Status of Research on Sestrin2 and Prospects for its Application in Therapeutic Strategies Targeting Myocardial Aging.

Cardiac aging is accompanied by changes in the heart at the cellular and molecular levels, leading to alterations in cardiac structure and function. Given today's increasingly aging population, the decline in cardiac function caused by cardiac aging has a significant impact on quality of life. Antiaging therapies to slow the aging process and attenuate changes in cardiac structure and function have become an important research topic. Treatment with drugs, including metformin, spermidine, rapamycin, resveratrol, astaxanthin, Huolisu oral liquid, and sulforaphane, has been demonstrated be effective in delaying cardiac aging by stimulating autophagy, delaying ventricular remodeling, and reducing oxidative stress and the inflammatory response. Furthermore, caloric restriction has been shown to play an important role in delaying aging of the heart. Many studies in cardiac aging and cardiac aging-related models have demonstrated that Sestrin2 has antioxidant and anti-inflammatory effects, stimulates autophagy, delays aging, regulates mitochondrial function, and inhibits myocardial remodeling by regulation of relevant signaling pathways. Therefore, Sestrin2 is likely to become an important target for antimyocardial aging therapy.

Sestrin2 is an endogenous antioxidant that improves contractile function in the heart during exposure to ischemia and reperfusion stress.

Sestrin2 (Sesn2) is a stress-inducible protein that plays a critical role in the response to ischemic stress. We recently recognized that Sesn2 may protect the heart against ischemic insults by reducing the generation of reactive oxygen species (ROS). After 45 min of ischemia followed by 24 h of reperfusion, myocardial infarcts were significantly larger in Sesn2 KO hearts than in wild-type hearts. Isolated cardiomyocytes from wild-type hearts treated with hypoxia and reoxygenation (H/R) stress showed significantly greater Sesn2 levels, compared with normoxic hearts (p < 0.05). Intriguingly, the administration of adeno-associated virus 9-Sesn2 into Sesn2 knockout (KO) hearts rescued Sesn2 protein levels and significantly improved the cardiac function of Sesn2 KO mice exposed to ischemia and reperfusion. The rescued levels of Sesn2 in Sesn2 KO hearts significantly ameliorated ROS generation and the activation of ROS-related stress signaling pathways during ischemia and reperfusion. Moreover, the rescued Sesn2 levels in Sesn2 KO cardiomyocytes improved the maximal velocity of cardiomyocyte shortening by H/R stress. Rescued Sesn2 levels also improved peak height, peak shortening amplitude, and maximal velocity of the re-lengthening of Sesn2 KO cardiomyocytes subjected to H/R. Finally, the rescued Sesn2 levels significantly augmented intracellular calcium levels and reduced the mean time constant of transient calcium decay in Sesn2 KO cardiomyocytes exposed to H/R. Overall, these findings indicated that Sesn2 can act as an endogenous antioxidant to maintain intracellular redox homeostasis under ischemic stress conditions.

Sestrin 2, a potential star of antioxidant stress in cardiovascular diseases.

Physiological reactive oxygen species (ROS) play an important role in cellular signal transduction. However, excessive ROS is an important pathological mechanism in most cardiovascular diseases (CVDs), such as myocardial aging, cardiomyopathy, ischemia/reperfusion injury (e.g., myocardial infarction) and heart failure. Programmed cell death, hypertrophy and fibrosis may be due to oxidative stress. Sestrin 2 (Sesn2), a stress-inducible protein associated with various stress conditions, is a potential antioxidant. Sesn2 can suppress the process of heart damage caused by oxidative stress, promote cell survival and play a key role in a variety of CVDs. This review discusses the effect of Sesn2 on the redox signal, mainly via participation in the signaling pathway of nuclear factor erythroid 2-related factor 2, activation of adenosine monophosphate-activated protein kinase and inhibition of mammalian target of rapamycin complex 1. It also discusses the effect of Sesn2's antioxidant activity on different CVDs. We speculate that Sesn2 plays an important role in CVDs by stimulating the process of antioxidation and promoting the adaptation of cells to stress conditions and/or the environment, opening a new avenue for related therapeutic strategies.

Substrate metabolism regulated by Sestrin2-mTORC1 alleviates pressure overload-induced cardiac hypertrophy in aged heart.

Sestrin2 (Sesn2) is a stress sensor for the mammalian target of rapamycin complex 1 (mTORC1) pathway. Aging impairs cardiac mTORC1 activation, thereby sensitizing the heart to hypertrophy. C57BL/6 J young wild-type (young WT; 4-6 months), aged WT (24-26 months), and young Sestrin2 knockout mice (Y-Sesn2 KO; 4-6 months) underwent transverse aortic constriction (TAC) for pressure overload. Cardiac expression of Sesn2 decreased with age. At 4 weeks after TAC, aged WT and Y-Sesn2 KO exhibited larger hearts and impaired cardiac function, compared with young WT mice. Augmented phosphorylation of mTOR and downstream effectors; damaged mitochondria and elevated redox markers, as well as and impaired glucose and fatty acid oxidation were observed in aged WT and Y-Sesn2 KO hearts. A pressure overload-induced interaction between Sesn2 and GTPase-activating protein activity toward Rags 2 (GATOR2), which positively regulates mTORC1, was impaired in aged WT hearts. Adeno-associated virus 9-Sesn2 treatment rescued Sesn2 expression, attenuated mTORC1 activation, and increased pressure overload tolerance in aged WT and Y-Sesn2 KO hearts. These results indicated that cardiac Sesn2 acts as a pressure overload sensor for mTORC1. Furthermore, Sesn2 deficiency may cause increased sensitivity to hypertrophy in elderly individuals.

Sestrin 2 controls the cardiovascular aging process via an integrated network of signaling pathways.

As an inevitable biological process, cardiovascular aging is the greatest risk factor for cardiovascular diseases (CVDs). Sestrin 2 (Sesn2), a stress-inducible and age-related protein associated with various stress conditions, plays a pivotal role in slowing this process. It acts as an anti-aging agent, mainly through its antioxidant enzymatic activity and regulation of antioxidant signaling pathways, as well as by activating adenosine monophosphate-activated protein kinase and inhibiting mammalian target of rapamycin complex 1. In this review, we first introduce the biochemical functions of Sesn2 in the cardiovascular aging process, and describe how Sesn2 expression is regulated under various stress conditions. Next, we emphasize the role of Sesn2 signal transduction in a series of age-related CVDs, including hypertension, myocardial ischemia and reperfusion, atherosclerosis, and heart failure, as well as provide potential mechanisms for the association of Sesn2 with CVDs. Finally, we present the potential therapeutic applications of Sesn2-directed therapy and future prospects.

Sestrin2 modulates cardiac inflammatory response through maintaining redox homeostasis during ischemia and reperfusion.

Ischemia heart disease is the leading cause of death world-widely and has increased prevalence and exacerbated myocardial infarction with aging. Sestrin2, a stress-inducible protein, declines with aging in the heart and the rescue of Sestrin2 in the aged mouse heart improves the resistance to ischemic insults caused by ischemia and reperfusion. Here, through a combination of transcriptomic, physiological, histological, and biochemical strategies, we found that Sestrin2 deficiency shows an aged-like phenotype in the heart with excessive oxidative stress, provoked immune response, and defected myocardium structure under physiological condition. While challenged with ischemia and reperfusion stress, the transcriptomic alterations in Sestrin2 knockout mouse heart resembled aged wild type mouse heart. It suggests that Sestrin2 is an age-related gene in the heart against ischemia reperfusion stress. Sestrin2 plays a crucial role in modulating inflammatory response through maintaining the intracellular redox homeostasis in the heart under ischemia reperfusion stress condition. Together, the results indicate that Sestrin2 is a potential target for treatment of age-related ischemic heart disease.

The Emerging Role of Sestrin2 in Cell Metabolism, and Cardiovascular and Age-Related Diseases.

Sestrins (Sesns), including Sesn1, Sesn2, and Sesn3, are cysteine sulfinyl reductases that play critical roles in the regulation of peroxide signaling and oxidant defense. Sesn2 is thought to regulate cell growth, metabolism, and survival response to various stresses, and act as a positive regulator of autophagy. The anti-oxidative and anti-aging roles of Sesn2 have been the focus of many recent studies. The role of Sesn2 in cellular metabolism and cardiovascular and age-related diseases must be analyzed and discussed. In this review, we discuss the physiological and pathophysiological roles and signaling pathways of Sesn2 in different stress-related conditions, such as oxidative stress, genotoxic stress, and hypoxia. Sesn2 is also involved in aging, cancer, diabetes, and ischemic heart disease. Understanding the actions of Sesn2 in cell metabolism and age-related diseases will provide new evidence for future experimental research and aid in the development of novel therapeutic strategies for Sesn2-related diseases.

The value of plasma fibrillin-1 level in patients with spontaneous coronary artery dissection.

BACKGROUND: Spontaneous coronary artery dissection (SCAD) has emerged as an important etiology of myocardial infarction and sudden death, especially in young women. Early diagnosis is essential for appropriate management. OBJECTIVES: To explore the value of plasma fibrillin-1 (FBN1) levels in patients with SCAD. METHODS: 70 patients with non-atherosclerotic SCAD between January 2014 and September 2018 were age and sex matched with 70 patients with non-SCAD acute coronary syndrome (ACS) and 70 healthy controls. The plasma FBN1 level was measured and compared among three groups. The value of FBN1 for prognosis and treatment decision making was further explored. RESULTS: The plasma FBN1 level of SCAD group (58.44 ± 7.06 ng/mL) was higher than that of non-SCAD ACS group (52.39 ± 6.92 ng/mL, P < 0.001) or healthy controls (50.56 ± 4.48 ng/mL, P < 0.001). Compared with controls, significantly higher percentages of patients with SCAD were found in the highest compared with lowest quartile of FBN1 concentration. The area under the curve (AUC) for plasma FBN1 level to discriminate patients with SCAD from non-SCAD ACS was 0.81 (95% CI 0.74-0.88, P < 0.001). A cut-off value of 54.64 ng/mL was determined to differentiate SCAD from non-SCAD ACS with a sensitivity of 0.77 (95%CI: 0.66-0.86) and specificity of 0.76 (95%CI: 0.64-0.85). After a median follow-up of 28.35 (14.07 ± 44.69) months, 11 (15.7%) cases suffered from major adverse cardiac events (MACE). Higher FBN1 level was detected in patients with MACE (63.71 ± 7.49 vs. 57.45 ± 6.58 ng/mL) (P = 0.006). A cut-point of 58.14 was determined for SCAD patients to identify MACE. At this point, FBN1 might also have potential use for decision making in SCAD patients. CONCLUSION: Plasma FBN1 is a promising biomarker for aiding the diagnosis of SCAD and have potential value in prognosis prediction.

Mitochondrial Complex I Inhibition by Metformin Limits Reperfusion Injury.

Transient, reversible blockade of complex I during early reperfusion after ischemia limits cardiac injury. We studied the cardioprotection of high dose of metformin in cultured cells and mouse hearts via the novel mechanism of acute downregulation of complex I. The effect of high dose of metformin on complex I activity was studied in isolated heart mitochondria and cultured H9c2 cells. Protection with metformin was evaluated in H9c2 cells at reoxygenation and at early reperfusion in isolated perfused mouse hearts and in vivo regional ischemia reperfusion. Acute, high-dose metformin treatment inhibited complex I in ischemia-damaged mitochondria and in H9c2 cells following hypoxia. Accompanying the complex I modulation, high-dose metformin at reoxygenation decreased death in H9c2 cells. Acute treatment with high-dose metformin at the end of ischemia reduced infarct size following ischemia reperfusion in vitro and in vivo, including in the AMP kinase-dead mouse. Metformin treatment during early reperfusion improved mitochondrial calcium retention capacity, indicating decreased permeability transition pore (MPTP) opening. Acute, high-dose metformin therapy decreased cardiac injury through inhibition of complex I accompanied by attenuation of MPTP opening. Moreover, in contrast to chronic metformin treatment, protection by acute, high-dose metformin is independent of AMP-activated protein kinase activation. Thus, a single, high-dose metformin treatment at reperfusion reduces cardiac injury via modulation of complex I.

Dichloroacetate Ameliorates Cardiac Dysfunction Caused by Ischemic Insults Through AMPK Signal Pathway-Not Only Shifts Metabolism.

Dichloroacetate (DCA), an inhibitor of pyruvate dehydrogenase kinase (PDK), regulates substrate metabolism in the heart. AMP-activated protein kinase (AMPK) is an age-related energy sensor that protects the heart from ischemic injury. This study aims to investigate whether DCA can protect the heart from ischemic injury through the AMPK signaling pathway. Young (3-4 months) and aged (20-24 months) male C57BL/6J mice were subjected to ligation of the left anterior descending coronary artery (LAD) for an in vivo ischemic model. The systolic function of the hearts was significantly decreased in both young and aged mice after 45 min of ischemia and 24 h of reperfusion. DCA treatment significantly improved cardiac function in both young and aged mice. The myocardial infarction analysis demonstrated that DCA treatment significantly reduced the infarction size caused by ischemia/reperfusion (I/R) in both young and aged mice. The isolated-cardiomyocyte experiments showed that DCA treatment ameliorated contractile dysfunction and improved the intracellular calcium signal of cardiomyocytes under hypoxia/reoxygenation (H/R) conditions. These cardioprotective functions of DCA can be attenuated by inhibiting AMPK activation. Furthermore, the metabolic measurements with an ex vivo working heart system demonstrated that the effects of DCA treatment on modulating the metabolic shift response to ischemia and reperfusion stress can be attenuated by inhibiting AMPK activity. The immunoblotting results showed that DCA treatment triggered cardiac AMPK signaling pathway by increasing the phosphorylation of AMPK's upstream kinase liver kinase B1 (LKB1) under both sham operations and I/R conditions. Thus, except from modulating metabolism in hearts, the cardioprotective function of DCA during I/R was mediated by the LKB1-AMPK pathway.

Cardiomyocyte-specific deletion of Sirt1 gene sensitizes myocardium to ischaemia and reperfusion injury.

Aims: 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 of this study 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 wild-type C57BL/6 J (WT, 4-6 months), aged WT C57BL/6 J (24-26 months), and young inducible cardiomyocyte-specific SIRT1 knockout (icSIRT1 KO) (4-6 months) mice under physiological conditions. However, after 45 mins ischaemia and 24-h reperfusion, the ejection fraction of aged WT and icSIRT1 KO mice was impaired. The aged WT and icSIRT1 KO hearts vs. young WT hearts also show an impaired post-ischemic contractile function in a Langendorff perfusion system. The infarct size of aged WT and icSIRT1 KO hearts was larger than that of young WT hearts. The immunoblotting data demonstrated that aged WT and icSIRT1 KO hearts vs. young WT hearts had impaired phosphorylation of AMPK and downstream acetyl-CoA carboxylase during ischaemia. Intriguingly, AMPK upstream LKB1 is hyper-acetylated in both aged WT and icSIRT1 KO hearts; this could blunt activation of LKB1, leading to an impaired AMPK activation. The working heart perfusion results demonstrated that SIRT1 deficiency significantly impaired substrate metabolism in the hearts; fatty acid oxidation is augmented and glucose oxidation is blunted during ischaemia and reperfusion. Adeno-associated virus (AAV9)-Sirt1 was delivered into the aged hearts via a coronary delivery approach, which significantly rescued the protein level of SIRT1 and the ischemic tolerance of aged hearts. Furthermore, AMPK agonist can rescue the tolerance of aged heart and icSIRT1 KO heart to ischemic insults. Conclusions: Cardiac SIRT1 mediates AMPK activation via LKB1 deacetylation, and AMPK modulates SIRT1 activity via regulation of NAD+ level during ischaemia. SIRT1 and AMPK agonists have therapeutic potential for treatment of aging-related ischemic heart disease.

Targeting ALDH2 for Therapeutic Interventions in Chronic Pain-Related Myocardial Ischemic Susceptibility.

Clinical observations have demonstrated a link between chronic pain and increased ischemic heart disease mortality, but the mechanisms remain elusive. Reactive aldehydes have recently been confirmed as a new player in pain pathologies, while our previous study demonstrated that reactive aldehydes (4-HNE) induced carbonyl stress contributing to myocardial ischemic intolerance. The aim of this study was to explore whether chronic pain increases susceptibility to myocardial ischemia/reperfusion (MI/R) injury and to investigate the underlying mechanisms focusing on toxic aldehyde and carbonyl stress. Methods: Chronic pain was induced by chronic compression of the dorsal root ganglion (CCD). After 2 weeks CCD, aldehyde dehydrogenase (ALDH2) KO or wild-type (WT) littermate mice were then subjected to in vivo MI/R. Results: In CCD-WT mice, heightened nociception paralleled circulating aldehyde (4-HNE) accumulation and cardiac protein carbonylation. Mechanistically, CCD-induced 4-HNE overload provoked cardiac Sirtuin 1 (SIRT1) carbonylative inactivation and inhibited Liver kinase B1 (LKB1) - AMP-activated protein kinase (LKB1-AMPK) interaction, which resulted in exacerbated MI/R injury and higher mortality compared with non-CCD WT mice. ALDH2 deficiency further aggravated CCD-induced susceptibility to MI/R injury. Exogenous 4-HNE exposure in peripheral tissue mimicked chronic pain-induced aldehyde overload, elicited sustained allodynia and increased MI/R injury. However, cardiac-specific ALDH2 upregulation by AAV9-cTNT-mediated gene delivery significantly ameliorated chronic pain-induced SIRT1 carbonylative inactivation and decreased MI/R injury (minor infarct size, less apoptosis, and improved cardiac function). Conclusion: Collectively, chronic pain-enhanced carbonyl stress promotes myocardial ischemic intolerance by SIRT1 carbonylative inactivation and impairment of LKB1-AMPK interaction. ALDH2 activation and prevention of protein carbonylation may be a potential therapeutic target for myocardial ischemic vulnerability in chronic pain patients. Our results newly provided overlapping cellular mechanisms of chronic pain and myocardial dysfunction interplay.

Sestrin2 prevents age-related intolerance to post myocardial infarction via AMPK/PGC-1α pathway.

We have revealed that a novel stress-inducible protein, Sestrin2, declines in the heart with aging. Moreover, there is an interaction between Sestrin2 and energy sensor AMPK in the heart in response to ischemic stress. The objective of this study is to determine whether Sestrin2-AMPK complex modulates PGC-1α in the heart and protects the heart from ischemic insults. In order to characterize the role of cardiac Sestrin2-AMPK signaling cascade in aging, C57BL/6 wild type young mice (3-4months), aged mice (24-26months) and young Sestrin2 KO mice were subjected to left anterior descending coronary artery occlusion for in vivo regional ischemia. Intriguingly, ischemic AMPK activation was blunted in aged WT and young Sesn2 KO hearts as compared with young WT hearts. In addition, the AMPK downstream PGC-1α was down-regulated in the aged and Sestrin2 KO hearts during post myocardial infarction. To further determine the regulation of AMPK on mitochondrial functions in aging, the downstream of mitochondrial biogenesis PGC-1α transcriptional factor were measured. The results demonstrated that the PGC-1α downstream effectors TFAM and UCP2 were impaired in the aged and Sestrin2 KO post-MI hearts as compared to the young hearts. While the apoptotic flux markers such as AIF, Bax/Bcl-2 were up-regulated in both aged and Sestrin2 KO hearts versus young hearts. Furthermore, both Sestrin2 KO and aged hearts demonstrated more susceptible to ischemic insults as compared to young hearts. Additionally, the adeno-associated virus (AAV9)-Sestrin2 delivered to the aged hearts via a coronary delivery approach significantly rescued the ischemic tolerance of aged hearts. Taken together, the decreased Sestrin2 levels in aging lead to an impaired AMPK/PGC-1α signaling cascade and an increased sensitivity to ischemic insults.

Activated protein C protects against pressure overload-induced hypertrophy through AMPK signaling.

We found that the anticoagulant plasma protease, activated protein C (APC), stimulates the energy sensor kinase, AMPK, in the stressed heart by activating protease-activated receptor 1 (PAR1) on cardiomyocytes. Wild-type (WT) and AMPK-kinase dead (KD) transgenic mice were subjected to transverse aortic constriction (TAC) surgery. The results demonstrated that while no phenotypic differences can be observed between WT and AMPK-KD mice under normal physiological conditions, AMPK-KD mice exhibit significantly larger hearts after 4 weeks of TAC surgery. Analysis by echocardiography suggested that the impairment in the cardiac function of AMPK-KD hearts is significantly greater than that of WT hearts. Immunohistochemical staining revealed increased macrophage infiltration and ROS generation in AMPK-KD hearts after 4 weeks of TAC surgery. Immunoblotting results demonstrated that the redox markers, pShc66, 4-hydroxynonenal and ERK, were all up-regulated at a higher extent in AMPK-KD hearts after 4 weeks of TAC surgery. Administration of APC-WT and the signaling selective APC-2Cys mutant, but not the anticoagulant selective APC-E170A mutant, significantly attenuated pressure overload-induced hypertrophy and fibrosis. Macrophage infiltration and pShc66 activation caused by pressure overload were also inhibited by APC and APC-2Cys but not by APC-E170A. Therefore, the cardiac AMPK protects against pressure overload-induced hypertrophy and the signaling selective APC-2Cys may have therapeutic potential for treating hypertension-related hypertrophy without increasing the risk of bleeding.

The endotoxemia cardiac dysfunction is attenuated by AMPK/mTOR signaling pathway regulating autophagy.

AMP-activated protein kinase (AMPK), an enzyme that plays a role in cellular energy homeostasis, modulates myocardial signaling in the heart. Myocardial dysfunction is a common complication of sepsis. Autophagy is involved in the aging related cardiac dysfunction. However, the role of AMPK in sepsis-induced cardiotoxicity has yet to be clarified, especially in aging. In this study, we explored the role of AMPK in lipopolysaccharide (LPS)-induced myocardial dysfunction and elucidated the potential mechanisms of AMPK/mTOR pathway regulating autophagy in young and aged mice. We harvested cardiac tissues by intraperitoneal injection of LPS treatment. The results by echocardiography, pathology, contractile and intracellular Ca2+ property as well as western blot analysis revealed that LPS induced remarkable cardiac dysfunction and cardiotoxicity in mice hearts and cardiomyocytes, which were more seriously in the aged mice. Western blot analysis indicated that the underlying mechanisms included inhibition autophagy mediated by AMPK/mTOR activation. LPS overtly promoted the expression of AMPK upstream regulator PP2A and PP2Cα. Pharmacological activation of AMPK improved cardiac function and upregulated cardiac autophagy induced by LPS in the aged mice. Collectively, our findings suggest that upregulation of autophagy by administration of AMPK could attenuate LPS-induced cardiotoxicity, which enhances our knowledge to explore new drugs and strategies for combating cardiac dysfunction induced by sepsis.

Sestrin2 prevents age-related intolerance to ischemia and reperfusion injury by modulating substrate metabolism.

A novel stress-inducible protein, Sestrin2 (Sesn2), declines in the heart with aging. AMPK has emerged as a pertinent stress-activated kinase that has been shown to have cardioprotective capabilities against myocardial ischemic injury. We identified the interaction between Sesn2 and AMPK in the ischemic heart. To determine whether ischemic AMPK activation-modulated by the Sesn2-AMPK complex in the heart-is impaired in aging that sensitizes the heart to ischemic insults, young C57BL/6 mice (age 3-4 mo), middle-aged mice (age 10-12 mo), and aged mice (age 24-26 mo) were subjected to left anterior descending coronary artery occlusion for in vivo regional ischemia. The ex vivo working heart system was used for measuring substrate metabolism. The protein level of Sesn2 in hearts was gradually decreased with aging. Of interest, ischemic AMPK activation was blunted in aged hearts compared with young hearts (P < 0.05); the AMPK downstream glucose uptake and the rate of glucose oxidation were significantly impaired in aged hearts during ischemia and reperfusion (P < 0.05 vs. young hearts). Myocardial infarction size was larger in aged hearts (P < 0.05 vs. young hearts). Immunoprecipitation with Sesn2 Ab revealed that cardiac Sesn2 forms a complex with AMPK and upstream liver kinase B1 (LKB1) during ischemia. Of interest, the binding affinity between Sesn2 and AMPK upstream LKB1 is impaired in aged hearts during ischemia (P < 0.05 vs. young hearts). Furthermore, Sesn2-knockout hearts demonstrate a cardiac phenotype and response to ischemic stress that is similar to wild-type aged hearts (i.e., impaired ischemic AMPK activation and higher sensitivity to ischemia- and reperfusion- induced injury). Adeno-associated virus-Sesn2 was delivered to aged hearts via a coronary delivery approach and significantly rescued the protein level of Sesn2 and the ischemic tolerance of aged hearts; therefore, Sesn2 is a scaffold protein that mediates AMPK activation in the ischemic myocardium via an interaction with AMPK upstream LKB1. Decreased Sesn2 levels in aging lead to a blunted ischemic AMPK activation, alterations in substrate metabolism, and an increased sensitivity to ischemic insults-Quan, N., Sun, W., Wang, L., Chen, X., Bogan, J. S., Zhou, X., Cates, C., Liu, Q., Zheng, Y., Li J. Sestrin2 prevents age-related intolerance to ischemia and reperfusion injury by modulating substrate metabolism.

Cardioprotective actions of Notch1 against myocardial infarction via LKB1-dependent AMPK signaling pathway.

AMP-activated protein kinase (AMPK) signaling pathway plays a pivotal role in intracellular adaptation to energy stress during myocardial ischemia. Notch1 signaling in the adult myocardium is also activated in response to ischemic stress. However, the relationship between Notch1 and AMPK signaling pathways during ischemia remains unclear. We hypothesize that Notch1 as an adaptive signaling pathway protects the heart from ischemic injury via modulating the cardioprotective AMPK signaling pathway. C57BL/6J mice were subjected to an in vivo ligation of left anterior descending coronary artery and the hearts from C57BL/6J mice were subjected to an ex vivo globe ischemia and reperfusion in the Langendorff perfusion system. The Notch1 signaling was activated during myocardial ischemia. A Notch1 γ-secretase inhibitor, dibenzazepine (DBZ), was intraperitoneally injected into mice to inhibit Notch1 signaling pathway by ischemia. The inhibition of Notch1 signaling by DBZ significantly augmented cardiac dysfunctions caused by myocardial infarction. Intriguingly, DBZ treatment also significantly blunted the activation of AMPK signaling pathway. The immunoprecipitation experiments demonstrated that an interaction between Notch1 and liver kinase beta1 (LKB1) modulated AMPK activation during myocardial ischemia. Furthermore, a ligand of Notch1 Jagged1 can significantly reduce cardiac damage caused by ischemia via activation of AMPK signaling pathway and modulation of glucose oxidation and fatty acid oxidation during ischemia and reperfusion. But Jagged1 did not have any cardioprotections on AMPK kinase dead transgenic hearts. Taken together, the results indicate that the cardioprotective effect of Notch1 against ischemic damage is mediated by AMPK signaling via an interaction with upstream LKB1.

Cardiac-Specific Deletion of the Pdha1 Gene Sensitizes Heart to Toxicological Actions of Ischemic Stress.

Pyruvate dehydrogenase (PDH) plays a key role in aerobic energy metabolism and occupies a central crossroad between glycolysis and the tricarboxylic acid cycle. We generated inducible cardiac-specific PDH E1α knockout (CreER(T2)-PDH(flox/flox)) mice that demonstrated a high mortality rate. It was hypothesized that PDH modulating cardiac glucose metabolism is crucial for heart functions under normal physiological and/or stress conditions. The myocardial infarction was conducted by a ligation of the left anterior descending coronary arteries. Cardiac PDH E1α deficiency caused large myocardial infarcts size and macrophage infiltration in the hearts (P < .01 vs wild-type [WT]). Wheat germ agglutinin and Masson trichrome staining revealed significantly increased hypertrophy and fibrosis in PDH E1α-deficient hearts (P < .05 vs WT). Measurements of heart substrate metabolism in an ex vivo working heart perfusion system demonstrated a significant impairment of glucose oxidation in PDH E1α-deficient hearts during ischemia/reperfusion (P < .05 vs WT). Dichloroacetate, a PDH activator, increased glucose oxidation in WT hearts during ischemia/reperfusion and reduced myocardial infarct size in WT, but not in PDH E1α-deficient hearts. Immunoblotting results demonstrated that cardiac PDH E1α deficiency leads to an impaired ischemic AMP-activated protein kinase activation through Sestrin2-liver kinase B1 interaction which is responsible for an increased susceptibility of PDH E1α-deficient heart to ischemic insults. Thus, cardiac PDH E1α deficiency impairs ischemic AMP-activated protein kinase signaling and sensitizes hearts to the toxicological actions of ischemic stress.