Abstract 622: Increased Mitochondrial Oxidative Stress and Activated AMP- Kinase In the Brain Dorsal Medulla of Hypertensive (mRen2)27 Transgenic Rats

Abstract

The deleterious actions of angiotensin (Ang) II are generally thought to be mediated by NADPH oxidase (NOX)-derived reactive oxygen species (ROS) which may stimulate mitochondrial oxidant release leading to impaired energy metabolism. Hypertensive transgenic (mRen2)27 rats (mRen2) exhibit high NOX activity in brain dorsal medullary tissue compared to normotensive Hannover Sprague-Dawley (SD) control rats; however, the extent of mitochondrial involvement is unknown. Therefore, the present study evaluated mitochondrial ROS levels, ATP and mitochondrial content in the brain dorsal medulla of age-matched mRen2 and SD rats. Additional studies assessed AMP-activated kinase (AMPK) activation since altered mitochondrial oxidant and/or energy levels are associated with a stimulated AMPK pathway that is known to be activated in response to depleted cellular energy levels. Freshly isolated mitochondria from the dorsal medulla of 20 week old male heterozygous mRen2 [systolic blood pressure (SBP): 211 ± 4 mmHg] and SD [SBP: 120 ± 3 mmHg] rats were loaded with the sensitive ROS indicator dihydroethidium (HEt). Basal HEt fluorescence intensity was ∼16% higher in mRen2 as compared to SD rats suggesting higher ROS levels in mitochondria of the hypertensive strain [mRen2: 83 ± 4 vs. SD: 70 ± 4 mean fluorescence intensity; p=0.02, n=3]. Although ATP levels and mitochondrial content were similar between strains, AMPK was significantly activated (phosphorylated AMPK-α and β 1 subunits) in the mRen2 compared to normotensive SD rats [AMPKα- mRen2: 3.5 ± 0.4 arbitary units vs. SD: 1.0 ± 0.2; p = 0.001, n = 5; and AMPKβ 1 - mRen2: 1.6 ± 0.04 arbitary units vs. SD: 1.0 ± 0.2; p = 0.05, n = 3]. The activation of AMPK may contribute to enhanced mitochondrial biogenesis since ATP and mitochondrial content were unchanged, thus representing a compensatory response to increased energy requirements in the hypertensive strain. We conclude that targeting of mitochondrial oxidants and increased AMPK activation may serve as a potential therapy to improve mitochondrial energy metabolism in hypertension.