Response of Bovine Cumulus-Oocytes Complexes to Energy Pathway Inhibition during In Vitro Maturation

Energy metabolism disorders during in vitro maturation of bovine cumulus-oocyte complexes interfere with blastocyst quality and metabolism

Glucose and fatty acids (FA) metabolism disturbances during oocyte in vitro maturation (IVM) affect their metabolism and surrounding cumulus cells, but only inhibition of glucose metabolism decreases embryo culture efficiency. Therefore, the present experiment aimed to reveal if glucose or FA metabolism inhibition leads to the disruption of embryo developmental potential, and to characterize the metabolic landscape of embryos reaching the blastocyst stage. Inhibitors of glucose (IO + DHEA) or FA (ETOMOXIR) metabolism were applied during IVM, and the control group was matured under standard conditions. Blastocysts obtained from experimental and control groups were analyzed with regard to lipidome and metabolome (mass spectrometry), transcriptome (RNA-Seq) and fluorescence lipid droplets staining (BODIPY). We showed that inhibition of glucose and fatty acid metabolism leads to cellular stress response compromising the quality of preimplantation embryos. The inhibition of energy metabolism affects membrane fluidity as well as downregulates fatty acids biosynthesis and gene expression of trophectoderm cell line markers. Therefore, we conclude that oocyte maturation environment exerts a substantial effect on preimplantation development programming at cellular and molecular levels.

Effect of a low ethanol concentration during in vitro maturation of bovine oocytes and subsequent embryo development

The present study investigated the effects of low ethanol exposure on bovine oocytes. Cumulus-oocyte complexes (COCs) were aspirated for the antral follicles of slaughterhouse-derived ovaries. These COCs were incubated in maturation medium containing 0, 0.1, and 0.2% ethanol for 21 h and subjected to fertilization and in vitro development, and then the rates of nuclear maturation, mitochondrial DNA copy number (Mt-cn) and protein (TOMM40), ATP content and lipid content in oocyte, fertilization, and blastulation were examined. Furthermore, COCs were incubated with 0 or 0.1% ethanol and then mitochondrial membrane potential (MMP) and the glucose consumption of COCs was determined. In addition, gene expression in oocytes was examined by RNA sequencing. Ethanol (0.1 and 0.2%) increased Mt-cn and Mt-protein levels whereas 0.2% ethanol increased the blastulation rate and ATP content in oocytes and decreased lipid content in oocytes. Ethanol (0.1%) increased MMP in oocytes and decreased glucose consumption of COCs. Eight stage embryos derived from 0.1% ethanol treated oocytes had higher levels of trimethyl-H3K9 compared with that of nontreated counterpart. RNA sequencing revealed that differentially expressed genes were associated with glycolysis/gluconeogenesis, carbon metabolism, sphingolipid metabolism, amino acid metabolism, and fatty acid degradation pathways. In conclusion, even 0.1% concentrations of ethanol during in vitro maturation considerably affects oocyte metabolism and histone configuration of embryos.

Species and embryo genome origin affect lipid droplets in preimplantation embryos

Mammalian embryo development is affected by multiple metabolism processes, among which energy metabolism seems to be crucial. Therefore the ability and the scale of lipids storage in different preimplantation stages might affect embryos quality. The aim of the present studies was to show a complex characterization of lipid droplets (LD) during subsequent embryo developmental stages. It was performed on two species (bovine and porcine) as well as on embryos with different embryo origin [after in vitro fertilization (IVF) and after parthenogenetic activation (PA)]. Embryos after IVF/PA were collected at precise time points of development at the following stages: zygote, 2-cell, 4-cell, 8/16-cell, morula, early blastocyst, expanded blastocyst. LD were stained with BODIPY 493/503 dye, embryos were visualized under a confocal microscope and images were analyzed with the ImageJ Fiji software. The following parameters were analyzed: lipid content, LD number, LD size and LD area within the total embryo. The most important results show that lipid parameters in the IVF vs. PA bovine embryos differ at the most crucial moments of embryonic development (zygote, 8-16-cell, blastocyst), indicating possible dysregulations of lipid metabolism in PA embryos. When bovine vs. porcine species are compared, we observe higher lipid content around EGA stage and lower lipid content at the blastocyst stage for bovine embryos, which indicates different demand for energy depending on the species. We conclude that lipid droplets parameters significantly differ among developmental stages and between species but also can be affected by the genome origin.

Bovine in vitro oocyte maturation and embryo culture in liquid marbles 3D culture system

Despite the advances in in vitro embryo production (IVP) over the years, the technique still has limitations that need to be overcome. In cell cultures, it is already well established that three-dimensional culture techniques are more physiological and similar to the in vivo development. Liquid marble (LM) is a three-dimensional system based on the use of a hydrophobic substance to create in vitro microbioreactors. Thus, we hypothesized that the LM system improves bovine in vitro oocyte maturation and embryo culture. In experiment I, bovine cumulus-oocyte complexes (COCs) were placed for in vitro maturation for 22h in two different groups: control (conventional 2D culture) and LM (three-dimensional culture). We found that oocyte nuclear maturation was not altered by the LM system, however it was observed a decrease in expression of genes important in the oocyte maturation process in cumulus cells of LM group (BCL2, EIF4E, and GAPDH). In experiment II, the COCs were conventionally matured and fertilized, and for culture, they were divided into LM or control groups. There was a decrease in blastocyst rate and cell counting, a down-regulation of miR-615 expression, and an increase in the DNA global methylation and hydroxymethylation in embryos of LM group. Therefore, for the bovine in vitro embryo production, this specific three-dimensional system did not present the advantages that we expected, but demonstrated that the embryos changed their development and epigenetics according to the culture system.