Rett syndrome is a debilitating autistic spectrum disorder affecting one in ten thousand girls. Patients develop normally for up to eighteen months before a period of regression involving stagnation in head growth, loss of speech, hand use and mobility. It is almost exclusively caused by mutation in Methyl CpG binding Protein 2 (MeCP2). MeCP2 has traditionally been thought of as a transcriptional repressor, although its exact function remains unknown and it has recently been shown that the protein can also bind to hydroxymethylation and non-CpG methylation, which occurs predominantly at CAC sites in the mature nervous system. Genotype-phenotype studies of the most common Rett-causing mutations in affected patients revealed that a missense mutation, R133C results in a milder form of Rett syndrome. The reasons for this are unclear, as the mutation lies right in the heart of the methylated DNA binding domain. Previous in vitro studies of R133C showed a severe deficit in binding to methylated cytosine. A subsequent study found that R133C binding to hydroxymethylated cytosine was specifically impaired, whereas binding to methylated cytosine was indistinguishable from wildtype. Defining the DNA binding impairment of MeCP2R133C would yield important insights into Rett disease pathophysiology and provide an explanation for the phenotypic spectrum seen in patients. To shed light on these matters, a novel mouse model of the R133C mutation was created. The R133C mouse had a phenotype that was less severe than other missense mutant mice, in terms of survival, growth, Rett-like phenotypic score and some behavioural paradigms thus recapitulating the patient data. At the molecular level in adult mouse brain, MeCP2R133C protein abundance was reduced. Immunohistochemistry showed that MeCP2R133C had an abnormal pattern of localisation in the nucleus of neurons. In vitro electrophoretic mobility shift assays suggested that MeCP2R133C binding to (hydroxy)methyl-CAC may be reduced to a greater extent than binding to mCpG. Chromatin immunoprecipitation experiments confirmed the deficit in binding to methylated sites and supported a disproportionate reduction in binding to methylation in a CAC sequence context. Analysis of adult mouse cerebellar gene expression revealed a subtle upregulation of long genes and downregulation of short genes. Based on these data, it is proposed that Rett syndrome caused by the R133C mutation results from a combination of protein instability and defective binding to methylated DNA. Methyl-CAC binding is potentially abolished. The downstream biological consequence of this is a length-dependent deregulation of gene expression in the brain.

Methyl-CpG binding protein 2 (MeCP2) was discovered as a protein binding to methylated DNA more than 20 years ago. It is very abundant in the brain and was shown to be able to repress transcription. The mutations in MeCP2 cause Rett syndrome, an autism-spectrum neurological disorder affecting girls. Yet, the exact role of MeCP2 in Rett disease, its function and mechanism of action are not fully elucidated. In order to shed some light on its role in the disease the aim of this project was to identify proteins interacting with MeCP2. Affinity purification of MeCP2 from mouse brains and mass spectrometry analysis revealed new interactions between MeCP2 and protein complexes. Detailed analysis confirmed the findings and narrowed down the top interactions to distinct regions of MeCP2. One of the domains interacts with identified NCoR/SMRT co-repressor complex and is mutated in many patients with Rett syndrome. In vitro assays proved that these mutations abolish the putative transcriptional repressor function of MeCP2. We propose a model in which Rett syndrome is caused by two types of mutations: either disrupting the interaction with DNA or affecting the interaction with the identified complex, which has an effect on the global state of chromatin. The presented findings can help to develop new therapies for Rett syndrome in the future.

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La méthylation de l’ADN est une modification majeure du génome des eucaryotes permettant de moduler l’expression génique et contrôler le développement des mammifères. La protéine Mecp2 (Methyl CpG binding protein 2), dont le gène est situé sur le chromosome X, appartient à la famille des protéines de liaison à l’ADN méthylé. Sur la base de sa structure et de ses interactions Mecp2 a été décrit comme un répresseur de l’expression des gènes. A l’heure actuelle, son implication en tant qu’activateur de la transcription et organisateur de la structure chromatinienne lui confère un rôle plus global dans la régulation de l’épigénome. Des mutations de MECP2 conduisent à des troubles neurologiques dont le principal est le syndrome de Rett (RTT). Cette pathologie dominante liée à l’X affecte principalement les jeunes filles (incidence: 1/15000 naissances). Même si les causes précises du phénotype RTT ne sont pas connues, le profil d’expression de Mecp2 est en lien avec la synaptogenèse, la maturation et la maintenance des réseaux neuronaux. A mon arrivée en thèse l’équipe qui m’a accueilli venait d’identifier des déficits neuronaux, affectant notamment les groupes catécholaminergiques bulbaires et périphériques, à l’origine de troubles respiratoires chez un modèle murin de cette pathologie. Mon travail de thèse a permis de caractériser l’évolution postnatale des déficits moteurs et physiologiques affectant la souris Mecp2-déficiente. L’étude de structures catécholaminergiques d’intérêt telles que la Substantia Nigra et le Locus Coeruleus a révélé que les neurones dopaminergiques et noradrénergiques centraux ont un métabolisme affecté. Le nombre de neurones immunomarqués apparait significativement réduit dans ces groupes ce qui résulterait d’une perte progressive du phénotype « catécholaminergique », en l’absence de mort cellulaire. Nos données suggèrent que ces atteintes constituent un corrélat neuropathologique aux troubles comportementaux observés chez les souris Mecp2-déficientes. Ainsi certains troubles moteurs ont pu être améliorés, à l’aide d’un agent pharmacologique pro-dopaminergique, la L-Dopa. En relation avec les déficits en Bdnf (Brain-derived neurotrophic factor) décrits chez les patientes et les souris Mecp2-déficientes, nous avons identifié qu’une modification du dosage de Mecp2 induit une dérégulation de gènes (Htt, Hap1) codant des protéines impliquées dans le transport intracellulaire des vésicules de Bdnf. Nos travaux nous permettent de postuler que chez la souris Mecp2-déficiente, une altération de la dynamique de transport des vésicules chargées en Bdnf pourrait exacerber le déficit d’expression de cette neurotrophine. Notre traitement des souris Mecp2-déficientes par la cystéamine, une molécule capable d’agir sur les contenus, la libération et la sécrétion du Bdnf permet d’augmenter la survie des animaux et de réduire leurs troubles moteurs. Nos résultats montrent que les déficiences en Mecp2 entrainent des déficits de transport axonal du Bdnf qui s’ajoutent aux déficits de production du Bdnf. Par ailleurs, avec l’utilisation d’agents pharmacologiques agissant sur ce transport, nous offrons de nouvelles perspectives thérapeutiques. / DNA methylation is the major modification of eukaryotic genomes and plays an essential role in mammalian development. The protein Mecp2 (Methyl CpG binding protein 2), encoded by a gene located on the X chromosome, belongs to the ‘Methyl Binding domain’ protein family. Based on its structure and its interactions Mecp2 has historically been described as a repressor of expression for many genes. Currently, its involvement as an activator of transcription and its role in chromatin architecture suggests that it could be a global regulator of the epigenome. Mutations in MECP2 lead to neurological disorders, among which Rett syndrome (RTT). This dominant X-linked pathology mainly affects girls (incidence: 1/15000 live births). Although the precise causes of the RTT phenotype are unknown, the pattern of Mecp2 expression is related to synaptogenesis, maturation and neuromaintenance. Before my integration in the ‘Human Neurogenetics’ team, this group identified neural deficits, affecting brainstem and peripheral catecholaminergic cell groups, causing respiratory disturbances in a mouse model of this disease. My thesis work enabled the characterization of the postnatal physiological and motor deficits affecting the Mecp2-deficient mice. The study of catecholaminergic structures of interest such as the substantia nigra pars compacta and the locus coeruleus has revealed that the central noradrenergic and dopaminergic neurons are affected in their metabolism. The number of immunolabelled neurons of these groups appears significantly reduced and would result in a gradual loss of the mature ‘catecholaminergic’ phenotype, in the absence of cell death. Our data suggest that these defects are a neuropathological correlate for behavioral disorders observed in Mecp2-deficient mice. Some motor deficits have been improved, with L-Dopa, a pro-dopaminergic drug. In relation with Bdnf (Brain-derived neurotrophic factor) reduction described in patients and Mecp2-deficient mice, we identified that a change in the dosage of Mecp2 deregulates genes (Htt, Hap1) encoding proteins involved in the intracellular transport of Bdnf. Our work allows to postulate that in the Mecp2-deficient neurons, an altered dynamics of Bdnf vesicles transport could exacerbate the deficit of expression of this neurotrophin. Our treatment of Mecp2-deficient mice with cysteamine, a molecule able to increase Bdnf contents and enhancing its release and secretion, increased the survival of the animals and reduced their motor defects. Our results show that the Mecp2-deficiencies lead to alteration in the axonal transport of Bdnf in addition to deficits in Bdnf production. In addition, by the use of pharmacological agents that affect this transport, we offer new therapeutic perspectives.

A síndrome de Rett (SR) é um distúrbio neurológico progressivo de causa genética que afeta quase exclusivamente o sexo feminino. É causada por mutações, geralmente esporádicas, do gene MECP2, localizado no cromossomo X. Apresenta como características principais: estagnação no desenvolvimento neuropsicomotor, perda de comunicação, do contato visual, do interesse por pessoas e objetos e estereotipias manuais. Em conseqüência do grave comprometimento cognitivo e motor, as portadoras de SR têm muita dificuldade em realizar as tarefas do dia-a-dia. O objetivo desse trabalho foi avaliar as habilidades funcionais e averiguar as necessidades de assistência do cuidador, conforme determinadas pelo Inventário de Avaliação Pediátrica de Incapacidade (PEDI). Esse instrumento de avaliação, que possui 197 itens nas áreas de autocuidado, mobilidade e função social, foi aplicado em 64 portadoras de SR que preenchiam os critérios para a forma clássica da doença. Elas tinham idade entre 2 e 26 anos, com média de 10 anos. Entre as 73 atividades da área de autocuidado do PEDI, 52 (71,2%) não foram realizadas por qualquer criança; na área de mobilidade, entre as 59 atividades propostas, 8 (13,5%) não foram feitas pelas portadoras de SR; e finalmente na área de função social, nenhuma das 50 (76,9%) entre 65 atividades foi realizada. O desempenho médio ajustado em escala de 0 a 100 para a área de autocuidado foi de 8,9/100, variando de 0 a 26; para a de mobilidade, foi em média de 30,2/100, variando de 1,7 a 74,5; e a de função social foi de 5,2/100, com variação de 0 a 21,5. A necessidade de assistência foi, de forma complementar, maior nas áreas de autocuidado e função social do que na de mobilidade. Não encontramos, em nossa amostra, uma relação entre a idade e o grau de incapacidade, sugerindo que as portadoras de SR apresentam um nível de comprometimento que é, desde o início, bastante grave. Infelizmente, o menor comprometimento da mobilidade, comparado com as áreas de autocuidado e função social, não traz vantagens adaptativas ou maior independência às portadoras de SR. / Rett syndrome (RS) is a progressive neurological disturbance of genetic cause that affects females almost exclusively. It is caused by mutations, usually sporadic, of the MECP2 gene located in the X chromosome. Presented as main characteristics: stagnation in neuromotor development; losses of communication, visual contact, interest for people and objects; and manual stereotypes. In consequence to the serious cognitive and motor compromise, the RS patients have great difficulty in accomplishing day-to-day tasks. The objective of this work was to evaluate the functional abilities and to discover the needs of assistance by the caregiver, conforming to the established Pediatric Evaluation of Disability Inventory (PEDI). That evaluation instrument, which possesses 197 items in the areas of self-care, mobility and social function, was applied to 64 individuals with RS that matched the criteria for the classic form of the disease. Their ages ranged between 2 years and 26 years, with an average of 10 years. Among the 73 PEDI activities in the area of self-care, 52 (71.2%) were not accomplished by any child; in the area of mobility, among the 59 proposed activities, 8 (13.5%) were not done by any RS patient; and finally in the area of social function, none of the 50 (76.9%) activities among 65 were accomplished. The average performance adjusted in a scale from 0 to 100 for the area of self-care was of 8.9/100, varying from 0 to 26; for mobility, it was an average of 30.2/100, varying from 1.7 to 74.5; and of social function was 5.2/100, with variation from 0 to 21.5. The need of attendance was, in a complementary way, greater in the self-care areas and social function than in mobility. We didn\'t find, in our sample, a relationship between the age and the degree of incapacity, suggesting that RS individual present a compromising level that is from the beginning quite serious. Unfortunately, the smallest compromise of mobility, compared with the areas of self-care and social function, doesn\'t bring adaptive advantages or greater independence to the RS patients.

Thesis advisor: Thomas N. Seyfried / Epilepsy is a prevalent disabling chronic and socially isolating neurological disorder that involves recurrent abnormal discharges of neurons. Despite seizures afflicting about 10% of people worldwide, antiepileptic drugs (AEDs) are largely unable to manage seizures in many persons with epilepsy. As an alternative to AEDs, dietary therapies possess a broad therapeutic potential in both humans and animals models of various neurological and neurodegenerative disease etiologies. My research focus was to identify the therapeutic efficacy and potential mechanism(s) of action of calorie restriction (CR) and the ketogenic diet (KD) in both the epileptic EL mouse model and the Mecp2<super>308/y<super/> mouse model of Rett syndrome. My findings indicate that both the KD and CR can reduce seizure susceptibility in EL mice, a natural model for multifactorial idiopathic generalized epilepsy. CR and circulating glucose and ketone levels significantly influence the therapeutic efficacy of the KD. A concurrent reduction in circulating plasma glucose levels and elevation in circulating plasma &beta-hydroxybutyrate levels was predicted to associate with the anticonvulsant effect of these diets in EL mice. For the first time, I was able to show that a KD fed in unrestricted amount is able to reduce seizure threshold in EL mice. Interestingly, supplementation of calories in the form of carbohydrate in the water of calorie-restricted EL mice results in a diminished anticonvulsant efficacy of the KD. In my effort to elucidate the neuroprotective mechanism(s) associated with these changes in metabolite availability, I started investigating the complex alterations occurring in multiple integrated neural and metabolic processes. Furthermore, I showed that a restricted KD diet improves aspects of the behavioral abnormalities seen in Rett mice, in particular with respect to anxiety. Finally, for the first time, I provide a standardized protocol for the implementation of diet therapies in the management of an array of neurological and neurodegenerative diseases, which ultimately may help elucidate the complex neuroprotective mechanism(s) of CR and the KD. This research overall has provided a new understanding in the therapeutic efficacy of diets in epilepsy and Rett Syndrome. / Thesis (PhD) — Boston College, 2010. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Biology.

The prevalence of Autism Spectrum Disorder (ASD) and its defining features has been increasingly investigated in genetic syndromes associated with intellectual disability, with syndrome specific profiles reported. The experience of catatonia and other movement disorders in people with ASD has been increasing highlighted within both research and diagnostic guidelines. However, these issues have not typically been investigated alongside other features of ASD within research into genetic syndromes. The first paper in this thesis provides a review of the literature on movement disorders in genetic syndromes associated with ASD, which focuses on the prevalence of reported movement disorders, the methods of assessment used, and the quality of research to date. An empirical study is reported in Paper 2. Within a cohort of individuals with Cornelia de Lange and Fragile X syndromes the prevalence of attenuated behaviour [autistic catatonia] is examined, based on parent/carer report, and the extent to which features of ASD predict later attenuated behaviour is investigated. Paper 3 provides a critical reflection on the first two papers as well as some wider considerations on undertaking research in this area. The results of both the literature review and the empirical study indicated that across a number of genetic syndromes (Angelman syndrome, Cornelia de Lange syndrome, Fragile X syndrome and Rett syndrome) attenuated behaviour [autistic catatonia] and/or movement disorders affect a substantial proportion of individuals. Furthermore, repetitive behaviours, one of the characteristic features of ASD, appear to predict later attenuated behaviour in Cornelia de Lange and Fragile X syndromesThe results presented in this thesis have important implications for the way services support individuals with specific genetic syndromes. Paper 1 confirms the high prevalence of movement problems in Angelman and Rett syndromes, and Paper 2 provides a new insight into movement problems in Cornelia de Lange and Fragile X syndromes. Movement disorders are reported to impact negatively on wellbeing and quality of life in people with ASD, and are likely to have a similar impact on the lives of people with genetic syndromes. Greater awareness and recognition of movement problems in CdLS and FXS is required, and although specialist services may already be aware of some of the above issues, there should be an increased emphasis on ensuring that community services are aware of the needs of individuals with genetic syndromes, including the implications of movement problems for support needs and quality of life.