Background: Oxidative stress is one of the important mediators of vascular complications in diabetes including nephropathy. High glucose (HG) generates reactive oxygen species (ROS) as a result of glucose auto-oxidation, metabolism, and formation of advanced glycosylation end products. The concept of ROS-induced tissue injury has recently been revised with the appreciation of new roles for ROS in signaling pathways and gene expression.
Methods and results: High glucose rapidly generated dichlorofluorescein-sensitive cytosolic ROS in rat and mouse mesangial cells. Neither L-glucose nor 3-O-methyl-D-glucose increased cytosolic ROS and cytochalasin B, an inhibitor of glucose transporter, effectively inhibited HG-induced ROS generation, suggesting that glucose uptake and subsequent metabolism are required in HG-induced cytosolic ROS generation. H2O2 up-regulated fibronectin mRNA expression and protein synthesis; this up-regulation was effectively inhibited by protein kinase C (PKC) inhibitor or by depletion of PKC. The HG-induced generation of ROS was, in turn, related to activation of PKC and transcription factors nuclear factor-kappaB (NF-kappaB) and activator protein-1 (AP-1) as well as to the up-regulation of transforming growth factor-beta1 (TGF-beta1), fibronectin mRNA expression and protein synthesis, because antioxidants effectively inhibited HG-induced PKC, NF-kappaB, AP-1 activation, and TGF-beta1 and fibronectin expression in mesangial cells cultured under HG.
Conclusions: Although signal transduction pathways linking HG, ROS, PKC, transcription factors, and extracellular matrix (ECM) protein synthesis in mesangial cells have not been fully elucidated, the current data provide evidence that ROS generated by glucose metabolism may act as integral signaling molecules under HG as in other membrane receptor signaling.