Mechanisms that regulate erythroid differentiation of hematopoietic stem cells

造血干细胞(HSCs)能够再生整个造血系统。此容量为 然而，充分释放骨髓移植的最新研究表明，包括我们在内的造血干细胞 在动态平衡期间对造血的贡献要有限得多。而来自以下来源的压力 化疗或炎症增加了HSCs对多个造血系的贡献，很少 已知造血干细胞如何应对导致贫血的压力源。鉴定祖细胞群体和 促进红系再生的信号可能导致更好地利用造血干细胞进行治疗的新策略 贫血和再生医学的总体情况。使用HSC血统追踪模型，我们发现溶血素 贫血特异性地增强了HSCs对红系的贡献，表明HSCs对红系应激有反应 通过启动红血球生成。溶血性贫血后，HSCs表达更多的红细胞生成相关基因和 在体外和体内均表现出促进红系分化的作用。有趣的是，HSCs的铁含量增加了 溶血性贫血和铁络合后，阻止了偏红分化。铁是营养不良的一个辅因 铁(II)/α-酮戊二酸依赖的双加氧酶TET2使DNA去甲基化，与红细胞生成相关 DNA去甲基化。我们发现，在贫血和缺氧时，HSCs中TET2蛋白表达增加，而不是mRNA表达增加。 TET2的缺失抑制了我们观察到的溶血后HSC向红系分化的增强 贫血。因此，我们假设HSC对贫血的反应是通过增加铁摄取、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HSC的异质性，并鉴定HSCs中偏向红系的部分。在目标2中，我们 将研究TET2在促进脾HSC红系承诺方面的作用。在目标3中，我们将调查 TET2蛋白在贫血期间稳定在HSCs中的机制。完成这项研究将提供 对骨髓和脾造血干细胞在应对贫血方面的差异的新见解，以及 铁和TET2指示造血干细胞致力于红系血统的机制。

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.