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

描述（由申请人提供）：跟腱病影响美国大部分人口的健康。随着对肌腱修复过程的深入了解，更好的治疗策略可能会为跟腱愈合带来更好的结果。本研究的总体目标是描述哪些祖细胞被招募来启动跟腱修复，哪些基质成分对愈合过程中胶原纤维的组织化至关重要。在该提议中，假设在跟腱修复期间，祖细胞被募集，分化成腱细胞，并且开始形成基质，其方式与肌腱发育期间发生的祖细胞定型基质形成相似但不完全相同。假设跟腱内存在祖细胞，并且具有启动内在修复机制的能力。还假设小的富含亮氨酸的蛋白聚糖（SLRP），在肌腱龛内发现的基质分子，是修复过程中胶原纤维形成和重塑所必需的。具体而言，假设II类SLRP纤调蛋白对于修复期间的胶原原纤维形成是必需的。在本培训项目中，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和表征跟腱的祖细胞;此外，将通过标记转基因（巩膜轴启动子/绿色荧光蛋白，ScxGFP）小鼠中的增殖细胞来定位肌腱内和周围的祖细胞，以表征内源性和/或外源性修复候选细胞。然后将确定哪种细胞群负责通过使用转基因ScxGFP小鼠的穿孔损伤模型在跟腱中的常见断裂部位处的合适愈合应答（Aim 2）。此外，将在整个穿孔损伤模型中检查SLRP在修复期间胶原纤维形成中的作用（目的3.1），特别是将在纤调蛋白缺陷小鼠中检查跟腱损伤的愈合反应（目的3.2）。这里提出的研究旨在确定肌腱修复的增殖阶段中跟腱内和周围的每个细胞群的修复作用。此外，通过这种损伤模型，SLRP参与肌腱愈合的阐明是预期的。对祖细胞和SLRP在其生态位内的参与的更好理解可能会导致改善治疗策略，以促进愈合或预防过度使用引起的进一步退行性变化。 公共卫生相关性：跟腱修复需要细胞在病变内增殖，然后合成和重塑胶原纤维。这项培训计划中提出的研究将更好地了解哪些细胞参与其中，哪些基质分子调节愈合。更好地了解肌腱修复的机制可能会导致更强的治疗策略和更好的患者结局。

DESCRIPTION (provided by applicant): 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. PUBLIC HEALTH RELEVANCE: Achilles tendon repair requires cells to proliferate within the lesion and then collagen fibrils to be synthesized and remodeled. Research proposed in this training program will provide a better understanding of just which cells are involved and just which matrix molecules regulate healing. Better knowledge of the mechanisms of tendon repair could lead to stronger treatment strategies and better patient outcomes.