Abstract
Synovial fibroblasts freshly isolated from the rheumatoid joint are characterized by their marked connective tissue degradative ability. This phenotype includes the ability to secrete large amounts of the matrix-degrading metalloproteinases, collagenase, and stromelysin. We have found that another aspect of this phenotype is the constitutive expression at both protein and mRNA levels of a 92-kD gelatinolytic metalloproteinase, which is not secreted by normal dermal or lung fibroblasts and is immunologically cross-reactive with a type V collagenase expressed by activated macrophages and neutrophils. Expression of this 92-kD metalloproteinase confers upon the fibroblasts the capacity to degrade collagenase- and stromelysin-resistant interstitial elements, such as collagen types IV, V and XI. In contrast to the 92-kD metalloproteinase, a 68-kD gelatinase (type IV collagenase) was expressed by all fibroblast types studied, indicating that its regulation is distinct from that of the 92-kD gelatinase. To identify what cytokines may be important in the induction of the rheumatoid synovial phenotype, including expression of the 92-kD gelatinase, we exposed normal dermal fibroblasts to a number of cytokines including many known or considered likely to be present in rheumatoid synovial fluid and tissue. Although IL-1 beta, tumor necrosis factor-alpha, lymphotoxin, platelet-derived growth factor, and basic fibroblast growth factor were capable of stimulating fibroblasts to secrete collagenase, only tumor necrosis factor-alpha, lymphotoxin, and IL-1 beta were able to induce expression of the 92-kD gelatinase, demonstrating discordant regulation of the two metalloproteinases. Expression of the 68-kD gelatinase was independent of that of the 92-kD gelatinase, as demonstrated at the protein and mRNA levels. Late passage rheumatoid synovial fibroblasts, which no longer constitutively expressed the 92-kD gelatinase, displayed an accentuated response to IL-1 beta when compared to normal dermal fibroblasts. Thus, in addition to IL-1 beta, tumor necrosis factor-alpha or lymphotoxin may contribute to the expression of a specific rheumatoid synovial phenotype in vivo that is associated with progressive matrix destruction.