Role of NADPH oxidase-NOX5 and associated ROS-sensitive pathways in human diabetic kidney disease

Background: Enhanced level of reactive oxygen species (ROS) in diabetes is considered a major contributor in aggravating renal injury. We aimed to evaluate the role of pro-oxidant enzyme NOX5 and associated redox-sensitive pathways in diabetic kidney disease (DKD).
Methods: We examined the expression of NOX5 and associated redox-sensitive factors including NOX4, thioredoxin-interacting protein (TXNIP), a transcription factor, EGR1 (early growth response 1) and a protein kinase, PKC-α as well as ROS production in human kidney biopsies and in human renal cell lines as well as in human kidney organoids. We also assessed the effect of NOX5 expression independent of NOX4 in Nox5 transgenic mice in the presence or absence of diabetes.
Results: We identified increased expression of renal NOX5 in diabetic patients in association with upregulation of ROS-sensitive factors including EGR-1, PKC-α and TXNIP. We also observed upregulation of human NOX5 and TXNIP in renal organoids exposed to high glucose. Silencing of Nox5 attenuated high glucose induced gene expression of markers of fibrosis and inflammation as well as downregulation of EGR-1, PKC-α and TXNIP. Our data also suggest that Nox5 is upstream of Nox4 and that Nox5 inhibition also downregulates Nox4, but not vice versa. In vivo, overexpression of Nox5 independent of NOX4 pathways demonstrated an increase in albuminuria, renal fibrosis and inflammation in association with upregulation of EGR-1, PKC-α and TXNIP and enhanced ROS production in comparison to diabetic mice not expressing Nox5.
Conclusions: These findings suggest that NOX5 plays a key pathogenic role in DKD, thereby providing impetus for the development of NOX5 specific inhibitor to combat DKD.