Association between DNA Methylation in Whole Blood and Measures of Glucose Metabolism: KORA F4 Study

Epigenetic regulation has been postulated to affect glucose metabolism, insulin sensitivity and the risk of type 2 diabetes. Therefore, we performed an epigenome-wide association study for measures of glucose metabolism in whole blood samples of the population-based Cooperative Health Research in the Region of Augsburg F4 study using the Illumina HumanMethylation 450 BeadChip. We identified a total of 31 CpG sites where methylation level was associated with measures of glucose metabolism after adjustment for age, sex, smoking, and estimated white blood cell proportions and correction for multiple testing using the Benjamini-Hochberg (B-H) method (four for fasting glucose, seven for fasting insulin, 25 for homeostasis model assessment-insulin resistance [HOMA-IR]; B-H-adjusted p-values between 9.2x10-5 and 0.047). In addition, DNA methylation at cg06500161 (annotated to ABCG1) was associated with all the aforementioned phenotypes and 2-hour glucose (B-H-adjusted p-values between 9.2x10-5 and 3.0x10-3). Methylation status of additional three CpG sites showed an association with fasting insulin only after additional adjustment for body mass index (BMI) (B-H-adjusted p-values = 0.047). Overall, effect strengths were reduced by around 30% after additional adjustment for BMI, suggesting that this variable has an influence on the investigated phenotypes. Furthermore, we found significant associations between methylation status of 21 of the aforementioned CpG sites and 2-hour insulin in a subset of samples with seven significant associations persisting after additional adjustment for BMI. In a subset of 533 participants, methylation of the CpG site cg06500161 (ABCG1) was inversely associated with ABCG1 gene expression (B-H-adjusted p-value = 1.5x10-9). Additionally, we observed an enrichment of the top 1,000 CpG sites for diabetes-related canonical pathways using Ingenuity Pathway Analysis. In conclusion, our study indicates that DNA methylation and diabetes-related traits are associated and that these associations are partially BMI-dependent. Furthermore, the interaction of ABCG1 with glucose metabolism is modulated by epigenetic processes.

表观遗传调控（Epigenetic regulation）已被推测可影响葡萄糖代谢、胰岛素敏感性以及2型糖尿病（type 2 diabetes）的发病风险。因此，本研究基于奥格斯堡地区基于人群的合作健康研究F4队列（Cooperative Health Research in the Region of Augsburg F4 study）的全血样本，使用Illumina人类甲基化450微珠芯片（Illumina HumanMethylation 450 BeadChip）开展了针对葡萄糖代谢相关指标的全表观基因组关联研究（epigenome-wide association study）。经校正年龄、性别、吸烟史、估算白细胞比例，并采用本雅明尼-霍赫贝格（Benjamini-Hochberg, B-H）法进行多重检验校正后，本研究共鉴定出31个CpG位点（CpG sites），其甲基化水平与葡萄糖代谢相关指标存在显著关联：其中4个关联于空腹血糖（fasting glucose）、7个关联于空腹胰岛素（fasting insulin）、25个关联于稳态模型评估-胰岛素抵抗（homeostasis model assessment-insulin resistance, HOMA-IR）；经B-H校正的P值范围为9.2×10^-5至0.047。此外，cg06500161位点（注释至ABCG1基因）的DNA甲基化水平与上述所有表型以及餐后2小时血糖（2-hour glucose）均存在显著关联，经B-H校正的P值范围为9.2×10^-5至3.0×10^-3。另有3个CpG位点的甲基化状态仅在额外校正体重指数（body mass index, BMI）后，才显示出与空腹胰岛素的关联，其经B-H校正的P值为0.047。整体而言，在额外校正BMI后，效应量（effect strengths）平均降低约30%，提示该变量对本研究关注的表型存在影响。此外，在亚样本分析中，本研究发现上述21个CpG位点的甲基化状态与餐后2小时胰岛素存在显著关联，其中7个关联在额外校正BMI后仍具有统计学意义。在533名参与者组成的亚组中，cg06500161位点（ABCG1）的甲基化水平与ABCG1基因表达呈负相关，经B-H校正的P值为1.5×10^-9。此外，通过Ingenuity通路分析（Ingenuity Pathway Analysis），本研究发现排名前1000的CpG位点显著富集于糖尿病相关经典通路。综上，本研究表明DNA甲基化与糖尿病相关表型存在关联，且此类关联部分依赖于BMI；此外，ABCG1与葡萄糖代谢的相互作用可受表观遗传过程调控。