PhD Defence by Ida W. Strand

Principal supervisor

• Professor Terje Svingen

Co-supervisors

• Senior Researcher Marta Axelstad
• Postdoc Monica K. Draskau

Examiners

• Senior Researcher Lea Sletting Jakobsen, DTU Food
• Professor Jean-Baptiste Fini, National Muséum of Natural History, France
• Senior Researcher Sofia Boeg Winge, Department of Growth and Reproduction, Copenhagen University Hospital (Rigshospitalet)

Chairperson at defence

• Associate Professor Hanna Katarina Lilith Johansson

Resume
Male reproductive health has declined in recent decades, raising concerns about the possible contribution of environmental factors, such as endocrine disrupting chemicals. Thyroid hormone (TH) signaling is known to regulate testis development in early life, and disruptions can delay in maturation and impar testis function. However, the involvement of TH signaling in male reproductive toxicity remains insufficiently addressed in the context of chemical regulation. Further, the molecular mechanisms linking TH system disruption to altered testis development are not well understood.

This PhD thesis investigates how reduced TH levels during development affect the testis. The rat was used as a model to analyze changes in gene expression levels, tissue structure, and hormone levels, providing a detailed understanding of how chemically induced hypothyroidism alters testis development. Additionally, an ex vivo rat testis model was used to explore whether simpler laboratory systems can capture relevant biological responses. The results show that disruption of TH signaling leads to consistent changes in gene expression that are linked to the observed testis effects and reproducible across chemicals and studies. The study further demonstrates that TH system disruption can influence other hormone systems.

Overall, this research provides important mechanistic insight into how TH system disruption affects testis development, that can be used in development of new methods for chemical testing, to account for the interactions between different hormone systems.

A copy of the PhD thesis is available for reading at the department