The Effects of Vitamin D Receptor Silencing on the Expression of LVSCC-A1C and LVSCC-A1D and the Release of NGF in Cortical Neurons

Recent studies have suggested that vitamin D can act on cells in the nervous system. Associations between polymorphisms in the vitamin D receptor (VDR), age-dependent cognitive decline, and insufficient serum 25 hydroxyvitamin D(3) levels in Alzheimer's patients and elderly people with cognitive decline have been reported. We have previously shown that amyloid β (Aβ) treatment eliminates VDR protein in cortical neurons. These results suggest a potential role for vitamin D and vitamin D-mediated mechanisms in Alzheimer's disease (AD) and neurodegeneration. Vitamin D has been shown to down-regulate the L-type voltage-sensitive calcium channels, LVSCC-A1C and LVSCC-A1D, and up-regulate nerve growth factor (NGF). However, expression of these proteins when VDR is repressed is unknown. The aim of this study is to investigate LVSCC-A1C, LVSCC-A1D expression levels and NGF release in VDR-silenced primary cortical neurons prepared from Sprague-Dawley rat embryos.qRT-PCR and western blots were performed to determine VDR, LVSCC-A1C and -A1D expression levels. NGF and cytotoxicity levels were determined by ELISA. Apoptosis was determined by TUNEL. Our findings illustrate that LVSCC-A1C mRNA and protein levels increased rapidly in cortical neurons when VDR is down-regulated, whereas, LVSCC-A1D mRNA and protein levels did not change and NGF release decreased in response to VDR down-regulation. Although vitamin D regulates LVSCC-A1C through VDR, it may not regulate LVSCC-A1D through VDR.Our results indicate that suppression of VDR disrupts LVSCC-A1C and NGF production. In addition, when VDR is suppressed, neurons could be vulnerable to aging and neurodegeneration, and when combined with Aβ toxicity, it is possible to explain some of the events that occur during neurodegeneration

Effects of estrogen and tamoxifen on the ultrastructural characteristics of female rat prolactin cells as evaluated by immunogold technique

Estrogens and antiestrogens are known to have effects on protactin (PRL)-producing cells in the anterior pituitary. This study was planned to investigate the effects of estrogen and tamoxifen at immunohistochemical. and immunoelectron microscopic levels on PRL cells of female rat pituitary. Animals were divided into three groups of eight adult female rats each. The first group was the control. group. 200-mu g/day of estrogen was administered subcutaneously for 11 weeks to 16 rats. Tamoxifen was administered to eight of them for the Last 15 days. In diethylstilbestrol (DES)-induced group, serum PRL levels and pituitary weights were found to be elevated when compared with the control group. In the DES plus tamoxifen group the readings were close to that of the control group. PRL-positive cells were enlarged and strongly immunostained in DES-induced group when assessed by tight microscopy. Tamoxifen prevented this effect. At the ultrastructural. level., in the tamoxifen treated group, PRL-producing cells contained both immunopositive and immunonegative secretory granules. Numerous PRL-producing cells exhibited progressive morphological changes in the nuclei compatible with the apoptotic process. The results of this study indicate that tamoxifen prevents not only the proliferative effect of estrogen but also inhibits the secretion mechanism of the cells. (c) 2005 Elsevier GmbH. ALL rights reserved

The Influence of Vitamin D Treatment on the Inducible Nitric Oxide Synthase (INOS) Expression in Primary Hippocampal Neurons

Introduction: Neurodegeneration is a process that is characterized by the loss of neuronal structure and function and eventually ends with neuronal death. An elevated level of inducible nitric oxide synthase (iNOS) is suggested to accompany this process by inducing oxidative and nitrosative damage. Vitamin D is reported to protect glial cells against neurotoxicity via suppressing iNOS synthesis. Though there was no data about whether iNOS is regulated by vitamin D in hippocampal neurons. In this study our aim was to determine any alteration in iNOS expression of hippocampal neurons in response to vitamin D treatment

A New Mechanism for Amyloid-beta Induction of iNOS: Vitamin D-VDR Pathway Disruption

The inflammatory process in Alzheimer's disease (AD) has been suggested to include oxidative and nitrosative damage caused by elevated levels of nitric oxide (NO) and inducible nitric oxide synthase (iNOS). Here, we investigated iNOS expression in cortical neurons following amyloid-beta (A beta) treatment, vitamin D treatment, A beta combined with vitamin D treatment, and vitamin D signaling disruption via silencing of nuclear (vitamin D receptor-VDR) or membrane vitamin D (1,25-MARRS) receptors. We observed that A beta induced iNOS expression. Vitamin D prevented A beta-induced cytotoxicity and iNOS upregulation in cortical neurons. Our silencing experiments suggest that vitamin D regulates iNOS via VDR, not 1,25-MARRS, in cortical neurons. Consequently, VDR absence induces iNOS expression in either the absence or presence of A beta. While our previous work demonstrates that A beta pathology includes VDR suppression, our present work demonstrates that A beta induces iNOS and that this effect is mediated via disruption of the vitamin D-VDR pathway. These data suggest the existence of crosstalk between A beta pathology and VDR. Thus, vitamin D supplementation should be considered a candidate in both the treatment and prevention of AD