Expression and enzymatic activity of MMP-2 during healing process of the acute supraspinatus tendon tear in rabbits.

We investigated the spontaneous healing process of a surgically created supraspinatus tendon tear in rabbits with specific reference to the expression of matrix metalloproteinase-2 (MMP-2) and its time-course change in enzymatic activity along with the expression of tissue inhibitors of metalloproteinases (TIMPs). A transverse, full thickness tear of the supraspinatus tendon was created and examined. Immunohistochemical analysis revealed that MMP-2 positive cells were mainly localized at both cutting ends of the tendon, and reparative tissue encroached into the gap from the bursal side. The expression of TIMP-1 was induced in the cells at not only the tendon edges but also the reparative tissue during the healing process. TIMP-2 was constitutively expressed in both the tendon and the reparative tissue. Gelatin zymography using tissue culture media demonstrated latent and active forms of MMP-2 and characteristic time-linked changes of the enzymatic activity. Western blotting confirmed the bands as the latent form of MMP-2. These results suggest that MMP-2 is expressed and activated during the healing process of acute supraspinatus tendon tear and can play an important role in the remodeling process.