Abstract 060: POLDIP-2/NOX-4 Generates Hydrogen Peroxide that Impairs Myogenic Response of Afferent Arterioles from Mice with the Reduced Renal Mass Model of Chronic Kidney Disease

Abstract

Background: Because we have found that myogenic contractions are stimulated by superoxide (O 2 .- ) but inhibited by hydrogen peroxide (H 2 O 2 ), we tested the hypothesis that H 2 O 2 is the cause of the impaired myogenic responses of afferent arterioles from mice with the reduced renal mass (RRM) model of chronic kidney disease (CKD). Methods: Mice were subjected to 5/6 surgical nephrectomy or sham operations and fed 6% salt for 3 months. Single afferent arterioles were perfused, their diameter measured directly and O 2 .- and H 2 O 2 measured by fluorescence microscopy. Results: The perfusion pressure of isolated afferent arterioles was increased from 40 to 80 mmHg to study myogenic responses. Arterioles from mice with RRM (vs sham) had a greater increase in O 2 .- (21.2 ± 1.9 versus 11.3 ± 2.5%; p < 0.01) and especially H 2 O 2 (28.7 ± 3.7 versus 4.2 ± 0.4%, P<0.005), but a reduction in myogenic contraction (-1.7 ± 4.3 versus -14.4 ± 3.6%; p < 0.005) . Myogenic contractions were paradoxically reversed in afferent arterioles from mice with RRM after reduction in O 2 .- by PEG-SOD (+3.3 ± 1.5 versus -1.7 ± 4.3%, P<0.05) or deletion of p47 phox (+2.5 ± 1.4 versus -1.7 ± 4.3%, P<0.05). In contrast, myogenic responses were increased even above the levels of shams in arterioles from mice with RRM after reduction in H 2 O 2 by PEG-catalase (-19.1 ± 1.6 versus -1.7 ± 4.3%, P<0.005) or transgenic overexpression of catalase in smooth muscle cells (-10.7 ± 1.3 versus -1.7 ± 4.3%, P<0.01). Gene expression for NOX-4 and POLDIP-2 (main source of H 2 O 2 ) was increased 40-50% (P<0.05) in individual afferent arterioles from mice with RRM. Moreover, the myogenic contractions in the arterioles from POLDIP-2+/- mice with RRM were similar to POLDIP-2+/- with sham operations (-7.7 ± 0.9 versus -8.0 ± 0.6, P=NS). Conclusions: Afferent arterioles from mice with RRM had severely impaired myogenic responses that were attributed to increased H 2 O 2 generation from POLDIP-2/NOX-4 that may therefore be novel targets to maintain autoregulation and protect kidneys from barotrauma in CKD.