TRANSCRIPTIONAL MODULATION OF CARTILAGE-SPECIFIC COLLAGEN GENE-EXPRESSION BY INTERFERON-GAMMA AND TUMOR-NECROSIS-FACTOR-ALPHA IN CULTURED HUMAN CHONDROCYTES

To examine the possibility that cytokines produced in inflamed joint t issues may contribute to the loss of articular cartilage by causing in hibition of synthesis of cartilage-specific matrix macromolecules, we studied the effects of interferon gamma (IFNgamma) and tumour necrosis factor alpha (TNFalpha), alone and in combination, on the expression of the genes for types-II, -IX and -XI collagens in cultured human cho ndrocytes. Chondrocytes isolated from human fetal epiphyseal cartilage by sequential enzymic digestions were cultured in the presence of IFN gamma (30 pM), TNFalpha (15 pM) or a combination of suboptimal concent rations of both cytokines (1.5 pM IFNgamma plus 0.3 pM TNFalpha). IFNg amma caused a maximal decrease of 23.3-32.6 % in the biosynthesis of c ollagen by chondrocytes. TNFalpha was a more potent inhibitor causing a 42.8-45.3 % decrease at one-half the concentration of IFNgamma. A sy nergistic inhibitory effect of 58.2 % was observed with the combinatio n of 1.5 pM IFNgamma plus 0.3 pM TNFalpha. Electrophoretic analysis of the biosynthesized proteins showed a coordinate decrease in the produ ction of the three cartilage-specific collagen types II, IX and XI. Th ese effects were accompanied by parallel changes in the steady-state l evels of their corresponding mRNAs. In vitro transcription assays show ed that the collagen inhibitory effects of the cytokines occurred larg ely at the transcriptional level. Similar effects of the cytokines wer e observed on biosynthesis of types-II, -IX and -XI collagens and stea dy-state mRNA levels for type-II collagen by chondrocytes obtained fro m adult articular cartilage. These observations indicate that IFNgamma and TNFalpha can induce a synergistic inhibition of the synthesis of cartilage-specific collagens by fetal and adult human chondrocytes and suggest that these effects may contribute to the articular cartilage loss that occurs in inflammatory joint diseases.