Identification of matrix metalloproteinases (MMPs) in synovial fluid from patients with temporomandibular disorder

Proteolytic enzymes with gelatinolytic activity in the synovial fluid (SF) of temporomandibular joint (TMJ) arthropathies were assayed by gelatin-impregnated gel enzymography. SF samples were collected from 10 TMJs in patients with closed lock (CL) condition and 5 TMJs from asymptomatic healthy volunteers. Two proteinases with gelatinolytic activities at 92 kDa and 72 kDa were detected in both the normal and the diseased TMJs. Also detected were weak bands at molecular weights of 83 kDa and 66 kDa. All of these proteinase activities were inhibited by EDTA and tissue inhibitor of metalloproteinases (TIMP), required Ca2+ for activation, and were detected with gelatin but not casein as substrate, suggesting that these enzymes were matrix metalloproteinases (MMPs). The 72 kDa and 66 kDa bands further reacted with anti-MMP-2 antibody by Western blot analysis, and the proteinases in the TMJ-SF could cleave type IV collagen in vitro without any activation. These four activities identified by enzymography were, therefore, identified as 92 kDa-gelatinase (proMMP-9), 83 kDa-gelatinase (active MMP-9), 72 kDa-gelatinase (proMMP-2) and 66 kDa-gelatinase (active MMP-2). Densitometric analyses of these bands revealed higher levels of the active form of MMP-9 in the CL patients compared to controls. These findings suggest that MMP-2 and -9 could be dominant proteinases in the TMJ-SF and possibly reflect TMJ pathology.