Effect of TNF-α, IL-17 and prostaglandin E2 on PPARγ1 protein expression in osteoarthritis chondrocytes. Cells were treated with IL-1 (100 pg/ml), TNF-α (1 and 10 ng/ml), IL-17 (10 and 100 ng/ml), and prostaglandin E2 (0.1 and 1 μM). After 24 hours, cell lysates were prepared and analyzed for peroxisome proliferator-activated receptor γ1 (PPARγ1) protein expression by Western blotting. In the lower panel, the blots were stripped and reprobed with a specific anti-β-actin antibody. The blots are representative of similar results obtained from four independent experiments.