Abstract
Glucose or fatty acids (FAs) metabolisms may alter the ovarian follicle environment and thus determine oocyte and the nascent embryo quality. The aim of the experiment was to investigate the effect of selective inhibition of glucose (iodoacetate + DHEA) or FA (etomoxir) metabolism on in vitro maturation (IVM) of bovine COCs (cumulus–oocyte complexes) to investigate oocyte’s development, quality, and energy metabolism. After in vitro fertilization, embryos were cultured to the blastocyst stage. Lipid droplets, metabolome, and lipidome were analyzed in oocytes and cumulus cells. mRNA expression of the selected genes was measured in the cumulus cells. ATP and glutathione relative levels were measured in oocytes. Changes in FA content in the maturation medium were evaluated by mass spectrometry. Our results indicate that only glucose metabolism is substantial to the oocyte during IVM since only glucose inhibition decreased embryo culture efficiency. The most noteworthy differences in the reaction to the applied inhibition systems were observed in cumulus cells. The upregulation of ketone body metabolism in the cumulus cells of the glucose inhibition group suggest possibly failed attempts of cells to switch into lipid consumption. On the contrary, etomoxir treatment of the oocytes did not affect embryo development, probably due to undisturbed metabolism in cumulus cells. Therefore, we suggest that the energy pathways analyzed in this experiment are not interchangeable alternatives in bovine COCs.
Highlights
Female fertility is a complex trait affected by numerous factors of environmental and physiological origin
The described experiment was conducted on the control group (IVM in basic medium) and two experimental groups: (1) IO+DHEA—in vitro maturation (IVM) medium supplemented with two inhibitors of glucose metabolism [1.5 μM iodoacetate diluted in water and 150 μM DHEA diluted in DMSO] and (2) ETOMOXIR—IVM medium supplemented with an inhibitor of fatty acid metabolism (150 μM etomoxir diluted in DMSO)
The obtained results indicate that glucose metabolism during in vitro maturation is substantial for the oocyte since only IO+DHEA inhibition significantly decreased embryo culture efficiency determined by reduced cleavage, blastocyst, and hatched blastocyst rate
Summary
Female fertility is a complex trait affected by numerous factors of environmental and physiological origin. Negative energy balance negatively impacts ovarian follicle growth and oocyte quality [2]. The physiological consequences are characterized by alternations in plasma metabolite levels and further modifications of follicular fluid composition [3]. Experiments revealed a substantial influence of non-esterified fatty acids (NEFAs) concentrations in the follicular fluid (in vivo) or maturation media (in case of the in vitro embryo production systems) on oocyte quality, with a key role of cumulus cells (CCs) in protection against lipotoxicity [4,5]. An optimal physiological concentration of glucose and fatty acids (FAs) is crucial for proper oocyte development and maturation, which, in the future, may have an impact on embryo developmental potential
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