The effect of folic acid deficiency on Mest/Peg1 in neural tube defects

Epigenetic regulation by TET1 in gene-environmental interactions influencing susceptibility to congenital malformations

The etiology of neural tube defects (NTDs) involves complex gene-environmental interactions. Folic acid (FA) prevents NTDs, but the mechanisms remain poorly understood and at least 30% of human NTDs resist the beneficial effects of FA supplementation. Here, we identify the DNA demethylase TET1 as a nexus of folate-dependent one-carbon metabolism and genetic risk factors post-neural tube closure. We determine that cranial NTDs in Tet1 -/- embryos occur at two to three times higher penetrance in genetically heterogeneous than in homogeneous genetic backgrounds, suggesting a strong impact of genetic modifiers on phenotypic expression. Quantitative trait locus mapping identified a strong NTD risk locus in the 129S6 strain, which harbors missense and modifier variants at genes implicated in intracellular endocytic trafficking and developmental signaling. NTDs across Tet1 -/- strains are resistant to FA supplementation. However, both excess and depleted maternal FA diets modify the impact of Tet1 loss on offspring DNA methylation primarily at neurodevelopmental loci. FA deficiency reveals susceptibility to NTD and other structural brain defects due to haploinsufficiency of Tet1. In contrast, excess FA in Tet1 -/- embryos drives promoter DNA hypermethylation and reduced expression of multiple membrane solute transporters, including a FA transporter, accompanied by loss of phospholipid metabolites. Overall, our study unravels interactions between modified maternal FA status, Tet1 gene dosage and genetic backgrounds that impact neurotransmitter functions, cellular methylation and individual susceptibilities to congenital malformations, further implicating that epigenetic dysregulation may underlie NTDs resistant to FA supplementation.

Perspectives on folate with special reference to epigenetics and neural tube defects

Folate is a micronutrient essential for DNA synthesis, cell division, fetal growth and development. Folate deficiency leads to genomic instability. Inadequate intake of folate during conception may lead to neural tube defects (NTDs) in the offspring. Folate influences the DNA methylation, histone methylation and homocysteine mediated gene methylation. DNA methylation influences the expression of microRNAs (miRNAs). Folate deficiency may be associated with miRNAs misregulation leading to NTDs. Mitochondrial epigenetics and folate metabolism has proved to be involved in embryogenesis and neural tube development. Folate related genetic variants also cause the occurrence of NTDs. Unmetabolized excessive folate may affect health adversely. Hence estimation of folate levels in the blood plays an important role in high-risk cases.

Implementing micronutrient fortification programs as a potential practical contribution to achieving sustainable diets

Due to sustainability concerns related to current diets and environmental challenges, it is crucial to have sound policies to protect human and planetary health. It is proposed that sustainable diets will improve public health and food security and decrease the food system's effect on the environment. Micronutrient deficiencies are a well-known major public health concern. One-third to half of the world's population suffers from nutrient deficiencies, which have a negative impact on society in terms of unrealised potential and lost economic productivity. Large-scale fortification with different micronutrients has been found to be a useful strategy to improve public health. As a cost-effective strategy to improve micronutrient deficiency, this review explores the role of micronutrient fortification programmes in ensuring the nutritional quality (and affordability) of diets that are adjusted to help ensure environmental sustainability in the face of climate change, for example by replacing some animal-sourced foods with nutrient-dense, plant-sourced foods fortified with the micronutrients commonly supplied by animal-sourced foods. Additionally, micronutrient fortification considers food preferences based on the dimensions of a culturally sustainable diet. Thus, we conclude that investing in micronutrient fortification could play a significant role in preventing and controlling micronutrient deficiencies, improving diets and being environmentally, culturally and economically sustainable.

High dietary folate and low vitamin B12 in the parental diet disturbed the epigenetics of imprinted genes MEST and PHLDA2 in mice placenta

To elucidate the dietary effects of vitamin B12 and folic acid on fetal and placental epigenetics, different dietary combinations of folic acid and low vitamin B12 (four groups) were fed to the animals (C57BL/6 mice), and mating was carried out within each group in the F0 generation. After weaning for 3 weeks in the F1 generation one group of mice was continued on the same diet (sustained group) while the other was shifted to a normal diet (transient group) for 6-8 weeks (F1). Mating was carried out again within each group, and on day 20 of gestation, the maternal placenta (F1) and fetal tissues (F2) were isolated. Expression of imprinted genes and various epigenetic mechanisms, including global and gene-specific DNA methylation and post-translational histone modifications, were studied. Evaluation of mRNA levels of MEST and PHLDA2 in placental tissue revealed that their expression is maximally influenced by vitamin B12 deficiency and high folate conditions. The gene expression of MEST and PHLDA2 was found significantly decreased in the F0 generation, with the over-expression of the genes in BDFO dietary groups. These dietary combinations also resulted in DNA methylation changes in both generations, which may not play a role in gene expression regulation. However, altered histone modifications were found to be the major regulatory factor in controlling the expression of genes in the F1 generation. The imbalance of low vitamin B12 and high folate leads to increased levels of activating histone marks, contributing to increased gene expression.

Effect of epigenetic activating of Dlk1-Dio3 imprinted cluster on miR-370 expression due to folate deficiency during nerve development

Proper Dlk1-Dio3 imprinting plays a critical role in embryogenesis, and folic acid deficiency may affect the imprinting of this locus through epigenetic regulation. However, whether and how folic acid directly impacts the imprinting status of Dlk1-Dio3 to affect neural development remain unclear. Here, we found decreased IG-DMR (intergenic -differentially methylated regions) methylation in the folate-deficient encephalocele in humans, suggesting that abnormal Dlk1-Dio3 imprinting status is related to neural tube defects (NTDs) caused by folate deficiency. Similar results were obtained with folate-deficient embryonic stem cells. By miRNA chip analysis, folic acid deficiency led to changes in multiple miRNAs, including the upregulation of 15 miRNAs located in the Dlk1-Dio3 locus. Real-time PCR confirmed that seven of these miRNAs were upregulated, especially miR-370. In contrast to normal embryonic development, in which expression of miR-370 is highest at E9.5, the abnormally high and sustained expression of miRNA-370 in folate-deficient E13.5 embryos may contribute to NTDs. In addition, we found that DNMT3A (de novo DNA methyltransferases 3A) is a direct target gene of miR-370 in neural cells, and DNMT3A participates in the role of miR-370 in inhibiting cell migration. Finally, in the folate-deficient mouse model, Dlk1-Dio3 epigenetic activation was found in fetal brain tissue, along with the upregulation of miR-370 and the downregulation of DNMT3A. Collectively, our findings demonstrate a pivotal role of folate in the epigenetic regulation of Dlk1-Dio3 imprinting during neurogenesis, revealing an elegant mechanism for the activation of Dlk1-Dio3 locus miRNAs in folic acid deficiency.

Folate deficiency disturbs PEG10 methylation modifications in human spina bifida

BACKGROUND

Paternally expressed gene 10 (PEG10) is believed to be a key imprinted gene involved in placenta formation. However, its role in human folate-related spina bifida (SB) remains unclear.

METHODS

The methylation status of the germline differentially methylated region (gDMR) in the PEG10/sarcoglycan epsilon (SGCE) imprinted cluster was compared between SB patients and control samples. Moreover, the influence of ectopic PEG10 expression on apoptosis was assessed to explore the underlying mechanisms related to folate deficiency-induced aberrant gDMR methylation in SB.

RESULTS

The case group exhibited a significant increase in the methylation level of the gDMR and a marked reduction in the mRNA and protein expression of PEG10 compared with the control group. A prominent negative correlation was found between the folate level in brain tissue and gDMR methylation status (r = -0.62, P = 0.001). A cell model treated with a demethylating agent showed a significant elevation of PEG10 transcription level, as well as other imprinted genes in this cluster. In addition, the inhibition of PEG10 was found to be accompanied by aberrant activation of apoptosis in SB.

CONCLUSIONS

Our findings suggest that disturbed gDMR methylation of the PEG10/SGCE cluster due to folate deficiency is involved in SB through aberrant activation of apoptosis.

IMPACT

Disturbed genomic imprinting has been verified to be involved in neural tube defects (NTDs). However, little is known about the effect of ectopic expression of imprinted gene PEG10 on human NTDs. Aberrant methylation status of the germline differentially methylated region (gDMR) of PEG10/SGCE cluster due to folate deficiency has been found to result in the inhibition of PEG10 and has a marked association with an increased occurrence of spina bifida. Inhibited expression of PEG10 partly is found to be related to the abnormal activation of apoptosis in spina bifida.