Four-repeat Tau Isoforms Research Articles

In vitro evaluation of [3H]PI-2620 and structural derivatives in non-Alzheimer's tauopathies

Alzheimer's disease (AD) and non-AD tauopathies such as chronic traumatic encephalopathy (CTE), progressive supranuclear palsy (PSP), and corticobasal degeneration (CBD) are characterized by the abnormal aggregation of three-repeat (3R) and/or four-repeat (4R) tau isoforms. Several tau-PET tracers have been applied for human imaging of AD and non-AD tauopathies including [18F]PI-2620. Our objective is to evaluate [3H]PI-2620 and two promising structural derivatives, [3H]PI-2014 and [3H]F-4, using in vitro saturation assays and competitive binding assays against new chemical entities based on this scaffold in human AD tissues for comparison with PSP, CBD and CTE tissues. Thin section autoradiography was employed to assess specific binding and distribution of [3H]PI-2620 and [3H]F-4 in fresh-frozen human post-mortem AD, PSP, CBD and CTE tissues. Immunohistochemistry was performed for phospho-tau (AT8) and 4R-tau (RD4). Homogenate filtration binding assays were performed for saturation analysis and competitive binding studies against [3H]PI-2620. All compounds bound with high affinity in AD tissue. In PSP tissue [3H]PI-2620 demonstrated the highest affinity (5.3 nM) and in CBD tissue [3H]F-4 bound with the highest affinity (9.4 nM). Over 40 fluorinated derivatives based on PI-2620 and F-4 were screened in AD and PSP tissue. Notably, compound 2 was the most potent derivative in PSP tissue (Ki = 7.3 nM). By autoradiography, [3H]PI-2620 and [3H]F-4 demonstrated positive signals similar in intensity in AD, PSP and CTE tissues that were displaced by homologous blockade. Binding of both radiotracers aligned with immunostaining for 4R-tau. This work demonstrates that [3H]PI-2620 and [3H]F-4 show promise for imaging 4R-tau aggregates in non-AD tauopathies. PI-2620 continues to serve as a structural scaffold for PET radiotracers with higher affinity for non-AD tau over AD tau.

Correlation of 18F-PM-PBB3 (18F-florzolotau) Tau PET Imaging with Postmortem Neuropathological Findings in A Case with Progressive Supranuclear Palsy (P9-11.015)

<h3>Objective:</h3> To examine correlations between <i>in vivo</i> positron emission tomography (PET) imaging with 18F-PM-PBB3 (18F-florzolotau) and postmortem neuropathological findings in a patient with progressive supranuclear palsy (PSP). <h3>Background:</h3> There have been no reports demonstrating tight PET-pathology associations in the same individual with non-Alzheimer-type neurodegenerative disorders, including PSP, characterized by aggregations of four-repeat tau isoforms only. 18F-florzolotau is a PET probe allowing high-contrast imaging of Alzheimer’s and non-Alzheimer tau pathologies irrespective of isoform compositions, while the utility of this tracer for quantifying the abundance of tau deposits in living cases is yet to be verified. <h3>Design/Methods:</h3> <h3>Patient:</h3> A 65-year-old male with a clinical diagnosis of PSP Richardson syndrome underwent 11C-PiB amyloid and 18F-florzolotau tau PET scans one year before autopsy. Clinical, neuroimaging, and neuropathological findings in this case were briefly summarized elsewhere (K Tagai, et al. Neuron 2021). <h3>Image analysis:</h3> The standardized uptake value ratio (SUVR) image was generated from averaged PET images at 90–110 min after injecting 18F-florzolotau. The reference region was determined using an optimized reference tissue method (K Tagai, et al. medRxiv DOI: https://doi.org/10.1101/2022.02.13.22270135). <h3>Neuropathological analysis:</h3> Quantitative analysis of tau burden was performed using an anti-phosphorylated tau antibody (AT8). A threshold-based binarization method was used for determining the mean AT-8-positive area (%area tau burden). <h3>Results:</h3> 18F-florzolotau PET showed enhanced radiosignals in the brainstem, subthalamic nucleus, and basal ganglia, and the presence of PSP-characteristic tau deposits, including the globose neurofibrillary tangle, tufted astrocytes and coiled bodies, primarily in these areas was confirmed by neuropathological assays. There was a close correlation between regional radioprobe SUVR and %area tau burden (<i>r</i><i>_s</i> = 0.63, <i>p</i> &lt;0.0001). Amyloid PET was negative by visual read. <h3>Conclusions:</h3> 18F-florzolotau PET measures reflect the abundance of tau pathologies in PSP. <b>Disclosure:</b> Dr. Endo has received personal compensation in the range of $500-$4,999 for serving as a Consultant for APRINOIA Therapeutics. Dr. Endo has received personal compensation in the range of $0-$499 for serving on a Speakers Bureau for AbbVie Inc.. The institution of Dr. Endo has received research support from JSPS KAKENHI 21K15705. Dr. Araki has nothing to disclose. Dr. Takeda has nothing to disclose. Dr. Takado has nothing to disclose. Dr. Tagai has nothing to disclose. Dr. Matsuoka has nothing to disclose. Dr. Seki has nothing to disclose. Dr. Takahata has nothing to disclose. Dr. Sahara has nothing to disclose. Hitoshi Shinotoh has nothing to disclose. Mr. Kawamura has nothing to disclose. Dr. Zhang has nothing to disclose. Dr. Honda has nothing to disclose. Prof. SHIMADA has received personal compensation in the range of $500-$4,999 for serving as a Consultant for Guidepoint. Prof. SHIMADA has received personal compensation in the range of $500-$4,999 for serving on a Scientific Advisory or Data Safety Monitoring board for eli lilly. Prof. SHIMADA has received personal compensation in the range of $500-$4,999 for serving on a Speakers Bureau for Takeda Pharmaceutical . Prof. SHIMADA has received personal compensation in the range of $500-$4,999 for serving on a Speakers Bureau for Eisai. Prof. SHIMADA has received personal compensation in the range of $500-$4,999 for serving on a Speakers Bureau for Nihon Medi-Physics. Prof. SHIMADA has received personal compensation in the range of $500-$4,999 for serving on a Speakers Bureau for Biogen. Prof. SHIMADA has received personal compensation in the range of $500-$4,999 for serving on a Speakers Bureau for FUJIFILM Toyama Chemical. Prof. SHIMADA has received personal compensation in the range of $500-$4,999 for serving on a Speakers Bureau for Sunplanet . Prof. SHIMADA has received personal compensation in the range of $500-$4,999 for serving on a Speakers Bureau for NIPPON CHEMIPHAR. Prof. SHIMADA has received personal compensation in the range of $500-$4,999 for serving on a Speakers Bureau for Sumitomo Pharma. Prof. SHIMADA has received personal compensation in the range of $500-$4,999 for serving on a Speakers Bureau for GE Healthcare. Prof. SHIMADA has received personal compensation in the range of $500-$4,999 for serving as an Expert Witness for CHUGAI PHARMACEUTICAL. Prof. SHIMADA has received intellectual property interests from a discovery or technology relating to health care. Prof. SHIMADA has received publishing royalties from a publication relating to health care. Prof. SHIMADA has received publishing royalties from a publication relating to health care. Prof. SHIMADA has received publishing royalties from a publication relating to health care. The institution of Dr. Higuchi has received research support from APRINOIA Therapeutics.

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.

Three-repeat and four-repeat tau isoforms form different oligomers.

Different tauopathies are characterized by the isoform-specific composition of the aggregates found in the brain and by structurally distinct tau strains. Although tau oligomers have been implicated as important neurotoxic species, little is known about how the primary structures of the six human tau isoforms affect tau oligomerization because the oligomers are metastable and difficult to analyze. To address this knowledge gap, here, we analyzed the initial oligomers formed by the six tau isoforms in the absence of posttranslational modifications or other manipulations using dot blots probed by an oligomer-specific antibody, native-PAGE/western blots, photo-induced cross-linking of unmodified proteins, mass-spectrometry, and ion-mobility spectroscopy. We found that under these conditions, three-repeat (3R) isoforms are more prone than four-repeat (4R) isoforms to form oligomers. We also tested whether known inhibitors of tau aggregation affect its oligomerization using three small molecules representing different classes of tau aggregation inhibitors, Methylene Blue (MB), the molecular tweezer CLR01, and the all-D peptide TLKIVW, for their ability to inhibit or modulate the oligomerization of the six tau isoforms. Unlike their reported inhibitory effect on tau fibrillation, the inhibitors had little or no effect on the initial oligomerization. Our study provides novel insight into the primary-quaternary structure relationship of human tau and suggests that 3R-tau oligomers may be an important target for future development of compounds targeting pathological tau assemblies.

Tau isoform–specific stabilization of intermediate states during microtubule assembly and disassembly

The microtubule (MT)-associated protein tau regulates the critical growing and shortening behaviors of MTs, and its normal activity is essential for neuronal development and maintenance. Accordingly, aberrant tau action is tightly associated with Alzheimer's disease and is genetically linked to several additional neurodegenerative diseases known as tauopathies. Although tau is known to promote net MT growth and stability, the precise mechanistic details governing its regulation of MT dynamics remain unclear. Here, we have used the slowly-hydrolyzable GTP analog, guanylyl-(α,β)-methylene-diphosphonate (GMPCPP), to examine the structural effects of tau at MT ends that may otherwise be too transient to observe. The addition of both four-repeat (4R) and three-repeat (3R) tau isoforms to pre-formed GMPCPP MTs resulted in the formation of extended, multiprotofilament-wide projections at MT ends. Furthermore, at temperatures too low for assembly of bona fide MTs, both tau isoforms promoted the formation of long spiral ribbons from GMPCPP tubulin heterodimers. In addition, GMPCPP MTs undergoing cold-induced disassembly in the presence of 4R tau (and to a much lesser extent 3R tau) also formed spirals. Finally, three pathological tau mutations known to cause neurodegeneration and dementia were differentially compromised in their abilities to stabilize MT disassembly intermediates. Taken together, we propose that tau promotes the formation/stabilization of intermediate states in MT assembly and disassembly by promoting both longitudinal and lateral tubulin-tubulin contacts. We hypothesize that these activities represent fundamental aspects of tau action that normally occur at the GTP-rich ends of GTP/GDP MTs and that may be compromised in neurodegeneration-causing tau variants.

Tau isoform expression and phosphorylation in marmoset brains

Tau is a microtubule-associated protein expressed in neuronal axons. Hyperphosphorylated tau is a major component of neurofibrillary tangles, a pathological hallmark of Alzheimer's disease (AD). Hyperphosphorylated tau aggregates are also found in many neurodegenerative diseases, collectively referred to as "tauopathies," and tau mutations are associated with familial frontotemporal lobar degeneration (FTLD). Previous studies have generated transgenic mice with mutant tau as tauopathy models, but nonhuman primates, which are more similar to humans, may be a better model to study tauopathies. For example, the common marmoset is poised as a nonhuman primate model for investigating the etiology of age-related neurodegenerative diseases. However, no biochemical studies of tau have been conducted in marmoset brains. Here, we investigated several important aspects of tau, including expression of different tau isoforms and its phosphorylation status, in the marmoset brain. We found that marmoset tau does not possess the "primate-unique motif" in its N-terminal domain. We also discovered that the tau isoform expression pattern in marmosets is more similar to that of mice than that of humans, with adult marmoset brains expressing only four-repeat tau isoforms as in adult mice but unlike in adult human brains. Of note, tau in brains of marmoset newborns was phosphorylated at several sites associated with AD pathology. However, in adult marmoset brains, much of this phosphorylation was lost, except for Ser-202 and Ser-404 phosphorylation. These results reveal key features of tau expression and phosphorylation in the marmoset brain, a potentially useful nonhuman primate model of neurodegenerative diseases.

Distinct differences in prion-like seeding and aggregation between Tau protein variants provide mechanistic insights into tauopathies

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

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

BackgroundThe MAPT c.1216C > T (p.Arg406Trp; R406W) mutation is a known cause of frontotemporal dementia with Parkinsonism linked to chromosome 17 tau with Alzheimer’s disease-like clinical features.MethodsWe compiled clinical data from a new Swedish kindred with R406W mutation. Seven family members were followed longitudinally for up to 22 years. Radiological examinations were performed in six family members and neuropathological examinations in three. We systematically reviewed the literature and compiled clinical, radiological, and neuropathological data on 63 previously described R406W heterozygotes and 3 homozygotes.ResultsFor all cases combined, the median age of onset was 56 years and the median disease duration was 13 years. Memory impairment was the most frequent symptom, behavioral disturbance and language impairment were less common, and Parkinsonism was rare. Disease progression was most often slow. The most frequent clinical diagnosis was Alzheimer’s disease. R406W homozygotes had an earlier age at onset and a higher frequency of behavioral symptoms and Parkinsonism than heterozygotes. In the new Swedish kindred, a consistent imaging finding was ventromedial temporal lobe atrophy, which was evident also in early disease stages as a widening of the collateral sulcus with ensuing atrophy of the parahippocampal gyrus. Unlike previously published R406W carriers, all three autopsied patients from the novel family showed neuropathological similarities with progressive supranuclear palsy, with predominant four-repeat (exon 10+) tau isoform (4R) tauopathy and neurofibrillary tangles accentuated in the basal-medial temporal lobe. Amyloid-β pathology was absent.ConclusionsDominance of 4R over three-repeat (exon 10−) tau isoforms contrasts with earlier reports of R406W patients and was not sufficiently explained by the presence of H1/H2 haplotypes in two of the autopsied patients. R406W patients often show a long course of disease with marked memory deficits. Both our neuropathological results and our imaging findings revealed that the ventromedial temporal lobes were extensively affected in the disease. We suggest that this area may represent the point of origin of tau deposition in this disease with relatively isolated tauopathy.

Accumulation of multiple neurodegenerative disease-related proteins in familial frontotemporal lobar degeneration associated with granulin mutation

In 2006, mutations in the granulin gene were identified in patients with familial Frontotemporal Lobar Degeneration. Granulin transcript haploinsufficiency has been proposed as a disease mechanism that leads to the loss of functional progranulin protein. Granulin mutations were initially found in tau-negative patients, though recent findings indicate that these mutations are associated with other neurodegenerative disorders with tau pathology, including Alzheimer’s disease and corticobasal degeneration. Moreover, a reduction in progranulin in tau transgenic mice is associated with increasing tau accumulation. To investigate the influence of a decline in progranulin protein on other forms of neurodegenerative-related protein accumulation, human granulin mutation cases were investigated by histochemical and biochemical analyses. Results showed a neuronal and glial tau accumulation in granulin mutation cases. Tau staining revealed neuronal pretangle forms and glial tau in both astrocytes and oligodendrocytes. Furthermore, phosphorylated α-synuclein-positive structures were also found in oligodendrocytes and the neuropil. Immunoblot analysis of fresh frozen brain tissues revealed that tau was present in the sarkosyl-insoluble fraction, and composed of three- and four-repeat tau isoforms, resembling Alzheimer’s disease. Our data suggest that progranulin reduction might be the cause of multiple proteinopathies due to the accelerating accumulation of abnormal proteins including TDP-43 proteinopathy, tauopathy and α-synucleinopathy.

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.

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

Non-taxoid site microtubule-stabilizing drugs work independently of tau overexpression in mouse N2a neuroblastoma cells

Microtubule-stabilizing drugs are useful in cancer therapy and show promise for treatment of neurodegenerative diseases. An overlapping binding site between tau and taxoid site drugs has led to a number of research papers investigating the competitive interaction between these drugs and the microtubule. This has implications for cancer treatment since increased tau could confer resistance to paclitaxel. Variations in the tau isoform ratio have also been reported in tauopathies, especially the rise in the levels of the four-repeat tau isoform. Therefore, in conditions of increased or altered expression of tau and its isoforms, a therapy that is not directly affected by changes in tau is desirable. Peloruside A and laulimalide are of particular interest in this respect because of their distinct binding site on the microtubule in relation to the clinically used drugs paclitaxel and ixabepilone. In the present study, we show that peloruside A and laulimalide stabilize microtubules independently of tau overexpression; whereas, the effects of paclitaxel and ixabepilone are masked by the presence of extra tau in the cell.

MicroRNA-132 loss is associated with tau exon 10 inclusion in progressive supranuclear palsy

Tauopathies represent a large class of neurological and movement disorders characterized by abnormal intracellular deposits of the microtubule-associated protein tau. It is now well established that mis-splicing of tau exon 10, causing an imbalance between three-repeat (3R) and four-repeat (4R) tau isoforms, can cause disease; however, the underlying mechanisms affecting tau splicing in neurons remain poorly understood. The small noncoding microRNAs (miRNAs), known for their critical role in posttranscriptional gene expression regulation, are increasingly acknowledged as important regulators of alternative splicing. Here, we identified a number of brain miRNAs, including miR-124, miR-9, miR-132 and miR-137, which regulate 4R:3R-tau ratios in neuronal cells. Analysis of miRNA expression profiles from sporadic progressive supranuclear palsy (PSP) patients, a major 4R-tau tauopathy, showed that miR-132 is specifically down-regulated in disease. We demonstrate that miR-132 directly targets the neuronal splicing factor polypyrimidine tract-binding protein 2 (PTBP2), which protein levels were increased in PSP patients. miR-132 overexpression or PTBP2 knockdown similarly affected endogenous 4R:3R-tau ratios in neuronal cells. Finally, we provide evidence that miR-132 is inversely correlated with PTBP2 during post-natal brain development at the time when 4R-tau becomes expressed. Taken together, these results suggest that changes in the miR-132/PTBP2 pathway could contribute to the abnormal splicing of tau exon 10 in the brain, and sheds light into the potential role played by miRNAs in a subset of tauopathies.

Increased expression of three-repeat isoforms of tau contributes to tau pathology in a rat model of chronic type 2 diabetes

The imbalance between three-repeat (3R) and four-repeat (4R) tau isoforms produced by the alternative splicing of tau exon 10 leads to neuronal instability and eventual neurodegeneration in tauopathy. However, the role of altered 3R/4R tau ratio in Alzheimer's disease (AD) remains controversial. It has been shown that the expression of 3R tau is modulated by peptide amyloid β (Aβ) and that 3R tau levels increase with the progression of AD. The incidence of AD increases in patients with type 2 diabetes mellitus (T2DM), and the comorbidity of these disorders is closely associated with both aging and disease duration. To investigate whether changes in 3R and 4R tau isoforms are involved in AD pathology pertaining to age-related T2DM, the expression of tau isoforms and their relationship with AD-like tau pathology were examined in a spontaneous T2DM model using aged Otsuka Long–Evans Tokushima Fatty (OLETF) rats with obesity. An AD-like pathology consisting of increased aggregates in the neuronal cytoplasm and a loss of synaptic proteins was observed in these rats. The aggregates were reactive with a 3R tau-specific, but not 4R tau-specific, antibody. In contrast to 4R tau, the level of 3R tau profoundly increased and the proteins were prone to taking toxic phosphorylated and truncated forms. Taken together, these findings suggest that increased 3R tau may contribute to AD-like tau pathology in a chronic T2DM model. Thus, the restoration of normal 3R tau expression should be considered as an important therapeutic strategy in the treatment of AD.

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.

P2-174: Expression of three-repeat and four-repeat tau isoforms and mRNA levels in control and progressive supranuclear palsy brains

Alternative splicing of exon 2, 3 and 10 of the tau gene results in six isoforms of tau in the adult CNS. Exon 10 inclusion results in tau isoforms containing four microtubule binding repeats (4R-tau) and exclusion results in three repeats (3R-tau). The tauopathies including PSP, FTDP-17, CBD and Pick's disease are linked to differential expression of 3R- and 4R-tau. The aim of the study was to measure the levels of 3R and 4R tau protein in PSP and control brains using a sandwich ELISA and to quantify tau mRNA isoforms by real-time PCR. Protein and mRNA levels of 3R- and 4R- tau in frontal cortex, caudate nucleus, globus pallidus (affected regions) and occipital lobe (unaffected regions) from confirmed PSP cases and control brains were measured using sandwich ELISAs and real-time PCR respectively. Monoclonal antibodies: RD3 or RD4 were used as coating antigens in the ELISAs and affinity purified- anti-TAU peptide HRP conjugate as the detector antibody. Total RNA from selected regions was extracted and real-time quantitative PCR was carried out using Sybr Green. There is no statistically significant difference in tau protein and mRNA levels between an affected area (frontal cortex) and an unaffected area (occipital lobe) of control brains. A significant increase (1.6-fold) in 4R-tau protein levels (ng/mg of total protein) as well as a trend for increased 4R- tau mRNA were observed in the PSP frontal cortex compared to control brains. However, there are no differences in 3R-tau levels in the frontal cortices between PSP and control brains. Furthermore, we observed no differences in both 3R- and 4R-tau levels in the occipital lobe (area spared from tau pathology) of PSP and control brains. In summary, we have used a recently developed sandwich ELISA for direct quantification of 3R- and 4R- tau in pathological samples. We have also used real-time PCR to measure mRNA expression of these tau isoforms. In this study, we have shown that abnormalities in protein levels as well as mRNA expression of 3R- and 4R- tau are both involved in the pathogenesis of PSP.

Tau-Based Treatment Strategies in Neurodegenerative Diseases

Neurofibrillary tangles are a characteristic hallmark of Alzheimer's and other neurodegenerative diseases, such as Pick's disease (PiD), progressive supranuclear palsy (PSP), corticobasal degeneration (CBD), and frontotemporal dementia and parkinsonism linked to chromosome 17 (FTDP-17). These diseases are summarized as tauopathies, because neurofibrillary tangles are composed of intracellular aggregates of the microtubule-associated protein tau. The molecular mechanisms of tau-mediated neurotoxicity are not well understood; however, pathologic hyperphosphorylation and aggregation of tau play a central role in neurodegeneration and neuronal dysfunction. The present review, therefore, focuses on therapeutic approaches that aim to inhibit tau phosphorylation and aggregation or to dissolve preexisting tau aggregates. Further experimental therapy strategies include the enhancement of tau clearance by activation of proteolytic, proteasomal, or autophagosomal degradation pathways or anti-tau directed immunotherapy. Hyperphosphorylated tau does not bind microtubules, leading to microtubule instability and transport impairment. Pharmacological stabilization of microtubule networks might counteract this effect. In several tauopathies there is a shift toward four-repeat tau isoforms, and interference with the splicing machinery to decrease four-repeat splicing might be another therapeutic option.

14‐3‐3 protein beta isoform is associated with 3‐repeat tau neurofibrillary tangles in Alzheimer's disease

14-3-3 proteins play roles in phosphorylation of tau proteins in neurofibrillary tangles (NFT) in Alzheimer's disease (AD). Tau is phosphorylated at serine (pSer) and threonine (pThr) in NFT, and NFT morphology varies according to phosphorylated sites and tau isoform. The roles of 14-3-3 proteins in NFT morphology remain unknown. This study was performed to examine the relationships between 14 and 3-3 proteins and tau phosphorylation of NFT. NFT were labeled with Gallyas impregnation, tau and 14-3-3 immunohistochemistry in paraffin-embedded hippocampal sections from seven AD and three control brains. Anti-tau antisera included monoclonal antisera that recognize pSer262 (pSer262), pSer422 (pSer422), pSer202/pThr205 (AT8), Thr231 (AT180), three-repeat (RD3) and four-repeat (RD4) tau isoform. Anti-14-3-3 protein isoform antisera included polyclonal antisera to beta, gamma, zeta, epsilon, tau, mu and sigma isoforms and monoclonal antiserum to beta antiserum (H8-beta). NFT density was obtained by counting labeled NFT in cornu ammonis (CA) 1-CA4, subiculum and entorhinal cortex. H8-beta and zeta isoforms were strongly expressed in NFT. Regional densities of NFT positive for pSer262, AT8, AT180, and Gallyas impregnation were similar to RD3-positive NFT density with high densities in CA1 and entorhinal cortex. NFT positive for pSer422 showed a similar regional distribution to RD4-positive NFT with high NFT density in CA2-CA4. H8-beta-positive NFT showed a similar regional distribution to RD3-positive NFT. In contrast, zeta isoform-positive NFT showed no specific distribution. In conclusion, H8-beta isoform is associated with development of 3-repeats NFT but a role of 14-3-3 zeta isoform in NFT could not be specified.

P2-155: Development of sensitive and specific ELISAs for three-repeat and four-repeat tau isoforms

Tau has been investigated in CSF as a potential diagnostic biomarker in neurodegenerative disorders associated with tau inclusions. Commercially available ELISA kits for quantification of total and phosphorylated tau have shown increased CSF t–tau and p–tau levels in Alzheimer's disease. In other tauopathies such as FTDP–17, four–repeat (4R) isoforms are abnormally elevated in brain. In such cases, the quantity and ratio of three–repeat (3R) and four–repeat (4R) tau isoforms could be reflected in CSF and could potentially serve as an early diagnostic biomarker. Previously, we developed two monoclonal antibodies; RD3 and RD4, specific for 3R and 4R tau isoforms, and these were effectively validated in several neuropathological studies. To develop highly specific and sensitive ELISAs for three–repeat (3R) and four–repeat (4R) tau isoforms. The current study describes the development of both competitive and sandwich ELISAs for 3R and 4R tau isoforms using RD3 and RD4. Peptide–protein conjugates are used as plate coating antigens in competitive ELISAs. Recombinant 3R and 4R tau isoforms are used as standards to compete against the solid phase antigen for antibody binding. In the sandwich format, several polyclonal and monoclonal antibodies have been tested to capture the tau isoforms, while RD3 and RD4 are respectively used as detector antibodies. In both assay formats, HRP has been used as label for quantification of bound antibodies onto the solid phase. The titres of RD3 and RD4 are found to be 1 in 150,000 and 1 in 6,000 respectively using peptide–protein conjugates as plate coating antigens. Both 3R and 4R tau isoforms are shown to effectively inhibit the binding of RD3 and RD4 towards the appropriate plate coating antigen in competitive ELISAs. We have achieved minimum detection limits for the tau isoforms in competitive ELISAs in the pg/mL range. Results of this study suggest that the current 3R tau and 4R tau ELISAs are feasible for rapid and sensitive detection of tau isoforms in CSF and corresponding biological matrices from patients with suspected tauopathies. These tests can potentially aid the diagnosis of tauopathies associated with differential expression of 3R and 4R tau isoforms.

A 62‐year‐old man with a family history of dementia, showing dementia and parkinsonism, presented with personality change and behavioral abnormality

The patient was a 62-year-old man. His mother, maternal uncle and grandfather had suffered from dementia. At the age of 57, the patient developed hypobulia, apathy and mental irritability, and showed disinhibited and stereotypical behaviors. At the age of 58, he showed personality change, poor understanding, restless and aimless walking, perseveration and echolalia as well as memory disturbance and disorientation. There was amnestic aphasia but no apraxia or agnosia. A CT scan and MRI disclosed localized symmetrical atrophy of the frontal and temporal lobes. Thereafter, he became mutistic and developed bradykinesia, rigidity of the extremities and impairment of vertical ocular pursuit movement. Sucking and grasp reflexes were positive with forced crying. He also revealed increased deep tendon reflexes in the extremities and bilateral Babinski signs. At the age of 59, he showed an oral tendency and could no longer walk. At the age of 60, he became bedridden, and tube feeding was started because of pseudobulbar palsy. At the terminal stage, he had repeated episodes of bronchopneumonia and died with akinetic mutism after a disease duration of about 5 years.