Nutrient preference and diet-induced adiposity in C57BL/6ByJ and 129P3/J mice

Light: An Extrinsic Factor Influencing Animal-based Research

Light is an environmental factor that is extrinsic to animals themselves and that exerts a profound influence on the regulation of circadian, neurohormonal, metabolic, and neurobehavioral systems of all animals, including research animals. These widespread biologic effects of light are mediated by distinct photoreceptors-rods and cones that comprise the conventional visual system and melanopsin-containing intrinsically photosensitive retinal ganglion cells (ipRGCs) of the nonvisual system that interact with the rods and cones. The rods and cones of the visual system, along with the ipRGCs of the nonvisual system, are species distinct in terms of opsins and opsin concentrations and interact with one another to provide vision and regulate circadian rhythms of neurohormonal and neurobehavioral responses to light. Here, we review a brief history of lighting technologies, the nature of light and circadian rhythms, our present understanding of mammalian photoreception, and current industry practices and standards. We also consider the implications of light for vivarium measurement, production, and technological application and provide simple recommendations on artificial lighting for use by regulatory authorities, lighting manufacturers, designers, engineers, researchers, and research animal care staff that ensure best practices for optimizing animal health and well-being and, ultimately, improving scientific outcomes.

Intermuscular adipose tissue in obesity and related disorders: cellular origins, biological characteristics and regulatory mechanisms

Intermuscular adipose tissue (IMAT) is a unique adipose depot interspersed between muscle fibers (myofibers) or muscle groups. Numerous studies have shown that IMAT is strongly associated with insulin resistance and muscular dysfunction in people with metabolic disease, such as obesity and type 2 diabetes. Moreover, IMAT aggravates obesity-related muscle metabolism disorders via secretory factors. Interestingly, researchers have discovered that intermuscular brown adipocytes in rodent models provide new hope for obesity treatment by acting on energy dissipation, which inspired researchers to explore the underlying regulation of IMAT formation. However, the molecular and cellular properties and regulatory processes of IMAT remain debated. Previous studies have suggested that muscle-derived stem/progenitor cells and other adipose tissue progenitors contribute to the development of IMAT. Adipocytes within IMAT exhibit features that are similar to either white adipocytes or uncoupling protein 1 (UCP1)-positive brown adipocytes. Additionally, given the heterogeneity of skeletal muscle, which comprises myofibers, satellite cells, and resident mesenchymal progenitors, it is plausible that interplay between these cellular components actively participate in the regulation of intermuscular adipogenesis. In this context, we review recent studies associated with IMAT to offer insights into the cellular origins, biological properties, and regulatory mechanisms of IMAT. Our aim is to provide novel ideas for the therapeutic strategy of IMAT and the development of new drugs targeting IMAT-related metabolic diseases.

Vivarium Lighting as an Important Extrinsic Factor Influencing Animal-based Research

Light is an extrinsic factor that exerts widespread influence on the regulation of circadian, physiologic, hormonal, metabolic, and behavioral systems of all animals, including those used in research. These wide-ranging biologic effects of light are mediated by distinct photoreceptors, the melanopsin-containing intrinsically photosensitive retinal ganglion cells of the nonvisual system, which interact with the rods and cones of the conventional visual system. Here, we review the nature of light and circadian rhythms, current industry practices and standards, and our present understanding of the neurophysiology of the visual and nonvisual systems. We also consider the implications of this extrinsic factor for vivarium measurement, production, and technological application of light, and provide simple recommendations on artificial lighting for use by regulatory authorities, lighting manufacturers, designers, engineers, researchers, and research animal care staff that ensure best practices for optimizing animal health and wellbeing and, ultimately, improving scientific outcomes.

Ketogenic Diet Increases Serum and White Adipose Tissue SIRT1 Expression in Mice

Overnutrition and its sequelae have become a global concern due to the increasing incidence of obesity and insulin resistance. A ketogenic diet (KD) is widely used as a dietary treatment for metabolic disorders. Sirtuin1 (SIRT1), a metabolic sensor which regulates fat homeostasis, is modulated by dietary interventions. However, the influence of nutritional ketosis on SIRT1 is still debated. We examined the effect of KD on adipose tissue, liver, and serum levels of SIRT1 in mice. Adult C57BL/6J male mice were randomly assigned to two isocaloric dietary groups and fed with either high-fat KD or normal chow (NC) for 4 weeks. Serum SIRT1, beta-hydroxybutyrate (βHB), glucose, and triglyceride levels, as well as SIRT1 expression in visceral (VAT), subcutaneous (SAT), and brown (BAT) adipose tissues, and in the liver, were measured. KD-fed mice showed an increase in serum βHB in parallel with serum SIRT1 (r = 0.732, p = 0.0156), and increased SIRT1 protein expression in SAT and VAT. SIRT1 levels remained unchanged in BAT and in the liver, which developed steatosis. Normal glycemia and triglycerides were observed. Under a KD, serum and white fat phenotypes show higher SIRT1, suggesting that one of the molecular mechanisms underlying a KD's potential benefits on metabolic health involves a synergistic interaction with SIRT1.

Type 2 Diabetes Mellitus: Pathogenic Features and Experimental Models in Rodents

Type 2 diabetes mellitus (T2DM) is the most common endocrine disorder (90%) in the world; it has numerous clinical, immunological, and genetic differences from type 1 diabetes mellitus. The pathogenesis of T2DM is complex and not fully clear. To date, animal models remain the main tool by which to study the pathophysiology and therapy of T2DM. Rodents are considered the best choice among animal models, because they are characterized by a small size, short induction period, easy diabetes induction, and economic efficiency. This review summarizes data on experimental models of T2DM that are currently used, evaluates their advantages and disadvantages vis-a-vis research, and describes in detail the factors that should be taken into account when using these models. Selection of a suitable model for tackling a particular issue is not always trivial; it affects study results and their interpretation.

Effects of Daytime Blue-Enriched LED Light on Physiologic Parameters of Three Common Mouse Strains Maintained on an IVC System

Light has been a crucial part of everyday life since the beginning of time. Most recently, light-emitting diode (LED) light enriched in the blue-appearing portion of the visible spectrum (465 to 485 nm), which is more efficient in energy use, is becoming the normal lighting technology in facilities around the world. Previous reports revealed that blue-enriched LED light at day (bLAD) enhances animal health and wellbeing as compared with cool white fluorescent (CWF) lighting. We hypothesized that bLAD, compared with CWF light, has a positive influence on basic physiologic indices such as food consumption, water consumption, weight gain, nesting behavior, complete blood count, and blood chemistry profile. To test this, we allocated 360 mice into equal-sized groups by sex, strain (C3H/HeNCrl, C57BL/6NCrl, BALB/cAnNCrl), lighting conditions, and 6 blood collection time points (n = 5 mice/sex/strain/lighting condition/time point). Food consumption, water consumption, body weight, nest location, and nest type were recorded every 3 d. At the end of the study, all mice were anesthetized over a period of 1 wk and blood was collected via cardiocentesis at 6 different time points. Overall, male C3H/HeNCrl consumed more food under bLAD conditions as compared with CWF conditions; male C3H/HeNCrl had lower cholesterol levels under bLAD conditions than under CWF conditions; female BALB/cAnNCrl mice had higher serum total protein under bLAD conditions than under CWF conditions; female C57BL/6NCrl mice had higher phosphorus levels under bLAD conditions than under CWF conditions, and female C3H/HeNCrl mice had a higher neutrophil count under bLAD conditions as compared with CWF conditions. Although sex and strain differences were found in various physiologic parameters under bLAD as compared with CWF lighting conditions, the differences were minimal. Thus, this study suggests that for these strains of mice, bLAD and CWF are largely equivalent with regard to indices of health and wellbeing, although some differences could affect research outcomes.

Genetic controls of Tas1r3-independent sucrose consumption in mice

We have previously used crosses between C57BL/6ByJ (B6) and 129P3/J (129) inbred strains to map a quantitative trait locus (QTL) on mouse chromosome (Chr) 4 that affects behavioral and neural responses to sucrose. We have named it the sucrose consumption QTL 2 (Scon2), and shown that it corresponds to the Tas1r3 gene, which encodes a sweet taste receptor subunit TAS1R3. To discover other sucrose consumption QTLs, we have intercrossed B6 inbred and 129.B6-Tas1r3 congenic mice to produce F₂ hybrids, in which Scon2 (Tas1r3) does not segregate, and hence does not contribute to phenotypical variation. Chromosome mapping using this F₂ intercross identified two main-effect QTLs, Scon3 (Chr9) and Scon10 (Chr14), and an epistatically interacting QTL pair Scon3 (Chr9)-Scon4 (Chr1). Using serial backcrosses, congenic and consomic strains, we conducted high-resolution mapping of Scon3 and Scon4 and analyzed their epistatic interactions. We used mice with different Scon3 or Scon4 genotypes to understand whether these two QTLs influence sucrose intake via gustatory or postoral mechanisms. These studies found no evidence for involvement of the taste mechanisms, but suggested involvement of energy metabolism. Mice with the B6 Scon4 genotype drank less sucrose in two-bottle tests, and also had a higher respiratory exchange ratio and lower energy expenditure under basal conditions (when they had only chow and water available). Our results provide evidence that Scon3 and Scon4 influence mouse-to-mouse variation in sucrose intake and that both likely act through a common postoral mechanism.

Examining the role of olfaction in dietary choice

Obesity is frequently caused by calorie-rich dietary choices across the animal kingdom. As prandial preference toward a high-fat diet develops in mice, an anti-preference or devaluation of a nutritionally balanced but less palatable standard chow diet occurs concomitantly. Although mechanistic insights underlying devaluation have been observed physiologically in the brain, it is unclear how peripheral sensory processing affects food choice. Because olfactory cues and odor perception help coordinate food preference and intake, we determine the role of smell in the targeted consumption of a high-fat diet and simultaneous devaluation of a standard chow diet. Using inaccessible food and loss-of-function manipulations, we find that olfactory information is neither sufficient nor necessary for both the acute and chronic selection of high-fat diet and coincident diminished value of standard diet. This work suggests alternative means are behind the immediate and sustained consumption of high-fat diet and concurrent standard diet devaluation.

Olfaction is considered integral to food choice and preference formation. Boone et al. use a behavioral approach to determine the salience of olfactory cues in diet selection. They find that olfaction is neither sufficient nor required for both high-fat-diet preference and standard diet devaluation.

Neuronal Activity Regulates Blood-Brain Barrier Efflux Transport through Endothelial Circadian Genes

The blood vessels in the central nervous system (CNS) have a series of unique properties, termed the blood-brain barrier (BBB), which stringently regulate the entry of molecules into the brain, thus maintaining proper brain homeostasis. We sought to understand whether neuronal activity could regulate BBB properties. Using both chemogenetics and a volitional behavior paradigm, we identified a core set of brain endothelial genes whose expression is regulated by neuronal activity. In particular, neuronal activity regulates BBB efflux transporter expression and function, which is critical for excluding many small lipophilic molecules from the brain parenchyma. Furthermore, we found that neuronal activity regulates the expression of circadian clock genes within brain endothelial cells, which in turn mediate the activity-dependent control of BBB efflux transport. These results have important clinical implications for CNS drug delivery and clearance of CNS waste products, including Aβ, and for understanding how neuronal activity can modulate diurnal processes.

Food-added azodicarbonamide alters haematogical parameters, antioxidant status and biochemical/histomorphological indices of liver and kidney injury in rats

OBJECTIVES

Azodicarbonamide (ADA) is a dough enhancer currently used as a replacement for potassium bromate in the process of bread-making in countries such as Nigeria. However, comprehensive information on the toxicological profile of ADA is not readily available. The present study investigated the toxicological effects of ADA in rats.

METHODS

Twenty-four adult rats were randomly assigned into four groups of six rats each. Animals in group A served as the control (administered standard diet), whereas animals in groups B, C and D were fed ADA in food at 1, 2 and 4%, respectively. Standard or ADA diet was fed to the animals daily for a period of 28 days. Body weight was measured weekly, whereas food and water consumption was measured daily. On day 28, animals were fasted overnight after which they were euthanised. Blood samples taken were used for assessment of fasting blood glucose, haematological parameters, serum lipids, antioxidant status, lipid peroxidation status, electrolytes and urea, plasma proteins and biochemical parameters of liver and kidney injury. The liver and kidneys were then excised and processed for general histological study.

RESULTS

The results showed that repeated administration of ADA was associated with dose-related decrease in weight gain, decrease in overall food consumption, decreased superoxide dismutase activity/glutathione level and increased lipid peroxidation. There was also biochemical and morphological evidence of liver and kidney injury.

CONCLUSIONS

These findings suggest that food-added ADA could be injurious to the body cells and organs in rats.

White Kidney Bean (Phaseolus Vulgaris L.) Consumption Reduces Fat Accumulation in a Polygenic Mouse Model of Obesity

Clinical studies indicate that eating common bean, Phaseolus vulgaris L., plays a role in body weight regulation but mechanisms have yet to be elucidated. Here, we investigated the anti-obesogenic activity of white kidney bean in a mouse model of dietary-induced obesity. Bean consumption reduced the accumulation of adipose tissue in male and female C57BL6 mice. The anti-obesogenic effect of white kidney bean was not due to alterations in energy intake, energy excreted in the feces, or feed efficiency ratio. While bean consumption increased the mass of the intestine, no marked differences were consistently observed in crypt height, mucin content of goblet cells, proliferation index or zone of proliferation. However, significantly higher concentrations of total bacteria and of Akkermansia muciniphila were detected in cecal content of bean-fed mice, and the ratio of Firmicutes to Bacteroidetes was reduced. Bile acid content was higher in the ileum of bean-fed mice, but transcript levels of farnesoid X receptor were not significantly affected. Whether changes in bile-acid-mediated cell signaling play a role in bean-related differences in fat accumulation and/or overall metabolic health requires further investigation.

Influence of Daytime LED Light Exposure on Circadian Regulatory Dynamics of Metabolism and Physiology in Mice

Light is a potent biologic force that profoundly influences circadian, neuroendocrine, and neurobehavioral regulation in animals. Previously we examined the effects of light-phase exposure of rats to white light-emitting diodes (LED), which emit more light in the blue-appearing portion of the visible spectrum (465 to 485 nm) than do broad-spectrum cool white fluorescent (CWF) light, on the nighttime melatonin amplitude and circadian regulation of metabolism and physiology. In the current studies, we tested the hypothesis that exposure to blue-enriched LED light at day (bLAD), compared with CWF, promotes the circadian regulation of neuroendocrine, metabolic, and physiologic parameters that are associated with optimizing homeostatic regulation of health and wellbeing in 3 mouse strains commonly used in biomedical research (C3H [melatonin-producing], C57BL/6, and BALB/c [melatonin-non-producing]). Compared with male and female mice housed for 12 wk under 12:12-h light:dark (LD) cycles in CWF light, C3H mice in bLAD evinced 6-fold higher peak plasma melatonin levels at the middark phase; in addition, high melatonin levels were prolonged 2 to 3 h into the light phase. C57BL/6 and BALB/c strains did not produce nighttime pineal melatonin. Body growth rates; dietary and water intakes; circadian rhythms of arterial blood corticosterone, insulin, leptin, glucose, and lactic acid; pO₂ and pCO₂; fatty acids; and metabolic indicators (cAMP, DNA, tissue DNA 3H-thymidine incorporation, fat content) in major organ systems were significantly lower and activation of major metabolic signaling pathways (mTOR, GSK3β, and SIRT1) in skeletal muscle and liver were higher only in C3H mice in bLAD compared with CWF. These data show that exposure of C3H mice to bLAD compared with CWF has a marked positive effect on the circadian regulation of neuroendocrine, metabolic, and physiologic parameters associated with the promotion of animal health and wellbeing that may influence scientific outcomes. The absence of enhancement in amelatonic strains suggests hyperproduction of nighttime melatonin may be a key component of the physiology.

Profound differences in fat versus carbohydrate preferences in CAST/EiJ and C57BL/6J mice: Role of fat taste

In a nutrient self-selection study, CAST/EiJ mice consumed more carbohydrate than fat while C57BL/6J (B6) mice showed the opposite preference. The present study revealed similar strain differences in preferences for isocaloric fat (Intralipid) and carbohydrate (sucrose, maltodextrin) solutions in chow-fed mice. In initial 2-day choice tests, percent fat intakes of CAST and B6 mice were 4-9% and 71-81% respectively. In subsequent nutrient vs. water tests, CAST mice consumed considerably less fat but not carbohydrate compared to B6 mice. Orosensory rather than postoral factors are implicated in the very low fat preference and intake of CAST mice. This is supported by results of a choice test with Intralipid mixed with non-nutritive sweeteners vs. non-sweet maltodextrin. The preference of CAST mice for sweetened fat exceeded that of B6 mice (94 vs. 74%) and absolute fat intakes were similar in the two strains. When given unsweetened Intralipid vs. water tests at ascending fat concentrations CAST mice displayed reduced fat preferences at 0.1-5% and reduced intakes at 0.5-5% concentrations, compared to B6 mice. The differential fat preferences of CAST and B6 mice may reflect differences in fat taste sensing or in central neural processes related to fat selection.

Adiposity and metabolic health in mice deficient in intestinal alkaline phosphatase

Intestinal alkaline phosphatase 3 (AKP3) is an enzyme that was reported to play a role in lipid metabolism and to prevent high fat diet-induced metabolic syndrome in mice. To investigate a potential functional role of AKP3 in diet-induced adiposity and metabolic health, we have kept male and female wild-type or AKP3 deficient mice on a high fat diet for 15 weeks to induce obesity and compared those with mice kept on standard fat diet. Body weight as well as adipose tissue mass were statistically significantly higher upon high fat diet feeding for mice of both genders and genotypes. Female mice of either genotype kept on high fat diet gained less weight, resulting in smaller adipose tissue depots with smaller adipocytes. However, AKP3 deficiency had no significant effect on body weight gain or adipose tissue mass and did not affect adipocyte size or density. Gene expression analysis revealed no effect of the genotype on inflammatory parameters in adipose tissue, except for tumor necrosis factor alpha, which was higher in mesenteric adipose tissue of female obese mice. Plasma glucose and insulin levels were also not affected in obese AKP3 deficient mice. Overall, our data do not support a functional role of AKP3 in adipose tissue development, or insulin sensitivity.

Burly1 is a mouse QTL for lean body mass that maps to a 0.8-Mb region of chromosome 2

To fine map a mouse QTL for lean body mass (Burly1), we used information from intercross, backcross, consomic, and congenic mice derived from the C57BL/6ByJ (host) and 129P3/J (donor) strains. The results from these mapping populations were concordant and showed that Burly1 is located between 151.9 and 152.7 Mb (rs33197365 to rs3700604) on mouse chromosome 2. The congenic region harboring Burly1 contains 26 protein-coding genes, 11 noncoding RNA elements (e.g., lncRNA), and 4 pseudogenes, with 1949 predicted functional variants. Of the protein-coding genes, 7 have missense variants, including genes that may contribute to lean body weight, such as Angpt41, Slc52c3, and Rem1. Lean body mass was increased by the B6-derived variant relative to the 129-derived allele. Burly1 influenced lean body weight at all ages but not food intake or locomotor activity. However, congenic mice with the B6 allele produced more heat per kilogram of lean body weight than did controls, pointing to a genotype effect on lean mass metabolism. These results show the value of integrating information from several mapping populations to refine the map location of body composition QTLs and to identify a short list of candidate genes.

Diet with high content of advanced glycation end products induces systemic inflammation and weight gain in experimental mice: Protective role of curcumin and gallic acid

The present study was aimed to investigate the effect of diet derived AGEs (dAGEs) on the circulatory levels of pro-inflammatory cytokines, chemokines and to evaluate the protective efficacy of natural anti-oxidants curcumin (CU) and gallic acid (GA) respectively against the dAGEs-induced systemic inflammation in experimental Swiss albino mice. The experimental mice were fed with dAGEs in the presence and absence of CU and GA for 6 months. The levels of 40 circulatory pro-inflammatory cytokines and chemokines were evaluated using Proteome-Cytokine Array kit. In addition, serum levels of N-ɛCML, CRP and HbA1c were estimated by ELISA method. Among the sixteen pro- and anti-inflammatory cytokines analysed, five (IL-16, IL-1α, ICAM, TIMP-1 and C5a) were found to be highly expressed (3.5-fold) and eleven cytokines were moderately expressed (2-fold) in dAGEs fed mice. In case of chemokines, three (BLC, SDF-1 and MCP-1) were found to be highly expressed (4-fold) and ten showed moderate expression (2-fold) as compared with basal diet fed mice. Interestingly, CU or GA co-treatment normalized the levels of circulatory pro- and anti-inflammatory cytokines, chemokines, N-ɛCML, CRP and HbA1c levels. Together, the present study suggests that dAGEs are positively associated with the development of systemic inflammation in experimental mice.

Functional role of ADAMTS5 in adiposity and metabolic health

Previous studies with gene-deficient mice (ADAMTS5-P) revealed that ADAMTS5 (A Disintegrin And Metalloproteinase with Thrombospondin type 1 motifs, member 5) plays a functional role in adiposity and metabolic health. To confirm these observations, we have performed similar studies with an independently generated strain of ADAMTS5 deficient mice (ADAMTS5-J). Upon cold exposure as well as after high-fat diet feeding (diet-induced obesity or DIO model), these knockout (KO) mice developed less subcutaneous and gonadal white adipose tissue (WAT) as compared to their wild-type (WT) littermates (reduction was more pronounced in ADAMTS5-P mice). Enhanced browning of WAT, as monitored by expression of UCP-1 was seen in the ADAMTS5-J KO mice upon cold exposure but not in the DIO model (seen in both conditions with the ADAMTS5-P mice). Brown adipose tissue (BAT) mass was not different between KO and WT ADAMTS5-J mice, either upon cold exposure or in the DIO model (in contrast to the enhanced BAT mass with the ADAMTS5-P mice). Energy expenditure and thermogenesis were not significantly different between KO and WT ADAMTS5-J mice (in contrast to somewhat enhanced levels in ADAMTS5-P mice). Insulin sensitivity was improved in the ADAMTS5-J KO mice, and they were protected against non-alcoholic steatohepatitis in the DIO model (as the ADAMTS5-P mice). These data are thus similar for both strains of KO mice, confirming specificity of the phenotype, but some quantitative and qualitative differences are also observed.

C57BL/6J mice as a polygenic developmental model of diet-induced obesity

Susceptibility to obesity changes during the course of life. We utilized the C57BL/6J (B6) and 129S mouse as a genetic model for variation in diet‐induced obesity to define the adiposity phenotypes from birth to maturity at 8 weeks‐of‐age. From birth to 8 weeks‐of‐age, both male and female 129S mice had significantly higher fat mass and adiposity index than B6 mice, although they were not obese. After 8 weeks‐of‐age, B6 had greater adiposity/obesity than 129S mice in response to a high fat (HF). We sought to determine the mechanism activating the fat accumulation in B6 mice at 8‐weeks‐of‐age. We used microarray analysis of gene expression during development of inguinal fat to show that molecular networks of lipogenesis were maximally expressed at 8 weeks‐of‐age. In addition, the DNA methylation analysis of the Sfrp5 promoter and binding of acetylated histones to Sfrp5 and Acly promoter regions showed that major differences in the expression of genes of lipogenesis and chromatin structure occur during development. Differences in lipogenesis networks could account for the strain‐dependent differences in adiposity up to 8 weeks‐of‐age; however, changes in the expression of genes in these networks were not associated with the susceptibility to DIO in B6 male mice beyond 8 weeks‐of‐age.

Adiposity QTL Adip20 decomposes into at least four loci when dissected using congenic strains

An average mouse in midlife weighs between 25 and 30 g, with about a gram of tissue in the largest adipose depot (gonadal), and the weight of this depot differs between inbred strains. Specifically, C57BL/6ByJ mice have heavier gonadal depots on average than do 129P3/J mice. To understand the genetic contributions to this trait, we mapped several quantitative trait loci (QTLs) for gonadal depot weight in an F2 intercross population. Our goal here was to fine-map one of these QTLs, Adip20 (formerly Adip5), on mouse chromosome 9. To that end, we analyzed the weight of the gonadal adipose depot from newly created congenic strains. Results from the sequential comparison method indicated at least four rather than one QTL; two of the QTLs were less than 0.5 Mb apart, with opposing directions of allelic effect. Different types of evidence (missense and regulatory genetic variation, human adiposity/body mass index orthologues, and differential gene expression) implicated numerous candidate genes from the four QTL regions. These results highlight the value of mouse congenic strains and the value of this sequential method to dissect challenging genetic architecture.

Detection of maltodextrin and its discrimination from sucrose are independent of the T1R2 + T1R3 heterodimer

Maltodextrins, such as Maltrin and Polycose, are glucose polymer mixtures of varying chain lengths that are palatable to rodents. Although glucose and other sugars activate the T1R2 + T1R3 "sweet" taste receptor, recent evidence from T1R2- or T1R3-knockout (KO) mice suggests that maltodextrins, despite their glucose polymer composition, activate a separate receptor mechanism to generate a taste percept qualitatively distinguishable from that of sweeteners. However, explicit discrimination of maltodextrins from prototypical sweeteners has not yet been psychophysically tested in any murine model. Therefore, mice lacking T1R2 + T1R3 and wild-type controls were tested in a two-response taste discrimination task to determine whether maltodextrins are 1) detectable when both receptor subunits are absent and 2) perceptually distinct from that of sucrose irrespective of viscosity, intensity, and hedonics. Most KO mice displayed similar Polycose sensitivity as controls. However, some KO mice were only sensitive to the higher Polycose concentrations, implicating potential allelic variation in the putative polysaccharide receptor or downstream pathways unmasked by the absence of T1R2 + T1R3. Varied Maltrin and sucrose concentrations of approximately matched viscosities were then presented to render the oral somatosensory features, intensity, and hedonic value of the solutions irrelevant. Although both genotypes competently discriminated Maltrin from sucrose, performance was apparently driven by the different orosensory percepts of the two stimuli in control mice and the presence of a Maltrin but not sucrose orosensory cue in KO mice. These data support the proposed presence of an orosensory receptor mechanism that gives rise to a qualitatively distinguishable sensation from that of sucrose.

Dietary treatment of fatty liver: High dietary protein content has an antisteatotic and antiobesogenic effect in mice

Few studies have assessed the effect of changing ratios of dietary macronutrients on fat accumulation in adipose tissue and organs such as the liver in a 3×n(n≥3) factorial design. We investigated the effects of 7 diets from a single manufacturer containing 11-58en% protein (casein), 0-81en% carbohydrates (CHO; sucrose, maltrodextrin-10 and corn starch), and 8-42en% fat (triheptanoin, olive oil or cocoa butter) in C57BL/6J mice, a good model for diet-induced obesity and fatty liver. The diets were fed for 3weeks to wild-type and hyperlipidemic male and female mice. Caloric intake was mainly determined by dietary fat. Body weight, liver lipid and cholesterol content, NFκB activation, and fat-pad size decreased only in mice fed a high-protein diet. A high dietary protein:CHO ratio reduced plasma FGF21 concentration, and increased liver PCK1 protein content and plasma triglyceride concentration. The dietary protein:CHO ratio determined hepatic expression of Pck1 and Ppargc1a in males, and Fgf21 in females, whereas the dietary CHO:fat ratio determined that of Fasn, Acaca1, and Scd1 in females. Hepatic glycogen content was determined by all three dietary components. Both hepatic PCK1 and plasma FGF21 correlated strongly and inversely with hepatic TG content, suggesting a key role for PCK1 and increased gluconeogenesis in resolving steatosis with a high-protein diet, with FGF21 expression reflecting declining cell stress. We propose that a diet containing ~35en% protein, 5-10en% fat, and 55-60en% carbohydrate will prevent fatty liver in mice without inducing side effects.

Caloric Restriction Protects against Lactacystin-Induced Degeneration of Dopamine Neurons Independent of the Ghrelin Receptor

Parkinson’s disease (PD) is a neurodegenerative disorder, characterized by a loss of dopamine (DA) neurons in the substantia nigra pars compacta (SNc). Caloric restriction (CR) has been shown to exert ghrelin-dependent neuroprotective effects in the 1-methyl-4-phenyl-1,2,3,6-tetrathydropyridine (MPTP)-based animal model for PD. We here investigated whether CR is neuroprotective in the lactacystin (LAC) mouse model for PD, in which proteasome disruption leads to the destruction of the DA neurons of the SNc, and whether this effect is mediated via the ghrelin receptor. Adult male ghrelin receptor wildtype (WT) and knockout (KO) mice were maintained on an ad libitum (AL) diet or on a 30% CR regimen. After 3 weeks, LAC was injected unilaterally into the SNc, and the degree of DA neuron degeneration was evaluated 1 week later. In AL mice, LAC injection significanty reduced the number of DA neurons and striatal DA concentrations. CR protected against DA neuron degeneration following LAC injection. However, no differences were observed between ghrelin receptor WT and KO mice. These results indicate that CR can protect the nigral DA neurons from toxicity related to proteasome disruption; however, the ghrelin receptor is not involved in this effect.

Hepatocytes Are the Principal Source of Circulating RBP4 in Mice

RBP4 is produced mainly by hepatocytes. In type 2 diabetes and obesity, circulating RBP4 is increased and may act systemically to cause insulin resistance and glucose intolerance. Observations that adipocyte RBP4 mRNA increases in parallel with circulating RBP4 in these conditions, whereas liver RBP4 mRNA does not, led to a widely held hypothesis that elevated circulating RBP4 is a direct result of increased production by adipocytes. To test this, we generated mice with hepatocyte-specific deletion of RBP4 (liver RBP4 knockout or LRKO mice). Adipose tissue RBP4 expression and secretion remained intact in LRKO mice and increased as expected in the setting of diet-induced insulin resistance. However, circulating RBP4 was undetectable in LRKO mice. We conclude that adipocyte RBP4 is not a significant source of circulating RBP4, even in the setting of insulin resistance. Adipocyte RBP4, therefore, may have a more important autocrine or paracrine function that is confined within the adipose tissue compartment.

Alterations in behaviour, cerebral cortical morphology and cerebral oxidative stress markers following aspartame ingestion

OBJECTIVE

The study evaluated changes in open field behaviours, cerebral cortical histomorphology and biochemical markers of oxidative stress following repeated administration of aspartame in mice.

METHODOLOGY

Adult mice were assigned into five groups of twelve each. Vehicle (distilled water), or aspartame (20, 40, 80 and 160mg/kg body weight) were administered orally for 28days. Horizontal locomotion, rearing and grooming were assessed after the first and last dose of aspartame. Sections of the cerebral cortex were processed and stained for general histology, and also examined for neuritic plaques using the Bielschwosky's protocol. Glial fibrillary acidic protein (GFAP) and neuron specific enolase (NSE) immunoreactivity were assessed using appropriate antibodies. Aspartate and antioxidant levels were also assayed from cerebral cortex homogenates. Data obtained were analysed using descriptive and inferential statistics.

RESULTS

Body weight and food consumption decreased significantly with aspartame consumption. Locomotion, rearing and grooming increased significantly after first dose, and with repeated administration of aspartame. Histological changes consistent with neuronal damage were seen at 40, 80 and 160mg/kg. Neuritic plaque formation was not evident; while GFAP-reactive astrocytes and NSE-reactive neurons increased at 40 and 80mg/kg but decreased at 160mg/kg. Superoxide dismutase and nitric oxide increased with increasing doses of aspartame, while aspartate levels showed no significant difference.

CONCLUSION

The study showed morphological alterations consistent with neuronal injury and biochemical changes of oxidative stress. These data therefore supports the need for caution in the indiscriminate use of aspartame as a non-nutritive sweetener.

Maltodextrin and sucrose preferences in sweet-sensitive (C57BL/6J) and subsensitive (129P3/J) mice revisited

Mice are attracted to the tastes of sugar and maltodextrin solutions. Sugar taste is mediated by the T1R2/T1R3 sweet taste receptor, while maltodextrin taste is dependent upon a different as yet unidentified receptor. In a prior study sweet-sensitive C57BL/6J (B6) mice displayed similar preferences for sucrose and maltodextrin solutions in 24-h saccharide vs. water choice tests that exceeded those of sweet-subsensitive 129P3/J (129) mice. In a subsequent experiment reported here, sucrose and maltodextrin (Polycose) preference and acceptance were compared in the two strains in saccharide vs. saccharide choice tests with isocaloric concentrations (0.5-32%). The 129 mice displayed significantly greater maltodextrin preferences than B6 mice at mid-range concentrations (2-8%), while the mice displayed an opposite preference profile at the highest concentration (32%). As in prior studies, 129 mice consumed less total saccharide than B6 mice at lower concentrations. These findings show that the conclusions reached from tastant vs. water tests may differ from those pitting one tastant against another. The increased sucrose preference and intake of B6 mice, relative to 129 mice, is consistent with their sweet-sensitive phenotype.

No insulating effect of obesity

The development of obesity may be aggravated if obesity itself insulates against heat loss and thus diminishes the amount of food burnt for body temperature control. This would be particularly important under normal laboratory conditions where mice experience a chronic cold stress (at ≈20°C). We used Scholander plots (energy expenditure plotted against ambient temperature) to examine the insulation (thermal conductance) of mice, defined as the inverse of the slope of the Scholander curve at subthermoneutral temperatures. We verified the method by demonstrating that shaved mice possessed only half the insulation of nonshaved mice. We examined a series of obesity models [mice fed high-fat diets and kept at different temperatures, classical diet-induced obese mice, ob/ob mice, and obesity-prone (C57BL/6) vs. obesity-resistant (129S) mice]. We found that neither acclimation temperature nor any kind or degree of obesity affected the thermal insulation of the mice when analyzed at the whole mouse level or as energy expenditure per lean weight. Calculation per body weight erroneously implied increased insulation in obese mice. We conclude that, in contrast to what would be expected, obesity of any kind does not increase thermal insulation in mice, and therefore, it does not in itself aggravate the development of obesity. It may be discussed as to what degree of effect excess adipose tissue has on insulation in humans and especially whether significant metabolic effects are associated with insulation in humans.

Partial Reversal of Obesity-Induced Insulin Resistance Owing to Anti-Inflammatory Immunomodulatory Potential of Flaxseed Oil

The present study was designed to assess the potential of supplementation of diet with Flaxseed (Linum usitatissimum, L.) oil (FXO), on obesity-related inflammation and reversal of obesity-induced insulin resistance. Swiss Albino mice, C57bl/6 mice and co-culture of 3T3-L1 adipocytes - RAW 264.7 macrophages to mimick obese adipose tissue environment were used for the study. Oral gavage of FXO at concentrations of 4, 8 or 16 mg/kg body weight (bwt) for 4 weeks or high-fat diet (HFD, 60% energy as fat) supplemented with dietary FXO (4, 8 or 16 mg/kg bwt) was given to the mice. FXO was characterised using gas chromatography - mass spectrometry. FXO supplemented HFD-fed mice (4 mg/kg bwt exhibited reduced adiposity index, serum glucose levels and triglycerides (8 and 16 mg/kg bwt) and improvement in insulin sensitisation (4, 8 and 16 mg/kg bwt) when compared with HFD mice. The co-culture showed a dose-dependent shift in cytokines towards anti-inflammatory (IL-4) state, with a decrease in pro-inflammatory TNF-α (p < 0.05). For immunomodulatory studies a dose-dependent increase (p < 0.05) was observed in antigen-specific levels of Th2 (IL-4) cytokine, serum anti-ova IgG1 and IgE levels. Suppression in anti-ova IgG2a, IgG2b, and IgG3 and antigen-specific Th1 cytokines like TNF-α and IFN-γ significantly (p < 0.05) was observed at 16 mg/kg bwt dosage. The results indicate that FXO exhibits an anti-inflammatory immunomodulatory potential and may partially relieve symptoms of obesity-associated insulin resistance.

Sulforaphane improves dysregulated metabolic profile and inhibits leptin-induced VSMC proliferation: Implications toward suppression of neointima formation after arterial injury in western diet-fed obese mice

Sulforaphane (SFN), a dietary phase-2 enzyme inducer that mitigates cellular oxidative stress through nuclear factor erythroid 2-related factor 2 (Nrf2) activation, is known to exhibit beneficial effects in the vessel wall. For instance, it inhibits vascular smooth muscle cell (VSMC) proliferation, a major event in atherosclerosis and restenosis after angioplasty. In particular, SFN attenuates the mitogenic and pro-inflammatory actions of platelet-derived growth factor (PDGF) and tumor necrosis factor-α (TNFα), respectively, in VSMCs. Nevertheless, the vasoprotective role of SFN has not been examined in the setting of obesity characterized by hyperleptinemia and insulin resistance. Using the mouse model of western diet-induced obesity, the present study demonstrates for the first time that subcutaneous delivery of SFN (0.5mg/Kg/day) for~3weeks significantly attenuates neointima formation in the injured femoral artery [↓ (decrease) neointima/media ratio by~60%; n=5-8]. This was associated with significant improvements in metabolic parameters, including ↓ weight gain by~52%, ↓ plasma leptin by~42%, ↓ plasma insulin by~63%, insulin resistance [↓ homeostasis model assessment of insulin resistance (HOMA-IR) index by~73%], glucose tolerance (↓ AUCGTT by~24%), and plasma lipid profile (e.g., ↓ triglycerides). Under in vitro conditions, SFN significantly decreased leptin-induced VSMC proliferation by~23% (n=5) with associated diminutions in leptin-induced cyclin D1 expression and the phosphorylation of p70S6kinase and ribosomal S6 protein (n=3-4). The present findings reveal that, in addition to improving systemic metabolic parameters, SFN inhibits leptin-induced VSMC proliferative signaling that may contribute in part to the suppression of injury-induced neointima formation in diet-induced obesity.

Large Neutral Amino Acid Supplementation Exerts Its Effect through Three Synergistic Mechanisms: Proof of Principle in Phenylketonuria Mice

Background

Phenylketonuria (PKU) was the first disorder in which severe neurocognitive dysfunction could be prevented by dietary treatment. However, despite this effect, neuropsychological outcome in PKU still remains suboptimal and the phenylalanine-restricted diet is very demanding. To improve neuropsychological outcome and relieve the dietary restrictions for PKU patients, supplementation of large neutral amino acids (LNAA) is suggested as alternative treatment strategy that might correct all brain biochemical disturbances caused by high blood phenylalanine, and thereby improve neurocognitive functioning.

Objective

As a proof-of-principle, this study aimed to investigate all hypothesized biochemical treatment objectives of LNAA supplementation (normalizing brain phenylalanine, non-phenylalanine LNAA, and monoaminergic neurotransmitter concentrations) in PKU mice.

Methods

C57Bl/6 Pah-enu2 (PKU) mice and wild-type mice received a LNAA supplemented diet, an isonitrogenic/isocaloric high-protein control diet, or normal chow. After six weeks of dietary treatment, blood and brain amino acid and monoaminergic neurotransmitter concentrations were assessed.

Results

In PKU mice, the investigated LNAA supplementation regimen significantly reduced blood and brain phenylalanine concentrations by 33% and 26%, respectively, compared to normal chow (p<0.01), while alleviating brain deficiencies of some but not all supplemented LNAA. Moreover, LNAA supplementation in PKU mice significantly increased brain serotonin and norepinephrine concentrations from 35% to 71% and from 57% to 86% of wild-type concentrations (p<0.01), respectively, but not brain dopamine concentrations (p = 0.307).

Conclusions

This study shows that LNAA supplementation without dietary phenylalanine restriction in PKU mice improves brain biochemistry through all three hypothesized biochemical mechanisms. Thereby, these data provide proof-of-concept for LNAA supplementation as a valuable alternative dietary treatment strategy in PKU. Based on these results, LNAA treatment should be further optimized for clinical application with regard to the composition and dose of the LNAA supplement, taking into account all three working mechanisms of LNAA treatment.

Body Composition QTLs Identified in Intercross Populations Are Reproducible in Consomic Mouse Strains

Genetic variation contributes to individual differences in obesity, but defining the exact relationships between naturally occurring genotypes and their effects on fatness remains elusive. As a step toward positional cloning of previously identified body composition quantitative trait loci (QTLs) from F2 crosses of mice from the C57BL/6ByJ and 129P3/J inbred strains, we sought to recapture them on a homogenous genetic background of consomic (chromosome substitution) strains. Male and female mice from reciprocal consomic strains originating from the C57BL/6ByJ and 129P3/J strains were bred and measured for body weight, length, and adiposity. Chromosomes 2, 7, and 9 were selected for substitution because previous F2 intercross studies revealed body composition QTLs on these chromosomes. We considered a QTL confirmed if one or both sexes of one or both reciprocal consomic strains differed significantly from the host strain in the expected direction after correction for multiple testing. Using these criteria, we confirmed two of two QTLs for body weight (Bwq5-6), three of three QTLs for body length (Bdln3-5), and three of three QTLs for adiposity (Adip20, Adip26 and Adip27). Overall, this study shows that despite the biological complexity of body size and composition, most QTLs for these traits are preserved when transferred to consomic strains; in addition, studying reciprocal consomic strains of both sexes is useful in assessing the robustness of a particular QTL.

Regulation of Adipose Tissue Inflammation and Insulin Resistance by MAPK Phosphatase 5

Obesity and metabolic disorders such as insulin resistance and type 2 diabetes have become a major threat to public health globally. The mechanisms that lead to insulin resistance in type 2 diabetes have not been well understood. In this study, we show that mice deficient in MAPK phosphatase 5 (MKP5) develop insulin resistance spontaneously at an early stage of life and glucose intolerance at a later age. Increased macrophage infiltration in white adipose tissue of young MKP5-deficient mice correlates with the development of insulin resistance. Glucose intolerance in MKP5-deficient mice is accompanied by significantly increased visceral adipose weight, reduced AKT activation, enhanced p38 activity, and increased inflammation in visceral adipose tissue when compared with wild-type (WT) mice. Deficiency of MKP5 resulted in increased inflammatory activation in macrophages. These findings thus demonstrate that MKP5 critically controls inflammation in white adipose tissue and the development of metabolic disorders.

Dietary stearic acid leads to a reduction of visceral adipose tissue in athymic nude mice

Stearic acid (C18:0) is a long chain dietary saturated fatty acid that has been shown to reduce metastatic tumor burden. Based on preliminary observations and the growing evidence that visceral fat is related to metastasis and decreased survival, we hypothesized that dietary stearic acid may reduce visceral fat. Athymic nude mice, which are used in models of human breast cancer metastasis, were fed a stearic acid, linoleic acid (safflower oil), or oleic acid (corn oil) enriched diet or a low fat diet ad libitum. Total body weight did not differ significantly between dietary groups over the course of the experiment. However visceral fat was reduced by ∼70% in the stearic acid fed group compared to other diets. In contrast total body fat was only slightly reduced in the stearic acid diet fed mice when measured by dual-energy x-ray absorptiometry and quantitative magnetic resonance. Lean body mass was increased in the stearic acid fed group compared to all other groups by dual-energy x-ray absorptiometry. Dietary stearic acid significantly reduced serum glucose compared to all other diets and increased monocyte chemotactic protein-1 (MCP-1) compared to the low fat control. The low fat control diet had increased serum leptin compared to all other diets. To investigate possible mechanisms whereby stearic acid reduced visceral fat we used 3T3L1 fibroblasts/preadipocytes. Stearic acid had no direct effects on the process of differentiation or on the viability of mature adipocytes. However, unlike oleic acid and linoleic acid, stearic acid caused increased apoptosis (programmed cell death) and cytotoxicity in preadipocytes. The apoptosis was, at least in part, due to increased caspase-3 activity and was associated with decreased cellular inhibitor of apoptosis protein-2 (cIAP2) and increased Bax gene expression. In conclusion, dietary stearic acid leads to dramatically reduced visceral fat likely by causing the apoptosis of preadipocytes.

Genetic variation in the ovine uncoupling protein 1 gene: association with carcass traits in New Zealand (NZ) Romney sheep, but no association with growth traits in either NZ Romney or NZ Suffolk sheep

The uncoupling protein 1 (UCP1) plays an important role in the regulation of lipolysis and thermogenesis in adipose tissues. Genetic variation within three regions (the promoter, intron 2 and exon 5) of the ovine UCP1 gene (UCP1) was investigated using polymerase chain reaction-single-strand conformational polymorphism (PCR-SSCP) analyses. These revealed three promoter variants (designated A, B and C) and two intron 2 variants (a and b). The association of this genetic variation with variation in lamb carcass traits and postweaning growth was investigated in New Zealand (NZ) Romney and Suffolk sheep. The presence of B in a lamb's genotype was associated with decreased subcutaneous carcass fat depth (V-GR) (p = 0.004) and proportion of total lean meat yield of loin meat (p = 0.005), and an increased proportion of total lean meat yield of hind-leg meat (p = 0.018). In contrast, having two copies of C was associated with increased V-GR (p < 0.001) and proportion of total lean meat yield of shoulder meat (p = 0.009), and a decreased hind-leg yield (p = 0.032). No associations were found with postweaning growth. These results suggest that ovine UCP1 is a potential gene marker for carcass traits.

Maltodextrin and fat preference deficits in "taste-blind" P2X2/P2X3 knockout mice

Adenosine triphosphate is a critical neurotransmitter in the gustatory response to the 5 primary tastes in mice. Genetic deletion of the purinergic P2X2/P2X3 receptor greatly reduces the neural and behavioral response to prototypical primary taste stimuli. In this study, we examined the behavioral response of P2X double knockout mice to maltodextrin and fat stimuli, which appear to activate additional taste channels. P2X double knockout and wild-type mice were given 24-h choice tests (vs. water) with ascending concentrations of Polycose and Intralipid. In Experiment 1, naive double knockout mice, unlike wild-type mice, were indifferent to dilute (0.5-4%) Polycose solutions but preferred concentrated (8-32%) Polycose to water. In a retest, the Polycose-experienced double knockout mice, like wild-type mice, preferred all Polycose concentrations. In Experiment 2, naive double knockout mice, unlike wild-type mice, were indifferent to dilute (0.313-2.5%) Intralipid emulsions but preferred concentrated (5-20%) Intralipid to water. In a retest, the fat-experienced double knockout mice, like wild-type mice, strongly preferred 0.313-5% Intralipid to water. These results indicate that the inherent preferences of mice for maltodextrin and fat are dependent upon adenosine triphosphate taste cell signaling. With experience, however, P2X double knockout mice develop strong preferences for the nontaste flavor qualities of maltodextrin and fat conditioned by the postoral actions of these nutrients.

Role of human pregnane X receptor in high fat diet-induced obesity in pre-menopausal female mice

Obesity is a complex metabolic disorder that is more prevalent among women. Until now, the only relevant rodent models of diet-induced obesity were via the use of ovariectomized ("postmenopausal") females. However, recent reports suggest that the xenobiotic nuclear receptor pregnane X receptor (PXR) may contribute to obesity. Therefore, we compared the roles of mouse and human PXRs in diet-induced obesity between wild type (WT) and PXR-humanized (hPXR) transgenic female mice fed either control or high-fat diets (HFD) for 16 weeks. HFD-fed hPXR mice gained weight more rapidly than controls, exhibited hyperinsulinemia, and impaired glucose tolerance. Fundamental differences were observed between control-fed hPXR and WT females: hPXR mice possessed reduced estrogen receptor α (ERα) but enhanced uncoupling protein 1 (UCP1) protein expression in white adipose tissue (WAT); increased protein expression of the hepatic cytochrome P450 3A11 (CYP3A11) and key gluconeogenic enzymes phosphoenolpyruvate carboxykinase and glucose 6-phosphatase, and increased total cholesterol. Interestingly, HFD ingestion induced both UCP1 and glucokinase protein expression in WT mice, but inhibited these enzymes in hPXR females. Unlike WT mice, CYP3A11 protein, serum 17β-estradiol levels, and WAT ERα expression were unaffected by HFD in hPXR females. Together, these studies indicate that the hPXR gene promotes obesity and metabolic syndrome by dysregulating lipid and glucose homeostasis while inhibiting UCP1 expression. Furthermore, our studies indicate that the human PXR suppresses the protective role of estrogen in metabolic disorders. Finally, these data identify PXR-humanized mice as a promising in vivo research model for studying obesity and diabetes in women.

Brucella pinnipedialis hooded seal (Cystophora cristata) strain in the mouse model with concurrent exposure to PCB 153

Brucellosis, a worldwide zoonosis, is linked to reproductive problems in primary hosts. A high proportion of Brucella-positive hooded seals (Cystophora cristata) have been detected in the declined Northeast Atlantic stock. High concentrations of polychlorinated biphenyls (PCBs) have also been discovered in top predators in the Arctic, including the hooded seal, PCB 153 being most abundant. The aim of this study was to assess the pathogenicity of Brucella pinnipedialis hooded seal strain in the mouse model and to evaluate the outcome of Brucella spp. infection after exposure of mice to PCB 153. BALB/c mice were infected with B. pinnipedialis hooded seal strain or Brucella suis 1330, and half from each group was exposed to PCB 153 through the diet. B. pinnipedialis showed a reduced pathogenicity in the mouse model as compared to B. suis 1330. Exposure to PCB 153 affected neither the immunological parameters, nor the outcome of the infection. Altogether this indicates that it is unlikely that B. pinnipedialis contribute to the decline of hooded seals in the Northeast Atlantic.

Adipose tissue browning and metabolic health

Accumulation of excess white adipose tissue (WAT) has deleterious consequences for metabolic health. The activation of brown adipose tissue (BAT), the primary organ for heat production, confers beneficial effects on adiposity, insulin resistance and hyperlipidaemia, at least in mice. As the amount of metabolically active BAT seems to be particularly low in patients with obesity or diabetes mellitus who require immediate therapy, new avenues are needed to increase the capacity for adaptive thermogenesis. In this light, we review the findings that BAT in human adults might consist of not only classic brown adipocytes but also inducible brown adipocytes (also called beige, brown-in-white, or brite adipocytes), which are phenotypically distinct from both white and brown adipocytes. Stimulating the development of beige adipocytes in WAT (so called 'browning') might reduce adverse effects of WAT and could help to improve metabolic health. This article focuses on the development and regulatory control of beige adipocytes at the transcriptional and hormonal levels. Emerging insights into the metabolic role of beige adipocytes are also discussed, along with the developments that can be expected from these promising targets for therapy of metabolic disease in the future.

QTL analysis of dietary obesity in C57BL/6byj X 129P3/J F2 mice: diet- and sex-dependent effects

Obesity is a heritable trait caused by complex interactions between genes and environment, including diet. Gene-by-diet interactions are difficult to study in humans because the human diet is hard to control. Here, we used mice to study dietary obesity genes, by four methods. First, we bred 213 F₂ mice from strains that are susceptible [C57BL/6ByJ (B6)] or resistant [129P3/J (129)] to dietary obesity. Percent body fat was assessed after mice ate low-energy diet and again after the same mice ate high-energy diet for 8 weeks. Linkage analyses identified QTLs associated with dietary obesity. Three methods were used to filter candidate genes within the QTL regions: (a) association mapping was conducted using >40 strains; (b) differential gene expression and (c) comparison of genomic DNA sequence, using two strains closely related to the progenitor strains from Experiment 1. The QTL effects depended on whether the mice were male or female or which diet they were recently fed. After feeding a low-energy diet, percent body fat was linked to chr 7 (LOD = 3.42). After feeding a high-energy diet, percent body fat was linked to chr 9 (Obq5; LOD = 3.88), chr 12 (Obq34; LOD = 3.88), and chr 17 (LOD = 4.56). The Chr 7 and 12 QTLs were sex dependent and all QTL were diet-dependent. The combination of filtering methods highlighted seven candidate genes within the QTL locus boundaries: Crx, Dmpk, Ahr, Mrpl28, Glo1, Tubb5, and Mut. However, these filtering methods have limitations so gene identification will require alternative strategies, such as the construction of congenics with very small donor regions.

High-fat feeding rapidly induces obesity and lipid derangements in C57BL/6N mice

C57BL/6N (B6N) is becoming the standard background for genetic manipulation of the mouse genome. The B6N, whose genome is very closely related to the reference C57BL/6J genome, is versatile in a wide range of phenotyping and experimental settings and large repositories of B6N ES cells have been developed. Here, we present a series of studies showing the baseline characteristics of B6N fed a high-fat diet (HFD) for up to 12 weeks. We show that HFD-fed B6N mice show increased weight gain, fat mass, and hypercholesterolemia compared to control diet-fed mice. In addition, HFD-fed B6N mice display a rapid onset of lipid accumulation in the liver with both macro- and microvacuolation, which became more severe with increasing duration of HFD. Our results suggest that the B6N mouse strain is a versatile background for studying diet-induced metabolic syndrome and may also represent a model for early nonalcoholic fatty liver disease.

Impact of T1r3 and Trpm5 on carbohydrate preference and acceptance in C57BL/6 mice

Knockout (KO) mice missing the sweet taste receptor subunit T1r3 or the signaling protein Trpm5 have greatly attenuated sweetener preferences but learn to prefer sucrose in 24-h tests. Here, we examined 24-h preferences of T1r3 KO, Trpm5 KO, and C57BL/6J wild-type (WT) mice for glucose, fructose, galactose, and corn starch. Unlike glucose, fructose has little postoral reward effect in WT mice, whereas conflicting data have been obtained with galactose. Naïve KO mice were initially indifferent to dilute glucose solutions (0.5-4%) but exhibited strong preferences for 8-32% concentrations. In a second test, they strongly preferred (~90%) all glucose concentrations although they drank less sugar than WT mice. Naïve KO mice were indifferent to 0.5-8% fructose and avoided 16-32% fructose. However, the glucose-experienced KO mice displayed significant preferences for all fructose solutions. Naïve KO mice preferred only 8% galactose, whereas WT mice preferred 4-16% galactose, and all mice avoided 32% galactose. Galactose experience enhanced the preference for this sugar in KO and WT mice. Naïve T1r3 KO and WT mice displayed similar preferences for 0.5-32% corn starch, which were enhanced by starch experience. Naïve Trpm5 KO mice did not prefer starch but did so after 1-bottle starch experience. The results confirm the sweet taste deficits of T1r3 KO and Trpm5 KO mice but demonstrate their ability to develop strong glucose and milder galactose preferences attributed to the postoral actions of these sugars. The acquired preference for the non-sweet flavor properties of glucose generalized to those of fructose. The findings further demonstrate that although Trpm5 (but not T1r3) signaling is essential for starch preference, Trpm5 KO mice can learn to prefer starch based on its postoral effects.

Automated video analysis system reveals distinct diurnal behaviors in C57BL/6 and C3H/HeN mice

Advances in rodent behavior dissection using automated video recording and analysis allows detailed phenotyping. This study compared and contrasted 15 diurnal behaviors recorded continuously using an automated behavioral analysis system for a period of 14 days under a 14/10 light/dark cycle in single housed C3H/HeN (C3H) or C57BL/6 (C57) male mice. Diurnal behaviors, recorded with minimal experimental interference and analyzed using phenotypic array and temporal distribution analysis showed bimodal and unimodal profiles in the C57 and C3H mice, respectively. Phenotypic array analysis revealed distinct behavioral rhythms in Activity-Like Behaviors (i.e. walk, hang, jump, come down) (ALB), Exploration-Like Behaviors (i.e. dig, groom, rear up, sniff, stretch) (ELB), Ingestion-Like Behaviors (i.e. drink, eat) (ILB) and Resting-Like Behaviors (i.e. awake, remain low, rest, twitch) (RLB) of C3H and C57 mice. Temporal distribution analysis demonstrated that strain and time of day affects the magnitude and distribution of the spontaneous homecage behaviors. Wheel running activity, water and food measurements correlated with timing of homecage behaviors. Subcutaneous (3 mg/kg, sc) or oral (0.02 mg/ml, oral) melatonin treatments in C57 mice did not modify either the total 24 h magnitude or temporal distribution of homecage behaviors when compared with vehicle treatments. We conclude that C3H and C57 mice show different spontaneous activity and behavioral rhythms specifically during the night period which are not modulated by melatonin.

Angiotensin AT(2) receptor contributes towards gender bias in weight gain

Obesity is a major disease condition, in turn leading to pathological changes collectively recognized as metabolic syndrome. Recently angiotensin receptor AT(2)R has been associated negatively with body weight (BW) gain in male mice. However, the gender differences in AT(2)R and BW changes have not been studied. To understand the gender based role of AT(2)R involving BW changes, we fed male and female wild type (WT) and AT(2)R knock out (AT(2)KO) mice with C57BL6 background with high fat diet (HFD) for 16 weeks. The male AT(2)KO had higher HFD calorie intake (WT: 1280±80; AT(2)KO:1680±80 kcal) but gained less BW compared with the WT (WT: 13; AT(2)KO: 6 g). Contrary to the male animals, the female AT(2)KO mice with equivalent caloric intake (WT: 1424±48; AT(2)KO:1456±80 kcal) gained significantly more BW than the WT mice (WT: 9 g; AT(2)KO: 15 g). The male AT(2)KO on HFD displayed lower plasma insulin level, less impaired glucose tolerance (GT), and higher plasma T3 compared with WT males on HFD; whereas the female AT(2)KO mice on HFD showed elevated levels of plasma insulin, more impaired GT, lower plasma T3 and higher free fatty acid and hepatic triglycerides compared with WT females on HFD. Interestingly, compared with WT, AT(2)KO female mice had significantly lower estrogen, which was further reduced by HFD. These results suggest that AT(2)R in female mice via potentially regulating estrogen may have protective role against BW gain and impaired glucose tolerance and lipid metabolism.

The use of animal models in diabetes research

Diabetes is a disease characterized by a relative or absolute lack of insulin, leading to hyperglycaemia. There are two main types of diabetes: type 1 diabetes and type 2 diabetes. Type 1 diabetes is due to an autoimmune destruction of the insulin-producing pancreatic beta cells, and type 2 diabetes is caused by insulin resistance coupled by a failure of the beta cell to compensate. Animal models for type 1 diabetes range from animals with spontaneously developing autoimmune diabetes to chemical ablation of the pancreatic beta cells. Type 2 diabetes is modelled in both obese and non-obese animal models with varying degrees of insulin resistance and beta cell failure. This review outlines some of the models currently used in diabetes research. In addition, the use of transgenic and knock-out mouse models is discussed. Ideally, more than one animal model should be used to represent the diversity seen in human diabetic patients.

Autophagy in adipose tissue biology

Obesity, which predisposes individuals to type II diabetes and cardiovascular diseases, results from accumulation of white adipose tissue (WAT). WAT comprises mainly white adipocytes that have a unique cellular structure in which almost the entire intracellular space is occupied by one single lipid droplet. The cytoplasm envelopes this lipid droplet and occupies negligible space. Differentiation of WAT, or adipogenesis, requires dramatic cytoplasmic reorganization, including a dynamic change in mitochondrial mass. Autophagy is a major cytoplasmic degradation pathway and a primary pathway for mitochondrial degradation. Recent studies indicate that autophagy is implicated in adipogenesis. In this review, we summarize our current knowledge on autophagy in adipose tissue biology, with the emphasis on its role in mitochondrial degradation. Adipose tissue is a central component for whole-body energy homeostasis regulation. Advancement in this research area may provide novel venues for the intervention of obesity and obesity related diseases.

Differences in triglyceride and cholesterol metabolism and resistance to obesity in male and female vitamin D receptor knockout mice

A lean phenotype has been detected in vitamin D receptor (VDR) knockout mice; however, the gender differences in fat metabolism between male and female mice both with age and in response to a high-fat diet have not been studied before. The objective of our study was to assess changes in body and fat tissue weight, food intake and serum cholesterol and triglyceride in VDR knockout mice from weaning to adulthood and after a challenge of adult animals with a high-fat diet. Although VDR knockout mice of both sexes consumed more food than wild-type and heterozygous littermates, their body weight and the weight of fat depots was lower after 6 months on a diet with 5% crude fat content. When adult animals were challenged with a high-fat diet containing 21% crude fat content for 8 weeks, VDR knockout mice of both sexes had a significantly higher food intake but gained less weight than their wild-type littermates. Cholesterol levels were higher after 2 days on the high-fat diet in both sexes, but in the VDR knockout mice, less cholesterol was detected in the serum after 8 weeks. Wild-type male mice showed signs of fatty liver disease at the end of the experiment, which was not detected in the other groups. In conclusion, lack of the VDR receptor results in reduced fat accumulation with age and when adult mice are fed a high-fat diet, despite a higher food intake of VDR knockout mice relative to their wild-type littermates. These effects can be detected in both sexes. Wild-type male mice react with the highest weight gain and cholesterol levels of all groups and develop fatty liver disease after 8 weeks on a high-fat diet, while male VDR knockout mice appear to be protected.

Age-related increase in food spilling by laboratory mice may lead to significant overestimation of actual food consumption: implications for studies on dietary restriction, metabolism, and dose calculations

It is widely accepted that food consumption in humans declines with advanced age; however, data from mice remain controversial. Based on our previous observation that mice spill a considerable amount of food while eating, we hypothesized that increased food spillage in old mice masks actual food intake. To investigate whether mice exhibit age-associated declines in food consumption, we evaluated the actual food consumption of C57BL/6 mice at various ages by measuring both the amount of food in the food receptacle and the amount dropped to the cage bottom during feeding. We found that old mice dropped significantly more food (36% ± 8%) than young mice (18% ± 5%), which led to overestimations of food consumption, particularly in old mice. Although actual food consumption decreased in very old mice, food intake per body weight did not significantly change. These findings suggest that caution should be taken to accurately quantify food consumption by aged animals.