Perinatal exposure to environmental tobacco smoke is associated with changes in DNA methylation that precede the adult onset of lung disease in a mouse model

Abstract

Prenatal and early-life environmental tobacco smoke (ETS) exposure can induce epigenetic alterations associated with inflammation and respiratory disease. The objective of this study was to address the long-term epigenetic consequences of perinatal ETS exposure on latent respiratory disease risk, which are still largely unknown. C57BL/6 mice were exposed to prenatal and early-life ETS; offspring lung pathology, global DNA, and gene-specific methylation were measured at two adult ages. Significant alterations in global DNA methylation and promoter methylation of IFN-γ and Thy-1 were found in ETS-exposed offspring at 10-12 and 20 weeks of age. These sustained epigenetic alterations preceded the onset of significant pulmonary pathologies observed at 20 weeks of age. This study suggests that perinatal ETS exposure induces persistent epigenetic alterations in global DNA, as well as IFN-γ and Thy-1 promoter methylation that precede the adult onset of fibrotic lung pathology. These epigenetic findings could represent potential biomarkers of latent respiratory disease risk.

Keywords: Inflammation; early life; environmental tobacco smoke; methylation; prenatal; respiratory disease.

Figure 1.

Timeline of experiment. Upon confirmation of a vaginal plug, female mice were exposed to either FA only or 1.0 mg/m³ ETS 6h/day, 7 days/week for the duration of pregnancy. Dams and pups were exposed to FA only (pups born from FA and Pre ETS) or continued to receive ETS exposure (Pre/Post ETS) for three weeks post-birth. In equal sex-ratio, mice lungs were harvested at 10–12 weeks of age and again at 18–20 weeks of age.

Figure 2.

Representative pictures of interstitial collagen deposition of 20 week aged offspring for each group. Collagen (arrowed) was stained in light blue. (A) FA, (B) Pre ETS, and (C) Pre/Post ETS

Figure 3.

Lung collagen deposition and pathology scores. (A) Lung interstitium collagen deposition percentage from 18- to 20-week old offspring, n = 3 mice per group, presented as means ± SEM. (B) Lung pathology scoring from 18–20 week old offspring, n = 3 mice per group, presented as medians ± interquartile range for all scores, *p < 0.05.

Figure 4.

(A) Global and promoter methylation of each group in 10- to 12-week old offspring. Data shown as means ± SEM percent methylation, n = 3–6 per group, ***p < 0.001, **p < 0.01, *p < 0.05. (B) Global and promoter methylation of each group in 20-week old offspring. Data shown as means ± SEM percent methylation, n = 3 per group, **p < 0.01, *p < 0.05.