Divergent roles of 25-hydroxyvitamin D3 and 1α,25-dihydroxyvitamin D3 in neural fate determination: A CYP27B1-dependent neuron formation and VDR-dependent astrocyte development

Vitamin D plays a crucial role in neural differentiation, yet its precise mechanisms remain unclear. In this study, we investigated the effects of vitamin D metabolites, 25-hydroxyvitamin D₃ (25D₃) and 1α,25-dihydroxyvitamin D₃ (1α,25D₃), on neural differentiation using Cyp27b1^-/- and Vdr^-/- knockout mice-derived neural stem cells. We found that 1α,25D₃ promotes neuronal differentiation via vitamin D receptor (VDR), whereas some of its effects occur independently of VDR. Additionally, 25D₃ requires conversion to 1α,25D₃ by CYP27B1 to induce neuronal differentiation. In contrast, both 25D₃ and 1α,25D₃ promoted astrocyte differentiation regardless of CYP27B1 expression but required VDR. Furthermore, using vitamin D derivatives, we demonstrated that VDR binding affinity does not directly correlate with neurogenic potential. These findings reveal distinct VDR-dependent and VDR-independent pathways in neural differentiation, highlighting a previously unrecognized role of vitamin D metabolism in neural fate determination.