Impact of non-esterified fatty acids during in vitro fertilisation on bovine preimplantation embryo development : implications for reproductive medicine/

Abstract

Background: In vitro bovine models have shown that exposure to high NEFA concentrations (i.e., stearic acid [SA], palmitic acid [PA], oleic acid [OA]) impair oocyte competence and embryo quality. However, the effect of high NEFA exposure exclusively during the fertilisation process per se is less certain. The aim of this thesis was to investigate the effects of high NEFA (SA, PA, and OA) concentrations exclusively during in vitro fertilisation (IVF) on preimplantation embryo development and spermatozoa quality. Methods: Bovine oocytes were in vitro matured, followed by IVF in physiological (control 1) and high NEFA concentrations. A second control group contained solvent. Zygotes were cultured for eight days (Day 0=IVF) and resultant preimplantation embryos examined. Spermatozoa were incubated for four hours under the same IVF conditions. Data were analysed with ANOVA. Results: High NEFA exposure impaired fertilisation rate, cleavage, and blastocyst formation. Cell number in blastocysts was decreased, but reactive oxygen species production in zygotes was not affected. H3K27me3 was examined in early embryos, a repressive epigenetic mark that undergoes erasure from fertilisation to the time of embryonic genome activation to allow progression to the blastocyst stage. The expected lack of difference in H3K27me3 levels between 2- and 4-cell embryos was observed in the control groups. However, in the high-NEFA group levels in 2-cell embryos were still higher than in 4-cell embryos on day 2, suggesting that activation of developmentally important genes needed to progress to the blastocyst stage was potentially delayed, explaining partially the low blastocyst production. Spermatozoa exposed to high NEFA concentrations displayed damaged plasma membrane and acrosome, along with impaired mitochondrial membrane potential and increased DNA damage. Conclusion: High NEFA concentrations can induce detrimental effects during the fertilisation process via both the oocyte and the spermatozoon resulting in impaired preimplantation embryo development.