Vitamin D Receptor Regulates Amyloid Beta 1–42 Production with Protein Disulfide Isomerase A3

Abstract

The challenge of understanding the biology of neuronal amyloid processing could provide a basis for understanding the amyloid pathology in Alzheimer's disease (AD). Based on our previous studies, we have suggested that AD might be the consequence of a hormonal imbalance in which the critical hormone is vitamin D. The present study primarily focused on the creation of a condition that prevents the genomic or nongenomic action of vitamin D by disrupting vitamin D receptors (VDR or PDIA3/1,25MARRS); the effects of these disruptions on the series of proteins involved in secretases that play a crucial role in amyloid pathology and on amyloid beta (Aβ) production in primary cortical neurons were observed. VDR and PDIA3/1,25MARRS genes were silenced separately or simultaneously in E16 primary rat cortical neurons. The expression of target genes involved in APP processing, including Presenilin1, Presenilin2, Nicastrin, BACE1, ADAM10, and APP, was investigated with qRT-PCR and Western blot in this model. 1,25-Dihydroxyvitamin D treatments were used to verify any transcriptional regulation data gathered from siRNA treatments by determining the mRNA expression of the target genes. Immunofluorescence labeling was used for the verification of silencing experiments and intracellular Aβ1-42 production. Extracellular Aβ1-42 level was assessed with ELISA. mRNA and protein expression results showed that 1,25-dihydroxyvitamin D might affect the transcriptional regulation of the genes involved in APP processing. The intracellular and extracellular Aβ1-42 measurements in our study support this suggestion. Consequently, we suggest that 1,25-dihydroxyvitamin D and its receptors are important parts of the amyloid processing pathway in neurons.

Vitamin D receptor is present on the neuronal plasma membrane and is co-localized with amyloid precursor protein, ADAM10 or Nicastrin

“…Therefore, we labelled VDR and PDIA3/1,25MARRS on the surface of living neuronal cells and determined that VDR was abundantly localized on the neuronal membrane. Note that we have confirmed the specificity of the anti-VDR antibody which was used in immunofluorescent labeling and cell surface staining, in our previous study [ 9 ]. The presence of VDR on the plasma membrane was also confirmed in SH-SY5Y cells.…”

“…The results of our previous study [ 9 ] led to questions about the VDR-dependent regulation of APP processing proteins. One potential regulatory mechanism was transcriptional regulation by VDR [ 9 ], and the other was the possible rapid response (RR) activity of the VDR.…”

“…The results of our previous study [ 9 ] led to questions about the VDR-dependent regulation of APP processing proteins. One potential regulatory mechanism was transcriptional regulation by VDR [ 9 ], and the other was the possible rapid response (RR) activity of the VDR. Some studies indicate that the RR properties, which are defined as non-genomic effects of steroid hormones, are mediated by receptors located near or associated with the plasma membrane or its caveolae components [ 25 – 27 ].…”

“…Our in vivo and in vitro studies [ 2 – 8 ] and other publications in the field support the effect of vitamin D on neurodegeneration and Alzheimer’s disease (AD), but the cellular mechanisms involved in this effect is still unknown. The intriguingly complex effects of vitamin D receptor (VDR) silencing or 1,25-Dihydroxyvitamin D 3 treatments on α-, β-, γ-secretases, APP and the obvious result on amyloid production that we demonstrated in our previous study [ 9 ] indicated that some of the vitamin D/its receptors depended regulations might not be explained solely by transcriptional regulation. This suggestion led us to investigate the localization of VDR in the neuronal plasma membrane, possibly as a part of a signal relaying mechanism or as a partner of the enzyme complexes (i.e: APP processing enzymes).…”

Hypovitaminosis D and Aging: Is There a Role in Muscle and Brain Health?

“…It has been suggested that vitamin D increases the AB clearance by the blood-brain barrier, increasing its brain-to-blood efflux though both genomic and non-genomic action [57,58]. Moreover, in vitro primary cultures of cortical neurons show that vitamin D is directly implicated in the production of Aβ and can downregulate its expression [59]. Several genes involved in the pathogenesis of AD have a vitamin D responding element within their sequences [60].…”