Role of PLC in PTH Signaling: Mutant Receptors in Vivo

PTH/PTHrP受体通过激活Gs和Gq家族通过至少两种不同的信号传导途径起作用。先前的研究提供了提示性但非决定性的证据，关于特定的第二信息途径和特定的PTH和PTHrP在肾脏和骨骼中的远端作用的联系。该建议的目的是建立特定的第二信使途径在PTH和PTHrP体内作用的生理作用。已经建立了小鼠品系，其中正常PTH/PTHrP受体基因被突变受体基因取代。在该突变受体中，四个相邻残基的改变导致Gq的活化显著钝化，而不影响Gs的活化。在完整的动物中失活Gq通路对组织反应性的影响的分析将确立Gq通路在PTH和PTHrP的作用中的生理作用。结果可能 帮助设计控制高钙血症的方法，并利用PTH的合成代谢作用治疗骨质疏松症。 该提案的具体目标I将是确定生长板中PTH/PTHrP受体的PLC信号传导的作用，随后发现这些小鼠具有异常生长板。特定目标II将评估突变对PTH骨反应的影响。特别关注PTH的合成代谢作用的调节和PTH对骨吸收的刺激。特定目标III将研究突变对PTH肾反应的影响，因为当这些小鼠用低钙饮食挑战时，钙和磷稳态被破坏。将特别关注钠-磷酸盐共转运和25-羟基维生素D 1 α-羟基化的调节。

The PTH/PTHrP receptor works through at least two distinct signaling pathways by activation both Gs and the Gq family. Previous studies have provided suggestive but inconclusive evidence concerning the linkage of specific second message pathways and particular distal actions of PTH and PTHrP in kidney and bone. The goal of this proposal is to establish the physiologic roles of specific second messenger pathways in PTH and PTHrP action in vivo. Lines of mice have been established in which the normal PTH/PTHrP receptor gene is replaced with a mutant receptor gene. In this mutant receptor, the alteration of four adjacent residues leads to dramatic blunting of activation of Gq without affecting the activation of Gs. Analysis of the effects of inactivating the Gq pathway on tissue responsiveness in intact animals will establish the physiologic roles of the Gq pathway in the actions of PTH and PTHrP. The results may help in the design of ways to control hypercalcemia and to use the anabolic actions of PTH to treat osteoporosis. Specific Aim I of the proposal will be to determine the role of PLC signaling by the PTH/PTHrP receptor in the growth plate, following up the discovery that these mice have abnormal growth plates. Specific Aim II will evaluate the effects of the mutation on the bone responses to PTH. Particular focus will be placed on the regulation of the anabolic effect of PTH and the stimulation by PTH of bone resorption. Specific Aim III will study the effects of the mutation on the renal responses to PTH, since calcium and phosphorus homeostasis are disrupted when these mice are challenged with a low calcium diet. Particular focus will be placed on the regulation of sodium-phosphate co-transport and of 25-hydroxyvitamin D 1alpha-hydroxylation.