Mechanisms that regulate erythroid differentiation of hematopoietic stem cells

造血干细胞（HSC）能够再生整个造血系统。这个容量是 然而，最近的研究（包括我们的研究）表明，HSC 在骨髓移植后完全释放 在稳态期间对造血的贡献要有限得多。虽然来自以下来源的压力 化疗或炎症会增加 HSC 对多种造血谱系的贡献，但影响很小 众所周知，造血干细胞如何应对导致贫血的压力源。鉴定祖细胞群和 促进红细胞再生的信号可能会导致更好地利用造血干细胞进行治疗的新策略 贫血和再生医学的整体。使用 HSC 谱系追踪模型，我们发现溶血 贫血特别增强 HSC 的红细胞贡献，表明 HSC 对红细胞应激有反应 通过启动红细胞生成。溶血性贫血后，HSC 表达更多红细胞生成相关基因， 在体外和体内表现出增强的红细胞分化。有趣的是，HSC 的铁含量增加了 溶血性贫血和铁螯合阻止了红系偏向分化。铁是一种辅助因子 铁 (II)/α-酮戊二酸依赖性双加氧酶 TET2 使 DNA 去甲基化，并与红细胞生成相关 与 DNA 去甲基化。我们发现，在贫血和贫血期间，HSC 中的 TET2 蛋白（而非 mRNA）增加。 Tet2 的缺失抑制了我们在溶血后观察到的 HSC 的红系分化增强 贫血。因此，我们假设 HSC 通过增加铁摄取、TET2 表达和 DNA去甲基化，从而增加红细胞生成基因的表达。在目标 1 中，我们将研究 贫血期间脾脏 HSC 的异质性并确定 HSC 的红系偏向部分。在目标 2 中，我们 将检查 TET2 在促进脾 HSC 红细胞定型中的作用。在目标 3 中，我们将调查 贫血期间 TET2 蛋白在 HSC 中稳定的机制。完成本研究将提供 关于骨髓和脾脏 HSC 在应对贫血方面的差异的新见解，以及 铁和 TET2 指导 HSC 致力于红系谱系的机制。

Hematopoietic stem cells (HSCs) are capable of regenerating the entire hematopoietic system. This capacity is fully unleashed upon bone marrow transplantation, however, recent studies including ours indicate that HSCs have a much more limited contribution to hematopoiesis during homeostasis. While stress from sources like chemotherapies or inflammation increases the contribution from HSCs to multiple hematopoietic lineages, little is known about how HSCs respond to stressors that cause anemia. Identifying the progenitor cell population and signals that promote erythroid regeneration may lead to novel strategies to better harness HSCs for the treatment of anemia and regenerative medicine overall. Using a HSC lineage tracing model, we found that hemolytic anemia specifically enhances erythroid contribution by HSCs, indicating that HSCs respond to erythroid stress by initiating erythropoiesis. After hemolytic anemia, HSCs expressed more erythropoiesis-related genes and exhibited enhanced erythroid differentiation in vitro and in vivo. Interestingly, HSCs had increased iron content after hemolytic anemia and iron chelation prevented erythroid-biased differentiation. Iron is a cofactor for the iron(II)/α-ketoglutarate-dependent dioxygenase TET2 that demethylates DNA, and erythropoiesis is associated with DNA demethylation. We found that TET2 protein, but not mRNA, is increased in HSCs during anemia and deletion of Tet2 suppressed the enhanced erythroid differentiation of HSCs we observed following hemolytic anemia. We thus hypothesized that HSCs respond to anemia by increasing iron uptake, TET2 expression, and DNA demethylation, thereby increasing the expression of erythropoiesis genes. In Aim 1, we will study the heterogeneity of splenic HSCs during anemia and identify the erythroid-biased fraction of HSCs. In Aim 2, we will examine the role of TET2 in promoting erythroid commitment of splenic HSC. In Aim 3, we will investigate the mechanism by which TET2 protein is stabilized in HSCs during anemia. Completion of this study will provide novel insights into the differences between bone marrow and splenic HSCs in responding to anemia, and the mechanism by which iron and TET2 instructs HSCs to become committed to the erythroid lineage.