Inhalation exposure to cigarette smoke and inflammatory agents induces epigenetic changes in the lung

Abstract

Smoking-related lung tumors are characterized by profound epigenetic changes including scrambled patterns of DNA methylation, deregulated histone acetylation, altered gene expression levels, distorted microRNA profiles, and a global loss of cytosine hydroxymethylation marks. Here, we employed an enhanced version of bisulfite sequencing (RRBS/oxRRBS) followed by next generation sequencing to separately map DNA epigenetic marks 5-methyl-dC and 5-hydroxymethyl-dC in genomic DNA isolated from lungs of A/J mice exposed whole-body to environmental cigarette smoke for 10 weeks. Exposure to cigarette smoke significantly affected the patterns of cytosine methylation and hydroxymethylation in the lungs. Differentially hydroxymethylated regions were associated with inflammatory response/disease, organismal injury, and respiratory diseases and were involved in regulation of cellular development, function, growth, and proliferation. To identify epigenetic changes in the lung associated with exposure to tobacco carcinogens and inflammation, A/J mice were intranasally treated with the tobacco carcinogen 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK), the inflammatory agent lipopolysaccharide (LPS), or both. NNK alone caused minimal epigenetic alterations, while exposure either to LPS or NNK/LPS in combination led to increased levels of global cytosine methylation and formylation, reduced cytosine hydroxymethylation, decreased histone acetylation, and altered expression levels of multiple genes. Our results suggest that inflammatory processes are responsible for epigenetic changes contributing to lung cancer development. Lung cancer is responsible for 30% of all cancer deaths worldwide and is expected to kill 154,050 Americans this year, with over 80% of cases directly attributable to smoking 1. Cigarette smoke contains over 60 known carcinogens, such as the tobacco specific nitrosamine 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK, 75 ng/cigarette) 2,3 , as well as non-genotoxic co-carcinogens including the inflammatory agent lipopolysaccharide (LPS, 120 ng/cigarette) 4. Chronic inflammation plays a central role in the pathogenesis of smoking-induced lung cancer 5. Smoking is characterized by neutrophilic inflammation and reduced mucociliary clearance in the lung, which, at least in part, can be explained by exposure to LPS and other endotoxins 6 .

Multi-Omics Characterization of Inflammatory Bowel Disease-Induced Hyperplasia/Dysplasia in the Rag2−/−/Il10−/− Mouse Model

“…By comparing the oxRRBS dataset with RRBS datasets, an accurate 5hmC fraction can be calculated ( Figure 2 A). Previously, we successfully employed this approach to characterize methylation and hydroxymethylation changes in an animal model of lung cancer (A/J mice treated with lipopolysaccharide) [ 52 ].…”

“…In the murine IBD model with significant dysplasia and hyperplasia prior to solid tumor formation, these results suggest an early effect of DNA epigenetic marks on triggering altered expression of cancer-related genes. Our recent study involving a murine model of inflammation-induced lung cancer analogously revealed early epigenetic changes within tumor suppressor genes Rassf1, Cdh13, and Dapk1 [ 52 ]. Future functional studies will establish whether such epigenetic dysregulation directly contributes to initiation and progression of cancer.…”

Small Airways Disease, Biomarkers and COPD: Where are We?

“… 45 Exposure to toxicants, such as prolonged cigarette smoke inhalation, may influence biomarkers by having direct effects on the small airway epithelium (SAE). 46 …”

Epigenetic underpinnings of inflammation: Connecting the dots between pulmonary diseases, lung cancer and COVID-19

“…These studies are further corroborated by in vivo and translational studies. Mice intranasally exposed to inflammatory agent lipopolysaccharide (LPS) for two weeks reduced the global levels of cytosine hydroxymethylation (5hmc) in lung tissue [ 168 ]. Six weeks exposure to LPS increased cytosine methylation (5mc) in CDH13 (cell adhesion molecule), Ahrr, Tet1 and Rassf1 (tumor suppressors) and DAPK1 (pro-oncogene) which together highlight involvement of complex inflammatory stimulus involving methylation-based regulation of inflammation as well as tumor suppressors and oncogenes in progression of lung cancer.…”