327 - Inactivation of Mitochondrial Deacetylase Sirt3 Promotes Vascular Oxidative Stress, Increases Endothelial Dysfunction and Exacerbates Hypertension

Abstract

Endothelial dysfunction is associated with aging, diabetes, hyperlipidemia, obesity and these risk factors affect the expression and activity of the mitochondrial energy regulator deacetylase Sirt3. Sirt3 activates major mitochondrial antioxidant enzyme SOD2 by deacetylation of specific lysine residues and Sirt3 depletion increases oxidative stress. We hypothesized that loss of vascular Sirt3 activity increases vascular oxidative stress and endothelial dysfunction and that this promotes hypertension and end organ damage. The role of vascular Sirt3 was studied in wild-type C57Bl/6J mice and tamoxifen-inducible smooth muscle specific Sirt3 knockout mice (Smc Sirt3KO ) using angiotensin II model of hypertension (Ang II, 0.7 mg/kg/day). Western blot analysis of aorta showed 30% reduction of vascular Sirt3 and increased SOD2 acetylation by 2-fold after onset of hypertension. We have tested if ex vivo treatment of aorta with Sirt3 activator resveratrol reduces SOD2 acetylation, diminishes mitochondrial O 2 ●– , and increases the production of endothelial NO. Indeed, however, ex vivo incubation with resveratrol (10 µM) significantly reduced SOD2 acetylation, diminished mitochondrial O 2 ●– and increased endothelial NO to normal level while Sirt3-inactive analog dihydroresveratrol had no effect. Specific role of vascular Sirt3 was studied in Smc Sirt3KO mice by crossing floxed Sirt3 mice with mice carrying gene for inducible cre in the vascular smooth muscle (inducible SMMHC cre). Wild-type and Smc Sirt3KO mice were injected daily for 5 days with tamoxifen and Ang II osmotic pumps were installed 10 days later. Deletion of Sirt3 in smooth muscle exacerbates hypertension (165 mm Hg vs 155 mm Hg in wild-type) and significantly increased mortality in Ang II-infused Smc Sirt3KO mice (60% vs 10% in wild-type) associated with severe edema and aortic aneurysm formation (100% vs 20% in wild-type). Decrease of NO is a hallmark of endothelial dysfunction in hypertension due to vascular oxidative stress. Indeed, Ang II infusion increased vascular O 2 ●– by 2-fold and reduced endothelial NO by 2-fold. Interestingly, Ang II infusion in Smc Sirt3KO mice caused severe vascular oxidative stress (3-fold increase in O 2 ●– ) and exacerbated endothelial dysfunction (4-fold decrease in NO). These data indicate that reduced vascular Sirt3 activity occurs in hypertension and this leads to SOD2 hyperacetylation and inactivation, promotes vascular oxidative stress, increases endothelial dysfunction, exacerbates hypertension, increases end-organ-damage and mortality. It is conceivable that Sirt3 agonists and SOD2 mimetics may have therapeutic potential in cardiovascular disease.