Mechanistic and metabolomic underpinnings of ALDH1L1 polymorphisms in the regulation of glycine metabolism

ALDH1L1是叶酸代谢中的一种常见酶，可将10-甲酰四氢叶酸（10-甲酰THF）转化为四氢叶酸（THF）。已知该反应调节从头嘌呤生物合成和叶酸依赖的同型半胱氨酸再甲基化循环。它也可能在控制单碳基团到合成代谢途径的通量方面发挥关键作用。为了支持在叶酸代谢调节中的作用，我们最近表明，敲除小鼠中ALDH1L1基因的缺失会导致功能性叶酸缺乏，即使小鼠摄入了足够的叶酸。对Aldh1l1基因敲除小鼠的分析也表明，该酶是肝脏中甘氨酸代谢的主要调节剂：KO小鼠的甘氨酸和甘氨酸偶联物水平较低，表明该酶参与了依赖叶酸的丝氨酸合成甘氨酸的过程。我们进一步报道了人类ALDH1L1在多态性位点rs3796191、rs2886059、rs9282691、rs2276724、rs1127717和rs4646750上有6个共同的非同义外显子snp，并且这些snp相关的单倍型在不同民族人群中的发生率存在显著差异。我们对西班牙裔儿童Viva La Familia队列的分析显示，rs2276724和rs3796191患儿血清甘氨酸显著降低，丝氨酸/甘氨酸比值显著升高，表明丝氨酸向甘氨酸转化的解除，并与我们的小鼠研究结果一致。在该队列中，ALDH1L1非同义snp也与代谢应激和肥胖标志物相关。基于我们的研究结果，我们假设非同义ALDH1L1 snp产生的酶变体具有改变的催化活性和/或稳定性，从而影响其代谢10-甲酰基四氢呋喃的能力，从而解除对甘氨酸代谢的调节。因此，具有特定单倍型的个体具有不同的THF/10-甲酰基THF和丝氨酸/甘氨酸比率，以及甘氨酸及其偶联物水平的改变，代谢型的扰动代表代谢健康的标志。该提案将通过追求以下特定目标来解决单倍型特异性ALDH1L1变异如何影响叶酸代谢和整体细胞代谢型的问题，以及叶酸补充如何修改单倍型特异性效应。目的1。从人类常见单倍型中鉴定ALDH1L1酶变异的功能特征。目标2。确定主要ALDH1L1单倍型对细胞代谢和单倍型对不同叶酸补充的特异性反应的影响。目标3。将ALDH1L1单倍型与叶酸依赖的甘氨酸代谢调节和人类健康结果联系起来。ALDH1L1变异在不同人群中非常常见，但它们在叶酸稳态和代谢性疾病的病因学中的作用在很大程度上尚未被探索。预计ALDH1L1单倍型对膳食叶酸的代谢反应有不同的介导作用，这可能需要对携带特定ALDH1L1 snp的个体调整叶酸摄入量。通过填补这一知识空白，拟议的研究将为ALDH1L1 snp的代谢调节提供机制见解，并将为评估人群特异性ALDH1L1单倍型作为疾病危险因素奠定基础。

ALDH1L1, a common enzyme in folate metabolism, converts 10-formyltetrahydrofolate (10-formyl-THF) to tetrahydrofolate (THF). This reaction is known to regulate the de novo purine biosynthesis and folate-dependent homocysteine re-methylation cycle. It could also play a key role in controlling the flux of one-carbon groups to anabolic pathways. In support of the role in the regulation of folate metabolism, we have recently shown that the loss of the ALDH1L1 gene in knockout mice causes functional folate deficiency, even when the mice had sufficient folate intake. Analysis of Aldh1l1 knockout mice also showed that the enzyme is the main regulator of glycine metabolism in the liver: KO mice have lower levels of glycine and glycine conjugates, indicating that the enzyme is involved in the folate-dependent synthesis of glycine from serine. We have further reported that human ALDH1L1 has six common non-synonymous exonic SNPs at the polymorphic loci rs3796191, rs2886059, rs9282691, rs2276724, rs1127717 and rs4646750 with the occurrence of haplotypes associated with these SNPs being remarkably different between ethnic populations. Our analysis of an established cohort of Hispanic children, Viva La Familia, has shown a significant reduction of serum glycine and increase in serine/glycine ratio in children with rs2276724 and rs3796191, indicating deregulation of serine to glycine conversion and re- capitulating our mouse findings. ALDH1L1 non-synonymous SNPs were also associated with markers of metabolic stress and adiposity in this cohort. Based on our findings, we hypothesize that non-synonymous ALDH1L1 SNPs produce enzyme variants with altered catalytic activity and/or stability that affects their ability to metabolize 10-formyl-THF and thus deregulates glycine metabolism. Accordingly, individuals with specific haplotypes have different ratios of THF/10-formyl-THF and serine/glycine, and altered levels of glycine and its conjugates, with perturbations in the metabotype representing a signature of metabolic health. This proposal will address the question of how haplotype-specific ALDH1L1 variants affect folate metabolism and the overall cellular metabotype, and how the haplotype-specific effect is modified by folate supplementation, by pursuing the following specific aims. Aim 1. Functionally characterize the ALDH1L1 enzyme variants from common human haplotypes. Aim 2. Determine the impact of major ALDH1L1 haplotypes on cellular metabolism and haplotype- specific responses to various folate supplementations. Aim 3. Link ALDH1L1 haplotypes to the folate-dependent regulation of glycine metabolism and health outcomes in humans. ALDH1L1 variants are very common in different populations but their role in folate homeostasis and in the etiology of metabolic disease is largely unexplored. It is expected that ALDH1L1 haplotypes differently mediate the metabolic response to dietary folate that might require adjustments of folate intake for individuals bearing certain ALDH1L1 SNPs. By filling this knowledge gap, the proposed research will provide mechanistic insight into the metabolic regulation by ALDH1L1 SNPs and will lay ground for the evaluation of population-specific ALDH1L1 haplotypes as a disease risk factor.