This Reprint May Differ from the Original in Pagination and Typographic Detail. Aerobic Fitness Does Not Modify the Effect of Fto Variation on Body Composition Traits

All material supplied via JYX is protected by copyright and other intellectual property rights, and duplication or sale of all or part of any of the repository collections is not permitted, except that material may be duplicated by you for your research use or educational purposes in electronic or print form. You must obtain permission for any other use. Electronic or print copies may not be offered, whether for sale or otherwise to anyone who is not an authorised user. (2012). Aerobic fitness does not modify the effect of FTO variation on body composition traits. Abstract Purpose: Poor physical fitness and obesity are risk factors for all cause morbidity and mortality. We aimed to clarify whether common genetic variants of key energy intake determinants in leptin (LEP), leptin receptor (LEPR), and fat mass and obesity-associated (FTO) are associated with aerobic and neuromuscular performance, and whether aerobic fitness can alter the effect of these genotypes on body composition. Methods: 846 healthy Finnish males of Caucasian origin were genotyped for FTO (rs8050136), LEP (rs7799039) and LEPR (rs8179183 and rs1137101) single nucleotide polymorphisms (SNPs), and studied for associations with maximal oxygen consumption, body fat percent, serum leptin levels, waist circumference and maximal force of leg extensor muscles. Results: Genotype AA of the FTO SNP rs8050136 associated with higher BMI and greater waist circumference compared to the genotype CC. In general linear model, no significant interaction for FTO genotype-relative VO 2 max (mL?kg 21 ?min 21) or FTO genotype-absolute VO 2 max (L?min 21) on BMI or waist circumference was found. Main effects of aerobic performance on body composition traits were significant (p,0.001). Logistic regression modelling found no significant interaction between aerobic fitness and FTO genotype. LEP SNP rs7799039, LEPR SNPs rs8179183 and rs1137101 did not associate with any of the measured variables, and no significant interactions of LEP or LEPR genotype with aerobic fitness were observed. In addition, none of the studied SNPs associated with aerobic or neuromuscular performance. Conclusions: Aerobic fitness may not modify the effect of FTO variation on body composition traits. However, relative aerobic capacity associates with lower BMI and waist circumference regardless of the FTO genotype. FTO, LEP and LEPR genotypes unlikely associate with physical performance. Copyright: ß 2012 Huuskonen et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the …


Introduction
Obesity and low physical fitness frequently associate with each other, and are individual risk factors for many pathological conditions and cardiovascular mortality [1,2].Body composition and physical performance are outcomes of cumulative effects of common and rare variants in a large number of genes with environmental and gene-gene interactions [3].The effects of behavioural factors on human performance, including physical activity and dietary habits have been widely studied, yet knowledge on genetic background is sparse.The heritability estimates for obesity range from 40% to 70% [3], from 20 to 40% for aerobic performance [4,5], and approximately 60% for muscle force [6].Single nucleotide polymorphisms (SNPs) represent the most common type of genetic variation in the human genome [7].However, it is not known whether genetic variants in genes encoding fat and obesity-associated (FTO), leptin (LEP), and leptin receptor (LEPR) associate with physical performance, and whether fitness level modifies the risk for obesity associated with these gene variants.
Genome-wide association studies have identified the FTO gene as the first susceptibility locus for common obesity [8,9].Minor allele of this variant is associated with increased risk for obesity and elevated body weight [8,9].In a recent meta-analysis, physical activity level was shown to modify the relationship between the FTO risk variant and body weight and risk of obesity [10].However, effects of FTO genotype and its interaction with aerobic fitness on body composition have not been reported so far.Despite the fact that FTO is under extensive research, the role and function of the FTO gene product remains incompletely understood.
Leptin is a peptide hormone secreted mainly from white adipose tissue.It regulates hunger, body temperature and energy metabolism, and has been used as a biomarker of energy deficiency [11,12].Recent studies have shown that obese individuals are in fact leptin resistant [12], and that physical exercise may restore leptin sensitivity [13].Associations of leptin receptor gene (LEPR) SNP Gln223Arg (rs1137101) and leptin (LEP) promoter region SNP -2548G/A (rs7799039) with BMI and other body composition-related traits have been reported [14][15][16][17][18].We previously demonstrated that the rs7799039 associates with changes in body composition in response to physical training [19].Furthermore, another LEPR SNP Lys656Asn (rs8179183) has been reported to associate with substrate oxidation and basal metabolic rate [20,21].However, the interaction effects of these SNPs with aerobic performance on body composition are not known.
The present study investigated the association of selected SNPs in FTO, LEP and LEPR with body composition, neuromuscular and cardiorespiratory performance and plasma leptin levels in 846 healthy male subjects.In addition, genotype-aerobic fitness interactions on body composition traits were studied.Our hypothesis was that these common variants are associated with human performance, body composition and health-related risk factors.Furthermore, we hypothesized that aerobic fitness modifies the relationship between the genetic variants and body composition.The information this study provides may be used to identify those individuals having higher health risks and tendency for poor physical fitness, and for better understanding of the effect of genetic factors on human physical performance.

Study Subjects
The subjects of Caucasian origin were 846 healthy male Finnish volunteers with mean age (SD) of 2565 years.All subjects were informed on the purpose of the study, gave a written informed consent and underwent medical examination prior to the tests.This study was approved by the ethics committee of the University of Jyva ¨skyla ¨and the hospital district of Central Finland.Anthropometric data and blood samples were collected after an overnight fast.The subjects consumed light breakfast 1 to 2 hours before the exercise tests.

Physical Performance and Body Composition
Height, weight and waist circumference were recorded, and body mass index (BMI, kg?m 22 ) was calculated.Body fat and lean mass percentage were recorded by using the eight-polar bioimpedance method with multifrequency current (InBody 720; Biospace Company, Seoul, Korea).Bioimpedance was recorded after an overnight fast and with at least one day off from any intensive physical activity.
Maximal isometric force production of the leg extensor muscles was measured with a dynamometer (Department of Biology of Physical Activity, University of Jyva ¨skyla ¨, Finland).The test was performed in sitting position with 107-degree knee angle.The subjects were supervised to generate maximal force as fast as possible and maintain this force for 3 seconds.The data were analysed with a 16-bit AD converter (CED power 1401, Cambridge Electronic Design ltd, England) and Signal (2.16) software.

Blood Samples and Genotyping
The fasting blood samples were collected and analysed immediately with a hemacytometer (Sysmex Co., Kobe, Japan).Plasma was separated from the whole blood and stored at -80Cu until analysis.Plasma leptin concentrations were assayed by commercial ELISA according to the manufacturer's instructions (Quantikine, R&D Systems, Minneapolis, MN, USA).Assay specifications were as follows: sensitivity limit 7.8 pg?mL 21 , and maximum intra-and interassay CV% 3.3% and 5.4%, respectively.

Statistics
Calculations were performed with SPSS software (Illinois, Chicago, USA) by using one-way ANCOVA or non-parametric tests, when appropriate.Age, smoking and earlier physical activity were set as covariates.Smoking (smoker or non-smoker) and physical activity (vigorous physical activity more than 3 times per week) were set as dichotomous variables, whereas age VO 2 max, BMI, waist circumference were set as continuous variables.
Genotype-VO 2 max interaction on BMI, waist circumference and fat percent were analyzed by using general linear model.The general linear model included main effects terms for earlier physical activity, smoking, age, genotype, VO 2 max and genotype-VO 2 max interaction.Physical activity and smoking were set as dichotomous variables, and VO 2 max, age and body composition traits were set as continuous variables.Genotype was set as discrete variable in every analysis.
Additionally, the FTO genotype and FTO genotype-VO 2 max interaction related odds for overweight (BMI over 25 kg?m 22 ) and abdominal obesity (waist circumference over 90 cm) were analyzed by logistic regression.Recessive model was applied in analysis (AA genotype vs. CA and CC genotype).Age, smoking and physical activity were set as covariates.The subjects were divided into quartiles according to VO 2 max.The 75% percentile limits for VO 2 max were 3.7 L?min 21 and 46.9 mL?kg 21 ?min 21.The subjects in the highest 25% quartile were defined as high aerobic fitness group, and compared with the 75% percentile of subjects (VO 2 max ,3.7 L?min 21 or ,46.9 mL?kg 21 ?min 21).
Data are presented as mean 6 standard deviation unless otherwise stated.Statistical significance was set at p,0.0125 to account for multiple testing.Bonferroni correction was applied to post-hoc comparisons.Statistical power and sample sizes were estimated with SISA web calculator [24].A 90% level was chosen for power calculations, and the number of subjects needed to demonstrate 1 S.D. difference in continuous parameters was estimated.

Results
All SNPs conformed to Hardy-Weinberg's equilibrium.None of the SNPs were associated with earlier physical activity estimated with IPAQ.
In ANCOVA analysis, the FTO SNP rs8050136 associated with BMI and waist circumference (Table 1).Genotype AA carriers had significantly higher BMI and greater waist circumference compared to the genotype CC carriers.In general linear model, the main effects of relative and absolute VO 2 max on BMI and waist circumference were significant (p,0.001).However, no significant FTO genotype-relative VO 2 max (mL?kg 21 ?min 21) interaction on BMI (p = 0.081) or waist circumference (p = 0.093) was found.In addition, the test result was insignificant when FTO genotype-absolute VO 2 max (L?min 21 ) interaction on BMI (p = 0.937) or waist circumference (p = 0.262) were analyzed (Figures 1-4).In logistic regression, genotype AA increased odds for waist circumference over 90 cm.However, the interaction of genotype AA with high VO 2 max was insignificant (Table 2).No association was found with aerobic fitness (VO 2 max expressed as L?min 21 or mL?kg 21 ?min 21) (Table 1).
In ANCOVA analysis, LEP SNP rs7799039 did not associate with any variable (Table 3).No interactions were observed between aerobic fitness and genotype.LEPR SNP rs1137101 did not associate with BMI, body fat, leptin levels or physical performance in ANCOVA (Table 3), and no aerobic performance-genotype interactions were observed in the general linear model.In ANCOVA analysis, LEPR Lys656Asn SNP rs8179183 Figure 1.Linear regression analysis.The main effect of VO 2 max (mL?kg 21 ?min 21) on BMI was significant (p,0.001).The main effects of FTO genotype and FTO genotype-VO 2 max (mL?kg 21 ?min 21) interaction were not significant (p = 0.029 and p = 0.081, respectively).doi:10.1371/journal.pone.0051635.g001Earlier physical activity, smoking and age were set as covariates.Bonferroni correction was accounted for multiple post-hoc comparisons.BMI: p = 0.007 for main effect, *p = 0.005 between the genotype groups CC and AA.
Waist circumference: p = 0.012 for main effect, #p = 0.012 between the genotype groups CC and AA.p.0.0125 for main effect between genotype groups for rest of the variables.doi:10.1371/journal.pone.0051635.t001 did not associate with any variable (Table 3).In addition, no interactions were observed between genotype and aerobic fitness in the general linear model.

Discussion
The main finding of the present study was that aerobic fitness does not modify the effect of FTO variation on BMI or waist circumference.However, relative aerobic capacity did associate   There are certain limitations to the present study.First, the sample size was moderate for genetic association analyses.The relatively large confidence intervals may bias identification of a true interaction in logistic regression analysis.In addition, all subjects were males, which may affect generalization of the results to other populations.Our study design was cross-sectional, which may increase risk for selection bias.However, earlier physical activity status was assessed with IPAQ survey, and no associations with pre-study physical activity and genotypes were found.The bioimpedance method is both sensitive and specific for analysis of body fat mass, but may have limitations for accurate evaluation of muscle mass [39].The method for assessing aerobic fitness was indirect, whereas direct gas exchange analysis would provide greater accuracy.
In conclusion, aerobic fitness may not modify the effect of FTO variation on body composition traits.However, relative aerobic capacity had a favourable effect on BMI and waist circumference, regardless of the FTO genotype.It is unlikely that FTO, LEP and LEPR genotypes associate with physical performance.These findings can be applied in sports medicine to decrease risk for diseases related to sedentary lifestyle and obesity, where improved aerobic fitness is beneficial regardless of the FTO-related predisposition to obesity.

Table 1 .
Showing the results of ANCOVA-analysis according to FTO genotype.

Table 2 .
Showing results of the logistic regression analysis.Waist circumference over 90 cm adjusted for age, smoking, physical activity and absolute aerobic fitness (L?min21 ) OR and 95% C.I. for the genotype AA (vs.genotype CA and CC) of the FTO rs8050136 according to overweight and abdominal obesity.doi:10.1371/journal.pone.0051635.t002