Nuclear lipid microdomains regulate nuclear vitamin D 3 uptake and influence embryonic hippocampal cell differentiation

Despite recent advances in the understanding of the role of 1,25-dihydroxyvitamin D-3 (1,25-(OH)(2)D-3) in the CNS, the mechanism of action remains obscure. We demonstrate that some 1,25-(OH)(2)D-3 receptor (VDR) is localized in the cell nucleus in specialized microdomains enriched in sphingomyelin and cholesterol; the integrity of these microdomains is necessary for embryonic hippocampal cell differentiation. Sphingomyelinase (SMase) treatment reduces both VDR and labeled 1,25-(OH)(2)D-3 content in nuclear microdomains. We have previously shown that HN9.10e embryonic hippocampal cells differentiate when incubated with 100 nM 1,25-(OH)(2)D-3 in the presence of 10% fetal calf serum, while serum deprivation induces cell death. In this study, we have investigated whether conditions that alter lipid content of nuclear microdomains modify 1,25-(OH)(2)D-3-induced differentiation. Serum deprivation activates SMase and modifies the composition of nuclear microdomains, which lose the 1,25-(OH)(2) vitamin D-3 receptor. The incubation of serum-deprived cells with 100 nM 1,25-(OH)(2)D-3 prevents differentiation. However, treatment with 400 nM 1,25-(OH)(2)D-3 during serum withdrawal increases the lipid content of the nuclear microdomains, allows the interaction of 1,25-(OH)(2)D-3 with its receptor, and results in differentiation. These results suggest the presence of VDR in nuclear microdomains is necessary for 1,25-(OH)(2)D-3-induced differentiation in embryonic hippocampal cells.