Researchers from the University of Newcastle and HMRI Infertility and Reproduction are investigating the effects of heat stress on sperm, a study that could have important implications for male fertility. Led by Dr. Natalie Trigg, Dr. John Schjenken, and Professor Brett Nixon, their recent research, published in PNAS, sheds light on sperm health under extreme temperature conditions typical of Australian summers.
The team focused on the impact of sustained heat waves, with temperatures reaching 35°C during the day and 25°C at night, on sperm after they leave the testes and enter the epididymis. Dr. Trigg explained that while previous studies have shown heat affects sperm development in the testes, the team wanted to explore how heat influences sperm during its maturation in the male reproductive tract.
The study revealed that although the heat stress did not hinder sperm motility or its ability to fertilize an egg in laboratory models, it did result in significant changes to the small RNA molecules within the sperm. These small RNAs are crucial because they regulate gene expression in the embryo and can influence the health of offspring.
Under heat wave conditions, the team found notable changes in embryonic gene expression, including faster pre-implantation development, altered blastocyst hatching, and an increased fetal-to-placental weight ratio, which indicates changes in placental efficiency. These findings underscore how sensitive sperm are to environmental stressors like heat, even those that might seem relatively mild.
Dr. Trigg emphasized the importance of paternal health prior to conception, noting that sperm health has a direct impact on the health of future offspring. Moving forward, the research team plans to investigate potential strategies to protect sperm during heat waves and examine how quickly small RNAs return to normal once the heat stress subsides.
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