FOXO3 est un facteur de transcription important pour la réponse au stress, la régulation de la différenciation et de la survie cellulaires qui a des effets neuroprotecteurs dans plusieurs modèles de maladies neurodégénératives, dont la maladie de Huntington (MH). Les effets neuroprotecteurs de FOXO3 sont réprimés dans la MH par une activité anormale de Ryk, un récepteur Wnt important pour la neurogenèse, par la liaison du domaine intracellulaire de Ryk à la ?-caténine, un co-facteur de FOXO3. L'objectif principal de ce travail est d'étudier les effets de la huntingtine mutée (mHTT) sur le répertoire des cibles directes humaines de FOXO3 à l'aide d'un modèle des phases développementales de la MH, à savoir des cellules souches neurales isogéniques issues de cellules souches pluripotentes induites. En formant un complexe tripartite avec la ?-caténine et FOXO3, Ryk agit comme un co-régulateur de FOXO3 en conditions normales ou pathologiques. L'analyse des cibles directes de FOXO3 montre une reprogrammation de ces cibles avec des pertes et des gains dans des voies de signalisation qui sont connues pour leur rôle dans la MH, notamment les voies de régulation de la prolifération cellulaire. Ces résultats montrent que la régulation des gènes par FOXO3 est fortement modifiée dans les cellules qui expriment la mHTT. Cela ouvre la voie à l'étude des mécanismes d'homéostase cellulaire sous contrôle de FOXO3 dans les neurones en différenciation et leur impact sur l'activité des neurones adultes. Plus largement, ces résultats permettent de mieux comprendre la dynamique moléculaire de la MH et les effets de reprogrammation moléculaire sur la différenciation et l'activité neuronale. / FOXO3 is an important transcription factor for stress response, the regulation of differentiation and cell survival that has neuroprotective effects in several models of neurodegenerative diseases, including Huntington’s disease (HD). The neuroprotective effects of FOXO3 in HD are repressed by abnormal signaling from the Wnt receptor Ryk by the binding of the intracellular domain of Ryk to the β-catenin, a cofactor of FOXO3.The aim of this work was to explore the effect of the mutant huntingtin (mHTT) on the repertoire of direct FOXO3 targets (F3Ts) using a model of developmental stage of HD, namely HD isogenic neural stem cells derived from Huntington’s Induced Pluripotent Stem cells. Forming a tripartite complex with β-catenin and FOXO3, Ryk acts as a co-regulator of FOXO3 in normal or pathological condition. Analysis of direct FOXO3 targets shows reprogramming of these targets with losses and gains in signaling pathways that are known to role in HD, including regulatory pathways of cell proliferation. These results show that gene regulation by FOXO3 is heavily modified in cells expressing the mutant huntingtin. Our findings open the way for a comprehensive study of cellular homeostasis mechanisms under the control of FOXO3 in neural differentiation and their impact on the activity of adult neurons. More broadly, these results provide insight into the molecular dynamics of MH and the effects of molecular reprogramming in differentiation and neuronal activity.

Les astrocytes deviennent réactifs dans les maladies neurodégénératives (MND) comme la maladie d’Alzheimer (MA) et de Huntington (MH) mais les conséquences fonctionnelles de cette réactivité sont peu connues. Dans cette étude, nous avons évalué 1) les voies de signalisation impliquées dans la réactivité astrocytaire, 2) la contribution des astrocyte réactifs (AR) à la dysfonction neuronale dans des modèles de MND et 3) les caractéristiques fonctionnelles des AR.Nous avons montré que la voie JAK2/STAT3 est responsable de la réactivité astrocytaire dans des modèles murins de la MA et la MH. Nous avons développé de nouveaux vecteurs viraux ciblant cette voie dans les astrocytes, in vivo. Grâce à ces outils, nous avons étudié la contribution des AR à la dysfonction neuronale dans deux modèles murins de la MH. Nos résultats suggèrent que les AR ne jouent pas un rôle central dans ces modèles de pathologie. En ciblant la voie JAK2/STAT3, nous avons induit la réactivité astrocytaire chez la souris sauvage et avons montré que cette voie régule la transcription de gènes impliqués dans des fonctions cellulaires importantes. De plus, nous avons observé que l’activation des astrocytes conduit à une diminution de la plasticité synaptique dans le cerveau de souris.En conclusion, nous avons montré que la voie JAK2/STAT3 est une voie centrale dans les AR. Nous avons développé des vecteurs viraux innovants pour évaluer 1) la contribution des AR à la dysfonction neuronale dans des modèles de MND et 2) les propriétés fonctionnelles des AR in vivo. L’étude des AR permettra d’identifier de nouvelles cibles moléculaires pour manipuler ces cellules pléiotropes à des fins thérapeutiques. / Astrocyte reactivity is a hallmark of pathological conditions in the CNS including neurodegenerative diseases (ND) such as Alzheimer’s (AD) and Huntington’s (HD) diseases. Reactive astrocytes (RA) are identified by morphological changes but their functional features and influence on neurons are poorly understood, especially in ND. Therefore, we aimed at 1) identifying the signaling cascades involved in astrocyte reactivity in ND, 2) evaluating RA contribution to disease phenotype in ND models and 3) deciphering RA functional features. The JAK2/STAT3 pathway is a known trigger of astrocyte reactivity in CNS injuries. Here, we show that this pathway is a common inducer of astrocyte reactivity in AD and HD models. We developed new viral vectors to target this cascade in astrocytes and manipulate astrocyte reactivity in vivo. We used these vectors to determine the contribution of RA to neuronal dysfunction in HD mouse models. We found that RA do not primarily influence disease phenotype in HD. Last, we targeted the JAK2/STAT3 pathway in WT mice to characterize RA functional features in vivo. We show RA undergo transcriptional changes of numerous genes involved in metabolism, protein degradation pathways and immune response. Moreover, we show that astrocyte reactivity alters synaptic plasticity in the mouse hippocampus. Our results identify the JAK2/STAT3 pathway as a central cascade for astrocyte reactivity. The viral vectors developed in this project represent powerful tools to decipher the roles of RA in various ND models and to characterize RA functional features in vivo. Better understanding RA functions may lead to the identification of new therapeutic targets for ND.

Huntington's disease (HD) belongs to neurodegenerative disorders. It is a monogenic disease caused by trinucleotic CAG expansion in exon 1 of gene coding protein huntingtin. Even though the cause of HD is known since 1993, the pathophysiology and cure for HD reminds to be found. The animal models are being used for better understanding of HD. The most common animal models for HD are rodents, especially mice but it was also important to create large animal models, which will be more like human. Therefore, TgHD minipig was created in Academic of Science in Liběchov in 2009. This model was created by microinjection of lentiviral vector carrying N-terminal part of human HTT with 124 repetitive CAG in exon 1. This model is viable and in every generation, is part of the offspring transgenic. In this thesis, I specialized to biochemical and behavioral changes of this model. I compared transgenic and wild type siblings. I found that biochemical changes are manifested mostly by increased level of mtHtt fragments in testes and brain. In behavioral part of this thesis I established new methods for testing behavioral changes in this model. The introduced methods showed some changes between wild type and transgenic animals at the tested ages but these changes were not significant due to the low number of...

Huntington's disease (HD) is inherited fatal disorder caused by CAG triplet expansions in the huntingtin gene resulting in the expression of mutated huntingtin protein (mtHtt). The main symptoms of HD are neurodegeneration, osteoporosis, testicular degeneration, loss of muscle tissue and heart muscle malfunction, weight loss, metabolic changes, and sleeping disturbances. Since huntingtin protein (Htt) has a role in several biological processes, many molecular mechanisms, like oxidative stress, mitochondrial dysfunction, DNA-damage, and others, are affected by mtHtt. However, its exact pathogenic mechanisms in HD are still not well understood. Transgenic minipig model of HD (TgHD) serves an opportunity to isolate unlimited number of primary cells and unlike primary cells obtained from HD patients, often in the late stages of the disease, the TgHD minipig model allows to monitor molecular changes occurring gradually with age and progression of the disease. Thus, TgHD minipig model and primary cells isolated from it play an important role in investigating and understanding the underlying mechanistic cause of HD. We focused on molecular and cellular changes in primary cells isolated from TgHD minipigs and their wild type (WT) controls at different ages (24, 36, and 48 months). In mesenchymal stem cells...

Huntington's disease is a dominantly-inherited autosomal neurodegenerative disease manifested by disorders of motility, cognitive function, behaviour, and weight loss, which is conditioned multifactorially. The aim of the study was to determine whether there are eating disorders in Huntington's disease, as well as its etiology and severity. Neurological scaling, anthropometric examinations, evaluation of three-day diet records, measurements with a manual dynamometer, bioimpedance analyses, indirect colorimetry and predictions of energy expenditure were performed on 10 patients. Algorithms were applied for the diagnosis of sarcopenia and malnutrition. Unwanted weight loss was observed in all patients and 4 out of 10 showed malnutrition. No difference was found between the values of measured resting metabolism and calculated according to the predictive equation. However, it has been shown that strict nutritional recommendations based on this data can be misleading for some patients with HN, as real energy consumption can be significantly higher. All our patients had a positive energy balance. A new diagnostic algorithm for the early diagnosis of sarcopenia has proven its worth. Using bioimpedance analysis and examination of the force of the handshake, we identified possible sarcopenia and already-present...

Huntington’s disease (HD) is an autosomal dominant inherited neurodegenerative disease that specifically affects the striatum of the human brain. HD is characterized by a chorea-like movement disorder, cognitive decline, and psychiatric symptoms. In Europe, it has a relatively high prevalence of about 2.17-7.33 per 100,000 people compared with other continents. By far, there is no cure for HD. The mean survival time of patients after the diagnosis of HD is 15 to 20 years. Although the mutant form of the Huntingtin (HTT) as the cause of HD has been confirmed for decades, the exact pathogenesis of HD is still elusive. More recently, large global genome-wide association studies (GWAS) and several other studies provided new insights for HD mechanism, by highlighting several genes involved in DNA damage repair mechanisms as modifiers of age at onset and disease severity in HD. Thus, this project focused on the investigation of DNA damage response and repair in HD in vitro models. Fused in sarcoma (FUS) was the protein of our interest, as it has been confirmed to participate in DNA damage response and repair in multiple ways. Furthermore, FUS protein was implicated to have a relationship with neurodegenerative diseases, as it was found to play a role in the pathogenesis of subtypes of amyotrophic lateral sclerosis and frontotemporal dementia. FUS was also found to co-localize with mutant huntingtin protein in intracellular aggregates in HD mice models. In this project, donor/patient-specific induced pluripotent cells (iPSCs) and its derived striatal neurons were the main materials. By immunofluorescence staining approach of γH2AX and 53BP1, DNA double-strand breaks (DSBs) damage was investigated on iPSCs-derived in vitro striatal neurons. HD neurons showed an obvious and excessive accumulation of DNA DSBs damage. Then, in order to visualize FUS protein during DNA damage response procedure, eGFP tagged endogenous wild-type FUS iPSCs were generated, and later were differentiated into striatal neurons. UVA laser micro-irradiation was applied onto both hiPSCs and their differentiated striatal neurons in vitro models, simultaneously conducting with live-cell imaging approach. FUS was found to recruit to the DNA damage site induced by laser irradiation. For studying the kinetics of wild-type FUS protein during the response to laser irradiation, a novel and robust workflow was generated. By this workflow, the kinetics of FUS protein was characterized into four phases and a real-time scale of the kinetics was offered. After comparisons, a prominent change of FUS kinetics in HD at neuron-stage but not iPSC-stage was found. Furthermore, an intriguing different performance of FUS protein was found in different types of in vitro cellular models. In iPSCs, not all the laser-irradiated cells recruited FUS at the DNA damage site. The kinetics of the FUS protein also differed in different models. In conclusion, first, our in vitro striatal neuron model recapitulated the impaired DNA damage repair phenotype that published by other models. Second, new evidence was offered that wild-type FUS was involved in the pathogenesis of HD. Third, depending on cell-type, FUS performed differently during the response to the laser irradiation-induced DNA damage. Thus, these results suggest that the impaired DNA damage response and repair would be crucial to the mechanism of HD. Furthermore, the role of FUS protein playing especially the functional part in DNA damage response and repair might be a potential target for further investigation of neurodegenerative diseases including HD.

Indiana University-Purdue University Indianapolis (IUPUI) / Huntington disease (HD) is an autosomal dominant disorder characterized by progressive decline of motor, cognitive, and behavioral function. Saccades (rapid, gaze-shifting eye movements) are affected before a clinical diagnosis of HD is certain (i.e. during the premanifest period of the disease). Fundamental questions remain regarding the neural substrates of abnormal saccades and the course of premanifest disease. This work addressed these questions using magnetic resonance imaging (MRI) and a longitudinal study of premanifest disease progression. Gray matter atrophy is a characteristic of HD that can be reliably detected during the premanifest period, but it is not known how such changes influence saccadic behavior. We evaluated antisaccades (AS) and memory guided saccades (MG) in premanifest and manifest HD, then tested for associations between impaired saccadic measures and gray matter atrophy in brain regions involved in these saccadic tasks. The results suggest that slowed vertical AS responses indicate cortical and subcortical atrophy and may be a noninvasive marker of atrophic changes in the brain. We also investigated the brain changes that underlie AS impairment using an event-related AS design with functional MRI (fMRI). We found that, in premanifest and manifest HD, blood oxygenation level dependent (BOLD) response was abnormally absent in the pre-supplementary motor area and dorsal anterior cingulate cortex following incorrect AS responses. These results are the first to suggest that abnormalities in an error-related response network underlie early disease-related saccadic changes, and they emphasize the important influence of regions outside the striatum and frontal cortex in disease manifestations. Though saccadic abnormalities have been repeatedly observed cross sectionally, they have not yet been studied longitudinally in premanifest HD. We found different patterns of decline; for some measures the rate of decline increased as individuals approached onset, while for others the rate was constant throughout the premanifest period. These results establish the effectiveness of saccadic measures in tracking premanifest disease progression, and argue for their use in clinical trials. Together, these studies establish the utility of saccade measures as a marker of HD neurodegeneration and suggest that they would be a valuable component of batteries evaluating the efficacy of neuroprotective therapies.

No description available.

Huntington disease (HD) is a devastating and fatal neurodegenerative disease. At the moment, no disease modifying therapies are available, with only symptomatic treatment offered to alleviate psychiatric and some types of motor deficits. As a result, many people will continue to suffer and die from this disease. Small molecule therapies have failed to provide benefit in HD, necessitating more complex gene therapy approaches and the identification of less traditional therapeutic targets. A previous study demonstrated that preventing cleavage of the huntingtin (HTT) protein, the protein that when mutated causes HD, by caspase 6 (C6) at amino acid 586 prevents the onset of disease in transgenic HD model mice. This suggests that inhibiting the toxicity initiated by N586 cleavage could be a promising therapeutic strategy, but a safe and specific way to do this in humans has not been identified. General C6 inhibition is not a feasible strategy due to the vital functions it plays throughout life. Thus, the purpose of this study was to investigate whether the C6 cleavage fragment of HTT, N586, is itself a toxic species of HTT or if it initiates a toxic proteolytic pathway in order to identify more viable therapeutic strategies for HD. To accomplish this, we are using novel and highly sensitive immunoprecipitation and flow cytometry (IP-FCM) protein detection assays, specific for the N586 neoepitope of HTT, to evaluate the in vivo persistence of N586 in HD model mice. If N586 is detected, it is likely that it is itself toxic and promoting its degradation may be beneficial. Conversely, if it is not detected, N586 cleavage likely initiates a toxic degradation pathway and promoting its stability may be beneficial. The results of these studies have the potential to define new therapeutic strategies for HD that can be addressed more specifically than generalized C6 inhibition for the prevention of N586-mediated toxicity. The selective targeting of N586 toxicity, either to promote or prevent its degradation depending on our results, would ensure that therapeutic activity is restricted to HTT and reduce the potential for deleterious off-target effects

<p>Huntington’s disease (HD) is a progressive, neurodegenerative disorder that leads to the selective loss of neurons in the striatum and the cerebral cortex. HD is caused by a CAG trinucleotide repeat expansion beyond the normal length in the <em>IT15 </em>(<em>Htt</em>) gene. The CAG stretch codes for an elongated polyglutamine tract within the amino‐terminus of the huntingtin protein. Polyglutamine tracts with lengths exceeding 37 repeats cause HD whereas repeat lengths below do not. This phenomenon has plagued the HD community since the discovery of the gene in 1993. In this thesis, we sought to elucidate the molecular mechanism by which huntingtin becomes toxic at polyglutamine lengths above 37. Using Förster resonance energy transfer (FRET) techniques, we describe an intramolecular proximity between the first 17 residues (N17) and the proline-rich regions, which flank the polyglutamine tract of huntingtin. We report that we can precisely measure differences between the conformations adopted by the huntingtin protein with polyglutamine tracts below and above the pathogenic repeat threshold of 37 repeats. Our data supports the hypothesis that polyglutamine tracts below the pathogenic threshold can act as a flexible hinge allowing the N17 domain to freely fold back upon huntingtin and come into close 3D proximity with the polyproline region. This flexibility is lost in polyglutamine tracts with >37 repeats resulting in a diminished spatial proximity between N17 and the polyproline domain.</p> / Doctor of Philosophy (PhD)