Aims: Mesenchymal stem cells (MSCs) with multilineage differentiation capacity and immunomodulatory properties are novel sources for cell therapy. However, in vitro expansion of these rare somatic stem cells leads to senescence, resulting in declines of differentiation and proliferative capacities. We therefore investigated the mechanisms mediating senescence in human fetal MSCs termed placenta-derived multipotent cells (PDMCs).
Results: Long-term cultured PDMCs underwent senescence, with increased levels of hydrogen peroxide (H2O2; a reactive oxygen species), positive β-galactosidase staining, decreased sirtuin-1 expression, increased p21 expression, and cell cycle arrest at the G0/G1 phase. Senescent PDMCs also showed decreased osteogenic capacity. Mechanistically, increased p21 expression and proliferative decline were not due to elevated H2O2 levels nor mediated by p53. Instead, inhibition of protein kinase C (PKC)-α and -β in senescent PDMCs decreased p21 expression and reversed cell cycle arrest. H2O2 was involved in the alteration of differentiation potential, since scavenging of H2O2 restored expression of c-MAF, an osteogenic and age-sensitive transcription factor, and osteogenic capacity in senescent PDMCs.
Innovation: Our findings not only show the effects of senescence on MSCs, but also reveal mechanisms involved in mediating decreased proliferation and differentiation capacity. Moreover, targeting increased levels of H2O2 associated with senescence may reverse the decreased osteogenic capacity of senescent MSCs.
Conclusion: Our study suggests that the two biological consequences of senescence, differentiation alteration, and proliferative decline, in fetal MSCs are distinctly regulated by the H2O2-c-MAF and PKC-p21 pathways, respectively.