Synthesis, secretion, and deposition of fibronectin in cultured human synovium

We examined fibronectin synthesis, secretion, and deposition in vitro by primary explants of rheumatoid synovium. Primary cultures initiated from tissue with monocytic infiltrates had higher levels of fibronectin synthesis; addition of dexamethasone at concentrations known to stimulate other tissue fibroblasts increased fibronectin synthesis and secretion. Newly synthesized fibronectin recovered from primary rheumatoid culture medium had a higher apparent molecular weight (240-245 kd), on sodium dodecyl sulfate-polyacrylamide gel electrophoresis, compared with fibronectin recovered from passaged normal and rheumatoid cultures (230 kd). Primary rheumatoid explant cultures had a characteristic morphology which correlated with fibronectin deposition. Dense deposits of fibronectin extracellular matrix covered overlapping synoviocytes adjacent to esterase-positive mononuclear cells. Dexamethasone-treated cultures showed little fibronectin deposited as extracellular matrix and did not develop overlapping cellular networks. Characteristic patterns of fibronectin synthesis and deposition in primary rheumatoid cultures appear to result from interaction between fibroblastic and monocytic cells. This culture system may provide a model by which to study interactions between cells and extracellular matrix components that regulate synovial cell function.