Abstract 345: Effects Of Endothelial-targeted Overexpression Of Nox4 On Vascular Tone And Blood Pressure In Mice
NADPH oxidases (Noxs) are major sources of reactive oxygen species (ROS) that are involved in the pathophysiology of several cardiovascular disorders. Of the 5 Nox isoforms identified to date, Nox2 and Nox4 are the main isoforms expressed in the endothelium. Whereas Nox2 has been implicated in the genesis of endothelial dysfunction, the role of Nox4 remains unclear. Interestingly, the activation mechanisms of Nox2 and Nox4 appear to be distinct. To specifically examine the function of endothelial Nox4 in vivo, we generated transgenic mice with endothelial-targeted overexpression of Nox4 using a Tie2 promoter construct. Nox4 transgenic mice (TG) backcrossed onto a C57BL/6J background had increased Nox4 mRNA in endothelial-rich tissues and in isolated coronary microvascular endothelial cells (CMEC) compared to wild-type littermates (WT) (2-fold increase in CMEC; p<0.001). Aortic Nox4 protein levels were 3-fold higher in TG compared to WT. CMEC isolated from TG mice had increased NADPH-dependent superoxide production compared to WT (237.6 ± 2.7 vs. 186.5 ± 7.1 integrated RLU; n = 3, p<0.01) as well as increased H2O2 production (7.60 ± 0.70 vs. 3.22 ± 0.42 μM H2O2 /105 cells; n=3, p<0.01). No changes were detected in mRNA expression of SOD1, SOD2, SOD3, catalase or eNOS in aorta of TG compared to WT mice. Isolated aortic rings from TG mice exhibited enhanced endothelial-dependent vasorelaxation to cumulative addition of acetylcholine compared to WT (−log EC50 7.76 ± 0.07 vs. 7.20 ± 0.05; n =12, p<0.001), a difference that was abolished by catalase (1500 units/ml). There was no difference in endothelial-independent responses to sodium nitroprusside (−log EC50 8.57 ± 0.11 vs. 8.54 ± 0.09; n = 12, p = NS). In vivo blood pressure measured both by tail-cuff plethysmography and ambulatory telemetry was significantly lower in TG compared to WT (systolic 117.4 ± 1.9 vs. 125.5 ± 2.1 mmHg and diastolic 90.1 ± 2.0 vs. 98.1 ± 2.1 mmHg by telemetry; n =5, p<0.05). These results indicate that modest endothelium-targeted overexpression of Nox4 in vivo enhances endothelium-dependent relaxation and reduces blood pressure, probably through increased generation of H2O2. These in vivo effects are quite distinct from those that have been found with Nox2 overexpression.