Long-term Chronic Intermittent Hypoxia Research Articles

Carotid body ablation restores astrocyte/microglia morphology in the NTS and reduces hypertension following long-term intermittent hypoxia

Chronic intermittent hypoxia (CIH) heightened carotid body (CB) chemosensory discharges, which contributes to hypertension development. Previously, we reported that CB ablation significantly reduced blood pressure after 21 days of CIH; however, whether CB-mediated glial cell activation in the caudal Nucleus of the Solitary Tract (cNTS) following long-term CIH contribute to maintain high blood pressure and enhanced ventilatory chemoreflex remains unknown. To test this hypothesis, we exposed male C57BL6 mice to CIH (5% FIO2, 12 times/h, 8 h/day) for 60 days. At 45 days of CIH, CBs were selectively denervated, and animals returned to CIH for 15 more days. At the end of the experimental protocol, we measured arterial blood pressure, hypoxic ventilatory response (HVR) in awake mice and characterized astrocyte and microglia morphological features using Sholl analysis. CIH induces hypertension (MABP: 83.47±1.39 vs. 95.00±2.18 mmHg; Sham vs. CIH), increases the HVR (1.69±0.17 vs. 4.31±0.87 ΔVE/min; Sham vs. CIH), modify cNTS astrocytes phenotype (N° of branches: 13.01±0.66 vs. 11.31±0.52; cable length: 181.00±8.90 vs 148.10±1.48 μm, convex hull: 788.10±37.60 vs. 584.30±23.75 μm3; Sham vs. CIH), and microglia arborization (N° of branches: 196.10±8.35 vs. 376.30±16.80; cable length: 667.4±29.63 vs. 1267±60.47 μm, convex hull: 6177±362 vs. 9721±564 μm3; Sham vs. CIH). Importantly, CB denervation normalized the elevated blood pressure (MABP: 83.47±1.38 mmHg; CIHd), the altered peripheral chemoreflex response (HVR: 1.63±0.43 ΔVE/min; CIHd) and morphological changes in astrocytes (N °of branches: 17.23±0.88, cable length: 231.70±12.87, convex hull: 982.70±55.55 μm3) and microglia located in the cNTS (N° of branches 126.20±13.34; cable length: 126.2±13.3, Convex hull size: 3584±380 μm3; CIHd). Present results suggest that CBs play a crucial role in the maintenance of high arterial pressure and respiratory alterations induced by long-term CIH and may contribute to the formation of a neuroinflammatory niche at the cNTS by modifying glial cell activity. Supported by Fondecyt Grants 1211443 and 1220950. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Regulation of the CB1R/AMPK/PGC-1α signaling pathway in mitochondria of mouse hearts and cardiomyocytes with chronic intermittent hypoxia.

This study evaluated the effects of chronic intermittent hypoxia (CIH) at different times on the mitochondria of mouse hearts and H9C2 cardiomyocytes to determine the role of the cannabinoid receptor 1 (CB1R)/adenosine 5'-monophosphate-activated protein kinase (AMPK)/peroxisome proliferator-activated receptor-γ coactivator-1α (PGC-1α) signaling pathway. Animal and cellular CIH models were prepared inan intermittent hypoxia chamber at different times. The cardiac function of mice was determined, and heart tissue and ultrastructural changes were observed. Apoptosis, reactive oxygen species (ROS), and mitochondrial membrane potential were detected, and MitoTracker™ staining was performed to observe cardiomyocyte mitochondria. Western blot, immunohistochemistry, and cellular immunofluorescence were also performed. In the short-term CIH group, increases in mouse ejection fraction (EF) and heart rate (HR); mitochondrial division; ROS and mitochondrial membrane potential; and the expression levels of CB1R, AMPK, and PGC-1α were observed in vivo and in vitro. In the long-term CIH group, the EF and HR increased, the myocardial injury and mitochondrial damage were more severe, mitochondrial synthesis decreased, the apoptosis percentage and ROS increased, mitochondrial fragmentation increased, membrane potential decreased, CB1R expression increased, and AMPK and PGC-1α expression levels decreased. Targeted blocking of CB1R can increase AMPK and PGC-1α, reduce damage attributed to long-term CIH in mouse hearts and H9C2 cells, and promote mitochondrial synthesis. Short-term CIH can directly activate the AMPK/PGC-1α pathway, promote mitochondrial synthesis in cardiomyocytes, and protect cardiac structure and function. Long-term CIH can increase CB1R expression and inhibit the AMPK/PGC-1α pathway, resulting in structural damage, the disturbance of myocardial mitochondria synthesis, and further alterations in the cardiac structure. After targeted blocking of CB1R, levels of AMPK and PGC-1α increased, alleviating damage to the heart and cardiomyocytes caused by long-term CIH.

Long-term intermittent hypoxia induces anxiety-like behavior and affects expression of orexin and its receptors differently in the mouse brain.

Studies have revealed a possible connection between orexin, narcolepsy, and obstructive sleep apnea (OSA). Orexin has an important role in the maintenance of arousal and wakefulness/sleeping states. To better understand the pathophysiological mechanism of OSA, we used a chronic intermittent hypoxia (CIH) model in mice to mimic OSA. In this way, we explored the effect of CIH on the locomotor activity and orexin system in the hypothalamus, cerebral cortex, and brainstem of mice. Male C57BL/6J mice (8weeks) in the CIH group were exposed in a hypoxia chamber for 8h/day for 28weeks. The re-oxygenation groups comprised the W2 group and W4 group, which were exposed to 28weeks of CIH followed by 2weeks and 4weeks of re-oxygenation, respectively. The open field test was undertaken to observe locomotor activity. mRNA expression of orexin, orexin receptor type 1 (OX1R), and OX2R mRNA was evaluated by real-time reverse transcription-quantitative polymerase chain reaction. Mice subjected to long-term CIH exhibited significant anxiety-like behavior during the light period, and this behavior lasted until 4weeks of re-oxygenation. mRNA expression of orexin was upregulated in the hypothalamus. mRNA expression of OX1R mRNA in the cerebral cortex and brainstem was downregulated by CIH. Two weeks and 4weeks of re-oxygenation could not reverse these alternations. Long-term CIH may induce anxiety-like behavior and re-oxygenation cannot reverse these behavior. Moreover, OX1R has a significant role in the anxiety-related symptoms observed in long-term CIH.

The theranostic value of acetylation gene signatures in obstructive sleep apnea derived by machine learning

Epigenetic modifications are implicated in the onset and progression of obstructive sleep apnea (OSA) and its complications through their bidirectional relationship with long-term chronic intermittent hypoxia (IH). However, the exact role of epigenetic acetylation in OSA is unclear. Here we explored the relevance and impact of acetylation-related genes in OSA by identifying molecular subtypes modified by acetylation in OSA patients. Twenty-nine significantly differentially expressed acetylation-related genes were screened in a training dataset (GSE135917). Six common signature genes were identified using the lasso and support vector machine algorithms, with the powerful SHAP algorithm used to judge the importance of each identified feature. DSCC1, ACTL6A, and SHCBP1 were best calibrated and discriminated OSA patients from normal in both training and validation (GSE38792) datasets. Decision curve analysis showed that patients could benefit from a nomogram model developed using these variables. Finally, a consensus clustering approach characterized OSA patients and analyzed the immune signatures of each subgroup. OSA patients were divided into two acetylation patterns (higher acetylation scores in Group B than in Group A) that differed significantly in terms of immune microenvironment infiltration. This is the first study to reveal the expression patterns and key role played by acetylation in OSA, laying the foundation for OSA epitherapy and refined clinical decision-making.

Chronic intermittent hypoxia accelerates cardiac dysfunction and cardiac remodeling during cardiac pressure overload in mice and can be alleviated by PHD3 overexpression.

Obstructive sleep apnea (OSA) accelerates the progression of chronic heart failure (CHF). OSA is characterized by chronic intermittent hypoxia (CIH), and CIH exposure accelerates cardiac systolic dysfunction and cardiac remodeling in a cardiac afterload stress mouse model. Mechanistic experiments showed that long-term CIH exposure activated hypoxia-inducible factor 1α (HIF-1α) expression in the mouse heart and upregulated miR-29c expression and that both HIF-1α and miR-29c simultaneously inhibited sarco-/endoplasmic reticulum calcium ATPase 2a (SERCA2a) expression in the mouse heart. Cardiac HIF-1α activation promoted cardiomyocyte hypertrophy. SERCA2a expression was suppressed in mouse heart in middle- and late-stage cardiac afterload stress, and CIH exposure further downregulated SERCA2a expression and accelerated cardiac systolic dysfunction. Prolyl hydroxylases (PHDs) are physiological inhibitors of HIF-1α, and PHD3 is most highly expressed in the heart. Overexpression of PHD3 inhibited CIH-induced HIF-1α activation in the mouse heart while decreasing miR-29c expression, stabilizing the level of SERCA2a. Although PHD3 overexpression did not reduce mortality in mice, it alleviated cardiac systolic dysfunction and cardiac remodeling induced by CIH exposure.

Lower Body Weight in Rats Under Hypobaric Hypoxia Exposure Would Lead to Reduced Right Ventricular Hypertrophy and Increased AMPK Activation.

BackgroundBoth chronic hypoxia (CH) and long-term chronic intermittent hypoxia (CIH) exposure lead to right ventricular hypertrophy (RVH). Weight loss is an effective intervention to improve cardiac function and energy metabolism in cardiac hypertrophy. Likewise, caloric restriction (CR) also plays an important role in this cardioprotection through AMPK activation. We aimed to determine the influence of body weight (BW) on RVH, AMPK and related variables by comparing rats exposed to both hypoxic conditions.MethodsSixty male adult rats were separated into two groups (n = 30 per group) according to their previous diet: a caloric restriction (CR) group and an ad libitum (AL) group. Rats in both groups were randomly assigned to 3 groups: a normoxic group (NX, n = 10), a CIH group (2 days hypoxia/2 days normoxia; n = 10) and a CH group (n = 10). The CR group was previously fed 10 g daily, and the other was fed ad libitum. Rats were exposed to simulated hypobaric hypoxia in a hypobaric chamber set to 428 Torr (the equivalent pressure to that at an altitude of 4,600 m above sea level) for 30 days. Measurements included body weight; hematocrit; serum insulin; glycemia; the degree of RVH (Fulton’s index and histology); and AMPK, mTOR, and PP2C expression levels in the right ventricle determined by western blotting.ResultsA lower degree of RVH, higher AMPK activation, and no activation of mTOR were found in the CR groups exposed to hypobaric hypoxia compared to the AL groups (p < 0.05). Additionally, decreased glycemia and serum insulin levels were observed. Interestingly, PP2C expression showed an increase in the AL groups but not in the CR groups (p < 0.05).ConclusionMaintaining a low weight before and during exposure to high-altitude hypoxia, during either CH or CIH, could prevent a major degree of RVH. This cardioprotection would likely be due to the activation of AMPK. Thus, body weight is a factor that might contribute to RVH at high altitudes.

Potential Role of mRNAs and LncRNAs in Chronic Intermittent Hypoxia Exposure-Aggravated Atherosclerosis.

Atherosclerosis is the pathological basis of cardiovascular disease. Obstructive sleep apnea (OSA) aggravates atherosclerosis, and chronic intermittent hypoxia (CIH) as a prominent feature of OSA plays an important role during the process of atherosclerosis. The mechanisms of CIH in the development of atherosclerosis remain unclear. In the current study, we used microarray to investigate differentially expressed mRNAs and long non-coding RNAs (lncRNAs) in aorta from five groups of ApoE–/– mice fed with a high-fat diet and exposed to various conditions: normoxia for 8 weeks, CIH for 8 weeks, normoxia for 12 weeks, CIH for 12 weeks, or CIH for 8 weeks followed by normoxia for 4 weeks. Selected transcripts were validated in aorta tissues and RT-qPCR analysis showed correlation with the microarray data. Gene Ontology analysis and pathway enrichment analysis were performed to explore the mRNA function. Bioinformatic analysis indicated that short-term CIH induced up-regulated mRNAs involved in inflammatory response. Pathway enrichment analysis of lncRNA co-localized mRNAs and lncRNA co-expressed mRNAs were performed to explore lncRNA functions. The up-regulated mRNAs, lncRNA co-localized mRNAs and lncRNA co-expressed mRNAs were significantly associated with protein processing in endoplasmic reticulum pathway in atherosclerotic vascular tissue with long-term CIH exposure, suggesting that differentially expressed mRNAs and lncRNAs play important roles in this pathway. Moreover, a mRNA-lncRNA co-expression network with 380 lncRNAs, 508 mRNAs and 3238 relationships was constructed based on the correlation analysis between the differentially expressed mRNAs and lncRNAs. In summary, our study provided a systematic perspective on the potential function of mRNAs and lncRNAs in CIH-aggravated atherosclerosis, and may provide novel molecular candidates for future investigation on atherosclerosis exposed to CIH.

Long-Term Chronic Intermittent Hypobaric Hypoxia Induces Glucose Transporter (GLUT4) Translocation Through AMP-Activated Protein Kinase (AMPK) in the Soleus Muscle in Lean Rats.

Background: In chronic hypoxia (CH) and short-term chronic intermittent hypoxia (CIH) exposure, glycemia and insulin levels decrease and insulin sensitivity increases, which can be explained by changes in glucose transport at skeletal muscles involving GLUT1, GLUT4, Akt, and AMPK, as well as GLUT4 translocation to cell membranes. However, during long-term CIH, there is no information regarding whether these changes occur similarly or differently than in other types of hypoxia exposure. This study evaluated the levels of AMPK and Akt and the location of GLUT4 in the soleus muscles of lean rats exposed to long-term CIH, CH, and normoxia (NX) and compared the findings.Methods: Thirty male adult rats were randomly assigned to three groups: a NX (760 Torr) group (n = 10), a CIH group (2 days hypoxia/2 days NX; n = 10) and a CH group (n = 10). Rats were exposed to hypoxia for 30 days in a hypobaric chamber set at 428 Torr (4,600 m). Feeding (10 g daily) and fasting times were accurately controlled. Measurements included food intake (every 4 days), weight, hematocrit, hemoglobin, glycemia, serum insulin (by ELISA), and insulin sensitivity at days 0 and 30. GLUT1, GLUT4, AMPK levels and Akt activation in rat soleus muscles were determined by western blot. GLUT4 translocation was measured with confocal microscopy at day 30.Results: (1) Weight loss and increases in hematocrit and hemoglobin were found in both hypoxic groups (p < 0.05). (2) A moderate decrease in glycemia and plasma insulin was found. (3) Insulin sensitivity was greater in the CIH group (p < 0.05). (4) There were no changes in GLUT1, GLUT4 levels or in Akt activation. (5) The level of activated AMPK was increased only in the CIH group (p < 0.05). (6) Increased GLUT4 translocation to the plasma membrane of soleus muscle cells was observed in the CIH group (p < 0.05).Conclusion: In lean rats experiencing long-term CIH, glycemia and insulin levels decrease and insulin sensitivity increases. Interestingly, there is no increase of GLUT1 or GLUT4 levels or in Akt activation. Therefore, cellular regulation of glucose seems to primarily involve GLUT4 translocation to the cell membrane in response to hypoxia-mediated AMPK activation.