Oxidative stress stimulates autophagic flux during ischemia/reperfusion

Autophagy-monitoring and autophagy-deficient mice

Discovery of yeast autophagy-related (ATG) genes and subsequent identification of their homologs in other organisms have enabled researchers to investigate physiological functions of macroautophagy/autophagy using genetic techniques. Specific identification of autophagy-related structures is important to evaluate autophagic activity, and specific ablation of autophagy-related genes is a critical means to determine the requirements of autophagy. Here, we review currently available mouse models, particularly focusing on autophagy (and mitophagy) indicator models and systemic autophagy-related gene-knockout mouse models.

Roles of Autophagy in Ischemic Heart Diseases and the Modulatory Effects of Chinese Herbal Medicine

Autophagy is an evolutionarily conserved degradation process which eliminates dysfunctional proteins and cytoplasmic components to maintain homeostasis for cell survival. Increasing evidence has demonstrated the modulatory role of autophagy in ischemic heart diseases (IHDs). Traditionally, this process has been recognized as having protective functions, such as inhibiting atherosclerosis progression and reducing cell death during the ischemic phase. However, recent studies have suggested its dual roles in myocardial ischemia/reperfusion (MIR) injury. Excessive autophagy may play a deleterious role in cardiac function, due to overwhelming clearance of cellular constituents and proteins. Hence modulation of autophagy to increase cardiomyocyte survival and improve cardiac function is meaningful for the treatment of IHD. Chinese herbal medicine, including extractive compounds and patented drugs, has shown its potential role in treating IHD by addressing autophagy-related mechanisms. This review summarizes the updated knowledge on the molecular basis and modulatory role of autophagy in IHD and the recent progress of Chinese herbal medicine in its treatment.

Monitoring and Measuring Autophagy

Autophagy is a cytoplasmic degradation system, which is important for starvation adaptation and cellular quality control. Recent advances in understanding autophagy highlight its importance under physiological and pathological conditions. However, methods for monitoring autophagic activity are complicated and the results are sometimes misinterpreted. Here, we review the methods used to identify autophagic structures, and to measure autophagic flux in cultured cells and animals. We will also describe the existing autophagy reporter mice that are useful for autophagy studies and drug testing. Lastly, we will consider the attempts to monitor autophagy in samples derived from humans.

Association of catalase polymorphisms with primary open-angle glaucoma in a Chinese population

PURPOSE

Many genes have been associated with primary open-angle glaucoma (POAG). This study was conducted to investigate whether catalase (CAT) polymorphisms play a significant role in POAG in a Chinese population.

METHODS

A cohort of 416 unrelated POAG patients and 997 unrelated control subjects was included in this case-control association study. CAT functional single-nucleotide polymorphisms (SNPs), including rs1001179, rs7943316, and rs769217, were genotyped by SNaPshot method. The genotype and allele frequencies were evaluated using the χ² tests. The linkage disequilibrium (LD) and haplotype block structure association were examined using the program Haploview (Broad Institute, Cambridge, MA).

RESULTS

There was a statistically significant difference for CAT functional SNP rs769217 between POAG cases and controls in the allelic model (p = 0.004, OR = 1.27, 95% CI 1.08-1.49). At this SNP, the allele frequency of the C allele in POAG cases was 0.587, which was higher than that in controls (0.528). However, no association was found for rs1001179 and rs7943316 with POAG. Pairwise LD analysis showed high LD between rs769217 and rs7943316 (D' = 0.857, r² = 0.252, confidence bounds 0.71-0.93). After the association analysis for haplotype block structure generated from rs769217 with rs7943316, the data showed no significant association between the cases and controls.

CONCLUSIONS

This study showed that CAT functional SNP rs769217 was significantly associated with POAG, implying that the CAT gene variants may play a role in the pathogenesis of POAG in the Chinese population.

HIV-1 Nef-induced cardiotoxicity through dysregulation of autophagy

Cardiovascular disease is a leading cause of co-morbidity in HIV-1 positive patients, even those in whom plasma virus levels are well-controlled. The pathogenic mechanism of HIV-1-associated cardiomyopathy is unknown, but has been presumed to be mediated indirectly, owing to the absence of productive HIV-1 replication in cardiomyocytes. We sought to investigate the effect of the HIV-1 auxiliary protein, Nef, which is suspected of extracellular release by infected CD4+ T cells on protein quality control and autophagy in cardiomyocytes. After detection of Nef in the serum of HIV-1 positive patients and the accumulation of this protein in human and primate heart tissue from HIV-1/SIV-infected cells we employed cell and molecular biology approaches to investigate the effect of Nef on cardiomyocyte-homeostasis by concentrating on protein quality control (PQC) pathway and autophagy. We found that HIV-1 Nef-mediated inhibition of autophagy flux leads to cytotoxicity and death of cardiomyocytes. Nef compromises autophagy at the maturation stage of autophagosomes by interacting with Beclin 1/Rab7 and dysregulating TFEB localization and cellular lysosome content. These effects were reversed by rapamycin treatment. Our results indicate that HIV-1 Nef-mediated inhibition of cellular PQC is one possible mechanism involved in the development of HIV-associated cardiomyopathy.

Circular RNA HIPK2 regulates astrocyte activation via cooperation of autophagy and ER stress by targeting MIR124-2HG

Circular RNAs are a subclass of noncoding RNAs in mammalian cells; however, whether these RNAs are involved in the regulation of astrocyte activation is largely unknown. Here, we have shown that the circular RNA HIPK2 (circHIPK2) functions as an endogenous microRNA-124 (MIR124-2HG) sponge to sequester MIR124-2HG and inhibit its activity, resulting in increased sigma non-opioid intracellular receptor 1 (SIGMAR1/OPRS1) expression. Knockdown of circHIPK2 expression significantly inhibited astrocyte activation via the regulation of autophagy and endoplasmic reticulum (ER) stress through the targeting of MIR124-2HG and SIGMAR1. These findings were confirmed in vivo in mouse models, as microinjection of a circHIPK2 siRNA lentivirus into mouse hippocampi inhibited astrocyte activation induced by methamphetamine or lipopolysaccharide (LPS). These findings provide novel insights regarding the specific contribution of circHIPK2 to astrocyte activation in the context of drug abuse as well as for the treatment of a broad range of neuroinflammatory disorders.

Bisphenol a induces autophagy and apoptosis concurrently involving the Akt/mTOR pathway in testes of pubertal SD rats

Bisphenol A (BPA), a typical endocrine disrupting chemical (EDC), has been proven to cause male reproductive toxicity. However, the precise mechanisms of this effect are still unclear. Puberty is a crucial period of reproductive development, and adolescents are more susceptible to xenobiotics. This research was designed to explore the mechanism of BPA toxicity on pubertal male reproduction. Rats were exposed to 0, 2, 10, 50 mg kg^-1 bw BPA, then the levels of sex hormones, oxidative stress, and semen quality were detected. HE staining, TUNEL assay and transmission electron microscopy were used to investigate the morphological changes, apoptosis, and autophagy in testes, respectively. Expressions of relevant genes and proteins were measured by RT-PCR, western blotting, and immunohistochemical staining. The results indicated that BPA exposure led to oxidative stress and endocrine disorders in pubertal male SD rats, caused apoptosis and autophagy in testes, and then damaged spermatogenesis ultimately. The Akt pathway was activated and the mTOR pathway was inhibited in the process. Taken together, BPA induced apoptosis and autophagy concurrently in pubertal testes, and this added a new layer to our understanding on male reproductive toxicity of BPA. © 2016 Wiley Periodicals, Inc. Environ Toxicol 32: 1977-1989, 2017.

Efficacy and Mechanisms of Chinese Medicine on the Modulation of Myocardial Autophagy in Cardiovascular Disease

Autophagy refers to the process in which the cellular lysosome degrades the cell’s own damaged organelles and related macromolecule substances. It plays important roles in the homeostasis of organs, cell survival, and stable development. Previous studies indicate that the process of cardiopathology is closely associated with autophagy and some of Chinese medicines (active compounds and formulae) are found to have beneficial effects on injured cardiomyocytes via the modulation of autophagy. This review highlights the efficacy of the action of Chinese medicine on the regulation of myocardial autophagy and summarizes the related molecular and signal mechanisms. Our study discovers that some active compounds and formulae of Chinese medicines react on the specific targets of autophagy in related signal pathways to exert protective effects in the processes of ischemia and reperfusion, as well as, in other cardiopathological models. Parts of these compounds even have the characteristics of multiple targets in autophagic signal pathways and dual-directional regulated actions on autophagy, suggesting that Chinese medicines, which possess the ability to modulate autophagy, might improve effective cardio protection in the treatment of cardiovascular disease.

Potential signaling pathways of acute endurance exercise-induced cardiac autophagy and mitophagy and its possible role in cardioprotection

Cardiac myocytes are terminally differentiated cells and possess extremely limited regenerative capacity; therefore, preservation of mature cardiac myocytes throughout the individual's entire life span contributes substantially to healthy living. Autophagy, a lysosome-dependent cellular catabolic process, is essential for normal cardiac function and mitochondria maintenance. Therefore, it may be reasonable to hypothesize that if endurance exercise promotes cardiac autophagy and mitochondrial autophagy or mitophagy, exercise-induced cardiac autophagy (EICA) or exercise-induced cardiac mitophagy (EICM) may confer propitious cellular environment and thus protect the heart against detrimental stresses, such as an ischemia-reperfusion (I/R) injury. However, although the body of evidence supporting EICA and EICM is growing, the molecular mechanisms of EICA and EICM and their possible roles in cardioprotection against an I/R injury are poorly understood. Here, we introduce the general mechanisms of autophagy in an attempt to integrate potential molecular pathways of EICA and EICM and also highlight a potential insight into EICA and EICM in cardioprotection against an I/R insult.

Sitagliptin Attenuates Endothelial Dysfunction of Zucker Diabetic Fatty Rats: Implication of the Antiperoxynitrite and Autophagy

Although the contributions of sitagliptin to endothelial function in diabetes mellitus were previously reported, the potential mechanisms still remain undefined. Our research was intended to explore the underlying mechanisms of protective effects of sitagliptin treatment on endothelial dysfunction in Zucker diabetic fatty (ZDF) rats. Male lean nondiabetic Zucker rats were used as control and male obese ZDF rats were randomly divided into ZDF and ZDF + sitagliptin groups. The significant decrease in endothelium-dependent relaxation induced by acetylcholine was observed in mesenteric arteries and thoracic aorta rings of ZDF rats. The administration of sitagliptin restored the vascular function effectively. The morphology study showed severe endothelial injuries in thoracic aortas of ZDF rats, and sitagliptin treatment attenuated these changes. The increased malondialdehyde levels and decreased superoxide dismutase activities in serum of ZDF rats were reversed by sitagliptin treatment. Sitagliptin also increased the expression of endothelial nitric oxide synthase and microtubule-associated protein 1 light chain 3 (LC3) and decreased the expression of inducible nitric oxide synthase, 3-nitrotyrosine, and p62 in ZDF rats. After giving Fe (III) tetrakis (1-methyl-4-pyridyl) porphyrin pentachloride porphyrin pentachloride (FeTMPyP, a peroxynitrite [ONOO^-] scavenger) or sitagliptin to high-glucose (30 mmol/L, 48 hours) cultured human umbilical vein endothelial cells (HUVECs), the increased levels of Beclin-1 and lysosome-associated membrane protein type 2 were detected. Both FeTMPyP and sitagliptin also significantly increased the number of mRFP-GFP-LC3 dots per cell, suggesting that autophagic flux was increased in HUVECs. Our study indicated that sitagliptin treatment can improve the endothelium-dependent relaxation and attenuate the endothelial impairment of ZDF rats. The protective effects of sitagliptin are possibly related to antiperoxynitrite and promoting autophagy.

Methods for Measuring Autophagy in Mice

Autophagy is a dynamic intracellular process that mediates the degradation of damaged cytoplasmic components by the lysosome. This process plays important roles in maintaining normal cellular homeostasis and energy balance. Measuring autophagy activity is critical and although the determination of autophagic flux in isolated cells is well documented, there is a need to have reliable and quantitative assays to evaluate autophagy in whole organisms. Because mouse models have been precious in establishing the functional significance of autophagy under physiological or pathological conditions, we present in this chapter a compendium of the current available methods to measure autophagy in mice, and discuss their advantages and limitations.

RLIP76 Depletion Enhances Autophagic Flux in U251 Cells

Our previous study showed that RalA-binding protein 1 (RLIP76) is overexpressed in gliomas and is associated with higher tumour grade and decreased patient survival. Furthermore, RLIP76 downregulation increases chemosensitivity of glioma cells to temozolomide by inducing apoptosis. However, other mechanisms underlying RLIP76-associated chemoresistance are unknown. In this study, we investigated the effect of RLIP76 depletion on autophagy. RLIP76 was knocked down in U251 glioma cells using shRNA and autophagy-related proteins, and PI3K/Akt signalling components were evaluated. RLIP76 depletion significantly increased cell autophagy as demonstrated by a significant increase in LC3 II, autophagy protein 5 (ATG-5), and Beclin1, and a decrease in p62 expression levels. Furthermore, RLIP76 knockdown increased autophagic flux in U251 cells as autolysosome numbers increased relative to autophagosome numbers. Autophagy induced by RLIP76 knockdown resulted in increased apoptosis that was independent of temozolomide treatment. Moreover, RLIP76 knockdown decreased PI3K and Akt activation. RLIP76 depletion also resulted in decreased levels of the anti-apoptotic protein Bcl2. LY294002, a PI3K/Akt pathway inhibitor, led to increased autophagy and apoptosis in U251 RLIP76-depleted cells. Therefore, RLIP76 knockdown increased autophagic flux and apoptosis in U251 glioma cells, possibly through inhibition of the PI3K/Akt pathway. Thus, this study provides a novel mechanism for the role of RLIP76 in glioma pathogenesis and chemoresistance.

Effects of a novel ascorbate-based protocol on infarct size and ventricle function in acute myocardial infarction patients undergoing percutaneous coronary angioplasty

INTRODUCTION

This study was designed to test the hypothesis that high-dose ascorbate prior to reperfusion followed by low chronic oral doses ameliorate myocardial reperfusion injury (MRI) in acute myocardial infarction patients subjected to primary percutaneous coronary angioplasty (PCA).

MATERIAL AND METHODS

A randomized double-blind placebo-controlled and multicenter clinical trial was performed on acute myocardial infarction (AMI) patients who underwent PCA. Sodium ascorbate (320 mmol/l, n = 53) or placebo (n = 46) was infused 30 min prior to PCA. Blood samples were drawn at enrolment (M1), after balloon deflation (M2), 6-8 h after M2 (M3) and at discharge (M4). Total antioxidant capacity of plasma (ferric reducing ability of plasma - FRAP), erythrocyte reduced glutathione (GSH) and plasma ascorbate levels were determined in blood samples. Cardiac magnetic resonance (CMR) was performed at 7-15 days and 2-3 months following PCA. Ninety-nine patients were enrolled. In 67 patients, the first CMR was performed, and 40 patients completed follow-up.

RESULTS

The ascorbate group showed significantly higher ascorbate and FRAP levels and a decrease in the GSH levels at M2 and M3 (p < 0.05). There were no significant differences in the infarct size, indexed end-systolic volume and ejection fraction at both CMRs. There was a significant amelioration in the decreased ejection fraction between the first and second CMR in the ascorbate group (p < 0.05).

CONCLUSIONS

Ascorbate given prior to reperfusion did not show a significant difference in infarct size or ejection fraction. However, it improved the change in ejection fraction determined between 7-15 days and 2-3 months. This result hints at a possible functional effect of ascorbate to ameliorate MRI.

Myocardial stress and autophagy: mechanisms and potential therapies

Autophagy is a ubiquitous cellular catabolic process responsive to energy stress. Research over the past decade has revealed that cardiomyocyte autophagy is a prominent homeostatic pathway, important in adaptation to altered myocardial metabolic demand. The cellular machinery of autophagy involves targeted direction of macromolecules and organelles for lysosomal degradation. Activation of autophagy has been identified as cardioprotective in some settings (that is, ischaemia and ischaemic preconditioning). In other situations, sustained autophagy has been linked with cardiopathology (for example, sustained pressure overload and heart failure). Perturbation of autophagy in diabetic cardiomyopathy has also been observed and is associated with both adaptive and maladaptive responses to stress. Emerging research findings indicate that various forms of selective autophagy operate in parallel to manage various types of catabolic cellular cargo including mitochondria, large proteins, glycogen, and stored lipids. In this Review, induction of autophagy associated with cardiac benefit or detriment is considered. The various static and dynamic approaches used to measure autophagy are critiqued, and current inconsistencies in the understanding of autophagy regulation in the heart are highlighted. The prospects for pharmacological intervention to achieve therapeutic manipulation of autophagic processes are also discussed.

Hypercholesterolemia downregulates autophagy in the rat heart

BACKGROUND

We have previously shown that efficiency of ischemic conditioning is diminished in hypercholesterolemia and that autophagy is necessary for cardioprotection. However, it is unknown whether isolated hypercholesterolemia disturbs autophagy or the mammalian target of rapamycin (mTOR) pathways. Therefore, we investigated whether isolated hypercholesterolemia modulates cardiac autophagy-related pathways or programmed cell death mechanisms such as apoptosis and necroptosis in rat heart.

METHODS

Male Wistar rats were fed either normal chow (NORM; n = 9) or with 2% cholesterol and 0.25% cholic acid-enriched diet (CHOL; n = 9) for 12 weeks. CHOL rats exhibited a 41% increase in plasma total cholesterol level over that of NORM rats (4.09 mmol/L vs. 2.89 mmol/L) at the end of diet period. Animals were sacrificed, hearts were excised and briefly washed out. Left ventricles were snap-frozen for determination of markers of autophagy, mTOR pathway, apoptosis, and necroptosis by Western blot.

RESULTS

Isolated hypercholesterolemia was associated with a significant reduction in expression of cardiac autophagy markers such as LC3-II, Beclin-1, Rubicon and RAB7 as compared to controls. Phosphorylation of ribosomal S6, a surrogate marker for mTOR activity, was increased in CHOL samples. Cleaved caspase-3, a marker of apoptosis, increased in CHOL hearts, while no difference in the expression of necroptotic marker RIP1, RIP3 and MLKL was detected between treatments.

CONCLUSIONS

This is the first comprehensive analysis of autophagy and programmed cell death pathways of apoptosis and necroptosis in hearts of hypercholesterolemic rats. Our data show that isolated hypercholesterolemia suppresses basal cardiac autophagy and that the decrease in autophagy may be a result of an activated mTOR pathway. Reduced autophagy was accompanied by increased apoptosis, while cardiac necroptosis was not modulated by isolated hypercholesterolemia. Decreased basal autophagy and elevated apoptosis may be responsible for the loss of cardioprotection reported in hypercholesterolemic animals.

Protein Quality Control Dysfunction in Cardiovascular Complications Induced by Anti-Cancer Drugs

Cardiovascular complications, including heart failure, hypertension, ischemic syndromes and venous thromboembolism, have been identified in patients treated with anti-cancer drugs. Oxidative stress, mitochondrial dysfunction and DNA synthesis inhibition are considered to be responsible for the cardiotoxicity induced by these agents. Protein quality control (PQC) has 3 major components, including the endoplasmic reticulum (ER), the ubiquitin-proteasome system (UPS) and the autophagy-lysosome system, and participates in protein folding and degradation to maintain protein homeostasis. We have demonstrated that PQC dysfunction is a new causal mechanism for the development of cardiac hypertrophy and failure. Increasing evidence shows that anti-cancer drugs, such as tyrosine kinase inhibitors, proteasome inhibitors, anthracyclines and autophagy inhibitors, cause PQC dysfunction. Here, we provide an overview of the potential role of PQC dysfunction in the development of cardiovascular complications induced by anti-cancer drugs.

Regulation of autophagy by some natural products as a potential therapeutic strategy for cardiovascular disorders

Autophagy is a lysosomal degradation process through which long-lived and misfolded proteins and organelles are sequestered, degraded by lysosomes, and recycled. Autophagy is an essential part of cardiomyocyte homeostasis and increases the survival of cells following cellular stress and starvation. Recent studies made clear that dysregulation of autophagy in the cardiovascular system leads to heart hypertrophy and failure. In this manner, autophagy seems to be an attractive target in the new treatment of cardiovascular diseases. Although limited activation of autophagy is generally considered to be cardioprotective, excessive autophagy leads to cell death and cardiac atrophy. Natural products such as resveratrol, berberine, and curcumin that are present in our diet, can trigger autophagy via canonical (Beclin-1-dependent) and non-canonical (Beclin-1-independent) pathways. The autophagy-modifying capacity of these compounds should be taken into consideration for designing novel therapeutic agents. This review focuses on the role of autophagy in the cardioprotective effects of these compounds.

Berbamine postconditioning protects the heart from ischemia/reperfusion injury through modulation of autophagy

Pretreatment of berbamine protects the heart from ischemia/reperfusion (I/R) injury. However it is unknown whether it has cardioprotection when given at the onset of reperfusion (postconditioning (PoC)), a protocol with more clinical impact. Autophagy is upregulated in I/R myocardium and exacerbates cardiomyocyte death during reperfusion. However, it is unknown whether the autophagy during reperfusion is regulated by berbamine. Here we investigated whether berbamine PoC (BMPoC) protects the heart through regulation of autophagy by analyzing the effects of BMPoC on infarct size and/or cell death, functional recovery and autophagy in perfused rat hearts and isolated cardiomyocytes subjected to I/R. Berbamine from 10 to 100 nM given during the first 5 min of reperfusion concentration-dependently improved post-ischemic myocardial function and attenuated cell death. Similar protections were observed in cardiomyocytes subjected to simulated I/R. Meanwhile, BMPoC prevented I/R-induced impairment of autophagosome processing in cardiomyocytes, characterized by increased LC3-II level and GFP-LC3 puncta, and decreased p62 degradation. Besides, lysosomal inhibitor chloroquine did not induce additional increase of LC3-II and P62 abundance after I/R but it reversed the effects of BMPoC in those parameters in cardiomyocytes, suggesting that I/R-impaired autophagic flux is restored by BMPoC. Moreover, I/R injury was accompanied by enhanced expression of Beclin 1, which was significantly inhibited by BMPoC. In vitro and in vivo adenovirus-mediated knockdown of Beclin 1 in myocardium and cardiomyocytes restored I/R-impaired autophagosome processing, associated with an improvement of post-ischemic recovery of myocardial contractile function and a reduction of cell death, but it did not have additive effects to BMPoC. Conversely, overexpression of Beclin 1 abolished the cardioprotection of BMPoC as did by overexpression of an essential autophagy gene Atg5. Furthermore, BMPoC-mediated cardioprotection was abolished by a specific Akt1/2 inhibitor A6730. Our results demonstrate that BMPoC confers cardioprotection by modulating autophagy during reperfusion through the activation of PI3K/Akt signaling pathway.

Autophagic flux, a possible mechanism for delayed gentamicin-induced ototoxicity

Aminoglycoside antibiotics including gentamicin (GM) induce delayed ototoxic effects such as hearing loss after long-term use, unlike the early-onset ototoxicity caused by cisplatin. The purpose of the study was to identify the mechanism of the delayed GM-induced ototoxicity by exploring the role of autophagy in vitro and in vivo. Treating HEI-OC1 auditory cells with GM led to a time-dependent increase of the autophagosome marker LC3-II, which was accompanied by cell death. In contrast, cisplatin and penicillin caused a rapid increase and had no effect on LC3-II levels, respectively. LC3-II-expressing autophagosomes co-localized with the labeled GM. GM-treated autophagosomes expressed reduced levels of Rab7, which is necessary for the fusion of autophagosomes with lysosomes. When the autophagic flux enhancer rapamycin was applied to GM-treated cells, Rab7 and the lysosomal enzyme cathepsin D were upregulated, and increased cell survival was observed. In animal studies, the intraperitoneal injection of GM worsened hearing thresholds and induced the accumulation of LC3 in the organ of Corti. This hearing impairment was attenuated by rapamycin. These findings suggest that the delayed onset-ototoxicity of GM may be closely related to the accumulation of autophagosomes via impaired autophagy. This GM-induced auditory cell death could be inhibited by enhancing autophagic flux.

Autophagy in Diabetic Retinopathy

Autophagy is an important homeostatic cellular process encompassing a number of consecutive steps indispensable for degrading and recycling cytoplasmic materials. Basically autophagy is an adaptive response that under stressful conditions guarantees the physiological turnover of senescent and impaired organelles and, thus, controls cell fate by various cross-talk signals. Diabetic retinopathy (DR) is a serious microvascular complication of diabetes and accounts for 5% of all blindness. Although, various metabolic disorders have been linked with the onset of DR, due to the complex character of this multi-factorial disease, a connection between any particular defect and DR becomes speculative. Diabetes increases inflammation, advanced glycation end products (AGEs) and oxidative stress in the retina and its capillary cells. Particularly, a great number of evidences suggest a mutual connection between oxidative stress and other major metabolic abnormalities implicated in the development of DR. In addition, the intricate networks between autophagy and apoptosis establish the degree of cellular apoptosis and the progression of DR. Growing data underline the crucial role of reactive oxygen species (ROS) in the activation of autophagy. Depending on their delicate balance both redox signaling and autophagy, being detrimental or beneficial, retain opposing effects. The molecular mechanisms of autophagy are very complex and involve many signaling pathways cooperating at various steps. This review summarizes recent advances of the possible molecular mechanisms in autophagic process that are involved in pathophysiology of DR. In-depth analysis on the molecular mechanisms leading to autophagy in the retinal pigment epithelial (RPE) will be helpful to plan new therapies aimed at preventing or improving the progression of DR.

Regulation of SREBP-2 intracellular trafficking improves impaired autophagic flux and alleviates endoplasmic reticulum stress in NAFLD

Sterol regulatory element-binding protein 2 (SREBP-2), is a well-known transcriptional regulator of cholesterol metabolism. SREBP-2 is activated unconventionally to promote excessive cholesterol accumulation in non-alcoholic fatty liver disease (NAFLD). In addition, recent studies suggested that excessive lipid and cholesterol accumulation can weaken cellular autophagy function and promote endoplasmic reticulum stress (ERS). However, it remains unknown whether regulation of SREBP-2 processing modulates autophagy and ERS. In this study, we demonstrated that inhibition of SREBP-2 intracellular trafficking by site-1 protease (S1P) and site-2 protease (S2P) specific inhibitors, or shRNAs targeting S1P and S2P, upregulated gene and protein expression of autophagy markers, and improved the impaired autophagic flux induced in both cell and mouse models of NAFLD. Furthermore, increased lipid degradation by autophagy could repress PERK-P-EIF2α signaling. Taken together, these findings suggest that regulating the nuclear transport of SREBP-2 reduces lipid deposition and ERS via an autophagy-dependent pathway.

Focal Adhesion Kinase-mediated Phosphorylation of Beclin1 Protein Suppresses Cardiomyocyte Autophagy and Initiates Hypertrophic Growth

Autophagy is an evolutionarily conserved intracellular degradation/recycling system that is essential for cellular homeostasis but is dysregulated in a number of diseases, including myocardial hypertrophy. Although it is clear that limiting or accelerating autophagic flux can result in pathological cardiac remodeling, the physiological signaling pathways that fine-tune cardiac autophagy are poorly understood. Herein, we demonstrated that stimulation of cardiomyocytes with phenylephrine (PE), a well known hypertrophic agonist, suppresses autophagy and that activation of focal adhesion kinase (FAK) is necessary for PE-stimulated autophagy suppression and subsequent initiation of hypertrophic growth. Mechanistically, we showed that FAK phosphorylates Beclin1, a core autophagy protein, on Tyr-233 and that this post-translational modification limits Beclin1 association with Atg14L and reduces Beclin1-dependent autophagosome formation. Remarkably, although ectopic expression of wild-type Beclin1 promoted cardiomyocyte atrophy, expression of a Y233E phosphomimetic variant of Beclin1 failed to affect cardiomyocyte size. Moreover, genetic depletion of Beclin1 attenuated PE-mediated/FAK-dependent initiation of myocyte hypertrophy in vivo Collectively, these findings identify FAK as a novel negative regulator of Beclin1-mediated autophagy and indicate that this pathway can facilitate the promotion of compensatory hypertrophic growth. This novel mechanism to limit Beclin1 activity has important implications for treating a variety of pathologies associated with altered autophagic flux.

Necroptotic cell death in failing heart: relevance and proposed mechanisms

As cardiomyocytes have a limited capability for proliferation, renewal, and repair, the loss of heart cells followed by replacement with fibrous tissue is considered to result in the development of ventricular dysfunction and progression to heart failure (HF). The loss of cardiac myocytes in HF has been traditionally believed to occur mainly due to programmed apoptosis or unregulated necrosis. While extensive research work is being carried out to define the exact significance and contribution of both these cell death modalities in the development of HF, recent knowledge has indicated the existence and importance of a different form of cell death called necroptosis in the failing heart. This new cell damaging process, resembling some of the morphological features of passive necrosis as well as maladaptive autophagy, is a programmed process and is orchestrated by a complex set of proteins involving receptor-interacting protein kinase 1 and 3 (RIP1, RIP3) and mixed lineage kinase domain-like protein (MLKL). Activation of the RIP1-RIP3-MLKL signaling pathway leads to disruption of cation homeostasis, plasma membrane rupture, and finally cell death. It seems likely that inhibition of any site in this pathway may prove as an effective pharmacological intervention for preventing the necroptotic cell death in the failing heart. This review is intended to describe general aspects of the signaling pathway associated with necroptosis, to describe its relationship with cardiac dysfunction in some models of cardiac injury and discuss its potential relevance in various types of HF with respect to the underlying pathologic mechanisms.

CLOCK Promotes Endothelial Damage by Inducing Autophagy through Reactive Oxygen Species

A number of recent studies have implicated that autophagy was activated by reactive oxygen species (ROS). Our previous report indicated that CLOCK increased the accumulation of ROS under hypoxic conditions. In this study, we investigated the mechanisms by which CLOCK mediated endothelial damage, focusing on the involvement of oxidative damage and autophagy. Overexpression of CLOCK in human umbilical vein endothelial cells (HUVECs) showed inhibition of cell proliferation and higher autophagosome with an increased expression of Beclin1 and LC3-I/II under hypoxic conditions. In contrast, CLOCK silencing reversed these effects. Interestingly, pretreatment with 3-methyladenine (3-MA) resulted in the attenuation of CLOCK-induced cell autophagy and but did not influence the production of intracellular reactive oxygen species (ROS). Furthermore, Tiron (4,5-dihydroxy-1,3-benzene disulfonic acid-disodium salt), a ROS scavenger, significantly attenuated CLOCK-induced cell autophagy. In addition, we found that overexpression of CLOCK had no significant effects on the production of ROS and expression of Beclin1 and LC3-I/II under normoxic conditions in HUVEC. In this present investigation, our results suggested a novel mechanism of action of CLOCK in HUVECs, opening up the possibility of targeting CLOCK for the treatment of vascular diseases.

Ischemia/Reperfusion

Ischemic disorders, such as myocardial infarction, stroke, and peripheral vascular disease, are the most common causes of debilitating disease and death in westernized cultures. The extent of tissue injury relates directly to the extent of blood flow reduction and to the length of the ischemic period, which influence the levels to which cellular ATP and intracellular pH are reduced. By impairing ATPase-dependent ion transport, ischemia causes intracellular and mitochondrial calcium levels to increase (calcium overload). Cell volume regulatory mechanisms are also disrupted by the lack of ATP, which can induce lysis of organelle and plasma membranes. Reperfusion, although required to salvage oxygen-starved tissues, produces paradoxical tissue responses that fuel the production of reactive oxygen species (oxygen paradox), sequestration of proinflammatory immunocytes in ischemic tissues, endoplasmic reticulum stress, and development of postischemic capillary no-reflow, which amplify tissue injury. These pathologic events culminate in opening of mitochondrial permeability transition pores as a common end-effector of ischemia/reperfusion (I/R)-induced cell lysis and death. Emerging concepts include the influence of the intestinal microbiome, fetal programming, epigenetic changes, and microparticles in the pathogenesis of I/R. The overall goal of this review is to describe these and other mechanisms that contribute to I/R injury. Because so many different deleterious events participate in I/R, it is clear that therapeutic approaches will be effective only when multiple pathologic processes are targeted. In addition, the translational significance of I/R research will be enhanced by much wider use of animal models that incorporate the complicating effects of risk factors for cardiovascular disease. © 2017 American Physiological Society. Compr Physiol 7:113-170, 2017.

Cardioprotection and lifespan extension by the natural polyamine spermidine

Aging is associated with an increased risk of cardiovascular disease and death. Here we show that oral supplementation of the natural polyamine spermidine extends the lifespan of mice and exerts cardioprotective effects, reducing cardiac hypertrophy and preserving diastolic function in old mice. Spermidine feeding enhanced cardiac autophagy, mitophagy and mitochondrial respiration, and it also improved the mechano-elastical properties of cardiomyocytes in vivo, coinciding with increased titin phosphorylation and suppressed subclinical inflammation. Spermidine feeding failed to provide cardioprotection in mice that lack the autophagy-related protein Atg5 in cardiomyocytes. In Dahl salt-sensitive rats that were fed a high-salt diet, a model for hypertension-induced congestive heart failure, spermidine feeding reduced systemic blood pressure, increased titin phosphorylation and prevented cardiac hypertrophy and a decline in diastolic function, thus delaying the progression to heart failure. In humans, high levels of dietary spermidine, as assessed from food questionnaires, correlated with reduced blood pressure and a lower incidence of cardiovascular disease. Our results suggest a new and feasible strategy for protection against cardiovascular disease.

Cinnamaldehyde ameliorates LPS-induced cardiac dysfunction via TLR4-NOX4 pathway: The regulation of autophagy and ROS production

Cinnamaldehyde (CA), a major bioactive compound extracted from the essential oil of Cortex Cinnamomi, exhibits anti-inflammatory activity on endotoxemia. Accumulating evidence indicates reactive oxygen species (ROS) and autophagy play a vital role in the cardiac dysfunction during endotoxemia. The aim of this study was to unveil the mechanism of CA on ROS production and autophagy during endotoxemia. Male Sprague-Dawley rats were stimulated by LPS (20mg/kg i.v.) with or without treatment of CA. Cardiac function and histopathological staining were preformed 4h after LPS stimulation. The levels of TNF-α, IL-1β and IL-6 were detected by ELISA. The expression of p-JNK, p-ERK, p-p38, TLR4, NOX4, NOX2, ATG5 and LC3 proteins were determined by Western blot. The results showed that CA inhibited cardiac dysfunction, inflammatory infiltration and the levels of TNF-α, IL-1β and IL-6 in LPS stimulated rats by blocking the TLR4, NOX4, MAPK and autophagy signalings. In order to obtain further confirmation of the mechanism of CA on endotoxemia in vitro, a limited time-course study was firstly performed by Western blot. TLR4, NOX4 and LC3 were significantly increased after 4h LPS stimulation. CA reversed the intracellular ROS production and MAPK signaling activation induced by LPS. Electron microscopy, mRFP-GFP-LC3 transfection and western blot results revealed autophagic flux were attenuated after CA treatment. The siRNA and molecular docking results suggest that CA can suppress both TLR4 and NOX4 during endotoxemia. Our data revealed that CA ameliorated LPS-induced cardiac dysfunction by inhibiting ROS production and autophagy through TLR4-NOX4 pathway.

Clearance of autophagy-associated dying retinal pigment epithelial cells - a possible source for inflammation in age-related macular degeneration

Retinal pigment epithelial (RPE) cells can undergo different forms of cell death, including autophagy-associated cell death during age-related macular degeneration (AMD). Failure of macrophages or dendritic cells (DCs) to engulf the different dying cells in the retina may result in the accumulation of debris and progression of AMD. ARPE-19 and primary human RPE cells undergo autophagy-associated cell death upon serum depletion and oxidative stress induced by hydrogen peroxide (H₂O₂). Autophagy was revealed by elevated light-chain-3 II (LC3-II) expression and electron microscopy, while autophagic flux was confirmed by blocking the autophago-lysosomal fusion using chloroquine (CQ) in these cells. The autophagy-associated dying RPE cells were engulfed by human macrophages, DCs and living RPE cells in an increasing and time-dependent manner. Inhibition of autophagy by 3-methyladenine (3-MA) decreased the engulfment of the autophagy-associated dying cells by macrophages, whereas sorting out the GFP-LC3-positive/autophagic cell population or treatment by the glucocorticoid triamcinolone (TC) enhanced it. Increased amounts of IL-6 and IL-8 were released when autophagy-associated dying RPEs were engulfed by macrophages. Our data suggest that cells undergoing autophagy-associated cell death engage in clearance mechanisms guided by professional and non-professional phagocytes, which is accompanied by inflammation as part of an in vitro modeling of AMD pathogenesis.

Does growth differentiation factor 11 protect against myocardial ischaemia/reperfusion injury? A hypothesis

The pathogenesis of myocardial ischaemia/reperfusion injury is multifactorial. Understanding the mechanisms of myocardial ischaemia/reperfusion will benefit patients with ischaemic heart disease. Growth differentiation factor 11 (GDF11), a member of the secreted transforming growth factor-β superfamily, has been found to reverse age-related hypertrophy, revealing the important role of GDF11 in cardiovascular disease. However, the functions of GDF11 in myocardial ischaemia/reperfusion have not been elucidated yet. A number of signalling molecules are known to occur downstream of GDF11, including mothers against decapentaplegic homolog 3 (SMAD3) and forkhead box O3a (FOXO3a). A hypothesis is presented that GDF11 has protective effects in acute myocardial ischaemia/reperfusion injury through suppression of oxidative stress, prevention of calcium ion overload and promotion of the elimination of abnormal mitochondria via both canonical (SMAD3) and non-canonical (FOXO3a) pathways. Since circulating GDF11 may mainly derive from the spleen, the lack of a spleen may make the myocardium susceptible to damaging insults. Administration of GDF11 may be an efficacious therapy to protect against cardiovascular diseases in splenectomized patients.

Inhibition of autophagy ameliorates pulmonary microvascular dilation and PMVECs excessive proliferation in rat experimental hepatopulmonary syndrome

Hepatopulmonary syndrome (HPS) is a defective liver-induced pulmonary vascular disorder with massive pulmonary microvascular dilation and excessive proliferation of pulmonary microvascular endothelial cells (PMVECs). Growing evidence suggests that autophagy is involved in pulmonary diseases, protectively or detrimentally. Thus, it is interesting and important to explore whether autophagy might be involved in and critical in HPS. In the present study, we report that autophagy was activated in common bile duct ligation (CBDL) rats and cultured pulmonary PMVECs induced by CBDL rat serum, two accepted in vivo and in vitro experimental models of HPS. Furthermore, pharmacological inhibition of autophagy with 3-methyladenine (3-MA) significantly alleviated pathological alterations and typical symptom of HPS in CBDL rats in vivo, and consistently 3-MA significantly attenuated the CBDL rat serum-induced excessive proliferation of PMVECs in vitro. All these changes mediated by 3-MA might explain the observed prominent improvement of pulmonary appearance, edema, microvascular dilatation and arterial oxygenation in vivo. Collectively, these results suggest that autophagy activation may play a critical role in the pathogenesis of HPS, and autophagy inhibition may have a therapeutic potential for this disease.

Lipocalin-2 inhibits autophagy and induces insulin resistance in H9c2 cells

Lipocalin-2 (Lcn2; also known as neutrophil gelatinase associated lipocalin, NGAL) levels are increased in obesity and diabetes and associate with insulin resistance. Correlations exist between Lcn2 levels and various forms or stages of heart failure. Insulin resistance and autophagy both play well-established roles in cardiomyopathy. However, little is known about the impact of Lcn2 on insulin signaling in cardiomyocytes. In this study, we treated H9c2 cells with recombinant Lcn2 for 1 h followed by dose- and time-dependent insulin treatment and found that Lcn2 attenuated insulin signaling assessed via phosphorylation of Akt and p70S6K. We used multiple assays to demonstrate that Lcn2 reduced autophagic flux. First, Lcn2 reduced pULK1 S555, increased pULK1 S757 and reduced LC3-II levels determined by Western blotting. We validated the use of DQ-BSA to assess autolysosomal protein degradation and this together with MagicRed cathepsin B assay indicated that Lcn2 reduced lysosomal degradative activity. Furthermore, we generated H9c2 cells stably expressing tandem fluorescent RFP/GFP-LC3 and this approach verified that Lcn2 decreased autophagic flux. We also created an autophagy-deficient H9c2 cell model by overexpressing a dominant-negative Atg5 mutant and found that reduced autophagy levels also induced insulin resistance. Adding rapamycin after Lcn2 could stimulate autophagy and recover insulin sensitivity. In conclusion, our study indicated that acute Lcn2 treatment caused insulin resistance and use of gain and loss of function approaches elucidated a causative link between autophagy inhibition and regulation of insulin sensitivity by Lcn2.

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

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

Danshensu alleviates cardiac ischaemia/reperfusion injury by inhibiting autophagy and apoptosis via activation of mTOR signalling

The traditional Chinese medicine Danshensu (DSS) has a protective effect on cardiac ischaemia/reperfusion (I/R) injury. However, the molecular mechanisms underlying the DSS action remain undefined. We investigated the potential role of DSS in autophagy and apoptosis using cardiac I/R injury models of cardiomyocytes and isolated rat hearts. Cultured neonatal rat cardiomyocytes were subjected to 6 hrs of hypoxia followed by 18 hrs of reoxygenation to induce cell damage. The isolated rat hearts were used to perform global ischaemia for 30 min., followed by 60 min. reperfusion. Ischaemia/reperfusion injury decreased the haemodynamic parameters on cardiac function, damaged cardiomyocytes or even caused cell death. Pre-treatment of DSS significantly improved cell survival and protected against I/R-induced deterioration of cardiac function. The improved cell survival upon DSS treatment was associated with activation of mammalian target of rapamycin (mTOR) (as manifested by increased phosphorylation of S6K and S6), which was accompanied with attenuated autophagy flux and decreased expression of autophagy- and apoptosis-related proteins (including p62, LC3-II, Beclin-1, Bax, and Caspase-3) at both protein and mRNA levels. These results suggest that alleviation of cardiac I/R injury by pre-treatment with DSS may be attributable to inhibiting excessive autophagy and apoptosis through mTOR activation.

Neutrophil gelatinase-associated lipocalin worsens ischemia/reperfusion damage of kidney cells by autophagy

This study aimed to explore the influence of neutrophil gelatinase-associated lipocalin on autophagy and its role in ischemia/reperfusion injury in human kidney-2 (HK-2) cells during acute kidney injury (AKI). HK-2 cells were given hypoxia/reoxygenation treatment for different times to simulate ischemia/reperfusion injury. Autophagy was evaluated by western blot and immunofluorescence of GFP-LC3. Cell viability was tested to reflect the degree of cell damage. The autophagy inhibitor 3-MA was used to inhibit autophagy and determine the role of autophagy in ischemia/reperfusion injury. HK-2 cells were hypoxia for 1 h, followed by reoxygenation treatment for 24 h. These cells were then exposed to human recombinant protein neutrophil gelatinase-associated lipocalin (NGAL) (50, 100, 200, 400, or 1000 ng/mL) with or without 3-MA. Our results showed that autophagy was induced by hypoxia treatment and was further enhanced by reoxygenation after hypoxia treatment. Cell viability was decreased with the inhibition of autophagy in the process. Autophagic flux was further induced with NGAL (>200 ng/mL), while cell viability declined in this condition. Cell viability was recovered when autophagy was inhibited. These results indicate that autophagy plays, in part, a protective role in renal ischemia/reperfusion injury. Furthermore, the data suggest that NGAL strengthens the level of autophagy in this process. Overall, a large quantity of NGAL produced by renal proximal tubular epithelial cells may induce excessive autophagy and increase renal ischemia/reperfusion injury in acute kidney injury.

Epigallocatechin gallate exerts protective effects against myocardial ischemia/reperfusion injury through the PI3K/Akt pathway-mediated inhibition of apoptosis and the restoration of the autophagic flux

Epigallocatechin gallate (EGCG), a polyphenol derived from green tea, exhibits a wide range of biological activities, including antioxidant, atherosclerosis and antitumor activities. In this study, the cardioprotective effects of EGCG on myocardial ischemia/reperfusion (I/R) injury in rats and the underlying mechanisms were investigated. A rat model of I/R injury was established by ligating the left anterior descending coronary artery for 30 min, followed by reperfusion for 2 h. The levels of I/R-induced creatine kinase-MB (CK-MB) and the release of lactate dehydrogenase (LDH), as well as the infarct size, cardiomyocyte apoptosis and cardiac functional impairment were examined and compared. Western blot analysis was carried out to elucidate the potential molecular mechanisms of action of EGCG. The results revealed that EGCG post-conditioning significantly decreased the levels of CK-MB and the release of LDH, reduced the myocardial infarct size, decreased the apoptotic rate and partially preserved heart function. Furthermore, EGCG decreased the expression of cleaved caspase-3 concomitantly with the upregulation of PI3K, and the phosphorylation of Akt and endothelial nitric oxide synthase (eNOS). It also inhibited I/R-induced overautophagy and promoted the clearance of autophagosomes, as evidenced by a decrease in the ratio of microtubule-associated protein 1 light chain 3 (LC3)-II/LC3-I, the downregulation of Beclin1, Atg5 and p62, and the upregulation of active cathepsin D. Additionally, we observed an increase in the phosphorylation levels of the mammalian target of rapamycin (mTOR) following treatment with EGCG. Taken together, the findings of this study demonstrate that, EGCG post-conditioning alleviates myocardial I/R injury by inhibiting apoptosis and restoring the autophagic flux, which is associated with several targets of the PI3K/Akt signaling pathway.

Therapeutic targeting of autophagy in myocardial infarction and heart failure

INTRODUCTION

Myocardial infarction (MI) is the leading cause of death. When MI is not lethal, heart failure (HF) is a major consequence with high prevalence and poor prognosis. The targeting of autophagy represents a potentially therapeutic approach for the treatment of both pathologies.

AREAS COVERED

PubMed searches were performed to discuss the current state of the art regarding the role of autophagy in MI and HF. We review available and potential approaches to modulate autophagy from a pharmacological and genetic perspective. We also discuss the targeting of autophagy in myocardial regeneration. Expert commentary: The targeting of autophagy has potential for the treatment of MI and HF. Autophagy is a process that takes place in virtually all cells of the body and thus, in order to evaluate this therapeutic approach in clinical trials, strategies that specifically target this process in the myocardium is required to avoid unwanted effects in other organs.

NQO1 Deficiency Leads Enhanced Autophagy in Cisplatin-Induced Acute Kidney Injury Through the AMPK/TSC2/mTOR Signaling Pathway

AIMS

Recent studies have revealed that autophagy is induced under various disease conditions; however, the role of autophagy in pathological states is controversial.

NAD(P)H

quinone oxidoreductase 1 (NQO1) is a highly inducible cytoprotective gene that regulates reactive oxygen species (ROS) generation. In this study, we examined whether NQO1 deficiency affects the autophagy process in response to cisplatin-induced nephrotoxicity.

RESULTS

In vitro, NQO1 and autophagy-associated proteins were induced after cisplatin treatment and the autophagosomes markedly increased in the cisplatin-treated NQO1-knockdown ACHN cells together with increased ROS production. In vivo, NQO1-KO mice displayed a significant increase in cisplatin-induced acute kidney injury (AKI), as indicated by elevated tubular damage and apoptosis as well as by suppressed cytoprotective signals. In agreement with the in vitro findings, NQO1-KO cisplatin-treated mice displayed a notable increase in autophagy-associated protein expression compared with their wild-type counterparts. Meanwhile, the expression of Ras-related protein 7, which participates in autophagosome maturation and lysosome fusion, markedly decreased in NQO1-KO mice, indicating hampered progress in late autophagy, and was accompanied by increased p62 protein expression. Moreover, NQO1 deletion enhanced the effect of the mammalian target of the rapamycin inhibitor, rapamycin, and led to enhanced tuberous sclerosis complex 2 phosphorylation through AMP-activated protein kinase activation.

INNOVATION AND CONCLUSION

These results indicate that autophagy may be enhanced to counter the increased stress due to NQO1 deficiency, an oxidative stress barrier. The present results demonstrate the significant influence of NQO1 on the autophagy process and support the hypothesis that autophagy plays a protective role under oxidative stress conditions. Antioxid. Redox Signal. 24, 867-883.

Aging and Autophagy in the Heart

The aging population is increasing in developed countries. Because the incidence of cardiac disease increases dramatically with age, it is important to understand the molecular mechanisms through which the heart becomes either more or less susceptible to stress. Cardiac aging is characterized by the presence of hypertrophy, fibrosis, and accumulation of misfolded proteins and dysfunctional mitochondria. Macroautophagy (hereafter referred to as autophagy) is a lysosome-dependent bulk degradation mechanism that is essential for intracellular protein and organelle quality control. Autophagy and autophagic flux are generally decreased in aging hearts, and murine autophagy loss-of-function models develop exacerbated cardiac dysfunction that is accompanied by the accumulation of misfolded proteins and dysfunctional organelles. On the contrary, stimulation of autophagy generally improves cardiac function in mouse models of protein aggregation by removing accumulated misfolded proteins, dysfunctional mitochondria, and damaged DNA, thereby improving the overall cellular environment and alleviating aging-associated pathology in the heart. Increasing lines of evidence suggest that autophagy is required for many mechanisms that mediate lifespan extension, such as caloric restriction, in various organisms. These results raise the exciting possibility that autophagy may play an important role in combating the adverse effects of aging in the heart. In this review, we discuss the role of autophagy in the heart during aging, how autophagy alleviates age-dependent changes in the heart, and how the level of autophagy in the aging heart can be restored.

Chlorin p6-Based Water-Soluble Amino Acid Derivatives as Potent Photosensitizers for Photodynamic Therapy

The development of novel photosensitizer with high phototoxicity, low dark toxicity, and good water solubility is a challenging task for photodynamic therapy (PDT). A series of chlorin p6-based water-soluble amino acid conjugates were synthesized and investigated for antitumor activity. Among them, aspartylchlorin p6 dimethylester (7b) showed highest phototoxicity against melanoma cells with weakest dark toxicity, which was more phototoxic than verteporfin while with less dark toxicity. It also exhibited better in vivo PDT antitumor efficacy on mice bearing B16-F10 tumor than verteporfin. The biological assays revealed that 7b was localized in multiple subcellular organelles and could cause both cell necrosis and apoptosis after PDT in a dose-dependent manner, resulting in more effective cell destruction. As a result, 7b represents a promising photosensitizer for PDT applications because of its strong absorption in the phototherapeutic window, relatively high singlet oxygen quantum yield, highest dark toxicity/phototoxicity ratio, good water solubility, and excellent in vivo PDT antitumor efficacy.

Crocin-Elicited Autophagy Rescues Myocardial Ischemia/Reperfusion Injury via Paradoxical Mechanisms

Crocin, the main effective component of saffron, exerts protective effects against ischemia/reperfusion injury during strokes. However, the effects of crocin in myocardial ischemia/reperfusion injury, and the mechanisms involved, remain unknown. Pretreated with crocin for 7 days, C57BL/6N mice were subjected to 30 min of myocardial ischemia followed by 12[Formula: see text]h of reperfusion (for cardiac function and infarct size, cell apoptosis and necrosis). Neonatal mouse cardiomyocytes were subjected to 2 h of hypoxia followed by 4 h of reoxygenation. NMCM's survival was assessed during hypoxia and reoxygenation in the presence or absence of the autophagy inhibitor 3-methyladenine or the inducer rapamycin. Western blotting was used to evaluate AMPK, Akt, and autophagy-related proteins. Autophagosome was observed using electron microscopy. In the in vivo experiment, crocin pretreatment significantly attenuated infarct size, myocardial apoptosis and necrosis, and improved left ventricular function following ischemia/reperfusion. In vitro data revealed that autophagy was induced during hypoxia, the levels of which were intensely elevated during reoxygenation. Crocin significantly promoted autophagy during ischemia, accompanied with the activation of AMPK. In contrast, crocin overtly inhibited autophagy during reperfusion, accompanied with Akt activation. Induction and inhibition of autophagy mitigated crocin induced protection against NMCMs injury during hypoxia and reoxygenation, respectively. Our data suggest that crocin demonstrated a myocardial protective effect via AMPK/mTOR and Akt/mTOR regulated autophagy against ischemia and reperfusion injury, respectively.

SIRT3-SOD2-mROS-dependent autophagy in cadmium-induced hepatotoxicity and salvage by melatonin

Cadmium is one of the most toxic metal compounds found in the environment. It is well established that Cd induces hepatotoxicity in humans and multiple animal models. Melatonin, a major secretory product of the pineal gland, has been reported to protect against Cd-induced hepatotoxicity. However, the mechanism behind this protection remains to be elucidated. We exposed HepG2 cells to different concentrations of cadmium chloride (2.5, 5, and 10 μM) for 12 h. We found that Cd induced mitochondrial-derived superoxide anion-dependent autophagic cell death. Specifically, Cd decreased SIRT3 protein expression and activity and promoted the acetylation of SOD2, superoxide dismutase 2, mitochondrial, thus decreasing its activity, a key enzyme involved in mitochondrial ROS production, although Cd did not disrupt the interaction between SIRT3 and SOD2. These effects were ameliorated by overexpression of SIRT3. However, a catalytic mutant of SIRT3 (SIRT3^H248Y) lacking deacetylase activity lost the capacity to suppress Cd-induced autophagy. Notably, melatonin treatment enhanced the activity but not the expression of SIRT3, decreased the acetylation of SOD2, inhibited mitochondrial-derived O₂^•− production and suppressed the autophagy induced by 10 μM Cd. Moreover, 3-(1H-1,2,3-triazol-4-yl)pyridine, a confirmed selective SIRT3 inhibitor, blocked the melatonin-mediated suppression of autophagy by inhibiting SIRT3-SOD2 signaling. Importantly, melatonin suppressed Cd-induced autophagic cell death by enhancing SIRT3 activity in vivo. These results suggest that melatonin exerts a hepatoprotective effect on mitochondrial-derived O₂^•−-stimulated autophagic cell death that is dependent on the SIRT3/SOD2 pathway.