Targeted GLUT-4 deficiency in the heart induces cardiomyocyte hypertrophy and impaired contractility linked with Ca2+ and proton flux dysregulation

TIGAR Deficiency Blunts Angiotensin-II-Induced Cardiac Hypertrophy in Mice

Hypertension is the key contributor to pathological cardiac hypertrophy. Growing evidence indicates that glucose metabolism plays an essential role in cardiac hypertrophy. TP53-induced glycolysis and apoptosis regulator (TIGAR) has been shown to regulate glucose metabolism in pressure overload-induced cardiac remodeling. In the present study, we investigated the role of TIGAR in cardiac remodeling during Angiotensin II (Ang-II)-induced hypertension. Wild-type (WT) and TIGAR knockout (KO) mice were infused with Angiotensin-II (Ang-II, 1 µg/kg/min) via mini-pump for four weeks. The blood pressure was similar between the WT and TIGAR KO mice. The Ang-II infusion resulted in a similar reduction of systolic function in both groups, as evidenced by the comparable decrease in LV ejection fraction and fractional shortening. The Ang-II infusion also increased the isovolumic relaxation time and myocardial performance index to the same extent in WT and TIGAR KO mice, suggesting the development of similar diastolic dysfunction. However, the knockout of TIGAR significantly attenuated hypertension-induced cardiac hypertrophy. This was associated with higher levels of fructose 2,6-bisphosphate, PFK-1, and Glut-4 in the TIGAR KO mice. Our present study suggests that TIGAR is involved in the control of glucose metabolism and glucose transporters by Ang-II and that knockout of TIGAR attenuates the development of maladaptive cardiac hypertrophy.

Mapping the cellular and molecular landscape of cardiac non-myocytes in murine diabetic cardiomyopathy

Diabetes is associated with a significantly elevated risk of heart failure. However, despite extensive efforts to characterize the phenotype of the diabetic heart, the molecular and cellular protagonists that underpin cardiac pathological remodeling in diabetes remain unclear, with a notable paucity of data regarding the impact of diabetes on non-myocytes within the heart. Here we aimed to define key differences in cardiac non-myocytes between spontaneously type-2 diabetic (db/db) and healthy control (db/h) mouse hearts. Single-cell transcriptomic analysis revealed a concerted diabetes-induced cellular response contributing to cardiac remodeling. These included cell-specific activation of gene programs relating to fibroblast hyperplasia and cell migration, and dysregulation of pathways involving vascular homeostasis and protein folding. This work offers a new perspective for understanding the cellular mediators of diabetes-induced cardiac pathology, and pathways that may be targeted to address the cardiac complications associated with diabetes.

Gut-derived short-chain fatty acids bridge cardiac and systemic metabolism and immunity in heart failure

Heart failure (HF) represents a group of complex clinical syndromes with high morbidity and mortality and has a significant global health burden. Inflammation and metabolic disorders are closely related to the development of HF, which are complex and depend on the severity and type of HF and common metabolic comorbidities such as obesity and diabetes. An increasing body of evidence indicates the importance of short-chain fatty acids (SCFAs) in regulating cardiac function. In addition, SCFAs represent a unique class of metabolites and play a distinct role in shaping systemic immunity and metabolism. In this review, we reveal the role of SCFAs as a link between metabolism and immunity, which regulate cardiac and systemic immune and metabolic systems by acting as energy substrates, inhibiting the expression of histone deacetylase (HDAC) regulated genes and activating G protein-coupled receptors (GPCRs) signaling. Ultimately cardiac efficiency is improved, cardiac inflammation alleviated and cardiac function in failing hearts enhanced. In conclusion, SCFAs represent a new therapeutic approach for HF.

Extracellular matrix remodelling in obesity and metabolic disorders

Obesity causes extracellular matrix (ECM) remodelling which can develop into serious pathology and fibrosis, having metabolic effects in insulin-sensitive tissues. The ECM components may be increased in response to overnutrition. This review will focus on specific obesity-associated molecular and pathophysiological mechanisms of ECM remodelling and the impact of specific interactions on tissue metabolism. In obesity, complex network of signalling molecules such as cytokines and growth factors have been implicated in fibrosis. Increased ECM deposition contributes to the pathogenesis of insulin resistance at least in part through activation of cell surface integrin receptors and CD44 signalling cascades. These cell surface receptors transmit signals to the cell adhesome which orchestrates an intracellular response that adapts to the extracellular environment. Matrix proteins, glycoproteins, and polysaccharides interact through ligand-specific cell surface receptors that interact with the cytosolic adhesion proteins to elicit specific actions. Cell adhesion proteins may have catalytic activity or serve as scaffolds. The vast number of cell surface receptors and the complexity of the cell adhesome have made study of their roles challenging in health and disease. Further complicating the role of ECM-cell receptor interactions is the variation between cell types. This review will focus on recent insights gained from studies of two highly conserved, ubiquitously axes and how they contribute to insulin resistance and metabolic dysfunction in obesity. These are the collagen-integrin receptor-IPP (ILK-PINCH-Parvin) axis and the hyaluronan-CD44 interaction. We speculate that targeting ECM components or their receptor-mediated cell signalling may provide novel insights into the treatment of obesity-associated cardiometabolic complications.

Transcriptional analysis reveals that the intracellular lipid accumulation impairs gene expression profiles involved in insulin response-associated cardiac functionality

Cardiovascular disease (CVD) is a multisystemic and multicellular pathology that is generally associated with high levels of atherogenic lipoproteins in circulation. These lipoproteins tend to be retained and modified, for example, aggregated low-density lipoprotein (aggLDL), in the extracellular matrix of different tissues, such as the vascular wall and heart. The uptake of aggLDL generates a significant increase in cholesteryl ester (CE) in these tissues. We previously found that the accumulation of CE generates alterations in the insulin response in the heart. Although the insulin response is mainly associated with the uptake and metabolism of glucose, other studies have shown that insulin would fulfill functions in this tissue, such as regulating the calcium cycle and cardiac contractility. Here, we found that aggLDL induced-lipid accumulation altered the gene expression profile involved in processes essential for cardiac functionality, including insulin response and glucose uptake (Insr, Ins1, Pik3ip1, Slc2a4 gene expression), calcium cycle (Cacna1s and Gjc2 gene expression) and calcium-dependent cardiac contractility (Myh3), and cholesterol efflux (Abca1), in HL-1 cardiomyocytes. These observations were recapitulated using an in vivo model of hypercholesterolemic ApoE-KO mice. Altogether, these results may explain the deleterious effect of lipid accumulation in the myocardium, with important implications for lipid-overloaded associated CVD, including impaired insulin response, disrupted lipid metabolism, altered cardiac structure, and increased susceptibility to cardiovascular events.

Transcriptional analysis reveals that the intracellular lipid accumulation impairs gene expression profiles involved in insulin response-associated cardiac functionality

Cardiovascular disease (CVD) is a multisystemic and multicellular pathology that is generally associated with high levels of atherogenic lipoproteins in circulation. These lipoproteins tend to be retained and modified, for example, aggregated low-density lipoprotein (aggLDL), in the extracellular matrix of different tissues, such as the vascular wall and heart. The uptake of aggLDL generates a significant increase in cholesteryl ester (CE) in these tissues. We previously found that the accumulation of CE generates alterations in the insulin response in the heart. Although the insulin response is mainly associated with the uptake and metabolism of glucose, other studies have shown that insulin would fulfill functions in this tissue, such as regulating the calcium cycle and cardiac contractility. Here, we found that aggLDL induced-lipid accumulation altered the gene expression profile involved in processes essential for cardiac functionality, including insulin response and glucose uptake ( Insr , Ins1 , Pik3ip1 , Slc2a4 gene expression), calcium cycle ( Cacna1s and Gjc2 gene expression) and calcium-dependent cardiac contractility ( Myh3 ), and cholesterol efflux ( Abca1 ), in HL-1 cardiomyocytes. These observations were recapitulated using an in vivo model of hypercholesterolemic ApoE-KO mice. Altogether, these results may explain the deleterious effect of lipid accumulation in the myocardium, with important implications for lipid-overloaded associated CVD.

Activated Alpha-2 Macroglobulin Improves Insulin Response via LRP1 in Lipid-Loaded HL-1 Cardiomyocytes

Activated alpha-2 Macroglobulin (α₂M*) is specifically recognized by the cluster I/II of LRP1 (Low-density lipoprotein Receptor-related Protein-1). LRP1 is a scaffold protein for insulin receptor involved in the insulin-induced glucose transporter type 4 (GLUT4) translocation to plasma membrane and glucose uptake in different types of cells. Moreover, the cluster II of LRP1 plays a critical role in the internalization of atherogenic lipoproteins, such as aggregated Low-density Lipoproteins (aggLDL), promoting intracellular cholesteryl ester (CE) accumulation mainly in arterial intima and myocardium. The aggLDL uptake by LRP1 impairs GLUT4 traffic and the insulin response in cardiomyocytes. However, the link between CE accumulation, insulin action, and cardiac dysfunction are largely unknown. Here, we found that α₂M* increased GLUT4 expression on cell surface by Rab4, Rab8A, and Rab10-mediated recycling through PI₃K/Akt and MAPK/ERK signaling activation. Moreover, α₂M* enhanced the insulin response increasing insulin-induced glucose uptake rate in the myocardium under normal conditions. On the other hand, α₂M* blocked the intracellular CE accumulation, improved the insulin response and reduced cardiac damage in HL-1 cardiomyocytes exposed to aggLDL. In conclusion, α₂M* by its agonist action on LRP1, counteracts the deleterious effects of aggLDL in cardiomyocytes, which may have therapeutic implications in cardiovascular diseases associated with hypercholesterolemia.

Run for your life: can exercise be used to effectively target GLUT4 in diabetic cardiac disease?

The global incidence, associated mortality rates and economic burden of diabetes are now such that it is considered one of the most pressing worldwide public health challenges. Considerable research is now devoted to better understanding the mechanisms underlying the onset and progression of this disease, with an ultimate aim of improving the array of available preventive and therapeutic interventions. One area of particular unmet clinical need is the significantly elevated rate of cardiomyopathy in diabetic patients, which in part contributes to cardiovascular disease being the primary cause of premature death in this population. This review will first consider the role of metabolism and more specifically the insulin sensitive glucose transporter GLUT4 in diabetic cardiac disease, before addressing how we may use exercise to intervene in order to beneficially impact key functional clinical outcomes.

Cardiometabolism as an Interlocking Puzzle between the Healthy and Diseased Heart: New Frontiers in Therapeutic Applications

Cardiac metabolism represents a crucial and essential connecting bridge between the healthy and diseased heart. The cardiac muscle, which may be considered an omnivore organ with regard to the energy substrate utilization, under physiological conditions mainly draws energy by fatty acids oxidation. Within cardiomyocytes and their mitochondria, through well-concerted enzymatic reactions, substrates converge on the production of ATP, the basic chemical energy that cardiac muscle converts into mechanical energy, i.e., contraction. When a perturbation of homeostasis occurs, such as an ischemic event, the heart is forced to switch its fatty acid-based metabolism to the carbohydrate utilization as a protective mechanism that allows the maintenance of its key role within the whole organism. Consequently, the flexibility of the cardiac metabolic networks deeply influences the ability of the heart to respond, by adapting to pathophysiological changes. The aim of the present review is to summarize the main metabolic changes detectable in the heart under acute and chronic cardiac pathologies, analyzing possible therapeutic targets to be used. On this basis, cardiometabolism can be described as a crucial mechanism in keeping the physiological structure and function of the heart; furthermore, it can be considered a promising goal for future pharmacological agents able to appropriately modulate the rate-limiting steps of heart metabolic pathways.

Multilayer global longitudinal strain assessment of subclinical myocardial dysfunction related to insulin resistance

Myocardial tissue is sensitive to insulin resistance (IR) due to its interactions with insulin levels. Previous studies demonstrated that heart failure prevalence was higher in IR patients. Evaluation of myocardial deformation by multilayer global longitudinal strain (MGLS) might provide more information about IR related left ventricular dysfunction. In this study, we aimed to investigate subclinical LV dysfunction with MGLS in patients with IR. The study was designed as a prospective cross-sectional study. The present study included 64 patients with IR (+), and 54 subjects without IR (-) prospectively. The homeostasis model of insulin resistance (HOMA-IR) was used to quantify insulin resistance. Specific analysis for endocardial, mid-myocardial and epicardial layers were performed by two-dimensional (2D) speckle tracking echocardiography (STE) for multilayer global longitudinal strain. MGLS (Endocard-Mid-myocard-Epicard) values were significantly lower in the IR (+) group compared to IR (-) group ((GLS-endocard; - 15.1 ± 1.5 vs. - 18.7 ± 1.3, p < 0.001), (GLS-mid-myocard; - 16.0 ± 2.0 vs. - 18.0 ± 2.0, p < 0.001), (GLS-epicard; - 17.0 ± 1.7 vs. - 18.01 ± 1.94, p = 0.004)). GLS-endocard levels were significantly and positively correlated with HOMA-IR levels (r = 0.643, p < 0.001). HOMA-IR and age were found to be independent factors in detecting a decrease in GLS-endocard level in regression analysis. In conclusion, our data reveal that IR (+) patients had significantly lower strain values compared to IR (-) group. Besides, we presented that the HOMA-IR value was an independent predictor of subclinical left ventricular dysfunction.

Effect of delay in transportation of extracellular glucose into cardiomyocytes under diabetic condition: a study through mathematical model

A four-dimensional model was built to mimic the cross-talk among plasma glucose, plasma insulin, intracellular glucose and cytoplasmic calcium of a cardiomyocyte. A time delay was considered to represent the time required for performing various cellular mechanisms between activation of insulin receptor and subsequent glucose entry from extracellular region into intracellular region of a cardiac cell. We analysed the delay-induced model and deciphered conditions for stability and bifurcation. Extensive numerical computations were performed to validate the analytical results and give further insights. Sensitivity study of the system parameters using LHS-PRCC method reveals that some rate parameters, which represent the input of plasma glucose, absorption of glucose by noncardiac cells and insulin production, are sensitive and may cause significant change in the system dynamics. It was observed that the time taken for transportation of extracellular glucose into the cell through GLUT4 plays an important role in maintaining physiological oscillations of the state variables. Parameter recalibration exercise showed that reduced input rate of glucose in the blood plasma or an alteration in transportation delay may be used for therapeutic targets in diabetic-like condition for maintaining normal cardiac function.

Prevalence and Clinical Characteristics of Children and Adolescents with Metabolically Healthy Obesity: Role of Insulin Sensitivity

Obesity represents a major risk factor for metabolic disorders, but some individuals, "metabolically healthy" (MHO), show less clinical evidence of these complications, in contrast to "metabolically unhealthy" (MUO) individuals. The aim of this cross-sectional study is to assess the prevalence of the MHO phenotype in a cohort of 246 overweight/obese Italian children and adolescents, and to evaluate their characteristics and the role of insulin resistance. Homeostasis model assessment-insulin resistance (HOMA-IR), insulin sensitivity index (ISI), insulinogenic index (IGI) and disposition index (DI) were all calculated from the Oral Glucose Tolerance Test (OGTT). MHO was defined by either: (1) HOMA-IR < 2.5 (MHO-IRes), or (2) absence of the criteria for metabolic syndrome (MHO-MetS). The MHO prevalence, according to MHO-MetS or MHO-IRes criteria, was 37.4% and 15.8%, respectively. ISI was the strongest predictor of the MHO phenotype, independently associated with both MHO-IRes and MHO-MetS. The MHO-MetS group was further subdivided into insulin sensitive or insulin resistant on the basis of HOMA-IR (either < or ≥ 2.5). Insulin sensitive MHO-MetS patients had a better metabolic profile compared to both insulin resistant MHO-MetS and MUO-MetS individuals. These data underscore the relevance of insulin sensitivity to identifying, among young individuals with overweight/obesity, the ones who have a more favorable metabolic phenotype.

Changes in Myocardial Metabolism Preceding Sudden Cardiac Death

Heart disease is widely recognized as a major cause of death worldwide and is the leading cause of mortality in the United States. Centuries of research have focused on defining mechanistic alterations that drive cardiac pathogenesis, yet sudden cardiac death (SCD) remains a common unpredictable event that claims lives in every age group. The heart supplies blood to all tissues while maintaining a constant electrical and hormonal feedback communication with other parts of the body. As such, recent research has focused on understanding how myocardial electrical and structural properties are altered by cardiac metabolism and the various signaling pathways associated with it. The importance of cardiac metabolism in maintaining myocardial function, or lack thereof, is exemplified by shifts in cardiac substrate preference during normal development and various pathological conditions. For instance, a shift from fatty acid (FA) oxidation to oxygen-sparing glycolytic energy production has been reported in many types of cardiac pathologies. Compounded by an uncoupling of glycolysis and glucose oxidation this leads to accumulation of undesirable levels of intermediate metabolites. The resulting accumulation of intermediary metabolites impacts cardiac mitochondrial function and dysregulates metabolic pathways through several mechanisms, which will be reviewed here. Importantly, reversal of metabolic maladaptation has been shown to elicit positive therapeutic effects, limiting cardiac remodeling and at least partially restoring contractile efficiency. Therein, the underlying metabolic adaptations in an array of pathological conditions as well as recently discovered downstream effects of various substrate utilization provide guidance for future therapeutic targeting. Here, we will review recent data on alterations in substrate utilization in the healthy and diseased heart, metabolic pathways governing cardiac pathogenesis, mitochondrial function in the diseased myocardium, and potential metabolism-based therapeutic interventions in disease.

Precocious Preclinical Cardiovascular Sonographic Markers in Metabolically Healthy and Unhealthy Childhood Obesity

Background: Childhood obesity is related to a wide spectrum of cardiovascular and metabolic comorbidities. Objectives: (1) To identify precocious, preclinical, cardiovascular sonographic modifications, in a cohort of overweight (OW) and obese (OB) children and adolescents compared to lean controls; (2) to investigate the association between clinical and metabolic variables and cardiovascular sonographic parameters; (3) to evaluate their relation with two different phenotypes of obesity: metabolically healthy obesity (MHO) and metabolically unhealthy obesity (MUO). Materials and Methods: Fifty-nine OW and OB children and adolescents (9.8 ± 2.9 years) and 20 matched lean controls underwent anthropometric, biochemical, echocardiography assessment, and sonographic evaluation of carotid artery and ascending aorta (AA). OW and OB subjects were divided in MHO and MUO, according to the Camhi et al. definition. Results: OW and OB children showed significantly higher left ventricular (LV) dimensions and mass, carotid artery intima-media thickness (CIMT), carotid stiffness [β-index, pulse wave velocity (PWV)], significantly lower mitral peak early (E) and late (A) velocity ratio (E/A ratio), and significantly impaired global longitudinal strain (GLS) compared to controls. BMI SD and HOMA-IR were positively significantly related to LV dimensions, LA volume and epicardial adipose tissue (EAT), and negative to E/A ratio. Waist circumference (WC) was positively correlated to LV dimensions, LA volume, CIMT, PWV, AA diameter, and EAT. Furthermore, WC was a strong predictor of LV dimensions, LA volume and strain, AA stiffness and diameter; BMI SD was significantly associated with EAT, LVM index, and E/A ratio; HOMA-IR and triglycerides were significant predictors of GLS. MUO patients showed higher BMI SD (p = 0.02), WC (p = 0.001), WHtR (p = 0.001), HOMA-IR (p = 0.004), triglycerides (p = 0.01), SBP (p = 0.001), as well as LV dimensions, EAT (p = 0.03), CIMT (p = 0.01), AA diameter (p = 0.02), β-index (p = 0.03) and PWV (p = 0.002), AA stiffness (p = 0.006), and significantly impaired GLS (p = 0.042) compared to MHO. Conclusions: Severity of overweight, abdominal obesity, insulin resistance, and MUO phenotype negatively affect cardiovascular remodeling and subclinical myocardial dysfunction in OW and OB children. MUO phenotype is likely to increase the risk of developing cardiometabolic complications since the pediatric age. Distinction between MHO and MUO phenotypes might be useful in planning a personalized follow-up approach in obese children.

Heart Failure in Type 2 Diabetes Mellitus

Patients with diabetes mellitus have >2× the risk for developing heart failure (HF; HF with reduced ejection fraction and HF with preserved ejection fraction). Cardiovascular outcomes, hospitalization, and prognosis are worse for patients with diabetes mellitus relative to those without. Beyond the structural and functional changes that characterize diabetic cardiomyopathy, a complex underlying, and interrelated pathophysiology exists. Despite the success of many commonly used antihyperglycemic therapies to lower hyperglycemia in type 2 diabetes mellitus the high prevalence of HF persists. This, therefore, raises the possibility that additional factors beyond glycemia might contribute to the increased HF risk in diabetes mellitus. This review summarizes the state of knowledge about the impact of existing antihyperglycemic therapies on HF and discusses potential mechanisms for beneficial or deleterious effects. Second, we review currently approved pharmacological therapies for HF and review evidence that addresses their efficacy in the context of diabetes mellitus. Dysregulation of many cellular mechanisms in multiple models of diabetic cardiomyopathy and in human hearts have been described. These include oxidative stress, inflammation, endoplasmic reticulum stress, aberrant insulin signaling, accumulation of advanced glycated end-products, altered autophagy, changes in myocardial substrate metabolism and mitochondrial bioenergetics, lipotoxicity, and altered signal transduction such as GRK (g-protein receptor kinase) signaling, renin angiotensin aldosterone signaling and β-2 adrenergic receptor signaling. These pathophysiological pathways might be amenable to pharmacological therapy to reduce the risk of HF in the context of type 2 diabetes mellitus. Successful targeting of these pathways could alter the prognosis and risk of HF beyond what is currently achieved using existing antihyperglycemic and HF therapeutics.

Vitamin D Deficiency in Rats Causes Cardiac Dysfunction by Inducing Myocardial Insulin Resistance

SCOPE

Cause-effect relationship between vitamin D deficiency and cardiometabolic abnormalities remains undefined. The aim is to investigate the role of vitamin D deficiency in cardiac failure, through possible involvement in myocardial insulin signaling.

METHODS AND RESULTS

Male SD rats (n = 6) are fed a normal diet (Con), vitamin D-deficient diet [Con(-)], or high-fat, high fructose diet (HFHFrD) for 20 weeks. Cardiac hypertrophy and fetal gene program are confirmed in Con(-) group. Cardiac dysfunction is assessed by echocardiography. Elevated renin, TGF-β and collagen-1α mRNAs, p-ERK1/2, and perivascular fibrosis indicate cardiac remodeling in Con(-) group. Increased serum insulin, triglycerides, and blood pressure, and decreased glucose tolerance and HDL cholesterol are observed in Con(-) rats. Decreased p-Akt/Akt, GLUT4, SOD2, and catalase, and increased NF-κB, TNF-α, and IL-6 are observed in Con(-) hearts. In H9c2 cells, calcitriol attenuates palmitate-induced insulin resistance. VDR-silenced H9c2 cells show reduced Akt phosphorylation, GLUT4 translocation, and 2-NBDG uptake. Findings in Con(-) and HFHFrD groups are comparable.

CONCLUSION

Vitamin D deficiency in rats mimic high-fat-, high-fructose-induced metabolic syndrome and cardiac dysfunction. This study demonstrates that vitamin D deficiency is an independent risk factor for heart failure, at least in part, through induction of myocardial insulin resistance.

AMPK: a therapeutic target of heart failure-not only metabolism regulation

Heart failure (HF) is a serious disease with high mortality. The incidence of this disease has continued to increase over the past decade. All cardiovascular diseases causing dysfunction of various physiological processes can result in HF. AMP-activated protein kinase (AMPK), an energy sensor, has pleiotropic cardioprotective effects and plays a critical role in the progression of HF. In this review, we highlight that AMPK can not only improve the energy supply in the failing heart by promoting ATP production, but can also regulate several important physiological processes to restore heart function. In addition, we discuss some aspects of some potential clinical drugs which have effects on AMPK activation and may have value in treating HF. More studies, especially clinical trials, should be done to evaluate manipulation of AMPK activation as a potential means of treating HF.

Alteration in cardiac PI3K/Akt/mTOR and ERK signaling pathways with the use of growth hormone and swimming, and the roles of miR21 and miR133

Athletes misuse recombinant human growth hormone (r-hGH) to enhance their performance. Although r-hGH is known to increase cardiac hypertrophy, the underlying molecular mechanism remains unclear. The aim of the present study was to investigate the role of r-hGH in cardiac intracellular signaling pathways and of miR-21 and miR-133 expression in rat hearts during exercise. A total of 36 adult male Sprague-Dawley rats were divided into sedentary control (SC, n=9), swimming exercise (SE, n=8), r-hGH (GH, n=10) and swimming exercise plus r-hGH (SE-GH, n=9) groups. The exercise groups completed a 1-h swimming exercise 5 times a week for 8 weeks. Subcutaneous r-hGH was administered as 0.3 mg/kg/day. Phosphoinositide-3-kinase (PI3K), serine/threonine protein kinase 1 (AKT1), extracellular signal-regulated kinase (ERK), microRNA (miR)-21 and miR-133 expression was evaluated in ventricular muscle by real-time quantitative polymerase chain reaction. Protein expression of PI3K, AKT1, ERK and mechanistic target of rapamycin (mTOR) was also assessed by immunohistochemistry. Statistical differences were analyzed by two-way ANOVA. PI3K and AKT1 expression and the gene and protein levels was notably increased in the SE-GH group compared with in SC ventricular tissues (P<0.05). mTOR protein expression was higher in the GH, SE and SE-GH groups compared with in the SC group (P<0.05, <0.05 and <0.001, respectively). ERK gene/protein expression was similar across all groups. miR-21 and miR-133 levels in ventricular muscle were higher in the SE and GH groups than those in the SC group. In summary, growth hormone application coupled with swimming exercise appeared to affect the PI3K/AKT/mTOR signaling pathway in the left ventricular tissue of rats; however, ERK signaling pathway appeared inactive in physiological left ventricular hypertrophy caused by swimming and GH administration over 8 weeks. Furthermore, GH treatment resulted in increased miR-21 and miR-133 expression. Future study by our group will aim to assess the effects of higher dose GH treatment.

Cardiomyocyte Functional Etiology in Heart Failure With Preserved Ejection Fraction Is Distinctive-A New Preclinical Model

Background

Among the growing numbers of patients with heart failure, up to one half have heart failure with preserved ejection fraction (HFpEF). The lack of effective treatments for HFpEF is a substantial and escalating unmet clinical need—and the lack of HFpEF‐specific animal models represents a major preclinical barrier in advancing understanding of HFpEF. As established treatments for heart failure with reduced ejection fraction (HFrEF) have proven ineffective for HFpEF, the contention that the intrinsic cardiomyocyte phenotype is distinct in these 2 conditions requires consideration. Our goal was to validate and characterize a new rodent model of HFpEF, undertaking longitudinal investigations to delineate the associated cardiac and cardiomyocyte pathophysiology.

Methods and Results

The selectively inbred Hypertrophic Heart Rat (HHR) strain exhibits adult cardiac enlargement (without hypertension) and premature death (40% mortality at 50 weeks) compared to its control strain, the normal heart rat. Hypertrophy was characterized in vivo by maintained systolic parameters (ejection fraction at 85%–90% control) with marked diastolic dysfunction (increased E/E′). Surprisingly, HHR cardiomyocytes were hypercontractile, exhibiting high Ca²⁺ operational levels and markedly increased L‐type Ca²⁺ channel current. In HHR, prominent regions of reparative fibrosis in the left ventricle free wall adjacent to the interventricular septum were observed.

Conclusions

Thus, the cardiomyocyte remodeling process in the etiology of this HFpEF model contrasts dramatically with the suppressed Ca²⁺ cycling state that typifies heart failure with reduced ejection fraction. These findings may explain clinical observations, that treatments considered appropriate for heart failure with reduced ejection fraction are of little benefit for HFpEF—and suggest a basis for new therapeutic strategies.

Mitochondrial oxidative stress and cardiac ageing

According with different international organizations, cardiovascular diseases are becoming the first cause of death in western countries. Although exposure to different risk factors, particularly those related to lifestyle, contribute to the etiopathogenesis of cardiac disorders, the increase in average lifespan and aging are considered major determinants of cardiac diseases events. Mitochondria and oxidative stress have been pointed out as relevant factors both in heart aging and in the development of cardiac diseases such as heart failure, cardiac hypertrophy and diabetic cardiomyopathy. During aging, cellular processes related with mitochondrial function, such as bioenergetics, apoptosis and inflammation are altered leading to cardiac dysfunction. Increasing our knowledge about the mitochondrial mechanisms related with the aging process, will provide new strategies in order to improve this process, particularly the cardiovascular ones.

Mitochondrial Function in Non-ischemic Heart Failure

Provision for the continuous demand for energy from the beating heart relies heavily on efficient mitochondrial activity. Non-ischemic cardiomyopathy in which oxygen supply is not limiting results from etiologies such as pressure overload. It is associated with progressive development of metabolic stress culminating in energy depletion and heart failure. The mitochondria from the ventricular walls undergoing non-ischemic cardiomyopathy are subjected to long periods of adaptation to support the changing metabolic milieu, which has been described as mal-adaptation since it ultimately results in loss of cardiac contractile function. While the chronicity of exposure to metabolic stressors, co-morbidities and thereby adaptive changes in mitochondria maybe different between ischemic and non-ischemic heart failure, the resulting pathology is very similar, especially in late stage heart failure. Understanding of the mitochondrial changes in early-stage heart failure may guide the development of mitochondrial-targeted therapeutic options to prevent progression of non-ischemic heart failure. This chapter reviews findings of mitochondrial functional changes in animal models and humans with non-ischemic heart failure. While most animal models of non-ischemic heart failure exhibit cardiac mitochondrial dysfunction, studies in humans have been inconsistent despite confirmed reduction in ATP production. This chapter also reviews the possibility of impairment of substrate supply processes upstream of the mitochondria in heart failure, and discusses potential metabolism-targeted therapeutic options.

Insulin Signaling and Heart Failure

Heart failure is associated with generalized insulin resistance. Moreover, insulin-resistant states such as type 2 diabetes mellitus and obesity increases the risk of heart failure even after adjusting for traditional risk factors. Insulin resistance or type 2 diabetes mellitus alters the systemic and neurohumoral milieu, leading to changes in metabolism and signaling pathways in the heart that may contribute to myocardial dysfunction. In addition, changes in insulin signaling within cardiomyocytes develop in the failing heart. The changes range from activation of proximal insulin signaling pathways that may contribute to adverse left ventricular remodeling and mitochondrial dysfunction to repression of distal elements of insulin signaling pathways such as forkhead box O transcriptional signaling or glucose transport, which may also impair cardiac metabolism, structure, and function. This article will review the complexities of insulin signaling within the myocardium and ways in which these pathways are altered in heart failure or in conditions associated with generalized insulin resistance. The implications of these changes for therapeutic approaches to treating or preventing heart failure will be discussed.

Mitochondria and oxidative stress in heart aging

As average lifespan of humans increases in western countries, cardiac diseases become the first cause of death. Aging is among the most important risk factors that increase susceptibility for developing cardiovascular diseases. The heart has very aerobic metabolism, and is highly dependent on mitochondrial function, since mitochondria generate more than 90 % of the intracellular ATP consumed by cardiomyocytes. In the last few decades, several investigations have supported the relevance of mitochondria and oxidative stress both in heart aging and in the development of cardiac diseases such as heart failure, cardiac hypertrophy, and diabetic cardiomyopathy. In the current review, we compile different studies corroborating this role. Increased mitochondria DNA instability, impaired bioenergetic efficiency, enhanced apoptosis, and inflammation processes are some of the events related to mitochondria that occur in aging heart, leading to reduced cellular survival and cardiac dysfunction. Knowing the mitochondrial mechanisms involved in the aging process will provide a better understanding of them and allow finding approaches to more efficiently improve this process.

The Effect of a High-Protein Diet and Exercise on Cardiac AQP7 and GLUT4 Gene Expression

High-protein (HP) diets are commonly consumed by athletes despite their potential health hazard, which is postulated to enforce a negative effect on bone and renal health. However, its effects on heart have not been known yet. Aquaporin-7 (AQP7) is an aquaglyceroporin that facilitates glycerol and water transport. Glycerol is an important cardiac energy production substrate, especially during exercise, in conjunction with fatty acids and glucose. Glucose transporter 4 (GLUT4) is an insulin-sensitive glucose transporter in heart. We aimed to investigate the effect of HPD on AQP7 and GLUT4 levels in the rat heart subjected to exercise. Male Sprague-Dawley rats were divided into control (n = 12), exercise (E) training (n = 10), HPD (n = 12), and HPD-E training (n = 9) groups. The HPD groups were fed a 45 % protein-containing diet 5 weeks. The HPD-E and E groups were performed the treadmill exercise during the 5-week study period. Real-time polymerase chain reaction and immunohistochemistry techniques were used to determine the gene expression and localization of AQP7 and GLUT4 in heart tissue. Results of relative gene expression were calculated by the 'Pfaffl' mathematical method using the REST program. Differences in AQP7 and GLUT4 gene expression were expressed as fold change compared to the control group. Heart weight/tibia ratio and ventricular wall thickness were evaluated as markers of cardiac hypertrophy. Further, serum glucose, glycerol, and insulin levels were also measured. AQP7 gene expression was found to be increased in the E (3.47-fold, p < 0.001), HPD (5.59-fold, p < 0.001), and HPD-E (3.87-fold, p < 0.001) groups compared to the control group. AQP7 protein expression was also increased in the HPD and HPD-E groups (p < 0.001). Additionally, cardiac mRNA expression levels of GLUT4 showed a significant increase in the E (2.16-fold, p < 0.003), HPD (7.14-fold, p < 0.001), and HPD-E (3.43-fold, p < 0.001) groups compared to the control group. GLUT4 protein expression was significantly increased in the E, HPD, and HPD-E groups compared to the control group (p = 0.024, p < 0.001, and p < 0.001, respectively). Furthermore, Serum glucose levels were significantly different between groups (p < 0.005). This difference was observed between the HPD groups and normal-protein diet groups (C and E). Serum insulin levels were higher for HPD groups compared with the normal-protein diet groups (p < 0.001), whereas no differences were observed between the exercise and sedentary groups (p = 0.111). Serum glycerol levels were significantly increased in the HPD groups compared with control and E groups (p < 0.05 and p < 0.05, respectively). Consumption of HPD supplementation caused the increased effects on AQP7 and GLUT4 expression in rat heart.

Cardiac LXRα protects against pathological cardiac hypertrophy and dysfunction by enhancing glucose uptake and utilization

Pathological cardiac hypertrophy is characterized by a shift in metabolic substrate utilization from fatty acids to glucose, but the molecular events underlying the metabolic remodeling remain poorly understood. Here, we investigated the role of liver X receptors (LXRs), which are key regulators of glucose and lipid metabolism, in cardiac hypertrophic pathogenesis. Using a transgenic approach in mice, we show that overexpression of LXRα acts to protect the heart against hypertrophy, fibrosis, and dysfunction. Gene expression profiling studies revealed that genes regulating metabolic pathways were differentially expressed in hearts with elevated LXRα. Functionally, LXRα overexpression in isolated cardiomyocytes and murine hearts markedly enhanced the capacity for myocardial glucose uptake following hypertrophic stress. Conversely, this adaptive response was diminished in LXRα-deficient mice. Transcriptional changes induced by LXRα overexpression promoted energy-independent utilization of glucose via the hexosamine biosynthesis pathway, resulting in O-GlcNAc modification of GATA4 and Mef2c and the induction of cytoprotective natriuretic peptide expression. Our results identify LXRα as a key cardiac transcriptional regulator that helps orchestrate an adaptive metabolic response to chronic cardiac stress, and suggest that modulating LXRα may provide a unique opportunity for intervening in myocyte metabolism.

Molecular switches under TGFβ signalling during progression from cardiac hypertrophy to heart failure

Cardiac hypertrophy is a mechanism to compensate for increased cardiac work load, that is, after myocardial infarction or upon pressure overload. However, in the long run cardiac hypertrophy is a prevailing risk factor for the development of heart failure. During pathological remodelling processes leading to heart failure, decompensated hypertrophy, death of cardiomyocytes by apoptosis or necroptosis and fibrosis as well as a progressive dysfunction of cardiomyocytes are apparent. Interestingly, the induction of hypertrophy, cell death or fibrosis is mediated by similar signalling pathways. Therefore, tiny changes in the signalling cascade are able to switch physiological cardiac remodelling to the development of heart failure. In the present review, we will describe examples of these molecular switches that change compensated hypertrophy to the development of heart failure and will focus on the importance of the signalling cascades of the TGFβ superfamily in this process. In this context, potential therapeutic targets for pharmacological interventions that could attenuate the progression of heart failure will be discussed.

Chronic high fat diet induces cardiac hypertrophy and fibrosis in mice

BACKGROUND

Obesity can cause pathological changes in organs. We determined the effects of chronic high fat diet (HFD) and intermittent fasting, a paradigm providing organ protection, on mouse heart.

METHODS

Seven-week old CD1 male mice were randomly assigned to control, HFD and intermittent fasting groups. Control mice had free access to regular diet (RD). RD was provided every other day to mice in the intermittent fasting group. Mice in HFD group had free access to HFD. Their left ventricles were harvested 11 months after they had been on these diet regimens.

RESULTS

HFD increased cardiomyocyte cross-section area and fibrosis. HFD decreased active caspase 3, an apoptosis marker, and the ratio of microtubule-associated protein 1A/1B-light chain 3 (LC3) II/LC3I, an autophagy marker. HFD increased the phospho-glycogen synthase kinase-3β (GSK-3β) at Ser9, a sign of GSK-3β inhibition. Nuclear GATA binding protein 4 and yes-associated protein, two GSK-3β targeting transcription factors that can induce hypertrophy-related gene expression, were increased in HFD-fed mice. Mice on intermittent fasting did not have these changes except for the increased active caspase 3 and decreased ratio of LC3II/LC3I.

CONCLUSIONS

These results suggest that chronic HFD induces myocardial hypertrophy and fibrosis, which may be mediated by GSK-3β inhibition.

SERCA2 Haploinsufficiency in a Mouse Model of Darier Disease Causes a Selective Predisposition to Heart Failure

Null mutations in one copy of ATP2A2, the gene encoding sarco/endoplasmic reticulum Ca(2+)-ATPase isoform 2 (SERCA2), cause Darier disease in humans, a skin condition involving keratinocytes. Cardiac function appears to be unimpaired in Darier disease patients, with no evidence that SERCA2 haploinsufficiency itself causes heart disease. However, SERCA2 deficiency is widely considered a contributing factor in heart failure. We therefore analyzed Atp2a2 heterozygous mice to determine whether SERCA2 haploinsufficiency can exacerbate specific heart disease conditions. Despite reduced SERCA2a levels in heart, Atp2a2 heterozygous mice resembled humans in exhibiting normal cardiac physiology. When subjected to hypothyroidism or crossed with a transgenic model of reduced myofibrillar Ca(2+)-sensitivity, SERCA2 deficiency caused no enhancement of the disease state. However, when combined with a transgenic model of increased myofibrillar Ca(2+)-sensitivity, SERCA2 haploinsufficiency caused rapid onset of hypertrophy, decompensation, and death. These effects were associated with reduced expression of the antiapoptotic Hax1, increased levels of the proapoptotic genes Chop and Casp12, and evidence of perturbations in energy metabolism. These data reveal myofibrillar Ca(2+)-sensitivity to be an important determinant of the cardiac effects of SERCA2 haploinsufficiency and raise the possibility that Darier disease patients are more susceptible to heart failure under certain conditions.

GLUT12 deficiency during early development results in heart failure and a diabetic phenotype in zebrafish

Cardiomyopathies-associated metabolic pathologies (e.g., type 2 diabetes and insulin resistance) are a leading cause of mortality. It is known that the association between these pathologies works in both directions, for which heart failure can lead to metabolic derangements such as insulin resistance. This intricate crosstalk exemplifies the importance of a fine coordination between one of the most energy-demanding organs and an equilibrated carbohydrate metabolism. In this light, to assist in the understanding of the role of insulin-regulated glucose transporters (GLUTs) and the development of cardiomyopathies, we have developed a model for glut12 deficiency in zebrafish. GLUT12 is a novel insulin-regulated GLUT expressed in the main insulin-sensitive tissues, such as cardiac muscle, skeletal muscle, and adipose tissue. In this study, we show that glut12 knockdown impacts the development of the embryonic heart resulting in abnormal valve formation. Moreover, glut12-deficient embryos also exhibited poor glycemic control. Glucose measurements showed that these larvae were hyperglycemic and resistant to insulin administration. Transcriptome analysis demonstrated that a number of genes known to be important in cardiac development and function as well as metabolic mediators were dysregulated in these larvae. These results indicate that glut12 is an essential GLUT in the heart where the reduction in glucose uptake due to glut12 deficiency leads to heart failure presumably due to the lack of glucose as energy substrate. In addition, the diabetic phenotype displayed by these larvae after glut12 abrogation highlights the importance of this GLUT during early developmental stages.

Updating experimental models of diabetic cardiomyopathy

Diabetic cardiomyopathy entails a serious cardiac dysfunction induced by alterations in structure and contractility of the myocardium. This pathology is initiated by changes in energy substrates and occurs in the absence of atherothrombosis, hypertension, or other cardiomyopathies. Inflammation, hypertrophy, fibrosis, steatosis, and apoptosis in the myocardium have been studied in numerous diabetic experimental models in animals, mostly rodents. Type I and type II diabetes were induced by genetic manipulation, pancreatic toxins, and fat and sweet diets, and animals recapitulate the main features of human diabetes and related cardiomyopathy. In this review we update and discuss the main experimental models of diabetic cardiomyopathy, analysing the associated metabolic, structural, and functional abnormalities, and including current tools for detection of these responses. Also, novel experimental models based on genetic modifications of specific related genes have been discussed. The study of specific pathways or factors responsible for cardiac failures may be useful to design new pharmacological strategies for diabetic patients.

Hydrogen sulfide improves glucose metabolism and prevents hypertrophy in cardiomyocytes

INTRODUCTION

Hydrogen sulfide (H2S) has been reported to inhibit myocardial hypertrophy in a cell model of cardiomyocyte hypertrophy. Our previous study also shows an H2S-induced increase in glucose metabolism in insulin-targeting cells. The present study aims to examine the hypothesis that H2S attenuates myocardial hypertrophy and promotes glucose utilization in cardiomyocytes.

METHODS

The cell model of cardiomyocyte hypertrophy was induced by application of phenylephrine and cardiomyocyte hypertrophy was examined using leucine incorporation assay. Protein levels were measured using Western blot analysis. The activity of related enzymes was measured with enzyme-linked immunosorbent assay (ELISA).

RESULTS

NaHS (an H2S donor) treatment increased the activity of cultured cardiomyocytes and reduced hypertrophy in cultured cardiomyocytes at concentrations ranging from 25 to 200 µmol/L. NaHS treatment increased glucose uptake and the efficiency of glycolysis and the citric acid cycle. The key enzymes in these reactions, including lactate dehydrogenase and pyruvate kinase and succinate dehydrogenase, were activated by NaHS treatment (100 µmol/L). Some intermediates of glycolysis and the citric acid cycle, including lactic acid, cyclohexylammonium, oxaloacetic acid, succinate, L-dimalate, sodium citrate, cis-aconitic acid, ketoglutarate and DL-isocitric acid trisodium also showed anti-hypertrophic effects in cardiomyocytes.

CONCLUSIONS

H2S improves glucose utilization and inhibits cardiomyocyte hypertrophy.

Ablation of plasma membrane Ca(2+)-ATPase isoform 4 prevents development of hypertrophy in a model of hypertrophic cardiomyopathy

The mechanisms linking the expression of sarcomeric mutant proteins to the development of pathological hypertrophy in hypertrophic cardiomyopathy (HCM) remain poorly understood. We investigated the role of the plasma membrane Ca(2+)-ATPase PMCA4 in the HCM phenotype using a transgenic model that expresses mutant (Glu180Gly) α-tropomyosin (Tm180) in heart. Immunoblot analysis revealed that cardiac PMCA4 expression was upregulated early in Tm180 disease pathogenesis. This was accompanied by an increase in levels of the L-type Ca(2+)-channel, which is implicated in pathological hypertrophy. When Tm180 mice were crossed with a PMCA4-null line, loss of PMCA4 caused the abrogation of hypertrophy in Tm180/PMCA4-null double mutant mice. RT-PCR analysis of Tm180/PMCA4-null hearts revealed blunting of the fetal program and reversion of pro-fibrotic Col1a1 and Col3a1 gene expression to wild-type levels. This was accompanied by evidence of reduced L-type Ca(2+)-channel expression, and diminished calcineurin activity. Expression of the metabolic substrate transporters glucose transporter 4 and carnitine palmitoyltransferase 1b was preserved and Tm180-related changes in mRNA levels of various contractile stress-related proteins including the cardiac ankyrin protein CARP and the N2B isoform of titin were reversed in Tm180/PMCA4-null hearts. cGMP levels were increased and phosphorylation of vasodilator-stimulated phosphoprotein was elevated in Tm180/PMCA4-null hearts. These changes were associated with a sharp reduction in left ventricular end-diastolic pressure in Tm180/PMCA4-null hearts, which occurred despite persistence of Tm180-related impairment of relaxation dynamics. These results reveal a novel and specific role for PMCA4 in the Tm180 hypertrophic phenotype, with the "protective" effects of PMCA4 deficiency encompassing multiple determinants of HCM-related hypertrophy.

Insulin resistance and subclinical abnormalities of global and regional left ventricular function in patients with aortic valve sclerosis

Background

Insulin resistance, as a key mediator of metabolic syndrome, is thought to be associated with pathogenesis of calcific aortic valve disease and altered left ventricular (LV) function and structure. However, in patients with aortic valve sclerosis (AVS), the association between insulin resistance and subclinical impairment of LV function is not fully elucidated.

Methods

We studied 57 patients (mean age 70 ± 8 years, 22 women) with asymptomatic AVS but normal LV ejection fraction in echocardiography. LV longitudinal and circumferential strain and strain rate was analyzed using two-dimensional speckle tracking echocardiography. Patients with uncontrolled hypertension and diabetes mellitus, chronic kidney disease, and concomitant coronary artery disease were excluded. They were divided into the insulin-resistant group (AVS+IR; N = 28) and no insulin-resistant group (AVS-IR; N = 29) according to the median value of homeostatic model assessment index. Computed tomography scans were also performed to measure the aortic valve calcium score and the visceral adipose tissue (VAT) area. In addition, age- and sex- adjusted 28 control subjects were recruited for the comparison.

Results

There were no significant differences in LV ejection fraction or mass index among the groups. The AVS+IR group had a higher aortic valve calcium score (median 94 versus 21, P = 0.022) and a larger VAT area (113 ± 42 cm² versus 77 ± 38 cm², P = 0.001) than the AVS-IR group. Notably, LV global longitudinal strain, strain rate (SR), and early diastolic SR were significantly lower in the AVS+IR group than in the AVS-IR group and in control subjects (strain: -16.2 ± 1.6% versus -17.2 ± 1.2% and -18.9 ± 0.8%; SR: -1.18 ± 0.26 s^-1 versus -1.32 ± 0.21 s^-1 and -1.52 ± 0.08 s^-1; early diastolic SR: -1.09 ± 0.23 s^-1 versus -1.23 ± 0.18 s^-1 and -1.35 ± 0.12 s^-1; P < 0.05 for all comparison), whereas circumferential function were not significantly different. Multiple linear regression analyses revealed insulin resistance as an independent determinant of LV longitudinal strain (P = 0.017), SR (P = 0.047), and early diastolic SR (P = 0.049) regardless of LV mass index or VAT area.

Conclusions

Insulin resistance is a powerful independent predictor of subclinical LV dysfunction regardless of concomitant visceral obesity and LV hypertrophy. Thus, it may be a novel therapeutic target to prevent subsequent heart failure in patients with AVS.

GLUT1 deficiency in cardiomyocytes does not accelerate the transition from compensated hypertrophy to heart failure

The aim of this study was to determine whether endogenous GLUT1 induction and the increased glucose utilization that accompanies pressure overload hypertrophy (POH) are required to maintain cardiac function during hemodynamic stress, and to test the hypothesis that lack of GLUT1 will accelerate the transition to heart failure. To determine the contribution of endogenous GLUT1 to the cardiac adaptation to POH, male mice with cardiomyocyte-restricted deletion of the GLUT1 gene (G1KO) and their littermate controls (Cont) were subjected to transverse aortic constriction (TAC). GLUT1 deficiency reduced glycolysis and glucose oxidation by 50%, which was associated with a reciprocal increase in fatty acid oxidation (FAO) relative to controls. Four weeks after TAC, glycolysis increased and FAO decreased by 50% in controls, but were unchanged in G1KO hearts relative to shams. G1KO and controls exhibited equivalent degrees of cardiac hypertrophy, fibrosis, and capillary density loss after TAC. Following TAC, in vivo left ventricular developed pressure was decreased in G1KO hearts relative to controls, but+dP/dt was equivalently reduced in Cont and G1KO mice. Mitochondrial function was equivalently impaired following TAC in both Cont and G1KO hearts. GLUT1 deficiency in cardiomyocytes alters myocardial substrate utilization, but does not substantially exacerbate pressure-overload induced contractile dysfunction or accelerate the progression to heart failure.

Myocardial insulin resistance, metabolic stress and autophagy in diabetes

Clinical studies in humans strongly support a link between insulin resistance and non-ischaemic heart failure. The occurrence of a specific insulin-resistant cardiomyopathy, independent of vascular abnormalities, is now recognized. The progression of cardiac pathology linked with insulin resistance is poorly understood. Cardiac insulin resistance is characterized by reduced availability of sarcolemmal Glut-4 transporters and consequent lower glucose uptake. A shift away from glycolysis towards fatty acid oxidation for ATP supply is apparent and is associated with myocardial oxidative stress. Reliance of cardiomyocyte excitation-contraction coupling on glycolytically derived ATP supply potentially renders cardiac function vulnerable to the metabolic remodelling adaptations observed in diabetes development. Findings from Glut-4-knockout mice demonstrate that cardiomyocytes with extreme glucose uptake deficiency exhibit cardiac hypertrophy and marked excitation-contraction coupling abnormalities characterized by reduced sarcolemmal Ca(2+) influx and sarcoplasmic reticulum Ca(2+) uptake. The 'milder' phenotype fructose-fed mouse model of type 2 diabetes does not show evidence of cardiac hypertrophy, but cardiomyocyte loss linked with autophagic activation is evident. Fructose feeding induces a marked reduction in intracellular Ca(2+) availability with myofilament adaptation to preserve contractile function in this setting. The cardiac metabolic adaptations of two load-independent models of diabetes, namely the Glut-4-deficient mouse and the fructose-fed mouse are contrasted. The role of autophagy in diabetic cardiopathology is evaluated and anomalies of type 1 versus type 2 diabetic autophagic responses are highlighted.

Cardiac insulin-resistance and decreased mitochondrial energy production precede the development of systolic heart failure after pressure-overload hypertrophy

BACKGROUND

Cardiac hypertrophy is accompanied by significant alterations in energy metabolism. Whether these changes in energy metabolism precede and contribute to the development of heart failure in the hypertrophied heart is not clear.

METHODS AND RESULTS

Mice were subjected to cardiac hypertrophy secondary to pressure-overload as a result of an abdominal aortic constriction (AAC). The rates of energy substrate metabolism were assessed in isolated working hearts obtained 1, 2, and 3 weeks after AAC. Mice subjected to AAC demonstrated a progressive development of cardiac hypertrophy. In vivo assessment of cardiac function (via echocardiography) demonstrated diastolic dysfunction by 2 weeks (20% increase in E/E'), and systolic dysfunction by 3 weeks (16% decrease in % ejection fraction). Marked cardiac insulin-resistance by 2 weeks post-AAC was evidenced by a significant decrease in insulin-stimulated rates of glycolysis and glucose oxidation, and plasma membrane translocation of glucose transporter 4. Overall ATP production rates were decreased at 2 and 3 weeks post-AAC (by 37% and 47%, respectively) because of a reduction in mitochondrial oxidation of glucose, lactate, and fatty acids that was not accompanied by an increase in myocardial glycolysis rates. Reduced mitochondrial complex V activity was evident at 3 weeks post-AAC, concomitant with a reduction in the ratio of phosphocreatine to ATP.

CONCLUSIONS

The development of cardiac insulin-resistance and decreased mitochondrial oxidative metabolism are early metabolic changes in the development of cardiac hypertrophy, which create an energy deficit that may contribute to the progression from hypertrophy to heart failure.

Sex, sex steroids, and diabetic cardiomyopathy: making the case for experimental focus

More than three decades ago, the Framingham study revealed that cardiovascular risk is elevated for all diabetics and that this jeopardy is substantially accentuated for women in particular. Numerous studies have subsequently documented worsened cardiac outcomes for women. Given that estrogen and insulin exert major regulatory effects through common intracellular signaling pathways prominent in maintenance of cardiomyocyte function, a sex-hormone:diabetic-disease interaction is plausible. Underlying aspects of female cardiovascular pathophysiology that exaggerate cardiovascular diabetic risk may be identified, including increased vulnerability to coronary microvascular disease, age-dependent impairment of insulin-sensitivity, and differential susceptibility to hyperglycemia. Since Framingham, considerable progress has been made in the development of experimental models of diabetic disease states, including a diversity of genetic rodent models. Ample evidence indicates that animal models of both type 1 and 2 diabetes variably recapitulate aspects of diabetic cardiomyopathy including diastolic and systolic dysfunction, and cardiac structural pathology including fibrosis, loss of compliance, and in some instances ventricular hypertrophy. Perplexingly, little of this work has explored the relevance and mechanisms of sexual dimorphism in diabetic cardiomyopathy. Only a small number of experimental studies have addressed this question, yet the prospects for gaining important mechanistic insights from further experimental enquiry are considerable. The case for experimental interrogation of sex differences, and of sex steroid influences in the aetiology of diabetic cardiomyopathy, is particularly compelling-providing incentive for future investigation with ultimate therapeutic potential.

Reduced cardiac fructose 2,6 bisphosphate increases hypertrophy and decreases glycolysis following aortic constriction

This study was designed to test whether reduced levels of cardiac fructose-2,6-bisphosphate (F-2,6-P₂) exacerbates cardiac damage in response to pressure overload. F-2,6-P₂ is a positive regulator of the glycolytic enzyme phosphofructokinase. Normal and Mb transgenic mice were subject to transverse aortic constriction (TAC) or sham surgery. Mb transgenic mice have reduced F-2,6-P₂ levels, due to cardiac expression of a transgene for a mutant, kinase deficient form of the enzyme 6-phosphofructo-2-kinase/fructose-2,6-bisphosphatase (PFK-2) which controls the level of F-2,6-P₂. Thirteen weeks following TAC surgery, glycolysis was elevated in FVB, but not in Mb, hearts. Mb hearts were markedly more sensitive to TAC induced damage. Echocardiography revealed lower fractional shortening in Mb-TAC mice as well as larger left ventricular end diastolic and end systolic diameters. Cardiac hypertrophy and pulmonary congestion were more severe in Mb-TAC mice as indicated by the ratios of heart and lung weight to tibia length. Expression of α-MHC RNA was reduced more in Mb-TAC hearts than in FVB-TAC hearts. TAC produced a much greater increase in fibrosis of Mb hearts and this was accompanied by 5-fold more collagen 1 RNA expression in Mb-TAC versus FVB-TAC hearts. Mb-TAC hearts had the lowest phosphocreatine to ATP ratio and the most oxidative stress as indicated by higher cardiac content of 4-hydroxynonenal protein adducts. These results indicate that the heart’s capacity to increase F-2,6-P₂ during pressure overload elevates glycolysis which is beneficial for reducing pressure overload induced cardiac hypertrophy, dysfunction and fibrosis.

Absence of glucose transporter 4 diminishes electrical activity of mouse hearts during hypoxia

Insulin resistance, which characterizes type 2 diabetes, is associated with reduced translocation of glucose transporter 4 (GLUT4) to the plasma membrane following insulin stimulation, and diabetic patients with insulin resistance show a higher incidence of ischaemia, arrhythmias and sudden cardiac death. The aim of this study was to examine whether GLUT4 deficiency leads to more severe alterations in cardiac electrical activity during cardiac stress due to hypoxia. To fulfil this aim, we compared cardiac electrical activity from cardiac-selective GLUT4-ablated (G4H-/-) mouse hearts and corresponding control (CTL) littermates. A custom-made cylindrical 'cage' electrode array measured potentials (Ves) from the epicardium of isolated, perfused mouse hearts. The normalized average of the maximal downstroke of Ves ( (|d Ves/dt(min)|na), which we previously introduced as an index of electrical activity in normal, ischaemic and hypoxic hearts, was used to assess the effects of GLUT4 deficiency on electrical activity. The |d Ves/dt(min)|na of G4H −/− and CTL hearts decreased by 75 and 47%, respectively (P < 0.05), 30 min after the onset of hypoxia. Administration of insulin attenuated decreases in values of |d Ves/dt(min)|na in G4H −/− hearts as well as in CTL hearts, during hypoxia. In general, however, G4H −/− hearts showed a severe alteration of the propagation sequence and a prolonged total activation time. Results of this study demonstrate that reduced glucose availability associated with insulin resistance and a reduction in GLUT4-mediated glucose transport impairs electrical activity during hypoxia, and may contribute to cardiac vulnerability to arrhythmias in diabetic patients.

Mitochondrial function in cardiac hypertrophy

Cardiac hypertrophic program is a chronic, complex process, and occurs in response to long-term increases of hemodynamic load related to a variety of pathophysiological conditions. Mitochondria, known as "the cellular power plants", occupy about one-third of cardiomyocyte volume and supply roughly 90% of the adenosine triphosphate (ATP). Impairment of energy metabolism has been regarded as one of the main pathogenesis of cardiac hypertrophy. Thus, we summarize here the molecular events of mitochondrial adaptations, including the mitochondrial genesis, ATP generation, ROS signaling and Ca(2+) homeostasis in cardiac hypertrophy, expecting that this effort will shed new light on understanding the maladaptive cardiac remodeling.

Insulin resistance and heart failure: molecular mechanisms

This article addresses the issue of insulin resistance and associated reductions in cardiac insulin metabolic signaling, which is emerging as a major factor in the development of heart failure, and assumes more importance because of an epidemic increase in obesity and the cardiorenal metabolic syndrome in our aging population. The effects of cardiac insulin resistance are exacerbated by metabolic, endocrine, and cytokine alterations associated with systemic insulin resistance. Understanding the molecular mechanisms linking insulin resistance and heart failure may help to design new and more effective mechanism-based drugs to improve myocardial and systemic insulin resistance.

Regulation of sarco(endo)plasmic reticulum Ca2+-ATPase and calsequestrin gene expression in the heart

The precise control of Ca2+levels during the contraction–relaxation cycle in cardiac myocytes is extremely important for normal beat-to-beat contractile activity. The sarcoplasmic reticulum (SR) plays a key role controlling calcium concentration in the cytosol. The SR Ca2+-ATPase (SERCA2) transports Ca2+inside the SR lumen during relaxation of the cardiac myocyte. Calsequestrin (Casq2) is the main protein in the SR lumen, functioning as a Ca2+buffer and participating in Ca2+release by interacting with the ryanodine receptor 2 (RyR2) Ca2+-release channel. Alterations in normal Ca2+handling significantly contribute to the contractile dysfunction observed in cardiac hypertrophy and in heart failure. Transcriptional regulation of the SERCA2 gene has been extensively studied and some of the mechanisms regulating its expression have been elucidated. Overexpression of Sp1 factor in cardiac hypertrophy downregulates SERCA2 gene expression and increased levels of thyroid hormone up-regulates its transcription. Other hormones such norepinephrine, angiotensin II, endothelin-1, parathyroid hormone, prostaglandin-F2α, as well the cytokines tumor necrosis factor-α and interleukin-6 also downregulate SERCA2 expression. Calcium acting through the calcineurin–NFAT (nuclear factor of activated T cells) pathway has been suggested to regulate SERCA2 and CASQ2 gene expression. This review focuses on the current knowledge regarding transcriptional regulation of SERCA2 and CASQ2 genes in the normal and pathologic heart.

Targeting myocardial substrate metabolism in heart failure: potential for new therapies

The incidence and prevalence of heart failure have increased significantly over the past few decades. Available data suggest that patients with heart failure independent of the aetiology have viable but dysfunctional myocardium that is potentially salvageable. Although a great deal of research effort has focused on characterizing the molecular basis of heart failure, cardiac metabolism in this disorder remains an understudied discipline. It is known that many aspects of cardiomyocyte energetics are altered in heart failure. These include a shift from fatty acid to glucose as a preferred substrate and a decline in the levels of ATP. Despite these demonstrated changes, there are currently no approved drugs that target metabolic enzymes or proteins in heart failure. This is partly due to our limited knowledge of the mechanisms and pathways that regulate cardiac metabolism. Better characterization of these pathways may potentially lead to new therapies for heart failure. Targeting myocardial energetics in the viable and potentially salvageable tissue may be particularly effective in the treatment of heart failure. Here, we will review metabolic changes that occur in fatty acid and glucose metabolism and AMP-activated kinase in heart failure. We propose that cardiac energetics should be considered as a potential target for therapy in heart failure and more research should be done in this area.

Myocyte enhancer factor-2 and cardiac muscle gene expression during hibernation in thirteen-lined ground squirrels

Many small mammals turn to hibernation to survive the winter, cycling through bouts of prolonged torpor where metabolic rate and body temperature fall to low levels. Remarkably, hypertrophy is promoted in cardiac muscle to support the stronger contractions needed in the cold. We proposed that altered expression of mRNA/protein levels of myocyte enhancer factor-2 (MEF2A, MEF2C) transcription factors and downstream targets (e.g., desmin, glucose transporter 4, and myomesin 1) would aid cardiac muscle of thirteen-lined ground squirrels (Ictidomys tridecemlineatus) in meeting challenges associated with hibernation. Gene and protein responses were compared over six conditions: control (euthermic animals in a 5 °C cold room), entrance into torpor, short and long torpors, arousal and interbout. Mef2a relative transcript levels were significantly elevated from controls contributing to increases in MEF2A protein levels throughout the torpor-arousal bout. In addition, levels of phosphorylated, activated MEF2A (Thr312) correlated with increases in MEF2A-DNA binding. MEF2C transcript/protein levels were significantly elevated over controls at selected sampling points whereas phosphorylated/activated MEF2C (Ser387) levels rose during torpor and DNA binding was most prominent during entrance into torpor. Some gene targets of MEF2 action were also upregulated. Desmin transcript levels remained constant whereas enhanced protein expression occurred during entrance into torpor. Glut4 transcript levels were enhanced in arousal and protein expression was elevated over all five sampling points during torpor/arousal. Myomesin 1 transcript levels increased between early torpor and early arousal and protein levels increased during entrance and deep torpor. These data provide insights into the changes in gene/protein in expression that help to prepare cardiac muscle for hibernation.