Exploring the cellular and molecular landscape underlying tendon fibrosis in horses

马产业每年为加拿大经济贡献近200亿美元，支持超过15万个工作岗位。在所有的马学科中，肌肉骨骼损伤一直被报道为表现不佳、提前退休和过早死亡的主要原因。其中，肌腱损伤是最常见和最具挑战性的治疗之一。与人类相似，随着年龄的增长和重复使用，从再生到纤维化肌腱修复的逐渐转变会导致进行性虚弱。这种“退行性肌腱病”使组织易于发生急性损伤，持续的性能导致在损伤部位产生进一步的生物力学下瘢痕组织（纤维化）。由于肌腱在运动活动期间通常在其生物力学极限附近发挥作用，因此纤维化代表了实质性的弱点，易于在典型的内源性修复后发生慢性再损伤1。尽管对马产业具有重要意义，但这种再生能力下降并转向肌腱纤维化反应的根本原因尚未阐明2。 凭借我在加拿大西部马产业内的完善网络，我的计划将独特地定位于收集来自马的组织（因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（新生儿和年轻的马进入运动训练）到退化（衰老的运动员），最终受伤。肌腱健康将通过磁共振成像进行结构表征;此后，组织将从肌腱的中央承重区域收获，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观结构的二次谐波生成成像3。接下来，我们将部署这些新的见解来进行早期肌腱愈合的细胞活动的体内监测，从而提供有关马运动员自然肌腱损伤中纤维化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比较老年马（已知对损伤产生纤维化反应）与小马（已知在其他结缔组织中表现出上级愈合）的愈合结果。在这样做的过程中，我们将开发和定义一种新的模型，上级成人肌腱愈合密切模拟自然发生的损伤，在马。 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逐渐发作以及随后的肌腱损伤相关的事件，并开发马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，这些研究将为未来开发能够在马肌肉骨骼愈合期间促进促再生（抗纤维化）反应的兽医治疗提供基础知识。

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.