Air pollution may impact male fertility through epigenetic changes by Jen Willow

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Air pollution is associated with epigenetic changes in sperm DNA, according to research presented at the 42nd Annual Meeting of the European Society of Human Reproduction and Embryology (ESHRE) in London.

US researchers found that sperm that developed during periods of higher air pollution were more likely to carry methylation changes on parts of their DNA. These changes do not affect the DNA sequence itself, but can impact how genes are turned on or off.

'Our findings suggest that air pollution exposure during key stages of sperm development may be associated with changes in sperm DNA methylation, including in genes involved in spermatogenesis and early developmental processes,' said lead author Dr Carrie Nobles from the University of Massachusetts Amherst, who presented the research.

The researchers studied methylation in semen samples from over 1220 men in Salt Lake City, Utah, between 2013-2017. They were able to compare the findings with estimates of air pollution from the three-month period before the sample was collected, when the sperm were developing. Among genes affected by methylation changes was GNAS, which is known to be associated with sperm quality and is also imprinted. Imprinting means that the gene carries specific epigenetic marks denoting whether a particular copy came from the egg or sperm.

'The association with changes in the imprinted gene GNAS was particularly important. Because imprinted genes can persist through early embryonic development, this raises important questions about whether fathers' environmental exposures may influence not only fertility, but pregnancy and offspring health,' said Dr Nobles.

The study looked at levels of four specific pollutants: ozone, nitrogen dioxide, sulphur dioxide and fine particulate matter, concluding that ozone and nitrogen dioxide levels appeared to have stronger associations with methylation changes.

Professor Karen Sermon, a recent chair of ESHRE, said: 'This is another piece of the puzzle... We know that couples exposed to air pollution often have difficulties becoming pregnant, and this may be one of the explanations amongst the myriad ways that pollution impacts our reproductive health.'

'There has been growing evidence in recent years that aspects of human health can be impacted by air pollution, and this includes male infertility. However, we have not really understood much about the likely mechanism by which this occurs,' said andrologist Professor Allan Pacey, from the University of Manchester, who was not involved in the research.

He told BioNews he welcomes this research but added that: 'At present, it is not possible to conclude whether the observed changes to sperm DNA methylation are clinically meaningful for male infertility and further work will need to be done to confirm or refute that.'

Dr Nobles agreed: 'We also need to understand whether air pollution-associated changes in sperm DNA methylation have measurable downstream impacts on men's fertility and couples' pregnancy health.'