Abstract 12050: Cardiomyocyte Specific Deletion of Sirt1 Gene Alters Substrate Metabolism and Sensitizes Myocardium to Ischemia and Reperfusion Injury

Abstract

Introduction: A longevity gene, sirtuin 1 (SIRT1) is a conserved NAD + -dependent protein deacetylase. AMP-activated protein kinase (AMPK) is an energy sensor. AMPK and SIRT1 signaling pathways have common activators such as caloric restriction, oxidative stress and exercise. Hypothesis: Aging-related impaired ischemic AMPK activation and increased susceptibility to ischemic insults are due to a decreased SIRT1 levels in aging. Methods: Mice were subjected to ligation of left anterior descending coronary artery for in vivo ischemic models. The glucose and fatty acid oxidation were measured in a working heart perfusion system. Results: The cardiac functions by echocardiography show no difference in young (SIRT1 flox/flox ), aged (SIRT1 flox/flox ) and young inducible cardiomyocyte specific SIRT1 knockout (icSIRT1 KO) mice under physiological conditions, but after 45 mins ischemia and 24 hours reperfusion, the ejection fraction of aged and icSIRT1 KO mice were impaired. The aged and icSIRT1 KO hearts versus young hearts also show an impaired post-ischemic contractile function in Langendorff perfusion system. The infarct size of aged and icSIRT1 KO hearts was larger than that of young hearts (p<0.05). The immunoblotting data demonstrated that aged and icSIRT1 KO hearts versus young hearts had impaired phosphorylation of AMPK and downstream acetyl-CoA carboxylase during ischemia. Intriguingly, AMPK upstream LKB1 is hyper-acetylated in both aged and icSIRT1 KO hearts that could blunt activation of LKB1, leading to an impaired AMPK activation. The working heart perfusion results demonstrated that SIRT1 deficiency significantly impair substrate metabolism in the hearts, fatty acid oxidation is augmented and glucose oxidation is blunted during ischemia and reperfusion. Aged and icSIRT1 KO hearts versus young hearts demonstrated significant cardiac fibrosis and macrophage infiltration during ischemia and reperfusion. Furthermore, AMPK agonist A769662 treatment can rescue the tolerance of aged heart but not icSIRT1 KO hearts to ischemic insults. Conclusions: Cardiac SIRT1 mediates AMPK activation via LKB1 deacetylation during ischemia. SIRT1 and AMPK agonists have therapeutic potential for treatment of aging-related ischemic heart disease.