The effect of chronic intermittent hypoxia in cardiovascular gene expression is modulated by age in a mice model of sleep apnea

Association between serum α-synuclein levels and neurocognitive deficits in patients with obstructive sleep apnea: A case-control study

BACKGROUND

Obstructive sleep apnea (OSA) is increasingly recognized as a contributor to neurocognitive dysfunction, yet the underlying biological mechanisms remain insufficiently understood. α-Synuclein, a presynaptic protein implicated in neurodegenerative processes, may be involved in OSA-related cognitive impairment, but its peripheral expression and diagnostic utility have not been fully elucidated.

METHODS

In this case-control study, 108 untreated OSA patients and 100 age- and sex-matched healthy controls underwent overnight polysomnography and neurocognitive assessments, including the Mini-Mental State Examination (MMSE) and Montreal Cognitive Assessment (MoCA). Serum α-synuclein levels were measured using ELISA. Logistic and linear regression analyses were conducted to assess associations between α-synuclein levels and cognitive performance, while ROC curve analysis evaluated the biomarker's predictive accuracy.

RESULTS

Serum α-synuclein levels were significantly elevated in OSA patients compared to controls (385.62 ± 125.47 pg/mL vs. 215.30 ± 78.65 pg/mL, p < 0.001). Elevated α-synuclein levels were independently associated with cognitive impairment in OSA (adjusted OR = 1.832, 95 % CI: 1.624-1.995, p = 0.013). Linear regression showed a significant inverse relationship between α-synuclein and MMSE scores (β = -0.459, p = 0.005). ROC analysis revealed strong predictive value for cognitive deficits (AUC = 0.892, sensitivity = 84.0 %, specificity = 86.0 %).

CONCLUSION

Elevated serum α-synuclein levels are independently associated with neurocognitive impairment in OSA and may serve as a potential biomarker for early detection and risk stratification. Future longitudinal and interventional studies are warranted to validate its clinical utility.

Intermittent Hypoxia as a Model of Obstructive Sleep Apnea: Present and Future

Intermittent hypoxia (IH) is an extremely frequent condition characterized by recurrent episodes of reduced oxygen levels interspersed with periods of normoxia, often seen in conditions like obstructive sleep apnea (OSA) and lung diseases. Among OSA patients, IH occurs due to periodic airway obstructions during sleep, leading to transient drops in blood oxygen saturation followed by reoxygenation. Future directions involve standardizing IH protocols, incorporating patient variability into the IH profiles being administered, and utilizing strategically developed animal models to enhance the reliability and applicability of IH-related research.

The role of Klotho and sirtuins in sleep-related cardiovascular diseases: a review study

The prevalence of sleep disorders has been reported from 1.6% to 56.0%, worldwide. Sleep deprivation causes cardiovascular diseases (CVDs) including atherosclerosis, vascular aging, hypertension, heart dysfunction, reduced heart rate variability, and cardiac arrhythmia. Reduced tissue oxygen causes various CVDs by activating pro-inflammatory factors and increasing oxidative stress. Sleep disorders are more important and prevalent in older people and cause more severe cardiovascular complications. On the other hand, the reduction of Klotho level, an age-dependent protein whose expression decreases with age, is associated with age-related diseases. Sirtuins, class III histone deacetylases, also are among the essential factors in postponing cellular aging and increasing the lifespan of organisms, and they do this by regulating different pathways in the cell. Sirtuins and Klotho play an important role in the pathophysiology of CVDS and both have anti-oxidative stress and anti-inflammatory activity. Studies have shown that the levels of Klotho and sirtuins are altered in sleep disorders. In this article, alterations of Klotho and sirtuins in sleep disorders and in the development of sleep-related CVDs were reviewed and the possible signaling pathways were discussed. The inclusion criteria were studies with keywords of different types of sleep disorders and CVDs, klotho, SIRT1-7, and sirtuins in PubMed, Scopus, Embase، Science Direct، Web of Sciences and Google Scholar by the end of 2023. The studies revealed there is a bidirectional relationship between sleep disorders and the serum and tissue levels of Klotho and sirtuins and sleep related-CVDs.

TRPC5-mediated NLRP3 inflammasome activation contributes to myocardial cell pyroptosis in chronic intermittent hypoxia rats

BACKGROUND

Chronic intermittent hypoxia (CIH) is the primary cause of myocardial inflammation in obstructive sleep apnea-hypopnea syndrome (OSAHS). Pyroptosis is a newly discovered form of programmed cell death accompanying inflammatory reactions. Our previous study showed that TRPC5 is upregulated in the myocardial injury of CIH rats. The present study aimed to explore the role of TRPC5 in CIH-induced myocardial cell pyroptosis.

METHODS

A model of CIH in OSA rats was established. SD rats were randomly divided into control group(8rats) and OSA group(8rats). Scanning electron microscope(SEM) was performed on left ventricular tissues slides. Western blot were used to detect the expression levels of pyroptosis-related factors and TRPC5 and its downstream proteins in myocardia tissue.

RESULTS

The pyroptosis of myocardial cells by SEM revealed damaged cell membrane integrity of OSA group rats, with fibrous tissue attached to the cell membrane surface, and vesicular protrusions and pyroptotic bodies were observed. Compared to the control group, the expression of pyroptosis-related proteins, such as caspase1, pro-IL-1β, IL-1β, IL-18, GSDMD, and GSDMD-N was upregulated in the OSA group (p < 0.05). Compared to the control group, the expression of TRPC5, NLPR3, p-CaMKIIβ + δ+γ, and HDAC4 was higher in the OSA group (p < 0.05).

CONCLUSIONS

These findings indicated that the pyroptosis response increases in CIH-induced myocardial injury, and the mechanism that TRPC5 is upregulated, promoting the expression of NLRP3 and inflammasome formation through CaMKII phosphorylation and HDAC4 cytoplasmic translocation. This might be a potential target for the treatment of OSA-induced myocardial injury.

Berberine ameliorates chronic intermittent hypoxia-induced cardiac remodelling by preserving mitochondrial function, role of SIRT6 signalling

Chronic intermittent hypoxia (CIH) is associated with an increased risk of cardiovascular diseases. Previously, we have shown that berberine (BBR) is a potential cardioprotective agent. However, its effect and mechanism on CIH-induced cardiomyopathy remain uncovered. This study was designed to determine the effects of BBR against CIH-induced cardiac damage and to explore the molecular mechanisms. Mice were exposed to 5 weeks of CIH with or without the treatment of BBR and adeno-associated virus 9 (AAV9) carrying SIRT6 or SIRT6-specific short hairpin RNA. The effect of BBR was evaluated by echocardiography, histological analysis and western blot analysis. CIH caused the inactivation of myocardial SIRT6 and AMPK-FOXO3a signalling. BBR dose-dependently ameliorated cardiac injury in CIH-induced mice, as evidenced by increased cardiac function and decreased fibrosis. Notably, SIRT6 overexpression mimicked these beneficial effects, whereas infection with recombinant AAV9 carrying SIRT6-specific short hairpin RNA abrogated them. Mechanistically, BBR reduced oxidative stress damage and preserved mitochondrial function via activating SIRT6-AMPK-FOXO3a signalling, enhancing mitochondrial biogenesis as well as PINK1-Parkin-mediated mitophagy. Taken together, these data demonstrate that SIRT6 activation protects against the pathogenesis of CIH-induced cardiac dysfunction. BBR attenuates CIH-induced myocardial injury by improving mitochondrial biogenesis and PINK1-Parkin-dependent mitophagy via the SIRT6-AMPK-FOXO3a signalling pathway.

Plasma levels of Sirtuin 7 are decreased in patients with essential hypertension

BACKGROUND

Sirtuin 7 (SIRT7), as a nicotinamide adenine dinucleotide-dependent protein/histone deacetylase, has been implicated in the pathogenesis of cardiovascular diseases. However, whether SIRT7 is related to hypertension remains largely unclear. Thus, this study aims to explore the effects and correlation between SIRT7 and hypertension.

METHODS

A total of 72 patients with essential hypertension and 82 controls with non-hypertension were recruited at Beijing Tongren Hospital Affiliated with Capital Medical University from July 2022 to June 2023. Plasma SIRT7 expression was measured using enzyme-linked immunosorbent assay analysis. Clinical baseline characteristics, laboratory measurements, echocardiographic data, and medical therapy were collected.

RESULTS

Plasma levels of SIRT7 were lower in hypertensive patients compared with non-hypertensive patients [0.97 (0.58-1.30) vs. 1.24 (0.99-1.46) ng/mL, P < 0.001, respectively]. Furthermore, compared with the low SIRT7 group, there were lower levels of systolic blood pressure, hyperlipidemia, and the ultrasonic electrocardiogram parameters left ventricular end-diastolic diameter and left atrial in diastole in the high SIRT7 group (P < 0.05, respectively). More importantly, multivariate logistic regression analyses indicated that plasma SIRT7 was a predictor of hypertension [OR: 0.06, 95 % CI (0.02-0.19), P < 0.001]. Receiver operating characteristics curve analysis revealed that the optimal cutoff value for plasma SIRT7 levels in detecting hypertension was determined as 0.85 ng/mL with a sensitivity of 73.6 % and a specificity of 89.0 %. The area under the curve for SIRT7 was 0.821 (95 % CI, 0.751-0.878; P < 0.001).

CONCLUSION

Plasma levels of SIRT7 are decreased in patients with essential hypertension, implying its potential as a biomarker for diagnosing essential hypertension..

4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxyl (Tempol) alleviates lung injury by inhibiting SIRT6-HIF-1α signaling pathway activation through the upregulation of miR-212-5p expression

OBJECTIVE

Obstructive sleep apnea is closely related to oxidative stress. 4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxyl (Tempol) can scavenge reactive oxygen species (ROS) and ameliorate oxidative damage in the body. The mechanism by which Tempol alleviates chronic intermittent hypoxia-induced lung injury has rarely been reported. This study aimed to confirm the molecular mechanism by which Tempol alleviates lung injury.

METHODS

The levels of miR-212-5p and Sirtuin 6 (SIRT6) in injured lungs were analyzed using bioinformatics. In vitro, intermittent hypoxia (IH) treatment induced hypoxia in BEAS-2B cells and we established a model of chronic intermittent hypoxia (CIH) in mouse using a programmed hypoxia chamber. We used HE staining to observe the morphology of lung tissue, and the changes in lung fibers were observed by Masson staining. The levels of inflammatory factors in mouse serum were detected by ELISA, and the levels of the oxidative stress indicators GSH, MDA, SOD and ROS were detected using commercially available kits. Moreover, a real-time qPCR assay was used to detect miR-212-5p expression, and Western blotting was used to detect the levels of SIRT6, HIF-1α and apoptosis-related proteins. CCK-8 was used to detect cell proliferation. Subsequently, we used flow cytometry to detect cell apoptosis. Dual-luciferase gene reporters determine the on-target binding relationship of miR-212-5p and SIRT6.

RESULTS

SIRT6 was highly expressed in CIH-induced lung injury, as shown by bioinformatics analysis; however, miR-212-5p expression was decreased. Tempol promoted miR-212-5p expression, and the levels of SIRT6 and HIF-1α were inhibited. In BEAS-2B cells, Tempol also increased proliferation, inhibited apoptosis and inhibited oxidative stress in BEAS-2B cells under IH conditions. In BEAS-2B cells, these effects of Tempol were reversed after transfection with an miR-212-5p inhibitor. miR-212-5p targeted and negatively regulated the level of SIRT6 and overexpression of SIRT6 effectively reversed the enhanced influence of the miR-212-5p mimic on Tempol's antioxidant activity. Tempol effectively ameliorated lung injury in CIH mice and inhibited collagen deposition and inflammatory cell infiltration. Likewise, the therapeutic effect of Tempol could be effectively reversed by interference with the miR-212-5p inhibitor.

CONCLUSION

Inhibition of the SIRT6-HIF-1α signaling pathway could promote the effect of Tempol by upregulating the level of miR-212-5p, thereby alleviating the occurrence of lung injury and providing a new underlying target for the treatment of lung injury.

Lifestyle effects on aging and CVD: A spotlight on the nutrient-sensing network

Aging is widespread worldwide and a significant risk factor for cardiovascular disease (CVD). Mechanisms underlying aging have attracted considerable attention in recent years. Remarkably, aging and CVD overlap in numerous ways, with deregulated nutrient sensing as a common mechanism and lifestyle as a communal modifier. Interestingly, lifestyle triggers or suppresses multiple nutrient-related signaling pathways. In this review, we first present the composition of the nutrient-sensing network (NSN) and its metabolic impact on aging and CVD. Secondly, we review how risk factors closely associated with CVD, including adverse life states such as sedentary behavior, sleep disorders, high-fat diet, and psychosocial stress, contribute to aging and CVD, with a focus on the bridging role of the NSN. Finally, we focus on the positive effects of beneficial dietary interventions, specifically dietary restriction and the Mediterranean diet, on the regulation of nutrient metabolism and the delayed effects of aging and CVD that depend on the balance of the NSN. In summary, we expound on the interaction between lifestyle, NSN, aging, and CVD.

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.

Obesity-related kidney disease: Beyond hypertension and insulin-resistance

Chronic kidney disease (CKD) causes considerable morbidity, mortality, and health expenditures worldwide. Obesity is a significant risk factor for CKD development, partially explained by the high prevalence of diabetes mellitus and hypertension in obese patients. However, adipocytes also possess potent endocrine functions, secreting a myriad of cytokines and adipokines that contribute to insulin resistance and induce a chronic low-grade inflammatory state thereby damaging the kidney. CKD development itself is associated with various metabolic alterations that exacerbate adipose tissue dysfunction and insulin resistance. This adipose-renal axis is a major focus of current research, given the rising incidence of CKD and obesity. Cellular senescence is a biologic hallmark of aging, and age is another significant risk factor for obesity and CKD. An elevated senescent cell burden in adipose tissue predicts renal dysfunction in animal models, and senotherapies may alleviate these phenotypes. In this review, we discuss the direct mechanisms by which adipose tissue contributes to CKD development, emphasizing the potential clinical importance of such pathways in augmenting the care of CKD.

Experimental Models to Study End-Organ Morbidity in Sleep Apnea: Lessons Learned and Future Directions

Sleep apnea (SA) is a very prevalent sleep breathing disorder mainly characterized by intermittent hypoxemia and sleep fragmentation, with ensuing systemic inflammation, oxidative stress, and immune deregulation. These perturbations promote the risk of end-organ morbidity, such that SA patients are at increased risk of cardiovascular, neurocognitive, metabolic and malignant disorders. Investigating the potential mechanisms underlying SA-induced end-organ dysfunction requires the use of comprehensive experimental models at the cell, animal and human levels. This review is primarily focused on the experimental models employed to date in the study of the consequences of SA and tackles 3 different approaches. First, cell culture systems whereby controlled patterns of intermittent hypoxia cycling fast enough to mimic the rates of episodic hypoxemia experienced by patients with SA. Second, animal models consisting of implementing realistic upper airway obstruction patterns, intermittent hypoxia, or sleep fragmentation such as to reproduce the noxious events characterizing SA. Finally, human SA models, which consist either in subjecting healthy volunteers to intermittent hypoxia or sleep fragmentation, or alternatively applying oxygen supplementation or temporary nasal pressure therapy withdrawal to SA patients. The advantages, limitations, and potential improvements of these models along with some of their pertinent findings are reviewed.

Temporal changes in coronary artery function and flow velocity reserve in mice exposed to chronic intermittent hypoxia

Study Objectives

Obstructive sleep apnea (OSA) is a chronic condition characterized by intermittent hypoxia (IH) that is implicated in an increased risk of cardiovascular disease (i.e., coronary heart disease, CHD) and associated with increased overall and cardiac-specific mortality. Accordingly, we tested the hypothesis that experimental IH progressively impairs coronary vascular function and in vivo coronary flow reserve.

Methods

Male C57BL/6J mice (8-week-old) were exposed to IH (FiO2 21% 90 s–6% 90 s) or room air (RA; 21%) 12 h/day during the light cycle for 2, 6, 16, and 28 weeks. Coronary artery flow velocity reserve (CFVR) was measured at each time point using a Doppler system. After euthanasia, coronary arteries were micro-dissected and mounted on wire myograph to assess reactivity to acetylcholine (ACh) and sodium nitroprusside (SNP).

Results

Endothelium-dependent coronary relaxation to ACh was preserved after 2 weeks of IH (80.6 ± 7.8%) compared to RA (87.8 ± 7.8%, p = 0.23), but was significantly impaired after 6 weeks of IH (58.7 ± 16.2%, p = 0.02). Compared to ACh responses at 6 weeks, endothelial dysfunction was more pronounced in mice exposed to 16 weeks (48.2 ± 5.3%) but did not worsen following 28 weeks of IH (44.8 ± 11.6%). A 2-week normoxic recovery after a 6-week IH exposure reversed the ACh abnormalities. CFVR was significantly reduced after 6 (p = 0.0006) and 28 weeks (p &lt; 0.0001) of IH when compared to controls.

Conclusion

Chronic IH emulating the hypoxia-re-oxygenation cycles of moderate-to-severe OSA promotes coronary artery endothelial dysfunction and CFVR reductions in mice, which progressively worsen until reaching asymptote between 16 and 28 weeks. Normoxic recovery after 6 weeks exposure reverses the vascular abnormalities.

Effects of chronic intermittent hypoxia on left cardiac function in young and aged mice

Obstructive sleep apnea (OSA) is an independent risk factor for cardiovascular disease that is characterized by chronic intermittent hypoxia (CIH), and its impact is related to age. This study aims to assess the age-related impact of CIH on cardiac function and to further explore the mechanism. After 8 weeks of severe CIH exposure, the hearts of young mice showed slight physiological hypertrophy, decreased diastolic function, and collagen I accumulation but no obvious change in contractile function. However, the contractile function of the hearts of aged mice was severely decreased. CIH exposure promoted the fragmentation of mitochondria in the hearts of aged mice and decreased the mitochondrial membrane potential of cardiomyocytes, but these effects were not observed in young mice exposed to the same conditions. CIH induced significant decreases in basal respiration, maximum respiration and ATP production in cardiac mitochondria of aged mice compared to those of young mice. The assessment of mitochondrial-related proteins showed that young mouse hearts had upregulated adaptive nuclear respiratory factors (Nrf)1/2 sirtuin (SIRT)1/3 and transcription factor A (TFAM) expression that stabilized mitochondrial function in response to CIH exposure. Aged mouse hearts exhibited maladaptation to CIH exposure, and downregulation of SIRT1 and TFAM expression resulted in mitochondrial dysfunction.

Obesity and Obstructive Sleep Apnea

Obstructive sleep apnea (OSA) is characterized by upper airway collapse during sleep. Chronic intermittent hypoxia, sleep fragmentation, and inflammatory activation are the main pathophysiological mechanisms of OSA. OSA is highly prevalent in obese patients and may contribute to cardiometabolic risk by exerting detrimental effects on adipose tissue metabolism and potentiating the adipose tissue dysfunction typically found in obesity. This chapter will provide an update on: (a) the epidemiological studies linking obesity and OSA; (b) the studies exploring the effects of intermittent hypoxia and sleep fragmentation on the adipose tissue; (c) the effects of OSA treatment with continuous positive airway pressure (CPAP) on metabolic derangements; and (d) current research on new anti-diabetic drugs that could be useful in the treatment of obese OSA patients.