Identification of an obesity quantitative trait locus on mouse chromosome 2 and evidence of linkage to body fat and insulin on the human homologous region 20q

Protein tyrosine phosphatase 1B in metabolic diseases and drug development

Protein tyrosine phosphatase 1B (PTP1B), a non-transmembrane phosphatase, has a major role in a variety of signalling pathways, including direct negative regulation of classic insulin and leptin signalling pathways, and is implicated in the pathogenesis of several cardiometabolic diseases and cancers. As such, PTP1B has been a therapeutic target for over two decades, with PTP1B inhibitors identified either from natural sources or developed throughout the years. Some of these inhibitors have reached phase I and/or II clinical trials in humans for the treatment of type 2 diabetes mellitus, obesity and/or metastatic breast cancer. In this Review, we summarize the cellular processes and regulation of PTP1B, discuss evidence from in vivo preclinical and human studies of the association between PTP1B and different disorders, and discuss outcomes of clinical trials. We outline challenges associated with the targeting of this phosphatase (which was, until the past few years, viewed as difficult to target), the current state of the field of PTP1B inhibitors (and dual phosphatase inhibitors) and future directions for manipulating the activity of this key metabolic enzyme.

High-resolution genomic profiling and locus-specific FISH in subcutaneous and visceral adipose tissue of obese patients

Obesity is known as a heterogeneous and multifactorial disease. The distribution of body fat is crucial for the development of metabolic complications. Comprehensive genetic analyses on different fat tissues are rare but necessary to provide more detailed information. Therefore, we performed genetic analyses of three patients with obesity using high resolution genome wide SNP array (blood, visceral fat tissue) and fluorescence in situ hybridization (FISH) analyses (visceral and subcutaneous fat tissue). Altogether, we identified 31 small Copy Number Variations (losses: 1p31.1, 1p22.2, 1q21.3, 2q34, 2q37.1, 3q28, 6p25.3, 7q31.33, 7q33, 8p23.3, 10q22.3, 11p15.4, 11p15.1, 11p14.2, 11p12, 13q12.3, 15q11.2-q13.1, 15q13.3, 20q13.2, 22q11.21; gains: 2q22.1-q22.2, 3p14.3, 4p16.3, 4q32.2, 6q27, 7p14.3, 7q34, 11p12, 12p11.21, 16p11.2-p11.1, 17q21.31) and 289 small copy-neutral Loss of Heterozygosity (cn-LOH). For the chromosomal region 15q11.2-q13.1, we detected a microdeletion (Prader-Willi-Syndrome) in one patient. Interestingly, we identified chromosomal SNP differences between EDTA-blood and visceral fat tissue (deletion and gain). Small losses of 7q31.33, 7q33, 11p14.2, 11p12, 13q12.3 as well as small gain of 7q34 were detected only in fat tissue and not in blood. Furthermore, FISH analyses on 7q31.33, 7q33 and 11p12 revealed differences between subcutaneous and visceral fat tissue. Generally, the deletions were detected more frequent in visceral fat tissue. Predominantly detected cn-LOH vs. CNV suggests a meaning of these cn-LOH for the pathogenesis of obesity. We conclude that the SNP array and FISH analyses used is applicable to generate more information for basic research on difficult cell subpopulations (e.g., visceral adipose tissue) and could opens up new diagnostic aspects in the field of obesity. Altogether, the significance of these mostly not yet described genetic aberrations in different fat tissues needs to confirmed in a larger series.

Programming With Varying Dietary Fat Content Alters Cardiac Insulin Receptor, Glut4 and FoxO1 Immunoreactivity in Neonatal Rats, Whereas High Fat Programming Alters Cebpa Gene Expression in Neonatal Female Rats

Fetal programming refers to an intrauterine stimulus or insult that shapes growth, development and health outcomes. Dependent on the quality and quantity, dietary fats can be beneficial or detrimental for the growth of the fetus and can alter insulin signaling by regulating the expression of key factors. The effects of varying dietary fat content on the expression profiles of factors in the neonatal female and male rat heart were investigated and analyzed in control (10% fat), 20F (20% fat), 30F (30% fat) and 40F (40% fat which was a high fat diet used to induce high fat programming) neonatal rats. The whole neonatal heart was immunostained for insulin receptor, glucose transporter 4 (Glut4) and forkhead box protein 1 (FoxO1), followed by image analysis. The expression of 84 genes, commonly associated with the insulin signaling pathway, were then examined in 40F female and 40F male offspring. Maintenance on diets, varying in fat content during fetal life, altered the expression of cardiac factors, with changes induced from 20% fat in female neonates, but from 30% fat in male neonates. Further, CCAAT/enhancer-binding protein alpha (Cebpa) was upregulated in 40F female neonates. There was, however, differential expression of several insulin signaling genes in 40F (high fat programmed) offspring, with some tending to significance but most differences were in fold changes (≥1.5 fold). The increased immunoreactivity for insulin receptor, Glut4 and FoxO1 in 20F female and 30F male neonatal rats may reflect a compensatory response to programming to maintain cardiac physiology. Cebpa was upregulated in female offspring maintained on a high fat diet, with fold increases in other insulin signaling genes viz. Aebp1, Cfd (adipsin), Adra1d, Prkcg, Igfbp, Retn (resistin) and Ucp1. In female offspring maintained on a high fat diet, increased Cebpa gene expression (concomitant with fold increases in other insulin signaling genes) may reflect cardiac stress and an adaptative response to cardiac inflammation, stress and/or injury, after high fat programming. Diet and the sex are determinants of cardiac physiology and pathophysiology, reflecting divergent mechanisms that are sex-specific.

Pathophysiology of melanocortin receptors and their accessory proteins

The melanocortin receptors (MCRs) and their accessory proteins (MRAPs) are involved in regulation of a diverse range of endocrine pathways. Genetic variants of these components result in phenotypic variation and disease. The MC1R is expressed in skin and variants in the MC1R gene are associated with ginger hair color. The MC2R mediates the action of ACTH in the adrenal gland to stimulate glucocorticoid production and MC2R mutations result in familial glucocorticoid deficiency (FGD). MC3R and MC4R are involved in metabolic regulation and their gene variants are associated with severe pediatric obesity, whereas the function of MC5R remains to be fully elucidated. MRAPs have been shown to modulate the function of MCRs and genetic variants in MRAPs are associated with diseases including FGD type 2 and potentially early onset obesity. This review provides an insight into recent advances in MCRs and MRAPs physiology, focusing on the disorders associated with their dysfunction.

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.

Polymorphisms and mutations in the melanocortin-3 receptor and their relation to human obesity

Inactivating mutations in the melanocortin 3 receptor (Mc3r) have been described as causing obesity in mice, but the physiologic effects of MC3R mutations in humans have been less clear. Here we review the MC3R polymorphisms and mutations identified in humans, and the in vitro, murine, and human cohort studies examining their putative effects. Some, but not all, studies suggest that the common human MC3R variant T6K+V81I, as well as several other rare, function-altering mutations, are associated with greater adiposity and hyperleptinemia with altered energy partitioning. In vitro, the T6K+V81I variant appears to decrease MC3R expression and therefore cAMP generation in response to ligand binding. Knockin mouse studies confirm that the T6K+V81I variant increases feeding efficiency and the avidity with which adipocytes derived from bone or adipose tissue stem cells store triglycerides. Other MC3R mutations occur too infrequently in the human population to make definitive conclusions regarding their clinical effects. This article is part of a Special Issue entitled: Melanocortin Receptors - edited by Ya-Xiong Tao.

Molecular genetics of human obesity: A comprehensive review

Obesity and its related health complications is a major problem worldwide. Hypothalamus and their signalling molecules play a critical role in the intervening and coordination with energy balance and homeostasis. Genetic factors play a crucial role in determining an individual's predisposition to the weight gain and being obese. In the past few years, several genetic variants were identified as monogenic forms of human obesity having success over common polygenic forms. In the context of molecular genetics, genome-wide association studies (GWAS) approach and their findings signified a number of genetic variants predisposing to obesity. However, the last couple of years, it has also been noticed that alterations in the environmental and epigenetic factors are one of the key causes of obesity. Hence, this review might be helpful in the current scenario of molecular genetics of human obesity, obesity-related health complications (ORHC), and energy homeostasis. Future work based on the clinical discoveries may play a role in the molecular dissection of genetic approaches to find more obesity-susceptible gene loci.

MC3R gene polymorphisms are associated with early childhood adiposity gain and infant appetite in an Asian population

BACKGROUND

Polymorphic variants within human melanocortin-3 receptor gene (MC3R) gene have been associated with obesity. However, its influence on infancy and early childhood adiposity has not been reported before.

OBJECTIVES

We assessed associations between genotype at polymorphic sites within MC3R with early childhood adiposity and interaction with early childhood appetitive traits.

METHODS

We studied 1090 singletons in an Asian mother-offspring cohort genotyped for MC3R and in a subgroup (n = 422) who had completed Child Eating Behaviour Questionnaires (CEBQ) at 12 months. Children were followed from birth to 48 months, and up to 10 measurements of body mass index and five measures of triceps and subscapular skin-folds were obtained.

RESULTS

Independent of potential confounders, each additional MC3R minor allele copy was associated with greater body mass index standard deviation score [B{95% confidence interval}: 0.004 units/month {0.001,0.007}; p = 0.007], triceps [0.009 mm/month {0.001,0.02}; p = 0.021] and subscapular skin-fold [0.008 mm/month {0.002,0.01}; p = 0.011] gain velocity in the first 48 months. Each additional MC3R minor allele copy was also associated with increased odds of overweight [odds ratio {95% confidence interval}: 1.48{1.17-1.88}] and obesity [1.58{1.10-2.28}] in the first 48 months. Every additional copy of MC3R minor allele was positively associated with 'slowness-in-eating' appetitive trait [0.24{0.06,0.39}, p = 0.006]; however, the relationship between 'slowness-in-eating' with adiposity gain was not statistically significant.

CONCLUSIONS

Our findings support the role of MC3R genetic variants in adiposity gain during early childhood.

Evaluation of hypothalamic murine and human melanocortin 3 receptor transcript structure

The melanocortin 3 receptor (MC3R) is involved in regulation of energy homeostasis. However, its transcript structure is not well understood. We therefore studied initiation and termination sites for hypothalamic murine Mc3r and human MC3R transcripts. Rapid Amplification of cDNA Ends (RACE) was performed for the 5' and 3' ends of murine and human hypothalamic RNA. 5' RACE experiments using hypothalamic murine RNA indicated mouse hypothalamus expresses two major Mc3r transcription start sites: one with a 5' UTR approximately 368 bases in length and another previously unknown transcript with a 5' UTR approximately 440 bases in length. 5' RACE experiments using human hypothalamic RNA identified a 5' UTR beginning 533 bases upstream of the start codon with a 248 base splice. 3' RACE experiments using hypothalamic murine RNA indicated the 3' UTR terminates approximately 1286 bases after the translational stop codon, with a previously unknown 787 base splice between consensus splice donor and acceptor sites. 3' RACE experiments using human MC3R transcript indicated the 3' UTR terminates approximately 115-160 bases after the translational stop codon. These data provide insight into melanocortin 3 receptor transcript structure.

PTPRT regulates high-fat diet-induced obesity and insulin resistance

Obesity is a risk factor for many human diseases. However, the underlying molecular causes of obesity are not well understood. Here, we report that protein tyrosine phosphatase receptor T (PTPRT) knockout mice are resistant to high-fat diet-induced obesity. Those mice avoid many deleterious side effects of high-fat diet-induced obesity, displaying improved peripheral insulin sensitivity, lower blood glucose and insulin levels. Compared to wild type littermates, PTPRT knockout mice show reduced food intake. Consistently, STAT3 phosphorylation is up-regulated in the hypothalamus of PTPRT knockout mice. These studies implicate PTPRT-modulated STAT3 signaling in the regulation of high-fat diet-induced obesity.

Genetic dissection of quantitative trait Loci for hemostasis and thrombosis on mouse chromosomes 11 and 5 using congenic and subcongenic strains

Susceptibility to thrombosis varies in human populations as well as many inbred mouse strains. Only a small portion of this variation has been identified, suggesting that there are unknown modifier genes. The objective of this study was to narrow the quantitative trait locus (QTL) intervals previously identified for hemostasis and thrombosis on mouse distal chromosome 11 (Hmtb6) and on chromosome 5 (Hmtb4 and Hmtb5). In a tail bleeding/rebleeding assay, a reporter assay for hemostasis and thrombosis, subcongenic strain (6A-2) had longer clot stability time than did C57BL/6J (B6) mice but a similar time to the B6-Chr11^A/J consomic mice, confirming the Hmtb6 phenotype. Six congenic and subcongenic strains were constructed for chromosome 5, and the congenic strain, 2A-1, containing the shortest A/J interval (16.6 cM, 26.6 Mbp) in the Hmtb4 region, had prolonged clot stability time compared to B6 mice. In the 3A-2 and CSS-5 mice bleeding time was shorter than for B6, mice confirming the Hmtb5 QTL. An increase in bleeding time was identified in another congenic strain (3A-1) with A/J interval (24.8 cM, 32.9 Mbp) in the proximal region of chromosome 5, confirming a QTL for bleeding previously mapped to that region and designated as Hmtb10. The subcongenic strain 4A-2 with the A/J fragment in the proximal region had a long occlusion time of the carotid artery after ferric chloride injury and reduced dilation after injury to the abdominal aorta compared to B6 mice, suggesting an additional locus in the proximal region, which was designated Hmtb11 (5 cM, 21.4 Mbp). CSS-17 mice crossed with congenic strains, 3A-1 and 3A-2, modified tail bleeding. Using congenic and subcongenic analysis, candidate genes previously identified and novel genes were identified as modifiers of hemostasis and thrombosis in each of the loci Hmtb6, Hmtb4, Hmtb10, and Hmtb11.

Developing 'integrative' zebrafish models of behavioral and metabolic disorders

Recently, the pathophysiological overlap between metabolic and mental disorders has received increased recognition. Zebrafish (Danio rerio) are rapidly becoming a popular model organism for translational biomedical research due to their genetic tractability, low cost, quick reproductive cycle, and ease of behavioral, pharmacological or genetic manipulation. High homology to mammalian physiology and the availability of well-developed assays also make the zebrafish an attractive organism for studying human disorders. Zebrafish neurobehavioral and endocrine phenotypes show promise for the use of zebrafish in studies of stress, obesity and related behavioral and metabolic disorders. Here, we discuss the parallels between zebrafish and other model species in stress and obesity physiology, as well as outline the available zebrafish models of weight gain, metabolic deficits, feeding, stress, anxiety and related behavioral disorders. Overall, zebrafish demonstrate a strong potential for modeling human behavioral and metabolic disorders, and their comorbidity.

Systems Biology Approaches and Applications in Obesity, Diabetes, and Cardiovascular Diseases

The metabolically connected triad of obesity, diabetes, and cardiovascular diseases is a major public health threat, and is expected to worsen due to the global shift toward energy-rich and sedentary living. Despite decades of intense research, a large part of the molecular pathogenesis behind complex metabolic diseases remains unknown. Recent advances in genetics, epigenomics, transcriptomics, proteomics and metabolomics enable us to obtain large-scale snapshots of the etiological processes in multiple disease-related cells, tissues and organs. These datasets provide us with an opportunity to go beyond conventional reductionist approaches and to pinpoint the specific perturbations in critical biological processes. In this review, we summarize systems biology methodologies such as functional genomics, causality inference, data-driven biological network construction, and higher-level integrative analyses that can produce novel mechanistic insights, identify disease biomarkers, and uncover potential therapeutic targets from a combination of omics datasets. Importantly, we also demonstrate the power of these approaches by application examples in obesity, diabetes, and cardiovascular diseases.

The Human Obesity Gene Map: The 2003 Update

This is the tenth update of the human obesity gene map, incorporating published results up to the end of October 2003 and continuing the previous format. Evidence from single-gene mutation obesity cases, Mendelian disorders exhibiting obesity as a clinical feature, quantitative trait loci (QTLs) from human genome-wide scans and animal crossbreeding experiments, and association and linkage studies with candidate genes and other markers is reviewed. Transgenic and knockout murine models relevant to obesity are also incorporated (N = 55). As of October 2003, 41 Mendelian syndromes relevant to human obesity have been mapped to a genomic region, and causal genes or strong candidates have been identified for most of these syndromes. QTLs reported from animal models currently number 183. There are 208 human QTLs for obesity phenotypes from genome-wide scans and candidate regions in targeted studies. A total of 35 genomic regions harbor QTLs replicated among two to five studies. Attempts to relate DNA sequence variation in specific genes to obesity phenotypes continue to grow, with 272 studies reporting positive associations with 90 candidate genes. Fifteen such candidate genes are supported by at least five positive studies. The obesity gene map shows putative loci on all chromosomes except Y. Overall, more than 430 genes, markers, and chromosomal regions have been associated or linked with human obesity phenotypes. The electronic version of the map with links to useful sites can be found at http://obesitygene.pbrc.edu.

The Human Obesity Gene Map: The 2004 Update

This paper presents the eleventh update of the human obesity gene map, which incorporates published results up to the end of October 2004. Evidence from single-gene mutation obesity cases, Mendelian disorders exhibiting obesity as a clinical feature, transgenic and knockout murine models relevant to obesity, quantitative trait loci (QTLs) from animal cross-breeding experiments, association studies with candidate genes, and linkages from genome scans is reviewed. As of October 2004, 173 human obesity cases due to single-gene mutations in 10 different genes have been reported, and 49 loci related to Mendelian syndromes relevant to human obesity have been mapped to a genomic region, and causal genes or strong candidates have been identified for most of these syndromes. There are 166 genes which, when mutated or expressed as transgenes in the mouse, result in phenotypes that affect body weight and adiposity. The number of QTLs reported from animal models currently reaches 221. The number of human obesity QTLs derived from genome scans continues to grow, and we have now 204 QTLs for obesity-related phenotypes from 50 genome-wide scans. A total of 38 genomic regions harbor QTLs replicated among two to four studies. The number of studies reporting associations between DNA sequence variation in specific genes and obesity phenotypes has also increased considerably with 358 findings of positive associations with 113 candidate genes. Among them, 18 genes are supported by at least five positive studies. The obesity gene map shows putative loci on all chromosomes except Y. Overall, >600 genes, markers, and chromosomal regions have been associated or linked with human obesity phenotypes. The electronic version of the map with links to useful publications and genomic and other relevant sites can be found at http://obesitygene.pbrc.edu.

Protein Tyrosine Phosphatase 1B Variant Associated with Fat Distribution and Insulin Metabolism

Protein tyrosine phosphatase 1B (PTPN1) affects the regulation of insulin signaling and energy metabolism. We studied whether polymorphisms in the PTPN1 gene impact body fat distribution in the HERITAGE Family Study cohort in 502 white and 276 black subjects. Insulin sensitivity index, glucose disappearance index, acute insulin response to glucose (AIR(glucose)), and the disposition index (DI) were obtained from the frequently sampled intravenous glucose tolerance test. White subjects with the G82G at the PTPN1 IVS6+G82A polymorphism had higher body fat levels (p = 0.031) and sum of eight skinfolds (p = 0.003) and highest subcutaneous fat on the limbs (p = 0.002). G82A subjects had the lowest AIR(glucose) (p = 0.005) and disposition index (p = 0.040). Interaction effects between PTPN1 and leptin receptor gene variants influenced insulin sensitivity index and AIR(glucose) (p from 0.006 to 0.010). The variant PTPN1 Pro387Leu was associated with lower fasting insulin level (p = 0.035) and glucose disappearance index (p = 0.038). In summary, PTPN1 IVS6+G82G homozygotes showed higher levels of all measures of adiposity. G82 allele heterozygotes are potentially at higher risk for type 2 diabetes. Gene-gene interactions between the PTPN1 and leptin receptor genes contributed to the phenotypic variability of insulin sensitivity. The PTPN1 Pro387Leu variant was associated with lower glucose tolerance.

Phenotypic and gene expression differences between DA, BN and WOKW rats

BACKGROUND

Because inbred rat strains are widely used as laboratory models, knowledge of phenotypic and genetic variations between strains will be useful to obtain insight into the relationship between different strains.

METHODS AND RESULTS

We studied phenotypic traits: of each strain--BN/K, DA/K and WOKW--10 male rats were studied for body weight and serum constituents at an age of 10 and 30 weeks. In addition, a total of 95 rats were studied for life expectancy. At an age of 30 weeks, these male rats were killed by an overdose of anesthetic (Sevofluran, Abbott), and the subcutaneous and visceral adipose tissue as well as bone tissue were removed to study the expression of 20 genes. There were significant differences in body weight, serum lipids and leptin at an age of 30 weeks between strains. Regarding life expectancy, BN rats lived longest (1072±228d). The highest gene expression was found in bone of BN rats. In adipose tissues, Nfkb1 is only expressed in subcutaneous adipocytes, and 5 genes, Col2a1, Mmp9, Tnfa, Ins1 and Cyp24a1, are not expressed in adipocytes. The ranking BN = DA>WOKW was observed in only one gene in subcutaneous (Fto) and visceral adipocytes (Col6a1). There were no significant differences in gene expression of one gene in subcutaneous adipocytes and of 3 genes in visceral adipocytes. Comparing the gene expression in visceral and subcutaneous adipocytes, only one gene showed a comparable behavior (Bmp1).

CONCLUSION

From these results, it can be concluded that obvious phenotypic differences are caused by genetic differences between three rat strains, BN, DA and WOKW, as supported by gene expression studies in bone and adipose tissues. Especially BN rats can be used to study the genetic basis of long life.

Elevated adenosine deaminase activity in overweight and obese Indian subjects

OBJECTIVE

To determine adenosine deaminase activity in overweight and obese Indian subjects.

METHODS

This study comprised of 100 subjects. The body mass index (BMI) of subjects was calculated and adenosine deaminase activity was determined in their fasting blood sample. The study was divided into three groups depending upon BMI: Control (n = 40, BMI < 25 kg/m(2)), Overweight (n = 30, BMI 25-29.9 kg/m(2)) and Obese (n = 30, BMI ≥ 30 kg/m(2)).

RESULTS

The serum adenosine deaminase activity was significantly increased in overweight and obese subjects and as well as in combined overweight and obese group as compared to control (P < 0.0001).

CONCLUSION

Adenosine, an endogenous anti-inflammatory metabolite, is increased in response to inflammation produced by adipose tissue in obesity. However, adenosine deaminase acts on adenosine to convert it into inosine, thereby increasing adenosine deaminase activity in overweight and obese Indian subjects.

Comparative analysis of a putative tuberculosis-susceptibility gene, MC3R, and pseudogene sequences in cattle, African buffalo, hyena, rhinoceros and other African bovids and ruminants

Studies in humans have suggested the possible involvement of melanocortin-3-receptor (MC3R) and other components of the central melanocortin system in host defense against mycobacteria. We report a genomic DNA nucleotide sequence highly homologous to human MC3R in several bovids and non-bovid African wildlife species. Nucleotide sequence analysis indicates that the orthologous genes of cattle and buffalo are highly homologous (89.4 and 90%, respectively) to the human MC3R gene. Sequence results also identified a typical non-functional, duplicated pseudogene, MC3RP, in 7 species from the family Bovidae. No pseudogene was found in animals outside Bovidae. The presence of the pseudogene in tuberculosis-susceptible species could have possible immunomodulatory effects on susceptibility to bovine tuberculosis infection, as well as a considerable influence on energy metabolism and food conversion efficiency.

The Genetics of PTPN1 and Obesity: Insights from Mouse Models of Tissue-Specific PTP1B Deficiency

The protein tyrosine phosphatase PTP1B is a negative regulator of both insulin and leptin signaling and is involved in the control of glucose homeostasis and energy expenditure. Due to its prominent role in regulating metabolism, PTP1B is a promising therapeutic target for the treatment of human obesity and type 2 diabetes. The PTP1B protein is encoded by the PTPN1 gene on human chromosome 20q13, a region that shows linkage with insulin resistance, type 2 diabetes, and obesity in human populations. In this paper, we summarize the genetics of the PTPN1 locus and associations with metabolic disease. In addition, we discuss the tissue-specific functions of PTP1B as gleaned from genetic mouse models.

Allelic variants of melanocortin 3 receptor gene (MC3R) and weight loss in obesity: a randomised trial of hypo-energetic high- versus low-fat diets

Introduction

The melanocortin system plays an important role in energy homeostasis. Mice genetically deficient in the melanocortin-3 receptor gene have a normal body weight with increased body fat, mild hypophagia compared to wild-type mice. In humans, Thr6Lys and Val81Ile variants of the melanocortin-3 receptor gene (MC3R) have been associated with childhood obesity, higher BMI Z-score and elevated body fat percentage compared to non-carriers. The aim of this study is to assess the association in adults between allelic variants of MC3R with weight loss induced by energy-restricted diets.

Subjects and Methods

This research is based on the NUGENOB study, a trial conducted to assess weight loss during a 10-week dietary intervention involving two different hypo-energetic (high-fat and low-fat) diets. A total of 760 obese patients were genotyped for 10 single nucleotide polymorphisms covering the single exon of MC3R gene and its flanking regions, including the missense variants Thr6Lys and Val81Ile. Linear mixed models and haplotype-based analysis were carried out to assess the potential association between genetic polymorphisms and differential weight loss, fat mass loss, waist change and resting energy expenditure changes.

Results

No differences in drop-out rate were found by MC3R genotypes. The rs6014646 polymorphism was significantly associated with weight loss using co-dominant (p = 0.04) and dominant models (p = 0.03). These p-values were not statistically significant after strict control for multiple testing. Haplotype-based multivariate analysis using permutations showed that rs3827103–rs1543873 (p = 0.06), rs6014646–rs6024730 (p = 0.05) and rs3746619–rs3827103 (p = 0.10) displayed near-statistical significant results in relation to weight loss. No other significant associations or gene*diet interactions were detected for weight loss, fat mass loss, waist change and resting energy expenditure changes.

Conclusion

The study provided overall sufficient evidence to support that there is no major effect of genetic variants of MC3R and differential weight loss after a 10-week dietary intervention with hypo-energetic diets in obese Europeans.

A role for miR-296 in the regulation of lipoapoptosis by targeting PUMA

Saturated free fatty acids (FFA) induce hepatocyte lipoapoptosis, a key mediator of liver injury in nonalcoholic fatty liver disease (NAFLD). Lipoapoptosis involves the upregulation of the BH3-only protein PUMA, a potent pro-apoptotic protein. Given that dysregulation of hepatic microRNA expression has been observed in NAFLD, we examined the role of miRNA in regulating PUMA expression during lipotoxicity. By in silico analysis, we identified two putative binding sites for miR-296-5p within the 3' untranslated region (UTR) of PUMA mRNA. Enforced miR-296-5p levels efficiently reduced PUMA protein expression in Huh-7 cells, while antagonism of miR-296-5p function increased PUMA cellular levels. Reporter gene assays identified PUMA 3'UTR as a direct target of miR-296-5p. The saturated FFA, palmitate, repressed miR-296-5p expression; and Huh-7 cells were sensitized to palmitate-induced lipotoxicity by antagonism of miR-296-5p function using a targeted locked nucleic acid (LNA). Finally, miR-296-5p was reduced in liver samples from nonalcoholic steatohepatitis (NASH) patients compared with patients with simple steatosis (SS) or controls. Also miR-296-5p levels inversely varied with PUMA mRNA levels in human liver specimens. Our results implicate miR-296-5p in the regulation of PUMA expression during hepatic lipoapoptosis. We speculate that enhancement of miR-296-5p expression may represent a novel approach to minimize apoptotic damage in human fatty liver diseases.

Physiological roles of the melanocortin MC₃ receptor

The melanocortin MC(3) receptor remains the most enigmatic of the melanocortin receptors with regard to its physiological functions. The receptor is expressed both in the CNS and in multiple tissues in the periphery. It appears to be an inhibitory autoreceptor on proopiomelanocortin neurons, yet global deletion of the receptor causes an obesity syndrome. Knockout of the receptor increases adipose mass without a readily measurable increase in food intake or decrease in energy expenditure. And finally, no melanocortin MC(3) receptor null humans have been identified and associations between variant alleles of the melanocortin MC(3) receptor and diseases remain controversial, so the physiological role of the receptor in humans remains to be determined.

Association of a common LAMA5 variant with anthropometric and metabolic traits in an Italian cohort of healthy elderly subjects

Laminins are large heterotrimeric glycoproteins found in basement membranes where they play an essential role in cell-matrix adhesion, migration, growth, and differentiation of various cell types. Previous work reported that a genetic variant located within the intron 1 of LAMA5 (rs659822) was associated with anthropometric traits and HDL-cholesterol levels in a cohort of premenopausal women. The present study aimed to investigate the effect of LAMA5 rs659822 on anthropometric traits, lipid profile, and fasting glucose levels in an Italian cohort of 667 healthy elderly subjects (aged 64-107years). We also tested for association between these traits and the single nucleotide polymorphism (SNP) rs13043313, which was previously shown to control variation in LAMA5 transcript abundance in the liver of Caucasians. In age- and gender-adjusted linear regression analyses, we did not find association of rs13043313 with any of the traits. However, under an additive model, the minor C-allele of LAMA5 rs659822 was associated with shorter stature (p = 0.007) and higher fasting glucose levels (p = 0.02). Moreover, subjects homozygous for the C-allele showed on average 6% and 10% lower total cholesterol (p = 0.034) and LDL-cholesterol (p = 0.016) levels, respectively, than those carrying at least one T allele, assuming a recessive model. Finally, in analyses stratified by age groups (age range 64-89 and 90-107 years), we found that the C-allele was additively associated with increased body weight (p = 0.018) in the age group 64-89 years, whereas no association was found in the age group 90-107 years. In conclusion, this study provides evidence that LAMA5 rs659822 regulates anthropometric and metabolic traits in elderly people. Future studies are warranted to replicate these findings in independent and larger populations and to investigate whether rs659822 is the causal variant responsible for the observed associations.

Comparison of three strains of diabetic rats with respect to the rate at which retinopathy and tactile allodynia develop

PURPOSE

We compared three rat strains to determine if different strains develop early-stage diabetic retinopathy or sensory neuropathy at different rates.

METHODS

Sprague Dawley, Lewis, and Wistar rats were made diabetic with streptozotocin. Diabetic and nondiabetic animals had retinal vascular pathology measured at eight months of diabetes. The number of cells in the retinal ganglion cell layer (GCL), retinal function (using electroretinography [ERG]), and retinal levels of inducible nitric oxide synthase (iNOS), cyclooxygenase2 (COX2), and vascular endothelial growth factor (VEGF) were measured at four months of diabetes. Tactile allodynia was assessed in hind paws at two months of diabetes.

RESULTS

Diabetes of eight months' duration resulted in a significant increase in retinal degenerate capillaries and pericyte ghosts in Lewis and Wistar rats, but not in Sprague Dawley rats. A significant loss of cells in the GCL occurred only in diabetic Lewis rats, whereas Wistar and Sprague Dawley rats showed little change. Diabetes-induced iNOS and VEGF were statistically significant in all strains. Cyclooxygenase 2 (COX2) was significantly elevated in the Sprague Dawley and Wistar strains. Lewis rats showed a similar trend, however, the results were not statistically significant. All strains tended to show diabetes-induced impairment of dark-adapted b-wave amplitude, but only Sprague Dawley and Lewis strains had a significant reduction in latency. All strains showed significant tactile allodynia in peripheral nerves.

CONCLUSIONS

At the durations studied, Lewis rats showed accelerated loss of both retinal capillaries and ganglion cells in diabetes, whereas diabetic Wistar rats showed degeneration of the capillaries without significant neurodegeneration, and Sprague Dawley rats showed neither lesion. Identification of strains that develop retinal lesions at different rates should be of value in investigating the pathogenesis of retinopathy.

Mouse chromosome 17 candidate modifier genes for thrombosis

Two overlapping quantitative trait loci (QTLs) for clot stability, Hmtb8 and Hmtb9, were identified on mouse chromosome 17 in an F2 intercross derived from C57BL/6J (B6) and B6-Chr17(A/J) (B6-Chr17) mouse strains. The intervals were in synteny with a QTL for thrombotic susceptibility on chromosome 18 in a human study, and there were 23 homologs between mouse and human. The objective of this study was to determine whether any of these genes in the syntenic region are likely candidates as modifiers for clot stability. Seven genes, Twsg1, Zfp161, Dlgap1, Ralbp1, Myom1, Rab31, and Emilin2, of the 23 genes with single nucleotide polymorphisms (SNPs) in the mRNA-UTR had differential expression in B6 and A/J mice. Dlgap1, Ralbp1, Myom1, and Emilin2 also had nonsynonymous SNPs. In addition, two other genes had nonsynonymous SNPs, Lama1 and Ndc80. Of these nine candidate genes, Emilin2 was selected for further analysis since other EMILIN (Elastin Microfibril Interface Located Protein) proteins have known functions in vascular structure and coagulation. Differences were found between B6 and A/J mice in vessel wall architecture and EMILIN2 protein in plasma, carotid vessel wall, and thrombi formed after ferric chloride injury. In B6-Chr17(A/J) mice both clot stability and Emilin2 mRNA expression were higher compared to those in B6 and A/J mice, suggesting the exposure of epistatic interactions. Although other homologous genes in the QTL region cannot be ruled out as causative genes, further investigation of Emilin2 as a candidate gene for thrombosis susceptibility is warranted.

Fine mapping of the chicken salmonellosis resistance locus (SAL1)

Salmonella enterica serovar Typhimurium is a Gram-negative bacterium that has a significant impact on both human and animal health. It is one of the most common food-borne pathogens responsible for a self-limiting gastroenteritis in humans and a similar disease in pigs, cattle and chickens. In contrast, intravenous challenge with S. Typhimurium provides a valuable model for systemic infection, often causing a typhoid-like infection, with bacterial replication resulting in the destruction of the spleen and liver of infected animals. Resistance to systemic salmonellosis in chickens is partly genetically determined, with bacterial numbers at systemic sites in resistant lines being up to 1000-fold fewer than in susceptible lines. Identification of genes contributing to disease resistance will enable genetic selection of resistant lines that will reduce Salmonella levels in poultry flocks. We previously identified a novel resistance locus on Chromosome 5, designated SAL1. Through the availability of high-density SNP panels in the chicken, combined with advanced back-crossing of the resistant and susceptible lines, we sought to refine the SAL1 locus and identify potential positional candidate genes. Using a 6(th) generation backcross mapping population, we have confirmed and refined the SAL1 locus as lying between 54.0 and 54.8 Mb on the long arm of Chromosome 5 (F = 8.72, P = 0.00475). This region spans 14 genes, including two very striking functional candidates; CD27-binding protein (Siva) and the RAC-alpha serine/threonine protein kinase homolog, AKT1 (protein kinase B, PKB).

CCAAT/enhancer binding protein alpha, beta and delta gene variants: associations with obesity related phenotypes in the Leeds Family Study

OBJECTIVE

To identify novel polymorphisms in the genes encoding the transcription factors CCAAT/enhancer binding protein alpha, beta and delta ( CEBPA, CEBPB, CEBPD) and investigate associations between polymorphisms and obesity-related phenotypes.

METHODS

Denaturing high-performance liquid chromatography (HPLC) was used to screen for novel gene variants and polymorphisms were genotyped in stored DNA from participants of the Leeds Family Study (537 subjects from 89 families). Genotype and haplotype analyses were carried out in STATA and PBAT, respectively.

RESULTS

Twenty-five polymorphisms were identified; 11 in CEBPA, 12 in CEBPB and 2 in CEBPD. Several allelic variants were associated at a nominal 5% level with waist-to-hip ratio (-919G>A in CEBPA, -412G>T and 646C>T in CEBPB), leptin (1558G>A in CEBPA, -1051A>G and 1383T>- in CEBPB) and adiponectin (1382G>T and 1903G>T in CEBPB). Effects of CEBPA and CEBPB allelic variants were independent, but variants within each gene were in linkage disequilibrium. Several associations were observed between other obesity-related traits and allelic variants in CEBPA and CEBPB, but not CEBPD.

CONCLUSION

These findings suggest that common allelic variants in CEBPA and CEBPB could influence abdominal obesity and related metabolic abnormalities associated with type 2 diabetes and cardiovascular disease in healthy White Northern European families, although results require independent confirmation.

Functions for pro-opiomelanocortin-derived peptides in obesity and diabetes

Melanocortin peptides, derived from POMC (pro-opiomelanocortin) are produced in the ARH (arcuate nucleus of the hypothalamus) neurons and the neurons in the commissural NTS (nucleus of the solitary tract) of the brainstem, in anterior and intermediate lobes of the pituitary, skin and a wide range of peripheral tissues, including reproductive organs. A hypothetical model for functional roles of melanocortin receptors in maintaining energy balance was proposed in 1997. Since this time, there has been an extraordinary amount of knowledge gained about POMC-derived peptides in relation to energy homoeostasis. Development of a Pomc-null mouse provided definitive proof that POMC-derived peptides are critical for the regulation of energy homoeostasis. The melanocortin system consists of endogenous agonists and antagonists, five melanocortin receptor subtypes and receptor accessory proteins. The melanocortin system, as is now known, is far more complex than most of us could have imagined in 1997, and, similarly, the importance of this system for regulating energy homoeostasis in the general human population is much greater than we would have predicted. Of the known factors that can cause human obesity, or protect against it, the melanocortin system is by far the most significant. The present review is a discussion of the current understanding of the roles and mechanism of action of POMC, melanocortin receptors and AgRP (agouti-related peptide) in obesity and Type 2 diabetes and how the central and/or peripheral melanocortin systems mediate nutrient, leptin, insulin, gut hormone and cytokine regulation of energy homoeostasis.

Evaluation of DOK5 as a susceptibility gene for type 2 diabetes and obesity in North Indian population

BACKGROUND

Type 2 diabetes is a complex metabolic disorder with obesity being a major contributing factor in its development. Susceptibility loci for type 2 diabetes and obesity have been localized on different chromosomal regions by various genome-wide linkage scans. Of these chromosomal regions, 20q13 is one of the strongest linked regions for type 2 diabetes as well as obesity. On 20q13 lies DOK5 that seems to be a strong functional and positional candidate for type 2 diabetes and obesity because of its involvement in insulin signaling and immune responses. Hence, for the first time, we explored DOK5 as a potential type 2 diabetes and obesity susceptibility gene.

METHODS

We sequenced 43 subjects for polymorphisms in functionally relevant regions of DOK5. A total of 10 SNPs that included 5 that were identified by sequencing and 5 additional SNPs from NCBI Variation Database were genotyped in 2,115 participants comprising of 1,073 patients with type 2 diabetes and 1,042 controls of Indo-European ethnicity from North India.

RESULTS

We identified a novel variant in intron 7 referred to as DK176673. We found nominal association of three SNPs-rs6064099 (OR = 0.75, P = 0.019), rs873079 (OR = 0.76, P = 0.036) and DK176673 (OR = 1.55, P = 0.037) with type 2 diabetes among normal-weight subjects [BMI < 23 kg/m2]. The haplotype GGC harboring rs6068916, rs6064099 and rs873079 showed strong association with type 2 diabetes among normal-weight subjects (OR = 1.37, P/Pperm = 5.8 x 10-3/0.037). Association analysis with obesity revealed that rs6064099 is associated with reduced susceptibility for obesity (OR = 0.48, P = 6.8 x 10-3). Also, haplotype GGC conferred increased susceptibility for obesity (OR = 1.27, P/Pperm = 9.0 x 10-3/0.039). Also, rs6064099 was significantly associated with reduced BMI [median(IQR) = 24.0(20.7-27.1) vs 23.9(20.2-26.8) vs 21.8(19.2-24.7) for GG vs GC vs CC, P = 7.0 x 10-3].

CONCLUSIONS

We identified DOK5 as a novel susceptibility gene for obesity and type 2 diabetes in North Indian subjects. Association of DOK5 variants both with obesity and type 2 diabetes suggests that these variants might modulate type 2 diabetes susceptibility through obesity.

Energy intake and energy expenditure among children with polymorphisms of the melanocortin-3 receptor

BACKGROUND

Homozygosity for 2 protein-altering polymorphisms in the melanocortin-3 receptor gene (MC3R) coding sequence, C17A and G241A, has been reported to be associated with an obesity phenotype in children, yet how these polymorphisms affect energy homeostasis is unknown. Association between adult body weight and +2138InsCAGACC, another variant in the 3' untranslated region of MC3R, has also been described.

OBJECTIVE

The objective of this study was to examine associations of C17A + G241A and +2138InsCAGACC MC3R variants with children's energy balance.

DESIGN

Children aged 6-19 y were genotyped for MC3R C17A, G241A, and +2138InsCAGACC. Subjects underwent studies of energy intake from a 9835-kcal food array (n = 185), resting energy expenditure (REE) by using indirect calorimetry (n = 302), or total daily energy expenditure (TEE) by using doubly labeled water (n = 120). Linear regression was used to examine the associations between MC3R polymorphisms and the measures of energy balance.

RESULTS

Body mass index and fat mass were greater in those with double homozygosity for C17A + G241A (P = 0.001). After accounting for covariates (including body composition), the number of minor C17A + G241A alleles was associated with significantly greater energy intake (beta = +0.15, P = 0.02) but not altered REE or TEE. No significant associations were observed between +2138InsCAGACC and measures of either fat mass or energy balance.

CONCLUSIONS

C17A + G241A polymorphisms may be associated with pediatric obesity because of greater energy intake rather than because of diminished energy expenditure. +2138InsCAGACC does not appear to be associated with obesity or measures of energy balance in children.

The two faces of PTP1B in cancer

PTP1B is a classical non-transmembrane protein tyrosine phosphatase that plays a key role in metabolic signaling and is a promising drug target for type 2 diabetes and obesity. Accumulating evidence also indicates that PTP1B is involved in cancer, but contrasting findings suggest that it can exert both tumor suppressing and tumor promoting effects depending on the substrate involved and the cellular context. In this review, we will discuss the diverse mechanisms by which PTP1B may influence tumorigenesis as well as recent in vivo data on the impact of PTP1B deficiency in murine cancer models. Together, these results highlight not only the great potential of PTP1B inhibitors in cancer therapy but also the need for a better understanding of PTP1B function prior to use of these compounds in human patients.

Genes on rat chromosomes 3, 5, 10, and 16 are linked with facets of metabolic syndrome

WOKW (Wistar Ottawa Karlsburg W) rats develop metabolic syndrome closely resembling human disorder. In crossing studies between disease-prone WOKW and disease-resistant DA (Dark Agouti) rats, several quantitative trait loci (QTLs) were mapped. To prove the in vivo relevance of QTLs, congenic DA.WOKW rats, briefly termed DA.3aW, DA.3bW, DA.5W, DA.10W, and DA.16W, were generated by transferring chromosomal regions of WOKW chromosomes 3, 5, 10, and 16 onto DA genetic background. Male (n=12) and female (n=12) rats of each congenic strain and their parental strain DA were characterized for adiposity index (AI), serum leptin, and serum insulin as well as serum cholesterol and serum triglycerides as single facets of metabolic syndrome at the age of 30 weeks. The data showed a significant higher AI for male and female DA.3aW and female DA.16W compared with DA. Serum leptin was significantly elevated in male and female DA.3aW, DA.10W, and DA.16W rats in comparison with DA. Rats of both sexes of DA.10W and female DA.16W showed significantly elevated serum insulin in comparison to DA. Female rats of all congenics had significantly higher serum cholesterol compared with DA, while males did not differ. Finally, triglycerides were only elevated in male DA.16W. The results demonstrate an involvement of WOKW chromosomes 3, 5, 10, and 16 in developing facets of the metabolic syndrome.

Agreement among type 2 diabetes linkage studies but a poor correlation with results from genome-wide association studies

AIMS/HYPOTHESIS

Little of the genetic basis for type 2 diabetes has been explained, despite numerous genetic linkage studies and the discovery of multiple genes in genome-wide association (GWA) studies. To begin to resolve the genetic component of this disease, we searched for sites at which genetic results had been corroborated in different studies, in the expectation that replication among studies should direct us to the genomic locations of causative genes with more confidence than the results of individual studies.

METHODS

We have mapped the physical location of results from 83 linkage reports (for type 2 diabetes and diabetes precursor quantitative traits [QTs, e.g. plasma insulin levels]) and recent large GWA reports (for type 2 diabetes) onto the same human genome sequence to identify replicated results in diabetes genetic 'hot spots'.

RESULTS

Genetic linkage has been found at least ten times at 18 different locations, and at least five times in 56 locations. All replication clusters contained study populations from more than one ethnic background and most contained results for both diabetes and QTs. There is no close relationship between the GWA results and linkage clusters, and the nine best replication clusters have no nearby GWA result.

CONCLUSIONS/INTERPRETATION

Many of the genes for type 2 diabetes remain unidentified. This analysis identifies the broad location of yet to be identified genes on 6q, 1q, 18p, 2q, 20q, 17pq, 8p, 19q and 9q. The discrepancy between the linkage and GWA studies may be explained by the presence of multiple, uncommon, mildly deleterious polymorphisms scattered throughout the regulatory and coding regions of genes for type 2 diabetes.

A histone map of human chromosome 20q13.12

Background

We present a systematic search for regulatory elements in a 3.5 Mb region on human chromosome 20q13.12, a region associated with a number of medical conditions such as type II diabetes and obesity.

Methodology/Principal Findings

We profiled six histone modifications alongside RNA polymerase II (PolII) and CTCF in two cell lines, HeLa S3 and NTERA-2 clone D1 (NT2/D1), by chromatin immunoprecipitation using an in-house spotted DNA array, constructed with 1.8 kb overlapping plasmid clones. In both cells, more than 90% of transcription start sites (TSSs) of expressed genes showed enrichments with PolII, di-methylated lysine 4 of histone H3 (H3K4me2), tri-methylated lysine 4 of histone H3 (H3K4me3) or acetylated H3 (H3Ac), whereas mono-methylated lysine 4 of histone H3 (H3K4me1) signals did not correlate with expression. No TSSs were enriched with tri-methylated lysine 27 of histone H3 (H3K27me3) in HeLa S3, while eight TSSs (4 expressed) showed enrichments in NT2/D1. We have also located several CTCF binding sites that are potential insulator elements.

Conclusions/Significance

In summary, we annotated a number of putative regulatory elements in 20q13.12 and went on to verify experimentally a subset of them using dual luciferase reporter assays. Correlating this data to sequence variation can aid identification of disease causing variants.

The Role of Leptin-Melanocortin System and Human Weight Regulation: Lessons from Experiments of Nature

Introduction: Common obesity is a multi-factorial trait, contributed by the “obesogenic” environment of caloric abundance and increasing automation, sedentary lifestyle and an underlying genetic susceptibility. There have been major advances in the past decade in our understanding of the human weight regulation mechanism and pathogenesis of obesity, abetted by discoveries of genetic defects which lead to human obesity. Materials and Methods: Reports of genetic mutations causing obesity in humans and murine models were reviewed Results: Humans with genetic defects resulting in leptin deficiency, leptin receptor deficiency, pro-opiomelanocortin deficiency (POMC), and melanocortin 4 receptor (MC4R) deficiency developed severe obesity as the dominant phenotypic feature, though these are rare autosomal recessive conditions, except MC4R deficiency which is inherited in an autosomal co-dominant fashion. Common and rare variants of the POMC and melanocortin 3 receptor genes may be pre-disposing factors in the development of common obesity. Recent reports of human obesity associated with thyrosine kinase B (TrkB) defect and brain derived neurotrophic factor (BDNF) disruption, coupled with other murine studies, supported the role of BDNF/TrkB as effectors downstream of the melanocortin receptors. Conclusions: Despite exciting discoveries of single gene mutations resulting in human obesity, most cases of obesity are likely the result of subtle interactions of several related genetic variants with environmental factors which favour the net deposition of calories as fat, culminating in the obese phenotype. The mechanisms of action of these genes in the development of obesity are now being examined, with the aim of eventually discovering a therapeutic intervention for obesity. Key words: Leptin, Melanocortin, Obesity

Genetic influences on growth and body composition in mice: multilocus interactions

BACKGROUND

The genetic architecture of body weight and body composition is complex because these traits are normally influenced by multiple genes and their interactions, even after controlling for the environment. Bayesian methodology provides an efficient way of estimating these interactions.

SUBJECTS AND MEASUREMENTS

We used Bayesian model selection techniques to simultaneously estimate the main effects, epistasis and gene-sex interactions on age-related body weight (at 3, 6 and 10 weeks, denoted as WT3wk, WT6wk and WT10wk) and body composition (organ weights and fat-related traits) in an F(2) sample obtained from a cross between high-growth (M16i) mice and low-growth (L6) mice.

RESULTS

We observed epistatic and main-effect quantitative trait loci (QTL) that controlled both body weight and body composition. Epistatic effects were generally more significant for WT6wk than WT10wk. Chromosomes 5 and 13 interacted strongly to control body weight at 3 weeks. A pleiotropic QTL on chromosome 2 was associated with body weight and some body composition phenotypes. Testis weight was regulated by a QTL on chromosome 13 with a significantly large main effect (2log(e)BF approximately 15).

CONCLUSION

By analyzing epistatic interactions, we detected QTL not found in a previous analysis of this mouse population. Hence, the detection of gene-gene interactions may provide new information about the genetic architecture of complex obesity-related traits and may lead to the detection of additional obesity genes.

Contribution of the transmembrane domain 6 of melanocortin-4 receptor to peptide [Pro5, DNal (2')8]-gamma-MSH selectivity

The melanocortin receptor (MCR) subtype family is a member of the GPCR superfamily and each of them has a different pharmacological profile regarding the relative potency of the endogenous and synthetic melanocortin peptides. Substitution of Trp with DNal (2') in gamma-MSH resulted in the loss of binding affinity and potency at hMC4R. However, the molecular mechanism of this ligand selectivity is unclear. In this study, we utilized chimeric receptors and site-directed mutagenesis approaches to investigate the molecular basis of MC4R responsible for peptide [Pro5, DNal (2')8]-gamma-MSH selectivity. Cassette substitutions of the second, third, fourth, fifth, and sixth TM of the human MC4R (hMC4R) with the homologous regions of hMC1R were constructed and the binding affinity of peptide [Pro5, DNal (2')8]-gamma-MSH at these chimeric receptors was evaluated. Our results indicate that the cassette substitutions of TM2, TM3, TM4 and TM5 of hMC4R with homologous regions of the hMC1R did not significantly increase peptide [Pro5, DNal (2')8]-gamma-MSH binding affinity and potency but substitution of the TM6 of the hMC4R with the same region of the hMC1R significantly enhances [Pro5, DNal (2')8]-gamma-MSH binding affinity and potency. Further site-directed mutagenesis study indicates that four amino acid residues, Phe267, Tyr268, Ile269 and Ser270, in TM6 of the hMC4R may play an important role in [Pro5, DNal (2')-gamma-MSH selective activity at MC4R.

Further evidence for the role of ENPP1 in obesity: association with morbid obesity in Finns

The aim of this study was to investigate a series of single-nucleotide polymorphisms (SNPs) in the genes MC2R, MC3R, MC4R, MC5R, POMC, and ENPP1 for association with obesity. Twenty-five SNPs (2-7 SNPs/gene) were genotyped in 246 Finns with extreme obesity (BMI > or = 40 kg/m2) and in 481 lean subjects (BMI 20-25 kg/m2). Of the obese subjects, 23% had concomitant type 2 diabetes. SNPs and SNP haplotypes were tested for association with obesity and type 2 diabetes. Allele frequencies differed between obese and lean subjects for two SNPs in the ENPP1 gene, rs1800949 (P = 0.006) and rs943003 (P = 0.0009). These SNPs are part of a haplotype (rs1800949 C-rs943003 A), which was observed more frequently in lean subjects compared to obese subjects (P = 0.0007). Weaker associations were detected between the SNPs rs1541276 in the MC5R, rs1926065 in the MC3R genes and obesity (P = 0.04 and P = 0.03, respectively), and between SNPs rs2236700 in the MC5R, rs2118404 in the POMC, rs943003 in the ENPP1 genes and type 2 diabetes (P = 0.03, P = 0.02 and P = 0.02, respectively); these associations did not, however, remain significant after correction for multiple testing. In conclusion, a previously unexplored ENPP1 haplotype composed of SNPs rs1800949 and rs943003 showed suggestive evidence for association with adult-onset morbid obesity in Finns. In this study, we did not find association between the frequently studied ENPP1 K121Q variant, nor SNPs in the MCR or POMC genes and obesity or type 2 diabetes.

Genome-wide linkage analysis for circulating levels of adipokines and C-reactive protein in the Quebec family study (QFS)

Adipose tissue synthesizes and secretes a wide range of biologically active molecules considered as inflammatory markers whose dysregulation in obesity plays a role in the development of insulin resistance and vascular disorders. Thus, finding genes that influence circulating levels of inflammatory biomarkers may provide insights into the genetic determinants of obesity-related metabolic diseases. We performed linkage analyses for fasting plasma levels of adiponectin, C-reactive protein (CRP), interleukin-6 (IL-6) and tumor-necrosis factor-alpha (TNF-alpha) in 764 subjects enrolled in the Quebec family study (QFS). A maximum of 393 pairs of siblings from 211 nuclear families were available for analyses. A total of 443 markers spanning the 22 autosomal chromosomes with an average inter-marker distance of 6.24 Mb were genotyped. Linkage was tested using both allele-sharing (SIBPAL) and variance component linkage methods (MERLIN). We showed suggestive evidence of linkage for plasma adiponectin levels on chromosome 15q21.1 [D15S659; logarithm of the odds (LOD) score = 2.23], 3q13.33 (D3S3023; LOD = 2.09), 20q13.2 (D20S197; LOD = 1.96) and 14q32.2 (D14S1426; LOD = 1.79). Evidence of linkage (SIBPAL) was also found for CRP on 12p11.23 (P = 0.001) and 12q15 (P = 0.0005) and for IL-6 on 14q12 (P = 0.002). None of these linkages remained significant after adjustment for body mass index. No evidence of linkage was found for TNF-alpha plasma levels. These results suggest that several QTLs can influence plasma levels of adiponectin and CRP, partly via their effects on adiposity.

Fine mapping of mouse QTLs for fatness using SNP data

Quantitative trait loci (QTLs), as determined in crossbred studies, are a valuable resource to identify genes responsible for the corresponding phenotypic variances. Due to their broad chromosomal extension of some dozens of megabases, further steps are necessary to bring the number of candidate genes that underlie the detected effects to a reasonable order of magnitude. We use a set of 13,370 SNPs to identify informative haplotype blocks in 22 mouse QTLs for fatness. About half of the genes in a typical QTL overlap with haplotype blocks, which are different for the two base mouse lines, and which, thus, qualify for further analysis. For these genes we collect four more pieces of evidence for association with fat accumulation, namely (1) homology to genes identified in a Caenorhabditis elegans knock-out experiment as fat decreasing or fat increasing, (2) the overexpression of the genes in mouse fat, liver, muscle, or hypothalamus tissues, (3) the occurrence of a gene in several independently found QTLs, and (4) the information provided by gene ontology, to achieve a ranked list of 131 candidate genes. Ten genes fulfill three or four of the above sketched criteria and are discussed briefly, 121 further genes fulfilling two criteria are provided as on-line material. Viewing the genomic region of fatness-related QTLs under several different aspects is appropriate to assess the many thousands of genes that reside in such QTLs and to produce lists of more robust candidate genes.

Identification of a novel modulator of thyroid hormone receptor-mediated action

Background

Diabetes is characterized by reduced thyroid function and altered myogenesis after muscle injury. Here we identify a novel component of thyroid hormone action that is repressed in diabetic rat muscle.

Methodology/Principal Findings

We have identified a gene, named DOR, abundantly expressed in insulin-sensitive tissues such as skeletal muscle and heart, whose expression is highly repressed in muscle from obese diabetic rats. DOR expression is up-regulated during muscle differentiation and its loss-of-function has a negative impact on gene expression programmes linked to myogenesis or driven by thyroid hormones. In agreement with this, DOR enhances the transcriptional activity of the thyroid hormone receptor TR_α1. This function is driven by the N-terminal part of the protein. Moreover, DOR physically interacts with TR _α1 and to T₃-responsive promoters, as shown by ChIP assays. T₃ stimulation also promotes the mobilization of DOR from its localization in nuclear PML bodies, thereby indicating that its nuclear localization and cellular function may be related.

Conclusions/Significance

Our data indicate that DOR modulates thyroid hormone function and controls myogenesis. DOR expression is down-regulated in skeletal muscle in diabetes. This finding may be of relevance for the alterations in muscle function associated with this disease.

Adenosine deaminase gene polymorphism is associated with obesity in Iranian population

SUMMARY

OBJECTIVE

Adenosine deaminase (ADA) is a polymorphic enzyme which has an important role in modulation of insulin bioactivity. It has been suggested that an excess of adenosine A1 receptor activity may contribute to adiposity in type 2 diabetes. Adenosine seems to have a role in facilitating insulin action on the adipocytes. ADA gene polymorphism seems to contribute to the degree of obesity in type 2 diabetes patients.

AIM

The aim of this study was to examine the role of adenosine deaminase gene polymorphism in randomly selected obese subjects in an Iranian population.

RESULTS

A significant increase in the frequency of ADA, AA genotype was observed in obese people compared to the controls (AA versus CA + CC, p = 0.01, OR: 3.4, 95% CI: [1.08-12.8]). There was also a significant increase in ADA gene allele A and AA genotype frequencies in patients with higher plasma cholesterol level compared to the normal controls (p = 0.0007, OR: 8.4, 95% CI [1.6-41.6]; AA versus CA + CC, p = 0.005, OR: 3.0, 95% CI [1.2-7.7], respectively). When we compared the ADA allele frequency in patients with obesity and higher plasma cholesterol level and patients with obesity and lower plasma cholesterol level there was also a significant difference (p = 0.01, OR: 2.6, 95% CI [1.08-6.8]). Also we examined the association between the frequency of ADA allele and genotype frequencies with triglyceride (TG) levels in obese patients and normal controls. We observed a significant increase in the ADA gene AA genotype frequency in obese patients with TG level ≥150 mg/dl compared to the normal controls (AA versus CA + CC, p = 0.008, OR: 4.5, 95% CI [1.2-18.7]).

CONCLUSION

Our data is supportive of a role for ADA in obesity and also points to its association with abnormal level of TG and cholesterol. Also our findings recommend adenosine receptors as important targets for new therapeutic approach in obesity and dislipidemia.