Hippocampal mitogen-activated protein kinase activation is associated with intermittent hypoxia in a rat model of obstructive sleep apnea syndrome

Role of Oxidative Stress in the Occurrence and Development of Cognitive Dysfunction in Patients with Obstructive Sleep Apnea Syndrome

Obstructive sleep apnea syndrome (OSAS) causes recurrent apnea and intermittent hypoxia at night, leading to several complications such as cognitive dysfunction. However, the molecular mechanisms underlying cognitive dysfunction in OSAS are unclear, and oxidative stress mediated by intermittent hypoxia is an important mechanism. In addition, the improvement of cognitive dysfunction in patients with OSAS varies by different treatment regimens; among them, continuous positive airway pressure therapy (CPAP) is mostly recognized for improving cognitive dysfunction. In this review, we discuss the potential mechanisms of oxidative stress in OSAS, the common factors of affecting oxidative stress and the Links between oxidative stress and inflammation in OSAS, focusing on the potential links between oxidative stress and cognitive dysfunction in OSAS and the potential therapies for neurocognitive dysfunction in patients with OSAS mediated by oxidative stress. Therefore, further analysis on the relationship between oxidative stress and cognitive dysfunction in patients with OSAS will help to clarify the etiology and discover new treatment options, which will be of great significance for early clinical intervention.

Acetylome analyses provide novel insights into the effects of chronic intermittent hypoxia on hippocampus-dependent cognitive impairment

Introduction

Chronic intermittent hypoxia (CIH) can negatively affect hippocampal function through various molecular mechanisms. Protein acetylation, a frequently occurring modification, plays crucial roles in synaptic plasticity and cognitive processes. However, the global protein acetylation induced by CIH in the hippocampus and its specific effects on hippocampal function and behavior remain poorly understood.

Methods

To address this gap, we conducted a study using liquid chromatography-tandem mass spectrometry to analyze the lysine acetylome and proteome of the hippocampus in healthy adult mice exposed to intermittent hypoxia for 4 weeks (as a CIH model) compared to normoxic mice (as a control).

Results

We identified and quantified a total of 2,184 lysine acetylation sites in 1,007 proteins. Analysis of these acetylated proteins revealed disturbances primarily in oxidative phosphorylation, the tricarboxylic acid (TCA) cycle, and glycolysis, all of which are localized exclusively to mitochondria. Additionally, we observed significant changes in the abundance of 21 proteins, some of which are known to be associated with cognitive impairments.

Discussion

This study helps to elucidate the molecular mechanisms underlying CIH-induced changes in protein acetylation in the hippocampus. By providing valuable insights into the pathophysiological processes associated with CIH and their impacts on hippocampal function, our findings contribute to a better understanding of the consequences of CIH-induced changes in protein acetylation in the hippocampus and the potential role of CIH in cognitive impairment.

Development and validation of a genomic nomogram based on a ceRNA network for comprehensive analysis of obstructive sleep apnea

Objectives: Some ceRNA associated with lncRNA have been considered as possible diagnostic and therapeutic biomarkers for obstructive sleep apnea (OSA). We intend to identify the potential hub genes for the development of OSA, which will provide a foundation for the study of the molecular mechanism underlying OSA and for the diagnosis and treatment of OSA.

Methods: We collected plasma samples from OSA patients and healthy controls for the detection of ceRNA using a chip. Based on the differential expression of lncRNA, we identified the target genes of miRNA that bind to lncRNAs. We then constructed lncRNA-related ceRNA networks, performed functional enrichment analysis and protein-protein interaction analysis, and performed internal and external validation of the expression levels of stable hub genes. Then, we conducted LASSO regression analysis on the stable hub genes, selected relatively significant genes to construct a simple and easy-to-use nomogram, validated the nomogram, and constructed the core ceRNA sub-network of key genes.

Results: We successfully identified 282 DElncRNAs and 380 DEmRNAs through differential analysis, and we constructed an OSA-related ceRNA network consisting of 292 miRNA-lncRNAs and 41 miRNA-mRNAs. Through PPI and hub gene selection, we obtained 7 additional robust hub genes, CCND2, WT1, E2F2, IRF1, BAZ2A, LAMC1, and DAB2. Using LASSO regression analysis, we created a nomogram with four predictors (CCND2, WT1, E2F2, and IRF1), and its area under the curve (AUC) is 1. Finally, we constructed a core ceRNA sub-network composed of 74 miRNA-lncRNA and 7 miRNA-mRNA nodes.

Conclusion: Our study provides a new foundation for elucidating the molecular mechanism of lncRNA in OSA and for diagnosing and treating OSA.

Dexmedetomidine improved one-lung ventilation-induced cognitive dysfunction in rats

BACKGROUND

One-lung ventilation (OLV) is widely used in thoracic surgery. However, OLV may also increase CERO₂ and aggravate delayed cognitive recovery. Here, we aimed to investigate the effect of dexmedetomidine (DEX) on cognitive function in rats undergoing OLV.

METHODS

Sprague-Dawley rats were randomly divided into two-lung ventilation (TLV) group, OLV group and OLV treated with DEX group. Group DEX received 25 μg/kg DEX i.p. 30 min before induction. After mechanical ventilation (MV), Morris water maze (MWM) test was carried out to examine spatial memory function. Western blotting was used to detect pERK1/2, pCREB, Bcl-2 and BAX in hippocampal tissues. Transmission electron microscopy (TEM) was used to observe the hippocampal CA1 region.

RESULTS

Post-MV, compared with group OLV, group DEX showed increases in percentage of target quadrant time (P < 0.05), platform crossings (P < 0.05), a reduction in CERO₂ (P < 0.05), and pERK1/2, pCREB, and Bcl-2 significantly increased (P < 0.01 or P < 0.05), while BAX significantly decreased (P < 0.01), besides, a less damaged synaptic structure was observed in group DEX.

CONCLUSIONS

DEX improved post-MV cognitive function in rats undergoing OLV, reduced cerebral oxygen consumption, protected synaptic structure and upregulated ERK1/2-CREB anti-apoptotic signaling pathway in hippocampal CA1 region.

Inhibition of ERK1/2 regulates cognitive function by decreasing expression levels of PSD-95 in the Hippocampus of CIH Rats

Obstructive sleep apnea syndrome (OSAS) is a potentially severe sleep disorder characterized by intermittent hypoxia, and there is growing evidence that OSAS can lead to cognitive decline. Extracellular signal-regulated protein kinase 1/2 (ERK1/2) plays a key role in synaptic plasticity. We established CIH model in male SD rats and examined their expression of p-ERK1/2 and PSD-95, as well as in CIH group, the effect of SL327 on the expression of p-ERK1/2 and PSD-95 in hippocampus of CIH model rats was observed by pretreating the experimental rats with SL327 during peak time of p-ERK1/2 expression. Mean oxygen saturation in the tail artery was lower in the CIH group. In the CIH groups exhibited increased escape latencies in the navigation test and decreased numbers of platform crossings in the space exploration test. Reduced volume, irregular structure, deepened cytoplasmic eosinophilic staining in the cytoplasm, and decreased nuclear size were found in hippocampal neurons in the 28-d CIH 、28-d CIH + SL327 group. The hippocampus of CIH rats^, p-ERK expressions gradually increased with prolonged CIH exposure but decreased after SL327 treatment. Moreover, PSD-95 expressions gradually reduced in the 14-d CIH, 21-d CIH, and 28-d CIH groups but increased in the SL327-treated group. The SL327 intervention decreased p-ERK1/2 expression, increased PSD-95 expression, and improved cognitive function in CIH rats. The present findings provide some insights into the mechanisms underlying OSAS-associated cognitive impairment.

Novel proteins associated with chronic intermittent hypoxia and obstructive sleep apnea: From rat model to clinical evidence

OBJECTIVE

To screen for obstructive sleep apnea (OSA) biomarkers, isobaric tags for relative and absolute quantitation (iTRAQ)-labeled quantitative proteomics assay was used to identify differentially expressed proteins (DEPs) during chronic intermittent hypoxia (CIH).

METHOD

The iTRAQ technique was applied to compare DEPs in the serum of a CIH rat model and control group. Biological analysis of DEPs was performed using Gene Ontology and Kyoto Encyclopedia to explore related biological functions and signaling pathways. Enzyme-linked immunosorbent assay (ELISA) was performed to validate their expression in sera from patients with OSA and CIH rats.

RESULTS

Twenty-three DEPs (fold change ≥1.2 or ≤0.833, p<0.05) were identified, and two DEPs (unique peptides>3 and higher coverage) were further verified by ELISA in the CIH rat model and OSA subject: apolipoprotein A-IV (APOA4, p<0.05) and Tubulin alpha-1A chain (TUBA1A, p<0.05). Both groups showed significant differences in the expression levels of DEPs between the CIH and control groups and the severe OSA and non-OSA groups. APOA4 was found to be upregulated and TUBA1A downregulated in both the sera from OSA patients and CIH rats, on comparing proteomics results with clinical results. There were two pathways that involved three DEPs, the mitogen-activated protein kinase (MAPK) signaling pathway (p<0.05) and cytokine-cytokine receptor interaction (p<0.05).

CONCLUSION

APOA4 and TUBA1A may be potential novel biomarkers for CIH and OSA, and may play an important role in the development of OSA complications.

Endothelial Dysfunction in a Cell Culture Model Exposed to Various Intermittent Hypoxia Modes

Wang, Juan, Jiahui Wang, Xin Li, Wanju Hou, Jie Cao, and Jing Feng. Endothelial dysfunction in a cell culture model exposed to various intermittent hypoxia modes. High Alt Med Biol. 21:388-395, 2020. Objective: To construct an in vitro model of endothelial cells exposed to various intermittent hypoxia (IH) modes, and determine whether different frequencies and degrees can cause different effects on endothelial cells. Methods: EA.hy926 cells were used to set up the cell model. A program-controlled gas delivery system was designed to regulate the flow of premixed air into the cell culture chamber. The cells were divided into eight groups exposed to various IH modes: standard cell culture group, intermittent normoxia (IN) group (21% O₂ 15 seconds/21% O₂ 3 minutes 45 seconds for 12 cycles/h), IH1 group (1.5% O₂ 15 seconds/21% O₂ 8 minutes 15 seconds for 6.32 cycles/h), IH2 group (1.5% O₂ 15 seconds/21% O₂ 5 minutes 15 seconds for 9.23 cycles/h), IH3 group (1.5% O₂ 15 seconds/21% O₂ 3 minutes 45 seconds for 12 cycles/h), IH4 group (1.5% O₂ 15 seconds/21% O₂ 1 minute 45 seconds for 20 cycles/h), IH5 group (1.5% O₂ 15 seconds/21% O₂ 15 seconds for 40 cycles/h), and IH6 group (10% O₂ 15 seconds/21% O₂ 3 minutes 45 seconds for 12 cycles/h). Results: Nuclear factor κB (NFκB) p65, c-fos, tumor necrosis factor-alpha (TNFα), malondialdehyde (MDA), and endothelin-1 (ET-1) were higher in the IH3 group or IH6 group than those in IN group, and they were much higher in IH3 group than those in IH6 group. Superoxide dismutase (SOD) and nitric oxide (NO) were the opposite results. In IH1, IH2, IH3, IH4, and IH5 groups, the frequencies increased gradually. NFκB p65, TNFα, and c-fos were the highest in IH3 group. MDA and ET-1 were the highest in IH2 group. SOD and NO were the lowest in IH2 group. Conclusions: Different IH frequencies and degrees could cause different effects on endothelial cells. The endothelial responses varied with the duration of reoxygenation. So, the duration of reoxygenation was the key phase for endothelial dysfunction.

Role of the Nrdp1 in Brain Injury Induced by Chronic Intermittent Hypoxia in Rats via Regulating the Protein Levels of ErbB3

Obstructive sleep apnea syndrome (OSAS) is known as a repeated obstruction of the upper airway during sleep, leading to generalized hypoxia episodes and associated with cardiovascular and cerebrovascular diseases. We mainly explored the role of neuregulin receptor degradation protein-1 (Nrdp1, also known as FLRF) in brain injury induced by chronic intermittent hypoxia (CIH) in rats. Wistar rats were randomly divided into 4 groups (n = 12 per group), including the sham + adeno-associated virus-NC (AAV-NC) group, the sham + AAV-siNrdp1 group, the IH-4w (intermittent hypoxia for 4 weeks) + AAV-NC group, and the IH-4w + AAV-siNrdp1 group. Morphologic changes in brain tissue were observed by hematoxylin and eosin (HE) staining. Apoptosis in the hippocampus was detected by terminal deoxynucleotidyl transferase-mediated dUTP nick end-labeling (TUNEL) staining. Spatial learning and memory were assessed by the Morris water maze test. The expression of Nrdp1 mRNA and protein in the hippocampus was detected by qualitative real-time polymerase chain reaction (qRT-PCR) and Western blotting. The concentration of interleukin-6 (IL-6) and tumor necrosis factor-α (TNF-α) in serum was detected via enzyme-linked immunosorbent assay (ELISA) kits. Nrdp1 expression was increased after intermittent hypoxia exposure over time. Western blotting and H&E results showed that pathological changes of hippocampus neurons in chronic intermittent hypoxia rat were diminished by shNrdp1. Western blotting and TUNEL staining showed that apoptotic cells in the hippocampus of CIH rats were decreased by shNrdp1. The Morris water maze results proved that shNrdp1 improved spatial learning performance of chronic intermittent hypoxia rats. ELISA kits results showed that CIH-induced inflammatory response was decreased by shNrdp1. Western blotting and qRT-PCR results showed protein expression of ErbB3 in the hippocampus of CIH rats. Nrdp1 could regulate ErbB3 protein levels in brain-injured rats with CIH, which demonstrates that Nrdp1 is a potential therapeutic target in the cognition deficits associated with OSAS.

Protective Effects and Mechanisms of MicroRNA-182 on Oxidative Stress in RHiN

To explore protective effects and related mechanisms of microRNA-182 (miR-182) on oxidative stress in rat hippocampal neurons (RHiN), RHiN cells. As the results, the survival rate and superoxide dismutase levels in H₂O₂ group were significantly lower than H₂O₂+miR-182 group (all P<0.05). The malondialdehyde levels and apoptosis rate in H₂O₂+miR-182 group were significantly lower than H2O2 group (all P<0.05). The mRNA levels and expression levels of mTOR and PI3K in H₂O₂+miR-182 group were higher than those in H₂O₂ group (both P<0.05). The experiment of cerebral ischemic oxidative stress model rats showed that the survival rate, apoptosis rate, malondialdehyde and superoxide dismutase levels in miR-182 group were better than model control group. The positive staining intensity of phosphoinositide 3-kinase (mTOR) and phosphoinositide 3-kinase (PI3K) in model control group were significantly lower than miR-182 group (all P<0.05). Increased levels of miR-182 can reduce the damage of H2O2 treatments in RHiN cells. Oxidative stress is decreased in the neuronal cells possibly by activation of the PI3K-AKT-mTOR pathway.

Tempol Alleviates Chronic Intermittent Hypoxia-Induced Pancreatic Injury Through Repressing Inflammation and Apoptosis

Obstructive sleep apnea (OSA) has been demonstrated to be implicated in disorder of insulin secretion and diabetes mellitus. In this study, we aimed to evaluate the protective role of tempol, a powerful antioxidant, in chronic intermittent hypoxia (IH)-induced pancreatic injury. The rat model of OSA was established by IH exposure. The pathological changes, increased blood-glucose level, and raised proinsulin/insulin ratio in pancreatic tissues of rats received IH were effectively relieved by tempol delivery. In addition, the enhanced levels of pro-inflammatory cytokines, TNF-α, IL-1β, IL-6, and inflammatory mediators, PGE2, cyclooxygenase-2 (COX-2), NO, and inducible nitric oxide synthase (iNOS) in pancreatic tissue were suppressed by tempol. Moreover, tempol inhibited IH-induced apoptosis in pancreatic tissue as evidenced by upregulated Bcl-2 level, and downregulated Bax and cleaved caspase-3 levels. Finally, the abnormal activation of mitogen-activated protein kinase (MAPK) and nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) signaling pathways induced by IH was restrained by tempol administration. In summary, our study demonstrates that tempol relieves IH-induced pancreatic injury by inhibiting inflammatory response and apoptosis, which provides theoretical basis for tempol as an effective treatment for OSA-induced pancreatic injury.

Endothelin-1 enhanced carotid body chemosensory activity in chronic intermittent hypoxia through PLC, PKC and p38MAPK signaling pathways

Endothelin-1 (ET-1), as it functions as a neuromodulator, has been associated with hypertension in chronic intermittent hypoxia (CIH) which attribute to enhanced carotid body sensibility to hypoxia. However, the molecular mechanism of ET-1 on carotid body sensibility in CIH is still not clear. Here, effect of ET-1 on carotid body chemosensory stimulation in rats exposed to either CIH or room air (Normoxia) was explored. Furthermore, Phospholipase C (PLC), Protein kinase C (PKC) or p38 MAPK antagonists were adopted to clarify the signalling pathways involved. Results showed that ET-1 induced a higher increase of carotid sinus nerve activity (CSNA) in animals exposed to CIH. Both ETA and ETB receptor expression were up-regulated by CIH exposure, but only ETA is responsible for ET-1 induced CSNA increase. Additional, the increase was inhibited by PLC, PKC, p38 MAPK antagonists and calcium channel blocker. Our findings support that ETA receptor mediates ET-1-induced CSNA increase through PLC, PKC and p38 MAPK signalling pathways in chronic intermittent hypoxia. Also, our study indicated that calcium influx was necessary for enhancing effect of ET-1 on CSNA.

Obstructive Sleep Apnea With or Without Excessive Daytime Sleepiness: Clinical and Experimental Data-Driven Phenotyping

Introduction: Obstructive sleep apnea (OSA) is a serious and prevalent medical condition with major consequences for health and safety. Excessive daytime sleepiness (EDS) is a common-but not universal-accompanying symptom. The purpose of this literature analysis is to understand whether the presence/absence of EDS is associated with different physiopathologic, prognostic, and therapeutic outcomes in OSA patients. Methods: Articles in English published in PubMed, Medline, and EMBASE between January 2000 and June 2017, focusing on no-EDS OSA patients, were critically reviewed. Results: A relevant percentage of OSA patients do not complain of EDS. EDS is a significant and independent predictor of incident cardiovascular disease (CVD) and is associated with all-cause mortality and an increased risk of metabolic syndrome and diabetes. Male gender, younger age, high body mass index, are predictors of EDS. The positive effects of nasal continuous positive airway pressure (CPAP) therapy on blood pressure, insulin resistance, fatal and non-fatal CVD, and endothelial dysfunction risk factors have been demonstrated in EDS-OSA patients, but results are inconsistent in no-EDS patients. The most sustainable cause of EDS is nocturnal hypoxemia and alterations of sleep architecture, including sleep fragmentation. These changes are less evident in no-EDS patients that seem less susceptible to the cortical effects of apneas. Conclusions: There is no consensus if we should consider OSA as a single disease with different phenotypes with or without EDS, or if there are different diseases with different genetic/epigenetic determinants, pathogenic mechanisms, prognosis, and treatment.The small number of studies focused on this issue indicates the need for further research in this area. Clinicians must carefully assess the presence or absence of EDS and decide accordingly the treatment. This approach could improve combination therapy targeted to a patient's specific pathology to enhance both efficacy and long-term adherence to OSA treatment and significantly reduce the social, economic, and health negative impact of OSA.

Spatial and temporal expression of SP-B and TGF-β1 in hyperoxia-induced neonatal rat lung injury

OBJECTIVE

Bronchopulmonary dysplasia (BPD) is a severe complication of extreme prematurity that can be caused by hyperoxia inhalation. SP-B and TGF-β have been reported to be implicated in the development of lung. This study aimed to reveal the spatial and temporal expression patterns of these two factors in an animal model of BPD.

METHODS

Newborn Sprague-Dawley (SD) rats were subjected to hyperoxia conditions to establish an animal model of BPD. The levels of SP-B, TGF-β, MDA and TAOC, as well as the activations of MAPK and PI3K/AKT pathways in lung tissues were monitored during newborn rats prolonged exposure to hyperoxia.

RESULTS

We found that hyperoxia exposure significantly induced body weight loss of SD rats. H&E staining for morphometric analyses revealed that hyperoxia arrested alveolar development or loss of alveoli, with fewer and dysmorphic capillaries. mRNA and protein levels of SP-B and TGF-β were high expressed in hyperoxic lung tissues. The concentrations of SP-B and TGF-β in bronchoalveolar lavage fluid were also increased. All these increases begin at the 3th day of hyperoxia exposure. MDA content was increased while TAOC content was decreased in response to hyperoxia. Furthermore, hyperoxia activated p38, and deactivated PI3K and AKT expression.

CONCLUSION

Our research demonstrated that SP-B and TGF-β1 were highly expressed in three levels: mRNA and protein levels in lung tissues, and the release of SP-B and TGF-β1 in bronchoalveolar lavage fluid, beginning at the 3th day of hyperoxia exposure.

Effect of Hypoxic Injury in Mood Disorder

Hypoxemia is a common complication of the diseases associated with the central nervous system, and neurons are highly sensitive to the availability of oxygen. Neuroplasticity is an important property of the neural system controlling breathing, memory, and cognitive ability. However, the underlying mechanism has not yet been clearly elucidated. In recent years, several pieces of evidence have highlighted the effect of hypoxic injury on neuronal plasticity in the pathogenesis and treatment of mood disorder. Therefore, the present study reviewed the relevant articles regarding hypoxic injury and neuronal plasticity and discussed the pathological changes and physiological functions of neurons in hypoxemia in order to provide a translational perspective to the relevance of hypoxic injury and mood disorder.

Intermittent hypoxia caused cognitive dysfunction relate to miRNAs dysregulation in hippocampus

Intermittent hypoxia (IH) is a characteristic pathophysiological change of obstructive sleep apnea (OSA), a commonly diagnosed chronic sleep disorder. With the process of OSA, patients will suffer from the nervous system damage and appear to multiple cognitive dysfunction. The mechanism that how IH causes cognitive impairment is still unknown. Both control and experimental rats were placed in conditions absence and presence of intermittent hypoxia (IH) for 8h a day for a week, two weeks and four weeks, and then followed by behavioral assessments with Morris Water Maze (MWM) test. The results showed that the escape latency of the tested animals to IH significantly increased the escape latency on the last four training days in comparison to the control group. Consistent with this, the expressions of apoptosis/anti-apoptosis proteins were both changed in the hippocampus. Then we utilized the miRNA microarray assay to investigate the level of miRNA expression in rat hippocampus which suffered from intermittent hypoxia. It is noteworthy that the expressions of miR-26b and miR-207 were consistently dysregulated in all the experimental groups post IH. And we utilized qRT-PCR methods to verify the microarray results. Our results showed that microarray based analysis of microRNA expression in rat hippocampus after IH has shown that some microRNAs such as miR-26b and miR-207 could be involved in the OSA-induced cognitive impairments.