Dynamic changes of histone acetylation and methylation in bovine oocytes, zygotes, and preimplantation embryos

Preconception Diet Interventions in Obese Outbred Mice and the Impact on Female Offspring Metabolic Health and Oocyte Quality

Obese individuals often suffer from metabolic health disorders and reduced oocyte quality. Preconception diet interventions in obese outbred mice restore metabolic health and oocyte quality and mitochondrial ultrastructure. Also, studies in inbred mice have shown that maternal obesity induces metabolic alterations and reduces oocyte quality in offspring (F1). Until now, the effect of maternal high-fat diet on F1 metabolic health and oocyte quality and the potential beneficial effects of preconception dietary interventions have not been studied together in outbred mice. Therefore, we fed female mice a high-fat/high-sugar (HF/HS) diet for 7 weeks and switched them to a control (CONT) or caloric-restriction (CR) diet or maintained them on the HF/HS diet for 4 weeks before mating, resulting in three treatment groups: diet normalization (DN), CR, and HF/HS. In the fourth group, mice were fed CONT diet for 11 weeks (CONT). HF/HS mice were fed an HF/HS diet from conception until weaning, while all other groups were then fed a CONT diet. After weaning, offspring were kept on chow diet and sacrificed at 11 weeks. We observed significantly elevated serum insulin concentrations in female HF/HS offspring and a slightly increased percentage of mitochondrial ultrastructural abnormalities, mitochondrial size, and mitochondrial mean gray intensity in HF/HS F1 oocytes. Also, global DNA methylation was increased and cellular stress-related proteins were downregulated in HF/HS F1 oocytes. Mostly, these alterations were prevented in the DN group, while, in CR, this was only the case for a few parameters. In conclusion, this research has demonstrated for the first time that a maternal high-fat diet in outbred mice has a moderate impact on female F1 metabolic health and oocyte quality and that preconception DN is a better strategy to alleviate this compared to CR.

Effect of lipotoxicity on mitochondrial function and epigenetic programming during bovine in vitro embryo production

Maternal metabolic disorders may cause lipotoxic effects on the developing oocyte. Understanding the timing at which this might disrupt embryo epigenetic programming and how this is linked with mitochondrial dysfunction is crucial for improving assisted reproductive treatments, but has not been investigated before. Therefore, we used a bovine in vitro model to investigate if pathophysiological palmitic acid (PA) concentrations during in vitro oocyte maturation and in vitro embryo culture alter embryo epigenetic patterns (DNA methylation (5mC) and histone acetylation/methylation (H3K9ac/H3K9me2)) compared to control (CONT) and solvent control (SCONT), at the zygote and morula stage. Secondly, we investigated if these epigenetic alterations are associated with mitochondrial dysfunction and changes in ATP production rate, or altered expression of epigenetic regulatory genes. Compared to SCONT, H3K9ac and H3K9me2 levels were increased in PA-derived zygotes. Also, 5mC and H3K9me2 levels were increased in PA-exposed morulae compared to SCONT. This was associated with complete inhibition of glycolytic ATP production in oocytes, increased mitochondrial membrane potential and complete inhibition of glycolytic ATP production in 4-cell embryos and reduced SOD2 expression in PA-exposed zygotes and morulae. For the first time, epigenetic alterations in metabolically compromised zygotes and morulae have been observed in parallel with mitochondrial dysfunction in the same study.

Micro-vibration results in vitro-derived bovine blastocysts with greater cryotolerance, epigenetic abnormalities, and a massive transcriptional change

Much effort has been employed to improve the quality of embryos obtained by in vitro production (IVP) given the relevance of this technology to current livestock systems. In this context, dynamic IVP systems have proved beneficial to the embryo once they mimic fluid flows and mechanical forces resulting from the movement of ciliated cells and muscle contraction in the reproductive tract. In the present study, we sought to confirm these initial findings as well as assess potential molecular consequences to the embryo by applying micro-vibration (45 Hz for 5 s once per 60 min) during both oocyte maturation and embryo culture in cattle. As a result, micro-vibration led to lower incidence of apoptosis in blastocysts following vitrification-thawing. Further analyses revealed epigenetic and transcriptional changes in blastocysts derived from the micro-vibration treatment, with a total of 502 differentially expressed genes. Enrichment analyses linked differentially expressed genes to 'Oxidative phosphorylation', 'Cytokine-cytokine receptor interaction', and 'Signaling pathways regulating pluripotency of stem cells'. Yet, a meta-analysis indicated that the transcriptional changes induced by micro-vibration were not toward that of in vivo-derived embryos. In conclusion, micro-vibration increases the cryoresistance of bovine embryos, but caution should be taken given the unclear consequences of epigenetic and transcriptional abnormalities induced by the treatment.

Metabolism-epigenetic interactions on in vitro produced embryos

Metabolism and epigenetics, which reciprocally regulate each other in different cell types, are fundamental aspects of cellular adaptation to the environment. Evidence in cancer and stem cells has shown that the metabolic status modifies the epigenome while epigenetic mechanisms regulate the expression of genes involved in metabolic processes, thereby altering the metabolome. This crosstalk occurs as many metabolites serve as substrates or cofactors of chromatin-modifying enzymes. If we consider the intense metabolic dynamic and the epigenetic remodelling of the embryo, the comprehension of these regulatory networks will be important not only for understanding early embryonic development, but also to determine in vitro culture conditions that support embryo development and may insert positive regulatory marks that may persist until adult life. In this review, we focus on how metabolism may affect epigenetic reprogramming of the early stages of development, in particular acetylation and methylation of histone and DNA. We also present other metabolic modifications in bovine embryos, such as lactylation, highlighting the promising epigenetic and metabolic targets to improve conditions for in vitro embryo development.

New Wenshen Shengjing Decoction Improves Early Embryonic Development by Maintaining Low Levels of H3K4me3 in Sperm

Background

New Wenshen Shengjing Decoction (NWSSJD), a traditional Chinese compound medicine, has significant effect on spermatogenesis disorder and can significantly improve sperm quality. Many components in NWSSJD can induce epigenetic modifications of different types of cells. It is not yet known whether they can cause epigenetic modifications in sperm or early embryos.

Objective

This study investigated the effect of NWSSJD on mouse early embryonic development and its regulation of H3K4me3 in mouse sperm and early embryos.

Methods

Spermatogenesis disorder was induced in male mice with CPA (cyclophosphamide). NWSSJD was administrated for 30 days. Then, the male mice were mated with the female mice with superovulation, and the embryo degeneration rate of each stage was calculated. Immunofluorescence staining was used to detect the expression of H3K4me3 in sperm and embryos at various stages. Western blotting was performed to detect methyltransferase SETD1B expression. The expressions of development-related genes (OCT-4, NANOG, and CDX2) and apoptosis-related genes (BCL-2 and p53) were measured with qRT-PCR.

Results

Compared with the CPA group, NWSSJD significantly reduced the H3K4me3 level in sperms, significantly increased the number of normal early embryos (2-cell embryos, 3-4-cell embryos, 8-16-cell embryos, and blastocysts) per mouse, and reduced the degeneration rate of the embryos. The expression levels of H3K4me3 and methyltransferase SETD1B in early embryos were significantly elevated by NWSSJD. Additionally, NWSSJD significantly promoted BCL-2 expression, while reducing p53 expression, thus inhibiting embryonic cell apoptosis. Moreover, the expressions of development-related genes OCT-4 and CDX2 were significantly increased by NWSSJD, but NANOG expression had no significant difference.

Conclusion

NWSSJD may promote early embryonic development possibly by maintaining low H3K4me3 levels in sperms and normal H3K4me3 modification in early embryos and by inhibiting embryonic cell apoptosis.

Cumulus Cell DNA Damage as an Index of Human Oocyte Competence

The determination of oocyte quality is crucial for achieving effective syngamy post-sperm injection and embryonic development. Cumulus cells (CCs) have been proposed as biomarkers of oocyte quality because of their close bio-dynamic relationship with the oocyte. To determine the quality of the oocyte, CCs were sampled during oocyte preparation for ICSI to determine a CC DNA fragmentation index (CCDFI) of each individual oocyte using a variant of the chromatin dispersion test. One hundred and thirty oocytes were selected and studied from two Spanish fertility clinics, 90 of which were fertilized and developed to embryos. Significant differences were found between the CCDFI of unfertilized and fertilized oocytes (p < .001) and between the CCDFI of embryos that were discarded and those that developed suitable for transfer or cryopreservation (p < .001). Oocyte quality was negatively correlated with CCDFI (Spearman’s rho =  − 0.45; p < .001). Receiver operator characteristics curves (ROC) suggested that a cut-off value of 24% CCDFI was able to discriminate the capacity of the gametes to result in syngamy with a sensitivity and specificity of 75.6% and 65%, respectively. This cut-off supports the application of CCDFI as potential index for the evaluation of the reproductive potential of oocytes prior to fertilization.

Dynamic changes of histone methylation in mammalian oocytes and early embryos

Histone methylation is a key epigenetic mechanism and plays a major role in regulating gene expression during oocyte maturation and early embryogenesis. This mechanism can be briefly defined as the process by which methyl groups are transferred to lysine and arginine residues of histone tails extending from nucleosomes. While methylation of the lysine residues is catalyzed by histone lysine methyltransferases (KMTs), protein arginine methyltransferases (PRMTs) add methyl groups to the arginine residues. When necessary, the added methyl groups can be reversibly removed by histone demethylases (HDMs) by a process called histone demethylation. The spatiotemporal regulation of methylation and demethylation in histones contributes to modulating the expression of genes required for proper oocyte maturation and early embryonic development. In this review, we comprehensively evaluate and discuss the functional importance of dynamic histone methylation in mammalian oocytes and early embryos, regulated by KMTs, PRMTs, and HDMs.