A role for peroxisome proliferator-activated receptor alpha (PPARalpha ) in the control of cardiac malonyl-CoA levels: reduced fatty acid oxidation rates and increased glucose oxidation rates in the hearts of mice lacking PPARalpha are associated with higher concentrations of malonyl-CoA and reduced expression of malonyl-CoA decarboxylase

Fatty acid metabolism in the placentae of gestational diabetes mellitus

The prevalence of gestational diabetes mellitus (GDM), a metabolic complication during pregnancy is increasing rapidly. It exerts various short and long term effects on the mother and the child. Nonetheless, the mechanisms underlying the pathophysiology of GDM are still not clear. Placenta is a key 'programming' agent and any impairment in placental structure and function may hamper the fetal growth and development. Omega-3 and omega-6 fatty acids are key nutrients involved in placental and fetal development. The fatty acids transport from maternal circulation towards the fetus depends on the fatty acid status of the mother, fatty acid metabolism of the placenta and placental transport of fatty acids. Alteration in any of these could influence the fatty acids transport towards the fetus thereby affecting the fetal brain development and leading to impairment in cognitive function in the off-spring. We propose a role for placental fatty acid metabolism in influencing fetal growth and development which in turn can have an impact on cognitive development of the offspring born to GDM women.

Ketone Catabolism is Essential for Maintaining Normal Heart Function During Aging

The heart utilizes various nutrient sources for energy production, primarily favoring fatty acid oxidation. While ketones can be fuel substrates, ketolysis has been shown to be dispensable for heart development and function in mice. However, the long-term consequences of ketolysis downregulation in the heart remain unknown. Here we demonstrate that ketone catabolism is essential for preserving cardiac function during aging. The cardiac expression of succinyl-CoA:3-ketoacid CoA transferase (SCOT), a rate-limiting enzyme in ketolysis, decreases with aging in female mice. SCOT cardiomyocyte-specific knockout (cKO) mice exhibit normal heart function at 10 weeks of age but progressively develop cardiac dysfunction and remodeling as they age, without overt hypertrophy in both sexes. Notably, ketone supplementation via a ketogenic diet partially rescues contractile dysfunction in SCOT cKO mice, suggesting ketone oxidation-independent mechanisms contribute to the development of cardiomyopathy caused by SCOT downregulation. These findings indicate that ketone catabolism is crucial for maintaining heart function during aging, and that ketones confer cardioprotection independently of ketone oxidation.

Molecular Targets and Small Molecules Modulating Acetyl Coenzyme A in Physiology and Diseases

Acetyl coenzyme A (acetyl-CoA), a pivotal regulatory metabolite, is a product of numerous catabolic reactions and a substrate for various anabolic responses. Its role extends to crucial physiological processes, such as glucose homeostasis and free fatty acid utilization. Moreover, acetyl-CoA plays a significant part in reshaping the metabolic microenvironment and influencing the progression of several diseases and conditions, including cancer, insulin resistance, diabetes, heart failure, fear, and neuropathic pain. This Review delves into the role of acetyl-CoA in both physiological and pathological conditions, shedding light on the key players in its formation within the cytosol. We specifically focus on the physiological impact of malonyl-CoA decarboxylase (MCD), acetyl-CoA synthetase2 (ACSS2), and ATP-citrate lyase (ACLY) on metabolism, glucose homeostasis, free fatty acid utilization, and post-translational modification cellular processes. Additionally, we present the pathological implications of MCD, ACSS2, and ACLY in various clinical manifestations. This Review also explores the potential and limitations of targeting MCD, ACSS2, and ACLY using small molecules in different clinical settings.

Oleoylethanolamide mitigates cardiometabolic disruption secondary to obesity induced by high-fat diet in mice

Chronic lipid overnutrition has been demonstrated to promote cardiac dysfunction resulting from metabolic derangement, inflammation, and fibrosis. Oleoylethanolamide (OEA), an endogenous peroxisome proliferator activating receptor (PPAR)-α agonist, has been extensively studied for its metabolic properties. The aim of this study was to determine if OEA has beneficial effects on high-fat diet (HFD)-induced cardiac disruption in obese mice, focusing on the underlying pathological mechanisms. OEA treatment restores the metabolic pattern, improving serum glycaemic and lipid profile. OEA also reduces heart weight and serum creatine kinase-myocardial band (CK-MB), a marker of cardiac damage. Accordingly, OEA modulates cardiac metabolism, increasing insulin signaling and reducing lipid accumulation. OEA increases AMPK and AKT phosphorylation, converging in the rise of AS160 activation and glucose transporter (GLUT)4 protein level. Moreover, OEA reduces the transcription of the cardiac fatty acid transporter CD36 and fatty acid synthase and increases PPAR-α mRNA levels. Adiponectin and meteorite-like protein transcription levels were significantly reduced by OEA in HFD mice, as well as those of inflammatory cytokines and pro-fibrotic markers. An increased autophagic process was also shown, contributing to OEA's cardioprotective effects. Metabolomic analyses of cardiac tissue revealed the modulation of different lipids, including triglycerides, glycerophospholipids and sphingomyelins by OEA treatment. In vitro experiments on HL-1 cardiomyocytes showed OEA's capability in reducing inflammation and fibrosis following palmitate challenge, demonstrating a direct activity of OEA on cardiac cells, mainly mediated by PPAR-α activation. Our results indicate OEA as a potential therapeutic to restrain cardiac damage associated with metabolic disorders.

Effects of In Ovo Taurine Injection on Embryo Development, Antioxidant Status, and Bioactive Peptide Content in Chicken Embryos (Gallus gallus domesticus)

Stress in birds disrupts the homeostasis of the organism, leading to an inability to neutralize reactive oxygen species. Taurine, an effective antioxidant, affects various cellular mechanisms, including cation modulation, protein phosphorylation, and cell proliferation. The aim of the study was to evaluate the effect of colloid with taurine applied in ovo to Albumin on embryonic development, oxidative stress indicators and the content of bioactive peptides-carnosine and anserine-in the pectoral muscle. The research materials were eggs of the parent flock (Ross 308) divided into four groups (K (without injection), T50-concentration of taurine hydrocolloid 50 ppm (mg/L); T100-colloid concentration 100 ppm (mg/L) taurine; T500-colloid concentration of 500 ppm (mg/L) taurine). The experimental solutions were injected in an amount of 0.3 mL into egg white. Eggs were incubated under standard incubation conditions. The addition of 100 and 500 ppm taurine had a highly significant (p = 0.001) effect on the plasma antioxidant potential in chicks. The level of anserine increased with increasing concentrations of taurine. These changes were highly significant (p = 0.007). The level of anserine in the T2 and T3 groups was determined to be 2.5 times higher than in the pectoral muscles of embryos not treated with taurine colloid. An analysis of the results showed that the administration of an increased dose of hydrocolloid with taurine increased the content of carnosine and anserine in the pectoral muscle. Colloid with taurine applied in ovo to chicken white egg reduces oxidative stress and increases homeostasis of the organism.

Ferroptosis and its Potential Determinant Role in Myocardial Susceptibility to Ischemia/Reperfusion Injury in Diabetes

Myocardial ischemia/reperfusion injury (MIRI) is a major cause of cardiac death particularly in patients with diabetes. When the coronary artery is partially or completely blocked, restoration of blood perfusion can normally be achieved within a certain time due to the development of advanced techniques such as percutaneous coronary intervention (PCI) and coronary artery bypass grafting (CABG) surgery. However, cardiac tissue injury may aggravate progressively even after the ischemic myocardium is restored to normal perfusion. MIRI is often associated with various forms of cell death, including apoptosis, autophagy, programmed necrosis, pyroptosis, and ferroptosis, among others. Ferroptosis is known as iron-dependent cell death that is distinct from other programmed modes of cell death. Ferroptosis is under constitutive control by glutathione peroxidase 4 (GPX4), and the reduction of GPX4 may result in ferroptosis even if iron homeostasis is physiologically maintained. The essences of ferroptosis are substantial iron accumulation and lipid peroxidation that trigger cell death. Under impaired antioxidant system, cellular reactive oxygen species (ROS) accumulation leads to lipid peroxidation which consequently results in ferroptosis. Ferroptosis shares a few common features with several types of cell death and interplays with various forms of cell death such as autophagy and apoptosis in the development of cardiovascular diseases. More and more recent studies have demonstrated that ferroptosis plays an important role in MIRI. However, few studies have addressed the relative importance of ferroptosis in MIRI relative to other forms of cell deaths. In this review, we summarized the basic aspects and advances regarding the molecular pathogenesis of ferroptosis, evaluated its role in MIRI, and propose that the levels of ferroptosis may function as a major determinant of myocardial susceptibility to ischemia/reperfusion injury (IRI) in general and of the enhanced vulnerability to MIRI specifically in diabetes.

Metabolic remodeling in cardiac hypertrophy and heart failure with reduced ejection fraction occurs independent of transcription factor EB in mice

Background

A metabolic shift from fatty acid (FAO) to glucose oxidation (GO) occurs during cardiac hypertrophy (LVH) and heart failure with reduced ejection fraction (HFrEF), which is mediated by PGC-1α and PPARα. While the transcription factor EB (TFEB) regulates the expression of both PPARGC1A/PGC-1α and PPARA/PPARα, its contribution to metabolic remodeling is uncertain.

Methods

Luciferase assays were performed to verify that TFEB regulates PPARGC1A expression. Cardiomyocyte-specific Tfeb knockout (cKO) and wildtype (WT) male mice were subjected to 27G transverse aortic constriction or sham surgery for 21 and 56 days, respectively, to induce LVH and HFrEF. Echocardiographic, morphological, and histological analyses were performed. Changes in markers of cardiac stress and remodeling, metabolic shift and oxidative phosphorylation were investigated by Western blot analyses, mass spectrometry, qRT-PCR, and citrate synthase and complex II activity measurements.

Results

Luciferase assays revealed that TFEB increases PPARGC1A/PGC-1α expression, which was inhibited by class IIa histone deacetylases and derepressed by protein kinase D. At baseline, cKO mice exhibited a reduced cardiac function, elevated stress markers and a decrease in FAO and GO gene expression compared to WT mice. LVH resulted in increased cardiac remodeling and a decreased expression of FAO and GO genes, but a comparable decline in cardiac function in cKO compared to WT mice. In HFrEF, cKO mice showed an improved cardiac function, lower heart weights, smaller myocytes and a reduction in cardiac remodeling compared to WT mice. Proteomic analysis revealed a comparable decrease in FAO- and increase in GO-related proteins in both genotypes. A significant reduction in mitochondrial quality control genes and a decreased citrate synthase and complex II activities was observed in hearts of WT but not cKO HFrEF mice.

Conclusions

TFEB affects the baseline expression of metabolic and mitochondrial quality control genes in the heart, but has only minor effects on the metabolic shift in LVH and HFrEF in mice. Deletion of TFEB plays a protective role in HFrEF but does not affect the course of LVH. Further studies are needed to elucidate if TFEB affects the metabolic flux in stressed cardiomyocytes.

Mechanism of Obesity-Related Lipotoxicity and Clinical Perspective

The link between cellular exposure to fatty acid species and toxicity phenotypes remains poorly understood. However, structural characterization and functional profiling of human plasma free fatty acids (FFAs) analysis has revealed that FFAs are located either in the toxic cluster or in the cluster that is transcriptionally responsive to lipotoxic stress and creates genetic risk factors. Genome-wide short hairpin RNA screen has identified more than 350 genes modulating lipotoxicity. Hypertrophic adipocytes in obese adipose are both unable to expand further to store excess lipids in the diet and are resistant to the antilipolytic action of insulin. In addition to lipolysis, the inability of packaging the excess lipids into lipid droplets causes circulating fatty acids to reach toxic levels in non-adipose tissues. Deleterious effects of accumulated lipid in non-adipose tissues are known as lipotoxicity. Although triglycerides serve a storage function for long-chain non-esterified fatty acid and their products such as ceramide and diacylglycerols (DAGs), overloading of palmitic acid fraction of saturated fatty acids (SFAs) raises ceramide levels. The excess DAG and ceramide load create harmful effects on multiple organs and systems, inducing chronic inflammation in obesity. Thus, lipotoxic inflammation results in β cells death and pancreatic islets dysfunction. Endoplasmic reticulum stress stimuli induce lipolysis by activating cyclic adenosine monophosphate (cAMP)/protein kinase A (PKA) and extracellular signal-regulated kinase (Erk) 1/2 signaling in adipocytes. However, palmitic acid-induced endoplasmic reticulum stress-c-Jun N-terminal kinase (JNK)-autophagy axis in hypertrophic adipocytes is a pro-survival mechanism against endoplasmic reticulum stress and cell death induced by SFAs. Endoplasmic reticulum-localized acyl-coenzyme A (CoA): glycerol-3-phosphate acyltransferase (GPAT) enzymes are mediators of lipotoxicity, and inhibiting these enzymes has therapeutic potential for lipotoxicity. Lipotoxicity increases the number of autophagosomes, which engulf palmitic acid, and thus suppress the autophagic turnover. Fatty acid desaturation promotes palmitate detoxification and storages into triglycerides. As therapeutic targets of glucolipotoxicity, in addition to caloric restriction and exercise, there are four different pharmacological approaches, which consist of metformin, glucagon-like peptide 1 (GLP-1) receptor agonists, peroxisome proliferator-activated receptor-gamma (PPARγ) ligands thiazolidinediones, and chaperones are still used in clinical practice. Furthermore, induction of the brown fat-like phenotype with the mixture of eicosapentanoic acid and docosahexaenoic acid appears as a potential therapeutic application for treatment of lipotoxicity.

Obesity-induced metabolic imbalance allosterically modulates CtBP2 to inhibit PPAR-alpha transcriptional activity

Maintenance of metabolic homeostasis is secured by metabolite-sensing systems, which can be overwhelmed by constant macronutrient surplus in obesity. Not only the uptake processes but also the consumption of energy substrates determine the cellular metabolic burden. We herein describe a novel transcriptional system in this context comprised of peroxisome proliferator-activated receptor alpha (PPARα), a master regulator for fatty acid oxidation, and C-terminal binding protein 2 (CtBP2), a metabolite-sensing transcriptional co-repressor. CtBP2 interacts with PPARα to repress its activity, and the interaction is enhanced upon binding to malonyl-CoA, a metabolic intermediate increased in tissues in obesity and reported to suppress fatty acid oxidation through inhibition of carnitine palmitoyltransferase 1 (CPT1). In line with our preceding observations that CtBP2 adopts a monomeric configuration upon binding to acyl-CoAs, we determined that mutations in CtBP2 that shift the conformational equilibrium toward monomers increase the interaction between CtBP2 and PPARα. In contrast, metabolic manipulations that reduce malonyl-CoA decreased the formation of the CtBP2/PPARα complex. Consistent with these in vitro findings, we found that the CtBP2/PPARα interaction is accelerated in obese livers while genetic deletion of CtBP2 in the liver causes derepression of PPARα target genes. These findings support our model where CtBP2 exists primarily as a monomer in the metabolic milieu of obesity to repress PPARα, representing a liability in metabolic diseases that can be exploited to develop therapeutic approaches.

Adriamycin downregulates the expression of KLF4 in cardiomyocytes in vitro and contributes to impaired cardiac energy metabolism in Adriamycin-induced cardiomyopathy

Adriamycin is a well-known anthracycline chemotherapeutic agent widely used in treating a variety of malignancies. However, Adriamycin's clinical use is limited due to its adverse side-effects, most importantly cardiomyopathy. Adriamycin-induced cardiotoxicity reportedly includes mitochondrial dysfunction. We hypothesize that modulation of KLF4, a key regulator of cardiac mitochondrial homeostasis might play a role in the development of Adriamycin-induced cardiomyopathy. Therefore, in the current work, we evaluated the interaction of Adriamycin with KLF4 and its subsequent downstream targets. Molecular docking revealed that Adriamycin interacts strongly with KLF4 at residues Thr 448, Arg 452, Ser 444 falls within C2H2 motif which is the active site. Quantitative real-time PCR also revealed that KLF4 is downregulated by Adriamycin in cardiomyocytes in vitro. The expression of KLF4 is downregulated in a dose-dependent manner, with a 0.12 ± 0.09-fold (p ≤ 0.05, n = 3) downregulation at a low dosage and 0.21 ± 0.02-fold (p ≤ 0.05, n = 3) downregulation at high dosage. Deficiency of KLF4 leads to an impairment of PPARγ that consequently supresses the proteins/enzymes involved in the fatty acid metabolism. Adriamycin-mediated suppression of KLF4 also affected the expression of PPARα in vitro. PPARα dysfunction is likely to cause defects in β-oxidation which ultimately results in impaired ATP synthesis. Cardiac cells are thus forced to switch over the substrate from free fatty acid to glucose. Moreover, Adriamycin elevates the expression of PPARβ due to downregulation of KLF4 leads to increased myocardial glucose utilization. Thus, a change in substrate preference affects the flexibility of metabolic network culminating in diminished energy production and other regulatory activities, altogether contributing to the development of cardiomyopathy. Thus, we conclude that the effect of Adriamycin on KLF4 disrupts mitochondrial homeostasis and lipid/glucose homeostasis resulting in a reduction of ATP synthesis which ultimately results in dilated cardiomyopathy.

Role of Stearoyl-CoA Desaturase 1 in Cardiovascular Physiology

Stearoyl-CoA desaturase is a rate-limiting enzyme in the synthesis of monounsaturated fatty acids. Monounsaturated fatty acids limit the toxicity of exogenous saturated fats. Studies have shown that stearoyl-CoA desaturase 1 is involved in the remodeling of cardiac metabolism. The loss of stearoyl-CoA desaturase 1 reduces fatty acid oxidation and increases glucose oxidation in the heart. Such a change is protective under conditions of a high-fat diet, which reduces reactive oxygen species-generating β-oxidation. In contrast, stearoyl-CoA desaturase 1 deficiency predisposes individuals to atherosclerosis under conditions of hyperlipidemia but protects against apnea-induced atherosclerosis. Stearoyl-CoA desaturase 1 deficiency also impairs angiogenesis after myocardial infarction. Clinical data show a positive correlation between blood stearoyl-CoA Δ-9 desaturation rates and cardiovascular disease and mortality. Moreover, stearoyl-CoA desaturase inhibition is considered an attractive intervention in some obesity-associated pathologies, and the importance of stearoyl-CoA desaturase in the cardiovascular system might be a limitation for developing such therapy. This review discusses the role of stearoyl-CoA desaturase 1 in the regulation of cardiovascular homeostasis and the development of heart disease and presents markers of systemic stearoyl-CoA desaturase activity and their predictive potential in the diagnosis of cardiovascular disorders.

Fatty Acid Amide Hydrolase Deficiency Is Associated with Deleterious Cardiac Effects after Myocardial Ischemia and Reperfusion in Mice

Ischemic cardiomyopathy leads to inflammation and left ventricular (LV) dysfunction. Animal studies provided evidence for cardioprotective effects of the endocannabinoid system, including cardiomyocyte adaptation, inflammation, and remodeling. Cannabinoid type-2 receptor (CB2) deficiency led to increased apoptosis and infarctions with worsened LV function in ischemic cardiomyopathy. The aim of our study was to investigate a possible cardioprotective effect of endocannabinoid anandamide (AEA) after ischemia and reperfusion (I/R). Therefore, fatty acid amide hydrolase deficient (FAAH)^−/− mice were subjected to repetitive, daily, 15 min, left anterior descending artery (LAD) occlusion over 3 and 7 consecutive days. Interestingly, FAAH^−/− mice showed stigmata such as enhanced inflammation, cardiomyocyte loss, stronger remodeling, and persistent scar with deteriorated LV function compared to wild-type (WT) littermates. As endocannabinoids also activate PPAR-α (peroxisome proliferator-activated receptor), PPAR-α mediated effects of AEA were eliminated with PPAR-α antagonist GW6471 i.v. in FAAH^−/− mice. LV function was assessed using M-mode echocardiography. Immunohistochemical analysis revealed apoptosis, macrophage accumulation, collagen deposition, and remodeling. Hypertrophy was determined by cardiomyocyte area and heart weight/tibia length. Molecular analyses involved Taqman^® RT-qPCR and immune cells were analyzed with fluorescence-activated cell sorting (FACS). Most importantly, collagen deposition was reduced to WT levels when FAAH^−/− mice were treated with GW6471. Chemokine ligand-2 (CCL2) expression was significantly higher in FAAH^−/− mice compared to WT, followed by higher macrophage infiltration in infarcted areas, both being reversed by GW6471 treatment. Besides restoring antioxidative properties and contractile elements, PPAR-α antagonism also reversed hypertrophy and remodeling in FAAH^−/− mice. Finally, FAAH^−/−-mice showed more substantial downregulation of PPAR-α compared to WT, suggesting a compensatory mechanism as endocannabinoids are also ligands for PPAR-α, and its activation causes lipotoxicity leading to cardiomyocyte apoptosis. Our study gives novel insights into the role of endocannabinoids acting via PPAR-α. We hypothesize that the increase in endocannabinoids may have partially detrimental effects on cardiomyocyte survival due to PPAR-α activation.

A Hypothesis Concerning the role of PPAR family on Cardiac Energetics in Adriamycin-Induced Cardiomyopathy

Adriamycin is an effective anti-neoplastic drug against a variety of cancer types. However, the drug causes adverse side-effects in a number of organ systems. Cardiomyopathy is one of the life-threatening side-effects of Adriamycin. In the current work, we have derived the possible involvement of PPAR family members in the development of Adriamycin-induced cardiomyopathy. Dysregulation of PPAR family by Adriamycin causes impairment in the transport and β-oxidation of fatty acids, the key substrate for ATP synthesis in heart. Evidences suggest that dysregulation of PPAR family results in alters the recruitment of glucose transporters. Furthermore, Hemeoxygenase-1 is a crucial enzyme regulating the iron homeostasis in the heart whose expression is regulated by PPAR family. Inverse relationship exists between the expression levels of PPARγ and hemeoxygenase-1. Adriamycin upregulates the expression of hemeoxygenase-1 which in turn disrupts the iron homeostasis in cardiomyocytes. Our molecular docking results show that Adriamycin has high affinity for iron binding sites of hemeoxygenase-1, thereby hindering formation of iron-sulfur complex. Lack of iron-sulfur complex impairs the electron transport chain. In addition, succinate dehydrogenase subunit A is downregulated by Adriamycin. The lack of this subunit uncouples Krebs cycle from ETC. Further lack of this subunit causes increases the concentration of succinate which further alters the mitochondrial membrane potential. Overall, in the present work we hypothesize that alteration in the expression of PPAR family members is one of the major causes of metabolic chaos and oxidative stress caused by Adriamycin during the development of cardiomyopathy.

Plin5, a New Target in Diabetic Cardiomyopathy

Abnormal lipid accumulation is commonly observed in diabetic cardiomyopathy (DC), which can create a lipotoxic microenvironment and damage cardiomyocytes. Lipid toxicity is an important pathogenic factor due to abnormal lipid accumulation in DC. As a lipid droplet (LD) decomposition barrier, Plin5 can protect LDs from lipase decomposition and regulate lipid metabolism, which is involved in the occurrence and development of cardiovascular diseases. In recent years, studies have shown that Plin5 expression is involved in the pathogenesis of DC lipid toxicity, such as oxidative stress, mitochondrial dysfunction, endoplasmic reticulum (ER) stress, and insulin resistance (IR) and has become a key target of DC research. Therefore, understanding the relationship between Plin5 and DC progression as well as the mechanism of this process is crucial for developing new therapeutic approaches and exploring new therapeutic targets. This review is aimed at exploring the latest findings and roles of Plin5 in lipid metabolism and DC-related pathogenesis, to explore possible clinical intervention approaches.

Exploring the Pattern of Metabolic Alterations Causing Energy Imbalance via PPARα Dysregulation in Cardiac Muscle During Doxorubicin Treatment

Cardiotoxicity by anthracycline antineoplastic drug doxorubicin is one of the systemic toxicity of the cardiovascular system. The mechanism responsible for doxorubicin cardiotoxicity and lipid metabolism remains elusive. The current study tested the hypotheses that the role of peroxisome proliferator-activated receptor α (PPARα) in the progress of doxorubicin-induced cardiomyopathy and its mechanism behind lipid metabolism. In the present study, male rats were subjected to intraperitoneal injection (5-week period) of doxorubicin with different dosages such as low dosage (1.5 mg/kg body weight) and high dosage (15 mg/kg body weight) to induce doxorubicin cardiomyopathy. Myocardial PPARα was impaired in both low dosage and high dosage of doxorubicin-treated rats in a dose-dependent manner. The attenuated level of PPARα impairs the expression of the genes involved in mitochondrial transporter, fatty acid transportation, lipolysis, lipid metabolism, and fatty acid oxidation. Moreover, it disturbs the reverse triacylglycerol transporter apolipoprotein B-100 (APOB) in the myocardium. Doxorubicin elevates the circulatory lipid profile and glucose. Further aggravated lipid profile in circulation impedes the metabolism of lipid in cardiac tissue, which causes a lipotoxic condition in the heart and subsequently associated disease for the period of doxorubicin treatment. Elevated lipids in the circulation translocate into the heart dysregulates lipid metabolism in the heart, which causes augmented oxidative stress and necro-apoptosis and mediates lipotoxic conditions. This finding determines the mechanistic role of doxorubicin-disturbed lipid metabolism via PPARα, which leads to cardiac dysfunction.

Signaling Pathways Related to Oxidative Stress in Diabetic Cardiomyopathy

Diabetes is a chronic metabolic disease that is increasing in prevalence and causes many complications. Diabetic cardiomyopathy (DCM) is a complication of diabetes that is associated with high mortality, but it is not well defined. Nevertheless, it is generally accepted that DCM refers to a clinical disease that occurs in patients with diabetes and involves ventricular dysfunction, in the absence of other cardiovascular diseases, such as coronary atherosclerotic heart disease, hypertension, or valvular heart disease. However, it is currently uncertain whether the pathogenesis of DCM is directly attributable to metabolic dysfunction or secondary to diabetic microangiopathy. Oxidative stress (OS) is considered to be a key component of its pathogenesis. The production of reactive oxygen species (ROS) in cardiomyocytes is a vicious circle, resulting in further production of ROS, mitochondrial DNA damage, lipid peroxidation, and the post-translational modification of proteins, as well as inflammation, cardiac hypertrophy and fibrosis, ultimately leading to cell death and cardiac dysfunction. ROS have been shown to affect various signaling pathways involved in the development of DCM. For instance, OS causes metabolic disorders by affecting the regulation of PPARα, AMPK/mTOR, and SIRT3/FOXO3a. Furthermore, OS participates in inflammation mediated by the NF-κB pathway, NLRP3 inflammasome, and the TLR4 pathway. OS also promotes TGF-β-, Rho-ROCK-, and Notch-mediated cardiac remodeling, and is involved in the regulation of calcium homeostasis, which impairs ATP production and causes ROS overproduction. In this review, we summarize the signaling pathways that link OS to DCM, with the intention of identifying appropriate targets and new antioxidant therapies for DCM.

PPAR control of metabolism and cardiovascular functions

Peroxisome proliferator-activated receptor-α (PPARα), PPARδ and PPARγ are transcription factors that regulate gene expression following ligand activation. PPARα increases cellular fatty acid uptake, esterification and trafficking, and regulates lipoprotein metabolism genes. PPARδ stimulates lipid and glucose utilization by increasing mitochondrial function and fatty acid desaturation pathways. By contrast, PPARγ promotes fatty acid uptake, triglyceride formation and storage in lipid droplets, thereby increasing insulin sensitivity and glucose metabolism. PPARs also exert antiatherogenic and anti-inflammatory effects on the vascular wall and immune cells. Clinically, PPARγ activation by glitazones and PPARα activation by fibrates reduce insulin resistance and dyslipidaemia, respectively. PPARs are also physiological master switches in the heart, steering cardiac energy metabolism in cardiomyocytes, thereby affecting pathological heart failure and diabetic cardiomyopathy. Novel PPAR agonists in clinical development are providing new opportunities in the management of metabolic and cardiovascular diseases.

Dapagliflozin Mediates Plin5/PPARα Signaling Axis to Attenuate Cardiac Hypertrophy

Objective: The purpose of this study was to investigate the effect of dapagliflozin (DAPA), a sodium-glucose cotransporter 2 inhibitor, on relieving cardiac hypertrophy and its potential molecular mechanism.

Methods: Cardiac hypertrophy induced by abdominal aortic constriction (AAC) in mice, dapagliflozin were administered in the drinking water at a dose of 25 mg/kg/d for 12 weeks was observed. Echocardiography was used to detect the changes of cardiac function, including LVEF, LVFS, LVEDd, LVEDs, HR and LV mass. Histological morphological changes were evaluated by Masson trichrome staining and wheat germ agglutinin (WGA) staining. The enrichment of differential genes and signal pathways after treatment was analyzed by gene microarray cardiomyocyte hypertrophy was induced by AngII (2 μM) and the protective effect of dapagliflozin (1 μM) was observed in vitro. The morphological changes of myocardial cells were detected by cTnI immunofluorescence staining. ELISA and qRT-PCR assays were performed to detect the expressions levels of cardiac hypertrophy related molecules.

Results: After 12 weeks of treatment, DAPA significantly ameliorated cardiac function and inhibited cardiac hypertrophy in AAC-induced mice. In vitro, DAPA significantly inhibited abnormal hypertrophy in AngII-induced cardiacmyocytes. Both in vivo and in vitro experiments have confirmed that DAPA could mediate the Plin5/PPARα signaling axis to play a protective role in inhibiting cardiac hypertrophy.

Conclusion: Dapagliflozin activated the Plin5/PPARα signaling axis and exerts a protective effect against cardiac hypertrophy.

Preoperative plasma biomarkers associated with atrial fibrillation after coronary artery bypass surgery

OBJECTIVES

Postoperative atrial fibrillation (POAF) is a common complication in coronary artery bypass grafting (CABG) procedures. This prospective study aimed to investigate predisposition of proteins and metabolites correlated to POAF after CABG and related cellular pathways.

METHODS

Preoperative plasma samples from patients undergoing CABG procedures were prospectively collected. After CABG, the patients were grouped to POAF or sinus rhythm (N = 170; n = 90 in the discovery set and n = 80 in the validation set). The plasma samples were analyzed using proteomics, metabolomics, and bioinformatics to identify the differential proteins and differential metabolites. The correlation between differential proteins and POAF was also investigated by multivariable regression analysis and receiver operator characteristic analysis.

RESULTS

In the POAF(+) group, 29 differential proteins and 61 differential metabolites were identified compared with the POAF(-) group. The analysis of integrated omics revealed that preoperative alteration of peroxisome proliferators-activated receptor α and glutathione metabolism pathways increased the susceptibility of POAF after CABG. There was a correlation between plasma levels of apolipoprotein-C3, phospholipid transfer protein, glutathione peroxidase 3, cholesteryl ester transfer protein, and POAF.

CONCLUSIONS

The present study for first time at multi-omics levels explored the mechanism of POAF and validated the results in a new cohort of patients, suggesting preexisting differential proteins and differential metabolites in the plasma of patients prone to POAF after CABG. Dysregulation of peroxisome proliferators-activated receptor α and glutathione metabolism pathways related to metabolic remodeling and redox imbalance-associated electrical remodeling may play a key role in the pathogenesis of POAF. Lower plasma phospholipid transfer protein, apolipoprotein-C3, higher cholesteryl ester transfer protein and glutathione peroxidase 3 levels are linked with POAF. These proteins/metabolites may be developed as biomarkers to predict POAF.

Untangling the Cooperative Role of Nuclear Receptors in Cardiovascular Physiology and Disease

The heart is the first organ to acquire its physiological function during development, enabling it to supply the organism with oxygen and nutrients. Given this early commitment, cardiomyocytes were traditionally considered transcriptionally stable cells fully committed to contractile function. However, growing evidence suggests that the maintenance of cardiac function in health and disease depends on transcriptional and epigenetic regulation. Several studies have revealed that the complex transcriptional alterations underlying cardiovascular disease (CVD) manifestations such as myocardial infarction and hypertrophy is mediated by cardiac retinoid X receptors (RXR) and their partners. RXRs are members of the nuclear receptor (NR) superfamily of ligand-activated transcription factors and drive essential biological processes such as ion handling, mitochondrial biogenesis, and glucose and lipid metabolism. RXRs are thus attractive molecular targets for the development of effective pharmacological strategies for CVD treatment and prevention. In this review, we summarize current knowledge of RXR partnership biology in cardiac homeostasis and disease, providing an up-to-date view of the molecular mechanisms and cellular pathways that sustain cardiomyocyte physiology.

The Glitazars Paradox: Cardiotoxicity of the Metabolically Beneficial Dual PPARα and PPARγ Activation

The most common complications in patients with type-2 diabetes are hyperglycemia and hyperlipidemia that can lead to cardiovascular disease. Alleviation of these complications constitutes the major therapeutic approach for the treatment of diabetes mellitus. Agonists of peroxisome proliferator-activated receptor (PPAR) alpha and PPARγ are used for the treatment of hyperlipidemia and hyperglycemia, respectively. PPARs belong to the nuclear receptors superfamily and regulate fatty acid metabolism. PPARα ligands, such as fibrates, reduce circulating triglyceride levels, and PPARγ agonists, such as thiazolidinediones, improve insulin sensitivity. Dual-PPARα/γ agonists (glitazars) were developed to combine the beneficial effects of PPARα and PPARγ agonism. Although they improved metabolic parameters, they paradoxically aggravated congestive heart failure in patients with type-2 diabetes via mechanisms that remain elusive. Many of the glitazars, such as muraglitazar, tesaglitazar, and aleglitazar, were abandoned in phase-III clinical trials. The objective of this review article pertains to the understanding of how combined PPARα and PPARγ activation, which successfully targets the major complications of diabetes, causes cardiac dysfunction. Furthermore, it aims to suggest interventions that will maintain the beneficial effects of dual PPARα/γ agonism and alleviate adverse cardiac outcomes in diabetes.

Loss of Acot12 contributes to NAFLD independent of lipolysis of adipose tissue

In this study, we hypothesized that deregulation in the maintenance of the pool of coenzyme A (CoA) may play a crucial role in the pathogenesis of nonalcoholic fatty liver disease (NAFLD). Specific deletion of Acot12 (Acot12-/-), the major acyl-CoA thioesterase, induced the accumulation of acetyl-CoA and resulted in the stimulation of de novo lipogenesis (DNL) and cholesterol biosynthesis in the liver. KEGG pathway analysis suggested PPARα signaling as the most significantly enriched pathway in Acot12-/- livers. Surprisingly, the exposure of Acot12-/- hepatocytes to fenofibrate significantly increased the accumulation of acetyl-CoA and resulted in the stimulation of cholesterol biosynthesis and DNL. Interaction analysis, including proximity-dependent biotin identification (BioID) analysis, suggested that ACOT12 may directly interact with vacuolar protein sorting-associated protein 33A (VPS33A) and play a role in vesicle-mediated cholesterol trafficking and the process of lysosomal degradation of cholesterol in hepatocytes. In summary, in this study, we found that ACOT12 deficiency is responsible for the pathogenesis of NAFLD through the accumulation of acetyl-CoA and the stimulation of DNL and cholesterol via activation of PPARα and inhibition of cholesterol trafficking.

Therapeutic Manipulation of Myocardial Metabolism: JACC State-of-the-Art Review

The mechanisms responsible for the positive and unexpected cardiovascular effects of sodium-glucose cotransporter-2 inhibitors and glucagon-like peptide-1 receptor agonists in patients with type 2 diabetes remain to be defined. It is likely that some of the beneficial cardiac effects of these antidiabetic drugs are mediated, in part, by altered myocardial metabolism. Common cardiometabolic disorders, including the metabolic (insulin resistance) syndrome and type 2 diabetes, are associated with altered substrate utilization and energy transduction by the myocardium, predisposing to the development of heart disease. Thus, the failing heart is characterized by a substrate shift toward glycolysis and ketone oxidation in an attempt to meet the high energetic demand of the constantly contracting heart. This review examines the metabolic pathways and clinical implications of myocardial substrate utilization in the normal heart and in cardiometabolic disorders, and discusses mechanisms by which antidiabetic drugs and metabolic interventions improve cardiac function in the failing heart.

Transcriptional Regulation of Postnatal Cardiomyocyte Maturation and Regeneration

During the postnatal period, mammalian cardiomyocytes undergo numerous maturational changes associated with increased cardiac function and output, including hypertrophic growth, cell cycle exit, sarcomeric protein isoform switching, and mitochondrial maturation. These changes come at the expense of loss of regenerative capacity of the heart, contributing to heart failure after cardiac injury in adults. While most studies focus on the transcriptional regulation of embryonic or adult cardiomyocytes, the transcriptional changes that occur during the postnatal period are relatively unknown. In this review, we focus on the transcriptional regulators responsible for these aspects of cardiomyocyte maturation during the postnatal period in mammals. By specifically highlighting this transitional period, we draw attention to critical processes in cardiomyocyte maturation with potential therapeutic implications in cardiovascular disease.

Role of Warburg Effect in Cardiovascular Diseases: A Potential Treatment Option

Background:

Under normal conditions, the heart obtains ATP through the oxidation of fatty acids, glucose, and ketones. While fatty acids are the main source of energy in the heart, under certain conditions, the main source of energy shifts to glucose where pyruvate converts into lactate, to meet the energy demand. The Warburg effect is the energy shift from oxidative phosphorylation to glycolysis in the presence of oxygen. This effect is observed in tumors as well as in diseases, including cardiovascular diseases. If glycolysis is more dominant than glucose oxidation, the two pathways uncouple, contributing to the severity of the heart condition. Recently, several studies have documented changes in metabolism in several cardiovascular diseases; however, the specific mechanisms remain unclear.

Methods:

This literature review was conducted by an electronic database of Pub Med, Google Scholar, and Scopus published until 2020. Relevant papers are selected based on inclusion and exclusion criteria.

Results:

A total of 162 potentially relevant articles after the title and abstract screening were screened for full-text. Finally, 135 papers were included for the review article.

Discussion:

This review discusses the effects of alterations in glucose metabolism, particularly the Warburg effect, on cardiovascular diseases, including heart failure, atrial fibrillation, and cardiac hypertrophy.

Conclusion:

Reversing the Warburg effect could become a potential treatment option for cardiovascular diseases.

Yulink, predicted from evolutionary analysis, is involved in cardiac function

Background

The comparative evolutionary genomics analysis was used to study the functions of novel Ka/Ks-predicted human exons in a zebrafish model. The Yulink (MIOS, Entrez Gene: 54,468), a conserved gene from zebrafish to human with WD40 repeats at N-terminus, was identified and found to encode an 875 amino acid in human. The biological function of this Yulink gene in cardiomyocytes remains unexplored. The purpose of this study is to determine the involvement of Yulink in the functions of cardiomyocytes and to investigate its molecular regulatory mechanism.

Methods

Knockdown of Yulink was performed using morpholino or shRNA in zebrafish, mouse HL-1 cardiomyocytes, and human iPSC-derived cardiomyocytes. The expression levels of mRNA and protein were quantified by qPCR and western blots. Other methods including DNA binding, ligand uptake, agonists treatment and Ca²⁺ imaging assays were used to study the molecular regulatory mechanism by Yulink. Statistical data were shown as mean ± SD or mean ± standard error.

Results

The knockdown of yulink with three specific morpholinos in zebrafish resulted in cardiac dysfunctions with pericardial edema, decreased heart beats and cardiac output. The Yulink knockdown in mouse HL-1 cardiomyocytes disrupted Ca²⁺ cycling, reduced DNA binding activity of PPARγ (peroxisome proliferator-activated receptor gamma) and resulted in a reduction of Serca2 (sarcoplasmic reticulum Ca²⁺ ATPase 2) expression. Expression of Serca2 was up-regulated by PPARγ agonists and down-regulated by PPARγ-shRNA knockdown, suggesting that Yulink regulates SERCA2 expression through PPARγ in mouse HL-1 cardiomyocytes. On the other hand, YULINK, PPARγ or SERCA2 over-expression rescued the phenotypes of Yulink KD cells. In addition, knockdown of YULINK in human iPSC-derived cardiomyocytes also disrupted Ca²⁺ cycling via decreased SERCA2 expression.

Conclusions

Overall, our data showed that Yulink is an evolutionarily conserved gene from zebrafish to human. Mechanistically Yulink regulated Serca2 expression in cardiomyocytes, presumably mediated through PPARγ nuclear entry. Deficiency of Yulink in mouse and human cardiomyocytes resulted in irregular Ca²⁺ cycling, which may contribute to arrhythmogenesis.

Impact of peroxisome proliferator-activated receptor-α on diabetic cardiomyopathy

The prevalence of cardiomyopathy is higher in diabetic patients than those without diabetes. Diabetic cardiomyopathy (DCM) is defined as a clinical condition of abnormal myocardial structure and performance in diabetic patients without other cardiac risk factors, such as coronary artery disease, hypertension, and significant valvular disease. Multiple molecular events contribute to the development of DCM, which include the alterations in energy metabolism (fatty acid, glucose, ketone and branched chain amino acids) and the abnormalities of subcellular components in the heart, such as impaired insulin signaling, increased oxidative stress, calcium mishandling and inflammation. There are no specific drugs in treating DCM despite of decades of basic and clinical investigations. This is, in part, due to the lack of our understanding as to how heart failure initiates and develops, especially in diabetic patients without an underlying ischemic cause. Some of the traditional anti-diabetic or lipid-lowering agents aimed at shifting the balance of cardiac metabolism from utilizing fat to glucose have been shown inadequately targeting multiple aspects of the conditions. Peroxisome proliferator-activated receptor α (PPARα), a transcription factor, plays an important role in mediating DCM-related molecular events. Pharmacological targeting of PPARα activation has been demonstrated to be one of the important strategies for patients with diabetes, metabolic syndrome, and atherosclerotic cardiovascular diseases. The aim of this review is to provide a contemporary view of PPARα in association with the underlying pathophysiological changes in DCM. We discuss the PPARα-related drugs in clinical applications and facts related to the drugs that may be considered as risky (such as fenofibrate, bezafibrate, clofibrate) or safe (pemafibrate, metformin and glucagon-like peptide 1-receptor agonists) or having the potential (sodium-glucose co-transporter 2 inhibitor) in treating DCM.

Mitochondria and Calcium Homeostasis: Cisd2 as a Big Player in Cardiac Ageing

The ageing of human populations has become a problem throughout the world. In this context, increasing the healthy lifespan of individuals has become an important target for medical research and governments. Cardiac disease remains the leading cause of morbidity and mortality in ageing populations and results in significant increases in healthcare costs. Although clinical and basic research have revealed many novel insights into the pathways that drive heart failure, the molecular mechanisms underlying cardiac ageing and age-related cardiac dysfunction are still not fully understood. In this review we summarize the most updated publications and discuss the central components that drive cardiac ageing. The following characters of mitochondria-related dysfunction have been identified during cardiac ageing: (a) disruption of the integrity of mitochondria-associated membrane (MAM) contact sites; (b) dysregulation of energy metabolism and dynamic flexibility; (c) dyshomeostasis of Ca²⁺ control; (d) disturbance to mitochondria–lysosomal crosstalk. Furthermore, Cisd2, a pro-longevity gene, is known to be mainly located in the endoplasmic reticulum (ER), mitochondria, and MAM. The expression level of Cisd2 decreases during cardiac ageing. Remarkably, a high level of Cisd2 delays cardiac ageing and ameliorates age-related cardiac dysfunction; this occurs by maintaining correct regulation of energy metabolism and allowing dynamic control of metabolic flexibility. Together, our previous studies and new evidence provided here highlight Cisd2 as a novel target for developing therapies to promote healthy ageing

Fetal cardiomyocyte phenotype, ketone body metabolism, and mitochondrial dysfunction in the pathology of atrial fibrillation

Atrial fibrillation (AF) is the most common cardiac arrhythmia diagnosed in clinical practice. Even though hypertension, congestive heart failure, pulmonary disease, and coronary artery disease are the potential risk factors for AF, the underlying molecular pathology is largely unknown. The reversion of the mature cardiomyocytes to fetal phenotype, impaired ketone body metabolism, mitochondrial dysfunction, and the cellular effect of reactive oxygen species (ROS) are the major underlying biochemical events associated with the molecular pathology of AF. On this background, the present manuscript sheds light into these biochemical events in regard to the metabolic derangements in cardiomyocyte leading to AF, especially with respect to structural, contractile, and electrophysiological properties. In addition, the article critically reviews the current understanding, potential demerits, and translational strategies in the management of AF.

Alcohol and Liver Clock Disruption Increase Small Droplet Macrosteatosis, Alter Lipid Metabolism and Clock Gene mRNA Rhythms, and Remodel the Triglyceride Lipidome in Mouse Liver

Heavy alcohol drinking dysregulates lipid metabolism, promoting hepatic steatosis – the first stage of alcohol-related liver disease (ALD). The molecular circadian clock plays a major role in synchronizing daily rhythms in behavior and metabolism and clock disruption can cause pathology, including liver disease. Previous studies indicate that alcohol consumption alters liver clock function, but the impact alcohol or clock disruption, or both have on the temporal control of hepatic lipid metabolism and injury remains unclear. Here, we undertook studies to determine whether genetic disruption of the liver clock exacerbates alterations in lipid metabolism and worsens steatosis in alcohol-fed mice. To address this question, male liver-specific Bmal1 knockout (LKO) and flox/flox (Fl/Fl) control mice were fed a control or alcohol-containing diet for 5 weeks. Alcohol significantly dampened diurnal rhythms of mRNA levels in clock genes Bmal1 and Dbp, phase advanced Nr1d1/REV-ERBα, and induced arrhythmicity in Clock, Noct, and Nfil3/E4BP4, with further disruption in livers of LKO mice. Alcohol-fed LKO mice exhibited higher plasma triglyceride (TG) and different time-of-day patterns of hepatic TG and macrosteatosis, with elevated levels of small droplet macrosteatosis compared to alcohol-fed Fl/Fl mice. Diurnal rhythms in mRNA levels of lipid metabolism transcription factors (Srebf1, Nr1h2, and Ppara) were significantly altered by alcohol and clock disruption. Alcohol and/or clock disruption significantly altered diurnal rhythms in mRNA levels of fatty acid (FA) synthesis and oxidation (Acaca/b, Mlycd, Cpt1a, Fasn, Elovl5/6, and Fads1/2), TG turnover (Gpat1, Agpat1/2, Lpin1/2, Dgat2, and Pnpla2/3), and lipid droplet (Plin2/5, Lipe, Mgll, and Abdh5) genes, along with protein abundances of p-ACC, MCD, and FASN. Lipidomics analyses showed that alcohol, clock disruption, or both significantly altered FA saturation and remodeled the FA composition of the hepatic TG pool, with higher percentages of several long and very long chain FA in livers of alcohol-fed LKO mice. In conclusion, these results show that the liver clock is important for maintaining temporal control of hepatic lipid metabolism and that disrupting the liver clock exacerbates alcohol-related hepatic steatosis.

Silencing of peroxisome proliferator-activated receptor-alpha alleviates myocardial injury in diabetic cardiomyopathy by downregulating 3-hydroxy-3-methylglutaryl-coenzyme A synthase 2 expression

Diabetic cardiomyopathy (DCM) is a cardiac disorder, which affects around 12% diabetic patients, resulting in overt heart death. Our initial bioinformatic analysis identified the differentially expressed gene 3-hydroxy-3-methylglutaryl-coenzyme A synthase 2 (HMGCS2) in DCM, which may be activated by peroxisome proliferator-activated receptor-alpha (PPARα) based on previous evidence. Therefore, the present study aims to explore the effect of PPARα on the development of DCM through regulating HMGCS2. The expression of PPARα and HMGCS2 was detected by reverse transcription quantitative polymerase chain reaction in cardiomyocytes and high-glucose-cultured cardiomyocytes. The proliferation and apoptosis of cardiomyocytes were examined by 5-ethynyl-2'-deoxyuridine assay and flow cytometry, separately. Mitoehondrial membrane potential (MMP) and intracellular reactive oxygen species (ROS) levels were determined. Then, the protein levels of B-cell lymphoma 2, Bcl-2-associated X protein, and cleaved Caspase-3 were detected by Western blot analysis. The myocardial apoptosis index, heart weight, and serum lipids of rats were examined. At last, the expressions of atrial natriuretic peptide (ANP), brain natriuretic peptide (BNP), transforming growth factor β1 (TGFβ1), peroxisome proliferator activator receptor gamma coactivator-1 alpha (PGC1α), nuclear respiratory factor (NRF)-1, NRF-2, NAD(P)H oxidase 1, and superoxide dismutase-1 were examined. HMGCS2 was the most differentially expressed gene in DCM. The levels of HMGCS2 and PPARα were upregulated in patients with DCM. HMGCS2 silencing was shown to inhibit HMGCS2 expression to suppress the apoptosis of high-glucose-induced cardiomyocytes and the loss of MMP, reduce the accumulation of ROS, and promote cardiomyocyte proliferation. Silencing of HMGCS2 and PPARα alleviated myocardial injury, decreased blood glucose, and lipid in DCM rats, downregulated the expression of ANP, BNP, and TGFβ1 to reduce myocardial injury, and elevated PGC1α, NRF-1, and NRF-2 levels to enhance oxidative stress levels. Our results demonstrated that silencing of PPARα could alleviate cardiomyocyte injury and oxidative stress via a mechanism related to the downregulation of HMGCS2, which could provide a novel target for DCM treatment.

Downregulation of PPARα during Experimental Left Ventricular Hypertrophy Is Critically Dependent on Nox2 NADPH Oxidase Signalling

Pressure overload-induced left ventricular hypertrophy (LVH) is initially adaptive but ultimately promotes systolic dysfunction and chronic heart failure. Whilst underlying pathways are incompletely understood, increased reactive oxygen species generation from Nox2 NADPH oxidases, and metabolic remodelling, largely driven by PPARα downregulation, are separately implicated. Here, we investigated interaction between the two as a key regulator of LVH using in vitro, in vivo and transcriptomic approaches. Phenylephrine-induced H9c2 cardiomyoblast hypertrophy was associated with reduced PPARα expression and increased Nox2 expression and activity. Pressure overload-induced LVH and systolic dysfunction induced in wild-type mice by transverse aortic constriction (TAC) for 7 days, in association with Nox2 upregulation and PPARα downregulation, was enhanced in PPARα-/- mice and prevented in Nox2-/- mice. Detailed transcriptomic analysis revealed significantly altered expression of genes relating to PPARα, oxidative stress and hypertrophy pathways in wild-type hearts, which were unaltered in Nox2-/- hearts, whilst oxidative stress pathways remained dysregulated in PPARα-/- hearts following TAC. Network analysis indicated that Nox2 was essential for PPARα downregulation in this setting and identified preferential inflammatory pathway modulation and candidate cytokines as upstream Nox2-sensitive regulators of PPARα signalling. Together, these data suggest that Nox2 is a critical driver of PPARα downregulation leading to maladaptive LVH.

Metabolism, Epigenetics, and Causal Inference in Heart Failure

Eukaryotes must balance the metabolic and cell death actions of mitochondria via control of gene expression and cell fate by chromatin, thereby functionally binding the metabolome and epigenome. This interaction has far-reaching implications for chronic diseases in humans, the most common of which are those of the cardiovascular system. The most devastating consequence of cardiovascular disease, heart failure, is not a single disease, diagnosis, or endpoint. Human and animal studies have revealed that, regardless of etiology and symptoms, heart failure is universally associated with abnormal metabolism and gene expression - to frame this as cause or consequence, however, may be to wrongfoot the question. This essay aims to challenge current thinking on metabolic-epigenetic crosstalk in heart failure, presenting hypotheses for how chronic diseases arise, take hold, and persist. We unpack assumptions about the order of operations for gene expression and metabolism, exploring recent findings in noncardiac systems that link metabolic intermediates directly to chromatin remodeling. Lastly, we discuss potential mechanisms by which chromatin may serve as a substrate for metabolic memory, and how changes in cellular transcriptomes (and hence in cellular behavior) in response to stress correspond to global changes in chromatin accessibility and structure.

Positioning Metabolism as a Central Player in the Diabetic Heart

In type 2 diabetes (T2D), the leading cause of death is cardiovascular complications. One mechanism contributing to cardiac pathogenesis is alterations in metabolism, with the diabetic heart exhibiting increased fatty acid oxidation and reduced glucose utilisation. The processes classically thought to underlie this metabolic shift include the Randle cycle and changes to gene expression. More recently, alternative mechanisms have been proposed, most notably, changes in post-translational modification of mitochondrial proteins in the heart. This increased understanding of how metabolism is altered in the diabetic heart has highlighted new therapeutic targets, with an aim to improve cardiac function in T2D. This review focuses on metabolism in the healthy heart and how this is modified in T2D, providing evidence for the mechanisms underlying this shift. There will be emphasis on the current treatments for the heart in diabetes, alongside efforts for metabocentric pharmacological therapies.

Allosteric, transcriptional and post-translational control of mitochondrial energy metabolism

The heart is the organ with highest energy turnover rate (per unit weight) in our body. The heart relies on its flexible and powerful catabolic capacity to continuously generate large amounts of ATP utilizing many energy substrates including fatty acids, carbohydrates (glucose and lactate), ketones and amino acids. The normal health mainly utilizes fatty acids (40-60%) and glucose (20-40%) for ATP production while ketones and amino acids have a minor contribution (10-15% and 1-2%, respectively). Mitochondrial oxidative phosphorylation is the major contributor to cardiac energy production (95%) while cytosolic glycolysis has a marginal contribution (5%). The heart can dramatically and swiftly switch between energy-producing pathways and/or alter the share from each of the energy substrates based on cardiac workload, availability of each energy substrate and neuronal and hormonal activity. The heart is equipped with a highly sophisticated and powerful mitochondrial machinery which synchronizes cardiac energy production from different substrates and orchestrates the rate of ATP production to accommodate its contractility demands. This review discusses mitochondrial cardiac energy metabolism and how it is regulated. This includes a discussion on the allosteric control of cardiac energy metabolism by short-chain coenzyme A esters, including malonyl CoA and its effect on cardiac metabolic preference. We also discuss the transcriptional level of energy regulation and its role in the maturation of cardiac metabolism after birth and cardiac adaptability for different metabolic conditions and energy demands. The role post-translational modifications, namely phosphorylation, acetylation, malonylation, succinylation and glutarylation, play in regulating mitochondrial energy metabolism is also discussed.

Nanotized PPARα Overexpression Targeted to Hypertrophied Myocardium Improves Cardiac Function by Attenuating the p53-GSK3β-Mediated Mitochondrial Death Pathway

AIMS

Metabolic remodeling of cardiac muscles during pathological hypertrophy is characterized by downregulation of fatty acid oxidation (FAO) regulator, peroxisome proliferator-activated receptor alpha (PPARα). Thereby, we hypothesized that a cardiac-specific induction of PPARα might restore the FAO-related protein expression and resultant energy deficit. In the present study, consequences of PPARα augmentation were evaluated for amelioration of chronic oxidative stress, myocyte apoptosis, and cardiac function during pathological cardiac hypertrophy.

RESULTS

Nanotized PPARα overexpression targeted to myocardium was done by a stearic acid-modified carboxymethyl-chitosan (CMC) conjugated to a 20-mer myocyte-targeted peptide (CMCP). Overexpression of PPARα ameliorated pathological hypertrophy and improved cardiac function. Augmented PPARα in hypertrophied myocytes revealed downregulated p53 acetylation (lys 382), leading to reduced apoptosis. Such cells showed increased binding of PPARα with p53 that in turn reduced interaction of p53 with glycogen synthase kinase-3β (GSK3β), which upregulated inactive phospho-GSK3β (serine [Ser]9) expression within mitochondrial protein fraction. Altogether, the altered molecular milieu in PPARα-overexpressed hypertrophy groups restored mitochondrial structure and function both in vitro and in vivo.

INNOVATION

Cardiomyocyte-targeted overexpression of a protein of interest (PPARα) by nanotized plasmid has been described for the first time in this study. Our data provide a novel insight towards regression of pathological hypertrophy by ameliorating mitochondrial oxidative stress in targeted PPARα-overexpressed myocardium.

CONCLUSION

PPARα-overexpression during pathological hypertrophy showed substantial betterment of mitochondrial structure and function, along with downregulated apoptosis. Myocardium-targeted overexpression of PPARα during pathological cardiac hypertrophy led to an overall improvement of cardiac energy deficit and subsequent cardiac function, thereby, opening up a potential avenue for cardiac tissue engineering during hypertrophic cardiac pathophysiology.

MiR-30c/PGC-1β protects against diabetic cardiomyopathy via PPARα

BACKGROUND

Metabolic abnormalities have been implicated as a causal event in diabetic cardiomyopathy (DCM). However, the mechanisms underlying cardiac metabolic disorder in DCM were not fully understood.

RESULTS

Db/db mice, palmitate treated H9c2 cells and primary neonatal rat cardiomyocytes were employed in the current study. Microarray data analysis revealed that PGC-1β may play an important role in DCM. Downregulation of PGC-1β relieved palmitate induced cardiac metabolism shift to fatty acids use and relevant lipotoxicity in vitro. Bioinformatics coupled with biochemical validation was used to confirm that PGC-1β was one of the direct targets of miR-30c. Remarkably, overexpression of miR-30c by rAAV system improved glucose utilization, reduced excessive reactive oxygen species production and myocardial lipid accumulation, and subsequently attenuated cardiomyocyte apoptosis and cardiac dysfunction in db/db mice. Similar effects were also observed in cultured cells. More importantly, miR-30c overexpression as well as PGC-1β knockdown reduced the transcriptional activity of PPARα, and the effects of miR-30c on PPARα was almost abated by PGC-1β knockdown.

CONCLUSIONS

Our data demonstrated a protective role of miR-30c in cardiac metabolism in diabetes via targeting PGC-1β, and suggested that modulation of PGC-1β by miR-30c may provide a therapeutic approach for DCM.

GCN2 deficiency ameliorates cardiac dysfunction in diabetic mice by reducing lipotoxicity and oxidative stress

Excessive myocardial lipid accumulation is a major feature of diabetic cardiomyopathy (DCM). Although general control nonderepressible 2 (GCN2) has been identified as a sensor of amino acid availability, it also functions as an important regulator of hepatic lipid metabolism. Our previous studies have reported that GCN2 promotes pressure overload or doxorubicin-induced cardiac dysfunction by increasing cardiomyocyte apoptosis and myocardial oxidative stress. However, the impact of GCN2 on the development of DCM remains unclear. In this study, we investigated the effect of GCN2 on DCM in type 1 and type 2 diabetes animal models. After streptozotocin (STZ) or high-fat diet (HFD) plus low-dose STZ treatments, GCN2^-/- mice developed less cardiac dysfunction, hyperlipidemia, myocardial hypertrophy, fibrosis, lipid accumulation, oxidative stress, inflammation and apoptosis compared with wild-type (WT) mice. In diabetic hearts, GCN2 deficiency attenuated the upregulation of peroxisome proliferator-activated receptor alpha (PPARα) and gamma (PPARγ), the phosphorylation of eIF2α and the induction of activating transcription factor 4 (ATF4) and C/EBP homologous protein (CHOP), as well as the reduction of Bcl-2. Furthermore, we found that knockdown of GCN2 attenuated, whereas overexpression of GCN2 exacerbated, high glucose or palmitic acid-induced cell death, oxidative and endoplasmic reticulum stress and lipid accumulation in H9C2 cells. Collectively, our data provide evidence that GCN2 deficiency protects cardiac function by reducing lipid accumulation, oxidative stress and cell death. Our findings suggest that strategies to inhibit GCN2 activity in the heart may be novel approaches for DCM therapy.

Elucidating the Beneficial Role of PPAR Agonists in Cardiac Diseases

Peroxisome proliferator-activated receptors (PPARs) are nuclear hormone receptors that bind to DNA and regulate transcription of genes involved in lipid and glucose metabolism. A growing number of studies provide strong evidence that PPARs are the promising pharmacological targets for therapeutic intervention in various diseases including cardiovascular disorders caused by compromised energy metabolism. PPAR agonists have been widely used for decades as lipid-lowering and anti-inflammatory drugs. Existing studies are mainly focused on the anti-atherosclerotic effects of PPAR agonists; however, their role in the maintenance of cellular bioenergetics remains unclear. Recent studies on animal models and patients suggest that PPAR agonists can normalize lipid metabolism by stimulating fatty acid oxidation. These studies indicate the importance of elucidation of PPAR agonists as potential pharmacological agents for protection of the heart from energy deprivation. Here, we summarize and provide a comprehensive analysis of previous studies on the role of PPARs in the heart under normal and pathological conditions. In addition, the review discusses the PPARs as a therapeutic target and the beneficial effects of PPAR agonists, particularly bezafibrate, to attenuate cardiomyopathy and heart failure in patients and animal models.

Impaired Energy Production Contributes to Development of Failure in Taurine Deficient Heart

Taurine forms a conjugate in the mitochondria with a uridine residue in the wobble position of tRNALeu(UUR). The resulting product, 5-taurinomethyluridine tRNALeu(UUR), increases the interaction between the UUG codon and AAU anticodon of tRNALeu(UUR), thereby improving the decoding of the UUG codon. We have shown that the protein most affected by the taurine conjugation product is ND6, which is a subunit of complex I of the respiratory chain. Thus, taurine deficiency exhibits reduced respiratory chain function. Based on these findings, we proposed that the taurine deficient heart is energy deficient. To test this idea, hearts were perfused with buffer containing acetate and glucose as substrates. The utilization of both substrates, as well as the utilization of endogenous lipids, was significantly reduced in the taurine deficient heart. This led to a 25% decrease in ATP production, an effect primarily caused by diminished aerobic metabolism and respiratory function. In addition, inefficient oxidative phosphorylation causes a further decrease in ATP generation. The data support the idea that reductions in energy metabolism, including oxidative phosphorylation, ATP generation and high energy phosphate content, contribute to the severity of the cardiomyopathy. The findings are also consistent with the hypothesis that taurine deficiency and reduced myocardial energy content increases mortality of the taurine deficient, failing heart. The clinical implications of these findings are addressed.

Role for Taurine in Development of Oxidative Metabolism After Birth

The heart undergoes a major metabolic transition after birth, a change largely caused by alterations in substrate availability, hormone levels and transcription factor content. However, another factor that could contribute to the resulting upregulation of oxidative metabolism is the increase in taurine levels. We proposed that by increasing UUG decoding and the biosynthesis of mitochondria encoded proteins, elevations in taurine content enhance electron transport flux and increase oxidative metabolism. To test our hypothesis, the effect of reduced taurine content on oxidative metabolism of myocardial mitochondria and neonatal cardiomyocytes was examined. Taurine deficient neonatal mitochondria exhibited impaired oxidation of complex I specific- but not complex II specific-substrates, indicating that taurine deficiency regulates complex I activity. Taurine deficiency also reduced respiration of neonatal cardiomyocytes oxidizing carbohydrate (glucose, lactate and pyruvate). However, cardiomyocytes from 2-3 day-old hearts respiring either β-hydroxybutyrate, an important substrate in the neonatal heart, or palmitate, which is poorly metabolized during the early neonatal period, were resistant to the metabolic defects of taurine deficiency, These data support the hypothesis that taurine contributes to development of respiratory chain function after birth, which is required for oxidative metabolism of multiple substrates.

Glucagon-like peptide-1 ameliorates cardiac lipotoxicity in diabetic cardiomyopathy via the PPARα pathway

Lipotoxicity cardiomyopathy is the result of excessive accumulation and oxidation of toxic lipids in the heart. It is a major threat to patients with diabetes. Glucagon-like peptide-1 (GLP-1) has aroused considerable interest as a novel therapeutic target for diabetes mellitus because it stimulates insulin secretion. Here, we investigated the effects and mechanisms of the GLP-1 analog exendin-4 and the dipeptidyl peptidase-4 inhibitor saxagliptin on cardiac lipid metabolism in diabetic mice (DM). The increased myocardial lipid accumulation, oxidative stress, apoptosis, and cardiac remodeling and dysfunction induced in DM by low streptozotocin doses and high-fat diets were significantly reversed by exendin-4 and saxagliptin treatments for 8 weeks. We found that exendin-4 inhibited abnormal activation of the (PPARα)-CD36 pathway by stimulating protein kinase A (PKA) but suppressing the Rho-associated protein kinase (ROCK) pathway in DM hearts, palmitic acid (PA)-treated rat h9c2 cardiomyocytes (CMs), and isolated adult mouse CMs. Cardioprotection in DM mediated by exendin-4 was abolished by combination therapy with the PPARα agonist wy-14643 but mimicked by PPARα gene deficiency. Therefore, the PPARα pathway accounted for the effects of exendin-4. This conclusion was confirmed in cardiac-restricted overexpression of PPARα mediated by adeno-associated virus serotype-9 containing a cardiac troponin T promoter. Our results provide the first direct evidence that GLP-1 protects cardiac function by inhibiting the ROCK/PPARα pathway, thereby ameliorating lipotoxicity in diabetic cardiomyopathy.

Pharmacologic activation of peroxisome proliferator-activating receptor-α accelerates hepatic fatty acid oxidation in neonatal pigs

Up-regulation of peroxisome proliferator-activating receptor-α (PPARα) and increasing fatty acid oxidation are important for reducing pre-weaning mortality of pigs. We examined the time-dependent regulatory effects of PPARα activation via oral postnatal clofibrate administration (75 mg/(kg-BW·d) for up to 7 days) on mitochondrial and peroxisomal fatty acid oxidation in pigs, a species with limited hepatic fatty acid oxidative capacity due to low ketogenesis. Hepatic oxidation was increased by 44-147% (depending on fatty acid chain-length) and was attained after only 4 days of clofibrate treatment. Acyl-CoA oxidase (ACO) and carnitine palmitoyltransferase I (CPTI) activities accelerated in parallel. The increase in CPTI activity was accompanied by a rapid reduction in the sensitivity of CPTI to malonyl-CoA inhibition. The mRNA abundance of CPTI and ACO, as well as peroxisomal keto-acyl-CoA thiolase (KetoACoA) and mitochondrial malonyl-CoA decarboxylase (MCD), also were augmented greatly. However, the increase in ACO activity and MCD expression were different from CPTI, and significant interactions were observed between postnatal age and clofibrate administration. Furthermore, the expression of acetyl-CoA carboxylase β (ACCβ) decreased with postnatal age and clofibrate had no effect on its expression. Collectively these results demonstrate that the expression of PPARα target genes and the increase in fatty acid oxidation induced by clofibrate are time- and age-dependent in the liver of neonatal pigs. Although the induction patterns of CPTI, MCD, ACO, KetoACoA, and ACCβ are different during the early postnatal period, 4 days of exposure to clofibrate were sufficient to robustly accelerate fatty acid oxidation.

Alterations in fatty acid metabolism and sirtuin signaling characterize early type-2 diabetic hearts of fructose-fed rats

Despite the fact that skeletal muscle insulin resistance is the hallmark of type‐2 diabetes mellitus (T2DM), inflexibility in substrate energy metabolism has been observed in other tissues such as liver, adipose tissue, and heart. In the heart, structural and functional changes ultimately lead to diabetic cardiomyopathy. However, little is known about the early biochemical changes that cause cardiac metabolic dysregulation and dysfunction. We used a dietary model of fructose‐induced T2DM (10% fructose in drinking water for 6 weeks) to study cardiac fatty acid metabolism in early T2DM and related signaling events in order to better understand mechanisms of disease. In early type‐2 diabetic hearts, flux through the fatty acid oxidation pathway was increased as a result of increased cellular uptake (CD36), mitochondrial uptake (CPT1B), as well as increased β‐hydroxyacyl‐CoA dehydrogenase and medium‐chain acyl‐CoA dehydrogenase activities, despite reduced mitochondrial mass. Long‐chain acyl‐CoA dehydrogenase activity was slightly decreased, resulting in the accumulation of long‐chain acylcarnitine species. Cardiac function and overall mitochondrial respiration were unaffected. However, evidence of oxidative stress and subtle changes in cardiolipin content and composition were found in early type‐2 diabetic mitochondria. Finally, we observed decreased activity of SIRT1, a pivotal regulator of fatty acid metabolism, despite increased protein levels. This indicates that the heart is no longer capable of further increasing its capacity for fatty acid oxidation. Along with increased oxidative stress, this may represent one of the earliest signs of dysfunction that will ultimately lead to inflammation and remodeling in the diabetic heart.

Dioxygen and Metabolism; Dangerous Liaisons in Cardiac Function and Disease

The heart must consume a significant amount of energy to sustain its contractile activity. Although the fuel demands are huge, the stock remains very low. Thus, in order to supply its daily needs, the heart must have amazing adaptive abilities, which are dependent on dioxygen availability. However, in myriad cardiovascular diseases, “fuel” depletion and hypoxia are common features, leading cardiomyocytes to favor low-dioxygen-consuming glycolysis rather than oxidation of fatty acids. This metabolic switch makes it challenging to distinguish causes from consequences in cardiac pathologies. Finally, despite the progress achieved in the past few decades, medical treatments have not improved substantially, either. In such a situation, it seems clear that much remains to be learned about cardiac diseases. Therefore, in this review, we will discuss how reconciling dioxygen availability and cardiac metabolic adaptations may contribute to develop full and innovative strategies from bench to bedside.

Proteomics landscape of radiation-induced cardiovascular disease: somewhere over the paradigm

INTRODUCTION

Epidemiological studies clearly show that thoracic or whole body exposure to ionizing radiation increases the risk of cardiac morbidity and mortality. Radiation-induced cardiovascular disease (CVD) has been intensively studied during the last ten years but the underlying molecular mechanisms are still poorly understood. Areas covered: Heart proteomics is a powerful tool holding promise for the future research. The central focus of this review is to compare proteomics data on radiation-induced CVD with data arising from proteomics of healthy and diseased cardiac tissue in general. In this context we highlight common and unique features of radiation-related and other heart pathologies. Future prospects and challenges of the field are discussed. Expert commentary: Data from comprehensive cardiac proteomics have deepened the knowledge of molecular mechanisms involved in radiation-induced cardiac dysfunction. State-of-the-art proteomics has the potential to identify novel diagnostic and therapeutic markers of this disease.

What Is Lipotoxicity?

Enlarged fat cells in obese adipose tissue diminish capacity to store fat and are resistant to the anti-lipolytic effect of insulin. Insulin resistance (IR)-associated S-nitrosylation of insulin-signaling proteins increases in obesity. In accordance with the inhibition of insulin-mediated anti-lipolytic action, plasma free fatty acid (FFA) levels increase. Additionally, endoplasmic reticulum stress stimuli induce lipolysis by activating cyclic adenosine monophosphate/Protein kinase A (cAMP/PKA) and extracellular signal-regulated kinase ½ (ERK1/2) signaling in adipocytes. Failure of packaging of excess lipid into lipid droplets causes chronic elevation of circulating fatty acids, which can reach to toxic levels within non-adipose tissues. Deleterious effects of lipid accumulation in non-adipose tissues are known as lipotoxicity. In fact, triglycerides may also serve a storage function for long-chain non-esterified fatty acids and their products such as ceramides and diacylglycerols (DAGs). Thus, excess DAG, ceramide and saturated fatty acids in obesity can induce chronic inflammation and have harmful effect on multiple organs and systems. In this context, chronic adipose tissue inflammation, mitochondrial dysfunction and IR have been discussed within the scope of lipotoxicity.

Thyroid Hormone Stimulation of Adult Brain Fatty Acid Oxidation

Thyroid hormone is a critical modulator of brain metabolism, and it is highly controlled in the central nervous system. Recent research has uncovered an important role of thyroid hormone in the regulation of fatty acid oxidation (FAO), an energetic process essential for neurodevelopment that continues to support brain metabolism during adulthood. Thyroid hormone stimulation of FAO has been shown to be protective in astrocytes and mouse models of brain injury, yet a clear mechanism of this relationship has not been elucidated. Thyroid hormone interacts with multiple receptors located in the nucleus and the mitochondria, initiating rapid and long-term effects via both genomic and nongenomic pathways. This has complicated efforts to isolate and study-specific interactions. This chapter presents the primary signaling pathways that have been identified to play a role in the thyroid hormone-mediated increase in FAO. Investigation of the impact of thyroid hormone on FAO in the adult brain has challenged classical models of brain metabolism and widened the window of potential neuroprotective strategies. A detailed understanding of these pathways is essential for any researchers aiming to expand the field of neuroenergetics.