Abstract
The positive effect of n-3 polyunsaturated fatty acids (FAs) on fertility in ruminants seems to be partly mediated through direct effects on the oocyte developmental potential. We aimed to investigate whether supplementation with physiological levels of docosahexaenoic acid (DHA, C22:6 n-3 polyunsaturated fatty acids) during IVM has an effect on oocyte maturation and in vitro embryo development in cattle. We reported that DHA (0, 1, 10, or 100 μM) had no effect on oocyte viability or maturation rate after 22-hour IVM. Incubation of oocyte-cumulus complexes with 1-μM DHA during IVM significantly increased (P < 0.05) oocyte cleavage rate as compared with control (86.1% vs. 78.8%, respectively) and the greater than 4-cell embryo rate at Day 2 after parthenogenetic activation (39.1% vs. 29.7%, respectively). Supplementation with 1 μM DHA during IVM also induced a significant increase in the blastocyst rate at Day 7 after IVF as compared with control (30.6% vs. 17.6%, respectively) and tended to increase the number of cells in the blastocysts (97.1 ± 4.9 vs. 81.2 ± 5.3, respectively; P = 0.08). On the contrary, 10-μM DHA had no effects, whereas 100-μM DHA significantly decreased the cleavage rate compared with control (69.5% vs.78.8%, respectively) and the greater than 4-cell embryo rate at Day 2 after parthenogenetic activation (19.5% vs. 29.7%). As was shown by real-time polymerase chain reaction, negative effects of 100-μM DHA were associated with significant increase of progesterone synthesis by oocyte-cumulus complexes, a three-fold increase in expression level of FA transporter CD36 and a two-fold decrease of FA synthase FASN genes in cumulus cells (CCs) of corresponding oocytes. Docosahexaenoic acid at 1 and 10 μM had no effect on expression of those and other key lipid metabolism-related genes in CC. In conclusion, administration of a low physiological dose of DHA (1 μM) during IVM may have beneficial effects on oocyte developmental competence in vitro without affecting lipid metabolism gene expression in surrounding CCs, contrarily to 100 μM DHA which diminished oocyte quality associated with perturbation of lipid and steroid metabolism in CC.
Highlights
Oocyte competence to develop into viable embryo after fertilization is mainly acquired during final oocyte growth and meiotic maturation
243 In our experiments, oocyte-cumulus complexes (OCC) were matured in vitro with or without DHA (1, 10, or 100 μM) and 244 in vitro embryo development was compared between conditions
We chose to assess oocyte developmental competence by using parthenogenetic activation (PA) first, because, in this case, embryo development only relies on oocyte maternal factors
Summary
Oocyte competence to develop into viable embryo after fertilization is mainly acquired during final oocyte growth and meiotic maturation. The oocyte lipid content, in terms of FA composition, has been shown to influence oocyte maturation and developmental competence [6, 7]. The highest concentrations of NEFA in the OCC environment, in vivo and in vitro led to low oocyte quality and embryo developmental rate after in vitro fertilization (IVF) [8,9,10]. FA are essential to oocyte quality as energy source [11, 12], but in the case of elevated FA concentration in the environment (follicular fluid or maturation medium), CC are required to protect the oocyte by incorporating excessive FA and transforming them into storage droplets [13, 14]. During oocyte maturation CC ensure active lipid metabolism through modulation of expression of FA metabolism related genes [15]
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