The Role of Matrix Metalloproteinases in Tendon Growth

描述(申请人提供)：肌腱是一种动态组织，连接肌肉和骨骼，并允许在运动过程中进行力传递。尽管肌腱在肌肉骨骼系统的整体功能中占有重要地位，但人们对肌腱生长、维持和修复的细胞和分子机制知之甚少。临床上，肌腱损伤和疾病是最常见和最令人衰弱的肌肉骨骼疾病之一，导致数十亿美元的治疗成本和生产力损失。肌腱主要由I型胶原纤维组成的致密网络组成，为肌腱提供结构支持，结合和释放调节多种细胞功能的生长因子，并作为细胞渗透的天然屏障。肌腱中的主要细胞是成纤维细胞，几乎所有肌腱疾病的主要特征是成纤维细胞形态异常和肌腱细胞外基质(ECM)的严重破坏。因此，了解肌腱成纤维细胞与其ECM环境之间的相互作用可能会为开发针对这些疼痛状况的新的有效治疗方法提供重要的基础。在肌腱生长期间，成纤维细胞表达基质金属蛋白酶(MMPs)，这是一个依赖锌的酶家族，共同降解多种ECM成分，包括I型胶原。虽然已经描述了20多种MMPs，但之前在其他组织中的研究发现，膜型MMPs亚群(MT-MMPs)是允许成纤维细胞通过其ECM迁移的蛋白。在MT-MMP亚组中，MT1-和MT2-MMPs似乎是对细胞运动最重要的MMPs，因为缺乏MT1-或MT2-MMPs的细胞失去了迁移能力。MT1-和MT2-MMP在肌腱中均有表达，但这些蛋白在肌腱成纤维细胞迁移中的作用尚不清楚，它们在肌腱生长中的重要性也是未知的。使用一个信息丰富的肌腱过载模型，该模型概括了肌腱生长的关键因素，MT1-MMP表达的变化与生长反应中的关键事件相关。此外，MT1-MMP的表达似乎仅限于新形成的肌腱组织区域。虽然MT2-MMP2在肌腱中也有表达，但作为MT1-MMPs的研究较少，其表达模式和功能目前尚不清楚。我们推测，MT1-MMP2单独或与MT2-MMP协同作用，是肌腱成纤维细胞对肌腱机械负荷反应的关键调节因子。我的中心假设是，MT1-和MT2-MMP都是肌腱生长所必需的，并协同发挥作用，允许肌腱成纤维细胞通过肌腱ECM迁移。这一假设将在两个特定的目标上进行严格的检验，采用多学科方法，包括在肌腱超负荷模型中进行分子生物学和组织力学实验的组合。这项提议的发现将为肌腱成纤维细胞生物学提供重要的见解，并有可能导致未来专注于MT-MMPs治疗肌腱损伤和疾病的翻译研究。

DESCRIPTION (provided by applicant): Tendon is a dynamic tissue that connects muscle to bone and allows for force transmission during locomotion. Despite the importance of tendon in the overall function of the musculoskeletal system, relatively little is known about the cellular and molecular mechanisms that control its growth, maintenance and repair. Clinically, tendon injuries and diseases are among the most frequent and debilitating musculoskeletal conditions, resulting in billions of dollars in treatment costs and lost productivity. Tendon is primarily composed of a dense network of type I collagen fibrils that provides structural support to the tendon, binds and releases growth factors that regulate multiple cellular functions, and acts as a natural barrier to the infiltration of cells. The predominant cells in tendon are fibroblasts, and central feature to nearly all tendon disorders is abnormal fibroblast morphology and grossly disrupted appearance of the tendon extracellular matrix (ECM). Thus, understanding the interaction between tendon fibroblasts and their ECM environment will likely provide an important basis for the development of novel and effective therapies for these painful conditions. During periods of tendon growth, fibroblasts express matrix metalloproteinases (MMPs), a family of zinc-dependent enzymes that collectively degrade multiple ECM components, including type I collagen. While more than 20 MMPs have been described, previous studies in other tissues have identified the subgroup of membrane-type MMPs (MT-MMPs) as the proteinases that allow fibroblasts to migrate through their ECM. Within the MT-MMP subgroup, MT1- and MT2-MMP are the MMPs that appear most important for cellular movement, as cells that are deficient in either MT1- or MT2-MMP lose their ability to migrate. Both MT1- and MT2-MMP are expressed in tendon, but the role of these proteinases in tendon fibroblast migration is unknown, as is their overall importance in tendon growth. Using an informative tendon overload model that recapitulates the key elements of tendon growth, changes in MT1-MMP expression correlate with pivotal events in the growth response. Furthermore, MT1-MMP expression appears to be restricted to areas of newly formed tendon tissue. While MT2-MMP is also expressed in tendon, it has been less extensively studied as MT1-MMP, and both its pattern of expression and function is presently unclear. We posit that MT1-MMP, working alone or in concert with MT2- MMP, is a key regulator of tendon fibroblast function in response to mechanical loading of tendons. My central hypothesis is that MT1- and MT2-MMP are both required for tendon growth and function cooperatively to allow tendon fibroblast migration through the tendon ECM. This hypothesis will be rigorously tested in two Specific Aims using a multidisciplinary approach involving a combination of molecular biology and tissue mechanics experiments in a tendon overload model. Findings from this proposal will provide important insights into basic tendon fibroblast biology and potentially lead to future translational studies focused on MT-MMPs in the treatment of tendon injuries and diseases.