BACKGROUND Active smoking is the main risk factor for COPD. Here, epigenetic mechanisms may play a role, since cigarette smoking is associated with differential DNA methylation in whole blood. So far, it is unclear whether epigenetics also play a role in subjects with COPD who never smoked. Therefore, we aimed to identify differential DNA methylation associated with lung function in never smokers. METHODS We determined epigenome-wide DNA methylation levels of 396,243 CpG-sites (Illumina 450 K) in blood of never smokers in four independent cohorts, LifeLines COPD&C (N = 903), LifeLines DEEP (N = 166), Rotterdam Study (RS)-III (N = 150) and RS-BIOS (N = 206). We meta-analyzed the cohort-specific methylation results to identify differentially methylated CpG-sites with FEV1/FVC. Expression Quantitative Trait Methylation (eQTM) analysis was performed in the Biobank-based Integrative Omics Studies (BIOS). RESULTS A total of 36 CpG-sites were associated with FEV1/FVC in never smokers at p-value< 0.0001, but the meta-analysis did not reveal any epigenome-wide significant CpG-sites. Of interest, 35 of these 36 CpG-sites have not been associated with lung function before in studies including subjects irrespective of smoking history. Among the top hits were cg10012512, cg02885771, annotated to the gene LTV1 Ribosome Biogenesis factor (LTV1), and cg25105536, annotated to Kelch Like Family Member 32 (KLHL32). Moreover, a total of 11 eQTMS were identified. CONCLUSIONS With the identification of 35 CpG-sites that are unique for never smokers, our study shows that DNA methylation is also associated with FEV1/FVC in subjects that never smoked and therefore not merely related to smoking.

中文翻译：

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在从未吸烟者中，DNA甲基化与肺功能有关。

背景技术积极吸烟是COPD的主要危险因素。在这里，表观遗传机制可能起作用，因为吸烟与全血中的差异DNA甲基化有关。到目前为止，尚不清楚表观遗传学是否还在从未吸烟的COPD受试者中发挥作用。因此，我们旨在确定从不吸烟者与肺功能相关的差异DNA甲基化。方法我们确定了四个独立队列中永不吸烟者血液中396,243个CpG位点（Illumina 450 K）的表观基因组范围内的DNA甲基化水平，这四个独立队列分别是LifeLines COPD＆C（N = 903），LifeLines DEEP（N = 166），鹿特丹研究（RS） -III（N = 150）和RS-BIOS（N = 206）。我们对队列特定的甲基化结果进行荟萃分析，以鉴定FEV1 / FVC差异甲基化的CpG位点。在基于生物库的综合组学研究（BIOS）中进行了表达定量性状甲基化（eQTM）分析。结果在从未吸烟者中，共有36个CpG位点与FEV1 / FVC相关，p值<0.0001，但荟萃分析未发现任何表观基因组范围内的重要CpG位点。有趣的是，在包括受试者在内的研究中，这36个CpG位点中有35个与肺功能无关，而与吸烟史无关。其中最热门的是注释为基因LTV1核糖体生物发生因子（LTV1）的cg10012512，cg02885771和注释为Kelch Like Family Member 32（KLHL32）的cg25105536。此外，总共鉴定出11个eQTMS。结论确定了35个从未吸烟者的独特CpG位点，