Effect of PPARγ blockade on the inhibition of IL-1β-induced responses by 15d-PGJ2. Chondrocytes were pretreated for 4 hours with 10 μM 15-deoxy-Δ12,14prostaglandin J2 (15d-PGJ2) in the presence or absence of 10 μM GW9662 (a specific antagonist of peroxisome-proliferator-activated receptor γ (PPARγ)), then stimulated with 10 ng/ml IL-1β for 24 hours before analysis of prostaglandin production and mPGES-1 expression. (a) PGE2 and 6-keto-PGF1α levels assayed by ELISA in culture supernatant; (b) relative abundance of microsomal prostaglandin E synthase-1 (mPGES-1) mRNA analysed by real-time PCR and normalized to S29 mRNA; (c) mPGES-1 protein level assessed by western blotting and normalized to β-actin level; (d) modulation of adiponectin (a PPARγ target gene) mRNAs by PPARγ ligands, analysed by real-time PCR and normalized to S29 mRNA. Results are expressed as means ± SD for at least three independent experiments. Statistically significant differences (P < 0.05): *, comparison with non stimulated controls; #comparison with IL-1β-stimulated cells; †, comparison with PPARγ agonists alone or in combination with PPARγ antagonist.