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The strongest BMI–associated GWAS locus in humans is the FTO gene. Rodent studies demonstrate a role for FTO in energy homeostasis and body composition. The phenotypes observed in loss of expression studies are complex with perinatal lethality, stunted growth from weaning, and significant alterations in body composition. Thus understanding how and where Fto regulates food intake, energy expenditure, and body composition is a challenge. To address this we generated a series of mice with distinct temporal and spatial loss of Fto expression. Global germline loss of Fto resulted in high perinatal lethality and a reduction in body length, fat mass, and lean mass. When ratio corrected for lean mass, mice had a significant increase in energy expenditure, but more appropriate multiple linear regression normalisation showed no difference in energy expenditure. Global deletion of Fto after the in utero and perinatal period, at 6 weeks of age, removed the high lethality of germline loss. However, there was a reduction in weight by 9 weeks, primarily as loss of lean mass. Over the subsequent 10 weeks, weight converged, driven by an increase in fat mass. There was a switch to a lower RER with no overall change in food intake or energy expenditure. To test if the phenotype can be explained by loss of Fto in the mediobasal hypothalamus, we sterotactically injected adeno-associated viral vectors encoding Cre recombinase to cause regional deletion. We observed a small reduction in food intake and weight gain with no effect on energy expenditure or body composition. Thus, although hypothalamic Fto can impact feeding, the effect of loss of Fto on body composition is brought about by its actions at sites elsewhere. Our data suggest that Fto may have a critical role in the control of lean mass, independent of its effect on food intake.

Author Summary

The fat mass and obesity (FTO) gene has one of the strongest links with body mass index (BMI) in the human population. One in six people have the “risk” alteration and weigh 3 kg more than those with the unaltered gene, but it is not understood how this gene influences BMI and obesity. We set out to understand how and where in the body FTO affects food intake, energy expenditure, and body composition using a mouse model that can be manipulated to lack FTO at particular times and/or places. Removing FTO everywhere from conception had a dramatic effect on body composition and resulted in stunted growth and some lethality. Removing FTO everywhere but only in adult animals resulted in better viability and normal growth but, surprisingly, reduced lean mass and increased fat mass with a change in the type of metabolic fuel being used. Finally, we removed FTO from the hypothalamus of adult animals, an important brain region involved in energy metabolism. These animals showed a mild reduction in food intake and weight gain. Our experiments show that FTO has an important role in body composition and that other brain areas outside of the hypothalamus are also important in determining its effects.

OBJECTIVE

Single nucleotide polymorphisms (SNPs) in intron 1 of fat mass– and obesity-associated gene (FTO) are strongly associated with human adiposity, whereas Fto−/− mice are lean and Fto+/− mice are resistant to diet-induced obesity. We aimed to determine whether FTO mutations are disproportionately represented in lean or obese humans and to use these mutations to understand structure-function relationships within FTO.

RESEARCH DESIGN AND METHODS

We sequenced all coding exons of FTO in 1,433 severely obese and 1,433 lean individuals. We studied the enzymatic activity of selected nonsynonymous variants.

RESULTS

We identified 33 heterozygous nonsynonymous variants in lean (2.3%) and 35 in obese (2.4%) individuals, with 8 mutations unique to the obese and 11 unique to the lean. Two novel mutations replace absolutely conserved residues: R322Q in the catalytic domain and R96H in the predicted substrate recognition lid. R322Q was unable to catalyze the conversion of 2-oxoglutarate to succinate in the presence or absence of 3-methylthymidine. R96H retained some basal activity, which was not enhanced by 3-methylthymidine. However, both were found in lean and obese individuals.

CONCLUSIONS

Heterozygous, loss-of-function mutations in FTO exist but are found in both lean and obese subjects. Although intron 1 SNPs are unequivocally associated with obesity in multiple populations and murine studies strongly suggest that FTO has a role in energy balance, it appears that loss of one functional copy of FTO in humans is compatible with being either lean or obese. Functional analyses of FTO mutations have given novel insights into structure-function relationships in this enzyme.

The fat mass and obesity associated, FTO, gene has been shown to be associated with obesity in human in several genome-wide association scans. In vitro studies suggest that Fto may function as a single-stranded DNA demethylase. In addition, homologous recombination-targeted knockout of Fto in mice resulted in growth retardation, loss of white adipose tissue, and increase energy metabolism and systemic sympathetic activation. Despite these intense investigations, the exact function of Fto remains unclear. We show here that Fto is a transcriptional coactivator that enhances the transactivation potential of the CCAAT/enhancer binding proteins (C/EBPs) from unmethylated as well as methylation-inhibited gene promoters. Fto also exhibits nuclease activity. We showed further that Fto enhances the binding C/EBP to unmethylated and methylated DNA. The coactivator role of FTO in modulating the transcriptional regulation of adipogenesis by C/EBPs is consistent with the temporal progressive loss of adipose tissue in the Fto-deficient mice, thus suggesting a role for Fto in the epigenetic regulation of the development and maintenance of fat tissue. How FTO reactivates transcription from methyl-repressed gene needs to be further investigated.

Obesity is an important risk factor for cardiovascular disease, diabetes and certain cancers. The fat mass– and obesity-associated (FTO) gene is tightly associated with the pathophysiology of obesity, whereas the exact role of FTO remains poorly understood. Here, we investigated the alternations of FTO mRNA and protein expression in the peripheral metabolic tissues and the brain upon energy restriction (ER) and explored the involvement of the leptin signaling pathway in FTO regulation under ER status. ER decreased the FTO mRNA and protein expression in hypothalamus and brainstem but not in periphery. Using double-immunofluorescence staining, FTO was found to be colocalized with the leptin receptor long isoform (LepRb) in arcuate nucleus of hypothalamus and the nucleus of the solitary tract. In LepRb mutant db/db mice, the FTO downregulation in brain and body weight reduction induced by ER were completely abolished. The enhanced phosphorylation of signal transducer and activator of transcription 3 (STAT3) induced by ER was also impaired in db/db mice. Moreover, leptin directly activated the STAT3 signaling pathway and downregulated FTO in in vitro arcuate nucleus of hypothalamus cultures and in vivo wild-type mice but not db/db mice. Thus, our results provide the first evidence that the LepRb-STAT3 signaling pathway is involved in the brain FTO downregulation during ER.

In 2007, an association of single nucleotide polymorphisms (SNPs) in the fat mass and obesity-associated (FTO) gene region with body mass index (BMI) and risk of obesity was identified in multiple populations, making FTO the first locus unequivocally associated with adiposity. At the time, FTO was a gene of unknown function and it was not known whether these SNPs exerted their effect on adiposity by affecting FTO or neighboring genes. Therefore, this breakthrough association inspired a wealth of in silico, in vitro, and in vivo analyses in model organisms and humans to improve knowledge of FTO function. These studies suggested that FTO plays a role in controlling feeding behavior and energy expenditure. Here, we review the approaches taken that provide a blueprint for the study of other obesity-associated genes in the hope that this strategy will result in increased understanding of the biological mechanisms underlying body weight regulation.

Objective:

Recent genome-wide association studies have identified a strong association between obesity and common variants in the fat mass and obesity associated (FTO) gene. FTO has been detected in the hypothalamus, but little is known about its regulation in that particular brain structure. The present study addressed the hypothesis that hypothalamic FTO expression is regulated by nutrients, specifically by glucose, and that its regulation by nutrients is impaired in obesity.

Research design and methods:

The effect of intraperitoneal (i.p.) or intracerebroventricular (i.c.v.) administration of glucose on hypothalamic Fto mRNA levels was examined in fasted mice. Additionally, the effect of glucose on Fto mRNA levels was also investigated ex vivo using mouse hypothalamic explants. Lastly, the effect of i.p. glucose injection on hypothalamic Fto immunoreactivity and food intake was compared between lean wild-type and obese ob/ob mice.

Results:

In wild-type mice, fasting reduced both Fto mRNA levels and the number of Fto-immunoreactive cells in the hypothalamus, whereas i.p. glucose treatment reversed this effect of fasting. Furthermore, i.c.v. glucose treatment also increased hypothalamic Fto mRNA levels in fasted mice. Incubation of hypothalamic explants at high glucose concentration increased Fto mRNA levels. In ob/ob mice, both fasting and i.p. glucose treatment failed to alter the number of Fto-immunoreactive cells in the hypothalamus. Glucose-induced feeding suppression was abolished in ob/ob mice.

Conclusion:

Reduction in hypothalamic Fto expression after fasting likely arises at least partly from reduced circulating glucose levels and/or reduced central action of glucose. Obesity is associated with impairments in glucose-mediated regulation of hypothalamic Fto expression and anorexia. Hypothalamic Fto-expressing neurons may have a role in the regulation of metabolism by monitoring metabolic states of the body.

Single-nucleotide polymorphisms in the first intron of the ubiquitously expressed FTO gene are associated with obesity. Although the physiological functions of FTO remain unclear, food intake is often altered when Fto expression levels are manipulated. Furthermore, deletion of FTO from neurones alone has a similar effect on food intake to deletion of FTO in all tissues. These results indicate that FTO expression in the brain is particularly important. Considerable focus has been placed on the dynamic regulation of Fto mRNA expression in the hypothalamus after short-term (16–48 hour) fasting, but results have been controversial. There are no studies that quantify FTO protein levels across the brain, and assess its alteration following short-term fasting. Using immunohistochemistry, we found that FTO protein is widely expressed in mouse brain, and present in the majority of neurones. Using quantitative Western blotting and RT-qPCR we show that FTO protein and mRNA levels in the hypothalamus, cerebellum and rostral brain are relatively uniform, and levels in the brain are higher than in skeletal muscles of the lower limbs. Fasting for 18 hours does not alter the expression pattern, or levels, of FTO protein and mRNA. We further show that the majority of POMC neurones, which are critically involved in food intake regulation, also express FTO, but that the percentage of FTO-positive POMC neurones is not altered by fasting. In summary, we find no evidence that Fto/FTO expression is regulated by short-term (18-hour) fasting. Thus, it is unlikely that the hunger and increased post-fasting food intake caused by such food deprivation is driven by alterations in Fto/FTO expression. The widespread expression of FTO in neurones also suggests that physiological studies of this protein should not be limited to the hypothalamus.

Human FTO gene variants are associated with body mass index and type 2 diabetes. Because the obesity-associated SNPs are intronic, it is unclear whether changes in FTO expression or splicing are the cause of obesity or if regulatory elements within intron 1 influence upstream or downstream genes. We tested the idea that FTO itself is involved in obesity. We show that a dominant point mutation in the mouse Fto gene results in reduced fat mass, increased energy expenditure, and unchanged physical activity. Exposure to a high-fat diet enhances lean mass and lowers fat mass relative to control mice. Biochemical studies suggest the mutation occurs in a structurally novel domain and modifies FTO function, possibly by altering its dimerisation state. Gene expression profiling revealed increased expression of some fat and carbohydrate metabolism genes and an improved inflammatory profile in white adipose tissue of mutant mice. These data provide direct functional evidence that FTO is a causal gene underlying obesity. Compared to the reported mouse FTO knockout, our model more accurately reflects the effect of human FTO variants; we observe a heterozygous as well as homozygous phenotype, a smaller difference in weight and adiposity, and our mice do not show perinatal lethality or an age-related reduction in size and length. Our model suggests that a search for human coding mutations in FTO may be informative and that inhibition of FTO activity is a possible target for the treatment of morbid obesity.

Author Summary

Geneticists have identified many gene regions that cause human disease by using multiple genetic markers in large populations to find gene regions associated with disease. However, it is often not clear precisely which gene in any given region causes the disease or how the gene exerts its functional effect. For example, a gene variant in the non-coding region of FTO enhances obesity risk, but it is not clear if this is an effect of the FTO gene itself or another gene located nearby. We therefore tested whether FTO regulates body weight in the mouse. We found that a single change (mutation) in the sequence coding for the mouse FTO protein decreases the functional activity of FTO and causes reduced fat mass and body weight. Food intake and activity were normal, but the mutant mice had a higher metabolic rate. In addition, their fat mass was lower than that of normal mice when both were fed a high-fat diet. Our study provides direct evidence that FTO directly affects fat mass and thus is likely to have a role in human obesity. As reduced FTO function decreases body weight in mice, it is worth exploring if pharmaceutical agents that inhibit FTO activity might help reduce human obesity.

Fat mass and obesity associated gene (FTO) is the first gene associated with body mass index (BMI) and risk for diabetes. FTO is highly expressed in the brain and pancreas, and is involved in regulating dietary intake and energy expenditure. To investigate the transcriptional regulation of FTO expression, we created 5′-deletion constructs of the FTO promoter to determine which transcription factors are most relevant to FTO expression. The presence of an activation region at −201/+34 was confirmed by luciferase activity analysis. A potential Foxa2 (called HNF-3β) binding site and an upstream stimulatory factor (USF)-binding site was identified in the −100 bp fragment upstream of the transcription start site (TSS). Furthermore, using mutagenesis, we identified the Foxa2 binding sequence (−26/−14) as a negative regulatory element to the activity of the human FTO promoter. The USF binding site did not affect the FTO promoter activity. Chromatin immunoprecipitation (ChIP) assays were performed to confirm Foxa2 binding to the FTO promoter. Overexpression of Foxa2 in HEK 293 cells significantly down-regulated FTO promoter activity and expression. Conversely, knockdown of Foxa2 by siRNA significantly up-regulated FTO expression. These findings suggest that Foxa2 negatively regulates the basal transcription and expression of the human FTO gene.

OBJECTIVE

Common variants in FTO (the fat mass– and obesity-associated gene) associate with obesity and type 2 diabetes. The regulation and biological function of FTO mRNA expression in target tissue is unknown. We investigated the genetic and nongenetic regulation of FTO mRNA in skeletal muscle and adipose tissue and their influence on in vivo glucose and fat metabolism.

RESEARCH DESIGN AND METHODS

The FTO rs9939609 polymorphism was genotyped in two twin cohorts: 1) 298 elderly twins aged 62–83 years with glucose tolerance ranging from normal to type 2 diabetes and 2) 196 young (25–32 years) and elderly (58–66 years) nondiabetic twins examined by a hyperinsulinemic-euglycemic clamp including indirect calorimetry. FTO mRNA expression was determined in subcutaneous adipose tissue (n = 226) and skeletal muscle biopsies (n = 158).

RESULTS

Heritability of FTO expression in both tissues was low, and FTO expression was not influenced by FTO rs9939609 genotype. FTO mRNA expression in skeletal muscle was regulated by age and sex, whereas age and BMI were predictors of adipose tissue FTO mRNA expression. FTO mRNA expression in adipose tissue was associated with an atherogenic lipid profile. In skeletal muscle, FTO mRNA expression was negatively associated to fat and positively to glucose oxidation rates as well as positively correlated with expression of genes involved in oxidative phosphorylation including PGC1α.

CONCLUSIONS

The heritability of FTO expression in adipose tissue and skeletal muscle is low and not influenced by obesity-associated FTO genotype. The age-dependent decline in FTO expression is associated with peripheral defects of glucose and fat metabolism.

Background

Intrauterine and postnatal overnutrition program hyperphagia, adiposity and glucose intolerance in offspring. Single-nucleotide polymorphisms (SNPs) of the fat mass and obesity associated (FTO) gene have been linked to increased risk of obesity. FTO is highly expressed in hypothalamic regions critical for energy balance and hyperphagic phenotypes were linked with FTO SNPs. As nutrition during fetal development can influence the expression of genes involved in metabolic function, we investigated the impact of maternal obesity on FTO.

Methods

Female Sprague Dawley rats were exposed to chow or high fat diet (HFD) for 5 weeks before mating, throughout gestation and lactation. On postnatal day 1 (PND1), some litters were adjusted to 3 pups (vs. 12 control) to induce postnatal overnutrition. At PND20, rats were weaned onto chow or HFD for 15 weeks. FTO mRNA expression in the hypothalamus and liver, as well as hepatic markers of lipid metabolism were measured.

Results

At weaning, hypothalamic FTO mRNA expression was increased significantly in offspring of obese mothers and FTO was correlated with both visceral and epididymal fat mass (P<0.05); body weight approached significance (P = 0.07). Hepatic FTO and Fatty Acid Synthase mRNA expression were decreased by maternal obesity. At 18 weeks, FTO mRNA expression did not differ between groups; however body weight was significantly correlated with hypothalamic FTO. Postnatal HFD feeding significantly reduced hepatic Carnitine Palmitoyltransferase-1a but did not affect the expression of other hepatic markers investigated. FTO was not affected by chronic HFD feeding.

Significance

Maternal obesity significantly impacted FTO expression in both hypothalamus and liver at weaning. Early overexpression of hypothalamic FTO correlated with increased adiposity and later food intake of siblings exposed to HFD suggesting upregulation of FTO may contribute to subsequent hyperphagia, in line with some human data. No effect of maternal obesity was observed on FTO in adulthood.

Variants in the FTO (fat mass and obesity associated) gene are associated with increased body mass index in humans. Here, we show by bioinformatics analysis that FTO shares sequence motifs with Fe(II)- and 2-oxoglutarate–dependent oxygenases. We find that recombinant murine Fto catalyzes the Fe(II)- and 2OG-dependent demethylation of 3-methylthymine in single-stranded DNA, with concomitant production of succinate, formaldehyde, and carbon dioxide. Consistent with a potential role in nucleic acid demethylation, Fto localizes to the nucleus in transfected cells. Studies of wild-type mice indicate that Fto messenger RNA (mRNA) is most abundant in the brain, particularly in hypothalamic nuclei governing energy balance, and that Fto mRNA levels in the arcuate nucleus are regulated by feeding and fasting. Studies can now be directed toward determining the physiologically relevant FTO substrate and how nucleic acid methylation status is linked to increased fat mass.

Genome-wide association studies have identified SNPs within the human FTO gene that display a strong association with obesity. Individuals homozygous for the at-risk rs9939609 A allele weigh ~3kg more. Loss of function and/or expression of FTO in mice leads to increased energy expenditure and a lean phenotype. We show here that ubiquitous overexpression of Fto leads to a dose-dependent increase in body and fat mass, irrespective of whether mice are fed a standard or high fat diet. The increased body mass results primarily from increased food intake. Glucose intolerance develops with increased Fto expression on a high fat diet. This study provides the first direct evidence that increased Fto expression causes obesity in mice.

Sequence variants in the first intron of FTO are strongly associated with human obesity and human carriers of the risk alleles show evidence for increased appetite and food intake. Mice globally lacking Fto display a complex phenotype characterised by both increased energy expenditure and increased food intake. The site of action of FTO on energy balance is unclear. Fasting reduces levels of Fto mRNA in the arcuate nucleus (ARC) of the hypothalamus, a site where Fto expression is particularly high. In this study, we have extended this nutritional link by demonstrating that consumption of a high fat diet (45%) results in a 2.5 fold increase in Arc Fto expression. We have further explored the role of hypothalamic Fto in the control of food intake by using stereotactic injections coupled with AAV technology to bi-directionally modulate Fto expression. An over expression of Fto protein by 2.5-fold in the ARC results in a 14% decrease in average daily food intake in the first week. In contrast, knocking down Arc Fto expression by 40% increases food intake by 16%. mRNA levels of Agrp, Pomc and Npy, ARC-expressed genes classically associated with the control of food intake, were not affected by the manipulation of Fto expression. However, over expression of Fto resulted in a 4-fold increase in the mRNA levels of Stat3, a signalling molecule critical for leptin receptor signalling, suggesting a possible candidate for the mediation of Fto's actions. These data provide further support for the notion that FTO itself can influence key components of energy balance, and is therefore a strong candidate for the mediation of the robust association between FTO intronic variants and adiposity. Importantly, this provide the first indication that selective alteration of FTO levels in the hypothalamus can influence food intake, a finding consistent with the reported effects of FTO alleles on appetite and food intake in man.

Background

The Fat mass and obesity gene (FTO) has been identified through genome wide association studies as an important genetic factor contributing to a higher body mass index (BMI). However, the molecular context in which this effect is mediated has yet to be determined. We investigated the potential molecular network for FTO by analyzing co-expression and protein-protein interaction databases, Coxpresdb and IntAct, as well as the functional coupling predicting multi-source database, FunCoup. Hypothalamic expression of FTO-linked genes defined with this bioinformatics approach was subsequently studied using quantitative real time-PCR in mouse feeding models known to affect FTO expression.

Results

We identified several candidate genes for functional coupling to FTO through database studies and selected nine for further study in animal models. We observed hypothalamic expression of Profilin 2 (Pfn2), cAMP-dependent protein kinase catalytic subunit beta (Prkacb), Brain derived neurotrophic factor (Bdnf), neurotrophic tyrosine kinase, receptor, type 2 (Ntrk2), Signal transducer and activator of transcription 3 (Stat3), and Btbd12 to be co-regulated in concert with Fto. Pfn2 and Prkacb have previously not been linked to feeding regulation.

Conclusions

Gene expression studies validate several candidates generated through database studies of possible FTO-interactors. We speculate about a wider functional role for FTO in the context of current and recent findings, such as in extracellular ligand-induced neuronal plasticity via NTRK2/BDNF, possibly via interaction with the transcription factor CCAAT/enhancer binding protein β (C/EBPβ).

Background

Obesity has been shown to increase breast cancer risk. FTO is a novel gene which has been identified through genome wide association studies (GWAS) to be related to obesity. Our objective was to evaluate tissue expression of FTO in breast and the role of FTO SNPs in predicting breast cancer risk.

Methods

We performed a case-control study of 354 breast cancer cases and 364 controls. This study was conducted at Northwestern University. We examined the role of single nucleotide polymorphisms (SNPs) of intron 1 of FTO in breast cancer risk. We genotyped cases and controls for four SNPs: rs7206790, rs8047395, rs9939609 and rs1477196. We also evaluated tissue expression of FTO in normal and malignant breast tissue.

Results

We found that all SNPs were significantly associated with breast cancer risk with rs1477196 showing the strongest association. We showed that FTO is expressed both in normal and malignant breast tissue. We found that FTO genotypes provided powerful classifiers to predict breast cancer risk and a model with epistatic interactions further improved the prediction accuracy with a receiver operating characteristic (ROC) curves of 0.68.

Conclusion

In conclusion we have shown a significant expression of FTO in malignant and normal breast tissue and that FTO SNPs in intron 1 are significantly associated with breast cancer risk. Furthermore, these FTO SNPs are powerful classifiers in predicting breast cancer risk.

Background

The rs9939609 single-nucleotide polymorphism (SNP) in the fat mass and obesity (FTO) gene has previously been associated with higher BMI levels in children and young adults. In contrast, this association was not found in elderly men. BMI is a measure of overweight in relation to the individuals' height, but offers no insight into the regional body fat composition or distribution.

Objective

To examine whether the FTO gene is associated with overweight and body composition-related phenotypes rather than BMI, we measured waist circumference, total fat mass, trunk fat mass, leg fat mass, visceral and subcutaneous adipose tissue, and daily energy intake in 985 humans (493 women) at the age of 70 years. In total, 733 SNPs located in the FTO gene were genotyped in order to examine whether rs9939609 alone or the other SNPs, or their combinations, are linked to obesity-related measures in elderly humans.

Design

Cross-sectional analysis of the Prospective Investigation of the Vasculature in Uppsala Seniors (PIVUS) cohort.

Results

Neither a single SNP, such as rs9939609, nor a SNP combination was significantly linked to overweight, body composition-related measures, or daily energy intake in elderly humans. Of note, these observations hold both among men and women.

Conclusions

Due to the diversity of measurements included in the study, our findings strengthen the view that the effect of FTO on body composition appears to be less profound in later life compared to younger ages and that this is seemingly independent of gender.

Background

Polymorphism in the FTO gene is strongly associated with obesity, but little is known about the molecular bases of this relationship. We investigated whether hypothalamic FTO is involved in energy-dependent overconsumption of food. We determined FTO mRNA levels in rodent models of short- and long-term intake of palatable fat or sugar, deprivation, diet-induced increase in body weight, baseline preference for fat versus sugar as well as in same-weight animals differing in the inherent propensity to eat calories especially upon availability of diverse diets, using quantitative PCR. FTO gene expression was also studied in organotypic hypothalamic cultures treated with anorexigenic amino acid, leucine. In situ hybridization (ISH) was utilized to study FTO signal in reward- and hunger-related sites, colocalization with anorexigenic oxytocin, and c-Fos immunoreactivity in FTO cells at initiation and termination of a meal.

Results

Deprivation upregulated FTO mRNA, while leucine downregulated it. Consumption of palatable diets or macronutrient preference did not affect FTO expression. However, the propensity to ingest more energy without an effect on body weight was associated with lower FTO mRNA levels. We found that 4-fold higher number of FTO cells displayed c-Fos at meal termination as compared to initiation in the paraventricular and arcuate nuclei of re-fed mice. Moreover, ISH showed that FTO is present mainly in hunger-related sites and it shows a high degree of colocalization with anorexigenic oxytocin.

Conclusion

We conclude that FTO mRNA is present mainly in sites related to hunger/satiation control; changes in hypothalamic FTO expression are associated with cues related to energy intake rather than feeding reward. In line with that, neurons involved in feeding termination express FTO. Interestingly, baseline FTO expression appears linked not only with energy intake but also energy metabolism.

Single nucleotide polymorphisms (SNPs) in the fat mass and obesity associated (FTO) gene are associated with body mass index (BMI) in populations of European descent. The FTO rs9939609 variant, first detected in a genome-wide association study of diabetes, conferred an increased disease risk that was abolished after adjustment for BMI, suggesting that the association may be due to variation in adiposity. The relationship between diabetes, four previously identified FTO polymorphisms that span a 19.6-kb genomic region, and obesity was therefore evaluated in the biracial population-based Atherosclerosis Risk in Communities Study with the goal of further refining the association by comparing results between the two ethnic groups. The prevalence of diabetes and obesity (BMI ≥30 kg/m2) was established at baseline, and diabetes was determined by either self-report, a fasting glucose level ≥126 mg/dL, or non-fasting glucose ≥200 mg/dL. There were 1,004 diabetes cases and 10,038 non-cases in whites, and 670 cases and 2,780 non-cases in African-Americans. Differences in mean BMI were assessed by a general linear model, and multivariable logistic regression was used to predict the risk of diabetes and obesity. For white participants, the FTO rs9939609 A allele was associated with an increased risk of diabetes (odds ratio (OR)  = 1.19, p<0.001) and obesity (OR = 1.22, p<0.001) under an additive genetic model that was similar for all of the SNPs analyzed. In African-Americans, only the rs1421085 C allele was a determinant of obesity risk (OR = 1.17, p = 0.05), but was found to be protective against diabetes (OR = 0.79, p = 0.03). Adjustment for BMI did not eliminate any of the observed associations with diabetes. Significant statistical interaction between race and the FTO variants suggests that the effect on diabetes susceptibility may be context dependent.

Background

Genome-wide association studies (GWAS) are useful to reveal an association between single nucleotide polymorphisms and different measures of obesity. A multitude of new loci has recently been reported, but the exact function of most of the according genes is not known. The aim of our study was to start elucidating the function of some of these genes.

Methods

We performed an expression analysis of fourteen genes, namely BDNF, ETV5, FAIM2, FTO, GNPDA2, KCTD15, LYPLAL1, MCR4, MTCH2, NEGR1, NRXN3, TMEM18, SEC16B and TFAP2B, via real-time RT-PCR in adipose tissue of the kidney capsule, the mesenterium and subcutaneum as well as the hypothalamus of obese Zucker diabetic fatty (ZDF) and Zucker lean (ZL) rats at an age of 22 weeks.

Results

All of our target genes except for SEC16B showed the highest expression in the hypothalamus. This suggests a critical role of these obesity-related genes in the central regulation of energy balance. Interestingly, the expression pattern in the hypothalamus showed no differences between obese ZDF and lean ZL rats. However, LYPLAL1, TFAP2B, SEC16B and FAIM2 were significantly lower expressed in the kidney fat of ZDF than ZL rats. NEGR1 was even lower expressed in subcutaneous and mesenterial fat, while MTCH2 was higher expressed in the subcutaneous and mesenterial fat of ZDF rats.

Conclusion

The expression pattern of the investigated obesity genes implies for most of them a role in the central regulation of energy balance, but for some also a role in the adipose tissue itself. For the development of the ZDF phenotype peripheral rather than central mechanisms of the investigated genes seem to be relevant.

OBJECTIVE

A strong association between genetic variants and obesity was found for the fat mass and obesity-associated gene (FTO). However, few details are known concerning the expression and function of FTO in skeletal muscle of patients with metabolic diseases.

RESEARCH DESIGN AND METHODS

We investigated basal FTO expression in skeletal muscle from obese nondiabetic subjects and type 1 and type 2 diabetic patients, compared with age-matched control subjects, and its regulation in vivo by insulin, glucose, or rosiglitazone. The function of FTO was further studied in myotubes by overexpression experiments.

RESULTS

We found a significant increase of FTO mRNA and protein levels in muscle from type 2 diabetic patients, whereas its expression was unchanged in obese or type 1 diabetic patients. Moreover, insulin or glucose infusion during specific clamps did not regulate FTO expression in skeletal muscle from control or type 2 diabetic patients. Interestingly, rosiglitazone treatment improved insulin sensitivity and reduced FTO expression in muscle from type 2 diabetic patients. In myotubes, adenoviral FTO overexpression increased basal protein kinase B phosphorylation, enhanced lipogenesis and oxidative stress, and reduced mitochondrial oxidative function, a cluster of metabolic defects associated with type 2 diabetes.

CONCLUSIONS

This study demonstrates increased FTO expression in skeletal muscle from type 2 diabetic patients, which can be normalized by thiazolidinedione treatment. Furthermore, in vitro data support a potential implication of FTO in oxidative metabolism, lipogenesis and oxidative stress in muscle, suggesting that it could be involved in the muscle defects that characterize type 2 diabetes.

A common T/A polymorphism (rs9939609) in the fat mass and obesity associated (FTO) gene was found associated with early-onset and severe obesity in both adults and children. However, recent observations failed to find associations of FTO with obesity. To investigate the genetic background of early obesity, we analysed the single nucleotide polymorphism (SNP) rs9939609 of FTO in 371 styrian adolescents towards degree of obesity, subcutaneous adipose tissue (SAT)-distribution determined by lipometry, early metabolic and preatherosclerotic symptoms. The percentage of AA homozygotes for the rs9939609 SNP of FTO was significantly increased in the obese adolescents. Compared to the TT wildtype, AA homozygotes showed significantly elevated values of SAT thickness at the trunk-located lipometer measure points neck and frontal chest, body weight, body mass index, waist, and hip circumference. No associations were found with carotis communis intima media thickness, systolic, diastolic blood pressure, ultrasensitive C-reactive protein (US-CRP), homocystein, total cholesterol, triglycerides, HDL cholesterol, oxidized LDL, fasted glucose, insulin, HOMA-index, liver transaminases, uric acid, and adipokines like resistin, leptin, and adiponectin. Taken together, to the best of our knowledge we are the first to report that the rs9939609 FTO SNP is associated with trunk weighted obesity as early as in adolescence.

Background

Fat-mass and obesity-associated (FTO) gene is a gene located in chromosome region 16q12.2. Genetic variants in FTO are associated with the obesity phenotype in European and Hispanic populations. However, this association still remains controversial in Asian population. We aimed to test the association of FTO genetic variants with obesity and obesity-related metabolic traits among children living in Beijing, China.

Methods

We genotyped FTO variants rs9939609 in 670 children (332 girls and 338 boys) aged 8-11 years living in Beijing, and analyzed its association with obesity and obesity-related metabolic traits. Overweight and obesity were defined by age- and sex-specific BMI reference for Chinese children. Obesity-related metabolic traits included fasting plasma glucose, lipid profiles, leptin, ghrelin, adiponectin and blood pressures.

Results

The frequency of rs9939609 A allele was 12.2%, which was 21.9% for the heterozygote and 1.2% for the homozygote of the A allele. The obesity prevalence among the carriers of AA/AT genotypes was significantly higher than that among those with TT genotype (36.4% vs. 22.6%, P = 0.004). Compared to the carrier of TT genotype, the likelihood of obesity was 1.79 (95% confidence interval (95% CI) 1.20-2.67, P = 0.004) for the carrier of AA/AT genotype, after adjustment of sex, age and puberty stages. The BMI Z-score of children with AA/AT genotype were significantly higher than that of their counterparts with the TT genotype (1.1 ± 0.1 vs. 0.8 ± 0.1, P = 0.02). The concentration of triglyceride was 1.03 ± 0.52 mmol/L among TT carrier and 1.13 ± 0.68 mmol/L among AA/AT carrier (P = 0.045). While, the concentrations of adiponectin were 18.0 ± 0.4 μg/ml among carriers of TT and 16.2 ± 0.7 μg/ml among subjects with AA/AT genotype (P = 0.03). The level of glucose marginally increased in the AA/AT genotype subjects (4.67 ± 0.40 mmol/L vs. 4.60 ± 0.35 mmol/L, P = 0.08). The evidence of association was reduced after adjustment for BMI (P = 0.38 for triglyceride, P = 0.20 for adiponectin and glucose). There was weak evidence of association between rs9939609 and other obesity-related metabolic traits including total cholesterol (3.92 ± 0.03 mmol/L vs. 4.02 ± 0.05 mmol/L, P = 0.10), insulin (2.69 ± 1.77 ng/ml vs. 3.12 ± 2.91 ng/ml, P = 0.14), and insulin resistance (HOMA-IR 0.56 ± 0.03 vs. 0.66 ± 0.05, P = 0.10).

Conclusions

Genetic variation in the FTO gene associates with obesity in Chinese children.

Background

FTO and NAMPT/PBEF/visfatin are thought to play a role in obesity but their transcriptional regulation in adipocytes is not fully understood. In this study, we evaluated the transcriptional regulation of FTO and NAMPT in preadipocytes and adipocytes by metabolic regulators.

Methodology and Principal Findings

We assessed FTO mRNA expression during human adipocyte differentiation of Simpson-Golabi-Behmel syndrome (SGBS) cells and primary subcutaneous preadipocytes in vitro and evaluated the effect of the metabolic regulators glucose, insulin, dexamethasone, IGF-1 and isoproterenol on FTO and NAMPT mRNA expression in SGBS preadipocytes and adipocytes. FTO mRNA levels were not significantly modulated during adipocyte differentiation. Also, metabolic regulators had no impact on FTO expression in preadipocytes or adipocytes. In SGBS preadipocytes NAMPT expression was more than 3fold induced by dexamethasone and isoproterenol and 1.6fold by dexamethasone in adipocytes. Complete glucose restriction caused an increase in NAMPT mRNA expression by more than 5fold and 1.4fold in SGBS preadipocytes and adipocytes, respectively.

Conclusion

FTO mRNA expression is not significantly affected by differentiation or metabolic regulators in human adipocytes. The stimulation of NAMPT expression by dexamethasone, isoproterenol and complete glucose restriction may indicate a regulation of NAMPT by metabolic stress, which was more pronounced in preadipocytes compared to mature adipocytes.

Genetic variants in intron 1 of the fat mass– and obesity-associated (FTO) gene have been consistently associated with body mass index (BMI) in Europeans. However, follow-up studies in African Americans (AA) have shown no support for some of the most consistently BMI–associated FTO index single nucleotide polymorphisms (SNPs). This is most likely explained by different race-specific linkage disequilibrium (LD) patterns and lower correlation overall in AA, which provides the opportunity to fine-map this region and narrow in on the functional variant. To comprehensively explore the 16q12.2/FTO locus and to search for second independent signals in the broader region, we fine-mapped a 646–kb region, encompassing the large FTO gene and the flanking gene RPGRIP1L by investigating a total of 3,756 variants (1,529 genotyped and 2,227 imputed variants) in 20,488 AAs across five studies. We observed associations between BMI and variants in the known FTO intron 1 locus: the SNP with the most significant p-value, rs56137030 (8.3×10−6) had not been highlighted in previous studies. While rs56137030was correlated at r2>0.5 with 103 SNPs in Europeans (including the GWAS index SNPs), this number was reduced to 28 SNPs in AA. Among rs56137030 and the 28 correlated SNPs, six were located within candidate intronic regulatory elements, including rs1421085, for which we predicted allele-specific binding affinity for the transcription factor CUX1, which has recently been implicated in the regulation of FTO. We did not find strong evidence for a second independent signal in the broader region. In summary, this large fine-mapping study in AA has substantially reduced the number of common alleles that are likely to be functional candidates of the known FTO locus. Importantly our study demonstrated that comprehensive fine-mapping in AA provides a powerful approach to narrow in on the functional candidate(s) underlying the initial GWAS findings in European populations.

Author Summary

Genetic variants within the fat mass– and obesity-associated (FTO) gene are associated with increased risk of obesity. To better understand which specific genetic variant(s) in this genetic region is associated with obesity risk, we attempt to genotype or impute all known genetic variants in the region and test for association with body mass index as a measurement of obesity in over 20,000 African Americans. We identified 29 potential candidate variants, of which one variant (rs1421085) is a particularly interesting candidate for future functional follow-up studies. Our example shows the powerful approach of studying a large African American population, substantially reducing the number of possible functional variants compared with European descent populations.