To clarify the interaction of tissue destruction and repair of articular cartilage during inflammation, the effects of interleukin-1 beta (IL-1 beta) on the expression of insulin-like growth factor I (IGF-I), its receptor, and its binding proteins were examined.
Articular chondrocytes from five week rats were cultured in serum free medium treated with IL-1 beta (1-100 U/ml) for 24 hours. The concentration of IGF-1 in the conditioned medium was measured by RIA, and IGFBP were analysed by immunoligand blotting method. IGF-I receptors were also examined by [125I]IGF-I binding study.
IL-1 beta induced the secretion of IGF-I and IGF-binding protein in chondrocytes; this was not inhibited by indomethacin (5 micrograms/ml). IL-1 beta also increased the number of IGF-I receptors but had no effect on receptor affinity. IL-1 beta inhibited chondrocyte proliferation, while exogenous IGF-I and growth hormone stimulated chondrocyte cell growth. IL-1 beta did not change IGF-I mRNA levels.
IL-1 beta up-regulated the IGF-I autocrine/paracrine axis in cultured articular chondrocytes. These observations provide insight into the critical role played by IL-1 beta in tissue destruction and repair, and into the direct interaction between cytokines and growth factors associated with inflammatory arthropathy.