MicroRNA therapy stimulates uncontrolled cardiac repair after myocardial infarction in pigs.

Prompt coronary catheterization and revascularization have markedly improved the outcomes of myocardial infarction, but have also resulted in a growing number of surviving patients with permanent structural damage of the heart, which frequently leads to heart failure. There is an unmet clinical need for treatments for this condition1, particularly given the inability of cardiomyocytes to replicate and thereby regenerate the lost contractile tissue2. Here we show that expression of human microRNA-199a in infarcted pig hearts can stimulate cardiac repair. One month after myocardial infarction and delivery of this microRNA through an adeno-associated viral vector, treated animals showed marked improvements in both global and regional contractility, increased muscle mass and reduced scar size. These functional and morphological findings correlated with cardiomyocyte de-differentiation and proliferation. However, subsequent persistent and uncontrolled expression of the microRNA resulted in sudden arrhythmic death of most of the treated pigs. Such events were concurrent with myocardial infiltration of proliferating cells displaying a poorly differentiated myoblastic phenotype. These results show that achieving cardiac repair through the stimulation of endogenous cardiomyocyte proliferation is attainable in large mammals, however dosage of this therapy needs to be tightly controlled.

Extracellular vesicle-mediated bidirectional communication between heart and other organs.

In recent years, a wealth of studies has identified various molecular species released by cardiac muscle under physiological and pathological conditions that exert local paracrine and/or remote endocrine effects. Conversely, humoral factors, principally produced by organs such as skeletal muscle, kidney, or adipose tissue, may affect the function and metabolism of normal and diseased hearts. Although this cross communication within cardiac tissue and between the heart and other organs is supported by mounting evidence, research on the role of molecular mediators carried by exosomes, microvesicles, and apoptotic bodies, collectively defined as extracellular vesicles (EVs), is at an early stage of investigation. Once released in the circulation, EVs can potentially reach any organ where they transfer their cargo of proteins, lipids, and nucleic acids that exert potent biological effects on recipient cells. Although there are a few cases where such signaling was clearly demonstrated, the results from many other studies can only be tentatively inferred based on indirect evidence obtained by infusing exogenous EVs in experimental animals or by adding them to cell cultures. This area of research is in rapid expansion and most mechanistic interpretations may change in the near future; hence, the present review on the role played by EV-carried mediators in the two-way communication between heart and skeletal muscle, kidneys, bone marrow, lungs, liver, adipose tissue, and brain is necessarily limited. Nonetheless, the available data are already unveiling new, intriguing, and ample scenarios in cardiac physiology and pathophysiology.

Proteome Dynamics and Bioinformatics Reveal Major Alterations in the Turnover Rate of Functionally Related Cardiac and Plasma Proteins in a Dog Model of Congestive Heart Failure.

Protein pool turnover is a critically important cellular homeostatic component, yet it has been little explored in the context of heart failure (HF) pathophysiology. We used in vivo 2H labeling/proteome dynamics for the nonbiased discovery of turnover alterations involving functionally linked cardiac and plasma proteins in canine tachypacing-induced HF, an established preclinical model of dilated cardiomyopathy. Compared with controls, dogs with congestive HF displayed bidirectional turnover changes of 28 cardiac proteins, that is, a reduced half-life of several key enzymes involved in glycolysis, homocysteine metabolism and glycogenesis, and increased half-life of proteins involved in proteolysis. Changes in plasma proteins were more modest: only 5 proteins, involved in various functions including proteolysis inhibition, hemoglobin, calcium and ferric iron binding, displayed increased or decreased turnover rates. In other dogs undergoing cardiac tachypacing, we infused for 2 weeks the myokine Follistatin-like protein 1, known for its ameliorative effects on HF-induced alterations. Proteome dynamics proved very sensitive in detecting the partial or complete prevention, by Follistatin-like protein 1, of cardiac and plasma protein turnover alterations. In conclusion, our study unveiled, for the first time in a large mammal, numerous HF-related alterations that may serve as the basis for future mechanistic research and/or as conceptually new molecular markers.

Creatine deficiency and heart failure.

Impaired cardiac energy metabolism has been proposed as a mechanism common to different heart failure aetiologies. The energy-depletion hypothesis was pursued by several researchers, and is still a topic of considerable interest. Unlike most organs, in the heart, the creatine kinase system represents a major component of the metabolic machinery, as it functions as an energy shuttle between mitochondria and cytosol. In heart failure, the decrease in creatine level anticipates the reduction in adenosine triphosphate, and the degree of myocardial phosphocreatine/adenosine triphosphate ratio reduction correlates with disease severity, contractile dysfunction, and myocardial structural remodelling. However, it remains to be elucidated whether an impairment of phosphocreatine buffer activity contributes to the pathophysiology of heart failure and whether correcting this energy deficit might prove beneficial. The effects of creatine deficiency and the potential utility of creatine supplementation have been investigated in experimental and clinical models, showing controversial findings. The goal of this article is to provide a comprehensive overview on the role of creatine in cardiac energy metabolism, the assessment and clinical value of creatine deficiency in heart failure, and the possible options for the specific metabolic therapy.

Post-mortem CMR in a model of sudden death due to myocardial ischemia: validation with connexin-43.

OBJECTIVES: We sought to evaluate the effectiveness of post-mortem cardiac magnetic resonance (PM-CMR) for the identification of myocardial ischemia as cause of sudden cardiac death (SCD) when the time interval between the onset of ischemia and SCD is ≤ 90 min. METHODS: PM-CMR was performed in 8 hearts explanted from pigs with spontaneous death caused by occlusion of the left anterior descending coronary artery: 4 with SCD after ≤ 40 min of coronary occlusion and 4 between 40 and 90 min. PM-CMR included conventional T1 and T2-weighted image and T1, T2, and T2* mapping techniques. Imaging data were compared and validated with immunohistochemical evaluation of the altered proportion and redistribution of phosphorylated versus non-phosphorylated connexin 43 (CX43 and npCX43, respectively), an established molecular marker of myocardial ischemia. RESULTS: At T2-weighted images, the ischemic core was hypointense (core/remote ratio 0.67 ± 0.11) and surrounded by and hyperintense border zone. Compared to remote myocardium, the ischemic core had higher T1 (p = 0.0008), and lower T2 (p = 0.007) and T2* (p = 0.002). Cytoplasmatic npX43 and the npCX43/CX43 ratio were significantly higher in animals deceased > 40 min than in others. CONCLUSION: PM-CMR can reliably detect early signs of myocardial damage induced by ischemia, based on conventional pulse sequences complemented by a novel ad hoc application of quantitative mapping techniques. KEY POINTS: • Post-mortem MRI may help to understand cause of sudden cardiac death. • Post-mortem MRI allows detection of signs of myocardial ischemia as cause of sudden cardiac death within 90 and 40 min following coronary occlusion as demonstrated in a pig model of myocardial ischemia. • Signs of myocardial ischemia using conventional and mapping MRI technique are associated with the immunohistochemical changes of phosphorylated and dephosphorylated connexin-43 which is an established molecular marker of myocardial ischemia.

Calculation of the Protein Turnover Rate Using the Number of Incorporated 2H Atoms and Proteomics Analysis of a Single Labeled Sample.

Rate constant estimation with heavy water requires a long-term experiment with data collection at multiple time points (3-4 weeks for mitochondrial proteome dynamics in mice and much longer in other species). When tissue proteins are analyzed, this approach requires euthanizing animals at each time point or multiple tissue biopsies in humans. Although short-term protocols are available, they require knowledge of the maximum number of isotope labels (N) and accurate quantification of observed 2H-enrichment in the peptide. The high-resolution accurate mass spectrometers used for proteome dynamics studies are characterized by a systematic spectral error that compromises these measurements. To circumvent these issues, we developed a simple algorithm for the rate constant calculation based on a single labeled sample and comparable unlabeled (time 0) sample. The algorithm determines N for all proteogenic amino acids from a long-term experiment to calculate the predicted plateau 2H-labeling of peptides for a short-term protocol and estimates the rate constant based on the measured baseline and the predicted plateau 2H-labeling of peptides. The method was validated based on the rate constant estimation in a long-term experiment in mice and dogs. The improved 2 time-point method enables the rate constant calculation with less than 10% relative error compared to the bench-marked multi-point method in mice and dogs and allows us to detect diet-induced subtle changes in ApoAI turnover in mice. In conclusion, we have developed and validated a new algorithm for protein rate constant calculation based on 2-time point measurements that could also be applied to other biomolecules.

Guidelines for experimental models of myocardial ischemia and infarction.

Myocardial infarction is a prevalent major cardiovascular event that arises from myocardial ischemia with or without reperfusion, and basic and translational research is needed to better understand its underlying mechanisms and consequences for cardiac structure and function. Ischemia underlies a broad range of clinical scenarios ranging from angina to hibernation to permanent occlusion, and while reperfusion is mandatory for salvage from ischemic injury, reperfusion also inflicts injury on its own. In this consensus statement, we present recommendations for animal models of myocardial ischemia and infarction. With increasing awareness of the need for rigor and reproducibility in designing and performing scientific research to ensure validation of results, the goal of this review is to provide best practice information regarding myocardial ischemia-reperfusion and infarction models. Listen to this article's corresponding podcast at ajpheart.podbean.com/e/guidelines-for-experimental-models-of-myocardial-ischemia-and-infarction/.

Assessing Cardiac Metabolism: A Scientific Statement From the American Heart Association.

In a complex system of interrelated reactions, the heart converts chemical energy to mechanical energy. Energy transfer is achieved through coordinated activation of enzymes, ion channels, and contractile elements, as well as structural and membrane proteins. The heart's needs for energy are difficult to overestimate. At a time when the cardiovascular research community is discovering a plethora of new molecular methods to assess cardiac metabolism, the methods remain scattered in the literature. The present statement on "Assessing Cardiac Metabolism" seeks to provide a collective and curated resource on methods and models used to investigate established and emerging aspects of cardiac metabolism. Some of those methods are refinements of classic biochemical tools, whereas most others are recent additions from the powerful tools of molecular biology. The aim of this statement is to be useful to many and to do justice to a dynamic field of great complexity.

Gene Therapy for Heart Failure: New Perspectives.

PURPOSE OF REVIEW: The current knowledge of pathophysiological and molecular mechanisms responsible for the genesis and development of heart failure (HF) is absolutely vast. Nonetheless, the hiatus between experimental findings and therapeutic options remains too deep, while the available pharmacological treatments are mostly seasoned and display limited efficacy. The necessity to identify new, non-pharmacological strategies to target molecular alterations led investigators, already many years ago, to propose gene therapy for HF. Here, we will review some of the strategies proposed over the past years to target major pathogenic mechanisms/factors responsible for severe cardiac injury developing into HF and will provide arguments in favor of the necessity to keep alive research on this topic. RECENT FINDINGS: After decades of preclinical research and phases of enthusiasm and disappointment, clinical trials were finally launched in recent years. The first one to reach phase II and testing gene delivery of sarcoendoplasmic reticulum calcium ATPase did not yield encouraging results; however, other trials are ongoing, more efficient viral vectors are being developed, and promising new potential targets have been identified. For instance, recent research is focused on gene repair, in vivo, to treat heritable forms of HF, while strong experimental evidence indicates that specific microRNAs can be delivered to post-ischemic hearts to induce regeneration, a result that was previously thought possible only by using stem cell therapy. Gene therapy for HF is aging, but exciting perspectives are still very open.

Proteomics-based network analysis characterizes biological processes and pathways activated by preconditioned mesenchymal stem cells in cardiac repair mechanisms.

BACKGROUND: We have demonstrated that intramyocardial delivery of human mesenchymal stem cells preconditioned with a hyaluronan mixed ester of butyric and retinoic acid (MSCp+) is more effective in preventing the decay of regional myocardial contractility in a swine model of myocardial infarction (MI). However, the understanding of the role of MSCp+ in proteomic remodeling of cardiac infarcted tissue is not complete. We therefore sought to perform a comprehensive analysis of the proteome of infarct remote (RZ) and border zone (BZ) of pigs treated with MSCp+ or unconditioned stem cells. METHODS: Heart tissues were analyzed by MudPIT and differentially expressed proteins were selected by a label-free approach based on spectral counting. Protein profiles were evaluated by using PPI networks and their topological analysis. RESULTS: The proteomic remodeling was largely prevented in MSCp+ group. Extracellular proteins involved in fibrosis were down-regulated, while energetic pathways were globally up-regulated. Cardioprotectant pathways involved in the production of keto acid metabolites were also activated. Additionally, we found that new hub proteins support the cardioprotective phenotype characterizing the left ventricular BZ treated with MSCp+. In fact, the up-regulation of angiogenic proteins NCL and RAC1 can be explained by the increase of capillary density induced by MSCp+. CONCLUSIONS: Our results show that angiogenic pathways appear to be uniquely positioned to integrate signaling with energetic pathways involving cardiac repair. GENERAL SIGNIFICANCE: Our findings prompt the use of proteomics-based network analysis to optimize new approaches preventing the post-ischemic proteomic remodeling that may underlie the limited self-repair ability of adult heart.

Class I Histone Deacetylase Inhibition for the Treatment of Sustained Atrial Fibrillation.

Current therapies are less effective for treating sustained/permanent versus paroxysmal atrial fibrillation (AF). We and others have previously shown that histone deacetylase (HDAC) inhibition reverses structural and electrical atrial remodeling in mice with inducible, paroxysmal-like AF. Here, we hypothesize an important, specific role for class I HDACs in determining structural atrial alterations during sustained AF. The class I HDAC inhibitor N-acetyldinaline [4-(acetylamino)-N-(2-amino-phenyl) benzamide] (CI-994) was administered for 2 weeks (1 mg/kg/day) to Hopx transgenic mice with atrial remodeling and inducible AF and to dogs with atrial tachypacing-induced sustained AF. Class I HDAC inhibition prevented atrial fibrosis and arrhythmia inducibility in mice. Dogs were divided into three groups: 1) sinus rhythm, 2) sustained AF plus vehicle, and 3) sustained AF plus CI-994. In group 3, the time in AF over 2 weeks was reduced by 30% compared with group 2, along with attenuated atrial fibrosis and intra-atrial adipocyte infiltration. Moreover, group 2 dogs had higher atrial and serum inflammatory cytokines, adipokines, and atrial immune cells and adipocytes compared with groups 1 and 3. On the other hand, groups 2 and 3 displayed similar left atrial size, ventricular function, and mitral regurgitation. Importantly, the same histologic alterations found in dogs with sustained AF and reversed by CI-994 were also present in atrial tissue from transplanted patients with chronic AF. This is the first evidence that, in sustained AF, class I HDAC inhibition can reduce the total time of fibrillation, atrial fibrosis, intra-atrial adipocytes, and immune cell infiltration without significant effects on cardiac function.

Acetylation mediates Cx43 reduction caused by electrical stimulation.

Communication between cardiomyocytes depends upon gap junctions (GJ). Previous studies have demonstrated that electrical stimulation induces GJ remodeling and modifies histone acetylase (HAT) and deacetylase (HDAC) activities, although these two results have not been linked. The aim of this work was to establish whether electrical stimulation modulates GJ-mediated cardiac cell-cell communication by acetylation-dependent mechanisms. Field stimulation of HL-1 cardiomyocytes at 0.5 Hz for 24 h significantly reduced connexin43 (Cx43) expression and cell-cell communication. HDAC activity was down-regulated whereas HAT activity was not modified resulting in increased acetylation of Cx43. Consistent with a post-translational mechanism, we did not observe a reduction in Cx43 mRNA in electrically stimulated cells, while the proteasomal inhibitor MG132 maintained Cx43 expression. Further, the treatment of paced cells with the HAT inhibitor Anacardic Acid maintained both the levels of Cx43 and cell-cell communication. Finally, we observed increased acetylation of Cx43 in the left ventricles of dogs subjected to chronic tachypacing as a model of abnormal ventricular activation. In conclusion, our findings suggest that altered electrical activity can regulate cardiomyocyte communication by influencing the acetylation status of Cx43.

Chronic ß1-adrenergic blockade enhances myocardial ß3-adrenergic coupling with nitric oxide-cGMP signaling in a canine model of chronic volume overload: new insight into mechanisms of cardiac benefit with selective ß1-blocker therapy.

The ß1-adrenergic antagonist metoprolol improves cardiac function in animals and patients with chronic heart failure, isolated mitral regurgitation (MR), and ischemic heart disease, though the molecular mechanisms remain incompletely understood. Metoprolol has been reported to upregulate cardiac expression of ß3-adrenergic receptors (ß3AR) in animal models. Myocardial ß3AR signaling via neuronal nitric oxide synthase (nNOS) activation has recently emerged as a cardioprotective pathway. We tested whether chronic ß1-adrenergic blockade with metoprolol enhances myocardial ß3AR coupling with nitric oxide-stimulated cyclic guanosine monophosphate (ß3AR/NO-cGMP) signaling in the MR-induced, volume-overloaded heart. We compared the expression, distribution, and inducible activation of ß3AR/NO-cGMP signaling proteins within myocardial membrane microdomains in dogs (canines) with surgically induced MR, those also treated with metoprolol succinate (MR+ßB), and unoperated controls. ß3AR mRNA transcripts, normalized to housekeeping gene RPLP1, increased 4.4 × 10(3)- and 3.2 × 10(2)-fold in MR and MR+ßB hearts, respectively, compared to Control. Cardiac ß3AR expression was increased 1.4- and nearly twofold in MR and MR+ßB, respectively, compared to Control. ß3AR was detected within caveolae-enriched lipid rafts (Cav3(+)LR) and heavy density, non-lipid raft membrane (NLR) across all groups. However, in vitro selective ß3AR stimulation with BRL37344 (BRL) triggered cGMP production within only NLR of MR+ßB. BRL induced Ser (1412) phosphorylation of nNOS within NLR of MR+ßB, but not Control or MR, consistent with detection of NLR-specific ß3AR/NO-cGMP coupling. Treatment with metoprolol prevented MR-associated oxidation of NO biosensor soluble guanylyl cyclase (sGC) within NLR. Metoprolol therapy also prevented MR-induced relocalization of sGCß1 subunit away from caveolae, suggesting preserved NO-sGC-cGMP signaling, albeit without coupling to ß3AR, within MR+ßB caveolae. Chronic ß1-blockade is associated with myocardial ß3AR/NO-cGMP coupling in a microdomain-specific fashion. Our canine study suggests that microdomain-targeted enhancement of myocardial ß3AR/NO-cGMP signaling may explain, in part, ß1-adrenergic antagonist-mediated preservation of cardiac function in the volume-overloaded heart.

Cardiac mitochondrial proteome dynamics with heavy water reveals stable rate of mitochondrial protein synthesis in heart failure despite decline in mitochondrial oxidative capacity.

We recently developed a method to measure mitochondrial proteome dynamics with heavy water ((2)H2O)-based metabolic labeling and high resolution mass spectrometry. We reported the half-lives and synthesis rates of several proteins in the two cardiac mitochondrial subpopulations, subsarcolemmal and interfibrillar (SSM and IFM), in Sprague Dawley rats. In the present study, we tested the hypothesis that the mitochondrial protein synthesis rate is reduced in heart failure, with possible differential changes in SSM versus IFM. Six to seven week old male Sprague Dawley rats underwent transverse aortic constriction (TAC) and developed moderate heart failure after 22weeks. Heart failure and sham rats of the same age received heavy water (5% in drinking water) for up to 80days. Cardiac SSM and IFM were isolated from both groups and the proteins were separated by 1D gel electrophoresis. Heart failure reduced protein content and increased the turnover rate of several proteins involved in fatty acid oxidation, electron transport chain and ATP synthesis, while it decreased the turnover of other proteins, including pyruvate dehydrogenase subunit in IFM, but not in SSM. Because of these bidirectional changes, the average overall half-life of proteins was not altered by heart failure in both SSM and IFM. The kinetic measurements of individual mitochondrial proteins presented in this study may contribute to a better understanding of the mechanisms responsible for mitochondrial alterations in the failing heart.

Regional mapping of myocardial hibernation phenotype in idiopathic end-stage dilated cardiomyopathy.

Myocardial hibernation (MH) is a well-known feature of human ischaemic cardiomyopathy (ICM), whereas its presence in human idiopathic dilated cardiomyopathy (DCM) is still controversial. We investigated the histological and molecular features of MH in left ventricle (LV) regions of failing DCM or ICM hearts. We examined failing hearts from DCM (n = 11; 41.9 ± 5.45 years; left ventricle-ejection fraction (LV-EF), 18 ± 3.16%) and ICM patients (n = 12; 58.08 ± 1.7 years; LVEF, 21.5 ± 6.08%) undergoing cardiac transplantation, and normal donor hearts (N, n = 8). LV inter-ventricular septum (IVS) and antero-lateral free wall (FW) were transmurally (i.e. sub-epicardial, mesocardial and sub-endocardial layers) analysed. LV glycogen content was shown to be increased in both DCM and ICM as compared with N hearts (P < 0.001), with a U-shaped transmural distribution (lower values in mesocardium). Capillary density was homogenously reduced in both DCM and ICM as compared with N (P < 0.05 versus N), with a lower decrease independent of the extent of fibrosis in sub-endocardial and sub-epicardial layers of DCM as compared with ICM. HIF1-α and nestin, recognized ischaemic molecular hallmarks, were similarly expressed in DCM-LV and ICM-LV myocardium. The proteomic profile was overlapping by ~50% in DCM and ICM groups. Morphological and molecular features of MH were detected in end-stage ICM as well as in end-stage DCM LV, despite epicardial coronary artery patency and lower fibrosis in DCM hearts. Unravelling the presence of MH in the absence of coronary stenosis may be helpful to design a novel approach in the clinical management of DCM.

Beneficial effects of acute inhibition of the oxidative pentose phosphate pathway in the failing heart.

In vitro studies suggested that glucose metabolism through the oxidative pentose phosphate pathway (oxPPP) can paradoxically feed superoxide-generating enzymes in failing hearts. We therefore tested the hypothesis that acute inhibition of the oxPPP reduces oxidative stress and enhances function and metabolism of the failing heart, in vivo. In 10 chronically instrumented dogs, congestive heart failure (HF) was induced by high-frequency cardiac pacing. Myocardial glucose consumption was enhanced by raising arterial glycemia to levels mimicking postprandial peaks, before and after intravenous administration of the oxPPP inhibitor 6-aminonicotinamide (80 mg/kg). Myocardial energy substrate metabolism was measured with radiolabeled glucose and oleic acid, and cardiac 8-isoprostane output was used as an index of oxidative stress. A group of five chronically instrumented, normal dogs served as control. In HF, raising glycemic levels from ∼ 80 to ∼ 170 mg/dL increased cardiac isoprostane output by approximately twofold, whereas oxPPP inhibition normalized oxidative stress and enhanced cardiac oxygen consumption, glucose oxidation, and stroke work. In normal hearts glucose infusion did not induce significant changes in cardiac oxidative stress. Myocardial tissue concentration of 6P-gluconate, an intermediate metabolite of the oxPPP, was significantly reduced by ∼ 50% in treated versus nontreated failing hearts, supporting the inhibitory effect of 6-aminonicotinamide. Our study indicates an important contribution of the oxPPP activity to cardiac oxidative stress in HF, which is particularly pronounced during common physiological changes such as postprandial glycemic peaks.

Impact of glucose-6-phosphate dehydrogenase deficiency on the pathophysiology of cardiovascular disease.

Glucose-6-phosphate dehydrogenase (G6PD) catalyzes the rate-determining step in the pentose phosphate pathway and produces NADPH to fuel glutathione recycling. G6PD deficiency is the most common enzyme deficiency in humans and affects over 400 million people worldwide; however, its impact on cardiovascular disease is poorly understood. The glutathione pathway is paramount to antioxidant defense, and G6PD-deficient cells do not cope well with oxidative damage. Limited clinical evidence indicates that G6PD deficiency may be associated with hypertension. However, there are also data to support a protective role of G6PD deficiency in decreasing the risk of heart disease and cardiovascular-associated deaths, perhaps through a decrease in cholesterol synthesis. Studies in G6PD-deficient (G6PDX) mice are mixed and provide evidence for both protective and deleterious effects. G6PD deficiency may provide a protective effect through decreasing cholesterol synthesis, superoxide production, and reductive stress. However, recent studies indicate that G6PDX mice are moderately more susceptible to ventricular dilation in response to myocardial infarction or pressure overload-induced heart failure. Furthermore, G6PDX hearts do not recover as well as nondeficient mice when faced with ischemia-reperfusion injury, and G6PDX mice are susceptible to the development of age-associated cardiac hypertrophy. Overall, the limited available data indicate a complex interplay in which adverse effects of G6PD deficiency may outweigh potential protective effects in the face of cardiac stress. Definitive clinical studies in large populations are needed to determine the effects of G6PD deficiency on the development of cardiovascular disease and subsequent outcomes.

Tachycardia-induced metabolic rewiring as a driver of contractile dysfunction.

Prolonged tachycardia-a risk factor for cardiovascular morbidity and mortality-can induce cardiomyopathy in the absence of structural disease in the heart. Here, by leveraging human patient data, a canine model of tachycardia and engineered heart tissue generated from human induced pluripotent stem cells, we show that metabolic rewiring during tachycardia drives contractile dysfunction by promoting tissue hypoxia, elevated glucose utilization and the suppression of oxidative phosphorylation. Mechanistically, a metabolic shift towards anaerobic glycolysis disrupts the redox balance of nicotinamide adenine dinucleotide (NAD), resulting in increased global protein acetylation (and in particular the acetylation of sarcoplasmic/endoplasmic reticulum Ca2+-ATPase), a molecular signature of heart failure. Restoration of NAD redox by NAD+ supplementation reduced sarcoplasmic/endoplasmic reticulum Ca2+-ATPase acetylation and accelerated the functional recovery of the engineered heart tissue after tachycardia. Understanding how metabolic rewiring drives tachycardia-induced cardiomyopathy opens up opportunities for therapeutic intervention.

Acute vagal stimulation attenuates cardiac metabolic response to ß-adrenergic stress.

The effects of vagal stimulation (VS) on cardiac energy substrate metabolism are unknown. We tested the hypothesis that acute VS alters the balance between free fatty acid (FFA) and carbohydrate oxidation and opposes the metabolic effects of ß-adrenergic stimulation. A clinical-type selective stimulator of the vagal efferent fibres was connected to the intact right vagus in chronically instrumented dogs. VS was set to reduce heart rate by 30 beats min(-1), and the confounding effects of bradycardia were then eliminated by pacing the heart at 165 beats min(-1). [(3)H]Oleate and [(14)C]glucose were infused to measure FFA and glucose oxidation. The heart was subjected to ß-adrenergic stress by infusing dobutamine at 5, 10 and 15 µg kg(-1) min(-1) before and during VS. VS did not significantly affect baseline cardiac performance, haemodynamics or myocardial metabolism. However, at peak dobutamine stress, VS attenuated the increase in left ventricular pressure-diameter area from 235.9 ± 72.8 to 167.3 ± 55.8%, and in cardiac oxygen consumption from 173.9 ± 23.3 to 127.89 ± 6.2% (both P < 0.05), and thus mechanical efficiency was not enhanced. The increase in glucose oxidation fell from 289.3 ± 55.5 to 131.1 ± 20.9% (P < 0.05), while FFA oxidation was not increased by ß-adrenergic stress and fell below baseline during VS only at the lowest dose of dobutamine. The functional and in part the metabolic changes were reversed by 0.1 mg kg(-1) atropine i.v. Our data show that acute right VS does not affect baseline cardiac metabolism, but attenuates myocardial oxygen consumption and glucose oxidation in response to adrenergic stress, thus functioning as a cardio-selective antagonist to ß-adrenergic activation.