70 Energy metabolites induce differential DNA methylation levels and transcription in trophectoderm and inner cell mass
Authors: Ispada J. , de Lima C. B. , dos Santos E. C. , Junior A. M. da Fonseca , da Silva J. V. Alcantara , da Rocha H. Cale , Milazzoto M. P. 
Published: January 2021

DNA methylation/demethylation is one of several epigenetic mechanisms by which metabolism regulates gene expression. More specifically, α-ketoglutarate (αKG) and succinate (Suc) are tricarboxylic acid cycle metabolites that may decrease and increase, respectively, the activity of DNA demethylases. Because pre-implantation embryos undergo reprogramming in both DNA methylation and metabolic pathways, it is possible that metabolic changes influence this epigenetic mark. To test that hypothesis, bovine embryos were invitro produced by using standard protocols and, 8h after fertilization, zygotes were transferred to synthetic oviductal fluid (SOF)-based culture medium (control, CO) or culture medium containing 4mM dimethyl-αKG, or 4mM dimethyl-Suc, where they remained until Day 4. Embryos were collected at Day 4 or remained in culture until Day 7, in control medium. Day 4 embryos were evaluated for DNA methylation levels by immunofluorescence detection of 5-methylcytosine (5mC) and cleavage rate. Day 7 embryos were also assessed for DNA methylation by immunofluorescence of 5mC, total cell number, blastocyst rates, and quantification of ACTB (housekeeping), DNMT1, DNMT3A, and DNMT3B transcript by RT-qPCR in trophectoderm (TE) and inner cell mass (ICM) separated by immunosurgery. The mRNA expression levels of were normalized to internal control ACTB and subsequently calculated using the 2−ΔΔCT method, using the control group for comparisons. All data were submitted to outlier detection using ROUT with Q=1% followed by one-way analysis of variance (ANOVA) and Fisher’s least significant difference (l.s.d.) test in GraphPad Prism. αKG and Suc did not influence cleavage or blastocyst rates, total cell number, or cell allocation. αKG supplementation reduced 5mC fluorescence intensity in embryos assessed at Day 4 (CO: 12.8±0.4 AU; αKG: 9.0±0.2AU; P&lt;0.0001) and Day 7 (CO: 36.5±0.7 AU; αKG: 23.5±0.4 AU; P&lt;0.0001), whereas Suc incubation increased DNA methylation levels in embryos at Day 4 (CO: 12.8±0.4 AU; Suc: 15.7±0.3 AU; P&lt;0.0001) and Day 7 (CO: 36.5±0.7 AU; Suc: 70.5±0.5 AU; P&lt;0.0001). αKG increased expression of DNMT1 (P=0.0438) in the ICM and led to lower levels of DNMT1 (P&lt;0.0001), DNMT3A (P=0.0013), and DNMT3B (P=0.0015) in TE cells. The culture with Suc increased DNMT1 (P=0.0074), DNMT3A (P=0.0186), and DNMT3B (P=0.0286) in ICM. Regarding TE, Suc resulted in lower expression of DNMT1 (P&lt;0.0001), DNMT3A (P=0.0017), and DNMT3B (P=0.0052). In conclusion, both supplementations resulted in global DNA methylation changes without affecting embryo development rates or morphology. These changes were accompanied by alterations in transcript profiles between ICM and TE, with differences among treatments being more pronounced in transcripts from ICM. This is the first report of DNA demethylation–induced changes by analogues of TCA cycle metabolites during early reprogramming of the bovine embryo with prolonged effects in TE and ICM cells.
This research was funded by FAPESP: 2017/18384-0; 2018/11668-6.