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产生所有类型成熟血细胞的祖细胞，这种细胞的存在已被发现超过半个世纪。最近，内皮干祖细胞也已被鉴定。对于更完整地理解这些干祖细胞自我更新和分化的分子机制，仍然存在几个主要障碍。首先，这些细胞以低丰度存在，并且难以从其更分化的后代中纯化。需要技术来扩增这些细胞，同时保持它们随后分化的能力，以便它们可以更好地被研究和治疗利用。其次，在内皮干细胞-祖细胞的情况下，迄今为止还不可能建立类似于造血细胞所描述的分层谱系。第三，成人骨髓中的造血干细胞和内皮干祖细胞本身是否是一种常见的干细胞（成血管细胞）的后代尚不清楚。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阐述。调节基因表达的两个中心机制是转录因子和microRNA，转录因子决定DNA序列转录成mRNA的速率，microRNA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祖细胞的自我更新和分化中发挥关键作用。这些细胞对于血管生成、血液和血管的形成是必不可少的，而血管生成又是将O2持续输送到身体所有细胞所必需的。在骨髓内，未分化的细胞沿着骨内膜分布，而分化程度较高的细胞则分布在高度血管化的骨髓腔附近，从那里它们进入外周血。骨内膜龛是缺氧的，可以促进干细胞的维持，而血管龛中的O2水平增加可以促进增殖和分化。我们假设O2作为血管生成细胞的发育调节剂发挥作用，因此干细胞与祖细胞群体可能需要不同的O2浓度。转录调节因子缺氧诱导因子1（HIF-1）介导的适应性发育和生理反应，缺氧和发挥重要的，但只有部分确定的作用，血管生成。在这项资助申请中，我们提出描绘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;指导干细胞和祖细胞分化为所需的细胞命运;并开发用于体内造血和血管化的这些细胞的治疗利用的新策略。

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.