In rheumatoid arthritis, synovial expression of urokinase (uPA) activity is greatly increased (Busso, N., V. Péclat, A. So, and A.-P. Sappino. 1997. Ann. Rheum. Dis. 56:550-557). We report the same effect in murine antigen-induced arthritis. uPA-mediated plasminogen activation in arthritic joints may have deleterious effects via degradation of cartilage and bone matrix proteins as well as beneficial effects via fibrin degradation. We evaluated these contrasting effects in vivo by analyzing the phenotype of uPA-deficient (uPA Ϫ / Ϫ ) and control mice during antigen-induced arthritis.Joint inflammation was comparable in both groups up to day 3 and subsequently declined in control mice, remaining significantly elevated in uPA Ϫ / Ϫ mice on days 10 and 30 after arthritis onset. Likewise, synovial thickness was markedly increased in uPA-deficient mice persisting for up to 2 mo, whereas it subsided in control animals. Bone erosion was exacerbated in uPA Ϫ / Ϫ mice on day 30. By contrast, no difference in articular cartilage proteoglycan content was found between both groups. Significantly increased accumulation of fibrin was observed by day 30 in arthritic joints of uPA Ϫ / Ϫ mice. We hypothesized that synovial fibrin deposition plays a role in joint inflammation. Accordingly, defibrinogenation of uPA Ϫ / Ϫ mice by ancrod significantly decreased the sustained joint inflammation. All the above observations were reproducible in plasminogen-deficient (Pln Ϫ / Ϫ ) mice.In conclusion, synovial fibrin deposition plays a role as a nonimmunological mechanism which sustains chronic arthritis. ( J. Clin. Invest. 1998. 102:41-50.)

Objective-To analyse the functional activity of the plasminogen activators urokinase (uPA) and tissue type plasminogen activator (tPA) in human synovial membrane, and to compare the pattern of expression between normal, osteoarthritic, and rheumatoid synovium. The molecular mechanisms underlying diVerences in PA activities between normal and pathological synovial tissues have been further examined. Methods-Synovial membranes from seven normal (N) subjects, 14 osteoarthritis (OA), and 10 rheumatoid arthritis (RA) patients were analysed for plasminogen activator activity by conventional zymography and in situ zymography on tissue sections. The tissue distribution of uPA, tPA, uPA receptor (uPAR), and plasminogen activator inhibitor type-1 (PAI-1) was studied by immunohistochemistry. uPA, tPA, uPAR, and PAI-1 mRNA values and mRNA distribution were assessed by northern blot and in situ hybridisations respectively. Results-All normal and most OA synovial tissues expressed predominantly tPA catalysed proteolytic activity mainly associated to the synovial vasculature. In some OA, tPA activity was expressed together with variable amounts of uPA mediated activity. By contrast, most RA synovial tissues exhibited considerably increased uPA activity over the proliferative lining areas, while tPA activity was reduced when compared with N and OA synovial tissues. This increase in uPA activity was associated with increased levels of uPA antigen and its corresponding mRNA, which were localised over the synovial proliferative lining areas. In addition, in RA tissues, expression of the specific uPA receptor (uPAR) and of the plasminogen activator inhibitor-type 1 (PAI-1) were also increased. Conclusion-Taken together, these results show an alteration of the PA/plasmin system in RA synovial tissues, resulting in increased uPA catalytic activity that may play a part in tissue destruction in RA.

The deleterious role of fibrin deposition in arthritic joints prompted us to explore the effect of the thrombin inhibition on the course of collagen-induced arthritis (CIA) in the mouse. CIA was induced in male DBA/1J mice using native chicken type II collagen. The thrombin inhibitor polyethyleneglycol-hirudin (PEG-hirudin) was given for 16 days, starting 20 days after the first immunization (preventive treatment) or at the onset of clinical signs of arthritis (curative treatment). All the mice treated with PEG-hirudin had a significantly prolonged clotting time compared with control mice. PEG-hirudin, administered in a preventive way, led to significantly reduced incidence and severity of CIA during most of the treatment period, as assessed by clinical scoring. Accordingly, histological features showed a significant diminution of synovial hyperplasia in PEG-hirudin-treated mice compared with untreated mice. There was also a significant downmodulation of the synovial proinflammatory IL-1β and IL-12p35 cytokine mRNAs in treated mice. Intra-articular fibrin, evaluated by immunohistochemistry, was significantly reduced in treated mice compared with control mice and correlated with both clinical and histological scorings. Most importantly, once arthritis was established, PEG-hirudin also showed a curative effect. In conclusion, PEG-hirudin can both prevent the onset of CIA in a dose-dependent manner and ameliorate established arthritis, suggesting that thrombin inhibition may offer a new therapeutic approach in arthritis.

Hirudin reduces joint inflammation associated with AIA by fibrin-dependent and independent mechanisms.

Serum MMP-3 is not an independent marker of joint damage, but is correlated with systemic inflammation. Its precise role in joint damage in RA remains to be elucidated.