Involvement of sex, strain and age factors in high fat diet-induced obesity in C57BL/6J and BALB/cA mice.

Although a number of obesity animal models have been reported, each model possesses different characteristics of obesity, suggesting care should be taken in choosing an animal model suitable for the experimental purpose. In this report, we fed 4-(young) and 52-week-old (middle-aged) C57BL/6J (B6) and young BALB/cA (BALB/c) mice with a high fat diet (HFD) for 9 weeks, and investigated the clinical and histological characteristics of obesity. In BALB/c mice, males gained more body weight and body fat weight and had higher energy intake than females by HFD feeding. Comparing the effect of HFD feeding between the strains of mice, BALB/c male mice accumulated more hepatic lipid than B6 male mice. In addition, middle-aged B6 mice increased the ratio of fat to body weight and hepatic lipid accumulation more than young mice. In conclusion, the characteristics of obesity induced by HFD feeding were influenced by the sex, strain and age of mice. Sex steroid hormones, hepatic lipid metabolism and systemic metabolism might be involved in these factors. The basic data in this study will be useful for the development of animal models of high fat diet-induced obesity.     

Genetic basis of murine antibacterial defense to streptococcal lung infection

To evaluate the effect of genetic background on antibacterial defense to streptococcal infection, eight genetically diverse strains of mice (A/J, DBA/2J, CAST/Ei, FVB/NJ, BALB/cJ, C57BL/6J, 129/SvImJ, and C3H/HeJ) and tlr2-deficient mice (C57BL/6^tlr2−/−) were infected with three doses of Streptococcus zooepidemicus (500, 5,000, or 50,000 colony-forming units) by alveolar challenge. There was a range of susceptibility between the strains at each dose and time point (6, 24, and 96 h). At the lowest dose, the 129/SvImJ and C3H/HeJ strains had significantly higher bacterial counts at all time points after infection, when compared to A/J, DBA/2J, CAST/Ei, FVB/NJ, which were resistant to infection at the low dose of innoculum. At the medium dose, 129/SvImJ and C3H/HeJ had higher bacterial counts, while A/J, DBA/2J, and BALB/cJ showed reduced streptococcal growth. After the highest dose of Streptococcus, there were minimal differences between strains, suggesting the protective impact of modifier genes can be overcome. TLR2-deficient animals contained increased bacterial load with reduced cytokines after 96 h when compared to C57BL/6J controls suggesting a role of innate immunity in late antibacterial defense. Overall, we identify vulnerable (129/SvlmJ and C3H/HeJ) and resistant (A/J, FVB, and DBA) mouse strains to streptococcal lung infection, which demonstrate divergent genetic expression profiles. These results demonstrate that innate differences in pulmonary host defense to S. zooepidemicus are dependent on host genetic factors.     

Genetic differences in leverpress escape/avoidance conditioning in seven mouse strains

Studies of inbred mouse strains can provide us with important information about the genetic basis of learning and memory. The present experiment studies the acquisition of a leverpress escape/avoidance task in six commonly studied inbred mouse strains (C57BL/6NCrlBR, DBA/2NCrlBR, C3H/HeJ, FVB/NJ, BALB/cByJ and 129S6/SvEvTac), and one outbred strain, the CD1. Results indicated that the strains formed three discrete performance clusters. The C57BL/6NCrlBR, C3HeB/FeJ, BALB/cByJ, and CD1 strains acquired the avoidance response comparably to Sprague-Dawley rats, avoiding approximately 40% of shocks by the fourth and final training session. The 129S6/SvEvTac and FVB/NJ were extremely poor at the avoidance task throughout training. The FVB/NJ strain remained in an escape mode, while the 129S6/SvEvTac animals performed few responses of any type. Finally, the DBA/2NCrlBR strain performed exceptionally well, avoiding over 90% of the shocks by the final session. Results are discussed in terms of genetic differences in learning and how the nigrostriatal dopamine system may mediate the observed differences.     

Regulation of glucose homeostasis and insulin action by ceramide acyl-chain length: A beneficial role for very long-chain sphingolipid species

In a recent study, we showed that in response to high fat feeding C57BL/6, 129X1, DBA/2 and FVB/N mice all developed glucose intolerance, while BALB/c mice displayed minimal deterioration in glucose tolerance and insulin action. Lipidomic analysis of livers across these five strains has revealed marked strain-specific differences in ceramide (Cer) and sphingomyelin (SM) species with high-fat feeding; with increases in C16-C22 (long-chain) and reductions in C > 22 (very long-chain) Cer and SM species observed in the four strains that developed HFD-induced glucose intolerance. Intriguingly, the opposite pattern was observed in sphingolipid species in BALB/c mice. These strain-specific changes in sphingolipid acylation closely correlated with ceramide synthase 2 (CerS2) protein content and activity, with reduced CerS2 levels/activity observed in glucose intolerant strains and increased content in BALB/c mice. Overexpression of CerS2 in primary mouse hepatocytes induced a specific elevation in very long-chain Cer, but despite the overall increase in ceramide abundance, there was a substantial improvement in insulin signal transduction, as well as decreased ER stress and gluconeogenic markers. Overall our findings suggest that very long-chain sphingolipid species exhibit a protective role against the development of glucose intolerance and hepatic insulin resistance.     

C57BL/6JRj mice are protected against diet induced obesity (DIO)

The C57BL/6 (B6) is one of the oldest inbred mouse strains. It has been widely used as control strain in metabolism research for many decades. Preliminary data from our lab indicated that C57BL/6JRj mice are not responding to diet induced obesity. Therefore, the aim of this study was to compare the two different B6 substrains, C57BL/6NTac and C57BL/6JRj, in regard to their response to diet induced obesity (DIO) and to investigate genetic differences which may explain such phenotypic differences. Sixteen male mice of C57BL/6NTac and C57BL/6JRj were fed a high fat diet (HFD) or standard chow diet (SD) for 10 weeks. Phenotypic characterization included measurements of bodyweight, physical activity, food intake and relative epigonadal fat mass. Genetic differences between both substrains were analyzed using a panel of 1449 single nucleotide polymorphism (SNP) markers. Our study revealed that C57BL/6JRj mice are protected against DIO independently from food intake and physical activity. Genetic SNP analysis among C57BL/6 mice identified genetic differences in at least 11 SNPs. Our data strongly support the importance of attention on the genetic background in obesity research.     

Cyclophosphamide-Induced IN VIVO Sister Chromatid Exchanges (Sce) in MUS MUSCULUS. III. Quantitative Genetic Analysis

In vivo cyclophosphamide (CP)-induced sister chromatid exchanges (SCEs) were evaluated in females from five genetic strains of mice (C57BL/6J, C3H/S, 129/ReJ, BALB/c and DBA/2) and their F₁ hybrids. Baseline (noninduced) SCE values differ significantly among strains, 129/ReJ having the lowest and DBA/2 having the highest mean SCE per cell values. In general, the baseline SCE of a given F₁ is within the range of its corresponding parental strains or near the lower parental value. Furthermore, there is a genotype-dependent increase in mean SCEs per cell with CP dose. Strain differences in SCE induction are noted particularly at the two higher CP doses (4.50 and 45.0 mg/kg). In general, F₁ hybrids involving a strain with high induced SCEs and a strain with low induced SCEs exhibit mean SCE values that are closer to the value of the lower strain. F₁ s involving two strains with high SCEs or two strains with low SCEs yield SCEs not different from parental strains. The method of diallel cross analysis showed the order of dominance of these strains in SCE induction to be 129/ReJ BALB/c C3H/S DBA/2 C57BL/6J. These results support the involvement of predominantly nonadditive genetic factors as major gene(s) in SCE induction. In addition, involvement of random and independent events in SCE induction is suggested by the distribution of SCEs which follows a Poisson distribution.     

Bacillary growth, interleukin 2 production defect, and specific antibody secretion governed by different genetical factors in mice infected subcutaneously with Mycobacterium lepraemurium

Different mouse strains were infected subcutaneously in the footpad with 10(7) Mycobacterium lepraemurium (MLM). At various stages of the infection, the number of acid-fast bacilli (AFB) in different organs, spleen cell interleukin 2 production, and specific IgM and IgG serum antibodies to MLM sonicate were assessed. Strains were separable into two distinct groups depending on the number of AFB recovered from the different organs, without any obvious influence of the Bcg gene. Thus C57BL/6, DBA/2, (C57BL/6 X DBA/2)F1 and C3H/Pas mice belonged to the high resistance group and DBA/1, BALB/c, and CBA strains to the low resistance group. Interleukin 2 production was depressed only in C57BL/6 and C3H/Pas mice. Anti-MLM antibody response also markedly varied according to strains, in terms of antibody titers, Ig class distribution, and species specificity, but with a different genetic pattern from that observed for MLM growth control.     

Macronutrient diet selection in thirteen mouse strains

The strain distribution for macronutrient diet selection was described in 13 mouse strains (AKR/J, NZB/B1NJ, C57BL/6J, C57BL/6ByJ, DBA/2J, SPRET/Ei, CD-1, SJL/J, SWR/J, 129/J, BALB/cByJ, CAST/Ei, and A/J) with the use of a self-selection protocol in which separate carbohydrate, fat, and protein diets were simultaneously available for 26-30 days. Relative to carbohydrate, nine strains consumed significantly more calories from the fat diet; two strains consumed more calories from carbohydrate than from fat (BALB/cByJ, CAST/Ei). Diet selection by SWR/J mice was variable over time, resulting in a lack of preference. One strain (A/J) failed to adapt to the diet paradigm due to inadequate protein intake. Comparisons of proportional fat intake across strains revealed that fat selection/consumption ranged from 26 to 83% of total energy. AKR/J, NZB/B1NJ, and C67BL/6J mice self-selected the highest proportion of dietary fat, whereas the CAST/Ei and BALB/cByJ strains chose the lowest. Finally, epididymal fat depot weight was correlated with fat consumption. There were significant positive correlations in AKR/J and C57BL/6J mice, which are highly sensitive to dietary obesity. However, absolute fat intake was inversely correlated with epididymal fat in two of the lean strains: SWR/J and CAST/Ei. We hypothesize that the SWR/J and CAST/Ei strains are highly sensitive to a negative feedback signal generated by increasing body fat, but the AKR/J and C67BL/6J mice are not. The variation in dietary fat selection across inbred strains provides a tool for dissecting the complex genetics of this trait.     

Mice with MCH ablation resist diet-induced obesity through strain-specific mechanisms

Genetics and environment contribute to the development of obesity, in both humans and rodents. However, the potential interaction between genes important in energy balance, strain background, and dietary environment has been only minimally explored. We investigated the effects of genetic ablation of melanin-concentrating hormone (MCH), a neuropeptide with a key role in energy balance, with chow and a high-fat diet (HFD) in two different mouse strains, one obesity-prone (C57BL/6) and the other obesity-resistant (129). Substantial differences were seen in wild-type (WT) animals of different strains. 129 animals had significantly lower levels of spontaneous locomotor activity than C57BL/6; however, 129 mice gained less weight on both chow and HFD. In both strains, deletion of MCH led to attenuated weight gain compared with WT counterparts, an effect secondary to increased energy expenditure. In both strains, feeding a HFD led to further increases in energy expenditure in both WT and MCH-KO mice; however, this increase was more pronounced in 129 mice. In addition, mice lacking MCH have a phenotype of increased locomotor activity, an effect also seen in both strains. The relative increase in activity in MCH(-/-) mice is modest in animals fed chow but increases substantially when animals are placed on HFD. These studies reinforce the important role of MCH in energy homeostasis and indicate that MCH is a plausible target for antiobesity therapy.     

Targeted proteomics reveals strain‐specific changes in the mouse insulin and central metabolic pathways after a sustained high‐fat diet

The metabolic syndrome is a collection of risk factors including obesity, insulin resistance and hepatic steatosis, which occur together and increase the risk of diseases such as diabetes, cardiovascular disease and cancer. In spite of intense research, the complex etiology of insulin resistance and its association with the accumulation of triacylglycerides in the liver and with hepatic steatosis remains not completely understood. Here, we performed quantitative measurements of 144 proteins involved in the insulin‐signaling pathway and central metabolism in liver homogenates of two genetically well‐defined mouse strains C57BL/6J and 129Sv that were subjected to a sustained high‐fat diet. We used targeted mass spectrometry by selected reaction monitoring (SRM) to generate accurate and reproducible quantitation of the targeted proteins across 36 different samples (12 conditions and 3 biological replicates), generating one of the largest quantitative targeted proteomics data sets in mammalian tissues. Our results revealed rapid response to high‐fat diet that diverged early in the feeding regimen, and evidenced a response to high‐fat diet dominated by the activation of peroxisomal β‐oxidation in C57BL/6J and by lipogenesis in 129Sv mice.     

NaCl taste thresholds in 13 inbred mouse strains

Molecular mechanisms of salty taste in mammals are not completely understood. We use genetic approaches to study these mechanisms. Previously, we developed a high-throughput procedure to measure NaCl taste thresholds, which involves conditioning mice to avoid LiCl and then examining avoidance of NaCl solutions presented in 48-h 2-bottle preference tests. Using this procedure, we measured NaCl taste thresholds of mice from 13 genealogically divergent inbred stains: 129P3/J, A/J, BALB/cByJ, C3H/HeJ, C57BL/6ByJ, C57BL/6J, CBA/J, CE/J, DBA/2J, FVB/NJ, NZB/BlNJ, PWK/PhJ, and SJL/J. We found substantial strain variation in NaCl taste thresholds: mice from the A/J and 129P3/J strains had high thresholds (were less sensitive), whereas mice from the BALB/cByJ, C57BL/6J, C57BL/6ByJ, CE/J, DBA/2J, NZB/BINJ, and SJL/J had low thresholds (were more sensitive). NaCl taste thresholds measured in this study did not significantly correlate with NaCl preferences or amiloride sensitivity of chorda tympani nerve responses to NaCl determined in the same strains in other studies. To examine whether strain differences in NaCl taste thresholds could have been affected by variation in learning ability or sensitivity to toxic effects of LiCl, we used the same method to measure citric acid taste thresholds in 4 inbred strains with large differences in NaCl taste thresholds but similar acid sensitivity in preference tests (129P3/J, A/J, C57BL/6J, and DBA/2J). Citric acid taste thresholds were similar in these 4 strains. This suggests that our technique measures taste quality-specific thresholds that are likely to represent differences in peripheral taste responsiveness. The strain differences in NaCl taste sensitivity found in this study provide a basis for genetic analysis of this phenotype.     

Variations in the behaviors to novel objects among five inbred strains of mice

Novelty stimuli cause various behavioral responses, such as exploration and avoidance, and contextual variables may contribute to the behavioral outputs. Here, we tried to compare the behavioral responses to novel objects of five inbred strains of mice (C57BL/6J, 129/svJae, C3H/HeJ, BALB/cJ and DBA/2J) by using a modified novel object test where a small light-weight cube wrapped with paper was presented to mice in a home cage without beddings. In response to these objects, the C57BL/6J, 129/svJae and C3H/HeJ mice showed mild exploratory behaviors, such as approaching, sniffing or brief contact. In striking contrast, the BALB/cJ and DBA/2J mice, which have been known to show high avoidance/low exploration in other behavioral paradigms, exhibited play-like secondary reactions toward the objects after initial primary exploratory behaviors. Specifically, DBA/2J mice would move the object around in the cage, holding it with their mouths, and BALB/cJ mice would gnaw the object, eventually stripping off the wrapping paper. Such behaviors decreased when similar objects were presented repeatedly. The present results suggest that active manipulations of novel objects may be a relevant parameter for measuring novelty-induced behaviors in mice and appear to be strongly influenced by genetic factors.     

Genetic differences in BCG-induced resistance to Schistosoma mansoni are not controlled by genes within the major histocompatibility complex of the mouse.

Induction of nonspecific resistance to Schistosoma mansoni infection after the i.v. injection of viable BCG was investigated in outbred mice and a panel of inbred and H-2 congenic strains. Significant protection was induced in CF1, A/J, C57BL/6, C57BL/10, DBA/2, C57BR, and SJL mice. BALB/c mice were not protected whereas CBA and C3H mice expressed intermediate degrees of protection. Expression of the protective phenomenon is not controlled by genes within the MHC as shown by the marked differences in response between BALB/c and DBA/2 (H-2d) as well as between C57BR and C3H (H-2k) mice. H-2 congenic strains with C57BL/10 background (B10.A and B10.D2) were high responders. BALB.B10 mice carrying the high responder (B10) MHC on the nonresponder (BALB/c) background were not protected. The degree of splenic hypertrophy did not correlate with the expression of nonspecific resistance. These results demonstrate that, in addition to controlling specific immune responses, genetic differences influence the nonspecific protective phenomena related to BCG administration as well.     

Genetic control of ATGL-mediated lipolysis modulates adipose triglyceride stores in leptin-deficient mice

Dissecting the genetics of complex traits such as obesity allows the identification of causal genes for disease. Here, we show that the BALB/c mouse strain carries genetic variants that confer resistance to obesity induced by leptin-deficiency or a high-fat diet (HFD). We set out to identify the physiological and genetic bases underlying this phenotype. When compared with C57BL6/J ob/ob mice (B6), BALB/c ob/ob mice exhibited decreased food intake, increased thermogenic capacity, and improved fat catabolism, each of which can potentially modify obesity. Interestingly, analysis of F1 ob/ob (progeny of B6 ob/+ × BALB/c ob+) mice revealed that obesity resistance in BALB/c ob/ob mice principally relied upon improved fat mobilization. This was mechanistically explained by increased adipose triglyceride lipase (ATGL) content in adipocytes, along with increased lipolysis and fatty acid oxidation. We conducted a genome-wide scan and defined a quantitative trait locus (QTL) on chromosome 2. BALB/c alleles on chromosome 2 not only associated with the obesity resistance phenotype but also supported increased ATGL content in adipose tissue. In summary, our study provides evidence that leptin-independent control of adipocyte lipolysis rates directly modifies the balance of macronutrient handling and is sufficient to regulate fat mass in the absence of alterations in food intake and energy expenditure.-Marcelin, G., S-M. Liu, X. Li, G. J. Schwartz, and S. Chua.     

Genetic analysis of intestinal cholesterol absorption in inbred mice.

A genetic mapping strategy was employed to identify chromosomal regions harboring genes that influence the absorption of intestinal cholesterol in the mouse. Analysis of seven inbred strains of male mice (129P3, AKR, BALB/c, C3H/He, C57BL/6, DBA/2, and SJL, all from Jackson Laboratories) revealed substantial differences in their abilities to absorb a bolus of cholesterol delivered by gavage. Crosses between high (AKR, 129) and low (DBA/2, SJL) absorbing strains revealed evidence for the presence of dominant genes that increase and decrease cholesterol absorption. Backcrosses between F1 offspring and parental strains (DBA/2xAKD2F1 and 129xSJL129F1) followed by linkage analyses revealed four quantitative trait loci that influenced cholesterol absorption. Analyses of recombinant inbred strains identified an additional three loci affecting this phenotype. These seven quantitative trait loci, which map to different chromosomes and are termed Cholesterol absorption 1-7 (Chab1-7) loci, together influence the absorption of intestinal cholesterol in mice and are likely to be involved in different steps of this complex pathway.     

C57BL/6J and A/J mice fed a high-fat diet delineate components of metabolic syndrome

Objective: The aim of this study was to assess the suitability of A/J and C57BL/6J mice of both sexes as models of some components of the human metabolic syndrome (MetS) under nutritional conditions more comparable with the actual worldwide diet responsible for the increased incidence of the MetS. Research Methods: We fed large cohorts (n = 515) of two strains of mice, A/J and the C57BL/6J, and of both sexes a high‐fat diet (HFD; 60% fat) that, in contrast with most previous reports using saturated fats, was enriched in mono‐ and polyunsaturated fatty acids, thus more closely mimicking most Western diets, or a control diet (10% fat), for 20 weeks. Results: In sharp contrast to previous reports, weight gain and hyperleptinemia were similar in both strains and sexes. Hyperinsulinemia, glucose tolerance, insulin resistance, and hypercholesterolemia were observed, although with important differences between strains and sexes. A/J males displayed severely impaired glucose tolerance and insulin resistance. However, in contrast with C57BL6/J mice, which displayed overt type 2 diabetes, A/J mice of both sexes remained normoglycemic. Discussion: With important differences in magnitude and time course, the phenotypic and metabolic characteristics of both strains and both sexes on this HFD demonstrate that these models are very useful for identifying the mechanisms underlying progression or resistance to subsequent type 2 diabetes.     

Obesity‐Induced Diabetes in Mouse Strains Treated With Gold Thioglucose: A Novel Animal Model for Studying β‐Cell Dysfunction

An obesity‐induced diabetes model using genetically normal mouse strains would be invaluable but remains to be established. One reason is that several normal mouse strains are resistant to high‐fat diet‐induced obesity. In the present study, we show the effectiveness of gold thioglucose (GTG) in inducing hyperphagia and severe obesity in mice, and demonstrate the development of obesity‐induced diabetes in genetically normal mouse strains. GTG treated DBA/2, C57BLKs, and BDF1 mice gained weight rapidly and exhibited significant increases in nonfasting plasma glucose levels 8–12 weeks after GTG treatment. These mice showed significantly impaired insulin secretion, particularly in the early phase after glucose load, and reduced insulin content in pancreatic islets. Interestingly, GTG treated C57BL/6 mice did not become diabetic and retained normal early insulin secretion and islet insulin content despite being as severely obese and insulin resistant as the other mice. These results suggest that the pathogenesis of obesity‐induced diabetes in GTG‐treated mice is attributable to the inability of their pancreatic β‐cells to secrete enough insulin to compensate for insulin resistance. Mice developing obesity‐induced diabetes after GTG treatment might be a valuable tool for investigating obesity‐induced diabetes. Furthermore, comparing the genetic backgrounds of mice with different susceptibilities to diabetes may lead to the identification of novel genetic factors influencing the ability of pancreatic β‐cells to secrete insulin.     

Strain distribution pattern of susceptibility to immune-mediated nephritis

The genetic basis of immune-mediated nephritis is poorly understood. Recent studies have demonstrated that the NZW mouse strain is more prone to immune-mediated nephritis compared with C57BL/6 and BALB/c strains. The present study extends these findings by challenging 12 additional inbred strains of mice with rabbit anti-mouse glomerular basement membrane (GBM) reactive sera. Compared with control sera-injected mice and anti-GBM-injected A/J, AKR/J, C3H/HeJ, DBA/2J, MRL/MpJ, NOD/LtJ, P/J, SJL/J, and SWR/J mice, the anti-GBM-injected BUB/BnJ, DBA/1J, and 129/svJ mice developed severe proteinuria and azotemia. Their kidneys exhibited pronounced glomerulonephritis, with crescent formation, as well as tubulointerstitial disease, with these phenotypes being particularly profound in 129/svJ mice. However, these strains did not appear to differ in the nature of their xenogeneic immune response to the administered rabbit sera, either quantitatively or qualitatively. Collectively, these findings allude to the presence of genetic elements in the BUB/BnJ, DBA/1J, and 129/svJ genomes that may potentially confer susceptibility to immune-mediated nephritis. Detailed studies to dissect out the immunological and genetic basis of renal disease in these three strains are clearly warranted.     

Behavioral differences among fourteen inbred mouse strains commonly used as disease models

We compared the behavior of 14 inbred mouse strains and an F1 hybrid commonly used in transgenic and knockout production. These strains were 129P3/J, 129S1/SvImJ, 129S6/SvEvTac, 129T2/SvEmsJ, 129X1/SvJ (formerly 129/J, 129/Sv-p+Tyr+Kitl+/J, 129/SvEvTac, 129SvEmsJ, and 129/SvJ, respectively), A/JCrTac, BALB/cAnNTac, C3H/HeNTac, C57BL/6J, C57BL/6NTac, DBA/2NTac, FVB/NTac, NOD/MrkTac, SJL/JCrNTac, and the hybrid B6129S6F1Tac. Performance in three behavioral tests (rotorod, open-field activity-habituation, and contextual and cued fear conditioning) was determined. On the rotorod assay, SJL/JCrNTac mice had the shortest latencies to fall on the first day of testing, and DBA/2NTac mice showed impaired motor learning. Open-field behavior was analyzed using the parameters total distance, center distance, velocity, and vertical activity. 129T2/EvEmsJ and A/JCrTac were least active in the open field, whereas NOD/MrkTac mice were most active. Contrary to earlier studies, we found that all strains habituated to the open field in at least one of these parameters. In contextual and cued fear conditioning, all strains displayed activity suppression. However, FVB/NTac mice reacted less strongly to both context and cue than did most of the other strains. There were no significant behavioral differences between C57BL/6J and C57BL/6NTac, except for higher open-field activity in C57BL/6J female mice. These findings illustrate the importance of the appropriate selection of background strain for transgenic, gene targeting, or drug research.