Assembly Of Tau Research Articles

Essential tremor with tau pathology features seeds indistinguishable in conformation from Alzheimer's disease and primary age-related tauopathy.

Neurodegenerative tauopathies are characterized by the deposition of distinct fibrillar tau assemblies whose rigid core structures correlate with defined neuropathological phenotypes. Essential tremor (ET) is a progressive neurological disease that, in some cases, is associated with cognitive impairment and tau accumulation. Consequently, we explored the tau assembly conformation in ET patients with tau pathology using cytometry-based tau biosensor assays. These assays quantify tau prion seeding activity present in brain homogenates based on conversion of intracellular tau-fluorescent protein fusions from a soluble to an aggregated state. Prions exhibit seeding barriers, whereby a specific assembly structure cannot serve as a template for a native monomer if the amino acids are not compatible. We recently exploited the tau prion species barrier to define tauopathies by systematically substituting alanine (Ala) in the tau monomer and measuring its incorporation into seeded aggregates within biosensor cells. The Ala scan precisely classified the conformation of tau seeds from diverse tauopathies. We next studied 18 ET patient brains with tau pathology. Only one case had concurrent high amyloid-β plaque pathology consistent with Alzheimer's disease (AD). We detected robust tau seeding activity in 9 (50%) of the patients. This predominantly localized to the temporal pole and temporal cortex. We examined 8 ET cases with the Ala scan and determined that the amino acid requirements for tau monomer incorporation into aggregates seeded from these ET brain homogenates were identical to those of AD and primary age-related tauopathy (PART), and completely distinct from other tauopathies such as corticobasal degeneration, chronic traumatic encephalopathy, and progressive supranuclear palsy. Based on these studies, tau assembly cores in a pathologically confined subset of ET cases with high tau pathology are identical to AD and PART. This could facilitate more precise diagnosis and therapy for ET patients with cognitive impairment.

Co-opting templated aggregation to degrade pathogenic tau assemblies and improve motor function

Protein aggregation causes a wide range of neurodegenerative diseases. Targeting and removing aggregates, but not the functional protein, is a considerable therapeutic challenge. Here, we describe a therapeutic strategy called "RING-Bait," which employs an aggregating protein sequence combined with an E3 ubiquitin ligase. RING-Bait is recruited into aggregates, whereupon clustering dimerizes the RING domain and activates its E3 function, resulting in the degradation of the aggregate complex. We exemplify this concept by demonstrating the specific degradation of tau aggregates while sparing soluble tau. Unlike immunotherapy, RING-Bait is effective against both seeded and cell-autonomous aggregation. RING-Bait removed tau aggregates seeded from Alzheimer's disease (AD) and progressive supranuclear palsy (PSP) brain extracts and was also effective in primary neurons. We used a brain-penetrant adeno-associated virus (AAV) to treat P301S tau transgenic mice, reducing tau pathology and improving motor function. A RING-Bait strategy could be applied to other neurodegenerative proteinopathies by replacing the Bait sequence to match the target aggregate.

Novel tau filament folds in individuals with MAPT mutations P301L and P301T.

Mutations in MAPT, the microtubule-associated protein tau gene, give rise to cases of frontotemporal dementia and parkinsonism linked to chromosome 17 (FTDP-17) with abundant filamentous tau inclusions in brain cells. Individuals with pathological MAPT variants exhibit behavioural changes, cognitive impairment and signs of parkinsonism. Missense mutations of residue P301, which are the most common MAPT mutations associated with FTDP-17, give rise to the assembly of mutant four-repeat tau into filamentous inclusions, in the absence of extracellular deposits. Here we report the cryo-EM structures of tau filaments from five individuals belonging to three unrelated families with mutation P301L and from one individual belonging to a family with mutation P301T. A novel three-lobed tau fold resembling the two-layered tau fold of Pick's disease was present in all cases with the P301L tau mutation. Two different tau folds were found in the case with mutation P301T, the less abundant of which was a variant of the three-lobed fold. The major P301T tau fold was V-shaped, with partial similarity to the four-layered tau folds of corticobasal degeneration and argyrophilic grain disease. These findings suggest that FTDP-17 with mutations in P301 should be considered distinct inherited tauopathies and that model systems with these mutations should be used with caution in the study of sporadic tauopathies.

Triggering Tau Fibrillization by Electroreduction: A New Tool for Studying Amyloid Diseases

The pathological aggregation of the microtubule-associated protein tau is a hallmark of various neurodegenerative disorders, including Alzheimer’s disease (AD), Pick’s disease and frontotemporal dementia. Tau protein’s reversible assembly and binding to microtubules in brain neurons are regulated by charge-neutralizing phosphorylation. Hyperphosphorylation, on the other hand, leads to irreversible formation of cytotoxic filaments. Under physiological conditions, tau remains remarkably stable, exhibiting intrinsically disordered behavior and reversible assembly. Irreversible aggregation requires specific mutations, preformed seeds or nucleating polyanionic cofactors. However, heparin-induced fibrils differ structurally from brain-derived filaments, and the presence of such cofactors can impede therapeutic agent development. We have developed a quick and easy method to generate cofactor-free filaments using heterogeneous electroreduction as a surrogate for charge-neutralization by hyperphosphorylation. We combine electrochemistry with in situ UV absorbance, circular dichroism and dynamic light scattering spectroscopies to dynamically follow tau’s conformational changes and assembly. Electroreduction of positively charged residues of the protein leads to rapid formation of b-rich structures, even at times as short as 15 minutes. The extent of assembly can be controlled by fine-tuning electroreductive potentials and electrolyte conditions. Relevance of this new method was confirmed by examining the impact of an early-onset AD-causing tau mutant and known inhibitors on aggregation kinetics. Our results demonstrate comparable effects to heparin-induced fibrils, as assessed by thioflavin-T fluorescence, dynamic light scattering, circular dichroism and electron microscopy. Low-voltage electroreduction provides a platform to study the effects of tau mutations and effectors, as well as to develop rapid assays to test how additional effectors may inhibit, disassemble or direct the trajectory of tau assembly. The versatility of our approach also suggests its potential applicability to a broader spectrum of neurodegenerative amyloid diseases.

Interaction of full-length Tau with negatively charged lipid membranes leads to polymorphic aggregates.

The Tau protein is implicated in various diseases collectively known as tauopathies, including Alzheimer's disease and frontotemporal dementia. The precise mechanism underlying Tau pathogenicity remains elusive. Recently, the role of lipids has garnered interest due to their implications in Tau aggregation, secretion, uptake, and pathogenic dysregulation. Previous investigations have highlighted critical aspects: (i) Tau's tendency to aggregate into fibers when interacting with negatively charged lipids, (ii) its ability to form structured species upon contact with anionic membranes, and (iii) the potential disruption of the membrane upon Tau binding. In this study, we examine the disease-associated P301L mutation of the 2N4R isoform of Tau and its effects on membranes composed on phosphatidylserine (PS) lipids. Aggregation studies and liposome leakage assays demonstrate Tau's ability to bind to anionic lipid vesicles, leading to membrane disruption. Attenuated total reflection Fourier-transform infrared spectroscopy (ATR-FTIR) reveals the accumulation of Tau on the membrane surface without protein insertion, structuration, or lipid removal. Plasmon waveguide resonance (PWR) demonstrates a strong binding of Tau on PS bilayers with an apparent Kd in the micromolar range, indicating the deposition of a thick protein layer. Atomic force microscopy (AFM) real-time imaging allows the observation of partial lipid solubilization and the deposition of polymorphic aggregates in the form of thick patches and fibrillary structures resembling amyloid fibers, which could grow from a combination of extracted anionic phospholipids from the membrane and Tau protein. This study deepens our understanding of full-length Tau's multifaceted interactions with lipids, shedding light on potential mechanisms leading to the formation of pathogenic Tau assemblies.

Tau and neurodegeneration.

First identified in 1975, tau was implicated in Alzheimer's disease 10 years later. Filamentous tangle inclusions were known to be made of hyperphosphorylated tau by 1991, with similar inclusions gaining recognition for being associated with other neurodegenerative diseases. In 1998, mutations in MAPT, the gene that encodes tau, were identified as the cause of a dominantly inherited form of frontotemporal dementia with abundant filamentous tau inclusions. While this result indicated that assembly of tau into aberrant filaments is sufficient to drive neurodegeneration and dementia, most cases of tauopathy are sporadic. More recent work in experimental systems showed that filamentous assemblies of tau may first form in one brain area, and then spread to others in a prion-like fashion. Beginning in 2017, work on human brains using high-resolution techniques has led to a structure-based classification of tauopathies, which has opened the door to a better understanding of the significance of tau filament formation.

Tau seeding without tauopathy

Neurodegenerative tauopathies such as Alzheimer’s disease (AD) are caused by brain accumulation of tau assemblies. Evidence suggests tau functions as a prion, and cells and animals efficiently propagate unique, transmissible tau pathology. This suggests a dedicated cellular replication machinery, potentially with a normal physiologic function for tau seeds. Consequently, we hypothesized that healthy control brains would have seeding activity. We have recently developed a novel monoclonal antibody (MD3.1) specific for tau seeds. We used this antibody to immunopurify tau from the parietal and cerebellar cortices of 19 healthy subjects without any neuropathology, ranging 19-65 years. We detected seeding in lysates from the parietal cortex, but not in the cerebellum. We also detected no seeding in brain homogenates from wild-type or human tau knockin mice, suggesting that cellular/genetic context dictates development of seed-competent tau. Seeding did not correlate with subject age or brain tau levels. We confirmed our essential findings using an orthogonal assay, RTQuIC, which amplifies tau seeds in vitro. Dot blot analyses revealed no AT8 immunoreactivity above background levels in parietal and cerebellar extracts and ∼1/100 of that present in AD. Based on binding to a panel of antibodies, the conformational characteristics of control seeds differed from AD, suggesting a unique underlying assembly, or structural ensemble. Tau’s ability to adopt self-replicating conformations under non-pathogenic conditions may reflect a normal function that goes awry in disease states.

Disease-Associated Mutations in Tau Encode for Changes in Aggregate Structure Conformation.

The accumulation of tau fibrils is associated with neurodegenerative diseases, which are collectively termed tauopathies. Cryo-EM studies have shown that the packed fibril core of tau adopts distinct structures in different tauopathies, such as Alzheimer's disease, corticobasal degeneration, and progressive supranuclear palsy. A subset of tauopathies are linked to missense mutations in the tau protein, but it is not clear whether these mutations impact the structure of tau fibrils. To answer this question, we developed a high-throughput protein purification platform and purified a panel of 37 tau variants using the full-length 0N4R splice isoform. Each of these variants was used to create fibrils in vitro, and their relative structures were studied using a high-throughput protease sensitivity platform. We find that a subset of the disease-associated mutations form fibrils that resemble wild-type tau, while others are strikingly different. The impact of mutations on tau structure was not clearly associated with either the location of the mutation or the relative kinetics of fibril assembly, suggesting that tau mutations alter the packed core structures through a complex molecular mechanism. Together, these studies show that single-point mutations can impact the assembly of tau into fibrils, providing insight into its association with pathology and disease.

Amyloid beta and tau pathology compared within different Alzheimer’s disease mouse models after inoculation with Alzheimer’s disease brain tissue

AbstractBackgroundAlzheimer’s disease (AD), the leading cause of dementia worldwide, is associated with two proteins known as amyloid beta (Aβ) and tau. Both proteins are thought to have prion‐like properties, resulting in the seeded propagation and spread of disease‐related assemblies. We have investigated three different AD knock‐in mouse models containing humanised versions of Aβ and tau to further our understanding of how AD progresses after the inoculation of Aβ/tau assemblies or seeds. These transmissions would also aid in deciphering the prion‐like properties of both Aβ and tau. These included the APPNL‐F/NL‐F model, which contains a Swedish and Iberian mutation (NL‐F) in the amyloid precursor protein (APP), expressing elevated levels of human Aβ42, and the human (h)TauKI/KI model, which contains all six human isoforms of human tau. Moreover, the AppNL‐F/NL‐F/hTauKI/KI mouse model expresses both human tau and human Aβ42, allowing a side‐to‐side comparison of all three models to provide an informative insight into the best model to study Aβ and tau pathology after inoculation with AD cases.MethodWe previously characterised three AD cases for prion‐like properties, in terms of protease resistance and conformational stability, and inoculated each of the cases into the different AD mouse models. Aβ and tau seeding was determined via histological and western blot analysis, via probing for 82E1 and AT8, to determine the presence of human Aβ and phosphorylated tau respectively.ResultUsing transmission studies, significant differences were seen for Aβ and tau seeding within the APPNL‐F/NL‐F, human (h)TauKI/KI and AppNL‐F/NL‐F/hTauKI/KI mouse models. We show that the AppNL‐F/NL‐F/hTauKI/KI mouse model demonstrates both Aβ and tau seeding from the inoculation of AD cases at earlier time points compared to its retrospective APPNL‐F/NL‐F and hTauKI/KI mouse models in vivo.ConclusionAfter comparing the three different mouse models, our data suggests that the AppNL‐F/NL‐F/hTauKI/KI mouse model may be a superior model for studying prion‐like behaviour and the role of Aβ and tau assemblies within AD. With regards to future characterisation of possible Aβ and tau strains, we anticipate that this model will be able to distinguish any potential strains indicated from serial passages in vivo using the AppNL‐F/NL‐F/hTauKI/KI model.

Immunotherapy against tau pathology in mouse models requires cytosolic Fc receptor TRIM21

AbstractBackgroundThe passive transfer of monoclonal antibodies reduces tau pathology in mouse models and is under evaluation as a potential immunotherapeutic strategy against Alzheimer’s disease and other tauopathies. The mechanisms that drive therapeutic protection of anti‐tau antibodies are not well understood.MethodP301S tau transgenic animals were treated with antibodies against pS422 and analysed for tau pathology by biochemical fractionation. Organotypic hippocampal slice cultures were used as a model of tau seeding and neutralisation. AAV serotypes were used to deliver tau‐selective degraders.ResultGenetic deletion of the cytosolic antibody receptor and E3 ubiquitin ligase TRIM21 rendered tau immunotherapy ineffective in animal models. In organotypic slices, expression of TRIM21 was essential for protection against seeded aggregation of tau. Cytosolic antibody‐tau complexes were visible inside neurons in complex with TRIM21 shortly after application of tau assemblies and antibodies to the cell exterior. Nanobody‐based degraders were developed using TRIM21 and found to protect against tau pathology.ConclusionAnti‐tau antibodies can engage extracellular tau seeds and enter neurons as a complex. Following cytosolic entry, TRIM21 engages the antibodies and mediates neutralisation of tau seeding activity. The results reveal a mechanism that can be optimised for future immunotherapeutics. In this direction, AAV‐delivered degraders reveal a route by which tau aggregates may be selectively removed from the brain.

Travels with tau prions.

Tau was originally identified as a microtubule associated protein, and subsequently recognized to constitute the fibrillar assemblies found in Alzheimer disease and related neurodegenerative tauopathies. Point mutations in the microtubule associated protein tau (MAPT) gene cause dominantly inherited tauopathies, and most predispose it to aggregate. This indicates tau aggregation underlies pathogenesis of tauopathies. Our work has suggested that tau functions as a prion, forming unique intracellular pathological assemblies that subsequently move to other cells, inducing further aggregation that underlies disease progression. Remarkably, in simple cells tau forms stably propagating aggregates of distinct conformation, termed strains. Each strain induces a unique and, in some cases, transmissible, neuropathological phenotype upon inoculation into a mouse model. After binding heparan sulfate proteoglycans on the plasma membrane, tau assemblies enter cells via macropinocytosis. From within a vesicle, if not trafficked to the endolysosomal system, tau subsequently enters the cytoplasm, where it becomes a template for its own replication, apparently after processing by valosin containing protein. The smallest seed unit is a stable monomer, which suggests that initial folding events in tau presage subsequent pathological aggregation. The study of tau prions has raised important questions about basic cell biological processes that underlie their replication and propagation, with implications for therapy of tauopathies.

Molecular pathology of neurodegenerative diseases by cryo-EM of amyloids.

Abnormal assembly of tau, α-synuclein, TDP-43 and amyloid-β proteins into amyloid filaments defines most human neurodegenerative diseases. Genetics provides a direct link between filament formation and the causes of disease. Developments in cryo-electron microscopy (cryo-EM) have made it possible to determine the atomic structures of amyloids from postmortem human brains. Here we review the structures of brain-derived amyloid filaments that have been determined so far and discuss their impact on research into neurodegeneration. Whereas a given protein can adopt many different filament structures, specific amyloid folds define distinct diseases. Amyloid structures thus provide a description of neuropathology at the atomic level and a basis for studying disease. Future research should focus on model systems that replicate the structures observed in disease to better understand the molecular mechanisms of disease and develop improved diagnostics and therapies.

Amyloid fibril structures of tau: Conformational plasticity of the second microtubule-binding repeat.

The intrinsically disordered protein tau associates with microtubules in neurons but aggregates into cross-β amyloid fibrils that propagate in neurodegenerative brains. Different tauopathies have different structures for the rigid fibril core. To understand the molecular basis of tau assembly into different polymorphs, here we use solid-state nuclear magnetic resonance (NMR) spectroscopy to determine the structure of a tau protein that includes all microtubule-binding repeats and a proline-rich domain. This P2R tau assembles into well-ordered filaments when induced by heparin. Two- and three-dimensional NMR spectra indicate that R2 and R3 repeats constitute the rigid β-sheet core of the fibril. Unexpectedly, the amino-terminal half of R2 forms a β-arch at ambient temperature (24°C) but a continuous β-strand at 12°C, which dimerizes with the R2 of another protofilament. This temperature-dependent structure indicates that R2 is conformationally more plastic than the R3 domain. The distinct conformational stabilities of different microtubule-binding repeats give insight into the energy landscape of tau fibril formation.

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 5h inside HEK cells and 1day 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.

Structurally and Morphologically Distinct Pathological Tau Assemblies Differentially Affect GVB Accumulation.

Tau aggregation is central to the pathogenesis of a large group of neurodegenerative diseases termed tauopathies, but it is still unclear in which way neurons respond to tau pathology and how tau accumulation leads to neurodegeneration. A striking neuron-specific response to tau pathology is presented by granulovacuolar degeneration bodies (GVBs), lysosomal structures that accumulate specific cargo in a dense core. Here we employed different tau aggregation models in primary neurons to investigate which properties of pathological tau assemblies affect GVB accumulation using a combination of confocal microscopy, transmission electron microscopy, and quantitative automated high-content microscopy. Employing GFP-tagged and untagged tau variants that spontaneously form intraneuronal aggregates, we induced pathological tau assemblies with a distinct subcellular localization, morphology, and ultrastructure depending on the presence or absence of the GFP tag. The quantification of the GVB load in the different models showed that an increased GVB accumulation is associated with the untagged tau aggregation model, characterized by shorter and more randomly distributed tau filaments in the neuronal soma. Our data indicate that tau aggregate structure and/or subcellular localization may be key determinants of GVB accumulation.

Disease-associated patterns of acetylation stabilize tau fibril formation

Assembly of tau into beta-sheet-rich amyloids dictates the pathology of a diversity of diseases. Lysine acetylation has been proposed to drive tau amyloid assembly, but no direct mechanism has emerged. Using tau fragments, we identify patterns of acetylation that flank amyloidogenic motifs on the tau fragments that promote rapid fibril assembly. We determined a 3.9Å cryo-EM amyloid fibril structure assembled from an acetylated tau fragment uncovering how lysine acetylation can mediate gain-of-function interactions. Comparison of the structure to an exvivo tauopathy fibril reveals regions of structural similarity. Finally, we show that fibrils encoding disease-associated patterns of acetylation are active in cell-based tau aggregation assays. Our data uncover the dual role of lysine residues in limiting tau aggregation while their acetylation leads to stabilizing pro-aggregation interactions. Design of tau sequence with specific acetylation patterns may lead to controllable tau aggregation to direct folding of tau into distinct amyloid folds.

Alzheimers Disease Mechanism in Neuroimmunology Perspective

Among the several neurodegenerative illnesses, one of these is the illness Alzheimer's (AD). it is hard to cure completely for now. To find fresh targets for the therapy of AD, neuroimmunology have been getting attention gradually. Neuroimmunology response, which happened in the central nervous system (CNS), is innate immune response of human. In the AD, microglia activated by damage signals lead to a series of cellular cascade responses. Then, a large number of chemokines and inflammatory cytokines are released by microglial cells. The cytokines have neurotoxic effects on the certain brain areas, causing neuronal degeneration. Since microglia can be activated by tau aggregation in addition to alarm signals, with tau protein aggregation releasing from the degenerative neurons, it provokes a positive feedback mechanism of neuroimmunology in hippocampal area. Microglia mainly play a role of neuroprotective by clearing -amyloid (A) on early stage of AD and have a neurotoxic effects induced by an A-induced phenotypic change on late stage of AD. TREM2 mainly expressed on microglia, it may downregulate the inflammatory response in AD. The review has explained clearly and demonstrated that tau assembly and clearance of A are effective therapeutic targets on AD. In addition, it explained AD nosogenesis from the new view of TREM2 mutations.

Conformation‐specific anti‐tau antibodies distinguish human tauopathies

AbstractBackgroundNeurodegenerative tauopathies are defined by progressive brain accumulation of tau aggregates, and include Alzheimer disease (AD), progressive supranuclear palsy (PSP), corticobasal degeneration (CBD), and Pick disease (PiD). Tau is an intrinsically disordered protein, yet it adopts diverse, highly ordered amyloid assemblies in disease states. These may amplify within cells by acting as “seeds,” or templates for their own replication. Evidence suggests that tau assemblies transfer between cells of the brain, which has inspired the development of immunotherapies that are in clinical trials. Analyses by cryo‐EM of insoluble tau filaments from tauopathies have revealed distinct fibril core structures, but these are not readily distinguished by immunohistochemistry. The tau repeat domain (RD) consists of three or four repeated segments and contains the amino acids comprising each tau filament core. The RD is required for tau assembly and has a different conformation in seed‐competent tau than in inert tau. Antibodies specific for distinct RD conformations have promise as diagnostic and therapeutic agents.MethodWe generated novel anti‐tau monoclonal antibodies against structurally defined synthetic linear peptide epitopes predicted to be exposed in seed‐competent tau. We employed a screening protocol using biosensor cell‐based seeding assays to select antibodies for sensitivity and specificity in binding soluble tau seeds from AD and non‐AD tauopathies.ResultTwo antibodies, MD2.2 and MD3.1, preferentially bind soluble tau seeds versus inert tau monomer, and distinguish seeds in AD and PSP from those of CBD and PiD. They stain tauopathy brain tissue with a pattern distinct from that of AT8.ConclusionWe have generated novel anti‐tauRD antibodies with specificity for seed‐competent conformations and which distinguish tauopathies. These may be valuable for biochemical and neuropathological investigation of tauopathies and may also improve development of immunotherapy for AD and PSP.

Aβ oligomer elimination decreases tau oligomer concentration in CSF and enhances cognition in cognitively impaired aged Beagle dogs ‐ a model of sporadic Alzheimer’s disease

AbstractBackgroundDisease‐modifying therapies to treat Alzheimer’s disease (AD) are of fundamental interest for aging humans, societies, and health care systems. More and more data suggest that the toxic protein assemblies of Aβ and tau behave prion like. The drug candidate RD2 (alias PRI‐002) has been developed to directly disassemble and disrupt toxic Aβ oligomer prions. The anti‐prionic compound is BBB penetrable and has demonstrated target engagement in vitro, ex vivo and in vivo. Treatment with RD2 has yielded improved cognition and deceleration of neurodegeneration in three different transgenic mouse models in three different laboratories. Cognitively impaired aged Beagle dogs are one of the very few non‐transgenic AD animal models that may simulate the situation of spontaneous late onset AD, i.e. sporadic AD, which is the most common form of AD in humans. The aim of this study was to investigate the efficacy of RD2 to enhance short‐term memory and cognition in cognitively impaired aged Beagle dogs ‐ a non‐transgenic model of sporadic AD.Method36 cognitively impaired aged Beagle dogs have been randomized for five months in three cohorts, placebo, low dose (3 mg/kg RD2 once daily) and high dose (30 mg/kg RD2 once daily). Treatment was done orally and for three months, followed by two months without treatment. Cognitive testing, blood and CSF drawing was done at baseline and then monthly.ResultWe demonstrate that once daily oral treatment with RD2 significantly reduced cognitive deficits in cognitively impaired aged Beagle dogs even beyond the end of the treatment. This and treatment dependent CSF tau oligomer decrease clearly suggest a neuroprotective and truly disease‐modifying effect of RD2 treatment.ConclusionDirect elimination of Aβ oligomers by disassembling them into monomers is an interesting therapeutic strategy for AD disease modification including beneficial symptomatic effects.

Brain Derived Biologically Relevant Tau Oligomers

AbstractBackgroundNeurodegenerative Tauopathies, including Alzheimer’s disease (AD), are characterized by the appearance of extracellular lesions composed of aggregated and post‐translationally modified tau proteins. The resulting tau pathology is an established marker for differential disease diagnosis and staging, a surrogate marker for neurodegeneration, a potential vector for disease propagation, and a source of toxicity in biological models. In comparison to the well‐established methods for isolation/preparation and biochemical and structural characterization of stable tau filaments from tauopathy brain, the characterization of smaller and much dynamic oligomeric tau aggregates has not been investigated to the same degree. As a result, tau oligomers that may associate most closely with disease propagation and toxicity as suggested by a large body of research, are not fully established.MethodHerein, we leverage our well‐optimized brain‐derived tau oligomers (BDTOs) from well‐vetted human tauopathy cases of AD, progressive supranuclear palsy (PSP) and dementia with Lewy bodies (DLB). In addition to our rigorous biochemical characterization of the BDTOs by immunological probing, and structural characterization by proteolysis and microscopic analyses, we have optimized Fluorescent Amyloid Multi Emission Spectra (FLAMES) microscopy for cataloging and comparing tau conformational variants across a wide range of samples, from brain tissue sections and BDTOs to in vitro aggregated tau assemblies. For selective immunodetection of the BDTOs, we have used our novel four fully sequenced and epitope mapped Tau Oligomer Monoclonal Antibodies (TOMAs), which recognize non‐continuous sequences on tau. Furthermore, the bioactivity of the BDTOs was assessed by evaluating their seeding propensity in biosensor cells and primary cortical neurons from tauopathy mice and their effects on synaptic function by electrophysiological studies.ResultWe observed that the BDTOs differed in their immunological properties, morphology, and sensibility/stability to proteolysis. The BDTOs were distinguished based on FLAMES spectral signature. Distinct seeding propensity and impairment of long‐term potentiation (LTP) indicated their differences in bioactivity as well.ConclusionOur thorough investigation/characterization of biologically active disease‐relevant tau oligomers will provide new opportunities to diagnose and evaluate therapeutics beyond the current capabilities for AD and related tauopathies by developing specific tau aggregation inhibitors and/or diagnostic probes for pathological tau protein.