Human iPSC 4R tauopathy model uncovers modifiers of tau propagation.

Tauopathies are age-associated neurodegenerative diseases whose mechanistic underpinnings remain elusive, partially due to a lack of appropriate human models. Here, we engineered human induced pluripotent stem cell (hiPSC)-derived neuronal lines to express 4R Tau and 4R Tau carrying the P301S MAPT mutation when differentiated into neurons. 4R-P301S neurons display progressive Tau inclusions upon seeding with Tau fibrils and recapitulate features of tauopathy phenotypes including shared transcriptomic signatures, autophagic body accumulation, and reduced neuronal activity. A CRISPRi screen of genes associated with Tau pathobiology identified over 500 genetic modifiers of seeding-induced Tau propagation, including retromer VPS29 and genes in the UFMylation cascade. In progressive supranuclear palsy (PSP) and Alzheimer's Disease (AD) brains, the UFMylation cascade is altered in neurofibrillary-tangle-bearing neurons. Inhibiting the UFMylation cascade in vitro and in vivo suppressed seeding-induced Tau propagation. This model provides a robust platform to identify novel therapeutic strategies for 4R tauopathy.

Transcriptional programs mediating neuronal toxicity and altered glial-neuronal signaling in a Drosophila knock-in tauopathy model.

Missense mutations in the gene encoding the microtubule-associated protein TAU (current and approved symbol is MAPT) cause autosomal dominant forms of frontotemporal dementia. Multiple models of frontotemporal dementia based on transgenic expression of human TAU in experimental model organisms, including Drosophila, have been described. These models replicate key features of the human disease but do not faithfully recreate the genetic context of the human disorder. Here we use CRISPR-Cas-mediated gene editing to model frontotemporal dementia caused by the TAU P301L mutation by creating the orthologous mutation, P251L, in the endogenous Drosophila tau gene. Flies heterozygous or homozygous for Tau P251L display age-dependent neurodegeneration, display metabolic defects, and accumulate DNA damage in affected neurons. To understand the molecular events promoting neuronal dysfunction and death in knock-in flies, we performed single-cell RNA sequencing on approximately 130,000 cells from brains of Tau P251L mutant and control flies. We found that expression of disease-associated mutant tau altered gene expression cell autonomously in all neuronal cell types identified. Gene expression was also altered in glial cells, suggestive of non-cell-autonomous regulation. Cell signaling pathways, including glial-neuronal signaling, were broadly dysregulated as were brain region and cell type-specific protein interaction networks and gene regulatory programs. In summary, we present here a genetic model of tauopathy that faithfully recapitulates the genetic context and phenotypic features of the human disease, and use the results of comprehensive single-cell sequencing analysis to outline pathways of neurotoxicity and highlight the potential role of non-cell-autonomous changes in glia.

TMEM16F exacerbates tau pathology and mediates phosphatidylserine exposure in phospho-tau-burdened neurons.

TMEM16F is a calcium-activated phospholipid scramblase and nonselective ion channel, which allows the movement of lipids bidirectionally across the plasma membrane. While the functions of TMEM16F have been extensively characterized in multiple cell types, the role of TMEM16F in the central nervous system remains largely unknown. Here, we sought to study how TMEM16F in the brain may be involved in neurodegeneration. Using a mouse model that expresses the pathological P301S human tau (PS19 mouse), we found reduced tauopathy and microgliosis in 6- to 7-mo-old PS19 mice lacking TMEM16F. Furthermore, this reduction of pathology can be recapitulated in the PS19 mice with TMEM16F removed from neurons, while removal of TMEM16F from microglia of PS19 mice did not significantly impact tauopathy at this time point. Moreover, TMEM16F mediated aberrant phosphatidylserine exposure in neurons with phospho-tau burden. These studies raise the prospect of targeting TMEM16F in neurons as a potential treatment of neurodegeneration.

Subcortical tau is linked to hypoperfusion in connected cortical regions in 4-repeat tauopathies.

Four-repeat (4R) tauopathies are neurodegenerative diseases characterized by cerebral accumulation of 4R tau pathology. The most prominent 4R tauopathies are progressive supranuclear palsy (PSP) and corticobasal degeneration characterized by subcortical tau accumulation and cortical neuronal dysfunction, as shown by PET-assessed hypoperfusion and glucose hypometabolism. Yet, there is a spatial mismatch between subcortical tau deposition patterns and cortical neuronal dysfunction, and it is unclear how these two pathological brain changes are interrelated. Here, we hypothesized that subcortical tau pathology induces remote neuronal dysfunction in functionally connected cortical regions to test a pathophysiological model that mechanistically links subcortical tau accumulation to cortical neuronal dysfunction in 4R tauopathies. We included 51 Aß-negative patients with clinically diagnosed PSP variants (n = 26) or corticobasal syndrome (n = 25) who underwent structural MRI and 18F-PI-2620 tau-PET. 18F-PI-2620 tau-PET was recorded using a dynamic one-stop-shop acquisition protocol to determine an early 0.5-2.5 min post tracer-injection perfusion window for assessing cortical neuronal dysfunction, as well as a 20-40 min post tracer-injection window to determine 4R-tau load. Perfusion-PET (i.e. early window) was assessed in 200 cortical regions, and tau-PET was assessed in 32 subcortical regions of established functional brain atlases. We determined tau epicentres as subcortical regions with the highest 18F-PI-2620 tau-PET signal and assessed the connectivity of tau epicentres to cortical regions of interest using a resting-state functional MRI-based functional connectivity template derived from 69 healthy elderly controls from the ADNI cohort. Using linear regression, we assessed whether: (i) higher subcortical tau-PET was associated with reduced cortical perfusion; and (ii) cortical perfusion reductions were observed preferentially in regions closely connected to subcortical tau epicentres. As hypothesized, higher subcortical tau-PET was associated with overall lower cortical perfusion, which remained consistent when controlling for cortical tau-PET. Using group-average and subject-level PET data, we found that the seed-based connectivity pattern of subcortical tau epicentres aligned with cortical perfusion patterns, where cortical regions that were more closely connected to the tau epicentre showed lower perfusion. Together, subcortical tau-accumulation is associated with remote perfusion reductions indicative of neuronal dysfunction in functionally connected cortical regions in 4R-tauopathies. This suggests that subcortical tau pathology may induce cortical dysfunction, which may contribute to clinical disease manifestation and clinical heterogeneity.

Truncated tau interferes with the autophagy and endolysosomal pathway and results in lipid accumulation.

The autophagy-lysosomal pathway plays a critical role in the clearance of tau protein aggregates that deposit in the brain in tauopathies, and defects in this system are associated with disease pathogenesis. Here, we report that expression of Tau35, a tauopathy-associated carboxy-terminal fragment of tau, leads to lipid accumulation in cell lines and primary cortical neurons. Our findings suggest that this is likely due to a deleterious block of autophagic clearance and lysosomal degradative capacity by Tau35. Notably, upon induction of autophagy by Torin 1, Tau35 inhibited nuclear translocation of transcription factor EB (TFEB), a key regulator of lysosomal biogenesis. Both cell lines and primary cortical neurons expressing Tau35 also exhibited changes in endosomal protein expression. These findings implicate autophagic and endolysosomal dysfunction as key pathological mechanisms through which disease-associated tau fragments could lead to the development and progression of tauopathy.

Validity and value of metabolic connectivity in mouse models of ß-amyloid and tauopathy.

Among functional imaging methods, metabolic connectivity (MC) is increasingly used for investigation of regional network changes to examine the pathophysiology of neurodegenerative diseases such as Alzheimer's disease (AD) or movement disorders. Hitherto, MC was mostly used in clinical studies, but only a few studies demonstrated the usefulness of MC in the rodent brain. The goal of the current work was to analyze and validate metabolic regional network alterations in three different mouse models of neurodegenerative diseases (ß-amyloid and tau) by use of 2-deoxy-2-[18F]fluoro-d-glucose positron emission tomography (FDG-PET) imaging. We compared the results of FDG-µPET MC with conventional VOI-based analysis and behavioral assessment in the Morris water maze (MWM). The impact of awake versus anesthesia conditions on MC read-outs was studied and the robustness of MC data deriving from different scanners was tested. MC proved to be an accurate and robust indicator of functional connectivity loss when sample sizes ≥12 were considered. MC readouts were robust across scanners and in awake/ anesthesia conditions. MC loss was observed throughout all brain regions in tauopathy mice, whereas ß-amyloid indicated MC loss mainly in spatial learning areas and subcortical networks. This study established a methodological basis for the utilization of MC in different ß-amyloid and tau mouse models. MC has the potential to serve as a read-out of pathological changes within neuronal networks in these models.

Changes in lipid metabolism track with the progression of neurofibrillary pathology in tauopathies.

BACKGROUND: Accumulation of tau leads to neuroinflammation and neuronal cell death in tauopathies, including Alzheimer's disease. As the disease progresses, there is a decline in brain energy metabolism. However, the role of tau protein in regulating lipid metabolism remains less characterized and poorly understood. METHODS: We used a transgenic rat model for tauopathy to reveal metabolic alterations induced by neurofibrillary pathology. Transgenic rats express a tau fragment truncated at the N- and C-terminals. For phenotypic profiling, we performed targeted metabolomic and lipidomic analysis of brain tissue, CSF, and plasma, based on the LC-MS platform. To monitor disease progression, we employed samples from transgenic and control rats aged 4, 6, 8, 10, 12, and 14 months. To study neuron-glia interplay in lipidome changes induced by pathological tau we used well well-established multicomponent cell model system. Univariate and multivariate statistical approaches were used for data evaluation. RESULTS: We showed that tau has an important role in the deregulation of lipid metabolism. In the lipidomic study, pathological tau was associated with higher production of lipids participating in protein fibrillization, membrane reorganization, and inflammation. Interestingly, significant changes have been found in the early stages of tauopathy before the formation of high-molecular-weight tau aggregates and neurofibrillary pathology. Increased secretion of pathological tau protein in vivo and in vitro induced upregulated production of phospholipids and sphingolipids and accumulation of lipid droplets in microglia. We also found that this process depended on the amount of extracellular tau. During the later stages of tauopathy, we found a connection between the transition of tau into an insoluble fraction and changes in brain metabolism. CONCLUSION: Our results revealed that lipid metabolism is significantly affected during different stages of tau pathology. Thus, our results demonstrate that the dysregulation of lipid composition by pathological tau disrupts the microenvironment, further contributing to the propagation of pathology.

Overexpression of pathogenic tau in astrocytes causes a reduction in AQP4 and GLT1, an immunosuppressed phenotype and unique transcriptional responses to repetitive mild TBI without appreciable changes in tauopathy.

Epidemiological studies have unveiled a robust link between exposure to repetitive mild traumatic brain injury (r-mTBI) and elevated susceptibility to develop neurodegenerative disorders, notably chronic traumatic encephalopathy (CTE). The pathogenic lesion in CTE cases is characterized by the accumulation of hyperphosphorylated tau in neurons around small cerebral blood vessels which can be accompanied by astrocytes that contain phosphorylated tau, the latter termed tau astrogliopathy. However, the contribution of tau astrogliopathy to the pathobiology and functional consequences of r-mTBI/CTE or whether it is merely a consequence of aging remains unclear. We addressed these pivotal questions by utilizing a mouse model harboring tau-bearing astrocytes, GFAPP301L mice, subjected to our r-mTBI paradigm. Despite the fact that r-mTBI did not exacerbate tau astrogliopathy or general tauopathy, it increased phosphorylated tau in the area underneath the impact site. Additionally, gene ontology analysis of tau-bearing astrocytes following r-mTBI revealed profound alterations in key biological processes including immunological and mitochondrial bioenergetics. Moreover, gene array analysis of microdissected astrocytes accrued from stage IV CTE human brains revealed an immunosuppressed astroglial phenotype similar to tau-bearing astrocytes in the GFAPP301L model. Additionally, hippocampal reduction of proteins involved in water transport (AQP4) and glutamate homeostasis (GLT1) was found in the mouse model of tau astrogliopathy. Collectively, these findings reveal the importance of understanding tau astrogliopathy and its role in astroglial pathobiology under normal circumstances and following r-mTBI. The identified mechanisms using this GFAPP301L model may suggest targets for therapeutic interventions in r-mTBI pathogenesis in the context of CTE.

Nanoligomers targeting NF-κB and NLRP3 reduce neuroinflammation and improve cognitive function with aging and tauopathy.

Neuroinflammation contributes to impaired cognitive function in brain aging and neurodegenerative disorders like Alzheimer's disease, which is characterized by the aggregation of pathological tau. One major driver of both age- and tau-associated neuroinflammation is the NF-κB and NLRP3 signaling axis. However, current treatments targeting NF-κB or NLRP3 may have adverse/systemic effects, and most have not been clinically translatable. In this study, we tested the efficacy of a novel, nucleic acid therapeutic (Nanoligomer) cocktail specifically targeting both NF-κB and NLRP3 in the brain for reducing neuroinflammation and improving cognitive function in old (aged 19 months) wildtype mice, and in rTg4510 tau pathology mice (aged 2 months). We found that 4 weeks of NF-κB/NLRP3-targeting Nanoligomer treatment strongly reduced neuro-inflammatory cytokine profiles in the brain and improved cognitive-behavioral function in both old and rTg4510 mice. These effects of NF-κB/NLRP3-targeting Nanoligomers were also associated with reduced glial cell activation and pathology, favorable changes in transcriptome signatures of glia-associated inflammation (reduced) and neuronal health (increased), and positive systemic effects. Collectively, our results provide a basis for future translational studies targeting both NF-κB and NLRP3 in the brain, perhaps using Nanoligomers, to inhibit neuroinflammation and improve cognitive function with aging and neurodegeneration.

Biochemical approaches to assess the impact of post-translational modifications on pathogenic tau conformations using recombinant protein.

Tau protein is associated with many neurodegenerative disorders known as tauopathies. Aggregates of tau are thought of as a main contributor to neurodegeneration in these diseases. Increasingly, evidence points to earlier, soluble conformations of abnormally modified monomers and multimeric tau as toxic forms of tau. The biological processes driving tau from physiological species to pathogenic conformations remain poorly understood, but certain avenues are currently under investigation including the functional consequences of various pathological tau changes (e.g. mutations, post-translational modifications (PTMs), and protein-protein interactions). PTMs can regulate several aspects of tau biology such as proteasomal and autophagic clearance, solubility, and aggregation. Moreover, PTMs can contribute to the transition of tau from normal to pathogenic conformations. However, our understating of how PTMs specifically regulate the transition of tau into pathogenic conformations is partly impeded by the relative lack of structured frameworks to assess and quantify these conformations. In this review, we describe a set of approaches that includes several in vitro assays to determine the contribution of PTMs to tau's transition into known pathogenic conformations. The approaches begin with different methods to create recombinant tau proteins carrying specific PTMs followed by validation of the PTMs status. Then, we describe a set of biochemical and biophysical assays that assess the contribution of a given PTM to different tau conformations, including aggregation, oligomerization, exposure of the phosphatase-activating domain, and seeding. Together, these approaches can facilitate the advancement of our understanding of the relationships between PTMs and tau conformations.

Comparative interactome mapping of Tau-protein in classical and rapidly progressive Alzheimer's disease identifies subtype-specific pathways.

AIMS: Tau is a key player in Alzheimer's disease (AD) and other Tauopathies. Tau pathology in the brain directly correlates with neurodegeneration in AD. The recent identification of a rapid variant of AD demands an urgent need to uncover underlying mechanisms leading to differential progression in AD. Accordingly, we aimed to dissect the underlying differential mechanisms of toxicity associated with the Tau protein in AD subtypes and to find out subtype-dependent biomarkers and therapeutic targets. METHODS: To identify and characterise subtype-specific Tau-associated mechanisms of pathology, we performed comparative interactome mapping of Tau protein in classical AD (cAD) and rapidly progressive AD (rpAD) cases using co-immunoprecipitation coupled with quantitative mass spectrometry. The mass spectrometry data were extensively analysed using several bioinformatics approaches. RESULTS: The comparative interactome mapping of Tau protein revealed distinct and unique interactors (DPYSL4, ARHGEF2, TUBA4A and UQCRC2) in subtypes of AD. Interestingly, an analysis of the Tau-interacting proteins indicated enrichment of mitochondrial organisation processes, including negative regulation of mitochondrion organisation, mitochondrial outer membrane permeabilisation involved in programmed cell death, regulation of autophagy of mitochondrion and necroptotic processes, specifically in the rpAD interactome. While, in cAD, the top enriched processes were related to oxidation-reduction process, transport and monocarboxylic acid metabolism. CONCLUSIONS: Overall, our results provide a comprehensive map of Tau-interacting protein networks in a subtype-dependent manner and shed light on differential functions/pathways in AD subtypes. This comprehensive map of the Tau-interactome has provided subsets of disease-related proteins that can serve as novel biomarkers/biomarker panels and new drug targets.

Synaptic gene expression changes in frontotemporal dementia due to the MAPT 10 + 16 mutation.

AIMS: Mutations in the MAPT gene encoding tau protein can cause autosomal dominant neurodegenerative tauopathies including frontotemporal dementia (often with Parkinsonism). In Alzheimer's disease, the most common tauopathy, synapse loss is the strongest pathological correlate of cognitive decline. Recently, Positron Emission Tomography (PET) imaging with synaptic tracers revealed clinically relevant loss of synapses in primary tauopathies; however, the molecular mechanisms leading to synapse degeneration in primary tauopathies remain largely unknown. In this study, we examined post-mortem brain tissue from people who died with frontotemporal dementia with tau pathology (FTDtau) caused by the MAPT intronic exon 10 + 16 mutation, which increases splice variants containing exon 10 resulting in higher levels of tau with four microtubule-binding domains. METHODS: We used RNA sequencing and histopathology to examine temporal cortex and visual cortex, to look for molecular phenotypes compared to age, sex and RNA integrity matched participants who died without neurological disease (n = 12 FTDtau10 + 16 and 13 controls). RESULTS: Bulk tissue RNA sequencing reveals substantial downregulation of gene expression associated with synaptic function. Upregulated biological pathways in human MAPT 10 + 16 brain included those involved in transcriptional regulation, DNA damage response and neuroinflammation. Histopathology confirmed increased pathological tau accumulation in FTDtau10 + 16 cortex as well as a loss of presynaptic protein staining and region-specific increased colocalization of phospho-tau with synapses in temporal cortex. CONCLUSIONS: Our data indicate that synaptic pathology likely contributes to pathogenesis in FTDtau10 + 16 caused by the MAPT 10 + 16 mutation.

Ageing-related tau astrogliopathy severely affecting the substantia nigra.

AIMS: Astrocytic tau pathology is a major feature of tauopathies and ageing-related tau astrogliopathy (ARTAG). The substantia nigra (SN) is one of the important degenerative areas in tauopathies with parkinsonism. Nigral tau pathology is usually reported as neuronal predominant with less prominent astrocytic involvement. We aimed to identify cases with prominent astrocytic tau pathology in the SN. METHODS: We use the term nigral tau-astrogliopathy (NITAG) to describe cases showing an unusually high density of ARTAG with less neuronal tau pathology in the SN. We collected clinical information and studied the distribution of tau pathology, morphological features and immunostaining profiles in three cases. RESULTS: Three cases, all males with parkinsonism, were identified with the following clinicopathological diagnoses: (i) atypical parkinsonism with tau pathology reminiscent to that in postencephalitic parkinsonism (69-year-old); (ii) multiple system atrophy (73-year-old); (iii) traumatic encephalopathy syndrome/chronic traumatic encephalopathy (84-year-old). Double-labelling immunofluorescence confirmed co-localization of GFAP and phosphorylated tau in affected astrocytes. Staining profiles of NITAG revealed immunopositivity for various phosphorylated tau antibodies. Some astrocytic tau lesions were also seen in other brainstem regions and cerebral grey matter. CONCLUSIONS: We propose NITAG is a rare neuropathological feature, and not a distinct disease entity, in the frame of multiple system ARTAG, represented by abundant tau-positive astrocytes in various brain regions but having the highest density in the SN. The concept of NITAG allows the stratification of cases with various background pathologies to understand its relevance and contribution to neuronal dysfunction.

MSUT2 regulates tau spreading via adenosinergic signaling mediated ASAP1 pathway in neurons.

Inclusions comprised of microtubule-associated protein tau (tau) are implicated in a group of neurodegenerative diseases, collectively known as tauopathies, that include Alzheimer's disease (AD). The spreading of misfolded tau "seeds" along neuronal networks is thought to play a crucial role in the progression of tau pathology. Consequently, restricting the release or uptake of tau seeds may inhibit the spread of tau pathology and potentially halt the advancement of the disease. Previous studies have demonstrated that the Mammalian Suppressor of Tauopathy 2 (MSUT2), an RNA binding protein, modulates tau pathogenesis in a transgenic mouse model. In this study, we investigated the impact of MSUT2 on tau pathogenesis using tau seeding models. Our findings indicate that the loss of MSUT2 mitigates human tau seed-induced pathology in neuron cultures and mouse models. In addition, MSUT2 regulates many gene transcripts, including the Adenosine Receptor 1 (A1AR), and we show that down regulation or inhibition of A1AR modulates the activity of the "ArfGAP with SH3 Domain, Ankyrin Repeat, and PH Domain 1 protein" (ASAP1), thereby influencing the internalization of pathogenic tau seeds into neurons resulting in reduction of tau pathology.

TMEM106B coding variant is protective and deletion detrimental in a mouse model of tauopathy.

TMEM106B is a risk modifier of multiple neurological conditions, where a single coding variant and multiple non-coding SNPs influence the balance between susceptibility and resilience. Two key questions that emerge from past work are whether the lone T185S coding variant contributes to protection, and if the presence of TMEM106B is helpful or harmful in the context of disease. Here, we address both questions while expanding the scope of TMEM106B study from TDP-43 to models of tauopathy. We generated knockout mice with constitutive deletion of TMEM106B, alongside knock-in mice encoding the T186S knock-in mutation (equivalent to the human T185S variant), and crossed both with a P301S transgenic tau model to study how these manipulations impacted disease phenotypes. We found that TMEM106B deletion accelerated cognitive decline, hind limb paralysis, tau pathology, and neurodegeneration. TMEM106B deletion also increased transcriptional correlation with human AD and the functional pathways enriched in KO:tau mice aligned with those of AD. In contrast, the coding variant protected against tau-associated cognitive decline, synaptic impairment, neurodegeneration, and paralysis without affecting tau pathology. Our findings reveal that TMEM106B is a critical safeguard against tau aggregation, and that loss of this protein has a profound effect on sequelae of tauopathy. Our study further demonstrates that the coding variant is functionally relevant and contributes to neuroprotection downstream of tau pathology to preserve cognitive function.

Severe neurodegeneration in brains of transgenic rats producing human tau prions.

Both wild-type and mutant tau proteins can misfold into prions and self-propagate in the central nervous system of animals and people. To extend the work of others, we investigated the molecular basis of tau prion-mediated neurodegeneration in transgenic (Tg) rats expressing mutant human tau (P301S); this line of Tg rats is denoted Tg12099. We used the rat Prnp promoter to drive the overexpression of mutant tau (P301S) in the human 0N4R isoform. In Tg12099(+/+) rats homozygous for the transgene, ubiquitous expression of mutant human tau resulted in the progressive accumulation of phosphorylated tau inclusions, including silver-positive tangles in the frontal cortices and limbic system. Signs of central nervous system dysfunction were found in terminal Tg12099(+/+) rats exhibiting severe neurodegeneration and profound atrophy of the amygdala and piriform cortex. The greatest increases in tau prion activity were found in the corticolimbic structures. In contrast to the homozygous Tg12099(+/+) rats, we found lower levels of mutant tau in the hemizygous rats, resulting in few neuropathologic changes up to 2 years of age. Notably, these hemizygous rats could be infected by intracerebral inoculation with recombinant tau fibrils or precipitated tau prions from the brain homogenates of sick, aged homozygous Tg12099(+/+) rats. Our studies argue that the regional propagation of tau prions and neurodegeneration in the Tg12099 rats resembles that found in human primary tauopathies. These findings seem likely to advance our understanding of human tauopathies and may lead to effective therapeutics for Alzheimer's disease and other tau prion disorders.

Head-to-head comparison of [18F]-Flortaucipir, [18F]-MK-6240 and [18F]-PI-2620 postmortem binding across the spectrum of neurodegenerative diseases.

We and others have shown that [18F]-Flortaucipir, the most validated tau PET tracer thus far, binds with strong affinity to tau aggregates in Alzheimer's (AD) but has relatively low affinity for tau aggregates in non-AD tauopathies and exhibits off-target binding to neuromelanin- and melanin-containing cells, and to hemorrhages. Several second-generation tau tracers have been subsequently developed. [18F]-MK-6240 and [18F]-PI-2620 are the two that have garnered most attention. Our recent data indicated that the binding pattern of [18F]-MK-6240 closely parallels that of [18F]-Flortaucipir. The present study aimed at the direct comparison of the autoradiographic binding properties and off-target profile of [18F]-Flortaucipir, [18F]-MK-6240 and [18F]-PI-2620 in human tissue specimens, and their potential binding to monoamine oxidases (MAO). Phosphor-screen and high resolution autoradiographic patterns of the three tracers were studied in the same postmortem tissue material from AD and non-AD tauopathies, cerebral amyloid angiopathy, synucleopathies, transactive response DNA-binding protein 43 (TDP-43)-frontotemporal lobe degeneration and controls. Our results show that the three tracers show nearly identical autoradiographic binding profiles. They all strongly bind to neurofibrillary tangles in AD but do not seem to bind to a significant extent to tau aggregates in non-AD tauopathies pointing to their limited utility for the in vivo detection of non-AD tau lesions. None of them binds to lesions containing ß-amyloid, α-synuclein or TDP-43 but they all show strong off-target binding to neuromelanin and melanin-containing cells, as well as weaker binding to areas of hemorrhage. The autoradiographic binding signals of the three tracers are only weakly displaced by competing concentrations of selective MAO-B inhibitor deprenyl but not by MAO-A inhibitor clorgyline suggesting that MAO enzymes do not appear to be a significant binding target of any of them. These findings provide relevant insights for the correct interpretation of the in vivo behavior of these three tau PET tracers.

Tau filaments with the chronic traumatic encephalopathy fold in a case of vacuolar tauopathy with VCP mutation D395G.

Dominantly inherited mutation D395G in the gene encoding valosin-containing protein causes vacuolar tauopathy, a type of behavioural-variant frontotemporal dementia, with marked vacuolation and abundant filamentous tau inclusions made of all six brain isoforms. Here we report that tau inclusions were concentrated in layers II/III of the frontotemporal cortex in a case of vacuolar tauopathy. By electron cryomicroscopy, tau filaments had the chronic traumatic encephalopathy (CTE) fold. Tau inclusions of vacuolar tauopathy share this cortical location and the tau fold with CTE, subacute sclerosing panencephalitis and amyotrophic lateral sclerosis/parkinsonism-dementia complex, which are believed to be environmentally induced. Vacuolar tauopathy is the first inherited disease with the CTE tau fold.

Neuropathological hallmarks in the post-mortem retina of neurodegenerative diseases.

The retina is increasingly recognised as a potential source of biomarkers for neurodegenerative diseases. Hallmark protein aggregates in the retinal neuronal tissue could be imaged through light non-invasively. Post-mortem studies have already shown the presence of specific hallmark proteins in Alzheimer's disease, primary tauopathies, synucleinopathies and frontotemporal lobar degeneration. This study aims to assess proteinopathy in a post-mortem cohort with different neurodegenerative diseases and assess the presence of the primary pathology in the retina. Post-mortem eyes were collected in collaboration with the Netherlands Brain Bank from donors with Alzheimer's disease (n = 17), primary tauopathies (n = 8), synucleinopathies (n = 27), frontotemporal lobar degeneration (n = 8), mixed pathology (n = 11), other neurodegenerative diseases (n = 6), and cognitively normal controls (n = 25). Multiple cross sections of the retina and optic nerve tissue were immunostained using antibodies against pTau Ser202/Thr205 (AT8), amyloid-beta (4G8), alpha-synuclein (LB509), pTDP-43 Ser409/410 and p62-lck ligand (p62) and were assessed for the presence of aggregates and inclusions. pTau pathology was observed as a diffuse signal in Alzheimer's disease, primary tauopathies and controls with Alzheimer's disease neuropathological changes. Amyloid-beta was observed in the vessel wall and as cytoplasmic granular deposits in all groups. Alpha-synuclein pathology was observed as Lewy neurites in the retina in synucleinopathies associated with Lewy pathology and as oligodendroglial cytoplasmic inclusions in the optic nerve in multiple system atrophy. Anti-pTDP-43 generally showed typical neuronal cytoplasmic inclusion bodies in cases with frontotemporal lobar degeneration with TDP-43 and also in cases with later stages of limbic-associated TDP-43 encephalopathy. P62 showed inclusion bodies similar to those seen with anti-pTDP-43. Furthermore, pTau and alpha-synuclein pathology were significantly associated with increasing Braak stages for neurofibrillary tangles and Lewy bodies, respectively. Mixed pathology cases in this cohort consisted of cases (n = 6) with high Braak LB stages (> 4) and low or moderate AD pathology, high AD pathology (n = 1, Braak NFT 6, Thal phase 5) with moderate LB pathology, or a combination of low/moderate scores for different pathology scores in the brain (n = 4). There were no cases with advanced co-pathologies. In seven cases with Braak LB ≥ 4, LB pathology was observed in the retina, while tau pathology in the retina in the mixed pathology group (n = 11) could not be observed. From this study, we conclude that the retina reflects the presence of the major hallmark proteins associated with neurodegenerative diseases. Although low or moderate levels of copathology were found in the brains of most cases, the retina primarily manifested protein aggregates associated with the main neurodegenerative disease. These findings indicate that with appropriate retinal imaging techniques, retinal biomarkers have the potential to become highly accurate indicators for diagnosing the major neurodegenerative diseases of the brain.