Vitamin D Inquiry in Hippocampal Neurons: Consequences of Vitamin D-VDR Pathway Disruption on Calcium Channel and the Vitamin D Requirement

Vitamin D receptor (VDR) and the enzymes involved in bioactivation of vitamin D, shown to be expressed in the central nervous system, particularly in areas affected by neurodegenerative disorders, especially in hippocampus. We showed that amyloid beta (Aβ) pathology includes VDR protein depletion and vitamin D-VDR pathway disruption either induced by Aβ or by VDR siRNA have very similar effects on cortical neurons. The goal of this study is to show the presence of 25 hydroxy vitamin D3-24 hydroxylase (24OHase) which is essential for vitamin D catabolism in hippocampal and cortical neurons. Additional goal is to compare the expression pattern of VDR and 24OHase both in hippocampal and in cortical neurons and to investigate the effects of VDR suppression in hippocampal neurons in order to see whether similar mechanisms work in hippocampus and cerebral cortex. Primary neuronal cultures were prepared from Sprague-dawley rat embryos. qRT-PCR was performed to determine VDR, 24OHase, and LVSCC-A1C mRNA expression levels. Cytotoxicity levels were determined by ELISA. Our findings illustrate that 24OHase mRNA was present both in hippocampal and in cortical neurons. VDR and 24OHase mRNA were higher in hippocampal neurons than the cortical ones. LVSCC-A1C mRNA levels increased in hippocampal neurons when VDR is down-regulated. Our results indicate that hippocampal neurons response to VDR suppression similar as cortical neurons, regarding calcium channel regulation. Higher gene expression of 24OHase and VDR might indicate "higher requirement of vitamin D" in hippocampus and potential consequences of vitamin D deficiency in cognitive decline, neurodegeneration, and Alzheimer's disease.