How dad’s stress affects sperm quality, makes offspring less resilient to pressure

The children of overly-stressed men may be less resilient and more prone to sensitivity to stress and even post traumatic stress disorder (PTSD), new research suggests.

A new study demonstrated how even mild to moderate stress may affect the way that men’s sperm develops.The resulting changes meant that these fathers passed down genetic coding for a less effective hormonal response to stress to their children.

This so-called ‘blunted’ hormonal response has been associated with those who develop certain neuropsychological disorders, including PTSD and autism.Historically, most research on how a parent’s lifestyle, behavior and environment can affect their children has focused on the mother. But scientists have recently been paying increasing attention to how a father’s health impacts his children.

Previous research linked stressed out male mice to offspring with the weaker hormonal response to stress, but did not uncover the exact mechanism that caused this phenomenon.

Three major hormones are released by the nervous system when the body is under stress. These are adrenaline, cortisol and norepinephrine. Collectively, these hormones send our bodies into ‘fight or flight’ mode, which is important to the body’s ability to cope with the effects of stress.

In humans, cortisol is the dominant steroid in the set, and in rodents its analogue is called corticosterone. In the University of Pennsylvania study, the researchers simulated ‘mild’ stress in cells taken from mice by exposing them to corticosterone.

In males, the same tract where sperm matures also releases vesicles which contain microRNA. RNA is Ribo Nucleic Acid/genetic material. MicroRNA can bond with sperm itself to change its composition, and, therefore, to change the genetic information passed on to offspring. The study revealed important mechanisms behind ‘how stress is transmitted across generations,’ says senior study author Dr. Tracy Bale at the University of Pennsylvania.

The researchers found that even the amount of corticosteroid released by males in a state of only mild stress had an effect on that tract. The stress on the reproductive tract caused it to release vesicles of microRNA that behaved like they were stressed.

If those microRNA bonded to the father’s developing sperm, he would pass along the same tendency to be overly-sensitive to stress – in the hormonal sense – to his children.

“These findings suggest that paternal stress may affect future generations’ by influencing ‘sperm maturation and content,” the study authors wrote.
Led by doctoral candidate Jennifer Chen, the researchers also found that when live male mice were placed under stress for four weeks, the hormonal effects would be present weeks later.

“It may be as much about the stress experience itself – that there’s stress, and that it ends – [that generates] effects that are long lasting,” says Bale.She says that now that her team has figured out what the ‘signals’ of stress carried to future generations are, they can begin to ask: ‘then how would you reverse those signals, how dynamic are the cells to this environment… and how the interaction of mom’s and dad’s genes effects [the translation of stress].’

Eventually, understanding these mechanisms could lead to the prevention – or at least mitigation – of many disorders. “Stress underlies all neuropsychological disease,” says Bayle.“Even mild environmental challenges can have lasting effects on future offspring health,” Chan says.

“An improved understanding of how a father’s life exposures to stress can affect his offspring is essential in understanding disease risk and improving the detection and prevention for these disorders,” she added.