Hematopoietic-Osteoblastic Interactions

描述（由申请人提供）：造血干细胞（HSC）所处的微环境或生态位对其调控至关重要。由于造血干细胞数量限制了其临床应用，通过操纵生态位增加造血干细胞的策略可以增加其治疗应用的范围。该建议的长期目标是操纵骨髓微环境以增加HSC数量，从而提高其临床应用价值。为了实现这一目标，我们建立了一个新的实验模型，在该模型中，用甲状旁腺激素（PTH）和/或激活成骨细胞中的PTH1R受体（PTH1R）治疗可扩大长期HSC (LT-HSC)，从而确定成骨细胞是HSC的关键调节因子。在确定PTH在生态位中的作用介质时，我们发现成骨细胞在PTH治疗时释放的前列腺素E2 （PGE2）在体内选择性地扩大短期HSC （ST-HSC）。这种对HSC亚群的精细和专门化调节以前尚未实现，但我们相信它将具有重要的治疗意义。因此，我们开发了两个独特的实验工具来定义HSC调节。根据我们的观察，我们假设独立的机制选择性地调节LT-HSC和ST-HSC，并且它们对HSC的调节有不同的影响。为了证明这一假设，本提案将追求三个具体目标。在ai1中，将通过药理学和遗传学手段在体内确定介导t - hsc扩增以响应PTH的特定细胞和分子机制。在Aim2中，将在体内和体外确定介导pge2依赖性ST-HSC扩增的特定细胞和分子机制。在Aim 3中，将建立LT-HSC和ST-HSC调控之间的相互作用。本申请中提出的研究数据将1)确定PTH和pge2激活的调节LT-HSC和ST-HSC的机制；2)确定这些机制之间的相互作用，这些机制可以在特定治疗需要的情况下用于靶向调节HSC亚群。因此，提出的研究旨在得出的结果不仅可以促进对干细胞调控的理解，而且还可以设计出可以带回患者的药理学策略，直接影响他们的临床护理。PTH和PGE2受体特异性激动剂的可用性使得这些研究特别及时地用于未来的人类治疗。使用两种新颖的体内实验工具，该项目将确定具体的调节机制，直接和间接，控制HSC的行为，并可以刺激具有不同性质的HSC的不同亚群。由于造血干细胞产生所有的血细胞，这些调节机制可以在治疗上用于在血细胞损伤或缺乏的特定情况下增加造血干细胞。

DESCRIPTION (provided by applicant): The microenvironment, or niche, in which hematopoietic stem cells (HSC) reside, is essential for their regulation. Since HSC number limits their clinical use, strategies to increase HSC through niche manipulation could increase the scope of their therapeutic application. The long-term objective of this proposal is to manipulate the bone marrow microenvironment to increase HSC numbers and thereby their clinical utility. To meet this objective, we established a novel experimental model in which treatment with parathyroid hormone (PTH) and/or activation of its receptor (PTH1R) in osteoblastic cells expands Long-term HSC (LT-HSC), thus identifying osteoblastic cells as key regulators of HSC. While defining mediators of PTH action in the niche, we discovered that Prostaglandin E2 (PGE2), which is released by osteoblastic cells upon PTH treatment, selectively expands Short-term HSC (ST-HSC) in vivo. Such exquisite and specialized regulation of HSC subsets has not previously been achieved, but we believe that it will have important therapeutic implications. Therefore, we have developed two unique experimental tools to define HSC regulation. Based on our observations, we hypothesize that independent mechanisms selectively regulate LT-HSC and ST-HSC and that these have different effects on HSC regulation. To demonstrate this hypothesis, this proposal will pursue three specific aims. In Aim1, the specific cellular and molecular mechanisms that mediate LT-HSC expansion in response to PTH will be defined in vivo by pharmacologic and genetic means. In Aim2, the specific cellular and molecular mechanisms that mediate PGE2-dependent ST-HSC expansion will be defined in vivo and in vitro. In Aim 3, interactions between regulation of LT-HSC and ST-HSC will be established. Data from the studies proposed in this application will 1) define the PTH and PGE2-activated mechanisms regulating LT-HSC and ST-HSC; 2) identify interactions between these mechanisms which could be exploited for targeted regulation of HSC subsets in the setting of specific therapeutic need. The studies proposed are therefore designed to result in findings that not only advance the understanding of stem cell regulation, but also devise pharmacologic strategies that can be brought back to patients, directly impacting their clinical care. The availability of PTH and PGE2 receptor specific agonists makes these studies particularly timely for future translation to human therapy. Using two novel in vivo experimental tools, this project will determine specific regulatory mechanisms, direct and indirect, that control HSC behavior, and that can stimulate differentially subsets of HSC which have different properties. Since HSC give rise to all blood cells, these regulatory mechanisms could be therapeutically exploited to increase HSC in specific situations of blood cell injury or deficiency.