ABSTRACT
This chapter reviews recent progress in understanding how synoviocytes regulate the metabolism of chondrocytes. Synovium comprises a collagenous matrix penetrated by lymphatic vessels, blood capillaries, and nerve endings, together with at least two types of resident synoviocytes. Synovial fibroblasts produce very little TNF-a, suggesting that type A synoviocytes account for most of the synovial production of TNF-a. Although TNF-a is present in synovial fluid, a recent study suggests that normal synovial fluids contain greater concentrations of TNF-a than fluids obtained from arthritic joints. TGF-ß increases the synthesis of proteoglycans by articular cartilage in organ culture and by monolayers of articular and growth plate chondrocytes. However, the synthesis of GAGs by lapine articular chondrocytes cultured in soft agar is reduced by TGF-ß. Human articular chondrocytes obtained from osteoarthritic joints produce superoxide in response to TNF-a. Stromelysin production in response to IL-1 is considerably greater in Ia positive chondrocytes, although collagenase induction is unaltered.
