Parathyroid Hormone Signaling in Bone Cells

描述（申请人提供）：骨质疏松症是人类最常见的骨骼疾病。据估计，美国有超过1000万女性和男性患有骨质疏松症，还有2000多万人有骨质疏松性骨折的风险。动物和人体研究表明，间歇低剂量给药时，甲状旁腺激素和甲状旁腺激素相关蛋白（PTHrP）都能有效刺激骨形成。PTH和PTHrP的骨合成代谢活性与其刺激1型PTH/PTHrP受体（PTHI Rc）的能力有关，PTH/PTHrP受体在成骨细胞和骨髓基质细胞中均表达。PTH1 Rc与多种信号通路偶联，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信号通路对于刺激骨骼的合成代谢反应似乎是必要的，而且可能是充分的，但最近的研究已经确定PKC和β -arrestin2在PTH 1 Rc功能脱敏中的联合作用。本研究建议的中心假设是，细胞对PTH和PTHrP的反应不仅依赖于PTH1 rc介导的信号转导，而且还依赖于与阻滞蛋白、内吞作用和配体/受体β -阻滞蛋白2复合物的细胞运输的额外相互作用。具体来说，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。非脱敏PTHrP类似物的发展显示选择性和持续的CAMP信号可以直接验证这一假设。因此，我们建议：1)确定PTH1 Rc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PTH 1Rc信号转导和细胞运输中的作用；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，并可能导致新型PTH/PTHrP合成代谢化合物的发展。

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.