Expression and Metabolic Profiles in a Panel of Five Neural Tube Defect Mouse Models

Neural tube defects (NTDs) are serious birth defects with an estimated worldwide incidence of 1 per 1,000 live births. The multifactorial nature of NTDs in humans has made it difficult to elucidate pathogenesis mechanisms. However, a strong relationship has been established between folate-homocysteine metabolism and NTD risk. Prevention of a substantial proportion of fetal NTDs can be achieved through maternal folic acid (FA) supplementation. However the mechanism by which FA exerts its beneficial effect remains unclear. METHODS: To improve our understanding of the underlying mechanisms of NTD pathogenesis and the ways in which folate exerts its beneficial effect, we analyzed mRNA profiles as well as folate and vitamin B12 levels in five NTD mouse mutants whose response to dietary FA was previously established. RESULTS: Differentially expressed genes representing the effect of each NTD-causing mutation were identified and associated with biologic pathways. Interestingly, the panel of NTD mutants collectively revealed pathways related to two nuclear receptors, retinoid X receptor (RXR) and pregnane X receptor (PXR), suggesting that these pathways may be related to a shared mechanism of NTD development. Moreover, the NTD-causing mutations that were associated with FA responsiveness had expression profiles that were related to folate-homocysteine metabolic pathways. These pathways were not strongly associated with mutants that do not respond to FA supplementation, implying that FA may be beneficial when the NTD mutation affects pathways related to folate-homocysteine metabolism. 5 groups of NTD mutants were studied. From each mutant group Heterozygous (test) and wild-type (control) female pups were used for this study at 6-8 weeks of age. 4 biological replicates were used for each of the test and control groups of each mutant. All mice used for the experiments were fasted 4-5 hours before dissection. A total of 36 samples were analyzed.神经管缺陷（Neural tube defects, NTDs）是一类严重的出生缺陷，据估算全球活产儿发病率约为1/1000。人类神经管缺陷具有多因素致病特性，这使得阐明其发病机制颇具挑战。不过，现已明确叶酸-同型半胱氨酸代谢与NTD患病风险之间存在密切关联。通过母体补充叶酸（folic acid, FA）可有效预防相当比例的胎儿神经管缺陷，但叶酸发挥有益作用的具体机制仍未明确。 研究方法：为加深对神经管缺陷发病机制以及叶酸发挥有益作用途径的理解，本研究分析了5种已被证实对膳食叶酸存在应答反应的神经管缺陷小鼠突变体的mRNA表达谱，以及叶酸和维生素B12水平。 研究结果：我们鉴定出了代表每种致NTD突变效应的差异表达基因，并将其与生物学通路进行关联分析。值得注意的是，该组神经管缺陷突变体共同揭示出与两类核受体相关的通路——视黄酸X受体（retinoid X receptor, RXR）和孕烷X受体（pregnane X receptor, PXR），提示这些通路可能与NTD发生的共同致病机制相关。此外，与叶酸应答相关的致NTD突变体，其表达谱与叶酸-同型半胱氨酸代谢通路密切相关；而此类通路在对叶酸补充无应答的突变体中并未呈现显著关联，这意味着当NTD突变影响叶酸-同型半胱氨酸代谢相关通路时，叶酸或可发挥有益防治作用。本研究共纳入5组神经管缺陷突变体，每组均选取6~8周龄的杂合子（实验组）与野生型（对照组）雌性幼鼠开展实验。每种突变体的实验组与对照组均设置4个生物学重复。所有实验用小鼠在解剖取材前均禁食4~5小时，最终共分析36份样本。