Autosomal dominant dementia with widespread neurofibrillary tangles

Tau filaments with the Alzheimer fold in cases with MAPT mutations V337M and R406W

Frontotemporal dementia (FTD) and Alzheimer's disease are the most common forms of early-onset dementia. Dominantly inherited mutations in MAPT, the microtubule-associated protein tau gene, cause FTD and parkinsonism linked to chromosome 17 (FTDP-17). Individuals with FTDP-17 develop abundant filamentous tau inclusions in brain cells. Here we used electron cryo-microscopy to determine the structures of tau filaments from the brains of individuals with MAPT mutations V337M and R406W. Both mutations gave rise to tau filaments with the Alzheimer fold, which consisted of paired helical filaments in all V337M and R406W cases and of straight filaments in two V337M cases. We also identified a new assembly of the Alzheimer fold into triple tau filaments in a V337M case. Filaments assembled from recombinant tau(297-391) with mutation V337M had the Alzheimer fold and showed an increased rate of assembly.

Frontotemporal Dementia-Parkinsonism Due to MAPT Gene Variant Presenting with Rest and Action Tremor

A 50-year-old male presented with a four-year history of gradually progressive rest tremor in the distal right lower limb and then spreading to the left lower limb in last 10-12 months. He developed right arm rest and action tremor two years later. Magnetic resonance imaging scans showed progressive frontotemporal and asymmetrical mesial temporal atrophy. Genetic testing revealed a heterozygous c.915+16C>T pathogenic variant in intron 9 of the MAPT gene. Presentation with rest tremor should not exclude frontotemporal dementia-parkinsonism due to a MAPT variant as a differential diagnosis though rest tremor is a rare presentation.

Neural atrophy produced by AAV tau injections into hippocampus and anterior cortex of middle-aged mice

Animal models of tauopathy help in understanding the role of mutations in tau pathobiology. Here, we used adeno-associated viral (AAV) vectors to administer three tau genetic variants (tauwild-type, tauP301L, and tauR406W) intracranially into 12-month-old C57BL/6Nia mice and collected tissue at 16 months. Vectors designed to express green fluorescent protein controlled for surgical procedures and exogenous protein expression by AAV. The tau genetic variants produced considerably different phenotypes. Tauwild-type and tauP301L caused memory impairments. The tauP301L caused increased amounts of aggregated tau, measured both neurochemically and histologically. Tauwild-type produced elevated levels of soluble tau and phosphorylated tau by ELISA and increased staining for phosphorylated forms of tau histologically. However, only the tauwild-type caused localized atrophy of brain tissue at the sites near the injection. The tauR406W had low protein expression and produced no atrophy or memory impairments. This supports the potential use of AAV expressing tauwild-type in aged mice to examine events leading to neurodegeneration in Alzheimer's disease pathology.

Contributions of rare and common variation to early-onset and atypical dementia risk

We collected and analyzed genomic sequencing data from individuals with clinician- diagnosed early-onset or atypical dementia. Thirty-two patients were previously described, with sixty-eight newly described in this report. Of those sixty-eight, sixty-two patients reported Caucasian, non-Hispanic ethnicity and six reported as African American, non-Hispanic. Fifty-three percent of patients had a returnable variant. Five patients harbored a pathogenic variant as defined by the American College of Medical Genetics criteria for pathogenicity. A polygenic risk score was calculated for Alzheimer's patients in the total cohort and compared to the scores of a late-onset Alzheimer's cohort and a control set. Patients with early-onset Alzheimer's had higher non- APOE polygenic risk scores than patients with late onset Alzheimer's, supporting the conclusion that both rare and common genetic variation associate with early-onset neurodegenerative disease risk.

Genotype-phenotype correlation in the spectrum of frontotemporal dementia-parkinsonian syndromes and advanced diagnostic approaches

The term frontotemporal dementia (FTD) refers to a group of progressive neurodegenerative disorders characterized mainly by atrophy of the frontal and anterior temporal lobes. Based on clinical presentation, three main clinical syndromes have traditionally been described: behavioral variant frontotemporal dementia (bvFTD), non-fluent/agrammatic primary progressive aphasia (nfPPA), and semantic variant PPA (svPPA). However, over the last 20 years, it has been recognized that cognitive phenotypes often overlap with motor phenotypes, either motor neuron diseases or parkinsonian signs and/or syndromes like progressive supranuclear palsy (PSP) and cortico-basal syndrome (CBS). Furthermore, FTD-related genes are characterized by genetic pleiotropy and can cause, even in the same family, pure motor phenotypes, findings that underlie the clinical continuum of the spectrum, which has pure cognitive and pure motor phenotypes as the extremes. The genotype-phenotype correlation of the spectrum, FTD-motor neuron disease, has been well defined and extensively investigated, while the continuum, FTD-parkinsonism, lacks a comprehensive review. In this narrative review, we describe the current knowledge about the genotype-phenotype correlation of the spectrum, FTD-parkinsonism, focusing on the phenotypes that are less frequent than bvFTD, namely nfPPA, svPPA, PSP, CBS, and cognitive-motor overlapping phenotypes (i.e. PPA + PSP). From a pathological point of view, they are characterized mainly by the presence of phosphorylated-tau inclusions, either 4 R or 3 R. The genetic correlate of the spectrum can be heterogeneous, although some variants seem to lead preferentially to specific clinical syndromes. Furthermore, we critically review the contribution of genome-wide association studies (GWAS) and next-generation sequencing (NGS) in disentangling the complex heritability of the FTD-parkinsonism spectrum and in defining the genotype-phenotype correlation of the entire clinical scenario, owing to the ability of these techniques to test multiple genes, and so to allow detailed investigations of the overlapping phenotypes. Finally, we conclude with the importance of a detailed genetic characterization and we offer to patients and families the chance to be included in future randomized clinical trials focused on autosomal dominant forms of FTLD.

Defective proteostasis in induced pluripotent stem cell models of frontotemporal lobar degeneration

Impaired proteostasis is associated with normal aging and is accelerated in neurodegeneration. This impairment may lead to the accumulation of protein, which can be toxic to cells and tissue. In a subset of frontotemporal lobar degeneration with tau pathology (FTLD-tau) cases, pathogenic mutations in the microtubule-associated protein tau (MAPT) gene are sufficient to cause tau accumulation and neurodegeneration. However, the pathogenic events triggered by the expression of the mutant tau protein remain poorly understood. Here, we show that molecular networks associated with lysosomal biogenesis and autophagic function are disrupted in brains from FTLD-tau patients carrying a MAPT p.R406W mutation. We then used human induced pluripotent stem cell (iPSC)-derived neurons and 3D cerebral organoids from patients carrying the MAPT p.R406W mutation and CRISPR/Cas9, corrected controls to evaluate proteostasis. MAPT p.R406W was sufficient to induce morphological and functional deficits in the lysosomal pathway in iPSC-neurons. These phenotypes were reversed upon correction of the mutant allele with CRISPR/Cas9. Treatment with mTOR inhibitors led to tau degradation specifically in MAPT p.R406W neurons. Together, our findings suggest that MAPT p.R406W is sufficient to cause impaired lysosomal function, which may contribute to disease pathogenesis and serve as a cellular phenotype for drug screening.

Studies of neurodegenerative diseases using Drosophila and the development of novel approaches for their analysis

The use of Drosophila in neurodegenerative disease research has contributed to the identification of modifier genes for the pathology. The basis for neurodegenerative disease occurrence in Drosophila is the conservation of genes across species and the ability to perform rapid genetic analysis using a compact brain. Genetic findings previously discovered in Drosophila can reveal molecular pathologies involved in human neurological diseases in later years. Disease models using Drosophila began to be generated during the development of genetic engineering. In recent years, results of reverse translational research using Drosophila have been reported. In this review, we discuss research on neurodegenerative diseases; moreover, we introduce various methods for quantifying neurodegeneration in Drosophila.

Structures of tau and α-synuclein filaments from brains of patients with neurodegenerative diseases

Intracellular accumulations and aggregates of abnormal protein, consisting of amyloid-like fibrils, are common neuropathological features of many neurodegenerative diseases. The distributions and spreading of these pathological proteins are closely correlated with clinical symptoms and progression. Recent evidence supports the idea that template-mediated amplification of amyloid-like fibrils and intracellular propagation of fibril seeds are the main mechanisms by which pathological features spread along the neural circuits in the brain. Here, we review recent developments in the structural analysis of amyloid-like fibrils from brains of patients with various types of tauopathy and alpha-synucleinopathy, focusing on cryo-electron microscopy and mass analysis, and we discuss their relevance to the mechanisms of template-mediated amplification and intracellular propagation.

Human Induced Pluripotent Stem Cell Models of Frontotemporal Dementia With Tau Pathology

Neurodegenerative dementias are the most common group of neurodegenerative diseases affecting more than 40 million people worldwide. One of these diseases is frontotemporal dementia (FTD), an early onset dementia and one of the leading causes of dementia in people under the age of 60. FTD is a heterogeneous group of neurodegenerative disorders with pathological accumulation of particular proteins in neurons and glial cells including the microtubule-associated protein tau, which is deposited in its hyperphosphorylated form in about half of all patients with FTD. As for other patients with dementia, there is currently no cure for patients with FTD and thus several lines of research focus on the characterization of underlying pathogenic mechanisms with the goal to identify therapeutic targets. In this review, we provide an overview of reported disease phenotypes in induced pluripotent stem cell (iPSC)-derived neurons and glial cells from patients with tau-associated FTD with the aim to highlight recent progress in this fast-moving field of iPSC disease modeling. We put a particular focus on genetic forms of the disease that are linked to mutations in the gene encoding tau and summarize mutation-associated changes in FTD patient cells related to tau splicing and tau phosphorylation, microtubule function and cell metabolism as well as calcium homeostasis and cellular stress. In addition, we discuss challenges and limitations but also opportunities using differentiated patient-derived iPSCs for disease modeling and biomedical research on neurodegenerative diseases including FTD.

MAPT R406W increases tau T217 phosphorylation in absence of amyloid pathology

Objective

Tau hyperphosphorylation at threonine 217 (pT217) in cerebrospinal fluid (CSF) has recently been linked to early amyloidosis and could serve as a highly sensitive biomarker for Alzheimer’s disease (AD). However, it remains unclear whether other tauopathies induce pT217 modifications. To determine if pT217 modification is specific to AD, CSF pT217 was measured in AD and other tauopathies.

Methods

Using immunoprecipitation and mass spectrometry methods, we compared CSF T217 phosphorylation occupancy (pT217/T217) and amyloid‐beta (Aβ) 42/40 ratio in cognitively normal individuals and those with symptomatic AD, progressive supranuclear palsy, corticobasal syndrome, and sporadic and familial frontotemporal dementia.

Results

Individuals with AD had high CSF pT217/T217 and low Aβ42/40. In contrast, cognitively normal individuals and the majority of those with 4R tauopathies had low CSF pT217/T217 and normal Aβ 42/40. We identified a subgroup of individuals with increased CSF pT217/T217 and normal Aβ 42/40 ratio, most of whom were MAPT R406W mutation carriers. Diagnostic accuracies of CSF Aβ 42/40 and CSF pT217/T217, alone and in combination were compared. We show that CSF pT217/T217 × CSF Aβ 42/40 is a sensitive composite biomarker that can separate MAPT R406W carriers from cognitively normal individuals and those with other tauopathies.

Interpretation

MAPT R406W is a tau mutation that leads to 3R+4R tauopathy similar to AD, but without amyloid neuropathology. These findings suggest that change in CSF pT217/T217 ratio is not specific to AD and might reflect common downstream tau pathophysiology common to 3R+4R tauopathies.

Diagnostic Performance of RO948 F 18 Tau Positron Emission Tomography in the Differentiation of Alzheimer Disease From Other Neurodegenerative Disorders

Question

How does RO948 F 18 positron emission tomographic scanning discriminate between Alzheimer disease and other neurodegenerative disorders in comparison with magnetic resonance imaging and cerebrospinal fluid measures?

Findings

In this diagnostic study including 613 patients from the Swedish BioFINDER-2 clinical trial, standard uptake value ratios of RO948 F 18 were higher in patients with Alzheimer disease dementia compared with cognitively unimpaired controls and patients with other neurodegenerative disorders; furthermore, RO948 F 18 outperformed magnetic resonance imaging and cerebrospinal fluid measures. Generally, tau positron emission tomographic positivity was confined to amyloid β–positive cases or MAPT R406W mutation carriers in this cohort; in patients with semantic variant primary progressive aphasia, RO948 F 18 retention was lower than that for flortaucipir F 18.

Meaning

These findings suggest that RO948 F 18 has a high specificity for Alzheimer disease–type tau and highlight its potential as a diagnostic marker in the workup of patients treated in memory clinics.

Importance

The diagnostic performance of second-generation tau positron emission tomographic (PET) tracers is not yet known.

Objective

To examine the novel tau PET tracer RO948 F 18 ([¹⁸F]RO948) performance in discriminating Alzheimer disease (AD) from non-AD neurodegenerative disorders.

Design, Setting, and Participants

In this diagnostic study, 613 participants in the Swedish BioFINDER-2 study were consecutively enrolled in a prospective cross-sectional study from September 4, 2017, to August 28, 2019. Participants included 257 cognitively unimpaired controls, 154 patients with mild cognitive impairment, 100 patients with AD dementia, and 102 with non-AD neurodegenerative disorders. Evaluation included a comparison of tau PET tracer [¹⁸F]RO948 with magnetic resonance imaging (MRI) and cerebrospinal fluid and a head-to-head comparison between [¹⁸F]RO948 and flortaucipir F 18 ([¹⁸F]flortaucipir) in patients with semantic variant primary progressive aphasia (svPPA).

Exposures

[¹⁸F]RO948 (all patients) and [¹⁸F]flortaucipir (3 patients with svPPA) tau PET; MRI (hippocampal volume, composite temporal lobe cortical thickness, whole-brain cortical thickness) and cerebrospinal fluid measures (p-tau181 and amyloid Aβ42 and Aβ40 ratio[Aβ42/Aβ40], and Aβ42/p-tau181 ratio).

Main Outcomes and Measures

Standard uptake value ratios (SUVRs) in 4 predefined regions of interest (ROIs) reflecting Braak staging scheme for tau pathology and encompass I-II (entorhinal cortex), III-IV (inferior/middle temporal, fusiform gyrus, parahippocampal cortex, and amygdala), I-IV, and V-VI (widespread neocortical areas), area under the receiver operating characteristic curve (AUC) values, and subtraction images between [¹⁸F]RO948 and [¹⁸F]flortaucipir.

Results

Diagnostic groups among the 613 participants included cognitively unimpaired (mean [SD] age, 65.8 [12.1] years; 117 men [46%]), mild cognitive impairment (age, 70.8 [8.3] years; 82 men [53%]), AD dementia (age, 73.5 [6.7] years; 57 men [57%]), and non-AD disorders (age, 70.5 [8.6] years; 41 men [40%]). Retention of [¹⁸F]RO948 was higher in AD dementia compared with all other diagnostic groups. [¹⁸F]RO948 could distinguish patients with AD dementia from individuals without cognitive impairment and those with non-AD disorders, and the highest AUC was obtained using the I-IV ROI (AUC = 0.98; 95% CI, 0.96-0.99 for AD vs no cognitive impairment and AUC = 0.97; 95% CI, 0.95-0.99 for AD vs non-AD disorders), which outperformed MRI (highest AUC = 0.91 for AD vs no cognitive impairment using whole-brain thickness, and AUC = 0.80 for AD vs non-AD disorders using temporal lobe thickness) and cerebrospinal fluid measures (highest AUC = 0.94 for AD vs no cognitive impairment using Aβ42/p-tau181, and AUC = 0.93 for AD vs non-AD disorders using Aβ42/Aβ40). Generally, tau PET positivity using [¹⁸F]RO948 was observed only in Aβ-positive cases or in MAPT R406W mutation carriers. Retention of [¹⁸F]RO948 was not pronounced in patients with svPPA, and head-to-head comparison revealed lower temporal lobe uptake than with [¹⁸F]flortaucipir.

Conclusions and Relevance

In this study, elevated [¹⁸F]RO948 SUVRs were most often seen among Aβ-positive cases, which suggests that [¹⁸F]RO948 has high specificity for AD-type tau and highlights its potential as a diagnostic marker in the differential diagnosis of AD.

A Single-Chain Variable Fragment Antibody Inhibits Aggregation of Phosphorylated Tau and Ameliorates Tau Toxicity in vitro and in vivo

BACKGROUND

Alzheimer's disease (AD) is a common cause of dementia among elderly people. Hyperphosphorylation and aggregation of tau correlates with the clinical progression of AD; therefore, therapies targeting the aggregation of tau may have potential applications for anti-AD drug development. Several inhibitors of tau aggregation, including small molecules and antibodies, have been found to decrease the aggregation of tau and the corresponding pathology.

OBJECTIVE

To screen one kind of single-chain variable fragment (scFv) antibody which could inhibit the aggregation of tau and ameliorate its cytotoxicity.

METHODS/RESULTS

Using phosphorylated tau (pTau) as an antigen, we obtained a scFv antibody via the screening of a high-capacity phage antibody library. Biochemical analysis revealed that this scFv antibody (scFv T1) had a strong ability to inhibit pTau aggregation both in dilute solutions and under conditions of macromolecular crowding. ScFv T1 could also depolymerize preformed pTau aggregates in vitro. Furthermore, scFv T1 was found to be able to inhibit the cytotoxicity of extracellular pTau aggregates and ameliorate tau-mediated toxicity when coexpressed with a hTauR406W mutant in the eye of transgenic Drosophila flies.

CONCLUSION

This scFv T1 antibody may be a potential new therapeutic agent against AD. Our methods can be used to develop novel strategies against protein aggregation for the treatment of neurodegenerative diseases.

Brain volumetric deficits in MAPT mutation carriers: a multisite study

OBJECTIVE

MAPT mutations typically cause behavioral variant frontotemporal dementia with or without parkinsonism. Previous studies have shown that symptomatic MAPT mutation carriers have frontotemporal atrophy, yet studies have shown mixed results as to whether presymptomatic carriers have low gray matter volumes. To elucidate whether presymptomatic carriers have lower structural brain volumes within regions atrophied during the symptomatic phase, we studied a large cohort of MAPT mutation carriers using a voxelwise approach.

METHODS

We studied 22 symptomatic carriers (age 54.7 ± 9.1, 13 female) and 43 presymptomatic carriers (age 39.2 ± 10.4, 21 female). Symptomatic carriers' clinical syndromes included: behavioral variant frontotemporal dementia (18), an amnestic dementia syndrome (2), Parkinson's disease (1), and mild cognitive impairment (1). We performed voxel-based morphometry on T1 images and assessed brain volumetrics by clinical subgroup, age, and mutation subtype.

RESULTS

Symptomatic carriers showed gray matter atrophy in bilateral frontotemporal cortex, insula, and striatum, and white matter atrophy in bilateral corpus callosum and uncinate fasciculus. Approximately 20% of presymptomatic carriers had low gray matter volumes in bilateral hippocampus, amygdala, and lateral temporal cortex. Within these regions, low gray matter volumes emerged in a subset of presymptomatic carriers as early as their thirties. Low white matter volumes arose infrequently among presymptomatic carriers.

INTERPRETATION

A subset of presymptomatic MAPT mutation carriers showed low volumes in mesial temporal lobe, the region ubiquitously atrophied in all symptomatic carriers. With each decade of age, an increasing percentage of presymptomatic carriers showed low mesial temporal volume, suggestive of early neurodegeneration.

Tau Protein and Frontotemporal Dementias

Filamentous inclusions of tau protein are found in cases of inherited and sporadic frontotemporal dementias (FTDs). Mutations in MAPT, the tau gene, cause approximately 5% of cases of FTD. They proved that dysfunction of tau protein is sufficient to cause neurodegeneration and dementia. Clinically and pathologically, cases with MAPT mutations can resemble sporadic diseases, such as Pick's disease, globular glial tauopathy, progressive supranuclear palsy and corticobasal degeneration. The structures of tau filaments from Pick's disease and corticobasal degeneration, determined by electron cryo-microscopy, revealed the presence of specific tau folds in each disease, with no inter-individual variation. The same was true of chronic traumatic encephalopathy.

Comparison of Common and Disease-Specific Post-translational Modifications of Pathological Tau Associated With a Wide Range of Tauopathies

Tauopathies are the most common type of neurodegenerative proteinopathy, being characterized by cytoplasmic aggregates of hyperphosphorylated tau protein. The formation and morphologies of these tau inclusions, the distribution of the lesions and related metabolic changes in cytoplasm differ among different tauopathies. The aim of this study was to examine whether there are differences in the post-translational modifications (PTMs) in the pathological tau proteins. We analyzed sarkosyl-insoluble pathological tau proteins prepared from brains of patients with Alzheimer's disease, Pick's disease, progressive supranuclear palsy, corticobasal degeneration, globular glial tauopathy, and frontotemporal dementia and parkinsonisms linked to chromosome 17 with tau inclusions using liquid chromatography mass spectrometry. In pathological tau proteins associated with a wide range of tauopathies, 170 PTMs in total were identified including new PTMs. Among them, common PTMs were localized in the N- and C-terminal flanking regions of the microtubule binding repeats and PTMs, which were considered to be disease-specific, were found in microtubule binding repeats forming filament core. These suggested that the differences in PTMs reflected the differences in tau filament core structures in each disease.

Tau proteinopathies and the prion concept

The ordered assembly of a small number of proteins into amyloid filaments is central to age-related neurodegenerative diseases. Tau is the most commonly affected of these proteins. In sporadic diseases, assemblies of tau form in a stochastic manner in certain brain regions, from where they appear to spread in a deterministic way, giving rise to disease symptoms. Over the past decade, multiple lines of evidence have shown that assembled tau behaves like a prion. More recently, electron cryo-microscopy of tau filaments has shown that distinct conformers are present in different diseases, with no inter-individual variation for a given disease.

Genetic Testing for Amyotrophic Lateral Sclerosis and Frontotemporal Dementia: Impact on Clinical Management

Amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD) are devastating neurodegenerative disorders that share clinical, pathologic, and genetic features. Persons and families affected by these conditions frequently question why they developed the disease, the expected disease course, treatment options, and the likelihood that family members will be affected. Genetic testing has the potential to answers these important questions. Despite the progress in gene discovery, the offer of genetic testing is not yet "standard of care" in ALS and FTD clinics. The authors review the current genetic landscape and present recommendations for the laboratory genetic evaluation of persons with these conditions.

Non-coding and Loss-of-Function Coding Variants in TET2 are Associated with Multiple Neurodegenerative Diseases

We conducted genome sequencing to search for rare variation contributing to early-onset Alzheimer's disease (EOAD) and frontotemporal dementia (FTD). Discovery analysis was conducted on 435 cases and 671 controls of European ancestry. Burden testing for rare variation associated with disease was conducted using filters based on variant rarity (less than one in 10,000 or private), computational prediction of deleteriousness (CADD) (10 or 15 thresholds), and molecular function (protein loss-of-function [LoF] only, coding alteration only, or coding plus non-coding variants in experimentally predicted regulatory regions). Replication analysis was conducted on 16,434 independent cases and 15,587 independent controls. Rare variants in TET2 were enriched in the discovery combined EOAD and FTD cohort (p = 4.6 × 10-8, genome-wide corrected p = 0.0026). Most of these variants were canonical LoF or non-coding in predicted regulatory regions. This enrichment replicated across several cohorts of Alzheimer's disease (AD) and FTD (replication only p = 0.0029). The combined analysis odds ratio was 2.3 (95% confidence interval [CI] 1.6-3.4) for AD and FTD. The odds ratio for qualifying non-coding variants considered independently from coding variants was 3.7 (95% CI 1.7-9.4). For LoF variants, the combined odds ratio (for AD, FTD, and amyotrophic lateral sclerosis, which shares clinicopathological overlap with FTD) was 3.1 (95% CI 1.9-5.2). TET2 catalyzes DNA demethylation. Given well-defined changes in DNA methylation that occur during aging, rare variation in TET2 may confer risk for neurodegeneration by altering the homeostasis of key aging-related processes. Additionally, our study emphasizes the relevance of non-coding variation in genetic studies of complex disease.

A Comprehensive Resource for Induced Pluripotent Stem Cells from Patients with Primary Tauopathies

Primary tauopathies are characterized neuropathologically by inclusions containing abnormal forms of the microtubule-associated protein tau (MAPT) and clinically by diverse neuropsychiatric, cognitive, and motor impairments. Autosomal dominant mutations in the MAPT gene cause heterogeneous forms of frontotemporal lobar degeneration with tauopathy (FTLD-Tau). Common and rare variants in the MAPT gene increase the risk for sporadic FTLD-Tau, including progressive supranuclear palsy (PSP) and corticobasal degeneration (CBD). We generated a collection of fibroblasts from 140 MAPT mutation/risk variant carriers, PSP, CBD, and cognitively normal controls; 31 induced pluripotent stem cell (iPSC) lines from MAPT mutation carriers, non-carrier family members, and autopsy-confirmed PSP patients; 33 genome engineered iPSCs that were corrected or mutagenized; and forebrain neural progenitor cells (NPCs). Here, we present a resource of fibroblasts, iPSCs, and NPCs with comprehensive clinical histories that can be accessed by the scientific community for disease modeling and development of novel therapeutics for tauopathies.

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A collection of fibroblasts from 140 MAPT mutation carriers, PSP, CBD, and controls

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31 iPSC lines reprogrammed from MAPT mutation carriers, PSP patients, and controls

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33 iPSC lines engineered with CRISPR/Cas9 or TALENs

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Comprehensive resource for tauopathy modeling and discovery of novel therapeutics

Tauopathy in the periaqueductal gray, kölliker-fuse nucleus and nucleus retroambiguus is not predicted by ultrasonic vocalization in tau-P301L mice

Upper airway and vocalization control areas such as the periaqueductal gray (PAG), kölliker-fuse nucleus (KF) and nucleus retroambiguus (NRA) are prone to developing tauopathy in mice expressing the mutant human tau P301L protein. Consequently, impaired ultrasonic vocalization (USV) previously identified in tau-P301L mice at the terminal disease stage of 8-9 months of age, was attributed to the presence of tauopathy in these regions. Our aim was to establish whether the onset of USV disorders manifest prior to the terminal stage, and if USV disorders are predictive of the presence of tauopathy in the PAG, KF and NRA. USVs produced by tau-P301L and wildtype mice aged 3-4, 5-6 or 8-9 months were recorded during male-female interaction. Immunohistochemistry was then performed to assess the presence or degree of tauopathy in the PAG, KF and NRA of mice displaying normal or abnormal USV patterns. Comparing various USV measurements, including the number, duration and frequency of calls, revealed no differences between tau-P301L and wildtype mice across all age groups, and linear discriminant analysis also failed to identify separate USV populations. Finally, the presence of tauopathy in the PAG, KF and NRA in individual tau-P301L mice did not reliably associate with USV disorders. Our findings that tauopathy in designated mammalian vocalization centres, such as the PAG, KF and NRA, did not associate with USV disturbances in tau-P301L mice questions whether USV phenotypes in this transgenic mouse are valid for studying tauopathy-related human voice and speech disorders.

Novel P397S MAPT variant associated with late onset and slow progressive frontotemporal dementia

Mutations in the MAPT gene cause frontotemporal dementia with tau deposits. We report the novel p.P397S MAPT variant in eight subjects from five apparently nonrelated families suffering from frontotemporal dementia with autosomal dominant pattern of inheritance. In silico analysis reported conflicting evidence of pathogenicity. The segregation analysis support that this variant is likely pathogenic. The mean age at onset (61.4 years) and mean disease duration (13.9 years) of these subjects and their affected relatives were significantly higher compared with our series of p.P301L MAPT mutation carriers. These findings suggest that p.P397S variant could be a new MAPT mutation associated with a less aggressive phenotype than other MAPT mutations.

Decreased synthesis of ribosomal proteins in tauopathy revealed by non-canonical amino acid labelling

Tau is a scaffolding protein that serves multiple cellular functions that are perturbed in neurodegenerative diseases, including Alzheimer's disease (AD) and frontotemporal dementia (FTD). We have recently shown that amyloid-β, the second hallmark of AD, induces de novo protein synthesis of tau. Importantly, this activation was found to be tau-dependent, raising the question of whether FTD-tau by itself affects protein synthesis. We therefore applied non-canonical amino acid labelling to visualise and identify newly synthesised proteins in the K369I tau transgenic K3 mouse model of FTD. This revealed massively decreased protein synthesis in neurons containing pathologically phosphorylated tau, a finding confirmed in P301L mutant tau transgenic rTg4510 mice. Using quantitative SWATH-MS proteomics, we identified changes in 247 proteins of the de novo proteome of K3 mice. These included decreased synthesis of the ribosomal proteins RPL23, RPLP0, RPL19 and RPS16, a finding that was validated in both K3 and rTg4510 mice. Together, our findings present a potential pathomechanism by which pathological tau interferes with cellular functions through the dysregulation of ribosomal protein synthesis.

Autoradiography validation of novel tau PET tracer [F-18]-MK-6240 on human postmortem brain tissue

[F-18]-MK-6240, a novel tau positron emission tomography (PET) tracer recently discovered for the in vivo detection of neurofibrillary tangles, has the potential to improve diagnostic accuracy in the detection of Alzheimer disease. We have examined regional and substrate-specific binding patterns as well as possible off-target binding of this tracer on human brain tissue to advance towards its validation. We applied [F-18]-MK-6240 phosphor screen and high resolution autoradiography to postmortem samples from patients with a definite pathological diagnosis of Alzheimer disease, frontotemporal lobar degeneration-tau (Pick's disease, progressive supranuclear palsy and corticobasal degeneration), chronic traumatic encephalopathy, frontotemporal lobar degeneration-Tar DNA-binding protein 43 (TDP-43), dementia with Lewy bodies, cerebral amyloid angiopathy and elderly controls free of pathologic changes of neurodegenerative disease. We also directly compared the binding properties of [F-18]-MK-6240 and [F-18]-AV-1451 in human tissue, and examined potential nonspecific binding of both tau tracers to monoamine oxidases (MAO) by using autoradiography in the presence of selective monoamine oxidase A (MAO-A) and monoamine oxidase B (MAO-B) inhibitors. Our data indicate that MK-6240 strongly binds to neurofibrillary tangles in Alzheimer disease but does not seem to bind to a significant extent to tau aggregates in non-Alzheimer tauopathies, suggesting that it may have a limited utility for the in vivo detection of these pathologies. There is no evidence of binding to lesions containing β-amyloid, α-synuclein or TDP-43. In addition, we identified MK-6240 strong off-target binding to neuromelanin and melanin-containing cells, and some weaker binding to areas of hemorrhage. These binding patterns are nearly identical to those previously reported by our group and others for [F-18]-AV-1451. Of note, [F-18]-MK-6240 and [F-18]-AV-1451 autoradiographic binding signals were only weakly displaced by competing concentrations of selective MAO-B inhibitor deprenyl but not by MAO-A inhibitor clorgyline, suggesting that MAO enzymes do not appear to be a significant binding target of any of these two tracers. Together these novel findings provide relevant insights for the correct interpretation of in vivo [F-18]-MK-6240 PET imaging.

Integrative system biology analyses of CRISPR-edited iPSC-derived neurons and human brains reveal deficiencies of presynaptic signaling in FTLD and PSP

Mutations in the microtubule-associated protein tau (MAPT) gene cause autosomal dominant frontotemporal lobar degeneration with tau inclusions (FTLD-tau). MAPT p.R406W carriers present clinically with progressive memory loss and neuropathologically with neuronal and glial tauopathy. However, the pathogenic events triggered by the expression of the mutant tau protein remain poorly understood. To identify the genes and pathways that are dysregulated in FTLD-tau, we performed transcriptomic analyses in induced pluripotent stem cell (iPSC)-derived neurons carrying MAPT p.R406W and CRISPR/Cas9-corrected isogenic controls. We found that the expression of the MAPT p.R406W mutation was sufficient to create a significantly different transcriptomic profile compared with that of the isogeneic controls and to cause the differential expression of 328 genes. Sixty-one of these genes were also differentially expressed in the same direction between MAPT p.R406W carriers and pathology-free human control brains. We found that genes differentially expressed in the stem cell models and human brains were enriched for pathways involving gamma-aminobutyric acid (GABA) receptors and pre-synaptic function. The expression of GABA receptor genes, including GABRB2 and GABRG2, were consistently reduced in iPSC-derived neurons and brains from MAPT p.R406W carriers. Interestingly, we found that GABA receptor genes, including GABRB2 and GABRG2, are significantly lower in symptomatic mouse models of tauopathy, as well as in brains with progressive supranuclear palsy. Genome wide association analyses reveal that common variants within GABRB2 are associated with increased risk for frontotemporal dementia (P < 1 × 10^-3). Thus, our systems biology approach, which leverages molecular data from stem cells, animal models, and human brain tissue can reveal novel disease mechanisms. Here, we demonstrate that MAPT p.R406W is sufficient to induce changes in GABA-mediated signaling and synaptic function, which may contribute to the pathogenesis of FTLD-tau and other primary tauopathies.

Genetic Variation in Genes Underlying Diverse Dementias May Explain a Small Proportion of Cases in the Alzheimer's Disease Sequencing Project

BACKGROUND/AIMS

The Alzheimer's Disease Sequencing Project (ADSP) aims to identify novel genes influencing Alzheimer's disease (AD). Variants within genes known to cause dementias other than AD have previously been associated with AD risk. We describe evidence of co-segregation and associations between variants in dementia genes and clinically diagnosed AD within the ADSP.

METHODS

We summarize the properties of known pathogenic variants within dementia genes, describe the co-segregation of variants annotated as "pathogenic" in ClinVar and new candidates observed in ADSP families, and test for associations between rare variants in dementia genes in the ADSP case-control study. The participants were clinically evaluated for AD, and they represent European, Caribbean Hispanic, and isolate Dutch populations.

RESULTS/CONCLUSIONS

Pathogenic variants in dementia genes were predominantly rare and conserved coding changes. Pathogenic variants within ARSA, CSF1R, and GRN were observed, and candidate variants in GRN and CHMP2B were nominated in ADSP families. An independent case-control study provided evidence of an association between variants in TREM2, APOE, ARSA, CSF1R, PSEN1, and MAPT and risk of AD. Variants in genes which cause dementing disorders may influence the clinical diagnosis of AD in a small proportion of cases within the ADSP.

Slowly progressive dementia caused by MAPT R406W mutations: longitudinal report on a new kindred and systematic review

Background

The MAPT c.1216C > T (p.Arg406Trp; R406W) mutation is a known cause of frontotemporal dementia with Parkinsonism linked to chromosome 17 tau with Alzheimer’s disease-like clinical features.

Methods

We compiled clinical data from a new Swedish kindred with R406W mutation. Seven family members were followed longitudinally for up to 22 years. Radiological examinations were performed in six family members and neuropathological examinations in three. We systematically reviewed the literature and compiled clinical, radiological, and neuropathological data on 63 previously described R406W heterozygotes and 3 homozygotes.

Results

For all cases combined, the median age of onset was 56 years and the median disease duration was 13 years. Memory impairment was the most frequent symptom, behavioral disturbance and language impairment were less common, and Parkinsonism was rare. Disease progression was most often slow. The most frequent clinical diagnosis was Alzheimer’s disease. R406W homozygotes had an earlier age at onset and a higher frequency of behavioral symptoms and Parkinsonism than heterozygotes. In the new Swedish kindred, a consistent imaging finding was ventromedial temporal lobe atrophy, which was evident also in early disease stages as a widening of the collateral sulcus with ensuing atrophy of the parahippocampal gyrus. Unlike previously published R406W carriers, all three autopsied patients from the novel family showed neuropathological similarities with progressive supranuclear palsy, with predominant four-repeat (exon 10+) tau isoform (4R) tauopathy and neurofibrillary tangles accentuated in the basal-medial temporal lobe. Amyloid-β pathology was absent.

Conclusions

Dominance of 4R over three-repeat (exon 10−) tau isoforms contrasts with earlier reports of R406W patients and was not sufficiently explained by the presence of H1/H2 haplotypes in two of the autopsied patients. R406W patients often show a long course of disease with marked memory deficits. Both our neuropathological results and our imaging findings revealed that the ventromedial temporal lobes were extensively affected in the disease. We suggest that this area may represent the point of origin of tau deposition in this disease with relatively isolated tauopathy.

Electronic supplementary material

The online version of this article (doi:10.1186/s13195-017-0330-2) contains supplementary material, which is available to authorized users.

Frontotemporal dementia

Frontotemporal dementia (FTD) is a neurodegenerative disorder characterized by progressive changes in behavior, personality, and language with involvement of the frontal and temporal regions of the brain. About 40% of FTD cases have a positive family history, and about 10% of these cases are inherited in an autosomal-dominant pattern. These gene defects present with distinct clinical phenotypes. As the diagnosis of FTD becomes more recognizable, it will become increasingly important to keep these gene mutations in mind. In this chapter, we review the genes with known associations to FTD. We discuss protein functions, mutation frequencies, clinical phenotypes, imaging characteristics, and pathology associated with these genes.

Caenorhabditis elegans models of tauopathy

One of the hallmarks of the tauopathies, which include the neurodegenerative disorders, such as Alzheimer disease (AD), corticobasal degeneration, frontotemporal dementia, and progressive supranuclear palsy (PSP), is the abnormal accumulation of post-translationally modified, insoluble tau. The result is a loss of neurons, decreased mental function, and complete dependence of patients on others. Aggregation of tau, which under physiologic conditions is a highly soluble protein, is thought to be central to the pathogenesis of these diseases. Indeed one of the strongest lines of evidence is the MAPT gene polymorphisms that lead to the familial forms of tauopathy. Extensive research in animal models over the years has contributed some of the most important findings regarding the pathogenesis of these diseases. Despite this, the precise molecular mechanisms that lead to abnormal tau folding, accumulation, and spreading remain unknown. Owing to the fact that most of the biochemical pathways are conserved, Caenorhabditis elegans provides an alternative approach to identify cellular mechanisms and druggable genes that operate in such disorders. Many human genes implicated in neurodegenerative diseases have counterparts in C. elegans, making it an excellent model in which to study their pathogenesis. In this article, we review some of the important findings gained from C. elegans tauopathy models.-Pir, G. J., Choudhary, B., Mandelkow, E. Caenorhabditiselegans models of tauopathy.

A Conserved Cytoskeletal Signaling Cascade Mediates Neurotoxicity of FTDP-17 Tau Mutations In Vivo

The microtubule binding protein tau is strongly implicated in multiple neurodegenerative disorders, including frontotemporal dementia and parkinsonism linked to chromosome 17 (FTDP-17), which is caused by mutations in tau. In vitro, FTDP-17 mutant versions of tau can reduce microtubule binding and increase the aggregation of tau, but the mechanism by which these mutations promote disease in vivo is not clear. Here we take a combined biochemical and in vivo modeling approach to define functional properties of tau driving neurotoxicity in vivo We express wild-type human tau and five FTDP-17 mutant forms of tau in Drosophila using a site-directed insertion strategy to ensure equivalent levels of expression. We then analyze multiple markers of neurodegeneration and neurotoxicity in transgenic animals, including analysis of both males and females. We find that FTDP-17 mutations act to enhance phosphorylation of tau and thus promote neurotoxicity in an in vivo setting. Further, we demonstrate that phosphorylation-dependent excess stabilization of the actin cytoskeleton is a key phosphorylation-dependent mediator of the toxicity of wild-type tau and of all the FTDP-17 mutants tested. Finally, we show that important downstream pathways, including autophagy and the unfolded protein response, are coregulated with neurotoxicity and actin cytoskeletal stabilization in brains of flies expressing wild-type human and various FTDP-17 tau mutants, supporting a conserved mechanism of neurotoxicity of wild-type tau and FTDP-17 mutant tau in disease pathogenesis.SIGNIFICANCE STATEMENT The microtubule protein tau aggregates and forms insoluble inclusion bodies known as neurofibrillary tangles in the brain tissue of patients with a variety of neurodegenerative disorders, including Alzheimer's disease. The tau protein is thus widely felt to play a key role in promoting neurodegeneration. However, precisely how tau becomes toxic is unclear. Here we capitalize on an "experiment of nature" in which rare missense mutations in tau cause familial neurodegeneration and neurofibrillary tangle formation. By comparing the biochemical activities of different tau mutations with their in vivo toxicity in a well controlled Drosophila model system, we find that all mutations tested increase phosphorylation of tau and trigger a cascade of neurotoxicity critically impinging on the integrity of the actin cytoskeleton.

Energy and the Alzheimer brain

The high energy demands of the poorly myelinated long axon hippocampal and cortical neurons render these neurons selectively vulnerable to degeneration in Alzheimer's disease. However, pathology engages all of the major elements of the neurovascular unit of the mature Alzheimer brain, the neurons, glia and blood vessels. Neurons present with retrograde degeneration of the axodendritic tree, capillaries with string vessels and markedly reduced densities and glia with signs of inflammatory activation. The neurons, capillaries and astrocytes of the mature Alzheimer brain harbor structurally defective mitochondria. Clinically, reduced glucose utilization, decades before cognitive deterioration, betrays ongoing energy insufficiency. β-hydroxybutyrate and γ-hydroxybutyrate can both provide energy to the brain when glucose utilization is blocked. Early work in mouse models of Alzheimer's disease demonstrate their ability to reverse the pathological changes in the Alzheimer brain and initial clinical trials reveal their ability to improve cognition and every day function. Supplying the brain with energy holds great promise for delaying the onset of Alzheimer's disease and slowing its progress.

Pathological correlations of [F-18]-AV-1451 imaging in non-alzheimer tauopathies

OBJECTIVE

Recent studies have shown that positron emission tomography (PET) tracer AV-1451 exhibits high binding affinity for paired helical filament (PHF)-tau pathology in Alzheimer's brains. However, the ability of this ligand to bind to tau lesions in other tauopathies remains controversial. Our goal was to examine the correlation of in vivo and postmortem AV-1451 binding patterns in three autopsy-confirmed non-Alzheimer tauopathy cases.

METHODS

We quantified in vivo retention of [F-18]-AV-1451 and performed autoradiography, [H-3]-AV-1451 binding assays, and quantitative tau measurements in postmortem brain samples from two progressive supranuclear palsy (PSP) cases and a MAPT P301L mutation carrier. They all underwent [F-18]-AV-1451 PET imaging before death.

RESULTS

The three subjects exhibited [F-18]-AV-1451 in vivo retention predominantly in basal ganglia and midbrain. Neuropathological examination confirmed the PSP diagnosis in the first two subjects; the MAPT P301L mutation carrier had an atypical tauopathy characterized by grain-like tau-containing neurites in gray and white matter with heaviest burden in basal ganglia. In all three cases, autoradiography failed to show detectable [F-18]-AV-1451 binding in multiple brain regions examined, with the exception of entorhinal cortex (reflecting incidental age-related neurofibrillary tangles) and neuromelanin-containing neurons in the substantia nigra (off-target binding). The lack of a consistent significant correlation between in vivo [F-18]-AV-1541 retention and postmortem in vitro binding and tau measures in these cases suggests that this ligand has low affinity for tau lesions primarily made of straight tau filaments.

INTERPRETATION

AV-1451 may have limited utility for in vivo selective and reliable detection of tau aggregates in these non-Alzheimer tauopathies. ANN NEUROL 2017;81:117-128.

FTDP-17 with Pick body-like inclusions associated with a novel tau mutation, p.E372G

Mutations in microtubule-associated protein tau gene (MAPT) cause frontotemporal dementia with parkinsonism linked to chromosome 17 (FTDP-17). Here, we describe a patient with FTDP-17 and a novel missense mutation in exon 13 of MAPT, p.E372G. We compare clinicopathologic features of this patient to two previously unreported patients with another exon 13 mutation, p.G389R. The patient with the p.E372G mutation was a 40-year-old man with behavioral variant frontotemporal dementia (bvFTD), who subsequently developed agrammatic speech and parkinsonism. One of the FTDP-17 patients with p.G389R mutation presented at age 24 with agrammatic variant of primary progressive aphasia, and subsequently behavioral dysfunction. The other presented at age 53 with bvFTD, followed by agrammatic speech and corticobasal syndrome. Neuropathologic features of FTDP-17 due to p.E372G were similar to those of p.G389R, including tau-immunoreactive Pick body-like neuronal inclusions and swollen, tapering thread-like processes in white matter immunoreactive for 3-repeat and 4-repeat tau. Biochemical analysis of insoluble tau showed similar isoform compositions in p.E372G and p.G389R. Functional studies of the p.E372G mutation showed marked increase in tau filament formation and its reduced ability to promote microtubule assembly. Together these findings indicate that p.E372G is a pathogenic MAPT mutation that causes FTDP-17 similar to p.G389R.

Quantitative and combinatory determination of in situ phosphorylation of tau and its FTDP-17 mutants

Tau is hyperphosphorylated in the brains of patients with tauopathies, such as Alzheimer's disease and frontotemporal dementia and parkinsonism linked to chromosome 17 (FTDP-17). However, neither the mechanism of hyperphosphorylation nor its contribution to pathogenesis is known. We applied Phos-tag SDS-PAGE, a phosphoaffinity electrophoresis, to the analysis of tau phosphorylation in vitro by Cdk5, in cultured cells and in mouse brain. Here, we found that Cdk5-p25 phosphorylated tau in vitro at Ser404, Ser235, Thr205 and Ser202 in this order. In contrast in cultured cells, Ser404 was preferentially phosphorylated by Cdk5-p35, whereas Thr205 was not phosphorylated. Ser202 and Ser235 were phosphorylated by endogenous kinases. Tau exhibited ~12 phosphorylation isotypes in COS-7 cells with different combinations of phosphorylation at Thr181, Ser202, Thr231, Ser235 and Ser404. These phosphorylation sites were similar to tau phosphorylated in mouse brains. FTDP-17 tau with a mutation in the C-terminal region had different banding patterns, indicating a different phosphorylation pattern. In particular, it was clear that the R406W mutation causes loss of Ser404 phosphorylation. These results demonstrate the usefulness of the Phos-tag technique in the quantitative analysis of site-specific in vivo phosphorylation of tau and provide detailed information on in situ combinatory phosphorylation of tau.

4-Hydroxyisophthalic acid from Decalepis hamiltonii rescues the neurobehavioral deficit in transgenic Drosophila model of taupathies

Oxidative stress is one of the major etiological factors implicated in pathogenesis of neurodegenerative diseases. Since neurons are more sensitive to oxidative damage there is an increasing interest in developing novel antioxidant therapies, especially herbal preparations due to their safety profile and high efficiency. In this regard, the neuroprotective potential of a novel antioxidant compound, 4-hydroxyisophthalic acid (4-HIPA) isolated from aqueous extract of Decalepis hamiltonii roots was examined using transgenic Drosophila model of taupathy expressing wild-type and mutant forms of 2N4R isoform of human microtubule associated protein tau (MAPT). Taupathy model flies showed cognitive deficits in olfactory memory and deteriorated circadian rhythm of locomotory activities. Administration of 0.1 mg/ml 4-HIPA, markedly enhanced their olfactory memory performance and restored circadian rhythmicity of the transgenic flies locomotory behavior to the normal range. The mechanism of action that underlies 4-HIPA neuroprotection involves enhancement in efficiency of cellular antioxidant defense system by means of elevation in antioxidant enzyme activities and attenuation of oxidative stress. The molecule could positively affect the activity of neurotransmitter enzymes, which in turn enhances neuronal function and ameliorates the Tau-induced neurobehavioral deficits. Our findings showed that 4-HIPA can be considered as a suitable therapeutic candidate for drug development towards treatment of neurodegenerative disorders.

18F-AV-1451 tau PET imaging correlates strongly with tau neuropathology in MAPT mutation carriers

Tau positron emission tomography ligands provide the novel possibility to image tau pathology in vivo. However, little is known about how in vivo brain uptake of tau positron emission tomography ligands relates to tau aggregates observed post-mortem. We performed tau positron emission tomography imaging with ¹⁸F-AV-1451 in three patients harbouring a p.R406W mutation in the MAPT gene, encoding tau. This mutation results in 3- and 4-repeat tau aggregates similar to those in Alzheimer’s disease, and many of the mutation carriers initially suffer from memory impairment and temporal lobe atrophy. Two patients with short disease duration and isolated memory impairment exhibited ¹⁸F-AV-1451 uptake mainly in the hippocampus and adjacent temporal lobe regions, correlating with glucose hypometabolism in corresponding regions. One patient died after 26 years of disease duration with dementia and behavioural deficits. Pre-mortem, there was ¹⁸F-AV-1451 uptake in the temporal and frontal lobes, as well as in the basal ganglia, which strongly correlated with the regional extent and amount of tau pathology in post-mortem brain sections. Amyloid-β (¹⁸F-flutemetamol) positron emission tomography scans were negative in all cases, as were stainings of brain sections for amyloid. This provides strong evidence that ¹⁸F-AV-1451 positron emission tomography can be used to accurately quantify in vivo the regional distribution of hyperphosphorylated tau protein.

Behind the curtain of tauopathy: a show of multiple players orchestrating tau toxicity

tau, a microtubule-associated protein, directly binds with microtubules to dynamically regulate the organization of cellular cytoskeletons, and is especially abundant in neurons of the central nervous system. Under disease conditions such as Pick's disease, progressive supranuclear palsy, frontotemporal dementia, parkinsonism linked to chromosome 17 and Alzheimer's disease, tau proteins can self-assemble to paired helical filaments progressing to neurofibrillary tangles. In these diseases, collectively referred to as "tauopathies", alterations of diverse tau modifications including phosphorylation, metal ion binding, glycosylation, as well as structural changes of tau proteins have all been observed, indicating the complexity and variability of factors in the regulation of tau toxicity. Here, we review our current knowledge and hypotheses from relevant studies on tau toxicity, emphasizing the roles of phosphorylations, metal ions, folding and clearance control underlining tau etiology and their regulations. A summary of clinical efforts and associated findings of drug candidates under development is also presented. It is hoped that a more comprehensive understanding of tau regulation will provide us with a better blueprint of tau networking in neuronal cells and offer hints for the design of more efficient strategies to tackle tau-related diseases in the future.

Three dimensions of the amyloid hypothesis: time, space and 'wingmen'

The amyloid hypothesis, which has been the predominant framework for research in Alzheimer's disease (AD), has been the source of considerable controversy. The amyloid hypothesis postulates that amyloid-β peptide (Aβ) is the causative agent in AD. It is strongly supported by data from rare autosomal dominant forms of AD. However, the evidence that Aβ causes or contributes to age-associated sporadic AD is more complex and less clear, prompting criticism of the hypothesis. We provide an overview of the major arguments for and against the amyloid hypothesis. We conclude that Aβ likely is the key initiator of a complex pathogenic cascade that causes AD. However, we argue that Aβ acts primarily as a trigger of other downstream processes, particularly tau aggregation, which mediate neurodegeneration. Aβ appears to be necessary, but not sufficient, to cause AD. Its major pathogenic effects may occur very early in the disease process.

Invited review: Frontotemporal dementia caused by microtubule-associated protein tau gene (MAPT) mutations: a chameleon for neuropathology and neuroimaging

Hereditary frontotemporal dementia associated with mutations in the microtubule-associated protein tau gene (MAPT) is a protean disorder. Three neuropathologic subtypes can be recognized, based on the presence of inclusions made of tau isoforms with three and four repeats, predominantly three repeats and mostly four repeats. This is relevant for establishing a correlation between structural magnetic resonance imaging and positron emission tomography using tracers specific for aggregated tau. Longitudinal studies will be essential to determine the evolution of anatomical alterations from the asymptomatic stage to the various phases of disease following the onset of symptoms.

Frontotemporal dementia with parkinsonism linked to chromosome 17 with the MAPT R406W mutation presenting with a broad distribution of abundant senile plaques

We report the autopsy results of a patient with familial dementia who was diagnosed as having frontotemporal dementia with parkinsonism linked to chromosome 17 (FTDP-17) with an R406W mutation in the microtubule-associated protein tau (MAPT) gene. This patient showed Alzheimer's disease (AD)-like clinical manifestations from the age of 59, with reduced β-amyloid1-42 (Aβ42 ) and elevated total and phosphorylated tau levels in the cerebrospinal fluid. He did not present with any apparent parkinsonism throughout the disease course. His autopsy at age 73 showed atrophy and neurodegeneration in many brain regions, particularly in the antero-medial temporal cortex and hippocampus, followed by the frontal lobes, with abundant neurofibrillary tangles. In addition, a diffuse distribution of Aβ-positive senile plaques, including many neuritic plaques, was observed and classified as stage C according to the Consortium to Establish a Registry for Alzheimer's Disease (CERAD) criteria. These results suggest that analyzing of the MAPT gene is essential for diagnosing familial dementia, even if amyloid markers such as Aβ42 in the cerebrospinal fluid and amyloid imaging are positive, or if neuropathological findings indicate a diagnosis of AD.

Alzheimer's disease genetics: from the bench to the clinic

Alzheimer's disease (AD) is a clinically heterogeneous neurodegenerative disease with a strong genetic component. Several genes have been associated with AD risk for nearly 20 years. However, it was not until the recent technological advances that allow for the analysis of millions of polymorphisms in thousands of subjects that we have been able to advance our understanding of the genetic complexity of AD susceptibility. Genome-wide association studies and whole-exome and whole-genome sequencing have revealed more than 20 loci associated with AD risk. These studies have provided insights into the molecular pathways that are altered in AD pathogenesis, which have, in turn, provided insight into novel therapeutic targets.

Zinc binding directly regulates tau toxicity independent of tau hyperphosphorylation

Tau hyperphosphorylation is thought to underlie tauopathy. Working in a Drosophila tauopathy model expressing a human Tau mutant (hTauR406W, or Tau*), we show that zinc contributes to the development of Tau toxicity through two independent actions: by increasing Tau phosphorylation and, more significantly, by directly binding to Tau. Elimination of zinc binding through amino acid substitution of Cys residues has a minimal effect on phosphorylation levels yet essentially eliminates Tau toxicity. The toxicity of the zinc-binding-deficient mutant Tau* (Tau*C2A) and overexpression of native Drosophila Tau, also lacking the corresponding zinc-binding Cys residues, are largely impervious to zinc concentration. Importantly, restoration of zinc-binding ability to Tau* by introduction of a zinc-binding residue (His) into the original Cys positions restores zinc-responsive toxicities in proportion to zinc-binding affinities. These results indicate zinc binding is a substantial contributor to tauopathy and have implications for therapy development.

Cerebrolysin™ efficacy in a transgenic model of tauopathy: role in regulation of mitochondrial structure

Background

Alzheimer’s Disease (AD) and Fronto temporal lobar dementia (FTLD) are common causes of dementia in the aging population for which limited therapeutical options are available. These disorders are associated with Tau accumulation. We have previously shown that Cerebrolysin^TM (CBL), a neuropeptide mixture with neurotrophic effects, ameliorates the behavioral deficits and neuropathological alterations in amyloid precursor protein (APP) transgenic (tg) mouse model of AD by reducing hyper-phosphorylated Tau. CBL has been tested in clinical trials for AD, however it’s potential beneficial effects in FTLD are unknown. For this purpose we sought to investigate the effects of CBL in a tg model of tauopathy. Accordingly, double tg mice expressing mutant Tau under the mThy-1 promoter and GSK3β (to enhance Tau phosphorylation) were treated with CBL and evaluated neuropathologically.

Results

Compared to single Tau tg mice the Tau/GSK3β double tg model displayed elevated levels of Tau phosphorylation and neurodegeneration in the hippocampus. CBL treatment reduced the levels of Tau phosphorylation in the dentate gyrus and the degeneration of pyramidal neurons in the temporal cortex and hippocampus of the Tau/GSK3β double tg mice. Interestingly, the Tau/GSK3β double tg mice also displayed elevated levels of Dynamin-related protein-1 (Drp-1), a protein that hydrolyzes GTP and is required for mitochondrial division. Ultrastructural analysis of the mitochondria in the Tau/GSK3β double tg mice demonstrated increased numbers and fragmentation of mitochondria in comparison to non-tg mice. CBL treatment normalized levels of Drp-1 and restored mitochondrial structure.

Conclusions

These results suggest that the ability of CBL to ameliorate neurodegenerative pathology in the tauopathy model may involve reducing accumulation of hyper-phosphorylated Tau and reducing alterations in mitochondrial biogenesis associated with Tau.

Parkinsonism and distinct dementia patterns in a family with the MAPT R406W mutation

BACKGROUND

The Arg406Trp (R406W) missense mutation in the microtubule-associated protein-tau gene (MAPT) is a known cause of early-onset dementia. Various dementia phenotypes have been described, including frontotemporal dementia (FTD), FTD with parkinsonism, and early-onset Alzheimer disease (EOAD)-like presentations.

METHODS

Using whole-exome capture with subsequent sequencing, we identified the R406W mutation in a family with multiple individuals with clinically diagnosed EOAD, in a pattern suggesting autosomal dominant inheritance. We reevaluated all available family members clinically.

RESULTS

Each of the affected individuals had a course meeting clinical criteria for EOAD. Two distinct disease trajectories were apparent: one rapidly progressive, and the other long and gradual. Four of five affected individuals also manifested parkinsonian symptoms. FTD features were not prominent and, when present, appeared only late in the course of dementia.

CONCLUSIONS

The MAPT R406W mutation is associated with EOAD-like symptoms and parkinsonism without FTD, as well as distinct cognitive courses.

C9orf72 hexanucleotide repeat expansions in clinical Alzheimer disease

IMPORTANCE

Hexanucleotide repeat expansions in the chromosome 9 open reading frame 72 (C9orf72) gene underlie a significant fraction of frontotemporal dementia and amyotrophic lateral sclerosis.

OBJECTIVE

To investigate the frequency of C9orf72 repeat expansions in clinically diagnosed late-onset Alzheimer disease (AD).

DESIGN, SETTING, AND PATIENTS

This case-control study genotyped the C9orf72 repeat expansion in 872 unrelated familial AD cases and 888 control subjects recruited as part of the National Institute on Aging Late-Onset Alzheimer Disease Family Study cohort, a multisite collaboration studying 1000 families with 2 or more individuals clinically diagnosed as having late-onset AD.

MAIN OUTCOMES AND MEASURES

We determined the presence or absence of the C9orf72 repeat expansion by repeat-primed polymerase chain reaction, the length of the longest nonexpanded allele, segregation of the genotype with disease, and clinical features of repeat expansion carriers. RESULTS Three families showed large C9orf72 hexanucleotide repeat expansions. Two additional families carried more than 30 repeats. Segregation with disease could be demonstrated in 3 families. One affected expansion carrier had neuropathology compatible with AD. In the National Institute on Aging Late-Onset Alzheimer Disease Family Study series, the C9orf72 repeat expansions constituted the second most common pathogenic mutation, just behind the PSEN1 A79V mutation, highlighting the heterogeneity of clinical presentations associated with repeat expansions.

CONCLUSIONS AND RELEVANCE

C9orf72 repeat expansions explain a small proportion of patients with a clinical presentation indistinguishable from AD, and they highlight the necessity of screening frontotemporal dementia genes in clinical AD cases with strong family history.

Frontotemporal dementia: implications for understanding Alzheimer disease

Frontotemporal dementia (FTD) comprises a group of behavioral, language, and movement disorders. On the basis of the nature of the characteristic protein inclusions, frontotemporal lobar degeneration (FTLD) can be subdivided into the common FTLD-tau and FTLD-TDP as well as the less common FTLD-FUS and FTLD-UPS. Approximately 10% of cases of FTD are inherited in an autosomal-dominant manner. Mutations in seven genes cause FTD, with those in tau (MAPT), chromosome 9 open reading frame 72 (C9ORF72), and progranulin (GRN) being the most common. Mutations in MAPT give rise to FTLD-tau and mutations in C9ORF72 and GRN to FTLD-TDP. The other four genes are transactive response-DNA binding protein-43 (TARDBP), fused in sarcoma (FUS), valosin-containing protein (VCP), and charged multivesicular body protein 2B (CHMP2B). Mutations in TARDBP and VCP give rise to FTLD-TDP, mutations in FUS to FTLD-FUS, and mutations in CHMP2B to FTLD-UPS. The discovery that mutations in MAPT cause neurodegeneration and dementia has important implications for understanding Alzheimer disease.

Transgenic expression of the FTDP-17 tauV337M mutation in brain dissociates components of executive function in mice

Frontotemporal lobe dementia (FTD) is a heterogeneous range of disorders, a subset of which arise from fully penetrant, autosomal dominant point mutations in the gene coding for the microtubule associated protein tau. These genetic tauopathies are associated with complex behavioural/cognitive disturbances, including compromised executive function. In the present study, we modelled the effects of the FTD with Parkinsonism linked to chromosome 17 (FTDP-17) tauV337M mutation (known as the Seattle Family A mutation) expressed in mice on executive processes using a novel murine analogue of the Stroop task. Employing biconditional discrimination procedures, Experiment 1 showed that normal mice, but not mice with excitotoxic lesions of the medial prefrontal cortex, were able to use context cues to resolve response conflict generated by incongruent stimulus compounds. In contrast to predictions, response conflict resolution was not disrupted by the tauV337M mutation (Experiment 2). However, while context appropriate actions were goal-directed in wild-type mice, performance of tauV337M mice was not goal-directed (Experiment 3). The results indicate that the tauV337M mutation in mice disrupts, selectively, a subset of processes related to executive function.

New approaches to genetic counseling and testing for Alzheimer's disease and frontotemporal degeneration

The discovery of new autosomal dominant and susceptibility genes for Alzheimer's disease (AD) and frontotemporal degeneration (FTD) is revealing important new information about the neurodegenerative process and the risk for acquiring these diseases. It is becoming increasingly clear that both the mechanisms that drive these diseases and their phenotypes overlap. New technologies will assist access to genetic testing but may increase difficulty with genetic test interpretation. Thus, the process of genetic counseling and testing for these diseases is becoming more complex. This article will review current knowledge on the genetics of AD and FTD and suggest clinical guidelines for helping families to navigate through these complexities. The implications of future discoveries will be offered.