Chavaunne T . Thorpe , John fragmentation age - and 1 injury - specific matrix withchanges in tendon matrix composition ,

Energy storing tendons, such as the human Achilles and equine superficial digital flexor tendon (SDFT), are highly prone to injury, the incidence of which increases with ageing. The cellular and molecular mechanisms that result in increased injury in aged tendons are not well established, but are thought to result in altered matrix turnover. However, little attempt has been made to fully characterise the tendon proteome, nor determine how the abundance of specific tendon proteins changes with ageing and/or injury. The aim of this study was therefore to assess the protein profile of normal SDFTs from young and old horses, using label free relative quantification to identify differentially abundant proteins and peptide fragments between age groups. The protein profile of injured SDFTs from young and old horses was also assessed. The results demonstrate distinct proteomic profiles in young and old tendon, with alterations in the levels of proteins involved in matrix organisation and regulation of cell tension. Further, we identified several new peptide fragments (neopeptides) present in aged tendons, suggesting that there are agespecific cleavage patterns within the SDFT. Proteomic profile also differed between young and old injured tendon, with a greater number of neopeptides identified in young injured tendon. This study has increased the knowledge of molecular events associated with tendon ageing and injury, suggesting that maintenance and repair of tendon tissue may be reduced in aged individuals, and may help to explain why the risk of injury increases with