273 CONSEQUENCE OF HIGH NONESTERIFIED FATTY ACID CONCENTRATIONS DURING BOVINE OOCYTE IN VITRO MATURATION ON mRNA TRANSCRIPT ABUNDANCE OF BLASTOCYSTS

Abstract

In recent years, high nonesterified fatty acid (NEFA) concentrations have been intensively discussed as an important metabolic cue linking negative energy balance in high yielding dairy cows early postpartum to disappointing fertility. Previous research has shown that high NEFA concentrations during in vitro oocyte maturation not only induce significant negative effects on the developmental capacity of oocytes but also reduce the quality and viability of the subsequent embryos that do survive until 7 days post-insemination. Because NEFA are known to regulate gene expression, the objective of this study was to investigate the effect of NEFA exposure during bovine in vitro oocyte maturation on the relative transcript abundance in the resultant day 7 blastocysts. This study focused on key genes related to embryonic quality, apoptosis, adaptation to stress, metabolism, DNA methylation, growth factors, and fatty acid synthesis. During a serum-free maturation period of 24 h, bovine cumulus–oocyte complexes were exposed to maturation medium (0.75% BSA) supplemented with 1) physiological NEFA concentrations (control; 150 μM of total NEFA, i.e. oleic, stearic, and palmitic acid), 2) elevated stearic acid concentrations (HSA; 75 μM of stearic acid), and 3) elevated NEFA concentrations (HCOMBI; 425 μM of total NEFA). Following IVF using semen from a bull of proven fertility, zygotes were cultured in SOF (+5% of FCS) medium for 7 days. Studied mRNA transcripts were quantified by real-time quantitative RT-PCR. Experiments were conducted to determine levels of each transcript relative to H2AZ in every sample. Relative mRNA abundance differences among groups were analysed by one-way ANOVA. Significant increases (P < 0.05) in relative mRNA abundance of the HCOMBI embryos were found for genes related to DNA methylation (DNMT3A), growth factors (IGF2R), glucose transport (SLC2A1), and fatty acid synthesis (ACSL1 and ACACA) compared with control embryos. Furthermore, HCOMBI embryos revealed a significantly higher expression (P < 0.05) of IGF2R and ACSL1 than did HSA embryos. The level of transcripts of genes related to mitochondrial biogenesis (TFAM) and the adaptation to stress (MNSOD) also tended to be increased in HCOMBI embryos compared with control embryos (P = 0.09 and P = 0.10, respectively). In conclusion, there is ample evidence that embryos originating from oocytes matured under negative energy balance conditions show aberrant transcriptional activities. These results might improve our current understanding of the possible mechanisms through which NEFA exposure during oocyte maturation affects the developmental capacity, quality, and viability of the resultant embryo.