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

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

The Inside-Out Amyloid Hypothesis and Synapse Pathology in Alzheimer's Disease.

Cumulative evidence in brains and cultured neurons of Alzheimer's disease (AD) transgenic mouse models, as well as in human postmortem AD brains, highlights that age-related increases in β-amyloid peptide (Aβ), particularly in endosomes near synapses, are involved in early synapse dysfunction. Our immunoelectron microscopy and high-resolution immunofluorescence microscopy studies show that this early subcellular Aβ accumulation leads to progressive Aβ aggregation and pathology, particularly within dystrophic neurites and synapses. These studies confirm that neuritic/synaptic Aβ accumulation is the nidus of plaque formation. Aβ-dependent synapse pathology in AD models is modulated by synaptic activity and is plaque independent. The amyloid precursor protein (APP) is normally transported down neurites and appears to be preferentially processed to Aβ at synapses. Synapses are sites of early Aβ accumulation and aberrant tau phosphorylation in AD, which alter the synaptic composition at early stages of the disease. Elucidating the normal role of APP, and potentially of Aβ, at synapses should provide important insights into the mechanism(s) of Aβ-induced synapse dysfunction in AD and how to therapeutically mitigate these dysfunctions. © 2013 S. Karger AG, Basel

Expression of ephrinA5 during development and potential involvement in the guidance of the mesostriatal pathway

(IF : 3,974)International audienceIdentifying guidance cues that direct axon growth to their final connections during development is of crucial interest if we aim to repair circuits damaged in adulthood following neurodegenerative disorders or common traumatic injuries. In this work, we set out to determine the ephrinA5 guidance molecule involvement in the establishment of the mouse mesostriatal pathway during development. We showed, in vitro and in vivo, that a proportion of mesencephalic dopaminergic cells express the ephrinA5 receptor, EphA5. Moreover, we observed, using stripe assays, that ephrinA5 purified protein has a repulsive effect on most of the mesencephalic dopaminergic projections. In vivo, we detected rostro-caudal and ventro-dorsal ephrinA5 protein expression gradients in the vicinity of the dopaminergic axons in the ventral telencephalon and in the striatum, during the embryonic and early postnatal development. In addition, other EphA5 ligands were also detected in the mesostriatal pathway. Together, these expression patterns suggest that, ephrinAs and more specifically ephrinA5, may be actors in the guidance of dopaminergic projections. Further studies will focus on identifying the molecular specificity of these guidance cues, taking into account the mesencephalic dopaminergic heterogeneous neuronal population. This may help increase the integration of neuronal transplants in the mature lesioned brain or provide tools to re-establish mesostriatal circuits in vivo

Detection of pre-plaque amyloid aggregation using FTIR

Background: Alzheimer's disease (AD) is characterized by misfolding and aggregation of naturally occurring beta-amyloid peptides (Aβ). These aggregates are thought to be pathogenic to neurons, although the conformation of the pathogenic Aβ species remains unclear. Biochemical extraction methods and different microscopy techniques (TEM, confocal) can be used to identify pathogenic Aβ species in the brain, although such methods can alter protein conformation or are n ot designed to determine structural details of protein assemblies

The Blood–Brain Barrier Is Unaffected in the Ndufs4−/− Mouse Model of Leigh Syndrome

International audienceMitochondrial dysfunction plays a major role in physiological aging and in many pathological conditions. Yet, no study has explored the consequence of primary mitochondrial deficiency on the blood–brain barrier (BBB) structure and function. Addressing this question has major implications for pharmacological and genetic strategies aimed at ameliorating the neurological symptoms that are often predominant in patients suffering from these conditions. In this study, we examined the permeability of the BBB in the Ndufs4−/− mouse model of Leigh syndrome (LS). Our results indicated that the structural and functional integrity of the BBB was preserved in this severe model of mitochondrial disease. Our findings suggests that pharmacological or gene therapy strategies targeting the central nervous system in this mouse model and possibly other models of mitochondrial dysfunction require the use of specific tools to bypass the BBB. In addition, they raise the need for testing the integrity of the BBB in complementary in vivo models

Glutamine Synthetase Stability and Subcellular Distribution in Astrocytes are Regulated by G-Aminobutyric Type B Receptors.

Emerging evidence suggests that functional γ-aminobutyric acid B receptors (GABABRs) are expressed by astrocytes within the mammalian brain. GABABRs are heterodimeric G-protein coupled receptors that are composed of R1/R2 subunits. To date, they have been characterized in neurons as the principal mediators of sustained inhibitory signaling, however their roles in astrocytic physiology have been ill defined. Here we reveal that the cytoplasmic tail of the GABABR2 subunit binds directly to the astrocytic protein glutamine synthetase (GS) and that this interaction determines the subcellular localization of GS. We further demonstrate that the binding of GS to GABABR2 increases the steady state expression levels of GS in heterologous cells and in mouse primary astrocyte culture. Mechanistically this increased stability of GS in the presence of GABABR2 occurs via reduced proteasomal degradation. Collectively, our results suggest a novel role for GABABRs as regulators of GS stability. Given the critical role that GS plays in the glutamine-glutamate cycle, astrocytic GABABRs may play a critical role in supporting both inhibitory and excitatory neurotransmission