SECOND MESSENGERS IN PARATHYROID HORMONE ACTION

描述：(直接取自应用)甲状旁腺激素(PTH)对骨骼的作用是多种多样的，可能会导致骨骼质量的净增加或减少，这取决于循环激素的时间和浓度分布。间歇性(每天一次)甲状旁腺激素显示出治疗骨质疏松的前景，但需要更多关于甲状旁腺素在骨骼中的细胞作用的知识来增强这种方法的有效性。PTH可激活成骨细胞(OBS)和骨髓基质细胞(MSCs)表达的PTH/PTHrP受体(PTHR)，但不能激活成熟破骨细胞(OCL)表达的PTH/PTHrP受体，尽管它可能直接影响OBS和OCL的早期祖细胞。PTHR可激活多个平行效应因子--腺苷环化酶(AC)、磷脂酶-C(PLC)和胞浆游离钙瞬变--调节骨靶细胞的增殖、分化和其他功能，但具体的PTHR信号或信号模式之间的联系，以及每组靶细胞中细胞反应的独特程序之间的联系尚不清楚。以前在体外研究这些问题的努力受到同质的、未转化的正常甲状旁腺激素靶细胞群体以及调节其甲状旁腺素受体信号的特定技术的限制。该项目的主要目标是利用新的、有条件转化的、克隆的OB、MSC和OCL祖细胞系，其中PTHR的表达和信号可以被特异性地修饰，以确定PTHR和单个PTHR信号在激素的关键细胞效应中的作用。通过基因消融消除内源性PTHR，并用正常或信号选择性突变PTHR取而代之，将创建一组每种类型的完全相同的克隆骨细胞系，用于评估细胞对特定PTHR信号的反应。与新的信号选择性甲状旁腺素类似物一起，可以指示正常的甲状旁腺激素受体信号异常，这些细胞系统将能够在体外直接分析甲状旁腺素及其信使信号在控制OB和OCL分化中的作用，包括脉动性和连续性甲状旁腺激素暴露对体内骨骼产生相反影响的可能的不同影响。进入PTHR阴性细胞也可以清楚地检测到其他种类的PTH受体的影响，这些细胞可能正常表达这些细胞。这些研究对甲状旁腺素作用的新理解对于进一步开发具有骨骼活性的甲状旁腺素类似物将是非常有价值的。

Description:(Taken directly from the application) The actions of parathyroid hormone (PTH) on bone are diverse and may cause a net gain or loss of skeletal mass, depending upon the temporal and concentration profiles of the circulating hormone. Intermittent (once daily) PTH shows promise for therapy of osteoporosis, but more knowledge of the cellular actions of PTH in bone is needed to enhance the efficacy of this approach. PTH activates PTH/PTHrP receptors (PTHRs) expressed by osteoblasts (OBs) and marrow stromal cells (MSCs) but not by mature osteoclasts (OCLs), although it may exert direct effects on early progenitors of both OBs and OCLs. PTHRs activate multiple parallel effectors-adenylyl cyclase (AC), phospholipase-C (PLC) and cytosolic free calcium transients-that modulate proliferation, differentiation and other functions in target cells of bone, but the links between specific PTHR signals, or patterns of signals, and distinctive programs of cellular responses in each population of target cells are poorly understood. Previous efforts to approach these issues in vitro were constrained by unavailability of homogeneous, nontransformed populations of normal PTH target cells and of specific techniques for modulating their PTHR signaling. The main goal of this project is to utilize novel, conditionally transformed, clonal OB, MSC and OCL progenitor cell lines, in which PTHR expression and signaling can be specifically modified, to determine the roles of the PTHR and of individual PTHR signals in the key cellular effects of the hormone. By eliminating endogenous PTHRs through gene ablation and replacing them with normal or signal-selective mutant PTHRs, a panel of otherwise-identical clonal bone cell lines of each type will be created with which to assess the cellular responses to specific PTHR signals. Together with new signal-selective PTH analogs that can instruct normal PTHRs to signal aberrantly, these cell systems will enable direct in vitro assays of the role of the PTHR and its messenger signals in controlling OB and OCL differentiation, including the possible differential impact of pulsatile and continuous PTH exposures that have opposite effects on bone in vivo. Access to PTHR-null cells also will allow unobscured detection of the effects of other species of PTH receptors that may be expressed normally by these cells. The new understanding of PTH action that should flow from these studies will be invaluable for further development of skeletally active PTH analogs.