Vitamins, folic acid and the cause and prevention of neural tube defects

The loop-tail mouse model displays open and closed caudal neural tube defects

Neural tube defects (NTDs) are the second most common cause of congenital malformations and are often studied in animal models. Loop-tail (Lp) mice carry a mutation in the Vangl2 gene, a member of the Wnt-planar cell polarity pathway. In Vangl2+/Lp embryos, the mutation induces a failure in the completion of caudal neural tube closure, but only a small percentage of embryos develop open spina bifida. Here, we show that the majority of Vangl2+/Lp embryos developed caudal closed NTDs and presented cellular aggregates that may facilitate the sealing of these defects. The cellular aggregates expressed neural crest cell markers and, using these as a readout, we describe a systematic method to assess the severity of the neural tube dorsal fusion failure. We observed that this defect worsened in combination with other NTD mutants, Daam1 and Grhl3. Besides, we found that in Vangl2+/Lp embryos, these NTDs were resistant to maternal folic acid and inositol supplementation. Loop-tail mice provide a useful model for research on the molecular interactions involved in the development of open and closed NTDs and for the design of prevention strategies for these diseases.

Integrated Bioinformatics Analysis Reveals Potential Pathway Biomarkers and Their Interactions for Clubfoot

Background

Congenital talipes equinovarus (clubfoot), one of the most regular pediatric congenital skeletal anomalies, seriously affects the normal growth and development of about 1 in 1000 newborns. Although it has been investigated widely, the etiology and pathogenesis of clubfoot are still controversial.

Material/Methods

g: Profiler, NetworkAnalyst and WebGestalt were used to probe the enriched signaling pathways by using the Gene Ontology (GO), Human Phenotype Ontology (HP), Kyoto Encyclopedia of Genes and Genomes (KEGG), Reactome (REAC), and WikiPathways (WP) databases. Large numbers of enriched signaling pathways were identified using the integrated bioinformatics enrichment analyses.

Results

Apoptosis or programmed cell death (PCD), disease, muscle contraction, metabolism, and immune system were the top functions. Embryo or organ morphogenesis and development, cell or muscle contraction, and apoptosis were the top biological processes, and cell/muscle contraction and apoptosis were the top molecular functions using enriched GO terms analysis. There were a large number of complex interactions in the genes, enriched pathways, and transcription factor (TF)-miRNA co-regulatory networks. Transcription factors such as FOXN3, GLI3, HOX, and NCOR2 family regulated the gene expression of APAF1, BCL2, BID, CASP, MTHFR, and TPM family.

Conclusions

The results of bioinformatics enrichment analysis not only supported the previously proposed hypotheses, e.g., extracellular matrix (ECM) abnormality, fetal movement reducing, genetic abnormality, muscle abnormality, neurological abnormality, skeletal abnormality and vascular abnormality, but also indicated that cellular or immune responses to external stimulus, molecular transport and metabolism may be new etiological mechanisms in clubfoot.

Myoinositol: The Bridge (PONTI) to Reach a Healthy Pregnancy

The use of folic acid in the periconceptional period can prevent about 70% of neural tube defects (NTDs). In the remaining cases, no medical prevention is available, and those conditions should be defined as folate-resistant NTDs. Rodent models suggest that some folate-resistant NTDs can be prevented by inositol (myoinositol and chiroinositol) supplementation prior to pregnancy. Should folic acid be combined with myoinositol periconceptional supplementation to reduce the overall risk of NTDs even in humans? Hereafter, we discuss the results from the PONTI study that strongly support both the effectiveness and safety of myoinositol periconceptional supplementation in preventing human NTDs. We further report on the largest case series of pregnancies treated with myoinositol and folic acid. At our institution, a sequential study during 12 years involved mothers at risk of fetal NTDs, and 29 babies from 27 pregnancies were born after periconceptional combined myoinositol and folic acid supplementation. No case of NTDs was observed, despite the high recurrence risk in the mothers. Taken together, those data suggest that periconceptional folic acid plus myoinositol can reduce both the occurrence and recurrence risks of NTDs in a greater number of cases than folic acid alone.

Formate supplementation enhances folate-dependent nucleotide biosynthesis and prevents spina bifida in a mouse model of folic acid-resistant neural tube defects

The curly tail mouse provides a model for neural tube defects (spina bifida and exencephaly) that are resistant to prevention by folic acid. The major ct gene, responsible for spina bifida, corresponds to a hypomorphic allele of grainyhead-like 3 (Grhl3) but the frequency of NTDs is strongly influenced by modifiers in the genetic background. Moreover, exencephaly in the curly tail strain is not prevented by reinstatement of Grhl3 expression. In the current study we found that expression of Mthfd1L, encoding a key component of mitochondrial folate one-carbon metabolism (FOCM), is significantly reduced in ct/ct embryos compared to a partially congenic wild-type strain. This expression change is not attributable to regulation by Grhl3 or the genetic background at the Mthfd1L locus. Mitochondrial FOCM provides one-carbon units as formate for FOCM reactions in the cytosol. We found that maternal supplementation with formate prevented NTDs in curly tail embryos and also resulted in increased litter size. Analysis of the folate profile of neurulation-stage embryos showed that formate supplementation resulted in an increased proportion of formyl-THF and THF but a reduction in proportion of 5-methyl THF. In contrast, THF decreased and 5-methyl THF was relatively more abundant in the liver of supplemented dams than in controls. In embryos cultured through the period of spinal neurulation, incorporation of labelled thymidine and adenine into genomic DNA was suppressed by supplemental formate, suggesting that de novo folate-dependent biosynthesis of nucleotides (thymidylate and purines) was enhanced. We hypothesise that reduced Mthfd1L expression may contribute to susceptibility to NTDs in the curly tail strain and that formate acts as a one-carbon donor to prevent NTDs.

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Neural tube defects in curly tail (ct/ct) embryos are not preventable by folic acid.

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Expression of Mthfd1L is diminished in ct/ct (Grhl3 hypomorph) embryos.

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Mthfd1L acts in mitochondrial folate one-carbon metabolism to generate formate.

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Supplemental formate reduces the frequency of neural tube defects in ct/ct embryos.

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Formate alters folate profiles of maternal liver and embryos and enhances folate-dependent nucleotide biosynthesis.

Neural tube defects induced by folate deficiency in mutant curly tail (Grhl3) embryos are associated with alteration in folate one-carbon metabolism but are unlikely to result from diminished methylation

BACKGROUND

Folate one-carbon metabolism has been implicated as a determinant of susceptibility to neural tube defects (NTDs), owing to the preventive effect of maternal folic acid supplementation and the higher risk associated with markers of diminished folate status.

METHODS

Folate one-carbon metabolism was compared in curly tail (ct/ct) and genetically matched congenic (+(ct)/+(ct)) mouse strains using the deoxyuridine suppression test in embryonic fibroblast cells and by quantifying s-adenosylmethionine (SAM) and s-adenosylhomocysteine (SAH) in embryos using liquid chromatography tandem mass spectrometry. A possible genetic interaction between curly tail and a null allele of 5,10-methylenetetrahydrofolate reductase (MTHFR) was investigated by generation of compound mutant embryos.

RESULTS

There was no deficit in thymidylate biosynthesis in ct/ct cells, but incorporation of exogenous thymidine was lower than in +(ct)/+(ct) cells. In +(ct)/+(ct) embryos the SAM/SAH ratio was diminished by dietary folate deficiency and normalized by folic acid or myo-inositol treatment, in association with prevention of NTDs. In contrast, folate deficiency caused a significant increase in the SAM/SAH ratio in ct/ct embryos. Loss of MTHFR function in curly tail embryos significantly reduced the SAM/SAH ratio but did not cause cranial NTDs or alter the frequency of caudal NTDs.

CONCLUSIONS

Curly tail fibroblasts and embryos, in which Grhl3 expression is reduced, display alterations in one-carbon metabolism, particularly in the response to folate deficiency, compared to genetically matched congenic controls in which Grhl3 is unaffected. However, unlike folate deficiency, diminished methylation potential appears to be insufficient to cause cranial NTDs in the curly tail strain, nor does it increase the frequency of caudal NTDs.

The genetic background of the curly tail strain confers susceptibility to folate-deficiency-induced exencephaly

BACKGROUND: Suboptimal maternal folate status is considered a risk factor for neural tube defects (NTDs). However, the relationship between dietary folate status and risk of NTDs appears complex, as experimentally induced folate deficiency is insufficient to cause NTDs in nonmutant mice. In contrast, folate deficiency can exacerbate the effect of an NTD-causing mutation, as in splotch mice. The purpose of the present study was to determine whether folate deficiency can induce NTDs in mice with a permissive genetic background which do not normally exhibit defects. METHODS: Folate deficiency was induced in curly tail and genetically matched wild-type mice, and we analyzed the effect on maternal folate status, embryonic growth and development, and frequency of NTDs. RESULTS: Folate-deficient diets resulted in reduced maternal blood folate, elevated homocysteine, and a diminished embryonic folate content. Folate deficiency had a deleterious effect on reproductive success, resulting in smaller litter sizes and an increased rate of resorption. Notably, folate deficiency caused a similar-sized, statistically significant increase in the frequency of cranial NTDs among both curly tail (Grhl3 mutant) embryos and background-matched embryos that are wild type for Grhl3. The latter do not exhibit NTDs under normal dietary conditions. Maternal supplementation with myo-inositol reduced the incidence of NTDs in the folate-deficient wild-type strain. CONCLUSIONS: Dietary folate deficiency can induce cranial NTDs in nonmutant mice with a permissive genetic background, a situation that likely parallels gene-nutrient interactions in human NTDs. Our findings suggest that inositol supplementation may ameliorate NTDs resulting from insufficient dietary folate. Birth Defects Research (Part A), 2010. © 2009 Wiley-Liss, Inc.

Mechanistic insights into folate supplementation from Crooked tail and other NTD-prone mutant mice

Despite two decades of research since Smithells and colleagues began exploring its benefits, the mechanisms through which folic acid supplementation supports neural tube closure and early embryonic development are still unclear. The greatest progress toward a molecular-genetic understanding of folate effects on neural tube defect (NTD) pathogenesis has come from animal models. The number of NTD-associated mouse mutants accumulated and studied over the past decade has illuminated the complexity of both genetic factors contributing to NTDs and also NTD-gene interactions with folate metabolism. This article discusses insights gained from mouse models into how folate supplementation impacts neurulation. A case is made for renewed efforts to systematically screen the folate responsiveness of the scores of NTD-associated mouse mutations now identified. Designed after Crooked tail, supplementation studies of additional mouse mutants could build the molecular network maps that will ultimately enable tailoring of therapeutic regimens to individual families.

Curly tail: a 50-year history of the mouse spina bifida model

This paper reviews 50 years of progress towards understanding the aetiology and pathogenesis of neural tube defects (NTD) in the curly tail (ct) mutant mouse. More than 45 papers have been published on various aspects of curly tail with the result that it is now the best understood mouse model of NTD pathogenesis. The failure of closure of the spinal neural tube, which leads to spina bifida in this mouse, has been traced back to a tissue-specific defect of cell proliferation in the tail bud of the E9.5 embryo. This cell proliferation defect results in a growth imbalance in the caudal region that generates ventral curvature of the body axis. Neurulation movements are opposed, leading to delayed neuropore closure and spina bifida, or tail defects. It is interesting to reflect that these advances have been achieved in the absence of information on the nature of the ct gene product, which remains unidentified. In addition to the principal ct gene, which maps to distal Chromosome 4, the curly tail phenotype is influenced by several modifier genes and by environmental factors. NTD in curly tail are resistant to folic acid, as is thought to be the case in 30% of human NTD, whereas they can be prevented by myo-inositol. These and other features of NTD in this system bear striking similarities to the situation in humans, making curly tail a model for understanding a sub-type folic acid-resistant human NTD.

Homocysteine induces congenital defects of the heart and neural tube: effect of folic acid

The biological basis or mechanism whereby folate supplementation protects against heart and neural tube defect is unknown. It has been hypothesized that the amino acid homocysteine may be the teratogenic agent, since serum homocysteine increases in folate depletion; however, this hypothesis has not been tested. In this study, avian embryos were treated directly with D,L-homocysteine or with L-homocysteine thiolactone, and a dose response was established. Of embryos treated with 50 microliters of the teratogenic dose (200 mM D,L-homocysteine or 100 mM L-homocysteine thiolactone) on incubation days 0, 1, and 2 and harvested at 53 h (stage 14), 27% showed neural tube defects. To determine the effect of the teratogenic dose on the process of heart septation, embryos were treated during incubation days 2, 3, and 4; then they were harvested at day 9 following the completion of septation. Of surviving embryos, 23% showed ventricular septal defects, and 11% showed neural tube defects. A high percentage of the day 9 embryos also showed a ventral closure defect. The teratogenic dose was shown to raise serum homocysteine to over 150 nmol/ml, compared with a normal level of about 10 nmol/ml. Folate supplementation kept the rise in serum homocysteine to approximately 45 nmol/ml, and prevented the teratogenic effect. These results support the hypothesis that homocysteine per se causes dysmorphogenesis of the heart and neural tube, as well as of the ventral wall.

Neural tube defects and abnormal brain development in F52-deficient mice

F52 is a myristoylated, alanine-rich substrate for protein kinase C. We have generated F52-deficient mice by the gene targeting technique. These mutant mice manifest severe neural tube defects that are not associated with other complex malformations, a phenotype reminiscent of common human neural tube defects. The neural tube defects observed include both exencephaly and spina bifida, and the phenotype exhibits partial penetrance with about 60% of homozygous embryos developing neural tube defects. Exencephaly is the prominent type of defect and leads to high prenatal lethality. Neural tube defects are observed in a smaller percentage of heterozygous embryos (about 10%). Abnormal brain development and tail formation occur in homozygous mutants and are likely to be secondary to the neural tube defects. Disruption of F52 in mice therefore identifies a gene whose mutation results in isolated neural tube defects and may provide an animal model for common human neural tube defects.