Impact of Intrafollicular Sulfated Steroids on Follicular Cells and the Oocyte's Developmental Capacity in Cattle
Final Report Abstract
Within the antral follicle, numerous events affect oocyte maturation and the acquisition of developmental competency, including interactions between somatic cells of the follicle (in particular cumulus cells) and the oocyte, as well as the composition of follicular fluid. Many of these factors change with follicle size and oocyte growth. In contrast, culture conditions for in vitro maturation (IVM) often do not reflect the follicular environment, and/or have complex compositions or additives such as macromolecule supplements that are undefined in nature. Steroid hormones are essential in orchestrating oocyte maturation. During the final maturation period a switch from estradiol to progesterone dominance within the follicle is well-described. Steroid hormone concentration and property can be modulated via different processes. Sulfoconjugation via sulfotransferases (SULTs) changes steroids from hydrophobic to hydrophilic, necessitating transport systems for plasma membrane passage. Steroid sulfatase (StS) can remove the sulfate moiety from conjugated steroids, transforming them to the free active form. The research project aimed at a better understanding of local effects of sulfated steroids in the female reproductive tract. Their concentration has been determined during important developmental stages of the sexual cycle in peripheral plasma and the female reproductive tract (follicular fluid). This has then been correlated to the presence of biologically active free steroids as well as of steroid sulfate transporter such as the sodium-dependent organic anion transporter SOAT and intracellular metabolizing enzymes (e.g. StS and SULT1E1). Information on the role of steroid sulfonation and the hydrolysis of sulfonated steroids as local regulatory mechanisms in follicular steroidogenesis show that the estrogen-specific sulfotransferase SULT1E1 was not detectable in ovarian tissue and expression of StS was very low. The hypothesis of sulfonated steroids as functionally relevant precursors, intermediates or products of ovarian steroidogenesis is also clearly challenged by their low or undetectable concentrations in blood and follicular fluid. During IVM, progesterone concentrations increased in the medium, whereas the estradiol concentrations stayed similar. Even after supplementation of IVM medium with three different compounds of gonadotropins, the temporal pattern of both hormones did not correspond with the pattern during final maturation in vivo. In addition, most transcripts related to steroid synthesis and metabolism were down-regulated during the period of IVM with different gonadotropin supplements with exception of the progesterone receptor (PGR). Furthermore, most transcripts follow a timely regulated mRNA expression pattern during the entire IVM period. For the analyses of bile acids in follicular fluid a liquid chromatography-tandem mass spectrometry (LC–MS/MS) method was developed and validated and revealed unexpectedly high concentrations. Taken together, these data underline that present conditions of IVM do not reflect the in vivo situation and require further optimization. Manipulation of these factors and application of gained knowledge of the in vivo environment may result in improved in vitro oocyte maturation and overall in vitro embryo production.
Publications
- (2017) Occurrence of sulfonated steroids and ovarian expression of steroid sulfatase and SULT1E1 in cyclic cows. J Steroid Biochem Mol Biol
Blaschka C, Schuler G, Sánchez-Guijo A, Zimmer B, Feller S, Kotarski F, Wudy SA, Wrenzycki C
(See online at https://doi.org/10.1016/j.jsbmb.2017.12.010)
