Activation Of Brown Adipose Tissue Thermogenesis Research Articles

76-OR: Axon Guidance Molecule Slit3 Is Essential for Cold-Induced Remodeling of BAT Neurovasculature and Thermogenesis

Brown adipose tissue (BAT) is primarily responsible for regulating body temperature through adaptive thermogenesis. Enhancing energy expenditure through the activation of BAT thermogenesis is a promising strategy to prevent and reverse obesity and its cardiometabolic sequelae. Brown adipocytes are embedded in a dense network of blood vessels and sympathetic nerves that supports their thermogenic activity. Increasing the density of blood vessels and sympathetic innervation is essential for enhanced thermogenesis in cold. However, how these distinct processes are spatiotemporally regulated is not clear. To define the mediators of intercellular crosstalk in the BAT, we used single-cell transcriptomic analysis of BAT to build a network of ligand-receptor interactions. We identified Slit guidance ligand 3 (Slit3) as a new adipokine that mediates the crosstalk among adipocyte progenitors, endothelial cells, and sympathetic nerves. Using a combination of in vivo gain and loss of function studies, we showed that Slit3 is essential for cold-induced angiogenesis and sympathetic innervation in BAT. Loss of Slit3 reduced the density of blood vessels and sympathetic neurites in BAT. Consequently, mice lacking Slit3 expression in BAT exhibited severe cold intolerance, increased lipid accumulation and whitening of BAT, and reduced expression of thermogenic and mitochondrial genes in BAT. Conversely, the overexpression of Slit3 enhanced cold-induced BAT thermogenesis. Our mechanistic studies identified the key regulatory events that control Slit3 signaling in BAT. Collectively, these findings established the essential role of Slit3 signaling in regulation of BAT thermogenesis and introduced Slit3 as a new niche factor that promotes adipose tissue health. These studies introduced a potential node of intervention for improving systemic metabolism through the expansion of thermogenic fat. Disclosure T.Duarte afonso serdan: None. H.E.Cervantes: None. F.M.Neto: None. Y.Tseng: Consultant; Cellarity, LyGenesis. F.Shamsi: None. Funding National Institutes of Health (K01DK125608)

Loureirin B protects against obesity via activation of adipose tissue ω3 PUFA-GPR120-UCP1 axis in mice

Obesity and related metabolic disorders are worldwide epidemics. Current lifestyle interventions and drug treatment for obesity seem insufficient. Here, we show that Loureirin B (LB), a major flavonoid molecule extracted from Sanguis Draxonis, prevents diet-induced obesity and ameliorates concomitant metabolic abnormalities including fatty liver, insulin resistance and systemic inflammation in mice. Mechanistically, LB treatment increases the proportion of ω3 polyunsaturated fatty acids (PUFAs) in brown adipose tissue (BAT) and white adipose tissue (WAT), which subsequently activates the key lipid sensor GPR120. In line with this, LB treatment promotes browning of WAT and activates BAT thermogenesis through upregulation of UCP1, a downstream effector of GPR120. Conversely, inhibition of GPR120 abolishes the thermogenic effect of LB in primary cultured brown adipocytes. Together, these results suggest that LB possesses anti-obesity property by enhancing adipose tissue thermogenesis via activation of ω3 PUFA-GPR120-UCP1 axis and holds promises for combating obesity and its related metabolic syndrome.

An estrogen-sensitive hypothalamus-midbrain neural circuit controls thermogenesis and physical activity.

Estrogen receptor–α (ERα) expressed by neurons in the ventrolateral subdivision of the ventromedial hypothalamic nucleus (ERαvlVMH) regulates body weight in females, but the downstream neural circuits mediating this biology remain largely unknown. Here we identified a neural circuit mediating the metabolic effects of ERαvlVMH neurons. We found that selective activation of ERαvlVMH neurons stimulated brown adipose tissue (BAT) thermogenesis, physical activity, and core temperature and that ERαvlVMH neurons provide monosynaptic glutamatergic inputs to 5-hydroxytryptamine (5-HT) neurons in the dorsal raphe nucleus (DRN). Notably, the ERαvlVMH → DRN circuit responds to changes in ambient temperature and nutritional states. We further showed that 5-HTDRN neurons mediate the stimulatory effects of ERαvlVMH neurons on BAT thermogenesis and physical activity and that ERα expressed by DRN-projecting ERαvlVMH neurons is required for the maintenance of energy balance. Together, these findings support a model that ERαvlVMH neurons activate BAT thermogenesis and physical activity through stimulating 5-HTDRN neurons.

HIF3A Inhibition Triggers Browning of White Adipocytes via Metabolic Rewiring.

Maintenance of energy balance between intake and expenditure is a prerequisite of human health, disrupted in severe metabolic diseases, such as obesity and type 2 diabetes (T2D), mainly due to accumulation of white adipose tissue (WAT). WAT undergoes a morphological and energetic remodelling toward brown adipose tissue (BAT) and the BAT activation has anti-obesity potential. The mechanisms or the regulatory factors able to activate BAT thermogenesis have been only partially deciphered. Identifying novel regulators of BAT induction is a question of great importance for fighting obesity and T2D. Here, we evaluated the role of Hif3α in murine pre-adipocyte 3T3-L1 cell line, a versatile and well characterized biological model of adipogenesis, by gain- and loss-of function approaches and in thermogenesis-induced model in vivo. HIF3A is regulated by inflammation, it modulates lypolysis in adipose tissue of obese adults, but its role in energy metabolism has not previously been investigated. We characterized gene and protein expression patterns of adipogenesis and metabolic activity in vitro and mechanistically in vivo. Overexpression of Hif3α in differentiating adipocytes increases white fat cells, whereas silencing of Hif3α promotes “browning” of white cells, activating thermogenesis through upregulation of Ucp1, Elovl3, Prdm16, Dio2 and Ppargc1a genes. Investigating cell metabolism, Seahorse Real-Time Cell Metabolism Analysis showed that silencing of Hif3α resulted in a significant increase of mitochondrial uncoupling with a concomitant increase in acetyl-CoA metabolism and Sirt1 and Sirt3 expression. The causal Hif3α/Ucp1 inverse relation has been validated in Cannabinoid receptor 1 (CB1) knockout, a thermogenesis-induced model in vivo. Our data indicate that Hif3α inhibition triggers “browning” of white adipocytes activating the beneficial thermogenesis rewiring energy metabolism in vitro and in vivo. HIF3A is a novel player that controls the energy metabolism with potential applications in developing therapy to fight metabolic disorders, as obesity, T2D and ultimately cancer.

Precision Nutrition to Activate Thermogenesis as a Complementary Approach to Target Obesity and Associated-Metabolic-Disorders.

Simple SummaryRegarding the pandemic of obesity and chronic diseases associated to metabolic alterations that occur nowadays worldwide, here, we review the most recent studies related to bioactive compounds and diet derived ingredients with potential effects to augment the systemic energy expenditure. We specifically focus in two processes: the activation of thermogenesis in adipose tissue and the enhancement of the mitochondrial oxidative phosphorylation capacity in muscles. This may provide relevant information to develop diets and supplements to conduct nutritional intervention studies with the objective to ameliorate the metabolic and chronic inflammation in the course of obesity and related disorders.Obesity is associated to increased incidence and poorer prognosis in multiple cancers, contributing to up to 20% of cancer related deaths. These associations are mainly driven by metabolic and inflammatory changes in the adipose tissue during obesity, which disrupt the physiologic metabolic homeostasis. The association between obesity and hypercholesterolemia, hypertension, cardiovascular disease (CVD) and type 2 diabetes mellitus (T2DM) is well known. Importantly, the retrospective analysis of more than 1000 epidemiological studies have also shown the positive correlation between the excess of fatness with the risk of cancer. In addition, more important than weight, it is the dysfunctional adipose tissue the main driver of insulin resistance, metabolic syndrome and all cause of mortality and cancer deaths, which also explains why normal weight individuals may behave as “metabolically unhealthy obese” individuals. Adipocytes also have direct effects on tumor cells through paracrine signaling. Downregulation of adiponectin and upregulation of leptin in serum correlate with markers of chronic inflammation, and crown like structures (CLS) associated to the adipose tissue disfunction. Nevertheless, obesity is a preventable risk factor in cancer. Lifestyle interventions might contribute to reduce the adverse effects of obesity. Thus, Mediterranean diet interventional studies have been shown to reduce to circulation inflammatory factors, insulin sensitivity and cardiovascular function, with durable responses of up to 2 years in obese patients. Mediterranean diet supplemented with extra-virgin olive oil reduced the incidence of breast cancer compared with a control diet. Physical activity is another important lifestyle factor which may also contribute to reduced systemic biomarkers of metabolic syndrome associated to obesity. In this scenario, precision nutrition may provide complementary approaches to target the metabolic inflammation associated to “unhealthy obesity”. Herein, we first describe the different types of adipose tissue -thermogenic active brown adipose tissue (BAT) versus the energy storing white adipose tissue (WAT). We then move on precision nutrition based strategies, by mean of natural extracts derived from plants and/or diet derived ingredients, which may be useful to normalize the metabolic inflammation associated to “unhealthy obesity”. More specifically, we focus on two axis: (1) the activation of thermogenesis in BAT and browning of WAT; (2) and the potential of augmenting the oxidative capacity of muscles to dissipate energy. These strategies may be particularly relevant as complementary approaches to alleviate obesity associated effects on chronic inflammation, immunosuppression, angiogenesis and chemotherapy resistance in cancer. Finally, we summarize main studies where plant derived extracts, mainly, polyphenols and flavonoids, have been applied to increase the energy expenditure.

An update on brown adipose tissue biology: a discussion of recent findings.

Brown adipose tissue (BAT) has been encouraged as a potential treatment for obesity and comorbidities due to its thermogenic activity capacity and contribution to energy expenditure. Some interventions such as cold and β-adrenergic drugs are able to activate BAT thermogenesis as well as promote differentiation of white adipocytes into brown-like cells (browning), enhancing the thermogenic activity of these cells. In this mini-review, we discuss new mechanisms related to BAT and energy expenditure. In this regard, we will also discuss recent studies that have revealed the existence of important secretory molecules from BAT "batokines" that act in autocrine, paracrine, and endocrine mechanisms, which in turn may explain some of the beneficial roles of BAT on whole body glucose and fat metabolism. Finally, we will discuss new insights related to BAT thermogenesis with an additional focus on the distinct features of BAT metabolism between rodents and humans.

Brain-derived neurotrophic factor modulates mitochondrial dynamics and thermogenic phenotype on 3T3-L1 adipocytes

Obesity is a growing threat. In recent years, the finding of functional brown adipose tissue (BAT) in adult humans implemented the studies of anti-obesity therapies based on triggering energy expenditure. The activation of BAT thermogenesis and the recruitment of brite (brown-in-white) adipocytes are under noradrenergic control. Brain-derived neurotrophic factor (BDNF), if centrally administered, enhances thermogenesis through sympathetic activation, but its direct effect on adipocytes is still unclear. The phenotypic change from fat storing to thermogenic adipocytes is recognized by the presence of multilocular lipid droplets (LDs) and fissed mitochondria that tend to surround LDs, maximizing the efficiency of fatty acid release for thermogenesis. BDNF treatment on differentiated 3T3-L1 adipocytes was compared to negative (CTRL) and positive (norepinephrine, NE) controls. BDNF significantly increased small globular mitochondria percentage (>150% CTRL), while the area surface and elongation index of branched tubules were respectively 55% and 10% lower than NE. Canonical discriminant analysis of mitochondria morphological data clearly separated differentially treated cells with 85% of the total variance. The expression of brown markers and mitochondrial dynamic genes was significantly affected by BDNF. Investigating the pathways involved in adipocyte BDNF stimulation could clarify its role in thermogenesis and its possible local regulation.

Switching on the furnace: Regulation of heat production in brown adipose tissue

Endothermy requires a source of endogenous heat production. In birds, this is derived primarily from shivering, but in mammals it is mostly non-shivering thermogenesis (NST). Brown adipose tissue (BAT) is a specialized tissue found in Eutherian mammals that is the source of most NST. Heat production in BAT depends primarily on the activity of uncoupling protein 1 (UCP1), which decouples transport of protons across the inner mitochondrial membrane from synthesis of ATP. UCP1 and hence heat production of BAT is regulated by many factors. In this paper we discuss the main factors activating UCP1 and increasing heat production. Probably the most well-known activator is the catecholamine norepinephrine (NE) which is released from sympathetic nerve endings and binds to adrenergic receptors that are abundantly expressed on BAT. NE stimulates release of free-fatty acids. It was previously thought that such FFAs were essential for activation of UCP1. However recent work has suggested intracellular lipolysis is not essential and FFAs can be derived from extracellular sources. Thyroid hormones also exert impacts on metabolic rate via effects on brown adipocytes which express type 2 deiodinase. Knocking out DIO2 makes mice cold intolerant. Parathyroid hormone appears to also be a potent regulator of BAT activity and may be an important mediator of elevated expenditure during cancer cachexia, although this is disputed by observations that cachexia wasting is not blunted in UCP1 KO mice. Cardiac natriuretic peptides have also been implicated in regulating BAT thermogenesis and the interconversion of beige adipocytes from their white to brown form. Activation of BAT thermogenesis may be an important component of the post-ingestion rise in heat production. Recent work suggests the gut derived hormone secretin may play a key role in this effect, directly linking BAT activation to the alimentary tract. Not only gut hormones but also metabolites derived from gut microbiota such as butyrate may be an important activator of BAT during cold exposure. Additional regulatory factors include bone morphogenic proteins, fibroblast growth factor 21, Vascular endothelial growth factors and transient receptor potential vanilloid receptors which are important components of thermal sensing and hence how brown adipose tissue responds to the cold. In the future the main challenge is to understand how these regulatory factors combine with each other and with inhibitory factors to control heat production from BAT, and what their relative importance is in differing circumstances. Knocking out UCP1 has revealed other sources of heat production in BAT including creatine-dependent cycles and a futile cycle of Ca2+ shuttling into and out of the endoplasmic reticulum via the SERCA and ryanodine receptors.

1796-P: A Ventral Medial Hypothalamus Estrogen Receptor a Neural Circuit Controlling Energy Expenditure

Multiple estrogen receptor α (ERα) neuron populations in the brain are required to maintain normal body weight. While the metabolic effects of these ERα neuron populations have been investigated, the neural circuit and associated neurotransmitter signaling underlying the regulatory effects of ERα neurons on energy balance are unknown. Here we combined retrograde and anterograde trans-synaptic tracers, chemogenetics, optogenetic circuit mapping, and genetic mouse models to functionally map the downstream neural circuits of ERα neurons. We found that selective activation of ERα neurons in the ventral medial hypothalamus (VMH) stimulated brown adipose tissue (BAT) thermogenesis and physical activity without affecting food intake. We also showed that VMH ERα neurons provide monosynaptic glutamatergic inputs to serotonergic neurons in the dorsal Raphe nuclei (DRN). Inhibition of DRN serotonergic neurons partially attenuated the stimulatory effects of VMH ERα neurons on BAT thermogenesis and physical activity. More intriguingly, specific deletion of ERα or vesicular glutamate transporter 2 (vGluT2) from a subpopulation of VMH neurons projecting to the DRN results in decreased BAT thermogenesis and physical activity with normal food intake. Together, these findings suggest a model that VMH ERα neurons activate BAT thermogenesis and physical activity by stimulating DRN serotonergic neurons. Disclosure P. Xu: None. Y. He: None. C. Wang: None. Y. Yang: None. X. Cai: None. Y. Xu: None. Funding American Diabetes Association (1-17-PDF-138 to Y.H.); National Institutes of Health (R01DK093587), (R01DK101379 to Y.X.); (R00DK107008 to P.X.); U.S. Department of Agriculture (3092-5-001-059 to Y.X.); American Heart Association (17GRNT32960003 to Y.X.)

Octacosanol and policosanol prevent high-fat diet-induced obesity and metabolic disorders by activating brown adipose tissue and improving liver metabolism

Brown adipose tissue (BAT) is an attractive therapeutic target for treating obesity and metabolic diseases. Octacosanol is the main component of policosanol, a mixture of very long chain aliphatic alcohols obtained from plants. The current study aimed to investigate the effect of octacosanol and policosanol on high-fat diet (HFD)-induced obesity. Mice were fed on chow, or HFD, with or without octacosanol or policosanol treatment for four weeks. HFD-fed mice showed significantly higher body weight and body fat compared with chow-fed mice. However, mice fed on HFD treated with octacosanol or policosanol (HFDo/p) showed lower body weight gain, body fat gain, insulin resistance and hepatic lipid content. Lower body fat gain after octacosanol or policosanol was associated with increased BAT activity, reduced expression of genes involved in lipogenesis and cholesterol uptake in the liver, and amelioration of white adipose tissue (WAT) inflammation. Moreover, octacosanol and policosanol significantly increased the expression of Ffar4, a gene encoding polyunsaturated fatty acid receptor, which activates BAT thermogenesis. Together, these results suggest that octacosanol and policosanol ameliorate diet-induced obesity and metabolic disorders by increasing BAT activity and improving hepatic lipid metabolism. Thus, these lipids represent promising therapeutic targets for the prevention and treatment of obesity and obesity-related metabolic disorders.

Chinese medicine Jinlida granules improve high-fat-diet induced metabolic disorders via activation of brown adipose tissue in mice

AimsActivation of brown adipose tissue (BAT) thermogenesis could contribute to energy expenditure, which is critical for the treatment of obesity and type 2 diabetes mellitus (T2DM). In the present study, we aimed to systematically investigate whether traditional Chinese medication Jinlida (JLD) granules could improve metabolic disorders and activate BAT thermogenesis in C57BL/6 J mice fed with a high-fat diet (HFD). MethodsIn the present study, JLD (3.8 g/kg) in 0.5% of carboxymethyl cellulose (CMC) solution was administrated daily by oral gavage to HFD-induced mice for 15 weeks. The body weight, biochemical analysis, histology analysis, intraperitoneal glucose and insulin tolerance (OGTT and ITT) tests were measured to explore metabolic disorders. Cold tolerance test, real-time PCR (qRT-PCR), immunohistochemistry, and western blot were performed to evaluate BAT function. ResultsAs results, JLD treatment significantly ameliorated HFD-induced obesity and fat mass gain, maintained glucose and lipid homeostasis, and improved hepatic steatosis and inflammation. More importantly, we observed that JLD markedly activated BAT thermogenesis in HFD-induced obese mice. Moreover, our data confirmed that JLD promoted mitochondrial biogenesis and fatty acid oxidation metabolism in BAT. ConclusionsThese data suggested that JLD could improve metabolic disorders in associated with activation of BAT thermogenesis via enhancement of mitochondrial biogenesis and fatty acid oxidation metabolism, thus providing a new pharmacological evidence for the clinical usage of JLD in T2DM treatment.

Neurons in ventral tegmental area tonically inhibit sympathetic outflow to brown adipose tissue: possible mediation of thermogenic signals from lateral habenula.

The lateral habenula (LHb), a nucleus involved in the response to salient, especially adverse, environmental events, is implicated in brown adipose tissue (BAT) thermogenesis caused by these events. LHb-elicited thermogenesis involves a neural pathway to the lower brain stem sympathetic control center in the medullary raphé. There are no direct connections from the LHb to the medullary raphé. LHb-mediated behavioral responses involve inhibitory control over the dopamine neurons in the ventral tegmental area (VTA), mediated via an excitatory drive from the LHb to GABAergic neurons in the tail of the VTA. We hypothesized that inhibition of the VTA is also involved in LHb-mediated BAT thermogenesis. To test this hypothesis, inhibition of neurons in the VTA with muscimol increased BAT sympathetic nerve discharge by 22.0 ± 9.2 dBμV ( n = 24, P < 0.0001) and BAT temperature by 1.2 ± 0.1°C ( P < 0.001). This response was abolished by inhibition of the medullary raphé neurons with muscimol. BAT thermogenesis initiated with focal injections of bicuculline in the LHb was reversed by subsequent blockade of GABAA receptors in the VTA with bicuculline. These results suggest that, at least in anesthetized rats, neurons in the VTA tonically inhibit BAT thermogenesis via a link, presently unknown, to the medullary raphé. Removal of this VTA-initiated inhibition is an important mechanism whereby LHb neurons activate BAT thermogenesis.

Physiological Responses to Daily Use of Beta-Three Adrenergic Receptor Agonist, Mirabegron

Background: Brown Adipose Tissue (BAT) in adult humans has become increasingly recognized to contribute to energy consumption and modulate metabolism. To date, BAT stimulation has predominately relied on cold exposure. However, long-term cold exposure is impractical as a treatment option for obesity and diabetes. Thus, we investigated if a chronic pharmacotherapeutic approach could stimulate BAT and contribute to metabolic health. Methods: In an ongoing study, 6 healthy female volunteers received 4 weeks of daily mirabegron (Myrbetriq, Astellas Pharma) 100 mg, a β3 adrenergic receptor (AR) agonist. Acute responses were determined by comparing effects before and then five hours after dosing. Chronic changes were assessed after 4 weeks of treatment. The primary endpoint was the change in BAT metabolic activity measured by 18F-FDG PET/CT. Secondary endpoints included resting energy expenditure (REE), insulin and glucose sensitivity, liver steatosis, and cardiovascular stimulation. Results: Acute effects of mirabegron included consistent increases in rate pressure product (RPP), REE, and serum non-esterified fatty acids (NEFA) (p&amp;lt;0.05, p=0.06, p&amp;lt;.05). After 4 weeks, there was a wide range of changes in BAT volume (41 ± 223 mL, p=0.86). Body weight was unchanged (0.3 ± 0.62 kg). Several physiological responses after chronic treatment were blunted, including smaller mirabegron-induced increases in RPP, NEFA, and REE. Yet, there were significant increases in sleeping EE (72 ± 23 kcal/d, p=0.03), insulin sensitivity (1.5 ± .6 (mU/L*min, p=0.05), and liver steatosis (30 ± 10 dB/m, p = 0.04) after 4 weeks. Conclusions: Acute treatment with mirabegron in women successfully activates BAT thermogenesis. Preliminary data show chronic treatment resulted in a blunting of several responses, consistent with physiological attenuation of β-AR signaling. The increases in sleeping EE and improved insulin sensitivity suggest chronic mirabegron treatment may help alleviate metabolic disease. Disclosure A. O'Mara: None. A. Cypess: None. C. Cero: None. J.W. Johnson: None. J.D. Linderman: None. B. Leitner: None. L. Fletcher: None. R. Brychta: None. D. Kapuria: None. S. McGehee: None. Y. Rotman: None.

Effects of cold exposure on metabolites in brown adipose tissue of rats

Brown adipose tissue (BAT) plays an important role in regulation of energy expenditure while adapting to a cold environment. BAT thermogenesis depends on uncoupling protein 1 (UCP1), which is expressed in the inner mitochondrial membranes of BAT. Gene expression profiles induced by cold exposure in BAT have been studied, but the metabolomic biological pathway that contributes to the activation of thermogenesis in BAT remains unclear. In this study, we comprehensively compared the relative levels of metabolites between the BAT of rats kept at room temperature (22 °C) and of those exposed to a cold temperature (4 °C) for 48 h using capillary electrophoresis (CE) time-of-flight mass spectrometry (TOFMS) and liquid chromatography (LC)-TOFMS. We identified 218 metabolites (137 cations and 81 anions) by CE-TOFMS and detected 81 metabolites (47 positive and 34 negative) by LC-TOFMS in BAT. We found that cold exposure highly influenced the BAT metabolome. We showed that the cold environment lead to lower levels of glycolysis and gluconeogenesis intermediates and higher levels of the tricarboxylic acid (TCA) cycle metabolites, fatty acids, and acyl-carnitine metabolites than control conditions in the BAT of rats. These results indicate that glycolysis and β-oxidation of fatty acids in BAT are positive biological pathways that contribute to the activation of thermogenesis by cold exposure, thereby facilitating the generation of heat by UCP1. These data provide useful information for understanding the basal metabolic functions of BAT thermogenesis in rats in response to cold exposure.

The Cannabinoid Receptor-1 Is an Imaging Biomarker of Brown Adipose Tissue.

Recently, the existence of significant deposits of brown adipose tissue (BAT) in human adults was confirmed. Its role in the human metabolism is unknown but could be substantial. Inhibition of the cannabinoid receptor-1 (CB1) by the antagonist rimonabant (SR141716) has been associated with activation of BAT thermogenesis and weight loss in mice and rats. The role of peripheral and central CB1 in the activation of BAT merits further investigation. Here we developed a technique for quantifying CB1 in BAT by PET. Sections of rat BAT and subcutaneous white adipose tissue (WAT) were stained for CB1 and uncoupling protein-1 by immunofluorescent staining. Binding of the radiolabeled CB1 antagonist (3R,5R)-5-(3-(18F-fluoromethoxy)phenyl)-3-(((R)-1-phenylethyl)amino)-1-(4-(trifluoromethyl)-phenyl)pyrrolidin-2-one ((18)F-FMPEP-d2) to BAT in vivo and in vitro was assessed in rats by PET. We found that CB1 was colocalized with uncoupling protein-1 in BAT, but neither protein was found in WAT. Binding of the radiotracer to BAT sections (but not WAT) in vitro was high and displaceable by pretreatment with rimonabant. Deposits of BAT in rats had significant binding of (18)F-FMPEP-d2 in vivo, indicating high CB1 density. WAT deposits were negative for (18)F-FMPEP-d2, consistent with the immunofluorescent staining and in vitro results. (18)F-FMPEP-d2 PET can quantify CB1 density noninvasively in vivo in rats. CB1 is therefore a promising surrogate imaging biomarker for assessing the presence of BAT deposits as well as for elucidating the mechanism of CB1 antagonist-mediated weight loss.

3,5-Diiodo-L-thyronine activates brown adipose tissue thermogenesis in hypothyroid rats.

3,5-diiodo-l-thyronine (T2), a thyroid hormone derivative, is capable of increasing energy expenditure, as well as preventing high fat diet-induced overweight and related metabolic dysfunction. Most studies to date on T2 have been carried out on liver and skeletal muscle. Considering the role of brown adipose tissue (BAT) in energy and metabolic homeostasis, we explored whether T2 could activate BAT thermogenesis. Using euthyroid, hypothyroid, and T2-treated hypothyroid rats (all maintained at thermoneutrality) in morphological and functional studies, we found that hypothyroidism suppresses the maximal oxidative capacity of BAT and thermogenesis, as revealed by reduced mitochondrial content and respiration, enlarged cells and lipid droplets, and increased number of unilocular cells within the tissue. In vivo administration of T2 to hypothyroid rats activated BAT thermogenesis and increased the sympathetic innervation and vascularization of tissue. Likewise, T2 increased BAT oxidative capacity in vitro when added to BAT homogenates from hypothyroid rats. In vivo administration of T2 to hypothyroid rats enhanced mitochondrial respiration. Moreover, UCP1 seems to be a molecular determinant underlying the effect of T2 on mitochondrial thermogenesis. In fact, inhibition of mitochondrial respiration by GDP and its reactivation by fatty acids were greater in mitochondria from T2-treated hypothyroid rats than untreated hypothyroid rats. In vivo administration of T2 led to an increase in PGC-1α protein levels in nuclei (transient) and mitochondria (longer lasting), suggesting a coordinate effect of T2 in these organelles that ultimately promotes net activation of mitochondrial biogenesis and BAT thermogenesis. The effect of T2 on PGC-1α is similar to that elicited by triiodothyronine. As a whole, the data reported here indicate T2 is a thyroid hormone derivative able to activate BAT thermogenesis.

Brown fat fuel use and regulation of energy homeostasis.

New evidence has recently supported the notion that brown adipose tissue (BAT) is present in adult humans and can play a prominent role in the regulation of body weight and metabolism. This has renewed the efforts to understand the physiologic mechanisms by which BAT is activated, which in turn could provide new therapeutic strategies for obesity and diabetes. BAT mass and activity are positively correlated with measures of metabolic health in rodents and humans; however, the amount of functional BAT in adult humans is highly variable with less found in overweight and obese individuals. The impact of BAT in the uptake and utilization of circulating nutrients is systemic, with major effects on whole-body insulin sensitivity and glucose tolerance as illustrated by BAT transplantation in rodents. Furthermore, a host of physiologic conditions and novel peptides/hormones have been implicated in the activation of BAT thermogenesis and/or 'browning' of white adipocytes. These new findings open the way for novel strategies aimed at increasing BAT mass and activity in obese humans as an important clinical goal in the midst of unprecedented high prevalence of obesity and associated metabolic disorders.

Grains of paradise (Aframomum melegueta) extract activates brown adipose tissue and increases whole-body energy expenditure in men

Brown adipose tissue (BAT) is responsible for cold- and diet-induced thermogenesis, and thereby contributes to the control of whole-body energy expenditure (EE) and body fat content. BAT activity can be assessed by fluoro-2-deoxyglucose (FDG)-positron emission tomography (PET) in human subjects. Grains of paradise (GP, Aframomum melegueta), a species of the ginger family, contain pungent, aromatic ketones such as 6-paradol, 6-gingerol and 6-shogaol. An alcohol extract of GP seeds and 6-paradol are known to activate BAT thermogenesis in small rodents. The present study aimed to examine the effects of the GP extract on whole-body EE and to analyse its relation to BAT activity in men. A total of nineteen healthy male volunteers aged 20-32 years underwent FDG-PET after 2 h of exposure to cold at 19°C with light clothing. A total of twelve subjects showed marked FDG uptake into the adipose tissue of the supraclavicular and paraspinal regions (BAT positive). The remaining seven showed no detectable uptake (BAT negative). Within 4 weeks after the FDG-PET examination, whole-body EE was measured at 27°C before and after oral ingestion of GP extract (40 mg) in a single-blind, randomised, placebo-controlled, crossover design. The resting EE of the BAT-positive group did not differ from that of the BAT-negative group. After GP extract ingestion, the EE of the BAT-positive group increased within 2 h to a significantly greater (P<0·01) level than that of the BAT-negative group. Placebo ingestion produced no significant change in EE. These results suggest that oral ingestion of GP extract increases whole-body EE through the activation of BAT in human subjects.

Brown Adipose Tissue Responds to Cold and Adrenergic Stimulation by Induction of FGF21

Fibroblast growth factor-21 (FGF21) is a pleiotropic protein involved in glucose, lipid metabolism and energy homeostasis, with main tissues of expression being the liver and adipose tissue. Brown adipose tissue (BAT) is responsible for cold-induced thermogenesis in rodents. The role of FGF21 in BAT biology has not been investigated. In the present study, wild-type C57BL/6J mice as well as a brown adipocyte cell line were used to explore the potential role of cold exposure and β3-adrenergic stimulation in the expression of FGF21 in BAT. Our results demonstrate that short-term exposure to cold, as well as β3-adrenergic stimulation, causes a significant induction of FGF21 mRNA levels in BAT, without a concomitant increase in FGF21 plasma levels. This finding opens new routes for the potential use of pharmaceuticals that could induce FGF21 and, hence, activate BAT thermogenesis.

Different populations of prostaglandin EP3 receptor-expressing preoptic neurons project to two fever-mediating sympathoexcitatory brain regions

The central mechanism of fever induction is triggered by an action of prostaglandin E2 (PGE2) on neurons in the preoptic area (POA) through the EP3 subtype of prostaglandin E receptor. EP3 receptor (EP3R)-expressing POA neurons project directly to the dorsomedial hypothalamus (DMH) and to the rostral raphe pallidus nucleus (rRPa), key sites for the control of thermoregulatory effectors. Based on physiological findings, we hypothesize that the febrile responses in brown adipose tissue (BAT) and those in cutaneous vasoconstrictors are controlled independently by separate neuronal pathways: PGE2 pyrogenic signaling is transmitted from EP3R-expressing POA neurons via a projection to the DMH to activate BAT thermogenesis and via another projection to the rRPa to increase cutaneous vasoconstriction. In this case, DMH-projecting and rRPa-projecting neurons would constitute segregated populations within the EP3R-expressing neuronal group in the POA. Here, we sought direct anatomical evidence to test this hypothesis with a double-tracing experiment in which two types of the retrograde tracer, cholera toxin b-subunit (CTb), conjugated with different fluorophores were injected into the DMH and the rRPa of rats and the resulting retrogradely labeled populations of EP3R-immunoreactive neurons in the POA were identified with confocal microscopy. We found substantial numbers of EP3R-immunoreactive neurons in both the DMH-projecting and the rRPa-projecting populations. However, very few EP3R-immunoreactive POA neurons were labeled with both the CTb from the DMH and that from the rRPa, although a substantial number of neurons that were not immunoreactive for EP3R were double-labeled with both CTbs. The paucity of the EP3R-expressing neurons that send collaterals to both the DMH and the rRPa suggests that pyrogenic signals are sent independently to these caudal brain regions from the POA and that such pyrogenic outputs from the POA reflect different control mechanisms for BAT thermogenesis and for cutaneous vasoconstriction by distinct sets of POA neurons.