Chronic Folate Deficiency in the Mouse Hippocampus

Short-term folate deficiency has been linked to cognitive defects. Given folate’s role in regulating nucleotide synthesis and DNA and histone methylation, these changes are often linked to altered gene expression. We hypothesize that chronic folate deficiency will induce memory deficits that can be linked to tissue-specific changes in gene expression. This study placed mice on folic acid deficient or replete diets, containing either no source of folate or AIN-93G normal folic acid intake, beginning post-weaning and persisting through the end of adult life at 18 months. Cognitive outcomes were assessed using the novel object test for memory. Changes in hippocampal gene expression were examined by RNA microarray analysis and confirmed by qPCR. qPCR was also use to compare a subset of significant hippocampal genes to potential changes in liver and heart expression. Ontological categories were determined using GeneCodis for genes whose expression significantly changed in the deficient condition. Significantly enriched motifs in the deficient genes were examined using the HOMER bioinformatics analysis tool to identify transcription factors associated with changing genes. Folic acid deficient mice showed significant memory impairment (P<0.05) compared to replete counterparts beginning at 5 mo and persisting through 17 mo. These deficits were associated with 363 significantly downregulated and 101 significantly upregulated genes (P<0.05, fold change > 2) in the deficient condition. Of the 16 genes whose differential hippocampal expression was confirmed by qPCR, none were also differentially regulated in the heart, and only one was differentially regulated in the liver (P<0.05). Significant ontological categories for differential genes included nucleotide regulation, ion channel activity, and MAPK signaling. Two enriched motifs were identified and determined to be associated with MafB and Zfp410 binding sites. These genes and enriched motifs may represent targets for treatment or investigation of memory-related diseases. Samples from 12 different mice were analyzed in the study, including 3 mice from each of the following categories: 6 months of folic acid deficiency, 6 months of folic acid supplementation, 18 months of folic acid deficiency, and 18 months of folic acid supplementation. The 6 month dietary groups were compared to one another for analysis, as were the 18 month dietary groups. Each of the 3 mice within a dietary group was used as a biological replicated for the given time/condition. The mice used were outbred CD1 mice. Folic acid (FA) replete mice were used as controls, which FA deficient mcie were considered the experimental group.