Abstract
Fas apoptotic inhibitory molecule 2 (
Introduction
In recent years, overweight and obesity have become more widespread in most areas of the world, including China. 1 The rising incidence of obesity is a major threat to public health. Overweight children exhibit a higher risk for severe adult obesity, 2 and childhood obesity strongly predisposes to several adult diseases, such as hypertension, type 2 diabetes and cardiovascular disease.
Fas apoptotic inhibitory molecule 2 (FAIM2) is a nervous system-specific inhibitor of Fas/CD95-mediated apoptosis that directly binds to the Fas receptor to protect cells against apoptosis.
3
Genome-wide association (GWA) studies in Caucasians identified that the single nucleotide polymorphism (SNP) rs7138803 near
Obesity most likely results from the complex interaction between genetic and environmental factors. Epigenetic alterations, especially DNA methylation, have been suggested to be associated with the development of obesity.7–9 We hypothesized that changes in the DNA methylation of the
Materials and methods
Subjects and ethics
The cohort included 59 obese (BMI > 30 kg/m2 and fat mass percentage (FMP) > 40) and 39 lean (BMI < 18 kg/m2 and FMP < 15) subjects selected from a cross-sectional survey of Beijing children aged 8–18 years in 2013.
We obtained written informed consent from all participants (or their parents/guardians). This study was approved by the ethics committees of the Capital Institute of Pediatrics.
Measurement of anthropometric parameters and biochemical analyses
The anthropometric measurements included weight, height and FMP. All instruments were validated according to the standard methods of the manufacturers. Weight and FMP were measured using a body composition analyser (InBody 720; Biospace Co., Ltd, Seoul, Korea). BMI was calculated as weight in kilograms divided by the square of height in metres. Blood pressure was measured via auscultation using a standard clinical sphygmomanometer.
The levels of triglycerides (TG), high-density lipoprotein cholesterol (HDL-C), low-density lipoprotein cholesterol (LDL-C), total cholesterol (TC) and fasting plasma glucose (FPG) were analysed using an automatic biochemical analyser (Olympus Chemistry Analyser AU640; Olympus Optical Co., Ltd, Tokyo, Japan) using commercial kits (Olympus Optical Co., Ltd).
We classified the lipid profiles as abnormal based on the Chinese criteria as follows: TG ⩿ 1.7 mmol/L, HDL-C ⩾ 1.04 mmol/L, LDL-C ⩿ 3.37 mmol/L and TC ⩿ 5.18 mmol/L. A diagnosis of dyslipidaemia was made if any of these four criteria was met. A high FPG level was defined as FPG ⩿ 5.6 mmol/L.
DNA methylation analysis
Genomic DNA was extracted from peripheral blood leukocytes using a QIAamp® DNA Blood Mini Kit according to the manufacturer’s protocol (QIAGEN Inc., Valencia, CA, USA).
The Sequenom MassARRAY platform (BioMiao Biological Technology, Beijing, China) was used to quantitatively analyse the methylation of
Statistical analysis
The continuous variables are presented as the mean ± standard deviation (SD), and the differences between the groups were assessed using analysis of variance (ANOVA). The categorical variables are presented as the percentages, and differences between the groups were assessed using the Chi-square test. A general linear model was used to investigate the difference in the methylation levels between the obese and lean subjects after adjusting for age and gender. Logistic regression was performed to evaluate the associations between abnormal lipid traits (high TG, low HDL-C, high LDL-C or high TC) or dyslipidaemia and the methylation levels after adjusting for age, gender and BMI;
Results
The characteristics of the study participants are summarized in Supplementary Table 2. In addition to BMI and FMP, the obese subjects exhibited higher levels of systolic blood pressure (SBP), diastolic blood pressure (DBP), TG and LDL-C and lower level of HDL-C in comparison with the lean subjects.
We investigated the methylation level of the
The methylation levels of the
All
Supplementary Table 3 shows the associations between the methylation variations at the examined CpG sites and dyslipidaemia and its four components. The methylation levels at several of the examined CpG sites were significantly associated with high TG, low HDL-C, high LDL-C and high TC levels and dyslipidaemia after adjusting for age, gender and BMI. The methylation levels at two CpG sites (sites -362 and -360 and site -164) were highly significantly associated with high TG level (
Discussion
FAIM2 is a 35.1 kDa membrane protein that is highly expressed in the hippocampus and that regulates Fas ligand-mediated apoptosis in neurons. 3 Reich et al. 10 provided evidence that FAIM2 acts as a neuroprotective molecule after transient brain ischaemia. The function of FAIM2 in the hypothalamus is unclear.
The SNP rs7138803 near
Because of the emerging evidence that the development of obesity is epigenetically regulated,7–9 we hypothesized that changes in the DNA methylation of the
There are a few limitations to this study. First, because of the lack of gene expression data from leukocytes or tissues, this study may not provide direct evidence that the expression of
In this study, we explored for the first time that the methylation levels of the
Footnotes
Acknowledgements
The authors thank the children and their parents for their participation in this study. We also thank Ping Yang, Guimin Huang, Zhongjian Su, Xinying Shan, Fangfang Chen and Wenpeng Wang for their help with blood sample collection.
Author contributions
Lijun Wu and Xiaoyuan Zhao contributed equally to this work.
Declaration of conflicting interests
The authors declare that there is no conflict of interest.
Funding
This work was supported by the National Natural Science Foundation of China (grant no. 81200624), the National Basic Research Program of China (973 Program, grant no. 2013CB530605) and the Beijing Training Project for the Leading Talents in S&T (grant no. 2011LJ07).