Novel DNA methylation changes in mouse lungs associated with chronic smoking

Smoking is a potent cause of asthma exacerbations, chronic obstructive pulmonary disease (COPD) and many other health defects, and changes in DNA methylation (DNAm) have been identified as a potential link between smoking and these health outcomes. However, most studies of smoking and DNAm have been done using blood and other easily accessible tissues in humans, while evidence from more directly affected tissues such as the lungs is lacking. Here, we identified DNAm patterns in the lungs that are altered by smoking. We used an established mouse model to measure the effects of chronic smoke exposure first on lung phenotype immediately after smoking and then after a period of smoking cessation. Next, we determined whether our mouse model recapitulates previous DNAm patterns observed in smoking humans, specifically measuring DNAm at a candidate gene responsive to cigarette smoke, Cyp1a1. Finally, we carried out epigenome-wide DNAm analyses using the newly released Illumina mouse methylation microarrays. Our results recapitulate some of the phenotypes and DNAm patterns observed in human studies but reveal 32 differentially methylated genes specific to the lungs which have not been previously associated with smoking. The affected genes are associated with nicotine dependency, tumorigenesis and metastasis, immune cell dysfunction, lung function decline, and COPD. This research emphasizes the need to study CS-mediated DNAm signatures in directly affected tissues like the lungs, to fully understand mechanisms underlying CS-mediated health outcomes.

吸烟是哮喘急性发作、慢性阻塞性肺疾病（chronic obstructive pulmonary disease, COPD）及多种其他健康损害的重要致病因素。DNA甲基化（DNA methylation, DNAm）的改变被证实是吸烟与上述健康结局之间的潜在关联机制。然而，现有关于吸烟与DNA甲基化的研究多采用人类血液及其他易获取的组织开展，来自肺等直接受影响组织的相关证据仍较为匮乏。
本研究鉴定了吸烟诱导的肺组织DNA甲基化模式变化。我们采用已建立的小鼠模型，先后评估了慢性烟雾暴露即刻及戒烟一段时间后对肺表型的影响。随后，我们验证了该小鼠模型能否复现吸烟人群中已报道的DNA甲基化模式，重点检测了香烟烟雾响应候选基因Cyp1a1的DNA甲基化水平。最后，我们利用最新发布的Illumina小鼠甲基化微阵列开展了全表观基因组DNA甲基化分析。
本研究结果复现了人类研究中报道的部分表型与DNA甲基化模式，同时鉴定出32个肺组织特异性差异甲基化基因，这些基因此前未被发现与吸烟相关。上述受影响基因与尼古丁依赖、肿瘤发生与转移、免疫细胞功能异常、肺功能下降及慢性阻塞性肺疾病密切相关。
本研究强调，需在肺等直接受影响组织中开展香烟烟雾（cigarette smoke, CS）介导的DNA甲基化特征研究，以全面解析香烟烟雾诱导健康损害的潜在分子机制。