Stimulation by glucocorticoid of the synthesis of cartilage-matrix proteoglycans produced by rabbit costal chondrocytes in vitro.

The effect of glucocorticoids on sulfated proteoglycan synthesis by rabbit costal chondrocyte cultures exposed to serum-free conditions has been examined. Low density cultures of rabbit costal chondrocytes were maintained on dishes coated with extracellular matrix produced by bovine corneal endothelial cells and exposed to a 9:1 mixture (v/v) of Dulbecco's modified Eagle's medium and Ham's F-12 medium supplemented with transferrin, high density lipoproteins, fibroblast growth factor, and insulin (Medium A). Chondrocytes maintained in the presence of Medium A supplemented with 10(-7) M hydrocortisone reorganized, at confluence, into a homogeneous cartilage-like tissue composed of round cells surrounded by a refractile matrix in which abundant thin collagen fibrils characteristic of type II collagen were observed. The cell ultrastructure and fibrils of the pericellular matrix were similar to those seen in vivo. In contrast, cells maintained in the presence of Medium A alone, once they reached confluence, formed a fibroblastic multilayer and produced thick collagen bundles. The level of 35SO4(2-) incorporated into large cartilage-specific proteoglycans in glucocorticoid-supplemented cultures was 33-fold higher than that of glucocorticoid-free cultures. The level of 35SO4(2-) incorporated into small ubiquitous proteoglycans was only 4-fold higher than that of glucocorticoid-free cultures. On the other hand, the level of [3H]glucosamine incorporated into hyaluronate in glucocorticoid-supplemented cultures was 4.5-fold lower than that of glucocorticoid-free cultures. Within 24 h of their addition to confluent cultures, hydrocortisone or dexamethasone markedly stimulated proteoglycan synthesis. This effect was not mimicked by androgens, estrogens, progesterone, or an inactive form of glucocorticoids such as deoxycorticosterone. This suggests that glucocorticoids have a direct and specific stimulatory effect on cartilage-specific proteoglycan synthesis and are essential for the maintenance of this synthesis in low density chondrocyte cultures.