Les connexions entre les cellules sensorielles et les neurones primaires de l’oreille interne, appelées synapses sont essentielles à l’encodage et la transmission des informations auditives et vestibulaires vers le cerveau. C’est aussi une zone extrêmement exposée et fragile qui semble impliquée dans de nombreuses atteintes de l’audition et de l’équilibration, mais également au cours du vieillissement. Des récupérations spontanées de l’audition et de l’équilibre ont été observées suite à ces différentes atteintes chez l’Homme. Dans le cadre de ma thèse, j’ai étudié d’une part, comment des atteintes sélectives de ces synapses pouvaient générer des troubles de l’oreille interne chez l’animal, et d’autre part, comment des mécanismes de réparation spontanée de ces synapses supportent la récupération des fonctions auditives et vestibulaires. Nous avons constaté qu’il existe une hétérogénéité dans les capacités de réparations synaptiques entre la cochlée et le vestibule. L’étude des mécanismes moléculaires mis en jeu dans cette réparation synaptique pourrait ouvrir la voie au développement de nouvelles stratégies thérapeutiques pour les atteintes de l’oreille interne. / Inner ear connections between primary neurons and sensory cells, called synapses are essential for encoding and transmitting auditory and vestibular information to the brain. It is also an extremely exposed and fragile area that is involved in many hearing and balance disorders, but also during aging. Spontaneous hearing and balance recoveries have been observed following these different injuries in humans. In the context of my thesis, I studied, on the one hand, how selective lesions of these synapses could generate inner ear disorders in animals, and on the other hand, how spontaneous repair mechanisms of these synapses support auditory and vestibular functions recovery. We found that there is heterogeneity in synaptic repair capabilities between the cochlea and the vestibule. The study of the molecular mechanisms involved in this synaptic repair could pave the way for the development of new therapeutic strategies against various inner ear disorders.

Hearing loss of various types is increasingly plaguing our modern world (Geneva: World Health Organization 2018). As the life expectancy increased in the industrialized world, age-related hearing loss (ARHL) has become more prevalent. The wars and terrorism of the modern world also created a significant body of blast-induced hearing loss (BIHL) patients. Both types of hearing loss present significant challenges for listeners even at suprathreshold sound levels. However, increasing bodies of clinical and laboratory evidence have suggested that the difficulties in the processing of time-varying auditory features in speech and other natural sounds may not be sufficiently diagnosed by threshold changes and simple auditory electrophysiological measures (Snell and Frisina 2000; Saunders et al. 2015; Bressler et al. 2017; Guest et al. 2018).<br>Studies have emphasized that excitatory/inhibitory neurotransmission imbalance plays important roles in ARHL (Caspary et al. 2008) and may also be key in BIHL, as hinted by the strong presence of GABA regulation in non-blast TBI (O’Dell et al. 2000; Cantu et al. 2015; Guerriero et al. 2015). The current studies focus on age-related and blast-induced hearing deficits by examining changes in the processing of simple, brief stimuli and complex, sustained, temporally modulated sounds.<br>Through post hoc circular analysis of single-unit, in vivo recording of young and aged inferior colliculus (IC) neurons responding to amplitude modulation (AM) stimuli and modulation depth changes, we observed evidence of central compensation in the IC manifesting as increased sensitivity to presynaptic input, which was measured via local field potentials (LFPs). We also found decreased sensitivity to decreasing modulation depth. Age-related central gain in the IC single units, while preserving and even overcompensating for temporal phase coding in the form of vector strength, was unable to make up for the loss of envelope shape coding.<br>Through careful, longitudinal measurements of auditory evoked potential (AEP) responses towards simple sounds, AM and speech-like iterated rippled noise (IRN), we documented the development and recovery of BIHL induced by a single mild blast in a previously established (Song et al. 2015; Walls et al. 2016; Race et al. 2017) rat blast model over the course of two months. We identified crucial acute (day 1-4 post-exposure) and early recovery (day 7-14) time windows in which drastic changes in electrophysiology take place. Challenging conditions and broadband, speech-like stimuli can better elucidate mild bTBI-induced auditory deficits during the sub-acute period. The anatomical significance of the aforementioned time windows was demonstrated with immunohistochemistry methods, showing two distinct waves of GABA inhibitory transmission changes taking place in the auditory brainstem, the IC, and the auditory thalamus. These changes were in addition to axonal and oxidative damage evident in the acute phase. We examined the roles and patterns of excitatory/inhibitory imbalance in BIHL, its distinction compared to that of ARHL, and demonstrated the complexity of its electrophysiological consequences. Blast traumatizes the peripheral auditory system and auditory brainstem, evident through membrane damage and acrolein-mediated oxidative stress. These initial traumas kickstart a unique, interlocking cascade of excitatory/inhibitory imbalances along the auditory neuraxis that is more complex and individually varied than the gradual, non-traumatic degradations in ARHL. Systemic treatment with the FDA-approved acrolein scavenger Hydralazine (HZ) was attempted with limited effects.<br>Taken together, the current study provided insights into the similarities and distinctions between the mechanisms of ARHL and BIHL and called for innovative and individual diagnostic and therapeutic measures.<br>

No description available.

No description available.

Auditorische Synaptopathien verursachen sensorineurale Schwerhörigkeit unterschiedlicher Ausprägung. Dabei sind sowohl erworbene, als auch angeborene Formen bekannt. Eine häufige Form ist die rezessive, nichtsyndromale Taubheitsform DFNB9, die auf einer Mutation des für Otoferlin kodierenden Gens beruht. Otoferlin ist ein Transmembranprotein, das essentiell für die stimulusabhängige Transmitterausschüttung an der Bändersynapse der Haarzellen ist . Um die Prognose von Patienten mit auditorischen Synaptopathien einschätzen zu können, ist es wichtig, den zeitlichen Verlauf der neuronalen Degeneration zu kennen. Aufgrund des Fehlens von protektiven Mittelohr und olivocochleären Reflexen könnte zusätzlich eine erhöhte Lärmempfindlichkeit bestehen, die einen frühen Verlust der Funktion der äußeren Haarzellen begünstigen wurde. Wir haben Otoferlin-Knockout-Mäuse im Alter von 6 Tagen bis 12 Monaten untersucht und die Funktion des Corti-Organs mittels Hirnstammaudiometrie und Messung der otoakustischen Emissionen getestet. In immunhistochemischen Färbungen von Corti-Organ Präparaten wurde die Degeneration von inneren und äußeren Haarzellen, Bändersynapsen und Spiralganglienneuronen beobachtet. Weiterhin wurden bei 2 Monate alten Otoferlin-Knockout-Mäusen die Auswirkungen eines leichten oder schweren Lärmtraumas quantifiziert. Wir beobachteten bei den Mutanten eine frühere und schnellere Degeneration der inneren und äußeren Haarzellen, insbesondere in der basalen Windung der Kochlea. Die Lärmtraumaversuche zeigten keinen Unterschied in der Empfindlichkeit von Otoferlin-Knockout-Mäusen und Wildtyp-Kontrollen, so dass die Ursache des Haarzellverlustes ungeklärt bleibt. Die Zahl der Bändersynapsen war ab Beginn des Hörens auf die Hälfte reduziert und blieb dann konstant, dennoch waren Spiralganglienneurone auch bei 12 Monate alten Tieren kaum reduziert. Das lässt auf einen relativ langen Erhalt des Hörnerven schließen Wir beschrieben hier zum ersten Mal die Degeneration des Corti-Organs in Otoferlin-Knockout-Mäusen. Gleichzeitig erfolgte die systematische Quantifizierung der synaptischen Degeneration von C57BL/6-Mäusen im Zusammenhang mit deren Altersschwerhörigkeit.

No description available.

Movement is a prerequisite for normal fetal development and growth. Intrauterine movement restrictions cause a broad spectrum of disorders in which the unifying feature is a reduction or lack of fetal movement, giving rise to the term fetal akinesia deformations sequence (FADS [OMIM 208150]). FADS corresponds to a clinically and genetically heterogeneous constellation of properties and is characterized by multiple joint contractures, facial abnormalities, and lung hypoplasia as a result of the decreased in utero movement of the fetuses. Affected babies are often prematurely and stillborn, and those born alive typically die within minutes or hours after birth. The genetic causes for this fatal disorder are ill-defined as a genetic diagnosis is rarely executed, but mutations in three genes, namely RAPSN, DOK7, and MUSK, as well as in the subunits of the muscular nicotinic acetylcholine receptor (AChR) have been described. These mutations are thought to affect neuromuscular junctions, although this has not been proven experimentally.The nucleoporin NUP88 is a constituent of the nuclear pore complex (NPC), the gate for all trafficking between the nucleus and the cytoplasm. NUP88 resides on both the cytoplasmic and the nuclear side of NPCs, and it is found in two distinct subcomplexes. It associates with NUP214 and NUP62 on the cytoplasmic face, while on the nuclear side NUP88 binds NUP98 and the intermediate filament protein lamin A. The NUP88-NUP214-NUP62 complex plays an essential role in the nuclear export of a subset of proteins and pre-ribosomes, which is mediated by the nuclear export receptor CRM1. NUP88 in particular somewhat participates in the nuclear export of NF-κB proteins in a CRM1-dependent manner. Moreover, NUP88 is frequently overexpressed in a variety of human cancers, and its role in cancer appears linked to the deregulation of the anaphase-promoting complex. Here, we report the first Mendelian disorders caused by mutations in NUP88 and with that the first lethal developmental human disease due to mutations in a nuclear pore component. We demonstrate that biallelic mutations in NUP88 are likely to cause fetal akinesia of the Pena-Shokeir subtype. We confirm in zebrafish that loss of NUP88 impairs movement and the mutations identified in the affected individuals resemble a loss-of-function phenotype. We show that loss of NUP88 affects expression and localization of rapsyn, the protein encoded by RAPSN, in human and mouse cell lines, and patient samples. Consistent with altered rapsyn, AChR clustering and neuromuscular junction formation in zebrafish are abnormal. We therefore propose that defective NUP88 function cause FADS by affecting neuromuscular junction formation.Keywords: Nuclear pore complex, NUP88, Fetal Akinesia Deformation Sequence, rapsyn, acetylcholine receptor clustering, synaptic transmission, fetal development, inherited developmental disorder. / Doctorat en Sciences / info:eu-repo/semantics/nonPublished

La surdité professionnelle constitue un problème de santé publique important, avec une prévalence estimée de 10 à 16%. Les études animales ont mis en évidence une perte des synapses entre les cellules ciliées internes et le nerf auditif et des fibres auditives présentant une activité spontanée faible. Cette synaptopathie cochléaire se manifesterait avant la dégradation des seuils auditifs et la perte des cellules ciliées externes, étant ainsi un précurseur à la surdité professionnelle. L’audiogramme utilisé en milieu clinique ne permet pas de mesurer la synaptopathie cochléaire, se contentant seulement de quantifier la perte d’audibilité causée par l’exposition au bruit. Des études post-mortem humaines ont permis d’identifier une synaptopathie cochléaire, similaire à celle observée dans le modèle animal. Étant donné que la quantification des synapses chez l'humain vivant n'est pas possible, les chercheurs se sont concentrés sur le développement d’outils pouvant servir de marqueur indirect de la synaptopathie cochléaire. À cet égard, les résultats sont divergents d’une étude à l’autre. Il est possible que ces outils ne soient pas sensibles ou que l’exposition au bruit investiguée dans la littérature ne soit pas suffisante pour entraîner une synaptopathie cochléaire chez l’humain. L’objectif de cette thèse est donc d’évaluer les effets d’une exposition au bruit industriel continu et au bruit impulsionnel, qui pourraient s’avérer plus nocives et entraîner un processus précoce de synaptopathie cochléaire. Des individus présentant des seuils auditifs et des émissions otoacoustiques dans la normale ont été investigués à l’aide de mesures électrophysiologiques et psychoacoustiques. Dans la première étude, 40 participants exposés au bruit industriel continu et 40 participants sans exposition au bruit industriel continu ont été recrutés et évalués à l’aide d’un test de perception de la parole dans le bruit (SPiN) et de différentes composantes du potentiels évoqués auditifs du tronc cérébral (PEATC). L’exposition au bruit des participants a été mesurée par dosimétrie. Les résultats ne montrent pas d’association entre l’exposition au bruit et les variables du PEATC et du SPiN. Dans la deuxième étude, 27 participants militaires exposés au bruit impulsionnel et 13 participants sans exposition au bruit impulsionnel ont été recrutés. Les PEATC, l’électrocochléographie, le SPiN et la largeur des filtres auditifs rectangulaires équivalents (ERB) ont été mesurés. L’exposition au bruit des participants a été quantifiée à l’aide du Noise Exposure Structured Interview. Les résultats montrent une réduction de l’amplitude de l’onde I, un allongement de la latence de l’onde V, des performances réduites de SPiN et un ERB plus large à 4 kHz chez les militaires exposés au bruit impulsionnel, en comparaison aux participants sans exposition au bruit impulsionnel. Cette thèse est importante d’un point de vue de santé publique puisqu’elle suggère que certains outils cliniques simples, comme la mesure des filtres auditifs, pourraient permettre de détecter les premiers signes d’un dommage auditif avant l’apparition d’une surdité professionnelle mesurée par l’audiogramme. Les résultats renforcent l’importance de la sensibilisation aux risques induits par l’exposition au bruit afin de prévenir l’apparition des troubles de communication et des situations de handicap découlant de la présence d’une surdité professionnelle. / Occupational hearing loss constitutes an important public health problem, with an estimated prevalence of 10 to 16%. Animal studies have shown a phenomenon of synapses dysfunction between the inner hair cells and the auditory nerve and a preferential loss of low spontaneous rate auditory fibers. This cochlear synaptopathy manifests itself before the degradation of hearing thresholds and the loss of outer hair cells, thus being a precursor damage to occupational hearing loss. The audiogram used in a clinical setting does not measure cochlear synaptopathy, only quantifying the loss of audibility caused by noise exposure. In humans, post-mortem studies have identified a process of cochlear synaptopathy, similar to that observed in the animal model. Since quantification of synapses in living humans is not possible, researchers focused on developing a noninvasive measurement that could serve as an indirect marker for cochlear synaptopathy. Several tools have been proposed, but the results vary from one study to another. It is possible that these tools are not sensitive or that noise exposures investigated in the literature is not sufficient to cause cochlear synaptopathy in humans. The objective of this thesis is therefore to evaluate the effects of exposure to continuous industrial noise and impulse noise, which could prove to be more harmful and lead to an accelerated process of cochlear synaptopathy. To this end, individuals with normal hearing thresholds and otoacoustic emissions were investigated using electrophysiological and psychoacoustical measurements. In the first study, 40 participants with occupational noise exposure and 40 participants without occupational noise exposure were recruited and evaluated using a speech perception in noise (SPiN) test and different components of the auditory brainstem response (ABR). Participants’ noise exposure was measured by dosimetry. The results do not show an association between noise exposure and the ABR and SPiN variables. In the second study, 27 military participants exposed to impulse noise and 13 participants without exposure to impulse noise were recruited. ABR, electrocochleography, SPiN and the equivalent rectangular bandwidth (ERB) of auditory filters were measured. Participants' noise exposure was quantified using the Noise Exposure Structured Interview. Results show a reduced wave I amplitude, a lengthened wave V latency, a reduced SPiN performance, and a broader ERB at 4 kHz in military recruits exposed to impulse noise, compared to participants without exposure to impulse noise. This thesis is important from a public health point of view since it suggests that certain simple clinical tools, such as the measurement of auditory filters, might make it possible to detect the first signs of auditory damage before the onset of hearing loss measured by the audiogram. Results reinforce the importance of raising awareness to the risks induced by noise exposure in order to prevent the appearance of communication disorders and handicaps resulting from the presence of occupational hearing loss.