Tendon Repair: Contributions of Progenitors and Small Leucine-Rich Proteoglycans

跟腱病影响了许多美国人的健康。随着对跟腱修复过程的了解的提高，更好的治疗策略可以带来更好的跟腱愈合结果。本研究的总体目的是描述哪些祖细胞被招募来启动跟腱修复，哪些基质成分在愈合过程中对胶原原纤维的组织至关重要。在这一提议中，假设在跟腱修复过程中，祖细胞被招募，分化成腱细胞，并开始形成基质，其方式与跟腱发育过程中祖细胞承诺基质的形成相似，但并不完全相同。假设跟腱内的祖细胞存在并具有启动内在修复机制的能力。也有假设认为，小的富含亮氨酸的蛋白聚糖（slrp）是肌腱生态位中发现的基质分子，在修复过程中对胶原纤维的形成和重塑至关重要。具体来说，我们假设II类SLRP纤维调节蛋白在修复过程中对胶原纤维形成至关重要。在本训练项目中，将通过分子生物学和免疫组织化学技术在小鼠组织中分离并表征跟腱祖细胞；此外，通过在转基因（巩膜启动子/绿色荧光蛋白，ScxGFP）小鼠中标记增殖细胞来定位肌腱内和周围的祖细胞，从而可以表征内在和/或外在修复候选细胞。然后，通过转基因ScxGFP小鼠穿孔损伤模型，确定哪些细胞群负责跟腱常见断裂部位的适当愈合反应（目的2）。此外，slrp在修复过程中胶原纤维形成中的作用将在穿孔损伤模型中进行研究（Aim 3.1），特别是在纤维调素缺乏的小鼠中，将研究跟腱损伤的愈合反应（Aim 3.2）。本文提出的研究旨在确定跟腱增殖期跟腱修复过程中跟腱内和周围各细胞群的修复作用。此外，通过该损伤模型，slrp在肌腱愈合中的作用有望得到阐明。更好地了解祖细胞和slrp在其生态位中的作用，可以改善治疗策略，以加强愈合或预防过度使用引起的进一步退行性改变。

Achilles tendinopathies affect the health of much of the population of the United States. With improved understanding of the tendon repair process, better treatment strategies could lead to better outcomes for Achilles tendon healing. The overall aims of this study are to delineate which progenitor cells are recruited to initiate Achilles tendon repair and which matrix components are essential to the organization of collagen fibrils during the healing process. In this proposal, it is hypothesized that during Achilles tendon repair progenitors are recruited, differentiate into tenocytes, and begin forming matrix in a manner similar yet not definitively identical to progenitor cell commitment matrix formation which occurs during tendon development. It is hypothesized that progenitors within the Achilles tendon exist and have the capacity to initiate an intrinsic repair mechanism. It is also hypothesized that small leucine-rich proteoglycans (SLRPs), matrix molecules found within the tendon niche, are essential to collagen fibrillogenesis and remodeling during repair. Specifically, it is hypothesized that Class II SLRP fibromodulin is essential to collagen fibrillogenesis during repair. In this training project, progenitor cells of the Achilles tendon will be isolated and characterized in mouse tissue through molecular biological and immunohistochemical techniques; moreover, progenitors in and around the tendon will be localized by labeling of proliferating cells in transgenic (scleraxis promoter/green fluorescent protein, ScxGFP) mice to allow for characterization of intrinsic and/or extrinsic repair candidate cells. Then it will be determined which cell population(s) is/are responsible for suitable healing responses at the common site of rupture in the Achilles tendon via punch lesion injury model with transgenic ScxGFP mice (Aim 2). Moreover, the roles of SLRPs in collagen fibrillogenesis during repair will examined throughout the punch lesion model (Aim 3.1), and specifically the healing response of Achilles tendon injuries will be examined in fibromodulin-deficient mice (Aim 3.2). Studies proposed here are designed to determine the reparative role of each cell population in and around the Achilles tendon during the proliferative phase of tendon repair. Moreover, through this injury model, elucidation of the involvement of SLRPs in tendon healing is anticipated. Improved understanding of the involvement of progenitors and SLRPs within their niche could lead to improved therapeutic strategies for bolstered healing or prevention of further degenerative changes caused by overuse.