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

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.

Chronic intermittent hypoxia induces cardiac hypertrophy by impairing autophagy through the adenosine 5'-monophosphate-activated protein kinase pathway

Autophagy is tightly regulated to maintain cardiac homeostasis. Impaired autophagy is closely associated with pathological cardiac hypertrophy. However, the relationship between autophagy and cardiac hypertrophy induced by chronic intermittent hypoxia (CIH) is not known. In the present study, we measured autophagy-related genes and autophagosomes during 10 weeks of CIH in rats, and 6 days in H9C2 cardiomyocytes, and showed that autophagy was impaired. This conclusion was confirmed by the autophagy flux assay. We detected significant hypertrophic changes in myocardium with impaired autophagy. Rapamycin, an autophagy enhancer, attenuated the cardiac hypertrophy induced by CIH. Moreover, silencing autophagy-related gene 5 (ATG5) exerted the opposite effect. The role of adenosine monophosphate-activated protein kinase (AMPK) in regulating autophagy under CIH was confirmed using AICAR to upregulate this enzyme and restore autophagy flux. Restoring autophagy by AICAR or rapamycin significantly reversed the hypertrophic changes in cardiomyocytes. To investigate the mechanism of autophagy impairment, we compared phospho (p)-AMPK, p-Akt, cathepsin D, and NFAT3 levels, along with calcineurin activity, between sham and CIH groups. CIH activated calcineurin, and inhibited AMPK and AMPK-mediated autophagy in an Akt- and NFAT3-independent manner. Collectively, these data demonstrated that impaired autophagy induced by CIH through the AMPK pathway contributed to cardiac hypertrophy.

Oxalicumone A, a new dihydrothiophene-condensed sulfur chromone induces apoptosis in leukemia cells through endoplasmic reticulum stress pathway

Oxalicumone A (POA1), a novel dihydrothiophene-condensed sulfur chromone isolated from the marine fungus Penicillium oxalicum SCSGAF 0023, showed cytotoxicity against several cancer cells previously. In this study, its anti-cancer activity and underlying mechanism of this action were investigated in leukemia cells like KG-1a, HL60, U937, and K562. The results showed that POA1 inhibited dose-/time-dependently cell growth and induced apoptosis in leukemia cells. Also, POA1 caused cleavages of caspase-3, 8, 9 and PARP1, loss of mitochondrial membrane potential, up-regulations of phosphorylated p38 and JNK, and activation of endoplasmic reticulum stress (ER stress). Furthermore, 4-PBA (an ER stress inhibitor) but not SP600125 and SB203580 (JNK and p38 inhibitor, respectively) could largely inhibit POA1-induced growth suppression. Additionally, 4-PBA obstructed mitochondrial depolarization and cleavage of PARP1. These data suggested that ER stress pathway might be an important mediator in POA1-induced apoptosis. In conclusion, POA1 may have antitumor effects in leukemia cells through the induction of ER stress pathway.

Adiponectin protects the kidney against chronic intermittent hypoxia-induced injury through inhibiting endoplasmic reticulum stress

PURPOSE

The current study was carried out to assess the effects of chronic intermittent hypoxia (CIH) on the kidney, the intervention roles of adiponectin (Ad), and the associated mechanisms.

METHODS

Sixty Wistar rats were randomly divided into four groups: the normal control (NC), normal control plus Ad supplement (NC + Ad), CIH, and CIH plus Ad supplement (CIH + Ad) groups. The rats in both CIH and CIH + Ad groups were submitted to a CIH environment for 4 months, while the rats in NC and NC + Ad groups were housed with the normal air for 4 months. In addition, the rats in NC + Ad and CIH + Ad groups were treated with an intravenous injection of Ad at a dosage of 10 μg per injection, twice a week, for four successive months.

RESULTS

The production level of reactive oxygen species (ROS) and the protein levels of endoplasmic reticulum (ER) stress, as well as the cell apoptosis level in kidney, were all higher in the CIH group than in the NC and NC + Ad groups (all p < 0.05). However, the ROS production, the protein of ER stress, and cell apoptosis levels in kidney were all lower in the CIH + Ad group than those in the CIH group (all p < 0.05).

CONCLUSION

Ad could protect against CIH-induced renal cell apoptosis through inhibiting ROS-related ER stress.

Endoplasmic reticulum stress as a novel inducer of hypoxia inducible factor-1 activity: its role in the susceptibility to myocardial ischemia-reperfusion induced by chronic intermittent hypoxia

BACKGROUND

Obstructive sleep apnea (OSA) is a highly prevalent disease and a risk factor for myocardial infarction expansion in humans. Intermittent hypoxia (IH) is known to be the most important OSA feature in terms of cardiovascular morbi-mortality. Since ER stress and HIF-1 are known to be involved in cardiomyocyte life or death, this study investigates the role of ER stress on HIF-1 activation in myocardial susceptibility to ischemia-reperfusion (I/R) induced by IH.

METHODS

C57Bl6J, HIF-1α(+/-) and their respective control mice were exposed to 14 days of IH (21-5% FiO2, 60 scycle, 8h/day). Myocardial inter-organelle calcium exchanges, ER stress and HIF-1 activity were investigated and in vivo I/R was performed to measure infarct size. In additional groups, tauroursodeoxycholic acid (TUDCA, 75 mg·kg(-1)), an ER stress inhibitor, was administered daily during exposure.

RESULTS

In C57Bl6J mice, chronic IH induced an increase in ER-Ca(2+) content, ER stress markers and HIF-1 activity, associated with an enhanced infarct size (33.7 ± 9.4 vs. 61.0 ± 5.6% in N and IH, respectively, p<0.05). IH failed to increase infarct size in HIF-1α deficient mice (42.4 ± 2.7 and 24.7 ± 3.4% N and IH, respectively). Finally, TUDCA totally abolished the IH-induced increase in HIF-1 activity (1.3 ± 0.04 vs. 0.14 ± 0.02 fold increase in IH vs. IH-TUDCA respectively, p<0.0001) and in infarct size (55.5 ± 7.6 vs. 49.9 ± 3.0 in N-TUDCA and IH-TUDCA, respectively).

CONCLUSION

This novel regulatory mechanism of HIF-1 activity by ER stress should be considered as a potential diagnostic tool for cardiovascular complications in OSA patients as well as a therapeutic target to limit myocardial ischemic damage.

High-intensity training reduces intermittent hypoxia-induced ER stress and myocardial infarct size

Chronic intermittent hypoxia (IH) is described as the major detrimental factor leading to cardiovascular morbimortality in obstructive sleep apnea (OSA) patients. OSA patients exhibit increased infarct size after a myocardial event, and previous animal studies have shown that chronic IH could be the main mechanism. Endoplasmic reticulum (ER) stress plays a major role in the pathophysiology of cardiovascular disease. High-intensity training (HIT) exerts beneficial effects on the cardiovascular system. Thus, we hypothesized that HIT could prevent IH-induced ER stress and the increase in infarct size. Male Wistar rats were exposed to 21 days of IH (21-5% fraction of inspired O2, 60-s cycle, 8 h/day) or normoxia. After 1 wk of IH alone, rats were submitted daily to both IH and HIT (2 × 24 min, 15-30m/min). Rat hearts were either rapidly frozen to evaluate ER stress by Western blot analysis or submitted to an ischemia-reperfusion protocol ex vivo (30 min of global ischemia/120 min of reperfusion). IH induced cardiac proapoptotic ER stress, characterized by increased expression of glucose-regulated protein kinase 78, phosphorylated protein kinase-like ER kinase, activating transcription factor 4, and C/EBP homologous protein. IH-induced myocardial apoptosis was confirmed by increased expression of cleaved caspase-3. These IH-associated proapoptotic alterations were associated with a significant increase in infarct size (35.4 ± 3.2% vs. 22.7 ± 1.7% of ventricles in IH + sedenary and normoxia + sedentary groups, respectively, P < 0.05). HIT prevented both the IH-induced proapoptotic ER stress and increased myocardial infarct size (28.8 ± 3.9% and 21.0 ± 5.1% in IH + HIT and normoxia + HIT groups, respectively, P = 0.28). In conclusion, these findings suggest that HIT could represent a preventive strategy to limit IH-induced myocardial ischemia-reperfusion damages in OSA patients.

A novel endoplasmic reticulum stress‑induced apoptosis model using tunicamycin in primary cultured neonatal rat cardiomyocytes

Endoplasmic reticulum (ER) stress is key in the development of cardiovascular diseases. However, there is a lack of a systemic ER stress‑induced cardiomyocyte apoptosis model. In the present study, primary cultured neonatal rat cardiomyocytes were exposed to tunicamycin. Cell viability was determined by an MTT assay, and cell damage was detected by a lactose dehydrogenase assay. Flow cytometry was used and the activity of caspase‑3 was analyzed in order to measure apoptosis. Reverse transcription-quantitative polymerase chain reaction and western blotting were used to examine the expression of glucose‑regulated protein 78‑kDa (GRP78) and C/EBP homologous protein (CHOP). As a result, tunicamycin significantly increased cardiomyocyte injury, which occurred in a time- and concentration‑dependent manner. In addition, tunicamycin treatment resulted in apoptosis of cardiomyocytes. Molecularly, tunicamycin (100 ng/ml) increased the levels of GRP78 and CHOP 6 h after administration. In addition, GRP78 and CHOP reached maximum mRNA and protein levels 24 h after administration. In conclusion, the results implicate that the tunicamycin‑induced ER stress‑induced apoptotic model was successfully constructed in cultured neonatal rat cardiomyocytes. A 100 ng/ml concentration of tunicamycin was selected, and MTT, LDH release and flow cytometry assay was at 72 h. In addition, GRP78 and GRP94 were detected 24 h following administration. The results of the present study indicate a novel experimental basis for the investigation of ERS-induced cardiac apoptosis.

Alterations in left ventricular function during intermittent hypoxia: Possible involvement of O-GlcNAc protein and MAPK signaling

Obstructive sleep apnea, characterized by recurrent episodes of hypoxia [intermittent hypoxia (IH)], has been identified as a risk factor for cardiovascular diseases. The O-linked β-N-acetylglucosamine (O-GlcNAc) modification (O-GlcNAcylation) of proteins has important regulatory implications on the pathophysiology of cardiovascular disorders. In this study, we examined the role of O-GlcNAcylation in cardiac architecture and left ventricular function following IH. Rats were randomly assigned to a normoxia and IH group (2 min 21% O₂; 2 min 6–8% O₂). Left ventricular function, myocardial morphology and the levels of signaling molecules were then measured. IH induced a significant increase in blood pressure, associated with a gradually abnormal myocardial architecture. The rats exposed to 2 or 3 weeks of IH presented with augmented left ventricular systolic and diastolic function, which declined at week 4. Consistently, the O-GlcNAc protein and O-GlcNAcase (OGA) levels in the left ventricular tissues steadily increased following IH, reaching peak levels at week 3. The O-GlcNAc transferase (OGT), extracellular signal-regulated kinase 1/2 (ERK1/2) and the p38 mitogen-activated protein kinase (p38 MAPK) phosphorylation levels were affected in an opposite manner. The phosphorylation of calcium/calmodulin-dependent protein kinase II (CaMKII) remained unaltered. In parallel, compared with exposure to normoxia, 4 weeks of IH augmented the O-GlcNAc protein, OGT, phosphorylated ERK1/2 and p38 MAPK levels, accompanied by a decrease in OGA levels and an increase in the levels of myocardial nuclear factor-κB (NF-κB), inflammatory cytokines, caspase-3 and cardiomyocyte apoptosis. Taken together, our suggest a possible involvement of O-GlcNAc protein and MAPK signaling in the alterations of left ventricular function and cardiac injury following IH.

The ER stress-mediated mitochondrial apoptotic pathway and MAPKs modulate tachypacing-induced apoptosis in HL-1 atrial myocytes

Background and Object

Cell apoptosis is a contributing factor in the initiation, progression and relapse of atrial fibrillation (AF), a life-threatening illness accompanied with stroke and heart failure. However, the regulatory cascade of apoptosis is intricate and remains unidentified, especially in the setting of AF. The aim of this study was to explore the roles of endoplasmic reticulum (ER) stress, mitochondrial apoptotic pathway (MAP), mitogen-activated protein kinases (MAPKs), and their cross-talking in tachypacing-induced apoptosis.

Methods and Results

HL-1 cells were cultured in the presence of tachypacing for 24 h to simulate atrial tachycardia remodeling. Results showed that tachypacing reduced cell viability measured by the cell counting kit-8, dissipated mitochondrial membrane potential detected by JC-1 staining and resulted in approximately 50% apoptosis examined by Hoechst staining and annexin V/propidium iodide staining. In addition, the proteins involved in ER stress, MAP and MAPKs were universally up-regulated or activated via phosphorylation, as confirmed by western blotting; and reversely silencing of ER stress, caspase-3 (the ultimate executor of MAP) and MAPKs with specific inhibitors prior to pacing partially alleviated apoptosis. An inhibitor of ER stress was applied to further investigate the responses of mitochondria and MAPKs to ER stress, and results indicated that suppression of ER stress comprehensively but incompletely attenuated the activation of MAP and MAPKs aroused by tachypacing, with the exception of ERK1/2, one branch of MAPKs.

Conclusions

Our study suggested tachypacing-induced apoptosis is regulated by ER stress-mediated MAP and MAPKs. Thus, the above three components are all promising anti-apoptotic targets in AF patients and ER stress appears to play a dominant role due to its comprehensive effects.

Adiponectin as a potential biomarker of vascular disease

The increasing prevalence of diabetes and its complications heralds an alarming situation worldwide. Obesity-associated changes in circulating adiponectin concentrations have the capacity to predict insulin sensitivity and are a link between obesity and a number of vascular diseases. One obvious consequence of obesity is a decrease in circulating levels of adiponectin, which are associated with cardiovascular disorders and associated vascular comorbidities. Human and animal studies have demonstrated decreased adiponectin to be an independent risk factor for cardiovascular disease. However, in animal studies, increased circulating adiponectin alleviates obesity-induced endothelial dysfunction and hypertension, and also prevents atherosclerosis, myocardial infarction, and diabetic cardiac tissue disorders. Further, metabolism of a number of foods and medications are affected by induction of adiponectin. Adiponectin has beneficial effects on cardiovascular cells via its antidiabetic, anti-inflammatory, antioxidant, antiapoptotic, antiatherogenic, vasodilatory, and antithrombotic activity, and consequently has a favorable effect on cardiac and vascular health. Understanding the molecular mechanisms underlying the regulation of adiponectin secretion and signaling is critical for designing new therapeutic strategies. This review summarizes the recent evidence for the physiological role and clinical significance of adiponectin in vascular health, identification of the receptor and post-receptor signaling events related to the protective effects of the adiponectin system on vascular compartments, and its potential use as a target for therapeutic intervention in vascular disease.

Factors affecting high-sensitivity cardiac troponin T elevation in Japanese metabolic syndrome patients

PURPOSE

The blood concentration of cardiac troponin T (ie, high-sensitivity cardiac troponin T [hs-cTnT]), measured using a highly sensitive assay, represents a useful biomarker for evaluating the pathogenesis of heart failure or predicting cardiovascular events. However, little is known about the clinical significance of hs-cTnT in metabolic syndrome. The aim of this study was to examine the factors affecting hs-cTnT elevation in Japanese metabolic syndrome patients.

PATIENTS AND METHODS

We enrolled 258 metabolic syndrome patients who were middle-aged males without a history of cardiovascular events. We examined relationships between hs-cTnT and various clinical parameters, including diagnostic parameters of metabolic syndrome.

RESULTS

There were no significant correlations between hs-cTnT and diagnostic parameters of metabolic syndrome. However, hs-cTnT was significantly correlated with age (P<0.01), blood concentrations of brain natriuretic peptide (P<0.01), reactive oxygen metabolites (markers of oxidative stress, P<0.001), and the cardio-ankle vascular index (marker of arterial function, P<0.01). Furthermore, multiple regression analysis revealed that these factors were independent variables for hs-cTnT as a subordinate factor.

CONCLUSION

The findings of this study indicate that in vivo oxidative stress and abnormality of arterial function are closely associated with an increase in hs-cTnT concentrations in Japanese metabolic syndrome patients.

Telmisartan attenuates myocardial apoptosis induced by chronic intermittent hypoxia in rats: modulation of nitric oxide metabolism and inflammatory mediators

PURPOSE

NO and NO synthase (NOS) are known to play key roles in the development of myocardial apoptosis induced by ischemia/hypoxia. Current evidence suggests that angiotensin II type 1 receptor blockers, such as telmisartan, lower blood pressure and produce beneficial regulatory effects on NO and NOS. Here, we examined the protective role of telmisartan in myocardial apoptosis induced by chronic intermittent hypoxia (CIH).

METHODS

Adult male Sprague-Dawley rats were subjected to 8 h of intermittent hypoxia/day, with/without telmisartan for 8 weeks. Myocardial apoptosis, NO and NOS activity, and levels of inflammatory mediators and radical oxygen species were determined.

RESULTS

Treatment with telmisartan preserved endothelial NOS expression and inhibited inducible NOS and excessive NO generation, while reducing oxidation/nitration stress and inflammatory responses. Administration of telmisartan before CIH significantly ameliorated the CIH-induced myocardial apoptosis.

CONCLUSIONS

This study show that pre-CIH telmisartan administration ameliorated myocardial injury following CIH by attenuating CIH-induced myocardial apoptosis via regulation of NOS activity and inhibition of excessive NO generation, oxidation/nitration stress, and inflammatory responses.

Adiponectin protects rat heart from left ventricular remodeling induced by chronic intermittent hypoxia via inhibition of TGF-β/smad2/3 pathway

OBJECTIVE

Obstructive sleep apnea syndrome (OSAS) is associated with many cardiovascular disorders. Chronic intermittent hypoxia (CIH) is the primary player in OSAS of the many associated factors. This study was in order to investigate the effects of the Adiponectin (Ad) on left ventricular remodeling induced by CIH.

METHODS

Forty-five rats were randomly divided into three groups: normal control (NC) group, CIH group and CIH plus Ad supplemented (CIH + Ad) group. After 35 days' CIH exposure, masson analysis was used to detect the left ventricular fibrosis and western blot was used to measure the protein expression of collagen I, collagen III and TGF-β/smad2/3 pathway. Gene analysis by RT-PCR was used to study the MMP2 and TIMP2.

RESULTS

After CIH exposure, the fibrosis of left ventricular in CIH group was significantly remarkable than that in both NC and CIH + Ad groups (P<0.05), although statistical difference existed between NC and CIH + Ad groups (P<0.05). In addition, the protein expression of collagen I as well as collagen III and the ratio of mRNA levels of MMP2/TIMP2 were the highest in CIH group but the lowest in NC group, with CIH + Ad group in between. There was a significant difference among three groups (all P<0.05). The TGF-β/smad2/3 pathway was activated obviously in CIH group, but less noticeably in CIH + Ad group (P<0.05) with a significant difference in the two groups.

CONCLUSIONS

The present study showed that Ad could ameliorate the left ventricular remodeling induced by CIH via inhibition of the expression of TGF-β/smad2/3 pathway.

Chronic obstructive sleep apnea causes atrial remodeling in canines: mechanisms and implications

Obstructive sleep apnea (OSA) is closely related to atrial fibrillation (AF). However, the roles and mechanisms of chronic OSA in atrial remodeling are still unclear. Canine model of chronic OSA was simulated by stopping the ventilator and closing the airway for 4 h per day and lasting for 12 weeks. AF inducibility and duration was increased while atrial effective refractory period (AERP) was shortened after chronic apnea. Meanwhile, upregulation of proteins encoding inward rectifier K(+) current (IK1), delayed rectifier K(+) current (IKr and IKs), acetylcholine activated K(+) current (IKACh), transient outward K(+) current (Ito) and ultra-rapid delayed rectifier potassium current (IKur) as well as downregulation of protein encoding L-type Ca(2+) current (ICa,L) were found after chronic OSA. Besides abnormal electrical activity, chronic OSA induced apoptosis and interstitial fibrosis of atrial myocytes, which was partly mediated by caspase 9, phosphorylation of extracellular-regulated kinase 1/2, and α-smooth muscle actin. In addition, atrial sympathetic and parasympathetic hyperinnervation were found manifesting by enhanced growth-associated protein 43, tyrosine hydroxylase and elevated choline acetyltransferase. Moreover, protein expression of β1, β2, and M2 receptor were markedly increased by chronic OSA. In summary, we firstly demonstrated in canine model that chronic OSA could shorten AERP and lead to altered expression of important channel proteins, moreover, induce atrial structure remodeling by increased atrial apoptosis, fibrosis, and autonomic remodeling, eventually promoting the development of a substrate of AF. Our findings suggested that reversing atrial remodeling might be a potential therapeutic strategy for OSA-induced AF.