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）：最近令人信服的证据表明，sclerostin -骨中骨细胞专门表达的Sost基因产物-拮抗Wnts和BMP的促成骨细胞作用;提供了骨细胞调节骨形成的长期寻求的分子手段。PI和合作者的研究表明，甲状旁腺激素（PTH）的慢性升高可有效降低体内和体外骨细胞中Sost/sclerostin的表达，这表明骨细胞介导的PTH依赖性成骨细胞生成的新机制。机械负荷也增加成骨细胞的数量;这种合成代谢作用的潜在介质是PTH相关肽（PTHrP），因为其表达通过机械刺激增加。值得注意的是，Sost表达在体外被机械刺激抑制，在体内被骨负荷抑制。此外，在骨细胞（DMP 1-caPTHR 1）中过度表达组成型活性PTH 1受体（PTHR 1）的转基因小鼠表现出Sost表达降低和骨量显著增加。基于这些证据，假设骨细胞中PTHR 1信号传导的激活导致Sost基因表达的快速和直接抑制，这反过来又负责响应于全身PTH升高以及通过PTHrP局部增加的骨负荷而增加的骨形成。该假设将通过使用体外生成的骨细胞和真实骨细胞的体外研究以及使用转基因和敲除小鼠的体内方法的组合进行测试。目的1中的研究将阐明负责通过PTH和PTHrP快速抑制Sost表达的信号通路。在目标2中，将确定通过拉伸或振荡流体流动诱导的机械刺激在体外抑制Sost表达是否需要PTHR 1信号传导和PTHrP;以及骨负荷导致的sclerostin表达减少是否与PTHrP增加和骨形成增加在空间上相关使用模型小鼠尺骨负荷。在目标3中，将通过互补的转基因和敲除方法建立体内骨细胞中PTHR 1激活或缺失的后果。还将检查由PTH升高或负荷诱导的成骨反应或DMP 1- caPTHRI小鼠的高骨量表型是否通过Sost过表达或通过阻断Wnt信号传导途径而逆转或至少改善。此外，还将确定在骨细胞中特异性敲除PTHR 1的小鼠（DMP 1 - 10 kb-Cre/PTHR 1小鼠）中，Sost表达的减少以及对PTH或机械负荷的成骨细胞反应是否被消除。这些研究将促进了解骨细胞的骨形成的控制，并将阐明这些细胞的成骨细胞的PTH，PTHrP，和机械刺激的作用。我们期望这项工作将为开发新的治疗方法提供机会，通过对骨细胞的作用来实现骨修复。