Mechanisms of mitochondrial folate metabolism in neural tube closure

描述（由申请人提供）：神经管缺陷（NTDs）是人类最常见的出生缺陷之一，被认为有多因素导致。改变NTD易感性的最强联系之一是与母亲叶酸状态有关。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被忽视热带病及其他人类疾病（包括先天性疾病和在生命后期发生的疾病）做出明智的卫生政策决定的能力。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神经管疾病的发展。本提案的目的是确定一种特定叶酸依赖酶（线粒体MTHFD1L）的丢失导致NTDs的机制。我的主要假设是，在mthfd11失合小鼠中观察到的NTDs是由线粒体叶酸依赖的一碳（1C）代谢缺陷引起的，该代谢为新生嘌呤、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中叶酸依赖的特定代谢机制。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，以减少或预防人类被忽视的热带病。我将验证我的中心假设，

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.