Parathyroid Hormone Signaling in Bone Cells

描述(申请人提供)：骨质疏松症是最常见的人类骨骼疾病。据估计，美国有1000多万男女患有骨质疏松症，还有2000万人面临骨质疏松性骨折的风险。动物和人体研究表明，当低剂量间歇给药时，甲状旁腺素和甲状旁腺激素相关蛋白(PTHrP)都能有效地刺激骨形成。PTH和PTHrP的骨合成活性与其刺激成骨细胞和骨髓基质细胞表达的1型PTH/PTHrP受体(PTHI RC)有关。PTH1RC连接到多个信号通路，导致蛋白激酶A(PKA)、PKC和丝裂原活化蛋白激酶ERK1和ERK2的激活。虽然Gs/cAMP/PKA信号通路似乎是刺激骨骼中合成代谢反应所必需的，也可能是足够的，但最近的研究证实，PKC和β-arrestin2在PTH1RC功能脱敏中的联合作用。这项研究的中心假设是，细胞对PTH和PTHrP的反应不仅依赖于PTH1RC介导的信号转导，还依赖于与拦阻蛋白的额外相互作用、内吞作用和配体/受体β-拦阻蛋白2复合体的细胞转运。具体地说，我们假设Gs/cAMP/PKA通路的持续和选择性激活将诱导与骨合成代谢活性相关的基因、蛋白质和细胞反应的表达。显示选择性和持续性cAMP信号的非脱敏PTHrP类似物的开发使这一假说的直接检验成为可能。因此，我们建议：1)确定PTH1RC和β-arrestin2之间的特定相互作用；2)确定β-arrestin2在成骨细胞和基质细胞中介导PTH1Rc信号转导和细胞转运中的作用；3)确定选择性和持续刺激cAMP信号对成骨细胞和基质细胞基因/蛋白表达的影响；4)确定选择性和持续刺激cAMP信号对成骨细胞和基质细胞增殖和凋亡的影响。这些研究将促进对PTH和PTHrP细胞作用的分子机制的理解，并可能导致基于PTH/PTHrP的新型合成代谢化合物的开发。

DESCRIPTION (provided by applicant): Osteoporosis is the most common human bone disorder. It is estimated that more than 10 million women and men in the United States have osteoporosis and 20 million more are at risk for osteoporotic fractures. Animal and human studies have shown that, when administered intermittently at low doses, both PTH and PTH-related protein (PTHrP) effectively stimulate bone formation. The bone anabolic activity of PTH and PTHrP is associated with their capacity to stimulate the type 1 PTH/PTHrP receptor (PTHI Rc), expressed in both osteoblasts and bone marrow stromal cells. PTH1 Rc is coupled to several signaling pathways, leading to activation of protein kinase A (PKA), PKC and mitogen-activated protein kinases ERK1 and ERK2. While the Gs/cAMP/PKA signaling pathway seems to be necessary, and possibly sufficient, to stimulate an anabolic response in the skeleton, recent studies have established the combined actions of PKC and beta-arrestin2 in the desensitization of PTH 1 Rc function. The central hypothesis of this research proposal is that the cellular responses to PTH and PTHrP depend not only on PTH1 Rc-mediated signal transduction, but also on additional interactions with arrestins, endocytosis and cellular trafficking of ligand/receptor beta-arrestin2 complexes. Specifically, we hypothesize that continuous and selective activation of the Gs/camp/PKA pathway will induce expression of genes, proteins and cellular responses associated with the anabolic activity on bone. The development of non-desensitizing PTHrP analogs displaying selective and sustained CAMP signaling permits the direct testing of this hypothesis. We therefore propose to: 1) identify specific interactions between PTH1 Rc and beta-arrestin2; 2) determine the role of beta-arrestin2 in mediating PTH 1Rc signal transduction and cellular trafficking in osteoblasts and stromal cells; 3) determine the effect of selective and continuous stimulation of cAMP signaling on gene/protein expression by osteoblasts and stromal cells; 4) determine the effect of selective and continuous stimulation of cAMP signaling on osteoblasts and stromal cells proliferation and apoptosis. These studies will advance the understanding of the molecular mechanisms underlying the cellular actions of PTH and PTHrP and may lead to the development of novel PTH/PTHrP-based anabolic compounds.