Embryo vitrification disturbs the pre-implantation DNA demethylation process and affects hepatic functions to threaten long-term metabolic health in mice.

INTRODUCTION

Embryo vitrification has been linked to an increased incidence of large-for-gestational-age offspring. Investigating how epigenetic regulation transmits vitrification-induced abnormalities to postnatal stages could provide valuable insights for the control and prevention of metabolic disorders in offspring derived from vitrified-thawed embryos, yet the underlying mechanisms remain poorly understood.

OBJECTIVES

This study aimed to investigate vitrification-induced aberrations in gene expression and DNA methylation remodeling during pre-implantation stages, and to explore how these abnormalities affect the postnatal metabolic health of the offspring.

METHODS

8-cell mouse embryos were vitrified and thawed, and transcriptome profiling was conducted using SMART-seq2 with 16-cell embryos, morulae and blastocysts. DNA methylome profiling of blastocysts using low-input bisulfite sequencing (LI-BS) was then performed. After embryo transfer, glucose tolerance tests (GTT) and insulin tolerance tests (ITT) were conducted on the offspring, and blood metabolite levels were measured by ELISA. Histological analyses, RNA-seq, and whole-genome bisulfite sequencing (WGBS) were then performed on hepatic tissues of the offspring.

RESULTS

Here, we found delayed progression of vitrified-thawed embryos, with downregulated expression of Tet2. Consistently, we observed genome-wide DNA hypermethylation, with the hypermethylated genes being enriched in metabolic processes. Our data further demonstrated that offsprings from vitrified-thawed embryos exhibited metabolic disturbances including insulin resistance, lipid deposition and mitochondrial dysfunction. Interestingly, genes associated with arachidonic acid metabolism remained dysregulated in the hepatic tissues of these offspring, although DNA methylation had been restored to the normal level in these terminally differentiated tissues.

CONCLUSIONS

Overall, our study uncovers the negative impact of vitrification on DNA methylation remodeling during early embryo development, which may partially account for the elevated susceptibility to metabolic diseases in offspring. Our findings also suggest that the Tet2 gene is a potential therapeutic target for improving the developmental competence of vitrified-thawed embryos.