Reduced MTHFD1 activity in male mice perturbs folate- and choline-dependent one-carbon metabolism as well as transsulfuration

Abstract

Impaired utilization of folate is caused by insufficient dietary intake and/or genetic variation and has been shown to prompt changes in related pathways, including choline and methionine metabolism. These pathways have been shown to be sensitive to variation within the Mthfd1 gene, which codes for a folate-metabolizing enzyme responsible for generating 1-carbon (1-C)-substituted folate derivatives. The Mthfd1(gt/+) mouse serves as a potential model of human Mthfd1 loss-of-function genetic variants that impair MTHFD1 function. This study investigated the effects of the Mthfd1(gt/+) genotype and folate intake on markers of choline, folate, methionine, and transsulfuration metabolism. Male Mthfd1(gt/+) and Mthfd1(+/+) mice were randomly assigned at weaning (3 wk of age) to either a control (2 mg/kg folic acid) or folate-deficient (0 mg/kg folic acid) diet for 5 wk. Mice were killed at 8 wk of age following 12 h of food deprivation; blood and liver samples were analyzed for choline, methionine, and transsulfuration biomarkers. Independent of folate intake, mice with the Mthfd1(gt/+) genotype had higher hepatic concentrations of choline (P = 0.005), betaine (P = 0.013), and dimethylglycine (P = 0.004) and lower hepatic concentrations of glycerophosphocholine (P = 0.002) relative to Mthfd1(+/+) mice. Mthfd1(gt/+) mice also had higher plasma concentrations of homocysteine (P = 0.0016) and cysteine (P < 0.001) as well as lower plasma concentrations of methionine (P = 0.0003) and cystathionine (P = 0.011). The metabolic alterations observed in Mthfd1(gt/+) mice indicate perturbed choline and folate-dependent 1-C metabolism and support the future use of Mthfd1(gt/+) mice as a tool to investigate the impact of impaired 1-C metabolism on disease outcomes.

FIGURE 1

A working model of the metabolic effects of Mthfd1 deficiency on choline- and folate-mediated 1-C metabolism. The product of the Mthfd1 gene is C1THF synthase, which contains FTHFS, MTHFC, and MTHFD enzymatic activities. The “X” indicates enzymatic activities that are reduced by 50% in the Mthfd1^gt/+ mouse model. Boxed metabolites are those that were measured in this study: a double-lined box indicates that the metabolite was measured in the liver, a single-lined box indicates that the metabolite was measured in plasma. Thicker arrow, process enhanced by reduced MTHFD1 activity; dashed arrow, process attenuated by reduced MTHFD1 activity. AdoHcy, S-adenosylhomocyteine; AdoMet, S-adenosylmethionine; 1-C, 1-carbon; CBS, cystathionine β-synthase; DMG, dimethylglycine; FTHFS, 10-formyltetrahydrofolate synthetase; GPC, glycerophosphocholine; Hcy, homocysteine; Met, methionine; MTHFC, methenyltetrahydrofolate cyclohydrolase; MTHFD, methylenetetrahydrofolate dehydrogenase; MTHFR, 5,10-methylenetetrahdyrofolate reductase; PC, phosphatidylcholine; SHMT, serine hydoxymethyltransferase; THF, tetrahydrofolate.