With Australia known for its hot conditions, University of Newcastle and HMRI Infertility and Reproduction researchers Dr Natalie Trigg, Dr John  Schjenken, and Professor Brett Nixon are looking to find out the impact heat stress has on sperm.

The team, who had their recent findings published in the journal PNAS, focused on what happens to sperm after they have left the testes during heat wave conditions of 35 degrees during the day and 25 degrees overnight.  

Dr Trigg says, “We know that heat affects sperm development in the testes but we were interested in finding out what happens to sperm during their subsequent maturation in the male reproductive tract (i.e. epididymis).  

“We found that while the emulated heat wave conditions didn’t affect the ability of sperm to swim or to fertilise an egg in laboratory models, there were changes to the small RNAs that the heat-exposed sperm carry” says Dr Trigg.  

HMRI Infertility and Reproduction researchers, Dr John Schjenken, Professor Brett Nixon and Dr Natalie Trigg.

What does this mean if the sperm goes on to fertilise an egg? 

Small RNA molecules carried by sperm and delivered to the egg are known to regulate gene expression in the embryo and program offspring health. In the heat model, there are changes to the embryonic gene expression, there’s accelerated pre-implantation development, altered blastocyst hatching, and there is increased feotal:placental weight ratio, a marker of placental efficiency.  

The findings highlight the fact that even a relatively modest alteration in ambient temperature can affect male reproductive function, demonstrating the acute sensitivity of sperm small RNAs to environmental stress. 

“We know that paternal preconception health has an impact on the health of the offspring so the next steps will be exploring strategies to protect sperm during heatwave conditions, as well as understanding how quickly the small RNAs revert to normal once the heat episode ends,” says Dr Trigg.