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.

National Institute of Health (NIH)
National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK)
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Integrative Nutrition and Metabolic Processes Study Section (INMP)
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Maruvada, Padma
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Vanderbilt University Medical Center
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Luka, Zigmund; Pakhomova, Svetlana; Loukachevitch, Lioudmila V et al. (2014) Crystal structure of the histone lysine specific demethylase LSD1 complexed with tetrahydrofolate. Protein Sci 23:993-8
Luka, Zigmund; Pakhomova, Svetlana; Loukachevitch, Lioudmila V et al. (2012) Differences in folate-protein interactions result in differing inhibition of native rat liver and recombinant glycine N-methyltransferase by 5-methyltetrahydrofolate. Biochim Biophys Acta 1824:286-91
Luka, Zigmund; Moss, Frank; Loukachevitch, Lioudmila V et al. (2011) Histone demethylase LSD1 is a folate-binding protein. Biochemistry 50:4750-6
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Varela-Rey, Marta; Martinez-Lopez, Nuria; Fernandez-Ramos, David et al. (2010) Fatty liver and fibrosis in glycine N-methyltransferase knockout mice is prevented by nicotinamide. Hepatology 52:105-14
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Luka, Zigmund; Capdevila, Antonieta; Mato, Jose M et al. (2006) A glycine N-methyltransferase knockout mouse model for humans with deficiency of this enzyme. Transgenic Res 15:393-7