Stress impacts sperm and brain development of offspring

Prolonged paternal stress may impact the composition of sperm and have far-reaching effects on any resulting offspring. 

Researchers at the University of Maryland School of Medicine looked at the biological effects of paternal stress on structures called extracellular vesicles that interact with maturing sperm in the reproductive tract. 

'There are so many reasons that reducing stress is beneficial especially now when our stress levels are chronically elevated and will remain so for the next few months,' said study author Tracy Bale, Professor of Pharmacology at University of Maryland School of Medicine, alluding to the coronavirus pandemic. 'Properly managing stress can not only improve mental health and other stress-related ailments, but it can also help reduce the potential lasting impact on the reproductive system that could impact future generations.'  

Extracellular vesicles transport proteins, nucleic acids and lipids between cells.  

The study published in Nature Communications details how the researchers examined the extracellular vesicles in mice following treatment with corticosterone – a key stress hormone. Following this hormonal treatment, the vesicles exhibited dramatic changes in size as well as protein and small RNA content. 

When sperm was incubated with the 'stressed' extracellular vesicles and then used to fertilise eggs, the resultant mice pups exhibited changes in early brain development patterns, and as they grew into adults, the mice responded to stressors very differently to control mice.  

The study found the changes in the male reproductive system occur at least a month after the stress is reduced - and life has resumed its normal patterns.  

To see if the results might also apply to humans, the team recruited students from the University of Pennsylvania to donate sperm samples over a six-month period, and complete a self-questionnaire assessing their perceived stress levels the month before each donation. Their findings show that those with elevated stress levels in the months leading to their donation had significant changes to the small RNA content in their sperm, compared to the students who had little to no stress prior to donating.  

'Our study shows that the baby's brain develops differently if the father experienced a chronic period of stress before conception, but we still do not know the implications of these differences,' said Professor Bale. 'Could this prolonged higher level of stress raise the risk for mental health issues in future offspring, or could experiencing stress and managing it well help to promote stress resilience? We don't really know at this point, but our data highlight why further studies are necessary.'