Brown Fat Depots Research Articles

THU297 Metformin Treatment Of Juvenile Mice Alters Aging-Related Developmental And Metabolic Phenotypes In Sex-Dependent And -Independent Manners

Abstract Disclosure: Y. Zhu: None. M. Engmann: None. D. Medina: None. A. Bartke: None. B.S. Ellsworth: None. R. Yuan: None. Metformin is a widely used drug for the treatment of type 2 diabetes that also has a strong potential for long-term effects which may extend healthspan and longevity. In the current study, C57BL/6J (B6) juvenile female and male mice were treated with metformin between the ages of 15 and 56 days. Saline was used as the control. The results show that early-life treatment with metformin has profound effects on developmental and metabolic traits. Body weight was significantly reduced by metformin treatment in both sexes (P<0.05, t test). At 10 weeks of age, mice were euthanized, and organ weights were recorded. In treated males, weights of epididymal, perirenal, and brown fat depots were significantly reduced (P<0.05, t test). Pancreas weight was significantly reduced in both sexes (P<0.05, t test). Hypothalamus weight was significantly reduced in the females, and whole brain weight was significantly reduced in the males. Tail length as well as age of sexual maturation were not significantly altered in either sex. No significant difference was found in circulating insulin-like growth factor 1 (IGF1) or adiponectin. Circulating insulin was significantly reduced by the treatment under fasting and non-fasting conditions in the male mice, while in the females no significant difference was detected. Insulin sensitivity, calculated by the quantitative insulin-sensitivity check index (QUICKI), was suggestively increased in the male mice (P=0.062, t test). Glucose tolerance test (GTT) did not show a significant difference in treated female mice; however, comparing the area under curve, metformin treatment significantly improved the glucose tolerance of male mice (P=0.014, t test). Insulin tolerance test (ITT) showed no significant difference in the male mice; but, unexpectedly, in female mice, metformin treatment significantly reduced insulin sensitivity. This study revealed that early-life metformin treatment alters development and metabolism of mice in both sex-specific and non-specific manners, which may have long-term impacts on metabolism in aging. Interestingly, comparing the results of this study with previous studies of metformin-treated heterogenous UM-HET3 mice, further analyses revealed that metformin effects on body weight, age of sexual maturation, body size, IGF1, adiponectin, insulin, GTT, and ITT, are genetically dependent. Funding: SIU collaborative grant to Rong Yuan and Buffy S. Ellsworth. SIU Geriatric foundation by Andrzej Bartke Presentation: Thursday, June 15, 2023

77-OR: Targeting JunB Induces a Shift from Low- to High-Thermogenic Adipocytes and Ameliorates Diet-Induced Insulin Resistance

The coexistence of brown adipocytes with low and high thermogenic activity is a fundamental feature of brown adipose tissue (BAT) heterogeneity and plasticity. However, the mechanisms that govern thermogenic adipocyte heterogeneity and its significance in obesity and metabolic disease remain poorly understood. In the current study, we identified a population of JunB-enriched adipocytes (JunB+ adipocytes) within the brown fat depot that exhibits lower thermogenic capacity and fewer and smaller lipid droplets compared to high-thermogenic adipocytes. This population of JunB+ adipocytes exhibited marked expansion during obesity, in part through induction of pro-inflammatory cytokines TNFα and IL-6. Depletion of JunB in adipocytes or UCP1+ adipocytes increased the fraction of adipocytes exhibiting high mitochondrial content and thermogenic capacity, leading to enhanced basal and cold-induced energy expenditure and protection against diet-induced obesity and insulin resistance. Mechanistically, JunB directly binds to the promoter of estrogen-related receptor α (Errα), a downstream effector of PGC1α, and suppresses its transcriptional function. JunB antagonizes the stimulatory effects of PGC1α-ERRα on mitochondrial biogenesis and high-thermogenic adipocyte development. Taken together, our studies uncover a novel mechanism involving JunB that shapes thermogenic adipocyte heterogeneity and serves a critical role in maintaining systemic metabolic health. Disclosure X.Zhang: None. C.Wang: None. M.Liu: None. Funding National Institute of Diabetes and Digestive and Kidney Diseases (DK110439); American Heart Association (20POST35120020)

Pathological bile acid concentrations in chronic cholestasis cause adipose mitochondrial defects

Although fat loss is observed in patients with cholestasis, how chronically elevated bile acids (BAs) impact white and brown fat depots remains obscure. To determine the direct effect of pathological levels of BAs on lipid accumulation and mitochondrial function, primary white and brown adipocyte cultures along with fat depots from two separate mouse models of cholestatic liver diseases, namely (i) genetic deletion of farnesoid X receptor (Fxr); small heterodimer (Shp) double knockout (DKO) and (ii) injury by 3,5-diethoxycarbonyl-1,4-dihydrocollidine (DDC), were used. As expected, cholestatic mice accumulate high systemic BA levels and exhibit fat loss. Here, we demonstrate that chronic exposure to pathological BA levels results in mitochondrial dysfunction and defective thermogenesis. Consistently, both DKO and DDC-fed mice exhibit lower body temperature. Importantly, thermoneutral (30°C) housing of the cholestatic DKO mice rescues the decrease in brown fat mass, and the expression of genes responsible for lipogenesis and regulation of mitochondrial function. To overcome systemic effects, primary adipocyte cultures were treated with pathological BA concentrations. Mitochondrial permeability and respiration analysis revealed that BA overload is sufficient to reduce mitochondrial function in primary adipocytes, which is not as a result of cytotoxicity. Instead, we found robust reductions in uncoupling protein 1 (Ucp1), PR domain containing 16 (Prdm16), and deiodinase, iodothyronine, type II (Dio2) transcripts in brown adipocytes upon treatment with chenodeoxycholic acid, whereas taurocholic acid led to the suppression of Dio2 transcript. This BA-mediated decrease in transcripts was alleviated by pharmacological activation of UCP1. High concentrations of BAs cause defective thermogenesis by reducing the expression of crucial regulators of mitochondrial function, including UCP1, which may explain the clinical features of hypothermia and fat loss observed in patients with cholestatic liver diseases. We uncover a detrimental effect of chronic bile acid overload on adipose mitochondrial function. Pathological concentration of different BAs reduces the expression of distinct genes involved in energy expenditure, which can be mitigated with pharmacological UCP1 activation.

It Is Not Just Fat: Dissecting the Heterogeneity of Adipose Tissue Function.

The purpose of the current review is to summarize findings from the most recent and impactful studies which investigated human and mouse adipose tissue transcriptomes at a single-cell level. We provide perspective about the potential importance of data derived from these single-cell technologies in improving our understanding of the adipose organ and metabolic disease and likely future directions of this approach. The majority of single-cell or single-nuclei studies of the adipose organ so far have focused on investigating the stromal-vascular fraction (SVF) of mouse subcutaneous and intraabdominal white and interscapular brown fat depots. Few studies have also evaluated the impact of additional factors as drivers of adipose phenotypes, such as high-fat diet-induced obesity, adolescence, aging, and cold exposure. Recent studies have also investigated human cell lines and human fat biopsies across a range of body mass index (BMI) and in response to insulin resistance or T2D. These studies have identified numerous previously unexplored subpopulations of adipocyte progenitors, immune cells, and mature adipocytes in both mice and men. Single-cell and single-nuclei technologies have brought an explosion of data that have advanced our understanding of the adipose organ in health and disease. However, we are still at the dawn of achieving a complete and comprehensive map of the mouse and human adipose organ. Multi-modal single-cell approaches to identify both anatomic localization of specific cellular populations and epigenetic mechanisms responsible for observed transcriptomic patterns are underway and will likely provide an even deeper understanding of the adipose organ in response to health and disease.

Global Adipose Tissue Remodeling During the First Month of Postnatal Life in Mice.

During the first month of postnatal life, adipose tissue depots of mice go through a drastic, but transient, remodeling process. Between postnatal days 10 and 20, several white fat depots display a strong and sudden surge in beige adipocyte emergence that reverts until day 30. At the same time, brown fat depots appear to undergo an opposite phenomenon. We comprehensively describe these events, their depot specificity and known environmental and genetic interactions, such as maternal diet, housing temperature and mouse strain. We further discuss potential mechanisms and plausible purposes, including the tempting hypothesis that postnatal transient remodeling creates a lasting adaptive capacity still detectable in adult animals. Finally, we propose postnatal adipose tissue remodeling as a model process to investigate mechanisms of beige adipocyte recruitment advantageous to cold exposure or adrenergic stimulation in its entirely endogenous sequence of events without external manipulation.

201-LB: Arx and Nr2f6 Transcriptionally Regulate Visceral and Brown Fat Phenotype

Mammals possess fat in three distinct depots- brown, subcutaneous and visceral fat depots. While brown fat contains thermogenic brown fat cells, the subcutaneous and visceral fat depots contain lipid-storing white fat cells. Excess visceral fat is associated with increased insulin resistance and type 2 diabetes, whereas the presence of brown fat corelates with lower odds of type 2 diabetes. These differences likely arise due to distinct developmental origins of brown and white fat cells. Expression of co-factors such as PRDM16 and PGC1α is limited to brown fat cells. Brown and white fat cells also have distinct sets of open chromatin. I hypothesize that epigenetic variations between brown and white fat can reveal fat depot-enriched factors that are essential to establishing fat identity and phenotype, and therefore, influence obesity and type 2 diabetes. Adipoq-NuTrap mice, that have labeled adipocytes, were used to isolate adipocyte nuclei from brown and visceral fat. ATAC-sequencing of these nuclei uncovered fat cell-specific open regions, which were then subjected to bioinformatic analysis to identify depot-enriched transcription factors. These analyses resulted in the discovery of two factors: Arx and Nr2f6. Arx is dramatically enriched in visceral gonadal fat, compared to brown and subcutaneous fat. Pathway analysis of Arx target genes reveal that Arx may regulate inflammation, cell shape and motility. Adipose-specific Arx knockout mice have lesser visceral fat and will be used to study the role of Arx in insulin tolerance and obesity. On the other hand, Nr2f6 expression is enriched in brown fat, increases with cold exposure and is dependent on PRDM16 expression. Pathway analysis of Nr2f6 target genes show that Nr2f6 regulates mitochondrial, thermogenic and lipolytic genes, genes central to brown fat function. Nr2f6 overexpression dampened thermogenic response, suggesting a novel regulatory mechanism in brown fat function. Nr2f6-null mice will be used to assess the role of Nr2f6 in brown fat function. Disclosure A. Maganti: None. J. Chi: None. P. Cohen: None. Funding American Diabetes Association (1-19-PDF-024 to A.M.)

FXR Regulates Adipose Tissue Remodeling during Obesity

Obesity is a major epidemic and results in adipose tissue expansion and dysregulated glucose and lipid metabolism. Farnesoid X receptor (FXR) is a nuclear receptor expressed in many tissues that transcriptionally regulates energy homeostasis. However, the role of FXR in adipose tissue remains elusive. We identified Fxr expression in adipocytes isolated from both white (WAT) and brown (BAT) adipose tissues, and uncovered that adipocyte-specific Fxr knockout (Ad-FxrKO) mice recently generated in our laboratory exhibit adipocyte hypertrophy and concomitant reductions in lipolysis and the expression of lipolytic genes in both white and brown fat depots, which is correlated with ectopic fat accumulation in the liver and systemic glucose intolerance when challenged with a 60% high fat diet (HFD) or high fat/high sucrose western diet. Further, transcriptomic analysis of WAT from Ad-FxrKO and control mice upon chow or HFD revealed that many genes enriched in pathways associated with lipid and glucose homeostasis are misregulated in Ad-FxrKO mice with distinct patterns under normal and obese conditions. These data suggest that adipocyte-specific FXR may play a crucial role in regulating fat accumulation and the subsequent glucose homeostasis during diet-induced obesity. In addition to the energy storage and distribution properties of adipose tissue, BAT has high mitochondrial content and burns energy to produce heat and combat obesity. We found that Ad-FxrKO mice display reductions in energy expenditure and the expression of mitochondrial genes, revealing a key role of FXR in controlling BAT mitochondrial function and the consequent thermogenesis. Overall, we demonstrate that FXR can control fat breakdown and regulate mitochondrial functions in the adipose tissue, which in turn, modulates whole-body lipid and glucose metabolism.

SAT-603 Growth Hormone-Releasing Hormone (GHRH) Antagonists Stimulate Feeding in Mice

Growth hormone-releasing hormone (GHRH) is a hypothalamic neuropeptide which stimulates the synthesis and secretion of growth hormone (GH) in pituitary gland. GHRH was also found to modulate food intake in mammals. MIA-690 is a synthetic GHRH antagonist of the Miami (MIA) series with potent antitumor effects. To date, its role in hypothalamic feeding modulation has not been evaluated. In the present study, we aimed to investigate the effects of chronic MIA-690 administration on feeding behavior, locomotor activity and hypothalamic dopamine (DA), norepinephrine (NE), serotonin (5-hydroxytriptamine, 5-HT), orexigenic peptides [agouti-related peptide (AgRP) and neuropeptide Y (NPY)] and anorexigenic peptides [cocaine and amphetamine-regulated transcript (CART) and proopiomelanocortin (POMC)] activity.Adult C57/BL6 mice were treated daily for 4 weeks by subcutaneous administration of (5 µg) MIA-690 or vehicle solution. Food intake and body weight were recorded every 4 days throughout the study. Immediately after the last injection, locomotor activity in the home cage was recorded, and thereafter animals were sacrificed. Visceral, subcutaneous and brown fat depots were quickly excised and weighed. Hypothalamus was also dissected for evaluating gene expression of AgRP, NPY, CART and POMC by real-time reverse transcription polymerase chain reaction. In addition, hypothalamic DA, NE and 5-HT levels were measured by high performance liquid chromatography (HPLC) coupled to electrochemical detection.Our findings show that administration of MIA-690 increased food intake and body weight, without affecting locomotor activity. No difference was observed in visceral, subcutaneous and brown fat mass in animals treated with MIA-690 or vehicle. As for neuromodulatory effects, a significant increase of AgRP gene expression and NE levels, along with a reduction of 5-HT levels were found after MIA-690 treatment. On the other hand, we did not observe any alteration in NPY, POMC and CART gene expression, as well as DA levels, following MIA-690 administration.In conclusion, chronic peripheral administration of MIA-690 could play an orexigenic role paralleled by increased body weight. The stimulation of feeding could be mediated, at least in part, by increased AgRP gene expression and NE levels and decreased 5-HT levels, in the hypothalamus.

Ablation of uncoupling protein 1 causes opposing changes of glucose uptake in brown and brite fat compatible with regulation of Glut 4 gene expression

BackgroundRecruitment and activation of uncoupling protein 1 – dependent thermogenesis in brown and brite fat is a candidate mechanism to promote negative energy balance and improve systemic glucose homeostasis. Non‐shivering thermogenesis mediated by UCP1 is mainly sustained by fatty acid oxidation and to lesser extent by glucose. Glucose supply, however, is essential to run serial and parallel metabolic pathways involved in thermogenesis, including glycolysis, glyceroneogenesis, anabolic bolstering of the citric acid cycle and de novo lipogenesis. Norepinephrine release in the cold stimulates glucose uptake via GLUT1 to support thermogenesis, while insulin stimulates uptake via GLUT4 for the storage of glycogen and triglyceride. It is unclear, however, whether glucose uptake depends on the presence of UCP1.ObjectiveWe aimed to quantify the effect of UCP1 ablation on insulin sensitivity, glucose tolerance and glucose uptake in brown and brite adipose tissues of mice fed either low, intermediate or high fat diets.MethodsWe assessed insulin sensitivity and oral glucose tolerance, and measured 2‐deoxyglucose uptake in different brown and white fat depots of UCP1‐KO and WT mice (B6 and 129 background) housed at thermoneutral temperature. Mice were fed low, intermediate and high fat diets. Transcriptomes of interscapular brown fat and inguinal brite fat were sequenced (RNA‐SEQ) and subjected to bioinformatic analysis.Results and DiscussionIn UCP1‐KO mice fed intermediate and high fat diets, body weight trajectories and body fat mass were rather unchanged or decreased. They rather showed reduced metabolic efficiency when fed the high fat diet, thus challenging a role of UCP1‐dependent thermogenesis in diet‐induced obesity resistance. Oral glucose tolerance, when analyzed as incremental area under the curve, was robustly impaired in UCP1‐KO mice fed intermediate and high fat diets, whereas insulin sensitivity was unchanged. In WT mice, brown fat showed the highest mass‐specific glucose uptake, with total uptake in the interscapular brown fat depot attaining up to 70% of the amount of glucose uptake measured in liver. Glucose uptake in UCP1‐KO mice was reduced in different brown fat depots, irrespective of diet. In contrast, glucose uptake was increased in inguinal brite fat of UCP1‐KO mice fed low fat diet. This increase was attenuated in mice fed intermediate or high fat diets. These differential genotype effects on glucose uptake in brown and brite fat were strongly associated with corresponding changes in Glut4 expression. Our results demonstrate a role of UCP1 in post‐prandial glucose homeostasis, most likely due to the reduced uptake into brown fat. Increased glucose uptake in inguinal brite fat of UCP1‐KO further corroborates the recruitment of alternative UCP1‐independent thermogenic capacity. We conclude that UCP1 is a modulator of adipose tissue glucose uptake and systemic glucose homeostasis.Support or Funding InformationThis work was supported by the EU FP7 project DIABAT (HEALTH‐F2‐2011‐278373), the Deutsche Forschungsgemeinschaft (KL973/13‐1, NUTRIBRITE) and the Else Kröner‐Fresenius Stiftung (EKFS).

Whole-body and adipose tissue-specific mechanisms underlying the metabolic effects of fibroblast growth factor 21 in the Siberian hamster

ObjectiveFibroblast growth factor 21 (FGF21) has been shown to rapidly lower body weight in the Siberian hamster, a preclinical model of adiposity. This induced negative energy balance mediated by FGF21 is associated with both lowered caloric intake and increased energy expenditure. Previous research demonstrated that adipose tissue (AT) is one of the primary sites of FGF21 action and may be responsible for its ability to increase the whole-body metabolic rate. The present study sought to determine the relative importance of white (subcutaneous AT [sWAT] and visceral AT [vWAT]), and brown (interscapular brown AT [iBAT]) in governing FGF21-mediated metabolic improvements using the tissue-specific uptake of glucose and lipids as a proxy for metabolic activity. MethodsWe used positron emission tomography-computed tomography (PET-CT) imaging in combination with both glucose (18F-fluorodeoxyglucose) and lipid (18F-4-thiapalmitate) tracers to assess the effect of FGF21 on the tissue-specific uptake of these metabolites and compared responses to a control group pair-fed to match the food intake of the FGF21-treated group. In vivo imaging was combined with ex vivo tissue-specific functional, biochemical, and molecular analyses of the nutrient uptake and signaling pathways. ResultsConsistent with previous findings, FGF21 reduced body weight via reduced caloric intake and increased energy expenditure in the Siberian hamster. PET-CT studies demonstrated that FGF21 increased the uptake of glucose in BAT and WAT independently of reduced food intake and body weight as demonstrated by imaging of the pair-fed group. Furthermore, FGF21 increased glucose uptake in the primary adipocytes, confirming that these in vivo effects may be due to a direct action of FGF21 at the level of the adipocytes. Mechanistically, the effects of FGF21 are associated with activation of the ERK signaling pathway and upregulation of GLUT4 protein content in all fat depots. In response to treatment with FGF21, we observed an increase in the markers of lipolysis and lipogenesis in both the subcutaneous and visceral WAT depots. In contrast, FGF21 was only able to directly increase the uptake of lipid into BAT. ConclusionsThese data identify brown and white fat depots as primary peripheral sites of action of FGF21 in promoting glucose uptake and also indicate that FGF21 selectively stimulates lipid uptake in brown fat, which may fuel thermogenesis.

The Beige Adipocyte as a Therapy for Metabolic Diseases.

Adipose tissue is traditionally categorized into white and brown relating to their function and morphology. The classical white adipose tissue builds up energy in the form of triglycerides and is useful for preventing fatigue during periods of low caloric intake and the brown adipose tissue more energetically active, with a greater number of mitochondria and energy production in the form of heat. Since adult humans possess significant amounts of active brown fat depots and its mass inversely correlates with adiposity, brown fat might play an important role in human obesity and energy homeostasis. New evidence suggests two types of thermogenic adipocytes with distinct developmental and anatomical features: classical brown adipocytes and beige adipocytes. Beige adipocyte has recently attracted special interest because of its ability to dissipate energy and the possible ability to differentiate themselves from white adipocytes. The presence of brown and beige adipocyte in human adults has acquired attention as a possible therapeutic intervention for metabolic diseases. Importantly, adult human brown appears to be mainly composed of beige-like adipocytes, making this cell type an attractive therapeutic target for obesity and obesity-related diseases, such as atherosclerosis, arterial hypertension and diabetes mellitus type 2. Because many epigenetics changes can affect beige adipocyte differentiation from adipose progenitor cells, the knowledge of the circumstances that affect the development of beige adipocyte cells may be important to new pathways in the treatment of metabolic diseases. New molecules have emerged as possible therapeutic targets, which through the impulse to develop beige adipocytes can be useful for clinical studies. In this review will discuss some recent observations arising from the unique physiological capacity of these cells and their possible role as ways to treat obesity and diabetes mellitus type 2.

Congenital lipodystrophy induces severe osteosclerosis.

Berardinelli-Seip congenital generalized lipodystrophy is associated with increased bone mass suggesting that fat tissue regulates the skeleton. Because there is little mechanistic information regarding this issue, we generated "fat-free" (FF) mice completely lacking visible visceral, subcutaneous and brown fat. Due to robust osteoblastic activity, trabecular and cortical bone volume is markedly enhanced in these animals. FF mice, like Berardinelli-Seip patients, are diabetic but normalization of glucose tolerance and significant reduction in circulating insulin fails to alter their skeletal phenotype. Importantly, the skeletal phenotype of FF mice is completely rescued by transplantation of adipocyte precursors or white or brown fat depots, indicating that adipocyte derived products regulate bone mass. Confirming such is the case, transplantation of fat derived from adiponectin and leptin double knockout mice, unlike that obtained from their WT counterparts, fails to normalize FF bone. These observations suggest a paucity of leptin and adiponectin may contribute to the increased bone mass of Berardinelli-Seip patients.

Sympathetic innervation of the interscapular brown adipose tissue in mouse.

The recent discovery of significant brown fat depots in adult humans has revived discussion of exploiting brown fat thermogenesis in the control of energy balance and body weight. The sympathetic nervous system (SNS) has a key role in the activation of brown fat and functional mapping of its components will be crucial for the development of specific neuromodulation techniques. The mouse is an important species used for molecular genetic modulations, but its small size is not ideal for anatomical dissections, thus brown fat innervation studies are mostly available in larger rodents such as rats and hamsters. Here, we use pseudorabies virus retrograde tracing, whole tissue clearing, and confocal/light sheet microscopy to show the location of pre‐ and postganglionic neurons selectively innervating the interscapular brown adipose tissue (iBAT) in the mouse. Using iDISCO whole tissue clearing, we identified iBAT projecting postganglionic neurons in the caudal parts of the ipsilateral fused stellate/T1, as well as the T2−T5 sympathetic chain ganglia and preganglionic neurons between levels T2 and T6 of the ipsilateral spinal cord. The methodology enabled high‐resolution imaging and 3D rendering of the specific SNS innervation of iBAT and will be helpful to discern peripheral nervous system innervation of other organs and tissues.

Initial age-associated metabolic alterations in white and brown fat depots: effect of long-term caloric restriction.

Initial age-associated metabolic alterations in white and brown fat depots: effect of long-term caloric restriction.

Clonal derivation of white and brown adipocyte progenitor cell lines from human pluripotent stem cells

BackgroundThe role of brown fat in non-shivering thermogenesis and the discovery of brown fat depots in adult humans has made it the subject of intense research interest. A renewable source of brown adipocyte (BA) progenitors would be highly valuable for research and therapy. Directed differentiation of human pluripotent stem (hPS) cells to white or brown adipocytes is limited by lack of cell purity and scalability. Here we describe an alternative approach involving the identification of clonal self-renewing human embryonic progenitor (hEP) cell lines following partial hPS cell differentiation and selection of scalable clones.MethodsWe screened a diverse panel of hPS cell-derived clonal hEP cell lines for adipocyte markers following growth in adipocyte differentiation medium. The transcriptome of the human hES-derived clonal embryonic progenitor cell lines E3, C4ELS5.1, NP88, and NP110 representing three class of definitive adipocyte progenitors were compared to the relatively non-adipogenic line E85 and adult-derived BAT and SAT-derived cells using gene expression microarrays, RT-qPCR, metabolic analysis and immunocytochemistry. Differentiation conditions were optimized for maximal UCP1 expression.ResultsMany of the differentiated hEP cell lines expressed the adipocyte marker, FAPB4, but only a small subset expressed definitive adipocyte markers including brown adipocyte marker, UCP1. Class I cells (i.e., E3) expressed CITED1, ADIPOQ, and C19orf80 but little to no UCP1. Class II (i.e., C4ELS5.1) expressed CITED1 and UCP1 but little ADIPOQ and LIPASIN. Class III (i.e., NP88, NP110) expressed CITED1, ADIPOQ, C19orf80, and UCP1 in a similar manner as fetal BAT-derived (fBAT) cells. Differentiated NP88 and NP110 lines were closest to fBAT cells morphologically in adiponectin and uncoupling protein expression. But they were more metabolically active than fBAT cells, had higher levels of 3-hydroxybutyrate, and lacked expression of fetal/adult marker, COX7A1. The hEP BA progenitor lines were scalable to 17 passages without loss of differentiation capacity and could be readily rederived.ConclusionsTaken together, these data demonstrate that self-renewing adipocyte progenitor cells can be derived from hES cells and that they are functionally like BAT cells but with unique properties that might be advantageous for basic research and for development of cell-based treatments for metabolic diseases.

Adipose and skeletal muscle thermogenesis: studies from large animals

The balance between energy intake and energy expenditure establishes and preserves a 'set-point' body weight. The latter is comprised of three major components including metabolic rate, physical activity and thermogenesis. Thermogenesis is defined as the cellular dissipation of energy via heat production. This process has been extensively characterised in brown adipose tissue (BAT), wherein uncoupling protein 1 (UCP1) creates a proton leak across the inner mitochondrial membrane, diverting protons away from ATP synthesis and resulting in heat dissipation. In beige adipocytes and skeletal muscle, thermogenesis can occur independent of UCP1. Beige adipocytes have been shown to produce heat via UCP1 as well as via both futile creatine and calcium cycling pathways. On the other hand, the UCP1 homologue UCP3 is abundant in skeletal muscle and post-prandial thermogenesis has been associated with UCP3 and the futile calcium cycling. This review will focus on the differential contributions of adipose tissue and skeletal muscle in determining total thermogenic output and energy expenditure in large mammals. Sheep and pigs do not have a circumscribed brown fat depot but rather possess white fat depots that contain brown and beige adipocytes interspersed amongst white adipose tissue. This is representative of humans, where brown, beige and white adipocytes have been identified in the neck and supraclavicular regions. This review will describe the mechanisms of thermogenesis in pigs and sheep and the relative roles of skeletal muscle and adipose tissue thermogenesis in controlling body weight in larger mammals.

The Mechanism FA-Dependent H+ Transport by UCP1.

Uncoupling protein 1 (UCP1) is an integral protein of the inner mitochondrial membrane (IMM) that is expressed specifically in brown and beige fat depots. UCP1 is responsible for the production of heat to control core body temperature, the regulation of fat metabolism, and the energy balance. As an uncoupling protein, UCP1 transports H+ across the IMM in presence of long-chain fatty acids (FA), which makes brown fat mitochondria produce heat at the expense of ATP. However, the exact mechanism of UCP1 action has remained difficult to elucidate, because direct methods for studying currents generated by UCP1 were unavailable. Recently, the patch-clamp technique was successfully applied to brown and beige fat mitochondria to directly study H+ currents across the IMM and characterize UCP1 function. A new model of the UCP1 mechanism was proposed based on the patch-clamp analysis. In this model, both FA anions (FA-) and H+ are transport substrates of UCP1, and UCP1 operates as a non-canonical FA-/H+ symporter. Here, we summarize recent findings obtained with the patch-clamp technique that describe how UCP1 can transport not only H+ but also FA-.

Infrared thermal imaging as a method to evaluate heat loss in newborn lambs

Thermal imaging technology has been identified as a potential method for non-invasive study of thermogenesis in the neonatal lamb. In comparison to measurement of the core body temperature, infrared thermography may observe thermal loss and thermogenesis linked to subcutaneous brown fat depots. This study aimed to identify a suitable method to measure heat loss in the neonatal lamb under a cold challenge. During late pregnancy (day 125), ewes were subjected to either shearing (n=15) or mock handling (sham-shorn for 2min mimicking the shearing movements) (n=15). Previous studies have shown an increase in brown adipose tissue deposition in lambs born to ewes shorn during pregnancy and we hypothesized that the shearing treatment would impact thermoregulatory capacities in newborn lambs. Lambs born to control ewes (n=14; CONTROL) and shorn ewes (n=13; SHORN) were subjected to a cold challenge of 1h duration at 4h after birth. During the cold challenge, thermography images were taken every 10min, from above, at a fixed distance from the dorsal midline. On each image, four fixed-size areas were identified (shoulder, mid loin, hips and rump) and the average and maximum temperatures of each recorded. In all lambs, body surface temperature decreased over time. Overall the SHORN lambs appeared to maintain body surface temperature better than CONTROL lambs, while CONTROL lambs appeared to have higher core temperature. At 30min post cold challenge SHORN lambs tended to have higher body surface temperatures than lambs (P=0.0474). Both average and maximum temperatures were highest at the hips. Average temperature was lowest at the shoulder (P<0.05), while maximum temperatures were lowest at both shoulder and rump (P<0.005). These results indicate that lambs born to shorn ewes maintained their radiated body surface temperature better than CONTROL lambs. In conjunction with core temperature changes under cold challenge, this insight will allow us to understand whether increased body surface temperature contributes to increased overall heat loss or whether increased body surface temperature is indeed a mechanism contributing to maintenance of core body temperature under cold challenge conditions. This study has confirmed the utility of infrared thermography images to capture and identify different levels of thermoregulatory capacity in newborn lambs.

The Sense of Smell Impacts Metabolic Health and Obesity

Olfactory inputs help coordinate food appreciation and selection, but their role in systemic physiology and energy balance is poorly understood. Here we demonstrate that mice upon conditional ablation of mature olfactory sensory neurons (OSNs) are resistant to diet-induced obesity accompanied by increased thermogenesis in brown and inguinal fat depots. Acute loss of smell perception after obesity onset not only abrogated further weight gain but also improved fat mass and insulin resistance. Reduced olfactory input stimulates sympathetic nerve activity, resulting in activation of β-adrenergic receptors on white and brown adipocytes to promote lipolysis. Conversely, conditional ablation of the IGF1 receptor in OSNs enhances olfactory performance in mice and leads to increased adiposity and insulin resistance. These findings unravel a new bidirectional function for the olfactory system in controlling energy homeostasis in response to sensory and hormonal signals.

Brown fat depots in adult humans remain static in their locations on PET/CT despite changes in seasonality.

Active brown adipose tissue (BAT) in humans has been demonstrated through use of positron emission tomography with 2‐deoxy‐2‐(fluorine‐18) fluoro‐D‐glucose integrated with computed tomography (18F‐FDG PET/CT) scans. The aim of our study was to determine whether active human BAT depots shown on 18F‐FDG PET/CT scans remain static in their location over time. This was a retrospective study. Adult human subjects (n = 15) who had had 18F‐FDG PET/CT imaging (n = 38 scans in total) for clinical reasons were included on the basis of 18F‐FDG uptake patterns consistent with BAT activity. For each subject, 18F‐FDG BAT uptake pattern on serial 18F‐FDG PET/CT images was compared to an index 18F‐FDG PET/CT image with the largest demonstrable BAT volume. Object‐based colocalization was expressed as Mander's correlation coefficient (where 1 = 100% overlap, 0 = no overlap). Distribution of 18F‐FDG BAT activity over time and across multiple 18F‐FDG BAT scans was equivalent in 60% (n = 9) of the subjects. The degree of consistency in the pattern of 18F‐FDG BAT uptake in each subject over time was greater than expected by chance in 87% (n = 13) of the subjects (pair‐wise agreement 75–100%, Fleiss’ κ 0.4–1). The degree of BAT colocalization on serial scans was greater than that expected by chance in 93% (n = 14) of the subjects (mean Mander's coefficient 0.81 ± 0.21 [95% CI]). To our knowledge, our study provides the most conclusive evidence to date to support the notion that active BAT depots in humans (volumes and activities of which were measured through use of 18F‐FDG PET/CT scans) remain static in location over sustained periods.