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AMPK is critical for mitochondrial function during reperfusion after myocardial ischemia.

ABSTRACT: AMP-activated kinase (AMPK) is a stress responsive kinase that regulates cellular metabolism and protects against cardiomyocyte injury during ischemia-reperfusion (IR). Mitochondria play an important role in cell survival, but the specific actions of activated AMPK in maintaining mitochondrial integrity and function during reperfusion are unknown. Thus, we assessed the consequences of AMPK inactivation on heart mitochondrial function during reperfusion. Mouse hearts expressing wild type (WT) or kinase-dead (KD) AMPK were studied. Mitochondria isolated from KD hearts during reperfusion had intact membrane integrity, but demonstrated reduced oxidative capacity, increased hydrogen peroxide production and decreased resistance to mitochondrial permeability transition pore opening compared to WT. KD hearts showed increased activation of the mitogen activated protein kinase kinase 4 (MKK4) and downstream c-Jun terminal kinase (JNK) and greater necrosis during reperfusion after coronary occlusion. Transgenic expression of mitochondrial catalase (MCAT) prevented the excessive cardiac JNK activation and attenuated the increased myocardial necrosis observed during reperfusion in KD mice. Inhibition of JNK increased the resistance of KD hearts to mPTP opening, contractile dysfunction and necrosis during IR. Thus, intrinsic activation of AMPK is critical to prevent excess mitochondrial reactive oxygen production and consequent JNK signaling during reperfusion, thereby protecting against mPTP opening, irreversible mitochondrial damage and myocardial injury.

SUBMITTER: Zaha VG

PROVIDER: S-EPMC4839186 | biostudies-literature | 2016 Feb

REPOSITORIES: biostudies-literature

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AMPK is critical for mitochondrial function during reperfusion after myocardial ischemia.

Zaha Vlad G VG Qi Dake D Su Kevin N KN Palmeri Monica M Lee Hui-Young HY Hu Xiaoyue X Wu Xiaohong X Shulman Gerald I GI Rabinovitch Peter S PS Russell Raymond R RR Young Lawrence H LH

Journal of molecular and cellular cardiology 20151230

AMP-activated kinase (AMPK) is a stress responsive kinase that regulates cellular metabolism and protects against cardiomyocyte injury during ischemia-reperfusion (IR). Mitochondria play an important role in cell survival, but the specific actions of activated AMPK in maintaining mitochondrial integrity and function during reperfusion are unknown. Thus, we assessed the consequences of AMPK inactivation on heart mitochondrial function during reperfusion. Mouse hearts expressing wild type (WT) or ...[more]

PMID: 26746142

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Project description:Mitochondrial dysfunction is a salient feature of myocardial ischemia/reperfusion injury (MIRI), while the potential mechanism of mitochondrial dynamics disorder remains unclear. This study sought to explore whether activation of Adenosine monophosphate-activated protein kinase (AMPK) could alleviate MIRI by regulating GTPase dynamin-related protein 1 (Drp1)-mediated mitochondrial dynamics. Isolated mouse hearts in a Langendorff perfusion system were subjected to ischemia/reperfusion (I/R) treatment, and H9C2 cells were subjected to hypoxia /reoxygenation (H/R) treatment in vitro. The results showed that AICAR, the AMPK activator, could significantly improve the function of left ventricular, decrease arrhythmia incidence and myocardial infarction area of isolated hearts. Meanwhile, AICAR increased superoxide dismutase (SOD) activity and decreased malondialdehyde (MDA) content in myocardial homogenate. Mechanistically, AICAR inhibited the phosphorylation of Drp1 at Ser 616 while enhanced phosphorylation of Drp1 at Ser 637. In addition, AICAR reduced the expression of inflammatory cytokines including TNF-ɑ, IL-6, and IL-1β, as well as mitochondrial fission genes Mff and Fis1, while improved the expression of mitochondrial fusion genes Mfn1 and Mfn2. Similar results were also observed in H9C2 cells. AICAR improved mitochondrial membrane potential (MMP), reduced reactive oxygen species (ROS) production, and inhibited mitochondrial damage. To further prove if Drp1 regulated mitochondrial dynamics mediated AMPK protection effect, the mitochondrial fission inhibitor Mdivi-1 was utilized. We found that Mdivi-1 significantly improved MMP, inhibited ROS production, reduced the expression of TNF-a, IL-6, IL-1β, Fis1, and Mff, and improved the expression of Mfn1 and Mfn2. However, the protection effect of Mdivi-1 was not reversed by AMPK inhibitor Compound C. In conclusion, this study confirmed that activation of AMPK exerted the protective effects on MIRI, which were largely dependent on the inhibition of Drp1-mediated mitochondrial fission.

Project description:RationaleAMPK (AMP-activated protein kinase) is a heterotrimeric protein that plays an important role in energy homeostasis and cardioprotection. Two isoforms of each subunit are expressed in the heart, but the isoform-specific function of AMPK remains unclear.ObjectiveWe sought to determine the role of γ2-AMPK in cardiac stress response using bioengineered cell lines and mouse models containing either isoform of the γ-subunit in the heart.Methods and resultsWe found that γ2 but not γ1 or γ3 subunit translocated into nucleus on AMPK activation. Nuclear accumulation of AMPK complexes containing γ2-subunit phosphorylated and inactivated RNA Pol I (polymerase I)-associated transcription factor TIF-IA at Ser-635, precluding the assembly of transcription initiation complexes for rDNA. The subsequent downregulation of pre-rRNA level led to attenuated endoplasmic reticulum (ER) stress and cell death. Deleting γ2-AMPK led to increases in pre-rRNA level, ER stress markers, and cell death during glucose deprivation, which could be rescued by inhibition of rRNA processing or ER stress. To study the function of γ2-AMPK in the heart, we generated a mouse model with cardiac-specific deletion of γ2-AMPK (cardiac knockout [cKO]). Although the total AMPK activity was unaltered in cKO hearts because of upregulation of γ1-AMPK, the lack of γ2-AMPK sensitizes the heart to myocardial ischemia/reperfusion injury. The cKO failed to suppress pre-rRNA level during ischemia/reperfusion and showed a greater infarct size. Conversely, cardiac-specific overexpression of γ2-AMPK decreased ribosome biosynthesis and ER stress during ischemia/reperfusion insult, and the infarct size was reduced.ConclusionsThe γ2-AMPK translocates into the nucleus to suppress pre-rRNA transcription and ribosome biosynthesis during stress, thus ameliorating ER stress and cell death. Increased γ2-AMPK activity is required to protect against ischemia/reperfusion injury. Our study reveals an isoform-specific function of γ2-AMPK in modulating ribosome biosynthesis, cell survival, and cardioprotection.

Project description:BackgroundReperfusion of ischemic tissue has adverse impact on the myocardium. Dexmedetomidine (Dex) is a α2-adrenergic receptor (α2-AR) agonist with sedative and analgesic effects. Macrophage migration inhibition factor (MIF) is a pressure-regulating cytokine and is responsible for inflammatory and immune diseases. This study aims to reveal the consequences of Dex on myocardial ischemia-reperfusion injury (IRI) in young mice.MethodsFifty mice were raised and examined. At the end of the experiment, all mice were euthanized. The anterior descending department of the left coronary artery in mice was under ischemia for 60 min, then the ligation line was released and reperfused for 120 min to establish the IRI model. Mice were randomly divided into Sham, control, treatment using 4,5-dihydro-3-(4-hydroxyphenyl)-5-isoxazoleacetic acid (ISO-1), Dex treatment, and Dex combined ISO-1 treatment groups. Interleukin (IL)-6, IL-10 and tumor necrosis factor (TNF-α) were determined by enzyme-linked immunosorbent assay (ELISA). Reactive oxygen species (ROS) and ATP levels were recorded. The expressions of MIF, P-adenosine monophosphate-activated kinase α (AMPKα), glucose transporter (GLUT)4, Bax and Bcl-2 were detected by Western Blot (WB). Hematoxylin and Eosin (H&E) staining was used to study cell morphology. Apoptosis was detected by terminal deoxynucleotidyl transferase dUTP nick end labelling (TUNEL) assay. Echocardiography was carried out at the end of reperfusion, and the infarct size was calculated by Electron microscopy.ResultsI/R + Dex group showed significantly increased IL-6 and TNF-α levels and reduced myocardial cell necrosis and apoptosis. H&E staining showed alleviated myocardial disorder, myocardial cell swelling, myocardial fiber fracture, and inflammatory cell infiltration in I/R + Dex group. Myocardial cell necrosis and apoptosis were significantly reduced in I/R + Dex group. ATP level in myocardial tissue of mice in I/R group was substantially decreased, while that in Dex group was increased. WB results showed that MIF, P-AMPK α, GLUT4 and Bcl-2 levels were increased and Bax levels were decreased in I/R + Dex group.ConclusionDex may exert myocardial protection in young mice through MIF/AMPK/GLUT4 axis.

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AMPK is critical for mitochondrial function during reperfusion after myocardial ischemia.

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AMPK is critical for mitochondrial function during reperfusion after myocardial ischemia.

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