Mechanisms of mitochondrial folate metabolism in neural tube closure

描述（由申请人提供）：神经管缺陷（NTD）是人类最常见的出生缺陷之一，被认为具有多因素原因。改变 NTD 易感性的最强联系之一是母体叶酸状况。然而，这些叶酸依赖性过程背后的生化机制尚不清楚。我们知识上的这一差距阻碍了我们就叶酸强化和预防 NTD 和其他人类疾病（先天性和晚年发生的疾病）做出明智的健康政策决策的能力。我的长期目标是了解叶酸支持正常神经管发育的机制，以及叶酸代谢的改变如何导致 NTD 的发展。该提案的目的是确定特定叶酸依赖性酶（线粒体 MTHFD1L）缺失导致 NTD 的机制。我的中心假设是，在 Mthfd1l 无效小鼠中观察到的 NTD 是由线粒体叶酸依赖性一碳 (1C) 代谢缺陷引起的，该代谢为从头嘌呤、胸苷酸、甘氨酸和甲基生物合成等基本过程提供 1C 单位。这项研究的基本原理是，Mthfd1l 小鼠模型提供了一个独特的机会来发现正常神经管发育的叶酸依赖性基础的特定代谢机制。更重要的是，更好的机制理解可能会带来新的和创新的叶酸强化方法或其他治疗干预措施，以减少或预防人类 NTD。我将检验我的中心假设， 从而通过一个具体目标实现本提案的目标：识别导致 Mthfd1l 无效胚胎中神经管缺陷的生化缺陷。在此目标下，我将使用生化测定来分析正常 (/)、杂合 (/-) 和无效 (-/-) 胚胎以及源自三种 Mthfd1l 基因型的胚胎干 (ES) 细胞中的叶酸依赖性代谢过程。这一目标的预期结果是确定导致 Mthfd1l 无效胚胎中观察到的 NTD 的特定代谢机制。在我看来，该申请中提出的研究具有创新性，因为它专注于一种新的小鼠 NTD 模型（Mthfd1l 敲除），该模型紧密复制人类 NTD 表型，并且不需要额外的营养干预来表达疾病表型。此外，人类 Mthfd1l 的常见变体已被证明与某些人群患 NTD 的风险增加有关。这一贡献意义重大，因为特定代谢机制的识别将从根本上促进对叶酸反应性 NTD 的理解，并且也将为非叶酸反应性 NTD 提供急需的新见解。当我们评估当前叶酸强化计划在降低人类 NTD 患病率方面的有效性和安全性时，这些详细的机制信息至关重要。 公共健康相关性：拟议的研究与公共健康相关，因为虽然我们知道膳食补充叶酸可以降低神经管缺陷的发生率；人们对这种保护背后的机制知之甚少。了解该基因与神经管缺陷发展之间的联系将为这些毁灭性的出生缺陷和叶酸代谢之间提供机制联系。因此，拟议的研究与 NIH 的使命相关，即增进我们对生命过程的理解，为疾病诊断、治疗和预防的进步奠定基础。

DESCRIPTION (provided by applicant): Neural tube defects (NTDs), among the most common birth defects in humans, are believed to have multifactorial causes. One of the strongest links to modifying NTD susceptibility is to maternal folic acid status. However, the biochemical mechanisms that underlie these folate-dependent processes are not understood. This gap in our knowledge hinders our ability to make informed health policy decisions about folic acid fortification and prevention of NTDs and other human diseases, both congenital and those occurring later in life. My long term goal is to understand the mechanisms by which folic acid supports normal neural tube development, and how altered folate metabolism leads to the development of NTDs. The objective of this proposal is to identify the mechanism(s) by which loss of a specific folate-dependent enzyme (mitochondrial MTHFD1L) leads to NTDs. My central hypothesis is that the NTDs observed in the Mthfd1l nullizygous mouse are caused by defects in mitochondrial folate-dependent one-carbon (1C) metabolism, which supplies 1C units for essential processes such as de novo purine, thymidylate, glycine, and methyl group biosynthesis. The rationale for this research is that the Mthfd1l mouse model provides a unique opportunity to discover the specific metabolic mechanism(s) that underlie the folate dependence of normal neural tube development. More importantly, a better mechanistic understanding is likely to lead to new and innovative approaches to folate fortification or other therapeutic interventions in the effort to reduce or prevent NTDs in humans. I will test my central hypothesis, and thereby accomplish the objective of this proposal, through one Specific Aim: Identify the biochemical defects responsible for neural tube defects in Mthfd1l nullizygous embryos. Under this aim, I will use biochemical assays to analyze the folate-dependent metabolic processes in normal (+/+), heterozygous (+/-), and nullizygous (-/-) embryos and in embryonic stem (ES) cells derived from the three Mthfd1l genotypes. The expected outcome of this aim is the identification of specific metabolic mechanisms responsible for the NTDs observed in Mthfd1l nullizygous embryos. The research proposed in this application is innovative, in my opinion, because it focuses on a new mouse NTD model (Mthfd1l knockout) that closely replicates the human NTD phenotype, and does not require additional nutritional intervention to express the disease phenotype. Moreover, a common variant of human Mthfd1l has been shown to be associated with increased risk of NTDs in some populations. This contribution is significant because identification of specific metabolic mechanisms will fundamentally advance understanding of folate-responsive NTDs, and will provide much needed new insight into non-folate-responsive NTDs as well. This detailed mechanistic information will be essential as we evaluate the efficacy and safety of the current folic acid fortification program in reducing the prevalence of human NTDs. PUBLIC HEALTH RELEVANCE: The proposed research is relevant to public health because while we know that dietary supplementation with folic acid reduces the incidence of neural tube defects; the mechanism behind this protection is very poorly understood. Understanding the link between this gene and development of neural tube defects will provide a mechanistic link between these devastating birth defects and folate metabolism. Thus, the proposed research is relevant to NIH's mission of increasing our understanding of life processes to lay the foundation for advances in disease diagnosis, treatment and prevention.