Effect of elevated homocysteine on cardiac neural crest migration in vitro

Deciphering the enigma of the function of alpha-tocopherol as a vitamin

α-Tocopherol (α-T) is a vitamin, but the reasons for the α-T requirement are controversial. Given that α-T deficiency was first identified in embryos, we studied to the premier model of vertebrate embryo development, the zebrafish embryo. We developed an α-T-deficient diet for zebrafish and used fish consuming this diet to produce α-T deficient (E-) embryos. We showed that α-T deficiency causes increased lipid peroxidation, leading to metabolic dysregulation that impacts both biochemical and morphological changes at very early stages in development. These changes occur at an early developmental window, which takes place prior to an analogous time to when a human knows she is pregnant. We found that α-T limits the chain reaction of lipid peroxidation and protects metabolic pathways and integrated gene expression networks that control embryonic development. Importantly, not only is α-T critical during early development, but the neurodevelopmental process is highly dependent on α-T trafficking by the α-T transfer protein (TTPa). Data from both gene expression and evaluation of the metabolome in E- embryos suggest that the activity of the mechanistic Target of Rapamycin (mTOR) signaling pathway is dysregulated-mTOR is a master regulatory mechanism, which controls both metabolism and neurodevelopment. Our findings suggest that TTPa is needed not only for regulation of plasma α-T in adults but is a key regulator during embryogenesis.

Expanding role of vitamin E in protection against metabolic dysregulation: Insights gained from model systems, especially the developing nervous system of zebrafish embryos

This review discusses why the embryo requires vitamin E (VitE) and shows that its lack causes metabolic dysregulation and impacts morphological changes at very early stages in development, which occur prior to when a woman knows she is pregnant. VitE halts the chain reactions of lipid peroxidation (LPO). Metabolomic analyses indicate that thiols become depleted in E- embryos because LPO generates products that require compensation using limited amino acids and methyl donors that are also developmentally relevant. Thus, VitE protects metabolic networks and the integrated gene expression networks that control development. VitE is critical especially for neurodevelopment, which is dependent on trafficking by the α-tocopherol transfer protein (TTPa). VitE-deficient (E-) zebrafish embryos initially appear normal, but by 12 and 24 h post-fertilization (hpf) E- embryos are developmentally abnormal with expression of pax2a and sox10 mis-localized in the midbrain-hindbrain boundary, neural crest cells and throughout the spinal neurons. These patterning defects indicate cells that are especially in need of VitE-protection. They precede obvious morphological abnormalities (cranial-facial malformation, pericardial edema, yolksac edema, skewed body-axis) and impaired behavioral responses to locomotor activity tests. The TTPA gene (ttpa) is expressed at the leading edges of the brain ventricle border. Ttpa knockdown using morpholinos is 100% lethal by 24 hpf, while E- embryo brains are often over- or under-inflated at 24 hpf. Further, E- embryos prior to 24 hpf have increased expression of genes involved in glycolysis and the pentose phosphate pathway, and decreased expression of genes involved in anabolic pathways and transcription. Combined data from both gene expression and the metabolome in E- embryos at 24 hpf suggest that the activity of the mechanistic Target of Rapamycin (mTOR) signaling pathway is decreased, which may impact both metabolism and neurodevelopment. Further evaluation of VitE deficiency in neurogenesis and its subsequent impact on learning and behavior is needed.

Structure, Function, and Pharmacology of Glutamate Receptor Ion Channels

Many physiologic effects of l-glutamate, the major excitatory neurotransmitter in the mammalian central nervous system, are mediated via signaling by ionotropic glutamate receptors (iGluRs). These ligand-gated ion channels are critical to brain function and are centrally implicated in numerous psychiatric and neurologic disorders. There are different classes of iGluRs with a variety of receptor subtypes in each class that play distinct roles in neuronal functions. The diversity in iGluR subtypes, with their unique functional properties and physiologic roles, has motivated a large number of studies. Our understanding of receptor subtypes has advanced considerably since the first iGluR subunit gene was cloned in 1989, and the research focus has expanded to encompass facets of biology that have been recently discovered and to exploit experimental paradigms made possible by technological advances. Here, we review insights from more than 3 decades of iGluR studies with an emphasis on the progress that has occurred in the past decade. We cover structure, function, pharmacology, roles in neurophysiology, and therapeutic implications for all classes of receptors assembled from the subunits encoded by the 18 ionotropic glutamate receptor genes. SIGNIFICANCE STATEMENT: Glutamate receptors play important roles in virtually all aspects of brain function and are either involved in mediating some clinical features of neurological disease or represent a therapeutic target for treatment. Therefore, understanding the structure, function, and pharmacology of this class of receptors will advance our understanding of many aspects of brain function at molecular, cellular, and system levels and provide new opportunities to treat patients.

Vitamin E is necessary for zebrafish nervous system development

Vitamin E (VitE) deficiency results in embryonic lethality. Knockdown of the gene ttpa encoding for the VitE regulatory protein [α-tocopherol transfer protein (α-TTP)] in zebrafish embryos causes death within 24 h post-fertilization (hpf). To test the hypothesis that VitE, not just α-TTP, is necessary for nervous system development, adult 5D strain zebrafish, fed either VitE sufficient (E+) or deficient (E-) diets, were spawned to obtain E+ and E- embryos, which were subjected to RNA in situ hybridization and RT-qPCR. Ttpa was expressed ubiquitously in embryos up to 12 hpf. Early gastrulation (6 hpf) assessed by goosecoid expression was unaffected by VitE status. By 24 hpf, embryos expressed ttpa in brain ventricle borders, which showed abnormal closure in E- embryos. They also displayed disrupted patterns of paired box 2a (pax2a) and SRY-box transcription factor 10 (sox10) expression in the midbrain-hindbrain boundary, spinal cord and dorsal root ganglia. In E- embryos, the collagen sheath notochord markers (col2a1a and col9a2) appeared bent. Severe developmental errors in E- embryos were characterized by improper nervous system patterning of the usually carefully programmed transcriptional signals. Histological analysis also showed developmental defects in the formation of the fore-, mid- and hindbrain and somites of E- embryos at 24 hpf. Ttpa expression profile was not altered by the VitE status demonstrating that VitE itself, and not ttpa, is required for development of the brain and peripheral nervous system in this vertebrate embryo model.

Temperature-activated ion channels in neural crest cells confer maternal fever-associated birth defects

Birth defects of the heart and face are common, and most have no known genetic cause, suggesting a role for environmental factors. Maternal fever during the first trimester is an environmental risk factor linked to these defects. Neural crest cells are precursor populations essential to the development of both at-risk tissues. We report that two heat-activated transient receptor potential (TRP) ion channels, TRPV1 and TRPV4, were present in neural crest cells during critical windows of heart and face development. TRPV1 antagonists protected against the development of hyperthermia-induced defects in chick embryos. Treatment with chemical agonists of TRPV1 or TRPV4 replicated hyperthermia-induced birth defects in chick and zebrafish embryos. To test whether transient TRPV channel permeability in neural crest cells was sufficient to induce these defects, we engineered iron-binding modifications to TRPV1 and TRPV4 that enabled remote and noninvasive activation of these channels in specific cellular locations and at specific developmental times in chick embryos with radio-frequency electromagnetic fields. Transient stimulation of radio frequency-controlled TRP channels in neural crest cells replicated fever-associated defects in developing chick embryos. Our data provide a previously undescribed mechanism for congenital defects, whereby hyperthermia activates ion channels that negatively affect fetal development.

Effects of Folic Acid and Homocysteine on the Morphogenesis of Mouse Cephalic Neural Crest Cells In Vitro

Folate deficiency and hyperhomocysteinemia have long been associated with developmental anomalies, particularly neural tube defects and neurocristopathies-a group of diverse disorders that result from defective growth, differentiation, and migration of neural crest (NC) cells. However, the exact mechanisms by which homocysteine (Hcys) and/or folate deficiencies disrupt NC development are still poorly understood in mammals. In this work, we employed a well-defined culture system to investigate the effects of Hcys and folic acid (FA) supplementation on the morphogenetic processes of murine NC cells in vitro. We demonstrated that Hcys increases outgrowth and proliferation of cephalic NC cells and impairs their differentiation into smooth muscle cells. In addition, we showed that FA alone does not directly affect the developmental dynamics of the cephalic NC cells but is able to prevent the Hcys-induced effects. Our results, therefore, suggest that elevated Hcys levels per se cause dysmorphogenesis of the cephalic NC and might contribute to neurocristopathies in mammalian embryos.

5-Mehtyltetrahydrofolate rescues alcohol-induced neural crest cell migration abnormalities

Background

Alcohol is detrimental to early development. Fetal alcohol spectrum disorders (FASD) due to maternal alcohol abuse results in a series of developmental abnormalities including cranial facial dysmorphology, ocular anomalies, congenital heart defects, microcephaly and intellectual disabilities. Previous studies have been shown that ethanol exposure causes neural crest (NC) apoptosis and perturbation of neural crest migration. However, the underlying mechanism remains elusive. In this report we investigated the fetal effect of alcohol on the process of neural crest development in the Xenopus leavis.

Results

Pre-gastrulation exposure of 2-4% alcohol induces apoptosis in Xenopus embryo whereas 1% alcohol specifically impairs neural crest migration without observing discernible apoptosis. Additionally, 1% alcohol treatment considerably increased the phenotype of small head (43.4% ± 4.4%, total embryo n = 234), and 1.5% and 2.0% dramatically augment the deformation to 81.2% ± 6.5% (n = 205) and 91.6% ± 3.0% (n = 235), respectively (P < 0.05). Significant accumulation of Homocysteine was caused by alcohol treatment in embryos and 5-mehtyltetrahydrofolate restores neural crest migration and alleviates homocysteine accumulation, resulting in inhibition of the alcohol-induced neurocristopathies.

Conclusions

Our study demonstrates that prenatal alcohol exposure causes neural crest cell migration abnormality and 5-mehtyltetrahydrofolate could be beneficial for treating FASD.

The N-methyl-d-aspartate receptor in heart development: a gene knockdown model using siRNA

Antagonists of the N-methyl-d-aspartate receptor (NMDAR) may disrupt the development of the cardiac neural crest (CNC) and contribute to conotruncal heart defects. To test this interaction, a loss-of-function model was generated using small interfering RNAs (siRNA) directed against the critical NR1-subunit of this receptor in avian embryos. The coding sequence of the chicken NR1 gene and predicted protein sequences were characterized and found to be homologous with other vertebrate species. Analysis of its spatiotemporal expression demonstrated its expression within the neural tube at pre-migratory CNC sites. siRNA targeted to the NR1-mRNA in pre-migratory CNC lead to a significant decrease in NR1 protein expression. However, embryo survival and heart development were not adversely affected. These results indicate that the CNC may function normally in the absence of functional NMDAR, and that NMDAR antagonists may have a complex impact upon the CNC that transcends impairment of a single receptor type.

Can we prevent diabetic birth defects with micronutrients?

Congenital malformations are more common in infants of diabetic women than in children of non-diabetic women. The mechanisms behind diabetes-induced congenital anomalies are not known. Disturbed micronutrient metabolism, in concert with oxidative stress, has been suggested as a cause of diabetes-induced malformations by several studies. In experimental work, administration of inositol, arachidonic acid and several antioxidative compounds, as well as folic acid, to the embryo, has proven to attenuate the teratogenic effects of a diabetic environment. Future therapeutic efforts may include supplementation with antioxidants or micronutrients, such as folic acid, to the pregnant diabetic woman, although exact compounds and doses need to be determined.

Homocysteine enhances cardiac neural crest cell attachment in vitro by increasing intracellular calcium levels

Elevated homocysteine (Hcys) increases the risk of neurocristopathies. Previous studies show Hcys inhibits neural crest (NC) cell migration in vivo. However, the mechanisms responsible for this effect are unknown. Here, we evaluated the effect of Hcys on NC cell attachment in vitro and determined if any of the effects were due to altered Ca2+ signaling. We found Hcys enhanced NC cell attachment in a dose and substrate-dependent manner. Ionomycin mimicked the effect of Hcys while BAPTA-AM and 2-APB blocked the effect of Hcys on NC attachment. In contrast, inhibitors of plasma membrane Ca2+ channels had no effect on NC attachment. Hcys also increased the emission of the intracellular Ca2+-sensitive probe, Fluo-4. These results show Hcys alters NC attachment by triggering an increase in intracellular Ca2+ possibly by generating inositol triphosphate. Hence, the teratogenic effect ascribed to Hcys may be due to perturbation of intracellular Ca2+ signaling.

Maternal intake of fat, riboflavin and nicotinamide and the risk of having offspring with congenital heart defects

BACKGROUND

With the exception of studies on folic acid, little evidence is available concerning other nutrients in the pathogenesis of congenital heart defects (CHDs). Fatty acids play a central role in embryonic development, and the B-vitamins riboflavin and nicotinamide are co-enzymes in lipid metabolism.

AIM OF THE STUDY

To investigate associations between the maternal dietary intake of fats, riboflavin and nicotinamide, and CHD risk in the offspring.

METHODS

A case-control family study was conducted in 276 mothers of a child with a CHD comprising of 190 outflow tract defects (OTD) and 86 non-outflow tract defects (non-OTD) and 324 control mothers of a non-malformed child. Mothers filled out general and food frequency questionnaires at 16 months after the index-pregnancy, as a proxy of the habitual food intake in the preconception period. Nutrient intakes (medians) were compared between cases and controls by Mann-Whitney U test. Odds ratios (OR) for the association between CHDs and nutrient intakes were estimated in a logistic regression model.

RESULTS

Case mothers, in particular mothers of a child with OTD, had higher dietary intakes of saturated fat, 30.9 vs. 29.8 g/d; P < 0.05. Dietary intakes of riboflavin and nicotinamide were lower in mothers of a child with an OTD than in controls (1.32 vs. 1.41 mg/d; P < 0.05 and 14.6 vs. 15.1 mg/d; P < 0.05, respectively). Energy, unsaturated fat, cholesterol and folate intakes were comparable between the groups. Low dietary intakes of both riboflavin (<1.20 mg/d) and nicotinamide (<13.5 mg/d) increased more than two-fold the risk of a child with an OTD, especially in mothers who did not use vitamin supplements in the periconceptional period (OR 2.4, 95%CI 1.4-4.0). Increasing intakes of nicotinamide (OR 0.8, 95%CI 0.7-1.001, per unit standard deviation increase) decreased CHD risk independent of dietary folate intake.

CONCLUSIONS

A maternal diet high in saturated fats and low in riboflavin and nicotinamide seems to contribute to CHD risk, in particular OTDs.

Microarray analysis of homocysteine-responsive genes in cardiac neural crest cells in vitro

The amino acid homocysteine increases in the serum when there is insufficient folic acid or vitamin B(12), or with certain mutations in enzymes important in methionine metabolism. Elevated homocysteine is related to increased risk for cardiovascular and other diseases in adults and elevated maternal homocysteine increases the risk for certain congenital defects, especially those that result from abnormal development of the neural crest and neural tube. Experiments with the avian embryo model have shown that elevated homocysteine perturbs neural crest/neural tube migration in vitro and in vivo. Whereas there have been numerous studies of homocysteine-induced changes in gene expression in adult cells, there is no previous report of a homocysteine-responsive transcriptome in the embryonic neural crest. We treated neural crest cells in vitro with exogenous homocysteine in a protocol that induces significant changes in neural crest cell migration. We used microarray analysis and expression profiling to identify 65 transcripts of genes of known function that were altered by homocysteine. The largest set of effected genes (19) included those with a role in cell migration and adhesion. Other major groups were genes involved in metabolism (13); DNA/RNA interaction (11); cell proliferation/apoptosis (10); and transporter/receptor (6). Although the genes identified in this experiment were consistent with prior observations of the effect of homocysteine upon neural crest cell function, none had been identified previously as response to homocysteine in adult cells.

Failure of homocysteine to induce neural tube defects in a mouse model

BACKGROUND

Folate deficiencies have been associated with many adverse congenital abnormalities. It is not clear, however, whether these defects are due to a folate deficiency or to an increase in homocysteine. Homocysteine has been shown to be teratogenic in the chicken-embryo model and it has been suggested that homocysteine-induced defects are mediated by inhibiting the N-methyl-D-aspartate (NMDA) receptor on neural crest cells. The majority of the teratology studies have been carried out using the chicken embryo model. In an effort to develop a murine model of homocysteine-induced neural tube defects, several inbred mouse strains were treated with homocysteine or the NMDA inhibitor MK801 and the fetuses examined for any induced-NTD.

METHODS

Several in-bred mouse strains were administered homocysteine once on gestational day (GD) E8.5 or once daily on GD 6.5-10.5. Additionally, because homocysteine was been reported to mediate its effects through the NMDA receptor, the effect of MK801, an antagonist of this receptor, was also investigated.

RESULTS

Regardless of the mouse treatment time, homocysteine failed to induce neural tube defects in our in-bred mouse strains. Homocysteine also failed to increase the number of neural tube defects in the splotch strain, regardless of the genotype.

CONCLUSIONS

Irrespective of the mouse strain or treatment, homocysteine failed to induce neural tube defects in our mouse models, which is in contrast to what has been reported in the chicken embryo models.

The expression of the NR1-subunit of the NMDA receptor during mouse and early chicken development

It has been suggested that homocysteine-induced defects are mediated by the inhibition of the N-methyl-d-aspartate (NMDA) receptor on neural crest cells. However, the majority of this work has been performed using the chicken embryo model. In an effort to better understand the molecular events involved a murine model of homocysteine-induced defects was sought. However, it has been previously shown that homocysteine failed to induce congenital defects in several strains of mouse. Therefore, in an effort to better understand the difference in the susceptibility between these two species we investigated the ontogeny of the NMDA receptor in the mouse and chicken. To determine the expression of the NMDA receptor we performed Western blot analysis using an antibody to the NR1-subunit of the NMDA receptor in both the chicken and mouse embryos. Further, we used RT-PCR to determine the temporal expression of this subunit in the murine embryos from gestational day 8.5 to 18.5 to confirm our Western blot analysis. Results from these studies demonstrated that the expression of the NMDA receptor was expressed during the early stages of development in the chick embryo but neither the transcript nor the protein was detected in mouse embryos until later in development. These results demonstrate that during the stages of neurulation and/or early heart development the expression of the NR1-subunit of the NMDA receptor was not detected. The expression of this gene increased and was detectable by gestational days 14.5-15.5 and continued to increase in its expression until term. Therefore, these experiments suggest that homocysteine-induced defects may be mediated via the NMDA receptor.

Connexin43 levels are increased in mouse neural crest cells exposed to homocysteine

BACKGROUND

Elevated homocysteine levels during embryonic development can result in neural tube and cardiovascular defects. The mechanisms that underlie the toxic effect of homocysteine are largely unknown.

METHODS

We cultured mouse neural tube explants to study the effects of homocysteine on the migratory behavior of neural crest cells and on the levels of the gap junction protein Connexin43 (Cx43) and the actin- and Cx43-interacting protein ZO-1.

RESULTS

Homocysteine exposure resulted in a significantly augmented maximal migration distance (MMD). The level of Cx43 immunolabeling was 2 times higher in the cytoplasm and cell protrusions of neural crest cells in homocysteine-treated cultures than in control cultures. Furthermore, colocalization of Cx43 and ZO-1 was increased in neural crest cell protrusions by this treatment.

CONCLUSION

Increased Cx43 levels were previously shown to result in abnormal embryonic development. Our data raises the hypothesis that the embryotoxic effects of homocysteine may be mediated in part by its effects on Cx43 expression level and gap junction function in neural crest cells.

Cardiac neural crest

Neural crest cells (NCCs) contribute to many organs and tissues during embryonic development. Amongst these, the cardiovascular system represents a fascinating example. In this review, recent advances in our understanding of the developmental biology and molecular genetics regulating cardiac NCC maturation will be summarized. While the existence of a significant neural crest (NC) contribution to the developing heart has been appreciated for more than 20 years, only in the last few years have molecular pathways regulating this process been elucidated and the significant contribution of these mechanisms to the etiology of congenital heart disease in man become apparent. Emerging data suggest that ongoing studies will reveal complex inductive interactions between cardiac NC and a series of other cell types contributing to the developing cardiovascular system.

Do maternal folate and homocysteine levels play a role in neurodevelopmental processes that increase risk for schizophrenia?

OBJECTIVE

Evidence from many different lines of research supports the hypothesis that schizophrenia is a disorder of development with etiological factors implicated as early as the second trimester in utero. We suggest that low maternal folate, acting to increase homocysteine levels, may provide a functional link between many of the identified prenatal risk factors and the hypothesized mechanisms whereby neurodevelopmental patterning deviates toward a schizophrenic potential.

METHODS

PubMed was searched from the present back to 1963, when elevated homocysteine was identified as a pathogen in homocystinuria as first described by Carson and colleagues (Arch Dis Child 1963;38:425-36). All articles for homocystinuria, homocysteine, folate, and development with schizophrenia were evaluated.

RESULTS

The findings from this review support the hypothesis that maternal low folate and high homocysteine levels may provide a potential teratogenic mechanism that increases the risk for developing schizophrenia.

CONCLUSION

The potential role of maternal folate deficiency and hyperhomocystinemia in the genesis of schizophrenia would extend the range of their known teratogenic effects. Given the potential for preventive treatment offered by this hypothesis, we believe further investigation into this mechanism is warranted.

Effects of trichloroethylene and its metabolite trichloroacetic acid on the expression of vimentin in the rat H9c2 cell line

Trichloroethylene (TCE) and its metabolite trichloroacetic acid (TCAA) are environmental contaminants with specific toxicity for the embryonic heart. In an effort to identify the cellular pathways disrupted by TCE and TCAA during heart development, we investigated their effects on expression of vimentin, a marker of cardiac differentiation. Previous studies had shown that the level of vimentin transcript was inhibited in rat embryonic heart after maternal exposure to TCE via drinking water. In the same study, maternal exposure to TCAA produced the opposite effect, inducing an increased level of vimentin mRNA. In this study, we selected an in vitro system, the rat cardiac myoblast cell line H9c2, to further characterize the molecular mechanisms used by TCE and TCAA to disrupt normal heart development. In particular, we investigated the effects of both toxicants on vimentin, at both the RNA and protein levels, using dose-response and time course curves. Our experimental findings indicate that vimentin expression is affected by TCE and TCAA in H9c2 cells similarly as in vivo. The work is significant because it provides a suitable in vitro model for studies looking at toxicant effects on myocardiac cells, and it suggests that vimentin is a good marker of TCE exposure in the embryonic heart.

The High Atherosclerotic Risk Among Epileptics: the Atheroprotective Role of Multivitamins

Neurologists have little concern about the high atherosclerotic risk among epileptics. Recent evidences mount that chronic epilepsy and prolonged use of antiepileptic drugs (AEDs) are associated with multiple risk factors that are critically implicated in pathobiology and dysfunction of the vessel wall through complex molecular mechanisms that promote atherogenesis. This review is concerned with three metabolic alterations, which are attributed as major risk factors for atherosclerosis among epileptics: altered metabolism of a) homocysteine (Hcy), b) lipids and lipoproteins, and c) uric acid. Most conventional AEDs reduce folic acid levels, thereby raising Hcy levels. Hyperhomosysteinemia is recently believed to induce endothelial dysfunction and promote atherosclerosis through complex oxidative and excitatory neurotoxic molecular mechanisms. However, Hcy itself is a convulsing substance with increased seizure recurrence and intractability to antiepileptic medications. AEDs can disturb lipid metabolism with resultant hypercholestrolemia and dyslipidemia, common recognized risks for atherosclerosis. Altered uric acid metabolism is common among epileptics. Uric acid has been implicated in endothelial cell damage and decreased endothelial nitric oxide bioavailability. In the presence of atherosclerotic milieu, uric acid interacts with other substrate toxicities and increased reactive oxygen species, accelerating atherosclerosis. The above information forms the rationale for future routine screening and correction of such metabolic alterations in epileptics. A convincing argument now develops that routine polyvitamin supplementation (folic acid, vitamin B12, vitamin B6, vitamin C, vitamin E, and beta-carotene) becomes increasingly important for women and men receiving AEDs at all ages. The atheroprotective effect of multivitamins is through their antioxidant and anti-inflammatory effects together with their lipid and Hcy lowering effects.

Folic acid and homocysteine affect neural crest and neuroepithelial cell outgrowth and differentiation in vitro

The beneficial effect of additional folic acid in the periconceptional period to prevent neural tube defects, orofacial clefts, and conotruncal heart defects in the offspring has been shown. Folate shortage results in homocysteine accumulation. Elevated levels of homocysteine have been related to neural tube defects. We studied the behavior of neuroepithelial cells and cranial and cardiac neural crest cells in vitro. Neural tube explants were cultured for 24 and 48 hr in medium after addition of folic acid and/or homocysteine. Folic acid addition increased neuroepithelial cell outgrowth and increased neural crest cell differentiation into nerve and smooth muscle cells. Addition of homocysteine increased neural crest cell outgrowth and migration from the neural tube and inhibited neural crest cell differentiation. Our findings suggest that neural tube defects caused by folate deficiency and hyperhomocysteinemia develop due to increased neuroepithelial to neural crest cell transformation. This increased transformation leads to a shortage of neuroepithelial cells in the neural tube. Defects in orofacial and conotruncal development are explained by abnormal differentiation of neural crest cells in the presence of high homocysteine concentrations. Our findings supports a critical role for folic acid and homocysteine in the development of neural tube defects and neural crest related heart malformations.

Nutrient-gene interactions in early pregnancy: a vascular hypothesis

It is hypothesized that the following periconceptional and early pregnancy nutrient-gene interactions link vascular-related reproductive complications and cardiovascular diseases in adulthood: (1) Maternal and paternal genetically controlled nutrient status affects the quality of gametes and fertilization capacity; (2) The embryonic genetic constitution, derived from both parents, and the maternal genetically controlled nutrient environment determine embryogenesis and fetal growth; (3) Trophoblast invasion of decidua and spiral arteries is driven by genes derived from both parents as well as by maternal nutritional factors; (4) Angiogenesis, vasculogenesis and vascular function are dependent on the genetic constitution of the embryo, derived from both parents, and the maternal genetically controlled nutritional environment.Early intra-uterine programming of vessels may concern the same (in)dependent determinants of vascular-related complications during pregnancy and cardiovascular diseases in later life.

Homocysteine inhibits cardiac neural crest cell formation and morphogenesis in vivo

Elevated homocysteine increases the risk of neurocristopathies. Here, we determined whether elevating homocysteine altered the proliferation or number of chick neural crest cells that form between the midotic and third somite in vivo. Homocysteine increased the number of neural tube cells but decreased neural crest cell number. However, the sum total of cells was not different from controls. In controls, the 5-bromo-2'-deoxyuridine-labeling index was higher in newly formed neural crest cells than in their progenitors, paralleling reports showing these progenitors must pass the restriction point before undergoing epithelial-mesenchymal transition. Homocysteine decreased the labeling index of newly formed neural crest cells, suggesting that it inhibited cell cycle progression of neural crest progenitors or the S-phase entry of newly formed neural crest cells. Homocysteine also inhibited neural crest dispersal and decreased the distance they migrated from the neural tube. These results show neural crest morphogenesis is directly altered by elevated homocysteine in vivo. Developmental Dynamics 229:63-73, 2004.