Modulation of collagenase 3 in human osteoarthritic cartilage by activation of extracellular transforming growth factor beta - Role of furin convertase

Objective. Treatment of normal cartilage with transforming growth factor be ta (TGF beta) can increase the synthesis of collagenase 3 by chondrocytes a nd mimic the in situ distribution of this enzyme in osteoarthritic (OA) car tilage, which occurs predominantly in the deep zone. In this study, we exam ined the elements of the TGF beta system that are potentially relevant to t his effect. Methods. TGF beta 1 and TGF beta 2 levels in cultured cartilage explants we re determined by enzyme-linked immunosorbent assay (ELISA), OA cartilage ex plants were treated with small latent TGF beta 1 complex in the presence of various inhibitors, and collagenase 3 levels were determined by ELISA. The inhibitors were against serine proteases, plasmin, cathepsins, furin, and a neutralizing antibody against the mannose-6 phosphate/ insulin-like growt h factor 2 receptor (M6P/IGF-2R). Small latent TGF beta 1, TGF beta recepto r types I, II, and III (TGF beta RI, RII, and RIII), M6P/IGF-2R, and furin were immunolocalized in cartilage. Results. Our data showed that latent TGF beta 1 is the major isoform that i s synthesized; levels of 17.2 +/- 1.7 pg/mg and 1.1 +/- 0.3 pg/mg tissue we t weight (mean +/- SEM) were found for total TGF beta 1 and TGF beta 2, res pectively, in OA cartilage. A general serine protease inhibitor abrogated a ctivation of both endogenous and exogenous small latent TGF beta 1, Plasmin and furin inhibitors and anti-M6P/IGF-2R reduced the levels of exogenous s mall latent TGF beta 1 complex-induced collagenase 3 by 33%, 95%, and 76%, respectively, but the cathepsin inhibitor had no effect. Immunolocalization of the small latent TGF beta 1 complex as well as of TGF beta RI and RII r evealed a statistically significant increase in the chondrocyte score in on ly the deep zone of OA cartilage. The M6P/IGF-2R level was significantly hi gher in OA cartilage in both the superficial and deep zones. Furin was foun d in normal cartilage exclusively in the superficial zone, whereas in OA ca rtilage, a level similar to that in normal. cartilage was found in the supe rficial zone, but a significantly higher cell score (mean +/- SEM 23.6 +/- 4.7%) was registered in the deep zone. Conclusion. The mechanisms of TGF beta activation/ activity with regard to collagenase 3 modulation in cartilage appear to be controlled by furin conv ertase with or without M6P/IGF-2R. These factors and the small latent TGF b eta complex are increased in the deep zone of OA cartilage, corresponding t o the preferential site of collagenase 3 production.