Les nouvelles stratégies thérapeutiques du traumatisme sonore par bruit d'arme chez le cobaye.

This research work regroups several studies about new therapeutic strategies following impulsional noise (gunshot) acoustic trauma on guinea pigs. The aim is the evaluation of different treatment methods (administration route and kinetic) after a gunshot noise acoustic trauma. The first study is about the usual treatment based on corticoids administration in humans. Corticoids are known to cross with difficulty the hematocochlear barrier. The goal of this work is to evaluate an intra-cochlear perfusion for the treatment. The direct perfusion of methylprednisolone continuously during 7 days, following a gunshot noise acoustic trauma, accelerates the hearing recovery and preserves most of the hair cells from the death. The second study concerns magnesium supplementation as treatment by the systemic route and particularly focuses on a long-term administration (1 month). The long-term administration of magnesium was the most effective treatment in terms of hair cell preservation. Hair cells death caused by gunshot noise is the subject of the last study. Hair cells death appears during the first 24 hours following the noise exposure (gunshot noise/continuous noise). With these results, two anti-apoptotic treatments (leupeptin and z-VAD-FMK) were tested. 1 hour following the gunshot noise exposure, the direct intra-cochlear route was used during 7 days continuously. The effectiveness of the treatment was assessed on auditory function (audiograms) and on hair cells survival (histology, died cells counting). The intra-cochlear administration of z-VAD-FMK continuously during 7 days following gunshot noise trauma accelerates hearing recovery and preserves hair cells from death. However, leupeptin was not effective in this model of trauma. These results suggest that one of the early steps in gunshot noise-induced trauma may involve the caspase rather than the calpain pathway. Caspase inhibitors are, therefore, potential candidates for new therapy in order to limit gunshot noise-induced hair loss. The present study confirms the importance of a fast and early administration of pharmacological agent after a traumatic noise over-exposure. These results give us a better understanding on the auditory physiopathology following a gunshot noise acoustic trauma and led us to evaluate a therapeutic windows for humans treatment.Ce travail de recherche regroupe plusieurs études portant sur de nouvelles stratégies thérapeutiques après traumatisme sonore par bruit impulsionnel (arme) chez le cobaye. Il a pour objectif d'évaluer différents protocoles thérapeutiques (traitement, voie d'administration et durée). La première étude s'intéresse au traitement commun actuellement utilisé chez l'Homme: l'administration de corticoïdes. Ceux-ci sont connus pour passer difficilement la barrière hémato-cochléaire. Le but de l'étude est d'évaluer leur administration intra-cochléaire directe. La méthylprednisolone, administrée en continu durant 7 jours, après un traumatisme sonore par bruit d'arme, accélère la récupération et préserve en partie la survie des cellules ciliées auditives. La seconde étude porte sur l'efficacité du magnésium à long terme (1 mois) administré par voie systémique. Le magnésium durant un mois est le traitement le plus efficace en termes de préservation des cellules ciliées. La dernière étude s'intéresse à la mort des cellules ciliées consécutive au traumatisme sonore. La mort cellulaire apparaît dans les 24 premières heures après l'exposition au bruit (bruit d'arme/bruit continu). Suite à ce résultat, deux traitements utilisant des anti-apoptotiques (leupeptine et z-VAD-FMK) ont été testés par voie intra-cochléaire directe 1 heure après le traumatisme et leur diffusion a duré 7 jours. L'efficacité du traitement a été évaluée sur la fonctionnalité des cellules auditives (audiogrammes) et sur la survie de ces cellules en fin d'expérimentation (histologie, comptage des cellules apoptotiques). L'administration intra-cochléaire de z-VAD-FMK de façon continue pendant 7 jours après un traumatisme sonore par bruit d'arme accélère la récupération auditive et permet la survie des cellules ciliées. A contrario, la leupeptine n'a pas été efficace dans notre modèle. Ces résultats suggèrent qu'une des premières étapes dans la physiopathologie du traumatisme sonore par bruit d'arme implique la mort des cellules ciliées par la voie des caspases plutôt que par la voie des calpaines. Les inhibiteurs de caspases sont donc de bons candidats thérapeutiques pour limiter les pertes cellulaires consécutives au bruit d'arme. Les résultats de ce travail de thèse permettent de mieux comprendre la physiopathologie auditive après traumatisme sonore par bruit d'arme et d'évaluer les différentes fenêtres thérapeutiques afin de tirer la meilleure stratégie utilisable chez l'Homme

Therapeutic efficacy of intra-cochlear administration of methylprednisolone after acoustic trauma caused by gunshot noise in guinea pigs.

International audienceThe therapeutic efficacy of cochlear infusion of methylprednisolone (MP) after an impulse noise trauma (170dB SPL peak) was evaluated in guinea pigs. The compound action potential threshold shifts were measured over a 14 days recovery period after the gunshot exposure. For each animal, one of the cochlea was perfused directly into the scala tympani with MP during 7 days via a mini-osmotic pump, whereas the other cochlea was not pump-implanted. The functional study of hearing was supplemented by histological analysis. Forty eight hours after the trauma, significant differences between auditory threshold shifts in the implanted and non-implanted ears were observed for frequencies above 8kHz. At day 7, the difference was significant for only one frequency and no difference was observed after 14 days recovery. Cochleograms showed that the hair cell losses were significantly lower in the MP treated ears. This work indicates that direct infusion of MP into perilymphatic space accelerates hearing recovery, reduces hair cell losses after impulse noise trauma but does not limit permanent threshold shifts

Evidence for a subventricular zone neural stem cell phagocytic activity stimulated by the vitamin K-dependent factor protein S.

article dans une revue avec comité de lectureInternational audienceNeural stem cells, whose major reservoir in the adult mammalian brain is the subventricular zone (SVZ), ensure neuropoiesis, a process during which many generated cells die. Removal of dead cells and debris by phagocytes is necessary for tissue homeostasis. Using confocal and electron microscopy, we demonstrate that cultured SVZ cells phagocytose both 1 and 2 µm latex beads and apoptotic cell-derived fragments. We determine by flow cytometry that phagocytic cells represent more than 10% of SVZ cultured cells. Phenotyping of SVZ cells using nestin, GFAP, Sox2, or LeX/SSEA and quantification of aldehyde dehydrogenase (ALDH) activity, reveals that cells with neural stem-cell features phagocytose and represent more than 30% of SVZ phagocytic cells. In vivo, nestin-, Sox2-, and ALDH-expressing neural stem-like cells engulfed latex beads or apoptotic cell-derived fragments that were injected into mice lateral brain ventricles. We show also that SVZ cell phagocytic activity is an active process, which depends both on cytoskeleton dynamic and on recognition of phosphatidylserine eat-me signal, and is stimulated by the vitamin K-dependent factor protein S (ProS). ProS neutralizing antibodies inhibit SVZ cell phagocytic activity and exposure of SVZ cells to apoptotic cell-derived fragments induces a transient Mer tyrosine kinase receptor (MerTK) phosphorylation. Conversely, MerTK blocking antibodies impair both basal and ProS-stimulated SVZ cell phagocytic activity. By revealing that neural stem-like cells act within the SVZ neurogenic niche as phagocytes and that the ProS/MerTK path represents an endogenous regulatory mechanism for SVZ cell phagocytic activity, the present report opens-up new perspectives for both stem cell biology and brain physiopathology