Intracerebroventricular administration of urotensin II regulates food intake and sympathetic nerve activity in brown adipose tissue

To clarify the functional roles of urotensin II in regulating energy balance, we investigated the effects of a central infusion of urotensin II on food intake, uncoupling protein (UCP) 1 mRNA expression, temperature, and sympathetic nervous system activity in brown adipose tissue (BAT), a site that regulates energy expenditure in rodents. A bolus central infusion of urotensin II at a dose of 1 nmol/rat into the third cerebral ventricle decreased food intake (p<0.05). Additionally, urotensin II induced c-Fos-like-immunoreactivity (c-FLI) in the paraventricular nucleus (PVN) as compared with that in the control (phosphate buffered saline [PBS]-treated) group. Furthermore, urotensin II increased BAT UCP 1 mRNA expression (p<0.05). Finally, central infusion of urotensin II significantly increased BAT sympathetic nerve activity, which was accompanied by a significant elevation in BAT temperature (p<0.05) in rats. Taken together, central infusion of urotensin II regulates food intake and BAT sympathetic nerve activity in rats.     

Leptin selectively reduces white adipose tissue in mice via a UCP1-dependent mechanism in brown adipose tissue

We tested the hypothesis that leptin, in addition to reducing body fat by restraining food intake, reduces body fat through a peripheral mechanism requiring uncoupling protein 1 (UCP1). Leptin was administered to wild-type (WT) mice and mice with a targeted disruption of the UCP1 gene (UCP1 deficient), while vehicle-injected control animals of each genotype were pair-fed to each leptin-treated group. Leptin reduced the size of white adipose tissue (WAT) depots in WT mice but not in UCP1-deficient animals. This was accompanied by a threefold increase in the amount of UCP1 protein and mRNA in the brown adipose tissue (BAT) of WT mice. Leptin also increased UCP2 mRNA in WAT of both WT and UCP1-deficient mice but increased UCP2 and UCP3 mRNA only in BAT from UCP1-deficient mice. These results indicate that leptin reduces WAT through a peripheral mechanism requiring the presence of UCP1, with little or no involvement of UCP2 or UCP3.     

Ghrelin affects gastrectomy-induced decrease in UCP1 and beta3-AR mRNA expression in mice

In this study we investigated the effects of gastrectomy (Gx) and of the gastric hormone, ghrelin, on the expression of proteins in brown adipose tissue (BAT) that are thought to be involved in thermogenesis. Heat production in BAT is known to depend upon activation and increased expression of beta3-adrenergic receptors (beta3-AR) and the consequent up-regulation of uncoupling protein 1 (UCP1). Mice were subjected to Gx or sham operation. One week later they started to receive daily subcutaneous injections of either saline or ghrelin (12 nmol) for two or eight weeks. Neither Gx nor ghrelin affected daily food intake. Gx did not lower body weight gain (except during the first post-operative week) but Gx mice responded to eight weeks of ghrelin treatment with a greater body weight increase (37%, p<0.05) than saline-injected Gx mice; sham-operated mice did not respond to ghrelin. Gx resulted in a greatly reduced expression of both UCP1 and beta3-AR mRNA in BAT (50% reduction or more, p<0.01) compared to sham-operated mice. Eight weeks of ghrelin treatment raised the UCP1 as well as the beta3-AR mRNA expression in the Gx mice, whereas two weeks of ghrelin treatment decreased UCP1 and beta3-AR mRNA expression compared to Gx mice receiving saline. In fact, mRNA expression in Gx mice after treatment with ghrelin for eight weeks was similar to that in saline-treated sham-operated mice. Ghrelin did not affect UCP1 and beta3-AR mRNA in sham-operated mice neither two nor eight weeks after the operation. The results suggest 1) that signals from the stomach stimulate BAT UCP1 (and possibly thermogenesis) and 2) that ghrelin may contribute to the control of UCP1 expression.     

Effects of growth hormone (GH) on mRNA levels of uncoupling proteins 1, 2, and 3 in brown and white adipose tissues and skeletal muscle in obese mice.

We have investigated whether GH treatment influences the expression of UCP1, 2 and 3 mRNA in a KK-Ay obese mouse model. KK-Ay mice (n = 10) and C57Bl/6J control mice (n = 10) were injected subcutaneously with human GH (1.0 mg/kg/day and 3.5 mg/kg/day) for 10 days, and compared with mice injected with physical saline. The KK-Ay obese mice weighed significantly less (p < 0.01 : 1.0 mg/kg/day, p < 0.05 : 3.5 mg/kg/day) and had smaller inguinal subcutaneous and perimetric white adipose tissue (WAT) pads (p < 0.05 : 3.5 mg/kg/day), but increased skeletal muscle weight (p < 0.05). The brown adipose tissue (BAT) weight did not change significantly. Not only plasma free fatty acid and glucose levels but also plasma insulin levels decreased. The reduced HOMA-IR (homeostasis model assessment-insulin resistance) values suggested that insulin resistance was improved by GH treatment. UCP1 mRNA levels increased after the 3.5 mg GH treatment by 2.8-fold (p < 0.01 vs. saline controls) and 2.0-fold (p < 0.05 vs. 1 mg GH treatment) in BAT, and by 6.0-fold in subcutaneous WAT (p < 0.05 vs. controls). UCP2 mRNA levels increased 2.2-fold (p < 0.05 vs. control) and 2.1-fold (p < 0.05 vs. 1 mg GH treatment) in BAT, and 2.0-fold (p < 0.05 vs. controls) in skeletal muscle. One mg GH administration also stimulated UCP1 mRNA expression by 2.5-fold (p < 0.05 vs. controls) and UCP3 mRNA expression by 2.8-fold (p < 0.05 vs. controls) in the muscle. On the other hand, lean mice showed no significant difference in body composition or plasma parameters. UCP1, 2 and 3 mRNA expression in lean mice did not show any significant change after treatment with GH. We conclude that GH treatment increased mRNA levels for not only UCP1, but also UCP 2 and 3 in BAT, WAT and muscle in a KK-Ay obese mouse model. These findings suggest that GH-induced thermogenesis may contribute to the reduction in WAT and energy expenditure.     

Dietary vitamin A supplementation in rats: suppression of leptin and induction of UCP1 mRNA

All-trans-retinoic acid (RA), an active metabolite of vitamin A, induces the gene expression of uncoupling protein 1 (UCP1) in brown adipose tissue (BAT) and suppresses leptin gene expression in white adipose tissue (WAT) when given as an acute dose. These contrasting effects of RA leave in doubt the overall effect of chronic RA or vitamin A supplementation on energy homeostasis. To investigate the effects of dietary vitamin A supplementation on leptin and UCP1 gene expression, rats were fed either a normal diet (2.6 retinol/kg diet) or a vitamin A-supplemented diet (129 mg retinol/kg diet) for 8 weeks, and adiposity, serum leptin levels, leptin mRNA levels in perirenal WAT, UCP1 and UCP2 mRNA levels in BAT, and beta3-adrenergic receptor mRNA levels in BAT and WAT were examined. Rats on both diets gained a similar amount of weight, but there was a small 9% decrease in the adiposity index in the vitamin A-supplemented rats. Dietary vitamin A supplementation increased UCP1 gene expression in BAT by 31%, but suppressed leptin gene expression by 44% and serum leptin levels by 65%. UCP2 and beta3-adrenergic receptor gene expression in BAT and perirenal WAT were unchanged by the vitamin A diet. These data suggest that dietary vitamin A has a role in regulating energy homeostasis by enhancing UCP1 gene expression and decreasing serum leptin levels.     

Regulation of UCP1, UCP2, and UCP3 mRNA expression in brown adipose tissue, white adipose tissue, and skeletal muscle in rats by estrogen

The effects of ovariectomy (OVX) and estrogen substitution on body weight, body composition, food intake, weight gain, and expression of uncoupling proteins (UCPs) in brown adipose tissue (BAT), white adipose tissue (WAT), and skeletal muscle were studied in four groups of rats: (1) Sham-operated rats (N = 8), (2) ovariectomized rats (OVX - E) (N = 8), (3) estrogen-treated OVX rats (OVX + E) (N = 8), and (4) OVX rats on energy restriction (OVX - E + D) (N = 8). OVX was associated with an increase in food intake and body weight gain during a 5-week study period compared to sham-operated rats. The estrogen-substituted rats had a significantly lower food intake and weight gain during the 5 weeks compared to the sham-operated group. However, we also included a nontreated OVX group that was allowed to eat only enough chow to match the weight gain of the sham-operated group. To match the weight gain in the two groups, the OVX group had to consume 16% less chow than the sham-operated group. In BAT, the UCP1 expression was significantly lower in estrogen-deficient rats compared to either intact rats or estrogen-substituted rats, whereas UCP2 and UCP3 mRNA expression was similar in BAT from all four groups. In WAT, both estrogen-deficient groups had significantly lower UCP2 mRNA expression compared to the control rats and estrogen-treated rats; In contrast, the UCP3 mRNA expression in WAT was similar in all four groups. Finally, in skeletal muscle the OVX group on mild energy restriction had reduced UCP3 mRNA expression compared to control, OVX, and estrogen-treated rats. In contrast, the UCP2 mRNA expression in skeletal muscle was similar in all four groups. Thus, the findings that estrogen deficiency is followed by reduced UCP1 expression in BAT and reduced UCP2 expression in WAT in association with weight gain probably caused by a decrease in energy expenditure might indicate that UCPs play a role for the estrogen-mediated changes in body weight and energy expenditure.     

Chronic dietary vitamin A supplementation regulates obesity in an obese mutant WNIN/Ob rat model

Objective: To understand the possible role of chronic dietary high vitamin A supplementation in body weight regulation and obesity using a novel WNIN/Ob obese rat model developed at the National Centre for Laboratory Animal Sciences of National Institute of Nutrition, India. Research Methods and Procedures: Thirty‐six 7‐month‐old male rats of lean, carrier, and obese phenotypes were broadly divided into two groups; each group was subdivided into three subgroups consisting of six lean, six carrier, and six obese rats and received diets containing either 2.6 or 129 mg vitamin A/kg of diet for 2 months. Body weight gain, food intake, and weights of various organs were recorded. Adiposity index and BMI were calculated. Serum and liver retinol and brown adipose tissue (BAT)‐uncoupling protein1 (UCP1) mRNA expression levels were quantified. Results: Chronic feeding of high but non‐toxic doses of vitamin A through diet significantly reduced (P ≤ 0.05) body weight gain, adiposity index, and retroperitoneal white adipose tissue mass (without affecting food intake) in obese rats compared with their lean and carrier counterparts. In general, vitamin A treatment significantly improved hepatic retinol stores (P ≤ 0.05) in all phenotypes without affecting serum free retinol levels. However, augmented BAT‐UCP1 expression was observed only in carrier and obese rats (whose basal expression was low). Discussion: Our data suggest that chronic dietary vitamin A supplementation at high doses effectively regulates obesity in obese phenotype of the WNIN/Ob strain, possibly through up‐regulation of the BAT‐UCP1 gene and associated adipose tissue loss. However, in vitamin A‐supplemented lean and carrier rats, changes in adiposity could not be related to BAT‐UCP1 expression levels.     

Acute central infusion of leptin modulates fatty acid mobilization by affecting lipolysis and mRNA expression for uncoupling proteins

Chronic administration of leptin has been shown to reduce adiposity through energy intake and expenditure. The present study aims to examine how acute central infusion of leptin regulates peripheral lipid metabolism, as assessed by markers indicative of their mobilization and utilization. A bolus infusion of 1 microg/rat leptin into the third cerebroventricle increased the expression of mRNA for hormone-sensitive lipase (HSL), an indicator of lipolysis, in white adipose tissue (WAT). This was accompanied by elevation of plasma levels of glycerol, but not of free fatty acids, as compared to the saline control (P < 0.03). The same treatment with leptin decreased plasma insulin levels but did not affect the plasma glucose level (P < 0.05 for insulin). Among the major regulators of the transportation or utilization of energy substrates, leptin treatment increased expression of mRNA for uncoupling protein 1 (UCP1) in brown adipose tissue (BAT), UCP2 in WAT, and UCP3 in quadriceps skeletal muscle, but not those for fatty acid-binding protein in WAT, carnitine phosphate transferase-1, a marker for beta oxidation of fatty acids in muscle, nor glucose transporter 4 in WAT and muscle (P < 0.01 for HSL, P < 0.05 for UCP1, and P < 0.005 for UCP2 and UCP3). These results indicate that, even in a single bolus, leptin may regulate the mobilization and/or utilization of energy substrates such as fatty acids by affecting lipolytic activity in WAT and by increasing the expression of UCPs in BAT, WAT, and muscle.     

Tea catechins enhance the mRNA expression of uncoupling protein 1 in rat brown adipose tissue

The aim of the present study was to determine whether the antiobesity effects of tea catechins (TCs) are associated with the expression of uncoupling protein 1 (UCP1) in brown adipose tissue (BAT). Male Sprague–Dawley rats were fed a high-fat (HF; 35% fat) diet for 5 weeks, then divided into four groups and fed an HF, HF with 0.5% TC (HFTC), normal-fat (NF; 5% fat) or NF with 0.5% TC (NFTC) diet for 8 weeks. At the end of the experimental period, perirenal and epididymal white adipose tissues (WATs) and interscapular BAT were isolated. The NFTC group had significantly lower perirenal WAT weights than the NF group (NF: 12.7±0.53 g; NFTC: 10.2±0.43 g; P<.01), but the HF and HFTC groups did not differ significantly. TC intake had no effects on epididymal WAT weights. The NFTC and HFTC groups had significantly lower BAT weights than the NF and HF groups, respectively. The NFTC group had significantly higher UCP1 mRNA levels in BAT than the NF group (NF: 0.35±0.02; NFTC: 0.60±0.11; P<.05), but the HF and HFTC groups did not differ significantly. Thus, TC intake in the context of the NF diet reduced perirenal WAT weight and up-regulated UCP1 mRNA expression in BAT. These results suggest that the suppressive effect of TC on body fat accumulation is associated with UCP1 expression in BAT.     

Fucoxanthin from edible seaweed, Undaria pinnatifida, shows antiobesity effect through UCP1 expression in white adipose tissues

Mitochondrial uncoupling protein 1 (UCP1) is usually expressed only in brown adipose tissue (BAT) and a key molecule for metabolic thermogenesis to avoid an excess of fat accumulation. However, there is little BAT in adult humans. Therefore, UCP1 expression in tissues other than BAT is expected to reduce abdominal fat. Here, we show reduction of abdominal white adipose tissue (WAT) weights in rats and mice by feeding lipids from edible seaweed, Undaria pinnatifida. Clear signals of UCP1 protein and mRNA were detected in WAT of mice fed the Undaria lipids, although there is little expression of UCP1 in WAT of mice fed control diet. The Undaria lipids mainly consisted of glycolipids and seaweed carotenoid, fucoxanthin. In the fucoxanthin-fed mice, WAT weight significantly decreased and UCP1 was clearly expressed in the WAT, while there was no difference in WAT weight and little expression of UCP1 in the glycolipids-fed mice. This result indicates that fucoxanthin upregulates the expression of UCP1 in WAT, which may contribute to reducing WAT weight.     

Upregulation of uncoupling protein 2 mRNA in genetic obesity: lack of an essential role for leptin, hyperphagia, increased tissue lipid content, and TNF-alpha

Uncoupling protein 2 (UCP2) has been proposed to play a prominent role in the regulation of energy balance. UCP2 mRNA expression is upregulated in white adipose tissue (WAT) and liver, but is not altered in skeletal muscle in genetically obese ob/ob mice. The mechanisms involved in the upregulation of UCP2 in obesity have not been investigated. We have now examined the potential role of leptin, hyperphagia, increased tissue lipid content, and overexpression of tumor necrosis factor (TNF)-alpha in the upregulation of UCP2 mRNA expression in the liver and WAT in ob/ob mice. Treatment of ob/ob mice with leptin for 3 days significantly reduced their food intake but had no effect on the upregulation of UCP2 mRNA levels in the liver or WAT. To investigate the effect of feeding and higher tissue lipid content on the upregulation of UCP2 in liver and WAT, we compared UCP2 mRNA levels in ad-libitum fed and 72-h fasted control and ob/ob mice. In controls, fasting had no effect on UCP2 mRNA levels in liver, but increased UCP2 mRNA in WAT suggesting that the effects of fasting on UCP2 mRNA levels are tissue-specific. In ob/ob mice, fasting did not lower UCP2 mRNA levels in liver or WAT suggesting that the upregulation of UCP2 in ob/ob mice is not merely a direct consequence of increased food intake. 72-h fasting lowered hepatic total lipid content by 34% and 36% in control and ob/ob mice, respectively, without any corresponding decrease in hepatic UCP2 mRNA levels, suggesting that the enhanced UCP2 expression in the liver of ob/ob mice is not secondary to lipid accumulation in their livers. Although TNF-alpha has been shown to acutely increase UCP2 mRNA levels in liver and WAT, and is overexpressed in adipose tissue in obesity, deletion of the genes for both TNF receptors in ob/ob mice produces a further increase in UCP2 mRNA expression in liver and adipose tissue indicating a paradoxical inhibitory role. Taken together, these results suggest that the upregulation of UCP2 mRNA levels in the liver and WAT of ob/ob mice is not due to the lack of leptin, hyperphagia, increased tissue lipid content, or over-expression of TNF-alpha.     

Individual severity of dietary obesity in unselected Wistar rats: relationship with hyperphagia

We investigated the relative importance of overeating, thermogenesis, and uncoupling protein (UCP) expression in determining the severity of obesity in male Wistar rats fed a highly palatable diet. After 2 wk of feeding, body weight did not differ significantly from controls (248 +/- 4 vs. 229 +/- 3 g; P > 0.3), but rectal temperature, brown adipose tissue (BAT) mass, UCP3 expression in gastrocnemius muscle, and UCP2 expression in white adipose tissue (WAT) were all elevated in diet-fed animals. In a further study, rats fed a palatable diet for 8 wk exhibited higher energy intake and rectal temperature than controls. Dietary-obese rats were divided into high (427-490 g; n = 8) and low (313-410 g; n = 10) weight gainers. The high gainers ate significantly more than the low gainers, and energy intake was positively correlated with weight gain (r(2) = 0.72, P < 0.01). UCP2 and UCP3 mRNA levels in gastrocnemius muscle were significantly increased above lean controls in all diet-fed animals, whereas UCPs in WAT and BAT did not differ significantly from controls. Whereas rats fed palatable food exhibited a thermogenic response, there was no significant difference in core temperature between high and low gain groups (37. 5 +/- 0.1 vs. 37.6 +/- 0.1 degrees C; P > 0.5). We conclude that a higher energy intake is the critical factor determining susceptibility to dietary obesity in unselected Wistar rats.     

Systemic administration of epidermal growth factor increases UCP3 mRNA levels in skeletal muscle and adipose tissue in rats

We have previously reported that systemic epidermal growth factor (EGF) treatment in rats reduces the amount of adipose tissue despite an unaltered food intake. The mitochondrial uncoupling proteins (UCP2 and UCP3) are thought to uncouple the respiratory chain and thus to increase energy expenditure. In order to find out whether the UCP system was involved in the EGF-induced weight loss, the effects of EGF on UCP2 and UCP3 in adipose tissue and skeletal muscle were investigated in the present study. Eight rats were treated with placebo or EGF (150 microg/kg/day) for seven days via mini-osmotic pumps. The EGF-treated rats gained significantly less body weight during the study period than the placebo-treated animals and had significantly less adipose tissue despite a similar food intake. The placebo group and the EGF group had similar UCP2 mRNA expression (in both adipose tissue and skeletal muscle), whereas the EGF-treated group compared to the placebo group had significantly higher UCP3 mRNA expression in both skeletal muscle (3.76 +/- 0.90 vs 8.41 +/- 0.87, P < 0.05) and in adipose tissue (6.38 +/- 0.71 vs 12.48 +/- 1.79, P < 0.05). In vitro studies with adipose tissue fragments indicated that the EGF effect probably is mediated indirectly as incubations with EGF (10 microM) were unable to affect adipose tissue UCP expression, whereas incubations with bromopalmitate stimulated both UCP2 and UCP3 mRNA expression twofold. Thus, EGF treatment in vivo was found to enhance UCP3 mRNA expression in both adipose tissue and skeletal muscle, which may indicate that the EGF effect on body composition might involve up-regulation of UCP3 in skeletal muscle and adipose tissue.     

Up-regulation of liver uncoupling protein-2 mRNA by either fish oil feeding or fibrate administration in mice

Fish oil feeding showed less obesity in rodents, relative to other dietary oils. N-3 fatty acids rich in fish oil and fibrate compounds are peroxisome proliferator-activated receptor alpha (PPARalpha) ligands that stimulate beta-oxidation of fatty acids in liver and are used for treatment of hypertriglycemic patients. Since UCP-2, a member of an uncoupling protein family, has been shown to express in hepatocytes, the effects of these agents on the expression of UCP2 mRNA were investigated. C57BL/6J mice were divided into three groups; the first group was given a high-carbohydrate diet, and the other two groups were given a high-fat diet (60% of total energy) as safflower oil or fish oil for 5 months. Safflower oil diet fed mice developed obesity, but those fed fish oil diet did not. Therefore, the effects of fish oil feeding on the expression of UCP1, UCP2 and UCP3 in liver, skeletal muscle (gastrocnemius), white adipose tissue (WAT) and brown adipose tissue (BAT) were assessed by Northern blotting. Compared with safflower oil feeding, fish oil feeding up-regulated liver UCP2, BAT UCP2 and skeletal muscle UCP3 mRNA, while down-regulated WAT UCP2 and BAT UCP3 mRNA. Among these alterations, 5-fold up-regulation of liver UCP2 mRNA, relative to carbohydrate feeding, was noteworthy. Fenofibrate administration (about 500 mg/kg BW/d) for 2 wks also induced liver UCP2 expression by 9-fold. These data indicated that fish oil feeding and fibrate administration each up-regulated UCP2 mRNA expression in liver possibly via PPARalpha and hence each has the potential of increasing energy expenditure for prevention of obesity.     

Peroxisome proliferator-activated receptors as regulators of lipid metabolism; tissue differential expression in adipose tissues during cold acclimatization and hibernation of jerboa (Jaculus orientalis)

Brown (BAT) and white (WAT) adipose tissues play a key role in the body energy balance orchestrated by the central nervous system. Hibernators have developed a seasonal obesity to respond to inhospitable environment. Jerboa is one of the deep hibernator originated from sub-desert highlands. Thus, this animal represents an excellent model to study cold adaptation mechanism. We report that the adipogenic factor PPARgamma exhibits a differential expression between BAT and WAT at mRNA level. A specific induction was only seen in WAT of pre-hibernating jerboa. Interestingly, PPAR beta/delta is specifically induced in BAT and brain of pre-hibernating jerboa, highlighting for the first time the possible key role of this ubiquitous isoform in the cold adaptation of this true hibernator. Inductions of PPARgamma(2) in WAT and PPAR beta/delta in BAT are blunted by a hypolipemic drug, the ciprofibrate. These changes may be correlated with hibernation arrest and death of treated jerboa. Mitochondrial acyl-CoA dehydrogenase and peroxisomal acyl-CoA oxidase activities in brown and white adipose tissues are decreased up to 85% during cold acclimatization (without food privation). These enzyme activities are subject to a strong induction in BAT and in WAT (3.4-7.5 fold) during the hibernation period. The BAT thermogenesis marker is also largely induced (approximately 4 fold of UCP1 mRNA level) during pre-hibernation period. Unexpectedly, treatment with ciprofibrate deeply affects lipolysis in BAT by increasing acyl-CoA dehydrogenase activity (3.4 fold) and acyl-CoA oxidase at both activity and mRNA levels (2.8 and 3.8 fold, respectively) and enhances strongly UCP1 mRNA level (9.5 fold) during pre-hibernation.     

Conjugated linoleic acid reduces adiposity and increases markers of browning and inflammation in white adipose tissue of mice

The objective of this study was to examine the mechanism by which conjugated linoleic acid (CLA) reduces body fat. Young male mice were fed three combinations of fatty acids at three doses (0.06%, 0.2%, and 0.6%, w/w) incorporated into AIN76 diets for 7 weeks. The types of fatty acids were linoleic acid (control), an equal mixture of trans-10, cis-12 (10,12) CLA plus linoleic acid, and an equal isomer mixture of 10,12 plus cis-9, trans-11 (9,11) CLA. Mice receiving the 0.2% and 0.6% dose of 10,12 CLA plus linoleic acid or the CLA isomer mixture had decreased white adipose tissue (WAT) and brown adipose tissue (BAT) mass and increased incorporation of CLA isomers in epididymal WAT and liver. Notably, in mice receiving 0.2% of both CLA treatments, the mRNA levels of genes associated with browning, including uncoupling protein 1 (UCP1), UCP1 protein levels, and cytochrome c oxidase activity, were increased in epididymal WAT. CLA-induced browning in WAT was accompanied by increases in mRNA levels of markers of inflammation. Muscle cytochrome c oxidase activity and BAT UCP1 protein levels were not affected by CLA treatment. These data suggest a linkage between decreased adiposity, browning in WAT, and low-grade inflammation due to consumption of 10,12 CLA.     

Role of adipogenic and thermogenic genes in susceptibility or resistance to develop diet-induced obesity in rats

The aim of the present work was to assess whether changes in adipose tissue gene expression related with adipogenesis and/or thermogenesis could be involved in the mechanism conferring susceptibility or resistance to develop obesity in high-fat fed outbreed rats. For this purpose, male Wistar rats were fed with standard laboratory diet (control group) or high fat diet. After 15 days, two groups of rats with significant differences on body weight gain in response to the high fat diet were characterized and identified as diet-induced obesity (DIO) and diet resistant (DR) rats. A significant increase in visceral white adipose tissue (WAT) PPARgamma and aP2 (p < 0.05) mRNA levels associated to a decrease in RARgamma expression (p < 0.05) was observed in DIO rats, suggesting an increase of adipogenesis. Furthermore, our data showed a marked increase in brown adipose tissue (BAT) of UCP1 mRNA in DIO animals (p < 0.01) (without affecting PGC-1alpha gene expression), whereas no changes were found in WAT UCP2 gene expression. All these data suggest that the variations found in the expression pattern of PPARgamma, aP2 and RARgamma by high-fat diet could be involved, at least in part, in the differences in body weight gain and adiposity observed between DR and DIO animals. The compensatory adaptations through the increase in energy expenditure by changes on the expression levels of UCP1 seem not to be enough to avoid the obesity onset in the DIO group.     

Ablation of ghrelin receptor reduces adiposity and improves insulin sensitivity during aging by regulating fat metabolism in white and brown adipose tissues

Aging is associated with increased adiposity in white adipose tissues and impaired thermogenesis in brown adipose tissues; both contribute to increased incidences of obesity and type 2 diabetes. Ghrelin is the only known circulating orexigenic hormone that promotes adiposity. In this study, we show that ablation of the ghrelin receptor (growth hormone secretagogue receptor, GHS-R) improves insulin sensitivity during aging. Compared to wild-type (WT) mice, old Ghsr(-/-) mice have reduced fat and preserve a healthier lipid profile. Old Ghsr(-/-) mice also exhibit elevated energy expenditure and resting metabolic rate, yet have similar food intake and locomotor activity. While GHS-R expression in white and brown adipose tissues was below the detectable level in the young mice, GHS-R expression was readily detectable in visceral white fat and interscapular brown fat of the old mice. Gene expression profiles reveal that Ghsr ablation reduced glucose/lipid uptake and lipogenesis in white adipose tissues but increased thermogenic capacity in brown adipose tissues. Ghsr ablation prevents age-associated decline in thermogenic gene expression of uncoupling protein 1 (UCP1). Cell culture studies in brown adipocytes further demonstrate that ghrelin suppresses the expression of adipogenic and thermogenic genes, while GHS-R antagonist abolishes ghrelin's effects and increases UCP1 expression. Hence, GHS-R plays an important role in thermogenic impairment during aging. Ghsr ablation improves aging-associated obesity and insulin resistance by reducing adiposity and increasing thermogenesis. Growth hormone secretagogue receptor antagonists may be a new means of combating obesity by shifting the energy balance from obesogenesis to thermogenesis.     

White adipose tissue contributes to UCP1-independent thermogenesis

Beta3-adrenergic receptors (AR) are nearly exclusively expressed in brown and white adipose tissues, and chronic activation of these receptors by selective agonists has profound anti-diabetes and anti-obesity effects. This study examined metabolic responses to acute and chronic beta3-AR activation in wild-type C57Bl/6 mice and congenic mice lacking functional uncoupling protein (UCP)1, the molecular effector of brown adipose tissue (BAT) thermogenesis. Acute activation of beta3-AR doubled metabolic rate in wild-type mice and sharply elevated body temperature and BAT blood flow, as determined by laser Doppler flowmetry. In contrast, beta3-AR activation did not increase BAT blood flow in mice lacking UCP1 (UCP1 KO). Nonetheless, beta3-AR activation significantly increased metabolic rate and body temperature in UCP1 KO mice, demonstrating the presence of UCP1-independent thermogenesis. Daily treatment with the beta3-AR agonist CL-316243 (CL) for 6 days increased basal and CL-induced thermogenesis compared with naive mice. This expansion of basal and CL-induced metabolic rate did not require UCP1 expression. Chronic CL treatment of UCP1 KO mice increased basal and CL-stimulated metabolic rate of epididymal white adipose tissue (EWAT) fourfold but did not alter BAT thermogenesis. After chronic CL treatment, CL-stimulated thermogenesis of EWAT equaled that of interscapular BAT per tissue mass. The elevation of EWAT metabolism was accompanied by mitochondrial biogenesis and the induction of genes involved in lipid oxidation. These observations indicate that chronic beta3-AR activation induces metabolic adaptation in WAT that contributes to beta3-AR-mediated thermogenesis. This adaptation involves lipid oxidation in situ and does not require UCP1 expression.     

Characterization of MCH-mediated obesity in mice

Melanin-concentrating hormone (MCH) is a cyclic orexigenic peptide expressed in the lateral hypothalamus. Recently, we demonstrated that chronic intracerebroventricular infusion of MCH induced obesity accompanied by sustained hyperphagia in mice. Here, we analyzed the mechanism of MCH-induced obesity by comparing animals fed ad libitum with pair-fed and control animals. Chronic infusion of MCH significantly increased food intake, body weight, white adipose tissue (WAT) mass, and liver mass in ad libitum-fed mice on a moderately high-fat diet. In addition, a significant increase in lipogenic activity was observed in the WAT of the ad libitum-fed group. Although body weight gain was marginal in the pair-fed group, MCH infusion clearly enhanced the lipogenic activity in liver and WAT. Plasma leptin levels were also increased in the pair-fed group. Furthermore, MCH infusion significantly reduced rectal temperatures in the pair-fed group. In support of these findings, mRNA expression of uncoupling protein-1, acyl-CoA oxidase, and carnitine palmitoyltransferase I, which are key molecules involved in thermogenesis and fatty acid oxidation, were reduced in the brown adipose tissue (BAT) of the pair-fed group, suggesting that MCH infusion might reduce BAT functions. We conclude that the activation of MCH neuronal pathways stimulated adiposity, in part resulting from increased lipogenesis in liver and WAT and reduced energy expenditure in BAT. These findings confirm that modulation of energy homeostasis by MCH may play a critical role in the development of obesity.