Rett syndrome (RTT) is a severe neurological disorder that affects approximately 1:10000 girls. Classical RTT is defined by a developmental regression phase and subsequent stabilisation of diagnostic criteria, which include partial or complete loss of spoken language, dyspraxic gait and stereotypic hand movements such as hand mouthing. RTT is a monogenic disorder, with the majority of cases being due to loss-of-function mutations in MeCP2 (methyl-CpG binding protein 2). Due to this clear genotype-phenotype link multiple RTT mouse models have been used to elucidate the molecular details, and consequent neuropathogenesis, of this complex neurological disease, as well as for the development of potential therapeutics for RTT. However, as the molecular details become clearer, the need for a simpler model system becomes evident. Human induced pluripotent stem cells (hiPSCs) generated from RTT patient fibroblasts are an option; however the handling of these cells is laborious, time-consuming and expensive and they often differentiate into a heterogeneous population of cells. To explore an alternative human model system I have been genetically engineering and experimenting with the human dopaminergic LUHMES cell line. LUHMES cells are an immortalised pre-neuronal cell line derived from an 8-week old, female foetus and can readily be differentiated into a homogeneous population of mature, electrically active neurons in just one week. In this thesis I have assessed the phenotypic properties of the wild-type cell line, demonstrated the ease of genetic manipulation of LUHMES cells by CRISPR/Cas9 approaches, generated seven mutant MECP2 LUHMES cell lines and explored the potential of protein therapy as a therapeutic approach for RTT. The LUHMES cell line proves to be extremely easy to handle and robust and has yielded novel molecular insights into the function of MeCP2 in human neurons. In particular, MeCP2-null cells show a striking relationship between the level of gene body methylation and the extent of transcriptional upregulation when compared to wild-type neurons. In contrast neurons that express a form of MeCP2 that can bind to DNA but cannot recruit a transcriptional corepressor complex (the R306C mutant) do not exhibit substantial gene expression alterations, yet do display a consistent decrease in total RNA amount. This decrease in total RNA is recapitulated in MeCP2-null LUHMES-derived neurons and in brain regions from MeCP2-R306C mice. The requirement for functional DNA binding for normal gene-body methylation dependent gene repression is demonstrated by assessing LUHMES cells that overexpress MeCP2-R111G, a protein that cannot bind to DNA. Furthermore, overexpression of the MeCP2-R306C protein highlights the importance of NCoR binding for normal gene repression, but also demonstrates that MeCP2-R306C protein retains some gene repression activity. Thinking more broadly, this cell line also has applications as a model system for a variety of other neurological disorders; as a simplified model system to elucidate molecular and neurological phenotypes, and as a relevant human system that can be cultured in a high-throughput manner for testing therapeutic strategies.

Rett syndrome is a neurodevelopmental disorder that is predominately caused by mutations of the MECP2 gene. As neuronal apoptosis is not observed in RTT patients and MeCP2-deficient mice, the neurological deficits may be reversible. To address this, we reactivated MeCP2 expression ubiquitously in MeCP2-deficient mice after symptom onset. Our results showed that life span, behavioural performances, EEG activity, thermoregulation, and daily rhythmic activity were significantly improved after MeCP2 reactivation. Furthermore, the extent of improvement was dependent upon the efficiency of MeCP2 reactivation. To assess the role of the catecholaminergic system in Rett syndrome pathophysiology, we selectively preserved MeCP2 function within tyrosine hydroxylase expressing cells. We observed a significant improvement in the life span of male rescue mice and reduced sudden unexplained death rates in female rescue mice. Behavioural performances and EEG patterns were also significantly improved.

Rett syndrome is a neurodevelopmental disorder that is predominately caused by mutations of the MECP2 gene. As neuronal apoptosis is not observed in RTT patients and MeCP2-deficient mice, the neurological deficits may be reversible. To address this, we reactivated MeCP2 expression ubiquitously in MeCP2-deficient mice after symptom onset. Our results showed that life span, behavioural performances, EEG activity, thermoregulation, and daily rhythmic activity were significantly improved after MeCP2 reactivation. Furthermore, the extent of improvement was dependent upon the efficiency of MeCP2 reactivation. To assess the role of the catecholaminergic system in Rett syndrome pathophysiology, we selectively preserved MeCP2 function within tyrosine hydroxylase expressing cells. We observed a significant improvement in the life span of male rescue mice and reduced sudden unexplained death rates in female rescue mice. Behavioural performances and EEG patterns were also significantly improved.

Für das Rett Syndrom, eine der häufigsten genetischen Ursachen für mentale Retardie-rung bei Frauen, gibt es bisher keine kausale Therapie, obwohl gentherapeutische Studi-en mit konditionellen knockout Mäusen gezeigt haben, dass es sich um eine therapierbare Erkrankung handelt. Um neue Therapien entwickeln zu können, werden Mausmodelle benötigt, die auf den beim Menschen am häufigsten gefundenen Mutation beruhen. In der vorliegenden Arbeit wurde ein Mausmodell mit der häufigsten humanen Nonsense-Mutation R168X im Mecp2 Gen charakterisiert. Mit Hilfe dieses Mausmodells wurden dann die Therapieansätze der „Stop-Codon Readthrough-Therapie“ und einer Knochenmarktransplantation auf ihre Wirksamkeit in vitro und in vivo untersucht. Die Charakterisierung der Mauslinie zeigte, dass männliche MeCP2R168X-Mäuse im Gegensatz zu anderen MeCP2-Mausmodellen kein verkürztes MeCP2 Protein exprimieren. Desweiteren weisen männliche MeCP2R168X-Mäuse einen Phänotyp, inklu-sive der drastisch verkürzten Lebenspanne, auf, wie er bei bereits etablierten Mausmo-dellen für das Rett Syndrom beschrieben wurde. Dagegen zeigten weibliche, heterozy-gote MeCP2R168X-Mäuse nur einen sehr mild ausgeprägten Phänotyp verglichen mit bereits etablierten MeCP2-Mauslinien. Für die „Stop-Codon Readthrough-Therapie“ wurde die Effizienz der Aminoglykoside Geniticin, Gentamicin und Neomycin, der Komponenten NB54, NB84 und NB124, sowie der niedermolekularen Substanz PTC124 auf ihre Wirksamkeit bei der Induktion eines Readthroughs mit transfizierten HeLa-Zellen und MeCP2R168X/y-Mausohrfibroblasten in vitro untersucht. Dabei zeigte sich eine deutliche Steigerung der Readthrough-Effizienz der NB-Komponenten, gemessen an der detektierbaren Menge an MeCP2, mit zunehmender Generation (NB54 --> NB84 --> NB124) und gegenüber dem klinisch angewandten Gentamicin. Während die Behandlung mit Neomycin zu einem minimalen Readthrough-Produkt führte, zeigte die Behandlung mit PTC124 kei-nen messbaren Readthrough. Anschließend wurden männliche MeCP2R168X-Mäuse mit den in vitro getesteten Sub-stanzen, mit Ausnahme von Geniticin, behandelt. Die Expression eines MeCP2-Proteins voller Länge konnte durch keine der applizierten Substanzen induziert werden. Auch bei Behandlungen über einen längeren Zeitraum mit hohen Dosierungen, im Fall von Gentamicin nahe der LD50-Dosis und nachweisbarer intrazellulärer Aufnahme, konnte in den behandelten Tieren weder ein verkürztes noch ein MeCP2 Protein nativer Länge detektiert werden. Die Ergebnisse dieser Arbeit zeigen, dass für die „Stop-Codon Readthrough-Therapie“ für das Rett Syndrom neue Komponenten entwickelt werden oder andere Applikationswege gewählt werden müssen, da mit den derzeit verfügbaren Substanzen kein therapeutischer Erfolg erzielt werden kann. Im letzten Teil dieser Arbeit wurde die Theorie einer gestörten Phagozytose MeCP2-defizienter Mikroglia, sowie die Therapie von MeCP2-defizienten Mäusen durch eine Knochenmarktransplantation überprüft. Dabei konnte weder in vitro noch in vivo eine Veränderung der Phagozytoseaktivität der MeCP2-defizienten Mikroglia nachgewiesen werden, wie sie von Derecki und Kollegen publiziert wurde. Die Transplantation von gesundem Knochenmark führte bei männlichen MeCP2R168X-Tieren zu keiner Verlängerung der Überlebensspanne oder einer allgemeinen Abmilde-rung der Symptomatik, wie sie ebenfalls von Derecki und Kollegen publiziert wurde. Bei weiblichen Tieren führte die Transplantation gesunden Knochenmarks zu einer Verschlechterung der motorischen Fähigkeiten. Diese Ergebnisse sind im Einklang mit denen Ergebnissen der Arbeitsgruppen von An-drew Pieper, Antonio Bedalov und Jeffrey Neul, die in anderen Mausmodellen die Wir-kung der Knochenmarktransplantation untersuchten. Die Ergebnisse aller beteiligten Arbeitsgruppen legen daher nahe, dass eine Knochen-marktransplantation nach einer Ganzkörperbestrahlung keine geeignete Therapie für das Rett Syndroms darstellt.

Das Rett Syndrom (RTT) gehört zu den tiefgreifenden Entwicklungsstörungen des Gehirns von dem fast ausschließlich Mädchen betroffen sind (ICD-10, F84.10). Ursächlich für die Pathogenese sind Mutationen im X-chromsomalen MECP2-Gen, welches für den Transkriptionsfaktor Methyl-CpG binding protein 2 (MeCP2) kodiert. Unterschiedliche neurologische Symptome treten zwischen 6 und 18 Monaten nach der Geburt auf, wobei schwere Rhythmussstörungen der Atmung für ein Viertel plötzlicher Todesfälle bei Rett-Patientinnen verantwortlich gemacht werden. Der neuronale Atmungsrhythmus bei Säugern wird in verschieden Regionen des ponto-medullären Hirnstammes generiert, wobei der Prä-Bötzinger Komplex als essentiell für die Rhythmogenese der Atmung angesehen wird. Mittels Genexpressionsstudien in der Ventralen Respiratorischen Gruppe (VRG), die den Prä-Bötzinger-Komplex einschließt, zeigte sich eine massiv erhöhte, pathologische Expression des Serotoninrezeptor 5B sowohl auf mRNA-, als auch auf Proteinebene bei MeCP2-defizienten Mäusen zum postnatalen Entwicklungstag P40. Der Serotoninrezeptor 5B (5-HTR5B) gehört zur Klasse der G-Protein-gekoppelten Rezeptoren. Durch detaillierte Analysen des 5-HTR5B-Proteins konnte eine natürliche Trunkierung des Rezeptors nachgewiesen werden. Des Weiteren wurde eine ungewöhnliche intrazelluläre Lokalisierung in Membranen von vesikulären und tubulären Kompartimenten beobachtet. Trotz dieser ungewöhnlichen Eigenschaften besitzt der Rezeptor weiterhin die Fähigkeit, das inhibitorische G-Protein Gαi3 konstitutiv zu aktivieren und somit den Anstieg von cAMP zu verhindern. Durch genetisches Ausschalten des 5-HTR5B Proteins (knockout) konnte gezeigt werden, dass die durch 5-HTR5B-verminderte cAMP-Konzentration in der VRG ursächlich für den gestörten Atmungsrhythmus MeCP2-defizienter Mäuse ist. Die sich aus diesen Ergebnissen ableitende pharmakologische Strategie, die cAMP Konzentration zu erhöhen, führte zu einem deutlich verbesserten Atmungsrhythmus. Die Ergebnisse dieser Arbeit implizieren neue Therapieansätze zur Behandlung der Atmungs-störungen von Rett-Patienten.

No description available.

No description available.

Rett Syndrome (RTT, OMIM 312750) is a pervasive autism spectrum disorder affecting 1 in 10,000 females. The majority of cases are caused by mutations in the X-linked gene MECP2. The RTT phenotype appears to be caused by impaired synapse maturation or maintenance, resulting in disrupted autonomic nervous system function, mental retardation, ataxia, apraxia, and movement stereotypies. While not a neurodegenerative disorder RTT is marked by region-specific reductions in brain volume. We examined the morphology of YFP-expressing Layer 5 pyramidal neurons in the motor cortex of a MeCP2 mutant RTT mouse model. Mutant mice exhibited smaller somata and reduced dendritic lengths in both the apical tuft and basal arbor. Basal dendritic branching was also reduced proximal to the soma. These changes are consistent with the motor deficits observed in mutant mice and in human RTT patients. Altered expression of a Thy-1-YFP reporter transgene in MeCP2 mutant mice is also described.

Rett Syndrome (RTT) is a developmental disorder that affects numerous neuronal systems that underlie problems with breathing, movement, cognition and sleep. RTT is caused by mutations in the methyl-CpG-binding protein 2 (Mecp2) gene. MeCP2 is a ubiquitous protein that is found in all mature neurons and binds to methylated DNA to repress transcription; thus regulating protein expression levels in neurons. The mutations in Mecp2 affect a large number of proteins that are crucial for regulating neuronal activity. Despite the abnormal expression of many of these proteins, mice with a total loss of MeCP2 can live to adulthood and some people with RTT can live to a very late age as well. It is possible that mutations in the Mecp2 gene not only cause widespread defects, but also elicit neuroadaptive processes that may limit the impact of the MeCP2 dysfunction. To test this hypothesis we performed these studies in which we focused on how synaptic and membrane currents were altered to maintain normal neuronal activity in Mecp2-null mice. We show two examples from different neurons where neuroadaptations of ion channel expression allowed the neuron to remain viable. First, the properties of the nicotinic acetylcholine receptor (nAChR) current were altered in LC neurons in Mecp2-null mice. This was caused by changes in the nicotinic receptor subunit expression. Despite the changes in the nAChR current, the cholinergic modulation of LC neuron activity in WT and Mecp2-null mice were similar. Secondly, we show that the fast Na+ voltage-gated and the hyperpolarization-activated currents were altered in mesencephalic trigeminal V (Me5) propriosensory neurons. The changes in the hyperpolarization-activated current caused a smaller sag and post-inhibitory rebound. Opposite to what we expected, these cells were hyperexcitable. The hyperexcitability was due to changes in the fast Na+ voltage-gated current causing a decreased action potential threshold. Alterations in the ionic currents in Me5 neurons seem to be due to changes in subunit expression patterns. These results indicate that despite the complications caused by defects in the Mecp2 gene, neurons respond by rearranging receptor / ion channel expression. This reorganization allows neurons to remain viable despite the MeCP2 deficiency.

Made available in DSpace on 2016-03-15T19:40:30Z (GMT). No. of bitstreams: 1 Renata de Lima Velloso.pdf: 575032 bytes, checksum: 2ded8ecbcde5b280b54ac0be7c3a6a35 (MD5) Previous issue date: 2008-01-29 / Fundo Mackenzie de Pesquisa / Children with Rett Syndrome (RS) are supposed to present progressive regression of psychomotor development and speech abilities as well as spontaneous hand movement loss, resulting in severe difficulties for their communication. Several studies have been reporting that RS girls use the eyes with intentional purpose for communicating or expressing desires, and these findings make possible the use of eyes movements as a tool for assessing other RS aspects, such as the cognitive aspects. Ten girls aged 4y8m to 12y10m with RS were assessed for this investigation with a computer system for visual tracking regarding their ability of recognizing concepts of color (red, yellow and blue), shape (circle, square and triangle), size (big and small) and spatial position (over and under). Results from comparing the time of eyes fixation on required and not required concepts did not differ significantly. Correlation between age advancement and ability for recognizing the concept of the color "blue" could be observed. Children did not show to recognize the most part of the required concepts when assessed with eye tracking system. / Crianças com Síndrome de Rett (SR) apresentam regressão progressiva do desenvolvimento psicomotor e das habilidades de linguagem verbal e perda das habilidades manuais voluntárias, o que lhes dificulta a comunicação. Estudos relatam que meninas com SR utilizam o olhar com finalidade intencional, como forma de comunicação ou de expressão de desejos, o que levanta a possibilidade de avaliação de outros aspectos por meio do olhar, como os aspectos cognitivos. O objetivo deste estudo foi avaliar, em crianças com SR, o reconhecimento dos conceitos de cor (vermelho, amarelo e azul), forma (círculo, quadrado e triângulo), tamanho (grande e pequeno) e posição espacial (em cima e embaixo), com a utilização de equipamento computadorizado de rastreamento ocular. Participaram do estudo 10 crianças com diagnóstico de SR com idade entre 4 anos e 8 meses e 12 anos e 10 meses. Comparando-se o tempo de fixação do olhar das crianças para o conceito solicitado com o tempo de fixação para outros conceitos não solicitados, os resultados não indicaram muitas diferenças significativas. Houve correlação entre o conceito cor "azul" e o aumento da idade, indicando que as crianças mais velhas aprendem o conceito "azul". Concluiu-se que, com o método de avaliação utilizado, as crianças não reconheceram a maior parte dos conceitos de cor, forma, tamanho e posição.