Canonical Wnt Signaling Mediates Enhanced Renal Afferent Arteriolar Reactive Oxygen Species and Contractility in Diabetic Mice.

Background: Canonical Wnt signaling is involved in oxidative stress and diabetes but its role in diabetic renal microvascular dysfunction is unclear. We tested the hypothesis that enhanced canonical Wnt signaling in renal afferent arterioles from diabetic mice increases reactive oxygen species (ROS) and contractions to endothelin-1 (ET-1). Methods: Diabetic or control C57Bl/6 mice received vehicle or sulindac (40 mg·kg -1 ·day -1 ) to block canonical Wnt signaling for 4 weeks. ET-1 contractions were measured in diameter changes and H 2 O 2 and O 2 .- by fluorescence microscopy. Arteriolar protein expression and enzymatic activity were examined by standard methods. Results: Compared to control, diabetic mouse afferent arteriole had significantly increased O 2 .- (+84%) and H 2 O 2 (+91%) and enhanced sensitivity to ET-1 at 10 -8 mol·l -1 (-72±4% versus -43±4%, P<0.05) accompanied by significantly (P<0.005) reduced protein expressions and activities for catalase and superoxide dismutase 2 (SOD2). Incubation of afferent arterioles from normal or diabetic mice with PEG-SOD reduced responses to ET-1 whereas incubation with PEG-catalase reduced sensitivity to ET-1 selectively in arterioles from diabetic mice. The arteriolar protein expressions for canonical Wnt signaling indicated overactivation of this pathway in diabetic mice (2.6-fold increase in p-GSK-3β/GSK-3β and 3.3-fold decrease in p-β-catenin/β-catenin). Sulindac given to diabetic mice normalized the canonical Wnt signaling protein and arteriolar O 2 .- , H 2 O 2 and ET-1 contractions while doubling (P<0.05) microvascular catalase and SOD2. Conclusions: Increased ROS, notably H 2 O 2 , mediated by canonical Wnt signaling contributes to enhanced afferent arteriolar sensitivity to ET-1 in diabetes. Thus, antioxidant pharmacological strategies targeting canonical Wnt signaling may improve vascular function in diabetic nephropathy.