Follicular fluid extracellular vesicles and their effects on bovine oocyte maturation and quality

Abstract

In vitro production (IVP) of embryos is a widely used reproductive biotechnique, but quality of embryos is still suboptimal; such embryos show greater sensibility to cryopreservation and increased cytoplasmic lipid accumulation. In vitro culture (IVC) of embryos with extracellular vesicles (EVs) from bovine oviductal fluid (oEVs), as well as the use of fetal calf serum (FCS) depleted from its EVs (dFCS), improved embryo quality and cryotolerance. Sequential IVC with oEVs followed by EVs from uterine fluid (uEVs) resulted in embryos with lower lipid amounts and modulated lipid metabolism related genes and lipase protein. Addition of EVs isolated from follicular fluid (ffEVs) and supplemented to in vitro maturation (IVM) medium, also improved embryo development and quality, but lipid metabolism effects were not studied on cumulus-oocyte complexes (COCs). Therefore, the aim of the present study is to investigate the role of ffEVs on lipid metabolism of COCs, as well as effects on maturation and developmental competence. For this purpose, effects of ffEVs during IVM on COCs will be assessed in terms of maturation rates (% of oocytes reaching metaphase II stage), lipids contents and mitochondrial activity of oocytes. Expression of lipid metabolism genes in oocytes will be assessed by PCR (FASN, PPARGC1B, ACACA, FASN and HSL). Moreover, developmental competence will be assessed by in vitro fertilization and culture, by measuring cleavage rate on day 2 (Day 0=day of fertilization) and blastocysts yield on days 6, 7 and 8. Knowledge on bovine COCs and embryo lipid metabolism and the role of EVs may contribute to improve quality of IVP embryos.