The double-edged sword of intermittent hypoxia-can intermittent hypoxia be both deleterious and protective in OSA? Focus on "Frequency and magnitude of intermittent hypoxia modulate endothelial wound healing in a cell culture model of sleep apnea"

My voyage in the enchanted world of sleep

In this paper, I describe my 45-year career in sleep research. I started my undergraduate studies at Tel Aviv University, where I was first introduced to the enchanted world of sleep, continued to my graduate studies with Wilse B. Webb at the University of Florida, and then to post-doctoral training with Dan Kripke at the University of California at San Diego. Then, I describe the evolution of my academic career at the Technion-Israel Institute of Technology, where I started in 1975 as an Assistant Professor and retired in 2019 as the President of the Institute. I describe the areas of research that I pursued and how the research developed, emphasizing unexpected results that guided me and my lab team in new directions. This includes my early studies on ultradian rhythms, inspired by Nathaniel Kleitman's Basic Rest Activity Cyle hypothesis, utilizing the ultrashort sleep-wake paradigm to chart the 24-hour sleep propensity function, and how these studies led us to explore the role of melatonin in sleep regulation. I also explain why we directed our attention to sleep apnea, and how clinical observations led to the provocative hypothesis that sleep apnea-typically seen as a disorder-may also play a protective role. Under the leadership of my research partner and wife, Lena, we confirmed this hypothesis. Also in this article, I describe my enthusiasm for the history of our field and, as derived from my experience as a Dean of Medicine and President of a university, I share my philosophy about the role of members of academia in society. I emphasize that none of my achievements could have been accomplished without the hard work and motivation of my students and research partners, who shared my enthusiasm and passion for the enchanted world of sleep. This paper is part of the Living Legends in Sleep Research series, which is sponsored by Idorsia Pharmaceuticals and Jazz Pharmaceuticals.

Cardiac consequences of intermittent hypoxia: a matter of dose? A systematic review and meta-analysis in rodents

Aim

Intermittent hypoxia (IH) is considered to be a major contributor to obstructive sleep apnoea-related cardiovascular consequences. The present meta-analysis aimed to assess the effects of IH on cardiac remodelling, function and infarct size after myocardial ischaemia across different rodent species and IH severities.

Methods and results

Relevant articles from PubMed, Embase and Web of Science were screened. We performed a random effect meta-analysis to assess the effect of IH on myocardium in rodents by using standardised mean difference (SMD). Studies using rodents exposed to IH and outcomes related to cardiac remodelling, contractile function and response to myocardial ischaemia–reperfusion were included. 5217 articles were screened and 92 were included, demonstrating that IH exposure induced cardiac remodelling, characterised by cardiomyocyte hypertrophy (cross-sectional area: SMD=2.90, CI (0.82–4.98), I²=94.2%), left ventricular (LV) dilation (LV diameter: SMD=0.64, CI (0.18–1.10), I²=88.04%), interstitial fibrosis (SMD=5.37, CI (3.22–7.53), I²=94.8) and apoptosis (terminal deoxynucleotidyl transferase dUTP nick end labelling: SMD=6.70, CI (2.96–10.44), I²=95.9). These structural changes were accompanied by a decrease in LV ejection fraction (SMD=−1.82, CI (−2.52–−1.12), I²=94.22%). Importantly, most of the utilised IH protocols mimicked extremely severe hypoxic disease. Concerning infarct size, meta-regression analyses highlighted an ambivalent role of IH, depending on its severity. Indeed, IH exposure with inspiratory oxygen fraction (F_IO2) <7% was associated with an increase in infarct size, whereas a reduced infarct size was reported for F_IO2 levels above 10%. Heterogeneity between studies, small study effect and poor reporting of methods in included articles limited the robustness of the meta-analysis findings.

Conclusion

This meta-analysis demonstrated that severe IH systematically induces cardiac remodelling and contractile dysfunction in rodents, which might trigger or aggravate chronic heart failure. Interestingly, this meta-analysis showed that, depending on stimulus severity, IH exhibits both protective and aggravating effects on infarct size after experimental ischaemia–reperfusion procedures.

This meta-analysis shows that IH induces cardiac remodelling and contractile dysfunction in rodents, independently of IH characteristics. Conversely, the dual response to myocardial ischaemia–reperfusion seems to be related to IH intensity and duration.https://bit.ly/3rdnR32

Intermittent Hypoxia Activates Duration-Dependent Protective and Injurious Mechanisms in Mouse Lung Endothelial Cells

Intermittent hypoxia is a major factor in clinical conditions like the obstructive sleep apnea syndrome or the cyclic recruitment and derecruitment of atelectasis in acute respiratory distress syndrome and positive pressure mechanical ventilation. In vivo investigations of the direct impact of intermittent hypoxia are frequently hampered by multiple co-morbidities of patients. Therefore, cell culture experiments are important model systems to elucidate molecular mechanisms that are involved in the cellular response to alternating oxygen conditions and could represent future targets for tailored therapies. In this study, we focused on mouse lung endothelial cells as a first frontier to encounter altered oxygen due to disturbances in airway or lung function, that play an important role in the development of secondary diseases like vascular disease and pulmonary hypertension. We analyzed key markers for endothelial function including cell adhesion molecules, molecules involved in regulation of fibrinolysis, hemostasis, redox balance, and regulators of gene expression like miRNAs. Results show that short-time exposure to intermittent hypoxia has little impact on vitality and health of cells. At early timepoints and up to 24 h, many endothelial markers are unchanged in their expression and some indicators of injury are even downregulated. However, in the long-term, multiple signaling pathways are activated, that ultimately result in cellular inflammation, oxidative stress, and apoptosis.

Intermittent hypoxia-induced insulin resistance is associated with alterations in white fat distribution

Sleep apnea syndrome is characterized by repetitive upper airway collapses during night leading to intermittent hypoxia (IH). The latter is responsible for metabolic disturbances that rely, at least in part, on abdominal white fat inflammation. Besides qualitative alterations, we hypothesized that IH could also modify body fat distribution, a key factor for metabolic complications. C57BL6 mice exposed to IH (21-5% FiO₂, 60 s cycle, 8 h/day) or air for 6 weeks were investigated for topographic fat alterations (whole-body MRI). Specific role of epididymal fat in IH-induced metabolic dysfunctions was assessed in lipectomized or sham-operated mice exposed to IH or air. Whereas total white fat volume was unchanged, IH induced epididymal adipose tissue (AT) loss with non-significant increase in subcutaneous and mesenteric fat. This was associated with impaired insulin sensitivity and secretion. Epididymal lipectomy led to increased subcutaneous fat in the perineal compartment and prevented IH-induced metabolic disturbances. IH led to reduced epididymal AT and impaired glucose regulation. This suggests that, rather than epididymal AT volume, qualitative fat alterations (i.e. inflammation) could represent the main determinant of metabolic dysfunction. This deterioration of glucose regulation was prevented in epididymal-lipectomized mice, possibly through prevention of IH-induced epididymal AT alterations and compensatory increase in subcutaneous AT.