Activation of Ras-ERK Signaling and GSK-3 by Amyloid Precursor Protein and Amyloid Beta Facilitates Neurodegeneration in Alzheimer's Disease

MAMs and Mitochondrial Quality Control: Overview and Their Role in Alzheimer's Disease

Alzheimer's disease (AD) represents the most widespread neurodegenerative disorder, distinguished by a gradual onset and slow progression, presenting a substantial challenge to global public health. The mitochondrial-associated membrane (MAMs) functions as a crucial center for signal transduction and material transport between mitochondria and the endoplasmic reticulum, playing a pivotal role in various pathological mechanisms of AD. The dysregulation of mitochondrial quality control systems is considered a fundamental factor in the development of AD, leading to mitochondrial dysfunction and subsequent neurodegenerative events. Recent studies have emphasized the role of MAMs in regulating mitochondrial quality control. This review will delve into the molecular mechanisms underlying the imbalance in mitochondrial quality control in AD and provide a comprehensive overview of the role of MAMs in regulating mitochondrial quality control.

Protective effects of 2,4-dinitrophenol in okadaic acid-induced cellular model of Alzheimer's disease

Alzheimer's disease (AD) research started several decades ago and despite the many efforts employed to develop new treatments or approaches to slow and/or revert disease progression, AD treatment remains an unsolved issue. Knowing that mitochondria loss of function is a central hub for many AD-associated pathophysiological processes, there has been renewed interest in exploring mitochondria as targets for intervention. In this perspective, the present study was aimed to investigate the possible beneficial effects of 2,4 dinitrophenol (DNP), a mitochondrial uncoupler agent, in an in vitro model of AD. Retinoic acid-induced differentiated SH-SY5Y cells were incubated with okadaic acid (OA), a neurotoxin often used as an AD experimental model, and/or with DNP. OA caused a decrease in neuronal cells viability, induced multiple mitochondrial anomalies including increased levels of reactive oxygen species, decreased bioenergetics and mitochondria content markers, and an altered mitochondria morphology. OA-treated cells also presented increased lipid peroxidation levels, and overactivation of tau related kinases (GSK3β, ERK1/2 and AMPK) alongside with a significant augment in tau protein phosphorylation levels. Interestingly, DNP co-treatment ameliorated and rescued OA-induced detrimental effects not only on mitochondria but also but also reinstated signaling pathways homeostasis and ameliorated tau pathology. Overall, our results show for the first time that DNP has the potential to preserve mitochondria homeostasis under a toxic insult, like OA exposure, as well as to reestablish cellular signaling homeostasis. These observations foster the idea that DNP, as a mitochondrial modulator, might represent a new avenue for treatment of AD.

Establishment of a novel cellular model for Alzheimer's disease in vitro studies

Alzheimer's disease (AD) is a neurodegenerative disease characterized by memory loss, cognitive impairment, and behavioral and psychological symptoms of dementia. The limited efficacy of drugs for the treatment of neurodegenerative diseases reflects their complex etiology and pathogenesis. A novel in vitro model may help to bridge the gap between existing preclinical animal models and human clinical trials, thus identifying promising therapeutic targets that can be explored in upcoming clinical trials. By assisting in the identification of the mechanism of action and potential dangers, in vitro testing can also shorten the time and expense of translation.

AIM

As a result of these factors, our objective is to develop a powerful and informative cellular model of AD within a short period of time. Through triggering the MAPK and NF-κβ signaling pathways with the aid of small chemical compounds (PAF C-16 and BetA), respectively, in mouse microglial (SIM-A9) and neuroblast Neuro-2a (N2a) cell lines.

RESULTS

PAF C-16, initiated an activation effect at a concentration of 3.12 nM to 25 nM in the SIM-A9 and N2a cell lines after 72 h. BetA, activated the NF-κβ pathway with a concentration of 12.5 nM to 25 nM in the SIM-A9 and N2a cell lines after 72 h. The combination of the activator chemicals provided suitable activation for MEK1/2-ERK and NF-κβ in more than three subcultures. Activators significantly initiate APP and MAPT gene expression, as well as the expression of proteins APP, β. Amyloid, tau, and p-tau. The activation of the targeted pathways leads to significant morphological changes.

CONCLUSION

We can infer that the MEK1/2-ERK and NF-κβ pathways, respectively, are directly activated by the PAF C-16 and BetA chemicals. The activation of MEK1/2-ERK pathway results in the activation of the APP gene, which in turn activates the β. Amyloid protein, which in turn results in plaque. Furthermore, NF-κβ activation results in the activation of the MAPT gene, which leads to Tau and p-Tau protein activation, which ultimately results in tangles. This can be put into practice in just three days, with a high level of activity and stability that is passed down to the next three generations (subculture), with significant morphological changes. In microglial and neuroblast cell lines, we were successful in creating a novel AD-cell model.

Role of 14-3-3 protein family in the pathobiology of EBV in immortalized B cells and Alzheimer's disease

Background and Aims

Several studies have revealed that Epstein-Barr virus (EBV) infection raised the likelihood of developing Alzheimer's disease (AD) via infecting B lymphocytes. The purpose of the current investigation was to assess the possible association between EBV infection and AD.

Methods

The microarray datasets GSE49628, GSE126379, GSE122063, and GSE132903 were utilized to extract DEGs by using the GEO2R tool of the GEO platform. The STRING tool was used to determine the interaction between the DEGs, and Cytoscape was used to visualize the results. The DEGs that were found underwent function analysis, including pathway and GO, using the DAVID 2021 and ClueGo/CluePedia. By using MNC, MCC, Degree, and Radiality of cytoHubba, we identified seven common key genes. Gene co-expression analysis was performed through the GeneMANIA web tool. Furthermore, expression analysis of key genes was performed through GTEx software, which have been identified in various human brain regions. The miRNA-gene interaction was performed through the miRNet v 2.0 tool. DsigDB on the Enrichr platform was utilized to extract therapeutic drugs connected to key genes.

Results

In GEO2R analysis of datasets with |log2FC|≥ 0.5 and p-value <0.05, 8386, 10,434, 7408, and 759 genes were identified. A total of 141 common DEGs were identified by combining the extracted genes of different datasets. A total of 141 nodes and 207 edges were found during the PPI analysis. The DEG GO analysis with substantial alterations disclosed that they are associated to molecular functions and biological processes, such as positive regulation of neuron death, autophagy regulation of mitochondrion, response of cell to insulin stimulus, calcium signaling regulation, organelle transport along microtubules, protein kinase activity, and phosphoserine binding. Kyoto Encyclopedia of Genes and Genomes analysis discovered the correlation between the DEGs in pathways of neurodegeneration: multiple disease, cell cycle, and cGMP-PKG signaling pathway. Finally, YWHAH, YWHAG, YWHAB, YWHAZ, MAP2K1, PPP2CA, and TUBB genes were identified that are strongly linked to EBV and AD. Three miRNAs, i.e., hsa-mir-15a-5p, hsa-let-7a-5p, and hsa-mir-7-5p, were identified to regulate most of hub genes that are associated with EBV and AD. Further top 10 significant therapeutic drugs were predicted.

Conclusion

We have discovered new biomarkers and therapeutic targets for AD, as well as the possible biological mechanisms whereby infection with EBV may be involved in AD susceptibility for the first time.

The duality of amyloid-β: its role in normal and Alzheimer's disease states

Alzheimer's disease (AD) is a degenerative neurological condition that gradually impairs cognitive abilities, disrupts memory retention, and impedes daily functioning by impacting the cells of the brain. A key characteristic of AD is the accumulation of amyloid-beta (Aβ) plaques, which play pivotal roles in disease progression. These plaques initiate a cascade of events including neuroinflammation, synaptic dysfunction, tau pathology, oxidative stress, impaired protein clearance, mitochondrial dysfunction, and disrupted calcium homeostasis. Aβ accumulation is also closely associated with other hallmark features of AD, underscoring its significance. Aβ is generated through cleavage of the amyloid precursor protein (APP) and plays a dual role depending on its processing pathway. The non-amyloidogenic pathway reduces Aβ production and has neuroprotective and anti-inflammatory effects, whereas the amyloidogenic pathway leads to the production of Aβ peptides, including Aβ40 and Aβ42, which contribute to neurodegeneration and toxic effects in AD. Understanding the multifaceted role of Aβ, particularly in AD, is crucial for developing effective therapeutic strategies that target Aβ metabolism, aggregation, and clearance with the aim of mitigating the detrimental consequences of the disease. This review aims to explore the mechanisms and functions of Aβ under normal and abnormal conditions, particularly in AD, by examining both its beneficial and detrimental effects.

Therapeutic effects of Tanshinone IIA and Tetramethylpyrazine nanoemulsions on cognitive impairment and neuronal damage in Alzheimer's disease rat models

OBJECTIVES

The aim of this study was to investigate the therapeutic effects and related mechanisms of Tanshinone IIA and Tetramethylpyrazine O/W composite nanoemulsions on Alzheimer's disease (AD) rats.

METHODS

The therapeutic effect of TSN/TMP O/W NEs on AD rats was evaluated by behavioral tests, H&E, Nissl, and Immunohistochemistry staining. ELISA and Western blot were used to analyze the mechanism.

KEY FINDINGS

The results showed that TSN/TMP O/W NEs could down-regulate the expression of Bax and Caspase-3 proteins, decrease the level of MDA, increase the expression of SOD and GSH-Px, and alleviate cognitive impairment in AD rats.

CONCLUSIONS

TSN/TMP O/W NEs can inhibit MAPK/ERK/CREB signaling pathway and effectively alleviate cognitive impairment, oxidative stress injury, and neuronal apoptosis in AD rats.

Profiling of the Proteins Interacting with Amyloid Beta Peptides in Clinical Samples by PACTS-TPP

The accumulation of amyloid beta (Aβ1-42) results in neurotoxicity and is strongly related to neurodegenerative disorders, especially Alzheimer's disease (AD), but the underlying molecular mechanism is still poorly understood. Therefore, there is an urgent need for researchers to discover the proteins that interact with Aβ1-42 to determine the molecular basis. Previously, we developed peptide-ligand-induced changes in the abundance of proTeinS (PACTS)-assisted thermal proteome profiling (TPP) to identify proteins that interact with peptide ligands. In the present study, we applied this technique to analyze clinical samples to identify Aβ1-42-interacting proteins. We detected 115 proteins that interact with Aβ1-42 in human frontal lobe tissue. Pathway enrichment analysis revealed that the differentially expressed proteins were involved mainly in neurodegenerative diseases. Further orthogonal validation revealed that Aβ1-42 interacted with the AD-associated protein mitogen-activated protein kinase 3 (MAPK3), and knockdown of the Aβ1-42 amyloid precursor protein (APP) inhibited the MAPK signaling pathway, suggesting potential functional roles for Aβ1-42 in interacting with MAPK3. Overall, this study demonstrated the application of the PACTS-TPP in clinical samples and provided a valuable data source for research on neurodegenerative diseases.

Intranasal Administration of Apelin-13 Ameliorates Cognitive Deficit in Streptozotocin-Induced Alzheimer's Disease Model via Enhancement of Nrf2-HO1 Pathways

BACKGROUND

The discovery of novel diagnostic methods and therapies for Alzheimer's disease (AD) faces significant challenges. Previous research has shed light on the neuroprotective properties of Apelin-13 in neurodegenerative disorders. However, elucidating the mechanism underlying its efficacy in combating AD-related nerve injury is imperative. In this study, we aimed to investigate Apelin-13's mechanism of action in an in vivo model of AD induced by streptozocin (STZ).

METHODS

We utilized an STZ-induced nerve injury model of AD in mice to investigate the effects of Apelin-13 administration. Apelin-13 was administered intranasally, and cognitive impairment was assessed using standardized behavioral tests, primarily, behavioral assessment, histological analysis, and biochemical assays, in order to evaluate synaptic plasticity and oxidative stress signaling pathways.

RESULTS

Our findings indicate that intranasal administration of Apelin-13 ameliorated cognitive impairment in the STZ-induced AD model. Furthermore, we observed that this effect was potentially mediated by the enhancement of synaptic plasticity and the attenuation of oxidative stress signaling pathways.

CONCLUSIONS

The results of this study suggest that intranasal administration of Apelin-13 holds promise as a therapeutic strategy for preventing neurodegenerative diseases such as AD. By improving synaptic plasticity and mitigating oxidative stress, Apelin-13 may offer a novel approach to neuroprotection in AD and related conditions.

Alterations in Immune Responses Are Associated with Dysfunctional Intracellular Signaling in Peripheral Blood Mononuclear Cells of Men and Women with Mild Cognitive Impairment and Alzheimer's disease

Deficits in the neuroendocrine-immune network in the periphery associated with the onset and progression of mild cognitive impairment (MCI) and Alzheimer's disease (AD) have not been extensively studied. The present study correlatively examines the association between cell-mediated immune responses, stress hormones, amyloid precursor protein (APP) expression, peripheral blood mononuclear cells (PBMC), and intracellular signaling molecules in the pathophysiology of MCI and AD compared to adults. Serum APP, lymphocyte proliferation, total cholinesterase (TChE), butyrylcholinesterase (BChE) activities, cytokines (IL-2, IFN-γ, IL-6, and TNF-α), and intracellular signaling molecules (p-ERK, p-CREB, and p-Akt) were measured in the PBMCs of adult, old, MCI, and AD men and women initially and after 3 years in the same population. An age- and disease-associated decline in mini-mental state examination (MMSE) scores and lymphocyte proliferation of MCI and AD men and women were observed. An age- and disease-related increase in serum APP, cortisol levels, and TChE activity were observed in men and women. Enhanced production of Th1 cytokine, IL-2, pro-inflammatory cytokines, and suppressed intracellular transcription factors may promote the inflammatory environment in MCI and AD patients. The expression of CREB and Akt was lower in MCI and AD men, while the expression of p-ERK was higher, and p-CREB was lower in MCI and AD women after 3 years. These results suggest that changes in specific intracellular signaling pathways may influence alterations in cell-mediated immunity to promote disease progression in MCI and AD patients.

Transsynaptic degeneration of ventral horn motor neurons exists but plays a minor role in lower motor system dysfunction in acute ischemic rats

BACKGROUND

As a leading cause of mortality and long-term disability, acute ischemic stroke can produce far-reaching pathophysiological consequences. Accumulating evidence has demonstrated abnormalities in the lower motor system following stroke, while the existence of Transsynaptic degeneration of contralateral spinal cord ventral horn (VH) neurons is still debated.

METHODS

Using a rat model of acute ischemic stroke, we analyzed spinal cord VH neuron counts contralaterally and ipsilaterally after stroke with immunofluorescence staining. Furthermore, we estimated the overall lower motor unit abnormalities after stroke by simultaneously measuring the modified neurological severity score (mNSS), compound muscle action potential (CMAP) amplitude, repetitive nerve stimulation (RNS), spinal cord VH neuron counts, and the corresponding muscle fiber morphology. The activation status of microglia and extracellular signal-regulated kinase 1/2 (ERK 1/2) in the spinal cord VH was also assessed.

RESULTS

At 7 days after stroke, the contralateral CMAP amplitudes declined to a nadir indicating lower motor function damage, and significant muscle disuse atrophy was observed on the same side; meanwhile, the VH neurons remained intact. At 14 days after focal stroke, lower motor function recovered with alleviated muscle disuse atrophy, while transsynaptic degeneration occurred on the contralateral side with elevated activation of ERK 1/2, along with the occurrence of neurogenic muscle atrophy. No apparent decrement of CMAP amplitude was observed with RNS during the whole experimental process.

CONCLUSIONS

This study offered an overview of changes in the lower motor system in experimental ischemic rats. We demonstrated that transsynaptic degeneration of contralateral VH neurons occurred when lower motor function significantly recovered, which indicated the minor role of transsynaptic degeneration in lower motor dysfunction during the acute and subacute phases of focal ischemic stroke.

Potential diagnostic markers and therapeutic targets for periodontitis and Alzheimer's disease based on bioinformatics analysis

BACKGROUND AND OBJECTIVE

As a chronic inflammatory disease, periodontitis threatens oral health and is a risk factor for Alzheimer's disease (AD). There is growing evidence that these two diseases are closely related. However, current research is still incomplete in understanding the common genes and common mechanisms between periodontitis and AD. In this study, we aimed to identify common genes in periodontitis and AD and analyze the relationship between crucial genes and immune cells to provide new therapeutic targets for clinical treatment.

MATERIALS AND METHODS

We evaluated differentially expressed genes (DEGs) specific to periodontitis and AD. Co-expressed genes were identified by obtaining gene expression profile data from the Gene Expression Omnibus (GEO) database. Using the STRING database, protein-protein interaction (PPI) networks were constructed, and essential genes were identified. We also used four algorithms to identify critical genes and constructed regulatory networks. The association of crucial genes with immune cells and potential therapeutic effects was also assessed.

RESULTS

PDGFRB, VCAN, TIMP1, CHL1, EFEMP2, and IGFBP5 were obtained as crucial common genes. Immune infiltration analysis showed that Natural killer cells and Myeloid-derived suppressor cells were significantly differentially expressed in patients with PD and AD compared with the normal group. FOXC1 and GATA2 are important TFs for PD and AD. MiR-23a, miR-23b, miR-23a, and miR-23b were associated with AD and PD. Finally, the hub genes retrieved from the DSigDB database indicate multiple drug molecule and drug-target interactions.

CONCLUSION

This study reveals commonalities in common hub genes and immune infiltration between periodontitis and AD, and the analysis of six hub genes and immune cells may provide new insights into potential therapeutic directions for the pathogenesis of periodontitis complicated by AD.

Recent insights from non-mammalian models of brain injuries: an emerging literature

Traumatic brain injury (TBI) is a major global health concern and is increasingly recognized as a risk factor for neurodegenerative diseases including Alzheimer's disease (AD) and chronic traumatic encephalopathy (CTE). Repetitive TBIs (rTBIs), commonly observed in contact sports, military service, and intimate partner violence (IPV), pose a significant risk for long-term sequelae. To study the long-term consequences of TBI and rTBI, researchers have typically used mammalian models to recapitulate brain injury and neurodegenerative phenotypes. However, there are several limitations to these models, including: (1) lengthy observation periods, (2) high cost, (3) difficult genetic manipulations, and (4) ethical concerns regarding prolonged and repeated injury of a large number of mammals. Aquatic vertebrate model organisms, including Petromyzon marinus (sea lampreys), zebrafish (Danio rerio), and invertebrates, Caenorhabditis elegans (C. elegans), and Drosophila melanogaster (Drosophila), are emerging as valuable tools for investigating the mechanisms of rTBI and tauopathy. These non-mammalian models offer unique advantages, including genetic tractability, simpler nervous systems, cost-effectiveness, and quick discovery-based approaches and high-throughput screens for therapeutics, which facilitate the study of rTBI-induced neurodegeneration and tau-related pathology. Here, we explore the use of non-vertebrate and aquatic vertebrate models to study TBI and neurodegeneration. Drosophila, in particular, provides an opportunity to explore the longitudinal effects of mild rTBI and its impact on endogenous tau, thereby offering valuable insights into the complex interplay between rTBI, tauopathy, and neurodegeneration. These models provide a platform for mechanistic studies and therapeutic interventions, ultimately advancing our understanding of the long-term consequences associated with rTBI and potential avenues for intervention.

Bridging neurotrophic factors and bioactive peptides to Alzheimer's disease

Alzheimer's disease (AD) is a neurodegenerative disorder. As the demographic shifting towards an aging population, AD has emerged as a prominent public health concern. The pathogenesis of AD is complex, and there are no effective treatment methods for AD until now. In recent years, neurotrophic factors and bioactive peptides including brain-derived neurotrophic factor (BDNF) and nerve growth factor (NGF), irisin, melatonin, have been discovered to exert neuroprotective functions for AD. Bioactive peptides can be divided into two categories based on their sources: endogenous and exogenous. This review briefly elaborates on the pathogenesis of AD and analyzes the regulatory effects of endogenous and exogenous peptides on the pathogenesis of AD, thereby providing new therapeutic targets for AD and a theoretical basis for the application of bioactive peptides as adjunctive therapies for AD.

Targeting protein kinases for the treatment of Alzheimer's disease: Recent progress and future perspectives

Alzheimer's disease (AD) is a serious neurodegenerative disease characterized by memory impairment, mental retardation, impaired motor balance, loss of self-care and even death. Among the complex and diverse pathological changes in AD, protein kinases are deeply involved in abnormal phosphorylation of Tau proteins to form intracellular neuronal fiber tangles, neuronal loss, extracellular β-amyloid (Aβ) deposits to form amyloid plaques, and synaptic disturbances. As a disease of the elderly, the growing geriatric population is directly driving the market demand for AD therapeutics, and protein kinases are potential targets for the future fight against AD. This perspective provides an in-depth look at the role of the major protein kinases (GSK-3β, CDK5, p38 MAPK, ERK1/2, and JNK3) in the pathogenesis of AD. At the same time, the development of different protein kinase inhibitors and the current state of clinical advancement are also outlined.

Tau-targeting therapies for Alzheimer disease: current status and future directions

Alzheimer disease (AD) is the most common cause of dementia in older individuals. AD is characterized pathologically by amyloid-β (Aβ) plaques and tau neurofibrillary tangles in the brain, with associated loss of synapses and neurons, which eventually results in dementia. Many of the early attempts to develop treatments for AD focused on Aβ, but a lack of efficacy of these treatments in terms of slowing disease progression led to a change of strategy towards targeting of tau pathology. Given that tau shows a stronger correlation with symptom severity than does Aβ, targeting of tau is more likely to be efficacious once cognitive decline begins. Anti-tau therapies initially focused on post-translational modifications, inhibition of tau aggregation and stabilization of microtubules. However, trials of many potential drugs were discontinued because of toxicity and/or lack of efficacy. Currently, the majority of tau-targeting agents in clinical trials are immunotherapies. In this Review, we provide an update on the results from the initial immunotherapy trials and an overview of new therapeutic candidates that are in clinical development, as well as considering future directions for tau-targeting therapies.

Nuclear ERK1/2 signaling potentiation enhances neuroprotection and cognition via Importinα1/KPNA2

Cell signaling is central to neuronal activity and its dysregulation may lead to neurodegeneration and cognitive decline. Here, we show that selective genetic potentiation of neuronal ERK signaling prevents cell death in vitro and in vivo in the mouse brain, while attenuation of ERK signaling does the opposite. This neuroprotective effect mediated by an enhanced nuclear ERK activity can also be induced by the novel cell penetrating peptide RB5. In vitro administration of RB5 disrupts the preferential interaction of ERK1 MAP kinase with importinα1/KPNA2 over ERK2, facilitates ERK1/2 nuclear translocation, and enhances global ERK activity. Importantly, RB5 treatment in vivo promotes neuroprotection in mouse models of Huntington's (HD), Alzheimer's (AD), and Parkinson's (PD) disease, and enhances ERK signaling in a human cellular model of HD. Additionally, RB5-mediated potentiation of ERK nuclear signaling facilitates synaptic plasticity, enhances cognition in healthy rodents, and rescues cognitive impairments in AD and HD models. The reported molecular mechanism shared across multiple neurodegenerative disorders reveals a potential new therapeutic target approach based on the modulation of KPNA2-ERK1/2 interactions.

Trametinib activates endogenous neurogenesis and recovers neuropathology in a model of Alzheimer's disease

Enhancing adult neurogenesis in the brain has been suggested as a potential therapeutic strategy for AD. We developed a screening platform, ATRIVIEW®, for molecules that activate neuronal differentiation of adult mouse NSCs. The most potent hit from an FDA-approved drug library was SNR1611 (trametinib), a selective MEK1/2 inhibitor. We found that trametinib increases the levels of P15INK4b and Neurog2, suggesting a mechanism by which MEK1/2 inhibition induces neuronal differentiation. Oral administration of trametinib increased adult neurogenesis in the dentate gyrus and subventricular zone of the 5XFAD AD mouse model. Surprisingly, we also found that trametinib enhanced adult neurogenesis in the cortex. Consequently, trametinib rescued AD pathologies such as neuronal loss and cognitive impairment in 5XFAD mice. Finally, trametinib induced neurogenic differentiation of NSCs derived from AD patient iPSCs, which suggests its potential therapeutic application. Altogether, we suggest that restoration of endogenous adult neurogenesis by trametinib may be a promising therapeutic approach to AD.

GPR34 Knockdown Relieves Cognitive Deficits and Suppresses Neuroinflammation in Alzheimer's Disease via the ERK/NF-κB Signal

Alzheimer's disease (AD) is a serious neurodegenerative disease characterized by amyloid-β (Aβ) aggregation and neuroinflammation. G-protein-coupled receptor 34 (Gpr34) was found highly expressed in the hippocampus of APP/PS1 mice. However, its role in AD remains unclear. Herein, the role of Gpr34 as well as its molecular mechanism was explored. Data in GSE85162 were analyzed and the differently expressed genes in the hippocampus tissues of APP/PS1 mouse model of AD were subjected to GO, KEGG and GSEA enrichment analyses. APP/PS1 mice were used as an animal model of AD and the cognitive impairment was evaluated by a water maze test. The level of Gpr34 in hippocampus and BV-2 cells as well as the activation of ERK/NF-κB signal was determined by quantitative real-time PCR, western blot or immunofluorescence. Our results showed that, in BV-2 cells exposed to Aβ1-42, Gpr34 knockdown decreased the levels of TNF-α, IL-1β, IL-6 and iNOS and suppressed the activation of ERK/NF-κB signal. Moreover, the Gpr34-overexpression-induced activation of ERK/NF-κB signal and up-regulated levels of TNF-α, IL-1β, IL-6 and iNOS were abolished by FR180204, an ERK inhibitor. On the other hand, the in vivo study showed that Gpr34 knockdown ameliorated the cognitive impairment in APP/PS1 mice, decreased the levels of TNF-α, IL-1β and IL-6, the activation of microglia and ERK/NF-κB signal. In conclusion, Gpr34 knockdown relieved cognitive deficits in APP/PS1 mice and suppressed neuroinflammation and microglial activation, maybe via the ERK/NF-κB signal. It is indicated that the high level of Grp34 in hippocampus may contribute to the pathogenesis of AD.

Multiomics profiling of human plasma and cerebrospinal fluid reveals ATN-derived networks and highlights causal links in Alzheimer's disease

INTRODUCTION

This study employed an integrative system and causal inference approach to explore molecular signatures in blood and CSF, the amyloid/tau/neurodegeneration [AT(N)] framework, mild cognitive impairment (MCI) conversion to Alzheimer's disease (AD), and genetic risk for AD.

METHODS

Using the European Medical Information Framework (EMIF)-AD cohort, we measured 696 proteins in cerebrospinal fluid (n = 371), 4001 proteins in plasma (n = 972), 611 metabolites in plasma (n = 696), and genotyped whole-blood (7,778,465 autosomal single nucleotide epolymorphisms, n = 936). We investigated associations: molecular modules to AT(N), module hubs with AD Polygenic Risk scores and APOE4 genotypes, molecular hubs to MCI conversion and probed for causality with AD using Mendelian randomization (MR).

RESULTS

AT(N) framework associated with protein and lipid hubs. In plasma, Proprotein Convertase Subtilisin/Kexin Type 7 showed evidence for causal associations with AD. AD was causally associated with Reticulocalbin 2 and sphingomyelins, an association driven by the APOE isoform.

DISCUSSION

This study reveals multi-omics networks associated with AT(N) and causal AD molecular candidates.

Proteomic responses in the human dopaminergic LUHMES cell line to imidacloprid and its metabolites imidacloprid-olefin and desnitro-imidacloprid

Neonicotinoids (neonics) are amongst the most commonly used class of pesticides globally. In the United States, imidacloprid (IMI) is extensively used for agriculture and in other common applications such as house-hold pest control. Regular exposure to IMI, and several of its known metabolites including IMI-olefin and desnitro-imidacloprid (DN-IMI), has been shown to be harmful to many organisms including mammals, birds, and fish. Studies show that neonics bind human nicotinicacetylcholine receptors (nAChRs) and cause cellular toxicity. In the dopaminergic Lund human mesencephalic (LUHMES) cell line, IMI and other neonics (10-100 μM) have been recently shown to activate intracellular calcium signaling through nAChRs. Thus, we examined proteomic responses of LUHMES cells to a 48-h treatment with 50 μM IMI, IMI-olefin, or DN-IMI. Our findings show differential effects of these neonics on cellular protein expression. Bioinformatic analysis of significantly altered proteins indicates an effect of IMI, IMI-olefin, and DN-IMI on protein synthesis and ribosomal function. These findings suggest a role for protein synthesis and transcriptional regulation in neonic-mediated dopaminergic neurotoxicity.

P38 MAPK Signaling in the Retina: Effects of Aging and Age-Related Macular Degeneration

Age-related macular degeneration (AMD) is the leading cause of irreversible visual impairment worldwide. Age is the greatest risk factor for AMD but the underlying mechanism remains unascertained, resulting in a lack of effective therapies. Growing evidence shows that dysregulation of the p38 MAPK signaling pathway (SP) contributes to aging and neurodegenerative diseases; however, information about its alteration in the retina with age and during AMD development is limited. To assess the contribution of alterations in p38 MAPK signaling to AMD, we compared age-associated changes in p38 MAPK SP activity in the retina between Wistar rats (control) and OXYS rats, which develop AMD-like retinopathy spontaneously. We analyzed changes in the mRNA levels of genes of this SP in the retina (data of RNA-seq) and evaluated the phosphorylation/activation of key kinases using Western blotting at different stages of AMD-like pathology including the preclinical stage. p38 MAPK SP activity increased in the retinas of healthy Wistar rats with age. The manifestation and dramatic progression of AMD-like pathology in OXYS rats was accompanied by hyperphosphorylation of p38 MAPK and MK2 as key p38 MAPK SP kinases. Retinopathy progression co-occurred with the enhancement of p38 MAPK-dependent phosphorylation of CryaB at Ser59 in the retina.

O-GlcNAcylation regulates extracellular signal-regulated kinase (ERK) activation in Alzheimer's disease

Introduction

Aberrant activation of Extracellular Signal-Regulated Kinase (ERK) signaling is associated with Alzheimer's disease (AD) pathogenesis. For example, enhanced ERK signal activation mediated by Apolipoprotein E4 (APOE4), which is a critical genetic risk factor for AD, increases the transcription of amyloid precursor protein (APP). We hypothesize that O-linked N-acetylglucosamine (O-GlcNAc) regulates the phosphorylation and activation of ERK. O-GlcNAc is a single sugar post-translational modification that dynamically cycles on and off proteins in response to nutrient changes by the action of the enzymes O-GlcNAc transferase (OGT) and O-GlcNAcase (OGA), respectively. However, O-GlcNAc quickly returns to a baseline level after stimulus removal (called O-GlcNAc homeostasis).

Methods

We did a serum reactivation time-course followed by western blot in SH-SY5Y neuroblastoma cells after long-term O-GlcNAcase (OGA) inhibition by Thiamet-G (TMG) treatment, O-GlcNAc transferase (OGT) knock-down (KD) and OGA KD. Brain tissues of C57BL6/J mice and 5XFAD Alzheimer's disease mice intra-peritoneally injected with TMG for 1 month and C57BL6/J mice intra-peritoneally injected with TMG for 6 months were also used for western blot.

Results

We found that ERK1/2 phosphorylation at Thr 202/Tyr204 and Thr183/Tyr185 (p-ERK) are amplified and hence ERK1/2 are activated after long-term OGA inhibition in SH-SY5Y cells. In addition to pharmacological treatment, genetic disruption of O-GlcNAc by OGT KD and OGA KD also increased p-ERK in SH-SY5Y cells suggesting O-GlcNAc homeostasis controls ERK signaling. To determine how O-GlcNAc regulates p-ERK, we probed the expression of phosphorylated mitogen-activated protein kinase-kinase (p-MEK) which phosphorylates and activates ERK and Dual specificity phosphatase-4 (DUSP4) which dephosphorylates and inactivates ERK in SH-SY5Y cells. p-MEK increases in TMG treated and OGT KD cells whereas total DUSP4 decreases in OGT KD and OGA KD cells with serum reactivation time course. Next, we probed the role of OGA inhibition in regulating ERK activation using mice brain-tissue samples. Interestingly, 6-month intra-peritoneal TMG injection in C57BL/6J mice showed an increase in amplitude of p-ERK and APP protein levels, indicating long-term OGA inhibition potentially contributes to AD progression. Furthermore, 1-month TMG injection was sufficient to increase the amplitude of p-ERK in 5XFAD AD mice brains suggesting AD phenotype contributes to the acceleration of ERK activation mediated by OGA inhibition.

Conclusion

Together, these results indicate that disruptions to O-GlcNAc homeostasis amplify ERK signal activation in AD.

Agmatine prevents the memory impairment and the dysfunction of hippocampal GSK-3β and ERK signaling induced by aluminum nanoparticle in mice

The growing usage of aluminum nanoparticles (Al-NP) and their exposure may influence body function. Considering the proposed relationship between Al and the pathogenesis of Alzheimer's disease and the concern about the effect of this nanoparticle on brain health and cognitive function, the use of neuroprotective agents might be helpful. According to the reported neuroprotective effects of agmatine, in the present study, the possible protective effect of agmatine was assessed in mice model of Al-NP-induced memory impairment. In addition, due to the roles of hippocampal Glycogen synthase kinase-3 beta (GSK-3β) and ERK signaling in memory and its disorders, these pathways were also investigated. Al-NP (10 mg/kg/p.o.) with/without agmatine (5 or 10 mg/kg/i.p.) was administered to adult male NMRI mice for 5 days. Novel object recognition (NOR) test session was used to assess cognitive function. Following the behavioral assessments, the hippocampi were used to determine the phosphorylated and total levels of GSK-3β and ERK as well as GAPDH using western blot analysis. The results showed that Al-NP impaired NOR memory in mice while agmatine 10 mg/kg prevented the memory deficit induced by Al-NP. Furthermore, Al-NP activated GSK-3β as well as ERK signals within the hippocampus while agmatine prevented the effects of Al-NP on GSK-3β and ERK signals within the hippocampus. Besides supporting the neuroprotective effects of agmatine, these findings suggest the possibility of the connection of hippocampal GSK-3β and ERK signaling in the neuroprotective effect of this polyamine against Al-NP.

Molecular crosstalk between COVID-19 and Alzheimer's disease using microarray and RNA-seq datasets: A system biology approach

Objective

Coronavirus disease 2019 (COVID-19) is an infectious disease caused by Severe Acute Respiratory Syndrome Coronavirus-2 (SARS-CoV-2). The clinical and epidemiological analysis reported the association between SARS-CoV-2 and neurological diseases. Among neurological diseases, Alzheimer's disease (AD) has developed as a crucial comorbidity of SARS-CoV-2. This study aimed to understand the common transcriptional signatures between SARS-CoV-2 and AD.

Materials and methods

System biology approaches were used to compare the datasets of AD and COVID-19 to identify the genetic association. For this, we have integrated three human whole transcriptomic datasets for COVID-19 and five microarray datasets for AD. We have identified differentially expressed genes for all the datasets and constructed a protein-protein interaction (PPI) network. Hub genes were identified from the PPI network, and hub genes-associated regulatory molecules (transcription factors and miRNAs) were identified for further validation.

Results

A total of 9,500 differentially expressed genes (DEGs) were identified for AD and 7,000 DEGs for COVID-19. Gene ontology analysis resulted in 37 molecular functions, 79 cellular components, and 129 biological processes were found to be commonly enriched in AD and COVID-19. We identified 26 hub genes which includes AKT1, ALB, BDNF, CD4, CDH1, DLG4, EGF, EGFR, FN1, GAPDH, INS, ITGB1, ACTB, SRC, TP53, CDC42, RUNX2, HSPA8, PSMD2, GFAP, VAMP2, MAPK8, CAV1, GNB1, RBX1, and ITGA2B. Specific miRNA targets associated with Alzheimer's disease and COVID-19 were identified through miRNA target prediction. In addition, we found hub genes-transcription factor and hub genes-drugs interaction. We also performed pathway analysis for the hub genes and found that several cell signaling pathways are enriched, such as PI3K-AKT, Neurotrophin, Rap1, Ras, and JAK-STAT.

Conclusion

Our results suggest that the identified hub genes could be diagnostic biomarkers and potential therapeutic drug targets for COVID-19 patients with AD comorbidity.

Study on multi-target effects of PIMPC on Aβ/Cu2+-induced Alzheimer's disease model of rats

Glycogen synthase kinase-3 (GSK-3), a key role in the pathogenesis of Alzheimer's disease (AD), has been linked with the formation of β-amyloid (Aβ), tubulin-associated unit (tau) protein phosphorylation and apoptosis. Moreover, the excessive presence of elements such as copper (Cu) can promote Aβ aggregation and increase the risk of AD. Combined with the role of GSK-3 and metal elements in AD, a metal-chelating imine GSK-3 inhibitor N-(4-{[(2-amino-5-phenylpyridin-3-ylidene)imino]methyl}pyridin-2-yl)cyclopropanecarboxamide (PIMPC) was designed and synthesized. In our study, Aβ/Cu²⁺-induced AD rat model was established and treated with PIMPC. The results indicated that PIMPC can not only down-regulate the high expression levels of Aβ, tau and p-tau proteins of the AD rats, but also chelate Cu and aluminum (Al) elements in the brain. In addition, PIMPC may play an anti-apoptotic effect by down-regulating the high expression of cleaved Caspase-3 protein, and it can modulate ATPase and nitric oxide synthase (NOS) levels, oxidative stress and neurotransmitter disturbance. In summary, PIMPC acts on multiple targets to relieve the learning and memory impairment of AD rats induced by Aβ/Cu²⁺.

MicroRNAs and MAPKs: Evidence of These Molecular Interactions in Alzheimer's Disease

Alzheimer's disease (AD) is a neurodegenerative disorder known to be the leading cause of dementia worldwide. Many microRNAs (miRNAs) were found deregulated in the brain or blood of AD patients, suggesting a possible key role in different stages of neurodegeneration. In particular, mitogen-activated protein kinases (MAPK) signaling can be impaired by miRNA dysregulation during AD. Indeed, the aberrant MAPK pathway may facilitate the development of amyloid-beta (Aβ) and Tau pathology, oxidative stress, neuroinflammation, and brain cell death. The aim of this review was to describe the molecular interactions between miRNAs and MAPKs during AD pathogenesis by selecting evidence from experimental AD models. Publications ranging from 2010 to 2023 were considered, based on PubMed and Web of Science databases. According to obtained data, several miRNA deregulations may regulate MAPK signaling in different stages of AD and conversely. Moreover, overexpressing or silencing miRNAs involved in MAPK regulation was seen to improve cognitive deficits in AD animal models. In particular, miR-132 is of particular interest due to its neuroprotective functions by inhibiting Aβ and Tau depositions, as well as oxidative stress, through ERK/MAPK1 signaling modulation. However, further investigations are required to confirm and implement these promising results.

Royal jelly improves learning and memory deficits in an amyloid β-induced model of Alzheimer's disease in male rats: Involvement of oxidative stress

Alzheimer's disease (AD) as the commonest type of dementia is associated with the cognitive function failure. Oxidative stress performs an essential role in the progression of AD. Royal jelly (RJ) is a natural product of bees with antioxidant and anti-inflammatory properties. The present research aimed to investigate the possible protective effect of RJ on learning and memory in a rat model of Aβ-induced AD. Forty male adult Wistar rats were equally distributed into five groups: control, sham-operated, Aβ (receiving intracerebroventricular (ICV) injection of amyloid beta (Aβ1-40)), Aβ + RJ 50 mg/kg, and Aβ + RJ 100 mg/kg. RJ was administered daily post-surgery by oral gavage for four weeks. Behavioral learning and memory were examined using the novel object recognition (NOR) and passive avoidance learning (PAL) tests. Also, oxidative stress markers, such as malondialdehyde (MDA), total oxidant status (TOS) and total antioxidant capacity (TAC), were assessed in the hippocampus. Aβ reduced step-through latency (STLr) and increased time spent in the dark compartment (TDC) in the PAL task and also decreased discrimination index in the NOR test. Administration of RJ ameliorated the Aβ-related memory impairment in both NOR and PAL tasks. Aβ decreased TAC and increased MDA and TOS levels in the hippocampus, whereas RJ administration reversed these Aβ-induced alterations. Our results indicated that RJ has the potential to ameliorate learning and memory impairment in the Aβ model of AD via attenuating oxidative stress.

Using Optogenetics to Model Cellular Effects of Alzheimer's Disease

Across the world a dementia case is diagnosed every three seconds. Alzheimer's disease (AD) causes 50-60% of these cases. The most prominent theory for AD correlates the deposition of amyloid beta (Aβ) with the onset of dementia. Whether Aβ is causative remains unclear due to findings such as the recently approved drug Aducanumab showing effective clearance of Aβ, but not improving cognition. New approaches for understanding Aβ function, are therefore necessary. Here we discuss the application of optogenetic techniques to gain insight into AD. Optogenetics, or genetically encoded, light-dependent on/off switches, provides precise spatiotemporal control to regulate cellular dynamics. This precise control over protein expression and oligomerization or aggregation could provide a better understanding of the etiology of AD.

Alteration of the MEK1/2–ERK1/2 Signaling Pathway in the Retina Associated with Age and Development of AMD-Like Retinopathy

Age-related macular degeneration (AMD) is a complex neurodegenerative disease and a major cause of irreversible visual impairment in patients in developed countries. Although age is the greatest risk factor in AMD, molecular mechanisms involved in AMD remain unknown. Growing evidence shows that dysregulation of MAPK signaling contributes to aging and neurodegenerative diseases; however, the information on the role of MAPK upregulation in these processes is controversial. ERK1 and ERK2 participate in the maintenance of proteostasis through the regulation of protein aggregation induced by the endoplasmic reticulum stress and other stress-mediated cell responses. To assess the contribution of alterations in the ERK1/2 signaling to the AMD development, we compared age-associated changes in the activity of ERK1/2 signaling pathway in the retina of Wistar rats (control) and OXYS rats that develop AMD-like retinopathy spontaneously. The activity of the ERK1/2 signaling increased during physiological aging in the retina of Wistar rats. The manifestation and progression of the AMD-like pathology in the retina of OXYS rats was accompanied by hyperphosphorylation of ERK1/2 and MEK1/2, the key kinases of the ERK1/2 signaling pathway. The progression of the AMD-like pathology was also associated with the ERK1/2-dependent tau protein hyperphosphorylation and increase in the ERK1/2-dependent phosphorylation of alpha B crystallin at Ser45 in the retina.

Network pharmacology and bioinformatics approach reveals the therapeutic mechanism of action of curcumin in Alzheimer disease

Curcumin is a natural anti-inflammatory and antioxidant substance which plays a major role in reducing the amyloid plaques formation, which is the major cause of Alzheimer's disease (AD). Consequently, a methodical approach was used to select the potential protein targets of curcumin in AD through network pharmacology. In this study, through integrative methods, AD targets of curcumin through SwissTargetPrediction database, STITCH database, BindingDB, PharmMapper, Therapeutic Target Database (TTD), Online Mendelian Inheritance in Man (OMIM) database were predicted followed by gene enrichment analysis, network construction, network topology, and docking studies. Gene ontology analysis facilitated identification of a list of possible AD targets of curcumin (74 targets genes). The correlation of the obtained targets with AD was analysed by using gene ontology (GO) pathway enrichment analyses and Kyoto Encyclopaedia of Genes and Genomes (KEGG). We have incorporated the applied network pharmacological approach to identify key genes. Furthermore, we have performed molecular docking for analysing the mechanism of curcumin. In order to validate the temporospatial expression of key genes in human central nervous system (CNS), we searched the Human Brain Transcriptome (HBT) dataset. We identified top five key genes namely, PPARγ, MAPK1, STAT3, KDR and APP. Further validated the expression profiling of these key genes in publicly available brain data expression profile databases. In context to a valuable addition in the treatment of AD, this study is concluded with novel insights into the therapeutic mechanisms of curcumin, will ease the treatment of AD with the clinical application of curcumin.

A Function of Amyloid-β in Mediating Activity-Dependent Axon/Synapse Competition May Unify Its Roles in Brain Physiology and Pathology

Amyloid-β protein precursor (AβPP) gives rise to amyloid-β (Aβ), a peptide at the center of Alzheimer's disease (AD). AβPP, however, is also an ancient molecule dating back in evolution to some of the earliest forms of metazoans. This suggests a possible ancestral function that may have been obscured by those that evolve later. Based on literature from the functions of Aβ/AβPP in nervous system development, plasticity, and disease, to those of anti-microbial peptides (AMPs) in bacterial competition as well as mechanisms of cell competition uncovered first by Drosophila genetics, I propose that Aβ/AβPP may be part of an ancient mechanism employed in cell competition, which is subsequently co-opted during evolution for the regulation of activity-dependent neural circuit development and plasticity. This hypothesis is supported by foremost the high similarities of Aβ to AMPs, both of which possess unique, opposite (i.e., trophic versus toxic) activities as monomers and oligomers. A large body of data further suggests that the different Aβ oligomeric isoforms may serve as the protective and punishment signals long predicted to mediate activity-dependent axonal/synaptic competition in the developing nervous system and that the imbalance in their opposite regulation of innate immune and glial cells in the brain may ultimately underpin AD pathogenesis. This hypothesis can not only explain the diverse roles observed of Aβ and AβPP family molecules, but also provide a conceptual framework that can unify current hypotheses on AD. Furthermore, it may explain major clinical observations not accounted for and identify approaches for overcoming shortfalls in AD animal modeling.

The Interplay Between Cholesterol and Amyloid-β on HT22 Cell Viability, Morphology, and Receptor Tyrosine Kinase Signaling

BACKGROUND

There is a lack of understanding in the molecular and cellular mechanisms of Alzheimer's disease that has hindered progress on therapeutic development. The focus has been on targeting toxic amyloid-β (Aβ) pathology, but these therapeutics have generally failed in clinical trials. Aβ is an aggregation-prone protein that has been shown to disrupt cell membrane structure in molecular biophysics studies and interfere with membrane receptor signaling in cell and animal studies. Whether the lipid membrane or specific receptors are the primary target of attack has not been determined.

OBJECTIVE

This work elucidates some of the interplay between membrane cholesterol and Aβ42 on HT22 neuronal cell viability, morphology, and platelet-derived growth factor (PDGF) signaling pathways.

METHODS

The effects of cholesterol depletion by methyl-β-cyclodextrin followed by treatment with Aβ and/or PDGF-AA were assessed by MTT cell viability assays, western blot, optical and AFM microscopy.

RESULTS

Cell viability studies show that cholesterol depletion was mildly protective against Aβ toxicity. Together cholesterol reduction and Aβ42 treatment compounded the disruption of the PDGFα receptor activation. Phase contrast optical microscopy and live cell atomic force microscopy imaging revealed that cytotoxic levels of Aβ42 caused morphological changes including cell membrane damage, cytoskeletal disruption, and impaired cell adhesion; cell damage was ameliorated by cellular cholesterol depletion.

CONCLUSIONS

Cholesterol depletion impacted the effects of Aβ42 on HT22 cell viability, morphology, and receptor tyrosine kinase signaling.

Enhanced activity of Alzheimer disease-associated variant of protein kinase Cα drives cognitive decline in a mouse model

Exquisitely tuned activity of protein kinase C (PKC) isozymes is essential to maintaining cellular homeostasis. Whereas loss-of-function mutations are generally associated with cancer, gain-of-function variants in one isozyme, PKCα, are associated with Alzheimer's disease (AD). Here we show that the enhanced activity of one variant, PKCα M489V, is sufficient to rewire the brain phosphoproteome, drive synaptic degeneration, and impair cognition in a mouse model. This variant causes a modest 30% increase in catalytic activity without altering on/off activation dynamics or stability, underscoring that enhanced catalytic activity is sufficient to drive the biochemical, cellular, and ultimately cognitive effects observed. Analysis of hippocampal neurons from PKCα M489V mice reveals enhanced amyloid-β-induced synaptic depression and reduced spine density compared to wild-type mice. Behavioral studies reveal that this mutation alone is sufficient to impair cognition, and, when coupled to a mouse model of AD, further accelerates cognitive decline. The druggability of protein kinases positions PKCα as a promising therapeutic target in AD.

AR12 increases BAG3 expression which is essential for Tau and APP degradation via LC3-associated phagocytosis and macroautophagy

We defined the mechanisms by which the chaperone ATPase inhibitor AR12 and the multi-kinase inhibitor neratinib interacted to reduce expression of Tau and amyloid-precursor protein (APP) in microglia and neuronal cells. AR12 and neratinib interacted to increase the phosphorylation of eIF2A S51 and the expression of BAG3, Beclin1 and ATG5, and in parallel, enhanced autophagosome formation and autophagic flux. Knock down of BAG3, Beclin1 or ATG5 abolished autophagosome formation and significantly reduced degradation of p62, LAMP2, Tau, APP, and GRP78 (total and plasma membrane). Knock down of Rubicon, a key component of LC3-associated phagocytosis (LAP), significantly reduced autophagosome formation but not autophagic flux and prevented degradation of Tau, APP, and cell surface GRP78, but not ER-localized GRP78. Knock down of Beclin1, ATG5 or Rubicon or over-expression of GRP78 prevented the significant increase in eIF2A phosphorylation. Knock down of eIF2A prevented the increase in BAG3 expression and significantly reduced autophagosome formation, autophagic flux, and it prevented Tau and APP degradation. We conclude that AR12 has the potential to reduce Tau and APP levels in neurons and microglia via the actions of LAP, endoplasmic reticulum stress signaling and macroautophagy. We hypothesize that the initial inactivation of GRP78 catalytic function by AR12 facilitates an initial increase in eIF2A phosphorylation which in turn is essential for greater levels of eIF2A phosphorylation, greater levels of BAG3 and macroautophagy and eventually leading to significant amounts of APP/Tau degradation.

Interferon beta attenuates recognition memory impairment and improves brain glucose uptake in a rat model of Alzheimer's disease: Involvement of mitochondrial biogenesis and PI3K pathway

Interferon beta (IFNβ) is a cytokine with anti-apoptotic and anti-inflammatory properties, and its beneficial effects on Alzheimer's disease (AD) have been recently shown. The alterations in cerebral glucose uptake are closely linked to memory deficit and AD progression. The current study was designed to determine if IFNβ can improve recognition memory and brain glucose uptake in a rat model of AD. The lentiviruses expressing mutant human amyloid precursor protein were injected bilaterally to the rat hippocampus. From day 23 after virus injection, rats were intranasally treated with recombinant IFNβ protein (68,000 IU/rat) every other day until day 50. Recognition memory performance was evaluated by novel object recognition test on days 46-49. The 18F-2- fluoro-deoxy-d-glucose positron emission tomography (18F-FDG-PET) was used to determine changes in brain glucose metabolism on day 50. The expression of the PI3K/Akt pathway components, neurotrophins and mitochondrial biogenesis factors were also measured by qPCR in the hippocampus. Our results showed that IFNβ treatment improves recognition memory performance in parallel with increased glucose uptake and neuronal survival in the hippocampus of the AD rats. The neuroprotective effect of IFNβ could be attributed, at least partly, to activation of PI3K-Akt-mTOR signaling pathway, increased expression of NGF, and mitochondrial biogenesis. Taken together, our findings suggest the therapeutic potential of IFNβ for AD.

Irisin stimulates protective signaling pathways in rat hippocampal neurons

Physical exercise stimulates neuroprotective pathways, has pro-cognitive actions, and alleviates memory impairment in Alzheimer’s disease (AD). Irisin is an exercise-linked hormone produced by cleavage of fibronectin type III domain containing protein 5 (FNDC5) in skeletal muscle, brain and other tissues. Irisin was recently shown to mediate the brain benefits of exercise in AD mouse models. Here, we sought to obtain insight into the neuroprotective actions of irisin. We demonstrate that adenoviral-mediated expression of irisin promotes extracellular brain derived neurotrophic factor (BDNF) accumulation in hippocampal cultures. We further show that irisin stimulates transient activation of extracellular signal-regulated kinase 1/2 (ERK 1/2), and prevents amyloid-β oligomer-induced oxidative stress in primary hippocampal neurons. Finally, analysis of RNA sequencing (RNAseq) datasets shows a trend of reduction of hippocampal FNDC5 mRNA with aging and tau pathology in humans. Results indicate that irisin activates protective pathways in hippocampal neurons and further support the notion that stimulation of irisin signaling in the brain may be beneficial in AD.

Behavioral and Molecular Effects of Thapsigargin-Induced Brain ER- Stress: Encompassing Inflammation, MAPK, and Insulin Signaling Pathway

Accumulation of misfolded proteins, known as endoplasmic reticulum (ER) stress, is known to participate in Alzheimer’s disease (AD). AD is also correlated with impaired central insulin signaling. However, few studies have probed the relationship between memory, central ER stress, inflammation, hippocampal mitogen-activated protein kinase (MAPK) activity and insulin resistance. The present study aimed to investigate the causative role and underlying mechanisms of brain ER stress in memory impairment and develop a reliable animal model for ER-mediated memory loss. Thapsigargin (TG), a known ER stress activator, was centrally administered. The cognitive function of animals was evaluated by the Morris Water Maze (MWM). To verify the induction of central ER stress, we investigated the mRNA expression of UPR markers in the hippocampus. In addition, the activation of ER stress markers, including Bip, CHOP, and some related apoptosis and pro-inflammatory proteins, such as caspase-3, Bax, Bcl-2, TNF-α, MAPK, and insulin signaling markers, were assessed by Western-blots. The results demonstrated that TG impairs spatial cognition and hippocampal insulin signaling. Meanwhile, molecular results showed a concurrent increment of hippocampal UPR markers, apoptosis, P38 activity, and TNF-α. This study introduced TG-induced ER stress as a pharmacological model for memory impairment in rats and revealed some underlying mechanisms.

Ras Inhibitor Lonafarnib Rescues Structural and Functional Impairments of Synapses of Aβ1-42 Mice via α7nAChR-Dependent BDNF Upregulation

Alzheimer's disease (AD) is characterized pathologically by the structural and functional impairments of synapses in the hippocampus, inducing the learning and memory deficiencies. Ras GTPase is closely related to the synaptic function and memory. This study was to investigate the effects of farnesyl transferase inhibitor lonafarnib on the synaptic structure and function in AD male mice and explore the potential mechanism. Our results showed 50 mg/kg lonafarnib (intraperitoneal) rescued the impaired spatial memory and improved the damaged synaptic transmission and plasticity of Aβ1-42 mice. In addition, lonafarnib ameliorated the morphology of synaptic dendrites and spines in Aβ1-42 mice. Furthermore, lonafarnib enhanced α7nAChR cell surface expression and phosphorylation of downstream Akt and CaMKII in Aβ1-42 mice, which were inhibited by α7nAChR antagonist methyl lycaconitine (MLA), and increased the phosphorylation of CREB in a CaMKII- but not ERK-dependent way. Lonafarnib enhanced hippocampal brain-derived neurotrophic factor (BDNF) concentration in Aβ1-42 mice, which was sensitive to MLA and KN93 (an inhibitor of CaMKII), but not related to ERK and Akt pathways. H-Ras, but not Rhes, was related to the lonafarnib induced improvement of α7nAChR cell surface expression and BDNF content. Interestingly, lonafarnib induced improvement of synaptic transmission, plasticity and spatial cognition in Aβ1-42 mice was abolished by BDNF deprivation with TrkB/Fc chimera protein. Our results indicate that lonafarnib can rescue the structural and functional impairments of synapses in the Aβ1-42 mice, which may be related to the improvement of BDNF content through the H-Ras-α7nAChR-dependent CaMKII-CREB pathway, leading to the improvement of spatial cognition.SIGNIFICANCE STATEMENT Alzheimer's disease (AD) is characterized pathologically by the structural and functional impairments of synapses in the hippocampus, inducing the learning and memory deficiencies. However, no effective drugs have not been developed for the treatment of AD synaptic. This study for the first time reported the beneficial effects of Ras inhibitor lonafarnib on the synaptic structure and function in AD mice, providing an alternative way for the treatment of "synaptic disease" in AD patients.

Amyloid precursor protein (APP) and amyloid β (Aβ) interact with cell adhesion molecules: Implications in Alzheimer’s disease and normal physiology

Alzheimer’s disease (AD) is an incurable neurodegenerative disorder in which dysfunction and loss of synapses and neurons lead to cognitive impairment and death. Accumulation and aggregation of neurotoxic amyloid-β (Aβ) peptides generated via amyloidogenic processing of amyloid precursor protein (APP) is considered to play a central role in the disease etiology. APP interacts with cell adhesion molecules, which influence the normal physiological functions of APP, its amyloidogenic and non-amyloidogenic processing, and formation of Aβ aggregates. These cell surface glycoproteins also mediate attachment of Aβ to the neuronal cell surface and induce intracellular signaling contributing to Aβ toxicity. In this review, we discuss the current knowledge surrounding the interactions of cell adhesion molecules with APP and Aβ and analyze the evidence of the critical role these proteins play in regulating the processing and physiological function of APP as well as Aβ toxicity. This is a necessary piece of the complex AD puzzle, which we should understand in order to develop safe and effective therapeutic interventions for AD.

Modulation of MAPK- and PI3/AKT-Dependent Autophagy Signaling by Stavudine (D4T) in PBMC of Alzheimer’s Disease Patients

Background: Aβ₄₂ deposition plays a pivotal role in AD pathogenesis by inducing the activation of microglial cells and neuroinflammation. This process is antagonized by microglia-mediated clearance of Aβ plaques. Activation of the NLRP3 inflammasome is involved in neuroinflammation and in the impairments of Aβ-plaque clearance. On the other hand, stavudine (D4T) downregulates the NLRP3 inflammasome and stimulates autophagy-mediated Aβ-clearing in a THP-1-derived macrophages. Methods: We explored the effect of D4T on Aβ autophagy in PBMC from AD patients that were primed with LPS and stimulated with Aβ oligomers in the absence/presence of D4T. We analyzed the NLRP3 activity by measuring NLRP3-ASC complex formation by AMNIS FlowSight and pro-inflammatory cytokine (IL-1β, IL-18 and Caspase-1) production by ELISA. The phosphorylation status of p38, ERK, AKT, p70, and the protein expression of CREB, LAMP2A, beclin-1, Caspase-3 and Bcl2 were analyzed by Western blot. Results: Data showed that D4T: (1) downregulates NLRP3 inflammasome activation and the production of down-stream pro-inflammatory cytokines in PBMC; (2) stimulates the phosphorylation of AKT, ERK and p70 as well as LAMP2A, beclin-1 and Bcl2 expression and reduces Caspase-3 expression, suggesting an effect of this compound on autophagy; (3) increases phospho-CREB, which is a downstream target of p-ERK and p-AKT, inducing anti-inflammatory cytokine production and resulting in a possible decrease of Aβ-mediated cytotoxicity; and (4) reduces the phosphorylation of p38, a protein involved in the production of pro-inflammatory cytokines and tau hyperphosphorylation. Conclusions: D4T reduces the activation of the NLRP3 inflammasome, and it might stimulate autophagy as well as the molecular mechanism that modulates Aβ cytotoxicity, and D4T might reduce inflammation in the cells of AD patients. It could be very interesting to check the possible beneficial effects of D4T in the clinical scenario.

Alzheimer's Disease Blood Biomarkers Associated With Neuroinflammation as Therapeutic Targets for Early Personalized Intervention

The definitive diagnosis of Alzheimer's Disease (AD) without the need for neuropathological confirmation remains a challenge in AD research today, despite efforts to uncover the molecular and biological underpinnings of the disease process. Furthermore, the potential for therapeutic intervention is limited upon the onset of symptoms, providing motivation for studying and treating the AD precursor mild cognitive impairment (MCI), the prodromal stage of AD instead. Applying machine learning classification to transcriptomic data of MCI, AD, and cognitively normal (CN) control patients, we identified differentially expressed genes that serve as biomarkers for the characterization and classification of subjects into MCI or AD groups. Predictive models employing these biomarker genes exhibited good classification performances for CN, MCI, and AD, significantly above random chance. The PI3K-Akt, IL-17, JAK-STAT, TNF, and Ras signaling pathways were also enriched in these biomarker genes, indicating their diagnostic potential and pathophysiological roles in MCI and AD. These findings could aid in the recognition of MCI and AD risk in clinical settings, allow for the tracking of disease progression over time in individuals as part of a therapeutic approach, and provide possible personalized drug targets for early intervention of MCI and AD.

REPS1 as a Potential Biomarker in Alzheimer’s Disease and Vascular Dementia

Vascular dementia (VD) and Alzheimer’s disease (AD) are common types of dementia for which no curative therapies are known. In this study, we identified hub genes associated with AD and VD in order to explore new potential therapeutic targets. Genes differentially expressed in VD and AD in all three datasets (GSE122063, GSE132903, and GSE5281) were identified and used to construct a protein–protein interaction network. We identified 10 modules containing 427 module genes in AD and VD. Module genes showing an area under the diagnostic curve > 0.60 for AD or VD were used to construct a least absolute shrinkage and selection operator model and were entered into a support vector machine-recursive feature elimination algorithm, which identified REPS1 as a hub gene in AD and VD. Furthermore, REPS1 was associated with activation of pyruvate metabolism and inhibition of Ras signaling pathway. Module genes, together with differentially expressed microRNAs from the dataset GSE46579, were used to construct a regulatory network. REPS1 was predicted to bind to the microRNA hsa_miR_5701. Single-sample gene set enrichment analysis was used to explore immune cell infiltration, which suggested a negative correlation between REPS1 expression and infiltration by plasmacytoid dendritic cells in AD and VD. In conclusion, our results suggest core pathways involved in both AD and VD, and they identify REPS1 as a potential biomarker of both diseases. This protein may aid in early diagnosis, monitoring of treatment response, and even efforts to prevent these debilitating disorders.

Neurogenesis Is Increased in Human Neural Stem Cells by Aβ40 Peptide

Amyloid-β 40 peptides [Aβ1-40 (Aβ40)] are present within amyloid plaques in the brains of patients with Alzheimer's disease (AD). Even though Aβ peptides are considered neurotoxic, they can mediate many biological processes, both in adult brains and throughout brain development. However, the physiological function of these Aβ peptides remains poorly understood, and the existing data are sometimes controversial. Here, we analyze and compare the effects of monomeric Aβ40 on the biology of differentiating human neural stem cells (human NSCs). For that purpose, we used a model of human NSCs called hNS1. Our data demonstrated that Aβ40 at high concentrations provokes apoptotic cellular death and the damage of DNA in human NSCs while also increasing the proliferation and favors neurogenesis by raising the percentage of proliferating neuronal precursors. These effects can be mediated, at least in part, by β-catenin. These results provide evidence of how Aβ modulate/regulate human NSC proliferation and differentiation, suggesting Aβ40 may be a pro-neurogenic factor. Our data could contribute to a better understanding of the molecular mechanisms involved in AD pathology and to the development of human NSC-based therapies for AD treatment, since these results could then be used in diagnosing the disease at early stages and be applied to the development of new treatment options.

Intranasal Oxytocin Attenuates Cognitive Impairment, β-Amyloid Burden and Tau Deposition in Female Rats with Alzheimer's Disease: Interplay of ERK1/2/GSK3β/Caspase-3

Oxytocin is a neuropeptide hormone that plays an important role in social bonding and behavior. Recent studies indicate that oxytocin could be involved in the regulation of neurological disorders. However, its role in modulating cognition in Alzheimer’s disease (AD) has never been explored. Hence, the present study aims to investigate the potential of chronic intranasal oxytocin in halting memory impairment & AD pathology in aluminum chloride-induced AD in female rats. Morris water maze was used to assess cognitive dysfunction in two-time points throughout the treatment period. In addition, neuroprotective effects of oxytocin were examined by assessing hippocampal acetylcholinesterase activity, β-amyloid 1–42 protein, and Tau levels. In addition, ERK1/2, GSK3β, and caspase-3 levels were assessed as chief neurobiochemical mediators in AD. Hippocampi histopathological changes were also evaluated. These findings were compared to the standard drug galantamine alone and combined with oxytocin. Results showed that oxytocin restored cognitive functions and improved animals’ behavior in the Morris test. This was accompanied by a significant decline in acetylcholinesterase activity, 1–42 β-amyloid and Tau proteins levels. Hippocampal ERK1/2 and GSK3β were also reduced, exceeding galantamine effects, thus attenuating AD pathological hallmarks formation. Determination of caspase-3 revealed low cytoplasmic positivity, indicating the ceasing of neuronal death. Histopathological examination confirmed these findings, showing restored hippocampal cells structure. Combined galantamine and oxytocin treatment showed even better biochemical and histopathological profiles. It can be thus concluded that oxytocin possesses promising neuroprotective potential in AD mediated via restoring cognition and suppressing β-amyloid, Tau accumulation, and neuronal death.

Identification and Validation of Aging-Related Genes in Alzheimer’s Disease

Aging is recognized as the key risk factor for Alzheimer’s disease (AD). This study aimed to identify and verify potential aging-related genes associated with AD using bioinformatics analysis. Aging-related differential expression genes (ARDEGs) were determined by the intersection of limma test, weighted correlation network analysis (WGCNA), and 1153 aging and senescence-associated genes. Potential biological functions and pathways of ARDEGs were determined by GO, KEGG, GSEA, and GSVA. Then, LASSO algorithm was used to identify the hub genes and the diagnostic ability of the five ARDEGs in discriminating AD from the healthy control samples. Further, the correlation between hub ARDEGs and clinical characteristics was explored. Finally, the expression level of the five ARDEGs was validated using other four GEO datasets and blood samples of patients with AD and healthy individuals. Five ARDEGs (GFAP, PDGFRB, PLOD1, MAP4K4, and NFKBIA) were obtained. For biological function analysis, aging, cellular senescence, and Ras protein signal transduction regulation were enriched. Diagnostic ability of the five ARDEGs in discriminating AD from the control samples demonstrated a favorable diagnostic value. Eventually, quantitative real-time reverse transcription-polymerase chain reaction (qRT-PCR) validation test revealed that compared with healthy controls, the mRNA expression level of PDGFRB, PLOD1, MAP4K4, and NFKBIA were elevated in AD patients. In conclusion, this study identified four ARDEGs (PDGFRB, PLOD1, MAP4K4, and NFKBIA) associated with AD. They provide an insight into potential novel biomarkers for diagnosing AD and monitoring progression.

Baicalin Attenuated Aβ1-42-Induced Apoptosis in SH-SY5Y Cells by Inhibiting the Ras-ERK Signaling Pathway

Alzheimer's disease (AD) is a serious neurodegenerative disease. It is widely believed that the accumulation of amyloid beta (Aβ) in neurons around neurofibrillary plaques is the main pathological characteristic of AD; however, the molecular mechanism underlying these pathological changes is not clear. Baicalin is a flavonoid extracted from the dry root of Scutellaria baicalensis Georgi. Studies have shown that baicalin exerts excellent anti-inflammatory and neuroprotective effects. In this study, an AD cell model was established by exposing SH-SY5Y cells to Aβ_1-42 and treating them with baicalin. Cell survival, cell cycle progression, and apoptosis were measured by MTT, flow cytometry, and immunofluorescence assays, respectively. The expression levels of Ras, ERK/ERK phosphorylation (p-ERK), and cyclin D1 were measured by Western blotting. In addition, whether the MEK activator could reverse the regulatory effect of baicalin on Ras-ERK signaling was investigated using Western blotting. We found that baicalin improved the survival, promoted the proliferation, and inhibited the apoptosis of SH-SY5Y cells after Aβ_1-42 treatment. Baicalin also ameliorated Aβ_1-42-induced cell cycle arrest at the S phase and induced apoptosis. Furthermore, baicalin inhibited the levels of Ras, p-ERK, and cyclin D1 induced by Aβ, and this effect could be reversed by the MEK activator. Therefore, we suggest that baicalin may regulate neuronal cell cycle progression and apoptosis in Aβ_1-42-treated SH-SY5Y cells by inhibiting the Ras-ERK signaling pathway. This study suggested that baicalin might be a useful therapeutic agent for senile dementia, especially AD.

Identification of Potential Key circRNAs in Aged Mice With Postoperative Delirium

Postoperative delirium (POD) is a common postoperative complication in elderly patients and seriously affects postoperative recovery. The exact mechanism of POD is still unclear. Therefore, it is necessary to explore the mechanism of POD in transcriptional regulation. At present, circRNAs have been proven to play an important role in a variety of mental health and cognitive disorders, such as Alzheimer’s disease, depression and schizophrenia. To reveal the effect of circRNA on POD, we used microarray to analyze the differential expression profiles of circRNAs in the hippocampus of 12-month-old mice between the tibial fracture and control groups. A total of 1,4236 circRNAs were identified. Compared with the control group, there were 500 circRNAs with increased expression and 187 with decreased expression. The accuracy of the microarray data was further verified by qRT–PCR. Finally, GO enrichment and KEGG pathway analyses indicated that changes in axon orientation, ubiquitin-mediated proteolysis, glutamate synapses, the estrogen signaling pathway, the RAS signaling pathway and other systems may be important potential pathological mechanisms in the progression of POD. In particular, we found that the HOMER1 gene and its transcript mmu_circRNA_26701 are specifically expressed in the glutamate synapse, which may provide new clues and intervention targets for the progression of this refractory disease.

Aβ Assemblies Promote Amyloidogenic Processing of APP and Intracellular Accumulation of Aβ42 Through Go/Gβγ Signaling

Alzheimer’s disease (AD) is characterized by the deposition of aggregated species of amyloid beta (Aβ) in the brain, which leads to progressive cognitive deficits and dementia. Aβ is generated by the successive cleavage of the amyloid precursor protein (APP), first by β-site APP cleaving enzyme 1 (BACE1) and subsequently by the γ-secretase complex. Those conditions which enhace or reduce its clearance predispose to Aβ aggregation and the development of AD. In vitro studies have demonstrated that Aβ assemblies spark a feed-forward loop heightening Aβ production. However, the underlying mechanism remains unknown. Here, we show that oligomers and fibrils of Aβ enhance colocalization and physical interaction of APP and BACE1 in recycling endosomes of human neurons derived from induced pluripotent stem cells and other cell types, which leads to exacerbated amyloidogenic processing of APP and intracellular accumulation of Aβ42. In cells that are overexpressing the mutant forms of APP which are unable to bind Aβ or to activate Go protein, we have found that treatment with aggregated Aβ fails to increase colocalization of APP with BACE1 indicating that Aβ-APP/Go signaling is involved in this process. Moreover, inhibition of Gβγ subunit signaling with βARKct or gallein prevents Aβ-dependent interaction of APP and BACE1 in endosomes, β-processing of APP, and intracellular accumulation of Aβ42. Collectively, our findings uncover a signaling mechanism leading to a feed-forward loop of amyloidogenesis that might contribute to Aβ pathology in the early stages of AD and suggest that gallein could have therapeutic potential.

Oncogenic Pathways in Neurodegenerative Diseases

Cancer and neurodegenerative diseases are two of the leading causes of premature death in modern societies. Their incidence continues to increase, and in the near future, it is believed that cancer will kill more than 20 million people per year, and neurodegenerative diseases, due to the aging of the world population, will double their prevalence. The onset and the progression of both diseases are defined by dysregulation of the same molecular signaling pathways. However, whereas in cancer, these alterations lead to cell survival and proliferation, neurodegenerative diseases trigger cell death and apoptosis. The study of the mechanisms underlying these opposite final responses to the same molecular trigger is key to providing a better understanding of the diseases and finding more accurate treatments. Here, we review the ten most common signaling pathways altered in cancer and analyze them in the context of different neurodegenerative diseases such as Alzheimer's (AD), Parkinson's (PD), and Huntington's (HD) diseases.

Research Progress on Mechanism of Neuroprotective Roles of Apelin-13 in Prevention and Treatment of Alzheimer's Disease

Alzheimer's disease (AD) is the most common type of dementia. Currently, more than 50 million people live with dementia worldwide, and this number is expected to increase. Some of the typical pathological changes of AD include amyloid plaque, hyperphosphorylation of tau protein, secretion of inflammatory mediators, and neuronal apoptosis. Apelin is a neuroprotective peptide that is widely expressed in the body. Among members of apelin family, apelin-13 is the most abundant with a high neuroprotective function. Apelin-13/angiotensin domain type 1 receptor-associated proteins (APJ) system regulates several physiological and pathophysiological cell activities, such as apoptosis, autophagy, synaptic plasticity, and neuroinflammation. It has also been shown to prevent AD development. This article reviews the research progress on the relationship between apelin-13 and AD to provide new ideas for prevention and treatment of AD.