A PKM2 signature in the failing heart

Tissue-specific regulation of p53 by PKM2 is redox dependent and provides a therapeutic target for anthracycline-induced cardiotoxicity

Chemotherapy-induced cardiotoxicity (CIC) is a common clinical problem that compromises effective anticancer therapies. Many chemotherapeutics (including anthracyclines, such as doxorubicin) induce the proapoptotic transcription factor p53 in the tumor and nonspecifically in the heart, promoting heart failure. Although inhibition of p53 shows benefit in preclinical heart failure models, it would not be an attractive adjuvant therapy for CIC, because it would prevent tumor regression. A p53-targeting therapy that would decrease chemotherapy-induced apoptosis in the myocardium and, at the same time, enhance apoptosis in the tumor would be ideal. Here, we propose that differences in oxygen tension between the myocardium and the tumor could provide a platform for redox-dependent tissue-specific therapies. We show by coimmunoprecipitation and mass spectrometry that the redox-regulated pyruvate kinase muscle 2 (PKM2) directly binds with p53 and that the redox status of cysteine-423 of tetrameric (but not monomeric) PKM2 is critical for the differential regulation of p53 transcriptional activity. Tetrameric PKM2 suppresses p53 transcriptional activity and apoptosis in a high oxidation state but enhances them in a low oxidation one. We show that the oxidation state (along with cysteine-423 oxidation) is higher in the heart compared to the tumor of the same animal. Treatment with TEPP-46 (a compound that stabilizes tetrameric PKM2) suppressed doxorubicin-induced cardiomyocyte apoptosis, preventing cardiac dysfunction, but enhanced cancer cell apoptosis and tumor regression in the same animals in lung cancer models. Thus, our work suggests that redox-dependent differences in common proteins expressed in the myocardium and tumor can be exploited therapeutically for tissue selectivity in CIC.

Biventricular Increases in Mitochondrial Fission Mediator (MiD51) and Proglycolytic Pyruvate Kinase (PKM2) Isoform in Experimental Group 2 Pulmonary Hypertension-Novel Mitochondrial Abnormalities

Introduction: Group 2 pulmonary hypertension (PH), defined as a mean pulmonary arterial pressure ≥25 mmHg with elevated pulmonary capillary wedge pressure >15 mmHg, has no approved therapy and patients often die from right ventricular failure (RVF). Alterations in mitochondrial metabolism, notably impaired glucose oxidation, and increased mitochondrial fission, contribute to right ventricle (RV) dysfunction in PH. We hypothesized that the impairment of RV and left ventricular (LV) function in group 2 PH results in part from a proglycolytic isoform switch from pyruvate kinase muscle (PKM) isoform 1 to 2 and from increased mitochondrial fission, due either to upregulation of expression of dynamin-related protein 1 (Drp1) or its binding partners, mitochondrial dynamics protein of 49 or 51 kDa (MiD49 or 51).

Methods and Results: Group 2 PH was induced by supra-coronary aortic banding (SAB) in 5-week old male Sprague Dawley rats. Four weeks post SAB, echocardiography showed marked reduction of tricuspid annular plane systolic excursion (2.9 ± 0.1 vs. 4.0 ± 0.1 mm) and pulmonary artery acceleration time (24.3 ± 0.9 vs. 35.4 ± 1.8 ms) in SAB vs. sham rats. Nine weeks post SAB, left and right heart catheterization showed significant biventricular increases in end systolic and diastolic pressure in SAB vs. sham rats (LV: 226 ± 15 vs. 103 ± 5 mmHg, 34 ± 5 vs. 7 ± 1 mmHg; RV: 40 ± 4 vs. 22 ± 1 mmHg, and 4.7 ± 1.5 vs. 0.9 ± 0.5 mmHg, respectively). Picrosirius red staining showed marked biventricular fibrosis in SAB rats. There was increased muscularization of small pulmonary arteries in SAB rats. Confocal microscopy showed biventricular mitochondrial depolarization and fragmentation in SAB vs. sham cardiomyocytes. Transmission electron microscopy confirmed a marked biventricular reduction in mitochondria size in SAB hearts. Immunoblot showed marked biventricular increase in PKM2/PKM1 and MiD51 expression. Mitofusin 2 and mitochondrial pyruvate carrier 1 were increased in SAB LVs.

Conclusions: SAB caused group 2 PH. Impaired RV function and RV fibrosis were associated with increases in mitochondrial fission and expression of MiD51 and PKM2. While these changes would be expected to promote increased production of reactive oxygen species and a glycolytic shift in metabolism, further study is required to determine the functional consequences of these newly described mitochondrial abnormalities.

Endothelial pyruvate kinase M2 maintains vascular integrity

The M2 isoform of pyruvate kinase (PKM2) is highly expressed in most cancer cells, and has been studied extensively as a driver of oncogenic metabolism. In contrast, the role of PKM2 in nontransformed cells is little studied, and nearly nothing is known of its role, if any, in quiescent cells. We show here that endothelial cells express PKM2 almost exclusively over PKM1. In proliferating endothelial cells, PKM2 is required to suppress p53 and maintain cell cycle progression. In sharp contrast, PKM2 has a strikingly different role in quiescent endothelial cells, where inhibition of PKM2 leads to degeneration of tight junctions and barrier function. Mechanistically, PKM2 regulates barrier function independently of its canonical activity as a pyruvate kinase. Instead, PKM2 suppresses NF-kB and its downstream target, the vascular permeability factor angiopoietin 2. As a consequence, loss of endothelial cell PKM2 in vivo predisposes mice to VEGF-induced vascular leak, and to severe bacteremia and death in response to sepsis. Together, these data demonstrate new roles of PKM2 in quiescent cells, and highlight the need for caution in developing cancer therapies that target PKM2.

Proteomic analysis of rat serum revealed the effects of chronic sleep deprivation on metabolic, cardiovascular and nervous system

Sleep is an essential and fundamental physiological process that plays crucial roles in the balance of psychological and physical health. Sleep disorder may lead to adverse health outcomes. The effects of sleep deprivation were extensively studied, but its mechanism is still not fully understood. The present study aimed to identify the alterations of serum proteins associated with chronic sleep deprivation, and to seek for potential biomarkers of sleep disorder mediated diseases. A label-free quantitative proteomics technology was used to survey the global changes of serum proteins between normal rats and chronic sleep deprivation rats. A total of 309 proteins were detected in the serum samples and among them, 117 proteins showed more than 1.8-folds abundance alterations between the two groups. Functional enrichment and network analyses of the differential proteins revealed a close relationship between chronic sleep deprivation and several biological processes including energy metabolism, cardiovascular function and nervous function. And four proteins including pyruvate kinase M1, clusterin, kininogen1 and profilin-1were identified as potential biomarkers for chronic sleep deprivation. The four candidates were validated via parallel reaction monitoring (PRM) based targeted proteomics. In addition, protein expression alteration of the four proteins was confirmed in myocardium and brain of rat model. In summary, the comprehensive proteomic study revealed the biological impacts of chronic sleep deprivation and discovered several potential biomarkers. This study provides further insight into the pathological and molecular mechanisms underlying sleep disorders at protein level.

Cilostazol ameliorates heart failure with preserved ejection fraction and diastolic dysfunction in obese and non-obese hypertensive mice

Cilostazol (Ciloz) a potent Type III phosphodiesterase inhibitor is effective against inflammation, insulin resistance and cardiomyopathy. However, the effect of Ciloz on obesity-associated left ventricular diastolic dysfunction has not been explored yet. Hence, we examined the effect of Ciloz on cardiac remodelling and dysfunction in non-obese and obese-insulin resistant mice infused with AngiotensinII (AngII). Male C57BL/6 J mice were initially subjected to 19 weeks of chow or high fat diet (HFD) regimen and thereafter animals were randomised for AngII (1500 ng/kg/min, s.c) infusion or saline and Ciloz (50 mg/kg, p.o) for another 1 week. Obese and non-obese mice infused with AngII exhibited significant diastolic dysfunction and features of heart failure with preserved ejection fraction (HFpEF) since a decrease in fractional shortening and no change in ejection fraction were observed when compared with respective controls. Administration of AngII and Ciloz in HFD fed mice significantly improved the left ventricular function compared with AngII infused HFD mice as evinced from the echocardiographic data. Further, Ciloz treatment significantly reduced cardiomyocyte area, interstitial and perivascular fibrosis; and collagen deposition. Moreover, Ciloz reduced the inflammatory milieu in the heart as evinced by decreased F4/80⁺ and CD68⁺ cells; IL-1β and IL-6 gene transcripts. Quantitative assessment of the expression levels revealed substantial upregulation of MMP-9 (pro- and mature-forms) and α-SMA in the left ventricle of AngII infused HFD-fed mice, which was considerably suppressed by Ciloz regimen. The beneficial effect of Ciloz was associated with the normalization in gene expression of hypertrophic and fibrotic markers. Likewise, Ciloz administration markedly reduced the AngII and HFD induced TGF-β1/SMAD3 and Akt/mTOR signalling. Additionally, AngII administered and HFD-fed mice showed increased glycolytic flux, which was considerably diminished by Ciloz treatment as indicated from suppressed PKM2, HK-2, PDK-2, HIF-1α mRNA and GLUT-1 protein expression. Taken together, Ciloz might be therapeutically exploited against AngII and obesity-associated diastolic dysfunction thereby preventing overt heart failure.

HIF1 mediates a switch in pyruvate kinase isoforms after myocardial infarction

Alternative splicing of RNA is an underexplored area of transcriptional response. We expect that early changes in alternatively spliced genes may be important for responses to cardiac injury. Hypoxia inducible factor 1 (HIF1) is a key transcription factor that rapidly responds to loss of oxygen through alteration of metabolism and angiogenesis. The goal of this study was to investigate the transcriptional response after myocardial infarction (MI) and to identify novel, hypoxia-driven changes, including alternative splicing. After ligation of the left anterior descending artery in mice, we observed an abrupt loss of cardiac contractility and upregulation of hypoxic signaling. We then performed RNA sequencing on ischemic heart tissue 1 and 3 days after infarct to assess early transcriptional changes and identified 89 transcripts with altered splicing. Of particular interest was the switch in Pkm isoform expression (pyruvate kinase, muscle). The usually predominant Pkm1 isoform was less abundant in ischemic hearts, while Pkm2 and associated splicing factors (hnRNPA1, hnRNPA2B1, Ptbp1) rapidly increased. Despite increased Pkm2 expression, total pyruvate kinase activity remained reduced in ischemic myocardial tissue. We also demonstrated HIF1 binding to PKM by chromatin immunoprecipitation, indicating a direct role for HIF1 in mediating this isoform switch. Our study provides a new, detailed characterization of the early transcriptome after MI. From this analysis, we identified an HIF1-mediated alternative splicing event in the PKM gene. Pkm1 and Pkm2 play distinct roles in glycolytic metabolism and the upregulation of Pkm2 is likely to have important consequences for ATP synthesis in infarcted cardiac muscle.

Cardiotoxicity with vascular endothelial growth factor inhibitor therapy

Angiogenesis inhibitors targeting the vascular endothelial growth factor (VEGF) signaling pathway (VSP) have been important additions in the therapy of various cancers, especially renal cell carcinoma and colorectal cancer. Bevazicumab, the first VSP to receive FDA approval in 2004 targeting all circulating isoforms of VEGF-A, has become one of the best-selling drugs of all times. The second wave of tyrosine kinase inhibitors (TKIs), which target the intracellular site of VEGF receptor kinases, began with the approval of sorafenib in 2005 and sunitinib in 2006. Heart failure was subsequently noted, in 2-4% of patients on bevacizumab and in 3-8% of patients on VSP-TKIs. The very fact that the single-targeted monoclonal antibody bevacizumab can induce cardiotoxicity supports a pathomechanistic role for the VSP and the postulate of the "vascular" nature of VSP inhibitor cardiotoxicity. In this review we will outline this scenario in greater detail, reflecting on hypertension and coronary artery disease as risk factors for VSP inhibitor cardiotoxicity, but also similarities with peripartum and diabetic cardiomyopathy. This leads to the concept that any preexisting or coexisting condition that reduces the vascular reserve or utilizes the vascular reserve for compensatory purposes may pose a risk factor for cardiotoxicity with VSP inhibitors. These conditions need to be carefully considered in cancer patients who are to undergo VSP inhibitor therapy. Such vigilance is not to exclude patients from such prognostically extremely important therapy but to understand the continuum and to recognize and react to any cardiotoxicity dynamics early on for superior overall outcomes.

Cardiac Metabolic Deregulation Induced by the Tyrosine Kinase Receptor Inhibitor Sunitinib is rescued by Endothelin Receptor Antagonism

The growing field of cardio-oncology addresses the side effects of cancer treatment on the cardiovascular system. Here, we explored the cardiotoxicity of the antiangiogenic therapy, sunitinib, in the mouse heart from a diagnostic and therapeutic perspective. We showed that sunitinib induces an anaerobic switch of cellular metabolism within the myocardium which is associated with the development of myocardial fibrosis and reduced left ventricular ejection fraction as demonstrated by echocardiography. The capacity of positron emission tomography with [18F]fluorodeoxyglucose to detect the changes in cardiac metabolism caused by sunitinib was dependent on fasting status and duration of treatment. Pan proteomic analysis in the myocardium showed that sunitinib induced (i) an early metabolic switch with enhanced glycolysis and reduced oxidative phosphorylation, and (ii) a metabolic failure to use glucose as energy substrate, similar to the insulin resistance found in type 2 diabetes. Co-administration of the endothelin receptor antagonist, macitentan, to sunitinib-treated animals prevented both metabolic defects, restored glucose uptake and cardiac function, and prevented myocardial fibrosis. These results support the endothelin system in mediating the cardiotoxic effects of sunitinib and endothelin receptor antagonism as a potential therapeutic approach to prevent cardiotoxicity. Furthermore, metabolic and functional imaging can monitor the cardiotoxic effects and the benefits of endothelin antagonism in a theranostic approach.

Involvement of the Warburg effect in non-tumor diseases processes

Warburg effect, as an energy shift from mitochondrial oxidative phosphorylation to aerobic glycolysis, is extensively found in various cancers. Interestingly, increasing researchers show that Warburg effect plays a crucial role in non-tumor diseases. For instance, inhibition of Warburg effect can alleviate pulmonary vascular remodeling in the process of pulmonary hypertension (PH). Interference of Warburg effect improves mitochondrial function and cardiac function in the process of cardiac hypertrophy and heart failure. Additionally, the Warburg effect induces vascular smooth muscle cell proliferation and contributes to atherosclerosis. Warburg effect may also involve in axonal damage and neuronal death, which are related with multiple sclerosis. Furthermore, Warburg effect significantly promotes cell proliferation and cyst expansion in polycystic kidney disease (PKD). Besides, Warburg effect relieves amyloid β-mediated cell death in Alzheimer's disease. And Warburg effect also improves the mycobacterium tuberculosis infection. Finally, we also introduce some glycolytic agonists. This review focuses on the newest researches about the role of Warburg effect in non-tumor diseases, including PH, tuberculosis, idiopathic pulmonary fibrosis (IPF), failing heart, cardiac hypertrophy, atherosclerosis, Alzheimer's diseases, multiple sclerosis, and PKD. Obviously, Warburg effect may be a potential therapeutic target for those non-tumor diseases.

A Novel Positron Emission Tomography (PET) Approach to Monitor Cardiac Metabolic Pathway Remodeling in Response to Sunitinib Malate

Sunitinib is a tyrosine kinase inhibitor approved for the treatment of multiple solid tumors. However, cardiotoxicity is of increasing concern, with a need to develop rational mechanism driven approaches for the early detection of cardiac dysfunction. We sought to interrogate changes in cardiac energy substrate usage during sunitinib treatment, hypothesising that these changes could represent a strategy for the early detection of cardiotoxicity. Balb/CJ mice or Sprague-Dawley rats were treated orally for 4 weeks with 40 or 20 mg/kg/day sunitinib. Cardiac positron emission tomography (PET) was implemented to investigate alterations in myocardial glucose and oxidative metabolism. Following treatment, blood pressure increased, and left ventricular ejection fraction decreased. Cardiac [¹⁸F]-fluorodeoxyglucose (FDG)-PET revealed increased glucose uptake after 48 hours. [¹¹C]Acetate-PET showed decreased myocardial perfusion following treatment. Electron microscopy revealed significant lipid accumulation in the myocardium. Proteomic analyses indicated that oxidative metabolism, fatty acid β-oxidation and mitochondrial dysfunction were among the top myocardial signalling pathways perturbed. Sunitinib treatment results in an increased reliance on glycolysis, increased myocardial lipid deposition and perturbed mitochondrial function, indicative of a fundamental energy crisis resulting in compromised myocardial energy metabolism and function. Our findings suggest that a cardiac PET strategy may represent a rational approach to non-invasively monitor metabolic pathway remodeling following sunitinib treatment.

Role of microRNA in metabolic shift during heart failure

Heart failure (HF) is an end point resulting from a number of disease states. The prognosis for HF patients is poor with survival rates precipitously low. Energy metabolism is centrally linked to the development of HF, and it involves the proteomic remodeling of numerous pathways, many of which are targeted to the mitochondrion. microRNAs (miRNA) are noncoding RNAs that influence posttranscriptional gene regulation. miRNA have garnered considerable attention for their ability to orchestrate changes to the transcriptome, and ultimately the proteome, during HF. Recently, interest in the role played by miRNA in the regulation of energy metabolism at the mitochondrion has emerged. Cardiac proteome remodeling during HF includes axes impacting hypertrophy, oxidative stress, calcium homeostasis, and metabolic fuel transition. Although it is established that the pathological environment of hypoxia and hemodynamic stress significantly contribute to the HF phenotype, it remains unclear as to the mechanistic underpinnings driving proteome remodeling. The aim of this review is to present evidence highlighting the role played by miRNA in these processes as a means for linking pathological stimuli with proteomic alteration. The differential expression of proteins of substrate transport, glycolysis, β-oxidation, ketone metabolism, the citric acid cycle (CAC), and the electron transport chain (ETC) are paralleled by the differential expression of miRNA species that modulate these processes. Identification of miRNAs that translocate to cardiomyocyte mitochondria (miR-181c, miR-378) influencing the expression of the mitochondrial genome-encoded transcripts as well as suggested import modulators are discussed. Current insights, applications, and challenges of miRNA-based therapeutics are also described.

How cardiomyocytes sense pathophysiological stresses for cardiac remodeling

In the past decades, the cardiovascular community has laid out the fundamental signaling cascades that become awry in the cardiomyocyte during the process of pathologic cardiac remodeling. These pathways are initiated at the cell membrane and work their way to the nucleus to mediate gene expression. Complexity is multiplied as the cardiomyocyte is subjected to cross talk with other cells as well as a barrage of extracellular stimuli and mechanical stresses. In this review, we summarize the signaling cascades that play key roles in cardiac function and then we proceed to describe emerging concepts of how the cardiomyocyte senses the mechanical and environmental stimuli to transition to the deleterious genetic program that defines pathologic cardiac remodeling. As a highlighting example of these processes, we illustrate the transition from a compensated hypertrophied myocardium to a decompensated failing myocardium, which is clinically manifested as decompensated heart failure.

Quantitative Non-canonical Amino Acid Tagging (QuaNCAT) Proteomics Identifies Distinct Patterns of Protein Synthesis Rapidly Induced by Hypertrophic Agents in Cardiomyocytes, Revealing New Aspects of Metabolic Remodeling

Cardiomyocytes undergo growth and remodeling in response to specific pathological or physiological conditions. In the former, myocardial growth is a risk factor for cardiac failure and faster protein synthesis is a major factor driving cardiomyocyte growth. Our goal was to quantify the rapid effects of different pro-hypertrophic stimuli on the synthesis of specific proteins in ARVC and to determine whether such effects are caused by alterations on mRNA abundance or the translation of specific mRNAs. Cardiomyocytes have very low rates of protein synthesis, posing a challenging problem in terms of studying changes in the synthesis of specific proteins, which also applies to other nondividing primary cells. To study the rates of accumulation of specific proteins in these cells, we developed an optimized version of the Quantitative Noncanonical Amino acid Tagging LC/MS proteomic method to label and selectively enrich newly synthesized proteins in these primary cells while eliminating the suppressive effects of pre-existing and highly abundant nonisotope-tagged polypeptides. Our data revealed that a classical pathologic (phenylephrine; PE) and the recently identified insulin stimulus that also contributes to the development of pathological cardiac hypertrophy (insulin), both increased the synthesis of proteins involved in, e.g. glycolysis, the Krebs cycle and beta-oxidation, and sarcomeric components. However, insulin increased synthesis of many metabolic enzymes to a greater extent than PE. Using a novel validation method, we confirmed that synthesis of selected candidates is indeed up-regulated by PE and insulin. Synthesis of all proteins studied was up-regulated by signaling through mammalian target of rapamycin complex 1 without changes in their mRNA levels, showing the key importance of translational control in the rapid effects of hypertrophic stimuli. Expression of PKM2 was up-regulated in rat hearts following TAC. This isoform possesses specific regulatory properties, so this finding indicates it may be involved in metabolic remodeling and also serve as a novel candidate biomarker. Levels of translation factor eEF1 also increased during TAC, likely contributing to faster cell mass accumulation. Interestingly those two candidates were not up-regulated in pregnancy or exercise induced CH, indicating PKM2 and eEF1 were pathological CH specific markers. We anticipate that the methodologies described here will be valuable for other researchers studying protein synthesis in primary cells.

MicroRNA and receptor mediated signaling pathways as potential therapeutic targets in heart failure

INTRODUCTION

Cardiac remodelling is a complex pathogenetic pathway involving genome expression, molecular, cellular, and interstitial changes that cause changes in size, shape and function of the heart after cardiac injury. Areas covered: We will review recent advances in understanding the role of several receptor-mediated signaling pathways and micro-RNAs, in addition to their potential as candidate target pathways in the pathogenesis of heart failure. The myocyte is the main target cell involved in the remodelling process via ischemia, cell necrosis and apoptosis (by means of various receptor pathways), and other mechanisms mediated by micro-RNAs. We will analyze the role of some receptor mediated signaling pathways such as natriuretic peptides, mediators of glycogen synthase kinase 3 and ERK1/2 pathways, beta-adrenergic receptor subtypes and relaxin receptor signaling mechanisms, TNF/TNF receptor family and TWEAK/Fn14 axis, and some micro-RNAs as candidate target pathways in pathogenesis of heart failure. These mediators of receptor-mediated pathways and micro-RNA are the most addressed targets of emerging therapies in modern heart failure treatment strategies. Expert opinion: Future treatment strategies should address mediators involved in multiple steps within heart failure pathogenetic pathways.

3,3',5-triiodothyroxine inhibits apoptosis and oxidative stress by the PKM2/PKM1 ratio during oxygen-glucose deprivation/reperfusion AC16 and HCM-a cells: T3 inhibits apoptosis and oxidative stress by PKM2/PKM1 ratio

Oxidative stress (OS) plays a crucial role in the development of myocardial disease, which can induce the dysfunction of cardiac muscle cells. 3,3',5-triiodothyroxine (T3) is a hormone secreted from the thyroid gland that has been shown to protect cells by improving the redox state and to regulate the expression of pyruvate kinase muscle isozyme (PKM, including two isoforms PKM1 and PKM2). The present study aimed to reveal the key effects of T3 on protecting human myocardial cell lines from oxidative stress and the downstream molecular mechanism. An oxygen-glucose deprivation/reperfusion model (OGDR) and three subtypes of the deiodinase family (DIO1, DIO2, and DIO3), which convert thyroxine (T4) to T3, were tested in this model. Our results show that the expression of DIO1, DIO2 and T3 was downregulated, but DIO3 was upregulated in OGDR-treated AC16 and HCM-a cells. Then, OGDR-treated cells were treated with T3 and T4. The results show that T3 inhibited the expression of reactive oxygen species (ROS) and malonic dialdehyde (MDA), but upregulated glutathione peroxidase (GSH-Px) and superoxide dismutase (SOD). The effects of T4 were not notable. T3 also protected OGDR cells from apoptosis and upregulated the PKM2/PKM1 ratio. Further mechanistic studies found that PKM2 inhibition by small interfering RNA (siRNA) could attenuate the anti-OS and anti-apoptotic effects of T3. These findings suggest that T3 can inhibit apoptosis and oxidative stress in OGDR-treated AC16 and HCM-a cells by regulating the PKM2/PKM1 ratio.

Fuel availability and fate in cardiac metabolism: A tale of two substrates

The heart's extraordinary metabolic flexibility allows it to adapt to normal changes in physiology in order to preserve its function. Alterations in the metabolic profile of the heart have also been attributed to pathological conditions such as ischemia and hypertrophy; however, research during the past decade has established that cardiac metabolic adaptations can precede the onset of pathologies. It is therefore critical to understand how changes in cardiac substrate availability and use trigger events that ultimately result in heart dysfunction. This review examines the mechanisms by which the heart obtains fuels from the circulation or from mobilization of intracellular stores. We next describe experimental models that exhibit either an increase in glucose use or a decrease in FA oxidation, and how these aberrant conditions affect cardiac metabolism and function. Finally, we highlight the importance of alternative, relatively under-investigated strategies for the treatment of heart failure. This article is part of a Special Issue entitled: Heart Lipid Metabolism edited by G.D. Lopaschuk.

c-Myc Alters Substrate Utilization and O-GlcNAc Protein Posttranslational Modifications without Altering Cardiac Function during Early Aortic Constriction

Hypertrophic stimuli cause transcription of the proto-oncogene c-Myc (Myc). Prior work showed that myocardial knockout of c-Myc (Myc) attenuated hypertrophy and decreased expression of metabolic genes after aortic constriction. Accordingly, we assessed the interplay between Myc, substrate oxidation and cardiac function during early pressure overload hypertrophy. Mice with cardiac specific, inducible Myc knockout (MycKO-TAC) and non-transgenic littermates (Cont-TAC) were subjected to transverse aortic constriction (TAC; n = 7/group). Additional groups underwent sham surgery (Cont-Sham and MycKO-Sham, n = 5 per group). After two weeks, function was measured in isolated working hearts along with substrate fractional contributions to the citric acid cycle by using perfusate with ¹³C labeled mixed fatty acids, lactate, ketone bodies and unlabeled glucose and insulin. Cardiac function was similar between groups after TAC although +dP/dT and -dP/dT trended towards improvement in MycKO-TAC versus Cont-TAC. In sham hearts, Myc knockout did not affect cardiac function or substrate preferences for the citric acid cycle. However, Myc knockout altered fractional contributions during TAC. The unlabeled fractional contribution increased in MycKO-TAC versus Cont-TAC, whereas ketone and free fatty acid fractional contributions decreased. Additionally, protein posttranslational modifications by O-GlcNAc were significantly greater in Cont-TAC versus both Cont-Sham and MycKO-TAC. In conclusion, Myc alters substrate preferences for the citric acid cycle during early pressure overload hypertrophy without negatively affecting cardiac function. Myc also affects protein posttranslational modifications by O-GlcNAc during hypertrophy, which may regulate Myc-induced metabolic changes.