Effects of osteocyte specific Gs alpha signaling on bone mass and hematopoiesis

描述(申请人提供)：骨细胞占所有骨细胞的90%以上，但对其功能或系统激素参与调节其活动知之甚少(S)。最近的研究支持这样一种理论，即骨细胞起着主要的“机械感觉”作用。骨细胞究竟如何感觉到施加在骨骼上的机械力，然后将这种机械刺激转化为生物功能，目前尚不完全清楚。几种激素，特别是前列腺素E2(PGE2)和甲状旁腺激素(PTH)参与了这一过程。这项建议将探讨骨细胞中的GSA信号对适当的机械转导和骨稳态至关重要的假说。此外，我们的初步数据显示，骨细胞中缺乏GSA信号会导致造血异常。这项建议的第一个目标将检验这样一个假设，即骨细胞中的GSA信号对于适当的骨获取和骨骼动态平衡是重要的。第二个目标将研究GSA介导的骨细胞信号是机械转导的重要调节因子的假说。最后，在目标III中，我们将研究GSA在造血中的作用。为了解决这些问题，已经产生了在骨细胞中特异性地消融GSA表达的小鼠。为了将GSA的消融限于骨细胞，我们使用已知在骨细胞中特异表达的牙本质基质蛋白-1(DMP-1)的10kb上游启动子来驱动Cre重组酶，其中GNas的外显子1两侧是Lox-P位点。这种动物模型将使人们能够更好地了解GSA对骨骼和造血系统的作用，并可能指导新的治疗药物的开发。本文提出的研究将扩展目前关于骨细胞中GSA信号的知识，并将调查这些细胞中的GSA依赖通路在多大程度上参与正常骨骼发育、造血和矿质离子稳态。通过这样做，他们承诺将显著扩大对骨细胞和骨生物学的理解。我们想要验证的假设是，骨细胞中通过GSA的信号直接影响骨稳态和机械感觉，并直接或间接地控制髓系细胞的发育和造血。如果我们的假设成立，这将是第一次有证据表明骨细胞可以调节造血。

DESCRIPTION (provided by applicant): Osteocytes comprise over 90% of all bone cells, yet little is known of their function(s) or of the involvement of systemic hormones in regulating their activity. Recent studies support the theory that osteocytes play a major "mechanosensory" role. How exactly the osteocyte can sense the mechanical forces applied to the bone and then transform this mechanical stimulus into a biological function remains incompletely understood. Several hormones, particularly prostaglandin E2 (PGE2) and parathyroid hormone (PTH) had been implicated in this process. This proposal will investigate the hypothesis that Gsa- signaling in osteocytes is critical for proper mechano-transduction and bone homeostasis. Moreover, our initial data revealed that lack of Gsa-signaling in osteocytes induce hematopoietic abnormalities. The first aim of this proposal will test the hypothesis that Gsa-signaling in osteocytes is important for proper bone acquisition and skeletal homeostasis. The second aim will investigate the hypothesis that Gsa-mediated signaling in osteocyte is an important regulator of mechano-transduction. Lastly, in aim III we will investigate the role of Gsa in hematopoiesis. To address these questions, mice in which Gsa expression is specifically ablated in osteocytes have been generated. To restrict ablation of Gsa to osteocytes, we used the 10Kb upstream promoter of Dentin Matrix Protein-1 (DMP-1), known to be expressed specifically in osteocytes, to drive the Cre-recombinase in mice in which Exon1 of Gnas is flanked by Lox-P sites. This animal model will enable enhanced understanding of Gsa action on bone and on the hematopoietic system and could direct the development of novel therapeutic agents. The studies proposed here will expand the current knowledge on Gsa-signaling in osteocytes and will investigate the extent to which Gsa-dependent pathways in these cells is involved in normal skeletal development, hematopoiesis and mineral-ion homeostasis. In so doing, they promise to significantly expand understanding of osteocyte and bone biology. The hypothesis that we wish to test is that signaling via Gsa in osteocytes directly affects bone homeostasis and mechanosensation and directly, or indirectly controls myeloid cells development and hematopoiesis. If our hypothesis holds true it will be the first time that osteocytes are shown to regulate hematopoiesis.