Cardiomyocyte-specific Deletion Of SIRT1 Gene Sensitizes Myocardium To Ischaemia And Reperfusion Injury

Cardiovascular diseases are diseases caused by cardiac and vascular dysfunction,including acute myocardial infarction,hypertension,coronary heart disease,etc.,and are currently the number one killer of human death.Acute myocardial infarction remains the most common cause of sudden cardiac death.China currently has a large aging population and is gradually increasing.Population aging is one of the most important reasons for the increased incidence and mortality of cardiovascular disease.An aged heart will show a more vulnerable state than a young heart,and it will significantly reduce the response to various stimuli,leading to a significant increase in the disability and mortality rates associated with aged heart disease,so it is more urgent to study aging heart disease.In the course of acute myocardial infarction,the heart needs to quickly adapt to the state of hypoxia and ischemia,and undergo an important transition from aerobic metabolism to anaerobic metabolism.In this process,it plays a key role in maintaining a certain level of ATP in the heart,and it is also necessary to maintain the normal systolic function,normal ion channel activity and myocardial cell integrity of the heart.Therefore,it is of great clinical significance to study the mechanism of the effect of cardio metabolism on myocardial ischemia.The aging process itself has been described as being associated with decreased SIRT1 and AMPK activity.SIRT1 gene belongs to the nicotinamide adenine dinucleotide(NAD)dependent protein family and is considered to be the gatekeeper of oxidative stress and cardiovascular aging,so it is also known as longevity protein.SIRT1 protects the heart against ischemia/reperfusion injury and myocardial cell apoptosis.AMPK is one of the most important energy sensors that regulate cell metabolism.SIRT1 is related to the key energy-switching protein AMPK,which is closely related to each other and cannot be separated.This suggests that AMPK and SIRT1 interact closely in cardiac energy.There is growing evidence that AMPK plays a role in regulating glucose and fatty acid metabolism in favor of the heart's tolerance to ischemic stress.We have reported the response of myocardial AMPK signaling to ischemic stress caused by aging,so we sought to elucidate the role of AMPK and SIRT1 activation induced by ischemia-reperfusion injury(I/R)in the elderly heart.In addition,we investigated whether small-molecule AMPK agonist or SIRT1 agonist can enhance cardiac AMPK-SIRT1 signal to improve cardiac function and enhance cardiac resistance to ischemic stress in the elderly.Aim: A longevity gene,SIRTuin 1(SIRT1)and energy sensor AMP-activated protein kinase(AMPK)have common activators such as caloric restriction,oxidative stress and exercise.The objective is to characterize the role of cardiomyocyte SIRT1 in age-related impaired ischemic AMPK activation and increased susceptibility to ischemic insults.Methods and Results: 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.The cardiac functions by echocardiography show no difference in young(4-6 months),aged(24-26 months)and young inducible cardiomyocyte specific SIRT1 knockout(icSIRT1 KO)(4-6 months)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.Adeno-associated virus(AAV9)-SIRT1 were delivered into the aged hearts via a coronary delivery approach significantly rescued the protein level of SIRT1 and the ischemic tolerance of aged hearts.Furthermore,AMPK agonist can rescue the tolerance of aged heart but not icSIRT1 KO hearts to ischemic insults.Conclusions: Cardiac SIRT1 mediates AMPK activation via LKB1 deacetylation and AMPK modulates SIRT1 activity via regulation of NAD level during ischemia.SIRT1 and AMPK agonists have therapeutic potential for treatment of aging-related ischemic heart disease.