BMP4, SCF, and hypoxia cooperatively regulate the expansion of murine stress erythroid progenitors

The erythrold response to acute anemia relies on the rapid expansion in the spleen of a specialized population of erythroid progenitors termed stress BFU-E. This expansion requires BMN/Madh5-dependent signaling in vivo; however, in vitro, BMP4 alone cannot recapitulate the expansion of stress BFU-E observed in vivo, which suggests that other signals are required. In this report we show that mutation of the Kit receptor results in a severe defect in the expansion of stress BFU-E, indicatIng a role for the Kit/SCF signaling pathway in stress erythropoiesis. In vitro analysis showed that BMP4 and SCIF are necessary for the expansion of stress BFU-E, but only when spleen cells were cultured in BMP4 + SCIF at low-oxygen concentrations did we recapitulate the expansion of stress BFU-E observed in vivo. Culturing spleen cells in BMP4, SCIF under hypoxic conditions resulted in the preferential expansion of erythrold progenitors characterized by the expression of Kit, CD71, and TER119. This expression pattern is also seen in stress erythroid progenitors isolated from patients with sickle cell anemia and patients with beta-thalassemia. Taken together these data demonstrate that SCIF and hypoxia synergize with BMP4 to promote the expansion and differentiation of stress BFU-E during the recovery from acute anemia.