Troglitazone ameliorates high glucose-induced EMT and dysfunction of SGLTs through PI3K/Akt, GSK-3β, Snail1, and β-catenin in renal proximal tubule cells

Lee YJ, Han HJ. Troglitazone ameliorates high glucose-induced EMT and dysfunction of SGLTs through PI3K/Akt, GSK-3 beta, Snail1, and beta-catenin in renal proximal tubule cells. Am J Physiol Renal Physiol 298: F1263-F1275, 2010. First published December 16, 2009; doi:10.1152/ajprenal.00475.2009.-Peroxisome proliferatoractivated receptor-gamma (PPAR gamma) agonists ameliorate renal fibrotic lesions in diabetic nephropathy. However, the effects of the agonists on the epithelial-mesenchymal transition (EMT) linked to membrane transport dysfunction are unknown. The present study aimed to verify the effects of the PPAR gamma agonist troglitazone on high glucose (HG)induced EMT in primary cultured renal proximal tubular epithelial cells (PTCs). HG (25 mM) as well as hydrogen peroxide (H2O2) and transforming growth factor-beta 1 (TGF-beta 1) decreased expression of epithelial cell marker E-cadherin and increased the expression of the mesenchymal markers vimentin and alpha-smooth muscle actin (alpha-SMA). HG, H2O2, and TGF-beta 1 decreased Na+/H+ exchangers (NHEs) or Na+-glucose cotransporters (SGLTs) and glucose uptake, showing membrane transport dysfunction. HG stimulated the production of cellular reactive oxygen species (ROS), and antioxidants blocked the HG-induced increase in phosphatidylinositol 3-kinase (PI3K)/Akt activation. Antioxidants and inhibitors of PI3K/Akt reversed HGinduced EMT protein expression. Inhibition of PI3K/Akt also blocked HG-induced glycogen synthase kinase-3 beta (GSK-3 beta) phosphorylation. HG and lithium chloride (GSK-3 beta inhibitor) blocked Snail1 and beta-catenin activation. Moreover, transfection with Snail1 or beta-catenin small interfering RNA (siRNA) reversed HG-induced EMT protein expression. Importantly, HG decreased PPAR gamma activation and troglitazone reversed HG-induced expression of PI3K/Akt, GSK-3 beta, Snail1, and beta-catenin as well as EMT proteins. Finally, inhibitors of PI3K/Akt, Snail1/beta-catenin siRNA, and troglitazone blocking the HG-induced EMT restored glucose uptake in PTCs. In conclusion, HG induces EMT through ROS, PI3K/Akt, GSK-3 beta, Snail, and beta-catenin. Subsequently, HG-induced EMT may result in SGLT dysfunction that is restored by the PPAR gamma agonist troglitazone in primary cultured PTCs.