Functional characterization of the Ucp1-associated oxidative phenotype of human epicardial adipose tissue

Navigating Lipodystrophy: Insights from Laminopathies and Beyond

Recent research into laminopathic lipodystrophies-rare genetic disorders caused by mutations in the LMNA gene-has greatly expanded our knowledge of their complex pathology and metabolic implications. These disorders, including Hutchinson-Gilford progeria syndrome (HGPS), Mandibuloacral Dysplasia (MAD), and Familial Partial Lipodystrophy (FPLD), serve as crucial models for studying accelerated aging and metabolic dysfunction, enhancing our understanding of the cellular and molecular mechanisms involved. Research on laminopathies has highlighted how LMNA mutations disrupt adipose tissue function and metabolic regulation, leading to altered fat distribution and metabolic pathway dysfunctions. Such insights improve our understanding of the pathophysiological interactions between genetic anomalies and metabolic processes. This review merges current knowledge on the phenotypic classifications of these diseases and their associated metabolic complications, such as insulin resistance, hypertriglyceridemia, hepatic steatosis, and metabolic syndrome, all of which elevate the risk of cardiovascular disease, stroke, and diabetes. Additionally, a range of published therapeutic strategies, including gene editing, antisense oligonucleotides, and novel pharmacological interventions aimed at addressing defective adipocyte differentiation and lipid metabolism, will be explored. These therapies target the core dysfunctional lamin A protein, aiming to mitigate symptoms and provide a foundation for addressing similar metabolic and genetic disorders.

Is stimulation of browning of human adipose tissue a relevant therapeutic target?

Brown adipose tissue (BAT) and beige adipose tissues are important contributors to cold-induced whole body thermogenesis in rodents. The documentation in humans of cold- and ß-adrenergic receptor agonist-stimulated BAT glucose uptake using positron emission tomography (PET) and of a decrease of this response in individuals with cardiometabolic disorders led to the suggestion that BAT/beige adipose tissues could be relevant targets for prevention and treatment of these conditions. In this brief review, we will critically assess this question by first describing the basic rationale for this affirmation, second by examining the evidence in human studies, and third by discussing the possible means to activate the thermogenic response of these tissues in humans.

Radiomics of pericardial fat: a new frontier in heart failure discrimination and prediction

OBJECTIVES

To use pericardial adipose tissue (PAT) radiomics phenotyping to differentiate existing and predict future heart failure (HF) cases in the UK Biobank.

METHODS

PAT segmentations were derived from cardiovascular magnetic resonance (CMR) studies using an automated quality-controlled model to define the region-of-interest for radiomics analysis. Prevalent (present at time of imaging) and incident (first occurrence after imaging) HF were ascertained using health record linkage. We created balanced cohorts of non-HF individuals for comparison. PyRadiomics was utilised to extract 104 radiomics features, of which 28 were chosen after excluding highly correlated ones (0.8). These features, plus sex and age, served as predictors in binary classification models trained separately to detect (1) prevalent and (2) incident HF. We tested seven modeling methods using tenfold nested cross-validation and examined feature importance with explainability methods.

RESULTS

We studied 1204 participants in total, 297 participants with prevalent (60 ± 7 years, 21% female) and 305 with incident (61 ± 6 years, 32% female) HF, and an equal number of non-HF comparators. We achieved good discriminative performance for both prevalent (voting classifier; AUC: 0.76; F1 score: 0.70) and incident (light gradient boosting machine: AUC: 0.74; F1 score: 0.68) HF. Our radiomics models showed marginally better performance compared to PAT area alone. Increased PAT size (maximum 2D diameter in a given column or slice) and texture heterogeneity (sum entropy) were important features for prevalent and incident HF classification models.

CONCLUSIONS

The amount and character of PAT discriminate individuals with prevalent HF and predict incidence of future HF.

CLINICAL RELEVANCE STATEMENT

This study presents an innovative application of pericardial adipose tissue (PAT) radiomics phenotyping as a predictive tool for heart failure (HF), a major public health concern. By leveraging advanced machine learning methods, the research uncovers that the quantity and characteristics of PAT can be used to identify existing cases of HF and predict future occurrences. The enhanced performance of these radiomics models over PAT area alone supports the potential for better personalised care through earlier detection and prevention of HF.

KEY POINTS

•PAT radiomics applied to CMR was used for the first time to derive binary machine learning classifiers to develop models for discrimination of prevalence and prediction of incident heart failure. •Models using PAT area provided acceptable discrimination between cases of prevalent or incident heart failure and comparator groups. •An increased PAT volume (increased diameter using shape features) and greater texture heterogeneity captured by radiomics texture features (increased sum entropy) can be used as an additional classifier marker for heart failure.

Epicardial Adipose Tissue: A Precise Biomarker for Cardiovascular Risk, Metabolic Diseases, and Target for Therapeutic Interventions

Epicardial adipose tissue (EAT) is located between the heart muscle and visceral pericardium, where it has direct contact with coronary blood vessels. Elevated thickness of this tissue can induce local inflammation affecting the myocardium and the underlying coronary arteries, contributing to various cardiovascular diseases such as coronary artery disease, atrial fibrillation, or heart failure with preserved ejection fraction. Recent studies have identified EAT thickness as a simple and reliable biomarker for certain cardiovascular outcomes. Examples include the presence of atherosclerosis, incident cardiovascular disease (CVD) in individuals with type 2 diabetes mellitus (T2DM), and the prevalence of atrial fibrillation. Furthermore, EAT measurements can help to identify patients with a higher risk of developing metabolic syndrome. Since the EAT thickness can be easily measured using echocardiography, such examinations could serve as a useful and cost-effective preventive tool for assessing cardiovascular health. This review also summarizes therapeutical interventions aimed at reducing EAT. Reducing EAT thickness has been shown to be possible through pharmacological, surgical, or lifestyle-change interventions. Pharmaceutical therapies, including thiazolidinediones, glucagon-like peptide 1-receptor agonists, sodium-glucose cotransporter 2 inhibitors, dipeptidyl peptidase-4 inhibitors, and statins, have been shown to influence EAT thickness. Additionally, EAT thickness can also be managed more invasively through bariatric surgery, or noninvasively through lifestyle changes to diet and exercise routines.

Role of Epicardial Adipose Tissue Secretome on Cardiovascular Diseases

Obesity and insulin resistance are associated with the inflamed and defective adipose tissue (AT) phenotype, and are established risk factors for cardiovascular diseases (CVDs). Extracellular vesicles (EVs) are a heterogeneous group of cell-derived lipid membrane vesicles involved in the onset and development of many pathologies, including insulin resistance, diabetes, and CVDs. The inflammation associated with overweight and obesity triggers the transition of the AT secretome from healthy to pathological, with a consequent increased expression of pro-inflammatory mediators. Epicardial adipose tissue (EAT) is a specialized fat depot that surrounds the heart, in direct contact with the myocardium. Recently, the role of EAT in regulating the physiopathology of many heart diseases has been increasingly explored. In particular, the EAT phenotype and derived EVs have been associated with the onset and exacerbation of CVDs. In this review, we will focus on the role of the AT secretome in the case of CVDs, and will discuss the beneficial effects of EVs released by AT as promising therapeutic candidates.

The evolving view of thermogenic fat and its implications in cancer and metabolic diseases

The incidence of metabolism-related diseases like obesity and type 2 diabetes mellitus has reached pandemic levels worldwide and increased gradually. Most of them are listed on the table of high-risk factors for malignancy, and metabolic disorders systematically or locally contribute to cancer progression and poor prognosis of patients. Importantly, adipose tissue is fundamental to the occurrence and development of these metabolic disorders. White adipose tissue stores excessive energy, while thermogenic fat including brown and beige adipose tissue dissipates energy to generate heat. In addition to thermogenesis, beige and brown adipocytes also function as dynamic secretory cells and a metabolic sink of nutrients, like glucose, fatty acids, and amino acids. Accordingly, strategies that activate and expand thermogenic adipose tissue offer therapeutic promise to combat overweight, diabetes, and other metabolic disorders through increasing energy expenditure and enhancing glucose tolerance. With a better understanding of its origins and biological functions and the advances in imaging techniques detecting thermogenesis, the roles of thermogenic adipose tissue in tumors have been revealed gradually. On the one hand, enhanced browning of subcutaneous fatty tissue results in weight loss and cancer-associated cachexia. On the other hand, locally activated thermogenic adipocytes in the tumor microenvironment accelerate cancer progression by offering fuel sources and is likely to develop resistance to chemotherapy. Here, we enumerate current knowledge about the significant advances made in the origin and physiological functions of thermogenic fat. In addition, we discuss the multiple roles of thermogenic adipocytes in different tumors. Ultimately, we summarize imaging technologies for identifying thermogenic adipose tissue and pharmacologic agents via modulating thermogenesis in preclinical experiments and clinical trials.

Epicardial fat and atrial fibrillation: the perils of atrial failure

Obesity is a heterogeneous condition, characterized by different phenotypes and for which the classical assessment with body mass index may underestimate the real impact on cardiovascular (CV) disease burden. An epidemiological link between obesity and atrial fibrillation (AF) has been clearly demonstrated and becomes even more tight when ectopic (i.e. epicardial) fat deposition is considered. Due to anatomical and functional features, a tight paracrine cross-talk exists between epicardial adipose tissue (EAT) and myocardium, including the left atrium (LA). Alongside-and even without-mechanical atrial stretch, the dysfunctional EAT may determine a pro-inflammatory environment in the surrounding myocardial tissue. This evidence has provided a new intriguing pathophysiological link with AF, which in turn is no longer considered a single entity but rather the final stage of atrial remodelling. This maladaptive process would indeed include structural, electric, and autonomic derangement that ultimately leads to overt disease. Here, we update how dysfunctional EAT would orchestrate LA remodelling. Maladaptive changes sustained by dysfunctional EAT are driven by a pro-inflammatory and pro-fibrotic secretome that alters the sinoatrial microenvironment. Structural (e.g. fibro-fatty infiltration) and cellular (e.g. mitochondrial uncoupling, sarcoplasmic reticulum fragmentation, and cellular protein quantity/localization) changes then determine an electrophysiological remodelling that also involves the autonomic nervous system. Finally, we summarize how EAT dysfunction may fit with the standard guidelines for AF. Lastly, we focus on the potential benefit of weight loss and different classes of CV drugs on EAT dysfunction, LA remodelling, and ultimately AF onset and recurrence.

Integrated Analysis of the microRNA–mRNA Network Predicts Potential Regulators of Atrial Fibrillation in Humans

Atrial fibrillation (AF) is a form of sustained cardiac arrhythmia and microRNAs (miRs) play crucial roles in the pathophysiology of AF. To identify novel miR–mRNA pairs, we performed RNA-seq from atrial biopsies of persistent AF patients and non-AF patients with normal sinus rhythm (SR). Differentially expressed miRs (11 down and 9 up) and mRNAs (95 up and 82 down) were identified and hierarchically clustered in a heat map. Subsequently, GO, KEGG, and GSEA analyses were run to identify deregulated pathways. Then, miR targets were predicted in the miRDB database, and a regulatory network of negatively correlated miR–mRNA pairs was constructed using Cytoscape. To select potential candidate genes from GSEA analysis, the top-50 enriched genes in GSEA were overlaid with predicted targets of differentially deregulated miRs. Further, the protein–protein interaction (PPI) network of enriched genes in GSEA was constructed, and subsequently, GO and canonical pathway analyses were run for genes in the PPI network. Our analyses showed that TNF-α, p53, EMT, and SYDECAN1 signaling were among the highly affected pathways in AF samples. SDC-1 (SYNDECAN-1) was the top-enriched gene in p53, EMT, and SYDECAN1 signaling. Consistently, SDC-1 mRNA and protein levels were significantly higher in atrial samples of AF patients. Among negatively correlated miRs, miR-302b-3p was experimentally validated to suppress SDC-1 transcript levels. Overall, our results suggested that the miR-302b-3p/SDC-1 axis may be involved in the pathogenesis of AF.

A preliminary coronary computed tomography angiography-based study of perivascular fat attenuation index: relation with epicardial adipose tissue and its distribution over the entire coronary vasculature

OBJECTIVES

To investigate the perivascular fat attenuation index (FAI) in association with epicardial adipose tissue (EAT) parameters and its distribution over the entire coronary vasculature in patients with known or suspected coronary artery disease (CAD).

METHODS

Patients with known or suspected CAD who underwent coronary computed tomography angiography from January 1, 2019, to June 1, 2019, were retrospectively included. The perivascular FAI was quantified on four main epicardial coronary arteries and seven coronary segments. Moreover, EAT density and volume were measured.

RESULTS

We included 192 consecutive patients (55 without coronary plaque [mean age 46.4 ± 13.2 years, 69.1% male] and 137 with coronary plaque [mean age 57.9 ± 13.0 years, 84.7% male]). EAT density was lower than perivascular FAI in both groups, but they exhibited substantial correlation (- 83.33 ± 4.54 vs. - 78.22 ± 6.52 HU, p < 0.001; r = 0.667 in plaque- patients and - 83.11 ± 4.48 vs. - 77.81 ± 5.63 HU, p < 0.001; r = 0.778 in plaque+ patients). The left main coronary artery had the highest perivascular FAI, followed by the left circumflex artery. The perivascular FAI in proximal segments was significantly higher compared to that in distal segments (all p < 0.05). Furthermore, the presence of plaque did not alter perivascular FAI on the patient or segmental level.

CONCLUSION

The perivascular FAI was significantly higher than EAT density and correlated substantially with EAT density. The perivascular FAI distribution over the entire coronary tree varied and prompted for vessel-specific or segment-specific thresholds to determine abnormal perivascular FAI in practice.

KEY POINTS

• The perivascular FAI correlated well with EAT density and had higher values than EAT density. • The distributions of perivascular FAI differ between coronary vessels or segments; considering segment and vessel confounding factors while conducting a perivascular FAI study is necessary. • No significant difference of perivascular FAI was observed between patients without and with coronary plaque, nor between coronary segments without plaque and those with plaque.

Multiparametric CMR imaging of myocardial structure and function changes in diabetic mini-pigs with preserved LV function: a preliminary study

Background

The purpose of this study is to dynamically monitor the myocardial structure and function changes in diabetic mini-pigs by 1.5 T cardiac magnetic resonance.

Methods

Three male mini-pigs underwent cardiac magnet resonance (CMR) imaging, and histologic examination. T1-mapping was acquired at basal, mid and apical segments. CMR feature-tracking (CMR-FT) is used to quantify left ventricle global longitudinal (LVGLS), circumferential (LVGCS) and radial strain (LVGRS). Epicardial adipose tissue (EAT) was evaluated using a commercially available software.

Results

Left ventricular mass (LVM), myocardial native T1 value, extracellular volume (ECV) value and EAT were increased gradually after 6 months of modeling, while LVGLS decreased gradually after 6 months of modeling (LVM: 24.5 (23.4, 26.7) vs. 42.7 (41.4, 44.6) g/m², p < 0.001; Native T1: 1005.5 (992.6, 1010.7) vs. 1028.7 (1015.5, 1035.6) ms, p = 0.041; EAT: 16.1 (14.5, 18.2) vs. 24.6 (20.8, 26.9) mL, p = 0.020; ECV: 21.4 (20.2, 23.9) vs. 28.9 (26.7, 30.3) %, p = 0.011; LVGLS: − 22.8 (− 21.4, − 23.9) vs. − 17.4 (− 17.2, − 19.2)%, p = 0.008). The diffuse myocardial interstitial fibrosis was found in histology samples.

Conclusion

The progressive impairments in LV structure and myocardial deformation occurs in diabetic mini-pigs. T1 mapping and CMR-FT technology are promising to monitor abnormal changes of diabetic myocardium in the early stage of diabetic cardiomyopathy.

Meta-Analysis of Non-Alcoholic Fatty Liver Disease and Electromechanical Reconstruction of Myocardium

In developed countries, non-alcoholic fatty liver disease (NAFLD), which results from obesity, has become endemic and kills many adults annually. Health research centers in most countries are looking to examine the relationship between metabolic syndrome (MetS) and metabolic biomarkers. A bleeding-prone standard liver biopsy or costly magnetic resonance imaging scan is used to diagnose NAFLD. The present study aimed to analyze medical databases using various scientific articles; moreover, this experiment analyzed medical databases using published scientific articles related to NAFLD, endovascular treatment, cardiac arrhythmias and conduction disorders, changes in the geometry of atria and ventricles, changes in myocardial mass volume as well as diastolic flow left and right ventricular systolic functions, coronary blood flow, analysis of the dependence of epicardial fat tissue (EFT) thickness, and the presence of chronic heart failure (CHF). It is demonstrated that the index of EFT in NAFLD positively correlated with the criteria of cardiovascular health, values of the carotid intima-media thickness, and calcification of the coronary arteries on the coronary artery calcium scale (P<0.0001). The index of per EFT significantly correlated with the factor of the age of the NAFLD patients (P=0.04), hemoglobin A1C level (P<0.001), systemic inflammatory index (P=0.02), the index of impaired glucose tolerance (P=0.03), and especially, the patient's diabetes factor (P<0.001). In addition, adiponectin levels were significantly lower in individuals with NAFLD (P=0.001) and patients with MetS (P=0.02). NAFLD in association with an increase in epicardial adipose tissue (EAT) is an independent risk factor for atherosclerosis, coronary heart disease, CHF, as well as structural and electrophysiological myocardial remodeling. The study of pathogenetic mechanisms in the context of the role of EAT and clinical monitoring of its condition are urgent problems of modern medicine.

Role of Epicardial Adipose Tissue in Cardiovascular Diseases: A Review

Cardiovascular diseases (CVDs) are the leading causes of death worldwide. Epicardial adipose tissue (EAT) is defined as a fat depot localized between the myocardial surface and the visceral layer of the pericardium and is a type of visceral fat. EAT is one of the most important risk factors for atherosclerosis and cardiovascular events and a promising new therapeutic target in CVDs. In health conditions, EAT has a protective function, including protection against hypothermia or mechanical stress, providing myocardial energy supply from free fatty acid and release of adiponectin. In patients with obesity, metabolic syndrome, or diabetes mellitus, EAT becomes a deleterious tissue promoting the development of CVDs. Previously, we showed an adverse modulation of gene expression in pericoronary adipose tissue in patients with coronary artery disease (CAD). Here, we summarize the currently available evidence regarding the role of EAT in the development of CVDs, including CAD, heart failure, and atrial fibrillation. Due to the rapid development of the COVID-19 pandemic, we also discuss data regarding the association between EAT and the course of COVID-19. Finally, we present the potential therapeutic possibilities aiming at modifying EAT's function. The development of novel therapies specifically targeting EAT could revolutionize the prognosis in CVDs.

Physical Exercise Potentially Targets Epicardial Adipose Tissue to Reduce Cardiovascular Disease Risk in Patients with Metabolic Diseases: Oxidative Stress and Inflammation Emerge as Major Therapeutic Targets

Excess epicardial adiposity, within a state of obesity and metabolic syndrome, is emerging as an important risk factor for the development of cardiovascular diseases (CVDs). Accordingly, increased epicardial fat thickness (EFT) implicates the exacerbation of pathological mechanisms involving oxidative stress and inflammation within the heart, which may accelerate the development of CVDs. This explains increased interest in targeting EFT reduction to attenuate the detrimental effects of oxidative stress and inflammation within the setting of metabolic syndrome. Here, we critically discuss clinical and preclinical evidence on the impact of physical exercise on EFT in correlation with reduced CVD risk within a setting of metabolic disease. This review also brings a unique perspective on the implications of oxidative stress and inflammation as major pathological consequences that link increased EFT to accelerated CVD risk in conditions of metabolic disease.

Are Interactions between Epicardial Adipose Tissue, Cardiac Fibroblasts and Cardiac Myocytes Instrumental in Atrial Fibrosis and Atrial Fibrillation?

Atrial fibrillation is very common among the elderly and/or obese. While myocardial fibrosis is associated with atrial fibrillation, the exact mechanisms within atrial myocytes and surrounding non-myocytes are not fully understood. This review considers the potential roles of myocardial fibroblasts and myofibroblasts in fibrosis and modulating myocyte electrophysiology through electrotonic interactions. Coupling with (myo)fibroblasts in vitro and in silico prolonged myocyte action potential duration and caused resting depolarization; an optogenetic study has verified in vivo that fibroblasts depolarized when coupled myocytes produced action potentials. This review also introduces another non-myocyte which may modulate both myocardial (myo)fibroblasts and myocytes: epicardial adipose tissue. Epicardial adipocytes are in intimate contact with myocytes and (myo)fibroblasts and may infiltrate the myocardium. Adipocytes secrete numerous adipokines which modulate (myo)fibroblast and myocyte physiology. These adipokines are protective in healthy hearts, preventing inflammation and fibrosis. However, adipokines secreted from adipocytes may switch to pro-inflammatory and pro-fibrotic, associated with reactive oxygen species generation. Pro-fibrotic adipokines stimulate myofibroblast differentiation, causing pronounced fibrosis in the epicardial adipose tissue and the myocardium. Adipose tissue also influences myocyte electrophysiology, via the adipokines and/or through electrotonic interactions. Deeper understanding of the interactions between myocytes and non-myocytes is important to understand and manage atrial fibrillation.

Epicardial fat thickness in infants of diabetic mothers

BACKGROUND

Epicardial fat thickness (EFT) in adults and children has been related to the metabolic syndrome and other cardiovascular risk factors; however, scarce studies have evaluated it in infants of diabetic mothers (IDM) in whom, alterations in the thickness of the interventricular septum have been reported. This study compares the EFT in IDM versus infants of non-diabetic mothers (INDM) and its association with others echocardiographic parameters.

METHODS

We performed a cross sectional study in 93 infants (64 IDM and 29 INDM). To evaluate EFT dimensions, an echocardiogram was performed within the first 24h of extrauterine life in both groups. In diabetic mothers, HbA1c was also determined.

RESULTS

There was no significant difference in birth weight between the groups although gestational age was lower in IDM. The EFT (3.6 vs. 2.5 mm, p <  0.0001), the interventricular septum thickness (IVST) (6.2 vs. 5.2 mm, p <  0.0001) and the IVST / left ventricle posterior wall (1.3 vs. 1.1, p = 0.001) were higher in the IDM; while the left ventricular expulsion fraction [LVFE] (71.1 vs. 77.8; p <  0.0001) was lower than in the INDM, respectively. We found a positive correlation between EFT with IVST (r = 0.577; p = 0.0001), LVPW (r = 0.262; p = 0.011), IVST/LVPW index (r = 0.353; p = 0.001), and mitral integral early velocity (r = 0.313; p = 0.002), while a negative correlation with LVFE was observed (r = -0.376; p = 0.0001).

CONCLUSIONS

The EFT is higher in IDM than in INDM. It was positively related with echocardiographic parameters of left ventricular thickness and negatively with left ventricular ejection function.

Regional Heterogeneity of Perivascular Adipose Tissue: Morphology, Origin, and Secretome

Perivascular adipose tissue (PVAT) is a unique fat depot with local and systemic impacts. PVATs are anatomically, developmentally, and functionally different from classical adipose tissues and they are also different from each other. PVAT adipocytes originate from different progenitors and precursors. They can produce and secrete a wide range of autocrine and paracrine factors, many of which are vasoactive modulators. In the context of obesity-associated low-grade inflammation, these phenotypic and functional differences become more evident. In this review, we focus on the recent findings of PVAT’s heterogeneity by comparing commonly studied adipose tissues around the thoracic aorta (tPVAT), abdominal aorta (aPVAT), and mesenteric artery (mPVAT). Distinct origins and developmental trajectory of PVAT adipocyte potentially contribute to regional heterogeneity. Regional differences also exist in ways how PVAT communicates with its neighboring vasculature by producing specific adipokines, vascular tone regulators, and extracellular vesicles in a given microenvironment. These insights may inspire new therapeutic strategies targeting the PVAT.

Dual role for angiotensin-converting enzyme 2 in Severe Acute Respiratory Syndrome Coronavirus 2 infection and cardiac fat

Angiotensin-converting enzyme 2 (ACE2) has been an increasingly prevalent target for investigation since its discovery 20 years ago. The finding that it serves a counterregulatory function within the traditional renin-angiotensin system, implicating it in cardiometabolic health, has increased its clinical relevance. Focus on ACE2's role in cardiometabolic health has largely centered on its apparent functions in the context of obesity. Interest in ACE2 has become even greater with the discovery that it serves as the cell receptor for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), opening up numerous mechanisms for deleterious effects of infection. The proliferation of ACE2 within the literature coupled with its dual role in SARS-CoV-2 infection and obesity necessitates review of the current understanding of ACE2's physiological, pathophysiological, and potential therapeutic functions. This review highlights the roles of ACE2 in cardiac dysfunction and obesity, with focus on epicardial adipose tissue, to reconcile the data in the context of SARS-CoV-2 infection.

Different Expression of Mitochondrial and Endoplasmic Reticulum Stress Genes in Epicardial Adipose Tissue Depends on Coronary Atherosclerosis

The aim of our study was to analyze mitochondrial and endoplasmic reticulum (ER) gene expression profiles in subcutaneous (SAT) and epicardial (EAT) adipose tissue, skeletal muscle, and myocardium in patients with and without CAD undergoing elective cardiac surgery. Thirty-eight patients, 27 with (CAD group) and 11 without CAD (noCAD group), undergoing coronary artery bypass grafting and/or valvular surgery were included in the study. EAT, SAT, intercostal skeletal muscle, and right atrium tissue and blood samples were collected at the start and end of surgery; mRNA expression of selected mitochondrial and ER stress genes was assessed using qRT-PCR. The presence of CAD was associated with decreased mRNA expression of most of the investigated mitochondrial respiratory chain genes in EAT, while no such changes were seen in SAT or other tissues. In contrast, the expression of ER stress genes did not differ between the CAD and noCAD groups in almost any tissue. Cardiac surgery further augmented mitochondrial dysfunction in EAT. In our study, CAD was associated with decreased expression of mitochondrial, but not endoplasmic reticulum stress genes in EAT. These changes may contribute to the acceleration of coronary atherosclerosis.

Exploring the Role of Epicardial Adipose Tissue in Coronary Artery Disease From the Difference of Gene Expression

Objectives

Epicardial adipose tissue (EAT) is closely adjacent to the coronary arteries and myocardium, its role as an endocrine organ to affect the pathophysiological processes of the coronary arteries and myocardium has been increasingly recognized. However, the specific gene expression profiles of EAT in coronary artery disease (CAD) has not been well characterized. Our aim was to investigate the role of EAT in CAD at the gene level.

Methods

Here, we compared the histological and gene expression difference of EAT between CAD and non-CAD. We investigated the gene expression profiles in the EAT of patients with CAD through the high-throughput RNA sequencing. We performed bioinformatics analysis such as functional enrichment analysis and protein-protein interaction network construction to obtain and verify the hub differentially expressed genes (DEGs) in the EAT of CAD.

Results

Our results showed that the size of epicardial adipocytes in the CAD group was larger than in the control group. Our findings on the EAT gene expression profiles of CAD showed a total of 747 DEGs (fold change >2, p value <0.05). The enrichment analysis of DEGs showed that more pro-inflammatory and immunological genes and pathways were involved in CAD. Ten hub DEGs (GNG3, MCHR1, BDKRB1, MCHR2, CXCL8, CXCR5, CCR8, CCL4L1, TAS2R10, and TAS2R41) were identified.

Conclusion

Epicardial adipose tissue in CAD shows unique gene expression profiles and may act as key regulators in the CAD pathological process.

The Role of Brown Adipose Tissue Dysfunction in the Development of Cardiovascular Disease

Brown adipose tissue (BAT), consisted of brown adipocytes and stromal vascular fraction, which includes endothelial cells, lymphocytes, fibroblasts and stem cells, plays a vital role in regulating cardiovascular health and diseases. As a thermogenic organ, BAT can influence body through strengthening energy expenditure by promoting glucose and lipid metabolism. In addition, BAT is also an endocrine organ which is able to secret adipokines in an autocrine and/or paracrine fashion. BAT plays a protective role in cardiovascular system through attenuating cardiac remodeling and suppressing inflammatory response. In this review, we summarize the advances from the discovery of BAT to the present and provide an overview on the role of BAT dysfunction in cardiovascular diseases.

Adipose Tissue Immunomodulation: A Novel Therapeutic Approach in Cardiovascular and Metabolic Diseases

Adipose tissue is a critical regulator of systemic metabolism and bodily homeostasis as it secretes a myriad of adipokines, including inflammatory and anti-inflammatory cytokines. As the main storage pool of lipids, subcutaneous and visceral adipose tissues undergo marked hypertrophy and hyperplasia in response to nutritional excess leading to hypoxia, adipokine dysregulation, and subsequent low-grade inflammation that is characterized by increased infiltration and activation of innate and adaptive immune cells. The specific localization, physiology, susceptibility to inflammation and the heterogeneity of the inflammatory cell population of each adipose depot are unique and thus dictate the possible complications of adipose tissue chronic inflammation. Several lines of evidence link visceral and particularly perivascular, pericardial, and perirenal adipose tissue inflammation to the development of metabolic syndrome, insulin resistance, type 2 diabetes and cardiovascular diseases. In addition to the implication of the immune system in the regulation of adipose tissue function, adipose tissue immune components are pivotal in detrimental or otherwise favorable adipose tissue remodeling and thermogenesis. Adipose tissue resident and infiltrating immune cells undergo metabolic and morphological adaptation based on the systemic energy status and thus a better comprehension of the metabolic regulation of immune cells in adipose tissues is pivotal to address complications of chronic adipose tissue inflammation. In this review, we discuss the role of adipose innate and adaptive immune cells across various physiological and pathophysiological states that pertain to the development or progression of cardiovascular diseases associated with metabolic disorders. Understanding such mechanisms allows for the exploitation of the adipose tissue-immune system crosstalk, exploring how the adipose immune system might be targeted as a strategy to treat cardiovascular derangements associated with metabolic dysfunctions.

Functional characterization of human brown adipose tissue metabolism

Brown adipose tissue (BAT) has long been described according to its histological features as a multilocular, lipid-containing tissue, light brown in color, that is also responsive to the cold and found especially in hibernating mammals and human infants. Its presence in both hibernators and human infants, combined with its function as a heat-generating organ, raised many questions about its role in humans. Early characterizations of the tissue in humans focused on its progressive atrophy with age and its apparent importance for cold-exposed workers. However, the use of positron emission tomography (PET) with the glucose tracer [18F]fluorodeoxyglucose ([18F]FDG) made it possible to begin characterizing the possible function of BAT in adult humans, and whether it could play a role in the prevention or treatment of obesity and type 2 diabetes (T2D). This review focuses on the in vivo functional characterization of human BAT, the methodological approaches applied to examine these features and addresses critical gaps that remain in moving the field forward. Specifically, we describe the anatomical and biomolecular features of human BAT, the modalities and applications of non-invasive tools such as PET and magnetic resonance imaging coupled with spectroscopy (MRI/MRS) to study BAT morphology and function in vivo, and finally describe the functional characteristics of human BAT that have only been possible through the development and application of such tools.

Inflammation and adiposity: new frontiers in atrial fibrillation

The aetiology of atrial fibrillation (AF) remains poorly understood, despite its growing prevalence and associated morbidity, mortality, and healthcare costs. Obesity is implicated in myriad different disease processes and is now recognized a major risk factor in the pathogenesis of AF. Moreover, the role of distinct adipose tissue depots is a matter of intense scientific interest with the depot directly surrounding the heart—epicardial adipose tissue (EAT) appearing to have the greatest correlation with AF presence and severity. Similarly, inflammation is implicated in the pathophysiology of AF with EAT thought to act as a local depot of inflammatory mediators. These can easily diffuse into atrial tissue with the potential to alter its structural and electrical properties. Various meta-analyses have indicated that EAT size is an independent risk factor for AF with adipose tissue expansion being inevitably associated with a local inflammatory process. Here, we first briefly review adipose tissue anatomy and physiology then move on to the epidemiological data correlating EAT, inflammation, and AF. We focus particularly on discussing the mechanistic basis of how EAT inflammation may precipitate and maintain AF. Finally, we review how EAT can be utilized to help in the clinical management of AF patients and discuss future avenues for research.

Insulin sensing by astrocytes is critical for normal thermogenesis and body temperature regulation

The important role of astrocytes in the central control of energy balance and glucose homeostasis has recently been recognized. Changes in thermoregulation can lead to metabolic dysregulation, but the role of astrocytes in this process is not yet clear. Therefore, we generated mice congenitally lacking insulin receptors (Ir) in astrocytes (IrKOGFAP mice) to investigate the involvement of astrocyte insulin signaling. IrKOGFAP mice displayed significantly lower energy expenditure and a strikingly lower basal and fasting body temperature. When exposed to cold, however, they were able to mount a thermogenic response. IrKOGFAP mice displayed sex differences in metabolic function and thermogenesis that may contribute to the development of obesity and type II diabetes as early as 2 months of age. While brown adipose tissue exhibited higher adipocyte size in both sexes, more apoptosis was seen in IrKOGFAP males. Less innervation and lower BAR3 expression levels were also observed in IrKOGFAP brown adipose tissue. These effects have not been reported in models of astrocyte Ir deletion in adulthood. In contrast, body weight and glucose regulatory defects phenocopied such models. These findings identify a novel role for astrocyte insulin signaling in the development of normal body temperature control and sympathetic activation of BAT. Targeting insulin signaling in astrocytes has the potential to serve as a novel target for increasing energy expenditure.

Human Brown Adipocyte Thermogenesis Is Driven by β2-AR Stimulation

Stimulation of brown adipose tissue (BAT) thermogenesis in humans has emerged as an attractive target to improve metabolic health. Pharmacological stimulations targeting the β₃-adrenergic receptor (β₃-AR), the adrenergic receptor believed to mediate BAT thermogenesis, have historically performed poorly in human clinical trials. Here we report that, in contrast to rodents, human BAT thermogenesis is not mediated by the stimulation of β₃-AR. Oral administration of the β₃-AR agonist mirabegron only elicited increases in BAT thermogenesis when ingested at the maximal allowable dose. This led to off-target binding to β₁-AR and β₂-AR, thereby increasing cardiovascular responses and white adipose tissue lipolysis, respectively. ADRB2 was co-expressed with UCP1 in human brown adipocytes. Pharmacological stimulation and inhibition of the β₂-AR as well as knockdown of ADRB1, ADRB2, or ADRB3 in human brown adipocytes all confirmed that BAT lipolysis and thermogenesis occur through β₂-AR signaling in humans (ClinicalTrials.govNCT02811289).

Cerasus humilis Cherry Polyphenol Reduces High-Fat Diet-Induced Obesity in C57BL/6 Mice by Mitigating Fat Deposition, Inflammation, and Oxidation

This study aimed to determine the anti-obesity effects and mechanisms of Cerasus humilis polyphenol (CHP) in C57BL/6 obese mice and 3T3-L1 cells. High-performance liquid chromatography-electrospray ionization-tandem mass spectrometry was used for the qualitative and quantitative identification of CHP components. The obese mice, induced by feeding high-fat diet (HFD), were treated with CHP (250 mg/kg/day) by gavage for 12 weeks. Orlistat was gavaged at 15.6 mg/kg bw/day, as a positive control group. The analysis revealed that the main components of CHP were procyanidin B2, cyanidin-3-glucoside, and pelargonidin-3-glucoside. CHP dietary supplementation significantly reduced body weight and improved blood lipid measurements in HFD-fed mice (p < 0.01). Moreover, it inhibited mRNA expression of miR-122, Srebp-1c, and Cpt1a (p < 0.01) and reduced hepatic lipid deposition, as seen by hematoxylin and eosin staining. CHP downregulated the protein expression of PPARγ and C/EBPα in HFD-induced obese mice and inhibited adipocyte differentiation (p < 0.01). Compared with the HFD group, CHP supplementation had an obvious anti-inflammatory effect (decreased protein expression, such as TNF-α, IL-6, and MCP1), reducing leptin levels and TNF-α secretion in serum and cells (p < 0.01). CHP significantly inhibited the expression of miR-27a/b (53.3 and 29.9%, p < 0.01) in mice retroperitoneal white adipocytes, enhancing the expression of the target gene Prdm16 and significantly upregulating Sirt1 (105.5%, p < 0.01) compared with the HFD group. Moreover, CHP supplementation effectively improved oxidative stress (ROS, T-AOC, SOD, CAT, and GSH-Px) induced by HFD in obese mice (p < 0.01). Thus, CHP mitigates adipocyte differentiation, browning of white adipocytes, and reduction of inflammation and antioxidant activity to reduce obesity. Consequently, these results provide novel insights into the anti-obesity roles of CHP in HFD-induced obesity.

Comprehensive analysis of differential immunocyte infiltration and the potential ceRNA networks during epicardial adipose tissue development in congenital heart disease

Background

To detect the development, function and therapeutic potential of epicardial adipose tissue (EAT); analyze a related gene expression dataset, including data from neonates, infants, and children with congenital heart disease (CHD); compare the data to identify the codifferentially expressed (DE) mRNAs and lncRNAs and the corresponding miRNAs; generate a potential competitive endogenous RNA (ceRNA) network; and assess the involvement of immunocyte infiltration in the development of the EAT.

Methods

Multiple algorithms for linear models for microarray data algorithms (LIMMA), CIBERSORT, gene-set enrichment analysis (GSEA), and gene set variation analysis (GSVA) were used. The miRcode, miRDB, miRTarBase, and TargetScan database were used to construct the ceRNA network. The Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analyses of the DE mRNAs were performed.

Results

Thirteen co-DE mRNAs and 47 co-DE lncRNAs were subsequently identified. The related categories included negative regulation of myoblast differentiation, regulation of ion transmembrane transport, and heart development, which were primarily identified for further pathway enrichment analysis. Additionally, the hub ceRNA network in EAT development involving MIR210HG, hsa-miR-449c-5p, and CACNA2D4 was generated and shown to target monocyte infiltration.

Conclusion

These findings suggest that the pathways of myoblast differentiation and ion transmembrane transport may be potential hub pathways involved in EAT development in CHD patients. In addition, the network includes monocytes, MIR210HG, and CACNA2D4, which were shown to target the RIG-I-like receptor signaling pathway and PPAR signaling pathway, indicating that these factors may be novel regulators and therapeutic targets in EAT development.

Acute interaction between human epicardial adipose tissue and human atrial myocardium induces arrhythmic susceptibility

Epicardial adipose tissue (EAT) deposition has a strong clinical association with atrial arrhythmias; however, whether a direct functional interaction exists between EAT and the myocardium to induce atrial arrhythmias is unknown. Therefore, we aimed to determine whether human EAT can be an acute trigger for arrhythmias in human atrial myocardium. Human trabeculae were obtained from right atrial appendages of patients who have had cardiac surgery (n = 89). The propensity of spontaneous contractions (SCs) in the trabeculae (proxy for arrhythmias) was determined under physiological conditions and during known triggers of SCs (high Ca²⁺, β-adrenergic stimulation). To determine whether EAT could trigger SCs, trabeculae were exposed to superfusate of fresh human EAT, and medium of 24 h-cultured human EAT treated with β_1/2 (isoproterenol) or β₃ (BRL37344) adrenergic agonists. Without exposure to EAT, high Ca²⁺ and β_1/2-adrenergic stimulation acutely triggered SCs in, respectively, 47% and 55% of the trabeculae that previously were not spontaneously active. Acute β₃-adrenergic stimulation did not trigger SCs. Exposure of trabeculae to either superfusate of fresh human EAT or untreated medium of 24 h-cultured human EAT did not induce SCs; however, specific β₃-adrenergic stimulation of EAT did trigger SCs in the trabeculae, either when applied to fresh (31%) or cultured (50%) EAT. Additionally, fresh EAT increased trabecular contraction and relaxation, whereas media of cultured EAT only increased function when treated with the β₃-adrenergic agonist. An acute functional interaction between human EAT and human atrial myocardium exists that increases the propensity for atrial arrhythmias, which depends on β₃-adrenergic rather than β_1/2-adrenergic stimulation of EAT.

Depot-specific UCP1 expression in human white adipose tissue and its association with obesity-related markers

BACKGROUND

This study investigated depot-specific mRNA expression of uncoupling protein 1 (UCP1) in human white adipose tissue (WAT) and its association with obesity-related markers.

METHODS

We recruited 39 normal-weight, 41 nondiabetic obese, and 22 diabetic obese women. We measured UCP1 mRNA expression in abdominal visceral adipose tissue (VAT) and subcutaneous adipose tissue (SAT), and investigated the associations between UCP1 mRNA expression in VAT and SAT, and obesity-related markers including mRNA expression of leptin, adiponectin, CCAAT-enhancer-binding protein homologous protein (CHOP), and positive regulatory domain-containing protein 16 (PRDM16). We also evaluated UCP1 mRNA expression in differentiated human white adipocytes after treatment with various stressors and metabolic improvement agents in vitro.

RESULTS

UCP1 mRNA in VAT was significantly higher than in SAT in all groups. UCP1 mRNA in SAT was negatively correlated with BMI, total abdominal fat area, visceral fat area, blood pressure, fasting glucose, insulin, HOMA-IR score, triglyceride, hsCRP, fasting leptin levels, and adipocyte size. UCP1 mRNA in SAT was positively correlated with fasting adiponectin levels. UCP1 mRNA in VAT was negatively correlated with visceral-to-subcutaneous fat ratio (VSR), fasting glucose, and triglyceride levels. In SAT, UCP1 mRNA was negatively correlated with mRNA expression of leptin and CHOP, and positively correlated with mRNA expression of adiponectin. The expression of PRDM16 was positively correlated with UCP1 mRNA in both VAT and SAT. UCP1 mRNA expression in differentiated human white adipocytes was significantly reduced after incubation with thapsigargin, tunicamycin, homocysteine, TNF-α, or IL-β, and significantly increased after incubation with exendin 4, dapagliflozin, and telmisartan.

CONCLUSIONS

This study demonstrated depot-specific mRNA expression of UCP1 and its association with obesity-related markers in human WAT. UCP1 mRNA in human white adipocytes was suppressed by inflammatory agents and enhanced by metabolic improvement agents. UCP1 in human WAT might participate in the pathogenesis of obesity-related metabolic diseases.

The role of adipose tissue in cardiovascular health and disease

Accumulating knowledge on the biology and function of the adipose tissue has led to a major shift in our understanding of its role in health and disease. The adipose tissue is now recognized as a crucial regulator of cardiovascular health, mediated by the secretion of several bioactive products, including adipocytokines, microvesicles and gaseous messengers, with a wide range of endocrine and paracrine effects on the cardiovascular system. The adipose tissue function and secretome are tightly controlled by complex homeostatic mechanisms and local cell-cell interactions, which can become dysregulated in obesity. Systemic or local inflammation and insulin resistance lead to a shift in the adipose tissue secretome from anti-inflammatory and anti-atherogenic towards a pro-inflammatory and pro-atherogenic profile. Moreover, the interplay between the adipose tissue and the cardiovascular system is bidirectional, with vascular-derived and heart-derived signals directly affecting adipose tissue biology. In this Review, we summarize the current knowledge of the biology and regional variability of adipose tissue in humans, deciphering the complex molecular mechanisms controlling the crosstalk between the adipose tissue and the cardiovascular system, and their possible clinical translation. In addition, we highlight the latest developments in adipose tissue imaging for cardiovascular risk stratification and discuss how therapeutic targeting of the adipose tissue can improve prevention and treatment of cardiovascular disease.

The emerging roles of lactate as a redox substrate and signaling molecule in adipose tissues

Thermogenic (brown and beige) adipose tissues improve glucose and lipid homeostasis and therefore represent putative targets to cure obesity and related metabolic diseases including type II diabetes. Beside decades of research and the very well-described role of noradrenergic signaling, mechanisms underlying adipocytes plasticity and activation of thermogenic adipose tissues remain incompletely understood. Recent studies show that metabolites such as lactate control the oxidative capacity of thermogenic adipose tissues. Long time viewed as a metabolic waste product, lactate is now considered as an important metabolic substrate largely feeding the oxidative metabolism of many tissues, acting as a signaling molecule and as an inter-cellular and inter-tissular redox carrier. In this review, we provide an overview of the recent findings highlighting the importance of lactate in adipose tissues, from its production to its role as a browning inducer and its metabolic links with brown adipose tissue. We also discuss additional function(s) than thermogenesis ensured by brown and beige adipose tissues, i.e., their ability to dissipate high redox pressure and oxidative stress thanks to the activity of the uncoupling protein-1, helping to maintain tissue and whole organism redox homeostasis and integrity.

Epicardial adipose tissue: an emerging biomarker of cardiovascular complications in type 2 diabetes?

Type 2 diabetes (T2D) is associated with an increased risk of cardiovascular disease and heart failure, which highlights the need for improved understanding of factors contributing to the pathophysiology of these complications as they are the leading cause of mortality in T2D. Patients with T2D have high levels of epicardial adipose tissue (EAT). EAT is known to secrete inflammatory factors, lipid metabolites, and has been proposed to apply mechanical stress on the cardiac muscle that may accelerate atherosclerosis, cardiac remodeling, and heart failure. High levels of EAT in patients with T2D have been associated with atherosclerosis, diastolic dysfunction, and incident cardiovascular events, and this fat depot has been suggested as an important link coupling diabetes, obesity, and cardiovascular disease. Despite this, the predictive potential of EAT in general, and in patients with diabetes, is yet to be established, and, up until now, the clinical relevance of EAT is therefore limited. Should this link be established, importantly, studies show that this fat depot can be modified both by pharmacological and lifestyle interventions. In this review, we first introduce the role of adipose tissue in T2D and present mechanisms involved in the pathophysiology of EAT and pericardial adipose tissue (PAT) in general, and in patients with T2D. Next, we summarize the evidence that these fat depots are elevated in patients with T2D, and discuss whether they might drive the high cardiometabolic risk in patients with T2D. Finally, we discuss the clinical potential of cardiac adipose tissues, address means to target this depot, and briefly touch upon underlying mechanisms and future research questions.

Novel imaging biomarkers: epicardial adipose tissue evaluation

Epicardial adipose tissue (EAT) is a metabolically activated beige adipose tissue, non-homogeneously surrounding the myocardium. Physiologically, EAT regulates toxic fatty acids, protects the coronary arteries against mechanical strain, regulates proinflammatory cytokines, stimulates the production of nitric oxide, reduces oxidative stress, and works as a thermogenic source against hypothermia. Conversely, EAT has pathologic paracrine interactions with the surrounded vessels, and might favour the onset of atrial fibrillation. In addition, initial atherosclerotic lesions can promote inflammation and trigger the EAT production of cytokines increasing vascular inflammation, which, in turn, may help the development of collateral vessels but also of self-stimulating, dysregulated inflammatory process, increasing coronary artery disease severity. Variations in EAT were also linked to metabolic syndrome. Echocardiography first estimated EAT measuring its thickness on the free wall of the right ventricle but does not allow accurate volumetric EAT estimates. Cardiac CT (CCT) and cardiac MR (CMR) allow for three-dimensional EAT estimates, the former showing higher spatial resolution and reproducibility but being limited by radiation exposure and long segmentation times, the latter being radiation-free but limited by lower spatial resolution and reproducibility, higher cost, and difficulties for obese patients. EAT radiodensity at CCT could to be related to underlying metabolic processes. The correlation between EAT and response to certain pharmacological therapies has also been investigated, showing promising results. In the future, semi-automatic or fully automatic techniques, machine/deep-learning methods, if validated, will facilitate research for various EAT measures and may find a place in CCT/CMR reporting.

Statins Reduce Epicardial Adipose Tissue Attenuation Independent of Lipid Lowering: A Potential Pleiotropic Effect

Background

High epicardial adipose tissue (EAT) attenuation (Hounsfield units [HUs]) on computed tomography is considered a marker of inflammation and is associated with an increased risk of cardiovascular events. Statins reduce the volume of EAT, but it is unknown whether they affect EAT HUs.

Methods and Results

We reviewed the chest computed tomographic scans of 420 postmenopausal women randomized to either 80 mg of atorvastatin or 40 mg of pravastatin daily and rescanned after 1 year to measure change in coronary artery calcium score. EAT HUs were measured near the proximal right coronary artery and remote from any area of coronary artery calcium. Computed tomographic images were also queried for subcutaneous adipose tissue (SubQ) attenuation (HUs) change over time. The mean patients’ age was 65±6 years. The baseline EAT HU value was higher than the SubQ HU value (−89.4±24.0 HU versus −123.3±30.4 HU; P<0.001). The EAT HU value decreased significantly in the entire cohort (−5.4±29.7 HU [−6% change]; P<0.001), but equally in the patients given atorvastatin and pravastatin (−6.35+31 HU and −4.55+28 HU; P=0.55). EAT HU change was not associated with change in total cholesterol, low‐density lipoprotein cholesterol, coronary artery calcium, and EAT volume (all P=not significant). Change in high‐density lipoprotein cholesterol was marginally associated with EAT HU change (P=0.07). Statin treatment did not induce a change in SubQ HUs.

Conclusions

Statins induced a decrease in EAT HUs over time, independent of intensity of low‐density lipoprotein cholesterol lowering. The positive effect on EAT and the neutral effect on SubQ suggest that statins induced a decrease in metabolic activity in EAT by reduction in cellularity, vascularity, or inflammation. The clinical significance of the observed change in EAT HUs remains to be demonstrated.

UCP1 expression-associated gene signatures of human epicardial adipose tissue

Multiple reports of uncoupling protein 1 (UCP1) expression have established its presence in human epicardial adipose tissue (eAT). Its functional relevance to eAT, however, remains largely unknown. In a recent study, we reported that adrenergic stimulation of eAT was associated with downregulation of secreted proteins involved in oxidative stress-related and immune-related pathways. Here, we explored the UCP1-associated features of human eAT using next-generation deep sequencing. Paired biopsies of eAT, mediastinal adipose tissue (mAT), and subcutaneous adipose tissue (sAT) obtained from cardiac surgery patients, with specific criteria of high and low expression of UCP1 in eAT, were subjected to RNA sequencing. Although eAT exhibited a depot-specific upregulation in the immune-related pathways relative to mAT and sAT, high UCP1 expression in eAT was specifically associated with differential gene expression that functionally corresponded with downregulation in the production of reactive oxygen species and immune responses, including T cell homeostasis. Our data indicate that UCP1 and adaptive immunity share a reciprocal relationship at the whole-transcriptome level, thereby supporting a plausible role for UCP1 in maintaining tissue homeostasis in human eAT.

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.

Inflammation of brown/beige adipose tissues in obesity and metabolic disease

Many of the comorbidities of obesity, including type 2 diabetes and cardiovascular diseases, are related to the low-grade chronic inflammation of white adipose tissue. Under white adipocyte stress, local infiltration of immune cells and enhanced production of pro-inflammatory cytokines together reduce metabolic flexibility and lead to insulin resistance in obesity. Whereas white adipocytes act in energy storage, brown and beige adipocytes specialize in energy expenditure. Brown and beige activity protects against obesity and associated metabolic disorders, such as hyperglycaemia and hyperlipidaemia. Compared to white fat, brown adipose tissue depots are less susceptible to developing local inflammation in response to obesity; however, strong obesogenic insults ultimately induce a locally pro-inflammatory environment in brown fat. This condition directly alters the thermogenic activity of brown fat by impairing its energy expenditure mechanism and uptake of glucose for use as a fuel substrate. Pro-inflammatory cytokines also impair beige adipogenesis, which occurs mainly in subcutaneous adipose tissue. There is evidence that inflammatory processes occurring in perivascular adipose tissues alter their brown-versus-white plasticity, impair the extent of browning in these depots and favour the local release of vasculature damaging signals. In summary, the targeting of brown and beige adipose tissues by pro-inflammatory signals and the subsequent impairment of their thermogenic and metabolite draining activities appears to represent obesity-driven disturbances that contribute to metabolic syndrome and cardiovascular alterations in obesity.

Uncoupling proteins as a therapeutic target to protect the diabetic heart

Myocardial remodeling and dysfunction caused by accelerated oxidative damage is a widely reported phenomenon within a diabetic state. Altered myocardial substrate preference appears to be the major cause of enhanced oxidative stress-mediated cell injury within a diabetic heart. During this process, exacerbated free fatty acid flux causes an abnormal increase in mitochondrial membrane potential leading to the overproduction of free radical species and subsequent cell damage. Uncoupling proteins (UCPs) are expressed within the myocardium and can protect against free radical damage by modulating mitochondrial respiration, leading to reduced production of reactive oxygen species. Moreover, transgenic animals lacking UCPs have been shown to be more susceptible to oxidative damage and display reduced cardiac function when compared to wild type animals. This suggests that tight regulation of UCPs is necessary for normal cardiac function and in the prevention of diabetes-induced oxidative damage. This review aims to enhance our understanding of the pathophysiological mechanisms relating to the role of UCPs in a diabetic heart, and further discuss known pharmacological compounds and hormones that can protect a diabetic heart through the modulation of UCPs.

Brown adipose tissue development and function and its impact on reproduction

Although brown adipose tissue (BAT) is one of the smallest organs in the body, it has the potential to have a substantial impact on both heat production as well as fat and carbohydrate metabolism. This is most apparent at birth, which is characterised with the rapid appearance and activation of the BAT specific mitochondrial uncoupling protein (UCP)1 in many large mammals. The amount of brown fat then gradually declines with age, an adaptation that can be modulated by the thermal environment. Given the increased incidence of maternal obesity and its potential transmission to the mother's offspring, increasing BAT activity in the mother could be one mechanism to prevent this cycle. To date, however, all rodent studies investigating maternal obesity have been conducted at standard laboratory temperature (21°C), which represents an appreciable cold challenge. This could also explain why offspring weight is rarely increased, suggesting that future studies would benefit from being conducted at thermoneutrality (~28°C). It is also becoming apparent that each fat depot has a unique transcriptome and show different developmental pattern, which is not readily apparent macroscopically. These differences could contribute to the retention of UCP1 within the supraclavicular fat depot, the most active depot in adult humans, increasing heat production following a meal. Despite the rapid increase in publications on BAT over the past decade, the extent to which modifications in diet and/or environment can be utilised to promote its activity in the mother and/or her offspring remains to be established.

Brown and beige fat: From molecules to physiology and pathophysiology

The adipose organ portrays adipocytes of diverse tones: white, brown and beige, each type with distinct functions. Adipocytes orchestrate their adaptation and expansion to provide storage to excess nutrients, the quick mobilisation of fuel to supply peripheral functional demands, insulation, and, in their thermogenic form, heat generation to maintain core body temperature. Thermogenic adipocytes could be targets for anti-obesity and anti-diabetic therapeutic approaches aiming to restore adipose tissue functionality and increase energy dissipation. However, for thermogenic adipose tissue to become therapeutically relevant, a better understanding of its development and origins, its progenitors and their characteristics and the composition of its niche, is essential. Also crucial is the identification of stimuli and molecules promoting its specific differentiation and activation. Here we highlight the structural/cellular differences between human and rodent brown adipose tissue and discuss how obesity and metabolic complication affects brown and beige cells as well as how they could be targeted to improve their activation and improve global metabolic homeostasis. Finally, we describe the limitations of current research models and the advantages of new emerging approaches.

Neck adipose tissue - tying ties in metabolic disorders

Upper body adipose tissue accumulation has been associated with clustering of metabolic disorders and increased cardiovascular risk. Neck circumference (NC) indicated that subcutaneous adipose tissue (SAT) in that region is an independent pathogenic depot that might account for the additional risk missed by visceral adipose tissue (VAT). Neck adipose tissue (NAT) is not only one more ectopic depot but has several particular features that might modulate its metabolic role. Besides a controversial impact on obstructive apnea syndrome, neck fat encompasses carotid arteries as an important perivascular adipose tissue (PVAT) depot. With dysfunctional changes in obesity, physiologic vascular regulation is lost and inflammatory signals accelerate atherogenesis. Unexpected was the discovery of brown and beige adipocytes in the neck of human adults. When stimulated, brown adipose tissue (BAT) dissipates energy through thermogenesis and it is associated with other favorable metabolic effects. Moreover, the neck is the region where the browning mechanism was disclosed. With this unique plastic nature, NAT revealed multiple ties, challenging dynamics and potential new therapeutic targets that might have significant implications on metabolic outcomes and vascular risk.