Fat Mass And Obesity-associated Protein Research Articles

FTO rs9939609 polymorphism is associated with metabolic disturbances and response to HCV therapy in HIV/HCV-coinfected patients

BackgroundThe Fat Mass and Obesity-Associated Protein (FTO) gene rs9939609 single nucleotide polymorphism (SNP) has been associated with obesity, metabolic syndrome, insulin resistance (IR), and type 2 diabetes mellitus in the general population. The aim of our study was to examine for the first time the association of the rs9939609 polymorphism with metabolic disturbances, liver disease and virologic response to hepatitis C virus (HCV) therapy with pegylated-interferon-alpha plus ribavirin (pegIFNα/RBV) in human immunodeficiency virus (HIV)/HCV coinfected patients.MethodsWe carried out a cross-sectional study in 261 patients, of whom 178 were subsequently treated with pegIFNα/RBV therapy. FTO rs9939609 and IFNL3 rs12980275 polymorphisms were genotyped by GoldenGate®. The main outcomes were: 1) metabolic disturbances: insulin resistance (homeostatic model assessment (HOMA-IR)) and overweight (body mass index (BMI)); 2) liver disease (Metavir score): significant fibrosis (F ≥2) and steatosis (>10% fatty hepatocytes); and 3) virologic response to HCV treatment: sustained virologic response (SVR).ResultsThe rs9939609 AA genotype was associated with higher values of BMI (adjusted arithmetic mean ratio (aAMR) = 1.08; 95% confidence interval (95%CI) = 1.03 to 1.14; P = 0.002) and HOMA-IR (aAMR = 1.32; 95%CI = 1.03 to 1.69; P = 0.027). Patients with an rs9939609 AA genotype had higher likelihoods of achieving values of BMI ≥27.5 kg/m2 (adjusted odds ratio (aOR) = 3.46; 95%CI =1.17 to 10.21; P = 0.024), HOMA-IR ≥2.5 (aOR = 2.09; 95%CI = 1.02 to 4.32; P = 0.045), significant fibrosis (aOR = 2.34; 95%CI =1.02 to 5.36; P = 0.045) and steatosis (aOR = 3.65; 95%CI = 1.29 to 10.36; P = 0.015). The rs9939609 AT/AA genotype decreased the likelihood of achieving SVR (aOR = 0.58; 95%CI = 0.34 to 0.99; P = 0.044). A decision tree was performed with the genotypes of HCV, IFNL3 and FTO. The incorporation of rs9939609 significantly improves the prediction of SVR (P <0.05). The overall accuracy was 68.2%.ConclusionsPatients carrying the unfavourable AT/AA genotype of rs9939609 polymorphism had higher odds of metabolic disturbances and a lower likelihood of achieving successful virologic response to HCV therapy.

Genetic Susceptibility to Type 2 Diabetes and Obesity: Follow-Up of Findings from Genome-Wide Association Studies

Elucidating the underlying genetic variations influencing various complex diseases is one of the major challenges currently facing clinical genetic research. Although these variations are often difficult to uncover, approaches such as genome-wide association studies (GWASs) have been successful at finding statistically significant associations between specific genomic loci and disease susceptibility. GWAS has been especially successful in elucidating genetic variants that influence type 2 diabetes (T2D) and obesity/body mass index (BMI). Specifically, several GWASs have confirmed that a variant in transcription factor 7-like 2 (TCF7L2) confers risk for T2D, while a variant in fat mass and obesity-associated protein (FTO) confers risk for obesity/BMI; indeed both of these signals are considered the most statistically associated loci discovered for these respective traits to date. The discovery of these two key loci in this context has been invaluable for providing novel insight into mechanisms of heritability and disease pathogenesis. As follow-up studies of TCF7L2 and FTO have typically lead the way in how to follow up a GWAS discovery, we outline what has been learned from such investigations and how they have implications for the myriad of other loci that have been subsequently reported in this disease context.

M6A mRNA Methylation: A New Circadian Pacesetter

The purpose of m(6)A methylation of RNA, first observed in the 1970s, has been a longstanding mystery. Fustin et al. now show that it regulates RNA processing and determines the period and oscillatory stability of the mammalian circadian clockwork.

Identification of Fat Mass and Obesity Associated (FTO) Protein Expression in Cardiomyocytes: Regulation by Leptin and Its Contribution to Leptin-Induced Hypertrophy

The recently-identified fat mass and obesity-associated (FTO) protein is associated with various physiological functions including energy and body weight regulation. Ubiquitously expressed, FTO was identified in heart homogenates although its function is unknown. We studied whether FTO is specifically expressed within the cardiac myocyte and its potential role pertaining to the hypertrophic effect of the adipokine leptin. Most experiments were performed using cultured neonatal rat cardiomyocytes which showed nuclei-specific FTO expression. Leptin significantly increased FTO expression which was associated with myocyte hypertrophy although both events were abrogated by FTO knockdown with siRNA. Administration of a leptin receptor antibody to either normal or obese rats significant reduced myocardial FTO protein expression. Responses in cardiomyocytes were accompanied by JAK2/STAT3 activation whereas JAK2/STAT3 inhibition abolished these effects. Expression of the cut-like homeobox 1(CUX1) transcriptional factor was significantly increased by leptin although this was restricted to the cathepsin L-dependent, proteolytically-derived shorter p110CUX1 isoform whereas the longer p200CUX1 protein was not significantly affected. Cathepsin L expression and activity were both significantly increased by leptin whereas a cathepsin L peptide inhibitor or siRNA specific for CUX1 completely prevented the leptin-induced increase in FTO expression. The cathepsin L peptide inhibitor or siRNA-induced knockdown of either CUX1 or FTO abrogated the hypertrophic response to leptin. Two other pro-hypertrophic factors, endothelin-1 or angiotensin II had no effect on FTO expression and FTO knockdown did not alter the hypertrophic response to either agent. This study demonstrates leptin-induced FTO upregulation in cardiomyocytes via JAK2/STAT3- dependent CUX1 upregulation and suggests an FTO regulatory function of leptin. It also demonstrates for the first time a functional role of FTO in the cardiomyocyte.

Clinical and genetic predictors of weight gain in patients diagnosed with breast cancer

Background:Post-diagnosis weight gain in breast cancer patients has been associated with increased cancer recurrence and mortality. Our study was designed to identify risk factors for this weight gain and create a predictive model to identify a high-risk population for targeted interventions.Methods:Chart review was conducted on 459 breast cancer patients from Northwestern Robert H. Lurie Cancer Centre to obtain weights and body mass indices (BMIs) over an 18-month period from diagnosis. We also recorded tumour characteristics, demographics, clinical factors, and treatment regimens. Blood samples were genotyped for 14 single-nucleotide polymorphisms (SNPs) in fat mass and obesity-associated protein (FTO) and adiponectin pathway genes (ADIPOQ and ADIPOR1).Results:In all, 56% of patients had >0.5 kg m–2 increase in BMI from diagnosis to 18 months, with average BMI and weight gain of 1.9 kg m–2 and 5.1 kg, respectively. Our best predictive model was a primarily SNP-based model incorporating all 14 FTO and adiponectin pathway SNPs studied, their epistatic interactions, and age and BMI at diagnosis, with area under receiver operating characteristic curve of 0.85 for 18-month weight gain.Conclusion:We created a powerful risk prediction model that can identify breast cancer patients at high risk for weight gain.

The biology of FTO: from nucleic acid demethylase to amino acid sensor

Genome-wide association studies have revealed that single-nucleotide polymorphisms in the first intron of the gene encoding fat mass and obesity-associated protein (FTO) are robustly associated with BMI and obesity. Subsequently, this association with body weight, which is replicable across multiple populations and different age groups, has been unequivocally linked to increased food intake. Although evidence from a number of animal models with perturbed FTO expression indicates a role for FTO in energy homeostasis, to date, no conclusive link has been made between the risk alleles and FTO expression or its physiological role. FTO is a nucleic acid demethylase, and a deficiency in FTO leads to a complex phenotype highlighted by postnatal growth retardation, pointing to some fundamental developmental role. Recent emerging data now points to a role for FTO in the sensing of nutrients and the regulation of translation and growth. In this review, we explore the in vivo and in vitro evidence detailing the complex biology of FTO and discuss how these might link to the regulation of body weight.

The expression of FTO in human adipose tissue is influenced by fat depot, adiposity, and insulin sensitivity

The fat mass and obesity associated (FTO) gene is related to obesity, but the regulation of FTO expression in adipose tissue is not fully understood. We investigated FTO expression in paired subcutaneous and omental adipose tissues (SAT and OAT) from healthy women undergoing gynecological surgeries, and its relation with adiposity and insulin sensitivity. FTO expression in SAT of type 2 diabetic patients treated or not with Rosiglitazone was also compared. Both the mRNA and protein levels of FTO were higher in OAT from women than in SAT. Only OAT FTO protein levels negatively correlated with BMI and body fat mass, whereas SAT FTO mRNA levels were negatively correlated with subcutaneous fat deposition. In addition, SAT FTO mRNA and protein levels were increased in insulin resistant women (high HOMA) compared to insulin sensitive women (low HOMA), whereas OAT FTO expression was not different between these two subgroups. Interestingly, FTO mRNA levels were increased in SAT of type 2 diabetic patients, and treatment of diabetics with Rosiglitazone improved insulin sensitivity and reduced SAT FTO mRNA levels. Lastly, FTO expression was transiently increased in the early phase of 3T3-L1 cell differentiation, which coincides with the induction of PPARγ2 expression. However, partial reduction of FTO did not impact PPARγ2 expression and adipocyte differentiation. Therefore, FTO gene expression is higher in OAT than in SAT in lean to moderately obese women. OAT FTO expression is associated with adiposity, whereas SAT FTO expression is associated with insulin sensitivity. These associations are independent of an effect of FTO on adipocyte differentiation.

Clinical and genetic predictors of weight gain in patients diagnosed with breast cancer.

1561 Background: Obesity and weight gain in breast cancer patients has been associated with decreased quality of life, decreased response to chemotherapy, increased cancer recurrence, and higher all-cause mortality. Our study was designed to identify factors that contribute to this weight gain. Methods: Chart review was conducted on 565 breast cancer patients to obtain weights and BMIs over an 18 month period from diagnosis, tumor characteristics (ER/PR/Her2 status, grade, presence of LN metastases, stage), demographics (age, race), clinical factors (menopausal status), and treatment regimens (chemotherapy, hormone therapy, radiation). Blood samples were genotyped for polymorphisms in FTO (fat mass and obesity-associated protein) and the adiponectin pathway, two pathways found to be associated with obesity and breast cancer risk. Results: See table. For genetic analysis, one statistically significant epistatic and three gene x environmental interactions were detected for adiponectin SNPs: rs822396d x BMI at diagnosis (effect size 8.65), rs2232853a x age (2.75), rs1501299a x BMI at diagnosis (3.63), and rs266729d x rs7539542d (6.40). Conclusions: We have identified multiple clinical and genetic variables that are likely predictors of weight gain in breast cancer patients. We are conducting a prospective study of 200 breast cancer patients to validate the findings of this retrospective study. By identifying a high risk patient population, we hope to target them for aggressive lifestyle interventions to prevent weight gain and thereby improve their mortality and morbidity. [Table: see text]

Lose Weight with Traditional Chinese Medicine? Potential Suppression of Fat Mass and Obesity-Associated Protein

Overweight and obesity are common health problems in modern society, particularly in developed countries. Excessive body mass has been linked to numerous diseases, such as cardiovascular diseases, diabetes, and cancer. Fat mass and obesity-associated protein (FTO) activity have direct impact on food intake and results in obesity. Inhibition of FTO activity may cause weight loss and reduce obese-linked health risks. We investigated the potential weight loss effects of traditional Chinese medicine (TCM), particularly by inhibiting FTO functions. Molecular docking was performed to screen TCM compounds from TCM Database@Taiwan (http://tcm.cmu.edu.tw). Three candidates were identified that contained either a tetrahydropyridine group or potent electronegative phenol group in the structure scaffold. Molecular dynamics simulation analysis of the docking poses of each complex indicated stabilizing trends in the protein-ligand complex movements. In addition, the number of hydrogen bonds increased throughout the 20 ns simulation. These results suggest that these TCM candidates could be potential FTO inhibitors through competitive inhibition.

N6-methyladenosine in nuclear RNA is a major substrate of the obesity-associated FTO.

We report here that FTO (fat mass and obesity-associated protein) exhibits efficient oxidative demethylation activity of abundant N6-methyladenosine (m6A) residues in RNA in vitro. FTO knockdown with siRNA led to an increased level of m6A in mRNA, whereas overexpression of FTO resulted in a decreased level of m6A in human cells. We further show that FTO partially colocalizes with nuclear speckles, supporting m6A in nuclear RNA as a physiological substrate of FTO.

FTO mRNA Expression in Extremely Obese and Type 2 Diabetic Human Omental and Subcutaneous Adipose Tissues

Fat mass and obesity-associated protein (FTO) gene expression is known to correlate with obesity. Our aim was to investigate the FTO gene expression in paired omental and subcutaneous human adipose tissues from morbid and obese patients. To understand the role of CD68-positive macrophages in adipose tissues, the correlation with adiposity parameters such as adipocyte diameter and adipocyte radius was also measured. Drug and adiposity correlations were also analyzed. Paired omental and subcutaneous adipose tissue were excised during elective surgery from morbidly obese (n = 9) and obese (n = 5) patients. FTO expressions were determined by quantitative PCR. Tissue sections were analyzed for their CD68 protein expressions by immunuhistochemistry. Omental and subcutaneous adipose tissue FTO gene expression levels were not found to differ significantly among morbidly obese and obese study groups. Serum aspartate aminotransferase e and alanine transaminase levels were found to be in negative correlation with subcutaneous fat tissue FTO expression rate. Antidiabetic drug use was found to be in correlation with adiposity. Both subcutaneous and omental fat cell diameters were found to have correlation with antidiabetic drug use. Omental fat cell diameter was found to enlarge together with omental CD68 protein expression. Subcutaneous macrophage number decreased while omental fat cell radius increased. Omental macrophage number was found in correlation with subcutaneous macrophage number. Antidiabetic therapy was found to increase adiposity in omental and subcutaneous fat. Further research is needed with larger samples to explore the exact role of FTO in obesity.

Involvement of Leptin Receptor Long Isoform (LepRb)-STAT3 Signaling Pathway in Brain Fat Mass- and Obesity-Associated (FTO) Downregulation during Energy Restriction

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.

Involvement of leptin receptor long isoform (LepRb)-STAT3 signaling pathway in brain fat mass- and obesity-associated (FTO) downregulation during energy restriction.

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.

Conditional expression of the FTO gene product in rat INS-1 cells reveals its rapid turnover and a role in the profile of glucose-induced insulin secretion

Common polymorphisms within the FTO (fat mass and obesity-associated) gene correlate with increased BMI (body mass index) and a rising risk of Type2 diabetes. FTO is highly expressed in the brain but has also been detected in peripheral tissues, including the endocrine pancreas, although its function there is unclear. The aim of the present study was to investigate the role of FTO protein in pancreatic β-cells using a conditional expression system developed in INS-1 cells. INS-1 cells were stably transfected with FTO-HA (haemagluttinin) incorporated under the control of a tetracycline-inducible promoter. Induction of FTO protein resulted in localization of the tagged protein to the nucleus. The level of FTO-HA protein achieved in transfected cells was tightly regulated, and experiments with selective inhibitors revealed that FTO-HA is rapidly degraded via the ubiquitin/proteasome pathway. The nuclear localization was not altered by proteasome inhibitors, although following treatment with PYR-41, an inhibitor of ubiquitination, some of the protein adopted a perinuclear localization. Unexpectedly, modestly increased expression of FTO-HA selectively enhanced the first phase of insulin secretion when INS-1 monolayers or pseudoislets were stimulated with 20mM glucose, whereas the second phase remained unchanged. The mechanism responsible for the potentiation of glucose-induced insulin secretion is unclear; however, further experiments revealed that it did not involve an increase in insulin biosynthesis or any changes in STAT3 (signal transducer and activator of transcription 3) expression. Taken together, these results suggest that the FTO protein may play a hitherto unrecognized role in the control of first-phase insulin secretion in pancreatic β-cells.

The Fat Mass and Obesity Associated Gene FTO Functions in the Brain to Regulate Postnatal Growth in Mice

FTO (fat mass and obesity associated) was identified as an obesity-susceptibility gene by several independent large-scale genome association studies. A cluster of SNPs (single nucleotide polymorphism) located in the first intron of FTO was found to be significantly associated with obesity-related traits, such as body mass index, hip circumference, and body weight. FTO encodes a protein with a novel C-terminal α-helical domain and an N-terminal double-strand β-helix domain which is conserved in Fe(II) and 2-oxoglutarate-dependent oxygenase family. In vitro, FTO protein can demethylate single-stranded DNA or RNA with a preference for 3-methylthymine or 3-methyluracil. Its physiological substrates and function, however, remain to be defined. Here we report the generation and analysis of mice carrying a conditional deletion allele of Fto. Our results demonstrate that Fto plays an essential role in postnatal growth. The mice lacking Fto completely display immediate postnatal growth retardation with shorter body length, lower body weight, and lower bone mineral density than control mice, but their body compositions are relatively normal. Consistent with the growth retardation, the Fto mutant mice have reduced serum levels of IGF-1. Moreover, despite the ubiquitous expression of Fto, its specific deletion in the nervous system results in similar phenotypes as the whole body deletion, indicating that Fto functions in the central nerve system to regulate postnatal growth.

OBESITY CLUE IN VIEW

WITH X-RAY CRYSTALLOGRAPHY, researchers have determined the structure of FTO (fat-mass and obesity-associated protein), an enzyme that removes methyl groups from DNA and RNA and that has been linked with an increased risk of obesity. The structure suggests an explanation for the enzyme’s choice of substrates and could help researchers develop small molecules to address questions about its activity. In some groups of people, adults with specific variations in the gene for FTO are heavier than similar people with the normal FTO gene. And inactivating FTO in mice makes the animals leaner. But it’s not clear how the enzyme is connected to metabolism and body mass. FTO eschews double-stranded nucleic acids in favor of single-stranded substrates. Its exact sites of action in the body remain a mystery. Now, a team led by Jijie Chai of the National Institute of Biological Sciences and Tsinghua University, both in China, has probed FTO’s specificity ( Nature, DOI:10.1038/nature08921). In ...

Crystal structure of the FTO protein reveals basis for its substrate specificity

Recent studies have unequivocally associated the fat mass and obesity-associated (FTO) gene with the risk of obesity. In vitro FTO protein is an AlkB-like DNA/RNA demethylase with a strong preference for 3-methylthymidine (3-meT) in single-stranded DNA or 3-methyluracil (3-meU) in single-stranded RNA. Here we report the crystal structure of FTO in complex with the mononucleotide 3-meT. FTO comprises an amino-terminal AlkB-like domain and a carboxy-terminal domain with a novel fold. Biochemical assays show that these two domains interact with each other, which is required for FTO catalytic activity. In contrast with the structures of other AlkB members, FTO possesses an extra loop covering one side of the conserved jelly-roll motif. Structural comparison shows that this loop selectively competes with the unmethylated strand of the DNA duplex for binding to FTO, suggesting that it has an important role in FTO selection against double-stranded nucleic acids. The ability of FTO to distinguish 3-meT or 3-meU from other nucleotides is conferred by its hydrogen-bonding interaction with the two carbonyl oxygen atoms in 3-meT or 3-meU. Taken together, these results provide a structural basis for understanding FTO substrate-specificity, and serve as a foundation for the rational design of FTO inhibitors.

Obesity and the brain: a possible genetic link

Structural brain deficits have been repeatedly linked to body mass index and obesity, which itself is controlled by the effects of a number of independent genetic loci. One of the most consistently replicated of these putative obesity genes is fat mass and obesity-associated protein (FTO). A recent study by investigators from the Alzheimer's Disease Neuroimaging Initiative set out to assess whether polymorphisms in FTO are directly correlated with brain volume in a collection of over 200 healthy older individuals. The authors found a modest but significant reduction in brain volume in the frontal and occipital lobes exerted by the same FTO alleles that also predispose to obesity. Although potentially providing a novel genetic link between obesity and brain structure, the relevance of these findings for normal brain function and disease remains to be determined.