Placental promoter methylation of DNA repair genes and prenatal exposure to particulate air pollution: an ENVIRONAGE cohort study.

Abstract

BACKGROUND: Exposure to particulate air pollution has been linked with risk of carcinogenesis. Damage to repair pathways might have long-term adverse health effects. We aimed to investigate the association of prenatal exposure to air pollution with placental mutation rate and the DNA methylation of key placental DNA repair genes.

METHODS: This cohort study used data from the ongoing ENVironmental Influence ON early AGEing (ENVIRONAGE) birth cohort, which enrols pairs of mothers and neonates (singleton births only) at the East-Limburg Hospital (Genk, Belgium). Placental DNA samples were collected after birth. We used bisulfite-PCR-pyrosequencing to investigate the mutation rate of Alu (a marker for overall DNA mutation) and DNA methylation in the promoter genes of key DNA repair and tumour suppressor genes (APEX1, OGG1, PARP1, ERCC1, ERCC4, p53, and DAPK1). We used a high-resolution air pollution model to estimate exposure to particulate matter with a diameter less than 2·5 μm (PM2·5), black carbon, and NO2 over the entire pregnancy on the basis of maternal address. Alu mutation was analysed with a linear regression model, and methylation values of the selected genes were analysed in mixed-effects models. Effect estimates are presented as the relative percentage change in methylation for an ambient air pollution increment of one IQR (ie, the difference between the first and third quartiles of exposure in the entire cohort).

FINDINGS: 500 biobanked placental DNA samples were randomly selected from 814 pairs of mothers and neonates who were recruited to the cohort between Feb 1, 2010, and Dec 31, 2014, of which 463 samples met the pyrosequencing quality control criteria. IQR exposure increments were 3·84 μg/m3 for PM2·5, 0·36 μg/m3 for black carbon, and 5·34 μg/m3 for NO2. Among these samples, increased Alu mutation rate was associated with greater exposure to PM2·5 (r=0·26, p<0·0001) and black carbon (r=0·33, p<0·0001), but not NO2. Promoter methylation was positively associated with PM2·5 in APEX1 (7·34%, 95% CI 0·52 to 14·16, p=0·009), OGG1 (13·06, 3·88 to 22·24, p=0·005), ERCC4 (16·31%, 5·43 to 27·18, p=0·01), and p53 (10·60%, 4·46 to 16·74, p=0·01), whereas promoter methylation of DAPK1 (-12·92%, -22·35 to -3·49, p=0·007) was inversely associated with PM2·5 exposure. Black carbon exposure was associated with elevated promoter methylation in APEX1 (9·16%, 4·06 to 14·25, p=0·01) and ERCC4 (27·56%, 17·58 to 37·55, p<0·0001). Promoter methylation was not associated with pollutant exposure in PARP1 and ERCC1, and NO2 exposure was not associated with methylation in any of the genes studied.

INTERPRETATION: Transplacental in-utero exposure to particulate matter is associated with an increased overall placental mutation rate (as measured with Alu), which occurred in concert with epigenetic alterations in key DNA repair and tumour suppressor genes. Our results suggest that exposure to air pollution can induce changes to fetal and neonatal DNA repair capacity. Future studies will be essential to elucidate whether these changes persist and have a role in carcinogenic insults later in life.