Regulation of Erythroid Cell Progenitors by the Nuclear Receptor Transcription Factor VDR

摘要：调节红系祖细胞形成和分化为红血球的途径 人们对细胞的理解还不完全。我们发现维生素D受体(VDR)核激素转录 因子基因在胎儿期和成人期表达，但在胚胎发育阶段不表达， 在成熟过程中下调。VDR被其配体维生素D3激活导致构象变化 这稳定了蛋白质，并诱导其移位到细胞核，在那里它招募了共同调节复合体。 VDR信号通路主要在骨骼中被研究，但在很大程度上还没有被探索。 红细胞生成：已发表的研究几乎全部在白血病细胞系(非正常原代细胞)中进行 单元格)。维生素D3激动剂骨化三醇激活VDR信号增加EryD集落生长 来自胎肝和成人骨髓，维持祖细胞潜能，并延迟红系成熟。这个 刺激红系祖细胞生长可使成熟红血球数量显著增加 细胞。Linneg cKit+细胞早期(CD71lo/neg)而不是晚期(CD71hi)EryD祖细胞亚群有反应 骨化三醇，不受其降钙剂作用的影响。VDR的激活可以部分替代和 与应激糖皮质激素地塞米松协同促进祖细胞增殖的比较 两种配基中的任何一种，都表明在应激性红细胞生成中起作用。我们的发现支持了这种可能性 VDR中的红系特异性缺失干扰DNA结合，导致网织红细胞增多 比对照动物对压力的反应更早，而且更明显。RNA对VDR表达的抑制作用 取消骨化三醇对早期红系祖细胞生长的刺激作用。这些发现表明，VDR具有 早期红系祖细胞的细胞固有功能。骨化三醇激活VDR阻断血管紧张素转换酶上调 红系转录因子基因GATA1、Fog1和KLF1。有趣的是，昼夜节律基因 VDR和糖皮质激素受体Gr的激活以及Clock表达的振荡而上调 PER1基因在红系祖细胞中被激活。时钟基因BMal1是增殖所必需的 对地塞米松的反应。因此，该提案的首要假设是VDR和GR 部分通过调节Clock基因表达来调节红系祖细胞，并具有部分冗余 功能。这项应用将使用动物和细胞培养模型来探索生物钟的调节 GR和VDR在红系祖细胞中的基因表达及其与核功能的关系 激素受体转铁蛋白。这些研究可能导致在红系中识别新的分子靶点 可以被利用来开发治疗贫血和其他红细胞疾病的新疗法的祖细胞。一种能力 以新的方式调控RBC前体细胞的体外扩增或分化将具有明显的临床应用价值。

ABSTRACT: The pathways that regulate the formation and differentiation of erythroid progenitors to red blood cells are incompletely understood. We found that the vitamin D receptor (Vdr) nuclear hormone transcription factor gene is expressed in fetal and adult stages but not at the embryonic stage of development and is downregulated during maturation. VDR activation by its ligand vitamin D3 results in conformational changes that stabilize the protein and induce its translocation into the nucleus, where it recruits coregulatory complexes. The VDR signaling pathway has been studied mostly in bone but has been largely unexplored in erythropoiesis: published studies were performed almost entirely in leukemic cell lines (not normal primary cells). Activation of Vdr signaling by the vitamin D3 agonist calcitriol increased the outgrowth of EryD colonies from fetal liver and adult bone marrow, maintained progenitor potential, and delayed erythroid maturation. The stimulation in growth of erythroid progenitors resulted in a large increase in the numbers of mature red blood cells. The early (CD71lo/neg) but not the late (CD71hi) EryD progenitor subset of Linneg cKit+ cells was responsive to calcitriol, independently of its calcemic effects. Activation of VDR could partially substitute for and synergize with the stress glucocorticoid dexamethasone in enhancing progenitor proliferation compared to either ligand alone, suggesting a role in stress erythropoiesis. This possibility is supported by our finding that an erythroid specific deletion in Vdr that interferes with DNA binding results in a reticulocytosis that occurs earlier and is more pronounced than in control animals in response to stress. RNA inhibition of Vdr expression abrogated the stimulation of early erythroid progenitor growth by calcitriol. These findings suggest that Vdr has a cell-intrinsic function in early erythroid progenitors. Activation of Vdr by calcitriol blocked the upregulation of erythroid transcription factor genes Gata1, Fog1 and Klf1. Intriguingly, circadian rhythm genes are upregulated by activation of Vdr and the glucocorticoid receptor Gr and oscillations in expression of the clock gene Per1 are promoted in erythroid progenitors. The clock gene Bmal1 is required for the proliferative response to dexamethasone. Therefore, the overarching hypothesis of this proposal is that Vdr and Gr regulate erythroid progenitors in part by modulating clock gene expression and have partially redundant functions. This application will use animal and cell culture models to explore the modulation of circadian clock gene expression by Gr and Vdr in erythroid progenitors and functional relationships between these two nuclear hormone receptor TFs. These studies may lead to the identification of novel molecular targets in erythroid progenitors that can be exploited to develop new therapies for anemias and other red cell disorders. The ability to modulate ex vivo expansion or differentiation of RBC progentors in new ways would have clear clinical utility.