Since we found that MMP-2 is mostly found in its proform in SF, our results favour the implication of MMP-13 Interestingly, MMP-13, which is responsible for cleavage of type II collagen [36,37], aggrecan [38], and fibrinogen [39], has been shown to be increased in RA SF [3] and to be linked to synovial inflammation and bone destruction [40]. The gene discussed is ACAN; the disease is rheumatoid arthritis.