Uncoupling Protein 1 Expression In Brown Adipose Tissue Research Articles

OR07-03 UCP1 Expression In Human Brown Adipose Tissue Is Inversely Associated With Cardiometabolic Risk Factors

Abstract Disclosure: T. Kwok: None. L.E. Ramage: None. K.J. Suchacki: None. C. Gray: None. K. Alexandra: None. L.D. Boyle: None. R.K. Semple: None. S.I. Semple: None. T. MacGillivray: None. E.J. van Beek: None. S. Wakelin: None. R.H. Stimson: None. Brown adipose tissue (BAT) is a promising therapeutic target for obesity. 18F-Fluorodeoxyglucose positron emission tomography (18F-FDG PET) is the most commonly used imaging modality to quantify human BAT activity. 18F-FDG uptake may be reduced in obesity but insulin resistance has been suggested as a potential confounding factor. Uncoupling protein 1 (UCP1) is the key thermogenic protein in BAT and thus serves as a surrogate measure of BAT thermogenic capacity. We quantified UCP1 expression in paired BAT and white adipose tissue (WAT) samples from 141 patients undergoing elective neck surgery. UCP1 mRNA was quantified in whole tissue (n=53) and differentiated pre-adipocytes (n=88). Data are presented as mean ± SEM. Individuals with high UCP1 expression in whole BAT (>2 arbitrary units) were younger (44.2 ± 3.5 vs 55.7 ± 2.0 years) with lower BMI (26.5 ± 1.2 vs 30.1 ± 1.0kg/m2), waist circumference (87.9 ± 2.9 vs 101.1 ± 2.6cm), waist-hip ratio (0.86 ± 0.01 vs 0.92 ± 0.01), fat percentage (29.1 ± 2.6 vs 35.3 ± 1.7%), insulin resistance (HOMA-IR 1.44 ± 0.18 vs 2.69 ± 0.35), systolic (131 ± 6 vs 143 ± 4mmHg) and diastolic blood pressure (79 ± 3 vs 86 ± 2mmHg) (all P<0.05). BAT UCP1 expression was lower in subjects on beta-blockers or with existing hypertension. BAT (but not WAT) UCP1 expression correlated negatively with age (r=−0.305), weight (r=−0.374), waist circumference (r=−0.296), fat mass (r=−0.388) and BMI (r=−0.282) (all P<0.05). However, UCP1 levels in differentiated brown adipocytes were not associated with any of the above measurements. In multiple regression, age was the only independent predictor of high BAT UCP1 expression. Interestingly, BAT UCP1 levels were not reduced in obese subjects aged <40 years. To determine whether BAT activity was preserved in young obese subjects in vivo, we performed 18F-FDG-PET/MR scanning during mild cold exposure (16-17°C) in 6 normal weight (BMI 22 ± 1kg/m2) and 6 obese (BMI 32 ± 1kg/m2) age-matched (22 ± 1 years) subjects. BAT 18F-FDG uptake (standard uptake value 5.1 ± 0.5 vs 4.2 ± 0.6 g/mL) and volume (69 ± 14 vs 72 ± 32 cm3) were similar between weight groups, despite greater insulin resistance in obese subjects (fasting glucose 5.5 ± 0.2 vs 4.3 ± 0.1mmol/L, insulin 11.9 ± 1.3 vs 5.8 ± 0.9mU/L, HOMA-IR 2.9 ± 0.3 vs 1.1 ± 0.2, free fatty acids 465 ± 78 vs 240 ± 34µM, all P<0.05), suggesting that 18F-FDG uptake by BAT is not significantly affected by insulin resistance. In conclusion, BAT UCP1 expression is reduced in individuals with adverse cardiometabolic risk factors, but these subjects retain brown pre-adipocytes with the capacity to form new thermogenic adipocytes after appropriate stimulation. UCP1 expression and cold-induced 18F-FDG uptake by BAT is preserved in young obese subjects. These data highlight the therapeutic potential of BAT mass expansion and activation as a therapeutic strategy to ameliorate the cardiometabolic consequences of obesity. Presentation: Thursday, June 15, 2023

The nonshivering thermogenesis of brown adipose tissue and fat mobilization of striped hamsters exposed to cycles of cold and warm temperatures

The adaptive adjustments in the capacity for metabolic thermogenesis are critical for the survival in many small mammals that are acclimated to cold winter conditions. In this study the striped hamsters (Cricetulus barabensis) were subjected to repeated cycles of cold (5°C) and warm (23°C) temperatures. Resting metabolic rate (RMR), nonshivering thermogenesis (NST) and energy intake, as well as the expression of uncoupling protein 1 (UCP1) of brown adipose tissue (BAT) and serum thyroid hormone levels were measured. Both RMR and NST were significantly increased in striped hamsters subjected to repeated cycles of short-term cold (5°C, 72 h) – warm (23°C, 4 days) temperatures compared to that of the hamsters consistently kept at 23°C. In these cycled hamsters, BAT UCP1 expression was significantly upregulated, whereas serum T3 and T4 concentration did not change significantly. Moreover, gross energy intake was considerably increased during both cold exposure and warm phases, whereas fat deposition was significantly decreased in these cycled hamsters compared to those consistently kept at 23°C. This indicates that small mammals may both increase energy intake and mobilize fat depots to cope with frequent cold exposure. Thyroid hormone may be not involved in the BAT UCP1-mediated thermogenesis and fat mobilization.

The effects of mirabegron on obesity-induced inflammation and insulin resistance are associated with brown adipose tissue activation but not beiging in the subcutaneous white adipose tissue.

Mirabegron is a selective β₃-adrenergic receptors agonist, which has been recently shown to improve metabolic health in rodents and humans. In this study, we investigated the effects of 2-week mirabegron treatment on the metabolic parameters of mice with a diet-induced obesity (DIO). C57BL/6JUnib mice were divided into control (CTR) and obese (OB) groups treated with vehicle, and an OB group treated with mirabegron (OB+MIRA). The obese groups were fed a high-fat diet for 12weeks. Mirabegron (10mg/kg/day) was administrated orally by gavage from weeks 10-12. After 2weeks of mirabegron treatment, the energy expenditure was assessed with indirect calorimetry. Blood glucose, insulin, glycerol, free fatty acids (FFA), thiobarbituric acid reactive substance (TBAR), and tumour necrosis factor (TNF)-α levels were also assessed, and the HOMA index was determined. Liver tissue, brown adipose tissue (BAT), and inguinal white adipose tissue (iWAT) samples were collected for histological examination. The protein expressions of uncoupling protein 1 (UCP1) and mitochondrial transcription factor A (TFAM) were assessed using western blotting of the BAT and iWAT samples. In this study, mirabegron increased the energy expenditure and decreased adiposity in OB+MIRA. Increased UCP1 expression in BAT without changes in iWAT was also found. Mirabegron decreased circulating levels of FFA, glycerol, insulin, TNF-α, TBARS and HOMA index. DIO significantly increased the lipid deposits in the liver and BAT, but mirabegron partially reversed this change. Our findings indicate that treatment with mirabegron decreased inflammation and improved metabolism in obese mice. This effect was associated with increased BAT-mediated energy expenditure, but not iWAT beiging, which suggests that mirabegron might be useful for the treatment of obesity and diabetes.

Supplementary prenatal copper increases plasma triiodothyronine and brown adipose tissue uncoupling protein-1 gene expression but depresses thermogenesis in newborn lambs.

ObjectiveWe tested the hypothesis that increasing dietary copper (Cu) to gravid ewes would enhance brown adipose tissue (BAT) thermogenesis in their offspring.MethodsTwin-bearing ewes were assigned on d 70 of gestation to diets containing 3, 10, or 20 ppm dietary Cu (n = 8 per group). Twin lambs were assigned at birth to a cold (6°C) or warm (28°C) environmental chamber for 48 h. Blood was collected from ewes and from lambs and perirenal BAT was collected after 48 h in the environmental chambers.ResultsPrenatal Cu exposure increased ewe plasma triiodothyronine (T3) and thyroxine concentration (T4) (p<0.01) but prenatal Cu exposure had no effect on lamb plasma concentrations of T3, T4, glucose, or nonesterified fatty acid concentration (p≥0.08). The high level of prenatal Cu exposure depressed 48-h rectal temperature (p = 0.03). Cold exposure decreased BAT norepinephrine (NE) and increased BAT dopamine (p≤0.01), but prenatal Cu exposure had no effect on BAT cytochrome C oxidase activity or BAT NE or dopamine (p≥0.07). However, BAT of lambs from high-Cu ewes maintained higher uncoupling protein-1 (UCP1) gene expression than BAT of lambs from low- and medium-Cu ewes following warm or cold exposure in environmental chambers (p = 0.02). Cold exposure caused near depletion of BAT lipid by 48 h (p<0.001), increased BAT cytochrome c oxidase activity (p< 0.01), and depressed plasma fatty acid concentrations (p<0.001).ConclusionAlthough prenatal Cu exposure increased BAT UCP1 expression during warm and cold exposure, prenatal cold Cu exposure depressed 48-h rectal temperature. Cold exposure decreased BAT lipid content by over 80% and decreased lamb plasma fatty acid concentration by over 40%, indicating that fuel reserves for thermogenesis were nearly depleted by 48 h of cold exposure.

ZW290 Increases Cold Tolerance by Inducing Thermogenesis via the Upregulation of Uncoupling Protein 1 in Brown Adipose Tissue In Vitro and In Vivo.

To provide molecular evidence on the thermogenic mechanism of primary brown adipocytes, western blot analysis was used to detect brown adipose tissue (BAT)-specific gene expressions. BAT protects the mammals from hypothermia injury with a large amount of mitochondria and high expression of uncoupling Protein 1 (UCP1), which is the vital protein to determine the heat production in BAT. In our previous study, the compound ZW290 (the structure shown in Fig. 1) was obtained by molecular docking with a UCP1 inducer. In the present study, ZW290 not only significantly upregulated the expression of UCP1 protein (p < 0.01) and its related signaling pathway in the primary brown adipocytes, but also remarkably decreased the mitochondrial membrane potential and the concentration of adenosine triphosphate (ATP) (p < 0.01). Kunming (KM) mice were kept under acute cold exposure (-20°C) to evaluate the preventive and protective effects of ZW290 on cold injury, and revealed its regulating mechanism in vitro. The rectal and body temperatures of ZW290-treated mice were significantly higher than those of the control (or model) group both at room temperature and at -20°C (p < 0.001). Hematoxylin-eosin (HE) staining and immunohistochemistry indicated that ZW290 notably decreased the size of lipid droplets in BAT and increased the content of mitochondria and the expression of UCP1 in BAT and white adipose tissue (WAT). Furthermore, the survival rate showed that ZW290 could prolong the overall survival of mice. Therefore, we obtained the conclusion that ZW290 might transform energy into heat by inhibiting ATP synthesis and increasing the expression of UCP1. Additionally, ZW290 may enhance cold tolerance by increasing heat production through increasing the content of mitochondria and the expression of UCP1 in BAT and WAT.

Dietary Curcumin Intervention Targets Mouse White Adipose Tissue Inflammation and Brown Adipose Tissue UCP1 Expression.

This study aimed to determine whether dietary curcumin intervention targets both white adipose tissue (WAT) inflammation and brown adipose tissue (BAT)-mediated energy expenditure. C57BL/6J mice were fed with a low-fat diet, high-fat diet (HFD), or HFD plus curcumin. In addition to assessing the effect of curcumin intervention on metabolic profiles, this study assessed WAT macrophage infiltration and composition and inflammatory cytokine production. Metabolic cages were applied for determining energy expenditure. Raw264.7 (ATCC, Manassas, Virginia) and other cell models were utilized to test the in vitro effect of curcumin treatment. Curcumin intervention reduced WAT macrophage infiltration and altered macrophage functional polarity, as the ratio of M2-like versus M1-like macrophages increased after curcumin intervention. Curcumin treatment reduced M1-like macrophage markers or proinflammation cytokine expression in both macrophages and adipocytes. Curcumin intervention also increased energy expenditure and body temperature in response to a cold challenge. Finally, the in vivo and in vitro investigations suggested that curcumin increased expression of uncoupling protein 1 (UCP1), possibly involving PPAR-dependent and -independent mechanisms. Curcumin intervention targets both WAT inflammation and BAT UCP1 expression. These observations advanced our knowledge on the metabolic beneficial effects of the curry compound curcumin, bringing us a novel perspective on dietary polyphenol research.

Effects of Nigella sativa Extracts on the Lipid Profile and Uncoupling Protein-1 Gene Expression in Brown Adipose Tissue of Mice.

Background:Uncoupling protein-1 (UCP-1) is the index protein of the brown adipose tissue (BAT), used in the obesity studies. We evaluated the effects of thymoquinone (TQ), hydroalcoholic, and hexane extracts of Nigella sativa, on the UCP-1 gene expression in BAT, and also on the recovery from oxidative stress, due to a high-fat diet.Materials and Methods:Fifty mice were divided into five groups: the first group was fed with a usual diet and the second, third, fourth, and fifth groups with a high-fat diet, hydroalcoholic extract, hexane extract, and TQ, respectively. After completing the course, the lipid profile, paraoxonase 1 (PON1), serum total antioxidant capacity (TAC), and malondialdehyde (MDA) were measured. UCP-1 expression in BAT was evaluated at the gene and protein level.Results:The weight of mice, receiving TQ, hydroalcoholic, and hexane extracts, was decreased (P < 0.05), compared to the second group (P < 0.05). MDA was increased in the second group, compared to the first group (P < 0.05); however, TAC, liver catalase enzyme, and PON1 were decreased (P < 0.05). Furthermore, MDA of the third, fourth, and fifth groups had decreased, and the activity of PON1, liver catalase enzyme, and the amount of TAC was increased (P < 0.05). UCP-1 expression of the third and fourth groups was increased, compared to the second group (P < 0.05).Conclusion:The results suggest that TQ, hydroalcoholic, and hexane extracts of N. sativa have a protective and therapeutic role in the oxidative stress, caused by high-fat diets. The hydroalcoholic and hexane extracts can induce weight loss, by positively affecting UCP-1, at the gene and protein level.

Nesfatin-1 in the Lateral Parabrachial Nucleus Inhibits Food Intake, Modulates Excitability of Glucosensing Neurons, and Enhances UCP1 Expression in Brown Adipose Tissue.

Nesfatin-1, an 82-amino acid neuropeptide, has been shown to induce anorexia and energy expenditure. Food intake is decreased in ad libitum-fed rats following injections of nesfatin-1 into the lateral, third, or fourth ventricles of the brain. Although the lateral parabrachial nucleus (LPBN) is a key regulator of feeding behavior and thermogenesis, the role of nesfatin-1 in this structure has not yet been delineated. We found that intra-LPBN microinjections of nesfatin-1 significantly reduced nocturnal cumulative food intake and average meal sizes without affecting meal numbers in rats. Because glucose sensitive neurons are involved in glucoprivic feeding and glucose homeostasis, we examined the effect of nesfatin-1 on the excitability of LPBN glucosensing neurons. In vivo electrophysiological recordings from LPBN glucose sensitive neurons showed that nesfatin-1 (1.5 × 10−8 M) excited most of the glucose-inhibited neurons. Chronic administration of nesfatin-1 into the LPBN of rats reduced body weight gain and enhanced the expression of uncoupling protein 1 (UCP1) in brown adipose tissue (BAT) over a 10-day period. Furthermore, the effects of nesfatin-1 on food intake, body weight, and BAT were attenuated by treatment with the melanocortin antagonist SHU9119. These results demonstrate that nesfatin-1 in LPBN inhibited food intake, modulated excitability of glucosensing neurons and enhanced UCP1 expression in BAT via the melanocortin system.

427 - Reduced Mitochondrial Oxidative Stress Impairs Brown Adipose Tissue-Mediated Thermogenesis in Mice

Our recent work identified oxidative stress in adipocyte as a prerequisite for diet-induced thermogenesis and uncoupling protein 1 (UCP1) induction in white and brown adipose tissue of mice. To further confirm this observation, we used mice that overexpressed human catalase targeted to mitochondria (mCAT mice). Similar to the heart, catalase activity was significantly increased in brown adipose tissue (BAT) of mCAT mice compared to wild-type (WT) mice. WT and mCAT mice were fed high fat diet (HFD, 45% calories from fat) or normal chow diet (NCD, 4% calories from fat) for 20 weeks. Oxidative stress markers such as 4-hydroxynonenal and nitrotyrosine were only elevated in BAT of WT mice fed HFD. HFD induced similar weight gain and adiposity in WT and mCAT mice but mCAT mice produced less heat especially when housed at colder temperatures (15°C) or when given a beta-adrenergic agonist to activate thermogenesis. UCP1 expression in BAT was similarly induced by HFD in both WT and mCAT. However, mitochondrial uncoupling, as assessed by proton leak, was reduced in brown preadipocytes isolated from HFD-fed mCAT mice compared to those isolated from WT mice on HFD. To determine if the changes in BAT function affected whole body glucose and insulin homeostasis, we performed glucose and insulin tolerance tests. HFD similarly impaired glucose and insulin tolerance in WT and mCAT mice but induced adipose tissue inflammation only in WT mice. Taken together, these data suggest that oxidative stress is required for diet and cold-induced thermogenesis in mice.

The Gq signalling pathway inhibits brown and beige adipose tissue.

Brown adipose tissue (BAT) dissipates nutritional energy as heat via the uncoupling protein-1 (UCP1) and BAT activity correlates with leanness in human adults. Here we profile G protein-coupled receptors (GPCRs) in brown adipocytes to identify druggable regulators of BAT. Twenty-one per cent of the GPCRs link to the Gq family, and inhibition of Gq signalling enhances differentiation of human and murine brown adipocytes. In contrast, activation of Gq signalling abrogates brown adipogenesis. We further identify the endothelin/Ednra pathway as an autocrine activator of Gq signalling in brown adipocytes. Expression of a constitutively active Gq protein in mice reduces UCP1 expression in BAT, whole-body energy expenditure and the number of brown-like/beige cells in white adipose tissue (WAT). Furthermore, expression of Gq in human WAT inversely correlates with UCP1 expression. Thus, our data indicate that Gq signalling regulates brown/beige adipocytes and inhibition of Gq signalling may be a novel therapeutic approach to combat obesity.

Apelin Enhances Brown Adipogenesis and Browning of White Adipocytes

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

Concerted expression of the thermogenic and bioenergetic mitochondrial protein machinery in brown adipose tissue

Brown adipose tissue (BAT) is specialized in non-shivering thermogenesis through the expression of the mitochondrial uncoupling protein-1 (UCP1). In this paper, we describe the relationship between UCP1 and proteins involved in ATP synthesis. By the use of BATIRKO mice, which have enhanced UCP1 expression in BAT, an increase in ATP synthase as well as in ubiquinol cytochrome c reductase levels was observed. Alterations in mitochondrial mass or variations in ATP levels were not observed in BAT of these mice. In addition, using a protocol of brown adipocyte differentiation, the concerted expression of UCP1 with ATP synthase was found. These two scenarios revealed that increases in the uncoupling machinery of brown adypocites must be concomitantly followed by an enhancement of proteins involved in ATP synthesis. These concerted changes reflect the need to maintain ATP production in an essentially uncoupling cell type.

The Isoflavone-Rich Fraction of the Crude Extract of the Puerariae Flower Increases Oxygen Consumption and BAT UCP1 Expression in High-Fat Diet-Fed Mice

Puerariae flower extract (PFE) is a crude extract of the Kudzu flower. Previous studies have shown that PFE supplementation exerts anti-obesity and anti-fatty liver effects in high-fat diet-fed mice. In this study, we aimed to identify the PFE components responsible for these effects and to determine their influence on energy expenditure and uncoupling protein 1 (UCP1) expression. Experiments were conducted on C57BL/6J male mice classified into 3 groups: (1) high-fat diet-fed (HFD), (2) high-fat diet-fed given PFE (HFD + PFE), and (3) high-fat diet-fed given the PFE isoflavone-rich fraction (HFD + ISOF). All groups were fed for 42 days. The HFD + PFE and HFD + ISOF groups showed significant resistance to increases in body weight, hepatic triglyceride level, and visceral fat compared to the HFD group. These groups also exhibited significant increases in oxygen consumption and UCP1-positive brown adipose tissue (BAT) area. Our results demonstrate that the active ingredients in PFE are present in the ISOF and that these compounds may increase energy expenditure by upregulation of BAT UCP1 expression. These findings provide valuable information regarding the anti-obesity effects of isoflavones.

Maximal thermogenic capacity and non-shivering thermogenesis in the South American subterranean rodent Ctenomys talarum

Subterranean rodents inhabit closed tunnel systems that are hypoxic and hypercapnic and buffer aboveground ambient temperature. In contrast to other strictly subterranean rodents, Ctenomys talarum exhibits activity on the surface during foraging and dispersion and hence, is exposed also to the aboveground environment. In this context, this species is a valuable model to explore how the interplay between underground and aboveground use affects the relationship among basal metabolic rate (BMR), cold-induced maximum metabolic rate (MMR), shivering (ST), and non-shivering thermogenesis (NST). In this work, we provide the first evidence of the presence of NST, including the expression of uncoupling proteins in brown adipose tissue (BAT), and shivering thermogenesis in Ctenomys talarum, a species belonging to the most numerous subterranean genus, endemic to South America. Our results show no differences in BMR, cold-induced MMR, and NST between cold- (15 °C) and warm- (25 °C) acclimated individuals. Furthermore, thermal acclimation had no effect on the expression of mitochondrial uncoupling protein 1 (UCP1) in BAT. Only cytochrome c oxidase (COX) content and activity increased during cold acclimation. When interscapular BAT was removed, NST decreased more than 30%, whereas cold-induced MMR remained unchanged. All together, these data suggest that cold-induced MMR reaches a maximum in warm-acclimated individuals and so a probable ceiling in NST and UCP1 expression in BAT. Possible thermogenic mechanisms explaining the increase in the oxidative capacity, mediated by COX in BAT of cold-acclimated individuals and the role of ST in subterranean life habits are proposed.

Effects of ileal interposition on glucose metabolism in obese rats with diabetes

Ileal interposition (IT), in which the distal ileum is transposed isoperistaltically into the proximal jejunum, is considered as a procedure for metabolic or antidiabetes surgery. Our aim was to study the effects of IT on glycemic control, fat metabolism, and hormonal changes in obese rats with spontaneous diabetes. Animals were divided into either an IT or a sham (SH) group. They underwent an oral glucose tolerance test (OGTT) before and 4 and 8 weeks after the operation. All animals were killed 10 weeks after operation for analyses of tissue weight (liver, pancreas, epididymal fat, brown fat), immunoblotting of uncoupling protein-1 (UCP1) protein in brown adipose tissue (BAT), and fasting plasma levels of glucose, insulin, glucagon-like peptide (GLP)-1, peptide YY (PYY), glucose-dependent insulinotropic polypeptide (GIP), and leptin. Body weight increased postoperatively in both groups compared with preoperative weight, but it did not differ between the 2 groups. Eight weeks postoperatively, integrated blood glucose levels during the OGTT were decreased in IT compared with SH (P < .05). Fasting plasma levels of insulin, GLP-1, and GIP did not differ between the 2 groups, but PYY levels were higher in the IT animals (P < .01). The weight of epididymal and BATs, homeostasis model assessment insulin resistance, and fasting plasma leptin levels were decreased in the IT group (P < .05). Expression of UCP1 was higher in IT than SH animals (P < .05). These results suggest that IT improves glucose and lipid metabolism by decreasing insulin resistance and epididymal fat, and increased expression of UCP1 in BAT might be among the mechanisms responsible.

Rhein Protects against Obesity and Related Metabolic Disorders through Liver X Receptor-Mediated Uncoupling Protein 1 Upregulation in Brown Adipose Tissue

Liver X receptors (LXRs) play important roles in regulating cholesterol homeostasis, and lipid and energy metabolism. Therefore, LXR ligands could be used for the management of metabolic disorders. We evaluated rhein, a natural compound from Rheum palmatum L., as an antagonist for LXRs and investigated its anti-obesity mechanism in high-fat diet-fed mice. Surface plasmon resonance assays were performed to examine the direct binding of rhein to LXRs. LXR target gene expression was assessed in 3T3-L1 adipocytes and HepG2 hepatic cells in vitro. C57BL/6J mice fed a high-fat diet were orally administered with rhein for 4 weeks, and then the expression levels of LXR-related genes were analyzed. Rhein bound directly to LXRs. The expression levels of LXR target genes were suppressed by rhein in 3T3-L1 and HepG2 cells. In white adipose tissue, muscle and liver, rhein reprogrammed the expression of LXR target genes related to adipogenesis and cholesterol metabolism. Rhein activated uncoupling protein 1 (UCP1) expression in brown adipose tissue (BAT) in wild-type mice, but did not affect UCP1 expression in LXR knockout mice. In HIB-1B brown adipocytes, rhein activated the UCP1 gene by antagonizing the repressive effect of LXR on UCP1 expression. This study suggests that rhein may protect against obesity and related metabolic disorders through LXR antagonism and regulation of UCP1 expression in BAT.

Leucine Deprivation Stimulates Fat Loss via Increasing CRH Expression in the Hypothalamus and Activating The Sympathetic Nervous System

We previously showed that leucine deprivation decreases abdominal fat mass largely by increasing energy expenditure, as demonstrated by increased lipolysis in white adipose tissue (WAT) and uncoupling protein 1 (UCP1) expression in brown adipose tissue (BAT). The goal of the present study was to investigate the possible involvement of central nervous system (CNS) in this regulation and elucidate underlying molecular mechanisms. For this purpose, levels of genes and proteins related to lipolysis in WAT and UCP1 expression in BAT were analyzed in wild-type mice after intracerebroventricular administration of leucine or corticotrophin-releasing hormone antibodies, or in mice deleted for three β-adrenergic receptors, after being maintained on a leucine-deficient diet for 7 d. Here, we show that intracerebroventricular administration of leucine significantly attenuates abdominal fat loss and blocks activation of hormone sensitive lipase in WAT and induction of UCP1 in BAT in leucine-deprived mice. Furthermore, we provide evidence that leucine deprivation stimulates fat loss by increasing expression of corticotrophin-releasing hormone in the hypothalamus via activation of stimulatory G protein/cAMP/protein kinase A/cAMP response element-binding protein pathway. Finally, we show that the effect of leucine deprivation on fat loss is mediated by activation of the sympathetic nervous system. These results suggest that CNS plays an important role in regulating fat loss under leucine deprivation and thereby provide novel and important insights concerning the importance of CNS leucine in the regulation of energy homeostasis.

Crossing the Hurdles of Thyroid Hormone Receptor-α Activation

Thyroid hormone acts in virtually every biological system in vertebrates by controlling the expression of different sets of genes. To achieve this, thyroid hormone interacts with two receptors (TR), TR and TR , located in the nucleus of its target cells, which turn gene transcription on or offand thusmediate thebiological effectsassociatedwith the thyroid secretion (1, 2). The distribution of TR and TR among different target tissues is not homogeneous: TR pathways are implicated in the brain, skeletal muscle, heart, and bone, whereas the TR pathways play a metabolic role in liver and adipose tissue (3). Together both TR isoforms control avastnetworkofbiologicalprocesses that includescritical roles in development, growth, and metabolic homeostasis (4). The determination of the TR structure made it clear that differences in the ligand binding pocket of the receptors would allow for the development of small molecules with a reasonable degree of binding selectivity (5). This was achieved in the late 1990s and GC-1, the first of such molecules to exhibit TR selectivity, was tested in cell systems and in animals (6). Today an array of TR -selective ligands exists, expanding not only our understanding of thyroid hormone action but also the exciting possibility of pharmacological intervention in disease states (7). The latter is based on the fact that beneficial metabolic effects can be obtained by activating TR pathways in liver and adipose tissue and avoiding the undesirable side effects of the TR pathway activation in the brain, heart, and bone (8). In the current issue of Endocrinology, GrijotaMartinez et al. (9) report the analysis of TR-dependent pathways in developing hypothyroid rats using GC-24, a highly TR -selective molecule, and CO23, a thyromimetic with reportedly TR -specific effects in vitro and in tadpoles (10). Whereas GC-24 exhibited the expected selectivity for TR pathways, equimolar amounts of CO23 failed to activate either TR-dependent pathway. Only at much higher doses did CO23 exhibit thyromimetic activity, without the expected selectivity for TR pathways. Such a failure is hard to explain but could be the result of unfavorable pharmacokinetics in mammals unforeseen from the GC series experience. Any of several small problems could be killing the effects of CO23, including impaired absorption, distribution, and/or transport into target cells and accelerated metabolism or excretion, resulting in death by a thousand cuts. That different TR isoforms control separate biological processes became clear from a series of studies in mice with inactivation or mutation of different TR isoforms as well as studies in patients with the syndrome of resistance to thyroid hormone (3). However, a landmark in this field was established with the demonstration that treatment of hypothyroid rats with GC-1 normalizes serum cholesterol and triglycerides through TR activation in the liver without increasing heart rate or expression of typical T3 target genes in the heart, all TR -dependent processes (11). Later an additional key observation was made: that chronic treatment with GC-1 in euthyroid female rats lowered serum cholesterol by approximately 20% and spared bone mass as assessed by histomorphometry and dual-x-ray bone absorptiometry (12). Further studies illustrated that a substantial degree of TR selectivity could be achieved with GC-1, even in tissues with active TR and TR pathways, such as the brown adipose tissue (BAT). In hypothyroid mice, treatment with GC-1 normalized BAT uncoupling protein-1 expression (a highly T3 responsive

Lipocalin 2 is a selective modulator of peroxisome proliferator‐activated receptor‐γ activation and function in lipid homeostasis and energy expenditure

We have previously identified lipocalin 2 (Lcn2) as a cytokine playing a critical role in the regulation of body fat mass, lipid metabolism, and insulin resistance. Lcn2 deficiency reduces PPARγ gene expression in adipocytes. In this study, we investigated the role of Lcn2 in PPARγ activation and function via assessing the insulin sensitization and fatty acid (FA) homeostasis of PPARγ agonist in high-fat diet (HFD)-induced obesity in Lcn2(-/-) mice. We found that rosiglitazone (Rosi) significantly improved insulin sensitivity in Lcn2(-/-) mice as effectively as in wild-type (WT) mice; unfed-state levels of blood glucose, free FAs, and triglycerides (TGs) were significantly reduced after a 25-d treatment of Rosi in Lcn2(-/-) mice. However, Rosi action on fat deposition and FA homeostasis was altered; Rosi-induced body weight and subcutaneous fat gain and liver lipid accumulation were markedly lessened in Lcn2(-/-) mice. The results of in vivo metabolic labeling showed that Rosi markedly reduced de novo lipogenesis in adipose tissue of Lcn2(-/-) mice. In brown adipose tissue (BAT), the expression of the genes functioning in TG hydrolysis and mitochondrial oxidation was up-regulated more in Lcn2(-/-) than in WT mice. Most strikingly, Rosi stimulated significantly higher levels of uncoupling protein-1 expression in BAT, and completely rescued cold intolerance in Lcn2(-/-) mice. We demonstrate that Lcn2 is a critical selective modulator of PPARγ activation and function in lipid homeostasis and energy expenditure.

Adaptive character of metabolism in Eothenomys miletus in Hengduan Mountains region during cold acclimation

Environmental factors play an important role in the seasonal adaptation of body mass and thermogenesis in small, wild mammals. The purpose of the present study was to test the hypothesis that ambient temperature was a cue to trigger the seasonal adjustments in body mass, energy intake, uncoupling protein 1 (UCP1) in brown adipose tissue (BAT), and other biochemical characteristics of Eothenomys miletus during 49 days of cold exposure. Our data demonstrated that cold acclimation induced a remarkable decrease in body mass, a significant increase in energy intake and metabolic rate, and high expression of UCP1 in BAT of E. miletus. Biochemical characteristics of BAT and liver respiration were also increased following cold acclimation. These data suggest that E. miletus reduced the body mass and increased energy intake and expenditure under cold acclimation. Increased expression of UCP1 was potentially involved in the regulation of energy metabolism and thermogenic capacity following cold acclimation.