Mapping the glucocorticoids during reproductive eventschecks and balances in their expression across species

Abstract

The assisted reproduction techniques have greatly improved over the last decades. However, there is still a long way to go until acceptable success rates are achieved. Developing strategies for reducing the cellular stress in vitro, together with a better understanding of signaling pathways involved in reproductive physiology and fertility, can provide new valuable insights in the field. The regulation of glucocorticoids (GCs) can be a candidate signaling pathway in this regard. GCs are steroid hormones that can inhibit reproduction during stress responses, but are also essential at baseline levels for important events of the female reproductive physiology, including ovulation, oocyte maturation or implantation. The role of GCs in reproduction is complex and seems to be different among species. The mechanisms involved in their regulation remain unclear, but most of their actions are attributed to the GC receptor, NR3C1, to the enzymes controlling GC availability, and immunophilins FKBP4 and FKBP5, involved in the regulation of the NR3C1 actions in the nucleus. Accordingly, the present thesis studies the role of the gene and protein expression of the GC receptor -and molecules involved in GC regulation- in the reproductive function, by determining its modulation in the female reproductive tract during reproductive events in vivo and in vitro. In this regard, we studied the GC regulatory expression in bovine oocytes and cumulus during in vitro maturation, vitrification, and supplementation with coenzyme Q10 (Q10), an endogenous molecule with important mitochondrial properties. Thus, we demonstrated that Q10 is beneficial for preserving the oocyte integrity after vitrification, exerts positive effects against apoptosis, and can influence the regulation of GCs in the female gamete. Moreover, we determined the changes in GC-related expression occurring at baseline level in the bovine endometrium and ampulla across different stages of the estrous cycle. These changes showed a spatiotemporal pattern that matched with reproductive events, suggesting a relevant role of GCs in the oviduct during the postovulatory phase. After this approach, we aimed to understand the influence of the male-female interaction in the expression of the GC regulation, by assessing the effects of natural mating, artificial insemination and seminal plasma infusion in the reproductive tract of preovulatory sows. According to our results, the natural mating induces a tight regulation for the restriction of the GC actions in the sperm reservoir which is not mimicked by artificial insemination. Finally, in the rabbit, an induced-ovulation species, we evaluated the modulation of NR3C1 in the female reproductive tract caused by the influence of the male-female interactions, and during different time points, corresponding to reproductive events such as ovulation, fertilization and presumed embryo developmental stages. We concluded that seminal plasma could trigger NR3C1 expression in the infundibulum, and mating increased NR3C1 in a spatiotemporal sequence corresponding to the assumed location of rabbit embryos. Overall, this thesis provides new knowledge about the complex GC regulation in reproduction and its modulation during reproductive events in different species. A better comprehension of this pathway may help to unravel the underlying mechanisms behind the stress influence on reproduction, find novel fertility biomarkers, and develop new potential strategies with reproductive purposes.