Welcome to the AD/PD™ 2022 Interactive Program

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Displaying One Session

Session Type
SYMPOSIUM
Date
Sat, 19.03.2022
Session Time
09:10 AM - 11:10 AM
Room
ONSITE: 114

FUNCTIONAL GENETIC CLASSIFICATION OF ASSEMBLY STRUCTURES IN TAUOPATHIES

Session Type
SYMPOSIUM
Date
Sat, 19.03.2022
Session Time
09:10 AM - 11:10 AM
Room
ONSITE: 114
Lecture Time
09:10 AM - 09:25 AM

Abstract

Abstract Body

Classification of tauopathies is based on immunohistochemical analyses of brain tissue. Conformations of tau assemblies, or seeds, in tauopathy brain lysate could provide a complementary metric for standard neuropathology. Biosensor cells that express tau repeat domain fused to fluorescent proteins will propagate self-replicating tau assemblies (strains) derived from patient material. Certain strains propagate indefinitely, and produce faithfully transmissible neuropathology upon inoculation into mice. Thus tau can be reasonably considered a mammalian prion. We hypothesize that, as for PrP prions, a “ground truth” of diagnosis in tauopathy could derive from underlying tau assembly conformation, rather than patterns of neuropathology. To build a relatively unbiased classification system, we have created a library of mutants with an alanine scan through the tau repeat domain. Using biosensor cells we have probed assembly of each alanine mutant onto existing stable strains, and onto transient intracellular assemblies induced by exposure to brain lysates. The relative incorporation of alanine mutants into intracellular aggregates is dictated by artificial “species barriers” they create. We thus derive a “fingerprint” of amino acids critical to build a given tau assembly. This unbiased, functional genetic dendrogram of tau prions predicts patterns of neuropathology following inoculation into a tauopathy mouse model. For human brain extracts, this method readily distinguishes different tauopathies. It also implicates amino acids outside the amyloid core defined by cryoEM as critical for stability. In ongoing work we are testing the validity of this structure-based classification scheme.

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TAU MICROANGIOPATHY: FROM NETWORK DYSFUNCTION TO DISORDERED NEUROVASCULAR COUPLING

Session Type
SYMPOSIUM
Date
Sat, 19.03.2022
Session Time
09:10 AM - 11:10 AM
Room
ONSITE: 114
Lecture Time
09:25 AM - 09:40 AM

Abstract

Abstract Body

The mechanisms of the cognitive dysfunction caused by vascular factors (vascular cognitive impairment) or neurodegeneration (Alzheimer’s disease, AD) have traditionally been considered distinct, but there is increasing evidence that alterations in cerebral blood vessels play a role both in vascular and neurodegenerative dementias. Indeed, amyloid-beta and tau, major pathogenic factors in AD, have profound cerebrovascular effects. While the cerebrovascular effects of amyloid-beta are well described, recent data indicate that also tau has a profound impact on neurovascular regulation. However, the cerebrovascular dysfunction of tau is mechanistically distinct from that of amyloid beta. In mouse models of tau accumulation tau suppresses the increase in cerebral blood flow produced by neural activity in the somatosensory cortex but, at variance with amyloid-beta, does not impair the ability of cerebral endothelial cells to regulate blood flow. The mechanisms of the effect involve tau-mediated uncoupling of neuronal nitric oxide from NMDA receptors, leading to suppression of glutamate-dependent nitric oxide production, which, in turn, dampens the increase in blood flow produced by synaptic activity. The deficit of neuronal nitric oxide also leads to interneuron network dysfunction and increased neuronal excitability. These finding indicate that both tau and amyloid-beta target the cerebral microvasculature through mechanistically distinct pathogenic processes. The resulting vascular dysfunction may cooperate with amyloid-beta and tau-induced synaptic dysfunction and contribute to cognitive impairment. In the absence of mechanism-based approaches to counteract dementia, targeting cerebrovascular function may offer the opportunity to mitigate the public health impact of one of the most disabling human afflictions.

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WOLFRAMIN-1–EXPRESSING NEURONS IN THE ENTORHINAL CORTEX PROPAGATE TAU TO CA1 NEURONS, INDUCE NEUROINFLAMMATION AND IMPAIR HIPPOCAMPAL MEMORY, MIMICKING EARLY BRAAK STAGES OF ALZHEIMER’S DISEASE

Session Type
SYMPOSIUM
Date
Sat, 19.03.2022
Session Time
09:10 AM - 11:10 AM
Room
ONSITE: 114
Lecture Time
09:40 AM - 09:55 AM

Abstract

Aims

We have recently reported that wolframin-1-expressing (Wfs1+) pyramidal neurons in the layer II entorhinal cortex (ECII) that project to the CA1 propagate phosphorylated tau (pTau) via the temporoammonic pathway in a mouse model (ECII-CA1 tau mouse), mimicking early stages of tau pathology in early-stage Alzheimer’s disease (AD). We examined if this phenomenon is recapitulated in human brains. Using the mouse model, we characterized tau transfer between ECII axons and CA1 dendrites and determined the pathological phenotype via multi-modal approaches.

Methods

Human brain tissues from 12 postmortem early-stage AD cases were examined for Wfs1 and pTau expression. ECII-CA1 tau mice were developed using Wfs1-Cre mice injected with Cre-inducible AAV expressing human P301L mutant tau in the ECII. At 4 weeks post-injection, the mice underwent behavioral tests and their brains were subject to immunohistochemistry, electrophysiology, electron microscopy, and RNA-sequencing analysis.

Results

High numbers of pTau+ Wfs1+ neurons were detected in EC of human brains at early-stage AD stages. The ECII-CA1 tau mice displayed tau pathology specifically propagating in CA1, avoiding the dentate gyrus. Reduced measures of excitability in the CA1, determined by field recording and multielectrode array, were accompanied by deficits in trace and contextual memory and enhanced expression of neuroinflammatory genes.

Conclusions

Wfs1+ pyramidal neurons are conserved in the human EC and contain pTau in early AD stages. The ECII-CA1 tau mice mimic early Braak stages of AD in tau propagation to the CA1 via monosynaptic transmission, accompanied by neuroinflammation and cognitive deficits.

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CHRONIC PHARMACOLOGICAL INHIBITION OF GLYMPHATIC FUNCTION EXACERBATES PROPAGATION OF TAU PATHOLOGY IN AN ANIMAL MODEL

Session Type
SYMPOSIUM
Date
Sat, 19.03.2022
Session Time
09:10 AM - 11:10 AM
Room
ONSITE: 114
Lecture Time
09:55 AM - 10:10 AM

Abstract

Aims

The glymphatic system describes the exchange of peri-arterial cerebrospinal fluid (CSF) with interstitial fluid in the parenchymal extracellular space, and peri-venous clearance out of the brain. Facilitated by astrocytic aquaporin-4 channels, this pathway has been shown to effectively clear proteins prone to propagation and aggregation in neurodegenerative diseases, such as amyloid-β, tau, and α-synuclein. Here, we tested proof-of-principle, that modulation of glymphatic function affects propagation of tau pathology in an animal model of such pathological aetiology.

Methods

Tau propagation was initiated in young (2 m.o.) Thy1-hTau.P301S mice (P301S mice), by injection of aged P301S mouse brain homogenate, into the hippocampus and overlying cortex. Animals subsequently received chronic treatment with the pharmacological aquaporin-4 inhibitor, TGN-020 (50mg/kg, i.p., 3 times/week) or vehicle for 10 weeks. Behavioural performance was accessed at baseline, 2, 4 and 10 weeks post-injection, after which in vivo structural brain MRI scans were acquired, and CSF and brains were collected for quantification of tau propagation, aggregation and resultant neurodegeneration following chronic impairment of glymphatic function.

Results

Mice chronically treated with TGN-020 exhibited exacerbated outcomes in hippocampal dependent cognitive memory tasks compared to vehicle treated controls. This was accompanied by intensified atrophy in treated brains, and a greater extent of tau aggregation and neurodegeneration following chronic drug treatment.

Conclusions

These data suggest that modulation of the function of the water channel aquaporin-4, and by extension the function of the glymphatic system, is capable of altering the extent to which tau is able to propagate throughout the brain.

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METHYLATED RNA AND THE EPITRANSCRIPTOME: HIDDEN FACTORS DIRECTING THE STRESS RESPONSE AND TAUOPATHY

Session Type
SYMPOSIUM
Date
Sat, 19.03.2022
Session Time
09:10 AM - 11:10 AM
Room
ONSITE: 114
Lecture Time
10:10 AM - 10:25 AM

Abstract

Aims

Tau is known to oligomerize and fibrillize, but the target of oligomeric tau (oTau) in the neuron is unclear. We sought to determine the protein interaction network for oTau, and then use this to understand the mechanisms of action of oTau.

Methods

Light induced Cry2 tau oligomerization was combined with mass spectrometry to generate the oTau protein interaction network. Subsequent work used immunochemical methods with human and mouse brains, combined with knockdown in P301S tau mice.

Results

HNRNPA2B1, an indirect reader for N6-methyl adenosine (m6A), was the top oTau network member. The oTau::HNRNPA2B1::m6A complex was validated by imaging and immunoprecipitation in human and mouse brains. oTau co-localized with m6A in a disease-dependent manner, increasing with disease progression over 4-fold in P301S tau mice and in human cases of Alzheimer’s disease. Colocalization of oTau with m6A (as well as HNRNPA2B1) was confirmed by proximity ligation assays. We will present transcripts and circRNAs that exhibit disease-dependent differential methylation. Knockdown of HNRNPA2B1 or m6A reduced the complex, rescued protein synthesis and inhibited neurodegeneration in P301S tau mice.

Conclusions

Little is known about the role of m6A in neurodegenerative diseases. These results identify a novel complex containing oTau, HNRNPA2B1 and m6A that contributes to the integrated stress response and the pathophysiology of oTau. The protection arising from knockdown of the oTau::HNRNPA2B1::m6A complex components suggests that this complex plays an important role in disease progression. Discovery of robust disease-dependent increases of m6A in AD opens novel areas of investigation and presents a novel target for diagnosis and therapy.

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QUANTIFICATION OF MULTIPLE TAU PHOSPHORYLATIONS AND ISOFORMS ACROSS DIFFERENT TAUOPATHIES IN HUMAN BRAIN USING HIGH-RESOLUTION MASS SPECTROMETRY

Session Type
SYMPOSIUM
Date
Sat, 19.03.2022
Session Time
09:10 AM - 11:10 AM
Room
ONSITE: 114
Lecture Time
10:25 AM - 10:40 AM

Abstract

Aims

Alzheimer’s disease (AD), progressive supranuclear palsy (PSP), Pick’s disease (PiD), and corticobasal degeneration (CBD) are neurodegenerative disorders characterized by the aggregation and spreading of tau protein. Due to similarities, it is currently problematic to chemically characterize the tau pathology in these diseases. Our aim was to develop a multiplex assay to quantify isoform-specific and phospho-tau species in brain and cerebrospinal fluid (CSF) of these diseases.

Methods

CSF, soluble (tris-buffered saline, TBS), and sarkosyl-insoluble (SI) brain extracts from the aforementioned tauopathies were immunoprecipitated using antibodies targeting all four tau regions. More than 50 tryptic peptides were monitored by liquid chromatography/high-resolution mass spectrometry, using isotope-labelled protein and peptide standards for quantification.

Results

In both brain fractions, all tau isoforms were detected, while only N-terminal peptides were observed in CSF. The 0N and 1N isoforms were most abundant in all samples. Preliminary data from the SI fraction of pooled brain extracts, 3R was more abundant in PiD, 4R in PSP and CBD, while in AD and controls they had similar abundance. Further, peptides from the microtubule-binding region were markedly more abundant in AD, indicating aggregation of these species. In the TBS fraction, immunoprecipitated with the HT7 antibody, phosphorylated tau was markedly increased in AD compared with the other groups; in particular doubly (p212+p217 and p231+p235) and triply (p231+p235+p238) phosphorylated peptides.

Conclusions

This novel assay can identify isoform differences across tauopathies. Measurement of multiply phosphorylated peptides could clearly differentiate AD from the other tauopathies. Additional data from the sample set is under way and will be presented.

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EFFICIENT INTERCELLULAR DISSEMINATION OF PROTEOPATHIC SEEDS MEDIATED BY VIRAL GLYCOPROTEINS

Session Type
SYMPOSIUM
Date
Sat, 19.03.2022
Session Time
09:10 AM - 11:10 AM
Room
ONSITE: 114
Lecture Time
10:40 AM - 10:55 AM

Abstract

Aims

Cell-to-cell propagation of protein misfolding likely underlies the stereotypical pattern of disease progression in neurodegenerative disorders. Mechanisms of intercellular protein aggregate spreading are ill-defined, but include secretion of free protein aggregates, direct cell contact or release of pathologic protein aggregates in association with extracellular vesicles (EV). To which extent these pathways contribute to proteopathic seed spreading is so far unknown. Interestingly, EV can increase the dissemination of enveloped viruses by shuttling partial or whole genomes and even viral particles to uninfected cells. Here we tested the hypothesis if decoration of EV with viral glycoproteins could also contribute to the spreading of protein aggregates between cells.

Methods

Permanent and primary cells propagating self-templating protein aggregates and expressing viral glycoproteins served as donor cells to test their capacity to spread protein misfolding to cocultured recipient cells. Futher, recipient cells were exposed to viral glycoprotein-decorated donor EV.

Results

We here demonstrate that coating donor cells or EV with viral ligands from vesicular stomatitis virus or Cov-2 strongly increases aggregate induction in recipients. Increased aggregate induction was observed for both tau and prion models, arguing that viral glycoproteins affect intercellular spreading of diverse types of protein aggregates.

Conclusions

In light of findings that some viruses are upregulated in brains of patients suffering from neurodegenerative diseases, viral infections could potentially contribute to the dissemination of proteopathic seeds and ultimately modulate disease progression.

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DISCUSSION

Session Type
SYMPOSIUM
Date
Sat, 19.03.2022
Session Time
09:10 AM - 11:10 AM
Room
ONSITE: 114
Lecture Time
10:55 AM - 11:10 AM