Methylenetetrahydrofolate reductase 677C→T polymorphism affects DNA methylation in response to controlled folate intake in young women

https://doi.org/10.1016/j.jnutbio.2004.04.003Get rights and content

Abstract

DNA methylation is critical for normal genomic structure and function and is dependent on adequate folate status. A polymorphism (677C→T) in a key folate enzyme, methylenetetrahydrofolate reductase (MTHFR), may impair DNA methylation when folate intake is inadequate and may increase the risk of reproductive abnormalities. The present study was designed to evaluate the effect of the MTHFR 677C→T polymorphism on changes in global DNA methylation in young women consuming a low folate diet followed by repletion with the current Recommended Dietary Allowance (RDA). Women (age 20–30 years) with the TT (variant; n = 19) or CC (n = 22) genotype for the MTHFR 677C→T polymorphism participated in a folate depletion-repletion study (7 weeks, 115 μg DFE/day; 7 weeks, 400 μg DFE/day). DNA methylation was measured at baseline, week 7, and week 14 using a [3H]methyl acceptance assay and a novel liquid chromatography tandem mass spectrometry assay of the DNA bases methylcytosine and cytosine. [3H]Methyl group acceptance tended to increase (P = 0.08) during depletion in all subjects, indicative of a decrease in global DNA methylation. During repletion, the raw change and the percent change in the methylcytosine/total cytosine ratio increased (P = 0.03 and P = 0.04, respectively) only in the subjects with the TT genotype. Moderate folate depletion in young women may cause a decrease in overall DNA methylation. The response to folate repletion suggests that following folate depletion women with the MTHFR 677 TT genotype have a greater increase in DNA methylation with folate repletion than women with the CC genotype.

Introduction

Folate functions in the formation of S-adenosylmethionine (SAM), the methylating agent for DNA methylation, a key epigenetic modification critical for genome stability [1], gene expression [2], and thus normal development [3], [4]. To ensure maintenance of normal DNA methylation, it is important to understand the interrelationship among folate status, genetic factors that may impair the synthesis of folate coenzymes, and the methyl group donor SAM. SAM synthesis is dependent in part on the availability of 5-methyltetrahydrofolate (5-methylTHF), which may be limited because of dietary folate restriction or reduced activity of methylenetetrahydrofolate reductase (MTHFR), the enzyme that converts 5,10-methyleneTHF to 5-methylTHF. MTHFR activity is affected negatively by a common genetic variant in the gene that codes for MTHFR. A C→T base transition at base pair 677 causes an alanine to valine substitution [5], which impairs stability as a result of less avid binding of FAD to the variant form of the MTHFR enzyme under conditions of low folate concentration [6]. The MTHFR 677C→T polymorphism affects a large percentage of the population with an estimated frequency of ∼12% for the homozygous (TT) genotype with considerable variation among different ethnic groups [7], [8]. The potential for the MTHFR 677C→T transition to reduce global DNA methylation when coupled with poor folate status has been evaluated in observational, population-based studies [9], [10]. There are, however, no previous reports of the effect of the MTHFR 677C→T polymorphism on global DNA methylation in response to controlled dietary folate intake. Because the intake of other nutrients involved in one carbon metabolism may affect DNA methylation, it is important to evaluate the effect of dietary folate intake alone in individuals with the TT or CC MTHFR 677C→T genotype under controlled dietary conditions. The responsiveness of DNA methylation to changes in folate status under controlled metabolic conditions has not been previously reported for women of reproductive age.

Inadequate folate status has been linked to abnormal fetal growth and development [11] as well as pregnancy complications [12]. In addition, it is well established that periconceptional folic acid supplementation significantly reduces the risk for neural tube defects [13], [14], [15]. Although the mechanism behind the relationship between folate status and pregnancy outcome is unknown, one possibility could be the role of folate in SAM synthesis. A decrease in folate status may affect SAM availability, resulting in decreased DNA methylation [16]. Reduced global DNA methylation has been associated with impaired fetal development and viability [3], [4], emphasizing the crucial need to maintain normal DNA methylation in women of reproductive age.

The potential for impaired folate status coupled with the MTHFR 677 TT genotype to negatively influence DNA methylation [9], [10] provided the incentive for this study. We investigated the differences in response to folate depletion and repletion with the current RDA in leukocyte DNA methylation between women of childbearing age (20–30 years) with the TT or CC MTHFR 677C→T genotype. This is the first study in young women in which changes in DNA methylation were evaluated in response to controlled folate intake.

Section snippets

Subjects

Young (age 20–30 years), healthy, nonpregnant women were recruited and screened for this study. Only women with the TT or CC MTHFR 677 genotype were eligible. Exclusion criteria were chronic use of alcohol or tobacco products; use of medications including oral contraceptives; recent use of vitamin–mineral supplements; history of chronic disease or major surgery; body weight >120% of ideal; and abnormal blood chemistry profile. Serum and red blood cell folate, plasma vitamin B12, pyridoxal

Serum and red blood cell folate and plasma homocysteine concentrations

The results for serum and red blood cell folate and plasma homocysteine concentrations at baseline, postdepletion, and postrepletion by genotype and overall have been previously described [17].

DNA methylation

No differences were detected between the means ± SD for [3H]methyl group acceptance (Table 1) at weeks 0, 7, or 14 between genotype groups (P > 0.05). The overall mean percent change in [3H]methyl group acceptance tended (P = 0.08) to increase from baseline to postdepletion (5% ± 19%), suggesting a trend

Discussion

The primary objective of this metabolic study was to evaluate the influence of the MTHFR 677C→T variant on DNA methylation response to a low-folate diet followed by repletion with the current folate RDA for nonpregnant women using a controlled feeding protocol. Previous studies have been primarily observational, population-based studies in which the combined effect of the MTHFR polymorphism and folate status was evaluated. The women in the current study had baseline folate values well above

Acknowledgements

The authors acknowledge Karen Novak, MS, RN, for assistance in subject recruitment and sample collection during this study, and Steven Zeisel, PhD, for analysis of the choline content in the diet. This research was supported by the Florida Agricultural Experiment Station and grants from the U.S. Department of Agriculture (USDA)–National Research Initiative (NRI) grant 00-3500-9102, USDA-NRI grant 00-3500-9113, National Institutes of Health (NIH) grant DK56724, and NIH General Clinical Research

References (35)

  • R.A. Jacob et al.

    Moderate folate depletion increases plasma homocysteine and decreases lymphocyte DNA methylation in postmenopausal women

    J Nutr

    (1998)
  • S.-W. Choi et al.

    Biochemical and molecular aberrations in the rat colon due to folate depletion are age-specific

    J Nutr

    (2003)
  • B.C. Richardson

    Role of DNA methylation in the regulation of cell functionAutoimmunity, aging and cancer

    J Nutr

    (2002)
  • B. Richardson

    Impact of aging on DNA methylation

    Ageing Res Rev

    (2003)
  • R.L. Adams

    DNA methylation. The effect of minor bases on DNA-protein interactions

    Biochem J

    (1990)
  • P.A. Jones et al.

    The role of DNA methylation in mammalian epigenetics

    Science

    (2001)
  • P. Frosst et al.

    A candidate genetic risk factor for vascular diseaseA common mutation in methylenetetrahydrofolate reductase

    Nat Genet

    (1995)
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