EFFECTS OF INTERFERON-GAMMA AND TUMOR-NECROSIS-FACTOR-ALPHA ON THE EXPRESSION OF THE GENES ENCODING AGGRECAN, BIGLYCAN, AND DECORIN CORE PROTEINS IN CULTURED HUMAN CHONDROCYTES

Objective. To determine the effects of interferon-gamma (IFN gamma) an d tumor necrosis factor alpha (TNF alpha), alone or in combination, on the expression of aggrecan, biglycan, and decorin core protein genes in human chondrocytes. Methods. Isolated human chondrocytes were cultu red on poly(2-hydroxyethyl methacrylate)-coated plastic dishes to prev ent the loss of cartilage-specific phenotype, and the effects of IFN g amma and TNF alpha, alone or in combination, on aggrecan, biglycan, an d decorin core protein gene transcription and steady-state messenger R NA (mRNA) levels were examined. Results. The addition of IFN gamma (1. 5 pM) or TNF alpha (0.3 pM) caused a decrease in the steady-state leve l of aggrecan mRNA (-25% and -15%, respectively), and the combination of these low-concentration cytokines caused a potent inhibition (-66%) . These effects were the result of a decrease (-50%) in the transcript ion rate of the corresponding gene, At the concentrations used, IFN ga mma did not alter the levels of biglycan mRNA or the transcription rat es of the biglycan core protein gene. In contrast, TNF alpha decreased biglycan steady-state mRNA levels (-62%) and the biglycan core protei n gene transcription rate (-18%). The combination of IFN gamma and TNF alpha resulted in a potentiation of the inhibitory effects of TNF alp ha on biglycan mRNA levels (-79%) and transcription rate of the biglyc an core protein gene (-46%). IFN gamma produced a modest decrease in d ecorin mRNA levels (-23%) and decorin core protein gene transcription rate (-17%). In contrast, TNF alpha resulted in a marked increase in d ecorin mRNA levels (+260%) that was not the result of transcriptional regulation. Notably, the combination of IFN gamma and TNF alpha potent iated the inhibitory effects of IFN gamma on decorin mRNA (-80%) and o n the transcription of the corresponding gene (-43%). Similar results were obtained in fetal and adult articular chondrocytes. Conclusion. T hese data demonstrate that 1) the expression of the core protein genes encoding the cartilage proteoglycans aggrecan, biglycan, and decorin is differentially regulated by IFN gamma and TNF alpha; 2) these effec ts are mediated by transcriptional and posttranscriptional mechanisms; and 3) the combination of the 2 cytokines causes a potent inhibitory effect on the expression of the genes for the core proteins of these 3 proteoglycans, which occurs largely at the transcriptional level. The inhibition of aggrecan, decorin, and biglycan core protein gene expre ssion by the combination of IFN gamma and TNF alpha may contribute to the cartilage destruction that is characteristic of inflammatory joint diseases.