Intermittent-hypoxia induced autophagy attenuates contractile dysfunction and myocardial injury in rat heart

Optimizing myocardial cell protection with xanthine derivative KMUP-3 potentiates autophagy through the PI3K/Akt/eNOS axis

BACKGROUND

Autophagy can have either beneficial or detrimental effects on various heart diseases. Pharmacological interventions improve cardiac function, which is correlated with enhanced autophagy. To assess whether a xanthine derivative (KMUP-3) treatment coincides with enhanced autophagy while also providing cardio-protection, we investigated the hypothesis that KMUP-3 treatment activation of autophagy through PI3K/Akt/eNOS signalling offered cardioprotective properties.

METHODS

The pro-autophagic effect of KMUP-3 was performed in a neonatal rat model targeting cardiac fibroblasts and cardiomyocytes, and by assessing the impact of KMUP-3 treatment on cardiotoxicity, we used antimycin A-induced cardiomyocytes.

RESULTS

As determined by transmission electron microscopy observation, KMUP-3 enhanced autophagosome formation in cardiac fibroblasts. Furthermore, KMUP-3 significantly increased the expressions of autophagy-related proteins, LC3 and Beclin-1, both in a time- and dose-dependent manner; moreover, the pro-autophagy and nitric oxide enhancement effects of KMUP-3 were abolished by inhibitors targeting eNOS and PI3K in cardiac fibroblasts and cardiomyocytes. Notably, KMUP-3 ameliorated cytotoxic effects induced by antimycin A, demonstrating its protective autophagic response.

CONCLUSION

These findings enable the core pathway of PI3K/Akt/eNOS axis in KMUP-3-enhanced autophagy activation and suggest its principal role in safeguarding against cardiotoxicity.

Mitochondrial dysfunction and skeletal muscle atrophy: Causes, mechanisms, and treatment strategies

Skeletal muscle, which accounts for approximately 40% of total body weight, is one of the most dynamic and plastic tissues in the human body and plays a vital role in movement, posture and force production. More than just a component of the locomotor system, skeletal muscle functions as an endocrine organ capable of producing and secreting hundreds of bioactive molecules. Therefore, maintaining healthy skeletal muscles is crucial for supporting overall body health. Various pathological conditions, such as prolonged immobilization, cachexia, aging, drug-induced toxicity, and cardiovascular diseases (CVDs), can disrupt the balance between muscle protein synthesis and degradation, leading to skeletal muscle atrophy. Mitochondrial dysfunction is a major contributing mechanism to skeletal muscle atrophy, as it plays crucial roles in various biological processes, including energy production, metabolic flexibility, maintenance of redox homeostasis, and regulation of apoptosis. In this review, we critically examine recent knowledge regarding the causes of muscle atrophy (disuse, cachexia, aging, etc.) and its contribution to CVDs. Additionally, we highlight the mitochondrial signaling pathways involvement to skeletal muscle atrophy, such as the ubiquitin-proteasome system, autophagy and mitophagy, mitochondrial fission-fusion, and mitochondrial biogenesis. Furthermore, we discuss current strategies, including exercise, mitochondria-targeted antioxidants, in vivo transfection of PGC-1α, and the potential use of mitochondrial transplantation as a possible therapeutic approach.

Effect of renal denervation on cardiac remodelling and function in rats with chronic intermittent hypoxia

Chronic intermittent hypoxia (CIH) mimicking obstructive sleep apnea elicits divergent outcomes in the cardiovascular systems. The effect of renal denervation (RDN) on the heart during CIH remains unclear. We aimed to explore the effect of RDN on cardiac remodelling in rats exposed to CIH and to discuss the underlying mechanisms. Adult Sprague Dawley rats were divided into four groups: control, control+RDN, CIH (CIH exposure for 6 weeks, nadir of 5%-7% to peak of 21% O2, 20 cycles/h, 8 h/day) and CIH+ RDN group. Echocardiography, cardiac fibrosis, left ventricle (LV) expressions of nuclear factor-E2-related factor 2 (Nrf2)/heme oxygenase-1 (HO-1) pathway and inflammatory factors were tested at the end of the study. Cardiac structural remodelling and dysfunction were induced by CIH and attenuated by RDN. Myocardial fibrosis was more severe in the CIH group than in the control group and improved in the CIH + RDN group. Sympathetic activity reflected by tyrosine hydroxylase (TH) expression and noradrenaline were significantly elevated after CIH but blunted by RDN. CIH downregulated LV protein expressions of Nrf2 and HO-1, which was activated by RDN. The downstream of Nrf2/HO-1, such as NQO1 and SOD expression, elevated following RDN. RDN also decreased the mRNA expression of IL-1β and IL-6. Notably, control+RDN did not affect cardiac remodelling and Nrf2/HO-1 compared with the control. Taken together, we found that RDN exerted cardio-protective effects in a rat model of CIH involving Nrf2/HO-1 pathway and inflammation.

Autophagy impairment in patients with obstructive sleep apnea modulates intermittent hypoxia-induced oxidative stress and cell apoptosis via hypermethylation of the ATG5 gene promoter region

BACKGROUND

Autophagy is a catabolic process that recycles damaged organelles and acts as a pro-survival mechanism, but little is known about autophagy dysfunction and epigenetic regulation in patients with obstructive sleep apnea (OSA).

METHODS

Protein/gene expressions and DNA methylation levels of the autophagy-related genes (ATG) were examined in blood leukocytes from 64 patients with treatment-naïve OSA and 24 subjects with primary snoring (PS).

RESULTS

LC3B protein expression of blood monocytes, and ATG5 protein expression of blood neutrophils were decreased in OSA patients versus PS subjects, while p62 protein expression of cytotoxic T cell was increased, particularly in those with nocturia. ATG5, ULK1, and BECN1 gene expressions of peripheral blood mononuclear cells were decreased in OSA patients versus PS subjects. LC3B gene promoter regions were hypermethylated in OSA patients, particularly in those with excessive daytime sleepiness, while ATG5 gene promoter regions were hypermethylated in those with morning headache or memory impairment. LC3B protein expression of blood monocytes and DNA methylation levels of the LC3B gene promoter region were negatively and positively correlated with apnea hyponea index, respectively. In vitro intermittent hypoxia with re-oxygenation exposure to human THP-1/HUVEC cell lines resulted in LC3B/ATG5/ULK1/BECN1 down-regulations and p62 up-regulation along with increased apoptosis and oxidative stress, while rapamycin and umbilical cord-mesenchymal stem cell treatment reversed these abnormalities through de-methylation of the ATG5 gene promoter.

CONCLUSIONS

Impaired autophagy activity in OSA patients was regulated by aberrant DNA methylation, correlated with clinical phenotypes, and contributed to increased cell apoptosis and oxidative stress. Autophagy enhancers may be novel therapeutics for OSA-related neurocognitive dysfunction.

Metabolic dysregulation and decreased capillarization in skeletal muscles of male adolescent offspring rats exposed to gestational intermittent hypoxia

Gestational intermittent hypoxia (IH) is a hallmark of obstructive sleep apnea that occurs frequently during pregnancy, and effects caused by this environmental change during pregnancy may be transmitted to the offspring. In this study, we aimed to clarify the effects of IH in pregnant rats on the skeletal muscle of adolescent offspring rats. Mother rats underwent IH from gestation day 7-21, and their 5-weeks-old male offspring were analyzed. All male offspring rats were born and raised under normoxia conditions. Although no general growth retardation was observed, we found that exposure to gestational IH reduces endurance running capacity of adolescent offspring rats. Both a respiratory muscle (diaphragm; DIA) and a limb muscle (tibialis anterior; TA) showed no histological abnormalities, including fiber size and fiber type distribution. To identify the possible mechanism underlying the reduced running capacity, regulatory factors associated with energy metabolism were analyzed in different parts of skeletal muscles. Compared with rats born under conditions of gestational normoxia, gestational IH offspring rats showed significantly lower expression of genes associated with glucose and lipid metabolism, and lower protein levels of phosphorylated AMPK and AKT. Furthermore, gene expression of adiponectin receptors one and two was significantly decreased in the DIA and TA muscles. In addition, the DIA muscle from adolescent rats had significantly decreased capillary density as a result of gestational IH. However, these changes were not observed in a sucking muscle (geniohyoid) and a masticating muscle (masseter) of these rats. These results suggest that respiratory and limb muscles are vulnerable to gestational IH, which induces altered energy metabolism with decreased aerobic motor function. These changes were partially owing to the decreased expression of adiponectin receptors and decreased capillary density in adolescent offspring rats.

Selective β2-Adrenoceptor Blockade Rescues Mandibular Growth Retardation in Adolescent Rats Exposed to Chronic Intermittent Hypoxia

Activation of the sympathoadrenal system is associated with sleep apnea-related symptoms and metabolic dysfunction induced by chronic intermittent hypoxia (IH). IH can induce hormonal imbalances and growth retardation of the craniofacial bones. However, the relationship between IH and β2-adrenergic receptor signaling in the context of skeletal growth regulation is unclear. This study aimed to investigate the role of β2-adrenergic receptors in IH-induced mandibular growth retardation and bone metabolic alterations. Male 7-week-old Sprague–Dawley rats were subjected to IH for 3 weeks. IH conditions were established using original customized hypoxic chambers; IH was induced at a rate of 20 cycles per hour (oxygen levels changed from 4 to 21% in one cycle) for 8 h per day during the 12 h “lights on” period. The rats received intraperitoneal administration of a β2-adrenergic antagonist (butoxamine) or saline. To exclude dietary effects on general growth, the normoxic rats with saline, normoxic rats with butoxamine, and IH rats with butoxamine were subjected to food restriction to match the body weight gains between IH and other three groups. Body weight, heart rate, blood pressure, and plasma concentrations of leptin, serotonin, and growth hormone were measured. Bone growth and metabolism were evaluated using radiography, microcomputed tomography, and immunohistochemical staining. Plasma leptin levels were significantly increased, whereas that of serotonin and growth hormone were significantly decreased following IH exposure. Leptin levels recovered following butoxamine administration. Butoxamine rescued IH-induced mandibular growth retardation, with alterations in bone mineral density at the condylar head of the mandible. Immunohistochemical analysis revealed significantly lower expression levels of receptor activator of nuclear factor-kappa B ligand (RANKL) in the condylar head of IH-exposed rats. Conversely, recovery of RANKL expression was observed in IH-exposed rats administered with butoxamine. Collectively, our findings suggest that the activation of β2-adrenergic receptors and leptin signaling during growth may be involved in IH-induced skeletal growth retardation of the mandible, which may be mediated by concomitant changes in RANKL expression at the growing condyle.

Intermittent hypoxia-induced autophagy via AMPK/mTOR signaling pathway attenuates endothelial apoptosis and dysfunction in vitro

PURPOSE

The aim of this study was to examine whether or not intermittent hypoxia (IH) upregulated autophagy and the contributions of autophagy to endothelial apoptosis and dysfunction in human umbilical vein endothelial cells (HUVECs).

METHOD

HUVECs were incubated under normoxia and IH conditions. After 3-, 6-, 12-, and 24-h exposure, the autophagic vacuoles and autophagosomes were observed by transmission electron microscopy and monodansylcadaverine staining. The protein levels of autophagy-related biomarkers and AMPK/mTOR pathway were measured by Western blot. The apoptosis-related proteins and the percentage of apoptotic cells were evaluated by Western blot and flow cytometry, respectively, while the levels of endothelial function biomarkers were assessed by ELISA.

RESULTS

IH induced autophagy, as determined by the increased numbers of the autophagic vacuoles, autophagosomes, and by the elevated levels of Beclin-1 protein, the LC3II/LC3I ratio, and p62 degradation. IH-induced autophagic flux peaked at 12-h duration and weakened at 24 h. IH increased the ratio of p-AMPK/AMPK and decreased the ratio of p-mTOR/mTOR, while compound C restored the alteration. A significant decrease in the Bcl-2 level and the Bcl-2/Bax ratio and a significant increase in the protein expression levels of Bax and cleaved caspase 3 and in the percentage of apoptosis were observed under IH exposure. Moreover, the NO level was reduced, while the ET-1 and VEGF levels were raised under IH condition. These alterations were suppressed by the pretreatment of 3-methyladenine.

CONCLUSIONS

IH upregulates autophagy through AMPK/mTOR pathway in HUVECs in vitro, which might be protective against endothelial apoptosis and dysfunction caused by IH.

The importance of autophagy regulation in obstructive sleep apnea

PURPOSE

Autophagy, the self-renewal process of cells, is dependent on lysosomes to degrade damaged organelles and proteins. The increased or damaged level of autophagy is proven to relate to a number of disorders, including metabolic disorders, malignant tumors, pulmonary diseases, and neurodegenerative disorders. This review aims to examine the effects of autophagy on the pathogenic mechanism of obstructive sleep apnea (OSA) in order to guide relevant disease treatment.

METHODS

We conducted a search of the literature using the electronic database, focusing on articles that explored the association between OSA and autophagy.

CONCLUSION

OSA can induced autophagy through hypoxia, oxidative stress, endoplasmic reticulum stress, endothelial dysfunction, miRNA, etc. We propose that the mechanism of the autophagy in patients with OSA should be eclucidated in further studies.

Nuclear factor kappa B activation in cardiomyocytes by serum of children with obstructive sleep apnea syndrome

Obstructive sleep apnea syndrome (OSA) is associated with cardiovascular morbidity in adults and children. NFκB activity is enhanced in circulating monocytes of adults with OSA, that decreases following positive pressure therapy. OSA children’s serum activates NFκB in a cell line. We hypothesized that OSA children’s serum can activate NFκB in cardiomyocytes (CM) and effect their viability. In order to explore the role played by NFκB in OSA cardiovascular pathophysiology, rat, mouse and human immortalized CM were exposed to human serum drawn from OSA children and matched controls. Increased expression of NFκB classical subunits p65/p50 as well as major morphological changes occurred in cardiomyocytes following OSA’s serum exposure. OSA children’s serum induced NFκB activity as measured by p65 nuclear translocation in immortalized human CM and rat cardiomyocytes as well as dense immunostaining of the nucleus. Trypan blue and XTT assays showed that OSA sera induced CM apoptosis. We conclude that NFκB is systemically activated in cardiomyocytes, who also demonstrate decreased viability and contractility following exposure to OSA serum. It supports the hypothesis NFκB plays a role in the evolution of cardiovascular morbidity in OSA. It may support the search for new therapeutic interventions controlling NFκB activation in OSA.

Intermittent hypoxia induces turbinate mucosal hypertrophy via upregulating the gene expression related to inflammation and EMT in rats

PURPOSE

Chronic intermittent hypoxia (IH) plays a pivotal role in the consequences of obstructive sleep apnea (OSA). It has been demonstrated that IH impairs nasomaxillary complex growth to reduce nasal airway cavity size in rodent models. Although turbinate dysfunction with inflammatory mucosal hypertrophy is related to OSA, the role of IH in turbinate hypertrophy with inflammation-driven fibrosis is unknown. Here, we aimed to clarify the pathogenesis of inflammatory mucosal hypertrophy and epithelial-mesenchymal transition (EMT) in the nasal turbinate under IH.

METHODS

Seven-week-old male Sprague-Dawley rats were exposed to IH (4% O₂ to 21% O₂ with 0% CO₂) at a rate of 20 cycles/h.

RESULTS

Hypertrophy of the turbinate mucosa occurred after 3 weeks, with the turbinate mucosa of the experimental group becoming significantly thicker than in the control group. Immunostaining showed that IH increased the expression of TGFβ and N-cadherin and decreased E-cadherin expression in the turbinate mucosa. Quantitative PCR analysis demonstrated that IH enhanced the expression of not only the inflammatory markers Tnf-a, Il-1b, and Nos2 but also the EMT markers Tgf-b1, Col1a1, and Postn.

CONCLUSIONS

Collectively, these results suggest that IH induced turbinate hypertrophy via upregulation of gene expression related to inflammation and EMT in the nasal mucosa.

Exogenous supplement of glucagon like peptide-1 protects the heart against aortic banding induced myocardial fibrosis and dysfunction through inhibiting mTOR/p70S6K signaling and promoting autophagy

Mammalian target of rapamycin (mTOR) and a ribosomal protein S6 kinase (p70S6K) mediate tissue fibrosis and negatively regulate autophagy. This study aims to investigate whether glucagon-like peptide-1 (GLP-1) analog liraglutide protects the heart against aortic banding-induced cardiac fibrosis and dysfunction through inhibiting mTOR/p70S6K signaling and promoting autophagy activity. Male SD rats were randomly divided into four groups (n = 6/each group): sham operated control; abdominal aortic constriction (AAC); liraglutide treatment during AAC (0.3 mg/kg, injected subcutaneously twice daily); rapamycin treatment during AAC (0.2 mg/kg/day, administered by gastric gavage). Relative to the animals with AAC on week 16, liraglutide treatment significantly reduced heart/body weight ratio, inhibited cardiomyocyte hypertrophy, and augmented plasma GLP-1 level and tissue GLP-1 receptor expression. Phosphorylation of mTOR/p70S6K, populations of myofibroblasts and synthesis of collagen I/III in the myocardium were simultaneously inhibited. Furthermore, autophagy regulating proteins: LC3-II/LC3-I ratio and Beclin-1 were upregulated, and p62 was downregulated by liraglutide. Compared with liraglutide group, treatment with rapamycin, a specific inhibitor of mTOR, compatibly augmented GLP-1 receptor level, inhibited phosphorylation of mTOR/p70S6K and expression of p62 as well as increased level of LC3-II/LC3-I ratio and Beclin-1, suggesting that there is an interaction between GLP-1 and mTOR/p70S6K signaling in the regulation of autophagy. In line with these modifications, treatment with liraglutide and rapamycin significantly reduced perivascular/interstitial fibrosis, and preserved systolic/diastolic function. These results suggest that the inhibitory effects of liraglutide on cardiac fibrosis and dysfunction are potentially mediated by inhibiting mTOR/p70S6K signaling and enhancing autophagy activity.

Cardiac effects and toxicity of chloroquine: a short update

There is currently increased interest in the use of the antimalarial drugs chloroquine and hydroxychloroquine for the treatment of other diseases, including cancer and viral infections such as coronavirus disease 2019 (COVID-19). However, the risk of cardiotoxic effects tends to limit their use. In this review, the effects of these drugs on the electrical and mechanical activities of the heart as well as on remodelling of cardiac tissue are presented and the underlying molecular and cellular mechanisms are discussed. The drugs can have proarrhythmic as well as antiarrhythmic actions resulting from their inhibition of ion channels, including voltage-dependent Na⁺ and Ca²⁺ channels, background and voltage-dependent K⁺ channels, and pacemaker channels. The drugs also exert a vagolytic effect due at least in part to a muscarinic receptor antagonist action. They also interfere with normal autophagy flux, an effect that could aggravate ischaemia/reperfusion injury or post-infarct remodelling. Most of the toxic effects occur at high concentrations, following prolonged drug administration or in the context of drug associations.

Critical examination of mechanisms underlying the reduction in heart failure events with SGLT2 inhibitors: identification of a molecular link between their actions to stimulate erythrocytosis and to alleviate cellular stress

Sodium-glucose co-transporter 2 (SGLT2) inhibitors reduce the risk of serious heart failure events, even though SGLT2 is not expressed in the myocardium. This cardioprotective benefit is not related to an effect of these drugs to lower blood glucose, promote ketone body utilization or enhance natriuresis, but it is linked statistically with their action to increase haematocrit. SGLT2 inhibitors increase both erythropoietin and erythropoiesis, but the increase in red blood cell mass does not directly prevent heart failure events. Instead, erythrocytosis is a biomarker of a state of hypoxia mimicry, which is induced by SGLT2 inhibitors in manner akin to cobalt chloride. The primary mediators of the cellular response to states of energy depletion are sirtuin-1 and hypoxia-inducible factors (HIF-1α/HIF-2α). These master regulators promote the cellular adaptation to states of nutrient and oxygen deprivation, promoting mitochondrial capacity and minimizing the generation of oxidative stress. Activation of sirtuin-1 and HIF-1α/HIF-2α also stimulates autophagy, a lysosome-mediated degradative pathway that maintains cellular homoeostasis by removing dangerous constituents (particularly unhealthy mitochondria and peroxisomes), which are a major source of oxidative stress and cardiomyocyte dysfunction and demise. SGLT2 inhibitors can activate SIRT-1 and stimulate autophagy in the heart, and thereby, favourably influence the course of cardiomyopathy. Therefore, the linkage between erythrocytosis and the reduction in heart failure events with SGLT2 inhibitors may be related to a shared underlying molecular mechanism that is triggered by the action of these drugs to induce a perceived state of oxygen and nutrient deprivation.

Inhibition of Autophagy Signaling via 3-methyladenine Rescued Nicotine-Mediated Cardiac Pathological Effects and Heart Dysfunctions

Rationale: Cigarette smoking is a well-established risk factor for myocardial infarction and sudden cardiac death. The deleterious effects are mainly due to nicotine, but the mechanisms involved and theranostics remain unclear. Thus, we tested the hypothesis that nicotine exposure increases the heart sensitivity to ischemia/reperfusion injury and dysfunction, which can be rescued by autophagy inhibitor.

Methods: Nicotine or saline was administered to adult rats via subcutaneous osmotic minipumps in the absence or presence of an autophagy inhibitor, 3-methyladenine (3-MA). After 30 days of nicotine treatment, the rats underwent the cardiac ischemia/reperfusion (I/R) procedure and echocardiography analysis, and the heart tissues were isolated for molecular biological studies.

Results: Nicotine exposure increased I/R-induced cardiac injury and cardiac dysfunction as compared to the control. The levels of autophagy-related proteins including LC3 II, P62, Beclin1, and Atg5 were upregulated in the reperfused hearts isolated from nicotine-treated group. In addition, nicotine enhanced cardiac and plasma ROS production, and increased the phosphorylation of GSK3β (ser9) in the left ventricle tissues. Treatment with 3-MA abolished nicotine-mediated increase in the levels of autophagy-related proteins and phosphorylation of GSK3β, but had no effect on ROS production. Of importance, 3-MA ameliorated the augmented I/R-induced cardiac injury and dysfunction in the nicotine-treated group as compared to the control.

Conclusion: Our results demonstrate that nicotine exposure enhances autophagy signaling pathway, resulting in development of ischemic-sensitive phenotype of heart. It suggests a potentially novel therapeutic strategy of autophagy inhibition for the treatment of ischemic heart disease.

Autophagy during left ventricular redilation after ventriculoplasty: Insights from a rat model of ischemic cardiomyopathy

OBJECTIVES

Myocardial autophagy has been recognized as an important factor in heart failure. It is not known whether changes in ventricular geometry by left ventriculoplasty influence autophagy in ischemic cardiomyopathy. We hypothesized that myocardial autophagy plays an important role in left ventricular (LV) redilation after ventriculoplasty.

METHODS

Four weeks after ligation of the left anterior descending artery, ventriculoplasty or sham operation was performed. The animals were euthanized at 2 days (early) or 28 days (late) after the second operation. Ventricular autophagy was evaluated by protein expression of microtubule-associated protein light chain 3 II, an autophagosome marker. Cardiomyocyte area was assessed by histologic examination. LV function was evaluated by echocardiography. To examine the implications of autophagy, an autophagy inhibitor (3-methyladenine) was injected intraperitoneally for 3 weeks before sacrifice.

RESULTS

The LV was reduced in size early and redilated late after ventriculoplasty. LV systolic function was improved early and later worsened after ventriculoplasty. Light chain 3 II expression decreased early after ventriculoplasty and increased in the late period. Myocyte area increased from the early to late stage after ventriculoplasty. Autophagic inhibition exaggerated the increased myocyte hypertrophy and LV redilation.

CONCLUSIONS

In a rat model of myocardial infarction, autophagy decreased early after ventriculoplasty and increased again during LV redilation. These results provide new insights into the mechanism underlying the late failure of ventriculoplasty.

Up-regulating autophagy by targeting the mTOR-4EBP1 pathway: a possible mechanism for improving cardiac function in mice with experimental dilated cardiomyopathy

Background

Autophagy plays a crucial role in the pathological process of cardiovascular diseases. However, little is known about the pathological mechanism underlying autophagy regulation in dilated cardiomyopathy (DCM).

Methods

We explored whether up-regulating autophagy could improve cardiac function in mice with experimental DCM through the mTOR-4EBP1 pathway. Animal model of DCM was established in BALB/c mice by immunization with porcine cardiac myosin. Both up- or down-regulation of autophagy were studied by administration of rapamycin or 3-MA in parallel. Morphology, Western blotting, and echocardiography were applied to confirm the pathological mechanisms.

Results

Autophagy was activated and autophagosomes were significantly increased in the rapamycin group. The collagen volume fraction (CVF) was decreased in the rapamycin group compared with the DCM group (9.21 ± 0.82% vs 14.38 ± 1.24%, P < 0.01). The expression of p-mTOR and p-4EBP1 were significantly decreased in rapamycin-induced autophagy activation, while the levels were increased by down-regulating autophagy with 3-MA. In the rapamycin group, the LVEF and FS were significantly increased compared with the DCM group (54.12 ± 6.48% vs 45.29 ± 6.68%, P < 0.01; 26.89 ± 4.04% vs 22.17 ± 2.82%, P < 0.05). As the inhibitor of autophagy, 3-MA aggravated the progress of maladaptive cardiac remodeling and declined cardiac function in DCM mice.

Conclusions

The study indicated a possible mechanism for improving cardiac function in mice with experimental DCM by up-regulating autophagy via the mTOR-4EBP1 pathway, which could be a promising therapeutic strategy for DCM.

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.

Autophagy inhibition plays a protective role against 3, 4-methylenedioxymethamphetamine (MDMA)-induced loss of serotonin transporters and depressive-like behaviors in rats

The 3,4-methylenedioxymethamphetamine (MDMA) is a popular recreational drug, which ultimately leads to serotonergic (5-HT) neurotoxicity and psychiatric disorders. Previous in vitro studies have consistently demonstrated that MDMA provokes autophagic activation, as well as damage of 5-HT axons and nerve fibers. So far, whether autophagy, a well-conserved cellular process that is critical for cell fate, also participates in MDMA-induced neurotoxicity in vivo remains elusive. Here, we first examined time-course of autophagy-related changes during repeated administration of MDMA (10 mg/kg s.c. twice daily for 4 consecutive days) using immunofluorescent staining for tryptophan hydroxylase and microtubule-associated protein 1 light chain 3 beta in rats. We also evaluated the protective effects of 3-methyadanine (3-MA, an autophagy inhibitor, 15 mg/kg i.p.) against MDMA-induced acute and long-term reductions in serotonin transporters (SERT) density in various brain regions using immunohistochemical staining and positron emission tomography (PET) imaging respectively. Plasma corticosterone measurements and forced swim tests were performed to evaluate the depressive performance. The staining results showed that repeated administration of MDMA increased expression of autophagosome and caused reduction in SERT densities of striatum and frontal cortex, which was ameliorated in the presence of 3-MA. PET imaging data also revealed that 3-MA could ameliorate MDMA-induced long-term decreased SERT availability in various brain regions of rats. Furthermore, immobility time of forced swim tests and plasma corticosterone levels were less in the group of MDMA co-injected with 3-MA compared with that of MDMA group. Together, these findings suggest that autophagy inhibition may confer protection against neurobiological and behavioral changes induced by MDMA.

Carvedilol alleviates diabetic cardiomyopathy in diabetic rats

Diabetic cardiomyopathy (DCM) is characterized by structural and functional changes in the myocardium. Several studies have revealed that myocardial apoptosis and fibrosis occur during DCM. Studies have also indicated that oxidative stress may be a major factor associated with the development of DCM. Protein kinase C (PKC)β₂ has been demonstrated to be activated in diabetic rats, and overexpression of PKCβ₂ in the myocardium may result in cardiac hypertrophy and fibrosis. The P66^shc adaptor protein, which is mediated by PKCβ, serves an important role in apoptosis during oxidative stress. The aim of the present study was to investigate whether the PKCβ₂/P66^shc oxidative stress pathway is associated with DCM, and to investigate the role and mechanisms of carvedilol in preserving cardiac function. Experimental diabetic rat models were induced by streptozotocin treatment accompanied by high energy intake. Carvedilol was orally administrated at a dose of 1 or 10 mg/kg/day. Cardiac function was evaluated by serum N-terminal pro-B-type natriuretic peptide level and cardiac ultrasound. Myocardial inflammation, oxidative stress, apoptosis and fibrosis were assessed by histopathological and echocardiographic analyses and tests for oxidative markers. Associated proteins and factors were examined by immunohistochemical and western blot analyses. Rats in the diabetes mellitus group exhibited significantly decreased systolic cardiac function along with elevated expression levels of phosphorylated (p)-PKCβ₂, phos-P66^shc, caspase-3, malondialdehyde, collagen type I, tumor necrosis factor-α and interleukin-1β, which were accompanied by disorder in metabolic processes. Treatment with carvedilol reversed these changes. Thus, the present results suggest that the PKCβ₂/P66^shc signaling pathway may be associated with diabetic cardiomyopathy; furthermore, carvedilol, as a novel β-receptor blocker, may protect the myocardium from injury by suppressing the myocardial inflammatory response, fibrosis, P66^shc-mediated oxidative stress and subsequent apoptosis in myocardial tissue. Consequently, carvedilol may have potential as a therapy for the treatment of DCM.

Hydrogen gas reduces chronic intermittent hypoxia-induced hypertension by inhibiting sympathetic nerve activity and increasing vasodilator responses via the antioxidation

Molecular hydrogen is reported to be used medically to ameliorate various systemic pathological conditions. This study aimed to investigate the effect of hydrogen (H₂ ) gas on hypertension induced by intermittent hypoxia in rats. The adult rats were exposed to chronic intermittent hypoxia (CIH) 8 hours/day for 5 weeks and/or H ₂ gas 2 hours/day. We found that the systolic and diastolic blood pressure (BP) increased significantly in rats exposed to intermittent hypoxia, both of which were markedly attenuated after H treatment. Furthermore, intermittent hypoxia exposure elevated renal sympathetic nerve activity, consistent with plasma norepinephrine. Additionally, H ₂ gas significantly improved CIH-induced abnormal vascular relaxation. Nevertheless, inhalation of H ₂ gas alone did not cause such changes. Moreover, H ₂ gas-treated rats exposed to CIH showed a significant reduction in 8-hydroxy-2 deoxyguanosine content and increases in superoxide dismutase activity, indicating improved oxidative stress. Taken together, these results indicate that H ₂ gas has significant effects on the reduction of BP without any side effects. Mechanistically, inhibition of sympathetic activity and reduction of systemic vascular resistance may participate in this process via the antioxidant activity of H ₂ .

Lysophosphatidic Acid Is Associated With Cardiac Dysfunction and Hypertrophy by Suppressing Autophagy via the LPA3/AKT/mTOR Pathway

Background: Lysophosphatidic acid (LPA), as a phospholipid signal molecule, participates in the regulation of various biological functions. Our previous study demonstrated that LPA induces cardiomyocyte hypertrophy in vitro; however, the functional role of LPA in the post-infarct heart remains unknown. Growing evidence has demonstrated that autophagy is involved in regulation of cardiac hypertrophy. The aim of the current work was to investigate the effects of LPA on cardiac function and hypertrophy during myocardial infarction (MI) and determine the regulatory role of autophagy in LPA-induced cardiomyocyte hypertrophy.

Methods:In vivo experiments were conducted in Sprague-Dawley rats subjected to MI surgery or a sham operation, and rats with MI were assigned to receive an intraperitoneal injection of LPA (1 mg/kg) or vehicle for 5 weeks. The in vitro experiments were conducted in H9C2 cardiomyoblasts.

Results: LPA treatment aggravated cardiac dysfunction, increased cardiac hypertrophy, and reduced autophagy after MI in vivo. LPA suppressed autophagy activation, as indicated by a decreased LC3II-to-LC3I ratio, increased p62 expression, and reduced autophagosome formation in vitro. Rapamycin, an autophagy enhancer, attenuated LPA-induced autophagy inhibition and H9C2 cardiomyoblast hypertrophy, while autophagy inhibition with Beclin1 siRNA did not further enhance the hypertrophic response in LPA-treated cardiomyocytes. Moreover, we demonstrated that LPA suppressed autophagy through the AKT/mTOR signaling pathway because mTOR and PI3K inhibitors significantly prevented LPA-induced mTOR phosphorylation and autophagy inhibition. In addition, we found that knockdown of LPA3 alleviated LPA-mediated autophagy suppression in H9C2 cardiomyoblasts, suggesting that LPA suppresses autophagy through activation of the LPA3 and AKT/mTOR pathways.

Conclusion: These findings suggest that LPA plays an important role in mediating cardiac dysfunction and hypertrophy after a MI, and that LPA suppresses autophagy through activation of the LPA3 and AKT/mTOR pathways to induce cardiomyocyte hypertrophy.

NR4A2 protects cardiomyocytes against myocardial infarction injury by promoting autophagy

Myocardial infarction (MI), characterized by ischemia-induced cardiomyocyte apoptosis, is the leading cause of mortality worldwide. NR4A2, a member of the NR4A orphan nucleus receptor family, is upregulated in mouse hearts with MI injury. Furthermore, NR4A2 knockdown aggravates heart injury as evidenced by enlarged hearts and increased apoptosis. To elucidate the underlying mechanisms of NR4A2-regulated apoptosis, we used H9c2 cardiomyocytes deprived of serum and neonatal rat cardiomyocytes (NRCMs) exposed to hypoxia to mimic ischemic conditions in vivo. As NR4A2 knockdown aggravates cardiomyocyte apoptosis, while NR4A2 overexpression ameliorates it, NR4A2 upregulation was considered an adaptive response to ischemia-induced cardiomyocyte apoptosis. By detecting changes in LC3 and using autophagy detection tools including Bafilomycin A1, 3MA and rapamycin, we found that NR4A2 knockdown promoted apoptosis through blocking autophagic flux. This apoptotic response was phenocopied by downregulation of NR4A2 after autophagic flux was impaired by Bafilomycin A1. Further study showed that NR4A2 binds to p53 directly and decreases its levels when it inhibits apoptosis; thus, p53/Bax is the downstream effector of NR4A2-mediated apoptosis, as previously reported. Changes in p53/Bax that were regulated by NR4A2 were also detected in injured hearts with NR4A2 knockdown. In addition, miR-212-3p is the upstream regulator of NR4A2, and it could downregulate the expression of NR4A2, as well as p53/Bax. The mechanism underlying the role of NR4A2 in apoptosis and autophagy was elucidated, and NR4A2 may be a therapeutic drug target for heart failure.

Acute hypoxic preconditioning prevents palmitic acid-induced cardiomyocyte apoptosis via switching metabolic GLUT4-glucose pathway back to CD36-fatty acid dependent

Metabolic syndrome is a risk factor for the development of cardiovascular diseases. Myocardial cell damage leads to an imbalance of energy metabolism, and many studies have indicated that short-term hypoxia during myocardial cell injury has a protective effect. In our previous animal studies, we found that short-term hypoxia in the heart has a protective effect, but long-term hypoxia increases myocardial cell injury. Palmitic acid (PA)-treated H9c2 cardiomyoblasts and neonatal rat ventricle cardiomyocytes were used to simulate hyperlipidemia model, which suppress cluster of differentiation 36 (CD36) and activate glucose transporter type 4 (GLUT4). We exposed the cells to short- and long-term hypoxia and investigated the protective effects of hypoxic preconditioning on PA-induced lipotoxicity in H9c2 cardiomyoblasts and neonatal rat cardiomyocytes. Preconditioning with short-term hypoxia enhanced both CD36 and GLUT4 metabolism pathway protein levels. Expression levels of phospho-PI3K, phospho-Akt, phospho-AMPK, SIRT1, PGC1α, PPARα, CD36, and CPT1β induced by PA was reversed by short-term hypoxia in a time-dependent manner. PA-induced increased GLUT4 membrane protein level was reduced in the cells exposed to short-term hypoxia and si-PKCζ. Short-term hypoxia, resveratrol and si-PKCζ rescue H9c2 cells from apoptosis induced by PA and switch the metabolic pathway from GLUT4 dependent to CD36 dependent. We demonstrate short-term hypoxic preconditioning as a more efficient way as resveratrol in maintaining the energy metabolism of hearts during hyperlipidemia and can be used as a therapeutic strategy.

Intermittent hypoxia causes mandibular growth retardation and macroglossia in growing rats

INTRODUCTION

In this study, we aimed to examine the role of intermittent hypoxia (IH) in dentofacial morphologic changes in growing rats.

METHODS

Seven-week-old male rats were exposed to IH at 20 cycles per hour (nadir of 4% oxygen to peak of 21% oxygen) for 8 hours per day for 6 weeks. Control rats were exposed to normoxia (N). Maxillofacial growth was compared between the 2 groups by linear measurements on cephalometric radiographs. To examine the dental arch morphology, study models and microcomputed tomography images of the jaws were taken. Additionally, tongue size was measured.

RESULTS

The gonial angle and the ramus of the mandible were smaller in the IH group than in the N group, whereas the body weights were not different between the 2 groups. Morphometric analysis of the dentition showed a significantly wider mandibular dentition and narrower maxillary dentition in the IH than in the N group. The relative width (+4.2 %) and length (tongue apex to vallate papillae, +3.5 %) of the tongue to the mandible were significantly greater in the IH group than in the N group.

CONCLUSIONS

IH induced dentofacial morphologic discrepancies in growing rats.

Hydroxytyrosol regulates the autophagy of vascular adventitial fibroblasts through the SIRT1-mediated signaling pathway

Hydroxytyrosol (HT), a phenolic compound in olive oil, exerts an anti-inflammatory effect in cardiovascular diseases. Recent studies found that autophagy was a therapeutic target of diseases. However, the effect of HT on autophagy in vascular adventitial fibroblasts (VAFs) remains unknown. Thus, in this study, we aimed to determine the effect of HT on cell autophagy and related signaling pathway and whether HT regulates the inflammatory response through autophagy in VAFs. Our results showed that HT promoted cell autophagy by increasing the conversion of LC3 and Beclin1 expression and the autophagic flux in VAFs stimulated with tumor necrosis factor-α (TNF-α). HT also upregulated the expression of the deacetylase sirtuin 1 (SIRT1) protein and mRNA compared with the TNF-α group. The molecular docking studies showed the good compatibility between HT and SIRT1, indicating that HT might act through SIRT1. Further study found that HT regulated autophagy through SIRT1-mediated Akt/mTOR suppression in VAFs. In addition, HT inhibited TNF-α-induced inflammatory response in VAFs through SIRT1. Furthermore, the study showed that HT inhibited the inflammatory response of VAFs through autophagy. These findings indicate that HT regulates the autophagy of VAFs through SIRT1-mediated Akt/mTOR suppression and then inhibits the inflammatory response of VAFs.

Effect of different levels of intermittent hypoxia on autophagy of hippocampal neurons

PURPOSE

The current study was carried out to assess the effects of different levels of intermittent hypoxia (IH) on autophagy in hippocampal neurons, and explore the extent, frequency and duration of IH for researching on autophagy in hippocampal neurons.

METHODS

Hippocampal neurons were exposed to different levels of IH. To analyze the oxygen level of neuronal exposure environment, we detected the oxygen concentration in the chamber by O₂ analyzer, and monitored the oxygen partial pressure (PO₂), carbon dioxide partial pressure (PCO₂), and pH in the culture media by blood gas analyzer. After 4-, 8-, and 12-h IH, the morphology and quantity of neurons, as well as the expression of light chain 3 (LC3)-II positive dots were observed by immunofluorescence. The expression of apoptosis marker protein cleaved caspase-3 and autophagy marker protein LC3 were examined by western blotting.

RESULTS

The oxygen level in the chamber and the neuronal culture media both reached to the values set previously in three models. The level of cleaved caspase-3 and LC3 had no significant changes in IH-1 group. The morphology and quantity had no significant changes, while the levels of cleaved caspase-3 and LC3 were both increased in IH-2 group. The quantity of neurons was reduced significantly, and the chromatin condensed and nuclei fragmented in IH-3 group.

CONCLUSIONS

The effects of varying degrees of IH on autophagy in hippocampal neurons are different. The IH model, hypoxia phase (1.5% O₂, 5% CO₂, and balance N₂) for 5 min and reoxygenation phase (21% O₂, 5% CO₂, and balance N₂) for 10 min, may be the best condition for researching on autophagy in hippocampal neurons.

High intensity aerobic exercise training improves chronic intermittent hypoxia-induced insulin resistance without basal autophagy modulation

Chronic intermittent hypoxia (IH) associated with obstructive sleep apnea (OSA) is a major risk factor for cardiovascular and metabolic diseases (insulin resistance: IR). Autophagy is involved in the pathophysiology of IR and high intensity training (HIT) has recently emerged as a potential therapy. We aimed to confirm IH-induced IR in a tissue-dependent way and to explore the preventive effect of HIT on IR-induced by IH. Thirty Swiss 129 male mice were randomly assigned to Normoxia (N), Intermittent Hypoxia (IH: 21-5% FiO₂, 30 s cycle, 8 h/day) or IH associated with high intensity training (IH HIT). After 8 days of HIT (2*24 min, 50 to 90% of Maximal Aerobic Speed or MAS on a treadmill) mice underwent 14 days IH or N. We found that IH induced IR, characterized by a greater glycemia, an impaired insulin sensitivity and lower AKT phosphorylation in adipose tissue and liver. Nevertheless, MAS and AKT phosphorylation were greater in muscle after IH. IH associated with HIT induced better systemic insulin sensitivity and AKT phosphorylation in liver. Autophagy markers were not altered in both conditions. These findings suggest that HIT could represent a preventive strategy to limit IH-induced IR without change of basal autophagy.

Autophagy, Metabolic Disease, and Pathogenesis of Heart Dysfunction

In normal physiology, autophagy is recognized as a protective housekeeping mechanism that enables elimination of unhealthy organelles, protein aggregates, and invading pathogens, as well as recycling cell components and producing new building blocks and energy for cellular renovation and homeostasis. However, overactive or depressed autophagy is often associated with the pathogenesis of multiple disorders, including cardiac disease. During metabolic disorders, such as diabetes and obesity, dysregulation of autophagy frequently leads to cell death, cardiomyopathy, and cardiac dysfunction. In this article, we summarize the current understanding of autophagy-its classification, progression, and regulation; its roles in both physiological and pathophysiological conditions; and the balance between autophagy and apoptosis. We also explore how dysregulation of autophagy leads to cell death in models of metabolic disease and its contributing factors-including nutrient state, hyperglycemia, dyslipidemia, insulin inefficiency, and oxidative stress-and outline some recent efforts to restore normal autophagy in pathophysiological states. This information could provide potential targets for the prevention of, or intervention in, cardiac failure in metabolic disorders such as diabetes and obesity.

The Effects of Carvedilol on Cardiac Function and the AKT/XIAP Signaling Pathway in Diabetic Cardiomyopathy Rats

OBJECTIVES

Diabetic cardiomyopathy (DCM) is characterized by cardiac dysfunction, myocardial inflammation, interstitial fibrosis and cardiomyocytes apoptosis. The present study aimed to investigate the effects of carvedilol on cardiac function and the AKT/XIAP signaling pathway in DCM rats.

METHODS

Male Wistar rats were randomly divided into 3 groups: the control group, diabetic mellitus (DM) group and DM with carvedilol treatment group. DM rats were induced by streptozotocin accompanied by high energy intake. Carvedilol was orally administered at a dose of 10 mg/kg/day. After 16 weeks, the interrelated blood data were detected by biochemical analysis. Cardiac function was evaluated by echocardiography and the serum NT-proBNP level. The changes of myocardium ultrastructural and fibrosis were determined by electron microscopy and Masson's staining. Apoptotic cells were examined by TUNEL staining and interrelated proteins were measured by immunohistochemical and Western blots.

RESULTS

Rats in the DM group showed significant serum elevation of glucose, cholesterol, triglyceride, NT-proBNP, IL-1β and TNF-α, along with decreased cardiac function. Moreover, in the DM group, the levels of myocardial apoptosis and fibrosis were all increased accompanied by upregulation of caspase-3 and downregulation of phos-AKT and phos-XIAP, whereas carvedilol treatment prevented or reversed all the changes without influencing plasma levels of glucose, cholesterol and triglyceride.

CONCLUSIONS

The AKT/XIAP signaling pathway may be involved in DCM. Carvedilol can improve cardiac function, possibly not only by upregulating the AKT/XIAP antiapoptotic signaling pathway and subsequently attenuating myocardial fibrosis, but also through suppressing the myocardial inflammation response.

Intermittent Hypoxia Influences Alveolar Bone Proper Microstructure via Hypoxia-Inducible Factor and VEGF Expression in Periodontal Ligaments of Growing Rats

Intermittent hypoxia (IH) recapitulates morphological changes in the maxillofacial bones in children with obstructive sleep apnea (OSA). Recently, we found that IH increased bone mineral density (BMD) in the inter-radicular alveolar bone (reflecting enhanced osteogenesis) in the mandibular first molar (M1) region in the growing rats, but the underlying mechanism remains unknown. In this study, we focused on the hypoxia-inducible factor (HIF) pathway to assess the effect of IH by testing the null hypothesis of no significant differences in the mRNA-expression levels of relevant factors associated with the HIF pathway, between control rats and growing rats with IH. To test the null hypothesis, we investigated how IH enhances mandibular osteogenesis in the alveolar bone proper with respect to HIF-1α and vascular endothelial growth factor (VEGF) in periodontal ligament (PDL) tissues. Seven-week-old male Sprague-Dawley rats were exposed to IH for 3 weeks. The microstructure and BMD in the alveolar bone proper of the distal root of the mandibular M1 were evaluated using micro-computed tomography (micro-CT). Expression of HIF-1α and VEGF mRNA in PDL tissues were measured, whereas osteogenesis was evaluated by measuring mRNA levels for alkaline phosphatase (ALP) and bone morphogenetic protein-2 (BMP-2). The null hypothesis was rejected: we found an increase in the expression of all of these markers after IH exposure. The results provided the first indication that IH enhanced osteogenesis of the mandibular M1 region in association with PDL angiogenesis during growth via HIF-1α in an animal model.

Sheng-Mai-San attenuates contractile dysfunction and structural damage induced by chronic intermittent hypoxia in mice

Sheng-Mai-San (SMS), a well-known Chinese medicinal plant formula, is widely used for the treatment of cardiac diseases characterized by deficiency of Qi and Yin syndrome. A mouse chronic intermittent hypoxia (CIH) model was established to mimic the primary clinical features of deficiency of Qi and Yin syndrome. Mice experienced CIH for 28 days (nadir 7% to peak 8% oxygen, 20 min per day), resulting in left ventricle (LV) dysfunction and structure abnormalities. After administration of SMS (0.55, 1.1, and 5.5 g·kg(-1)·d(-1)) for four weeks, improved cardiac function was observed, as indicated by the increase in the ejection fraction from the LV on echocardiography. SMS also preserved the structural integrity of the LV against eccentric hypotrophy, tissue vacuolization, and mitochondrial injury as measured by histology, electron microscopy, and ultrasound assessments. Mechanistically, the antioxidant effects of SMS were demonstrated; SMS was able to suppress mitochondrial apoptosis as indicated by the reduction of several pro-apoptotic factors (Bax, cytochrome c, and cleaved caspase-3) and up-regulation of the anti-apoptosis factor Bcl-2. In conclusion, these results demonstrate that SMS treatment can protect the structure and function of the LV and that the protective effects of this formula are associated with the regulation of the mitochondrial apoptosis pathway.

Autophagy and Obesity-Related Lung Disease

Obesity-related disease is a significant source of premature death and economic burden globally. It is also a common comorbidity in patients suffering from lung disease, affecting both severity and treatment success. However, this complex association between obesity and the lung is poorly understood. Autophagy is a self-recycling homeostatic process that has been linked to beneficial or deleterious effects, depending on the specific lung disease. Obesity affects autophagy in a tissue-specific manner, activating autophagy in adipocytes and impairing autophagy in hepatocytes, immune cells, and pancreatic β-cells, among others. Obesity is also characterized by chronic low-grade inflammation that can be modulated by the pro- and antiinflammatory effects of the autophagic machinery. Scant evidence exists regarding the impact of autophagy in obesity-related lung diseases, but there are communal pathways that could be related to disease pathogenesis. Important signaling molecules in obesity, including IL-17, leptin, adiponectin, NLRP3 inflammasome, and TLR-4, have been implicated in the pathogenesis of lung disease. These mediators are known to be modulated by autophagy activity. In this perspective, we highlight the recent advances in the understanding of autophagy in obesity-related conditions, as well as the potential mechanisms that can link autophagy and obesity in the pathogenesis of lung disease.

Intermittent hypoxia upregulates hepatic heme oxygenase-1 and ferritin-1, thereby limiting hepatic pathogenesis in rats fed a high-fat diet

Non-alcoholic fatty liver disease (NAFLD) is prevalent in patients with sleep apnea syndrome (SAS). Intermittent hypoxia (IH) and a high-fat diet (HFD) reproduce SAS and NAFLD, respectively, in rodents. In this study, rats were fed either an HFD or a standard diet (SD) for 2 weeks, and breathed either IH air or normoxic air for 4 days (early phase) or 6 weeks (late phase), with the same diets maintained during the exposure. HFD increased hepatic lipid accumulation, as detected by oil-red staining and triglyceride content. However, IH exposure reversed the hepatic steatosis at the late phase in these HFD-rats. IH exposure also increased hepatic expression of HO-1 and iron-binding protein ferritin-1 at the late phase, in association with increase in serum iron, bilirubin, and hepatic levels of lipid peroxides, such as 4-hydroxy-2-nonenal (HNE). IH exposure increased serum levels of hemoglobin (Hb) at the early phase and immunofluorescence of Hb and HO-1 in CD68-positive Kupffer cells (KCs) at the late phase. These findings support that IH induces erythrocytosis, erythro-phagocytosis, and generation of Hb in the KCs. The Hb promotes HO-1 expression in KCs, thereby produces iron, bilirubin, and carbon monoxide (CO). The iron would be either sequestrated by ferritin-1, transferred to the bone marrow for erythropoiesis, or would produce hydroxyradicals and HNE in the liver of rats fed an HFD. HNE might also contribute to the upregulation of HO-1, transferrin-1, and IκB, thereby limiting hepatic steatosis and inflammation via inhibition of nuclear factor κB (NFκB) activation.

Autophagy Promotes Peripheral Nerve Regeneration and Motor Recovery Following Sciatic Nerve Crush Injury in Rats

Autophagy maintains cellular homeostasis by stimulating the lysosomal degradation of cytoplasmic structures, including damaged organelles and dysfunctional proteins. The role of autophagy in the renewal and regeneration of injured peripheral nerves remains poorly understood. The current study investigated the role of autophagy in peripheral nerve regeneration and motor function recovery following sciatic nerve crush injury in rats by stimulating or suppressing autophagy and detecting the presence of autophagosomes and LC3-II expression by electron microscopy and Western blotting, respectively. Neurobehavioral function was tested by CatWalk gait analysis 1, 2, 3, and 6 weeks after injury, and the expression of neurofilament (NF)-200 and myelin basic protein (MBP) at the injury site was examined by immunocytochemistry. Apoptosis at the lesion site was determined by the terminal deoxynucleotidyl transferase dUTP nick end labeling assay. Treatment of injured rats with the autophagy inducer rapamycin increased the number of autophagosomes and LC3-II expression while reducing the number of apoptotic cells at the lesion; this was associated with an upregulation of MBP and NF-200 expression and increased motor function recovery as compared to sham-operated rats and those that were subjected to crush injury but untreated. The opposite effects were observed in rats treated with the autophagy inhibitor 3-methyladenine. These data indicate that the modulation of autophagy in peripheral nerve injury could be an effective pharmacological approach to promote nerve regeneration and reestablish motor function.

Autophagy activation attenuates angiotensin II-induced cardiac fibrosis

Autophagy has been involved in numerous diseases processes. However, little is known about the role of autophagy in cardiac fibrosis. Thus, whether or not angiotensin II (Ang II)-induced autophagy has a regulatory function on cardiac fibrosis was detected in vitro and in vivo. In rat cardiac fibroblasts (CFs) stimulated with Ang II, activated autophagy was observed using transmission electron microscopic analysis (TEM), immunofluorescence and Western blot. In Ang II-infused mice, increased co-localization of LC3 puncta with vimentin was observed. In rat CFs, co-treated with rapamycin (Rapa), an autophagy inducer, Ang II-induced the upregulation of type I collagen (Col-I), fibronectin (FN) was decreased. Conversely, inhibition of autophagy by chloroquine (CQ), an autophagy inhibitor, or knockdown of ATG5, a key component of the autophagy pathway by specific siRNA, aggravated Ang II-mediated the accumulation of Col-I and FN. Furthermore, in C57 BL/6 mice with Ang II infusion, intraperitoneal administration of Rapa ameliorated Ang II-induced cardiac fibrosis and cardiac dysfunction, while CQ treatment not only exacerbated Ang II-mediated cardiac fibrosis and cardiac dysfunction, but also impaired cardiac function. These findings suggest that autophagy may exert a protective role to attenuate excess extracellular matrix (ECM) accumulation in the heart.

Intermittent hypoxia induces disturbances in craniofacial growth and defects in craniofacial morphology

OBJECTIVES

To investigate intermittent hypoxia (IH) induced changes in craniofacial morphology and bone mineral density (BMD) in the mandible of growing rats.

DESIGN

Seven-week-old male Sprague-Dawley rats were exposed to IH for 4 days or 3 weeks. Sham-operated rats simultaneously breathed room air. Lateral and transverse cephalometric radiographs of the craniofacial region were obtained, and the linear distances between cephalometric landmarks were statistically analyzed. BMD and bone microstructure of the mandible were evaluated using micro-computed tomography (micro-CT).

RESULTS

Cephalometric analyses demonstrated that exposure to IH only in the two groups for 3 weeks decreased the size of the mandibular and viscerocranial bones, but not that of the neurocranial bones, in early adolescent rats. These findings are consistent with upper airway narrowing and obstructive sleep apnea (OSA). Micro-CT showed that IH increased the BMD in the cancellous bone of the mandibular condyle and the inter-radicular alveolar bone in the mandibular first molar (M1) region.

CONCLUSIONS

This study is the first to identify growth retardation of the craniofacial bones in an animal model of sleep apnea. Notably, 3 weeks of IH can induce multiple changes in the bones around the upper airway in pubertal rats, which can enhance upper airway narrowing and the development of OSA. The reproducibility of these results supports the validity and usefulness of this model. These findings also emphasize the critical importance of morphometric evaluation of patients with OSA.

Apelin Gene Therapy Increases Autophagy via Activation of Sirtuin 3 in Diabetic Heart

Heart failure is the leading cause of death in diabetic patients. Recently we showed that apelin gene therapy attenuates heart failure following myocardial infarction. This study further explored the potential mechanisms by which apelin may reduce cardiac injury in Postmyocardial infarction (MI)) model of diabetes. Wild type and Sirt3 knockout (Sirt3 KO) mice were induced into diabetes by intra-peritoneal (i.p.) Streptozotocin (STZ). STZ mice were then subjected to MI followed by immediate intramyocardial injection with Adenovirus-apelin (Ad-apelin). Ad-apelin treatment resulted in over expression of apelin in the ischemic hearts of STZ mice. Apelin over expression led to a significant increase in Sirt3 expression. Apelin over expression significantly reduced gp91^phox expression. This was accompanied by a significant reduction of reactive oxygen species formation. Ad-apelin treatment also dramatically reduced NF-κb-p65 expression in WT-STZ mice. Over expression of apelin further enhanced autophagy markers (LC3-II and beclin-1) expression in post-MI heart. Most intriguingly, knockout of Sirt3 in STZ mice abolished these beneficial effects of apelin treatment. In vitro, knockout of Sirt3 in EPCs significantly enhanced high glucose-induced ROS formation. Conversely, treatment of Sirt3 KO-EPCs with NADPH oxidase inhibitor led to two fold increase in LC3-II levels. Our studies demonstrate that apelin increases autophagy via up regulation of Sirt3 and suppression of ROS-NF-κb pathway in diabetic heart.

Autophagy-associated atrophy and metabolic remodeling of the mouse diaphragm after short-term intermittent hypoxia

BACKGROUND

Short-term intermittent hypoxia (IH) is common in patients with acute respiratory disorders. Although prolonged exposure to hypoxia induces atrophy and increased fatigability of skeletal muscle, the response to short-term IH is less well known. We hypothesized that the diaphragm and limb muscles would adapt differently to short-term IH given that hypoxia stimulates ventilation and triggers a superimposed exercise stimulus in the diaphragm.

METHODS

We determined the structural, metabolic, and contractile properties of the mouse diaphragm after 4 days of IH (8 hours per day, 30 episodes per hour to a FiO2 nadir=6%), and compared responses in the diaphragm to a commonly studied reference limb muscle, the tibialis anterior. Outcome measures included muscle fiber size, assays of muscle proteolysis (calpain, ubiquitin-proteasome, and autophagy pathways), markers of oxidative stress and mitochondrial function, quantification of intramyocellular lipid and lipid metabolism genes, type I myosin heavy chain (MyHC) expression, and in vitro contractile properties.

RESULTS

After 4 days of IH, the diaphragm alone demonstrated significant atrophy (30% decrease of myofiber size) together with increased LC3B-II protein (2.4-fold) and mRNA markers of the autophagy pathway (LC3B, Gabarapl1, Bnip3), whereas active calpain and E3 ubiquitin ligases (MuRF1, atrogin-1) were unaffected in both muscles. Succinate dehydrogenase activity was significantly reduced by IH in both muscles. However, only the diaphragm exhibited increased intramyocellular lipid droplets (2.5-fold) after IH, along with upregulation of genes linked to activated lipid metabolism. In addition, although the diaphragm showed evidence for acute fatigue immediately following IH, it underwent an adaptive fiber type switch toward slow type I MyHC-expressing fibers, associated with greater intrinsic endurance of the muscle during repetitive stimulation in vitro.

CONCLUSIONS

Short-term IH induces preferential atrophy in the mouse diaphragm together with increased autophagy and a rapid compensatory metabolic adaptation associated with enhanced fatigue resistance.

Cardioprotective effects of fucoidan against hypoxia-induced apoptosis in H9c2 cardiomyoblast cells

CONTEXT

Cardiomyocyte apoptosis plays a critical role in the progress of heart diseases. Fucoidan, a complex-sulfated polysaccharide, has been reported to possess potential cardioprotective efficacy in vivo.

OBJECTIVE

The present study determines whether fucoidan could provide cardioprotection on hypoxia-induced cardiomyocyte apoptosis.

MATERIALS AND METHODS

H9c2 cardiomyoblast cells were incubated with various concentrations (15, 30, and 60 μg/ml) of fucoidan in a humidified incubator at 37 °C with 95% O2 and 5% CO2. After 6 h, hypoxia was processed and the cardioprotective effects of fucoidan were evaluated by applying MTT, ELISA, Hoechst 33258 nucleus staining, and western blot.

RESULTS

Following a 6 h exposure of H9c2 to hypoxic condition, significant reduction was found in cell survival (0.57-fold) and superoxide dismutase (SOD) activity (0.56-fold), which were associated with the increase of malondialdehyde (MDA) level (2.58-fold), creatine phosphokinase (CK, 3.57-fold), and lactate dehydrogenase (LDH) activities (2.39-fold). Moreover, hypoxia-induced apoptosis was confirmed by Hoechst 33258 nuclear staining, and these changes were accompanied by the increase of Bcl-2 (1.27-fold) and Bax expression (2.6-fold). However, preincubation of the cells with fucoidan prior to hypoxia exposure elevated the cell viability (30 μg/ml, 1.18-fold; 60 μg/ml, 1.32-fold) and SOD activity (30 μg/ml, 1.12-fold; 60 μg/ml, 1.25-fold), but decreased the MDA level (30 μg/ml, 0.70-fold; 60 μg/ml, 0.80-fold), CK (30 μg/ml, 0.69-fold; 60 μg/ml, 0.76-fold), and LDH (30 μg/ml, 0.67-fold; 60 μg/ml, 0.86-fold) leakages. Hoechst 33258 nuclear staining observations demonstrated the same protective effect of fucoidan on hypoxia-induced myocardial injury. Also, cardioprotective effects of fucoidan were reflected by increasing Bcl-2 (60 μg/ml, 1.84-fold), as well as decreasing Bax (60 μg/ml, 0.6-fold).

CONCLUSION

Fucoidan had protective effect against hypoxia-induced cardiomyocytes apoptosis, and the mechanism might involve protections of the cell from oxidative injury.

Hydrogen gas attenuates embryonic gene expression and prevents left ventricular remodeling induced by intermittent hypoxia in cardiomyopathic hamsters

The prevalence of sleep apnea is very high in patients with heart failure (HF). The aims of this study were to investigate the influence of intermittent hypoxia (IH) on the failing heart and to evaluate the antioxidant effect of hydrogen gas. Normal male Syrian hamsters (n = 22) and cardiomyopathic (CM) hamsters (n = 33) were exposed to IH (repeated cycles of 1.5 min of 5% oxygen and 5 min of 21% oxygen for 8 h during the daytime) or normoxia for 14 days. Hydrogen gas (3.05 vol/100 vol) was inhaled by some CM hamsters during hypoxia. IH increased the ratio of early diastolic mitral inflow velocity to mitral annulus velocity (E/e', 21.8 vs. 16.9) but did not affect the LV ejection fraction (EF) in normal Syrian hamsters. However, IH increased E/e' (29.4 vs. 21.5) and significantly decreased the EF (37.2 vs. 47.2%) in CM hamsters. IH also increased the cardiomyocyte cross-sectional area (672 vs. 443 μm(2)) and interstitial fibrosis (29.9 vs. 9.6%), along with elevation of oxidative stress and superoxide production in the left ventricular (LV) myocardium. Furthermore, IH significantly increased the expression of brain natriuretic peptide, β-myosin heavy chain, c-fos, and c-jun mRNA in CM hamsters. Hydrogen gas inhalation significantly decreased both oxidative stress and embryonic gene expression, thus preserving cardiac function in CM hamsters. In conclusion, IH accelerated LV remodeling in CM hamsters, at least partly by increasing oxidative stress in the failing heart. These findings might explain the poor prognosis of patients with HF and sleep apnea.

Rosuvastatin alleviates diabetic cardiomyopathy by inhibiting NLRP3 inflammasome and MAPK pathways in a type 2 diabetes rat model

PURPOSE

Nucleotide-binding oligomerization domain-like receptor protein 3 (NLRP3) inflammasome is important in inflammation of several diabetic complications. However, the potential role of NLRP3 inflammasome in the inflammatory process of diabetic cardiomyopathy (DCM) remains unclear. Although rosuvastatin (RSV) has an anti-inflammatory effect on some cardiovascular diseases, its influence on DCM is incompletely understood. We aimed to explore the effect on and underlying mechanism of RSV in DCM, and whether NLRP3 is a target for RSV.

METHODS

Type 2 diabetes was induced in rat. The characteristics of type 2 DCM were evaluated by metabolic tests, echocardiography and histopathology. The expression of factors was determined by real-time RT-PCR and western blot. Eight-week RSV treatment and NLRP3 gene silencing were used to investigate the effect and underlying target of RSV in DCM.

RESULTS

Compared with controls, diabetic rats showed severe metabolic disorder, cardiac dysfunction, fibrosis, disorganized ultrastructure, and excessive activation of thioredoxin interacting/inhibiting protein (TXNIP, p < 0.05), NLRP3 inflammasome (NLRP3, p < 0.01; apoptosis-associated speck-like protein containing a caspase recruitment domain [ASC], p < 0.05; caspase-1, p < 0.01), interleukin-1β (p < 0.01) and mitogen-activated protein kinases (MAPKs, all p < 0.01). Compared with diabetes alone, RSV ameliorated the overexpression of NLRP3 inflammasome (NLRP3, p < 0.05; ASC, p < 0.05; pro-caspase-1 p < 0.05, caspase-1 p20, p < 0.01) and MAPKs (all p < 0.05), which paralleled the cardiac protection of RSV. Silencing NLRP3 ameliorated cardiac remodeling and dysfunction. The beneficial effects of RSV in vehicle-treated rats were all abrogated in NLRP3-silenced rats.

CONCLUSIONS

The beneficial effect of RSV on DCM depended on inhibited NLRP3 inflammasome, and correlated with suppression of the MAPKs.

The microbiota protects against ischemia/reperfusion-induced intestinal injury through nucleotide-binding oligomerization domain-containing protein 2 (NOD2) signaling

Nucleotide-binding oligomerization domain-containing protein 2 (NOD2), an intracellular pattern recognition receptor, induces autophagy on detection of muramyl dipeptide (MDP), a component of microbial cell walls. The role of bacteria and NOD2 signaling toward ischemia/reperfusion (I/R)-induced intestinal injury response is unknown. Herein, we report that I/R-induced intestinal injury in germ-free (GF) C57BL/6 wild-type (WT) mice is worse than in conventionally derived mice. More important, microbiota-mediated protection against I/R-induced intestinal injury is abrogated in conventionally derived Nod2(-/-) mice and GF Nod2(-/-) mice. Also, WT mice raised in specific pathogen-free (SPF) conditions fared better against I/R-induced injury than SPF Nod2(-/-) mice. Moreover, SPF WT mice i.p. administered 10 mg/kg MDP were protected against injury compared with mice administered the inactive enantiomer, l-MDP, an effect lost in Nod2(-/-) mice. However, MDP administration failed to protect GF mice from I/R-induced intestinal injury compared with control, a phenomenon correlating with undetectable Nod2 mRNA level in the epithelium of GF mice. More important, the autophagy-inducer rapamycin protected Nod2(-/-) mice against I/R-induced injury and increased the levels of LC3(+) puncta in injured tissue of Nod2(-/-) mice. These findings demonstrate that NOD2 protects against I/R and promotes wound healing, likely through the induction of the autophagy response.

NLRP3 gene silencing ameliorates diabetic cardiomyopathy in a type 2 diabetes rat model

BACKGROUND

Nucleotide-binding oligomerization domain-like receptor protein 3 (NLRP3) inflammasome is associated with metabolic disorder and cell death, which are important triggers in diabetic cardiomyopathy (DCM). We aimed to explore whether NLRP3 inflammasome activation contributes to DCM and the mechanism involved.

METHODS

Type 2 diabetic rat model was induced by high fat diet and low dose streptozotocin. The characteristics of type 2 DCM were evaluated by metabolic tests, echocardiography and histopathology. Gene silencing therapy was used to investigate the role of NLRP3 in the pathogenesis of DCM. High glucose treated H9c2 cardiomyocytes were used to determine the mechanism by which NLRP3 modulated the DCM. The cell death in vitro was detected by TUNEL and EthD-III staining. TXNIP-siRNA and pharmacological inhibitors of ROS and NF-kB were used to explore the mechanism of NLRP3 inflammasome activation.

RESULTS

Diabetic rats showed severe metabolic disorder, cardiac inflammation, cell death, disorganized ultrastructure, fibrosis and excessive activation of NLRP3, apoptosis-associated speck-like protein containing a caspase recruitment domain (ASC), pro-caspase-1, activated caspase-1 and mature interleukin-1β (IL-1β). Evidence for pyroptosis was found in vivo, and the caspase-1 dependent pyroptosis was found in vitro. Silencing of NLRP3 in vivo did not attenuate systemic metabolic disturbances. However, NLRP3 gene silencing therapy ameliorated cardiac inflammation, pyroptosis, fibrosis and cardiac function. Silencing of NLRP3 in H9c2 cardiomyocytes suppressed pyroptosis under high glucose. ROS inhibition markedly decreased nuclear factor-kB (NF-kB) phosphorylation, thioredoxin interacting/inhibiting protein (TXNIP), NLRP3 inflammasome, and mature IL-1β in high glucose treated H9c2 cells. Inhibition of NF-kB reduced the activation of NLRP3 inflammasome. TXNIP-siRNA decreased the activation of caspase-1 and IL-1β.

CONCLUSION

NLRP3 inflammasome contributed to the development of DCM. NF-κB and TXNIP mediated the ROS-induced caspase-1 and IL-1β activation, which are the effectors of NLRP3 inflammasome. NLRP3 gene silencing may exert a protective effect on DCM.

Impairment of nasal airway under intermittent hypoxia during growth period in rats

OBJECTIVE

To clarify the influences of intermittent hypoxia (IH) on the growth and development of the midfacial area, including the nasal cavity, in growing rats.

DESIGN

Seven-week-old male Sprague-Dawley rats were divided into two groups: the experimental group (n=5), which was exposed to IH for 8h during light periods at a rate of 20 cycles/h (nadir, 4% O₂ to peak, 21% O₂ with 0% CO₂), and the control group (n=5), which was exposed to room air. After 3 weeks, the maxillofacial structures in both groups were evaluated with respect to the height, width, length, surface area, cross-sectional area, and volume of the nasal cavity using soft X-ray and micro-CT.

RESULTS

The experimental group showed a significantly smaller cross-sectional area and volume than did the control group. The surface area exhibited no significant differences between the two groups, although it tended to be smaller in the experimental group than in the control group. The nasal volume divided by the length of the tibia (for comparison with whole-body growth) was significantly smaller in the experimental group than in the control group.

CONCLUSIONS

These data suggest that IH exposure suppresses growth and development of the nasal cavity and may result in nasal breathing disturbance.