High-Phytate Diets Increase Amyloid β Deposition and Apoptotic Neuronal Cell Death in a Rat Model

Amyloid-β (Aβ) accumulation in the hippocampus is an essential event in the pathogenesis of Alzheimer’s disease. Insoluble Aβ is formed through the sequential proteolytic hydrolysis of the Aβ precursor protein, which is cleaved by proteolytic secretases. However, the pathophysiological mechanisms of Aβ accumulation remain elusive. Here, we report that rats fed high-phytate diets showed Aβ accumulation and increased apoptotic neuronal cell death in the hippocampus through the activation of the amyloidogenic pathway in the hippocampus. Immunoblotting and immunohistochemical analyses confirmed that the overexpression of BACE1 β-secretase, a critical enzyme for Aβ generation, exacerbated the hippocampal Aβ accumulation in rats fed high-phytate diets. Moreover, we identified that parathyroid hormone, a physiological hormone responding to the phytate-mediated dysregulation of calcium and phosphate homeostasis, plays an essential role in the transcriptional activation of the Aβ precursor protein and BACE1 through the vitamin D receptor and retinoid X receptor axis. Thus, our findings suggest that phytate-mediated dysregulation of calcium and phosphate is a substantial risk factor for elevated Aβ accumulation and apoptotic neuronal cell death in rats.

Switched Aβ43 generation in familial Alzheimer’s disease with presenilin 1 mutation

Presenilin (PS) with a genetic mutation generates abundant β-amyloid protein (Aβ) 43. Senile plaques are formed by Aβ43 in the cerebral parenchyma together with Aβ42 at middle ages. These brains cause the early onset of Alzheimer’s disease (AD), which is known as familial Alzheimer’s disease (FAD). Based on the stepwise processing model of Aβ generation by γ-secretase, we reassessed the levels of Aβs in the cerebrospinal fluid (CSF) of FAD participants. While low levels of Aβ38, Aβ40, and Aβ42 were generated in the CSF of FAD participants, the levels of Aβ43 were unchanged in some of them compared with other participants. We sought to investigate why the level of Aβ43 was unchanged in FAD participants. These characteristics of Aβ generation were observed in the γ-secretase assay in vitro using cells, which express FAD mutations in PS1. Aβ38 and Aβ40 generation from their precursors, Aβ42 and Aβ43, was decreased in PS1 mutants compared with wild-type (WT) PS1, as observed in the CSF. Both the ratios of Aβ38/Aβ42 and Aβ40/Aβ43 in PS1 mutants were lower than those in the WT. However, the ratio of Aβ43/amyloid precursor protein intracellular domain (AICD) increased in the PS1 mutants in an onset age dependency, while other Aβ/AICD ratios were decreased or unchanged. Importantly, liquid chromatography–mass spectrometry found that the generation of Aβ43 was stimulated from Aβ48 in PS1 mutants. This result indicates that PS1 mutants switched the Aβ43 generating line, which reflects the level of Aβ43 in the CSF and forming senile plaques.

Crocin inhibited amyloid-beta (Aβ) generation via promoting non-amyloidogenic APP processing and suppressed ER stress UPR signaling in N2a/APP cells

Background: Crocin is a major active component of saffron (Crocus sativus) with many beneficial effects. More recently, crocin has been proposed for management of neurodegenerative diseases such as Alzheimer's disease (AD). Here, we demonstrated for the first time that crocin reduced amyloid-beta generation through promoting alpha cleavage of APP processing and inhibited ER stress by attenuating UPR signaling in N2a/APP cells. Methodology: Mouse neuroblastoma N2a cells stably transfected with the Swedish mutant APP (N2a/APP) was used as a cellular model for AD pathogenesis. Vector transfected cells (N2a/vector) were employed to serve as control. The toxicity of crocin was first evaluated and non-toxic treatment of crocin (>30 micromolar for 24 h) was used for further investigations. Amyloid beta levels were determined by ELISA. Expression levels of UPR signaling proteins were determined by using Western blot. Results: Crocin significantly inhibited the protein expression of total APP in N2a/APP cells and promoted alpha cleavage of APP processing to increase sAPPalpha generation, but only modestly reduced BACE-1 and PS1, suggesting amyloid beta reduction by crocin was mainly associated with the non-amyloidogenic APP processing. Further investigation on ER stress related protein expressions showed that GRP78, CHOP, p-PERK, p-eIF2alpha, p-IREalpha, XBP1, ATF6alpha, and PDI were all significantly elevated in N2a/APP cells compared to N2a/vector. Crocin effectively reduced the levels of GRP78 and CHOP, and significantly inhibited p-PERK/p-eIF2, and AT6, while slightly reduced p-IRE1alpha. Conclusion: The present study showed that crocin was effective at blocking amyloid beta generation and inhibiting ER stress associated overactivation of UPR signaling in AD cell model N2a/APP. The results provided evidence for crocin as useful natural product for the treatment of AD.

Caesalpinia mimosoides Leaf Extract Promotes Neurite Outgrowth and Inhibits BACE1 Activity in Mutant APP-Overexpressing Neuronal Neuro2a Cells

Alzheimer’s disease (AD) is implicated in the imbalance of several proteins, including Amyloid-β (Aβ), amyloid precursor protein (APP), and BACE1. APP overexpression interferes with neurite outgrowth, while BACE1 plays a role in Aβ generation. Medicinal herbs with effects on neurite outgrowth stimulation and BACE1 inhibition may benefit AD. This study aimed to investigate the neurite outgrowth stimulatory effect, along with BACE1 inhibition of Caesalpinia mimosoides (CM), using wild-type (Neuro2a) and APP (Swedish mutant)-overexpressing (Neuro2a/APPSwe) neurons. The methanol extract of CM leaves stimulated neurite outgrowth in wild-type and APP-overexpressing cells. After exposure to the extract, the mRNA expression of the neurite outgrowth activation genes growth-associated protein-43 (GAP-43) and teneurin-4 (Ten-4) was increased in both Neuro2a and Neuro2a/APPSwe cells, while the mRNA expression of neurite outgrowth negative regulators Nogo receptor (NgR) and Lingo-1 was reduced. Additionally, the extract suppressed BACE1 activity in the APP-overexpressing neurons. Virtual screening demonstrated that quercetin-3′-glucuronide, quercetin-3-O-glucoside, clausarinol, and theogallin were possible inhibitors of BACE1. ADMET was analyzed to predict drug-likeness properties of CM-constituents. These results suggest that CM extract promotes neurite outgrowth and inhibits BACE1 activity in APP-overexpressing neurons. Thus, CM may serve as a source of drugs for AD treatment. Additional studies for full identification of bioactive constituents and to confirm the neuritogenesis in vivo are needed for translation into clinic of the present findings.

Copper, Iron, Selenium and Lipo-Glycemic Dysmetabolism in Alzheimer’s Disease

The aim of the present review is to discuss traditional hypotheses on the etiopathogenesis of Alzheimer’s disease (AD), as well as the role of metabolic-syndrome-related mechanisms in AD development with a special focus on advanced glycation end-products (AGEs) and their role in metal-induced neurodegeneration in AD. Persistent hyperglycemia along with oxidative stress results in increased protein glycation and formation of AGEs. The latter were shown to possess a wide spectrum of neurotoxic effects including increased Aβ generation and aggregation. In addition, AGE binding to receptor for AGE (RAGE) induces a variety of pathways contributing to neuroinflammation. The existing data also demonstrate that AGE toxicity seems to mediate the involvement of copper (Cu) and potentially other metals in AD pathogenesis. Specifically, Cu promotes AGE formation, AGE-Aβ cross-linking and up-regulation of RAGE expression. Moreover, Aβ glycation was shown to increase prooxidant effects of Cu through Fenton chemistry. Given the role of AGE and RAGE, as well as metal toxicity in AD pathogenesis, it is proposed that metal chelation and/or incretins may slow down oxidative damage. In addition, selenium (Se) compounds seem to attenuate the intracellular toxicity of the deranged tau and Aβ, as well as inhibiting AGE accumulation and metal-induced neurotoxicity.

Mechanism of Cellular Formation and In Vivo Seeding Effects of Hexameric β-amyloid Assemblies

The β-amyloid peptide (Aβ) is the main constituent of senile plaques, a typical hallmark of Alzheimer’s disease (AD). Monomeric Aβ is generated through sequential processing of the amyloid precursor protein (APP), with a final step involving γ-secretase activity. In AD, Aβ monomers assemble in oligomers and ultimately fibrils depositing in plaques. Importantly, Aβ toxicity appears related to its soluble oligomeric intermediates. In particular, recombinant Aβ studies described Aβ hexamers as critical oligomeric nuclei. We recently identified hexameric Aβ assemblies in a cellular model, and revealed their ability to enhance recombinant Aβ aggregation in vitro. Here, we assessed the contribution of similar hexameric-like Aβ assemblies to the development of amyloid pathology. We report their early presence in both transgenic mice brains exhibiting human Aβ pathology and cerebrospinal fluid of AD patients, suggesting hexameric Aβ as a putative novel AD biomarker. Using isolated cell-derived hexameric Aβ, we report the potential of these assemblies to seed other human Aβ species, resulting in neuronal toxicity in vitro and amyloid deposition aggravation in vivo. In order to identify key contributors to their formation in a cellular context, we investigated the role of presenilin-1 (PS1) and presenilin-2 (PS2) in the formation of hexameric-like Aβ assemblies. As catalytic subunits of the γ-secretase complex, PS1 and PS2 can differentially participate in Aβ generation. Using CRISPR-Cas9-modified neuronal-like cell lines knockdown for each of the two presenilins, we present experimental evidence suggesting a direct link between the PS2-dependent pathway and the release of hexameric-like Aβ assemblies in extracellular vesicles.

Amyloid beta oligomers modulate neuronal autophagy through the primary cilium

The major neurodegenerative diseases, like Alzheimer disease (AD), accumulate neuropathogenic proteins that compromise autophagic function. In AD, autophagy contributes to intracellular APP processing and amyloid beta (Aβ) generation by mutant presenilin-1 (PS1). However, how extracellular soluble Aβ oligomers (Aβo) impact intracellular autophagy is not well understood. The primary cilium (PC), a signaling organelle on the surface of mature neurons and glia, is able to bind Aβ. Since PC signaling pathways knowingly modify autophagy in non-brain cells, we here investigated the role of neuronal PC in the modulation of autophagy during acute extracellular Aβo overload. Our results show that, in vivo, recombinant Aβo require the presence of neuronal PC to modulate early autophagy and to induce the accumulation of autophagic vacuoles in an age-dependent manner. We show that activated Akt mediates these effects in an age-dependent manner, and that ciliary p75NTR receptor is required to block autophagy by Aβo. These findings demonstrate that neuronal PC in the adult brain participates in the deleterious effects mediated by soluble Aβo. The PC should therefore be considered as a target organelle to modulate autophagy for the treatment of neurodegenerative diseases.

The Role of PGC1α in Alzheimer’s Disease and Therapeutic Interventions

The peroxisome proliferator-activated receptor co-activator-1α (PGC1α) belongs to a family of transcriptional regulators, which act as co-activators for a number of transcription factors, including PPARs, NRFs, oestrogen receptors, etc. PGC1α has been implicated in the control of mitochondrial biogenesis, the regulation of the synthesis of ROS and inflammatory cytokines, as well as genes controlling metabolic processes. The levels of PGC1α have been shown to be altered in neurodegenerative disorders. In the brains of Alzheimer’s disease (AD) patients and animal models of amyloidosis, PGC1α expression was reduced compared with healthy individuals. Recently, it was shown that overexpression of PGC1α resulted in reduced amyloid-β (Aβ) generation, particularly by regulating the expression of BACE1, the rate-limiting enzyme involved in the production of Aβ. These results provide evidence pointing toward PGC1α activation as a new therapeutic avenue for AD, which has been supported by the promising observations of treatments with drugs that enhance the expression of PGC1α and gene therapy studies in animal models of AD. This review summarizes the different ways and mechanisms whereby PGC1α can be neuroprotective in AD and the pre-clinical treatments that have been explored so far.