Rheumatoid arthritis synovial fibroblasts: Cytokine-induced invasive phenotype and associated mechanism(s) of tissue destruction.

Abstract

The invasive and destructive properties of pannus tissue contribute to the loss of cartilage and bone in rheumatoid arthritis (RA). To further analyze the process of cartilage degradation, we have developed an in vitro model which allows for observations of cellular degradation and invasion of a cartilage matrix isolated from porcine knee joints. This matrix contains collagen type II, proteoglycans and glycosaminoglycans, and is similar in composition to human cartilage. Synovial fibroblasts isolated from the pannus tissue of patients with aggressive RA, based on clinical evaluation, demonstrated a highly invasive phenotype in this in vitro model; whereas synovial fibroblasts isolated from pannus tissue of less aggressive RA, based on clinical evaluation, showed a less invasive phenotype. Further characterization of cell-cartilage matrix interactions reveal that RA and normal synovial fibroblasts adhere to a similar degree to cartilage matrix, but this adhesion can be inhibited with arginine-glycine-aspartic acid (RGD) peptides, thus implicating integrins in this attachment process. During the subsequent process of spreading on cartilage matrix, highly invasive RA synovial fibroblasts maintained a round phenotype for a longer duration than normal synovial fibroblasts. Furthermore, with respect to the degradative ability of these cells, the level of expression and secretion of key metalloproteinases was measured, and interstitial collagenase activity was shown to correlate with the RA phenotype, while no expression was detected in normal synovial fibroblasts. By comparison, there was no differential expression of stromelysin, gelatinase A and gelatinase B found in normal synovial fibroblasts versus RA synovial fibroblasts. Normal synovial fibroblast invasion was augmented by culturing these cells in the presence of 5 U/ml IL-1β or 18 U/ml TGFβ whereas, PDGF at 100 ng/ml did not affect normal synovial fibroblast invasion. In addition, normal synovial fibroblasts cultured in 150 U/ml TNFα demonstrated a significant decrease in their ability to invade cartilage matrix. Collectively, these in vitro data suggest that highly invasive synovial fibroblasts correlate with advanced RA clinical disease. Moreover, this invasive phenotype may be due, in part, to decreased spreading ability on the cartilage matrix in addition to interstitial collagenase activity. This model allows for further molecular characterization of the invasive properties of the synovial fibroblast.