Extracellular matrix synthesis by articular chondrocytes and synovial fibroblasts in long-term monolayer culture.

Synthesis of collagen and proteoglycan by rabbit articular chondrocytes and synovial fibroblasts has been studied over a 12-week period in primary monolayer culture. Chondrocytes, but not fibroblasts, accumulate large quantities of proteoglycan over the culture period studied. Radiolabeling studies with [35S]sulfate have shown that the major proteoglycan synthesized by cultured chondrocytes is similar to the proteoglycan of cartilage matrix. Chondrocytes also synthesize a smaller dermatan sulfate proteoglycan, which is apparently the only proteoglycan species produced by synovial fibroblasts. Collagen synthesis was studied by radiolabeling with [3H]proline. Cultured chondrocytes produce mainly Type II collagen, with lesser amounts of Type I, whereas synovial fibroblasts produce Type I collagen and some low molecular weight collagenous species. Therefore, long-term monolayer culture permits the production of extensive chondroid matrix by chondrocytes, but not fibroblasts.