TGF-beta1 differentially modulates the collagen VI alpha5 and alpha6 chains in human tendon cultures.

Collagen VI is a microfibrillar collagen with a potential regulatory role in tendon repair mechanism. We studied the expression of collagen VI alpha5 and alpha6 chains in normal human tendon fibroblast cultures, both under basal condition and in response to TGF-beta1, a potent regulator of tendon healing. Under basal condition, we found that the alpha5 chain was expressed, although to a lesser extent with respect to the alpha3 chain; in contrast, the alpha6 chain was absent. The treatment with TGFbeta1 induced an opposite effect on the expression of the alpha5 and alpha6 chains; in fact, while the alpha5 chain was dramatically reduced, the alpha6 chain was induced and released in the culture medium. These data indicate that collagen VI alpha5 and alpha6 chains are differentially involved in tendon matrix homeostasis. The alpha6 chain may represent a new potential biomarker for monitoring TGFbeta1-related events in tendon, as healing and fibrotic scar formation.