Chronic intermittent hypoxia elicits distinct transcriptomic responses among neurons and oligodendrocytes within the brainstem of mice

Chronic intermittent hypoxia (CIH) is a prevalent condition characterized by recurrent episodes of oxygen deprivation, linked to respiratory and neurological disorders. Prolonged CIH is known to have adverse effects, including endothelial dysfunction, chronic inflammation, oxidative stress, and impaired neuronal function. These factors can contribute to serious comorbidities, including metabolic disorders and cardiovascular diseases. To investigate the molecular impact of CIH, we examined male C57BL/6J mice exposed to CIH for 21 days, comparing with normoxic controls. We used single-nucleus RNA sequencing to comprehensively examine the transcriptomic impact of CIH on key cell classes within the brainstem, specifically excitatory neurons, inhibitory neurons, and oligodendrocytes. These cell classes regulate essential physiological functions, including autonomic tone, cardiovascular control, and respiration. Through analysis of 10,995 nuclei isolated from pontine-medullary tissue, we identified seven major cell classes, further subdivided into 24 clusters. Our findings among these cell classes, revealed significant differential gene expression, underscoring their distinct responses to CIH. Notably, neurons exhibited transcriptional dysregulation of genes associated with synaptic transmission, and structural remodeling. In addition, we found dysregulated genes encoding ion channels and inflammatory response. Concurrently, oligodendrocytes exhibited dysregulated genes associated with oxidative phosphorylation and oxidative stress. Utilizing CellChat network analysis, we uncovered CIH-dependent altered patterns of diffusible intercellular signaling. These insights offer a comprehensive transcriptomic cellular atlas of the pons-medulla and provide a fundamental resource for the analysis of molecular adaptations triggered by CIH.NEW & NOTEWORTHY This study on chronic intermittent hypoxia (CIH) from pons-medulla provides initial insights into the molecular effects on excitatory neurons, inhibitory neurons, and oligodendrocytes, highlighting our unbiased approach, in comparison with earlier studies focusing on single target genes. Our findings reveal that CIH affects cell classes distinctly, and the dysregulated genes in distinct cell classes are associated with synaptic transmission, ion channels, inflammation, oxidative stress, and intercellular signaling, advancing our understanding of CIH-induced molecular responses.

Chromium picolinate supplementation improves cardiac performance in hypoxic rats

BACKGROUND

Conditions associated with chronic hypoxia increase morbidity and mortality attributable to cardiovascular complications. Myocardial hypoxia is a common feature in several diseases including: stroke, infarction, anaemia, chronic lung diseases, obstructive sleep apnoea and cyanotic congenital heart defects. The present study was planned to investigate the cardiovascular effects of chronic intermittent hypoxia and its association with increased myocardial oxidative stress. In addition, to evaluate the protective effect of chromium supplementation, aiming at achieving an alternative that may enable to devise a therapy for hypoxic patients.

METHODS

Male rats were allocated into three groups: control group (normoxic), untreated hypoxic group (exposed to hypoxia 8 h/day, 5 days/week for 6 weeks) and hypoxic group supplemented with chromium picolinate (90 µg/kg/day by gavage). Rats were subjected to measurement of body weight, haematocrit value, mean arterial blood pressure, heart rate and ECG recording. Cardiac activities of isolated hearts were studied on Langendorff preparation under basal conditions and in response to ischaemia/reperfusion. Thereafter, cardiac weights were determined and cardiac tissue catalase activity as well as malondialdhyde level were assessed.

RESULTS

Significant results were obtained upon exposure to hypoxia including; low body weight, increased haematocrit, elevated blood pressure, left ventricular hypertrophy and impaired cardiac activities, basally and in response to ischaemia/reperfusion challenges, associated with increased oxidative stress in cardiac tissue. At the same time, chromium supplementation increased body weight, lowered blood pressure, reduced ventricular hypertrophy and significantly improved the cardiac performance.

CONCLUSION

Chromium supplementation confers protection against hypoxia-induced cardiovascular dysfunction by improvement of the antioxidant capacity.

Ferrostatin-1 Reversed Chronic Intermittent Hypoxia-Induced Ferroptosis in Aortic Endothelial Cells via Reprogramming Mitochondrial Function

Purpose

Chronic intermittent hypoxia (CIH) related arterial endothelium injury is a common cause of cardiovascular system injury. However, the mechanism still needs to be clarified. In this study, we aimed to clarify the role and mechanism of ferrostatin-1 (Fer-1) in CIH-related rat arterial endothelial cells (ROAEC) ferroptosis.

Methods

ROAEC was divided into control group, CIH group, and CIH+ Fer-1 group. Cell viability was detected by cell counting kit 8 kits (CCK8). The apoptotic rate, reactive oxygen species (ROS) levels, Fe2+ levels, and lipid ROS levels were detected by flow cytometry. Malondialdehyde (MDA) levels and nicotinamide adenine dinucleotide (NAD+)/NADH ratio were detected via Elisa kits. The mRNA and protein levels of cystine/glutamate antiporter solute carrier family 7 member 11 (SLC7A11) and glutathione peroxidase 4 (GPX4) were detected by qRT-PCR and Western blot. Mitochondrial structure and function were observed by transmission electron microscope (TEM) and mitochondrial membrane potential (MMP). Central carbon metabolism was measured to compare metabolites among each group.

Results

After the CIH exposure, ROAEC cell viability decreased; The levels of cell apoptosis, ROS, Fe2+, MDA, and lip ROS increased; The levels of NAD+/NADP ratio decreased; The mRNA and protein levels of GPX4 and SLC7A11 decreased (all p<0.05). Co-cultured with Fer-1 reversed the levels of apoptosis rate, cell viability, ROS, Fe2+, MAD, lipid ROS, NAD+/NADH ratio and the mRNA and protein expression of GPX4 and SLC7A11 (all p<0.05). The TEM results showed that damaged mitochondrial membrane and the matrix spillover in the CIH group. The results of the JC-1 assay showed decreased MMP in the CIH group. Fer-1 treatment ameliorated the mitochondrial injury. The results of central carbon metabolism found that CIH altered the metabolites in the TCA cycle, which were reversed by Fer-1 treatment.

Conclusion

CIH-induced ferroptosis in ROAEC, which were reversed by Fer-1 via reprogramming mitochondrial function.

NLRP3-GSDMD-dependent IL-1β Secretion from Microglia Mediates Learning and Memory Impairment in a Chronic Intermittent Hypoxia-induced Mouse Model

Hypoxia/reoxygenation caused by chronic intermittent hypoxia (CIH) plays an important role in cognitive deficits in patients with obstructive sleep apnea. However, the precise underlying mechanism remains unclear. This study investigated whether the NOD-like receptor family pyrin domain-containing 3 (NLRP3) inflammasome is involved in CIH-induced spatial learning and memory impairment in mice, and the possible underlying upstream and downstream mechanisms. The C57BL/6 male mice were exposed to CIH (21% O2-6% O2, 4 min/cycle, 8 h/day) for 9 weeks to investigate the role of NLRP3 in CIH-induced spatial learning and memory impairment in mice. BV2 cells were exposed to intermittent hypoxia (21% O2-1% O2, 90 min/cycle) for 48 h to investigate the possible mechanisms in vitro. We found that: 1) inhibition of NLRP3 inflammasome activation improved CIH-induced spatial learning and memory impairment in mice. 2) CIH damaged hippocampal neurons but increased the number of microglia in mice hippocampi; CIH activated microglia-specific NLRP3 inflammasome, leading to upregulation of matured IL-1β and N-GSDMD. 3) intermittent hypoxia activated NLRP3 inflammasome via the ROS-NF-κB signaling pathway to promote the release of matured IL-1β from microglia in a GSDMD-dependent manner without pyroptosis. 4) The IL-1β released from microglia might impair the synaptic plasticity of hippocampal CA3-CA1 synapses by acting on IL-1 receptors in hippocampal neurons. Our findings reveal that ROS-NF-κB-NLRP3 inflammasome-GSDMD dependent IL-1β release from microglia may participate in CIH-induced spatial learning and memory impairment by acting on hippocampal neuronal IL-1 receptor, leading to synaptic plasticity impairment.

Gut microbiota and metabolic profiles in chronic intermittent hypoxia-induced rats: disease-associated dysbiosis and metabolic disturbances

Aim

Chronic intermittent hypoxia (CIH) is a key characteristic of obstructive sleep apnea (OSA) syndrome, a chronic respiratory disorder. The mechanisms of CIH-induced metabolic disturbance and histopathological damage remain unclear.

Methods

CIH-induced rats underwent daily 8-h CIH, characterized by oxygen levels decreasing from 21% to 8.5% over 4 min, remaining for 2 min, and quickly returning to 21% for 1 min. The control rats received a continuous 21% oxygen supply. The levels of hypersensitive C reactive protein (h-CRP), tumor necrosis factor-α (TNF-α), interleukin 6 (IL-6), interleukin 8 (IL-8), and nuclear factor kappa-B (NF-κB) were measured by ELISA. Histological analysis of the soft palates was conducted using HE staining. The microbial profiling of fecal samples was carried out by Accu16STM assay. Untargeted metabolomics of serum and soft palate tissue samples were analyzed by UPLC-MS. The protein expression of cAMP-related pathways in the soft palate was determined by Western blot.

Results

After 28 h of CIH induction, a significant increase in pro-inflammatory cytokines was observed in the serum, along with mucosal layer thickening and soft palate tissue hypertrophy. CIH induction altered the diversity and composition of fecal microbiota, specifically reducing beneficial bacteria while increasing harmful bacteria/opportunistic pathogens. Notably, CIH induction led to a significant enrichment of genera such as Dorea, Oscillibacter, Enteractinococcus, Paenibacillus, Globicatella, and Flaviflexus genera. Meanwhile, Additionally, CIH induction had a notable impact on 108 serum marker metabolites. These marker metabolites, primarily involving amino acids, organic acids, and a limited number of flavonoids or sterols, were associated with protein transport, digestion and absorption, amino acid synthesis and metabolism, as well as cancer development. Furthermore, these differential serum metabolites significantly affected 175 differential metabolites in soft palate tissue, mainly related to cancer development, signaling pathways, amino acid metabolism, nucleotide precursor or intermediate metabolism, respiratory processes, and disease. Importantly, CIH induction could significantly affect the expression of the cAMP pathway in soft palate tissue.

Conclusions

Our findings suggest that targeting differential metabolites in serum and soft palate tissue may represent a new approach to clinical intervention and treatment of OSA simulated by the CIH.

Chronic intermittent hypoxia remodels catecholaminergic nerve innervation in mouse atria

Chronic intermittent hypoxia (CIH, a model for sleep apnoea) is a major risk factor for several cardiovascular diseases. Autonomic imbalance (sympathetic overactivity and parasympathetic withdrawal) has emerged as a causal contributor of CIH-induced cardiovascular disease. Previously, we showed that CIH remodels the parasympathetic pathway. However, whether CIH induces remodelling of the cardiac sympathetic innervation remains unknown. Mice (male, C57BL/6J, 2-3 months) were exposed to either room air (RA, 21% O2 ) or CIH (alternating 21% and 5.7% O2 , every 6 min, 10 h day-1 ) for 8-10 weeks. Flat-mounts of their left and right atria were immunohistochemically labelled for tyrosine hydroxylase (TH, a sympathetic marker). Using a confocal microscope (or fluorescence microscope) and Neurlocudia 360 digitization and tracing system, we scanned both the left and right atria and quantitatively analysed the sympathetic axon density in both groups. The segmentation data was mapped onto a 3D mouse heart scaffold. Our findings indicated that CIH significantly remodelled the TH immunoreactive (-IR) innervation of the atria by increasing its density at the sinoatrial node, the auricles and the major veins attached to the atria (P < 0.05, n = 7). Additionally, CIH increased the branching points of TH-IR axons and decreased the distance between varicosities. Abnormal patterns of TH-IR axons around intrinsic cardiac ganglia were also found following CIH. We postulate that the increased sympathetic innervation may further amplify the effects of enhanced CIH-induced central sympathetic drive to the heart. Our work provides an anatomical foundation for the understanding of CIH-induced autonomic imbalance. KEY POINTS: Chronic intermittent hypoxia (CIH, a model for sleep apnoea) causes sympathetic overactivity, cardiovascular remodelling and hypertension. We determined the effect of CIH on sympathetic innervation of the mouse atria. In vivo CIH for 8-10 weeks resulted in an aberrant axonal pattern around the principal neurons within intrinsic cardiac ganglia and an increase in the density, branching point, tortuosity of catecholaminergic axons and atrial wall thickness. Utilizing mapping tool available from NIH (SPARC) Program, the topographical distribution of the catecholaminergic innervation of the atria were integrated into a novel 3D heart scaffold for precise anatomical distribution and holistic quantitative comparison between normal and CIH mice. This work provides a unique neuroanatomical understanding of the pathophysiology of CIH-induced autonomic remodelling.

Ferroptosis-related genes are considered as potential targets for CPAP treatment of obstructive sleep apnea

Obstructive sleep apnea (OSA) is a common syndrome characterized by upper airway dysfunction during sleep. Continuous positive airway pressure (CPAP) is the most frequently utilized non-surgical treatment for OSA. Ferroptosis play a crucial role in the physiological diseases caused by chronic intermittent hypoxia, but its involvement in the development of OSA and the exact mechanisms have incompletely elucidated. GSE75097 microarray dataset was used to identify differentially expressed genes between OSA patients and CPAP-treated OSA patients. Subsequently, Gene Ontology (GO) annotation, Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway, STRING database, and FerrDb database were conducted to analyze the biological functions of differentially expressed genes and screen ferroptosis-related genes. Finally, GSE135917 dataset employed for validation. There were 1,540 differentially expressed genes between OSA patients and CPAP-treated OSA patients. These differentially expressed genes were significantly enriched in the regulation of interleukin-1-mediated signaling pathway and ferroptosis-related signaling pathway. Subsequently, 13 ferroptosis-related genes (DRD5, TSC22D3, TFAP2A, STMN1, DDIT3, MYCN, ELAVL1, JUN, DUSP1, MIB1, PSAT1, LCE2C, and MIR27A) were identified from the interaction between differentially expressed genes and FerrDb database, which are regarded as the potential targets of CPAP-treated OSA. These ferroptosis-related genes were mainly involved in cell proliferation and apoptosis and MAPK signaling pathway. Furthermore, DRD5 and TFAP2A were downregulated in OSA patients, which showed good diagnostic properties for OSA, but these abnormal signatures are not reversed with short-term effective CPAP therapy. In summary, the identification of 13 ferroptosis-related genes as potential targets for the CPAP treatment of OSA provides valuable insights into the development of novel, reliable, and accurate therapeutic options.

Hydrogen Attenuates Chronic Intermittent Hypoxia-Induced Cardiac Hypertrophy by Regulating Iron Metabolism

The present study aimed to investigate the impact of hydrogen (H2) on chronic intermittent hypoxia (CIH)-induced cardiac hypertrophy in mice by modulating iron metabolism. C57BL/6N mice were randomly allocated into four groups: control (Con), CIH, CIH + H2, and H2. The mice were exposed to CIH (21-5% FiO2, 3 min/cycle, 8 h/d), and received inhalation of a hydrogen-oxygen mixture (2 h/d) for 5 weeks. Cardiac and mitochondrial function, levels of reactive oxygen species (ROS), and iron levels were evaluated. The H9C2 cell line was subjected to intermittent hypoxia (IH) and treated with H2. Firstly, we found H2 had a notable impact on cardiac hypertrophy, ameliorated pathological alterations and mitochondrial morphology induced by CIH (p < 0.05). Secondly, H2 exhibited a suppressive effect on oxidative injury by decreasing levels of inducible nitric oxide synthase (i-NOS) (p < 0.05) and 4-hydroxynonenal (4-HNE) (p < 0.01). Thirdly, H2 demonstrated a significant reduction in iron levels within myocardial cells through the upregulation of ferroportin 1 (FPN1) proteins (p < 0.01) and the downregulation of transferrin receptor 1 (TfR1), divalent metal transporter 1 with iron-responsive element (DMT1(+ire)), and ferritin light chain (FTL) mRNA or proteins (p < 0.05). Simultaneously, H2 exhibited the ability to decrease the levels of Fe2+ and ROS in H9C2 cells exposed to IH (p < 0.05). Moreover, H2 mediated the expression of hepcidin, hypoxia-inducible factor-1α (HIF-1α) (p < 0.01), and iron regulatory proteins (IRPs), which might be involved in the regulation of iron-related transporter proteins. These results suggested that H2 may be beneficial in preventing cardiac hypertrophy, a condition associated with reduced iron toxicity.

Chronic intermittent hypoxia-induced cardiovascular and renal dysfunction: from adaptation to maladaptation

Chronic intermittent hypoxia (CIH) is the dominant pathological feature of human obstructive sleep apnoea (OSA), which is highly prevalent and associated with cardiovascular and renal diseases. CIH causes hypertension, centred on sympathetic nervous overactivity, which persists following removal of the CIH stimulus. Molecular mechanisms contributing to CIH-induced hypertension have been carefully delineated. However, there is a dearth of knowledge on the efficacy of interventions to ameliorate high blood pressure in established disease. CIH causes endothelial dysfunction, aberrant structural remodelling of vessels and accelerates atherosclerotic processes. Pro-inflammatory and pro-oxidant pathways converge on disrupted nitric oxide signalling driving vascular dysfunction. In addition, CIH has adverse effects on the myocardium, manifesting atrial fibrillation, and cardiac remodelling progressing to contractile dysfunction. Sympatho-vagal imbalance, oxidative stress, inflammation, dysregulated HIF-1α transcriptional responses and resultant pro-apoptotic ER stress, calcium dysregulation, and mitochondrial dysfunction conspire to drive myocardial injury and failure. CIH elaborates direct and indirect effects in the kidney that initially contribute to the development of hypertension and later to chronic kidney disease. CIH-induced morphological damage of the kidney is dependent on TLR4/NF-κB/NLRP3/caspase-1 inflammasome activation and associated pyroptosis. Emerging potential therapies related to the gut-kidney axis and blockade of aryl hydrocarbon receptors (AhR) are promising. Cardiorenal outcomes in response to intermittent hypoxia present along a continuum from adaptation to maladaptation and are dependent on the intensity and duration of exposure to intermittent hypoxia. This heterogeneity of OSA is relevant to therapeutic treatment options and we argue the need for better stratification of OSA phenotypes.

Shedding light on neurofilament involvement in cognitive decline in obstructive sleep apnea and its possible role as a biomarker

Obstructive sleep apnea is one of the most common sleep disorders with a high estimated global prevalence and a large number of associated comorbidities in general as well as specific neuropsychiatric complications such as cognitive impairment. The complex pathogenesis and effects of the disorder including chronic intermittent hypoxia and sleep fragmentation may lead to enhanced neuronal damage, thereby contributing to neuropsychiatric pathologies. Obstructive sleep apnea has been described as an independent risk factor for several neurodegenerative diseases, including Alzheimer's disease and all-cause dementia. The influence of obstructive sleep apnea on cognitive deficits is still a topic of recent debate, and several mechanisms, including neurodegeneration and depression-related cognitive dysfunction, underlying this correlation are taken into consideration. The differentiation between both pathomechanisms of cognitive impairment in obstructive sleep apnea is a complex clinical issue, requiring the use of multiple and costly diagnostic methods. The studies conducted on neuroprotection biomarkers, such as brain-derived neurotrophic factors and neurofilaments, are recently gaining ground in the topic of cognition assessment in obstructive sleep apnea patients. Neurofilaments as neuron-specific cytoskeletal proteins could be useful non-invasive indicators of brain conditions and neurodegeneration, which already are observed in many neurological diseases leading to cognitive deficits. Additionally, neurofilaments play an important role as a biomarker in other sleep disorders such as insomnia. Thus, this review summarizes the current knowledge on the involvement of neurofilaments in cognitive decline and neurodegeneration in obstructive sleep apnea patients as well as discusses its possible role as a biomarker of these changes.

[Quantitative analysis of differential proteins in renal tissues of rats with chronic intermittent hypoxic exposure based on TMT and PRM technology]

OBJECTIVE

To screen the differentially expressed proteins in the kidneys of rats exposed to chronic intermittent hypoxia (CIH) based on TMT-PRM technology to identify the potential biomarkers of renal injuries induced by CIH.

METHODS

Twenty SD rats were randomized into two groups (n=10) and exposed to CIH or normoxia. After 12 weeks of exposure, the kidneys of the rats were collected for observing pathological changes. The renal proteins were extracted, enzymatically digested and labelled with TMT, and LC-MS/MS was used to identify the proteins. The data were processed using Proteome Discoverer2.4 for bioinformatic analysis of the differentially expressed proteins. PRM technology was used to verify the expression of the candidate proteins.

RESULTS

CIH induced obvious renal injury in the rats, manifested by irregular glomerulus and swelling of the epithelial cells of the renal tubules. A total of 31 differentially expressed proteins were identified in CIH rats, including 22 up-regulated and 9 down-regulated proteins. Enrichment analysis of GO function and KEGG pathway analysis showed that the differentially expressed proteins participated mainly in the biological processes of cell adhesion, hypoxic stress, and calcium ions and were involved in the PPAR, AMPK, and metabolic pathways. In PRM quantitative analysis, 3 proteins, namely P07379 (PCK1), P19132 (Fth1) and Q5XI79 (Ndufaf7), showed results consistent with those of TMT-quantitative proteomic analysis.

CONCLUSION

Thirty-one differentially expressed proteins were identified in the renal tissues of rats with CIH exposure, and among them P07379 (PCK1), P19132 (Fth1), and Q5XI79 (Ndufaf7) may be the key proteins closely related to the renal injury in induced by CIH.

Chronic intermittent hypoxia due to obstructive sleep apnea slightly alters nutritional status: a pre-clinical study

Obstructive sleep apnea syndrome (OSAS) is associated with chronic intermittent hypoxia (cIH) that causes disturbances in glucose and lipid metabolism. Animals exposed to cIH show lower body weight and food intake, but the protein-energy metabolism has never been investigated. Here, to address the gap, we studied the impact of cIH on nutritional status in rats. A total of 24 male Wistar rats were randomized into 3 groups (n = 8): a control group (Ctrl), a cIH group (cIH) exposed to cIH (30 s 21-30 s 5% fraction of inspired oxygen, 8 h per day, for 14 days), and a pair-fed group (PF) exposed to normoxia with food intake adjusted to the intake of the cIH group rats with anorexia. Body weight and food intake were measured throughout the study. After 14 days, the rats were euthanized, the organs were collected, weighed, and the liver, intestine mucosa, and muscles were snap-frozen to measure total protein content. Food intake was decreased in the cIH group. Body weight was significantly lower in the cIH group only (-11%, p < 0.05). Thymus and liver weight as well as EDL protein content tended to be lower in the cIH group than in the Ctrl and PF groups. Jejunum and ileum mucosa protein contents were lower in the cIH group compared to the PF group. cIH causes a slight impairment of nutritional status and immunity. This pre-clinical work argues for greater consideration of malnutrition in care for OSAS patients. Further studies are warranted to devise an adequate nutritional strategy.

Chronic Intermittent Hypoxia-Induced Dysmetabolism Is Associated with Hepatic Oxidative Stress, Mitochondrial Dysfunction and Inflammation

The association between obstructive sleep apnea (OSA) and metabolic disorders is well-established; however, the underlying mechanisms that elucidate this relationship remain incompletely understood. Since the liver is a major organ in the maintenance of metabolic homeostasis, we hypothesize that liver dysfunction plays a crucial role in the pathogenesis of metabolic dysfunction associated with obstructive sleep apnea (OSA). Herein, we explored the underlying mechanisms of this association within the liver. Experiments were performed in male Wistar rats fed with a control or high fat (HF) diet (60% lipid-rich) for 12 weeks. Half of the groups were exposed to chronic intermittent hypoxia (CIH) (30 hypoxic (5% O2) cycles, 8 h/day) that mimics OSA, in the last 15 days. Insulin sensitivity and glucose tolerance were assessed. Liver samples were collected for evaluation of lipid deposition, insulin signaling, glucose homeostasis, hypoxia, oxidative stress, antioxidant defenses, mitochondrial biogenesis and inflammation. Both the CIH and HF diet induced dysmetabolism, a state not aggravated in animals submitted to HF plus CIH. CIH aggravates hepatic lipid deposition in obese animals. Hypoxia-inducible factors levels were altered by these stimuli. CIH decreased the levels of oxidative phosphorylation complexes in both groups and the levels of SOD-1. The HF diet reduced mitochondrial density and hepatic antioxidant capacity. The CIH and HF diet produced alterations in cysteine-related thiols and pro-inflammatory markers. The results obtained suggest that hepatic mitochondrial dysfunction and oxidative stress, leading to inflammation, may be significant factors contributing to the development of dysmetabolism associated with OSA.

Ginsenoside Rb1 alleviates chronic intermittent hypoxia-induced diabetic cardiomyopathy in db/db mice by regulating the adenosine monophosphate-activated protein kinase/Nrf2/heme oxygenase-1 signaling pathway

OBJECTIVE

To examine the protective effect of ginsenoside Rb1 (Rb1), the main component of Renshen (), on cardiomyopathy in db/db mice exposed to chronic intermittent hypoxia (CIH) and explore the potential underlying mechanism of Rb1 in treating diabetic cardiomyopathy (DCM).

METHODS

The db/db mice were randomly separated into five groups: normal control group, model group, Rb1 20 mg/kg group, Rb1 40 mg/kg group, and glucagon-like peptide-1 (GLP-1) group. Mice were exposed to air-condition or CIH for 8 weeks, and Rb1 and GLP-1 were administrated before CIH exposure every day. Oral glucose tolerance test (OGTT), intraperitoneal insulin tolerance test (IPITT), total cholesterol (TC), triglyceride (TG), and high-density lipoprotein cholesterol (HDL-C) were detected to evaluate glycolipid metabolism. The level of insulin was detected by a mouse enzyme-linked immunosorbent assay (ELISA). Cardiac function was detected by echocardiography, and myocardial pathology was observed by hematoxylin-eosin and Masson staining. The expression of collagen Ⅰ and collagen Ⅲ was detected by immunohistochemistry. Adenosine monophosphate-activated protein kinase (AMPK)/Nrf2/heme oxygenase-1 (HO-1) signaling pathway was detected by Western blot and immunofluorescence.

RESULTS

Rb1 treatment could improve glucose tolerance and the level of cardiac function indexes, and inhibit the level of oxidative stress indexes and the expression of collagen Ⅰ and collagen Ⅲ. Moreover, Rb1 treatment enhanced AMPK phosphorylation and increased Nrf2 and HO-1 expression.

CONCLUSION

Rb1 treatment alleviated CIH-induced diabetic cardiomyopathy and glycolipid metabolism disorders in db/db mice by inhibiting oxidative stress and regulating the AMPK/Nrf2/HO-1 signaling pathway.

[Characterization of metabotropic glutamate receptor 7 and 8 in rat superior cervical ganglion and their changes following chronic intermittent hypoxia]

OBJECTIVE

To investigate the expression and localization of metabotropic glutamate receptors 7 and 8 (mGluR7/8) in rat superior cervical ganglion (SCG) and their changes in response to chronic intermittent hypoxia (CIH).

METHODS

We detected the expressions of mGluR7 and mGluR8 in the SCG of 8-week-old male SD rats using immunohistochemistry and characterized their distribution with immunofluorescence staining. The expression of mGluR7 and mGluR8 in the cytoplasm and nucleus was detected using Western blotting. A 6-week CIH rat model was established by exposure to intermittent hypoxia (6% oxygen for 30 s followed by normoxia for 4 min) for 8 h daily, and the changes in systolic blood pressure, diastolic blood pressure and mean arterial pressure were measured. The effect of CIH on expression levels of mGluR7 and mGluR8 in the SCG was analyzed using Western blotting.

RESULTS

Positive expressions of mGluR7 and mGluR8 were detected in rat SCG. mGluR7 was distributed in the neurons and small fluorescent (SIF) cells with positive staining in both the cytoplasm and nuclei, but not expressed in satellite glial cells (SGCs), nerve fibers or blood vessels; mGluR8 was localized in the cytoplasm of neurons and SIF cells, but not expressed in SGCs, nerve fibers, or blood vessels. Western blotting of the nuclear and cytoplasmic fractions of rat SCG further confirmed that mGluR7 was expressed in both the cytoplasm and the nucleus, while mGluR8 exists only in the cytoplasm. Exposure to CIH significantly increased systolic blood pressure, diastolic blood pressure and mean arterial pressure of the rats (all P < 0.001) and augmented the protein expressions of mGluR7 and mGluR8 in the SCG (P < 0.05).

CONCLUSION

mGluR7 and mGluR8 are present in rat SCG but with different localization patterns. CIH increases blood pressure of rats and enhanced protein expressions of mGluR7 and mGluR8 in rat SCG.

Chronic Intermittent Hypoxia-Induced Diaphragm Muscle Weakness Is NADPH Oxidase-2 Dependent

Chronic intermittent hypoxia (CIH)-induced redox alterations underlie diaphragm muscle dysfunction. We sought to establish if NADPH oxidase 2 (NOX2)-derived reactive oxygen species (ROS) underpin CIH-induced changes in diaphragm muscle, which manifest as impaired muscle performance. Adult male mice (C57BL/6J) were assigned to one of three groups: normoxic controls (sham); chronic intermittent hypoxia-exposed (CIH, 12 cycles/hour, 8 h/day for 14 days); and CIH + apocynin (NOX2 inhibitor, 2 mM) administered in the drinking water throughout exposure to CIH. In separate studies, we examined sham and CIH-exposed NOX2-null mice (B6.129S-Cybb^TM1Din/J). Apocynin co-treatment or NOX2 deletion proved efficacious in entirely preventing diaphragm muscle dysfunction following exposure to CIH. Exposure to CIH had no effect on NOX2 expression. However, NOX4 mRNA expression was increased following exposure to CIH in wild-type and NOX2 null mice. There was no evidence of overt CIH-induced oxidative stress. A NOX2-dependent increase in genes related to muscle regeneration, antioxidant capacity, and autophagy and atrophy was evident following exposure to CIH. We suggest that NOX-dependent CIH-induced diaphragm muscle weakness has the potential to affect ventilatory and non-ventilatory performance of the respiratory system. Therapeutic strategies employing NOX2 blockade may function as an adjunct therapy to improve diaphragm muscle performance and reduce disease burden in diseases characterised by exposure to CIH, such as obstructive sleep apnoea.

Role of TRPC3 in Right Ventricular Dilatation under Chronic Intermittent Hypoxia in 129/SvEv Mice

Patients with obstructive sleep apnea (OSA) exhibit a high prevalence of pulmonary hypertension and right ventricular (RV) hypertrophy. However, the exact molecule responsible for the pathogenesis remains unknown. Given the resistance to RV dilation observed in transient receptor potential canonical 3(Trpc3)^-/- mice during a pulmonary hypertension model induced by phenylephrine (PE), we hypothesized that TRPC3 also plays a role in chronic intermittent hypoxia (CIH) conditions, which lead to RV dilation and dysfunction. To test this, we established an OSA mouse model using 8- to 12-week-old 129/SvEv wild-type and Trpc3^-/- mice in a customized breeding chamber that simulated sleep and oxygen cycles. Functional parameters of the RV were evaluated through analysis of cardiac cine magnetic resonance images, while histopathological examinations were conducted on cardiomyocytes and pulmonary vessels. Following exposure to 4 weeks of CIH, Trpc3^-/- mice exhibited significant RV dysfunction, characterized by decreased ejection fraction, increased end-diastole RV wall thickness, and elevated expression of pathological cardiac markers. In addition, reactive oxygen species (ROS) signaling and the endothelin system were markedly increased solely in the hearts of CIH-exposed Trpc3^-/- mice. Notably, no significant differences in pulmonary vessel thickness or the endothelin system were observed in the lungs of wild-type (WT) and Trpc3^-/- mice subjected to 4 weeks of CIH. In conclusion, our findings suggest that TRPC3 serves as a regulator of RV resistance in response to pressure from the pulmonary vasculature, as evidenced by the high susceptibility to RV dilation in Trpc3^-/- mice without notable changes in pulmonary vasculature under CIH conditions.

Mechanisms of Atrial Fibrillation in Obstructive Sleep Apnoea

Obstructive sleep apnoea (OSA) is a strong independent risk factor for atrial fibrillation (AF). Emerging clinical data cite adverse effects of OSA on AF induction, maintenance, disease severity, and responsiveness to treatment. Prevention using continuous positive airway pressure (CPAP) is effective in some groups but is limited by its poor compliance. Thus, an improved understanding of the underlying arrhythmogenic mechanisms will facilitate the development of novel therapies and/or better selection of those currently available to complement CPAP in alleviating the burden of AF in OSA. Arrhythmogenesis in OSA is a multifactorial process characterised by a combination of acute atrial stimulation on a background of chronic electrical, structural, and autonomic remodelling. Chronic intermittent hypoxia (CIH), a key feature of OSA, is associated with long-term adaptive changes in myocyte ion channel currents, sensitising the atria to episodic bursts of autonomic reflex activity. CIH is also a potent driver of inflammatory and hypoxic stress, leading to fibrosis, connexin downregulation, and conduction slowing. Atrial stretch is brought about by negative thoracic pressure (NTP) swings during apnoea, promoting further chronic structural remodelling, as well as acutely dysregulating calcium handling and electrical function. Here, we provide an up-to-date review of these topical mechanistic insights and their roles in arrhythmia.

Sex and age differences in social and cognitive function in offspring exposed to late gestational hypoxia

Background

Gestational sleep apnea affects 8-26% of pregnancies and can increase the risk for autism spectrum disorder (ASD) in offspring. ASD is a neurodevelopmental disorder associated with social dysfunction, repetitive behaviors, anxiety, and cognitive impairment. To examine the relationship between gestational sleep apnea and ASD-associated behaviors, we used a chronic intermittent hypoxia (CIH) protocol between gestational days (GD) 15-19 in pregnant rats to model late gestational sleep apnea. We hypothesized that late gestational CIH would produce sex- and age-specific social, mood, and cognitive impairments in offspring.

Methods

Timed pregnant Long-Evans rats were exposed to CIH or room air normoxia from GD 15-19. Behavioral testing of offspring occurred during either puberty or young adulthood. To examine ASD-associated phenotypes, we quantified ASD-associated behaviors (social function, repetitive behaviors, anxiety-like behaviors, and spatial memory and learning), hippocampal activity (glutamatergic NMDA receptors, dopamine transporter, monoamine oxidase-A, EGR-1, and doublecortin), and circulating hormones in offspring.

Results

Late gestational CIH induced sex- and age-specific differences in social, repetitive and memory functions in offspring. These effects were mostly transient and present during puberty. In female pubertal offspring, CIH impaired social function, increased repetitive behaviors, and increased circulating corticosterone levels, but did not impact memory. In contrast, CIH transiently induced spatial memory dysfunction in pubertal male offspring but did not impact social or repetitive functions. Long-term effects of gestational CIH were only observed in female offspring, wherein CIH induced social disengagement and suppression of circulating corticosterone levels in young adulthood. No effects of gestational CIH were observed on anxiety-like behaviors, hippocampal activity, circulating testosterone levels, or circulating estradiol levels, regardless of sex or age of offspring.

Conclusions

Our results indicate that hypoxia-associated pregnancy complications during late gestation can increase the risk for ASD-associated behavioral and physiological outcomes, such as pubertal social dysfunction, corticosterone dysregulation, and memory impairments.

Contrast Enhanced Ultrasonography of Kidney in Chronic Intermittent Hypoxia Rat Model

OBJECTIVES

The objective of our study was to assess the ability of contrast-enhanced ultrasound (CEUS) in evaluating renal microperfusion in an animal model.

METHODS

Twenty Sprague-Dawley rats were subdivided into two groups: the normal and chronic intermittent hypoxia (CIH) groups. In the CIH model, 10 Sprague-Dawley rats were exposed to CIH for 8 weeks to mimic obstructive sleep apnea (OSA). The CEUS parameters of the renal cortex and medulla were obtained and compared between groups. The pathological changes of the kidney tissues were examined by histological staining such as hematoxylin and eosin (H&E) and Masson's trichrome.

RESULTS

CIH caused morphological damage to kidneys. In the cortex, the peak intensity (PI) (P = .009) was significantly lower and time to peak (Ttop) (P = .019) was significantly prolonged in the CIH group compared with the controls. The area under ascending curve (WiAUC) in the medulla and cortex were both significantly lower in the CIH group than those in the control group (P both <.05). CEUS parameters (including PI and WiAUC of the cortex and WiAUC of the medulla) were negatively correlated with serum creatinine (P all <.05). In the medulla, the area under descending curve (WoAUC) was positively correlated with serum creatinine (P = .027), PI was negatively correlated with uric acid (P = .034).

CONCLUSION

CEUS parameters (including Ttop, PI, WoAUC, and WiAUC) reflect renal microvascular changes in CIH. CEUS could be a safe and accurate imaging method to assess renal microvascular damage in CIH rats.

Activation of the High Mobility Group Box 1/Receptor for Advanced Glycation Endproducts /NOD-like Receptor Family Pyrin Domain-Containing 3 Axis Under Chronic Intermittent Hypoxia Induction Promotes the Progression of Atherosclerosis in ApoE-/- Mice

Background Chronic intermittent hypoxia (CIH) has been regarded as an important cause of atherosclerotic disease. In our study, we set out to investigate whether CIH regulated the high mobility group box 1/receptor for advanced glycation endproducts/NOD-like receptor family pyrin domain-containing 3 (HMGB1/RAGE/NLRP3) axis to affect the progression of atherosclerosis. Methods and Results Initially, peripheral blood samples were collected from patients with single obstructive sleep apnea, atherosclerosis complicated with obstructive sleep apnea, and healthy volunteers. In vitro cell experiments were conducted using human monocyte cell line THP-1 and human umbilical vein endothelial cells to explore the role of HMGB1 in cell migration, apoptosis, adhesion, and transendothelial migration. In addition, a CIH-induced atherosclerosis mouse model was established for further identifying the critical role of the HMGB1/RAGE/NLRP3 axis in atherosclerosis. Upregulated HMGB1 and RAGE were found in patients with atherosclerosis complicated with obstructive sleep apnea. CIH induction increased HMGB1 expression by inhibiting HMGB1 methylation, activating the RAGE/NLRP3 axis. After inhibition of the HMGB1/RAGE/NLRP3 axis, monocyte chemotaxis and adhesion were repressed, and macrophage-derived foam cell formation was inhibited, accompanied by suppression of endothelial and foam cell apoptosis and inflammatory factor secretion. In vivo animal experiments also noted that the progression of atherosclerosis was prevented by inhibition of the HMGB1/RAGE/NLRP3 axis in CIH-induced ApoE^-/- mice. Conclusions Taken together, CIH induction can upregulate HMGB1 through inhibition of HMGB1 methylation, which activates the RAGE/NLRP3 axis to promote inflammatory factor secretion, thereby promoting the progression of atherosclerosis.

Rearrangement of cell types in the rat carotid body neurogenic niche induced by chronic intermittent hypoxia

The carotid body (CB) is a prototypical acute oxygen (O₂ )-sensing organ that mediates reflex hyperventilation and increased cardiac output in response to hypoxaemia. CB overactivation, secondary to the repeated stimulation produced by the recurrent episodes of intermittent hypoxia, is believed to contribute to the pathogenesis of sympathetic hyperactivity present in sleep apnoea patients. Although CB functional plasticity induced by chronic intermittent hypoxia (CIH) has been demonstrated, the underlying mechanisms are not fully elucidated. Here, we show that CIH induces a small increase in CB volume and rearrangement of cell types in the CB, characterized by a mobilization of immature quiescent neuroblasts, which enter a process of differentiation into mature, O₂ -sensing and neuron-like, chemoreceptor glomus cells. Prospective isolation of individual cell classes has allowed us to show that maturation of CB neuroblasts is paralleled by an upregulation in the expression of specific glomus cell genes involved in acute O₂ -sensing. CIH enhances mitochondrial responsiveness to hypoxia in maturing neuroblasts as well as in glomus cells. These data provide novel perspectives on the pathogenesis of CB-mediated sympathetic overflow that may lead to the development of new pharmacological strategies of potential applicability in sleep apnoea patients. KEY POINTS: Obstructive sleep apnoea is a frequent condition in the human population that predisposes to severe cardiovascular and metabolic alterations. Activation of the carotid body, the main arterial oxygen-sensing chemoreceptor, by repeated episodes of hypoxaemia induces exacerbation of the carotid body-mediated chemoreflex and contributes to sympathetic overflow characteristic of sleep apnoea patients. In rats, chronic intermittent hypoxaemia induces fast neurogenesis in the carotid body with rapid activation of neuroblasts, which enter a process of proliferation and maturation into O₂ -sensing chemoreceptor glomus cells. Maturing carotid body neuroblasts and glomus cells exposed to chronic intermittent hypoxia upregulate genes involved in acute O₂ sensing and enhance mitochondrial responsiveness to hypoxia. These findings provide novel perspectives on the pathogenesis of carotid body-mediated sympathetic hyperactivation. Pharmacological modulation of carotid body fast neurogenesis could help to ameliorate the deleterious effects of chronic intermittent hypoxaemia in sleep apnoea patients.

Huperzine A-Liposomes Efficiently Improve Neural Injury in the Hippocampus of Mice with Chronic Intermittent Hypoxia

Background

Chronic intermittent hypoxia (CIH) could cause neuronal damage, accelerating the progression of dementia. However, safe and effective therapeutic drugs and delivery are needed for successful CIH therapy.

Purpose

To investigate the neuroprotective effect of Huperzine A (HuA) packaged with nanoliposomes (HuA-LIP) on neuronal damage induced by CIH.

Methods

The stability and release of HuA-LIP in vitro were identified. Mice were randomly divided into the Control, CIH, HuA-LIP, and HuA groups. The mice in the HuA and HuA-LIP groups received HuA (0.1 mg/kg, i.p.), and HuA-LIP was administered during CIH exposure for 21 days. HuA-LIP contains the equivalent content of HuA.

Results

We prepared a novel formulation of HuA-LIP that had good stability and controlled release. First, HuA-LIP significantly ameliorated cognitive dysfunction and neuronal damage in CIH mice. Second, HuA-LIP elevated T-SOD and GSH-Px abilities and decreased MDA content to resist oxidative stress damage induced by CIH. Furthermore, HuA-LIP reduced brain iron levels by downregulating TfR1, hepcidin, and FTL expression. In addition, HuA-LIP activated the PKAα/Erk/CREB/BDNF signaling pathway and elevated MAP2, PSD95, and synaptophysin to improve synaptic plasticity. Most importantly, compared with HuA, HuA-LIP showed a superior performance against neuronal damage induced by CIH.

Conclusion

HuA-LIP has a good sustained-release effect and targeting ability and efficiently protects against neural injury caused by CIH.

Advances in animal models of obstructive sleep apnea

Animal experiments play an important role in the study of the pathogenesis of human diseases and new methods of diagnosis and treatment. Due to the great differences in the anatomical structure and physiology of the upper airway between animals and humans, there is currently no animal model that can fully simulate the pathological anatomy and pathophysiological characteristics of human obstructive sleep apnea (OSA) patients. Herein, we summarizes the construction methods of several OSA animal models that have been widely used in the studies published in the last 5 years, the advantages and limitations of each model as well as related evaluation techniques are described. This information has potential to provide further guide for the development of OSA related animal experiments.

Long noncoding RNA HOXA-AS2 ameliorates chronic intermittent hypoxia-induced lung inflammation by regulating miR-17-5p/tipe2 axis

PURPOSE

The purpose is to confirm whether long noncoding RNA HOXA-AS2 relieves chronic intermittent hypoxia (CIH)-induced lung inflammation.

METHODS

Male Sprague Dawley rats were used to establisha CIH rat model. Hematoxylin and Eosin staining was used on the lung tissue injury to determine the successful construction of CIH animal model. Arterial partial pressure of oxygen (PaO₂) and carbon dioxide (PaCO₂) were measured. HOXA-AS2 was overexpressed to evaluate its role in the progression and development of CIH. T cell differentiation and cytokine production were determined using flow cytometry. Cell apoptosis was determined using terminal deoxynucleotidyl transferase dUTP nick end labelling assay kit. The target of HOXA-AS2 and miR-17-5p was predicted by the Encyclopedia of RNA Interactomes (ENCORI) and confirmed using luciferase assay.

RESULTS

HOXA-AS2 was downregulated in CIH rat models. Lung tissue injury was observed in CIH rats, and the injury was attenuated by the overexpression of HOXA-AS2. PaO₂ was reduced and PaCO₂ was induced in CIH rats, which was reversed by the overexpression of HOXA-AS2. The overexpression of HOXA-AS2 inhibited CIH-induced cell apoptosis. It also reversed alterations in the levels of interferon gamma (IFNγ), interleukin (IL)-2, IL-6, IL-1β, tumor necrosis factor alpha (TNF-α), and transforming growth factor beta1 (TGF-β1) in rats caused by CIH. The overexpression of HOXA-AS2 prevented the induction in CD4⁺ IFN-γ⁺ T cells and reduction in CD4⁺TGF-β1⁺ T cells. The overexpression of HOXA-AS2 upregulated tumor necrosis factor-alpha-induced protein 8-like 2 (tipe2) key regulator through directly targeting miR-17-5p. Further experiments proved that tipe2 was the direct target of miR-17-5p.

CONCLUSION

This study manifested that HOXA-AS2 acted as an anti-inflammatory regulator and protected lung tissue injury from CIH in the rat model; this was mediated by upregulation of tipe2 through directly targeting miR-17-5p. HOXA-AS2 upregulated the expression of tipe2, providing new understanding and therapeutic target for CIH.

Association Between Metabolic-Associated Fatty Liver Disease and Obstructive Sleep Apnea: A Cross-Sectional Study

AIM

Emerging evidence has revealed that obstructive sleep apnea (OSA) is an independent risk factor for the development of a variety of adverse metabolic disease states. In this study, we evaluated the association between OSA severity and metabolic dysfunction-associated fatty liver disease (MAFLD) among Asian populations.

MATERIALS AND METHODS

This was a cross-sectional, single-center study. The study cohort consisted of patients undergoing polysomnography and abdominal ultrasonography. Logistic regression analysis was used to evaluate the independent risk factors of MAFLD in patients with OSA.

RESULTS

A total of 1065 patients (277 non-MAFLD and 788 MAFLD) were included in the study. The prevalence of MAFLD in non-OSA, mild-moderate OSA, and severe OSA patients was 58.16%, 72.41%, and 78.0%, respectively (p < 0.001). We identified significant differences in body mass index (BMI), apnea-hypopnea index (AHI), oxygen desaturation index (ODI), and lowest O₂ saturation (LaSO₂) between non-MAFLD and MAFLD patients (all p < 0.001). After adjusting for confounding variables, we used multivariate regression analysis to show that BMI, ODI, and triglyceride (TG) levels independently predicted the occurrence of MAFLD (odds ratio [OR] = 1.234, p < 0.001; OR = 1.022, p = 0.013; OR = 1.384, p = 0.001, respectively). Moreover, stratified analysis according to BMI indicated that TG levels were the predominant risk factor for MAFLD in a group of patients with a BMI < 23 kg/m², while BMI, ODI, TG levels, and total cholesterol (TC) were the major risk factors for MAFLD in a group of patients with a BMI ≥ 23 kg/m² (all p < 0.05).

CONCLUSION

OSA-associated chronic intermittent hypoxia was independently associated with the risk of MAFLD, especially in OSA patients with a BMI ≥ 23 kg/m², suggesting that oxidative stress might play an important role in the pathogenesis of MAFLD in patients with OSA.

Chronic intermittent hypoxia promotes early intrahepatic endothelial impairment in rats with nonalcoholic fatty liver disease

Nonalcoholic fatty liver disease (NAFLD) is a progressive disease that ranges from simple steatosis to cirrhosis. Obstructive sleep apnea syndrome (OSAS) and chronic intermittent hypoxia (CIH) are implicated in the pathogenesis of NAFLD. However, the overlapping consequences of CIH on liver sinusoidal endothelial function over time in NAFLD are largely unknown. We explored endothelial dysfunction in a rat model of NAFLD with a high-fat diet exposed to CIH [12 h/day, every 30 s to fractional concentration of oxygen ([Formula: see text] 8%-10%]. The livers were isolated and perfused, and the endothelial function was determined by testing the vasodilation of the liver circulation to increased concentrations of acetylcholine and von Willebrand factor (vWF) and intercellular adhesion molecule 1 (ICAM-1) expression. Phosphorylated endothelial nitric oxide synthase (p-eNOS), cGMP, and oxidative stress were assessed to determine nitric oxide bioavailability. Inflammation and fibrosis were evaluated by transaminases, myeloperoxidase activity, hydroxyproline, and histological evaluation. Hypoxia-inducible factors (HIFs) were studied as a marker of hypoxia and after a second insult with acetaminophen. CIH exposure provoked typical systemic features of OSAS and provoked a decreased response in vasodilation to acetylcholine. This was associated with increased oxidative stress and reduced p-eNOS and cGMP. The microcirculation impairment due to CIH preceded significant hepatic inflammation and fibrotic changes, despite the presence of HIF expression. In conclusion, CIH exacerbates endothelial dysfunction in NAFLD rats associated with increased oxidative stress and reduced nitric oxide bioavailability. This occurs before inflammation and fibrosis establish. Our results suggest that with CIH endothelial dysfunction should be considered an early target.NEW & NOTEWORTHY We believe the findings are of relevance because we demonstrate that chronic intermittent hypoxia further augments impaired hepatic endothelial dysfunction in nonalcoholic fatty liver disease rats. Because obstructive sleep apnea syndrome is associated with systemic endothelial dysfunction in cardiovascular disorders, and chronic intermittent hypoxia is an independent and reversible risk factor for hypertension and coronary artery disease, we hypothesized that this entity may be of potential relevance in the pathophysiology of nonalcoholic fatty liver disease.

[Effects of Bu Zhong Yi Qi decoction on CIH-induced interstitial lung fibrosis in mice]

OBJECTIVE

To investigate the effects of chronic intermittent hypoxia (CIH) on the expression of transforming growth factor-β (TGF-β), P-samd3, serum laminin (LN) and hyaluronidase (HA) in mouse lung tissues and the protective effects of Bu Zhong Yi Qi decoction on lung interstitial deposition damage in CIH mice.

METHODS

Fifty SPF-grade C57BL mice were randomly divided into five groups (n=10): blank control group, CIH model group, and CIH+ low, medium and high doses of Bu Zhong Yi Qi decoction group. Mice were placed under normoxia or CIH conditions, respectively. The Chinese medicine group was given the corresponding doses of drugs. HE staining was performed to assess pathological changes and Masson staining was performed to assess collagen deposition. Western blot was performed to detect the expressions of channel proteins such as TGF-β1, P-smad3 and down stream α-SMA and Collagen I. ELISA was performed to detect the serum levels of TGF-β1, LN and HA.

RESULTS

HE staining showed alveolar collapse, septal thickening and epithelial cell necrosis in CIH mice, Masson showed massive collagen fiber proliferation and deposition in lung interstitium, while the above changes in lung tissues were significantly improved in the CIH + Bu Zhong Yi Qi decoction groups compared with the CIH group. TGF-β1, P-smad3 and Collagen I, Collagen Ⅲ, and α-SMA expression levels were increased compared with the blank control group (P＜0.05), and the expressions of TGF-β1 and LN in serum were upregulated (P＜0.05). The expressions of TGF-β1, P-smad3, Collagen I protein and SMA-α in the lung tissues of the CIH+ Bu Zhong Yi Qi decoction groups were downregulated significantly compared with those of the CIH group (P＜0.05), and the improvement of multiple indexes in the CIH+high-dose CIH intervention group was better than those of the low-dose group (P＜0.05).

CONCLUSION

Bu Zhong Yi Qi decoction can inhibit alveolar structural changes and excessive collagen deposition in the interstitium of CIH mice, and then improve lung function in CIH mice. The mechanism may be related to the down-regulation of protein expression related to TGF-β/smads signaling pathway by Bu Zhong Yi Qi decoction.

[Effects of chronic intermittent hypoxia on atrial electrical remodeling in rats]

OBJECTIVE

The aim of this study was to investigate the effects of chronic intermittent hypoxia (CIH) on atrial electrical remodeling in Sprague-Dawley (SD) rats, which provide the explication for the mechanisms of CIH promoting atrial fibrillation (AF).

METHODS

Eighty SD rats were randomly divided into 2 groups: control group and CIH group (n=40). CIH rats were subjected to CIH 8 h/d for 30 days. After the echocardiography and hemodynamics examination, cardiac electrophysiological experiments, histological experiments, and molecular biological experiments were executed. AF susceptibility was measured by isolated heart electrophysiological experiments. Masson's trichrome stain was used to assess the degree of atrial fibrosis. The protein expression levels of sodium voltage-gated channel alpha subunit 5 (SCN5A/Na_v1.5), calcium voltage-gated channel subunit alpha1 C (CACNA1C/Ca_v1.2) and potassium voltage-gated channel subfamily D member 3 (KCND3/K_v4.3) were measured by Western blot. In whole-cell patch clamp experiments, current clamp mode was used to record AP, and APD₉₀ and APD₅₀ were analyzed and compared between the two groups. In voltage clamp mode, I_Na, I_Ca-L, I_to and their kinetic parameters were recorded and compared between the two groups.

RESULTS

Compared to the control rats, atrial interstitial collagen deposition (P＜0.01) and AF inducibility (P＜0.05) were increased in CIH rats, whereas the expression levels of Na_v1.5, Ca_v1.2 and K_v4.3 were decreased (P＜0.05). APD₉₀ and APD₅₀ in CIH rats' atrial myocytes were longer than those of control rats, and CIH rats showed decreased current density of I_Na, I_Ca-L(P＜0.01) and I_to(P＜0.01).

CONCLUSION

CIH-induced changes in the protein expression levels of ion channel subunits, current intensity, APD, and AF susceptibility, which may be the mechanisms of CIH promoting AF.

Optogenetic stimulation of pre-Bötzinger complex reveals novel circuit interactions in swallowing-breathing coordination

The coordination of swallowing with breathing, in particular inspiration, is essential for homeostasis in most organisms. While much has been learned about the neuronal network critical for inspiration in mammals, the pre-Bötzinger complex (preBötC), little is known about how this network interacts with swallowing. Here we activate within the preBötC excitatory neurons (defined as Vglut2 and Sst neurons) and inhibitory neurons (defined as Vgat neurons) and inhibit and activate neurons defined by the transcription factor Dbx1 to gain an understanding of the coordination between the preBötC and swallow behavior. We found that stimulating inhibitory preBötC neurons did not mimic the premature shutdown of inspiratory activity caused by water swallows, suggesting that swallow-induced suppression of inspiratory activity is not directly mediated by the inhibitory neurons in the preBötC. By contrast, stimulation of preBötC Dbx1 neurons delayed laryngeal closure of the swallow sequence. Inhibition of Dbx1 neurons increased laryngeal closure duration and stimulation of Sst neurons pushed swallow occurrence to later in the respiratory cycle, suggesting that excitatory neurons from the preBötC connect to the laryngeal motoneurons and contribute to the timing of swallowing. Interestingly, the delayed swallow sequence was also caused by chronic intermittent hypoxia (CIH), a model for sleep apnea, which is 1) known to destabilize inspiratory activity and 2) associated with dysphagia. This delay was not present when inhibiting Dbx1 neurons. We propose that a stable preBötC is essential for normal swallow pattern generation and disruption may contribute to the dysphagia seen in obstructive sleep apnea.

[Effects of NLRP3/Caspase-1 pathway on Banxia Houpu decoction in the intervention of chronic intermittent hypoxia in mice with renal inflammatory injury]

Objective: To investigate the effects of Banxia Houpo decoction on the renal NLRP3/Caspase-1/IL-1β signaling pathway in chronic intermittent hypoxia mice. Methods: C57BL/6 mice were randomly divided into 3 groups, normal control group (Control), chronic intermittent hypoxia group (CIH), and Banxia Houpo decoction treatment group (BHD), with 10 mice in each group. Mice in the CIH group and BHD group were placed in a hypoxic chamber. The oxygen volume fraction in the cabin was decreased from 21% to 9% in 90 s, and then oxygen was filled in 90 s to gradually increase the oxygen volume fraction in the cabin to 21%, while the mice in the control group were placed in the cabin and filled with normal air, processing 8 hours per day for 21 days. The mice in BHD group were treated with Banxia Houpu decoction by gavage before entering the cabin every day, and the control group and CIH group were given an equal volume of normal saline. After modeling, the changes of renal function indexes in each group were detected; HE and Masson staining were used to observe the pathological conditions of the kidney; Western blot and immunohistochemical staining were used to detect the protein expression levels of the nucleotide-binding oligomerization domain-like receptor protein 3(NLRP3), aspartate-specific cysteine protein 1(Caspase-1) and interleukine-1beta(IL-1β). Results: Compared with control group, the contents of serum renal functional indexes UA, BUN and SCr in CIH group were increased significantly (P<0.01), and after BHD treatment, they all were decreased significantly compared with CIH group (P<0.01). Compared with control group, the results of HE staining showed that in the CIH group, glomerular endothelial cells were degenerated and necrotic, and vacuoles of different sizes appeared in renal tubular epithelial cells, and a small amount of renal tubular epithelial cells fell off and died. The pathological condition of the BHD group was improved compared with CIH group, the glomerular morphology gradually returned to normal, and a small amount of renal tubular epithelial cells fell off and died. Compared with control group, Masson staining results showed that there was obvious fibrosis around the glomeruli in the CIH group, the fibrosis was significantly reduced in the BHD group. The expression levels of NLRP3, Caspase-1, IL-1β and IL-18 were increased significantly compared with control group (P<0.05 or P<0.01), and immunohistochemical staining showed that NLRP3 was mainly expressed in renal tubular epithelial cells and interstitial macrophages, caspase-1 and IL-1β were mainly found in the cytoplasm of renal tubular epithelial cells. After BHD treatment, the expression levels of each protein were decreased compared with CIH group (P<0.05). Conclusion: Banxia Houpu decoction can reduce the kidney damage by inhibiting the expression of related molecules in the NLRP3/Casapse-1/IL-1β signaling pathway.

NADPH oxidase-2 is necessary for chronic intermittent hypoxia-induced sternohyoid muscle weakness in adult male mice

New Findings

What is the central question of this study?

Exposure to chronic intermittent hypoxia (CIH) evokes redox changes, culminating in impaired upper airway muscle function: what is the specific source of CIH‐induced reactive oxygen species?

What is the main finding and its importance?

Profound sternohyoid muscle dysfunction following exposure to CIH was entirely prevented by apocynin co‐treatment or NADPH oxidase 2 (NOX2) deletion. The results have implications for human obstructive sleep apnoea syndrome and point to antioxidant intervention, potentially targeting NOX2 blockade, as a therapeutic strategy.

Abstract

Exposure to chronic intermittent hypoxia (CIH) evokes redox changes, culminating in impaired upper airway muscle function. We sought to determine if NADPH oxidase 2 (NOX2)‐derived reactive oxygen species underpin CIH‐induced maladaptive changes in upper airway (sternohyoid) muscle performance. Adult male mice (C57BL/6J) were assigned to one of three groups: normoxic controls (sham); CIH‐exposed (CIH, 12 cycles/hour, 8 h/day for 14 days); and CIH + apocynin (NOX2 inhibitor, 2 mM) given in the drinking water throughout exposure to CIH. In addition, we studied sham and CIH‐exposed NOX2‐null mice (B6.129S‐CybbTM^1Din/J). Profound sternohyoid muscle dysfunction following exposure to CIH was entirely prevented by apocynin co‐treatment or NOX2 deletion. Exposure to CIH increased sternohyoid muscle NOX enzyme activity, with no alteration to the gene or protein expression of NOX subunits. There was no evidence of overt oxidative stress, muscle regeneration, inflammation or atrophy following exposure to CIH. We suggest that NOX‐dependent CIH‐induced upper airway muscle weakness increases vulnerability to upper airway obstruction. Our results have implications for human obstructive sleep apnoea syndrome and point to antioxidant intervention, potentially targeting NOX2 blockade, as a therapeutic strategy.

Chronic Intermittent Hypoxia Exposure Alternative to Exercise Alleviates High-Fat-Diet-Induced Obesity and Fatty Liver

Obesity often concurs with nonalcoholic fatty liver disease (NAFLD), both of which are detrimental to human health. Thus far, exercise appears to be an effective treatment approach. However, its effects cannot last long and, moreover, it is difficult to achieve for many obese people. Thus, it is necessary to look into alternative remedies. The present study explored a noninvasive, easy, tolerable physical alternative. In our experiment, C57BL/6 mice were fed with a high-fat diet (HFD) to induce overweight/obesity and were exposed to 10% oxygen for one hour every day. We found that hypoxia exerted protective effects. First, it offset HFD-induced bodyweight gain and insulin resistance. Secondly, hypoxia reversed the HFD-induced enlargement of white and brown adipocytes and fatty liver, and protected liver function. Thirdly, HFD downregulated the expression of genes required for lipolysis and thermogenesis, such as UCP1, ADR3(beta3-adrenergic receptor), CPT1A, ATGL, PPARα, and PGC1α, M2 macrophage markers arginase and CD206 in the liver, and UCP1 and PPARγ in brown fat, while these molecules were upregulated by hypoxia. Furthermore, hypoxia induced the activation of AMPK, an energy sensing enzyme. Fourthly, our results showed that hypoxia increased serum levels of epinephrine. Indeed, the effects of hypoxia on bodyweight, fatty liver, and associated changes in gene expression ever tested were reproduced by injection of epinephrine and prevented by propranolol at varying degrees. Altogether, our data suggest that hypoxia triggers stress responses where epinephrine plays important roles. Therefore, our study sheds light on the hope to use hypoxia to treat the daunting disorders, obesity and NAFLD.

Cardiac Autonomic Modulation and Response to Sub-Maximal Exercise in Chilean Hypertensive Miners

Cardiac autonomic modulation in workers exposed to chronic intermittent hypoxia (CIH) has been poorly studied, especially considering hypertensive ones. Heart rate variability (HRV) has been proven as valuable tool to assess cardiac autonomic modulation under different conditions. The aim of this study is to investigate the cardiac autonomic response related to submaximal exercise (i.e., six-minute walk test, 6MWT) in hypertensive (HT, n = 9) and non-hypertensive (NT, n = 10) workers exposed for > 2 years to CIH. Participants worked on 7-on 7-off days shift between high altitude (HA: > 4.200 m asl) and sea level (SL: < 500 m asl). Data were recorded with electrocardiography (ECG) at morning upon awakening (10 min supine, baseline), then at rest before and after (5 min sitting, pre and post) the 6MWT, performed respectively on the first day of their work shift at HA, and after the second day of SL sojourn. Heart rate was higher at HA in both groups for each measurement (p < 0.01). Parasympathetic indices of HRV were lower in both groups at HA, either in time domain (RMSSD, p < 0.01) and in frequency domain (log HF, p < 0.01), independently from measurement's time. HRV indices in non-linear domain supported the decrease of vagal tone at HA and showed a reduced signal's complexity. ECG derived respiration frequency (EDR) was higher at HA in both groups (p < 0.01) with interaction group x altitude (p = 0.012), i.e., higher EDR in HT with respect to NT. No significant difference was found in 6MWT distance regarding altitude for both groups, whereas HT covered a shorter 6MWT distance compared to NT (p < 0.05), both at HA and SL. Besides, conventional arm-cuff blood pressure and oxygen blood saturation values (recorded before, at the end and after 5-min recovery from 6MWT), reported differences related to HA only. HA is the main factor affecting cardiac autonomic modulation, independently from hypertension. However, presence of hypertension was associated with a reduced physical performance independently from altitude, and with higher respiratory frequency at HA.

Sulforaphane Attenuates Chronic Intermittent Hypoxia-Induced Brain Damage in Mice via Augmenting Nrf2 Nuclear Translocation and Autophagy

Obstructive sleep apnea–hypopnea syndrome (OSAHS), typically characterized by chronic intermittent hypoxia (CIH), is associated with neurocognitive dysfunction in children. Sulforaphane (SFN), an activator of nuclear factor E2-related factor 2 (Nrf2), has been demonstrated to protect against oxidative stress in various diseases. However, the effect of SFN on OSAHS remains elusive. In this research, we investigated the neuroprotective role of SFN in CIH-induced cognitive dysfunction and underlying mechanisms of regulation of Nrf2 signaling pathway and autophagy. CIH exposures for 4 weeks in mice, modeling OSAHS, contributed to neurocognitive dysfunction, manifested as increased working memory errors (WMEs), reference memory errors (RMEs) and total memory errors (TEs) in the 8-arm radial maze test. The mice were intraperitoneally injected with SFN (0.5 mg/kg) 30 min before CIH exposure everyday. SFN treatment ameliorated neurocognitive dysfunction in CIH mice, which demonstrates less RME, WME, and TE. Also, SFN effectively alleviated apoptosis of hippocampal neurons following CIH by decreased TUNEL-positive cells, downregulated cleaved PARP, cleaved caspase 3, and upregulated Bcl-2. SFN protects hippocampal tissue from CIH-induced oxidative stress as evidenced by elevated superoxide dismutase (SOD) activities and reduced malondialdehyde (MDA). In addition, we found that SFN enhanced Nrf2 nuclear translocation to hold an antioxidative function on CIH-induced neuronal apoptosis in hippocampus. Meanwhile, SFN promoted autophagy activation, as shown by increased Beclin1, ATG5, and LC3II/LC3I. Overall, our findings indicated that SFN reduced the apoptosis of hippocampal neurons through antioxidant effect of Nrf2 and autophagy in CIH-induced brain damage, which highlights the potential of SFN as a novel therapy for OSAHS-related neurocognitive dysfunction.

Expression of p11 and TASK1 Channels in Rat Carotid Body Glomus Cells Subjected to Chronic Intermittent Hypoxia

Chronic intermittent hypoxia (CIH) has been used as a model to mimic nocturnal apnea, which is associated with hypertension. One of the mechanisms for hypertension in patients with nocturnal apnea is an enhancement of the plasma membrane response to acute hypoxia in carotid body glomus cells. Hypoxia is known to induce depolarization via inhibiting TWIK-related acid-sensitive K⁺ (TASK) channels, one type of leak K⁺ channels, in glomus cells. The present experiment was undertaken to immunocytochemically investigate the effects of CIH on the expression and intracellular localization of TASK1 channels and p11 that critically affect the trafficking of TASK1 to the cell surface. The expression levels of TASK1 proteins and p11 and their intracellular localization in rat carotid body glomus cells were not noticeably affected by CIH, suggesting that the enhanced membrane response to acute hypoxia is not due to an increase in surface TASK channels.

Reduced circulating growth hormone and insulin-like growth factor-1 and delayed growth of premature rats are aggravated by longer daily duration of chronic intermittent hypoxia exposure

OBJECTIVE

This study mainly aimed to investigate the effect of daily duration of chronic intermittent hypoxia (CIH) exposure on circulating growth hormone (GH)/insulin-like growth factor-1 (IGF-1) concentrations and body weight changes of premature rats.

METHODS

40 healthy male SD rats aged six weeks were enrolled in this study. These rats were randomly divided into four groups (n = 10 per group), including normal control (NC) group (normal oxygen exposure every day), CIH-1 group (daily CIH exposure for 2 h), CIH-2 group (daily CIH exposure for 4 h), and CIH-3 group (daily CIH exposure for 8 h). The serum GH/IGF-1 concentrations and body weights in all rats were determined after 30 days of normal oxygen or CIH exposure.

RESULTS

No significant difference was found with respect to the baseline body weight among the four groups of rats. After establishments of animal models with a duration of 30 days, significant differences were found respect to body weight, body weight changes, and serum GH/IGF-1 concentrations among the four groups of rats with a same trend (all P < 0.05): the highest values were all in NC group rats, followed CIH-1 group, CIH-2 group, and CIH-3 group rats. Among all the rats, the body weight changes correlated significantly with both serum GH and IGF-1 concentrations (both P < 0.05).

CONCLUSION

CIH decreases circulating GH/IGF-1 concentrations and causes growth delay in premature rats. Such effects could be aggravated by increased daily duration of CIH exposures.

Gender Differences in the Context of Obstructive Sleep Apnea and Metabolic Diseases

The relationship between obstructive sleep apnea (OSA) and endocrine and metabolic disease is unequivocal. OSA, which is characterized by intermittent hypoxia and sleep fragmentation, leads to and exacerbates obesity, metabolic syndrome, and type 2 diabetes (T2D) as well as endocrine disturbances, such as hypothyroidism and Cushing syndrome, among others. However, this relationship is bidirectional with endocrine and metabolic diseases being considered major risk factors for the development of OSA. For example, polycystic ovary syndrome (PCOS), one of the most common endocrine disorders in women of reproductive age, is significantly associated with OSA in adult patients. Several factors have been postulated to contribute to or be critical in the genesis of dysmetabolic states in OSA including the increase in sympathetic activation, the deregulation of the hypothalamus-pituitary axis, the generation of reactive oxygen species (ROS), insulin resistance, alteration in adipokines levels, and inflammation of the adipose tissue. However, probably the alterations in the hypothalamus-pituitary axis and the altered secretion of hormones from the peripheral endocrine glands could play a major role in the gender differences in the link between OSA-dysmetabolism. In fact, normal sleep is also different between men and women due to the physiologic differences between genders, with sex hormones such as progesterone, androgens, and estrogens, being also connected with breathing pathologies. Moreover, it is very well known that OSA is more prevalent among men than women, however the prevalence in women increases after menopause. At the same time, the step-rise in obesity and its comorbidities goes along with mounting evidence of clinically important sex and gender differences. Metabolic and cardiovascular diseases, seen as a men's illness for decades, presently are more common in women than in men and obesity has a higher association with insulin-resistance-related risk factors in women than in men. In this way, in the present manuscript, we will review the major findings on the overall mechanisms that connect OSA and dysmetabolism giving special attention to the specific regulation of this relationship in each gender. We will also detail the gender-specific effects of hormone replacement therapies on metabolic control and sleep apnea.

Effects of Chronic Intermittent Hypoxia and Chronic Sleep Fragmentation on Gut Microbiome, Serum Metabolome, Liver and Adipose Tissue Morphology

Chronic intermittent hypoxia (CIH) and chronic sleep fragmentation (CSF) are two cardinal pathological features of obstructive sleep apnea (OSA). Dietary obesity is a crucial risk intermediator for OSA and metabolic disorders. Gut microbiota affect hepatic and adipose tissue morphology under conditions of CIH or CSF through downstream metabolites. However, the exact relationship is unclear. Herein, chow and high-fat diet (HFD)-fed mice were subjected to CIH or CSF for 10 weeks each and compared to normoxia (NM) or normal sleep (NS) controls. 16S rRNA amplicon sequencing, untargeted liquid chromatography-tandem mass spectrometry, and histological assessment of liver and adipose tissues were used to investigate the correlations between the microbiome, metabolome, and lipid metabolism under CIH or CSF condition. Our results demonstrated that CIH and CSF regulate the abundance of intestinal microbes (such as Akkermansia mucinphila, Clostridium spp., Lactococcus spp., and Bifidobacterium spp.) and functional metabolites, such as tryptophan, free fatty acids, branched amino acids, and bile acids, which influence adipose tissue and hepatic lipid metabolism, and the level of lipid deposition in tissues and peripheral blood. In conclusion, CIH and CSF adversely affect fecal microbiota composition and function, and host metabolism; these findings provide new insight into the independent and synergistic effects of CIH, CSF, and HFD on lipid disorders.

Cannabinoid receptors promote chronic intermittent hypoxia-induced breast cancer metastasis via IGF-1R/AKT/GSK-3β

The progression of breast cancer is closely related to obstructive sleep apnea-hypopnea syndrome (OSAHS). Low concentrations of cannabinoids promote tumor proliferation. However, the role of cannabinoid receptors (CBs) in chronic intermittent hypoxia (CIH)-induced breast cancer has not been reported. The migration and invasion of breast cancer cell lines (MCF-7 and T47D) were measured by scratch assay and transwell assay. Gene and protein expressions were analyzed by qPCR and western blotting. Tumor xenograft mice model were established to evaluate the function of CBs. We observed that chronic hypoxia (CH) and CIH increased CBs expression and promoted migration and invasion in breast cancer. Mice grafted with MCF-7 exhibited obvious tumor growth, angiogenesis, and lung metastasis in CIH compared with CH and control. In addition, CIH induced CBs expression, which subsequently activated insulin-like growth factor-1 receptor (IGF-1R)/AKT/glycogen synthase kinase-3β (GSK-3β) axis. Knockdown of CBs alleviated CIH-induced migration and invasion of breast cancer in vitro. Furthermore, CIH exaggerated the malignancy of breast cancer and silencing of CBs suppressed tumor growth and metastasis in vivo. Our study contributed to understanding the role of CIH in breast cancer development modulation.

Association of Genes of the NO Pathway with Altitude Disease and Hypoxic Pulmonary Hypertension

Chronic intermittent hypoxia leads to high-altitude pulmonary hypertension, which is associated with high asymmetric dimethylarginine (ADMA), an endogenous inhibitor of nitric oxide synthesis. Therefore, we aimed to understand the relation of single nucleotide polymorphisms in this pathway to high-altitude pulmonary hypertension (HAPH). We genotyped 69 healthy male Chileans subjected to chronic intermittent hypoxia. Acclimatization to altitude was determined using the Lake Louise Score and the presence of acute mountain sickness. Echocardiography was performed after six months in 24 individuals to estimate pulmonary arterial pressure. The minor allele of dimethylarginine dimethylaminohydrolase (DDAH)1 rs233112 was associated with high-baseline plasma ADMA concentration, while individuals homozygous for the major allele of DDAH2 rs805304 had a significantly greater increase in ADMA during chronic intermittent hypoxia. The major allele of alanine glyoxylate aminotransferase-2 (AGXT2) rs37369 was associated with a greater reduction of plasma symmetric dimethylarginine (SDMA). Several genes were associated with high-altitude pulmonary hypertension, and the nitric oxide synthase (NOS)3 and DDAH2 genes were related to acute mountain sickness. In conclusion, DDAH1 determines baseline plasma ADMA, while DDAH2 modulates ADMA increase in hypoxia. AGXT2 may be up-regulated in hypoxia. Genomic variation in the dimethylarginine pathway affects the development of HAPH and altitude acclimatization.

Enhanced Ocular Surface and Intraoral Nociception via a Transient Receptor Potential Vanilloid 1 Mechanism in a Rat Model of Obstructive Sleep Apnea

Obstructive sleep apnea (OSA), characterized by low arterial oxygen saturation during sleep, is associated with an increased risk of orofacial pain. In this study, we simulated chronic intermittent hypoxia (CIH) during the sleep/rest phase (light phase) to determine the role of transient receptor potential vanilloid 1 (TRPV1) in mediating enhanced orofacial nocifensive behavior and trigeminal spinal subnucleus caudalis (Vc) neuronal responses to capsaicin (a TRPV1 agonist) stimulation in a rat model of OSA. Rats were subjected to CIH (nadir O₂, 5%) during the light phase for 8 or 16 consecutive days. CIH yielded enhanced behavioral responses to capsaicin after application to the ocular surface and intraoral mucosa, which was reversed under normoxic conditions. The percentage of TRPV1-immunoreactive trigeminal ganglion neurons was greater in CIH rats than in normoxic rats and recovered under normoxic conditions after CIH. The ratio of large-sized TRPV1-immunoreactive trigeminal ganglion neurons increased in CIH rats. The density of TRPV1 positive primary afferent terminals in the superficial laminae of Vc was higher in CIH rats. Phosphorylated extracellular signal-regulated kinase (pERK)-immunoreactive cells intermingled with the central terminal of TRPV1-positive afferents in the Vc. The number of pERK-immunoreactive cells following low-dose capsaicin (0.33 µM) application to the tongue was significantly greater in the middle portion of the Vc of CIH rats than of normoxic rats and recovered under normoxic conditions after CIH. These data suggest that CIH during the sleep (light) phase is sufficient to transiently enhance pain on the ocular surface and intraoral mucosa via TRPV1-dependent mechanisms.

Circular RNA Expression Profiles and Bioinformatic Analysis in Mouse Models of Obstructive Sleep Apnea-Induced Cardiac Injury: Novel Insights Into Pathogenesis

Circular RNAs (circRNAs) participate in the development of various kinds of diseases. However, the function and roles of circRNAs in obstructive sleep apnea (OSA)-induced cardiovascular disease remain poorly understood. Therefore, we sought to explore the circRNA expression profiles and predict their functions in OSA-induced cardiac injury with the use of bioinformatics analysis. The model of OSA was established in mouse treated by chronic intermittent hypoxia (CIH) exposure. Then, we screened the circRNA profile using circRNA microarray. By comparing circRNA expression in three matched pairs of CIH-treated cardiac tissues and controls, differentially expressed circRNAs were identified in the CIH groups. Comparison of the selected circRNAs expression levels was performed between qRT-PCR and microarray. Meanwhile, we employed Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analyses to predict the functions of these selected circRNAs. Finally, we constructed a circRNA-miRNA-mRNA network based on the target prediction. It was found that a total of 124 circRNAs were differentially expressed in CIH-treated cardiac tissues (p ≤ 0.05, fold-change ≥ 1.5). Among them, 23 circRNAs were significantly down-regulated, and the other 101 were up-regulated. Then, ten circRNAs were randomly selected to validate the reliability of the microarray results by using qRT-PCR. Next, we conducted the GO and KEGG pathway analysis to explore the parental genes functions of differentially expressed circRNA. Finally, two significantly differentially expressed circRNAs (mmu_circRNA_014309 and mmu_circRNA_21856) were further selected to create a circRNA-miRNA-mRNA regulation network. Our study did first reveal that the differentially expressed circRNAs played a vital role in the pathogenesis of OSA-induced cardiac damage. Thus, our findings bring us closer to unraveling the pathophysiologic mechanisms and eliciting novel therapeutic targets for the treatment of OSA-associated cardiovascular diseases.

Brown Adipose Tissue Activation Is Involved in Atherosclerosis of ApoE-/- Mice Induced by Chronic Intermittent Hypoxia

Background: Obstructive sleep apnea is an atherogenesis factor of which chronic intermittent hypoxia is a prominent feature. Chronic intermittent hypoxia (CIH) exposure can sufficiently activate the sympathetic system, which acts on the β3 adrenergic receptors of brown adipose tissue (BAT). However, the activity of BAT and its function in CIH-induced atherosclerosis have not been fully elucidated.

Methods: This study involved ApoE^−/− mice which were fed with a high-fat diet for 12 weeks and grouped into control and CIH group. During the last 8 weeks, mice in the CIH group were housed in cages to deliver CIH (12 h per day, cyclic inspiratory oxygen fraction 5–20.9%, 180 s cycle). Atherosclerotic plaques were evaluated by Oil Red O, hematoxylin and eosin, Masson staining, and immunohistochemistry. Afterward, we conducted immunohistochemistry, western blotting, and qRT-PCR of uncoupling protein 1 (UCP1) to investigate the activation of BAT. The level of serum total cholesterol (TC), triglyceride, low-density lipoprotein cholesterol (LDL-c), high-density lipoprotein cholesterol (HDL-c), and free fatty acid (FFA) were measured. Finally, RNA-Sequencing was deployed to explore the differentially expressed genes (DEGs) and their enriched pathways between control and CIH groups.

Results: Chronic intermittent hypoxia exposure promoted atherosclerotic plaque area with increasing CD68, α-SMA, and collagen in plaques. BAT activation was presented during CIH exposure with UCP1 up-regulated. Serum TC, triglyceride, LDL-c, and FFA were increased accompanied by BAT activation. HDL-c was decreased. Mechanistically, 43 lipolysis and lipid metabolism-associated mRNA showed different expression profiling between the groups. Calcium, MAPK, and adrenergic signaling pathway included the most gene number among the significantly enriched pathways.

Conclusion: This study first demonstrated that BAT activation is involved in the progression of CIH-induced atherosclerosis, possibly by stimulating lipolysis.

Hypoxia-Inducible Factors as Key Players in the Pathogenesis of Non-alcoholic Fatty Liver Disease and Non-alcoholic Steatohepatitis

Non-alcoholic fatty liver disease (NAFLD) and its more severe form non-alcoholic steatohepatitis (NASH) are a major public health concern with high and increasing global prevalence, and a significant disease burden owing to its progression to more severe forms of liver disease and the associated risk of cardiovascular disease. Treatment options, however, remain scarce, and a better understanding of the pathological and physiological processes involved could enable the development of new therapeutic strategies. One process implicated in the pathology of NAFLD and NASH is cellular oxygen sensing, coordinated largely by the hypoxia-inducible factor (HIF) family of transcription factors. Activation of HIFs has been demonstrated in patients and mouse models of NAFLD and NASH and studies of activation and inhibition of HIFs using pharmacological and genetic tools point toward important roles for these transcription factors in modulating central aspects of the disease. HIFs appear to act in several cell types in the liver to worsen steatosis, inflammation, and fibrosis, but may nevertheless improve insulin sensitivity. Moreover, in liver and other tissues, HIF activation alters mitochondrial respiratory function and metabolism, having an impact on energetic and redox homeostasis. This article aims to provide an overview of current understanding of the roles of HIFs in NAFLD, highlighting areas where further research is needed.

Health Effects of Chronic Intermittent Hypoxia at a High Altitude among Chilean Miners: Rationale, Design, and Baseline Results of a Longitudinal Study

OBJECTIVES

This study aims to assess the health effects on mining workers of exposure to chronic intermittent hypoxia (CIH) at high- and very high-altitude mining compared with similar work at lower altitudes in Chile, and it also aims to constitute the baseline of a 5-year follow-up study.

METHODS

We designed a cross-sectional study to assess health conditions in 483 miners working at 2 levels of altitude exposure: 336 working at a very high or high altitude (HA; 247 above 3900-4400 m, and 89 at 3000-3900 m), and 147 below 2400 m. Subjects were randomly selected in two stages. First, a selection of mines from a census of mines in each altitude stratum was made. Secondly, workers with less than 2 years of employment at each of the selected mines were recruited. The main outcomes measured at the baseline were mountain sickness, sleep alterations, hypertension, body mass index, and neurocognitive functions.

RESULTS

Prevalence of acute mountain sickness (AMS) was 28.4% in the very high-altitude stratum (P = 0.0001 compared with the low stratum), and 71.7% experienced sleep disturbance (P = 0.02). The adjusted odds ratio for AMS was 9.2 (95% confidence interval: 5.2-16.3) when compared with the very high- and low-altitude groups. Motor processing speed and spatial working memory score were lower for the high-altitude group. Hypertension was lower in the highest-altitude subjects, which may be attributed to preoccupational screening even though this was not statistically significant.

CONCLUSIONS

Despite longer periods of acclimatization to CIH, subjects continue to present AMS and sleep disturbance. Compromise of executive functions was detected, including working memory at HA. Further rigorous research is warranted to understand long-term health impacts of high-altitude mining, and to provide evidence-based policy recommendations.

Role of the p38MAPK signaling pathway in hippocampal neuron autophagy in rats with chronic intermittent hypoxia

This study explored the role of the p38 mitogen-activated protein kinase (MAPK) signaling pathway in hippocampal neuron autophagy in rats with chronic intermittent hypoxia (CIH). Male Sprague-Dawley rats were randomly divided to normoxic control (CON), CIH (optimal modeling time was determined prior by measuring the expression of several proteins after 2-, 4-, and 6-wk intermittent hypoxia), solvent (CIH+Veh), or p38MAPK inhibitor (CIH+SB203580) groups. DMSO and SB203580 were injected intraperitoneally 30 min before hypoxia in CIH+Veh and CIH+SB203580 group rats, respectively. Rat learning and memory were evaluated via the Morris water maze test. Ultrastructural changes in the hippocampal CA1 region autophagic vesicles and neurons were observed under transmission electron and light microscopy. Hippocampal microtubule-associated proteins were detected by western blot. Morris water maze test showed that CIH+SB203580 group rats spent significantly more time on the platform quadrant and crossed the platform more times than CIH+Veh group rats (P < 0.01). Hematoxylin-eosin (HE) staining showed greater rat cell damage in the CIH+SB group than in the CIH and CIH+Veh groups. Western blot analysis showed that CIH+SB group rats had significantly lower p-p38MAPK/p38MAPK, LC3I, and p62 expression and higher beclin-1 expression than CIH+Veh group rats (P < 0.01). Electron microscopy showed that CIH+SB203580 group rats had several small hippocampal neuron autophagic vesicles. On immunofluorescence analyses, it showed a higher LC3II expression in CIH+SB203580 group rats than in CIH+Veh group rats (P < 0.01). These results indicate that inhibition of the CIH p38MAPK signaling pathway can activate autophagy and protect hippocampal neurons in rats.NEW & NOTEWORTHY The pathophysiological processes related to autophagy obstructive sleep apnea-hypopnea syndrome (OSAHS) are unclear. This study clarified that the inhibition of the p38MAPK signaling pathway could further activate autophagy in hippocampal nerve cells, thus reducing nerve cell injury.

Adiponectin Ameliorated Pancreatic Islet Injury Induced by Chronic Intermittent Hypoxia through Inhibiting the Imbalance in Mitochondrial Fusion and Division

Objective This study aimed to assess the protective value of adiponectin (APN) in pancreatic islet injury induced by chronic intermittent hypoxia (CIH). Methods Sixty rats were randomly divided into three groups: normal control (NC) group, CIH group, and CIH with APN supplement (CIH+APN) group. After 5 weeks of CIH exposure, we conducted oral glucose tolerance tests (OGTT) and insulin released test (IRT), examined and compared the adenosine triphosphate (ATP) levels, mitochondrial membrane potential (MMP) levels, reactive oxygen species (ROS) levels, enzymes gene expression levels of Ant1, Cs, Hmox1, and Cox4i1 which represented mitochondrial tricarboxylic acid cycle function, the protein and gene expression levels of DRP1, FIS1, MFN1, and OPA1 which represented mitochondrial fusion and division, and the protein expression levels of BAX, BCL-2, cleaved Caspase-3, and cleaved PARP which represented mitochondrial associated apoptosis pathway of pancreatic islet. Results OGTT and IRT showed blood glucose and insulin levels had no differences among the NC, CIH and CIH+APN groups (both P>0.05) at 0 min, 20 min, 30 min, 60 min, 120 min. However, we found that compared to NC group, CIH increased the ROS level, reduced ATP level and MMP level. The islets of CIH exposed rats showed reduced gene expression levels of Ant1, Cs, Hmox1, and Cox4i1, decreased protein and gene expression levels of MFN1 and OPA1, increased protein and gene expression levels of DRP1 and FIS1, increased protein expression levels of cleaved Caspase-3 and cleaved PARP, with lower ratio of BCL-2/BAX at protein expression level. All the differences among three groups were statistically significant. APN treated CIH rats showed mitigated changes in the above measurements associated with islet injuries. Conclusion APN may ameliorate the pancreatic islet injury induced by CIH via inhibiting the imbalance in mitochondrial fusion and division.

Chronic Intermittent Hypoxia Reduces the Effects of Glucosteroid in Asthma via Activating the p38 MAPK Signaling Pathway

Aims

Obstructive sleep apnea (OSA) is a risk factor for steroid-resistant (SR) asthma. However, the underlying mechanism is not well defined. This study aimed to investigate how chronic intermittent hypoxia (CIH), the main pathophysiology of OSA, influenced the effects of glucocorticoids (GCs) on asthma.

Main Methods

The effects of dexamethasone (Dex) were determined using the ovalbumin (OVA)-challenged mouse model of asthma and transforming growth factor (TGF)-β treated airway smooth muscle cells (ASMCs), with or without CIH. The p38 MAPK signaling pathway activity was then detected in the mouse (n = 6) and ASMCs models (n = 6), which were both treated with the p38 MAPK inhibitor SB239063.

Key Findings

Under CIH, mouse pulmonary resistance value, inflammatory cells in bronchoalveolar lavage fluid (BALF), and inflammation scores increased in OVA-challenged combined with CIH exposure mice compared with OVA-challenged mice (p < 0.05). These indicators were similarly raised in the OVA + CIH + Dex group compared with the OVA + Dex group (P < 0.05). CIH exposure enhanced the activation of the p38 MAPK pathway, oxidative stress injury, and the expression of NF-κB both in lung tissue and ASMCs, which were reversed by treatment with Dex and SB239063. In the in vitro study, treatment with Dex and SB239063 decreased ASMCs proliferation induced by TGF-β combined with CIH and suppressed activation of the p38 MAPK pathway, oxidative stress injury, and NF-κB nuclear transcription (p < 0.05).

Significance

These results indicated that CIH decreased GC sensitivity by activating the p38 MAPK signaling pathway.