IL-1 downregulates PPARγ1 expression at the transcriptional level. (a) Osteoarthritis (OA) chondrocytes were treated with increasing concentrations of IL-1 for 12 hours. Total RNA was isolated and reverse transcribed into cDNA, and peroxisome proliferator-activated receptor γ1 (PPARγ1) and glyceraldehyde-3-phosphate dehydrogenase mRNAs were quantified by real-time PCR. All experiments were performed in triplicate, and negative controls without template RNA were included in each experiment. (b) OA chondrocytes were co-transfected with 1 μg per well of the PPARγ1 promoter (pGL3-PPARγ1p3000) and 0.5 μg per well of the internal control pSV40-β-galactosidase, using FuGene 6 transfection reagent. The next day, transfected cells were treated with increasing concentrations of IL-1 for 18 hours. Luciferase activity values were determined and normalized to β-galactosidase activity. Results are expressed as percentage changes, taking the value of untreated cells as 100%, and show means ± SEM for four independent experiments. *p < 0.05 compared with untreated cells.