GENETIC EFFECTS-FOLATE-DEPENDENT ONE-CARBON METABOLISM

描述：一碳(氯)代谢由碳的生成组成。 细胞过程中使用的单位，包括DNA合成、再生 甲硫氨酸(Met)来源于同型半胱氨酸(Hcy)，以及多种生物的甲基化 化合物。损害一碳代谢的条件(如叶酸 缺乏)与血浆同型半胱氨酸升高和罹患 血管疾病、某些癌症和神经管缺陷。一种常见的突变 亚甲基四氢叶酸还原酶(MTHFR)，被称为“不耐热”或 C677T突变，与血浆I-ICE升高有关(尤其是 处于低叶酸状态)，血浆叶酸降低，红细胞分布改变 叶酸，潜在地增加了血管疾病的风险，降低了 结肠癌。C677T突变对体内代谢的影响尚未得到证实 直接确定。我们的总体假设是，收购的速度和 减少了从丝氨酸(C1单元的主要来源)生成甲基 在纯合子个体中C677T突变，以及基因分型的影响 当叶酸营养不足时，效果最好。我们还假设 依赖于叶酸的核苷酸(嘌呤和胸苷)的合成速率 在叶酸缺乏时会减少，但可能会因C677T突变而增强。 拟议的研究将确定儿童的营养和遗传依赖性。 氯单位从丝氨酸(Ser)流向蛋氨酸(Met)以及从Ser流向核苷酸。这 协议还将允许测量同型半胱氨酸的硫化途径 分解代谢在处理过量同型半胱氨酸方面很重要。明确的目标。要确定，请执行以下操作： (A)丝氨酸作为甲基氯单位供体的动力学 合成和核苷酸合成以及可能引起的损伤程度 由C677T突变和/或低叶酸状态引起。(B)C677T的影响 突变和叶酸状态对细胞氯状态的影响 红细胞中叶酸物种的分布。(C)C677T的影响 同型半胱氨酸分解代谢的突变和叶酸状态。(D)亲属 胞质和线粒体代谢在氯离子生成中的作用 甲基和核苷酸的合成单位。(E) 线粒体甘氨酸在氯单位生成中的裂解作用。协议：基本 根据协议，健康、营养充足的受试者(20-30岁)将 按MTHFR基因分型(纯合子对照和纯合子突变)。 受试者最初将接受13C-丝氨酸作为主要前体的输注 并在饮食耗尽8周后补充120微克叶酸以评估其效果。 营养和基因对氯离子动力学的影响。它的两个变种 将进行研究，以确定线粒体和 丝氨酸产生氯的胞质途径及线粒体的作用 甘氨酸裂解途径。总之，这些研究将产生新的功能 关于叶酸缺乏的影响的数据，以及共同的 亚甲基四氢叶酸还原酶基因多态性。

DESCRIPTION: One-carbon (Cl) metabolism consists of the generation of carbon units for use in cellular processes including DNA synthesis, regeneration of methionine (Met) from homocysteine (Hcy), and methylation of many biological compounds. Conditions that impair one-carbon metabolism (e.g. folate deficiency) are associated with elevation in plasma Hcy and increased risk of vascular disease, certain cancers, and neural tube defects. A common mutation of methylene-tetrahydrofolate reductase (MTHFR), known as the "thermolabile" or C677T mutant, has been associated with elevations in plasma I-Icy (especially in low folate status), lower plasma folate, altered distribution of erythrocyte folate, potentially increased risk of vascular disease, and decreased risk of colon cancer. The in vivo metabolic effects of the C677T mutation have not been determined directly. Our overall hypothesis is that the rate of acquisition and generation of methyl groups from serine (primary source of C1 units) is reduced in individuals homozygous for the C677T mutation, and that the genotypic effect is greatest when folate nutriture is inadequate. We also hypothesize that the rate of folate-dependent synthesis of nucleotides (purines and thymidylate) will be reduced in folate deficiency but may be enhanced by the C677T mutation. The proposed studies will determine nutritional and genetic dependence of the flow of Cl units from serine (Ser) to Met and from Ser to nucleotides. This protocol also will allow measurement of the transsulfuration pathway of Hcy catabolism important in disposal of excess Hcy. Specific aims. To determine: (a) The kinetics by which Ser serves as a donor of Cl units for methyl group synthesis and nucleotide synthesis and the possible degree of impairment caused by the C677T mutation and/or low folate status. (b) The influence of the C677T mutation and folate status on cellular Cl status as reflected by the distribution of folate species in erythrocytes. (C) The influence of the C677T mutation and folate status on homocysteine catabolism. (d) The relative contributions of cytosolic and mitochondrial metabolism in the generation of Cl units for synthesis of methyl groups and nucleotides. (e) The significance of mitochondrial glycine cleavage in generation of Cl units. Protocol: In the main protocol, healthy adequately nourished human subjects (20-30 yr) will be classified by MTHFR genotype, (homozygous control and homozygous mutant). Subjects will be given infusions with 13C-serine as primary precursor initially and following 8-wk dietary depletion of 120 ugld folate to evaluate the effect of nutritional and genotypic effects on Cl kinetics. Two variations of this study will be conducted to determine the relative roles of mitochondrial and cytosolic routes of Cl generation from serine and the role of the mitochondrial glycine cleavage pathway. In total, these studies will yield new functional data regarding the effects of folate deficiency, and the influence of common polymorphism of MTHFR.