Stress-induced events boost sperm performance after the event has passed, study finds

A study by researchers at the University of Colorado Anschutz Medical Campus reveals that stress-induced changes in sperm motility occur after a stressful event, rather than during it, and improve sperm performance. This finding is critical to understanding how stress affects the reproductive process in order to improve fetal development outcomes.

The study was published in Nature Communications.

Over the past five decades, sperm quality has declined dramatically, due to environmental stressors. This new study identifies how stress affects the ability of sperm to move through a woman’s reproductive system to fertilize an egg (motility).

The researchers observed changes in extracellular vesicles (EVs), small particles released by the male reproductive tract that play a role in sperm development and maturation. These changes occurred after the stressor disappeared, not during the stress experience.

“Our results show a significant, time-dependent increase in sperm motility following perceived stress, which is consistent with previous studies of microRNA changes in human sperm,” said Tracy Bale, Ph.D., lead author and the Anschutz Foundation Chair in Integrated Women’s Mental and Physical Health at the Ludeman Center at CU Anschutz.

“This timing of improved sperm function after stress could be evolutionarily beneficial for increasing birth rates, especially after difficult times like those experienced during the COVID pandemic.”

Studies have been conducted in humans and animal models. In both cases, stress-induced EVs enhanced sperm motility and mitochondrial respiration, the chemical energy needed to fuel the cell’s biochemical reactions.

“Imagine you have a car that struggles to climb a steep hill. When the engine is stressed, the car becomes less efficient. However, with a little more gas, you can improve overall performance for a smoother ride. Just as your car becomes more efficient under stress, with the right tuning, cells improve their energy production and movement when stress-induced factors are present,” said Nickole Moon, Ph.D., first author of the study and a CU Anschutz graduate student who is part of the research team.

Given that the results were the same in humans and animal models, the findings suggest that this may be a universal adaptation mechanism across species, which could offer insights into broader implications for reproductive health.

Although the study focused on men, the researchers emphasize the importance of exploring how stress affects both partners in the fertility process. Additionally, the researchers are ultimately interested in how these differences affect fetal development, particularly the brain.

“The impact of stress on germ cells, fertility and the mechanisms underlying the transmission of parental stress experiences across generations are not well understood,” said Neill Epperson, MD, professor and chair of the CU Department of Psychiatry and Bale’s partner in the studies.

“By continuing to recruit participants for these trials and conducting in-depth stress assessments alongside the laboratory work, we hope to gain a better understanding of how past stressors may affect future offspring.”

Bale reiterates the importance of increasing awareness of the impact of stress on reproduction.

“Because stress is an integral part of daily life, understanding its effects on reproduction and development will be essential to improving fertility and addressing broader ecological impacts on threatened species,” Bale said.

The team is conducting further studies to understand how stress information is transmitted to EVs and how this influences fertilization. They are also investigating the impact on brain development. In addition, they will launch a pilot study to test this model and further investigate the relationship between EVs and sperm in seminal fluid.