(P-112) Metabolic characterisation of the roe deer uterine fluid during diapause and elongation

Abstract Authors: Sara Elsafadi¹, Anna-Katharina Hankele¹, Pieter Giesbertz², Susanne E. Ulbrich<sup>1

1</sup> ETH Zurich, Animal Physiology, Institute of Agricultural Sciences, Zurich, Switzerland

² Else Kröner-Fresenius-Center of Nutritional Medicine, TUM School of Life Sciences, Technical University of Munich, Freising, Germany

Abstract Text: Embryonic diapause is a peculiar developmental phenomenon in which the usual consecutive progression from fertilization to implantation is halted. In the case of the European roe deer (Capreolus capreolus), the blastocysts enter a four-month period of reduced embryonic growth and minimal metabolism, during which the blastocyst floats freely in the uterus surrounded by the nutrient-rich histotroph. Exit from diapause is marked by the elongation of the embryo, setting the stage for implantation. We theorized that the uterine fluid (UF), which undergoes changes to support early embryonic development, creates a nurturing environment that either actively slows embryo development during diapause or accompanies its reduced developmental velocity to facilitate elongation upon reactivation. Therefore, we performed targeted and untargeted metabolomics via mass spectrometry to characterise the metabolome of roe deer UF during diapause and reactivation. By analysing non-polar lipids, polar metabolites, acylcarnitines, and polyamines, we aimed to provide a comprehensive view of the metabolic landscape within the UF before implantation to understand intricate molecular interactions and metabolic changes. Our results indicate that fatty acid degradation increases during elongation, possibly for membrane synthesis rather than energy production. Elevated glycolysis/gluconeogenesis may compensate for energy needs during elongation. We also observed increases in sphingomyelin, prostaglandin precursors, and the amino acids asparagine, glutamine, and methionine during elongation. Metabolomic Pathway Analysis (MetPA) revealed the importance of sphingolipid and glycerophospholipid metabolism pathways during elongation. We particularly found that the polyamines spermidine and spermine, but not putrescine, significantly increased 7- and 1.3-fold respectively in the UF during elongation, indicating their importance for reactivation and/or proliferation. Indeed, it was previously shown that putrescine is implicated in the diapause of mink. Whether polyamines are cause or result of embryo reactivation in roe deer requires further investigation. Overall, our research uncovered dynamic changes in the roe deer uterine fluid composition and proposed their role in supporting the energy- and resource-intensive process of embryo elongation. It provided insights into the role of the intrauterine environment on roe deer embryo development. This study will not only improve our knowledge of roe deer reproduction, but also shed light into embryonic diapause regulation with broader implications for understanding fertility issues and furthering conservation efforts.