Exposure to a chronic high-fat diet promotes atrial structure and gap junction remodeling in rats

Epicardial fat and ventricular arrhythmias

The arrhythmogenic role of epicardial adipose tissue (EAT) in atrial arrhythmias is well established, but its effect on ventricular arrhythmias has been significantly less investigated. Since ventricular arrhythmias are thought to cause 75%-80% of cases of sudden cardiac death, this is not a trivial issue. We provide an overview of clinical data as well as experimental and molecular data linking EAT to ventricular arrhythmias, attempting to dissect possible mechanisms and indicate future directions of research and possible clinical implications. However, despite a wealth of data indicating the role of epicardial and intramyocardial fat in the induction and propagation of ventricular arrhythmias, unfortunately there is currently no direct evidence that indeed EAT triggers arrhythmia or can be a target for antiarrhythmic strategies.

MicroRNA-205-5p plays a suppressive role in the high-fat diet-induced atrial fibrosis through regulation of the EHMT2/IGFBP3 axis

Objective

MicroRNAs (miRNAs) targeting has been revealed to be an appealing strategy for the treatment and management of atrial fibrillation (AF). In this research, we aimed to explore the mechanisms of miR-205-5p in reducing the high-fat diet (HFD)-induced atrial fibrosis through the EHMT2/IGFBP3 axis.

Methods

Expression levels of miR-205-5p, IGFBP3 and EHMT2 were determined in AF patients, cell fibrosis models and mouse atrial fibrosis models. Luciferase activity and RIP assays were performed to detect the binding between miR-205-5p and EHMT2, and ChIP assays were implemented to detect the enrichment of H3K9me2 and H3K4me3 in the promoter region of IGFBP3 in cells. The related experiments focusing on the inflammatory response, atrial fibrosis, mitochondrial damage, and metabolic abnormalities were performed to figure out the roles of miR-205-5p, IGFBP3, and EHMT2 in cell and mouse atrial fibrosis models.

Results

Low expression levels of miR-205-5p and IGFBP3 and a high expression of EHMT2 were found in AF patients, cell fibrosis models and mouse atrial fibrosis models. Upregulation of miR-205-5p reduced the expression of TGF-β1, α-SMA, Col III and other fibrosis-related proteins. miR-205-5p overexpression targeted EHMT2 to regulate the methylation of H3 histones to promote IGFBP3 expression, which in turn affected the fibrosis of atrial muscle cells. In HFD-induced atrial fibrosis mice, upregulated miR-205-5p or elevated IGFBP3 alleviated atrial fibrosis, mitochondrial damage, and metabolic abnormalities.

Conclusion

This study suggests that miR-205-5p attenuates HFD-induced atrial fibrosis via modulating the EHMT2/IGFBP3 axis.

Graphical Abstract

miR-205-5p alleviates high-fat diet-induced atrial fibrosis in mice via EHMT2/IGFBP3.

Genetic inhibition of serum glucocorticoid kinase 1 prevents obesity-related atrial fibrillation

Obesity is an important risk factor for atrial fibrillation (AF), but a better mechanistic understanding of obesity-related atrial fibrillation is required. Serum glucocorticoid kinase 1 (SGK1) is a kinase positioned within multiple obesity-related pathways, and prior work has shown a pathologic role of SGK1 signaling in ventricular arrhythmias. We validated a mouse model of obesity-related AF using wild-type mice fed a high-fat diet. RNA sequencing of atrial tissue demonstrated substantial differences in gene expression, with enrichment of multiple SGK1-related pathways, and we showed upregulated of SGK1 transcription, activation, and signaling in obese atria. Mice expressing a cardiac specific dominant-negative SGK1 were protected from obesity-related AF, through effects on atrial electrophysiology, action potential characteristics, structural remodeling, inflammation, and sodium current. Overall, this study demonstrates the promise of targeting SGK1 in a mouse model of obesity-related AF.

Atrial cardiomyopathy: from cell to bedside

Atrial cardiomyopathy refers to structural and electrical remodelling of the atria, which can lead to impaired mechanical function. While historical studies have implicated atrial fibrillation as the leading cause of cardioembolic stroke, atrial cardiomyopathy may be an important, underestimated contributor. To date, the relationship between atrial cardiomyopathy, atrial fibrillation, and cardioembolic stroke remains obscure. This review summarizes the pathogenesis of atrial cardiomyopathy, with a special focus on neurohormonal and inflammatory mechanisms, as well as the role of adipose tissue, especially epicardial fat in atrial remodelling. It reviews the current evidence implicating atrial cardiomyopathy as a cause of embolic stroke, with atrial fibrillation as a lagging marker of an increased thrombogenic atrial substrate. Finally, it discusses the potential of antithrombotic therapy in embolic stroke with undetermined source and appraises the available diagnostic techniques for atrial cardiomyopathy, including imaging techniques such as echocardiography, computed tomography, and magnetic resonance imaging as well as electroanatomic mapping, electrocardiogram, biomarkers, and genetic testing. More prospective studies are needed to define the relationship between atrial cardiomyopathy, atrial fibrillation, and embolic stroke and to establish a prompt diagnosis and specific treatment strategies in these patients with atrial cardiomyopathy for the secondary and even primary prevention of embolic stroke.

Epicardial adipose tissue as a mediator of cardiac arrhythmias

Obesity is associated with higher risks of cardiac arrhythmias. Although this may be partly explained by concurrent cardiometabolic ill-health, growing evidence suggests that increasing adiposity independently confers risk for arrhythmias. Among fat depots, epicardial adipose tissue (EAT) exhibits a proinflammatory secretome and, given the lack of fascial separation, has been implicated as a transducer of inflammation to the underlying myocardium. The present review explores the mechanisms underpinning adverse electrophysiological remodeling as a consequence of EAT accumulation and the consequent inflammation. We first describe the physiological and pathophysiological function of EAT and its unique secretome and subsequently discuss the evidence for ionic channel and connexin expression modulation as well as fibrotic remodeling induced by cytokines and free fatty acids that are secreted by EAT. Finally, we highlight how weight reduction and regression of EAT volume may cause reverse remodeling to ameliorate arrhythmic risk.

Enhancing Fatty Acids Oxidation via L-Carnitine Attenuates Obesity-Related Atrial Fibrillation and Structural Remodeling by Activating AMPK Signaling and Alleviating Cardiac Lipotoxicity

Atrial fibrillation (AF) is the most common sustained cardiac arrhythmia in clinical setting. Its pathogenesis was associated with metabolic disorder, especially defective fatty acids oxidation (FAO). However, whether promoting FAO could prevent AF occurrence and development remains elusive. In this study, we established a mouse model of obesity-related AF through high-fat diet (HFD) feeding, and used l-carnitine (LCA, 150 mg/kg⋅BW/d), an endogenous cofactor of carnitine palmitoyl-transferase-1B (CPT1B; the rate-limiting enzyme of FAO) to investigate whether FAO promotion can attenuate the AF susceptibility in obesity. All mice underwent electrophysiological assessment for atrial vulnerability, and echocardiography, histology and molecular evaluation for AF substrates and underlying mechanisms, which were further validated by pharmacological experiments in vitro. HFD-induced obese mice increased AF vulnerability and exhibited apparent atrial structural remodeling, including left atrial dilation, cardiomyocyte hypertrophy, connexin-43 remodeling and fibrosis. Pathologically, HFD apparently leads to defective cardiac FAO and subsequent lipotoxicity, thereby evoking a set of pathological reactions including oxidative stress, DNA damage, inflammation, and insulin resistance. Enhancing FAO via LCA attenuated lipotoxicity and lipotoxicity-induced pathological changes in the atria of obese mice, resulting in restored structural remodeling and ameliorated AF susceptibility. Mechanistically, LCA activated AMPK/PGC1α signaling both in vivo and in vitro, and pharmacological inhibition of AMPK via Compound C attenuated LCA-induced cardio-protection in palmitate-treated primary atrial cardiomyocytes. Taken together, our results demonstrated that FAO promotion via LCA attenuated obesity-mediated AF and structural remodeling by activating AMPK signaling and alleviating atrial lipotoxicity. Thus, enhancing FAO may be a potential therapeutic target for AF.

New Insights on the Role of Connexins and Gap Junctions Channels in Adipose Tissue and Obesity

Due to the inability to curb the excessive increase in the prevalence of obesity and overweight, it is necessary to comprehend in more detail the factors involved in the pathophysiology and to appreciate more clearly the biochemical and molecular mechanisms of obesity. Thus, understanding the biological regulation of adipose tissue is of fundamental relevance. Connexin, a protein that forms intercellular membrane channels of gap junctions and unopposed hemichannels, plays a key role in adipogenesis and in the maintenance of adipose tissue homeostasis. The expression and function of Connexin 43 (Cx43) during the different stages of the adipogenesis are differentially regulated. Moreover, it has been shown that cell–cell communication decreases dramatically upon differentiation into adipocytes. Furthermore, inhibition of Cx43 degradation or constitutive overexpression of Cx43 blocks adipocyte differentiation. In the first events of adipogenesis, the connexin is highly phosphorylated, which is likely associated with enhanced Gap Junction (GJ) communication. In an intermediate state of adipocyte differentiation, Cx43 phosphorylation decreases, as it is displaced from the membrane and degraded through the proteasome; thus, Cx43 total protein is reduced. Cx is involved in cardiac disease as well as in obesity-related cardiovascular diseases. Different studies suggest that obesity together with a high-fat diet are related to the production of remodeling factors associated with expression and distribution of Cx43 in the atrium.

Necroptosis is required for atrial fibrillation and involved in aerobic exercise-conferred cardioprotection

Necroptosis, a novel programmed cell death, plays a critical role in the development of fibrosis, yet its role in atrial fibrillation (AF) remains elusive. Mounting evidence demonstrates that aerobic exercise improves AF-related symptoms and quality of life. Therefore, we explored the role of necroptosis in AF pathogenesis and exercise-conferred cardioprotection. A mouse AF model was established either by calcium chloride and acetylcholine (CaCl₂ -Ach) administration for 3 weeks or high-fat diet (HFD) feeding for 12 weeks, whereas swim training was conducted 60 min/day, for 3-week duration. AF susceptibility, heart morphology and function and atrial fibrosis were assessed by electrophysiological examinations, echocardiography and Masson's trichrome staining, respectively. Both CaCl₂ -Ach administration and HFD feeding significantly enhanced AF susceptibility (including frequency and duration of episodes), left atrial enlargement and fibrosis. Moreover, protein levels of necroptotic signaling (receptor-interacting protein kinase 1, receptor-interacting protein kinase 3, mixed lineage kinase domain-like protein and calcium/calmodulin-dependent protein kinase II or their phosphorylated forms) were markedly elevated in the atria of AF mice. However, inhibiting necroptosis with necrostatin-1 partly attenuated CaCl₂ -Ach (or HFD)-induced fibrosis and AF susceptibility, implicating necroptosis as contributing to AF pathogenesis. Finally, we found 3-week swim training inhibited necroptotic signaling, consequently decreasing CaCl₂ -Ach-induced AF susceptibility and atrial structural remodeling. Our findings identify necroptosis as a novel mechanism in AF pathogenesis and highlight that aerobic exercise may confer benefits on AF via inhibiting cardiac necroptosis.

Atrial Remodeling in Atrial Fibrillation. Comorbidities and Markers of Disease Progression Predict Catheter Ablation Outcome

Atrial fibrillation is the most common supraventricular arrhythmia affecting an increasing proportion of the population in which mainstream therapy, i.e. catheter ablation, provides freedom from arrhythmia in only a limited number of patients. Understanding the mechanism is key in order to find more effective therapies and to improve patient selection. In this review, the structural and electrophysiological changes of the atrial musculature that constitute atrial remodeling in atrial fibrillaton and how risk factors and markers of disease progression can predict catheter ablation outcome will be discussed in detail.

Cadherin-11 deficiency mitigates high-fat diet-induced inflammatory atrial remodeling and vulnerability to atrial fibrillation

Atrial fibrillation (AF) is the most common cardiac arrhythmia nowadays. The occurrence of AF is closely associated with obesity. Cadherin-11 (Cad-11), as a member of the cadherin family, can make a contribution to diet-induced obesity and it will be informative to know whether Cad-11 exerts its effects on atrial remodeling and AF vulnerability in a diet-induced obesity model. In this study, we demonstrated that the expression of Cad-11 was significantly upregulated in the left atrium of AF patients with obesity and mice following 16 weeks of high-fat diet (HFD) feeding. Further confirmed that Cad-11 could regulate the activity of atrial fibroblasts by participating in inducing proinflammatory cytokines production. At animal levels, we found that although there was a lack of statistical difference in body weight, Cad-11^-/- mice could markedly improve impaired glucose tolerance and hyperlipidemia. Adverse atrial structural remodeling, including atrial enlargement, inflammation, and fibrosis provoked by HFD feeding were mitigated in Cad-11^-/- mice. Mechanistically, Cad-11 activated mitogen-activated protein kinases and nuclear factor-κB for interleukin-6 production in atrial fibroblasts that may contribute to the atrial fibrosis process in obesity-related AF, suggesting Cad-11 might be a new therapeutic target for obesity-related AF.

Inhibition of endoplasmic reticulum stress prevents high-fat diet mediated atrial fibrosis and fibrillation

Obesity is a significant risk factor for atrial fibrillation (AF), which is the most common sustained arrhythmia with increased mortality and morbidity. High-fat diet (HFD)-induced obesity is associated with the activation of endoplasmic reticulum stress (ERS). However, the role of ERS in HFD-induced AF remains elusive. Human atrium samples were examined for the ERS activation test. C57BL/6J mice were divided into four groups, including the control group, the HFD group, the 4-phenylbutyric acid (4-PBA) group, and the HFD + 4-PBA group. At the age of 4 weeks, the HFD group and the HFD + 4-PBA group were given HFD to construct the obesity model, while the other two groups were given a normal diet (ND). Transesophageal programmed electrical stimulation was conducted to evaluate the AF inducibility and duration. Atrial fibrosis and ERS activation were also investigated.We found that CHOP and GRP-78 protein were significantly higher in overweight patients than the controls (both P < 0.05). AF inducibility and duration of the HFD group were significantly higher than the other groups (both P < 0.05), while there was no difference between those groups (P > 0.05). The mice of the HFD group had significantly higher collagen volume fraction (CVF%) than the other groups (P < 0.05). ERS marker protein of GRP78, p-PERK, ATF6 and CHOP protein expression level was increased in the HFD group, which were significantly mitigated in the HFD + 4-PBA group. In summary, HFD-induced ERS activation facilitates atrial fibrosis and AF. The inhibition of ERS might alleviate atrial fibrosis and reduce the incidence of AF-associated obesity.

Mechanisms of Chronic Metabolic Stress in Arrhythmias

Cardiac arrhythmias are responsible for many cardiovascular disease-related deaths worldwide. While arrhythmia pathogenesis is complex, there is increasing evidence for metabolic causes. Obesity, diabetes, and chronically consuming high-fat foods significantly increase the likelihood of developing arrhythmias. Although these correlations are well established, mechanistic explanations connecting a high-fat diet (HFD) to arrhythmogenesis are incomplete, although oxidative stress appears to be critical. This review investigates the metabolic changes that occur in obesity and after HFD. Potential therapies to prevent or treat arrhythmias are discussed, including antioxidants.

Hydrogen-rich saline mitigates pressure overload-induced cardiac hypertrophy and atrial fibrillation in rats via the JAK-STAT signalling pathway

Objective

To investigate if hydrogen-rich saline (HRS), which has been shown to have antioxidant and anti-inflammatory properties, could mitigate cardiac remodelling and reduce the incidence of atrial fibrillation (AF) in the rat model of cardiac hypertrophy.

Methods

Pressure overload was induced in rats by abdominal aortic constriction (AAC). The animals were separated into four groups: sham; AAC group; AAC plus low dose HRS (LHRS); AAC plus high dose HRS (HHRS). The sham and AAC groups received normal saline intraperitoneally and the LHRS and HHRS groups received 3 or 6 ml/kg HRS daily for six weeks, respectively. In vitro research was also performed using cardiotrophin-1 (CT-1)-induced hypertrophy of cultured neonatal rat cardiomyocytes.

Results

Cardiac hypertrophy was successfully induced by AAC and low and high dose HRS mitigated the pressure overload as shown by lower heart and atrial weights in these treatment groups. AF incidence and duration of the HRS groups were also significantly lower in the HRS groups compared with the AAC group. Atrial fibrosis was also reduced in the HRS groups and the JAK-STAT signalling pathway was down-regulated. In vitro experiments showed that hydrogen-rich medium mitigated the CT-1-induced cardiomyocyte hypertrophy with a similar effect as the JAK specific antagonists AG490.

Conclusions

HRS was found to mitigate cardiac hypertrophy induced by pressure overload in rats and reduce atrial fibrosis and AF which was possibly achieved via inhibition of the JAK-STAT signalling pathway.

Ion Channel and Structural Remodeling in Obesity-Mediated Atrial Fibrillation

BACKGROUND

Epidemiological studies have established obesity as an independent risk factor for atrial fibrillation (AF), but the underlying pathophysiological mechanisms remain unclear. Reduced cardiac sodium channel expression is a known causal mechanism in AF. We hypothesized that obesity decreases Nav1.5 expression via enhanced oxidative stress, thus reducing INa, and enhancing susceptibility to AF.

METHODS

To elucidate the underlying electrophysiological mechanisms a diet-induced obese mouse model was used. Weight, blood pressure, glucose, F2-isoprostanes, NOX2 (NADPH oxidase 2), and PKC (protein kinase C) were measured in obese mice and compared with lean controls. Invasive electrophysiological, immunohistochemistry, Western blotting, and patch clamping of membrane potentials was performed to evaluate the molecular and electrophysiological phenotype of atrial myocytes.

RESULTS

Pacing-induced AF in 100% of diet-induced obese mice versus 25% in controls (P<0.01) with increased AF burden. Cardiac sodium channel expression, INa and atrial action potential duration were reduced and potassium channel expression (Kv1.5) and current (IKur) and F2-isoprostanes, NOX2, and PKC-α/δ expression and atrial fibrosis were significantly increased in diet-induced obese mice as compared with controls. A mitochondrial antioxidant reduced AF burden, restored INa, ICa,L, IKur, action potential duration, and reversed atrial fibrosis in diet-induced obese mice as compared with controls.

CONCLUSIONS

Inducible AF in obese mice is mediated, in part, by a combined effect of sodium, potassium, and calcium channel remodeling and atrial fibrosis. Mitochondrial antioxidant therapy abrogated the ion channel and structural remodeling and reversed the obesity-induced AF burden. Our findings have important implications for the management of obesity-mediated AF in patients. Graphic Abstract: A graphic abstract is available for this article.

Exogenous hydrogen sulfide reduces atrial remodeling and atrial fibrillation induced by diabetes mellitus via activation of the PI3K/Akt/eNOS pathway

Diabetes mellitus (DM) facilitates atrial fibrosis and increases the risk of atrial fibrillation (AF). The underlying mechanism of DM in causing AF remains mostly unknown and potential therapeutic targets for DM‑induced AF are rarely reported. Hydrogen sulfide (H2S) has drawn considerable attention in recent years for its potential as a cardiovascular protector. Thus, the aim of the present study was to investigate the effect of H2S on DM‑induced AF and the mechanism of action. Sprague‑Dawley rats were divided into four groups, including the control group, the DM group, the H2S group and the DM+H2S group. The DM group and the DM+H2S group were administered streptozotocin to induce DM, whereas the other two groups were given citrate buffer as a control. The H2S group and the DM+H2S group were administered with an intraperitoneal injection of sodium hydrosulfide (precursor of H2S). AF inducibility, AF duration, atrial fibrosis and vital protein expression of oxidative stress were compared among the four groups. The DM group showed significantly higher AF incidence rates and duration (P<0.05). Histology results demonstrated severe atrial fibrosis in the DM group, and the PI3K/Akt/endothelial nitric oxide synthase (eNOS) pathway was significantly downregulated (P<0.05). However, when H2S was administered, the rats showed lower AF incidence and duration compared with the DM group. Additionally, H2S was able to mitigate the atrial fibrosis induced by DM, as well as the proliferation and migration of cardiac fibroblasts, as demonstrated by an MTT assay and real‑time cell analyzer migration experiment. Western blotting showed that the expression levels of the PI3K/Akt/eNOS pathway in the DM+H2S group were significantly upregulated compared with those of the DM group (P<0.05). In summary, DM status can lead to the structural remodeling of atrial fibrosis, facilitating AF incidence and persistence. Administration of H2S does not affect the glucose level, but can significantly mitigate atrial fibrosis and reduce the incidence of AF induced by DM, probably via activation of the PI3K/Akt/eNOS pathway.

Autophagy inhibition blunts PDGFRA adipose progenitors' cell-autonomous fibrogenic response to high-fat diet

Adipose tissue (AT) fibrosis in obesity compromises adipocyte functions and responses to intervention-induced weight loss. It is driven by AT progenitors with dual fibro/adipogenic potential, but pro-fibrogenic pathways activated in obesity remain to be deciphered. To investigate the role of macroautophagy/autophagy in AT fibrogenesis, we used Pdgfra-Cre^Ert2 transgenic mice to create conditional deletion of Atg7 alleles in AT progenitor cells (atg7 cKO) and examined sex-dependent, depot-specific AT remodeling in high-fat diet (HFD)-fed mice. Mice with atg7 cKO had markedly decreased extracellular matrix (ECM) gene expression in visceral, subcutaneous, and epicardial adipose depots compared to Atg7^lox/lox littermates. ECM gene program regulation by autophagy inhibition occurred independently of changes in the mass of fat tissues or adipocyte numbers of specific depots, and cultured preadipocytes treated with pharmacological or siRNA-mediated autophagy disruptors could mimic these effects. We found that autophagy inhibition promotes global cell-autonomous remodeling of the paracrine TGF-BMP family landscape, whereas ECM gene modulation was independent of the autophagic regulation of GTF2IRD1. The progenitor-specific mouse model of ATG7 inhibition confirms the requirement of autophagy for white/beige adipocyte turnover, and combined to in vitro experiments, reveal progenitor autophagy dependence for AT fibrogenic response to HFD, through the paracrine remodeling of TGF-BMP factors balance. Abbreviations: CQ: chloroquine; ECM: extracellular matrix; EpiAT: epididymal adipose tissue; GTF2IRD1: general transcription factor II I repeat domain-containing 1; HFD: high-fat diet; KO: knockout; OvAT: ovarian adipose tissue; PDGFR: platelet derived growth factor receptor; ScAT: subcutaneous adipose tissue; TGF-BMP: transforming growth factor-bone morphogenic protein.

Chronic consumption of a high-fat diet rich in corn oil activates intrinsic cell death pathway and induces several ultrastructural changes in the atria of healthy and type 1 diabetic rat

This study investigates the effect of chronic consumption of a high-fat diet rich in corn oil (CO-HFD) on atrial cells ultrastructure, antioxidant levels and markers of intrinsic cell death of both control and type 1 diabetes mellitus (T1DM)-induced rats. Adult male rats (10 rats/group) were divided into four groups: control fed standard diet (STD) (3.82 kcal/g, 9.4% fat), CO-HFD (5.4 kcal/g, 40% fat), T1DM fed STD, and T1DM + CO-HFD. CO-HFD and T1DM alone or in combination impaired systolic and diastolic functions of rats and significantly reduced levels of GSH and the activity of SOD, enhanced lipid peroxidation, increased protein levels of P53, Bax, cleaved caspase-3, and ANF and decreased levels of Bcl-2 in their atria. Concomitantly, atrial cells exhibited fragmentation of the myofibrils, disorganized mitochondria, decreased number of atrionatriuretic factor (ANF) granules, and loss of gap junctions accompanied by changes in capillary walls. Among all treatments, the severity of all these findings was more severe in T1DM and most profound in the atria of T1DM + CO-HFD. In conclusion, chronic consumption of CO-HFD by T1DM-induced rats elicits significant biochemical and ultrastructural damage to rat atrial cells accompanied by elevated oxidative stress and mitochondria-mediated cell death.

Linking Arrhythmias and Adipocytes: Insights, Mechanisms, and Future Directions

Obesity and atrial fibrillation have risen to epidemic levels worldwide and may continue to grow over the next decades. Emerging evidence suggests that obesity promotes atrial and ventricular arrhythmias. This has led to trials employing various strategies with the ultimate goal of decreasing the atrial arrhythmic burden in obese patients. The effectiveness of these interventions remains to be determined. Obesity is defined by the expansion of adipose mass, making adipocytes a prime candidate to mediate the pro-arrhythmogenic effects of obesity. The molecular mechanisms linking obesity and adipocytes to increased arrhythmogenicity in both the atria and ventricles remain poorly understood. In this focused review, we highlight areas of potential molecular interplay between adipocytes and cardiomyocytes. The effects of adipocytes may be direct, local or remote. Direct effect refers to adipocyte or fatty infiltration of the atrial and ventricular myocardium itself, possibly causing increased dispersion of normal myocardial electrical signals and fibrotic substrate of adipocytes that promote reentry or adipocytes serving as a direct source of aberrant signals. Local effects may originate from nearby adipose depots, specifically epicardial adipose tissue (EAT) and pericardial adipose tissue, which may play a role in the secretion of adipokines and chemokines that can incite inflammation given the direct contact and disrupt the conduction system. Adipocytes can also have a remote effect on the myocardium arising from their systemic secretion of adipokines, cytokines and metabolites. These factors may lead to mitochondrial dysfunction, oxidative stress, autophagy, mitophagy, autonomic dysfunction, and cardiomyocyte death to ultimately produce a pro-arrhythmogenic state. By better understanding the molecular mechanisms connecting dysfunctional adipocytes and arrhythmias, novel therapies may be developed to sever the link between obesity and arrhythmias.

Obesity-associated alterations in cardiac connexin-43 and PKC signaling are attenuated by melatonin and omega-3 fatty acids in female rats

We aimed to explore whether specific high-sucrose intake in older female rats affects myocardial electrical coupling protein, connexin-43 (Cx43), protein kinase C (PKC) signaling, miR-1 and miR-30a expression, and susceptibility of the heart to malignant arrhythmias. Possible benefit of the supplementation with melatonin (40 µg/ml/day) and omega-3 polyunsaturated fatty acids (Omacor, 25 g/kg of rat chow) was examined as well. Results have shown that 8 weeks lasting intake of 30% sucrose solution increased serum cholesterol, triglycerides, body weight, heart weight, and retroperitoneal adipose tissues. It was accompanied by downregulation of cardiac Cx43 and PKCε signaling along with an upregulation of myocardial PKCδ and miR-30a rendering the heart prone to ventricular arrhythmias. There was a clear benefit of melatonin or omega-3 PUFA supplementation due to their antiarrhythmic effects associated with the attenuation of myocardial Cx43, PKC, and miR-30a abnormalities as well as adiposity. The potential impact of these findings may be considerable, and suggests that high-sucrose intake impairs myocardial signaling mediated by Cx43 and PKC contributing to increased susceptibility of the older obese female rat hearts to malignant arrhythmias.