Osteoblastic Activation in the Hematopoietic Stem Cell

描述（由申请人提供）：骨髓基质微环境是一个复杂的细胞网络，对于控制造血干细胞（HSC）至关重要，造血干细胞是个体一生中所有血细胞谱系的原始细胞。在骨髓中，HSC通过激活甲状旁腺激素(PTH) /PTHrP受体（PPR），与成骨细胞（骨形成细胞）密切相关。定义造血干细胞生态位细胞成分及其影响造血干细胞行为的机制一直很困难。近年来的研究表明，成骨细胞在造血干细胞的调控中起着至关重要的作用，成骨细胞PPR的激活使造血干细胞扩张。我们使用pth处理过的小鼠以及将组成性活性PPR靶向成骨细胞（col1-caPPR）的转基因小鼠，证明通过Jagged1-Notch信号激活成骨细胞中的PPR可使造血干细胞数量加倍。因此，本研究的主要目标是确定成骨细胞Jagged1在ppr介导的HSC扩增中的功能。我们假设成骨细胞Jagged1的表达对于ppr依赖的HSC扩增是必要的，并且它有助于扩增特定的成骨细胞亚群，这最能支持HSC。这些假设将通过实验来检验：1)描述ppr依赖性基质成骨细胞Jagged1的表达；2)确定ppr介导的HSC扩增是否受成骨细胞Jagged1的控制；3)定义Notch信号对HSC微环境的影响。这些研究将确定pth依赖的Jagged1和Notch信号在HSC生态位中的作用，促进对HSC自我更新的骨髓微环境控制的基本机制的理解，并为开发促进HSC扩展的新方法提供基础，以改善骨髓移植和骨髓衰竭状态的临床恢复。

DESCRIPTION (provided by applicant): The bone marrow stromal microenvironment is a complex cellular network essential for the control of hematopoietic stem cells (HSC), primitive cells giving rise to all blood cell lineages throughout the life of an individual. In the bone marrow, HSC are found in close proximity to osteoblasts, bone-forming cells which are the main target of parathyroid hormone (PTH) in bone, through activation of the PTH/PTHrP receptor (PPR). Definition of HSC niche cellular components and of the mechanisms by which they influence HSC behavior has been difficult. Recent studies have shown that osteoblastic cells play a crucial role in HSC regulation and that osteoblastic PPR activation expands HSC. We have used PTH-treated mice as well as transgenic mice in which a constitutively active PPR is targeted to osteoblastic cells (col1-caPPR) to show that activation of the PPR in osteoblastic cells through Jagged1-Notch signaling doubles hematopoietic stem cell numbers. The primary goal of this proposal is therefore to determine the function of osteoblastic Jagged1 in PPR-mediated HSC expansion. We hypothesize that osteoblastic Jagged1 expression is necessary for PPR-depended HSC expansion, and that it is instrumental in expanding a specific subpopulation of osteoblastic cells, which best support HSC. These hypotheses will be examined through experiments designed to: 1) delineate PPR-dependent stromal osteoblastic Jagged1 expression; 2) determine whether PPR-mediated HSC expansion is controlled by osteoblastic Jagged1; and 3) define the effects of Notch signaling on the HSC microenvironment. These studies will determine the role of PTH-dependent Jagged1 and Notch signaling in the HSC niche, advance the understanding the basic mechanisms underlying the bone marrow microenvironmental control of HSC self-renewal, and provide the basis for developing novel approaches to facilitate HSC expansion, with the goal of improving clinical recovery from bone marrow transplantation and bone marrow failure states.