NOX1 abet mesangial fibrogenesis via iNOS induction in diabetes

Both NADPH oxidase (NOX) and inducible nitric oxide synthase (iNOS) are the main sources of reactive oxygen species in kidney. However, their interactions in oxidative stress and contributions to kidney fibrosis during diabetic nephropathy have not been studied. Human mesangial cells were treated with normal glucose (5.6 mmol/L), high glucose (30 mmol/L) in the presence or absence of AGE (200 mg/L). Protein expressions of NOX1, NOX2, NOX4, and iNOS were examined by immunoblotting. NOX was genetically silenced with specific RNAi to study the interactions between NOX and iNOS in diabetic milieu. Superoxide (O center dot-) and peroxynitrite (ONOO center dot-) productions were assessed by dihydroethidium and hydroxyphenyl fluorescein, respectively. Fibrotic factors were determined by biochemistry assay. Superoxide, peroxynitrite, TGF-beta, and fibronectin productions as well as the protein expressions of NOX1, NOX2, NOX4, and iNOS were increased in the diabetic milieu (high glucose 30 mmol/L plus AGE 200 mg/L). However, abolishment of iNOS induction with 1400W or iNOS RNAi would restore peroxynitrite, TGF-beta, and fibronectin productions completely to basal level and attenuate superoxide production. Moreover, NOX1 inhibition not only prevented iNOS induction but also abrogated changes consequent to iNOS induction such as mesangial fibrogenesis.