Maladie neurodégénérative | EPFL Graph Search

Les maladies neurodégénératives, telles que la maladie d'Alzheimer, la maladie à corps de Lewy, la maladie de Parkinson, la maladie de Huntington, l'atrophie corticale postérieure ou encore la sclérose latérale amyotrophique sont des maladies chroniques invalidantes à évolution lente et discrète. Elles provoquent généralement une détérioration du fonctionnement des cellules nerveuses, en particulier les neurones, pouvant conduire à la mort cellulaire (ou neurodégénérescence). Les troubles induits par les maladies neurodégénératives sont variés et peuvent être d'ordre cognitivo-comportemental, sensoriel et moteur. En France en 2014, les maladies neurodégénératives touchent plus d'un million de personnes et ont donné lieu à différents plans dont le plan maladies neuro-dégénératives 2014-2019. En Europe, un important programme de recherches sur ces maladies est également en place. Au fur et à mesure que la recherche progresse, de nombreuses similitudes apparaissent reliant ces maladies

Role of the FoxO3a Transcription Factor in alpha-synuclein Induced Neurodegeneration

Emilda Pino

Increased expression of α-synuclein and point mutations in its amino acid sequence play a causative role in familial forms of Parkinson's disease (PD). In addition, circumstances affecting the level of α-synuclein expression significantly increase the risk of developing sporadic PD. This is further corroborated by the abundance of α-synuclein in protein aggregates called Lewy bodies (LBs), a histological hallmark of the disease. Aging constitutes the most prominent risk factor in the pathogenesis of PD and other synucleinopathies. Protective stress response and repair pathways gradually decline over time, a process likely to contribute to the appearance of neurodegenerative disease. Studies in lower organisms, such as the yeast and the worm Caenorhabditis elegans, have highlighted the role of the evolutionarily conserved transcription factor FoxO3a in the aging process, increasing life span and reducing molecular processes that possibly underlie neurodegeneration in higher organisms. This transcription factor is mainly controlled by insulin/Insulin-like growth factor (IGF) signaling (IIS) and impacts a broad range of disease-related responses involving neuronal apoptosis and adaptation to stress. We have hypothesized that FoxO3a activity may regulate the response of dopaminergic neurons to PD-related stress such as reactive oxygen species (ROS) and α-synuclein proteotoxicity. To address this question, AAV2/6 vectors encoding various forms of FoxO3a were used to modulate the activity of this transcription factor in the adult rat substantia nigra pars compacta (SNpc). We determined a viral dose where expression of the wild-type form of FoxO3a did not impair the survival of nigral neurons and their striatal projections. In contrast, a constitutively active FoxO3a mutant (FoxOm), with an Akt-independent nuclear import, led to a significant loss of dopaminergic cell bodies, consistent with the pro-apoptotic activity of FoxO3a. Expression of a dominant-negative competitor composed of the FoxO DNA-binding domain (FoxODBD) did not significantly impair the survival of nigral neurons. However, at a high viral dose, FoxO inhibition led to neuronal accumulation of 4-hydroxynonenal (HNE), an indicator of chronic oxidative stress, and to a loss of neurons positive for dopaminergic markers. Altogether, these results confirm in nigral neurons the critical role of FoxO3a activity at the intersection between apoptotic response and neuronal resistance to oxidative stress. Next, we hypothesized that FoxO3a may regulate the response of dopaminergic neurons to α-synuclein proteotoxicity. To investigate the effect of FoxO3a on α-synuclein accumulation, we co-injected AAV2/6 vectors modulating FoxO3a activity with a wild-type human α-synuclein vector. When compared to control and FoxOm, both wild-type FoxO3a and FoxODBD significantly reduced the α-synuclein-induced loss of neurons positive for dopaminergic markers. Importantly, the injection of vectors activating FoxO3a (wild-type and FoxOm) led to an overall reduction in soluble α-synuclein monomeric forms, concomitant with the formation of dense proteinase K-resistant aggregates found in the neuronal cell soma. With the dominant negative FoxODBD, we observed an accumulation of α-synuclein, with a diffuse distribution of proteinase K-resistant immunoreactivity in both axon and neuronal soma. These data point to FoxO3a as an important regulator of neuronal survival in the SNpc, which can oppose α-synuclein accumulation and proteotoxicity. The role of FoxO3a in α-synuclein toxicity may provide some clues about the role of the aging process in PD neurodegeneration.

EPFL2012

A viral vector based in vivo model of tauopathy to explore therapeutic strategies against tau pathology

Sameer Mohammad Khaleel Nazeeruddin

Tauopathies are neurodegenerative diseases whose common pathological feature is the intraneuronal accumulation of tau aggregates. Tau protein has various roles in the neuron, among which stabilization of microtubules (MT), regulation of synaptic activity or axonal transport. Subsequently, tau pathology exerts toxicity through mechanisms that likely involve the loss of normal function or the gain of toxic functions. In tauopathies, tau undergoes post-translational modifications (PTM), which are thought to promote the detachment from the MT, change its subcellular localization, and induce conformational changes that favor its assembly with other tau monomers, forming oligomers and fibrils. Furthermore, both normal and pathological forms of tau can be transferred from neuron to neuron. This process may have an important role in disease progression, by propagating the pathology along synaptically connected brain regions, which reflects the evolution of the symptoms. Therefore, the aggregation of tau protein and its propagation are promising targets for potential treatments. In the present thesis, our objective was to assess the efficacy of two treatments using a mouse model of tauopathy based on local overexpression of the 4R0N human tau (hTau) wild-type (WT) induced by intracerebral injection of an adeno-associated viral (AAV) vector. In the first part of the thesis, we overexpressed tau in the entorhinal cortex (EC) of WT mice to induce pathology and assess the effects of aggregation inhibitor compounds orally administered. Although we did not observe any effect on markers of tau aggregation, likely because the induced pathology was still at an early stage, the treatment was found to enhance phosphorylation of the Ser202/Thr205 residues in the EC and ipsilateral hippocampus (HPC). Additionally, we measured an increase in the density of microglial cells in the HPC, and significantly decreased levels of total hTau in the cerebrospinal fluid of the treated mice. These findings suggest a potential positive effect of this treatment on the clearance of hTau. In the second part of the thesis, we unilaterally overexpressed hTau in the mouse CA3 HPC and used the connectivity between both hemispheres to quantify the propagation of tau from neuron-to-neuron to the contralateral HPC. We found neurons labelled for hTau in the contralateral HPC, the number of which was increased in 5xFAD mice carrying the amyloid pathology. Next, to induce an antibody response against pathological tau, we subcutaneously injected a vaccine against the phospho-Ser396/404 tau epitope. The vaccine induced a potent antibody response in WT mice, but antibody titers remained low in the 5xFAD mice. In the treated WT mice, immunohistochemistry showed a decreased PHF-1 immunoreactivity in the HPC, indicating that the generated antibodies indeed recognized the phospho-Ser396/404 epitope. Remarkably, the vaccine decreased the number of neurons positive for hTau in the contralateral HPC, suggesting an effect of immunotherapy on tau propagation. Furthermore, the vaccine also showed potential neuroprotective effects, by decreasing the level of neurodegeneration in the dentate gyrus of treated mice as a function of the anti-phospho-tau antibody titer. In this work, using adapted AAV8-based models of local tau overexpression in the mouse brain, we reveal the effects of two treatments on different aspects of tau pathology related to the progression of the symptoms in tauopathies.

EPFL2019

Motor Deficits upon Alpha-Synuclein Expression in the Nigrostriatal System Are Due to a Loss of Dopaminergic Vesicles and Reduced Dopamine Release at an early Stage of Neurodegeneration

Meret Gaugler

Alpha-synuclein is linked to both sporadic and familial forms of Parkinson's disease. The protein represents the major component of Lewy bodies – one of the hallmarks of the disease. Additionally, several point mutations and locus multiplications in the gene for α-synuclein lead to familial parkinsonism. Interestingly, in conditions of a hereditary excess of wild-type protein, the difference in clinical severity between duplication and triplication carriers seems to suggest a direct relation to gene dosage. In the adult brain, where the protein is highly expressed, α-synuclein is thought to participate in regulating multiple crucial cellular functions related to neurotransmission. While the clinical motor symtoms of Parkinson's disease are usually attributed to a massive cell loss in the substantia nigra, we investigate how a pathogenic overabundance of wild-type α-synuclein can lead to parkinsonian symptoms as a direct result of a perturbation in its normal endogenous functions, and before an overt lesion. We show that mild overexpression of wild-type α-synuclein in the rat substantia nigra induces motor behavior attributable to disturbances in dopamine transmission, concomitant with early neurodegenerative events. Importantly, these changes are tied to the membrane association of α-synuclein, as they fail to appear upon overexpression of the binding-deficient A30P mutant. Moreover, we correlate behavioral deficits with a reduction of dopaminergic vesicles in nigrostriatal axons – showing ultrastructurally how overexpressed α-synuclein leads to deficits in neurotransmission. We demonstrate that impaired dopaminergic function can lead to Parkinson-related symtoms at an early stage of degeneration, and might indeed represent a primary step towards the demise of nigral neurons.

EPFL2010