CONSTITUTIVELY ACTIVE PTH/PTHRP RECEPTORS IN VIVO

描述（来自申请人的逐字描述）： PTH/PTHrP受体（PTH 1 R）及其基因，我们确定了激活突变， Jansen干骺端软骨发育不良（JMC）是一种遗传性疾病， 短肢侏儒症和严重的PTH/PTHrP非依赖性高钙血症。以来 PTH 1 R在肾脏、骨和生长板中大量表达， 突变型PTH 1 R在这些组织中的表达为 JMC的特征性实验室和放射学发现，以及转基因 突变型PTH 1 R（II型胶原启动子）在小鼠中的表达证实， 干骺端的变化确实是由组成性活性受体引起的。 令人惊讶的是，JMC患者的骨小梁体积似乎增加， 而皮质骨不变或减少;得出了相同的发现 在I型PTH 1 R控制下表达突变型PTH 1 R的转基因小鼠中， 胶原促进剂。总之，这些发现表明，骨内膜和 骨膜骨形成受到不同的调节。进一步开拓 PTH 1 Rs在骨形成中的作用，我们现在建议进行以下具体研究： 目标。在目标1中，我们提出通过以下方法建立詹森病的小鼠模型： 用含有激活的PTH 1 R的突变基因替换野生型PTH 1 R基因， 突变（即H223 R/M226 L突变，或具有更高突变频率的其他突变）。 组成活性）。这种动物可以让我们更详细地探索 活化的PTH 1 Rs对矿物质离子的影响 体内平衡、骨代谢和生长板发育。在目标2中，我们 确定反向激动剂是否可以降低细胞的组成性活性， 肾脏和骨骼中突变的PTH 1 R。除了进一步证实， 持续的受体激活确实负责所有JMC特异性 变化，“詹森”小鼠将因此提供一个模型，以探索细节， PTH 1 R在骨代谢中的作用，并确定其在骨代谢中的生物学作用。 其他组织。在目标3中，我们计划在大肠杆菌中寻找更多的PTH 1 R突变。 JMC患者，并在这些和先前表征的个体中进行评估 骨小梁和皮质骨形成的变化。

DESCRIPTION (Verbatim from the Applicant): After the molecular cloning of the PTH/PTHrP receptor (PTH1R) and its gene, we identified activating mutations in Jansen's metaphyseal chondrodysplasia (JMC), a genetic disorder characterized by short-limbed dwarfism and severe PTH-/PTHrP-independent hypercalcemia. Since the PTH1R is abundantly expressed in kidney, bone and growth plates, expression of mutant PTH1Rs in these tissues provided a plausible explanation for the characteristic laboratory and radiological findings in JMC, and the transgenic expression of mutant PTH1Rs (type II collagen promoter) in mice confirmed that the metaphyseal changes are indeed caused by constitutively active receptors. Surprisingly, trabecular bone volume appears to be increased in JMC patients, while cortical bone is unchanged or diminished; equivalent findings were made in transgenic mice expressing the mutant PTH1R under the control of the type I collagen promoter. Taken together these findings indicate that endosteal and periosteal bone formation are differently regulated. To further explore the PTH1Rs role in bone formation, we now propose to pursue the following Specific Aims. In Aim 1, we propose to develop a mouse model of Jansen's disease by replacing the wild-type PTH1R gene with a mutant gene containing an activating mutation (i.e. the H223R/M226L mutation, or other mutations with higher constitutive activity). This animal will allow us to explore, in more detail than is possible in patients, the impact of activated PTH1Rs on mineral ion homeostasis, bone metabolism, and growth plate development. In Aim 2, we will determine whether inverse agonists can reduce the constitutive activity of the mutant PTH1R in kidney and bone. Besides providing further confirmation that persistent receptor activation is indeed responsible for all JMC-specific changes, the "Jansen" mouse will thus provide a model to explore details of the PTH1R's role in bone metabolism, and to determine its biological role(s) in other tissues. In Aim 3, we plan to search for additional PTH1R mutations in JMC patients and to assess in these and previously characterized individuals the changes in trabecular and cortical bone formation.