Regulatory Crosstalk between Physiological Low O-2 Concentration and Notch Pathway in Early Erythropoiesis

Physiological low oxygen (O-2) concentration (<5%) favors erythroid development ex vivo. It is known that low O-2 concentration, via the stabilization of hypoxia-induced transcription factors (HIFs), intervenes with Notch signaling in the control of cell fate. In addition, Notch activation is implicated in the regulation of erythroid differentiation. We test here if the favorable effects of a physiological O-2 concentration (3%) on the amplification of erythroid progenitors implies a cooperation between HIFs and the Notch pathway. To this end, we utilized a model of early erythropoiesis ex vivo generated from cord blood CD34(+) cells transduced with shHIF1 alpha and shHIF2 alpha at 3% 02 and 20% O-2 in the presence or absence of the Notch pathway inhibitor. We observed that Notch signalization was activated by Notch2R-Jaggedl ligand interaction among progenitors. The inhibition of the Notch pathway provoked a modest reduction in erythroid cell expansion and promoted erythroid differentiation. ShHIF1 alpha and particularly shHIF2 alpha strongly impaired erythroid progenitors' amplification and differentiation. Additionally, HIF/NOTCH signaling intersects at the level of multipotent progenitor erythroid commitment and amplification of BFU-E. In that, both HIFs contribute to the expression of Notch2R and Notch target gene HES1. Our study shows that HIF, particularly HIF2, has a determining role in the early erythroid development program, which includes Notch signaling.