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Background In complex congenital heart disease patients such as those with tetralogy of Fallot, the right ventricle (RV) is subject to pressure overload, leading to RV hypertrophy and eventually RV failure. The mechanisms that promote the transition from stable RV hypertrophy to RV failure are unknown. We evaluated the role of mitochondrial bioenergetics in the development of RV failure. Methods and Results We created a murine model of RV pressure overload by pulmonary artery banding and compared with sham‐operated controls. Gene expression by RNA‐sequencing, oxidative stress, mitochondrial respiration, dynamics, and structure were assessed in pressure overload‐induced RV failure. RV failure was characterized by decreased expression of electron transport chain genes and mitochondrial antioxidant genes (aldehyde dehydrogenase 2 and superoxide dismutase 2) and increased expression of oxidant stress markers (heme oxygenase, 4‐hydroxynonenal). The activities of all electron transport chain complexes decreased with RV hypertrophy and further with RV failure (oxidative phosphorylation: sham 552.3±43.07 versus RV hypertrophy 334.3±30.65 versus RV failure 165.4±36.72 pmol/(s×mL), P Conclusions Pressure overload‐induced RV failure is characterized by decreased transcription and activity of electron transport chain complexes and increased oxidative stress which are associated with decreased energy generation. An improved understanding of the complex processes of energy generation could aid in developing novel therapies to mitigate mitochondrial dysfunction and delay the onset of RV failure.

The myocardium consists of different cell types, of which endothelial cells, cardiomyocytes, and fibroblasts are the most abundant. Communication between these different cell types, also called paracrine signaling, is essential for normal cardiac function, but also important in cardiac remodeling and heart failure. Systematic studies on the expression of ligands and their corresponding receptors in different cell types showed that for 60% of the expressed ligands in a particular cell, the receptor is also expressed. The fact that many ligand‐receptor pairs are present in most cells, including the major cell types in the heart, indicates that autocrine signaling is a widespread phenomenon. Autocrine signaling in cardiac remodeling and heart failure is involved in all pathophysiological mechanisms generally observed: hypertrophy, fibrosis, angiogenesis, cell survival, and inflammation. Herein, we review ligand‐receptor pairs present in the major cardiac cell types based on RNA‐sequencing expression databases, and we review current literature on extracellular signaling proteins with an autocrine function in the heart; these include C‐type natriuretic peptide, fibroblast growth factors 2, F21, and 23, macrophage migration inhibitory factor, heparin binding–epidermal growth factor, angiopoietin‐like protein 2, leptin, adiponectin, follistatin‐like 1, apelin, neuregulin 1, vascular endothelial growth factor, transforming growth factor β, wingless‐type integration site family, member 1‐induced secreted protein‐1, interleukin 11, connective tissue growth factor/cellular communication network factor, and calcitonin gene‒related peptide. The large number of autocrine signaling factors that have been studied in the literature supports the concept that autocrine signaling is an essential part of myocardial biology and disease.

Background The mutated α‐B‐Crystallin (CryAB R120G ) mouse model of desmin‐related myopathy (DRM) shows an age‐dependent onset of pathologic cardiac remodeling and progression of heart failure. CryAB R120G expression in cardiomyocytes affects the mitochondrial spatial organization within the myofibrils, but the molecular perturbation within the mitochondria in the relation of the overall course of the proteotoxic disease remains unclear. Methods and Results CryAB R120G mice show an accumulation of electron‐dense aggregates and myofibrillar degeneration associated with the development of cardiac dysfunction. Though extensive studies demonstrated that these altered ultrastructural changes cause cardiac contractility impairment, the molecular mechanism of cardiomyocyte death remains elusive. Here, we explore early pathological processes within the mitochondria contributing to the contractile dysfunction and determine the pathogenic basis for the heart failure observed in the CryAB R120G mice. In the present study, we report that the CryAB R120G mice transgenic hearts undergo altered mitochondrial dynamics associated with increased level of dynamin‐related protein 1 and decreased level of optic atrophy type 1 as well as mitofusin 1 over the disease process. In association with these changes, an altered level of the components of mitochondrial oxidative phosphorylation and pyruvate dehydrogenase complex regulatory proteins occurs before the manifestation of pathologic adverse remodeling in the CryAB R120G hearts. Mitochondria isolated from CryAB R120G transgenic hearts without visible pathology show decreased electron transport chain complex activities and mitochondrial respiration. Taken together, we demonstrated the involvement of mitochondria in the pathologic remodeling and progression of DRM‐associated cellular dysfunction. Conclusions Mitochondrial dysfunction in the form of altered mitochondrial dynamics, oxidative phosphorylation and pyruvate dehydrogenase complex proteins level, abnormal electron transport chain complex activities, and mitochondrial respiration are evident on the CryAB R120G hearts before the onset of detectable pathologies and development of cardiac contractile dysfunction.

Background Pediatric‐onset restrictive cardiomyopathy (RCM) is associated with high mortality, but underlying mechanisms of disease are under investigated. RCM‐associated diastolic dysfunction secondary to variants in TNNT2‐encoded cardiac troponin T (TNNT2) is poorly described. Methods and Results Genetic analysis of a proband and kindred with RCM identified TNNT2‐R94C, which cosegregated in a family with 2 generations of RCM, ventricular arrhythmias, and sudden death. TNNT2‐R94C was absent among large, population‐based cohorts Genome Aggregation Database (gnomAD) and predicted to be pathologic by in silico modeling. Biophysical experiments using recombinant human TNNT2‐R94C demonstrated impaired cardiac regulation at the molecular level attributed to reduced calcium‐dependent blocking of myosin's interaction with the thin filament. Computational modeling predicted a shift in the force‐calcium curve for the R94C mutant toward submaximal calcium activation compared within the wild type, suggesting low levels of muscle activation even at resting calcium concentrations and hypercontractility following activation by calcium. Conclusions The pathogenic TNNT2‐R94C variant activates thin‐filament–mediated sarcomeric contraction at submaximal calcium concentrations, likely resulting in increased muscle tension during diastole and hypercontractility during systole. This describes the proximal biophysical mechanism for development of RCM in this family.

Background Translocation of miR‐181c into cardiac mitochondria downregulates the mitochondrial gene, mt‐ COX 1. miR‐181c/d −/− hearts experience less oxidative stress during ischemia/reperfusion (I/R) and are protected against I/R injury. Additionally, miR‐181c overexpression can increase mitochondrial matrix Ca 2+ ([Ca 2+ ] m ), but the mechanism by which miR‐181c regulates [Ca 2+ ] m is unknown. Methods and Results By RNA sequencing and analysis, here we show that hearts from miR‐181c/d −/− mice overexpress nuclear‐encoded Ca 2+ regulatory and metabolic pathway genes, suggesting that alterations in miR‐181c and mt‐ COX 1 perturb mitochondria‐to‐nucleus retrograde signaling and [Ca 2+ ] m regulation. Quantitative polymerase chain reaction validation of transcription factors that are known to initiate retrograde signaling revealed significantly higher Sp1 (specificity protein) expression in the miR‐181c/d −/− hearts. Furthermore, an association of Sp1 with the promoter region of MICU 1 was confirmed by chromatin immunoprecipitation‐quantitative polymerase chain reaction and higher expression of MICU 1 was found in the miR‐181c/d −/− hearts. Conversely, downregulation of Sp1 by small interfering RNA decreased MICU 1 expression in neonatal mouse ventricular myocytes. Changes in PDH activity provided evidence for a change in [Ca 2+ ] m via the miR‐181c/ MICU 1 axis. Moreover, this mechanism was implicated in the pathology of I/R injury. When MICU 1 was knocked down in the miR‐181c/d −/− heart by lentiviral expression of a short‐hairpin RNA against MICU 1, cardioprotective effects against I/R injury were abrogated. Furthermore, using an in vitro I/R model in miR‐181c/d −/− neonatal mouse ventricular myocytes, we confirmed the contribution of both Sp1 and MICU 1 in ischemic injury. Conclusions miR‐181c regulates mt‐ COX 1, which in turn regulates MICU 1 expression through the Sp1‐mediated mitochondria‐to‐nucleus retrograde pathway. Loss of miR‐181c can protect the heart from I/R injury by modulating [Ca 2+ ] m through the upregulation of MICU 1.

Background Right ventricular ( RV ) failure because of chronic pressure load is an important determinant of outcome in pulmonary hypertension. Progression towards RV failure is characterized by diastolic dysfunction, fibrosis and metabolic dysregulation. Metabolic modulation has been suggested as therapeutic option, yet, metabolic dysregulation may have various faces in different experimental models and disease severity. In this systematic review and meta‐analysis, we aimed to identify metabolic changes in the pressure loaded RV and formulate recommendations required to optimize translation between animal models and human disease. Methods and Results Medline and EMBASE were searched to identify original studies describing cardiac metabolic variables in the pressure loaded RV . We identified mostly rat‐models, inducing pressure load by hypoxia, Sugen‐hypoxia, monocrotaline (MCT), pulmonary artery banding ( PAB ) or strain (fawn hooded rats, FHR ), and human studies. Meta‐analysis revealed increased Hedges’ g (effect size) of the gene expression of GLUT 1 and HK 1 and glycolytic flux. The expression of MCAD was uniformly decreased. Mitochondrial respiratory capacity and fatty acid uptake varied considerably between studies, yet there was a model effect in carbohydrate respiratory capacity in MCT ‐rats. Conclusions This systematic review and meta‐analysis on metabolic remodeling in the pressure‐loaded RV showed a consistent increase in glucose uptake and glycolysis, strongly suggest a downregulation of beta‐oxidation, and showed divergent and model‐specific changes regarding fatty acid uptake and oxidative metabolism. To translate metabolic results from animal models to human disease, more extensive characterization, including function, and uniformity in methodology and studied variables, will be required.

Background Myocardial infarction results in a large‐scale cardiomyocyte loss and heart failure due to subsequent pathological remodeling. Whereas zebrafish and neonatal mice have evident cardiomyocyte expansion following injury, adult mammalian cardiomyocytes are principally nonproliferative. Despite historical presumptions of stem cell–mediated cardiac regeneration, numerous recent studies using advanced lineage‐tracing methods demonstrated that the only source of cardiomyocyte renewal originates from the extant myocardium; thus, the augmented proliferation of preexisting adult cardiomyocytes remains a leading therapeutic approach toward cardiac regeneration. In the present study we investigate the significance of suppressing cell cycle inhibitors Rb1 and Meis2 to promote adult cardiomyocyte reentry to the cell cycle. Methods and Results In vitro experiments with small interfering RNA –mediated simultaneous knockdown of Rb1 and Meis2 in both adult rat cardiomyocytes, isolated from 12‐week‐old Fischer rats, and human induced pluripotent stem cell–derived cardiomyocytes showed a significant increase in cell number, a decrease in cell size, and an increase in mononucleated cardiomyocytes. In vivo, a hydrogel‐based delivery method for small interfering RNA –mediated silencing of Rb1 and Meis2 is utilized following myocardial infarction. Immunofluorescent imaging analysis revealed a significant increase in proliferation markers 5‐ethynyl‐2′‐deoxyuridine, PH 3, KI 67, and Aurora B in adult cardiomyocytes as well as improved cell survivability with the additional benefit of enhanced peri‐infarct angiogenesis. Together, this intervention resulted in a reduced infarct size and improved cardiac function post–myocardial infarction. Conclusions Silencing of senescence‐inducing pathways in adult cardiomyocytes via inhibition of Rb1 and Meis2 results in marked cardiomyocyte proliferation and increased protection of cardiac function in the setting of ischemic injury.

Background In murine heart failure models and in humans with diabetic‐related heart hypertrophy, inhibition of phosphodiesterase 5 ( PDE 5) by sildenafil improves cardiac outcomes. However, the mechanism by which sildenafil improves cardiac function is unclear. We have observed a relationship between PDE 5 and β2 adrenergic receptor (β2 AR ), which is characterized here as a novel mechanistic axis by which sildenafil improves symptoms of diabetic cardiomyopathy. Methods and Results Wild‐type and β2 AR knockout mice fed a high fat diet ( HFD ) were treated with sildenafil, and echocardiogram analysis was performed. Cardiomyocytes were isolated for excitation‐contraction (E‐C) coupling, fluorescence resonant energy transfer, and proximity ligation assays; while heart tissues were implemented for biochemical and histological analyses. PDE 5 selectively associates with β2 AR , but not β1 adrenergic receptor, and inhibition of PDE 5 with sildenafil restores the impaired response to adrenergic stimulation in HFD mice and isolated ventriculomyocytes. Sildenafil enhances β adrenergic receptor (βAR)‐stimulated cGMP and cAMP signals in HFD myocytes. Consequently, inhibition of PDE 5 leads to protein kinase G–, and to a lesser extent, calcium/calmodulin‐dependent kinase II –dependent improvements in adrenergically stimulated E‐C coupling. Deletion of β2 AR abolishes sildenafil's effect. Although the PDE 5‐β2 AR association is not altered in HFD , phosphodiesterase 3 displays an increased association with the β2 AR ‐ PDE 5 complex in HFD myocytes. Conclusions This study elucidates mechanisms by which the β2 AR ‐ PDE 5 axis can be targeted for treating diabetic cardiomyopathy. Inhibition of PDE 5 enhances β2 AR stimulation of cGMP and cAMP signals, as well as protein kinase G–dependent E‐C coupling in HFD myocytes.

Background Particulate matter (particles < 2.5 μm [PM 2.5]) exposure during the in utero and postnatal developmental periods causes cardiac dysfunction during adulthood. Here, we investigated the potential priming effects of preconception exposure of PM 2.5 on cardiac function in adult offspring. Methods and Results Male and female friend leukemia virus b (FVB) mice were exposed to either filtered air (FA) or PM 2.5 at an average concentration of 38.58 μg/m3 for 6 hours/day, 5 days/week for 3 months. Mice were then crossbred into 2 groups: (1) FA male×FA female (both parents were exposed to FA preconception) and, (2) PM 2.5male×PM 2.5female (both parents were exposed to PM 2.5 preconception). Male offspring were divided: (1) preconception FA (offspring born to FA exposed parents) and, (2) preconception PM 2.5 (offspring born to PM 2.5 exposed parents) and analyzed at 3 months of age. Echocardiography identified increased left ventricular end systolic volume and reduced posterior wall thickness, reduced %fractional shortening and %ejection fraction in preconception PM 2.5 offspring. Cardiomyocytes isolated from preconception PM 2.5 offspring showed reduced %peak shortening, −dL/dT, TPS90 and slower calcium reuptake (tau). Gene and protein expression revealed modifications in markers of inflammation (IL‐6, IL‐15, TNFα, NFқB, CRP, CD26E, CD26P, intercellular adhesion molecule 1, and monocyte chemoattractant protein‐1) profibrosis (collagen type III alpha 1 chain), oxidative stress (NOS2), antioxidants (Nrf2, SOD, catalase), Ca2+ regulatory proteins (SERCA2a, p‐PLN, NCX), and epigenetic regulators (Dnmt1, Dnmt3a, Dnmt3b, Sirt1, and Sirt2) in preconception PM 2.5 offspring. Conclusions Preconception exposure to PM 2.5 results in global cardiac dysfunction in adult offspring, suggesting that abnormalities during development are not limited to the prenatal or postnatal periods but can also be determined before conception., See Editorial by Stapleton

Background Cardiac hypertrophy is an adaptive remodeling event that may improve or diminish contractile performance of the heart. Physiologic and pathologic hypertrophy yield distinct outcomes, yet both are dependent on caspase‐directed proteolysis. This suggests that each form of myocardial growth may derive from a specific caspase cleavage event(s). We examined whether caspase 3 cleavage of the actin capping/severing protein gelsolin is essential for the development of pathologic hypertrophy. Methods and Results Caspase targeting of gelsolin was established through protein analysis of hypertrophic cardiomyocytes and mass spectrometry mapping of cleavage sites. Pathologic agonists induced late‐stage caspase‐mediated cleavage of gelsolin. The requirement of caspase‐mediated gelsolin cleavage for hypertrophy induction was evaluated in primary cardiomyocytes by cell size analysis, monitoring of prohypertrophy markers, and measurement of hypertrophy‐related transcription activity. The in vivo impact of caspase‐mediated cleavage was investigated by echo‐guided intramyocardial injection of adenoviral‐expressed gelsolin. Expression of the N‐terminal gelsolin caspase cleavage fragment was necessary and sufficient to cause pathologic remodeling in isolated cardiomyocytes and the intact heart, whereas expression of a noncleavable form prevents cardiac remodeling. Alterations in myocardium structure and function were determined by echocardiography and end‐stage cardiomyocyte cell size analysis. Gelsolin secretion was also monitored for its impact on naïve cells using competitive antibody trapping, demonstrating that hypertrophic agonist stimulation of cardiomyocytes leads to gelsolin secretion, which induces hypertrophy in naïve cells. Conclusions These results suggest that cell autonomous caspase cleavage of gelsolin is essential for pathologic hypertrophy and that cardiomyocyte secretion of gelsolin may accelerate this negative remodeling response.

Background Dilated cardiomyopathy (DCM) is a common cause of heart failure in adult and pediatric patients, but the underlying mechanism may vary in adults and children, with few studies conducted to date. The objective of the present study was to determine whether differential remodeling of the extracellular matrix contributes to the differences between pediatric and adult DCM hearts. Methods and Results Explanted hearts were procured from adult (age, 46–61 years) and pediatric (age, 2–8) patients with DCM‐related heart failure and nonfailing control hearts. Fibrillar and nonfibrillar extracellular matrix (proteoglycans, glycosaminoglycans, glycoprotein), their regulatory enzymes (matrix metalloproteinases, disintegrin and metalloproteinases, and disintegrin and metalloproteinases with a thrombospondin domain), and their inhibitors (tissue inhibitor of metalloproteinases) were assessed. Pediatric DCM hearts exhibited less fibrosis compared with adult DCMs. Total glycosaminoglycans increased similarly in both DCM groups but exhibited a significantly lower affinity for transforming growth factor‐β in adult DCMs versus pediatric DCMs, resulting in increased bioavailability of transforming growth factor‐β1 and a significantly higher activity of the Smad2/3 pathway in adult DCMs. Glycosylated biglycan and versican, and cleaved thrombospondin‐1 increased in both DCMs. Protein expression of disintegrin and metalloproteinases with thrombospondin domains (‐1, ‐2, ‐4, ‐7) and disintegrin and metalloproteinases (‐12, ‐15, ‐17, ‐19) were altered differently in pediatric and adult control and failing hearts. Total matrix metalloproteinase activity increased in both DCMs. Tissue inhibitor of metalloproteinase levels were altered similarly with heart failure in both age groups, and only tissue inhibitor of metalloproteinase 3 decreased in both DCM groups. Conclusions Differential remodeling of glycosaminoglycans in pediatric DCMs versus adult DCMs could underlie the enhanced activation of the transforming growth factor‐β pathway, leading to more fibrosis in adult DCM hearts. The distinct remodeling of the fibrillar and nonfibrillar extracellular matrix between pediatric and adult DCM hearts highlights a distinct pathophysiological basis for these cohorts.

Background A clear understanding of the molecular mechanisms underlying hemodynamic stress‐initiated cardiac hypertrophy is important for preventing heart failure. Interferon‐γ ( IFN ‐γ) has been suggested to play crucial roles in various diseases other than immunological disorders by modulating the expression of myriad genes. However, the involvement of IFN ‐γ in the pathogenesis of cardiac hypertrophy still remains unclear. Methods and Results In order to elucidate the roles of IFN ‐γ in pressure overload–induced cardiac pathology, we subjected Balb/c wild‐type ( WT ) or IFN ‐γ‐deficient ( Ifng −/− ) mice to transverse aortic constriction ( TAC ). Three weeks after TAC , Ifng −/− mice developed more severe cardiac hypertrophy, fibrosis, and dysfunction than WT mice. Bone marrow–derived immune cells including macrophages were a source of IFN ‐γ in hearts after TAC . The activation of PI 3K/Akt signaling, a key signaling pathway in compensatory hypertrophy, was detected 3 days after TAC in the left ventricles of WT mice and was markedly attenuated in Ifng −/− mice. The administration of a neutralizing anti‐ IFN ‐γ antibody abrogated PI 3K/Akt signal activation in WT mice during compensatory hypertrophy, while that of IFN ‐γ activated PI 3K/Akt signaling in Ifng −/− mice. TAC also induced the phosphorylation of Stat5, but not Stat1 in the left ventricles of WT mice 3 days after TAC . Furthermore, IFN ‐γ induced Stat5 and Akt phosphorylation in rat cardiomyocytes cultured under stretch conditions. A Stat5 inhibitor significantly suppressed PI 3K/Akt signaling activation in the left ventricles of WT mice, and aggravated pressure overload–induced cardiac hypertrophy. Conclusions The IFN ‐γ/Stat5 axis may be protective against persistent pressure overload–induced cardiac hypertrophy by activating the PI 3K/Akt pathway.

Background Aberrant Ca2+ handling is a prominent feature of heart failure. Elucidation of the molecular mechanisms responsible for aberrant Ca2+ handling is essential for the development of strategies to blunt pathological changes in calcium dynamics. The peptidyl‐prolyl cis‐trans isomerase peptidyl‐prolyl isomerase 1 (Pin1) is a critical mediator of myocardial hypertrophy development and cardiac progenitor cell cycle. However, the influence of Pin1 on calcium cycling regulation has not been explored. On the basis of these findings, the aim of this study is to define Pin1 as a novel modulator of Ca2+ handling, with implications for improving myocardial contractility and potential for ameliorating development of heart failure. Methods and Results Pin1 gene deletion or pharmacological inhibition delays cytosolic Ca2+ decay in isolated cardiomyocytes. Paradoxically, reduced Pin1 activity correlates with increased sarco(endo)plasmic reticulum calcium ATPase (SERCA2a) and Na2+/Ca2+ exchanger 1 protein levels. However, SERCA2a ATPase activity and calcium reuptake were reduced in sarcoplasmic reticulum membranes isolated from Pin1‐deficient hearts, suggesting that Pin1 influences SERCA2a function. SERCA2a and Na2+/Ca2+ exchanger 1 associated with Pin1, as revealed by proximity ligation assay in myocardial tissue sections, indicating that regulation of Ca2+ handling within cardiomyocytes is likely influenced through Pin1 interaction with SERCA2a and Na2+/Ca2+ exchanger 1 proteins. Conclusions Pin1 serves as a modulator of SERCA2a and Na2+/Ca2+ exchanger 1 Ca2+ handling proteins, with loss of function resulting in impaired cardiomyocyte relaxation, setting the stage for subsequent investigations to assess Pin1 dysregulation and modulation in the progression of heart failure.

Background Pulmonary arterial hypertension ( PAH ) is a lethal disease characterized by obstructive pulmonary vascular remodeling and right ventricular ( RV ) dysfunction. Although RV function predicts outcomes in PAH , mechanisms of RV dysfunction are poorly understood, and RV ‐targeted therapies are lacking. We hypothesized that in PAH , abnormal microtubular structure in RV cardiomyocytes impairs RV function by reducing junctophilin‐2 ( JPH 2) expression, resulting in t‐tubule derangements. Conversely, we assessed whether colchicine, a microtubule‐depolymerizing agent, could increase JPH 2 expression and enhance RV function in monocrotaline‐induced PAH . Methods and Results Immunoblots, confocal microscopy, echocardiography, cardiac catheterization, and treadmill testing were used to examine colchicine's (0.5 mg/kg 3 times/week) effects on pulmonary hemodynamics, RV function, and functional capacity. Rats were treated with saline (n=28) or colchicine (n=24) for 3 weeks, beginning 1 week after monocrotaline (60 mg/kg, subcutaneous). In the monocrotaline RV , but not the left ventricle, microtubule density is increased, and JPH 2 expression is reduced, with loss of t‐tubule localization and t‐tubule disarray. Colchicine reduces microtubule density, increases JPH 2 expression, and improves t‐tubule morphology in RV cardiomyocytes. Colchicine therapy diminishes RV hypertrophy, improves RV function, and enhances RV –pulmonary artery coupling. Colchicine reduces small pulmonary arteriolar thickness and improves pulmonary hemodynamics. Finally, colchicine increases exercise capacity. Conclusions Monocrotaline‐induced PAH causes RV ‐specific derangement of microtubules marked by reduction in JPH 2 and t‐tubule disarray. Colchicine reduces microtubule density, increases JPH 2 expression, and improves both t‐tubule architecture and RV function. Colchicine also reduces adverse pulmonary vascular remodeling. These results provide biological plausibility for a clinical trial to repurpose colchicine as a RV ‐directed therapy for PAH .

The immune system plays a pivotal role in myocardial homeostasis and response to injury. Interleukins-4 and -13 are anti-inflammatory type-2 cytokines, signaling via the common interleukin-13 receptor α1 chain and the type-2 interleukin-4 receptor. The role of interleukin-13 receptor α1 in the heart is unknown.We analyzed myocardial samples from human donors (n=136) and patients with end-stage heart failure (n=177). We found that the interleukin-13 receptor α1 is present in the myocardium and, together with the complementary type-2 interleukin-4 receptor chainThe results of our studies in humans and mice indicate, for the first time, a role of interleukin-13 receptor α1 in myocardial homeostasis and heart failure and suggests a new therapeutic target to treat heart disease.

Background High levels of ketone bodies are associated with improved survival as observed with regular exercise, caloric restriction, and—most recently—treatment with sodium–glucose linked transporter 2 inhibitor antidiabetic drugs. In heart failure, indices of ketone body metabolism are upregulated, which may improve energy efficiency and increase blood flow in skeletal muscle and the kidneys. Nevertheless, it is uncertain how ketone bodies affect myocardial glucose uptake and blood flow in humans. Our study was therefore designed to test whether ketone body administration in humans reduces myocardial glucose uptake ( MGU ) and increases myocardial blood flow. Methods and Results Eight healthy subjects, median aged 60 were randomly studied twice: (1) During 390 minutes infusion of Na‐3‐hydroxybutyrate ( KETONE ) or (2) during 390 minutes infusion of saline ( SALINE ), together with a concomitant low‐dose hyperinsulinemic–euglycemic clamp to inhibit endogenous ketogenesis. Myocardial blood flow was measured by 15 O‐H 2 O positron emission tomography/computed tomography, myocardial fatty acid metabolism by 11 C‐palmitate positron emission tomography/computed tomography and MGU by 18 F‐fluorodeoxyglucose positron emission tomography/computed tomography. Similar euglycemia, hyperinsulinemia, and suppressed free fatty acids levels were recorded on both study days; Na‐3‐hydroxybutyrate infusion increased circulating Na‐3‐hydroxybutyrate levels from zero to 3.8±0.5 mmol/L. MGU was halved by hyperketonemia ( MGU [nmol/g per minute]: 304±97 [ SALINE ] versus 156±62 [ KETONE ], P Conclusions Ketone bodies displace MGU and increase myocardial blood flow in healthy humans; these novel observations suggest that ketone bodies are important cardiac fuels and vasodilators, which may have therapeutic potentials.

Background Sphingosine‐1‐phosphate plays vital roles in cardiomyocyte physiology, myocardial ischemia–reperfusion injury, and ischemic preconditioning. The function of the cardiomyocyte sphingosine‐1‐phosphate receptor 1 (S1P1) in vivo is unknown. Methods and Results Cardiomyocyte‐restricted deletion of S1P1 in mice (S1P1 α MHCC re) resulted in progressive cardiomyopathy, compromised response to dobutamine, and premature death. Isolated cardiomyocytes from S1P1 α MHCC re mice revealed reduced diastolic and systolic Ca2+ concentrations that were secondary to reduced intracellular Na+ and caused by suppressed activity of the sarcolemmal Na+/H+ exchanger NHE‐1 in the absence of S1P1. This scenario was successfully reproduced in wild‐type cardiomyocytes by pharmacological inhibition of S1P1 or sphingosine kinases. Furthermore, Sarcomere shortening of S1P1 α MHCC re cardiomyocytes was intact, but sarcomere relaxation was attenuated and Ca2+ sensitivity increased, respectively. This went along with reduced phosphorylation of regulatory myofilament proteins such as myosin light chain 2, myosin‐binding protein C, and troponin I. In addition, S1P1 mediated the inhibitory effect of exogenous sphingosine‐1‐phosphate on β‐adrenergic–induced cardiomyocyte contractility by inhibiting the adenylate cyclase. Furthermore, ischemic precondtioning was abolished in S1P1 α MHCC re mice and was accompanied by defective Akt activation during preconditioning. Conclusions Tonic S1P1 signaling by endogenous sphingosine‐1‐phosphate contributes to intracellular Ca2+ homeostasis by maintaining basal NHE‐1 activity and controls simultaneously myofibril Ca2+ sensitivity through its inhibitory effect on adenylate cyclase. Cardioprotection by ischemic precondtioning depends on intact S1P1 signaling. These key findings on S1P1 functions in cardiac physiology may offer novel therapeutic approaches to cardiac diseases.

Background Nitric oxide synthase uncoupling occurs under conditions of oxidative stress modifying the enzyme's function so it generates superoxide rather than nitric oxide. Nitric oxide synthase uncoupling occurs with chronic pressure overload, and both are ameliorated by exogenous tetrahydrobiopterin ( BH 4)—a cofactor required for normal nitric oxide synthase function—supporting a pathophysiological link. Genetically augmenting BH 4 synthesis in endothelial cells fails to replicate this benefit, indicating that other cell types dominate the effects of exogenous BH 4 administration. We tested whether the primary cellular target of BH 4 is the cardiomyocyte or whether other novel mechanisms are invoked. Methods and Results Mice with cardiomyocyte‐specific overexpression of GTP cyclohydrolase 1 ( mGCH 1) and wild‐type littermates underwent transverse aortic constriction. The mGCH 1 mice had markedly increased myocardial BH 4 and, unlike wild type, maintained nitric oxide synthase coupling after transverse aortic constriction; however, the transverse aortic constriction–induced abnormalities in cardiac morphology and function were similar in both groups. In contrast, exogenous BH 4 supplementation improved transverse aortic constricted hearts in both groups, suppressed multiple inflammatory cytokines, and attenuated infiltration of inflammatory macrophages into the heart early after transverse aortic constriction. Conclusions BH 4 protection against adverse remodeling in hypertrophic cardiac disease is not driven by its prevention of myocardial nitric oxide synthase uncoupling, as presumed previously. Instead, benefits from exogenous BH 4 are mediated by a protective effect coupled to suppression of inflammatory pathways and myocardial macrophage infiltration.