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Microglia represent a population of resident macrophages in the central nervous system (CNS) involved in brain development and maintenance of homeostasis. As immune cells, microglial cells are the first line of defense against lesions and pathogens, contributing to tissue repair processes. Moreover, due to their direct involvement in numerous neuropathologies, microglia represent a major target for the development of new therapeutic approaches. In recent years, studies have considerably expanded our knowledge of microglia ontogeny, leading to the current model in which the microglial population, derived from early hematopoietic progenitors, is maintained locally by self-renewal. However, the molecular mechanisms underlying the differentiation, the self-renewal, and the maturation of microglial cells are still poorly understood. A precise understanding of how microglia development is regulated represents a major challenge in the field as it will help to improve reprogramming protocols for the generation of microglial cells in vitro for clinical purposes. In this work, our goal is to provide new insights into the molecular determinants underlying microglia ontogeny by taking advantage of the strengths of the zebrafish, an established model for the study of developmental hematopoiesis. We focused on two signaling pathways: Colony-stimulating factor 1 receptor (csf1r) and transforming growth factor b receptor (tgfbr), both previously identified as key regulators of microglia biology in vertebrates. As zebrafish possess two paralogous genes for CSF-1R, namely csf1ra and csf1rb, we have investigated their specific contribution to microglia ontogeny, which occurs in two successive waves in the zebrafish model. By combining the use of hematopoietic mutants for csf1ra and csf1rb with a transgenic approach, we have identified distinct functions for each paralog. According to our model, Csf1ra signaling is required for the establishment of primitive macrophage-derived embryoni, Doctorat en Sciences biomédicales et pharmaceutiques (Médecine), info:eu-repo/semantics/nonPublished

Primary congenital hydrocephalus (PCH) is characterized by ventriculomegaly, defined as a dilation of cerebral ventricles, and thought to be due to impaired cerebrospinal fluid (CSF) homeostasis. PCH, highly heterogenous in etiology, affects 1 in 1,000 live births, where its poor prognosis and lack of satisfactory treatments, underscores our incomplete understanding of PCH pathogenesis. While epidemiological data suggest an underlying genetic cause in up to 40% of congenital hydrocephalus cases, few genes have been discovered as causal of PCH where ventriculomegaly is the sole or primary clinical feature.The work presented within this thesis represents the study through whole-exome sequencing (WES) of a cohort of 28 inbred/outbred families with PCH. Analysis for rare transmitted or de novo mutations (MAF <0.005) uncovered novel mutations in known genes associated with PCH (POMT2, POMGNT1, CRADD, ARID1A and KIDINS220), thus broadening the spectrum of known mutations in PCH. In a consanguineous family we identified a mutation in KIDINS220 shared among the three fetuses presenting brain ventriculomegaly and limb contractures, a gene previously reported in one family with an identical phenotype. Through immunoprecipitation experiments, we showed that the mutation diminished the interaction of KIDINS220 with TrkA, a receptor important in cell survival signaling.In three PCH probands, we identified variants in three potential candidate genes, which reflect the heterogenous genetic landscape of PCH as they are involved in minor spliceosome (RNPC3), angiogenesis (TIE1) and ciliary structure (DNAH2). Though literature poses these genes as strong candidates, further investigation will be required to ascertain them as such.With the increasing number of reports demonstrating that disorders traditionally considered as monogenic are in fact caused by a combination of mutant genes, possible oligogenic inheritance of human PCH was investigated. As ciliary defects of motile and more, Doctorat en Sciences biomédicales et pharmaceutiques (Médecine), info:eu-repo/semantics/nonPublished

Sepsis-associated brain dysfunction (SABD) is the acute brain dysfunction that occurs during sepsis as a wide range of neurologic deficits - from intermittent episodes of disorientation to coma. SABD has been associated with mortality, but it is not clear whether brain dysfunction increases the risk of death per se in critically ill patients or is just a marker of sepsis severity. Furthermore, the neurologic status of septic patients is often fluctuating, but whether the trend in neurological condition has a prognostic value is not known. The impact of brain dysfunction on in-hospital mortality in critically ill patients has been investigated in the first part of this research project. Data from 7192 (2096 septic and 5096 non-septic) patients from multiple centres were analysed; brain failure was defined as neurological sequential organ failure assessment (nSOFA) score 3–4 (i.e. GCS ≤ 9). At multivariable analysis, sepsis and brain failure entailed an increased risk of death compared with non-septic patients with normal brain function, with an adjusted risk ratio (RR) and 95% confidence interval (95%CI) of 1.66 (1.31–2.09) and 4.85 (3.33–7.07), respectively. In case of simultaneous presence of sepsis and brain failure the RR was 5.61 (3.93–8.00). Brain deterioration – defined as an increased in nSOFA over the first 3 days of intensive care unit (ICU) stay - was associated with increased in-hospital mortality in both septic and non-septic patients. However, the risk of death septic patients who experienced brain improvement – defined as a decrease in nSOFA over the first 3 days of ICU stay - was the same as that of non-septic patients without brain dysfunction. Although pathogenesis of SABD is still unclear, cerebral perfusion alterations likely play a role. Cerebral perfusion pressure (CPP) is the difference between mean systemic arterial pressure (MAP) and intracranial pressure (ICP), thus MAP reductions or ICP increases might lead to reduced CPP. MAP is frequently, Doctorat en Sciences médicales (Médecine), info:eu-repo/semantics/nonPublished

The mechanisms underlying the human brain evolution constitute one of the mostfascinating unresolved questions of biology. Our lab recently identified more than 30human-specific gene families highly and dynamically expressed during human corticaldevelopment. We focus our study on one such family that contains human-specificparalogs to the ancestral gene WASH1, previously involved in actin polymerizationand endosome trafficking. Using in vivo analyses in the mouse and in vitro models,we present evidence that the WASH1 human-specific paralogs WASH1P affectscortical neuron migration and fate acquisition in vivo, which is phenocopied by loss offunction of WASH1 ancestral gene. Our data reveal the requirement of the WASH1complex for normal cortical development, and that it is influenced by human-specificmodifiers, with potential implication for human brain evolution., Les liens entre le développement et l’évolution du cerveau constituent l’un desmystères les plus fascinants de la biologie. Notre laboratoire a précédemment identifiéplus de 30 familles de gènes résultant de duplications chez les hominidés, exprimésau cours du développement du cortex cérébral humain. Dans ce travail, j’ai étudiél’une de ces familles de gènes, composée des paralogues spécifiquement humainsdu gène ancestral WASH1, précedemment impliqué dans la polymérisation d’actineet le contrôle du transport endosomal. Nous avons identifié plusieurs paralogues quisemblent être fortement exprimés au cours du développement cortical humain, enparticulier WASH1P, que nous avons identifié comme inhibiteur de la fonction deWASH1 dans le trafic des endosomes. De plus, nous montrons que le gain de fonctiondu paralogue WASH1P in vivo chez la souris affecte la migration des neuronescorticaux et favorise l’acquisition du destin neuronal des couches superficielles ducortex. Les mêmes phénotypes sont observés dans des souris déficientes pourWASH1, indiquant que WASH1P peut influencer la corticogenèse de la souris via uneinteraction avec WASH1. Les mécanismes moléculaires sous-jacents et leurpertinence potentielle pour l'évolution du cerveau humain sont également explorés., Doctorat en Sciences biomédicales et pharmaceutiques (Médecine), info:eu-repo/semantics/nonPublished

Friedreich ataxia is an autosomal recessive multisystem disorder with prominent neurological manifestations and cardiac involvement. The disease is caused by large GAA expansions in the first intron of the FXN gene, encoding the mitochondrial protein frataxin, resulting in downregulation of gene expression and reduced synthesis of frataxin. The selective loss of proprioceptive neurons is a hallmark of Friedreich ataxia, but the cause of the specific vulnerability of these cells is still unknown. We herein perform an in vitro characterization of human induced pluripotent stem cell-derived sensory neuronal cultures highly enriched for primary proprioceptive neurons. We employ neurons differentiated from healthy donors, Friedreich ataxia patients and Friedreich ataxia sibling isogenic control lines. The analysis of the transcriptomic and proteomic profile suggests an impairment of cytoskeleton organization at the growth cone, neurite extension and, at later stages of maturation, synaptic plasticity. Alterations in the spiking profile of tonic neurons are also observed at the electrophysiological analysis of mature neurons. Despite the reversal of the repressive epigenetic state at the FXN locus and the restoration of FXN expression, isogenic control neurons retain many features of Friedreich ataxia neurons. Our study suggests the existence of abnormalities affecting proprioceptors in Friedreich ataxia, particularly their ability to extend towards their targets and transmit proper synaptic signals. It also highlights the need for further investigations to better understand the mechanistic link between FXN silencing and proprioceptive degeneration in Friedreich ataxia., SCOPUS: ar.j, info:eu-repo/semantics/published

Résumé :La maladie d’Alzheimer (MA) est une maladie neurodégénérative, incurable, composée de deux lésions neuropathologiques :les plaques amyloïdes et les dégénérescences neurofibrillaires (DNF). Ces dernières sont composées de protéines tau hyperphosphorylées qui s’accumulent et s’agrègent dans le corps cellulaire des neurones en formant des filaments torsadés nommés « PHF » en anglais pour « Paired Helical Filaments ». Au cours de l’évolution de la maladie, la progression de la pathologie tau, mise en évidence par la présence des DNF dans le cerveau, semble être dépendante de voies neuroanatomiquement connectées. Cette observation a conduit à l’hypothèse que la protéine tau pourrait se comporter comme une protéine prion. Dans cette hypothèse, les protéines tau anormales doivent être internalisées par les cellules cibles pour opérer un changement physico-chimique des protéines tau endogènes (nucléation), qui, à leur tour acquièrent des caractéristiques pathologiques pouvant être transmises dans de nouvelles cellules (propagation). Néanmoins, contrairement aux prions, le caractère transmissible des protéines tau pathologiques n’a jamais été démontré.Des contaminations iatrogènes de protéines prions ont été reportées ou suspectées à la suite de transfusions sanguines ou de greffes de cornées. Afin d’évaluer les similitudes possibles entre les prions et la protéine tau, nous avons analysé la transmission éventuelle de la pathologie tau par le sang ou à la suite d’une chirurgie oculaire en procédant à des injections intravasculaires ou intraoculaires de PHF-tau, isolés de cerveaux de patients décédés de la MA, dans des souris sauvages (WT) ou transgéniques exprimant une protéine tau et/ou amyloïde humaine sauvage ou mutée.Les capacités de nucléation et de propagation des PHF-tau humains ont été validées in vitro à l’aide d’un modèle cellulaire de détection de l’activité de nucléation de la protéine tau et in vivo en utilisant des injections intracérébrales dans des so, Doctorat en Sciences biomédicales et pharmaceutiques (Médecine), info:eu-repo/semantics/nonPublished

Friedreich Ataxia (FRDA) is an autosomal recessive multisystem disorder with prominent neurological manifestations, which include the early and severe loss of large primary proprioceptive neurons (PPNs) of the Dorsal Root Ganglia (DRGs) and, at a later stage, the degeneration of cerebellar and pyramidal systems. The disease is caused by the hyperexpansion of a GAA triplet repeat in the first intron of the FXN gene, encoding the mitochondrial protein frataxin (FXN), which is involved in iron-sulfur cluster biogenesis. The expanded GAA tract promotes chromatin condensation and disrupts FXN mRNA transcription, leading to reduced FXN levels, impaired mitochondrial function and altered iron metabolism. Despite notable progress in the identification of the underlying causes of FRDA, neither the details of these pathogenic processes nor the reason for the specific vulnerability of the proprioceptive system and a limited number of other cell types are yet fully understood. Human induced pluripotent stem cells (iPSCs) are used to generate models of human diseases that recapitulate the pathogenic process as it occurs in affected cell types. Studies conducted so far in FRDA have mainly utilized iPSC-derived cortical neurons and cardiomyocytes, which have shown to recapitulate essential aspects of FRDA pathogenesis that are at least partially corrected by restoring FXN expression. However, those studies can only provide a limited view of the effects that FXN silencing has in vivo, because the neuronal type utilized so far is not affected in FRDA patients. On the other side, efforts to differentiate iPSCs into primary sensory neurons have only succeeded in generating an unselected mixed neuronal population with a small minority of proprioceptors.Having an in vitro source of PPNs would enable the study of the alterations which are specifically induced and the pathways which are impaired by frataxin deficiency in these cells, helping in the understanding of their unique neuronal p, L'ataxie de Friedreich (FRDA) est une pathologie héréditaire autosomale récessive caractérisée par des manifestations neurologiques importantes, qui comprennent la perte précoce et sévère des neurones proprioceptifs (PPN) des ganglions de la racine dorsale (DRG) et, à un stade ultérieur, l’atteinte des systèmes cérébelleux et pyramidaux.La maladie est causée par une expansion de triplets nucléotidiques GAA au sein du premier intron du gène FXN, qui code pour la protéine mitochondriale frataxine (FXN), impliquée dans la biogenèse des centres fer-soufre (Fe-S). Cette expansion GAA induit la formation d’hétérochromatine et perturbe la transcription du gène FXN, entraînant une réduction des niveaux de frataxine, une altération de la fonction mitochondriale et une altération du métabolisme du fer. Malgré des progrès notables dans l'identification des causes de la maladie, ni les détails de ces processus pathogènes ni la raison de la vulnérabilité spécifique du système proprioceptif et d'un nombre limité d'autres types de cellules ne sont encore entièrement élucidés.Les cellules souches pluripotentes induites (iPSC) sont utilisées pour générer des modèles de maladies humaines qui récapitulent le processus pathogénique tel qu'il se manifeste dans les cellules affectées. Les études menées jusqu'à présent dans l’ataxie de Friedreich ont principalement utilisé des neurones corticaux et des cardiomyocytes dérivés des iPSC FRDA, qui présentent les aspects essentiels de la pathogenèse de FRDA, qui sont partiellement corrigés après la restauration de l’expression du gène FXN. Cependant, ces études ne peuvent fournir qu'une vision limitée des effets de la diminution de la transcription du gène FXN, car le type neuronal utilisé n'est pas affecté dans la maladie. D'autre part, les efforts pour différencier les iPSC en neurones sensoriels primaires n'ont réussi qu'à générer une population neuronale mixte avec une faible proportion de neurones de type proprioceptif. Disposer d'une sou, Doctorat en Sciences biomédicales et pharmaceutiques (Médecine), info:eu-repo/semantics/nonPublished

The work at hand will describe the influence of the Glycine receptor alpha 2 subunit and the glycinergic system on the development of Medium Spiny Neurons (MSNs) in the dorsal striatum. We will begin by giving a short introduction into the different structures of the CNS with deeper focus on the structures relevant for this work. Furthermore, we will introduce the neurons we investigate in this work and the different chapters. Finally, a more in depth introduction will describe the glycinergic system in the CNS and its most known physiological functions. Eventually we can establish the context in which we did this research about the effect of the Glycine receptor alpha 2 subunit in the development in medium spiny neurons (MSNs)., Doctorat en Sciences biomédicales et pharmaceutiques (Médecine), info:eu-repo/semantics/nonPublished

The principal neurons of the striatum - the spiny projection neurons (SPNs) - make inhibitory synaptic connections with each other via collaterals of their main axon, forming a local lateral inhibition network. Serotonin, acting via the 5-HT1B receptor, modulates neurotransmitter release from SPN terminals in striatal output nuclei, but the role of 5-HT1B receptors in lateral inhibition among SPNs in the striatum is unknown. Here we report the effects of 5-HT1B receptor activation on lateral inhibition in the mouse striatum. Whole-cell recordings were made from SPNs in acute brain slices of either sex, while optogenetically activating presynaptic SPNs or fast-spiking interneurons (FSIs). Activation of 5-HT1B receptors significantly reduced the amplitude of inhibitory postsynaptic currents (IPSCs) evoked by optical stimulation of both direct and indirect pathway SPNs. This reduction was blocked by application of a 5-HT1B receptor antagonist. Activation of 5-HT1B receptors did not reduce the amplitude of IPSCs evoked from FSIs. These results suggest a new role for serotonin as a modulator of lateral inhibition among striatal SPNs. The 5-HT1B receptor may, therefore, be a suitable target for future behavioral experiments investigating the currently unknown role of lateral inhibition in the function of the striatum.Significance StatementWe show that stimulation of serotonin receptors reduces the efficacy of lateral inhibition between spiny projection neurons - one of the biggest GABAergic sources in the striatum - by activation of the serotonin 5-HT1B receptor. The striatum receives serotonergic input from the dorsal raphe nuclei and is important in behavioral brain functions like learning and action selection. Our findings suggest a new role for serotonin in modulating the dynamics of neural interactions in the striatum, which extends current knowledge of the mechanisms of the behavioral effects of serotonin., SCOPUS: ar.j, info:eu-repo/semantics/published

Pour pouvoir communiquer efficacement dans son environnement social naturel, l’être humain doit pouvoir isoler le discours de son interlocuteur des autres voix composants le bruit ambiant. Cette situation, connue sous l’expression « d’effet cocktail party », va engager notre cerveau dans différents processus auditifs et attentionnels lui permettant d’analyser spécifiquement le signal acoustique de son interlocuteur. La façon dont le cerveau procède pour extraire les attributs acoustiques de la voix d’intérêt de l’ensemble de la scène auditive restent toutefois méconnus. Cette méconnaissance est d’autant plus importante que certaines populations peuvent présenter des troubles de compréhension dans le bruit alors que leur système auditif périphérique ne présente aucun déficit (comme les enfants ou chez certains jeunes adultes). L’objectif de cette thèse de doctorat était d’identifier les mécanismes corticaux permettant la compréhension dans le bruit et d’évaluer si ceux-ci étaient déficitaires dans deux populations souffrant de troubles de compréhension dans le bruit sans atteinte auditive périphérique. Pour y parvenir, nous avons étudié par magnétoencéphalographie le couplage entre l’activité corticale d’un auditeur et les différentes voix constituant une scène auditive de type cocktail party. Ces investigations ont été menées chez des sujets sains (étude I), chez des enfants (étude II) ainsi que chez des jeunes adultes présentant des troubles isolés de la compréhension dans le bruit (étude III). Nos études ont révélé que le cortex auditif suit sélectivement la voix d’intérêt plutôt que la scène auditive globale. Ce couplage « cerveau-parole » se produit à des fréquences correspondant aux fluctuations rythmiques de la prosodie (<1 Hz), des mots (1–4 Hz) et des syllabes (4–8 Hz), et diminue lorsque le niveau de bruit augmente. De plus, le couplage « cerveau-parole » à <1 Hz est latéralisé dans l'hémisphère gauche en présence d’un bruit de type cocktail party. Enfin, u, Doctorat en Sciences médicales (Médecine), info:eu-repo/semantics/nonPublished