Effects of diesel exhaust particles and engineered nanoparticles on DNA methylation of genes associated with pathogenesis of Chronic Obstructive Pulmonary Disease (COPD) in bronchial epithelial cells

Inhaled particles such as diesel exhaust particles (DEP) and engineered nanoparticles (NP) create an important risk for respiratory health. Studies suggest that DEP and NP induce oxidative stress, cellular toxicity, and inflammation, which can lead to airway diseases. These particles are also shown to cause DNA methylation in various cellular systems. However, their effects on genes involved in chronic obstructive pulmonary disease (COPD) are not clear. We aimed to investigate the effects of DEP and NP on mRNA expression and DNA methylation of genes associated with the pathogenesis of COPD. BEAS-2B cells were incubated with DEP, Titanium Dioxide (TiO2), and Multi-walled Carbon Nanotubes (MWCNT) at concentrations of 0-100 µg/mL for 6, 24 and 48 hours, and viability of the cells was assessed using MTT assay. mRNA expression of COPD-associated genes (GCLC, CYP1B1, MUC5B, MUC5AC, FAM13A, SERPINA1) was analysed by qRT-PCR. CpG-targeted pyrosequencing was performed to understand DNA methylation status of differentially expressed genes. Particles did not cause a reduction in cell viability greater than 50%, except 100 µg/mL DEP at T48 hours of incubation. DEP and NP altered mRNA expression of GCLC and CYP1B1 genes, which are both involved in oxidative stress mechanisms. There were no significant DNA methylation changes in the promoter regions of the genes. However, DNA methylation changes were observed at CpG sites in exon 1 and intron 1. Although 50 µg/mL DEP increased DNA methylation of GCLC gene following 24 hours of incubation, this was decreased by MWCNT as the exposure time increased. TiO2 did not cause significant DNA methylation changes in GCLC gene. MWCNT (100 µg/mL)increased DNA methylation of CYP1B1 gene at T6 and T48 hours, whereas neither DEP nor TiO2 caused a significant change in DNA methylation of CYP1B1 gene. Our findings suggest that DEP and engineered NP may play a role in the pathogenesis of COPD by altering mRNA expression and DNA methylation of GCLC and CYP1B1 genes. Keywords: Bronchial Epithelial Cells, Diesel Exhaust Particles, Engineered Nanoparticles, DNA Methylation, COPD.