Ventilatory and Autonomic Regulation in Sleep Apnea Syndrome: A Potential Protective Role for Erythropoietin?

Obstructive sleep apnea (OSA) is the most common form of sleep disordered breathing and is associated with wide array of cardiovascular morbidities. It has been proposed that during OSA, the respiratory control center (RCC) is affected by exaggerated afferent signals coming from peripheral/central chemoreceptors which leads to ventilatory instability and may perpetuate apnea generation. Treatments focused on decreasing hyperactivity of peripheral/central chemoreceptors may be useful to improving ventilatory instability in OSA patients. Previous studies indicate that oxidative stress and inflammation are key players in the increased peripheral/central chemoreflex drive associated with OSA. Recent data suggest that erythropoietin (Epo) could also be involved in modulating chemoreflex activity as functional Epo receptors are constitutively expressed in peripheral and central chemoreceptors cells. Additionally, there is some evidence that Epo has anti-oxidant/anti-inflammatory effects. Accordingly, we propose that Epo treatment during OSA may reduce enhanced peripheral/central chemoreflex drive and normalize the activity of the RCC which in turn may help to abrogate ventilatory instability. In this perspective article we discuss the potential beneficial effects of Epo administration on ventilatory regulation in the setting of OSA

Effet aggravant de l’hypoxie intermittente chronique sur la fibrose pulmonaire induite par la bléomycine et les mécanismes moléculaires impliqués

Idiopathic pulmonary fibrosis (IPF) is a fibrotic lung disease characterized by an accumulation of connective tissue in the lungs leading to fatal restrictive respiratory failure. It appears to be the consequence of alveolar epithelial cells (AEC) dysfunction and fibroblast aberrant activation in response to repeated micro-injuries of the alveolar epithelium. In this pathophysiological mechanism, several molecular and cellular events are involved and actively participate in the loss of the epithelial phenotype. Among these events, endoplasmic reticulum (ER) stress seems to play a major role. In addition, a high prevalence of obstructive sleep apnea syndrome (OSA) has been reported in IPF patients. OSA is characterized by nocturnal intermittent hypoxia (IH) due to repeated upper airway obstructive events. The impact of OSA on the pathogenesis of IPF remains poorly understood.In the first study, we showed in a murine model of bleomycin-induced lung fibrosis exposed to IH an increase of pulmonary fibrosis severity through an exacerbation of lung inflammation and tissue damage. In the second study, we showed that ER stress, a pathogenetic element common to pulmonary fibrosis and IH, could be at least in part responsible for this aggravating effect of IH. We have also shown that other cellular events such as cellular senescence could be involved.During this PhD, we have demonstrated that IH induce an aggravating effects on pulmonary fibrogenesis at histological and molecular level and that ER stress and an induction of UPR pathways could be a crucial element. This work thus contributes to a better understanding of the impact of OSA in IPF patients.La fibrose pulmonaire idiopathique (FPI) est une pneumopathie fibrosante, caractérisée par l’accumulation de tissu conjonctif dans les poumons conduisant à une insuffisance respiratoire restrictive d’évolution fatale. Elle semble être la conséquence d’un dysfonctionnement de cellules épithéliales alvéolaires (CEA) et d’une activation aberrante des fibroblastes suite à des micro-agressions répétées de l’épithélium. Dans ce processus, un ensemble d’événements moléculaires et cellulaires sont mis en jeu et participent activement à la perte du phénotype épithélial. Parmi ces évènements, le stress réticulum endoplasmique (RE) semble jouer un rôle majeur et central. Par ailleurs, une forte prévalence du syndrome d’apnées obstructives du sommeil (SAOS) a été rapportée chez les patients FPI. Le SAOS se caractérise par une hypoxie intermittente (HI) nocturne due aux évènements obstructifs répétés des voies aériennes supérieures. L’impact du SAOS sur la pathogenèse de la FPI reste encore mal connu. Dans une première étude, nous avons montré dans un modèle murin de fibrose induite par la bléomycine et exposé à l’HI, une aggravation de la sévérité de la fibrose pulmonaire mise en évidence par une exacerbation de l’inflammation et des lésions tissulaires. Dans une seconde étude, nous avons montré que le stress du RE, élément pathogénique communs à la fibrose pulmonaire et à l’HI, pouvait être au moins en partie responsable de cet effet aggravant. Nous avons également mis en évidence que d’autres évènements cellulaires tels que la senescence pourraient être impliqués. Au cours de ce doctorat nous avons mis en évidence que l’HI avait des effets aggravants sur la fibrogènése pulmonaire au niveau tissulaire et moléculaire et que le stress du RE et l’induction des voies de l’UPR pourrait constituer un élément central critique. Ce travail contribue ainsi à la meilleure compréhension de l’impact du SAOS chez les patients FPI

Effet aggravant de l’hypoxie intermittente chronique sur la fibrose pulmonaire induite par la bléomycine et les mécanismes moléculaires impliqués

Idiopathic pulmonary fibrosis (IPF) is a fibrotic lung disease characterized by an accumulation of connective tissue in the lungs leading to fatal restrictive respiratory failure. It appears to be the consequence of alveolar epithelial cells (AEC) dysfunction and fibroblast aberrant activation in response to repeated micro-injuries of the alveolar epithelium. In this pathophysiological mechanism, several molecular and cellular events are involved and actively participate in the loss of the epithelial phenotype. Among these events, endoplasmic reticulum (ER) stress seems to play a major role. In addition, a high prevalence of obstructive sleep apnea syndrome (OSA) has been reported in IPF patients. OSA is characterized by nocturnal intermittent hypoxia (IH) due to repeated upper airway obstructive events. The impact of OSA on the pathogenesis of IPF remains poorly understood.In the first study, we showed in a murine model of bleomycin-induced lung fibrosis exposed to IH an increase of pulmonary fibrosis severity through an exacerbation of lung inflammation and tissue damage. In the second study, we showed that ER stress, a pathogenetic element common to pulmonary fibrosis and IH, could be at least in part responsible for this aggravating effect of IH. We have also shown that other cellular events such as cellular senescence could be involved.During this PhD, we have demonstrated that IH induce an aggravating effects on pulmonary fibrogenesis at histological and molecular level and that ER stress and an induction of UPR pathways could be a crucial element. This work thus contributes to a better understanding of the impact of OSA in IPF patients.La fibrose pulmonaire idiopathique (FPI) est une pneumopathie fibrosante, caractérisée par l’accumulation de tissu conjonctif dans les poumons conduisant à une insuffisance respiratoire restrictive d’évolution fatale. Elle semble être la conséquence d’un dysfonctionnement de cellules épithéliales alvéolaires (CEA) et d’une activation aberrante des fibroblastes suite à des micro-agressions répétées de l’épithélium. Dans ce processus, un ensemble d’événements moléculaires et cellulaires sont mis en jeu et participent activement à la perte du phénotype épithélial. Parmi ces évènements, le stress réticulum endoplasmique (RE) semble jouer un rôle majeur et central. Par ailleurs, une forte prévalence du syndrome d’apnées obstructives du sommeil (SAOS) a été rapportée chez les patients FPI. Le SAOS se caractérise par une hypoxie intermittente (HI) nocturne due aux évènements obstructifs répétés des voies aériennes supérieures. L’impact du SAOS sur la pathogenèse de la FPI reste encore mal connu. Dans une première étude, nous avons montré dans un modèle murin de fibrose induite par la bléomycine et exposé à l’HI, une aggravation de la sévérité de la fibrose pulmonaire mise en évidence par une exacerbation de l’inflammation et des lésions tissulaires. Dans une seconde étude, nous avons montré que le stress du RE, élément pathogénique communs à la fibrose pulmonaire et à l’HI, pouvait être au moins en partie responsable de cet effet aggravant. Nous avons également mis en évidence que d’autres évènements cellulaires tels que la senescence pourraient être impliqués. Au cours de ce doctorat nous avons mis en évidence que l’HI avait des effets aggravants sur la fibrogènése pulmonaire au niveau tissulaire et moléculaire et que le stress du RE et l’induction des voies de l’UPR pourrait constituer un élément central critique. Ce travail contribue ainsi à la meilleure compréhension de l’impact du SAOS chez les patients FPI

The aggravating effect of chronic intermitten hypoxia on pulmonary fibrosis induced by bleomycin and the involved molecular mechanisms

La fibrose pulmonaire idiopathique (FPI) est une pneumopathie fibrosante, caractérisée par l’accumulation de tissu conjonctif dans les poumons conduisant à une insuffisance respiratoire restrictive d’évolution fatale. Elle semble être la conséquence d’un dysfonctionnement de cellules épithéliales alvéolaires (CEA) et d’une activation aberrante des fibroblastes suite à des micro-agressions répétées de l’épithélium. Dans ce processus, un ensemble d’événements moléculaires et cellulaires sont mis en jeu et participent activement à la perte du phénotype épithélial. Parmi ces évènements, le stress réticulum endoplasmique (RE) semble jouer un rôle majeur et central. Par ailleurs, une forte prévalence du syndrome d’apnées obstructives du sommeil (SAOS) a été rapportée chez les patients FPI. Le SAOS se caractérise par une hypoxie intermittente (HI) nocturne due aux évènements obstructifs répétés des voies aériennes supérieures. L’impact du SAOS sur la pathogenèse de la FPI reste encore mal connu. Dans une première étude, nous avons montré dans un modèle murin de fibrose induite par la bléomycine et exposé à l’HI, une aggravation de la sévérité de la fibrose pulmonaire mise en évidence par une exacerbation de l’inflammation et des lésions tissulaires. Dans une seconde étude, nous avons montré que le stress du RE, élément pathogénique communs à la fibrose pulmonaire et à l’HI, pouvait être au moins en partie responsable de cet effet aggravant. Nous avons également mis en évidence que d’autres évènements cellulaires tels que la senescence pourraient être impliqués. Au cours de ce doctorat nous avons mis en évidence que l’HI avait des effets aggravants sur la fibrogènése pulmonaire au niveau tissulaire et moléculaire et que le stress du RE et l’induction des voies de l’UPR pourrait constituer un élément central critique. Ce travail contribue ainsi à la meilleure compréhension de l’impact du SAOS chez les patients FPI.Idiopathic pulmonary fibrosis (IPF) is a fibrotic lung disease characterized by an accumulation of connective tissue in the lungs leading to fatal restrictive respiratory failure. It appears to be the consequence of alveolar epithelial cells (AEC) dysfunction and fibroblast aberrant activation in response to repeated micro-injuries of the alveolar epithelium. In this pathophysiological mechanism, several molecular and cellular events are involved and actively participate in the loss of the epithelial phenotype. Among these events, endoplasmic reticulum (ER) stress seems to play a major role. In addition, a high prevalence of obstructive sleep apnea syndrome (OSA) has been reported in IPF patients. OSA is characterized by nocturnal intermittent hypoxia (IH) due to repeated upper airway obstructive events. The impact of OSA on the pathogenesis of IPF remains poorly understood.In the first study, we showed in a murine model of bleomycin-induced lung fibrosis exposed to IH an increase of pulmonary fibrosis severity through an exacerbation of lung inflammation and tissue damage. In the second study, we showed that ER stress, a pathogenetic element common to pulmonary fibrosis and IH, could be at least in part responsible for this aggravating effect of IH. We have also shown that other cellular events such as cellular senescence could be involved.During this PhD, we have demonstrated that IH induce an aggravating effects on pulmonary fibrogenesis at histological and molecular level and that ER stress and an induction of UPR pathways could be a crucial element. This work thus contributes to a better understanding of the impact of OSA in IPF patients

Sleep Apnea in Idiopathic Pulmonary Fibrosis: A Molecular Investigation in an Experimental Model of Fibrosis and Intermittent Hypoxia

International audienceBackground: High prevalence of obstructive sleep apnea (OSA) is reported in incident and prevalent forms of idiopathic pulmonary fibrosis (IPF). We previously reported that Intermittent Hypoxia (IH), the major pathogenic element of OSA, worsens experimental lung fibrosis. Our objective was to investigate the molecular mechanisms involved. Methods: Impact of IH was evaluated on C57BL/6J mice developing lung fibrosis after intratracheal instillation of Bleomycin (BLM). Mice were Pre-exposed 14 days to IH before induction of lung fibrosis or Co-challenged with IH and BLM for 14 days. Weight loss and survival were daily monitored. After experimentations, lungs were sampled for histology, and protein and RNA were extracted. Results: Co-challenge or Pre-exposure of IH and BLM induced weight loss, increased tissue injury and collagen deposition, and pro-fibrotic markers. Major worsening effects of IH exposure on lung fibrosis were observed when mice were Pre-exposed to IH before developing lung fibrosis with a strong increase in sXBP1 and ATF6N ER stress markers. Conclusion: Our results showed that IH exacerbates BLM-induced lung fibrosis more markedly when IH precedes lung fibrosis induction, and that this is associated with an enhancement of ER stress markers

A New Model of Acute Exacerbation of Experimental Pulmonary Fibrosis in Mice

Rationale: idiopathic pulmonary fibrosis (IPF) is the most severe form of fibrosing interstitial lung disease, characterized by progressive respiratory failure leading to death. IPF’s natural history is heterogeneous, and its progression unpredictable. Most patients develop a progressive decline of respiratory function over years; some remain stable, but others present a fast-respiratory deterioration without identifiable cause, classified as acute exacerbation (AE). Objectives: to develop and characterize an experimental mice model of lung fibrosis AE, mimicking IPF-AE at the functional, histopathological, cellular and molecular levels. Methods: we established in C57BL/6 male mice a chronic pulmonary fibrosis using a repetitive low-dose bleomycin (BLM) intratracheal (IT) instillation regimen (four instillations of BLM every 2 weeks), followed by two IT instillations of a simple or double-dose BLM challenge to induce AE. Clinical follow-up and histological and molecular analyses were done for fibrotic and inflammatory lung remodeling analysis. Measurements and main results: as compared with a low-dose BLM regimen, this AE model induced a late burst of animal mortality, worsened lung fibrosis and remodeling, and superadded histopathological features as observed in humans IPF-AE. This was associated with stronger inflammation, increased macrophage infiltration of lung tissue and increased levels of pro-inflammatory cytokines in lung homogenates. Finally, it induced in the remodeled lung a diffuse expression of hypoxia-inducible factor 1α, a hallmark of tissular hypoxia response and a major player in the progression of IPF. Conclusion: this new model is a promising model of AE in chronic pulmonary fibrosis that could be relevant to mimic IPF-AE in preclinical trials

Intermittent Hypoxia Increases the Severity of Bleomycin-Induced Lung Injury in Mice

Background. Severe obstructive sleep apnea (OSA) with chronic intermittent hypoxia (IH) is common in idiopathic pulmonary fibrosis (IPF). Here, we evaluated the impact of IH on bleomycin- (BLM-) induced pulmonary fibrosis in mice. Methods. C57BL/6J mice received intratracheal BLM or saline and were exposed to IH (40 cycles/hour; FiO2 nadir: 6%; 8 hours/day) or intermittent air (IA). In the four experimental groups, we evaluated (i) survival; (ii) alveolar inflammation, pulmonary edema, lung oxidative stress, and antioxidant enzymes; (iii) lung cell apoptosis; and (iv) pulmonary fibrosis. Results. Survival at day 21 was lower in the BLM-IH group (p<0.05). Pulmonary fibrosis was more severe at day 21 in BLM-IH mice, as assessed by lung collagen content (p=0.02) and histology. At day 4, BLM-IH mice developed a more severe neutrophilic alveolitis, (p<0.001). Lung oxidative stress was observed, and superoxide dismutase and glutathione peroxidase expression was decreased in BLM-IH mice (p<0.05 versus BLM-IA group). At day 8, pulmonary edema was observed and lung cell apoptosis was increased in the BLM-IH group. Conclusion. These results show that exposure to chronic IH increases mortality, lung inflammation, and lung fibrosis in BLM-treated mice. This study raises the question of the worsening impact of severe OSA in IPF patients