Pathogenesis Of Tauopathies Research Articles

Molecular Insights into the Differential Effects of Acetylation on the Aggregation of Tau Microtubule-Binding Repeats.

Aggregation of tau protein into intracellular fibrillary inclusions is characterized as the hallmark of tauopathies, including Alzheimer's disease and chronic traumatic encephalopathy. The microtubule-binding (MTB) domain of tau, containing either three or four repeats with sequence similarities, plays an important role in determining tau's aggregation. Previous studies have reported that abnormal acetylation of lysine residues displays a distinct effect on the formation of pathological tau aggregates. However, the underlying molecular mechanism remains mostly elusive. In this study, we performed extensive replica exchange molecular dynamics (REMD) simulations of 144 μs in total to systematically investigate the dimerization of four tau MTB repeats and explore the impacts of Lys280 (K280) or Lys321 (K321) acetylation on the conformational ensembles of the R2 or R3 dimer. Our results show that R3 is the most prone to aggregation among the four repeats, followed by R2 and R4, while R1 displays the weakest aggregation propensity with a disordered structure. Acetylation of K280 could promote the aggregation of R2 peptides by increasing the formation of β-sheet structures and strengthening the interchain interaction. However, K321 acetylation decreases the β-sheet content of the R3 dimer, reduces the ability of R3 peptides to form long β-strands, and promotes the stable helix structure formation. The salt bridge and Y310-Y310 π-π stacking interactions of the R3 dimer are greatly weakened by K321 acetylation, resulting in the inhibition of dimerization. This study uncovers the structural ensembles of tau MTB repeats and provides mechanistic insights into the influences of acetylation on tau aggregation, which may deepen the understanding of the pathogenesis of tauopathies.

A decrease in Fkbp52 alters autophagosome maturation and A152T-tau clearance in vivo.

The failure of the autophagy-lysosomal pathway to clear the pathogenic forms of Tau exacerbates the pathogenesis of tauopathies. We have previously shown that the immunophilin FKBP52 interacts both physically and functionally with Tau, and that a decrease in FKBP52 protein levels is associated with Tau deposition in affected human brains. We have also shown that FKBP52 is physiologically present within the lysosomal system in healthy human neurons and that a decrease in FKBP52 expression alters perinuclear lysosomal positioning and Tau clearance during Tau-induced proteotoxic stress in vitro. In this study, we generate a zebrafish fkbp4 loss of function mutant and show that axonal retrograde trafficking of Lamp1 vesicles is altered in this mutant. Moreover, using our transgenic HuC::mCherry-EGFP-LC3 line, we demonstrate that the autophagic flux is impaired in fkbp4 mutant embryos, suggesting a role for Fkbp52 in the maturation of autophagic vesicles. Alterations in both axonal transport and autophagic flux are more evident in heterozygous rather than homozygous fkbp4 mutants. Finally, taking advantage of the previously described A152T-Tau transgenic fish, we show that the clearance of pathogenic A152T-Tau mutant proteins is slower in fkbp4 +/- mutants in comparison to fkbp4 +/+ larvae. Altogether, these results indicate that Fkbp52 is required for the normal trafficking and maturation of lysosomes and autophagic vacuoles along axons, and that its decrease is sufficient to hinder the clearance of pathogenic Tau in vivo.

Inpp5d deficiency exacerbates tau pathology and cognitive deficits in MAPTP301S mouse

AbstractBackgroundAlzheimer’s disease (AD) is the most common cause of dementia and is characterized by the cerebral accumulation of amyloid plaques and tauopathy. The gene inositol polyphosphate‐5‐phosphatase D (INPP5D), which encodes Src homology 2‐containing‐inositol‐phosphatase‐1 (SHIP1), has been highlighted by multiple approaches as a gene that modulates the risk for AD. SHIP1 expression in brain is restricted to inflammatory cells called microglia that have been shown to play significant roles in the induction and spread of tauopathy. Therefore, the goal of the current study was to examine the effect of microglial Inpp5d/SHIP1 knockdown on a mouse model of tauopathy.MethodWe generated a mouse model of conditional Inpp5d knockdown in microglia to assess the impact on pathology in the MAPTP301S mouse model of tauopathy, using Inpp5dflox mice crossed with an inducible Cx3cr1CreER/+. To induce recombination, 3‐month‐old (mo) Inpp5dfl/fl/Cx3cr1CreER/+ mice, with and without the MAPTP301S transgene, were injected for 5 consecutive days with either tamoxifen (TAM) or corn oil (CO). At 8.5 mo, we assessed learning behavior using the Barnes Maze test and Novel Object Recognition test. Finally, we performed immunohistochemistry, immunoblotting, and quantitative real‐time PCR to assess neuroinflammation and tau pathology.ResultTAM treatment of Inpp5dfl/fl/Cx3cr1CreER/+ mice and MAPTP301S /Inpp5dfl/fl/Cx3cr1CreER/+ mice was used to induce microglial Inpp5d deficiency in both lines. Microglial Inpp5d deficiency in MAPTP301S mice was associated with increased levels of AT8+ hyperphosphorylated tau, yet the numbers of IBA1+ microglia and GFAP+ astrocytes were similar to MAPTP301S expressing normal levels of Inpp5d.ConclusionOur findings suggest that, in our mouse model, Inpp5d deficiency plays an important role in the pathogenesis of tauopathy, but fails to induce an obvious increase in the numbers of either IBA1+ microglia or GFAP+ astrocytes. Our results provide evidence for further evaluation of INPP5D/SHIP1 as a potential target for treating and/or preventing AD.

Modulation of the p75 neurotrophin receptor in the PS19 tauopathy mouse model regulates transcription profiles and inter‐cellular communication across multiple populations of non‐neuronal cells

AbstractBackgroundTau pathologies contribute to neurodegeneration in Alzheimer’s Disease (AD) and other disorders via a variety of mechanisms. In tauopathy mouse models, administration of LM11A‐31 (C31), a small molecule modulator of the p75 neurotrophin receptor (p75NTR), reduced tau post‐translational modifications, accumulation of pathological tau species and microglial activation; restored synaptic plasticity, and reversed synaptic spine loss. We examined long‐term dosing with C31 at the single‐cell transcriptional level to further elucidate cell types and cellular mechanisms affected by treatment.MethodTauopathy model tauP301S mice (PS19) and age‐matched wildtype (Wt) mice were dosed by oral gavage with C31 or vehicle once daily for 3 months from 6 months of age, when tau pathology was well established. Whole cortex single‐nucleus RNA‐sequencing was analyzed using Seurat, with automated cell type annotation, followed by manual curation. Additional analyses compared AD‐associated biodomains and risk scored genes from TREAT‐AD with individual cell types. Finally, cell‐to‐cell communication was assessed via Liana ligand‐receptor (LR) interaction analysis.ResultSeveral neuronal, glial, and vascular cell types showed inverse correlations between C31 differential expression and both PS19 differential expression and TREAT‐AD biodomains (Figure 1), suggesting shifts in expression profiles in the opposite direction from those in human AD cohorts and mouse tauopathy models. In LR interaction analysis, vascular and leptomeningeal cells (VLMCs) were highly active as a signaling source to most other cells—particularly neurons—in the PS19 vehicle mice compared to all other groups (Figure 2). VLMC LR signals that were stronger in PS19 vehicle mice versus Wt vehicle were enriched for Focal Adhesion/PI3K‐Akt signaling, TGF‐beta signaling, AD‐presenilin pathways and regulation of synapse organization (Figure 3). VLMC LR signals that were stronger in PS19 C31 versus PS19 vehicle showed similar pathway enrichments and included several neuropilin‐semaphorin‐plexin complexes which may direct neuronal wiring and development.ConclusionThese findings demonstrate that broad patterns of expression and LR signaling in multiple cell types impacted by tauopathy show substantial reversion to wildtype‐like patterns when treated with C31. Further they indicate a possible role for VLMC signaling in the pathogenesis of tauopathies.

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.

Tau protein modulates an epigenetic mechanism of cellular senescence in human SH-SY5Y neuroblastoma cells.

Introduction: Progressive Tau deposition in neurofibrillary tangles and neuropil threads is the hallmark of tauopathies, a disorder group that includes Alzheimer's disease. Since Tau is a microtubule-associated protein, a prevalent concept to explain the pathogenesis of tauopathies is that abnormal Tau modification contributes to dissociation from microtubules, assembly into multimeric β-sheets, proteotoxicity, neuronal dysfunction and cell loss. Tau also localizes in the cell nucleus and evidence supports an emerging function of Tau in DNA stability and epigenetic modulation. Methods: To better characterize the possible role of Tau in regulation of chromatin compaction and subsequent gene expression, we performed a bioinformatics analysis of transcriptome data obtained from Tau-depleted human neuroblastoma cells. Results: Among the transcripts deregulated in a Tau-dependent manner, we found an enrichment of target genes for the polycomb repressive complex 2. We further describe decreased cellular amounts of the core components of the polycomb repressive complex 2 and lower histone 3 trimethylation in Tau deficient cells. Among the de-repressed polycomb repressive complex 2 target gene products, IGFBP3 protein was found to be linked to increased senescence induction in Tau-deficient cells. Discussion: Our findings propose a mechanism for Tau-dependent epigenetic modulation of cell senescence, a key event in pathologic aging.

TRIM11 protects against tauopathies and is down-regulated in Alzheimer's disease.

Aggregation of tau into filamentous inclusions underlies Alzheimer's disease (AD) and numerous other neurodegenerative tauopathies. The pathogenesis of tauopathies remains unclear, which impedes the development of disease-modifying treatments. Here, by systematically analyzing human tripartite motif (TRIM) proteins, we identified a few TRIMs that could potently inhibit tau aggregation. Among them, TRIM11 was markedly down-regulated in AD brains. TRIM11 promoted the proteasomal degradation of mutant tau as well as superfluous normal tau. It also enhanced tau solubility by acting as both a molecular chaperone to prevent tau misfolding and a disaggregase to dissolve preformed tau fibrils. TRIM11 maintained the connectivity and viability of neurons. Intracranial delivery of TRIM11 through adeno-associated viruses ameliorated pathology, neuroinflammation, and cognitive impairments in multiple animal models of tauopathies. These results suggest that TRIM11 down-regulation contributes to the pathogenesis of tauopathies and that restoring TRIM11 expression may represent an effective therapeutic strategy.

Molecular activation of gliovascular signaling precedes blood‐brain barrier disruption and neuronal loss in a mouse model of tauopathy

AbstractBackgroundIncreasing evidence points to disruption of the blood‐brain barrier (BBB) as an inciting event in the pathogenesis of Alzheimer’s disease. The contribution of tau‐mediated pathways driving blood‐brain dysfunction are comparatively understudied.MethodUsing the P301S mouse model of tauopathy, we employed dynamic contrast enhanced MRI (DCE‐MRI) and quantitative spatial analysis using gadolinium‐based mass spectrometry imaging to demonstrate widespread BBB dysfunction in late stage tauopathy. To identify molecular pathways regulating intercellular signaling between neurons and gliovascular support cells that are dysregulated in advance of BBB disruption, we developed a cell‐specific viral approach for transcriptional profiling of novel pathways within the multicellular environment of the neurovascular unit (NVU) in tauopathy. Viral constructs using cell‐type specific promoters (hSynapsin, GFAP, or PDGFRb) to drive expression of antigen‐tagged ribosomes (TRAP) were used to study variance in spatial and temporal gene expression patterns in NVU cell types in P301S transgenic mice prior to widespread BBB disruption.ResultRegional disruption of BBB integrity involving the hippocampus, lateral temporal, and frontal cortices is prominent in 11 month‐old P301S mice. Cell‐specific profiling of early symptomatic 6 month‐old P301S mice identified a defined gene expression profile antecedent to BBB disruption in NVU cells comprised of 29 shared and 3299 unique genes across all cell types. In this early symptomatic stage of tauopathy, pericytes (1021 genes) and astrocytes (1717 genes) were remarkably more transcriptionally active than neurons (561 genes). Gene ontology analysis indicates that multiple molecular programs driving neuronal differentiation, neurite outgrowth, and synaptogenesis are expressed in gliovascular cells in the prodromal stage.ConclusionThe specific and temporally regulated coordination of pathways in pericytes and astrocytes in advance of BBB dysfunction implicates the neurovascular unit as a potential driver in the development of tauopathy. This suggests a paradigm exists for gliovascular rescue of neurodegeneration and implicates numerous novel perivascular molecular pathways in the pathogenesis of tauopathy and Alzheimer’s disease.

Limitations of human tau-expressing mouse models and novel approaches of mouse modeling for tauopathy.

Neurofibrillary tangles (NFTs) composed of hyperphosphorylated tau protein are primarily neuropathological features of a number of neurodegenerative diseases, collectively termed tauopathy. There is no disease-modifying drug available for tauopathy except anti-amyloid antibody therapies for Alzheimer's disease. For tau-targeting therapy, experimental models recapitulating human tau pathologies are indispensable. However, there are limited numbers of animal models that display intracellular filamentous tau aggregations. At present, several lines of P301L/S mutant tau-expressing transgenic mice successfully developed neurofibrillary pathology in the central nervous system, while most non-mutant tau-expressing transgenic mice rarely developed tau pathology. Importantly, recent studies have revealed that transgenes disrupt the coding sequence of endogenous genes, resulting in deletions and/or structural variations at the insertion site. Although any impact on the pathogenesis of tauopathy is unknown, gene disruptions may affect age-related neurodegeneration including tangle formation and brain atrophy. Moreover, some mouse lines show strain-dependent pathological features. These limitations (FTDP-17 mutations, insertion/deletion mutations, and genetic background) are a major hindrance to the establishment of a precise disease model of tauopathy. In this review, we noticed both the utility and the pitfalls of current P301L/S mutant tau-expressing transgenic mice, and we propose future strategies of mouse modeling to replicate human tauopathies.

Atomistic Insights into the Inhibitory Mechanism of Tyrosine Phosphorylation against the Aggregation of Human Tau Fragment PHF6.

Abnormal aggregation of the microtubule-associated protein tau into intracellular fibrillary inclusions is characterized as the hallmark of tauopathies, including Alzheimer's disease and chronic traumatic encephalopathy. The hexapeptide 306VQIVYK311 (PHF6) of R3 plays an important role in the aggregation of tau. Recent experimental studies reported that phosphorylation of residue tyrosine 310 (Y310) could decrease the propensity of PHF6 to form fibrils and inhibit tau aggregation. However, the underlying inhibitory mechanism is not well understood. In this work, we systematically investigated the influences of phosphorylation on the conformational ensembles and oligomerization dynamics of PHF6 by performing extensive all-atom molecular dynamics (MD) simulations. Our replica exchange MD simulations demonstrate that Y310 phosphorylation could effectively suppress the formation of β-structure and shift PHF6 oligomers toward coil-rich aggregates. The interaction analyses show that hydrogen bonding and hydrophobic interactions among PHF6 peptides, as well as Y310-Y310 π-π stacking and I308-Y310 CH-π interactions, are weakened by phosphorylation. Additional microsecond MD simulations show that Y310 phosphorylation could inhibit the oligomerization of PHF6 by preventing the formation of large β-sheet oligomers and multi-layer β-sheet aggregates. This study provides mechanistic insights into the phosphorylation-inhibited tau aggregation, which may be helpful for the in-depth understanding of the pathogenesis of tauopathies.

Tuberous sclerosis complex is associated with a novel human tauopathy.

Tuberous sclerosis complex (TSC) is a neurogenetic disorder leading to epilepsy, developmental delay, and neurobehavioral dysfunction. The syndrome is caused by pathogenic variants in TSC1 (coding for hamartin) or TSC2 (coding for tuberin). Recently, we reported a progressive frontotemporal dementia-like clinical syndrome in a patient with a mutation in TSC1, but the neuropathological changes seen in adults with TSC with or without dementia have yet to be systematically explored. Here, we examined neuropathological findings in adults with TSC (n = 11) aged 30-58years and compared them to age-matched patients with epilepsy unrelated to TSC (n = 9) and non-neurological controls (n = 10). In 3 of 11 subjects with TSC, we observed a neurofibrillary tangle-predominant "TSC tauopathy" not seen in epilepsy or non-neurological controls. This tauopathy was observed in the absence of pathological amyloid beta, TDP-43, or alpha-synuclein deposition. The neurofibrillary tangles in TSC tauopathy showed a unique pattern of post-translational modifications, with apparent differences between TSC1 and TSC2 mutation carriers. Tau acetylation (K274, K343) was prominent in both TSC1 and TSC2, whereas tau phosphorylation at a common phospho-epitope (S202) was observed only in TSC2. TSC tauopathy was observed in selected neocortical, limbic, subcortical, and brainstem sites and showed a 3-repeat greater than 4-repeat tau isoform pattern in both TSC1 and TSC2 mutation carriers, but no tangles were immunolabeled with MC1 or p62 antibodies. The findings suggest that individuals with TSC are at risk for a unique tauopathy in mid-life and that tauopathy pathogenesis may involve TSC1, TSC2, and related molecular pathways.

Identification and characterization of a MAPT-targeting locked nucleic acid antisense oligonucleotide therapeutic for tauopathies

Tau is a microtubule-associated protein (MAPT, tau) implicated in the pathogenesis of tauopathies, a spectrum of neurodegenerative disorders characterized by accumulation of hyperphosphorylated, aggregated tau. Because tau pathology can be distinct across diseases, a pragmatic therapeutic approach may be to intervene at the level of the tau transcript, as it makes no assumptions to mechanisms of tau toxicity. Here we performed a large library screen of locked-nucleic-acid (LNA)-modified antisense oligonucleotides (ASOs), where careful tiling of the MAPT locus resulted in the identification of hot spots for activity in the 3′ UTR. Further modifications to the LNA design resulted in the generation of ASO-001933, which selectively and potently reduces tau in primary cultures from hTau mice, monkey, and human neurons. ASO-001933 was well tolerated and produced a robust, long-lasting reduction in tau protein in both mouse and cynomolgus monkey brain. In monkey, tau protein reduction was maintained in brain for 20 weeks post injection and corresponded with tau protein reduction in the cerebrospinal fluid (CSF). Our results demonstrate that LNA-ASOs exhibit excellent drug-like properties and sustained efficacy likely translating to infrequent, intrathecal dosing in patients. These data further support the development of LNA-ASOs against tau for the treatment of tauopathies.

The effect of lipid composition on the dynamics of tau fibrils.

Knowledge of the interaction of the tau fibrils with the cell membrane is critical for the understanding of the underlying tauopathy pathogenesis. Lipid composition is found to affect the conformational ensemble of the tau fibrils. Using coarse-grained and all-atom molecular dynamics simulations we have shown the effect of the lipid composition in modulating the tau structure and dynamics. Molecular dynamics simulations show that tau proteins interact differentially with the zwitterionic compared to the charged lipid membranes. The negatively charged POPG lipid membranes increase the binding propensity of the tau fibrils. The addition of cholesterol is also found to modify the tau binding to the membrane. The binding of tau fibril leads to the concomitant loss of the β-sheet structures across the tau residues alongside the change in the membrane properties (like area per lipid, bilayer thickness, and order parameter of the lipid tails) over the pure bilayers.

Phosphorylation of Truncated Tau Promotes Abnormal Native Tau Pathology and Neurodegeneration.

Abnormal posttranslational modifications of tau play important roles in mediating neurodegeneration in tauopathies including Alzheimer's disease. Both phosphorylation and truncation are implicated in the pathogenesis of tauopathies. However, whether phosphorylation aggravates truncated tau-induced pathology and neurodegeneration remains elusive. Here, we construct different tau fragments cleaved by delta secretase, with either phosphorylation or non-phosphorylation mimic mutations, and evaluate the contributions of phosphorylation to truncated tau-induced pathological and behavioral alterations in vitro and in vivo through biochemical methods including detergent insoluble tau extraction, western blot, immunofluorescence, flow cytometry, and behavior tests. Our results show that the self-aggregation of phospho-truncated tau is significantly influenced by the domain it contains. N-terminal inhibits, proline-rich domain promotes, and C-terminus have no impact on phospho-truncated tau aggregation. Phosphorylation of truncated tau1-368, which contains the microtubule-binding repeat domain and the proline-rich domain, induces endogenous tau phosphorylation and aggregation. In vivo, phospho-tau1-368 but not non-phospho-tau1-368 leads to a decrease in body weight of C57BL/6J mice. Intriguingly, although tau1-368-induced anxiety behavior in C57BL/6J mice is phosphorylation-independent, the recognition memory of mice is impaired by phospho-tau1-368, but not by non-phospho-tau1-368. Immunofluorescence staining shows that overexpressing phospho-tau1-368 results in neuronal loss and gliosis in the hippocampus, while the transmission of tau1-368 is phosphorylation-independent as revealed by the flow cytometry results in vitro and immunofluorescence staining in vivo. Our findings indicate that phosphorylation of truncated tau significantly fosters endogenous tau pathology and neurodegeneration.

Does MAPT have anything new to say? Discovery of novel nonaggregative Tau isoforms that are decreased in Alzheimer’s disease.

Introduction: Tauopathies, including Alzheimer's disease (AD), are a group of neurodegenerative disorders characterised by Tau hyperphosphorylation. Post-translational modifications of Tau such as phosphorylation and truncation have been demonstrated to be an essential step in the molecular pathogenesis of tauopathies. Alternative splicing is the process by which a single gene can produce multiple transcripts and, potentially, as many different proteins. Tau isoforms are generated by alternative splicing from a single gene, MAPT. In this work, we demonstrate the existence of a new, human- specific truncated form of Tau generated by intron 12 retention. Materials and methods: Intron-12-retaining MAPT transcripts were detected using qPCR with SH-SY5Y neuroblastoma human cells and confirmed in human brain samples. Results were validated on a database of human RNA-seq samples (363 samples from three brain regions). Functional assays were carried out after cloning the isoform on the eukaryotic and prokariotic expression vectors pSG5 and pRK172. Functional analysis evaluated sarkosyl solubility, heparin-induced self-aggregation, microtubule stabilisation and binding affinity and epitope phosphorylation; all of them evaluated by Western blot. Heparin-induced aggregation and microtubule stabilisation were also analysed by electron microscopy. Protein levels on human samples were analysed by Western blot on Alzheimer’s brain classified according to Braak stages I (n = 3), II (n = 6), III (n = 4), IV (n = 1), V (n = 10) and VI (n = 8), and non-demented control subjects (n = 10). Results and conclusions: In this work, we demonstrated the existence of a previously undescribed, human-specific truncated tau isoform generated by intron 12 retention. RNA transcripts retaining intron 12 were detected in SHSY5Y cells and, to a greater extent, in human brains, which were then further confirmed on a larger RNAseq public database. Functional analysis demonstrated that, while this new Tau isoform exhibits similar post-transcriptional modifications by phosphorylation and affinity for microtubule binding, it is less prone to aggregate than other Tau isoforms. Importantly, diminished protein levels of this new Tau isoform are found in Alzheimer's patients' brains with respect to non-demented control subjects, suggesting that the lack of this truncated isoform may play an important role in the pathology. Our results open up new research avenues focused on the exploration of MAPT alternative splicing and the striking characteristics of novel isoforms, that may help develop future therapies for Alzheimer’s disease and other tauopathies

Altered Brain Arginine Metabolism and Polyamine System in a P301S Tauopathy Mouse Model: A Time-Course Study.

Altered arginine metabolism (including the polyamine system) has recently been implicated in the pathogenesis of tauopathies, characterised by hyperphosphorylated and aggregated microtubule-associated protein tau (MAPT) accumulation in the brain. The present study, for the first time, systematically determined the time-course of arginine metabolism changes in the MAPT P301S (PS19) mouse brain at 2, 4, 6, 8 and 12 months of age. The polyamines putrescine, spermidine and spermine are critically involved in microtubule assembly and stabilization. This study, therefore, further investigated how polyamine biosynthetic and catabolic enzymes changed in PS19 mice. There were general age-dependent increases of L-arginine, L-ornithine, putrescine and spermidine in the PS19 brain (particularly in the hippocampus and parahippocampal region). While this profile change clearly indicates a shift of arginine metabolism to favor polyamine production (a polyamine stress response), spermine levels were decreased or unchanged due to the upregulation of polyamine retro-conversion pathways. Our results further implicate altered arginine metabolism (particularly the polyamine system) in the pathogenesis of tauopathies. Given the role of the polyamines in microtubule assembly and stabilization, future research is required to understand the functional significance of the polyamine stress response and explore the preventive and/or therapeutic opportunities for tauopathies by targeting the polyamine system.

Hyperphosphorylated Tau Relates to Improved Cognitive Performance and Reduced Hippocampal Excitability in the Young rTg4510 Mouse Model of Tauopathy.

Tau hyperphosphorylation at several sites, including those close to its microtubule domain (MD), is considered a key pathogenic event in the development of tauopathies. Nevertheless, we recently demonstrated that at the very early disease stage, tau phosphorylation (pTau) at MD sites promotes neuroprotection by preventing seizure-like activity. To further support the notion that very early pTau is not detrimental, the present work evaluated the young rTg4510 mouse model of tauopathy as a case study. Thus, in mice at one month of age (PN30-35), we studied the increase of pTau within the hippocampal area as well as hippocampal and locomotor function. We used immunohistochemistry, T-maze, nesting test, novel object recognition test, open field arena, and electrophysiology. Our results showed that the very young rTg4510 mouse model has no detectable changes in hippocampal dependent tasks, such as spontaneous alternation and nesting, or in locomotor activity. However, at this very early stage the hippocampal neurons from PN30-35 rTg4510 mice accumulate pTau protein and exhibit changes in hippocampal oscillatory activity. Moreover, we found a significant reduction in the somatic area of pTau positive pyramidal and granule neurons in the young rTg4510 mice. Despite this, improved memory and increased number of dendrites per cell in granule neurons was found. Altogether, this study provides new insights into the early pathogenesis of tauopathies and provides further evidence that pTau remodels hippocampal function and morphology.

Deciphering the Effect of Lysine Acetylation on the Misfolding and Aggregation of Human Tau Fragment 171IPAKTPPAPK180 Using Molecular Dynamic Simulation and the Markov State Model.

The formation of neurofibrillary tangles (NFT) with β-sheet-rich structure caused by abnormal aggregation of misfolded microtubule-associated protein Tau is a hallmark of tauopathies, including Alzheimer’s Disease. It has been reported that acetylation, especially K174 located in the proline-rich region, can largely promote Tau aggregation. So far, the mechanism of the abnormal acetylation of Tau that affects its misfolding and aggregation is still unclear. Therefore, revealing the effect of acetylation on Tau aggregation could help elucidate the pathogenic mechanism of tauopathies. In this study, molecular dynamics simulation combined with multiple computational analytical methods were performed to reveal the effect of K174 acetylation on the spontaneous aggregation of Tau peptide 171IPAKTPPAPK180, and the dimerization mechanism as an early stage of the spontaneous aggregation was further specifically analyzed by Markov state model (MSM) analysis. The results showed that both the actual acetylation and the mutation mimicking the acetylated state at K174 induced the aggregation of the studied Tau fragment; however, the effect of actual acetylation on the aggregation was more pronounced. In addition, acetylated K174 plays a major contributing role in forming and stabilizing the antiparallel β-sheet dimer by forming several hydrogen bonds and side chain van der Waals interactions with residues I171, P172, A173 and T175 of the corresponding chain. In brief, this study uncovered the underlying mechanism of Tau peptide aggregation in response to the lysine K174 acetylation, which can deepen our understanding on the pathogenesis of tauopathies.

Functional study in the young rTg4510 mouse model of tauopathy

AbstractBackgroundTau hyperphosphorylation (pTau) is considered a key pathogenic event in the development of tauopathies. Nevertheless, we recently demonstrated that at the very early disease stage, pTau promotes neuroprotection by preventing seizure‐like activity.MethodTo further support the notion that very early pTau is not detrimental, the present work evaluated the young rTg4510 mouse model of tauopathy as a case study. Thus, in mice at one month of age (p30‐35), we studied the increase of pTau within the hippocampal area as well as hippocampal and locomotor function.ResultOur results showed that the very young rTg4510 model has no detectable changes in hippocampal dependent tasks, such as spontaneous alternation and nesting, or in locomotor activity. However, at this very early stage the hippocampal neurons from p30‐35 rTg4510 mice accumulate pTau protein and exhibit changes in hippocampal oscillatory activity. Moreover, we found an increased number of dendrites per cell in granule neurons.ConclusionAltogether, this study provides new insights into the early pathogenesis of tauopathies and provides further evidence that pTau remodels hippocampal function and morphology.

Biophysical properties of a tau seed

Pathogenesis of tauopathies involves conversion of tau monomer into pathological tau conformers that serve as templates to recruit native tau into growing assemblies. Small soluble tau seeds have been proposed to drive pathological tau assembly in vitro, in cells and in vivo. We have previously described the isolation of monomeric pathogenic tau seeds derived from recombinant samples and tauopathy tissues but in-depth biophysical characterization of these species has not been done. Here we describe a chromatographic method to isolate recombinant soluble tau seeds derived from heparin treatment. We used biochemical and biophysical approaches to show that the seeds are predominantly monomeric and have the capacity to nucleate aggregation of inert forms of tau in vitro and in cells. Finally, we used crosslinking mass spectrometry to identify the topological changes in tau as it converts from an inert state to a pathogenic seed. Future studies will reveal the relationship between soluble seeds and structural polymorphs derived from tauopathies to help diagnose and develop therapeutics targeting specific tauopathies.