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Single-nucleotide polymorphisms (SNPs), which are located in the first intron of the FTO gene, are reported to be associated with body weight and the body mass index (BMI). However, their effects on anthropometric measurements in adolescents are poorly understood. This study aimed to investigate the association of three adjacent polymorphisms (rs9930506, rs9930501, & rs9932754) in the FTO gene with anthropometric indices in Iranian adolescent males. The participants comprised a total of 237 adolescent males who were recruited randomly from two high schools in Tehran, Iran. The DNA samples were genotyped for the FTO gene polymorphisms by DNA sequencing. BMI, body fat percentage (BF%), and body muscle percentage (BM%) were determined using a validated bioelectrical impedance analysis scale. The association of the FTO polymorphisms with weight, height, BMI, BF%, and BM% was investigated. A haplotype of rs9930506, rs9930501, and rs9932754 (GGT) in the first intron of the FTO with complete linkage disequilibrium (LD) was found to be significantly associated with higher weight (OR = 1.32), BMI (OR = 5.36) and BF% (OR = 1.46), and lower BM% (OR = 3.59) (all P<0.001). None of the students with GGC genotypes were underweight, while all of the students with AAT genotypes had high muscle mass. A haplotype in the first intron of the FTO gene had a strong association with obesity indices in Iranian adolescent males. The FTO gene polymorphisms might have greater effects on anthropometric indices than what was previously imagined. Moreover, we suggested that the FTO gene exerted their effects on anthropometric measurements through haplotypes (and not single SNPs).

Obesity-associated noncoding sequences within FTO are functionally connected with IRX3 , and long-range enhancers in this region recapitulate aspects of IRX3 expression, suggesting that the obesity-associated interval is part of IRX3 regulation; Irx3 -deficient mice have lower body weight and are resistant to diet-induced obesity, suggesting IRX3 as a novel determinant of body mass and composition. Genetic links to obesity The search for genetic correlates of obesity has highlighted a noncoding region in the FTO gene: variations within this intron are associated with increased risk for obesity and type 2 diabetes. Although the biological actions of FTO have been intensely scrutinized, it is still not clear how these genetic variants influence FTO expression and biology. This paper shows that these noncoding sequences are functionally connected — at megabase distances — with the homeobox gene IRX3 . The obesity-associated interval appears to belong to the regulatory functions of IRX3 , rather than FTO . In addition, mice lacking Irx3 have reduced body weight and are resistant to diet-induced obesity. Taken together, the data suggest that IRX3 is an important metabolic regulator associated with human obesity and type 2 diabetes. Genome-wide association studies (GWAS) have reproducibly associated variants within introns of FTO with increased risk for obesity and type 2 diabetes (T2D) 1 , 2 , 3 . Although the molecular mechanisms linking these noncoding variants with obesity are not immediately obvious, subsequent studies in mice demonstrated that FTO expression levels influence body mass and composition phenotypes 4 , 5 , 6 . However, no direct connection between the obesity-associated variants and FTO expression or function has been made 7 , 8 , 9 . Here we show that the obesity-associated noncoding sequences within FTO are functionally connected, at megabase distances, with the homeobox gene IRX3 . The obesity-associated FTO region directly interacts with the promoters of IRX3 as well as FTO in the human, mouse and zebrafish genomes. Furthermore, long-range enhancers within this region recapitulate aspects of IRX3 expression, suggesting that the obesity-associated interval belongs to the regulatory landscape of IRX3 . Consistent with this, obesity-associated single nucleotide polymorphisms are associated with expression of IRX3 , but not FTO , in human brains. A direct link between IRX3 expression and regulation of body mass and composition is demonstrated by a reduction in body weight of 25 to 30% in Irx3- deficient mice, primarily through the loss of fat mass and increase in basal metabolic rate with browning of white adipose tissue. Finally, hypothalamic expression of a dominant-negative form of Irx3 reproduces the metabolic phenotypes of Irx3 -deficient mice. Our data suggest that IRX3 is a functional long-range target of obesity-associated variants within FTO and represents a novel determinant of body mass and composition.

The variation in weight within a shared environment is largely attributable to genetic factors. Whilst many genes/loci confer susceptibility to obesity, little is known about the genetic architecture of healthy thinness. Here, we characterise the heritability of thinness which we found was comparable to that of severe obesity (h2 = 28.07 vs 32.33% respectively), although with incomplete genetic overlap (r = -0.49, 95% CI [-0.17, -0.82], p = 0.003). In a genome-wide association analysis of thinness (n = 1,471) vs severe obesity (n = 1,456), we identified 10 loci previously associated with obesity, and demonstrate enrichment for established BMI-associated loci (pbinomial = 3.05x10-5). Simulation analyses showed that different association results between the extremes were likely in agreement with additive effects across the BMI distribution, suggesting different effects on thinness and obesity could be due to their different degrees of extremeness. In further analyses, we detected a novel obesity and BMI-associated locus at PKHD1 (rs2784243, obese vs. thin p = 5.99x10-6, obese vs. controls p = 2.13x10-6 pBMI = 2.3x10-13), associations at loci recently discovered with much larger sample sizes (e.g. FAM150B and PRDM6-CEP120), and novel variants driving associations at previously established signals (e.g. rs205262 at the SNRPC/C6orf106 locus and rs112446794 at the PRDM6-CEP120 locus). Our ability to replicate loci found with much larger sample sizes demonstrates the value of clinical extremes and suggest that characterisation of the genetics of thinness may provide a more nuanced understanding of the genetic architecture of body weight regulation and may inform the identification of potential anti-obesity targets.

Autophagy has been implicated in the ageing process, but whether autophagy activation extends lifespan in mammals is unknown. Here we show that ubiquitous overexpression of Atg5, a protein essential for autophagosome formation, extends median lifespan of mice by 17.2%. We demonstrate that moderate overexpression of Atg5 in mice enhances autophagy, and that Atg5 transgenic mice showed anti-ageing phenotypes, including leanness, increased insulin sensitivity and improved motor function. Furthermore, mouse embryonic fibroblasts cultured from Atg5 transgenic mice are more tolerant to oxidative damage and cell death induced by oxidative stress, and this tolerance was reversible by treatment with an autophagy inhibitor. Our observations suggest that the leanness and lifespan extension in Atg5 transgenic mice may be the result of increased autophagic activity. Changes in autophagy have been shown to modulate lifespan in lower organisms. Here, Pyo et al. show that mice globally overexpressing the autophagy protein Atg5 live longer and are leaner than normal mice, providing the first evidence that increased autophagy extends lifespan in mammals.

Significance A unique population of Foxp3 ⁺CD4 ⁺ regulatory T (T ᵣₑg) cells resides in visceral adipose tissue of lean mice. VAT T ᵣₑgₛ are important regulators of local and systemic inflammation and metabolism. Here, we show that the VAT T ᵣₑg signature is imposed early in life, well before the typical age-dependent expansion of the adipose-tissue T ᵣₑg population. VAT T ᵣₑgₛ in obese mice lose the signature typical of lean individuals but gain an additional set of over- and underrepresented transcripts. In striking parallel to a pathway recently elucidated in adipocytes, the obese mouse VAT T ᵣₑg signature depends on phosphorylation of a specific residue of PPARγ. These findings are important to consider in designing drugs to target type 2 diabetes and other features of the “metabolic syndrome.” A unique population of Foxp3 ⁺CD4 ⁺ regulatory T (T ᵣₑg) cells resides in visceral adipose tissue (VAT) of lean mice, especially in the epididymal fat depot. VAT T ᵣₑgₛ are unusual in their very high representation within the CD4 ⁺ T-cell compartment, their transcriptome, and their repertoire of antigen-specific T-cell receptors. They are important regulators of local and systemic inflammation and metabolism. The overall goal of this study was to learn how the VAT T ᵣₑg transcriptome adapts to different stimuli; in particular, its response to aging in lean mice, to metabolic perturbations associated with obesity, and to certain signaling events routed through PPARγ, the “master-regulator” of adipocyte differentiation. We show that the VAT T ᵣₑg signature is imposed early in life, well before age-dependent expansion of the adipose-tissue T ᵣₑg population. VAT T ᵣₑgₛ in obese mice lose the signature typical of lean individuals but gain an additional set of over- and underrepresented transcripts. This obese mouse VAT T ᵣₑg signature depends on phosphorylation of the serine residue at position 273 of PPARγ, in striking parallel to a pathway recently elucidated in adipocytes. These findings are important to consider in designing drugs to target type 2 diabetes and other features of the “metabolic syndrome.”

In these new reports, three different research groups independently find that various T cell populations are crucial mediators of obesity-induced metabolic dysfunction. They also show that pharmacological approaches that target these T cells are beneficial, thus opening the door to possible new therapeutic approaches to treating obesity-related diseases such as diabetes ( pages 846–847 , 914–920 and 921–929 ). Obesity is accompanied by chronic, low-grade inflammation of adipose tissue, which promotes insulin resistance and type-2 diabetes. These findings raise the question of how fat inflammation can escape the powerful armamentarium of cells and molecules normally responsible for guarding against a runaway immune response. CD4 + Foxp3 + T regulatory (T reg ) cells with a unique phenotype were highly enriched in the abdominal fat of normal mice, but their numbers were strikingly and specifically reduced at this site in insulin-resistant models of obesity. Loss-of-function and gain-of-function experiments revealed that these T reg cells influenced the inflammatory state of adipose tissue and, thus, insulin resistance. Cytokines differentially synthesized by fat-resident regulatory and conventional T cells directly affected the synthesis of inflammatory mediators and glucose uptake by cultured adipocytes. These observations suggest that harnessing the anti-inflammatory properties of T reg cells to inhibit elements of the metabolic syndrome may have therapeutic potential.

Genomic balance: underweight as a mirror image of obesity Underweight and obese phenotypes can both pose health risks. But whereas obesity has been associated with a number of genetic variants, little is known about the genetic basis of underweight. A large-scale screen of data from 28 cytogenetic centres in Europe and North America now shows that being underweight is frequently associated with duplication of a short region on chromosome 16. Deletion of this same chromosomal region has previously been associated with obesity. The observed associated phenotypes are opposites, or mirrors, of those reported in carriers of deletions at this locus, and correlate with changes in transcript levels for genes within the duplication but not within the adjacent regions. The suggestion is that severe obesity and being underweight could have mirror etiologies, possibly through contrasting effects on energy balance. Both obesity and being underweight have been associated with increased mortality 1 , 2 . Underweight, defined as a body mass index (BMI) ≤ 18.5 kg per m 2 in adults and ≤ −2 standard deviations from the mean in children, is the main sign of a series of heterogeneous clinical conditions including failure to thrive 3 , 4 , 5 , feeding and eating disorder and/or anorexia nervosa 6 , 7 . In contrast to obesity, few genetic variants underlying these clinical conditions have been reported 8 , 9 . We previously showed that hemizygosity of a ∼600-kilobase (kb) region on the short arm of chromosome 16 causes a highly penetrant form of obesity that is often associated with hyperphagia and intellectual disabilities 10 . Here we show that the corresponding reciprocal duplication is associated with being underweight. We identified 138 duplication carriers (including 132 novel cases and 108 unrelated carriers) from individuals clinically referred for developmental or intellectual disabilities (DD/ID) or psychiatric disorders, or recruited from population-based cohorts. These carriers show significantly reduced postnatal weight and BMI. Half of the boys younger than five years are underweight with a probable diagnosis of failure to thrive, whereas adult duplication carriers have an 8.3-fold increased risk of being clinically underweight. We observe a trend towards increased severity in males, as well as a depletion of male carriers among non-medically ascertained cases. These features are associated with an unusually high frequency of selective and restrictive eating behaviours and a significant reduction in head circumference. Each of the observed phenotypes is the converse of one reported in carriers of deletions at this locus. The phenotypes correlate with changes in transcript levels for genes mapping within the duplication but not in flanking regions. The reciprocal impact of these 16p11.2 copy-number variants indicates that severe obesity and being underweight could have mirror aetiologies, possibly through contrasting effects on energy balance.

Lean body mass, consisting mostly of skeletal muscle, is important for healthy aging. We performed a genome-wide association study for whole body (20 cohorts of European ancestry with n  = 38,292) and appendicular (arms and legs) lean body mass ( n  = 28,330) measured using dual energy X-ray absorptiometry or bioelectrical impedance analysis, adjusted for sex, age, height, and fat mass. Twenty-one single-nucleotide polymorphisms were significantly associated with lean body mass either genome wide ( p  < 5 × 10 −8 ) or suggestively genome wide ( p  < 2.3 × 10 −6 ). Replication in 63,475 (47,227 of European ancestry) individuals from 33 cohorts for whole body lean body mass and in 45,090 (42,360 of European ancestry) subjects from 25 cohorts for appendicular lean body mass was successful for five single-nucleotide polymorphisms in/near HSD17B11, VCAN, ADAMTSL3 , IRS1 , and FTO for total lean body mass and for three single-nucleotide polymorphisms in/near VCAN , ADAMTSL3 , and IRS1 for appendicular lean body mass. Our findings provide new insight into the genetics of lean body mass. Lean body mass is a highly heritable trait and is associated with various health conditions. Here, Kiel and colleagues perform a meta-analysis of genome-wide association studies for whole body lean body mass and find five novel genetic loci to be significantly associated.

Protection from obesity Variations in the human FTO gene have been linked to obesity-related traits in several genome-wide association studies. A functional correlation is now reported between Fto , the equivalent gene in the mouse, and obesity. In Fto -deficient mice there is postnatal growth retardation and a lean phenotype with high energy expenditure and reduced fat accumulation. This suggests that Fto/FTO is involved in homeostasis via the control of energy expenditure. This study shows that mice lacking the Fto gene do not grow properly after birth, and have less adipose tissue and lean body mass. This is due to increased energy expenditure and systemic sympathetic activation, even though these mice move less and eat lots. Several independent, genome-wide association studies have identified a strong correlation between body mass index and polymorphisms in the human FTO gene 1 , 2 , 3 , 4 . Common variants in the first intron define a risk allele predisposing to obesity, with homozygotes for the risk allele weighing approximately 3 kilograms more than homozygotes for the low risk allele 1 . Nevertheless, the functional role of FTO in energy homeostasis remains elusive. Here we show that the loss of Fto in mice leads to postnatal growth retardation and a significant reduction in adipose tissue and lean body mass. The leanness of Fto-deficient mice develops as a consequence of increased energy expenditure and systemic sympathetic activation, despite decreased spontaneous locomotor activity and relative hyperphagia. Taken together, these experiments provide, to our knowledge, the first direct demonstration that Fto is functionally involved in energy homeostasis by the control of energy expenditure.

Context:Recently, data on 2,000,000 people established that low body mass index (BMI) is associated with increased risk of dementia. Whether this observational association reflects a causal effect remains to be clarified.Objective:We tested the hypothesis that there is a causal association between low BMI and high risk of Alzheimer’s disease.Design, Setting, and Participants:Using a Mendelian randomization approach, we studied 95,578 individuals from the Copenhagen General Population Study (CGPS) with up to 36 years of follow-up and consortia data on 303,958 individuals from the Genetic Investigation of Anthropometric Traits (GIANT) and the International Genomics of Alzheimer's Project (IGAP).Main Outcome Measure:Risk of Alzheimer’s disease.Results:The causal odds ratio for a 1-kg/m2 genetically determined lower BMI was 0.98 [95% confidence interval (CI), 0.77 to 1.23] for a weighted allele score in the CGPS. Using 32 BMI-decreasing variants from GIANT and IGAP the causal odds ratio for Alzheimer’s disease for a 1-standard deviation (SD) lower genetically determined BMI was 1.02 (95% CI, 0.86 to 1.22). Corresponding observational hazard ratios from the CGPS were 1.07 (95% CI, 1.05 to 1.09) and 1.32 (95% CI, 1.20 to 1.46) for a 1-kg/m2 and a 1-SD lower BMI, respectively.Conclusions:Genetic and hence lifelong low BMI is not associated with increased risk of Alzheimer’s disease in the general population. These data suggest that low BMI is not a causal risk factor for Alzheimer’s disease and that the corresponding observational association likely is explained by reverse causation or confounding.In this Mendelian randomization study of 399,536 individuals, genetic and hence lifelong lower BMI was not associated with higher risk of Alzheimer’s disease, in contrast to observational associations.