Effect of IL-1 on PPARγ1 protein expression in osteoarthritis chondrocytes. (a) Osteoarthritis (OA) chondrocytes were treated with 100 pg/ml IL-1 for the indicated periods. (b) OA chondrocytes were treated with increasing concentrations of IL-1 for 24 hours. Cell lysates were prepared and analyzed for peroxisome proliferator-activated receptor γ1 (PPARγ1) protein by Western blotting (upper panels). The blots were stripped and reprobed with a specific anti-β-actin antibody (lower panels). The blots are representative of similar results obtained from four independent experiments.