MMP1 and rheumatoid arthritis: Matrix metalloproteinases-3 (MMP-3), a member of the matrix metalloproteinases, can degrade extracellular proteoglycans and type IV collagen; activate the activities of MMP-1, MMP-8 and MMP-9; accelerate articular cartilage aging; and exacerbate osteoarthritis (OA) and rheumatoid arthritis (RA).