The mechanistic control of bone extracellular matrix material properties by TGFb

描述(由申请人提供)：保护或恢复骨骼质量的新疗法具有显著改善骨骼健康的巨大潜力。这些疗法的发展需要确定调节骨骼质量的细胞和分子机制。因此，本研究的长期目标是确定生物和物理线索控制骨细胞外基质(ECM)材料特性的机制。为此，这一更新应用建立在我们的发现之上，即转化生长因子调节骨细胞外基质的材料特性，并且仍然是为数不多的几个因素之一。最近的工作，在第一个资金周期的支持下，确立了骨细胞和MMP13作为关键参与者，通过称为尺骨周围重塑(PLR)的动态过程来控制骨质量。在PLR中，骨细胞分泌MMP13等蛋白酶，以吸收髓周骨基质。PLR对于维持骨质量、全身矿物质平衡以及促进骨细胞滋养、沟通和机械感觉的管状通道是必不可少的。我们最近的数据表明，人类骨骼中PLR的破坏可能导致股骨头或颌骨放射性骨坏死等疾病的骨脆性。然而，对PLR在健康骨骼或骨骼疾病中的作用或调节的理解存在重大差距。初步数据表明，PLR受机械负荷和转化生长因子的调节，这是一种潜在的机制，可以将PLR维持骨骼质量与改变骨骼的物理和生物需求结合起来。这一建议验证了这样的假设，即骨细胞通过依赖负荷和转化生长因子的方式进行的楔周重塑来调节骨ECM材料的特性，从而控制骨质量和细胞张力。具体地说，本项目的目标是：1)确定楔周重塑是机械敏感的和受转化生长因子调节的程度；2)确定机械负荷调节转化生长因子对骨的影响的机制；以及3)确定PLR对骨ECM质量和骨细胞张力的功能影响。PLR活性和调节将使用组织学、放射学、生物工程和分子方法的组合进行评估。这些研究将评估骨细胞特异性MMP13缺乏、施加机械负荷和药物抑制转化生长因子βI型受体对PLR的影响。体内和体外功能获得和丧失的研究将用于 确定这些因素在上位性途径中的作用程度。此外，本项目还研究了动态调节的钩骨周围骨细胞外基质材料特性对骨细胞张力、信号和功能的影响。这个项目意义重大，因为它将阐明转化生长因子和物理线索对骨细胞介导的PLR和骨质量的调节，揭示可以作为治疗靶点的新机制，以预防骨脆性和维持骨骼健康。

DESCRIPTION (provided by applicant): New therapies that protect or restore bone quality have great potential to significantly improve skeletal health. Development of these therapies requires the identification of the cellular and molecular mechanisms that regulate bone quality. Therefore, the long-term goal of this research is to identify mechanisms by which biological and physical cues control bone extracellular matrix (ECM) material properties. To that end, this renewal application builds on our discovery that TGFß regulates the material properties of bone ECM and remains one of just a handful of factors yet shown to do so. Recent work, supported by the first funding cycle, establishes osteocytes and MMP13 as key participants in the control of bone quality through a dynamic process called perilacunar remodeling (PLR). In PLR, osteocytes secrete proteases such as MMP13 to resorb the perilacunar bone matrix. PLR is essential for the maintenance of bone quality, systemic mineral homeostasis, and the canalicular channels that facilitate osteocyte nourishment, communication, and mechanosensation. Our recent data suggests that disruption of PLR in human bone may contribute to the bone fragility in diseases such as osteonecrosis of the femoral head or osteoradionecrosis of the jaw. However, major gaps surround the understanding of the role or regulation of PLR in healthy bone or in skeletal disease. Preliminary data raise the possibility that PLR is regulated by mechanical load and by TGFß, a mechanism that has the potential to couple the maintenance of bone quality by PLR to changing physical and biological demands on the skeleton. This proposal tests the hypothesis that osteocytes regulate bone ECM material properties through perilacunar remodeling in a load- and TGFß-dependent manner to control bone quality and cellular tension. Specifically, this project aims to: 1) determine the extent to which perilacunar remodeling is mechanosensitive and TGFß-regulated, 2) identify mechanisms by which mechanical load regulates the effects of TGFß on bone, and 3) determine the functional impact of PLR on bone ECM quality and osteocyte tension. PLR activity and regulation will be evaluated using a combination of histologic, radiologic, bioengineering, and molecular approaches. These studies will assess the effects on PLR of osteocyte-specific MMP13-deficiency, applied mechanical loads, and pharmacologic inhibition of the TGFß type I receptor. In vivo and in vitro gain and loss of function studies will be used to determine the extent to which these factors operate in an epistatic pathway. In addition, this project examines the effect of dynamically regulated perilacunar bone ECM material properties on osteocyte cellular tension, signaling, and function. This project is significant because it will elucidate the regulation of osteocyte mediated PLR and bone quality by TGFß and physical cues, revealing new mechanisms that can be therapeutically targeted to prevent bone fragility and maintain skeletal health.