Effects of Pyridoxine Deficiency on Hippocampal Function and Its Possible Association with V-Type Proton ATPase Subunit B2 and Heat Shock Cognate Protein 70

Pyridoxine, one of the vitamin B6 vitamers, plays a crucial role in amino acid metabolism and synthesis of monoamines as a cofactor. In the present study, we observed the effects of pyridoxine deficiency on novel object recognition memory. In addition, we examined the levels of 5-hydroxytryptamine (5-HT), 5-hydroxyindoleacetic acid (5-HIAA), 3,4-dihydroxyphenethylamine (DA), 3,4-dihydroxyphenylacetic acid, and homovanillic acid and the number of proliferating cells and neuroblasts in the hippocampus. We also examined the effects of pyridoxine deficiency on protein profiles applying a proteomic study. Five-week-old mice fed pyridoxine-deficient diets for 8 weeks and showed a significant decrease in the serum and brain (cerebral cortex, hippocampus, and thalamus) levels of pyridoxal 5′-phosphate, a catalytically active form of vitamin-B6, and decline in 5-HT and DA levels in the hippocampus compared to controls fed a normal chow. In addition, pyridoxine deficiency significantly decreased Ki67-positive proliferating cells and differentiated neuroblasts in the dentate gyrus compared to controls. A proteomic study demonstrated that a total of 41 spots were increased or decreased more than two-fold. Among the detected proteins, V-type proton ATPase subunit B2 (ATP6V1B2) and heat shock cognate protein 70 (HSC70) showed coverage and matching peptide scores. Validation by Western blot analysis showed that ATP6V1B2 and HSC70 levels were significantly decreased and increased, respectively, in pyridoxine-deficient mice compared to controls. These results suggest that pyridoxine is an important element of novel object recognition memory, monoamine levels, and hippocampal neurogenesis. Pyridoxine deficiency causes cognitive impairments and reduction in 5-HT and DA levels, which may be associated with a reduction of ATP6V1B2 and elevation of HSC70 levels in the hippocampus.