| Objective:Obesity is rapidly increasing in prevalence worldwide,and has become a public health crisis of pandemic proportions.Studies have shown that,compared with body mass index（BMI）and waist circumference（WC）,body fat percentage（BF%）is the preferred indicator for accurately determining obesity.Altered DNA methylation triggered by genetic,environmental and stochastic effects accumulated over time can contribute to the development of individual susceptibility to complex diseases such as obesity.Monozygotic（MZ）twins share their genetic makeups,MZ twin pairs discordant for a disease or trait serve as ideal samples for epigenome-wide association studies（EWAS）on highly heritable phenotypes such as obesity advantaged by a perfect control over the genetic background.Hence,based on 29 BF%-discordant MZ twin pairs,we here investigated the association of DNA methylation in whole blood with BF%.Our results may help to elucidate the potential molecular mechanisms of obesity and provide new targets for the treatment of obesity-related diseases.Methods:The twin pairs in this study were drawn from the Qingdao Twin Registry.Prior written informed consent was achieved for all participants.BF%was measured by a standard procedure using the Tanita TBF-300A bioimpedance device.All participants were invited to complete a questionnaire and undertake a clinical examination after a10–12h overnight fast.The zygosity was identified by sex,ABO blood type and 16multiple short tandem sequence repeat DNA markers in Qingdao Blood Center.Methylation data from whole blood samples were collected using the reduced representation bisulfite sequencing technique.We used Re FACTor method to control for the cell-type composition effect on DNA methylation in EWAS.Linear mixed effect model adjusting for potential confounders（age,sex,BMI,diastolic blood pressure and cell-type composition et al.）was fitted to estimate the relationship between methylation level of single Cp G site and BF%.Differentially methylated regions（DMRs）were detected by comb-p python library.Weighted gene correlation network analysis（WGCNA）was conducted to identify co-methylation modules and genes associated with BF%.Genomic Regions Enrichment of Annotations Tool（GREAT）was used to predict the functions of cis-regulatory regions and ontology enrichments.Results:A total of 29 complete monozygotic twin pairs were included in the current sample,including 16 male and 13 female pairs.The mean age of twins was 52.79±7.69years,and themean BF%was around 27.96±8.52.A list of 26 Cp G sites were identified to reach the level of P<1×10-4,5 Cp Gs with P<1×10-5.Moreover,these top Cp G sites(P<1×10-4)were located at 4 genes（PCDHG,ALOX12,IGSF21 and LRAT）.In region-based analysis,we identified 5 DMRs potentially associated with BF%.The methylation levels of one DMR was negatively correlated with BF%and three DMRs were positively correlated with BF%.But it is difficult to determine the direction of association between one DMR and BF%.The identified DMRs located at 4 genes（ROCK1P1,PCDHG,SOX30,RGPD3）.Weighted gene correlation network analysis（WGCNA）identified 10 co-methylation modules.Several hub genes,such as GRIN1,TUSC1,EHMT1,AK128414,FAM219A,BC036431,SHC3,SPTLC1,CENPP were also identified.The GREAT enriched terms were mainly involved in pyruvate metabolism,pyridoxal phosphate salvage pathway,Notch signaling pathway,Mannose metabolism,Transcription regulation by b ZIP transcription factor,GABA-B receptor II signaling,Angiogenesis,Nicotinic acetylcholine receptor signaling pathway,Hedgehog signaling pathway,Wnt signaling pathway,mitochondrial L-carnitine shuttle pathway,L-serine degradation,thyroid hormone biosynthesis,etc.Conclusions:We detected multiple Cp G sites,DMRs,genes and pathways potentially related to BF%based on the DNA methylome profile data of Northern Han Chinese monozygotic twins.Our study is helpful to understand the relationship between DNA methylation and BF%,and provide a new reference for the pathological mechanism of obesity. |
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