Abstract 344: Endothelium-targetted Overexpression of Nox2 Accentuates Angiotensin II-induced Endothelial Dysfunction but not Hypertension
NADPH oxidase-derived reactive oxygen species (ROS) are involved in the pathophysiology of several vascular diseases. Nox1, 2 and 4 can all be expressed in the vessel wall but their cell-specific roles in vivo are poorly understood. To address the role of Noxs in the endothelium, we generated transgenic mice (TG) with endothelial-specific overexpression of Nox2. Endothelial-specific transgene expression was confirmed by RT-PCR, and TG mice had greater Nox2 protein expression in endothelial-rich tissues than wild-type littermates (WT), eg, 2.6-fold greater in lung. mRNA levels of Nox1, Nox4, p22phox, p67phox, p47phox and eNOS were unaltered in TG aorta compared to WT. Basal (unstimulated) NADPH oxidase activity was similar in TG and WT aorta, left ventricle (LV) or coronary microvascular endothelial cells. Similarly, there was no difference in endothelium-dependent relaxation to acetylcholine (Ach) in aortic rings of TG versus WT (Emax: 94.0 ± 2.1% vs. 87.9 ± 1.8%). Basal blood pressure assessed by telemetry was also unchanged in TG versus WT (123.1 ± 6.2 vs 128.5 ± 3.3 mmHg; P=NS). Exposure of isolated aortae to angiotensin II (100nM, 30 min) increased NADPH oxidase activity ~2-fold more in TG compared to WT and induced greater impairment of Ach-induced relaxation (LogEC50 for the Ach response after AngII −7.2 ± 0.0 in TG vs. −7.4 ± 0.1M in WT). In vivo angiotensin II infusion (1.1mg/kg/day) for 2 weeks resulted in an 80% increase in LV NADPH oxidase activity in TG cf. 33% in WT (P<0.05) but similar changes in blood pressure (145.5 ± 4.9 vs. 142.0 ± 4.8 mmHg; P=NS). Angiotensin II-induced activation of ERK1/2 is increased to a greater extent in TG versus WT aortae. These results indicate that overexpression of Nox2 in the endothelium (a) has no significant effect on oxidase activity, vasodilator function or blood pressure in the absence of agonist stimulation; (b) augments angiotensin II-induced increases in oxidase activity and endothelial dysfunction but does not augment blood pressure. Thus, agonist-stimulated endothelial Nox2 appears to specifically influence endothelial vasodilator function and redox-sensitive kinase activation rather than blood pressure.