4R Tau Isoforms Research Articles

Is it Useful to Classify Progressive Supranuclear Palsy and Corticobasal Degeneration as Different Disorders? No.

http://onlinelibrary.wiley.com/journal/10.1002/(ISSN)2330-1619/homepage/mdc312582-sup-v001.htm.

Tau Kinetics in Neurons and the Human Central Nervous System

We developed stable isotope labeling and mass spectrometry approaches to measure the kinetics of multiple isoforms and fragments of tau in the human central nervous system (CNS) and in human induced pluripotent stem cell (iPSC)-derived neurons. Newly synthesized tau is truncated and released from human neurons in 3days. Although most tau proteins have similar turnover, 4R tau isoforms and phosphorylated forms of tau exhibit faster turnover rates, suggesting unique processing of these forms that may have independent biological activities. The half-life of tau in control human iPSC-derived neurons is 6.74± 0.45days and in human CNS is 23± 6.4days. In cognitively normal and Alzheimer's disease participants, the production rate of tau positively correlates with the amount of amyloid plaques, indicating a biological link between amyloid plaques and tau physiology.

Detection of Alzheimer Disease (AD)-Specific Tau Pathology in AD and NonAD Tauopathies by Immunohistochemistry With Novel Conformation-Selective Tau Antibodies.

Aggregation of tau into fibrillar structures within the CNS is a pathological hallmark of a clinically heterogeneous set of neurodegenerative diseases termed tauopathies. Unique misfolded conformations of tau, referred to as strains, are hypothesized to underlie the distinct neuroanatomical and cellular distribution of pathological tau aggregates. Here, we report the identification of novel tau monoclonal antibodies (mAbs) that selectively bind to an Alzheimer disease (AD)-specific conformation of pathological tau. Immunohistochemical analysis of tissue from various AD and nonAD tauopathies demonstrate selective binding of mAbs GT-7 and GT-38 to AD tau pathologies and absence of immunoreactivity for tau aggregates that are diagnostic of corticobasal degenerations (CBD), progressive supranuclear palsy (PSP), and Pick's disease (PiD). In cases with co-occurring AD tauopathy, GT-7 and GT-38 distinguish comorbid AD tau from pathological tau in frontotemporal lobar degeneration characterized by tau inclusions (FTLD-Tau), as confirmed by the presence of both 3 versus 4 microtubule-binding repeat isoforms (3R and 4R tau isoforms, respectively), in AD neurofibrillary tangles but not in the tau aggregates of CBD, PSP, or PiD. These findings support the concept of an AD-specific tau strain. The mAbs described here enable the selective detection of AD tau pathology in nonAD tauopathies.

Increased Vulnerability of the Hippocampus in Transgenic Mice Overexpressing APP and Triple Repeat Tau.

Alzheimer's disease (AD) is the most common tauopathy, characterized by progressive accumulation of amyloid-β (Aβ) and hyperphosphorylated tau. While pathology associated with the 4-repeat (4R) tau isoform is more abundant in corticobasal degeneration and progressive supranuclear palsy, both 3R and 4R tau isoforms accumulate in AD. Many studies have investigated interactions between Aβ and 4R tau in double transgenic mice, but few, if any, have examined the effects of Aβ with 3R tau. To examine this relationship, we crossed our APP751 mutant line with our recently characterized 3R tau mutant model to create a bigenic line (hAPP-3RTau) to model AD neuropathology. Mice were analyzed at 3 and 6 months of age for pathological and behavioral endpoints. While both the 3RTau and the hAPP-3RTau mice showed neuronal loss, increased tau aggregation, Aβ plaques and exhibited more behavioral deficits compared to the non-tg control, the bigenic mice often displaying relatively worsening levels. We found that even in young animals we found that the presence of APP/Aβ increased the accumulation of 3R tau in the neocortex and hippocampus. This observation was accompanied by activation of GSK3 and neurodegeneration in the neocortex and CA1 region. These results suggest that in addition to 4R tau, APP/Aβ may also enhance accumulation of 3R tau, a process which may be directly relevant to pathogenic pathways in AD. Our results demonstrate that this bigenic model closely parallels the pathological course of AD and may serve as a valuable model for testing new pharmacological interventions.

Old cats : a naturally occuring model of tauopathy.

Old cats : a naturally occuring model of tauopathy.

A HUMAN 3D NEURAL CULTURE MODEL UTILISING INDUCED PLURIPOTENT STEM CELLS FROM AN ALZHEIMER’S PATIENT TO STUDY MECHANISMS OF ALZHEIMER DISEASE PATHOLOGY

Alzheimer's Disease (AD) is the leading cause of dementia and with a population of increasing longevity is set to become a major burden on health services. Currently human tissue from AD cases is only available for research from post mortem brain but we can now utilise iPSC technology to obtain neural stem cells from AD patients with the aim to produce mature neurons with the same genetic signature of AD patients. Using induced Pluripotent Stem Cells (iPSCs) from early onset AD patients containing Presenilin 1 mutations we have created a 3D human neural culture system for the study of some early onset Alzheimer's disease mechanisms. Using immunofluorescence, western blotting and electrophysiology we have characterised neuronal morphology and maturity, synaptic function and disease-protein profiles. Neural progenitors derived from AD iPSCs (Axol Biosciences) were plated in matrigel and self-organised into 3D structures by week 3. These cultures contained a heterogeneous cell population expressing differentiation markers for neurons and astrocytes and importantly AD-associated proteins, amyloid precursor protein/Abeta and tau. These 3D cultures were maintained in vitrofor 18+ weeks. They expressed the mature 4R tau isoform and Abeta oligomers by week 6 and exhibited repetitive firing by week 12. Together these results suggest the presence of mature neurons within these cultures and the expression of pathology-associated proteins. We have created 3D mature neural cultures derived from AD patients to study mechanisms of the disease pathology in a human cell model. This is a viable new in vitro 3D neural model for the study of neuropathology, which can serve as a powerful new translational tool in this area of research.

Transactive response DNA-binding protein 43 (TDP-43) regulates alternative splicing of tau exon 10: Implications for the pathogenesis of tauopathies

Hyperphosphorylation and aggregation of the neuronal protein tau are responsible for neurodegenerative diseases called tauopathies. Dysregulation of the alternative splicing of tau exon 10 results in alterations of the ratio of two tau isoforms, 3R-tau and 4R-tau, which have been seen in several tauopathies. Transactive response DNA-binding protein of 43 kDa (TDP-43) is involved in the regulation of RNA processing, including splicing. Cytoplasmic aggregation of TDP-43 has been observed in the brains of individuals with chronic traumatic encephalopathy or Alzheimer's disease, diseases in which neurofibrillary tangles of hyperphosphorylated tau are hallmarks. Here, we investigated the role of TDP-43 in tau exon 10 splicing. We found that TDP-43 promoted tau exon 10 inclusion, which increased production of the 4R-tau isoform. Moreover, TDP-43 could bind to intron 9 of tau pre-mRNA. Deletion of the TDP-43 N or C terminus promoted its cytoplasmic aggregation and abolished or diminished TDP-43-promoted tau exon 10 inclusion. Several TDP-43 mutations associated with amyotrophic lateral sclerosis or frontotemporal lobar degeneration with ubiquitin inclusions promoted tau exon 10 inclusion more effectively than wild-type TDP-43 but did not affect TDP-43 cytoplasmic aggregation in cultured cells. The ratio of 3R-tau/4R-tau was decreased in transgenic mouse brains expressing human TDP-43 and increased in the brains expressing the disease-causing mutation TDP-43M337V, in which cytoplasmic TDP-43 was increased. These findings suggest that TDP-43 promotes tau exon 10 inclusion and 4R-tau expression and that disease-related changes of TDP-43, truncations and mutations, affect its function in tau exon 10 splicing, possibly because of TDP-43 mislocalization to the cytoplasm.

FTDP‐17 mutants S320F and S352L have subtle differential effects on 4R tau isoform aggregation in vitro

Frontotemporal Dementia with Parkinsonism linked to chromosome‐17 (FTDP‐17) is a class of inherited neurodegenerative diseases caused by mutations in the tau gene. Tau protein is a microtubule associated protein that stabilizes microtubules in neurons. During neurodegeneration, tau protein aggregates to form toxic filaments. Tau isoforms have either three or four 18‐amino acid microtubule binding repeats, known as 3‐repeat tau (3R tau) or 4‐repeat tau (4R tau). The 4R and 3R tau isoforms are further classified into 0N, 1N and 2N isoforms based on the number of N‐terminal exons. Forty four different mutations in various positions of the tau gene have been reported. FTDP‐17 tau mutants 2N4R S320F and S352L cause neuropathology through different mechanisms of tau aggregation. The mutant S320F forms short tau oligomers while S352L forms long tau filaments in vitro. Here, we determined whether the 4R tau isoforms (0N, 1N, 2N) of S320F and S352L affect tau aggregation differently in vitro. We used right angle laser light scattering, thioflavin S florescence assay and transmission electron microscopy (TEM) to study arachidonic acid induced tau aggregation. All wild type 4R tau isoforms (0N, 1N, 2N) showed the same effect on polymerization of tau into filaments upon addition of arachidonic acid. All S320F isoforms (0N, 1N, 2N) showed a significant decrease (p < 0.01) and S352L isoforms (0N, 1N, 2N) showed no significant change in laser light scattering when compared to the corresponding wild type 4R isoforms. However, S320F isoform 1N showed a significant decrease (p < 0.01) in percentage change from the respective wild type isoform when compared to 0N, 2N S320F by one way ANOVA analysis of laser light scattering. S320F isoforms 0N, 2N showed an increase (p < 0.05, 0.01) and 2N S352L also showed an increase (p < 0.001) in thioflavin S fluorescence when compared to the corresponding wild type 4R isoform. TEM images of all 4R S320F filaments showed very short tau fibrils which could be tau oligomers while all S352L filaments showed an increase in length of tau polymer. The 2N S352L filaments were longer than filaments from 0N and 1N isoforms. Though the mutant isoforms have the same effect on tau polymerization, the extent of polymerization varies. These results show that the presence of N‐terminal exons have small, but significant, alterations in the pro‐aggregation properties of FTDP‐17 4R tau.Support or Funding InformationNIH grant R01NS083391

Ultrasensitive and selective detection of 3-repeat tau seeding activity in Pick disease brain and cerebrospinal fluid.

The diagnosis and treatment of diseases involving tau-based pathology such as Alzheimer disease and certain frontotemporal dementias is hampered by the inability to detect pathological forms of tau with sufficient sensitivity, specificity and practicality. In these neurodegenerative diseases, tau accumulates in self-seeding filaments. For example, Pick disease (PiD) is associated with frontotemporal degeneration and accumulation of 3-repeat (3R) tau isoforms in filaments constituting Pick bodies. Exploiting the self-seeding activity of tau deposits, and using a 3R tau fragment as a substrate, we have developed an assay (tau RT-QuIC) that can detect tau seeds in 2µl aliquots of PiD brain dilutions down to 10-7-10-9. PiD seeding activities were 100-fold higher in frontal and temporal lobes compared to cerebellar cortex. Strikingly, this test was 103- to 105-fold less responsive when seeded with brain containing predominant 4-repeat (4R) tau aggregates from cases of corticobasal degeneration, argyrophilic grain disease, and progressive supranuclear palsy. Alzheimer disease brain, with 3R+4R tau deposits, also gave much weaker responses than PiD brain. When applied to cerebrospinal fluid samples (5µl), tau RT-QuIC analyses discriminated PiD from non-PiD cases. These findings demonstrate that abnormal tau aggregates can be detected with high sensitivity and disease-specificity in crude tissue and fluid samples. Accordingly, this tau RT-QuIC assay exemplifies a new approach to diagnosing tauopathies and monitoring therapeutic trials using aggregated tau itself as a biomarker.

Mitochondrial hyperpolarization in iPSC-derived neurons from patients of FTDP-17 with 10+16 MAPT mutation leads to oxidative stress and neurodegeneration

Tau protein inclusions are a frequent hallmark of a variety of neurodegenerative disorders. The 10+16 intronic mutation in MAPT gene, encoding tau, causes frontotemporal dementia and parkinsonism linked to chromosome 17 (FTDP-17), by altering the splicing of the gene and inducing an increase in the production of 4R tau isoforms, which are more prone to aggregation. However, the molecular mechanisms linking increased 4R tau to neurodegeneration are not well understood.Here, we have used iPSC-derived neurons from patients of FTDP-17 carrying the 10+16 mutation to study the molecular mechanisms underlying neurodegeneration.We show that mitochondrial function is altered in the neurons of the patients. We found that FTDP-17 neurons present an increased mitochondrial membrane potential, which is partially maintained by the F1Fo ATPase working in reverse mode. The 10+16 MAPT mutation is also associated with lower mitochondrial NADH levels, partially supressed complex I-driven respiration, and lower ATP production by oxidative phosphorylation, with cells relying on glycolysis to maintain ATP levels. Increased mitochondrial membrane potential in FTDP-17 neurons leads to overproduction of the ROS in mitochondria, which in turn causes oxidative stress and cell death. Mitochondrial ROS overproduction in these cells is a major trigger for neuronal cell death and can be prevented by mitochondrial antioxidants

Astrocyte pathology in a human neural stem cell model of frontotemporal dementia caused by mutant TAU protein

Astroglial pathology is seen in various neurodegenerative diseases including frontotemporal dementia (FTD), which can be caused by mutations in the gene encoding the microtubule-associated protein TAU (MAPT). Here, we applied a stem cell model of FTD to examine if FTD astrocytes carry an intrinsic propensity to degeneration and to determine if they can induce non-cell-autonomous effects in neighboring neurons. We utilized CRISPR/Cas9 genome editing in human induced pluripotent stem (iPS) cell-derived neural progenitor cells (NPCs) to repair the FTD-associated N279K MAPT mutation. While astrocytic differentiation was not impaired in FTD NPCs derived from one patient carrying the N279K MAPT mutation, FTD astrocytes appeared larger, expressed increased levels of 4R-TAU isoforms, demonstrated increased vulnerability to oxidative stress and elevated protein ubiquitination and exhibited disease-associated changes in transcriptome profiles when compared to astrocytes derived from one control individual and to the isogenic control. Interestingly, co-culture experiments with FTD astrocytes revealed increased oxidative stress and robust changes in whole genome expression in previously healthy neurons. Our study highlights the utility of iPS cell-derived NPCs to elucidate the role of astrocytes in the pathogenesis of FTD.

Developmental Expression of 4-Repeat-Tau Induces Neuronal Aneuploidy in Drosophila Tauopathy Models

Tau-mediated neurodegeneration in Alzheimer’s disease and tauopathies is generally assumed to start in a normally developed brain. However, several lines of evidence suggest that impaired Tau isoform expression during development could affect mitosis and ploidy in post-mitotic differentiated tissue. Interestingly, the relative expression levels of Tau isoforms containing either 3 (3R-Tau) or 4 repeats (4R-Tau) play an important role both during brain development and neurodegeneration. Here, we used genetic and cellular tools to study the link between 3R and 4R-Tau isoform expression, mitotic progression in neuronal progenitors and post-mitotic neuronal survival. Our results illustrated that the severity of Tau-induced adult phenotypes depends on 4R-Tau isoform expression during development. As recently described, we observed a mitotic delay in 4R-Tau expressing cells of larval eye discs and brains. Live imaging revealed that the spindle undergoes a cycle of collapse and recovery before proceeding to anaphase. Furthermore, we found a high level of aneuploidy in post-mitotic differentiated tissue. Finally, we showed that overexpression of wild type and mutant 4R-Tau isoform in neuroblastoma SH-SY5Y cell lines is sufficient to induce monopolar spindles. Taken together, our results suggested that neurodegeneration could be in part linked to neuronal aneuploidy caused by 4R-Tau expression during brain development.

Optimization of in vitro conditions to study the arachidonic acid induction of 4R isoforms of the microtubule-associated protein tau.

The microtubule-associated protein tau exists in six different isoforms that accumulate as filamentous aggregates in a wide spectrum of neurodegenerative diseases classified as tauopathies. One potential source of heterogeneity between these diseases could arise from differential tau isoform aggregation. in vitro assays employing arachidonic acid as an inducer of aggregation have been pivotal in gaining an understanding of the longest four repeat tau isoform (2N4R). These approaches have been less successful for modeling the shorter 1N4R and 0N4R tau isoforms in vitro. Through a careful analysis of in vitro conditions for aggregation, we found that the differences in the acidity of tau isoform N-terminal projection domains determine whether tau filaments cluster into larger assemblies in solution. Beyond the potential biological implications of filament clustering, we provide optimized conditions for the arachidonic acid induction of shorter 4R tau isoforms aggregation in vitro that greatly reduce filament clustering and improved modeling results.

Neuropathological criteria of anti-IgLON5-related tauopathy.

We recently reported a novel neurological syndrome characterized by a unique NREM and REM parasomnia with sleep apnea and stridor, accompanied by bulbar dysfunction and specific association with antibodies against the neuronal cell-adhesion protein IgLON5. All patients had the HLA-DRB1*1001 and HLA-DQB1*0501 alleles. Neuropathological findings in two patients revealed a novel tauopathy restricted to neurons and predominantly involving the hypothalamus and tegmentum of the brainstem. The aim of the current study is to describe the neuropathological features of the anti-IgLON5 syndrome and to provide diagnostic levels of certainty based on the presence of associated clinical and immunological data. The brains of six patients were examined and the features required for the neuropathological diagnosis were established by consensus. Additional clinical and immunological criteria were used to define “definite”, “probable” and “possible” diagnostic categories. The brains of all patients showed remarkably similar features consistent with a neurodegenerative disease with neuronal loss and gliosis and absence of inflammatory infiltrates. The most relevant finding was the neuronal accumulation of hyperphosphorylated tau composed of both three-repeat (3R) and four-repeat (4R) tau isoforms, preferentially involving the hypothalamus, and more severely the tegmental nuclei of the brainstem with a cranio-caudal gradient of severity until the upper cervical cord. A “definite” diagnosis of anti-IgLON5-related tauopathy is established when these neuropathological features are present along with the detection of serum or CSF IgLON5 antibodies. When the antibody status is unknown, a “probable” diagnosis requires neuropathological findings along with a compatible clinical history or confirmation of possession of HLA-DRB1*1001 and HLA-DQB1*0501 alleles. A “possible” diagnosis should be considered in cases with compatible neuropathology but without information about a relevant clinical presentation and immunological status. These criteria should help to identify undiagnosed cases among archival tissue, and will assist future clinicopathological studies of this novel disorder.Electronic supplementary materialThe online version of this article (doi:10.1007/s00401-016-1591-8) contains supplementary material, which is available to authorized users.

Phosphorylation and isoform expression of microtubule-associated protein tau are regulated independently in the mouse brain

Event Abstract Back to Event Phosphorylation and isoform expression of microtubule-associated protein tau are regulated independently in the mouse brain Dilina Tuerde1*, Taeko Kimura1, Tomohiro Miyasaka2, Akiko Asada1, Kanae Ando1, Taro Saito1 and Shin-Ichi Hisanaga1* 1 Tokyo Metropolitan University, Department of Biological Sciences, Japan 2 Doshisha University, Faculty of Life and Medical Sciences Neuropathology, Japan Tau is a microtubule-associated protein, mainly expressed in axon of neurons. There are 6 isoforms in tau, which are produced by alternative mRNA splicing of N-terminal insertions and C-terminal microtubule-binding repeats. The C-terminal splicing produces 3-repeat (3R) and 4-repeart (4R) tau with different microtubule-binding ability. It is shown that isoforms and phosphorylation of tau change during neuronal development. In mouse brain 3R tau isoforms are expressed in embryonic and early postnatal days and replaced with 4R tau until postnatal day 20 (P20). Early postnatal tau resembles that of Alzheimer`s disease in their high phosphorylation states. Thus, it is important to understand the mechanism of highly phosphorylated postnatal tau. However, it is not entirely known how the changes in isoforms and phosphorylation of tau are regulated and related to each other. In order to address this question, we used Phos-tag SDS-PAGE, in which phosphorylated proteins are shifted upward remarkably depending on the number and site of phosphorylation. Phosphorylation of tau drops with the decrease in 3R tau expression during postnatal day 5 (P5) to 18 (P18). In contrast, 4R tau, whose expression began at around P9 and was not highly phosphorylated even when 3R tau was phosphorylated. Phosphorylation of 4R tau changed around P24, one week after 3R tau completed the change in phosphorylation. We also examined phosphorylation of human 3R tau which was knocked in mouse tau locus. Human 3R tau changed phosphorylation states at P20, slightly delayed after mouse tau even though its expression levels did not change. We also studied phosphorylation of tau in several brain regions, cerebral cortex, cerebellum, hippocampus and olfactory bulb. Tau was phosphorylated higher in olfactory bulb than other areas with stronger expression of 3R tau. Keywords: Brain, Phosphorylation, in vivo, neurone, protein Conference: 14th Meeting of the Asian-Pacific Society for Neurochemistry, Kuala Lumpur, Malaysia, 27 Aug - 30 Aug, 2016. Presentation Type: Poster Presentation Session Topic: 14th Meeting of the Asian-Pacific Society for Neurochemistry Citation: Tuerde D, Kimura T, Miyasaka T, Asada A, Ando K, Saito T and Hisanaga S (2016). Phosphorylation and isoform expression of microtubule-associated protein tau are regulated independently in the mouse brain. Conference Abstract: 14th Meeting of the Asian-Pacific Society for Neurochemistry. doi: 10.3389/conf.fncel.2016.36.00125 Copyright: The abstracts in this collection have not been subject to any Frontiers peer review or checks, and are not endorsed by Frontiers. They are made available through the Frontiers publishing platform as a service to conference organizers and presenters. The copyright in the individual abstracts is owned by the author of each abstract or his/her employer unless otherwise stated. Each abstract, as well as the collection of abstracts, are published under a Creative Commons CC-BY 4.0 (attribution) licence (https://creativecommons.org/licenses/by/4.0/) and may thus be reproduced, translated, adapted and be the subject of derivative works provided the authors and Frontiers are attributed. For Frontiers’ terms and conditions please see https://www.frontiersin.org/legal/terms-and-conditions. Received: 04 Aug 2016; Published Online: 11 Aug 2016. * Correspondence: Ms. Dilina Tuerde, Tokyo Metropolitan University, Department of Biological Sciences, Hachioji-shi, Tokyo, Japan, dilnara0616@gmail.com Dr. Shin-Ichi Hisanaga, Tokyo Metropolitan University, Department of Biological Sciences, Hachioji-shi, Tokyo, Japan, Shin-ichi.Hisanaga@frontiersin.org Login Required This action requires you to be registered with Frontiers and logged in. To register or login click here. Abstract Info Abstract The Authors in Frontiers Dilina Tuerde Taeko Kimura Tomohiro Miyasaka Akiko Asada Kanae Ando Taro Saito Shin-Ichi Hisanaga Google Dilina Tuerde Taeko Kimura Tomohiro Miyasaka Akiko Asada Kanae Ando Taro Saito Shin-Ichi Hisanaga Google Scholar Dilina Tuerde Taeko Kimura Tomohiro Miyasaka Akiko Asada Kanae Ando Taro Saito Shin-Ichi Hisanaga PubMed Dilina Tuerde Taeko Kimura Tomohiro Miyasaka Akiko Asada Kanae Ando Taro Saito Shin-Ichi Hisanaga Related Article in Frontiers Google Scholar PubMed Abstract Close Back to top Javascript is disabled. Please enable Javascript in your browser settings in order to see all the content on this page.

Deep clinical and neuropathological phenotyping of Pick disease.

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

Mitochondrial complex 1 inhibition increases 4-repeat isoform tau by SRSF2 upregulation.

Progressive Supranuclear Palsy (PSP) is a neurodegenerative disorder characterised by intracellular aggregation of the microtubule-associated protein tau. The tau protein exists in 6 predominant isoforms. Depending on alternative splicing of exon 10, three of these isoforms have four microtubule-binding repeat domains (4R), whilst the others only have three (3R). In PSP there is an excess of the 4R tau isoforms, which are thought to contribute significantly to the pathological process. The cause of this 4R increase is so far unknown. Several lines of evidence link mitochondrial complex I inhibition to the pathogenesis of PSP. We demonstrate here for the first time that annonacin and MPP+, two prototypical mitochondrial complex I inhibitors, increase the 4R isoforms of tau in human neurons. We show that the splicing factor SRSF2 is necessary to increase 4R tau with complex I inhibition. We also found SRSF2, as well as another tau splicing factor, TRA2B, to be increased in brains of PSP patients. Thereby, we provide new evidence that mitochondrial complex I inhibition may contribute as an upstream event to the pathogenesis of PSP and suggest that splicing factors may represent an attractive therapeutic target to intervene in the disease process.

Are cases with tau pathology occurring in the absence of Aβ deposits part of the AD-related pathological process?

and only at the same predilection sites as the tau lesions that are present in individuals with Aβ and in fully developed AD can represent possible preclinical (early) stages of the AD-related pathological process. In other words, an interim or transient absence of a minimum of Aβ deposits is not an adequate or compelling rationale for excluding tau-only cases from the developmental spectrum of the ADrelated process, nor is the existence of such cases in nonaged individuals (compare Table 3 here with Table 1 in [8]) consistent with the term ‘primary age-related tauopathy.’ The authors claim that PART, in contrast to AD, is probably not APOE e4 allele-driven. However, an earlier study showing that non-demented individuals with NFT stage I pathology displayed a significantly higher APOE e4 allele frequency than controls [11] reached the opposite conclusion. That study was retrospective (cross sectional), but so were the studies in the supporting literature (13, 67, 70, 122, 150, 151) cited by Crary et al. [8], who have not incorporated into their thinking the implications of recent original findings showing that neuronal injury develops independently of Aβ in APOE e4 allele carriers [7, 13]. The fundamental question whether 3R + 4R tau-only cases and cases with 3R + 4R tau plus Aβ deposits belong to essentially different pathological processes cannot be resolved without identifying potentially unique mechanisms for cases with tau-only pathology, e.g., by means of experimental models of tau seeding and neuron-to-neuron transmission [12], in which tau extracts are isolated not from AD brains but from brains of individuals with autopsy-confirmed 3R + 4R tau-only lesions. Biomarkerbased research and positron emission tomography (PET) imaging of brain Aβ and of tau that can quantify abnormalities in AD-associated neurodegeneration [19] have the developmental potential to reach the point at which the presence and progression of both pathological proteins can The current neuropathological diagnosis of clinically suspected Alzheimer’s disease (AD) requires the presence of advanced neurofibrillary tangle (NFT) stages and of Aβ deposits in the brain [15]. Both abnormal proteins (intraneuronal forms of aggregated and hyperphosphorylated tau and extracellular Aβ) develop at different times at different predilection sites and progress gradually but inexorably during the pathological process by sequential spreading into previously uninvolved regions. Tau pathology develops prior to Aβ deposits [1, 5, 6]. In their position paper, Crary et al. [8] present arguments for distinguishing two processes: an ‘AD-related process’ and a non-AD-related ‘primary age-related tauopathy’ (PART). Both are characterized by the presence of 3R and 4R tau isoforms as well as paired helical filaments but they differ in that the first displays the combined presence of tau and Aβ pathologies, whereas the second is marked by the presence of tau pathology alone. Nevertheless, application of the criteria required to confirm neuropathologically that the diagnosis of clinically manifest AD [15] does not warrant the disqualification of tau-only cases because the statement that “a diagnosis of AD neuropathologic changes requires at least a minimum threshold level of Aβ deposition” [8] is correct only in cases with clinically diagnosed AD but is inaccurate when applied to non-demented individuals. In the absence of Aβ deposits, tau pathology consisting of 3R and 4R isoforms that occurs in the same neuronal cell types as those known to be vulnerable to the pathological process underlying AD

3R and 4R tau isoforms in paired helical filaments in Alzheimer’s disease

3R and 4R tau isoforms in paired helical filaments in Alzheimer’s disease

Extensive deamidation at asparagine residue 279 accounts for weak immunoreactivity of tau with RD4 antibody in Alzheimer’s disease brain

BackgroundIntracytoplasmic inclusions composed of filamentous tau proteins are defining characteristics of neurodegenerative tauopathies, but it remains unclear why different tau isoforms accumulate in different diseases and how they induce abnormal filamentous structures and pathologies. Two tau isoform-specific antibodies, RD3 and RD4, are widely used for immunohistochemical and biochemical studies of tau species in diseased brains.ResultsHere, we show that extensive irreversible post-translational deamidation takes place at asparagine residue 279 (N279) in the RD4 epitope of tau in Alzheimer’s disease (AD), but not corticobasal degeneration (CBD) or progressive supranuclear palsy (PSP), and this modification abrogates the immunoreactivity to RD4. An antiserum raised against deamidated RD4 peptide specifically recognized 4R tau isoforms, regardless of deamidation, and strongly stained tau in AD brain. We also found that mutant tau with N279D substitution showed reduced ability to bind to microtubules and to promote microtubule assembly.ConclusionThe biochemical and structural differences of tau in AD from that in 4R tauopathies found in this study may therefore have implications for prion-like propagation of tau.