Secretome of atrial epicardial adipose tissue facilitates reentrant arrhythmias by myocardial remodeling

Exploring the role of epicardial adipose-tissue-derived extracellular vesicles in cardiovascular diseases

Epicardial adipose tissue (EAT) is a fat depot located between the myocardium and the visceral layer of the epicardium, which, owing to its location, can influence surrounding tissues and can act as a local transducer of systemic inflammation. The mechanisms upon which such influence depends on are however unclear. Given the role EAT undoubtedly has in the scheme of cardiovascular diseases (CVDs), understanding the impact of its cellular components is of upmost importance. Extracellular vesicles (EVs) constitute promising candidates to fill the gap in the knowledge concerning the unexplored mechanisms through which EAT promotes onset and progression of CVDs. Owing to their ability of transporting active biomolecules, EAT-derived EVs have been reported to be actively involved in the pathogenesis of ischemia/reperfusion injury, coronary atherosclerosis, heart failure, and atrial fibrillation. Exploring the precise functions EVs exert in this context may aid in connecting the dots between EAT and CVDs.

Adipocyte-mediated electrophysiological remodeling of human stem cell - derived cardiomyocytes

Adipocytes normally accumulate in the epicardial and pericardial layers around the human heart, but their infiltration into the myocardium can be proarrhythmic. METHODS AND RESULTS: Human adipose derived stem/stromal cells and human induced pluripotent stem cells (hiPSC) were differentiated, respectively into predominantly white fat-like adipocytes (hAdip) and ventricular cardiomyocytes (CMs). Adipocytes cultured in CM maintenance medium (CM medium) maintained their morphology, continued to express adipogenic markers, and retained clusters of intracellular lipid droplets. In contrast, hiPSC-CMs cultivated in adipogenic growth medium displayed abnormal cell morphologies and more clustering across the monolayer. Pre-plated hiPSC-CMs co-cultured in direct contact with hAdips in CM medium displayed prolonged action potential durations, increased triangulation, slowed conduction velocity, increased conduction velocity heterogeneity, and prolonged calcium transients. When hAdip-conditioned medium was added to monolayer cultures of hiPSC-CMs, results similar to those recorded with direct co-cultures were observed. Both co-culture and conditioned medium experiments resulted in increases in transcript abundance of SCN10A, CACNA1C, SLC8A1, and RYR2, with a decrease in KCNJ2. Human adipokine immunoblots revealed the presence of cytokines that were elevated in adipocyte-conditioned medium, including MCP-1, IL-6, IL-8 and CFD that could induce electrophysiological changes in cultured hiPSC-CMs. CONCLUSIONS: Co-culture of hiPSC-CMs with hAdips reveals a potentially pathogenic role of infiltrating human adipocytes on myocardial tissue. In the absence of structural changes, hAdip paracrine release alone is sufficient to cause CM electrophysiological dysfunction mirroring the co-culture conditions. These effects, mediated largely by paracrine mechanisms, could promote arrhythmias in the heart.

Interpretation of field and LEAP potentials recorded from cardiomyocyte monolayers

Multielectrode arrays (MEAs) are the method of choice for electrophysiological characterization of cardiomyocyte monolayers. The field potentials recorded using an MEA are like extracellular electrograms recorded from the myocardium using conventional electrodes. Nevertheless, different criteria are used to interpret field potentials and extracellular electrograms, which hamper correct interpretation and translation to the patient. To validate the criteria for interpretation of field potentials, we used neonatal rat cardiomyocytes to generate monolayers. We recorded field potentials using an MEA and simultaneously recorded action potentials using sharp microelectrodes. In parallel, we recreated our experimental setting in silico and performed simulations. We show that the amplitude of the local RS complex of a field potential correlated with conduction velocity in silico but not in vitro. The peak time of the T wave in field potentials exhibited a strong correlation with APD90 while the steepest upslope correlated well with APD50. However, this relationship only holds when the T wave displayed a biphasic pattern. Next, we simulated local extracellular action potentials (LEAPs). The shape of the LEAP differed markedly from the shape of the local action potential, but the final duration of the LEAP coincided with APD90. Criteria for interpretation of extracellular electrograms should be applied to field potentials. This will provide a strong basis for the analysis of heterogeneity in conduction velocity and repolarization in cultured monolayers of cardiomyocytes. Finally, a LEAP is not a recording of the local action potential but is generated by intracellular current provided by neighboring cardiomyocytes and is superior to field potential duration in estimating APD90.NEW & NOTEWORTHY We present a physiological basis for the interpretation of multielectrode array-derived, extracellular, electrical signals.

Epicardial adipose tissue, metabolic disorders, and cardiovascular diseases: recent advances classified by research methodologies

Epicardial adipose tissue (EAT) is located between the myocardium and visceral pericardium. The unique anatomy and physiology of the EAT determines its great potential in locally influencing adjacent tissues such as the myocardium and coronary arteries. Classified by research methodologies, this study reviews the latest research progress on the role of EAT in cardiovascular diseases (CVDs), particularly in patients with metabolic disorders. Studies based on imaging techniques demonstrated that increased EAT amount in patients with metabolic disorders is associated with higher risk of CVDs and increased mortality. Then, in-depth profiling studies indicate that remodeled EAT may serve as a local mediator of the deleterious effects of cardiometabolic conditions and plays a crucial role in CVDs. Further, in vitro coculture studies provided preliminary evidence that the paracrine effect of remodeled EAT on adjacent cardiomyocytes can promote the occurrence and progression of CVDs. Considering the important role of EAT in CVDs, targeting EAT might be a potential strategy to reduce cardiovascular risks. Several interventions have been proved effective in reducing EAT amount. Our review provides valuable insights of the relationship between EAT, metabolic disorders, and CVDs, as well as an overview of the methodological constructs of EAT-related studies.

MicroRNAs in extracellular vesicles released from epicardial adipose tissue promote arrhythmogenic conduction slowing

Background

Patients with excess epicardial adipose tissue (EAT) are at increased risk of developing cardiac arrhythmias. EAT promotes arrhythmias by depolarizing the resting membrane of cardiomyocytes, which slows down conduction and facilitates re-entrant arrhythmias. We hypothesized that EAT slows conduction by secreting extracellular vesicles (EVs) and their microRNA (miRNA) cargo.

Objective

We aimed to determine the role of EAT-derived EVs and their miRNA cargo in conduction slowing.

Methods

EAT and subcutaneous adipose tissue (SAT) were collected from patients with atrial fibrillation. Adipose tissue explants were incubated in culture medium and secretome was collected. The numbers of EVs in the EAT and SAT secretome were measured by calibrated flow cytometry. EVs in the EAT secretome were isolated by size exclusion chromatography and miRNAs were sequenced. Pathway analysis was performed to predict candidates involved in cardiac electrophysiology. The candidates were validated in the EAT and SAT by quantitative real-time polymerase chain reaction. Finally, miRNA candidates were overexpressed in neonatal rat ventricular myocytes.

Results

The EV concentration was higher in the EAT secretome than in the SAT and control secretomes. miRNA sequencing of EAT-derived EVs detected a total of 824 miRNAs. Pathway analysis led to the identification of 7 miRNAs potentially involved in regulation of cardiac resting membrane potential. Validation of those miRNA candidates showed that they were all expressed in EAT, and that miR-1-3p and miR-133a-3p were upregulated in EAT in comparison with SAT. Overexpression of miR-1-3p and miR-133a-3p in neonatal rat ventricular myocytes led to conduction slowing and reduced Kcnj2 and Kcnj12 expression.

Conclusion

miR-1-3p and miR-133a-3p are potential mediators of EAT arrhythmogenicity.

Epicardial adipose tissue, pulmonary veins anatomy, and the P-wave/PR interval ratio in young patients with atrial fibrillation

Background

Atrial fibrillation (AF) is uncommon in the youngest population. Epicardial adipose tissue (EAT) volume has been proposed as an independent AF risk factor.

Objective

The aim of this retrospective study was to evaluate the impact of the EAT, the anatomy of the pulmonary veins (PVs), and electrocardiogram (ECG) features in these young patients with AF.

Methods

Sixty-two patients divided in 2 groups, one with history of paroxysmal AF treated with ablation and the other, a control group, all younger than 30 years of age, were included. Computed tomography scans were performed in both groups to estimate the PVs anatomy and EAT volume. Twelve-lead ECGs were performed in all patients. Patients underwent follow-up in our outpatient clinic (35.9 ± 18.3 months).

Results

In the AF group, the EAT volume around the left atrium was 22.25 ± 9.3 cm3 compared with 12.61 ± 3.37 cm3, showing a statistically significance difference (P = .003). Family history resulted to be another significant risk factor (P = .009). During follow-up, 67.7% of the patients treated were still free of events. The anatomy and morphology of the right-sided PVs seemed to play a more consistent role in the patients with AF recurrences (P = .04). The P/PR ratio, a new ECG index, seemed predict AF recurrences after ablation (P = .03).

Conclusion

The abundance of EAT seems related to the risk of developing AF in young patients. The recurrence of AF is about 33% and does not seem related to the EAT volume, but rather to the anatomy of the PVs. A higher P/PR ratio might suggest recurrences.

The relationship between frequent premature ventricular complexes and epicardial adipose tissue volume

Background

Epicardial adipose tissue (EAT) is related to atrial fibrillation. The association between EAT volume and premature ventricular complexes (PVCs) remains unclear. Our study aimed to investigate the effect of EAT volume on the risk of frequent PVCs and burden levels of PVCs.

Methods

This observational study retrospectively recruited consecutive patients who had consultation between 2019 and 2021 at the First Affiliated Hospital of Zhengzhou University. Frequent PVC patients (n = 402) and control patients (n = 402) undergoing non-contrast computed tomography (CT) were enrolled. We selected evaluation criteria for the conduct of a 1:1 propensity score matching (PSM) analysis. Multivariable logistic analysis was used to investigate factors related to frequent PVCs. Furthermore, the determinants of EAT volume and the burden levels of PVCs were evaluated.

Results

Patients with PVCs had a significantly larger EAT volume than control patients. EAT volume was significantly larger in male PVC patients with BMI ≥24 kg/m2, diabetes mellitus, and E/A ratio <1. EAT volume was independently associated with PVCs. Moreover, the larger EAT volume was an independent predictor for the high burden level of PVCs. We revealed that the risk of high PVC burden level was increased with the rising of EAT volume by restricted cubic splines.

Conclusions

EAT volume was larger in frequent PVC patients than in control patients, regardless of other confounding factors. A large EAT volume was independently associated with high burden levels of PVCs. EAT volume may be a new mechanism to explain the pathogenesis of PVCs.

Atrial epicardial adipose tissue abundantly secretes myeloperoxidase and activates atrial fibroblasts in patients with atrial fibrillation

BACKGROUND

Epicardial adipose tissue (EAT) secretome induces fibrosis. Fibrosis, primarily extracellular matrix (ECM) produced by fibroblasts, creates a substrate for atrial fibrillation (AF). Whether the EAT secretome from patients with AF activates human atrial fibroblasts and through which components, remains unexplored.

RESEARCH AIMS

(a) To investigate if the EAT secretome from patients with versus without AF increases ECM production in atrial fibroblasts. (b) To identify profibrotic proteins and processes in the EAT secretome and EAT from patients with, who will develop (future onset), and without AF.

METHODS

Atrial EAT was obtainded during thoracoscopic ablation (AF, n = 20), or open-heart surgery (future onset and non-AF, n = 35). ECM gene expression of human atrial fibroblasts exposed to the EAT secretome and the proteomes of EAT secretome and EAT were assessed in patients with and without AF. Myeloperoxidase and neutrophil extracellular traps (NETs) were assessed immunohistochemically in patients with paroxysmal, persistent, future onset, and those who remain free of AF (non-AF).

RESULTS

The expression of COL1A1 and FN1 in fibroblasts exposed to secretome from patients with AF was 3.7 and 4.7 times higher than in patients without AF (p < 0.05). Myeloperoxidase was the most increased protein in the EAT secretome and EAT from patients with versus without AF (FC 18.07 and 21.57, p < 0.005), as was the gene-set neutrophil degranulation. Immunohistochemically, myeloperoxidase was highest in persistent (FC 13.3, p < 0.0001) and increased in future onset AF (FC 2.4, p = 0.02) versus non-AF. Myeloperoxidase aggregated subepicardially and around fibrofatty infiltrates. NETs were increased in patients with persistent versus non-AF (p = 0.03).

CONCLUSION

In AF, the EAT secretome induces ECM gene expression in atrial fibroblasts and contains abundant myeloperoxidase. EAT myeloperoxidase was increased prior to AF onset, and both myeloperoxidase and NETs were highest in persistent AF, highlighting the role of EAT neutrophils in the pathophysiology of AF.

Relationship between epicardial adipose tissue measured by computed tomography and premature ventricular complexes originating from different sites

AIMS

This study aims to explore the association between the features of epicardial adipose tissue (EAT) in different zones and premature ventricular complexes (PVCs) originating from different sites by computed tomography (CT).

METHODS AND RESULTS

A total of 136 patients who underwent radiofrequency ablation for PVCs were incorporated in this study. One hundred and thirty-six matched controls were included in this study using the case-control method (1:1 matching). PVCs were classified into four subgroups: (1) right ventricular outflow tract (RVOT-PVCs), (2) non-RVOT of the right ventricle (RV-PVCs), (3) left ventricular outflow tract (LVOT-PVCs), and (4) non-LVOT of the left ventricle (LV-PVCs). The volume and density of EAT were quantified by CT. Patients with PVCs had a significantly higher volume and lower density of EAT than the controls (P < 0.001). The LVOT-PVCs and LV-PVCs had a higher left ventricle periventricular EAT volume (LV-EATv) proportion (P < 0.05). The right ventricle periventricular EAT volume (RV-EATv) proportion was higher in ROVT-PVCs and LVOT-PVCs (P < 0.05). RVOT-PVC patients had a higher volume ratio and a smaller density differential (P < 0.05). Patients with LVOT-PVCs had a lower volume ratio and the LV-PVCs showed a greater density differential (P < 0.05).

CONCLUSION

Higher volume and lower density of EAT were significantly associated with frequent PVCs. The RVOT-PVC patients had a higher volume ratio and a smaller density differential. The LVOT-PVCs had a lower volume ratio and the LV-PVCs showed a greater density differential. These suggest a link between EAT structural properties and PVCs and a potential role for regional EAT in the development of PVCs.

Knockdown of Ift88 in fibroblasts causes extracellular matrix remodeling and decreases conduction velocity in cardiomyocyte monolayers

Background: Atrial fibrosis plays an important role in the development and persistence of atrial fibrillation by promoting reentry. Primary cilia have been identified as a regulator of fibroblasts (FB) activation and extracellular matrix (ECM) deposition. We hypothesized that selective reduction of primary cilia causes increased fibrosis and facilitates reentry.

Aim: The aim of this study was to disrupt the formation of primary cilia in FB and examine its consequences on ECM and conduction in a co-culture system of cardiomyocytes (CM) and FB.

Materials: Using short interfering RNA (siRNA), we removed primary cilia in neonatal rat ventricular FB by reducing the expression of Ift88 gene required for ciliary assembly. We co-cultured neonatal rat ventricular cardiomyocytes (CM) with FB previously transfected with Ift88 siRNA (siIft88) or negative control siRNA (siNC) for 48 h. We examined the consequences of ciliated fibroblasts reduction on conduction and tissue remodeling by performing electrical mapping, microelectrode, and gene expression measurements.

Results: Transfection of FB with siIft88 resulted in a significant 60% and 30% reduction of relative Ift88 expression in FB and CM-FB co-cultures, respectively, compared to siNC. Knockdown of Ift88 significantly increased the expression of ECM genes Fn1, Col1a1 and Ctgf by 38%, 30% and 18%, respectively, in comparison to transfection with siNC. Conduction velocity (CV) was significantly decreased in the siIft88 group in comparison to siNC [11.12 ± 4.27 cm/s (n = 10) vs. 17.00 ± 6.20 (n = 10) respectively, p &lt; 0.05]. The fraction of sites with interelectrode activation block was larger in the siIft88 group than in the siNC group (6.59 × 10−2 ± 8.01 × 10−2 vs. 1.18 × 10−2 ± 3.72 × 10−2 respectively, p &lt; 0.05). We documented spontaneous reentrant arrhythmias in two cultures in the siIft88 group and in none of the siNC group. Action potentials were not significantly different between siNC and siIft88 groups.

Conclusion: Disruption of cilia formation by siIft88 causes ECM remodeling and conduction abnormalities. Prevention of cilia loss could be a target for prevention of arrhythmias.

Diabesity in Elderly Cardiovascular Disease Patients: Mechanisms and Regulators

Cardiovascular disease (CVD) is the leading cause of death in the world. In 2019, 550 million people were suffering from CVD and 18 million of them died as a result. Most of them had associated risk factors such as high fasting glucose, which caused 134 million deaths, and obesity, which accounted for 5.02 million deaths. Diabesity, a combination of type 2 diabetes and obesity, contributes to cardiac, metabolic, inflammation and neurohumoral changes that determine cardiac dysfunction (diabesity-related cardiomyopathy). Epicardial adipose tissue (EAT) is distributed around the myocardium, promoting myocardial inflammation and fibrosis, and is associated with an increased risk of heart failure, particularly with preserved systolic function, atrial fibrillation and coronary atherosclerosis. In fact, several hypoglycaemic drugs have demonstrated a volume reduction of EAT and effects on its metabolic and inflammation profile. However, it is necessary to improve knowledge of the diabesity pathophysiologic mechanisms involved in the development and progression of cardiovascular diseases for comprehensive patient management including drugs to optimize glucometabolic control. This review presents the mechanisms of diabesity associated with cardiovascular disease and their therapeutic implications.