The L266V tau mutation is associated with frontotemporal dementia and Pick-like 3R and 4R tauopathy

Gene replacement-Alzheimer's disease (GR-AD): Modeling the genetics of human dementias in mice

INTRODUCTION

Genetic studies conducted over the past four decades have provided us with a detailed catalog of genes that play critical roles in the etiology of Alzheimer's disease (AD) and related dementias (ADRDs). Despite this progress, as a field we have had only limited success in incorporating this rich complexity of human AD/ADRD genetics findings into our animal models of these diseases. Our primary goal for the gene replacement (GR)-AD project is to develop mouse lines that model the genetics of AD/ADRD as closely as possible.

METHODS

To do this, we are generating mouse lines in which the genes of interest are precisely and completely replaced in the mouse genome by their full human orthologs.

RESULTS

Each model set consists of a control line with a wild-type human allele and variant lines that precisely match the human genomic sequence in the control line except for a high-impact pathogenic mutation or risk variant.

Disentangling tau: One protein, many therapeutic approaches

The tauopathies encompass over 20 adult neurodegenerative diseases and are characterized by the dysfunction and accumulation of insoluble tau protein. Among them, Alzheimer's disease, frontotemporal dementia, and progressive supranuclear palsy collectively impact millions of patients and their families worldwide. Despite years of drug development using a variety of mechanisms of action, no therapeutic directed against tau has been approved for clinical use. This raises important questions about our current model of tau pathology and invites thoughtful consideration of our approach to nonclinical models and clinical trial design. In this article, we review what is known about the biology and genetics of tau, placing it in the context of current and failed clinical trials. We highlight potential reasons for the lack of success to date and offer suggestions for new pathways in therapeutic development. Overall, our viewpoint to the future is optimistic for this important group of neurodegenerative diseases.

Unraveling Molecular and Genetic Insights into Neurodegenerative Diseases: Advances in Understanding Alzheimer's, Parkinson's, and Huntington's Diseases and Amyotrophic Lateral Sclerosis

Neurodegenerative diseases are, according to recent studies, one of the main causes of disability and death worldwide. Interest in molecular genetics has started to experience exponential growth thanks to numerous advancements in technology, shifts in the understanding of the disease as a phenomenon, and the change in the perspective regarding gene editing and the advantages of this action. The aim of this paper is to analyze the newest approaches in genetics and molecular sciences regarding four of the most important neurodegenerative disorders: Alzheimer's disease, Parkinson's disease, Huntington's disease, and amyotrophic lateral sclerosis. We intend through this review to focus on the newest treatment, diagnosis, and predictions regarding this large group of diseases, in order to obtain a more accurate analysis and to identify the emerging signs that could lead to a better outcome in order to increase both the quality and the life span of the patient. Moreover, this review could provide evidence of future possible novel therapies that target the specific genes and that could be useful to be taken into consideration when the classical approaches fail to shed light.

Isoform-specific patterns of tau burden and neuronal degeneration in MAPT-associated frontotemporal lobar degeneration

Frontotemporal lobar degeneration with MAPT pathogenic variants (FTLD-MAPT) has heterogeneous tau pathological inclusions postmortem, consisting of three-repeat (3R) or four-repeat (4R) tau isoforms, or a combination (3R + 4R). Here, we studied grey matter tau burden, its relation to neuronal degeneration, and regional patterns of pathology in different isoform groups of FTLD-MAPT. We included 38 FTLD-MAPT autopsy cases with 10 different MAPT pathogenic variants, grouped based on predominant tau isoform(s). In up to eleven regions (ten cortical and one striatal), we quantified grey matter tau burden using digital histopathological analysis and assigned semi-quantitative ratings for neuronal degeneration (i.e. 0-4) and separate burden of glial and neuronal tau inclusions (i.e. 0-3). We used mixed modelling to compare pathology measures (1) across the entire cohort and (2) within isoform groups. In the total cohort, tau burden and neuronal degeneration were positively associated and most severe in the anterior temporal, anterior cingulate and transentorhinal cortices. Isoform groups showed distinctive features of tau burden and neuronal degeneration. Across all regions, the 3R isoform group had lower tau burden compared to the 4R group (p = 0.008), while at the same time showing more severe neuronal degeneration than the 4R group (p = 0.002). The 3R + 4R group had an intermediate profile with relatively high tau burden along with relatively severe neuronal degeneration. Neuronal tau inclusions were most frequent in the 4R group (p < 0.001 vs. 3R), while cortical glial tau inclusions were most frequent in the 3R + 4R and 4R groups (p ≤ 0.009 vs. 3R). Regionally, neuronal degeneration was consistently most severe in the anterior temporal cortex within each isoform group. In contrast, the regions with the highest tau burden differed in isoform groups (3R: striatum; 3R + 4R: striatum, inferior parietal lobule, middle frontal cortex, anterior cingulate cortex; 4R: transentorhinal cortex, anterior temporal cortex, fusiform gyrus). We conclude that FTLD-MAPT isoform groups show distinctive features of overall neuronal degeneration and regional tau burden, but all share pronounced anterior temporal neuronal degeneration. These data suggest that distinct isoform-related mechanisms of genetic tauopathies, with slightly divergent tau distribution, may share similar regional vulnerability to neurodegeneration within the frontotemporal paralimbic networks.

Astrocytic 4R tau expression drives astrocyte reactivity and dysfunction

The protein tau and its isoforms are associated with several neurodegenerative diseases, many of which are characterized by greater deposition of the 4-repeat (4R) tau isoform; however, the role of 4R tau in disease pathogenesis remains unclear. We created antisense oligonucleotides (ASOs) that alter the ratio of 3R to 4R tau to investigate the role of specific tau isoforms in disease. Preferential expression of 4R tau in human tau-expressing (hTau-expressing) mice was previously shown to increase seizure severity and phosphorylated tau deposition without neuronal or synaptic loss. In this study, we observed strong colocalization of 4R tau within reactive astrocytes and increased expression of pan-reactive and neurotoxic genes following 3R to 4R tau splicing ASO treatment in hTau mice. Increasing 4R tau levels in primary astrocytes provoked a similar response, including a neurotoxic genetic profile and diminished homeostatic function, which was replicated in human induced pluripotent stem cell-derived (iPSC-derived) astrocytes harboring a mutation that exhibits greater 4R tau. Healthy neurons cultured with 4R tau-expressing human iPSC-derived astrocytes exhibited a higher firing frequency and hypersynchrony, which could be prevented by lowering tau expression. These findings support a potentially novel pathway by which astrocytic 4R tau mediates reactivity and dysfunction and suggest that astrocyte-targeted therapeutics against 4R tau may mitigate neurodegenerative disease progression.

A critical appraisal of tau-targeting therapies for primary and secondary tauopathies

INTRODUCTION

Primary tauopathies are neurological disorders in which tau protein deposition is the predominant pathological feature. Alzheimer's disease is a secondary tauopathy with tau forming hyperphosphorylated insoluble aggregates. Tau pathology can propagate from region to region in the brain, while alterations in tau processing may impair tau physiological functions.

METHODS

We reviewed literature on tau biology and anti-tau drugs using PubMed, meeting abstracts, and ClnicalTrials.gov.

RESULTS

The past 15 years have seen >30 drugs interfering with tau aggregation, processing, and accumulation reaching the clinic. Initial results with tau aggregation inhibitors and anti-tau monoclonal antibodies have not shown clinical efficacy.

DISCUSSION

The reasons for these clinical failures are unclear but could be linked to the clearing of physiological forms of tau by non-specific drugs. Research is now concentrating efforts on developing reliable translational animal models and selective compounds targeting specific tau epitopes, neurotoxic tau aggregates, and post-translational tau modifications.

Mutant three-repeat tau expression initiates retinal ganglion cell death through Caspase-2

The microtubule-associated protein tau is implicated in multiple degenerative diseases including retinal diseases such as glaucoma; however, the way tau initiates retinopathy is unclear. Previous retinal assessments in mouse models of tauopathy suggest that mutations in four-repeat (4R) tau are associated with disease-induced retinal dysfunction, while shifting tau isoform ratio to favor three-repeat (3R) tau production enhanced photoreceptor function. To further understand how alterations in tau expression impact the retina, we analyzed the retinas of transgenic mice overexpressing mutant 3R tau (m3R tau-Tg), a model known to exhibit Pick's Disease pathology in the brain. Analysis of retinal cross-sections from young (3 month) and adult (9 month) mice detected asymmetric 3R tau immunoreactivity in m3R tau-Tg retina, concentrated in the retinal ganglion and amacrine cells of the dorsal retinal periphery. Accumulation of hyperphosphorylated tau was detected specifically in the detergent insoluble fraction of the adult m3R tau-Tg retina. RNA-seq analysis highlighted biological pathways associated with tauopathy that were uniquely altered in m3R tau-Tg retina. The upregulation of transcript encoding apoptotic protease caspase-2 coincided with increased immunostaining in predominantly 3R tau positive retinal regions. In adult m3R tau-Tg, the dorsal peripheral retina of the adult m3R tau-Tg exhibited decreased cell density in the ganglion cell layer (GCL) and reduced thickness of the inner plexiform layer (IPL) compared to the ventral peripheral retina. Together, these data indicate that mutant 3R tau may mediate toxicity in retinal ganglion cells (RGC) by promoting caspase-2 expression which results in RGC degeneration. The m3R tau-Tg line has the potential to be used to assess tau-mediated RGC degeneration and test novel therapeutics for degenerative diseases such as glaucoma.

Phenotype Heterogeneity and Genotype Correlation of MAPT Mutations in a Chinese PUMCH Cohort

Frontotemporal dementia (FTD) is a heterogeneous disease both clinically and pathologically. Genetic mutation in microtubule-associated protein tau (MAPT) is the most common cause of FTD, and the phenotype is related to the mutation location. However, the phenotype and genotype correlation varies somewhat among different cohorts and ethnicities. Whole-genome next-generation sequencing (NGS) was carried out for 1351 patients with dementia at Peking Union Medical College Hospital. MAPT variations classified as pathogenic and of uncertain significance were identified. Demographic information, clinical presentations, and neuroimaging were collected, and the phenotype-genotype correlation was analyzed with a concurrent literature review. Twenty-four patients were enrolled; 8 patients carrying the D177V mutation are discussed separately. The average onset age was young, and most of them had a positive family history. Cognitive dysfunction, behavior, and personality changes as well as aphasia were the most common presentations. Most structural MRIs showed asymmetrical atrophy of the temporal lobe, with/without similar changes in the frontal lobe. L266V carriers presented with youngest onset typical behavior variant FTD or aphasia; P301L carriers presented with behavior variant FTD or aphasia. Functional MRI and molecular imaging also showed that the involved areas were similar to those with structural atrophy. D296N carriers presented atypical parkinsonism and cognitive dysfunction at older ages. Eight D177V carriers had extraordinarily different manifestations. The clinical phenotype of most of them was not FTD, though cerebral vascular lesions were obvious in some of them. MAPT mutation is rare in Chinese dementia patients. The phenotype and genotype correlation is specific and overlaps. The D177V mutation is possibly not directly pathogenic in our cohort. Some of the variants might increase the genetic risk of neurodegenerative diseases.

Novel mGluR4 agonist Rapitalam ameliorates motor dysfunction in mice with tau-associated neurodegeneration

Introduction: Tau protein is classically involved in the pathogenesis of a neurodegenerative processes, such as Parkinson’s disease. This study was aimed at testing the novel mGluR4 selective agonist using it in transgenic mice with tau-associated neurodegeneration.

Materials and methods: Mice with Human P301S Tau hyperexpression were divided into 3 groups: Rapitalam 6 mg/kg and 20 mg/kg by gavage 3 times a week; and Control (Sham). The motor functions of animals were evaluated at 12th, 14th, 16th, 18th, and 20th weeks of life using the grip-test, rotarod and hanging wire test. In addition, the time of symptoms onset and death was recorded.

Research results: The use of Rapitalam at a dose of 6 mg/kg and 20 mg/kg significantly restored the holding impulse on a hanging wire, increasing it from 5.06±1.25 kg×sec to 6.42±0.97 kg×sec and 8.84±1.17 kg×sec, respectively. A similar trend was observed in the grip test: Rapitalam recovered grip strength from 28.43±5.04 N in the control group to 44.27±5.54 N (6 mg/kg) and 59.53±7.95 (20 mg/kg). Finally, the two-month use of Rapitalam neither delayed the manifestation of symptoms, nor increased the survival of mice.

Discussion: The cause of the loss of nerve cells in the mouse-tau line is autophagy. Apparently, Rapitalam is not able to simulate this process by reducing excitotoxicity, but against the background of the neurodegenerative process, it increases the activity of the nerve cells.

Conclusion: Rapitalam improves motor dysfunction in mice with tauopathy, with no effect on the survival of animals.

MAPT mutations, tauopathy, and mechanisms of neurodegeneration

In multiple neurodegenerative diseases, including Alzheimer's disease (AD), a prominent pathological feature is the aberrant aggregation and inclusion formation of the microtubule-associated protein tau. Because of the pathological association, these disorders are often referred to as tauopathies. Mutations in the MAPT gene that encodes tau can cause frontotemporal dementia with parkinsonism linked to chromosome 17 (FTDP-17), providing the clearest evidence that tauopathy plays a causal role in neurodegeneration. However, large gaps in our knowledge remain regarding how various FTDP-17-linked tau mutations promote tau aggregation and neurodegeneration, and, more generally, how the tauopathy is linked to neurodegeneration. Herein, we review what is known about how FTDP-17-linked pathogenic MAPT mutations cause disease, with a major focus on the prion-like properties of wild-type and mutant tau proteins. The hypothesized mechanisms by which mutations in the MAPT gene promote tauopathy are quite varied and may not provide definitive insights into how tauopathy arises in the absence of mutation. Further, differences in the ability of tau and mutant tau proteins to support prion-like propagation in various model systems raise questions about the generalizability of this mechanism in various tauopathies. Notably, understanding the mechanisms of tauopathy induction and spread and tau-induced neurodegeneration has important implications for tau-targeting therapeutics.

Disease-modifying therapies for tauopathies: agents in the pipeline

INTRODUCTION

Tauopathies are heterogeneous clinicopathological entities characterized by abnormal neuronal and/or glial inclusions of the microtubule-binding protein tau. Primary tauopathies considered to be diseases correspond to a major class of frontotemporal lobar degeneration (FTLD) neuropathology (FTLD-Tau), including several forms of frontotemporal dementia (FTD) clinical syndromes. Little progress has been made in the past 20 years in developing effective disease-modifying drugs for primary tauopathies and available symptomatic treatments have limited efficacy. Areas covered: Potential disease-modifying drugs in clinical development to slow neuropathological progression of primary tauopathies. Expert opinion: Since the underlying pathology of primary tauopathies consists of abnormal tau protein aggregates, treatments are being developed to interfere with the aggregation process or to promote the clearance of this protein. Unfortunately, disease-modifying treatments remain years away as demonstrated by the recent negative Phase III findings of a tau aggregation inhibitor (LMTM) for treating the behavioral variant of FTD. Further evidence will come from ongoing Phase I/II trials on novel drugs and immunotherapeutics with various targets - prevention of deposition or removal of tau aggregates, inhibition of tau phosphorylation/acetylation, modulation of O-GlcNAcylation, activation of autophagy or ubiquitin-proteasome system pathways, and rescue of selected tau loss of function or suppression of tau gene expression.

Heritability in frontotemporal tauopathies

Introduction

Exploring the degree of heritability in a large cohort of frontotemporal lobar degeneration with tau-immunopositive inclusions (FTLD-tau) and determining if different FTLD-tau subtypes are associated with stronger heritability will provide important insight into disease pathogenesis.

Methods

Using modified Goldman pedigree classifications, heritability was examined in pathologically proven FTLD-tau cases with dementia at any time (n = 124) from the Sydney-Cambridge collection.

Results

Thirteen percent of the FTLD-tau cohort have a suggested autosomal dominant pattern of inheritance, 25% have some family history, and 62% apparently sporadic. MAPT mutations were found in 9% of cases. Globular glial tauopathy was associated with the strongest heritability with 40% having a suggested autosomal dominant pattern of inheritance followed by corticobasal degeneration (19%), Pick's disease (8%), and progressive supranuclear palsy (6%).

Discussion

Similar to clinical frontotemporal dementia syndromes, heritability varies between pathological subtypes. Further identification of a genetic link in cases with strong heritability await discovery.

Tau Pathology in Parkinson's Disease

Tau protein—a member of the microtubule-associated protein family—is a key protein involved in many neurodegenerative diseases. Tau pathology in neurodegenerative diseases is characterized by pathological tau aggregation in neurofibrillary tangles (NFTs). Diseases with this typical pathological feature are called tauopathies. Parkinson's disease (PD) was not initially considered to be a typical tauopathy. However, recent studies have demonstrated increasing evidence of tau pathology in PD. A genome-wide association (GWA) study indicated a potential association between tauopathy and sporadic PD. The aggregation and deposition of tau were also observed in ~50% of PD brains, and it seems to be transported from neuron to neuron. The aggregation of NFTs, the abnormal hyperphosphorylation of tau protein, and the interaction between tau and alpha-synuclein may all contribute to the cell death and poor axonal transport observed in PD and Parkinsonism.

Protein astrogliopathies in human neurodegenerative diseases and aging

Neurodegenerative diseases are characterized by progressive dysfunction and loss of neurons associated with depositions of pathologically altered proteins showing hierarchical involvement of brain regions. The role of astrocytes in the pathogenesis of neurodegenerative diseases is explored as contributors to neuronal degeneration or neuroprotection pathways, and also as potential mediators of the transcellular spreading of disease-associated proteins. Protein astrogliopathy (PAG), including deposition of amyloid-β, prion protein, tau, α-synuclein, and very rarely transactive response DNA-binding protein 43 (TDP-43) is not unprecedented or unusual in neurodegenerative diseases. Morphological characterization of PAG is considered, however, only for the neuropathological diagnosis and classification of tauopathies. Astrocytic tau pathology is seen in primary frontotemporal lobar degeneration (FTLD) associated with tau pathologies (FTLD-Tau), and also in the form of aging-related tau astrogliopathy (ARTAG). Importantly, ARTAG shares common features with primary FTLD-Tau as well as with the astroglial tau pathologies that are thought to be hallmarks of a brain injury-related tauopathy known as chronic traumatic encephalopathy (CTE). Supported by experimental observations, the morphological variability of PAG might reflect distinct pathogenic involvement of different astrocytic populations. PAG might indicate astrocytic contribution to spreading or clearance of disease-associated proteins, however, this might lead to astrocytic dysfunction and eventually contribute to the degeneration of neurons. Here, we review recent advances in understanding ARTAG and other related forms of PAG.

Tau in Oligodendrocytes Takes Neurons in Sickness and in Health

Oligodendrocytes (OLGs), the myelin-forming cells of the central nervous system (CNS), are lifelong partners of neurons. They adjust to the functional demands of neurons over the course of a lifetime to meet the functional needs of a healthy CNS. When this functional interplay breaks down, CNS degeneration follows. OLG processes are essential features for OLGs being able to connect with the neurons. As many as fifty cellular processes from a single OLG reach and wrap an equal number of axonal segments. The cellular processes extend to meet and wrap axonal segments with myelin. Further, transport regulation, which is critical for myelination, takes place within the cellular processes. Because the microtubule-associated protein tau plays a crucial role in cellular process extension and myelination, alterations of tau in OLGs have deleterious effects, resulting in neuronal malfunction and CNS degeneration. Here, we review current concepts on the lifelong role of OLGs and myelin for brain health and plasticity. We present key studies of tau in OLGs and select important studies of tau in neurons. The extensive work on tau in neurons has considerably advanced our understanding of how tau promotes either health or disease. Because OLGs are crucial to neuronal health at any age, an understanding of the functions and regulation of tau in OLGs could uncover new therapeutics for selective CNS neurodegenerative diseases.

Retiring the term FTDP-17 as MAPT mutations are genetic forms of sporadic frontotemporal tauopathies

See Josephs (doi:10.1093/brain/awx367) for a scientific commentary on this article.In many neurodegenerative disorders, familial forms have provided important insights into the pathogenesis of their corresponding sporadic forms. The first mutations associated with frontotemporal lobar degeneration (FTLD) were found in the microtubule-associated protein tau (MAPT) gene on chromosome 17 in families with frontotemporal degeneration and parkinsonism (FTDP-17). However, it was soon discovered that 50% of these families had a nearby mutation in progranulin. Regardless, the original FTDP-17 nomenclature has been retained for patients with MAPT mutations, with such patients currently classified independently from the different sporadic forms of FTLD with tau-immunoreactive inclusions (FTLD-tau). The separate classification of familial FTLD with MAPT mutations implies that familial forms cannot inform on the pathogenesis of the different sporadic forms of FTLD-tau. To test this assumption, this study pathologically assessed all FTLD-tau cases with a known MAPT mutation held by the Sydney and Cambridge Brain Banks, and compared them to four cases of four subtypes of sporadic FTLD-tau, in addition to published case reports. Ten FTLD-tau cases with a MAPT mutation (K257T, S305S, P301L, IVS10+16, R406W) were screened for the core differentiating neuropathological features used to diagnose the different sporadic FTLD-tau subtypes to determine whether the categorical separation of MAPT mutations from sporadic FTLD-tau is valid. Compared with sporadic cases, FTLD-tau cases with MAPT mutations had similar mean disease duration but were younger at age of symptom onset (55 ± 4 years versus 70 ± 6 years). Interestingly, FTLD-tau cases with MAPT mutations had similar patterns and severity of neuropathological features to sporadic FTLD-tau subtypes and could be classified into: Pick's disease (K257T), corticobasal degeneration (S305S, IVS10‰+‰16, R406W), progressive supranuclear palsy (S305S) or globular glial tauopathy (P301L, IVS10‰+‰16). The finding that the S305S mutation could be classified into two tauopathies suggests additional modifying factors. Assessment of our cases and previous reports suggests that distinct MAPT mutations result in particular FTLD-tau subtypes, supporting the concept that they are likely to inform on the varied cellular mechanisms involved in distinctive forms of sporadic FTLD-tau. As such, FTLD-tau cases with MAPT mutations should be considered familial forms of FTLD-tau subtypes rather than a separate FTDP-17 category, and continued research on the effects of different mutations more focused on modelling their impact to produce the very different sporadic FTLD-tau pathologies in animal and cellular models.

The impact of Snoezelen in pediatric complex continuing care: A pilot study

PURPOSE

Snoezelen is an environment that provides sensory stimulation to individuals in health care and rehabilitative settings. With the presentation of various instruments and materials, individuals can encounter a range of sensory experiences including visual, tactile, and auditory with the purpose of inducing relaxation and restoration. Little is known about how children and adolescents experience this form of sensory stimulation, particularly those in complex continuing care who may have limited verbal and mobility capacity.

METHODS

This pilot study examined autonomic physiological responses and observational data on five children and adolescents in complex continuing care within a large rehabilitation hospital. Responses to Snoezelen and watching television were compared against baseline data collected during pre-intervention phases.

RESULTS

Using a single-subject design, this preliminary study found that individual participant responses varied considerably. Four of the five participants exhibited significant changes between sessions on one or two distinct physiological measures. The authors call on additional studies that apply unique and multiple methods capable of accessing the preferences of children and adolescent in rehabilitative care.

CONCLUSIONS

As an outcome, contributions to evidence-based practice can be made while supporting children's participation rights in health care decision making.

Current Understanding of Neurodegenerative Diseases Associated With the Protein Tau

Primary tauopathies are a group of neurodegenerative diseases in which tau is believed to be the major contributing factor of the neurodegenerative process. In primary tauopathies, there is a disassociation between tau (a microtubule-associated protein) and microtubules as a result of tau hyperphosphorylation. This disassociation between tau and microtubules results in tau fibrillization and inclusion formation as well as in microtubule dysfunction. There are different clinical syndromes associated with different primary tauopathies, and some clinical syndromes can be associated with multiple primary tauopathies. Hence, although some clinical syndromes are highly specific and almost diagnostic of a primary tauopathy, many are not, making it difficult to diagnose a primary tauopathy. Recently, radioligands that bind to tau and can be combined with positron emission tomography to detect fibrillary tau antemortem have been developed, although preliminary data suggest that these ligands may not be sensitive in detecting tau associated with many primary tauopathies. Another recent advancement in the field is evidence suggesting that tau may exhibit properties similar to those of prions, although infective transmission has not been shown. There have been a few clinical trials targeting tau and microtubule dysfunction, although none have had any disease-modifying effects. Understanding tau biology is critical to the development of pharmacological agents that could have disease-modifying effects on primary tauopathies.

Frontotemporal lobar degeneration: Pathogenesis, pathology and pathways to phenotype

Frontotemporal Lobar Degeneration (FTLD) is a clinically, pathologically and genetically heterogeneous group of disorders that affect principally the frontal and temporal lobes of the brain. There are three major associated clinical syndromes, behavioral variant frontotemporal dementia (bvFTD), semantic dementia (SD) and progressive non-fluent aphasia (PNFA); three principal histologies, involving tau, TDP-43 and FUS proteins; and mutations in three major genes, MAPT, GRN and C9orf72, along with several other less common gene mutations. All three clinical syndromes can exist separately or in combination with Amyotrophic Lateral Sclerosis (ALS). SD is exclusively a TDP-43 proteinopathy, and PNFA may be so, with both showing tight clinical, histological and genetic inter-relationships. bvFTD is more of a challenge with overlapping histological and genetic features, involvement of any of the three aggregating proteins, and changes in any of the three major genes. However, when ALS is present, all cases show a clear histological phenotype with TDP-43 aggregated proteins, and familial forms are associated with expansions in C9orf72. TDP-43 and FUS are nuclear carrier proteins involved in the regulation of RNA metabolism, whereas tau protein - the product of MAPT - is responsible for the assembly/disassembly of microtubules, which are vital for intracellular transport. Mutations in TDP-43 and FUS genes are linked to clinical ALS rather than FTLD (with or without ALS), suggesting that clinical ALS may be a disorder of RNA metabolism. Conversely, the protein products of GRN and C9orf72, along with those of the other minor genes, appear to form part of the cellular protein degradation machinery. It is possible therefore that FTLD is a reflection of dysfunction within lysosomal/proteasomal systems resulting in failure to remove potentially neurotoxic (TDP-43 and tau) aggregates, which ultimately overwhelm capacity to function. Spread of aggregates along distinct pathways may account for the different clinical phenotypes, and patterns of progression of disease.

ALS/FTLD: experimental models and reality

Amyotrophic lateral sclerosis is characterised by a loss of upper and lower motor neurons and characteristic muscle weakness and wasting, the most common form being sporadic disease with neuronal inclusions containing the tar DNA-binding protein 43 (TDP-43). Frontotemporal lobar degeneration is characterised by atrophy of the frontal and/or temporal lobes, the most common clinical form being the behavioural variant, in which neuronal inclusions containing either TDP-43 or 3-repeat tau are most prevalent. Although the genetic mutations associated with these diseases have allowed various experimental models to be developed, the initial genetic forms identified remain the most common models employed to date. It is now known that these first models faithfully recapitulate only some aspects of these diseases and do not represent the majority of cases or the most common overlapping pathologies. Newer models targeting the main molecular pathologies are still rare and in some instances, lack significant aspects of the molecular pathology. However, these diseases are complex and multigenic, indicating that experimental models may need to be targeted to different disease aspects. This would allow information to be gleaned from a variety of different yet relevant models, each of which has the capacity to capture a certain aspect of the disease, and together will enable a more complete understanding of these complex and multi-layered diseases.

Glial Tau Pathology in Tauopathies: Functional Consequences

Tauopathies are a class of neurodegenerative diseases characterized by the presence of hyperphosphorylated and aggregated tau pathology in neuronal and glial cells. Though the ratio of neuronal and glial tau aggregates varies across diseases, glial tau aggregates can populate the same degenerating brain regions as neuronal tau aggregates. While much is known about the deleterious consequences of tau pathology in neurons, the relative contribution of glial tau pathology to these diseases is less clear. Recent studies using a number of model systems implicate glial tau pathology in contributing to tauopathy pathogenesis. This review aims to highlight the functional consequences of tau overexpression in glial cells and explore the potential contribution of glial tau pathology in the pathogenesis of neurodegenerative tauopathies.

Deep clinical and neuropathological phenotyping of Pick disease

OBJECTIVE

To characterize sequential patterns of regional neuropathology and clinical symptoms in a well-characterized cohort of 21 patients with autopsy-confirmed Pick disease.

METHODS

Detailed neuropathological examination using 70μm and traditional 6μm sections was performed using thioflavin-S staining and immunohistochemistry for phosphorylated tau, 3R and 4R tau isoforms, ubiquitin, and C-terminally truncated tau. Patterns of regional tau deposition were correlated with clinical data. In a subset of cases (n = 5), converging evidence was obtained using antemortem neuroimaging measures of gray and white matter integrity.

RESULTS

Four sequential patterns of pathological tau deposition were identified starting in frontotemporal limbic/paralimbic and neocortical regions (phase I). Sequential involvement was seen in subcortical structures, including basal ganglia, locus coeruleus, and raphe nuclei (phase II), followed by primary motor cortex and precerebellar nuclei (phase III) and finally visual cortex in the most severe (phase IV) cases. Behavioral variant frontotemporal dementia was the predominant clinical phenotype (18 of 21), but all patients eventually developed a social comportment disorder. Pathological tau phases reflected the evolution of clinical symptoms and degeneration on serial antemortem neuroimaging, directly correlated with disease duration and inversely correlated with brain weight at autopsy. The majority of neuronal and glial tau inclusions were 3R tau-positive and 4R tau-negative in sporadic cases. There was a relative abundance of mature tau pathology markers in frontotemporal limbic/paralimbic regions compared to neocortical regions.

INTERPRETATION

Pick disease tau neuropathology may originate in limbic/paralimbic cortices. The patterns of tau pathology observed here provide novel insights into the natural history and biology of tau-mediated neurodegeneration.

Neuroprotective effects of Cerebrolysin in triple repeat Tau transgenic model of Pick's disease and fronto-temporal tauopathies

BACKGROUND

Tauopathies are a group of neurodegenerative disorders with accumulation of three-repeat (3R) or four-repeat (4R) Tau. While 3R tau is found in Pick's disease and Alzheimer's disease (AD), 4R tau is more abundant in corticobasal degeneration, progressive supranuclear palsy, and AD. We have previously shown that Cerebrolysin™ (CBL), a neuropeptide mixture with neurotrophic effects, ameliorates the pathology in amyloid precursor protein transgenic (tg) mouse model of AD and 4R tau, however it is unclear if CBL ameliorates the deficits and neuropathology in the mouse model of Pick's disease over expressing 3R tau.

RESULTS

Mice expressing 3R tau (L266V and G272V mutations) under the mThy-1 promoter were treated with CBL in two separate groups, the first was 3 months old (treated for 3 months, IP) and the second was 6 months old (treated for 3 months, IP) at the start of the treatment. We found that although the levels of total 3R tau were unchanged, CBL reduced the levels of hyper-phosphorylated tau in both groups of mice. This was accompanied by reduced neurodegenerative pathology in the neocortex and hippocampus in both groups and by improvements in the behavioral deficits in the nest-building test and water maze in the 3-6 month group.

CONCLUSION

Taken together these results support the notion that CBL may be beneficial in other taupathy models by reducing the levels of aberrantly phosphorylated tau.

Semi-Automated Digital Image Analysis of Pick's Disease and TDP-43 Proteinopathy

Digital image analysis of histology sections provides reliable, high-throughput methods for neuropathological studies but data is scant in frontotemporal lobar degeneration (FTLD), which has an added challenge of study due to morphologically diverse pathologies. Here, we describe a novel method of semi-automated digital image analysis in FTLD subtypes including: Pick's disease (PiD, n=11) with tau-positive intracellular inclusions and neuropil threads, and TDP-43 pathology type C (FTLD-TDPC, n=10), defined by TDP-43-positive aggregates predominantly in large dystrophic neurites. To do this, we examined three FTLD-associated cortical regions: mid-frontal gyrus (MFG), superior temporal gyrus (STG) and anterior cingulate gyrus (ACG) by immunohistochemistry. We used a color deconvolution process to isolate signal from the chromogen and applied both object detection and intensity thresholding algorithms to quantify pathological burden. We found object-detection algorithms had good agreement with gold-standard manual quantification of tau- and TDP-43-positive inclusions. Our sampling method was reliable across three separate investigators and we obtained similar results in a pilot analysis using open-source software. Regional comparisons using these algorithms finds differences in regional anatomic disease burden between PiD and FTLD-TDP not detected using traditional ordinal scale data, suggesting digital image analysis is a powerful tool for clinicopathological studies in morphologically diverse FTLD syndromes.

A novel triple repeat mutant tau transgenic model that mimics aspects of pick's disease and fronto-temporal tauopathies

Tauopathies are a group of disorders leading to cognitive and behavioral impairment in the aging population. While four-repeat (4R) Tau is more abundant in corticobasal degeneration, progressive supranuclear palsy, and Alzheimer’s disease, three-repeat (3R) Tau is the most abundant splice, in Pick's disease. A number of transgenic models expressing wild-type and mutant forms of the 4R Tau have been developed. However, few models of three-repeat Tau are available. A transgenic mouse model expressing three-repeat Tau was developed bearing the mutations associated with familial forms of Pick's disease (L266V and G272V mutations). Two lines expressing high (Line 13) and low (Line 2) levels of the three-repeat mutant Tau were analyzed. By Western blot, using antibodies specific to three-repeat Tau, Line 13 expressed 5-times more Tau than Line 2. The Tau expressed by these mice was most abundant in the frontal-temporal cortex and limbic system and was phosphorylated at residues detected by the PHF-1, AT8, CP9 and CP13 antibodies. The higher-expressing mice displayed hyperactivity, memory deficits in the water maze and alterations in the round beam. The behavioral deficits started at 6-8 months of age and were associated with a progressive increase in the accumulation of 3R Tau. By immunocytochemistry, mice from Line 13 displayed extensive accumulation of 3R Tau in neuronal cells bodies in the pyramidal neurons of the neocortex, CA1-3 regions, and dentate gyrus of the hippocampus. Aggregates in the granular cells had a globus appearance and mimic Pick’s-like inclusions. There were abundant dystrophic neurites, astrogliosis and synapto-dendritic damage in the neocortex and hippocampus of the higher expresser line. The hippocampal lesions were moderately argyrophilic and Thioflavin-S negative. By electron microscopy, discrete straight filament aggregates were detected in some neurons in the hippocampus. This model holds promise for better understanding the natural history and progression of 3R tauopathies and their relationship with mitochondrial alterations and might be suitable for therapeutical testing.

Cellular factors modulating the mechanism of tau protein aggregation

Pathological accumulation of the microtubule-associated protein tau, in the form of neurofibrillary tangles, is a major hallmark of Alzheimer's disease, the most prevalent neurodegenerative condition worldwide. In addition to Alzheimer's disease, a number of neurodegenerative diseases, called tauopathies, are characterized by the accumulation of aggregated tau in a variety of brain regions. While tau normally plays an important role in stabilizing the microtubule network of the cytoskeleton, its dissociation from microtubules and eventual aggregation into pathological deposits is an area of intense focus for therapeutic development. Here we discuss the known cellular factors that affect tau aggregation, from post-translational modifications to molecular chaperones.

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.

Lost after translation: missorting of Tau protein and consequences for Alzheimer disease

Tau is a microtubule-associated-protein that is sorted into neuronal axons in physiological conditions. In Alzheimer disease (AD) and other tauopathies, Tau sorting mechanisms fail and Tau becomes missorted into the somatodendritic compartment. In AD, aberrant amyloid-β (Aβ) production might trigger Tau missorting. The physiological axonal sorting of Tau depends on the developmental stage of the neuron, the phosphorylation state of Tau and the microtubule cytoskeleton. Disease-associated missorting of Tau is connected to increased phosphorylation and aggregation of Tau, and impaired microtubule interactions. Disease-causing mechanisms involve impaired transport, aberrant kinase activation, non-physiological interactions of Tau, and prion-like spreading. In this review we focus on the physiological and pathological (mis)sorting of Tau, the underlying mechanisms, and effects in disease.

αB-crystallin and HSP27 in glial cells in tauopathies

Tauopathies are neurodegenerative diseases characterized by hyper-phosphorylated tau deposition in neurons and glial cells. Chaperones, such as small heat shock proteins αB-crystallin and HSP27 highly expressed in normal glial cells, have been postulated as putative molecules preventing abnormal deposition and folding in glial cells in tauopathies. The objective of this work was to assess the expression of αB-crystallin, phosphorylated αB-crystallin at Ser59 and HSP27 in glial cells with and without tau deposits in progressive supranuclear palsy, corticobasal degeneration (CBD), argyrophilic grain disease (AGD), Pick's disease (PiD), Alzheimer's disease, frontotemporal lobar degeneration associated with mutations in the tau gene (FTLD-tau), globular glial tauopathy (GGT) and tauopathy in the elderly. Immunohistochemistry, and double-labeling immunofluorescence and confocal microscopy have been used for this purpose. Increased expression of αB-crystallin and phosphorylated αB-crystallin at Ser59 occurs in a subpopulation of glial cells with and without hyper-phosphorylated tau deposition in all the analyzed tauopathies, but their expression in neurons is restricted to ballooned neurons in CBD, AGD and PiD. HSP27 barely co-localizes with tau and with phosphorylated αB-crystallin at Ser59, thus making the formation of active dimers operating as chaperones unlikely. Results suggest a limited function of αB-crystallin and HSP27 in preventing abnormal tau protein deposition in glial cells and neurons; in addition, the expression of αB-crystallin phosphorylated at Ser59 may act as a protective factor in glial cells.

Regulation of alternative splicing of tau exon 10

The neuronal microtubule-associated protein tau is abnormally hyperphosphorylated and aggregated into neurofibrillary tangles in the brains of individuals with Alzheimer's disease and related neurodegenerative disorders. The adult human brain expresses six isoforms of tau generated by alternative splicing of exons 2, 3, and 10 of its pre-mRNA. Exon 10 encodes the second microtubule-binding repeat of tau. Its alternative splicing produces tau isoforms with either three or four microtubule-binding repeats, termed 3R-tau and 4Rtau. In the normal adult human brain, the level of 3R-tau is approximately equal to that of 4R-tau. Several silent and intronic mutations of the tau gene associated with FTDP-17T (frontotemporal dementia with Parkinsonism linked to chromosome 17 and specifically characterized by tau pathology) only disrupt exon 10 splicing, but do not influence the primary sequence of the tau protein. Thus, abnormal exon 10 splicing is sufficient to cause neurodegeneration and dementia. Here, we review the regulation of tau exon 10 splicing by cis-elements and trans-factors and summarize all the mutations associated with FTDP-17T and related tauopathies. The findings suggest that correction of exon 10 splicing may be a potential target for tau exon 10 splicing-related tauopathies.

Glial and neuronal tau pathology in tauopathies: characterization of disease-specific phenotypes and tau pathology progression

Tauopathies are degenerative diseases characterized by the accumulation of phosphorylated tau in neurons and glial cells. With some exceptions, tau deposits in neurons are mainly manifested as pretangles and tangles unrelated to the tauopathy. It is thought that abnormal tau deposition in neurons occurs following specific steps, but little is known about the progression of tau pathology in glial cells in tauopathies. We compared tau pathology in different astrocyte phenotypes and oligodendroglial inclusions with that in neurons in a large series of tauopathies, including progressive supranuclear palsy, corticobasal degeneration, argyrophilic grain disease, Pick disease, frontotemporal lobar degenerations (FTLD) associated with mutations in the tau gene, globular glial tauopathy (GGT), and tauopathy in the elderly. Our findings indicate that disease-specific astroglial phenotypes depend on i) the primary amino acid sequence of tau (mutated tau, 3Rtau, and 4Rtau); ii) phospho-specific sites of tau phosphorylation, tau conformation, tau truncation, and ubiquitination in that order (which parallel tau modifications related to pretangle and tangle stages in neurons); and iii) modifications of the astroglial cytoskeleton. In contrast to astrocytes, coiled bodies in oligodendrocytes have similar characteristics whatever the tauopathy, except glial globular inclusions in GGT, and coiled bodies and globular oligodendroglial inclusions in FTLD-tau/K317M. These observations indicate that tau pathology in glial cells largely parallels, but is not identical to, that in neurons in many tauopathies.

Alzheimer disease therapeutics: focus on the disease and not just plaques and tangles

The bulk of AD research during the last 25 years has been Aβ-centric based on a strong faith in the Amyloid Cascade Hypothesis which is not supported by the data on humans. To date, Aβ-based therapeutic clinical trials on sporadic cases of AD have been negative. Although most likely the major reason for the failure is that Aβ is not an effective therapeutic target for sporadic AD, initiation of the treatment at mild to moderate stages of the disease is blamed as too late to be effective. Clinical trials on presymptomatic familial AD cases have been initiated with the logic that Aβ is a trigger of the disease and hence initiation of the Aβ immunotherapies several years before any clinical symptoms would be effective. There is an urgent need to explore targets other than Aβ. There is now increasing interest in inhibiting tau pathology, which does have a far more compelling rationale than Aβ. AD is multifactorial and over 99% of the cases are the sporadic form of the disease. Understanding of the various etiopathogenic mechanisms of sporadic AD and generation of the disease-relevant animal models are required to develop rational therapeutic targets and therapies. Treatment of AD will require both inhibition of neurodegeneration and regeneration of the brain.

A novel MAPT mutation, G55R, in a frontotemporal dementia patient leads to altered Tau function

Over two dozen mutations in the gene encoding the microtubule associated protein tau cause a variety of neurodegenerative dementias known as tauopathies, including frontotemporal dementia (FTD), PSP, CBD and Pick's disease. The vast majority of these mutations map to the C-terminal region of tau possessing microtubule assembly and microtubule dynamics regulatory activities as well as the ability to promote pathological tau aggregation. Here, we describe a novel and non-conservative tau mutation (G55R) mapping to an alternatively spliced exon encoding part of the N-terminal region of the protein in a patient with the behavioral variant of FTD. Although less well understood than the C-terminal region of tau, the N-terminal region can influence both MT mediated effects as well as tau aggregation. The mutation changes an uncharged glycine to a basic arginine in the midst of a highly conserved and very acidic region. In vitro, 4-repeat G55R tau nucleates microtubule assembly more effectively than wild-type 4-repeat tau; surprisingly, this effect is tau isoform specific and is not observed in a 3-repeat G55R tau versus 3-repeat wild-type tau comparison. In contrast, the G55R mutation has no effect upon the abilities of tau to regulate MT growing and shortening dynamics or to aggregate. Additionally, the mutation has no effect upon kinesin translocation in a microtubule gliding assay. Together, (i) we have identified a novel tau mutation mapping to a mutation deficient region of the protein in a bvFTD patient, and (ii) the G55R mutation affects the ability of tau to nucleate microtubule assembly in vitro in a 4-repeat tau isoform specific manner. This altered capability could markedly affect in vivo microtubule function and neuronal cell biology. We consider G55R to be a candidate mutation for bvFTD since additional criteria required to establish causality are not yet available for assessment.

Tau as a therapeutic target in neurodegenerative disease

Tau is a microtubule-associated protein thought to help modulate the stability of neuronal microtubules. In tauopathies, including Alzheimer's disease and several frontotemporal dementias, tau is abnormally modified and misfolded resulting in its disassociation from microtubules and the generation of pathological lesions characteristic for each disease. A recent surge in the population of people with neurodegenerative tauopathies has highlighted the immense need for disease-modifying therapies for these conditions, and new attention has focused on tau as a potential target for intervention. In the current work we summarize evidence linking tau to disease pathogenesis and review recent therapeutic approaches aimed at ameliorating tau dysfunction. The primary therapeutic tactics considered include kinase inhibitors and phosphatase activators, immunotherapies, small molecule inhibitors of protein aggregation, and microtubule-stabilizing agents. Although the evidence for tau-based treatments is encouraging, additional work is undoubtedly needed to optimize each treatment strategy for the successful development of safe and effective therapeutics.

Neuropathology of frontotemporal lobar degeneration-tau (FTLD-tau)

A clinically and pathologically heterogeneous type of frontotemporal lobar degeneration has abnormal tau pathology in neurons and glia (FTLD-tau). Familial FTLD-tau is usually due to mutations in the tau gene (MAPT). Even FTLD-tau determined by MAPT mutations has clinical and pathologic heterogeneity. Tauopathies are subclassified according to the predominant species of tau that accumulates, with respect to alternative splicing of MAPT, with tau proteins containing three (3R) or four repeats (4R) of ~32 amino acids in the microtubule binding domain. In Pick's disease (PiD), 3R tau predominates, whereas 4R tau is characteristic of corticobasal degeneration (CBD) and progressive supranuclear palsy (PSP). Depending upon the specific mutation in MAPT, familial FTLD-tau can have 3R, 4R or a combination of 3R and 4R tau. PiD is the least common FTLD-tau characterized by neuronal Pick bodies in a stereotypic neuroanatomical distribution. PSP and CBD are more common than PiD and have extensive clinical and pathologic overlap, with no distinctive clinical syndrome or biomarker that permits their differentiation. Diagnosis rests upon postmortem examination of the brain and demonstration of globose tangles, oligodendroglial coiled bodies and tufted astrocytes in PSP or threads, pretangles and astrocytic plaques in CBD. The anatomical distribution of tau pathology determines the clinical presentation of PSP and CBD, as well as PiD. The basis for this selective cortical vulnerability in FTLD-tau is unknown.

Curcumin labeling of neuronal fibrillar tau inclusions in human brain samples

The study aimed to characterize curcumin (CCM) (fluorescent yellow curry pigment) labeling of neuronal fibrillar tau inclusions (FTIs) in representative cases of 3 main tauopathies: Alzheimer disease (AD), progressive supranuclear palsy, and Pick disease. After identification of FTIs in hematoxylin and eosin-stained brain sections, sequential labeling and signal colocalization image analysis were used to compare CCM with thioflavine S (ThS), monoclonal antibody AT8 immunofluorescence, and Gallyas silver staining by visualizing the same FTIs. Curcumin preference for specific tau isoforms was tested with 3-repeat tau and 4-repeat tau isoform-specific immunofluorescence. Curcumin proved highly comparable to ThS and Gallyas staining in its detection of FTIs. When comparing CCM with AT8, ThS, and Gallyas staining in AD and progressive supranuclear palsy, 3 types of neuronal tau deposits were observed: nonfibrillar intracellular material labeled only with AT8, fibrillar intracellular inclusions labeled by all the methods, and fibrillar extracellular FTIs labeled with CCM, ThS, and Gallyas staining but not with AT8. Although CCM labeling overlapped with both 3-repeat tau and 4-repeat tau in AD, it did not label 3-repeat tau FTIs in Pick disease probably because of their different ultrastructural characteristics. In summary, CCM fluorescence reliably detected neuronal FTIs in AD and progressive supranuclear palsy and surpassed AT8 immunolabeling in visualizing later stages of FTIs, including ghost tangles. These results provide the basis for potential future applications of CCM binding of tau aggregates in diagnostic pathology and in vivo.

Frontotemporal lobar degeneration: epidemiology, pathophysiology, diagnosis and management

Frontotemporal lobar degeneration (FTLD) is a clinically and pathologically heterogeneous syndrome, characterized by progressive decline in behaviour or language associated with degeneration of the frontal and anterior temporal lobes. While the seminal cases were described at the turn of the 20th century, FTLD has only recently been appreciated as a leading cause of dementia, particularly in patients presenting before the age of 65 years. Three distinct clinical variants of FTLD have been described: (i) behavioural-variant frontotemporal dementia, characterized by changes in behaviour and personality in association with frontal-predominant cortical degeneration; (ii) semantic dementia, a syndrome of progressive loss of knowledge about words and objects associated with anterior temporal neuronal loss; and (iii) progressive nonfluent aphasia, characterized by effortful language output, loss of grammar and motor speech deficits in the setting of left perisylvian cortical atrophy. The majority of pathologies associated with FTLD clinical syndromes include either tau-positive (FTLD-TAU) or TAR DNA-binding protein 43 (TDP-43)-positive (FTLD-TDP) inclusion bodies. FTLD overlaps clinically and pathologically with the atypical parkinsonian disorders corticobasal degeneration and progressive supranuclear palsy, and with amyotrophic lateral sclerosis. The majority of familial FTLD cases are caused by mutations in the genes encoding microtubule-associated protein tau (leading to FTLD-TAU) or progranulin (leading to FTLD-TDP). The clinical and pathological heterogeneity of FTLD poses a significant diagnostic challenge, and in vivo prediction of underlying histopathology can be significantly improved by supplementing the clinical evaluation with genetic tests and emerging biological markers. Current pharmacotherapy for FTLD focuses on manipulating serotonergic or dopaminergic neurotransmitter systems to ameliorate behavioural or motor symptoms. However, recent advances in FTLD genetics and molecular pathology make the prospect of biologically driven, disease-specific therapies for FTLD seem closer than ever.

Development of a sensitive ELISA for quantification of three- and four-repeat tau isoforms in tauopathies

Tau protein plays an important role in stabilising and assembling neuronal microtubules. Pathological changes in expression and aggregation of tau isoforms containing three (3R-tau) and four (4R-tau) microtubule-binding repeat domains are associated with several tauopathies. This paper describes novel sandwich ELISAs for quantification of 3R- and 4R-tau in brain. The assays are constructed using well-characterised isoform-specific antibodies (RD3 and RD4) as capture antibodies and an affinity-purified HRP-anti-tau peptide antibody and biotin-tyramide amplification for detection. For 3R-tau, we achieved a minimal detection limit in buffer of 460 pg mL(-1) and a recovery of 81.0% using 500 pg mL(-1) recombinant 3R-tau spiked in diluted brain homogenate. Mean intra- and inter-assay variation of the 3R-tau ELISA was 8.8 and 10.5%, respectively. For 4R-tau, the detection limit was 780 pg mL(-1) and the recovery of 5 ng mL(-1) spiked recombinant 4R-tau was 86.0% and the mean intra- and inter-assay variation was 10.4 and 15.6%, respectively. With these assays, we showed that in progressive supranuclear palsy (PSP) brains, 4R-tau is significantly increased in frontal cortex and caudate, the two regions that are usually associated with 4R-tau-dominant pathology. This increase was not observed in occipital lobe, a region that is spared of tau inclusions. No differences in 3R-tau levels were found between PSP and control brains in all regions tested. With this, we have for the first time developed ELISAs for quantification of 3R- and 4R-tau isoforms in pathological samples. These could prove useful in the pathological investigation and differential diagnosis of tauopathies.

Pathogenic missense MAPT mutations differentially modulate tau aggregation propensity at nucleation and extension steps

Mutations in the MAPT gene encoding tau protein lead to neurofibrillary lesion formation, neurodegeneration, and cognitive decline associated with frontotemporal lobar degeneration. While some pathogenic mutations affect MAPT introns, resulting in abnormal splicing patterns, the majority occur in the tau coding sequence leading to single amino acid changes in tau primary structure. Depending on their location within the polypeptide chain, tau missense mutations have been reported to augment aggregation propensity. To determine the mechanisms underlying mutation-associated changes in aggregation behavior, the fibrillization of recombinant pathogenic mutants R5L, G272V, P301L, V337M, and R406W prepared in a full-length four-repeat human tau background was examined in vitro as a function of time and submicromolar tau concentrations using electron microscopy assay methods. Kinetic constants for nucleation and extension phases of aggregation were then estimated by direct measurement and mathematical simulation. Results indicated that the mutants differ from each other and from wild-type tau in their aggregation propensity. G272V and P301L mutations increased the rates of both filament nucleation and extension reactions, whereas R5L and V337M increased only the nucleation phase. R406W did not differ from wild-type in any kinetic parameter. The results show that missense mutations can directly promote tau filament formation at different stages of the aggregation pathway.

Microtubule-associated protein tau in development, degeneration and protection of neurons

As a principal neuronal microtubule-associated protein, tau has been recognized to play major roles in promoting microtubule assembly and stabilizing the microtubules and to maintain the normal morphology of the neurons. Recent studies suggest that tau, upon alternative mRNA splicing and multiple posttranslational modifications, may participate in the regulations of intracellular signal transduction, development and viability of the neurons. Furthermore, tau gene mutations, aberrant mRNA splicing and abnormal posttranslational modifications, such as hyperphosphorylation, have also been found in a number of neurodegenerative disorders, collectively known as tauopathies. Therefore, changes in expression of the tau gene, alternative splicing of its mRNA and its posttranslational modification can modulate the normal architecture and functions of neurons as well as in a situation of tauopathies, such as Alzheimer's disease. The primary aim of this review is to summarize the latest developments and perspectives in our understanding about the roles of tau, especially hyperphosphorylation, in the development, degeneration and protection of neurons.