Mutant Tau Research Articles

Reconfigured metabolism brain network in asymptomatic microtubule‐associated protein tau mutation carriers: A graph‐theoretical analysis

AbstractBackgroundStudies exploring topologic properties of the metabolic network in the presymptomatic stage of genetic frontotemporal dementia (FTD) are scarce, which may be important for understanding brain function and disease pathogenesis. This study aimed to explore FTD‐specific patterns of metabolism topology reconfiguration in asymptomatic microtubule‐associated protein tau (MAPT) mutation carriers.MethodSix asymptomatic carriers of MAPT P301L mutation were compared with 12 non‐carriers who were all from the same large family of FTD. For comparison, we included 32 behavioral‐variant FTD (bvFTD) patients and 33 unrelated healthy controls. Each participant underwent neuropsychological assessments, genetic testing, and hybrid PET/MRI scan. Voxel‐wise gray matter volume and standardized uptake value ratio were calculated and compared for structural MRI and FDG‐PET, separately. The sparse inverse covariance estimation (SICE) method was applied to topologic properties and metabolic connectomes of brain functional networks derived from 18F‐fluorodeoxyglucose PET/MRI data. Independent component analysis was used to explore metabolic connectivity in the salience (SN) and default mode networks (DMN).ResultThe mean estimated years from symptom onset was 8.33 ± 1.875 years in the mutation carrier group. The asymptomatic MAPT carriers show no significant differences in cognitive tests, gray matter volume and FDG uptake compared to non‐carriers. They also retained normal global parameters of metabolism network, but not for bvFTD patients. However, we revealed lost hubs in the ventromedial prefrontal, orbitofrontal, and anterior cingulate cortices and reconfigured hubs in the anterior insula, precuneus, and posterior cingulate cortex in asymptomatic carriers, which is consistent with the findings in bvFTD patients. Similarly, significant differences in local parameters of these nodes were observed in asymptomatic carriers. The reduction in connectivity was marked in lost hub regions during the asymptomatic stage. Functional connectivity within the SN and DMN was enhanced in asymptomatic carriers, while reduced in bvFTD patients.ConclusionOur findings showed that asymptomatic MAPT carriers were initially involved in medial prefrontal areas and actively compensated in task‐related regions. Topologic properties of the metabolic network may contribute to further investigations and monitoring of the earliest stages of FTD in individuals with genetic backgrounds.

Overexpression of Aha1 and FKBP52 does not affect learning or mood‐like behavior in human tau (hTau) mice

AbstractBackgroundTau plays a critical role in neurodegeneration, thus targeting this protein to control its accumulation is important to prevent or delay neurotoxicity in tauopathies like Alzheimer’s disease (AD). Discrete molecular chaperones, like Aha1 and FKBP52, are known to affect the stability of tau by promoting its phosphorylation, aggregation and, in some mouse models, neuronal death. However, one limitation of preclinical tau models is that various contain tau mutations which do not represent most AD cases. Our study is important because it investigates biological mechanisms and behavioral phenotype in a humanized tau (hTau) mouse model absent of tau mutations. We hypothesize that overexpression of Aha1 in in hTau mice will accelerate tau tangle formation and cognitive deficits.MethodTo test this, Tau KO and hTau mice were bilaterally injected into the hippocampus with AAV9‐Aha1, AAV9‐FKBP52, and AAV9‐mKate (control) virus. At 11 and 13 months of age, animals were tested for cognitive and behavioral phenotypes.ResultsWe found that overexpression of these chaperones does not affect anxiety, spatial working memory, and locomotion in hTau mice. We further confirmed that short‐term working memory in the learning and extinction of fear memories remained unaltered by the high levels of Aha1 and FKBP52 at these ages. Ongoing analyses will examine tau pathology in these brains by measuring tau levels, neuronal density, and cell death markers.ConclusionAt this timepoint, Aha1 and FKBP52 did not induce behavioral differences in these mice. We recently reported that overexpression of these chaperones promotes tau pathological changes in 16‐months‐old wild‐type. Thus, it is possible that behavioral differences can be detected as tau pathology progresses at an older age.

Multidisciplinary characterization of potential inhibitors of the MSUT‐2 protein using molecular dynamics, mechanosensation assays, and deep AI‐based hit optimization for the treatment of Alzheimer’s disease

AbstractBackgroundAlzheimer’s disease is a type of tauopathy, which is a broad category of diseases marked by abnormal aggregation and hyperphosphorylation of the tau protein. The MSUT‐2 protein has gained traction as a promising target for the treatment of tauopathies, given the protein’s RNA‐binding activity linked to tau aggregation. Previously in this research endeavor, using techniques like Quantum Machine Learning and Virtual Screening, 5 potential MSUT‐2 inhibitors have been identified from an initial set of 500,000 candidate compounds. The primary research aim is to further analyze these 5 potential hits using a new combination of computational methodologies and laboratory characterization.MethodA myriad of tests were performed with strains of C. elegans (microscopic roundworms that are established models for neurodegeneration) to validate previous computational indications. A series of motion evaluations, mechanosensation assays, and behavioral assessments were performed with CL2319 C. elegans (mutated to overexpress neuronal tau) with all 5 compounds. One of the compounds, named R128, was found to improve the health and behavior of tau mutant worms across experimental assessments at increasing doses of the compound. A 100 nanosecond simulation of the MSUT2‐R128 complex using the GROMOS96 43a1 force field and SPC Water Model was used to computationally validate protein‐ligand stability based on RMSD fluctuation values. DeepFrag, a fragment‐based lead optimization tool with a deep convolutional neural network backend, was then used to generate 20 potential optimized compounds, nine of which were found to retain R128’s druglikeliness profile yet have improved binding affinities to MSUT‐2.ResultThis multidisciplinary workflow has uncovered a promising hit for the MSUT‐2 protein, named R128, with 9 optimized derivatives with improved drug‐like qualities. This methodology can be used to efficiently identify promising treatment candidates for new protein targets involved in neurodegenerative diseases, with the prospect of expediting the drug discovery process significantly.ConclusionTo conclude, a translational approach, combining molecular dynamics, mechanosensation assessments with C. elegans, and an AI‐based hit optimization strategy has been used to identify new treatment candidates for Alzheimer’s disease. R128, a promising inhibitor for MSUT‐2 (an understudied target for Alzheimer’s disease), has also been identified in this study.

Tau mutation S356T in the three repeat isoform leads to microtubule dysfunction and promotes prion-like seeded aggregation.

Tauopathies are a group of neurodegenerative diseases, which include frontotemporal dementia (FTD) and Alzheimer's disease (AD), broadly defined by the development of tau brain aggregates. Both missense and splicing tau mutations can directly cause early onset FTD. Tau protein is a microtubule-associated protein that stabilizes and regulates microtubules, but this function can be disrupted in disease states. One contributing factor is the balance of different tau isoforms, which can be categorized into either three repeat (3R) or four repeat (4R) isoforms based on the number of microtubule-binding repeats that are expressed. Imbalance of 3R and 4R isoforms in either direction can cause FTD and neurodegeneration. There is also increasing evidence that 3R tauopathies such as Pick's disease form tau aggregates predominantly comprised of 3R isoforms and these can present differently from 4R and mixed 3R/4R tauopathies. In this study, multiple mutations in 3R tau were assessed for MT binding properties and prion-like aggregation propensity. Different missense tau mutations showed varying effects on MT binding depending on molecular location and properties. Of the mutations that were surveyed, S356T tau is uniquely capable of prion-like seeded aggregation and forms extensive Thioflavin positive aggregates. This unique prion-like tau strain will be useful to model 3R tau aggregation and will contribute to the understanding of diverse presentations of different tauopathies.

Reversal of Tau-Dependent Cognitive Decay by Blocking Adenosine A1 Receptors: Comparison of Transgenic Mouse Models with Different Levels of Tauopathy.

The accumulation of tau is a hallmark of several neurodegenerative diseases and is associated with neuronal hypoactivity and presynaptic dysfunction. Oral administration of the adenosine A1 receptor antagonist rolofylline (KW-3902) has previously been shown to reverse spatial memory deficits and to normalize the basic synaptic transmission in a mouse line expressing full-length pro-aggregant tau (TauΔK) at low levels, with late onset of disease. However, the efficacy of treatment remained to be explored for cases of more aggressive tauopathy. Using a combination of behavioral assays, imaging with several PET-tracers, and analysis of brain tissue, we compared the curative reversal of tau pathology by blocking adenosine A1 receptors in three mouse models expressing different types and levels of tau and tau mutants. We show through positron emission tomography using the tracer [18F]CPFPX (a selective A1 receptor ligand) that intravenous injection of rolofylline effectively blocks A1 receptors in the brain. Moreover, when administered to TauΔK mice, rolofylline can reverse tau pathology and synaptic decay. The beneficial effects are also observed in a line with more aggressive tau pathology, expressing the amyloidogenic repeat domain of tau (TauRDΔK) with higher aggregation propensity. Both models develop a progressive tau pathology with missorting, phosphorylation, accumulation of tau, loss of synapses, and cognitive decline. TauRDΔK causes pronounced neurofibrillary tangle assembly concomitant with neuronal death, whereas TauΔK accumulates only to tau pretangles without overt neuronal loss. A third model tested, the rTg4510 line, has a high expression of mutant TauP301L and hence a very aggressive phenotype starting at ~3 months of age. This line failed to reverse pathology upon rolofylline treatment, consistent with a higher accumulation of tau-specific PET tracers and inflammation. In conclusion, blocking adenosine A1 receptors by rolofylline can reverse pathology if the pathological potential of tau remains below a threshold value that depends on concentration and aggregation propensity.

Amisulpride as a potential disease-modifying drug in the treatment of tauopathies.

Hyperphosphorylation and aggregation of the microtubule-associated protein tau cause the development of tauopathies, such as Alzheimer's disease and frontotemporal dementia (FTD). We recently uncovered a causal link between constitutive serotonin receptor 7 (5-HT7R) activity and pathological tau aggregation. Here, we evaluated 5-HT7R inverse agonists as novel drugs in the treatment of tauopathies. Based on structural homology, we screened multiple approved drugs for their inverse agonism toward 5-HT7R. Therapeutic potential was validated using biochemical, pharmacological, microscopic, and behavioral approaches in different cellular models including tau aggregation cell line HEK293 tau bimolecular fluorescence complementation, primary mouse neurons, and human induced pluripotent stem cell-derived neurons carrying an FTD-associated tau mutation as well as in two mouse models of tauopathy. Antipsychotic drug amisulpride is a potent 5-HT7R inverse agonist. Amisulpride ameliorated tau hyperphosphorylation and aggregation in vitro. It further reduced tau pathology and abrogated memory impairment in mice. Amisulpride may be a disease-modifying drug for tauopathies.

Genetically Engineered Triple MAPT-Mutant Human-Induced Pluripotent Stem Cells (N279K, P301L, and E10+16 Mutations) Exhibit Impairments in Mitochondrial Bioenergetics and Dynamics

Pathological abnormalities in the tau protein give rise to a variety of neurodegenerative diseases, conjointly termed tauopathies. Several tau mutations have been identified in the tau-encoding gene MAPT, affecting either the physical properties of tau or resulting in altered tau splicing. At early disease stages, mitochondrial dysfunction was highlighted with mutant tau compromising almost every aspect of mitochondrial function. Additionally, mitochondria have emerged as fundamental regulators of stem cell function. Here, we show that compared to the isogenic wild-type triple MAPT-mutant human-induced pluripotent stem cells, bearing the pathogenic N279K, P301L, and E10+16 mutations, exhibit deficits in mitochondrial bioenergetics and present altered parameters linked to the metabolic regulation of mitochondria. Moreover, we demonstrate that the triple tau mutations disturb the cellular redox homeostasis and modify the mitochondrial network morphology and distribution. This study provides the first characterization of disease-associated tau-mediated mitochondrial impairments in an advanced human cellular tau pathology model at early disease stages, ranging from mitochondrial bioenergetics to dynamics. Consequently, comprehending better the influence of dysfunctional mitochondria on the development and differentiation of stem cells and their contribution to disease progression may thus assist in the potential prevention and treatment of tau-related neurodegeneration.

Tau Lysine Pseudomethylation Regulates Microtubule Binding and Enhances Prion-like Tau Aggregation.

Alzheimer's disease (AD) and frontotemporal dementia (FTD) can be classified as tauopathies, which are a group of neurodegenerative diseases that develop toxic tau aggregates in specific brain regions. These pathological tau inclusions are altered by various post-translational modifications (PTMs) that include phosphorylation, acetylation, and methylation. Tau methylation has emerged as a target of interest for its potential involvement in tau pathomechanisms. Filamentous tau aggregates isolated from patients with AD are methylated at multiple lysine residues, although the exact methyltransferases have not been identified. One strategy to study the site-specific effects of methylation is to create methylation mimetics using a KFC model, which replaces lysine (K) with a hydrophobic group such as phenylalanine (F) to approximate the effects of lysine methylation (C or methyl group). In this study, tau methylmimetics were used to model several functional aspects of tau methylation such as effects on microtubule binding and tau aggregation in cell models. Overall, several tau methylmimetics displayed impaired microtubule binding, and tau methylmimetics enhanced prion-like seeded aggregation in the context of the FTD tau mutation P301L. Like other PTMs, tau methylation is a contributing factor to tau pathogenesis and could be a potential therapeutic drug target for the treatment of different tauopathies.

Mutations in α-synuclein, TDP-43 and tau prolong protein half-life through diminished degradation by lysosomal proteases

BackgroundAutosomal dominant mutations in α-synuclein, TDP-43 and tau are thought to predispose to neurodegeneration by enhancing protein aggregation. While a subset of α-synuclein, TDP-43 and tau mutations has been shown to increase the structural propensity of these proteins toward self-association, rates of aggregation are also highly dependent on protein steady state concentrations, which are in large part regulated by their rates of lysosomal degradation. Previous studies have shown that lysosomal proteases operate precisely and not indiscriminately, cleaving their substrates at very specific linear amino acid sequences. With this knowledge, we hypothesized that certain coding mutations in α-synuclein, TDP-43 and tau may lead to increased protein steady state concentrations and eventual aggregation by an alternative mechanism, that is, through disrupting lysosomal protease cleavage recognition motifs and subsequently conferring protease resistance to these proteins.ResultsTo test this possibility, we first generated comprehensive proteolysis maps containing all of the potential lysosomal protease cleavage sites for α-synuclein, TDP-43 and tau. In silico analyses of these maps indicated that certain mutations would diminish cathepsin cleavage, a prediction we confirmed utilizing in vitro protease assays. We then validated these findings in cell models and induced neurons, demonstrating that mutant forms of α-synuclein, TDP-43 and tau are degraded less efficiently than wild type despite being imported into lysosomes at similar rates.ConclusionsTogether, this study provides evidence that pathogenic mutations in the N-terminal domain of α-synuclein (G51D, A53T), low complexity domain of TDP-43 (A315T, Q331K, M337V) and R1 and R2 domains of tau (K257T, N279K, S305N) directly impair their own lysosomal degradation, altering protein homeostasis and increasing cellular protein concentrations by extending the degradation half-lives of these proteins. These results also point to novel, shared, alternative mechanism by which different forms of neurodegeneration, including synucleinopathies, TDP-43 proteinopathies and tauopathies, may arise. Importantly, they also provide a roadmap for how the upregulation of particular lysosomal proteases could be targeted as potential therapeutics for human neurodegenerative disease.

Acetylated tau exacerbates learning and memory impairment by disturbing with mitochondrial homeostasis

Increased tau acetylation at K274 and K281 has been observed in the brains of Alzheimer's disease (AD) patients and animal models, and mitochondrial dysfunction are noticeable and early features of AD. However, the effect of acetylated tau on mitochondria has been unclear until now. Here, we constructed three type of tau forms, acetylated tau mutant by mutating its K274/K281 into Glutamine (TauKQ) to mimic disease-associated lysine acetylation, the non-acetylation tau mutant by mutating its K274/K281 into Arginine (TauKR) and the wild-type human full-length tau (TauWT). By overexpression of these tau forms in vivo and in vitro, we found that, TauKQ induced more severe cognitive deficits with neuronal loss, dendritic plasticity damage and mitochondrial dysfunctions than TauWT. Unlike TauWT induced mitochondria fusion, TauKQ not only induced mitochondria fission by decreasing mitofusion proteins, but also inhibited mitochondrial biogenesis via reduction of PGC-1a/Nrf1/Tfam levels. TauKR had no significant difference in the cognitive and mitochondrial abnormalities compared with TauWT. Treatment with BGP-15 rescued impaired learning and memory by attenuation of mitochondrial dysfunction, neuronal loss and dendritic complexity damage, which caused by TauKQ. Our data suggested that, acetylation at K274/281 was an important post translational modification site for tau neurotoxicity, and BGP-15 is a potential therapeutic drug for AD.

Can accelerated ageing models inform us on age-related tauopathies?

Ageing is the greatest risk factor of late-onset neurodegenerative diseases. In the realm of sporadic tauopathies, modelling the process of biological ageing in experimental animals forms the foundation of searching for the molecular origin of pathogenic tau and developing potential therapeutic interventions. Although prior research into transgenic tau models offers valuable lessons for studying how tau mutations and overexpression can drive tau pathologies, the underlying mechanisms by which ageing leads to abnormal tau accumulation remains poorly understood. Mutations associated with human progeroid syndromes have been proposed to be able to mimic an aged environment in animal models. Here, we summarise recent attempts in modelling ageing in relation to tauopathies using animal models that carry mutations associated with human progeroid syndromes, or genetic elements unrelated to human progeroid syndromes, or have exceptional natural lifespans, or a remarkable resistance to ageing-related disorders.

Effect of Nrf2 loss on senescence and cognition of tau-based P301S mice.

Cellular senescence may contribute to chronic inflammation involved in the progression of age-related diseases such as Alzheimer's disease (AD), and its removal prevents cognitive impairment in a model of tauopathy. Nrf2, the major transcription factor for damage response pathways and regulators of inflammation, declines with age. Our previous work showed that silencing Nrf2 gives rise to premature senescence in cells and mice. Others have shown that Nrf2 ablation can exacerbate cognitive phenotypes of some AD models. In this study, we aimed to understand the relationship between Nrf2 elimination, senescence, and cognitive impairment in AD, by generating a mouse model expressing a mutant human tau transgene in an Nrf2 knockout (Nrf2KO) background. We assessed senescent cell burden and cognitive decline of P301S mice in the presence and absence of Nrf2. Lastly, we administered 4.5-month-long treatments with two senotherapeutic drugs to analyze their potential to prevent senescent cell burden and cognitive decline: the senolytic drugs dasatinib and quercetin (DQ) and the senomorphic drug rapamycin. Nrf2 loss accelerated the onset of hind-limb paralysis in P301S mice. At 8.5months of age, P301S mice did not exhibit memory deficits, while P301S mice without Nrf2 were significantly impaired. However, markers of senescence were not elevated by Nrf2 ablation in any of tissues that we examined. Neither drug treatment improved cognitive performance, nor did it reduce expression of senescence markers in brains of P301S mice. Contrarily, rapamycin treatment at the doses used delayed spatial learning and led to a modest decrease in spatial memory. Taken together, our data suggests that the emergence of senescence may be causally associated with onset of cognitive decline in the P301S model, indicate that Nrf2 protects brain function in a model of AD through mechanisms that may include, but do not require the inhibition of senescence, and suggest possible limitations for DQ and rapamycin as therapies for AD.

Cortical iron accumulation in MAPT- and C9orf 72-associated frontotemporal lobar degeneration.

Neuroinflammation has been implicated in frontotemporal lobar degeneration (FTLD) pathophysiology, including in genetic forms with microtubule-associated protein tau (MAPT) mutations (FTLD-MAPT) or chromosome 9 open reading frame 72(C9orf72) repeat expansions (FTLD-C9orf72). Iron accumulation as a marker of neuroinflammation has, however, been understudied in genetic FTLD to date. To investigate the occurrence of cortical iron accumulation in FTLD-MAPT and FTLD-C9orf72, iron histopathology was performed on the frontal and temporal cortex of 22 cases (11 FTLD-MAPT and 11 FTLD-C9orf72). We studied patterns of cortical iron accumulation and its colocalization with the corresponding underlying pathologies (tau and TDP-43), brain cells (microglia and astrocytes), and myelination. Further, with ultrahigh field ex vivo MRI on a subset (four FTLD-MAPT and two FTLD-C9orf72), we examined the sensitivity of T2*-weighted MRI for iron in FTLD. Histopathology showed that cortical iron accumulation occurs in both FTLD-MAPT and FTLD-C9orf72 in frontal and temporal cortices, characterized by a diffuse mid-cortical iron-rich band, and by a superficial cortical iron band in some cases. Cortical iron accumulation was associated with the severity of proteinopathy (tau or TDP-43) and neuronal degeneration, in part with clinical severity, and with the presence of activated microglia, reactive astrocytes and myelin loss. Ultra-high field T2*-weighted MRI showed a good correspondence between hypointense changes on MRI and cortical iron observed on histology. We conclude that iron accumulation is a feature of both FTLD-MAPT and FTLD-C9orf72 and is associated with pathological severity. Therefore, in vivo iron imaging using T2*-weighted MRI or quantitative susceptibility mapping may potentially be used as a noninvasive imaging marker to localize pathology in FTLD.

FTD-tau S320F mutation stabilizes local structure and allosterically promotes amyloid motif-dependent aggregation

Amyloid deposition of the microtubule-associated protein tau is associated with neurodegenerative diseases. In frontotemporal dementia with abnormal tau (FTD-tau), missense mutations in tau enhance its aggregation propensity. Here we describe the structural mechanism for how an FTD-tau S320F mutation drives spontaneous aggregation, integrating data from in vitro, in silico and cellular experiments. We find that S320F stabilizes a local hydrophobic cluster which allosterically exposes the 306VQIVYK311 amyloid motif; identify a suppressor mutation that destabilizes S320F-based hydrophobic clustering reversing the phenotype in vitro and in cells; and computationally engineer spontaneously aggregating tau sequences through optimizing nonpolar clusters surrounding the S320 position. We uncover a mechanism for regulating tau aggregation which balances local nonpolar contacts with long-range interactions that sequester amyloid motifs. Understanding this process may permit control of tau aggregation into structural polymorphs to aid the design of reagents targeting disease-specific tau conformations.

Spermidine Rescues Bioenergetic and Mitophagy Deficits Induced by Disease-Associated Tau Protein

Abnormal tau build-up is a hallmark of Alzheimer's disease (AD) and more than 20 other serious neurodegenerative diseases. Mitochondria are paramount organelles playing a predominant role in cellular bioenergetics, namely by providing the main source of cellular energy via adenosine triphosphate generation. Abnormal tau impairs almost every aspect of mitochondrial function, from mitochondrial respiration to mitophagy. The aim of our study was to investigate the effects of spermidine, a polyamine which exerts neuroprotective effects, on mitochondrial function in a cellular model of tauopathy. Recent evidence identified autophagy as the main mechanism of action of spermidine on life-span prolongation and neuroprotection, but the effects of spermidine on abnormal tau-induced mitochondrial dysfunction have not yet been investigated. We used SH-SY5Y cells stably expressing a mutant form of human tau protein (P301L tau mutation) or cells expressing the empty vector (control cells). We showed that spermidine improved mitochondrial respiration, mitochondrial membrane potential as well as adenosine triphosphate (ATP) production in both control and P301L tau-expressing cells. We also showed that spermidine decreased the level of free radicals, increased autophagy and restored P301L tau-induced impairments in mitophagy. Overall, our findings suggest that spermidine supplementation might represent an attractive therapeutic approach to prevent/counteract tau-related mitochondrial impairments.

A novel gene therapy for methamphetamine- induced cognitive disorder with a hyper-acidified fusion variant of DnaJB1

Methamphetamine (MA) is spread worldwide and is a highly addictive psychostimulant that can induce neurodegeneration and cognitive disorder, which lacks effective treatments. We and other researchers have found that the crucial member of Hsp70 chaperone machinery, DnaJ, is liable to be co-aggregated with aberrant proteins, which has been confirmed a risk factor to promote neurodegeneration. In the current study, we demonstrated that tailing with a hyper-acidic fusion partner, tua2, human DnaJB1 could resist the formation of toxic mutant Tau aggregates both in prokaryote and eukaryote models. We found that aberrant Tau aggregates could deplete the antioxidant enzyme pool and disturb Hsp70 molecular chaperone system by co-aggregating with the principal members of these systems. Stability-enhanced DnaJB1-tua2 could stop the chain reaction of Tau aggregates as well as maintain redox balance and protein homeostasis. With an MA-induced cognitive disorder mouse model, we found that the cognitive disorder of MA mice was rescued and the overactivated inflammatory response was relieved by the expression of DnaJB1-tua2 in the hippocampus. Furthermore, the Tau neurofibrillary tangles and apoptotic neurons were diminished with the escorting of DnaJB1-tua2. These findings demonstrate that delivering DnaJB1-tua2 in hippocampus may have a therapeutic potential in the treatment of MA-induced cognitive disorder.

Common mouse models of tauopathy reflect early but not late human disease

BackgroundMouse models that overexpress human mutant Tau (P301S and P301L) are commonly used in preclinical studies of Alzheimer’s Disease (AD) and while several drugs showed therapeutic effects in these mice, they were ineffective in humans. This leads to the question to which extent the murine models reflect human Tau pathology on the molecular level.MethodsWe isolated insoluble, aggregated Tau species from two common AD mouse models during different stages of disease and characterized the modification landscape of the aggregated Tau using targeted and untargeted mass spectrometry-based proteomics. The results were compared to human AD and to human patients that suffered from early onset dementia and that carry the P301L Tau mutation.ResultsBoth mouse models accumulate insoluble Tau species during disease. The Tau aggregation is driven by progressive phosphorylation within the proline rich domain and the C-terminus of the protein. This is reflective of early disease stages of human AD and of the pathology of dementia patients carrying the P301L Tau mutation. However, Tau ubiquitination and acetylation, which are important to late-stage human AD are not represented in the mouse models.ConclusionAD mouse models that overexpress human Tau using risk mutations are a suitable tool for testing drug candidates that aim to intervene in the early formation of insoluble Tau species promoted by increased phosphorylation of Tau.

Characterization of pseudophosphorylated tau protein.

Tau protein facilitates assembly, organization, and stability of microtubules found in neuronal axons. Hyperphosphorylation results in a loss of tau function from decreased microtubule binding affinity which is prominent in Alzheimer's Disease. The current study employed 7-Phos—a tau mutant with seven specific site pseudophosphorylation mutations—to mimic the characteristic changes found in hyperphosphorylation. In vivo, tau has six naturally occurring isoforms that vary in the length of the N-terminal projection domains, three of which were investigated in this study. Biophysical characterization of these isoforms was accomplished with several techniques. SDS-PAGE was used to identify an upward band shift, a feature of 7-Phos. A thioflavin fluorescence assay was performed to compare the arachidonic acid induced polymerization of the 7-Phos variants with their wild-type counterparts. Atomic force microscopy was used to measure the length of 7-Phos tau polymers over several days and to analyze the intermolecular interactions between molecules of 7-Phos. We determined that the total amount of polymerization measured by thioflavin fluorescence of the two longer 7-Phos isoforms, 1N4R and 2N4R, were similar to their corresponding wild-type proteins. The total amount of polymerization of the shortest isoform, 0N4R, was greater than its wild-type. Atomic force microscopy (AFM) imaging revealed that 7-Phos isoforms form longer polymers than their wild-type. Atomic force microscopy of immobilized tau layers allowed comparison of projection domain lengths between 7-Phos and wild-type. These results demonstrate some novel AFM-based measurements to characterize tau polymerization, projection domain extension/conformation and intermolecular interactions.

Investigations into the phase separation and nuclear role of tau.

Tau is a microtubule-associated protein and pathological hallmark of Alzheimer's disease (AD), most infamous for becoming hyperphosphorylated and fibrilizing into neurofibrillary tangles (NFTs). Beyond this role, mounting evidence suggests that tau localizes into the nucleus and plays unknown roles in DNA protection and heterochromatin regulation. Intriguingly, frontotemporal dementia mutants (P301L) of tau show loss of genetically silent heterochromatin clusters. This has been associated with aberrant expression of heterochromatic genes and in other studies, of transposable element activation in AD patient brain tissue. Similar effects of heterochromatin relaxation and gene dysregulation have been observed in tau knockouts, suggesting that loss of tau is pathologically relevant. Recent literature showed that tau undergoes liquid-liquid phase separation (LLPS). Studies have not fully described the functional role of nuclear tau in gene regulation, and whether this involves LLPS. My work demonstrates that tau has an intrinsic ability to phase separate with, compact, and oligomerize chromatin, likely through its DNA-binding domain, and this is regulated by phosphorylation. In addition, tau phase separates with heterochromatin protein 1α (HP1α), an essential heterochromatin constituent, which may promote its partitioning into heterochromatin despite its lack of DNA-sequence specificity. These data imply a potential role for tau LLPS in the maintenance of chromatin compaction with aging.

Understanding the effect of tau protein phosphorylation on nucleosome array compaction.

Tau is an intrinsically disordered, microtubule associated protein that is mainly expressed in neurons and responsible for stabilizing microtubules in axons. The hyperphosphorylation of tau causes it to dissociate from microtubules which promotes its aggregation into neurofibrillary tangles (NFTs). This can significantly affect brain function. Tau is also found in the nucleus and plays an important role in DNA protection, chromosome stability, and heterochromatin regulation. Recent work has found a correlation between disease-relevant mutations of tau with heterochromatin relaxation, destabilization, and aberrant gene expression. Understanding how tau interacts with nucleosome arrays would give us insight into tau's role in gene expression and regulation. Here, we investigate the question of how the concentration and phosphorylation state of tau affects interactions with nucleosome arrays and their compaction state? We explored this question by using micrococcal nuclease digestion assays to determine the extent of tau's protection on nucleosome arrays. We found that an increase in wild type tau concentration leads to a dramatic increase in array protection but phosphorylated tau shows less dramatic protection patterns. These results provide insights into how tau might be involved in DNA protection and how this process might be disrupted in disease.