MODULATION OF THE CATABOLIC EFFECTS OF INTERLEUKIN-1-BETA ON HUMAN ARTICULAR CHONDROCYTES BY TRANSFORMING GROWTH-FACTOR-BETA

The effects of IL-1 beta and TGF-beta on the biosynthesis of extracell ular matrix structural components relative to the metalloproteinases a nd their inhibitor TIMP1 in human articular chondrocytes were investig ated. It has been proposed that TGF-beta, acting as a positive regulat or of matrix accretion, can counteract the increased loss of cartilage matrix induced by IL-1 beta. To allow a comparison of their effects o n mRNA levels for these different components, quantitation by competit ive RT/PCR was employed. This method was found to give reproducible es timates of mRNA levels and the observed effects of IL-1 beta and TGF-b eta on individual components of this system agree with qualitative dat a obtained by northern blotting. IL-1 beta had a more pronounced effec t on aggrecan mRNA levels than on those for type II collagen. Similar quantitative differences were observed between collagenase and stromel ysin mRNA levels. TGF-beta generally counteracted the effects of IL-1 beta, and new steady state levels were attained within 24 h. However, the reversal of IL-1 beta induced suppression of matrix protein mRNA l evels appeared more effective than its suppression of the increase in stromelysin and collagenase mRNA levels. Similarly TGF-beta did not re duce the extent of IL-1 beta induced secretion of stromelysin at the p rotein level. TIMP1 mRNA levels were only slightly reduced by IL-1 bet a; however this cytokine effectively surpressed its induction by TGF-b eta. The higher concentrations of TGF-beta and longer exposure times r equired to overcome the surpressive effects of IL-1 beta suggest that the interaction between IL-1 beta and TGF-P in the regulation of TIMP1 expression follows a different mechanism to that operating for the me talloproteinases and matrix proteins. Thus the overall potential of TG F-beta to inhibit proteolysis is attenuated by its much slower effect on TIMP1 mRNA levels. (C) 1996 Wiley-Liss, Inc.