Inhibition of IGF-I-related intracellular signaling pathways by proinflammatory cytokines in growth plate chondrocytes

BACKGROUND: Children with chronic inflammatory diseases suffer from severe growth failure associated with resistance toward the anabolic action of insulin-like growth factor I (IGF-I). We hypothesized that proinflammatory cytokines interfere with IGF-I signaling. METHODS: We used the mesenchymal chondrogenic cell line RCJ3.1C5.18 as a model of the growth plate. Cell proliferation was assessed by [H-3]-thymidine-uptake and differentiation by gene expression (quantitative reverse-transcriptase PCR) of specific differentiation markers. Key signaling molecules of the respective IGF-I related intracellular pathways were determined by western immunoblotting. RESULTS: Coincubation of the proinflammatory cytokines interleukin (1L)-beta (10 ng/ml), IL-6 (100 ng/ml), or tumor necrosis factor-a (50 ng/ml) with ICE-I inhibited IGF-I driven cell proliferation by 50%, while baseline cell proliferation was not altered. These cytokines attenuated the IGF-I induced phosphorylation of AKT as a key signaling molecule of the phosphatidylinositol-3 kinase pathway by 30-50% and the phosphorylation of ERK as a key signaling molecule of the mitogen-activated protein kinase/extracellular signal regulated kinase pathway by 50-75%. Also, IGF-I enhanced chondrocyte differentiation was inhibited by these proinflammatory cytokines. CONCLUSION:The insensitivity toward the anabolic action of IGF-I in the growth plate in conditions of chronic inflammation is partially due to inhibition of ICE-I specific signaling pathways by proinflammatory cytokines, which affect both IGF-I driven,chondrocyte proliferation and differentiation.