Stimulation of tendon repair by retinoid nuclear receptor agonists

描述（由申请人提供）：由于受伤的肌腱不能完全愈合和再生，迫切需要创造新的和更有效的肌腱修复疗法。在急性肌腱损伤中，修复是由固有的肌腱细胞和从周围组织和循环中迁移的外源性细胞进行的。细胞在损伤部位增殖，合成细胞外基质，产生致密排列的胶原纤维，并不同程度地重组肌腱结构。随着时间的推移，修复后的肌腱也会出现疤痕和退化，其特征是细胞增多、排列错误和胶原纤维数量减少，以及软骨特异性蛋白聚糖的产生增加，以及其他缺陷。这些改变会导致正常机械强度、柔韧性和弹性的丧失。目前尚不清楚哪些细胞负责多步骤修复过程，哪些细胞行为应该被增强或抑制，以防止退行性变化和改善愈合。这些和相关问题的阐明无疑会导致新的治疗工具的发展，以改善和刺激肌腱修复。我们最近发现，小鼠肌腱损伤部位的细胞群表现出祖细胞样特征，包括集落形成能力、多能性和间充质干细胞表面标记物的表达。有趣的是，这些受伤的肌腱相关祖细胞，在这里被称为intpc，具有比从未受伤的肌腱中分离的祖细胞更强的分化成软骨细胞的能力。此外，我们发现核维甲酸受体的激动剂？（RAR?）刺激培养intpc的成肌腱分化，同时抑制其体外成软骨分化和体内小鼠断裂肌腱的软骨变性。此外，我们发现小鼠intpc参与了小鼠断裂肌腱的修复过程和退行性变化，并且在受伤的人类肌腱中也存在类似的细胞群。这些和其他结果直接支持并导致了我们的新假设，即急性损伤肌腱中出现的祖细胞在肌腱修复中发挥重要作用，但也在肌腱退化中发挥重要作用，RAR？激动剂可以控制其差电位，改善肌腱修复。这个高风险高回报的R21项目将在受伤的小鼠和人类肌腱中使用肌腱祖细胞来测试这些新的可能性，并将开始开发通过控制这些祖细胞向腱源性谱系分化来刺激肌腱修复的方法。我们的目标是：(1)确定RAR的影响？激动剂对小鼠肌腱损伤模型中inTPCs和肌腱修复的影响(2)确定人类intpc是否有助于损伤肌腱的修复和退行性改变，并对RAR有反应？受体激动剂。这些探索性实验的结果将为设计更广泛的项目铺平道路，在这些项目中，可以更深入地研究上述治疗策略及其潜在的作用机制，从而在肌腱修复中获得创新的转化医学成果。

DESCRIPTION (provided by applicant): There is an urgent need to create new and more effective therapies for tendon repair since injured tendons do not fully heal and regenerate. In acute tendon injuries, repair is carried out by intrinsic tendon cells and extrinsic cells that migrate from surrounding tissues and the circulation. The cells proliferate at the injured site, synthesize extracellular matrix, produce dense and aligned collagen fibers, and reorganize tendon structure to varying degrees. The repaired tendons can also undergo scarring and degeneration over time that are characterized by hypercellularity, mis-alignment and reduced number of collagen fibers, and increased production of cartilage-specific proteoglycans, among other defects. These alterations can result in loss of normal mechanical strength, flexibility and elasticity. It remains unclear as to which cells are responsible for the multistep repair process and which cellular actions should be enhanced or suppressed to prevent degenerative changes and improve healing. The elucidation of these and related issues could undoubtedly lead to development of new therapeutic tools to improve and stimulate tendon repair. We recently found that a cell population present at the injury site in mouse tendons exhibited progenitor-like traits including colony forming ability, multipotency and expression of mesenchymal stem cell surface markers. Interestingly, these injured tendon-associated progenitor cells, herein called inTPCs, possessed a much stronger ability to differentiate into chondrogenic cells than progenitor cells isolated from uninjured tendons. Furthermore, we found that agonists for the nuclear retinoic acid receptor ? (RAR?) stimulated tenogenic differentiation in cultured inTPCs, while they inhibited their chondrogenic differentiation in vitro and chondroid degeneration in ruptured mouse tendons in vivo. In addition, we found that mouse inTPCs participated in both repair process and degenerative changes in ruptured mouse tendons and that a similar cell population was present in injured human tendons. These and other results directly support and lead to our novel hypotheses that progenitor cells appearing in acutely injured tendons play important roles in tendon repair but also degeneration and that RAR? agonists can control their differential potential and improve tendon repair. This high risk-high return R21 project will test these novel possibilities using tendon progenitor cells in injured mouse and human tendons and will begin to develop methods to stimulate tendon repair by controlling differentiation of these progenitors toward a tenogenic lineage. Our aims are: (1) To determine the effects of RAR? agonists on inTPCs and tendon repair in a mouse tendon injury model; and (2) To determine whether human inTPCs contribute to repair and degenerative changes in injured tendons and respond to RAR? agonists. The outcome of these exploratory experiments will pave the way toward designing more encompassing projects in which the above therapeutic strategies and their underlying mechanisms of action can be studied in greater depth, leading to innovative translational medicine outcomes in tendon repair.