De nouveaux enjeux émergent dans le domaine de la Santé en raison du vieillissement de la population et du développement inquiétant de la Maladie d’Alzheimer (MA). Chez le sujet sain ou pathologique, peu d’études ont porté sur le vieillissement du contrôle nerveux de la respiration, en dépit de son rôle crucial pour l’oxygénation du cerveau. Cette thèse présente des recherches translationnelles, réalisées chez la souris, pour étudier le vieillissement physiologique et pathologique du contrôle nerveux de la respiration. Chez des souris transgéniques, modèles reconnus de la MA et du syndrome de Rett, nous décrivons le développement de neuropathologies respiratoires graves, conduisant à un décès prématuré. Nous montrons pour la première fois qu’une tauopathie du tronc cérébral altère le fonctionnement des voies aériennes supérieures, la vocalisation et la respiration. De plus, nos travaux suggèrent un rôle délétère de l’anesthésie pour la MA et identifient des pistes thérapeutiques nouvelles. En conclusion, nos travaux chez la souris peuvent avoir des retombées particulièrement intéressantes notamment pour la MA. / New issues are emerging in the field of Health care due to ageing of the population and the alarming development of Alzheimer’s Disease (AD). In healthy or pathological living being, very few studies are dealing with the ageing of the respiratory nervous control, in spite of the crucial role of respiration for brain oxygenation. This thesis presents translational research performed in mice to examine the physiological and pathological ageing of the respiratory nervous control. In mice from two transgenic strains, recognized models for AD and Rett syndrome, we describe the development of drastic respiratory neuropathologies leading to premature death. In the AD mouse model, we show for the first time that brainstem tauopathy triggers dysfunctions of the upper airways, impairs vocalization and alters respiration and respiratory control. In addition, our work suggests a deleterious effect of anaesthesia for AD and identifies new therapeutic strategies. This mouse research could well contribute to significant improvements in AD care.

No description available.

Rett Syndrome (RTT) is a neurodevelopmental disorder affecting 1 out of 10,000 females worldwide. Mutations of the X-linked MECP2 gene encoding methyl CpG binding protein 2 (MeCP2) accounts for >90% of RTT cases. People with RTT and mice with Mecp2 disruption show autonomic dysfunction, especially life-threatening breathing disorders, which involves defects in brainstem neurons for breathing controls, including neurons in the locus coeruleus (LC). Accumulating evidence obtained from Mecp2−/Y mice suggests that imbalanced excitation/inhibition or the impaired synaptic communications in central neurons plays a major role. LC neurons in Mecp2−/Ymice are hyperexcited, attributable to the deficiency in GABA synaptic inhibition. Several previous studies indicate that augmenting synaptic GABA receptors (GABARs) leads to a relief of RTT-like symptoms in mice. The extrasynaptic GABARs located outside synaptic cleft, which have the capability to produce sustained inhibition, and may be a potential therapeutic target for the rebalance of excitation/inhibition in RTT. In contrast to the rich information of the synaptic GABARs in RTT research, however, whether Mecp2 gene disruption affects the extrasynaptic GABARs remains unclear. In this study, we show evidence that the extrasynaptic GABAR mediated tonic inhibition of LC neurons was enhanced in Mecp2−/Ymice, which seems attributable to the augmented δ subunit expression. Low-dose THIP exposure, an agonist specific to δ subunit containing extrasynaptic GABARs, extended the lifespan, alleviated breathing abnormalities, enhanced motor function, and improved social behaviors of Mecp2−/Ymice. Such beneficial effects were associated with stabilization of brainstem neuronal hyperexcitability, including neurons in the LC and the mesencephalic trigeminal V nucleus (Me5), and improvement of norepinephrine (NE) biosynthesis. Such phenomena were found in symptomatic Mecp2+/− (sMecp2+/−) female mice model as well, in which the THIP exposure alleviated the hyperexcitability of both LC and Me5 neurons to a similar level as their counterparts in Mecp2−/Y mice, and improved breathing function. In identified LC neurons of sMecp2+/− mice, the hyperexcitability appeared to be determined by both MeCP2 expression and their environmental cues. In conclusion, intervention to extrasynaptic GABAAR by chronic treatment with THIP might be a therapeutic approach to RTT-like symptoms in both Mecp2−/Y and Mecp2+/− mice models and perhaps in people with RTT as well.

No description available.

Methyl-CpG-binding protein 2 (MeCP2 is) is an epigenetic regulator that binds to methylated DNA. Initially identified as transcriptional repressor, MeCP2 also binds to different proteins functioning as gene activator. Importantly, MecCP2 gene mutations and changes in MeCP2 levels are associated to several forms of mental retardation and autism-related disorders; including Rett, a neurodevelopmental disorder affecting primarily girls. While brain MeCP2 was considered to be exclusively neuronal, this regulator is also present in glia. We found that oligodendrocytes, the myelinating cells of the central nervous system (CNS), express particularly high MeCP2 levels at a developmental stage that precedes their final maturation. Moreover, downregulation of MeCP2 levels by treatment of immature oligodendrocytes with small interference RNA (siRNA), reduced the expression of 14 kDa myelin basic protein (MBP) and MOG, two markers of mature oligodendrocytes. These observations raise the possibility that oligodendrocytes have a direct participation in Rett syndrome and other autism-related disorders.

Induced pluripotent stem (iPS) cells generated from patients hold great promise for studying diseases that affect the central nervous system, as differentiation into the neuronal lineage creates a limitless supply of affected cells for disease study. Rett syndrome (RTT) is a neurodevelopmental autism spectrum disorder primarily caused by mutations in the methyl-CpG-binding protein 2 (MECP2) gene. Due to the inaccessibility of patient neurons, most of what is known about underlying phenotypes has been described using mouse models. iPS cells provide a potential solution, but reprogramming of patient cells is hampered by low efficiency, and early methods of identifying iPS cells involve transgenic techniques that are not translatable to human patient samples. The first part of this thesis describes the generation and characterization of a pluripotency reporter to address this issue. The EOS lentiviral reporter allows real-time observation of pluripotency changes during reprogramming, and is a useful tool for more efficient isolation of reprogrammed cell lines. Further, the EOS selection system can be used in a disease context to reproducibly mark and maintain disease-specific iPS cell lines for future use in disease modelling. Though iPS cells have been used to study RTT in vitro, extensive assessments of neuron function and electrophysiology have not yet been performed. In the second part of this thesis, iPS cell lines generated from a RTT mouse model were tested for their ability to model disease in vitro. Directed differentiation of multiple Mecp2-deficient and wild-type iPS cell lines to glutamatergic neurons revealed neurons that lack Mecp2 have a smaller soma size, diminished sodium currents, and are less excitable, firing fewer, prolonged action potentials that are smaller in magnitude. This deficiency in intrinsic excitability was accompanied by a dysfunction at excitatory glutamatergic synapses, which together recapitulate changes previously observed in the Mecp2-deficient mouse brain. Having accumulated counts and recordings from hundreds of neurons with consistent responses among lines, the iPS cell system is a representative model of the neuronal and synaptic defects in RTT. These results illustrate the requirement of MeCP2 in normal neuronal function, and suggest altered neuronal homeostasis or aberrant network circuitry may underlie RTT pathogenesis.

Patients with Rett Syndrome (RTT) show severe breathing disorders in addition to other neuropathological features, contributing to the high incidence of sudden unexplained death and abnormal brain development. However, the molecular and cellular mechanisms underlying the breathing disorders are still unknown. Recent studies indicate that the dysfunction of brainstem norepinephrine (NE) systems are closely associated with breathing disorders in RTT patients as well as its mice model, the Mecp2-null (Mecp2─/Y) mice. This as well as the fact the major group of NE-ergic neurons in the locus coeruleus (LC) is CO2 chemosensitive suggests that the breathing disorders in RTT may be related these LC neurons. To test this hypothesis, we took a multidisciplinary approach and systematically studied these neurons using molecular biology, in-vitro brain slices, acutely dissociated neurons, immunocytochemistry, and whole-body plethysmograph. To facilitate the electrophysiological studies, we developed a new strain of transgenic mice with GFP expression selectively in the LC neurons of both WT and Mecp2─/Y mice. Breathing activity of the Mecp2─/Y mice showed selective disruptions in responses to mild hypercapnia. The defect was alleviated with the NE uptake blocker desipramine, suggesting the involvement of NE in central CO2 chemosensitivity. In the LC region, the expressions of tyrosine hydroxylase (TH) and dopamine beta-hydroxylase (DBH) at both protein and mRNA levels reduced by ~50% in Mecp2─/Y mice. No evidence was found for selective deficiency in TH- or DBH-containing neurons in Mecp2─/Y mice, and no major loss of NE-ergic LC cells were found, indicating that the NE defect is likely to result from deficient expression of biosynthetic enzymes rather than a loss of neurons in the LC. Several intrinsic membrane properties were abnormal in Mecp2─/Y LC neurons in comparison to wild type cells, including stronger inward rectification, shorter time constant, extended action potential duration, smaller amplitude of medium afterhyperpolarization (AHP) and over-expression of fast AHP. These abnormalities seem to be associated with the altered K+ and Na+ currents. Most importantly, Mecp2─/Y LC neurons displayed defective CO2 chemosensitivity in agreement of in vivo CO2 response, likely due to excessive expression of the homomeric Kir4.1 channel. Thus, it seems that the global effect of MeCP2 on the A6 NE system contributes to the impaired systemic CO2 response as well as the breathing irregularities in Mecp2─/Y mice. Such an alteration allowed CO2 to be detected only when hypercapnia became severe, leading to periodical hyper- and hypoventilation. These findings not only provide a novel etiology for the breathing disturbances of Mecp2─/Y mice but also show direct evidence for the first time on a molecular mechanism for the central CO2 chemosensitivity.

Rett syndrome (RTT) is a rare, severe neurodevelopmental disorder, which partly develops in a predictable way, and influences many bodily functions. Regression, i.e. loss of earlier achieved abilities, is one of the clinical criteria for RTT. Research on motor function has to some extent focused on this loss, and less on the possibility to keep, regain or develop abilities. RTT is mainly verified in girls/women, and the prevalence of classic RTT in Sweden for girls born between 1965 and 1976 was 1 in 10.000-12.000. Clinical criteria are used for diagnosis, but since 1999 RTT can be confirmed by a genetic test. As there is no cure so far, development of clinical intervention and management is important, and with good treatment it is possible to improve quality of life. The main aim was to acquire more knowledge about motor development in RTT, both, early development, and development over time. Another aim was to study if there were deviating orthostatic reactions when rising from sitting to standing, and during standing, compared with normally developed, healthy people, matched by sex and age. Clinical experience as well as reports from parents showed that some people with RTT had lost abilities, some had been able to keep abilities, and some had been able to learn new abilities after regression. For good results, the person with RTT had to be motivated, and the intervention jointly planned; it was also important to realize that dyspraxia causes dependence on other people’s initiatives. Information about one person with RTT, collected over several years, showed the possibility to develop in some areas over time and the tendency to deteriorate in other areas. Studying orthostatic reactions when rising to standing, and standing for three minutes, revealed that those with RTT mainly had the same reactions as the healthy controls. The quicker initial drop in systolic blood pressure in people with RTT, when rising, has not been documented earlier.   In conclusion, this thesis shows that it is possible for some people with RTT to keep abilities, regain abilities, and also learn new abilities after regression. Since those with RTT recovered their blood pressure in the same way as the healthy controls, there is no reason to recommend limitations in standing, though the quicker initial drop in systolic blood pressure should be noted. The deterioration in walking found in our previous studies does not seem to be due to deviation in orthostatic reactions. Individual analysis, as well as good knowledge about the development of the disorder and variation in its expression, is essential. Since many people with RTT live to adulthood, planning for lifelong intervention and care is most important.

Rett Syndrome (RTT) is a neurodevelopmental disorder primarily caused by mutations in the X-linked gene methyl-CpG-binding protein 2 (MECP2). The mosaic brain environment in heterozygous (MECP2+/-) females consists of both MeCP2-wildtype (MeCP2+) and Mecp2-mutant (MeCP2-) neurons. To separate possible cell autonomous and cell non-autonomous effects three-dimensional morphological analysis was performed on individually genotyped layer V pyramidal neurons in the primary motor cortex of heterozygous (Mecp2+/-) and wild-type (Mecp2+/+) mature female mice (>8 months old) from the Mecp2tm1.1Jae line. Mecp2+/+ neurons and Mecp2+ were found to be indistinguishable while Mecp2- neurons have significantly reduced basal dendritic length (p<0.05), predominantly in the region 70-130 μm from the cell body, culminating in a total reduction of 15%. Mecp2- neurons have three (17%) fewer total branch points, lost specifically at the second and third branch orders. Thus the reduced total dendritic length in Mecp2- neurons is a result of fewer higher-order branches. Soma and nuclear areas of 30 Mecp2+/- female mice (5-21 months) with X chromosome inactivation (XCI) ratios ranging from 12% to 56% were analyzed. On average Mecp2- somata and nuclei were 15% and 13% smaller than Mecp2+ neurons respectively. The variation observed in the soma and nuclear sizes of Mecp2- neurons was not due to age, but was found to be correlated with the XCI ratio. Animals with a balanced XCI ratio (approximately 50% Mecp2-) were found to have Mecp2- neurons with a less severe cellular phenotype (11-17% smaller than Mecp2+). Animals with a highly skewed XCI ratio favouring expression of the wild-type allele (less than 30% Mecp2-) were found to have a more severe Mecp2- cellular phenotype (17-22% smaller than Mecp2+). These data support indicate that mutations in Mecp2 exert both cell autonomous and cell non- autonomous effects on neuronal morphology. / Graduate

Induced pluripotent stem (iPS) cells generated from patients hold great promise for studying diseases that affect the central nervous system, as differentiation into the neuronal lineage creates a limitless supply of affected cells for disease study. Rett syndrome (RTT) is a neurodevelopmental autism spectrum disorder primarily caused by mutations in the methyl-CpG-binding protein 2 (MECP2) gene. Due to the inaccessibility of patient neurons, most of what is known about underlying phenotypes has been described using mouse models. iPS cells provide a potential solution, but reprogramming of patient cells is hampered by low efficiency, and early methods of identifying iPS cells involve transgenic techniques that are not translatable to human patient samples. The first part of this thesis describes the generation and characterization of a pluripotency reporter to address this issue. The EOS lentiviral reporter allows real-time observation of pluripotency changes during reprogramming, and is a useful tool for more efficient isolation of reprogrammed cell lines. Further, the EOS selection system can be used in a disease context to reproducibly mark and maintain disease-specific iPS cell lines for future use in disease modelling. Though iPS cells have been used to study RTT in vitro, extensive assessments of neuron function and electrophysiology have not yet been performed. In the second part of this thesis, iPS cell lines generated from a RTT mouse model were tested for their ability to model disease in vitro. Directed differentiation of multiple Mecp2-deficient and wild-type iPS cell lines to glutamatergic neurons revealed neurons that lack Mecp2 have a smaller soma size, diminished sodium currents, and are less excitable, firing fewer, prolonged action potentials that are smaller in magnitude. This deficiency in intrinsic excitability was accompanied by a dysfunction at excitatory glutamatergic synapses, which together recapitulate changes previously observed in the Mecp2-deficient mouse brain. Having accumulated counts and recordings from hundreds of neurons with consistent responses among lines, the iPS cell system is a representative model of the neuronal and synaptic defects in RTT. These results illustrate the requirement of MeCP2 in normal neuronal function, and suggest altered neuronal homeostasis or aberrant network circuitry may underlie RTT pathogenesis.