Human mediastinal adipose tissue displays certain characteristics of brown fat

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.

White adipocyte dysfunction and obesity-associated pathologies in humans

The prevalence of obesity and associated chronic diseases continues to increase worldwide, negatively impacting on societies and economies. Whereas the association between excess body weight and increased risk for developing a multitude of diseases is well established, the initiating mechanisms by which weight gain impairs our metabolic health remain surprisingly contested. In order to better address the myriad of disease states associated with obesity, it is essential to understand adipose tissue dysfunction and develop strategies for reinforcing adipocyte health. In this Review we outline the diverse physiological functions and pathological roles of human white adipocytes, examining our current knowledge of why white adipocytes are vital for systemic metabolic control, yet poorly adapted to our current obesogenic environment.

Severity of coronary artery disease is associated with diminished circANRIL expression: A possible blood based transcriptional biomarker in East Africa

Antisense Noncoding RNA in the INK4 Locus (ANRIL) is the prime candidate gene at Chr9p21, the well-defined genetic risk locus associated with coronary artery disease (CAD). ANRIL and its transcript variants were investigated for the susceptibility to CAD in adipose tissues (AT) and peripheral blood mononuclear cells (PBMCs) of the study group and the impact of 9p21.3 locus mutations was further analysed. Expressions of ANRIL, circANRIL (hsa_circ_0008574), NR003529, EU741058 and DQ485454 were detected in epicardial AT (EAT) mediastinal AT (MAT), subcutaneous AT (SAT) and PBMCs of CAD patients undergoing coronary artery bypass grafting and non-CAD patients undergoing heart valve surgery. ANRIL expression was significantly upregulated, while the expression of circANRIL was significantly downregulated in CAD patients. Decreased circANRIL levels were significantly associated with the severity of CAD and correlated with aggressive clinical characteristics. rs10757278 and rs10811656 were significantly associated with ANRIL and circANRIL expressions in AT and PBMCs. The ROC-curve analysis suggested that circANRIL has high diagnostic accuracy (AUC: 0.9808, cut-off: 0.33, sensitivity: 1.0, specificity: 0.88). circANRIL has high diagnostic accuracy (AUC: 0.9808, cut-off: 0.33, sensitivity: 1.0, specificity: 0.88). We report the first data demonstrating the presence of ANRIL and its transcript variants expressions in the AT and PBMCs of CAD patients. circANRIL having a synergetic effect with ANRIL plays a protective role in CAD pathogenesis. Therefore, altered circANRIL expression may become a potential diagnostic transcriptional biomarker for early CAD diagnosis.

The quantity and quality of cardiovascular fat at mid-life and future cognitive performance among women: The SWAN cardiovascular fat ancillary study

INTRODUCTION

Cardiovascular fat is a novel risk factor that may link to dementia. Fat volume and radiodensity are measurements of fat quantity and quality, respectively. Importantly, high fat radiodensity could indicate healthy or adverse metabolic processes.

METHODS

The associations of cardiovascular fat (including epicardial, paracardial, and thoracic perivascular adipose tissue [PVAT]) quantity and quality assessed at mean age of 51 with subsequent cognitive performance measured repeatedly over 16 years of follow-up were examined using mixed models among 531 women.

RESULTS

Higher thoracic PVAT volume was associated with a higher future episodic memory (β[standard error (SE)] = 0.08 [0.04], P = 0.033), while higher thoracic PVAT radiodensity with lower future episodic (β[SE] = -0.06 [0.03], P = 0.045) and working (β[SE] = -0.24 [0.08], P = 0.003) memories. The latter association is prominent at higher volume of thoracic PVAT.

DISCUSSION

Mid-life thoracic PVAT may have a distinct contribution to future cognition possibly due to its distinct adipose tissue type (brown fat) and anatomical proximity to the brain circulation.

HIGHLIGHTS

Higher mid-life thoracic perivascular adipose tissue (thoracic PVAT) volume is related to a better future episodic memory in women. Higher mid-life thoracic PVAT radiodensity is related to worse future working and episodic memories. Negative association of high thoracic PVAT radiodensity with working memory is prominent at higher thoracic PVAT volume. Mid-life thoracic PVAT is linked to future memory loss, an early sign of Alzheimer's disease. Mid-life women's epicardial and paracardial fat are not related to future cognition.

Of mice and men: Pinpointing species differences in adipose tissue biology

The prevalence of obesity and metabolic diseases continues to rise, which has led to an increased interest in studying adipose tissue to elucidate underlying disease mechanisms. The use of genetic mouse models has been critical for understanding the role of specific genes for adipose tissue function and the tissue’s impact on other organs. However, mouse adipose tissue displays key differences to human fat, which has led, in some cases, to the emergence of some confounding concepts in the adipose field. Such differences include the depot-specific characteristics of visceral and subcutaneous fat, and divergences in thermogenic fat phenotype between the species. Adipose tissue characteristics may therefore not always be directly compared between species, which is important to consider when setting up new studies or interpreting results. This mini review outlines our current knowledge about the cell biological differences between human and mouse adipocytes and fat depots, highlighting some examples where inadequate knowledge of species-specific differences can lead to confounding results, and presenting plausible anatomic explanations that may underlie the differences. The article thus provides critical insights and guidance for researchers working primarily with only human or mouse fat tissue, and may contribute to new ideas or concepts in the important and evolving field of adipose biology.

Preparation of Cell-Seeded Heart Patch In Vitro; Co-Culture of Adipose-Derived Mesenchymal Stem Cell and Cardiomyocytes in Amnion Bilayer Patch

INTRODUCTION

Cardiovascular disease is the second killer across the globe, while coronary disease is the major cause. Cell therapy is one alternative to regenerate the infarcted heart wall.

MATERIALS AND METHODS

In this study, the cardiomyogenesis capacity of human adipose stem cells (hAdSC) and human cardiomyocytes (hCardio) cultured in a 3-D biological scaffold (decellularised amnion bilayer) for nine days in a static condition was investigated. The cardiomyogenesis capacity of hAdSC were identified using immunohistochemistry and RT-PCR. The population of the cells isolated from the heart tissue expressed cTnT-1 (13.38 ± 11.38%), cKit (7.85 ± 4.2%), ICAM (85.53 ± 8.69%), PECAM (61.63 ± 7.18%) and VCAM (35.9 ± 9.11%), while from the fat tissue expressed the mesenchymal phenotypes (CD73, CD90, CD105, but not CD45, CD34, CD11b, CD19 and HLA-DR). Two age groups of hAdSC donors were compared, the youngsters (30-40yo) and the elderly (60-70 yo).

RESULTS

The co-culture showed that after 5-day incubation, the seeded graft in the hAdSC-30 group had a tube-like appearance while the hAdSC-60 group demonstrated a disorganised pattern, despite of the MSC expressions of the hAdSC-60 were significantly higher. Initial co-culture showed no difference of ATP counts among all groups, however the hAdSC-30 group had the highest ATP count after 9 days culture (p = 0.004). After normalising to the normal myocardium, only the hAdSC-60 group expressed cTnT and MHC, very low, seen during the initial cultivation, but then disappeared. Meanwhile, the hAdSC-30 group expressed α-actinin, MHC and cTnT in the Day-5. The PPAR also was higher in the Day-5 compared to the Day-9 (p < 0.005).

CONCLUSION

Cardiomyogenesis capacity of hAdSC co-cultured with hCardio in a 3-D scaffold taken from the 30-40yo donor showed better morphology and viability than the 60-70yo group, but maintained less than 5 days in this system.

Defining the lineage of thermogenic perivascular adipose tissue

Brown adipose tissue can expend large amounts of energy, and therefore increasing its size or activity is a promising therapeutic approach to combat metabolic disease. In humans, major deposits of brown fat cells are found intimately associated with large blood vessels, corresponding to perivascular adipose tissue (PVAT). However, the cellular origins of PVAT are poorly understood. Here, we determine the identity of perivascular adipocyte progenitors in mice and humans. In mice, thoracic PVAT develops from a fibroblastic lineage, consisting of progenitor cells (Pdgfra+, Ly6a+ and Pparg-) and preadipocytes (Pdgfra+, Ly6a+ and Pparg+), which share transcriptional similarity with analogous cell types in white adipose tissue. Interestingly, the aortic adventitia of adult animals contains a population of adipogenic smooth muscle cells (Myh11+, Pdgfra- and Pparg+) that contribute to perivascular adipocyte formation. Similarly, human PVAT contains presumptive fibroblastic and smooth muscle-like adipocyte progenitor cells, as revealed by single-nucleus RNA sequencing. Together, these studies define distinct populations of progenitor cells for thermogenic PVAT, providing a foundation for developing strategies to augment brown fat activity.

Homeobox A5 and C10 genes modulate adaptation of brown adipose tissue during exercise training in juvenile rats

NEW FINDINGS

What is the central question of this study? Exercise can stimulate brown adipose tissue (BAT) with subsequent increase in uncoupling protein 1 expression and mitochondrial biogenesis. In that case, do BAT-specific Hox genes modify BAT functioning and cause uncoupling protein expression changes due to exercise? What is the main finding and its importance? Exercise enhanced brown adipocyte markers, with significant upregulation of HoxA5 and downregulation of HoxC10 mRNA expression in rat BAT. HoxA5 and HoxC10 are thus likely to play distinct roles in exercise-induced changes in BAT markers during the early postnatal period. These findings provide new insight into the mechanisms underlying exercise-induced changes in BAT function.

ABSTRACT

Brown adipose tissue (BAT) recruitment is involved in increased energy expenditure associated with cold exposure and exercise training. We explored whether exercise training induced changes in expression levels of brown adipocyte-selective factors and Homeobox (Hox) genes during the post-weaning growth period of male Wistar rats. Relative to total body weight, BAT weights alone were lower in exercise-trained (EX) rats compared to sedentary control (SED) rats. mRNA expression of HoxA5 was higher and that of HoxC10 was lower in EX rats than in SED rats, accompanied by both higher citrate synthase activity and protein expression levels for uncoupling protein 1 (UCP1), peroxisome proliferator-activated receptor (PPAR) α, and PPARγ-coactivator (PGC)-1α. HoxA5 knockdown with siRNA reduced the expression of PR-domain containing 16 (Prdm16), cell death-inducing DNA fragmentation factor-α-like effector A (Cidea) gene, type 2 deiodinase mRNA, and PRDM16 protein. Comparatively, HoxC10 knockdown with siRNA enhanced mRNA expression of Prdm16, Pparα and Pgc1α and protein expression of UCP1, PPARα and PGC1α in brown adipocytes. The stimulation of brown adipocytes with isoproterenol, a β-adrenoceptor agonist, caused a phenomenon similar to the effect of exercise training on the genes tested: upregulation of HoxA5 mRNA, downregulation of HoxC10 mRNA, and increased protein expression for UCP1 and PGC1α. Collectively, HoxA5 and HoxC10 may have unique functions that contribute to modulating the expression of BAT-selective markers in BAT of juvenile rats during exercise training. The study findings regarding activation and recruitment of BAT during exercise training have implications for anti-obesity management.

Cardiac Adipose Tissue Contributes to Cardiac Repair: a Review

Cardiac adipose tissue is a metabolically active adipose tissue in close proximity to heart. Recent studies emphasized the benefits of cardiac adipose tissue in heart remodeling, such as reducing infarction size, enhancing neovascularization and regulating immune response, through a series of cellular mechanisms. In the present manuscript, we provide a comprehensive review regarding the role of cardiac adipose tissue in cardiac repair. We focus on different cardiac adipose tissues according to their distinguished anatomical structures. This review summarizes the latest evidence on the relationship between cardiac adipose tissue and cardiac repair. Cardiac adipose tissues (CAT) were systematically reviewed in the current manuscript which focused on the components of CAT, debates about cardiac adipose stem cells and their effect on heart.

No Effect of Dietary Fish Oil Supplementation on the Recruitment of Brown and Brite Adipocytes in Mice or Humans under Thermoneutral Conditions

SCOPE

Brown and brite adipocytes within the mammalian adipose organ provide non-shivering thermogenesis and thus, have an exceptional capacity to dissipate chemical energy as heat. Polyunsaturated fatty acids (PUFA) of the n3-series, abundant in fish oil, have been repeatedly demonstrated to enhance the recruitment of thermogenic capacity in these cells, consequently affecting body adiposity and glucose tolerance. These effects are scrutinized in mice housed in a thermoneutral environment and in a human dietary intervention trial.

METHODS AND RESULTS

Mice are housed in a thermoneutral environment eliminating the superimposing effect of mild cold-exposure on thermogenic adipocyte recruitment. Dietary fish oil supplementation in two different inbred mouse strains neither affects body mass trajectory nor enhances the recruitment of brown and brite adipocytes, both in the presence and absence of a β3-adrenoreceptor agonist imitating the effect of cold-exposure on adipocytes. In line with these findings, dietary fish oil supplementation of persons with overweight or obesity fails to recruit thermogenic adipocytes in subcutaneous adipose tissue.

CONCLUSION

Thus, the authors' data question the hypothesized potential of n3-PUFA as modulators of adipocyte-based thermogenesis and energy balance regulation.

Association of Pericardiac Adipose Tissue With Coronary Artery Disease

BACKGROUND AND AIM

Coronary artery disease (CAD) poses a worldwide health threat. Compelling evidence shows that pericardial adipose tissue (PAT), a brown-like adipose adjacent to the external surface of the pericardium, is associated with CAD. However, the specific molecular mechanisms of PAT in CAD are elusive. This study aims to characterize human PAT and explore its association with CAD.

METHODS

We acquired samples of PAT from 31 elective cardiac surgery patients (17 CAD patients and 14 controls). The transcriptome characteristics were assessed in 5 CAD patients and 4 controls via RNA-sequencing. Cluster profile R package, String database, Cytoscape were applied to analyze the potential pathways and PPI-network key to DEGS, whereas the hubgenes were predicted via Metascape, Cytohubba, and MCODE. We use Cibersort, ENCORI, and DGIDB to predict immunoinfiltration, mRNA-miRNA target gene network, and search potential drugs targeting key DEGs. The predictable hubgenes and infiltrating inflammatory cells were validated in 22 patients (12 CAD samples and 10 control samples) through RT-qPCR and immunohistochemistry.

RESULTS

A total of 147 different genes (104 up-regulated genes and 43 down-regulated genes) were identified in CAD patients. These different genes were associated with immunity and inflammatory dysfunction. Cibersort analysis showed monocytes and macrophages were the most common subsets in immune cells, whereas immunohistochemical results revealed there were more macrophages and higher proportion of M1 subtype cells in PAT of CAD patients. The PPI network and module analysis uncovered several crucial genes, defined as candidate genes, including Jun, ATF3, CXCR4, FOSB, CCl4, which were validated through RT-qPCR. The miRNA-mRNA network implicated hsa-miR-185-5p as diagnostic targets and drug-gene network showed colchicine, fenofibrate as potential therapeutic drugs, respectively.

CONCLUSION

This study demonstrates that PAT is mainly associated with the occurrence of CAD following the dysfunction of immune and inflammatory processes. The identified hubgenes, predicted drugs and miRNAs are promising biomarkers and therapeutic targets for CAD.

Mechanisms linking adipose tissue inflammation to cardiac hypertrophy and fibrosis

Adipose tissue is classically recognized as the primary site of lipid storage, but in recent years has garnered appreciation for its broad role as an endocrine organ comprising multiple cell types whose collective secretome, termed as adipokines, is highly interdependent on metabolic homeostasis and inflammatory state. Anatomical location (e.g. visceral, subcutaneous, epicardial etc) and cellular composition of adipose tissue (e.g. white, beige, and brown adipocytes, macrophages etc.) also plays a critical role in determining its response to metabolic state, the resulting secretome, and its potential impact on remote tissues. Compared with other tissues, the heart has an extremely high and constant demand for energy generation, of which most is derived from oxidation of fatty acids. Availability of this fatty acid fuel source is dependent on adipose tissue, but evidence is mounting that adipose tissue plays a much broader role in cardiovascular physiology. In this review, we discuss the impact of the brown, subcutaneous, and visceral white, perivascular (PVAT), and epicardial adipose tissue (EAT) secretome on the development and progression of cardiovascular disease (CVD), with a particular focus on cardiac hypertrophy and fibrosis.

The Serosal Immune System of the Thorax in Toxicology

The thoracic cavities receive increasing attention in toxicology, because inhaled fibers and (nano)particles can reach these cavities and challenge the local lymphoid tissues. The thoracic and abdominopelvic cavities are controlled by the serosal immune system with its special, loosely organized lymphoid clusters, namely the fat-associated lymphoid clusters and milky spots, which together can be denoted as serosa-associated lymphoid clusters. These clusters house numerous innate lymphoid cells, namely the nonconventional, innate B lymphoid cell and innate lymphocyte type 2 populations. The fat depots in the thorax play a significant role in the serosal immunity, and they can be modulated by health issues such as metabolic syndrome. The serosal immune system operates in a unique way at the interface of the innate and acquired immunity and therefore exposure-related modulation of the system may have a distinct impact on the body's immunity. To add to the investigation of the serosal immune system in the thorax, this review describes the (micro)anatomy of the immune system in relation to exposure, with a focus on the rat and mouse as preferred species in toxicology and immunology.

RPS3A positively regulates the mitochondrial function of human periaortic adipose tissue and is associated with coronary artery diseases

Pericardial adipose tissue, which comprises both epicardial adipose tissue (EAT) and paracardial adipose tissue (PAT), has recently been recognized as a novel factor in the pathophysiology of cardiovascular diseases, especially coronary artery disease (CAD). The goal of this study was to evaluate differences in the brown-like characteristic and proteome among human EAT, PAT, and subcutaneous adipose tissue (SAT) to identify candidate molecules causing CAD. Uncoupling protein 1 (UCP-1) and other brown-related proteins were highly expressed in pericardial adipose tissue but was weakly expressed in SAT from the same non-CAD patient. Moreover, pericardial adipose tissues displayed a higher thermogenesis than SAT. However, brown-related genes were lower in CAD pericardial fat. Remarkably, there were lower levels of metabolic enzymes involved in glycolysis, tricarboxylic acid cycle, and fatty acid metabolism in pericardial adipose tissues of CAD. EAT is an organ adjacent to aortic root without anatomy barriers, which differs from PAT. We found that the expression of ribosomal protein S3A (RPS3A) was decreased in human EAT as well as in mouse perivascular adipose tissue (PVAT). Knockdown of RPS3A significantly inhibited adipocyte differentiation in preadipocytes and impaired the function of mitochondria in mature adipocytes. Moreover, RPS3A knockdown in mouse periaortic adipose tissue impaired browning of PVAT, accelerated vascular inflammation, and atherosclerosis progression. Mechanistically, RPS3A can migrate to the mitochondria to maintain the function of brown adipocytes. These findings provide compelling evidence that RPS3A was a key factor for modulating the brown fat-specific gene UCP-1 and carbon metabolic enzymes in EAT for preventing CAD.

Thermogenic capacity of human periaortic adipose tissue is transformed by body weight

The anatomical location of adipose tissue might have direct implications for its functionality and risk of cardiovascular disease. Adipose tissue surrounding blood vessels may be thermogenically more active in specific areas of the body, releasing substances that regulate vascular metabolism. In humans, the phenotypic characteristics of adipose tissue surrounding the aorta and the cardiovascular disease risk that it might entail remain largely unknown. Here, we compared thermogenesis-related molecular features of human periaortic adipose tissue samples with those of subcutaneous adipose tissue, obtained by sternotomy from 42 patients undergoing cardiovascular surgery. To determine the expression of genes related to energy expenditure and the levels of some adipokines, histological examinations, quantitative PCR, and protein expression measurements in adipocyte precursor cells were performed. Periaortic adipocytes were smaller than those from subcutaneous tissue. Moreover, weight gain induced periaortic adipocyte hypertrophy (r = -0.91, p<0.01). Compared to subcutaneous tissue, adiponectin, FABP4, IL-4 and IL-6 was decreased in periaortic adipocytes, whereas FGF21, UCP-1, PGC-1a, CITED1, Omentin and TFAM (Mitochondrial protein) increased. Upon analyzing patients’ clinical conditions, it emerged that the levels of PGC-1a both in male (r = -0.48 p<0.04) and female (r = -0.61, p<0.05) and TFAM in male (r = -0.72, p<0.0008) and female (r = -0.86, p<0.002) decreased significantly with progressive weight gain. However, no differences were observed in patients with diabetes mellitus 2 or Hyperlipidemia. Adipocytes surrounding the ascending aorta present markers of major thermogenic activity than those in subcutaneous tissue. Nevertheless, this characteristic might change, due to unfavorable metabolic conditions such as obesity, which is a risk factor for cardiovascular disease.

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

Brown fat presence and metabolic activity has been associated with lower body mass index, higher insulin sensitivity and better cardiometabolic profile in humans. We, and others, have previously reported the presence of Ucp1, a marker of brown adipocytes, in human epicardial adipose tissue (eAT). Characterization of the metabolic activity and associated physiological relevance of Ucp1 within eAT, however, is still awaited. Here, we validate the presence of Ucp1 within human eAT and its ‘beige’ nature. Using in-vitro analytical approaches, we further characterize its thermogenic potential and demonstrate that human eAT is capable of undergoing enhanced uncoupling respiration upon stimulation. Direct biopsy gene expression analysis reveals a negative association between thermogenic markers and oxidative stress-related genes in this depot. Consistently, isoproterenol (Iso) stimulation of eAT leads to a downregulation of secreted proteins included in the GO terms ‘cell redox homeostasis’ and ‘protein folding’. In addition, cardiac endothelial cells exhibit a downregulation in the expression of adhesion markers upon treatment with Iso-stimulated eAT derived conditioned media. Overall, these observations suggest that Ucp1- associated metabolic activity plays a significant role in local tissue homeostasis within eAT and can plausibly alter its communication with neighboring cells of the cardiovascular system.

Altered Protein Composition of Subcutaneous Adipose Tissue in Chronic Kidney Disease

Introduction

Loss of renal function is associated with high mortality from cardiovascular disease (CVD). Patients with chronic kidney disease (CKD) have altered circulating adipokine and nonesterified fatty acid concentrations and insulin resistance, which are features of disturbed adipose tissue metabolism. Because dysfunctional adipose tissue contributes to the development of CVD, we hypothesize that adipose tissue dysfunctionality in patients with CKD could explain, at least in part, their high rates of CVD. Therefore we characterized adipose tissue from patients with CKD, in comparison to healthy controls, to search for signs of dysfunctionality.

Methods

Biopsy samples of subcutaneous adipose tissue from 16 CKD patients and 11 healthy controls were analyzed for inflammation, fibrosis, and adipocyte size. Protein composition was assessed using 2-dimensional gel proteomics combined with multivariate analysis.

Results

Adipose tissue of CKD patients contained significantly more CD68-positive cells, but collagen content did not differ. Adipocyte size was significantly smaller in CKD patients. Proteomic analysis of adipose tissue revealed significant differences in the expression of certain proteins between the groups. Proteins whose expression differed the most were α-1-microglobulin/bikunin precursor (AMBP, higher in CKD) and vimentin (lower in CKD). Vimentin is a lipid droplet−associated protein, and changes in its expression may impair fatty acid storage/mobilization in adipose tissue, whereas high levels of AMBP may reflect oxidative stress.

Discussion

These findings demonstrate that adipose tissue of CKD patients shows signs of inflammation and disturbed functionality, thus potentially contributing to the unfavorable metabolic profile and increased risk of CVD in these patients.

Impact of the cardiovascular system-associated adipose tissue on atherosclerotic pathology

Cardiac obesity makes an important contribution to the pathogenesis of cardiovascular disease. One of the important pathways of this contribution is the inflammatory process that takes place in the adipose tissue. In this review, we consider the role of the cardiovascular system-associated fat in atherosclerotic cardiovascular pathology and a non-atherosclerotic cause of coronary artery disease, such as atrial fibrillation. Cardiovascular system-associated fat not only serves as the energy store, but also releases adipokines that control local and systemic metabolism, heart/vascular function and vessel tone, and a number of vasodilating and anti-inflammatory substances. Adipokine appears to play an important protective role in cardiovascular system. Under chronic inflammation conditions, the repertoire of signaling molecules secreted by cardiac fat can be altered, leading to a higher amount of pro-inflammatory messengers, vasoconstrictors, profibrotic modulators. This further aggravates cardiovascular inflammation and leads to hypertension, induction of the pathological tissue remodeling and cardiac fibrosis. Contemporary imaging techniques showed that epicardial fat thickness correlates with the visceral fat mass, which is an established risk factor and predictor of cardiovascular disease in obese subjects. However, this correlation is no longer present after adjustment for other covariates. Nevertheless, recent studies showed that pericardial fat volume and epicardial fat thickness can probably serve as a better indicator for atrial fibrillation.

'Browning' the cardiac and peri-vascular adipose tissues to modulate cardiovascular risk

Excess visceral adiposity, in particular that located adjacent to the heart and coronary arteries is associated with increased cardiovascular risk. In the pathophysiological state, dysfunctional adipose tissue secretes an array of factors modulating vascular function and driving atherogenesis. Conversely, brown and beige adipose tissues utilise glucose and lipids to generate heat and are associated with improved cardiometabolic health. The cardiac and thoracic perivascular adipose tissues are now understood to be composed of brown adipose tissue in the healthy state and undergo a brown-to-white transition i.e. during obesity which may be a driving factor of cardiovascular disease. In this review we discuss the risks of excess cardiac and vascular adiposity and potential mechanisms by which restoring the brown phenotype i.e. “re-browning” could potentially be achieved in clinically relevant populations.

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Epicardial, paracardial and thoracic perivascular adipose tissues resemble BAT at birth.

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Despite ‘whitening’ in early life these depots remain metabolically active and potentially thermogenic into adulthood.

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Obesity induces further ‘whitening’ and inflammation in these depots likely driving the atherogenesis.

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Maintaining or inducing the brown phenotype in these depots could prevent atherosclerotic disease.

The adipose tissue of origin influences the biological potential of human adipose stromal cells isolated from mediastinal and subcutaneous fat depots

Indirect evidence suggests that adipose tissue-derived stromal cells (ASCs) possess different physiological and biological variations related to the anatomical localization of the adipose depots. Accordingly, to investigate the influence of the tissue origin on the intrinsic properties of ASCs and to assess their response to specific stimuli, we compared the biological, functional and ultrastructural properties of two ASC pools derived from mediastinal and subcutaneous depots (thoracic compartment) by means of supplements such as platelet lysate (PL) and FBS. Subcutaneous ASCs exhibited higher proliferative and clonogenic abilities than mediastinal counterpart, as well as increased secreted levels of IL-6 combined with lower amount of VEGF-C. In contrast, mediastinal ASCs displayed enhanced pro-angiogenic and adipogenic differentiation properties, increased cell diameter and early autophagic processes, highlighted by electron microscopy. Our results further support the hypothesis that the origin of adipose tissue significantly defines the biological properties of ASCs, and that a homogeneric function for all ASCs cannot be assumed.

Cardiac Adipose-Derived Stem Cells Exhibit High Differentiation Potential to Cardiovascular Cells in C57BL/6 Mice

Adipose-derived stem cells (AdSCs) have recently been shown to differentiate into cardiovascular lineage cells. However, little is known about the fat tissue origin-dependent differences in AdSC function and differentiation potential. AdSC-rich cells were isolated from subcutaneous, visceral, cardiac (CA), and subscapular adipose tissue from mice and their characteristics analyzed. After four different AdSC types were cultured with specific differentiation medium, immunocytochemical analysis was performed for the assessment of differentiation into cardiovascular cells. We then examined the in vitro differentiation capacity and therapeutic potential of AdSCs in ischemic myocardium using a mouse myocardial infarction model. The cell density and proliferation activity of CA-derived AdSCs were significantly increased compared with the other adipose tissue-derived AdSCs. Immunocytochemistry showed that CA-derived AdSCs had the highest appearance rates of markers for endothelial cells, vascular smooth muscle cells, and cardiomyocytes among the AdSCs. Systemic transfusion of CA-derived AdSCs exhibited the highest cardiac functional recovery after myocardial infarction and the high frequency of the recruitment to ischemic myocardium. Moreover, long-term follow-up of the recruited CA-derived AdSCs frequently expressed cardiovascular cell markers compared with the other adipose tissue-derived AdSCs. Cardiac adipose tissue could be an ideal source for isolation of therapeutically effective AdSCs for cardiac regeneration in ischemic heart diseases. Significance: The present study found that cardiac adipose-derived stem cells have a high potential to differentiate into cardiovascular lineage cells (i.e., cardiomyocytes, endothelial cells, and vascular smooth muscle cells) compared with stem cells derived from other adipose tissue such as subcutaneous, visceral, and subscapular adipose tissue. Notably, only a small number of supracardiac adipose-derived stem cells that were systemically transplanted sufficiently improved cardiac functional recovery after myocardial infarction, differentiating into cardiovascular cells in the ischemic myocardium. These findings suggest a new autologous stem cell therapy for patients with myocardial ischemia, especially those with secondary myocardial ischemia after cardiovascular open chest surgery.

Evaluation of reference genes for gene expression studies in human brown adipose tissue

Human brown adipose tissue (BAT) has during the last 5 year been subjected to an increasing research interest, due to its putative function as a target for future obesity treatments. The most commonly used method for molecular studies of human BAT is the quantitative polymerase chain reaction (qPCR). This method requires normalization to a reference gene (genes with uniform expression under different experimental conditions, e.g. similar expression levels between human BAT and WAT), but so far no evaluation of reference genes for human BAT has been performed. Two different microarray datasets with samples containing human BAT were used to search for genes with low variability in expression levels. Seven genes (FAM96B, GNB1, GNB2, HUWE1, PSMB2, RING1 and TPT1) identified by microarray analysis, and 8 commonly used reference genes (18S, B2M, GAPDH, LRP10, PPIA, RPLP0, UBC, and YWHAZ) were selected and further analyzed by quantitative PCR in both BAT containing perirenal adipose tissue and subcutaneous adipose tissue. Results were analyzed using 2 different algorithms (Normfinder and geNorm). Most of the commonly used reference genes displayed acceptably low variability (geNorm M-values <0.5) in the samples analyzed, but the novel reference genes identified by microarray displayed an even lower variability (M-values <0.25). Our data suggests that PSMB2, GNB2 and GNB1 are suitable novel reference genes for qPCR analysis of human BAT and we recommend that they are included in future gene expression studies of human BAT.

Thermogenic potential and physiological relevance of human epicardial adipose tissue

Epicardial adipose tissue is a unique fat depot around the heart that shares a close anatomic proximity and vascular supply with the myocardium and coronary arteries. Its accumulation around the heart, measured using various imaging modalities, has been associated with the onset and progression of coronary artery disease in humans. Epicardial adipose tissue is also the only fat depot around the heart that is known to express uncoupling protein 1 at both mRNA and protein levels in the detectable range. Recent advances have further indicated that human epicardial fat exhibits beige fat-like features. Here we provide an overview of the physiological and pathophysiological relevance of human epicardial fat, and further discuss whether its thermogenic properties can serve as a target for the therapeutic management of coronary heart disease in humans.

A stringent validation of mouse adipose tissue identity markers

The nature of brown adipose tissue in humans is presently debated: whether it is classical brown or of brite/beige nature. The dissimilar developmental origins and proposed distinct functions of the brown and brite/beige tissues make it essential to ascertain the identity of human depots with the perspective of recruiting and activating them for the treatment of obesity and type 2 diabetes. For identification of the tissues, a number of marker genes have been proposed, but the validity of the markers has not been well documented. We used established brown (interscapular), brite (inguinal), and white (epididymal) mouse adipose tissues and corresponding primary cell cultures as validators and examined the informative value of a series of suggested markers earlier used in the discussion considering the nature of human brown adipose tissue. Most of these markers unexpectedly turned out to be noninformative concerning tissue classification (Car4, Cited1, Ebf3, Eva1, Fbxo31, Fgf21, Lhx8, Hoxc8, and Hoxc9). Only Zic1 (brown), Cd137, Epsti1, Tbx1, Tmem26 (brite), and Tcf21 (white) proved to be informative in these three tissues. However, the expression of the brite markers was not maintained in cell culture. In a more extensive set of adipose depots, these validated markers provide new information about depot identity. Principal component analysis supported our single-gene conclusions. Furthermore, Zic1, Hoxc8, Hoxc9, and Tcf21 displayed anteroposterior expression patterns, indicating a relationship between anatomic localization and adipose tissue identity (and possibly function). Together, the observed expression patterns of these validated marker genes necessitates reconsideration of adipose depot identity in mice and humans.

A clinical approach to brown adipose tissue in the para-aortic area of the human thorax

BACKGROUND

Human thoracic brown adipose tissue (BAT), composed of several subdivisions, is a well-known target organ of many clinical studies; however, the functional contribution of each part of human thoracic BAT remains unknown. The present study analyzed the significance of each part of human thoracic BAT in the association between regional distribution, cellularity, and factors involved in the functional regulation of thoracic BAT.

METHODS

We analyzed 1550 healthy adults who underwent medical check-ups by positron-emission tomography and computed tomography (PET-CT) imaging, 8 cadavers, and 78 autopsy cases in an observational study. We first characterized the difference between the mediastinum and the supraclavicular areas using counts of BAT detection and conditions based on PET-CT outcomes. The measurable important area was then subjected to systematic anatomical and immunohistochemical analyses using anti-uncoupling protein 1 (UCP1) antibody to characterize the cellularity in association with age and sex.

RESULTS

In PET-CT scanning, the main site of thoracic BAT was the mediastinum rather than the supraclavicular area (P < 0.05). Systemic macroanatomy revealed that the thumb-sized BAT in the posterior mediastinal descending para-aortic area (paBAT) had feeding vessels from the posterior intercostal arteries and veins and sympathetic/parasympathetic innervation from trunks of the sympathetic and vagus nerves, respectively. Immunohistochemical analysis indicated that the paBAT exhibited immunoreactivity for tyrosine hydroxylase and vesicular acetylcholine transporter located in the pericellular nervous fibers and intracellular UCP1. The brown adipose cells of paBAT showed age-dependent decreases in UCP1 expression (P < 0.05), accompanied by a significant increase in vacuole formation, indicating fat accumulation (P < 0.05), from 10 to 37 years of age (P < 0.01).

CONCLUSIONS

paBAT may be one of the essential sites for clinical application in BAT study because of its visible anatomy with feeding vessels and sympathetic/parasympathetic innervation functionally affected by outer condition and senescence.

Role of developmental transcription factors in white, brown and beige adipose tissues

In this review we discuss the role of developmental transcription factors in adipose tissue biology with a focus on how these developmental genes may contribute to regional variation in adipose tissue distribution and function. Regional, depot-specific, differences in lipid handling and signalling (lipolysis, lipid storage and adipokine/lipokine signalling) are important determinants of metabolic health. At a cellular level, preadipocytes removed from their original depot and cultured in vitro retain depot-specific functional properties, implying that these are intrinsic to the cells and not a function of their environment in situ. High throughput screening has identified a number of developmental transcription factors involved in embryological development, including members of the Homeobox and T-Box gene families, that are strongly differentially expressed between regional white adipose tissue depots and also between brown and white adipose tissue. However, the significance of depot-specific developmental signatures remains unclear. Developmental transcription factors determine body patterning during embryogenesis. The divergent developmental origins of regional adipose tissue depots may explain their differing functional characteristics. There is evidence from human genetics that developmental genes determine adipose tissue distribution: in GWAS studies a number of developmental genes have been identified as being correlated with anthropometric measures of adiposity and fat distribution. Additionally, compelling functional studies have recently implicated developmental genes in both white adipogenesis and the so-called 'browning' of white adipose tissue. Understanding the genetic and developmental pathways in adipose tissue may help uncover novel ways to intervene with the function of adipose tissue in order to promote health.

Lack of adenovirus DNA in mediastinal adipose tissue of obese/overweight adults with cardiovascular disorders?

Mediastinal adipose tissue can be found on the anterior surface of pericardial sac below the remnants of the thymus. On the basis of previous studies describing adenoviruses (AdVs) as a causative factor of obesity, the causative relation between the presence of AdVs and an increased accumulation of mediastinal adipose tissue was studied. The study included 25 obese/overweight subjects with cardiac disorders. Specimens from fat deposits from the anterior mediastinum were collected during cardiac surgery procedures. Afterwards, PCR was used to detect AdV-DNA. No AdV-DNA could be detected in adipose tissue. An association between an excessive accumulation of mediastinal adipose tissue and an AdV-infection in the development of accompanying cardiac disorders was excluded.

Exercise training does not increase muscle FNDC5 protein or mRNA expression in pigs

BACKGROUND

Exercise training elevates circulating irisin and induces the expression of the FNDC5 gene in skeletal muscles of mice. Our objective was to determine whether exercise training also increases FNDC5 protein or mRNA expression in the skeletal muscles of pigs as well as plasma irisin.

METHODS

Castrated male pigs of the Rapacz familial hypercholesterolemic (FHM) strain and normal (Yucatan miniature) pigs were sacrificed after 16-20 weeks of exercise training. Samples of cardiac muscle, deltoid and triceps brachii muscle, subcutaneous and epicardial fat were obtained and FNDC5 mRNA, along with that of 6 other genes, was measured in all tissues of FHM pigs by reverse transcription polymerase chain reaction. FNDC protein in deltoid and triceps brachii was determined by Western blotting in both FHM and normal pigs. Citrate synthase activity was measured in the muscle samples of all pigs as an index of exercise training. Irisin was measured by an ELISA assay.

RESULTS

There was no statistically significant effect of exercise training on FNDC5 gene expression in epicardial or subcutaneous fat, deltoid muscle, triceps brachii muscle or heart muscle. Exercise-training elevated circulating levels of irisin in the FHM pigs and citrate synthase activity in deltoid and triceps brachii muscle. A similar increase in citrate synthase activity was seen in muscle extracts of exercise-trained normal pigs but there was no alteration in circulating irisin.

CONCLUSION

Exercise training in pigs does not increase FNDC5 mRNA or protein in the deltoid or triceps brachii of FHM or normal pigs while increasing circulating irisin only in the FHM pigs. These data indicate that the response to exercise training in normal pigs is not comparable to that seen in mice.