Sympathetic innervation of the supraclavicular brown adipose tissue: A detailed anatomical study.

BACKGROUND: The supraclavicular fossa is the dominant location for human brown adipose tissue (BAT). Activation of BAT promotes non-shivering thermogenesis by utilization of glucose and free fatty acids and has been the focus of pharmacological and non-pharmacological approaches for modulation in order to improve body weight and glucose homeostasis. Sympathetic neural control of supraclavicular BAT has received much attention, but its innervation has not been extensively investigated in humans. METHODS: Dissection of the cervical region in human cadavers was performed to find the distribution of sympathetic nerve branches to supraclavicular fat pad. Furthermore, proximal segments of the 4th cervical nerve were evaluated histologically to assess its sympathetic components. RESULTS: Nerve branches terminating in supraclavicular fat pad were identified in all dissections, including those from the 3rd and 4th cervical nerves and from the cervical sympathetic plexus. Histology of the proximal segments of the 4th cervical nerves confirmed tyrosine hydroxylase positive thin nerve fibers in all fascicles with either a scattered or clustered distribution pattern. The scattered pattern was more predominant than the clustered pattern (80% vs. 20%) across cadavers. These sympathetic nerve fibers occupied only 2.48% of the nerve cross sectional area on average. CONCLUSIONS: Human sympathetic nerves use multiple pathways to innervate the supraclavicular fat pad. The present finding serves as a framework for future clinical approaches to activate human BAT in the supraclavicular region.

Role of adropin in arterial stiffening associated with obesity and type 2 diabetes.

Adropin is a peptide largely secreted by the liver and known to regulate energy homeostasis; however, it also exerts cardiovascular effects. Herein, we tested the hypothesis that low circulating levels of adropin in obesity and type 2 diabetes (T2D) contribute to arterial stiffening. In support of this hypothesis, we report that obesity and T2D are associated with reduced levels of adropin (in liver and plasma) and increased arterial stiffness in mice and humans. Establishing causation, we show that mesenteric arteries from adropin knockout mice are also stiffer, relative to arteries from wild-type counterparts, thus recapitulating the stiffening phenotype observed in T2D db/db mice. Given the above, we performed a set of follow-up experiments, in which we found that 1) exposure of endothelial cells or isolated mesenteric arteries from db/db mice to adropin reduces filamentous actin (F-actin) stress fibers and stiffness, 2) adropin-induced reduction of F-actin and stiffness in endothelial cells and db/db mesenteric arteries is abrogated by inhibition of nitric oxide (NO) synthase, and 3) stimulation of smooth muscle cells or db/db mesenteric arteries with a NO mimetic reduces stiffness. Lastly, we demonstrated that in vivo treatment of db/db mice with adropin for 4 wk reduces stiffness in mesenteric arteries. Collectively, these findings indicate that adropin can regulate arterial stiffness, likely via endothelium-derived NO, and thus support the notion that "hypoadropinemia" should be considered as a putative target for the prevention and treatment of arterial stiffening in obesity and T2D.NEW & NOTEWORTHY Arterial stiffening, a characteristic feature of obesity and type 2 diabetes (T2D), contributes to the development and progression of cardiovascular diseases. Herein we establish that adropin is decreased in obese and T2D models and furthermore provide evidence that reduced adropin may directly contribute to arterial stiffening. Collectively, findings from this work support the notion that "hypoadropinemia" should be considered as a putative target for the prevention and treatment of arterial stiffening in obesity and T2D.

Recruitment and remodeling of peridroplet mitochondria in human adipose tissue.

Beige adipocyte mitochondria contribute to thermogenesis by uncoupling and by ATP-consuming futile cycles. Since uncoupling may inhibit ATP synthesis, it is expected that expenditure through ATP synthesis is segregated to a disparate population of mitochondria. Recent studies in mouse brown adipocytes identified peridroplet mitochondria (PDM) as having greater ATP synthesis and pyruvate oxidation capacities, while cytoplasmic mitochondria have increased fatty acid oxidation and uncoupling capacities. However, the occurrence of PDM in humans and the processes that result in their expansion have not been elucidated. Here, we describe a novel high-throughput assay to quantify PDM that is successfully applied to white adipose tissue from mice and humans. Using this approach, we found that PDM content varies between white and brown fat in both species. We used adipose tissue from pheochromocytoma (Pheo) patients as a model of white adipose tissue browning, which is characterized by an increase in the capacity for energy expenditure. In contrast with control subjects, PDM content was robustly increased in the periadrenal fat of Pheo patients. Remarkably, bioenergetic changes associated with browning were primarily localized to PDM compared to cytoplasmic mitochondria (CM). PDM isolated from periadrenal fat of Pheo patients had increased ATP-linked respiration, Complex IV content and activity, and maximal respiratory capacity. We found similar changes in a mouse model of re-browning where PDM content in whitened brown adipose tissue was increased upon re-browning induced by decreased housing temperature. Taken together, this study demonstrates the existence of PDM as a separate functional entity in humans and that browning in both mice and humans is associated with a robust expansion of peri-droplet mitochondria characterized by increased ATP synthesis linked respiration.

A Thermogenic-Like Brown Adipose Tissue Phenotype Is Dispensable for Enhanced Glucose Tolerance in Female Mice.

The prevailing dogma is that thermogenic brown adipose tissue (BAT) contributes to improvements in glucose homeostasis in obesogenic animal models, though much of the evidence supporting this premise is from thermostressed rodents. Determination of whether modulation of the BAT morphology/function drives changes in glucoregulation at thermoneutrality requires further investigation. We used loss- and gain-of-function approaches including genetic manipulation of the lipolytic enzyme Pnpla2, change in environmental temperature, and lifestyle interventions to comprehensively test the premise that a thermogenic-like BAT phenotype is coupled with enhanced glucose tolerance in female mice. In contrast to this hypothesis, we found that 1) compared to mice living at thermoneutrality, enhanced activation of BAT and its thermogenic phenotype via chronic mild cold stress does not improve glucose tolerance in obese mice, 2) silencing of the Pnpla2 in interscapular BAT causes a brown-to-white phenotypic shift accompanied with inflammation but does not disrupt glucose tolerance in lean mice, and 3) exercise and low-fat diet improve glucose tolerance in obese mice but these effects do not track with a thermogenic BAT phenotype. Collectively, these findings indicate that a thermogenic-like BAT phenotype is not linked to heightened glucose tolerance in female mice.

Removal of interscapular brown adipose tissue increases aortic stiffness despite normal systemic glucose metabolism in mice.

Brown adipose tissue (BAT) is considered protective against obesity and related cardiometabolic dysfunction. Indeed, activation of BAT improves glucose homeostasis and attenuates cardiovascular disease development. However, whether a reduction in BAT mass perturbs metabolic function and increases risk for cardiovascular disease remains largely unknown. To address this question, C57BL/6J male mice underwent a sham procedure or surgical bilateral excision of interscapular BAT (iBATx) and were fed a normal chow or a Western diet for 18 wk, creating four groups ( n = 10/group). Mice were housed at 25°C. As expected, the Western diet increased final body weight and adiposity; however, contrary to our hypothesis, iBATx did not potentiate adiposity independent of diet. Furthermore, iBATx did not affect indexes of glycemic control (HbA1c, fasting glucose and insulin, and glucose area under the curve during a glucose tolerance test) and produced minimal-to-no effects on lipid homeostasis. The absence of metabolic disturbances with iBATx was not attributed to regrowth of iBAT or a "browning" or proliferative compensatory response of other BAT depots. Notably, iBATx caused an increase in aortic stiffness in normal chow-fed mice only, which was associated with an increase in aortic uncoupling protein-1. Collectively, we demonstrated that, at 25°C (i.e., limited thermal stress conditions), a substantial reduction in BAT mass via iBATx does not disrupt systemic glucose metabolism, challenging the current dogma that preservation of BAT is obligatory for optimal metabolic function. However, iBATx caused aortic stiffening in lean mice, hence supporting the existence of an interplay between iBAT and aortic stiffness, independent of alterations in glucose homeostasis.

Deletion of UCP1 enhances ex vivo aortic vasomotor function in female but not male mice despite similar susceptibility to metabolic dysfunction.

Females are typically more insulin sensitive than males, which may be partly attributed to greater brown adipose tissue (BAT) activity and uncoupling protein 1 (UCP1) content. Accordingly, we tested the hypothesis that UCP1 deletion would abolish sex differences in insulin sensitivity and that whitening of thoracic periaortic BAT caused by UCP1 loss would be accompanied with impaired thoracic aortic function. Furthermore, because UCP1 exerts antioxidant effects, we examined whether UCP1 deficiency-induced metabolic dysfunction was mediated by oxidative stress. Compared with males, female mice had lower HOMA- and AT-insulin resistance (IR) despite no significant differences in BAT UCP1 content. UCP1 ablation increased HOMA-IR, AT-IR, and whitening of BAT in both sexes. Expression of UCP1 in thoracic aorta was greater in wild-type females compared with males. Importantly, deletion of UCP1 enhanced aortic vasomotor function in females only. UCP1 ablation did not promote oxidative stress in interscapular BAT. Furthermore, daily administration of the free radical scavenger tempol for 8 wk did not abrogate UCP1 deficiency-induced increases in adiposity, hyperinsulinemia, or liver steatosis. Collectively, we report that 1) in normal chow-fed mice housed at 25°C, aortic UCP1 content was greater in females than males and its deletion improved ex vivo aortic vasomotor function in females only; 2) constitutive UCP1 content in BAT was similar between females and males and loss of UCP1 did not abolish sex differences in insulin sensitivity; and 3) the metabolic disruptions caused by UCP1 ablation did not appear to be contingent upon increased oxidative stress in mice under normal dietary conditions.

Epicardial Adipose Tissue Removal Potentiates Outward Remodeling and Arrests Coronary Atherogenesis.

BACKGROUND: Pericoronary epicardial adipose tissue (cEAT) serves as a metabolic and paracrine organ that contributes to inflammation and is associated with macrovascular coronary artery disease (CAD) development. Although there is a strong correlation in humans between cEAT volume and CAD severity, there remains a paucity of experimental data demonstrating a causal link of cEAT to CAD. The current study tested the hypothesis that surgical resection of cEAT attenuates inflammation and CAD progression. METHODS: Female Ossabaw miniature swine (n = 12) were fed an atherogenic diet for 8 months and randomly allocated into sham (n = 5) or adipectomy (n = 7) groups. Both groups underwent a thoracotomy, opening of the pericardial sac, and placement of radioopaque clips to mark the proximal left anterior descending artery. Adipectomy swine underwent removal of 1 to 1.5 cm2 of cEAT from the proximal artery. After sham or adipectomy, CAD severity was assessed with intravascular ultrasonography. Swine recovered for an additional 3 months on an atherogenic diet, and CAD was assessed immediately before euthanasia. Artery sections were processed for histologic and immunohistochemical analysis. RESULTS: Severity of CAD as assessed by percent stenosis was reduced in the adipectomy cohort compared with shams; however, plaque size remained unaltered, whereas larger plaque sizes developed in sham-operated swine. Adipectomy resulted in an expanded arterial diameter, similar to the Glagov phenomenon of positive outward remodeling. No differences in inflammatory marker expression were observed. CONCLUSIONS: These data indicate that cEAT resection did not alter inflammatory marker expression, but arrested CAD progression through increased positive outward remodeling and arrest of atherogenesis.

Loss of UCP1 exacerbates Western diet-induced glycemic dysregulation independent of changes in body weight in female mice.

We tested the hypothesis that female mice null for uncoupling protein 1 (UCP1) would have increased susceptibility to Western diet-induced "whitening" of brown adipose tissue (AT) and glucose intolerance. Six-week-old C57BL/6J wild-type (WT) and UCP1 knockout (UCP1-/-) mice, housed at 25°C, were randomized to either a control diet (10% kcal from fat) or Western diet (45% kcal from fat and 1% cholesterol) for 28 wk. Loss of UCP1 had no effect on energy intake, energy expenditure, spontaneous physical activity, weight gain, or visceral white AT mass. Despite similar susceptibility to weight gain compared with WT, UCP1-/- exhibited whitening of brown AT evidenced by a striking ~500% increase in mass and appearance of large unilocular adipocytes, increased expression of genes related to inflammation, immune cell infiltration, and endoplasmic reticulum/oxidative stress (P < 0.05), and decreased mitochondrial subunit protein (COX I, II, III, and IV, P < 0.05), all of which were exacerbated by Western diet (P < 0.05). UCP1-/- mice also developed liver steatosis and glucose intolerance, which was worsened by Western diet. Collectively, these findings demonstrate that loss of UCP1 exacerbates Western diet-induced whitening of brown AT, glucose intolerance, and induces liver steatosis. Notably, the adverse metabolic manifestations of UCP1-/- were independent of changes in body weight, visceral adiposity, and energy expenditure. These novel findings uncover a previously unrecognized metabolic protective role of UCP1 that is independent of its already established role in energy homeostasis.

'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.

Adipocyte Browning and Higher Mitochondrial Function in Periadrenal But Not SC Fat in Pheochromocytoma.

CONTEXT: Patients with pheochromocytoma (pheo) show presence of multilocular adipocytes that express uncoupling protein 1 within periadrenal (pADR) and omental (OME) fat depots. It has been hypothesized that this is due to adrenergic stimulation by catecholamines produced by the pheo tumors. OBJECTIVE: To characterize the prevalence and respiratory activity of brown-like adipocytes within pADR, OME, and SC fat depots in human adult pheo patients. DESIGN: This was an observational cohort study. SETTING: The study took place in a university hospital. PATIENTS: We studied 46 patients who underwent surgery for benign adrenal tumors (21 pheos and 25 controls with adrenocortical adenomas). MAIN OUTCOME MEASURE: We characterized adipocyte browning in pADR, SC, and OME fat depots for histological and immunohistological features, mitochondrial respiration rate, and gene expression. We also determined circulating levels of catecholamines and other browning-related hormones. RESULTS: Eleven of 21 pheo pADR adipose samples, but only one of 25 pADR samples from control patients exhibited multilocular adipocytes. The pADR browning phenotype was associated with higher plasma catecholamines and raised uncoupling protein 1. Mitochondria from multilocular pADR fat of pheo patients exhibited increased rates of coupled and uncoupled respiration. Global gene expression analysis in pADR fat revealed enrichment in ß-oxidation genes in pheo patients with multilocular adipocytes. No SC or OME fat depots exhibited aspects of browning. CONCLUSION: Browning of the pADR depot occurred in half of pheo patients and was associated with increased catecholamines and mitochondrial activity. No browning was detected in other fat depots, suggesting that other factors are required to promote browning in these depots.

Epicardial adipose excision slows the progression of porcine coronary atherosclerosis.

BACKGROUND: In humans there is a positive association between epicardial adipose tissue (EAT) volume and coronary atherosclerosis (CAD) burden. We tested the hypothesis that EAT contributes locally to CAD in a pig model. METHODS: Ossabaw miniature swine (n=9) were fed an atherogenic diet for 6 months to produce CAD. A 15 mm length by 3-5 mm width coronary EAT (cEAT) resection was performed over the middle segment of the left anterior descending artery (LAD) 15 mm distal to the left main bifurcation. Pigs recovered for 3 months on atherogenic diet. Intravascular ultrasound (IVUS) was performed in the LAD to quantify atheroma immediately after adipectomy and was repeated after recovery before sacrifice. Coronary wall biopsies were stained immunohistochemically for atherosclerosis markers and cytokines and cEAT was assayed for atherosclerosis-related genes by RT-PCR. Total EAT volume was measured by non-contrast CT before each IVUS. RESULTS: Circumferential plaque length increased (p<0.05) in the proximal and distal LAD segments from baseline until sacrifice whereas plaque length in the middle LAD segment underneath the adipectomy site did not increase. T-cadherin, scavenger receptor A and adiponectin were reduced in the intramural middle LAD. Relative to control pigs without CAD, 11ß-hydroxysteroid dehydrogenase (11ßHSD-1), CCL19, CCL21, prostaglandin D2 synthase, gp91phox [NADPH oxidase], VEGF, VEGFGR1, and angiotensinogen mRNAs were up-regulated in cEAT. EAT volume increased over 3 months. CONCLUSION: In pigs used as their own controls, resection of cEAT decreased the progression of CAD, suggesting that cEAT may exacerbate coronary atherosclerosis.

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.

Adult epicardial fat exhibits beige features.

CONTEXT: Human epicardial fat has been designated previously as brown-like fat. The supraclavicular fat depot in man has been defined as beige coexistent with classical brown based on its gene expression profile. OBJECTIVE: The aim of the study was to establish the gene expression profile and morphology of human epicardial and visceral paracardial fat compared with sc fat. SETTING: The study was conducted at a tertiary care hospital cardiac center. PATIENTS: Epicardial, visceral paracardial, and sc fat samples had been taken from middle-aged patients with severe coronary atherosclerosis or valvular heart disease. INTERVENTIONS: Gene expression was determined by reverse transcription-quantitative PCR and relative abundance of the mitochondrial uncoupling protein-1 (UCP-1) by Western blotting. Epicardial tissue sections from patients were examined by light microscopy, UCP-1 immunohistochemistry, and cell morphometry. MAIN OUTCOME MEASURES: We hypothesized that epicardial fat has a mixed phenotype with a gene expression profile similar to that described for beige cell lineage. RESULTS: Immunoreactive UCP-1 was clearly measurable in each epicardial sample analyzed but was undetectable in each of the 4 other visceral and sc depots. Epicardial fat exhibited high expression of genes for UCP-1, PRDM16, PGC-1α, PPARγ, and the beige adipocyte-specific marker CD137, which were also expressed in visceral paracardial fat but only weakly in sternal, upper abdominal, and lower extremity sc fat. Histology of epicardial fat showed small unilocular adipocytes without UCP-1 immunostaining. CONCLUSION: UCP-1 is relatively abundant in epicardial fat, and this depot possesses molecular features characteristic of those found in vitro in beige lineage adipocytes.

Human epicardial fat: what is new and what is missing?

1. Putative physiological functions of human epicardial adipose tissue (EAT) include: (i) lipid storage for the energy needs of the myocardium; (ii) thermoregulation, whereby brown fat components of EAT generate heat by non-shivering thermogenesis in response to core cooling; (iii) neuroprotection of the cardiac autonomic ganglia and nerves; and (iv) regulation of vasomotion and luminal size of the coronary arteries. Under pathophysiological circumstances, EAT may play an adverse paracrine role in cardiac arrhythmias and in lipotoxic cardiomyopathy, but of major current interest is its hypothetical role as an immunological organ contributing to inflammation around coronary artery disease (CAD). 2. The amount of EAT measured either by echocardiographic thickness over the free wall of the right ventricle or as volume by computed tomography expands in patients with obesity both without and with CAD. The mechanisms other than obesity governing the increase in EAT volume in CAD are unknown, but EAT around CAD is infiltrated by chronic inflammatory cells and overexpresses genes for adipokines that have pro- or anti-inflammatory actions and regulate oxidative stress plus angiogenesis. 3. Many cross-sectional studies have shown positive associations between increased EAT mass and stable CAD burden. One prospective population-based epidemiological study suggested that EAT volume at baseline is a predictor of acute myocardial infarction, but was without significant incremental predictive value after adjustment for established cardiovascular risk factors. However, strategies are needed to obtain robust epidemiological, interventional and experimental evidence to prove or disprove the hypothesis that EAT is a cardiovascular risk factor locally contributing to CAD.

Depot-specific overexpression of proinflammatory, redox, endothelial cell, and angiogenic genes in epicardial fat adjacent to severe stable coronary atherosclerosis.

BACKGROUND: Pro- and antiinflammatory genes are expressed in epicardial adipose tissue (EAT). Our objectives were to characterize genes in EAT that may contribute specifically to coronary atherogenesis and to measure circulating adipokines matched to their messenger RNAs (mRNAs) in EAT. We hypothesized that severe coronary atherosclerosis (CAD) would preferentially affect gene expression in EAT as compared to substernal fat or subcutaneous thoracic adipose tissue (SAT), as well as circulating levels of adipokines. METHODS: Fat mRNA was quantified using reverse transcription polymerase chain reaction (RT-PCR), and circulating adipokines were measured by enzyme-linked immunosorbent assays (ELISAs) in patients with severe stable CAD and controls without severe CAD undergoing open heart surgery. RESULTS: A total of 39 of 70 mRNAs in EAT were significantly increased in CAD. Only 4 and 3 of these mRNAs were increased in substernal fat and SAT, respectively. Of the mRNAs increased in EAT, 17 were either inflammatory adipokines or proteins known to be involved in inflammatory processes, 7 were involved in oxidative stress and or oxygen species regulation, whereas 15 were proteins involved in metabolism and regulation of gene transcription or proteins unique to fat cells. The largest increases, over three-fold, were seen in GPX3, gp91 phox, p47phox, heme oxygenase, and interleukin-8 (IL-8). Tpl2 mRNA was uniquely elevated in all three fat depots from CAD patients, and its expression in SAT, but not in EAT or substernal fat, was directly correlated with homeostasis model assessment of insulin resistance (HOMA-IR) values. Compared to controls, there were no associations between circulating levels of IL-8, lipocalin-2, nerve growth factor (NGF), RANTES, CD-163, GPX-3, monocyte chemotactic protein-1 (MCP-1)/CCL2, leptin, soluble vascular endothelial growth factor receptor-1 (sFLT1), fatty acid binding protein-4 (FABP-4), and plasminogen activator inhibitor-1 (PAI-1) and increases in their gene expression in EAT adjacent to CAD. CONCLUSIONS: Expression of proinflammatory, redox, endothelial cell, and angiogenic genes in EAT is depot specific and supports the hypothesis that pathophysiologically EAT contributes locally to CAD. CAD links with these fat depots might involve Tpl2 as a primary response indicator.

Inflammatory genes in epicardial fat contiguous with coronary atherosclerosis in the metabolic syndrome and type 2 diabetes: changes associated with pioglitazone.

OBJECTIVE: To determine changes in gene expression in epicardial adipose tissue (EAT) associated with coronary atherosclerosis (CAD) and effects of pioglitazone therapy. RESEARCH DESIGN AND METHODS: Genes were quantified by RT-PCR in EAT and thoracic subcutaneous adipose tissue (SAT) obtained during surgery in CAD patients with metabolic syndrome (MS) or type 2 diabetes and control subjects with minimal or no CAD and no MS or type 2 diabetes. RESULTS: Increased expression of interleukin-1 receptor antagonist (IL-1Ra) and IL-10, a trend for higher IL-1ß, and no change in peroxisome proliferator-activated receptor-γ (PPARγ) was found in EAT from MS or type 2 diabetes. Only PPARγ mRNA was reduced in SAT. Pioglitazone therapy in type 2 diabetes was associated with decreased expression of IL-1ß, IL-1Ra, and IL-10 in EAT; decreased IL-10 in SAT; and increased PPARγ in SAT. CONCLUSIONS: In MS and type 2 diabetes with CAD, proinflammatory and anti-inflammatory genes were differentially increased in EAT and selectively reduced in association with pioglitazone treatment.

Epicardial fat gene expression after aerobic exercise training in pigs with coronary atherosclerosis: relationship to visceral and subcutaneous fat.

Epicardial adipose tissue (EAT) is contiguous with coronary arteries and myocardium and potentially may play a role in coronary atherosclerosis (CAD). Exercise is known to improve cardiovascular disease risk factors. The purpose of this study was to investigate the effect of aerobic exercise training on the expression of 18 genes, measured by RT-PCR and selected for their role in chronic inflammation, oxidative stress, and adipocyte metabolism, in peri-coronary epicardial (cEAT), peri-myocardial epicardial (mEAT), visceral abdominal (VAT), and subcutaneous (SAT) adipose tissues from a castrate male pig model of familial hypercholesterolemia with CAD. We tested the hypothesis that aerobic exercise training for 16 wk would reduce the inflammatory profile of mRNAs in both components of EAT and VAT but would have little effect on SAT. Exercise increased mEAT and total heart weights. EAT and heart weights were directly correlated. Compared with sedentary pigs matched for body weight to exercised animals, aerobic exercise training reduced the inflammatory response in mEAT but not cEAT, had no effect on inflammatory genes but preferentially decreased expression of adiponectin and other adipocyte-specific genes in VAT, and had no effect in SAT except that IL-6 mRNA went down and VEGFa mRNA went up. We conclude that 1) EAT is not homogeneous in its inflammatory response to aerobic exercise training, 2) cEAT around CAD remains proinflammatory after chronic exercise, 3) cEAT and VAT share similar inflammatory expression profiles but different metabolic mRNA responses to exercise, and 4) gene expression in SAT cannot be extrapolated to VAT and heart adipose tissues in exercise intervention studies.

Human epicardial adipokine messenger RNAs: comparisons of their expression in substernal, subcutaneous, and omental fat.

We compared the gene expression of inflammatory and other proteins by real-time quantitative polymerase chain reaction in epicardial, substernal (mediastinal) and subcutaneous sternal, upper abdominal, and leg fat from coronary bypass patients and omental (visceral) fat from extremely obese women undergoing bariatric surgery. We hypothesized that (1) epicardial fat would exhibit higher expression of inflammatory messenger RNAs (mRNAs) than substernal and subcutaneous fat and (2) epicardial mRNAs would be similar to those in omental fat. Epicardial fat was clearly different from substernal fat because there was a far higher expression of haptoglobin, prostaglandin D(2) synthase, nerve growth factor beta, the soluble vascular endothelial growth factor receptor (FLT1), and alpha1 glycoprotein but not of inflammatory adipokines such as monocyte chemoattractant protein-1, interleukin (IL)-8, IL-1beta, tumor necrosis factor alpha, serum amyloid A, plasminogen activator inhibitor-1, or adiponectin despite underlying coronary atherosclerosis. However, the latter inflammatory adipokines as well as most other mRNAs were overexpressed in epicardial fat as compared with the subcutaneous depots except for IL-8, fatty acid binding protein 4, the angiotensin II receptor 1, IL-6, and superoxide dismutase-2. Relative to omental fat, about one third of the genes were expressed at the same levels, whereas monocyte chemoattractant protein-1, cyclooxygenase-2, plasminogen activator inhibitor-1, IL-1beta, and IL-6 were expressed at far lower levels in epicardial fat. In conclusion, epicardial fat does not appear to be a potentially more important source of inflammatory adipokines than substernal mediastinal fat. Furthermore, the expression of inflammatory cytokines such as IL-6 and IL-1beta is actually higher in omental fat from obese women without coronary atherosclerosis. The data do not support the hypothesis that most of the inflammatory adipokines are expressed at high levels in epicardial fat of humans.

Uncoupling protein-1 and related messenger ribonucleic acids in human epicardial and other adipose tissues: epicardial fat functioning as brown fat.

CONTEXT: Uncoupling protein-1 (UCP-1) is the inner mitochondrial membrane protein that is a specific marker for and mediator of nonshivering thermogenesis in brown adipocytes. OBJECTIVE: This study was performed to better understand the putative thermogenic function of human epicardial fat. DESIGN: We measured the expression of UCP-1 and brown adipocyte differentiation transcription factors PR-domain-missing 16 (PRDM16) and peroxisome-proliferator-activated receptor gamma co-activator-1 alpha (PGC-1 alpha) in epicardial, substernal, and sc thoracic, abdominal, and leg fat. SETTING: The study was conducted at a tertiary care hospital cardiac center. PATIENTS: Forty-four patients had coronary artery bypass surgery, and six had heart valve replacement. INTERVENTIONS: Fat samples were taken at open heart surgery. RESULTS: UCP-1 expression was 5-fold higher in epicardial fat than substernal fat and barely detectable in sc fat. Epicardial fat UCP-1 expression decreased with age, increased with body mass index, was similar in women and men and patients on and not on statin therapy, and showed no relationship to epicardial fat volume or waist circumference. UCP-1 expression was similar in patients without and with severe coronary atherosclerosis and metabolic syndrome or type 2 diabetes. PRDM16 and PGC-1 alpha expression was 2-fold greater in epicardial than sc fat. Epicardial fat UCP-1, PRDM16, and PGC1-alpha mRNAs were similar in diabetics treated with thiazolidinediones compared to diabetics not treated with thiazolidinediones. CONCLUSION: Because UCP-1 is expressed at high levels in epicardial fat as compared to other fat depots, the possibility should be considered that epicardial fat functions like brown fat to defend the myocardium and coronary vessels against hypothermia. This process could be blunted in the elderly.