Hypermethylated CpG sites in the MTR gene promoter in preterm placenta

The one-carbon metabolism as an underlying pathway for placental DNA methylation - a systematic review

Epigenetic modifications, including DNA methylation, are proposed mechanisms explaining the impact of parental exposures to foetal development and lifelong health. Micronutrients including folate, choline, and vitamin B12 provide methyl groups for the one-carbon metabolism and subsequent DNA methylation processes. Placental DNA methylation changes in response to one-carbon moieties hold potential targets to improve obstetrical care. We conducted a systematic review on the associations between one-carbon metabolism and human placental DNA methylation. We included 22 studies. Findings from clinical studies with minimal ErasmusAGE quality score 5/10 (n = 15) and in vitro studies (n = 3) are summarized for different one-carbon moieties. Next, results are discussed per study approach: (1) global DNA methylation (n = 9), (2) genome-wide analyses (n = 4), and (3) gene specific (n = 14). Generally, one-carbon moieties were not associated with global methylation, although conflicting outcomes were reported specifically for choline. Using genome-wide approaches, few differentially methylated sites associated with S-adenosylmethionine (SAM), S-adenosylhomocysteine (SAH), or dietary patterns. Most studies taking a gene-specific approach indicated site-specific relationships depending on studied moiety and genomic region, specifically in genes involved in growth and development including LEP, NR3C1, CRH, and PlGF; however, overlap between studies was low. Therefore, we recommend to further investigate the impact of an optimized one-carbon metabolism on DNA methylation and lifelong health.

Emerging role of toll-like receptors signaling and its regulators in preterm birth: a narrative review

INTRODUCTION

Despite intensive research, preterm birth (PTB) rates have not decreased significantly in recent years due to a lack of understanding of the underlying causes and insufficient treatment options for PTB. We are committed to finding promising biomarkers for the treatment of PTB.

METHODS

An extensive search of the literature was conducted with MEDLINE/PubMed, and in total, 151 studies were included and summarized in the present review.

RESULTS

Substantial evidence supports that the infection and/or inflammatory cascade associated with infection is an early event in PTB. Toll-like receptor (TLR) is a prominent pattern recognition receptor (PRR) found on both immune and non-immune cells, including fetal membrane cells. The activation of TLR downstream molecules, followed by TLR binding to its ligand, is critical for infection and inflammation, leading to the involvement of the TLR signaling pathway in PTB. TLR ligands are derived from microbial components and molecules released by damaged and dead cells. Particularly, TLR4 is an essential TLR because of its ability to recognize lipopolysaccharide (LPS). In this comprehensive overview, we discuss the role of TLR signaling in PTB, focus on numerous host-derived genetic and epigenetic regulators of the TLR signaling pathway, and cover ongoing research and prospective therapeutic options for treating PTB by inhibiting TLR signaling.

CONCLUSION

This is a critical topic because TLR-related molecules and mechanisms may enable obstetricians to better understand the physiological changes in PTB and develop new treatment and prevention strategies.

Causes of preterm birth: Genetic factors in preterm birth and preterm infant phenotypes

AIM

The aim is to provide an overview of recent research on genetic factors that influence preterm birth in the context of neonatal phenotypic assessment.

METHODS

This is a nonsystematic review of the recent scientific literature.

RESULTS

Maternal and fetal genetic diversity and rare genome variants are linked with crucial immune response sites. In addition, more frequent in preterm neonates, de novo variants may lead to attention deficits, hyperactivity, autism spectrum disorders, and infertility of both sexes later in life. Environmental factors may also greatly burden fetal, and consequently, neonatal development and neurodevelopment through a failure in the fetal epigenome reprogramming process and even influence the initiation of spontaneous preterm pregnancy termination. Minimally invasive analysis of the transcription factors associated with preterm birth helps elucidate labor mechanisms and predict its timing. We also provide valuable summaries of genomic and transcriptomic factors that contribute to preterm birth.

CONCLUSIONS

Investigation of the human genome, epigenome, and transcriptome helps to identify molecular mechanisms linked with preterm delivery and premature newborn clinical appearance in early and late neonatal life and even predict developmental outcomes. Further studies are needed to fully understand the implications of genetic changes in preterm births. These data could be used to develop targeted interventions aimed at selecting the most effective individual treatment and rehabilitation plan.

METTL3-Mediated m6A RNA Methylation of ZBTB4 Interferes With Trophoblast Invasion and Maybe Involved in RSA

N⁶-methyladenosine (m⁶A) was the most abundant modification of mRNA and lncRNA in mammalian cells and played an important role in many biological processes. However, whether m⁶A modification was associated with recurrent spontaneous abortion (RSA) and its roles were still unclear.

Methods: Methylated RNA immunoprecipitation sequencing (MeRIP-Seq) was used to study the global m⁶A modification pattern in RSAs and controls. RNA sequencing (RNA-Seq) was used to study the level of global mRNA in two groups. Real-time quantitative PCR (RT-qPCR) was used to verify the level of mRNA of METTL3 and ZBTB4. MeRIP–qPCR was conducted to test the level of ZBTB4 m⁶A modification in two groups. In order to further explore whether ZBTB4 was the substrate of METTL3, the HTR-8/SVneo (HTR-8) cell line was selected for the knockdown and overexpression of METTL3. To study whether METTL3 regulated the ZBTB4 expression by recognizing ZBTB4 mRNA m⁶A motifs in coding sequences (CDS), dual-luciferase reporter assay was conducted. RNA stability assays using actinomycin D were conducted to study the RNA stability of the HTR-8 cell line with METTL3 overexpression and knockdown. To illustrate the role of METTL3 in the invasion of trophoblast, matrigel invasion assays and transwell migration assays were conducted using the HTR-8 cell line with METTL3 overexpression and knockdown.

Results: A total of 65 genes were found with significant differences both in m⁶A modification and mRNA expression. We found m⁶A methyltransferase METTL3 was significantly down-regulated in the RSA group. Through gene function analysis, RT-qPCR, MeRIP–qPCR validation experiment, knockdown, and overexpression of METTL3 in the HTR-8 cell line, ZBTB4 was selected as one target of METTL3. Furthermore, we clarified that METTL3 regulated the expression of ZBTB4 by recognizing ZBTB4 mRNA m⁶A motifs in the CDS using the dual-luciferase reporter assay and METTL3 regulated the invasion of trophoblast by altering the stability and expression of ZBTB4 by RNA stability, matrigel invasion, and transwell migration assays.

Conclusion: Our study revealed the mechanism by which METTL3 regulated the stability and expression of ZBTB4 and the trophoblast migration ability of RSA. A new perspective was provided for exploring the mechanism of embryonic development in RSA patients.

A narrative review on the role of folate-mediated one-carbon metabolism and its associated gene polymorphisms in posing risk to preeclampsia

Preeclampsia (PE) presents a major obstetrical problem for mother and fetus which is characterized by the onset of hypertension and proteinuria in formerly normotensive women. Altered folate-mediated one-carbon metabolism is one of the factors for PE development either due to nutritional insufficiencies such as folate deficiency or polymorphisms in genes that code for the key enzymes of the cycle. Commonly, there are four genes in the cycle whose polymorphisms have been described in relation to PE. These factors could cause elevation of homocysteine; the toxic metabolite, which subsequently leads to the development of PE. Sufficient levels of folate have been considered important during pregnancy and may reduce the risk of development of PE. This review aims at discussing genetic polymorphisms and nutritional deficiencies as probable predisposing factors and suggests considering fetal genotypes, varied ethnicities, and interaction of various other factors involved to render better conclusiveness to the present studies.

Correlation of methylation status in MTHFR promoter region with recurrent pregnancy loss

Background

DNA methylation is an epigenetic process for modifying transcription factors in various genes. Methylenetetrahydrofolate reductase (MTHFR) stimulates synthesis of methyl radical in the homocysteine cycle and delivers methyl groups needed in DNA methylation. Furthermore, numerous studies have linked gene polymorphisms of this enzyme with a larger risk of recurrent pregnancy loss (RPL), yet scarce information is available concerning the association between epigenetic deviations in this gene and RPL. Hypermethylation at precise DNA sequences can function as biomarkers for a diversity of diseases. We aimed by this study to evaluate the methylation status of the promoter region of MTHFR gene in women with RPL compared to healthy fertile women. It is a case–control study. Hundred RPL patients and hundred healthy fertile women with no history of RPL as controls were recruited. MTHFR C677T was assessed by polymerase chain reaction-restriction fragment length polymorphism (RFLP). Quantitative evaluation of DNA methylation was performed by high-resolution melt analysis by real-time PCR.

Results

The median of percentage of MTHFR promoter methylation in RPL cases was 6.45 [0.74–100] vs. controls was 4.50 [0.60–91.7], P value < 0.001. In the case group, 57 hypermethylated and 43 normo-methylated among RPL patients vs. 40 hypermethylated and 60 normo-methylated among controls, P< 0.005. Frequency of T allele in C677T MTHFR gene among RPL patients was 29% vs. 23% among the control group; C allele vs. T allele: odds ratio (OR) = 1.367 (95% confidence interval (CI) 0.725–2.581).

Conclusion

Findings suggested a significant association between hypermethylation of the MTHFR promoter region in RPL patients compared to healthy fertile women.

Epigenetic biomarkers and preterm birth

Preterm birth (PTB) is a major public health challenge, and novel, sensitive approaches to predict PTB are still evolving. Epigenomic markers are being explored as biomarkers of PTB because of their molecular stability compared to gene expression. This approach is also relatively new compared to gene-based diagnostics, which relies on mutations or single nucleotide polymorphisms. The fundamental principle of epigenome diagnostics is that epigenetic reprogramming in the target tissue (e.g. placental tissue) might be captured by more accessible surrogate tissue (e.g. blood) using biochemical epigenome assays on circulating DNA that incorporate methylation, histone modifications, nucleosome positioning, and/or chromatin accessibility. Epigenomic-based biomarkers may hold great potential for early identification of the majority of PTBs that are not associated with genetic variants or mutations. In this review, we discuss recent advances made in the development of epigenome assays focusing on its potential exploration for association and prediction of PTB. We also summarize population-level cohort studies conducted in the USA and globally that provide opportunities for genetic and epigenetic marker development for PTB. In addition, we summarize publicly available epigenome resources and published PTB studies. We particularly focus on ongoing genome-wide DNA methylation and epigenome-wide association studies. Finally, we review the limitations of current research, the importance of establishing a comprehensive biobank, and possible directions for future studies in identifying effective epigenome biomarkers to enhance health outcomes for pregnant women at risk of PTB and their infants.

Maternal vitamin D deficiency increases the thromboxane/prostacyclin ratio through alterations in the one-carbon cycle in Wistar rats

This study aims to test the hypothesis that vitamin D deficiency can influence long-chain polyunsaturated fatty acid metabolism through alterations in the one-carbon cycle. Wistar rats (n = 8 per group) were given either a control (1,000 IU D3/kg diet) or a vitamin D deficient (VDD) (0 IU D3/kg diet) diet from pre-pregnancy to delivery. On day 20 of gestation, pregnant female rats were delivered by C-section to collect placenta and blood. VDD group demonstrated high serum parathyroid hormone, low serum phosphate, low plasma folate, higher plasma homocysteine, and higher plasma malondialdehyde levels (P < 0.05 for all) as compared to control. Lower protein levels of placental cystathionine-β-synthase enzyme (P < 0.05) were observed in the VDD group as compared to control. VDD group demonstrated higher placental mRNA levels of the enzymes phospholipase A₂ and cyclooxygenase-2 (P < 0.05 for both) as compared to control. Protein levels of the enzymes phospholipase A₂ and cyclooxygenase-2 were lower (P < 0.05 for both) in the VDD group as compared to the control group. The ratio of thromboxane B₂ and 6-keto prostaglandin F_1α in serum was higher (P < 0.05) in the VDD group as compared to control; although the serum levels of 6-keto prostaglandin F_1α and thromboxane B₂ were similar in both the groups. Our findings suggest that increased oxidative stress due to maternal vitamin D deficiency results in the imbalance between the vasoconstrictor (thromboxane B₂ ) and vasodilator (6-keto prostaglandin F_1α ) eicosanoids, which may lead to endothelial dysfunction and poor pregnancy outcome. © 2019 BioFactors, 45 (4):548-555, 2019.

Recurrent pregnancy losses vis-à-vis anemia and vitamin (Folate/B12) imbalance

Purpose

Recurrent pregnancy losses (RPL), a major contributor of reproductive wastage, affect maternal health both physically and mentally. Folate and B12 (Vitamin B12) deficiency anemia is common in the reproductive age group women in developing countries like India. And due to proven role of folate in various maternal and fetal anomalies, women are routinely prescribed folic acid under various national policies. However, B12 supplementation is rare, despite known deleterious effects of its deficiency. The purpose of this paper is to understand RPL through anemia with special reference to folate and B12 imbalance.

Design/methodology/approach

Multiparous women with normal obstetric outcomes (n=135) and women with Idiopathic RPL (n=105) were recruited in the study. All women were non-pregnant and belonged to North Indian population. Hb, serum folate and B12 and plasma homocysteine were measured in all the women. Anemia was classified according to WHO guidelines (Hemoglobin (Hb)<12g/dL).

Findings

The incidence of Anemia was more among normal multiparous women (73 percent) as compared to women with RPL (60 percent). However, unlike folate deficiency anemia among controls, B12 deficiency anemia was observed in women with RPL. Moreover, these women, despite being less anemic, with high B12 deficiency and folate sufficiency (presumably due to folate supplementation) had more imbalanced vitamin metabolism, as evident from homocysteine levels. The study suggests that anemic or non-anemic deficiencies of B12 and folate among women with RPL may be combated by screening for both vitamins, rather than supplementing folate indiscriminately to all.

Research limitations/implications

One of the limitations is that ferritin levels for iron deficiency anemia could not be measured in this study.

Originality/value

The present study is the first study, to the best of our knowledge, where we looked for the role of imbalance of folate and B12 in women with RPL.