Exploring the cellular and molecular landscape underlying tendon fibrosis in horses

马匹产业每年为加拿大经济贡献近200亿美元，支持15万个工作岗位。在所有马术项目中，肌肉骨骼损伤一直被报告为表现不佳、过早退休和过早死亡的主要原因。在这些损伤中，肌腱损伤是最常见和最具挑战性的治疗之一。与人类相似，肌腱修复从再生到纤维性逐渐转变，随着年龄的增长和重复使用，会导致渐进性虚弱。这种“退行性肌腱病”使组织容易受到急性损伤，并持续表现，导致损伤部位产生进一步的生物力学下部瘢痕组织(纤维化)。由于肌腱在运动过程中通常处于接近其生物力学极限的状态，纤维化是一种严重的弱点，容易在典型的内源性修复后再次损伤。尽管这对马业意义重大，但肌腱再生能力下降并转向纤维化反应的根本原因尚未阐明。凭借我在加拿大西部马匹行业内建立的良好网络，我的项目将独一无二地收集马匹的组织(由于与研究无关的原因而被安乐死)，代表广泛的肌腱健康，从再生能力强(新生和年轻的马进入运动训练)到退行性(老年运动员)，最终到受伤。肌腱健康的结构特征将通过磁共振成像进行表征；此后，将从肌腱的中央承重区采集组织，并使用我们建立的单细胞RNA测序管道进行严格询问，然后进行原位验证和微结构的二次谐波成像3。接下来，我们将利用这些新的见解对肌腱早期愈合背后的细胞活动进行活体监测，从而提供关于马匹运动员自然肌腱损伤的纤维性愈合的详细、时间数据。最后，我们将使用实验性肌腱损伤模型来比较老年马(已知会对损伤产生纤维化反应)和小马(已知在其他结缔组织中表现出更好的愈合)的愈合结果。在此过程中，我们将开发和定义一种新的成年高级肌腱愈合模型，该模型接近于模拟马的自然损伤。总之，我的研究计划将详细描述目前未知的与退行性肌腱病以及随后的肌腱损伤相关的事件，并建立马匹运动员肌腱损伤后再生和纤维化愈合的强大成人模型。最终，这些研究将为未来兽医疗法的发展提供基础知识，这些疗法能够在马的肌肉骨骼愈合过程中促进促再生(抗纤维化)反应。

The equine industry contributes nearly $20B annually to the Canadian economy, supporting >150K jobs. Across all equine disciplines, musculoskeletal injuries have been consistently reported as a leading cause of poor performance, early retirement and premature loss of life. Of these, tendon injuries are among the most common and challenging to treat. Similar to humans, a gradual shift from regenerative to fibrotic tendon repair leads to progressive weakness with advancing age and repetitive use. This "degenerative tendinopathy", predisposes the tissue to acute injury with continued performance resulting in the production of further biomechanically inferior scar tissue (fibrosis) at the injury site. As tendons typically function at near their biomechanical limits during athletic activity, fibrosis represents a substantial weakness, predisposing to chronic re-injury following typical endogenous repair1. Despite the significance to the equine industry, the underlying causes of this decline in regenerative capacity and switch to fibrotic response of tendons have not been elucidated2. With my well-established network within the equine industry of western Canada, my program will be uniquely positioned to collect tissues from horses (euthanized for reasons unrelated to research) representing a wide spectrum of tendon health, ranging from regeneration competent (neonatal and young horses entering athletic training) through degenerative (aging athletes) and ultimately to injured. Tendon health will be structurally characterized by magnetic resonance imaging; thereafter, tissue will harvested from the tendon's central, load-bearing region and rigorously interrogated using our established single cell RNA-sequencing pipeline, followed by in situ validation and second harmonic generation imaging of microstructure3. Next, we will deploy these new insights to conduct in vivo monitoring of cellular activities underlying early tendon healing, thus providing detailed, temporal data regarding fibrotic healing in natural tendon injuries of equine athletes. Lastly, we will use an experimental tendon injury model to compare healing outcomes in aged horses (known to produce a fibrotic response to injury) with ponies (known to exhibit superior healing in other connective tissues). In doing so, we will develop and define a novel model of superior adult tendon healing closely simulating naturally occurring injury in equines. Together, my research program will describe, in detail, currently unknown events associated with the gradual onset of degenerative tendinopathy as well as subsequent tendon injury and develop robust adult models of both regenerative and fibrotic healing after tendon injury in equine athletes. Ultimately, these studies will provide the foundational knowledge for future development of veterinary therapeutics capable of fostering a pro-regenerative (anti-fibrotic) response during musculoskeletal healing in horses.