DJ-1 activates autophagy in the repression of cardiac hypertrophy

Emerging markers of inflammation and oxidative stress as potential predictors of coronary artery disease

BACKGROUND AND AIMS

The multi-ligand receptor for advanced glycation end products (RAGE) and its ligands AGEs and S100/calgranulin proteins are important mediators of inflammation and oxidative stress whereas the soluble form of RAGE (sRAGE) by acting as a decoy and the antioxidant PARK7/DJ-1 exert antiatherogenic effects. We examined whether sRAGE and its ligands AGEs, S100A8/A9, S100B, S100A12 and DJ-1 are associated with the presence of angiographic coronary artery disease (CAD) in asymptomatic patients with and without diabetes.

METHODS AND RESULTS

Plasma levels of RAGE ligands, sRAGE and DJ-1 were determined in 50 patients with angiographically proven CAD and in 50 age-matched healthy controls. In the whole cohort, lower levels of sRAGE and higher levels of interleukin-6 (IL-6), the RAGE ligands S100B, S100A12 and the AGEs/sRAGE ratio were associated with CAD. In patients without diabetes (n = 72), lower levels of sRAGE and DJ-1 and higher levels of IL-6 and AGEs/sRAGE ratio were associated with CAD. In multivariable analysis, AGEs/sRAGE ratio was an independent predictor of CAD both in the whole cohort (p = 0.034, OR = 1.247, [95%CI: 1.024, 1.0519]) and in the subgroup of patients without diabetes (p = 0.021, OR = 1.363, 95%CI [1.048, 1.771]) on top of established cardiovascular risk factors.

CONCLUSION

Alterations in plasma RAGE axis inflammatory mediators are associated with atherosclerosis, and higher levels of AGEs/sRAGE ratio are independently associated with CAD in asymptomatic patients and may act as a novel biomarker for predicting CAD. DJ-1 emerges as promising marker of oxidative stress in CAD patients without diabetes, a finding that deserves further study.

DJ-1 promotes energy balance by regulating both mitochondrial and autophagic homeostasis

The protein DJ-1 is mutated in rare familial forms of recessive Parkinson's disease and in parkinsonism accompanied by amyotrophic lateral sclerosis symptoms and dementia. DJ-1 is considered a multitasking protein able to confer protection under various conditions of stress. However, the precise cellular function still remains elusive. In the present work, we evaluated fruit flies lacking the expression of the DJ-1 homolog dj-1β as compared to control aged-matched individuals. Behavioral evaluations included lifespan, locomotion in an open field arena, sensitivity to oxidative insults, and resistance to starvation. Molecular analyses were carried out by analyzing the mitochondrial morphology and functionality, and the autophagic response. We demonstrated that dj-1β null mutant flies are hypoactive and display higher sensitivity to oxidative insults and food deprivation. Analysis of mitochondrial homeostasis revealed that loss of dj-1β leads to larger and more circular mitochondria, characterized by impaired complex-I-linked respiration while preserving ATP production capacity. Additionally, dj-1β null mutant flies present an impaired autophagic response, which is suppressed by treatment with the antioxidant molecule N-Acetyl-L-Cysteine. Overall, our data point to a mechanism whereby DJ-1 plays a critical role in the maintenance of energy homeostasis, by sustaining mitochondrial homeostasis and affecting the autophagic flux through the maintenance of the cellular redox state. In light of the involvement of DJ-1 in neurodegenerative diseases and considering that neurons are highly energy-demanding cells, particularly sensitive to redox stress, our study sheds light on a key role of DJ-1 in the maintenance of cellular homeostasis.

Disuse-associated loss of the protease LONP1 in muscle impairs mitochondrial function and causes reduced skeletal muscle mass and strength

Mitochondrial proteolysis is an evolutionarily conserved quality-control mechanism to maintain proper mitochondrial integrity and function. However, the physiological relevance of stress-induced impaired mitochondrial protein quality remains unclear. Here, we demonstrate that LONP1, a major mitochondrial protease resides in the matrix, plays a role in controlling mitochondrial function as well as skeletal muscle mass and strength in response to muscle disuse. In humans and mice, disuse-related muscle loss is associated with decreased mitochondrial LONP1 protein. Skeletal muscle-specific ablation of LONP1 in mice resulted in impaired mitochondrial protein turnover, leading to mitochondrial dysfunction. This caused reduced muscle fiber size and strength. Mechanistically, aberrant accumulation of mitochondrial-retained protein in muscle upon loss of LONP1 induces the activation of autophagy-lysosome degradation program of muscle loss. Overexpressing a mitochondrial-retained mutant ornithine transcarbamylase (ΔOTC), a known protein degraded by LONP1, in skeletal muscle induces mitochondrial dysfunction, autophagy activation, and cause muscle loss and weakness. Thus, these findings reveal a role of LONP1-dependent mitochondrial protein quality-control in safeguarding mitochondrial function and preserving skeletal muscle mass and strength, and unravel a link between mitochondrial protein quality and muscle mass maintenance during muscle disuse.

Mitochondrial function is important for muscle maintenance and function, and mitochondrial proteolysis maintains mitochondrial integrity and function. Here the authors report that that loss of LONP1-dependent mitochondrial proteolysis in muscle causes reduced muscle mass and strength via activation of autophagy.

MiR-100-5p regulates cardiac hypertrophy through activation of autophagy by targeting mTOR

Autophagy has been proved to play a vital role in cardiac hypertrophy. The present study was designed to investigate the relationship between miR-100-5p and autophagy in the development of cardiac hypertrophy. Here, miR-100-5p expression was detected in abdominal aortic coarctation (AAC)-induced cardiac hypertrophy rats and Angiotensin II (Ang II)-stimulated cardiomyocytes. In vitro and in vivo experiments were performed to explore the function of miR-100-5p on autophagy and cardiac hypertrophy. We also investigated the mechanism of miR-100-5p on autophagy with dual-luciferase reporter assays, RNA immunoprecipitation (RIP), quantitative real-time PCR (qRT-PCR), western blot, immunofluorescence, and transmission electron microscopy (TEM). The results showed that miR-100-5p was highly expressed in hypertrophic hearts and Ang II-induced cardiomyocytes. Overexpression of miR-100-5p promoted the expression of cardiac hypertrophy markers ANP, BNP and β-MHC and cell surface area, while those were suppressed by miR-100-5p inhibitor. Knockdown of miR-100-5p by antagomiR significantly improves cardiac function and attenuate cardiac hypertrophy in vivo. Mechanistic investigation has found that miR-100-5p promote autophagy by targeting mTOR. Inhibition of autophagy by 3-methyladenine (3-MA) or mTOR overexpression could reverse the function of miR-100-5p in cardiac hypertrophy. These results elucidate that miR-100-5p promoted the pathogenesis of cardiac hypertrophy through autophagy activation by targeting mTOR.

DJ-1 activates the noncanonical NF-κB pathway via interaction with Cezanne to inhibit the apoptosis and promote the proliferation of Ishikawa cells

BACKGROUND

Endometrial cancer is generally one of the most evident malignant tumours of the female reproductive system, and the mechanisms underlying its cell proliferation and apoptosis are key to research in gynaecological oncology. In the paper, the in-depth molecular mechanism by which DJ-1 protein regulates the proliferation and apoptosis of Ishikawa cells was investigated.

METHODS AND RESULTS

DJ-1 knockdown and overexpressing Ishikawa stable cell lines were established by lentiviral transduction. The levels of DJ-1 and noncanonical NF-κB signaling key proteins were evaluated by Western blotting. Cell counting kit-8 (CCK-8) and flow cytometry were applied to analyze the cell viability and apoptosis. Co-immunoprecipitation experiment was utilized to assess the DJ-1-Cezanne interaction. The results showed that DJ-1 overexpression conferred apoptosis resistance and high proliferation on Ishikawa cells, while DJ-1 knockdown in Ishikawa cells produced the opposite results. These findings again suggested that DJ-1 inhibits the apoptosis and promotes the proliferation of Ishikawa cells. More crucially, further data showed that the noncanonical NF-κB activation was required for the regulation of Ishikawa cell proliferation and apoptosis by DJ-1. Meanwhile, it was found that noncanonical NF-κB pathway may be activated by DJ-1 interacting with and negatively regulating Cezanne in Ishikawa cells.

CONCLUSIONS

Overall, this work revealed that DJ-1 associates with and negatively regulates Cezanne and consequently triggers the noncanonical NF-κB activation, thereby regulating Ishikawa cell proliferation and apoptosis.

Cytoprotective Mechanisms of DJ-1: Implications in Cardiac Pathophysiology

DJ-1 was originally identified as an oncogene product while mutations of the gene encoding DJ-1/PARK7 were later associated with a recessive form of Parkinson's disease. Its ubiquitous expression and diversity of function suggest that DJ-1 is also involved in mechanisms outside the central nervous system. In the last decade, the contribution of DJ-1 to the protection from ischemia-reperfusion injury has been recognized and its involvement in the pathophysiology of cardiovascular disease is attracting increasing attention. This review describes the current and gaps in our knowledge of DJ-1, focusing on its role in regulating cardiovascular function. In parallel, we present original data showing an association between increased DJ-1 expression and antiapoptotic and anti-inflammatory markers following cardiac and vascular surgical procedures. Future studies should address DJ-1's role as a plausible novel therapeutic target for cardiovascular disease.

Mechanism of N-acetylcysteine in alleviating diabetic myocardial ischemia reperfusion injury by regulating PTEN/Akt pathway through promoting DJ-1

Ischemic heart disease is the main cardiovascular complication of diabetes patients which is mainly caused by oxidative stress. DJ-1 is the key regulator for myocardial protection through inhibiting phosphatase and tensin homolog deleted on chromosome 10 (PTEN) and activating Akt (also known as PKB or protein kinase B). This research is to investigate whether the antioxidant N-acetylcysteine (NAC) could alleviate diabetic myocardial ischemia/reperfusion (I/R) injury by the protective molecule DJ-1. DJ-1 in rat myocardial H9c2 cells and cardiac tissue was respectively knocked down by siRNA and adeno-associated virus (AAV). From the present study, it could be found that compared with high glucose (HG)-normal (N)/DM group, hypoxia/reoxygenation (H/R) or I/R injury can aggravate oxidative stress injury and apoptosis rate of myocardial cells, inhibit the expression of Bcl-2, activate the BAX and cleaved caspase-3 (c-caspase-3) protein and PTEN/Akt pathway. However, in the groups of HG-N, DM, HG-N+I/R and DM+I/R, NAC can significantly reduce oxidative stress injury and apoptosis rate of myocytes, promote the Bcl-2 and DJ-1 molecules, inhibit BAX and c-caspase-3 protein and PTEN/Akt pathway. Compared with HG-N+I/R+NAC and DM+I/R+NAC groups, the oxidative stress injury, apoptosis rate of myocardial cells and heart tissues increased after the knockdown of DJ-1, the expression of Bcl-2 and DJ-1 were inhibited, the BAX and c-caspase-3 expression was increased, and PTEN/Akt pathway was activated. Taken together, the findings suggest that NAC can reduce I/R injury in diabetic myocardium by up-regulating the PTEN/Akt pathway through the level of DJ-1.

DJ-1 Deficiency in Hepatocytes Improves Liver Ischemia-Reperfusion Injury by Enhancing Mitophagy

BACKGROUND & AIMS

DJ-1 is universally expressed in various tissues and organs and is involved in the physiological processes in various liver diseases. However, the role of DJ-1 in liver ischemia-reperfusion (I/R) injury is largely unknown.

METHODS

In this study, we first examined the DJ-1 expression changes in the liver tissues of mice and clinical donor after hepatic I/R by both quantitative polymerase chain reaction and Western blotting assays. Then we investigated the role of DJ-1 in I/R injury by using a murine liver I/R model.

RESULTS

We demonstrated that DJ-1 down-regulation in both human and mouse liver tissues in response to I/R injury and Dj-1 deficiency in hepatocytes but not in myeloid cells could significantly ameliorate I/R induced liver injury and inflammatory responses. This hepatoprotective effect was dependent on enhanced autophagy in Dj-1 knockout mice, because inhibition of autophagy by 3-methyladenine and chloroquine could reverse the protective effect on hepatic I/R injury in Dj-1 knockout mice.

CONCLUSIONS

Dj-1 deficiency in hepatocytes significantly enhanced mitochondrial accumulation and protein stability of PARKIN, which in turn promotes the onset of mitophagy resulting in elevated clearance of damaged mitochondria during I/R injury.

Bcl-2 Is Involved in Cardiac Hypertrophy through PI3K-Akt Pathway

Cardiac hypertrophy (CH) is a common cause of sudden cardiac death and heart failure, resulting in a significant medical burden. The present study is aimed at exploring potential CH-related pathways and the key downstream effectors. The gene expression profile of GSE129090 was obtained from the Gene Expression Omnibus database (GEO), and 1325 differentially expressed genes (DEGs) were identified, including 785 upregulated genes and 540 downregulated genes. Kyoto Encyclopedia of Genes and Genomes (KEGG) and Reactome pathway enrichment analysis of DEGs were then performed. Although there were no pathways enriched by downregulated genes, many CH-related pathways were identified by upregulated genes, including PI3K-Akt signaling pathway, extracellular matrix- (ECM-) receptor interaction, regulation of actin cytoskeleton, and hypertrophic cardiomyopathy (HCM). In the deeper analysis of PI3K-Akt signaling pathway, we found all the signaling transduction pointed to B cell lymphoma-2- (Bcl-2-) mediated cell survival. We then demonstrated that PI3K-Akt signaling pathway was indeed activated in cardiac hypertrophy. Furthermore, no matter LY294002, an inhibitor of the PI3K/AKT signaling pathway, or Venetoclax, a selective Bcl-2 inhibitor, protected against cardiac hypertrophy. In conclusion, these data indicate that Bcl-2 is involved in cardiac hypertrophy as a key downstream effector of PI3K-Akt signaling pathway, suggesting a potential therapeutic target for the clinical management of cardiac hypertrophy.

Myocardial proteomic profile in pulmonary arterial hypertension

Pulmonary arterial hypertension (PAH) is a rare, fatal, and incurable disorder. Although advances in the understanding of the PAH pathobiology have been seen in recent years, molecular processes underlying heart remodelling over the course of PAH are still insufficiently understood. Therefore, the aim of this study was to investigate myocardial proteomic profile of rats at different stages of monocrotaline-induced PAH. Samples of left and right ventricle (LV and RV) free wall collected from 32 Wistar rats were subjected to proteomic analysis using an isobaric tag for relative quantitation method. Hemodynamic parameters indicated development of mild elevation of pulmonary artery pressure in the early PAH group (27.00 ± 4.93 mmHg) and severe elevation in the end-stage PAH group (50.50 ± 11.56 mmHg). In early PAH LV myocardium proteins that may be linked to an increase in inflammatory response, apoptosis, glycolytic process and decrease in myocardial structural proteins were differentially expressed compared to controls. During end-stage PAH an increase in proteins associated with apoptosis, fibrosis and cardiomyocyte Ca2+ currents as well as decrease in myocardial structural proteins were observed in LV. In RV during early PAH, especially proteins associated with myocardial structural components and fatty acid beta-oxidation pathway were upregulated. During end-stage PAH significant changes in RV proteins abundance related to the increased myocardial structural components, intensified fibrosis and glycolytic processes as well as decreased proteins related to cardiomyocyte Ca2+ currents were observed. At both PAH stages changes in RV proteins linked to apoptosis inhibition were observed. In conclusion, we identified changes of the levels of several proteins and thus of the metabolic pathways linked to the early and late remodelling of the left and right ventricle over the course of monocrotaline-induced PAH to delineate potential therapeutic targets for the treatment of this severe disease.

Identification of New Targets and the Virtual Screening of Lignans against Alzheimer's Disease

Alzheimer's disease (AD) is characterized by the progressive disturbance in cognition and affects approximately 36 million people, worldwide. However, the drugs used to treat this disease are only moderately effective and do not alter the course of the neurodegenerative process. This is because the pathogenesis of AD is mainly associated with oxidative stress, and current drugs only target two enzymes involved in neurotransmission. Therefore, the present study sought to identify potential multitarget compounds for enzymes that are directly or indirectly involved in the oxidative pathway, with minimal side effects, for AD treatment. A set of 159 lignans were submitted to studies of QSAR and molecular docking. A combined analysis was performed, based on ligand and structure, followed by the prediction of absorption, distribution, metabolism, excretion, and toxicity (ADMET) properties. The results showed that the combined analysis was able to select 139 potentially active and multitarget lignans targeting two or more enzymes, among them are c-Jun N-terminal kinase 3 (JNK-3), protein tyrosine phosphatase 1B (PTP1B), nicotinamide adenine dinucleotide phosphate oxidase 1 (NOX1), NADPH quinone oxidoreductase 1 (NQO1), phosphodiesterase 5 (PDE5), nuclear factor erythroid 2-related factor 2 (Nrf2), cycloxygenase 2 (COX-2), and inducible nitric oxide synthase (iNOS). The authors conclude that compounds (06) austrobailignan 6, (11) anolignan c, (19) 7-epi-virolin, (64) 6-[(2R,3R,4R,5R)-3,4-dimethyl-5-(3,4,5-trimethoxyphenyl)oxolan-2-yl]-4-methoxy-1,3-benzodioxole, (116) ococymosin, and (135) mappiodoinin b have probabilities that confer neuroprotection and antioxidant activity and represent potential alternative AD treatment drugs or prototypes for the development of new drugs with anti-AD properties.

Inhibiting SLC26A4 reverses cardiac hypertrophy in H9C2 cells and in rats

Background

It has been confirmed that mutations in solute carrier family 26 member 4 (SLC26A4) contribute to pendred syndrome. However, the role of SLC26A4 in cardiac hypertrophy and the signaling pathways remain unclear.

Methods

Cardiomyocytes were treated by 200 µM phenylephrine (PE) to induce cardiac hypertrophy. Also, the expression of SLC26A4, GSK3, cardiac hypertrophy markers including atrial natriuretic peptide (ANP) and brain natriuretic peptide (BNP) was detected through real-time quantitative polymerase chain reaction (RT-qPCR). Flow cytometry assay was used to test the apoptosis of PE-induced cardiomyocytes transfected by small interfere RNA (siRNA)-SLC26A4. Furthermore, we detected the expression of autophagy-related markers including light chain 3 (LC3) and P62. Finally, we established a rat model of abdominal aortic constriction (AAC)-induced cardiac hypertrophy in vivo.

Results

RT-qPCR results showed that the mRNA expression of SLC26A4 was significantly up-regulated in PE-induced cardiac hypertrophy. After inhibiting SLC26A4, the release of ANP and BNP was significantly decreased and GSK3β was elevated in vivo and in vitro. Furthermore, inhibiting SLC26A4 promoted apoptosis of cardiac hypertrophy cells. In addition, LC3 was down-regulated and P62 was enhanced after transfection of siRNA-SLC26A4.

Conclusion

Our findings revealed that SLC26A4 increases cardiac hypertrophy, and inhibiting SLC26A4 could decrease the release of ANP/BNP and promote the expression of GSK-3β in vitro and in vivo. Moreover, SLC26A4 silencing inhibits autophagy of cardiomyocytes and induces apoptosis of cardiomyocytes. Therefore, SLC26A4 possesses potential value to be a therapeutic target of cardiac hypertrophy, and our study provides new insights into the mechanisms of cardiac hypertrophy.

Protective effect of hyperoside on heart failure rats via attenuating myocardial apoptosis and inducing autophagy

Heart failure (HF) is one of the most severe heart conditions, which lacks effective therapies. Therefore, it is necessary to develop more efficient drugs for HF. In this study, we investigated the cardioprotective effects of hyperoside against the pathological progression of HF. Thoracic aortic constriction (TAC) was performed to induce HF in rats. Hyperoside treatment improved cardiac function, decreased cardiomyocyte cross-sectional area and heart weight to body weight (HW/BW) ratio in HF rats. Moreover, hyperoside administration repressed apoptosis as evidenced by changing apoptosis-related protein levels, and promoted autophagy in TAC rats and angiotensin II (AngII)-induced H9C2 cells. Inhibition of autophagy by 3-methyladenine (3-MA) attenuated the beneficial effect of hyperoside against apoptosis in H9C2 cells. In summary, these data confirm that hyperoside effectively alleviates HF via suppressing apoptosis and inducing autophagy, which provides evidence that hyperoside may serve as a promising natural drug for treating HF.

Ulinastatin Reduces the Severity of Intestinal Damage in the Neonatal Rat Model of Necrotizing Enterocolitis

Background

Ulinastatin is a protease inhibitor derived from urine that has shown anti-inflammatory effects in human disease, including in sepsis. Necrotizing enterocolitis (NEC) is a common gastrointestinal disease in premature infants. Our aim was to explore the effects of ulinastatin on a neonatal NEC rat model.

Material/Methods

Forty-five neonatal rats were divided into 3 groups: normal control; NEC+sepsis-induced kidney injury (SIRS); NEC/SIRS+ulinastatin. The NEC/SIRS model was induced by injection of intraperitoneal saline, enteral formula feeding, hypoxia-hyperoxide, and cold stress exposure. The NEC/SIRS neonatal rats were perfused with ulinastatin at a dose of 10 000 u/kg/day. Giemsa staining and hematoxylin and eosin (H&E) were performed to evaluate the severity of intestinal damage. To assess intestinal cell apoptosis, we examined the expression of caspase-3 by TUNEL staining and western blot analysis. Intestinal levels of inflammatory cytokines (IL-1β, IL-6, and TNF-α) were examined using ELISA assay.

Results

Rats in the NEC treated with ulinastatin group had better physiological status and histological score compared to the NEC/SIRS group. Ulinastatin reduced NEC-induced weight loss. Macroscopic and microscopic morphology analyses showed that rats in the NEC treated with ulinastatin group had lower severity of intestinal damage compared to the NEC/SIRS group. TUNEL staining and caspase-3 expression detection results revealed that ulinastatin significantly inhibited intestinal cell apoptosis of NEC. Furthermore, ulinastatin decreased the intestinal levels of IL-1β, IL-6, and TNF-α in NEC.

Conclusions

Ulinastatin could ameliorate the severity of intestinal damage in NEC and possess anti-apoptosis and anti-inflammation effects.

DJ-1 Suppresses Cytoplasmic TDP-43 Aggregation in Oxidative Stress-Induced Cell Injury

DJ-1 (also called PARK7) is a multifunctional redox-sensitive protein that is protective against oxidative stress-induced cell death. TAR DNA-binding protein 43 (TDP-43) is a major protein component of pathological inclusions in amyotrophic lateral sclerosis and frontotemporal dementia. Reducing aberrant aggregation of TDP-43 is a potential approach to prevent cell death. To investigate whether DJ-1 might inhibit TDP-43 aggregation to exert a protective effect in oxidative stress-induced injury, we tested the protein level and subcellular localization of TDP-43 and DJ-1 in SH-SY5Y cells transfected with wild-type DJ-1, DJ-1 mutant (L166P) cDNA, or DJ-1 siRNA. We show that oxidative stress induced by paraquat leads to the formation of cytosolic TDP-43 aggregation in SH-SY5Y cells. DJ-1 overexpression decreases paraquat-induced cytoplasmic accumulation of TDP-43 in SH-SY5Y cells and protects against paraquat-induced cell death. Transfection of DJ-1 L166P mutant or DJ-1 siRNA leads to increased cytosolic aggregation of TDP-43 in paraquat-treated SH-SY5Y cells and promotes cell death. These data suggest that DJ-1 may protect against oxidative stress-induced cell death through the suppression of cytoplasmic TDP-43 aggregation.

Park 7: A Novel Therapeutic Target for Macrophages in Sepsis-Induced Immunosuppression

Sepsis remains a serious and life-threatening condition with high morbidity and mortality due to uncontrolled inflammation together with immunosuppression with few therapeutic options. Macrophages are recognized to play essential roles throughout all phases of sepsis and affect both immune homeostasis and inflammatory processes, and macrophage dysfunction is considered to be one of the major causes for sepsis-induced immunosuppression. Currently, Parkinson disease protein 7 (Park 7) is known to play an important role in regulating the production of reactive oxygen species (ROS) through interaction with p47^phox, a subunit of NADPH oxidase. ROS are key mediators in initiating toll-like receptor (TLR) signaling pathways to activate macrophages. Emerging evidence has strongly implicated Park 7 as an antagonist for sepsis-induced immunosuppression, which suggests that Park 7 may be a novel therapeutic target for reversing immunosuppression compromised by sepsis. Here, we review the main characteristics of sepsis-induced immunosuppression caused by macrophages and provide a detailed mechanism for how Park 7 antagonizes sepsis-induced immunosuppression initiated by the macrophage inflammatory response. Finally, we further discuss the most promising approach to develop innovative drugs that target Park 7 in patients whose initial presentation is at the late stage of sepsis.

Irisin alleviates pressure overload-induced cardiac hypertrophy by inducing protective autophagy via mTOR-independent activation of the AMPK-ULK1 pathway

In hypertrophic hearts, autophagic flux insufficiency is recognized as a key pathology leading to maladaptive cardiac remodeling and heart failure. This study aimed to illuminate the cardioprotective role and mechanisms of a new myokine and adipokine, irisin, in cardiac hypertrophy and remodeling. Adult male wild-type, mouse-FNDC5 (irisin-precursor)-knockout and FNDC5 transgenic mice received 4 weeks of transverse aortic constriction (TAC) alone or combined with intraperitoneal injection of chloroquine diphosphate (CQ). Endogenous FNDC5 ablation aggravated and exogenous FNDC5 overexpression attenuated the TAC-induced hypertrophic damage in the heart, which was comparable to the protection of irisin against cardiomyocyte hypertrophy induced by angiotensin II (Ang II) or phenylephrine (PE). Accumulated autophagosome and impaired autophagy flux occurred in the TAC-treated myocardium and Ang II- or PE-insulted cardiomyocytes. Irisin deficiency caused reduced autophagy and aggravated autophagy flux failure, whereas irisin overexpression or supplementation induced protective autophagy and improved autophagy flux, which were reversed by autophagy inhibitors Atg5 siRNA, 3-MA and CQ. Irisin boosted the activity of only AMPK but not Akt and MAPK family members in hypertrophic hearts and cultured cardiomyocytes and further activated ULK1 at Ser555 but not Ser757 and did not affect the mTOR-S6K axis. Blockage of AMPK and ULK1 with compund C and SBI-0206965, respectively, both abrogated irisin's protection against cardiomyocyte hypertrophic injury and reversed its induction of both autophagy and autophagy flux. Our results suggest that irisin protects against pressure overload-induced cardiac hypertrophy by inducing protective autophagy and autophagy flux via activating AMPK-ULK1 signaling.