Transforming growth factor-beta1 (TGF-beta1) promotes tissue fibrosis by upregulating genes encoding extracellular matrix proteins and by increasing the synthesis of plasminogen activator inhibitor-1 (PAI-1). TGF-beta1 induces cellular reactive oxygen species (ROS) and PAI-1 promoter region has binding sites for redox sensitive transcription factors. We, therefore, hypothesized that TGF-beta1-induced upregulation of PAI-1 is ROS-dependent. Using cultured glomerular mesangial cells, we confirmed that TGF-beta1 induces cellular ROS, upregulates PAI-1 mRNA and protein expression, and suppresses plasmin activity. We further demonstrated that H2O2 Stimulates PAI-1 expression and suppresses plasmin activity and that N-acetylcysteine effectively reverses TGF-beta1- and H2O2-induced changes in PAI-1 expression and plasmin activity. Basal as well as TGF-beta1- and H2O2-induced PAI-1 expression was by depletion of intracellular GSH. The present data demonstrate that TGF-beta1-induced PAI-1 in mesangial cells is ROS-dependent and imply that cellular ROS may be potential therapeutic targets in glomerular fibrosis. (C) 2003 Elsevier Inc. All rights reserved.