Tenascin-C in the pathobiology and healing process of musculoskeletal tissue injury.

Tenascin-C (TN-C) is a hexabrachion-shaped extracellular matrix (ECM) protein which has very restricted expression in normal musculoskeletal tissues, but is expressed in large quantities in these tissues during embryogenesis as well as during regenerative and healing processes. TN-C is an elastic protein which has a number of binding sites for other extracellular matrix proteins as well as for cell membrane adhesion receptors. In addition, it can be stretched to several times its resting length, the ability of which is attributed to the stretch-induced unfolding of its fibronectin type III domains. In the musculoskeletal tissues, TN-C is present in the regions where high mechanical forces are transmitted from one tissue component to another, such as the myotendinous and osteotendinous junctions. Not surprisingly, it was recently presented that the expression of TN-C in the musculoskeletal tissues is regulated by the mechanical strain applied to their cells. Thus, taking into account the flexible structure of the TN-C and its site-specific expression pattern at sites exposed to heavy mechanical loads, TN-C is likely to play an important role in providing elasticity to the musculoskeletal tissues. This feature has a special significance in the degenerative and regenerative processes where the normal biomechanical environment of the musculoskeletal tissue is temporarily interrupted by injury. The rapidly increasing understanding of the structure and function of the ECM protein TN-C may well bring important insights into the clinical treatment of sports injuries in the future.