Two for tau: Automated model discovery reveals two-stage tau aggregation dynamics in Alzheimer’s disease

Amyloid Activates GSK-3β to Aggravate Neuronal Tauopathy in Bigenic Mice

The accumulation of aberrantly aggregated MAPT (microtubule-associated protein Tau) defines a spectrum of tauopathies, including Alzheimer's disease. Mutations in the MAPT gene cause frontotemporal dementia with Parkinsonism linked to chromosome 17 (FTDP-17), characterized by neuronal pathological Tau inclusions in the form of neurofibrillary tangles and Pick bodies and in some cases glial Tau pathology. Increasing evidence points to the importance of prion-like seeding as a mechanism for the pathological spread in tauopathy and other neurodegenerative diseases. Herein, using a cell culture model, we examined a multitude of genetic FTDP-17 Tau variants for their ability to be seeded by exogenous Tau fibrils. Our findings revealed stark differences between FTDP-17 Tau variants in their ability to be seeded, with variants at Pro301 and Ser320 showing robust aggregation with seeding. Similarly, we elucidated the importance of certain Tau protein regions and unique residues, including the role of Pro301 in inhibiting Tau aggregation. We also revealed potential barriers in cross-seeding between three-repeat and four-repeat Tau isoforms. Overall, these differences alluded to potential mechanistic differences between wildtype and FTDP-17 Tau variants, as well as different Tau isoforms, in influencing Tau aggregation. Furthermore, by combining two FTDP-17 Tau variants (either P301L or P301S with S320F), we generated aggressive models of tauopathy that do not require exogenous seeding. These models will allow for rapid screening of potential therapeutics to alleviate Tau aggregation without the need for exogenous Tau fibrils. Together, these studies provide novel insights in the molecular determinants that modulate Tau aggregation.

Accelerated Human Mutant Tau Aggregation by Knocking Out Murine Tau in a Transgenic Mouse Model

Classification of diseases with accumulation of Tau protein.

Labeling Pathological Tau: An Important Quest for the Unknown.

Aggregation of tau proteins underlies several neurodegenerative diseases, notably Alzheimer’s disease (AD). Protein aggregation is a complex multi-step process where normal soluble proteins self-assemble in an ordered fashion into higher order conglomerates of low solubility. Experimental evidence suggests that not only the large tau aggregates, known as neurofibrillary tangles (NFTs), are involved in neuronal death, but also small tau oligomers are more likely contributed to the neuronal toxicity.1-3 While in the recent years substantial progress has been made in the design of drugs that interfere with tau aggregation, there is a lack of methods available that allow rapid screening of potential drug candidates which is critical for the future successful clinical trial.4-6 The heterogeneous nature of protein aggregation is the key challenge for testing the aggregation inhibition.Our previous studies showed the capability of surface-based electrochemistry to monitor the conformational changes of tau film on the gold surface by interrogating the electrochemical properties of tau-modified surface using the ferro/ferricyanide redox couple.7 We also clearly demonstrated that electrochemistry is a highly useful tool to monitor tau-metal and tau-tau interactions.7 Thus, we proposed that this approach can be expanded to monitor changes in the current/impedance as a result of the interaction of surface-linked tau proteins with tau protein in solution or with drug candidates. The former will provide information about tau dimerization and aggregation, while the latter will give information about tau-drug interactions and can potentially be further developed into a drug screening tool by following two different strategies. The first approach examines the affinity of the drug to bind to tau, followed by determining the effectiveness of the drug to prevent the tau dimerization. The second strategy monitors tau oligomerization and aggregation in an attempt to examine the inhibitory activity of potential drug candidates.We utilized Screen printed gold electrodes to reduce the sample size and the preparation time. A commercially available tau aggregation inhibitor, Cpd16 (amino thienopyridazine) was chosen to evaluate the developed biosensor. Since the orientation of the protein molecules on the surface has a significant impact on the efficiency and robustness of the biosensor, two different approaches were employed to anchor tau proteins on the electrode surface. First, full-length tau protein was chemically linked to the gold surface using lipoic acid N-hydroxysuccinimide ester (Lip-NHS), in which tau molecules randomly immobilize on the gold electrode. Although, results obtained from this approach was promising, non-specific adsorption is one of the biggest challenges that might have contributed to the false positive results. Therefore, biotin-tagged tau proteins were immobilized on the gold surface through the anchor NeutrAvidin to provide an oriented self-assembled monolayer as a biorecognition element. The non-specific adsorption can be minimized by this approach due to highly specific interaction of biotin with NeutrAvidin. This is the first report of using biotin-tagged tau for modification of a protein-based electrochemical biosensor. The oriented film has the advantages of higher sensitivity and reproducibility compared to the random orientation film on the gold surface. Also, the time for surface modification was significantly reduce by this approach.For both surface modification, a range of different electrochemical techniques has been exploited to study tau-tau interaction as well as tau-Cpd16 interaction by monitoring the redox activities of ferro/ferricyanide redox couple. Also changes in the film resistance as a result of such biomolecular interactions were conveniently monitored by electrochemical impedance spectroscopy. Circular dichroism spectroscopy and transmission electron microscopy were utilized as supporting techniques to monitor tau aggregation kinetics. The IC50 of Cpd16 obtained from the developed biosensors is comparable with the reported IC50, which shows the ability of this biosensor to predict the IC50 of the drug candidate for the in vitro model of AD.This project represents a significant achievement that contributes to our understanding of tau protein aggregation and provides a highly sensitive analytical tool that makes it possible to rapidly screen drug candidates that target tau aggregation. It can be expected that such a tool will be critical to identify the efficient drug candidates for AD therapy.

New unexpected role for Wolfram Syndrome protein WFS1: a novel therapeutic target for Alzheimer's disease?

Aggregated and highly phosphorylated tau protein is a pathological hallmark of Alzheimer's disease (AD) and other tauopathies. We identified motifs of alternating polar and apolar amino acids within the microtubule-binding repeats of tau which were interrupted by small breaking stretches. Minimal mutation of these breaking sequences yielded a unique instantly aggregating tau mutant containing longer stretches of polar/apolar amino acids without losing its microtubule-binding capacity. These modifications produced rapid aggregation and cytotoxicity with accompanying occurrence of pathologic tau phosphoepitopes (AT8, AT180, AT270, AT100, Ser(422), and PHF-1) and conformational epitopes (MC-1 and Alz50) in cells. Similar to pathological tau in the pretangle state, toxicity appeared to occur early without the requirement for extensive fibril formation. Thus, our mutant protein provides a novel platform for the investigation of the molecular mechanisms for toxicity and cellular behavior of pathologically aggregated tau proteins and the identification of its interaction partners.

Zinc(Ⅱ) induced Alzheimer’s Disease (AD) prevention and suppressive progression with early, middle, and lately stages are elucidated, and subsequently zinc binding molecular mechanism on each Aβ peptide and Tau protein in progressing stages is clarified. Zinc homeostasis regulates MCI and AD prevention, in which ZnCl2 could prevent AD pathology by that zinc can reduce β-Amyloid (Aβ) and Tau proteins. Zinc transporters may allow the novel therapies that ZnT-6 functions to a likely site of Aβ generation. At AD progression with early stage, zinc-induced aggregation of Aβ peptides and tau hyperphosphorylation on amyloid and tau aggregation consider the involvement of environmental zinc in Aβ and tau pathology. Zinc can suppress spreading of the Aβ peptide and the Tau protein that elemental zinc 150 mg daily is showed to be evident for an improvement of memory, understanding, communication, and social contact in AD. Zinc induced middle stage AD progression is pathologically characterized by the deposition of Aβ plaques and hyperphosphorylated Tau Proteins (p-tau). Zinc Finger Proteins (ZNFs) regulate the accumulation of tau proteins to affect the Neurofibrillary Tangles (NFTs), resulting in the formation of NFTs, and can inhibit protein phosphatase, promoted abnormal phosphorylation of tau protein. Zinc(Ⅱ) can prevent heavy stage AD with pathological deposits of Senile Plaques (SPs) and NFTs that the tau-zinc interaction will help understanding the zinc-related tau regulation or aggregation processes in both physiological and pathological conditions. Zinc accelerates the fibrillization of human Tau and thereby increases Tau toxicity in neuronal cells with zinc exacerbated tauopathic deficits. Zinc induced toxic Reactive Oxygen Species (ROS) generation and hyperphosphorylated tau cause oxidative stress and neurotoxicity, leading to hyperphosphorylated tau damages. Zinc(Ⅱ) binding AD molecular mechanism on Aβ and Tau proteins is that Zn2+ ions which having Zn2+ ions-centered tetrahedral geometric coordination pattern and Zn-CysHis Ligands complexes with tetrahedral geometry formed, bind with Aβ and Tau proteins in each three AD progressing stages, causing Zn2+ ions-each stages protein complex formations and oxidative stress to Aβ and Tau protein cells, leading the Zn-CysHis Ligands complexes to molecular and apoptosis activities of synaptic cells.

Optimization of tracer dose regimes in positron emission tomography (PET) imaging is a trade-off between diagnostic image quality and radiation exposure. The challenge lies in defining minimal tracer doses that still result in sufficient diagnostic image quality. In order to find such minimal doses, it would be useful to simulate tracer dose reduction as this would enable to study the effects of tracer dose reduction on image quality in single patients without repeated injections of different amounts of tracer. The aim of our study was to introduce and validate a method for simulation of low-dose PET images enabling direct comparison of different tracer doses in single patients and under constant influencing factors. (18)F-fluoride PET data were acquired on a combined PET/magnetic resonance imaging (MRI) scanner. PET data were stored together with the temporal information of the occurrence of single events (list-mode format). A predefined proportion of PET events were then randomly deleted resulting in undersampled PET data. These data sets were subsequently reconstructed resulting in simulated low-dose PET images (retrospective undersampling of list-mode data). This approach was validated in phantom experiments by visual inspection and by comparison of PET quality metrics contrast recovery coefficient (CRC), background-variability (BV) and signal-to-noise ratio (SNR) of measured and simulated PET images for different activity concentrations. In addition, reduced-dose PET images of a clinical (18)F-FDG PET dataset were simulated using the proposed approach. (18)F-PET image quality degraded with decreasing activity concentrations with comparable visual image characteristics in measured and in corresponding simulated PET images. This result was confirmed by quantification of image quality metrics. CRC, SNR and BV showed concordant behavior with decreasing activity concentrations for measured and for corresponding simulated PET images. Simulation of dose-reduced datasets based on clinical (18)F-FDG PET data demonstrated the clinical applicability of the proposed data. Simulation of PET tracer dose reduction is possible with retrospective undersampling of list-mode data. Resulting simulated low-dose images have equivalent characteristics with PET images actually measured at lower doses and can be used to derive optimal tracer dose regimes.

In Vivo Spreading of Tau Pathology

Old cats : a naturally occuring model of tauopathy.

Alzheimer's Disease-Like Tau Neuropathology Leads to Memory Deficits and Loss of Functional Synapses in a Novel Mutated Tau Transgenic Mouse without Any Motor Deficits

Microtubule-associated protein tau (MAPT) hyperphosphorylation and aggregation, are two hallmarks of a family of neurodegenerative disorders collectively referred to as tauopathies. In many tauopathies, including Alzheimer’s disease (AD), progressive supranuclear palsy (PSP) and Pick’s disease, tau aggregates are found associated with highly sulfated polysaccharides known as heparan sulfates (HSs). In AD, amyloid beta (Aβ) peptide aggregates associated with HS are also characteristic of disease. Heparin, an HS analog, promotes misfolding, hyperphosphorylation and aggregation of tau protein in vitro. HS also provides cell surface receptors for attachment and uptake of tau seeds, enabling their propagation. These findings point to HS-tau interactions as potential therapeutic targets in tauopathies. The zebrafish genome contains genes paralogous to MAPT, genes orthologous to HS biosynthetic and chain modifier enzymes, and other genes implicated in AD. The nervous system in the zebrafish bears anatomical and chemical similarities to that in humans. These homologies, together with numerous technical advantages, make zebrafish a valuable model for investigating basic mechanisms in tauopathies and identifying therapeutic targets. Here, we comprehensively review current knowledge on the role of HSs in tau pathology and HS-targeting therapeutic approaches. We also discuss novel insights from zebrafish suggesting a role for HS 3-O-sulfated motifs in tau pathology and establishing HS antagonists as potential preventive agents or therapies for tauopathies.

We report on a novel transgenic mouse model expressing human full-length Tau with the Tau mutation A152T (hTau(AT)), a risk factor for FTD-spectrum disorders including PSP and CBD Brain neurons reveal pathological Tau conformation, hyperphosphorylation, mis-sorting, aggregation, neuronal degeneration, and progressive loss, most prominently in area CA3 of the hippocampus. The mossy fiber pathway shows enhanced basal synaptic transmission without changes in short- or long-term plasticity. In organotypic hippocampal slices, extracellular glutamate increases early above control levels, followed by a rise in neurotoxicity. These changes are normalized by inhibiting neurotransmitter release or by blocking voltage-gated sodium channels. CA3 neurons show elevated intracellular calcium during rest and after activity induction which is sensitive to NR2B antagonizing drugs, demonstrating a pivotal role of extrasynaptic NMDA receptors. Slices show pronounced epileptiform activity and axonal sprouting of mossy fibers. Excitotoxic neuronal death is ameliorated by ceftriaxone, which stimulates astrocytic glutamate uptake via the transporter EAAT2/GLT1. In summary, hTau(AT) causes excitotoxicity mediated by NR2B-containing NMDA receptors due to enhanced extracellular glutamate.