Tau forms oligomeric complexes on microtubules that are distinct from tau aggregates

Electrostatic Effects on Tau Nanocondensates

Biomolecular condensates (BMCs) are membrane-less protein compartments with physiological and pathological relevance. The formation of BMCs is driven by a process known as liquid-liquid phase separation (LLPS), a field that has largely focused on the study of micron-sized condensates. However, there have been recent studies showing that proteins that undergo LLPS also form nanometer-sized condensates. These nanometer-sized condensates, or nanocondensates, are distinct from microcondensates and potentially exhibit more relevance in cell biology. The field of nanocondensate research is in its infancy, with limited biophysical studies of these structures. Here, we studied condensate formation and dissolution of wild-type and disease-linked (hyperphosphorylated and missense mutated) Tau. We investigated the effects of solution condition modulation on nanocondensate formation and dissolution, and observed that Tau condensation is strongly regulated by electrostatic forces and less affected by hydrophobic disruption. We observed that all three Tau variants studied shared condensate formation properties when in solution conditions with the same ionic strength. However, hyperphosphorylated and missense-mutated Tau exhibited higher resistance to dissolution compared to wild-type Tau. This study uncovers additional distinctions between different types of condensates, which provides further insight into the distinctions between physiological and pathological condensates.

Distinct neuronal vulnerability and metabolic dysfunctions are characteristic features of fast-progressing Alzheimer's patients with Lewy bodies

Tau protein accumulation is linked to dementia progression in Alzheimer's disease (AD), with potential co-pathologies contributing to it. The progression of dementia in patients with AD varies between individuals, and the association between co-pathology and heterogeneity in dementia progression rate remains unclear. We used longitudinal cohort data, postmortem brain tissues, and biochemical methods such as immunoassays and proteomic profiling to investigate the molecular components associated with progression rate. We report that AD with comorbidities, such as dementia with Lewy bodies (DLB) and TDP-43 pathology, progress faster than AD alone. Patients with AD-DLB had higher levels of soluble oligomeric tau proteins and lower levels of insoluble tau proteins compared to those with AD alone. Our data suggest that α-synuclein fibrils may enhance tau aggregation through cross-seeding. The prefrontal cortex is more vulnerable to Lewy body pathology than the temporal cortex, and Tau and α-synuclein aggregate in distinct neuronal populations, indicating selective neuronal and regional vulnerability to their respective pathologies. Dysfunctional metabolic pathways were more strongly associated with patients having fast-progressing AD-DLB. Our study suggests that comorbidities, such as α-synuclein aggregation and metabolic dysfunctions, are associated with rapidly progressing AD patients, highlighting the importance of patient subgrouping for clinical trials.

Tubulin transforms Tau and α-synuclein condensates from pathological to physiological

Proteins phase-separate to form condensates that partition and concentrate biomolecules into membraneless compartments. These condensates can exhibit dichotomous behaviors in biology by supporting cellular physiology or instigating pathological protein aggregation 1-3 . Tau and α- synuclein (αSyn) are neuronal proteins that form heterotypic (Tau:αSyn) condensates associated with both physiological and pathological processes. Tau and αSyn functionally regulate microtubules 8-12 , but are also known to misfold and co-deposit in aggregates linked to various neurodegenerative diseases 4,5,6,7 , which highlights the paradoxically ambivalent effect of Tau:αSyn condensation in health and disease. Here, we show that tubulin modulates Tau:αSyn condensates by promoting microtubule interactions, competitively inhibiting the formation of homotypic and heterotypic pathological oligomers. In the absence of tubulin, Tau-driven protein condensation accelerates the formation of toxic Tau:αSyn heterodimers and amyloid fibrils. However, tubulin partitioning into Tau:αSyn condensates modulates protein interactions, promotes microtubule polymerization, and prevents Tau and αSyn oligomerization and aggregation. We distinguished distinct Tau and αSyn structural states adopted in tubulin-absent (pathological) and tubulin-rich (physiological) condensates, correlating compact conformations with aggregation and extended conformations with function. Furthermore, using various neuronal cell models, we showed that loss of stable microtubules, which occurs in Alzheimer's disease and Parkinsons disease patients 13,14 , results in pathological oligomer formation and loss of neurites, and that functional condensation using an inducible optogenetic Tau construct resulted in microtubule stablization. Our results identify that tubulin is a critical modulator in switching Tau:αSyn pathological condensates to physiological, mechanistically relating the loss of stable microtubules with disease progression. Tubulin restoration strategies and Tau-mediated microtubule stabilization can be potential therapies targeting both Tau-specific and Tau/αSyn mixed pathologies.

Tau Oligomers Resist Phase Separation

Tau is a microtubule-associated protein that undergoes liquid-liquid phase separation (LLPS) to form condensates under physiological conditions, facilitating microtubule stabilization and intracellular transport. LLPS has also been implicated in pathological Tau aggregation, which contributes to tauopathies such as Alzheimer's disease. While LLPS is known to promote Tau aggregation, the relationship between Tau's structural states and its phase separation behavior remains poorly defined. Here, we examine how oligomerization modulates Tau LLPS and uncover key distinctions between monomeric, oligomeric, and amyloidogenic Tau species. Using dynamic light scattering and fluorescence microscopy, we monitored oligomer formation over time and assessed oligomeric Tau's ability to undergo LLPS. We found that Tau monomers readily phase separate and form condensates. As oligomerization progresses, Tau's propensity to undergo LLPS diminishes, with oligomers still being able to phase separate, albeit with reduced efficiency. Interestingly, oligomeric Tau is recruited into condensates formed with 0-day-aged Tau, with this recruitment depending on the oligomer state of maturation. Early-stage, Thioflavin T (ThT)-negative oligomers co-localize with 0-day-aged Tau condensates, whereas ThT-positive oligomers resist condensate recruitment entirely. This study highlights a dynamic interplay between Tau LLPS and aggregation, providing insight into how Tau's structural and oligomeric states influence its pathological and functional roles. These findings underscore the need to further explore LLPS as a likely modulator of Tau pathogenesis and distinct pathogenic oligomers as viable therapeutic targets in tauopathies.

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.

A pathological phosphorylation pattern enhances tau cooperativity on microtubules and facilitates tau filament assembly

Phosphorylation plays a crucial role in both normal and disease processes involving the microtubule-associated protein tau. Physiologically, phosphorylation regulates tau's subcellular localization within neurons and is involved in fetal development and animal hibernation. However, abnormal phosphorylation of tau is linked to the formation of neurofibrillary tangles (NFTs) in various human tauopathies. Interestingly, the patterns of tau phosphorylation are similar in both normal and abnormal processes, leaving unclear whether phosphorylated tau retains its functional role in normal processes. The relationship between tau phosphorylation and NFT assembly in tauopathies is also still debated. To address these questions, we investigated the effects of tau phosphorylation on microtubule binding, cooperative protein envelope formation, and NFT filament assembly relevant to tauopathies. Consistent with previous results, our findings show that tau phosphorylation decreases tau's overall affinity for microtubules, but we reveal that phosphorylation more dramatically impacts the cooperativity between tau molecules during tau envelope formation along microtubules. Additionally, we observed that the specific pattern of phosphorylation, rather than overall phosphorylation level, strongly impacts the assembly of tau filaments in vitro . Our results reveal new insights into how tau phosphorylation impacts tau's physiological roles on microtubules and its pathoconversion into NFTs.

Multimer Detection System: A Universal Assay System for Differentiating Protein Oligomers from Monomers

Depositions of protein aggregates are typical pathological hallmarks of various neurodegenerative diseases (NDs). For example, amyloid-beta (Aβ) and tau aggregates are present in the brain and plasma of patients with Alzheimer's disease (AD); α-synuclein in Parkinson's disease (PD), dementia with Lewy bodies (DLB), and multiple system atrophy (MSA); mutant huntingtin protein (Htt) in Huntington's disease (HD); and DNA-binding protein 43 kD (TDP-43) in amyotrophic lateral sclerosis (ALS), frontotemporal dementia (FTD), and limbic-predominant age-related TDP-43 encephalopathy (LATE). The same misfolded proteins can be present in multiple diseases in the form of mixed proteinopathies. Since there is no cure for all these diseases, understanding the mechanisms of protein aggregation becomes imperative in modern medicine, especially for developing diagnostics and therapeutics. A Multimer Detection System (MDS) was designed to distinguish and quantify the multimeric/oligomeric forms from the monomeric form of aggregated proteins. As the unique epitope of the monomer is already occupied by capturing or detecting antibodies, the aggregated proteins with multiple epitopes would be accessible to both capturing and detecting antibodies simultaneously, and signals will be generated from the oligomers rather than the monomers. Hence, MDS could present a simple solution for measuring various conformations of aggregated proteins with high sensitivity and specificity, which may help to explore diagnostic and treatment strategies for developing anti-aggregation therapeutics.

Structures of Oligomeric States of Tau Protein, Amyloid-β, α-Synuclein and Prion Protein Implicated in Alzheimer's Disease, Parkinson's Disease and Prionopathies

In this review, we focus on the biophysical and structural aspects of the oligomeric states of physiologically intrinsically disordered proteins and peptides tau, amyloid-β and α-synuclein and partly disordered prion protein and their isolations from animal models and human brains. These protein states may be the most toxic agents in the pathogenesis of Alzheimer's and Parkinson's disease. It was shown that oligomers are important players in the aggregation cascade of these proteins. The structural information about these structural states has been provided by methods such as solution and solid-state NMR, cryo-EM, crosslinking mass spectrometry, AFM, TEM, etc., as well as from hybrid structural biology approaches combining experiments with computational modelling and simulations. The reliable structural models of these protein states may provide valuable information for future drug design and therapies.

Exploring the protective effect and molecular mechanism of betulin in Alzheimer's disease based on network pharmacology, molecular docking and experimental validation

Alzheimer's disease (AD) is a neurodegenerative disorder that impairs learning and memory, with high rates of mortality. Birch bark has been traditionally used in the treatment of various skin ailments. Betulin (BT) is a key compound of birch bark that exhibits diverse pharmacological benefits and therapeutic potential in AD. However, the therapeutic effects and molecular mechanisms of BT in AD remain unclear. The present study aimed to predict the potential therapeutic targets of BT in the treatment of AD, and to determine the specific underlying molecular mechanisms through network pharmacology analysis and experimental validation. PharmMapper was used to predict the target genes of BT, and four disease databases were searched to screen for AD targets. The intersection targets were identified using the jveen website. Drug‑disease target protein‑protein interaction networks and hub genes were obtained and visualized using the Search Tool for the Retrieval of Interacting Genes/Proteins database and Cytoscape. The Database for Annotation, Visualization and Integrated Discovery was used for Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analyses, and AutoDock was used for molecular docking analysis of BT and hub genes. Subsequently, the network‑predicted mechanisms of BT in AD were verified in vitro. A total of 495 BT and 1,386 AD targets were identified, and 120 were identified as potential targets of BT in the treatment of AD. The results of the molecular docking analysis revealed a strong binding affinity between BT and the hub genes. In addition, enrichment analyses of GO and KEGG pathways indicated that the neuroprotective effects of BT mainly involved the 'PI3K‑Akt signaling pathway'. The results of in vitro experiments demonstrated that pretreatment with BT for 2 h may ameliorate formaldehyde (FA)‑induced cytotoxicity and morphological changes in HT22 cells, and decrease FA‑induced Tau hyperphosphorylation and reactive oxygen species levels. Furthermore, the PI3K/AKT signaling pathway was activated and the expression levels of downstream proteins, namely GSK3β, Bcl‑2 and Bax, were modified following pre‑treatment with BT. Overall, the results of network pharmacology and in vitro analyses revealed that BT may reduce FA‑induced AD‑like pathology by modulating the PI3K/AKT signaling pathway, highlighting it as a potential multi‑target drug for the treatment of AD.

The structure of a Tau fragment bound to tubulin prompts new hypotheses on Tau mechanism and oligomerization

Tau is a protein involved in the regulation of axonal microtubules in neurons. In pathological conditions, it forms filamentous aggregates which are molecular markers of neurodegenerative diseases known as tauopathies. Structures of Tau in fibrils or bound to the microtubule have been reported. We present here a structure of a Tau construct comprising the PHF6 motif, an oligopeptide involved in Tau aggregation, as a complex with tubulin. This Tau fragment binds as a dimer to a new site which, when transposed to the microtubule, would correspond to a pore between protofilaments. These results raise new hypotheses on Tau-induced microtubule assembly and stabilization and on Tau oligomerization.

Inducing aggresome and stable tau aggregation in Neuro2a cells with an optogenetic tool

Tauopathy is a spectrum of diseases characterized by fibrillary tau aggregate formation in neurons and glial cells in the brain. Tau aggregation originates in the brainstem and entorhinal cortex and then spreads throughout the brain in Alzheimer's disease (AD), which is the most prevalent type of tauopathy. Understanding the mechanism by which locally developed tau pathology propagates throughout the brain is crucial for comprehending AD pathogenesis. Therefore, a novel model of tau pathology that artificially induces tau aggregation in targeted cells at specific times is essential. This study describes a novel optogenetic module, OptoTau, which is a human tau with the P301L mutation fused with a photosensitive protein CRY2olig, inducing various forms of tau according to the temporal pattern of blue light illumination pattern. Continuous blue light illumination for 12 h to Neuro2a cells that stably express OptoTau (OptoTauKI cells) formed clusters along microtubules, many of which eventually accumulated in aggresomes. Conversely, methanol-resistant tau aggregation was formed when alternating light exposure and darkness in 30-min cycles for 8 sets per day were repeated over 8 days. Methanol-resistant tau was induced more rapidly by repeating 5-min illumination followed by 25-min darkness over 24 h. These results indicate that OptoTau induced various tau aggregation stages based on the temporal pattern of blue light exposure. Thus, this technique exhibits potential as a novel approach to developing specific tau aggregation in targeted cells at desired time points.

Intracellular tau fragment droplets serve as seeds for tau fibrils

Intracellular tau aggregation requires a local protein concentration increase, referred to as "droplets". However, the cellular mechanism for droplet formation is poorly understood. Here, we expressed OptoTau, a P301L mutant tau fused with CRY2olig, a light-sensitive protein that can form homo-oligomers. Under blue light exposure, OptoTau increased tau phosphorylation and was sequestered in aggresomes. Suppressing aggresome formation by nocodazole formed tau granular clusters in the cytoplasm. The granular clusters disappeared by discontinuing blue light exposure or 1,6-hexanediol treatment suggesting that intracellular tau droplet formation requires microtubule collapse. Expressing OptoTau-ΔN, a species of N-terminal cleaved tau observed in the Alzheimer's disease brain, formed 1,6-hexanediol and detergent-resistant tau clusters in the cytoplasm with blue light stimulation. These intracellular stable tau clusters acted as a seed for tau fibrils in vitro. These results suggest that tau droplet formation and N-terminal cleavage are necessary for neurofibrillary tangles formation in neurodegenerative diseases.

ECLiPSE: a versatile classification technique for structural and morphological analysis of 2D and 3D single-molecule localization microscopy data

Single-molecule localization microscopy (SMLM) has gained widespread use for visualizing the morphology of subcellular organelles and structures with nanoscale spatial resolution. However, analysis tools for automatically quantifying and classifying SMLM images have lagged behind. Here we introduce Enhanced Classification of Localized Point clouds by Shape Extraction (ECLiPSE), an automated machine learning analysis pipeline specifically designed to classify cellular structures captured through two-dimensional or three-dimensional SMLM. ECLiPSE leverages a comprehensive set of shape descriptors, the majority of which are directly extracted from the localizations to minimize bias during the characterization of individual structures. ECLiPSE has been validated using both unsupervised and supervised classification on datasets, including various cellular structures, achieving near-perfect accuracy. We apply two-dimensional ECLiPSE to classify morphologically distinct protein aggregates relevant for neurodegenerative diseases. Additionally, we employ three-dimensional ECLiPSE to identify relevant biological differences between healthy and depolarized mitochondria. ECLiPSE will enhance the way we study cellular structures across various biological contexts.

New therapies on the horizon: Targeted protein degradation in neuroscience

This minireview explores the burgeoning field of targeted protein degradation (TPD) and its promising applications in neuroscience and clinical development. TPD offers innovative strategies for modulating protein levels, presenting a paradigm shift in small-molecule drug discovery and therapeutic interventions. Importantly, small-molecule protein degraders specifically target and remove pathogenic proteins from central nervous system cells without the drug delivery challenges of genomic and antibody-based modalities. Here, we review recent advancements in TPD technologies, highlight proteolysis targeting chimera (PROTAC) protein degrader molecules with proximity-induced degradation event-driven and iterative pharmacology, provide applications in neuroscience research, and discuss the high potential for translation of TPD into clinical settings.

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.

Reelin links Apolipoprotein E4, Tau, and Amyloid-β in Alzheimer's disease

Alzheimer's disease (AD) is the most common neurodegenerative disorder that affects the cerebral cortex and hippocampus, and is characterised by progressive cognitive decline and memory loss. A recent report of a patient carrying a novel gain-of-function variant of RELN (H3447R, termed RELN-COLBOS) who developed resilience against presenilin-linked autosomal-dominant AD (ADAD) has generated enormous interest. The RELN-COLBOS variant enhances interactions with the apolipoprotein E receptor 2 (ApoER2) and very-low-density lipoprotein receptor (VLDLR), which are associated with delayed AD onset and progression. These findings were validated in a transgenic mouse model. Reelin is involved in neurodevelopment, neurogenesis, and neuronal plasticity. The evidence accumulated thus far has demonstrated that the Reelin pathway links apolipoprotein E4 (ApoE4), amyloid-β (Aβ), and tubulin-associated unit (Tau), which are key proteins that have been implicated in AD pathogenesis. Reelin and key components of the Reelin pathway have been highlighted as potential therapeutic targets and biomarkers for AD.

Initiation of hnRNPA1 Low-Complexity Domain Condensation Monitored by Dynamic Light Scattering

Biomolecular condensates (BMCs) exhibit physiological and pathological relevance in biological systems. Both liquid and solid condensates play significant roles in the spatiotemporal regulation and organization of macromolecules and their biological activities. Some pathological solid condensates, such as Lewy Bodies and other fibrillar aggregates, have been hypothesized to originate from liquid condensates. With the prevalence of BMCs having functional and dysfunctional roles, it is imperative to understand the mechanism of biomolecular condensate formation and initiation. Using the low-complexity domain (LCD) of heterogenous ribonuclear protein A1 (hnRNPA1) as our model, we monitored initial assembly events using dynamic light scattering (DLS) while modulating pH and salt conditions to perturb macromolecule and condensate properties. We observed the formation of nanometer-sized BMCs (nano-condensates) distinct from protein monomers and micron-sized condensates. We also observed that conditions that solubilize micron-sized protein condensates do not solubilize nano-condensates, indicating that the balance of forces that stabilize nano-condensates and micron-sized condensates are distinct. These findings provide insight into the forces that drive protein phase separation and potential nucleation structures of macromolecular condensation.

The types and numbers of kinesins and dyneins transporting endocytic cargoes modulate their motility and response to tau

Organelles and vesicular cargoes are transported by teams of kinesin and dynein motors along microtubules. We isolated endocytic organelles from cells at different stages of maturation and reconstituted their motility along microtubules in vitro. We asked how the sets of motors transporting a cargo determine its motility and response to the microtubule-associated protein tau. Here, we find that phagosomes move in both directions along microtubules, but the directional bias changes during maturation. Early phagosomes exhibit retrograde-biased transport while late phagosomes are directionally unbiased. Correspondingly, early and late phagosomes are bound by different numbers and combinations of kinesins-1, -2, -3, and dynein. Tau stabilizes microtubules and directs transport within neurons. While single-molecule studies show that tau differentially regulates the motility of kinesins and dynein in vitro, less is known about its role in modulating the trafficking of endogenous cargoes transported by their native teams of motors. Previous studies showed that tau preferentially inhibits kinesin motors, which biases late phagosome transport towards the microtubule minus-end. Here, we show that tau strongly inhibits long-range, dynein-mediated motility of early phagosomes. Tau reduces forces generated by teams of dynein motors on early phagosomes and accelerates dynein unbinding under load. Thus, cargoes differentially respond to tau, where dynein complexes on early phagosomes are more sensitive to tau inhibition than those on late phagosomes. Mathematical modeling further explains how small changes in the number of kinesins and dynein on cargoes impact the net directionality but also that cargoes with different sets of motors respond differently to tau.

A Simple Sandwich Electrochemical Immunosensor for Rapid Detection of the Alzheimer's Disease Biomarker Tau Protein

As a typical biomarker of Alzheimer's disease, rapid and specific detection of tau protein can help improve the early diagnosis and prognosis of the disease. In this study, a simple sandwich electrochemical immunosensor was developed for rapid detection of tau protein. Primary monoclonal antibodies (mAb1) against the middle domain of tau protein (amino acids 189-195) were immobilized on the gold electrode surface through a self-assembled monolayer (SAM) of 3,3'-dithiobis (sulfosuccinimidyl propionate) (DTSSP). Then the tau protein was captured through the specific adsorption between the antigen and the antibody, resulting in a change in the impedance. Secondary monoclonal antibodies (mAb2) against the N-terminal region of tau protein were used for further amplification of the binding reaction between mAb1 and tau protein. A linear correlation between the total change in impedance and the logarithm of tau concentration was found from 2 × 10-6 mg mL-1 to 2 × 10-3 mg mL-1, with a detection limit as low as 1 × 10-6 mg mL-1. No significant interference was observed from human serum albumin. Furthermore, the fabricated sandwich immunosensor successfully detected target tau protein in artificial cerebrospinal fluid (aCSF) samples, indicating good potential for clinical applications in the future.

Single-Molecule Characterization and Super-Resolution Imaging of Alzheimer's Disease-Relevant Tau Aggregates in Human Samples

Hyperphosphorylation and aggregation of the protein tau play key roles in the development of Alzheimer's disease (AD). While the molecular structure of the filamentous tau aggregates has been determined to atomic resolution, there is far less information available about the smaller, soluble aggregates, which are believed to be more toxic. Traditional techniques are limited to bulk measures and struggle to identify individual aggregates in complex biological samples. To address this, we developed a novel single-molecule pull-down-based assay (MAPTau) to detect and characterize individual tau aggregates in AD and control post-mortem brain and biofluids. Using MAPTau, we report the quantity, as well as the size and circularity of tau aggregates measured using super-resolution microscopy, revealing AD-specific differences in tau aggregate morphology. By adapting MAPTau to detect multiple phosphorylation markers in individual aggregates using two-color coincidence detection, we derived compositional profiles of the individual aggregates. We find an AD-specific phosphorylation profile of tau aggregates with more than 80 % containing multiple phosphorylations, compared to 5 % in age-matched non-AD controls. Our results show that MAPTau is able to identify disease-specific subpopulations of tau aggregates phosphorylated at different sites, that are invisible to other methods and enable the study of disease mechanisms and diagnosis.

The Enigma of Tau Protein Aggregation: Mechanistic Insights and Future Challenges

Tau protein misfolding and aggregation are pathological hallmarks of Alzheimer's disease and over twenty neurodegenerative disorders. However, the molecular mechanisms of tau aggregation in vivo remain incompletely understood. There are two types of tau aggregates in the brain: soluble aggregates (oligomers and protofibrils) and insoluble filaments (fibrils). Compared to filamentous aggregates, soluble aggregates are more toxic and exhibit prion-like transmission, providing seeds for templated misfolding. Curiously, in its native state, tau is a highly soluble, heat-stable protein that does not form fibrils by itself, not even when hyperphosphorylated. In vitro studies have found that negatively charged molecules such as heparin, RNA, or arachidonic acid are generally required to induce tau aggregation. Two recent breakthroughs have provided new insights into tau aggregation mechanisms. First, as an intrinsically disordered protein, tau is found to undergo liquid-liquid phase separation (LLPS) both in vitro and inside cells. Second, cryo-electron microscopy has revealed diverse fibrillar tau conformations associated with different neurodegenerative disorders. Nonetheless, only the fibrillar core is structurally resolved, and the remainder of the protein appears as a "fuzzy coat". From this review, it appears that further studies are required (1) to clarify the role of LLPS in tau aggregation; (2) to unveil the structural features of soluble tau aggregates; (3) to understand the involvement of fuzzy coat regions in oligomer and fibril formation.

Super-Resolution Imaging Uncovers Nanoscale Tau Aggregate Hyperphosphorylation Patterns in Human Alzheimer's Disease Brain Tissue

Tau aggregation plays a critical role in Alzheimer's Disease (AD), where tau neurofibrillary tangles (NFTs) are a key pathological hallmark. While much attention has been given to NFTs, emerging evidence underscores nano-sized pre-NFT tau aggregates as potentially toxic entities in AD. By leveraging DNA-PAINT super-resolution microscopy, we visualized and quantified nanoscale tau aggregates (nano-aggregates) in human postmortem brain tissues from intermediate and advanced AD, and Primary Age-Related Tauopathy (PART). Nano-aggregates were predominant across cases, with AD exhibiting a higher burden compared to PART. Hyperphosphorylated tau residues (p-T231, p-T181, and p-S202/T205) were present within nano-aggregates across all AD Braak stages and PART. Moreover, nano-aggregates displayed morphological differences between PART and AD, and exhibited distinct hyperphosphorylation patterns in advanced AD. These findings suggest that changes in nano-aggregate morphology and hyperphosphorylation patterns may exacerbate tau aggregation and AD progression. The ability to detect and profile nanoscale tau aggregates in human brain tissue opens new avenues for studying the molecular underpinnings of tauopathies.

Current Insights of Nanocarrier-Mediated Gene Therapeutics to Treat Potential Impairment of Amyloid Beta Protein and Tau Protein in Alzheimer's Disease

Alzheimer's disease (AD), is the major type of dementia and most progressive, irreversible widespread neurodegenerative disorder affecting the elderly worldwide. The prime hallmarks of Alzheimer's disease (AD) are beta-amyloid plaques (Aβ) and neurofibrillary tangles (NFT). In spite of recent advances and developments in targeting the hallmarks of AD, symptomatic medications that promise neuroprotective activity against AD are currently unable to treat degenerating brain clinically or therapeutically and show little efficacy. The extensive progress of AD therapies over time has resulted in the advent of disease-modifying medications with the potential to alleviate AD. However, due to the presence of a defensive connection between the vascular system and the neural tissues known as the blood-brain barrier (BBB), directing these medications to the site of action in the degenerating brain is the key problem. BBB acts as a highly selective semipermeable membrane that prevents any type of foreign substance from entering the microenvironment of neurons. To overcome this limitation, the revolutionary approach of nanoparticle(NP)/nanocarrier-mediated drug delivery system has marked the era with its unique property to cross, avoid, or disrupt the defensive BBB efficiently and release the modified drug at the target site of action. After comprehensive data mining, this review focuses on the detailed understanding of different types of nanoparticle(NP)/nanocarrier-mediated drug delivery system like liposomes, micelles, gold nanoparticles(NP), polymeric NPs, etc. which have promising potential in carrying the desired drug(cargo) to the location in the degenerated brain thus mitigating the Alzheimer's disease.

Korean red ginseng polysaccharide as a potential therapeutic agent targeting tau pathology in Alzheimer's disease

Tau is a microtubule-associated protein that plays a critical role in the stabilization and modulation of neuronal axons. Tau pathology is stronger associated with cognitive decline in patients with Alzheimer's disease (AD) than amyloid beta (Aβ) pathology. Hence, tau targeting is a promising approach for the treatment of AD. Previous studies have demonstrated that the non-saponin fraction with rich polysaccharide (NFP) from Korean red ginseng (KRG) can modulate tau aggregation and exert a therapeutic effect on AD. Therefore, we investigated the efficacy of NFP isolated from KRG on tau pathology in experimental models of AD. Our results showed that NFP from KRG ameliorated deposition and hyperphosphorylation of tau in the brain of 3xTg mice. Moreover, NFP from KRG modulated the aggregation and dissociation of tau K18 in vitro. We demonstrated the alleviatory effects of NFP from KRG on hyperphosphorylated tau and tau kinase in okadaic acid-treated HT22 cells. Furthermore, NFP from KRG mitigated Aβ deposition, neurodegeneration, and neuroinflammation in 3xTg mice. We revealed the neuroprotective effects of NFP from KRG on tau-induced neuronal loss in HT22 cells. Our results indicate that NFP extracted from KRG is a novel therapeutic agent for the treatment of AD associated with tau pathology.

Lung endothelium, tau, and amyloids in health and disease

Lung endothelia in the arteries, capillaries, and veins are heterogeneous in structure and function. Lung capillaries in particular represent a unique vascular niche, with a thin yet highly restrictive alveolar-capillary barrier that optimizes gas exchange. Capillary endothelium surveys the blood while simultaneously interpreting cues initiated within the alveolus and communicated via immediately adjacent type I and type II epithelial cells, fibroblasts, and pericytes. This cell-cell communication is necessary to coordinate the immune response to lower respiratory tract infection. Recent discoveries identify an important role for the microtubule-associated protein tau that is expressed in lung capillary endothelia in the host-pathogen interaction. This endothelial tau stabilizes microtubules necessary for barrier integrity, yet infection drives production of cytotoxic tau variants that are released into the airways and circulation, where they contribute to end-organ dysfunction. Similarly, beta-amyloid is produced during infection. Beta-amyloid has antimicrobial activity, but during infection it can acquire cytotoxic activity that is deleterious to the host. The production and function of these cytotoxic tau and amyloid variants are the subject of this review. Lung-derived cytotoxic tau and amyloid variants are a recently discovered mechanism of end-organ dysfunction, including neurocognitive dysfunction, during and in the aftermath of infection.

Targeting vulnerable microcircuits in the ventral hippocampus of male transgenic mice to rescue Alzheimer-like social memory loss

BACKGROUND

Episodic memory loss is a prominent clinical manifestation of Alzheimer's disease (AD), which is closely related to tau pathology and hippocampal impairment. Due to the heterogeneity of brain neurons, the specific roles of different brain neurons in terms of their sensitivity to tau accumulation and their contribution to AD-like social memory loss remain unclear. Therefore, further investigation is necessary.

METHODS

We investigated the effects of AD-like tau pathology by Tandem mass tag proteomic and phosphoproteomic analysis, social behavioural tests, hippocampal electrophysiology, immunofluorescence staining and in vivo optical fibre recording of GCaMP6f and iGABASnFR. Additionally, we utilized optogenetics and administered ursolic acid (UA) via oral gavage to examine the effects of these agents on social memory in mice.

RESULTS

The results of proteomic and phosphoproteomic analyses revealed the characteristics of ventral hippocampal CA1 (vCA1) under both physiological conditions and AD-like tau pathology. As tau progressively accumulated, vCA1, especially its excitatory and parvalbumin (PV) neurons, were fully filled with mislocated and phosphorylated tau (p-Tau). This finding was not observed for dorsal hippocampal CA1 (dCA1). The overexpression of human tau (hTau) in excitatory and PV neurons mimicked AD-like tau accumulation, significantly inhibited neuronal excitability and suppressed distinct discrimination-associated firings of these neurons within vCA1. Photoactivating excitatory and PV neurons in vCA1 at specific rhythms and time windows efficiently ameliorated tau-impaired social memory. Notably, 1 month of UA administration efficiently decreased tau accumulation via autophagy in a transcription factor EB (TFEB)-dependent manner and restored the vCA1 microcircuit to ameliorate tau-impaired social memory.

CONCLUSION

This study elucidated distinct protein and phosphoprotein networks between dCA1 and vCA1 and highlighted the susceptibility of the vCA1 microcircuit to AD-like tau accumulation. Notably, our novel findings regarding the efficacy of UA in reducing tau load and targeting the vCA1 microcircuit may provide a promising strategy for treating AD in the future.

Single-molecule imaging of Tau reveals how phosphorylation affects its movement and confinement in living cells

Tau is a microtubule-associated protein that is regulated by post-translational modifications. The most studied of these modifications is phosphorylation, which affects Tau's aggregation and loss- and gain-of-functions, including the interaction with microtubules, in Alzheimer's disease and primary tauopathies. However, little is known about how Tau's phosphorylation state affects its dynamics and organisation at the single-molecule level. Here, using quantitative single-molecule localisation microscopy, we examined how mimicking or abrogating phosphorylation at 14 disease-associated serine and threonine residues through mutagenesis influences the behaviour of Tau in live Neuro-2a cells. We observed that both pseudohyperphosphorylated Tau (TauE14) and phosphorylation-deficient Tau (TauA14) exhibit a heterogeneous mobility pattern near the plasma membrane. Notably, we found that the mobility of TauE14 molecules was higher than wild-type Tau molecules, while TauA14 molecules displayed lower mobility. Moreover, TauA14 was organised in a filament-like structure resembling cytoskeletal filaments, within which TauA14 exhibited spatial and kinetic heterogeneity. Our study provides a direct visualisation of how the phosphorylation state of Tau affects its spatial and temporal organisation, presumably reflecting the phosphorylation-dependent changes in the interactions between Tau and its partners. We suggest that alterations in Tau dynamics resulting from aberrant changes in phosphorylation could be a critical step in its pathological dysregulation.

Phase 1 Studies of the Anti-Tau Monoclonal Antibody JNJ-63733657 in Healthy Participants and Participants with Alzheimer's Disease

BACKGROUND

JNJ-63733657 (posdinemab) is a humanized IgG1/kappa monoclonal anti-phospho tau antibody that binds with high affinity to phosphorylated amino acid 217 (pT217) in the proline-rich domain. The parent molecule, PT3, was raised against Alzheimer's disease brain purified paired helical filament, and preclinical studies with the humanized version, JNJ-63733657, have demonstrated reductions in tau seeding. The results of the first-in-human clinical trial of JNJ-63733657 and a separate single ascending dose study in Japanese participants are presented.

OBJECTIVES

To evaluate the safety and tolerability, pharmacokinetics, immunogenicity, and pharmacodynamics of JNJ-63733657 after single and multiple intravenous dose administrations in healthy participants and participants with prodromal or mild Alzheimer's disease.

DESIGN

A two part first-in-human, phase 1, randomized, double-blind, placebo-controlled trial: Single ascending dose (Part 1) and multiple ascending dose (Part 2). And a phase 1, randomized, double-blind, placebo-controlled single ascending dose trial in healthy Japanese participants.

SETTING

7 sites in Belgium, Netherlands, Spain, and Germany; 1 site in Japan.

PARTICIPANTS

A total of 40 healthy participants aged 55-75 were enrolled in Part 1 of the first-in-human study; a total of 16 healthy participants and 13 participants with prodromal or mild AD aged 55-80 years were enrolled in Part 2. In the Japanese trial, a total of 24 participants aged 55-75 were enrolled.

INTERVENTION

In Part 1, single doses of 1, 3, 10, 30, or 60 mg/kg of JNJ-63733657 or placebo were administered to healthy participants. In Part 2, two dose levels of JNJ-63733657 (5 mg/kg or 50 mg/kg) or placebo were evaluated in healthy participants, and 2 dose levels (15 mg/kg or 30 mg/kg) or placebo were evaluated in participants with Alzheimer's disease; doses were administered on Days 1, 29, and 57. In the Japanese trial, single doses of 3, 15, or 60 mg/kg of JNJ-63733675 or placebo were administered. All doses were administered intravenously.

MEASUREMENTS

Safety assessments, serum and cerebrospinal fluid pharmacokinetic parameters, immunogenicity, and cerebrospinal fluid pharmacodynamic changes in free and total p217+tau, total tau, and p181tau were evaluated.

RESULTS

JNJ-63733657 was generally safe and well-tolerated in healthy participants and participants with Alzheimer's disease. In healthy participants and participants with Alzheimer's disease, JNJ-63733657 demonstrated linear PK, and serum Cmax and AUC were approximately dose proportional following single and multiple doses. Dose-dependent reductions in free and total p217+tau in cerebrospinal fluid were observed. No changes in total tau or p181tau were observed in healthy participants whereas Alzheimer's disease participants showed decreases in these tau species following administration of JNJ-63733657.

CONCLUSION

In these Phase 1 trials, no safety or tolerability concerns were identified, and dose dependent reductions in p217+tau in the cerebrospinal fluid were demonstrated following administration of JNJ-63733657. The safety and biomarker profiles support the continued investigation of this compound for the slowing of disease progression in Alzheimer's disease.

Phase separation on microtubules: from droplet formation to cellular function?

Microtubules are cytoskeletal polymers that play important roles in numerous cellular processes, ranging from the control of cell shape and polarity to cell division and intracellular transport. Many of these roles rely on proteins that bind to microtubule ends and shafts, carry intrinsically disordered regions, and form complex multivalent interaction networks. A flurry of recent studies demonstrated that these properties allow diverse microtubule-binding proteins to undergo liquid-liquid phase separation (LLPS) in vitro. It is proposed that LLPS could potentially affect multiple microtubule-related processes, such as microtubule nucleation, control of microtubule dynamics and organization, and microtubule-based transport. Here, we discuss the evidence in favor and against the occurrence of LLPS and its functional significance for microtubule-based processes in cells.

Interplay between stochastic enzyme activity and microtubule stability drives detyrosination enrichment on microtubule subsets

Microtubules in cells consist of functionally diverse subpopulations carrying distinct post-translational modifications (PTMs). Akin to the histone code, the tubulin code regulates a myriad of microtubule functions, ranging from intracellular transport to chromosome segregation. However, how individual PTMs only occur on subsets of microtubules to contribute to microtubule specialization is not well understood. In particular, microtubule detyrosination, the removal of the C-terminal tyrosine on α-tubulin subunits, marks the stable population of microtubules and modifies how microtubules interact with other microtubule-associated proteins to regulate a wide range of cellular processes. Previously, we found that in certain cell types, only ∼30% of microtubules are highly enriched with the detyrosination mark and that detyrosination spans most of the length of a microtubule, often adjacent to a completely tyrosinated microtubule. How the activity of a cytosolic detyrosinase, vasohibin (VASH), leads to only a small subpopulation of highly detyrosinated microtubules is unclear. Here, using quantitative super-resolution microscopy, we visualized nascent microtubule detyrosination events in cells consisting of 1-3 detyrosinated α-tubulin subunits after nocodazole washout. Microtubule detyrosination accumulates slowly and in a dispersed pattern across the microtubule length. By visualizing single molecules of VASH in live cells, we found that VASH engages with microtubules stochastically on a short timescale, suggesting limited removal of tyrosine per interaction, consistent with the super-resolution results. Combining these quantitative imaging results with simulations incorporating parameters from our experiments, we provide evidence for a stochastic model for cells to establish a subset of detyrosinated microtubules via a detyrosination-stabilization feedback mechanism.

Oligomeric, phosphorylated, and truncated tau and spliceosome pathology within the entorhinal-hippocampal connectome across stages of Alzheimer's disease

Neurofibrillary tangles (NFTs) contain abnormally phosphorylated tau proteins, which spread within components of the medial temporal lobe (MTL) memory circuit in Alzheimer's disease (AD). Here, we used quantitative immunohistochemistry to determine the density of posttranslational oligomeric (TOC1 and TNT1), phosphorylated (AT8), and late truncated (TauC3) tau epitopes within the MTL subfields including entorhinal cortex (EC) layer II, subiculum, Cornu Ammonis (CA) subfields, and dentate gyrus (DG) in subjects who died with a clinical diagnosis of no cognitive impairment (NCI), mild cognitive impairment (MCI), and AD. We also examined whether alterations of the nuclear alternative splicing protein, SRSF2, are associated with tau pathology. Although a significant increase in TOC1, TNT1, and AT8 neuron density occurred in the EC in MCI and AD, subicular, DG granule cell, and CA1 and CA3 densities were only significantly higher in AD. TauC3 counts were not different between connectome regions and clinical groups. SRSF2 intensity in AT8-positive cells decreased significantly in all regions independent of the clinical groups examined. CA1 and subicular AT8, TauC3, and oligomeric densities correlated across clinical groups. EC AT8 counts correlated with CA subfields and subicular and DG values across clinical groups. Oligomeric and AT8 CA1, EC, and subicular density correlated with Braak stage. Decreased nuclear SRSF2 in the presence of cytoplasmic phosphorylated tau suggests a dual-hit process in NFT formation within the entorhinal hippocampal connectome during the onset of AD. Although oligomeric and phosphorylated tau follow a stereotypical pattern, clinical disease stage determined density of tau deposition and not anatomic location within the entorhinal-hippocampal connectome.

Tau forms synaptic nano-biomolecular condensates controlling the dynamic clustering of recycling synaptic vesicles

Neuronal communication relies on the release of neurotransmitters from various populations of synaptic vesicles. Despite displaying vastly different release probabilities and mobilities, the reserve and recycling pool of vesicles co-exist within a single cluster suggesting that small synaptic biomolecular condensates could regulate their nanoscale distribution. Here, we performed a large-scale activity-dependent phosphoproteome analysis of hippocampal neurons in vitro and identified Tau as a highly phosphorylated and disordered candidate protein. Single-molecule super-resolution microscopy revealed that Tau undergoes liquid-liquid phase separation to generate presynaptic nanoclusters whose density and number are regulated by activity. This activity-dependent diffusion process allows Tau to translocate into the presynapse where it forms biomolecular condensates, to selectively control the mobility of recycling vesicles. Tau, therefore, forms presynaptic nano-biomolecular condensates that regulate the nanoscale organization of synaptic vesicles in an activity-dependent manner.

Proteostasis and neurodegeneration: a closer look at autophagy in Alzheimer's disease

Alzheimer's disease (AD) is characterized by the accumulation of misfolded amyloid-beta and tau proteins. Autophagy acts as a proteostasis process to remove protein clumps, although it progressively weakens with aging and AD, thus facilitating the accumulation of toxic proteins and causing neurodegeneration. This review examines the impact of impaired autophagy on the progression of AD disease pathology. Under normal circumstances, autophagy removes abnormal proteins and damaged organelles, but any dysfunction in this process can lead to the exacerbation of amyloid and tau pathology, particularly in AD. There is increasing attention to therapeutic tactics to revitalize autophagy, including reduced caloric intake, autophagy-stimulating drugs, and genetic therapy. However, the translation of these strategies into clinical practice faces several hurdles. In summary, this review integrates the understanding of the intricate role of autophagy dysfunction in Alzheimer's disease progression and reinforces the promising prospects of autophagy as a beneficial target for treatments to modify the course of Alzheimer's disease.

Untangling Tau: Molecular Insights into Neuroinflammation, Pathophysiology, and Emerging Immunotherapies

Neuroinflammation, a core pathological feature observed in several neurodegenerative diseases, including Alzheimer's disease (AD), is rapidly gaining attention as a target in understanding the molecular underpinnings of these disorders. Glial cells, endothelial cells, peripheral immune cells, and astrocytes produce a variety of pro-inflammatory mediators that exacerbate the disease progression. Additionally, microglial cells play a complex role in AD, facilitating the clearance of pathological amyloid-beta peptide (Aβ) plaques and aggregates of the tau protein. Tau proteins, traditionally associated with microtubule stabilization, have come under intense scrutiny for their perturbed roles in neurodegenerative conditions. In this narrative review, we focus on recent advances from molecular insights that have revealed aberrant tau post-translational modifications, such as phosphorylation and acetylation, serving as pathological hallmarks. These modifications also trigger the activation of CNS-resident immune cells, such as microglia and astrocytes substantially contributing to neuroinflammation. This intricate relationship between tau pathologies and neuroinflammation fosters a cascading impact on neural pathophysiology. Furthermore, understanding the molecular mechanisms underpinning tau's influence on neuroinflammation presents a frontier for the development of innovative immunotherapies. Neurodegenerative diseases have been relatively intractable to conventional pharmacology using small molecules. We further comprehensively document the many alternative approaches using immunotherapy targeting tau pathological epitopes and structures with a wide array of antibodies. Clinical trials are discussed using these therapeutic approaches, which have both promising and disappointing outcomes. Future directions for tau immunotherapies may include combining treatments with Aβ immunotherapy, which may result in more significant clinical outcomes for neurodegenerative diseases.

Aggregation, Transmission, and Toxicity of the Microtubule-Associated Protein Tau: A Complex Comprehension

The microtubule-associated protein tau is an intrinsically disordered protein containing a few short and transient secondary structures. Tau physiologically associates with microtubules (MTs) for its stabilization and detaches from MTs to regulate its dynamics. Under pathological conditions, tau is abnormally modified, detaches from MTs, and forms protein aggregates in neuronal and glial cells. Tau protein aggregates can be found in a number of devastating neurodegenerative diseases known as "tauopathies", such as Alzheimer's disease (AD), frontotemporal dementia (FTD), corticobasal degeneration (CBD), etc. However, it is still unclear how the tau protein is compacted into ordered protein aggregates, and the toxicity of the aggregates is still debated. Fortunately, there has been considerable progress in the study of tau in recent years, particularly in the understanding of the intercellular transmission of pathological tau species, the structure of tau aggregates, and the conformational change events in the tau polymerization process. In this review, we summarize the concepts of tau protein aggregation and discuss the views on tau protein transmission and toxicity.

Zn2+ decoration of microtubules arrests axonal transport and displaces tau, doublecortin, and MAP2C

Intracellular Zn2+ concentrations increase via depolarization-mediated influx or intracellular release, but the immediate effects of Zn2+ signals on neuron function are not fully understood. By simultaneous recording of cytosolic Zn2+ and organelle motility, we find that elevated Zn2+ (IC50 ≈ 5-10 nM) reduces both lysosomal and mitochondrial motility in primary rat hippocampal neurons and HeLa cells. Using live-cell confocal microscopy and in vitro single-molecule TIRF imaging, we reveal that Zn2+ inhibits activity of motor proteins (kinesin and dynein) without disrupting their microtubule binding. Instead, Zn2+ directly binds to microtubules and selectively promotes detachment of tau, DCX, and MAP2C, but not MAP1B, MAP4, MAP7, MAP9, or p150glued. Bioinformatic predictions and structural modeling show that the Zn2+ binding sites on microtubules partially overlap with the microtubule binding sites of tau, DCX, dynein, and kinesin. Our results reveal that intraneuronal Zn2+ regulates axonal transport and microtubule-based processes by interacting with microtubules.

Super-resolution imaging unveils the self-replication of tau aggregates upon seeding

Tau is a soluble protein interacting with tubulin to stabilize microtubules. However, under pathological conditions, it becomes hyperphosphorylated and aggregates, a process that can be induced by treating cells with exogenously added tau fibrils. Here, we employ single-molecule localization microscopy to resolve the aggregate species formed in early stages of seeded tau aggregation. We report that entry of sufficient tau assemblies into the cytosol induces the self-replication of small tau aggregates, with a doubling time of 5 h inside HEK cells and 1 day in murine primary neurons, which then grow into fibrils. Seeding occurs in the vicinity of the microtubule cytoskeleton, is accelerated by the proteasome, and results in release of small assemblies into the media. In the absence of seeding, cells still spontaneously form small aggregates at lower levels. Overall, our work provides a quantitative picture of the early stages of templated seeded tau aggregation in cells.

ECLiPSE: A Versatile Classification Technique for Structural and Morphological Analysis of Super-Resolution Microscopy Data

We introduce a new automated machine learning analysis pipeline to precisely classify cellular structures captured through single molecule localization microscopy, which we call ECLiPSE (Enhanced Classification of Localized Pointclouds by Shape Extraction). ECLiPSE leverages 67 comprehensive shape descriptors encompassing geometric, boundary, skeleton and other properties, the majority of which are directly extracted from the localizations to accurately characterize individual structures. We validate ECLiPSE through unsupervised and supervised classification on a dataset featuring five distinct cellular structures, achieving exceptionally high classification accuracies nearing 100%. Moreover, we demonstrate the versatility of our approach by applying it to two novel biological applications: quantifying the clearance of tau protein aggregates, a critical marker for neurodegenerative diseases, and differentiating between two distinct morphological features (morphotypes) of TAR DNA-binding protein 43 proteinopathy, potentially associated to different TDP-43 strains, each exhibiting unique seeding and spreading properties. We anticipate that this versatile approach will significantly enhance the way we study cellular structures across various biological contexts, elucidating their roles in disease development and progression.

Quantitative Single-Molecule Localization Microscopy

Super-resolution fluorescence microscopy allows the investigation of cellular structures at nanoscale resolution using light. Current developments in super-resolution microscopy have focused on reliable quantification of the underlying biological data. In this review, we first describe the basic principles of super-resolution microscopy techniques such as stimulated emission depletion (STED) microscopy and single-molecule localization microscopy (SMLM), and then give a broad overview of methodological developments to quantify super-resolution data, particularly those geared toward SMLM data. We cover commonly used techniques such as spatial point pattern analysis, colocalization, and protein copy number quantification but also describe more advanced techniques such as structural modeling, single-particle tracking, and biosensing. Finally, we provide an outlook on exciting new research directions to which quantitative super-resolution microscopy might be applied.

Neurobiochemical, Peptidomic, and Bioinformatic Approaches to Characterize Tauopathy Peptidome Biomarker Candidates in Experimental Mouse Model of Traumatic Brain Injury

Traumatic brain injury (TBI) is a multidimensional damage, and currently, no FDA-approved medicine is available. Multiple pathways in the cell are triggered through a head injury (e.g., calpain and caspase activation), which truncate tau and generate variable fragment sizes (MW 400-45,000 K). In this study, we used an open-head TBI mouse model generated by controlled cortical impact (CCI) and collected ipsilateral (IC) and contralateral (CC) mice htau brain cortices at one (D1) three (D3), and seven (D7) days post-injury. We implemented immunological (antibody-based detection) and peptidomic approaches (nano-reversed-phase liquid chromatography/tandem mass spectrometry) to investigate proteolytic tau peptidome (low molecular weight (LMW) < 10 K)) and pathological phosphorylation sites (high-molecular-weight (HMW); > 10 K) derived from CCI-TBI animal models. Our immunoblotting analysis verified tau hyperphosphorylation, HMW, and HMW breakdown products (HMW-BDP) formation of tau (e.g., pSer₂₀₂, pThr₁₈₁, pThr₂₃₁, pSer₃₉₆, and pSer₄₀₄), following CCI-TBI. Peptidomic data revealed unique sequences of injury-dependent proteolytic peptides generated from human tau protein. Among the N-terminal tau peptides, EIPEGTTAEEAGIGDTPSLEDEAAGHVTQA (a.a. 96-125) and AQPHTEIPEGTTAEEAGIGDTPSLEDEAAGHVTQARM (a.a. 91-127). Examples of tau C-terminal peptides identified include NVSSTGSIDMVDSPQLATLADEVSASLAKQGL (a.a. 410-441) and QLATLADEVSASLAKQGL (a.a. 424-441). Our peptidomic bioinformatic tools showed the association of proteases, such as CAPN1, CAPN2, and CTSL; CASP1, MMP7, and MMP9; and ELANE, GZMA, and MEP1A, in CCI-TBI tau peptidome. In clinical trials for novel TBI treatments, it might be useful to monitor a subset of tau peptidome as targets for biomarker utility and use them for a "theranostic" approach.

Hyperphosphorylated tau (p-tau) and drug discovery in the context of Alzheimer's disease and related tauopathies

Alzheimer's disease (AD) is the most common form of dementia, characterized by intracellular neurofibrillary tangles (NFTs) and extracellular β-amyloid (βA) plaques. No disease-modifying therapy is currently available to prevent the progression of, or cure, the disease. Misfolded hyperphosphorylated tau (p-tau) is considered a pivotal point in the pathogenesis of AD and other tauopathies. Compelling evidence suggests that it is a key driver of the accumulation of NFTs and can be directly correlated with the extent of dementia in patients with AD. Therefore, inhibiting tau hyperphosphorylation-induced aggregation could be a viable strategy to discover and develop therapeutics for patients with AD.

Myo19 tethers mitochondria to endoplasmic reticulum-associated actin to promote mitochondrial fission

Mitochondrial homeostasis requires a dynamic balance of fission and fusion. The actin cytoskeleton promotes fission, and we found that the mitochondrially localized myosin, myosin 19 (Myo19), is integral to this process. Myo19 knockdown induced mitochondrial elongation, whereas Myo19 overexpression induced fragmentation. This mitochondrial fragmentation was blocked by a Myo19 mutation predicted to inhibit ATPase activity and strong actin binding but not by mutations predicted to affect the working stroke of the motor that preserve ATPase activity. Super-resolution imaging indicated a dispersed localization of Myo19 on mitochondria, which we found to be dependent on metaxins. These observations suggest that Myo19 acts as a dynamic actin-binding tether that facilitates mitochondrial fragmentation. Myo19-driven fragmentation was blocked by depletion of either the CAAX splice variant of the endoplasmic reticulum (ER)-anchored formin INF2 or the mitochondrially localized F-actin nucleator Spire1C (a splice variant of Spire1), which together polymerize actin at sites of mitochondria-ER contact for fission. These observations imply that Myo19 promotes fission by stabilizing mitochondria-ER contacts; we used a split-luciferase system to demonstrate a reduction in these contacts following Myo19 depletion. Our data support a model in which Myo19 tethers mitochondria to ER-associated actin to promote mitochondrial fission.

Cholesterol in the cargo membrane amplifies tau inhibition of kinesin-1-based transport

Intracellular cargos are often membrane-enclosed and transported by microtubule-based motors in the presence of microtubule-associated proteins (MAPs). Whereas increasing evidence reveals how MAPs impact the interactions between motors and microtubules, critical questions remain about the impact of the cargo membrane on transport. Here we combined in vitro optical trapping with theoretical approaches to determine the effect of a lipid cargo membrane on kinesin-based transport in the presence of MAP tau. Our results demonstrate that attaching kinesin to a fluid lipid membrane reduces the inhibitory effect of tau on kinesin. Moreover, adding cholesterol, which reduces kinesin diffusion in the cargo membrane, amplifies the inhibitory effect of tau on kinesin binding in a dosage-dependent manner. We propose that reduction of kinesin diffusion in the cargo membrane underlies the effect of cholesterol on kinesin binding in the presence of tau, and we provide a simple model for this proposed mechanism. Our study establishes a direct link between cargo membrane cholesterol and MAP-based regulation of kinesin-1. The cholesterol effects uncovered here may more broadly extend to other lipid alterations that impact motor diffusion in the cargo membrane, including those associated with aging and neurological diseases.

Discovery of Novel Acridane-Based Tubulin Polymerization Inhibitors with Anticancer and Potential Immunomodulatory Effects

A series of novel acridane-based tubulin polymerization inhibitors were designed, synthesized, and bioevaluated as anticancer agents. The most potent compound NT-6 exhibited high tubulin polymerization inhibitory activity (IC50 = 1.5 μM) and remarkable antiproliferative potency against four cancer cell lines with an average IC50 of 30 nM, better than colchicine and the hit compound 1f (IC50 of 65 and 126 nM, respectively). In addition, NT-6 (10 mg/kg) exerted excellent antitumor efficacy in a melanoma tumor model with a tumor growth inhibition (TGI) of 65.1% without apparent toxicity. Importantly, the combination of NT-6 with a small-molecule PD-L1 inhibitor NP-19 decreased tumor burden significantly (TGI% = 77.6%). Moreover, the combination of NT-6 with NP-19 enhanced the antitumor immune response, mediated by a decrease of PD-L1 expression levels and increased infiltration of antitumor CD8+ effector T cells in tumor tissues. Collectively, NT-6 represents a novel tubulin polymerization inhibitor with immunopotentiating effects.

Sequence-Dependent Conformational Properties of PGGG Motif in Tau Repeats: Insights from Molecular Dynamics Simulations of Narrow Pick Filament

Tauopathies are a class of neurodegenerative diseases correlated with the presence of pathological Tau fibrils as a diagnostic marker. The microtubule-binding repeat region of Tau protein, which includes R1, R2, R3, and R4 repeats, constitutes the core of these fibrils. Each repeat consists of a semiconserved C-terminal hexapeptide flanked by KxGS and PGGG motifs. Previous studies have shown the influence of these peptides on protein aggregation, yet their repeat-specific properties are less explored. Using molecular dynamics, we probed the sequence-specific influence of the C-terminal hexapeptide (²⁶⁴ENLKHQ²⁶⁹) in determining the compact local conformation of the R1 repeat of the narrow Pick filament (NPF) with a homologous E264G mutation. In addition to that, we also studied the influence of ²⁶²S phosphorylation on this conformation as the phosphorylation is proposed to alleviate the pathogenesis of Pick's disease. Interestingly, we determined that E264G mutation induces a conformational shift of ²⁷⁰PGGG²⁷³ from a turn to a random coil. This conformational dependence is experimentally verified with the R1R3-E264G mutant construct, which displayed accelerated aggregation compared with the R1R3 wild-type construct. A significant delay in aggregation of the R1R3-G326E mutant further demonstrates the importance of ³²⁶G in determining the conformation of the R3 repeat. Thus, we conclude that the conformational properties of the PGGG motif in Tau repeats are strongly dependent on the repeat-specific sequence of the C-terminal hexapeptide.

Oligomerization by co-assembly of β-amyloid and α-synuclein

Aberrant self-assembly of an intrinsically disordered protein is a pathological hallmark of protein misfolding diseases, such as Alzheimer's and Parkinson's diseases (AD and PD, respectively). In AD, the 40-42 amino acid-long extracellular peptide, β-amyloid (Aβ), self-assembles into oligomers, which eventually aggregate into fibrils. A similar self-association of the 140 amino acid-long intracellular protein, α-synuclein (αS), is responsible for the onset of PD pathology. While Aβ and αS are primarily extracellular and intracellular polypeptides, respectively, there is evidence of their colocalization and pathological overlaps of AD and PD. This evidence has raised the likelihood of synergistic, toxic protein-protein interactions between Aβ and αS. This mini review summarizes the findings of studies on Aβ-αS interactions related to enhanced oligomerization via co-assembly, aiming to provide a better understanding of the complex biology behind AD and PD and common pathological mechanisms among the major neurodegenerative diseases.

The N-terminal disease-associated R5L Tau mutation increases microtubule shrinkage rate due to disruption of microtubule-bound Tau patches

Regulation of the neuronal microtubule cytoskeleton is achieved through the coordination of microtubule-associated proteins (MAPs). MAP-Tau, the most abundant MAP in the axon, functions to modulate motor motility, participate in signaling cascades, as well as directly mediate microtubule dynamics. Tau misregulation is associated with a class of neurodegenerative diseases, known as tauopathies, including progressive supranuclear palsy, Pick's disease, and Alzheimer's disease. Many disease-associated mutations in Tau are found in the C-terminal microtubule-binding domain. These mutations decrease microtubule-binding affinity and are proposed to reduce microtubule stability, leading to disease. N-terminal disease-associated mutations also exist, but the mechanistic details of their downstream effects are not as clear. Here, we investigate the effect of the progressive supranuclear palsy–associated N-terminal R5L mutation on Tau-mediated microtubule dynamics using an in vitro reconstituted system. We show that the R5L mutation does not alter Tau interactions with tubulin by fluorescence correlation spectroscopy. Using total internal reflection fluorescence microscopy, we determined that the R5L mutation has no effect on microtubule growth rate, catastrophe frequency, or rescue frequency. Rather, the R5L mutation increases microtubule shrinkage rate. We determine this is due to disruption of Tau patches, larger order Tau complexes known to form on the GDP-microtubule lattice. Altogether, these results provide insight into the role of Tau patches in mediating microtubule dynamics and suggesting a novel mechanism by which mutations in the N-terminal projection domain reduce microtubule stability.

Single-molecule imaging reveals Tau trapping at nanometer-sized dynamic hot spots near the plasma membrane that persists after microtubule perturbation and cholesterol depletion

Accumulation of aggregates of the microtubule‐binding protein Tau is a pathological hallmark of Alzheimer's disease. While Tau is thought to primarily associate with microtubules, it also interacts with and localizes to the plasma membrane. However, little is known about how Tau behaves and organizes at the plasma membrane of live cells. Using quantitative, single‐molecule imaging, we show that Tau exhibits spatial and kinetic heterogeneity near the plasma membrane of live cells, resulting in the formation of nanometer‐sized hot spots. The hot spots lasted tens of seconds, much longer than the short dwell time (∼ 40 ms) of Tau on microtubules. Pharmacological and biochemical disruption of Tau/microtubule interactions did not prevent hot spot formation, suggesting that these are different from the reported Tau condensation on microtubules. Although cholesterol removal has been shown to reduce Tau pathology, its acute depletion did not affect Tau hot spot dynamics. Our study identifies an intrinsic dynamic property of Tau near the plasma membrane that may facilitate the formation of assembly sites for Tau to assume its physiological and pathological functions.