Oligomeric Tau-induced oxidative damage and functional alterations in cerebral endothelial cells: Role of RhoA/ROCK signaling pathway

Despite of yet unknown mechanism, microvascular deposition of oligomeric Tau (oTau) has been implicated in alteration of the Blood-Brain Barrier (BBB) function in Alzheimer's disease (AD) brains. In this study, we employed an in vitro BBB model using primary mouse cerebral endothelial cells (CECs) to investigate the mechanism underlying the effects of oTau on BBB function. We found that exposing CECs to oTau induced oxidative stress through NADPH oxidase, increased oxidative damage to proteins, decreased proteasome activity, and expressions of tight junction (TJ) proteins including occludin, zonula occludens-1 (ZO-1) and claudin-5. These effects were suppressed by the pretreatment with Fasudil, a RhoA/ROCK signaling inhibitor. Consistent with the biochemical alterations, we found that exposing the basolateral side of CECs to oTau in the BBB model disrupted the integrity of the BBB, as indicated by an increase in FITC-dextran transport across the model, and a decrease in trans endothelial electrical resistance (TEER). oTau also increased the transmigration of peripheral blood mononuclear cells (PBMCs) in the BBB model. These functional alterations in the BBB induced by oTau were also suppressed by Fasudil. Taken together, our findings suggest that targeting the RhoA/ROCK pathway can be a potential therapeutic strategy to maintain BBB function in AD.

The Effects of Ketogenic Diet on Brain Gene Expressions in Type 2 Diabetes Background

Type 2 diabetes mellitus (T2DM) is a major risk factor of a number of neurodegenerative diseases (NDDs). Ketogenic diet (KD) has significant beneficial effects on glycemic control and may act effectively against NDDs, but the mechanism remains unclear. In this study, we aimed to investigate the potential effects of KD on gene expressions in the brains of T2DM model mice. Male db/db mice at the age of 9 weeks were fed with KD or normal diet to the age of 6 months, and the whole brains were subjected to mRNA-seq analysis for differentially expressed genes. KD significantly lowered fasting glucose and body weights in db/db mice (P < 0.05), and the expression of 189 genes in the brain were significantly changed (P < 0.05, |log2| > 1). Gene Ontology and Kyoto Encyclopedia of Genes and Genomes enrichment analyses revealed that the differentially expressed genes upon KD are involved in inflammatory responses and the functions of biosynthesis. In inflammatory responses, NF-κB signaling pathway, viral protein interaction with cytokine and cytokine receptor, and cytokine-cytokine receptor interaction pathways were enriched, and in biosynthesis pathways, genes functioning in lipid and amino acid metabolism, protein synthesis, and energy metabolism were enriched. Moreover, consistent with the gene set enrichment analysis results, proteasomal activity measured biochemically were enhanced in KD-fed T2DM mice. These data may facilitate the understanding of how KD can be protective to the brain in T2DM background. KD could be a new strategy for the prevention of NDDs in T2DM patients.

Engineered Antibodies to Improve Efficacy against Neurodegenerative Disorders

Antibodies that can selectively remove rogue proteins in the brain are an obvious choice to treat neurodegenerative disorders (NDs), but after decades of efforts, only two antibodies to treat Alzheimer's disease are approved, dozens are in the testing phase, and one was withdrawn, and the other halted, likely due to efficacy issues. However, these outcomes should have been evident since these antibodies cannot enter the brain sufficiently due to the blood-brain barrier (BBB) protectant. However, all products can be rejuvenated by binding them with transferrin, preferably as smaller fragments. This model can be tested quickly and at a low cost and should be applied to bapineuzumab, solanezumab, crenezumab, gantenerumab, aducanumab, lecanemab, donanemab, cinpanemab, and gantenerumab, and their fragments. This paper demonstrates that conjugating with transferrin does not alter the binding to brain proteins such as amyloid-β (Aβ) and α-synuclein. We also present a selection of conjugate designs that will allow cleavage upon entering the brain to prevent their exocytosis while keeping the fragments connected to enable optimal binding to proteins. The identified products can be readily tested and returned to patients with the lowest regulatory cost and delays. These engineered antibodies can be manufactured by recombinant engineering, preferably by mRNA technology, as a more affordable solution to meet the dire need to treat neurodegenerative disorders effectively.

Proteasome inhibitors induce apoptosis by superoxide anion generation via NADPH oxidase 5 in human neuroblastoma SH-SY5Y cells

The ubiquitin-proteasome system (UPS) is a major proteolytic system that plays an important role in the regulation of various cell processes, such as cell cycle, stress response, and transcriptional regulation, especially in neurons, and dysfunction of UPS is considered to be a cause of neuronal cell death in neurodegenerative diseases. However, the mechanism of neuronal cell death caused by UPS dysfunction has not yet been fully elucidated. In this study, we investigated the mechanism of neuronal cell death induced by proteasome inhibitors using human neuroblastoma SH-SY5Y cells. Z-Leu-D-Leu-Leu-al (MG132), a proteasome inhibitor, induced apoptosis in SH-SY5Y cells in a concentration- and time-dependent manner. Antioxidants N-acetylcysteine and EUK-8 attenuated MG132-induced apoptosis. Apocynin and diphenyleneiodonium, inhibitors of NADPH oxidase (NOX), an enzyme that produces superoxide anions, also attenuated MG132-induced apoptosis. It was also found that MG132 treatment increased the expression of NOX5, a NOX family member, and that siRNA-mediated silencing of NOX5 and BAPTA-AM, which inhibits NOX5 by chelating calcium, suppressed MG132-induced apoptosis and production of reactive oxygen species in SH-SY5Y cells. These results suggest that MG132 induces apoptosis in SH-SY5Y cells through the production of superoxide anion by NOX5.

Role of PIM Kinase Inhibitor in the Treatment of Alzheimer's Disease

Alzheimer's disease (AD), a neurodegenerative disorder, is the most prevalent form of senile dementia, causing progressive deterioration of cognition, behavior, and rational skills. Neuropathologically, AD is characterized by two hallmark proteinaceous aggregates: amyloid beta (Aβ) plaques and neurofibrillary tangles (NFTs) formed of hyperphosphorylated tau. A significant study has been done to understand how Aβ and/or tau accumulation can alter signaling pathways that affect neuronal function. A conserved protein kinase known as the mammalian target of rapamycin (mTOR) is essential for maintaining the proper balance between protein synthesis and degradation. Overwhelming evidence shows mTOR signaling's primary role in age-dependent cognitive decline and the pathogenesis of AD. Postmortem human AD brains consistently show an upregulation of mTOR signaling. Confocal microscopy findings demonstrated a direct connection between mTOR and intraneuronal Aβ42 through molecular processes of PRAS40 phosphorylation. By attaching to the mTORC1 complex, PRAS40 inhibits the activity of mTOR. Furthermore, inhibiting PRAS40 phosphorylation can stop the Aβ-mediated increase in mTOR activity, indicating that the accumulation of Aβ may aid in PRAS40 phosphorylation. Physiologically, PRAS40 is phosphorylated by PIM1 which is a serine/threonine kinase of proto-oncogene PIM kinase family. Pharmacological inhibition of PIM1 activity prevents the Aβ-induced mTOR hyperactivity in vivo by blocking PRAS40 phosphorylation and restores cognitive impairments by enhancing proteasome function. Recently identified small-molecule PIM1 inhibitors have been developed as potential therapeutic to reduce AD-neuropathology. This comprehensive study aims to address the activity of PIM1 inhibitor that has been tested for the treatment of AD, in addition to the pharmacological and structural aspects of PIM1.

N-3 polyunsaturated fatty acids attenuate amyloid-beta-induced toxicity in AD transgenic Caenorhabditis elegans via promotion of proteasomal activity and activation of PPAR-gamma

Alzheimer's disease (AD) is a common neurodegenerative disease that causes progressive cognitive decline. A major pathological characteristic of AD brain is the presence of senile plaques composed of β-amyloid (Aβ), the accumulation of which induces toxic cascades leading to synaptic dysfunction, neuronal apoptosis, and eventually cognitive decline. Dietary n-3 polyunsaturated fatty acids (PUFAs), such as eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), are beneficial for patients with early-stage AD; however, the mechanisms are not completely understood. In this study, we investigated the effects of n-3 PUFAs on Aβ-induced toxicity in a transgenic AD Caenorhabditis elegans (C. elegans) model. The results showed that EPA and DHA significantly inhibited Aβ-induced paralytic phenotype and decreased the production of reactive oxygen species while reducing the levels of Aβ in the AD worms. Further studies revealed that EPA and DHA might reduce the accumulation of Aβ by restoring the activity of proteasome. Moreover, treating worms with peroxisome proliferator-activated receptor (PPAR)-γ inhibitor GW9662 prevented the inhibitory effects of n-3 PUFAs on Aβ-induced paralytic phenotype and diminished the elevation of proteasomal activity by n-3 PUFAs, suggesting that PPARγ-mediated signals play important role in the protective effects of n-3 PUFAs against Aβ-induced toxicity.

Ganoderma lucidum methyl ganoderate E extends lifespan and modulates aging-related indicators in Caenorhabditis elegans

Methyl Ganoderate E (MGE) is a triterpenoid derived from Ganoderma lucidum (Reishi), an edible mushroom, commonly processed into food forms such as soups, drinks, culinary dishes, and supplements. MGE has been shown to inhibit 3T3-L1 murine adipocyte differentiation when combined with other G. lucidum triterpenes. However, the specific effect of MGE on biological processes remains unknown. In this study, we present the first evidence of MGE's anti-aging effect in Caenorhabditis elegans. Through our screening process using the UPRER regulation ability, we evaluated a library of 74 pure compounds isolated from G. lucidum, and MGE exhibited the most promising results. Subsequent experiments demonstrated that MGE extended the lifespan by 26% at 10 μg ml-1 through daf-16, hsf-1, and skn-1-dependent pathways. MGE also enhanced resistance to various molecular stressors, improved healthspan, increased fertility, and reduced the aggregation of alpha-synuclein and amyloid-beta. Transcriptome data revealed that MGE promoted processes associated with proteolysis and neural activity, while not promoting cell death processes. Collectively, our findings suggest that G. lucidum MGE could be considered as a potential anti-aging intervention, adding to the growing list of such interventions.

Interactions of Cellular Energetic Gene Clusters in the Alzheimer's Mouse Brain

Alzheimer's disease (AD) is the most common cause of dementia in the aging population. The pathological characteristics include extracellular senile plaques and intracellular neurofibrillary tangles. In addition, mitochondrial dysfunction, oxidative stress, and neuroinflammation contribute to AD pathogenesis. In this study, we sought to determine the crosstalk between different pathways in the brain of 5XFAD mice, a mouse model for amyloid pathology, by RNA-seq analysis. We observed significant changes in the expression of genes (1288 genes; adj p value < 0.05; log2-fold > 1 and < 1) related to pathways including oxidation-reduction, oxidative phosphorylation, innate immune response, ribosomal protein synthesis, and ubiquitin proteosome system. The most striking feature was the downregulation of genes related to oxidation-reduction process with changes in the expression of a large number of mitochondrial genes. We also observed an upregulation of several immune response genes. Gene interaction network of oxidation-reduction related genes further confirmed a tight cluster of mitochondrial genes. Furthermore, gene interaction analysis of all the 1288 genes showed at least three distinct interaction clusters, with the predominant one relating to cellular energetics. In summary, we identified 1288 genes distinctly different in the 5XFAD brain compared to the WT brain and found cellular energetics to be the most distinct gene cluster in the AD mouse brain.

Raw Inonotus obliquus polysaccharide counteracts Alzheimer's disease in a transgenic mouse model by activating the ubiquitin-proteosome system

BACKGROUND/OBJECTIVES

Inonotus obliquus has been used as antidiabetic herb around the world, especially in the Russian and Scandinavian countries. Diabetes is widely believed to be a key factor in Alzheimer's disease (AD), which is widely considered to be type III diabetes. To investigate whether I. obliquus can also ameliorate AD, it would be interesting to identify new clues for AD treatment. We tested the anti-AD effects of raw Inonotus obliquus polysaccharide (IOP) in a mouse model of AD (3×Tg-AD transgenic mice).

MATERIALS/METHODS

SPF-grade 3×Tg-AD mice were randomly divided into three groups (Control, Metformin, and raw IOP groups, n = 5 per group). β-Amyloid deposition in the brain was analyzed using immunohistochemistry for AD characterization. Gene and protein expression of pertinent factors of the ubiquitin-proteasome system (UPS) was determined using real-time quantitative polymerase chain reaction and Western blotting.

RESULTS

Raw IOP significantly reduced the accumulation of amyloid aggregates and facilitated UPS activity, resulting in a significant reduction in AD-related symptoms in an AD mouse model. The presence of raw IOP significantly enhanced the expression of ubiquitin, E1, and Parkin (E3) at both the mRNA and protein levels in the mouse hippocampus. The mRNA level of ubiquitin carboxyl-terminal hydrolase isozyme L1, a key factor involved in UPS activation, also increased by approximately 50%.

CONCLUSIONS

Raw IOP could contribute to AD amelioration via the UPS pathway, which could be considered as a new potential strategy for AD treatment, although we could not exclude other mechanisms involved in counteracting AD processing.

Neuron-specific proteasome activation exerts cell non-autonomous protection against amyloid-beta (Aβ) proteotoxicity in Caenorhabditis elegans

Proteostasis reinforcement is a promising approach in the design of therapeutic interventions against proteinopathies, including Alzheimer's disease. Understanding how and which parts of the proteostasis network should be enhanced is crucial in developing efficient therapeutic strategies. The ability of specific tissues to induce proteostatic responses in distal ones (cell non-autonomous regulation of proteostasis) is attracting interest. Although the proteasome is a major protein degradation node, nothing is known on its cell non-autonomous regulation. We show that proteasome activation in the nervous system can enhance the proteasome activity in the muscle of Caenorhabditis elegans. Mechanistically, this communication depends on Small Clear Vesicles, with glutamate as one of the neurotransmitters required for the distal regulation. More importantly, we demonstrate that this cell non-autonomous proteasome activation is translated into efficient prevention of amyloid-beta (Αβ)-mediated proteotoxic effects in the muscle of C. elegans but notably not to resistance against oxidative stress. Our in vivo data establish a mechanistic link between neuronal proteasome reinforcement and decreased Aβ proteotoxicity in the muscle. The identified distal communication may have serious implications in the design of therapeutic strategies based on tissue-specific proteasome manipulation.

Antibody-Mediated Clearance of Brain Amyloid-β: Mechanisms of Action, Effects of Natural and Monoclonal Anti-Aβ Antibodies, and Downstream Effects

Immunotherapeutic efforts to slow the clinical progression of Alzheimer's disease (AD) by lowering brain amyloid-β (Aβ) have included Aβ vaccination, intravenous immunoglobulin (IVIG) products, and anti-Aβ monoclonal antibodies. Neither Aβ vaccination nor IVIG slowed disease progression. Despite conflicting phase III results, the monoclonal antibody Aducanumab received Food and Drug Administration (FDA) approval for treatment of AD in June 2021. The only treatments unequivocally demonstrated to slow AD progression to date are the monoclonal antibodies Lecanemab and Donanemab. Lecanemab received FDA approval in January 2023 based on phase II results showing lowering of PET-detectable Aβ; phase III results released at that time indicated slowing of disease progression. Topline results released in May 2023 for Donanemab's phase III trial revealed that primary and secondary end points had been met. Antibody binding to Aβ facilitates its clearance from the brain via multiple mechanisms including promoting its microglial phagocytosis, activating complement, dissolving fibrillar Aβ, and binding of antibody-Aβ complexes to blood-brain barrier receptors. Antibody binding to Aβ in peripheral blood may also promote cerebral efflux of Aβ by a peripheral sink mechanism. According to the amyloid hypothesis, for Aβ targeting to slow AD progression, it must decrease downstream neuropathological processes including tau aggregation and phosphorylation and (possibly) inflammation and oxidative stress. This review discusses antibody-mediated mechanisms of Aβ clearance, findings in AD trials involving Aβ vaccination, IVIG, and anti-Aβ monoclonal antibodies, downstream effects reported in those trials, and approaches which might improve the Aβ-clearing ability of monoclonal antibodies.

Amyloid-β Pathology-Specific Cytokine Secretion Suppresses Neuronal Mitochondrial Metabolism

Introduction

Neuroinflammation and metabolic dysfunction are early alterations in Alzheimer's disease (AD) brain that are thought to contribute to disease onset and progression. Glial activation due to protein deposition results in cytokine secretion and shifts in brain metabolism, which have been observed in AD patients. However, the mechanism by which this immunometabolic feedback loop can injure neurons and cause neurodegeneration remains unclear.

Methods

We used Luminex XMAP technology to quantify hippocampal cytokine concentrations in the 5xFAD mouse model of AD at milestone timepoints in disease development. We used partial least squares regression to build cytokine signatures predictive of disease progression, as compared to healthy aging in wild-type littermates. We applied the disease-defining cytokine signature to wild-type primary neuron cultures and measured downstream changes in gene expression using the NanoString nCounter system and mitochondrial function using the Seahorse Extracellular Flux live-cell analyzer.

Results

We identified a pattern of up-regulated IFNγ, IP-10/CXCL10, and IL-9 as predictive of advanced disease. When healthy neurons were exposed to these cytokines in proportions found in diseased brain, gene expression of mitochondrial electron transport chain complexes, including ATP synthase, was suppressed. In live cells, basal and maximal mitochondrial respiration were impaired following cytokine stimulation.

Conclusions

We identify a pattern of cytokine secretion predictive of progressing amyloid-β pathology in the 5xFAD mouse model of AD that reduces expression of mitochondrial electron transport complexes and impairs mitochondrial respiration in healthy neurons. We establish a mechanistic link between disease-specific immune cues and impaired neuronal metabolism, potentially causing neuronal vulnerability and susceptibility to degeneration in AD.

Supplementary Information

The online version contains supplementary material available at 10.1007/s12195-023-00782-y.

Orthogonal approaches required to measure proteasome composition and activity in mammalian brain tissue

Proteasomes are large macromolecular complexes with multiple distinct catalytic activities that are each vital to human brain health and disease. Despite their importance, standardized approaches to investigate proteasomes have not been universally adapted. Here, we describe pitfalls and define straightforward orthogonal biochemical approaches essential to measure and understand changes in proteasome composition and activity in the mammalian central nervous system. Through our experimentation in the mammalian brain, we determined an abundance of catalytically active proteasomes exist with and without a 19S cap(s), the regulatory particle essential for ubiquitin-dependent degradation. Moreover, we learned that in-cell measurements using activity-based probes (ABPs) are more sensitive in determining the available activity of the 20S proteasome without the 19S cap and in measuring individual catalytic subunit activities of each β subunit within all neuronal proteasomes. Subsequently, applying these tools to human brain samples, we were surprised to find that post-mortem tissue retained little to no 19S-capped proteasome, regardless of age, sex, or disease state. Comparing brain tissues (parahippocampal gyrus) from human Alzheimer's disease (AD) patients and unaffected subjects, available 20S proteasome activity was significantly elevated in severe cases of AD, an observation not previously noted. Taken together, our study establishes standardized approaches for comprehensive investigation of proteasomes in mammalian brain tissue, and we reveal new insight into brain proteasome biology.

Immortalized Alzheimer's Disease Astrocytes: Characterization of Their Proteolytic Systems

Alzheimer's disease (AD) is a progressive neurodegeneration with dysfunctions in both the ubiquitin-proteasome system (UPS) and autophagy. Astroglia participation in AD is an attractive topic of research, but molecular patterns are partially defined and available in vitro models have technical limitations. Immortalized astrocytes from the hippocampus of 3xTg-AD and wild-type mice (3Tg-iAstro and WT-iAstro, respectively) have been obtained as an attempt to overcome primary cell line limitations and this study aims at characterizing their proteolytic systems, focusing on UPS and autophagy. Both 26S and 20S proteasomal activities were downregulated in 3Tg-iAstro, in which a shift in catalytic subunits from constitutive 20S proteasome to immunoproteasome occurred, with consequences on immune functions. In fact, immunoproteasome is the specific complex in charge of clearing damaged proteins under inflammatory conditions. Parallelly, augmented expression and activity of the lysosomal cathepsin B, enhanced levels of lysosomal-associated membrane protein 1, beclin1, and LC3-II, together with an increased uptake of monodansylcadaverine in autophagic vacuoles, suggested autophagy activation in 3Tg-iAstro. The two proteolytic pathways were linked by p62 that accumulated in 3Tg-iAstro due to both increased synthesis and decreased degradation in the UPS defective astrocytes. Treatment with 4-phenylbutyric acid, a neuroprotective small chemical chaperone, partially restored proteasome and autophagy-mediated proteolysis in 3Tg-iAstro. Our data shed light on the impaired proteostasis in 3Tg-iAstro with proteasome inhibition and autophagic compensatory activation, providing additional validation of this AD in vitro model, and propose a new mechanism of action of 4-phenylbutyric acid in neurodegenerative disorders.

Alzheimer's disease-specific cytokine secretion suppresses neuronal mitochondrial metabolism

Introduction

Neuroinflammation and metabolic dysfunction are early alterations in Alzheimer's disease brain that are thought to contribute to disease onset and progression. Glial activation due to protein deposition results in cytokine secretion and shifts in brain metabolism, which have been observed in Alzheimer's disease patients. However, the mechanism by which this immunometabolic feedback loop can injure neurons and cause neurodegeneration remains unclear.

Methods

We used Luminex XMAP technology to quantify hippocampal cytokine concentrations in the 5xFAD mouse model of Alzheimer's disease at milestone timepoints in disease development. We used partial least squares regression to build cytokine signatures predictive of disease progression, as compared to healthy aging in wild-type littermates. We applied the disease-defining cytokine signature to wild-type primary neuron cultures and measured downstream changes in gene expression using the NanoString nCounter system and mitochondrial function using the Seahorse Extracellular Flux live-cell analyzer.

Results

We identified a pattern of up-regulated IFNγ, IP-10, and IL-9 as predictive of advanced disease. When healthy neurons were exposed to these cytokines in proportions found in diseased brain, gene expression of mitochondrial electron transport chain complexes, including ATP synthase, was suppressed. In live cells, basal and maximal mitochondrial respiration were impaired following cytokine stimulation.

Conclusions

An Alzheimer's disease-specific pattern of cytokine secretion reduces expression of mitochondrial electron transport complexes and impairs mitochondrial respiration in healthy neurons. We establish a mechanistic link between disease-specific immune cues and impaired neuronal metabolism, potentially causing neuronal vulnerability and susceptibility to degeneration in Alzheimer's disease.

Ubiquitin Is Not a Blood Biomarker of an Early Cognitive Decline in the Polish Elderly

Together with development of new pharmaceutical interventions, as well as the introduction of the concept of initial dementia phase, the demand for early diagnosis has been growing. Research on potential blood biomarkers, amazingly attractive, mainly due to the facility of deriving the material, has provided ambiguous results throughout. The existence of an association between ubiquitin and Alzheimer’s disease pathology suggests that it could be a potential neurodegeneration biomarker. The present study aims to identify and assess the relationship between ubiquitin with regard to the adequacy as a biomarker of an initial dementia and cognitive decline in the elderly. Method: The study sample was composed of 230 participants: 109 women and 121 men aged 65 and older. The relationships of plasma ubiquitin levels with cognitive performance, gender, and age were analyzed. The assessments were performed in three groups of cognitive functioning level: cognitively normal, mild cognitive impairment, and mild dementia, of which the subjects were divided with the Mini-Mental State Examination (MMSE). Results: No significant disparities in plasma ubiquitin levels for various levels of cognitive functioning were identified. Significantly higher plasma ubiquitin levels in women were found in comparison to men. No significant differences were found in ubiquitin concentrations based on age. Results suggest that ubiquitin does not meet the requirements for qualification as a blood biomarker of an early cognitive decline. In order to thoroughly evaluate the potential of research on ubiquitin in connection to an early neurodegenerative process, further studies are needed.

The Involvement of Post-Translational Modifications in Regulating the Development and Progression of Alzheimer's Disease

Post-translational modifications (PTMs) have been recently reported to be involved in the development and progression of Alzheimer's disease (AD). In detail, PTMs include phosphorylation, glycation, acetylation, sumoylation, ubiquitination, methylation, nitration, and truncation, which are associated with pathological functions of AD-related proteins, such as β-amyloid (Aβ), β-site APP-cleavage enzyme 1 (BACE1), and tau protein. In particular, the roles of aberrant PTMs in the trafficking, cleavage, and degradation of AD-associated proteins, leading to the cognitive decline of the disease, are summarized under AD conditions. By summarizing these research progress, the gaps will be filled between PMTs and AD, which will facilitate the discovery of potential biomarkers, leading to the establishment of novel clinical intervention methods against AD.

Beyond the classical amyloid hypothesis in Alzheimer's disease: Molecular insights into current concepts of pathogenesis, therapeutic targets, and study models

Alzheimer's disease (AD) is one of the progressive neurodegenerative disorders and the most common cause of dementia in the elderly worldwide causing difficulties in the daily life of the patient. AD is characterized by the aberrant accumulation of β-amyloid plaques and tau protein-containing neurofibrillary tangles (NFTs) in the brain giving rise to neuroinflammation, oxidative stress, synaptic failure, and eventual neuronal cell death. The total cost of care in AD treatment and related health care activities is enormous and pharmaceutical drugs approved by Food and Drug Administration have not manifested sufficient efficacy in protection and therapy. In recent years, there are growing studies that contribute a fundamental understanding to AD pathogenesis, AD-associated risk factors, and pharmacological intervention. However, greater molecular process-oriented research in company with suitable experimental models is still of the essence to enhance the prospects for AD therapy and cell lines as a disease model are still the major part of this milestone. In this review, we provide an insight into molecular mechanisms, particularly the recent concept in gut-brain axis, vascular dysfunction and autophagy, and current models used in the study of AD. Here, we emphasized the importance of therapeutic strategy targeting multiple mechanisms together with utilizing appropriate models for the discovery of novel effective AD therapy. This article is categorized under: Neurological Diseases > Molecular and Cellular Physiology.

Conformational Dynamics of an α-Synuclein Fibril upon Receptor Binding Revealed by Insensitive Nuclei Enhanced by Polarization Transfer-Based Solid-State Nuclear Magnetic Resonance and Cryo-Electron Microscopy

Many amyloid fibrils associated with neurodegenerative diseases consist of an ordered fibril core (FC) and disordered terminal regions (TRs). The former represents a stable scaffold, while the latter is rather active in binding with various partners. Current structural studies mainly focus on the ordered FC since the high flexibility of TRs hinders structural characterization. Here, by combining insensitive nuclei enhanced by polarization transfer-based ¹H-detected solid-state NMR and cryo-EM, we explored the intact structure of an α-syn fibril including both FC and TRs and further studied the conformational dynamics of the fibril upon binding to lymphocyte activation gene 3 (LAG3)─a cell surface receptor that is involved in α-syn fibril transmission in brains. We found that both the N- and C-TRs of α-syn are disordered in free fibrils featuring similar conformation ensembles as those in soluble monomers. While in the presence of the D1 domain of LAG3 (L3D1), the C-TR directly binds to L3D1, meanwhile the N-TR folds into a β-strand and further integrates with the FC, which leads to alteration of the overall fibril structure and surface property. Our work reveals synergistic conformational transition of the intrinsically disordered TRs of α-syn, which sheds light on mechanistic understanding of the essential role of TRs in regulating the structure and pathology of amyloid fibrils.

Inhibition of histone methyltransferase Smyd3 rescues NMDAR and cognitive deficits in a tauopathy mouse model

Pleiotropic mechanisms have been implicated in Alzheimer's disease (AD), including transcriptional dysregulation, protein misprocessing and synaptic dysfunction, but how they are mechanistically linked to induce cognitive deficits in AD is unclear. Here we find that the histone methyltransferase Smyd3, which catalyzes histone H3 lysine 4 trimethylation (H3K4me3) to activate gene transcription, is significantly elevated in prefrontal cortex (PFC) of AD patients and P301S Tau mice, a model of tauopathies. A short treatment with the Smyd3 inhibitor, BCI-121, rescues cognitive behavioral deficits, and restores synaptic NMDAR function and expression in PFC pyramidal neurons of P301S Tau mice. Fbxo2, which encodes an E3 ubiquitin ligase controlling the degradation of NMDAR subunits, is identified as a downstream target of Smyd3. Smyd3-induced upregulation of Fbxo2 in P301S Tau mice is linked to the increased NR1 ubiquitination. Fbxo2 knockdown in PFC leads to the recovery of NMDAR function and cognitive behaviors in P301S Tau mice. These data suggest an integrated mechanism and potential therapeutic strategy for AD.

Scrutinizing the Therapeutic Potential of PROTACs in the Management of Alzheimer's Disease

Finding an effective cure for Alzheimer's disease has eluded scientists despite intense research. The disease is a cause of suffering for millions of people worldwide and is characterized by dementia accompanied by cognitive and motor deficits, ultimately culminating in the death of the patient. The course of the disease progression has various underlying contributing pathways, with the first and foremost factor being the development and accumulation of aberrant and misfolded proteins exhibiting neurotoxic functions. The impairment of cellular clearance mechanisms adds to their accumulation, resulting in neuronal death. This is where the PROteolysis TArgeting Chimera (PROTAC) technology comes into play, bringing the UPS degradation machinery in the proximity of the target protein for initiating its degradation and clearing abnormal protein debris with unparalleled precision demonstrating an edge over traditional protein inhibitors in many respects. The technology is widely explored in cancer research and utilized in the treatment of various tumors and malignancies, and is now being applied in treating AD. This review explores the application of PROTAC technology in developing lead compounds for managing this deadly disease along with detailing the pieces of evidence justifying its utility and efficacy.

TRIM25 mutation (p.C168*), coding for an E3 ubiquitin ligase, is a cause of early-onset autosomal dominant dementia with amyloid load and parkinsonism

INTRODUCTION

Patients with familial early-onset dementia (EOD) pose a unique opportunity for gene identification studies.

METHODS

We present the phenotype and whole-exome sequencing (WES) study of an autosomal dominant EOD family. Candidate genes were examined in a set of dementia cases and controls (n = 3712). Western blotting was conducted of the wild-type and mutant protein of the final candidate.

RESULTS

Age at disease onset was 60 years (range 56 to 63). The phenotype comprised mixed amnestic and behavioral features, and parkinsonism. Cerebrospinal fluid and plasma biomarkers, and a positron emission tomography amyloid study suggested Alzheimer's disease. WES and the segregation pattern pointed to a nonsense mutation in the TRIM25 gene (p.C168*), coding for an E3 ubiquitin ligase, which was absent in the cohorts studied. Protein studies supported a loss-of-function mechanism.

DISCUSSION

This study supports a new physiopathological mechanism for brain amyloidosis. Furthermore, it extends the role of E3 ubiquitin ligases dysfunction in the development of neurodegenerative diseases.

HIGHLIGHTS

A TRIM25 nonsense mutation (p.C168*) is associated with autosomal dominant early-onset dementia and parkinsonism with biomarkers suggestive of Alzheimer's disease. TRIM25 protein studies support that the mutation exerts its effect through loss of function. TRIM25, an E3 ubiquitin ligase, is known for its role in the innate immune response but this is the first report of association with neurodegeneration. The role of TRIM25 dysfunction in development of amyloidosis and neurodegeneration merits a new line of research.

Gene expression changes implicate specific peripheral immune responses to Deep and Lobar Intracerebral Hemorrhages in humans

The peripheral immune system response to Intracerebral Hemorrhage (ICH) may differ with ICH in different brain locations. Thus, we investigated peripheral blood mRNA expression of Deep ICH, Lobar ICH, and vascular risk factor-matched control subjects (n = 59). Deep ICH subjects usually had hypertension. Some Lobar ICH subjects had cerebral amyloid angiopathy (CAA). Genes and gene networks in Deep ICH and Lobar ICH were compared to controls. We found 774 differentially expressed genes (DEGs) and 2 co-expressed gene modules associated with Deep ICH, and 441 DEGs and 5 modules associated with Lobar ICH. Pathway enrichment showed some common immune/inflammatory responses between locations including Autophagy, T Cell Receptor, Inflammasome, and Neuroinflammation Signaling. Th2, Interferon, GP6, and BEX2 Signaling were unique to Deep ICH. Necroptosis Signaling, Protein Ubiquitination, Amyloid Processing, and various RNA Processing terms were unique to Lobar ICH. Finding amyloid processing pathways in blood of Lobar ICH patients suggests peripheral immune cells may participate in processes leading to perivascular/vascular amyloid in CAA vessels and/or are involved in its removal. This study identifies distinct peripheral blood transcriptome architectures in Deep and Lobar ICH, emphasizes the need for considering location in ICH studies/clinical trials, and presents potential location-specific treatment targets.

Linking the Amyloid, Tau, and Mitochondrial Hypotheses of Alzheimer's Disease and Identifying Promising Drug Targets

Damage or loss of brain cells and impaired neurochemistry, neurogenesis, and synaptic and nonsynaptic plasticity of the brain lead to dementia in neurodegenerative diseases, such as Alzheimer's disease (AD). Injury to synapses and neurons and accumulation of extracellular amyloid plaques and intracellular neurofibrillary tangles are considered the main morphological and neuropathological features of AD. Age, genetic and epigenetic factors, environmental stressors, and lifestyle contribute to the risk of AD onset and progression. These risk factors are associated with structural and functional changes in the brain, leading to cognitive decline. Biomarkers of AD reflect or cause specific changes in brain function, especially changes in pathways associated with neurotransmission, neuroinflammation, bioenergetics, apoptosis, and oxidative and nitrosative stress. Even in the initial stages, AD is associated with Aβ neurotoxicity, mitochondrial dysfunction, and tau neurotoxicity. The integrative amyloid-tau-mitochondrial hypothesis assumes that the primary cause of AD is the neurotoxicity of Aβ oligomers and tau oligomers, mitochondrial dysfunction, and their mutual synergy. For the development of new efficient AD drugs, targeting the elimination of neurotoxicity, mutual potentiation of effects, and unwanted protein interactions of risk factors and biomarkers (mainly Aβ oligomers, tau oligomers, and mitochondrial dysfunction) in the early stage of the disease seems promising.

Artificial Intelligence Predictor for Alzheimer’s Disease Trained on Blood Transcriptome: The Role of Oxidative Stress

Alzheimer’s disease (AD) is an incurable neurodegenerative disease diagnosed by clinicians through healthcare records and neuroimaging techniques. These methods lack sensitivity and specificity, so new antemortem non-invasive strategies to diagnose AD are needed. Herein, we designed a machine learning predictor based on transcriptomic data obtained from the blood of AD patients and individuals without dementia (non-AD) through an 8 × 60 K microarray. The dataset was used to train different models with different hyperparameters. The support vector machines method allowed us to reach a Receiver Operating Characteristic score of 93% and an accuracy of 89%. High score levels were also achieved by the neural network and logistic regression methods. Furthermore, the Gene Ontology enrichment analysis of the features selected to train the model along with the genes differentially expressed between the non-AD and AD transcriptomic profiles shows the “mitochondrial translation” biological process to be the most interesting. In addition, inspection of the KEGG pathways suggests that the accumulation of β-amyloid triggers electron transport chain impairment, enhancement of reactive oxygen species and endoplasmic reticulum stress. Taken together, all these elements suggest that the oxidative stress induced by β-amyloid is a key feature trained by the model for the prediction of AD with high accuracy.

Mechanistic Insights into Selective Autophagy Subtypes in Alzheimer's Disease

Eukaryotic cells possess a plethora of regulatory mechanisms to maintain homeostasis and ensure proper biochemical functionality. Autophagy, a central, conserved self-consuming process of the cell, ensures the timely degradation of damaged cellular components. Several studies have demonstrated the important roles of autophagy activation in mitigating neurodegenerative diseases, especially Alzheimer's disease (AD). However, surprisingly, activation of macroautophagy has not shown clinical efficacy. Hence, alternative strategies are urgently needed for AD therapy. In recent years, selective autophagy has been reported to be involved in AD pathology, and different subtypes have been identified, such as aggrephagy, mitophagy, reticulophagy, lipophagy, pexophagy, nucleophagy, lysophagy and ribophagy. By clarifying the underlying mechanisms governing these various subtypes, we may come to understand how to control autophagy to treat AD. In this review, we summarize the latest findings concerning the role of selective autophagy in the pathogenesis of AD. The evidence overwhelmingly suggests that selective autophagy is an active mechanism in AD pathology, and that regulating selective autophagy would be an effective strategy for controlling this pathogenesis.

N-Acetyl-Cysteine: Modulating the Cysteine Redox Proteome in Neurodegenerative Diseases

In the last twenty years, significant progress in understanding the pathophysiology of age-associated neurodegenerative diseases has been made. However, the prevention and treatment of these diseases remain without clinically significant therapeutic advancement. While we still hope for some potential genetic therapeutic approaches, the current reality is far from substantial progress. With this state of the issue, emphasis should be placed on early diagnosis and prompt intervention in patients with increased risk of neurodegenerative diseases to slow down their progression, poor prognosis, and decreasing quality of life. Accordingly, it is urgent to implement interventions addressing the psychosocial and biochemical disturbances we know are central in managing the evolution of these disorders. Genomic and proteomic studies have shown the high molecular intricacy in neurodegenerative diseases, involving a broad spectrum of cellular pathways underlying disease progression. Recent investigations indicate that the dysregulation of the sensitive-cysteine proteome may be a concurrent pathogenic mechanism contributing to the pathophysiology of major neurodegenerative diseases, opening new therapeutic opportunities. Considering the incidence and prevalence of these disorders and their already significant burden in Western societies, they will become a real pandemic in the following decades. Therefore, we propose large-scale investigations, in selected groups of people over 40 years of age with decreased blood glutathione levels, comorbidities, and/or mild cognitive impairment, to evaluate supplementation of the diet with low doses of N-acetyl-cysteine, a promising and well-tolerated therapeutic agent suitable for long-term use.

Regulation of Neurodegeneration-associated Protein Fragments by the N-degron Pathways

Among the most salient features that underpin the development of aging-related neurodegenerative disorders are the accumulation of protein aggregates and the decrease in cellular degradation capacity. Mammalian cells have evolved sophisticated quality control mechanisms to repair or eliminate the otherwise abnormal or misfolded proteins. Chaperones identify unstable or abnormal conformations in proteins and often help them regain their correct conformation. However, if repair is not an option, abnormal proteins are selectively degraded to prevent undesired interactions with other proteins or oligomerization into toxic multimeric complexes. The autophagic-lysosomal system and the ubiquitin-proteasome system mediate the selective and targeted degradation of abnormal or aberrant protein fragments. Despite an increasing understanding regarding the molecular responses that counteract the formation and clearance of dysfunctional protein aggregates, the role of N-degrons in these processes is poorly understood. Previous work demonstrated that the Arg-N-end rule degradation pathway (Arg-N-degron pathway) mediates the degradation of neurodegeneration-associated proteins, thereby regulating crucial signaling hubs that modulate the progression of neurodegenerative diseases. Herein, we discuss the functional interconnection between N-degron pathways and proteins associated with neurodegenerative disorders, including Alzheimer's disease, amyotrophic lateral sclerosis, and Parkinson's disease. We also highlight some future prospects related to how the molecular insights gained from these processes will help unveil novel therapeutic approaches.

UCHL1 and Proteasome in Blood Serum in Relation to Dietary Habits, Concentration of Selected Antioxidant Minerals and Total Antioxidant Status among Patients with Alzheimer's Disease

Alzheimer's disease (AD) is an incurable neurodegenerative disease. It is the most common form of dementia among the elderly population. So far, no effective methods of its treatment have been found. Research to better understand the mechanism of pathology may provide new methods for early diagnosis. This, in turn, could enable early intervention that could slow or halt disease progression and improve patients' quality of life. Therefore, minimally invasive markers, including serum-based markers, are being sought to improve the diagnosis of AD. One of the important markers may be the concentration of UCHL1 and the proteasome in the blood serum. Their concentration can be affected by many factors, including eating habits. This study was conducted in 110 patients with early or moderate AD, with a mean age of 78.0 ± 8.1 years. The patients were under the care of the Podlasie Center of Psychogeriatrics and the Department of Neurology (Medical University of Białystok, Poland). The control group consisted of 60 healthy volunteers, matched for gender and age. The concentration of UCHL1 and the 20S proteasome subunit were measured by surface plasmon resonance imaging (SPRI). In addition, a nutritional interview was conducted with patients with AD, which assessed the frequency of consumption of 36 groups of products. In the group of patients with AD, compared to the control group, we showed a significantly higher concentration of UCHL1 (56.05 vs. 7.98 ng/mL) and the proteasome (13.02 vs. 5.72 µg/mL). Moreover, we found a low negative correlation between UCHL1 and the proteasome in the control group, and positive in the AD group. The analysis of eating habits showed that the consumption of selected groups of products may affect the concentration of the tested components, and therefore may have a protective effect on AD.

Altered succinylation of mitochondrial proteins, APP and tau in Alzheimer's disease

Abnormalities in brain glucose metabolism and accumulation of abnormal protein deposits called plaques and tangles are neuropathological hallmarks of Alzheimer's disease (AD), but their relationship to disease pathogenesis and to each other remains unclear. Here we show that succinylation, a metabolism-associated post-translational protein modification (PTM), provides a potential link between abnormal metabolism and AD pathology. We quantified the lysine succinylomes and proteomes from brains of individuals with AD, and healthy controls. In AD, succinylation of multiple mitochondrial proteins declined, and succinylation of small number of cytosolic proteins increased. The largest increases occurred at critical sites of amyloid precursor protein (APP) and microtubule-associated tau. We show that in vitro, succinylation of APP disrupted its normal proteolytic processing thereby promoting Aβ accumulation and plaque formation and that succinylation of tau promoted its aggregation to tangles and impaired microtubule assembly. In transgenic mouse models of AD, elevated succinylation associated with soluble and insoluble APP derivatives and tau. These findings indicate that a metabolism-linked PTM may be associated with AD.

Ursolic acid ameliorates amyloid β-induced pathological symptoms in Caenorhabditis elegans by activating the proteasome

BACKGROUND

Amyloid β induces pathological symptoms in various neurodegenerative disorders. It is the hallmark of these neurodegenerative disorders, such as Alzheimer's disease, and is reported to induce neurotoxicity leading to neuronal impairment. The continuous development of neurodegenerative disease accompanies pathological changes in amyloid β deposition in the brain. After amyloid β accumulates, the inadequate clearance of amyloid β further accelerates the development of events in the pathological cascade. In eukaryotes, the proteasome is responsible for the degradation of misfolded and damaged proteins to maintain proteostasis. Therefore, screening candidates that preserve proteasomal activity may promote amyloid β homeostasis, which is expected to provide new therapeutic opportunities for these neurodegenerative diseases. Ursolic acid, a natural triterpenoid, has prominent pharmacological antioxidant, anti-inflammatory, neuroprotective, and nontoxic activities. Here, we explored the protective effects of ursolic acid on amyloid β-induced pathological symptoms.

METHODS

This study investigated the therapeutic potential of ursolic acid and its underlying molecular mechanisms using a Caenorhabditis elegans transgenic pathological model.

RESULTS

In our study, ursolic acid successfully repressed amyloid β-induced paralysis and hypersensitivity to serotonin in Caenorhabditis elegans. The levels of amyloid β monomers, oligomers, and deposits were decreased after treatment with ursolic acid in transgenic nematodes overexpressing human amyloid β; however, ursolic acid did not affect exogenous transgene transcription and expression levels. Ursolic acid transcriptionally enhanced the ubiquitin-proteasome system and augmented proteasome activity in vivo. However, the proteasome inhibitor MG132 abolished the therapeutic effect of ursolic acid on behavioral paralysis, and Parkinson's disease-related-1 was required for the therapeutic effect of ursolic acid.

CONCLUSIONS

Our study revealed that ursolic acid prevented amyloid β-induced proteotoxic stress, specifically by reducing the amount of amyloid β and increasing proteasome activity in vivo. Furthermore, the therapeutic effect of ursolic acid on transgenic nematodes expressing amyloid β depended on the increased activity of the proteasome. This work provides an essential supplement to the information on the pharmacological mechanism of ursolic acid.

Roles and Mechanisms of the Protein Quality Control System in Alzheimer's Disease

Alzheimer's disease (AD) is characterized by the deposition of senile plaques (SPs) and the formation of neurofibrillary tangles (NTFs), as well as neuronal dysfunctions in the brain, but in fact, patients have shown a sustained disease progression for at least 10 to 15 years before these pathologic biomarkers can be detected. Consequently, as the most common chronic neurological disease in the elderly, the challenge of AD treatment is that it is short of effective biomarkers for early diagnosis. The protein quality control system is a collection of cellular pathways that can recognize damaged proteins and thereby modulate their turnover. Abundant evidence indicates that the accumulation of abnormal proteins in AD is closely related to the dysfunction of the protein quality control system. In particular, it is the synthesis, degradation, and removal of essential biological components that have already changed in the early stage of AD, which further encourages us to pay more attention to the protein quality control system. The review mainly focuses on the endoplasmic reticulum system (ERS), autophagy-lysosome system (ALS) and the ubiquitin-proteasome system (UPS), and deeply discusses the relationship between the protein quality control system and the abnormal proteins of AD, which can not only help us to understand how and why the complex regulatory system becomes malfunctional during AD progression, but also provide more novel therapeutic strategies to prevent the development of AD.

Putative Factors Interfering Cell Cycle Re-Entry in Alzheimer's Disease: An Omics Study with Differential Expression Meta-Analytics and Co-Expression Profiling

BACKGROUND

Neuronal cell cycle re-entry (CCR) is a mechanism, along with amyloid-β (Aβ) oligomers and hyperphosphorylated tau proteins, contributing to toxicity in Alzheimer's disease (AD).

OBJECTIVE

This study aimed to examine the putative factors in CCR based on evidence corroboration by combining meta-analysis and co-expression analysis of omic data.

METHODS

The differentially expressed genes (DEGs) and CCR-related modules were obtained through the differential analysis and co-expression of transcriptomic data, respectively. Differentially expressed microRNAs (DEmiRNAs) were extracted from the differential miRNA expression studies. The dysregulations of DEGs and DEmiRNAs as binary outcomes were independently analyzed by meta-analysis based on a random-effects model. The CCR-related modules were mapped to human protein-protein interaction databases to construct a network. The importance score of each node within the network was determined by the PageRank algorithm, and nodes that fit the pre-defined criteria were treated as putative CCR-related factors.

RESULTS

The meta-analysis identified 18,261 DEGs and 36 DEmiRNAs, including genes in the ubiquitination proteasome system, mitochondrial homeostasis, and CCR, and miRNAs associated with AD pathologies. The co-expression analysis identified 156 CCR-related modules to construct a protein-protein interaction network. Five genes, UBC, ESR1, EGFR, CUL3, and KRAS, were selected as putative CCR-related factors. Their functions suggested that the combined effects of cellular dyshomeostasis and receptors mediating Aβ toxicity from impaired ubiquitination proteasome system are involved in CCR.

CONCLUSION

This study identified five genes as putative factors and revealed the significance of cellular dyshomeostasis in the CCR of AD.

Autophagy in Alzheimer's disease pathogenesis: Therapeutic potential and future perspectives

Alzheimer's disease (AD) is a complex neurodegenerative disease in the elderly and the most common cause of human dementia. AD is characterized by accumulation of abnormal protein aggregates including amyloid plaques (composed of beta-amyloid (Aβ) peptides) and neurofibrillary tangles (formed by hyper-phosphorylated tau protein). Synaptic plasticity, neuroinflammation, calcium signaling etc. also show dysfunction in AD patients. Autophagy is an evolutionarily conserved lysosome-dependent cellular event in eukaryotes. It is closely linked to modulation of protein metabolism, through which damaged organelles and mis-folded proteins are degraded and then recycled to maintain protein homeostasis. Accumulating evidence has shown that impaired autophagy also contributes to AD pathogenesis. In the present review, we highlight the role of autophagy, including bulk and selective autophagy, in regulating metabolic circuits in AD pathogenesis. We also discuss the potential and future perspectives of autophagy-inducing strategies in AD therapeutics.

Advances in Proteasome Enhancement by Small Molecules

The proteasome system is a large and complex molecular machinery responsible for the degradation of misfolded, damaged, and redundant cellular proteins. When proteasome function is impaired, unwanted proteins accumulate, which can lead to several diseases including age-related and neurodegenerative diseases. Enhancing proteasome-mediated substrate degradation with small molecules may therefore be a valuable strategy for the treatment of various neurodegenerative diseases such as Parkinson's, Alzheimer's, and Huntington's diseases. In this review, we discuss the structure of proteasome and how proteasome's proteolytic activity is associated with aging and various neurodegenerative diseases. We also summarize various classes of compounds that are capable of enhancing, directly or indirectly, proteasome-mediated protein degradation.

RNF13 Dileucine Motif Variants L311S and L312P Interfere with Endosomal Localization and AP-3 Complex Association

Developmental and epileptic encephalopathies (DEE) are rare and serious neurological disorders characterized by severe epilepsy with refractory seizures and a significant developmental delay. Recently, DEE73 was linked to genetic alterations of the RNF13 gene, which convert positions 311 or 312 in the RNF13 protein from leucine to serine or proline, respectively (L311S and L312P). Using a fluorescence microscopy approach to investigate the molecular and cellular mechanisms affected by RNF13 protein variants, the current study shows that wild-type RNF13 localizes extensively with endosomes and lysosomes, while L311S and L312P do not extensively colocalize with the lysosomal marker Lamp1. Our results show that RNF13 L311S and L312P proteins affect the size of endosomal vesicles along with the temporal and spatial progression of fluorescently labeled epidermal growth factor, but not transferrin, in the endolysosomal system. Furthermore, GST-pulldown and co-immunoprecipitation show that RNF13 variants disrupt association with AP-3 complex. Knockdown of AP-3 complex subunit AP3D1 alters the lysosomal localization of wild-type RNF13 and similarly affects the size of endosomal vesicles. Importantly, our study provides a first step toward understanding the cellular and molecular mechanism altered by DEE73-associated genetic variations of RNF13.

A Mechanism for the Inhibition of Tau Neurotoxicity: Studies with Artificial Membranes, Isolated Mitochondria, and Intact Cells

It is currently believed that molecular agents that specifically bind to and neutralize the toxic proteins/peptides, amyloid β (Aβ42), tau, and the tau-derived peptide PHF6, hold the key to attenuating the progression of Alzheimer's disease (AD). We thus tested our previously developed nonaggregating Aβ42 double mutant (Aβ42_DM) as a multispecific binder for three AD-associated molecules, wild-type Aβ42, the tau_K174Q mutant, and a synthetic PHF6 peptide. Aβ42_DM acted as a functional inhibitor of these molecules in in vitro assays and in neuronal cell-based models of AD. The double mutant bound both cytotoxic tau_K174Q and synthetic PHF6 and protected neuronal cells from the accumulation of tau in cell lysates and mitochondria. Aβ42_DM also reduced toxic intracellular levels of calcium and the overall cell toxicity induced by overexpressed tau, synthetic PHF6, Aβ42, or a combination of PHF6and Aβ42. Aβ42_DM inhibited PHF6-induced overall mitochondrial dysfunction: In particular, Aβ42_DM inhibited PHF6-induced damage to submitochondrial particles (SMPs) and suppressed PHF6-induced elevation of the ζ-potential of inverted SMPs (proxy for the inner mitochondrial membrane, IMM). PHF6 reduced the lipid fluidity of cardiolipin/DOPC vesicles (that mimic the IMM) but not DOPC (which mimics the outer mitochondrial membrane), and this effect was inhibited by Aβ42_DM. This inhibition may be explained by the conformational changes in PHF6 induced by Aβ42_DM in solution and in membrane mimetics. On this basis, the paper presents a mechanistic explanation for the inhibitory activity of Aβ42_DM against Aβ42- and tau-induced membrane permeability and cell toxicity and provides confirmatory evidence for its protective function in neuronal cells.

Amyloid toxicity in a Drosophila Alzheimer's model is ameliorated by autophagy activation

Alzheimer's disease (AD) is the prevailing form of dementia. Protein degradation and antioxidant pathways have a critical role in preventing the accumulation of protein aggregation; thus, failure of proteostasis in neurons along with redox imbalance mark AD. Herein, we exploited an AD Drosophila model expressing human amyloid precursor (hAPP) and beta-secretase 1 (hBACE1) proteins, to better understand the role of proteostatic or antioxidant pathways in AD. Ubiquitous expression of hAPP, hBACE1 in flies caused more severe degenerative phenotypes versus neuronal targeted expression; it also, suppressed proteasome activity, increased oxidative stress and significantly enhanced stress-sensitivity. Overexpression of Prosβ5 proteasomal subunit or Nrf2 transcription factor in AD Drosophila flies partially restored proteasomal activity but did not rescue hAPP, hBACE1 induced neurodegeneration. On the other hand, expression of autophagy-related Atg8a in AD flies decelerated neurodegeneration, increased stress-resistance, and improved flies' health-/lifespan. Overall, our data suggest that the noxious effects of amyloid-beta aggregates can be alleviated by enhanced autophagy, thus dietary or pharmacological interventions that target autophagy should be considered in AD therapeutic approaches.

The proteasome and its role in the nervous system

Proteasomes are multisubunit complexes that catalyze the majority of protein degradation in mammalian cells to maintain protein homeostasis and influence the regulation of most cellular processes. The proteasome, a multicatalytic protease complex, is a ring-like structure with a narrow pore that exhibits regulated gating, enabling the selective degradation of target proteins into peptide fragments. This process of removing proteins is essential for eliminating proteins that are no longer wanted, such as unfolded or aggregated proteins. This is important for preserving cellular function relevant to brain health and disease. Recently, in the nervous system, specialized proteasomes have been shown to generate peptides with important cellular functions. These discoveries challenge the prevailing notion that proteasomes primarily operate to eliminate proteins and identify signaling-competent proteasomes. This review focuses on the structure, function, and regulation of proteasomes and sheds light on emerging areas of investigation regarding the role of proteasomes in the nervous system.

Thioredoxin-80 protects against amyloid-beta pathology through autophagic-lysosomal pathway regulation

Aggregation and accumulation of amyloid beta (Aβ) are believed to play a key role in the pathogenesis of Alzheimer's disease (AD). We previously reported that Thioredoxin-80 (Trx80), a truncated form of Thioredoxin-1, prevents the toxic effects of Aβ and inhibits its aggregation in vitro. Trx80 levels were found to be dramatically reduced both in the human brain and cerebrospinal fluid of AD patients. In this study, we investigated the effect of Trx80 expression using in vivo and in vitro models of Aβ pathology. We developed Drosophila melanogaster models overexpressing either human Trx80, human Aβ₄₂, or both Aβ₄₂/Trx80 in the central nervous system. We found that Trx80 expression prevents Aβ₄₂ accumulation in the brain and rescues the reduction in life span and locomotor impairments seen in Aβ₄₂ expressing flies. Also, we show that Trx80 induces autophagosome formation and reverses the inhibition of Atg4b-Atg8a/b autophagosome formation pathway caused by Aβ₄₂. These effects were also confirmed in human neuroblastoma cells. These results give insight into Trx80 function in vivo, suggesting its role in the autophagosome biogenesis and thus in Aβ₄₂ degradation. Our findings put Trx80 on the spotlight as an endogenous agent against Aβ₄₂-induced toxicity in the brain suggesting that strategies to enhance Trx80 levels in neurons could potentially be beneficial against AD pathology in humans.

Identification of hub ubiquitin ligase genes affecting Alzheimer's disease by analyzing transcriptome data from multiple brain regions

The ubiquitin-proteasome system (UPS) plays crucial roles in numerous cellular functions. Dysfunction of the UPS shows certain correlations with the pathological changes in Alzheimer's disease (AD). This study aimed to explore the different impairments of the UPS in multiple brain regions and identify hub ubiquitin ligase (E3) genes in AD. The brain transcriptome, blood transcriptome and proteome data of AD were downloaded from a public database. The UPS genes were collected from the Ubiquitin and Ubiquitin-like Conjugation Database. The hub E3 genes were defined as the differentially expressed E3 genes shared by more than three brain regions. E3Miner and UbiBrowser were used to predict the substrate of hub E3. This study shows varied impairment of the UPS in different brain regions in AD. Furthermore, we identify seven hub E3 genes (CUL1, CUL3, EIF3I, NSMCE1, PAFAH1B1, RNF175, and UCHL1) that are downregulated in more than three brain regions. Three of these genes (CUL1, EIF3I, and NSMCE1) showed consistent low expression in blood. Most of these genes have been reported to promote AD, whereas the impact of RNF175 on AD is not yet reported. Further analysis revealed a potential regulatory mechanism by which hub E3 and its substrate genes may affect transcription functions and then exacerbate AD. This study identified seven hub E3 genes and their substrate genes affect transcription functions and then exacerbate AD. These findings may be helpful for the development of diagnostic biomarkers and therapeutic targets for AD.

Polymorphism in the MAGI2 Gene Modifies the Effect of Amyloid β on Neurodegeneration

INTRODUCTION

A weak association between amyloid β (Aβ) deposition and neurodegeneration biomarkers, such as brain atrophy, has been repeatedly reported in a subset of patients with Alzheimer disease, suggesting individual differences in response to Aβ deposition.

METHODS

Here, we performed a genome-wide interaction study to identify single-nucleotide polymorphism (SNP) that modify the effect of Aβ (measured by 18F-florbetapir positron emission tomography) on brain atrophy (measured by cortical thickness using magnetic resonance imaging). We used magnetic resonance imaging, positron emission tomography, cerebrospinal fluid, and genetic data from the Alzheimer's Disease Neuroimaging Initiative (ADNI) database [discovery cohort, ADNI-GO/2 (n=723) and replication cohort, ADNI-1 (n=129)].

RESULTS

We identified a genome-wide suggestive interaction of rs3807779 SNP (β=-0.14, SE=0.029, P=9.08×10-7) in the discovery cohort. The greater dosage of rs3807779 SNP increased the detrimental effect of Aβ deposition on cortical thickness. In replication analyses, the congruent results were replicated to confirm our findings. Furthermore, rs3807779 SNP augmented the detrimental effect of Aβ deposition on cognitive function. Genetic profiling showed that rs3807779 has chromatin interactions with the promoter region of MAGI2 gene, suggesting its association with MAGI2 expression.

CONCLUSIONS

These findings demonstrate that subjects carrying the rs3807779 SNP are more susceptible to Aβ-related neurodegeneration.

Identifying the Mechanisms and Molecular Targets of Yizhiqingxin Formula on Alzheimer's Disease: Coupling Network Pharmacology with GEO Database

Background

Yizhiqingxin formula (YZQX) is a promising formula for the treatment of Alzheimer’s disease (AD) with significant clinical effects. Here, we coupled a network pharmacology approach with the Gene Expression Omnibus (GEO) database to illustrate comprehensive mechanisms and screen for molecular targets of YZQX for AD treatment.

Methods

First, active ingredients of YZQX were screened for the Traditional Chinese Medicine Systems Pharmacology (TCMSP) database with the absorption, distribution, metabolism, and excretion (ADME) parameters. Subsequently, putative targets of active ingredients were predicted using the DrugBank database. AD-related targets were retrieved by analyzing published microarray data (accession number GSE5281). Protein–protein interaction (PPI) networks of YZQX putative targets and AD-related targets were constructed visually and merged to identify candidate targets for YZQX against AD using Cytoscape 3.7.2 software. We performed gene ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis to further clarify the biological functions of the candidate targets. The gene-pathway network was established to filter for key target genes.

Results

Forty-three active ingredients were identified, and 193 putative target genes were predicted. Seven hundred and ten targets related to AD were screened with |log2 FC| > 1 and P < 0.05. Based on the PPI network, 110 target genes of YZQX against AD were identified. Moreover, 32 related pathways including the PI3K-Akt signaling pathway, MAPK signaling pathway, ubiquitin-mediated proteolysis, apoptosis and the NF-kappa B signaling pathway were significantly enriched. In the gene-pathway network, MAPK1, AKT1, TP53, MDM2, EGFR, RELA, SRC, GRB2, CUL1, and MYC targets are putative core genes for YZQX in AD treatment.

Conclusion

YZQX against AD may exert its neuroprotective effect via the PI3K-Akt signaling pathway, MAPK signaling pathway, and ubiquitin-mediated proteolysis. YZQX may be a promising drug that can be used in the treatment of AD.

Alignment of Alzheimer's Disease Amyloid-β Peptide and Herpes Simplex Virus-1 pUL15 C-Terminal Nuclease Domain

Background:

The cause of Alzheimer’s disease (AD) is poorly understood. Neurotropic microbes, particularly herpesviruses, might set off chronic neuroinflammation. Amyloid-β (Aβ) has antimicrobial properties and could represent a brain defense against infection.

Objective:

We searched for protein sequence alignment between herpes simplex virus type I (HSV-1) HSV-2, and Aβ.

Methods:

Protein data bank (pdb) structures for Aβ, HSV-1, and HSV-2 were searched on the RCSB Protein Data Bank. The protein structures were superimposed and aligned on PYMOL v 2.3.4.

Results:

For HSV-1 and Aβ, amino acid residues ser549 – his569 of HSV-1 aligned closely with residues asp7 - asn27 of Aβ. For HSV-2 and Aβ, amino acid residues of HSV-2 aligned less closely than those of HSV-1 with residues of Aβ.

Conclusion:

Conjugating and binding to the same alpha helix in the HSV-1 protease, Aβ could be marking HSV-1 for attack by the immune system, providing a rapid inherited immune response to a destructive neurotropic virus that would otherwise require the more time-consuming involvement of T-cells, B-cells, and the adaptive immune system. But older people do not respond to viral infections as well as younger individuals. When HSV-1 infection advances in an old person, more and more amyloid is produced, forming an adhesive web. As the brain tries to hold the pathologic process in check, neuroinflammation increases and spreads. Progressive neurodegeneration and cognitive decline are the outcome.

Abnormal Serum Bilirubin/Albumin Concentrations in Dementia Patients With Aβ Deposition and the Benefit of Intravenous Albumin Infusion for Alzheimer's Disease Treatment

Background

Our previous study in animal models revealed that bilirubin could induce Aβ formation and deposition. Bilirubin may be important in neurodegenerative dementia with Aβ deposition. Hence, lowering the concentration of the free bilirubin capable of crossing the blood brain-barrier may benefit the treatment of Alzheimer's disease (AD).

Objectives

The objectives of this study were to examine the change in the serum bilirubin and albumin concentrations of dementia patients with Aβ deposition, and to determine the effects of intravenous administration of albumin in the treatment of AD.

Methods

Bilirubin and albumin concentrations in dementia patients with Aβ deposition were examined. Cell viability and apoptosis were determined in dopaminergic neuron-like cells MN9D treated with bilirubin in the presence of diverse concentrations of serum. Human albumin at a dose of 10 g every 2 weeks for 24 weeks was administered intravenously to AD patients to examine the effect of albumin on AD symptoms.

Results

Significantly higher indirect bilirubin (IBIL) concentrations, lower albumin concentrations, and higher ratio of IBIL to albumin (IBIL/ALB) were observed in dementia patients with Aβ deposition, including AD, dementia with Lewy bodies, and general paresis of insane. In vitro assays showed that bilirubin-induced injury in cultured dopaminergic neuron-like cells negatively depends on the concentration of serum in the culture medium. General linear model with repeated measures analysis indicated a main effect of group on the change in albumin concentrations and Alzheimer's Disease Cooperative Study Activities of Daily Living Inventory scale (ADCS-ADL) scores, and the main effect of time and group, and group-by-time interaction on the change of Clinical Dementia Rating Scale-Sum of Boxes (CDR-SB) scores. Analysis of the combined data of the entire 28 weeks of assessment period using the area under curve convincingly showed significantly improvements in the change of albumin concentrations, ADCS-ADL scores, and CDR-SB scores.

Conclusion

IBIL and the IBIL/ALB ratio are significantly higher in dementia patients with Aβ deposition, and intravenous administration of albumin is beneficial to AD treatment.

Trial Registration

The intervention study was registered at http://www.chictr.org.cn (ChiCTR-IOR-17011539). Date of registration: June 1, 2017.

Ubiquitin biology in neurodegenerative disorders: From impairment to therapeutic strategies

The abnormal accumulation of neurotoxic proteins is the typical hallmark of various age-related neurodegenerative disorders (NDDs), including Alzheimer's disease, Parkinson's disease, Huntington's disease, Amyotrophic lateral sclerosis and Multiple sclerosis. The anomalous proteins, such as Aβ, Tau in Alzheimer's disease and α-synuclein in Parkinson's disease, perturb the neuronal physiology and cellular homeostasis in the brain thereby affecting the millions of human lives across the globe. Here, ubiquitin proteasome system (UPS) plays a decisive role in clearing the toxic metabolites in cells, where any aberrancy is widely reported to exaggerate the neurodegenerative pathologies. In spite of well-advancement in the ubiquitination research, their molecular markers and mechanisms for target-specific protein ubiquitination and clearance remained elusive. Therefore, this review substantiates the role of UPS in the brain signaling and neuronal physiology with their mechanistic role in the NDD's specific pathogenic protein clearance. Moreover, current and future promising therapies are discussed to target UPS-mediated neurodegeneration for better public health.

Molecular mechanisms underlying actions of certain long noncoding RNAs in Alzheimer's disease

Long non-coding RNAs (lncRNAs) are a group of non-protein coding RNAs that have more than 200 nucleotides. LncRNAs play an important role in the regulation of protein-coding genes at the transcriptional and post-transcriptional levels. They are found in most organs, with a high prevalence in the central nervous system. Accumulating data suggests that lncRNAs are involved in various neurodegenerative disorders, including the onset and progression of Alzheimer's disease (AD). Recent insights suggest lncRNAs, such as BACE1-AS, 51A, 17A, NDM29 and AS-UCHL1, are dysregulated in AD tissues. Furthermore, there are ongoing efforts to explore the clinical usability of lncRNAs as biomarkers in the disease. In this review, we explore the mechanisms by which aberrant expressions of the most studied lncRNAs contribute to the neuropathologies associated with AD, including amyloid β plaques and neurofibrillary tangles. Understanding the molecular mechanisms of lncRNAs in patients with AD will reveal novel diagnosis strategies and more effective therapeutic targets.

The impact of proteostasis dysfunction secondary to environmental and genetic causes on neurodegenerative diseases progression and potential therapeutic intervention

Aggregation of particular proteins in the form of inclusion bodies or plaques followed by neuronal death is a hallmark of neurodegenerative proteopathies such as primary Parkinsonism, Alzheimer's disease, Lou Gehrig's disease, and Huntington's chorea. Complex polygenic and environmental factors implicated in these proteopathies. Accumulation of proteins in these disorders indicates a substantial disruption in protein homeostasis (proteostasis). Proteostasis or cellular proteome homeostasis is attained by the synchronization of a group of cellular mechanisms called the proteostasis network (PN), which is responsible for the stability of the proteome and achieves the equilibrium between synthesis, folding, and degradation of proteins. In this review, we will discuss the different types of PN and the impact of PN component dysfunction on the four major neurodegenerative diseases mentioned earlier. Graphical abstract.