The ATM/p53/p21 pathway influences cell fate decision between apoptosis and senescence in reoxygenated hematopoietic progenitor cells

Hematopoietic cells are often exposed to transient hypoxia as they develop and migrate between blood and tissues. We tested the hypothesis that hypoxia-then-reoxygenation represent a stress for hematopoietic progenitor cells. Here we report that reoxygenation-generated oxidative stress induced senescence, tested as staining for SA-beta-galactosidase (SA-beta-gal), of bone marrow progenitor cells. Reoxygenation induced significant DNA damage and inhibited colony formation in lineage-depleted bone marrow cells enriched for progenitor cells. These reoxygenated cells exhibited a prolonged G(0)/G(1) accumulation without significant apoptosis after 24 h of treatments. Reoxygenated bone marrow progenitor cells expressed SA-beta-gal and senescence-associated proteins p53 and p21(WAF1). Reoxygenated Fancc-/- progenitor cells, which underwent significant apoptosis and senescence, tested as staining for SA-beta-gal, also expressed p16(INK4A). Suppression of apoptosis by the pan-caspase inhibitor benzyloxycarbonyl-VAD-fluoromethyl ketone dramatically increased senescent Fancc-/- progenitor cells. Senescence induction, tested as staining for SA-beta-gal, in reoxygenated progenitor cells was closely correlated with extent of DNA damage and phosphorylation of ATM at Ser-1981 and p53 at Ser-15. Moreover, inhibition of ATM signaling reduced SA-beta-gal positivity but increased apoptosis of reoxygenated progenitor cells. Thus, these results suggest that the ATM/p53/p21 pathway influences cell fate decision between apoptosis and senescence in reoxygenated hematopoietic progenitor cells.