The many manipulations and processes used in ART coincide with the timing of epigenetic reprogramming and imprinting during female gametogenesis and pre-implantation embryo development, leading to concerns that the actual ART could negatively affect epigenetic reprogramming and imprinting in gametes and early embryos. A growing body of literature suggests that ART may affect epigenetic marks, such as DNA methylation, in the fetus and placenta. Potentially, this may be responsible later in life for the increased risk of adverse outcomes associated with ART. Unfortunately, the conclusions are inconsistent and, despite the increasing usage of ART, its safety at the epigenetic level is still not established. To examine whether ART is associated with DNA methylation modifications and if these modifications persist throughout life, we provide an update on the current understanding of epigenetic reprogramming in human gametes and embryos, and then focus on the assessment of fetal and postnatal DNA methylation modifications that may remain until adulthood following the use of ART in humans. We reviewed studies using targeted or epigenome-wide techniques to assess the DNA methylation patterns of the conceptus after ART compared with natural conceptions. A search for relevant studies was performed in the PubMed and EMBASE databases on 15 July 2021 with an extensive search equation. Studies on animals, gametes and embryos were subsequently excluded. After an in-depth review of full-text articles, studies on specific populations with imprinting disorders were removed and not further discussed. Before comprehensive analysis, the risk of bias of each included study was assessed with the Newcastle–Ottawa scale and quality of evidence was graded using the Grading of Recommendations, Assessment, Development and Evaluations criteria. In total, 928 records were initially identified, and 51 were finally included in the systematic review. Given the variability in the genomic scale at which DNA methylation was measured in the different studies, they were separated into two categories: targeted DNA methylation or genome-wide DNA methylation study. The present systematic review has made it possible to assess a substantial number of children since more than 4000 DNA methylation profiles of ART concepti were compared to more than 7000 controls. There is evidence that ART conception is associated with aberrant DNA methylation in imprinted loci and other genes in various tissues. One isolated modification notably occur in the paternally expressed gene 1/mesoderm-specific transcript homologue (PEG1/MEST) region, and we cannot rule out other studied sequences owing to the heterogeneity of the evidence base. Differences in DNA methylation after ART conceptions are modest, and the functional relevance in adult tissues is unknown. Functional effects in terms of gene expression as well as the roles of other epigenetic marks need to be further explored. Moreover, there is little overlap of findings obtained in targeted and genome-scale analyses owing to the lack of comparability of CpGs analyzed between both techniques. This issue also stems from small sample sizes and marked differences in methodology and cohort characteristics. Standardization of methodologies and large collaborative efforts are required to reduce the inconsistency of results and increase the robustness of findings. Finally, further studies are required to determine the contribution of parental infertility per se from the ART treatment.

Endometriosis appears to have a multilayered etiology, with genetic and epigenetic factors each contributing half of the pathogenesis. The molecular processes that underlie the onset of endometriosis are yet unclear, but it is assumed that an important contributor in the etiopathology of the disease is DNA methylation. We conducted a systematic review of the literature regarding DNA methylation in endometriosis following PRISMA guidelines. Records were obtained from PubMed and Web of Science on May 31, 2024. Original research articles analyzing regional or genome-wide DNA methylation in patients with confirmed endometriosis (by surgery and/or histological examination) were given consideration for inclusion. Only human studies were included, and there were no restrictions on the types of tissue that was analyzed (i.e., endometrium, blood, or fetal tissue). The study selection process was run by two manual reviewers. In parallel, an adapted virtual artificial intelligence-powered reviewer operated study selection and results were compared with the manual reviewers’ selection. Studies were divided into targeted (e.g., single gene or region level) and epigenome-wide association studies. For each, we extracted a list of genes studied with precise location of CpGs analyzed and the DNA methylation status according to the groups compared. Quality assessment of studies was performed following the Newcastle–Ottawa scale. Quality of evidence was graded following the Grading of Recommendations Assessment, Development and Evaluation. A total of 955 studies were screened, and 70 were identified as relevant for systematic review. Our analyses displayed that endometriosis could be polyepigenetic and with alterations in specific genes implicated in major signaling pathways contributing to the disease etiopathology (cell proliferation, differentiation, and division [PI3K-Akt and Wnt-signaling pathway], cell division [MAPK pathway], cell adhesion, cell communication, developmental processes, response to hormone, apoptosis, immunity, neurogenesis, and cancer). Our systematic review indicates that endometriosis is associated with DNA methylation modifications at specific genes involved in key endometrial biological processes, particularly in the ectopic endometrium. As DNA methylation appears to be an integral component of the pathogenesis of endometriosis, the identification of DNA methylation biomarkers would likely help better understand its causes and aggravating factors as well as potentially facilitate its diagnosis and support the development of new therapeutic approaches. DNA methylation modifications are observed in both eutopic and ectopic endometrium in endometriosis compared to the healthy endometrium, and their localization may influence important biological pathways of the female reproductive system. DMP: Differentially methylated position. DMR: Differentially methylated region.

The oocyte transcriptome follows a tightly controlled dynamic that leads the oocyte to grow and mature. This succession of distinct transcriptional states determines embryonic development prior to embryonic genome activation. However, these oocyte maternal mRNA regulatory events have yet to be decoded in humans. We reanalyzed human single-oocyte RNA-seq datasets previously published in the literature to decrypt the transcriptomic reshuffles ensuring that the oocyte is fully competent. We applied trajectory analysis (pseudotime) and a meta-analysis and uncovered the fundamental transcriptomic requirements of the oocyte at any moment of oogenesis until reaching the metaphase II stage (MII). We identified a bunch of genes showing significant variation in expression from primordial-to-antral follicle oocyte development and characterized their temporal regulation and their biological relevance. We also revealed the selective regulation of specific transcripts during the germinal vesicle-to-MII transition. Transcripts associated with energy production and mitochondrial functions were extensively downregulated, while those associated with cytoplasmic translation, histone modification, meiotic processes, and RNA processes were conserved. From the genes identified in this study, some appeared as sensitive to environmental factors such as maternal age, polycystic ovary syndrome, cryoconservation, and in vitro maturation. In the future, the atlas of transcriptomic changes described in this study will enable more precise identification of the transcripts responsible for follicular growth and oocyte maturation failures.

Early life periconceptional exposures during assisted reproductive technology (ART) procedures could alter the DNA methylation profiles of ART children, notably in imprinted genes and repetitive elements. At the genome scale, DNA methylation differences have been reported in ART conceptions at birth, but it is still unclear if those differences remain at childhood. Here, we performed an epigenome-wide DNA methylation association study using Illumina InfiniumEPIC BeadChip to assess the effects of the mode of conception on the methylome of buccal cells from 7- to 8-year-old children (48 children conceived after ART or naturally (control, CTL)) and according to the embryo culture medium in which they were conceived. We identified 127 differentially methylated positions (DMPs) and 16 differentially methylated regions (DMRs) (FDR < 0.05) with low delta beta differences between the two groups (ART vs. CTL). DMPs were preferentially located inside promoter proximal regions and CpG islands and were mostly hypermethylated with ART. We highlighted that the use of distinct embryo culture medium was not associated with DNA methylation differences in childhood. Overall, we bring additional evidence that children conceived via ART display limited genome-wide DNA methylation variation compared with those conceived naturally.

We read the study by Cannarella et al.