CoCl2 induces apoptosis through the mitochondria- and death receptor-mediated pathway in the mouse embryonic stem cells

Embryonic hypoxia/ischemia is a major cause of a poor fetal outcome and future neonatal and adult handicaps. However, biochemical cellular events in mouse embryonic stem (mES) cells during hypoxia remains unclear. This study investigated the underlying mechanism of apoptosis in mES cells under CoCl₂-induced hypoxic/ischemic conditions. CoCl₂ enhanced the expression of hypoxia-inducible factor-1α (HIF-1α) and the accumulation of reactive oxygen species in mES cells. The CoCl₂-treated mES cells showed a decrease in cell viability as well as typical apoptotic changes, cell shrinkage, chromatin condensation, and nuclear fragmentation and an extended G₂/M phase of the cell cycle. CoCl₂ augmented the release of cytochrome c into the cytosol from the mitochondria with a concomitant loss of the mitochondrial transmembrane potential (ΔΨ_m) and upregulated the voltage-dependent anion channel. In addition, CoCl₂-induced caspase-3, -8, and -9 activation and upregulation of p53 level, whereas downregulated Bcl-2 and Bcl-xL, a member of the anti-apoptotic Bcl-2 family in mES cells. Furthermore, CoCl₂ led to the upregulation of Fas and Fas-ligand, which are the death receptor assemblies, as well as the cleavage of Bid in mES cells. These results suggest that CoCl₂ induces apoptosis through both mitochondria- and death receptor-mediated pathways that are regulated by the Bcl-2 family in mES cells.