β2-microglobulin induces MMP-1 but not TIMP-1 expression in human synovial fibroblasts

Background. beta(2)-Microglobulin (beta(2)m) amyloidosis is a destructive articular disease that causes significant morbidity in patients undergoing hemodialysis. The amyloid deposits contain beta(2)m, some of which is altered with advanced glycation end products (AGE-beta(2)m). The deposits are located principally in joint structures, with adjacent degradation of cartilage and bone. We hypothesized that one of the mechanisms by which beta(2)m induces joint destruction is to induce the release of matrix metalloproteinase-1 (MMP-1), but not tissue inhibitor of metalloproteinase-1 (TIMP-1), from synovial fibroblasts. Methods. To test this hypothesis and determine the role of AGE-beta(2)m, we incubated human osteoarthritic synovial fibroblasts in the presence and absence of beta(2)m and AGE-beta(2)m and measured the release of interstitial collagenase (MMP-1) and/or TIMP-1 by enzyme-linked immunosorbent assay and Northern blot analysis. Results. beta(2)m and AGE-beta(2)m at 10 and 25 mu g/mL induced the release of MMP-1 from human osteoarthritic synovial fibro blasts at 24 hours. Tn contrast, there was no increased release of TIMP-1, leading to an increase in the MMP-1/TIMP-1 ratio indicative of uncontrolled collagenolysis. A similar dose response was observed at 48 hours, except that AGE-beta(2)m had no effect over control cultures. MMP-1 mRNA expression by Northern blot analysis paralleled these findings. The source of the fibroblasts did not alter the results. Finally, we demonstrated that doxycycline, a treatment for arthritis, can inhibit the release of MMP-1 from synovial fibroblasts incubated with beta(2)m. Conclusion. beta(2)m, at physiologically relevant concentrations, induces the release of MMP-1 without concomitant release of TIMP-1 from human synovial fibroblasts, leading to uncontrolled collagenolysis. The alteration of beta(2)m with AGE did not alter this effect at 24 hours, but blocked the effect at 48 hours. These findings may account for the tissue destruction seen in beta(2)m amyloidosis.