161 Dichloroacetate influences the mitochondrial activity of bovine oocytes impairing meiotic progression

Abstract

Pyruvate is a key energy substrate for the oocyte during maturation and acquisition of developmental competence. Mitochondrial activity is also essential for oocyte competence. Dichloroacetate (DCA) is an inhibitor of pyruvate dehydrogenase kinase that indirectly stimulates pyruvate dehydrogenase (PDH), increasing pyruvate oxidation. PDH converts pyruvate into acetyl coenzyme A (acetyl-CoA) and thereby modulates the entry of glucose-derived carbons into the tricarboxylic acid (TCA) cycle, the main ATP production pathway within the oocyte. It was reported that DCA addition to embryo culture media improves embryo development in aged mice, by enhancing mitochondrial membrane potential (MMP) and decreasing oxidative stress (McPherson et al. 2014 Fertil. Steril. 101, 1458-1466). We hypothesised that increased pyruvate metabolism through the oxidative pathway, by stimulating PDH activity with DCA, could influence in vitro oocyte maturation. The aim of this work was to evaluate the effect of different concentrations of DCA during in vitro maturation (IVM) of bovine oocytes on maturation rate and mitochondrial activity, by assessing MMP and levels of flavin adenine dinucleotide (FADH₂), nicotinamide adenine dinucleotide hydride (NADH), and reactive oxygen species (ROS). Abattoir-derived bovine cumulus-oocytes complexes (COC; n = 360, over 4 replicates) were in vitro-matured with 0 (Control; n = 120), 0.5 mM (n = 120) and 5 mM (n = 120) of DCA. After maturation, all matured COC were denuded by mechanical pipetting and meiotic progression was assessed by Hoechst 33342 staining and MMP by MitoTracker Red CMXRos test (Thermo Fisher Scientific, Waltham, MA, USA). Moreover, FADH₂ and NADH levels were evaluated by autofluorescence (Dumollard et al. Development 134, 455-465) and ROS levels by CellRox® Green test (Thermo Fisher Scientific). Data were analysed by ANOVA, and the Tukey post hoc test was used to evaluate the difference among groups. The α-level was set at 0.05. Treatment with both concentrations of DCA decreased maturation rate (86.1, 67.8, and 67.6% in 0, 0.5, and 5 mM groups, respectively; P < 0.05). The MMP increased in oocytes matured with the highest concentration of DCA (3.42 ± 0.28, 4.44 ± 0.51, and 6.32 ± 0.89 pixel/mm², with 0, 0.5, and 5 mM DCA, respectively; P < 0.05). In line with this, higher levels of FADH₂ (3.16 ± 0.15, 3.96 ± 0.24, and 3.83 ± 0.20 pixel/mm², with 0, 0.5, and 5 mM DCA, respectively; P < 0.05) and NADH (3.86 ± 0.14, 4.80 ± 0.16, and 4.95 ± 0.17 pixel/mm², with 0, 0.5, and 5 mM DCA, respectively; P < 0.05) were found in both DCA-treated groups compared with the control. Unexpectedly, ROS levels increased in the presence of DCA (0.9 ± 0.07, 1.30 ± 0.12, and 1.54 ± 0.16 pixel/mm², with 0, 0.5, and 5 mM DCA, respectively; P < 0.05) compared with the control. These results suggest that DCA was effective in stimulating mitochondrial activity of bovine oocytes, but also resulting in increased oxidative stress that likely accounts for the decreased maturation rate. Therefore, alternative strategies should be identified for the manipulation of the oocyte metabolic profile to improve oocyte developmental competence.