Association of increased expression of macrophage elastase (matrix metalloproteinase 12) with rheumatoid arthritis

Abstract

Objective: Increased enzymatic activity of matrix metalloproteinases (MMPs) may promote the progression of rheumatoid arthritis (RA). We undertook this study to investigate the expression and localization of human macrophage elastase (MMP-12) in synovial tissue from RA patients and to compare MMP-12 levels in the synovial tissue and synovial fluid of RA patients with the corresponding levels in patients with osteoarthritis (OA).

Methods: We obtained synovial tissues from 23 RA patients and 29 OA patients and analyzed MMP-12 expression using immunohistochemistry, Western and Northern blotting analyses, and zymography. Furthermore, we quantified MMP-12 levels in synovial fluid by Western blotting and zymography.

Results: Northern blotting analysis demonstrated that RA synovial tissue contained higher levels of MMP-12 messenger RNA than did OA synovial tissue. Western blotting revealed that MMP-12 proteins were consistently and markedly increased in RA synovial tissue compared with OA synovial tissue. A greater amount of immunoreactive proteins corresponding to catalytic forms of MMP-12 was present in RA synovial tissue and synovial fluid, and the MMP-12 proteins exhibited caseinolytic activity in vitro. Immunohistochemical staining showed that the major cells expressing MMP-12 were synovial lining cells, many of which were inflammatory macrophages.

Conclusion: These results establish a possible mechanism by which macrophage-derived MMP-12 may play an important role in the destructive process in RA. Inhibition of MMP-12 may be a potential modality for the treatment of RA.