G PROTEIN SIGNALING IN OSTEOBLASTS

外源性因素如激素、生长因子和机械应力对骨骼肌的生长和功能产生影响， 通过对成骨细胞的作用来生长和重塑。因此，人们对如何界定 特定的细胞内信号传导途径介导这些因子在控制成骨细胞功能中的作用。 G蛋白信号发生在对许多骨骼刺激的反应中，并且这种信号的结果是 这取决于G蛋白的性质;信号的时间传递;和细胞的表型状态。 成骨细胞更清楚地了解促钙剂（如PTH）如何引起其在体内的复杂作用， 骨需要在体内环境中直接解决这些问题的研究。在本提案中，我们 将评估Gs和Gi信号在成骨细胞中介导合成代谢骨骼反应的作用。在一个 方法，新的G蛋白偶联受体称为RASSLs将靶向成骨细胞在转基因 小鼠RASSLs激活特定的G蛋白途径，以响应合成激动剂的施用。 Gs-和Gi RASSLs的激活将使我们能够剖析这些途径在骨骼反应中的作用。在 第二种方法，通过cre介导的切除成骨细胞中的Gs和Gi功能， 功能性GS-α等位基因和百日咳毒素催化亚基的靶向表达。 我们将确定切除这些信号通路对正常骨骼稳态的影响， 对PTH的合成代谢反应将进行机制研究以评估G蛋白的作用 在体内和分离的骨髓基质细胞（BMSCs）中对成骨细胞增殖和凋亡的信号 从转基因小鼠身上。最近显示，G蛋白信号与两种途径的会聚是 骨形成所必需的-LRP/经典wnt通路和最近鉴定的RSK 2/ATF 4 将在BMSC中探索。我们建议：1）评估成骨细胞Gs和Gi信号转导在骨形成中的作用。 调节成熟小鼠的骨骼稳态。我们将确定调节的，间歇的 不同分化阶段成骨细胞中的Gs和Gi信号传导;确定 Gs和Gi信号传导的条件性敲除;并评估Gs和Gi信号传导的操纵机制。 Gi信号转导增强了这些作用; 2）确定Gs和Gi信号转导对合成代谢的贡献。 对PTH的反应以及这些作用的机制。这些研究将为控制 通过G蛋白信号在不同分化阶段的成骨细胞中的骨形成和骨吸收。 它们还可能提供G蛋白信号与骨中合成代谢作用之间的新联系，从而识别 治疗骨质疏松症的新靶点。 说明：我们将探讨如何激活特定的信号在骨形成细胞可以导致 骨质增加。这些结果可能会导致骨质疏松症治疗的新方法。

Extrinsic factors such as hormones, growth factors, and mechanical strain produce their effects on skeletal growth and remodeling via actions on osteoblasts. Accordingly, there is great interest in defining how specific intracellular signaling pathways mediate the effects of these factors in controlling osteoblast function. G protein signaling occurs in response to many skeletal stimuli, and the consequence of this signaling depends on the nature of the G protein; the temporal delivery of the signal; and the phenotypic state of the osteoblast. A clearer understanding of how calciotropic agents such as PTH elicit their complex effects in bone requires studies that address these issues directly in an in vivo context. In the present proposal, we will assess the role of Gs and Gi signaling in osteoblasts in mediating anabolic skeletal responses. In one approach, novel G protein-coupled receptors termed RASSLs will be targeted to osteoblasts in transgenic mice. RASSLs activate specific G protein pathways in response to administration of synthetic agonists. Activation of Gs- and Gi RASSLs will allow us to dissect the role of these pathways in skeletal responses. In a second approach, Gs and Gi function will be ablated in osteoblasts in vivo by cre-mediated excision of functional Gs-alpha alleles and by targeted expression of the catalytic subunit of pertussis toxin, respectively. We will determine the effects of ablating these signaling pathways on normal skeletal homeostasis and on the anabolic response to PTH. Mechanistic studies will be carried out to assess the effects of G protein signals on osteoblast proliferation and apoptosis in vivo and in bone marrow stromal cells (BMSCs) isolated from the transgenic mice. Convergence of G protein signals with two pathways recently shown to be essential for bone formation - the LRP/canonical wnt pathway and the recently identified RSK2/ATF4 pathway- will be explored in BMSCs. We propose to: 1) assess the role of osteoblast Gs and Gi signaling in the regulation of skeletal homeostasis in mature mice. We will determine the effects of regulated, intermittent Gs and Gi signaling in osteoblasts at different stages of differentiation; determine the skeletal effect of conditional knockout of Gs and Gi signaling; and assess the mechanisms by which manipulation of Gs and Gi signaling elicits these effects; and 2) determine the contribution of Gs and Gi signaling to the anabolic response to PTH and the mechanisms of these effects. These studies will shed new light on the control of bone formation and bone resorption by G protein signaling in osteoblasts at different stages of differentiation. They may also provide new links between G protein signals and anabolic effects in bone, thereby identifying new therapeutic targets for the treatment of osteoporosis. LAY DESCRIPTION: We will explore how activation of specific signals in bone-forming cells can lead to increases in bone mass. The results may lead to new approaches to the treatment of osteoporosis.