CONSTITUTIVELY ACTIVE PTH/PTHRP RECEPTORS IN OSTEOBLAST

骨与肾是甲状旁腺激素的主要靶器官。它是 众所周知，甲状旁腺素可以增加骨转换，但它为什么会在体内存在还不清楚。 间歇给药有合成代谢作用，而它的 当以连续的方式给予时，分解代谢作用占上风。第PTH 增强破骨活性，但其是否具有争议性 对破骨细胞的影响仅通过成骨细胞介导，或者 它们也是直接的。成骨细胞是甲状旁腺素作用的主要靶点。 然而，成骨细胞谱系中的哪些细胞-来自 前成骨细胞和成熟成骨细胞的成骨前体细胞-介导 甲状旁腺激素在体内的各种作用是一个悬而未决的问题。它也是未知的 甲状旁腺素受体如何独立于其作用影响成骨细胞功能 软骨细胞分化。最后，克隆的甲状旁腺素/甲状旁腺素受体 能够激活至少两个不同的信号通路，腺苷 环化酶和磷脂酶C，然而，它们在 甲状旁腺激素对成骨细胞的作用机制尚需阐明。最近 甲状旁腺激素/甲状旁腺素受体两种不同突变的鉴定 在患有Jansen‘s干骺端软骨发育不良症(JMC)的患者中， 对配体不依赖的构成阵营的积累，给了我们一个强大的 通过实验探索上述至少一些问题的工具 问题。我们建议开发转基因小鼠，在其中突变 甲状旁腺素/甲状旁腺素受体将在两种不同的调控下表达 推动者。α1(I)胶原和骨钙素启动子，以允许其 靶向表达在成骨细胞中的表达 分别(具体目标一)。对这些动物的分析将会有所帮助 以确定和区分这些细胞在调节 对甲状旁腺素和甲状旁腺素受体的反应(特定目标II)。我们还建议交配 这些带有选择性缺失PTH基因的转基因小鼠， 确定甲状旁腺素对成骨细胞功能和成熟的影响 依赖于cAMP途径的PTH/PTHrP受体激活 (具体目标三)。最后，我们将对上述转基因动物进行配对 对胶原酶-3有抵抗力的小鼠裂解成 确认胶原酶-3诱导对骨骼的重要性 甲状旁腺激素在发育和成人中诱导的重塑过程 LIFE(具体目标四)。

Bone is, together with kidney, the major target organ of PTH. It is known that PTH increases bone turnover, but it is obscure why in vivo it has an anabolic effect when it is administered intermittently, while its catabolic action prevails when it is given in a continuous fashion. PTH augments osteoclastic activity, but it is controversial whether its effects on osteoclasts are only mediated through osteoblasts, or whether they are also direct. Osteoblasts are the major target of PTH action. Which cells, however, in the osteoblast lineage- a spectrum from osteoprogenitors to pre-osteoblasts and mature osteoblasts - mediate the various actions of PTH in vivo is an open question. It is also unknown how PTHrP influenced osteoblast function independently of its role on chondrocyte differentiation. Finally, the cloned PTH/PTHrP receptor is able to activate at least two different signaling pathways, adenylate cyclase and phospholipase C. However, their relative importance in mediating the PTH effect on osteoblasts needs to be clarified. Recently the identification of two different mutations in the PTH/PTHrP receptor in patients with Jansen's metaphyseal chondrodysplasia (JMC), that lead to ligand-independent constitutive cAMP accumulation, gave us a powerful tool to explore experimentally at least some of the above mentioned questions. We propose to develop transgenic mice in which mutant PTH/PTHrP receptors will be expressed under the control of two different promoters. alpha1(I) collagen and osteocalcin promoters, to allow their targeted expression in less mature and/or more mature osteoblasts respectively (Specific Aim I). The analysis of these animals will help to determine and distinguish the roles of these cells in mediating the response to PTH and PTHrP (Specific Aim II). We also propose to mate these transgenic mice with the ones that selectively lack the PTH gene, to identify PTH effects on osteoblast function and maturation that are dependent on the PTH/PTHrP receptor activation of the cAMP pathway (Specific Aim III). Lastly, we will mate the above described transgenic mice with the animals that are resistant to collagenase-3 cleavage to confirm the importance of collagenase-3 induction for the bone remodeling process induced by PTH, both during development and in adult life (Specific Aim IV).