Abstract 119: The Imbalance of Mitochondrial Superoxide Dismutase Activity and Superoxide Production in Endothelial Dysfunction and Hypertension

Abstract

Clinical studies have shown that Sirt3 expression declines by 40% by age 65 paralleling the increased incidence of hypertension and metabolic conditions further inactivate Sirt3 due to increased NADH and Acetyl-CoA. Sirt3 activates a major mitochondrial antioxidant enzyme, superoxide dismutase 2 (SOD2) by deacetylation of specific lysine residues. We hypothesized that loss of Sirt3 activity increases vascular oxidative stress due to SOD2 hyperacetylation and this promotes endothelial dysfunction and hypertension. Indeed, Western blot analysis showed 3-fold increase in SOD2 acetylation and 1.5-fold decrease in Sirt3 level in hypertensive human subjects. Infusion of angiotensin II (0.7 mg/kg/day) in C57Bl/6J mice increased acetylation of vascular SOD2 by 2-fold, reduced SOD2 activity to 52% and raised blood pressure to 156 mm Hg. We have tested if Sirt3 depletion exacerbates endothelial dysfunction and hypertension. Indeed, Western blot analysis of Sirt3-/- mice showed SOD2 hyperacetylation and reduced SOD2 activity, however, blood pressure and superoxide production was normal. Angiotensin II infusion in Sirt3-/- mice increased blood pressure to 182 mm Hg, increased superoxide, reduced endothelial nitric oxide and impaired acetylcholine-mediated vasodilatation compared with angiotensin II infused wild type mice. Treatment of hypertensive Sirt3-/- mice with SOD2 mimetic mitoTEMPO (1.4 mg/kg/day) after onset of angiotensin II-induced hypertension normalized blood pressure and restored endothelial dependent vasodilatation. We suggest that mitochondrial superoxide does not contribute to the basal vasodilation and blood pressure regulation however high salt, angiotensin II and inflammation increase mitochondrial superoxide. Indeed, superoxide production by complex I in submitochondrial particles was significantly increased in hypertensive mice and this was associated with complex I S-glutathionylation. Interestingly, SOD2 overexpression in transgenic mice prevents complex I S-glutathionylation, reduces superoxide production by complex I and attenuates hypertension. These data indicate that imbalance of SOD2 activity and mitochondrial superoxide production contributes to endothelial dysfunction and hypertension.