Abstract 5226: Endothelial Nox4 NADPH Oxidase Enhances Vasodilatation via Hydrogen Peroxide-induced Hyperpolarization and Reduces Blood Pressure
Introduction NADPH oxidases (Noxs) are reactive oxygen species-generating enzymes implicated in cardiovascular disease. Nox4 is the most abundantly expressed isoform in endothelial cells but its function is unclear. We investigated the role of endothelial Nox4 on vascular function in vivo.
Methods and Results We generated transgenic mice with endothelium-specific overexpression of Nox4 (Nox4TG) and studied the effects on endothelial function (aortic rings ex vivo) and blood pressure (BP, telemetry). Nox4 protein levels were 2-fold higher in Nox4TG aorta compared to wild-type littermates (WT), with no changes in expression of other Nox isoforms. Nox4TG had enhanced relaxation to acetylcholine (ACh) than WT (−log EC50 7.76±0.07 vs. 7.20±0.05; n=12; p<0.001) but similar relaxation to sodium nitroprusside. The ACh response in Nox4TG and WT was identical in the presence of catalase (1500U/ml) but remained greater in Nox4TG in the presence of inhibitors of nitric oxide synthesis (L-NMMA, 100μM; −log EC50 7.44±0.22 vs. 6.93±0.22; n=6; p<0.01), soluble guanylate cyclase (ODQ, 5μM; −log EC50 6.92±0.21 vs. 6.78±0.30; n=6; p<0.001) or protein kinase G (KT5823, 2μM; −log EC50 7.77±0.11 vs. 7.27±0.12; n=6; p<0.001). However, the difference between Nox4TG and WT was abolished in the presence of high extracellular potassium (30mM). Nox4TG also had significantly lower BP than WT (mean BP 102.5±1.8 vs. 109.5±2.0mmHg; n=10; P<0.05), which was abolished after chronic treatment with N-acetylcysteine or an SOD/catalase mimetic, EUK-8. Plasma nitrite/nitrate levels and aortic levels of phosphorylated VASP were identical and acute iv treatment with L-NMMA (10mg/kg) increased BP to a similar extent in Nox4TG and WT. The hypertensive response to chronic 14-day angiotensin II infusion (1.1mg/kg/d) was lower in Nox4TG compared to WT (mean BP 116.7±4.7 vs. 129.4±3.5mmHg; n=10; P<0.05).
Conclusions Nox4TG had significantly enhanced ACh-induced vasodilatation compared to WT as a result of H2O2-induced hyperpolarization. Nox4TG also had a lower BP, which was not attributable to altered nitric oxide bioactivity but was normalized by chronic antioxidant treatment. These results suggest that endothelial Nox4 has potentially beneficial effects on vascular tone and BP.