Troglitazone suppresses transforming growth factor-β1-induced collagen type I expression in keloid fibroblasts

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Abstract
Peroxisome proliferator-activated receptor (PPAR)-gamma agonists are increasingly used in patients with diabetes and some studies have suggested a beneficial effect on organ fibrosis. However their effects on dermal fibrosis in keloids are unknown. To investigate the effect of the PPAR-gamma agonist troglitazone on transforming growth factor (TGF)-beta1-induced collagen type I expression in keloid fibroblasts. Keloid fibroblasts were cultured and exposed to different concentrations of troglitazone in the presence of TGF-beta1. The mRNA expression of PPAR-gamma was determined by semiquantitative reverse transcriptase-polymerase chain reaction. The protein of PPAR-gamma, Smad2, Smad3, phoshpo-Smad2/3 and collagen type I was determined by Western blotting and collagen synthesis was evaluated by measuring (3)H-proline incorporation. The effect of troglitazone on cell viability was evaluated by the colorimetric conversion of 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide. PPAR-gamma was expressed at a moderate level in keloid fibroblasts. Troglitazone depressed TGF-beta1-stimulated collagen type I expression and collagen synthesis in keloid fibroblasts in a concentration-dependent manner. Moreover, troglitazone inhibited expression and phosphorylation of TGF-beta1-induced Smad2/3. Cell viability was unaffected. These inhibitory effects of troglitazone were reversed by the PPAR-gamma-specific antagonist GW9662. Our data suggest that PPAR-gamma is present in keloid fibroblasts and PPAR-gamma activation inhibits TGF-beta1-induced collagen type I expression at least in part by decreasing collagen synthesis. PPAR-gamma may be a promising therapeutic target for keloids.