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。这些疗法的开发需要确定调节骨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，这种更新应用建立在我们的发现基础上，即TGF β调节骨ECM的材料特性，并且仍然是少数几个因素之一。最近的工作，在第一个资助周期的支持下，建立了骨细胞和MMP 13作为通过一个动态过程控制骨质量的关键参与者，该过程被称为骨关节周围重塑（PLR）。在PLR中，骨细胞分泌蛋白酶，如MMP 13，以再吸收周围的骨基质。PLR对于维持骨质量、全身矿物质稳态以及促进骨细胞营养、通信和机械感觉的小管通道至关重要。我们最近的数据表明，PLR在人骨中的破坏可能会导致骨脆性的疾病，如股骨头坏死或放射性骨坏死的颌骨。然而，主要差距围绕PLR在健康骨或骨骼疾病中的作用或调节的理解。初步数据提出了PLR受机械负荷和TGF β调节的可能性，这是一种有可能将PLR对骨质量的维持与骨骼上不断变化的物理和生物需求相结合的机制。该提案测试了骨细胞通过以负荷和TGF β-依赖性方式的骨间隙重塑来调节骨ECM材料性质以控制骨质量和细胞张力的假设。具体而言，该项目旨在：1）确定半月板周围重塑是机械敏感性和TGF β调节的程度，2）确定机械负荷调节TGF β对骨作用的机制，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来评估。这些研究将评估骨细胞特异性MMP 13缺乏、施加的机械负荷和TGF β 1型受体的药理学抑制对PLR的影响。体内和体外功能获得和丧失研究将用于 确定这些因素在上位途径中起作用的程度。此外，该项目还研究了动态调节的骨外基质材料特性对骨细胞张力、信号传导和功能的影响。该项目意义重大，因为它将阐明TGF β 1和物理线索对骨细胞介导的PLR和骨质量的调节，揭示可用于预防骨脆性和维持骨骼健康的治疗靶向新机制。

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.