Joel B. Schachter

Internalized Tau Oligomers Cause Neurodegeneration by Inducing Accumulation of Pathogenic Tau in Human Neurons Derived from Induced Pluripotent Stem Cells.

Neuronal inclusions of hyperphosphorylated and aggregated tau protein are a pathological hallmark of several neurodegenerative tauopathies, including Alzheimers disease (AD). The hypothesis of tau transmission in AD has emerged from histopathological studies of the spatial and temporal progression of tau pathology in postmortem patient brains. Increasing evidence in cellular and animal models supports the phenomenon of intercellular spreading of tau. However, the molecular and cellular mechanisms of pathogenic tau transmission remain unknown. The studies described herein investigate tau pathology propagation using human neurons derived from induced pluripotent stem cells. Neurons were seeded with full-length human tau monomers and oligomers and chronic effects on neuronal viability and function were examined over time. Tau oligomer-treated neurons exhibited an increase in aggregated and phosphorylated pathological tau. These effects were associated with neurite retraction, loss of synapses, aberrant calcium homeostasis, and imbalanced neurotransmitter release. In contrast, tau monomer treatment did not produce any measureable changes. This work supports the hypothesis that tau oligomers are toxic species that can drive the spread of tau pathology and neurodegeneration. SIGNIFICANCE STATEMENT Several independent studies have implicated tau protein as central to Alzheimers disease progression and cell-to-cell pathology propagation. In this study, we investigated the ability of different tau species to propagate pathology in human neurons derived from induced pluripotent stem cells, which to date has not been shown. We demonstrated that tau oligomers, but not monomers, induce accumulation of pathological, hyperphosphorylated tau. This effect was accompanied with neurite degeneration, loss of synapses, aberrant calcium homeostasis, imbalanced neurotransmitter release, and ultimately with neuronal death. This study bridges various tau pathological phenotypes into a single and relevant induced pluripotent stem cell neuronal model of human disease that can be applied to the discovery of the mechanisms of tau-induced neurodegeneration.

Discovery of 6-(Fluoro-18F)-3-(1H-pyrrolo[2,3-c]pyridin-1-yl)isoquinolin-5-amine ([18F]-MK-6240): A Positron Emission Tomography (PET) Imaging Agent for Quantification of Neurofibrillary Tangles (NFTs)

Neurofibrillary tangles (NFTs) made up of aggregated tau protein have been identified as the pathologic hallmark of several neurodegenerative diseases including Alzheimers disease. In vivo detection of NFTs using PET imaging represents a unique opportunity to develop a pharmacodynamic tool to accelerate the discovery of new disease modifying therapeutics targeting tau pathology. Herein, we present the discovery of 6-(fluoro-(18)F)-3-(1H-pyrrolo[2,3-c]pyridin-1-yl)isoquinolin-5-amine, 6 ([(18)F]-MK-6240), as a novel PET tracer for detecting NFTs. 6 exhibits high specificity and selectivity for binding to NFTs, with suitable physicochemical properties and in vivo pharmacokinetics.

Targeting Post-translational Modifications on Tau as a Therapeutic Strategy for Alzheimer's Disease

Abstract: Alzheimers disease (AD) is a neurodegenerative disorder that causes early memory impairment, followed by profound progressive cognitive decline, and eventually death. Neurofibrillary tangles (NFTs) are one of the histopathological hallmarks of AD. NFTs are deposits of insoluble aggregates of the microtubule-binding protein tau, left behind following neuronal loss. Intracellular aggregates of tau, either in soluble or insoluble forms, are thought to disrupt cellular machinery and synaptic function and ultimately lead to neuronal death. As the ultimate pathological endpoint in AD is neuronal loss, there is significant interest in understanding the causes of tau aggregation and deposition in the brain as a potential therapeutic avenue for AD. Post-translational modifications on tau are thought to be an important regulatory mechanism that may contribute to the propensity of tau to aggregate and form NFTs. In addition to phosphorylation, numerous other post-translational modifications have been observed on tau protein. The mechanisms that cause aggregation of tau are unknown, but it is likely that post-translational modifications other than phosphorylation also regulate this process. This review will discuss several post-translational modifications of tau and their roles in modulation of tau function and aggregation in AD.

EARLY CLINICAL RESULTS AND PRECLINICAL VALIDATION OF THE O-GLCNACASE (OGA) INHIBITOR MK-8719 AS A NOVEL THERAPEUTIC FOR THE TREATMENT OF TAUOPATHIES

cant decrease of human Tau multimers (HT7/HT7 setup), as well as a significant decrease of a misfolded Tau (MC-1/HT7 setup) in a total brain fraction.A trend to decrease humanTau phosphorylated at pS396 in different brain fractions was also observed. ACI-35 treatment significantly improved the rotarod performance in both the transgenic hTauP301S-Tg model and the AAV-TauP301S spreading model. Conclusions: The study demonstrated that active immunization with ACI-35 significantly decreased human pathological Tau species in different brain fractions and ameliorated the clinical phenotype in two different mouse models of tauopathy.

High throughput monitoring of amyloid-β(42) assembly into soluble oligomers achieved by sensitive conformation state-dependent immunoassays.

Accumulation of small soluble assemblies of amyloid-β (Aβ)(42) in the brain is thought to play a key role in the pathogenesis of Alzheimers disease. As a result, there has been much interest in finding small molecules that inhibit the formation of synaptotoxic Aβ(42) oligomers that necessitates sensitive methods for detecting the initial steps in the oligomerization of Aβ(42). Modeling suggests that oligomerized Aβ(42) adopts a conformation in which the C-terminus is embedded in the center, whereas the N-terminus is exposed at the periphery of the oligomer. Here we report that an inverse change in Aβ(42) C-terminal and N-terminal epitope accessibility provides the basis of a sensitive method for assessing early steps in Aβ(42) oligomerization. Using ELISA and AlphaLISA, we found that Aβ(42) C-terminal immunoreactivity decreased in a time- and concentration-dependent manner under conditions favoring oligomerization. This reduction was accompanied by an increase in the N-terminal immunoreactivity, suggesting that assemblies with multiple exposed N-terminal epitopes were detected. Importantly the assay generates a robust window between monomers and oligomers at as low as 1 nM Aβ(42). Using this assay, known oligomerization inhibitors produced a dose-dependent unmasking of the Aβ(42) C-terminal epitope. After automation, the assay proved to be highly reproducible and effective for high throughput screening of small molecules that inhibit Aβ(42) oligomerization.

DISCOVERY AND FIRST-IN-HUMAN EVALUATION OF THE TAU-IMAGING PET RADIOTRACER [18F]MK-6240

Parametric [C]PBB3, and [C]PiB PET images were generated by calculation of target-to-cerebellar cortex standardized uptake value ratio (SUVR) at 30-50 min, and 50-70 min after radiotracer injection, respectively. [C]PiB retention was assessed by visual inspection of SUVR images. A two sample t-test was also performed on [C]PBB3 PET SUVR images between each patient and 13 HCs using SPM12. Neuropathological and autoradiographic examinations were performed in postmortem brain sections of other patients with three MAPT mutations. Results: All subjects were negative for amyloid PET. Five subjects with MAPT gene mutations exhibited increased [C]PBB3 binding in the brain compared with HCs. In the N279K mutation carriers, increased [C]PBB3 bindings were detected at an asymptomatic stage, and were spatially extended involving white matter with the progression of clinical manifestations. In contrast, patients with R406W and G272V mutations showed increased [C]PBB3 binding mostly restricted to gray matter in the brain. Autoradiographic signals and fluorescence labeling of brain sections revealed that PBB3 binds to various tau inclusions in the brain with these three mutations. Conclusions: [C]PBB3 PET can detect diverse tau inclusions, and may be useful for monitoring disease progression and therapeutic effect of anti-tau therapy in patients with MATP mutations, and other tauopathies.

Early intervention of tau pathology prevents behavioral changes in the rTg4510 mouse model of tauopathy

Although tau pathology, behavioral deficits, and neuronal loss are observed in patients with tauopathies, the relationship between these endpoints has not been clearly established. Here we found that rTg4510 mice, which overexpress human mutant tau in the forebrain, develop progressive age-dependent increases in locomotor activity (LMA), which correlates with neurofibrillary tangle (NFT) pathology, hyperphosphorylated tau levels, and brain atrophy. To further clarify the relationship between these endpoints, we treated the rTg4510 mice with either doxycycline to reduce mutant tau expression or an O-GlcNAcase inhibitor Thiamet G, which has been shown to ameliorate tau pathology in animal models. We found that both doxycycline and Thiamet G treatments starting at 2 months of age prevented the progression of hyperactivity, slowed brain atrophy, and reduced brain hyperphosphorylated tau. In contrast, initiating doxycycline treatment at 4 months reduced neither brain hyperphosphorylated tau nor hyperactivity, further confirming the relationship between these measures. Collectively, our results demonstrate a unique behavioral phenotype in the rTg4510 mouse model of tauopathy that strongly correlates with disease progression, and that early interventions which reduce tau pathology ameliorate the progression of the locomotor dysfunction. These findings suggest that better understanding the relationship between locomotor deficits and tau pathology in the rTg4510 model may improve our understanding of the mechanisms underlying behavioral disturbances in patients with tauopathies.