Traduction locale et dynamique dans les prolongements astrocytaires périsynaptiques de l'hippocampe

Les astrocytes sont les cellules gliales les plus nombreuses du système nerveux central. Elles présentent une morphologie très ramifiée, envoyant des prolongements vers les vaisseaux sanguins où elles régulent les fonctions vasculaires, et vers les neurones où elles contrôlent la formation, la maturation et l’élimination des synapses. Les mécanismes sous-jacents à ces fonctions polarisées restent peu connus. La présence d’une traduction locale aux interfaces périvasculaire et périsynaptique des astrocytes a été récemment décrite. L’objectif de cette thèse était donc de définir le répertoire complet d’ARNm polysomaux à l’interface périsynaptique des astrocytes de l’hippocampe dorsale, une région du cerveau impliquée dans la mémoire contextuelle. Nous avons ensuite comparé la distribution relative d’une vingtaine d’ARNm polysomaux entre les prolongements périsynaptiques et périvasculaires. Les astrocytes sont connus pour leur contribution aux mécanismes d’apprentissage et de mémoire. Nous avons donc étudié le rôle physiologique de la traduction locale dans les prolongements périsynaptiques astrocytaires en observant les changements de traduction locale chez des souris exposées à une tâche de conditionnement à la peur. Cette thèse révèle, pour la première fois, des changements de traduction locale liés à l’activité neuronale dans les prolongements périsynaptiques astrocytaires.Astrocytes are the most numerous glial cells in the central nervous system. They display a highly ramified morphology, with processes extending towards blood vessels, where they regulate vascular functions, and towards neurons where they control the formation, maturation and elimination of synapses. The mechanisms sustaining these polarized functions in astrocytes remain elusive. Local translation was recently identified in astroglial processes, at both the perisynaptic and perivascular interface. We therefore aimed at defining the entire repertoire of polysomal mRNAs translated in perisynaptic processes of the dorsal hippocampus, a region of the brain involved in contextual memory. We then compared the relative distribution of polysomal transcripts between perivascular and perisynaptic processes of hippocampal astrocytes. Finally, as astrocytes are known to contribute to memory and learning, we investigated the physiological implication of perisynaptic astrocytic protein synthesis in these processes by subjecting mice to a contextual fear conditioning paradigm and assessing the resulting changes in local translation. This thesis highlights, for the first time, the presence of activity-dependent local translation in perisynaptic processes of astrocytes

Traduction locale et dynamique dans les prolongements astrocytaires périsynaptiques de l'hippocampe

Astrocytes are the most numerous glial cells in the central nervous system. They display a highly ramified morphology, with processes extending towards blood vessels, where they regulate vascular functions, and towards neurons where they control the formation, maturation and elimination of synapses. The mechanisms sustaining these polarized functions in astrocytes remain elusive. Local translation was recently identified in astroglial processes, at both the perisynaptic and perivascular interface. We therefore aimed at defining the entire repertoire of polysomal mRNAs translated in perisynaptic processes of the dorsal hippocampus, a region of the brain involved in contextual memory. We then compared the relative distribution of polysomal transcripts between perivascular and perisynaptic processes of hippocampal astrocytes. Finally, as astrocytes are known to contribute to memory and learning, we investigated the physiological implication of perisynaptic astrocytic protein synthesis in these processes by subjecting mice to a contextual fear conditioning paradigm and assessing the resulting changes in local translation. This thesis highlights, for the first time, the presence of activity-dependent local translation in perisynaptic processes of astrocytes.Les astrocytes sont les cellules gliales les plus nombreuses du système nerveux central. Elles présentent une morphologie très ramifiée, envoyant des prolongements vers les vaisseaux sanguins où elles régulent les fonctions vasculaires, et vers les neurones où elles contrôlent la formation, la maturation et l’élimination des synapses. Les mécanismes sous-jacents à ces fonctions polarisées restent peu connus. La présence d’une traduction locale aux interfaces périvasculaire et périsynaptique des astrocytes a été récemment décrite. L’objectif de cette thèse était donc de définir le répertoire complet d’ARNm polysomaux à l’interface périsynaptique des astrocytes de l’hippocampe dorsale, une région du cerveau impliquée dans la mémoire contextuelle. Nous avons ensuite comparé la distribution relative d’une vingtaine d’ARNm polysomaux entre les prolongements périsynaptiques et périvasculaires. Les astrocytes sont connus pour leur contribution aux mécanismes d’apprentissage et de mémoire. Nous avons donc étudié le rôle physiologique de la traduction locale dans les prolongements périsynaptiques astrocytaires en observant les changements de traduction locale chez des souris exposées à une tâche de conditionnement à la peur. Cette thèse révèle, pour la première fois, des changements de traduction locale liés à l’activité neuronale dans les prolongements périsynaptiques astrocytaires

Connexin 30 is expressed in a subtype of mouse brain pericytes

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AstroDot -a new method for studying the spatial distribution of mRNA in astrocytes

International audienceAstrocytes are morphologically complex and use local translation to regulate distal functions. To study the distribution of mRNA in astrocytes, we combined mRNA detection via in situ hybridization with immunostaining of the astrocyte-specific intermediate filament glial fibrillary acidic protein (GFAP). mRNAs at the level of GFAP-immunolabelled astrocyte somata, and large and fine processes were analysed using AstroDot, an ImageJ plug-in and the R package AstroStat. Taking the characterization of mRNAs encoding GFAP-α and GFAP-δ isoforms as a proof of concept, we showed that they mainly localized on GFAP processes. In the APPswe/PS1dE9 mouse model of Alzheimer's disease, the density and distribution of both α and δ forms of Gfap mRNA changed as a function of the region of the hippocampus and the astrocyte's proximity to amyloid plaques. To validate our method, we confirmed that the ubiquitous Rpl4 (large subunit ribosomal protein 4) mRNA was present in astrocyte processes as well as in microglia processes immunolabelled for ionized calcium binding adaptor molecule 1 (Iba1; also known as IAF1). In summary, this novel set of tools allows the characterization of mRNA distribution in astrocytes and microglia in physiological or pathological settings

Physiopathological changes of ferritin mRNA density and distribution in hippocampal astrocytes in the mouse brain

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Local Translation in Perisynaptic Astrocytic Processes Is Specific and Changes after Fear Conditioning

International audienceLocal translation is a conserved mechanism conferring cells the ability to quickly respond to local stimuli. Inthe brain, it has been recently reported in astrocytes, whose fine processes contact blood vessels and synapses.Yet the specificity and regulation of astrocyte local translation remain unknown. We study hippocampalperisynaptic astrocytic processes (PAPs) and show that they contain the machinery for translation. Usinga refined immunoprecipitation technique, we characterize the entire pool of ribosome-bound mRNAs in PAPsand compare it with the one expressed in the whole astrocyte. We find that a specific pool of mRNAs is highlypolarized at the synaptic interface. These transcripts encode an unexpected molecular repertoire, composedof proteins involved in iron homeostasis, translation, cell cycle, and cytoskeleton. Remarkably, we observealterations in global RNA distribution and ribosome-bound status of some PAP-enriched transcripts afterfear conditioning, indicating the role of astrocytic local translation in memory and learning

Translation in astrocyte distal processes sets molecular heterogeneity at the gliovascular interface

International audienceAstrocytes send out long processes that are terminated by endfeet at the vascular surface and regulate vascular functions as well as homeostasis at the vascular interface. To date, the astroglial mechanisms underlying these functions have been poorly addressed. Here we demonstrate that a subset of messenger RNAs is distributed in astrocyte endfeet. We identified, among this transcriptome, a pool of messenger RNAs bound to ribosomes, the endfeetome, that primarily encodes for secreted and membrane proteins. We detected nascent protein synthesis in astrocyte endfeet. Finally, we determined the presence of smooth and rough endoplasmic reticulum and the Golgi apparatus in astrocyte perivascular processes and endfeet, suggesting for local maturation of membrane and secreted proteins. These results demonstrate for the first time that protein synthesis occurs in astrocyte perivascular distal processes that may sustain their structural and functional polarization at the vascular interface

Translation in astrocyte distal processes sets molecular heterogeneity at the gliovascular interface

International audienceAstrocytes send out long processes that are terminated by endfeet at the vascular surface and regulate vascular functions as well as homeostasis at the vascular interface. To date, the astroglial mechanisms underlying these functions have been poorly addressed. Here we demonstrate that a subset of messenger RNAs is distributed in astrocyte endfeet. We identified, among this transcriptome, a pool of messenger RNAs bound to ribosomes, the endfeetome, that primarily encodes for secreted and membrane proteins. We detected nascent protein synthesis in astrocyte endfeet. Finally, we determined the presence of smooth and rough endoplasmic reticulum and the Golgi apparatus in astrocyte perivascular processes and endfeet, suggesting for local maturation of membrane and secreted proteins. These results demonstrate for the first time that protein synthesis occurs in astrocyte perivascular distal processes that may sustain their structural and functional polarization at the vascular interface

mTORC1 signaling and primary cilia are required for brain ventricle morphogenesis

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