Poster Presentation ESA-SRB 2023 in conjunction with ENSA

Sub-chronic elevation of ambient temperature differentially alters male reproductive function depending on the duration of exposure (#388)

Shannon P Smyth 1 2 3 , Natalie A Trigg 1 2 4 , John E Schjenken 1 2 , Jacinta H Martin 1 2 , Amanda L Anderson 1 2 , Ilana R Bernstein 1 2 , David A Skerrett-Byrne 1 2 , Brett Nixon 1 2 , Elizabeth G Bromfield 1 2 3
  1. Infertility and Reproduction Research Program, Hunter Medical Research Institute, Newcastle, NSW, Australia
  2. School of Environmental and Life Sciences, College of Engineering, Science and Environment, University of Newcastle, Callaghan, NSW, Australia
  3. School of BioSciences, Faculty of Science, Bio21 Institute, University of Melbourne, Parkville, VIC, Australia
  4. Departments of Genetics and Pediatrics, University of Pennsylvania Perelman School of Medicine and Children's Hospital of Philadelphia Research Institute, Philadelphia, PA, USA

Extreme weather events associated with changes in climatic behaviour, including severe drought and heatwaves, are increasing in frequency, intensity, and duration. Despite compelling evidence that such weather events pose a potential risk to the reproductive capacity of ecologically and agriculturally significant animal species, our understanding of the impact of sub-chronic whole-body exposure to elevated temperatures remains limited. To address this, here we exposed male mice to heat stress conditions that mimic a prolonged heatwave (daily cycle of 8h at 35°C followed by 16h at 25°C) for a period of seven days. Neither the testes nor epididymides of heat-exposed mice exhibited gross histological changes or displayed significantly altered oxidative DNA damage, single-strand DNA lesions or apoptotic markers. Furthermore, spermatozoa of exposed males retained comparable functionality to sham controls and supported fertilisation and subsequent embryonic development. Intriguingly, however, the embryos sired by heat-exposed males experienced pronounced changes in gene expression linked to an acceleration of early embryonic development, aberrant blastocyst hatching and macrosomia. These data eloquently reveal the importance of stress signals encountered by sperm during transit through the epididymal environment and their role in modulating offspring outcomes. To expand on these findings, an extended fourteen-day exposure model was utilised to assess the impacts of sub-chronic heat stress when applied during both spermatogenesis and post-testicular sperm maturation. Preliminary data revealed a marked increase in TUNEL staining in the testes, and unexpectedly, an accumulation of immune cells within the epididymal lumen of heat-exposed males. In contrast to the seven-day model, spermatozoa from fourteen-day exposed males displayed significantly impaired motility and reduced viability compared to shams and age-matched controls. It is yet to be determined whether these changes impact offspring outcomes. Together, these in vivo models provide a new platform to extensively investigate the mechanisms through which increased ambient temperature alters male reproductive capacity.