Gelatinase A (MMP-2) and cysteine proteinases are essential for the degradation of collagen in soft connective tissue

The degradation of soft connective tissue collagen is considered to depend on the activity of various proteolytic enzymes, particularly those belonging to the group of matrix metalloproteinases and cysteine proteinases. In the present study, we investigated the contribution of these enzymes to this process. Using a general inhibitor of MMPs (SC44463), collagen degradation was strongly inhibited, by about 40% after 24 h and up to 80% after 72 h of culturing. Blockage of cysteine proteinase activity (with leupeptin or E-64) reduced breakdown at these time intervals by 50% and 20%, respectively. Given the abundant presence of gelatinases - in particular gelatinase A (MMP-2) - in the tissue, the effect of an inhibitor selective for gelatinases (CT1166) was studied. Gelatinase inhibition resulted in a dose-dependent decrease of collagen breakdown up to 90% after 48 h. The ability of gelatinase A to degrade collagens was demonstrated by the induction of breakdown in devitalized explants by addition of activated gelatinase A, or by activation of endogenous enzyme with 4-aminophenylmercuric acetate. This latter effect was not found with plasmin, an activator of MMPs other than gelatinase A. Finally, the relevance of gelatinase A to the in vivo degradation of soft connective tissue collagen was implicated by the significant correlation found between its activity aid the collagen turnover rates of four soft connective tissues (tooth pulp, periodontal ligament, molar gingiva and skin). We conclude that collagen degradation in soft connective tissue is mediated by MMPs and to a lesser extent by cysteine proteinases. Our data are the first to attach a key role to gelatinase A in this process.