Sirtuin(Sirt1/Sirt2) protect human pluripotent stem cells from DNA damage-induced apoptosis

Abstract

Sirtuin (Sirt1/2) NAD+ dependent deacetylase plays an important role in cell survival under stress conditions. Sirt1 recently has been found to be highly-expressed in embryonic stem cells and Sirt1/2 may play a key role in survival of pluripotent stem cells (PSCs, embryonic stem cells and induced pluripotent stem cells).1,2 In this study, the roles of Sirt1/2 were investigated in pluripotent stem cell survival by chemical inhibitions. Sirt1/2 inhibitors: Sirtuin, Salermide, and Teniovin-6 were tested in survival of PSCs. While Sirt1/2 inhibition led to apoptosis of undifferentiated PSCs, it did not affect differentiated cells. PSCs have similar characteristics with cancer cells especially in cell cycle.3,4 p53 in PSCs and cancer cells is not activated. To prove Sirt1/2 inhibition-mediated apoptosis in PSCs, the author tested DNA damage and p53-related pathway regulation by Sirt1/2 deacetylation. Sirt1/2 down regulation led to DNA damage increment and reactivation of p53 followed by over-expression of p53 target genes: PUMA and BAX. In the end, cleaved caspase-3 was clearly detected in PSCs treated with Sirt1/2 inhibitors. Pro-apoptotic gene (PUMA, BAX) up-regulations and caspase3 activation imply that the apoptosis is p53-mediated event in Pluripotent stem cells. Thus, PSCs are susceptible to Sirt1/2 inhibition-mediated DNA damage and p53 activation that leads to apoptosis of PSCs, but not of differentiated cells. To validate the PSC-specific apoptosis induction by Sirt1/2 inhibitors, embryoid bodies containing partial differentiated cells and undifferentiated cells and PSC survival was examined by PSC marker (Oct4, SSEA4) expressions. In day 4 EBs, Sirt1/2 inhibitors dramatically reduced Oct4 levels and activated caspase-3 was mostly detected in SSEA4+ cells within the partially differentiating cells. Our findings provide a novel strategy to eliminate undifferentiated cells by Sirt1/2 inhibition in the process of in vitro differentiation.