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Time-restricted feeding (TRF) has gained attention as a dietary regimen that promotes metabolic health. This study questioned if the health benefits of an intermittent TRF (iTRF) schedule require ketone flux specifically in skeletal and cardiac muscles. Notably, we found that the ketolytic enzyme beta-hydroxybutyrate dehydrogenase 1 (BDH1) is uniquely enriched in isolated mitochondria derived from heart and red/oxidative skeletal muscles, which also have high capacity for fatty acid oxidation (FAO). Using mice with BDH1 deficiency in striated muscles, we discover that this enzyme optimizes FAO efficiency and exercise tolerance during acute fasting. Additionally, iTRF leads to robust molecular remodeling of muscle tissues, and muscle BDH1 flux does indeed play an essential role in conferring the full adaptive benefits of this regimen, including increased lean mass, mitochondrial hormesis, and metabolic rerouting of pyruvate. In sum, ketone flux enhances mitochondrial bioenergetics and supports iTRF-induced remodeling of skeletal muscle and heart., Competing Interests: Declaration of interests D.M.M. is a member of the Cell Metabolism advisory board., (Copyright © 2024 Elsevier Inc. All rights reserved.)

Background: Accumulating evidence suggests that the failing heart reprograms fuel metabolism toward increased utilization of ketone bodies and that increasing cardiac ketone delivery ameliorates cardiac dysfunction. As an initial step toward development of ketone therapies, we investigated the effect of chronic oral ketone ester (KE) supplementation as a prevention or treatment strategy in rodent heart failure models., Methods: Two independent rodent heart failure models were used for the studies: transverse aortic constriction/myocardial infarction (MI) in mice and post-MI remodeling in rats. Seventy-five mice underwent a prevention treatment strategy with a KE comprised of hexanoyl-hexyl-3-hydroxybutyrate KE (KE-1) diet, and 77 rats were treated in either a prevention or treatment regimen using a commercially available β-hydroxybutyrate-(R)-1,3-butanediol monoester (DeltaG; KE-2) diet., Results: The KE-1 diet in mice elevated β-hydroxybutyrate levels during nocturnal feeding, whereas the KE-2 diet in rats induced ketonemia throughout a 24-hour period. The KE-1 diet preventive strategy attenuated development of left ventricular dysfunction and remodeling post-transverse aortic constriction/MI (left ventricular ejection fraction±SD, 36±8 in vehicle versus 45±11 in KE-1; P =0.016). The KE-2 diet therapeutic approach also attenuated left ventricular dysfunction and remodeling post-MI (left ventricular ejection fraction, 41±11 in MI-vehicle versus 61±7 in MI-KE-2; P <0.001). In addition, ventricular weight, cardiomyocyte cross-sectional area, and the expression of ANP (atrial natriuretic peptide) were significantly attenuated in the KE-2-treated MI group. However, treatment with KE-2 did not influence cardiac fibrosis post-MI. The myocardial expression of the ketone transporter and 2 ketolytic enzymes was significantly increased in rats fed KE-2 diet along with normalization of myocardial ATP levels to sham values., Conclusions: Chronic oral supplementation with KE was effective in both prevention and treatment of heart failure in 2 preclinical animal models. In addition, our results indicate that treatment with KE reprogrammed the expression of genes involved in ketone body utilization and normalized myocardial ATP production following MI, consistent with provision of an auxiliary fuel. These findings provide rationale for the assessment of KEs as a treatment for patients with heart failure.

Aims: The failing heart is energy-starved and inefficient due to perturbations in energy metabolism. Although ketone oxidation has been shown recently to increase in the failing heart, it remains unknown whether this improves cardiac energy production or efficiency. We therefore assessed cardiac metabolism in failing hearts and determined whether increasing ketone oxidation improves cardiac energy production and efficiency., Methods and Results: C57BL/6J mice underwent sham or transverse aortic constriction (TAC) surgery to induce pressure overload hypertrophy over 4-weeks. Isolated working hearts from these mice were perfused with radiolabelled β-hydroxybutyrate (βOHB), glucose, or palmitate to assess cardiac metabolism. Ejection fraction decreased by 45% in TAC mice. Failing hearts had decreased glucose oxidation while palmitate oxidation remained unchanged, resulting in a 35% decrease in energy production. Increasing βOHB levels from 0.2 to 0.6 mM increased ketone oxidation rates from 251 ± 24 to 834 ± 116 nmol·g dry wt-1 · min-1 in TAC hearts, rates which were significantly increased compared to sham hearts and occurred without decreasing glycolysis, glucose, or palmitate oxidation rates. Therefore, the contribution of ketones to energy production in TAC hearts increased to 18% and total energy production increased by 23%. Interestingly, glucose oxidation, in parallel with total ATP production, was also significantly upregulated in hearts upon increasing βOHB levels. However, while overall energy production increased, cardiac efficiency was not improved., Conclusions: Increasing ketone oxidation rates in failing hearts increases overall energy production without compromising glucose or fatty acid metabolism, albeit without increasing cardiac efficiency., (Published on behalf of the European Society of Cardiology. All rights reserved. © The Author(s) 2019. For permissions, please email: journals.permissions@oup.com.)

Evidence has emerged that the failing heart increases utilization of ketone bodies. We sought to determine whether this fuel shift is adaptive. Mice rendered incapable of oxidizing the ketone body 3-hydroxybutyrate (3OHB) in the heart exhibited worsened heart failure in response to fasting or a pressure overload/ischemic insult compared with WT controls. Increased delivery of 3OHB ameliorated pathologic cardiac remodeling and dysfunction in mice and in a canine pacing model of progressive heart failure. 3OHB was shown to enhance bioenergetic thermodynamics of isolated mitochondria in the context of limiting levels of fatty acids. These results indicate that the heart utilizes 3OHB as a metabolic stress defense and suggest that strategies aimed at increasing ketone delivery to the heart could prove useful in the treatment of heart failure.

The adult heart is uniquely designed and equipped to provide a continuous supply of energy in the form of ATP to support persistent contractile function. This high-capacity energy transduction system is the result of a remarkable surge in mitochondrial biogenesis and maturation during the fetal-to-adult transition in cardiac development. Substantial evidence indicates that nuclear receptor signaling is integral to dynamic changes in the cardiac mitochondrial phenotype in response to developmental cues, in response to diverse postnatal physiologic conditions, and in disease states such as heart failure. A subset of cardiac-enriched nuclear receptors serve to match mitochondrial fuel preferences and capacity for ATP production with changing energy demands of the heart. In this Review, we describe the role of specific nuclear receptors and their coregulators in the dynamic control of mitochondrial biogenesis and energy metabolism in the normal and diseased heart.

In developing hearts, changes in the cardiac metabolic milieu during the perinatal period redirect mitochondrial substrate preference from carbohydrates to fatty acids. Mechanisms responsible for this mitochondrial plasticity are unknown. Here, we found that PINK1-Mfn2-Parkin-mediated mitophagy directs this metabolic transformation in mouse hearts. A mitofusin (Mfn) 2 mutant lacking PINK1 phosphorylation sites necessary for Parkin binding (Mfn2 AA) inhibited mitochondrial Parkin translocation, suppressing mitophagy without impairing mitochondrial fusion. Cardiac Parkin deletion or expression of Mfn2 AA from birth, but not after weaning, prevented postnatal mitochondrial maturation essential to survival. Five-week-old Mfn2 AA hearts retained a fetal mitochondrial transcriptional signature without normal increases in fatty acid metabolism and mitochondrial biogenesis genes. Myocardial fatty acylcarnitine levels and cardiomyocyte respiration induced by palmitoylcarnitine were concordantly depressed. Thus, instead of transcriptional reprogramming, fetal cardiomyocyte mitochondria undergo perinatal Parkin-mediated mitophagy and replacement by mature adult mitochondria. Mitophagic mitochondrial removal underlies developmental cardiomyocyte mitochondrial plasticity and metabolic transitioning of perinatal hearts., (Copyright © 2015, American Association for the Advancement of Science.)

The mitochondrion is a complex organelle that serves essential roles in energy transduction, ATP production, and a myriad of cellular signaling events. A finely tuned regulatory network orchestrates the biogenesis, maintenance, and turnover of mitochondria. The high-capacity mitochondrial system in the heart is regulated in a dynamic way to generate and consume enormous amounts of ATP in order to support the constant pumping function in the context of changing energy demands. This review describes the regulatory circuitry and downstream events involved in mitochondrial biogenesis and its coordination with mitochondrial dynamics in developing and diseased hearts., (© 2015 Dorn et al.; Published by Cold Spring Harbor Laboratory Press.)

The heart is an omnivore organ that requires constant energy production to match its functional demands. In the adult heart, adenosine-5'-triphosphate (ATP) production occurs mainly through mitochondrial fatty acid and glucose oxidation. The heart must constantly adapt its energy production in response to changes in substrate supply and work demands across diverse physiologic and pathophysiologic conditions. The cardiac myocyte maintains a high level of mitochondrial ATP production through a complex transcriptional regulatory network that is orchestrated by the members of the peroxisome proliferator-activated receptor gamma coactivator-1 (PGC-1) family. There is increasing evidence that during the development of cardiac hypertrophy and in the failing heart, the activity of this network, including PGC-1, is altered. This review summarizes our current understanding of the perturbations in the gene regulatory pathways that occur during the development of heart failure. An appreciation of the role this regulatory circuitry serves in the regulation of cardiac energy metabolism may unveil novel therapeutic targets aimed at the metabolic disturbances that presage heart failure. This article is part of a Special Issue entitled:Cardiomyocyte Biology: Cardiac Pathways of Differentiation, Metabolism and Contraction., (Copyright © 2012 Elsevier B.V. All rights reserved.)

Fatty acid synthase (FAS) promotes energy storage through de novo lipogenesis and participates in signaling by the nuclear receptor PPARα in noncardiac tissues. To determine if de novo lipogenesis is relevant to cardiac physiology, we generated and characterized FAS knockout in the myocardium (FASKard) mice. FASKard mice develop normally, manifest normal resting heart function, and have normal cardiac PPARα signaling as well as fatty acid oxidation. However, they decompensate with stress. Most die within 1 h of transverse aortic constriction, probably due to arrhythmia. Voltage clamp measurements of FASKard cardiomyocytes show hyperactivation of L-type calcium channel current that could not be reversed with palmitate supplementation. Of the classic regulators of this current, Ca(2+)/calmodulin-dependent protein kinase II (CaMKII) but not protein kinase A signaling is activated in FASKard hearts, and knockdown of FAS in cultured cells activates CaMKII. In addition to being intolerant of the stress of acute pressure, FASKard hearts were also intolerant of the stress of aging, reflected as persistent CaMKII hyperactivation, progression to dilatation, and premature death by ∼1 year of age. CaMKII signaling appears to be pathogenic in FASKard hearts because inhibition of its signaling in vivo rescues mice from early mortality after transverse aortic constriction. FAS was also increased in two mechanistically distinct mouse models of heart failure and in the hearts of humans with end stage cardiomyopathy. These data implicate a novel relationship between FAS and calcium signaling in the heart and suggest that FAS induction in stressed myocardium represents a compensatory response to protect cardiomyocytes from pathological calcium flux.

Background: Currently, there are no specific therapies available to treat cardiac dysfunction caused by sepsis and other chronic inflammatory conditions. Activation of toll-like receptor 4 (TLR4) by lipopolysaccharide (LPS) is an early event in Gram-negative bacterial sepsis, triggering a robust inflammatory response and changes in metabolism. Peroxisome proliferator-activated receptor-γ coactivator-1 (PGC-1) α and β serve as critical physiological regulators of energy metabolic gene expression in heart., Methods and Results: Injection of mice with LPS triggered a myocardial fuel switch similar to that of the failing heart: reduced mitochondrial substrate flux and myocyte lipid accumulation. The LPS-induced metabolic changes were associated with diminished ventricular function and suppression of the genes encoding PGC-1α and β, known transcriptional regulators of mitochondrial function. This cascade of events required TLR4 and nuclear factor-κB activation. Restoration of PGC-1β expression in cardiac myocytes in culture and in vivo in mice reversed the gene regulatory, metabolic, and functional derangements triggered by LPS. Interestingly, the effects of PGC-1β overexpression were independent of the upstream inflammatory response, highlighting the potential utility of modulating downstream metabolic derangements in cardiac myocytes as a novel strategy to prevent or treat sepsis-induced heart failure., Conclusions: LPS triggers cardiac energy metabolic reprogramming through suppression of PGC-1 coactivators in the cardiac myocyte. Reactivation of PGC-1β expression can reverse the metabolic and functional derangements caused by LPS-TLR4 activation, identifying the PGC-1 axis as a candidate therapeutic target for sepsis-induced heart failure.

Diabetic cardiac dysfunction is associated with decreased rates of myocardial glucose oxidation (GO) and increased fatty acid oxidation (FAO), a fuel shift that has been shown to sensitize the heart to ischemic insult and ventricular dysfunction. We sought to evaluate the metabolic and functional consequences of chronic suppression of GO in heart as modeled by transgenic mice with cardiac-specific overexpression of pyruvate dehydrogenase kinase 4 (myosin heavy chain (MHC)-PDK4 mice), an inhibitor of pyruvate dehydrogenase. Hearts of MHC-PDK4 mice were shown to exhibit an insulin-resistant substrate utilization profile, characterized by low GO rates and high FAO flux. Surprisingly, MHC-PDK4 mice were not sensitized to cardiac ischemia-reperfusion injury despite a fuel utilization pattern that phenocopied the diabetic heart. In addition, MHC-PDK4 mice were protected against high fat diet-induced myocyte lipid accumulation, likely related to increased capacity for FAO. The high rates of mitochondrial FAO in the MHC-PDK4 heart were related to heightened activity of the AMP-activated protein kinase, reduced levels of malonyl-CoA, and increased capacity for mitochondrial uncoupled respiration. The expression of the known AMP-activated protein kinase target, peroxisome proliferator-activated receptor γ coactivator-1α (PGC-1α), a master regulator of mitochondrial function and biogenesis, was also activated in the MHC-PDK4 heart. These results demonstrate that chronic activation of PDK4 triggers transcriptional and post-transcriptional mechanisms that re-program the heart for chronic high rates of FAO without the expected deleterious functional or metabolic consequences.

Rationale: Long chain fatty acids (LCFAs) are the preferred substrate for energy provision in hearts. However, the contribution of endogenous triacylglyceride (TAG) turnover to LCFA oxidation and the overall dependence of mitochondrial oxidation on endogenous lipid is largely unstudied., Objective: We sought to determine the role of TAG turnover in supporting LCFA oxidation and the influence of the lipid-activated nuclear receptor, proliferator-activated receptor (PPAR)alpha, on this balance., Methods and Results: Palmitoyl turnover within TAG and palmitate oxidation rates were quantified in isolated hearts, from normal mice (nontransgenic) and mice with cardiac-specific overexpression of PPARalpha (MHC-PPARalpha). Turnover of palmitoyl units within TAG, and thus palmitoyl-coenzyme A recycling, in nontransgenic (4.5+/-2.3 micromol/min per gram dry weight) was 3.75-fold faster than palmitate oxidation (1.2+/-0.4). This high rate of palmitoyl unit turnover indicates preferential oxidation of palmitoyl units derived from TAG in normal hearts. PPARalpha overexpression augmented TAG turnover 3-fold over nontransgenic hearts, despite similar fractions of acetyl-coenzyme A synthesis from palmitate and oxygen use at the same workload. Palmitoyl turnover within TAG of MHC-PPARalpha hearts (16.2+/-2.9, P<0.05) was 12.5-fold faster than oxidation (1.3+/-0.2). Elevated TAG turnover in MHC-PPARalpha correlated with increased mRNA for enzymes involved in both TAG synthesis, Gpam (glycerol-3-phosphate acyltransferase, mitochondrial), Dgat1 (diacylglycerol acetyltransferase 1), and Agpat3 (1-acylglycerol-3-phospate O-acyltransferase 3), and lipolysis, Pnliprp1 (pancreatic lipase related protein 1)., Conclusions: The role of endogenous TAG in supporting beta-oxidation in the normal heart is much more dynamic than previously thought, and lipolysis provides the bulk of LCFA for oxidation. Accelerated palmitoyl turnover in TAG, attributable to chronic PPARalpha activation, results in near requisite oxidation of LCFAs from TAG.

Background: Emerging evidence in obesity and diabetes mellitus demonstrates that excessive myocardial fatty acid uptake and oxidation contribute to cardiac dysfunction. Transgenic mice with cardiac-specific overexpression of the fatty acid-activated nuclear receptor peroxisome proliferator-activated receptor-alpha (myosin heavy chain [MHC]-PPARalpha mice) exhibit phenotypic features of the diabetic heart, which are rescued by deletion of CD36, a fatty acid transporter, despite persistent activation of PPARalpha gene targets involved in fatty acid oxidation., Methods and Results: To further define the source of fatty acid that leads to cardiomyopathy associated with lipid excess, we crossed MHC-PPARalpha mice with mice deficient for cardiac lipoprotein lipase (hsLpLko). MHC-PPARalpha/hsLpLko mice exhibit improved cardiac function and reduced myocardial triglyceride content compared with MHC-PPARalpha mice. Surprisingly, in contrast to MHC-PPARalpha/CD36ko mice, the activity of the cardiac PPARalpha gene regulatory pathway is normalized in MHC-PPARalpha/hsLpLko mice, suggesting that PPARalpha ligand activity exists in the lipoprotein particle. Indeed, LpL mediated hydrolysis of very-low-density lipoprotein activated PPARalpha in cardiac myocytes in culture. The rescue of cardiac function in both models was associated with improved mitochondrial ultrastructure and reactivation of transcriptional regulators of mitochondrial function., Conclusions: MHC-PPARalpha mouse hearts acquire excess lipoprotein-derived lipids. LpL deficiency rescues myocyte triglyceride accumulation, mitochondrial gene regulatory derangements, and contractile function in MHC-PPARalpha mice. Finally, LpL serves as a source of activating ligand for PPARalpha in the cardiomyocyte.

To define the necessity of calcineurin (Cn) signaling for cardiac maturation and function, the postnatal phenotype of mice with cardiac-specific targeted ablation of the Cn B1 regulatory subunit (Ppp3r1) gene (csCnb1(-/-) mice) was characterized. csCnb1(-/-) mice develop a lethal cardiomyopathy, characterized by impaired postnatal growth of the heart and combined systolic and diastolic relaxation abnormalities, despite a lack of structural derangements. Notably, the csCnb1(-/-) hearts did not exhibit diastolic dilatation, despite the severe functional phenotype. Myocytes isolated from the mutant mice exhibited reduced rates of contraction/relaxation and abnormalities in calcium transients, consistent with altered sarcoplasmic reticulum loading. Levels of sarco(endo) plasmic reticulum Ca-ATPase 2a (Atp2a2) and phospholamban were normal, but phospholamban phosphorylation was markedly reduced at Ser(16) and Thr(17). In addition, levels of the Na/Ca exchanger (Slc8a1) were modestly reduced. These results define a novel mouse model of cardiac-specific Cn deficiency and demonstrate novel links between Cn signaling, postnatal growth of the heart, pathological ventricular remodeling, and excitation-contraction coupling.

High-capacity mitochondrial ATP production is essential for normal function of the adult heart, and evidence is emerging that mitochondrial derangements occur in common myocardial diseases. Previous overexpression studies have shown that the inducible transcriptional coactivator peroxisome proliferator-activated receptor-gamma coactivator (PGC)-1alpha is capable of activating postnatal cardiac myocyte mitochondrial biogenesis. Recently, we generated mice deficient in PGC-1alpha (PGC-1alpha(-/-) mice), which survive with modestly blunted postnatal cardiac growth. To determine if PGC-1alpha is essential for normal cardiac energy metabolic capacity, mitochondrial function experiments were performed on saponin-permeabilized myocardial fibers from PGC-1alpha(-/-) mice. These experiments demonstrated reduced maximal (state 3) palmitoyl-l-carnitine respiration and increased maximal (state 3) pyruvate respiration in PGC-1alpha(-/-) mice compared with PGC-1alpha(+/+) controls. ATP synthesis rates obtained during maximal (state 3) respiration in permeabilized myocardial fibers were reduced for PGC-1alpha(-/-) mice, whereas ATP produced per oxygen consumed (ATP/O), a measure of metabolic efficiency, was decreased by 58% for PGC-1alpha(-/-) fibers. Ex vivo isolated working heart experiments demonstrated that PGC-1alpha(-/-) mice exhibited lower cardiac power, reduced palmitate oxidation, and increased reliance on glucose oxidation, with the latter likely a compensatory response. (13)C NMR revealed that hearts from PGC-1alpha(-/-) mice exhibited a limited capacity to recruit triglyceride as a source for lipid oxidation during beta-adrenergic challenge. Consistent with reduced mitochondrial fatty acid oxidative enzyme gene expression, the total triglyceride content was greater in hearts of PGC-1alpha(-/-) mice relative to PGC-1alpha(+/+) following a fast. Overall, these results demonstrate that PGC-1alpha is essential for the maintenance of maximal, efficient cardiac mitochondrial fatty acid oxidation, ATP synthesis, and myocardial lipid homeostasis.

Common causes of heart failure are associated with derangements in myocardial fuel utilization. Evidence is emerging that metabolic abnormalities may contribute to the development and progression of myocardial disease. The peroxisome proliferator-activated receptor (PPAR) family of nuclear receptor transcription factors has been shown to regulate cardiac fuel metabolism at the gene expression level. The three PPAR family members (alpha, beta/delta and gamma) are uniquely suited to serve as transducers of developmental, physiological, and dietary cues that influence cardiac fatty acid and glucose metabolism. This review describes murine PPAR loss- and gain-of-function models that have shed light on the roles of these receptors in regulating myocardial metabolic pathways and have defined key links to disease states including the hypertensive and diabetic heart.

Diabetes is associated with increased risk of diastolic dysfunction, heart failure, QT prolongation and rhythm disturbances independent of age, hypertension or coronary artery disease. Although these observations suggest electrical remodeling in the heart with diabetes, the relationship between the metabolic and the functional derangements is poorly understood. Exploiting a mouse model (MHC-PPARalpha) with cardiac-specific overexpression of the peroxisome proliferator-activated receptor alpha (PPARalpha), a key driver of diabetes-related lipid metabolic dysregulation, the experiments here were aimed at examining directly the link(s) between alterations in cardiac fatty acid metabolism and the functioning of repolarizing, voltage-gated K(+) (Kv) channels. Electrophysiological experiments on left (LV) and right (RV) ventricular myocytes isolated from young (5-6 week) MHC-PPARalpha mice revealed marked K(+) current remodeling: I(to,f) densities are significantly (P<0.01) lower, whereas I(ss) densities are significantly (P<0.001) higher in MHC-PPARalpha, compared with age-matched wild type (WT), LV and RV myocytes. Consistent with the observed reductions in I(to,f) density, expression of the KCND2 (Kv4.2) transcript is significantly (P<0.001) lower in MHC-PPARalpha, compared with WT, ventricles. Western blot analyses revealed that expression of the Kv accessory protein, KChIP2, is also reduced in MHC-PPARalpha ventricles in parallel with the decrease in Kv4.2. Although the properties of the endogenous and the "augmented" I(ss) suggest a role(s) for two pore domain K(+) channel (K2P) pore-forming subunits, the expression levels of KCNK2 (TREK1), KCNK3 (TASK1) and KCNK5 (TASK2) in MHC-PPARalpha and WT ventricles are not significantly different. The molecular mechanisms underlying I(to,f) and I(ss) remodeling in MHC-PPARalpha ventricular myocytes, therefore, are distinct.

In the diabetic heart, chronic activation of the PPARalpha pathway drives excessive fatty acid (FA) oxidation, lipid accumulation, reduced glucose utilization, and cardiomyopathy. The related nuclear receptor, PPARbeta/delta, is also highly expressed in the heart, yet its function has not been fully delineated. To address its role in myocardial metabolism, we generated transgenic mice with cardiac-specific expression of PPARbeta/delta, driven by the myosin heavy chain (MHC-PPARbeta/delta mice). In striking contrast to MHC-PPARalpha mice, MHC-PPARbeta/delta mice had increased myocardial glucose utilization, did not accumulate myocardial lipid, and had normal cardiac function. Consistent with these observed metabolic phenotypes, we found that expression of genes involved in cellular FA transport were activated by PPARalpha but not by PPARbeta/delta. Conversely, cardiac glucose transport and glycolytic genes were activated in MHC-PPARbeta/delta mice, but repressed in MHC-PPARalpha mice. In reporter assays, we showed that PPARbeta/delta and PPARalpha exerted differential transcriptional control of the GLUT4 promoter, which may explain the observed isotype-specific effects on glucose uptake. Furthermore, myocardial injury due to ischemia/reperfusion injury was significantly reduced in the MHC-PPARbeta/delta mice compared with control or MHC-PPARalpha mice, consistent with an increased capacity for myocardial glucose utilization. These results demonstrate that PPARalpha and PPARbeta/delta drive distinct cardiac metabolic regulatory programs and identify PPARbeta/delta as a potential target for metabolic modulation therapy aimed at cardiac dysfunction caused by diabetes and ischemia.

High fatty acid oxidation (FAO) rates contribute to ischemia-reperfusion injury of the myocardium. Because peroxisome proliferator-activated receptor (PPAR)alpha regulates transcription of several FAO enzymes in the heart, we examined the response of mice with cardiac-restricted overexpression of PPARalpha (MHC-PPARalpha) or whole body PPARalpha deletion including the heart (PPARalpha-/-) to myocardial ischemia-reperfusion injury. Isolated working hearts from MHC-PPARalpha and nontransgenic (NTG) littermates were subjected to no-flow global ischemia followed by reperfusion. MHC-PPARalpha hearts had significantly higher FAO rates during aerobic and postischemic reperfusion (aerobic 1,479 +/- 171 vs. 699 +/- 117, reperfusion 1,062 +/- 214 vs. 601 +/- 70 nmol x g dry wt(-1) x min(-1); P < 0.05) and significantly lower glucose oxidation rates compared with NTG hearts (aerobic 225 +/- 36 vs. 1,563 +/- 165, reperfusion 402 +/- 54 vs. 1,758 +/- 165 nmol x g dry wt(-1) x min(-1); P < 0.05). In hearts from PPARalpha-/- mice, FAO was significantly lower during aerobic and reperfusion (aerobic 235 +/- 36 vs. 442 +/- 75, reperfusion 205 +/- 25 vs. 346 +/- 38 nmol x g dry wt(-1) x min(-1); P < 0.05) whereas glucose oxidation was significantly higher compared with wild-type (WT) hearts (aerobic 2,491 +/- 631 vs. 901 +/- 119, reperfusion 2,690 +/- 562 vs. 1,315 +/- 172 nmol x g dry wt(-1) x min(-1); P < 0.05). Increased FAO rates in MHC-PPARalpha hearts were associated with a markedly lower recovery of cardiac power (45 +/- 9% vs. 71 +/- 6% of preischemic levels in NTG hearts; P < 0.05). In contrast, the percent recovery of cardiac power of PPARalpha-/- hearts was not significantly different from that of WT hearts (80 +/- 8% vs. 75 +/- 9%). This study demonstrates that chronic activation of PPARalpha is detrimental to the cardiac recovery during reperfusion after ischemia.

Background: Downregulation of peroxisome proliferator-activated receptor-alpha (PPARalpha) in hypertrophied and failing hearts leads to the reappearance of the fetal metabolic pattern, ie, decreased fatty acid oxidation and increased reliance on carbohydrates. Here, we sought to elucidate the functional significance of this shift in substrate preference., Methods and Results: We assessed contractile function and substrate utilization using 13C nuclear magnetic resonance spectroscopy and high-energy phosphate metabolism using 31P nuclear magnetic resonance spectroscopy in perfused hearts isolated from genetically modified mice (PPARalpha(-/-)) that mimic the metabolic profile in myocardial hypertrophy. We found that the substrate switch from fatty acid to glucose (3-fold down) and lactate (3-fold up) in PPARalpha(-/-) hearts was sufficient for sustaining normal energy metabolism and contractile function at baseline but depleted the metabolic reserve for supporting high workload. Decreased ATP synthesis (measured by 31P magnetization transfer) during high workload challenge resulted in progressive depletion of high-energy phosphate content and failure to sustain high contractile performance. Interestingly, the metabolic and functional defects in PPARalpha(-/-) hearts could be corrected by overexpressing the insulin-independent glucose transporter GLUT1, which increased the capacity for glucose utilization beyond the intrinsic response to PPARalpha deficiency., Conclusions: These findings demonstrate that metabolic remodeling in hearts deficient in PPARalpha increases the susceptibility to functional deterioration during hemodynamic overload. Moreover, our results suggest that normalization of myocardial energetics by further enhancing myocardial glucose utilization is an effective strategy for preventing the progression of cardiac dysfunction in hearts with impaired PPARalpha activity such as hearts with pathological hypertrophy.

Diabetic heart failure may be causally associated with alterations in cardiac energy metabolism and insulin resistance. Mice with heart-specific overexpression of peroxisome proliferator-activated receptor (PPAR)alpha showed a metabolic and cardiomyopathic phenotype similar to the diabetic heart, and we determined tissue-specific glucose metabolism and insulin action in vivo during hyperinsulinemic-euglycemic clamps in awake myosin heavy chain (MHC)-PPARalpha mice (12-14 weeks of age). Basal and insulin-stimulated glucose uptake in heart was significantly reduced in the MHC-PPARalpha mice, and cardiac insulin resistance was mostly attributed to defects in insulin-stimulated activities of insulin receptor substrate (IRS)-1-associated phosphatidylinositol (PI) 3-kinase, Akt, and tyrosine phosphorylation of signal transducer and activator of transcription 3 (STAT3). Interestingly, MHC-PPARalpha mice developed hepatic insulin resistance associated with defects in insulin-mediated IRS-2-associated PI 3-kinase activity, increased hepatic triglyceride, and circulating interleukin-6 levels. To determine the underlying mechanism, insulin clamps were conducted in 8-week-old MHC-PPARalpha mice. Insulin-stimulated cardiac glucose uptake was similarly reduced in 8-week-old MHC-PPARalpha mice without changes in cardiac function and hepatic insulin action compared with the age-matched wild-type littermates. Overall, these findings indicate that increased activity of PPARalpha, as occurs in the diabetic heart, leads to cardiac insulin resistance associated with defects in insulin signaling and STAT3 activity, subsequently leading to reduced cardiac function. Additionally, age-associated hepatic insulin resistance develops in MHC-PPARalpha mice that may be due to altered cardiac metabolism, functions, and/or inflammatory cytokines.

The mitochondrion serves a critical role as a platform for energy transduction, signaling, and cell death pathways relevant to common diseases of the myocardium such as heart failure. This review focuses on the molecular regulatory events and downstream effector pathways involved in mitochondrial energy metabolic derangements known to occur during the development of heart failure.

The heart has a tremendous capacity for ATP generation, allowing it to function as an efficient pump throughout the life of the organism. The adult myocardium uses either fatty acid or glucose oxidation as its main energy source. Under normal conditions, the adult heart derives most of its energy through oxidation of fatty acids in mitochondria. However, the myocardium has a remarkable ability to switch between carbohydrate and fat fuel sources so that ATP production is maintained at a constant rate in diverse physiological and dietary conditions. This fuel selection flexibility is important for normal cardiac function. Although cardiac energy conversion capacity and metabolic flux is modulated at many levels, an important mechanism of regulation occurs at the level of gene expression. The expression of genes involved in multiple energy transduction pathways is dynamically regulated in response to developmental, physiological, and pathophysiological cues. This review is focused on gene transcription pathways involved in short- and long-term regulation of myocardial energy metabolism. Much of our knowledge about cardiac metabolic regulation comes from studies focused on mitochondrial fatty acid oxidation. The genes involved in this key energy metabolic pathway are transcriptionally regulated by members of the nuclear receptor superfamily, specifically the fatty acid-activated peroxisome proliferator-activated receptors (PPARs) and the nuclear receptor coactivator, PPARgamma coactivator-1alpha (PGC-1alpha). The dynamic regulation of the cardiac PPAR/PGC-1 complex in accordance with physiological and pathophysiological states will be described.

The expression of myocardial fatty acid beta-oxidation enzymes is downregulated at the gene transcriptional level in animal models of left ventricular hypertrophy and of heart failure. Humans with idiopathic dilated cardiomyopathy have decreased myocardial fatty acid oxidation. The extent to which molecular mechanisms, such as a reduction in myocardial fatty acid oxidation, regulate the cardiac hypertrophic response in humans in vivo is unknown. Positron emission tomography was used to measure myocardial blood flow, oxygen consumption, fatty acid utilization, and oxidation in two groups of patients: (1) hypertensive left ventricular hypertrophy (n=19; left ventricular mass, 211+/-39 g; left ventricular ejection fraction, 67+/-4%) and (2) left ventricular dysfunction (n=9; left ventricular mass, 210+/-36 g; left ventricular ejection fraction, 31+/-10%); these were compared with a normal control group (n=36; left ventricular mass, 139+/-25 g; left ventricular ejection fraction, 66+/-6%). Left ventricular mass showed significant correlation with gender, diastolic and systolic blood pressure, myocardial fatty acid uptake, utilization and oxidation, myocardial blood flow, body mass index, and left ventricular ejection fraction (all P<0.02). Independent predictors of increased left ventricular mass were male gender (r=0.38, P<0.001), myocardial fatty acid oxidation (r=-0.24, P<0.018), systolic blood pressure (r=0.41, P<0.001), and left ventricular ejection fraction (r=-0.29, P=0.005). Thus, myocardial fatty acid metabolism is an independent predictor of left ventricular mass in hypertension and in left ventricular dysfunction. The extent to which reduced myocardial fatty acid metabolism affects cardiovascular morbidity and mortality and whether pharmacologic modulation results in improved outcomes remains to be determined.

The transcriptional coactivator PPARgamma coactivator-1alpha (PGC-1alpha) has been characterized as a broad regulator of cellular energy metabolism. Although PGC-1alpha functions through many transcription factors, the PGC-1alpha partners identified to date are unlikely to account for all of its biologic actions. The orphan nuclear receptor estrogen-related receptor alpha (ERRalpha) was identified in a yeast two-hybrid screen of a cardiac cDNA library as a novel PGC-1alpha-binding protein. ERRalpha was implicated previously in regulating the gene encoding medium-chain acyl-CoA dehydrogenase (MCAD), which catalyzes the initial step in mitochondrial fatty acid oxidation. The cardiac perinatal expression pattern of ERRalpha paralleled that of PGC-1alpha and MCAD. Adenoviral-mediated ERRalpha overexpression in primary neonatal cardiac mycoytes induced endogenous MCAD expression. Furthermore, PGC-1alpha enhanced the transactivation of reporter plasmids containing an estrogen response element or the MCAD gene promoter by ERRalpha and the related isoform ERRgamma. In vitro binding experiments demonstrated that ERRalpha interacts with PGC-1alpha via its activation function-2 homology region. Mutagenesis studies revealed that the LXXLL motif at amino acid position 142-146 of PGC-1alpha (L2), necessary for PGC-1alpha interactions with other nuclear receptors, is not required for the PGC-1alpha.ERRalpha interaction. Rather, ERRalpha binds PGC-1alpha primarily through a Leu-rich motif at amino acids 209-213 (Leu-3) and utilizes additional LXXLL-containing domains as accessory binding sites. Thus, the PGC-1alpha.ERRalpha interaction is distinct from that of other nuclear receptor PGC-1alpha partners, including PPARalpha, hepatocyte nuclear factor-4alpha, and estrogen receptor alpha. These results identify ERRalpha and ERRgamma as novel PGC-1alpha interacting proteins, implicate ERR isoforms in the regulation of mitochondrial energy metabolism, and suggest a potential mechanism whereby PGC-1alpha selectively binds transcription factor partners.

The tremendous energy demands of the post-natal mammalian heart are fulfilled via dynamic flux through mitochondrial oxidative pathways. The capacity for energy production via fatty acid (FA) beta-oxidation pathway is determined, in part, by the regulated expression of genes encoding FA utilization enzymes and varies in accordance with diverse dietary and physiologic conditions. For example, fasting and diabetes activate the expression of cardiac FA oxidation (FAO). Peroxisome proliferator-activated receptor alpha (PPARalpha) is a ligand-activated transcription factor that is known to control the expression of many genes involved in cellular FA import and oxidation. Cardiac FA utilization rates are reduced in PPARalpha null mice due to diminished expression of genes encoding FAO enzymes. Recent work has shown that the PPARalpha regulatory pathway is deactivated in pathologic cardiac hypertrophy and hypoxia, two circumstances characterized by reduced FAO and increased dependence on glucose as a fuel source. Conversely, the activity of the PPARalpha gene regulatory pathway is increased in the diabetic heart, which relies primarily on FAO for energy production. In fact, evidence is emerging that excessive FA import and oxidation may be a cause of pathologic cardiac remodeling in the diabetic heart. This review summarizes the regulation of cardiac substrate utilization pathways via the PPARalpha complex in the normal and diseased heart.

Objectives: The purpose of this study was to determine whether patients with idiopathic dilated cardiomyopathy (IDCM) exhibit alterations in myocardial fatty acid and glucose metabolism., Background: Alterations in myocardial metabolism have been implicated in the pathogenesis of heart failure (HF); however, studies of myocardial metabolic function in human HF have yielded conflicting results. Animal models of HF have shown a downregulation of the expression of enzymes of fatty acid beta-oxidation that recapitulates the fetal energy metabolic program, in which fatty acid metabolism is decreased and glucose metabolism is increased., Methods: Seven patients with IDCM (mean left ventricular ejection fraction 27 +/- 8%) and 12 normal controls underwent positron emission tomography for measurements of myocardial blood flow (MBF), myocardial oxygen consumption (MVO(2)), myocardial glucose utilization (MGU), myocardial fatty acid utilization (MFAU) and myocardial fatty acid oxidation (MFAO)., Results: The systolic and diastolic blood pressures, plasma substrates and insulin levels, MBF and MVO(2), were similar between groups. The rates of MFAU and MFAO were significantly lower in IDCM than in the normal control group (MFAU: 134 +/- 44 vs. 213 +/- 49 nmol/g/min, p = 0.003; and MFAO: 113 +/- 50 vs. 205 +/- 49 nmol/g/min, p = 0.001) and the rates of MGU were significantly higher in IDCM than the normal control group (MGU: 247 +/- 63 vs. 125 +/- 64 nmol/g/min, p < 0.001)., Conclusions: Patients with IDCM exhibit alterations in myocardial metabolism characterized by decreased fatty acid metabolism and increased myocardial glucose metabolism, a pattern similar to that shown in animal models of HF. Whether alterations in myocardial metabolism constitute an adaptive response or mediate the development of HF remains to be determined.

Peroxisome proliferator-activated receptor alpha (PPARalpha) is a nuclear receptor transcription factor that has an important role in controlling cardiac metabolic gene expression. We determined whether mice lacking PPARalpha (PPARalpha (-/-) mice) have alterations in cardiac energy metabolism. Rates of palmitate oxidation were significantly decreased in isolated working hearts from PPARalpha (-/-) hearts compared with hearts from age-matched wild type mice (PPARalpha (+/+) mice), (62 +/- 12 versus 154 +/- 65 nmol/g dry weight/min, respectively, p < 0.05). This was compensated for by significant increases in the rates of glucose oxidation and glycolysis. The decreased fatty acid oxidation in PPARalpha (-/-) hearts was associated with increased levels of cardiac malonyl-CoA compared with PPARalpha (+/+) hearts (15.15 +/- 1.63 versus 7.37 +/- 1.31 nmol/g, dry weight, respectively, p < 0.05). Since malonyl-CoA is an important regulator of cardiac fatty acid oxidation, we also determined if the enzymes that control malonyl-CoA levels in the heart are under transcriptional control of PPARalpha. Expression of both mRNA and protein as well as the activity of malonyl-CoA decarboxylase, which degrades malonyl-CoA, were significantly decreased in the PPARalpha (-/-) hearts. In contrast, the expression and activity of acetyl-CoA carboxylase, which synthesizes malonyl-CoA and 5'-AMP-activated protein kinase, which regulates acetyl-CoA carboxylase, were not altered. Glucose transporter expression (GLUT1 and GLUT4) was not different between PPARalpha (-/-) and PPARalpha (+/+) hearts, suggesting that the increase in glycolysis and glucose oxidation in the PPARalpha null mice was not due to direct effects on glucose uptake but rather was occurring secondary to the decrease in fatty acid oxidation. This study demonstrates that PPARalpha is an important regulator of fatty acid oxidation in the heart and that this regulation of fatty acid oxidation may in part occur due to the transcriptional control of malonyl-CoA decarboxylase.

Recent evidence has defined an important role for PPARalpha in the transcriptional control of cardiac energy metabolism. To investigate the role of PPARalpha in the genesis of the metabolic and functional derangements of diabetic cardiomyopathy, mice with cardiac-restricted overexpression of PPARalpha (MHC-PPAR) were produced and characterized. The expression of PPARalpha target genes involved in cardiac fatty acid uptake and oxidation pathways was increased in MHC-PPAR mice. Surprisingly, the expression of genes involved in glucose transport and utilization was reciprocally repressed in MHC-PPAR hearts. Consistent with the gene expression profile, myocardial fatty acid oxidation rates were increased and glucose uptake and oxidation decreased in MHC-PPAR mice, a metabolic phenotype strikingly similar to that of the diabetic heart. MHC-PPAR hearts exhibited signatures of diabetic cardiomyopathy including ventricular hypertrophy, activation of gene markers of pathologic hypertrophic growth, and transgene expression-dependent alteration in systolic ventricular dysfunction. These results demonstrate that (a) PPARalpha is a critical regulator of myocardial fatty acid uptake and utilization, (b) activation of cardiac PPARalpha regulatory pathways results in a reciprocal repression of glucose uptake and utilization pathways, and (c) derangements in myocardial energy metabolism typical of the diabetic heart can become maladaptive, leading to cardiomyopathy.

Estrogen-related receptors (ERR) α and γ were shown recently to serve as regulators of cardiac maturation, yet the underlying mechanisms have not been delineated. Herein, we find that ERR signaling is necessary for induction of genes involved in mitochondrial and cardiac-specific contractile processes during human induced pluripotent stem cell-derived cardiomyocyte (hiPSC-CM) differentiation. Genomic interrogation studies demonstrate that ERRγ occupies many cardiomyocyte enhancers/super-enhancers, often co-localizing with the cardiogenic factor GATA4. ERRγ interacts with GATA4 to cooperatively activate transcription of targets involved in cardiomyocyte-specific processes such as contractile function, whereas ERRγ-mediated control of metabolic genes occurs independent of GATA4. Both mechanisms require the transcriptional coregulator PGC-1α. A disease-causing GATA4 mutation is shown to diminish PGC-1α/ERR/GATA4 cooperativity and expression of ERR target genes are downregulated in human heart failure samples suggesting that dysregulation of this circuitry may contribute to congenital and acquired forms of heart failure. Mature cardiac muscle requires high mitochondrial ATP production and specialized contractile proteins. Here the authors demonstrate that cardiomyocyte-specific contractile maturation involves cooperation between the nuclear receptor ERRγ and cardiogenic transcription factor GATA4, but ERRγ controls metabolic genes independently. [ABSTRACT FROM AUTHOR]

Cardiac muscle has the highest mitochondrial density of any human tissue, but mitochondrial dysfunction is not a recognized cause of isolated cardiomyopathy. Here, we determined that the rare mitofusin (MFN) 2 R400Q mutation is 15-20× over-represented in clinical cardiomyopathy, whereas this specific mutation is not reported as a cause of MFN2 mutant-induced peripheral neuropathy, Charcot-Marie-Tooth disease type 2A (CMT2A). Accordingly, we interrogated the enzymatic, biophysical, and functional characteristics of MFN2 Q400 versus wild-type and CMT2A-causing MFN2 mutants. All MFN2 mutants had impaired mitochondrial fusion, the canonical MFN2 function. Compared to MFN2 T105M that lacked catalytic GTPase activity and exhibited normal activation-induced changes in conformation, MFN2 R400Q and M376A had normal GTPase activity with impaired conformational shifting. MFN2 R400Q did not suppress mitochondrial motility, provoke mitochondrial depolarization, or dominantly suppress mitochondrial respiration like MFN2 T105M. By contrast to MFN2 T105M and M376A, MFN2 R400Q was uniquely defective in recruiting Parkin to mitochondria. CRISPR editing of the R400Q mutation into the mouse Mfn2 gene induced perinatal cardiomyopathy with no other organ involvement; knock-in of Mfn2 T105M or M376V did not affect the heart. RNA sequencing and metabolomics of cardiomyopathic Mfn2 Q/Q400 hearts revealed signature abnormalities recapitulating experimental mitophagic cardiomyopathy. Indeed, cultured cardiomyoblasts and in vivo cardiomyocytes expressing MFN2 Q400 had mitophagy defects with increased sensitivity to doxorubicin. MFN2 R400Q is the first known natural mitophagy-defective MFN2 mutant. Its unique profile of dysfunction evokes mitophagic cardiomyopathy, suggesting a mechanism for enrichment in clinical cardiomyopathy. [ABSTRACT FROM AUTHOR]

Estrogen-related receptors (ERRs) are orphan nuclear receptors activated by the transcriptional coactivator peroxisome proliferator-activated receptor γ (PPARγ) coactivator 1α (PGC-1α), a critical regulator of cellular energy metabolism. However, metabolic target genes downstream of ERRα have not been well defined. To identify ERRα-regulated pathways in tissues with high energy demand such as the heart, gene expression profiling was performed with primary neonatal cardiac myocytes overexpressing ERRα. ERRα upregulated a subset of PGC-1α target genes involved in multiple energy production pathways, including cellular fatty acid transport, mitochondrial and peroxisomal fatty acid oxidation, and mitochondrial respiration. These results were validated by independent analyses in cardiac myocytes, C2C12 myotubes, and cardiac and skeletal muscle of ERRα-/- mice. Consistent with the gene expression results, ERRα increased myocyte lipid accumulation and fatty acid oxidation rates. Many of the genes regulated by ERRα are known targets for the nuclear receptor PPARα, and therefore, the interaction between these regulatory pathways was explored. ERRα activated PPARα gene expression via direct binding of ERRα to the PPARα gene promoter. Furthermore, in fibroblasts null for PPARα and ERRα, the ability of ERRα to activate several PPARα targets and to increase cellular fatty acid oxidation rates was abolished. PGC-1α was also shown to activate ERRα gene expression. We conclude that ERRα serves as a critical nodal point in the regulatory circuitry downstream of PGC-1α to direct the transcription of genes involved in mitochondrial energy-producing pathways in cardiac and skeletal muscle. [ABSTRACT FROM AUTHOR]

To determine whether glutaminolysis inhibition is sufficient to revert myofibroblasts to a quiescent phenotype and reverse tissue fibrosis, we targeted I Gls1 i (glutaminase-1), the replace with committed step in of glutaminolysis, following fibroblast activation in a murine model of pressure-overload heart failure (HF). Keywords: fibrosis; glutamine; heart failure; metabolism; myofibroblasts EN fibrosis glutamine heart failure metabolism myofibroblasts 1625 1628 4 05/23/22 20220524 NES 220524 After injury, cardiac fibroblasts (CFs) differentiate into highly specialized myofibroblasts, essential for maintaining myocardial structural integrity by contracting surrounding tissue and remodeling the extracellular matrix network.[1] It was recently reported that withdrawal of stress stimuli is sufficient for some myofibroblasts to revert to a quiescent phenotype,[2] suggesting the potential for myofibroblast reversion by targeting the molecular pathways maintaining the fibrotic phenotype. [Extracted from the article]

To learn more about the targets of Cn (Cn) and calcium/calmodulin-dependent protein kinase in cardiac muscle, we investigated their actions in cultured cardiac myocytes and the hearts of mice in vivo. Adenoviral-mediated expression of constitutively active forms of either pathway induced expression of peroxisome proliferator-activated receptor γ coactivator 1α, a transcriptional coactivator involved in the control of multiple cellular energy metabolic pathways in cardiac myocytes. Transcriptional profiling studies demonstrated that Cn and calcium/calmodulin-dependent protein kinase activate distinct but overlapping metabolic gene regulatory programs. Expression of the nuclear receptor, peroxisome proliferator-activated receptor α, was markedly increased by Cn, but not calcium/calmodulin-dependent protein kinase, providing one mechanism whereby cellular fatty acid utilization genes are selectively activated by Cn. Transfection experiments demonstrated that Cn directly activates the mouse peroxisome proliferator-activated receptor α gene promoter. Co-transfection “add-back” experiments demonstrated that the transcription factors, myocyte enhancer factors 2C or 2D, were sufficient to confer Cn-mediated activation of the peroxisome proliferatoractivated receptor α gene. Cn was also shown to directly activate a known peroxisome proliferator-activated receptor α target, muscle-type carnitine palmitoyltransferase I, providing a second mechanism by which Cn activates genes of cellular fatty acid utilization. Lastly, the gene expression of peroxisome proliferator-activated receptor γ coactivator 1α and peroxisome proliferator-activated receptor α was reduced in the hearts of mice with cardiac-specific ablation of the Cn regulatory subunit. These data support a role for calcium-triggered signaling pathways in the regulation of cardiac energetics and identify pathway-specific control of metabolic targets. [ABSTRACT FROM AUTHOR]

Introduction: Recent Evidence indicates that circulating ketone bodies serve as an alternative myocardial substrate in heart failure (HF). Hypothesis: We tested the hypothesis that enhancing ketones delivery to the heart during early/compensated stages of HF delays the progression towards decompensation. Methods: Eight chronically instrumented dogs were subjected to cardiac tachypacing and infused with the ketone beta-hydroxybutyrate (BHB), starting after 2 weeks of pacing (HF+BHB group), i.e. during the early stages of cardiac dysfunction. A group of 8 dogs was subjected to cardiac pacing without BHB infusion (HF group). In 5 dogs per group, paired blood samples were withdrawn from aorta and coronary sinus to measure cardiac substrate utilization. 3H-oleate and 14C-glucose were co-infused to track the metabolic fate of free fatty acids (FFA) and glucose. Results: Blood BHB concentrations reached 190.3±19.7 microM in HF+BHB, approximately 4-fold the normal baseline values. This enhanced cardiac ketone uptake from 0.0091±0.002 to 0.022±0.005 umol/beat/100gr in HF+BHB vs HF (P<0.05). Cardiac glucose oxidation was more than doubled in HF vs control and but was suppressed in HF+BHB together with a 60% reduction in lactate uptake (all P<0.05). In contrast, FFA oxidation rates were modestly increased by the BHB infusion. These metabolic alterations were associated with marked functional protection: after 29±1 days of cardiac pacing, LV end-diastolic pressure was ≥25 mmHg in HF, indicating end-stage decompensation, while it remained at normal physiological values in HF+BHB. Cardiac output was also preserved and the fall in ejection fraction was significantly attenuated (56.1±1.5 vs 37.0±3.1%, P<0.05) in HF+BHB compared to HF. Beta-adrenergic response to dobutamine was also significantly higher in HF+BHB. However, BHB did not prevent alterations of other hemodynamic parameters, such as systemic blood pressures and dP/dtmax/min, typically occurring in HF. Conclusions: These results provide the first evidence that high levels of circulating BHB exert strong beneficial effects in HF opposing the progression toward decompensation, perhaps in part due to the shift of failing hearts from carbohydrate to ketones as a major source of energy. [ABSTRACT FROM AUTHOR]