Biochemistry and cell biology of tau protein in neurofibrillary degeneration

Inhibition of tau aggregation by the CCT3 and CCT7 apical domains

The eukaryotic chaperonin containing t-complex polypeptide 1 (CCT/TRiC) is a molecular chaperone that assists protein folding in an ATP-driven manner. It consists of two stacked identical rings that are each made up of eight distinct subunits. Here, we show that the apical domains of subunits CCT3 and CCT7 from humans are strong inhibitors of tau aggregation, which is associated with several neurological disorders such as Alzheimer's and Parkinson's diseases. Kinetic analyses and negative-stain electron microscopy indicate that the mechanism of inhibition of tau aggregation by the apical domains of subunits CCT3 and CCT7 differ. Aggregation of tau alone, or in the presence of the apical domain of subunit CCT7, can be described by a fragmentation model whereas in the presence of the apical domain of subunit CCT3, it fits a saturating elongation and fragmentation mechanism. Coarse-grained molecular dynamics simulations show that tau interacts with different regions in the apical domains of subunits CCT3 and CCT7, in agreement with their different inhibition mechanisms.

Inflammasome links traumatic brain injury, chronic traumatic encephalopathy, and Alzheimer's disease

Traumatic brain injury, chronic traumatic encephalopathy, and Alzheimer's disease are three distinct neurological disorders that share common pathophysiological mechanisms involving neuroinflammation. One sequela of neuroinflammation includes the pathologic hyperphosphorylation of tau protein, an endogenous microtubule-associated protein that protects the integrity of neuronal cytoskeletons. Tau hyperphosphorylation results in protein misfolding and subsequent accumulation of tau tangles forming neurotoxic aggregates. These misfolded proteins are characteristic of traumatic brain injury, chronic traumatic encephalopathy, and Alzheimer's disease and can lead to downstream neuroinflammatory processes, including assembly and activation of the inflammasome complex. Inflammasomes refer to a family of multimeric protein units that, upon activation, release a cascade of signaling molecules resulting in caspase-induced cell death and inflammation mediated by the release of interleukin-1β cytokine. One specific inflammasome, the NOD-like receptor protein 3, has been proposed to be a key regulator of tau phosphorylation where it has been shown that prolonged NOD-like receptor protein 3 activation acts as a causal factor in pathological tau accumulation and spreading. This review begins by describing the epidemiology and pathophysiology of traumatic brain injury, chronic traumatic encephalopathy, and Alzheimer's disease. Next, we highlight neuroinflammation as an overriding theme and discuss the role of the NOD-like receptor protein 3 inflammasome in the formation of tau deposits and how such tauopathic entities spread throughout the brain. We then propose a novel framework linking traumatic brain injury, chronic traumatic encephalopathy, and Alzheimer's disease as inflammasome-dependent pathologies that exist along a temporal continuum. Finally, we discuss potential therapeutic targets that may intercept this pathway and ultimately minimize long-term neurological decline.

Advances in Alzheimer's Therapy: Exploring Neuropathological Mechanisms to Revolutionize the Future Therapeutic Landscape

Alzheimer's disease (AD) is still an excessively complicated neurological disorder that impacts millions of individuals globally. The ideal defensive feature of the central nervous system (CNS) is the intimate junction of endothelial cells, which functions as a biological barrier to safely control molecular transport throughout the brain. The blood-brain barrier (BBB) comprises tightly locked astrocyte cell junctions on CNS blood capillaries. This biological barrier shields the brain from hazardous toxins by preventing the entry of polar medications, cells, and ions. However, it is very challenging to provide any treatment to the brain for neurodegenerative illnesses like Alzheimer's. Different causative mechanisms, such as amyloid-β (Aβ) plaques, tubulin-associated unit (Tau) tangles, and neuroinflammation, cause neuronal dysfunction, leading to dementia and memory loss in the subject. Several treatments are approved for AD therapy, whereas most only help treat related symptoms. Disappointingly, current remedies have not been able to control the progression of AD due to associated side effects. Specific pathogenic mechanisms are involved in the initiation and development of this disease. Therefore, the expected survival of a patient with AD is limited and is approximately ten years. Hence, the pathogenic mechanism behind AD progression must be understood to better comprehend and improve the overall survival rate. This review highlighted the recent insights into AD pathogenesis, molecular mechanisms, advancements in theragnostic techniques, the existing updates of clinical trials, and emerging innovations for AD medicinal development. That has helped researchers develop other strategies to address the shortcomings of traditional medications.

Navigating the complexities of neuronal signaling and targets in neurological disorders: From pathology to therapeutics

Neurological disorders arising from structural and functional disruptions in the nervous system present major global health challenges. This review examines the intricacies of various cellular signaling pathways, including Nrf2/Keap1/HO-1, SIRT-1, JAK/STAT3/mTOR, and BACE-1/gamma-secretase/MAPT, which play pivotal roles in neuronal health and pathology. The Nrf2-Keap1 pathway, a key antioxidant response mechanism, mitigates oxidative stress, while SIRT-1 contributes to mitochondrial integrity and inflammation control. Dysregulation of these pathways has been identified in neurodegenerative and neuropsychiatric disorders, including Alzheimer's and Parkinson's diseases, characterized by inflammation, protein aggregation, and mitochondrial dysfunction. Additionally, the JAK/STAT3 signaling pathway emphasizes the connection between cytokine responses and neuroinflammation, further compounding disease progression. This review explores the crosstalk among these signaling networks, elucidating how their disruption leads to neuronal decline. It also addresses the dual roles of these pathways, presenting challenges in targeting them for therapeutic purposes. Despite the potential benefits of activating neuroprotective pathways, excessive stimulation may cause deleterious effects, including tumorigenesis. Future research should focus on designing multi-targeted therapies that enhance the effectiveness and safety of treatments, considering individual variabilities and the obstacles posed by the blood-brain barrier to drug delivery. Understanding these complex signaling interactions is crucial for developing innovative and effective neuroprotective strategies that could significantly improve the management of neurological disorders.

High precision and cost-effective multiplex quantification of amyloid-β40, amyloid-β42, p181Tau, p217Tau, neurofilament light chain, and glial fibrillary acidic protein from plasma and serum

BackgroundCurrent methods to quantify blood biomarkers for Alzheimer's disease (AD) are expensive and are not widely available.ObjectiveTo develop a low-cost, sensitive, and accurate multiplex assay to quantify Aβ40, Aβ42, p181Tau, p217Tau, NfL, and GFAP biomarkers in plasma and serum based on a widely available technology.MethodsWe used commercial antibodies to Aβ40, Aβ42, p181Tau, p217Tau, NfL, and GFAP, and xMAP Luminex technology, and developed the multiplex 5ADCSI to quantify these biomarkers from plasma and serum. The utility of 5ADCSI was tested in matched cerebrospinal fluid (CSF) and plasma or serum of a cohort of cognitively normal (CN: n = 35), with mild cognitive impairment (MCI: n = 17), and with AD (n = 11) individuals.ResultsThe 5ADCSI demonstrated high specificity and sensitivity, with excellent precision. In clinical samples, moderate to strong correlation is observed between CSF and plasma or serum for Aβ42/40 (r = 0.78), p181Tau/Aβ42 (r = 0.57), p217Tau/Aβ42 (r = 0.72), p181Tau (r = 0.59), p217Tau (r = 0.75), and GFAP (r = 0.59). The AUC of receiver-operator characteristic curve for differentiating CN from AD for plasma/serum and CSF are 0.75, and 0.80 for Aβ42/40, 0.95, 0.91 for p217Tau, 0.76, 0.81 for p181Tau, and 0.73 and 0.78for GFAP, respectively.ConclusionsThe 5ADCSI assay is highly specific, sensitive, and accurate. The wide availability of the base technology of 5ADCSI is an advantage over other similar methods and would allow cost-effective large-scale studies for validation of blood biomarkers for early diagnosis of AD.

Water-directed pinning is key to tau prion formation

Tau forms fibrillar aggregates that are pathological hallmarks of a family of neurodegenerative diseases known as tauopathies. The synthetic replication of disease-specific fibril structures is a critical gap for developing diagnostic and therapeutic tools. This study debuts a strategy of identifying a critical and minimal folding motif in fibrils characteristic of tauopathies and generating seeding-competent fibrils from the isolated tau peptides. The 19-residue jR2R3 peptide (295 to 313) which spans the R2/R3 splice junction of tau, and includes the P301L mutation, is one such peptide that forms prion-competent fibrils. This tau fragment contains the hydrophobic VQIVYK hexapeptide that is part of the core of all known pathological tau fibril structures and an intramolecular counterstrand that stabilizes the strand-loop-strand (SLS) motif observed in 4R tauopathy fibrils. This study shows that P301L exhibits a duality of effects: it lowers the barrier for the peptide to adopt aggregation-prone conformations and enhances the local structuring of water around the mutation site to facilitate site-directed pinning and dewetting around sites 300-301 to achieve in-register stacking of tau to cross β-sheets. We solved a 3 Å cryo-EM structure of jR2R3-P301L fibrils in which each protofilament layer contains two jR2R3-P301L copies, of which one adopts a SLS fold found in 4R tauopathies and the other wraps around the SLS fold to stabilize it, reminiscent of the three- and fourfold structures observed in 4R tauopathies. These jR2R3-P301L fibrils are competent to template full-length 4R tau in a prion-like manner.

Decoupling Phase Separation and Fibrillization Preserves Activity of Biomolecular Condensates

Age-dependent transition of metastable, liquid-like protein condensates to amyloid fibrils is an emergent phenomenon of numerous neurodegeneration-linked protein systems. A key question is whether the thermodynamic forces underlying reversible phase separation and maturation to irreversible amyloids are distinct and separable. Here, we address this question using an engineered version of the microtubule-associated protein Tau, which forms biochemically active condensates. Liquid-like Tau condensates exhibit rapid aging to amyloid fibrils under quiescent, cofactor-free conditions. Tau condensate interface promotes fibril nucleation, impairing their activity to recruit tubulin and catalyze microtubule assembly. Remarkably, a small molecule metabolite, L-arginine, selectively impedes condensate-to-fibril transition without perturbing phase separation in a valence and chemistry-specific manner. By heightening the fibril nucleation barrier, L-arginine counteracts age-dependent decline in the biochemical activity of Tau condensates. These results provide a proof-of-principle demonstration that small molecule metabolites can enhance the metastability of protein condensates against a liquid-to-amyloid transition, thereby preserving condensate function.

Involvement of the VGF/BDNF axis in the neuropathology of Alzheimer's disease and its potential role in diagnosis and treatment

The brain is a highly plastic organ that continually receives and integrates signals to generate functional and structural changes and homeostatic adaptations throughout life. Alterations in some signaling pathways that mediate these responses can impact brain plasticity, accelerate brain aging and potentially lead to neurodegeneration. There is substantial evidence that two important signaling pathways activated by neurotrophins, nonacronymic (VGF) and brain-derived neurotrophic factor (BDNF), are involved in substantial functions stimulating neuronal growth, differentiation, and circuit establishment during development and neuronal maintenance and plasticity in the mature brain. In this review, we present evidence that these two pathways and their interactions are central players in cognitive performance and alterations in pathological aging, particularly in conditions such as Alzheimer's disease (AD). Finally, we suggest specific avenues for future research on the basis of recent findings suggesting these molecules are diagnostic biomarkers and putative therapeutic tools to prevent, delay or improve AD neuropathology.

Implications of Mucin-Type O-Glycosylation in Alzheimer's Disease

Alzheimer's disease (AD) is one of the most common neurodegenerative disorders linked to aging. Major hallmarks of AD pathogenesis include amyloid-β peptide (Aβ) plaques, which are extracellular deposits originating from the processing of the amyloid precursor protein (APP), and neurofibrillary tangles (NFTs), which are intracellular aggregates of tau protein. Recent evidence indicates that disruptions in metal homeostasis and impaired immune recognition of these aggregates trigger neuroinflammation, ultimately driving disease progression. Therefore, a more comprehensive approach is needed to understand the underlying causes of the disease. Patients with AD present abnormal glycan profiles, and most known AD-related molecules are either modified with glycans or involved in glycan regulation. A deeper understanding of how O-glycosylation influences the balance between amyloid-beta peptide production and clearance, as well as microglia's pro- and anti-inflammatory responses, is crucial for deciphering the early pathogenic events of AD. This review aims to provide a comprehensive summary of the extensive research conducted on the role of mucin-type O-glycosylation in the pathogenesis of AD, discussing its role in disease onset and immune recognition.

Grounding as a complementary intervention for Alzheimer's disease: Mechanisms, evidence, and potential therapeutic applications

Alzheimer's disease (AD) is a progressive neurodegenerative disorder characterized by cognitive decline, neuroinflammation, oxidative stress, and mitochondrial dysfunction. Despite extensive research efforts, effective curative treatments remain elusive, emphasizing the need for innovative therapeutic strategies. Grounding, or earthing, involves direct physical contact with the Earth's surface to facilitate the absorption of negatively charged electrons into the body. This practice has gained attention for its potential to reduce inflammation, oxidative stress, and cortisol dysregulation, which are significant contributors to AD pathology. This review examines the biological mechanisms by which grounding may influence AD, including its antioxidative effects that mitigate oxidative stress and its anti-inflammatory properties that reduce neuroinflammation. Grounding may also improve sleep quality and stress management, factors known to exacerbate AD progression. Evidence from preclinical and clinical studies highlights its potential to protect neuronal health by targeting oxidative and inflammatory pathways. Additionally, the safety, feasibility, and cost-effectiveness of grounding are discussed, making it a practical complementary approach to existing AD therapies. While the preliminary evidence is promising, the review emphasizes the need for robust clinical trials to validate grounding's efficacy specifically in AD populations. By integrating grounding into standard care protocols, it may be possible to enhance the overall therapeutic outcomes and improve the quality of life for individuals with AD. Grounding represents a novel, non-pharmacological intervention that could complement existing treatments by addressing both the physiological and psychological aspects of this complex disease.

Key biomarkers in Alzheimer's disease: Insights for diagnosis and treatment strategies

Alzheimer's disease (AD) remains a significant global health challenge, characterized by its progressive neurodegeneration and cognitive decline. The urgent need for early diagnosis and effective treatment necessitates the identification of reliable biomarkers that can illuminate the underlying pathophysiology of AD. This review provides a comprehensive overview of the latest advancements in biomarker research, focusing on their applications in diagnosis, prognosis, and therapeutic development. We delve into the multifaceted landscape of AD biomarkers, encompassing molecular, imaging, and fluid-based markers. The integration of these biomarkers, including amyloid-β and tau proteins, neuroimaging modalities, cerebrospinal fluid analysis, and genetic risk factors, offers a more nuanced understanding of AD's complex etiology. By leveraging the power of precision medicine, biomarker-driven approaches can enable personalized treatment strategies and enhance diagnostic accuracy. Moreover, this review highlights the potential of biomarker research to accelerate drug discovery and development. By identifying novel therapeutic targets and monitoring disease progression, biomarkers can facilitate the evaluation of experimental treatments and ultimately improve patient outcomes. In conclusion, this review underscores the critical role of biomarkers in advancing our comprehension of AD and driving the development of effective interventions. By providing a comprehensive overview of the current state-of-the-art, this work aims to inspire future research and contribute to the goal of conquering AD.

Neocortical tau propagation is a mediator of clinical heterogeneity in Alzheimer's disease

Heterogeneity in progression of clinical dementia obstructs the general therapeutic potential of current treatments for Alzheimer's disease (AD). Though the mechanisms of this heterogeneity remain unclear, the characterization of bioactive tau species and factors that regulate their seeding behavior might give valuable insight as pathological tau is well correlated with cognitive impairment. Here, we conducted an innovative investigation into the molecular basis of widespread, connectivity-based tau propagation that begins in the inferior temporal gyrus (ITG) and spreads to neocortical areas such as the prefrontal cortex (PFC). Biochemical analysis of human postmortem ITG and PFC tissues revealed individual variability in tau seeding, which correlated with cognitive decline, particularly in the ITG, a region known for promoting accelerated tau propagation. Notably, this study presents the first evidence that site-specific phosphorylation and isoform composition of both aggregation-prone high-molecular-weight (HMW) tau and the relatively unexplored, yet potentially crucial in AD progression low-molecular-weight (LMW) tau significantly contribute to tau propagation and cognitive decline. Our findings underscore the importance of comprehensively considering diverse tau forms including both HMW and LMW tau species in understanding AD progression. Additionally, these results are the first to identify distinct morphological strains within the AD brain associated with differing seeding propensity, potentially enabling patient stratification based on their tau profile. Furthermore, RNA-seq analyses of gene expression patterns in the ITG revealed molecular heterogeneity associated with tau seeding potential. Patients with higher levels of seed-competent tau displayed greater impairments in synaptic and neural plasticity, and increased neuroinflammation. This multidisciplinary study offers novel insights into various molecular mechanisms driving AD progression, suggesting potential molecular targets for early intervention and improved patient subtyping, which is critical for developing precision medicine approaches.

Molecular dynamics of amyloid-β transport in Alzheimer's disease: Exploring therapeutic plasma exchange with albumin replacement - Current insights and future perspectives

INTRODUCTION

The complex process of amyloid-β (Aβ) transportation across the blood-brain and blood-cerebrospinal fluid barriers is crucial for preventing Aβ accumulation, which linked to dementia and neurodegeneration. This review explores therapeutic plasma exchange with albumin replacement in Alzheimer's disease, based on the dynamics of amyloid-β between the brain, plasma, and cerebrospinal fluid.

METHODOLOGY

A comprehensive literature review was conducted using PubMed/Medline, Cochrane Library, and open databases (bioRxiv, MedRixv, preprint.org) up to April 30, 2023. The first search utilized the following MeSH terms and keywords: 'Plasma Exchange', 'Plasmapheresis', 'Therapeutic plasma exchange', 'Apheresis', 'Aβ', 'p-tau', 'Total-tau', 'Alzheimer's disease', 'Cognitive dysfunction', 'neurodegenerative diseases', 'centrifugation', 'membranous', and 'filtration' in the Title/Abstract, yielding 146 results. A second search with the keywords: 'Albumin', 'Aβ', 'BBB', 'Alzheimer's dementia', and 'Nerve degeneration' resulted in 125 additional articles for analysis. Finally, a third search using keywords: 'Albumin structural domains', 'Albumin-Aβ interactions', 'Albumin-endothelial interactions', and 'Post-Translational Modification' produced 193 results for further review.

RESULTS/DISCUSSION

Therapeutic plasma exchange shows potential as a disease-modifying therapy for dementia, specifically for Alzheimer's disease. Additionally, the promising role of albumin supplementation in cognitive improvement has attracted attention. However, clinical evidence supporting therapeutic plasma exchange for dementia remains limited, necessitating further research and development to mitigate potential adverse effects. A deeper understanding of the molecular dynamics of Aβ transportation and the mechanisms of therapeutic plasma exchange is essential. A critical evaluation of existing evidence highlights the importance of balancing potential benefits with associated risks, which will guide the development and application of these treatments in neurodegenerative diseases.

Brain injury plasma biomarkers in patients on veno-arterial extracorporeal membrane oxygenation: A pilot prospective observational study

IntroductionEarly diagnosis of acute brain injury (ABI) is critical for patients on veno-arterial extracorporeal membrane oxygenation (V-A ECMO) to guide anticoagulation strategy; however, neurological assessment in ECMO is often limited by patient sedation.MethodsIn this pilot study of adults from June 2018 to May 2019, plasma samples of glial fibrillary acidic protein (GFAP), neurofilament light chain (NFL), and tubulin associated unit (Tau) were collected daily after V-A ECMO cannulation and measured using a multiplex platform. Primary outcomes were occurrence of ABI, assessed clinically, and neurologic outcome, assessed by modified Rankin Scale (mRS).ResultsOf 20 consented patients (median age = 48.5°years; 55% female), 8 (40%) had ABI and 15 (75%) had unfavorable neurologic outcome at discharge. 10 (50%) patients were centrally cannulated. Median duration on ECMO was 4.5°days (IQR: 2.5-9.5). Peak GFAP, NFL, and Tau levels were higher in patients with ABI vs. without (AUC = 0.77; 0.85; 0.57, respectively) and in patients with unfavorable vs. favorable neurologic outcomes (AUC = 0.64; 0.59; 0.73, respectively). GFAP elevated first, NFL elevated to the highest degree, and Tau showed limited change regardless of ABI.ConclusionFurther studies are warranted to determine how plasma biomarkers may facilitate early detection of ABIs in V-A ECMO to assist timely clinical decision-making.

Detecting the Undetectable: Advances in Methods for Identifying Small Tau Aggregates in Neurodegenerative Diseases

Tau, a microtubule-associated protein, plays a critical role in maintaining neuronal structure and function. However, in neurodegenerative diseases such as Alzheimer's disease and other tauopathies, tau misfolds and aggregates into oligomers and fibrils, leading to neuronal damage. Tau oligomers are increasingly recognised as the most neurotoxic species, inducing synaptic dysfunction and contributing to disease progression. Detecting these early-stage aggregates is challenging due to their low concentration and high heterogeneity in biological samples. Traditional methods such as immunostaining and enzyme-linked immunosorbent assay (ELISA) lack the sensitivity and specificity to reliably detect small tau aggregates. Advanced single-molecule approaches, including single-molecule fluorescence resonance energy transfer (smFRET) and single-molecule pull-down (SiMPull), offer improved sensitivity for studying tau aggregation at the molecular level. These emerging tools provide critical insights into tau pathology, enabling earlier detection and characterisation of disease-relevant aggregates, thereby offering potential for the development of targeted therapies and diagnostic approaches for tauopathies.

Decoupling Phase Separation and Fibrillization Preserves Activity of Biomolecular Condensates

Age-dependent transition of metastable, liquid-like protein condensates to amyloid fibrils is an emergent phenomenon of numerous neurodegeneration-linked protein systems. A key question is whether the thermodynamic forces underlying reversible phase separation and maturation to irreversible amyloids are distinct and separable. Here, we address this question using an engineered version of the microtubule-associated protein Tau, which forms biochemically active condensates. Liquid-like Tau condensates exhibit rapid aging to amyloid fibrils under quiescent, cofactor-free conditions. Tau condensate interface promotes fibril nucleation, impairing their activity to recruit tubulin and catalyze microtubule assembly. Remarkably, a small molecule metabolite, L-arginine, selectively impedes condensate-to-fibril transition without perturbing phase separation in a valence and chemistry-specific manner. By heightening the fibril nucleation barrier, L-arginine counteracts age-dependent decline in the biochemical activity of Tau condensates. These results provide a proof-of-principle demonstration that small molecule metabolites can enhance the metastability of protein condensates against a liquid-to-amyloid transition, thereby preserving condensate function.

Biochemical characterization of Tau protein changes and amyloid dynamics in a novel non-transgenic rat model of tauopathy

In this study, we further characterized a non-transgenic model of tauopathy by examining tau protein changes using ELISA and Western blot upon inoculation of human tau oligomers (TO) and human tau synthetic pre-formed fibrils (TF) into the medial entorhinal cortex of Wistar rats. Our analyses showed that inoculation with TO did not significantly alter the ratio of phosphorylated tau at AT8 epitopes (pSer202/pThr205) to total tau protein in the hippocampus and entorhinal cortex, but only resulted in a decrease of phosphorylation at AT100 epitopes (pThr212/pSer214). As we previously observed an increase in AT8 immunostaining in both regions, this suggests method-dependent conformational alterations. In contrast, eleven months after inoculation, TF caused significant AT8 and PHF-1 (pSer396/pSer404) epitope-specific changes in tau phosphorylation in the hippocampus, but not in the entorhinal cortex, reflecting a more advanced stage of Alzheimer's disease (AD)-like changes compared to TO. Importantly, amyloid plaques appeared as early as four months post-inoculation with TO, preceding significant phosphorylation changes of tau, thus indicating that amyloid probably facilitates early tau seeding and spreading. This was corroborated by the observed dynamic changes in Aβ1-42 levels in cerebrospinal fluid, with initial decreases followed by increases, similar to patterns seen in transgenic mouse models of AD and in AD patients. Altogether, these findings lead us to conclude that changes in tau protein induce amyloid changes and vice versa, which is actually what defines AD as a unique neurodegenerative disease.

Tau PET probes for Alzheimer's disease detection and their structural characterization

There are two hallmarks for the Alzheimer's disease that are currently used to identify the disease- the presence of the proteins Amyloid-β and Tau. Amyloid PET has been studied for a long time and many effective probes have been introduced, some approved by the FDA, including [18F]-florbetaben (Neuraceq), [18F]-florbetapir (Amyvid), [18F]-flutemetamol (Vizamyl). However, it was found that imaging of NFTs could give more accurate results as the accumulation of Tau could directly be correlated with neurodegeneration, which isn't the case for Amyloid-β. Amyloid PET is thereby a diagnostic tool, which can rather be used for confirming the absence of Alzheimer's Disease. Tau PET, which was found to be a potentially useful diagnostic tool was explored further as it can directly be associated with the extent of spread of the disease. This led to the discovery of many probes for Tau PET. The initial ones were non-selective for Tau over Aβ. Further exploration suggested two generations of Tau probes, both with higher selectivity for Tau over Aβ. A second generation was introduced to overcome the shortcomings of the first generation which are examined in this review. Much research on effective Tau PET probes has led to an FDA-approved Tau probe, 18F-flortaucipir. This systematic review discusses the characteristics and effectiveness of the first-generation probes, second-generation probes and other newer probes. It discusses the structural changes made in the probes over time that led to the enhancement of their properties as a Tau probe, that is, increased affinity and selectivity for Tau. It also discusses the shortcomings of probes developed so far and the ideal characteristics for Tau probes.

Inspecting the Triazole Scaffold as Powerful Antifibril Agents against 2N4R Tau and α-Synuclein Aggregates

Alzheimer's (AD) and Parkinson's (PD) disease are neurodegenerative disorders that are considered to be a significant global health challenge due to their increasing prevalence and profound impact on both individuals and society. These disorders are characterized by the progressive loss of neuronal function, leading to cognitive and motor impairments. A key pathological feature of AD and PD is the abnormal accumulation of misfolded proteins within the brain. In AD, amyloid-beta aggregates into plaques, while tau proteins form neurofibrillary tangles (NFTs). Parkinson's disease, on the other hand, is marked by the accumulation of α-synuclein (α-syn) in the form of Lewy bodies (LBs). These protein aggregates are involved in neuronal dysfunction and neurodegeneration, contributing to disease progression. Research efforts are increasingly focused on identifying small molecules that can simultaneously target multiple pathological processes, offering the potential to not only alleviate symptoms but also modify the progression of neurodegeneration. Herein, a novel group of triazole-based compounds was designed and synthesized to curtail the aggregation of α-syn and tau proteins, which are closely linked to the physiopathology of PD and AD, respectively. A thioflavin T (ThT) fluorescence assay was used to measure fibril formation and assess the antiaggregation effects of various compounds. To further validate these findings, transmission electron microscopy (TEM) was employed as a direct method to visualize the impact of these compounds on fibril morphology. Inhibition of oligomer formation was evaluated using photoinduced cross-linking of unmodified proteins (PICUP), enabling the detection of early protein aggregation events. During fibril formation assays, three compounds (3e, 4b, 4d) demonstrated superior inhibitory activity as assessed by ThT fluorescence and TEM imaging. Subsequent evaluations, which included tests for antioligomer, anti-inclusion, and disaggregation effects identified compound 4d as the most promising candidate overall.

The Advancements of Marine Natural Products in the Treatment of Alzheimer's Disease: A Study Based on Cell and Animal Experiments

As life expectancy rises and the aging population grows, Alzheimer's disease (AD) has become a significant global health concern. AD is a complex neurodegenerative disorder with an unclear etiology. Current hypotheses primarily focus on β-amyloid (Aβ) aggregation, tau protein hyperphosphorylation, and neuroinflammation as key pathological processes. Given the limited efficacy of existing therapeutic strategies, there is an urgent need to explore novel treatment options. Marine natural products have garnered significant attention due to their unique chemical structures and diverse bioactivities, demonstrating potential for multi-target interventions in AD. This review systematically summarizes the roles of marine-derived compounds, including polysaccharides, carotenoids, and polyphenols, in modulating Aβ aggregation, mitigating tau protein pathology, and regulating gut-brain axis dysfunction. Furthermore, the challenges of current research are discussed, with an emphasis on improving blood-brain barrier permeability and optimizing drug delivery systems to facilitate clinical translation.

Temperature-Dependent Aggregation of Tau Protein Is Attenuated by Native PLGA Nanoparticles Under in vitro Conditions

Introduction

Hyperphosphorylation and aggregation of the microtubule-associated tau protein, which plays a critical role in many neurodegenerative diseases (ie, tauopathies) including Alzheimer's disease (AD), are known to be regulated by a variety of environmental factors including temperature. In this study we evaluated the effects of FDA-approved poly (D,L-lactide-co-glycolic) acid (PLGA) nanoparticles, which can inhibit amyloid-β aggregation/toxicity in cellular/animal models of AD, on temperature-dependent aggregation of 0N4R tau isoforms in vitro.

Methods

We have used a variety of biophysical (Thioflavin T kinetics, dynamic light scattering and asymmetric-flow field-flow fractionation), structural (fluorescence imaging and transmission electron microscopy) and biochemical (Filter-trap assay and detection of soluble protein) approaches, to evaluate the effects of native PLGA nanoparticles on the temperature-dependent tau aggregation.

Results

Our results show that the aggregation propensity of 0N4R tau increases significantly in a dose-dependent manner with a rise in temperature from 27°C to 40°C, as measured by lag time and aggregation rate. Additionally, the aggregation of 2N4R tau increases in a dose-dependent manner. Native PLGA significantly inhibits tau aggregation at all temperatures in a concentration-dependent manner, possibly by interacting with the aggregation-prone hydrophobic hexapeptide motifs of tau. Additionally, native PLGA is able to trigger disassembly of preformed 0N4R tau aggregates as a function of temperature from 27°C to 40°C.

Conclusion

These results, taken together, suggest that native PLGA nanoparticles can not only attenuate temperature-dependent tau aggregation but also promote disassembly of preformed aggregates, which increased with a rise of temperature. Given the evidence that temperature can influence tau pathology, we believe that native PLGA may have a unique potential to regulate tau abnormalities associated with AD-related pathology.

Internalization of extracellular Tau oligomers in Alzheimer's disease

A key factor in the progression of Alzheimer's disease (AD) is internalization of extracellular Tau oligomers (ecTauOs) by neuroglial cells. Aberrant hyperphosphorylation of Tau results in their dissociation from microtubules and formation of toxic intracellular Tau oligomers (icTauOs). These are subsequently released to the extracellular space following neuronal dysfunction and death. Although receptor mediated internalization of these ecTauOs by other neurons, microglia and astrocytes can facilitate elimination, incomplete degradation thereof promotes inflammation, exacerbates pathologic spread and accelerates neurodegeneration. Targeting Tau oligomer degradation pathways, blocking internalization receptors, and mitigating neuroinflammation are proposed as therapeutic strategies to control Tau propagation and toxicity. This review highlights the urgent need for innovative approaches to prevent the spread of Tau pathology, emphasizing its implications for AD and related neurodegenerative diseases.

Selenoproteins: Zoom-In to Their Metal-Binding Properties in Neurodegenerative Diseases

Selenoproteins contain selenium (Se), which is included in the 21st proteinogenic amino acid selenocysteine (Sec). Selenium (Se) is an essential trace element that exerts its biological actions mainly through selenoproteins. Selenoproteins have crucial roles in maintaining healthy brain activity. At the same time, brain-function-associated selenoproteins may also be involved in neurodegenerative diseases, such as Alzheimer's disease (AD) and Parkinson's disease (PD). The selenoproteins GPx4 (glutathione peroxidase 4), GPx1 (glutathione peroxidase 1), SELENOP (selenoprotein P), SELENOK (selenoprotein K), SELENOS (selenoprotein S), SELENOW (selenoprotein W), and SELENOT (selenoprotein T) are highly expressed, specifically in AD-related brain regions being closely correlated to brain function. Only a few selenoproteins, mentioned above (especially SELENOP), can bind transition and heavy metals. Metal ion homeostasis accomplishes the vital physiological function of the brain. Dyshomeostasis of these metals induces and entertains neurodegenerative diseases. In this review, we described some of the proposed and established mechanisms underlying the actions and properties of the above-mentioned selenoproteins having the characteristic feature of binding transition or heavy metals.

WITHDRAWN: Biomarker Detection and Therapy of Parkinson's and Alzheimer's disease using upconversion based approach: A Comprehensive Review

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Localized Reconstruction of Multimodal Distance Distribution from DEER Data of Biopolymers

Pulsed Dipolar ESR Spectroscopy (PDS) is a uniquely powerful technique to characterize the structural property of intrinsically disordered proteins (IDPs) and polymers and the conformational evolution of IDPs and polymers, e.g. during assembly, by offering the probability distribution of segment end-to-end distances. However, it is challenging to determine distance distribution P(r) of IDPs by PDS because of the uncertain and broad shape information that is intrinsic to the distance distribution of IDPs. We demonstrate here that the Srivastava-Freed Singular Value Decomposition (SF-SVD) point-wise mathematical inversion method along with wavelet denoising (WavPDS) can aid in obtaining reliable shapes for the distance distribution, P(r), for IDPs. We show that broad regions of P(r) as well as mixed narrow and broad features within the captured distance distribution range can be effectively resolved and differentiated without a priori knowledge. The advantage of SF-SVD and WavPDS is that the methods are transparent, requiring no adjustable parameters, the processing of the magnitude for the probability distribution is performed separately for each distance increment, and the outcome of the analysis is independent of the user's judgement. We demonstrate the performance and present the application of WavPDS and SF-SVD on model ruler molecules, model polyethylene glycol polymers with end-to-end spin labeling, and IDPs with pairwise labeling spanning different segments of the protein tau to generate the transparent solutions to the P(r)'s including their uncertainties and error analysis.

Mitochondrial bioenergetics stimulates autophagy for pathological MAPT/Tau clearance in tauopathy neurons

Hyperphosphorylation and aggregation of MAPT (microtubule-associated protein tau) is a pathogenic hallmark of tauopathies and a defining feature of Alzheimer disease (AD). Pathological MAPT/tau is targeted by macroautophagy/autophagy for clearance after being sequestered within autophagosomes, but autophagy dysfunction is indicated in tauopathy. While mitochondrial bioenergetic deficits have been shown to precede MAPT/tau pathology in tauopathy brains, it is unclear whether energy metabolism deficiency is involved in the pathogenesis of autophagy defects. Here, we reveal that stimulation of anaplerotic metabolism restores defective oxidative phosphorylation (OXPHOS) in tauopathy neurons which, strikingly, leads to pronounced MAPT/tau clearance by boosting autophagy functionality through enhancements of mitochondrial biosynthesis and supply of phosphatidylethanolamine for autophagosome biogenesis. Furthermore, early anaplerotic stimulation of OXPHOS elevates autophagy activity and attenuates MAPT/tau pathology, thereby counteracting memory impairment in tauopathy mice. Taken together, our study sheds light on a pivotal role of mitochondrial bioenergetic deficiency in tauopathy-related autophagy defects and suggests a new therapeutic strategy to prevent the buildup of pathological MAPT/tau in AD and other tauopathy diseases.Abbreviation: AA: antimycin A; AD, Alzheimer disease; ATP, adenosine triphosphate; AV, autophagosome/autophagic vacuole; AZ, active zone; Baf-A1: bafilomycin A1; CHX, cycloheximide; COX, cytochrome c oxidase; DIV, days in vitro; DRG, dorsal root ganglion; ETN, ethanolamine; FRET, Förster/fluorescence resonance energy transfer; FTD, frontotemporal dementia; Gln, glutamine; HA: hydroxylamine; HsMAPT/Tau, human MAPT; IMM, inner mitochondrial membrane; LAMP1, lysosomal-associated membrane protein 1; LIs, lysosomal inhibitors; MDAV, mitochondria-derived autophagic vacuole; MmMAPT/Tau, murine MAPT; NFT, neurofibrillary tangle; OCR, oxygen consumption rate; Omy: oligomycin; OXPHOS, oxidative phosphorylation; PPARGC1A/PGC-1alpha: peroxisome proliferative activated receptor, gamma, coactivator 1 alpha; PE, phosphatidylethanolamine; phospho-MAPT/tau, hyperphosphorylated MAPT; PS, phosphatidylserine; PISD, phosphatidylserine decarboxylase;SQSTM1/p62, sequestosome 1; STX1, syntaxin 1; SYP, synaptophysin; Tg, transgenic; TCA, tricarboxylic acid; TEM, transmission electron microscopy.

Neuronal plasma biomarkers in acute ischemic stroke

Early imaging-based detection of acute ischemic stroke (AIS) has improved in the era of reperfusion therapy. Despite of this, prognosis of outcome after AIS remains a challenge. Therefore, parameters that support clinical decision making are sought. Blood-based biomarkers have the potential to provide valuable information in addition to the established prognostic factors. Neuronal biomarkers of acute or degenerative neuronal injury have shown to be reliably detected in plasma. These biomarkers are well-established in neurodegenerative pathology, such as Alzheimer's disease. In this study, we explored the association between stroke diameter and plasma biomarkers for neuronal injury and tau pathophysiology (brain-derived tau [BD-tau], phosphorylated-tau-217 [p-tau21] and neurofilament light [NfL]) in patients (n = 193) admitted to the acute ward, Akershus University Hospital. All patients received a final diagnosis of AIS, transient ischemic attack or stroke mimics. Blood samples were obtained the day after admission. We find that levels of BD-tau (p = .004) and NfL (p = .011) were higher after AIS than in patients with stroke mimics. The cortical stroke diameter correlated with BD-tau (tau-b = 0.64, p < .001) and p-tau217 (tau-b = 0.36, p = .003). Linear regression confirmed BD-tau to be the strongest variable associated with stroke diameter, pointing to the potential clinical value of plasma BD-tau in outcome prediction after AIS.

Microglial APOE3 Christchurch protects neurons from Tau pathology in a human iPSC-based model of Alzheimer's disease

Alzheimer's disease (AD) is the most prevalent neurodegenerative disorder characterized by extracellular amyloid plaques and neuronal Tau tangles. A recent study found that the APOE3 Christchurch (APOECh) variant could delay AD progression. However, the underlying mechanisms remain unclear. In this study, we established neuron-microglia co-cultures and neuroimmune organoids using isogenic APOE3 and APOECh microglia derived from human induced pluripotent stem cells (hiPSCs) with PSEN1 mutant neurons or brain organoids. We show that APOECh microglia are resistant to Aβ-induced lipid peroxidation and ferroptosis and therefore preserve the phagocytic activity and promote pTau clearance, providing mechanistic insights into the neuroprotective role of APOE3Ch microglia. Moreover, we show that an APOE mimetic peptide can mimic the protective effects of APOECh microglia. These findings demonstrate that the APOECh microglia plays a causal role in microglial neuroprotection, which can be exploited for therapeutic development for AD.

The Search for a Universal Treatment for Defined and Mixed Pathology Neurodegenerative Diseases

The predominant neurodegenerative diseases, Alzheimer's disease, Parkinson's disease, dementia with Lewy Bodies, Huntington's disease, amyotrophic lateral sclerosis, and frontotemporal dementia, are rarely pure diseases but, instead, show a diversity of mixed pathologies. At some level, all of them share a combination of one or more different toxic biomarker proteins: amyloid beta (Aβ), phosphorylated Tau (pTau), alpha-synuclein (αSyn), mutant huntingtin (mHtt), fused in sarcoma, superoxide dismutase 1, and TAR DNA-binding protein 43. These toxic proteins share some common attributes, making them potentially universal and simultaneous targets for therapeutic intervention. First, they all form toxic aggregates prior to taking on their final forms as contributors to plaques, neurofibrillary tangles, Lewy bodies, and other protein deposits. Second, the primary enzyme that directs their aggregation is transglutaminase 2 (TGM2), a brain-localized enzyme involved in neurodegeneration. Third, TGM2 binds to calmodulin, a regulatory event that can increase the activity of this enzyme threefold. Fourth, the most common mixed pathology toxic biomarkers (Aβ, pTau, αSyn, nHtt) also bind calmodulin, which can affect their ability to aggregate. This review examines the potential therapeutic routes opened up by this knowledge. The end goal reveals multiple opportunities that are immediately available for universal therapeutic treatment of the most devastating neurodegenerative diseases facing humankind.

Interplay between Antimicrobial Peptides and Amyloid Proteins in Host Defense and Disease Modulation

The biological properties of antimicrobial peptides (AMPs) and amyloid proteins and their cross-talks have gained increasing attention due to their potential implications in both host defense mechanisms and amyloid-related diseases. However, complex interactions, molecular mechanisms, and physiological applications are not fully understood. The interplay between antimicrobial peptides and amyloid proteins is crucial for uncovering new insights into immune defense and disease mechanisms, bridging critical gaps in understanding infectious and neurodegenerative diseases. This review provides an overview of the cross-talk between AMPs and amyloids, highlighting their intricate interplay, mechanisms of action, and potential therapeutic implications. The dual roles of AMPs, which not only serve as key components of the innate immune system, combating microbial infections, but also exhibit modulatory effects on amyloid formation and toxicity, are discussed. The diverse mechanisms employed by AMPs to modulate amyloid aggregation, fibril formation, and toxicity are also discussed. Additionally, we explore emerging evidence suggesting that amyloid proteins may possess antimicrobial properties, adding a new dimension to the intricate relationship between AMPs and amyloids. This review underscores the importance of understanding the cross-talk between AMPs and amyloids to better understand the molecular processes underlying infectious diseases and amyloid-related disorders and to aid in the development of therapeutic avenues to treat them.

Intrinsic Disorder and Other Malleable Arsenals of Evolved Protein Multifunctionality

Microscopic evolution at the functional biomolecular level is an ongoing process. Leveraging functional and high-throughput assays, along with computational data mining, has led to a remarkable expansion of our understanding of multifunctional protein (and gene) families over the past few decades. Various molecular and intermolecular mechanisms are now known that collectively meet the cumulative multifunctional demands in higher organisms along an evolutionary path. This multitasking ability is attributed to a certain degree of intrinsic or adapted flexibility at the structure-function level. Evolutionary diversification of structure-function relationships in proteins highlights the functional importance of intrinsically disordered proteins/regions (IDPs/IDRs) which are highly dynamic biological soft matter. Multifunctionality is favorably supported by the fluid-like shapes of IDPs/IDRs, enabling them to undergo disorder-to-order transitions upon binding to different molecular partners. Other new malleable members of the protein superfamily, such as those involved in fold-switching, also undergo structural transitions. This new insight diverges from all traditional notions of functional singularity in enzyme classes and emphasizes a far more complex, multi-layered diversification of protein functionality. However, a thorough review in this line, focusing on flexibility and function-driven structural transitions related to evolved multifunctionality in proteins, is currently missing. This review attempts to address this gap while broadening the scope of multifunctionality beyond single protein sequences. It argues that protein intrinsic disorder is likely the most striking mechanism for expressing multifunctionality in proteins. A phenomenological analogy has also been drawn to illustrate the increasingly complex nature of modern digital life, driven by the need for multitasking, particularly involving media.

Targeting Protein Misfolding and Aggregation as a Therapeutic Perspective in Neurodegenerative Disorders

The abnormal deposition and intercellular propagation of disease-specific protein play a central role in the pathogenesis of many neurodegenerative disorders. Recent studies share the common observation that the formation of protein oligomers and subsequent pathological filaments is an essential step for the disease. Synucleinopathies such as Parkinson's disease (PD), dementia with Lewy bodies (DLB) or multiple system atrophy (MSA) are neurodegenerative diseases characterized by the aggregation of the α-synucleinprotein in neurons and/or in oligodendrocytes (glial cytoplasmic inclusions), neuronal loss, and astrogliosis. A similar mechanism of protein Tau-dependent neurodegeneration is a major feature of tauopathies, represented by Alzheimer's disease (AD), corticobasal degeneration (CBD), progressive supranuclear palsy (PSP), and Pick's disease (PD). The specific inhibition of the protein misfolding and their interneuronal spreading represents a promising therapeutic strategy against both disease pathology and progression. The most recent research focuses on finding potential applications targeting the pathological forms of proteins responsible for neurodegeneration. This review highlights the mechanisms relevant to protein-dependent neurodegeneration based on the most common disorders and describes current therapeutic approaches targeting protein misfolding and aggregation.

Untangling the role of tau in sex hormone responsive cancers: lessons learnt from Alzheimer's disease

Tubulin associated unit has been extensively studied in neurodegenerative diseases including Alzheimer's disease (AD), whereby its hyperphosphorylation and accumulation contributes to disease pathogenesis. Tau is abundantly expressed in the central nervous system but is also present in non-neuronal tissues and in tumours including sex hormone responsive cancers such as breast and prostate. Curiously, hormonal effects on tau also exist in an AD context from numerous studies on menopause, hormone replacement therapy, and androgen deprivation therapy. Despite sharing some risk factors, most importantly advancing age, there are numerous reports from population studies of, currently poorly explained inverse associations between cancer and Alzheimer's disease. We previously reviewed important components of the phosphoinositide-3-kinase/protein kinase B (PI3K/Akt) signalling pathway and their differential modulation in relation to the two diseases. Similarly, receptor tyrosine kinases, estrogen receptor and androgen receptor have all been implicated in the pathogenesis of both cancer and AD. In this review, we focus on tau and its effects in hormone responsive cancer in terms of development, progression, and treatment and in relation to sex hormones and PI3K/Akt signalling molecules including IRS-1, PTEN, Pin1, and p53.

Cellular and pathological functions of tau

Tau protein is involved in various cellular processes, including having a canonical role in binding and stabilization of microtubules in neurons. Tauopathies are neurodegenerative diseases marked by the abnormal accumulation of tau protein aggregates in neurons, as seen, for example, in conditions such as frontotemporal dementia and Alzheimer disease. Mutations in tau coding regions or that disrupt tau mRNA splicing, tau post-translational modifications and cellular stress factors (such as oxidative stress and inflammation) increase the tendency of tau to aggregate and interfere with its clearance. Pathological tau is strongly implicated in the progression of neurodegenerative diseases, and the propagation of tau aggregates is associated with disease severity. Recent technological advancements, including cryo-electron microscopy and disease models derived from human induced pluripotent stem cells, have increased our understanding of tau-related pathology in neurodegenerative conditions. Substantial progress has been made in deciphering tau aggregate structures and the molecular mechanisms that underlie protein aggregation and toxicity. In this Review, we discuss recent insights into the diverse cellular functions of tau and the pathology of tau inclusions and explore the potential for therapeutic interventions.

Age- and Sex-Associated Wnt Signaling Dysregulation is Exacerbated from the Early Stages of Neuropathology in an Alzheimer's Disease Model

Emerging studies suggest that Wnt signaling is dysregulated in the brains of AD patients, suggesting that this pathway may also contribute to disease progression. However, it remains to be determined whether alterations in the Wnt pathway are the cause or consequence of this disease and which elements of Wnt signaling mainly contribute to the appearance of AD histopathological markers early in disease compared to what occurs during normal aging. The present study aimed to describe the status of several canonical Wnt pathway components and the expression of the AD marker p-tau in the hippocampi of female and male 3xTg-AD mice during disease progression compared to those during normal aging. We analyzed the levels of the canonical Wnt components Wnt7a, Dkk-1, LRP6 and GSK3β as well as the levels of p-tau and BDNF at 3, 6, 9-12 and 18 months of age. We found a gradual increase in Dkk-1 levels during aging prior to Wnt7a and LRP5/6 depletion, which was strongly exacerbated in 3xTg-AD mice even at young ages and correlated with GSK3β activation and p-tau-S202/Thr205 expression. Dkk-1 upregulation, as well as the level of p-tau, was significantly greater in females than in males. Our results suggest that Dkk-1 upregulation is involved in the expression of several features of AD at early stages, which supports the possibility of positively modulating the canonical Wnt pathway as a therapeutic tool to delay this disease at early stages.

Brain aging and Alzheimer's disease, a perspective from non-human primates

Brain aging is compared between Cercopithecinae (macaques and baboons), non-human Hominidae (chimpanzees, orangutans, and gorillas), and their close relative, humans. β-amyloid deposition in the form of senile plaques (SPs) and cerebral β-amyloid angiopathy (CAA) is a frequent neuropathological change in non-human primate brain aging. SPs are usually diffuse, whereas SPs with dystrophic neurites are rare. Tau pathology, if present, appears later, and it is generally mild or moderate, with rare exceptions in rhesus macaques and chimpanzees. Behavior and cognitive impairment are usually mild or moderate in aged non-human primates. In contrast, human brain aging is characterized by early tau pathology manifested as neurofibrillary tangles (NFTs), composed of paired helical filaments (PHFs), progressing from the entorhinal cortex, hippocampus, temporal cortex, and limbic system to other brain regions. β-amyloid pathology appears decades later, involves the neocortex, and progresses to the paleocortex, diencephalon, brain stem, and cerebellum. SPs with dystrophic neurites containing PHFs and CAA are common. Cognitive impairment and dementia of Alzheimer's type occur in about 1-5% of humans aged 65 and about 25% aged 85. In addition, other proteinopathies, such as limbic-predominant TDP-43 encephalopathy, amygdala-predominant Lewy body disease, and argyrophilic grain disease, primarily affecting the archicortex, paleocortex, and amygdala, are common in aged humans but non-existent in non-human primates. These observations show that human brain aging differs from brain aging in non-human primates, and humans constitute the exception among primates in terms of severity and extent of brain aging damage.

Complement 3a induces the synapse loss via C3aR in mitochondria-dependent NLRP3 activating mechanisms during the development and progression of Alzheimer's disease

As a central molecule in complement system (CS), complement (C) 3 is upregulated in the patients and animal models of Alzheimer's disease (AD). C3 will metabolize to iC3b and C3a. iC3b is responsible for clearing β-amyloid protein (Aβ). In this scenario, C3 exerts neuroprotective effects against the disease via iC3b. However, C3a will inhibit microglia to clear the Aβ, leading to the deposition of Aβ and impair the functions of synapses. To their effects on AD, activation of C3a and C3a receptor (C3aR) will impair the mitochondria, leading to the release of reactive oxygen species (ROS), which activates the NOD-like receptor thermal protein domain associated protein 3 (NLRP3) inflammasomes. The overloading of NLRP3 inflammasomes activate microglia, leading to the formation of inflammatory environment. The inflammatory environment will facilitate the deposition of Aβ and abnormal synapse pruning, which results in the progression of AD. Therefore, the current review will decipher the mechanisms of C3a inducing the synapse loss via C3aR in mitochondria-dependent NLRP3 activating mechanisms, which facilitates the understanding the AD.

Structural Insights into the Role of the Proline Rich Region in Tau Function

Tau is a microtubule-associated protein that plays an important role in modulating axonal microtubules in neurons. Intracellular tau aggregates are found in a broad class of disorders, including Alzheimer's disease, termed tauopathies. Tau is an intrinsically disordered protein, and its structural disorder appears to be critical to its microtubule-related functions. Tubulin binding sites are found in tau's proline-rich region (PRR), microtubule binding repeats (MTBR: R1-R4), and pseudo-repeat, R'. While many post-translational modifications have been identified on tau, phosphorylation sites, which both regulate tubulin dimer and microtubule interactions and are correlated with disease, cluster with high frequency within the PRR. Here, we use fluorescence correlation spectroscopy and structural mass spectrometry techniques to characterize the impact of phosphomimic mutations in the PRR on tubulin dimer binding and probe the structure of the PRR-tubulin dimer complex. We find that phosphomimics cumulatively diminish tubulin dimer binding and slow microtubule polymerization. Additionally, we map two ∼15 residue regions of the PRR as primary tubulin dimer binding sites and propose a model in which PRR enhances lateral interactions between tubulin dimers, complementing the longitudinal interactions observed for MTBR. Together these measurements provide insight into the previously overlooked relevance of tau's PRR in functional interactions with tubulin.

GRAPHICAL ABSTRACT

Cadmium neurotoxicity: Insights into behavioral effect and neurodegenerative diseases

Cadmium (Cd) induced neurotoxicity has become a growing concern due to its potential adverse effects on the Central Nervous System. Cd is a Heavy Metal (HM) that is released into the environment, through several industrial processes. It poses a risk to the health of the community by polluting air, water, and soil. Cd builds up in the brain and other neural tissues, raising concerns about its effect on the nervous system due to its prolonged biological half-life. Cd can enter into the neurons, hence increasing the production of Reactive Oxygen Species (ROS) in them and impairing their antioxidant defenses. Cd disrupts the Calcium (Ca2+) balance in neurons, affects the function of the mitochondria, and triggers cell death pathways. As a result of these pathways, the path to the development of many neurological diseases affected by environmental factors, especially Cd, such as Alzheimer's Disease (AD) and Amyotrophic Lateral Sclerosis (ALS) is facilitated. There are cognitive deficits associated with long exposure to Cd. Memory disorders are present in both animals and humans. Cd alters the brain's function and performance in critical periods. There are lifelong consequences of Cd exposure during critical brain development stages. The susceptibility to neurotoxic effects is increased by interactions with a variety of risk factors. Cd poses risks to neuronal function and behavior, potentially contributing to neurodegenerative diseases like Parkinson's disease (PD) and AD as well as cognitive issues. This article offers a comprehensive overview of Cd-induced neurotoxicity, encompassing risk assessment, adverse effect levels, and illuminating intricate pathways.

Suppression of the amyloidogenic metabolism of APP and the accumulation of Aβ by alcadein α in the brain during aging

Generation and accumulation of amyloid-β (Aβ) protein in the brain are the primary causes of Alzheimer's disease (AD). Alcadeins (Alcs composed of Alcα, Alcβ and Alcγ family) are a neuronal membrane protein that is subject to proteolytic processing, as is Aβ protein precursor (APP), by APP secretases. Previous observations suggest that Alcs are involved in the pathophysiology of Alzheimer's disease (AD). Here, we generated new mouse AppNL-F (APP-KI) lines with either Alcα- or Alcβ-deficient background and analyzed APP processing and Aβ accumulation through the aging process. The Alcα-deficient APP-KI (APP-KI/Alcα-KO) mice enhanced brain Aβ accumulation along with increased amyloidogenic β-site cleavage of APP through the aging process whereas Alcβ-deficient APP-KI (APP-KI/Alcβ-KO) mice neither affected APP metabolism nor Aβ accumulation at any age. More colocalization of APP and BACE1 was observed in the endolysosomal pathway in neurons of APP-KI/Alcα-KO mice compared to APP-KI and APP-KI/Alcβ-KO mice. These results indicate that Alcα plays an important role in the neuroprotective function by suppressing the amyloidogenic cleavage of APP by BACE1 in the brain, which is distinct from the neuroprotective function of Alcβ, in which p3-Alcβ peptides derived from Alcβ restores the viability in neurons impaired by toxic Aβ.

Cellular and Molecular Responses to Mitochondrial DNA Deletions in Kearns-Sayre Syndrome: Some Underlying Mechanisms

Kearns-Sayre syndrome (KSS) is a rare multisystem mitochondrial disorder. It is caused by mitochondrial DNA (mtDNA) rearrangements, mostly large-scale deletions of 1.1-10 kb. These deletions primarily affect energy supply through impaired oxidative phosphorylation and reduced ATP production. This impairment gives rise to dysfunction of several tissues, in particular those with high energy demand like brain and muscles. Over the past decades, changes in respiratory chain complexes and energy metabolism have been emphasized, whereas little attention has been paid to other reports on ROS overproduction, protein synthesis inhibition, myelin vacuolation, demyelination, autophagy, apoptosis, and involvement of lipid raft and oligodendrocytes in KSS. Therefore, this paper draws attention towards these relatively underemphasized findings that might further clarify the pathologic cascades following deletions in the mtDNA.

Palmitic Acid Induces Posttranslational Modifications of Tau Protein in Alzheimer's Disease-Related Epitopes and Increases Intraneuronal Tau Levels

Metabolic diseases derived from an unhealthy lifestyle have been linked with an increased risk for developing cognitive impairment and even Alzheimer's disease (AD). Although high consumption of saturated fatty acids such as palmitic acid (PA) has been associated with the development of obesity and type II diabetes, the mechanisms connecting elevated neuronal PA levels and increased AD marker expression remain unclear. Among other effects, PA induces insulin resistance, increases intracellular calcium and reactive oxygen species (ROS) production, and reduces the NAD+/NADH ratio, resulting in decreased activity of the deacetylase Sirtuin1 (SIRT1) in neurons. These mechanisms may affect signaling pathways that impact the posttranslational modifications (PTMs) of the tau protein. To analyze the role played by PA in inducing the phosphorylation and acetylation of tau, we examined PTM changes in human tau in differentiated neurons from human neuroblastoma cells. We found changes in the phosphorylation state of several AD-related sites, namely, S199/202 and S214, that were mediated by a mechanism associated with the dysregulated activity of the kinases GSK3β and mTOR. PA also increased the acetylation of residue K280 and elevated total tau level after long exposure time. These findings provide information about the mechanisms by which saturated fatty acids cause tau PTMs that are similar to those observed in association with AD biochemical changes.

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

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

Alzheimer's Disease Neuropathological Change in Aged Non-Primate Mammals

Human brain aging is characterized by the production and deposition of β-amyloid (Aβ) in the form of senile plaques and cerebral amyloid angiopathy and the intracellular accumulation of hyper-phosphorylated tau (Hp-tau) to form neurofibrillary tangles (NFTs) and dystrophic neurites of senile plaques. The process progresses for years and eventually manifests as cognitive impairment and dementia in a subgroup of aged individuals. Aβ is produced and deposited first in the neocortex in most aged mammals, including humans; it is usually not accompanied by altered behavior and cognitive impairment. Hp-tau is less frequent than Aβ pathology, and NFTs are rare in most mammals. In contrast, NFTs are familiar from middle age onward in humans; NFTs first appear in the paleocortex and selected brain stem nuclei. NFTs precede for decades or years Aβ deposition and correlate with dementia in about 5% of individuals at the age of 65 and 25% at the age of 85. Based on these comparative data, (a) Aβ deposition is the most common Alzheimer's disease neuropathological change (ADNC) in the brain of aged mammals; (b) Hp-tau is less common, and NFTs are rare in most aged mammals; however, NFTs are the principal cytoskeletal pathology in aged humans; (c) NFT in aged humans starts in selected nuclei of the brain stem and paleocortical brain regions progressing to the most parts of the neocortex and other regions of the telencephalon; (d) human brain aging is unique among mammalian species due to the early appearance and dramatic progression of NFTs from middle age onward, matching with cognitive impairment and dementia in advanced cases; (e) neither mammalian nor human brain aging supports the concept of the amyloid cascade hypothesis.

Liquid-liquid phase separation in diseases

Liquid-liquid phase separation (LLPS), an emerging biophysical phenomenon, can sequester molecules to implement physiological and pathological functions. LLPS implements the assembly of numerous membraneless chambers, including stress granules and P-bodies, containing RNA and protein. RNA-RNA and RNA-protein interactions play a critical role in LLPS. Scaffolding proteins, through multivalent interactions and external factors, support protein-RNA interaction networks to form condensates involved in a variety of diseases, particularly neurodegenerative diseases and cancer. Modulating LLPS phenomenon in multiple pathogenic proteins for the treatment of neurodegenerative diseases and cancer could present a promising direction, though recent advances in this area are limited. Here, we summarize in detail the complexity of LLPS in constructing signaling pathways and highlight the role of LLPS in neurodegenerative diseases and cancers. We also explore RNA modifications on LLPS to alter diseases progression because these modifications can influence LLPS of certain proteins or the formation of stress granules, and discuss the possibility of proper manipulation of LLPS process to restore cellular homeostasis or develop therapeutic drugs for the eradication of diseases. This review attempts to discuss potential therapeutic opportunities by elaborating on the connection between LLPS, RNA modification, and their roles in diseases.

Time-Dependent Long-Term Effect of Memantine following Repetitive Mild Traumatic Brain Injury

Repetitive mild traumatic brain injury (rmTBI, e.g., sports concussions) may be associated with both acute and chronic symptoms and neurological changes. Despite the common occurrence of these injuries, therapeutic strategies are limited. One potentially promising approach is N-methyl-D-aspartate receptor (NMDAR) blockade to alleviate the effects of post-injury glutamatergic excitotoxicity. Initial pre-clinical work using the NMDAR antagonist, memantine, suggests that immediate treatment following rmTBI improves a variety of acute outcomes. It remains unclear (1) whether acute memantine treatment has long-term benefits and (2) whether delayed treatment following rmTBI is beneficial, which are both clinically relevant concerns. To test this, animals were subjected to rmTBI via a weight drop model with rotational acceleration (five hits in 5 days) and randomized to memantine treatment immediately, 3 months, or 6 months post-injury, with a treatment duration of one month. Behavioral outcomes were assessed at 1, 4, and 7 months post-injury. Neuropathological outcomes were characterized at 7 months post-injury. We observed chronic changes in behavior (anxiety-like behavior, motor coordination, spatial learning, and memory), as well as neuroinflammation (microglia, astrocytes) and tau phosphorylation (T231). Memantine treatment, either immediately or 6 months post-injury, appears to confer greater rescue of neuroinflammatory changes (microglia) than vehicle or treatment at the 3-month time point. Although memantine is already being prescribed chronically to address persistent symptoms associated with rmTBI, this study represents the first evidence of which we are aware to suggest a small but durable effect of memantine treatment in mild, concussive injuries. This effect suggests that memantine, although potentially beneficial, is insufficient to treat all aspects of rmTBI alone and should be combined with other therapeutic agents in a multi-therapy approach, with attention given to the timing of treatment.

Molecular Chaperones as Therapeutic Target: Hallmark of Neurodegenerative Disorders

Misfolded and aggregated proteins build up in neurodegenerative illnesses, which causes neuronal dysfunction and ultimately neuronal death. In the last few years, there has been a significant upsurge in the level of interest towards the function of molecular chaperones in the control of misfolding and aggregation. The crucial molecular chaperones implicated in neurodegenerative illnesses are covered in this review article, along with a variety of their different methods of action. By aiding in protein folding, avoiding misfolding, and enabling protein breakdown, molecular chaperones serve critical roles in preserving protein homeostasis. By aiding in protein folding, avoiding misfolding, and enabling protein breakdown, molecular chaperones have integral roles in preserving regulation of protein balance. It has been demonstrated that aging, a significant risk factor for neurological disorders, affects how molecular chaperones function. The aggregation of misfolded proteins and the development of neurodegeneration may be facilitated by the aging-related reduction in chaperone activity. Molecular chaperones have also been linked to the pathophysiology of several instances of neuron withering illnesses, enumerating as Parkinson's disease, Huntington's disease, and Alzheimer's disease. Molecular chaperones have become potential therapy targets concerning with the prevention and therapeutic approach for brain disorders due to their crucial function in protein homeostasis and their connection to neurodegenerative illnesses. Protein homeostasis can be restored, and illness progression can be slowed down by methods that increase chaperone function or modify their expression. This review emphasizes the importance of molecular chaperones in the context of neuron withering disorders and their potential as therapeutic targets for brain disorders.

Anti-acetylated-tau immunotherapy is neuroprotective in tauopathy and brain injury

BACKGROUND

Tau is aberrantly acetylated in various neurodegenerative conditions, including Alzheimer's disease, frontotemporal lobar degeneration (FTLD), and traumatic brain injury (TBI). Previously, we reported that reducing acetylated tau by pharmacologically inhibiting p300-mediated tau acetylation at lysine 174 reduces tau pathology and improves cognitive function in animal models.

METHODS

We investigated the therapeutic efficacy of two different antibodies that specifically target acetylated lysine 174 on tau (ac-tauK174). We treated PS19 mice, which harbor the P301S tauopathy mutation that causes FTLD, with anti-ac-tauK174 and measured effects on tau pathology, neurodegeneration, and neurobehavioral outcomes. Furthermore, PS19 mice received treatment post-TBI to evaluate the ability of the immunotherapy to prevent TBI-induced exacerbation of tauopathy phenotypes. Ac-tauK174 measurements in human plasma following TBI were also collected to establish a link between trauma and acetylated tau levels, and single nuclei RNA-sequencing of post-TBI brain tissues from treated mice provided insights into the molecular mechanisms underlying the observed treatment effects.

RESULTS

Anti-ac-tauK174 treatment mitigates neurobehavioral impairment and reduces tau pathology in PS19 mice. Ac-tauK174 increases significantly in human plasma 24 h after TBI, and anti-ac-tauK174 treatment of PS19 mice blocked TBI-induced neurodegeneration and preserved memory functions. Anti-ac-tauK174 treatment rescues alterations of microglial and oligodendrocyte transcriptomic states following TBI in PS19 mice.

CONCLUSIONS

The ability of anti-ac-tauK174 treatment to rescue neurobehavioral impairment, reduce tau pathology, and rescue glial responses demonstrates that targeting tau acetylation at K174 is a promising neuroprotective therapeutic approach to human tauopathies resulting from TBI or genetic disease.

In-vivo neuronal dysfunction by Aβ and tau overlaps with brain-wide inflammatory mechanisms in Alzheimer's disease

The molecular mechanisms underlying neuronal dysfunction in Alzheimer's disease (AD) remain uncharacterized. Here, we identify genes, molecular pathways and cellular components associated with whole-brain dysregulation caused by amyloid-beta (Aβ) and tau deposits in the living human brain. We obtained in-vivo resting-state functional MRI (rs-fMRI), Aβ- and tau-PET for 47 cognitively unimpaired and 16 AD participants from the Translational Biomarkers in Aging and Dementia cohort. Adverse neuronal activity impacts by Aβ and tau were quantified with personalized dynamical models by fitting pathology-mediated computational signals to the participant's real rs-fMRIs. Then, we detected robust brain-wide associations between the spatial profiles of Aβ-tau impacts and gene expression in the neurotypical transcriptome (Allen Human Brain Atlas). Within the obtained distinctive signature of in-vivo neuronal dysfunction, several genes have prominent roles in microglial activation and in interactions with Aβ and tau. Moreover, cellular vulnerability estimations revealed strong association of microglial expression patterns with Aβ and tau's synergistic impact on neuronal activity (q < 0.001). These results further support the central role of the immune system and neuroinflammatory pathways in AD pathogenesis. Neuronal dysregulation by AD pathologies also associated with neurotypical synaptic and developmental processes. In addition, we identified drug candidates from the vast LINCS library to halt or reduce the observed Aβ-tau effects on neuronal activity. Top-ranked pharmacological interventions target inflammatory, cancer and cardiovascular pathways, including specific medications undergoing clinical evaluation in AD. Our findings, based on the examination of molecular-pathological-functional interactions in humans, may accelerate the process of bringing effective therapies into clinical practice.

Role of Tau Protein in Neurodegenerative Diseases and Development of Its Targeted Drugs: A Literature Review

Tau protein is a microtubule-associated protein that is widely distributed in the central nervous system and maintains and regulates neuronal morphology and function. Tau protein aggregates abnormally and forms neurofibrillary tangles in neurodegenerative diseases, disrupting the structure and function of neurons and leading to neuronal death, which triggers the initiation and progression of neurological disorders. The aggregation of tau protein in neurodegenerative diseases is associated with post-translational modifications, which may affect the hydrophilicity, spatial conformation, and stability of tau protein, promoting tau protein aggregation and the formation of neurofibrillary tangles. Therefore, studying the role of tau protein in neurodegenerative diseases and the mechanism of aberrant aggregation is important for understanding the mechanism of neurodegenerative diseases and finding therapeutic approaches. This review describes the possible mechanisms by which tau protein promotes neurodegenerative diseases, the post-translational modifications of tau protein and associated influencing factors, and the current status of drug discovery and development related to tau protein, which may contribute to the development of new therapeutic approaches to alleviate or treat neurodegenerative diseases.