9-cis-Retinoic Acid and 1,25-dihydroxy Vitamin D3 Improve the Differentiation of Neural Stem Cells into Oligodendrocytes through the Inhibition of the Notch and Wnt Signaling Pathways

BACKGROUND: Differentiating oligodendrocyte precursor cells (OPCs) into oligodendrocytes could be improved by inhibiting signaling pathways such as Wnt and Notch. 9-cis-retinoic acid (9-cis-RA) and 1,25-dihydroxyvitamin D(3) (1,25[OH](2)D(3)) can ameliorate oligodendrogenesis. We investigated whether they could increase oligodendrogenesis by inhibiting the Wnt and Notch signaling pathways. METHODS: Cortical neural stem cells were isolated from 14-day-old rat embryos and cultured using the neurosphere assay. The cells were treated in 4 different conditions for 1 week: the negative control group received only the basic fibroblast growth factor, the positive control group received only T(3) without growth factors, the RA group was treated with 9-cis-RA, and the Vit D(3) group was treated with 1,25(OH)(2)D(3). The effects of 9-cis-RA and 1,25(OH)(2)D(3) on the level of the myelin basic protein (MBP) and the gene expression of the SOX10, MBP gene, HES5, and LRP6 were studied using flow cytometry and real-time PCR. The data were analyzed using one-way ANOVA with GraphPad Prism. A P value less than 0.05 was considered significant. RESULTS: The mRNA expressions of the SOX10, MBP, and MBP gene were significantly increased in the treated groups compared with the negative control group; the increase was similar in the 9-cis-RA group and the positive control group. Furthermore, 9-cis-RA significantly decreased the expression of the HES5 gene, a Notch signaling pathway transcription factor, and 1,25(OH)(2)D(3) significantly reduced the expression of the LRP6 gene, a Wnt signaling pathway co-receptor. CONCLUSION: It seems that 9-cis-RA and 1,25(OH)(2)D(3) are good candidates to improve the differentiation of OPCs into oligodendrocytes.