Role of PLC in PTH Signaling: Mutant Receptors in Vivo

PTH/PTHrP受体通过激活Gs和Gq家族，至少通过两条不同的信号通路发挥作用。以前的研究已经提供了关于肾脏和骨骼中特定的第二信息通路和甲状旁腺素和甲状旁腺素rP的特殊远端作用之间的联系的提示性但非确凿的证据。这项建议的目的是建立特定的第二信使通路在体内甲状旁腺素和甲状旁腺素rP作用中的生理学作用。已经建立了正常的PTH/PTHrP受体基因被突变的受体基因取代的小鼠品系。在这个突变的受体中，四个相邻残基的改变导致GQ的激活被戏剧性地钝化，而不影响Gs的激活。分析失活GQ通路对完整动物组织反应性的影响将建立GQ通路在PTH和PTHrP作用中的生理学作用。结果可能是 帮助设计控制高钙血症的方法，并利用甲状旁腺素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PLC信号在生长板中通过PTH/PTHrP受体的作用，这是继这些小鼠有异常生长板的发现之后。SPARTIC AIM II将评估该突变对甲状旁腺激素骨反应的影响。重点将放在甲状旁腺素的合成代谢作用的调节和甲状旁腺素对骨吸收的刺激上。特殊目的III将研究突变对甲状旁腺素肾脏反应的影响，因为当这些小鼠受到低钙饮食的挑战时，钙和磷的稳态被破坏。重点将特别放在钠-磷酸共转运和25-羟基维生素D_1α-羟化的调节上。

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.