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Profiling placental and fetal DNA methylation in human neural tube defects

ABSTRACT: The incidence of neural tube defects (NTDs) declined by about 40% in Canada with the introduction of national folic acid (FA) fortification programs. However, NTDs persist despite the fact that few Canadians currently exhibit folate deficiency. FA fortification may have aided in reducing NTDs by overcoming abnormal one carbon metabolism cycling, the process which provides one carbon units for methylation of DNA. We considered that NTDs persisting in a folate replete population may also occur in the context of compromised one carbon metabolism, and that this might manifest as abnormal DNA methylation (DNAm). Second trimester human placental chorionic villi, kidney, spinal cord, brain and muscle were collected from 19 control, 22 spina bifida and 15 anencephaly fetuses in British Columbia, Canada. DNA was extracted, assessed for methylenetetrahydrofolate reductase (MTHFR) genotype and for genome-wide DNAm using repetitive elements, in addition to the Illumina Infinium HumanMethylation450 (450k) array. No difference in repetitive element DNAm was noted. Using a false discovery rate <0.05 and average group difference in DNAm >0.05, differentially methylated array sites were only identified in (i) the comparison of anencephaly to controls in chorionic villi (n=4 sites) and (ii) the comparison of spina bifida to controls in kidney (n=3,342 sites). We suggest that the distinctive DNAm of spina bifida kidneys may be consequent to the neural tube defect. Although other studies have provided data to support altered DNAm in NTDs, this was not a major feature of British Columbian cases on a genome-wide or site specific level.

ORGANISM(S): Homo sapiens

PROVIDER: GSE69502 | GEO | 2016/01/23

SECONDARY ACCESSION(S): PRJNA285746

REPOSITORIES: GEO

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Project description:Background The vitamin A derivative, retinoic acid (RA), is a potent teratogenic agent that induces a variety of congenital abnormalities including neural tube defects. The embryopathology of RA has been extensively investigated and retinol receptors play important roles during organogenesis, development and neural tube closure. Still, the mechanisms by which RA influences these processes are not completely understood. Methods We used a custom-made mouse genome 32K oligonucleotide microarray to determine the gene expression profiles of mouse embryo spinal cord samples that had been exposed to vehicle or RA. Then, we performed a GSEA (gene set enrichment analysis) on the gene expression data by searching MSigDB (v2.5) c2 gene sets (canonical pathways) and c5 gene sets (curated GO terms), with set size restraints on the range to avoid over-narrow or over-broad categories. Results Using microarray technology, the present study identifies 85 genes in the spinal cord that exhibit at least a 1.5-fold change between control samples and samples with spina bifida aperta. A gene set enrichment analysis showed that maternal exposure to RA induced spinal bifida that were associated with altered expression of genes involved in pro- or anti-apoptosis, cell proliferation, migration, cytoskeleton components, and cell or focal adhesion, indicating that defective functions of these cell components and biological processes preceded the abnormal development of neural tube. Conclusions Maternal exposure to RA induced spinal bifida that were associated with altered expression of genes involved in pro- or anti-apoptosis, cell proliferation, migration, cytoskeleton components, and cell or focal adhesion. As shown in previous reports, defective functions of these cell components and biological processes preceded the abnormal development of the neural tube. Our study will help the understanding of the etiology and pathology of spinal bifida. However, it should be noted that the changes in gene expression induced by RA exposure may not be an effect on events other than neural tube closure; further study is required to fully understand the molecular mechanisms and consequence of neural tube defects in embryos exposed to RA. Our study provides a global analysis of gene expression patterns in spina bifida and will help the understanding of the etiology and pathology of neural tube defects. We assessed the changes in gene expression that coincide with spina bifida in RA-treated mouse fetuses. After generating an independent list of regulated genes, we analyzed samples by gene set enrichment analysis to expand our results. A pool of spinal cord tissue from spina bifida fetuses whose mothers were exposed to RA was compared to a pool of spinal cord tissue from fetuses whose mothers were exposed to olive oil vehicle. Three replicates each.

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Profiling placental and fetal DNA methylation in human neural tube defects

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