Adiponectin protects rat myocardium against chronic intermittent hypoxia-induced injury via inhibition of endoplasmic reticulum stress

TRPC5 channel participates in myocardial injury in chronic intermittent hypoxia

OBJECTIVE

The purpose of this study is to develop an animal model of Chronic Intermittent Hypoxia (CIH) and investigate the role of the TRPC5 channel in cardiac damage in OSAHS rats.

METHODS

Twelve male Sprague Dawley rats were randomly divided into the CIH group and the Normoxic Control (NC) group. Changes in structure, function, and pathology of heart tissue were observed through echocardiography, transmission electron microscopy, HE-staining, and TUNEL staining.

RESULTS

The Interventricular Septum thickness at diastole (IVSd) and End-Diastolic Volume (EDV) of rats in the CIH group significantly increased, whereas the LV ejection fraction and LV fraction shortening significantly decreased. TEM showed that the myofilaments in the CIH group were loosely arranged, the sarcomere length varied, the cell matrix dissolved, the mitochondrial cristae were partly flocculent, the mitochondrial outer membrane dissolved and disappeared, and some mitochondria were swollen and vacuolated. The histopathological examination showed that the cardiomyocytes in the CIH group were swollen with granular degeneration, some of the myocardial fibers were broken and disorganized, and most of the nuclei were vacuolar and hypochromic.

CONCLUSION

CIH promoted oxidative stress, the influx of Ca2+, and the activation of the CaN/NFATc signaling pathway, which led to pathological changes in the morphology and ultrastructure of cardiomyocytes, the increase of myocardial apoptosis, and the decrease of myocardial contractility. These changes may be associated with the upregulation of TRPC5.

IRE1α: from the function to the potential therapeutic target in atherosclerosis

Inositol requiring enzyme 1 (IRE1) is generally thought to control the most conserved pathway in the unfolded protein response (UPR). Two isoforms of IRE1, IRE1α and IRE1β, have been reported in mammals. IRE1α is a ubiquitously expressed protein whose knockout shows marked lethality. In contrast, the expression of IRE1β is exclusively restricted in the epithelial cells of the respiratory and gastrointestinal tracts, and IRE1β-knockout mice are phenotypically normal. As research continues to deepen, IRE1α was showed to be tightly linked to inflammation, lipid metabolism regulation, cell death and so on. Growing evidence also suggests an important role for IRE1α in promoting atherosclerosis (AS) progression and acute cardiovascular events through disrupting lipid metabolism balance, facilitating cells apoptosis, accelerating inflammatory responses and promoting foam cell formation. In addition, IRE1α was recognized as novel potential therapeutic target in AS prevention. This review provides some clues about the relationship between IRE1α and AS, hoping to contribute to further understanding roles of IRE1α in atherogenesis and to be helpful for the design of novel efficacious therapeutics agents targeting IRE1α-related pathways.

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.

Active metabolites and potential mechanisms of Notopterygium incisum against obstructive sleep apnea Syndrome (OSAS): network analysis and experimental assessment

Background: Notopterygium incisum K.C. Ting ex H.T. Chang, a synonym of Hansenia weberbaueriana (Fedde ex H. Wolff) Pimenov & Kljuykov, is an anti-inflammatory medicinal plant. Although abrnotopterol has been reported to be its primary active metabolite, the other metabolites and their mechanisms of action remain unclear. This study aims to investigate the potential mechanisms by which its active metabolites treat Obstructive Sleep Apnea Syndrome (OSAS) through network analysis and experimental assessment. Methods: The metabolites and potential targets of Notopterygium incisum were extracted from public databases. We searched for OSAS-related genes in the Genecards, OMIM, PharmGkb, TTD, and DrugBank databases. Cytoscape 3.9.0 was used to construct the drug-target-disease network and screen for hub genes. Human bronchial epithelial (HBE) cells were cultivated in normoxia and chronic intermittent hypoxia (CIH) medium for 24 h. Interleukin-6 (IL-6), tumor necrosis factor-alpha (TNF-α), and prostaglandin E2 (PGE2) were quantified using enzyme-linked immunosorbent assay (ELISA). Prostaglandin-endoperoxide synthase 2(PTGS2) mRNA was detected using RT-qPCR, while PTGS2 and nuclear factor-kappa B (NF-κB) proteins were identified using Western blot analysis. Co-Immunoprecipitation (CoIP) and Western blotting were utilized to evaluate the ubiquitination of PTGS2 in HBE cells. Results: Pterostilbene and notopterol, isolated from Notopterygium incisum, had potential therapeutic effects on OSAS. The PTGS2 and estrogen receptor alpha (ESR1) hub genes were associated with OSAS. The pathway enrichment analysis focuses on the NF-κB, apoptosis, and HIF-1A pathways. In response to CIH, pterostilbene and notopterol decreased IL-6, TNF-α, and PGE2 levels. The NF-κB pathway was activated by an increase in PTGS2 levels. Pterostilbene promoted proteasome-mediated ubiquitination of PTGS2 protein and reduced PTGS2 levels, inhibiting the NF-κB pathway. Conclusion: This study reveals the active metabolites of Notopterygium incisum and hub genes involved in treating OSAS, which provide a basis for the follow-up development and exploitation of the botanical drug.

Pathophysiological mechanisms and therapeutic approaches in obstructive sleep apnea syndrome

Obstructive sleep apnea syndrome (OSAS) is a common breathing disorder in sleep in which the airways narrow or collapse during sleep, causing obstructive sleep apnea. The prevalence of OSAS continues to rise worldwide, particularly in middle-aged and elderly individuals. The mechanism of upper airway collapse is incompletely understood but is associated with several factors, including obesity, craniofacial changes, altered muscle function in the upper airway, pharyngeal neuropathy, and fluid shifts to the neck. The main characteristics of OSAS are recurrent pauses in respiration, which lead to intermittent hypoxia (IH) and hypercapnia, accompanied by blood oxygen desaturation and arousal during sleep, which sharply increases the risk of several diseases. This paper first briefly describes the epidemiology, incidence, and pathophysiological mechanisms of OSAS. Next, the alterations in relevant signaling pathways induced by IH are systematically reviewed and discussed. For example, IH can induce gut microbiota (GM) dysbiosis, impair the intestinal barrier, and alter intestinal metabolites. These mechanisms ultimately lead to secondary oxidative stress, systemic inflammation, and sympathetic activation. We then summarize the effects of IH on disease pathogenesis, including cardiocerebrovascular disorders, neurological disorders, metabolic diseases, cancer, reproductive disorders, and COVID-19. Finally, different therapeutic strategies for OSAS caused by different causes are proposed. Multidisciplinary approaches and shared decision-making are necessary for the successful treatment of OSAS in the future, but more randomized controlled trials are needed for further evaluation to define what treatments are best for specific OSAS patients.

Chronic intermittent hypoxia-induced BNIP3 expression mitigates contractile dysfunction and myocardial injury in animal and cell model via modulating autophagy

Obstructive sleep apnea syndrome is generally associated with multiple cardiovascular disorders, such as myocardial hypertrophy. Autophagy is strictly modulated to maintain cardiac homeostasis. Post-injury autophagy is closely associated with pathological cardiac hypertrophy. BCL2 interacting protein 3 (BNIP3) and BNIP3-like protein (BNIP3L) can cause cell death and are important for hypoxia-elicited autophagy. Here, we evaluated whether BNIP3 could mitigate functional remodeling and cardiac hypertrophy through regulation of autophagy. Male WT rats or rats with BNIP3 knockout were subjected to chronic intermittent hypoxia (CIH) for 8 h/day over 5 weeks. Echocardiography and morphology were employed to assess the cardioprotective effects. Autophagy was assessed via transmission electron microscopy and detection of LC3, p62, and Beclin-1. Terminal deoxynucleotidyl transferase dUTP nick end labeling and the Bax/Bcl2 ratio were used to monitor apoptosis. Biochemical evaluations were performed to assess oxidative stress. Additionally, BNIP3-knockdown H9c2 cells that were subjected to CIH were used to examine autophagy and apoptosis to confirm the findings of the animal study. The CIH group showed elevated heart weight/body weight and left ventricle weight/body weight proportions, along with left ventricular remodeling. CIH-exposed rats exhibited dramatically higher fractional shortening and ejection fractions than the controls. In addition, the levels of autophagy markers Beclin-1 and LC3-II/I were increased, whereas the level of p62 was reduced by CIH treatment. The oxidative marker levels and the apoptosis index in the CIH group were markedly increased. Knockout of BNIP3 significantly aggravated the impairment in cardiac function, apoptosis, oxidative stress, and hypertrophy of CIH rats, while significantly reducing autophagy. The autophagy-associated PI3K/Akt/mTOR pathway was also deactivated by BNIP3 knockout. At the cellular level, CIH treatment significantly upregulated autophagy and apoptosis; however, BNIP3 silencing reduced autophagy and promoted apoptosis. CIH treatment-mediated upregulation of BNIP3 expression plays a crucial role in autophagy by targeting the PI3K/Akt/mTOR pathway, alleviating cardiac hypertrophy.

Intermittent Hypoxia-Induced Cardiomyocyte Death Is Mediated by HIF-1 Dependent MAM Disruption

Rationale: Intermittent hypoxia (IH) is one of the main features of sleep-disordered breathing (SDB). Recent findings indicate that hypoxia inducible factor-1 (HIF-1) promotes cardiomyocytes apoptosis during chronic IH, but the mechanisms involved remain to be elucidated. Here, we hypothesize that IH-induced ER stress is associated with mitochondria-associated ER membrane (MAM) alteration and mitochondrial dysfunction, through HIF-1 activation. Methods: Right atrial appendage biopsies from patients with and without SDB were used to determine HIF-1α, Grp78 and CHOP expressions. Wild-type and HIF-1α^+/− mice were exposed to normoxia (N) or IH (21–5% O₂, 60 cycles/h, 8 h/day) for 21 days. Expressions of HIF-1α, Grp78 and CHOP, and apoptosis, were measured by Western blot and immunochemistry. In isolated cardiomyocytes, we examined structural integrity of MAM by proximity ligation assay and their function by measuring ER-to-mitochondria Ca²⁺ transfer by confocal microscopy. Finally, we measured mitochondrial respiration using oxygraphy and calcium retention capacity (CRC) by spectrofluorometry. MAM structure was also investigated in H9C2 cells incubated with 1 mM CoCl₂, a potent HIF-1α inducer. Results: In human atrial biopsies and mice, IH induced HIF-1 activation, ER stress and apoptosis. IH disrupted MAM, altered Ca²⁺ homeostasis, mitochondrial respiration and CRC. Importantly, IH had no effect in HIF-1α^+/− mice. Similar to what observed under IH, HIF-1α overexpression was associated with MAM alteration in H9C2. Conclusion: IH-induced ER stress, MAM alterations and mitochondrial dysfunction were mediated by HIF-1; all these intermediate mechanisms ultimately inducing cardiomyocyte apoptosis. This suggests that HIF-1 modulation might limit the deleterious cardiac effects of SDB.

Adiponectin protects HL-1 cardiomyocytes against rotenone-induced cytotoxicity through AMPK activation

The relationship between mitochondrial dysfunction or ER stress with pathogenesis of cardiovascular disease is well documented, but the crosstalk between them in cardiovascular diseases is not clear. Adiponectin (APN) is reported to become a potential cardioprotective molecule, but whether and how APN regulates mitochondrial dysfunction and ER stress is not clear. In this study, we used rotenone-treated HL-1 atrial cardiomyocytes as an in vitro model of mitochondrial dysfunction to investigate the possible interactions between mitochondrial dysfunction and ER stress and explore the effects of APN on rotenone-induced cytotoxicity and the underlying mechanisms. It found that rotenone treatment significantly activated the ER stress PRK-like endoplasmic reticulum kinase (PERK)-dependent pathway, decreased autophagic flux and APN expression in a dose-dependent manner. Pretreatment of GSK2606414, an inhibitor of PERK kinase activity, attenuated the rotenone-induced decrease of APN expression. In return exogenous APN pretreatment inhibited rotenone-induced ER stress and activated autophagy via AMP-activated protein kinase (AMPK) activation and protected HL-1 cells against apoptosis and enhanced the viability after rotenone treatment. In conclusion, rotenone treatment induced significant cardiomyocyte cytotoxicity and ER stress, suppressed autophagy, and decreased APN expression in HL-1 cells. APN in return inhibited ER stress and activated autophagy through AMPK activation, thus alleviating rotenone induced HL-1 apoptosis.

Globular adiponectin alleviates chronic intermittent hypoxia-induced H9C2 cardiomyocytes apoptosis via ER-phagy induction

This study evaluated the effects of endoplasmic reticulum autophagy (ER-phagy) and globular adiponectin (gAPN) on chronic intermittent hypoxia (CIH)-induced H9C2 cardiomyocytes injury while investigating potential mechanisms of action. The CIH model of H9C2 cardiomyocytes was established in this study. CCK-8 assay was used to determine cell viability post-exposure to various CIH times and gAPN concentrations. Flow cytometry was used to observe H9C2 cardiomyocytes apoptosis and immunofluorescence was used to measure ER-phagy and SEC62 activation. Western blot was used to observe ER stress and AMPK pathway. Results indicated that ER stress was activated in H9C2 cardiomyocytes exposed to CIH. Inhibition of ER stress reduced CIH-induced cell apoptosis. gAPN attenuated CIH-induced ER stress and H9C2 cardiomyocytes apoptosis. ER-phagy and SEC62 protein level were induced by CIH, while gAPN highly enhanced these changes. Inhibition of SEC62 expression reduced ER-phagy and increased ER stress and H9C2 cardiomyocytes apoptosis. Moreover, gAPN induced AMPK expression. Inhibition of AMPK expression reduced SEC62-mediated ER-phagy and increased the H9C2 cardiomyocytes apoptosis. Altogether, our study suggested that gAPN upregulated SEC62-mediated ER-phagy to extenuate ER stress, and mitigated H9C2 cardiomyocytes apoptosis induced by CIH through AMPK activation.

Adipokines and Inflammation: Focus on Cardiovascular Diseases

It is well established that adipose tissue, apart from its energy storage function, acts as an endocrine organ that produces and secretes a number of bioactive substances, including hormones commonly known as adipokines. Obesity is a major risk factor for the development of cardiovascular diseases, mainly due to a low grade of inflammation and the excessive fat accumulation produced in this state. The adipose tissue dysfunction in obesity leads to an aberrant release of adipokines, some of them with direct cardiovascular and inflammatory regulatory functions. Inflammation is a common link between obesity and cardiovascular diseases, so this review will summarise the role of the main adipokines implicated in the regulation of the inflammatory processes occurring under the scenario of cardiovascular diseases.

Intermittent Hypoxia Triggers Early Cardiac Remodeling and Contractile Dysfunction in the Time-Course of Ischemic Cardiomyopathy in Rats

BACKGROUND Sleep-disordered breathing is associated with a poor prognosis (mortality) in patients with ischemic cardiomyopathy. The understanding of mechanisms linking intermittent hypoxia (IH), the key feature of sleep-disordered breathing, to ischemic cardiomyopathy progression is crucial for identifying specific actionable therapeutic targets. The aims of the present study were (1) to evaluate the impact of IH on the time course evolution of cardiac remodeling and contractile dysfunction in a rat model of ischemic cardiomyopathy; and (2) to determine the impact of IH on sympathetic activity, hypoxia inducible factor-1 activation, and endoplasmic reticulum stress in the time course of ischemic cardiomyopathy progression. METHODS AND RESULTS Ischemic cardiomyopathy was induced by a permanent ligature of the left coronary artery in male Wistar rats (rats with myocardial infarction). Rats with myocardial infarction were then exposed to either IH or normoxia for up to 12 weeks. Cardiac remodeling and function were analyzed by Sirius red and wheat germ agglutinin staining, ultrasonography, and cardiac catheterization. Sympathetic activity was evaluated by spectral analysis of blood pressure variability. Hypoxia-inducible factor-1α activation and burden of endoplasmic reticulum stress were characterized by Western blots. Long-term IH exposure precipitated cardiac remodeling (hypertrophy and interstitial fibrosis) and contractile dysfunction during the time course evolution of ischemic cardiomyopathy in rodents. Among associated mechanisms, we identified the early occurrence and persistence of sympathetic activation, associated with sustained hypoxia-inducible factor-1α expression and a delayed pro-apoptotic endoplasmic reticulum stress. CONCLUSIONS Our data provide the demonstration of the deleterious impact of IH on post-myocardial infarction remodeling and contractile dysfunction. Further studies are needed to evaluate whether targeting sympathetic nervous system or HIF-1 overactivities could limit these effects and improve management of coexisting ischemic cardiomyopathy and sleep-disordered breathing.

Leptin: Master Regulator of Biological Functions that Affects Breathing

Obesity is a global epidemic in developed countries accounting for many of the metabolic and cardiorespiratory morbidities that occur in adults. These morbidities include type 2 diabetes, sleep-disordered breathing (SDB), obstructive sleep apnea, chronic intermittent hypoxia, and hypertension. Leptin, produced by adipocytes, is a master regulator of metabolism and of many other biological functions including central and peripheral circuits that control breathing. By binding to receptors on cells and neurons in the brainstem, hypothalamus, and carotid body, leptin links energy and metabolism to breathing. In this comprehensive article, we review the central and peripheral locations of leptin's actions that affect cardiorespiratory responses during health and disease, with a particular focus on obesity, SDB, and its effects during early development. Obesity-induced hyperleptinemia is associated with centrally mediated hypoventilation with decrease CO₂ sensitivity. On the other hand, hyperleptinemia augments peripheral chemoreflexes to hypoxia and induces sympathoexcitation. Thus, "leptin resistance" in obesity is relative. We delineate the circuits responsible for these divergent effects, including signaling pathways. We review the unique effects of leptin during development on organogenesis, feeding behavior, and cardiorespiratory responses, and how undernutrition and overnutrition during critical periods of development can lead to cardiorespiratory comorbidities in adulthood. We conclude with suggestions for future directions to improve our understanding of leptin dysregulation and associated clinical diseases and possible therapeutic targets. Lastly, we briefly discuss the yin and the yang, specifically the contribution of relative adiponectin deficiency in adults with hyperleptinemia to the development of metabolic and cardiovascular disease. © 2020 American Physiological Society. Compr Physiol 10:1047-1083, 2020.

Curcumin prevents chronic intermittent hypoxia-induced myocardial injury

Background:

Chronic intermittent hypoxia (IH), the hallmark feature of obstructive sleep apnoea syndrome, contributes to infarct size enhancement after myocardial ischemia–reperfusion (I/R). Curcumin (Curc), the natural pigment of Curcuma longa, has been demonstrated to be beneficial in the context of myocardial injury. In this study, we assessed the effects of Curc on the maladaptive cardiac response to IH, and particularly on IH-induced hypoxia inducible factor-1 (HIF-1) expression, oxidative stress, inflammation, endoplasmic reticulum (ER) stress and apoptosis.

Methods:

Swiss/SV129 mice were exposed to normoxia or IH (21–5% FiO₂, 60 s cycles, 8 h per day, for 21 days) and treated orally with Curc (100 mg kg⁻¹ day⁻¹, oral gavage) or its vehicle. Mice were then either euthanised for heart sampling in order to perform biochemical and histological analysis, or subjected to an in vivo ischemia-reperfusion protocol in order to measure infarct size.

Results:

IH increased nuclear HIF-1α expression and superoxide anion (O₂^.–) production as well as nuclear factor kappa B (NF-kB) p65, glucose-regulated protein (Grp78) and C/EBP homologous protein (CHOP) expression. IH also induced apoptosis and increased infarct size after I/R . The IH-induced HIF-1 activation, oxidative stress, inflammation, ER stress and apoptosis were abolished by chronic Curc treatment. Curc also significantly decreased infarct size only in mice exposed to IH.

Conclusion:

Curc prevents IH-induced myocardial cell death signalling. Curc might be used as a combined therapy with continuous positive airway pressure in sleep apnoea patients with high cardiovascular risk.

Impact of Endoplasmic Reticulum Stress in Otorhinolaryngologic Diseases

The endoplasmic reticulum (ER) is an important organelle for normal cellular function and homeostasis in most living things. ER stress, which impairs ER function, occurs when the ER is overwhelmed by newly introduced immature proteins or when calcium in the ER is depleted. A number of diseases are associated with ER stress, including otorhinolaryngological diseases. The relationship between ER stress and otorhinolaryngologic conditions has been the subject of investigation over the last decade. Among otologic diseases associated with ER stress are otitis media and hearing loss. In rhinologic diseases, chronic rhinosinusitis, allergic rhinitis, and obstructive sleep apnea are also significantly associated with ER stress. In this review, we provide a comprehensive overview of the relationship between ER stress and otorhinolaryngological diseases, focusing on the current state of knowledge and mechanisms that link ER stress and otorhinolaryngologic diseases.

Adiponectin ameliorates lung injury induced by intermittent hypoxia through inhibition of ROS-associated pulmonary cell apoptosis

PURPOSE

Obstructive sleep apnea hypopnea syndrome has been reported to be associated with pulmonary hypertension (PH). Adiponectin (Ad) has many protective roles in the human body, including its function as an anti-inflammatory and an anti-oxidant, as well as its role in preventing insulin resistance and atherosclerosis. This study aimed to investigate the molecular mechanism of chronic intermittent hypoxia (CIH)-induced pulmonary injury and the protective role of Ad in experimental rats.

METHODS

Thirty male Sprague-Dawley rats were randomly divided into three groups with 10 rats in each group: normal control (NC) group, CIH group, and CIH + Ad group. Rats in the NC group were kept breathing room air for 12 weeks. Rats in the CIH group were intermittently exposed to a hypoxic environment for 8 h/day for 12 weeks. Rats in the CIH + Ad group received 10 μg Ad twice weekly via intravenous injection. After 12 weeks of CIH exposure, we detected the pulmonary function, pulmonary artery pressure, lung histology, pulmonary cell apoptosis, pulmonary artery endothelial cell apoptosis, mitochondrial membrane potential (MMP), and reactive oxygen species (ROS) level. We also analyzed expression proteins involved in the mitochondria-, endoplasmic reticulum (ER) stress-, and Fas receptor-associated pulmonary apoptosis pathways, as well as the SIRT3/SOD2 pathway.

RESULTS

CIH exposure for 12 weeks did not lead to abnormal pulmonary function, PH, or pulmonary artery endothelial cell apoptosis. However, we observed a significant increase in the rate of pulmonary cell apoptosis, the expression of proteins involved in mitochondria-, ER stress-, and Fas receptor-associated pulmonary apoptosis pathways, and the generation of ROS in the CIH group compared with the NC group. In contrast, the MMP and protein expressions of SIRT3/SOD2 pathway were significantly decreased in the CIH group compared with the NC group. Ad supplementation in the CIH + Ad group partially improved these changes induced by CIH.

CONCLUSION

Even though CIH did not cause abnormal pulmonary function or PH, early lung injury was detected at the molecular level in rats exposed to CIH. Treatment with Ad ameliorated the pulmonary injury by activating the SIRT3/SOD2 pathway, reducing ROS generation, and inhibiting ROS-associated lung cell apoptosis.

Attenuation of intermittent hypoxia-induced apoptosis and fibrosis in pulmonary tissues via suppression of ER stress activation

Background

Obstructive sleep apnea (OSA) is associated with pulmonary fibrosis and endothelial apoptosis in pulmonary tissues. Chronic intermittent hypoxia (IH) is considered to be the primary player in OSA, but the mechanisms underlying its effect on pulmonary tissues are unknown. Endoplasmic reticulum (ER) stress induced by IH treatment plays an important role in accelerating the process of fibrosis and induction of apoptosis.

Methods

Mice were placed in IH chambers for 4 weeks with an oscillating oxygen (O₂) concentration between 5 and 21%, cycling every 90s for 8 h daily. Mice were randomly divided into four groups: control group (normal oxygen), tauroursodeoxycholic acid (TUDCA) group (normal oxygen intraperitoneally injected with TUDCA), IH group and IH + TUDCA group. After 4 weeks, the proteins in three branch signaling pathways of ER stress, including protein kinase RNA (PKR)-like/Pancreatic ER kinase (PERK), activating transcription factor 6 (ATF-6) and inositol-requiring enzyme 1 (IRE-1), were evaluated. The cleaved caspase-3, caspase-12 and TUNNEL staining was assessed. Furthermore, the expression of transforming growth factor-β1 (TGF-β1) and thrombospondin-1(TSP-1), two extracellular matrix proteins that play critical role in fibrosis, were examined. Finally, Masson’s trichrome staining was performed to detect the expression of collagen.

Results

After 4 weeks of IH treatment, the expressions of two ER stress markers, glucose regulated protein-78 (Grp78) and transcription factor C/EBP homologous protein (CHOP) were increased which was prevented by administration of the ER stress attenuator, TUDCA. The expressions of PERK, but not those of ATF-6 and IRE-1, were increased. The effects of IH were accompanied by an increased number of apoptotic cells and increased expressions of cleaved caspase-3 and caspase-12 in pulmonary tissues. In addition, histological examination suggested the presence of fibrosis after chronic IH treatment, indicated by increased expression of collagen, which was associated with the up-regulation of TGF-β1 and TSP-1 that are known to promote fibrosis. Similarly, TUDCA could reduce the extent of fibrotic area and the expression levels of these proteins.

Conclusions

It reveals the roles of ER stress, especially the PERK pathway, in IH induced apoptosis and fibrosis in pulmonary tissues that might underlie the pulmonary complications observed in OSA.

Synergistic anti-atherosclerotic role of combined treatment of omega-3 and co-enzyme Q10 in hypercholesterolemia-induced obese rats

Hypercholesterolemia is a metabolic disorder associated with atherosclerosis. This study aimed to investigate the effects of omega-3 and/or coenzyme Q10 (CoQ10) on hypercholesterolemia-induced atherosclerosis. Rats were divided into five groups; (1): served as the negative control, (2): served as hypercholesterolemic (HC) control, (3): HC-rats administrated omega-3 orally, (4): HC-rats administrated CoQ10 orally, and (5): HC-rats administered the combination treatment of both omega-3 and CoQ10. Lipid profile was assayed and cardiovascular risk indices were calculated. Serum levels of Adiponectin (APN) and creatine kinase (CK-MB) were determined using ELISA. Besides, oxidative stress markers, malondialdehyde (MDA), nitric oxide (NO) and glutathione (GSH) were assayed in the heart homogenate. Histopathological investigation of the aortae and heart tissues were investigated. The results revealed that atherogenic HC-rats demonstrated a significant elevation in lipid profiles, except for HDL-C, along with decreased levels of APN, but increased CK-MB activities. Hypercholesterolemia increased lipid peroxidation, reduced NO production, and decreased GSH content in the cardiac tissue. Treatment of atherogenic HC-rats with omega-3 and/or CoQ10 improved dyslipidemia and ameliorated most of the HC-induced biochemical and histopathological changes. The histological observations of aortae and cardiac tissues validated our biochemical results. We concluded that the combined treatment of nutraceuticals such as omega-3 and CoQ10 demonstrated the best outcome, demonstrating their anti-hyperlipidemic, cardioprotective, and atheroprotective potentials. Together, this study supports a beneficial role of dietary co-administration of omega-3 and CoQ10 in obese patients who are prone to develop cardiovascular disorders.

Injury and Apoptosis in the Palatopharyngeal Muscle in Patients with Obstructive Sleep Apnea-Hypopnea Syndrome

Background

This study aimed to elucidate the possible activity of the mitochondrial-mediated apoptotic pathway (MMAP) in obstructive sleep apnea-hypopnea syndrome (OSAHS).

Material/Methods

A control group, a mild OSAHS group, a moderate OSAHS group, and a severe OSAHS group were included. Masson staining, hematoxylin and eosin staining, and terminal deoxynucleotidyl transferase dUTP nick-end labeling (TUNEL) assay were performed to assess collagen fiber hyperplasia, pathological morphology, and cell apoptosis, respectively, in muscle samples.

Results

In the OSAHS groups, the palatopharyngeal muscle fibers were larger, with apparent hypertrophy and increased elastic fiber content. The proportions of type I fibers were markedly higher in the control group than in the moderate and severe OSAHS groups (P<0.05). Moreover, apoptosis was significantly enhanced in the muscle cells of the OSAHS groups. The Bax expression levels gradually increased across the 4 groups (lowest in the control group and highest in the severe OSAHS group) (P<0.05); conversely, the p38 and p62 expression levels did not significantly differ among groups (P>0.05).

Conclusions

A decrease in the proportion of the different fiber types can result in collapse of the upper airway. The pathogenesis of OSAHS appears to involve muscle cell apoptosis via MMAP.

Adipose-Derived Stem Cells Protect Ischemia-Reperfusion and Partial Hepatectomy by Attenuating Endoplasmic Reticulum Stress

Ischemia-reperfusion (IR) is an inevitable complication of liver surgery. Recent studies indicate a critical role of endoplasmic reticulum stress (ERS) in hepatic IR. Mesenchymal stem cells (MSCs) have proven to be an effective tool for tissue regeneration and treatment of various diseases, including that of the liver. However, the mechanisms underlying the therapeutic effects of stem cells on hepatic IR injury (IRI) are still poorly understood, especially in the context of ERS. In this study, we established a porcine model of hepatic IRI and partial hepatectomy, and transplanted the animals with adipose-derived mesenchymal stem cells (ADSCs) isolated from miniature pigs. ADSCs not only alleviated the pathological changes in the liver parenchyma following IRI, but also protected the resident hepatocytes from damage. Mechanistically, the ADSCs significantly downregulated ERS-related proteins, including GRP78, p-eIF2α, ATF6 and XBP1s, as well as the proteins involved in ERS-induced apoptosis like p-JNK, ATF4 and CHOP. Taken together, ADSCs can alleviate hepatic IRI by inhibiting ERS and its downstream apoptotic pathways in the hepatocytes, indicating its therapeutic potential in liver diseases.

Mandibular Advancement Devices Prevent the Adverse Cardiac Effects of Obstructive Sleep Apnea-Hypopnea Syndrome (OSAHS)

Although considerable research highlights the interactions between obstructive sleep apnea-hypopnea syndrome (OSAHS) and cardiovascular diseases, the effect of mandibular advancement device (MAD) treatment on cardiovascular complications in OSAHS patients remains unclear. We evaluated the effect of OSAHS treatment with MADs on the myocardium. All methods in this study were in accordance with relevant guidelines and regulations of the medical ethics committee in Hospital of Stomatology, Hebei Medical University approved the work. Thirty New Zealand rabbits were randomized into three groups: the control group, Group OSAHS, and Group MAD. Hydrophilic polyacrylamide gel was injected into the soft palate of the rabbits to induce OSAHS. In Group MAD, a MAD was positioned after OSAHS induction. All animals were induced to sleep in a supine position for 4–6 h/day for 8 weeks. Echocardiography was used to determine the structure and function of the heart. The histological changes were detected by optical microscopy and transmission electron microscopy (TEM). The levels of ET-1(endothelin-1) and Ang II (Angiotensin II) in the plasma were measured by an enzyme-linked immunosorbent assay (ELISA). The expression of ET-1 mRNA in heart tissue was detected by RT-PCR. Histological abnormalities, left ventricular hypertrophy, and left ventricular dysfunctions were demonstrated in Group OSAHS, and the abnormities were rescued with MAD treatment. Higher levels of plasma ET-1 and Ang II and elevated expression of ET-1 mRNA in cardiac tissue were detected in Group OSAHS compared with Group MAD and the control group. The blood oxygen saturation was negatively correlated with the levels of ET-1 and Ang II. OSAHS-induced elevated levels of ET-1 and Ang II may be attributed to myocardial structural abnormalities and dysfunction. Early treatment of MADs may play an important role in preventing myocardial damage in OSAHS rabbit model.

Hydrogen Sulfide Plays an Important Protective Role through Influencing Endoplasmic Reticulum Stress in Diseases

The endoplasmic reticulum is an important organelle responsible for protein synthesis, modification, folding, assembly and transport of new peptide chains. When the endoplasmic reticulum protein folding ability is impaired, the unfolded or misfolded proteins accumulate to lead to endoplasmic reticulum stress. Hydrogen sulfide is an important signaling molecule that regulates many physiological and pathological processes. Recent studies indicate that H₂S plays an important protective role in many diseases through influencing endoplasmic reticulum stress, but its mechanism is not fully understood. This article reviewed the progress about the effect of H₂S on endoplasmic reticulum stress and its mechanisms involved in diseases in recent years to provide theoretical basis for in-depth study.

L-lysine protects C2C12 myotubes and 3T3-L1 adipocytes against high glucose damages and stresses

Hyperglycemia is a hallmark of diabetes, which is associated with protein glycation and misfolding, impaired cell metabolism and altered signaling pathways result in endoplasmic reticulum stress (ERS). We previously showed that L-lysine (Lys) inhibits the nonenzymatic glycation of proteins, and protects diabetic rats and type 2 diabetic patients against diabetic complications. Here, we studied some molecular aspects of the Lys protective role in high glucose (HG)-induced toxicity in C2C12 myotubes and 3T3-L1 adipocytes. C2C12 and 3T3-L1 cell lines were differentiated into myotubes and adipocytes, respectively. Then, they were incubated with normal or high glucose (HG) concentrations in the absence/presence of Lys (1 mM). To investigate the role of HG and/or Lys on cell apoptosis, oxidative status, unfolded protein response (UPR) and autophagy, we used the MTT assay and flow cytometry, spectrophotometry and fluorometry, RT-PCR and Western blotting, respectively. In both cell lines, HG significantly reduced cell viability and induced apoptosis, accompanying with the significant increase in reactive oxygen species (ROS) and nitric oxide (NO). Furthermore, the spliced form of X-box binding protein 1 (XBP1), at both mRNA and protein levels, the phosphorylated eukaryotic translation initiation factor 2α (p-eIf2α), and the Light chain 3 (LC3)II/LC3I ratio was also significantly increased. Lys alone had no significant effects on most of these parameters; but, treatment with HG plus Lys returned them all to, or close to, the normal values. The results indicated the protective role of Lys against glucotoxicity induced by HG in C2C12 myotubes and 3T3-L1 adipocytes.

Adiponectin Reverses the Hypothalamic Microglial Inflammation during Short-Term Exposure to Fat-Rich Diet

Adiponectin, an adipokine derived from the adipose tissue, manifests anti-inflammatory effects in the metabolically active organs and is, therefore, beneficial in various metabolic diseases associated with inflammation. However, the role of adiponectin in alleviating the hypothalamic inflammation connected to the pathogenesis of obesity has not yet been clearly interrogated. Here, we identified that the systemic administration of adiponectin suppresses the activation of microglia and thereby reverses the hypothalamic inflammation during short-term exposure to a high-fat diet. Additionally, we show that adiponectin induces anti-inflammatory effects in the microglial cell line subjected to an exogenous treatment with a saturated free fatty acid. In conclusion, the current study suggests that adiponectin suppresses the saturated free fatty acid-triggered the hypothalamic inflammation by modulating the microglial activation and thus maintains energy homeostasis.

Intermittent Hypoxia Induces Autophagy to Protect Cardiomyocytes From Endoplasmic Reticulum Stress and Apoptosis

Intermittent hypoxia (IH), characterized as cyclic episodes of short-period hypoxia followed by normoxia, occurs in many physiological and pathophysiological conditions such as pregnancy, athlete, obstructive sleep apnea, and asthma. Hypoxia can induce autophagy, which is activated in response to protein aggregates, in the proteotoxic forms of cardiac diseases. Previous studies suggested that autophagy can protect cells by avoiding accumulation of misfolded proteins, which can be generated in response to ischemia/reperfusion (I/R) injury. The objective of the present study was to determine whether IH-induced autophagy can attenuate endoplasmic reticulum (ER) stress and cell death. In this study, H9c2 cell line, rat primary cultured cardiomyocytes, and C57BL/6 male mice underwent IH with an oscillating O₂ concentration between 4 and 20% every 30 min for 1-4 days in an incubator. The levels of LC3, an autophagy indicator protein and CHOP and GRP78 (ER stress-related proteins) were measured by Western blotting analyses. Our data demonstrated that the autophagy-related proteins were upregulated in days 1-3, while the ER stress-related proteins were downregulated on the second day after IH. Treatment with H₂O₂ (100 μM) for 24 h caused ER stress and increased the level of ER stress-related proteins, and these effects were abolished by pre-treatment with IH condition. In response to the autophagy inhibitor, the level of ER stress-related proteins was upregulated again. Taken together, our data suggested that IH could increase myocardial autophagy as an adaptive response to prevent the ER stress and apoptosis.

Hydrogen and Oxygen Mixture to Improve Cardiac Dysfunction and Myocardial Pathological Changes Induced by Intermittent Hypoxia in Rats

Obstructive sleep apnea (OSA) can cause intermittent changes in blood oxygen saturation, resulting in the generation of many reactive oxygen species (ROS). To discover new antioxidants and clarify the endoplasmic reticulum (ER) stress involved in cardiac injury in OSA, we established a chronic intermittent hypoxia (CIH) rat model with a fraction of inspired O₂ (FiO₂) ranging from 21% to 9%, 20 times/h for 8 h/day, and the rats were treated with H₂-O₂ mixture (67% hydrogen and 33% oxygen) for 2 h/day for 35 days. Our results showed that H₂-O₂ mixture remarkably improved cardiac dysfunction and myocardial fibrosis. We found that H₂-O₂ mixture inhalation declined ER stress-induced apoptosis via three major response pathways: PERK-eIF2α-ATF4, IRE 1-XBP1, and ATF 6. Furthermore, we revealed that H₂-O₂ mixture blocked c-Jun N-terminal kinase- (JNK-) MAPK activation, increased the ratio of Bcl-2/Bax, and inhibited caspase 3 cleavage to protect against CIH-induced cardiac apoptosis. In addition, H₂-O₂ mixture considerably decreased ROS levels via upregulating superoxide dismutase (SOD) and glutathione (GSH) as well as downregulating NADPH oxidase (NOX 2) expression in the hearts of CIH rats. All the results demonstrated that H₂-O₂ mixture significantly reduced ER stress and apoptosis and that H₂ might be an efficient antioxidant against the oxidative stress injury induced by CIH.

AMPK: a therapeutic target of heart failure-not only metabolism regulation

Heart failure (HF) is a serious disease with high mortality. The incidence of this disease has continued to increase over the past decade. All cardiovascular diseases causing dysfunction of various physiological processes can result in HF. AMP-activated protein kinase (AMPK), an energy sensor, has pleiotropic cardioprotective effects and plays a critical role in the progression of HF. In this review, we highlight that AMPK can not only improve the energy supply in the failing heart by promoting ATP production, but can also regulate several important physiological processes to restore heart function. In addition, we discuss some aspects of some potential clinical drugs which have effects on AMPK activation and may have value in treating HF. More studies, especially clinical trials, should be done to evaluate manipulation of AMPK activation as a potential means of treating HF.

Adiponectin Relieves Human Adult Cardiac Myocytes Injury Induced by Intermittent Hypoxia

Background

Obstructive sleep apnea (OSA) is associated with many cardiovascular disorders. Intermittent hypoxia (IH) is a key pathological hallmark of OSA. This study was conducted to evaluate the potential therapeutic effects and the associated mechanisms of adiponectin (APN) on IH induced human adult cardiac myocytes (HACMs) injury.

Material/Methods

HACMs were exposed to normoxia or IH (1% to 21% O₂) using a novel cell culture bio-reactor with gas-permeable membranes. Cell viability was detected by Cell Counting Kit-8 assay. Cell membrane integrity was assessed by the detection of lactate dehydrogenase (LDH) release. Cell apoptosis was analyzed by flow cytometry. Malondialdehyde (MDA), superoxide dismutase (SOD), and glutathione peroxidase (GSH-Px) levels were determined using specific assay kits. P-AMPK (AMP-activated protein kinase), p-LKB1, and p-p65 protein levels were measured by western blotting. Pro-inflammatory factors including interleukin (IL)-1β, IL-6, IL-8 expressions were detected by enzyme-linked immunosorbent assay and quantitative real-time polymerase chain reaction.

Results

The results showed that APN had no cytotoxic to HACMs. Compared with the control group, HACMs cell viability significantly decreased, LDH release increased and cell apoptosis increased in the IH group. The levels of IL-1β, IL-6, IL-8, MDA, and p-p65 were higher, while the levels of SOD, GSH-Px, p-AMPK, and p-LKB1 were lower in HACMs cells in the IH group than that in the control group. However, APN treatment significantly rescued these effects compared with the IH group in a dose-dependent manner.

Conclusions

In conclusion, these results indicated that APN protected against IH induced HACMs injury possibly mediated by AMPK and NF-κB pathway.

4-phenylbutyric acid attenuates endoplasmic reticulum stress-mediated apoptosis and protects the hepatocytes from intermittent hypoxia-induced injury

PURPOSE

To investigate the effect of 4-phenylbutyric acid (4-PBA) on intermittent hypoxia (IH)-induced liver cell injury and to clarify the underlying mechanisms.

METHODS

L02 cells (normal human liver cells) were cultured in normoxic condition or subjected to intermittent hypoxia for 4, 8, and 12 h. A part of hypoxia-treated L02 cells was applied with 4-PBA 1 h before exposure to hypoxia. The effect of 4-PBA on liver injury, hepatocyte apoptosis, endoplasmic reticulum stress (ERS), and PERK-eIFa2-ATF4-CHOP apoptotic pathway was investigated.

RESULTS

(1) IH caused apoptosis in hepatocyte; (2) IH caused ERS in hepatocyte; (3) IH caused hepatic injury; (4) 4-PBA attenuated IH-induced liver cell injury; (5) 4-PBA protected liver cell from IH-induced apoptosis; (6) 4-PBA suppressed ERS-related apoptotic pathway (PERK-eIFa2-ATF4-CHOP), but did not suppress IH-induced unfold protein reaction (UPR).

CONCLUSIONS

4-PBA could protect liver cells by suppressing IH-induced apoptosis mediated by ERS, but not by reducing the UPR.

Hispidulin induces ER stress-mediated apoptosis in human hepatocellular carcinoma cells in vitro and in vivo by activating AMPK signaling pathway

Hispidulin (4',5,7-trihydroxy-6-methoxyflavone) is a phenolic flavonoid isolated from the medicinal plant S. involucrata, which exhibits anti-neoplastic activity against several types of cancer. However, the mechanism underlying its anti-cancer activity against hepatocellular carcinoma (HCC) has not been fully elucidated. In this study, we investigated whether and how hispidulin-induced apoptosis of human HCC cells in vitro and in vivo. We showed that hispidulin (10, 20 μmol/L) dose-dependently inhibited cell growth and promoted apoptosis through mitochondrial apoptosis pathway in human HCC SMMC7721 cells and Huh7 cells. More importantly, we revealed that its pro-apoptotic effects depended on endoplasmic reticulum stress (ERS) and unfolded protein response (UPR), as pretreatment with salubrinal, a selective ERS inhibitor, or shRNA targeting a UPR protein CHOP effectively abrogated hispidulin-induced cell apoptosis. Furthermore, we showed that hispidulin-induced apoptosis was mediated by activation of AMPK/mTOR signaling pathway as pretreatment with Compound C, an AMPK inhibitor, or AMPK-targeting siRNA reversed the pro-apoptotic effect of hispidulin. In HCC xenograft nude mice, administration of hispidulin (25, 50 mg/kg every day, ip, for 27 days) dose-dependently suppressed the tumor growth, accompanied by inducing ERS and apoptosis in tumor tissue. Taken together, our results demonstrate that hispidulin induces ERS-mediated apoptosis in HCC cells via activating the AMPK/mTOR pathway. This study provides new insights into the anti-tumor activity of hispidulin in HCC.

Obstructive Sleep Apnea Syndrome and Metabolic Diseases

With the rapid changes in lifestyle in modern society, including the high nutritional intake and reduced physical activity, the incidence of metabolic diseases has been increasing year by year. Obstructive sleep apnea syndrome (OSAS) is a sleep disorder, usually characterized by sudden pauses of breathing during sleep and an interrupted sleep rhythm. Although the pathological mechanism remains poorly understood, it has been strongly associated with metabolic diseases, including obesity, insulin resistance, type 2 diabetes mellitus (T2DM), and nonalcoholic fatty liver disease (NAFLD). In the present mini-review, we briefly summarize the connections between OSAS, obesity, T2DM, and NAFLD, which might help us to better understand the pathogenesis of human diseases.

Sinomenine Attenuates Chronic Intermittent Hypoxia-Induced Lung Injury by Inhibiting Inflammation and Oxidative Stress

Background

In the present study, we aimed to investigate the effects of sinomenine (SIN) on chronic intermittent hypoxia (CIH)- induced lung injury in rats, and to explore the underlying mechanisms.

Material/Methods

To perform the investigation, a CIH rat model was established. ELISA assay was applied to detect the level of inflammatory cytokines. Oxidative stress bio-markers (MDA, SOD, and CAT) were determined in lung tissues. In addition, the expression level of NADPH oxidase 2 (Nox2) was analyzed by Western blotting and qRT-PCR, respectively.

Results

The results showed that compared with other groups, more obvious pulmonary pathological changes were observed in the CIH group. The level of inflammatory cytokines in the CIH group was markedly higher than that in the control and Con-S groups. Compared with the control and Con-S groups, oxidative stress was notably increased in the CIH group. Expression of Nox2 was also increased in the CIH group. The effects caused by CIH in rats were attenuated by SIN treatment.

Conclusions

SIN can reverse chronic intermittent hypoxia-induced lung injury through inhibiting inflammation and oxidative stress.

Intermittent hypoxia promotes melanoma lung metastasis via oxidative stress and inflammation responses in a mouse model of obstructive sleep apnea

Background

Recently, increased tumor incidence and cancer-related mortality have been reported among patients with obstructive sleep apnea (OSA). Intermittent hypoxia (IH), the hallmark feature of OSA, contributes to the metastasis of tumors. However, the molecular mechanisms by which tumor metastasis is accelerated by OSA-like IH remain to be elucidated.

Methods

C57BL/6 J male mice were subjected to intravenous injection of B16F10 melanoma cells before receiving IH treatment. Then, the animals were randomly distributed into three groups (n = 8 each): normoxia (N) group, IH group, and antioxidant tempol group (IHT, exposed to IH after treatment with tempol). After the mice were sacrificed, the number and weight of lung metastatic colonies were assessed. The lung tissues with tumor metastasis were analyzed for markers of oxidative stress and inflammation and for HIF-1α using western blotting and real-time PCR (qRT-PCR). The level of reactive oxygen species (ROS) in B16F10 cell was also assessed after N, IH and IH with tempol treatments.

Results

Compared with normoxia, IH significantly increased the number and weight of mouse lung metastatic colonies. Treatment of B16F10 cells with IH significantly enhanced ROS generation. Lung tissues with tumor metastasis provided evidence of increased oxidative stress, as assessed by p22^phox and SOD mRNA levels and the NRF2 protein level, as well as increased inflammation, as assessed by TNF-α and IL-6 mRNA levels and the NF-κB P65 protein level. HIF-1α protein levels were increased in response to IH treatment. Tempol, an important antioxidant, ameliorated IH-induced melanoma lung metastasis in mice and reduced oxidative stress and inflammation responses.

Conclusions

These results support the hypothesis that oxidative stress and inflammation responses play an important role in the pathogenesis of OSA-like IH-induced melanoma lung metastasis in mice. Antioxidant intervention provides a novel strategy for the prevention and treatment of cancer in OSA populations.

Bisoprolol protects myocardium cells against ischemia/reperfusion injury by attenuating unfolded protein response in rats

Bisoprolol (B) exerts potential cardioprotective effects against myocardial ischemia/reperfusion (I/R) injury. Unfolded protein response (UPR) attenuates I/R injury induced apoptosis by reducing oxidative damage and inflammation response. The current study investigated whether the protective effects of bisoprolol resulted from modulating UPR and anti-inflammatory during myocardial I/R condition and elucidated its potential mechanisms. Sprague-Dawley rats were treated with B in the absence or presence of the injected UPR activator dithiothreitol (DTT) and then subjected to myocardial I/R surgery. In vitro, cultured H9C2 cells were pretreated with B or DTT and then subjected to simulate ischemia reperfusion (SIR) operation. Bisoprolol conferred cardioprotective effects by improving postischemic cardiac function, decreasing infarct size, reducing apoptotic index, diminishing serum creatine kinase and lactate dehydrogenase levels, suppressing TNF-α and IL-6 secretion, inhibiting UPR signal pathways and downregulating caspase-12 and caspase-3 expressions. Consistently, B conferred similar antioxidative and anti-inflammatory effects against SIR injury in cultured H9C2 cardiomyocytes. Pretreatment with DTT or C/EBP homologous protein (CHOP) overexpression mediated by lentivirus administration both abolished these effects. In summary, our results demonstrate that Bisoprolol protects myocardium cells against ischemia/reperfusion injury partly by attenuating unfolded protein response.

Tauroursodeoxycholic acid attenuates endoplasmic reticulum stress and protects the liver from chronic intermittent hypoxia induced injury

Obstructive sleep apnea that characterized by chronic intermittent hypoxia (CIH) has been reported to associate with chronic liver injury. Tauroursodeoxycholic acid (TUDCA) exerts liver-protective effects in various liver diseases. The purpose of this study was to test the hypothesis that TUDCA could protect liver against CIH injury. C57BL/6 mice were subjected to intermittent hypoxia for eight weeks and applied with TUDCA by intraperitoneal injection. The effect of TUDCA on liver histological changes, liver function, oxidative stress, inflammatory response, hepatocyte apoptosis and endoplasmic reticulum (ER) stress were investigated. The results showed that administration of TUDCA attenuated liver pathological changes, reduced serum alanine aminotransferase and aspartate aminotransferase level, suppressed reactive oxygen species activity, decreased tumor necrosis factor-α and interleukin-1β level and inhibited hepatocyte apoptosis induced by CIH. TUDCA also inhibited CIH-induced ER stress in liver as evidenced by decreased expression of ER chaperone 78 kDa glucose-related protein, unfolded protein response transducers and ER proapoptotic proteins. Altogether, the present study described a liver-protective effect of TUDCA in CIH mice model, and this effect seems at least partly through the inhibition of ER stress.

Genistein Protects Genioglossus Myoblast Against Hypoxia-induced Injury through PI3K-Akt and ERK MAPK Pathways

Obstructive sleep apnea and hypopnea syndrome (OSAHS) is a clinical syndrome characterized by recurrent episodes of obstruction of the upper airway during sleep that leads to a hypoxic condition. Genioglossus, an important pharyngeal muscle, plays an important role in maintaining an open upper airway for effective breathing. Our previous study found that genistein (a kind of phytoestrogen) protects genioglossus muscle from hypoxia-induced oxidative injury. However, the underlying mechanism is still unknown. In the present study, we examined the effects of hypoxia on genioglossus myoblast proliferation, viability and apoptosis, and the protective effect of genistein and its relationship with the PI3K/Akt and ERK MAPK pathways. Cell viability and Bcl-2 were reduced under hypoxic condition, while ROS generation, caspase-3, MDA, and DNA damage were increased following a hypoxia exposure. However, the effects of hypoxia were partially reversed by genistein in an Akt- and ERK- (but not estrogen receptor) dependent manner. In conclusion, genistein protects genioglossus myoblasts against hypoxia-induced oxidative injury and apoptosis independent of estrogen receptor. The PI3K-Akt and ERK1/2 MAPK signaling pathways are involved in the antioxidant and anti-apoptosis effect of genistein on genioglossus myoblasts.

Unfolded protein response plays a critical role in heart damage after myocardial ischemia/reperfusion in rats

The unfolded protein response (UPR) plays a critical role in cell death mediated by ischemia/reperfusion (I/R) injury. However, little is known about the exact mechanism of UPR signaling pathways after myocardial I/R injury in rats. An attempt was therefore made to assess whether the myocardial I/R induced UPR, and which branch of UPR (ATF6, IRE1 and PERK) signal pathway was activated. Sprague-Dawley rats were pretreated with UPR stimulator dithiothreitol (DTT) and UPR inhibitor 4-phenylbutyrate (4PBA) and then subjected to myocardial I/R surgery. Compared with sham-operated group, the expression of GRP78, ATF6, CHOP and sXBP1 in the I/R injured group is significantly increased at transcript and protein levels, which indicated that all the three signal pathways of UPR were activated in the myocardial I/R injury. Compared with the I/R injured group, treatment with 4PBA effectively decreased myocardium infarct size, reduced myocardial apoptosis, down-regulated caspase-12 expression, diminished serum creatine kinase and lactate dehydrogenase levels. In contrast, these effects were reversed in DTT treated group. In summary, these results demonstrated that myocardial I/R injury activates UPR and inhibiting cell UPR possesses a cardioprotective effect through the suppression of ER stress-induced apoptosis. Therefore, inhibition of UPR might be used as a therapeutic target during myocardial I/R injury.

Establishment of a Rabbit Model of Chronic Obstructive Sleep Apnea and Application in Cardiovascular Consequences

Background:

Although obstructive sleep apnea (OSA) has been recognized as a major risk factor for cardiovascular complications and its clinical features are well characterized, it is difficult to replicate the OSA hypoxic model in humans. We aimed to establish an experimental rabbit model for chronic OSA and to explore its application to measure blood pressure (BP), myocardial systolic function, and oxidative stress.

Methods:

The rabbit model for OSA was established by repeatedly closing the airway and then reopening it. A tube specially designed with a bag that could be alternately inflated and deflated according to a predetermined time schedule, resulting in recurrent airway occlusions and chronic intermittent hypoxia (CIH) imitating OSA patterns in humans, was used. Twenty-four rabbits were randomly divided into obstruction, sham, and control groups, and their upper airways were alternately closed for 15 s and then reopened for 105 s in a 120-s-long cycle, for 8 h each day over 12 consecutive weeks. Before and after the experiment, the BP of each rabbit was monitored. Levels of interleukin-6 (IL-6) and tumor necrosis factor-α (TNF-α) in the serum, superoxide dismutase (SOD) activity, malondialdehyde (MDA) and reactive oxygen species (ROS) contents, as well as Na⁺-K⁺-ATPase/Ca²⁺-ATPase activities in cardiac muscle were examined. In addition, cardiac functional parameters were measured using echocardiography.

Results:

After 3 months, all rabbits in the obstruction group manifested sleepiness performance similar to that observed in OSA patients. Traces of airflow and SpO₂ showed that this model mimicked the respiratory events involved in OSA, including increased respiratory effort and decreased oxygen saturation. Gradually, the BP rose each month. CIH led to obvious oxidative stress and injured myocardial systolic performance. The serum levels of IL-6 and TNF-α increased significantly (64.75 ± 9.05 pg/ml vs. 147.00 ± 19.24 pg/ml and 59.38 ± 8.21 pg/ml vs. 264.75 ± 25.54 pg/ml, respectively, both P < 0.001). Compared with the sham and the control groups, myocardial activities of Na⁺-K⁺-ATPase/Ca²⁺-ATPase and SOD in the obstruction group decreased markedly, while ROS and MDA content increased.

Conclusions:

These results show that the rabbit model for OSA simulates the pathophysiological characteristics of OSA in humans, which implies that this animal model is feasible and useful to study the mechanisms involved in the cardiovascular consequences of OSA.

Effects of phosphodiestrase type 5 inhibitors in epinephrine-induced arrhythmia in rats: Involvement of lactate dehydrogenase and creatine kinase downregulation and adiponectin expression

Cardiac arrhythmia is a common cause of mortality, and its progression may be due to abnormal sympathetic nerve activity and catecholamine release. Besides, lactate dehydrogenase (LDH) and creatine kinase (CK) downregulation and adiponectin expression play important roles in promoting coronary artery disease. The study aimed to examine the possible cardioprotective effect of members of phosphodiesterase type 5 (PDE-5) inhibitors in epinephrine-induced arrhythmia in rats. Arrhythmia was induced by cumulative boluses of epinephrine (4, 8, 16, 32, 64, and 128 mg/kg) given at 10-min intervals. Rats were randomly allocated into five groups. Group I: Normal control group received only saline. Group II: Rats injected with epinephrine and served as arrhythmia group. Groups III, IV, and V: Rats received daily oral sildenafil (0.5 mg/kg), vardenafil (3 mg/kg), and tadalafil (10 mg/kg), respectively, for 30 days prior to epinephrine injections. Injection of epinephrine to rats decreased heart rate and QTc interval but increased RR interval and duration of arrhythmia. Epinephrine group had lower serum reduced glutathione (GSH) and adiponectin levels and higher serum malondialdehyde (MDA), nitric oxide (NO), heart LDH, and CK contents. Histopathological investigations of epinephrine group provoked necrotic changes with strong positive immunoreactivity for caspases-3. While pretreatment of rats with PDE-5 inhibitors improved GSH and adiponectin contents, ameliorated serum MDA and NO levels and heart LDH and CK contents and corrected epinephrine-induced histopathological changes. PDE-5 inhibitors may delay epinephrine-induced arrhythmia through expression of adiponectin and downregulation of heart LDH and CK.

Endoplasmic Reticulum (ER) Stress and Endocrine Disorders

The endoplasmic reticulum (ER) is the organelle where secretory and membrane proteins are synthesized and folded. Unfolded proteins that are retained within the ER can cause ER stress. Eukaryotic cells have a defense system called the “unfolded protein response” (UPR), which protects cells from ER stress. Cells undergo apoptosis when ER stress exceeds the capacity of the UPR, which has been revealed to cause human diseases. Although neurodegenerative diseases are well-known ER stress-related diseases, it has been discovered that endocrine diseases are also related to ER stress. In this review, we focus on ER stress-related human endocrine disorders. In addition to diabetes mellitus, which is well characterized, several relatively rare genetic disorders such as familial neurohypophyseal diabetes insipidus (FNDI), Wolfram syndrome, and isolated growth hormone deficiency type II (IGHD2) are discussed in this article.

Hydrogen-rich saline attenuates hippocampus endoplasmic reticulum stress after cardiac arrest in rats

BACKGROUND

Hydrogen-rich saline can selectively scavenge reactive oxygen species (ROS) and protect brain against ischemia reperfusion (I/R) injury. Endoplasmic reticulum stress (ERS) has been implicated in the pathological process of cerebral ischemia. However, very little is known about the role of hydrogen-rich saline in mediating pathophysiological reactions to ERS after I/R injury caused by cardiac arrest.

METHODS

The rats were randomly divided into three groups, sham group (n=30), ischemia/reperfusion group (n=40) and hydrogen-rich saline group (n=40). The rats in experimental groups were subjected to 4min of cardiac arrest and followed by resuscitation. Then they were randomized to receive 5ml/kg of either hydrogen-rich saline or normal saline.

RESULTS

Hydrogen-rich saline significantly improves survival rate and neurological function. The beneficial effects of hydrogen-rich saline were associated with decreased levels of oxidative products, as well as the increased levels of antioxidant enzymes. Furthermore, the protective effects of hydrogen-rich saline were accompanied by the increased activity of glucose-regulated protein 78 (GRP78), the decreased activity of cysteinyl aspartate specific proteinase-12 (caspase-12) and C/EBP homologous protein (CHOP).

CONCLUSIONS

Hydrogen-rich saline attenuates brain I/R injury may through inhibiting hippocampus ERS after cardiac arrest in rats.

Upregulation of endoplasmic reticulum stress is associated with diaphragm contractile dysfunction in a rat model of sepsis

Sepsis often causes diaphragm contractile dysfunction. Endoplasmic reticulum (ER) stress has been implicated in muscle contractile dysfunction. However, it remains unknown if ER stress occurs in the diaphragm during sepsis. In the present study, rats were divided into 4 groups and received placebo or one of three durations of endotoxin treatment (24, 48 h and 7 days). Isometric contractile force of the diaphragm was measured and lung wet-to-dry ratio (W/D) was calculated. Hematoxylin and eosin (H&E) staining of lung tissue was performed and electron microscopy assessed ER damage in the diaphragm during sepsis. The mRNA and protein expression of glucose‑regulated protein 78 kDa (GRP78), glucose-regulated protein 94 kDa (GRP94), C/EBP homologous protein (CHOP), endoplasmic reticulum protein 44 (ERP44), protein disulfide-isomerase like protein (ERP57) and protein disulfide isomerase family A member 4 (ERP72) in diaphragm muscles were measured using reverse transcription‑quantitative polymerase chain reaction and western blot analysis. The level of cleaved caspase-12 was analyzed by western blot analysis. The results demonstrated that sepsis increased lung W/D. H&E staining revealed that sepsis caused alveolar congestion, hemorrhage and rupture. Swollen and distended ER was observed using electron microscopy during sepsis and decreased diaphragm contractile function was also observed. The expression levels of ER stress markers (GRP78, GRP94, CHOP, ERP44, ERP57 and ERP72) and the level of cleaved caspase‑12 were significantly elevated in septic rats compared with control rats, particularly in the 48 h group. In conclusion, the present study indicated that weakened diaphragm contraction and damaged ER in septic rats was associated with increased expression of ER stress markers.

Adiponectin protects the rats liver against chronic intermittent hypoxia induced injury through AMP-activated protein kinase pathway

This study was performed to assess the effect of chronic intermittent hypoxia (CIH) on the liver, the associated mechanisms and the potential therapeutic roles of adiponectin (Ad). Sixty rats were randomly assigned to four groups: the normal control (NC), NC and Ad supplement (NC + Ad), CIH, and CIH and Ad supplement (CIH + Ad) groups. The rats in the CIH and CIH + Ad groups were exposed to a hypoxic environment for 4 months. Rats in the NC + Ad and CIH + Ad groups were also treated with an intravenous injection of Ad (10 ug), twice a week. The plasma levels of hepatic enzymes, serum triglyceride, liver triglyceride, fasting blood glucose and hepatic cell apoptosis in hepatic tissue, were higher in the CIH group than in the NC and NC + Ad groups. However, the Ad supplementation in the CIH + Ad group rescued the hepatic tissue insult by activating the AMP-activated protein kinase (AMPK) pathway. In conclusion, Ad could protect against CIH-induced hepatic injury partly through the AMPK pathway.

Hypoxia in Atherogenesis

The anoxemia theory proposes that an imbalance between the demand for and supply of oxygen in the arterial wall is a key factor in the development of atherosclerosis. There is now substantial evidence that there are regions within the atherosclerotic plaque in which profound hypoxia exists; this may fundamentally change the function, metabolism, and responses of many of the cell types found within the developing plaque and whether the plaque will evolve into a stable or unstable phenotype. Hypoxia is characterized in molecular terms by the stabilization of hypoxia-inducible factor (HIF) 1α, a subunit of the heterodimeric nuclear transcriptional factor HIF-1 and a master regulator of oxygen homeostasis. The expression of HIF-1 is localized to perivascular tissues, inflammatory macrophages, and smooth muscle cells adjacent to the necrotic core of atherosclerotic lesions and regulates several genes that are important to vascular function including vascular endothelial growth factor, nitric oxide synthase, endothelin-1, and erythropoietin. This review summarizes the effects of hypoxia on the functions of cells involved in atherogenesis and the evidence for its potential importance from experimental models and clinical studies.

C1 inhibitor-mediated myocardial protection from chronic intermittent hypoxia-induced injury

The optimal treatment for chronic intermittent hypoxia (CIH)-induced cardiovascular injuries has yet to be determined. The aim of the current study was to explore the potential protective effect and mechanism of a C1 inhibitor in CIH in the myocardium. The present study used a rat model of CIH in which complement regulatory protein, known as C1 inhibitor (C1INH), was administered to the rats in the intervention groups. Cardiomyocyte apoptosis was detected by terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling. The expression of proteins associated with the apoptotic pathway, such as B-cell lymphoma 2 (Bcl-2), Bax and caspase-3 were detected by western blot analysis. The expression of complement C3 protein and RNA were also analyzed. C1INH was observed to improve the cardiac function in rats with CIH. Myocardial myeloperoxidase activity, a marker of neutrophil infiltration, was significantly decreased in the C1INH intervention group compared with the CIH control group, and cardiomyocyte apoptosis was significantly attenuated (P<0.05). Western blotting and reverse transcription-polymerase chain reaction analysis indicated that the protein expression levels of Bcl-2 were decreased and those of Bax were increased in the CIH group compared with the normal control group, but the protein expression levels of Bcl-2 were increased and those of Bax were decreased in the C1INH intervention group, as compared with the CIH group. Furthermore, the CIH-induced expression and synthesis of complement C3 in the myocardium were also reduced in the C1INH intervention group. C1INH, in addition to inhibiting complement activation and inflammation, preserved cardiac function in CIH-mediated myocardial cell injury through an anti-apoptotic mechanism.