L’ataxie de Friedreich (AF) est une maladie mitochondriale caractérisée par une ataxie spinocérébelleuse et sensitive, une cardiomyopathie et un diabète. L’AF est due à un déficit en frataxine (FXN), une protéine mitochondriale impliquée dans la synthèse des centres Fe-S et l’homéostasie mitochondriale. L’atteinte cardiaque, pour laquelle il n’existe aucun traitement, est la cause principale de décès. Nous avons montré que l’injection intraveineuse d’un vecteur adéno-associé (AAV) rh10 exprimant la FXN humaine prévient le développement de la cardiomyopathie d’un modèle souris de l’AF mais aussi que l’injection du vecteur à des animaux en insuffisance cardiaque permet la correction complète et rapide du phénotype cardiaque. Ces résultats démontrent la capacité des cardiomyocytes défectueux présentant un défaut bioénergétique à être rapidement corrigés. Nous avons ainsi établi la preuve de concept qu’un traitement par thérapie génique est une approche thérapeutique pertinente pour l’AF. / Friedreich ataxia (FRDA) is a mitochondrial disease with neurodegeneration, hypertrophic cardiomyopathy and diabetes. FRDA is caused by reduced level of frataxine (FXN), an essential mitochondrial protein involved in iron-sulfur cluster biogenesis and mitochondrial homeostasis. Cardiac failure is the most common cause of mortality in FRDA. To date, no treatment exists for FRDA cardiomyopathy. During my PhD, we showed that an adeno-associated vector (AAV) rh10 expressing human FXN injected intravenously not only prevented the onset of the cardiac disease in a faithful FRDA cardiac mouse model, but also, when administered in animals with cardiac failure, reversed rapidly and completely cardiac remodeling and insufficiency. Our results demonstrate the capacity of defective cardiomyocytes with severe energy failure and ultrastructure disorganization to be rapidly corrected and remodeled by gene therapy. Thus, we showed that gene therapy may be a relevant therapeutical approach for FRDA.

Introdução: A Ataxia Espinocerebelar tipo 3 (SCA3), também chamada de Doença de Machado - Joseph (DMJ) é uma doença neurodegenerativa autossômica dominante causada pela expansão de uma sequência repetitiva CAG no gene ATXN3 localizado no cromossomo 14q32.1. Alelos normais contêm 12 a 43 repetições CAG; alelos causadores da doença contêm 51 ou mais repetições CAG (CAGexp). Existe uma forte correlação entre o tamanho da expansão e a gravidade da doença, e a antecipação é um fenômeno comum. Com idade de início média entre os 32 e os 40 anos, a SCA3/DMJ se apresenta com ataxia, disartria, disfagia com uma expressão clínica heterogênea e manifestações clínicas abrangendo mú ltiplos sistemas neurológicos como as vias piramidais e extrapiramidais, a sensibilidade e o neurônio motor inferior. O curso da SCA3/DMJ é invariavelmente progressivo, levando os pacientes à dependência funcional e ao retraimento social e não há tratamentos específicos para a condição. Estima-se que a sobrevida média após o início da doença seja de 21 anos. O inicio da doença na infância raramente foi relatado na literatura, e a progressão e característ icas da doença nesses casos não são conhecidas. Objetivo: caracterizar as manifestações clínicas e a progressão da doença em sujeitos portadores de SCA3/DMJ com idade de inicio da doença na infância. Métod os: casos com idade de início do primeiro sintoma igual ou anterior aos 12 anos (DMl-início-na-infância) foram identificados a partir do registro de casos diagnosticados com exame molecular e acompanhados no ambulatório de Neurogenética do Hospital ele Clínicas de Porto Alegre ele 2000 a 2014. Após consentimento, os pacientes foram entrevistados e examinados através das escalas cl ínicas SARA e NESSCA. As variáveis gênero, idade de início (ii), duração da doença (DD), as repetições CAG dos dois alelos, o gênero do genitor transmissor, a CAGexp do genitor e a antecipação foram obtidas e comparadas com os dados da coorte geral de casos da institu ição. Quando possível, essas comparações foram fe itas através de testes de qui-quadrado para variáveis categóricas, e de testes não paramétricas como Sperman e Mann-Whitney, para variáveis quantitativas. Doze meses após a primeira avaliação (baseline), as escalas NESSCA e SARA foram novamente aplicadas. As taxas de progressão da NESSCA e da SARA nesse intervalo foram medida através do teste modelo misto de coeficientes aleatórios sendo comparadas com as taxas obtidas em duas observações prospectivas prévias, realizadas em pacientes SCA3/DMJ com ii após os 12 anos: o estudo da história natural da SCA3/DMJ uti lizando a escala NESSCA (Jardim et ai, 2010) gerou o grupo Controle-I-IN, e o grupo placebo do e nsaio clín ico randomizado sobre o lítio (Saute et al,2014) gerou o grupo Controle-PL. Resultados: No período, 1317 pacientes (189 famílias) com SCA3/DMJ foram identificados na nossa instituição. Os 367 que fizeram o exame molecular fo ram analisados. Sua ii média ± dp (variação) foi de 34,1 ± 11 (5 a 59) anos. Oito pacientes de 6 fa mílias, todos heterozigotos para a CAGexp, foram identificados com DMI-início-na-infância (2,2% ). Sete dos oito DMJin ício-na-infância (87,5%) eram do sexo feminino (p = 0,057), a ii dos sintomas do grupo DMJ-início-na-infância variou entre 5 e 10 anos com mediana de 8 e intervalo inter-quartil 3 anos. A CAGexp variou de 80 a 91 repetições. A progressão da NESSCA foi de 0,8 pontos anuais em média no grupo Controle-PL e 2 pontos anuais em média no grupo DMJ-início-nainfância (p=O,OO L). A progressão da SARA foi de 0,6 pontos anuais em média no controle-PL e 2,3 pontos em média no grupo DMJ-início na infância (p=O,OOl). A escala NESSCA foi dividida em subescalas considerando sinais piramidais, extrapiramidais, ataxia, sinais de comprometimento periférico, disfagia, disartria e alterações oculomotoras. A progressão dessas subescalas foi comparada entre os dois grupos. Foi observado uma piora na progressão do grupo DMJ-início-na-infância nos sintomas extrapiramidais (p=0,006) e na disfagia (p=O,OOl). Conclusão: A DMI-início-na-infância está associada ao sexo feminino e apresenta uma velocidade de progressão maior do que os demais sujeitos com SCA3/MJD. / lntroduction: Spinocerebellar Ataxia 3 (SCA3), also known as Machado-Joseph Disease (MJD), is an autosomal dominant neurodegenerative disorder, associated to a CAG repeated expansion at the ATXN3 gene coding region, located at chromosome 14q32.1. Normal alteies contain 12-43 CAG repeats; alleles causing disease contain 51 or more CAG repetitions (CAGexp). There is a strong correlation between the expansion size anel the severity of disease, and the anticipation is a common phenomenon. The average age of onset is 32 to 40 years old anel the SCA3/MJD presents with ataxia, dysarthria, dysphagia with a heterogcneous clinicai expression anel clinicai manifestations affect multiple neurological systems as pyramidal anel extrapyramidal pathways, sensitivity anel motor neuron lower. The course of SCA3/MJD is invariably progressive, leading patients to fu nctional dependency anel social withdrawal and there are no specific treatments for the condition. lt is estimated that the avcrage survival after elisease onset is 21 years. The onset of disease in childhood was rarely reported in the literature, anel the disease progression anel characteristics in patients under 12 years is not known. Objcctive: To characterize patients with heterozygous SCA3/MJD with age of onsct before 12 ycars old. Methods: cases with age of onset before 12 years old were ident ificcl from the registry of cases eliagnosecl molecularly anel accompanied in the Neurogcnctics Clinic of Hospital de Clínicas de Porto Alegre (HCPA) from 2000 to 2014. After consent, patients were interviewed anel examined with the cl inicai scales SARA anel NESSCA. The variables gender, age at onset (ao), clisease cluration (DD), CAG repeats of the two ali cies, transmitter parent gender, CAGexp of parent anel anticipation were obtained anel compareci with data of the general cohort of cases from institution. These comparisons were macle using chi-square tests for categorical variables anel non-parametric tests as Spearman anel Mann-Whitney test for quantitative variables. Twelve months after the first evaluation (baseline), the SARA and NESSCA scales were again applied. Progression rates of SARA and NESSCA in that range were measured using the mixed model of random coefficient test were compareci with the rates obtained in two previous prospective observations, made in SCA3 I MJD patients with ao after 12 years: the Natural His tory Study of SCA3/DMJ using NESSCA (Jardim et al, 2010) generaLed the Control-HN group and Lhe placebo group randomized clinicai trial of lithium (Saute et ai, 2014) generated Control-PL group. Results: During the period, 1317 patienLs (189 fami lies) with SCA3/MJD were identified at HCPA. The 367 patients who dicl the molecular examinaLion were analyzecl. Its average ao ± SD (range) was 34.1 ± 11 (5-59) years. Six families of eight patients, ali heterozygous for CAGexp were identified MJD-chilclhood-onset group (2.2% ). Seven of the eight MJDchildhood- onset group (87.5%) were female (p = 0.057), ao of the symptoms of MJDchildhood- onset group ranged between 5 and 10 years wiLh a median of 8 and interquartile range 3 years. The CAGexp ranged 80-91 repetitions. The ann ual progression of NESSCA was 0.8 poinLs on average in Lhe Control-PL group anel 2 points on average in MJDchildhood- onset group (p = 0.001). The progression of SARA was 0.6 points per year on average in the Controi-PL group anel 2.3 points in average MJD group in childhood-onset (p = 0.001). The scale NESSCA was divided in subscales considering pyramidal signs, extrapyramidal signs, ataxia, peripheral signs, dysphagia, dysarthria and oculomotor and compareci to progression in both groups. The progression of these subscales was compareci between the two groups.

Orientadores: Íscia Lopes-Cendes, Tiago Campos Pereira / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Ciências Médicas / Made available in DSpace on 2018-08-16T04:52:35Z (GMT). No. of bitstreams: 1 Lopes_CamilaMiranda_M.pdf: 829941 bytes, checksum: 12321a46db80c3af2cd6c71e4d97fd00 (MD5) Previous issue date: 2010 / Resumo: A ataxia espinocerebelar do tipo 3 (SCA3), também conhecida como doença de Machado-Joseph (DMJ), pertence ao grupo das doenças neurodegenerativas por expansão de poliglutamina e é o tipo de ataxia de herança autossômica dominante mais comum em muitos países. Os efeitos clínicos são variados, incluindo a coordenação motora anormal e morte precoce. O gene MJD1, responsável pela doença, codifica a proteína ataxina-3, uma ubiquitina protease do sistema ubiquitina-proteossomo. Esta proteína quando mutada contém uma expansão consecutiva de 51-86 glutaminas, em contraste com a ataxina-3 normal que apresenta 14-44 glutaminas. Os mecanismos envolvidos na doença estão principalmente relacionados ao mal enovelamento e consequente agregação da proteína mutada, disfunção neuronal e morte celular por apoptose nos neurônios afetados. A investigação de estratégias que interfiram diretamente nos efeitos citotóxicos da doença representa, portanto, um importante enfoque terapêutico. O objetivo deste trabalho foi desenvolver um modelo in vitro dos efeitos citotóxicos da ataxina-3 mutada a fim de avaliar diferentes estratégias terapêuticas para o controle desses efeitos. O modelo in vitro para a DMJ foi estabelecido com sucesso utilizando a sequência completa do cDNA da ataxina-3 expandida codificando 84 glutaminas. A análise fenotípica das culturas celulares mostrou que nosso modelo apresenta os principais efeitos fenotípicos e citotóxicos da doença, como a formação de agregados protéicos e indução de morte celular. Nós investigamos três estratégias terapêuticas com a finalidade de diminuir a morte celular no modelo in vitro. A primeira, utilizando uma chaperona química (glicerol) teve o intuito de estabilizar a conformação nativa da proteína, auxiliando no enovelamento correto da mesma. Os sais de lítio provavelmente atuam modulando a expressão gênica e poderiam reverter os efeitos citotóxicos causados pela ataxina-3 expandida que levam à disfunção neuronal e à morte celular. A terceira estratégia focou na atenuação da disfunção mitocondrial através de um cofator mitocondrial e antioxidante poderoso, a coenzima Q10. O glicerol, lítio e coenzima Q10 aumentaram a viabilidade das células expressando a ataxina-3 expandida em 16%, 17% e 11%, respectivamente. O aumento de viabilidade resultou da diminuição da população celular em apoptose. Atualmente não existem tratamentos eficazes contra a DMJ, daí a importância de se estudar compostos capazes de reduzirem os efeitos citotóxicos da doença. Esse trabalho estabeleceu um modelo in vitro para a DMJ, bem caracterizado, fácil de ser manipulado no laboratório e de análise fenotípica direta que poderá ser mais explorado futuramente quanto à investigação de novos alvos terapêuticos e à compreensão dos mecanismos moleculares envolvidos na patologia da doença. Nossos resultados indicam que o glicerol, o lítio e a coenzima Q10 são bons candidatos para prevenir a morte celular causada pela ataxina-3 expandida e, portanto, estudos adicionais utilizando esses 3 compostos devem ser considerados / Abstract: Spinocerebellar ataxia-3 (SCA3), also known as Machado-Joseph disease (MJD), belongs to a group of neurodegenerative disorders caused by expansion of a polyglutamine stretch, called polyglutamine diseases. MJD is the most frequent inherited autosomal dominant ataxia in many countries. Clinical manifestations are varied, including abnormal motor coordination and early death. The protein encoded by MJD1, ataxin-3, is an ubiquitin protease that belongs to the ubiquitin-proteasome system. The responsible for MJD is a trinucleotide repeat expansion (CAG), which leads to an elongated polyglutamine tract in the encoded ataxin-3 protein, varying from 51 to 86 glutamines. On the other hand, normal alleles range between 14 and 44. The mechanisms underlying the disease are mainly related to protein misfolding and aggregation, neuronal dysfunction followed by cell death within the affected neurons. Investigation of strategies that interfere directly with disease cytotoxic effects represents an important therapeutic approach. The objective of this study was to develop an in vitro model that presented the main expanded ataxin-3 cytotoxic effects in order to evaluate different therapeutic strategies to control these effects. The in vitro model for MJD was successfully established using the complete ataxin-3 cDNA coding 84 glutamines. We confirmed that the model presented the main phenotypic and cytotoxic effects of the disease, such as protein aggregates and induction of cell death. We investigated three therapeutic strategies aiming cell death reduction in our in vitro model. The first, using a chemical chaperone (glycerol), was designed to stabilize the native protein and help protein folding. Lithium probably acts by modulating gene expression, and it was used in order to reverse the cytotoxic effects resulted from the disease, such as neuronal dysfunction and cell death. The third strategy focused on attenuation of mitochondrial dysfunction via a mitochondrial cofactor and powerful antioxidant, coenzyme Q10. Glycerol, lithium and coenzyme Q10 increased the viability of cells expressing expanded ataxin-3 in 16%, 17% and 11%, respectively. This augmentation resulted from a decrease in cell population undergoing apoptosis. Currently, there are no effective treatments against MJD, hence the importance of studying compounds capable of reducing disease cytotoxic effects. This work established an in vitro model for MJD, well characterized, and easy to be manipulated and analyzed. This model can be further explored for therapeutic investigations and for better understanding of molecular mechanisms involved in disease pathology. Our results indicate that glycerol, lithium and coenzyme Q10 are good candidates for preventing cell death caused by expanded ataxin-3 and, therefore, further studies with these 3 compounds should be considered / Mestrado / Neurociencias / Mestre em Fisiopatologia Médica

The objectives of my PhD were to identify the spatial and the temporal dynamics of the brain areas involved in tactile change detection as well as the neural mechanisms responsible for the processing of tactile change detection. To that aim, three specific MEG studies were performed; each of them is addressing specific research aims.The first study investigated the spatiotemporal dynamics of the multilevel cortical processing of tactile change detection in human healthy subjects. This study disclosed a hierarchical organization from unimodal early tactile change detection at secondary somatosensory cortex to multi modal complex processing at bilateral temporo-parietal junctions, posterior parietal cortex and supplementary motor areas. The second study aimed at discriminating between debated neural mechanisms responsible for the genesis of the somatosensory mismatch negativity (sMMN). To do so, we manipulated the predictability of the deviant stimuli and the response to omissions in different kind of oddballs, the response to deviant stimuli paired with standards and occurring alone. We found out that mechanisms for early tactile change detection reflected by the sMMN were better explained by the predictive coding theory compared to the adaptation and adjustment theories. Finally we sought to characterize the alterations in early cortical tactile change detection in Friedreich Ataxia (FRDA); a neurological disorder characterized by somatosensory and cerebellar pathways degeneration. The aim of this work was to study the role of the cerebellum in the genesis of sMMN and its potential selectivity for somatosensory change detection compared to auditory. This study demonstrated that, in FRDA, both tactile and auditory pathways are affected at the level of primary sensory neurons and dorsal root/spiral ganglia in a genetically determined. By contrasts, early cortical sensory change detection in FRDA was impaired only in the tactile modality in line with the sMMN impairment described in patients with acquired cerebellar lesions or during cerebellar inhibition by trans cranial magnetic stimulation. These data brought novel empirical evidence supporting the contribution of spinocerebellar tracts in sMMN genesis at cSII cortex.In conclusion, this PhD contributed to identify the network responsible for tactile change detection that involves cuneocerebellar spinocerebellar tract and cSII cortex as somatosensory specific areas and TPJ, SMA & PPC as multimodal brain areas. We further provided evidence that early change detection mechanisms at SII cortex fall under the predictive coding framework and that change detection is hierarchically organized with inputs from low level areas for genesis of an adequate generative model of our environment and conscious representation of our body. / Doctorat en Sciences médicales (Médecine) / info:eu-repo/semantics/nonPublished

Les ataxies cérébelleuses héréditaires sont un ensemble de pathologies neurodégénératives ou neuro-développementales rares responsables d’un handicap fonctionnel important. Nous décrivons la découverte dans deux familles consanguines avec une ataxie cérébelleuse, une épilepsie et un retard mental deux mutations homozygotes dans le gène WWOX à l’aide du séquençage de l’exome d’un des patients de chaque famille. Ce gène était connu comme un gène suppresseur de tumeur. Par une stratégie de capture ciblée de 57 gènes d’ataxies cérébelleuses sur une série de 155 patients, nous avons posé un diagnostic dans 20,6% des cas dont des mutations d’ANO10 et SYNE1. Des études multicentriques ont permis d’étendre les connaissances sur ces maladies et montrer l’existence de phénotypes sévères dans ARCA1.A partir de cette série, nous avons validé en aveugle la pertinence d’un algorithme diagnostique clinico-biologique proposé par l’article de Anheim dans le New England Journal of Medicine en 2012. / Hereditary cerebellar ataxias are a group of neurodegenerative or neurodevelopemental diseases responsible of major disability. We found thanks to exome sequencing mutations in the WWOX gene in two consaguineous families presenting with cerebellar ataxia, epilepsy and mental retardation. This gene was until recently only recognized to be a tumor suppressor.With a 57 ataxia genes targeted capture strategy, next generation sequencing in 155 patients found 20,6% of positive diagnosis, including several new mutations in ANO10 and SYNE1. Multi center studies allow to extend clinical knowledge with severes phenotypes especially in ARCA1.We validate a clinico-biological algorithm for recesssive ataxias diagnosis published by Anheim in the in New England Journal of Medicine, 2012 in a blinded manner.

Expanded polyglutamine proteins are known to be the causative agents of a number of human neurodegenerative diseases but the molecular basis of their cytoxicity is still poorly understood. Polyglutamine tracts may impede the activity of the proteasome, and evidence from single cell imaging suggests that the sequestration of polyglutamine proteins into inclusion bodies can reduce the proteasomal burden and promote cell survival, at least in the short term. The presence of misfolded protein also leads to activation of stress kinases such as p38MAPK, which can be cytotoxic. The relationships of these systems are not well understood. We have used fluorescent reporter systems imaged in living cells, and stochastic computer modeling to explore the relationships of expanded polyglutamine proteins, p38MAPK activation, generation of reactive oxygen species (ROS), proteasome inhibition, and inclusion body formation. In cells expressing a polyglutamine protein, inclusion body formation was preceded by proteasome inhibition but cytotoxicity was greatly reduced by administration of a p38MAPK inhibitor. Computer simulations suggested that without the generation of ROS, the proteasome inhibition and activation of p38MAPK would have significantly reduced toxicity. Our data suggest a vicious cycle of stress kinase activation and proteasome inhibition that is ultimately lethal to cells. There was close agreement between experimental data and the predictions of a stochastic computer model, supporting a central role for proteasome inhibition and p38MAPK activation in inclusion body formation and ROS-mediated cell death.

L'ataxie spinocérébelleuse de type 7 (SCA7) est une maladie neurodégénerative due à une expansion de CAG traduit en polyQ dans la protéine ataxine-7. La SUMOylation, modification post-traductionnelle que nous avons identifiée moduler l'agrégation de la protéine mutante, est facilitée par une SUMO E3 ligase.Nous avons identifié RanBP2, une nucléoporine appartenant au complexe du pore nucléaire en tant que SUMO E3 ligase, via SUMO-1 de l'ataxine-7. En effet, le silencing de RanBP2 induit l'agrégation de l'ataxine-7 mutante, ce qui démontre l'implication de RanBP2 dans la physiopathologie de SCA7. Nous montrons également que l'ataxine-7 endogène est une cible modifiée par SUMO-1 et -2. L'ataxine-7 poly-SUMOylée, grâce à la présence de chaines SUMO2/3, est capable de recruter RNF4. Cette protéine conduit à la dégradation de l'ataxine-7 mutante par la voie du protéasome. La dégradation est abolie en présence d'un mutant de RNF4.Dans un modèle murin KI SCA7, nous avons quantifié l'expression des gènes impliqués dans la voie de la SUMOylation au niveau des régions les plus touchées du cerveau. Le niveau d'expression des ARNs messagers montre des altérations dépendantes des répétitions CAG du gène SCA7. A 6 mois (avant le début de la pathologie), les premières dérégulations sont observées; à 12 mois (à un stade avancé de la maladie), on note une diminution statistiquement significative de Sumo-1 dans le cervelet des souris Atxn7100Q/5Q. Ces résultats, alliés à l'observation de l'accumulation anormale des protéines SUMO-1 et RanBP2 dans le cervelet d'un patient SCA7, suggèrent que les voies de la SUMOylation in vivo peuvent être perturbées dans SCA7. / Spinocerebellar ataxia type 7 (SCA7) is a neurodegenerative disease caused by a CAG expansion (polyQ) in the protein ataxin-7. SUMOylation, a post-translational modification that we identified to modulate mutant protein aggregation in a SCA7 cellular model, is facilitated by a SUMO E3 ligase. Here, we identified RanBP2 (Nup358), a nucleoporin belonging to the nuclear pore complex, as the major E3 enzyme implicated in ataxin-7 modification by SUMO-1. Indeed, RanBP2 silencing renders mutant ataxin-7 more prone to aggregation, thus demonstrating the implication of RanBP2 in SCA7 pathophysiology. We also show that endogenous ataxin-7 is a target for both SUMO-1 and -2 modification. Poly-SUMOylated ataxin-7 presents a docking site composed of SUMO2/3 chains for the recruitment of RNF4: this protein is a SUMO E3 ubiquitin ligase that mediates degradation of mutant ataxin-7 by the proteasome pathway. The degradation is abolished in presence of a mutant form of RNF4. In a SCA7 knock-in mouse model we quantified expression of SUMO-pathway related genes in cerebellum and retina, the most affected regions using quantitative RT-PCR. SUMO-related genes show expanded repeat-dependent alterations in expression patterns. At 6 months (before onset), deregulations begin to occur; by 12 months (late stage of disease), there is a statistically significant impairment in Sumo-1 levels in Atxn7100Q/5Q cerebellum. These results, together with the observation that SUMO-1 and RanBP2 protein accumulate abnormally in the cerebellum of a SCA7 patient, suggest that in vivo SUMO-modifying pathways may be perturbed in SCA7.

京都大学 / 0048 / 新制・課程博士 / 博士(医科学) / 甲第22006号 / 医科博第104号 / 新制||医科||7(附属図書館) / 京都大学大学院医学研究科医科学専攻 / (主査)教授 井上 治久, 教授 伊佐 正, 教授 妻木 範行 / 学位規則第4条第1項該当 / Doctor of Medical Science / Kyoto University / DFAM

ARSACS est une maladie neurodégénérative autosomique récessive caractérisée par une ataxie cérébelleuse, une paraplégie spastique et une polyneuropathie sensitivo-motrice démyélinisante. Le gène SACS, responsable de la maladie, a été identifié en 2000. Depuis, de nombreux cas ont été décrits dans le monde entier. Le gène SACS code pour la sacsine, dont la fonction reste inconnue malgré l’identification de nombreux domaines protéiques et surtout la description récente d’un rôle dans la physiologie mitochondriale. Les objectifs de ma thèse étaient d’identifier des mutations dans SACS au sein d’une large cohorte de patients atteints d’ataxie grâce à plusieurs collaborations puis d’étudier leurs effets au niveau du compartiment mitochondrial en utilisant essentiellement des cellules de malades. Nous avons pu identifier 2 variants de SACS dans 10% des cas analysés recrutés via le réseau international SPATAX. Nous avons parallèlement confirmé les mutations de SACS identifiées par séquençage haut-débit chez 5 autres patients via le PHRC ATAXIC et analysé un dernier cas porteur d’une délétion complète de SACS découverte par CGH-array pangénomique. Des cultures primaires de fibroblastes ont été obtenues chez 11 patients pour l’analyse fonctionnelle. Une altération de la morphologie des mitochondries a été observée chez tous les patients sauf un. Ces anomalies du réseau mitochondrial semblent très utiles pour cheminer vers le diagnostic d’ARSACS qui peut s’avérer complexe dans les situations non exceptionnelles où les résultats moléculaires sont délicats à interpréter (mutations faux-sens). Nous proposons une définition graduelle d’ARSACS reposant sur des critères cliniques, génétiques et cellulaires intégrant ces anomalies du réseau. Enfin, nous avons débuté l’exploration des mécanismes impliqués dans cette altération de la dynamique du réseau mitochondrial. Nos résultats préliminaires font évoquer une action potentielle de la sacsine au niveau du renouvellement des mitochondries. / ARSACS is a recessive autosomal neurodegenerative condition characterized by cerebellar ataxia, spastic paraplegia and demyelinating sensitivo-motor polyneuropathy. ARSACS is caused by mutations in the SACS gene identified in 2000. Since then, cases have been reported worldwide. SACS encodes sacsin, a protein of still unknown function in spite of the description of numerous protein domains and of a recent focus on a potential implication in the regulation of mitochondrial physiology. Aims of this thesis were to identify new mutations in a large population of ataxic patients and then to functionally analyze their cellular effects in the mitochondrial compartment. We identified 2 variants in SACS in 10% of analyzed cases collected through the international SPATAX network. We also confirmed mutations in SACS in 5 patients identified using next-generation sequencing in the ATXAIC project, and studied a last case harbouring a large deletion encompassing the entire SACS gene identified by pangenomic CGH-array. For functional analyses, primary cultures of fibroblasts were obtained in 11 patients. A drastic and recurrent alteration of the mitochondrial network was observed in all patients except one. These anomalies seem very useful for the diagnosis of ARSACS when molecular results are difficult to interpret (missense variants). We therefore propose a grading diagnostic definition using clinical, genetic and cellular criteria for ARSACS. Finally, we started to study the mechanistic of the mitochondrial function of sacsin. Our preliminary data may suggest a potential role at the mitochondrial turn over level.

Background: Environmental and endogenous stresses induce genomic DNA damage. In order to combat cellular assaults and maintain genomic integrity, reparative processes including DNA damage repair (DDR) and autophagy are activated. A key protein involved in DDR is ataxia telangiectasia mutated kinase (ATM). Mutations in ATM gene cause a multi-systemic disease called ataxia telangiectasia. Approximately 1.4-2.0% of the population has heterozygous mutation in ATM gene, which associates with enhanced susceptibility to cancer and ischemic heart disease. Autophagy, a conserved catabolic process, functions to maintain genomic stability by the sequestration and removal of misfolded proteins and damaged organelles. Dysregulation of autophagy contributes to the pathogenesis of many diseases including heart disease. Previous work from our lab has demonstrated autophagic impairment in the myocardium of ATM deficient mice during an acute phase (4 hr) of myocardial infarction (MI). The objective of this study was to examine the role of ATM deficiency in autophagic impairment during a chronic phase (28 days) post-MI. Methods: Wildtype (WT) and ATM heterozygous knockout (hKO) mice underwent MI by the ligation of the left anterior descending artery. Expression and activity of proteins associated with autophagy were examined in the infarct left ventricular tissue 28 days post-MI using western blot analyses. The data were analyzed using ANOVA followed by Student-Newman-Keuls test. A p-value of Results: The ratio of microtubule-associated protein light chain 3 (LC3-II-to-LC3-I; an indicator of autophagic turnover) lower in hKO-sham vs WT-sham. MI led to significant decrease in this ratio in WT-MI vs WT-sham. Protein levels of p62 (an autophagic transport protein) remained unchanged among the four groups. Expression levels of beclin-1 (aids in the formation of the autophagophore) were similarly increased in both MI groups vs their sham controls. Levels of mature cathepsin D (a lysosomal protease involved in lysosomal degradation of misfolded proteins) were significantly higher in WT-MI vs WT-sham group. Interestingly, cathepsin D levels were significantly lower in hKO-MI vs WT-MI group. Activation of mTOR (a coordinator of autophagy, cell growth and metabolism) was significantly higher in hKO-MI, not in WT-MI, vs hKO-sham group. Activation of AMPK (a sensor and regulator of cellular energy homeostasis) was higher in WT-MI, not in hKO-MI, vs WT-sham. Conclusion: Thus, ATM deficiency alters autophagic response in the heart chronic post-MI.