Emerging Role of Neuronal Exosomes in the Central Nervous System

Exosomes are small extracellular vesicles, which stem from endosomes fusing with the plasma membrane, and can be recaptured by receiving cells. They contain lipids, proteins, and RNAs able to modify the physiology of receiving cells. Functioning of the brain relies on intercellular communication between neural cells. These communications can modulate the strength of responses at sparse groups of specific synapses, to modulate circuits underlying associations and memory. Expression of new genes must then follow to stabilize the long-term modifications of the synaptic response. Local changes of the physiology of synapses from one neuron driven by another, have so far been explained by classical signal transduction to modulate transcription, translation, and posttranslational modifications. In vitro evidence now demonstrates that exosomes are released by neurons in a way depending on synaptic activity; these exosomes can be retaken by other neurons suggesting a novel way for inter-neuronal communication. The efficacy of inter-neuronal transfer of biochemical information allowed by exosomes would be far superior to that of direct cell-to-cell contacts or secreted soluble factors. Indeed, lipids, proteins, and RNAs contained in exosomes secreted by emitting neurons could directly modify signal transduction and protein expression in receiving cells. Exosomes could thus represent an ideal mechanism for inter-neuronal transfer of information allowing anterograde and retrograde signaling across synapses necessary for plasticity. They might also allow spreading across the nervous system of pathological proteins like PrPsc, APP fragments, phosphorylated Tau, or Alpha-synuclein

Impact of anatase and rutile titanium dioxide nanoparticles on uptake carriers and efflux pumps in Caco-2 gut epithelial cells

International audienceTiO2 microparticles are widely used in food products, where they are added as a white food colouring agent. This food additive contains a significant amount of nanoscale particles; still the impact of TiO2 nanoparticles (TiO2-NPs) on gut cells is poorly documented. Our study aimed at evaluating the impact of rutile and anatase TiO2-NPs on the main functions of enterocytes, i.e. nutrient absorption driven by solute-liquid carriers (SLC transporters) and protection against other xenobiotics driven by efflux pumps from the ATP-binding cassette (ABC) family. We show that acute exposure of Caco-2 cells to both anatase (12 nm) and rutile (20 nm) TiO2-NPs induce early upregulation of a battery of efflux pumps and nutrient transporters. In addition they cause overproduction of reactive oxygen species and misbalance redox repair systems, without inducing cell mortality or DNA damage. Taken together, these data suggest that TiO2-NPs may increase the functionality of gut epithelial cells, particularly their property to form a protective barrier against exogenous toxicants and to absorb nutrients

Regulation of Postsynaptic Function by the Dementia-Related ESCRT-III Subunit CHMP2B

The charged multivesicular body proteins (Chmp1–7) are an evolutionarily conserved family of cytosolic proteins that transiently assembles into helical polymers that change the curvature of cellular membrane domains. Mutations in human CHMP2B cause frontotemporal dementia, suggesting that this protein may normally control some neuron-specific process. Here, we examined the function, localization, and interactions of neuronal Chmp2b. The protein was highly expressed in mouse brain and could be readily detected in neuronal dendrites and spines. Depletion of endogenous Chmp2b reduced dendritic branching of cultured hippocampal neurons, decreased excitatory synapse density in vitro and in vivo, and abolished activity-induced spine enlargement and synaptic potentiation. To understand the synaptic effects of Chmp2b, we determined its ultrastructural distribution by quantitative immuno-electron microscopy and its biochemical interactions by coimmunoprecipitation and mass spectrometry. In the hippocampus in situ, a subset of neuronal Chmp2b was shown to concentrate beneath the perisynaptic membrane of dendritic spines. In synaptoneurosome lysates, Chmp2b was stably bound to a large complex containing other members of the Chmp family, as well as postsynaptic scaffolds. The supramolecular Chmp assembly detected here corresponds to a stable form of the endosomal sorting complex required for transport-III (ESCRT-III), a ubiquitous cytoplasmic protein complex known to play a central role in remodeling of lipid membranes. We conclude that Chmp2b-containing ESCRT-III complexes are also present at dendritic spines, where they regulate synaptic plasticity. We propose that synaptic ESCRT-III filaments may function as a novel element of the submembrane cytoskeleton of spines

Etude du rôle dans le trafic membranaire de trois protéines qui lient les microtubules et qui sont associées à l'appareil de Golgi

L'appareil de Golgi est une structure dynamique dont la morphologie dépend conjointement du réseau de microtubules et du transport membranaire. Je me suis donc intéressée an rôle dans le trafic intracellulaire de trois protéines qui sont associées à l'appareil de Golgi et qui interagissent avec les microtubules. En premier lieu, j'ai étudié l'interaction de la rabkinésine-6 avec les membranes de l'appareil de Golgi. J'ai montré qua la domaine carboxy-terminal de ce moteur est suffisant pour lier les membranes in vitro. Néanmoins, cette liaison est sensible à la force ionique et ne permet pas d'adresser spécifiquement la rabkinésine-6 sur l'appareil de Golgi in vivo. En second lieu, j'ai analysé le phénotype de la surexpression de GMAP-210, une protéine localisée sur la face cis de l'appareil de Golgi qui interagit avec l'extrémité négative des microtubules. J'ai montré, an microscopie électronique, qua la transfection transitoire de cette protéine entraînait le désorganisation de l'appareil de Golgi et la formation concomitante d'amas de vésicules qui contiennent les enzymes de l'appareil de Golgi ainsi qua les protéines qui effectuent des cycles entre le RE et l'appareil de Golgi. De plus, j'ai montré que dans ces cellules le transport antérograde de même que le transport rétrograde entre le RE et l'appareil de Golgi est bloqué au niveau des amas de vésicules. Enfin, j'ai participé à la caractérisation de CLIPR-59, une nouvelle protéine qui contient deux sites de liaison aux microtubules et qui est localisée sur la face trans de l'appareil de Golgi. Par des expérience de transfection transitoire, j'ai aussi montré qua la surexpression de cette protéine entraînait l'accumulation de structures de type endosomale à proximité de l'appareil de Golgi. Ces résultats suggèrent que CLIPR-59 intervient dans la régulation du transport membranaire entre l'appareil do Golgi et le système endosomal.The Golgi apparatus is a dynamic structure which morphology depends both on the microtubule network and on membrane transport. I have therefore studied the role in membrane traffic of three proteins that are associated to the Golgi apparatus and that interact with microtubules. First I have studied the interaction of rabkinesin-6 with Golgi membranes. I have shown that the carboxy-terminal domain of this motor protein is sufficient to bind membranes in vitro. However, this interaction is salt sensitive and can not account for the targetting of rabkinesin-6 to Golgi membrane in vivo. Then I have analyzed the phenotype of GMAP-210 overexpressing cells. GMAP-210 is a protein that is localized on the cis side of the Golgi apparatus and that interacts with microtubule minus end. I have shown, by electron microscopy, that the transfection of this protein leads to the disassembly of the Golgi apparatus and induces the formation of vesicle clusters that contain both Golgi enzyme and proteins that cycle between the ER and the Golgi apparatus. Moreover, I have shown that in these cells both anterograde and retrograde transport between the ER and the Golgi apparatus are blocked at the level of these vesicle clusters. Finally, I have participated to the characterization of CLIPR-59, a new protein that has two microtubule binding sites and which is localized on the trans side of the Golgi apparatus. In addition, I have shown that the overexpression of this protein induces the accumulation of endosomal membrane in close apposition of the Golgi apparatus. These results suggest that CLIPR-59 is involved in the regulation of membrane transport between the Golgi apparatus and the endosomal system.ORSAY-PARIS 11-BU Sciences (914712101) / SudocSudocFranceF

Astrocyte-neuron interplay is critical for Alzheimer's disease pathogenesis and is rescued by TRPA1 channel blockade

International audienceAbstract The sequence of cellular dysfunctions in preclinical Alzheimer’s disease must be understood if we are to plot new therapeutic routes. Hippocampal neuronal hyperactivity is one of the earliest events occurring during the preclinical stages of Alzheimer’s disease in both humans and mouse models. The most common hypothesis describes amyloid-β accumulation as the triggering factor of the disease but the effects of this accumulation and the cascade of events leading to cognitive decline remain unclear. In mice, we previously showed that amyloid-β-dependent TRPA1 channel activation triggers hippocampal astrocyte hyperactivity, subsequently inducing hyperactivity in nearby neurons. In this work, we investigated the potential protection against Alzheimer's disease progression provided by early chronic pharmacological inhibition of the TRPA1 channel. A specific inhibitor of TRPA1 channel (HC030031) was administered intraperitoneally from the onset of amyloid-β overproduction in the APP/PS1-21 mouse model of Alzheimer’s disease. Short-, medium- and long-term effects of this chronic pharmacological TRPA1 blockade were characterized on Alzheimer’s disease progression at functional (astrocytic and neuronal activity), structural, biochemical and behavioural levels. Our results revealed that the first observable disruptions in the Alzheimer’s disease transgenic mouse model used correspond to aberrant hippocampal astrocyte and neuron hyperactivity. We showed that chronic TRPA1 blockade normalizes astrocytic activity, avoids perisynaptic astrocytic process withdrawal, prevents neuronal dysfunction and preserves structural synaptic integrity. These protective effects preserved spatial working memory in this Alzheimer’s disease mouse model. The toxic effect of amyloid-β on astrocytes triggered by TRPA1 channel activation is pivotal to Alzheimer’s disease progression. TRPA1 blockade prevents irreversible neuronal dysfunction, making this channel a potential therapeutic target to promote neuroprotection

Exosomes as a novel way of interneuronal communication.

International audienceExosomes are small extracellular vesicles which stem from endosomes fusing with the plasma membrane; they contain lipids, proteins and RNAs that are able to modify receiving cells. Functioning of the brain relies on synapses, and certain patterns of synaptic activity can change the strength of responses at sparse groups of synapses, to modulate circuits underlying associations and memory. These local changes of the synaptic physiology in one neuron driven by another have, so far, been explained by classical signal transduction modulating transcription, translation and post-translational modifications. We have accumulated in vitro evidence that exosomes released by neurons in a way depending on synaptic activity can be recaptured by other neurons. Some lipids, proteins and RNAs contained in exosomes secreted by emitting neurons could directly modify signal transduction and protein expression in receiving cells. Exosomes may be an ideal mechanism for anterograde and retrograde information transfer across synapses underlying local changes in synaptic plasticity. Exosomes might also participate in the spreading across the nervous system of pathological proteins such as PrPSc (abnormal disease-specific conformation of prion protein), APP (amyloid precursor protein) fragments, phosphorylated tau or α-synuclein

TCF12 controls oligodendroglial cell proliferation and regulates signaling pathways conserved in gliomas

International audienceAbstract Diffuse gliomas are primary brain tumors originating from the transformation of glial cells. In particular, oligodendrocyte precursor cells constitute the major tumor-amplifying population in the gliomagenic process. We previously identified the TCF12 gene, encoding a transcription factor of the E protein family, as being recurrently mutated in oligodendrogliomas. In this study, we sought to understand the function of TCF12 in oligodendroglial cells, the glioma lineage of origin. We first describe TCF12 mRNA and protein expression pattern in oligodendroglial development in the mouse brain. Second, by TCF12 genome wide chromatin profiling in oligodendroglial cells, we show that TCF12 binds active promoters of genes involved in proliferation, translation/ribosomes, and pathways involved in oligodendrocyte development and cancer. Finally, we perform OPC-specific Tcf12 inactivation in vivo and demonstrate by immunofluorescence and transcriptomic analyses that TCF12 is transiently required for OPC proliferation but dispensable for oligodendrocyte differentiation. We further show that Tcf12 inactivation results in deregulation of biological processes that are also altered in oligodendrogliomas. Together, our data suggest that TCF12 directly regulates transcriptional programs in oligodendroglia development that are relevant in a glioma context