Matrot, B. | Search bioRxiv

bioRxiv2022

Serotonin, Etonogestrel and breathing activity in murine Congenital Central Hypoventilation Syndrome

Congenital Central Hypoventilation Syndrome, a rare disease caused by PHOX2B mutation, is associated with absent or blunted CO2/H+ chemosensitivity due to the dysfunction of PHOX2B neurons of the retrotrapezoid nucleus. No pharmacological treatment is available. Clinical observations have reported non-systematic CO2/H+ chemosensitivity recovery under desogestrel. Here, we used a preclinical model of Congenital Central Hypoventilation Syndrome, the retrotrapezoid nucleus conditional Phox2b mutant mouse, to investigate whether etonogestrel, the active metabolite of desogestrel, led to a restoration of chemosensitivity by acting on serotonin neurons known to be sensitive to etonogestrel, or retrotrapezoid nucleus PHOX2B residual cells that persist despite the mutation. The effect of etonogestrel, alone or combined with serotonin drugs, on the respiratory rhythm of medullary-spinal cord preparations from Phox2b mutants and wildtype mice was analyzed under metabolic acidosis. c-FOS, serotonin and PHOX2B were immunodetected. Serotonin metabolic pathways were characterized by ultra-high-performance liquid chromatography. We observed etonogestrel restored chemosensitivity in Phox2b mutants in a non-systematic way. Histological differences between Phox2b mutants with restored chemosensitivity and others indicated greater activation of serotonin neurons of the raphe obscurus nucleus but no effect on retrotrapezoid nucleus PHOX2B residual cells. Pharmacology of serotonin systems modulated the respiratory effect of etonogestrel differently according to serotonin metabolic pathways. Etonogestrel induced a restoration of chemosensitivity in Phox2b mutants by acting on serotonin neurons. Our work thus highlights that the state of serotonin systems was critically important for the occurrence of an etonogestrel-restoration, an element to consider in potential therapeutic intervention in Congenital Central Hypoventilation Syndrome patients.

physiology↗

bioRxiv2021

OBSTRUCTIVE APNEAS IN A MOUSE MODEL OF CONGENITAL CENTRAL HYPOVENTILATION SYNDROME

RationaleCongenital Central Hypoventilation Syndrome (CCHS) is characterized by life-threatening sleep hypoventilation, and is caused by PHOX2B gene mutations, most frequently the PHOX2B27Ala/+ mutation, with patients requiring lifelong ventilatory support. It is unclear whether obstructive apneas are part of the syndrome. ObjectivesTo determine whether Phox2b27Ala/+ mice, which present the main symptoms of CCHS and die within hours after birth, also express obstructive apneas, and to investigate potential underlying mechanisms. MethodsApneas were classified as central, obstructive or mixed by using a novel system combining pneumotachography and laser detection of abdominal movement immediately after birth. Several respiratory nuclei involved in airway patency were examined by immunohistochemistry and electrophysiology in brainstem-spinal cord preparation. Measurements and Main ResultsThe median (interquartile range) of obstructive apnea frequency was 2.3/min (1.5-3.3) in Phox2b27Ala/+ pups versus 0.6/min (0.4-1.0) in wildtypes (P < 0.0001). Obstructive apnea duration was 2.7s (2.3-3.9) in Phox2b27Ala/+ pups versus 1.7s (1.1-1.9) in wildtypes (P < 0.0001). Central and mixed apneas presented similar, significant differences. In Phox2b27Ala/+ preparations, the hypoglossal nucleus had fewer (P < 0.05) and smaller (P < 0.01) neurons, compared to wildtypes. Importantly, coordination of phrenic and hypoglossal motor activities was disrupted, as evidenced by the longer and variable delay of hypoglossal with respect to phrenic activity onset (P < 0.001). ConclusionsThe Phox2b27Ala/+ mutation predisposed pups not only to hypoventilation and central apneas, but also to obstructive and mixed apneas, likely due to hypoglossal dysgenesis. These results thus demand attention towards obstructive events in infants with CCHS.

physiology↗