Preimplantation embryo development is accompanied by the restructuring of the epigenetic landscape to ensure appropriate gene activation for ongoing development. Nutrient availability modulates the levels of acetyl-CoA, a necessary cofactor for acetylation, linking metabolism with the regulation of the epigenome. Importantly, in vitro culture has recently been shown to significantly impact histone 3 lysine 9 acetylation (H3K9ac) levels. Plausibly, the detrimental effects of atmospheric oxygen on embryo development and metabolism are mediated in part via altered acetylation. Therefore, the aim of this study was to elucidate the impact of modulating oxygen, and acetyl-CoA directly using the pyruvate dehydrogenase kinase inhibitor dichloroacetic acid (DCA), on blastocyst formation, total cell numbers and acetylation.
Two PN embryos were collected from superovulated female mice and cultured in G1/G2 media, supplemented with or without 2 mM DCA under 5 or 20% oxygen. Day 4 blastocyst rates were calculated, with resultant embryos immunostained for H3K9ac and H3K27ac and counterstained with DAPI to quantify acetylation levels and total cell number. Blastocyst formation was not altered by oxygen or DCA treatment, however 20% oxygen significantly reduced total blastocyst cell number, relative to 5% cultured embryos (p<0.0001). Cell number was further reduced with DCA treatment under 20% oxygen (p= 0.0044). Significantly, both 20% oxygen and DCA treatment, alone or in combination, increased blastocyst H3K27ac (p<0.0001), while 20% oxygen alone and in combination with DCA also increased H3K9ac (p<0.0001).
These data reveal that 20% oxygen culture, and modulation of acetyl-CoA levels, significantly alters blastocyst H3K9ac and H3K27ac, highlighting how metabolite availability can markedly alter acetylation dynamics. Plausibly, increased H3K9 and H3K27 acetylation could alter fetal and placental development, and is currently being investigated.