Osteocyte control of bone formation via Sost

骨细胞通过Sost控制骨形成

• 批准号: 7650222
• 负责人: Teresita M. Bellido
• 金额: $ 34.37万
• 依托单位: INDIANA UNIV-PURDUE UNIV AT INDIANAPOLIS
• 依托单位国家: 美国
• 财政年份: 2007
• 资助国家: 美国
• 起止时间: 2007-08-05 至 2011-06-30
• 项目状态: 已结题
• 来源: https://reporter.nih.gov/project-details/7650222
• 关键词: Adult; Affect; Anabolism; Antibodies; Apoptosis; Attenuated; Calvaria; Catabolism; Cell Culture Techniques; Cell Lineage; Cells; Chronic; Development; Dietary Calcium; Disease; Event; Exhibits; Gene Expression; Genes; Genetic; Hormonal; Hormones; Human; Hyperparathyroidism; In Vitro; Infusion procedures; Inherited; Injection of therapeutic agent; Knock-out; Knockout Mice; Mechanical Stimulation; Mechanics; Mediating; Mediator of activation protein; Mesenchymal Stem Cells; Messenger RNA; Modeling; Molecular; Mus; Osteoblasts; Osteocytes; Osteogenesis; Parathyroid Hormone Receptor; Parathyroid Hormones; Phenotype; Regulation; Research Personnel; Signal Pathway; Signal Transduction; Stimulus; Stretching; Testing; Transgenes; Transgenic Mice; Transgenic Organisms; Van Buchem disease; Work; base; bone; bone mass; bone strength; fluid flow; human PTH protein; in vivo; novel; novel therapeutic intervention; osteogenic; overexpression; parathyroid hormone-related protein; prevent; response; skeletal; spatial relationship; transcription factor; ulna

DESCRIPTION (provided by applicant): Recent compelling evidence demonstrates that sclerostin - the product of the Sost gene exclusively expressed by osteocytes in bone - antagonizes the pro-osteoblastogenic actions of Wnts and BMPs; providing a long-sought molecular means by which osteocytes regulate bone formation. Work leading to this application by the PI and collaborators demonstrated that chronic elevation of parathyroid hormone (PTH) potently decreases Sost/sclerostin expression in osteocytes in vivo and in vitro, suggesting a novel mechanism for PTH-dependent osteoblastogenesis mediated by osteocytes. Mechanical loading also increases osteoblast number; and a potential mediator of this anabolic effect is PTH related peptide (PTHrP), as its expression is increased by mechanical stimulation. Notably, Sost expression in inhibited by mechanical stimuli in vitro and by bone loading in vivo. Moreover, transgenic mice overexpressing a constitutively active PTH 1 receptor (PTHR1) exclusively in osteocytes (DMP1-caPTHR1) exhibit decreased Sost expression and a remarkable increase in bone mass. Based on these lines of evidence, it is hypothesized that activation of PTHR1 signaling in osteocytes leads to a rapid and direct inhibition of Sost gene expression, which, in turn, is responsible for increased bone formation in response to systemic elevation of PTH as well as to bone loading through local increase in PTHrP. This hypothesis will be tested by a combination of in vitro studies using osteocytes generated in vitro and authentic osteocytes, and in vivo approaches using transgenic and knock out mice. Studies in Aim 1 will elucidate the signaling pathways responsible by the rapid inhibition of Sost expression by PTH and PTHrP. In Aim 2, it will be determined whether suppression of Sost expression in vitro by mechanical stimulation induced by stretching or oscillating fluid flow requires PTHR1 signaling and PTHrP; and whether the decreased sclerostin expression by bone loading is spatially related to increased PTHrP and increased bone formation using the model of ulna loading in mice. In Aim 3, the consequences of PTHR1 activation or deletion in osteocytes in vivo will be established by complementary transgenic and knock out approaches. It will be also examined whether the osteogenic response induced by PTH elevation or loading, or the high bone mass phenotype of DMP1- caPTHRI mice are reversed, or at least ameliorated, by Sost overexpression or by blocking the Wnt signaling pathway. Furthermore, it will be established whether the reduction in Sost expression and the osteoblastogenic response to PTH or mechanical loading are abrogated in mice in which the PTHR1 is knocked out specifically in osteocytes (DMP1-10kb-Cre/PTHR1 mice). These studies will advance understanding of the control of bone formation by osteocytes and will elucidate the contribution of these cells to the osteoblastogenic actions of PTH, PTHrP, and mechanical stimuli. We expect that this work will provide opportunities for the development of novel therapeutic approaches leading to bone anabolism through actions on osteocytes.

描述（由申请人提供）：最近的令人信服的证据表明，硬化素 - 骨中骨细胞独家表达的SOST基因的产物 - 拮抗Wnt和BMP的促稳态作用；提供了长期以来的分子手段，骨细胞调节骨形成。 PI和合作者导致这种应用的工作表明，甲状旁腺激素（PTH）的慢性升高会在体内和体外有效降低骨/硬化素的表达，并在体外和体外降低，这表明了PTH依赖性依赖性骨细胞生成的新型机制。机械载荷还增加了成骨细胞数。这种合成代谢作用的潜在介体是PTH相关的肽（PTHRP），因为它通过机械刺激增加了表达。值得注意的是，在体外机械刺激抑制和体内骨负荷的抑制作用。此外，在骨细胞（DMP1-CAPTHR1）中，过表达组成型活性PTH 1受体（PTHR1）的转基因小鼠表现出降低的表达和骨骼质量的显着增加。基于这些证据，假设骨细胞中的PTHR1信号传导的激活导致对SOST基因表达的快速而直接抑制，这反过来又导致骨骼形成增加，以响应PTH的系统性升高以及PTHRP中局部增加的骨负荷。该假设将通过在体外生成的骨细胞和真实的骨细胞以及使用转基因和敲除小鼠的体外接近的体外研究来检验。 AIM 1中的研究将阐明通过PTH和PTHRP快速抑制SOST表达的信号传导途径。在AIM 2中，将确定是否通过拉伸或振荡流体流引起的机械刺激在体外抑制SOST表达是否需要PTHR1信号传导和PTHRP；以及使用小鼠尺负荷模型在空间上与PTHRP增加和骨形成增加的硬化蛋白表达降低是否与骨形成增加有关。在AIM 3中，将通过互补的转基因和敲除方法来确定体内骨细胞中PTHR1激活或缺失的后果。还将检查是否是由PTH升高或负载诱导的成骨反应，还是DMP1- Capthri小鼠的高骨质量表型通过SOSSSSOST过表达或阻止WNT信号通路来逆转或至少改善。此外，将在小鼠中废除PTHR1在骨细胞（DMP1-10KB-CRE/PTHR1小鼠）中特异性敲除pTHR1的小鼠中，是否会消除对PTH或机械负荷的降低和对PTH或机械负荷的成骨细胞生成反应的降低或机械负荷的降低（将确定）。这些研究将通过骨细胞对控制骨形成的控制，并阐明这些细胞对PTH，PTHRP和机械刺激的成骨细胞生成作用的贡献。我们预计，这项工作将为开发新型治疗方法提供机会，从而通过对骨细胞的作用导致骨骼合成代谢。