Marie-Eve Grosjean

Targeting phospho-Ser422 by active Tau Immunotherapy in the THYTau22 mouse model: a suitable therapeutic approach.

Recent data indicate that Tau immunotherapy may be relevant for interfering with neurofibrillary degeneration in Alzheimer disease and related disorders referred to as Tauopathies. The key question for immunotherapy is the choice of the epitope to target. Abnormal phosphorylation is a well-described post-translational modification of Tau proteins and may be a good target. In the present study, we investigated the effects of active immunization against the pathological epitope phospho-Ser422 in the THY-Tau22 transgenic mouse model. Starting from 3-6 months of age, THY-Tau22 mice develop hippocampal neurofibrillary tangle-like inclusions and exhibit phosphorylation of Tau on several AD-relevant Tau epitopes. Three month-old THY-Tau22 mice were immunized with a peptide including the phosphoserine 422 residue while control mice received the adjuvant alone. A specific antibody response against the phospho-Ser422 epitope was observed. We noticed a decrease in insoluble Tau species (AT100- and pS422 immunoreactive) by both biochemical and immunohistochemical means correlated with a significant cognitive improvement using the Y-maze. This Tau immunotherapy may facilitate Tau clearance from the brain toward the periphery since, following immunization, an increase in Tau concentrations was observed in blood. Overall, the present work is, to our knowledge, the first one to demonstrate that active immunotherapy targeting a real pathological epitope such as phospho-Ser422 epitope is efficient. This immunotherapy allows for Tau clearance and improves cognitive deficits promoted by Tau pathology in a well-defined Tau transgenic model.

Beneficial effects of exercise in a transgenic mouse model of Alzheimer's disease-like Tau pathology.

Tau pathology is encountered in many neurodegenerative disorders known as tauopathies, including Alzheimers disease. Physical activity is a lifestyle factor affecting processes crucial for memory and synaptic plasticity. Whether long-term voluntary exercise has an impact on Tau pathology and its pathophysiological consequences is currently unknown. To address this question, we investigated the effects of long-term voluntary exercise in the THY-Tau22 transgenic model of Alzheimers disease-like Tau pathology, characterized by the progressive development of Tau pathology, cholinergic alterations and subsequent memory impairments. Three-month-old THY-Tau22 mice and wild-type littermates were assigned to standard housing or housing supplemented with a running wheel. After 9 months of exercise, mice were evaluated for memory performance and examined for hippocampal Tau pathology, cholinergic defects, inflammation and genes related to cholesterol metabolism. Exercise prevented memory alterations in THY-Tau22 mice. This was accompanied by a decrease in hippocampal Tau pathology and a prevention of the loss of expression of choline acetyltransferase within the medial septum. Whereas the expression of most cholesterol-related genes remained unchanged in the hippocampus of running THY-Tau22 mice, we observed a significant upregulation in mRNA levels of NPC1 and NPC2, genes involved in cholesterol trafficking from the lysosomes. Our data support the view that long-term voluntary physical exercise is an effective strategy capable of mitigating Tau pathology and its pathophysiological consequences.

Phosphorylation of amyloid precursor carboxy-terminal fragments enhances their processing by a gamma-secretase-dependent mechanism

In Alzheimers disease, the complex catabolism of amyloid precursor protein (APP) leads to the production of amyloid-beta (Abeta) peptide, the major component of amyloid deposits. APP is cleaved by beta- and alpha-secretases to generate APP carboxy-terminal fragments (CTFs). Abeta peptide and amyloid intracellular domain are resulting from the cleavage of APP-CTFs by the gamma-secretase. In the present study, we hypothesize that post-translational modification of APP-CTFs could modulate their processing by the gamma-secretase. Inhibition of the gamma-secretase was shown to increase the total amount of APP-CTFs. Moreover, we showed that this increase was more marked among the phosphorylated variants and directly related to the activity of the gamma-secretase, as shown by kinetics analyses. Phosphorylated CTFs were shown to associate to presenilin 1, a major protein of the gamma-secretase complex. The phosphorylation of CTFs at the threonine 668 resulting of the c-Jun N-terminal kinase activation was shown to enhance their degradation by the gamma-secretase. Altogether, our results demonstrated that phosphorylated CTFs can be the substrates of the gamma-secretase and that an increase in the phosphorylation of APP-CTFs facilitates their processing by gamma-secretase.

From tau phosphorylation to tau aggregation: what about neuronal death?

Tau pathology is characterized by intracellular aggregates of abnormally and hyperphosphorylated tau proteins. It is encountered in many neurodegenerative disorders, but also in aging. These neurodegenerative disorders are referred to as tauopathies. Comparative biochemistry of the tau aggregates shows that they differ in both tau isoform phosphorylation and content, which enables a molecular classification of tauopathies. In conditions of dementia, NFD (neurofibrillary degeneration) severity is correlated to cognitive impairment and is often considered as neuronal death. Using tau animal models, analysis of the kinetics of tau phosphorylation, aggregation and neuronal death in parallel to electrophysiological and behavioural parameters indicates a disconnection between cognition deficits and neuronal cell death. Tau phosphorylation and aggregation are early events followed by cognitive impairment. Neuronal death is not observed before the oldest ages. A sequence of events may be the formation of toxic phosphorylated tau species, their aggregation, the formation of neurofibrillary tangles (from pre-tangles to ghost tangles) and finally neuronal cell death. This sequence will last from 15 to 25 years and one can ask whether the aggregation of toxic phosphorylated tau species is a protection against cell death. Apoptosis takes 24 h, but NFD lasts for 24 years to finally kill the neuron or rather to protect it for more than 20 years. Altogether, these data suggest that NFD is a transient state before neuronal death and that therapeutic interventions are possible at that stage.

Hippocampal tauopathy in tau transgenic mice coincides with impaired hippocampus-dependent learning and memory, and attenuated late-phase long-term depression of synaptic transmission.

We evaluated various forms of hippocampus-dependent learning and memory, and hippocampal synaptic plasticity in THY-Tau22 transgenic mice, a murine tauopathy model that expresses double-mutated 4-repeat human tau, and shows neuropathological tau hyperphosphorylation and aggregation throughout the brain. Focussing on hippocampus, immunohistochemical studies in aged THY-Tau22 mice revealed prominent hyper- and abnormal phosphorylation of tau in CA1 region, and an increase in glial fibrillary acidic protein (GFAP) in hippocampus, but without signs of neuronal loss. These mice displayed spatial, social, and contextual learning and memory defects that could not be reduced to subtle neuromotor disability. The behavioral defects coincided with changes in hippocampal synaptic functioning and plasticity as measured in paired-pulse and novel long-term depression protocols. These results indicate that hippocampal tauopathy without neuronal cell loss can impair neural and behavioral plasticity, and further show that transgenic mice, such as the THY-Tau22 strain, might be useful for preclinical research on tauopathy pathogenesis and possible treatment.

NMDA receptor dysfunction contributes to impaired brain-derived neurotrophic factor-induced facilitation of hippocampal synaptic transmission in a Tau transgenic model

While the spatiotemporal development of Tau pathology has been correlated with occurrence of cognitive deficits in Alzheimers patients, mechanisms underlying these deficits remain unclear. Both brain‐derived neurotrophic factor (BDNF) and its tyrosine kinase receptor TrkB play a critical role in hippocampus‐dependent synaptic plasticity and memory. When applied on hippocampal slices, BDNF is able to enhance AMPA receptor‐dependent hippocampal basal synaptic transmission through a mechanism involving TrkB and N‐methyl‐d‐Aspartate receptors (NMDAR). Using THY‐Tau22 transgenic mice, we demonstrated that hippocampal Tau pathology is associated with loss of synaptic enhancement normally induced by exogenous BDNF. This defective response was concomitant to significant memory impairments. We show here that loss of BDNF response was due to impaired NMDAR function. Indeed, we observed a significant reduction of NMDA‐induced field excitatory postsynaptic potential depression in the hippocampus of Tau mice together with a reduced phosphorylation of NR2B at the Y1472, known to be critical for NMDAR function. Interestingly, we found that both NR2B and Src, one of the NR2B main kinases, interact with Tau and are mislocalized to the insoluble protein fraction rich in pathological Tau species. Defective response to BDNF was thus likely related to abnormal interaction of Src and NR2B with Tau in THY‐Tau22 animals. These are the first data demonstrating a relationship between Tau pathology and synaptic effects of BDNF and supporting a contribution of defective BDNF response and impaired NMDAR function to the cognitive deficits associated with Tauopathies.

Early Tau pathology involving the septo-hippocampal pathway in a Tau transgenic model: relevance to Alzheimer's disease.

Alzheimers disease is a neurodegenerative disorder characterized by amyloid deposits and neurofibrillary tangles. Cholinergic dysfunction is also a main pathological feature of the disease. Nevertheless, the links between cholinergic dysfunction and neuropathological hallmarks of Alzheimers are still unknown. In the present study, we aimed to further investigate Tau aggregation in cholinergic systems, in a Tau transgenic mouse model. THY-Tau22 mice have recently been described as a novel model of Alzheimer-like Tau pathology without motor deficits. This strain presents an age-dependent development of Tau pathology leading to synaptic dysfunctions as well as learning and memory impairments. In the present work, we observed that Tau pathology differentially affects cerebral structures. Interestingly, early Tau pathology was observed in both hippocampus and basal forebrain. Moreover, some morphological as well as functional alterations of the septohippocampal pathway suggest a disconnection between these two key brain regions in Alzheimers disease. Finally, these data suggest that Tau pathology may participate in cholinergic degeneration.

Chloroquine and chloroquinoline derivatives as models for the design of modulators of amyloid Peptide precursor metabolism.

The amyloid precursor protein (APP) plays a central role in Alzheimers disease (AD). Preventing deregulated APP processing by inhibiting amyloidogenic processing of carboxy-terminal fragments (APP-CTFs), and reducing the toxic effect of amyloid beta (Aβ) peptides remain an effective therapeutic strategy. We report the design of piperazine-containing compounds derived from chloroquine structure and evaluation of their effects on APP metabolism and ability to modulate the processing of APP-CTF and the production of Aβ peptide. Compounds which retained alkaline properties and high affinity for acidic cell compartments were the most effective. The present study demonstrates that (1) the amino side chain of chloroquine can be efficiently substituted by a bis(alkylamino)piperazine chain, (2) the quinoline nucleus can be replaced by a benzyl or a benzimidazole moiety, and (3) pharmacomodulation of the chemical structure allows the redirection of APP metabolism toward a decrease of Aβ peptide release, and increased stability of APP-CTFs and amyloid intracellular fragment. Moreover, the benzimidazole compound 29 increases APP-CTFs in vivo and shows promising activity by the oral route. Together, this family of compounds retains a lysosomotropic activity which inhibits lysosome-related Aβ production, and is likely to be beneficial for therapeutic applications in AD.

P1-21 Mécanismes sous jacents à l’immunothérapie anti-Tau dans la maladie d’Alzheimer

Introduction La maladie d’Alzheimer est une maladie neurodegenerative qui affecte pres de 10% de la population de plus de 65 ans. Elle se caracterise par des depots amyloides et une degenerescence neurofibrillaire (DNF). Cette derniere lesion resulte de l’accumulation intraneuronale des proteines Tau hyper- et anormalement phosphorylees. Il n’existe, a ce jour, aucun traitement reellement efficace contre la DNF. L’immunotherapie a deja permis de reduire, chez des souris transgeniques, l’accumulation de proteines telles que la huntingtine ou encore l’α-synucleine ; mais est-ce que cette approche d’immunotherapie serait capable de cibler Tau qui est une proteine neuronale ? Une premiere etude qui a consiste a injecter dans le cerveau de notre modele murin de DNF type Alzheimer (THY-Tau22) un anticorps anti-Tau nous a permis de valider le passage de l’anticorps dans le compartiment intraneuronal. Ainsi, une immunisation active est realisable dans notre lignee THY-Tau22. Materiel et methode Des souris THY-Tau22 et “littermates”, âgees de 3 mois, ont ete vaccinees avec un peptide contenant un site pathologique de la proteine Tau ou avec du PBS pendant 3 mois. La reponse immunitaire a ete evaluee par ELISA. Des etudes immunohistochimiques sur la pathologie Tau ont ete realisees. Resultats Les souris THY-Tau22 vaccinees avec le peptide produisent des anticorps anti-phospho-Tau. L’analyse immunohistochimique des neurones en DNF montre une tendance a la reduction chez les souris vaccinees avec le peptide. Conclusion A ce jour, les resultats preliminaires montrent qu’une approche d’immunisation active ciblant la proteine Tau intraneuronale tend a reduire la DNF dans notre lignee THY-Tau22.

P1-20 Effets de l’exercice volontaire à long terme dans un modèle de souris transgénique THY-Tau22 développant une pathologie Tau similaire à celle observée dans la maladie d’Alzheimer

Introduction La maladie d’Alzheimer est une maladie neurodegenerative caracterisee par des depots amyloides et une degenerescence neurofibrillaire (DNF). Cette derniere est constituee d’agregats de proteines Tau hyper- et anormalement phosphorylees et sa progression est correlee avec celle des deficits cognitifs. Afin de modeliser la pathologie Tau, nous avons genere un nouveau modele de souris transgenique Tau (THY-Tau22) dans lequel nous testons certains paradigmes. Ainsi, l’activite physique previent le declin cognitif et retarde le debut des demences. Materiels et methodes La lignee Thy-Tau22 a ete caracterisee dans une cinetique d’un point de vue comportemental (Y maze). Des etudes immunohistochimiques sur la pathologie Tau et le systeme cholinergique ont ete realisees. Des souris THY-Tau22 et “littermates” âgees de 3 mois ont ete soumises a l’exercice volontaire ad libitum durant 9 mois. Les memes etudes ont ensuite ete realisees. Resultats Dans les Thy-Tau22, la DNF se developpe progressivement dans l’hippocampe A l’âge de 12 mois, les souris THYTau22 presentent une pathologie Tau septo-hippocampique accompagnee par une alteration du transport retrograde au sein de ce tractus. Une perte des neurones cholinergiques est egalement observee. Nous avons evalue les effets de l’exercice volontaire dans notre lignee THY-Tau22. Apres cette periode d’exercice, nous avons observe, par le test du Y-maze, que les souris THY-Tau22 ayant acces a une roue presentaient une amelioration mnesique significative par rapport aux souris THY-Tau22 ne pratiquant pas d’exercice. Cette amelioration de la memoire est accompagnee d’une forte augmentation des niveaux de BDNF hippocampique suggerant que ce facteur puisse jouer un role important. De plus, la perte des neurones cholinergiques observee chez les souris THY-Tau22 est prevenue par l’exercice volontaire. L’analyse de l’agregation de la proteine Tau chez les souris THY-Tau22 sera presentee. Conclusions Dans l’ensemble, nos resultats montrent que l’exercice physique a long terme est capable d’ameliorer les deficits cognitifs engendres par la pathologie Tau et suggerant un effet benefique potentiel dans la maladie d’Alzheimer ainsi que dans les autres Tauopathies. Ce travail a beneficie du support du CNRS, Inserm, Region Nord/Pas-de-Calais, Univ. Lille2, CHU-Lille, Communaute Europeenne (FP7 MEMOSAD) et ANR (ADONTAGE et AMYTOXTAU).