Evidence that rosiglitazone acts as an antidegradative agent on cartilage cells in vitro

Recent studies have documented the role of the natural ligand (15d-PGJ2) of peroxisome proliferator-activated receptor gamma (PPARγ) as an anti-inflammatory agent in IL-1-treated cartilage cells and synovial fibroblasts in culture. Similar but less pronounced effects have been reported with pharmacological concentrations of synthetic PPARγ ligands, such as thiazolidinediones. These anti-IL-1 effects were attributed to the transcriptional inhibition of NF-κB and/or AP-1-dependent genes, while PPARγ implication remained questionable. We studied the effects of rosiglitazone, a thiazolidinedione with high affinity for PPARγ, in IL-1-treated rabbit articular chondrocytes (ARC) in culture. When used at 10 μM, rosiglitazone inhibited IL-1-induced nitric oxide production, COX-2 mRNA, decreased the degradative effect of IL-1 on ³⁵S-sulfated proteoglycans and the 55 kDa gelatinolytic activity secreted by ARC, and downregulated MMP-1 mRNA. By contrast, when used at 0.1–1 μM, rosiglitazone decreased proteoglycan degradation and MMP-1 gene expression, whereas it did not modify chondrocyte nitric oxide production nor COX-2 mRNA expression. Transient transfection of ARC with MMP-1-Luc showed that IL-1 stimulation was inhibited in a dose-dependent manner by rosiglitazone from 0.1 μM to 1 μM, indicating that rosiglitazone was acting at the transcriptional level. The electrophoretic mobility shift assay showed that IL-1-induced NF-κB binding activity was not changed by rosiglitazone, while IL-1-induced AP-1 binding activity was reduced. We analysed rosiglitazone's effect on MMP-1 promoter activation in cells transiently cotransfected with MMP-1-Luc vector. We showed that the inhibitory effect of rosiglitazone was significantly more pronounced in cells cotransfected with wild-type PPARγ than without, while this effect was completely suppressed by cotransfecting cells with the dominant-negative PPARγ. Altogether, these data show for the first time that rosiglitazone has a selective inhibitory effect on IL-1-induced MMP-1 in chondrocytes, which involves a mechanism whereby PPARγ and AP-1 are implicated.