Brown and beige adipocytes utilize a variety of substrates for cold-induced thermogenesis, contributing to the clearance of metabolites in circulation and, consequently, metabolic health. Food-derived compounds that exhibit agonistic activity at temperature-sensitive transient receptor potential channels may serve as cold mimics to elicit thermogenesis and substrate utilization in brown adipose tissue (BAT). In addition to fatty acids and glucose, branched-chain amino acids (BCAAs), which are essential amino acids obtained from foods, are actively catabolized in BAT through mitochondrial BCAA carrier (MBC). The relative contribution of BCAAs to fueling the tricarboxylic acid cycle as a substrate (i.e., anaplerosis) is estimated to be relatively small, yet BCAA catabolism in BAT exerts a critical role in systemic insulin sensitivity. The nature of this apparent tension remained unclear until the recent discovery that active BCAA catabolism in BAT through MBC is critical for the synthesis of metabolites such as glutathione, which is delivered to the liver to improve hepatic insulin sensitivity through redox homeostasis. Novel mechanistic insights into the control of BAT function and systemic metabolism reveal the therapeutic potential of food-derived compounds for improving metabolic flexibility and insulin sensitivity.

Since the 1960s, researchers have recognized an association between elevated plasma branched chain amino acids (BCAA) and metabolic disease, including type 2 diabetes mellitus and obesity, but the cause for it remained poorly understood. Recent advances in metabolomics, advanced imaging techniques, and genetic analyses over the past decade have enabled newfound insights into the mechanism of BCAA metabolic dysregulation across a variety of peripheral tissues and its impact on metabolic disease, suggesting a key role for brown adipose tissue (BAT) in determining BCAA metabolic homeostasis. Previous investigations into BAT have emphasized fatty acids and glucose as substrates for BAT thermogenesis. Here, we address the importance of BAT in systemic BCAA metabolism, driven via the newly identified mitochondrial BCAA carrier (MBC), as well as the impact of BAT-driven BCAA clearance on glucose homeostasis and metabolic disease. The newly identified MBC offers new therapeutic avenues by which BAT activity may be enhanced to improve metabolic and cardiovascular health, as well as other diseases in which increases of circulating BCAA may play a role in pathogenicity.

Compelling evidence shows that brown and beige adipose tissue are protective against metabolic diseases1,2. PR domain-containing 16 (PRDM16) is a dominant activator of the biogenesis of beige adipocytes by forming a complex with transcriptional and epigenetic factors and is therefore an attractive target for improving metabolic health3-8. However, a lack of knowledge surrounding the regulation of PRDM16 protein expression hampered us from selectively targeting this transcriptional pathway. Here we identify CUL2-APPBP2 as the ubiquitin E3 ligase that determines PRDM16 protein stability by catalysing its polyubiquitination. Inhibition of CUL2-APPBP2 sufficiently extended the half-life of PRDM16 protein and promoted beige adipocyte biogenesis. By contrast, elevated CUL2-APPBP2 expression was found in aged adipose tissues and repressed adipocyte thermogenesis by degrading PRDM16 protein. Importantly, extended PRDM16 protein stability by adipocyte-specific deletion of CUL2-APPBP2 counteracted diet-induced obesity, glucose intolerance, insulin resistance and dyslipidaemia in mice. These results offer a cell-autonomous route to selectively activate the PRDM16 pathway in adipose tissues.

Enhancer activation is essential for cell-type specific gene expression during cellular differentiation, however, how enhancers transition from a hypoacetylated "primed" state to a hyperacetylated-active state is incompletely understood. Here, we show SET domain-containing 5 (SETD5) forms a complex with NCoR-HDAC3 co-repressor that prevents histone acetylation of enhancers for two master adipogenic regulatory genes Cebpa and Pparg early during adipogenesis. The loss of SETD5 from the complex is followed by enhancer hyperacetylation. SETD5 protein levels were transiently increased and rapidly degraded prior to enhancer activation providing a mechanism for the loss of SETD5 during the transition. We show that induction of the CDC20 co-activator of the ubiquitin ligase leads to APC/C mediated degradation of SETD5 during the transition and this operates as a molecular switch that facilitates adipogenesis.

Abstract Branched-chain amino acids (BCAA) and their cognate α-ketoacids (BCKA) are elevated in an array of cardiometabolic diseases. Here we demonstrate that the major metabolic fate of uniformly-¹³C-labeled α-ketoisovalerate ([U-¹³C]KIV) in the heart is reamination to valine. Activation of cardiac branched-chain α-ketoacid dehydrogenase (BCKDH) by treatment with the BCKDH kinase inhibitor, BT2, does not impede the strong flux of [U-¹³C]KIV to valine. Sequestration of BCAA and BCKA away from mitochondrial oxidation is likely due to low levels of expression of the mitochondrial BCAA transporter SLC25A44 in the heart, as its overexpression significantly lowers accumulation of [¹³C]-labeled valine from [U-¹³C]KIV. Finally, exposure of perfused hearts to levels of BCKA found in obese rats increases phosphorylation of the translational repressor 4E-BP1 as well as multiple proteins in the MEK-ERK pathway, leading to a doubling of total protein synthesis. These data suggest that elevated BCKA levels found in obesity may contribute to pathologic cardiac hypertrophy via chronic activation of protein synthesis.

Importing necessary metabolites into the mitochondrial matrix is a crucial step of fuel choice during stress adaptation. Branched chain-amino acids (BCAAs) are essential amino acids needed for anabolic processes, but they are also imported into the mitochondria for catabolic reactions. What controls the distinct subcellular BCAA utilization during stress adaptation is insufficiently understood. The present study reports the role of SLC25A44, a recently identified mitochondrial BCAA carrier (MBC), in the regulation of mitochondrial BCAA catabolism and adaptive response to fever in rodents. We found that mitochondrial BCAA oxidation in brown adipose tissue (BAT) is significantly enhanced during fever in response to the pyrogenic mediator prostaglandin E₂ (PGE₂) and psychological stress in mice and rats. Genetic deletion of MBC in a BAT-specific manner blunts mitochondrial BCAA oxidation and non-shivering thermogenesis following intracerebroventricular PGE₂ administration. At a cellular level, MBC is required for mitochondrial BCAA deamination as well as the synthesis of mitochondrial amino acids and TCA intermediates. Together, these results illuminate the role of MBC as a determinant of metabolic flexibility to mitochondrial BCAA catabolism and optimal febrile responses. This study also offers an opportunity to control fever by rewiring the subcellular BCAA fate.

Increasing adaptive thermogenesis through the activation of brown adipose tissue (BAT) is a promising practical strategy for preventing obesity and related disorders. Ingestion of a single dose of 40 mg of an extract of Grains of Paradise (GP), a ginger family species, reportedly triggers BAT thermogenesis in individuals with high but not in those with low BAT activity. We hypothesized that prolonged treatment with GP might revive BAT in individuals who have lost active BAT. In the present study, we recruited 9 healthy young male volunteers with reduced BAT that was assessed by fluorodeoxyglucose positron emission tomography and computed tomography (FDG-PET/CT) following 2-h cold exposure at 19ºC. The subjects ingested GP extract (40 mg/d) or placebo every day for 5 wk. Before and after the treatment with either GP or placebo, their body composition and BAT-dependent cold-induced thermogenesis (CIT)-a non-invasive index of BAT-were measured in a single-blinded, randomized, placebo-controlled cross-over design. Their whole-body resting energy expenditure at a thermoneutral condition remained unchanged following GP treatment. However, CIT after treatment was significantly higher in GP-treated individuals than in placebo-treated individuals. Body weight and fat-free mass did not change significantly following GP or placebo treatment. Notably, body fat percentage slightly but significantly decreased after GP treatment but not after placebo treatment. These results suggest that repeated ingestion of GP elevates adaptive thermogenesis through the re-activation of BAT, thereby reducing body fat in individuals with low BAT activity.

Cold stimuli and the subsequent activation of β-adrenergic receptor (β-AR) potently stimulate adipose tissue thermogenesis and increase whole-body energy expenditure. However, systemic activation of the β3-AR pathway inevitably increases blood pressure, a significant risk factor for cardiovascular disease, and, thus, limits its application for the treatment of obesity. To activate fat thermogenesis under tight spatiotemporal control without external stimuli, here, we report an implantable wireless optogenetic device that bypasses the β-AR pathway and triggers Ca2+ cycling selectively in adipocytes. The wireless optogenetics stimulation in the subcutaneous adipose tissue potently activates Ca2+ cycling fat thermogenesis and increases whole-body energy expenditure without cold stimuli. Significantly, the light-induced fat thermogenesis was sufficient to protect mice from diet-induced body-weight gain. The present study provides the first proof-of-concept that fat-specific cold mimetics via activating non-canonical thermogenesis protect against obesity.

Thermogenesis in brown adipose tissue (BAT) declines with age; however, what regulates this process remains poorly understood. Here, we identify mitochondria lipoylation as a previously unappreciated molecular hallmark of aged BAT in mice. Using mitochondrial proteomics, we show that mitochondrial lipoylation is disproportionally reduced in aged BAT through a post-transcriptional decrease in the iron-sulfur (Fe-S) cluster formation pathway. A defect in the Fe-S cluster formation by the fat-specific deletion of Bola3 significantly reduces mitochondrial lipoylation and fuel oxidation in BAT, leading to glucose intolerance and obesity. In turn, enhanced mitochondrial lipoylation by α-lipoic acid supplementation effectively restores BAT function in old mice, thereby preventing age-associated obesity and glucose intolerance. The effect of α-lipoic acids requires mitochondrial lipoylation via the Bola3 pathway and does not depend on the anti-oxidant activity of α-lipoic acid. These results open up the possibility to alleviate the age-associated decline in energy expenditure by enhancing the mitochondrial lipoylation pathway.

Branched-chain amino acid (BCAA; valine, leucine and isoleucine) supplementation is often beneficial to energy expenditure; however, increased circulating levels of BCAA are linked to obesity and diabetes. The mechanisms of this paradox remain unclear. Here we report that, on cold exposure, brown adipose tissue (BAT) actively utilizes BCAA in the mitochondria for thermogenesis and promotes systemic BCAA clearance in mice and humans. In turn, a BAT-specific defect in BCAA catabolism attenuates systemic BCAA clearance, BAT fuel oxidation and thermogenesis, leading to diet-induced obesity and glucose intolerance. Mechanistically, active BCAA catabolism in BAT is mediated by SLC25A44, which transports BCAAs into mitochondria. Our results suggest that BAT serves as a key metabolic filter that controls BCAA clearance via SLC25A44, thereby contributing to the improvement of metabolic health.

Bone marrow provides progenitors of several types of cells, including muscle and white adipocytes, ensuring peripheral tissue homeostasis. However, the role of bone marrow-derived cells (BMCs) in induction of thermogenic adipocytes is unresolved. The purpose of this study is to examine whether BMCs are involved in the emergence of thermogenic adipocytes through adrenergic activation. Irradiation of mice with 8 Gy of X-ray-depleted BMCs and peripheral blood mononucleated cells (PBMCs), which in turn impaired induction of uncoupling protein 1 (UCP1) through administration of β3 adrenergic receptor agonist, CL 316,243 (CL), in inguinal white adipose tissue (iWAT). In contrast, CL-induced UCP1 induction in brown adipose tissue was unaffected by BMC depletion. Transplantation of normal BMCs into mice depleted of BMCs recovered PBMC levels and rescued the ability of iWAT browning by CL. Furthermore, analyses of mice transplanted with green fluorescent protein (GFP)-labeled BMCs revealed that the number of GFP-positive BMCs and PBMCs were significantly decreased by CL and that GFP-positive stromal cells and GFP-positive UCP1-expressing multilocular adipocytes appeared in iWAT after CL administration, demonstrating differentiation of BMC-derived preadipocytes into UCP1-expressing thermogenic adipocytes. These results unveiled a crucial role of the BMC as a nonresident origin for a subset of thermogenic adipocytes, contributing to browning of white adipose tissue.-Yoneshiro, T., Shin, W., Machida, K., Fukano, K., Tsubota, A., Chen, Y., Yasui, H., Inanami, O., Okamatsu-Ogura, Y., Kimura, K. Differentiation of bone marrow-derived cells toward thermogenic adipocytes in white adipose tissue induced by the β3 adrenergic stimulation.

Since the rediscovery of brown adipose tissue (BAT) in humans, its energy-dissipating ability has been well-recognized. The negative correlations of BAT activity with adiposity and insulin sensitivity provided an obvious rationale for discerning reliable and practical strategies for stimulating BAT. Though cold exposure or use of pharmacological adrenomimetics can activate BAT, they may have adverse effects. Therefore, determining alternative stimulants of BAT with lower risks such as commonly used food ingredients is highly desirable. Recent observations revealed that chemical activation of temperature-sensitive transient receptor potential (TRP) channels by food ingredients can recruit BAT in humans. Furthermore, animal studies have identified several food-derived stimulants of BAT acting through multiple mechanisms distinct from a TRP-mediated process. Dietary compounds acting as an activator of Sirtuin 1, a critical regulator of mitochondrial biogenesis and brown adipocyte differentiation, are one such class of promising food-derived BAT activators in humans. While the individual effects of various dietary factors are increasingly established in a laboratory setting, the potential synergistic effects of multiple stimulants on BAT remain to be tested in a clinical environment. These investigations may support the development of efficient, flexible dietary regimens capable of boosting BAT thermogenesis.

Environmental cues profoundly affect cellular plasticity in multicellular organisms. For instance, exercise promotes a glycolytic-to-oxidative fibre-type switch in skeletal muscle, and cold acclimation induces beige adipocyte biogenesis in adipose tissue. However, the molecular mechanisms by which physiological or pathological cues evoke developmental plasticity remain incompletely understood. Here we report a type of beige adipocyte that has a critical role in chronic cold adaptation in the absence of β-adrenergic receptor signalling. This beige fat is distinct from conventional beige fat with respect to developmental origin and regulation, and displays enhanced glucose oxidation. We therefore refer to it as glycolytic beige fat. Mechanistically, we identify GA-binding protein α as a regulator of glycolytic beige adipocyte differentiation through a myogenic intermediate. Our study reveals a non-canonical adaptive mechanism by which thermal stress induces progenitor cell plasticity and recruits a distinct form of thermogenic cell that is required for energy homeostasis and survival.

Dietary supplementation with melinjo (Gnetum gnemon L.) seed extract (MSE) has been proposed as an anti-obesity strategy. However, it remains unclear how MSE modulates energy balance. We tested the hypothesis that dietary MSE reduces energy intake and/or increases physical activity and metabolic thermogenesis in brown and white adipose tissue (BAT and WAT) in mice. Twenty-four C57BL/6 J mice were provided with normal diet, high-fat diet (HFD), or HFD with 1% MSE added, for 17 weeks. Food intake, spontaneous locomotor activity, hepatic triglyceride (TG) content, and blood parameters were examined. Mitochondrial thermogenesis-associated molecule and inflammatory marker expression levels in BAT and WAT were examined by quantitative PCR and western blotting. Dietary MSE did not affect energy intake or spontaneous locomotor activity, but significantly suppressed HFD-induced fat accumulation, hyperglycemia, and hyperinsulinemia. Homeostasis model assessment of insulin resistance score and hepatic TG content were both lower in the MSE-supplemented HFD-fed group than in the HFD-fed group, indicating reduced insulin resistance and a less fatty liver. Dietary MSE upregulated thermogenic uncoupling protein 1 (UCP1) and mitochondrial marker cytochrome c oxidase subunit IV protein expression in BAT; this was closely associated with sirtuin 1 mRNA induction. mRNAs of adipose inflammatory markers, such as monocyte chemotactic 1 and interleukin-1, were induced by HFD but suppressed by MSE. Considering that UCP1 protein expression is the most physiologically relevant parameter to assess the thermogenic capacities of BAT, our results indicate that dietary MSE supplementation induces BAT thermogenesis and reduces obesity-associated adipose tissue inflammation, hepatic steatosis, and insulin resistance.

Thermogenesis by brown and beige adipose tissue, which requires activation by external stimuli, can counter metabolic disease1. Thermogenic respiration is initiated by adipocyte lipolysis through cyclic AMP-protein kinase A signalling; this pathway has been subject to longstanding clinical investigation2-4. Here we apply a comparative metabolomics approach and identify an independent metabolic pathway that controls acute activation of adipose tissue thermogenesis in vivo. We show that substantial and selective accumulation of the tricarboxylic acid cycle intermediate succinate is a metabolic signature of adipose tissue thermogenesis upon activation by exposure to cold. Succinate accumulation occurs independently of adrenergic signalling, and is sufficient to elevate thermogenic respiration in brown adipocytes. Selective accumulation of succinate may be driven by a capacity of brown adipocytes to sequester elevated circulating succinate. Furthermore, brown adipose tissue thermogenesis can be initiated by systemic administration of succinate in mice. Succinate from the extracellular milieu is rapidly metabolized by brown adipocytes, and its oxidation by succinate dehydrogenase is required for activation of thermogenesis. We identify a mechanism whereby succinate dehydrogenase-mediated oxidation of succinate initiates production of reactive oxygen species, and drives thermogenic respiration, whereas inhibition of succinate dehydrogenase supresses thermogenesis. Finally, we show that pharmacological elevation of circulating succinate drives UCP1-dependent thermogenesis by brown adipose tissue in vivo, which stimulates robust protection against diet-induced obesity and improves glucose tolerance. These findings reveal an unexpected mechanism for control of thermogenesis, using succinate as a systemically-derived thermogenic molecule.

Uncoupling protein 1 (UCP1) plays a central role in nonshivering thermogenesis in brown fat; however, its role in beige fat remains unclear. Here we report a robust UCP1-independent thermogenic mechanism in beige fat that involves enhanced ATP-dependent Ca2+ cycling by sarco/endoplasmic reticulum Ca2+-ATPase 2b (SERCA2b) and ryanodine receptor 2 (RyR2). Inhibition of SERCA2b impairs UCP1-independent beige fat thermogenesis in humans and mice as well as in pigs, a species that lacks a functional UCP1 protein. Conversely, enhanced Ca2+ cycling by activation of α1- and/or β3-adrenergic receptors or the SERCA2b-RyR2 pathway stimulates UCP1-independent thermogenesis in beige adipocytes. In the absence of UCP1, beige fat dynamically expends glucose through enhanced glycolysis, tricarboxylic acid metabolism and pyruvate dehydrogenase activity for ATP-dependent thermogenesis through the SERCA2b pathway; beige fat thereby functions as a 'glucose sink' and improves glucose tolerance independently of body weight loss. Our study uncovers a noncanonical thermogenic mechanism through which beige fat controls whole-body energy homeostasis via Ca2+ cycling.

To date, 11 thermosensitive transient receptor potential (thermo-TRP) channels have been identified. Recent studies have characterized the mechanism of thermosensing by thermo-TRPs and the physiological role of thermo-TRPs in energy metabolism. In this review, we highlight the role of various thermo-TRPs in energy metabolism and hormone secretion. In the pancreas, TRPM2 and other TRPs regulate insulin secretion. TRPV2 expressed in brown adipocytes contributes to differentiation and/or thermogenesis. Sensory nerves that express TRPV1 promote increased energy expenditure by activating sympathetic nerves and adrenaline secretion. Here, we first show that capsaicin-induced adrenaline secretion is completely impaired in TRPV1 knockout mice. The thermogenic effects of TRPV1 agonists are attributable to brown adipose tissue (BAT) activation in mice and humans. Moreover, TRPA1- and TRPM8-expressing sensory nerves also contribute to potentiation of BAT thermogenesis and energy expenditure in mice. Together, thermo-TRPs are promising targets for combating obesity and metabolic disorders.

Background: The thermogenic effects of green tea catechin have been repeatedly reported, but their mechanisms are poorly understood.Objective: The aim of this study was to investigate the acute and chronic effects of catechin on brown adipose tissue (BAT), a site specialized for nonshivering thermogenesis, in humans.Design: Fifteen healthy male volunteers underwent fluorodeoxyglucose-positron emission tomography to assess BAT activity. To examine the acute catechin effect, whole-body energy expenditure (EE) after a single oral ingestion of a beverage containing 615 mg catechin and 77 mg caffeine (catechin beverage) was measured. Next, to investigate the chronic catechin effects, 10 men with low BAT activity were enrolled. Before and after ingestion of the catechin beverage 2 times/d for 5 wk, cold-induced thermogenesis (CIT) after 2 h of cold exposure at 19°C, which is proportional to BAT activity, was examined. Both the acute and chronic trials were single-blinded, randomized, placebo-controlled, season-matched crossover studies.Results: A single ingestion of the catechin beverage increased EE in 9 subjects who had metabolically active BAT (mean ± SEM: +15.24 ± 1.48 kcal, P < 0.01) but not in 6 subjects who had negligible activities (mean ± SEM: +3.42 ± 2.68 kcal). The ingestion of a placebo beverage containing 82 mg caffeine produced a smaller and comparative EE response in the 2 subject groups. Multivariate regression analysis revealed a significant interaction between BAT and catechin on EE (β = 0.496, P = 0.003). Daily ingestion of the catechin beverage elevated mean ± SEM CIT (from 92.0 ± 26.5 to 197.9 ± 27.7 kcal/d; P = 0.009), whereas the placebo beverage did not change it.Conclusion: Orally ingested tea catechin with caffeine acutely increases EE associated with increased BAT activity and chronically elevates nonshivering CIT, probably because of the recruitment of BAT, in humans. These trials were registered at www.umin.ac.jp/ctr/ as UMIN000016361.

Brown adipose tissue (BAT) contributes to whole-body energy expenditure (EE), especially cold-induced thermogenesis (CIT), in humans. Although it is known that EE and CIT vary seasonally, their relationship with BAT has not been investigated. In the present study, we examined the impact of BAT on seasonal variations of EE/CIT and thermal responses to cold exposure in a randomized crossover design. Forty-five healthy male volunteers participated, and their BAT was assessed by positron emission tomography and computed tomography. CIT, the difference of EE at 27ºC and after 2-h cold exposure at 19ºC, significantly increased in winter compared to summer, being greater in subjects with metabolically active BAT (High BAT, 185.6 kcal/d, 18.3 kcal/d, P<0.001) than those without (Low BAT, 90.6 kcal/d, -46.5 kcal/d, P<0.05). Multivariate regression analysis revealed a significant interaction effect between season and BAT on CIT (P<0.001). The cold-induced drop of tympanic temperature (Tty) and skin temperature (Tskin) in the forehead region and in the supraclavicular region close to BAT deposits were smaller in the High BAT group than in the Low BAT group in winter but not in summer. In contrast, the drop of Tskinin the subclavicular and peripheral regions distant from BAT was similar in the two groups in both seasons. In conclusion, CIT increased from summer to winter in a BAT-dependent manner, paralleling cold-induced changes in Tty/Tskin, indicating a role of BAT in seasonal changes in the thermogenic and thermal responses to cold exposure in humans.

Brown adipose tissue (BAT) is the site of sympathetically activated adaptive thermogenesis during cold exposure and after hyperphagia, thereby controlling whole-body energy expenditure (EE) and body fat. BAT thermogenesis is primarily dependent on the energy-dissipating activity of uncoupling protein 1 (UCP1). There are two types of UCP1-expressing adipocyte, classical brown and beige/brite adipocytes. Recent radionuclide studies have demonstrated the existence of metabolically active BAT composed of mainly beige/brite adipocytes in adult humans. Human BAT is activated by acute cold exposure, being positively correlated to cold-induced increases in EE. The inverse relationship between the BAT activity and body fatness suggests that BAT, because of its energy-dissipating activity, is protective against body fat accumulation. In fact, either repeated cold exposure or daily ingestion of some food ingredients acting on transient receptor potential channels recruited BAT in association with increased EE and decreased body fat. Moreover, possible contribution of BAT to glucose tolerance has been suggested. In addition to the sympathetic nervous system, some endocrine factors also have potential for activation/recruitment of BAT. Thus, BAT is a promising therapeutic target for combating human obesity and related metabolic disorders.

PURPOSE OF REVIEW: Cold exposure activates brown adipose tissue (BAT), the major site of sympathetically activated nonshivering thermognenesis, via transient receptor potential (TRP) channels. Capsaicin and its nonpungent analogue (capsinoids) are agonists for a vanilloid subtype one of TRP, and have the potential to increase whole-body energy expenditure and reduce body fat. This article reviews the regulatory roles of BAT for energy expenditure and body fat in humans, particularly focusing on food ingredients activating the TRP-BAT axis. RECENT FINDINGS: Acute cold exposure increased energy expenditure in humans with metabolically active BAT, but not those without it. Quite similar responses were found after a single oral ingestion of either capsinoids or an alcohol extract of Guinea pepper seeds, indicating that these food ingredients activate BAT and thereby increase energy expenditure. When individuals without active BAT were exposed to cold every day for 6 weeks, BAT was recruited in association with increased energy expenditure and decreased body fat. A 6-week daily ingestion of capsinoids mimicked the effects of repeated cold exposure. These findings indicate that human BAT can be reactivated/recruited, thereby increasing energy expenditure and decreasing body fat. SUMMARY: Human BAT recruited by prolonged ingestion of a vanilloid subtype one of TRP agonists increases energy expenditure and decreases body fat. In addition to capsinoids, there are numerous food ingredients acting as TRP agonists, which are expected to activate BAT and so be useful for the prevention of obesity in daily life.

Brown adipose tissue (BAT) burns fat to produce heat when the body is exposed to cold and plays a role in energy metabolism. Using fluorodeoxyglucose-positron emission tomography and computed tomography, we previously reported that BAT decreases with age and thereby accelerates age-related accumulation of body fat in humans. Thus, the recruitment of BAT may be effective for body fat reduction. In this study, we examined the effects of repeated stimulation by cold and capsinoids (nonpungent capsaicin analogs) in healthy human subjects with low BAT activity. Acute cold exposure at 19°C for 2 hours increased energy expenditure (EE). Cold-induced increments of EE (CIT) strongly correlated with BAT activity independently of age and fat-free mass. Daily 2-hour cold exposure at 17°C for 6 weeks resulted in a parallel increase in BAT activity and CIT and a concomitant decrease in body fat mass. Changes in BAT activity and body fat mass were negatively correlated. Similarly, daily ingestion of capsinoids for 6 weeks increased CIT. These results demonstrate that human BAT can be recruited even in individuals with decreased BAT activity, thereby contributing to body fat reduction.

Brown adipose tissue is attracting much attention due to its antiobestic effects; however, its development and involvement in metabolic improvement remain elusive. Here we established a method for a high-efficiency (>90%) differentiation of human pluripotent stem cells (hPSCs) into functional classical brown adipocytes (BAs) using specific hemopoietin cocktail (HC) without exogenous gene transfer. BAs were not generated without HC, and lack of a component of HC induced white adipocyte (WA) marker expressions. hPSC-derived BA (hPSCdBA) showed respiratory and thermogenic activation by β-adrenergic receptor (AdrRβ) stimuli and augmented lipid and glucose tolerance, whereas human multipotent stromal cell-derived WA (hMSCdWA) improved lipid but inhibited glucose metabolism. Cotransplantation of hPSCdBA normalized hMSCdWA-induced glucose intolerance. Surprisingly, hPSCdBAs expressed various hemopoietin genes, serving as stroma for myeloid progenitors. Moreover, AdrRβ stimuli enhanced recovery from chemotherapy-induced myelosuppression. Our study enhances our understanding of BA, identifying roles in metabolic and hemogenic regulation.

BACKGROUND: Capsinoids-nonpungent capsaicin analogs-are known to activate brown adipose tissue (BAT) thermogenesis and whole-body energy expenditure (EE) in small rodents. BAT activity can be assessed by [¹⁸F]fluorodeoxyglucose-positron emission tomography (FDG-PET) in humans. OBJECTIVES: The aims of the current study were to examine the acute effects of capsinoid ingestion on EE and to analyze its relation to BAT activity in humans. DESIGN: Eighteen healthy men aged 20-32 y underwent FDG-PET after 2 h of cold exposure (19°C) while wearing light clothing. Whole-body EE and skin temperature, after oral ingestion of capsinoids (9 mg), were measured for 2 h under warm conditions (27°C) in a single-blind, randomized, placebo-controlled, crossover design. RESULTS: When exposed to cold, 10 subjects showed marked FDG uptake into adipose tissue of the supraclavicular and paraspinal regions (BAT-positive group), whereas the remaining 8 subjects (BAT-negative group) showed no detectable uptake. Under warm conditions (27°C), the mean (±SEM) resting EE was 6114 ± 226 kJ/d in the BAT-positive group and 6307 ± 156 kJ/d in the BAT-negative group (NS). EE increased by 15.2 ± 2.6 kJ/h in 1 h in the BAT-positive group and by 1.7 ± 3.8 kJ/h in the BAT-negative group after oral ingestion of capsinoids (P < 0.01). Placebo ingestion produced no significant change in either group. Neither capsinoids nor placebo changed the skin temperature in various regions, including regions close to BAT deposits. CONCLUSION: Capsinoid ingestion increases EE through the activation of BAT in humans. This trial was registered at http://www.umin.ac.jp/ctr/ as UMIN 000006073.

Brown adipose tissue (BAT) can be identified by (18)F-fluorodeoxyglucose (FDG)-positron emission tomography (PET) combined with X-ray computed tomography (CT) in adult humans. The objective of this study was to clarify the relationship between BAT and adiposity in healthy adult humans, particularly to test the idea that decreased BAT activity may be associated with body fat accumulation with age. One hundred and sixty-two healthy volunteers aged 20-73 years (103 males and 59 females) underwent FDG-PET/CT after 2-h cold exposure at 19 °C with light clothing. Cold-activated BAT was detected in 41% of the subjects (BAT-positive). Compared with the BAT-negative group, the BAT-positive group was younger (P < 0.01) and showed a lower BMI (P < 0.01), body fat content (P < 0.01), and abdominal fat (P < 0.01). The incidence of cold-activated BAT decreased with age (P < 0.01), being more than 50% in the twenties, but less than 10% in the fifties and sixties. The adiposity-related parameters showed some sex differences, but increased with age in the BAT-negative group (P < 0.01), while they remained unchanged from the twenties to forties in the BAT-positive group, in both sexes. These results suggest that decreased BAT activity may be associated with accumulation of body fat with age.

Brown adipose tissue (BAT) can be identified by (18)F-fluorodeoxyglucose (FDG)-positron emission tomography (PET) in adult humans. Thirteen healthy male volunteers aged 20-28 years underwent FDG-PET after 2-h cold exposure at 19 °C with light-clothing and intermittently putting their legs on an ice block. When exposed to cold, 6 out of the 13 subjects showed marked FDG uptake into adipose tissue of the supraclavicular and paraspinal regions (BAT-positive group), whereas the remaining seven showed no detectable uptake (BAT-negative group). The BMI and body fat content were similar in the two groups. Under warm conditions at 27 °C, the energy expenditure of the BAT-positive group estimated by indirect calorimetry was 1,446 ± 97 kcal/day, being comparable with that of the BAT-negative group (1,434 ± 246 kcal/day). After cold exposure, the energy expenditure increased markedly by 410 ± 293 (P < 0.05) and slightly by 42 ± 114 kcal/day (P = 0.37) in the BAT-positive and -negative groups, respectively. A positive correlation (P < 0.05) was found between the cold-induced rise in energy expenditure and the BAT activity quantified from FDG uptake. After cold exposure, the skin temperature in the supraclavicular region close to BAT deposits dropped by 0.14 °C in the BAT-positive group, whereas it dropped more markedly (P < 0.01) by 0.60 °C in the BAT-negative group. The skin temperature drop in other regions apart from BAT deposits was similar in the two groups. These results suggest that BAT is involved in cold-induced increases in whole-body energy expenditure, and, thereby, the control of body temperature and adiposity in adult humans.

Adipocyte spheroids offer a promising three-dimensional (3D) cell culture model for obesity research, as they reproduce the structure and cell-cell interaction of adipose tissue more accurately compared to two-dimensional (2D) cultures. However, the mass production of uniform, small adipocyte spheroids remains challenging, limiting their use in large-scale analyses, such as drug screening. Here, we develop a method that combines simple microfluidics with templated emulsification to enable the large-scale production of small, uniform adipocyte spheroids. By encapsulating preadipocytes in hollow agarose microcapsules and incubating them for 2 days, we reproducibly generated more than 100,000 uniform spheroids with diameters of approximately 60 μm. These preadipocytes were subsequently differentiated into adipocyte spheroids through an 8-day induction period. This platform facilitates large-scale 3D analysis for obesity research and can be adapted to produce various other spheroid and organoid models, broadening its utility in biomedical research.

BACKGROUND: Adaptation to cold was essential for human migration across Eurasia. Non-shivering thermogenesis through brown adipose tissue (BAT) participates in cold adaptation because some genes involved in the differentiation and function of BAT exhibit signatures of positive natural selection in populations at high latitudes. Whether these genes are associated with the inter-individual variability in BAT thermogenesis remains unclear. In this study, we evaluated the potential associations between BAT activity and single nucleotide polymorphisms (SNPs) in candidate gene regions in East Asian populations. METHODS: BAT activity induced by mild cold exposure was measured in 399 healthy Japanese men and women using fluorodeoxyglucose-positron emission tomography and computed tomography (FDG-PET/CT). The capacity for cold-induced thermogenesis and fat oxidation was measured in 56 men. Association analyses with physiological traits were performed for 11 SNPs at six loci (LEPR, ANGPTL8, PLA2G2A, PLIN1, TBX15-WARS2, and FADS1) reported to be under positive natural selection. Associations found in the FDG-PET/CT population were further validated in 84 healthy East Asian men and women, in whom BAT activity was measured using infrared thermography. Associations between the SNP genotypes and BAT activity or other related traits were tested using multiple logistic and linear regression models. RESULTS: Of the 11 putative adaptive alleles of the six genes, two intronic SNPs in LEPR (rs1022981 and rs12405556) tended to be associated with higher BAT activity. However, these did not survive multiple test comparisons. Associations with lower body fat percentage, plasma triglyceride, insulin, and HOMA-IR levels were observed in the FDG-PET/CT population (P < 0.05). Other loci, including TBX15-WARS2, which is speculated to mediate cold adaptation in Greenland Inuits, did not show significant differences in BAT thermogenesis. CONCLUSIONS: Our results suggest a marginal but significant association between LEPR SNPs. However, robust supporting evidence was not established for the involvement of other loci under positive natural selection in cold adaptation through BAT thermogenesis in East Asian adults. Given the pleiotropic function of these genes, factors other than cold adaptation through BAT thermogenesis, such as diet adaptation, may contribute to positive natural selection at these loci.

Mitochondria play a vital role in non-shivering thermogenesis in both brown and subcutaneous white adipose tissues (BAT and scWAT, respectively). However, specific regulatory mechanisms driving mitochondrial function in these tissues have been unclear. Here we demonstrate that prolonged activation of β-adrenergic signaling induces epigenetic modifications in scWAT, specifically targeting the enhancers for the mitochondria master regulator genes Pgc1a/b. This is mediated at least partially through JMJD1A, a histone demethylase that in response to β-adrenergic signals, facilitates H3K9 demethylation of the Pgc1a/b enhancers, promoting mitochondrial biogenesis and the formation of beige adipocytes. Disruption of demethylation activity of JMJD1A in mice impairs activation of Pgc1a/b driven mitochondrial biogenesis and limits scWAT beiging, contributing to reduced energy expenditure, obesity, insulin resistance, and metabolic disorders. Notably, JMJD1A demethylase activity is not required for Pgc1a/b dependent thermogenic capacity of BAT especially during acute cold stress, emphasizing the importance of scWAT thermogenesis in overall energy metabolism.

BACKGROUND: Sympathetic activation of brown adipose tissue (BAT) thermogenesis can ameliorate obesity and related metabolic abnormalities. However, crucial subtypes of the β-adrenergic receptor (AR), as well as effects of its genetic variants on functions of BAT, remains unclear in humans. We conducted association analyses of genes encoding β-ARs and BAT activity in human adults. METHODS: Single nucleotide polymorphisms (SNPs) in β1-, β2-, and β3-AR genes (ADRB1, ADRB2, and ADRB3) were tested for the association with BAT activity under mild cold exposure (19 °C, 2 h) in 399 healthy Japanese adults. BAT activity was measured using fluorodeoxyglucose-positron emission tomography and computed tomography (FDG-PET/CT). To validate the results, we assessed the effects of SNPs in the two independent populations comprising 277 healthy East Asian adults using near-infrared time-resolved spectroscopy (NIRTRS) or infrared thermography (IRT). Effects of SNPs on physiological responses to intensive cold exposure were tested in 42 healthy Japanese adult males using an artificial climate chamber. RESULTS: We found a significant association between a functional SNP (rs1042718) in ADRB2 and BAT activity assessed with FDG-PET/CT (p < 0.001). This SNP also showed an association with cold-induced thermogenesis in the population subset. Furthermore, the association was replicated in the two other independent populations; BAT activity was evaluated by NIRTRS or IRT (p < 0.05). This SNP did not show associations with oxygen consumption and cold-induced thermogenesis under intensive cold exposure, suggesting the irrelevance of shivering thermogenesis. The SNPs of ADRB1 and ADRB3 were not associated with these BAT-related traits. CONCLUSIONS: The present study supports the importance of β2-AR in the sympathetic regulation of BAT thermogenesis in humans. The present collection of DNA samples is the largest to which information on the donor's BAT activity has been assigned and can serve as a reference for further in-depth understanding of human BAT function.

Protein kinase A promotes beige adipogenesis downstream from β-adrenergic receptor signaling by phosphorylating proteins, including histone H3 lysine 9 (H3K9) demethylase JMJD1A. To ensure homeostasis, this process needs to be reversible however, this step is not well understood. We show that myosin phosphatase target subunit 1- protein phosphatase 1β (MYPT1-PP1β) phosphatase activity is inhibited via PKA-dependent phosphorylation, which increases phosphorylated JMJD1A and beige adipogenesis. Mechanistically, MYPT1-PP1β depletion results in JMJD1A-mediated H3K9 demethylation and activation of the Ucp1 enhancer/promoter regions. Interestingly, MYPT1-PP1β also dephosphorylates myosin light chain which regulates actomyosin tension-mediated activation of YAP/TAZ which directly stimulates Ucp1 gene expression. Pre-adipocyte specific Mypt1 deficiency increases cold tolerance with higher Ucp1 levels in subcutaneous white adipose tissues compared to control mice, confirming this regulatory mechanism in vivo. Thus, we have uncovered regulatory cross-talk involved in beige adipogenesis that coordinates epigenetic regulation with direct activation of the mechano-sensitive YAP/TAZ transcriptional co-activators.

There is no evidence of the effect of exercise training on human brown-like adipose tissue vascular density (BAT-d). Here, we report whether whole-body strength training (ST) in a cold environment increased BAT-d. The participants were 18 men aged 20–31 years. They were randomly assigned to two groups: one that performed ST twice a week at 75% intensity of one-repetition maximum for 10 weeks during winter (EX; n = 9) and a control group that did not perform ST (CT; n = 9). The total hemoglobin concentration in the supraclavicular region determined by time-resolved near-infrared spectroscopy was used as a parameter of BAT-d. ST volume (Tvol) was defined as the mean of the weight x repetition x sets of seven training movements. The number of occasions where the room temperature was lower than the median (NRcold) was counted as an index of potential cold exposure during ST. There was no significant between-group difference in BAT-d. Multiple regression analysis using body mass index, body fat percentage, NRcold, and Tvol as independent variables revealed that NRcold and Tvol were determined as predictive of changes in BAT-d. An appropriate combination of ST with cold environments could be an effective strategy for modulating BAT.

The increase of whole-body energy expenditure seen after a single meal ingestion, referred to as diet-induced thermogenesis (DIT), substantially varies depending on the meal's macronutrient composition. Brown adipose tissue (BAT), a site of non-shivering thermogenesis, was reported to be involved in DIT. To examine the effects of meal composition on BAT-associated DIT in humans, healthy male participants underwent fluorodeoxyglucose-positron emission tomography to assess BAT activity, and respiratory gas analysis for 2 h after ingestion of a carbohydrate-, protein-, or fat-rich meal (C-meal, P-meal, and F-meal, respectively). The calculated DIT at 2 h was 6.44 ± 2.01%, 3.49 ± 2.00%, and 2.32 ± 0.90% of the ingested energy after the P-meal, C-meal, and F-meal, respectively. The DIT after C-meal ingestion correlated positively with BAT activity (P = 0.011), and was approximately twice greater in the group with high-BAT activity than in the group with low-BAT activity (4.35 ± 1.74% vs. 2.12 ± 1.76%, P < 0.035). Conversely, the DIT after F-meal or P-meal ingestion did not correlate with BAT activity, with no difference between the two groups. Thus, BAT has a significant role in DIT after ingestion of a carbohydrate-rich meal, but hardly after ingestion either protein- or fat-rich meal.

The gut microbiome has emerged as a key regulator of obesity; however, its role in brown adipose tissue (BAT) metabolism and association with obesity remain to be elucidated. We found that the levels of circulating branched-chain amino acids (BCAA) and their cognate α-ketoacids (BCKA) were significantly correlated with the body weight in humans and mice and that BCAA catabolic defects in BAT were associated with obesity in diet-induced obesity (DIO) mice. Pharmacological systemic enhancement of BCAA catabolic activity reduced plasma BCAA and BCKA levels and protected against obesity; these effects were reduced in BATectomized mice. DIO mice gavaged with Bacteroides dorei and Bacteroides vulgatus exhibited improved BAT BCAA catabolism and attenuated body weight gain, which were not observed in BATectomized DIO mice. Our data have highlighted a possible link between the gut microbiota and BAT BCAA catabolism and suggest that Bacteroides probiotics could be used for treating obesity.

KEY POINTS: Melanin-concentrating hormone (MCH) neuron-ablated mice exhibit increased energy expenditure and reduced fat weight. Increased brown adipose tissue (BAT) activity and locomotor activity-independent energy expenditure contributed to body weight reduction in MCH neuron-ablated mice. MCH neurons send inhibitory input to the medullary raphe nucleus to modulate BAT activity. ABSTRACT: Hypothalamic melanin-concentrating hormone (MCH) peptide robustly affects energy homeostasis. However, it is unclear whether and how MCH-producing neurons, which contain and release a variety of neuropeptides/transmitters, regulate energy expenditure in the central nervous system and peripheral tissues. We thus examined the regulation of energy expenditure by MCH neurons, focusing on interscapular brown adipose tissue (BAT) activity. MCH neuron-ablated mice exhibited reduced body weight, increased oxygen consumption, and increased BAT activity, which improved locomotor activity-independent energy expenditure. Trans-neuronal retrograde tracing with the recombinant pseudorabies virus revealed that MCH neurons innervate BAT via the sympathetic premotor region in the medullary raphe nucleus (MRN). MRN neurons were activated by MCH neuron ablation. Therefore, endogenous MCH neuron activity negatively modulates energy expenditure via BAT inhibition. MRN neurons might receive inhibitory input from MCH neurons to suppress BAT activity.

AIMS/INTRODUCTION: Brown adipose tissue (BAT) utilizes large amounts of fuel for thermogenesis, but the mechanism by which fuel substrates are switched in response to changes in energy status is poorly understood. We have now investigated the role of Kruppel-like factor 15 (KLF15), a transcription factor expressed at a high level in adipose tissue, in the regulation of fuel utilization in BAT. MATERIALS AND METHODS: Depletion or overexpression of KLF15 in HB2 differentiated brown adipocytes was achieved by adenoviral infection. Glucose and fatty acid oxidation were measured with radioactive substrates, pyruvate dehydrogenase complex activity was determined with a colorimetric assay, and gene expression was examined by reverse transcription and real-time polymerase chain reaction analysis. RESULTS: Knockdown of KLF15 in HB2 cells attenuated fatty acid oxidation in association with downregulation of the expression of genes related to this process including Acox1 and Fatp1, whereas it increased glucose oxidation. Expression of the gene for pyruvate dehydrogenase kinase 4 (PDK4), a negative regulator of pyruvate dehydrogenase complex, was increased or decreased by KLF15 overexpression or knockdown, respectively, in HB2 cells, with these changes being accompanied by a respective decrease or increase in pyruvate dehydrogenase complex activity. Chromatin immunoprecipitation showed that Pdk4 is a direct target of KLF15 in HB2 cells. Finally, fasting increased expression of KLf15, Pdk4 and genes involved in fatty acid utilization in BAT of mice, whereas refeeding suppressed Klf15 and Pdk4 expression. CONCLUSIONS: Our results implicate KLF15 in the regulation of fuel switching between glucose and fatty acids in response to changes in energy status in BAT.

While brown adipose tissue (BAT) is well-recognized for its ability to dissipate energy in the form of heat, recent studies suggest multifaced roles of BAT in the regulation of glucose and lipid homeostasis beyond stimulating thermogenesis. One of the functions involves interorgan communication with metabolic organs, such as the liver, through BAT-derived secretory factors, a.k.a., batokine. However, the identity and the roles of such mediators remain insufficiently understood. Here, we employed proteomics and transcriptomics in human thermogenic adipocytes and identified previously unappreciated batokines, including phospholipid transfer protein (PLTP). We found that increased circulating levels of PLTP, via systemic or BAT-specific overexpression, significantly improve glucose tolerance and insulin sensitivity, increased energy expenditure, and decrease the circulating levels of cholesterol, phospholipids, and sphingolipids. Such changes were accompanied by increased bile acids in the circulation, which in turn enhances glucose uptake and thermogenesis in BAT. Our data suggest that PLTP is a batokine that contributes to the regulation of systemic glucose and lipid homeostasis as a mediator of BAT-liver interorgan communication.

Since the recent rediscovery of brown adipose tissue (BAT) in adult humans, this thermogenic tissue has been attracting increasing interest. The inverse relationship between BAT activity and body fatness suggests that BAT, because of its energy dissipating activity, is protective against body fat accumulation. Cold exposure activates and recruits BAT, resulting in increased energy expenditure and decreased body fatness. The stimulatory effects of cold exposure are mediated through transient receptor potential (TRP) channels and the sympathetic nervous system (SNS). Most TRP members also function as chemesthetic receptors for various food ingredients, and indeed, agonists of TRP vanilloid 1 such as capsaicin and its analog capsinoids mimic the effects of cold exposure to decrease body fatness through the activation and recruitment of BAT. The antiobesity effect of other food ingredients including tea catechins may be attributable, at least in part, to the activation of the TRP-SNS-BAT axis. BAT is also involved in the facultative thermogenesis induced by meal intake, referred to as diet-induced thermogenesis (DIT), which is a significant component of the total energy expenditure in our daily lives. Emerging evidence suggests a crucial role for the SNS in BAT-associated DIT, particularly during the early phase, but several gut-derived humoral factors may also participate in meal-induced BAT activation. One intriguing factor is bile acids, which activate BAT directly through Takeda G-protein receptor 5 (TGR5) in brown adipocytes. Given the apparent beneficial effects of some TRP agonists and bile acids on whole-body substrate and energy metabolism, the TRP/TGR5-BAT axis represents a promising target for combating obesity and related metabolic disorders in humans.

Brown adipose tissue (BAT) mediates adaptive thermogenesis upon food intake and cold exposure, thus potentially contributing to the prevention of lifestyle-related diseases. 18F-fluorodeoxyglucose (FDG)-positron emission tomography (PET) with computed tomography (CT) (18FDG-PET/CT) is a standard method for assessing BAT activity and volume in humans. 18FDG-PET/CT has several limitations, including high device cost and ionizing radiation and acute cold exposure necessary to maximally stimulate BAT activity. In contrast, near-infrared spectroscopy (NIRS) has been used for measuring changes in O2-dependent light absorption in the tissue in a non-invasive manner, without using radiation. Among NIRS, time-resolved NIRS (NIRTRS) can quantify the concentrations of oxygenated and deoxygenated hemoglobin ([oxy-Hb] and [deoxy-Hb], respectively) by emitting ultrashort (100 ps) light pulses and counts photons, which are scattered and absorbed in the tissue. The basis for assessing BAT density (BAT-d) using NIRTRS is that the vascular density in the supraclavicular region, as estimated using Hb concentration, is higher in BAT than in white adipose tissue. In contrast, relatively low-cost continuous wavelength NIRS (NIRCWS) is employed for measuring relative changes in oxygenation in tissues. In this review, we provide evidence for the validity of NIRTRS and NIRCWS in estimating human BAT characteristics. The indicators (IndNIRS) examined were [oxy-Hb]sup, [deoxy-Hb]sup, total hemoglobin [total-Hb]sup, Hb O2 saturation (StO2sup), and reduced scattering coefficient ( μ s sup ' ) in the supraclavicular region, as determined by NIRTRS, and relative changes in corresponding parameters, as determined by NIRCWS. The evidence comprises the relationships between the IndNIRS investigated and those determined by 18FDG-PET/CT; the correlation between the IndNIRS and cold-induced thermogenesis; the relationship of the IndNIRS to parameters measured by 18FDG-PET/CT, which responded to seasonal temperature fluctuations; the relationship of the IndNIRS and plasma lipid metabolites; the analogy of the IndNIRS to chronological and anthropometric data; and changes in the IndNIRS following thermogenic food supplementation. The [total-Hb]sup and [oxy-Hb]sup determined by NIRTRS, but not parameters determined by NIRCWS, exhibited significant correlations with cold-induced thermogenesis parameters and plasma androgens in men in winter or analogies to 18FDG-PET. We conclude that NIRTRS can provide useful information for assessing BAT-d in a simple, rapid, non-invasive way, although further validation study is still needed.

F18-fluorodeoxyglucose (FDG)-positron emission tomography (PET) along with computed tomography (CT) is a standard method for assessing brown adipose tissue (BAT) activity. We tested the usefulness of near-infrared time-resolved spectroscopy (NIRTRS) as a simple and noninvasive method for evaluating BAT density (BAT-d) by examining the effects of some factors known to influence BAT activity. The total hemoglobin concentration as a parameter of BAT-d was evaluated using NIRTRS in the supraclavicular region in 413 Japanese individuals. The associations were analyzed between BAT-d and sex, age, the percentages of body fat (%BF), visceral fat (VF), and the seasonal ambient temperature (AmT) fluctuations. Age was associated with decreased BAT-d (P  <  0.05). There was no sex difference in the BAT-d, except for those in their twenties. Multivariate analyses revealed that %BF and VF were correlated with BAT-d, and the lower AmT (around 4°C or 5°C) for 4 and 6 weeks prior to the measurement day was associated with an increase in the BAT-d. Our NIRTRS results were analogous to those reported with FDG18-PET  /  CT, indicating the usefulness of NIRTRS. BAT-d might increase during the 4 and 6 weeks after the AmT decreases to lower than 4°C or 5°C.

Beige adipocytes are an inducible form of mitochondria-enriched thermogenic adipocytes that emerge in response to external stimuli, such as chronic cold exposure. We have previously shown that after the withdrawal of external stimuli, beige adipocytes directly acquire a white fat-like phenotype through autophagy-mediated mitochondrial degradation. We investigated the upstream pathway that mediates mitochondrial clearance and report that Parkin-mediated mitophagy plays a key role in the beige-to-white adipocyte transition. Mice genetically deficient in Park2 showed reduced mitochondrial degradation and retained thermogenic beige adipocytes even after the withdrawal of external stimuli. Norepinephrine signaling through the PKA pathway inhibited the recruitment of Parkin protein to mitochondria in beige adipocytes. However, mitochondrial proton uncoupling by uncoupling protein 1 (UCP1) was dispensable for Parkin recruitment and beige adipocyte maintenance. These results suggest a physiological mechanism by which external cues control mitochondrial homeostasis in thermogenic fat cells through mitophagy.

High-mobility group protein B1 (HMGB1) is a late inflammatory mediator released from inflammatory cells when stimulated, resulting in exaggerating septic symptoms. We recently demonstrated that full-length adiponectin, a potent anti-inflammatory adipokine, inhibits lipopolysaccharide-induced HMGB1 release. However, the effects of adiponectin on HMGB1-induced exaggerating signals currently remain unknown. This study aimed to investigate the effects of adiponectin on the pro-inflammatory function of HMGB1 in RAW264 macrophage cells. The treatment of RAW264 cells with HMGB1 significantly up-regulated the mRNA expression of tumour necrosis factor-α, interleukin-1β and C-X-C motif chemokine 10. HMGB1-induced cytokine expression was markedly suppressed by a toll-like receptor 4 (TLR4) antagonist and slightly suppressed by an antagonist of the receptor for advanced glycation end products. A prior treatment with full-length or globular adiponectin dose-dependently suppressed all types of HMGB1-induced cytokine expression, and this suppression was abolished by compound C, an AMPK inhibitor, but not by the haem oxygenase (HO)-1 inhibitor, zinc protoporphyrin IX. Both forms of adiponectin also reduced the mRNA expression of TLR4. These results suggest that full-length and globular adiponectin suppress HMGB1-induced cytokine expression through an AMPK-mediated HO-1-independent pathway.

18F-fluorodeoxyglucose positron emission tomography combined with computed tomography (FDGPET/CT) is widely used as a standard method for evaluating human brown adipose tissue (BAT), a recognized therapeutic target of obesity. However, a longitudinal BAT study using FDG-PET/CT is lacking owing to limitations of the method. Near-infrared time-resolved spectroscopy (NIR(TRS)) is a technique for evaluating human BAT density noninvasively. This study aimed to test whether NIRTRS could detect changes in BAT density during or after long-term intervention. First, using FDG-PET/CT, we confirmed a significant increase (+48.8%, P < 0.05) in BAT activity in the supraclavicular region after 6-week treatment with thermogenic capsaicin analogs, capsinoids. Next, 20 volunteers were administered either capsinoids or placebo daily for 8 weeks in a double-blind design, and BAT density was measured using NIR(TRS) every 2 weeks during the 8-week treatment period and an 8-week period after stopping treatment. Consistent with FDG-PET/CT results, NIR(TRS) successfully detected an increase in BAT density during the 8-week treatment (+46.4%, P < 0.05), and a decrease in the 8-week follow-up period (-12.5%, P = 0.07), only in the capsinoid-treated, but not the placebo, group. Thus, NIR(TRS) can be applied for quantitative assessment of BAT in longitudinal intervention studies in humans.

Since the recent re-discovery of brown adipose tissue (BAT) in adult humans, this thermogenic tissue has attracted increasing interest. The inverse relationship between the BAT activity and body fatness suggests that BAT, because of its energy dissipating activity, is protective against body fat accumulation. Cold exposure activates and recruits BAT in association with increased energy expenditure and decreased body fatness. The stimulatory effects of cold are mediated through transient receptor potential channels (TRP), most of which are also chemesthetic receptors for various food ingredients. In fact, capsaicin and its analog capsinoids, representative agonists of TRPV1, mimic the effects of cold to decrease body fatness through the activation and recruitment of BAT. The anti-obesity effect of some other food ingredients including tea catechins may also be attributable to the activation of the TRP-BAT axis. Thus, BAT is a promising target for combating obesity and related metabolic disorders in humans.

Human brown adipose tissue (BAT) activity (SUVmax) has been typically evaluated by 18F-fluorodeoxy glucose (FDG)-positron emission tomography (PET) combined with computed tomography (CT). In this study, the objective was to detect human BAT by near-infrared time-resolved spectroscopy (NIRTRS), a noninvasive and simple method for measuring total hemoglobin concentration [total-Hb] and reduced scattering coefficient (μs') in the tissue. The [total-Hb] in the supraclavicular region of the BAT (+) (SUVmax≥2.0) group was 95.0±28.2 μM (mean+/-SD), which was significantly higher than that of the BAT (-) (SUVmax<2.0) group (52.0±14.8 μM), but not in other regions apart from the BAT deposits. The μs' in the supraclavicular region of the BAT (+) group was 8.4±1.7 cm(-1), which was significantly higher than that of BAT (-) group (4.3±1.0 cm(-1)), but not in other regions. The area under the receiver operating characteristic curve closest to (0, 1) for [total-Hb] and μs' to discriminate BAT (+) from BAT (-) was 72.5 μM and 6.3 cm(-1), respectively. The sensitivity, specificity, and accuracy for both parameters were 87.5, 100, and 93.3%, respectively. Our novel NIRTRS method is noninvasive, simple, and inexpensive compared with FDG-PET/CT, and is reliable for detecting human BAT.

PURPOSE: Brown adipose tissue (BAT) contributes to the regulation of non-shivering thermogenesis and adiposity. Increasing BAT has recently attracted much attention as a countermeasure to obesity. Animal studies have shown that prolonged catechin treatment increases uncoupling protein 1, a thermogenic protein in BAT. On the other hand, supportable evidence in human is lacking. Thus, the purpose of this study was to examine whether BAT increases after catechin ingestion in humans. METHODS: Twenty-two healthy young women were given either a catechin-rich (540 mg/day; catechin) or placebo beverage every day for 12 weeks in a double-blind design. BAT density was measured using near-infrared time-resolved spectroscopy (NIRTRS), visceral fat area were measured using magnetic resonance imaging, extramyocellular lipids (EMCL) using proton magnetic resonance spectroscopy, and body fat mass using dual-energy X-ray absorptiometry scans. RESULTS: BAT density was significantly increased (18.8 %), and EMCL was decreased (17.4 %) after the 12-week ingestion. There was a significant negative correlation between the changes in BAT density and those in EMCL (r = -0.66, P < 0.05). There were no notable changes in other parameters. CONCLUSIONS: In conclusion, prolonged ingestion of a catechin-rich beverage increases the BAT density in parallel with a decrease in EMCL.

Brown adipose tissue (BAT) is a site of adaptive non-shivering thermogenesis after cold exposure, and is involved in the regulation of energy expenditure and body fatness. BAT can be activated and recruited by not only cold exposure but also by various food ingredients including capsaicin in chili pepper and catechins in green tea, which would be easily and safely applicable to our daily life for preventing obesity.

OBJECTIVE: Human brown adipose tissue (BAT) activity has been typically evaluated by (18) F-fluorodeoxyglucose (FDG)-positron emission tomography (PET) combined with computed tomography (CT). However, FDG-PET/CT has serious limitations (e.g., radiation and cold exposure). This study evaluated BAT density using near-infrared time-resolved spectroscopy (NIRTRS ), a simple and noninvasive method of measuring the indices of tissue hemoglobin concentration [total-Hb] and mitochondrial density (µs '). METHODS: The NIRTRS parameters at 760, 800, and 830 nm in the supraclavicular region potentially containing BAT were evaluated. First, the NIRTRS parameters were compared at 27 °C and during a 2-h cold exposure (19 °C) in 18 men. Then, NIRTRS parameters at 27 °C were compared with mean standardized uptake values (SUVmean ) assessed by FDG-PET/CT after the 2-h cold exposure (19 °C) in 29 men. RESULTS: There was no significant difference between the NIRTRS parameters at 27 °C and 19°C. The [total-Hb] and µs ' were significantly correlated to SUVmean (r = 0.73 and r = 0.64, respectively). A receiver operating characteristic analysis revealed that the sensitivity (75.0-82.4%), specificity (91.7-100%), and accuracy (82.8-86.2%) of the NIRTRS parameters were all good to determine the NIRTRS reliability. CONCLUSIONS: Our novel NIRTRS method is noninvasive and simple and can reliably assess human BAT density in the supraclavicular region.

Kaempferia parviflora extract (KP) has been reported to have a preventive effect on obesity in mice, probably by increasing energy expenditure (EE). The aims of the current study were to examine the acute effects of KP ingestion on whole-body EE in humans and to analyze its relation to the activity of brown adipose tissue (BAT), a site of non-shivering thermogenesis. After an oral ingestion of an ethanol extract of KP, EE increased significantly, showing a maximal increase of 229±69 kJ/d at 60 min, while it did not change after placebo ingestion. To evaluate BAT activity, the subjects underwent fluorodeoxyglucose-positron emission tomography, and divided into two groups with high- and low-BAT activities. A similar and greater response of EE to KP ingestion was observed in the high-BAT group (351±50 kJ/d at 60 min), but not in the low activity group. Placebo ingestion did not cause any significant EE change in either group. These results indicate that a single oral ingestion of the KP extract can potentially increase whole-body EE probably through the activation of BAT in healthy men, and may be useful as an anti-obesity regimen.

We reported previously that a single ingestion of an alcohol extract of grains of paradise (GP, Aframomum melegueta), a species of the ginger family, increases energy expenditure (EE) through the activation of brown adipose tissue, a site of sympathetically mediated metabolic theromogenesis. The present study aimed to examine a daily ingestion of GP extract on whole-body EE and body fat in humans. Whole-body EE and body fat content were measured before and after daily oral ingestion of GP extract (30 mg/d) for 4 wk in 19 non-obese female volunteers aged 20-22 y in a single-blind, randomized, placebo-controlled, crossover design. Four-week daily ingestion of GP and a placebo decreased and increased slightly the visceral fat area at the umbilicus level, respectively. The GP-induced change was significantly different from that induced by the placebo (p<0.05), and negatively correlated with the initial visceral fat area (r=-0.64, p<0.01). Neither GP nor placebo ingestion affected subcutaneous or total fat. The daily ingestion of GP, but not the placebo, increased whole-body EE (p<0.05). These results suggest that GP extract may be an effective and safe tool for reducing body fat, mainly by preventing visceral fat accumulation.

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.

PURPOSE OF REVIEW: Capsaicin and its nonpungent analog (capsinoids) are known to be food ingredients that increase energy expenditure and decrease body fat. This article reviews the role of brown adipose tissue (BAT) for the thermogenic effect of these compounds in humans and proposes the possibility of some other antiobesity food ingredients. RECENT FINDINGS: A single oral ingestion of capsinoids increases energy expenditure in human individuals with metabolically active BAT, but not those without it, indicating that capsinoids activate BAT and thereby increase energy expenditure. This finding gave a rational explanation for discrepant results of the effects of capsinoids in the previous studies. Human BAT may be largely composed of inducible 'beige' adipocytes more than typical brown adipocytes because its gene expression patterns are similar to beige cells isolated from murine white fat depots. In fact, preadipocytes isolated from supraclavicular fat deposits - where BAT is often detected - are capable of differentiating into brown-like adipocytes in vitro, providing evidence of inducible brown adipogenesis in adult humans. SUMMARY: As human BAT may be inducible, a prolonged ingestion of capsinoids would recruit active BAT and thereby increase energy expenditure and decrease body fat. In addition to capsinoids, there are numerous food ingredients that are expected to activate BAT and so be useful for the prevention of obesity in daily life.

OBJECTIVE: The significant roles of brown adipose tissue (BAT) in the regulation of energy expenditure and adiposity are established in small rodents but have been controversial in humans. The objective is to examine the prevalence of metabolically active BAT in healthy adult humans and to clarify the effects of cold exposure and adiposity. RESEARCH DESIGN AND METHODS: In vivo 2-[(18)F]fluoro-2-deoxyglucose (FDG) uptake into adipose tissue was measured in 56 healthy volunteers (31 male and 25 female subjects) aged 23-65 years by positron emission tomography (PET) combined with X-ray computed tomography (CT). RESULTS: When exposed to cold (19 degrees C) for 2 h, 17 of 32 younger subjects (aged 23-35 years) and 2 of 24 elderly subjects (aged 38-65 years) showed a substantial FDG uptake into adipose tissue of the supraclavicular and paraspinal regions, whereas they showed no detectable uptake when kept warm (27 degrees C). Histological examinations confirmed the presence of brown adipocytes in these regions. The cold-activated FDG uptake was increased in winter compared with summer (P < 0.001) and was inversely related to BMI (P < 0.001) and total (P < 0.01) and visceral (P < 0.001) fat areas estimated from CT image at the umbilical level. CONCLUSIONS: Our findings, being against the conventional view, indicate the high incidence of metabolically active BAT in adult humans and suggest a role in the control of body temperature and adiposity.