Collagen III differential roles in temporal regulation of tendon healing across ages

肌腱可以承受大的力量，由于高度对齐，致密的胶原蛋白基质。然而，其低 细胞结构和相对不能招募损伤后的修复细胞，以及对过度损伤的敏感性。 瘢痕形成导致肌腱结构和机械功能的丧失。I型胶原蛋白（Col 1）是主要的 健康肌腱的胶原蛋白和III型胶原蛋白（Col 3）是一种次要成分， 损伤在其他富含Col 1的组织中，如皮肤和骨骼，Col 3通过调节 早期细胞浸润，促进愈合，以及胶原蛋白沉积、构建和交联 形成，支持Col 3在伤口愈合中的早期关键作用，其尚未在肌腱中研究。 更重要的是了解Col 3在肌腱中的作用，Col 3在老化组织中的水平降低 在老年肌腱中，我们发现愈合不良，这增加了年龄引起的Col 3丢失的可能性。 增加老年人群中肌腱愈合不良的易感性。虽然Col 3可以协调细胞 活动和命运是至关重要的最佳修复反应后损伤的早期阶段，在肌腱，其 在重塑阶段的持续表达可能损害所需的愈合反应。所以我们的 总体目标是描述Col 3的时间表达调节损伤的机制， 在整个肌腱愈合过程中的反应，以及其在整个老化过程中的差异效应。具体来说，我们将测试 假设Col 3对早期肌腱愈合至关重要，但其在重建过程中的持续表达 是有害的。为了测试这一点，我们产生了一种新的诱导型Col 3缺陷型（即，Col 3a 1F/+、Col 3a 1F/F）小鼠 模型以通过Col 3的时间靶向来确定Col 3的剂量依赖性效应。使用这种方法，我们 将定义Col 3在损伤时肌腱愈合过程中的调节作用， 增殖期和重塑期。此外，通过敲除青年、中年和老年人中的Col 3， 动物，我们将评估老化对改变Col 3的肌腱愈合的影响。理解的作用 Col 3在整个愈合过程中将导致临床相关的见解，以改善肌腱损伤后的结局， 不同年龄的患者。本研究的目的是：目的1：确定Col 3的年龄敏感性机制作用 通过在肌腱损伤时敲低Col 3，在整个肌腱愈合过程中发挥作用。目的2：阐明年龄- Col 3在指导修复细胞活动和敲除效应延长中的敏感机制作用 在肌腱愈合的增殖阶段，Col 3下降。目的3：确定年龄敏感性机制 通过在肌腱愈合的重塑阶段敲低Col 3，来研究Col 3在肌腱修复中的作用。这 这项研究将确定Col 3在整个衰老过程中对肌腱损伤的反应中的关键时间作用。我们将利用 一种新的小鼠模型，结合严格的分级结构/功能测定，以确定Col 3在 指导肌腱愈合中细胞活性和基质组装/组织之间的相互作用。

Tendons can withstand large forces due to a highly aligned, dense collagen matrix. However, their low cellularity and relative inability to recruit reparative cells post-injury, as well as susceptibility to excessive scarring results in loss of tendon structure and mechanical function. Type I collagen (Col1) is the primary collagen of healthy tendon and type III collagen (Col3) is a minor constituent that increases in response to injury. In other Col1-rich tissues such as skin and bone, Col3 directs reparative cell activities by regulating early cellular infiltration to promote healing, as well as collagen deposition, architecture and crosslink formation, supporting an early critical role of Col3 in wound healing, which has not been studied in tendon. Adding to the importance of understanding a role for Col3 in tendon, Col3 levels in aging tissues are reduced and in aged tendon, we have shown inferior healing which raises the possibility that age-induced Col3 loss increases susceptibility to poor tendon healing in aging populations. While Col3 may orchestrate cellular activities and fate that are critical for an optimal reparative response post-injury at early stages in tendon, its persistent expression in the remodeling phase may compromise the desired healing response. Therefore, our overall objective is to delineate mechanisms by which the temporal expression of Col3 modulates the injury response throughout tendon healing, as well as its differential effect throughout aging. Specifically, we will test the hypothesis that Col3 is crucial for early tendon healing, but that its continued expression during remodeling is detrimental. To test this, we generated a novel inducible Col3 deficient (i.e., Col3a1F/+, Col3a1F/F) mouse model to determine the dose-dependent effects of Col3 by temporal targeting of Col3. Using this approach, we will define the regulatory roles of Col3 throughout tendon healing at the time of injury, during the early proliferative phase, and during remodeling. In addition, by knockdown of Col3 in young, middle-aged, and old animals, we will evaluate the effects of aging on tendon healing with altered Col3. Understanding the role of Col3 throughout healing will lead to clinically relevant insights to improve outcomes following tendon injury in patients of varying ages. The study aims are: Aim 1: To define the age-sensitive mechanistic role(s) of Col3 throughout tendon healing by knocking down Col3 at the time of tendon injury. Aim 2: To elucidate the age- sensitive mechanistic role(s) of Col3 in directing reparative cell activities and prolonged effects of knocking down Col3 during the proliferative phase of tendon healing. Aim 3: To define the age-sensitive mechanistic role(s) of Col3 in tendon repair by knocking down Col3 during the remodeling phase of tendon healing. This study will define the critical temporal roles of Col3 in response to tendon injury throughout aging. We will utilize a novel mouse model coupled with rigorous hierarchical structure/function assays to define the role of Col3 in directing interplay between cellular activities and matrix assembly/organization in tendon healing.