SECOND MESSENGERS IN PARATHYROID HORMONE ACTION

描述：（直接取自应用程序）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曲线。间歇性（每日一次）PTH显示出治疗骨质疏松症的希望，但需要更多的知识PTH在骨细胞的行动，以提高这种方法的疗效。PTH激活由成骨细胞（OB）和骨髓基质细胞（MSC）表达的PTH/PTHrP受体（PTHR），但不激活成熟破骨细胞（OCL），尽管它可能对OB和OCL的早期祖细胞产生直接影响。PTHR激活多个平行的效应腺苷酸环化酶（AC），磷脂酶C（PLC）和胞质游离钙瞬变，调节增殖，分化和其他功能的靶细胞骨，但具体的PTHR信号之间的联系，或模式的信号，并在每个群体的靶细胞的细胞反应的独特程序知之甚少。以前的努力，以解决这些问题在体外受到限制的同质，非转化群体的正常PTH靶细胞和特定的技术，用于调节他们的PTHR信号。该项目的主要目标是利用新的、条件转化的克隆OB、MSC和OCL祖细胞系，其中PTHR表达和信号传导可以被特异性地修饰，以确定PTHR和个体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替代它们，将创建一组其他方面相同的每种类型的克隆骨细胞系，用于评估对特定PTHR信号的细胞反应。与新的信号选择性PTH类似物，可以指导正常PTHR信号异常，这些细胞系统将能够直接在体外测定的PTHR和它的信使信号在控制OB和OCL分化的作用，包括可能的差异影响脉动和连续的PTH暴露，有相反的影响骨在体内。接近PTHR-无效细胞也将允许对可能由这些细胞正常表达的其他种类的PTH受体的作用的不模糊检测。从这些研究中对PTH作用的新认识将对进一步开发具有神经活性的PTH类似物非常宝贵。

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.