Abstract 19950: SIRT1-Mediated Deacetylation Promotes Akt Membrane Localization and Activation During Development of Cardiac Hypertrophy.
Introduction: SIRT1 is a prototype member of the sirtuin family, which has been implicated in regulation of many biological functions including, cell growth, survival and longevity of the organism. SIRT1 over expression protects cardiomyoctes from apoptosis but it induces hypertrophy. This study was designed to delineate the mechanism of pro-hypertrophic effects of SIRT1.
Methods and Results: We analyzed hearts of SIRT1-KO and SIRT1 transgenic (Tg) mice having cardiac-specific over expression of SIRT1. SIRT1-KO mice (4–6 wks old) had significantly reduced heart weight to body weight (HW/BW) ratio, and reduced size of cardiomyocytes. These hearts also had substantially reduced phosphorylation of Akt and GSK3β, compared to control hearts. On the other hand, SIRT1-Tg mice showed robust cardiac hypertrophy at adulthood, which was associated with massive phosphorylation of Akt and of its downstream targets like GSK3β, Foxo1, Foxo3a and mTOR. To test the effect of SIRT1 on Akt signaling directly, we examined acetylation of Akt in these hearts. Akt was immunoprecipitated from heart-lysates and analyzed by western analysis by use of an anti-acetyl-lysine antibody. Akt was highly acetylated in SIRT1-KO hearts, but not in SIRT1 over expressing hearts, suggesting that SIRT1 regulates reversible acetylation of Akt. Akt is known to bind to PIP3 (phosphatidylinositol-(3,4,5)-triphosphate) for membrane localization and activation. We therefore examined the ability of acetylated and deacetylated forms of Akt to bind to PIP3. The results showed that only Akt which was deacetylated by SIRT1 has the capacity to bind to PIP3, whereas the acetylated Akt does not. Confocal analysis of cells with or without SIRT1 showed that SIRT1 promotes the membrane localization of Akt. To demonstrate whether Akt activation was necessary for pro-hypertrophic effects of SIRT1, we examined the effect of an Akt-inhibitor, A15 in primary cultures of cardiomyocytes. Pretreatment of myocytes with A15 completely blocked the pro-hypertrophic effects of SIRT1.
Conclusions: These results uncovered an important step in Akt signaling and demonstrated that the pro-hypertrophic effects of SIRT1 are mediated through its ability to deacetylate Akt.
- © 2010 by American Heart Association, Inc.