Oxygen-induced alterations in the expression of chromatin modifying enzymes and the transcriptional regulation of imprinted genes

Abstract

Embryo culture and assisted reproductive technologies have been associated with a disproportionately high number of epigenetic abnormalities in the resulting offspring. However, the mechanisms by which these techniques influence the epigenome remain poorly defined. In this study, we evaluated the capacity of oxygen concentration to influence the transcriptional control of a selection of key enzymes regulating chromatin structure. In mouse embryonic stem cells, oxygen concentrations modulated the transcriptional regulation of the TET family of enzymes, as well as the de novo methyltransferase Dnmt3a. These transcriptional changes were associated with alterations in the control of multiple imprinted genes, including H19, Igf2, Igf2r, and Peg3. Similarly, exposure of in vitro produced bovine embryos to atmospheric oxygen concentrations was associated with disruptions in the transcriptional regulation of TET1, TET3, and DNMT3a, along with the DNA methyltransferase co-factor HELLS. In addition, exposure to high oxygen was associated with alterations in the abundance of transcripts encoding members of the Polycomb repressor complex (EED and EZH2), the histone methyltransferase SETDB1 and multiple histone demethylases (KDM1A, KDM4B, and KDM4C). These disruptions were accompanied by a reduction in embryo viability and suppression of the pluripotency genes NANOG and SOX2. These experiments demonstrate that oxygen has the capacity to modulate the transcriptional control of chromatin modifying genes involved in the establishment and maintenance of both pluripotency and genomic imprinting.

Changes in DNA methylation and imprinting disorders in E9.5 mouse fetuses and placentas derived from vitrified eight‐cell embryos

“…Thus, these results could partly explain the increased global methylation level observed in fetuses of the VET group. The TET family of genes is thought to play a role in active genomic demethylation and the resetting of the epigenome (Inoue & Zhang, ; Seiler et al, ; Skiles et al, ). According to our results, TET2 and TET3 were increased in fetuses of the IVC group compared with two other groups, which revealed the reason for the decreased global methylation level of the IVC group.…”

A positive feedback loop between EZH2 and NOX4 regulates nucleus pulposus cell senescence in age-related intervertebral disc degeneration

“…At the later stage of EZH2 downregulation, H3K27me3 is demethylated, which upregulates p16 and SASP-related genes [15][16][17]. Moreover, EZH2 has been shown to be associated with intracellular oxidative stress [18,19]. These results suggest that EZH2 plays potential roles in cell senescence induced by oxidative stress.…”

Embryo Culture Conditions and the Epigenome

“…Embryo culture at 5% O 2 , mimicking the hypoxic environment within the female reproductive tract, is believed to improve embryo development. 40,[81][82][83] Recently identified links between oxygen levels and transcriptional control of epigenetic regulators support data demonstrating a role of oxygen tension on imprint establishment [84][85][86] (►Table 3). In a study by de Waal et al, our collaborators found significant differences in placental DNA methylation at imprinted loci based on oxygen tension during embryo culture.…”

“…Epigenetic differences due to oxygen tension have also been documented in mouse embryonic stem cells, where differences in expression of imprinted genes H19, Igf2, Igf2r, and Peg3 were all noted after incubation at atmospheric oxygen compared with 5% O 2 . 84 Whole-genome effects of oxygen tension have also been examined in bovine embryos. Using a 5-methylcytosine antibody, Li et al found that culture of embryos at 20% O 2 resulted in global hypermethylation, though no changes in gene expression were examined.…”

“…88 Culture of bovine embryos at high oxygen (20% O 2 ) has also been found to alter gene expression of genes involved in DNA methylation as well as histone modifications. 84 For over a decade, our group has studied epigenetic changes in placenta and cord blood from infants conceived by IVF compared with those conceived by natural conception. In an attempt to identify specific modifiable factors responsible for the epigenetic perturbations seen with ART, we performed an analysis on human placental tissue and assessed global DNA methylation levels at repeated sequences (LINE1 elements) in the placenta of patients who conceived by natural conception compared with those who conceived by IVF.…”