Purpose: Matrix metalloproteinases (MMPs) play a major role in connective tissue remodelling, wound healing and embryogenesis. They have also been implicated in pathological tissue degradation in diseases such as rheumatoid arthritis (RA), osteoarthritis (OA), and tumor invasion. The aim of this study was to define the potential role of MMPs in the inflammatory process of uveitis by identifying these proteases in the aqueous humor (AH) of patients with uveitis and in rabbits with endotoxin-induced uveitis (EIU).
Methods: Aqueous humor samples from 6 patients with uveitis and 5 control patients who had undergone elective cataract surgery were examined. The profile of MMPs in the AH of experimentally-induced acute anterior uveitis in rabbits was also assessed. Western blot analysis and SDS-PAGE substrate zymography were used to detect metalloenzymes and their natural inhibitor, tissue inhibitor of metalloproteinase (TIMP-1) in aqueous samples.
Results: Aqueous humor from all patients contained interstitial collagenase (MMP-1), stromelysin (MMP-3), gelatinase B (MMP-9) and TIMP-1. Although the amount of MMPs varied considerably, TIMP-1 levels remained unchanged in the aqueous of uveitis patients. Using substrate gel zymography, we were able to reveal several gelatinolytic bands, including one major band at approximately 92-kDa whose activity differed between uveitis and cataract AH. The gelatinase activity found in human AH samples was shown to be inhibited by 10 mM EDTA and activated in vitro by APMA, indicating that these enzymes were indeed of the metalloproteinase class. Aqueous humor samples from the rabbit EIU model revealed a 100-kDa molecular weight species likely to correspond to gelatinase B. This gelatinolytic activity was maximal at 6 hours after the lipopolysaccharide (LPS) injection, declined at 12 and 24 hours post LPS, and was absent at later time points. The induction of gelatinase activity in rabbit AH preceded the increase in cell number during the inflammatory process in the anterior chamber.
Conclusions: Metalloproteinases found in normal human AH may participate in physiological turnover of extracellular matrix in the eye. Elevated levels of MMPs were found in the AH of patients with uveal inflammation and animals with LPS-induced uveitis, where they are likely to be critical to tissue destructive and repair processes. It is likely that pro-inflammatory cytokines such as tumor necrosis factor-alpha (TNF-alpha) and interleukin-1 alpha (IL-1 alpha), which are known modulators of MMPs, induce their secretion in acute anterior uveitis.