Fatty acid oxidation enzyme gene expression is downregulated in the failing heart

Thiazolidinedione drugs in the treatment of type 2 diabetes mellitus: past, present and future

Thiazolidinedione (TZD) drugs used in the treatment of type 2 diabetes mellitus (T2DM) have proven effective in improving insulin sensitivity, hyperglycemia, and lipid metabolism. Though well tolerated by some patients, their mechanism of action as ligands of peroxisome proliferator-activated receptors (PPARs) results in the activation of several pathways in addition to those responsible for glycemic control and lipid homeostasis. These pathways, which include those related to inflammation, bone formation, and cell proliferation, may lead to adverse health outcomes. As treatment with TZDs has been associated with adverse hepatic, cardiovascular, osteological, and carcinogenic events in some studies, the role of TZDs in the treatment of T2DM continues to be debated. At the same time, new therapeutic roles for TZDs are being investigated, with new forms and isoforms currently in the pre-clinical phase for use in the prevention and treatment of some cancers, inflammatory diseases, and other conditions. The aims of this review are to provide an overview of the mechanism(s) of action of TZDs, a review of their safety for use in the treatment of T2DM, and a perspective on their current and future therapeutic roles.

Cardiac metabolism - A promising therapeutic target for heart failure

Both heart failure with reduced ejection fraction (HFrEF) and with preserved ejection fraction (HFpEF) are associated with high morbidity and mortality. Although many established pharmacological interventions exist for HFrEF, hospitalization and death rates remain high, and for those with HFpEF (approximately half of all heart failure patients), there are no effective therapies. Recently, the role of impaired cardiac energetic status in heart failure has gained increasing recognition with the identification of reduced capacity for both fatty acid and carbohydrate oxidation, impaired function of the electron transport chain, reduced capacity to transfer ATP to the cytosol, and inefficient utilization of the energy produced. These nodes in the genesis of cardiac energetic impairment provide potential therapeutic targets, and there is promising data from recent experimental and early-phase clinical studies evaluating modulators such as carnitine palmitoyltransferase 1 inhibitors, partial fatty acid oxidation inhibitors and mitochondrial-targeted antioxidants. Metabolic modulation may provide significant symptomatic and prognostic benefit for patients suffering from heart failure above and beyond guideline-directed therapy, but further clinical trials are needed.

The role of sirtuins in mitochondrial function and doxorubicin-induced cardiac dysfunction

Anthracycline chemotherapeutics such as doxorubicin continue to be important treatments for many cancers. Through improved screening and therapy, more patients are surviving and living longer after the diagnosis of their cancer. However, anthracyclines are associated with both short- and long-term cardiotoxic effects. Doxorubicin-induced mitochondrial dysfunction is a central mechanism in the cardiotoxic effects of doxorubicin that contributes to impaired cardiac energy levels, increased reactive oxygen species production, cardiomyocyte apoptosis and the decline in cardiac function. Sirtuins are protein deacetylases that are activated by low energy levels and stimulate energy production through their activation of transcription factors and enzymatic regulators of cardiac energy metabolism. In addition, sirtuins activate oxidative stress resistance pathways. SIRT1 and SIRT3 are expressed at high levels in the cardiomyocyte. This review examines the function of sirtuins in the regulation of cardiac mitochondrial function, with a focus on their role in heart failure and an emphasis on their effects on doxorubicin-induced cardiotoxicity. We discuss the potential for sirtuin activation in combination with anthracycline chemotherapy in order to mitigate its cardiotoxic side-effects without reducing the antineoplastic activity of anthracyclines.

The ‘Goldilocks zone’ of fatty acid metabolism; to ensure that the relationship with cardiac function is just right

Fatty acids (FA) are the main fuel used by the healthy heart to power contraction, supplying 60–70% of the ATP required. FA generate more ATP per carbon molecule than glucose, but require more oxygen to produce the ATP, making them a more energy dense but less oxygen efficient fuel compared with glucose. The pathways involved in myocardial FA metabolism are regulated at various subcellular levels, and can be divided into sarcolemmal FA uptake, cytosolic activation and storage, mitochondrial uptake and β-oxidation. An understanding of the critical involvement of each of these steps has been amassed from genetic mouse models, where forcing the heart to metabolize too much or too little fat was accompanied by cardiac contractile dysfunction and hypertrophy. In cardiac pathologies, such as heart disease and diabetes, aberrations in FA metabolism occur concomitantly with changes in cardiac function. In heart failure, FA oxidation is decreased, correlating with systolic dysfunction and hypertrophy. In contrast, in type 2 diabetes, FA oxidation and triglyceride storage are increased, and correlate with diastolic dysfunction and insulin resistance. Therefore, too much FA metabolism is as detrimental as too little FA metabolism in these settings. Therapeutic compounds that rebalance FA metabolism may provide a mechanism to improve cardiac function in disease. Just like Goldilocks and her porridge, the heart needs to maintain FA metabolism in a zone that is ‘just right’ to support contractile function.

Cardiac mitochondrial dynamics: miR-mediated regulation during cardiac injury

Mitochondrial integrity is indispensable for cardiac health. With the advent of modern imaging technologies, mitochondrial motility and dynamics within the cell are extensively studied. Terminally differentiated and well-structured cardiomyocytes depict little mitochondrial division and fusion, questioning the contribution of mitochondrial fusion proteins (Mitofusin 1/2 and Optic Atrophy 1 protein) and fission factors (Dynamin-like protein 1 and mitochondrial fission 1 protein) in cardiomyocyte homeostasis. Emerging evidences suggest that alterations in mitochondrial morphology from globular, elongated network to punctate fragmented disconnected structures are a pathological response to ensuing cardiac stress and cardiomyocyte cell death, bringing forth the following question, "what maintains this balance between fusion and fission?" The answer hinges upon the classical "junk" DNA: microRNAs, the endogenous non-coding RNAs. Because of their essential role in numerous signaling pathways, microRNAs are considered to play major roles in the pathogenesis of various diseases. Mitochondria are not exempted from microRNA-mediated regulation. This review defines the importance of mitochondrial structural integrity and the microRNA-mitochondrial dynamics tandem, an imminent dimension of the cardiac homeostasis network. Elucidating their coordinated interaction could spur RNA-based therapeutics for resuscitating functional mitochondrial population during cardiovascular disorders.

Metabolic remodeling in hypertrophied and failing myocardium: a review

The energy starvation hypothesis proposes that maladaptive metabolic remodeling antedates, initiates, and maintains adverse contractile dysfunction in heart failure (HF). Better understanding of the cardiac metabolic phenotype and metabolic signaling could help identify the role metabolic remodeling plays within HF and the conditions known to transition toward HF, including "pathological" hypertrophy. In this review, we discuss metabolic phenotype and metabolic signaling in the contexts of pathological hypertrophy and HF. We discuss the significance of alterations in energy supply (substrate utilization, oxidative capacity, and phosphotransfer) and energy sensing using observations from human and animal disease models and models of manipulated energy supply/sensing. We aim to provide ways of thinking about metabolic remodeling that center around metabolic flexibility, capacity (reserve), and efficiency rather than around particular substrate preferences or transcriptomic profiles. We show that maladaptive metabolic remodeling takes multiple forms across multiple energy-handling domains. We suggest that lack of metabolic flexibility and reserve (substrate, oxidative, and phosphotransfer) represents a final common denominator ultimately compromising efficiency and contractile reserve in stressful contexts.

Proteomics of acute heart failure in a rat post-myocardial infarction model

The aim of the present study was to identify the mechanisms underlying the development of post-myocardial infarction (post-MI) heart failure. The left anterior descending coronary artery of rats was occluded to mimic human ischemic heart disease. Linear Trap Quadropole OrbiTrap mass spectrometry was used to profile the expressions of energy metabolism‑associated and calcium‑binding proteins in the post‑MI and control groups. Using the online Protein Analysis Through Evolutionary Relationships classification system, 78 differentially expressed proteins were identified, including 50 downregulated proteins and 28 upregulated proteins in post‑MI group when compared with the control group. The differentially expressed proteins were closely associated with energy metabolism, contractile function, calcium handling, pathological hypertrophy and cardiac remodeling. These results were further validated using western blotting. At different postoperative time points (1st and 14th day following surgery) during the progression of advanced heart failure post‑MI, dynamic alterations in differential protein expression were identified. The expression of the vitamin D protein was significantly upregulated on the 1st day post‑MI however, was then downregulated with progression of the disease on the 14th day post‑MI. These results identified various target proteins associated with the disease, which may be used as diagnostic markers.

Metabolic Origins of Heart Failure

For more than half a century, metabolic perturbations have been explored in the failing myocardium, highlighting a reversion to a more fetal-like metabolic profile (characterized by depressed fatty acid oxidation and concomitant increased reliance on use of glucose). More recently, alterations in ketone body and amino acid/protein metabolism have been described during heart failure, as well as mitochondrial dysfunction and perturbed metabolic signaling (e.g., acetylation, O-GlcNAcylation). Although numerous mechanisms are likely involved, the current review provides recent advances regarding the metabolic origins of heart failure, and their potential contribution toward contractile dysfunction of the heart.

Cardiac metabolic imaging: current imaging modalities and future perspectives

In this review, current imaging techniques and their future perspectives in the field of cardiac metabolic imaging in humans are discussed. This includes a range of noninvasive imaging techniques, allowing a detailed investigation of cardiac metabolism in health and disease. The main imaging modalities discussed are magnetic resonance spectroscopy techniques for determination of metabolite content (triglycerides, glucose, ATP, phosphocreatine, and so on), MRI for myocardial perfusion, and single-photon emission computed tomography and positron emission tomography for quantitation of perfusion and substrate uptake.

A systems genetics approach identifies Trp53inp2 as a link between cardiomyocyte glucose utilization and hypertrophic response

Cardiac failure has been widely associated with an increase in glucose utilization. The aim of our study was to identify factors that mechanistically bridge this link between hyperglycemia and heart failure. Here, we screened the Hybrid Mouse Diversity Panel (HMDP) for substrate-specific cardiomyocyte candidates based on heart transcriptional profile and circulating nutrients. Next, we utilized an in vitro model of rat cardiomyocytes to demonstrate that the gene expression changes were in direct response to substrate abundance. After overlaying candidates of interest with a separate HMDP study evaluating isoproterenol-induced heart failure, we chose to focus on the gene Trp53inp2 as a cardiomyocyte glucose utilization-specific factor. Trp53inp2 gene knockdown in rat cardiomyocytes reduced expression and protein abundance of key glycolytic enzymes. This resulted in reduction of both glucose uptake and glycogen content in cardiomyocytes stimulated with isoproterenol. Furthermore, this reduction effectively blunted the capacity of glucose and isoprotereonol to synergistically induce hypertrophic gene expression and cell size expansion. We conclude that Trp53inp2 serves as regulator of cardiomyocyte glycolytic activity and can consequently regulate hypertrophic response in the context of elevated glucose content.NEW & NOTEWORTHY Here, we apply a novel method for screening transcripts based on a substrate-specific expression pattern to identify Trp53inp2 as an induced cardiomyocyte glucose utilization factor. We further show that reducing expression of the gene could effectively blunt hypertrophic response in the context of elevated glucose content.

Cancer-induced cardiac cachexia: Pathogenesis and impact of physical activity (Review)

Cachexia is a wasting syndrome observed in many patients suffering from several chronic diseases including cancer. In addition to the progressive loss of skeletal muscle mass, cancer cachexia results in cardiac function impairment. During the severe stage of the disease, patients as well as animals bearing cancer cells display cardiac atrophy. Cardiac energy metabolism is also impeded with disruption of mitochondrial homeostasis and reduced oxidative capacity, although the available data remain equivocal. The release of inflammatory cytokines by tumor is a key mechanism in the initiation of heart failure. Oxidative stress, which results from the combination of chemotherapy, inadequate antioxidant consumption and chronic inflammation, will further foster heart failure. Protein catabolism is due to the concomitant activation of proteolytic systems and inhibition of protein synthesis, both processes being triggered by the deactivation of the Akt/mammalian target of rapamycin pathway. The reduction in oxidative capacity involves AMP-activated protein kinase and peroxisome proliferator-activated receptor gamma coactivator 1α dysregulation. The nuclear factor-κB transcription factor plays a prominent role in the coordination of these alterations. Physical exercise appears as an interesting non-pharmaceutical way to counteract cancer cachexia-induced-heart failure. Indeed, aerobic training has anti-inflammatory effects, increases anti-oxidant defenses, prevents atrophy and promotes oxidative metabolism. The present review points out the importance of better understanding the concurrent structural and metabolic changes within the myocardium during cancer and the protective effects of exercise against cardiac cachexia.

Complex Energy Metabolic Changes in Heart Failure With Preserved Ejection Fraction and Heart Failure With Reduced Ejection Fraction

Alterations in cardiac energy metabolism contribute to the severity of heart failure. However, the energy metabolic changes that occur in heart failure are complex, and are dependent not only on the severity and type of heart failure present, but also on the coexistence of common comorbidities such as obesity and type 2 diabetes. In this article we review the cardiac energy metabolic changes that occur in heart failure. An emphasis is made on distinguishing the differences in cardiac energy metabolism between heart failure with preserved ejection fraction (HFpEF) and heart failure with reduced ejection fraction (HFrEF) and in clarifying the common misconceptions surrounding the fate of fatty acids and glucose in the failing heart. The major key points from this article are: (1) mitochondrial oxidative capacity is reduced in HFpEF and HFrEF; (2) fatty acid oxidation is increased in HFpEF and reduced in HFrEF (however, oxidative metabolism of fatty acids in HFrEF still exceeds that of glucose); (3) glucose oxidation is decreased in HFpEF and HFrEF; (4) there is an uncoupling between glucose uptake and oxidation in HFpEF and HFrEF, resulting in an increased rate of glycolysis; (5) ketone body oxidation is increased in HFrEF, which might further reduce fatty acid and glucose oxidation; and finally, (6) branched chain amino acid oxidation is impaired in HFrEF. The understanding of these changes in cardiac energy metabolism in heart failure are essential to allow the development of metabolic modulators in the treatment of heart failure.

Cardiac nuclear receptors: architects of mitochondrial structure and function

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

Peroxisome proliferator-activated receptor-α expression induces alterations in cardiac myofilaments in a pressure-overload model of hypertrophy

Although alterations in fatty acid (FA) metabolism have been shown to have a negative impact on contractility of the hypertrophied heart, the targets of action remain elusive. In this study we compared the function of skinned fiber bundles from transgenic (Tg) mice that overexpress a relatively low level of the peroxisome proliferator-activated receptor α (PPARα), and nontransgenic (NTg) littermates. The mice (NTg-T and Tg-T) were stressed by transverse aortic constriction (TAC) and compared with shams (NTg-S and Tg-S). There was an approximate 4-fold increase in PPARα expression in Tg-S compared with NTg-S, but Tg-T hearts showed the same PPARα expression as NTg-T. Expression of PPARα did not alter the hypertrophic response to TAC but did reduce ejection fraction (EF) in Tg-T hearts compared with other groups. The rate of actomyosin ATP hydrolysis was significantly higher in Tg-S skinned fiber bundles compared with all other groups. Tg-T hearts showed an increase in phosphorylation of specific sites on cardiac myosin binding protein-C (cMyBP-C) and β-myosin heavy chain isoform. These results advance our understanding of potential signaling to the myofilaments induced by altered FA metabolism under normal and pathological states. We demonstrate that chronic and transient PPARα activation during pathological stress alters myofilament response to Ca²⁺ through a mechanism that is possibly mediated by MyBP-C phosphorylation and myosin heavy chain isoforms.NEW & NOTEWORTHY Data presented here demonstrate novel signaling to sarcomeric proteins by chronic alterations in fatty acid metabolism induced by PPARα. The mechanism involves modifications of key myofilament regulatory proteins modifying cross-bridge dynamics with differential effects in controls and hearts stressed by pressure overload.

Expert consensus document: Mitochondrial function as a therapeutic target in heart failure

Heart failure is a pressing worldwide public-health problem with millions of patients having worsening heart failure. Despite all the available therapies, the condition carries a very poor prognosis. Existing therapies provide symptomatic and clinical benefit, but do not fully address molecular abnormalities that occur in cardiomyocytes. This shortcoming is particularly important given that most patients with heart failure have viable dysfunctional myocardium, in which an improvement or normalization of function might be possible. Although the pathophysiology of heart failure is complex, mitochondrial dysfunction seems to be an important target for therapy to improve cardiac function directly. Mitochondrial abnormalities include impaired mitochondrial electron transport chain activity, increased formation of reactive oxygen species, shifted metabolic substrate utilization, aberrant mitochondrial dynamics, and altered ion homeostasis. In this Consensus Statement, insights into the mechanisms of mitochondrial dysfunction in heart failure are presented, along with an overview of emerging treatments with the potential to improve the function of the failing heart by targeting mitochondria.

Mechanotransduction and Metabolism in Cardiomyocyte Microdomains

Efficient contractions of the left ventricle are ensured by the continuous transfer of adenosine triphosphate (ATP) from energy production sites, the mitochondria, to energy utilization sites, such as ionic pumps and the force-generating sarcomeres. To minimize the impact of intracellular ATP trafficking, sarcomeres and mitochondria are closely packed together and in proximity with other ultrastructures involved in excitation-contraction coupling, such as t-tubules and sarcoplasmic reticulum junctions. This complex microdomain has been referred to as the intracellular energetic unit. Here, we review the literature in support of the notion that cardiac homeostasis and disease are emergent properties of the hierarchical organization of these units. Specifically, we will focus on pathological alterations of this microdomain that result in cardiac diseases through energy imbalance and posttranslational modifications of the cytoskeletal proteins involved in mechanosensing and transduction.

Potential beneficial effect of some adipokines positively correlated with the adipose tissue content on the cardiovascular system

Obesity is a risk factor of cardiovascular diseases. However, in the case of heart failure, obese and overweight patients have a more favourable prognosis compared to patients who have a normal body weight. This phenomenon is referred to as the "obesity paradox," and it is explained by, among others, a positive effect of adipokines produced by adipose tissue, particularly by the tissue located in the direct vicinity of the heart and blood vessels. The favourable effect on the cardiovascular system is mostly associated with adiponectin and omentin, but the levels of these substances are reduced in obese patients. Among the adipokines which levels are positively correlated with the adipose tissue content, favourable activity is demonstrated by apelin, progranulin, chemerin, TNF-α (tumour necrosis factor-)α, CTRP-3 (C1q/tumour necrosis factor (TNF) related protein), leptin, visfatin and vaspin. This activity is associated with the promotion of regeneration processes in the damaged myocardium, formation of new blood vessels, reduction of the afterload, improvement of metabolic processes in cardiomyocytes and myocardial contractile function, inhibition of apoptosis and fibrosis of the myocardium, as well as anti-inflammatory and anti-atheromatous effects. The potential use of these properties in the treatment of heart failure and ischaemic heart disease, as well as in pulmonary hypertension, arterial hypertension and the limitation of the loss of cardiomyocytes during cardioplegia-requiring cardiosurgical procedures, is studied. The most advanced studies focus on analogues of apelin and progranulin.

Preservation of myocardial fatty acid oxidation prevents diastolic dysfunction in mice subjected to angiotensin II infusion

RATIONALE

Diastolic dysfunction is a common feature in many heart failure patients with preserved ejection fraction and has been associated with altered myocardial metabolism in hypertensive and diabetic patients. Therefore, metabolic interventions to improve diastolic function are warranted. In mice with a germline cardiac-specific deletion of acetyl CoA carboxylase 2 (ACC2), systolic dysfunction induced by pressure-overload was prevented by maintaining cardiac fatty acid oxidation (FAO). However, it has not been evaluated whether this strategy would prevent the development of diastolic dysfunction in the adult heart.

OBJECTIVE

To test the hypothesis that augmenting cardiac FAO is protective against angiotensin II (AngII)-induced diastolic dysfunction in an adult mouse heart.

METHODS AND RESULTS

We generated a mouse model to induce cardiac-specific deletion of ACC2 in adult mice. Tamoxifen treatment (20mg/kg/day for 5days) was sufficient to delete ACC2 protein and increase cardiac FAO by 50% in ACC2 flox/flox-MerCreMer+ mice (iKO). After 4weeks of AngII (1.1mg/kg/day), delivered by osmotic mini-pumps, iKO mice showed normalized E/E' and E'/A' ratios compared to AngII treated controls (CON). The prevention of diastolic dysfunction in iKO-AngII was accompanied by maintained FAO and reduced glycolysis and anaplerosis. Furthermore, iKO-AngII hearts had a~50% attenuation of cardiac hypertrophy and fibrosis compared to CON. In addition, maintenance of FAO in iKO hearts suppressed AngII-associated increases in oxidative stress and sustained mitochondrial respiratory complex activities.

CONCLUSION

These data demonstrate that impaired FAO is a contributor to the development of diastolic dysfunction induced by AngII. Maintenance of FAO in this model leads to an attenuation of hypertrophy, reduces fibrosis, suppresses increases in oxidative stress, and maintains mitochondrial function. Therefore, targeting mitochondrial FAO is a promising therapeutic strategy for the treatment of diastolic dysfunction.

The TBX1 Transcription Factor in Cardiac Remodeling After Myocardial Infarction

INTRODUCTION AND OBJECTIVES

The transcription factor TBX1 plays an important role in the embryonic development of the heart. Nothing is known about its involvement in myocardial remodeling after acute myocardial infarction (AMI) and whether its expression can be modulated by a treatment with proven benefit such as mineralocorticoid receptor blockade.

METHODS

Acute myocardial infarction was induced in 60 rats via left coronary artery ligation: 50 animals were randomized to be euthanized after 1, 2, 4, 12, or 24 weeks; 10 animals were treated with eplerenone (100 mg/kg/days) 7 days before the AMI until their euthanasia (4 weeks later); 8 additional animals underwent surgery without ligation (control). We analyzed the cardiac expression of TBX1, fetal genes, and fibrosis markers.

RESULTS

The gene and protein expression of TBX1 was increased in the infarcted myocardium, peaking 1 week after AMI (P < .01), without changes in the noninfarcted myocardium. Levels of the fetal genes and fibrosis markers also increased, peaking 4 weeks (P < .001) and 1 week (P < .01) after AMI, respectively. The TBX1 expression was correlated with that of the fibrosis markers (P < .01) but not the fetal genes. Eplerenone reduced the TBX1 increase and fibrosis induced by AMI, with an association improvement in ventricular function and remodeling in echocardiography.

CONCLUSIONS

These results show the reactivated expression of TBX1 and indicate its involvement in cardiac fibrosis and remodeling after AMI and its participation in the benefit from mineralocorticoid receptor blockade.

Role of microRNA in metabolic shift during heart failure

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

Mitochondrial dysfunction and its impact on diabetic heart

Mitochondrial dysfunction and associated oxidative stress are strongly linked to cardiovascular, neurodegenerative, and age associated disorders. More specifically cardiovascular diseases are common in patients with diabetes and significant contributor to the high mortality rates associated with diabetes. Studies have shown that the heart failure risk is increased in diabetic patients even after adjusting for coronary artery disease and hypertension. Although the actual basis of the increased heart failure risk is multifactorial, increasing evidences suggest that imbalances in mitochondrial function and associated oxidative stress play an important role in this process. This review summarizes these abnormalities in mitochondrial function and discusses potential underlying mechanisms. This article is part of a Special Issue entitled: Oxidative Stress and Mitochondrial Quality in Diabetes/Obesity and Critical Illness Spectrum of Diseases - edited by P. Hemachandra Reddy.

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

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

Acetylation control of cardiac fatty acid β-oxidation and energy metabolism in obesity, diabetes, and heart failure

Alterations in cardiac energy metabolism are an important contributor to the cardiac pathology associated with obesity, diabetes, and heart failure. High rates of fatty acid β-oxidation with cardiac insulin resistance represent a cardiac metabolic hallmark of diabetes and obesity, while a marginal decrease in fatty acid oxidation and a prominent decrease in insulin-stimulated glucose oxidation are commonly seen in the early stages of heart failure. Alterations in post-translational control of energy metabolic processes have recently been identified as an important contributor to these metabolic changes. In particular, lysine acetylation of non-histone proteins, which controls a diverse family of mitochondrial metabolic pathways, contributes to the cardiac energy derangements seen in obesity, diabetes, and heart failure. Lysine acetylation is controlled both via acetyltransferases and deacetylases (sirtuins), as well as by non-enzymatic lysine acetylation due to increased acetyl CoA pool size or dysregulated nicotinamide adenine dinucleotide (NAD⁺) metabolism (which stimulates sirtuin activity). One of the important mitochondrial acetylation targets are the fatty acid β-oxidation enzymes, which contributes to alterations in cardiac substrate preference during the course of obesity, diabetes, and heart failure, and can ultimately lead to cardiac dysfunction in these disease states. This review will summarize the role of lysine acetylation and its regulatory control in the context of mitochondrial fatty acid β-oxidation. The functional contribution of cardiac protein lysine acetylation to the shift in cardiac energy substrate preference that occurs in obesity, diabetes, and especially in the early stages of heart failure will also be reviewed. This article is part of a Special Issue entitled: The role of post-translational protein modifications on heart and vascular metabolism edited by Jason R.B. Dyck & Jan F.C. Glatz.

Metabolomics - A wide-open door to personalized treatment in chronic heart failure?

Heart failure (HF) is a complex syndrome representing a final stage of various cardiovascular diseases. Despite significant improvement in the diagnosis and treatment (e.g. ACE-inhibitors, β-blockers, aldosterone antagonists, cardiac resynchronization therapy) of the disease, prognosis of optimally treated patients remains very serious and HF mortality is still unacceptably high. Therefore there is a strong need for further exploration of novel analytical methods, predictive and prognostic biomarkers and more personalized treatment. The metabolism of the failing heart being significantly impaired from its baseline state may be a future target not only for biomarker discovery but also for the pharmacologic intervention. However, an assessment of a particular, isolated metabolite or protein cannot be fully informative and makes a correct interpretation difficult. On the other hand, metabolites profile analysis may greatly assist investigator in an interpretation of the altered pathway dynamics, especially when combined with other lines of evidence (e.g. metabolites from the same pathway, transcriptomics, proteomics). Despite many prior studies on metabolism, the knowledge of peripheral and cardiac pathophysiological mechanisms responsible for the metabolic imbalance and progression of the disease is still insufficient. Metabolomics enabling comprehensive characterization of low molecular weight metabolites (e.g. lipids, sugars, organic acids, amino acids) that reflects the complete metabolic phenotype seems to be the key for further potential improvement in HF treatment (diet-based or biochemical-based). Will this -omics technique one day open a door to easy patients identification before they have a heart failure onset or its decompensation?

Arrhythmogenic and metabolic remodelling of failing human heart

Heart failure (HF) is a major cause of morbidity and mortality worldwide. The global burden of HF continues to rise, with prevalence rates estimated at 1-2% and incidence approaching 5-10 per 1000 persons annually. The complex pathophysiology of HF impacts virtually all aspects of normal cardiac function - from structure and mechanics to metabolism and electrophysiology - leading to impaired mechanical contraction and sudden cardiac death. Pharmacotherapy and device therapy are the primary methods of treating HF, but neither is able to stop or reverse disease progression. Thus, there is an acute need to translate basic research into improved HF therapy. Animal model investigations are a critical component of HF research. However, the translation from cellular and animal models to the bedside is hampered by significant differences between species and among physiological scales. Our studies over the last 8 years show that hypotheses generated in animal models need to be validated in human in vitro models. Importantly, however, human heart investigations can establish translational platforms for safety and efficacy studies before embarking on costly and risky clinical trials. This review summarizes recent developments in human HF investigations of electrophysiology remodelling, metabolic remodelling, and β-adrenergic remodelling and discusses promising new technologies for HF research.

Mitochondrial Function, Biology, and Role in Disease: A Scientific Statement From the American Heart Association

Cardiovascular disease is a major leading cause of morbidity and mortality in the United States and elsewhere. Alterations in mitochondrial function are increasingly being recognized as a contributing factor in myocardial infarction and in patients presenting with cardiomyopathy. Recent understanding of the complex interaction of the mitochondria in regulating metabolism and cell death can provide novel insight and therapeutic targets. The purpose of this statement is to better define the potential role of mitochondria in the genesis of cardiovascular disease such as ischemia and heart failure. To accomplish this, we will define the key mitochondrial processes that play a role in cardiovascular disease that are potential targets for novel therapeutic interventions. This is an exciting time in mitochondrial research. The past decade has provided novel insight into the role of mitochondria function and their importance in complex diseases. This statement will define the key roles that mitochondria play in cardiovascular physiology and disease and provide insight into how mitochondrial defects can contribute to cardiovascular disease; it will also discuss potential biomarkers of mitochondrial disease and suggest potential novel therapeutic approaches.

Physiological and pathological cardiac hypertrophy

The heart must continuously pump blood to supply the body with oxygen and nutrients. To maintain the high energy consumption required by this role, the heart is equipped with multiple complex biological systems that allow adaptation to changes of systemic demand. The processes of growth (hypertrophy), angiogenesis, and metabolic plasticity are critically involved in maintenance of cardiac homeostasis. Cardiac hypertrophy is classified as physiological when it is associated with normal cardiac function or as pathological when associated with cardiac dysfunction. Physiological hypertrophy of the heart occurs in response to normal growth of children or during pregnancy, as well as in athletes. In contrast, pathological hypertrophy is induced by factors such as prolonged and abnormal hemodynamic stress, due to hypertension, myocardial infarction etc. Pathological hypertrophy is associated with fibrosis, capillary rarefaction, increased production of pro-inflammatory cytokines, and cellular dysfunction (impairment of signaling, suppression of autophagy, and abnormal cardiomyocyte/non-cardiomyocyte interactions), as well as undesirable epigenetic changes, with these complex responses leading to maladaptive cardiac remodeling and heart failure. This review describes the key molecules and cellular responses involved in physiological/pathological cardiac hypertrophy.

Present and future pharmacotherapeutic agents in heart failure: an evolving paradigm

Many conditions culminate in heart failure (HF), a multi‐organ systemic syndrome with an intrinsically poor prognosis. Pharmacotherapeutic agents that correct neurohormonal dysregulation and haemodynamic instability have occupied the forefront of developments within the treatment of HF in the past. Indeed, multiple trials aimed to validate these agents in the 1980s and early 1990s, resulting in a large and robust evidence‐base supporting their use clinically. An established treatment paradigm now exists for the treatment of HF with reduced ejection fraction (HFrEF), but there have been very few notable developments in recent years. HF remains a significant health concern with an increasing incidence as the population ages. We may indeed be entering the surgical era for HF treatment, but these therapies remain expensive and inaccessible to many. Newer pharmacotherapeutic agents are slowly emerging, many targeting alternative therapeutic pathways, but with mixed results. Metabolic modulation and manipulation of the nitrate/nitrite/nitric oxide pathway have shown promise and could provide the answers to fill the therapeutic gap between medical interventions and surgery, but further definitive trials are warranted. We review the significant evidence base behind the current medical treatments for HFrEF, the physiology of metabolic impairment in HF, and discuss two promising novel agents, perhexiline and nitrite.

Effects of the Novel Long-Acting GLP-1 Agonist, Albiglutide, on Cardiac Function, Cardiac Metabolism, and Exercise Capacity in Patients With Chronic Heart Failure and Reduced Ejection Fraction

OBJECTIVES

This study sought to determine if glucagon-like peptide (GLP)-1 ameliorates myocardial metabolic abnormalities in chronic heart failure.

BACKGROUND

Albiglutide (GSK716155) is a GLP-1 agonist indicated for type 2 diabetes.

METHODS

We performed a randomized, placebo-controlled study evaluating 12 weeks of albiglutide in New York Heart Association II or III subjects with ejection fraction <40%. Subjects received weekly placebo (n = 30) or albiglutide 3.75 mg (n = 12), 15 mg (n = 13), or 30 mg (n = 27). The primary comparison was between albiglutide 30 mg and placebo. Assessments included echocardiography, 6-minute-walk test, and peak oxygen consumption. In a subgroup of patients, myocardial glucose and oxygen use were assessed. Endpoints are reported as change from baseline ± SE.

RESULTS

Albiglutide 30 mg compared with placebo did not improve change from baseline in left ventricular ejection fraction (2.4% [1.1%] vs. 4.4% [1.1%]; p = 0.22), 6-min walk test (18 [12] m vs. 9 [11] m; p = 0.58), myocardial glucose use (p = 0.59), or oxygen use (p = 0.25). In contrast, albiglutide 30 mg versus placebo improved change from baseline in peak oxygen consumption (0.9 [0.5] ml/kg/min vs. -0.6 [0.5] ml/kg/min; p = 0.02). Albiglutide was well tolerated.

CONCLUSIONS

Although there was no detectable effect of albiglutide on cardiac function or myocardial glucose use, there was a modest increase in peak oxygen consumption, which could have been mediated by noncardiac effects. (A Multi-center, Placebo-controlled Study to Evaluate the Safety of GSK716155 and Its Effects on Myocardial Metabolism, Myocardial Function, and Exercise Capacity in Patients With NYHA Class II/III Congestive Heart Failure; NCT01357850).

Triacylglycerol turnover in the failing heart

No longer regarded as physiologically inert the endogenous triacylglyceride (TAG) pool within the cardiomyocyte is now recognized to play a dynamic role in metabolic regulation. Beyond static measures of content, the relative rates of interconversion among acyl intermediates are more closely linked to dynamic processes of physiological function in normal and diseased hearts, with the potential for both adaptive and maladaptive contributions. Indeed, multiple inefficiencies in cardiac metabolism have been identified in the decompensated, hypertrophied and failing heart. Among the intracellular responses to physiological, metabolic and pathological stresses, TAG plays a central role in the balance of lipid handling and signaling mechanisms. TAG dynamics are profoundly altered from normal in both diabetic and pathologically stressed hearts. More than just expansion or contraction of the stored lipid pool, the turnover rates of TAG are sensitive to and compete against other enzymatic pathways, anabolic and catabolic, for reactive acyl-CoA units. The rates of TAG synthesis and lipolysis thusly affect multiple components of cardiomyocyte function, including energy metabolism, cell signaling, and enzyme activation, as well as the regulation of gene expression in both normal and diseased states. This review examines the multiple etiologies and metabolic consequences of the failing heart and the central role of lipid storage dynamics in the pathogenic process. This article is part of a Special Issue entitled: Heart Lipid Metabolism edited by G.D. Lopaschuk.

Normalization of cardiac substrate utilization and left ventricular hypertrophy precede functional recovery in heart failure regression

AIMS

Impaired cardiac substrate metabolism plays an important role in heart failure (HF) pathogenesis. Since many of these metabolic changes occur at the transcriptional level of metabolic enzymes, it is possible that this loss of metabolic flexibility is permanent and thus contributes to worsening cardiac function and/or prevents the full regression of HF upon treatment. However, despite the importance of cardiac energetics in HF, it remains unclear whether these metabolic changes can be normalized. In the current study, we investigated whether a reversal of an elevated aortic afterload in mice with severe HF would result in the recovery of cardiac function, substrate metabolism, and transcriptional reprogramming as well as determined the temporal relationship of these changes.

METHODS AND RESULTS

Male C57Bl/6 mice were subjected to either Sham or transverse aortic constriction (TAC) surgery to induce HF. After HF development, mice with severe HF (% ejection fraction < 30) underwent a second surgery to remove the aortic constriction (debanding, DB). Three weeks following DB, there was a near complete recovery of systolic and diastolic function, and gene expression of several markers for hypertrophy/HF were returned to values observed in healthy controls. Interestingly, pressure-overload-induced left ventricular hypertrophy (LVH) and cardiac substrate metabolism were restored at 1-week post-DB, which preceded functional recovery.

CONCLUSIONS

The regression of severe HF is associated with early and dramatic improvements in cardiac energy metabolism and LVH normalization that precede restored cardiac function, suggesting that metabolic and structural improvements may be critical determinants for functional recovery.

Cardiac mitochondrial energy metabolism in heart failure: Role of cardiolipin and sirtuins

Mitochondrial oxidation of fatty acids accounts for the majority of cardiac ATP production in the heart. Fatty acid utilization by cardiac mitochondria is controlled at the level of fatty acid uptake, lipid synthesis, mobilization and mitochondrial import and oxidation. Consequently defective mitochondrial function appears to be central to the development of heart failure. Cardiolipin is a key mitochondrial phospholipid required for the activity of the electron transport chain. In heart failure, loss of cardiolipin and tetralinoleoylcardiolipin helps to fuel the generation of excessive reactive oxygen species that are a by-product of inefficient mitochondrial electron transport chain complexes I and III. In this vicious cycle, reactive oxygen species generate lipid peroxides and may, in turn, cause oxidation of cardiolipin catalyzed by cytochrome c leading to cardiomyocyte apoptosis. Hence, preservation of cardiolipin and mitochondrial function may be keys to the prevention of heart failure development. In this review, we summarize cardiac energy metabolism and the important role that fatty acid uptake and metabolism play in this process and how defects in these result in heart failure. We highlight the key role that cardiolipin and sirtuins play in cardiac mitochondrial β-oxidation. In addition, we review the potential of pharmacological modulation of cardiolipin through the polyphenolic molecule resveratrol as a sirtuin-activator in attenuating mitochondrial dysfunction. Finally, we provide novel experimental evidence that resveratrol treatment increases cardiolipin in isolated H9c2 cardiac myocytes and tetralinoleoylcardiolipin in the heart of the spontaneously hypertensive rat and hypothesize that this leads to improvement in mitochondrial function. This article is part of a Special Issue entitled: Heart Lipid Metabolism edited by G.D. Lopaschuk.

Mitochondrial protein hyperacetylation in the failing heart

Myocardial fuel and energy metabolic derangements contribute to the pathogenesis of heart failure. Recent evidence implicates posttranslational mechanisms in the energy metabolic disturbances that contribute to the pathogenesis of heart failure. We hypothesized that accumulation of metabolite intermediates of fuel oxidation pathways drives posttranslational modifications of mitochondrial proteins during the development of heart failure. Myocardial acetylproteomics demonstrated extensive mitochondrial protein lysine hyperacetylation in the early stages of heart failure in well-defined mouse models and the in end-stage failing human heart. To determine the functional impact of increased mitochondrial protein acetylation, we focused on succinate dehydrogenase A (SDHA), a critical component of both the tricarboxylic acid (TCA) cycle and respiratory complex II. An acetyl-mimetic mutation targeting an SDHA lysine residue shown to be hyperacetylated in the failing human heart reduced catalytic function and reduced complex II-driven respiration. These results identify alterations in mitochondrial acetyl-CoA homeostasis as a potential driver of the development of energy metabolic derangements that contribute to heart failure.

The Failing Heart Relies on Ketone Bodies as a Fuel

BACKGROUND

Significant evidence indicates that the failing heart is energy starved. During the development of heart failure, the capacity of the heart to utilize fatty acids, the chief fuel, is diminished. Identification of alternate pathways for myocardial fuel oxidation could unveil novel strategies to treat heart failure.

METHODS AND RESULTS

Quantitative mitochondrial proteomics was used to identify energy metabolic derangements that occur during the development of cardiac hypertrophy and heart failure in well-defined mouse models. As expected, the amounts of proteins involved in fatty acid utilization were downregulated in myocardial samples from the failing heart. Conversely, expression of β-hydroxybutyrate dehydrogenase 1, a key enzyme in the ketone oxidation pathway, was increased in the heart failure samples. Studies of relative oxidation in an isolated heart preparation using ex vivo nuclear magnetic resonance combined with targeted quantitative myocardial metabolomic profiling using mass spectrometry revealed that the hypertrophied and failing heart shifts to oxidizing ketone bodies as a fuel source in the context of reduced capacity to oxidize fatty acids. Distinct myocardial metabolomic signatures of ketone oxidation were identified.

CONCLUSIONS

These results indicate that the hypertrophied and failing heart shifts to ketone bodies as a significant fuel source for oxidative ATP production. Specific metabolite biosignatures of in vivo cardiac ketone utilization were identified. Future studies aimed at determining whether this fuel shift is adaptive or maladaptive could unveil new therapeutic strategies for heart failure.

Dietary management of heart failure: room for improvement?

There is growing awareness of the role of diet in both health and disease management. Much data are available on the cardioprotective diet in the primary and secondary prevention of CVD. However, there is limited information on the role of diet in the management of heart failure (HF). Animal models of HF have provided interesting insight and potential mechanisms by which dietary manipulation may improve cardiac performance and delay the progression of the disease, and small-scale human studies have highlighted beneficial diet patterns. The aim of this review is to summarise the current data available on the role of diet in the management of human HF and to demonstrate that dietary manipulation needs to progress further than the simple recommendation of salt and fluid restriction.

PPARβ/δ and lipid metabolism in the heart

Cardiac lipid metabolism is the focus of attention due to its involvement in the development of cardiac disorders. Both a reduction and an increase in fatty acid utilization make the heart more prone to the development of lipotoxic cardiac dysfunction. The ligand-activated transcription factor peroxisome proliferator-activated receptor (PPAR)β/δ modulates different aspects of cardiac fatty acid metabolism, and targeting this nuclear receptor can improve heart diseases caused by altered fatty acid metabolism. In addition, PPARβ/δ regulates glucose metabolism, the cardiac levels of endogenous antioxidants, mitochondrial biogenesis, cardiomyocyte apoptosis, the insulin signaling pathway and lipid-induced myocardial inflammatory responses. As a result, PPARβ/δ ligands can improve cardiac function and ameliorate the pathological progression of cardiac hypertrophy, heart failure, cardiac oxidative damage, ischemia-reperfusion injury, lipotoxic cardiac dysfunction and lipid-induced cardiac inflammation. Most of these findings have been observed in preclinical studies and it remains to be established to what extent these intriguing observations can be translated into clinical practice. This article is part of a Special Issue entitled: Heart Lipid Metabolism edited by G.D. Lopaschuk.

Post-Translational Modifications of Cardiac Mitochondrial Proteins in Cardiovascular Disease: Not Lost in Translation

Protein post-translational modifications (PTMs) are crucial in regulating cellular biology by playing key roles in processes such as the rapid on and off switching of signaling network and the regulation of enzymatic activities without affecting gene expressions. PTMs lead to conformational changes in the tertiary structure of protein and resultant regulation of protein function such as activation, inhibition, or signaling roles. PTMs such as phosphorylation, acetylation, and S-nitrosylation of specific sites in proteins have key roles in regulation of mitochondrial functions, thereby contributing to the progression to heart failure. Despite the extensive study of PTMs in mitochondrial proteins much remains unclear. Further research is yet to be undertaken to elucidate how changes in the proteins may lead to cardiovascular and metabolic disease progression in particular. We aimed to summarize the various types of PTMs that occur in mitochondrial proteins, which might be associated with heart failure. This study will increase the understanding of cardiovascular diseases through PTM.

Mitochondrial biogenesis and dynamics in the developing and diseased heart

In this review, Dorn et al. describe the regulatory circuitry and downstream events involved in mitochondrial biogenesis and its coordination with mitochondrial dynamics in developing and diseased hearts.

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

In utero Undernutrition Programs Skeletal and Cardiac Muscle Metabolism

In utero undernutrition is associated with increased risk for insulin resistance, obesity, and cardiovascular disease during adult life. A common phenotype associated with low birth weight is reduced skeletal muscle mass. Given the central role of skeletal muscle in whole body metabolism, alterations in its mass as well as its metabolic characteristics may contribute to disease risk. This review highlights the metabolic alterations in cardiac and skeletal muscle associated with in utero undernutrition and low birth weight. These tissues have high metabolic demands and are known to be sites of major metabolic dysfunction in obesity, type 2 diabetes, and cardiovascular disease. Recent research demonstrates that mitochondrial energetics are decreased in skeletal and cardiac muscles of adult offspring from undernourished mothers. These effects apparently lead to the development of a thrifty phenotype, which may represent overall a compensatory mechanism programmed in utero to handle times of limited nutrient availability. However, in an environment characterized by food abundance, the effects are maladaptive and increase adulthood risks of metabolic disease.

Novel Perspectives in Redox Biology and Pathophysiology of Failing Myocytes: Modulation of the Intramyocardial Redox Milieu for Therapeutic Interventions-A Review Article from the Working Group of Cardiac Cell Biology, Italian Society of Cardiology

The prevalence of heart failure (HF) is still increasing worldwide, with enormous human, social, and economic costs, in spite of huge efforts in understanding pathogenetic mechanisms and in developing effective therapies that have transformed this syndrome into a chronic disease. Myocardial redox imbalance is a hallmark of this syndrome, since excessive reactive oxygen and nitrogen species can behave as signaling molecules in the pathogenesis of hypertrophy and heart failure, leading to dysregulation of cellular calcium handling, of the contractile machinery, of myocardial energetics and metabolism, and of extracellular matrix deposition. Recently, following new interesting advances in understanding myocardial ROS and RNS signaling pathways, new promising therapeutical approaches with antioxidant properties are being developed, keeping in mind that scavenging ROS and RNS tout court is detrimental as well, since these molecules also play a role in physiological myocardial homeostasis.

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.

Peroxisome Proliferator-Activated Receptors and the Heart: Lessons from the Past and Future Directions

Peroxisome proliferator-activated receptors (PPARs) belong to the nuclear family of ligand activated transcriptional factors and comprise three different isoforms, PPAR-α, PPAR-β/δ, and PPAR-γ. The main role of PPARs is to regulate the expression of genes involved in lipid and glucose metabolism. Several studies have demonstrated that PPAR agonists improve dyslipidemia and glucose control in animals, supporting their potential as a promising therapeutic option to treat diabetes and dyslipidemia. However, substantial differences exist in the therapeutic or adverse effects of specific drug candidates, and clinical studies have yielded inconsistent data on their cardioprotective effects. This review summarizes the current knowledge regarding the molecular function of PPARs and the mechanisms of the PPAR regulation by posttranslational modification in the heart. We also describe the results and lessons learned from important clinical trials on PPAR agonists and discuss the potential future directions for this class of drugs.

Modulation of fatty acid metabolism is involved in the alleviation of isoproterenol-induced rat heart failure by fenofibrate

Heart failure is a disease predominantly caused by an energy metabolic disorder in cardiomyocytes. The present study investigated the inhibitory effects of fenofibrate (FF) on isoproterenol (ISO)-induced hear failure in rats, and examined the underlying mechanisms. The rats were divided into CON, ISO (HF model), FF and FF+ISO (HF animals pretreated with FF) groups. The cardiac structure and function of the rats were assessed, and contents of free fatty acids and glucose metabolic products were determined. In addition, myocardial cells were isolated from neonatal rats and used in vitro to investigate the mechanisms by which FF relieves heart failure. Western blot analysis was performed to quantify the expression levels of peroxisome proliferator-activated receptor (PPAR)α and uncoupling protein 2 (UCP2). FF effectively alleviated the ISO-induced cardiac structural damage, functional decline, and fatty acid and carbohydrate metabolic abnormalities. Compared with the ISO group, the serum levels of brain natriuretic peptide (BNP), free fatty acids, lactic acid and pyruvic acid were decreased in the FF animals. In the cultured myocardial cells, lactic acid and pyruvic acid contents were lower in the supernatants obtained from the FF animals, with lower levels of mitochondrial ROS production and cell necrosis, compared with the ISO group, whereas PPARα upregulation and UCP2 downregulation occurred in the FF+ISO group. The results demonstrated that FF efficiently alleviated heart failure in the ISO-induced rat model, possibly via promoting fatty acid oxidation.

Bendavia restores mitochondrial energy metabolism gene expression and suppresses cardiac fibrosis in the border zone of the infarcted heart

AIMS

We have observed that Bendavia, a mitochondrial-targeting peptide that binds the phospholipid cardiolipin and stabilizes the components of electron transport and ATP generation, improves cardiac function and prevents left ventricular remodeling in a 6week rat myocardial infarction (MI) model. We hypothesized that Bendavia restores mitochondrial biogenesis and gene expression, suppresses cardiac fibrosis, and preserves sarco/endoplasmic reticulum (SERCA2a) level in the noninfarcted border zone of infarcted hearts.

MAIN METHODS

Starting 2h after left coronary artery ligation, rats were randomized to receive Bendavia (3mg/kg/day), water or sham operation. At 6weeks, PCR array and qRT-PCR was performed to detect gene expression. Picrosirius red staining was used to analyze collagen deposition.

KEY FINDINGS

There was decreased expression of 70 out of 84 genes related to mitochondrial energy metabolism in the border zone of untreated hearts. This down-regulation was largely reversed by Bendavia treatment. Downregulated mitochondrial biogenesis and glucose & fatty acid (FA) oxidation related genes were restored by administration of Bendavia. Matrix metalloproteinase (MMP9) and tissue inhibitor of metalloproteinase (TIMP1) gene expression were significantly increased in the border zone of untreated hearts. Bendavia completely prevented up-regulation of MMP9, but maintained TIMP1 gene expression. Picrosirius red staining demonstrated that Bendavia suppressed collagen deposition within border zone. In addition, Bendavia showed a trend toward restoring SERCA2a expression.

SIGNIFICANCE

Bendavia restored expression of mitochondrial energy metabolism related genes, prevented myocardial matrix remodeling and preserved SERCA2a expression in the noninfarcted border, which may have contributed to the preservation of cardiac structure and function.