Superoxide and hydrogen peroxide counterregulate myogenic contractions in renal afferent arterioles from a mouse model of chronic kidney disease

Myogenic contractions protect kidneys from barotrauma but are impaired in chronic kidney disease (CKD). Since myogenic contractions are enhanced by superoxide but impaired by hydrogen peroxide, we tested the hypothesis that they are counterregulated by superoxide and H 2 O 2 from NOX2/p47phox and/or NOX4/POLDIP2 in CKD. Myogenic contraction in isolated perfused afferent arterioles from mice with surgical 5/6 nephrectomy or sham operations fed a 6% sodium chloride diet was measured directly while superoxide and H 2 O 2 were measured by fluorescence microscopy. Compared to sham-operated animals, an increase in perfusion pressure of arterioles from CKD mice doubled superoxide (21 versus 11%), increased H 2 O 2 seven-fold (29 versus 4%), and reduced myogenic contractions profoundly (-1 versus -14%). Myogenic contractions were impaired further by PEG-superoxide dismutase or in arterioles from p47phox-/- (versus wild type) mice but became supra-normal by PEG-catalase or in mice with transgenic expression of catalase in vascular smooth muscle cells (-11 versus -1%). Single arterioles from mice with CKD expressed over 40% more mRNA and protein for NOX4 and POLDIP2. Myogenic responses in arterioles from POLDIP2 +/- (versus wild type) mice with CKD had over an 85% reduction in H 2 O 2 , but preserved superoxide and a normal myogenic response. Tempol administration to CKD mice for 3 months decreased afferent arteriolar superoxide and H 2 O 2 and maintained myogenic contractions. Thus, afferent arteriolar superoxide generated by NOX2/p47phox opposes H 2 O 2 generated by NOX4/POLDIP2 whose upregulation in afferent arterioles from mice with CKD accounts for impaired myogenic contractions.