Reactive oxygen species amplify glucose signalling in renal cells cultured under high glucose and in diabetic kidney

Diabetic nephropathy is characterized by excessive accumulation of extracellular matrix (ECM) in the kidney. Reactive oxygen species (ROS) play a central role in the ECM synthesis and degradation in the glomeruli and tubulointerstitium leading to renal fibrosis. High glucose (HG) induces cellular ROS through protein kinase C (PKC)-dependent activation of NADPH oxidase and through mitochondrial metabolism. ROS thus generated activate signal transduction cascade (PKC, mitogen-activated protein kinases, and Janus kinase/signal transducers and activators of transcription) and transcription factors (nuclear factor-κB, activated protein-1, and specificity protein-1), up-regulate transforming growth factor-β1 (TGF-β1), angiotensin II (Ang II), monocyte chemoattractant protein-1 (MCP-1), and plasminogen activator inhibitor-1 (PAI-1) gene and protein expression, and promote formation of advanced glycation end-products (AGE). PKC, TGF-β1, Ang II, and AGE also induce cellular ROS and signal through ROS leading to enhanced ECM synthesis. NF-κB-MCP-1 pathway is activated by ROS and promotes monocyte recruitment and profibrotic process in the kidney. HG- and TGF-β1-induced PAI-1 up-regulation is mediated by ROS and contribute to ECM accumulation via suppression of plasmin ativity. TGF-β1-induced myofibroblast transformation of renal tubular epithelial cells (epithelial-mesenchymal transition) is also mediated by ROS and contribute to tubulointerstitial fibrosis. In summary, ROS transduce and amplify glucose signalling in renal cells under high glucose environment and play a critical role in excessive ECM deposition in the diabetic kidney. A better understanding of ROS production and removal will allow more effective therapeutic strategies in diabetic renal and other vascular complications.