Combination of PKCε Activation and PTP1B Inhibition Effectively Suppresses Aβ-Induced GSK-3β Activation and Tau Phosphorylation

Does Metabolic Manager Show Encouraging Outcomes in Alzheimer's?: Challenges and Opportunity for Protein Tyrosine Phosphatase 1b Inhibitors

Protein tyrosine phosphatase 1b (PTP1b) is a member of the protein tyrosine phosphatase (PTP) enzyme group and encoded as PTP1N gene. Studies have evidenced an overexpression of the PTP1b enzyme in metabolic syndrome, anxiety, schizophrenia, neurodegeneration, and neuroinflammation. PTP1b inhibitor negatively regulates insulin and leptin pathways and has been explored as an antidiabetic agent in various clinical trials. Notably, the preclinical studies have shown that recuperating metabolic dysfunction and dyshomeostasis can reverse cognition and could be a possible approach to mitigate multifaceted Alzheimer's disease (AD). PTP1b inhibitor thus has attracted attention in neuroscience, though the development is limited to the preclinical stage, and its exploration in large clinical trials is warranted. This review provides an insight on the development of PTP1b inhibitors from different sources in diabesity. The crosstalk between metabolic dysfunction and insulin insensitivity in AD and type-2 diabetes has also been highlighted. Furthermore, this review presents the significance of PTP1b inhibition in AD based on pathophysiological facets, and recent evidences from preclinical and clinical studies.

Natural compounds from herbs and nutraceuticals as glycogen synthase kinase-3β inhibitors in Alzheimer's disease treatment

BACKGROUND

Alzheimer's disease (AD) pathogenesis is complex. The pathophysiology is not fully understood, and safe and effective treatments are needed. Glycogen synthase kinase 3β (GSK-3β) mediates AD progression through several signaling pathways. Recently, several studies have found that various natural compounds from herbs and nutraceuticals can significantly improve AD symptoms.

AIMS

This review aims to provide a comprehensive summary of the potential neuroprotective impacts of natural compounds as inhibitors of GSK-3β in the treatment of AD.

MATERIALS AND METHODS

We conducted a systematic literature search on PubMed, ScienceDirect, Web of Science, and Google Scholar, focusing on in vitro and in vivo studies that investigated natural compounds as inhibitors of GSK-3β in the treatment of AD.

RESULTS

The mechanism may be related to GSK-3β activation inhibition to regulate amyloid beta production, tau protein hyperphosphorylation, cell apoptosis, and cellular inflammation. By reviewing recent studies on GSK-3β inhibition in phytochemicals and AD intervention, flavonoids including oxyphylla A, quercetin, morin, icariin, linarin, genipin, and isoorientin were reported as potent GSK-3β inhibitors for AD treatment. Polyphenols such as schisandrin B, magnolol, and dieckol have inhibitory effects on GSK-3β in AD models, including in vivo models. Sulforaphene, ginsenoside Rd, gypenoside XVII, falcarindiol, epibrassinolides, 1,8-Cineole, and andrographolide are promising GSK-3β inhibitors.

CONCLUSIONS

Natural compounds from herbs and nutraceuticals are potential candidates for AD treatment. They may qualify as derivatives for development as promising compounds that provide enhanced pharmacological characteristics.

Understanding Glycogen Synthase Kinase-3: A Novel Avenue for Alzheimer's Disease

Alzheimer's Disease (AD) is the most prevalent form of age-related dementia. Even though a century has passed since the discovery of AD, the exact cause of the disease still remains unknown. As a result, this poses a major hindrance in developing effective therapies for treating AD. Glycogen synthase kinase-3 (GSK-3) is one of the kinases that has been investigated recently as a potential therapeutic target for the treatment of AD. It is also known as human tau protein kinase and is a proline-directed serine-threonine kinase. Since dysregulation of this kinase affects all the major characteristic features of the disease, such as tau phosphorylation, amyloid formation, memory, and synaptic function, it is thought to be a major player in the pathogenesis of AD. In this review, we present the most recent information on the role of this kinase in the onset and progression of AD, as well as significant findings that identify GSK-3 as one of the most important targets for AD therapy. We further discuss the potential of treating AD by targeting GSK-3 and give an overview of the ongoing studies aimed at developing GSK-3 inhibitors in preclinical and clinical investigations.

A systematic review and meta-analysis of tau phosphorylation in mouse models of familial Alzheimer's disease

Transgenic models of familial Alzheimer's disease (AD) serve as valuable tools for probing the molecular mechanisms associated with amyloid-beta (Aβ)-induced pathology. In this meta-analysis, we sought to evaluate levels of phosphorylated tau (p-tau) and explore potential age-related variations in tau hyperphosphorylation, within mouse models of AD. The PubMed and Scopus databases were searched for studies measuring soluble p-tau in 5xFAD, APPswe/PSEN1de9, J20 and APP23 mice. Data were extracted and analyzed using standardized procedures. For the 5xFAD model, the search yielded 36 studies eligible for meta-analysis. Levels of p-tau were higher in 5xFAD mice relative to control, a difference that was evident in both the carboxy-terminal (CT) and proline-rich (PR) domains of tau. Age negatively moderated the relationship between genotype and CT phosphorylated tau in studies using hybrid mice, female mice, and preparations from the neocortex. For the APPswe/PSEN1de9 model, the search yielded 27 studies. Analysis showed tau hyperphosphorylation in transgenic vs. control animals, evident in both the CT and PR regions of tau. Age positively moderated the relationship between genotype and PR domain phosphorylated tau in the neocortex of APPswe/PSEN1de9 mice. A meta-analysis was not performed for the J20 and APP23 models, due to the limited number of studies measuring p-tau levels in these mice (<10 studies). Although tau is hyperphosphorylated in both 5xFAD and APPswe/PSEN1de9 mice, the effects of ageing on p-tau are contingent upon the model being examined. These observations emphasize the importance of tailoring model selection to the appropriate disease stage when considering the relationship between Aβ and tau, and suggest that there are optimal intervention points for the administration of both anti-amyloid and anti-tau therapies.

Arsenic and Tau Phosphorylation: a Mechanistic Review

Arsenic poisoning can affect the peripheral nervous system and cause peripheral neuropathy. Despite different studies on the mechanism of intoxication, the complete process is not explained yet, which can prevent further intoxication and produce effective treatment. In the following paper, we would like to consider the idea that arsenic might cause some diseases via inflammation induction, and tauopathy in neurons. Tau protein, one of the microtubule-associated proteins expressed in neurons, contributes to neuronal microtubules structure. Arsenic may be involved in cellular cascades involved in modulating tau function or hyperphosphorylation of tau protein, which ultimately leads to nerve destruction. For proof of this assumption, some investigations have been planned to measure the association between arsenic and quantities of phosphorylation of tau protein. Additionally, some researchers have investigated the association between microtubule trafficking in neurons and the levels of tau protein phosphorylation. It should be noticed that changing tau phosphorylation in arsenic toxicity may add a new feature to understanding the mechanism of poisonousness and aid in discovering novel therapeutic candidates such as tau phosphorylation inhibitors for drug development.

Role of Non-Receptor-Type Tyrosine Phosphatases in Brain-Related Diseases

The non-receptor protein tyrosine phosphatase is a class of enzymes that catalyze the dephosphorylation of phosphotyrosines in protein molecules. They are involved in cellular signaling by regulating the phosphorylation status of a variety of receptors and signaling molecules within the cell, thereby influencing cellular physiological and pathological processes. In this article, we detail multiple non-receptor tyrosine phosphatase and non-receptor tyrosine phosphatase genes involved in the pathological process of brain disease. These include PTPN6, PTPN11, and PTPN13, which are involved in glioma signaling; PTPN1, PTPN5, and PTPN13, which are involved in the pathogenesis of Alzheimer's disease Tau protein lesions, PTPN23, which may be involved in the pathogenesis of Epilepsy and PTPN1, which is involved in the pathogenesis of Parkinson's disease. The role of mitochondrial tyrosine phosphatase in brain diseases was also discussed. Non-receptor tyrosine phosphatases have great potential for targeted therapies in brain diseases and are highly promising research areas.

The Role of IgLON Cell Adhesion Molecules in Neurodegenerative Diseases

In the brain, cell adhesion molecules (CAMs) are critical for neurite outgrowth, axonal fasciculation, neuronal survival and migration, and synapse formation and maintenance. Among CAMs, the IgLON family comprises five members: Opioid Binding Protein/Cell Adhesion Molecule Like (OPCML or OBCAM), Limbic System Associated Membrane Protein (LSAMP), neurotrimin (NTM), Neuronal Growth Regulator 1 (NEGR1), and IgLON5. IgLONs exhibit three N-terminal C2 immunoglobulin domains; several glycosylation sites; and a glycosylphosphatidylinositol anchoring to the membrane. Interactions as homo- or heterodimers in cis and in trans, as well as binding to other molecules, appear critical for their functions. Shedding by metalloproteases generates soluble factors interacting with cellular receptors and activating signal transduction. The aim of this review was to analyse the available data implicating a role for IgLONs in neuropsychiatric disorders. Starting from the identification of a pathological role for antibodies against IgLON5 in an autoimmune neurodegenerative disease with a poorly understood mechanism of action, accumulating evidence links IgLONs to neuropsychiatric disorders, albeit with still undefined mechanisms which will require future thorough investigations.

Abnormal phosphorylation of protein tyrosine in neurodegenerative diseases

Neurodegenerative diseases, including Alzheimer disease, Parkinson disease, amyotrophic lateral sclerosis, and multiple sclerosis, are chronic disorders of the CNS that are characterized by progressive neuronal dysfunction. These diseases have diverse clinical and pathological features and their pathogenetic mechanisms are not yet fully understood. Currently, widely accepted hypotheses include the accumulation of misfolded proteins, oxidative stress from reactive oxygen species, mitochondrial dysfunction, DNA damage, neurotrophin dysfunction, and neuroinflammatory processes. In the CNS of patients with neurodegenerative diseases, a variety of abnormally phosphorylated proteins play important roles in pathological processes such as neuroinflammation and intracellular accumulation of β-amyloid plaques and tau. In recent years, the roles of abnormal tyrosine phosphorylation of intracellular signaling molecules regulated by protein tyrosine kinases (PTKs) and protein tyrosine phosphatases (PTPs) in neurodegenerative diseases have attracted increasing attention. Here, we summarize the roles of signaling pathways related to protein tyrosine phosphorylation in the pathogenesis of neurodegenerative diseases and the progress of therapeutic studies targeting PTKs and PTPs that provide theoretical support for future studies on therapeutic strategies for these devastating and important neurodegenerative diseases.

Apolipoprotein E ε4 triggers neurotoxicity via cholesterol accumulation, acetylcholine dyshomeostasis, and PKCε mislocalization in cholinergic neuronal cells

The Apolipoprotein E (ApoE) has been known to regulate cholesterol and β-amyloid (Aβ) production, redistribution, and elimination, in the central nervous system (CNS). The ApoE ε4 polymorphic variant leads to impaired brain cholesterol homeostasis and amyloidogenic pathway, thus representing the major risk factor for Alzheimer's Disease (AD). Currently, less is known about the molecular mechanisms connecting ApoE ε4-related cholesterol metabolism and cholinergic system degeneration, one of the main AD pathological features. Herein, in vitro cholinergic neuron models were developed in order to study ApoE neuronal expression and investigate the possible interplay between cholesterol metabolism and cholinergic pathway impairment prompted by ε4 isoform. Particularly, alterations specifically occurring in ApoE ε4-carrying neurons (i.e. increased intracellular ApoE, amyloid precursor protein (APP), and Aβ levels, elevated apoptosis, and reduced cell survival) were recapitulated. ApoE ε4 expression was found to increase intracellular cholesterol accumulation, by regulating the related gene expression, while reducing cholesterol precursor acetyl-CoA, which in turn fuels the acetylcholine (ACh) synthesis route. In parallel, although the ACh intracellular signalling was activated, as demonstrated by the boosted extracellular ACh as well as increased IP₃ and Ca²⁺, the PKCε activation via membrane translocation was surprisingly suppressed, probably explained by the cholesterol overload in ApoE ε4 neuron-like cells. Consequently, the PKC-dependent anti-apoptotic and neuroprotective roles results impaired, reliably adding to other causes of cell death prompted by ApoE ε4. Overall, the obtained data open the way to further critical considerations of ApoE ε4-dependent cholesterol metabolism dysregulation in the alteration of cholinergic pathway, neurotoxicity, and neuronal death.

Ginsenoside compound K reduces ischemia/reperfusion-induced neuronal apoptosis by inhibiting PTP1B-mediated IRS1 tyrosine dephosphorylation

Background

Ginsenoside compound K (CK) stimulated activation of the PI3K-Akt signaling is one of the major mechanisms in promoting cell survival after stroke. However, the underlying mediators remain poorly understood. This study aimed to explore the docking protein of ginsenoside CK mediating the neuroprotective effects.

Materials and methods

Molecular docking, surface plasmon resonance, and cellular thermal shift assay were performed to explore ginsenoside CK interacting proteins. Neuroscreen-1 cells and middle cerebral artery occlusion (MCAO) model in rats were utilized as in-vitro and in-vivo models.

Results

Ginsenoside CK interacted with recombinant human PTP1B protein and impaired its tyrosine phosphatase activity. Pathway and process enrichment analysis confirmed the involvement of PTP1B and its interacting proteins in PI3K-Akt signaling pathway. PTP1B overexpression reduced the tyrosine phosphorylation of insulin receptor substrate 1 (IRS1) after oxygen-glucose deprivation/reoxygenation (OGD/R) in neuroscreen-1 cells. These regulations were confirmed in the ipsilateral ischemic hemisphere of the rat brains after MCAO/R. Ginsenoside CK treatment reversed these alterations and attenuated neuronal apoptosis.

Conclusion

Ginsenoside CK binds to PTP1B with a high affinity and inhibits PTP1B-mediated IRS1 tyrosine dephosphorylation. This novel mechanism helps explain the role of ginsenoside CK in activating the neuronal protective PI3K-Akt signaling pathway after ischemia-reperfusion injury.

Protein tyrosine phosphatase 1B (PTP1B) as a potential therapeutic target for neurological disorders

Protein tyrosine phosphatase 1B (PTP1B) is a typical member of the PTP family, considered a direct negative regulator of several receptor and receptor-associated tyrosine kinases. This widely localized enzyme has been involved in the pathophysiology of several diseases. More recently, PTP1B has attracted attention in the field of neuroscience, since its activation in brain cells can lead to schizophrenia-like behaviour deficits, anxiety-like effects, neurodegeneration, neuroinflammation and depression. Conversely, PTP1B inhibition has been shown to prevent microglial activation, thus exerting a potent anti-inflammatory effect and has also shown potential to increase the cognitive process through the stimulation of hippocampal insulin, leptin and BDNF/TrkB receptors. Notwithstanding, most research on the clinical efficacy of targeting PTP1B has been developed in the field of obesity and type 2 diabetes mellitus (TD2M). However, despite the link existing between these metabolic alterations and neurodegeneration, no clinical trials assessing the neurological advantages of PTP1B inhibition have been performed yet. Preclinical studies, though, have provided strong evidence that targeting PTP1B could allow to reach different pathophysiological mechanisms at once. herefore, specific interventions or trials should be designed to modulate PTP1B activity in brain, since it is a promising strategy to decelerate or prevent neurodegeneration in aged individuals, among other neurological diseases. The present paper fails to include all neurological conditions in which PTP1B could have a role; instead, it focuses on those which have been related to metabolic alterations and neurodegenerative processes. Moreover, only preclinical data is discussed, since clinical studies on the potential of PTP1B inhibition for treating neurological diseases are still required.

The role and therapeutic implication of protein tyrosine phosphatases in Alzheimer's disease

Protein tyrosine phosphatases (PTPs) are important regulator of neuronal signal transduction and a growing number of PTPs have been implicated in Alzheimer's disease (AD). In the brains of patients with AD, there are a variety of abnormally phosphorylated proteins, which are closely related to the abnormal expression and activity of PTPs. β-Amyloid plaques (Aβ) and hyperphosphorylated tau protein are two pathological hallmarks of AD, and their accumulation ultimately leads to neurodegeneration. Studies have shown that protein phosphorylation signaling pathways mediates intracellular accumulation of Aβ and tau during AD development and are involved in synaptic plasticity and other stress responses. Here, we summarized the roles of PTPs related to the pathogenesis of AD and analyzed their therapeutic potential in AD.

Mini-review: Role of the PI3K/Akt pathway and tyrosine phosphatases in Alzheimer's disease susceptibility

A variety of findings from in vitro experiments and animal models support the hypothesis that one contribution to pathogenesis in Alzheimer's disease (AD) is enhanced phosphorylation of tau protein, which may be triggered by amyloid β (Aβ) and mediated by impaired activity of the PI3K/Akt signaling pathway. A number of tyrosine phosphatases act to reduce PI3K/Akt activity, and inhibition of tyrosine phosphatases is protective against Aβ toxicity in cell cultures and whole animals. Results from analysis of exome sequenced late onset AD cases and controls similarly show that rare coding variants predicted to damage PI3K functioning increase AD risk, whereas those which are predicted to damage genes for tyrosine phosphatase genes are protective. Taken together, these results support the proposition that tyrosine phosphatase antagonists might be trialed as therapeutic agents to protect against the development of AD.

Resveratrol targeting tau proteins, amyloid-beta aggregations, and their adverse effects: An updated review

Resveratrol (Res) is a non-flavonoid compound with pharmacological actions such as antioxidant, antiinflammatory, hepatoprotective, antidiabetes, and antitumor. This plant-derived chemical has a long history usage in treatment of diseases. The excellent therapeutic impacts of Res and its capability in penetration into blood-brain barrier have made it an appropriate candidate in the treatment of neurological disorders (NDs). Tau protein aggregations and amyloid-beta (Aβ) deposits are responsible for the induction of NDs. A variety of studies have elucidated the role of these aggregations in NDs and the underlying molecular pathways in their development. In the present review, based on the recently published articles, we describe that how Res administration could inhibit amyloidogenic pathway and stimulate processes such as autophagy to degrade Aβ aggregations. Besides, we demonstrate that Res supplementation is beneficial in dephosphorylation of tau proteins and suppressing their aggregations. Then, we discuss molecular pathways and relate them to the treatment of NDs.

Weighted burden analysis of exome-sequenced late-onset Alzheimer's cases and controls provides further evidence for a role for PSEN1 and suggests involvement of the PI3K/Akt/GSK-3β and WNT signalling pathways

Previous studies have implicated common and rare genetic variants as risk factors for late-onset Alzheimer's disease (LOAD). Here, weighted burden analysis was applied to over 10,000 exome-sequenced subjects from the Alzheimer's Disease Sequencing Project. Analyses were carried out to investigate whether rare variants predicted to have a functional effect within a gene were more commonly seen in cases or in controls. Confirmatory results were obtained for TREM2, ABCA7, and SORL1. Additional support was provided for PSEN1 (p = 0.0002), which previously had been only weakly implicated in LOAD. There was suggestive evidence that functional variants in PIK3R1, WNT7A, C1R, and EXOC5 might increase risk and that variants in TIAF1 and/or NDRG2 might have a protective effect. Overall, there was strong evidence (p = 5 × 10-6 ) that variants in tyrosine phosphatase genes reduce the risk of developing LOAD. Because PIK3R1 variants are expected to impair PI3K/Akt/GSK-3β signalling while variants in tyrosine phosphatase genes would enhance it, these findings are in line with those from animal models, suggesting that this pathway is protective against Alzheimer's disease.

The Protective Effect of Vanadium on Cognitive Impairment and the Neuropathology of Alzheimer's Disease in APPSwe/PS1dE9 Mice

Alzheimer's disease (AD) is a widely distributed neurodegenerative disease characterized clinically by cognitive deficits and pathologically by formation of amyloid-β (Aβ) plaque and neurofibrillary tangles (NFTs) in the brain. Vanadium is a biological trace element that has a function to mimic insulin for diabetes. Bis(ethylmaltolato) oxidovanadium (IV) (BEOV) has been reported to have a hypoglycemic property, but its effect on AD remains unclear. In this study, BEOV was supplemented at doses of 0.2 and 1.0 mmol/L to the AD model mice APPSwe/PS1dE9 for 3 months. The results showed that BEOV substantially ameliorated glucose metabolic disorder as well as synaptic and behavioral deficits of the AD mice. Further investigation revealed that BEOV significantly reduced Aβ generation by increasing the expression of peroxisome proliferator-activated receptor gamma and insulin-degrading enzyme and by decreasing β-secretase 1 in the hippocampus and cortex of AD mice. BEOV also reduced tau hyperphosphorylation by inhibiting protein tyrosine phosphatase-1B and regulating the pathway of insulin receptor/insulin receptor substrate-1/protein kinase B/glycogen synthase kinase 3 beta. Furthermore, BEOV could enhance autophagolysosomal fusion and restore autophagic flux to increase the clearance of Aβ deposits and phosphorylated tau in the brains of AD mice. Collectively, the present study provides solid data for revealing the function and mechanism of BEOV on AD pathology.

Neurodegenerative Susceptibility During Maternal Nutritional Programing: Are Central and Peripheral Innate Immune Training Relevant?

Maternal overnutrition modulates body weight, development of metabolic failure and, potentially, neurodegenerative susceptibility in the offspring. Overnutrition sets a chronic pro-inflammatory profile that integrates peripheral and central immune activation nodes, damaging neuronal physiology and survival. Innate immune cells exposed to hypercaloric diets might experience trained immunity. Here, we address the role of maternal overnutrition as a trigger for central and peripheral immune training and its contribution to neurodegeneration and the molecular nodes implicated in the Nod-like receptor protein 3 (NLRP3) inflammasome pathway leading to immune training. We propose that maternal overnutrition leads to peripheral or central immune training that favor neurodegenerative susceptibility in the offspring.

Bis(ethylmaltolato)oxidovanadium(iv) inhibited the pathogenesis of Alzheimer's disease in triple transgenic model mice

Vanadium compounds have been reported to mimic the anti-diabetes effects of insulin on rodent models, but their effects on Alzheimer's disease (AD) have rarely been explored. In this paper, 9-month-old triple transgenic AD model mice (3×Tg-AD) received bis(ethylmaltolato)oxidovanadium(iv) (BEOV) at doses of 0.2 mmol L^-1 (68.4 μg mL^-1) and 1.0 mmol L^-1 (342 μg mL^-1) for 3 months. BEOV at both doses was found to improve contextual memory and spatial learning in AD mice. It also improved glucose metabolism and protected neuronal synapses in the AD brain, as evidenced respectively by ¹⁸F-labeled fluoro-deoxyglucose positron emission tomography (¹⁸F-FDG-PET) scanning and by transmission electron microscopy. Inhibitory effects of BEOV on β-amyloid (Aβ) plaques and neuronal impairment in the cortex and hippocampus of fluorescent AD mice were visualized three-dimensionally by applying optical clearing technology to brain slices before confocal laser scanning microscopy. Western blot analysis semi-quantitatively revealed the altered levels of Aβ₄₂ in the brains of wildtype, AD, and AD treated with 0.2 and 1.0 mmol L^-1 BEOV mice (70.3%, 100%, 83.2% and 56.8% in the hippocampus; 82.4%, 100%, 66.9% and 42% in the cortex, respectively). The mechanism study showed that BEOV increased the expression of peroxisome proliferator-activated receptor γ (PPARγ) (140%, 100%, 142% and 160% in the hippocampus; 167%, 100%, 124% and 133% in the cortex) to inactivate the JAK2/STAT3/SOCS-1 pathway and to block the amyloidogenesis cascade, thus attenuating Aβ-induced insulin resistance in AD models. BEOV also reduced protein tyrosine phosphatase 1B (PTP1B) expression (74.8%, 100%, 76.5% and 53.8% in the hippocampus; 71.8%, 100%, 94.2% and 81.8% in cortex) to promote insulin sensitivity and to stimulate the PI3K/Akt/GSK3β pathway, subsequently reducing tau hyperphosphorylation (phosphorylated tau396 levels were 51.1%, 100%, 56.1% and 50.2% in the hippocampus; 22.2%, 100%, 36.1%, and 24% in the cortex). Our results suggested that BEOV reduced the pathological hallmarks of AD by targeting the pathways of PPARγ and PTP1B in 3×Tg AD mice.

Nitazoxanide, an anti-parasitic drug, efficiently ameliorates learning and memory impairments in AD model mice

The pathogenesis of Alzheimer's disease (AD) is characterized by both accumulation of β-amyloid (Aβ) plaque and formation of neurofibrillary tangles in the brain. Recent evidence shows that autophagy activation may potently promote intracellular Aβ clearance. Thus targeting autophagy becomes a promising strategy for discovery of drug leads against AD. In the present study, we established a platform to discover autophagy stimulator and screened the lab in-house FDA-approved drug library. We found that anti-parasitic drug nitazoxanide (NTZ) was an autophagy activator and could efficiently improve learning and memory impairments in APP/PS1 transgenic mice. In BV2 cells and primary cortical astrocytes, NTZ stimulated autophagy and promoted Aβ clearance by inhibiting both PI3K/AKT/mTOR/ULK1 and NQO1/mTOR/ULK1 signaling pathways; NTZ treatment attenuated LPS-induced inflammation by inhibiting PI3K/AKT/IκB/NFκB signaling. In SH-SY5Y cells and primary cortical neurons, NTZ treatment restrained tau hyperphosphorylation through inhibition of PI3K/AKT/GSK3β pathway. The beneficial effects and related signaling mechanisms from the in vitro studies were also observed in APP/PS1 transgenic mice following administration of NTZ (90 mg·kg-1·d-1, ig) for 100 days. Furthermore, NTZ administration decreased Aβ level and senile plaque formation in the hippocampus and cerebral cortex of APP/PS1 transgenic mice, and improved learning and memory impairments in Morris water maze assay. In conclusion, our results highlight the potential of NTZ in the treatment of AD.

Epigenetic Modulation on Tau Phosphorylation in Alzheimer's Disease

Tau hyperphosphorylation is a typical pathological change in Alzheimer's disease (AD) and is involved in the early onset and progression of AD. Epigenetic modification refers to heritable alterations in gene expression that are not caused by direct changes in the DNA sequence of the gene. Epigenetic modifications, such as noncoding RNA regulation, DNA methylation, and histone modification, can directly or indirectly affect the regulation of tau phosphorylation, thereby participating in AD development and progression. This review summarizes the current research progress on the mechanisms of epigenetic modification associated with tau phosphorylation.

IL-33 suppresses GSK-3β activation through an ST2-independent MyD88/TRAF6/RIP/PI3K/Akt pathway

Aims

The present study was conducted to explore the effect of interleukin-33 (IL-33) on glycogen synthase kinase-3β (GSK-3β) activation involving Tau phosphorylation, a critical causative factor for Alzheimer's disease (AD).

Main methods

Experiments were performed using PC-12 cells. Target proteins were knocked-down by transfecting with the siRNA for each protein. The kinase activities were assessed by monitoring phosphorylation of Thr308 and Ser473 for Akt and phosphorylation of Ser9 and Tyr216 for GSK-3β in the Western blotting.

Key findings

Exogenously applied IL-33 activated Akt and inactivated GSK-3β. IL-33-induced Akt activation and GSK-3β inactivation were significantly inhibited by knocking-down myeloid differentiation factor 88 (MyD88), tumor necrosis factor receptor associated factor 6 (TRAF6), receptor-interacting protein (RIP), or phosphatidylinositol 3 kinase (PI3K). IL-33 neutralized amyloid β_1-42 (Aβ_1-42)-induced Akt inactivation and GSK-3β activation.

Significance

The results of the present study show that IL-33 inactivates GSK-3β through an ST2-independent MyD88/TRAF6/RIP/PI3K/Akt pathway and inhibits Aβ_1-42-induced GSK-3β activation. This suggests that IL-33 could restrain GSK-3β-mediated Tau phosphorylation in AD.

Divergent brain gene expression patterns associate with distinct cell-specific tau neuropathology traits in progressive supranuclear palsy

Progressive supranuclear palsy (PSP) is a neurodegenerative parkinsonian disorder characterized by tau pathology in neurons and glial cells. Transcriptional regulation has been implicated as a potential mechanism in conferring disease risk and neuropathology for some PSP genetic risk variants. However, the role of transcriptional changes as potential drivers of distinct cell-specific tau lesions has not been explored. In this study, we integrated brain gene expression measurements, quantitative neuropathology traits and genome-wide genotypes from 268 autopsy-confirmed PSP patients to identify transcriptional associations with unique cell-specific tau pathologies. We provide individual transcript and transcriptional network associations for quantitative oligodendroglial (coiled bodies = CB), neuronal (neurofibrillary tangles = NFT), astrocytic (tufted astrocytes = TA) tau pathology, and tau threads and genomic annotations of these findings. We identified divergent patterns of transcriptional associations for the distinct tau lesions, with the neuronal and astrocytic neuropathologies being the most different. We determined that NFT are positively associated with a brain co-expression network enriched for synaptic and PSP candidate risk genes, whereas TA are positively associated with a microglial gene-enriched immune network. In contrast, TA is negatively associated with synaptic and NFT with immune system transcripts. Our findings have implications for the diverse molecular mechanisms that underlie cell-specific vulnerability and disease risk in PSP.

Structural analysis of protein tyrosine phosphatase 1B reveals potentially druggable allosteric binding sites

Catalytic proteins such as human protein tyrosine phosphatase 1B (PTP1B), with conserved and highly polar active sites, warrant the discovery of druggable nonactive sites, such as allosteric sites, and potentially, therapeutic small molecules that can bind to these sites. Catalyzing the dephosphorylation of numerous substrates, PTP1B is physiologically important in intracellular signal transduction pathways in diverse cell types and tissues. Aberrant PTP1B is associated with obesity, diabetes, cancers, and neurodegenerative disorders. Utilizing clustering methods (based on root mean square deviation, principal component analysis, nonnegative matrix factorization, and independent component analysis), we have examined multiple PTP1B structures. Using the resulting representative structures in different conformational states, we determined consensus clustroids and used them to identify both known and novel binding sites, some of which are potentially allosteric. We report several lead compounds that could potentially bind to the novel PTP1B binding sites and can be further optimized. Considering the possibility for drug repurposing, we discovered homologous binding sites in other proteins, with ligands that could potentially bind to the novel PTP1B binding sites.

IL-33 Acts to Express Schaffer Collateral/CA1 LTP and Regulate Learning and Memory by Targeting MyD88

Interleukin-33 (IL-33) is recognized to transmit a signal through a heterodimeric receptor complex ST2/interleukin-1 receptor accessory protein (IL-1RAcP) bearing activation of myeloid differentiation factor 88 (MyD88). High-frequency stimulation to the Schaffer collateral induced long-term potentiation (LTP) in the CA1 region of hippocampal slices from wild-type control mice. Schaffer collateral/CA1 LTP in IL-33-deficient mice was significantly suppressed, which was neutralized by application with IL-33. Similar suppression of the LTP was found with MyD88-deficient mice but not with ST2-deficient mice. In the water maze test, the acquisition latency in IL-33-deficient and MyD88-deficient mice was significantly prolonged as compared with that in wild-type control mice. Moreover, the retention latency in MyD88-deficient mice was markedly prolonged. In contrast, the acquisition and retention latencies in ST2-deficient mice were not affected. Taken together, these results show that IL-33 acts to express Schaffer collateral/CA1 LTP relevant to spatial learning and memory in a MyD88-dependent manner and that the LTP might be expressed through an IL-1R1/IL-1RAcP-MyD88 pathway in the absence of ST2.

Resveratrol Ameliorates Tau Hyperphosphorylation at Ser396 Site and Oxidative Damage in Rat Hippocampal Slices Exposed to Vanadate: Implication of ERK1/2 and GSK-3β Signaling Cascades

The objective of this study was to investigate the effect of resveratrol (a natural polyphenolic phytostilbene) on tau hyperphosphorylation and oxidative damage induced by sodium orthovanadate (Na₃VO₄), the prevalent species of vanadium (vanadate), in rat hippocampal slices. Our results showed that resveratrol significantly inhibited Na₃VO₄-induced hyperphosphorylation of tau at the Ser396 (p-S396-tau) site, which is upregulated in the hippocampus of Alzheimer's disease (AD) brains and principally linked to AD-associated cognitive dysfunction. Subsequent mechanistic studies revealed that reduction of ERK1/2 activation was involved in the inhibitory effect of resveratrol by inhibiting the ERK1/2 pathway with SL327 mimicking the aforementioned effect of resveratrol. Moreover, resveratrol potently induced GSK-3β Ser9 phosphorylation and reduced Na₃VO₄-induced p-S396-tau levels, which were markedly replicated by pharmacologic inhibition of GSK-3β with LiCl. These results indicate that resveratrol could suppress Na₃VO₄-induced p-S396-tau levels via downregulating ERK1/2 and GSK-3β signaling cascades in rat hippocampal slices. In addition, resveratrol diminished the increased extracellular reactive oxygen species generation and hippocampal toxicity upon long-term exposure to Na₃VO₄ or FeCl₂. Our findings strongly support the notion that resveratrol may serve as a potential nutraceutical agent for AD.

Ferulic acid attenuates diabetes-induced cognitive impairment in rats via regulation of PTP1B and insulin signaling pathway

Cognitive impairment has been recognized as a typical characteristic of neurodegenerative disease in diabetes mellitus (DM) and this cognitive dysfunction may be a risk factor for Alzheimer's disease (AD). Ferulic acid, a phenolic compound commonly found in a range of plants, has emerged various properties including anti-inflammatory and neuroprotective effects. In the present study, the protective activities and relevant mechanisms of ferulic acid were evaluated in diabetic rats with cognitive deficits, which were induced by a high-glucose-fat (HGF) diet and low dose of streptozotocin (STZ). It was observed that ferulic acid significantly increased body weight and decreased blood glucose levels. Meanwhile, ferulic acid could markedly ameliorate spatial memory of diabetic rats in Morris water maze (MWM) and decrease AD-like pathologic changes (Aβ deposition and Tau phosphorylation) in the hippocampus, which might be correlated with the inhibition of inflammatory cytokines release and reduction of protein tyrosine phosphatase 1B (PTP1B) expression. Moreover, the levels of brain insulin signal molecules p-IRS, p-Akt and p-GSK3β were also investigated. We found that ferulic acid administration restored the alterations in insulin signaling. In conclusion, ferulic acid exhibited beneficial effects on diabetes-induced cognition lesions, which was involved in the regulation of PTP1B and insulin signaling pathway. We suppose that PTP1B inhibition may represent a promising approach to correct abnormal signaling linked to diabetes-induced cognitive impairment.

SLM, a novel carbazole-based fluorophore attenuates okadaic acid-induced tau hyperphosphorylation via down-regulating GSK-3β activity in SH-SY5Y cells

Phosphorylated tau dissociates from microtubules and aggregates to form neurofibrillary tangles resulting in neuronal toxicity and cognitive deficits. Attenuating tau hyperphosphorylation is considered as an effective therapeutic approach for Alzheimer's disease (AD). From our previous study, SLM, a carbazole-based fluorophore prevents Aβ aggregation, reduced glycogen synthase kinase-3β (GSK-3β) activity and tau hyperphosphorylation in triple transgenic mouse model of AD. However, the mechanism by which SLM attenuates tau hyperphosphorylation warrants further investigation. In the current study, we intend to evaluate the effects of SLM against okadaic acid (OA)-induced tau hyperphosphorylation and microtubules instability in human neuroblastoma (SH-SY5Y) cells. The results showed that, SLM reduced the OA-induced cell neurotoxicity and tau hyperphosphorylation in SH-SY5Y cells. SLM treatment down-regulated GSK-3β activity. However, in the presence of GSK-3β inhibitor (SB216763, 10μM), SLM treatment could not reduce GSK-3β activity and tau hyperphosphorylation as compared with SB216763 treatment alone. Furthermore, SLM treatment also ameliorated OA-induced microtubules instability and cytoskeleton damage. Collectively, SLM attenuated OA-induced tau hyperphosphorylation via down-regulating GSK-3β activity in SH-SY5Y cells. Therefore, this study supports SLM as a potential compound for AD and other tau pathology-related neurodegenerative disorders.

DCP-LA Exerts an Antiaging Action on the Skin

The present study assessed the possibility for the linoleic acid derivative 8-[2-(2-pentyl-cyclopropylmethyl)-cyclopropyl]-octanoic acid (DCP-LA) as an antiaging compound for the skin by assaying senescence-associated β-galactosidase (SA-β-Gal), a biomarker of senescence and cell viability. The nitric oxide (NO) donor sodium nitroprusside (SNP) increased in SA-β-Gal-positive cells in cultured human fibroblasts and mouse keratinocytes, and DCP-LA significantly inhibited the effect of SNP. Moreover, SNP induced cell death in cultured mouse keratinocytes, and DCP-LA significantly prevented NO stress-induced death of keratinocytes. Taken together, these results indicate that DCP-LA exerts an antiaging action on the skin.