Methyl Donor Supplementation Prevents a Folate Deficiency-induced Depression-like State and Neuronal Immaturity of the Dentate Gyrus in Mice

•SAM prevented increased immobility in low folate mice.•SAM prevented immaturity of the hippocampus in low folate mice.•SAM prevented disruption of expression of transcription factors in low folate mice. We have recently shown that folate deficiency induces depression-like behavior and neuronal immaturity in the dentate gyrus (DG) in mice. We also revealed that folate deficiency inhibits neuronal maturation, hypomethylates the promoter of certain neuronal genes and decreases intracellular levels of S-adenosylmethionine (SAM), a methyl donor, in cultured neural stem and progenitor cells. Based on these findings, we hypothesized that SAM reduction may be involved in a folate deficiency-induced depressive state and neural immaturity. In this study, we examined whether SAM supplementation prevents depression-like behavior and neural immaturity in low folate diet-fed mice. Intraperitoneal administration of SAM (50 mg/kg/day) for 14 days from 7 weeks old prevented increased immobility in low folate diet-fed mice. SAM supplementation also prevented an increase in the number of doublecortin (an immature neuron marker)-positive cells and a decrease in the number of NeuN (a mature neuron marker)/5-bromo-2′-deoxyuridine (a proliferation marker)-double positive cells in the DG of these mice. Furthermore, neurofunctional and neuromorphological abnormalities in the DG of low folate diet-fed mice, such as decreases in stress-induced expression of c-Fos (a neuronal activity marker), dendritic complexity and the number of mature spines, were improved by SAM supplementation. The disrupted expression of transcription factors involved in neuronal differentiation and maturation was also normalized by SAM supplementation. These results suggest that SAM reduction may be involved in a folate deficiency-induced depressive state.