Fibronectin and proteoglycan synthesis in long term cultures of cartilage explants in Ham's F12 supplemented with insulin and calcium: effects of the addition of TGF-beta.

Canine cartilage explants were maintained in a basal medium supplemented with a commercially available supplement (ITSCR+) which includes insulin for up to 12 days in culture. During this time it was found that proteoglycan synthesis, as measured by 35SO4 incorporation into high molecular weight proteoglycans, was maintained at levels comparable to those at Day O. This is in substantial agreement with the results of McQuillan et al. (1) for bovine cartilage explants. Since the basal medium which we used, Ham's F12, is low in calcium, we found that supplementation with additional calcium also was needed for maintenance of proteoglycan synthesis. This defined medium was not adequate to prevent a decrease in fibronectin, total protein, and collagen synthesis relative to Day O levels. The addition of transforming growth factor-beta (TGF-beta) at 2 and 10 ng/ml to the defined medium not only prevented the decline in fibronectin synthesis but progressively increased the rate of fibronectin synthesis until the Day O levels were exceeded by an average of fourfold. This TGF-beta-induced increase in fibronectin synthesis was contrasted with the increase in fibronectin synthesis previously reported for degenerated cartilage of osteoarthritic joints (2,3), and possible implications for understanding the disease were discussed.