Peroxisome Proliferator-Activated Receptor-γ Ligands Inhibit TGF-β1-Induced Fibronectin Expression in Glomerular Mesangial Cells

Peroxisome Proliferator-Activated Receptor-γ Ligands Inhibit TGF-β1-Induced Fibronectin Expression in Glomerular Mesangial Cells Baoliang Guo , Daisuke Koya , Motohide Isono , Toshiro Sugimoto , Atsunori Kashiwagi and Masakazu Haneda Department of Medicine, Shiga University of Medical Science, Otsu, Shiga, Japan Address correspondence and reprint requests to Masakazu Haneda, MD, Department of Medicine, Shiga University of Medical Science, Seta, Otsu, Shiga, Japan. E-mail: haneda{at}belle.shiga-med.ac.jp Abstract The thiazolidinedione (TZD) class of antidiabetic drugs, which are ligands for peroxisome proliferator-activated receptor (PPAR)-γ, has been shown to possess potent anti-inflammatory and antineoplastic actions. Here, we show in mesangial cells that PPAR-γ agonists inhibit fibronectin expression by transforming growth factor (TGF)-β1. TGF-β1 enhanced fibronectin mRNA expression, and this enhancement was abrogated by pretreatment with pioglitazone. Electrophoretic mobility shift assay identified that pioglitazone inhibited TGF-β1-induced DNA binding of activator protein-1 (AP-1). Pioglitazone inhibited AP-1 reporter activity but not Smad binding elements reporter activity without affecting TGF-β1-induced activation of mitogen-activated protein kinases (MAPKs) or Smad2. PPAR-γ overexpression inhibited TGF-β1-induced fibronectin expression as well as the activation of AP-1. 15-Deoxy-Δ 12,14 -prostaglandin J 2 (15d-PGJ 2 ), a natural PPAR-γ ligand, also inhibited TGF-β1-induced fibronectin expression by suppressing AP-1 activation by TGF-β1. 15d-PGJ 2 inhibited the TGF-β1-induced MAPK activation. Dominant-negative PPAR-γ (ΔPPAR-γ) completely abrogated the inhibitory effect of pioglitazone and incompletely blocked its effect of 15d-PGJ 2 on TGF-β1-induced AP-1 reporter activity. ΔPPAR-γ overexpression did not affect the inhibitory effect of 15d-PGJ 2 on TGF-β1-induced MAPK activation. In conclusion, pioglitazone inhibits TGF-β1-induced fibronectin expression by inhibiting AP-1 activation dependent on PPAR-γ, while 15d-PGJ 2 acts through a dual mechanism independent of and dependent on PPAR-γ activation in mouse mesangial cells. 15d-PGJ2, 15-deoxy-Δ12,14-prostaglandin J2 ΔPPAR dominant-negative peroxisome proliferator-activated receptor AP-1, activator protein-1 dCTP, deoxycytidine triphosphate DMEM, Dulbecco’s Modified Eagle’s Medium ECM, extracellular matrix EMSA, electrophoretic mobility shift analysis ERK, extracellular signal-regulated kinase FBS, fe