Human Brown Fat Research Articles

Endothelin 3/EDNRB signaling induces thermogenic differentiation of white adipose tissue

Thermogenic adipose tissue, consisting of brown and beige fat, regulates nutrient utilization and energy metabolism. Human brown fat is relatively scarce and decreases with obesity and aging. Hence, inducing thermogenic differentiation of white fat offers an attractive way to enhance whole-body metabolic capacity. Here, we show the role of endothelin 3 (EDN3) and endothelin receptor type B (EDNRB) in promoting the browning of white adipose tissue (WAT). EDNRB overexpression stimulates thermogenic differentiation of human white preadipocytes through cAMP-EPAC1-ERK activation. In mice, cold induces the expression of EDN3 and EDNRB in WAT. Deletion of EDNRB in adipose progenitor cells impairs cold-induced beige adipocyte formation in WAT, leading to excessive weight gain, glucose intolerance, and insulin resistance upon high-fat feeding. Injection of EDN3 into WAT promotes browning and improved whole-body glucose metabolism. The findings shed light on the mechanism of WAT browning and offer potential therapeutics for obesity and metabolic disorders.

EPAC1 enhances brown fat growth and beige adipogenesis

Brown adipose tissue (BAT) is a central thermogenic organ that enhances energy expenditure and cardiometabolic health. However, regulators that specifically increase the number of thermogenic adipocytes are still an unmet need. Here, we show that the cAMP-binding protein EPAC1 is a central regulator of adaptive BAT growth. In vivo, selective pharmacological activation of EPAC1 increases BAT mass and browning of white fat, leading to higher energy expenditure and reduced diet-induced obesity. Mechanistically, EPAC1 coordinates a network of regulators for proliferation specifically in thermogenic adipocytes, but not in white adipocytes. We pinpoint the effects of EPAC1 to PDGFRα-positive preadipocytes, and the loss of EPAC1 in these cells impedes BAT growth and worsens diet-induced obesity. Importantly, EPAC1 activation enhances the proliferation and differentiation of human brown adipocytes and human brown fat organoids. Notably, a coding variant of RAPGEF3 (encoding EPAC1) that is positively correlated with body mass index abolishes noradrenaline-induced proliferation of brown adipocytes. Thus, EPAC1 might be an attractive target to enhance thermogenic adipocyte number and energy expenditure to combat metabolic diseases.

Human brown fat and metabolic disease: a heated debate.

Human brown fat and metabolic disease: a heated debate.

Thermogenic Capacity of Human Supraclavicular Brown Fat and Cold-Stimulated Brain Glucose Metabolism.

Human brain metabolism is susceptible to temperature changes. It has been suggested that the supraclavicular brown adipose tissue (BAT) protects the brain from these fluctuations by regulating heat production through the presence of uncoupling protein 1 (UCP-1). It remains unsolved whether inter-individual variation in the expression of UCP-1, which represents the thermogenic capacity of the supraclavicular BAT, is linked with brain metabolism during cold stress. Ten healthy human participants underwent 18F-FDG PET scanning of the brain under cold stimulus to determine brain glucose uptake (BGU). On a separate day, an excision biopsy of the supraclavicular fat-the fat proximal to the carotid arteries supplying the brain with warm blood-was performed to determine the mRNA expression of the thermogenic protein UCP-1. Expression of UCP-1 in supraclavicular BAT was directly related to the whole brain glucose uptake rate determined under cold stimulation (rho = 0.71, p = 0.03). In sub-compartmental brain analysis, UCP-1 expression in supraclavicular BAT was directly related to cold-stimulated glucose uptake rates in the hypothalamus, medulla, midbrain, limbic system, frontal lobe, occipital lobe, and parietal lobe (all rho ≥ 0.67, p < 0.05). These relationships were independent of body mass index and age. When analysing gene expressions of BAT secretome, we found a positive correlation between cold-stimulated BGU and DIO2. These findings provide evidence of functional links between brain metabolism under cold stimulation and UCP-1 and DIO2 expressions in BAT in humans. More research is needed to evaluate the importance of these findings in clinical outcomes, for instance, in examining the supporting role of BAT in cognitive functions under cold stress.

Drug-Initiated Activity Metabolomics Identifies Myristoylglycine as a Potent Endogenous Metabolite for Human Brown Fat Differentiation.

Worldwide, obesity rates have doubled since the 1980s and in the USA alone, almost 40% of adults are obese, which is closely associated with a myriad of metabolic diseases such as type 2 diabetes and arteriosclerosis. Obesity is derived from an imbalance between energy intake and consumption, therefore balancing energy homeostasis is an attractive target for metabolic diseases. One therapeutic approach consists of increasing the number of brown-like adipocytes in the white adipose tissue (WAT). Whereas WAT stores excess energy, brown adipose tissue (BAT) can dissipate this energy overload in the form of heat, increasing energy expenditure and thus inhibiting metabolic diseases. To facilitate BAT production a high-throughput screening approach was developed on previously known drugs using human Simpson–Golabi–Behmel Syndrome (SGBS) preadipocytes. The screening allowed us to discover that zafirlukast, an FDA-approved small molecule drug commonly used to treat asthma, was able to differentiate adipocyte precursors and white-biased adipocytes into functional brown adipocytes. However, zafirlukast is toxic to human cells at higher dosages. Drug-Initiated Activity Metabolomics (DIAM) was used to investigate zafirlukast as a BAT inducer, and the endogenous metabolite myristoylglycine was then discovered to mimic the browning properties of zafirlukast without impacting cell viability. Myristoylglycine was found to be bio-synthesized upon zafirlukast treatment and was unique in inducing brown adipocyte differentiation, raising the possibility of using endogenous metabolites and bypassing the exogenous drugs to potentially alleviate disease, in this case, obesity and other related metabolic diseases.

Capsaicin directly promotes adipocyte browning in the chemical compound-induced brown adipocytes converted from human dermal fibroblasts

Human brown fat is a potential therapeutic target for preventing obesity and related metabolic diseases by dissipating energy as heat through uncoupling protein 1 (UCP1). We have previously reported a method to obtain chemical compound-induced brown adipocytes (ciBAs) converted from human dermal fibroblasts under serum-free conditions. However, pharmacological responses to bioactive molecules have been poorly characterised in ciBAs. This study showed that the treatment with Capsaicin, an agonist of transient receptor potential vanilloid 1, directly activated adipocyte browning such as UCP1 expression, mitochondrial biogenesis, energy consumption rates, and glycerol recycling in ciBAs. Furthermore, genome-wide transcriptome analysis indicated that Capsaicin activated a broad range of metabolic genes including glycerol kinase and glycerol 3-phosphate dehydrogenase 1, which could be associated with the activation of glycerol recycling and triglyceride synthesis. Capsaicin also activated UCP1 expression in immortalised human brown adipocytes but inhibited its expression in mesenchymal stem cell-derived adipocytes. Altogether, ciBAs successfully reflected the direct effects of Capsaicin on adipocyte browning. These findings suggested that ciBAs could serve as a promising cell model for screening of small molecules and dietary bioactive compounds targeting human brown adipocytes.

Human brown fat, adiposity, and cardiometabolic health: New pieces to the puzzle

Brown adipose tissue (BAT) is an emerging target against obesity and its related metabolic diseases. Wibmer et al.1 recently reported that human BAT is associated with a healthier fat distribution and improved cardiometabolic health independent of adiposity and fat distribution.

Bola3 Regulates Beige Adipocyte Thermogenesis via Maintaining Mitochondrial Homeostasis and Lipolysis

Mitochondrial iron-sulfur (Fe-S) cluster is an important cofactor for the maturation of Fe-S proteins, which are ubiquitously involved in energy metabolism; however, factors facilitating this process in beige fat have not been established. Here, we identified BolA family member 3 (Bola3), as one of 17 mitochondrial Fe-S cluster assembly genes, was the most significant induced gene in the browning program of white adipose tissue. Using lentiviral-delivered shRNA in vitro, we determined that Bola3 deficiency inhibited thermogenesis activity without affecting lipogenesis in differentiated beige adipocytes. The inhibition effect of Bola3 knockdown might be through impairing mitochondrial homeostasis and lipolysis. This was evidenced by the decreased expression of mitochondria related genes and respiratory chain complexes, attenuated mitochondrial formation, reduced mitochondrial maximal respiration and inhibited isoproterenol-stimulated lipolysis. Furthermore, BOLA3 mRNA levels were higher in human deep neck brown fat than in the paired subcutaneous white fat, and were positively correlated with thermogenesis related genes (UCP1, CIDEA, PRDM16, PPARG, COX7A1, and LIPE) expression in human omental adipose depots. This study demonstrates that Bola3 is associated with adipose tissue oxidative capacity both in mice and human, and it plays an indispensable role in beige adipocyte thermogenesis via maintaining mitochondrial homeostasis and adrenergic signaling-induced lipolysis.

The gut hormone secretin triggers a gut-brown fat-brain axis in the control of food intake.

What is the topic of this review? Brown fat's role in meal-associated thermogenesis and the related consequences for energy balance regulation with a focus on the gut hormone secretin, which has been identified as the endocrine molecular mediator of meal-associated brown fat thermogenesis. What advances does it highlight? The finding of the secretin-induced gut-brown fat-brain axis creates new opportunities to manipulate brown fat and thereby energy balance in a natural way while living in a thermoneutral environment. The role of brown fat as a mere catabolic heater organ needs to be revised and more attention should be directed towards the regulatory role of brown fat beyond energy expenditure. Brown fat research concentrates on the energy expenditure function of this heating organ, whereas previous evidence for a role of brown fat in regulating energy intake has been mostly neglected. Ingestion of a single mixed meal activates human brown fat thermogenesis to the same degree as cold. In mice, activation of brown fat thermogenesis with a β3 -adrenergic receptor agonist inhibits food intake. Pharmacological β-blockade, however, inhibits neither meal-associated thermogenesis nor food intake. We recently identified the gut hormone secretin as a non-adrenergic activator of brown fat. In vivo, secretin treatment acutely increases energy expenditure and inhibits food intake in wild-type, but not in uncoupling protein 1 (UCP1)-knockout (KO) mice, which lack thermogenic brown fat function. Concurrently, secretin alters gene expression of melanocortinergic peptides of hypothalamic neurons in wild-type mice, but not UCP1-KO. Blocking endogenous secretin with a neutralizing antibody attenuates brown fat thermogenesis during refeeding, increases food intake of mice, and alters ad libitum feeding behaviour. Taken together, these findings demonstrate that secretin triggers an endocrine gut-brown adipose tissue-brain axis in the control of satiation. We hypothesize that meal-associated activation of brown adipose tissue thermogenesis induced by secretin results in a rise in brain temperature and increased melanocortinergic signalling. Taken together, brown fat is not a mere heating organ dissipating excess calories but also involved in gut-brain communication in the control of food intake.

Cytoplasmic p16 Is Expressed in Normal Brown Fat and Hibernomas.

White adipose tissue browning has emerged as a putative therapy of obesity, and studies in mice have shown that Cdkn2a is implicated in white-to-brown transition. However, the role of Cdkn2a product p16 has been never studied in human brown fat tissue. The aim of the study is to investigate the expression of p16 in normal brown fat and in hibernoma, a lipoma containing brown fat-like adipocytes. Ten normal brown fat tissues and 5 hibernomas were immunohistochemically studied for p16 expression. Nearby white adipose tissue was used for comparison. All brown fat and hibernomas specimens express p16 in a cytoplasmic manner. Neighboring white adipose tissue is negative for p16 expression. Thus, cytoplasmic p16 may be associated with fat tissue browning.

NFIA Colocalizes with PPARgamma and Activates the Cell-Type–Specific Enhancers to Control the Brown Fat Gene Program

Brown fat dissipates energy as heat by means of the uncoupling protein-1 (UCP1) on the mitochondrial inner membrane. Brown fat activity is inversely correlated with body mass index in humans, and pilot studies have shown that interventions such as chronic cold exposure successfully recruit human brown fat and increase systemic energy expenditure. Therefore, stimulating development and/or function of brown fat would be a novel strategy for the treatment of obesity and its complications. Here, we identified nuclear factor I-A (NFIA) as a transcriptional regulator of brown fat by a genome-wide open chromatin analysis of murine brown and white fat followed by motif analysis of the brown-fat-specific open chromatin regions. Introduction of NFIA into myoblasts results in brown adipocyte differentiation. Conversely, the brown fat of NFIA knockout mice displays impaired expression of the brown-fat-specific genes and reciprocal elevation of muscle genes. In human brown fat, expression of NFIA and the brown-fat-specific genes including UCP1 is positively correlated. Mechanistically, NFIA co-localizes with the master transcriptional regulator of adipogenesis, PPARgamma, selectively at the brown-fat-specific enhancers. Moreover, the binding of NFIA precedes and facilitates the binding of PPARgamma, leading to increased chromatin accessibility and active transcription. Most recently, we performed mass spectrometry analysis of NFIA protein complex to identify and characterize the crucial partner of NFIA-dependent brown-fat-specific chromatin regulation. Collectively, these results indicate that NFIA is a key transcription factor that activates the cell-type-specific enhancers and facilitates the binding of PPARgamma for controlling the brown fat gene program. Disclosure Y. Hiraike: Speaker's Bureau; Self; Novo Nordisk A/S. Research Support; Self; Novo Nordisk A/S, Mitsubishi Tanabe Pharma Corporation. H. Waki: Research Support; Self; MSD K.K., Novartis Pharma K.K., Boehringer Ingelheim Pharmaceuticals, Inc., Sanofi K.K., Ono Pharmaceutical Co., Ltd., Kyowa Hakko Kirin Co., Ltd., Takeda PHarmaceutical Co., Ltd.. S. Tsutsumi: None. H. Aburatani: None. T. Yamauchi: Research Support; Self; Novo Nordisk Inc., Daiichi Sankyo Company, Limited, Sanofi, Takeda, Tanabe-Mitsubishi. T. Kadowaki: Consultant; Self; Novo Nordisk A/S, AstraZeneca, Merck Sharp &amp; Dohme Corp.. Research Support; Self; Kissei Pharmaceutical Co., Ltd., Taisho Pharmaceutical Co., Ltd., Sanofi, Kyowa Hakko Kirin Co., Ltd., Novo Nordisk A/S, Astellas Pharma, Daiichi Sankyo Company, Limited, Takeda, Mitsubishi Tanabe Pharma Corporation, Ono Pharmaceutical Co., Ltd., Merck Sharp &amp; Dohme Corp., Nippon Boehringer Ingelheim Co. Ltd.. Speaker's Bureau; Self; Astellas Pharma, AstraZeneca, Merck Sharp &amp; Dohme Corp., Ono Pharmaceutical Co., Ltd., Takeda, Eli Lilly and Company, Nippon Boehringer Ingelheim Co. Ltd., Novo Nordisk A/S.

CRISPR-Engineered Human Brown-Like Adipocytes Promotes Metabolic Homeostasis through Activation of Endogenous Brown Fat

Brown and brown-like beige adipocytes dissipate energy for thermogenesis and have been proposed to combat obesity and metabolic disorders. Uncoupling protein 1 (UCP1) is uniquely expressed in brown and beige adipocytes, and facilitates fuel utilization and energy expenditure. Ectopic UCP1 overexpression improves obesity and insulin resistance in mice. Recently, we utilized the CRISPR/Cas9 synergistic activation mediator and specific gRNAs to boost endogenous UCP1 expression in human white adipocytes. The CRISPR/Cas9 engineered human brown fat-like (referred to as HUMBLE, hereafter) cells had acquired human brown fat features when comparing bona fide human brown adipocytes derived from the same individual. Obese mice receiving a transplantation of HUMBLE cells showed improved glucose tolerance and insulin sensitivity, as well as increased energy expenditure. This was mediated, at least in part, via activation of endogenous brown fat, which showed an increase in heat production and glucose uptake in mice receiving HUMBLE cells. Co-culture with HUMBLE cells or treatment of conditional medium from HUMBLE cells promoted glucose uptake and thermogenesis in brown adipocytes. Metabolomic analysis identified an increased ratio of arginine and asymmetrical dimethylarginine (ADMA) in the sera of mice receiving HUMBLE cell transplantation. Arginine is known to promote nitric oxide biosynthesis, which can activate thermogenic function of brown fat. Consistently, the level of nitric oxide was increased in the endogenous brown fat of mice receiving HUMBLE cells. Inhibition of nitric oxide synthase abolished the HUMBLE cells-mediated activation of brown adipocytes in vitro and in vivo. In summary, CRISPR/Cas9-mediated activation of endogenous UCP1 expression in human white adipocytes creates brown fat-like features, and activates endogenous brown fat, potentially through arginine-related metabolites to improve the systemic glucose utilization. Disclosure C. Wang: None. M. Lundh: None. R. Kriszt: Employee; Self; QuintilesIMS. T. Huang: None. L.O. Leiria: None. F. Shamsi: None. M. Lynes: None. J. Darcy: None. B. Emanuelli: None. M. Kiebish: None. Y. Tseng: Other Relationship; Self; Chugai Pharmaceutical Co., Ltd.. Research Support; Self; MedImmune.

Derivation and characterization of a UCP1 reporter human ES cell line

Interest in human brown fat as a novel therapeutic target to tackle the growing obesity and diabetes epidemic has increased dramatically in recent years. While much insight into brown fat biology has been gained from murine cell lines and models, few resources are available to study human brown fat in vitro, which makes the need for new ways to derive and study human brown adipocytes imperative. Human ES cell based reporter systems present an excellent tool to identify, mark, and purify cell populations of choice. In this study, we detail the derivation and characterization of a novel human ES UCP1 reporter cell line that marks UCP1 positive adipocytes in vitro. We targeted a mCherry reporter to the UCP1 stop codon via CRISPR-Cas9 based gene targeting. The brown adipocytes derived from reporter cells express UCP1, display high mitochondrial content, multi-locular lipid morphology, and exhibit functional properties such as lipolysis. The mCherry positive cells purified after cell sorting show elevated expression of brown fat marker genes and a high similarity to isolated human brown fat via RNA-seq analysis. Finally, we demonstrate the utility of this reporter to real time monitor UCP1 expression upon stimulation. This reporter cell line thus presents new opportunities to study human brown fat biology by enabling future work to understand early human brown fat development, perform disease modeling, and facilitate drug screening.

Indomethacin Induces Browning and Brown Adipogenesis in Murine 3T3‐L1 White Adipocytes and Human Brown Fat Cells

Functional brown adipose tissue, including classical brown adipocytes and brown‐like or beige adipocytes, which develop within white adipose tissue in response to various stimuli, have emerged as novel targets for obesity treatment and prevention. Identifying strategies that increase UCP‐1 expression and induce browning and brown adipogenesis is key to unlocking thermogenic potential. Indomethacin (INDO) is a non‐selective Cox‐1/Cox‐2 inhibitor which is an approved NSAID used to treat and relief inflammatory diseases. It has been reported that INDO induced C3H10T1/2 mesenchymal stem cell differentiation into adipocytes by activating PPARg, which is also important for browning and brown adipogenesis. In this study, INDO was tested at various doses (2, 5, 10, 20, 50 mM) in 3T3‐L1 mouse pre‐adipocytes in a 7‐day differentiation process as well as human brown fat cells in a 21‐day differentiation process. Rosiglitazone (ROSI), a well‐known browning agent and PPARg agonist, was used as a positive control. At the end of differentiation, 3T3‐L1 cells were subjected to thermogenic activation by isoproterenol (ISO), a b‐adrenergic receptor agonist, or the control for 6–24 hours. Protein and mRNA expression of UCP‐1, PPARg, and PGC1a were measured. mRNA analysis of other brown and beige maker genes (PRDM16, Cidea, and CD137), and white marker genes (IGFBP3), as well as mitochondrial related genes (Nrf and Cox4a) were also measured. For mechanistic exploration, PPARg transactivation reporter gene assays were conducted. In addition, an adenovirus mediated PPARg knock down (KD) in 3T3‐L1 cells was generated. We report that similar to ROSI, INDO significantly induced UCP‐1 mRNA expression in 3T3‐L1 cells under basal and ISO stimulated condition compared to the controls (p&lt;0.05 for INDO at 10, 20, 50 μM under basal condition and INDO at 2, 5, 10, 20 μM under ISO stimulated condition). INDO also significantly induced mRNA expression of Nrf and PGC1a (p&lt;0.05). INDO also significantly induced UCP1 and PGC1α protein expression under basal condition (p&lt;0.05 INDO at 10 and 20 μM) while suppressing PPARg protein expression (p&lt;0.05 INDO at 10 and 20 μM). Mechanistically, INDO significantly activated PPARg in 3T3‐L1 cells (p&lt;0.01 for INDO at 20 and 50 μM), which is consistent with the previous report in C3H10T1/2 cells. Moreover, upregulation of UCP1 and other brown markers by INDO were decreased in PPARg KD cells compared to non‐targeting adenovirus infected control cells. Furthermore, we explored INDO's effects on promoting brown adipogenesis in human brown fat cells. We report that INDO significantly induced PPARg, PGC1α, and DIO2 at 20 μM (p&lt;0.05). INDO also significantly induced UCP1 mRNA and protein expression (p&lt;0.01 for INDO at 20 μM for mRNA and p&lt;0.05 for INDO at 2, 5, 10 μM, for protein). Taken together, despite INDO's potential systemic side‐effects, our results reveal a novel capacity for INDO to induce browning and brown adipogenesis through acting as a PPARg agonist.Support or Funding InformationThe work has been partially supported by NIH 1R15AT008733 award.This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Study of the association of Trp64Arg mutation of beta three adrenergic receptor with obesity in Saudi population

Introduction: Beta three adrenergic receptor (ADRB3) is an adrenergic receptor that induces activation of adenylate cyclase located mainly in adipose tissue and is involved in the thermogenesis of brown fat tissue and in the regulation of lipolysis. Agonists of ADRB3 are found to induce the thermogenesis process of human brown fat tissue and thus believed to be excellent anti-obesity targets. The most studied single nucleotide polymorphism (SNP) of ADRB3 is rs4994. Inconsistent findings have been found in earlier studies about the association of rs4994 polymorphisms with obesity among different populations. The association of ADRB3/rs4994 polymorphism with obesity among the Saudi population is unknown. This study aimed to investigate the association of ADRB3/rs4994 polymorphism with obesity, blood lipids and blood pressure in the Saudi population.&#x0D; Method: This study was a case control study involving 88 obese healthy volunteers and 84 non-obese (controls) volunteers recruited from the King Khaled University Hospital (KKUH), Riyadh City, Saudi Arabia. Using KASPTM (Competitive Allele-Specific PCR) the rs4994 genotype for each participant was determined. The frequency, distribution, and association of each genotype with body mass index (BMI) and lipid profile were calculated.&#x0D; Results: The distribution of CC, TT and CT genotypes in the study population was 0.37, 0.06 and 0.56, respectively. The heterozygote CT genotype was associated with a reduced risk of obesity (odds ratio (OR)=0.4398, 95%CI=0.2338 to 0.8277, P-value=0.010). It was more frequent in the non-obese participants compared to the obese participants (67.9% vs. 44.3%, respectively). Moreover, participants with the CT genotype had a significantly lower BMI (P=0.004). In contrast, the CC genotype was associated with an increased risk of obesity (OR=2.5, 95%CI=1.3467 to 4.8758, P-value=0.004). The frequency of the CC genotype was higher in obese participants compared to the non-obese ones (46.6% vs. 28.6%, respectively). Participants with the CC genotype demonstrated a significantly higher BMI than participants with the CT or TT genotypes (Q= 4.5, P=0.004). The TT genotype had no significant effects on the participants’ BMI (OR=2.9, 95%CI=0.7563 to 11.5759, P value=0.11), and it was higher in obese compared to non-obese participants (9.1% vs. 3.6%, respectively). No significant effect of ADRB3/rs4994 polymorphism on blood lipid profile or blood pressure was observed.&#x0D; Conclusion: The findings of this study suggested that the heterozygote CT genotype of the ADRB3/rs4994 polymorphism is associated with a reduced risk of obesity among the Saudi population. In the future, larger scale studies are required to further confirm these observations.

Peroxisome Proliferator Activated Receptor Gamma Controls Mature Brown Adipocyte Inducibility through Glycerol Kinase

Peroxisome proliferator-activated receptors (PPARs) have been suggested as the master regulators ofadipose tissue formation. However, their role in regulating brown fat functionality has not been resolved. To address this question, we generated mice with inducible brown fat-specific deletions of PPARα, β/δ, and γ, respectively. We found that both PPARα and β/δδ are dispensable for brown fat function. In contrast, we could show that ablation of PPARγ invitro and invivo led to a reduced thermogenic capacity accompanied by a loss of inducibility by β-adrenergic signaling, as well as a shift from oxidative fatty acid metabolism to glucose utilization. We identified glycerol kinase (Gyk) as a partial mediator of PPARγ function and could show that Gyk expression correlates with brown fat thermogenic capacity in human brown fat biopsies. Thus, Gyk might constitute the link between PPARγ-mediated regulation of brown fat function and activation by β-adrenergic signaling.

Brown Adipose Tissue Development and Metabolism.

Brown adipose tissue is well known to be a thermoregulatory organ particularly important in small rodents and human infants, but it was only recently that its existence and significance to metabolic fitness in adult humans have been widely realized. The ability of active brown fat to expend high amounts of energy has raised interest in stimulating thermogenesis therapeutically to treat metabolic diseases related to obesity and type 2 diabetes. In parallel, there has been a surge of research aimed at understanding the biology of rodent and human brown fat development, its remarkable metabolic properties, and the phenomenon of white fat browning, in which white adipocytes can be converted into brown like adipocytes with similar thermogenic properties. Here, we review the current understanding of the developmental and metabolic pathways involved in forming thermogenic adipocytes, and highlight some of the many unknown functions of brown fat that make its study a rich and exciting area for future research.

Loss of the tumour suppressor gene AIP mediates the browning of human brown fat tumours.

Human brown fat tumours (hibernomas) show concomitant loss of the tumour suppressor genes MEN1 and AIP. We hypothesized that the brown fat phenotype is attributable to these mutations. Accordingly, in this study, we demonstrate that silencing of AIP in human brown preadipocytic and white fat cell lines results in the induction of the brown fat marker UCP1. In human adipocytic tumours, loss of MEN1 was found both in white (one of 51 lipomas) and in brown fat tumours. In contrast, concurrent loss of AIP was always accompanied by a brown fat morphology. We conclude that this white-to-brown phenotype switch in brown fat tumours is mediated by the loss of AIP. Copyright © 2017 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

NFIA co-localizes with PPARγ and transcriptionally controls the brown fat gene program.

Brown fat dissipates energy as heat and protects against obesity. Here, we identified nuclear factor I-A (NFIA) as a transcriptional regulator of brown fat by a genome-wide open chromatin analysis of murine brown and white fat followed by motif analysis of brown-fat-specific open chromatin regions. NFIA and the master transcriptional regulator of adipogenesis, PPARγ, co-localize at the brown-fat-specific enhancers. Moreover, the binding of NFIA precedes and facilitates the binding of PPARγ, leading to increased chromatin accessibility and active transcription. Introduction of NFIA into myoblasts results in brown adipocyte differentiation. Conversely, the brown fat of NFIA-knockout mice displays impaired expression of the brown-fat-specific genes and reciprocal elevation of muscle genes. Finally, expression of NFIA and the brown-fat-specific genes is positively correlated in human brown fat. These results indicate that NFIA activates the cell-type-specific enhancers and facilitates the binding of PPARγ to control the brown fat gene program.

Optical visualisation of thermogenesis in stimulated single-cell brown adipocytes

The identification of brown adipose deposits in adults has led to significant interest in targeting this metabolically active tissue for treatment of obesity and diabetes. Improved methods for the direct measurement of heat production as the signature function of brown adipocytes (BAs), particularly at the single cell level, would be of substantial benefit to these ongoing efforts. Here, we report the first application of a small molecule-type thermosensitive fluorescent dye, ERthermAC, to monitor thermogenesis in BAs derived from murine brown fat precursors and in human brown fat cells differentiated from human neck brown preadipocytes. ERthermAC accumulated in the endoplasmic reticulum of BAs and displayed a marked change in fluorescence intensity in response to adrenergic stimulation of cells, which corresponded to temperature change. ERthermAC fluorescence intensity profiles were congruent with mitochondrial depolarisation events visualised by the JC-1 probe. Moreover, the averaged fluorescence intensity changes across a population of cells correlated well with dynamic changes such as thermal power, oxygen consumption, and extracellular acidification rates. These findings suggest ERthermAC as a promising new tool for studying thermogenic function in brown adipocytes of both murine and human origins.