Effect of glucose concentration in culture medium on the human preimplantation embryo methylome

Study questionDoes glucose concentration in culture medium have an impact on the DNA methylome of the early human embryo? Summary answerGlucose concentration is associated with changes in gene expression, global DNA methylation, methylation levels at CpG islands and at key histone modifications in human blastocysts. What is known alreadyPreimplantation human embryos are highly sensitive to their local environment, and this may have long term implications for the health of the developing embryo, fetus and offspring. Glucose is a standard component of human embryo culture media, due to its importance as a nutrient. However, concentrations of glucose differ widely between different commercially available types. The present study was designed to determine whether changes in glucose concentration could influence global methylation and gene expression in the human preimplantation embryo. Study design, size, durationHuman embryos were cultured in clinically relevant concentrations of glucose and global DNA methylation analysis was performed. The effect of glucose concentration on the embryo epigenome, specifically DNA methylation, was analysed. Participants/materials, setting, methodsHuman embryos surplus to treatment requirements were donated with informed consent from several ART centres. Embryos were cultured to the blastocyst stage in Vitrolife G-TL medium, either at 0.9 mM or 3.5 mM glucose, separated via immunosurgery into Inner Cell Mass (ICM) and trophectoderm (TE) samples, and compared for both DNA methylation and gene expression. This allowed us to evaluate the association between DNA methylation and previously importantly identified biological pathways. Main results and the role of chanceThe concentration of glucose in human embryo culture medium was associated with changes in gene expression and global DNA methylation in both ICM and TE, and methylation levels at CpG islands and key histone modifications. These results are significant because glucose is a major nutrient metabolised by human embryos in culture, and yet we know relatively little of its downstream effects on the genome and epigenome. Wider implications of the findingsCommercially available embryo culture media with varying glucose levels have also been associated with altered fetal growth, birthweight and postnatal development of IVF offspring. Our findings may have important ramifications for potential clinical markers of embryo quality and pregnancy initiation, and improve understanding of the mechanisms underlying the impact of the early environment on the long term health of ART offspring. Study funding/competing interest(s)This work was funded by the National Council for Science and Technology of Mexico (CONACyT), an NIHR pre-doctoral fellowship (PCAF) to MM, the NIHR Local Comprehensive Research Network and NIHR Manchester Clinical Research Facility, the University of Manchester and Manchester University NHS Foundation Trust. None of the authors has any conflict of interest to declare.