Long-term high-fat feeding induces greater fat storage in mice lacking UCP3

Uncoupling protein-3 (UCP3) is a mitochondrial inner-membrane protein highly expressed in skeletal muscle. While UCP3's function is still unknown, it has been hypothesized to act as a fatty acid (FA) anion exporter, protecting mitochondria against lipid peroxidation and/or facilitating FA oxidation. The aim of this study was to determine the effects of long-term feeding of a 45% fat diet on whole body indicators of muscle metabolism in congenic C57BL/6 mice that were either lacking UCP3 (Ucp3(-/-)) or had a transgenically induced approximately twofold increase in UCP3 levels (UCP3tg). Mice were fed the high-fat (HF) diet for a period of either 4 or 8 mo immediately following weaning. After long-term HF feeding, UCP3tg mice weighed an average of 15% less than wild-type mice (P < 0.05) and were 20% less metabolically efficient than both wild-type and Ucp3(-/-) mice (P < 0.01). Additionally, wild-type mice had 21% lower, whereas UCP3tg mice had 36% lower, levels of adiposity compared with Ucp3(-/-) mice (P < 0.05 and P < 0.001, respectively), indicating a protective effect of UCP3 against fat gain. No differences in whole body oxygen consumption were detected following long-term HF feeding. Glucose and insulin tolerance tests revealed that both the UCP3tg and Ucp3(-/-) mice were more glucose tolerant and insulin sensitive compared with wild-type mice after short-term HF feeding, but this protection was not maintained in the long term. Findings indicate that UCP3 is involved in protection from fat gain induced by long-term HF feeding, but not in protection from insulin resistance.     

Effects of the presence, absence, and overexpression of uncoupling protein-3 on adiposity and fuel metabolism in congenic mice

Uncoupling protein-3 (UCP3) is a poorly understood mitochondrial inner membrane protein expressed predominantly in skeletal muscle. The aim of this study was to examine the effects of the absence or constitutive physiological overexpression of UCP3 on whole body energy metabolism, glucose tolerance, and muscle triglyceride content. Congenic male UCP3 knockout mice (Ucp3-/-), wild-type, and transgenic UCP3 overexpressing (UCP3Tg) mice were fed a 10% fat diet for 4 or 8 mo after they were weaned. UCP3Tg mice had lower body weights and were less metabolically efficient than wild-type or Ucp3-/- mice, but they were not hyperphagic. UCP3Tg mice had smaller epididymal white adipose tissue and brown adipose tissue (BAT) depots; however, there were no differences in muscle weights. Glucose and insulin tolerance tests revealed that both UCP3Tg and Ucp3-/- mice were protected from development of impaired glucose tolerance and were more sensitive to insulin. 2-Deoxy-D-[1-3H]glucose tracer studies showed increased uptake of glucose into BAT and increased storage of liver glycogen in Ucp3-/- mice. Assessments of intramuscular triglyceride (IMTG) revealed decreases in quadriceps of UCP3Tg mice compared with wild-type and Ucp3-/- mice. When challenged with a 45% fat diet, Ucp3-/- mice showed increased accumulation of IMTG compared with wild-type mice, which in turn had greater IMTG than UCP3Tg mice. Results are consistent with a role for UCP3 in preventing accumulation of triglyceride in both adipose tissue and muscle.     

Inactivation of UCP1 and the glycerol phosphate cycle synergistically increases energy expenditure to resist diet-induced obesity

Our current paradigm for obesity assumes that reduced thermogenic capacity increases susceptibility to obesity, whereas enhanced thermogenic capacity protects against obesity. Here we report that elimination of two major thermogenic pathways encoded by the mitochondrial uncoupling protein (Ucp1) and mitochondrial glycerol-3-phosphate dehydrogenase (Gdm) result in mice with increased resistance to diet-induced obesity when housed at 28 degrees C, provided prior adaptation occurred at 20 degrees C. Obesity resistant Gdm(-/-).Ucp1(-/-) mice maintained at 28 degrees C have increased energy expenditure, in part through conversion of white to brown adipocytes in inguinal fat. Increased oxygen consumption in inguinal fat cell suspensions and the up-regulation of genes of mitochondrial function and fat metabolism indicated increased thermogenic activity, despite the absence of UCP1, whereas liver and skeletal muscle showed no changes in gene expression. Additionally, comparisons of energy expenditure in UCP1-deficient and wild type mice fed an obesogenic diet indicates that UCP1-based brown fat-based thermogenesis plays no role in so-called diet-induced thermogenesis. Accordingly, a new paradigm for obesity emerges in which the inactivation of major thermogenic pathways force the induction of alternative pathways that increase metabolic inefficiency.     

Npvf: Hypothalamic Biomarker of Ambient Temperature Independent of Nutritional Status

The mechanism by which mice, exposed to the cold, mobilize endogenous or exogenous fuel sources for heat production is unknown. To address this issue we carried out experiments using 3 models of obesity in mice: C57BL/6J+/+ (wild-type B6) mice with variable susceptibility to obesity in response to being fed a high-fat diet (HFD), B6. Ucp1-/- mice with variable diet-induced obesity (DIO) and a deficiency in brown fat thermogenesis and B6. Lep-/- with defects in thermogenesis, fat mobilization and hyperphagia. Mice were exposed to the cold and monitored for changes in food intake and body composition to determine their energy balance phenotype. Upon cold exposure wild-type B6 and Ucp1-/- mice with diet-induced obesity burned endogenous fat in direct proportion to their fat reserves and changes in food intake were inversely related to fat mass, whereas leptin-deficient and lean wild-type B6 mice fed a chow diet depended on increased food intake to fuel thermogenesis. Analysis of gene expression in the hypothalamus to uncover a central regulatory mechanism revealed suppression of the Npvf gene in a manner that depends on the reduced ambient temperature and degree of exposure to the cold, but not on adiposity, leptin levels, food intake or functional brown fat.     

Overexpression of constitutively active PKG-I protects female, but not male mice from diet-induced obesity

Cyclic guanosine monophosphate (cGMP)-dependent protein kinase I (PKG-I) is a multifunctional protein. The direct effects of PKG-I activation on energy homeostasis and obesity development are not well understood. Herein, we generated transgenic mice with expression of the constitutively active PKG-I in adipose tissue as well as in other tissues. Male and female PKG-I overexpressing mice were fed a low-fat (LF) or high-fat (HF) diet for 16 weeks. HF-fed female PKG-I transgenic mice had decreased body weight gain, lower percentage of body fat, and improved glucose tolerance compared to HF-fed wild-type (WT) controls. In contrast, male transgenic PKG-I mice were not resistant to the development of HF-diet-induced obesity, and exhibited similar levels of adiposity and glucose intolerance as HF-fed WT controls. Furthermore, we found that HF-fed female transgenic PKG-I mice had increased energy expenditure and cold-induced adaptive thermogenesis compared to HF-fed WT controls, which was associated with increased expression of uncoupling protein-1 (UCP1) in brown adipose tissue (BAT). In addition, the rates of lipolysis in white adipose tissue (WAT) were also increased in female transgenic PKG-I mice compared to WT controls due to increased phosphorylation of hormone-sensitive lipase (HSL). However, in male mice, adaptive thermogenesis or WAT lipolysis was similar between transgenic PKG-I mice and WT controls. Together, these data demonstrate sex differences in effects of PKG-I activation on the regulation of adipose tissue function and its contribution to diet induced obesity.     

Dietary modification dampens liver inflammation and fibrosis in obesity‐related fatty liver disease

Background: Alms1 mutant (foz/foz) mice develop hyperphagic obesity, diabetes, metabolic syndrome, and fatty liver (steatosis). High‐fat (HF) feeding converts pathology from bland steatosis to nonalcoholic steatohepatitis (NASH) with fibrosis, which leads to cirrhosis in humans. Objective: We sought to establish how dietary composition contributes to NASH pathogenesis. Design and Methods: foz/foz mice were fed HF diet or chow 24 weeks, or switched HF to chow after 12 weeks. Serum ALT, NAFLD activity score (NAS), fibrosis severity, neutrophil, macrophage and apoptosis immunohistochemistry, uncoupling protein (UCP)2, ATP, NF‐κB activation/expression of chemokines/adhesion molecules/fibrogenic pathways were determined. Result: HF intake upregulated liver fatty acid and cholesterol transporter, CD36. Dietary switch expanded adipose tissue and decreased hepatomegaly by lowering triglyceride, cholesterol ester, free cholesterol and diacylglyceride content of liver. There was no change in lipogenesis or fatty acid oxidation pathways; instead, CD36 was suppressed. These diet‐induced changes in hepatic lipids improved NAS, reduced neutrophil infiltration, normalized UCP2 and increased ATP; this facilitated apoptosis with a change in macrophage phenotype favoring M2 cells. Dietary switch also abrogated NF‐κB activation and chemokine/adhesion molecule expression, and arrested fibrosis by dampening stellate cell activation. Conclusion: Reversion to a physiological dietary composition after HF feeding in foz/foz mice alters body weight distribution but not obesity. This attenuates NASH severity and fibrotic progression by suppressing NF‐κB activation and reducing neutrophil and macrophage activation. However, adipose inflammation persists and is associated with continuing apoptosis in the residual fatty liver disease. Taken together, these findings indicate that other measures, such as weight reduction, may be required to fully reverse obesity‐related NASH.     

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.     

Differential regulation of leptin expression and function in A/J vs. C57BL/6J mice during diet-induced obesity

Obesity-resistant (A/J) and obesity-prone (C57BL/6J) mice were weaned onto low-fat (LF) or high-fat (HF) diets and studied after 2, 10, and 16 wk. Despite consuming the same amount of food, A/J mice on the HF diet deposited less carcass lipid and gained less weight than C57BL/6J mice over the course of the study. Leptin mRNA was increased in white adipose tissue (WAT) in both strains on the HF diet but to significantly higher levels in A/J compared with C57BL/6J mice. Uncoupling protein 1 (UCP1) and UCP2 mRNA were induced by the HF diet in brown adipose tissue (BAT) and WAT of A/J mice, respectively, but not in C57BL/6J mice. UCP1 mRNA was also significantly higher in retroperitoneal WAT of A/J compared with C57BL/6J mice. The ability of A/J mice to resist diet-induced obesity is associated with a strain-specific increase in leptin, UCP1, and UCP2 expression in adipose tissue. The findings indicate that the HF diet does not compromise leptin-dependent regulation of adipocyte gene expression in A/J mice and suggest that maintenance of leptin responsiveness confers resistance to diet-induced obesity.     

Uncoupling protein 1 expression and high-fat diets

Uncoupling protein 1 (Ucp1) is the key component of β-adrenergically controlled nonshivering thermogenesis in brown adipocytes. This process combusts stored and nutrient energy as heat. Cold exposure not only activates Ucp1-mediated thermogenesis to maintain normothermia but also results in adaptive thermogenesis, i.e., the recruitment of thermogenic capacity in brown adipose tissue. As a hallmark of adaptive thermogenesis, Ucp1 synthesis is increased proportionally to temperature and duration of exposure. Beyond this classical thermoregulatory function, it has been suggested that Ucp1-mediated thermogenesis can also be employed for metabolic thermogenesis to prevent the development of obesity. Accordingly, in times of excess caloric intake, one may expect a positive regulation of Ucp1. The general impression from an overview of the present literature is, indeed, an increased brown adipose tissue Ucp1 mRNA and protein content after feeding a high-fat diet (HFD) to mice and rats. The reported increases are very variable in magnitude, and the effect size seems to be independent of dietary fat content and duration of the feeding trial. In white adipose tissue depots Ucp1 mRNA is generally downregulated by HFD, indicating a decline in the number of interspersed brown adipocytes.     

Regulation of UCP1 and UCP3 in arctic ground squirrels and relation with mitochondrial proton leak.

Uncoupling protein (UCP) 1 (UCP1) catalyzes a proton leak in brown adipose tissue (BAT) mitochondria that results in nonshivering thermogenesis (NST), but the extent to which UCP homologs mediate NST in other tissues is controversial. To clarify the role of UCP3 in mediating NST in a hibernating species, we measured Ucp3 expression in skeletal muscle of arctic ground squirrels in one of three activity states (not hibernating, not hibernating and fasted for 48 h, or hibernating) and housed at 5 degrees C or -10 degrees C. We then compared Ucp3 mRNA levels in skeletal muscle with Ucp1 mRNA and UCP1 protein levels in BAT in the same animals. Ucp1 mRNA and UCP1 protein levels were increased on cold exposure and decreased with fasting, with the highest UCP1 levels in thermogenic hibernators. In contrast, Ucp3 mRNA levels were not affected by temperature but were increased 10-fold during fasting and >3-fold during hibernation. UCP3 protein levels were increased nearly fivefold in skeletal muscle mitochondria isolated from fasted squirrels compared with nonhibernators, but proton leak kinetics in the presence of BSA were unchanged. Proton leak in BAT mitochondria also did not differ between fed and fasted animals but did show classical inhibition by the purine nucleotide GDP. Levels of nonesterified fatty acids were highest during hibernation, and tissue temperatures during hibernation were related to Ucp1, but not Ucp3, expression. Taken together, these results do not support a role for UCP3 as a physiologically relevant mediator of NST in muscle.     

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.     

Quinoa extract enriched in 20-hydroxyecdysone protects mice from diet-induced obesity and modulates adipokines expression

Besides their well-known effect in the molting control in insects, ecdysteroids are steroid hormones that display potential pharmacologic and metabolic properties in mammals. The most common ecdysteroid, 20-hydroxyecdysone (20E) is found in many plants such as quinoa. The aim of the present study was to investigate the ability of quinoa extract (Q) enriched in 20E supplementation to prevent the onset of diet-induced obesity and to regulate the expression of adipocyte-specific genes in mice. Mice were fed a standard low-fat (LF) or a high-fat (HF) diet with or without supplementation by 20E-enriched Q or pure 20E for 3 weeks. Supplementation with Q reduced adipose tissue development in HF mice without modification of their body weight gain. This adipose tissue-specific effect was mainly associated with a reduced adipocyte size and a decrease in the expression of several genes involved in lipid storage, including lipoprotein lipase and phosphoenolpyruvate carboxykinase. Furthermore, Q-treated mice exhibited marked attenuation of mRNA levels of several inflammation markers (monocyte chemotactic protein-1, CD68) and insulin resistance (osteopontin, plasminogen activator inhibitor-1 (PAI-1)) as compared to HF mice. Q supplementation also reversed the effects of HF-induced downregulation of the uncoupling protein(s) (UCP(s)) mRNA levels in muscle. Similar results were obtained in mice fed a HF diet supplemented with similar amounts of pure 20E, suggesting that the latter accounted for most of the Q effects. Our study indicates that Q has an antiobesity activity in vivo and could be used as a nutritional supplement for the prevention and treatment of obesity and obesity-associated disorders.     

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.     

Sex‐Dependent Dietary Obesity,Induction of UCPs,and Leptin Expression in Rat Adipose Tissues

Objective: The aim of this study was to determine the sex‐dependent differences in the response of key parameters involved in thermogenesis and control of body weight in brown adipose tissue (BAT) and white adipose tissue (WAT) in postcafeteria‐fed rats, a model of dietary obesity. Research Methods and Procedures: BAT and WAT were obtained from male and female control and postcafeteria‐fed Wistar rats. Postcafeteria‐fed rats were initially fed with cafeteria diet from day 10 of life until day 110 (cafeteria period) and with standard chow diet from then until day 180 of life (postcafeteria period). Body mass and energy intake were evaluated. Biometric parameters were analyzed in interscapular BAT (IBAT). Levels of uncoupling protein 1 (UCP1), α₂‐adrenergic receptor (AR), and β₃‐AR proteins and UCP1, UCP2, UCP3, β₃‐AR, and leptin mRNAs, in IBAT or WAT, were studied by Western blot and Northern blot analyses, respectively. Results: Rats attained 59% (females) and 39% (males) increase in body weight at the end of the cafeteria period. During the postcafeteria period, the rats showed a loss of body weight, which was higher in females. Postcafeteria‐fed female rats also presented higher activation of thermogenic parameters in IBAT, including UCP1, UCP2, and UCP3 mRNAs. Female control rats showed lower levels of both α2 and β₃‐ARs in BAT compared with male rats, but these levels in postcafeteria‐fed female and male rats were the same, because males tended to down‐regulate them. Levels of leptin mRNA in response to the postcafeteria state depended on gender and the specific WAT depot studied. Discussion: It is suggested that in postcafeteria‐fed female rats, BAT thermogenic capacity becomes more efficiently activated than in males. Female rats also showed a bigger weight loss. The parallel regulation of the levels of UCP2 and UCP3 mRNAs, with respect to UCP1 mRNA, with higher activation in female postcafeteria‐fed rats, suggests a possible role of both UCP2 and UCP3 in the regulation of energy expenditure and in the control of body weight. The distinct responses to overweight of α2 and β₃‐ARs—which were sex dependent—and leptin mRNA—which depended on both sex and WAT depot—also support the different response of thermogenesis‐related parameters between overweight males and females.     

Lack of UCP1 stimulates fatty liver but mediates UCP1-independent action of beige fat to improve hyperlipidemia in Apoe knockout mice

Brown adipose tissue (BAT) plays a critical role in lipid metabolism and may protect from hyperlipidemia; however, its beneficial effect appears to depend on the ambient temperature of the environment. In this study, we investigated the effects of uncoupling protein 1 (UCP1) deficiency on lipid metabolism, including the pathophysiology of hyperlipidemia, in apolipoprotein E knockout (APOE-KO) mice at a normal (23 °C) and thermoneutral (30 °C) temperature. Unexpectedly, UCP1 deficiency caused improvements in hyperlipidemia, atherosclerosis, and glucose metabolism, regardless of an increase in hepatic lipid deposition, in Ucp1/Apoe double-knockout (DKO) mice fed a high-fat diet at 23 °C, with BAT hyperplasia and robust browning of inguinal white adipose tissue (IWAT) observed. Proteomics and gene expression analyses revealed significant increases in many proteins involved in energy metabolism and strong upregulation of brown/beige adipocyte-related genes and fatty acid metabolism-related genes in browned IWAT, suggesting an induction of beige fat formation and stimulation of lipid metabolism in DKO mice at 23 °C. Conversely, mRNA levels of fatty acid oxidation-related genes decreased in the liver of DKO mice. The favorable phenotypic changes were lost at 30 °C, with BAT whitening and disappearance of IWAT browning, while fatty liver further deteriorated in DKO mice compared with that in APOE-KO mice. Finally, longevity analysis revealed a significant lifespan extension of DKO mice compared with that of APOE-KO mice at 23 °C. Irrespective of the fundamental role of UCP1 thermogenesis, our results highlight the importance of beige fat for the improvement of hyperlipidemia and longevity under the atherogenic status at normal room temperature.     

Self‐Selected Macronutrient Diet Affects Energy and Glucose Metabolism in Brown Fat‐Ablated Mice

Objective: Obese transgenic UCP‐DTA mice have largely ablated brown adipose tissue and develop obesity and diabetes, which are highly susceptible to a high‐fat diet. We investigated macronutrient self‐selection and its effect on development of obesity, diabetes, and energy homeostasis in UCP‐DTA mice. Research Methods and Procedures: UCP‐DTA and wild‐type littermates were fed a semisynthetic macronutrient choice diet (CD) ad libitum from weaning until 17 weeks. Energy homeostasis was assessed by measurement of food intake, food digestibility, body composition, and energy expenditure. Diabetes was assessed by blood glucose measurements and insulin tolerance test. Results: Wild‐type and UCP‐DTA mice showed a high fat preference and increased energy digestion on CD compared with a low‐fat standard diet. On CD, wild‐type mice accumulated less body fat (16.9%) than UCP‐DTA (32.6%) mice, although they had a higher overall energy intake. Compared with wild‐type mice, resting metabolic rate was reduced in UCP‐DTA mice irrespective of diet. UCP‐DTA mice progressively decreased their carbohydrate intake, resulting in an almost complete avoidance of carbohydrate. UCP‐DTA mice developed severe insulin resistance but showed decreased fed and fasted blood glucose on CD. Discussion: In contrast to wild‐type mice, UCP‐DTA mice were not able to reduce their weight gain efficiency on CD. This suggests that, because of the high fat preference of the background strain and the increased metabolic efficiency, brown adipose tissue‐deficient mice still develop obesity and insulin resistance on a macronutrient CD even when decreasing overall energy intake. Through the avoidance of carbohydrates, however, they are able to maintain normoglycemia.     

Partial leptin deficiency favors diet-induced obesity and related metabolic disorders in mice

Partial leptin deficiency is not uncommon in the general population. We hypothesized that leptin insufficiency could favor obesity, nonalcoholic steatohepatitis (NASH), and other metabolic abnormalities, particularly under high calorie intake. Thus, mice partially deficient in leptin (ob/+) and their wild-type (+/+) littermates were fed for 4 mo with a standard-calorie (SC) or a high-calorie (HC) diet. Some ob/+ mice fed the HC diet were also treated weekly with leptin. Our results showed that, when fed the SC diet, ob/+ mice did not present significant metabolic abnormalities except for elevated levels of plasma adiponectin. Under high-fat feeding, increased body fat mass, hepatic steatosis, higher plasma total cholesterol, and glucose intolerance were observed in +/+ mice, and these abnormalities were further enhanced in ob/+ mice. Furthermore, some metabolic disturbances, such as blunted plasma levels of leptin and adiponectin, reduced UCP1 expression in brown adipose tissue, increased plasma liver enzymes, beta-hydroxybutyrate and triglycerides, and slight insulin resistance, were observed only in ob/+ mice fed the HC diet. Whereas de novo fatty acid synthesis in liver was decreased in +/+ mice fed the HC diet, it was disinhibited in ob/+ mice along with the restoration of the expression of several lipogenic genes. Enhanced expression of several genes involved in fatty acid oxidation was also observed only in ob/+ animals. Leptin supplementation alleviated most of the metabolic abnormalities observed in ob/+ fed the HC diet. Hence, leptin insufficiency could increase the risk of obesity, NASH, glucose intolerance, and hyperlipidemia in a context of calorie overconsumption.     

Dietary calcium attenuation of body fat gain during high-fat feeding in mice

Human epidemiological studies have supported the hypothesis that a dairy food-rich diet is associated with lower fat accumulation, although prospective studies and intervention trials are not so conclusive and contradictory data exist in animal models. The purpose of this study was to assess the effects on body weight and fat depots of dairy calcium (12 g/kg diet) in wild-type mice under ad libitum high-fat (43%) and normal-fat (12%) diets and to gain comprehension on the underlying mechanism of dairy calcium effects. Our results show that calcium intake decreases body weight and body fat depot gain under high-fat diet and accelerates weight loss under normal-fat diet, without differences in food intake. No differences in gene or protein expression of UCP1 in brown adipose tissue or UCP2 in white adipose tissue were found that could be related with calcium feeding, suggesting that calcium intake contributed to modulate body weight in wild-type mice by a mechanism that is not associated with activation of brown adipose tissue thermogenesis. UCP3 protein but not gene expression increased in muscle due to calcium feeding. In white adipose tissue there were effects of calcium intake decreasing the expression of proteins related to calcium signalling, in particular of stanniocalcin 2. CaSR levels could play a role in decreasing cytosolic calcium in adipocytes and, therefore, contribute to the diminution of fat accretion. Results support the anti-obesity effect of dietary calcium in male mice and indicate that, at least at the time-point studied, activation of thermogenesis is not involved.     

The role of uncoupling protein 1 in the metabolism and adiposity of RII beta-protein kinase A-deficient mice

Mice lacking the RII beta regulatory subunit of protein kinase A exhibit a 50% reduction in white adipose tissue stores compared with wild-type littermates and are resistant to diet-induced obesity. RII beta(-/-) mice also have an increase in resting oxygen consumption along with a 4-fold increase in the brown adipose-specific mitochondrial uncoupling protein 1 (UCP1). In this study, we examined the basis for UCP1 induction and tested the hypothesis that the induced levels of UCP1 in RII beta null mice are essential for the lean phenotype. The induction of UCP1 occurred at the protein but not the mRNA level and correlated with an increase in mitochondria in brown adipose tissue. Mice lacking both RII beta and UCP1 (RII beta(-/-)/Ucp1(-/-)) were created, and the key parameters of metabolism and body composition were studied. We discovered that RII beta(-/-) mice exhibit nocturnal hyperactivity in addition to the increased oxygen consumption at rest. Disruption of UCP1 in RII beta(-/-) mice reduced basal oxygen consumption but did not prevent the nocturnal hyperactivity. The double knockout animals also retained the lean phenotype of the RII beta null mice, demonstrating that induction of UCP1 and increased resting oxygen consumption is not the cause of leanness in the RII beta mutant mice.