Folate and S-adenosyimethionine in Methyl Group and One-carbon Metabolism

描述（由申请人提供）：甲基化调节与叶酸代谢密切相关。这两种代谢过程由甘氨酸n -甲基转移酶连接，该酶在肝脏、外分泌胰腺和前列腺中含量丰富，在肾脏和肠粘膜中含量较低。它通过s -腺苷蛋氨酸（AdoMet）对甘氨酸进行甲基化，形成n -甲基甘氨酸和s -腺苷同型半胱氨酸（AdoHcy）。该酶的功能被认为是调节AdoMet与adhcy的比例。AdoMet是甲基的主要组成部分，AdoMet/ adhcy比值是细胞甲基化能力的指标。该酶在体内和体外也能与5-甲基四氢叶酸五谷氨酸紧密结合，后者可作为该酶的抑制剂。这将预先形成的甲基（如蛋氨酸）的可用性与通过叶酸介导的反应重新合成甲基联系起来。我们开发了一种甘氨酸n -甲基转移酶敲除小鼠，与WT小鼠相比，其肝脏和血浆中的s -腺苷甲硫氨酸水平非常高。初步数据显示，肝脏DNA并非全局性高甲基化。这些-/-小鼠自发发展为脂肪肝。我们的第一个假设是，来自高水平甘氨酸N-甲基转移酶的-/-动物的肝外组织也会有异常的组织学和升高的AdoMet。我们的第一个特定目标是在WT和-/-小鼠的组织中检查胺组织学和测量蛋氨酸代谢物。我们的第二个假说是基因的启动子区域会被超甲基化，影响关键蛋白的表观遗传表达。我们的第二个特定目标是测量DNA的整体甲基化和启动子区域的基因参与脂肪性肝炎的发展和蛋氨酸代谢的组织从WT和小鼠。甘氨酸n -甲基转移酶在外分泌组织中最为丰富。我们的第三个假设是甘氨酸n -甲基转移酶在外分泌中很重要，我们的第三个特定目标是测量WT和-/-小鼠的外分泌。肝脏中最丰富的叶酸辅酶是5-甲基四氢叶酸。肝脏中的大部分叶酸与甘氨酸n -甲基转移酶紧密结合。我们的第四个假设是，在缺乏这种蛋白质的情况下，不同形式的叶酸将被重新分配，并导致叶酸介导反应的改变。我们的第四个具体目标是测量WT和-/-小鼠肝脏、胰腺和前列腺中各种形式叶酸的分布，以及叶酸缺乏是否会改变。AdoMet的水平在非/非动物中非常高，这表明蛋白质可能过度甲基化。我们的第五个假设是，他的音调可能在-/-动物中高度甲基化。我们的第五个特定目的是研究WT和-/-小鼠组蛋白的甲基化。我们的第六个假设是，有可能通过给药作为甲基受体的化合物来降低组织中AdoMet的高水平，并降低-/-小鼠肝脏疾病的严重程度。我们的第六个具体目标是确定是否给予烟酰胺或胍- noacetate会做到这一点。公共卫生相关性：该提案“甲基叶酸和s -腺苷蛋氨酸和一碳代谢”涉及酶，甘氨酸n -甲基转移酶，肝脏，胰腺和前列腺中的一种主要酶的损失的影响。我们已经在几个儿童身上发现了这种酶的突变，导致中度肝损伤，并开发了一种完全缺乏甘氨酸n -甲基转移酶的小鼠模型，随着年龄的增长，这种模型会发展为严重的肝脏疾病。本提案的目标之一是评估几种常见天然化合物在该小鼠模型中减少肝损伤发展的能力，从而提高治疗有缺陷的甘氨酸n -甲基转移酶的可能性，并防止严重的肝损伤。

DESCRIPTION (provided by applicant): Regulation of methylation is intimately associated with folate metabolism. These two metabolic processes are connected by the enzyme, glycine N-methyltransferase, which is abundant in liver, exocrine pancreas and prostate as well as in kidney and intestinal mucosa in lower amounts. It carries out the methylation of glycine by S-adenosylmethionine (AdoMet) to form N-methylglycine and S-adenosylhomocysteine (AdoHcy). The function of the enzyme is believed to be regulation of the ratio of AdoMet to AdoHcy. AdoMet is the major do- nor of methyl groups and the AdoMet/AdoHcy ratio an index of the methylating capacity of the cell. The enzyme also tightly binds 5-methyl-tetrahydrofolate pentaglutamate in vivo and in vitro, which acts as an inhibitor of the enzyme. This links the availability of preformed methyl groups, as methionine, to the de novo synthesis of methyl groups via folate-mediated reactions. We developed a glycine N-methyltransferase knockout mouse that has very high levels of S-adenosylmethionine in the livers and plasma compared to WT mice. Preliminary data showed that liver DNA is not globally hypermethylated. These -/- mice spontaneously develop fatty liver. Our First Hypothesis is that extra-hepatic tissues from -/- animals with high levels of glycine N- methyltransferase will also have abnormal histology and elevated AdoMet. Our First Specific Aim is to ex- amine histology and measure methionine metabolites in tissues from WT, and -/- mice. Our Second Hy- pothesis is that promoter regions of genes will be hypermethylated affecting the epigenetic expression of key proteins. Our second Specific Aim is to measure DNA for global methylation and the promoter regions of genes involved in the development of steatohepatitis and methionine metabolism in tissue from WT and mice. Glycine N-methyltransferase is most abundant in exocrine tissue. Our Third Hypothesis is that glycine N-methyltransferase is important in exocrine secretion and our Third Specific Aim is to measure exocrine se- cretion in WT and -/- mice. The most abundant folate coenzyme in liver is 5-methyltetrahydrofolate. Most of the folate in the liver is tightly bound to glycine N-methyltransferase. Our Fourth Hypothesis is that in the absence of this protein the different forms of folate will be redistributed and result in alterations in folate-mediated reac- tions. Our Fourth Specific Aim is to measure the distribution of the various forms of folate in liver, pancreas and prostate of WT and -/- mice and also whether it is changed in folate deficiency. The levels of AdoMet are very high in -/- animals suggesting that proteins may be overmethylated. Our Fifth Hypothesis is that his- tones may be hypermethylated in -/- animals. Our Fifth Specific Aim is to examine the methylation of histones in WT and -/- mice. Our Sixth Hypothesis is that it is possible to reduce the high levels of AdoMet in tissues by administration of compounds that serve as acceptors of methyl groups and reduce the severity of liver dis- ease in -/- mice. Our Sixth Specific Aim is to determine whether administration of nicotinamide or guanidi- noacetate will do this. PUBLIC HEALTH RELEVANCE: This proposal "Folate and S-adenosylmethionine in Methyl Group and One-carbon Metabolism" deals with the effects of the loss of the enzyme, glycine N-methyltransferase, a major enzyme in liver, pancreas and the prostate gland. We have discovered mutations of this enzyme in several children that result in moderate liver damage and have developed a mouse model that has a complete absence of glycine N-methyltransferase that progresses to severe liver disease as they get older. One of the goals of this proposal is to evaluate the use of several common natural compounds for their ability to diminish the development of liver damage in this mouse model thus raising the possibility of treating humans with defective glycine N-methyltransferase and prevent serious liver damage.