Obesity Quantitative Trait Locus Research Articles

Allograft inflammatory factor-1-like is a situational regulator of leptin levels, hyperphagia, and obesity

SummaryMouse models enable the study of genetic factors affecting the complex pathophysiology of metabolic disorders. Here, we identify reductions in leptin levels, food intake, and obesity due to high-fat diet, accompanied by increased leptin sensitivity, in mice that harbor the E2a-Cre transgene within Obrq2, an obesity quantitative trait locus (QTL) that includes the leptin gene. Interestingly, loss of allograft inflammatory factor-1-like (AIF1L) protein in these transgenic mice leads to similar leptin sensitivity, yet marked reversal of the obesity phenotype, with accelerated weight gain and increased food intake. Transgenic mice lacking AIF1L also have low circulating leptin, which suggests that benefits of enhanced leptin sensitivity are lost with further impairment of leptin expression due to loss of AIF1L. Together, our results identify AIF1L as a genetic modifier of Obrq2 and leptin that affects leptin levels, food intake, and obesity during the metabolic stress imposed by HFD.

A collective diabetes cross in combination with a computational framework to dissect the genetics of human obesity and Type 2 diabetes.

To explore the genetic determinants of obesity and Type 2 diabetes (T2D), the German Center for Diabetes Research (DZD) conducted crossbreedings of the obese and diabetes-prone New Zealand Obese mouse strain with four different lean strains (B6, DBA, C3H, 129P2) that vary in their susceptibility to develop T2D. Genome-wide linkage analyses localized more than 290 quantitative trait loci (QTL) for obesity, 190 QTL for diabetes-related traits and 100 QTL for plasma metabolites in the outcross populations. A computational framework was developed that allowed to refine critical regions and to nominate a small number of candidate genes by integrating reciprocal haplotype mapping and transcriptome data. The efficiency of the complex procedure was demonstrated for one obesity QTL. The genomic interval of 35 Mb with 502 annotated candidate genes was narrowed down to six candidates. Accordingly, congenic mice retained the obesity phenotype owing to an interval that contains three of the six candidate genes. Among these the phospholipase PLA2G4A exhibited an elevated expression in adipose tissue of obese human subjects and is therefore a critical regulator of the obesity locus. Together, our broad and complex approach demonstrates that combined- and comparative-cross analysis exhibits improved mapping resolution and represents a valid tool for the identification of disease genes.

Increased Ifi202b/IFI16 expression stimulates adipogenesis in mice and humans

Aims/hypothesisObesity results from a constant and complex interplay between environmental stimuli and predisposing genes. Recently, we identified the IFN-activated gene Ifi202b as the most likely gene responsible for the obesity quantitative trait locus Nob3 (New Zealand Obese [NZO] obesity 3). The aim of this study was to evaluate the effects of Ifi202b on body weight and adipose tissue biology, and to clarify the functional role of its human orthologue IFI16.MethodsThe impact of Ifi202b and its human orthologue IFI16 on adipogenesis was investigated by modulating their respective expression in murine 3T3-L1 and human Simpson-Golabi-Behmel syndrome (SGBS) pre-adipocytes. Furthermore, transgenic mice overexpressing IFI202b were generated and characterised with respect to metabolic traits. In humans, expression levels of IFI16 in adipose tissue were correlated with several variables of adipocyte function.ResultsIn mice, IFI202b overexpression caused obesity (Δ body weight at the age of 30 weeks: 10.2 ± 1.9 g vs wild-type mice) marked by hypertrophic fat mass expansion, increased expression of Zfp423 (encoding the transcription factor zinc finger protein [ZFP] 423) and white-selective genes (Tcf21, Tle3), and decreased expression of thermogenic genes (e.g. Cidea, Ucp1). Compared with their wild-type littermates, Ifi202b transgenic mice displayed lower body temperature, hepatosteatosis and systemic insulin resistance. Suppression of IFI202b/IFI16 in pre-adipocytes impaired adipocyte differentiation and triacylglycerol storage. Humans with high levels of IFI16 exhibited larger adipocytes, an enhanced inflammatory state and impaired insulin-stimulated glucose uptake in white adipose tissue.Conclusions/interpretationOur findings reveal novel functions of Ifi202b and IFI16, demonstrating their role as obesity genes. These genes promote white adipogenesis and fat storage, thereby facilitating the development of obesity-associated insulin resistance.

Characterization Of Expression Levels Of Genes Involved In Adipogenesis And Inflammation In Congenic Mice Carrying Obesity and Hyperlipidemia QTL on Chromosome 1

Obesity is an international health crisis and is considered the leading cause of preventable death. The development of obesity is likely due to interactions of susceptibility genes with obesity‐promoting environments such as high fat diets (HFD). These interactions lead to an expansion of adipose tissue, through an increase in adipocyte size and/or number. Adipose tissue inflammation is a well‐recognized characteristic of obesity. Previously, we identified quantitative trait loci (QTL) linked to obesity and hyperlipidemia on mouse chromosome (Chr) 1 in an intercross of obese and diabetic TALLYHO/Jng (TH) mice with C57BL/6 (B6) mice. Subsequently, we established a congenic mouse strain carrying the Chr1 QTL, 128 Mb in size, derived from TH on a B6 background (B6.TH‐Chr1–128Mb). The congenic mice were found to be more susceptible to diet‐induced obesity and hyperlipidemia than their B6 counterparts. The purpose of this study was to characterize the congenic mice by examining mRNA and protein levels of adipocyte differentiation and inflammation markers in white adipose tissue and liver. B6.TH‐Chr1–128Mb congenic and B6 mice were weaned onto chow and HFD and maintained until 16 weeks of age. Total RNA was isolated from adipose tissue and reverse‐transcribed with SUPERSCRIPT RT using oligo dT as primer to synthesize first‐strand cDNA. mRNA levels of peroxisome proliferator‐activated receptor gamma (Pparg), CCAAT/enhancer binding protein beta (Cebpb), preadipocyte factor 1 (Pref‐1), and Interleukin 6 (Il‐6) genes were measured by real‐time quantitative RT‐PCR. For protein levels, adipose tissue and liver were lysed in RIPA buffer and lysates subjected to SDA‐PAGE and Western blotting. Blots were probed with specific antibodies against PPARG and IL‐6, and detection of immunoreactive bands performed using enhanced chemiluminescence. Data analysis was conducted by ANOVA with GraphPad Prism 7. Congenic mice had a 2‐fold increase in gene expression level of Pparg, a major regulator of adipogenesis and lipogenesis, in adipose tissue compared to B6 mice on chow. HFD significantly increased the gene expression level of Pparg in both B6 and congenic mice, with greater degree in congenic mice. This trend was also the case for the protein expression level of PPARG in adipose tissue, as well as in liver, but it did not reach statistical significance. There were no significant differences in gene expression levels of Pref‐1, the most upstream repressor to adipocyte differentiation, and Cebpb, a major transcription factor during an early stage of adipogenesis, in adipose tissue between congenic and B6 mice for either diet. The gene expression level of Il‐6, a proinflammatory marker, was increased by HFD in both congenic and B6 mice, without genotype difference. A similar trend was also shown in IL‐6 protein levels in adipose tissue, as well as in liver, but it did not reach statistical significance. Collectively, we demonstrated that gene expression levels of Pparg were significantly upregulated in adipose tissue of B6.TH‐Chr1–128Mb congenic mice on chow and HFD.Support or Funding InformationThis work was supported by NASA WVSGC Graduate Fellowship to JKP and in part by NIH/NIDDK Grant R01DK077202 and institutional start‐up funding from Marshall University to JHK.

Whole genome sequence analysis of the TALLYHO/Jng mouse.

BackgroundThe TALLYHO/Jng (TH) mouse is a polygenic model for obesity and type 2 diabetes first described in the literature in 2001. The origin of the TH strain is an outbred colony of the Theiler Original strain and mice derived from this source were selectively bred for male hyperglycemia establishing an inbred strain at The Jackson Laboratory. TH mice manifest many of the disease phenotypes observed in human obesity and type 2 diabetes.ResultsWe sequenced the whole genome of TH mice maintained at Marshall University to a depth of approximately 64.8X coverage using data from three next generation sequencing runs. Genome-wide, we found approximately 4.31 million homozygous single nucleotide polymorphisms (SNPs) and 1.10 million homozygous small insertions and deletions (indels) of which 98,899 SNPs and 163,720 indels were unique to the TH strain compared to 28 previously sequenced inbred mouse strains. In order to identify potentially clinically-relevant genes, we intersected our list of SNP and indel variants with human orthologous genes in which variants were associated in GWAS studies with obesity, diabetes, and metabolic syndrome, and with genes previously shown to confer a monogenic obesity phenotype in humans, and found several candidate variants that could be functionally tested using TH mice. Further, we filtered our list of variants to those occurring in an obesity quantitative trait locus, tabw2, identified in TH mice and found a missense polymorphism in the Cidec gene and characterized this variant’s effect on protein function.ConclusionsWe generated a complete catalog of variants in TH mice using the data from whole genome sequencing. Our findings will facilitate the identification of causal variants that underlie metabolic diseases in TH mice and will enable identification of candidate susceptibility genes for complex human obesity and type 2 diabetes.Electronic supplementary materialThe online version of this article (doi:10.1186/s12864-016-3245-6) contains supplementary material, which is available to authorized users.

Identification of novel susceptibility genes for diabetes- and obesity-related traits in a backcross of obese NZO with lean C3 H mice

Background and aims: Type 2 diabetes (T2D) in humans is influenced by a combination of hundreds of adipogenic and diabetogenic alleles. In outcross experiments of obese and lean mouse strains, several QTL (Quantitative Trait Loci) for obesity and hyperglycaemia were separated. Mouse models could therefore help to identify several key obesity and diabetes modifier genes. In order to find further disease genes we performed a new crossbreeding approach and subsequent QTL analysis with obese New Zealand Obese (NZO) and lean C3HeB/FeJ mice.

Temporal pattern of circulating leptin levels and obesity in congenic mice carrying an obesity quantitative trait locus, tabw2

Previously, we established a congenic mouse strain that carries an obesity quantitative trait locus, tabw2, derived from TALLYHO/Jng (TH) on a C57BL/6 (B6) background. B6.TH-tabw2 congenic mice have a significantly larger fat mass than controls, which is exaggerated with high-fat high-sucrose (HFS) diets. Leptin is produced in adipocytes and the circulating leptin levels are positively correlated with fat mass. Under normal homeostasis conditions, leptin is secreted in a diurnal rhythm. Interestingly, this diurnal rhythm of circulating leptin levels is dampened in obese subjects. The objective of this study was to investigate the diurnal rhythm of circulating leptin levels in tabw2 mice. Control and tabw2 mice were fed either chow or HFS diets beginning at 4 weeks of age for 10 weeks. Mice were bled at 6 AM, 12 PM, 6 PM, and 12 AM, and the plasma leptin concentrations determined using ELISA. On chow, the 24-hour profile of circulating plasma levels of leptin was comparable between tabw2 and control mice. However, the average of the 24-hour leptin concentrations, as expressed as the area under the curve, was significantly increased in tabw2 mice compared to controls (62±8 vs. 36±4, P<0.05). On HFS diets, the average of the 24-hour leptin concentrations was increased in both tabw2 and control mice than on chow. However, the 24-hour pattern was altered in tabw2 mice from controls; control mice showed the highest magnitude of the leptin increase from 6 PM to 12 AM, whereas tabw2 mice showed it from 12 PM to 6 PM. In conclusion, it appears that body fat mass above a certain threshold causes an altered diurnal pattern in circulating leptin levels, accelerating progression of the obesity in tabw2 congenic mice on HFS diets.

Identification of a Loss-of-Function Mutation in Ube2l6 Associated With Obesity Resistance

We previously mapped a locus on BALB/c chromosome 2 associated with protection from leptin-deficiency–induced obesity. Here, we generated the corresponding congenic mouse strain by introgression of a segment of C57BL/6J chromosome 2 to the BALB/c background to confirm the genotype–phenotype associations. We found that the BALB/c alleles decreased fat mass expansion by limiting adipocyte hyperplasia and adipocyte hypertrophy. This was concomitant to an increase in adipocyte triglyceride lipase (ATGL)-mediated triglyceride breakdown and prolongation of ATGL half-life in adipose tissue. In addition, BALB/c alleles on chromosome 2 exerted a cell-autonomous role in restraining the adipogenic potential of preadipocytes. Within a 9.8-Mb critical interval, we identified a nonsynonymous coding single nucleotide polymorphism in the gene coding for the ubiquitin-conjugating enzyme E2L6 (Ube2l6, also known as Ubch8) and showed that the BALB/c allele of Ube2l6 is a hypomorph leading to the lack of UBE2L6 protein expression. Ube2l6 knockdown in 3T3-L1 adipocytes repressed adipogenesis. Thus, altered adipogenic potential caused by Ube2l6 knockdown is likely critically involved in BALB/c obesity resistance by inhibiting adipogenesis and reducing adipocyte numbers. Overall, we have identified a loss-of-function mutation in Ube2l6 that contributes to the chromosome 2 obesity quantitative trait locus.

Moo1 obesity quantitative trait locus in BTBR T+ Itpr3tf/J mice increases food intake

The rising prevalence of obesity is one of the greatest health challenges facing the world today. Discovery of genetic factors affecting obesity risk will provide important insight to its etiology that could suggest new therapeutic approaches. We have previously identified the Modifier of obese 1 (Moo1) quantitative trait locus (QTL) in a cross between leptin-deficient BTBR T(+) Itpr3(tf)/J (BTBR) and C57BL/6J (B6) mice. Understanding the mechanism by which this locus acts will aid in the identification of candidate genes. Here we refined the location of this QTL and sought to determine the mechanism by which Moo1 affects body weight. We found that the effects of Moo1 also alter high fat diet-induced obesity in mice having functional leptin. In detailed metabolic analyses we determined that this locus acts by increasing food intake in BTBR mice, without affecting energy expenditure. The expression levels of the main molecular mediators of food intake in the hypothalamus were not altered, suggesting this locus affects an independent pathway, consistent with its identification in mice lacking functional leptin. Finally, we show that the increased adiposity resulting from Moo1 is sufficient to affect glucose tolerance. These studies show that the Moo1 obesity QTL affects food intake, likely through a novel mechanism, and indicate that modulation of the underlying pathway may not only ameliorate obesity but also its clinical consequences.

An Interval of the Obesity QTL Nob3.38 within a QTL Hotspot on Chromosome 1 Modulates Behavioral Phenotypes

A region on mouse distal chromosome 1 (Chr. 1) that is highly enriched in quantitative trait loci (QTLs) controlling neural and behavioral phenotypes overlaps with the peak region of a major obesity QTL (Nob3.38), which we identified in an intercross of New Zealand Obese (NZO) mice with C57BL/6J (B6). By positional cloning we recently identified a microdeletion within this locus causing the disruption of Ifi202b that protects from adiposity by suppressing expression of 11β-Hsd1. Here we show that the Nob3.38 segment also corresponds with the QTL rich region (Qrr1) on Chr. 1 and associates with increased voluntary running wheel activity, Rota-rod performance, decreased grip strength, and anxiety-related traits. The characterization of a subcongenic line carrying 14.2 Mbp of Nob3.38 with a polymorphic region of 4.4 Mbp indicates that the microdeletion and/or other polymorphisms in its proximity alter body weight, voluntary activity, and exploration. Since 27 out of 32 QTL were identified in crosses with B6, we hypothesized that the microdeletion and or adjacent SNPs are unique for B6 mice and responsible for some of the complex Qrr1-mediated effects. Indeed, a phylogenic study of 28 mouse strains revealed a NZO-like genotype for 22 and a B6-like genotype for NZW/LacJ and 4 other C57BL strains. Thus, we suggest that a Nob3.38 interval (173.0–177.4 Mbp) does not only modify adiposity but also neurobehavioral traits by a haplotype segregating with C57BL strains.

QTL Mapping of Genes Controlling Plasma Insulin and Leptin Concentrations: Metabolic Effect of Obesity QTLs Identified in an F&lt;sub&gt;2&lt;/sub&gt; Intercross between C57BL/6J and DDD.Cg-&lt;i&gt;A&lt;sup&gt;y&lt;/sup&gt;&lt;/i&gt; Inbred Mice

DDD.Cg-A(y) female mice developed massive obesity as compared with B6.Cg-A(y) female mice. We previously identified quantitative trait loci (QTLs) for obesity on chromosomes 1, 6, 9 and 17 in F2 female mice, including F2A(y) (F2 mice with the A(y) allele) and F2 non- A(y) mice (F2 mice without the A(y) allele), produced by crossing C57BL/6J and DDD.Cg-A(y) strains. We here addressed the question whether the obesity QTLs share genetic bases with putative QTLs for plasma glucose, insulin and leptin concentrations. We performed QTL analyses for the first principal component (PC1) extracted from these metabolic measurements to identify the genes that contributed to the comprehensive evaluation of metabolic traits. By single QTL scans, we identified two significant QTLs for insulin concentration on chromosomes 6 and 12, three for leptin concentration on chromosomes 1, 6 and 17, and five for PC1 on chromosomes 1, 6, 12 (two loci) and 17. Although insulin and leptin concentrations and PC1 were not normally distributed in combined F2 mice, results of single QTL scans by parametric and non-parametric methods were very similar. Therefore, QTL scan by the parametric method was performed with the agouti locus genotype as a covariate. A significant QTL × covariate interaction was found for PC1 on chromosome 9. All obesity QTLs had significant metabolic effects. Thus, obesity- and diabetes-related traits in DDD.Cg-A(y) mice were largely controlled by QTLs on chromosomes 1, 6, 9, 12 and 17.

Subcongenic analysis of tabw2obesity QTL on mouse chromosome 6

BackgroundWe previously established a congenic mouse strain with TALLYHO/Jng (TH) donor segment on chromosome 6 in a C57BL/6 (B6) background that harbors an obesity quantitative trait locus, tabw2. The B6.TH-tabw2 congenic mice developed increased adiposity that became exacerbated upon feeding a high fat-high sucrose (HFS) diet. To fine map the tabw2, in this study we generated and characterized subcongenic lines with smaller TH donor segments.ResultsWe fixed four subcongenic lines, with maximum size of donor segment retained in the lines ranging from 10.8 – 92.5 Mb. For mapping, all the subcongenic mice, along with B6.TH-tabw2 congenic and B6-homozygous control mice were fed either chow or HFS diets, and their post-mortem fat pads were weighed. Mice were also characterized for energy expenditure, respiratory exchange ratio, locomotor activity, and food intake. As previously reported, B6.TH-tabw2 congenic mice showed a significantly larger fat mass than controls on both diets. On chow, a subcongenic line retaining the distal region of the TH donor congenic interval exhibited significantly larger fat mass than B6-homozygous controls, and comparable that to B6.TH-tabw2 congenic mice. Two nested subcongenic lines within that region suggested that the effect of tabw2 on obesity could be attributed to at least two subloci. On HFS diets, on the other hand, all the subcongenic mice had significantly larger fat mass than controls without genotype differences, but none of them had fat mass as large as the original congenic mice. This possibly implicates that further genetic complexity involves in the effect of tabw2 on diet-induced obesity. Significantly reduced locomotor activity was exhibited in B6.TH-tabw2 congenic and subcongenic mice compared to controls when animals were fed HFS diets. B6.TH-tabw2 congenic mice, but not subcongenic mice, also had significantly increased food intake on HFS diets.ConclusionsIt appears that at least two subloci explaining the tabw2 effect under chow feeding map to the distal region of the congenic interval, whereas the diet-induced obesity mediated by tabw2 is attributed to more complex genetic mechanism.

Loss of function of Ifi202b by a microdeletion on chromosome 1 of C57BL/6J mice suppresses 11β-hydroxysteroid dehydrogenase type 1 expression and development of obesity

Nob3 is a major obesity quantitative trait locus (QTL) identified in an intercross of New Zealand Obese (NZO) mice with C57BL/6J (B6), and by introgression of its 38 Mbp peak region into B6 (B6.NZO-Nob3.38). B6.NZO-Nob3.38 mice carrying the NZO allele exhibited markedly increased body weight, fat mass, lean mass and a lower energy expenditure, than the corresponding B6 allele carriers. For positional cloning of the responsible obesity gene, five additional congenic lines (RCS) were generated and characterized, allowing to define a critical genomic interval comprising 43 genes. mRNA profiling and western blotting indicated that Ifi202b, a member of the Ifi200 family of interferon inducible transcriptional modulators, was expressed in NZO-allele carriers but was undetectable in tissues of homozygous B6-allele carriers due to a microdeletion, including the first exon and the 5'-flanking region of Ifi202b in B6. Transcriptome analysis of adipose tissue of RCS revealed a marked induction of 11β-hydroxysteroid dehydrogenase type 1 (11β-Hsd1) expression in mice expressing Ifi202b. Furthermore, siRNA-mediated Ifi202b suppression in 3T3-L1 adipocytes resulted in a significant inhibition of 11β-Hsd1 expression, whereas an adenoviral-mediated overexpression of Ifi202b increased 11β-Hsd1 mRNA levels. Expression of human IFI orthologues was significantly increased in visceral adipose tissue of obese subjects. We suggest that the disruption of Ifi202b in B6 is responsible for the effects of the obesity QTL Nob3, and that Ifi202b modulates fat accumulation through expression of adipogenic genes such as 11β-Hsd1.

A Stratified Transcriptomics Analysis of Polygenic Fat and Lean Mouse Adipose Tissues Identifies Novel Candidate Obesity Genes

BackgroundObesity and metabolic syndrome results from a complex interaction between genetic and environmental factors. In addition to brain-regulated processes, recent genome wide association studies have indicated that genes highly expressed in adipose tissue affect the distribution and function of fat and thus contribute to obesity. Using a stratified transcriptome gene enrichment approach we attempted to identify adipose tissue-specific obesity genes in the unique polygenic Fat (F) mouse strain generated by selective breeding over 60 generations for divergent adiposity from a comparator Lean (L) strain.ResultsTo enrich for adipose tissue obesity genes a ‘snap-shot’ pooled-sample transcriptome comparison of key fat depots and non adipose tissues (muscle, liver, kidney) was performed. Known obesity quantitative trait loci (QTL) information for the model allowed us to further filter genes for increased likelihood of being causal or secondary for obesity. This successfully identified several genes previously linked to obesity (C1qr1, and Np3r) as positional QTL candidate genes elevated specifically in F line adipose tissue. A number of novel obesity candidate genes were also identified (Thbs1, Ppp1r3d, Tmepai, Trp53inp2, Ttc7b, Tuba1a, Fgf13, Fmr) that have inferred roles in fat cell function. Quantitative microarray analysis was then applied to the most phenotypically divergent adipose depot after exaggerating F and L strain differences with chronic high fat feeding which revealed a distinct gene expression profile of line, fat depot and diet-responsive inflammatory, angiogenic and metabolic pathways. Selected candidate genes Npr3 and Thbs1, as well as Gys2, a non-QTL gene that otherwise passed our enrichment criteria were characterised, revealing novel functional effects consistent with a contribution to obesity.ConclusionsA focussed candidate gene enrichment strategy in the unique F and L model has identified novel adipose tissue-enriched genes contributing to obesity.

Quantitative Trait Loci that Control Body Weight and Obesity in an F2 Intercross between C57BL/6J and DDD.Cg-Ay Mice

I have developed a congenic mouse strain for the A(y) allele at the agouti locus in an inbred DDD/Sgn strain, DDD.Cg-A(y). DDD.Cg-A(y) females are extremely obese and significantly heavier than B6.Cg-A(y) females. The objectives of this study were to determine the genetic basis of obesity in DDD.Cg-A(y) mice, and to determine whether or not their high body weight was due to the presence of DDD background-specific modifiers. I performed quantitative trait locus (QTL) analyses for body weight and body mass index in two types of F(2) mice [F2 A(y) (F(2) mice carrying the A(y) allele) and F(2) non-A(y) (F2 mice without the A(y) allele)] produced by crossing C57BL/6J females and DDD.Cg-A(y) males. The results of the QTL analysis of F(2) A(y) mice were very similar to those obtained for F(2) non-A(y) mice. It was unlikely that the high body weight of DDD.Cg-A(y) mice was due to the presence of specific modifiers. When both F(2) datasets were merged and analyzed, four significant body weight QTLs were identified on chromosomes 6, 9, and 17 (2 loci) and four significant obesity QTLs were identified on chromosomes 1, 6, 9, and 17. Although the presence of DDD background-specific modifiers was not confirmed, a multifactorial basis of obesity in DDD.Cg-A(y) females was thus revealed.

A wild derived quantitative trait locus on mouse chromosome 2 prevents obesity

BackgroundThe genetic architecture of multifactorial traits such as obesity has been poorly understood. Quantitative trait locus (QTL) analysis is widely used to localize loci affecting multifactorial traits on chromosomal regions. However, large confidence intervals and small phenotypic effects of identified QTLs and closely linked loci are impeding the identification of causative genes that underlie the QTLs. Here we developed five subcongenic mouse strains with overlapping and non-overlapping wild-derived genomic regions from an F2 intercross of a previously developed congenic strain, B6.Cg-Pbwg1, and its genetic background strain, C57BL/6J (B6). The subcongenic strains developed were phenotyped on low-fat standard chow and a high-fat diet to fine-map a previously identified obesity QTL. Microarray analysis was performed with Affymetrix GeneChips to search for candidate genes of the QTL.ResultsThe obesity QTL was physically mapped to an 8.8-Mb region of mouse chromosome 2. The wild-derived allele significantly decreased white fat pad weight, body weight and serum levels of glucose and triglyceride. It was also resistant to the high-fat diet. Among 29 genes residing within the 8.8-Mb region, Gpd2, Upp2, Acvr1c, March7 and Rbms1 showed great differential expression in livers and/or gonadal fat pads between B6.Cg-Pbwg1 and B6 mice.ConclusionsThe wild-derived QTL allele prevented obesity in both mice fed a low-fat standard diet and mice fed a high-fat diet. This finding will pave the way for identification of causative genes for obesity. A further understanding of this unique QTL effect at genetic and molecular levels may lead to the discovery of new biological and pathologic pathways associated with obesity.

Carbohydrate metabolic pathway genes associated with quantitative trait loci (QTL) for obesity and type 2 diabetes: Identification by data mining

Increasing consumption of refined carbohydrates is now being recognized as a primary contributor to the development of nutritionally related chronic diseases such as obesity and type 2 diabetes mellitus (T2DM). A data mining approach was used to evaluate the role of carbohydrate metabolic pathway genes in the development of obesity and T2DM. Data from public databases were used to map the position of the carbohydrate metabolic pathway genes to known quantitative trait loci (QTL) for obesity and T2DM and for examining the pathway genes for the presence of sequence and structural genetic variants such as single nucleotide polymorphisms (SNPs) and copy number variants (CNS), respectively. The results demonstrated that a majority of the genes of the carbohydrate metabolic pathways are associated with QTL for obesity and many for T2DM. In addition, some key genes of the pathways also encode non-synonymous SNPs that exhibit significant differences in population frequencies. This study emphasizes the significance of the metabolic pathways genes in the development of disease phenotypes, its differential occurrence across populations and between individuals, and a strategy for interpreting an individuals' risk for disease.

In this issue: Biotechnology Journal 9/2010

AbstractLinking obesity and colorectal cancerSung and Bae, Biotechnol. J. 2010, 5, 930–941Obesity is known as one of the most closely related risk factors of colorectal cancer (CRC). However, due to the complicated nature of the diet, it has been very difficult to provide clear explanations and molecular mechanisms for the role of dietary components in carcinogenesis. Nutrigenomics has become a powerful tool to study the relationships between food components and genes. It includes nutrigenetics (dealing with genetic variations related to phenotypic changes in response to diet), nutritional epigenomics and nutritional transcriptomics/proteomics/metabolomics. This review summarizes data on genes, proteins and metabolites that are related to either obesity or CRC and candidate molecules that may link obesity and CRC. The application of bioinformatics helps to perform large‐scale network analysis to study cause‐effect relationships between dietary components and CRC in the future.Hepatoprotective effects of oleuropeinKim et al., Biotechnol. J. 2010, 5, 950–960Oleuropein, an active constituent of olive leaf, has a variety of pharmacological activities associated with its capacity to scavenge reactive oxygen species and has a protective effect against non‐alcoholic fatty liver disease (NAFLD) in vivo. To gain insights into the molecular mechanisms of its hepatoprotective action the group of Taesun Park (Seoul, Korea) fed mice with a high fat diet supplemented with oleuropein. Then, liver tissue was subjected to DNA microarray analysis. Oleuropein in high fat diet reduced the mRNA level of regulators of hepatic fatty acid uptake and transport. The expression of a number of genes involved in oxidative stress responses, detoxification of lipid peroxidation products and proinflammatory cytokine genes were reduced, while highly regulated transcription factors were implicated in the lipogenesis, inflammation, insulin resistance and fibrosis, underlying the multifactorial effect of oleuropein on NAFLD.Genetic variations in obesity and diabetesVarma et al., Biotechnol. J. 2010, 5, 942–949Obesity is a state of metabolic deregulation and a leading cause for development of type 2 diabetes, which are complex polygenic diseases. Here, authors from the National Centre of Toxicological Research at the FDA (Jefferson, Arizona, USA) used a data mining approach to evaluate the role of carbohydrate metabolic pathway genes in the development of obesity and type 2 diabetes. Data from public databases were used to map the position of these genes to known quantitative trait loci (QTL) and to find sequence and structural genetic variants such as single nucleotide polymorphisms (SNPs). The results demonstrated that a majority of carbohydrate metabolic pathways genes are associated with QTL for obesity and many for type 2 diabetes. This data mining approach can establish a strategy for interpreting an individual's risk factor for disease development, instead of population attributable risks.

Calpain-10 is a component of the obesity-related quantitative trait locus Adip1

Calpain-10 is a component of the obesity-related quantitative trait locus Adip1

Calpain-10 is a component of the obesity-related quantitative trait locus Adip1

We previously mapped Adip1, an obesity quantitative trait locus (QTL), to the central portion of murine chromosome 1 containing the calpain-10 (Capn10) gene. Human studies have associated calpain-10 (CAPN10) variants with type 2 diabetes and various metabolic traits. We performed a quantitative hybrid complementation test (QHCT) to determine whether differences attributed to Adip1 are the result of variant Capn10 alleles in LG/J and SM/J mice. We crossed LG/J and SM/J to wild-type (C57BL/6J) and Capn10 knockout (Capn10(-/-)) mice to form four F(1) hybrid groups: LG/J by wild-type, LG/J by Capn10(-/-), SM/J by wild-type, and SM/J by Capn10(-/-). We performed a two-way ANOVA with the experimental strain, tester strain, and their interaction as the factors. Significant interaction indicates a quantitative failure to complement. We found failure to complement for fat, organ, and body weights, and leptin, female free fatty acid, and triglyceride levels. Capn10(-/-) resulted in heavier weights and higher serum levels in LG/J crosses but not in SM/J crosses. For glucose tolerance and insulin response tests, the Capn10(-/-) allele resulted in lower glucose levels in crosses with SM/J but had no effect in the LG/J crosses. Differences between the LG/J and SM/J Capn10 alleles are the likely source of some of the QTL effects mapped to Adip1 in the LG/J-by-SM/J cross. Capn10 plays an important role in regulating obesity and diabetes in mice.