EFFECT OF INTERLEUKIN-1 AND INSULIN-LIKE GROWTH FACTOR-I ON THE RELEASE OF PROTEOGLYCAN COMPONENTS AND HYALURONAN FROM PIG ARTICULAR-CARTILAGE IN EXPLANT CULTURE

The turnover of proteoglycans was investigated in articular cartilage in explant culture by analysing the components released into the culture medium. The effect of IL-1-alpha on the release of fragments derived from different proteoglycan domains and of hyaluronan (HA) was determined over 4 days in culture. The effect of IGF-1 (100 ng/ml) on matrix degradation of proteoglycan and its ability to inhibit the effects of IL-1 (10 ng/ml) was also assessed. The rate of release of G1 and G2 globular domains of proteoglycans into the culture medium was determined by radioimmunoassay. In unstimulated control cartilage there was a greater release of proteoglycan G2 domain than of G1 domain suggesting that cleavage occurred between them and that some G1 was preferentially retained bound in the matrix. Compared with control cartilage IL-1 stimulated the release of all proteoglycan components and hyaluronan. IL-1 had a greater effect on the release of G1 than on G2 domain, but also resulted in some net loss of these proteins (approximately 45% as detected in the immunoassays). In explants treated with both IL-1 and IGF-1 there was much less release of proteoglycan fragments and evidence for less extensive degradation. IGF-1 was particularly affective in preventing any increase in HA release and also preventing the apparent loss of G1 and G2 domains. It also partially inhibited the release of G1 and G2 domains and the sulphated glycosaminoglycan fragments. IGF-1 was therefore an effective antagonist of IL-1 action on cartilage. It is not known at what level it blocks the chondrocyte response to IL-1, but it clearly results in the suppression of matrix degradative activity.