Glutathione transferase isozyme A4 (GSTA4) exhibits high catalytic efficiency to metabolize 4-hydroxynonenal (4-HNE), a highly reactive lipid peroxidation product that has been implicated in the pathogenesis of various chronic diseases. We investigated the role of 4-HNE in the mechanisms of unilateral ureteral obstruction (UUO)induced fibrosis and its modulation by GSTA4-4 in a mouse model. Our data indicate that after UUO, accumulation of 4-HNE and its adducts were increased in renal tissues, with a concomitant decrease in the expression of GSTA4-4 in mice. As compared to wild-type (WT) mice, UUO caused an increased expression of fibroblast markers in the interstitium of GSTA4 KO mice. Additionally, increased autophagy and tubular cell damage were more severe in UUO-treated GSTA4 KO mice than in WT mice. Furthermore, GSK-3 beta phosphorylation and expression of Snail, a regulator of E-cadherin and Occludin, was found to be significantly higher in UUO-inflicted GSTA4 KO mice. GSTA4 over-expression prevented 4-HNE-induced autophagy activation, tubular cell damage and Snail nuclear translocation in vitro. The effects of long-term expression of GSTA4 in restoration of UUO-induced damage in mice with the GSTA4 inducible transposon system indicated that release of obstruction after 3 days of UUO resulted in the attenuation of interstitial SMA alpha and collagen I expression. This transposon-delivered GSTA4 expression also suppressed UUO-induced loss of tubular cell junction markers and autophagy activation. Together, these results indicate that 4-HNE significantly contributes to the mechanisms of tubule injury and fibrosis and that these effects can be inhibited by the enhanced expression of GSTA4-4. Copyright (C) 2012 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.