Welcome to the AD/PD™ 2022 Interactive Program
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AMYLOID FACILITATED TAU-SEEDING AND SUBSEQUENT TAU-INDUCED NEURODEGENERATION: RECAPITULATING THE A/T/N-AXIS IN VIVO
Abstract
Aims
Brains of AD patients are characterized by the presence of amyloid pathology, Tau-pathology and neurodegeneration, referred to as A-, T- and N-pathology respectively. These stages develop in a characteristic spatio-temporal way in AD patients. Previous publications demonstrated amyloid facilitated tau seeding of endogenous tau, highlighting the relevance of amyloid facilitated tau pathology. We now focused on the development of a preclinical model that recapitulates all aspects of ATN pathology, downstream of amyloid pathology.
Methods
Hereto, we analyzed the effect of amyloid pathology on Tau-seeded pathology, its propagation and subsequent neurodegeneration in crosses of TauP301S and 5xFAD mice.
Results
Tau-seeded Tau-pathology was significantly increased in the presence of amyloid pathology. Tau-pathology propagated more efficiently to functionally connected brain areas at the ipsi- and contralateral side, remote from the injection site in the presence of amyloid pathology. Most strikingly, in the presence of amyloid pathology, Tau-seeding induced significant hippocampal and cortical atrophy, correlating with the level of Tau-pathology. Finally, microgliosis significantly increased at the different stages of the ATN axis in this model.
Conclusions
Our in vivo model displays amyloid facilitated propagation of Tau-seeded pathology and Tau-induced neurodegeneration. We here present a model robustly recapitulating the ATN pathologies, providing a tool to gain mechanistic insights in the interrelation and synergism between A, T and N pathologies to gain insight in the progressive development of ATN pathologies in AD.
MILD TRAUMATIC BRAIN INJURY INDUCES A RAPID, KINASE-DEPENDENT MISLOCALIZATION OF TAU FROM AXONS TO THE SOMATODENDRITIC DOMAIN
Abstract
Aims
Chronic traumatic encephalopathy (CTE) is a neurodegenerative disease with prominent TAU pathologies caused by repeated brain traumas. The molecular modifications of TAU in CTE are essentially identical those found in AD tissues, but the spatial pattern of degeneration is different. We tested our hypothesis that mild traumatic brain injury (mTBI) can act as a pathogenic trigger of TAU modification and characterized the early-stage pattern and molecular consequences of these modifications.
Methods
We induced mTBI in the forebrains of MAPT-GR mice, in which the endogenous mouse Mapt gene is replaced by the full human MAPT (TAU) gene. Brain tissues were then examined for TAU phosphorylation and sub-cellular localization.
Results
Prior to mTBI, human TAU protein in MAPT-GR mice is unphosphorylated and primarily localized to axons. We found that TAU in neurons impacted by mTBI becomes phosphorylated and prominently mis-localized to the somatodendritic domain. TAU pathology is clearly detectable by day 3 post-mTBI, is fully developed by day 7, and in young animals is largely cleared by 1 month. Treatment of the brain tissue just prior to mTBI with specific kinase inhibitors blocked both the TAU phosphorylation and mislocalization. In control experiments with wt mice, mTBI did not induce phosphorylation nor mislocalization of the mouse TAU protein.
Conclusions
We conclude that physical damage to axons activates a pair of kinases to phosphorylate TAU and that this phosphorylation is a necessary component of the process that then moves the modified TAU protein from the axon to the somatodendritic domain.
INCREASED PRESENCE OF PHOSPHORYLATED TAU IN THE RETINA OF ALZHEIMER’S DISEASE AND OTHER TAUOPATHIES
Abstract
Aims
There is increased interest in in vivo labeling of Alzheimer’s disease (AD) pathology in the retina as a non-invasive, low-cost diagnostic approach. In this study we assessed the presence of different tau isoforms in post-mortem retinas of AD and controls, as well as other neurodegenerative diseases associated with or without tau pathology.
Methods
Post-mortem eyes were collected through the Netherlands Brain Bank from donors with AD (n=17), frontotemporal lobar degeneration (FTLD; n=6), other tauopathies (n=7), alpha-synucleinopathies (n=13), as well as non-neurodegenerative controls (n=16) and other neurodegenerative cases (n=3). Cross-sections of the superior-temporal quadrants were immunostained for total tau (HT7), early tau phosphorylation (AT8, AT100, AT270), 3R and 4R tau isoforms (RD3/RD4) and late tau phosphorylation (pS422).
Results
Total tau (HT-7) was observed in all cases. The presence of 3- and 4-repeat isoforms of tau varied within the inner plexiform layer (IPL) and outer plexiform layer (OPL) with more 3-repeat tau in the IPL and more 4-repeat tau in the OPL. In general, AD and other tauopathy cases showed positive immunoreactivity for AT8. Tau phosphorylated at Ser422 was negative in all groups.
Conclusions
In controls with cerebral cortical tau and neurodegenerative tauopathy cases, high levels of tau are present in the retina, mainly in the plexiform layers. Overall, tau phosphorylated at Ser202/Thr205 differentiates tauopathies from other neurodegenerative diseases and non-neurodegenerative controls. Depending on the epitope, phosphorylated tau is a potential retinal biomarker for AD and other tauopathies.
LOSS OF PRESENILIN FUNCTION CAUSES TAU PHOSPHORYLATION AND AGGREGATION IN MICE
Abstract
Aims
Mutations in the presenilin (PS/PSEN) genes encoding the catalytic components of γ-secretase accelerate amyloid-β (Aβ) and tau pathologies in familial Alzheimer’s disease (AD). The mechanisms by which PSEN mutations affect Aβ are well defined, but the precise role PS/γ-secretase on tau pathology in neurodegeneration independently of Aβ is largely unclear. Here, we aimed to define the cellular mechanisms by which PS regulates tau pathology during neurodegeneration.
Methods
We performed molecular, pathological and behavioral analyses in novel mutant Tau transgenic mice lacking presenilin-1 (PS1) or both PS genes in glutamatergic neurons.
Results
Neuronal PS deficiency in conditional knockout (cKO) mice results in age-dependent brain atrophy, inflammatory responses and accumulation of pathological tau in neurons and glial cells associated with altered tau kinases. Interestingly, genetic inactivation of PS1 or both PS genes in a mouse model of frontotemporal dementia expressing mutant human tau exacerbates memory deficits by accelerating phosphorylation and aggregation of tau in excitatory neurons of vulnerable AD brain regions. Remarkably, neurofilament (NF) light chain levels are abnormally accumulated in Tau mice lacking PS. Synchroton infrared microspectroscopy revealed aggregated and oligomeric β-sheet structures in amyloid plaque-free PS-deficient Tau mice. Hippocampal-dependent memory deficits are associated with synaptic tau accumulation and reduction of pre- and post-synaptic proteins in PS-deficient Tau mice.
Conclusions
Partial loss of PS/γ-secretase in neurons causes temporal- and spatial-dependent tau aggregation associated with memory and synaptic deficits and neurodegeneration. Our findings show that tau phosphorylation and aggregation are key pathological processes that may underlie neurodegeneration caused by familial AD-linked PS mutations.
EXTRACELLULAR VESICLES: MAJOR ACTORS OF HETEROGENEITY IN TAU SPREADING AMONG HUMAN TAUOPATHIES
Abstract
Aims
In somes tauopathies, the progression of neurodegeneration follows disease-specific hierarchical progression that may be linked to a prion-like propagation. Indeed, seed-competent tau species spread from cell to cell but the intercellular mechanisms of transfer are unclear. Extracellular vesicles represent a unique intercellular delivery vehicle for transferring pathological species from one neuronal population to another that could explain the differing cell vulnerability seen in tauopathies. Here, we compare tau seeding capacity from vesicles that have been isolated from brain derived fluid of patients with various tauopathies.
Methods
Brain extracts (AD, PSP, PiD, control) were obtained from the Lille Neurobank. Vesicles were characterized (electron microscopy, nanotracking analyses, mass spectrometry, biochemistry). Tau in brain-derived enriched-extracellular vesicles (BD-EVs) was evaluated by ELISA and EM. Seeding mediated by BD-EVs was tested using a cell seeding assay; BD-EVs were injected into the hippocampus of tau transgenic mice and tau lesions quantified (MC1 and AT100).
Results
Whereas vesicles concentration and the tau content did not differ among the tauopathies and controls, we observed considerable heterogeneity in their seeding capacities. The most striking evidence was coming from AD where the BD-EVs clearly contain pathological species that can induce tau lesions in vivo. For PSP and PiD patients, a weak FRET signal was observed which was consistent with neuropathology.
Conclusions
Together, our results support the hypothesis that BD-EVs contain tau variants that may participate to the prion-like propagation of tau pathology in tauopathies. Such observation may lead to reconsider diagnostic and therapeutic strategies.
INTERFERON REGULATORY FACTOR 5 (IRF5) MODULATES TAU ACCUMULATION IN ALZHEIMER’S DISEASE.
Abstract
Aims
The innate immune system reacts to tau accumulation to limit its spread. However, dysfunctional microglia activation may cause hyper-inflammation and worsened pathology. We identified the transcription factor interferon regulatory factor 5 (IRF5) as a new mediator of microglia activation in response to pathological tau and sought to define its role.
Methods
We analyzed human AD brains for IRF5 expression by Western blot and immunohistochemistry. In ageing wild-type and Irf5-/- mice intracranially injected with PHF-tau, we measured tau levels and characterized microglia numbers and function. In vitro, we assessed the response to PHF-Tau using imaging flow cytometry on AMNIS Imagestream. Last, we tested the feasibility of in-vivo IRF5 inhibition with a novel peptide inhibitor developed in our lab.
Results
We determined that: 1) IRF5 is overexpressed in AD brains and localizes in microglia, near plaque-like structures; 2) ageing Irf5-/- mice have higher levels of soluble tau; 3) after hippocampal injection of PHF tau, young Irf5-/- mice accumulate more soluble total tau in all brain regions than wild-type littermates; 4) PHF tau induces IRF5 nuclear translocation (i.e. activation) in cultured macrophages; 5) a novel IRF5 peptide inhibitor, N5-1, penetrated into the brain when injected IV, hence is a viable tool to modulate IRF5 function in vivo.
Conclusions
IRF5 is a regulator of microglia response to tau pathology. Modulation of IRF5 may be a key factor to maintain innate immune response to tau without causing hyper-inflammation.
CRYO-ELECTRON MICROSCOPY OF EXTRACELLULAR VESICLES CONTAINING AGGREGATED TAU IN ALZHEIMER'S DISEASE
Abstract
Aims
In Alzheimer’s disease tau aggregation begins in subcortical regions and spreads sequentially to the transentorhinal cortex, limbic system and neocortex along neuronal connections. It has been shown that extracellular vesicles, a heterogeneous group of secreted vesicles, can mediate cell to cell spreading of aggregated tau. However, the molecular identities of the aggregated tau species and extracellular vesicles are not known.
Methods
We used cryo-electron microscopy to visualise aggregated tau associated with extracellular vesicles from the brains of individuals with Alzheimer's disease. Cryo-electron tomography was used to reveal the molecular composition of intact extracellular vesicles and single particle cryo-electron microscopy was used to determine the structures of aggregated tau associated with extracellular vesicles.
Results
We found paired helical and straight tau filaments densely packed within double-membraned vesicles of between 300 and 750 nm in diameter. We found evidence for tethering of filaments to the inner vesicle membrane via adaptor proteins, with additional filaments tethered to one another and to internal vesicles in a network. Tau filaments were decorated with additional globular protein densities at ordered positions along the long filament axis. We determined the structure of the ordered core of tau filaments following detergent extraction from extracellular vesicles. This revealed the presence of negatively-charged molecules associated with the side chains of R349 and K375 that were not observed in filaments extracted from total brain homogenates.
Conclusions
Our results give molecular insights into extracellular vesicles containing aggregated tau in Alzheimer's disease, which will inform strategies to target the spread of aggregated tau.