Abstract 692: Endothelial Nox2 Overexpression Potentiates Vascular Oxidative Stress and Hemodynamic Response to Angiotensin II: Studies in Endothelial-Targeted Nox2 Transgenic Mice
Vascular disease states are associated with endothelial dysfunction and increased production of reactive oxygen species (ROS) derived from vascular NADPH oxidases in both vascular smooth muscle cells (VSMC) and endothelial cells. Recent evidence suggests an important role for VSMC NADPH oxidases in vascular ROS production. However, it is unclear whether increased NADPH oxidase activity in endothelial cells is alone sufficient to alter overall vascular ROS production. We addressed this question using mice with Tie2-driven endothelial-targeted overexpression of the catalytic subunit of NADPH oxidase, Nox2. Aortas of Nox2-Tg mice had increased total Nox2 mRNA and protein levels compared to wild-type littermates. Both aortic p22phox mRNA and protein levels were also significantly elevated in Nox2-Tg mice. Aortic and ventricular NADPH-dependent superoxide production, measured by lucigenin chemiluminescence, was significantly increased, by 2-fold, in Nox2-Tg mice compared to wild-type (aortic; 2592 ± 278 versus 1360 ± 178 relative light units/s/mg respectively), whereas superoxide production in endothelial denuded aortas was similar. Dihydroethidium fluorescence confirmed increased endothelial superoxide production in Nox2-Tg mice. MnSOD protein was significantly elevated in Nox2-Tg aortas compared with wild-type, and SOD inhibition increased superoxide release. Increased ROS production from endothelial Nox2 overexpression led to increased eNOS protein and MAPK phosphorylation in transgenic aortas. Basal blood pressure, measured by tail-cuff, was similar in Nox2-Tg and wild-type littermates. However, the pressor responses to both acute angiotensin II (intraperitoneal injection) and chronic angiotensin II (subcutaneous osmotic minipumps at 0.4mg/kg/day) were significantly increased in Nox2-Tg mice. These results demonstrate that endothelial-targeted Nox2 overexpression is sufficient to increase vascular NADPH oxidase activity, activate downstream signaling pathways and potentiate the hemodynamic response to angiotensin II, despite compensatory increases in antioxidant enzymes. Endothelial cell Nox2-containing NADPH oxidase plays an important functional role in vascular redox signaling.