Regulation of Hemangiogenesis by Hypoxia-Inducible Factor 1 and microRNAs

描述（由申请人提供）：造血干细胞-祖细胞存在于成人骨髓中，能够自我更新并分化为祖细胞，从而产生所有类型的成熟血细胞，半个多世纪前就已为人所知。最近，内皮干细胞-祖细胞也被发现。要更全面地了解干细胞自我更新和分化的分子机制，还存在几个主要障碍。首先，这些细胞的丰度很低，很难从分化程度更高的后代中纯化出来。需要技术来扩增这些细胞，同时保持其后续分化的能力，以便更好地研究和利用它们进行治疗。其次，在内皮干细胞祖细胞的情况下，到目前为止还不可能建立一个类似于造血细胞的等级谱系。第三，尚不清楚成人骨髓中的造血干细胞和内皮干细胞祖细胞本身是否是一种常见的干细胞，即成血管细胞的后代。发育的分子基础是每种细胞类型中基因表达的离散程序的细化。调控基因表达的两个主要机制是转录因子和microRNAs，前者决定DNA序列转录成mRNA的速率，后者决定mRNA转录成蛋白质的速率。我们假设有关键的转录因子和microrna在调节造血和内皮干细胞-祖细胞的自我更新和分化中发挥关键作用。这些细胞分别对血管生成、血液和血管的形成至关重要，而血管和血管的形成又对持续向身体所有细胞输送氧气至关重要。在骨髓内，未分化的细胞沿内皮分布，而分化程度较高的细胞位于血管化程度较高的骨髓腔附近，从那里进入外周血。内皮生态位是缺氧的，可能促进干细胞的维持，而血管生态位中氧气水平的升高可能促进增殖和分化。我们假设O2作为血管生成细胞的发育调节剂，因此干细胞和祖细胞群可能需要不同的O2浓度。转录调节因子缺氧诱导因子1 （HIF-1）介导对缺氧的适应性发育和生理反应，并在血管生成中发挥重要作用，但仅部分确定。在这项拨款申请中，我们建议描述HIF-1和microrna调节血管生成的分子机制。通过这样做，我们希望：更好地识别和表征血管生成祖细胞谱系；引导干细胞和祖细胞向理想的细胞命运分化；并开发新的策略来治疗利用这些细胞在体内造血和血管形成。

DESCRIPTION (provided by applicant): The existence of hematopoietic stem-progenitor cells, which are present in the adult marrow and capable of self-renewal and differentiation into the progenitors that give rise to all types of mature blood cells, has been known for over half a century. More recently, endothelial stem-progenitor cells have also been identified. There remain several major obstacles to a more complete understanding of the molecular mechanisms underlying the self-renewal and differentiation of these stem-progenitor cells. First, these cells are present in low abundance and are difficult to purify from their more differentiated progeny. Techniques are needed to expand these cells, while maintaining their capacity for subsequent differentiation, in order that they might be better studied and utilized therapeutically. Second, in the case of endothelial stem-progenitors, thus far it has not been possible to establish a hierarchical lineage similar to what has been described for hematopoietic cells. Third, it is not clear whether the hematopoietic and endothelial stem-progenitors in adult marrow are themselves the descendants of a common stem cell, the hemangioblast. The molecular basis for development is the elaboration of discrete programs of gene expression in each cell type. Two central mechanisms for regulating gene expression are transcription factors, which determine the rate at which DNA sequences are transcribed into mRNA, and microRNAs, which determine the rate at which mRNAs are transcribed into protein. We hypothesize that there are key transcription factors and microRNAs which play critical roles in regulating the self-renewal and differentiation of hematopoietic and endothelial stem-progenitor cells. These cells are essential for hemangiogenesis, the formation of blood and blood vessels, respectively, which in turn are essential for the continuous delivery of O2 to all cells of the body. Within the marrow, undifferentiated cells are located along the endosteum, whereas more differentiated cells are located in proximity to the highly vascularized marrow cavity, from whence they enter the peripheral blood. The endosteal niche is hypoxic and may promote stem cell maintenance, whereas increased O2 levels in the vascular niche may promote proliferation and differentiation. We hypothesize that O2 functions as a developmental regulator for hemangiogenic cells, such that stem vs progenitor cell populations may require different O2 concentrations. The transcriptional regulator hypoxia-inducible factor 1 (HIF-1) mediates adaptive developmental and physiological responses to hypoxia and plays an essential, but only partially defined role, in hemangiogenesis. In this grant application, we propose to delineate the molecular mechanisms whereby HIF-1 and microRNAs regulate hemangiogenesis. By doing so, we hope to: better identify and characterize hemangiogenic progenitor cell lineages; direct the differentiation of stem and progenitor cells to desired cell fates; and develop new strategies for therapeutic utilization of these cells for in vivo hematopoiesis and vascularization.