Paired Helical Tau Filaments Research Articles

Dual Modification of Tau by Pseudophosphorylation and Glycation Does Not Enhance Amorphous Aggregation

Background/Aims: The neurofibrillary tangles consisting of Tau protein are an important pathology in Alzheimer’s disease. The paired helical filaments of Tau form most of the NFTs. These PHFs of Tau are found to carry numerous post-translational modifications, which stabilize them and aid in aggregation. The mechanistic function of Tau is to bind and stabilize the axonal microtubules. Hyperphosphorylation of Tau causes it to compromise its physiological function and accumulate in the neurons in the form of aggregates. Such residue-specific phosphorylation has been studied by employing Tau pseudophosphorylation mutants. But in addition to phosphorylation, several other modifications also aid in stabilizing the Tau PHF. Glycation is one such non-enzymatic PTM caused by sugars and their reactive intermediates. In this study, we employed the pseudophosphorylated Tau double mutants (262/404D, 262/396D, and 231/262) for studying their modification by methyl glyoxal, a reactive intermediate of glucose metabolism. Methods: We studied various biophysical properties like aggregation propensity, Advanced glycation end-product formation, and global conformation of the Tau with dual modifications. Our study includes the use of in vitro techniques e.g., ThS fluorescence assay, electron microscopy, CD spectroscopy, SDS-PAGE. Results: The overall result of the study suggest that the MG-induced Tau aggregation is influenced by the residue-specific Tau phosphorylation. Conclusion: In conclusion, the combinatorial effect of discreet PTMs on Tau function could lead to a better understanding of Tauopathy.

Tau filaments from amyotrophic lateral sclerosis/parkinsonism-dementia complex adopt the CTE fold.

The amyotrophic lateral sclerosis/parkinsonism-dementia complex (ALS/PDC) of the island of Guam and the Kii peninsula of Japan is a fatal neurodegenerative disease of unknown cause that is characterized by the presence of abundant filamentous tau inclusions in brains and spinal cords. Here, we used electron cryo-microscopy to determine the structures of tau filaments from the cerebral cortex of three cases of ALS/PDC from Guam and eight cases from Kii, as well as from the spinal cord of two of the Guam cases. Tau filaments had the chronic traumatic encephalopathy (CTE) fold, with variable amounts of Type I and Type II filaments. Paired helical tau filaments were also found in three Kii cases and tau filaments with the corticobasal degeneration fold in one Kii case. We identified a new Type III CTE tau filament, where protofilaments pack against each other in an antiparallel fashion. ALS/PDC is the third known tauopathy with CTE-type filaments and abundant tau inclusions in cortical layers II/III, the others being CTE and subacute sclerosing panencephalitis. Because these tauopathies are believed to have environmental causes, our findings support the hypothesis that ALS/PDC is caused by exogenous factors.

Impact of disease stage and reference region selection on longitudinal tau 18F‐MK6240 PET in Alzheimer’s disease

AbstractBackgroundTau PET imaging enables prospective longitudinal observation of the rate and location of tau accumulation in Alzheimer’s disease (AD). 18F‐MK6240 is a newer, high affinity tracer for the paired helical filaments of tau in AD. It is widely used in clinical trials, despite sparse longitudinal natural history data. We aimed to evaluate the impact of two reference regions on the magnitude and effect size of regional change.MethodOne hundred and fifty‐eight participants: 83 Aβ‐ cognitively unimpaired (CU), 37 Aβ+ CU, 19 Aβ+ MCI, 19 Aβ+ AD had annual 18F‐MK6240 PET imaging for a mean of 1.6 years. Standardized uptake value ratios (SUVR) were generated for three in‐house composite ROI: mesial temporal (Me), temporoparietal (Te), and rest of neocortex (R), and a Free‐Surfer derived meta‐temporal (MT) ROI. Two reference regions were examined: cerebellar cortex (SUVRcb) and eroded subcortical white matter (SUVRwm).ResultFigure 1 shows the annual rate of tau SUVR change in composite ROI. In Aβ+ CU, tau accumulation was greatest in Me (2.8‐3.2%/ year) (vs Aβ‐ CU, Cohen’s d = 0.30 SUVRcb, 0.24 SUVRwm) and MT (3.2‐3.6%/year) (vs Aβ‐ CU, d = 0.36 SUVRcb, 0.31 SUVRwm). In Aβ+ MCI, tau accumulation was greatest in Te (2.3‐3.7%/year) (vs Aβ‐ CU, d = 0.34 SUVRcb, 0.41 SUVRwm). In Aβ+ AD, greatest increase was in Te and R, with a decrease in Me. In Aβ+ AD, SUVRcb showed marginally greater increase in these regions (e.g. 3.8%/year compared to 2.68%/year SUVRwm in R) (vs Aβ‐ CU, d = 0.60 SUVRcb, 0.27 SUVRwm). In the young Aβ+ AD dementia group, spill‐over from adjacent high cortical binding or an increase in white matter binding elevates signal in the reference region.ConclusionThe rate of tau accumulation varies according to brain region and baseline tau. Change is greatest in the MTL in preclinical AD, in the MTL and lateral temporal cortex in MCI, and Braak V‐VI regions in AD dementia. The PET measured change is greater and less variable using an eroded white matter reference region, except in AD dementia, where spill‐over from adjacent high cortical binding or increase in white matter binding elevates the reference region.

Rates of regional tau accumulation in ageing and across the Alzheimer's disease continuum: an AIBL 18F-MK6240 PET study.

Tau positron emission tomography (PET) imaging enables longitudinal observation of tau accumulation in Alzheimer's disease (AD). 18F-MK6240 is a high affinity tracer for the paired helical filaments of tau in AD, widely used in clinical trials, despite sparse longitudinal natural history data. We aimed to evaluate the natural history of tau accumulation, and the impact of disease stage and reference region on the magnitude and effect size of regional change. One hundred and eighty-four participants: 89 cognitively unimpaired (CU) beta-amyloid negative (Aβ-), 44 CU Aβ+, 51 cognitively impaired Aβ+ (26 with mild cognitive impairment [MCI] and 25 with dementia) had follow-up 18F-MK6240 PET for one to four years (median 1.48). Regional standardised uptake value ratios (SUVR) were generated. Two reference regions were examined: cerebellar cortex and eroded subcortical white matter. CU Aβ- participants had very low rates of tau accumulation in the mesial temporal lobe (MTL). In CU Aβ+, significantly higher rate of accumulation was seen in the MTL (particularly the amygdala), extending into the inferior temporal lobes. In MCI Aβ+, the rate of accumulation was greatest in the lateral temporal, parietal and lateral occipital cortex, and plateaued in the MTL. Accumulation was global in AD Aβ+, except for a plateau in the MTL. The eroded subcortical white matter reference region showed no significant advantage over the cerebellar cortex and appeared prone to spill-over in AD participants. Data fitting suggested approximately 15-20 years to accumulate tau to typical AD levels. Tau accumulation occurs slowly. Rates vary according to brain region, disease stage and tend to plateau at high levels. Rates of tau accumulation are best measured in the MTL and inferior temporal cortex in preclinical AD and in large neocortical areas, in MCI and AD. NHMRC; Cerveau Technologies.

Alzheimer’s disease biomarker roadmap 2020: [18F]flortaucipir

AbstractBackgroundIn the last decade, the research community focused on defining reliable biomarkers for the early detection of the pathological hallmarks of Alzheimer’s Disease (AD). In 2017, the Geneva AD Biomarker Roadmap Initiative adapted the framework for the systematic validation of oncological diagnostic biomarkers to AD, with the aim to accelerate their development and implementation in clinical practice. With this work we assess the maturity of [18F]flortaucipir and we define the research priorities.MethodIn a two‐day workshop (Geneva, November 2019), we convened a panel of experts in AD biomarkers. The level of maturity of [18F]flortaucipir has been assessed based on the Biomarker Roadmap (Frisoni et al., 2017). Biomarker maturity and research priorities were processed by thematic subgroups before the meeting, and presented and discussed during the workshopResult[18F]flortaucipir binds with high affinity to paired helical filaments of tau and has favorable kinetic properties. It accurately discriminates between AD and patients with non‐AD neurodegenerative disorders as well as healthy controls. Initial studies showed high correlations between ante mortem and post‐mortem tau pathology. Further research is needed to investigate the effects of covariates on tracer binding and its ability to detect tau pathology in the early phase of AD.Conclusion[18F]flortaucipir provide partial evidence for clinical utility. In vivo [18F]flortaucipir PET shows excellent discrimination for AD from controls and non‐AD neurodegenerative disorders and promising results for the validation with autopsy. However, completion of studies on analytical validity is a requirement to investigate clinical utility properly.

Reader response: In vivo [18F]-AV-1451 tau-PET imaging in sporadic Creutzfeldt-Jakob disease.

We read with interest the article by Day et al.,1 which indicated no specific pattern of [18F]-AV-1451 retention was found in patients with rapidly progressive dementia (RPD) resulting from sporadic Creutzfeldt-Jakob disease (sCJD). This finding was in line with a former study that showed that the frequency of tau pathologies could not precisely reflect the deposition of prion protein.2 This work further confirmed that abnormal prion protein deposition in sCJD was not a risk factor for Alzheimer disease (AD), which indicated the [18F]-AV-1451 PET tracer showed a good specificity for paired helical tau filaments observed in AD dementia. In spite of the negative findings of this study, this work may have potential implications concerning the specificity of [18F]-AV-1451 PET retention for paired helical tau filaments. However, a recent study using fluorodeoxyglucose PET (FDG-PET) indicated a close relationship between FDG-PET hypometabolism and neuropathology in cortical, not subcortical, regions in prion disease.3 Further studies are needed to recruit patients with additional causes of RPD to evaluate the clinical applications of in vivo [18F]-AV-1451 PET and FDG-PET imaging in clinical practice.

Positron emission tomography imaging of tau pathology in progressive supranuclear palsy

Progressive supranuclear palsy is a rare form of atypical Parkinsonism that differs neuropathologically from other parkinsonian disorders. While many parkinsonian disorders such as Parkinson’s disease, Lewy body dementia, and multiple system atrophy are classified as synucleinopathies, progressive supranuclear palsy is coined a tauopathy due to the aggregation of pathological tau in the brain. [18F]AV-1451 (also known as [18F]-T807) is a positron emission tomography radiotracer that binds to paired helical filaments of tau in Alzheimer’s disease. We investigated whether [18F]AV-1451 could be used as biomarker for the diagnosis and disease progression monitoring in progressive supranuclear palsy. Six progressive supranuclear palsy, six Parkinson’s disease, and 10 age-matched healthy controls were recruited. An anatomical MRI and a 90-min PET scan, using [18F]AV-1451, were acquired from all participants. The standardized uptake value ratio from 60 to 90 min post-injection was calculated in each region of interest, using the cerebellar cortex as a reference region. No significant differences in standardized uptake value ratios were detected in our progressive supranuclear palsy group compared to the two control groups. [18F]AV-1451 may bind selectivity to the paired helical filaments in Alzheimer’s disease, which differ from the straight conformation of tau filaments in progressive supranuclear palsy.

18F-AV1451 PET DETECTS TAU PATHOLOGY IN MAPT MUTATION CARRIERS AND CORRELATES STRONGLY WITH IMMUNOHISTOCHEMISTRY OF TAU AGGREGATES

Background: The Tau PET ligand 18F-AV1451 has been shown to reliably detect paired helical filaments of tau in Alzheimer's disease, but it is not yet known whether it binds to the tau aggregates present in patients with mutations in the gene (MAPT) coding for the tau protein. Further, no study has yet compared the cerebral retention of 18F -AV1451 with the tau aggregates revealed using neuropathology. Methods: Three patients from a Swedish family carrying the R406W mutation of MAPT were assessed with cognitive tests and subjects underwent 18F-AV1451 and 18F-Flutemetamol PET scans. Further one of younger subjects also underwent an 18F-FDG PET scan. The oldest subject died two weeks after the scan and the brain was processed for neuropathology. Tau immunohistochemistry was performed on brain sections from affected and unaffected brain regions. Results: Two mutation carriers, aged 56 and 60 years, had disease durations of 5-10 years and still only exhibited mild-moderate episodic memory impairment and no clear behavioural deficits. The MRI revealed only slight cortical atrophy and 18F-AV1451 PET imaging showed uptake in the hippocampus and the temporal lobes, especially in the inferior and anterior parts (Fig 1A, B). The uptake of 18F - AV1451 correlated well with hypometabolism revealed with FGD PET in one of the subjects. The third case, 76 years, had a disease duration of ≥20 years and exhibited clear cognitive impairment, behavioural disturbances, mutism and dysphagia. The CT scan showed generalised cortical atrophy with a pronounced temporal lobe atrophy and 18F -AV1451 PET imaging revealed uptake in the temporal and frontal lobes, as well as in the basal ganglia (Fig 1 C). The regional uptake of 18F -AV1451 correlated strongly with the tau aggregates revealed using immunohistochemistry (R2 = 0.80, P <0.01; Fig 2). All cases exhibited negative amyloid (18F -flutemetamol) PET scans. Conclusions: The in vivo uptake of 18F-AV1451 reflects the regional amount of tau aggregates revealed by neuropathological examination. Further, tau pathology in MAPT mutation carriers is accurately detected with 18F -AV1451 PET, which consequently can be used to track the effects of anti-tau therapies in this patient group. (Figure Presented) . (Less)

Multiple signaling factors and drugs alleviate neuronal death induced by expression of human and zebrafish tau proteins in vivo.

BackgroundThe axonal tau protein is a tubulin-binding protein, which plays important roles in the formation and stability of the microtubule. Mutations in the tau gene are associated with familial forms of frontotemporal dementia with Parkinsonism linked to chromosome-17 (FTDP-17). Paired helical filaments of tau and extracellular plaques containing beta-amyloid are found in the brain of Alzheimer’s disease (AD) patients.ResultsTransgenic models, including those of zebrafish, have been employed to elucidate the mechanisms by which tau protein causes neurodegeneration. In this study, a transient expression system was established to express GFP fusion proteins of zebrafish and human tau under the control of a neuron-specific HuC promoter. Approximately ten neuronal cells expressing tau-GFP in zebrafish embryos were directly imaged and traced by time-lapse recording, in order to evaluate the neurotoxicity induced by tau-GFP proteins. Expression of tau-GFP was observed to cause high levels of neuronal death. However, multiple signaling factors, such as Bcl2-L1, Nrf2, and GDNF, were found to effectively protect neuronal cells expressing tau-GFP from death. Treatment with chemical compounds that exert anti-oxidative or neurotrophic effects also resulted in a similar protective effect and maintained human tau-GFP protein in a phosphorylated state, as detected by antibodies pT212 and AT8.ConclusionsThe novel finding of this study is that we established an expression system expressing tau-GFP in zebrafish embryos were directly imaged and traced by time-lapse recording to evaluate the neurotoxicity induced by tau-GFP proteins. This system may serve as an efficient in vivo imaging platform for the discovery of novel drugs against tauopathy.

A concise radiosynthesis of the tau radiopharmaceutical, [18F]T807

Fluorine-18 labeled 7-(6-fluoropyridin-3-yl)-5H-pyrido[4,3-b]indole ([(18) F]T807) is a potent and selective agent for imaging paired helical filaments of tau and is among the most promising PET radiopharmaceuticals for this target in early clinical trials. The present study reports a simplified one-step method for the synthesis of [(18) F]T807 that is broadly applicable for routine clinical production using a GE TRACERlab™ FXFN radiosynthesis module. Key facets of our optimized radiosynthesis include development and use of a more soluble protected precursor, tert-butyl 7-(6-nitropyridin-3-yl)-5H-pyrido[4,3-b]indole-5-carboxylate, as well as new HPLC separation conditions that enable a facile one-step synthesis. During the nucleophilic fluorinating reaction with potassium cryptand [(18) F]fluoride (K[(18) F]/K222 ) in DMSO at 130 °C over 10 min the precursor is concurrently deprotected. Formulated [(18) F]T807 was prepared in an uncorrected radiochemical yield of 14 ± 3%, with a specific activity of 216 ± 60 GBq/µmol (5837 ± 1621 mCi/µmol) at the end of synthesis (60 min; n = 3) and validated for human use. This methodology offers the advantage of faster synthesis in fewer steps, with simpler automation that we anticipate will facilitate widespread clinical use of [(18) F]T807.

Age-related changes of Alzheimer’s disease-associated proteins in cynomolgus monkey brains

We characterized senile plaques (SPs) immunohistochemically in cynomolgus monkey brains and also examined age-related biochemical changes of Alzheimer’s disease (AD)-associated proteins in these brains from monkeys of various ages. In the neocortex of aged monkeys (>20 years old), we found SPs but no neurofibrillary tangles (NFTs). Antibodies against β-amyloid precursor protein (APP) or apolipoprotein E (ApoE) stained SPs; however, the pattern of immunostaining was different for the two antigens. APP was present only in swollen neurites, but ApoE was present throughout all parts of SPs. Western blot analysis revealed that the pattern of APP expression changed with age. Although full-length APP695 protein was mainly expressed in brains from young monkeys (4 years old), the expression of full-length APP751 protein was increased in brains from older monkeys (>20 years old). Biochemical analyses also showed that levels of various AD-associated proteins increased significantly with age in nerve ending fractions. Both SP-associated (APP) and NFT-associated proteins (tau, activated glycogen synthase kinase 3β, cyclin dependent kinase 5, p35, and p25) accumulated in the nerve ending fraction with increasing age; however, we found no NFTs or paired helical filaments of tau in aged cynomolgus monkey brains. This age-related accumulation of these proteins in the nerve ending fraction was similar to that observed in our laboratory previously for presenilin-1 (PS-1). The accumulation of these SP-associated proteins in this fraction may be a causal event in the spontaneous formation of SPs; thus, SPs may be formed initially in nerve endings. Taken together, these results suggest that intensive investigation of age-related changes in the nerve ending and in axonal transport will contribute to a better understanding of the pathogenesis of neurodegenerative disorders such as AD.

Frontotemporal dementia with novel tau pathology and a Glu342Valtau mutation

It is unclear how tau gene mutations cause frontotemporal dementia (FTD) with parkinsonism linked to chromosome 17 (FTDP-17), but those in exon 10 (E10) or the following intron may be pathogenic by altering E10 splicing, perturbing the normal 1:1 ratio of four versus three microtubule-binding repeat tau (4R:3R tau ratio) and forming tau inclusions. We report on a 55-year old woman with frontotemporal dementia and a family history of FTDP-17 in whom we found a novel E12 (Glu342Val) tau gene mutation, prominent frontotemporal neuron loss, intracytoplasmic tau aggregates, paired helical tau filaments, increased 4R tau messenger RNA, increased 4R tau without E2 or E3 inserts, decreased 4R tau with these inserts, and a 4R:3R tau ratio greater than 1 in gray and white matter. Thus, this novel Glu342Val mutation may cause FTDP-17 by unprecedented mechanisms that alter splicing of E2, E3, and E10 to preferentially increase 4R tau without amino terminal inserts and promote aggregation of tau filaments into cytopathic inclusions.

Frontotemporal dementia with novel tau pathology and a Glu342Val tau mutation

It is unclear how tau gene mutations cause frontotemporal dementia (FTD) with parkinsonism linked to chromosome 17 (FTDP-17), but those in exon 10 (E10) or the following intron may be pathogenic by altering E10 splicing, perturbing the normal 1:1 ratio of four versus three microtubule-binding repeat tau (4R:3R tau ratio) and forming tau inclusions. We report on a 55-year old woman with frontotemporal dementia and a family history of FTDP-17 in whom we found a novel E12 (Glu342Val) tau gene mutation, prominent frontotemporal neuron loss, intracytoplasmic tau aggregates, paired helical tau filaments, increased 4R tau messenger RNA, increased 4R tau without E2 or E3 inserts, decreased 4R tau with these inserts, and a 4R:3R tau ratio greater than 1 in gray and white matter. Thus, this novel Glu342Val mutation may cause FTDP-17 by unprecedented mechanisms that alter splicing of E2, E3, and E10 to preferentially increase 4R tau without amino terminal inserts and promote aggregation of tau filaments into cytopathic inclusions. Ann Neurol 2000;48:850–858