Venue: Centre Broca Nouvelle-Aquitaine
Defense in french
Gabriel Pitollat
Team: Development and Neurobiology of Neural Networks (DN3) (Thoby-Brisson, Barrière)
Thesis supervisor: Muriel Thoby-Brisson
Title
Congenital central hypoventilation syndrome: Pathophysiological mechanisms and search for pharmacological treatments in an animal model
Résumé
The Ondine syndrome, or congenital central hypoventilation syndrome (CCHS), is a rare genetic disorder caused by a heterozygous mutation of the PHOX2B gene. The main clinical manifestations are severe hypoventilation associated with a near complete loss of ventilatory response to hypercapnia. To date, mechanical ventilation by tracheostomy cannula is the only method of respiratory supplementary that is used to counteract these deficits. In order to improve patient’s everyday life, it is essential to develop research on molecules with potential therapeutic interests. In this perspective, my thesis project was devoted to test in vitro, on an animal model of CCHS (Phox2b27Ala/+ mice), the capacities of pharmacological agents to compensate for the respiratory deficits linked to Phox2b mutation and to identify their underlying mechanisms. By electrophysiological recordings of neural activities on isolated brainstem preparations from animals carrying the mutation and their wildtype congeners and containing the neural networks that control respiration, respiration-linked activities were measured in control condition and after pharmacological treatment. (1) Three compounds of the Heat Shock Protein (HSP) signalling family were studied, and more particularly ATS-002, that proved to be very effective in restoring both basal respiratory rate and a response to acidosis close to the values obtained in control animals. The effects of ATS002 on respiratory rhythm are mediated by an indirect action, via the involvement of microglia, on the activity of the Pre-Bötzinger complex known to control the respiratory rhythm generation. On the other hand, the mechanisms of the recovery of the acidosis response remain poorly identified, but preliminary experiments suggest that the retrotrapezoïd/parafacial respiratory group, known to be anatomically and functionally affected by Phox2b mutation and to be a major player in central chemosensitivity, would not be involved. (2) Using a purely anatomical approach, I also show in the mutant that brainstem microglia exhibit a morphological profile associated with a different activation state than in control animals that can be restored by ATS002 treatment. These data suggest an abnormal inflammatory state in Phox2b27Ala/+ animals that can be reversed by the known anti-inflammatory effect of this compound. (3) Furthermore, it has been shown in cell culture that polyalanine expansion of Phox2b leads to toxic accumulation of protein aggregates. ATS002 is known to have anti-aggregating effects due to its action on the HSP70/90 balance. By measuring the quantity of proteins in the brainstem (western blot) I was able to show that this balance is abnormal in mutant animals but can be restored after treatment. (4) Finally, in close collaboration with the Gallego team (Paris), we observed an abnormally high number of obstructive apneas in Phox2b27Ala/+ neonates, that can be associated with the existence of a morpho-functional alteration of the hypoglossal motor nucleus which controls the upper airways. This thesis work thus proposes original tracks for the research of pharmacological compounds likely to have a therapeutic interest within the framework of the syndrome of Ondine. It also brings new data on the probable existence of an inflammatory terrain and an alteration of the permeability of the upper airways in Ondine patients, which must now be taken into account in the therapeutic approaches applied in clinic.
Publication
Obstructive Apneas in a Mouse Model of Congenital Central
Amélia Madani, Gabriel Pitollat, Eléonore Sizun, Laura Cardoit, Maud Ringot, Thomas Bourgeois, Nelina Ramanantsoa, Christophe Delclaux, Stéphane Dauger, Marie-Pia d’Ortho, Muriel Thoby-Brisson, Jorge Gallego, Boris Matrot
Am J Respir Crit Care Med. – 2021 Nov 15
10.1164/rccm.202104-0887OC
Jury
Agnès NADJAR, présidente
Christian STRAUS, rapporteur
Jean-Charles VIEMARI, rapporteur
Christian GESTREAU, examinateur
Xénia PROTON DE LA CHAPELLE, membre invitée et présidente de la société AtmosR
Muriel THOBY-BRISSON, directrice de thèse,