Mechanistic Pathways of Sex Differences in Cardiovascular Disease
Abstract
Major differences between men and women exist in epidemiology, manifestation, pathophysiology, treatment, and outcome of cardiovascular diseases (CVD), such as coronary artery disease, pressure overload, hypertension, cardiomyopathy, and heart failure. Corresponding sex differences have been studied in a number of animal models, and mechanistic investigations have been undertaken to analyze the observed sex differences. We summarize the biological mechanisms of sex differences in CVD focusing on three main areas, i.e., genetic mechanisms, epigenetic mechanisms, as well as sex hormones and their receptors. We discuss relevant subtypes of sex hormone receptors, as well as genomic and nongenomic, activational and organizational effects of sex hormones. We describe the interaction of sex hormones with intracellular signaling relevant for cardiovascular cells and the cardiovascular system. Sex, sex hormones, and their receptors may affect a number of cellular processes by their synergistic action on multiple targets. We discuss in detail sex differences in organelle function and in biological processes. We conclude that there is a need for a more detailed understanding of sex differences and their underlying mechanisms, which holds the potential to design new drugs that target sex-specific cardiovascular mechanisms and affect phenotypes. The comparison of both sexes may lead to the identification of protective or maladaptive mechanisms in one sex that could serve as a novel therapeutic target in one sex or in both.
I. INTRODUCTION
In many frequent diseases, significant differences exist between men and women in epidemiology, clinical manifestation, pathophysiology, treatment and outcomes. A part of these differences is due to biological differences between men and women and is commonly designated as sex differences, whereas differences between men and women that depend on the interaction of the individual with the environment and society are referred to as gender differences. It is well known that sex hormones influence behavior and lifestyle. More recent findings demonstrate that environmental influences, such as lifestyle, nutrition, different forms of stress, dust, and heat, lead to epigenetic modifications in the developing fetus, the child, and the adult. These can be transmitted through the germline and affect the development of disease or determine resistance against disease. The psychosocial mechanisms contributing to disease are summarized as gender effects. Sex and gender effects are frequently interrelated and interact in many diseases (Figure 1).
FIGURE 1.Interaction of sex and gender during development and adulthood. X- and Y-linked genes determine the formation of ovaries or testes and subsequent production of sexual hormones. These, in turn, exert direct activational effects that are reversible after removal of sex hormones. In contrast, organizational effects, based on epigenetic modifications of DNA, persist for longer time periods in the absence of sex hormones. Other factors, such as nutrition and environmental factors, contribute to complex interactions.
This review focuses on the contribution of biology to sex differences in cardiovascular diseases (CVD) and on mechanistic pathways of sex differences in CVD. We first introduce CVD with significant differences between men and women that call for clinical attention. So far, this topic has been neglected by many regulatory, funding, research, and industrial policies, and the knowledge is rather limited in many aspects. We then discuss how experimental animals can serve as models for these diseases and the sex differences therein, acknowledging that these models are hampered by limited comparability between humans and animals regarding age and duration of disease manifestations, comorbidities, hormonal cycle, and pathophysiological mechanisms. Nevertheless, genetic manipulation of experimental animals provides mechanistic insights into disease processes. The main focus is to analyze genetic and epigenetic mechanisms leading to sex differences, the contributions of sex hormones and their receptors to sex differences in biological processes of cardiovascular cells.
II. CLINICAL BACKGROUND
A. Ischemic Heart Disease
Men and women are prone to develop different types of ischemic heart disease (IHD). While men suffer most frequently from occlusive coronary artery disease (CAD), women exhibit more frequently a nonobstructive CAD or microvascular dysfunction that is better described with the term IHD. The term IHD recognizes that the main pathophysiological problem is myocardial ischemia due to a disturbed balance between oxygen supply and demand of the myocardium (48). This may be located in the epicardial coronary arteries, due to atherosclerosis, which is more common in men and known as CAD, or pathological vasoreactivity, such as spasm and endothelial dysfunction, which is more common in women (29, 387). Perfusion problems may also arise from microvascular dysfunction, which appears to be more common in women. Women with recurrent chest pain syndromes without obstructive CAD but with microvascular dysfunction have a twofold increased risk to develop CAD events in the following 5-8 years and have a four times higher risk for rehospitalizations and recurrent angiograms after an acute event than women without these symptoms (171, 338). Pathophysiology of microvascular dysfunction is incompletely understood and needs more systematic investigation.
Other manifestations of IHD with sex-specific prevalence are spontaneous coronary artery dissection and the Takotsubo syndrome. Spontaneous coronary artery dissection occurs preferentially (>90%) in women below 60 years of age. It is frequently associated with immunologic and connective tissue diseases (295). Three-quarters of the manifestations of this syndrome occur in pregnancy (329, 345, 395). The relative high prevalence of this syndrome in pregnancy is the reason that acute coronary events in women that need coronary interventions should be treated with stents and not with thrombolysis (329). Furthermore, the Takotsubo syndrome affects predominantly women (196, 300, 355, 424). It manifests as an acute coronary syndrome and accounts for up to 8% of the acute coronary syndromes in women, but its etiopathology is not clear. The postmenopausal decrease in estrogen levels probably contributes to an increased sensitivity of the heart to circulating catecholamines. Takotsubo is often preceded by massive acute psychological or physical stress. The patients mostly recover with normalized ejection fraction. However, according to the most recent data, mortality is 8% per year, and recurrence is estimated at 5% (380).
Men develop CAD earlier and usually present with more severe atherosclerosis in their coronary arteries than women. As a consequence, myocardial infarction (MI) in general appears 10 years earlier and is associated with a more widespread CAD localization in men than in women. The reason for the relative protection of women against the development of atherosclerosis before menopause is poorly understood. A more beneficial lipid profile may contribute, and some protection seems to be conferred by sex hormones, since women with hormonal disturbances, such as polycystic ovarian syndrome, develop earlier atherosclerosis and MI than healthy women (219, 413). The role of estrogen and its receptor (ER) is substantiated by the fact that even men with a disruptive ERα (ESR1) mutation have early CAD (318, 374).
For unknown reasons, acute mortality in the first days after MI is greater in younger women than in age-matched men (397). Cardiac rupture at acute MI has been reported more frequently in women than in men in studies from the United States, Europe, and Japan. These studies have suggested that women have a higher mortality rate than men, even when controlled for age, and die less often from arrhythmia but more often from cardiac rupture independent of whether thrombolytic therapy is used or not (59, 151, 269, 433). In contrast, ischemic sudden death due to arrhythmia occurs more frequently in men than in women.
The risk of heart failure (HF) following MI is higher in women than men (211). Women also have more rehospitalization for acute coronary syndrome after MI than men (242). In some but not all studies, a higher total in-hospital mortality rate after MI in women than in men was accounted for on the basis of differences in age and comorbidities (207).
B. Pressure Overload
Female hearts adapt to pressure overload differently from male hearts. In particular, pressure overload-induced hypertrophy in women is associated with smaller internal cavity and relatively larger wall thickness than men (13, 80, 81). Women, independently of left ventricular size, more frequently preserve better ejection fraction and myocardial contractility than men during progression of aortic stenosis (AS) (55, 80, 99, 407). The better systolic function in women with AS may be due to a less pronounced induction in collagen remodeling than in men (406, 407). In our own study of patients undergoing aortic valve replacement, similar percentages of women and men had increased left ventricular (LV) diameters, but women more frequently exhibited LV hypertrophy than men (312). Increased LV diameters persisted 1 wk after surgery in 34% of men but only in 12% of women. LV hypertrophy reversed more frequently in women than in men. In LV tissue samples from AS patients, men had significantly higher collagen I (COL1A1) and III (COL3A1) and matrix metalloproteinase 2 (MMP2) gene expression than women (312). Less fibrosis prior to aortic valve replacement may enable faster regression following surgery (311). Overall, AS leads to sex-specific myocardial remodeling (Figure 2) with a more concentric form of myocardial hypertrophy, less fibrosis, and a better reversibility after unloading the ventricle by aortic valve replacement in women than in men (311, 312).
FIGURE 2.Paradigmatic changes in male and female hearts under pressure overload. Both men and women respond primarily with concentric myocardial hypertrophy (MH), but women stay more in concentric MH with maintained systolic function, whereas men develop more easily eccentric MH.
C. Hypertension
The number of hypertensive individuals in younger age groups is greater in the male population than in the female population, whereas in the elderly the percentage of hypertensive women doubles the numbers of men (290). Sex differences in hypertension are related to the renin-angiotensin system (RAS) and the bradykinin and nitric oxide (NO) system. Hypertensive LV hypertrophy regresses less well in women under RAS inhibition than in men (128). Hypertensive women sustain higher LV ejection fraction and other measures of systolic function than hypertensive men. Nevertheless, they have an estimated threefold higher risk of developing HF or stroke compared with men (223). Hypertensive women develop more vascular and myocardial stiffness than men at older ages and more often have isolated systolic hypertension, reflecting increased aortic stiffness (254).
D. Exercise-Induced Cardiac Hypertrophy
Cross-sectional studies of endurance athletes suggest that women develop a lower maximal oxygen uptake and less LV hypertrophy than men undergoing a similar training program (429). However, cross-sectional studies are limited by the different forms of competition, exercise, and training performed by male and female athletes. Only recently, a small longitudinal study was published that focused on sex differences in physiological adaptation using identical 1-year endurance training programs in six men and five women (152). The small sample size limits the power of this study; however, the use of cardiac magnetic resonance imaging for analyzing LV mass and the longitudinal character of the study may partially offset this disadvantage. As a first surprising result, the study found sex differences in metabolic adaptation. Women experienced a major reduction in body fat already after 6 mo of training, whereas men experienced a reduction in body fat only at 12 mo of training. Second, ventricular compliance and distensibility improved similarly in men and women. However, men demonstrated greater enhancement in the Frank-Starling mechanism. Third, men exhibited a greater increase in oxygen uptake and a greater increase in LV mass in month 12 of training. Noteworthy, women had the same or even greater increase in LV mass as men after 3 mo, but no further increase occurred up to month 12, leading to much lower total increase of LV mass over the 12-mo period. Myocardial hypertrophy in men could partially be due to testosterone, which is known to increase with regular exercise training (409). In women, estrogen may influence cardiac hypertrophy via pathways, such as phosphatidylinositol 3-kinase/AKT signaling or the β-catenin pathway that can act as a prohypertrophic as well as an antihypertrophic stimulus (discussed later) (143, 188). Premenopausal women are known to exhibit greater cardiac AKT activity than men with subsequent greater antihypertrophic effects (51). Nevertheless, no good mechanistic explanations are provided so far by rodent models, since in these models, female animals develop greater LV hypertrophy than males (discussed later) (108, 198). In summary, the cardiovascular adaptation to endurance training occurs differently between men and women, even with identical training programs. Clearly more data and larger studies are needed in this field.
E. Genetic Cardiomyopathies and Arrhythmia
Genetic cardiomyopathies due to autosomal gene variations are expected to occur with the same prevalence between men and women. Nevertheless, recent large-scale genome-wide studies associating genetic profiles with disease risk have revealed significant sex differences in genetic variation-disease associations (230, 276, 379). Furthermore, dilated cardiomyopathy and hypertrophic cardiomyopathy (HCM) have a greater prevalence in men than in women (10, 20, 75, 78, 129). Thus compensation for the genetic defect in these syndromes appears to be more efficient in women than in men. Sudden arrhythmic cardiac death is a frequent thread in HCM, and sudden death in young athletes is frequently attributed to undiagnosed HCM. Noteworthy, sudden cardiac death in young and middle-aged athletes affects almost only men (255).
Genetic defects leading to long QT syndromes (LQTS) are located on autosomes. Mutations in 13 genes have been associated with LQTS, but most of the LQTS are due to mutations in three ion channels (342). LQTS-induced tachycardia occurs with equal frequency in boys and girls. However, after puberty, arrhythmias are more frequent in women than men. Women are at higher risk than men for torsades de pointes with LQT type 1 and type 2, but LQT type 3 occurs in equal frequency between men and women (342). It has been hypothesized that testosterone contributes to shortening of the QT interval in men, whereas estrogen has smaller, QT prolonging effects in women (314, 449).
F. Heart Failure
HF is a typical clinical syndrome arising from different pathophysiological conditions, defined by clinical symptoms and signs that has a high prevalence in old age, affecting more than 10% of those above 70 years in western societies and typically more women than men. We now differentiate between HF with reduced ejection fraction, affecting typically men, and HF with preserved ejection fraction, affecting more women (73). In both syndromes, women have better clinical outcomes than men (222, 258). The heart of men and women also adapts differently in HF. In a large population-based German cohort, men with moderate or severe LV dysfunction developed a stronger increase in LV mass than women (236). In HF with preserved ejection fraction, women develop less ventricular dilation than men, but they have smaller and stiffer ventricles (330, 332), which may be due to different fibrous tissue composition or different relaxation kinetics due to sex differences in calcium (Ca2+) handling (97, 330). Men and women with HF with preserved ejection fraction differ mainly in their comorbidities. Aging, over- and undernutrition, diabetes, hypertension, salt loading, as well as inflammatory or autoimmune diseases are significant risk factors, which manifest differently between men and women and contribute to HF with preserved ejection fraction in a sex-dependent manner (133, 210, 262).
III. SEX DIFFERENCES IN EXPERIMENTAL ANIMALS AS MODELS FOR HUMAN CARDIOVASCULAR (PATHO)PHYSIOLOGY
The above described clinically relevant sex differences in many CVD await pathophysiological clarification that may lead to the development of sex-specific therapeutic strategies. Since studies in humans are limited, use of experimental animals that mimic human disease are necessary to advance our understanding (248). A number of models have been used to mechanistically investigate sex differences in pathophysiology and outcomes. In particular, models for ischemia, pressure overload, hypertension, exercise-induced hypertrophy, and cardiomyopathies have been developed and investigated for sex differences in their effects on myocardial remodeling in rodents (331). For heart failure with reduced ejection fraction, animal models have been developed for the underlying disease conditions, but they have frequently not been studied for sex differences. Due to the multifactorial and largely unknown origins of heart failure with preserved ejection fraction in humans, no good animal models are available for this syndrome. Therefore, sex differences in animal models do not always offer a one-to-one representation of sex differences in humans.
A. Myocardial Ischemia
Animal models for myocardial ischemia that investigated sex differences focused mainly on infarct size and on outcomes in the first days or weeks after acute occlusion of a coronary artery in vivo in mice, rats, rabbits, dogs, and pigs with and without reperfusion. Furthermore, an ex vivo system, the isolated beating heart, i.e., the Langendorff model, has been frequently used. In the Langendorff system, better postischemic recovery of LV function and smaller infarct sizes were found in females than in males (19). Isolated perfused female rat hearts have a better recovery and smaller infarct size than male hearts (46, 175). Female hearts also had improved recovery of contractility (+dP/dt) and compliance (−dP/dt) after ischemia and reperfusion and less necrosis compared with male hearts (123, 419).
In vivo studies of ischemia revealed smaller infarct size and less apoptotic cell death in female than in male rabbits (41). After coronary occlusion, female rats developed a concentric hypertrophy with no additional cavity dilation and no measurable scar thinning, while males showed eccentric hypertrophy, cavity dilation, and scar thinning (166). Smaller infarct size in females was also confirmed in a dog model (175, 218). Most studies agree that under ischemic stress, female mice, rats, and rabbits have a better survival than males in the first days after MI. This seems partially due to smaller infarct sizes and to lower rates of cardiac rupture in females than in males in the first 5 days after MI (58). Males have delayed myocardial healing, resulting in early cardiac rupture, and the survivors have poorer cardiac function and pronounced maladaptive remodeling, while females show a better outcome and less development of HF. Greater wall stress, partially due to greater volumes, greater inflammation and matrix metalloproteinase activation in males seem to be contributing causes of these sex differences (57, 113). Testosterone enhances early cardiac eccentric remodeling after MI, causing rupture and degrading cardiac function, while estrogen seems to have no significant protective effect in the acute phase after MI (58).
Most of these results were obtained in small studies that could not consider the effects of genetic background, age, body temperature, or other conditions. In a very large analysis of determinants of infarct size in mice that included these variables, female sex was still associated with reduced infarct size after ischemia/reperfusion (139). In our own large study with 400 mice, we also found that female sex improves early survival after MI, and we showed that males and females responded differently to a novel therapy with a transgenic approach (396). The whole study group and the subgroup of males responded with improved survival after acute coronary occlusion to the transgenic overexpression of melusin (Itgb1bp2) in the heart, but survival in the female subgroup was not affected by this treatment (396). However, chronic remodeling was positively affected in both sexes. Together, these results corroborate that sex has a major impact on infarct size and survival after MI in rodent models, and this needs to be taken into account when designing a study of MI in mice (139).
B. Pressure and Volume Overload
Pressure overload in mice may be introduced by constriction of the aorta at different levels (Figure 3). Male rats with chronic transverse aortic constriction (TAC) develop an unfavorable form of myocardial hypertrophy, i.e., more eccentric hypertrophy and fibrosis, whereas females develop less and more concentric myocardial hypertrophy (98). Contractile reserve and Ca2+ handling are better preserved in females than in males subjected to TAC. Furthermore, males develop HF at an earlier stage than females (426). This pattern is similar to human AS as discussed above. In line, our own studies have also revealed significant sex differences in a mouse model of TAC and found a more pronounced increase in myocardial hypertrophy and fibrosis in male animals. In contrast, female animals exhibited less downregulation of genes related to mitochondrial function and respiration (119). The changes in the transcriptional profile induced by pressure overload differed significantly between the sexes (119, 432).
FIGURE 3.Mouse model of myocardial hypertrophy and heart failure. Transverse aortic constriction (TAC) (A) leads to concentric myocardial hypertrophy with rounded apex after 2 wk and eccentric myocardial hypertrophy with LV dilation after 8 wk (B) in mice.
Sex differences in volume overload models have been less frequently studied so far. Female rats with atrioventricular shunt have less HF, maintain cardiac function, and have lower chamber size than males (127). Proapoptotic pathways are increased in males but not in females (91). Males have a greater mortality than females (25 vs. 3%), despite a similar degree of volume overload. Interestingly, ovariectomy abolished the biological advantage of females, and estrogen treatment restored the sex-associated patterns of remodeling in this model (45).
C. Hypertensive Models
Further animal models for other complex human CVD, such as hypertension, have also been analyzed for sex differences. In the spontaneous hypertensive rat (SHR) model, cardiac function declined faster in male than in female animals (313). Female SHR maintained normal cardiac dimensions and function, whereas males developed LV dysfunction and HF. At the age of 12 mo, female SHR have greater ejection fraction and cardiac index and smaller end-diastolic and -systolic volumes than males, despite similar systolic blood pressure values between the sexes (313). Female SHR also developed less LV hypertrophy and fibrosis than males, which was independent of blood pressure differences and was associated with greater generation of NO (339).
In the deoxycorticosterone (DOCA)-salt hypertension model, a model characterized by hyperaldosteronism, a blood pressure-independent sexual dimorphism was confirmed (190). Males developed more LV hypertrophy than females, and this was associated with greater calcineurin activation (140, 190).
D. Exercise
In models of voluntary or forced exercise, female mice develop more cardiac hypertrophy than males (88, 108, 120, 198). Surprisingly, female mice run on a cage wheel longer distances than males (88, 198). However, the greater hypertrophic response in females persists after normalization of cardiac mass to running distance (198). Our own recent studies revealed that the greater increase in physiological myocardial hypertrophy in females is mediated by induction of protein kinase B (PKB, also known as AKT) signaling, mitogen-activated protein kinase (MAPK) pathway, protein synthesis, and mitochondrial adaptation in an ERβ-dependent manner (108). Thus a veritable biological difference between the sexes in the hypertrophic response to exercise must be assumed. Another study also found increased cardiac hypertrophic responses to exercise in female mice and reported that this was associated with increased plasma free fatty acid levels and augmented adipose tissue lipolysis (120). In parallel, myocardial glucose uptake was reduced in female mice after exercise, analyzed by positron emission tomography, while cardiac glucose uptake was unaltered after exercise in males. Expression of genes involved in fatty acid uptake was increased in female compared with male mice. Thus sex differences in exercise-induced cardiac hypertrophy are associated with changes in cardiac substrate availability and utilization with a shift to greater use of fatty acids in females (120). Sex differences were also found in other species and exercise forms. In rats, females subjected to chronic swimming exhibited a marked increase in absolute heart mass associated with increased contractile performance compared with male mice (271, 347, 348). However, in studies of effects of exercise, the accompanying stress response, i.e., catecholamine liberation, must be considered, since mechanical load and catecholamine liberation may exert different effects on cardiac adaptation (349).
E. Genetic Models Leading to Sex Differences in Cardiac Function
Sex differences have also been found in animal models of genetic diseases leading to myocardial hypertrophy and HF. In most of these models, male mice appear more sensitive to genetic interventions than females, since female animals display a lower mortality, less severe hypertrophy, and better preserved function than males (Table 1) (102). Some of these models mimic human HCM. Mutations in the cardiac myosin heavy chain gene can cause familial HCM. In a transgenic model (missense R403Q allele), males develop more LV systolic dysfunction than females (294). Genetic deletion of Fkbp1b, encoding a sarcoplasmic reticulum (SR) protein that regulates cardiomyocyte Ca2+ handling, results in increased cardiac mass in male but not in female mice (436). Ablation of phospholamban (Pln), another gene involved in cardiac SR Ca2+ handling regulation, exacerbates ischemic injury to a lesser extent in female than male mice (82). Female mice with fourfold overexpression of phospholamban do not exhibit LV hypertrophy and mortality at 15 mo, while males do (87). Genetic deletion of peroxisome proliferator-activated receptor alpha (Ppara), a gene involved in cellular energy metabolism, led to cardiac lipid accumulation and death in all male mice, but only in 25% of females (95). This lipid accumulation could be prevented by estrogen administration (95). In another study, overexpression of a histone deacetylase (HDAC) in cardiomyocytes caused death in male but not in female mice (85). The transgene effect may have been mediated by alterations in mitochondrial function (85).
| Modification | Gene | Sex-Specific Phenotype | Reference Nos. |
|---|---|---|---|
| Genetic deletion | Fkbp1b | Cardiac mass increased in males but not females | 436 |
| Pln | More ischemic injury in males than females | 82 | |
| Ppara | Cardiac lipid accumulation and death in all males, but only in 25% of females | 95 | |
| Transgenic expression | Myh6 | More LV systolic dysfunction in males than females | 294 |
| Pln | LV hypertrophy and mortality at 15 mo in males but not females | 87 | |
| Hdac5 | Death in males but not females | 85 | |
| Tnf | HF and increased mortality predominantly in males | 167 |
Modulation of inflammatory pathways also lead to sex-specific effects. Overexpression of tumor necrosis factor-α (Tnf), a proinflammatory cytokine, caused HF and increased mortality predominantly in males (167, 177). This may be due to sex differences in the activation of proinflammatory pathways including TNF-α signaling in the heart. Sex hormones may lead to sex-specific activation or suppression of these pathways (438) and will be discussed later.
IV. MECHANISMS OF SEX DIFFERENCES
The large number of sex differences in humans and experimental animals have led to the study of these differences in more detail and to the search for underlying mechanisms. Obviously, (epi)genetic mechanisms, based on the differences in sex chromosomes, are expected to play a major role, as well as sex hormones and their receptors. The share of these mechanisms in contributing to sex differences is not easy to evaluate and frequently surprising. We discuss the most prominent concepts and findings.
A. Genetic Mechanisms
1. Male specific Y-chromosomal gene expression
Sex differences in the transcriptome may arise from the expression of Y-encoded genes and lead to male-specific cardiovascular phenotypes (Figure 4A). In the 2000s, observations linking gene variants on the Y chromosome to hypertension were reported, which could contribute to the higher incidence of CVD in males compared with females (62). Further results indicated that a locus on the Y chromosome may influence low-density lipoprotein (LDL) levels, independent of testosterone levels (61). Notably, it was reported that a severe form of CAD in men was linked to a Y-chromosomal gene variant possibly through interactions of immunity and inflammation (60). Next, it was suggested that the previously identified association between haplogroup I and CAD was not mediated by an abnormal regulation of sex steroids (33). In summary, these data demonstrate that gene variants on the Y chromosome contribute to cardiovascular phenotypes in men.
FIGURE 4.Sex chromosome-dependent gene regulation. Y chromosome-specific genes lead to male-specific gene expression (A), thereby resulting in male-specific traits. X chromosome inactivation (ca. 15% of genes) leads to female-specific gene dosage effects (B), thereby affecting (patho)physiology in a sex-specific manner. Only a part of the chromosome is indicatively shown with selected regions containing 3 genes.
2. Incomplete X-chromosomal gene inactivation
Escape of X-chromosomal genes from X-inactivation may contribute to a sex-specific imbalance in gene expression (Figure 4B). Under normal conditions, a balanced gene expression dosage between males (XY) and females (XX) is achieved by X inactivation. Mammals have evolved a compensatory mechanism to randomly inactivate one of the female X chromosomes, resulting in equalizing gene expression between males and females in the best case. However, despite this chromosome-wide silencing, a number of genes escape X inactivation. This is species-specific; in humans, ∼15% of X-linked genes are bi-allelically expressed and in mice, ∼3%. Expression from the inactive X allele varies from a few percent of that from the active allele to near equal expression. While most genes have a stable inactivation pattern, a subset of genes exhibit tissue-specific differences in escaping from X inactivation. Escaping genes appear to be protected from the repressive chromatin modifications associated with X inactivation. Differences in the identity and distribution of escape genes between species and tissues suggest a role for these genes in the evolution of sex differences in specific phenotypes.
The contribution of X-chromosomal genes to sex differences in cardiovascular phenotypes may have been underestimated, since genome-wide association studies have frequently not included the X chromosome. In fact, the X chromosome represents one potential source for the “missing heritability” for complex phenotypes, which so far has remained underanalyzed in genome-wide association studies. The results of a recent study have provided the first link between phenotypic variation in a population sample and a X chromosome inactivation-escaping locus (394). Interestingly enough, X chromosomal gene variation is associated with slow progression to AIDS in HIV-1-infected women (360). A single nucleotide polymorphism located at Xq21.1 in a conserved sequence element was identified as a significant genetic determinant of disease progression in women but not in men. These data provide a clear motivation for including the X chromosome in large-scale genetic studies of complex diseases and traits.
3. Sex-specific heterochromatizing effects of sex chromosomes
The presence of a large heterochromatic sex chromosome may alter the availability of heterochromatizing factors and thereby alter gene expression from autosomes. This is a theoretical mechanism that has not been conclusively shown in humans yet. Research suggesting a role for X and Y chromosome heterochromatin in regulating epigenetic states of autosomes has highlighted unorthodox mechanisms of gene regulation. They have been postulated to contribute to sex-specific susceptibilities to autoimmune and neurological diseases (361).
4. Sex-specific effects of autosomal genetic variants
Surprisingly, some genetic variants at autosomes act in a sex-specific manner. Newly identified genetic loci link adipose and insulin biology to body fat distribution. In a large study of more than 200,000 individuals, 49 loci were found to be associated with waist-to-hip ratio after adjustment for body mass index (359). Twenty of the 49 waist-to-hip ratio loci show significant sexual dimorphism, 19 of which display a stronger effect in women. The identified loci were enriched for genes expressed in adipose tissue and for putative regulatory elements in adipocytes. Pathway analysis implicated adipogenesis, angiogenesis, transcriptional regulation, and insulin resistance as processes affecting fat distribution, providing insight into potential pathophysiological mechanisms, but this analysis did not give an explanation why they had a stronger effect in women (359). Furthermore, common genetic polymorphisms and haplotypes of the chymase gene (CMA1) were associated with LV mass only in male but not in female patients with symptomatic AS (295). Polymorphisms in the bradykinin type 1 receptor (BDKRB1), a factor involved in the renin-angiotensin system, have also been associated with sex-specific effects (434).
5. Genome-wide expression profiling and proteomics
Genome-wide expression profiling has been used to analyze sex differences in gene expression. Under healthy conditions, genes located on sex chromosomes are usually the ones that exhibit sex-specific expression. Male-specific expression of Y-linked genes, such as DDX3Y, EIF2S3 (Y-linked), and KDM5D (also known as JARID1D), is generally observed in mouse hearts, as well as in the human myocardium. Higher expression levels of X-linked genes are detected in female mice, e.g., Xist, Timp1, and Ca5b, and in women, e.g., XIST, EIF2S3 (X-linked), and GPM6B. Nevertheless, genes on autosomal chromosomes encoding cytochromes of the monoxygenase family, such as Cyp2b10, carbonic anhydrases, such as Ca2 and Ca3, and natriuretic peptides, such as Nppb, have also been reported with sex-specific expression levels (164).
In diseased conditions, such as new-onset HF, females usually have higher expression of genes related to energy metabolism than males (35, 116, 142, 148), indicating that females may be able to maintain their metabolic function in response to a disease stimulus. Mouse models of MI (68) or dietary manipulation (76) have also revealed sex-specific gene regulation. Furthermore, in patients with AS, we recently reported significant sex differences in genes involved in the regulation of fibrosis and inflammation with a significant repression of these processes in women (184), indicating some protection in the female sex against deleterious effects of persistent fibrosis and inflammation. Importantly, rodent models of pressure overload demonstrate sex differences in a similar pattern, including apoptosis, cytoskeletal integrity, fibrosis, and metabolism (119, 185, 186, 425, 432), thereby making a case for the conservation of specific regulatory mechanisms between humans and rodents.
Sex differences were also found in gene expression in human umbilical vein endothelial cells (233, 367). This regulation is believed to reflect mainly the effect of fetal sex, but it could also be affected by the mother's hormones or those hormones produced by the fetus itself. However, these differences are small and under debate (205, 398), while in vitro experiments are performed after 3–4 wk of culturing; therefore, the hormonal effects are thought to be small. These interesting observations can be used to generate hypotheses on relevant pathways that contribute to sex differences in cardiovascular gene expression.
Proteomic approaches have also been taken to investigate cardiovascular sex differences. In a targeted approach, we analyzed extracellular matrix proteins in LV samples of individuals free of cardiovascular disease, which demonstrated an age-dependent sex-specific regulation (107). Overall, the levels of these proteins in younger individuals were lower in women than men, while in older individuals they were higher in women than men (107).
Other studies focusing on mechanisms involved in metabolism and oxidative stress regulation identified several proteins with sex-specific pattern, including members of the apolipoprotein family, carbonic anhydrase 2, desmin, nitrilase 1, and peroxiredoxin 2 (94), most of which are mitochondrial proteins with antioxidant function. Higher female-specific levels of such proteins may contribute to mechanisms resulting in better adaptation under (patho)physiological conditions and give females an advantage.
Considering the estrogen-dependent induction of antioxidant, longevity-related genes (408) and the significantly high levels of phytoestrogens in human diet (30), another study assessed the effect of phytoestrogens on the cardiac proteome also revealing significant sex differences under healthy conditions. In particular, the authors found that several enzymes of the fatty acid metabolism and their transcriptional regulators varied differentially between males and females (353). The role of phytoestrogens in males or females is still poorly understood, but they can influence cardiac mass in ovariectomized mice (281, 282). Nevertheless, an activation of mechanisms in males leading to deleterious effects has been reported. In particular, increased levels of enzyme species involved in oxidative phosphorylation and generation of reactive oxygen species (ROS) were accompanied by decreased amounts of antioxidants in male mice receiving genistein compared with male mice maintained on a phytoestrogen-free basic chow used as control, which have been previously associated with various pathological conditions (353). Similarly, in a model of endothelin-1 overexpression and endothelial NO synthase knockout (KO), cardiac proteome analysis revealed that the protein abundance of the oxidative stress related enzyme superoxide dismutase presented with sexual dimorphism potentially leading to decreased male-specific antioxidant capacity (405).
Recently, we determined global changes in protein abundance due to sex and ERβ in pressure overload and found major sex and ERβ-dependent differences together with a complex interaction of the two factors (185). The pathways involved include metabolism, p38 MAPK signaling, and cytoskeletal regulation revealing a better adaptation of female than male mice to pressure overload. Importantly, our study revealed previously unrelated proteins to the development and progression of pressure overload-induced LV hypertrophy. These include cofilin 2 (Cfl2) and pyruvate kinase 2 (Pkm2). Given the lack of information between regulation of these proteins and LV hypertrophy, we have postulated that the induction of these proteins in female mice deficient of ERβ might underlie a better structural and metabolic adaptation to pressure overload.
B. Epigenetic Mechanisms
A number of epigenetic DNA and histone modifications have been described that arise at specific time points in development and modulate gene expression. Environmental factors can modify epigenetic marks in a sex-specific manner leading to sex differences in CVD in the individual and following generations. We discuss epigenetic mechanisms that play an essential role in cardiovascular phenotypes, such as myocardial hypertrophy and HF. Figure 5 illustrates a novel hypothetical model of sex-specific DNA and histone modifications, which may also be affected by sex hormones and their receptors.
FIGURE 5.Sex- and sex hormone-specific DNA and histone modifications. Sex-specific epigenetic marks from the parent are transmitted to the offspring leading to sex-specific transcriptional (in)activation. Sex hormones may directly regulate DNA and histone-modifying enzymes to modulate the epigenetic profile in a sex-specific manner.
1. Histone and DNA modifications
Epigenetic changes include methylation of cytosines in the primary DNA sequence, or histone modifications, such as acetylation and methylation. These modifications can last long term, such that epigenetic modulation early in development can alter the phenotype much later in life (448). Some epigenetic modifications can persist in the germ cells and can influence subsequent generations (138, 275). A Dutch study showed that famine-induced epigenetic modifications occurred in a sex-specific manner (389). For 6 of 15 loci studied, significant differences in DNA methylation after famine exposure during pregnancy were observed. This association differed by sex for three loci (INSIGF, GNASAS, and LEP) with stronger methylation in men (389). In the Dutch birth cohorts from Amsterdam, Rotterdam, and Leiden examined at age 59 years, there was a moderate increase in systolic blood pressure and prevalent hypertension in men and women with prenatal famine exposure compared with unexposed controls (368). However, more studies are needed to establish robust associations between famine during pregnancy and clinical conditions (238).
Steroid hormones can induce, among others, modification of histones. Androgen or estrogen receptors act by binding to hormone response elements in the DNA and attract various cofactors that have inherent histone acetyltransferase or methyltransferase activity. This is particularly known for the CREB binding protein (CBP) and E1A binding protein p300 (EP300) (12, 121, 122, 134, 214, 215). The histone-modifying enzymes alter the epigenetic state of gene promoters to which the nuclear receptors bind, thereby changing gene expression.
The induction of DNA or histone demethylation or histone deacetylation has been implicated in CVD-dependent gene regulation. Histone acetyltransferases and deacetylases control cardiac hypertrophy, and a dysregulation of histone methylation profiles is found in HF (179, 392, 446). These mechanisms bear the potential for sex-specific regulation, since DNA modifying enzymes, e.g., histone acetyltransferases CBP and EP300, are recruited to the DNA by estrogen and androgen receptors. The X and Y chromosome encode some DNA demethylases, such as the Jarid family and others, that are activated by estrogen. Some of these genes undergo incomplete X inactivation or are only expressed from the Y chromosome and have therefore the potential to cause different effects between males and females. We therefore hypothesize that sex-specific DNA deacetylation or demethylation controls sex-specific gene transcription in the development of CVD and its course, thereby determining sex- and disease-specific cardiovascular phenotypes.
2. Non-coding RNA
Non-coding RNA species represent recently discovered mechanisms that control gene transcription by binding of RNA fragments to regulatory DNA sequences. Different types of non-coding RNA may contribute to sex differences. MicroRNAs (miRNAs) are small non-coding RNAs of ∼22 nucleotides that inhibit gene expression pairing to the 3' untranslated region (3' UTR) of target messenger RNAs (mRNAs). The expression of several 100s different miRNAs has been described in the mouse heart, many of which are regulated during the development of LV hypertrophy (53, 70, 346, 378, 390, 401). However, so far only few data exist about sex-specific regulation of miRNAs and their role in the observed sex differences in heart disease.
Our group has proposed sex-specific and estrogen-dependent regulation of miRNAs as a potential mechanism that may lead to sex differences particularly in fibrosis. Recently, we showed for the first time that TAC led to the sex-specific regulation of cardiac miRNAs (320). In particular, a large number of miRNAs were upregulated in males but not in females. In fact, we obtained evidence for the sex-specific expression of functionally related miRNA-21, -24, -27a, -27b, 106a, and -106b and the regulation of their expression by estrogen and ERβ (320). Functional target sites for these miRNAs are located on three repressors of the MAPK signaling pathway, i.e., Rasa1, Rasa2, and Spry1, which may all lead to cardiac fibrosis. miRNA-21 has already been linked to fibrosis (386). Our data suggest that the sex-specific expression of specific miRNAs is related to sex differences in fibrosis under pressure overload.
Recently, we also aimed at the analysis of cardiac miRNA regulation by sex and ERβ and their target proteins related to mitochondrial metabolism (343). After TAC, we found 34 miRNAs upregulated, 31 of which were induced only in males. Pathway enrichment analysis of potential targets of male-specific upregulated miRNAs identified mitochondrial metabolism, MAPK signaling, and extracellular matrix organization. Six mitochondrial proteins, i.e., Auh, Crat, Decr1, Hadha, Hadhb, and Ndufs4, carrying putative binding sites for the male-specific induced miRNAs were reduced only in males under pressure overload. The deletion of ERβ induced miRNAs in unstressed animals of both sexes. However, in ERβ-deficient mice, the upregulation of miRNAs in the males under pressure overload was abolished. Thus, under pressure overload, the regulation of miRNA expression and of relevant targets differs significantly between the sexes. ERβ plays a major role in this process by modifying pressure overload-induced regulation of miRNA in a sex-specific manner.
C. Sex Hormones and Sex Hormone Receptors
1. Synthesis and metabolism of sex hormones
Sex hormones are synthesized early in embryonic development and act through a number of different mechanisms. Sex hormones belong to a large family of endogenous signaling molecules that can modulate cellular processes via gene regulation and protein modification. In fact, androgens, estrogens, and progesterone affect the cardiovascular system leading to sex differences. The bulk of sex hormones is synthesized in the gonads, but extragonadal synthesis in cardiomyocytes or neurons, among others, also occurs. In particular, testosterone may be metabolized via aromatase to estrogen, thereby allowing estrogen to contribute to pathophysiology in males. In this review, we will mainly focus on estrogen and its receptors and to a lesser extent on androgens, while progesterone will not be addressed.
Androgens are mainly produced in the Leydig cells of the testis but also to a lesser extent by the adrenal gland, in the adipose tissue and bone (34, 268). In fact, it has been suggested that the rise in cardiovascular mortality in women following menopause may be due to an increased ovarian production of testosterone, which is in part stimulated by high levels of circulating gonadotropins (364). Nearly all organs, including the brain and cardiovascular tissues, express the androgen receptor (AR) and are responsive to androgens (4, 86, 257, 260).
Testosterone is the most important natural androgen. Testosterone's highly active metabolite is dihydrotestosterone (DHT), which also exerts its effects through binding to the AR, particularly with a two- to-fivefold higher binding capacity to the receptor (15). DHT is the most potent androgen in the body being ∼10-fold more potent in inducing AR-mediated signaling than testosterone (15, 371, 439). In fact, the main physiological role of DHT is expected to be the amplification of testosterone-dependent actions, such as the formation of reproductive organs (244).
DHT is converted from testosterone by isoforms 1–3 of the enzyme 5-α-reductase, which are expressed at similar levels in hearts of male and female mice (15, 431). However, it was recently shown that isoform 3 of 5-α-reductase (Srd5a3) is the predominant cardiac isoform (451). Nevertheless, it was reported that the expression of all 5-α-reductase isoforms is increased in human and mouse hypertrophic hearts, thereby leading to increased abundance of DHT (451). Similarly, increased levels of DHT were found in preparation of microsomes from human hypertrophic hearts (385). However, epidemiological studies and clinical trials have shown contradictory effects, where testosterone appears to improve functional exercise capacity in patients with HF (252, 296, 391). On the other hand, long-term anabolic-androgenic steroid use has been associated with myocardial hypertrophy and LV dysfunction (21, 341). A current hypothesis is that testosterone may be beneficial, while DHT may exert deleterious actions (40).
The major circulating estrogen is 17β-estradiol (E2), which binds equally to both ERα and ERβ (197). Other naturally occurring estrogens include estrone and estriol, the latter being the weakest of all estrogens, while E2 has the strongest potency. The primary sources of production of E2 are the theca and granulosa cells of the ovaries (136). However, E2 can also be produced locally as a result of the conversion of testosterone by the enzyme aromatase (362). Aromatase is present in a number of extragonadal tissues, such as the adipose tissue, bone, brain, heart, and the vasculature in both sexes (27, 370). Notably, there is a highly significant increase in E2 levels associated with inflammation and obesity. This increase results from aromatase conversion of androgen to estrogen in adipose tissue contributing significantly to the circulating pool of E2 (280). Consequently, in men, E2 is produced in significant quantities by local tissue aromatization of androgenic precursors from the testes and adrenal glands (241). In fact, in obese men, there is a marked increase of E2 production (74), and elderly men may have higher concentrations of E2 compared with age-matched women (54).
2. Sex hormone receptors in the cardiovascular system: relevant subtypes and regulation
Sex hormone-activated receptors, i.e., AR, ERα, ERβ, and the G protein-coupled receptor GPR30, affect a number of genomic and nongenomic pathways in a cell- and sex-specific manner. Regulation of these receptors in the cardiovascular system in different localizations and disease conditions is still not well understood.
The AR, ERα, and ERβ are members of the evolutionary related superfamily of nuclear steroid hormone receptors (206, 415). They are intracellular proteins that regulate gene expression in a hormone-dependent fashion upon their activation (47, 112, 206, 415). Like all steroid receptors, the AR, ERα, and ERβ have a conserved zinc finger-based DNA-binding domain (DBD) (C region), which contains regions that mediate dimerization, a COOH-terminal ligand-binding domain (LBD) (E region), which contains the ligand-dependent activation function (AF-2) domain and mediates ligand binding, and they bind to specific nucleotide sequences (112, 393). Additionally, they contain an NH2-terminal A/B domain with constitutive activation function (AF-1) and a hinge domain (D region) (393).
Several ER isoforms have been identified. The full-length 66-kDa ERα protein is composed of six domains (A to F), while there is a physiologically expressed 46-kDa isoform lacking the entire A and B domains, thereby being devoid of AF-1 (26). Alternative splicing events can generate a 55-kDa isoform, whose levels are enough to mediate several actions of E2 in the vessel wall of mice (307), as well as a 61-kDa isoform, whose transactivation capability can be as high as 75% of the WT ERα in uterine tissue of mice (201). Several polymorphisms for human ERα and ERβ have also been reported. In particular, ERα polymorphisms correlate with increased risk of MI (351, 356), while ERβ polymorphisms are associated with increased LV mass and LV wall thickness (309). In line, the human AR located on the X chromosome also exhibits polymorphisms, which are associated with higher maximal LV wall thickness (227).
Functional ERα and ERβ have been identified in the vascular endothelium, vascular smooth muscle cells, cardiac fibroblasts, and cardiomyocytes of male and female individuals (135, 189, 192, 234, 265, 402). Of interest, levels of ERα mRNA are similar in hearts of both men and women, while ERβ mRNA levels are higher in male than in female human hearts, including hearts without recognizable pathology that were not suitable for transplant due to technical reasons (286). We also demonstrated the implication of both ERs in human cardiac disease through the upregulation of mRNA levels of both receptors in the myocardium of patients with AS (286) and the elevated mRNA and protein levels of ERα in end-stage failing hearts (247). We also visualized a significant change in the intracellular localization of ERα in failing hearts, away from the intercalated disk, where it is also usually found in healthy hearts (247). We speculate that this may lead to mechanical instability of the intercalated disk in HF. Mechanistically, our studies identified that the nuclear factor κB (NF-κB) pathway is a part of the regulatory mechanism involved in ERα expression in the human heart (249) and atrial natriuretic peptide precursor A (NPPA) interacting with ERα in an E2-dependent manner (251). Studies in the vasculature revealed that ERα levels are lower in atherosclerotic coronary arteries compared with normal arteries of premenopausal women (234).
A pool of ERs is localized at the plasma membrane, which mediates the rapid extranuclear activity of E2 (11, 435). In addition to the membrane and nuclear localization of ERs, ERα and ERβ have also been detected in mitochondria (66, 440). Notably, in response to ischemia/reperfusion, myocardial mitochondria of ovariectomized rats and ERα KO mice showed noticeable ultrastructural damage and a decrease in mitochondrial respiratory chain function (444, 445). Treatment with E2 reversed the mitochondrial dysfunction (324, 376).
The first mouse models of ERα gene disruption included a global model showing effects on fertility and the reproductive system (106, 235), while the use of conditional site-specific recombination system enabled tissue-specific manipulation of ERα (264). These models have been extensively used to understand cardiovascular (patho)physiology, and several examples will be discussed in subsequent sections. Newer models have been generated to investigate potentially different functions specific to different localizations. In particular, to explore the role of the two activation functions (AFs), AF-1 and AF-2, mice lacking ERαAF-1 or ERαAF-2 were generated (1, 7, 31). More recently, a mouse model with a point mutation of the palmitoylation site of ERα (C451A-ERα) that leads to membrane-specific loss of function of ERα was generated, resulting in the abrogation of E2 vascular actions, such as rapid dilation, acceleration of endothelial repair, and endothelial NO synthase phosphorylation (3).
A third receptor, the G protein-coupled receptor (GPR30), has been proposed to be an ER mediating nongenomic effects of E2 (117, 118, 335), whose role, though, as an actual ER binding E2 in a direct manner or an interacting partner of the classical ER has been debated (221, 297). GPR30 has been shown to be expressed in certain endothelial cells (163); however, its role in mediating E2 actions in the endothelium is currently not understood mainly due to conflicting reports using several ER gain- or loss-of-function models (44, 141, 304).
3. Genomic actions of sex hormone receptors
The genomic actions of sex hormones are mainly mediated by their receptors that function as ligand-activated transcription factors. Following the diffusion of the sex hormone into the cell, it binds to the ligand-binding domain of the receptor, leading to the dissociation of the receptor from its cytoplasmic chaperones (365). Following nuclear translocation, the formation of a homodimer or a heterodimer ensues (79). The hormone-receptor complex then binds to hormone response elements situated in the promoter or enhancer region of target genes (279). The binding to hormone response elements is either direct or indirect through tethering with other transcription factor sites, such as activator protein 1 (AP-1) or specificity protein 1 (SP-1) (92). Interestingly, the interaction of the ER with NF-κB has been shown to mediate E2-dependent transcriptional regulation of genes that lack estrogen response elements (326). Recruitment of cell- and sex-specific cofactors is necessary and determines their action. In particular, interactions of the hormone-receptor complex with other transcriptional cofactors, i.e., co-activators and co-repressors, facilitate modulation of transcription of target genes (144, 251, 357). Our previous studies have shown that E2 regulates gene transcription in cardiac tissue and cells and that this regulation occurs in a sex-specific manner (182, 183, 188, 312). For example, E2 induces a female-specific increase in progesterone receptor levels, which might confer females protection (182). On the other hand, E2 induces a male-specific increase in myosin regulatory light-chain interacting protein (MYLIP), which leads to reduced contractility in males (183).
4. Nongenomic effects of sex hormone receptor activation
In addition to the classical genomic effects, sex hormones have been demonstrated to exert rapid nongenomic effects. These actions are mediated either by the classical receptors located in or adjacent to the plasma membrane or by other plasma membrane-bound receptors (89, 92). These effects are so rapid that phenotypical changes may occur in a matter of minutes following exposure to the sex hormones, and normally they affect signaling. For example, the nongenomic activities of estrogen include the activation of extracellular signal-regulated kinase 1 and 2 (ERK1/2) and Src, as well as the increased phosphorylation of c-Jun-NH2-terminal protein kinase (JNK) (246, 289, 366). Particularly in the myocyte, estrogen modulates signaling through phosphoinositide 3-kinase (PI3K), PKB, glycogen synthase kinase 3β (GSK3β), β-catenin, calcineurin, mechanistic target of rapamycin (mTOR), ERK1/2, p38 MAPK, JNK, and others. Together, these data demonstrate that estrogen interferes with a vast number of cytoplasmic signaling pathways through rapid nongenomic mechanisms, thereby altering cellular function. Notably, the nongenomic actions of sex hormones are not dependent on changes in gene expression for their action. However, the rapid induction of gene expression has also been reported (89, 246).
5. Manipulation of sex hormones in (patho)physiological animal models
To understand sex differences in animal models, several studies embarked on the analysis of the contribution of sex hormones to sex differences employing animal models and incorporating ovariectomy (OVX), orchiectomy, along with hormone substitution protocols. Most studies have focused on the effects of estrogen and related compounds, while testosterone has been less frequently studied. It is important, however, to consider the way of administration of the hormone, the hormonal levels reached in the circulation, and the limitation that these hormones are usually given transdermal or intramuscular to young animals, which is different to the situation in humans.
In ischemia, E2 administration has been shown to reduce infarct size and to improve postischemic myocardial function in a number of different animal models, including rabbits, mice, and rats (36, 37, 145, 216, 283, 303). The specificity of this effect was frequently documented by its blockade by the ER antagonist ICI182780 (36, 104). Furthermore, hearts from OVX mice and rats exhibited a greater infarct size, impaired functional recovery, and worse remodeling, which were reversed by E2 administration in physiological doses (195, 231, 283).
E2 supplementation has also been shown to exert antihypertrophic effects in different pressure overload models, and several mechanisms have been identified. In particular, E2-mediated inhibition of LV hypertrophy and prohypertrophic gene expression in the TAC model was reported (399). It was demonstrated that E2 exerts profound antihypertrophic effects, which were mediated through the regulation of atrial natriuretic factor (ANF) and myosin heavy chain beta (MHCβ) (16, 302). In another study, changes observed in OVX rats, such as a significant increase of LV hypertrophy, cardiomyocyte diameter and heart weight-to-body weight ratio, and a decrease in fractional shortening and ejection fraction, were largely reversed by administration of E2 (83). Our own studies have aimed to identify the receptor involved. We administered E2 and the selective ERα agonist 16α-LE2 for 9 wk after induction of pressure overload by TAC. Both slowed the progression of LV hypertrophy leading to reduced systolic dysfunction and fibrosis (427). We therefore concluded that ERα inhibits myocardial fibrosis in female mice under pressure overload.
While estrogen exerts antihypertrophic effects in the diseased heart, its role in the healthy heart is less studied. Recently, we found that long-term oral E2 administration induced physiological hypertrophic growth in the healthy C57BL/6J mouse heart, and this was characterized by an increase in nuclear β-catenin (188). In a model of cardiac β-catenin deletion, our surprising finding was that E2 had the opposite effects in WT littermates with a C57BL/6N background (188). Thus E2 exerts contradictory effects on postnatal cardiac growth in mice with distinct genetic backgrounds through the regulation of β-catenin.
In a mouse model of pressure overload-induced hypertrophy, treatment with finasteride, which inhibits the 5-α-reductase-dependent DHT generation, reduced mortality, inhibited pathological hypertrophy and fibrosis, LV dilation, and dysfunction in both male and female mice (451). Similarly, the removal of androgens through orchiectomy prevented adverse myocardial remodeling and dysfunction in response to several stressors (56, 126, 225, 272). Collectively, these data suggest that increased androgen levels play a major role in cardiac pathophysiology of both sexes.
6. Role of sex hormone receptors in cardiovascular disease models
To verify whether ERα and/or ERβ mediates the beneficial effects of E2, ERα- and ERβ-selective agonists have been used. A number of studies point to a cardioprotective effect of ERα agonists. Treatment with the ERα agonist 4,4′,4″-(4-propyl-[1H]-pyrazole-1,3,5-triyl)trisphenol (PPT) and E2, but not with the ERβ agonist 2,3-bis(4-hydroxyphenyl)-propionitrile (DPN), resulted in a significant reduction of infarct size in a rabbit model (38). Along the same lines, ERα agonism with PPT or ERA-45 reduced infarct size and accompanying inflammation (169, 287). In another model of MI, administration of PPT and a membrane-impermeable estrogen-albumin construct revealed that cardiac fibrosis was attenuated by inhibiting RhoA/ROCK/cofilin signaling through a membrane-bound ERα-mediated mechanism (217). Comparing ERα agonism with PPT and ERβ agonism with DPN in the same setting showed that both conferred protection following ischemia/reperfusion (412). However, agonism of ERβ also mediates strong cardiovascular effects. The ERβ agonist DPN improved postischemic recovery of isolated perfused hearts (283, 442). In a rat model of trauma-hemorrhage, DPN, as well as E2, protected against the consequences of ischemia (153).
Data on the potential role of GPR30 have also been emerging with postischemic contractile dysfunction and infarct size being significantly reduced in animals treated with the highly specific GPR30 agonist G1 compared with untreated controls (93). Assessment of the underlying mechanisms suggests that G1-mediated activation of GPR30 improves functional recovery and reduces infarct size in isolated rat hearts following ischemia/reperfusion through a PI3K-dependent, sex-independent mechanism (93). Interestingly, GPR30 seems to regulate contractile function through PI3K, among other signaling pathways, also in skeletal muscle (209).
7. Genetic deletion of sex hormone receptors
Hormone receptors have also been modulated genetically in models of myocardial ischemia, pressure overload, and others. Frequently, global KO models for sex hormone receptors have been used. However, such global KO models reflect effects in the whole body associated with counterregulatory effects, thereby being of limited use for cell-specific hypothesis testing. Therefore, cell-specific KO models have been developed more recently.
Several studies tried to verify the role of ERα and ERβ in mediating beneficial effects of E2 during LV hypertrophy using mice with genetic deletion of ERα (ERKO) and/or ERβ (BERKO). Early studies suggested a protective role for ERβ (17). In other studies, genetic deletion of ERα did not affect LV hypertrophy in TAC models, while deletion of ERβ did (363), suggesting a greater role for ERβ in attenuating the hypertrophic response to pressure overload. Due to these diverging findings, we investigated the effect of ERβ deletion under TAC conditions in males and females and found that WT males had more LV hypertrophy, greater cardiomyocyte hypertrophy, and more fibrosis (119). Deletion of ERβ increased LV hypertrophy and fibrosis in a different manner between males and females (119). In particular, we concluded that ERβ promotes fibrosis in males, but it inhibits fibrosis in females. ERβ limits cardiomyocyte hypertrophy and inhibits apoptosis in both sexes, but with a greater antiapoptotic effect in male hearts that actually exhibit more apoptosis than females. Thus, under pressure overload, the loss of ERβ is detrimental for both males and females but for different reasons.
Similarly, we found recently that sex differences in exercise-induced physiological myocardial hypertrophy are also modulated by ERβ (108). Physical exercise induces physiological myocardial hypertrophy. The sex-specific response of the heart to exercise is mediated by sex-specific regulation of PKB and MAPK signaling pathways, protein synthesis, and mitochondrial adaptation in an ERβ-dependent manner (108). In line, sex-specific modulation of adipose fatty acid metabolism during exercise may result in alterations of circulating free fatty acids, which leads to sexual dimorphic changes in cardiac substrate utilization and cardiac hypertrophy (120). Our recent studies have demonstrated that E2 also induces physiological cardiac growth via β-catenin signaling in an ERα-dependent manner (187, 188).
Several studies have also attempted to determine the role of ERα or ERβ in mediating the beneficial actions of E2 in ischemia/reperfusion using ERKO and/or BERKO mice. Under hypercontractile conditions, female BERKO mice exhibit a significantly greater degree of ischemia/reperfusion injury than ERKO or WT female mice (123), suggesting a protective role for ERβ. It was also shown that E2 treatment resulted in smaller infarct size in OVX ERKO mice than in OVX BERKO mice (18), again pointing towards an important role for ERβ. Similarly, deletion of ERβ in OVX mice subjected to chronic MI increased mortality and aggravated biochemical markers of HF (306). In another study, although no significant differences in overall mortality, infarct size, and parameters of LV remodeling were found when comparing infarcted ERKO and BERKO mice with infarcted WT mice, it was found that ERβ deficiency resulted in prolonged ventricular repolarization and decreased ventricular automaticity in female mice with chronic MI (200). These observations support a relevant role for ERβ in mediating an attenuated response to cardiovascular tissue injury in females.
Other studies have reported that the cardioprotective effects of E2 are mediated by ERα. For example, it was shown that female ERKO mice subjected to ischemia/reperfusion had a similar recovery with WT and ERKO males, while WT females had a worse recovery (417). In a similar study, it was demonstrated that the deletion of ERα is associated with more severe cardiac damage following ischemia/reperfusion injury (444). Endothelial ERα was also shown to play a crucial role in the E2-induced prevention of endothelial dysfunction after ischemia/reperfusion. In fact, it was demonstrated that targeting endothelial protection per se can confer cardiomyocyte protection under ischemia/reperfusion conditions (115). Although these studies utilizing ERKO and/or BERKO mice were not able to provide a clear consensus regarding which ER mediates the protection against cardiac injury, they actually suggest that both ERs may be involved in the cardioprotective effects of E2.
8. Overexpression of sex hormone receptors
Our own recent studies with a unique cardiac-specific overexpressing (OE) model of ERα show that this receptor protects the heart against ischemic injury (250). At baseline, unstressed male and female ERα-OE mice showed increased LV mass, LV volume, cardiomyocyte length, increased expression of markers of LV hypertrophy, as well as reduced markers of mitochondrial function and sarcoplasmatic Ca2+ transport compared with WT mice. Nevertheless, while ERα-OE mice exhibited a similar infarct size with WT mice, they had a lower increase in LV volumes and smaller loss in wall thickness, as well as a lower induction of profibrotic genes than WT mice. ERα-OE mice also exhibited enhanced expression of angiogenesis and lymphangiogenesis markers and neovascularization in the peri-infarct area in both sexes. Thus cardiomyocyte-specific ERα induces neovascularization and attenuates profibrotic gene expression probably through paracrine actions.
Recently, we have also overexpressed ERβ in cardiomyocytes (Figure 6) (352). We found that 2 wk after MI, ERβ-OE males and females showed improved survival. ERβ-OE was associated with attenuated LV dilation, smaller increase in heart weight and less lung congestion, as well as improved systolic and diastolic function in both sexes. Two potential pathways for ERβ-mediated myocardial protection were identified. First, male and female ERβ-OE mice had a lower reduction of the cardiac SR Ca2+-ATPase (SERCA2a) expression after MI, suggesting less reduction in diastolic Ca2+ reuptake into SR post MI. Second, male ERβ-OE revealed attenuated cardiac fibrosis in the remote LV tissue and expression of fibrosis markers, such as collagen type I and III, periostin and miRNA-21. Thus ERβ-OE led to improved survival, reduced maladaptive remodeling, improved cardiac function, and less HF development after MI in both sexes. These effects seem to be related, at least in part, to a better maintenance of Ca2+ cycling and a lower induction of cardiac fibrosis after MI.
FIGURE 6.Generation of an inducible cardiac-specific overexpression (OE) mouse model of ERβ. Crossing of a transactivator (tTA) mouse line that expresses a transactivator under a cardiomyocyte-specific promoter, i.e., myosin heavy chain (MHC), with a responder mouse that expresses ERβ under the control of the transactivator results in a double-transgenic (DT) ERβOE mouse line.
9. The four core genotype model: chromosomal versus hormonal effects
Even though a lot of meaningful results have been obtained by the aforementioned animal models, a lot of questions still remain open. Most studies have suggested that female sex, as well as estrogens, are protective. This has led the field to develop more sophisticated models to address whether differences in chromosomes or hormones mainly account for the observed sex differences. To this extent, the four core genotype (FCG) model has been developed and suggested that chromosomes, as well as hormones, play a major role and interact in a complicated manner.
In the FCG mouse model, gonadal sex and sex chromosome complement are uncoupled (90). In particular, the testis-determining gene, Sry, has been moved from the Y chromosome to an autosome. Consequently, FCG mice comprise XX and XY gonadal males (XXM and XYM) and XX and XY gonadal females (XXF and XYF) (243). Therefore, differences can be studied in XX versus XY mice that have the same sexual phenotype, same type of gonads, and same sex hormone levels. Consequently, it can be used to dissociate the effects of sex hormones from the sex chromosomes.
Sex hormones may exert acute effects, the so-called activational effects (8). On the other hand, sex hormones may also induce longer lasting effects, such as changes in DNA structure and chromatin remodeling, which are the so-called organizational effects (8). Androgens and estrogens together with their receptors induce sex-specific DNA modifications by recruiting DNA modifying enzymes, which lead to the induction of activational or repressive marks on target genes, ultimately regulating their expression. These marks can persist in the absence of sex hormones during cell division, thereby transmitting epigenetic regulation over the life span of a cell or an organism. If animals are gonadectomized, organizational and activational effects of sex hormones can be distinguished (9). Gonadectomy equalizes the levels of gonadal hormones among groups. Under these conditions, when effects of gonadal sex are found, they are most likely caused by organizational effects of gonadal hormones, i.e., effects of gonads in early development, before gonadectomy (9).
The FCG mouse model has been used to investigate protective mechanisms from cardiac ischemia/reperfusion injury and the role of sex chromosomes (224). It was shown that XX male and female mice are more susceptible to this type of injury compared with XY male and female mice attributed to the extra copy of X chromosome and not the absence of the Y chromosome (224). Similarly, the hearts of XY male and female mice were less vulnerable to coxsackie virus B3 than those of XX male and female mice, thereby developing significantly less myocarditis than XX mice (337). However, the levels of myocarditis measured were significantly higher in XY male mice compared with XX female mice, but the opposite occurred in XY male and XX female mice, which were gonadectomized, thereby suggesting a complex interaction of sex chromosome complement with sex hormones.
D. Sex Differences in Biological Processes in Cardiovascular Cells
As a result of the function of sex chromosomes, sex hormones, and their receptors, several cellular processes differ between male and female cells. Here, we discuss ion handling and rhythmicity, mitochondrial function and energy metabolism, cardiac lipid and carbohydrate metabolism, cell death and survival, inflammation, fibrosis, vascular function, and gene expression. An overview is given in Figure 7.
FIGURE 7.Interaction of sex hormones with intracellular signaling relevant for the cardiovascular system. Selected abbreviations: PKB, protein kinase B; CnA-β, calcineurin Aβ; ER, estrogen receptor; ERK, extracellular signal-regulated kinase; GSK3β, glycogen synthase kinase 3β; HSL, hormone-sensitive lipase; IGF, insulin-like growth factor; JNK, c-jun-NH2-terminal kinase; LTCC, L-type Ca2+ channel; MAPK, mitogen-activated protein kinase; MCIP, myocyte-enriched calcineurin interactin protein; MEF2, myocyte enhancer factor 2; mTOR, mammalian target of rapamycin; NFAT, nuclear factor of activated T-cells; NF-κB, nuclear factor κ, B cells; NOS, nitric oxide synthase; PGC-1, peroxisome proliferator-activated receptor gamma coactivator 1; PI3K, phosphatidylinositol 3-kinase; PTEN, phosphatase and tensin homolog.
1. Ion handling and rhythmicity
There are several electrophysiological differences between men and women, including faster resting heart rates and longer rate-corrected QT intervals in women than in men (2, 263, 325). Women are also more susceptible to drug-induced QT prolongation and torsades de pointes (100, 220, 333). On the other hand, ventricular arrhythmias and sudden cardiac death are more common in men than in women, and male sex is a strong predictor of risk for atrial fibrillation (6, 14, 28, 50, 180). These phenotypes can be caused by pathological mechanisms affecting ion channels or factors related to regulatory pathways of ion channels in a sex-specific manner.
In particular, there are marked sex differences in Ca2+ handling. These are expected to be due to sex-specific Ca2+ homeostasis protein regulation, thereby altering functional outcomes, such as force development and relaxation (72). To this extent, female rodents demonstrate smaller Ca2+ transients and have reduced cardiac reserve, smaller changes in shortening, and less SR Ca2+ loading compared with males in response to β-adrenergic stimulation (64, 411). Mechanistically, these sex differences are partly mediated by the cAMP/protein kinase A (PKA) pathway (299), which may be due to the function of sex chromosomes or sex hormones.
In particular, SR Ca2+ content and peak Ca2+ transient amplitudes are significantly increased in OVX rodents compared with sham-operated rodents, while these effects are reversed by E2 treatment (84, 114, 204, 239). It has also been shown that Ca2+ homeostasis is further regulated as a function of the estrous cycle (240).
In addition, S-nitrosylation of the L-type Ca2+ channel is increased in female hearts following ischemia/reperfusion, leading to reduced Ca2+ entry and SR loading, thereby reducing tissue injury (375). Conversely, OVX leads to decreased cardiac endothelial NO synthase levels and increased expression of the L-type Ca2+ channel in rats, while E2 treatment reversed these effects (71, 288). Furthermore, E2 reduced the Ca2+ current and intracellular Ca2+ concentration in guinea pig cardiomyocytes (172), while cardiomyocytes from ERKO mice exhibited an increased expression and activity of the L-type Ca2+ channel (174).
The sensitivity of myofilament response to Ca2+ is regulated by estrogen administration (49, 71, 384). In particular, myofilament Ca2+ sensitivity is increased in hearts of OVX rats compared with sham-operated rats, while this effect is reversed by E2 treatment (49, 422, 423). Similarly, CaV1.2 protein levels and the gain of excitation-contraction coupling are higher in hearts from OVX rats compared with those of sham-operated rats (71, 114).
Testosterone also modulates ion channel homeostasis. For example, in isolated cardiomyocytes, testosterone rapidly stimulates intracellular Ca2+ activating phospholipase C and the inositol-3-phosphate pathway (403). Gonadectomy leads to the downregulation of Ca2+ channel regulatory proteins in the hearts of male rodents, which is reversed by testosterone treatment (131–132). Along this line, L- and T-type Ca2+ currents are induced in neonatal rat cardiomyocytes treated with testosterone in an AR-dependent manner (110, 266). However, chronic testosterone treatment can have opposite effects from acute testosterone treatment on L- and T-type Ca2+ channels and Ca2+ sparks (110, 266). These contradictory effects are currently poorly understood, and the role of aromatase is not clear. In chronic testosterone treatment, aromatase converting testosterone to estrogen might contribute to the latter repressing L- and T-type Ca2+ channels. Testosterone may also shorten action potential duration by activating potassium channels leading to shorter QT interval (22, 232).
Female sex is associated with greater levels of the sarcolemmal and mitochondrial ATP-sensitive potassium (KATP) channels, whose inhibition during ischemia increases the degree of tissue injury (175, 323). Interestingly, E2 treatment led to increased sarcolemmal KATP channel levels and to the protection of cardiac cells against hypoxia/reoxygenation injury (218, 322).
Furthermore, E2 leading to the increased activity of large-conductance Ca2+-activated K+ channels in mitochondria of rat cardiomyocytes (292) and to the modulation of K+ currents in male diabetic rat cardiomyocytes by interacting with angiotensin (358) exerts antiarrhythmic effects. In fact, estrogen has been demonstrated to attenuate the occurrence of ischemia/reperfusion-induced arrhythmias through the modulation of NO and Ca2+-activated potassium channels (284, 420). However, the antiarrhythmic actions of acute E2 treatment are more prominent in females than in males (315).
Several genetic models of ion handling proteins also exhibit major sex differences. For example, deletion of the Fkbp1b gene, a SR protein regulating the ryanodine Ca2+ release channels, led to myocardial hypertrophy in males but not in females (436). Similarly, ablation of phospholamban (PLN) exacerbated ischemic injury to a higher extent in males than females (82). On the other hand, overexpression of PLN led to ventricular hypertrophy and mortality in male mice aged 15 mo, while there were no such effects in age-matched female mice (87).
2. Mitochondrial function and energy metabolism
Female mitochondria exhibit lower oxidative damage under stress underlain by higher antioxidant gene expression than male mitochondria (39). In cardiomyopathy induced by doxorubicin, which is a member of the anthracycline family and an effective broad-spectrum chemotherapeutic drug targeting topoisomerase-II to trigger cell death (382), male mice exhibit significantly higher mortality than female mice (277). The underlying mechanisms seem to include significant decreases in the levels of total adenosine monophosphate-activated protein kinase and in markers of mitochondrial biogenesis and cardiolipin content only in males (277). In vascular smooth muscle cells isolated from rat aorta, female cells show better survival and seem to be more resistant to oxidative stress than those isolated from males (253).
In addition, female mice displayed improved recovery of cardiac mitochondrial respiratory function and higher ATP levels versus males in response to acute oxygen deprivation, underlain by diminished transcript levels of Ppara, muscle-type carnitine palmitoyltransferase 1 (Cpt1b) and pyruvate dehydrogenase kinase 4 (Pdk4) (111). Cardiac-specific expression of a phosphorylation-deficient cyclic nucleotide regulatory element binding protein (Creb) mutant in transgenic mice led to significantly higher mortality and contractile dysfunction in female compared with male mice, which were underlain by a significant decrease in mitochondrial density and deterioration of mitochondrial structure, increased ROS were accompanied by decreases in the expression/activity of the mitochondrial antioxidants manganese superoxide dismutase (MnSOD) and glutathione peroxidase in female mice only (421). Sex differences in the phosphorylation of mitochondrial proteins, such as aldehyde dehydrogenase-2 (ALDH2), also play a major role in mitochondrial sex differences resulting in reduced production of ROS and cardioprotection in females (208).
Mitochondrial function and energy metabolism are also regulated by estrogen (155, 218, 369). Such estrogenic actions are expected to be mediated by the ER, as functional ERα and ERβ have been documented in mitochondria (66, 440). Subsequently, E2 may affect the expression of nuclear and mitochondrial DNA encoded proteins, lead to posttranslational modifications of mitochondrial proteins, and control free radical production, thereby affecting mitochondrial function and biogenesis (Figure 8).
FIGURE 8.Hypothetical scheme for E2/ER-induced activation of PI3K/PKB and p38-MAPK pathways in female hearts leading to increased mitochondrial biogenesis and function.
In particular, E2 treatment reversed the mitochondrial dysfunction associated with menopause and ovariectomy (324, 376). Notably, estrogen regulates the key activator of mitochondrial biogenesis and function peroxisome proliferator-activated receptor γ coactivator 1α (PGC-1α) (153, 154, 432). We postulate that a female-specific interaction between E2/ER and PGC-1α may at least partially maintain mitochondrial function in female hearts (Figure 8). In pathological LV hypertrophy, genome-wide expression profiling revealed less downregulation of metabolic genes dependent on PGC-1α in female hearts than in male hearts (119, 432). PGC-1α is located downstream of HDAC, and it is therefore of interest to study sex-specific HDAC activation. In a transgenic model of HDAC5, where myocyte enhancer factor-2 (MEF2) was repressed, all male mice died early, while female mice survived (85). In particular, male mice exhibited severe defects in mitochondrial number and structure, as well as a repression of PGC-1α and mitochondrial enzymes (85). On the other hand, female mice survived without mitochondrial damage, suggesting that female mice maintain their PGC-1α levels independent of MEF2.
Estrogen treatment of OVX rodents exposed to ischemia/reperfusion injury also restored mitochondrial respiratory function and attenuated mitochondrial and ultrastructural damage in an ERα-dependent manner (444, 445). These protective effects are also associated with E2-dependent induction of proteins involved in the activity of oxidative phosphorylation (OXPHOS) or tricarboxylic citric acid (TCA) cycle (162, 334). In fact, the E2/ER signaling axis is expected to play a major role in the regulation of OXPHOS by enhancing the expression of several nuclear- and mitochondrial-encoded OXPHOS proteins (65, 155) followed by direct binding of the ER to mitochondrial DNA and mitochondrial estrogen response elements in an E2-dependent manner (67, 334). Consequently, these ER-mediated effects on OXPHOS protein regulation protect against mitochondrial and cellular injury induced by oxidative stress (267, 369).
The protective actions of the E2/ER axis against oxidative stress may also be mediated through mechanisms exerting direct effects on mitochondrial enzymes. In particular, E2 induced the expression and activity of superoxide dismutase (SOD) in vascular smooth muscle cells, thereby diminishing the production of ROS (373). Along this line, E2 stimulated the activity of the mitochondrial antioxidant MnSOD and repressed superoxide generation in neonatal rat cardiomyocytes subjected to oxidative stress (229). In OVX Dahl salt-sensitive rats, the levels of the antioxidative enzymes glutathione peroxidase 1 and 4 that scavenge hydrogen peroxide were reduced, while E2 treatment reversed this effect (447). The induction of these mitochondrial antioxidants by the E2/ER axis detoxifies ROS and confers protection against ROS-induced cytotoxicity (65). E2-dependent posttranslational modifications in the heart, such as S-nitrosylation of several proteins, including mitochondrial F1-ATPase (226), have also been reported, thereby modulating mitochondrial bioenergetics. Collectively, these data exhibit the mechanisms that contribute to a sex-specific mitochondrial protein composition with higher levels of enzymes of the respiratory chain in females. Recent resources and tools, such as a functionally validated metabolic network of the human cardiomyocyte (191), will enable further studies of the mechanisms accounting for sex- and sex hormone-dependent regulation of cellular metabolic processes crucial for the maintenance of cardiovascular function.
3. Cardiac lipid and carbohydrate metabolism
Sex differences in cardiovascular pathophysiological processes could also be the consequence of sex hormone-specific alterations in glucose and fatty acid supply and/or changes in the uptake and catabolism of energy substrates in cardiovascular cells. In the cardiomyocyte, fatty acid uptake is mediated by the membrane transporter CD36 and fatty acid transport proteins FATP (237), which seem to be under the regulation of estrogen (199, 381). Free fatty acid levels are also kept low by estrogen (170), and it is expected that E2 directs fatty acids to beta oxidation, ultimately producing energy for high demand cardiac functions (245, 377).
Male transgenic mice lacking Ppara and overexpressing lipoprotein lipase (Lpl) in cardiac muscle displayed increased mortality, while their female counterparts were not affected (285). Importantly, E2 treatment rescued the lethal phenotype of mice lacking Ppara (95). Deletion of the Ppara gene resulted in massive cardiac lipid accumulation and death in all males with E2 being able to rescue this phenotype, while merely one-quarter of the females were affected (95). Notably, a reduction in lipid accumulation by estrogen in human macrophages has been reported (259). Estrogen has also been associated with lowered LDL cholesterol and raised high-density lipoprotein (HDL) cholesterol levels (261, 414), further implicating estrogen signaling in the regulation of lipid metabolism.
Sex-specific regulation of adipose triglyceride lipase (ATGL) and hormone-sensitive lipase contributes further to sex differences in energy metabolism (270, 278). Testosterone has also been shown to affect cardiomyocyte metabolism regulating the activity of hormone-sensitive lipase, thereby altering cardiac balance between lipid and carbohydrate metabolism (212). Notably, female sex is associated with increased rates of myocardial fatty acid oxidation in humans (310) and exercising rodents (120). Female rats also have higher cardiac docosahexaenoic acid (DHA, 22:6n-3) levels than males, but the expression of enzymes involved in the biosynthesis of docosahexaenoic acid from short-chain n-3 polyunsaturated fatty acids does not differ between the sexes (194), calling for a better understanding of the underlying mechanisms leading to cardiovascular sex differences.
Eicosanoid pathways are also differentially activated between males and females, leading to female protection via epoxyeicosatrienoic acids (EET) and male maladaptation via hydroxyeicosatetraenoic acid (HETE) (149, 278, 428). These pathways also seem to be involved in the actions of testosterone that lead to increased blood pressure in rats, while castration or blockade of the AR attenuate the development of hypertension (125, 158, 327, 328). In male mice with elevated plasma androgens, the CYP4A12 enzyme was induced and caused ω-hydroxylation of arachidonic acid and formation of 20-HETE leading to hypertension (150). Castration prevented the hypertension and enzyme induction, while testosterone treatment restored the hypertension and CYP4A12 enzyme activity (150).
4. Cell death and survival
Cell death also occurs in a sex-specific manner, where cardiomyocyte loss increases in men with aging but not in women (293), and cardiomyocyte death is higher in the male failing heart than in the female failing heart (137). Notably, young women have higher levels of nuclear-localized phosphorylated-PKB compared with aged men or postmenopausal women, which might contribute to the mechanisms conferring protection against cell death in young women (51). The female heart seems to be better protected also against ischemia-induced apoptosis. In particular, the peri-infarcted area displays a 10 times higher apoptosis rate in men than in women (32). In a rabbit ischemia/reperfusion model, apoptotic cell death was significantly higher in males than females (41). Mice subjected to ischemia/reperfusion demonstrated similar responses, where female hearts showed less necrosis compared with male hearts (123, 419). The mechanisms conferring the advantage to females seem to include male-specific reduction of the antiapoptotic protein Bcl2 and female-specific reduction of the proapoptotic protein Bax (63). Furthermore, genetic deletion of mammalian target of rapamycin complex 1 (mTORC1) downstream signaling molecule ribosomal protein S6 kinase 1 (Rps6kb1) inhibits cell senescence and favors longevity restricted to female mice (354). Consistent with the genetic deletion of Rps6kb1, pharmacological intervention with rapamycin has most prominent effects in female mice (147).
Sex hormones also exert antiapoptotic effects mediated through a number of different mechanisms. E2 treatment of OVX mice with MI reduced cardiomyocyte apoptosis (400). Such antiapoptotic effects of E2 in cardiomyocytes are partly mediated by activation of PI3K/PKB signaling (303), leading, for example, to the improvement of cardiac function following trauma-hemorrhage (441). E2 treatment also induces the nuclear localization of phosphorylated-PKB in cultured cardiomyocytes (51). The antiapoptotic effects of estrogen may also be mediated through the repression of TNF-α in the heart (438). Furthermore, E2 prevented cardiomyocyte apoptosis via the modulation of p38α and -β MAPKs in cultured rat cardiomyocytes (193), along with inhibiting p53 and its translocation to the mitochondria (228). Interestingly, estrogen preserved the integrity of ischemic tissue by augmenting the mobilization and incorporation of bone marrow-derived endothelial progenitor cells into sites of neovascularization (165). Studies with OVX rats and isolated perfused hearts from OVX rats showed that acute administration of E2 and ERα agonist significantly reduced oxidant stress and necrosis following ischemia/reperfusion (169, 287). Together, regulation of these factors by estrogens is a set of different mechanisms mediating antiapoptotic effects in a sex-specific manner.
Testosterone-induced increased PKB phosphorylation has also been reported and may be involved in the observed antiapoptotic effects of testosterone against doxorubicin-induced cardiotoxicity (159). However, depending on the model, the effects of testosterone may be opposing. In fact, in an ischemia/reperfusion model, acute testosterone infusion led to the downregulation of PKB and lower levels of MnSOD (157). Similarly, testosterone led to aggravated cardiac damage in both males and females exposed to ischemia/reperfusion injury, and the mechanism includes the downregulation of the antiapoptotic protein Bcl-xL (213) and the upregulation of the proinflammatory mediators TNF-α, IL-1β, and IL-6 (418).
Sex differences in autophagy have also been reported, where males display a lower level of autophagy than females (77). Stress seems to induce autophagy activity at a higher level in female cells compared with male cells (372). In rat neuronal cells, nutrient deprivation-induced autophagy death was higher in males than in females, with neurons from females surviving longer (101). Evidence for the crosstalk between the E2/ER axis and the autophagy pathway has been provided through the association of the autophagy mediator Beclin-1 with ERα downregulating E2 signaling, thereby contributing to the development of E2 resistance (173). However, the E2- and sex-specific regulation of autophagy in cardiac cells is currently not understood. In fact, a recent study suggested that the male heart has major constitutive autophagy (52).
E2 further activates signaling pathways that regulate protein metabolism (274), thereby regulating protein synthesis and protein degradation (178). In fact, estrogen regulates cardiomyocyte contractile function modifying the ubiquitin-proteasome system (UPS) (183). Another important effect of estrogen is the degradation of calcineurin, which leads to the attenuation of LV and cardiomyocyte hypertrophy by an ER-dependent pathway (96).
5. Inflammation
Men and women differ in the activation of adaptive and innate immune system. Women appear to be more efficient in fighting a primary pathogenic insult, but on the other hand they are more prone to the development of autoimmunity. A link between the activity of the adaptive immune system and cardiovascular function is illustrated in autoimmune diseases with severe cardiovascular manifestations, such as systemic sclerosis. Cytokine receptors and parts of the inflammasome are regulated in a sex-specific manner. These complex interactions may modify inflammatory reactions in the heart and the vasculature.
In animal models, females seem to be protected against tissue injury through decreased inflammatory cytokine production, such as TNF-α, IL-1, and IL-6 expression (113, 416, 438). As with other transgenic models described previously, overexpression of Tnf leads to increased mortality and HF to a greater extent in males than in females (167, 177). The receptor activator of NF-κB ligand (RANKL), its receptor RANK, and the decoy receptor osteoprotegerin also appear to be involved in the inflammatory process (146, 176, 350). RANK expression has been reported in the heart, which is actually one of the highest producing tissues of osteoprotegerin (TNFRSF11B), which, in turn, is expressed in a sex-specific manner (164). Together, these sex differences in inflammatory mediators play a major role in sex-specific inflammatory responses.
Estrogen also exerts a key role in immune responses, regulating proinflammatory cytokine expression through monocyte and macrophage regulation and affecting the expression of target genes (202, 388). In fact, cardioprotective effects of E2 on neutrophil infiltration, oxidant stress, and necrosis in an ER-dependent manner following ischemia/reperfusion have been reported (169). Notably, ERβ seems to be necessary for the strict regulation of the inflammatory response to cardiac insults (186). Monocyte chemoattractant protein (MCP)-1-dependent ROS production in monocytes is closely associated with LV dysfunction, and E2 is directly involved in the regulation of the MCP-1 gene (437). In OVX rats subjected to ischemia/reperfusion, a marked increase in the proinflammatory cytokine TNF-α occurred, while the treatment with E2 reduced TNF-α levels in the myocardium and further decreased its release after ischemia/reperfusion, which was associated with improved functional recovery and a decrease in markers of tissue injury and apoptosis (438).
Based on these findings, we postulate that estrogen and the ER may partly exert their effects via the modulation of key inflammatory mediators and cells, including mast cells, macrophages, and T cells (Figure 9). Along this line, in a KO model of ERβ under chronic pressure overload with evident sex differences (119), the presence of ERβ was necessary for the inhibition of inflammatory factors and ROS-mediated NF-κB regulation, and for the maintenance of the cytochrome P-450 pathway (186). Interestingly, NF-κB inhibits ERα transcription, but NF-κB may in turn be inhibited by the E2/ER axis (249). Other anti-inflammatory actions of estrogen may include the rescue of PPARγ-expression (388), which in turn functions as a transcriptional repressor of proinflammatory signaling pathways. In contrast, the actions of testosterone are rather conflicting, and it apparently activates the transcription factor NF-κB contributing to inflammatory mechanisms (316).
FIGURE 9.Estrogen regulates the inflammatory response. Low E2 levels induce a Th1 response leading to a proinflammatory response (A), while high E2 levels induce a Th2 response leading to an anti-inflammatory response (B).
6. Fibrosis
Profibrotic pathways exacerbate cardiovascular disease and lead to severe dysfunction. Recent studies have demonstrated that male patients with AS have increased levels of fibrosis mediators compared with female patients (184, 311). ERα, ERβ, and AR control fibrotic pathways, collagen, and matrix-metalloproteinase synthesis in a sex-specific manner (Figure 10). In addition, estrogen attenuates the development of cardiac fibrosis. This could be through direct effects of estrogen inhibiting collagen synthesis and directly regulating collagen type I and III levels (103, 251, 312, 450), along with matrix metalloproteinase expression via activation of the ERα and MAPK-ERK1/2 signaling pathway (246). E2-dependent induction of the progesterone receptor might also contribute to the antifibrotic actions of estrogen (182). Furthermore, the E2/ER axis regulates a network of miRNAs, thereby affecting fibrosis (320). Cardiomyocyte-specific ERα expression enhances angiogenesis and the reduction of fibrosis following myocardial infarction (250). Interestingly, the genetic deletion of the AR leads to the exacerbation of angiotensin II-induced cardiac dysfunction and fibrosis (160).
FIGURE 10.Interaction of sex hormones with fibrotic pathways. Sex hormones (SH) bound to their receptors (SHR) interact with other signaling pathways or directly target fibrosis-associated genes in a sex-specific manner. Consequently, there is a stronger transcriptional activation of collagen synthesis in males vs. females, thereby leading to higher collagen deposition and degree of fibrosis in male than in female hearts.
7. Sex differences in vascular function and gene expression
There are major physiological differences between males and females in vascular function, in aging arteries, and in disease. Atherosclerosis affects men earlier than women, but microvascular disease and dysfunction are more prominent in women. Notably, microvascular dysfunction may play a major role in the development of diastolic dysfunction. Patients with LV hypertrophy, a precursor of HF, often show an impaired coronary reserve despite angiographically normal coronary arteries (321). This microvascular dysfunction occurs particularly following menopause and has been linked to sex differences in chronic ischemia and diastolic HF (23, 256).
Research on sex differences in the vasculature has been so far largely focused on the effect of sex hormones. However, some studies have also considered the effect of sex beyond the effects of sex hormones when analyzing sex-specific gene regulation (319). The sex-specific effects of estrogen and testosterone on cardiovascular risk, the direct vascular effects of these sex hormones, and how these effects influence the development of atherosclerosis have been reviewed in detail previously (410). Here, we discuss a few interesting findings.
Estrogen attenuates atherosclerotic plaque progression by inducing prostacyclin production through the activation of cyclooxygenase-2 (109); it inhibits smooth muscle cell proliferation and matrix deposition (298); and it promotes angiogenesis (273) and reendothelialization (43, 203). Furthermore, estrogen treatment restores endothelium-dependent NO-mediated vasorelaxation and endothelial NO synthase expression (69, 340, 430). The vasodilatory effects of estrogen may also be partially mediated through its inhibitory actions on the renin-angiotensin system (42, 124) or its inducing effects on epoxyeicosatrienoic acids and vasodilator metabolites of cytochrome P-450 (156, 404). Estrogen treatment of OVX mice also rescued vascular PPARγ expression; reduced ROS generation, monocyte recruitment, and atherosclerotic lesion formation; and improved endothelial function (388). A similar E2 treatment of OVX mice abolished progressive growth and decreased severity of angiotensin II-induced abdominal aortic aneurysms through mechanisms acting on smooth muscle cell α-actin and transforming growth factor-β (TGF-β) (383). A study employing ERKO and BERKO mice revealed that ERα- and ERβ-dependent pathways regulate distinct and largely nonoverlapping sets of genes in aortas (291). Notably, while ERα seems to be required for most of the estrogen-mediated increase in gene expression, ERβ mediates the large majority of estrogen-dependent decrease in gene expression (291).
Hormonal regulation of NO production via endothelial NO synthase by estrogen or testosterone has implications in maintaining vascular health in combination with cardiovascular risk factors, such as diabetes and metabolic disorders (105). Reduced bioavailability and/or responsiveness to endogenously produced NO contributes to the development of cardiovascular disease. Interestingly, testosterone also appears to induce rapid vasorelaxation in both large arteries and smaller resistance vessels (308). Conversely, low plasma free testosterone levels are associated with endothelial dysfunction, while testosterone treatment leads to a rapid endothelium-dependent vasodilating effect (5, 443). The dependence on the AR of the testosterone-induced release of NO leading to vasorelaxation is not clear, as conflicting data have been reported (130, 161). However, the antiandrogen compound flutamide, which was used in those studies, has additional effects beyond AR blockade, probably mediated by a rapid-acting AR (24–25).
V. LIMITATIONS AND IMPLICATIONS FOR FUTURE RESEARCH
There is an ongoing debate whether experimental animals are informative models of human sex differences. Furthermore, as recently pointed out, studies of sex differences in permanent cell lines may not reflect sex differences in humans, since sex chromosomes may become modified (336). However, this may be overcome by switching to freshly isolated primary cells or by testing cell lines for sex chromosomes before the study of sex differences.
It is well known that sex differences in animal models mimic those in humans imperfectly. Age, duration of disease exposure, sex hormone and growth hormone profiles, many forms of stressors, and other factors differ between animal models and humans. Furthermore, menopause is a human phenomenon that is difficult to study in animal models, and surgical ovariectomy is an imperfect proxy for physiological menopause. Other models of menopause, such as slow chemical destruction of the ovaries, have been developed to mimic the human situation better, but they still have limitations (181). Nevertheless, these limitations do not apply only to the case of the investigation of sex differences, but rather to the whole research spectrum. Despite these limitations, animal models have been used successfully for drug development for decades. Consequently, we believe that animal models have their value for the understanding of human pathophysiology, including sex differences, and hold the potential for translational use, particularly when results are interpreted with caution and the model-inherent limitations are taken into consideration.
To improve future understanding of the role of sex in pathophysiology, we put forward that investigations in animal models are based on precise hypotheses on sex differences and include all possible confounders, such as housing, diet, environment, stress, and so on (317). This is, however, a requirement that does not apply only to the study of sex differences. Recent studies have shown that, against general belief, variability in female rodents is not bigger than in males, even when females have a proper hormonal cycle. A large amount of variability is due to housing conditions (317). Investigators have to consider this. Effect size may be different between both sexes, but such a finding may be very important for clinical translation and should be followed.
In human studies, various investigations have shown that abnormalities of sex hormone status may influence disease patterns. However, this has not received enough attention so far, and we put forward that hormonal status should be better documented and controlled in clinical studies. This refers to abnormal sex hormone profiles, such as in hypothalamic or stress-induced hypogonadism, polycystic ovary syndrome (PCOS), late menarche, early menopause, andropause, and other forms of sex hormone abnormalities (168, 301, 344). The same is true for pregnancy conditions and complications, particularly eclampsia, pregnancy-induced diabetes, and hypertension (329). Obesity and proinflammatory states, physiological and psychological stressors, environmental toxins or endocrine disruptors, such as bisphenols, affect sex hormone profiles in men and women and should be included in patient documentation (168). Transgender individuals frequently exhibit cardio-metabolic disease, supporting the view that abnormalities in sex hormones lead to CVD. Finally, measuring a proxy of self-estimated gender, which may be different from biological sex, can provide a novel cardiovascular risk factor (305). Considering these variables in clinical and epidemiological studies may be very important steps towards truly personalized medicine or precision medicine.
VI. CONCLUSION
Sex differences have consistently been confirmed throughout a large spectrum of experimental and clinical studies, in different species, and in (patho)physiological conditions. However, a more detailed understanding of sex differences and their underlying mechanisms is needed to design new drugs that target sex-specific cardiovascular mechanisms and affect phenotypes. The comparison of both sexes is essential for the identification of protective or maladaptive mechanisms. A knowledge of such mechanisms in gene transcription, intracellular signaling, organelle function, and interorgan cross-talk will reveal new targets for the activation or inhibition of specific aspects of the cardiovascular system that are linked to sex hormones or other differences between males and females.
GRANTS
We are grateful to the German Centre for Cardiovascular Research (DZHK), German Federal Ministry of Education and Research (BMBF), German Research Foundation (DFG), European Union, and the Margarete Ammon Foundation for financial support.
DISCLOSURES
No conflicts of interest, financial or otherwise, are declared by the authors.
acknowledgments
We thank the members of our working group M. L. Barcena de Arellano, E. Dworatzek and Y. Ladilov for help with Figures 9 and 10 and for valuable comments. We acknowledge A. Kühne for excellent work with the references.
Address for reprint requests and other correspondence: G. Kararigas, Institute of Gender in Medicine & Center for Cardiovascular Research, Charite University Hospital, Hessische Str 3–4, 10115 Berlin, Germany (e-mail: george.
REFERENCES
- 1. . The AF-1 activation function of estrogen receptor alpha is necessary and sufficient for uterine epithelial cell proliferation in vivo. Endocrinology 154: 2222–2233, 2013.
Crossref | PubMed | ISI | Google Scholar - 2. . The normal duration of the electrocardiographic ventricular complex. J Clin Invest 15: 335–342, 1936.
Crossref | PubMed | Google Scholar - 3. . Mutation of the palmitoylation site of estrogen receptor alpha in vivo reveals tissue-specific roles for membrane versus nuclear actions. Proc Natl Acad Sci USA 111: E283–290, 2014.
Crossref | PubMed | ISI | Google Scholar - 4. . Heavy resistance exercise training and skeletal muscle androgen receptor expression in younger and older men. Steroids 76: 183–192, 2011.
Crossref | PubMed | ISI | Google Scholar - 5. . Low testosterone level is an independent determinant of endothelial dysfunction in men. Hypertens Res 30: 1029–1034, 2007.
Crossref | PubMed | ISI | Google Scholar - 6. . Sex differences in cardiac arrest survivors. Circulation 93: 1170–1176, 1996.
Crossref | PubMed | ISI | Google Scholar - 7. . Estrogen receptor alpha AF-2 mutation results in antagonist reversal and reveals tissue selective function of estrogen receptor modulators. Proc Natl Acad Sci USA 108: 14986–14991, 2011.
Crossref | PubMed | ISI | Google Scholar - 8. . The organizational-activational hypothesis as the foundation for a unified theory of sexual differentiation of all mammalian tissues. Horm Behav 55: 570–578, 2009.
Crossref | PubMed | ISI | Google Scholar - 9. . What a difference an X or Y makes: sex chromosomes, gene dose, and epigenetics in sexual differentiation. Handb Exp Pharmacol 67–88, 2012.
Google Scholar - 10. . Epidemiology of idiopathic cardiomyopathies in children and adolescents. A nationwide study in Finland. Am J Epidemiol 146: 385–393, 1997.
Crossref | PubMed | ISI | Google Scholar - 11. . Structure-function relationship of estrogen receptor alpha and beta: impact on human health. Mol Aspects Med 27: 299–402, 2006.
Crossref | PubMed | Google Scholar - 12. . Epigenetic organization of brain sex differences and juvenile social play behavior. Horm Behav 59: 358–363, 2011.
Crossref | PubMed | ISI | Google Scholar - 13. . Impact of chamber geometry and gender on left ventricular systolic function in patients >60 years of age with aortic stenosis. Am J Cardiol 74: 794–798, 1994.
Crossref | PubMed | ISI | Google Scholar - 14.
AVID . A comparison of antiarrhythmic-drug therapy with implantable defibrillators in patients resuscitated from near-fatal ventricular arrhythmias. The Antiarrhythmics versus Implantable Defibrillators (AVID) Investigators. N Engl J Med 337: 1576–1583, 1997.
Crossref | PubMed | ISI | Google Scholar - 15. . Role of 5alpha-reductase inhibitors in prostate cancer prevention and treatment. Urology 79: 1197–1205, 2012.
Crossref | PubMed | ISI | Google Scholar - 16. . 17Beta-estradiol antagonizes cardiomyocyte hypertrophy by autocrine/paracrine stimulation of a guanylyl cyclase A receptor-cyclic guanosine monophosphate-dependent protein kinase pathway. Circulation 109: 269–276, 2004.
Crossref | PubMed | ISI | Google Scholar - 17. . Estrogen receptor beta protects the murine heart against left ventricular hypertrophy. Arterioscler Thromb Vasc Biol 26: 1524–1530, 2006.
Crossref | PubMed | ISI | Google Scholar - 18. . Oestrogen modulates cardiac ischaemic remodelling through oestrogen receptor-specific mechanisms. Acta Physiol 189: 23–31, 2007.
Crossref | PubMed | ISI | Google Scholar - 19. . Gender differences in cardioprotection against ischemia/reperfusion injury in adult rat hearts: focus on Akt and protein kinase C signaling. J Pharmacol Exp Ther 315: 1125–1135, 2005.
Crossref | PubMed | ISI | Google Scholar - 20. . Cardiomyopathy in western Denmark. Br Heart J 52: 327–331, 1984.
Crossref | PubMed | Google Scholar - 21. . Long-term anabolic-androgenic steroid use is associated with left ventricular dysfunction. Circ Heart Fail 3: 472–476, 2010.
Crossref | PubMed | ISI | Google Scholar - 22. . Nontranscriptional regulation of cardiac repolarization currents by testosterone. Circulation 112: 1701–1710, 2005.
Crossref | PubMed | ISI | Google Scholar - 23. ,
Wise Investigators . Insights from the NHLBI-Sponsored Women's Ischemia Syndrome Evaluation (WISE) Study. Part II: gender differences in presentation, diagnosis, and outcome with regard to gender-based pathophysiology of atherosclerosis and macrovascular and microvascular coronary disease. J Am Coll Cardiol 47: S21–29, 2006.
PubMed | ISI | Google Scholar - 24. . Abolition of end-organ damage by antiandrogen treatment in female hypertensive transgenic rats. Hypertension 41: 830–833, 2003.
Crossref | PubMed | ISI | Google Scholar - 25. . Abolition of hypertension-induced end-organ damage by androgen receptor blockade in transgenic rats harboring the mouse ren-2 gene. J Am Soc Nephrol 13: 2681–2687, 2002.
Crossref | PubMed | ISI | Google Scholar - 26. . Alternative initiation of translation accounts for a 67/45 kDa dimorphism of the human estrogen receptor ERalpha. Biochem Biophys Res Commun 257: 84–88, 1999.
Crossref | PubMed | ISI | Google Scholar - 27. . Aromatase deficiency confers paradoxical postischemic cardioprotection. Endocrinology 152: 4937–4947, 2011.
Crossref | PubMed | ISI | Google Scholar - 28. . Impact of atrial fibrillation on the risk of death: the Framingham Heart Study. Circulation 98: 946–952, 1998.
Crossref | PubMed | ISI | Google Scholar - 29. . Sex differences in mortality following acute coronary syndromes. JAMA 302: 874–882, 2009.
Crossref | PubMed | ISI | Google Scholar - 30. . Influence of sex hormones and phytoestrogens on heart disease in men and women. Womens Health 6: 77–95, 2010.
Google Scholar - 31. . The transactivating function 1 of estrogen receptor alpha is dispensable for the vasculoprotective actions of 17beta-estradiol. Proc Natl Acad Sci USA 106: 2053–2058, 2009.
Crossref | PubMed | ISI | Google Scholar - 32. . Reduced post-infarction myocardial apoptosis in women: a clue to their different clinical course? Heart 91: 99–101, 2005.
Crossref | PubMed | ISI | Google Scholar - 33. . Coronary artery disease predisposing haplogroup I of the Y chromosome, aggression and sex steroids–genetic association analysis. Atherosclerosis 233: 160–164, 2014.
Crossref | PubMed | ISI | Google Scholar - 34. . Androgen inactivation and steroid-converting enzyme expression in abdominal adipose tissue in men. J Endocrinol 191: 637–649, 2006.
Crossref | PubMed | ISI | Google Scholar - 35. . Sex- and age-dependent human transcriptome variability: implications for chronic heart failure. Proc Natl Acad Sci USA 100: 2754–2759, 2003.
Crossref | PubMed | ISI | Google Scholar - 36. . 17Beta-estradiol as a receptor-mediated cardioprotective agent. J Pharmacol Exp Ther 307: 395–401, 2003.
Crossref | PubMed | ISI | Google Scholar - 37. . The pathway-selective estrogen receptor ligand WAY-169916 reduces infarct size after myocardial ischemia and reperfusion by an estrogen receptor dependent mechanism. J Cardiovasc Pharmacol 49: 401–407, 2007.
Crossref | PubMed | ISI | Google Scholar - 38. . Activation of estrogen receptor-alpha protects the in vivo rabbit heart from ischemia-reperfusion injury. Am J Physiol Heart Circ Physiol 289: H2039–H2047, 2005.
Link | ISI | Google Scholar - 39. . Mitochondria from females exhibit higher antioxidant gene expression and lower oxidative damage than males. Free Radic Biol Med 34: 546–552, 2003.
Crossref | PubMed | ISI | Google Scholar - 40. . Musculoskeletal and prostate effects of combined testosterone and finasteride administration in older hypogonadal men: a randomized, controlled trial. Am J Physiol Endocrinol Metab 306: E433–E442, 2014.
Link | ISI | Google Scholar - 41. . Sex-related resistance to myocardial ischemia-reperfusion injury is associated with high constitutive ARC expression. Am J Physiol Heart Circ Physiol 298: H1510–H1517, 2010.
Link | ISI | Google Scholar - 42. . Estrogen protects transgenic hypertensive rats by shifting the vasoconstrictor-vasodilator balance of RAS. Am J Physiol Regul Integr Comp Physiol 273: R1908–R1915, 1997.
Link | ISI | Google Scholar - 43. . Estradiol accelerates reendothelialization in mouse carotid artery through estrogen receptor-alpha but not estrogen receptor-beta. Circulation 103: 423–428, 2001.
Crossref | PubMed | ISI | Google Scholar - 44. . Endothelium-dependent relaxation by G protein-coupled receptor 30 agonists in rat carotid arteries. Am J Physiol Heart Circ Physiol 298: H1055–H1061, 2010.
Link | ISI | Google Scholar - 45. . Gender mediated cardiac protection from adverse ventricular remodeling is abolished by ovariectomy. Mol Cell Biochem 251: 89–95, 2003.
Crossref | PubMed | ISI | Google Scholar - 46. . Susceptibility of the heart to ischaemia-reperfusion injury and exercise-induced cardioprotection are sex-dependent in the rat. J Physiol 564: 619–630, 2005.
Crossref | PubMed | ISI | Google Scholar - 47. . Estrogen receptor molecular biology. Hematol Oncol Clin N Am 8: 101–112, 1994.
Crossref | PubMed | ISI | Google Scholar - 48. . Angina with “normal” coronary arteries: a changing philosophy. JAMA 293: 477–484, 2005.
Crossref | PubMed | ISI | Google Scholar - 49. . Myofilament response to Ca2+ and Na+/H+ exchanger activity in sex hormone-related protection of cardiac myocytes from deactivation in hypercapnic acidosis. Am J Physiol Regul Integr Comp Physiol 292: R837–R843, 2007.
Link | ISI | Google Scholar - 50. . A randomized study of the prevention of sudden death in patients with coronary artery disease. Multicenter Unsustained Tachycardia Trial Investigators. N Engl J Med 341: 1882–1890, 1999.
Crossref | PubMed | ISI | Google Scholar - 51. . Myocardial Akt activation and gender: increased nuclear activity in females versus males. Circ Res 88: 1020–1027, 2001.
Crossref | PubMed | ISI | Google Scholar - 52. . Protein oxidation seems to be linked to constitutive autophagy: a sex study. Life Sci 93: 145–152, 2013.
Crossref | PubMed | ISI | Google Scholar - 53. . MicroRNA-133 controls cardiac hypertrophy. Nat Med 13: 613–618, 2007.
Crossref | PubMed | ISI | Google Scholar - 54. . Higher levels of plasma estradiol and testosterone in healthy elderly men compared with age-matched women may protect aspects of explicit memory. Menopause 7: 168–177, 2000.
Crossref | PubMed | ISI | Google Scholar - 55. . Sex-associated differences in left ventricular function in aortic stenosis of the elderly. Circulation 86: 1099–1107, 1992.
Crossref | PubMed | ISI | Google Scholar - 56. . Estrogen and testosterone have opposing effects on chronic cardiac remodeling and function in mice with myocardial infarction. Am J Physiol Heart Circ Physiol 284: H1560–H1569, 2003.
Link | ISI | Google Scholar - 57. . Gender differences in cardiac function during early remodeling after acute myocardial infarction in mice. Life Sci 75: 2181–2192, 2004.
Crossref | PubMed | ISI | Google Scholar - 58. . Testosterone enhances early cardiac remodeling after myocardial infarction, causing rupture and degrading cardiac function. Am J Physiol Heart Circ Physiol 290: H2043–H2050, 2006.
Link | ISI | Google Scholar - 59. . Observations of the treatment of women in the United States with myocardial infarction: a report from the National Registry of Myocardial Infarction-I. Arch Intern Med 158: 981–988, 1998.
Crossref | PubMed | Google Scholar - 60. . Inheritance of coronary artery disease in men: an analysis of the role of the Y chromosome. Lancet 379: 915–922, 2012.
Crossref | PubMed | ISI | Google Scholar - 61. . Association of the human Y chromosome with cholesterol levels in the general population. Arterioscler Thromb Vasc Biol 24: 308–312, 2004.
Crossref | PubMed | ISI | Google Scholar - 62. . Y is there a risk to being male? Trends Endocrinol Metab 14: 163–168, 2003.
Crossref | PubMed | ISI | Google Scholar - 63. . Apoptosis and autophagy contribute to gender difference in cardiac ischemia-reperfusion induced injury in rats. Life Sci 93: 265–270, 2013.
Crossref | PubMed | ISI | Google Scholar - 64. . Gender differences in sarcoplasmic reticulum calcium loading after isoproterenol. Am J Physiol Heart Circ Physiol 285: H2657–H2662, 2003.
Link | ISI | Google Scholar - 65. . Regulation of mitochondrial respiratory chain biogenesis by estrogens/estrogen receptors and physiological, pathological and pharmacological implications. Biochim Biophys Acta 1793: 1540–1570, 2009.
Crossref | PubMed | ISI | Google Scholar - 66. . Mitochondrial localization of ERalpha and ERbeta in human MCF7 cells. Am J Physiol Endocrinol Metab 286: E1011–E1022, 2004.
Link | ISI | Google Scholar - 67. . Binding of MCF-7 cell mitochondrial proteins and recombinant human estrogen receptors alpha and beta to human mitochondrial DNA estrogen response elements. J Cell Biochem 93: 358–373, 2004.
Crossref | PubMed | ISI | Google Scholar - 68. . An association between gene expression and better survival in female mice following myocardial infarction. J Mol Cell Cardiol 49: 801–811, 2010.
Crossref | PubMed | ISI | Google Scholar - 69. . Estrogen receptor alpha mediates the nongenomic activation of endothelial nitric oxide synthase by estrogen. J Clin Invest 103: 401–406, 1999.
Crossref | PubMed | ISI | Google Scholar - 70. . MicroRNAs are aberrantly expressed in hypertrophic heart: do they play a role in cardiac hypertrophy? Am J Pathol 170: 1831–1840, 2007.
Crossref | PubMed | ISI | Google Scholar - 71. . Effect of estrogen on calcium-handling proteins, beta-adrenergic receptors, and function in rat heart. Life Sci 79: 1257–1267, 2006.
Crossref | PubMed | ISI | Google Scholar - 72. . Sex differences in expression of calcium-handling proteins and beta-adrenergic receptors in rat heart ventricle. Life Sci 76: 2735–2749, 2005.
Crossref | PubMed | ISI | Google Scholar - 73. . The EuroHeart Failure survey programme—a survey on the quality of care among patients with heart failure in Europe. Part 1: patient characteristics and diagnosis. Eur Heart J 24: 442–463, 2003.
Crossref | PubMed | ISI | Google Scholar - 74. . Aromatase activity of membrane fractions of human adipose tissue stromal cells and adipocytes. Endocrinology 113: 2155–2160, 1983.
Crossref | PubMed | ISI | Google Scholar - 75. Epidemiology of idiopathic dilated and hypertrophic cardiomyopathy. A population-based study in Olmsted County, Minnesota, 1975–1984. Circulation 80: 564–572, 1989.
Crossref | PubMed | ISI | Google Scholar - 76. . Sex-dimorphism in cardiac nutrigenomics: effect of trans fat and/or monosodium glutamate consumption. BMC Genomics 12: 555, 2011.
Crossref | PubMed | ISI | Google Scholar - 77. . Sexual autophagic differences in the androgen-dependent flank organ of Syrian hamsters. J Androl 30: 113–121, 2009.
Crossref | PubMed | Google Scholar - 78. . Descriptive epidemiology of idiopathic dilated cardiomyopathy in Washington County, Maryland, 1975–1991. J Clin Epidemiol 46: 1003–1008, 1993.
Crossref | PubMed | ISI | Google Scholar - 79. . Estrogen receptors alpha and beta form heterodimers on DNA. J Biol Chem 272: 19858–19862, 1997.
Crossref | PubMed | ISI | Google Scholar - 80. . Factors influencing left ventricular structure and stress-corrected systolic function in men and women with asymptomatic aortic valve stenosis (a SEAS Substudy). Am J Cardiol 101: 510–515, 2008.
Crossref | PubMed | ISI | Google Scholar - 81. . Sex differences in cardiovascular outcome during progression of aortic valve stenosis. Heart 101: 209–214, 2015.
Crossref | PubMed | ISI | Google Scholar - 82. . Ablation of PLB exacerbates ischemic injury to a lesser extent in female than male mice: protective role of NO. Am J Physiol Heart Circ Physiol 284: H683–H690, 2003.
Link | ISI | Google Scholar - 83. . 17 Beta-estradiol attenuates pressure overload-induced myocardial hypertrophy through regulating caveolin-3 protein in ovariectomized female rats. Mol Biol Rep 38: 4885–4892, 2011.
Crossref | PubMed | ISI | Google Scholar - 84. . Effects of ovariectomy and 17 beta-oestradiol replacement on [Ca2+]i in female rat cardiac myocytes. Clin Exp Pharmacol Physiol 30: 489–494, 2003.
Crossref | PubMed | ISI | Google Scholar - 85. . Regulation of peroxisome proliferator-activated receptor gamma coactivator 1 alpha (PGC-1 alpha) and mitochondrial function by MEF2 and HDAC5. Proc Natl Acad Sci USA 100: 1711–1716, 2003.
Crossref | PubMed | ISI | Google Scholar - 86. . Visualising androgen receptor activity in male and female mice. PLoS One 8: e71694, 2013.
Crossref | PubMed | ISI | Google Scholar - 87. . Differential regulation of p38 mitogen-activated protein kinase mediates gender-dependent catecholamine-induced hypertrophy. Cardiovasc Res 57: 704–714, 2003.
Crossref | PubMed | ISI | Google Scholar - 88. . Novel quantitative phenotypes of exercise training in mouse models. Am J Physiol Regul Integr Comp Physiol 290: R926–R934, 2006.
Link | ISI | Google Scholar - 89. . Mechanisms of estrogen receptor action in the myocardium. Rapid gene activation via the ERK1/2 pathway and serum response elements. J Biol Chem 276: 27873–27880, 2001.
Crossref | PubMed | ISI | Google Scholar - 90. . A model system for study of sex chromosome effects on sexually dimorphic neural and behavioral traits. J Neurosci 22: 9005–9014, 2002.
Crossref | PubMed | ISI | Google Scholar - 91. . Gender differences in apoptotic signaling in heart failure due to volume overload. Apoptosis 15: 499–510, 2010.
Crossref | PubMed | ISI | Google Scholar - 92. . Estrogen receptors and human disease. J Clin Invest 116: 561–570, 2006.
Crossref | PubMed | ISI | Google Scholar - 93. . Activation of a novel estrogen receptor, GPER, is cardioprotective in male and female rats. Am J Physiol Heart Circ Physiol 297: H1806–H1813, 2009.
Link | ISI | Google Scholar - 94. . Heart protein expression related to age and sex in mice and humans. Int J Mol Med 20: 865–874, 2007.
PubMed | ISI | Google Scholar - 95. . A gender-related defect in lipid metabolism and glucose homeostasis in peroxisome proliferator-activated receptor alpha-deficient mice. J Clin Invest 102: 1083–1091, 1998.
Crossref | PubMed | ISI | Google Scholar - 96. . Estrogen attenuates left ventricular and cardiomyocyte hypertrophy by an estrogen receptor-dependent pathway that increases calcineurin degradation. Circ Res 104: 265–275, 2009.
Crossref | PubMed | ISI | Google Scholar - 97. . Interstitial fibrosis, left ventricular remodeling, and myocardial mechanical behavior in a population-based multiethnic cohort: the Multi-Ethnic Study of Atherosclerosis (MESA) study. Circ Cardiovasc Imaging 7: 292–302, 2014.
Crossref | PubMed | ISI | Google Scholar - 98. . Hypertrophic remodeling: gender differences in the early response to left ventricular pressure overload. J Am Coll Cardiol 32: 1118–1125, 1998.
Crossref | PubMed | ISI | Google Scholar - 99. . Gender differences in left ventricle geometry and function in patients undergoing balloon dilatation of the aortic valve for isolated aortic stenosis. NHLBI Balloon Valvuloplasty Registry. Br Heart J 73: 548–554, 1995.
Crossref | PubMed | Google Scholar - 100. . Cardiac actions of erythromycin: influence of female sex. JAMA 280: 1774–1776, 1998.
Crossref | PubMed | ISI | Google Scholar - 101. . Starving neurons show sex difference in autophagy. J Biol Chem 284: 2383–2396, 2009.
Crossref | PubMed | ISI | Google Scholar - 102. . Gender modulates cardiac phenotype development in genetically modified mice. Cardiovasc Res 63: 510–519, 2004.
Crossref | PubMed | ISI | Google Scholar - 103. . 17Beta-estradiol, its metabolites, and progesterone inhibit cardiac fibroblast growth. Hypertension 31: 522–528, 1998.
Crossref | PubMed | ISI | Google Scholar - 104. . Estradiol metabolites inhibit endothelin synthesis by an estrogen receptor-independent mechanism. Hypertension 37: 640–644, 2001.
Crossref | PubMed | ISI | Google Scholar - 105. . Hormonal modulation of endothelial NO production. Pflügers Arch 459: 841–851, 2010.
Crossref | PubMed | ISI | Google Scholar - 106. . Effect of single and compound knockouts of estrogen receptors alpha (ERalpha) and beta (ERbeta) on mouse reproductive phenotypes. Development 127: 4277–4291, 2000.
Crossref | PubMed | ISI | Google Scholar - 107. . Effects of aging on cardiac extracellular matrix in men and women. Proteomics Clin Appl 10: 84–91, 2016.
Crossref | PubMed | ISI | Google Scholar - 108. . Sex differences in exercise-induced physiological myocardial hypertrophy are modulated by oestrogen receptor beta. Cardiovasc Res 102: 418–428, 2014.
Crossref | PubMed | ISI | Google Scholar - 109. . COX-2-derived prostacyclin confers atheroprotection on female mice. Science 306: 1954–1957, 2004.
Crossref | PubMed | ISI | Google Scholar - 110. . Impact of testosterone on cardiac L-type calcium channels and Ca2+ sparks: acute actions antagonize chronic effects. Cell Calcium 41: 467–477, 2007.
Crossref | PubMed | ISI | Google Scholar - 111. . Metabolic gene switching in the murine female heart parallels enhanced mitochondrial respiratory function in response to oxidative stress. FEBS J 274: 5278–5284, 2007.
Crossref | PubMed | ISI | Google Scholar - 112. . The steroid and thyroid hormone receptor superfamily. Science 240: 889–895, 1988.
Crossref | PubMed | ISI | Google Scholar - 113. . Differences in inflammation, MMP activation and collagen damage account for gender difference in murine cardiac rupture following myocardial infarction. J Mol Cell Cardiol 43: 535–544, 2007.
Crossref | PubMed | ISI | Google Scholar - 114. . Ovariectomy enhances SR Ca2+ release and increases Ca2+ spark amplitudes in isolated ventricular myocytes. J Mol Cell Cardiol 52: 32–42, 2012.
Crossref | PubMed | ISI | Google Scholar - 115. . Endothelial estrogen receptor α plays an essential role in the coronary and myocardial protective effects of estradiol in ischemia/reperfusion. Arterioscler Thromb Vasc Biol 30: 2562–2567, 2010.
Crossref | PubMed | ISI | Google Scholar - 116. . Sex and age dimorphism of myocardial gene expression in nonischemic human heart failure. Circ Cardiovasc Genet 1: 117–125, 2008.
Crossref | PubMed | ISI | Google Scholar - 117. Estrogen-induced activation of Erk-1 and Erk-2 requires the G protein-coupled receptor homolog, GPR30, and occurs via trans-activation of the epidermal growth factor receptor through release of HB-EGF. Mol Endocrinol 14: 1649–1660, 2000.
Crossref | PubMed | Google Scholar - 118. . Estrogen action via the G protein-coupled receptor, GPR30: stimulation of adenylyl cyclase and cAMP-mediated attenuation of the epidermal growth factor receptor-to-MAPK signaling axis. Mol Endocrinol 16: 70–84, 2002.
Crossref | PubMed | Google Scholar - 119. . Female sex and estrogen receptor-beta attenuate cardiac remodeling and apoptosis in pressure overload. Am J Physiol Regul Integr Comp Physiol 298: R1597–R1606, 2010.
Link | ISI | Google Scholar - 120. . Sex differences in physiological cardiac hypertrophy are associated with exercise-mediated changes in energy substrate availability. Am J Physiol Heart Circ Physiol 301: H115–H122, 2011.
Link | ISI | Google Scholar - 121. . The androgen receptor acetylation site regulates cAMP and AKT but not ERK-induced activity. J Biol Chem 279: 29436–29449, 2004.
Crossref | PubMed | ISI | Google Scholar - 122. . Acetylation of nuclear receptors in cellular growth and apoptosis. Biochem Pharmacol 68: 1199–1208, 2004.
Crossref | PubMed | ISI | Google Scholar - 123. . Estrogen receptor beta mediates gender differences in ischemia/reperfusion injury. J Mol Cell Cardiol 38: 289–297, 2005.
Crossref | PubMed | Google Scholar - 124. . Estrogen regulation of angiotensin-converting enzyme mRNA. Hypertension 33: 323–328, 1999.
Crossref | PubMed | ISI | Google Scholar - 125. . Sexual dimorphism of blood pressure in spontaneously hypertensive rats: effects of anti-androgen treatment. J Hypertens 7: 721–726, 1989.
Crossref | PubMed | ISI | Google Scholar - 126. . Sex hormones and cardiomyopathic phenotype induced by cardiac beta 2-adrenergic receptor overexpression. Endocrinology 144: 4097–4105, 2003.
Crossref | PubMed | ISI | Google Scholar - 127. . Gender differences in cardiac remodeling secondary to chronic volume overload. J Card Fail 8: 101–107, 2002.
Crossref | PubMed | ISI | Google Scholar - 128. . Gender differences in left ventricular structure and function during antihypertensive treatment: the Losartan Intervention for Endpoint Reduction in Hypertension Study. Hypertension 51: 1109–1114, 2008.
Crossref | PubMed | ISI | Google Scholar - 129. . Idiopathic cardiomyopathy in the United States, 1970–1982. Am Heart J 111: 752–755, 1986.
Crossref | PubMed | ISI | Google Scholar - 130. . Endothelial regulation of eNOS, PAI-1 and t-PA by testosterone and dihydrotestosterone in vitro and in vivo. Mol Hum Reprod 16: 761–769, 2010.
Crossref | PubMed | ISI | Google Scholar - 131. . Castration reduces mRNA levels for calcium regulatory proteins in rat heart. Endocrine 19: 339–344, 2002.
Crossref | PubMed | ISI | Google Scholar - 132. . Gonadectomy of adult male rats reduces contractility of isolated cardiac myocytes. Am J Physiol Endocrinol Metab 285: E449–E453, 2003.
Link | ISI | Google Scholar - 133. . Sex-specific cardiovascular structure and function in heart failure with preserved ejection fraction. Eur J Heart Fail 16: 535–542, 2014.
Crossref | PubMed | ISI | Google Scholar - 134. . Oestrogen-receptor-mediated transcription and the influence of co-factors and chromatin state. Nat Rev Cancer 7: 713–722, 2007.
Crossref | PubMed | ISI | Google Scholar - 135. . Cardiac myocytes and fibroblasts contain functional estrogen receptors. FEBS Lett 416: 107–112, 1997.
Crossref | PubMed | ISI | Google Scholar - 136. . Production and actions of estrogens. N Engl J Med 346: 340–352, 2002.
Crossref | PubMed | ISI | Google Scholar - 137. . Myocyte death in the failing human heart is gender dependent. Circ Res 85: 856–866, 1999.
Crossref | PubMed | ISI | Google Scholar - 138. . Environmentally induced epigenetic transgenerational inheritance of phenotype and disease. Mol Cell Endocrinol 354: 3–8, 2012.
Crossref | PubMed | ISI | Google Scholar - 139. . Genetic background, gender, age, body temperature, and arterial blood pH have a major impact on myocardial infarct size in the mouse and need to be carefully measured and/or taken into account: results of a comprehensive analysis of determinants of infarct size in 1,074 mice. Basic Res Cardiol 107: 288, 2012.
PubMed | ISI | Google Scholar - 140. . Estrogen receptor-beta signals left ventricular hypertrophy sex differences in normotensive deoxycorticosterone acetate-salt mice. Hypertension 57: 648–654, 2011.
Crossref | PubMed | ISI | Google Scholar - 141. . Regulatory role of G protein-coupled estrogen receptor for vascular function and obesity. Circ Res 104: 288–291, 2009.
Crossref | PubMed | ISI | Google Scholar - 142. . Human cardiac-specific cDNA array for idiopathic dilated cardiomyopathy: sex-related differences. Physiol Genomics 33: 267–277, 2008.
Link | ISI | Google Scholar - 143. . Estrogens mediate cardiac hypertrophy in a stimulus-dependent manner. Endocrinology 153: 4480–4490, 2012.
Crossref | PubMed | ISI | Google Scholar - 144. . Estrogen receptor-associated proteins: possible mediators of hormone-induced transcription. Science 264: 1455–1458, 1994.
Crossref | PubMed | ISI | Google Scholar - 145. beta-Estradiol, but not alpha-estradiol, reduced myocardial necrosis in rabbits after ischemia and reperfusion. Am Heart J 132: 258–262, 1996.
Crossref | PubMed | ISI | Google Scholar - 146. . Central control of fever and female body temperature by RANKL/RANK. Nature 462: 505–509, 2009.
Crossref | PubMed | ISI | Google Scholar - 147. . Rapamycin fed late in life extends lifespan in genetically heterogeneous mice. Nature 460: 392–395, 2009.
Crossref | PubMed | ISI | Google Scholar - 148. . The gene expression profile of patients with new-onset heart failure reveals important gender-specific differences. Eur Heart J 31: 1188–1196, 2010.
Crossref | PubMed | ISI | Google Scholar - 149. . Cytochrome P450 subfamily 2J polypeptide 2 expression and circulating epoxyeicosatrienoic metabolites in preeclampsia. Circulation 126: 2990–2999, 2012.
Crossref | PubMed | ISI | Google Scholar - 150. . Alterations in the regulation of androgen-sensitive Cyp 4a monooxygenases cause hypertension. Proc Natl Acad Sci USA 98: 5211–5216, 2001.
Crossref | PubMed | ISI | Google Scholar - 151. . Trends in the clinical and pathological characteristics of cardiac rupture in patients with acute myocardial infarction over 35 years. J Am Heart Assoc 3: e000984, 2014.
Crossref | PubMed | ISI | Google Scholar - 152. . Females have a blunted cardiovascular response to one year of intensive supervised endurance training. J Appl Physiol 119: 37–46, 2015.
Link | ISI | Google Scholar - 153. . Inhibition of cardiac PGC-1alpha expression abolishes ERbeta agonist-mediated cardioprotection following trauma-hemorrhage. FASEB J 20: 1109–1117, 2006.
Crossref | PubMed | ISI | Google Scholar - 154. . PGC-1 upregulation via estrogen receptors: a common mechanism of salutary effects of estrogen and flutamide on heart function after trauma-hemorrhage. Am J Physiol Heart Circ Physiol 289: H2665–H2672, 2005.
Link | ISI | Google Scholar - 155. . Upregulation of mitochondrial respiratory complex IV by estrogen receptor-beta is critical for inhibiting mitochondrial apoptotic signaling and restoring cardiac functions following trauma-hemorrhage. J Mol Cell Cardiol 41: 511–521, 2006.
Crossref | PubMed | ISI | Google Scholar - 156. . Estrogen elicits cytochrome P450–mediated flow-induced dilation of arterioles in NO deficiency: role of PI3K-Akt phosphorylation in genomic regulation. Circ Res 94: 245–252, 2004.
Crossref | PubMed | ISI | Google Scholar - 157. . Testosterone-down-regulated Akt pathway during cardiac ischemia/reperfusion: a mechanism involving BAD, Bcl-2 and FOXO3a. J Surg Res 164: e1–11, 2010.
Crossref | PubMed | ISI | Google Scholar - 158. . Retardation in the development of spontaneous hypertension in SH rats by gonadectomy. J Lab Clin Med 90: 997–1003, 1977.
PubMed | Google Scholar - 159. . Androgen receptor counteracts Doxorubicin-induced cardiotoxicity in male mice. Mol Endocrinol 24: 1338–1348, 2010.
Crossref | PubMed | Google Scholar - 160. . Androgen receptor gene knockout male mice exhibit impaired cardiac growth and exacerbation of angiotensin II-induced cardiac fibrosis. J Biol Chem 280: 29661–29666, 2005.
Crossref | PubMed | ISI | Google Scholar - 161. . Androgen receptor independent cardiovascular action of the antiandrogen flutamide. J Mol Med 81: 420–427, 2003.
Crossref | PubMed | ISI | Google Scholar - 162. . Selective oestrogen receptor modulators differentially potentiate brain mitochondrial function. J Neuroendocrinol 24: 236–248, 2012.
Crossref | PubMed | ISI | Google Scholar - 163. . Expression pattern of G protein-coupled receptor 30 in LacZ reporter mice. Endocrinology 150: 1722–1730, 2009.
Crossref | PubMed | ISI | Google Scholar - 164. . Sexually dimorphic gene expression in the heart of mice and men. J Mol Med 86: 61–74, 2008.
Crossref | PubMed | ISI | Google Scholar - 165. . Estradiol enhances recovery after myocardial infarction by augmenting incorporation of bone marrow-derived endothelial progenitor cells into sites of ischemia-induced neovascularization via endothelial nitric oxide synthase-mediated activation of matrix metalloproteinase-9. Circulation 113: 1605–1614, 2006.
PubMed | ISI | Google Scholar - 166. . Influence of gender on the response to hemodynamic overload after myocardial infarction. Am J Physiol Heart Circ Physiol 283: H2544–H2550, 2002.
Link | ISI | Google Scholar - 167. . Morphological and functional changes in cardiac myocytes isolated from mice overexpressing TNF-alpha. Am J Physiol Heart Circ Physiol 284: H960–H969, 2003.
Link | ISI | Google Scholar - 168. . Circulating estradiol and mortality in men with systolic chronic heart failure. JAMA 301: 1892–1901, 2009.
Crossref | PubMed | ISI | Google Scholar - 169. . Oestrogen-mediated cardioprotection following ischaemia and reperfusion is mimicked by an oestrogen receptor (ER)alpha agonist and unaffected by an ER beta antagonist. J Endocrinol 197: 493–501, 2008.
Crossref | PubMed | ISI | Google Scholar - 170. . Effects of estrogen on free fatty acid metabolism in humans. Am J Physiol Endocrinol Metab 266: E914–E920, 1994.
Link | ISI | Google Scholar - 171. . Burden of hospital admission and repeat angiography in angina pectoris patients with and without coronary artery disease: a registry-based cohort study. PLoS One 9: e93170, 2014.
Crossref | PubMed | ISI | Google Scholar - 172. . Effect of 17 beta-oestradiol on contraction, Ca2+ current and intracellular free Ca2+ in guinea-pig isolated cardiac myocytes. Br J Pharmacol 106: 739–745, 1992.
Crossref | PubMed | ISI | Google Scholar - 173. . Regulation of estrogenic effects by beclin 1 in breast cancer cells. Cancer Res 68: 7855–7863, 2008.
Crossref | PubMed | ISI | Google Scholar - 174. . Increased expression of the cardiac L-type calcium channel in estrogen receptor-deficient mice. J Gen Physiol 110: 135–140, 1997.
Crossref | PubMed | ISI | Google Scholar - 175. . Sex differences in myocardial infarct size are abolished by sarcolemmal KATP channel blockade in rat. Am J Physiol Heart Circ Physiol 290: H2644–H2647, 2006.
Link | ISI | Google Scholar - 176. . Regulation of cancer cell migration and bone metastasis by RANKL. Nature 440: 692–696, 2006.
Crossref | PubMed | ISI | Google Scholar - 177. . Sex-related survival differences in murine cardiomyopathy are associated with differences in TNF-receptor expression. J Clin Invest 106: 589–597, 2000.
Crossref | PubMed | ISI | Google Scholar - 178. . Effect of Estradiol-17beta on protein synthesis and degradation rates in fused bovine satellite cell cultures. Domest Anim Endocrinol 39: 54–62, 2010.
Crossref | PubMed | ISI | Google Scholar - 179. . Genome-wide histone methylation profile for heart failure. Genes Cells 14: 69–77, 2009.
Crossref | PubMed | ISI | Google Scholar - 180. . Sudden coronary death in women. Am Heart J 136: 205–212, 1998.
Crossref | PubMed | ISI | Google Scholar - 181. . 4-Vinylcyclohexene diepoxide: a model chemical for ovotoxicity. Syst Biol Reprod Med 58: 57–62, 2012.
Crossref | PubMed | ISI | Google Scholar - 182. . Sex-specific modification of progesterone receptor expression by 17beta-oestradiol in human cardiac tissues. Biol Sex Differ 1: 2, 2010.
Crossref | PubMed | Google Scholar - 183. . Transcriptome characterization of estrogen-treated human myocardium identifies myosin regulatory light chain interacting protein as a sex-specific element influencing contractile function. J Am Coll Cardiol 59: 410–417, 2012.
Crossref | PubMed | ISI | Google Scholar - 184. . Sex-dependent regulation of fibrosis and inflammation in human left ventricular remodelling under pressure overload. Eur J Heart Fail 16: 1160–1167, 2014.
Crossref | PubMed | ISI | Google Scholar - 185. . Comparative proteomic analysis reveals sex and estrogen receptor beta effects in the pressure overloaded heart. J Proteome Res 13: 5829–5836, 2014.
Crossref | PubMed | ISI | Google Scholar - 186. . Role of the estrogen/estrogen-receptor-beta axis in the genomic response to pressure overload-induced hypertrophy. Physiol Genomics 43: 438–446, 2011.
Link | ISI | Google Scholar - 187. . Estrogen modulates cardiac growth through an estrogen receptor alpha-dependent mechanism in healthy ovariectomized mice. Mol Cell Endocrinol 382: 909–914, 2014.
Crossref | PubMed | ISI | Google Scholar - 188. . Genetic background defines the regulation of postnatal cardiac growth by 17beta-estradiol through a beta-catenin mechanism. Endocrinology 155: 2667–2676, 2014.
Crossref | PubMed | ISI | Google Scholar - 189. . Human vascular smooth muscle cells contain functional estrogen receptor. Circulation 89: 1943–1950, 1994.
Crossref | PubMed | ISI | Google Scholar - 190. . Deoxycorticosterone acetate-salt mice exhibit blood pressure-independent sexual dimorphism. Hypertension 51: 1177–1183, 2008.
Crossref | PubMed | ISI | Google Scholar - 191. . CardioNet: a human metabolic network suited for the study of cardiomyocyte metabolism. BMC Syst Biol 6: 114, 2012.
Crossref | PubMed | ISI | Google Scholar - 192. . Expression of an estrogen receptor by human coronary artery and umbilical vein endothelial cells. Circulation 94: 1402–1407, 1996.
Crossref | PubMed | ISI | Google Scholar - 193. . Estrogen prevents cardiomyocyte apoptosis through inhibition of reactive oxygen species and differential regulation of p38 kinase isoforms. J Biol Chem 281: 6760–6767, 2006.
Crossref | PubMed | ISI | Google Scholar - 194. . Tissue-specific sex differences in docosahexaenoic acid and Delta6-desaturase in rats fed a standard chow diet. Appl Physiol Nutr Metab 37: 1200–1211, 2012.
Crossref | PubMed | ISI | Google Scholar - 195. . Myocardial protection of contractile function after global ischemia by physiologic estrogen replacement in the ovariectomized rat. J Mol Cell Cardiol 29: 2403–2414, 1997.
Crossref | PubMed | ISI | Google Scholar - 196. . Takotsubo cardiomyopathy: Pathophysiology, diagnosis and treatment. World J Cardiol 6: 602–609, 2014.
Crossref | PubMed | Google Scholar - 197. . The effects of biological sex and diet on the development of heart failure. Circulation 116: 2747–2759, 2007.
Crossref | PubMed | ISI | Google Scholar - 198. . Sex modifies exercise and cardiac adaptation in mice. Am J Physiol Heart Circ Physiol 287: H2768–H2776, 2004.
Link | ISI | Google Scholar - 199. . Estradiol enhances effects of fructose rich diet on cardiac fatty acid transporter CD36 and triglycerides accumulation. Eur J Pharmacol 694: 127–134, 2012.
Crossref | PubMed | ISI | Google Scholar - 200. . Female mice lacking estrogen receptor beta display prolonged ventricular repolarization and reduced ventricular automaticity after myocardial infarction. Circulation 111: 2282–2290, 2005.
Crossref | PubMed | ISI | Google Scholar - 201. . Down but not out? A novel protein isoform of the estrogen receptor alpha is expressed in the estrogen receptor alpha knockout mouse. J Mol Endocrinol 29: 281–286, 2002.
Crossref | PubMed | ISI | Google Scholar - 202. . 17beta-Estradiol utilizes the estrogen receptor to regulate CD16 expression in monocytes. Mol Cell Endocrinol 279: 16–25, 2007.
Crossref | PubMed | ISI | Google Scholar - 203. . Estradiol accelerates functional endothelial recovery after arterial injury. Circulation 95: 1768–1772, 1997.
Crossref | PubMed | ISI | Google Scholar - 204. . Altered Ca2+ handling by ryanodine receptor and Na+-Ca2+ exchange in the heart from ovariectomized rats: role of protein kinase A. Am J Physiol Cell Physiol 292: C1625–C1635, 2007.
Link | ISI | Google Scholar - 205. . Reproductive hormone concentrations in pregnancy and neonates: a systematic review. Reprod Biomed Online 27: 33–63, 2013.
Crossref | PubMed | ISI | Google Scholar - 206. . Cloning of a novel receptor expressed in rat prostate and ovary. Proc Natl Acad Sci USA 93: 5925–5930, 1996.
Crossref | PubMed | ISI | Google Scholar - 207. . Gender and in-hospital mortality of ST-segment elevation myocardial infarction (from a multihospital nationwide registry study of 31,689 patients). Am J Cardiol 115: 303–306, 2015.
Crossref | PubMed | ISI | Google Scholar - 208. . Sex differences in the phosphorylation of mitochondrial proteins result in reduced production of reactive oxygen species and cardioprotection in females. Circ Res 106: 1681–1691, 2010.
Crossref | PubMed | ISI | Google Scholar - 209. . Estradiol modulates myosin regulatory light chain phosphorylation and contractility in skeletal muscle of female mice. Am J Physiol Endocrinol Metab 310: E724–E733, 2016.
Link | ISI | Google Scholar - 210. . Sex differences in clinical characteristics and outcomes in elderly patients with heart failure and preserved ejection fraction: the Irbesartan in Heart Failure with Preserved Ejection Fraction (I-PRESERVE) trial. Circ Heart Fail 5: 571–578, 2012.
Crossref | PubMed | ISI | Google Scholar - 211. . Sex differences in clinical characteristics and outcomes after myocardial infarction: insights from the Valsartan in Acute Myocardial Infarction Trial (VALIANT). Eur J Heart Fail 17: 301–312, 2015.
Crossref | PubMed | ISI | Google Scholar - 212. . Testosterone affects hormone-sensitive lipase (HSL) activity and lipid metabolism in the left ventricle. Biochem Biophys Res Commun 399: 670–676, 2010.
Crossref | PubMed | ISI | Google Scholar - 213. . Role of androgens in sex differences in cardiac damage during myocardial infarction. Endocrinology 155: 568–575, 2014.
Crossref | PubMed | ISI | Google Scholar - 214. . Epigenetic regulation of nuclear steroid receptors. Biochem Pharmacol 72: 1589–1596, 2006.
Crossref | PubMed | ISI | Google Scholar - 215. . Epigenetics and the estrogen receptor. Ann NY Acad Sci 1089: 73–87, 2006.
Crossref | PubMed | ISI | Google Scholar - 216. . Adjunctive 17beta-estradiol administration reduces infarct size by altered expression of canine myocardial connexin43 protein. Cardiovasc Res 63: 109–117, 2004.
Crossref | PubMed | ISI | Google Scholar - 217. . Membrane ERalpha attenuates myocardial fibrosis via RhoA/ROCK-mediated actin remodeling in ovariectomized female infarcted rats. J Mol Med 92: 43–51, 2014.
Crossref | PubMed | ISI | Google Scholar - 218. . Cardioprotective effects of 17 beta-estradiol produced by activation ofmitochondrial ATP-sensitive K+ channels in canine hearts. J Mol Cell Cardiol 32: 1147–1158, 2000.
Crossref | PubMed | ISI | Google Scholar - 219. . Polycystic ovary syndrome and cardiovascular disease: a premature association? Endocr Rev 24: 302–312, 2003.
Crossref | PubMed | ISI | Google Scholar - 220. . JTc prolongation with d,l-sotalol in women versus men. Am J Cardiol 83: 354–359, 1999.
Crossref | PubMed | ISI | Google Scholar - 221. . G protein-coupled receptor 30: estrogen receptor or collaborator? Endocrinology 150: 1563–1565, 2009.
Crossref | PubMed | ISI | Google Scholar - 222. . Long-term trends in the incidence of and survival with heart failure. N Engl J Med 347: 1397–1402, 2002.
Crossref | PubMed | ISI | Google Scholar - 223. . The progression from hypertension to congestive heart failure. JAMA 275: 1557–1562, 1996.
Crossref | PubMed | ISI | Google Scholar - 224. . The number of X chromosomes influences protection from cardiac ischaemia/reperfusion injury in mice: one X is better than two. Cardiovasc Res 102: 375–384, 2014.
Crossref | PubMed | ISI | Google Scholar - 225. . Androgen contributes to gender-related cardiac hypertrophy and fibrosis in mice lacking the gene encoding guanylyl cyclase-A. Endocrinology 145: 951–958, 2004.
Crossref | PubMed | ISI | Google Scholar - 226. . Estrogen receptor-beta activation results in S-nitrosylation of proteins involved in cardioprotection. Circulation 120: 245–254, 2009.
Crossref | PubMed | ISI | Google Scholar - 227. . Sex hormone receptor gene variation associated with phenotype in male hypertrophic cardiomyopathy patients. J Mol Cell Cardiol 45: 217–222, 2008.
Crossref | PubMed | ISI | Google Scholar - 228. . Oestrogen prevents cardiomyocyte apoptosis by suppressing p38alpha-mediated activation of p53 and by down-regulating p53 inhibition on p38beta. Cardiovasc Res 89: 119–128, 2011.
Crossref | PubMed | ISI | Google Scholar - 229. . Mitochondrial p38beta and manganese superoxide dismutase interaction mediated by estrogen in cardiomyocytes. PLoS One 9: e85272, 2014.
Crossref | PubMed | ISI | Google Scholar - 230. . Sex differences in disease risk from reported genome-wide association study findings. Hum Genet 131: 353–364, 2012.
Crossref | PubMed | ISI | Google Scholar - 231. . Influence of ovariectomy and 17beta-estradiol treatment on insulin sensitivity, lipid metabolism and post-ischemic cardiac function. Int J Cardiol 97: 485–493, 2004.
Crossref | PubMed | ISI | Google Scholar - 232. . In vivo androgen treatment shortens the QT interval and increases the densities of inward and delayed rectifier potassium currents in orchiectomized male rabbits. Cardiovasc Res 57: 28–36, 2003.
Crossref | PubMed | ISI | Google Scholar - 233. . Does cellular sex matter? Dimorphic transcriptional differences between female and male endothelial cells. Atherosclerosis 240: 61–72, 2015.
Crossref | PubMed | ISI | Google Scholar - 234. . Variable expression of the estrogen receptor in normal and atherosclerotic coronary arteries of premenopausal women. Circulation 89: 1501–1510, 1994.
Crossref | PubMed | ISI | Google Scholar - 235. . Alteration of reproductive function but not prenatal sexual development after insertional disruption of the mouse estrogen receptor gene. Proc Natl Acad Sci USA 90: 11162–11166, 1993.
Crossref | PubMed | ISI | Google Scholar - 236. . Gender-specific differences of cardiac remodeling in subjects with left ventricular dysfunction: a population-based study. Cardiovasc Res 53: 720–727, 2002.
Crossref | PubMed | ISI | Google Scholar - 237. . Regulation of cardiac long-chain fatty acid and glucose uptake by translocation of substrate transporters. Pflügers Arch 448: 1–15, 2004.
Crossref | PubMed | ISI | Google Scholar - 238. . Prenatal famine and adult health. Annu Rev Public Health 32: 237–262, 2011.
Crossref | PubMed | ISI | Google Scholar - 239. . Oestrogen confers cardioprotection by suppressing Ca2+/calmodulin-dependent protein kinase II. Br J Pharmacol 157: 705–715, 2009.
Crossref | PubMed | ISI | Google Scholar - 240. . Cardiac contraction, calcium transients, and myofilament calcium sensitivity fluctuate with the estrous cycle in young adult female mice. Am J Physiol Heart Circ Physiol 306: H938–H953, 2014.
Link | ISI | Google Scholar - 241. . Origin of estrogen in normal men and in women with testicular feminization. J Clin Endocrinol Metab 49: 905–916, 1979.
Crossref | PubMed | ISI | Google Scholar - 242. . Implantable cardioverter-defibrillator therapy in patients with ventricular fibrillation out of hospital cardiac arrest secondary to acute coronary syndrome. J Am Heart Assoc 4: 2015.
Crossref | PubMed | ISI | Google Scholar - 243. . Mouse homologues of the human AZF candidate gene RBM are expressed in spermatogonia and spermatids, and map to a Y chromosome deletion interval associated with a high incidence of sperm abnormalities. Hum Mol Genet 7: 715–727, 1998.
Crossref | PubMed | ISI | Google Scholar - 244. . Unexpected virilization in male mice lacking steroid 5 alpha-reductase enzymes. Endocrinology 142: 4652–4662, 2001.
Crossref | PubMed | ISI | Google Scholar - 245. . Men supplemented with 17beta-estradiol have increased beta-oxidation capacity in skeletal muscle. Physiol Genomics 42: 342–347, 2010.
Link | ISI | Google Scholar - 246. . 17beta-Estradiol inhibits matrix metalloproteinase-2 transcription via MAP kinase in fibroblasts. Cardiovasc Res 85: 719–728, 2010.
Crossref | PubMed | ISI | Google Scholar - 247. . Estrogen receptor alpha up-regulation and redistribution in human heart failure. FASEB J 20: 926–934, 2006.
Crossref | PubMed | ISI | Google Scholar - 248. . Sex differences in animal models for cardiovascular diseases and the role of estrogen. Handb Exp Pharmacol 23–48, 2012.
Google Scholar - 249. . Nuclear factor-kappaB regulates estrogen receptor-alpha transcription in the human heart. J Biol Chem 284: 24705–24714, 2009.
Crossref | PubMed | ISI | Google Scholar - 250. . Cardiomyocyte-specific estrogen receptor alpha increases angiogenesis, lymphangiogenesis and reduces fibrosis in the female mouse heart post-myocardial infarction. J Cell Sci Ther 5: 153, 2014.
Crossref | PubMed | Google Scholar - 251. . 17beta-Estradiol-induced interaction of ERalpha with NPPA regulates gene expression in cardiomyocytes. Cardiovasc Res 96: 411–421, 2012.
Crossref | PubMed | ISI | Google Scholar - 252. . Testosterone therapy in men with moderate severity heart failure: a double-blind randomized placebo controlled trial. Eur Heart J 27: 57–64, 2006.
Crossref | PubMed | ISI | Google Scholar - 253. . Redox state and gender differences in vascular smooth muscle cells. FEBS Lett 582: 635–642, 2008.
Crossref | PubMed | ISI | Google Scholar - 254. . Impact of isolated systolic hypertension on normalization of left ventricular structure during antihypertensive treatment (the LIFE study). Blood Pressure 23: 206–212, 2014.
Crossref | PubMed | ISI | Google Scholar - 255. . Sudden cardiac arrest during sports activity in middle age. Circulation 131: 1384–1391, 2015.
Crossref | PubMed | ISI | Google Scholar - 256. . Heterogeneity of microvascular dysfunction in women with chest pain not attributable to coronary artery disease: implications for clinical practice. Am Heart J 145: 628–635, 2003.
Crossref | PubMed | ISI | Google Scholar - 257. . Androgen receptors mediate hypertrophy in cardiac myocytes. Circulation 98: 256–261, 1998.
Crossref | PubMed | ISI | Google Scholar - 258. . Gender and survival in patients with heart failure: interactions with diabetes and aetiology. Results from the MAGGIC individual patient meta-analysis. Eur J Heart Fail 14: 473–479, 2012.
Crossref | PubMed | ISI | Google Scholar - 259. . Estrogen and progesterone reduce lipid accumulation in human monocyte-derived macrophages: a sex-specific effect. Circulation 100: 2319–2325, 1999.
Crossref | PubMed | ISI | Google Scholar - 260. . The heart is a target organ for androgen. Science 207: 775–777, 1980.
Crossref | PubMed | ISI | Google Scholar - 261. . The protective effects of estrogen on the cardiovascular system. N Engl J Med 340: 1801–1811, 1999.
Crossref | PubMed | ISI | Google Scholar - 262. . Noncardiac comorbidities in heart failure with reduced versus preserved ejection fraction. J Am Coll Cardiol 64: 2281–2293, 2014.
Crossref | PubMed | ISI | Google Scholar - 263. . Electrocardiographic quantitation of ventricular repolarization. Circulation 80: 1301–1308, 1989.
Crossref | PubMed | ISI | Google Scholar - 264. . Conditional site-specific recombination in mammalian cells using a ligand-dependent chimeric Cre recombinase. Proc Natl Acad Sci USA 92: 6991–6995, 1995.
Crossref | PubMed | ISI | Google Scholar - 265. . Rapid modulation of L-type calcium current by acutely applied oestrogens in isolated cardiac myocytes from human, guinea-pig and rat. Exp Physiol 83: 305–321, 1998.
Crossref | PubMed | ISI | Google Scholar - 266. . Long-term and immediate effect of testosterone on single T-type calcium channel in neonatal rat cardiomyocytes. Endocrinology 147: 5160–5169, 2006.
Crossref | PubMed | ISI | Google Scholar - 267. . Vascular actions of estrogens: functional implications. Pharmacol Rev 60: 210–241, 2008.
Crossref | PubMed | ISI | Google Scholar - 268. . The molecular biology, biochemistry, and physiology of human steroidogenesis and its disorders. Endocr Rev 32: 81–151, 2011.
Crossref | PubMed | ISI | Google Scholar - 269. . Specific and gender differences between hospitalized and out of hospital mortality due to myocardial infarction. Coll Antropol 32: 361–367, 2008.
PubMed | Google Scholar - 270. . Effect of gender on lipid kinetics during endurance exercise of moderate intensity in untrained subjects. Am J Physiol Endocrinol Metab 283: E58–E65, 2002.
Link | ISI | Google Scholar - 271. . Increased contractile potential of papillary muscles from exercise-trained rat hearts. Am J Physiol Heart Circ Physiol 234: H421–H425, 1978.
Link | ISI | Google Scholar - 272. . Androgens contribute to sex differences in myocardial remodeling under pressure overload by a mechanism involving TGF-beta. PLoS One 7: e35635, 2012.
Crossref | PubMed | ISI | Google Scholar - 273. . Estrogen promotes angiogenic activity in human umbilical vein endothelial cells in vitro and in a murine model. Circulation 91: 755–763, 1995.
Crossref | PubMed | ISI | Google Scholar - 274. . Estrogen receptor-alpha regulates the degradation of insulin receptor substrates 1 and 2 in breast cancer cells. Oncogene 22: 4007–4016, 2003.
Crossref | PubMed | ISI | Google Scholar - 275. . Early prenatal stress epigenetically programs dysmasculinization in second-generation offspring via the paternal lineage. J Neurosci 31: 11748–11755, 2011.
Crossref | PubMed | ISI | Google Scholar - 276. . Large-scale association analysis provides insights into the genetic architecture and pathophysiology of type 2 diabetes. Nat Genet 44: 981–990, 2012.
Crossref | PubMed | ISI | Google Scholar - 277. . Sexual dimorphism of doxorubicin-mediated cardiotoxicity: potential role of energy metabolism remodeling. Circ Heart Fail 8: 98–108, 2015.
Crossref | PubMed | ISI | Google Scholar - 278. . Mouse Cyp4a isoforms: enzymatic properties, gender- and strain-specific expression, and role in renal 20-hydroxyeicosatetraenoic acid formation. Biochem J 403: 109–118, 2007.
Crossref | PubMed | ISI | Google Scholar - 279. . Determinants of DNA sequence specificity of the androgen, progesterone, and glucocorticoid receptors: evidence for differential steroid receptor response elements. Mol Endocrinol 13: 2090–2107, 1999.
Crossref | PubMed | Google Scholar - 280. . Estrogen production and action. J Am Acad Dermatol 45: S116–124, 2001.
Crossref | PubMed | ISI | Google Scholar - 281. . Dose-dependent effects of a genistein-enriched diet in the heart of ovariectomized mice. Genes Nutr 8: 383–390, 2012.
Crossref | PubMed | ISI | Google Scholar - 282. . Long-term treatment of ovariectomized mice with estradiol or phytoestrogens as a new model to study the role of estrogenic substances in the heart. Planta Med 78: 6–11, 2012.
Crossref | PubMed | ISI | Google Scholar - 283. . Treatment with an estrogen receptor-beta-selective agonist is cardioprotective. J Mol Cell Cardiol 42: 769–780, 2007.
Crossref | PubMed | ISI | Google Scholar - 284. . Amelioration of ischemia- and reperfusion-induced myocardial injury by 17beta-estradiol: role of nitric oxide and calcium-activated potassium channels. Circulation 96: 1953–1963, 1997.
Crossref | PubMed | ISI | Google Scholar - 285. . Myocardial dysfunction and male mortality in peroxisome proliferator-activated receptor alpha knockout mice overexpressing lipoprotein lipase in muscle. Lab Invest 83: 259–269, 2003.
Crossref | PubMed | ISI | Google Scholar - 286. . Upregulation of myocardial estrogen receptors in human aortic stenosis. Circulation 110: 3270–3275, 2004.
Crossref | PubMed | ISI | Google Scholar - 287. . Rapid estrogen receptor-alpha activation improves ischemic tolerance in aged female rats through a novel protein kinase C epsilon-dependent mechanism. Endocrinology 150: 889–896, 2009.
Crossref | PubMed | ISI | Google Scholar - 288. . 17 Beta-estradiol stimulates expression of endothelial and inducible NO synthase in rat myocardium in-vitro and in-vivo. Cardiovasc Res 43: 666–674, 1999.
Crossref | PubMed | ISI | Google Scholar - 289. . Differential effects of 17beta-estradiol on mitogen-activated protein kinase pathways in rat cardiomyocytes. FEBS Lett 454: 271–276, 1999.
Crossref | PubMed | ISI | Google Scholar - 290. . Hypertension among adults in the United States: National Health and Nutrition Examination Survey, 2011–2012. NCHS Data Brief 1–8, 2013.
Google Scholar - 291. . Estrogen receptors alpha and beta mediate distinct pathways of vascular gene expression, including genes involved in mitochondrial electron transport and generation of reactive oxygen species. Mol Endocrinol 21: 1281–1296, 2007.
Crossref | PubMed | Google Scholar - 292. . Cardioprotective effects of estradiol include the activation of large-conductance Ca2+-activated K+ channels in cardiac mitochondria. Am J Physiol Heart Circ Physiol 289: H1635–H1642, 2005.
Link | ISI | Google Scholar - 293. . Gender differences and aging: effects on the human heart. J Am Coll Cardiol 26: 1068–1079, 1995.
Crossref | PubMed | ISI | Google Scholar - 294. . Gender and aging in a transgenic mouse model of hypertrophic cardiomyopathy. Am J Physiol Heart Circ Physiol 280: H1136–H1144, 2001.
Link | ISI | Google Scholar - 295. . Association of the common genetic polymorphisms and haplotypes of the chymase gene with left ventricular mass in male patients with symptomatic aortic stenosis. PLoS One 9: e96306, 2014.
Crossref | PubMed | ISI | Google Scholar - 296. . Testosterone and the cardiovascular system: a comprehensive review of the clinical literature. J Am Heart Assoc 2: e000272, 2013.
Crossref | PubMed | ISI | Google Scholar - 297. . G protein-coupled receptor 30 localizes to the endoplasmic reticulum and is not activated by estradiol. Endocrinology 149: 4846–4856, 2008.
Crossref | PubMed | ISI | Google Scholar - 298. . Estrogen receptor-alpha mediates the protective effects of estrogen against vascular injury. Circ Res 90: 1087–1092, 2002.
Crossref | PubMed | ISI | Google Scholar - 299. . Sex differences in SR Ca2+ release in murine ventricular myocytes are regulated by the cAMP/PKA pathway. J Mol Cell Cardiol 75: 162–173, 2014.
Crossref | PubMed | ISI | Google Scholar - 300. . Incidence, clinical findings, and outcome of women with left ventricular apical ballooning syndrome. Am J Cardiol 99: 182–185, 2007.
Crossref | PubMed | ISI | Google Scholar - 301. . Aspects of cardiometabolic risk in women with polycystic ovary syndrome. Curr Obes Rep 3: 377–386, 2014.
Crossref | PubMed | Google Scholar - 302. . 17 Beta-estradiol differentially affects left ventricular and cardiomyocyte hypertrophy following myocardial infarction and pressure overload. J Card Fail 14: 245–253, 2008.
Crossref | PubMed | ISI | Google Scholar - 303. . 17beta-estradiol reduces cardiomyocyte apoptosis in vivo and in vitro via activation of phospho-inositide-3 kinase/Akt signaling. Circ Res 95: 692–699, 2004.
Crossref | PubMed | ISI | Google Scholar - 304. . Nature of functional estrogen receptors at the plasma membrane. Mol Endocrinol 20: 1996–2009, 2006.
Crossref | PubMed | Google Scholar - 305. . A composite measure of gender and its association with risk factors in patients with premature acute coronary syndrome. Psychosom Med 77: 517–526, 2015.
Crossref | PubMed | ISI | Google Scholar - 306. . Increased mortality and aggravation of heart failure in estrogen receptor-beta knockout mice after myocardial infarction. Circulation 111: 1492–1498, 2005.
Crossref | PubMed | ISI | Google Scholar - 307. . The AF-1 activation-function of ERalpha may be dispensable to mediate the effect of estradiol on endothelial NO production in mice. Proc Natl Acad Sci USA 99: 2205–2210, 2002.
Crossref | PubMed | ISI | Google Scholar - 308. . Do androgens play a beneficial role in the regulation of vascular tone? Nongenomic vascular effects of testosterone metabolites. Am J Physiol Heart Circ Physiol 298: H1301–H1307, 2010.
Link | ISI | Google Scholar - 309. . Association of estrogen receptor beta gene polymorphisms with left ventricular mass and wall thickness in women. Am J Hypertens 18: 1388–1395, 2005.
Crossref | PubMed | ISI | Google Scholar - 310. . Impact of gender on the myocardial metabolic response to obesity. JACC Cardiovasc Imaging 1: 424–433, 2008.
Crossref | PubMed | ISI | Google Scholar - 311. . Maladaptive remodeling is associated with impaired survival in women but not in men after aortic valve replacement. JACC Cardiovasc Imaging 7: 1073–1080, 2014.
Crossref | PubMed | ISI | Google Scholar - 312. . Regression of myocardial hypertrophy after aortic valve replacement: faster in women? Circulation 122: S23–28, 2010.
Crossref | PubMed | ISI | Google Scholar - 313. . Favorable effects of therapy on cardiac performance in spontaneously hypertensive rats. Am J Physiol Heart Circ Physiol 242: H776–H784, 1982.
Link | ISI | Google Scholar - 314. . Impact of sex and gonadal steroids on prolongation of ventricular repolarization and arrhythmias induced by I(K)-blocking drugs. Circulation 103: 2207–2212, 2001.
Crossref | PubMed | ISI | Google Scholar - 315. . Greater antiarrhythmic activity of acute 17beta-estradiol in female than male anaesthetized rats: correlation with Ca2+ channel blockade. Br J Pharmacol 149: 233–242, 2006.
Crossref | PubMed | ISI | Google Scholar - 316. . Nuclear factor-kappaB activation leads to down-regulation of fatty acid oxidation during cardiac hypertrophy. J Biol Chem 280: 17464–17471, 2005.
Crossref | PubMed | ISI | Google Scholar - 317. . Female mice liberated for inclusion in neuroscience and biomedical research. Neurosci Biobehav Rev 40: 1–5, 2014.
Crossref | PubMed | ISI | Google Scholar - 318. . ESR1 in myocardial infarction. Clin Chim Acta 413: 81–87, 2012.
Crossref | PubMed | ISI | Google Scholar - 319. . Sex-specific regulation of gene expression in the aging monkey aorta. Physiol Genomics 29: 169–180, 2007.
Link | ISI | Google Scholar - 320. . Sex- and estrogen-dependent regulation of a miRNA network in the healthy and hypertrophied heart. Int J Cardiol 169: 331–338, 2013.
Crossref | PubMed | ISI | Google Scholar - 321. . Mechanisms of coronary microcirculatory dysfunction in patients with aortic stenosis and angiographically normal coronary arteries. Circulation 105: 470–476, 2002.
Crossref | PubMed | ISI | Google Scholar - 322. . 17Beta-estradiol regulates expression of K(ATP) channels in heart-derived H9c2 cells. J Am Coll Cardiol 40: 367–374, 2002.
Crossref | PubMed | ISI | Google Scholar - 323. . Gender-specific difference in cardiac ATP-sensitive K+ channels. J Am Coll Cardiol 38: 906–915, 2001.
Crossref | PubMed | ISI | Google Scholar - 324. . Significant role of estrogen in maintaining cardiac mitochondrial functions. J Steroid Biochem Mol Biol 147: 1–9, 2015.
Crossref | PubMed | ISI | Google Scholar - 325. . Sex differences in the evolution of the electrocardiographic QT interval with age. Can J Cardiol 8: 690–695, 1992.
PubMed | ISI | Google Scholar - 326. . Repression of interleukin-6 gene expression by 17 beta-estradiol: inhibition of the DNA-binding activity of the transcription factors NF-IL6 and NF-kappa B by the estrogen receptor. FEBS Lett 409: 79–85, 1997.
Crossref | PubMed | ISI | Google Scholar - 327. . Testosterone exacerbates hypertension and reduces pressure-natriuresis in male spontaneously hypertensive rats. Hypertension 31: 435–439, 1998.
Crossref | PubMed | ISI | Google Scholar - 328. . Gender differences in hypertension in spontaneously hypertensive rats: role of androgens and androgen receptor. Hypertension 34: 920–923, 1999.
Crossref | PubMed | ISI | Google Scholar - 329. ,
European Society of Gynecology, Association for European Paediatric Cardiology, German Society for Gender Medicine, and ESC Committee for Practice Guidelines . ESC Guidelines on the management of cardiovascular diseases during pregnancy: the Task Force on the Management of Cardiovascular Diseases during Pregnancy of the European Society of Cardiology (ESC). Eur Heart J 32: 3147–3197, 2011.
Crossref | PubMed | ISI | Google Scholar - 330. . Role of gender in heart failure with normal left ventricular ejection fraction. Prog Cardiovasc Dis 49: 241–251, 2007.
Crossref | PubMed | ISI | Google Scholar - 331. . Sex and sex hormone-dependent cardiovascular stress responses. Hypertension 61: 270–277, 2013.
Crossref | PubMed | ISI | Google Scholar - 332. . Cardiovascular therapy in women and men. In: Sex and Gender Differences in Pharmacoloy, edited by Regitz-Zagrosek V. Heidelberg: Springer Verlag, 2012.
Crossref | Google Scholar - 333. . Probucol-associated tachyarrhythmic events and QT prolongation: importance of gender. Am Heart J 131: 1184–1191, 1996.
Crossref | PubMed | ISI | Google Scholar - 334. . Estrogen: a master regulator of bioenergetic systems in the brain and body. Front Neuroendocrinol 35: 8–30, 2014.
Crossref | PubMed | ISI | Google Scholar - 335. . A transmembrane intracellular estrogen receptor mediates rapid cell signaling. Science 307: 1625–1630, 2005.
Crossref | PubMed | ISI | Google Scholar - 336. . Opinion: focus on preclinical sex differences will not address women's and men's health disparities. Proc Natl Acad Sci USA 112: 13419–13420, 2015.
Crossref | PubMed | ISI | Google Scholar - 337. . Sex chromosome complement contributes to sex differences in coxsackievirus B3 but not influenza A virus pathogenesis. Biol Sex Differ 2: 8, 2011.
Crossref | PubMed | Google Scholar - 338. . Cardiovascular risk in women with non-specific chest pain (from the Women's Health Initiative Hormone Trials). Am J Cardiol 102: 693–699, 2008.
Crossref | PubMed | ISI | Google Scholar - 339. . Sex differences in the beneficial cardiac effects of chronic treatment with atrial natriuretic peptide in spontaneously hypertensive rats. PLoS One 8: e71992, 2013.
Crossref | PubMed | ISI | Google Scholar - 340. . eNOS phosphorylation and translocation are altered in male but not female mice by increased activation of the Galphaq protein. Can J Physiol Pharmacol 88: 121–129, 2010.
Crossref | PubMed | ISI | Google Scholar - 341. . The effects of anabolic steroids on myocardial structure and cardiovascular fitness. Med Sci Sports Exerc 25: 1240–1245, 1993.
Crossref | PubMed | ISI | Google Scholar - 342. . Sex differences in the mechanisms underlying long QT syndrome. Am J Physiol Heart Circ Physiol 307: H640–H648, 2014.
Link | ISI | Google Scholar - 343. . ERbeta prevents up-regulation of miRNAs under pressure overload in LV of female mice. Cardiovasc Res 103: S11–S11, 2014.
Crossref | ISI | Google Scholar - 344. . Update in hyper- and hypogonadotropic amenorrhea. J Clin Endocrinol Metab 96: 3281–3288, 2011.
Crossref | PubMed | ISI | Google Scholar - 345. . Spontaneous coronary artery dissection: association with predisposing arteriopathies and precipitating stressors and cardiovascular outcomes. Circ Cardiovasc Interv 7: 645–655, 2014.
Crossref | PubMed | ISI | Google Scholar - 346. . MicroRNAs play an essential role in the development of cardiac hypertrophy. Circ Res 100: 416–424, 2007.
Crossref | PubMed | ISI | Google Scholar - 347. . Cardiac function in hypertrophied hearts from chronically exercised female rats. J Appl Physiol 50: 1140–1145, 1981.
Link | ISI | Google Scholar - 348. . Effects of physical training by running or swimming on ventricular performance of rat hearts. J Appl Physiol 46: 854–860, 1979.
Link | ISI | Google Scholar - 349. . Pressure overload and neurohumoral activation differentially affect the myocardial proteome. Proteomics 5: 1372–1381, 2005.
Crossref | PubMed | ISI | Google Scholar - 350. . Osteoclast differentiation factor RANKL controls development of progestin-driven mammary cancer. Nature 468: 98–102, 2010.
Crossref | PubMed | ISI | Google Scholar - 351. . Estrogen receptor alpha gene polymorphisms are associated with estradiol levels in postmenopausal women. Eur J Endocrinol 153: 327–334, 2005.
Crossref | PubMed | ISI | Google Scholar - 352. . Cardiomyocyte-specific overexpression of oestrogen receptor beta improves survival and cardiac function after myocardial infarction in female and male mice. Clin Sci 130: 365–376, 2016.
Crossref | PubMed | ISI | Google Scholar - 353. . Dietary phytoestrogen supplementation induces sex differences in the myocardial protein pattern of mice: a comparative proteomics study. Proteomics 11: 3887–3904, 2011.
Crossref | PubMed | ISI | Google Scholar - 354. . Ribosomal protein S6 kinase 1 signaling regulates mammalian life span. Science 326: 140–144, 2009.
Crossref | PubMed | ISI | Google Scholar - 355. . Epidemiology and clinical profile of Takotsubo cardiomyopathy. Circ J 78: 2119–2128, 2014.
Crossref | PubMed | ISI | Google Scholar - 356. . Estrogen receptor alpha gene variation is associated with risk of myocardial infarction in more than seven thousand men from five cohorts. Circ Res 98: 590–592, 2006.
Crossref | PubMed | ISI | Google Scholar - 357. . Role of co-activators and co-repressors in the mechanism of steroid/thyroid receptor action. Recent Prog Horm Res 52: 141–164, 1997.
PubMed | Google Scholar - 358. . Sex differences in the modulation of K+ currents in diabetic rat cardiac myocytes. J Physiol 550: 401–412, 2003.
Crossref | PubMed | ISI | Google Scholar - 359. . New genetic loci link adipose and insulin biology to body fat distribution. Nature 518: 187–196, 2015.
Crossref | PubMed | ISI | Google Scholar - 360. . X chromosomal variation is associated with slow progression to AIDS in HIV-1-infected women. Am J Hum Genet 85: 228–239, 2009.
Crossref | PubMed | ISI | Google Scholar - 361. . Sex-biased chromatin and regulatory cross-talk between sex chromosomes, autosomes, and mitochondria. Biol Sex Differ 5: 2, 2014.
Crossref | PubMed | ISI | Google Scholar - 362. . Aromatase expression in health and disease. Recent Prog Horm Res 52: 185–213, 1997.
PubMed | Google Scholar - 363. . Estrogen receptor-beta mediates male-female differences in the development of pressure overload hypertrophy. Am J Physiol Heart Circ Physiol 288: H469–H476, 2005.
Link | ISI | Google Scholar - 364. . Endocrine activity of the postmenopausal ovary: the effects of pituitary down-regulation and oophorectomy. J Clin Endocrinol Metab 80: 2163–2167, 1995.
PubMed | ISI | Google Scholar - 365. . Steroid receptors and their associated proteins. Mol Endocrinol 7: 4–11, 1993.
PubMed | Google Scholar - 366. . Estrogen rapid action via protein complex formation involving ERalpha and Src. Trends Endocrinol Metab 16: 347–353, 2005.
Crossref | PubMed | ISI | Google Scholar - 367. . LXR agonism improves TNF-alpha-induced endothelial dysfunction in the absence of its cholesterol-modulating effects. Atherosclerosis 232: 1–9, 2014.
Crossref | PubMed | ISI | Google Scholar - 368. . Exposure to famine during gestation, size at birth, and blood pressure at age 59 y: evidence from the Dutch Famine. Eur J Epidemiol 21: 759–765, 2006.
Crossref | PubMed | ISI | Google Scholar - 369. . Estrogen increases mitochondrial efficiency and reduces oxidative stress in cerebral blood vessels. Mol Pharmacol 68: 959–965, 2005.
Crossref | PubMed | ISI | Google Scholar - 370. . Tissue physiology and pathology of aromatase. Steroids 77: 27–35, 2012.
Crossref | PubMed | ISI | Google Scholar - 371. . The clinical development of a 5 alpha-reductase inhibitor, finasteride. J Steroid Biochem Mol Biol 37: 375–378, 1990.
Crossref | PubMed | ISI | Google Scholar - 372. . Cell sex determines anoikis resistance in vascular smooth muscle cells. FEBS Lett 583: 3448–3454, 2009.
Crossref | PubMed | ISI | Google Scholar - 373. . Modulation of antioxidant enzyme expression and function by estrogen. Circ Res 93: 170–177, 2003.
Crossref | PubMed | ISI | Google Scholar - 374. . Premature coronary artery disease associated with a disruptive mutation in the estrogen receptor gene in a man. Circulation 96: 3774–3777, 1997.
Crossref | PubMed | ISI | Google Scholar - 375. . Hypercontractile female hearts exhibit increased S-nitrosylation of the L-type Ca2+ channel alpha1 subunit and reduced ischemia/reperfusion injury. Circ Res 98: 403–411, 2006.
Crossref | PubMed | ISI | Google Scholar - 376. . MicroRNA-23a mediates mitochondrial compromise in estrogen deficiency-induced concentric remodeling via targeting PGC-1alpha. J Mol Cell Cardiol 75: 1–11, 2014.
Crossref | PubMed | ISI | Google Scholar - 377. . Gender differences in substrate metabolism during endurance exercise. Can J Appl Physiol 25: 312–327, 2000.
Crossref | PubMed | Google Scholar - 378. . Expression of microRNAs is dynamically regulated during cardiomyocyte hypertrophy. J Mol Cell Cardiol 42: 1137–1141, 2007.
Crossref | PubMed | ISI | Google Scholar - 379. . Investigation of gene-by-sex interactions for lipid traits in diverse populations from the population architecture using genomics and epidemiology study. BMC Genet 14: 33, 2013.
Crossref | PubMed | ISI | Google Scholar - 380. . Clinical features and outcomes of takotsubo (stress) cardiomyopathy. N Engl J Med 373: 929–938, 2015.
Crossref | PubMed | ISI | Google Scholar - 381. . Interaction between insulin and estradiol in regulation of cardiac glucose and free fatty acid transporters. Horm Metab Res 43: 524–530, 2011.
Crossref | PubMed | ISI | Google Scholar - 382. . Adriamycin-induced DNA damage mediated by mammalian DNA topoisomerase II. Science 226: 466–468, 1984.
Crossref | PubMed | ISI | Google Scholar - 383. . Exogenous 17-beta estradiol administration blunts progression of established angiotensin II-induced abdominal aortic aneurysms in female ovariectomized mice. Biol Sex Differ 6: 12, 2015.
Crossref | PubMed | ISI | Google Scholar - 384. . Hypersensitivity of myofilament response to Ca2+ in association with maladaptation of estrogen-deficient heart under diabetes complication. Am J Physiol Regul Integr Comp Physiol 292: R844–R851, 2007.
Link | ISI | Google Scholar - 385. . Testosterone, cytochrome P450, and cardiac hypertrophy. FASEB J 16: 1537–1549, 2002.
Crossref | PubMed | ISI | Google Scholar - 386. . MicroRNA-21 contributes to myocardial disease by stimulating MAP kinase signalling in fibroblasts. Nature 456: 980–984, 2008.
Crossref | PubMed | ISI | Google Scholar - 387. . Third universal definition of myocardial infarction. Circulation 126: 2020–2035, 2012.
Crossref | PubMed | ISI | Google Scholar - 388. . Estrogen improves vascular function via peroxisome-proliferator-activated-receptor-gamma. J Mol Cell Cardiol 53: 268–276, 2012.
Crossref | PubMed | ISI | Google Scholar - 389. . DNA methylation differences after exposure to prenatal famine are common and timing- and sex-specific. Hum Mol Genet 18: 4046–4053, 2009.
Crossref | PubMed | ISI | Google Scholar - 390. . Differential cardiac remodeling in preload versus afterload. Circulation 122: 993–1003, 2010.
Crossref | PubMed | ISI | Google Scholar - 391. . Testosterone supplementation in heart failure: a meta-analysis. Circ Heart Fail 5: 315–321, 2012.
Crossref | PubMed | ISI | Google Scholar - 392. . Hdac2 regulates the cardiac hypertrophic response by modulating Gsk3 beta activity. Nat Med 13: 324–331, 2007.
Crossref | PubMed | ISI | Google Scholar - 393. . Molecular mechanisms of action of steroid/thyroid receptor superfamily members. Annu Rev Biochem 63: 451–486, 1994.
Crossref | PubMed | ISI | Google Scholar - 394. . Chromosome X-wide association study identifies loci for fasting insulin and height and evidence for incomplete dosage compensation. PLoS Genet 10: e1004127, 2014.
Crossref | PubMed | ISI | Google Scholar - 395. . Clinical features, management, and prognosis of spontaneous coronary artery dissection. Circulation 126: 579–588, 2012.
Crossref | PubMed | ISI | Google Scholar - 396. . Melusin protects from cardiac rupture and improves functional remodelling after myocardial infarction. Cardiovasc Res 101: 97–107, 2014.
Crossref | PubMed | ISI | Google Scholar - 397. . Sex-based differences in early mortality after myocardial infarction. National Registry of Myocardial Infarction 2 Participants. N Engl J Med 341: 217–225, 1999.
Crossref | PubMed | ISI | Google Scholar - 398. . Relationships between sex hormones assessed in amniotic fluid, and maternal and umbilical cord serum: what is the best source of information to investigate the effects of fetal hormonal exposure? Horm Behav 46: 663–669, 2004.
Crossref | PubMed | ISI | Google Scholar - 399. . 17Beta-estradiol attenuates the development of pressure-overload hypertrophy. Circulation 104: 1419–1423, 2001.
Crossref | PubMed | ISI | Google Scholar - 400. . 17-Beta-estradiol increases cardiac remodeling and mortality in mice with myocardial infarction. J Am Coll Cardiol 41: 2084–2092, 2003.
Crossref | PubMed | ISI | Google Scholar - 401. . A signature pattern of stress-responsive microRNAs that can evoke cardiac hypertrophy and heart failure. Proc Natl Acad Sci USA 103: 18255–18260, 2006.
Crossref | PubMed | ISI | Google Scholar - 402. . Identification of authentic estrogen receptor in cultured endothelial cells. A potential mechanism for steroid hormone regulation of endothelial function. Circulation 94: 727–733, 1996.
Crossref | PubMed | ISI | Google Scholar - 403. . Testosterone induces an intracellular calcium increase by a nongenomic mechanism in cultured rat cardiac myocytes. Endocrinology 147: 1386–1395, 2006.
Crossref | PubMed | ISI | Google Scholar - 404. . Angiotensin II type 2 receptor mediates sex differences in mice renal interlobar arteries response to angiotensin II. J Hypertens 30: 1791–1798, 2012.
Crossref | PubMed | ISI | Google Scholar - 405. . Endothelin-1 overexpression and endothelial nitric oxide synthase knock-out induce different pathological responses in the heart of male and female mice. Life Sci 118: 219–225, 2014.
Crossref | PubMed | ISI | Google Scholar - 406. . Gender differences of echocardiographic and gene expression patterns in human pressure overload left ventricular hypertrophy. J Mol Cell Cardiol 46: 526–535, 2009.
Crossref | PubMed | ISI | Google Scholar - 407. . Sex-dependent differences in left ventricular function and structure in chronic pressure overload. Eur Heart J 16: 1410–1419, 1995.
Crossref | PubMed | ISI | Google Scholar - 408. . Females live longer than males: role of oxidative stress. Curr Pharm Des 17: 3959–3965, 2011.
Crossref | PubMed | ISI | Google Scholar - 409. . Testosterone physiology in resistance exercise and training: the up-stream regulatory elements. Sports Med 40: 1037–1053, 2010.
Crossref | PubMed | ISI | Google Scholar - 410. . Gender differences in the cardiovascular effect of sex hormones. Nat Rev Cardiol 6: 532–542, 2009.
Crossref | PubMed | ISI | Google Scholar - 411. . Mechanisms of sex differences in rat cardiac myocyte response to beta-adrenergic stimulation. Am J Physiol Heart Circ Physiol 282: H256–H263, 2002.
Link | ISI | Google Scholar - 412. . Acute postischemic treatment with estrogen receptor-alpha agonist or estrogen receptor-beta agonist improves myocardial recovery. Surgery 146: 145–154, 2009.
Crossref | PubMed | ISI | Google Scholar - 413. . Association of hyperandrogenemic and metabolic phenotype with carotid intima-media thickness in young women with polycystic ovary syndrome. J Clin Endocrinol Metab 90: 2740–2746, 2005.
Crossref | PubMed | ISI | Google Scholar - 414. . Effects of combination therapy with estrogen plus simvastatin on lipoprotein metabolism in postmenopausal women with type IIa hypercholesterolemia. Atherosclerosis 150: 103–111, 2000.
Crossref | PubMed | ISI | Google Scholar - 415. . Cloning of the human estrogen receptor cDNA. Proc Natl Acad Sci USA 82: 7889–7893, 1985.
Crossref | PubMed | ISI | Google Scholar - 416. . Sex differences in the myocardial inflammatory response to ischemia-reperfusion injury. Am J Physiol Endocrinol Metab 288: E321–E326, 2005.
Link | ISI | Google Scholar - 417. . Estrogen receptor-alpha mediates acute myocardial protection in females. Am J Physiol Heart Circ Physiol 290: H2204–H2209, 2006.
Link | ISI | Google Scholar - 418. . Role of endogenous testosterone in myocardial proinflammatory and proapoptotic signaling after acute ischemia-reperfusion. Am J Physiol Heart Circ Physiol 288: H221–H226, 2005.
Link | ISI | Google Scholar - 419. . 17-beta-Estradiol decreases p38 MAPK-mediated myocardial inflammation and dysfunction following acute ischemia. J Mol Cell Cardiol 40: 205–212, 2006.
Crossref | PubMed | ISI | Google Scholar - 420. . Protective effects of estrogen against reperfusion arrhythmias following severe myocardial ischemia in rats. Circ J 74: 634–643, 2010.
Crossref | PubMed | ISI | Google Scholar - 421. . Cardiac-specific overexpression of dominant-negative CREB leads to increased mortality and mitochondrial dysfunction in female mice. Am J Physiol Heart Circ Physiol 299: H2056–H2068, 2010.
Link | ISI | Google Scholar - 422. . Differential effects of ovariectomy on calcium activation of cardiac and soleus myofilaments. Am J Physiol Heart Circ Physiol 277: H467–H473, 1999.
Link | ISI | Google Scholar - 423. . Estrogen supplement prevents the calcium hypersensitivity of cardiac myofilaments in ovariectomized rats. Life Sci 66: 533–543, 2000.
Crossref | PubMed | ISI | Google Scholar - 424. . Tako-tsubo cardiomyopathy. Incidence in patients with acute coronary syndrome. Herz 31: 339–346, 2006.
Crossref | PubMed | ISI | Google Scholar - 425. . Sex dependence and temporal dependence of the left ventricular genomic response to pressure overload. Physiol Genomics 12: 113–127, 2003.
Link | ISI | Google Scholar - 426. . Gender differences in molecular remodeling in pressure overload hypertrophy. J Am Coll Cardiol 34: 264–273, 1999.
Crossref | PubMed | ISI | Google Scholar - 427. . Effects of estrogen, an ERalpha agonist and raloxifene on pressure overload induced cardiac hypertrophy. PLoS One 7: e50802, 2012.
Crossref | PubMed | ISI | Google Scholar - 428. . CYP2J2 overexpression protects against arrhythmia susceptibility in cardiac hypertrophy. PLoS One 8: e73490, 2013.
Crossref | PubMed | ISI | Google Scholar - 429. . The upper limit of physiological cardiac hypertrophy in elite male and female athletes: the British experience. Eur J Appl Physiol 92: 592–597, 2004.
Crossref | PubMed | ISI | Google Scholar - 430. . Improvement of endothelial dysfunction by selective estrogen receptor-alpha stimulation in ovariectomized SHR. Hypertension 42: 991–996, 2003.
Crossref | PubMed | ISI | Google Scholar - 431. . Reduced bone mass and muscle strength in male 5alpha-reductase type 1 inactivated mice. PLoS One 6: e21402, 2011.
Crossref | PubMed | ISI | Google Scholar - 432. . Sex-specific pathways in early cardiac response to pressure overload in mice. J Mol Med 86: 1013–1024, 2008.
Crossref | PubMed | ISI | Google Scholar - 433. ,
SHOCK Investigators . Absence of gender differences in clinical outcomes in patients with cardiogenic shock complicating acute myocardial infarction. A report from the SHOCK Trial Registry. J Am Coll Cardiol 38: 1395–1401, 2001.
Crossref | PubMed | ISI | Google Scholar - 434. . Genetic variation and gender determine bradykinin type 1 receptor responses in human tissue: implications for the ACE-inhibitor-induced effects in patients with coronary artery disease. Clin Sci 126: 441–449, 2014.
Crossref | PubMed | ISI | Google Scholar - 435. . Non-nuclear estrogen receptor signaling in the endothelium. J Biol Chem 286: 14737–14743, 2011.
Crossref | PubMed | ISI | Google Scholar - 436. . Oestrogen protects FKBP12.6 null mice from cardiac hypertrophy. Nature 416: 334–338, 2002.
Crossref | PubMed | ISI | Google Scholar - 437. . Estrogen modulates TNF-alpha-induced inflammatory responses in rat aortic smooth muscle cells through estrogen receptor-beta activation. Am J Physiol Heart Circ Physiol 292: H2607–H2612, 2007.
Link | ISI | Google Scholar - 438. . Estrogen improves cardiac recovery after ischemia/reperfusion by decreasing tumor necrosis factor-alpha. Cardiovasc Res 69: 836–844, 2006.
Crossref | PubMed | ISI | Google Scholar - 439. . Human type 3 5alpha-reductase is expressed in peripheral tissues at higher levels than types 1 and 2 and its activity is potently inhibited by finasteride and dutasteride. Horm Mol Biol Clin Invest 2: 293–299, 2010.
PubMed | Google Scholar - 440. . Correspondence regarding Schwend and Gustafsson, “False positives in MALDI-TOF detection of ERbeta in mitochondria.” Biochem Biophys Res Commun 345: 917–918, 2006.
Crossref | PubMed | ISI | Google Scholar - 441. . The PI3K/Akt pathway mediates the nongenomic cardioprotective effects of estrogen following trauma-hemorrhage. Ann Surg 245: 971–977, 2007.
Crossref | PubMed | ISI | Google Scholar - 442. . Mechanism of cardioprotection following trauma-hemorrhagic shock by a selective estrogen receptor-beta agonist: up-regulation of cardiac heat shock factor-1 and heat shock proteins. J Mol Cell Cardiol 40: 185–194, 2006.
Crossref | PubMed | ISI | Google Scholar - 443. . Testosterone relaxes rabbit coronary arteries and aorta. Circulation 91: 1154–1160, 1995.
Crossref | PubMed | ISI | Google Scholar - 444. . Myocardial ischemia-reperfusion injury in estrogen receptor-alpha knockout and wild-type mice. Am J Physiol Heart Circ Physiol 278: H1640–H1647, 2000.
Link | ISI | Google Scholar - 445. . Effect of estrogen on global myocardial ischemia-reperfusion injury in female rats. Am J Physiol Heart Circ Physiol 279: H2766–H2775, 2000.
Link | ISI | Google Scholar - 446. . Class II histone deacetylases act as signal-responsive repressors of cardiac hypertrophy. Cell 110: 479–488, 2002.
Crossref | PubMed | ISI | Google Scholar - 447. . Effect of oestrogen on reactive oxygen species production in the aortas of ovariectomized Dahl salt-sensitive rats. J Hypertens 25: 407–414, 2007.
Crossref | PubMed | ISI | Google Scholar - 448. . Epigenetics and the environmental regulation of the genome and its function. Annu Rev Psychol 61: 439–466, 2010.
Crossref | PubMed | ISI | Google Scholar - 449. . Sex-steroid hormones and electrocardiographic QT-interval duration: findings from the third National Health and Nutrition Examination Survey and the Multi-Ethnic Study of Atherosclerosis. Am J Epidemiol 174: 403–411, 2011.
Crossref | PubMed | ISI | Google Scholar - 450. . 17Beta-estradiol inhibits angiotensin II-induced collagen synthesis of cultured rat cardiac fibroblasts via modulating angiotensin II receptors. Eur J Pharmacol 567: 186–192, 2007.
Crossref | PubMed | ISI | Google Scholar - 451. . Antiandrogenic therapy with finasteride attenuates cardiac hypertrophy and left ventricular dysfunction. Circulation 131: 1071–1081, 2015.
Crossref | PubMed | ISI | Google Scholar
