Correlation of Internal Exposure Levels of Polycyclic Aromatic Hydrocarbons to Methylation of Imprinting Genes of Sperm DNA

Abstract

Human exposure to polycyclic aromatic hydrocarbons (PAHs) results in adverse health implications. However, the specific impact of paternal preconception PAHs exposure has not been fully studied. In this study, a total of 219 men aged 24–53 were recruited and an investigation was conducted using a questionnaire requesting information about age, occupation, education, family history, lifestyle, and dietary preferences. Urine and semen samples were examined for the levels of the hydroxyl metabolites of PAHs (OH-PAHs) using ultra-high-performance liquid chromatography–tandem mass spectrometry and sperm DNA methylation by pyrosequencing. The results from the correlation analysis using seven OH-PAHs and the average methylation levels of the imprinting genes H19, PEG3, and MEG3 indicated that 1-OHPH is positively correlated with H19/PEG3 methylation levels. We further examined the correlation between each OH-PAH and the methylation levels at the individual CpGs. The results showed 1-OHPH is specifically correlated with CpG4 and CpG6 of the imprinted gene H19, CpG1 and CpG2 of PEG3, and CpG2 of MEG3; whereas 1-OHP is positively correlated with PEG3 at CpG1. Multivariate regression model analysis confirmed that 1-OHPH and 1-OHP are independent risk factors for the methylation of H19. These data show that sperm DNA imprinting genes are sensitive to adverse environmental perturbations.

Methylation of Imprinted Genes in Sperm DNA Correlated to Urinary Polycyclic Aromatic Hydrocarbons (PAHs) Exposure Levels in Reproductive-Aged Men and the Birth Outcomes of the Offspring

“…Importantly, a similar pattern in methylation change of these genes was seen in their unexposed F1-2 male mice ( Zhang et al, 2019 ). In our recent human studies, paternal Hg and PAHs exposures are associated with altered methylation pattern in sperm ( Lu et al, 2018 ; Ma et al, 2019 ). However, whether paternal exposure to PAHs and the altered DNA methylation levels of imprinting genes in sperm are linked, and eventually lead to adverse birth outcomes, remains unknown.…”

Minor DNA methylation changes are observed in spermatozoa prepared using different protocols

“…The field of human reproduction is no exception in following this trend, as studying epigenetic changes in gametes is even more interesting considering that gametes are responsible for transferring genetic material to the next generation 11 . Lately, a number of studies exploring sperm DNA methylation from different angles have been published, 12‐18 but there is a lack of studies on how different sperm preparation methods could possibly influence the sperm DNA methylation profile. To our knowledge, only one study has explored the DNA methylation profile of spermatozoa after DGC sperm preparation, 22 which is one of the most often used sperm preparation method in assisted reproduction 23 .…”

“…Consequently, this can affect the outcome of in vitro fertilization (IVF) procedures in terms of abnormal embryogenesis and pregnancy rates 13,14 . In studies on sperm DNA methylation, whole‐genome methylation analysis can be performed 13‐15 but often, only particular regions or genes are examined exclusively, for instance, regions and genes that are known to have specific paternal or maternal imprinting 16‐18 . Thus, these genes or regions are expressed only from one parental allele and around 100 such imprints have been found in mammalian genomes 19 …”

Evidence for germline non-genetic inheritance of human phenotypes and diseases

“…Males with higher concentrations of urinary organophosphate metabolites, which originate from flameretardants, had significantly higher fractions of aberrantly methylated DNA in sperm at differentially methylated regions (DMRs) of multiple imprinted genes [75]. Various environmental exposures, including mercury [76] and polycyclic aromatic hydrocarbons [77] were associated with mild DNA methylation changes at imprinted genes in sperm; again, it is unclear the significance of these changes on affecting phenotypes or disease risk. Environmental exposure to bisphenol A, a chemical found in many plastics, was associated with changes in sperm hydroxymethylation, which is an intermediate modification in the process of DNA demethylation and is associated with active gene expression [78].…”