Impact of electrical defibrillation on infarct size and no-reflow in pigs subjected to myocardial ischemia-reperfusion without and with ischemic conditioning

Ventricular fibrillation (VF) occurs frequently during myocardial ischemia-reperfusion (I/R) and must then be terminated by electrical defibrillation. We have investigated the impact of VF/defibrillation on infarct size (IS) or area of no reflow (NR) without and with ischemic conditioning interventions. Anesthetized pigs were subjected to 60/180 min of coronary occlusion/reperfusion. VF, as identified from the ECG, was terminated by intrathoracic defibrillation. The area at risk (AAR), IS, and NR were determined by staining techniques (patent blue, triphenyltetrazolium chloride, and thioflavin-S). Four experimental protocols were analyzed: I/R ( n = 49), I/R with ischemic preconditioning (IPC; n = 22), I/R with ischemic postconditioning (POCO; n = 22), or I/R with remote IPC (RIPC; n = 34). The incidence of VF was not different between I/R (44%), IPC (45%), POCO (50%), and RIPC (33%). IS was reduced by IPC (23 ± 12% of AAR), POCO (31 ± 16%), and RIPC (22 ± 13%, all P < 0.05 vs. I/R: 41 ± 12%). NR was not different between protocols (I/R: 17 ± 15% of AAR, IPC: 15 ± 18%, POCO: 25 ± 16%, and RIPC: 18 ± 17%). In pigs with defibrillation, IS was 50% larger than in pigs without defibrillation but independent of the number of defibrillations. Analysis of covariance confirmed the established determinants of IS, i.e., AAR, residual blood flow during ischemia (RMBFi), and a conditioning protocol, and revealed VF/defibrillation as a novel covariate. VF/defibrillation in turn was associated with larger AAR and lower RMBFi. Lack of dose-response relation between IS and the number of defibrillations excluded direct electrical injury as the cause of increased IS. Obviously, AAR size and RMBFi account for both IS and the incidence of VF. IS and NR are mechanistically distinct phenomena. NEW & NOTEWORTHY Ventricular fibrillation/defibrillation is associated with increased infarct size. Electrical injury is unlikely the cause of such association, since there is no dose-response relation between infarct size and number of defibrillations. Ventricular fibrillation, in turn, is associated with a larger area at risk and lower residual blood flow.

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Metoprolol blunts the time-dependent progression of infarct size

Basic Research in Cardiology ◽

10.1007/s00395-020-0812-4 ◽

2020 ◽

Vol 115 (5) ◽

Cited By ~ 3

Author(s):

Manuel Lobo-Gonzalez ◽

Carlos Galán-Arriola ◽

Xavier Rossello ◽

Maribel González‐Del‐Hoyo ◽

Jean Paul Vilchez ◽

...

Keyword(s):

Infarct Size ◽

Ischemia Reperfusion Injury ◽

Ischemia Reperfusion ◽

Coronary Artery Occlusion ◽

Primary Angioplasty ◽

Primary Outcome Measure ◽

Artery Occlusion ◽

Area At Risk ◽

Perfusion Computed Tomography ◽

Myocardial Ischemia Reperfusion

Abstract Early metoprolol administration protects against myocardial ischemia–reperfusion injury, but its effect on infarct size progression (ischemic injury) is unknown. Eight groups of pigs (total n = 122) underwent coronary artery occlusion of varying duration (20, 25, 30, 35, 40, 45, 50, or 60 min) followed by reperfusion. In each group, pigs were randomized to i.v. metoprolol (0.75 mg/kg) or vehicle (saline) 20 min after ischemia onset. The primary outcome measure was infarct size (IS) on day7 cardiac magnetic resonance (CMR) normalized to area at risk (AAR, measured by perfusion computed tomography [CT] during ischemia). Metoprolol treatment reduced overall mortality (10% vs 26%, p = 0.03) and the incidence and number of primary ventricular fibrillations during infarct induction. In controls, IS after 20-min ischemia was ≈ 5% of the area AAR. Thereafter, IS progressed exponentially, occupying almost all the AAR after 35 min of ischemia. Metoprolol injection significantly reduced the slope of IS progression (p = 0.004 for final IS). Head-to-head comparison (metoprolol treated vs vehicle treated) showed statistically significant reductions in IS at 30, 35, 40, and 50-min reperfusion. At 60-min reperfusion, IS was 100% of AAR in both groups. Despite more prolonged ischemia, metoprolol-treated pigs reperfused at 50 min had smaller infarcts than control pigs undergoing ischemia for 40 or 45 min and similar-sized infarcts to those undergoing 35-min ischemia. Day-45 LVEF was higher in metoprolol-treated vs vehicle-treated pigs (41.6% vs 36.5%, p = 0.008). In summary, metoprolol administration early during ischemia attenuates IS progression and reduces the incidence of primary ventricular fibrillation. These data identify metoprolol as an intervention ideally suited to the treatment of STEMI patients identified early in the course of infarction and requiring long transport times before primary angioplasty.

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Long-term infusion of Met5-enkephalin fails to protect murine hearts against ischemia-reperfusion injury

AJP Heart and Circulatory Physiology ◽

10.1152/ajpheart.00257.2004 ◽

2005 ◽

Vol 288 (4) ◽

pp. H1717-H1723 ◽

Cited By ~ 6

Author(s):

Koh Kuzume ◽

Kazuyo Kuzume ◽

Zhiping Cao ◽

Lijuan Liu ◽

Donna M. Van Winkle

Keyword(s):

Myocardial Ischemia ◽

Infarct Size ◽

Ischemia Reperfusion Injury ◽

Ischemia Reperfusion ◽

Opioid Peptide ◽

Area At Risk ◽

Regional Myocardial Ischemia ◽

Chronic Infusion ◽

Myocardial Ischemia Reperfusion

Recently, we reported that exogenous administration of Met5-enkephalin (ME) for 24 h reduces infarct size after ischemia-reperfusion in rabbits. In the present study, we tested whether ME-induced cardioprotection is exhibited in murine hearts and whether chronic infusion of this peptide can render hearts tolerant to ischemia. Barbiturate-anesthetized open-chest mice (C57BL/6J) were subjected to regional myocardial ischemia-reperfusion (45 min of occlusion and 20 min of reperfusion). Mice received saline vehicle or ME for 24 h or 2 wk before undergoing regional myocardial ischemia-reperfusion or for 24 h followed by a 24-h delay before regional myocardial ischemia-reperfusion. Infarct size was measured with propidium iodide and is expressed as a percentage of the area at risk. Infarcts were smaller after infusion of ME for 24 h than with vehicle control: 49.2 ± 9.0% vs. 22.2 ± 3.2% ( P < 0.01). In contrast, administration of ME for 2 wk failed to elicit cardioprotection: 36.5 ± 9.1% and 41.4 ± 8.2% for control and ME, respectively ( P = not significant). When a 24-h delay was imposed between the end of drug treatment and the onset of the ischemic insult, cardioprotection was lost: 38.5 ± 6.1% and 42.8 ± 6.6% for control and ME, respectively ( P = not significant). Chronic sustained exogenous infusion of the endogenously produced opioid peptide ME is associated with loss of the cardioprotection that is observed with 24 h of infusion. Furthermore, in this in vivo murine model, ME failed to induce delayed tolerance to myocardial ischemia-reperfusion.

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Coronary endothelial P-selectin in pathogenesis of myocardial ischemia-reperfusion injury

AJP Heart and Circulatory Physiology ◽

10.1152/ajpheart.1998.275.5.h1865 ◽

1998 ◽

Vol 275 (5) ◽

pp. H1865-H1872 ◽

Cited By ~ 19

Author(s):

Anthony J. Palazzo ◽

Steven P. Jones ◽

Donald C. Anderson ◽

D. Neil Granger ◽

David J. Lefer

Keyword(s):

Myocardial Ischemia ◽

Infarct Size ◽

Ischemia Reperfusion Injury ◽

Myocardial Infarct ◽

Ischemia Reperfusion ◽

Myocardial Infarct Size ◽

Wild Type ◽

Area At Risk ◽

Myocardial Ischemia Reperfusion

We investigated in vivo coronary P-selectin expression and its pathophysiological consequences in a murine model of myocardial ischemia-reperfusion (MI/R) using wild-type and P-selectin deficient (−/−) mice. Coronary P-selectin expression [μg monoclonal antibody (MAb)/g tissue] was measured using a radiolabeled MAb method after 30 min of myocardial ischemia and 20 min of reperfusion. P-selectin expression in wild-type mice was significantly ( P< 0.01) elevated in the ischemic zone (0.070 ± 0.010) compared with the nonischemic zone (0.037 ± 0.008). Myocardial P-selectin expression was nearly undetectable in P-selectin −/− mice after MI/R. Furthermore, myocardial infarct size (% of area at risk) after 30 min of myocardial ischemia and 120 min of reperfusion was 42.5 ± 4.4 in wild-type mice and 24.4 ± 4.0 in P-selectin −/− mice ( P < 0.05). In additional experiments of prolonged myocardial ischemia (60 min) and reperfusion (120 min), myocardial infarct size was similar in P-selectin −/− mice and wild-type mice. Our results clearly demonstrate the involvement of coronary P-selectin in the development of myocardial infarction after MI/R.

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Adrenomedullin gene delivery attenuates myocardial infarction and apoptosis after ischemia and reperfusion

AJP Heart and Circulatory Physiology ◽

10.1152/ajpheart.00270.2003 ◽

2003 ◽

Vol 285 (4) ◽

pp. H1506-H1514 ◽

Cited By ~ 83

Author(s):

Kazuo Kato ◽

Hang Yin ◽

Jun Agata ◽

Hideaki Yoshida ◽

Lee Chao ◽

...

Keyword(s):

Myocardial Infarction ◽

Gene Transfer ◽

Gene Delivery ◽

Infarct Size ◽

P38 Mapk ◽

Ischemia Reperfusion ◽

Terminal Deoxynucleotidyl Transferase ◽

Area At Risk ◽

Calcitonin Gene ◽

Myocardial Ischemia Reperfusion

Adrenomedullin (AM) has been shown to protect against cardiac remodeling. In this study, we investigated the potential role of AM in myocardial ischemia-reperfusion (I/R) injury through adenovirus-mediated gene delivery. One week after AM gene delivery, rats were subjected to 30-min coronary occlusion, followed by 2-h reperfusion. AM gene transfer significantly reduced the ratio of infarct size to ischemic area at risk and the occurrence of sustained ventricular fibrillation compared with control rats. AM gene delivery also attenuated apoptosis, assessed by both terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling assay and DNA laddering. The effect of AM gene transfer on infarct size, arrhythmia, and apoptosis was abolished by an AM antagonist, calcitonin gene-related peptide [CGRP(8–37)]. Expression of human AM significantly increased cardiac cGMP levels and reduced superoxide production, superoxide density, NAD(P)H oxidase activity, p38 MAPK activation, and Bax levels. Moreover, AM increased Akt and Bad phosphorylation and Bcl-2 levels, but decreased caspase-3 activation. These results indicate that AM protects against myocardial infarction, arrhythmia, and apoptosis in I/R injury via suppression of oxidative stress-induced Bax and p38 MAPK phosphorylation and activation of the Akt-Bad-Bcl-2 signaling pathway. Successful application of this technology may have a protective effect in coronary artery diseases.

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Abstract 843: Cardiomyocyte Overexpression of the Hydrogen Sulfide Producing Enzyme Cystathioine gamma-Lyase Attenuates Myocardial Ischemia-Reperfusion Injury

Circulation ◽

10.1161/circ.116.suppl_16.ii_164 ◽

2007 ◽

Vol 116 (suppl_16) ◽

Author(s):

John W Elrod ◽

John W Calvert ◽

Chi-Wing Chow ◽

Joanna Morrison ◽

Jeannette E Doeller ◽

...

Keyword(s):

Hydrogen Sulfide ◽

Infarct Size ◽

Ischemia Reperfusion Injury ◽

Ischemia Reperfusion ◽

Fold Increase ◽

Area At Risk ◽

Physiological Processes ◽

Myocardial Ischemia Reperfusion Injury ◽

Myocardial Ischemia Reperfusion

Background : Hydrogen sulfide (H 2 S) was recently discovered to be an endogenously produced gaseous second messenger capable of modulating many physiological processes. We have previously demonstrated that administration of a H 2 S donor limits the extent of myocardial infarction. This prompted us to investigate the potential of endogenously generated H 2 S in acute cardioprotection utilizing mice with transgenic overexpression of an H 2 S producing enzyme. Methods: Mice with cardiac-specific overexpression of murine cystathionine γ-lyase (αMHC-CGL-Tg) were generated and analyzed for increased enzyme expression and H 2 S production utilizing a H 2 S specific polarographic electrode. αMHC-CGL-Tg and WT mice were then subjected to 45 min of in vivo LCA ischemia and 72 hr reperfusion and infarct size was evaluated using TTC staining. Results: αMHC-CGL-Tg mice displayed an increased level of myocardial CGL RNA, which translated into a (15 fold) increase in protein expression. This increase in CGL enzyme resulted in a significant (2 fold) increase in H 2 S production by myocardial homogenates of αMHC-CGL-Tg mice. αMHC-CGL-Tg mice were found to have a 47% reduction in infarct size per area-at-risk (INF/AAR) as compared to WT littermates. AAR was similar between both groups. Conclusions: This is the first evidence that overexpression of a H 2 S producing enzyme can decrease infarct size following MI-R injury. These findings demonstrate that modulation of endogenous H 2 S production may be of clinical benefit in ischemic disorders and that H 2 S generating enzymes may be viable therapeutic targets.

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Abstract 553: In Vivo Cardioprotection by Postconditioning is Mediated by Endogenous PAR2 Activation

Circulation ◽

10.1161/circ.116.suppl_16.ii_99 ◽

2007 ◽

Vol 116 (suppl_16) ◽

Author(s):

Rong Jiang ◽

Jeremiah Deneve ◽

Shady Eldaif ◽

Ning-Ping Wang ◽

Zhi-Qing Zhao ◽

...

Keyword(s):

Infarct Size ◽

Ex Vivo ◽

Ischemia Reperfusion ◽

List Type ◽

Area At Risk ◽

General Activation ◽

Sparing Effect ◽

Myocardial Ischemia Reperfusion ◽

Protease Activated Receptor 2

Background : Protease activated receptor 2 (PAR2) is a member of the seven transmembrane G-protein coupled receptor (GPCR) family. Activation of PAR2 is cardioprotective in ex vivo and in vivo myocardial ischemia reperfusion model, potentially by cognate ligands released at reperfusion (R). Postconditioning (postcon), defined as alternating brief (seconds) episodes of R and ischemia applied at the onset of R , is also cardioprotective. This cardioprotection involves activation of GPCR by adenosine, bradykinin and opioids. However, the role of the GPCR PAR2 in cardioprotection by postcon has not been investigated. Hypothesis : This study tested the hypothesis that cardioprotection by postcon is mediated in part by endogenous PAR2 activation. Methods : Rats were randomly assigned to one of 5 groups with 30 min left coronary artery (LCA) occlusion followed by 3 h reperfusion: Control: no intervention was applied either before or after LCA occlusion (n =8); Postcon alone: 3 cycles of 10-s full reperfusion and 10-s re-occlusion were initiated at the onset of R (n=8); PAR2 antagonist alone: the selective PAR2 antagonist (FSLLRY-NH2, 1 mg/Kg) was injected 5 min before R (n=8); PAR2 antagonist + Postcon: PAR2 antagonist (1 mg/Kg) was administered 5 min before Postcon (n=8); Delayed PAR2 antagonist: PAR2 antagonist (1 mg/Kg) was given 5 min after the postcon protocol (n=8). Results: Area at risk (AAR) was comparable in all groups (35–38%). Compared to control, infarct size (TTC, area of necrosis/AAR, %) was significantly reduced by postcon alone (39.0% ± 1.3% vs 53.7% ± 1.5%, P<0.05). The PAR2 antagonist alone administered just before R had no effect on infarct size (57.4% ± 2.4% vs 53.7% ± 1.5%). Interestingly, the infarct sparing effect of postcon was completely reversed by PAR2 antagonist administered before postcon to control values ( 56.7% ± 2.7% *). Furthermore, the infarct sparing effect of postcon was also blocked by PAR2 antagonist given after postcon (50.3% ± 3.3% *). These results suggest that endogenous PAR2 activation induced by postcon during the early moments of R is cardioprotective. Conclusions : Cardioprotection by postcon is mediated, in part, by activation of endogenous PAR2, and suggests a general activation of GPCR. *P<0.05 vs Postcon.

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Abstract 1098: Effect of Hypercholesterolemia on Myocardial Necrosis and Apoptosis in Response to Ischemia Reperfusion Injury

Circulation ◽

10.1161/circ.118.suppl_18.s_646-a ◽

2008 ◽

Vol 118 (suppl_18) ◽

Author(s):

Robert M Osipov ◽

Cesario Bianchi ◽

Jun Feng ◽

Yuhong Liu ◽

Richard T Clements ◽

...

Keyword(s):

Infarct Size ◽

Myocardial Function ◽

Ischemia Reperfusion Injury ◽

Ischemia Reperfusion ◽

Myocardial Necrosis ◽

Tunel Staining ◽

Area At Risk ◽

Survival Pathway ◽

Myocardial Ischemia Reperfusion ◽

Apoptosis Inducing Factor

OBJECTIVE: Myocardial ischemia-reperfusion(I/R) injury often results in necrosis and apoptosis and may lead to cardiac dysfunction or death. This study investigates impact of hypercholesterolemia in the setting of I/R injury on myocardium. METHODS: The mid-left anterior descending coronary artery in normocholesterolemic (NCn=7) and hypercholesterolemic (HCn=7) Yucatan males were occluded for 60 min, followed by reperfusion for 120 min. Hemodynamic values were recorded. Monastryl blue/TTC staining was utilized to assess the area-at-risk (AAR) and necrosis. The expression of Bcl2, apoptosis inducing factor (AIF), total & cleaved caspase3, total & cleaved PARP, bad, BNIP3, Akt and phospho-Akt measured. The TUNEL staining utilized to assess the magnitude of apoptosis. RESULTS: Hemodynamic values of MAP (p<0.01), DLVP (p<0.01), +dP/pt (p<0.01), and −dP/pt (p<0.01) were increased 1.2 fold in HC. In HC longitudinal and horizontal segmental shortening in the AAR decreased by 49% vs. 26% (p<0.01) and 68% vs. 48% (p<0.01) at the end. The AAR was similar in both groups (36% vs. 34%, p=0.61) whereas infarct size increased 45% in HC (42% vs. 61%, p=0.01). The expression of anti-apoptotic Bcl2 decreased 2.3-fold (p<0.01) whereas pro-apoptotic PARP and BNIP3 increased 2.8-fold (p<0.01) and 1.9 fold (p<0.01) respectively in HC. Ischemia decreased Akt expression 1.6-folds (p<0.01) and phospho-Akt 1.5 fold (p<0.01) in HC, whereas increased phospho-Akt 1.9 fold (p<0.01) in NC. In HC the TUNEL+ cells increased 3.8 fold (p=0.03) in the AAR. CONCLUSIONS: This study demonstrated that hypercholesterolemia have positive ionotropic effect on myocardial function, increase infarct size in AAR, mediate pro-apoptosis and attenuate survival pathway after I/R injury.

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Abstract 350: Toll-like Receptor 2 Activation, Especially In Circulating Leukocytes, Mediates Myocardial Ischemia/Reperfusion Injury In Mice

Circulation ◽

10.1161/circ.118.suppl_18.s_288 ◽

2008 ◽

Vol 118 (suppl_18) ◽

Author(s):

Fatih Arslan ◽

Gerard Pasterkamp ◽

Leo Timmers ◽

Ben van Middelaar ◽

Pieter A Doevendans ◽

...

Keyword(s):

At Risk ◽

Myocardial Ischemia ◽

Infarct Size ◽

Ischemia Reperfusion ◽

Myocardial Damage ◽

Blue Dye ◽

Tlr2 Expression ◽

Area At Risk ◽

Saline Treatment ◽

Myocardial Ischemia Reperfusion

OBJECTIVES. Myocardial ischemia/reperfusion (MI/R) injury is characterized by an inflammatory response through NF-κB, increase of infarct size and worsening of cardiac function. Toll-like receptors (TLRs) are part of innate immunity and initiate the same inflammatory reaction. Here we studied in vivo to what extent TLR2 is involved in myocardial damage and what the relative contribution is of TLR2 expression in parenchymal cells and leukocytes to myocardial damage during MI/R in mice. METHODS. C57Bl6J mice underwent 30 minutes ischemia - 24 hours of reperfusion. Four experimental groups were studied: TLR2 knock-out (TLR2 KO) mice (n=10), saline treated wild-type (WT) mice (n=10), generated chimeric WT mice with TLR2 KO bone marrow (BLOOD KO; n=7) and chimeric TLR2 KO mice with WT hematopoietic cells (ORGAN KO; n=7). Saline was administered via the tail vein 5 minutes prior to reperfusion. After 24 hours, the LCA was ligated again at the level marked by the suture left in place. Mice were terminated and infarct size (IS) was measured as a percentage of the area at risk (AAR) using 4% Evans’ blue dye injection in the aortic root and triphenyltetrazolium chloride (TTC) staining (fig. 1). Data are presented as Mean±SEM. RESULTS. The AAR as percentage of the left ventricle was similar between groups: TLR2 KO 41%, saline 41%, Blood KO 41%, Organ KO 42%. Saline treatment resulted in 34.5%±3.3 of infarction, whereas in TLR2 KO mice infarct size decreased to 23.0%±2.9 (p=0.029 vs. saline). Infarct size in BLOOD KO mice was 22.9%±2.7 (p=0.024 vs. saline), while ORGAN KO mice had 33.9%±3.2 (p=0.998 vs. saline) of infarction within the area at risk (fig. 2). CONCLUSION. TLR2 deficiency significantly reduces infarct size with ~33% compared to saline treatment in mice after 30 minutes of ischemia and 24 hours of reperfusion. We show for the first time that TLR2 expression in circulating leukocytes plays an important role in infarction after MI/R injury. Systemic inhibition of TLR2 may be a potential therapeutic target in the treatment of patients with acute myocardial infarction.

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Abstract 289: Cardiac-Specific Ectonucleoside Triphosphate Diphosphohydrolase 1 Overexpression Affords Protection from Myocardial Infarction and Reperfusion Injury

Circulation Research ◽

10.1161/res.111.suppl_1.a289 ◽

2012 ◽

Vol 111 (suppl_1) ◽

Author(s):

Zhaobin Xu ◽

Debra G Wheeler ◽

Shouvik D Mahamud ◽

Karen M Dwyer ◽

Simon C Robson ◽

...

Keyword(s):

Myocardial Ischemia ◽

Infarct Size ◽

Reperfusion Injury ◽

Ischemia Reperfusion Injury ◽

Myocardial Infarct ◽

Ischemia Reperfusion ◽

Myocardial Infarct Size ◽

Area At Risk ◽

Tetrazolium Chloride ◽

Myocardial Ischemia Reperfusion

Background: During myocardial stress, extracellular levels of adenosine triphosphate (ATP) and adenosine diphosphate (ADP) increase. These extracellular ATP and ADP levels are modulated via hydrolysis by ectonucleoside triphosphate diphosphohydrolase 1 (ENTDP-1/CD39) to adenosine monophosphate (AMP) subsequently converted by ecto-5'-nucleotidase (CD73) to the anti-thrombotic, cardioprotective nucleoside, adenosine. Previous data demonstrated significantly smaller infarcts in mice globally overexpressing CD39. The current objective was to determine whether tissue specific overexpression of CD39 in the heart would reduce myocardial ischemia/reperfusion injury. Methods: Myocardial ischemia/reperfusion (I/R) injury was evaluated in transgenic mice overexpressing human CD39 driven by the α-MHC promoter. I/R injury was induced by ligation of the left anterior descending (LAD) artery for 60 min followed by 24 hours of reperfusion. Myocardial infarct size was determined by staining with triphenyl tetrazolium chloride (TTC) and the area-at-risk was delineated by perfusion with 5% Phthalo Blue. Results: Expression of CD39 in the heart tissue was confirmed by Western blot analysis. In response to 60 minutes of ischemia followed by 24 hours of reperfusion, α-MHC CD39-OE animals displayed a marked reduction in infarct size (WT: 31.68%±4.64 vs TG: 6.14%± 2.48, N=5/group, P<0.01), relative to wild-type controls (Figure). Conclusions: Overexpression of CD39 in cardiac tissue alone significantly attenuates myocardial ischemic injury.

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Abstract 446: Activation of γ2-ampk Suppresses Ribosome Biogenesis and Protects Against Myocardial Ischemia-reperfusion Injury

Circulation Research ◽

10.1161/res.121.suppl_1.446 ◽

2017 ◽

Vol 121 (suppl_1) ◽

Author(s):

Yang Cao ◽

Naveen Bojjireddy ◽

Maengjo Kim ◽

Tao Li ◽

Peiyong Zhai ◽

...

Keyword(s):

Cell Death ◽

Myocardial Ischemia ◽

Infarct Size ◽

Er Stress ◽

Reperfusion Injury ◽

Ischemia Reperfusion ◽

Glucose Deprivation ◽

Area At Risk ◽

Stress Markers ◽

Myocardial Ischemia Reperfusion

AMP-activated protein kinase (AMPK) is a heterotrimeric protein that senses cellular energy status and maintains energy homeostasis by switching off biosynthetic pathways and increasing catabolism. The subcellular localization of AMPK has been shown to affect its activation and function. The γ2 subunit has both nuclear localization sequence and nuclear export sequence suggesting that it can shuttle between the two compartments. By overexpressing GFP-tagged γ subunits in COS7 cells followed by glucose deprivation or AMPK activation (A769662), we demonstrated that AMPK containing γ2 but not γ1 or γ3 subunit translocates into nucleus. Nuclear accumulation of AMPK complexes containing γ2-subunit phosphorylates and inactivates Pol I-associated transcription factor TIF-IA at Ser-635, precluding the assembly of transcription initiation complexes and lowering preribosomal RNA (pre-rRNA) level. Down-regulation of rRNA synthesis attenuated expression of ER stress markers (spliced X-box binding protein-1 and C/EBP homologous protein) and ER stress-induced cell death. Deleting γ2-AMPK using CRISPR-Cas9 system led to increases in pre-rRNA level, ER stress markers and cell death during glucose deprivation. To study the function of γ2-AMPK in the heart, we generated a mouse model with cardiac specific deletion of γ2-AMPK (cKO). Although the total AMPK activity was unaltered in cKO hearts due to upregulation of γ1-AMPK the lack of γ2-AMPK sensitizes the heart to myocardial ischemia-reperfusion (I/R, 30min ischemia followed by 24hr reperfusion) injury as evidenced by larger infarct size (Infarct size/area at risk: 34.7±5.7% vs. 50.6±8.9%, for control and cKO respectively, P<0.05). The cKO failed to suppress pre-rRNA level during I/R and showed higher levels of ER stress markers. Conversely, cardiac-specific overexpression (OE) of γ2-AMPK decreased ER stress markers and pre-rRNA level upon I/R injury and the infarct size was reduced (Infarct size/area at risk: 26.8±6.5% for control vs. 15.8±3.7% for OE, P<0.05), suggesting that γ2-AMPK protects against I/R injury and ER stress in the heart. Taken together, our study reveals isoform-specific functions of γ2-AMPK in modulating protein synthesis, cell survival and cardioprotection.

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