Increased Proteolysis of Collagen in an InVitro Tensile Overload Tendon Model

Presently, there is a lack of fundamental understanding regarding changes in collagen's molecular state due to mechanical damage. The bovine tail tendon (BTT; steers approximately 30months) was characterized and used as an invitro model for investigating the effect of tensile mechanical overload on collagen susceptibility to proteolysis by acetyltrypsin and a-chymotrypsin. Two strain rates with a 1000-fold difference (0.01 and 10s super(-1)) were used, since molecular mechanisms that determine mechanical behavior were presumed to be strain rate dependent. First, it was determined that the BTTs were normal but immature tendons. Water content and collagen content (approx. 60% of wet weight and 80% of dry weight, respectively) and mechanical properties were all within the expected range. The collagen crosslinking was dominated by the intermediate crosslink hydroxylysinonorleucine. Second, tensile overload damage significantly enhanced proteolysis by acetyltrypsin and, to a lesser degree, by a-chymotrypsin. Interestingly, proteolysis by acetyltrypsin was greatest for specimens ruptured at 0.01s super(-1) and seemed to occur throughout the specimen. Understanding damage is important for insight into injuries (as in sports and trauma) and for better understanding of collagen fiber stability, durability, and damage mechanisms, aiding in the development of durable tissue-based products for mechanically demanding surgical applications.