Alternative Oxidase Expression in the Mouse Enables Bypassing Cytochrome c Oxidase Blockade and Limits Mitochondrial ROS Overproduction

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Rôle du gène Phox2b dans le contrôle ventilatoire : application au syndrome d'ondine

Le syndrome d'ondine est une maladie génétique rare caractérisée par une hypoventilation pendant le sommeil, des apnées et une absence de réponse au CO2. La majorité des patients ont une mutation hétérozygote à expansion d'alanine du gène PHOX2B, important dans le développement du système nerveux autonome. Notre objectif est d'étudier le rôle de Phox2b dans le contrôle de la ventilation et de valider un modèle murin du syndrome d'Ondine. Grâce à une plateforme d'exploration fonctionnelle originale permettant les mesures non invasives dans un environnement contrôlé en température et en gaz des variables cardiorespiratoires chez le souriceau, nous avons analysé in vivo deux modèles de souris hétérozygotes pour Phox2b. Les souriceaux hétérozygotes Phox2b+/-, issus d'une invalidation d'un allèle Phox2b, présentent une instabilité ventilatoire associée à une activité tonique anormalement élevée de leurs chémorécepteurs périphériques. Leur phénotype ventilatoire dépend fortement de la température ambiante. La reproduction de la mutation humaine majoritaire, une insertion de 7 alanines (souriceaux Phox2b27Ala/+) chez le souriceau, produit un phénotype similaire au syndrome d'Ondine. Ces souriceaux meurent rapidement d'apnée centrale à la naissance. Ils ont une perte spécifique de neurones exprimant de neurones du noyau rétrotrapézoïde/groupe respiratoire parafacial (RTN/pFRG) impliqués dans la chémoréception centrale et la rythmogenèse, ce qui montre le rôle important du RTN/pFRG dans la chémosensibilité au CO2, et dans la rythmogénèse respiratoire néonataleOndine syndrome is a rare genetic disease characterized by hypoventilation during sleep, apneas and the absence of ventilatory response to CO2. The majority of patients carry a heterozygous mutation with polyalanine expansion of PHOX2B gene, which is important in the development of autonomous nervous system. We aim to study the role of Phox2b in ventilatory control and to validate a mouse model of Ondine syndrome. We used a platform that allows in vivo, non-invasive measurements of cardiorespiratory variables in newborn mice in controlled temperature and gas conditions. Heterozygous Phox2b+/- pups, which were obtained by invalidation of one allele of Phox2b, show ventilatory instability with augmented tonic activity of peripheral chemoreceptor. Their ventilatory phenotype strongly depends on ambient temperature. Reproducing in mice Phox2b mutation, which is frequently observed in patients, an insertion of 7 alanines (mutant pups Phox2b27Ala/+) produces a similar phenotype to Ondine syndrome. These newborn mice rapidly die of central apnea after birth. Phox2b27Ala/+ pups have a specific loss of neurons expressing Phox2b in retrotrapezoïd nucleus/parafacial respiratory group (RTN/pFRG) involved in central chemoreception and in rhythmogenesis, showing the important role of RTN/pFRG in CO2 chemosensitivity, and in respiratory rhythmogenesis at birt

Rôle du gène Phox2b dans le contrôle ventilatoire (application au syndrome d'ondine)

Le syndrome d'ondine est une maladie génétique rare caractérisée par une hypoventilation pendant le sommeil, des apnées et une absence de réponse au CO2. La majorité des patients ont une mutation hétérozygote à expansion d'alanine du gène PHOX2B, important dans le développement du système nerveux autonome. Notre objectif est d'étudier le rôle de Phox2b dans le contrôle de la ventilation et de valider un modèle murin du syndrome d'Ondine. Grâce à une plateforme d'exploration fonctionnelle originale permettant les mesures non invasives dans un environnement contrôlé en température et en gaz des variables cardiorespiratoires chez le souriceau, nous avons analysé in vivo deux modèles de souris hétérozygotes pour Phox2b. Les souriceaux hétérozygotes Phox2b+/-, issus d'une invalidation d'un allèle Phox2b, présentent une instabilité ventilatoire associée à une activité tonique anormalement élevée de leurs chémorécepteurs périphériques. Leur phénotype ventilatoire dépend fortement de la température ambiante. La reproduction de la mutation humaine majoritaire, une insertion de 7 alanines (souriceaux Phox2b27Ala/+) chez le souriceau, produit un phénotype similaire au syndrome d'Ondine. Ces souriceaux meurent rapidement d'apnée centrale à la naissance. Ils ont une perte spécifique de neurones exprimant de neurones du noyau rétrotrapézoïde/groupe respiratoire parafacial (RTN/pFRG) impliqués dans la chémoréception centrale et la rythmogenèse, ce qui montre le rôle important du RTN/pFRG dans la chémosensibilité au CO2, et dans la rythmogénèse respiratoire néonataleOndine syndrome is a rare genetic disease characterized by hypoventilation during sleep, apneas and the absence of ventilatory response to CO2. The majority of patients carry a heterozygous mutation with polyalanine expansion of PHOX2B gene, which is important in the development of autonomous nervous system. We aim to study the role of Phox2b in ventilatory control and to validate a mouse model of Ondine syndrome. We used a platform that allows in vivo, non-invasive measurements of cardiorespiratory variables in newborn mice in controlled temperature and gas conditions. Heterozygous Phox2b+/- pups, which were obtained by invalidation of one allele of Phox2b, show ventilatory instability with augmented tonic activity of peripheral chemoreceptor. Their ventilatory phenotype strongly depends on ambient temperature. Reproducing in mice Phox2b mutation, which is frequently observed in patients, an insertion of 7 alanines (mutant pups Phox2b27Ala/+) produces a similar phenotype to Ondine syndrome. These newborn mice rapidly die of central apnea after birth. Phox2b27Ala/+ pups have a specific loss of neurons expressing Phox2b in retrotrapezoïd nucleus/parafacial respiratory group (RTN/pFRG) involved in central chemoreception and in rhythmogenesis, showing the important role of RTN/pFRG in CO2 chemosensitivity, and in respiratory rhythmogenesis at birthPARIS-EST-Université (770839901) / SudocSudocFranceF

Emotional disorders in adult mice heterozygous for the transcription factor Phox2b

Phox2b is an essential transcription factor for the development of the autonomic nervous system. Mice carrying one invalidated Phox2b allele (Phox2b(+/-)) show mild autonomic disorders including sleep apneas, and impairments in chemosensitivity and thermoregulation that recover within 10days of postnatal age. Because Phox2b is not expressed above the pons nor in the cerebellum, this mutation is not expected to affect brain development and cognitive functioning directly. However, the transient physiological disorders in Phox2b(+/-) mice might impair neurodevelopment. To examine this possibility, we conducted a behavioral test battery of emotional, motor, and cognitive functioning in adult Phox2b(+/-) mice and their wildtype littermates (Phox2b(+/+)). Adult Phox2b(+/-) mice showed altered exploratory behavior in the open field and in the elevated plus maze, both indicative of anxiety. Phox2b(+/-) mice did not show cognitive or motor impairments. These results suggest that also mild autonomic control deficits may disturb long-term emotional development.publisher: Elsevier articletitle: Emotional disorders in adult mice heterozygous for the transcription factor Phox2b journaltitle: Physiology & Behavior articlelink: http://dx.doi.org/10.1016/j.physbeh.2015.01.012 content_type: article copyright: Copyright © 2015 Elsevier Inc. All rights reserved.status: publishe

Breathing without CO(2) chemosensitivity in conditional Phox2b mutants.

International audienceBreathing is a spontaneous, rhythmic motor behavior critical for maintaining O(2), CO(2), and pH homeostasis. In mammals, it is generated by a neuronal network in the lower brainstem, the respiratory rhythm generator (Feldman et al., 2003). A century-old tenet in respiratory physiology posits that the respiratory chemoreflex, the stimulation of breathing by an increase in partial pressure of CO(2) in the blood, is indispensable for rhythmic breathing. Here we have revisited this postulate with the help of mouse genetics. We have engineered a conditional mouse mutant in which the toxic PHOX2B(27Ala) mutation that causes congenital central hypoventilation syndrome in man is targeted to the retrotrapezoid nucleus, a site essential for central chemosensitivity. The mutants lack a retrotrapezoid nucleus and their breathing is not stimulated by elevated CO(2) at least up to postnatal day 9 and they barely respond as juveniles, but nevertheless survive, breathe normally beyond the first days after birth, and maintain blood PCO(2) within the normal range. Input from peripheral chemoreceptors that sense PO(2) in the blood appears to compensate for the missing CO(2) response since silencing them by high O(2) abolishes rhythmic breathing. CO(2) chemosensitivity partially recovered in adulthood. Hence, during the early life of rodents, the excitatory input normally afforded by elevated CO(2) is dispensable for life-sustaining breathing and maintaining CO(2) homeostasis in the blood

The vesicular glutamate transporter VGLUT3 contributes to protection against neonatal hypoxic stress

International audienceKey points Hypoxic stress is an important cause of morbidity and mortality in neonates. We examined the role of VGLUT3, an atypical transporter of glutamate present in serotonergic neurons involved in breathing and heat production, in the response to hypoxia. The respiratory responses to chemical stimuli and the turnover of serotonin in the brainstem were impaired in newborn mice lacking VGLUT3. Under cold conditions, metabolic rate, body temperature, baseline breathing and the ventilatory response to hypoxia were disrupted. Thus, VGLUT3 expression is required for optimal response to hypoxic stress in neonates. Abstract Neonates respond to hypoxia initially by increasing ventilation, and then by markedly decreasing both ventilation (hypoxic ventilatory decline) and oxygen consumption (hypoxic hypometabolism). This latter process, which vanishes with age, reflects a tight coupling between ventilatory and thermogenic responses to hypoxia. The neurological substrate of hypoxic hypometabolism is unclear, but it is known to be centrally mediated, with a strong involvement of the 5-hydroxytryptamine (5-HT, serotonin) system. To clarify this issue, we investigated the possible role of VGLUT3, the third subtype of vesicular glutamate transporter. VGLUT3 contributes to glutamate signalling by 5-HT neurons, facilitates 5-HT transmission and is expressed in strategic regions for respiratory and thermogenic control. We therefore assumed that VGLUT3 might significantly contribute to the response to hypoxia. To test this possibility, we analysed this response in newborn mice lacking VGLUT3 using anatomical, biochemical, electrophysiological and integrative physiology approaches. We found that the lack of VGLUT3 did not affect the histological organization of brainstem respiratory networks or respiratory activity under basal conditions. However, it impaired respiratory responses to 5-HT and anoxia, showing a marked alteration of central respiratory control. These impairments were associated with altered 5-HT turnover at the brainstem level. Furthermore, under cold conditions, the lack of VGLUT3 disrupted the metabolic rate, body temperature, baseline breathing and the ventilatory response to hypoxia. We conclude that VGLUT3 expression is dispensable under basal conditions but is required for optimal response to hypoxic stress in neonates

Obstructive Apneas in a Mouse Model of Congenital Central Hypoventilation Syndrome

International audienceRationale: Congenital central hypoventilation syndrome (CCHS) is characterized by life-threatening sleep hypoventilation and is caused by PHOX2B gene mutations, most frequently the PHOX2B 27Ala/1 mutation, with patients requiring lifelong ventilatory support. It is unclear whether obstructive apneas are part of the syndrome. Objectives: To determine if Phox2b 27Ala/1 mice, which present the main symptoms of CCHS and die within hours after birth, also express obstructive apneas, and to investigate potential underlying mechanisms.Methods: Apneas 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 preparations.Measurements and Main Results: The median (interquartile range) of obstructive apnea frequency was 2.3 (1.5-3.3)/min in Phox2b 27Ala/1 pups versus 0.6 (0.4-1.0)/min in wild types (P , 0.0001). Obstructive apnea duration was 2.7 seconds (2.3-3.9) in Phox2b 27Ala/1 pups versus 1.7 seconds (1.1-1.9) in wild types (P , 0.0001). Central and mixed apneas presented similar significant differences. In Phox2b 27Ala/1 preparations, the hypoglossal nucleus had fewer (P , 0.05) and smaller (P , 0.01) neurons, compared with wild-type preparations. Importantly, coordination of phrenic and hypoglossal motor activities was disrupted, as evidenced by the longer and variable delay of hypoglossal activity with respect to phrenic activity onset (P , 0.001).Conclusions: The Phox2b 27Ala/1 mutation predisposed pups not only to hypoventilation and central apneas, but also to obstructive and mixed apneas, likely because of hypoglossal dysgenesis. These results thus demand attention toward obstructive events in infants with CCHS

Resonant vibrational excitation of CH3X (X = F, Cl, Br and I) by low-energy electron impact

Perinatal inflammation is a major risk factor for neurological deficits in preterm infants. Several experimental studies have shown that systemic inflammation can alter the programming of the developing brain. However, these studies do not offer detailed pathophysiological mechanisms, and they rely on relatively severe infectious or inflammatory stimuli that most likely do not reflect the levels of systemic inflammation observed in many human preterm infants. The goal of the present study was to test the hypothesis that moderate systemic inflammation is sufficient to alter white matter development

Acetylcholine Modulates the Hormones of the Growth Hormone/Insulinlike Growth Factor-1 Axis During Development in Mice

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