Glial Glutamate Transporters and Maturation of the Mouse Somatosensory Cortex

In the adult nervous system, glutamatergic neurotransmission is tightly controlled by neuron-glia interactions through glial glutamate reuptake by the specific transporters GLT-1 and GLAST. Here, we have explored the role of these transporters in the structural and functional maturation of the somatosensory cortex of the mouse. We provide evidence that GLT-1 and GLAST are early and selectively expressed in barrels from P5 to P10. Confocal and electron microscopy confirm that the expression is restricted to the astroglial membrane. By P12, and despite an increased global expression as observed by immunoblotting, the barrel pattern of GLAST and GLT-1 staining is no longer evident. In P10 GLT-1 −/− and GLAST −/− mice, the cytoarchitectural segregation of the barrels is preserved. However, at P9-10, the functional response to whisker stimulation, measured by deoxyglucose uptake, is markedly decreased in GLT-1 −/− and GLAST −/− mice. The role of GLAST is transient since the metabolic response is already restored at P11-12 in GLAST −/− mice and remains unchanged in adulthood. However, deletion of GLT-1 seems to impair the functional metabolic response until adulthood. Our data suggest that astrocyte-neuron interactions via the glial glutamate transporters are involved in the functional maturation of the whisker representation in the somatosensory corte

Loss of the thyroid hormone-binding protein Crym renders striatal neurons more vulnerable to mutant huntingtin in Huntington's disease

The mechanisms underlying preferential atrophy of the striatum in Huntington's disease (HD) are unknown. One hypothesis is that a set of gene products preferentially expressed in the striatum could determine the particular vulnerability of this brain region to mutant huntingtin (mHtt). Here, we studied the striatal protein µ-crystallin (Crym). Crym is the NADPH-dependent p38 cytosolic T3-binding protein (p38CTBP), a key regulator of thyroid hormone (TH) T3 (3,5,3′-triiodo-l-thyronine) transportation. It has been also recently identified as the enzyme that reduces the sulfur-containing cyclic ketimines, which are potential neurotransmitters. Here, we confirm the preferential expression of the Crym protein in the rodent and macaque striatum. Crym expression was found to be higher in the macaque caudate than in the putamen. Expression of Crym was reduced in the BACHD and Knock-in 140CAG mouse models of HD before onset of striatal atrophy. We show that overexpression of Crym in striatal medium-size spiny neurons using a lentiviral-based strategy in mice is neuroprotective against the neurotoxicity of an N-terminal fragment of mHtt in vivo. Thus, reduction of Crym expression in HD could render striatal neurons more susceptible to mHtt suggesting that Crym may be a key determinant of the vulnerability of the striatum. In addition our work points to Crym as a potential molecular link between striatal degeneration and the THs deregulation reported in HD patient

STAT3-mediated astrocyte reactivity associated with brain metastasis contributes to neurovascular dysfunction

© 2020 American Association for Cancer Research. Astrocytes are thought to play a pivotal role in coupling neural activity and cerebral blood flow. However, it has been shown that astrocytes undergo morphologic changes in response to brain metastasis, switching to a reactive phenotype, which has the potential to significantly compromise cerebrovascular function and contribute to the neurological sequelae associated with brain metastasis. Given that STAT3 is a key regulator of astrocyte reactivity, we aimed here to determine the impact of STAT3- mediated astrocyte reactivity on neurovascular function in brain metastasis. Rat models of brain metastasis and ciliary neurotrophic factor were used to induce astrocyte reactivity. Multimodal imaging, electrophysiology, and IHC were performed to determine the relationship between reactive astrocytes and changes in the cerebrovascular response to electrical and physiological stimuli. Subsequently, the STAT3 pathway in astrocytes was inhibited with WP1066 to determine the role of STAT3- mediated astrocyte reactivity, specifically, in brain metastasis. Astrocyte reactivity associated with brain metastases impaired cerebrovascular responses to stimuli at both the cellular and functional level and disrupted astrocyte-endothelial interactions in both animal models and human brain metastasis samples. Inhibition of STAT3-mediated astrocyte reactivity in rats with brain metastases restored cerebrovascular function, as shown by in vivo imaging, and limited cerebrovascular changes associated with tumor growth. Together these findings suggest that inhibiting STAT3-mediated astrocyte reactivity may confer significant improvements in neurological outcome for patients with brain metastases and could potentially be tested in other brain tumors

Ciliary Neurotrophic Factor Protects Striatal Neurons against Excitotoxicity by Enhancing Glial Glutamate Uptake

Ciliary neurotrophic factor (CNTF) is a potent neuroprotective cytokine in different animal models of glutamate-induced excitotoxicity, although its action mechanisms are still poorly characterized. We tested the hypothesis that an increased function of glial glutamate transporters (GTs) could underlie CNTF-mediated neuroprotection. We show that neuronal loss induced by in vivo striatal injection of the excitotoxin quinolinic acid (QA) was significantly reduced (by ∼75%) in CNTF-treated animals. In striatal slices, acute QA application dramatically inhibited corticostriatal field potentials (FPs), whose recovery was significantly higher in CNTF rats compared to controls (∼40% vs. ∼7%), confirming an enhanced resistance to excitotoxicity. The GT inhibitor dl-threo-β-benzyloxyaspartate greatly reduced FP recovery in CNTF rats, supporting the role of GT in CNTF-mediated neuroprotection. Whole-cell patch-clamp recordings from striatal medium spiny neurons showed no alteration of basic properties of striatal glutamatergic transmission in CNTF animals, but the increased effect of a low-affinity competitive glutamate receptor antagonist (γ-d-glutamylglycine) also suggested an enhanced GT function. These data strongly support our hypothesis that CNTF is neuroprotective via an increased function of glial GTs, and further confirms the therapeutic potential of CNTF for the clinical treatment of progressive neurodegenerative diseases involving glutamate overflow

Targeted Activation of Astrocytes: A Potential Neuroprotective Strategy

International audienceAstrocytes are involved in many key physiological processes in the brain, including glutamatergic transmission, energy metabolism, and blood flow control. They become reactive in response to pathological situations, a response that involves well-described morphological alterations and less characterized functional changes. The functional consequences of astrocyte reactivity seem to depend on the molecular pathway involved and may result in the enhancement of several neuroprotective and neurotrophic functions. We propose that a selective and controlled activation of astrocytes may switch these highly pleiotropic cells into therapeutic agents to promote neuron survival and recovery. This may represent a potent therapeutic strategy for many brain diseases in which neurons would benefit from an increased support from activated astrocytes

Dysfonction des astrocytes du striatum induite par expression sélective de huntingtine mutée in vivo

La maladie de Huntington (MH) est une pathologie neurodégénérative héréditaire due à la mutation du gène codant la huntingtine (Htt). La mutation de la Htt (Httm) entraîne la perte sélective des neurones épineux de taille moyenne du striatum et ceci malgré son expression ubiquitaire. Plusieurs études suggèrent que les astrocytes pourraient participer à la pathologie en particulier dans les mécanismes d excitotoxicité impliqués dans la mort neuronale. Grâce à un nouveau vecteur lentiviral développé au laboratoire, nous avons exprimé un fragment court de la Httm dans les astrocytes du striatum de souris adulte. Nous avons observé une activation progressive des astrocytes, réaction jusqu à présent considérée comme secondaire à la dysfonction neuronale. L expression sélective de la Httm dans les astrocytes du striatum entraine une diminution d expression et d activité des transporteurs astrocytaires au glutamate GLT-1 et GLAST, 12 semaines après l injection des vecteurs. Ces résultats sont corrélés avec l observation de cerveaux de patients de la MH présentant une activation astrocytaire et une perte du transporteur de glutamate GLT-1 dès le stade pré-symptomatique. Ces résultats montrent que les astrocytes sont affectés par leur propre expression de Httm et qu ils pourraient participer précocement à la pathologie. Nous avons étudié le phénotype des neurones voisins des astrocytes dysfonctionnels et nous avons observé la diminution de deux marqueurs neuronaux, DARPP-32 et NR2B. La Httm astrocytaire pourrait donc altérer la fonction des neurones ce qui implique les interactions neurones-astrocytes dans la MH.PARIS-BIUSJ-Physique recherche (751052113) / SudocSudocFranceF

Développement d un vecteur lentiviral ciblant les astrocytes in vivo et mise en application dans l étude des transporteurs au glutamate GLAST et GLT-1

Les astrocytes remplissent de nombreuses fonctions primordiales dans le cerveau notamment la modulation de la transmission synaptique et le couplage neurométabolique qui impliquent les transporteurs astrocytaires au glutamate GLAST et GLT-1. Leur étude est essentielle, cependant, il existe peu d outils permettant l étude de leur fonction in vivo. Notre objectif a été de développer un nouveau vecteur lentiviral permettant un transfert de gène uniquement dans les astrocytes in vivo. Nous avons développé trois voies de recherche : le changement de l enveloppe du vecteur, du promoteur et une nouvelle méthode de régulation post-transcriptionnelle utilisant les microARN. Nos résultats montrent que la combinaison de l enveloppe Mokola avec des cibles d un microRNA spécifiquement neuronal permet un ciblage astrocytaire spécifique et efficace. La surexpression du transporteur GLAST permet une neuroprotection significative en condition excitotoxique tandis que l inhibition de GLT-1 induit une diminution du métabolisme énergétique cérébral. La mise au point de ce nouvel outil permettra une meilleure compréhension du fonctionnement des astrocytes in vivo.PARIS-BIUSJ-Thèses (751052125) / SudocPARIS-BIUSJ-Physique recherche (751052113) / SudocSudocFranceF

Astrocyte-neuron metabolic cooperation shapes brain activity

The brain has almost no energy reserve, but its activity coordinates organismal function, a burden that requires precise coupling between neurotransmission and energy metabolism. Deciphering how the brain accomplishes this complex task is crucial to understand central facets of human physiology and disease mechanisms. Each type of neural cell displays a peculiar metabolic signature, forcing the intercellular exchange of metabolites that serve as both energy precursors and paracrine signals. The paradigm of this biological feature is the astrocyte-neuron couple, in which the glycolytic metabolism of astrocytes contrasts with the mitochondrial oxidative activity of neurons. Astrocytes generate abundant mitochondrial reactive oxygen species and shuttle to neurons glycolytically derived metabolites, such as L-lactate and L-serine, which sustain energy needs, conserve redox status, and modulate neurotransmitter-receptor activity. Conversely, early disruption of this metabolic cooperation may contribute to the initiation or progression of several neurological diseases, thus requiring innovative therapies to preserve brain energetics.G.B. received grants from the Centre National de la Recherche Scientifique (CNRS), the Commissariat à l’Energie Atomique et aux Energies Alternatives (CEA), Agence Nationale de la Recherche (ANR 2011 MALZ-0003 MetALZ; ANR-18-C816-0008-03 ADORASTrAU), Association France Alzheimer, Fondation de France (Prix Spécial 2012), Fondation Alzheimer, and Infrastructure de Recherche Translationnelle pour les Biothérapies en Neurosciences (NeurATRIS ANR-11-INBS-0011). J.P.B. is funded by the Agencia Estatal de Investigación (PID2019-105699RB-I00 / AEI / 10.13039/501100011033 and RED2018-102576-T), Instituto de Salud Carlos III (CB16/10/00282), Junta de Castilla y León (CSI151P20 and Escalera de Excelencia CLU-2017-03), Ayudas Equipos Investigación Biomedicina 2017 Fundación BBVA, and Fundación Ramón Areces

Cell Metab

Recent work from Bonvento and colleagues indicated that synaptic and memory deficits in early Alzheimer's disease (AD) are related to a shortage in L-serine production in astrocytes. Here, the authors, responding to correspondence from Chen and colleagues, discuss how this deficiency does not necessarily require a decrease in PHGDH expression and conclude that the primary event leading to lower serine production is more likely related to altered glycolytic flux in early AD than to PHGDH expression