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它们的调节是必不可少的。由于HSC的数量限制了它们的临床应用，通过利基操作增加HSC的策略可能会扩大它们的治疗应用范围。这项建议的长期目标是操纵骨髓微环境，以增加HSC的数量，从而提高其临床效用。为了达到这一目的，我们建立了一种新的实验模型，在该模型中，成骨细胞中甲状旁腺激素(PTH)和/或其受体(PTH1R)的激活可以扩大长期HSC(LT-HSC)，从而确定成骨细胞是HSC的关键调节因子。在定义甲状旁腺素作用的中介时，我们发现成骨细胞在甲状旁腺素治疗时释放的前列腺素E2(PGE2)在体内选择性地扩张短期肝星状细胞(ST-HSC)。对HSC亚群进行如此精细和专门的调控以前从未实现过，但我们相信这将具有重要的治疗意义。因此，我们开发了两种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，并且这两种机制对HSC的调节具有不同的作用。为了证明这一假设，这项提议将追求三个具体目标。在Aim1中，通过药理学和遗传学手段在体内确定介导LT-HSC对PTH反应的特定的细胞和分子机制。在AIM2中，介导PGE2依赖的ST-HSC扩张的特定细胞和分子机制将在体内和体外确定。在目标3中，将建立LT-HSC和ST-HSC的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，这些机制可以用于在特定治疗需求的背景下对HSC亚群进行有针对性的调节。因此，拟议的研究旨在得出的结果不仅能促进对干细胞调节的理解，还能设计出可带回患者的药理学策略，直接影响他们的临床护理。甲状旁腺素和前列腺素E_2受体特异性激动剂的问世使得这些研究对于将来转化为人类治疗特别及时。利用两种新的体内实验工具，该项目将确定特定的调控机制，直接和间接，控制HSC的行为，并可以刺激不同的HSC亚群具有不同的特性。由于HSC产生了所有的血细胞，这些调节机制可以用于治疗在特定情况下增加HSC的血细胞损伤或缺乏。

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.