Osmotic Signaling in Chondrocyte Aging and Osteoarthritis

描述（由申请人提供）：骨关节炎（OA）是一种使人衰弱和疼痛的滑膜关节疾病，在美国估计有2100万人患有此病，超过10%的60岁以上人口患有此病。正常的软骨结构是通过软骨细胞介导的合成和软骨细胞外基质（ECM）的降解来维持的。通过关节载荷应用生物力学信号对于保持组织内稳态至关重要。然而，在生理和病理情况下，软骨细胞对软骨机械负荷的反应机制尚不完全清楚。近年来，瞬时受体电位香草样蛋白4 （TRPV4）离子通道作为一种Ca++优先阳离子通道，已成为软骨细胞渗透和机械刺激信号转导的中心焦点。在体外，TRPV4已被确定为软骨细胞基因表达和ECM产生的有效调节剂，并且在体内，自发性关节变性已被描述为具有全局TRPV4基因缺失。该信号通路中与年龄相关的变化可能解释了老化软骨对进行性退变和OA的脆弱性。本研究的目的是表征TRPV4在衰老过程中软骨维持中的作用。我们假设衰老过程中关节退行性变的发生和进展是由于trpv4介导的Ca++信号在响应渗透和机械刺激时发生改变。在Specific Aim 1中，我们将全面表征衰老和OA过程中软骨细胞TRPV4通道，包括TRPV4基因表达、TRPV4蛋白水平和TRPV4功能，并将其与相应形态和物质变化的定量分析联系起来。在Specific Aim 2中，我们将产生软骨靶向的、可诱导的trpv4敲除小鼠，进一步研究trpv4信号在成年软骨和OA发育中的具体作用，再次从宏观和微观角度观察软骨的trpv4依赖性变化。本研究旨在阐明软骨代谢是如何被机械因素调节的，以及在衰老和疾病过程中软骨的稳态是如何被破坏的。这项奖学金不仅将帮助我掌握作为骨科生物工程和转化研究的内科科学家的知识和工具，而且这里提出的项目将直接将这些人才用于开发新的诊断，制药和生物物理干预措施，以更好地治疗OA。

DESCRIPTION (provided by applicant): Osteoarthritis (OA) is a debilitating and painful disease of synovial joints that affects an estimated 21 million people in the United States and more than 10% of the population over 60 years old. Normal cartilage structure is maintained through chondrocyte-mediated synthesis and degradation of the cartilage extracellular matrix (ECM). The application of biomechanical signals through joint loading is known to be critical in preserving this tissue homeostasis. However, the mechanisms by which chondrocytes respond to mechanical loading of the cartilage, in both physiological and pathological settings, are not fully understood. Recently, the transient receptor potential vanilloid 4 (TRPV4) ion channel, a Ca++ preferred cation channel, has emerged as a central focus in chondrocyte osmotic and mechanical stimuli signal transduction. TRPV4 has been identified as a potent regulator of chondrocyte gene-expression and ECM production in vitro, and spontaneous joint degeneration has been described in vivo with global trpv4 gene deletion. Age-associated changes in this signaling pathway may explain the vulnerability of aging cartilage to progressive degeneration and OA. The goal of this study is to characterize the role of TRPV4 in cartilage maintenance during aging. We hypothesize that the initiation and progression of joint degeneration in aging is due to altered TRPV4-mediated Ca++ signaling in response osmotic and mechanical stimuli. In Specific Aim 1, we will comprehensively characterize the chondrocyte TRPV4 channel during aging and OA, including trpv4 gene expression, TRPV4 protein levels and TRPV4 function, and relate this to quantitative analyses of the corresponding morphological and material changes. In Specific Aim 2, we will generate cartilage-targeted, inducible trpv4 knockout mice to further study the specific role of TRPV4 signaling in adult cartilage and OA development, looking again at both macro and microscopic TRPV4-dependant changes of the cartilage. This study is intended to elucidate how cartilage metabolism is regulated by mechanical factors and how this cartilage homeostasis is disrupted during aging and disease. This fellowship will not only help equip me with the knowledge and tools to begin a productive career as a physician-scientist in orthopedic bioengineering and translational research, but the project proposed here will directly apply these talents towards the development of novel diagnostic, pharmaceutical, and biophysical interventions for better treatment of OA. PUBLIC HEALTH RELEVANCE: Aging is one of the primary risk factors for osteoarthritis (OA), although the mechanisms responsible for age-related joint degeneration are not well understood. The response of chondrocytes, the cells of cartilage, to mechanical loading is critical for articular cartilage resiliency and joint health. The Transient Receptor Potential Vanilloid 4 (TRPV4) ion channel, a transducer of osmotic and mechanical stimuli, may be the physiological link between aging and OA joint degeneration. We aim to characterize chondrocyte TRPV4 function during aging and OA pathogenesis, utilizing a novel TRPV4-deficient mouse model to further explore this relationship.