Protein synthesis in collagenous and non-collagenous fractions of human patellar tendon: Influence of tendinopathy and short-term exercise.

The dynamics of human tendon protein synthesis in response to short-term exercise and injury is poorly understood, and whether this occurs heterogeneously in the tendon remains an enigma. This study aimed to determine whether protein synthesis is affected by short-term exercise, and whether it is altered in patellar tendinopathy. Protein synthesis was studied in humans using an 8 day intake of deuterated water (D2O), and analyses of blood and tendon biopsies. Eighteen patients with chronic uni- or bilateral patellar tendinopathy (8 females and 10 males) and 18 healthy, matched participants (8 females and 10 males) were included. Both patellar tendons investigated in all participants, and the healthy participants additionally completed three bouts of unilateral heavy resistance training prior to biopsy sampling. Tendon protein synthesis rates were markedly higher (10-20 fold) in the soluble matrix fraction compared to the insoluble collagen fraction. Protein synthesis did not differ between tendinopathic and healthy tendons in either fraction. Unilateral resistance exercise had no significant impact on protein synthesis in either tendon fraction. Protein synthesis was not influenced by biological sex. The present study demonstrates that tendon protein synthesis predominantly occurs in the soluble matrix fraction compared to the insoluble collagen fraction of human patellar tendon, and chronic tendinopathy and short-term exercise do not appear to alter synthesis rates in healthy, physically active humans. These data increase our understanding of tendon protein synthesis, and could help explain why patellar tendinopathy becomes a chronic condition. KEY POINTS: The dynamics of human tendon protein synthesis in different protein fractions are not well-understood, and the effect of short-term exercise or tendinopathy remains largely unknown. In this study, protein synthesis was significantly higher in the soluble matrix proteins compared to the insoluble collagen fraction. No apparent differences in tendon protein synthesis in either fraction were observed between healthy and tendinopathic tendons. Unilateral short-term exercise had no measurable impact on tendon protein synthesis in either protein fraction. The results increase our understanding of protein dynamics in human tendon and suggest that neither chronic tendinopathy nor short-term exercise measurably alters tendon protein synthesis over an 8 day period.