The aim of this study was to define the relative regulation of matrix metalloproteinase-3 (MMP-3), and tissue inhibitor of metalloproteinases-1 (TIMP-1), in chondrocytes and synovium in experimental osteoarthritis (EOA).
Partial-meniscectomized (PM) rabbits, surgical sham controls (SH), and normal non-surgical controls (N) were killed at times corresponding to early degenerative lesions (4 weeks) and increasingly progressive stages of EOA at 8 and 12 weeks post-PM. MMP-3 activity was measured in conditioned media from chondrocytes and synovium using a peptide cleavage assay with substance P (SP) as the substrate. TIMP-1 was quantitated using an enzyme-linked immunosorbent assay (ELISA).
Early degenerative lesions (4 weeks post-PM) were characterized by inflammatory responses in the synovium accompanied by a significant rise of MMP-3 activity in synovial cultures (P < 0.05). At 8 weeks there was no discernible inflammation, and MMP-3 activity in EOA synovial cultures was comparable to that in the controls; this was followed by a second increase in MMP-3 activity in EOA samples at 12 weeks. MMP-3 activity was significantly elevated in EOA chondrocyte cultures at 8 weeks post-PM relative to N controls, corresponding to the most destructive phase of EOA, but not in the early phase (4 weeks) or 'late' degenerative phase (12 weeks). Medium derived from chondrocytes contained little or no TIMP-1. Synovia secreted relatively higher amounts of TIMP-1, and this was elevated at 8 weeks post-PM relative to the SH controls. The majority (approximately 90%) of MMP-3 activity could be inhibited using recombinant TIMP-1 or a hydroxamate MMP inhibitor. Complete inhibition was achieved with EDTA or 1,10 phenanthroline.
Together, these data indicate that in EOA, MMP-3 is initially upregulated in the synovium which may play a pivotal role in the pathogenesis of cartilage lesions. In contrast, chondrocyte-derived MMP-3 is upregulated in the later phases of EOA, contributing further to progression of cartilage lesions.