Rodent Brown Adipose Tissue Research Articles

The Role of β3-Adrenergic Receptors in Cold-Induced Beige Adipocyte Production in Pigs.

After exposure to cold stress, animals enhance the production of beige adipocytes and expedite thermogenesis, leading to improved metabolic health. Although brown adipose tissue in rodents is primarily induced by β3-adrenergic receptor (ADRB3) stimulation, the activation of major β-adrenergic receptors (ADRBs) in pigs has been a topic of debate. To address this, we developed overexpression vectors for ADRB1, ADRB2, and ADRB3 and silenced the expression of these receptors to observe their effects on the adipogenic differentiation stages of porcine preadipocytes. Our investigation revealed that cold stress triggers the transformation of subcutaneous white adipose tissue to beige adipose tissue in pigs by modulating adrenergic receptor levels. Meanwhile, we found that ADRB3 promotes the transformation of white adipocytes into beige adipocytes. Notably, ADRB3 enhances the expression of beige adipose tissue marker genes, consequently influencing cellular respiration and metabolism by regulating lipolysis and mitochondrial expression. Therefore, ADRB3 may serve as a pivotal gene in animal husbandry and contribute to the improvement of cold intolerance in piglets.

The ABA/LANCL1/2 Hormone/Receptor System Controls Adipocyte Browning and Energy Expenditure

The abscisic acid (ABA)/LANC-like protein 1/2 (LANCL1/2) hormone/receptor system regulates glucose uptake and oxidation, mitochondrial respiration, and proton gradient dissipation in myocytes. Oral ABA increases glucose uptake and the transcription of adipocyte browning-related genes in rodent brown adipose tissue (BAT). The aim of this study was to investigate the role of the ABA/LANCL system in human white and brown adipocyte thermogenesis. Immortalized human white and brown preadipocytes, virally infected to overexpress or silence LANCL1/2, were differentiated in vitro with or without ABA, and transcriptional and metabolic targets critical for thermogenesis were explored. The overexpression of LANCL1/2 increases, and their combined silencing conversely reduces mitochondrial number, basal, and maximal respiration rates; proton gradient dissipation; and the transcription of uncoupling genes and of receptors for thyroid and adrenergic hormones, both in brown and in white adipocytes. The transcriptional enhancement of receptors for browning hormones also occurs in BAT from ABA-treated mice, lacking LANCL2 but overexpressing LANCL1. The signaling pathway downstream of the ABA/LANCL system includes AMPK, PGC-1α, Sirt1, and the transcription factor ERRα. The ABA/LANCL system controls human brown and "beige" adipocyte thermogenesis, acting upstream of a key signaling pathway regulating energy metabolism, mitochondrial function, and thermogenesis.

β3-Adrenergic receptors regulate human brown/beige adipocyte lipolysis and thermogenesis.

β3-Adrenergic receptors (β3-ARs) are the predominant regulators of rodent brown adipose tissue (BAT) thermogenesis. However, in humans, the physiological relevance of BAT and β3-AR remains controversial. Herein, using primary human adipocytes from supraclavicular neck fat and immortalized brown/beige adipocytes from deep neck fat from 2 subjects, we demonstrate that the β3-AR plays a critical role in regulating lipolysis, glycolysis, and thermogenesis. Silencing of the β3-AR compromised genes essential for thermogenesis, fatty acid metabolism, and mitochondrial mass. Functionally, reduction of β3-AR lowered agonist-mediated increases in intracellular cAMP, lipolysis, and lipolysis-activated, uncoupling protein 1–mediated thermogenic capacity. Furthermore, mirabegron, a selective human β3-AR agonist, stimulated BAT lipolysis and thermogenesis, and both processes were lost after silencing β3-AR expression. This study highlights that β3-ARs in human brown/beige adipocytes are required to maintain multiple components of the lipolytic and thermogenic cellular machinery and that β3-AR agonists could be used to achieve metabolic benefit in humans.

Effects of Caffeine on Brown Adipose Tissue Thermogenesis and Metabolic Homeostasis: A Review.

The impact of brown adipose tissue (BAT) metabolism on understanding energy balance in humans is a relatively new and exciting field of research. The pathogenesis of obesity can be largely explained by an imbalance between caloric intake and energy expenditure, but the underlying mechanisms are far more complex. Traditional non-selective sympathetic activators have been used to artificially elevate energy utilization, or suppress appetite, however undesirable side effects are apparent with the use of these pharmacological interventions. Understanding the role of BAT, in relation to human energy homeostasis has the potential to dramatically offset the energy imbalance associated with obesity. This review discusses paradoxical effects of caffeine on peripheral adenosine receptors and the possible role of adenosine in increasing metabolism is highlighted, with consideration to the potential of central rather than peripheral mechanisms for caffeine mediated BAT thermogenesis and energy expenditure. Research on the complex physiology of adipose tissue, the embryonic lineage and function of the different types of adipocytes is summarized. In addition, the effect of BAT on overall human metabolism and the extent of the associated increase in energy expenditure are discussed. The controversy surrounding the primary β-adrenoceptor involved in human BAT activation is examined, and suggestions as to the lack of translational findings from animal to human physiology and human in vitro to in vivo models are provided. This review compares and distinguishes human and rodent BAT effects, thus developing an understanding of human BAT thermogenesis to aid lifestyle interventions targeting obesity and metabolic syndrome. The focus of this review is on the effect of BAT thermogenesis on overall metabolism, and the potential therapeutic effects of caffeine in increasing metabolism via its effects on BAT.

Magnetic Resonance Imaging Techniques for Brown Adipose Tissue Detection.

Magnetic resonance imaging (MRI) and magnetic resonance spectroscopy (MRS) methods can non-invasively assess brown adipose tissue (BAT) structure and function. Recently, MRI and MRS have been proposed as a means to differentiate BAT from white adipose tissue (WAT) and to extract morphological and functional information on BAT inaccessible by other means. Specifically, proton MR (1H) techniques, such as proton density fat fraction mapping, diffusion imaging, and intermolecular multiple quantum coherence imaging, have been employed to access BAT microstructure; MR thermometry, relaxometry, and MRI and MRS with 31P, 2H, 13C, and 129Xe have shown to provide complementary information on BAT function. The purpose of the present review is to provide a comprehensive overview of MR imaging and spectroscopy techniques used to detect BAT in rodents and in humans. The present work discusses common challenges of current methods and provides an outlook on possible future directions of using MRI and MRS in BAT studies.

2020-P: ß3-Adrenergic Receptors Regulate Lipolysis and Thermogenesis in Human Brown/Beige Adipocytes

Activation of rodent brown adipose tissue (BAT) via pharmacological stimulation of β3-adrenergic receptors (β3-AR) leads to metabolic benefit, however in humans, the physiological relevance of BAT and β3-AR remain controversial. To investigate the role of the β3-AR in human brown adipocytes, first, we established a human primary supraclavicular adipocyte in vitro model that upon differentiation preserved the physiological properties brown adipose tissue with increased β-ARs, adipogenic, thermogenic and brown/beige markers. Next, we selective silenced β3-AR expression in differentiated primary brown/beige adipocytes using a lipofectamine-based non-viral transfection. 48h of transfection of siRNA targeting ADRB3 (siRNA-ADRB3) resulted in a 90% reduction in ADRB3 mRNA levels, relative to control siRNA-transfected cells (siRNA-Ctrl). siRNA-ADRB3 also reduced genes of fatty acid metabolism, thermogenesis (UCP1, 90% decrease), and mitochondrial mass. Functionally, lower cAMP levels, lipolysis, oxygen consumption rates and higher glycolysis were caused by silencing β3-AR receptor. Immortalized brown adipocyte (hBA’s), from a separate subject, displayed a similar decrease in lipolysis and cellular respiration. Mirabegron, the selective human β3-AR agonist, stimulated BAT lipolysis and thermogenesis, that were lost after knockdown ADRB3. Similarly, selective subtype human β-AR agonists dobutamine (β1-AR agonist) and terbutaline (β2-AR agonist) treatment also increased lipolysis and thermogenesis, that were also attenuated when β3-AR was silenced. Thus, the β3-AR maintains multiple components of the human brown/beige adipocyte lipolytic and thermogenic cellular machinery. These findings indicate that ADRB3 and β3-AR agonists could be used to achieve metabolic benefit in humans. Disclosure C. Cero: None. H.J. Lea: None. K.Y. Zhu: None. A.M. Cypess: None.

Brown adipose tissue recruitment in a rodent model of severe burns

BackgroundSevere burns results in a prolonged hypermetabolic response. Brown adipose tissue (BAT), abundant in uncoupling protein 1 (UCP1), plays a key role in non-shivering thermogenesis. We set out to determine if BAT is recruited in response to severe burns. MethodsMale balb-c mice underwent scald burns on approximately 20–25% of their total body surface. BAT was harvested from the interscapular fat pad of sham and burned mice at 3h, 24h, 4 days, and 10 days after injury. High-resolution respirometry was used to determine mitochondrial respiratory function in BAT. BAT protein concentration, and mitochondrial enzyme activity were also determined. ResultsRespiration increased in BAT of burned mice, peaking at 24h after injury (after injury, P<0.001). While UCP1 independent respiration was not significantly altered by burn, UCP1 dependent respiration increased >2-fold at 24h after injury when compared to the 3h and sham group (P<0.01). Normalized to citrate synthase activity, total uncoupled (P<0.05) and UCP1 dependent (P<0.01) respiration remained elevated at 24h after injury. ConclusionsWe show a time-dependent recruitment of rodent BAT in response to severe burns. Given recent reports that humans, including patients with severe burns, have functional BAT, these data support a role for BAT in the hypermetabolic response to severe burns.

In vitro Radiopharmaceutical Evidence for MCHR1 Binding Sites in Murine Brown Adipocytes

[11C]SNAP-7941 and its radiofluorinated, fluoro-ethyl derivative [18F]FE@SNAP have been developed as the first positron emission tomography tracers for melanin-concentrating hormone receptor 1 (MCHR1) imaging. Accumulation of these MCHR1 PET-tracers in rat brown adipose tissue (BAT) in vivo provided first indication of MCHR1 expression in rodent BAT. To rule out off-target binding, affinity of both MCHR1 ligands toward adrenergic beta-3 receptors (ADRB3) was examined. Further, specific binding of [11C]SNAP-7941 to brown adipocytes and effects of MCHR1 ligands on brown adipocyte activation were investigated. SNAP-7941 and FE@SNAP evinced to be highly selective toward MCHR1. [11C]SNAP-7941 binding to brown adipocytes was shown to be mainly MCHR1-specific. This data strongly indicates MCHR1 expression in rodent BAT and moreover, a peripheral, anti-obesity effect of MCHR1 antagonists directly exerted in BAT is proposed. Moreover, MCHR1 expression in murine brown adipocytes was confirmed by protein and mRNA analysis. We conclude that MCHR1 PET imaging contributes to basic research in endocrinology by elucidating the involvement of the MCH system in peripheral tissues, such as BAT.

Adipose tissue browning in mice and humans

In the midst of an obesity epidemic, the promotion of brown adipose tissue (BAT) function and the browning of white adipose tissue (WAT) have emerged as promising therapeutic targets to increase energy expenditure and counteract weight gain. Despite the fact that the thermogenic potential of bone fide BAT in rodents is several orders of magnitudes higher than white fat containing brite/beige adipocytes, WAT browning represents a particularly intriguing concept in humans given the extreme amount of excess WAT in obese individuals. In addition, the clear distinction between classic brown and beige fat that has been proposed in mice does not exist in humans. In fact, studies of human BAT biopsies found controversial results suggesting both classic brown and beige characteristics. Irrespective of the true ‘color’, accumulating evidence suggests the induction of thermogenic adipocytes in human WAT depots in response to specific stimuli, highlighting that WAT browning may occur in both, mice and humans. These observations also emphasize the great plasticity of human fat depots and raise important questions about the metabolic properties of thermogenically active adipose tissue in humans and the potential therapeutic implications. We will first review the cellular and molecular aspects of selected adipose tissue browning concepts that have been identified in mouse models with emphasis on neuronal factors, the microbiome, immune cells and several hormones. We will also summarize the evidence for adipose tissue browning in humans including some experimental pharmacologic approaches.

Investigating the effects of Orexin-A on thermogenesis in human deep neck brown adipose tissue.

Despite successful preclinical testing, 85% of early clinical trials for novel drugs fail. Most futilities originate from molecular mechanisms of the drug(s) tested. It is critically important to develop validated human cell-based model systems in which animal-based research can be translated in order to complement the preclinical in vivo findings prior to implementation of a clinical trial. Obesity is associated with reduced circulating levels of Orexin-A (OX-A) in humans. OX-A increases thermogenesis in rodent brown adipose tissue (AT), yet this phenomenon has not been explored in humans. We established a cell-based model system of human brown and white adipocytes and tested the effects of OX-A on thermogenesis. Contrary to published in vivo and in vitro reports in rodents, OX-A treatment alone or in combination with an adrenergic stimulus did neither enhance thermogenesis nor its related transcriptional program in a human in vitro model of brown adipocytes or AT explants. Translating preclinical findings in human model systems poses a challenge that must be overcome for the development of effective therapeutic compounds and targets.

The significance of beige and brown fat in humans.

Promotion of brown adipose tissue (BAT) activity or browning of white adipose tissue has shown great potential as anti-obesity strategy in numerous preclinical models. The discovery of active BAT in humans and the recent advances in the understanding of human BAT biology and function have significantly propelled this field of research. Pharmacological stimulation of energy expenditure to counteract obesity has always been an intriguing therapeutic concept; with the identification of the specific molecular pathways of brown fat function, this idea has now become as realistic as ever. Two distinct strategies are currently being pursued; one is the activation of bone fide BAT, the other is the induction of BAT-like cells or beige adipocytes within white fat depots, a process called browning. Recent evidence suggests that both phenomena can occur in humans. Cold-induced promotion of BAT activity is strongly associated with enhanced thermogenesis and energy expenditure in humans and has beneficial effects on fat mass and glucose metabolism. Despite these encouraging results, a number of issues deserve additional attention including the distinct characteristics of human vs rodent BAT, the heterogeneity of human BAT depots or the identification of the adipocyte precursors that can give rise to thermogenic cells in human adipose tissue. In addition, many pharmaceutical compounds are being tested for their ability to promote a thermogenic program in human adipocytes. This review summarizes the current knowledge about the various cellular and molecular aspects of human BAT as well as the relevance for energy metabolism including its therapeutic potential for obesity.

Adipocyte arrestin domain-containing 3 protein (Arrdc3) regulates uncoupling protein 1 (Ucp1) expression in white adipose independently of canonical changes in β-adrenergic receptor signaling.

Adaptive thermogenesis and cold-induced activation of uncoupling protein 1 (Ucp1) in brown adipose tissue in rodents is well-described and attributed to sympathetic activation of β-adrenergic signaling. The arrestin domain containing protein Arrdc3 is a regulator of obesity in mice and also appears linked to obesity in humans. We generated a mouse with conditional deletion of Arrdc3, and here we present evidence that genetic ablation of Arrdc3 specifically in adipocytes results in increased Ucp1 expression in subcutaneous and parametrial adipose tissue. Although this increase in expression did not correspond with significant changes in body weight or energy expenditure, adipocyte-specific Arrdc3-null mice had improved glucose tolerance. It was previously hypothesized that Arrdc3 ablation leads to increased β-adrenergic receptor sensitivity; however, in vitro experiments show that Arrdc3-null adipocytes responded to β-adrenergic receptor agonist with decreased Ucp1 levels. Additionally, canonical β-adrenergic receptor signaling was not different in Arrdc3-null adipocytes. These data reveal a role for Arrdc3 in the regulation of Ucp1 expression in adipocytes. However, this adipocyte effect is insufficient to generate the obesity-resistant phenotype of mice with ubiquitous deletion of Arrdc3, indicating a likely role for Arrdc3 in cells other than adipocytes.

Human and Mouse Brown Adipose Tissue Mitochondria Have Comparable UCP1 Function

Brown adipose tissue (BAT) plays an important role in mammalian thermoregulation. The component of BAT mitochondria that permits this function is the inner membrane carrier protein uncoupling protein 1 (UCP1). To the best of our knowledge, no studies have directly quantified UCP1 function in human BAT. Further, whether human and rodent BAT have comparable thermogenic function remains unknown. We employed high-resolution respirometry to determine the respiratory capacity, coupling control, and, most importantly, UCP1 function of human supraclavicular BAT and rodent interscapular BAT. Human BAT was sensitive to the purine nucleotide GDP, providing the first direct evidence that human BATmitochondria have thermogenically functional UCP1. Further, our data demonstrate that human and rodent BAT have similar UCP1 function per mitochondrion. These data indicate that human and rodent BAT are qualitatively similar in terms of UCP1 function.

Apelin Enhances Brown Adipogenesis and Browning of White Adipocytes

Brown adipose tissue expends energy in the form of heat via the mitochondrial uncoupling protein UCP1. Recent studies showed that brown adipose tissue is present in adult humans and may be exploited for its anti-obesity and anti-diabetes actions. Apelin is an adipocyte-derived hormone that plays important roles in energy metabolism. Here, we report that apelin-APJ signaling promotes brown adipocyte differentiation by increasing the expressions of brown adipogenic and thermogenic transcriptional factors via the PI3K/Akt and AMPK signaling pathways. It is also found that apelin relieves the TNFα inhibition on brown adipogenesis. In addition, apelin increases the basal activity of brown adipocytes, as evidenced by the increased PGC1α and UCP1 expressions, mitochondrial biogenesis, and oxygen consumption. Finally, we provide both in vitro and in vivo evidence that apelin is able to increase the brown-like characteristics in white adipocytes. This study, for the first time, reveals the brown adipogenic and browning effects of apelin and suggests a potential therapeutic route to combat obesity and related metabolic disorders.

Activation of Human Brown Adipose Tissue by a β3-Adrenergic Receptor Agonist

Increasing energy expenditure through activation of endogenous brown adipose tissue (BAT) is a potential approach to treat obesity and diabetes. The class of β3-adrenergic receptor (AR) agonists stimulates rodent BAT, but this activity has never been demonstrated in humans. Here we determined the ability of 200mg oral mirabegron (Myrbetriq, Astellas Pharma, Inc.), a β3-AR agonist currently approved to treat overactive bladder, to stimulate BAT as compared to placebo. Mirabegron led to higher BAT metabolic activity as measured via (18)F-fluorodeoxyglucose ((18)F-FDG) using positron emission tomography (PET) combined with computed tomography (CT) in all twelve healthy male subjects (p= 0.001), and it increased resting metabolic rate (RMR) by 203± 40kcal/day (+13%; p= 0.001). BAT metabolic activity was also a significant predictor of the changes in RMR (p= 0.006). Therefore, a β3-AR agonist can stimulate human BAT thermogenesis and may be a promising treatment for metabolic disease.

Brown Adipose Tissue Quantification in Human Neonates Using Water-Fat Separated MRI

There is a major resurgence of interest in brown adipose tissue (BAT) biology, particularly regarding its determinants and consequences in newborns and infants. Reliable methods for non-invasive BAT measurement in human infants have yet to be demonstrated. The current study first validates methods for quantitative BAT imaging of rodents post mortem followed by BAT excision and re-imaging of excised tissues. Identical methods are then employed in a cohort of in vivo infants to establish the reliability of these measures and provide normative statistics for BAT depot volume and fat fraction. Using multi-echo water-fat MRI, fat- and water-based images of rodents and neonates were acquired and ratios of fat to the combined signal from fat and water (fat signal fraction) were calculated. Neonatal scans (n = 22) were acquired during natural sleep to quantify BAT and WAT deposits for depot volume and fat fraction. Acquisition repeatability was assessed based on multiple scans from the same neonate. Intra- and inter-rater measures of reliability in regional BAT depot volume and fat fraction quantification were determined based on multiple segmentations by two raters. Rodent BAT was characterized as having significantly higher water content than WAT in both in situ as well as ex vivo imaging assessments. Human neonate deposits indicative of bilateral BAT in spinal, supraclavicular and axillary regions were observed. Pairwise, WAT fat fraction was significantly greater than BAT fat fraction throughout the sample (ΔWAT-BAT = 38%, p<10−4). Repeated scans demonstrated a high voxelwise correlation for fat fraction (Rall = 0.99). BAT depot volume and fat fraction measurements showed high intra-rater (ICCBAT,VOL = 0.93, ICCBAT,FF = 0.93) and inter-rater reliability (ICCBAT,VOL = 0.86, ICCBAT,FF = 0.93). This study demonstrates the reliability of using multi-echo water-fat MRI in human neonates for quantification throughout the torso of BAT depot volume and fat fraction measurements.

Anatomical localization, gene expression profiling and functional characterization of adult human neck brown fat

The imbalance between energy intake and expenditure is the underlying cause of the current obesity and diabetes pandemics. Central to these pathologies is the fat depot: white adipose tissue (WAT) stores excess calories, and brown adipose tissue (BAT) consumes fuel for thermogenesis using tissue-specific uncoupling protein 1 (UCP1). BAT was once thought to have a functional role in rodents and human infants only, but it has been recently shown that in response to mild cold exposure, adult human BAT consumes more glucose per gram than any other tissue. In addition to this nonshivering thermogenesis, human BAT may also combat weight gain by becoming more active in the setting of increased whole-body energy intake. This phenomenon of BAT-mediated diet-induced thermogenesis has been observed in rodents and suggests that activation of human BAT could be used as a safe treatment for obesity and metabolic dysregulation. In this study, we isolated anatomically defined neck fat from adult human volunteers and compared its gene expression, differentiation capacity and basal oxygen consumption to different mouse adipose depots. Although the properties of human neck fat vary substantially between individuals, some human samples share many similarities with classical, also called constitutive, rodent BAT.

Noninvasive identification and assessment of functional brown adipose tissue in rodents using hyperpolarized 13C imaging

The recent identification of functional depots of brown adipose tissue (BAT) in adult humans has potential implications for the treatment of obesity. In order to evaluate new therapies aimed at inducing the production of more BAT or activating BAT in humans, it will be important to develop noninvasive methods to assess the functional state of the tissue in vivo. In this study, we investigate the feasibility of using hyperpolarized (13)C imaging to noninvasively identify functional, activated BAT in an in vivo rodent model, in less than 1 min, following an infusion of pre-polarized [1-(13)C] pyruvate. Hyperpolarized (13)C imaging was used to monitor BAT metabolic conversion of pre-polarized [1-(13)C] pyruvate in rats during baseline and norepinephrine (NE)-stimulated conditions. Activated BAT, stimulated by NE injection, can be detected in rats by increased conversion of pre-polarized [1-(13)C] pyruvate into its downstream products (13)C bicarbonate and [1-(13)C] lactate. The colocalization of the (13)C signal to interscapular BAT was validated using hematoxylin-eosin histological staining. The radiation-free nature and recent translation into the clinic of the hyperpolarized (13)C-imaging test may potentially facilitate trials of therapeutics targeting BAT activation in humans.

Excess cholesterol and fat in the diet: A dangerous liaison for energy expenditure and the liver

Excess cholesterol and fat in the diet: A dangerous liaison for energy expenditure and the liver

Differentiation and characterization in primary culture of white adipose tissue brown adipocyte-like cells

Rodent brown adipose tissue (BAT) is considered the main effector of adaptative thermogenesis as it contains a unique mitochondrial uncoupling protein, termed as uncoupling protein-1 (UCP1). The emergence of ectopic brown adipocytes in the white adipose tissue (WAT), called recruitment, might play an important role in the prevention of obesity. The recruitment phenomenon has until now been investigated mostly in vivo. This study is an attempt to mimic in vitro the recruitment phenomenon. It consisted in culturing the stroma vascular fractions of mouse BAT and WAT in a brown adipocyte differentiation medium. The multilocular cells obtained, referred to as BAT(B) and WAT(B) adipocytes, respectively, were compared. The BAT(B) and WAT(B) adipocytes were morphologically different. The expressions of UCP1, peroxisome proliferator-activated receptor-gamma coactivator-1alpha (PGC-1alpha), leptin and resistin mRNAs were low in WAT(B) adipocytes as compared with those in BAT(B) adipocytes. The expressions of UCP1 and PGC-1alpha proteins were, however, much higher in WAT(B) adipocytes, amounting 51% and 36% of those in BAT(B) adipocytes. The patterns of expression of UCP1, PGC-1alpha and leptin in the BAT(B) and in WAT(B) adipocytes were different with a higher relative expression of PGC-1alpha in the latter. Rosiglitazone increased UCP1 mRNA expression 4.5-fold in the BAT(B) and significantly more, 7.9-fold, in the WAT(B) adipocytes. Retinoic acid and triiodothyronine increased UCP1 mRNA expression in the BAT(B) adipocytes 1.6- and 2-fold, respectively but, surprisingly, slightly decreased UCP1 mRNA expression in the WAT(B) adipocytes. The study suggests that the nature and possibly the origin of WAT brown adipocytes is different from that of BAT brown adipocytes. It proposes an in vitro approach that could prove very useful to better characterize the WAT brown adipocyte-like cells.