The influence of follicular size on oocytes' lipid metabolism and FABP3 levels into extracellular vesicles of the follicular fluid in cattle

Abstract

Despite of decades of research on embryo in vitro production (IVP) we still have an incomplete understanding of the processes involved in generating oocytes that are competent to support embryonic development. However, it is known that the lipid accumulation is one of the major disadvantages of IVP embryos, since it compromises embryo cryotolerance and reduces pregnancy rates (Rizos et al., 2002). One of the hypothesis sustained by our research group is that the metabolic disturbances that lead to the excessive lipid accumulation are established as early as during the in vitro maturation (IVM) step. In all mammalian species, the IVM of oocytes retrieved from small follicles results in lower developmental rates (Trounson et al., 2002), indicating the importance of the follicular growth on the oocyte competence to sustain embryo development. Moreover, according to literature, there are differences in the content of oocyte cytoplasmic lipid droplets recovered from follicles of different diameters (Annes et al., 2018). One of the proteins involved with intraoocytic lipid accumulation, the Fatty Acid Binding Protein 3 (FABP3), was described to be into the transzonal projections (TZPs) during IVM, indicating that the cumulus cells might be the source of fatty acids that are transported to the oocyte (Del Collado et al., 2017). Additionally, our research group identified the FABP3 into extracellular vesicles (EVs) retrieved from the follicular fluid. Thus, this project will investigate the influence of the follicle diameter on FABP3 levels into follicular fluid-EVs. We expect that the results of this project allow to determine the existence of correlation between the follicular size and the lipid metabolism, and that contributes to elucidate the mechanisms driving the oocyte lipid accumulation during folliculogenesis.