Pharmacologic stabilization of HIF-1α increases hematopoietic stem cell quiescence in vivo and accelerates blood recovery after severe irradiation

Quiescent hematopoietic stem cells (HSCs) preferentially reside in poorly perfused niches that may be relatively hypoxic. Most of the cellular effects of hypoxia are mediated by O-2-labile hypoxia-inducible transcription factors (HIFs). To investigate the effects of hypoxia on HSCs, we blocked O-2-dependent HIF-1 alpha degradation in vivo in mice by injecting 2 structurally unrelated prolyl hydroxylase domain (PHD) enzyme inhibitors: dimethyloxalyl glycine and FG-4497. Injection of either of these 2 PHD inhibitors stabilized HIF-1 alpha protein expression in the BM. In vivo stabilization of HIF-1 alpha with these PHD inhibitors increased the proportion of phenotypic HSCs and immature hematopoietic progenitor cells in phase G(0) of the cell cycle and decreased their proliferation as measured by 5-bromo-2' -deoxyuridine incorporation. This effect was independent of erythropoietin, the expression of which was increased in response to PHD inhibitors. Finally, pretreatment of mice with a HIF-1 alpha stabilizer before severe, sublethal 9.0-Gy irradiation improved blood recovery and enhanced 89-fold HSC survival in the BM of irradiated mice as measured in long-term competitive repopulation assays. The results of the present study demonstrate that the levels of HIF-1 alpha protein can be manipulated pharmacologically in vivo to increase HSC quiescence and recovery from irradiation. (Blood. 2013;121(5):759-769)