Gene expression data of murine hematopoietic stem cells after anemic stress

Adult hematopoietic stem cells (HSCs) react to various stress conditions by rapidly proliferating and preferentially differentiating towards desired cell types. However, it is unclear whether and how HSCs respond to severe anemic conditions. Here we demonstrate that HSCs rapidly proliferate and enhance their erythroid potential upon induction of acute anemia. Under severe anemic conditions, the concentration of erythropoietin (EPO) does not increase in the bone marrow. Instead, lipoprotein profiles largely changed, and the concentration of apolipoprotein E (ApoE) increased. In HSCs, transcription levels of lipid metabolism-related genes such as very low-density lipoprotein receptor (Vldlr) were significantly up-regulated. Stimulation of HSCs with recombinant ApoE enhanced the erythroid potential, while HSCs of ApoE knockout mice did not respond to the hemolysis induction. We also found that VLDLRhighHSCs have higher erythroid differentiation potential, particularly after acute anemia induction. VLDLRhighHSCs were epigenetically distinct from VLDLRlowHSCs, as their chromatin accessibility was lower and more chromatin regions were closed upon acute anemia induction. Finally, we identified that the chromatin regions closed upon the acute anemia induction were mainly binding sites of a transcription factor Erg. Treatment of HSC with Erg inhibitor enhanced erythroid differentiation potential, as seen in the ApoE treatment. Our findings indicate that lipoprotein metabolism, particularly ApoE, plays a crucial role in HSC regulation under severe anemia conditions in a non-canonical fashion, unlike a conventional factor such as EPO. Ten weeks old C57BL/6JRj mice were injected with PBS or 60 mg/kg of phenylhydrazine, or phlebotomized, and 3 days later CD150+ CD48- c-Kit+ Sca-I+ Lineage- cells were sorted from the bone marrow of those mice.