Docosahexaenoic acid promotes neuronal differentiation by regulating basic helix–loop–helix transcription factors and cell cycle in neural stem cells

Recent studies have suggested that docosahexaenoic acid (DHA) enhances neuronal differentiation of neural stem cells (NSCs) isolated from rat embryonic day 14.5. However the underlying mechanism remains largely unknown. One hypothesis supported by DHA controls the expression level of basic helix–loop–helix (bHLH) transcription factors, such as hairy and enhancer of split 1 (Hes1), Mash1, neurogenin1, and NeuroD; another is that previous studies in retinal progenitor cells DHA affects the cell cycle. In this study, we show that treatment with DHA under differentiation conditions without basic fibroblast growth factor, (1) increases Tuj-1 and MAP2 positive cells in NSCs, (2) that the expression level of Hes1 mRNA and protein decreased significantly from day 1 to day 4, on the other hand, the NeuroD mRNA expression level increased from day 1 to day 4 after treatment with DHA and (3) decreased the percentage of S-phase cells, which correlated with prolonged expression of cyclin-dependent kinase inhibitor p27kip1, suggesting that DHA enhances neuronal differentiation of NSCs, in part, by controlling the bHLH transcription factors and promoting cell cycle exit. We therefore speculate that DHA is one of the essential key molecules for neuronal differentiation of NSCs.