4-repeat Tau Research Articles

Investigational therapeutics for the treatment of progressive supranuclear palsy

ABSTRACT Introduction Progressive supranuclear palsy (PSP) is a progressive neurodegenerative disease marked by a variety of movement, ocular, and cognitive symptoms. Currently, treatment is symptomatic, and there are no disease-modulating therapies. While clinical presentations can be variable, at autopsy, PSP shows 4-repeat (4 R) tau species that accumulate in brainstem, subcortical, and neocortical areas. Thus, several tau-directed therapies have been trialed in PSP but with disappointing results to date. Areas Covered We review PSP clinicopathological correlates and biomarkers and searched clinicaltrials.gov and pubmed.ncbi.nlm.nih.gov for disease-modulating trials in PSP from the preclinical stage to clinical stage 3 and reviewed their rationale and results in human trials. Expert Opinion Factors that may have hampered tau-directed therapies in PSP include patient selection, intervening in an advanced disease stage, lack of biomarkers for prodromal diagnosis, outcome measurements, target engagement measures, selection of specific tau epitopes, and brain penetration of trialed therapies. Coupled with early intervention, targets upstream of tau accumulation and corresponding cell death may need to be identified to modulate the disease course. PSP remains a promising disease to study tau-directed therapies, and several possible targets are being tackled using novel approaches bringing hope for future success.

Virtual Screening and Testing of GSK-3 Inhibitors Using Human SH-SY5Y Cells Expressing Tau Folding Reporter and Mouse Hippocampal Primary Culture under Tau Cytotoxicity.

Glycogen synthase kinase-3β (GSK-3β) is an important serine/threonine kinase that implicates in multiple cellular processes and links with the neurodegenerative diseases including Alzheimer's disease (AD). In this study, structure-based virtual screening was performed to search database for compounds targeting GSK-3β from Enamine's screening collection. Of the top-ranked compounds, 7 primary hits underwent a luminescent kinase assay and a cell assay using human neuroblastoma SH-SY5Y cells expressing Tau repeat domain (TauRD) with pro-aggregant mutation ΔK280. In the kinase assay for these 7 compounds, residual GSK-3β activities ranged from 36.1% to 90.0% were detected at the IC50 of SB-216763. In the cell assay, only compounds VB-030 and VB-037 reduced Tau aggregation in SH-SY5Y cells expressing ΔK280 TauRD-DsRed folding reporter. In SH-SY5Y cells expressing ΔK280 TauRD, neither VB-030 nor VB-037 increased expression of GSK-3α Ser21 or GSK-3β Ser9. Among extracellular signal-regulated kinase (ERK), AKT serine/threonine kinase 1 (AKT), mitogen-activated protein kinase 14 (P38) and mitogen-activated protein kinase 8 (JNK) which modulate Tau phosphorylation, VB-037 attenuated active phosphorylation of P38 Thr180/Tyr182, whereas VB-030 had no effect on the phosphorylation status of ERK, AKT, P38 or JNK. However, both VB-030 and VB-037 reduced endogenous Tau phosphorylation at Ser202, Thr231, Ser396 and Ser404 in neuronally differentiated SH-SY5Y expressing ΔK280 TauRD. In addition, VB-030 and VB-037 further improved neuronal survival and/or neurite length and branch in mouse hippocampal primary culture under Tau cytotoxicity. Overall, through inhibiting GSK-3β kinase activity and/or p-P38 (Thr180/Tyr182), both compounds may serve as promising candidates to reduce Tau aggregation/cytotoxicity for AD treatment.

Clinical, radiologic, and pathologic features of the globular glial tauopathy subtype of frontotemporal lobar degeneration in right temporal variant frontotemporal dementia with salient features of Geschwind syndrome

ABSTRACT Globular Glial Tauopathy (GGT) is a rare form of Frontotemporal Lobar Degeneration (FTLD) consisting of 4-repeat tau globular inclusions in astrocytes and oligodendrocytes. We present the pathological findings of GGT in a previously published case of a 73-year-old woman with behavioral symptoms concerning for right temporal variant frontotemporal dementia with initial and salient features of Geschwind syndrome. Clinically, she lacked motor abnormalities otherwise common in previously published GGT cases. Brain MRI showed focal right anterior temporal atrophy (indistinguishable from five FTLD-TDP cases) and subtle ipsilateral white matter signal abnormalities. Brain autopsy showed GGT type III and Alzheimer’s neuropathologic changes. .

Amyloid β, Tau, and α-Synuclein aggregates in the pathogenesis, prognosis, and therapeutics for neurodegenerative diseases.

Aggregation of specific proteins are histopathological hallmarks of several neurodegenerative diseases, such as, Amyloid β (Aβ) plaques and tau neurofibrillary tangles in Alzheimer's disease (AD); morphologically different inclusions of ratiometric 3 repeat (3R) and 4 repeat (4R) tau isoforms in progressive supranuclear palsy (PSP), corticobasal degeneration (CBD), and Pick's disease (PiD); α-Synuclein (α-Syn) containing Lewy bodies (LBs) and dystrophic Lewy neurites (LNs) in Parkinson's disease (PD) and dementia with Lewy bodies (DLB). However, mixed brain protein pathologies have been frequently observed in many of these diseases and in normal aging brains, among which Aβ/tau and tau/α-Syn crosstalks have received increased attention. Interestingly, studies have also shown synergistic interplay among Aβ, tau, and α-Syn in several neurodegenerative diseases, suggesting a protein triumvirate. In this review, we summarize the emerging evidence of Aβ, tau, and α-Syn aggregation in pathophysiology, and their overlap in a spectrum of neurodegenerative diseases including AD, PSP, PiD, CBD, PD and DLB. We discuss the prognostic advancements made in biomarker and imaging techniques in the triumvirate proteinopathies. Finally, we discuss the combined therapeutic modality involving biomarkers and imaging techniques for future combinatorial immunotherapeutic targeting more than one protein aggregates. We hope that such a multitarget therapeutic approach will have synergistic or additive effects to manage neurodegenerative diseases with two or more protein pathologies that might uncover a promising strategy for personalized combination therapies. Managing neurodegenerative diseases by optimizing the diagnostic criteria and the correct combination of immunotherapies will be a key factor in the success of future treatment.

Tau R2 and R3 are essential regions for tau aggregation, seeding and propagation

Tauopathies are characterised by intracellular deposits of fibrillar tau tangles. However, the interneuronal spread of pathological tau species precedes the development of major tau burdens. Two amyloid motifs, VQIINK in repeat 2 and VQIVYK in repeat 3, of tau repeat domain, assemble into β-sheet-rich fibrils on their own but alone do not form seed-competent fibrils. In contrast, the entire R3 region self-aggregates and forms seed-competent fibrils. Our study aimed to identify the minimal regions in the tau repeat domain that define seeding and its impact on intracellular tau phosphorylation and aggregation. Using peptides of individual repeats, we show that R2, like R3, forms seed-competent fibrils when assembled in the presence of heparin. However, R3, but not R2, forms seed-competent fibrils when assembled without heparin, even though both R2 and R3 have identical N-terminal hexapeptide and cysteine residue sequences. Moreover, cysteine to alanine substitution in R3 abrogates its self-aggregation and seeding potency. Tau RD P301S biosensor cells and Tau P301L (0N4R)-expressing HEK293 cells seeded with R2 and R3 fibrils show the induction of pathological phosphorylation of tau at Ser262/Ser396/Ser404 positions and oligomerisation of native tau. Protein fractions of biosensor cells seeded with R2 and R3 fibrils reseed endogenous tau aggregation when introduced into a fresh set of biosensor cells. Our findings suggest that R3 may be the minimal region for pathological seed generation under physiological conditions, whereas R2 might need polyanionic cofactors to generate pathogenic seeds. Lastly, R2 and R3 fibrils induce template-induced misfolding and pathological hyperphosphorylation of intracellular tau, making intracellular tau seed-competent.

Patterns of Mixed Pathologies in Down Syndrome.

Down syndrome (DS) is frequently associated with Alzheimer's disease (AD)-related neuropathological changes. There are few observations on the spectrum of mixed proteinopathies in DS patients. This study aimed to evaluate multiple disease-associated proteinopathies in a series of DS cases. We analyzed the distribution of neurodegenerative disease associated proteins in postmortem brain samples from 11 DS cases (6 females, median age 57, range 38-66 years). Sections were stained for phosphorylated tau, 3-repeat and 4-repeat tau, amyloid-β, alpha synuclein, phosphorylated TDP-43, and p62. A comprehensive anatomical mapping and staging were applied for all proteins. Tau and amyloid-β pathology was prevalent in all cases and compatible with that typically seen in AD with some subtle deviations. Four of 11 cases presented with Lewy-related pathology (LRP). Two cases followed the Braak staging (stage 4 and 5) whereas 2 cases presented with an atypical distribution. Two cases showed limbic predominant age-related TDP-43 encephalopathy (LATE) (stage 1 and stage 2) neuropathologic change. Two cases exhibited aging-related tau astrogliopathy (ARTAG). In addition to subtle deviations from AD regarding the morphology of amyloid-β deposition and distribution of neuronal tau pathology, we find that the spectrum of mixed-pathologies in DS show distinctive features such as deviations from the Braak staging of LRP and that LATE neuropathologic change and ARTAG pathology can be seen in individuals younger than in sporadic AD cases. Our observations support the notion that DS has distinctive pathogenic pathways from sporadic AD.

Independent distribution between tauopathy secondary to subacute sclerotic panencephalitis and measles virus: An immunohistochemical analysis in autopsy cases including cases treated with aggressive antiviral therapies.

Subacute sclerotic panencephalitis (SSPE) is a refractory neurological disorder after exposure to measles virus. Recently, SSPE cases have been treated with antiviral therapies, but data on the efficacy are inconclusive. Abnormal tau accumulation has been reported in the brain tissue of SSPE cases, but there are few reports in which this is amply discussed. Five autopsied cases diagnosed as definite SSPE were included in this study. The subject age or disease duration ranged from 7.6 to 40.9 years old or from 0.5 to 20.8 years, respectively. Cases 3 and 4 had been treated with antiviral therapies. All evaluated cases showed marked brain atrophy with cerebral ventricle dilatation; additionally, marked demyelination with fibrillary gliosis were observed in the cerebral white matter. The brainstem, cerebellum, and spinal cord were relatively preserved. Immunoreactivity (IR) against measles virus was seen in the brainstem tegmentum, neocortex, and/or limbic cortex of the untreated cases but was rarely seen in the two treated cases. Activated microglia were broadly observed from the cerebrum to the spinal cord and had no meaningful difference among cases. Neurofibrillary tangles characterized by a combination of 3- and 4-repeat tau were observed mainly in the oculomotor nuclei, locus coeruleus, and limbic cortex. IR against phosphorylated tau was seen mainly in the cingulate gyrus, oculomotor nuclei, and pontine tegmentum, and tended to be observed frequently in cases with long disease durations but also tended to decrease along with neuronal loss, as in Case 5, which had the longest disease duration. Since the distribution of phosphorylated tau was independent from that of measles virus, the tauopathy following SSPE was inferred to be the result of diffuse brain inflammation triggered by measles rather than a direct result of measles virus. Moreover, antiviral therapies seemed to suppress measles virus but not the progression of tauopathy.

18F-APN-1607 Tau Positron Emission Tomography Imaging for Evaluating Disease Progression in Alzheimer's Disease.

Purpose18F-APN-1607 is a novel tau positron emission tomography (PET) tracer characterized with high binding affinity for 3− and 4-repeat tau deposits. The aim was to analyze the spatial distribution of 18F-APN-1607 PET imaging in Alzheimer’s disease (AD) subjects with different stages and to investigate the relationship between the change of tau deposition and overall disease progression.MethodsWe retrospectively analyzed the 18F-APN-1607 PET imaging of 31 subjects with clinically and imaging defined as AD. According to the Mini-Mental State Examination (MMSE) score, patients were divided into three groups, namely, mild (≥21, n = 7), moderate (10–20, n = 16), and severe (≤9, n = 8). PET imaging was segmented to 70 regions of interest (ROIs) and extracted the standard uptake value (SUV) of each ROI. SUV ratio (SUVR) was calculated from the ratio of SUV in different brain regions to the cerebellar cortex. The regions were defined as positive and negative with unsupervised cluster analysis according to SUVR. The SUVRs of each region were compared among groups with the one-way ANOVA or Kruskal–Wallis H test. Furthermore, the correlations between MMSE score and regional SUVR were calculated with Pearson or Spearman correlation analysis.ResultsThere were no significant differences among groups in gender (χ2 = 3.814, P = 0.161), age of onset (P = 0.170), age (P = 0.109), and education level (P = 0.065). With the disease progression, the 18F-APN-1607 PET imaging showed the spread of tau deposition from the hippocampus, posterior cingulate gyrus (PCG), and lateral temporal cortex (LTC) to the parietal and occipital lobes, and finally to the frontal lobe. Between the mild and moderate groups, the main brain areas with significant differences in 18F-APN-1607 uptake were supplementary motor area (SMA), cuneus, precuneus, occipital lobule, paracentral lobule, right angular gyrus, and parietal, which could be used for early disease progression assessment (P < 0.05). There were significant differences in the frontal lobe, right temporal lobe, and fusiform gyrus between the moderate and severe groups, which might be suitable for the late-stage disease progression assessment (P < 0.05).Conclusion18F-APN-1607 PET may serve as an effective imaging marker for visualizing the change pattern of tau protein deposition in AD patients, and its uptake level in certain brain regions is closely related to the severity of cognitive impairment. These indicate the potential of 18F-APN-1607 PET for the in vivo evaluation of the progression of AD.

Non-invasive imaging of tau-targeted probe uptake by whole brain multi-spectral optoacoustic tomography

PurposeAbnormal tau accumulation within the brain plays an important role in tauopathies such as Alzheimer’s disease and frontotemporal dementia. High-resolution imaging of tau deposits at the whole-brain scale in animal disease models is highly desired.MethodsWe approached this challenge by non-invasively imaging the brains of P301L mice of 4-repeat tau with concurrent volumetric multi-spectral optoacoustic tomography (vMSOT) at ~ 115 μm spatial resolution using the tau-targeted pyridinyl-butadienyl-benzothiazole derivative PBB5 (i.v.). In vitro probe characterization, concurrent vMSOT and epi-fluorescence imaging of in vivo PBB5 targeting (i.v.) was performed in P301L and wild-type mice, followed by ex vivo validation using AT-8 antibody for phosphorylated tau.ResultsPBB5 showed specific binding to recombinant K18 tau fibrils by fluorescence assay, to post-mortem Alzheimer’s disease brain tissue homogenate by competitive binding against [11C]PBB3 and to tau deposits (AT-8 positive) in post-mortem corticobasal degeneration and progressive supranuclear palsy brains. Dose-dependent optoacoustic and fluorescence signal intensities were observed in the mouse brains following i.v. administration of different concentrations of PBB5. In vivo vMSOT brain imaging of P301L mice showed higher retention of PBB5 in the tau-laden cortex and hippocampus compared to wild-type mice, as confirmed by ex vivo vMSOT, epi-fluorescence, multiphoton microscopy, and immunofluorescence staining.ConclusionsWe demonstrated non-invasive whole-brain imaging of tau in P301L mice with vMSOT system using PBB5 at a previously unachieved ~ 115 μm spatial resolution. This platform provides a new tool to study tau spreading and clearance in a tauopathy mouse model, foreseeable in monitoring tau targeting putative therapeutics.

Nasal Rifampicin Halts the Progression of Tauopathy by Inhibiting Tau Oligomer Propagation in Alzheimer Brain Extract-Injected Mice.

The cell-to-cell transmission of tau aggregates is considered a mechanism underlying the intracerebral spreading of tau pathology in Alzheimer’s disease (AD) and other tauopathies. Recent studies suggest that tau oligomers, rather than fibrils, participate in this process. We previously showed that intranasal rifampicin inhibits tau oligomer accumulation and improves cognition in tauopathy mice. In the present study, we examined the effects of nasal rifampicin on tau propagation in a new mouse model of tauopathy. A tau oligomer-rich fraction prepared from the brain of an AD patient was injected into a unilateral hippocampus of tau264 mice that express both 3-repeat and 4-repeat wild-type human tau. Rifampicin administration was started one week after the injection and performed three times a week for 24 weeks. Cognitive function and tau pathology were assessed by the Morris water maze test and brain section staining. Rifampicin treatment inhibited the spreading of tau oligomers from the injection site to other brain regions and neurofibrillary tangle formation in the entorhinal cortex. Synapse and neuronal loss in the hippocampus were also prevented, and cognitive function remained normal. These results suggest that intranasal rifampicin could be a promising remedy that halts the progression of tauopathy by inhibiting tau oligomer propagation.

Astrocytic 4R tau expression drives astrocyte reactivity and dysfunction.

The protein tau and its isoforms are associated with several neurodegenerative diseases, many of which are characterized by greater deposition of the 4-repeat (4R) tau isoform; however, the role of 4R tau in disease pathogenesis remains unclear. We created antisense oligonucleotides (ASOs) that alter the ratio of 3R to 4R tau to investigate the role of specific tau isoforms in disease. Preferential expression of 4R tau in human tau–expressing (hTau-expressing) mice was previously shown to increase seizure severity and phosphorylated tau deposition without neuronal or synaptic loss. In this study, we observed strong colocalization of 4R tau within reactive astrocytes and increased expression of pan-reactive and neurotoxic genes following 3R to 4R tau splicing ASO treatment in hTau mice. Increasing 4R tau levels in primary astrocytes provoked a similar response, including a neurotoxic genetic profile and diminished homeostatic function, which was replicated in human induced pluripotent stem cell–derived (iPSC-derived) astrocytes harboring a mutation that exhibits greater 4R tau. Healthy neurons cultured with 4R tau–expressing human iPSC–derived astrocytes exhibited a higher firing frequency and hypersynchrony, which could be prevented by lowering tau expression. These findings support a potentially novel pathway by which astrocytic 4R tau mediates reactivity and dysfunction and suggest that astrocyte-targeted therapeutics against 4R tau may mitigate neurodegenerative disease progression.

Recent Developments in Positron Emission Tomography Tracers for Proteinopathies Imaging in Dementia.

An early detection and intervention for dementia represent tremendous unmet clinical needs and priorities in society. A shared feature of neurodegenerative diseases causing dementia is the abnormal accumulation and spreading of pathological protein aggregates, which affect the selective vulnerable circuit in a disease-specific pattern. The advancement in positron emission tomography (PET) biomarkers has accelerated the understanding of the disease mechanism and development of therapeutics for Alzheimer’s disease and Parkinson’s disease. The clinical utility of amyloid-β PET and the clinical validity of tau PET as diagnostic biomarker for Alzheimer’s disease continuum have been demonstrated. The inclusion of biomarkers in the diagnostic criteria has introduced a paradigm shift that facilitated the early and differential disease diagnosis and impacted on the clinical management. Application of disease-modifying therapy likely requires screening of patients with molecular evidence of pathological accumulation and monitoring of treatment effect assisted with biomarkers. There is currently still a gap in specific 4-repeat tau imaging probes for 4-repeat tauopathies and α-synuclein imaging probes for Parkinson’s disease and dementia with Lewy body. In this review, we focused on recent development in molecular imaging biomarkers for assisting the early diagnosis of proteinopathies (i.e., amyloid-β, tau, and α-synuclein) in dementia and discussed future perspectives.

Defective proteostasis in patient‐derived iPSC‐astrocytes and neurons carrying a MAPT IVS10+16 mutation

AbstractBackgroundImpaired proteostasis is associated with normal aging and is accelerated in neurodegeneration. This impairment may lead to the toxic protein accumulation. In a subset of frontotemporal dementia (FTD) cases, mutations in the microtubule‐associated protein tau (MAPT) that alter the relative levels of specific tau isoforms are sufficient to cause tau inclusions in neurons and astroglia and neurodegeneration without the presence of mutated protein (e.g. MAPTIVS10+16). However, the pathogenic events triggered by the expression of the alternatively spliced tau remain poorly understood.MethodTo determine whether altered tau splicing induced from MAPT IVS10+16 mutations is sufficient to alter proteostasis in neurons and glia, we used human induced pluripotent stem cell (iPSC)‐derived neurons and astrocytes from patients carrying the MAPT IVS10+16 mutation and CRISPR/Cas9, isogenic corrected controls.ResultWe found that neurons from MAPT IVS10+16 carriers exhibited significantly higher levels of 4 repeat tau, deficits in lysosomal trafficking, and reduced lysosomal acidity relative to isogenic‐control neurons. Additionally, MAPTIVS10+16 was sufficient to reduce genes associated with lysosomal biogenesis (regulated by TFEB). Interestingly, mutant astrocytes also produce elevated 4 repeat tau levels and exhibit several key hallmarks of cellular aging. Mutant astrocytes were larger in size with enlarged nuclei compared to isogenic controls. In addition to this hypertrophy phenotype, mutant astrocytes exhibited significantly elevated levels of senescence genes. Furthermore, markers of proteostasis were altered in mutant astrocytes: MAPT IVS10+16 carriers exhibited an increase in acidic lysosomes compared to isogenic‐control astrocytes, and TFEB‐regulated genes were upregulated MAPT IVS10+16 astrocytes.ConclusionOur findings suggest that altered tau splicing induced by the MAPT IVS10+16 mutation is sufficient to cause aging signatures, including hypertrophy, senescence, and altered proteostasis in a cell‐type specific manner.

Antitumour drugs targeting tau R3 VQIVYK and Cys322 prevent seeding of endogenous tau aggregates by exogenous seeds.

Emerging experimental evidence suggests tau pathology spreads between neuroanatomically connected brain regions in a prion-like manner in Alzheimer's disease (AD). Tau seeding, the ability of prion-like tau to recruit and misfold naïve tau to generate new seeds, is detected early in human AD brains before the development of major tau pathology. Many antitumour drugs have been reported to confer protection against neurodegeneration, supporting the repurposing of approved and experimental or investigational oncology drugs for AD therapy. In this study, we evaluated whether antitumour drugs that abrogate the generation of seed-competent aggregates of tau Repeat 3 (R3) domain peptides can prevent tau seeding and toxicity in Tau-RD P301S FRET Biosensor cells and Caenorhabditis elegans. We demonstrate that drugs that interact with the N-terminal VQIVYK or the C-terminal region housing the Cys322 prevent R3 dimerisation, abolishing the generation of prion-like R3 seeds. Preformed R3 seeds (fibrils) capped with, or R3 seeds formed in the presence of VQIVYK- or Cys322-targeting drugs have a reduced potency to cause aggregation of naïve tau in biosensor cells and protect worms from aggregate toxicity. These findings indicate that VQIVYK- or Cys322-targeting drugs may act as prophylactic agents against tau seeding.

Genome-wide association study and functional validation implicates JADE1 in tauopathy.

Primary age-related tauopathy (PART) is a neurodegenerative pathology with features distinct from but also overlapping with Alzheimer disease (AD). While both exhibit Alzheimer-type temporal lobe neurofibrillary degeneration alongside amnestic cognitive impairment, PART develops independently of amyloid-β (Aβ) plaques. The pathogenesis of PART is not known, but evidencesuggests anassociation with genes that promote tau pathology and others that protect from Aβ toxicity. Here, we performed a genetic association study in an autopsy cohort of individuals with PART (n = 647) using Braak neurofibrillary tangle stage as a quantitative trait. We found some significant associations with candidate loci associated with AD (SLC24A4, MS4A6A, HS3ST1) and progressive supranuclear palsy (MAPT and EIF2AK3). Genome-wide association analysis revealed a novel significant association with a single nucleotide polymorphism on chromosome 4 (rs56405341) in a locus containing three genes, including JADE1 which was significantly upregulated in tangle-bearing neurons by single-soma RNA-seq. Immunohistochemical studies using antisera targeting JADE1 protein revealed localization within tau aggregates in autopsy brains with four microtubule-binding domain repeats (4R) isoforms and mixed 3R/4R, but not with 3R exclusively. Co-immunoprecipitation in post-mortem human PART brain tissue revealed a specific binding of JADE1 protein to four repeat tau lacking N-terminal inserts (0N4R). Finally, knockdown of the Drosophila JADE1 homolog rhinoceros (rno) enhanced tau-induced toxicity and apoptosis in vivo in a humanized 0N4R mutant tau knock-in model, as quantified by rough eye phenotype and terminal deoxynucleotidyl transferase dUTP nick end-labeling (TUNEL) in the fly brain. Together, these findings indicate that PART has a genetic architecture that partially overlaps with AD and other tauopathies and suggests a novel role for JADE1 as a modifier of neurofibrillary degeneration.

Tau seeding in chronic traumatic encephalopathy parallels disease severity.

Chronic traumatic encephalopathy (CTE), a neurodegenerative tauopathy, is associated with behavioral, mood and cognitive impairment, including dementia. Tauopathies are neurodegenerative diseases whose neuropathological phenotypes are characterized by distinct histopathologic features of tau pathology, which progressively deposit throughout the brain. In certain tauopathies, especially Alzheimer's disease (AD), tau deposition appears to follow brain network connections. Experimental evidence suggests that the progression of tau pathology in humans, mouse and cell models could be explained by tau seeds that adopt distinct conformations and serve as templates for their own amplification to mediate transcellular propagation of pathology. Tau seeds are efficiently detected by the induction of aggregation in cell-based "biosensors" that express tau repeat domain (RD) with a disease-associated mutation (P301S) fused to complementary fluorescent protein tags (cyan and yellow fluorescent protein). Biosensors enable quantification of tau seeding in fixed and fresh-frozen brain tissue. Phospho-tau deposition in CTE follows progressive stages (I-IV), but the relationship of seeding to this deposition is unclear. We have used an established biosensor assay to independently quantify tau seeding as compared to AT8 phospho-tau histopathology in thin sections of fixed tissues of 11 brain regions from 27 patients with CTE, 5 with other tauopathies, and 5 negative controls. In contrast to prior studies of AD, we detected tau seeding late in the course of CTE (predominantly stages III and IV). It was less anatomically prevalent than AT8-positive inclusions, which were relatively widespread. We especially observed seeding in the limbic system (amygdala, thalamus, basal ganglia), which may explain the dominant cognitive and behavior impairments that characterize CTE.

Development of a novel tau propagation mouse model endogenously expressing 3 and 4 repeat tau isoforms.

The phenomenon of 'prion-like propagation' in which aggregates of abnormal amyloid-fibrilized protein propagate between neurons and spread pathology, is attracting attention as a new mechanism in neurodegenerative diseases. There is a strong correlation between the accumulation or spread of abnormal tau aggregates and the clinical symptoms of tauopathies. Microtubule-associated protein tau (MAPT) contains a microtubule-binding domain that consists of three or four repeats (3R/4R) due to alternative mRNA splicing of transcripts for the MAPT gene. Although a number of models for tau propagation have been reported, most use 4R human tau transgenic mice or adult wild-type mice expressing only endogenous 4R tau and these models have not been able to reproduce the pathology of Alzheimer's disease in which 3R and 4R tau accumulate simultaneously, or that of Pick's disease in which only 3R tau is aggregated. These deficiencies may reflect differences between human and rodent tau isoforms in the brain. To overcome this problem, we used genome editing techniques to generate mice that express an equal ratio of endogenous 3R and 4R tau, even after they become adults. We injected these mice with sarkosyl-insoluble fractions derived from the brains of human tauopathy patients such as those afflicted with Alzheimer's disease (3R and 4R tauopathy), corticobasal degeneration (4R tauopathy) or Pick's disease (3R tauopathy). At 8-9 months following intracerebral injection of mice, histopathological and biochemical analyses revealed that the abnormal accumulation of tau was seed-dependent, with 3R and 4R tau in Alzheimer's disease-injected brains, 4R tau only in corticobasal degeneration-injected brains and 3R tau only in Pick disease-injected brains, all of which contained isoforms related to those found in the injected seeds. The injected abnormal tau was seeded, and accumulated at the site of injection and at neural connections, predominantly within the same site. The abnormal tau newly accumulated was found to be endogenous in these mice and to have crossed the species barrier. Of particular importance, Pick's body-like inclusions were observed in Pick's disease-injected mice, and accumulations characteristic of Pick's disease were reproduced, suggesting that we have developed the first model that recapitulates the pathology of Pick's disease. These models are not only useful for elucidating the mechanism of propagation of tau pathology involving both 3R and 4R isoforms, but can also reproduce the pathology of tauopathies, which should lead to the discovery of new therapeutic agents.

Pathologic tau conformer ensembles induce dynamic, liquid-liquid phase separation events at the nuclear envelope

BackgroundThe microtubule-associated protein tau forms aggregates in different neurodegenerative diseases called tauopathies. Prior work has shown that a single P301L mutation in tau gene, MAPT, can promote alternative tau folding pathways that correlate with divergent clinical diagnoses. Using progressive chemical denaturation, some tau preparations from the brain featured complex transitions starting at low concentrations of guanidine hydrochloride (GdnHCl) denaturant, indicating an ensemble of differently folded tau species called conformers. On the other hand, brain samples with abundant, tangle-like pathology had simple GdnHCl unfolding profile resembling the profile of fibrillized recombinant tau and suggesting a unitary conformer composition. In studies here we sought to understand tau conformer progression and potential relationships with condensed liquid states, as well as associated perturbations in cell biological processes.ResultsAs starting material, we used brain samples from P301L transgenic mice containing tau conformer ensembles that unfolded at low GdnHCl concentrations and with signatures resembling brain material from P301L subjects presenting with language or memory problems. We seeded reporter cells expressing a soluble form of 4 microtubule-binding repeat tau fused to GFP or YFP reporter moieties, resulting in redistribution of dispersed fluorescence signals into focal assemblies that could fuse together and move within processes between adjacent cells. Nuclear envelope fluorescent tau signals and small fluorescent inclusions behaved as a demixed liquid phase, indicative of liquid-liquid phase separation (LLPS); these droplets exhibited spherical morphology, fusion events and could recover from photobleaching. Moreover, juxtanuclear tau assemblies were associated with disrupted nuclear transport and reduced cell viability in a stable cell line. Staining for thioflavin S (ThS) became more prevalent as tau-derived inclusions attained cross-sectional area greater than 3 μm2, indicating (i) a bipartite composition, (ii) in vivo progression of tau conformers, and (iii) that a mass threshold applying to demixed condensates may drive liquid-solid transitions.ConclusionsTau conformer ensembles characterized by denaturation at low GdnHCl concentration templated the production of condensed droplets in living cells. These species exhibit dynamic changes and develop in vivo, and the larger ThS-positive assemblies may represent a waystation to arrive at intracellular fibrillar tau inclusions seen in end-stage genetic tauopathies.

An autopsied FTDP-17 case with MAPT IVS 10+14C>T mutation presenting with frontotemporal dementia.

•We report the immunohistochemical and biochemical features of an FTDP-17 case with MAPT IVS 10+14C>T mutation.•Postmortem examination of the patient with bvFTD revealed diffuse neuronal and glial 4-repeat tau pathology similar to CBD.•The structure of tau filaments associated with MAPT IVS 10+14C>T mutation was characterized by electron microscopy.

Microtubule disruption upon CNS damage triggers mitotic entry via TNF signaling activation.

Repair after traumatic injury often starts with mitotic activation around the lesion edges. Early midline cells in the Drosophila embryonic CNS can enter into division following the traumatic disruption of microtubules. We demonstrate that microtubule disruption activates non-canonical TNF signaling by phosphorylation of TGF-β activated kinase 1 (Tak1) and its target IkappaB kinase (Ik2), culminating in Dorsal/NfkappaB nuclear translocation and Jra/Jun expression. Tak1 and Ik2 are necessary for the damaged-induced divisions. Microtubule disruption caused by Tau accumulation is also reported in Alzheimer's disease (AD). Human Tau expression in Drosophila midline cells is sufficient to induce Tak1 phosphorylation, Dorsal and Jra/Jun expression, and entry into mitosis. Interestingly, activation of Tak1 and Tank binding kinase 1 (Tbk1), the human Ik2 ortholog, and NfkappaB upregulation are observed in AD brains.