Abstract

Tendons are commonly injured, not only in athletes, but also during normal everyday activities, particularly in older age. Tendons are rich in extracellular matrix proteins, many of which are turned over extremely slowly during an individual's lifetime. As a result, tight regulation of the extracellular matrix is essential for tendons to remain resilient to the mechanical load placed on them. However, tendons are prone to age-associated functional decline, characterised by chronic inflammation, accumulation of damaged collagen, and matrix remodelling. These degenerative changes often precede injury, wherein additional inflammation and fibrotic tissue deposition make treatment difficult and reinjury highly likely. Understanding and preventing the causes of tendon functional decline is therefore vital to improving quality of life in the ageing population. Using an equine model, here we show that tendon fibroblasts, or tenocytes, isolated from aged tendons exhibit markers of senescence when cultured in vitro. Further, we describe how senescence in tenocytes drives inflammation, hypercontractility, and dysregulation of tendon matrix components. By replicatively senescing tenocytes isolated from young tendons, we observed that senescent tenocytes instigated proinflammatory signalling, had impaired capacity in wound healing assays, increased contractility, and secreted factors that induced senescence in healthy tenocytes. Further, tenocyte senescence dysregulated matrix turnover both at the gene and protein level. Finally, we demonstrate how senotherapeutic treatment of senescent tenocytes can reduce expression of senescence markers and restore proliferative capacity. Our results uncover systemic links between tendon ageing and cellular senescence, and identify mechanisms and therapeutic strategies for age-associated tendon degeneration.