The physical approximation of APP and BACE-1: A key event in alzheimer's disease pathogenesis

Ferroptosis: A new strategy for targeting Alzheimer's disease

Alzheimer's disease (AD) is a neurodegenerative disorder characterized by a complex pathogenesis, which involves the formation of amyloid plaques and neurofibrillary tangles. Many recent studies have revealed a close association between ferroptosis and the pathogenesis of AD. Factors such as ferroptosis-associated iron overload, lipid peroxidation, disturbances in redox homeostasis, and accumulation of reactive oxygen species have been found to contribute to the pathological progression of AD. In this review, we explore the mechanisms underlying ferroptosis, describe the link between ferroptosis and AD, and examine the reported efficacy of ferroptosis inhibitors in treating AD. Finally, we discuss the potential challenges to ferroptosis inhibitors use in the clinic, enabling their faster use in clinical treatment.

Proteomic Analysis Reveals Physiological Activities of Aβ Peptide for Alzheimer's Disease

With the rapid progress in deciphering the pathogenesis of Alzheimer's disease (AD), it has been widely accepted that the accumulation of misfolded amyloid β (Aβ) in the brain could cause the neurodegeneration in AD. Although much evidence demonstrates the neurotoxicity of Aβ, the role of Aβ in the nervous system are complex. However, more comprehensive studies are needed to understand the physiological effect of Aβ40 monomers in depth. To explore the physiological mechanism of Aβ, we employed mass spectrometry to investigate the altered proteomic events induced by a lower submicromolar concentration of Aβ. Human neuroblastoma SH-SY5Y cells were exposed to five different concentrations of Aβ1-40 monomers and collected at four time points. The proteomic analysis revealed the time-course behavior of proteins involved in biological processes, such as RNA splicing, nuclear transport and protein localization. Further biological studies indicated that Aβ40 monomers may activate PI3K/AKT signaling to regulate p-Tau, Ezrin and MAP2. These three proteins are associated with dendritic morphogenesis, neuronal polarity, synaptogenesis, axon establishment and axon elongation. Moreover, Aβ40 monomers may regulate their physiological forms by inhibiting the expression of BACE1 and APP via activation of the ERK1/2 pathway. A comprehensive exploration of pathological and physiological mechanisms of Aβ is beneficial for exploring novel treatment.

Sulfonamido, amido heterocyclic adducts of tetrazole derivatives as BACE1 inhibitors: in silico exploration

Alzheimer's disease is a neurodegenerative disorder accounting for 60-80% of dementia cases and is accompanied by a high mortality rate in patients above 70 years of age. The formation of senile plaques composed of amyloid-β protein is a hallmark of Alzheimer's disease. Beta-site APP cleaving enzyme 1 (BACE1) is a proteolytic enzyme involved in the degradation of amyloid precursor protein, which further degrades to form toxic amyloid-β fragments. Hence, inhibition of BACE1 was stated to be an effective strategy for Alzheimer's therapeutics. Keeping in mind the structures of different BACE1 inhibitors that had reached the clinical trials, we designed a library of compounds (total 164) based on a substituted 5-amino tetrazole scaffold which was an isosteric replacement of the cyclic amidine moiety, a common component of the BACE1 inhibitors which reached the clinical trials. The scaffold was linked to different structural moieties with the aid of an amide or sulfonamide bond to design some novel molecules. Molecular docking was initially performed and the top 5 molecules were selected based on docking scores and protein-ligand interactions. Furthermore, molecular dynamic simulations were performed for these molecules (3g, 7k, 8n, 9d, 9g) for 100 ns and MM-GBSA calculations were performed for each of these complexes. After critical evaluation of the obtained results, three potential molecules (9d, 8n, and 7k) were forwarded for prolonged stability studies by performing molecular dynamic simulations for 250 ns and simultaneous MM-GBSA calculations. It was observed that the compounds (9d, 8n, and 7k) were forming good interactions with the amino acid residues of the catalytic site of the enzyme with multiple non-covalent interactions. In MD simulations, the compounds have shown better stability and better binding energy throughout the runtime.

The relationship between Alzheimer disease and thyroiditis: A two-sample Mendelian randomization study

This study aims to investigate the causal effect of Alzheimer disease on thyroiditis using medical English and the Nature journal style. Genome-wide association data for Alzheimer disease and thyroiditis were obtained from the Mendelian Randomization (MR) platform. Single nucleotide polymorphisms (SNPs) significantly associated with Alzheimer disease were identified and used as instrumental variables (IVs) to examine the causal relationship between Alzheimer disease and thyroiditis, employing a 2-sample MR study design. Five statistical methods, including inverse-variance weighted (IVW) method, weighted median estimation, simple mode estimation, weighted mode estimation, and MR-Egger regression, were utilized. In the study, 13 single nucleotide polymorphisms (SNPs) were identified to be significantly associated with Alzheimer disease (P < 5 × 10-8, linkage disequilibrium r2 < 0.001). Upon evaluation using different methods, a consistent association between Alzheimer disease and thyroiditis was observed inverse variance-weighted method [IVW]: odds ratio [OR] 1.32, 95% confidence interval [CI] 1.01-1.72; weighted median estimator: OR 1.32, 95% CI 1.01-1.72; Mendelian randomization Egger regression: OR 1.29, 95% CI 0.92-1.81), indicating a positive correlation between Alzheimer disease and increased risk of thyroiditis. There was no evidence suggesting that the observed causal relationship between Alzheimer disease and thyroiditis risk could be influenced by pleiotropy (Mendelian randomization Egger intercept 0.0058, P = .88. Our MR analysis reveals causal association of Alzheimer disease and thyroiditis, despite observational studies reporting an association between Alzheimer disease and thyroiditis.

BACE1 and SCD1 are associated with neurodegeneration

Introduction

Proteolytic processing of amyloid protein precursor by β-site secretase enzyme (BACE1) is dependent on the cellular lipid composition and is affected by endomembrane trafficking in dementia and Alzheimer's disease (AD). Stearoyl-CoA desaturase 1 (SCD1) is responsible for the synthesis of fatty acid monounsaturation (MUFAs), whose accumulation is strongly associated with cognitive dysfunction.

Methods

In this study, we analyzed the relationship between BACE1 and SCD1 in vivo and in vitro neurodegenerative models and their association in familial AD (FAD), sporadic AD (SAD), and cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL) using microscopy, biochemical, and mass SPECT approach.

Results

Our findings showed that BACE1 and SCD1 immunoreactivities were increased and colocalized in astrocytes of the hippocampus in a rat model of global cerebral ischemia (2-VO). A synergistic effect of double BACE1/SCD1 silencing on the recovery of motor and cognitive functions was obtained. This neuroprotective regulation involved the segregation of phospholipids (PLs) associated with polyunsaturated fatty acids in the hippocampus, cerebrospinal fluid, and serum. The double silencing in the sham and ischemic groups was stronger in the serum, inducing an inverse ratio between total phosphatydilcholine (PC) and lysophosphatidylcholine (LPC), represented mainly by the reduction of PC 38:4 and PC 36:4 and an increase in LPC 16:0 and LPC 18:0. Furthermore, PC 38:4 and PC:36:4 levels augmented in pathological conditions in in vitro AD models. BACE1 and SCD1 increases were confirmed in the hippocampus of FAD, SAD, and CADASIL.

Conclusion

Therefore, the findings suggest a novel convergence of BACE-1 and SCD1 in neurodegeneration, related to pro-inflammatory phospholipids.

The Cleavage-Specific Tau 12A12mAb Exerts an Anti-Amyloidogenic Action by Modulating the Endocytic and Bioenergetic Pathways in Alzheimer's Disease Mouse Model

Beyond deficits in hippocampal-dependent episodic memory, Alzheimer's Disease (AD) features sensory impairment in visual cognition consistent with extensive neuropathology in the retina. 12A12 is a monoclonal cleavage specific antibody (mAb) that in vivo selectively neutralizes the AD-relevant, harmful N-terminal 20-22 kDa tau fragment(s) (i.e., NH₂htau) without affecting the full-length normal protein. When systemically injected into the Tg2576 mouse model overexpressing a mutant form of Amyloid Precursor Protein (APP), APPK670/671L linked to early onset familial AD, this conformation-specific tau mAb successfully reduces the NH₂htau accumulating both in their brain and retina and, thus, markedly alleviates the phenotype-associated signs. By means of a combined biochemical and metabolic experimental approach, we report that 12A12mAb downregulates the steady state expression levels of APP and Beta-Secretase 1 (BACE-1) and, thus, limits the Amyloid beta (Aβ) production both in the hippocampus and retina from this AD animal model. The local, antibody-mediated anti-amyloidogenic action is paralleled in vivo by coordinated modulation of the endocytic (BIN1, RIN3) and bioenergetic (glycolysis and L-Lactate) pathways. These findings indicate for the first time that similar molecular and metabolic retino-cerebral pathways are modulated in a coordinated fashion in response to 12A12mAb treatment to tackle the neurosensorial Aβ accumulation in AD neurodegeneration.

The Therapeutic Effects of Seven Lycophyte Compounds on Cell Models of Alzheimer’s Disease

Background: As an acetylcholinesterase inhibitor (AChEI), Huperzine-A (Hup-A) is marketed for treatment of mild to moderate Alzheimer’s disease (AD) for decades in China. However, Hup-A causes some side effects. To search for new analogs or derivatives of Hup-A, we produced five Lycophyte alkaloids and two analogues by chemical synthesis: Lyconadins A-E, H-R-NOB, and 2JY-OBZ4. Objective: To systematically evaluated the therapeutic effects of the seven compounds on AD cell models. Methods: We assessed the effects of the seven compounds on cell viability via CCK-8 kit and used HEK293-hTau cells and N2a-hAPP cells as AD cell models to evaluate their potential therapeutic effects. We examined their effects on cholinesterase activity by employing the mice primary neuron. Results: All compounds did not affect cell viability; in addition, Lyconadin A and 2JY-OBZ4 particularly increased cell viability. Lyconadin D and Lyconadin E restored tau phosphorylation at Thr231, and H-R-NOB and 2JY-OBZ4 restored tau phosphorylation at Thr231 and Ser396 in GSK-3β-transfected HEK293-hTau cells. 2JY-OBZ4 decreased the level of PP2Ac-pY307 and increased the level of PP2Ac-mL309, supporting that 2JY-OBZ4 may activate PP2A. Lyconadin B, Lyconadin D, Lyconadin E, H-R-NOB, and 2JY-OBZ4 increased sAβPPα level in N2a-hAPP cells. 2JY-OBZ4 decreased the levels of BACE1 and sAβPPβ, thereby reduced Aβ production. Seven compounds exhibited weaker AChE activity inhibition efficiency than Hup-A. Among them, 2JY-OBZ4 showed the strongest AChE inhibition activity with an inhibition rate of 17% at 10μM. Conclusion: Among the seven lycophyte compounds, 2JY-OBZ4 showed the most expected effects on promoting cell viability, downregulating tau hyperphosphorylation, and Aβ production and inhibiting AChE in AD.

Naturally-Occurring Antibodies Against Bim are Decreased in Alzheimer's Disease and Attenuate AD-type Pathology in a Mouse Model

Increased neuronal apoptosis is an important pathological feature of Alzheimer's disease (AD). The Bcl-2-interacting mediator of cell death (Bim) mediates amyloid-beta (Aβ)-induced neuronal apoptosis. Naturally-occurring antibodies against Bim (NAbs-Bim) exist in human blood, with their levels and functions unknown in AD. In this study, we found that circulating NAbs-Bim were decreased in AD patients. Plasma levels of NAbs-Bim were negatively associated with brain amyloid burden and positively associated with cognitive functions. Furthermore, NAbs-Bim purified from intravenous immunoglobulin rescued the behavioral deficits and ameliorated Aβ deposition, tau hyperphosphorylation, microgliosis, and neuronal apoptosis in APP/PS1 mice. In vitro investigations demonstrated that NAbs-Bim were neuroprotective against AD through neutralizing Bim-directed neuronal apoptosis and the amyloidogenic processing of amyloid precursor protein. These findings indicate that the decrease of NAbs-Bim might contribute to the pathogenesis of AD and immunotherapies targeting Bim hold promise for the treatment of AD.

Herpes Simplex Virus Infection Increases Beta-Amyloid Production and Induces the Development of Alzheimer's Disease

Background

Alzheimer's disease, a neurodegenerative memory disease, primarily results from the formation of amyloid plaques (Aβ) that gradually inhibit neuron communications. The entire mechanism of Aβ production remains unclear to date, and it is of particular interest among scientists to find out the exact mechanism that leads to amyloid precursor protein (APP) cleavage through the amyloidogenic pathway so that effective treatments can be developed.

Method

2 sets of experiments with the use of human H4-N cell lines are proposed to fully investigate the validity of the hypothesis. All of the experiments would involve immunoblotting of Aβ using an anti-Aβ antibody, and the results would be analyzed with the assistance of an image analyzer. A significant amount of Aβ would be expected to be present in the cytoplasm of cells with herpes simplex virus (HSV-1) applied, as APP endocytosis would be induced by HSV-1, which leads to higher Aβ levels inside the cell.

Results

In this paper, a new hypothesis is presented on how HSV-1 infection initiates APP endocytosis and causes an increase in APP cleavage and Aβ production inside the cells. It is also hypothesized that increased Aβ peptides exit the cell via exocytosis, therefore, leading to the development of Alzheimer's disease. The findings will support the hypothesis if intracellular Aβ concentration is significantly higher after the introduction of dHSV-1 and subsequently if extracellular Aβ concentration becomes higher without TeNT exocytosis inhibition.

Conclusion

The results of this study would provide valuable insights into the mechanisms underlying Alzheimer's disease and open new scopes of research for its potential treatments. Further studies on virus infection and the development of memory diseases should be conducted to investigate possible correlations.

Diosmetin Targeted at Peroxisome Proliferator-Activated Receptor Gamma Alleviates Advanced Glycation End Products Induced Neuronal Injury

The present study aimed to evaluate the role of diosmetin in alleviating advanced glycation end products (AGEs)-induced Alzheimer’s disease (AD)-like pathology and to clarify the action mechanisms. Before stimulation with AGEs (200 μg/mL), SH-SY5Y cells were treated with diosmetin (10 μmol/L), increasing cell viability. The induction of AGEs on the reactive oxygen species overproduction and downregulation of antioxidant enzyme activities, including superoxide dismutase, glutathione peroxidase, and catalase, were ameliorated by diosmetin. Amyloid precursor protein upregulation, accompanied by increased production of amyloid-β, caused by AGEs, was reversed by diosmetin. In the presence of diosmetin, not only β-site amyloid precursor protein cleaving enzyme1 expression was lowered, but the protein levels of insulin-degrading enzyme and neprilysin were elevated. Diosmetin protects SH-SY5Y cells from endoplasmic reticulum (ER) stress response to AGEs by suppressing ER stress-induced glucose regulated protein 78, thereby downregulating protein kinase R-like endoplasmic reticulum kinase, eukaryotic initiation factor 2 α, activating transcription factor 4, and C/EBP homologous protein. Diosmetin-pretreated cells had a lower degree of apoptotic DNA fragmentation; this effect may be associated with B-cell lymphoma (Bcl) 2 protein upregulation, Bcl-2-associated X protein downregulation, and decreased activities of caspase-12/-9/-3. The reversion of diosmetin on the AGEs-induced harmful effects was similar to that produced by pioglitazone. The peroxisome proliferator-activated receptor (PPAR)γ antagonist T0070907 (5 μmol/L) abolished the beneficial effects of diosmetin on AGEs-treated SH-SY5Y cells, indicating the involvement of PPARγ. We conclude that diosmetin protects neuroblastoma cells against AGEs-induced ER injury via multiple mechanisms and may be a potential option for AD.

Aging impact on amyloid precursor protein neuronal trafficking

Neurons live a lifetime. Neuronal aging may increase the risk of Alzheimer's disease. How does neuronal membrane trafficking maintain synapse function during aging? In the normal aged brain, intraneuronal beta-amyloid (Aβ) accumulates without Alzheimer's disease mutations or risk variants. However, do changes with neuronal aging potentiate Aβ accumulation? We reviewed the membrane trafficking of the amyloid precursor protein in neurons and highlighted its importance in Aβ production. Importantly, we reviewed the evidence supporting the impact of aging on neuronal membrane trafficking, APP processing, and consequently Aβ production. Dissecting the molecular regulators of APP trafficking during neuronal aging is required to identify strategies to delay synaptic decline and protect from Alzheimer's disease.

The neuronal-specific isoform of BIN1 regulates β-secretase cleavage of APP and Aβ generation in a RIN3-dependent manner

Genome-wide association studies have identified BIN1 (Bridging integrator 1) and RIN3 (Ras and Rab interactor 3) as genetic risk factors for late-onset Alzheimer's disease (LOAD). The neuronal isoform of BIN1 (BIN1V1), but not the non-neuronal isoform (BIN1V9), has been shown to regulate tau-pathology and Aβ generation via RAB5-mediated endocytosis in neurons. BIN1 directly interacts with RIN3 to initiate RAB5-mediated endocytosis, which is essential for β-secretase (BACE1)-mediated β-secretase cleavage of β-amyloid precursor protein (APP) to generate Amyloid-β (Aβ), the key component of senile plaques in AD. Understanding the regulatory roles of BIN1 (neuronal BIN1V1) and RIN3 in β-secretase mediated cleavage of APP and Aβ generation is key to developing novel therapeutics to delay or prevent AD progression. Neuronal and non-neuronal isoforms of BIN1 (BIN1V1 and BIN1V9, respectively) were introduced with RIN3 into an in vitro cell-based system to test RIN3-dependent effects of neuronal BIN1V1 and non-neuronal BIN1V9 on β-secretase-mediated cleavage of APP and Aβ generation. Confocal microscopy was performed to examine RIN3-dependent subcellular localization of BIN1V1 and BIN1V9. Western blot analysis was performed to assess the effects of RIN3 and BIN1V1/BIN1V9 on β-secretase mediated processing of APP. We enriched cells expressing BIN1V1 without or with RIN3 via FACS to measure Aβ generation using Aβ ELISA assay, and to evaluate APP internalization by chasing biotinylated or antibody-labeled cell surface APP. Neuronal BIN1V1 containing the CLAP domain and non-neuronal BIN1V9 lacking the CLAP domain are the major isoforms present in the brain. Employing confocal microscopy, we showed that RIN3 differentially regulates the recruitment of both BIN1V1 and BIN1V9 into RAB5-endosomes. We further showed that BIN1V1, but not BIN1V9, downregulates β-secretase (BACE1)-mediated processing of APP in a RIN3-dependent manner. Overexpression of BIN1V1 also attenuated Aβ generation in a RIN3-dependent manner. Using cell-based internalization assays, we show BIN1V1, but not BIN1V9, delays the endocytosis of APP, but not of BACE1, into early endosomes, thereby spatially and temporally separating these two proteins into different cellular compartments, resulting in reduced cleavage of APP by BACE1 and reduced Aβ generation-all in a RIN3-dependent manner. Finally, we show that RIN3 sequesters BIN1V1 in RAB5-positive early endosomes, likely via the CLAP-domain, resulting in attenuated β-secretase processing of APP and Aβ generation by delaying endocytosis of APP. Our findings provide new mechanistic data on how two AD-associated molecules, RIN3 and BIN1 (neuronal BIN1V1), interact to govern Aβ production, implicating these two proteins as potential therapeutic targets for the prevention and treatment of AD.

Impairment of the autophagy-lysosomal pathway in Alzheimer's diseases: Pathogenic mechanisms and therapeutic potential

Alzheimer's disease (AD), the most common neurodegenerative disorder, is characterized by memory loss and cognitive dysfunction. The accumulation of misfolded protein aggregates including amyloid beta (Aβ) peptides and microtubule associated protein tau (MAPT/tau) in neuronal cells are hallmarks of AD. So far, the exact underlying mechanisms for the aetiologies of AD have not been fully understood and the effective treatment for AD is limited. Autophagy is an evolutionarily conserved cellular catabolic process by which damaged cellular organelles and protein aggregates are degraded via lysosomes. Recently, there is accumulating evidence linking the impairment of the autophagy–lysosomal pathway with AD pathogenesis. Interestingly, the enhancement of autophagy to remove protein aggregates has been proposed as a promising therapeutic strategy for AD. Here, we first summarize the recent genetic, pathological and experimental studies regarding the impairment of the autophagy–lysosomal pathway in AD. We then describe the interplay between the autophagy–lysosomal pathway and two pathological proteins, Aβ and MAPT/tau, in AD. Finally, we discuss potential therapeutic strategies and small molecules that target the autophagy–lysosomal pathway for AD treatment both in animal models and in clinical trials. Overall, this article highlights the pivotal functions of the autophagy–lysosomal pathway in AD pathogenesis and potential druggable targets in the autophagy–lysosomal pathway for AD treatment.

The Alzheimer's gene SORL1 is a regulator of endosomal traffic and recycling in human neurons

BACKGROUND

Loss of the Sortilin-related receptor 1 (SORL1) gene seems to act as a causal event for Alzheimer's disease (AD). Recent studies have established that loss of SORL1, as well as mutations in autosomal dominant AD genes APP and PSEN1/2, pathogenically converge by swelling early endosomes, AD's cytopathological hallmark. Acting together with the retromer trafficking complex, SORL1 has been shown to regulate the recycling of the amyloid precursor protein (APP) out of the endosome, contributing to endosomal swelling and to APP misprocessing. We hypothesized that SORL1 plays a broader role in neuronal endosomal recycling and used human induced pluripotent stem cell-derived neurons (hiPSC-Ns) to test this hypothesis. We examined endosomal recycling of three transmembrane proteins linked to AD pathophysiology: APP, the BDNF receptor Tropomyosin-related kinase B (TRKB), and the glutamate receptor subunit AMPA1 (GLUA1).

METHODS

We used isogenic hiPSCs engineered to have SORL1 depleted or to have enhanced SORL1 expression. We differentiated neurons from these cell lines and mapped the trafficking of APP, TRKB and GLUA1 within the endosomal network using confocal microscopy. We also performed cell surface recycling and lysosomal degradation assays to assess the functionality of the endosomal network in both SORL1-depleted and -overexpressing neurons. The functional impact of GLUA1 recycling was determined by measuring synaptic activity. Finally, we analyzed alterations in gene expression in SORL1-depleted neurons using RNA sequencing.

RESULTS

We find that as with APP, endosomal trafficking of GLUA1 and TRKB is impaired by loss of SORL1. We show that trafficking of all three cargoes to late endosomes and lysosomes is affected by manipulating SORL1 expression. We also show that depletion of SORL1 significantly impacts the endosomal recycling pathway for APP and GLUA1 at the level of the recycling endosome and trafficking to the cell surface. This has a functional effect on neuronal activity as shown by multi-electrode array (MEA). Conversely, increased SORL1 expression enhances endosomal recycling for APP and GLUA1. Our unbiased transcriptomic data further support SORL1's role in endosomal recycling. We observe altered expression networks that regulate cell surface trafficking and neurotrophic signaling in SORL1-depleted neurons.

CONCLUSION

Collectively, and together with other recent observations, these findings suggest that one role for SORL1 is to contribute to endosomal degradation and recycling pathways in neurons, a conclusion that has both pathogenic and therapeutic implications for Alzheimer's disease.

Germacrone alleviates okadaic acid-induced neurotoxicity in PC12 cells via M1 muscarinic receptor-mediated Galphaq (Gq)/phospholipase C beta (PLCβ)/ protein kinase C (PKC) signaling

Alzheimer’s disease (AD) is a neurodegenerative disorder with prominent individual morbidity and mortality among elderly people. Germacrone (Germ) has been reported to exert dominant protective roles in multiple human diseases, and neurological diseases are also included. The intention of this paper is to determine the impacts of Germ on okadaic acid (OA)-treated PC12 cells and confirm the hidden regulatory mechanism. First, PC12 cells were induced by OA in the absence or presence of Germ. Cell counting kit-8 assay was to monitor cell proliferation. Western blot was to test the protein levels of cholinergic muscarinic M1 receptor (CHRM1), Galphaq (Gq), phospholipase C beta (PLCβ) and protein kinase C (PKC). The levels of reactive oxygen species (ROS) and other oxidative stress markers were evaluated using corresponding kits. ELISA was used to estimate the levels of AD markers. RT-qPCR was used to examine the mRNA levels of beta-site amyloid-precursor-protein-cleaving enzyme 1 (BACE-1) and apolipoprotein E (APOE). The results uncovered that Germ enhanced the proliferation of OA-insulted PC12 cells, elevated the protein level of CHRM1 and activated the Gq/PLCβ/PKC signaling. Moreover, after OA-induced PC12 cells were administered with Germ, insufficiency of CHRM1 impeded cell proliferation, enhanced oxidative stress and neuron injury and inactivated the Gq/PLCβ/PKC signaling. Furthermore, the addition of Gq inhibitor UBO-QIC, PLCβ inhibitor U73122 or PKC inhibitor Go6983 reversed the enhanced proliferation, the reduced oxidative stress and neuron injury in OA-treated PC12 cells caused by Germ. Collectively, Germ modulated M1 muscarinic receptor-mediated Gq/PLCβ/PKC signaling, thereby alleviating OA-induced PC12 cell injury.

Rab35 and glucocorticoids regulate APP and BACE1 trafficking to modulate Aβ production

Chronic stress and elevated glucocorticoids (GCs), the major stress hormones, are risk factors for Alzheimer’s disease (AD) and promote AD pathomechanisms, including overproduction of toxic amyloid-β (Aβ) peptides and intraneuronal accumulation of hyperphosphorylated Tau protein. The latter is linked to downregulation of the small GTPase Rab35, which mediates Tau degradation via the endolysosomal pathway. Whether Rab35 is also involved in Aβ overproduction remains an open question. Here, we find that hippocampal Rab35 levels are decreased not only by stress/GC but also by aging, another AD risk factor. Moreover, we show that Rab35 negatively regulates Aβ production by sorting amyloid precursor protein (APP) and β-secretase (BACE1) out of the endosomal network, where they interact to produce Aβ. Interestingly, Rab35 coordinates distinct intracellular trafficking steps for BACE1 and APP, mediated by its effectors OCRL and ACAP2, respectively. Finally, we demonstrate that Rab35 overexpression prevents the amyloidogenic trafficking of APP and BACE1 induced by high GC levels. These studies identify Rab35 as a key regulator of APP processing and suggest that its downregulation may contribute to stress-related and AD-related amyloidogenesis.

Self-Assembly of Superquenched Gold Nanoparticle Nanosensors for Lighting up BACE-1 in Live Cells

The β-site amyloid precursor protein-cleaving enzyme 1 (BACE-1) plays a key role in Alzheimer's disease (AD) pathogenesis and is regarded as a valuable biomarker for AD diagnosis and treatment. The reported BACE-1 assay often suffers from laborious procedures, large sample consumption, and unsatisfactory sensitivity with high background signals. Herein, we report the self-assembly of superquenched gold nanoparticle (AuNP) nanosensors for lighting up the BACE-1 in live cells. Through the self-assembly of both fluorophore-labeled peptide probes and quencher-labeled assistant DNAs on the surface of a single AuNP, a superquenched AuNP nanoprobe is obtained with a high quenching efficiency of 98.37% and a near-zero background fluorescence. The presence of target BACE-1 induces a distinct fluorescence signal as a result of the BACE-1-catalyzed cleavage of peptide probe and the subsequent release of abundant fluorophore moieties from the AuNP nanoprobe. The fluorescence signal can be directly visualized by single-molecule imaging and easily quantified by single-molecule counting. This nanosensor involves only a single nanoprobe for the one-step homogeneous detection of the BACE-1 activity without the requirements of any antibodies and separation steps, and it possesses good selectivity and high sensitivity with a low detection limit of 26.48 pM. Moreover, it can be employed to screen BACE-1 inhibitors and analyze kinetic parameters. Especially, this nanoprobe possesses good stability and can be easily transferred into live cells for the real-time imaging of cellular BACE-1 activity, providing a new platform for BACE-1-associated research and early diagnosis of Alzheimer's disease.

Phosphorylation and Glycosylation of Amyloid-β Protein Precursor: The Relationship to Trafficking and Cleavage in Alzheimer's Disease

Alzheimer's disease (AD) is a neurodegenerative disorder in the central nervous system, and this disease is characterized by extracellular senile plaques and intracellular neurofibrillary tangles. Amyloid-β (Aβ) peptide is the main constituent of senile plaques, and this peptide is derived from the amyloid-β protein precursor (AβPP) through the successive cleaving by β-site AβPP-cleavage enzyme 1 (BACE1) and γ-secretase. AβPP undergoes the progress of post-translational modifications, such as phosphorylation and glycosylation, which might affect the trafficking and the cleavage of AβPP. In the recent years, about 10 phosphorylation sites of AβPP were identified, and they play complex roles in glycosylation modification and cleavage of AβPP. In this article, we introduced the transport and the cleavage pathways of AβPP, then summarized the phosphorylation and glycosylation sites of AβPP, and further discussed the links and relationship between phosphorylation and glycosylation on the pathways of AβPP trafficking and cleavage in order to provide theoretical basis for AD research.

Binding of Inhibitors to BACE1 Affected by pH-Dependent Protonation: An Exploration from Multiple Replica Gaussian Accelerated Molecular Dynamics and MM-GBSA Calculations

To date, inhibiting the activity of β-amyloid cleaving enzyme 1 (BACE1) has been considered an efficient approach for treating Alzheimer's disease (AD). In the current work, multiple replica Gaussian accelerated molecular dynamics (MR-GaMD) simulations and the molecular mechanics general Born surface area (MM-GBSA) method were combined to investigate the effect of pH-dependent protonation on the binding of the inhibitors CS9, C6U, and 6WE to BACE1. Dynamic analyses based on the MR-GaMD trajectory show that pH-dependent protonation strongly affects the structural flexibility, correlated motions, and dynamic behavior of inhibitor-bound BACE1. According to the constructed free energy profiles, in the protonated state at low pH, inhibitor-bound BACE1 tends to populate at more conformations than in high pH. The binding free energies calculated by MM-GBSA suggest that inhibitors possess stronger binding abilities under the protonation conditions at high pH than under the protonation conditions at low pH. Moreover, pH-dependent protonation exerts a significant effect on the hydrogen bonding interactions of CS9, C6U, and 6WE to BACE1, which correspondingly alters the binding abilities of the three inhibitors to BACE1. Furthermore, in different protonated environments, three inhibitors share common interaction clusters and similar binding sites in BACE1, which are reliably used as efficient targets for the design of potent inhibitors of BACE1.

A review of the mechanisms underlying selected comorbidities in Alzheimer's disease

Alzheimer's disease (AD) is a progressive neurodegenerative disorder of the central nervous system (CNS) leading to mental deterioration and devastation, and eventually a fatal outcome. AD affects mostly the elderly. AD is frequently accompanied by hypercholesterolemia, hypertension, atherosclerosis, and diabetes mellitus, and these are significant risk factors of AD. Other conditions triggered by the progression of AD include psychosis, sleep disorders, epilepsy, and depression. One important comorbidity is Down’s syndrome, which directly contributes to the severity and rapid progression of AD. The development of new therapeutic strategies for AD includes the repurposing of drugs currently used for the treatment of comorbidities. A better understanding of the influence of comorbidities on the pathogenesis of AD, and the medications used in its treatment, might allow better control of disease progression, and more effective pharmacotherapy.

Age-Related Intraneuronal Aggregation of Amyloid-β in Endosomes, Mitochondria, Autophagosomes, and Lysosomes

 This work provides new insight into the age-related basis of Alzheimer’s disease (AD), the composition of intraneuronal amyloid (iAβ), and the mechanism of an age-related increase in iAβ in adult AD-model mouse neurons. A new end-specific antibody for Aβ₄₅ and another for aggregated forms of Aβ provide new insight into the composition of iAβ and the mechanism of accumulation in old adult neurons from the 3xTg-AD model mouse. iAβ levels containing aggregates of Aβ₄₅ increased 30-50-fold in neurons from young to old age and were further stimulated upon glutamate treatment. iAβ was 8 times more abundant in 3xTg-AD than non-transgenic neurons with imaged particle sizes following the same log-log distribution, suggesting a similar snow-ball mechanism of intracellular biogenesis. Pathologically misfolded and mislocalized Alz50 tau colocalized with iAβ and rapidly increased following a brief metabolic stress with glutamate. AβPP-CTF, Aβ₄₅, and aggregated Aβ colocalized most strongly with mitochondria and endosomes and less with lysosomes and autophagosomes. Differences in iAβ by sex were minor. These results suggest that incomplete carboxyl-terminal trimming of long Aβs by gamma-secretase produced large intracellular deposits which limited completion of autophagy in aged neurons. Understanding the mechanism of age-related changes in iAβ processing may lead to application of countermeasures to prolong dementia-free health span.

The interplay between lipid and Aβ amyloid homeostasis in Alzheimer's Disease: risk factors and therapeutic opportunities

Alzheimer's Diseases (AD) is characterized by the accumulation of amyloid deposits of Aβ peptide in the brain. Besides genetic background, the presence of other diseases and an unhealthy lifestyle are known risk factors for AD development. Albeit accumulating clinical evidence suggests that an impaired lipid metabolism is related to Aβ deposition, mechanistic insights on the link between amyloid fibril formation/clearance and aberrant lipid interactions are still unavailable. Recently, many studies have described the key role played by membrane bound Aβ assemblies in neurotoxicity. Moreover, it has been suggested that a derangement of the ubiquitin proteasome pathway and autophagy is significantly correlated with toxic Aβ aggregation and dysregulation of lipid levels. Thus, studies focusing on the role played by lipids in Aβ aggregation and proteostasis could represent a promising area of investigation for the design of valuable treatments. In this review we examine current knowledge concerning the effects of lipids in Aβ aggregation and degradation processes, focusing on the therapeutic opportunities that a comprehensive understanding of all biophysical, biochemical, and biological processes involved may disclose.

Gene-based therapies for neurodegenerative diseases

Gene therapy is making a comeback. With its twin promise of targeting disease etiology and 'long-term correction', gene-based therapies (defined here as all forms of genome manipulation) are particularly appealing for neurodegenerative diseases, for which conventional pharmacologic approaches have been largely disappointing. The recent success of a viral-vector-based gene therapy in spinal muscular atrophy-promoting survival and motor function with a single intravenous injection-offers a paradigm for such therapeutic intervention and a platform to build on. Although challenges remain, the newfound optimism largely stems from advances in the development of viral vectors that can diffusely deliver genes throughout the CNS, as well as genome-engineering tools that can manipulate disease pathways in ways that were previously impossible. Surely spinal muscular atrophy cannot be the only neurodegenerative disease amenable to gene therapy, and one can imagine a future in which the toolkit of a clinician will include gene-based therapeutics. The goal of this Review is to highlight advances in the development and application of gene-based therapies for neurodegenerative diseases and offer a prospective look into this emerging arena.

Chinese herbs and acupuncture to improve cognitive function in Alzheimer's disease

Alzheimer's disease (AD) is a neurodegenerative disease with a variety of causes. Traditional Chinese medicine (TCM), which includes the two main approaches of acupuncture and herbal medication, views the human body as a self-controlled system network. Fundamental theories, including "qi," the five elements, and the theory of viscera, form the basis for classification. Diseases in humans are considered to be caused by an imbalance of "yang qi" and "yin qi" that lead to the nonhomeostasis of organs. Acupuncture is derived from 12 main meridians and 365 acupuncture points characterized by "blood and qi." Needling of different positions corresponds to specific disease treatments to increase qi. Treatment with Chinese herbal medicines is based on syndrome differentiation characterized as "Zheng" which differs from the cause orientation approach of Western medicine. In this article, we review basic and clinical research studies that describe TCM herbs and acupuncture for the treatment of AD. Moreover, we propose that these two approaches be integrated to improve the outcomes for AD patients.

Multifaceted Role of Matrix Metalloproteinases in Neurodegenerative Diseases: Pathophysiological and Therapeutic Perspectives

Neurodegeneration is the pathological condition, in which the nervous system or neuron loses its structure, function, or both, leading to progressive degeneration or the death of neurons, and well-defined associations of tissue system, resulting in clinical manifestations. Neuroinflammation has been shown to precede neurodegeneration in several neurodegenerative diseases (NDs). No drug is yet known to delay or treat neurodegeneration. Although the etiology and potential causes of NDs remain widely indefinable, matrix metalloproteinases (MMPs) evidently have a crucial role in the progression of NDs. MMPs, a protein family of zinc (Zn²⁺)-containing endopeptidases, are pivotal agents that are involved in various biological and pathological processes in the central nervous system (CNS). The current review delineates the several emerging evidence demonstrating the effects of MMPs in the progression of NDs, wherein they regulate several processes, such as (neuro)inflammation, microglial activation, amyloid peptide degradation, blood brain barrier (BBB) disruption, dopaminergic apoptosis, and α-synuclein modulation, leading to neurotoxicity and neuron death. Published papers to date were searched via PubMed, MEDLINE, etc., while using selective keywords highlighted in our manuscript. We also aim to shed a light on pathophysiological effect of MMPs in the CNS and focus our attention on its detrimental and beneficial effects in NDs, with a special focus on Parkinson's disease (PD), amyotrophic lateral sclerosis (ALS), Alzheimer's disease (AD), multiple sclerosis (MS), and Huntington's disease (HD), and discussed various therapeutic strategies targeting MMPs, which could serve as potential modulators in NDs. Over time, several agents have been developed in order to overcome challenges and open up the possibilities for making selective modulators of MMPs to decipher the multifaceted functions of MMPs in NDs. There is still a greater need to explore them in clinics.

Resveratrol confers neuroprotection against high-fat diet in a mouse model of Alzheimer's disease via modulation of proteolytic mechanisms

Cumulative evidence indicates that excessive consumption of calories from saturated fat contributes to the development of Alzheimer's disease (AD). Here, we assess the triggering and progression of AD pathology induced by a high-fat diet (HFD), and the effects of resveratrol, a polyphenol found in common dietary sources with pleiotropic neuroprotective activities. Over 16 weeks, male wild type (WT) and AD transgenic 5XFAD mice were fed a control diet, HFD (60% kcal from fat), or HFD supplemented with 0.1% resveratrol. Resveratrol protected against HFD-induced memory loss in WT mice and prevented memory loss in 5XFAD mice. Resveratrol also reduced the amyloid burden aggravated by HFD in 5XFAD, and protected against HFD-induced tau pathology in both WT and 5XFAD strains. At the mechanistic level, resveratrol inhibited the HFD-increased amyloidogenic processing of the amyloid precursor protein in both strains; it also restored abnormal high levels in the proteolytic activity of the ubiquitin-proteasome system induced by HFD, suggesting the presence of a compensatory mechanism to counteract the accumulation of aberrant proteins. Thus, our data suggest that resveratrol can correct the harmful effects of HFD in the brain and may be a potential therapeutic agent against obesity-related disorders and AD pathology.

Alteration in synaptic nanoscale organization dictates amyloidogenic processing in Alzheimer's disease

Despite intuitive insights into differential proteolysis of amyloid precursor protein (APP), the stochasticity behind local product formation through amyloidogenic pathway at individual synapses remain unclear. Here, we show that the major components of amyloidogenic machinery namely, APP and secretases are discretely organized into nanodomains of high local concentration compared to their immediate environment in functional zones of the synapse. Additionally, with the aid of multiple models of Alzheimer's disease (AD), we confirm that this discrete nanoscale chemical map of amyloidogenic machinery is altered at excitatory synapses. Furthermore, we provide realistic models of amyloidogenic processing in unitary vesicles originating from the endocytic zone of excitatory synapses. Thus, we show how an alteration in the stochasticity of synaptic nanoscale organization contributes to the dynamic range of C-terminal fragments β (CTFβ) production, defining the heterogeneity of amyloidogenic processing at individual synapses, leading to long-term synaptic deficits as seen in AD.

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Components of amyloidogenic machinery are organized into nanodomains

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Assembly of nanodomains differs between functional zones of the synapse

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Stochasticity of nanoscale organization dictates dynamic range of APP proteolysis

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Variability in composition of amyloidogenic machinery is associated with AD

The Rab5 activator RME-6 is required for amyloid precursor protein endocytosis depending on the YTSI motif

Endocytosis of the amyloid precursor protein (APP) is critical for generation of β-amyloid, aggregating in Alzheimer's disease. APP endocytosis depending on the intracellular NPTY motif is well investigated, whereas involvement of the YTSI (also termed BaSS) motif remains controversial. Here, we show that APP lacking the YTSI motif (ΔYTSI) displays reduced localization to early endosomes and decreased internalization rates, similar to APP ΔNPTY. Additionally, we show that the YTSI-binding protein, PAT1a interacts with the Rab5 activator RME-6, as shown by several independent assays. Interestingly, knockdown of RME-6 decreased APP endocytosis, whereas overexpression increased the same. Similarly, APP ΔNPTY endocytosis was affected by PAT1a and RME-6 overexpression, whereas APP ΔYTSI internalization remained unchanged. Moreover, we could show that RME-6 mediated increase of APP endocytosis can be diminished upon knocking down PAT1a. Together, our data identify RME-6 as a novel player in APP endocytosis, involving the YTSI-binding protein PAT1a.

Exploring the Potential of Therapeutic Agents Targeted towards Mitigating the Events Associated with Amyloid-β Cascade in Alzheimer's Disease

One of the most commonly occurring neurodegenerative disorders, Alzheimer's disease (AD), encompasses the loss of cognitive and memory potential, impaired learning, dementia and behavioral defects, and has been prevalent since the 1900s. The accelerating occurrence of AD is expected to reach 65.7 million by 2030. The disease results in neural atrophy and disrupted inter-neuronal connections. Amongst multiple AD pathogenesis hypotheses, the amyloid beta (Aβ) cascade is the most relevant and accepted form of the hypothesis, which suggests that Aβ monomers are formed as a result of the cleavage of amyloid precursor protein (APP), followed by the conversion of these monomers to toxic oligomers, which in turn develop β-sheets, fibrils and plaques. The review targets the events in the amyloid hypothesis and elaborates suitable therapeutic agents that function by hindering the steps of plaque formation and lowering Aβ levels in the brain. The authors discuss treatment possibilities, including the inhibition of β- and γ-secretase-mediated enzymatic cleavage of APP, the immune response generating active immunotherapy and passive immunotherapeutic approaches targeting monoclonal antibodies towards Aβ aggregates, the removal of amyloid aggregates by the activation of enzymatic pathways or the regulation of Aβ circulation, glucagon-like peptide-1 (GLP-1)-mediated curbed accumulation and the neurotoxic potential of Aβ aggregates, bapineuzumab-mediated vascular permeability alterations, statin-mediated Aβ peptide degradation, the potential role of ibuprofen and the significance of natural drugs and dyes in hindering the amyloid cascade events. Thus, the authors aim to highlight the treatment perspective, targeting the amyloid hypothesis, while simultaneously emphasizing the need to conduct further investigations, in order to provide an opportunity to neurologists to develop novel and reliable treatment therapies for the retardation of AD progression.

Endosomal-Lysosomal Processing of Neurodegeneration-Associated Proteins in Astrocytes

Most common neurodegenerative diseases (NDs) are characterized by deposition of protein aggregates that are resulted from misfolding, dysregulated trafficking, and compromised proteolytic degradation. These proteins exert cellular toxicity to a broad range of brain cells and are found in both neurons and glia. Extracellular monomeric and oligomeric ND-associated proteins are taken up by astrocytes, the most abundant glial cell in the brain. Internalization, intracellular trafficking, processing, and disposal of these proteins are executed by the endosomal-lysosomal system of astrocytes. Endosomal-lysosomal organelles thus mediate the cellular impact and metabolic fate of these toxic protein species. Given the indispensable role of astrocytes in brain metabolic homeostasis, the endosomal-lysosomal processing of these proteins plays a fundamental role in altering the trajectory of neurodegeneration. This review aims at summarizing the mounting evidence that has established the essential role of astrocytic endosomal-lysosomal organelles in the processing of amyloid precursor proteins, Apolipoprotein E (ApoE), tau, alpha synuclein, and huntingtin, which are associated with NDs such as Alzheimer’s, Parkinson’s, and Huntington diseases.

Codonopsis pilosula polysaccharide attenuates Aβ toxicity and cognitive defects in APP/PS1 mice

Codonopsis pilosula Polysaccharides (CPPs), a traditional Chinese medicine used for thousands of years, is a potential neuroprotective polysaccharide via a relatively poorly understood mechanism. We previously reported that CPPs attenuated tau pathology in hTau transfected mice and therefore in the current work investigated the effect of CPPs on Aβ toxicity and cognitive defects in APP/PS1 mice model. It was found that one-month intragastric administration of CPPs significantly ameliorated cognitive defects in APP/PS1 mice. In addition, CPPs treatment mitigated the loss of the synaptic plasticity and increased the synaptic proteins including synaptotagmin and PSD95. The expression of Aβ42 and Aβ40 was remarkably decreased in the hippocampus of APP/PS1 mice after CPPs treatment. We also found that CPPs coincubation significantly reduced the amount of APPβ and Aβ42 expression in cells. Intriguingly, the activity of BACE1 was decreased following CPPs treatment in both the hippocampus of APP/PS1 mice and in vitro experiments. Collectively, these results indicated that CPPs attenuated Aβ pathology in APP/PS1 mice, and down-regulating BACE1 might be the underlaying mechanism which could be a therapeutic target for alleviating cognitive defects in AD pathology.

β-amyloid and Oxidative Stress: Perspectives in Drug Development

Alzheimer's Disease (AD) is a slow-developing neurodegenerative disorder in which the main pathogenic role has been assigned to β-amyloid protein (Aβ) that accumulates in extracellular plaques. The mechanism of action of Aβ has been deeply analyzed and several membrane structures have been identified as potential mediators of its effect. The ability of Aβ to modify neuronal activity, receptor expression, signaling pathways, mitochondrial function, and involvement of glial cells have been analyzed. In addition, extensive literature deals with the involvement of oxidative stress in Aβ effects. Herein we focus more specifically on the reciprocal regulation of Aβ, that causes oxidative stress, that favors Aβ aggregation and toxicity and negatively affects the peptide clearance. Analysis of this strict interaction may offer novel opportunities for therapeutic intervention. Both common and new molecules endowed with antioxidant properties deserve attention in this regard.

Berberine: A Plant-derived Alkaloid with Therapeutic Potential to Combat Alzheimer's disease

Berberine (a protoberberine isoquinoline alkaloid) has shown promising pharmacological activities, including analgesic, anti-inflammatory, anticancer, antidiabetic, anti-hyperlipidemic, cardioprotective, memory enhancement, antidepressant, antioxidant, anti-nociceptive, antimicrobial, anti- HIV and cholesterol-lowering effects. It is used in the treatment of the neurodegenerative disorder. It has strong evidence to serve as a potent phytoconstituent in the treatment of various neurodegenerative disorders such as AD. It limits the extracellular amyloid plaques and intracellular neurofibrillary tangles. It has also lipid-glucose lowering ability, hence can be used as a protective agent in atherosclerosis and AD. However, more detailed investigations along with safety assessment of berberine are warranted to clarify its role in limiting various risk factors and AD-related pathologies. This review highlights the pharmacological basis to control oxidative stress, neuroinflammation and protective effect of berberine in AD, which will benefit to the biological scientists in understanding and exploring the new vistas of berberine in combating Alzheimer's disease.

Dendritic Spines in Alzheimer's Disease: How the Actin Cytoskeleton Contributes to Synaptic Failure

Alzheimer’s disease (AD) is a neurodegenerative disorder characterized by Aβ-driven synaptic dysfunction in the early phases of pathogenesis. In the synaptic context, the actin cytoskeleton is a crucial element to maintain the dendritic spine architecture and to orchestrate the spine’s morphology remodeling driven by synaptic activity. Indeed, spine shape and synaptic strength are strictly correlated and precisely governed during plasticity phenomena in order to convert short-term alterations of synaptic strength into long-lasting changes that are embedded in stable structural modification. These functional and structural modifications are considered the biological basis of learning and memory processes. In this review we discussed the existing evidence regarding the role of the spine actin cytoskeleton in AD synaptic failure. We revised the physiological function of the actin cytoskeleton in the spine shaping and the contribution of actin dynamics in the endocytosis mechanism. The internalization process is implicated in different aspects of AD since it controls both glutamate receptor membrane levels and amyloid generation. The detailed understanding of the mechanisms controlling the actin cytoskeleton in a unique biological context as the dendritic spine could pave the way to the development of innovative synapse-tailored therapeutic interventions and to the identification of novel biomarkers to monitor synaptic loss in AD.

Role of Nuclear Factor Kappa B (NF-κB) Signalling in Neurodegenerative Diseases: An Mechanistic Approach

A transcriptional regulatory nuclear factor kappa B (NF-κB) protein is a modulator of cellular biological activity via binding to a promoter region in the nucleus and transcribing various protein genes. The recent research implicated the intensive role of nuclear factor kappa B (NF-κB) in diseases like autoimmune disorder, inflammatory, cardiovascular and neurodegenerative diseases. Therefore, targeting the nuclear factor kappa B (NF-κB) protein offers a new opportunity as a therapeutic approach. Activation of IκB kinase/NF-κB signaling pathway leads to the development of various pathological conditions in human beings, such as neurodegenerative, inflammatory disorders, autoimmune diseases, and cancer. Therefore, the transcriptional activity of IκB kinase/NF- κB is strongly regulated at various cascade pathways. The nuclear factor NF-kB pathway plays a major role in the expression of pro-inflammatory genes, including cytokines, chemokines, and adhesion molecules. In response to the diverse stimuli, the cytosolic sequestered NF-κB in an inactivated form by binding with an inhibitor molecule protein (IkB) gets phosphorylated and translocated into the nucleus further transcribing various genes necessary for modifying various cellular functions. The various researches confirmed the role of different family member proteins of NF-κB implicated in expressing various genes products and mediating various cellular cascades. MicroRNAs, as regulators of NF- κB microRNAs play important roles in the regulation of the inflammatory process. Therefore, the inhibitor of NF-κB and its family members plays a novel therapeutic target in preventing various diseases. Regulation of NF- κB signaling pathway may be a safe and effective treatment strategy for various disorders.

Histidine 131 in presenilin 1 is the pH-sensitive residue that causes the increase in Aβ42 level in acidic pH

Alzheimer disease (AD) is the most common neurodegenerative disease worldwide. The pathological hallmark of AD is the presence of senile plaques in the brain, which are accumulations of amyloid-β peptide (Aβ) ending at the 42nd residue (i.e. Aβ42), which is produced through multistep cleavage by γ-secretase. Thus, methods to regulate γ-secretase activity to attenuate the production of Aβ42 are in urgent demand towards the development of treatments for AD. We and others have demonstrated that γ-secretase activity is affected by its localization and ambient environment. In particular, an increase in Aβ42 production is correlated with the intracellular transport of γ-secretase and endosomal maturation-dependent luminal acidification. In this study, we focused on the mechanism by which γ-secretase affects Aβ42 production together with alterations in pH. Histidine is known to function as a pH sensor in many proteins, to regulate their activities through the protonation state of the imidazole side chain. Among the histidines facing the luminal side of presenilin (PS) 1, which is the catalytic subunit of γ-secretase, point mutations at H131 had no effect on the Aβ42 production ratio in an acidic environment. We also observed an increase in Aβ42 ratio when histidine was introduced into N137 of PS2, which is the corresponding residue of H131 in PS1. These results indicated that H131 serves as the pH sensor in PS1, which contains γ-secretase, to regulate Aβ42 production depending on the luminal pH. Our findings provide new insights into therapeutic strategies for AD targeting endosomes or the intracellular transport of γ-secretase.

On the Neuroprotective Effects of Naringenin: Pharmacological Targets, Signaling Pathways, Molecular Mechanisms, and Clinical Perspective

As a group of progressive, chronic, and disabling disorders, neurodegenerative diseases (NDs) affect millions of people worldwide, and are on the rise. NDs are known as the gradual loss of neurons; however, their pathophysiological mechanisms have not been precisely revealed. Due to the complex pathophysiological mechanisms behind the neurodegeneration, investigating effective and multi-target treatments has remained a clinical challenge. Besides, appropriate neuroprotective agents are still lacking, which raises the need for new therapeutic agents. In recent years, several reports have introduced naturally-derived compounds as promising alternative treatments for NDs. Among natural entities, flavonoids are multi-target alternatives affecting different pathogenesis mechanisms in neurodegeneration. Naringenin is a natural flavonoid possessing neuroprotective activities. Increasing evidence has attained special attention on the variety of therapeutic targets along with complex signaling pathways for naringenin, which suggest its possible therapeutic applications in several NDs. Here, in this review, the neuroprotective effects of naringenin, as well as its related pharmacological targets, signaling pathways, molecular mechanisms, and clinical perspective, are described. Moreover, the need to develop novel naringenin delivery systems is also discussed to solve its widespread pharmacokinetic limitation.

The Endolysosomal System and Proteostasis: From Development to Degeneration

How do neurons adapt their endolysosomal system to address the particular challenge of membrane transport across their elaborate cellular landscape and to maintain proteostasis for the lifetime of the organism? Here we review recent findings that address this central question. We discuss the cellular and molecular mechanisms of endolysosomal trafficking and the autophagy pathway in neurons, as well as their role in neuronal development and degeneration. These studies highlight the importance of understanding the basic cell biology of endolysosomal trafficking and autophagy and their roles in the maintenance of proteostasis within the context of neurons, which will be critical for developing effective therapies for various neurodevelopmental and neurodegenerative disorders.

Effects of MDMA on neuroplasticity, amyloid burden and phospho-tau expression in APPswe/PS1dE9 mice

BACKGROUND

3,4-Methylenedioxymethamphetamine (MDMA) is still one of the most consumed drugs by adolescents. Its abuse is related with cognitive impairment, which seems due to maladaptive plasticity and neural stress. In turn, new hypotheses suggest that Alzheimer's disease (AD) may be promoted by neural stressors.

AIMS AND METHODS

To test if there is an increase in vulnerability to AD after chronic MDMA consumption, we investigated the effects of this drug on recognition memory and its neurotoxic and neuroplastic effects in a transgenic mouse model of presymptomatic familiar AD (APP/PS1 dE9, Tg).

RESULTS

MDMA-treated animals showed recognition memory deficits, regardless of genotype, which were accompanied by changes in plasticity markers. Tg mice showed an impaired expression of Arc compared with wild-type animals, but exposure to MDMA induced an increase in the expression of this factor of the same percentage in both genotypes. However, the expression of c-fos, BDNF and p-CREB was not significantly altered by MDMA treatment in Tg mice. Although Tg mice had higher free choline levels than wild-type mice (about 123%), MDMA did not modify these levels in any case, ruling out any specific effect of this drug on the acetylcholine pathway. MDMA treatment significantly increased the presence of cortical amyloid plaques, as well as Aβ40, Aβ42 and secreted APPβ levels in Tg mice. These plaques were accompanied by increased tau phosphorylation (S199), which does not seem to occur via the canonic pathway involving AKT, CDK5 or GSK3β.

CONCLUSIONS

The present results support previous evidences that MDMA can contribute to the amyloid cascade.

Golgi Fragmentation in Neurodegenerative Diseases: Is There a Common Cause?

In most mammalian cells, the Golgi complex forms a continuous ribbon. In neurodegenerative diseases, the Golgi ribbon of a specific group of neurons is typically broken into isolated elements, a very early event which happens before clinical and other pathological symptoms become evident. It is not known whether this phenomenon is caused by mechanisms associated with cell death or if, conversely, it triggers apoptosis. When the phenomenon was studied in diseases such as Parkinson’s and Alzheimer’s or amyotrophic lateral sclerosis, it was attributed to a variety of causes, including the presence of cytoplasmatic protein aggregates, malfunctioning of intracellular traffic and/or alterations in the cytoskeleton. In the present review, we summarize the current findings related to these and other neurodegenerative diseases and try to search for clues on putative common causes.

Alzheimer's Disease as a Membrane Disorder: Spatial Cross-Talk Among Beta-Amyloid Peptides, Nicotinic Acetylcholine Receptors and Lipid Rafts

Biological membranes show lateral and transverse asymmetric lipid distribution. Cholesterol (Chol) localizes in both hemilayers, but in the external one it is mostly condensed in lipid-ordered microdomains (raft domains), together with saturated phosphatidyl lipids and sphingolipids (including sphingomyelin and glycosphingolipids). Membrane asymmetries induce special membrane biophysical properties and behave as signals for several physiological and/or pathological processes. Alzheimer’s disease (AD) is associated with a perturbation in different membrane properties. Amyloid-β (Aβ) plaques and neurofibrillary tangles of tau protein together with neuroinflammation and neurodegeneration are the most characteristic cellular changes observed in this disease. The extracellular presence of Aβ peptides forming senile plaques, together with soluble oligomeric species of Aβ, are considered the major cause of the synaptic dysfunction of AD. The association between Aβ peptide and membrane lipids has been extensively studied. It has been postulated that Chol content and Chol distribution condition Aβ production and posterior accumulation in membranes and, hence, cell dysfunction. Several lines of evidence suggest that Aβ partitions in the cell membrane accumulate mostly in raft domains, the site where the cleavage of the precursor AβPP by β- and γ- secretase is also thought to occur. The main consequence of the pathogenesis of AD is the disruption of the cholinergic pathways in the cerebral cortex and in the basal forebrain. In parallel, the nicotinic acetylcholine receptor has been extensively linked to membrane properties. Since its transmembrane domain exhibits extensive contacts with the surrounding lipids, the acetylcholine receptor function is conditioned by its lipid microenvironment. The nicotinic acetylcholine receptor is present in high-density clusters in the cell membrane where it localizes mainly in lipid-ordered domains. Perturbations of sphingomyelin or cholesterol composition alter acetylcholine receptor location. Therefore, Aβ processing, Aβ partitioning, and acetylcholine receptor location and function can be manipulated by changes in membrane lipid biophysics. Understanding these mechanisms should provide insights into new therapeutic strategies for prevention and/or treatment of AD. Here, we discuss the implications of lipid-protein interactions at the cell membrane level in AD.

The vexing complexity of the amyloidogenic pathway

The role of the amyloidogenic pathway in the etiology of Alzheimer's disease (AD), particularly the common sporadic late onset forms of the disease, is controversial. To some degree, this is a consequence of the failure of drug and therapeutic antibody trials based either on targeting the proteases in this pathway or its amyloid end products. Here, we explore the formidable complexity of the biochemistry and cell biology associated with this pathway. For example, we review evidence that the immediate precursor of amyloid-β, the C99 domain of the amyloid precursor protein (APP), may itself be toxic. We also review important new results that appear to finally establish a direct genetic link between mutations in APP and the sporadic forms of AD. Based on the complexity of amyloidogenesis, it seems possible that a major contributor to the failure of related drug trials is that we have an incomplete understanding of this pathway and how it is linked to Alzheimer's pathogenesis. If so, this highlights a need for further characterization of this pathway, not its abandonment.

Reciprocal modulation between amyloid precursor protein and synaptic membrane cholesterol revealed by live cell imaging

The amyloid precursor protein (APP) has been extensively studied because of its association with Alzheimer's disease (AD). However, APP distribution across different subcellular membrane compartments and its function in neurons remains unclear. We generated an APP fusion protein with a pH-sensitive green fluorescent protein at its ectodomain and a pH-insensitive blue fluorescent protein at its cytosolic domain and used it to measure APP's distribution, subcellular trafficking, and cleavage in live neurons. This reporter, closely resembling endogenous APP, revealed only a limited correlation between synaptic activities and APP trafficking. However, the synaptic surface fraction of APP was increased by a reduction in membrane cholesterol levels, a phenomenon that involves APP's cholesterol-binding motif. Mutations at or near binding sites not only reduced both the surface fraction of APP and membrane cholesterol levels in a dominant negative manner, but also increased synaptic vulnerability to moderate membrane cholesterol reduction. Our results reveal reciprocal modulation of APP and membrane cholesterol levels at synaptic boutons.

Trafficking and proteolytic processing of amyloid precursor protein and secretases in Alzheimer's disease development: An up-to-date review

Alzheimer's disease (AD), which is predicted to affect 1 in 85 persons worldwide by 2050, results in progressive loss of neuronal functions, leading to impairments in memory and cognitive abilities. As being one of the major neuropathological hallmarks of AD, senile plaques mainly consist of amyloid-β (Aβ) peptides, which are derived from amyloid precursor protein (APP) via the sequential cleavage by β- and γ-secretases. Although the overproduction and accumulation of Aβ peptides are at the center of AD research, the new discoveries point out to the complexity of the disease development. In this respect, it is crucial to understand the processing and the trafficking of APP, the enzymes involved in its processing, the cleavage products and their therapeutic potentials. This review summarizes the salient features of APP processing focusing on APP, the canonical secretases as well as the novel secretases and the cleavage products with an update of the recent developments. We also discussed the intracellular trafficking of APP and secretases in addition to their potential in AD therapy.

Novel Deoxyvasicinone-Donepezil Hybrids as Potential Multitarget Drug Candidates for Alzheimer's Disease

In this study, we designed and synthesized a series of deoxyvasicinone-donepezil hybrids and determined whether they could be used as novel multitarget inhibitors for Alzheimer's disease. In vitro studies showed that most of the hybrids demonstrated moderate to potent inhibition of hAChE, BACE1, and Aβ_1-42 aggregation. In particular, the hybrids 10a, 10d, 11a, and 11j exhibited excellent inhibitory activities against hAChE (IC₅₀ = 56.14, 5.91, 3.29, and 8.65 nM, respectively), BACE1 (IC₅₀ = 0.834, 0.167, 0.129, and 0.085 μM, respectively), and Aβ_1-42 aggregation (IC₅₀ = 13.26, 19.43, 9.26, and 5.41 μM, respectively). In addition, 10a and 11a exhibited very low cytotoxicity and showed remarkable neuroprotective activity against Aβ_1-42-induced damage in SH-SY5Y cells.

Expression of AHI1 Rescues Amyloidogenic Pathology in Alzheimer's Disease Model Cells

A hallmark of Alzheimer's disease (AD) pathogenesis is the accumulation of extracellular plaques mainly composed of amyloid-β (Aβ) derived from amyloid precursor protein (APP) cleavage. Recent reports suggest that transport of APP in vesicles with huntingtin-associated protein-1 (HAP1) negatively regulates Aβ production. In neurons, HAP1 forms a stable complex with Abelson helper integration site-1 (AHI1), in which mutations cause neurodevelopmental and psychiatric disorders. HAP1 and AHI1 interact with tropomyosin receptor kinases (Trks), which are also associated with APP and mediate neurotrophic signaling. In this study, we hypothesize that AHI1 participates in APP trafficking and processing to rescue AD pathology. Indeed, AHI1 was significantly reduced in mouse neuroblastoma N2a cells expressing human Swedish and Indiana APP (designed as AD model cells) and in 3xTg-AD mouse brain. The AD model cells as well as Ahi1-knockdown cells expressing wild-type APP-695 exhibited a significant reduction in viability. In addition, the AD model cells were reduced in neurite outgrowth. APP C-terminal fragment-β (CTFβ) and Aβ42 were increased in the AD cell lysates and the culture media, respectively. To investigate the mechanism how AHI1 alters APP activities, we overexpressed human AHI1 in the AD model cells. The results showed that AHI1 interacted with APP physically in mouse brain and transfected N2a cells despite APP genotypes. AHI1 expression facilitated intracellular translocation of APP and inhibited APP amyloidogenic process to reduce the level of APP-CTFβ in the total lysates of AD model cells as well as Aβ in the culture media. Consequently, AHI1-APP interactions enhanced neurotrophic signaling through Erk activation and led to restored cell survival and differentiation.

Novel Therapeutic Potentials of Taxifolin for Amyloid-β-associated Neurodegenerative Diseases and Other Diseases: Recent Advances and Future Perspectives

Amyloid-β (Aβ) has been closely implicated in the pathogenesis of cerebral amyloid angiopathy (CAA) and Alzheimer’s disease (AD), the major causes of dementia. Thus, Aβ could be a target for the treatment of these diseases, for which, currently, there are no established effective treatments. Taxifolin is a bioactive catechol-type flavonoid present in various plants, such as herbs, and it exhibits pleiotropic effects including anti-oxidant and anti-glycation activities. Recently, we have demonstrated that taxifolin inhibits Aβ fibril formation in vitro and have further shown that it improves cerebral blood flow, facilitating Aβ clearance in the brain and suppressing cognitive decline in a mouse model of CAA. These findings suggest the novel therapeutic potentials of taxifolin for CAA. Furthermore, recent extensive studies have reported several novel aspects of taxifolin supporting its potential as a therapeutic drug for AD and metabolic diseases with a high risk for dementia as well as for CAA. In this review, we have summarized the recent advances in taxifolin research based on in vitro, in vivo, and in silico approaches. Furthermore, we have discussed future research directions on the potential of taxifolin for use in novel therapeutic strategies for CAA, AD, and metabolic diseases with an increased risk for dementia.

Par3 regulates polarized convergence between APP and BACE1 in hippocampal neurons

The convergence between amyloid precursor protein (APP) and its β-secretase β-site APP cleaving enzyme 1 (BACE1) is a prerequisite for the generation of β-amyloid peptide, a key pathogenic agent for Alzheimer's disease. Yet the underlying molecular mechanisms regulating their convergence remain unclear. Here, we show that the polarity protein partitioning-defective 3 (Par3) regulates the polarized convergence between APP and BACE1 in hippocampal neurons. Par3 forms a complex with BACE1 through its first PDZ domain, which is important for regulating BACE1 endosome-to-TGN trafficking. In the absence of Par3, there is an increase in the convergence between internalized APP and BACE1. In hippocampal neurons, loss of Par3 leads to increased APP and BACE1 convergence in axons but not in dendrites. This polarized convergence mainly occurs in retrograde or stalled axonal late endocytic organelles and is likely due to compartment-specific regulation of APP trafficking by Par3. Together, our data show a novel function for Par3 in regulating polarized convergence between APP and BACE1 in hippocampal neurons.

Recent therapeutic strategies targeting beta amyloid and tauopathies in Alzheimer's disease

Alzheimer's disease (AD) has been a global concern for years due to its severe implications that affects the quality of life of the patients. The available line of therapy for treating Alzheimer's includes acetylcholinesterase inhibitors, NMDA(N-methyl-D-aspartate) antagonists and their combination which gives only symptomatic relief rather than treating the root cause of AD. Senile plaques and neurofibrillary tangles are the characteristic features underlying Alzheimer's pathology. Several attempts have been made towards exploring the niceties of these hallmarks and targeting various aspects of amyloid and tau pathology at different stages to eliminate the ultimate cause. Approaches targeting cleavage and formation of toxic amyloid fragments by secretases, aggregation of amyloid monofilaments, and immunotherapy against amyloid deposits has been extensively studied to treat amyloid pathology. Similarly, for tau pathology, tau hyperphosphorylation, microtubule stabilization, anti-tau immunotherapy has been explored. This article focuses on AD pathology and current pharmacotherapy, precisely for amyloid and tau. Furthermore, preclinical and clinical studies along with potential leads discovered under these approaches have also been included in this article. However, despite extensive research in drug development, overcoming clinical barrier still remain a major challenge for Alzheimer's pharmacotherapy.