3 Modulation of glycolysis alters histone acetylation and gene expression in bovine blastocysts produced invitro
Authors: Junior A. M. Fonseca , Paulson E. E. , Goszczynski D. E. , Ispada J. , Santos E. C. , Lima C. B. , Silva J. V. A. , Ross P. J. , Milazzotto M. P. 
Published: January 2021

Changes in the dynamics of energy metabolism can affect the sophisticated molecular control of different cell types including embryonic stem cells (Zhang et al. 2018 Cell Metab. 27, 332-338; https://doi.org/10.1016/j.cmet.2018.01.008). In this study, we modulated pathways related to acetyl-CoA generation, the major donor for histone acetylation, and explored how this affects histone acetylation and the transcriptional profile of bovine blastocysts. Embryos were produced invitro by conventional protocols. On Day 4 of culture (Fertilization=Day 0), embryos were randomly allocated into 3 experimental groups according to culture medium [synthetic oviductal fluid with amino acids (SOFaa) + 4% bovine serum albumin] supplementation: Control (no additional supplementation), sodium iodoacetate (IA; 2 µM; glycolysis inhibitor), and sodium dichloroacetate (DCA; 2 mM; acetyl-CoA conversion stimulator). Expanded blastocysts were collected on Day 7 and assessed for ATP levels (luminescence), mitochondrial activity (MitoTracker Red CMXRos; ThermoFisher Scientific), histone 3 lysine 9 and 27 acetylation (H3K9ac and H3K27ac; immunostaining) and transcriptional profiling by RNA sequencing (RNA-Seq) of isolated inner cell mass. Data were submitted to normality test and treatment groups were compared to control using t-test or Mann–Whitney test for non-parametric data (mean±s.e.) considering P&lt;0.05. RNA-Seq data were analysed by DESEqn 2 and transcripts with Padj &lt;0.05 were submitted to gene ontology by DAVID (https://david.ncifcrf.gov/). Mitochondrial activity was higher in DCA compared with Control (control: 53078±2747 AU vs. DCA: 57520±902 AU; P=0.0034), which explains the higher ATP levels found in this group (control: 1.49±0.65 µM vs. DCA: 41.56±15.69 µM; P=0.03). However, although mitochondrial activity was expectedly lower in IA compared to control (control: 53078±2747 A.U. vs. DCA: 36249±3200 A.U.; P=0.0013), we did not observe a decrease in ATP levels (control: 1.49±0.65µM vs. IA: 3.23±1.13 µM; P=0.12). Confirming our hypothesis, modulation of acetyl-CoA generation affected histone acetylation, with levels of H3K9ac and H3K27ac being higher in DCA and lower in IA compared with Control (H3K9ac Control: 988.3±22.82 AU, DCA: 1301±32.28 AU, IA: 684±23.7 AU; P&lt;0.0001 and H3K27ac Control: 502.5±13.64 AU, DCA: 667.2±12.19 AU, IA: 417.2±12.03 AU; P&lt;0.0001). Finally, 905 genes were differentially expressed, 599 up- and 306 downregulated in DCA compared with Control. Another 675 genes were differentially expressed between control and IA, (385 up- and 290 downregulated in IA). Gene ontology indicated that, compared with control, the biological functions upregulated in DCA were related to developmental process and the downregulated functions were associated with metabolism regulation, indicating a role of metabolic pathways in the developmental competence of the embryo. IA, in contrast, had catabolic activity upregulated and nucleotide metabolism downregulated compared with control, supporting the depletion of metabolic activity and lower acetylation. Taken together, our results demonstrate that the modulation of energy metabolism affects the epigenetic status of bovine embryos with consequences for the transcriptional profile of pathways involved in embryo quality and viability.