GENE-NUTRIENT INTERACTIONS AND EPIGENETICS. BIOCHEMICAL BASES OF THE ROLE OF PLASMA AND RED BLOOD CELL FOLATE, THE MTHFR C677T POLYMORPHISM AND GENOMIC DNA METHYLATION.

DNA methylation, an essential epigenetic feature of DNA that modulates gene expression and genomic integrity, is catalyzed by methyltransferases that utilize the universal methyl donor S-adenosyl-L-methionine (SAM). Methylenetetrahydrofolate reductase (MTHFR) catalyzes the synthesis of 5-methyltetrahydrofolate (5-methylTHF), the methyl donor for synthesis of methionine from homocysteine and precursor of SAM. In the present study we sought to determine the effect of folate status on genomic DNA methylation with an emphasis on the interaction with the common C677T mutation in the MTHFR gene. A newly developed sensitive and selective LC/ESI-MS method for the analysis of nucleotide bases was used to assess genomic DNA methylation in peripheral blood mononuclear cell DNA from 105 subjects homozygous for this mutation (T/T) and 187 homozygous for the wild-type (C/C) genotype. The results show that genomic DNA methylation directly correlates with folate status (P<0.01). T/T genotypes had a diminished level of DNA methylation compared to those with the C/C wild-type (32.23 vs.62.24 ng 5-methylcytosine/mg DNA, P<0.0001). Only the T/T subjects with low levels of folate, however, accounted for the diminished DNA methylation (P<0.0001). In T/T subjects DNA methylation status correlated with the methylated proportion of red blood cell folate (RBC) and was inversely related to the formylated proportion of RBC folates (P<0.03) that is known to be solely represented in those individuals. These results indicate that the MTHFR C677T polymorphism influences DNA methylation status through an interaction with folate status.