High Dietary Folate during Pregnancy Leads to Pseudo-MTHFR Deficiency and Short-term Memory Impairment in Murine Offspring
1. Department of Human Genetics, McGill University, Montreal, Quebec, Canada; 2. Department of Neuroscience, Carleton University, Ottawa, Ontario, Canada; 3. Division of Nutritional Sciences and Genomics, Cornell University, Ithaca, NY, USA; 4. Department of Pediatrics, McGill University Health Center, Montreal, Quebec, Canada
Severe deficiency of methylenetetrahydrofolate reductase (MTHFR) in mice is associated with brain dysfunction, short-term memory impairment and disturbed choline/acetylcholine metabolism. With the increased folate intake in the general population and in women of childbearing age in particular, due to food fortification and use of high dosage vitamin supplements, we have been studying the impact of high dietary folate on health. Recently we reported that male mice fed a high folate diet had a pseudo-MTHFR deficiency (decreased MTHFR immunoreactive protein on Western blots) in liver that led to lipid anomalies and liver injury.
The goal of this study was to determine whether a high folate diet during pregnancy and lactation would affect brain function in murine offspring. At weaning, female mice were placed on a control diet (CD; recommended level of folate for rodents) or folic acid- supplemented diet (FASD; 10-fold higher folate than recommended level for rodents) for 5 weeks prior to mating and maintained on the same diet during pregnancy and lactation. Male offspring were evaluated for memory impairment at 3 weeks of age and maternal tissue was collected. Pups from FASD mothers showed short-term memory impairment using the novel object recognition test (p<0.005, t-test). MTHFR protein levels in FASD maternal liver were significantly reduced (p=0.005, t-test) and there was an increase in the ratio of the phosphorylated (less active): non-phosphorylated MTHFR isoform (p<0.005). Since folate and choline metabolism are interrelated, we measured choline metabolites. We observed a trend towards decreased glycerophosphocholine in maternal plasma and in offspring hippocampus (p=0.06). There was an increase in protein levels of choline acetyltransferase (ChAT) in offspring hippocampus; this enzyme, which synthesizes acetylcholine, is often up-regulated when acetylcholine metabolism is disturbed. To assess these processes earlier in development, we followed the same experimental design and collected embryos and maternal tissues at E17.5. We observed decreased MTHFR protein in embryonic liver from FASD dams (p<0.05, t-test); additional assays are in progress. We suggest that high folate intake during pregnancy leads to a pseudo-MTHFR deficiency in dams and embryos, disturbs choline metabolism and results in memory impairment in offspring. These findings contribute to increased awareness of the unintended negative consequences when oversupplementing with folic acid and highlight the importance of appropriate public health recommendations for prenatal folate intake.