PROJECTS SUPPORTED FOR 2011
You can read the descriptions and results of each research project on Alzheimer’s disease funded by Fondation Vaincre Alzheimer.
Dr Faraj TERRO
Faculté de Médecine, Université de Limoges – Limoges
PP2A, Tau interaction with MAP1-LC3 and autophagy
SUMMARY OF PROPOSED RESEARCH
Objectives : To study the role of Tau in PP2A-dependent control of neuronal autophagy.
Hypothesis : We previously demonstrated that inactivation of protein phosphatase 2A (PP2A) inhibited autophagy in cultured neurons, resulted in intraneuronal accumulation of ubiquitinated proteins and altered the distribution of MAP1-LC3-I (LC3-I) between soluble and bound fractions (submitted for publication in Neurobiology of Aging). Moreover, our preliminary data demonstrated that Tau and LC3co-immunoprecipitate and this co-immunoprecipitation is lost when PP2A was inhibited by okadaic acid (OKA). Since, PP2A is the major Tau phosphatase in the brain, we hypothesize that Tau and LC3 directly interact and this interaction is phosphorylation-dependent and could play an important role in the regulation of neuronal autophagy. We also speculate that LC3 might be a PP2A substrate and LC3 phosphorylation might, by itself, alters LC3-I distribution and its activity in autophagy.
Specific aims : 1- To determine whether PP2A-dependent regulation of autophagy involves Tau and what is the role of Tau hyperphosphorylation and microtubule (MT) dynamics in PP2A-mediated regulation of autophagy? 2- To determine whether LC3 is a PP2A substrate and, if it is the case, to identify LC3 phosphorylation site(s) involved and what is the impact of LC3 phosphorylation on its functions in autophagy? 3- To determine whether Tau readily interacts directly with LC3-I and if it is the case to determine which domain(s) of LC3-I is (are) responsible for this interaction? we will dissect the role of LC3-I (and not Tau) domains because LC3-I is a small and less complex protein (121 aa) compared to Tau (441 aa for the longest human Tau isoform).
Experimental design and methods :
Aim 1: autophagy will be analyzed in cultured neurons from Tau-/, Tau+/- or Tau+/+ brains from mouse-embryos. The impact of Tau phosphorylation on autophagy will be assessed using Tau kinase inhibitors. The role of MT dynamics in autophagy will be determined using MT toxins (taxol, nocodazole or vinblastine). Aim 2. LC3 phosphorylation will be analyzed by 32P incorporation assay coupled to LC3 immunoprecipitation. Directed mutagenesis will enable to determine which phospho-LC3 site(s) is (are) involved in LC3 function in autophagy. Aim 3. Full length LC3construct, at least three LC3 constructs (which express N-ter, middle or C-ter parts of LC3-I) as well as a full-length Tau constructs will be generated and tested for interaction in yeast two-hybrid system and, by pull-down assay, in cell line co-expressing V5- or HA- tagged Tau and LC3 fragments for confirmation.
RELEVANCE OF PROPOSED RESEARCH TO ALZHEIMER’S DISEASE
This work can be relevant to Alzheirmer’s disease (AD), since it will provide possible links between pathological features of AD including PP2A downregulation, autophagy disruption and protein aggregation and Tau pathology. It will reveals a possible new role of Tau as a regulator of autophagy.
Autophagy constitutes a neuroprotection mechanism and has been shown to be downregulated in AD.
Therefore, down regulation of neuronal autophagy by the inhibition of PP2A may represents a model for intraneuronal protein aggregations and enhanced neuronal vulnerability to neurondegeneration. This model is useful for testing the drug ability to clear (through autophagy induction) protein aggregates and to protect neurons.
Publications :
November 1st, 2011 – October 31th, 2013 (2 years)
80 000€
Dr Frédéric CHECLER
CNRS, Institut de Pharmacologie Moléculaire et Cellulaire – Valbonne
Determinants of gamma-secretase neuronal trafficking
SUMMARY OF PROPOSED RESEARCH
g-secretase catalyses the final cleavage of the precursor protein APP into amyloid peptide (Aβ), the main component of senile plaques found in the brain of people affected by Alzheimer’s disease (AD). Four integral membrane proteins, presenilin (PS), nicastrin, APH1 and PEN2 are required and sufficient to achieve g-secretase activity. g-secretase localization in neurons is only partially characterized and the dynamic of g-secretase neuronal trafficking in response to physiological stimuli is still unknown. Additionally, APH1 is encoded by two genes in human that can be alternatively spliced. Also several g-secretase sub-complexes differing by their APH1 contents were identified and could co-exist within a cell. Whether these distinct sub-complexes reach similar or distinct subcellular neuronal compartments and how this process is regulated remains unknown.
The objective of this proposal is to determine using fluorescence microscopy and cultured hippocampal neurons where functional g-secretase is localized in neurons, if the complex is targeted to synapses depending on neuronal activity and the dynamic aspects of this trafficking. The first aim of this project is to identify the precise neuronal compartments where functional g-secretase is assembled and targeted and if neuronal activity modulates g-secretase trafficking. The second aim of this project is to characterized the molecular determinants required for g-secretase targeting to its neuronal locations (identified in aim 1), and in particular to determine if variants of APH1 (APH1aL, aS, b) affect g-secretase trafficking. Overall, this work should clarify where and how Aβ can be produced in neurons.
For the first aim of the project, we propose to generate nicastrin and PEN2 constructs labeled with fluorescent proteins that can be imaged simultaneously (e.g. GFP and mCherry) and will be transfected in hippocampal neurons in culture that will be processed for immunocytochemistry using several markers of neuronal compartments (axon, dendrites, pre-, postsynapses). These constructs will also be used to study the dynamic of g-secretase neuronal trafficking by live-imaging.
For the second aim of this project, we hypothesize that different APH1 isoforms interact with specific cytosolic partners that will affect APH1 and g-secretase subcellular trafficking and localization. Using the experimental approaches described for aim 1, we will determine if APH1 isoforms can affect g-secretase subcellular localization.
RELEVANCE OF PROPOSED RESEARCH TO ALZHEIMER’S DISEASE
The amyloid peptides (Aβ) are considered to play a central role in the pathogenesis of Alzheimer’s disease. In particular oligomers of these peptides were shown to alter synaptic plasticity and cognitive functions. Amyloid peptides were shown to be released from synapses and Aβ oligomers are able to bind synaptic sites. However, little is known about the neuronal localizations of the enzymes generating Aβ from the cleavages of its precursor protein APP. The goal of this proposal is to precisely identify the subcellular neuronal compartments where the g-secretase complex, that performs the last cut releasing Aβ, is targeted and determine the pathways and molecular determinants required for the trafficking of the complex to these locations. These information are crucial for a better understanding of Alzheimer’s disease pathogenesis as it should clarify where and how Aβ can be produced in neurons.
November 1st, 2011 – October 31th, 2013 (2 years)
80 000€
Dr Benoît DELATOUR
CNRS, Centre de Recherche de l’Institut du Cerveau et de la Moelle Epinière – Paris
Abeta oligomers in AD
SUMMARY OF PROPOSED RESEARCH
The amyloid cascade is still the predominant hypothesis of Alzheimer’s disease (AD) physiopathogeny. The identification of soluble oligomeric Aβ assemblies in promoting neuro- and synaptotoxicity and the association of these Aβ species with the onset and progression of cognitive disorders, has led to new conjecture and improvement of the amyloid cascade model.
The core of our research project will be the elucidation of the exact role of Aβ oligomers in AD. Our strategy will rely on the use of a multidisciplinary-transversal approach applied to different tissues (brain banks: AD brains, mouse models: transgenic APPxPS1 mice and mice brain-injected with Aβ oligomers). This will allow us to answer to two main questions:
(1) What is the topography of oligomeric species in the brain and how does this topography evolve with disease progression? We will use an immunohistochemical approach using validated conformational anti-Aβ antibodies to detect oligomers in brain sections. By using in vivo bi-photon microscopy we will concurrently analyze the diffusion of synthetic oligomers (coupled to a fluorochrome) after topic injections in the brain.
(2) What is the real in vivo toxicity of Aβ oligomers? In vitro data strongly suggest that oligomers induce synaptotoxic effects. We will confirm this in human and transgenic mouse by studying the colocalization of oligomers and synaptic markers in brain sections. To complement these postmortem studies we will use an interventionist approach to elucidate the effects of brain-injected oligomers on synaptic densities. We will determine the mechanisms of oligomers’ in vivo toxicity (direct or microglia-mediated?). The precise kinetic of oligomers toxicity will be documented by ex vivo analysis and by in vivo bi-photon imaging in Thy1-YFP mice injected with tagged oligomers. Finally the toxicity of Aβ oligomers will be appreciated in Aβ cerebro-injected animals through a) in vivo mapping of brain connectivity (MEMRI technique) and b) the cognitive assessment and evaluation of evoked neuronal activity (immediate early genes mapping).
To conclude, this research project will allow to better understand the in vivo role of Aβ oligomers in AD (and their participation to the amyloid cascade), at the earliest stage of the disease which is the optimal time window for efficient therapeutic intervention.
RELEVANCE OF PROPOSED RESEARCH TO ALZHEIMER’S DISEASE
Amyloid plaques are present in the brain of age non-demented people. The density of plaques is not associated with cognitive impairments and, up to now, their clearance in the brain of AD subjects has not been proved to lead to significant clinical effects. It remains clear that Aβ deposition is a pivotal event in the course of AD but it is becoming urgent to re-orient research efforts towards extra-plaques topographies and fibrillar conformations of the amyloid peptides. From a decade it has emerged that Aβ small assemblies could be particularly toxic, an assumption mainly derived from in vitro studies and that we propose to confirm and refine in vivo. Results will undoubtedly allow to gain access to new targets for both in vivo diagnosis and therapeutic intervention.
November 1st, 2011 – October 31th, 2013 (2 years)
80 000€
Dr David BLUM
INSERM, Centre de recherche J.P. Aubert – Lille
A2A receptor blockade in a Tau transgenic model
SUMMARY OF PROPOSED RESEARCH
Caffeine is the most widely consumed psychoactive compound. Epidemiological studies support that habitual caffeine consumption is associated with better cognitive performance at higher ages and even reduces risk for AD. Experimental studies support that caffeine prevents and reverses memory impairments and amyloid load in a model of the amyloid side of AD. Protective effect of caffeine towards β-amyloid toxicity seems mediated through blockade of adenosine A2A receptors (A2AR). However, whether blockade of A2AR impacts on the Tau side of AD has remained unknown so far. We have developed a transgenic mouse model (THY-Tau22) over-expressing mutated human Tau protein and exhibiting progressive hippocampal Tau pathology paralleling learning, memory and synaptic alterations and hippocampal inflammation. We observed that a preventive chronic treatment with caffeine reduces Tau phosphorylation in this model. Further, genetic invalidation of the A2AR leads to similar effect on Tau and reduces hippocampal inflammation as well as memory impairments. Thus, preventive blockade of A2AR can alleviate Tau pathology and associated deficits. In a therapeutical perspective, we now aim to evaluate whether pharmacological blockade of A2AR using caffeine and specific antagonists mitigate Tau pathology and/or associated inflammation and ultimately cognitive alterations in already altered Tau trangenic mice. We will use MSX-3 or MSX-4, prodrugs of the potent and highly selective A2AR antagonist MSX-2. We will first realize bio-avaibility studies of these compounds and caffeine in control mice to assess (i) side-effects after chronic peroral administration and (ii) plasma/organ/brain distributions using LCMS measurements as well as determine occupation of brain A2A receptors by ex-vivo radioligand binding studies. Then, we will orally and chronically administer caffeine or the chosen A2A receptor antagonist for two months to strongly altered THY-Tau22 mice (i.e. 7m of age) and evaluate outcome on Tau (Tau phosphorylation/solubility), hippocampal inflammation (qPCR, ELISA) and motor/cognitive abilities (Open field, Y-maze and Morris Water Maze). In addition, we will provide a microarray evaluation to uncover potential underlying mechanisms. Finally, we will correlate these changes with the plasma levels of the drugs and their degradation products. This pre-clinical collaborative project will thus give a proof-of-concept to use caffeine and/or specific A2AR antagonists as a therapy in AD and also to unravel possible molecular targets. Encouraging results will be unvaluable to give a basis for future clinical trials.
RELEVANCE OF PROPOSED RESEARCH TO ALZHEIMER’S DISEASE
Epidemiological and experimental studies indicate that caffeine, a non-selective adenosine receptor antagonist, may be protective in AD, particularly against amyloid toxicity, an effect ascribed to the blockade of A2A receptors. Our preliminary data support that caffeine and specific A2A receptor blockade are beneficial in a Tau transgenic mouse model. In a therapeutical perspective it is however mandatory to evaluate whether these compounds are also beneficial after disease onset. Importantly, caffeine is considered as a safe compound and A2A receptor antagonists are already clinically tested in Parkinson’s disease patients with good safety. The proof-of-concept studies proposed in the present project are thus important to go for pilot subsequent tolerability studies and clinical trials in AD patients in a reasonable time frame.
Publications :
November 1st, 2011 – October 31th, 2013 (2 years)
