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 tissues may contribute to the loss of articular cartilage by causing inhibition 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 chondrocytes. Chondrocytes isolated from human fetal epiphyseal cartilage by sequential enzymic digestions were cultured in the presence of IFNgamma (30 pM), TNFalpha (15 pM) or a combination of suboptimal concentrations of both cytokines (1.5 pM IFNgamma plus 0.3 pM TNFalpha). IFNgamma caused a maximal decrease of 23.3-32.6 % in the biosynthesis of collagen by chondrocytes. TNFalpha was a more potent inhibitor causing a 42.8-45.3 % decrease at one-half the concentration of IFNgamma. A synergistic inhibitory effect of 58.2 % was observed with the combination of 1.5 pM IFNgamma plus 0.3 pM TNFalpha. Electrophoretic analysis of the biosynthesized proteins showed a coordinate decrease in the production of the three cartilage-specific collagen types II, IX and XI. These effects were accompanied by parallel changes in the steady-state levels of their corresponding mRNAs. In vitro transcription assays showed that the collagen inhibitory effects of the cytokines occurred largely at the transcriptional level. Similar effects of the cytokines were observed on biosynthesis of types-II, -IX and -XI collagens and steady-state mRNA levels for type-II collagen by chondrocytes obtained from 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.