Epigenetic Genome Modifications during Pregnancy: The Impact of Essential Nutritional Supplements on DNA Methylation

Pregnancy is an extremely stressful period in a pregnant woman's life. Currently, women's awareness of the proper course of pregnancy and its possible complications is constantly growing. Therefore, a significant percentage of women increasingly reach for various dietary supplements during gestation. Some of the most popular substances included in multi-ingredient supplements are folic acid and choline. Those substances are associated with positive effects on fetal intrauterine development and fewer possible pregnancy-associated complications. Recently, more and more attention has been paid to the impacts of specific environmental factors, such as diet, stress, physical activity, etc., on epigenetic modifications, understood as changes occurring in gene expression without the direct alteration of DNA sequences. Substances such as folic acid and choline may participate in epigenetic modifications by acting via a one-carbon cycle, leading to the methyl-group donor formation. Those nutrients may indirectly impact genome phenotype by influencing the process of DNA methylation. This review article presents the current state of knowledge on the use of folic acid and choline supplementation during pregnancy, taking into account their impacts on the maternal-fetal unit and possible pregnancy outcomes, and determining possible mechanisms of action, with particular emphasis on their possible impacts on epigenetic modifications.

The role of maternal choline, folate and one-carbon metabolism in mediating the impact of prenatal alcohol exposure on placental and fetal development

Prenatal alcohol consumption (PAE) may be associated with a broad spectrum of impacts, ranging from no overt effects, to miscarriage, fetal growth restriction and fetal alcohol spectrum disorder. A major mechanism underlying the effects of PAE is considered to be altered DNA methylation and gene expression. Maternal nutritional status may be an important factor in determining the extent to which PAE impacts pregnancy outcomes, particularly the dietary micronutrients folate and choline because they provide methyl groups for DNA methylation via one carbon metabolism. This review summarises the roles of folate and choline in development of the blastocyst, the placenta and the fetal brain, and examines the evidence that maternal intake of these micronutrients can modify the effects of PAE on development. Studies of folate or choline deficiency have found reduced blastocyst development and implantation, reduced placental invasion, vascularisation and nutrient transport capability, impaired fetal brain development, and abnormal neurodevelopmental outcomes. PAE has been shown to reduce absorption and/or metabolism of folate and choline and to produce similar outcomes to maternal choline/folate deficiency. A few studies have demonstrated that the effects of PAE on brain development can be ameliorated by folate or choline supplementation; however, there is very limited evidence on the effects of supplementation in early pregnancy on the blastocyst and placenta. Further studies are required to support these findings and to determine optimal supplementation parameters.

Joint Effects of Prenatal Folic Acid Supplement with Prenatal Multivitamin and Iron Supplement on Obesity in Preschoolers Born SGA: Sex Specific Difference

Prenatal maternal nutrient supplementation has been reported to be associated with offspring obesity, but the reports are inconsistent and have mainly ignored the differences between the total children population and children born small for gestational age (SGA). This study aimed to examine the joint effects of folic acid, iron, and multivitamin supplementation during pregnancy on the risk of obesity in preschoolers born SGA. A total of 8918 children aged 3-6.5 years born SGA were recruited from Longhua District in Shenzhen of China in 2021. Their mothers completed a structured questionnaire about the child's and parents' socio-demographic characteristics, maternal prepregnant obesity, and mothers' prenatal supplementation of folic acid, iron, and multivitamin. In addition, the children's current weight and height were measured by trained nurses. Logistic regression models were used to analyze the associations between prenatal supplementations and the current presence of childhood obesity. After controlling for potential confounders, the results of the logistic regression analysis showed that prenatal supplement of folic acid (OR = 0.72, 95% CI = 0.55~0.93) was associated with a lower likelihood of being an obese preschooler born SGA. In contrast, the ingestion of multivitamin or iron supplements during pregnancy did not seem to be related to the likelihood of childhood obesity in preschoolers born SGA. Moreover, cross-over analysis of prenatal folic acid and multivitamin obtained significant negative associations of prenatal folic acid supplement only (OR = 0.73, 95% CI = 0.55~0.97) and combination supplement of folic acid and multivitamin (OR = 0.67, 95% CI = 0.50~0.90) with obesity of preschoolers born SGA; while the cross-over analysis of prenatal folic acid and iron observed significant negative associations between obesity of preschoolers born SGA and a combination supplement of folic acid and iron (OR = 0.70, 95% CI = 0.52~0.96). Furthermore, the aforementioned significant associations were only found in girls and not in boys when the analyses were stratified by sex. Our findings suggest that the prenatal folic acid supplementation may decrease the risk of obesity in preschool girls born SGA, and that this effect may be modified by prenatal multivitamin or iron supplementation.

The 677C > T variant in methylenetetrahydrofolate reductase causes morphological and functional cerebrovascular deficits in mice

Vascular contributions to cognitive impairment and dementia (VCID) particularly Alzheimer's disease and related dementias (ADRDs) are increasing; however, mechanisms driving cerebrovascular decline are poorly understood. Methylenetetrahydrofolate reductase (MTHFR) is a critical enzyme in the folate and methionine cycles. Variants in MTHFR, notably 677 C > T, are associated with dementias, but no mouse model existed to identify mechanisms by which MTHFR677C > T increases risk. Therefore, MODEL-AD created a novel knock-in (KI) strain carrying the Mthfr677C > T allele on the C57BL/6J background (Mthfr677C > T) to characterize morphology and function perturbed by the variant. Consistent with human clinical data, Mthfr677C > T mice have reduced enzyme activity in the liver and elevated plasma homocysteine levels. MTHFR enzyme activity is also reduced in the Mthfr677C > T brain. Mice showed reduced tissue perfusion in numerous brain regions by PET/CT as well as significantly reduced vascular density, pericyte number and increased GFAP-expressing astrocytes in frontal cortex. Electron microscopy revealed cerebrovascular damage including endothelial and pericyte apoptosis, reduced luminal size, and increased astrocyte and microglial presence in the microenvironment. Collectively, these data support a mechanism by which variations in MTHFR perturb cerebrovascular health laying the foundation to incorporate our new Mthfr677C > T mouse model in studies examining genetic susceptibility for cerebrovascular dysfunction in ADRDs.

Homocysteine Metabolism in Pregnancy and Developmental Impacts

Homocysteine is a metabolite generated by methionine cycle metabolism, comprising the demethylated derivative of methionine. Homocysteine can be metabolised by the transsulphuration pathway to cystathionine, which requires vitamin B6, or can undergo remethylation to methionine. Homocysteine remethylation to methionine is catalysed by methionine synthase activity which requires vitamin B12, regenerating methionine to allow synthesis of the universal methyl donor S-adenosylmethionine required for methylation and gene transcription regulation. The methyl-group donated for homocysteine remethylation comes from 5-methyltetrahydrofolate generated by the folate cycle, which allows tetrahydrofolate to be returned to the active folate pool for nucleotide biosynthesis. Therefore the integrated actions of the methionine and folate cycles, required to metabolise homocysteine, also perpetuate methylation and nucleotide synthesis, vitally important to support embryonic growth, proliferation and development. Dysregulated activities of these two interdependent metabolic cycles, arising from maternal suboptimal intake of nutrient co-factors such as folate and vitamin B12 or gene polymorphisms resulting in reduced enzymatic activity, leads to inefficient homocysteine metabolic conversion causing elevated concentrations, known as hyperhomocysteinemia. This condition is associated with multiple adverse pregnancy outcomes including neural tube defects (NTDs). Raised homocysteine is damaging to cellular function, binding to proteins thereby impairing their function, with perturbed homocysteine metabolism impacting negatively on embryonic development. This review discusses the "cross-talk" of maternal-fetal homocysteine interrelationships, describes the placental transport of homocysteine, homocysteine impacts on pregnancy outcomes, homocysteine and methylation effects linking to NTD risk and proposes a putative pathway for embryonic provision of folate and vitamin B12, homocysteine-modulating nutrients that ameliorate NTD risk.

Prenatal Choline Supplementation Alters One Carbon Metabolites in a Rat Model of Periconceptional Alcohol Exposure

Prenatal alcohol exposure disturbs fetal and placental growth and can alter DNA methylation (DNAm). Supplementation with the methyl donor choline can increase fetal and placental growth and restore DNAm, suggesting converging effects on one-carbon metabolism (1CM). We investigated the impact of periconceptional ethanol (PCE) exposure and prenatal choline supplementation on 1CM in maternal, placental, and fetal compartments. Female Sprague Dawley rats were given a liquid diet containing 12.5% ethanol (PCE) or 0% ethanol (control) for 4 days before and 4 days after conception. Dams were then placed on chow with different concentrations of choline (1.6 g, 2.6 g, or 7.2 g choline/kg chow). Plasma and tissues were collected in late gestation for the analysis of 1CM components by means of mass spectrometry and real-time PCR. PCE reduced placental components of 1CM, particularly those relating to folate metabolism, resulting in a 3−7.5-fold reduction in the ratio of s-adenosylmethionine:s-adenosylhomocysteine (SAM:SAH) (p < 0.0001). Choline supplementation increased placental 1CM components and the SAM:SAH ratio (3.5−14.5-fold, p < 0.0001). In the maternal and fetal compartments, PCE had little effect, whereas choline increased components of 1CM. This suggests that PCE impairs fetal development via altered placental 1CM, highlighting its role in modulating nutritional inputs to optimize fetal development.

Disruption of Folate Metabolism Causes Poor Alignment and Spacing of Mouse Conceptuses for Multiple Generations

Abnormal uptake or metabolism of folate increases risk of human pregnancy complications, though the mechanism is unclear. Here, we explore how defective folate metabolism influences early development by analysing mice with the hypomorphic Mtrr^gt mutation. MTRR is necessary for methyl group utilisation from folate metabolism, and the Mtrr^gt allele disrupts this process. We show that the spectrum of phenotypes previously observed in Mtrr^gt/gt conceptuses at embryonic day (E) 10.5 is apparent from E8.5 including developmental delay, congenital malformations, and placental phenotypes. Notably, we report misalignment of some Mtrr^gt conceptuses within their implantation sites from E6.5. The degree of misorientation occurs across a continuum, with the most severe form visible upon gross dissection. Additionally, some Mtrr^gt/gt conceptuses display twinning. Therefore, we implicate folate metabolism in blastocyst orientation and spacing at implantation. Skewed growth likely influences embryo development since developmental delay and heart malformations (but not defects in neural tube closure or trophoblast differentiation) associate with severe misalignment of Mtrr^gt/gt conceptuses. Typically, the uterus is thought to guide conceptus orientation. To investigate a uterine effect of the Mtrr^gt allele, we manipulate the maternal Mtrr genotype. Misaligned conceptuses were observed in litters of Mtrr^+/+, Mtrr^+/gt, and Mtrr^gt/gt mothers. While progesterone and/or BMP2 signalling might be disrupted, normal decidual morphology, patterning, and blood perfusion are evident at E6.5 regardless of conceptus orientation. These observations argue against a post-implantation uterine defect as a cause of conceptus misalignment. Since litters of Mtrr^+/+ mothers display conceptus misalignment, a grandparental effect is explored. Multigenerational phenotype inheritance is characteristic of the Mtrr^gt model, though the mechanism remains unclear. Genetic pedigree analysis reveals that severe conceptus skewing associates with the Mtrr genotype of either maternal grandparent. Moreover, the presence of conceptus skewing after embryo transfer into a control uterus indicates that misalignment is independent of the peri- and/or post-implantation uterus and instead is likely attributed to an embryonic mechanism that is epigenetically inherited. Overall, our data indicates that abnormal folate metabolism influences conceptus orientation over multiple generations with implications for subsequent development. This study casts light on the complex role of folate metabolism during development beyond a direct maternal effect.

Ability of dietary factors to affect homocysteine levels in mice: a review

Homocysteine is associated with several diseases, and a series of dietary factors are known to modulate homocysteine levels. As mice are often used as model organisms to study the effects of dietary hyperhomocysteinemia, we collected data about concentrations of vitamin B₁₂, vitamin B₆, folate, methionine, cystine, and choline in mouse diets and the associated plasma/serum homocysteine levels. In addition, we more closely examined the composition of the control diet, the impact of the mouse strain, sex and age, and the duration of the dietary intervention on homocysteine levels. In total, 113 out of 1103 reviewed articles met the inclusion criteria. In the experimental and control diets, homocysteine levels varied from 0.1 to 280 µmol/l. We found negative correlations between dietary vitamin B₁₂ (rho = − 0.125; p < 0.05), vitamin B₆ (rho = − 0.191; p < 0.01) and folate (rho = − 0.395; p < 0.001) and circulating levels of homocysteine. In contrast, a positive correlation was observed between dietary methionine and homocysteine (methionine: rho = 0.146; p < 0.05). No significant correlations were found for cystine or choline and homocysteine levels. In addition, there was no correlation between the duration of the experimental diets and homocysteine levels. More importantly, the data showed that homocysteine levels varied widely in mice fed control diets as well. When comparing control diets with similar nutrient concentrations (AIN-based), there were significant differences in homocysteine levels caused by the strain (ANOVA, p < 0.05) and age of the mice at baseline (r = 0.47; p < 0.05). When comparing homocysteine levels and sex, female mice tended to have higher homocysteine levels than male mice (9.3 ± 5.9 µmol/l vs. 5.8 ± 4.5 µmol/l; p = 0.069). To conclude, diets low in vitamin B₁₂, vitamin B₆, or folate and rich in methionine are similarly effective in increasing homocysteine levels. AIN recommendations for control diets are adequate with respect to the amounts of homocysteine-modulating dietary parameters. In addition, the mouse strain and the age of mice can affect the homocysteine level.

Maternal Folic Acid Deficiency Is Associated to Developing Nasal and Palate Malformations in Mice

Craniofacial development requires extremely fine-tuned developmental coordination of multiple specialized tissues. It has been evidenced that a folate deficiency (vitamin B9), or its synthetic form, folic acid (FA), in maternal diet could trigger multiple craniofacial malformations as oral clefts, tongue, or mandible abnormalities. In this study, a folic acid-deficient (FAD) diet was administered to eight-week-old C57/BL/6J female mouse for 2-16 weeks. The head symmetry, palate and nasal region were studied in 24 control and 260 experimental fetuses. Our results showed a significant reduction in the mean number of fetuses per litter according to maternal weeks on FAD diet (p < 0.01). Fetuses were affected by cleft palate (3.8%) as well as other severe congenital abnormalities, for the first time related to maternal FAD diet, as head asymmetries (4.6%), high arched palate (3.5%), nasal septum malformed (7.3%), nasopharynx duct shape (15%), and cilia and epithelium abnormalities (11.2% and 5.8%). Dysmorphologies of the nasal region were the most frequent, appearing at just four weeks following a maternal FAD diet. This is the first time that nasal region development is experimentally related to this vitamin deficiency. In conclusion, our report offers novel discoveries about the importance of maternal folate intake on midface craniofacial development of the embryos. Moreover, the longer the deficit lasts, the more serious the consequent effects appear to be.

Autophagy regulates abnormal placentation induced by folate deficiency in mice

Folate deficiency has been linked to a wide range of pregnancy disorders. Most research about folate-deficiency has focused on the embryo itself, little attention has been paid to possible effects on the placenta. According to our results, the morphology of the placenta, endocrine function, and the expression of genes involved in placental differentiation were all abnormal in folate-deficient mice on days 10, 12, and 14 of pregnancy. Similar results were found in human placenta explants cultured in folate-deficient medium. Autophagy is an inducible catabolic process activated by external nutrients starvation. Here we explored further, whether autophagy was involved in the abnormal placentation caused by folate-deficiency. The aberrant number of autophagosomes measured by transmission electron microscopy and the deviant expression of autophagy-related markers showed a disordered autophagy in placentas under conditions of folate-deficiency in vivo and in vitro dual-fluorescence mRFP-eGFP-LC3 analysis indicated enhanced autophagy was detected in HTR8/SVneo cells incubated in folate-deficient medium. Importantly, the placentation impairment in mice and human placenta explants could be recovered by inhibiting placental autophagy using 3-MA. In addition, the apoptosis and invasive capability of HTR8/SVneo cells were obviously suppressed by folate deficiency but notably elevated by 3-MA. These data suggest that folate deficiency can impair placentation and autophagy is a key factor in this. However, the signal pathway by which folate deficiency causes aberrant autophagy needs to be explored further.

Impact of mothers' early life exposure to low or high folate on progeny outcome and DNA methylation patterns

The dynamic patterning of DNA and histone methylation during oocyte development presents a potentially susceptible time for epigenetic disruption due to early life environmental exposure of future mothers. We investigated whether maternal exposure to folic acid deficient and supplemented diets starting in utero could affect oocytes and cause adverse developmental and epigenetic effects in next generation progeny. Female BALB/c mice (F0) were placed on one of four amino acid defined diets for 4 weeks before pregnancy and throughout gestation and lactation: folic acid control (rodent recommended daily intake; Ctrl), 7-fold folic acid deficient, 10-fold folic acid supplemented or 20-fold folic acid supplemented diets. F1 female pups were weaned onto Ctrl diets, mated to produce the F2 generation and the F2 offspring were examined at E18.5 for developmental and epigenetic abnormalities. Resorption rates were increased and litter sizes decreased amongst F2 E18.5-day litters in the 20-fold folic acid supplemented group. Increases in abnormal embryo outcomes were observed in all three folic acid deficient and supplemented groups. Subtle genome-wide DNA methylation alterations were found in the placentas and brains of F2 offspring in the 7-fold folic acid deficient , 10-fold folic acid supplemented and 20-fold folic acid supplemented groups; in contrast, global and imprinted gene methylation were not affected. The findings show that early life female environmental exposures to both low and high folate prior to oocyte maturation can compromise oocyte quality, adversely affecting offspring of the next generation, in part by altering DNA methylation patterns.

The Impact of Maternal Pre-Pregnancy Body Weight and Gestational Diabetes on Markers of Folate Metabolism in the Placenta

Dietary methyl donors, including folate, may modify the placenta and size at birth but the influence of maternal body weight has not been widely investigated. We therefore examined whether maternal or fetal folate status, together with indices of placental folate transport, were modulated by either maternal pre-pregnancy body mass index (BMI i.e., overweight: 25 ≤ BMI < 30 or obesity: BMI ≥ 30 kg/m²) and/or gestational diabetes mellitus (GD). We utilised a sub-sample of 135 pregnant women participating in the Spanish PREOBE survey for our analysis (i.e., 59 healthy normal weight, 29 overweight, 22 obese and 25 GD). They were blood sampled at 34 weeks gestation, and, at delivery, when a placental sample was taken together with maternal and cord blood. Placental gene expression of folate transporters and DNA methyltransferases (DNMT) were all measured. Folate plasma concentrations were determined with an electro-chemiluminescence immunoassay. Food diaries indicated that folate intake was unaffected by BMI or GD and, although all women maintained normal folate concentrations (i.e., 5–16 ng/mL), higher BMIs were associated with reduced maternal folate concentrations at delivery. Umbilical cord folate was not different, reflecting an increased concentration gradient between the mother and her fetus. Placental mRNA abundance for the folate receptor alpha (FOLR1) was reduced with obesity, whilst DNMT1 was increased with raised BMI, responses that were unaffected by GD. Multi-regression analysis to determine the best predictors for placental FOLR1 indicated that pre-gestational BMI had the greatest influence. In conclusion, the placenta’s capacity to maintain fetal folate supply was not compromised by either obesity or GD.

Maternal gene-micronutrient interactions related to one-carbon metabolism and the risk of myelomeningocele among offspring

BACKGROUND

Few studies have evaluated interactions between maternal genetic variation in 5,10-methylenetetrahydrofolate reductase (MTHFR) and micronutrient intake on the risk of myelomeningocele (MM) in offspring. Therefore, we sought to determine if the role of maternal MTHFR C677T and A1298C on MM risk is altered by maternal intake of micronutrients related to one-carbon metabolism.

METHODS

The study consisted of 220 MM case-parent trios recruited from 1996 to 2006. A dietary questionnaire was used to obtain information on maternal dietary intake on eight micronutrients including folate and cobalamin. TaqMan assays were used to generate MTHFR C677T and A1298C genotypes. Log-linear models were used to evaluate the joint effects of maternal genotype and micronutrient intake dichotomized as at or above versus below the United States Recommended Dietary Allowance (US RDA) on MM.

RESULTS

There was little evidence to suggest maternal MTHFR genotypes interacted with micronutrient intake to influence the risk of MM. For instance, the effect of MTHFR 677T was similar for mothers with cobalamin intake below US RDA (relative risk [RR] = 0.97) versus at or above US RDA cobalamin intake (RR = 0.81, interaction p = 0.87). However, some differences were noted. For example, the effect of MTHFR 1298C appeared to be different between those mothers below US RDA folate intake (RR = 0.98) versus those at or above US RDA folate intake (RR = 0.68), but the interaction was not statistically significant (interaction p = 0.27).

CONCLUSION

There did not appear to be strong effects of maternal micronutrient intake on the role of maternal genetic polymorphisms in MTHFR C677T and A1298C on MM risk. Birth Defects Research 109:99-105, 2017. © 2016 Wiley Periodicals, Inc.

Effects of micronutrients on placental function: evidence from clinical studies to animal models

Micronutrient deficiencies are common in pregnant women due to low dietary intake and increased requirements for fetal development. Low maternal micronutrient status is associated with a range of pregnancy pathologies involving placental dysfunction, including fetal growth restriction (FGR), small-for-gestational age (SGA), pre-eclampsia and preterm birth. However, clinical trials commonly fail to convincingly demonstrate beneficial effects of supplementation of individual micronutrients, attributed to heterogeneity and insufficient power, potential interactions and lack of mechanistic knowledge of effects on the placenta. We aimed to provide current evidence of relationships between selected micronutrients (vitamin D, vitamin A, iron, folate, vitamin B12) and adverse pregnancy outcomes, combined with understanding of actions on the placenta. Following a systematic literature search, we reviewed data from clinical, in vitro and in vivo studies of micronutrient deficiency and supplementation. Key findings are potential effects of micronutrient deficiencies on placental development and function, leading to impaired fetal growth. Studies in human trophoblast cells and rodent models provide insights into underpinning mechanisms. Interestingly, there is emerging evidence that deficiencies in all micronutrients examined induce a pro-inflammatory state in the placenta, drawing parallels with the inflammation detected in FGR, pre-eclampsia, stillbirth and preterm birth. Beneficial effects of supplementation are apparent in vitro and in animal models and for combined micronutrients in clinical studies. However, greater understanding of the roles of these micronutrients, and insight into their involvement in placental dysfunction, combined with more robust clinical studies, is needed to fully ascertain the potential benefits of supplementation in pregnancy.

Low Dietary Folate Interacts with MTHFD1 Synthetase Deficiency in Mice, a Model for the R653Q Variant, to Increase Incidence of Developmental Delays and Defects

Background

Suboptimal folate intake, a risk factor for birth defects, is common even in areas with folate fortification. A polymorphism in methylenetetrahydrofolate dehydrogenase 1 (MTHFD1), R653Q (MTHFD1 c.1958 G > A), has also been associated with increased birth defect risk, likely through reduced purine synthesis.

Objective

We aimed to determine if the interaction of MTHFD1 synthetase deficiency and low folate intake increases developmental abnormalities in a mouse model for MTHFD1 R653Q.

Methods

Female Mthfd1S+/+ and Mthfd1S+/- mice were fed control or low-folate diets (2 and 0.3 mg folic acid/kg diet, respectively) before mating and during pregnancy. Embryos and placentas were examined for anomalies at embryonic day 10.5. Maternal 1-carbon metabolites were measured in plasma and liver.

Results

Delays and defects doubled in litters of Mthfd1S+/- females fed low-folate diets compared to wild-type females fed either diet, or Mthfd1S+/- females fed control diets [P values (defects): diet 0.003, maternal genotype 0.012, diet × maternal genotype 0.014]. These adverse outcomes were associated with placental dysmorphology. Intrauterine growth restriction was increased by embryonic Mthfd1S+/- genotype, folate deficiency, and interaction of maternal Mthfd1S+/- genotype with folate deficiency (P values: embryonic genotype 0.045, diet 0.0081, diet × maternal genotype 0.0019). Despite a 50% increase in methylenetetrahydrofolate reductase expression in low-folate maternal liver (P diet = 0.0007), methyltetrahydrofolate concentration decreased 70% (P diet <0.0001) and homocysteine concentration doubled in plasma (P diet = 0.0001); S-adenosylmethionine decreased 40% and S-adenosylhomocysteine increased 20% in low-folate maternal liver (P diet = 0.002 and 0.0002, respectively).

Conclusions

MTHFD1 synthetase-deficient mice are more sensitive to low folate intake than wild-type mice during pregnancy. Reduced purine synthesis due to synthetase deficiency and altered methylation potential due to low folate may increase pregnancy complications. Further studies and individualized intake recommendations may be required for women homozygous for the MTHFD1 R653Q variant.

Effects of maternal folic acid supplementation on airway remodeling and allergic airway disease development

Objective: Maternal folic acid supplementation has been recommended prior to and during the first trimester of pregnancy to reduce the risk of infant neural tube defects. However, an uncertain relationship between folic acid supplementation during pregnancy and development of childhood asthma exists. Recent data show a methyl donor-rich diet could increase the risk of developing allergic airway disease through DNA methylation and aberrant gene transcription. This study evaluated the effect of folic acid supplementation during pregnancy on airway remodeling and allergic airway disease vulnerability in a mouse asthma model. Methods: BALB/c mice were divided into four groups according to gestational folic acid supplementation and postnatal ovalbumin (OVA) exposure: Group 1 (whole pregnancy folic acid supplementation + OVA-exposed group), Group 2 (first gestational week folic acid supplementation + OVA-exposed group), Group 3 (no folic acid supplementation + OVA-exposed group), and Group 4 (control group). Offspring were sacrificed on day 45 for immunohistological and ultrastructural tests. Results: In OVA challenged groups, folic acid supplementation led to a thicker epithelial and subepithelial smooth muscle layer than in the unsupplemented group. Moreover, folic acid supplementation during whole pregnancy (Group 1) was associated with a thicker epithelial and subepithelial smooth muscle layer than folic acid supplementation during the first week of pregnancy (Group 2), suggesting a duration-response relationship. Electron microscopic imaging revealed that structural changes including the loss of epithelial integrity, thickening of basement membrane, and subepithelial fibrosis were more prominent in the folic acid supplementation groups. Conclusions: This study suggested that maternal folic acid supplementation during pregnancy affects airway remodeling and increases the allergic responses induced by ovalbumin challenge in offspring. In addition, the effect size increased as the duration and cumulative dose increased.

Genome-wide survey reveals dynamic effects of folate supplement on DNA methylation and gene expression during C2C12 differentiation

Folic acid supplements taken during pregnancy can prevent neural tube defects and other developmental abnormalities. Here, we explored the effects of folate supplementation on gene expression and DNA methylation during C2C12 differentiation. Based on the folic acid concentration, this study comprised three groups: low folate (L), normal folate (N), and high-folate supplement (H). Our analyses revealed that differentiation and the mRNA expression of the gene myogenin in C2C12 cell were enhanced by folic acid; however, the overall methylation percentage in myogenin promoter between different treatment groups was not significantly different ( P > 0.05). The results of MeDIP-chip showed that hundreds of differentially methylated regions (DMRs) were identified between every two groups in both promoter and CpG islands, respectively. Genes with DMRs between N and L groups were mainly enriched in the processes of cell differentiation and cell development, whereas those with DMRs between H and N groups were frequently enriched in cellular process/cycle and cell metabolic processes. In addition, correlation analysis between methylation profile and expression profile revealed that some genes were regulated by methylation status directly. Together, these analyses suggest that folate deficiency and supplementation can influence the differentiation, genome-wide DNA methylation level and the expression of myogenesis-related genes including myogenin in the C2C12 cell line.

Multigenerational analysis of sex-specific phenotypic differences at midgestation caused by abnormal folate metabolism

The exposure to adverse environmental conditions (e.g. poor nutrition) may lead to increased disease risk in an individual and their descendants. In some cases, the results may be sexually dimorphic. A range of phenotypes has been associated with deficiency in or defective metabolism of the vitamin folate. However, the molecular mechanism linking folate metabolism to development is still not well defined nor is it clear whether phenotypes are sex-specific. The enzyme methionine synthase reductase (MTRR) is required for the progression of folate metabolism and the utilization of methyl groups from the folate cycle. Previously, we showed that the hypomorphic Mtrr^gt mutation in mice results in metabolic disruption, epigenetic instability, and a wide spectrum of developmental phenotypes (e.g. growth defects, congenital malformations) at midgestation that appear in subsequent wild-type generations. This transgenerational effect only occurs through the maternal lineage. Here, we explore whether the phenotypes that result from either intrinsic or ancestral Mtrr deficiency are sexually dimorphic. We found that no sexual dimorphism is apparent in either situation when the phenotypes were broadly or specifically defined. However, when we focused on the group of phenotypically normal conceptuses derived from maternal grandparental Mtrr deficiency, we observed an apparent increase in placental efficiency in each subsequent generation leading to F4 generation female embryos that weigh more than controls. These data suggest that ancestral abnormal folate metabolism may lead to male grandprogeny that are less able to adapt or female grandprogeny that are programmed to become more sensitive to folate availability in subsequent generations.

Moderate folic acid supplementation and MTHFD1-synthetase deficiency in mice, a model for the R653Q variant, result in embryonic defects and abnormal placental development

BACKGROUND

Moderately high folic acid intake in pregnant women has led to concerns about deleterious effects on the mother and fetus. Common polymorphisms in folate genes, such as methylenetetrahydrofolate dehydrogenase-methenyltetrahydrofolate cyclohydrolase-formyltetrahydrofolate synthetase (MTHFD1) R653Q, may modulate the effects of elevated folic acid intake.

OBJECTIVES

We investigated the effects of moderate folic acid supplementation on reproductive outcomes and assessed the potential interaction of the supplemented diet with MTHFD1-synthetase (Mthfd1S) deficiency in mice, which is a model for the R653Q variant.

DESIGN

Female Mthfd1S^+/+ and Mthfd1S^+/- mice were fed a folic acid-supplemented diet (FASD) (5-fold higher than recommended) or control diets before mating and during pregnancy. Embryos and placentas were assessed for developmental defects at embryonic day 10.5 (E10.5). Maternal folate and choline metabolites and gene expression in folate-related pathways were examined.

RESULTS

The combination of FASD and maternal MTHFD1-synthetase deficiency led to a greater incidence of defects in E10.5 embryos (diet × maternal genotype, P = 0.0016; diet × embryonic genotype, P = 0.054). The methylenetetrahydrofolate reductase (MTHFR) protein and methylation potential [ratio of S-adenosylmethionine (major methyl donor):S-adenosylhomocysteine) were reduced in maternal liver. Although 5-methyltetrahydrofolate (methylTHF) was higher in maternal circulation, the methylation potential was lower in embryos. The presence of developmental delays and defects in Mthfd1S^+/- embryos was associated with placental defects (P = 0.003). The labyrinth layer failed to form properly in the majority of abnormal placentas, which compromised the integration of the maternal and fetal circulation and presumably the transfer of methylTHF and other nutrients.

CONCLUSIONS

Moderately higher folate intake and MTHFD1-synthetase deficiency in pregnant mice result in a lower methylation potential in maternal liver and embryos and a greater incidence of defects in embryos. Although maternal circulating methylTHF was higher, it may not have reached the embryos because of abnormal placental development; abnormal placentas were observed predominantly in abnormally developed embryos. These findings have implications for women with high folate intakes, particularly if they are polymorphic for MTHFD1 R653Q.

Acute alcohol exposure during mouse gastrulation alters lipid metabolism in placental and heart development: Folate prevention

Background

Embryonic acute exposure to ethanol (EtOH), lithium, and homocysteine (HCy) induces cardiac defects at the time of exposure; folic acid (FA) supplementation protects normal cardiogenesis (Han et al., 2009, 2012; Serrano et al., 2010). Our hypothesis is that EtOH exposure and FA protection relate to lipid and FA metabolism during mouse cardiogenesis and placentation.

Methods

On the morning of conception, pregnant C57BL/6J mice were placed on either of two FA‐containing diets: a 3.3 mg health maintenance diet or a high FA diet of 10.5 mg/kg. Mice were injected a binge level of EtOH, HCy, or saline on embryonic day (E) 6.75, targeting gastrulation. On E15.5, cardiac and umbilical blood flow were examined by ultrasound. Embryonic cardiac tissues were processed for gene expression of lipid and FA metabolism; the placenta and heart tissues for neutral lipid droplets, or for medium chain acyl‐dehydrogenase (MCAD) protein.

Results

EtOH exposure altered lipid‐related gene expression on E7.5 in comparison to control or FA‐supplemented groups and remained altered on E15.5 similarly to changes with HCy, signifying FA deficiency. In comparison to control tissues, the lipid‐related acyl CoA dehydrogenase medium length chain gene and its protein MCAD were altered with EtOH exposure, as were neutral lipid droplet localization in the heart and placenta.

Conclusion

EtOH altered gene expression associated with lipid and folate metabolism, as well as neutral lipids, in the E15.5 abnormally functioning heart and placenta. In comparison to controls, the high FA diet protected the embryo and placenta from these effects allowing normal development. Birth Defects Research (Part A) 106:749–760, 2016. © 2016 The Authors Birth Defects Research Part A: Clinical and Molecular Teratology Published by Wiley Periodicals, Inc.

High Dietary Folate in Mice Alters Immune Response and Reduces Survival after Malarial Infection

Malaria is a significant global health issue, with nearly 200 million cases in 2013 alone. Parasites obtain folate from the host or synthesize it de novo. Folate consumption has increased in many populations, prompting concerns regarding potential deleterious consequences of higher intake. The impact of high dietary folate on the host’s immune function and response to malaria has not been examined. Our goal was to determine whether high dietary folate would affect response to malarial infection in a murine model of cerebral malaria. Mice were fed control diets (CD, recommended folate level for rodents) or folic acid-supplemented diets (FASD, 10x recommended level) for 5 weeks before infection with Plasmodium berghei ANKA. Survival, parasitemia, numbers of immune cells and other infection parameters were assessed. FASD mice had reduced survival (p<0.01, Cox proportional hazards) and higher parasitemia (p< 0.01, joint model of parasitemia and survival) compared with CD mice. FASD mice had lower numbers of splenocytes, total T cells, and lower numbers of specific T and NK cell sub-populations, compared with CD mice (p<0.05, linear mixed effects). Increased brain TNFα immunoreactive protein (p<0.01, t-test) and increased liver Abca1 mRNA (p<0.01, t-test), a modulator of TNFα, were observed in FASD mice; these variables correlated positively (r_s = 0.63, p = 0.01). Bcl-xl/Bak mRNA was increased in liver of FASD mice (p<0.01, t-test), suggesting reduced apoptotic potential. We conclude that high dietary folate increases parasite replication, disturbs the immune response and reduces resistance to malaria in mice. These findings have relevance for malaria-endemic regions, when considering anti-folate anti-malarials, food fortification or vitamin supplementation programs.

MTHFR deficiency or reduced intake of folate or choline in pregnant mice results in impaired short-term memory and increased apoptosis in the hippocampus of wild-type offspring

Genetic or nutritional disturbances in one-carbon metabolism, with associated hyperhomocysteinemia, can result in complex disorders including pregnancy complications and neuropsychiatric diseases. In earlier work, we showed that mice with a complete deficiency of methylenetetrahydrofolate reductase (MTHFR), a critical enzyme in folate and homocysteine metabolism, had cognitive impairment with disturbances in choline metabolism. Maternal demands for folate and choline are increased during pregnancy and deficiencies of these nutrients result in several negative outcomes including increased resorption and delayed development. The goal of this study was to investigate the behavioral and neurobiological impact of a maternal genetic deficiency in MTHFR or maternal nutritional deficiency of folate or choline during pregnancy on 3-week-old Mthfr(+/+) offspring. Mthfr(+/+) and Mthfr(+/-) females were placed on control diets (CD); and Mthfr(+/+) females were placed on folate-deficient diets (FD) or choline-deficient diets (ChDD) throughout pregnancy and lactation until their offspring were 3weeks of age. Short-term memory was assessed in offspring, and hippocampal tissue was evaluated for morphological changes, apoptosis, proliferation and choline metabolism. Maternal MTHFR deficiency resulted in short-term memory impairment in offspring. These dams had elevated levels of plasma homocysteine when compared with wild-type dams. There were no differences in plasma homocysteine in offspring. Increased apoptosis and proliferation was observed in the hippocampus of offspring from Mthfr(+/-) mothers. In the maternal FD and ChDD study, offspring also showed short-term memory impairment with increased apoptosis in the hippocampus; increased neurogenesis was observed in ChDD offspring. Choline acetyltransferase protein was increased in the offspring hippocampus of both dietary groups and betaine was decreased in the hippocampus of FD offspring. Our results reveal short-term memory deficits in the offspring of dams with MTHFR deficiency or dietary deficiencies of critical methyl donors. We suggest that deficiencies in maternal one-carbon metabolism during pregnancy can contribute to hippocampal dysfunction in offspring through apoptosis or altered choline metabolism.

Spina bifida

Spina bifida is a birth defect in which the vertebral column is open, often with spinal cord involvement. The most clinically significant subtype is myelomeningocele (open spina bifida), which is a condition characterized by failure of the lumbosacral spinal neural tube to close during embryonic development. The exposed neural tissue degenerates in utero, resulting in neurological deficit that varies with the level of the lesion. Occurring in approximately 1 per 1,000 births worldwide, myelomeningocele is one of the most common congenital malformations, but its cause is largely unknown. The genetic component is estimated at 60-70%, but few causative genes have been identified to date, despite much information from mouse models. Non-genetic maternal risk factors include reduced folate intake, anticonvulsant therapy, diabetes mellitus and obesity. Primary prevention by periconceptional supplementation with folic acid has been demonstrated in clinical trials, leading to food fortification programmes in many countries. Prenatal diagnosis is achieved by ultrasonography, enabling women to seek termination of pregnancy. Individuals who survive to birth have their lesions closed surgically, with subsequent management of associated defects, including the Chiari II brain malformation, hydrocephalus, and urological and orthopaedic sequelae. Fetal surgical repair of myelomeningocele has been associated with improved early neurological outcome compared with postnatal operation. Myelomeningocele affects quality of life during childhood, adolescence and adulthood, posing a challenge for individuals, families and society as a whole. For an illustrated summary of this Primer, visit: http://go.nature.com/fK9XNa.

Evidence of Paternal N5, N10 - Methylenetetrahydrofolate Reductase (MTHFR) C677T Gene Polymorphism in Couples with Recurrent Spontaneous Abortions (RSAs) in Kolar District- A South West of India

INTRODUCTION

Recurrent spontaneous abortion (RSA) is a multifactorial clinical obstetrics complication commonly occurring in pregnancy. Many research studies have noted the mutations such as C677T in N5, N10 - Methylenetetrahydrofolate reductase (MTHFR)gene which is regarded as RSA risk factor. This study was carried out to determine the occurrence of frequency of C677T of the MTHFR gene mutations with RSA.

AIM

The purpose of present study is to determine the frequency of MTHFR C677T polymorphisms in couples with recurrent pregnancy loss and the impact of paternal polymorphisms of MTHFR C677T in recurrent pregnancy loss in population of couples living in Kolar district of Karnataka with RSA.

DESIGN

A total of 15 couples with a history of two or more unexplained RSA were enrolled as subjects in the study and a total of 15 couples with normal reproductive history, having two or more children and no history of miscarriages were enrolled as controls.

MATERIALS AND METHODS

DNA extraction from samples case and control group couples and its quantification by Agarose gel electrophoresis, assessment of DNA purity, MTHFR C 677T gene mutation detection by PCR-RFLP method.

STATISTICAL ANALYSIS

Carried out by web based online SPSS tool.

RESULTS

The frequency of C677T genotype showed homozygous wild type CC (80%), heterozygous CT type (13.3%) and homozygous mutation TT type (6.67%) observed in males. Similarly from female's homozygous wild type CC (86.6%), heterozygous type (13.3%), and homozygous type mutations TT (0%) was recorded. In couple control groups, we observed homozygous wild type CC (86.6%), heterozygous CT type (13.3%) and homozygous type mutations TT type (0%).

CONCLUSION

We noticed a high frequency of MTHFR specifically T allele associated with paternal side.Therefore, the present study indicated the impact of paternal gene polymorphism of MTHFR C677T on screening in couples with recurrent pregnancy loss.

Neural tube defects

Neural tube defects (NTDs), including spina bifida and anencephaly, are severe birth defects of the central nervous system that originate during embryonic development when the neural tube fails to close completely. Human NTDs are multifactorial, with contributions from both genetic and environmental factors. The genetic basis is not yet well understood, but several nongenetic risk factors have been identified as have possibilities for prevention by maternal folic acid supplementation. Mechanisms underlying neural tube closure and NTDs may be informed by experimental models, which have revealed numerous genes whose abnormal function causes NTDs and have provided details of critical cellular and morphological events whose regulation is essential for closure. Such models also provide an opportunity to investigate potential risk factors and to develop novel preventive therapies.

Maternal micronutrients, omega-3 fatty acids, and placental PPARγ expression

An altered one-carbon cycle is known to influence placental and fetal development. We hypothesize that deficiency of maternal micronutrients such as folic acid and vitamin B12 will lead to increased oxidative stress, reduced long-chain polyunsaturated fatty acids, and altered expression of peroxisome proliferator activated receptor (PPARγ) in the placenta, and omega-3 fatty acid supplementation to these diets will increase the expression of PPARγ. Female rats were divided into 5 groups: control, folic acid deficient, vitamin B12 deficient, folic acid deficient + omega-3 fatty acid supplemented, and vitamin B12 deficient + omega-3 fatty acid supplemented. Dams were dissected on gestational day 20. Maternal micronutrient deficiency leads to lower (p < 0.05) levels of placental docosahexaenoic acid, arachidonic acid, PPARγ expression and higher (p < 0.05) levels of plasma malonidialdehyde, placental IL-6, and TNF-α. Omega-3 fatty acid supplementation to a vitamin B12 deficient diet normalized the expression of PPARγ and lowered the levels of placental TNF-α. In the case of supplementation to a folic acid deficient diet it lowered the levels of malonidialdehyde and placental IL-6 and TNF-α. This study has implications for fetal growth as oxidative stress, inflammation, and PPARγ are known to play a key role in the placental development.

Folate deficiency during early-mid pregnancy affects the skeletal muscle transcriptome of piglets from a reciprocal cross

Folate deficiency (FD) during pregnancy can cause fetal intrauterine growth restriction in pigs, of which the skeletal dysplasia is a major manifestation. Factors influencing muscle development are very important in the formation of porcine meat quality trait. However, the effect of folate deficiency on skeletal muscle development and its molecular mechanisms are unknown. The objective of this study is to determine the effect of maternal folate deficiency on the skeletal muscle transcriptome of piglets from a reciprocal cross, in which full-sibling Landrace (LR) and full-sibling Chinese local breed Laiwu (LW) pigs were used for reciprocal cross matings, and sows were fed either a folate deficient or a normal diet during early-mid gestation. In addition, the difference in the responsiveness of the piglets to folate deficiency during early-mid pregnancy between reciprocal cross groups was investigated. Longissimus dorsi (LD) muscle samples were collected from newborn piglets and a 4 × 44K Agilent porcine oligo microarray was used for transcriptome analysis of porcine LD muscle. The results showed that folate deficiency during early-mid pregnancy affected piglet body weight, LD muscle fiber number and content of intramuscular triglyceride. The microarray results indicated that 3154 genes were differentially expressed between folate deficient and normal piglets from the LR♂ × LW♀ cross, and 3885 differentially expressed genes (DEGs) in the ones from the LW♂ × LR♀ cross. From functional analyses, sow folate deficiency affected almost all biological processes in the progeny. Lipid metabolism-related genes and associated metabolic pathways were regulated extensively by folate deficiency, especially in LR♂ × LW♀ cross piglets. Most of the genes that are regulated by folate deficiency in the LD muscle of piglets were different between LR♂ × LW♀ and LW♂ × LR♀ crosses, suggesting some epigenetic effects of FD exist in genes underlying myogenesis and intramuscular fat deposition in piglets.

Lessons from the one-carbon metabolism: passing it along to the next generation

During development, a fetus and its placenta must respond to a changing maternal environment to ensure normal growth is achieved and survival is maintained. The mechanisms behind developmental programming involve complex interactions between epigenetic and physiological processes, which are not well understood. Importantly, when programming goes awry, it puts the fetus at risk for disease later in life and may, in some instances, affect subsequent generations via epigenetic processes including DNA methylation. The one-carbon metabolism, which includes the folate, methionine and choline pathways, provides methyl groups necessary for DNA methylation and a normal epigenetic landscape. Accordingly, disruptions in this pathway affect placental development and function leading to altered fetal programming. Remarkably, recent studies have revealed that abnormal folate metabolism causes transgenerational effects probably through epigenetic inheritance. The epigenetic mechanisms behind this phenomenon are not well understood but they have important implications for the influence of the metabolic environment on epigenetic stability and non-genetic inheritance of disease. Importantly, there are increasing concerns that assisted reproductive technologies cause aberrant epigenetic profiles in embryos leading to abnormal fetal programming. How the negative epigenetic consequences of assisted reproduction treatment affect subsequent generations requires further investigation.

Mutation in folate metabolism causes epigenetic instability and transgenerational effects on development

The importance of maternal folate consumption for normal development is well established, yet the molecular mechanism linking folate metabolism to development remains poorly understood. The enzyme methionine synthase reductase (Mtrr) is necessary for utilization of methyl groups from the folate cycle. We found that a hypomorphic mutation of the mouse Mtrr gene results in intrauterine growth restriction, developmental delay, and congenital malformations, including neural tube, heart, and placental defects. Importantly, these defects were dependent upon the Mtrr genotypes of the maternal grandparents. Furthermore, we observed widespread epigenetic instability associated with altered gene expression in the placentas of wild-type grandprogeny of Mtrr-deficient maternal grandparents. Embryo transfer experiments revealed that Mtrr deficiency in mice lead to two distinct, separable phenotypes: adverse effects on their wild-type daughters' uterine environment, leading to growth defects in wild-type grandprogeny, and the appearance of congenital malformations independent of maternal environment that persist for five generations, likely through transgenerational epigenetic inheritance.

A novel mouse model for genetic variation in 10-formyltetrahydrofolate synthetase exhibits disturbed purine synthesis with impacts on pregnancy and embryonic development

Genetic variants in one-carbon folate metabolism have been identified as risk factors for disease because they may impair the production or use of one-carbon folates required for nucleotide synthesis and methylation. p.R653Q (1958G>A) is a single-nucleotide polymorphism (SNP) in the 10-formyltetrahydrofolate (formylTHF) synthetase domain of the trifunctional enzyme MTHFD1; this domain produces the formylTHF which is required for the de novo synthesis of purines. Approximately 20% of Caucasians are homozygous for the Q allele. MTHFD1 p.R653Q has been proposed as a risk factor for neural tube defects (NTDs), congenital heart defects (CHDs) and pregnancy losses. We have generated a novel mouse model in which the MTHFD1 synthetase activity is inactivated without affecting protein expression or the other activities of this enzyme. Complete loss of synthetase activity (Mthfd1S(-/-)) is incompatible with life; embryos die shortly after 10.5 days gestation, and are developmentally delayed or abnormal. The proportion of 10-formylTHF in the plasma and liver of Mthfd1S(+/-) mice is reduced (P < 0.05), and de novo purine synthesis is impaired in Mthfd1S(+/-) mouse embryonic fibroblasts (MEFs, P < 0.005). Female Mthfd1S(+/-) mice had decreased neutrophil counts (P < 0.05) during pregnancy and increased incidence of developmental defects in embryos (P = 0.052). These findings suggest that synthetase deficiency may lead to pregnancy complications through decreased purine synthesis and reduced cellular proliferation. Additional investigation of the impact of synthetase polymorphisms on human pregnancy is warranted.

Moderately high intake of folic acid has a negative impact on mouse embryonic development

BACKGROUND

The incidence of neural tube defects has diminished considerably since the implementation of food fortification with folic acid (FA). However, the impact of excess FA intake, particularly during pregnancy, requires investigation. In a recent study, we reported that a diet supplemented with 20-fold higher FA than the recommended intake for rodents had adverse effects on embryonic mouse development at embryonic days (E)10.5 and 14.5. In this report, we examined developmental outcomes in E14.5 embryos after administering a diet supplemented with 10-fold higher FA than recommended to pregnant mice with and without a mild deficiency of methylenetetrahydrofolate reductase (MTHFR).

METHODS

Pregnant mice with or without a deficiency in MTHFR were fed a control diet (recommended FA intake of 2 mg/kg diet for rodents) or an FA-supplemented diet (FASD; 10-fold higher than the recommended intake [20 mg/kg diet]). At E14.5, mice were examined for embryonic loss and growth retardation, and hearts were assessed for defects and for ventricular wall thickness.

RESULTS

Maternal FA supplementation was associated with embryonic loss, embryonic delays, a higher incidence of ventricular septal defects, and thinner left and right ventricular walls, compared to mothers fed control diet.

CONCLUSIONS

Our work suggests that even moderately high levels of FA supplementation may adversely affect fetal mouse development. Additional studies are warranted to evaluate the impact of high folate intake in pregnant women. Birth Defects Research (Part A), 2013. © 2012 Wiley Periodicals, Inc.

Low dietary folate and methylenetetrahydrofolate reductase deficiency may lead to pregnancy complications through modulation of ApoAI and IFN-γ in spleen and placenta, and through reduction of methylation potential

SCOPE

Genetic or nutritional disturbances in folate metabolism lead to hyperhomocysteinemia and adverse reproductive outcomes. Folate-dependent homocysteine remethylation is required for methylation reactions and may influence choline/betaine metabolism. Hyperhomocysteinemia has been suggested to play a role in inflammation. The goal of this study was to determine whether folate-related pregnancy complications could be due to altered expression of some inflammatory mediators or due to disturbances in methylation intermediates.

METHODS AND RESULTS

Pregnant mice with or without a deficiency of methylenetetrahydrofolate reductase (MTHFR) were fed control diets or folate-deficient (FD) diets; tissues were collected at embryonic day 14.5. FD decreased plasma phosphocholine and increased plasma glycerophosphocholine and lysophosphatidylcholine. Liver betaine, phosphocholine, and S-adenosylmethionine:S-adenosylhomocysteine ratios were reduced in FD. In liver, spleen, and placenta, the lowest levels of apolipoprotein AI (ApoAI) were observed in Mthfr(+/-) mice fed FD. Increased interferon-gamma (IFN-γ) was observed in spleen and placentae due to FD or Mthfr genotype. Plasma homocysteine correlated negatively with liver and spleen ApoAI, and positively with IFN-γ.

CONCLUSION

Low dietary folate or Mthfr deficiency during pregnancy may result in adverse pregnancy outcomes by altering expression of the inflammatory mediators ApoAI and IFN-γ in spleen and placenta. Disturbances in choline metabolism or methylation reactions may also play a role.

DNA methyltransferase 1 (Dnmt1) mutation affects Snrpn imprinting in the mouse male germ line

DNA methylation and DNA methyltransferases are essential for spermatogenesis. Mutations in the DNA methyltransferase Dnmt1 gene exert a paternal effect on epigenetic states and phenotypes of offspring, suggesting that DNMT1 is important for the epigenetic remodeling of the genome that takes place during spermatogenesis. However, the specific role of DNMT1 in spermatogenesis and the establishment of genomic imprints in the male germ line remains elusive. To further characterize the effect of DNMT1 deficiency on the resetting of methylation imprints during spermatogenesis, we analyzed the methylation profiles of imprinted regions in the spermatozoa of mice that were heterozygous for a Dnmt1 loss-of-function mutation. The mutation did not affect the H19 or IG differentially methylated regions (DMRs) that are usually highly methylated but led to a partial hypermethylation of the Snrpn DMR, a region that should normally be unmethylated in mature spermatozoa. This defect does not appear in mouse models with mutations in Dnmt3a and Mthfr genes and, therefore, it is specific for the Dnmt1 gene and is suggestive of a role of DNMT1 in imprint resetting or maintenance in the male germ line.

Disturbed one-carbon metabolism causing adverse reproductive outcomes in mice is associated with altered expression of apolipoprotein AI and inflammatory mediators PPARα, interferon-γ, and interleukin-10

Low dietary choline or deficiency of methylenetetrahydrofolate reductase (Mthfr) leads to hyperhomocysteinemia (Hhcy) and adverse reproductive outcomes. Homocysteine reduces synthesis of ApoAI, the major lipoprotein in HDL-cholesterol; ApoAI is regulated by PPARα and has antiinflammatory properties. Our aim was to determine whether pregnancy complications due to genetic or nutritional deficiencies in 1-carbon metabolism could relate to dysregulation of ApoAI and inflammatory mediators. We fed pregnant mice, with or without a deficiency of Mthfr, control or choline-deficient (ChDD) diets for 10-12 wk and examined levels of ApoAI, PPARα, IFNγ, and IL-10. ApoAI mRNA was reduced in livers of Mthfr(+/-) mice and ApoAI protein was reduced due to Mthfr deficiency or choline deficiency in liver and plasma. Placental ApoAI protein was also reduced due to Mthfr genotype or choline-deficient diet and in developmentally delayed embryos. Reduced liver PPARα expression (mRNA and protein) was observed in ChDD-fed mice and was associated with increased methylation of a CpG dinucleotide in its promoter. Hepatic IFNγ increased due to genotype, and placental IFNγ was higher in Mthfr(+/-) ChDD-fed dams compared to Mthfr(+/+) mice fed ChDD or Mthfr(+/-) mice fed CD. IL-10 was reduced in livers of ChDD-fed mice. We propose that a deficiency of dietary choline or Mthfr leads to Hhcy and reduced expression of maternal ApoAI, with reduced ApoAI transfer to embryo. Disturbances in 1-carbon metabolism also reduce maternal PPARα expression, possibly through promoter hypermethylation, and increase IFNγ and decrease IL-10 levels. This disturbance of the T helper (Th1) (IFNγ):Th2 (IL-10) ratio and the increase in inflammatory mediators may contribute to pregnancy complications.

Spatial and temporal expression of folate-related transporters and metabolic enzymes during mouse placental development

It is well understood that maternal folate deficiency can cause abnormal fetal development. However, the extent to which placental development and function are also dependent upon folate uptake and metabolism remains unclear. To understand which trophoblast cell types may be affected by folate deficiency or abnormal folate metabolism, we completed a comprehensive spatial and temporal protein expression analysis of folate receptor (Folr), folate transporters (proton-coupled folate receptor [Slc46a1 or PCFT] and reduced folate carrier-1 [Rfc1]) and folate metabolic enzymes (5,10-methylenetetrahydrofolate reductase [Mthfr] and methionine synthase [Mtr]) in histological sections of mouse placentas from early development (E8.5) until term (E18.5). We observed that the highest level of protein expression was during early development (E8.5-E10.5), prior to the formation of the three main layers of the mature placenta suggesting that folate uptake and metabolism may be required for placental development, itself. As expected, the labyrinth trophoblast cells, which are responsible for nutrient transport, expressed these proteins throughout pregnancy, including robust expression in the sinusoidal trophoblast giant cells that line the maternal blood spaces. Other trophoblast giant cell (TGC) subtypes (parietal-TGCs and canal-TGCs), whose function does not include nutrient transport, expressed folate transporters and enzymes from E8.5 onwards. Remarkably, these proteins were also detected in glycogen trophoblast cells from E12.5-E18.5 suggesting a new role in folate uptake and metabolism for these cells. Together, these data provide evidence that folate may be necessary for normal placental development and function, and perturbations in its availability or metabolism may lead to secondary effects on fetal development.

Solute Carrier Family 19, member 1 (SLC19A1) polymorphisms (-43T>C, 80G>A, and 696C>T), and haplotypes in idiopathic recurrent spontaneous abortion in a Korean population

The objective was to investigate the association between idiopathic recurrent spontaneous abortion (RSA) and 3 SLC19A1 polymorphisms (-43T>C, 80G>A, and 696C>T). DNA from 269 patients with RSA and 125 controls were genotyped for the 3 SLC19A1 single nucleotide polymorphisms (SNPs) by polymerase chain reaction-restriction fragment length polymorphism. Homocysteine and folate levels of 100 patients with RSA were available for analysis. The combination genotypes of SLC19A1 -43TC/80GG, -43TC/80AA, and -43CC/80GA; 80GA/696TT, 80AA/696CC; and -43TC/696CC were less frequent in patients with RSA compared to controls (P < .05 for each). The -43C/80A/696 T and -43T/80G/696C haplotypes were more frequent in patients than controls, whereas -43T/80A/696C, -43C/80A/696C, -43C/80G/696C, -43C/80G/696T, and -43T/80G/696T haplotypes were less frequent in patients (P < .05 for each). The -43T/80G and 80A/696T haplotypes were more frequent in patients, while -43T/80A, -43C/80G, 80A/696C, 80G/696T, and -43C/696C haplotypes occurred less frequently in patients (P < .05 for each). The associations between idiopathic RSA occurrence and SLC19A1 -43T>C/80G>A/696C>T polymorphisms were identified and can be developed as biomarkers for RSA risk.

Targeted insertion of two Mthfr promoters in mice reveals temporal- and tissue-specific regulation

Methylenetetrahydrofolate reductase (MTHFR), a key enzyme in folate metabolism, synthesizes 5-methyltetrahydrofolate, the main circulatory form of folate which is required for maintaining nontoxic levels of homocysteine and providing one-carbon units for methylation. A common 677C → T variant in MTHFR confers mild MTHFR deficiency and has been associated with a number of human disorders, including neural tube defects and vascular disease. Two promoters of Mthfr, designated as upstream and downstream promoters, are located upstream of a transcription start site cluster and have previously demonstrated cell-specific activities. In this study we used a unique approach for targeted, single-copy transgene insertion to generate transgenic mice carrying a Mthfr upstream or Mthfr downstream promoter-reporter construct located 5' to the endogenous Hprt (hypoxanthine-guanine phosphoribosyltransferase) locus. The Mthfr downstream promoter demonstrated activity in the neural tube, neural crest cells, dorsal root ganglia, heart, and endothelial cells of blood vessels in 10.5-days post coitum embryos and placentas. Upstream promoter activity was absent at this developmental stage. Postnatally, both promoters demonstrated activity in the brain stem, hippocampus, and thalamus of 1-week-old brain that became stronger in the adult. The Mthfr upstream promoter also showed activity in the cerebellum and cerebral cortex. Both promoters were active in male reproductive tissues, including 1-week-old epididymides, and there was upstream promoter-specific activity in the adult testis. Our investigation of Mthfr regulation in an in vivo mouse model revealed temporal- and tissue-specific regulation that supports important roles for MTHFR in the developing embryo, and in postnatal brain and male reproductive tissues.

The emerging role of epigenetic mechanisms in the etiology of neural tube defects

The molecular requirements for neural tube closure are complex. This is illustrated by the occurrence of neural tube defects (NTDs) in many genetic mouse mutants, which implicate a variety of genes, pathways and cellular functions. NTDs are also prevalent birth defects in humans, affecting around 1 per 1000 pregnancies worldwide. In humans the causation is thought to involve the interplay of fetal genes and the effect of environmental factors. Recent studies on the aetiology of human NTDs, as well as analysis of mouse models, have raised the question of the possible involvement of epigenetic factors in determining susceptibility. A consideration of potential causative factors in human NTDs must now include both alterations in the regulation of gene expression, through mutation of promoter or regulatory elements, and the additional analysis of epigenetic regulation. Alterations in the epigenetic status can be directly modified by various environmental insults or maternal dietary factors.

Supplementation with apple juice can compensate for folate deficiency in a mouse model deficient in methylene tetrahydrofolate reductase activity

Folate insufficiency promotes developmental as well as age-related disorders of the nervous system. The C677T variant of 5',10' methylene tetrahydrofolate reductase (MTHFR; which utilizes folate to regenerate methionine from homocysteine) displays reduced activity, and therefore promotes functional folate deficiency. Mice heterozygously lacking this gene (MTHFR+/- mice) represent a useful model for analysis of the impact of MTHFR deficiency and potential compensatory approaches. Since consumption of apple products has benefited mouse models subjected to dietary and/or genetically-induced folate deficiency, we compared the impact of supplementation with apple juice on cognitive and neuromuscular performance of mice MTHFR+/+ and +/- mice with and without dietary folate deficiency. Mice were maintained for 1 month on a standard, complete diet, or a challenge diet lacking folate, and vitamin E and containing a 50 g iron/500 g total diet as a pro-oxidant. Additional groups received apple juice concentrate (AJC) diluted to 0.5% (vol/vol) in their sole source of drinking water. MTHFR+/- mice demonstrated significantly impaired cognitive performance in standard reward-based T maze and the non-reward-based Y maze tests as compared to MTHFR+/+ when maintained on the complete diet; supplementation with AJC improved the performance of MTHFR+/- to the level observed for MTHFR+/+ mice. Maintenance for 1 month on the deficient diet reduced the performance of both genotypes in both tests, but supplementation with AJC prevented these reductions. MTHFR+/+ and +/- displayed virtually identical neuromuscular performance in the standard paw grip endurance test when maintained on the complete diet, and displayed similar, non-significant declines in performance when maintained on the deficient diet. Supplementation of either diet with AJC dramatically improved the performance of both genotypes. The findings presented herein indicate that supplementation with AJCs can compensate for genetic as well as dietary insufficiency in folate in a murine model of genetic folate compromise, and support the notion that dietary supplementation may be more critical under conditions of latent genetic compromise.

Complete deficiency of methylenetetrahydrofolate reductase in mice is associated with impaired retinal function and variable mortality, hematological profiles, and reproductive outcomes

Severe deficiency of methylenetetrahydrofolate reductase (MTHFR) with homocystinuria can result in early demise or later-onset neurological impairment, including developmental delay, motor dysfunction, and seizures. We previously characterized BALB/c Mthfr (-/-)mice as a model for this disorder and have recently backcrossed the disrupted allele onto the C57Bl/6 background to examine the variable phenotypes in MTHFR deficiency. Compared with BALB/c Mthfr (-/-)mice, C57Bl/6 Mthfr (-/-)mice have enhanced survival rates (81% vs 26.5%). Four-day-old BALB/c mutant pups had lower body, brain, and spleen weights relative to their wild-type counterparts compared with C57Bl/6 mutants. Pregnant BALB/c Mthfr (+/-)mice had increased resorptions and embryonic delays compared with wild-type littermates, whereas these outcomes in C57Bl/6 c Mthfr (+/-)mice were similar to those of wild-type C57Bl/6 mice. BALB/c-mutant pups had altered hematological profiles (higher hematocrit, hemoglobin, and white blood cell counts, with lower platelet counts) compared with C57Bl/6 mutants. Mutants of both strains had similar degrees of hepatic steatosis, hepatic activity of betaine:homocysteine methyltransferase, and altered cerebellar histology. Electroretinograms (ERG) in C57Bl/6 Mthfr (-/-)mice revealed decreased amplitude of scotopic and photopic waves in 6-week-old mice, with normalized ERGs at 13 weeks. Plasma homocysteine was modestly higher in C57Bl/6 compared with BALB/c mice. Our results emphasize the variable presentation of MTHFR deficiency in different genetic backgrounds and suggest that plasma homocysteine is not a predictor of severity. In addition, our novel findings of decreased spleen weights, thrombocytopenia, and impaired retinal function warrant investigation in patients with severe MTHFR deficiency or other forms of homocystinuria.

Homocysteine is transported by the microvillous plasma membrane of human placenta

Elevated maternal plasma concentrations of homocysteine (Hcy) are associated with pregnancy complications and adverse neonatal outcomes. The postulate that we wish to advance here is that placental transport of Hcy, by competing with endogenous amino acids for transporter activity, may account for some of the damaging impacts of Hcy on placental metabolism and function as well as fetal development. In this article, we provide an overview of some recent studies characterising the transport mechanisms for Hcy across the microvillous plasma membrane (MVM) of the syncytiotrophoblast, the transporting epithelium of human placenta. Three Hcy transport systems have been identified, systems L, A and y(+)L. This was accomplished using a strategy of competitive inhibition to investigate the effects of Hcy on the uptake of well-characterised radiolabelled substrates for each transport system into isolated MVM vesicles. The reverse experiments were also performed, examining the effects of model substrates on [³⁵S]L-Hcy uptake. This article describes the evidence for systems L, A and y(+)L involvement in placental Hcy transport and discusses the physiological implications of these findings with respect to placental function and fetal development.

Homocysteine in pregnancy

The aim of this review is to evaluate the evidence for and against fasting plasma total homocysteine (tHcy) as a biomarker/risk factor of impaired reproductive function before and during pregnancy. Apart from nutritional and lifestyle factors, tHcy is also influenced by physiological factors specific to pregnancy such as hemodilution, increased glomerular filtration rate, and endocrinological changes. These lead to a considerable reduction under normal circumstances in tHcy by midpregnancy. Stimulating excess endogenous homocysteine production before and during pregnancy in animal experiments and adding exogenous homocysteine to cell cultures result in the impairment of reproductive and developmental processes from preconception throughout pregnancy and during subsequent development of the offspring. Different studies have confirmed that elevated tHcy is a risk factor for subfertility, congenital developmental defects, preeclampsia, and intrauterine growth retardation. There is conflicting evidence that elevated tHcy is a risk factor for miscarriage, gestational diabetes, premature rupture of the membranes, placental abruption, and offspring with Down syndrome. Prospective, sufficiently powered, studies from preconception/early pregnancy are required to determine whether tHcy is a risk factor for these pregnancy complications.

High intake of folic acid disrupts embryonic development in mice

BACKGROUND

Folic acid fortification and supplementation has increased folate intake and blood folate concentrations and successfully reduced the incidence of neural tube defects. However, the developmental consequences of high folate intake are unknown. This study investigated the impact of high folate intake, alone or with methylenetetrahydrofolate reductase (MTHFR) deficiency, on embryonic and placental development in mice.

METHODS

Mthfr +/+ or +/- pregnant mice on a control diet (CD; recommended intake of folic acid for rodents) or folic acid-supplemented diet (FASD; 20-fold higher than the recommended intake) were examined for embryonic loss, delay, and defects at 10.5 and 14.5 days post coitum (dpc); 10.5-dpc placenta, and 14.5-dpc embryo hearts were studied histologically.

RESULTS

Total plasma folate was 10-fold higher in FASD compared to CD mice; plasma homocysteine levels were not affected by diet. At 10.5 dpc, the FASD was associated with embryonic delay and growth retardation, and may confer susceptibility to embryonic defects. The FASD did not adversely affect 10.5-dpc placental development. At 14.5 dpc, embryos from the FASD Mthfr +/+ group were delayed and the FASD was associated with thinner ventricular walls in embryonic hearts. There was a significant interaction between maternal MTHFR deficiency and a high folate diet for several developmental outcomes.

CONCLUSIONS

Our study suggests that high folate intake may have adverse effects on fetal mouse development and that maternal MTHFR deficiency may improve or rescue some of the adverse outcomes. These findings underscore the need for additional studies on the potential negative impact of high folate intake during pregnancy.