Aggrecan degradation in osteoarthritis and rheumatoid arthritis

Aggrecan turnover is critically important to maintain extracellular matrix homeostasis in articular cartilage. Cartilage aggrecan metabolism has been studied in chondrocyte cell cultures, cartilage explant cultures, and in whole animal models. In many of these studies, matrix metalloproteinases (MMPs) are proposed to degrade cartilage aggrecan. MMP expression appears elevated in joint tissues from patients with osteoarthritis (OA) and rheumatoid arthritis (RA) (Dean et al. 1989, Wolfe et al. 1993) and inhibitors of both MMPs and thiol proteinases have been shown to block aggrecan (Buttle et al. 1992) and type II collagen (Mort et al. 1993) degradation in cartilage explant cultures. Using antibodies and cDNA probes, elevations in expression and concentration of many of these enzymes in animal models and in OA and RA have been described. Human cartilage aggrecan has now been cloned and sequenced (Doege et al. 1991). This information, in combination with the ability to sequence aggrecan and aggrecan fragments at the protein level, has resulted in the identification of several aggrecan fragments which appear to result from proteinase degradation. In this report, we describe data which suggest that MMPs may in part be responsible for aggrecan catabolism in normal articular cartilage, as well as in the elevated catabolism seen in OA and RA

Metalloproteinases, tissue inhibitor, and proteoglycan fragments in knee synovial fluid in human osteoarthritis

Objective. To determine the concentrations of human stromelysin-1, collagenase, tissue inhibitor of metalloproteinases (TIMP), and proteoglycan fragments in knee synovial fluid in patients with injury to the meniscus or anterior cruciate ligament, posttraumatic osteoarthritis, primary osteoarthritis, or pyrophosphate arthritis. Methods. Synovial fluid samples were collected from patients with knee disease diagnosed arthroscopically and radiologically. Concentrations of stromelysin-1, collagenase, and TIMP-1 were determined by sandwich immunoassay, using monoclonal and polyclonal antibodies. Fragments of cartilage proteoglycan containing the chondroitin sulfate-binding region were determined by immunoassay with a polyclonal antibody. Results. Average concentrations of metalloproteinases, TIMP, and proteoglycan fragments in joint fluid were significantly elevated in patients from all disease groups as compared with volunteers with healthy knees (reference group). Stromelysin concentrations in disease groups averaged 15-45 times that of the reference group. The molar ratios between stromelysin and collagenase varied between 10 and 150. The molar ratio between total stromelysin and free TIMP was 0.5 in the reference group and between 1.6 and 5.3 in the disease groups. Conclusion. Stromelysin concentration in joint fluid is a parameter that distinguishes diseased joints from healthy joints, with a sensitivity of 84% and a specificity of 90%. The high concentrations of metalloproteinase relative to TIMP in joint fluid from patients with the conditions studied may be associated with cartilage matrix degradation in these arthritides

Increased secretion and activity of matrix metalloproteinase-3 in synovial tissues and chondrocytes from experimental osteoarthritis

AbstractObjective: 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).Methods: 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).Results: 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.Conclusion: 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

Cartilage matrix metabolism in osteoarthritis : markers in synovial fluid, serum, and urine

Osteoarthritis is a major cause of disability and early retirement. Yet we lack the means to diagnose the disease in its early stages or to monitor the effects of treatment on the target tissue, the joint cartilage. Neither can we identify the disease mechanisms at the tissue or cell level. Current research focuses on the use of markers of cartilage matrix metabolism in body fluids as a means to diagnose and monitor osteoarthritis. Cartilage proteoglycan, collagen and glycoprotein fragments, as well as proteinases and their inhibitors, are being suggested for this purpose. Structural information on matrix molecule fragments released into body fluids may also help to identify the enzymes active in the destruction of the cartilage, a central issue in osteoarthritis