Autophagy and protein kinase C are required for cardioprotection by sulfaphenazole

Activation of the homeostatic intracellular repair response during cardiac surgery

BACKGROUND

The homeostatic intracellular repair response (HIR2) is an endogenous beneficial pathway that eliminates damaged mitochondria and dysfunctional proteins in response to stress. The underlying mechanism is adaptive autophagy. The purpose of this study was to determine whether the HIR2 response is activated in the heart in patients undergoing cardiac surgery and to assess whether it is associated with the duration of ischemic arrest and predicted surgical outcomes.

STUDY DESIGN

Autophagy was assessed in 19 patients undergoing coronary artery bypass or valve surgery requiring cardiopulmonary bypass. Biopsies of the right atrial appendage obtained before initiation of cardiopulmonary bypass and after weaning from cardiopulmonary bypass were analyzed for autophagy by immunoblotting for LC3, Beclin-1, autophagy 5-12, and p62. Changes in p62, a marker of autophagic flux, were correlated with duration of ischemia and with the mortality/morbidity risk scores obtained from the Society of Thoracic Surgeons Adult Cardiac Surgery Database (version 2.73).

RESULTS

Heart surgery was associated with a robust increase in autophagic flux indicated by depletion of LC3-I, LC3-II, Beclin-1, and autophagy 5-12; the magnitude of change for each of these factors correlated significantly with changes in the flux marker p62. In addition, changes in p62 correlated directly with cross-clamp time and inversely with the mortality and morbidity risk scores.

CONCLUSIONS

These findings are consistent with preclinical studies indicating that HIR2 is cardioprotective and reveal that it is activated in patients in response to myocardial ischemic stress. Strategies designed to amplify HIR2 during conditions of cardiac stress might have a therapeutic use and represent an entirely new approach to myocardial protection in patients undergoing heart surgery.

Mitochondrial pathways, permeability transition pore, and redox signaling in cardioprotection: therapeutic implications

Reperfusion therapy is the indispensable treatment of acute myocardial infarction (AMI) and must be applied as soon as possible to attenuate the ischemic insult. However, reperfusion is responsible for additional myocardial damage likely involving opening of the mitochondrial permeability transition pore (mPTP). A great part of reperfusion injury occurs during the first minute of reperfusion. The prolonged opening of mPTP is considered one of the endpoints of the cascade to myocardial damage, causing loss of cardiomyocyte function and viability. Opening of mPTP and the consequent oxidative stress due to reactive oxygen and nitrogen species (ROS/RNS) are considered among the major mechanisms of mitochondrial and myocardial dysfunction. Kinases and mitochondrial components constitute an intricate network of signaling molecules and mitochondrial proteins, which interact in response to stressors. Cardioprotective pathways are activated by stimuli such as preconditioning and postconditioning (PostC), obtained with brief intermittent ischemia or with pharmacological agents, which drastically reduce the lethal ischemia/reperfusion injury. The protective pathways converging on mitochondria may preserve their function. Protection involves kinases, adenosine triphosphate-dependent potassium channels, ROS signaling, and the mPTP modulation. Some clinical studies using ischemic PostC during angioplasty support its protective effects, and an interesting alternative is pharmacological PostC. In fact, the mPTP desensitizer, cyclosporine A, has been shown to induce appreciable protections in AMI patients. Several factors and comorbidities that might interfere with cardioprotective signaling are considered. Hence, treatments adapted to the characteristics of the patient (i.e., phenotype oriented) might be feasible in the future.

Autophagy, myocardial protection, and the metabolic syndrome

Autophagy is a housekeeping process that helps to maintain cellular energy homeostasis and remove damaged organelles. In the heart, autophagy is an adaptive process that is activated in response to stress including acute and chronic ischemia. Given the evidence that autophagy is suppressed in energy-rich conditions, the objective of this review is to examine autophagy and cardioprotection in the setting of the metabolic syndrome. Clinical approaches that involve the induction of cardiac autophagy pharmacologically to enhance the heart's tolerance to ischemia are also discussed.

Cell death pathways in acute ischemia/reperfusion injury

The consequence of myocardial ischemia is energetic stress, while reperfusion is accompanied by abrupt ionic shifts and considerable oxidative stress. Cells die by apoptotic and necrotic pathways. After the acute injury, the healing myocardium is subject to biomechanical stress and inflammation, which can trigger a smaller but more sustained wave of cell death, as well as changes in the metabolic and functional characteristics of surviving cells. The goal of cardioprotection is to prevent cell death during the acute injury as well as to modulate the detrimental processes that ensue during remodeling. This review will focus on acute injury, and the central premise is that mitochondria are the key determinant of cardiomyocyte fate.

Autophagy as a therapeutic target for ischaemia /reperfusion injury? Concepts, controversies, and challenges

Autophagy is the tightly orchestrated cellular 'housekeeping' process responsible for the degradation and disposal of damaged and dysfunctional organelles and protein aggregates. In addition to its established basal role in the maintenance of normal cellular phenotype and function, there is growing interest in the concept that targeted modulation of autophagy under conditions of stress (most notably, ischaemia/reperfusion) may represent an adaptive mechanism and render the myocardium resistant to ischaemia/reperfusion injury. Our aims in this review are to: (i) provide a balanced overview of the emerging hypothesis that perturbation of autophagy may serve as a novel, intriguing, and powerful cardioprotective treatment strategy and (ii) summarize the controversies and challenges in exploiting autophagy as a therapeutic target for ischaemia/reperfusion injury.

Pathophysiology of myocardial reperfusion injury: preconditioning, postconditioning, and translational aspects of protective measures

Heart diseases due to myocardial ischemia, such as myocardial infarction or ischemic heart failure, are major causes of death in developed countries, and their number is unfortunately still growing. Preliminary exploration into the pathophysiology of ischemia-reperfusion injury, together with the accumulation of clinical evidence, led to the discovery of ischemic preconditioning, which has been the main hypothesis for over three decades for how ischemia-reperfusion injury can be attenuated. The subcellular pathophysiological mechanism of ischemia-reperfusion injury and preconditioning-induced cardioprotection is not well understood, but extensive research into components, including autacoids, ion channels, receptors, subcellular signaling cascades, and mitochondrial modulators, as well as strategies for modulating these components, has made evolutional progress. Owing to the accumulation of both basic and clinical evidence, the idea of ischemic postconditioning with a cardioprotective potential has been discovered and established, making it possible to apply this knowledge in the clinical setting after ischemia-reperfusion insult. Another a great outcome has been the launch of translational studies that apply basic findings for manipulating ischemia-reperfusion injury into practical clinical treatments against ischemic heart diseases. In this review, we discuss the current findings regarding the fundamental pathophysiological mechanisms of ischemia-reperfusion injury, the associated protective mechanisms of ischemic pre- and postconditioning, and the potential seeds for molecular, pharmacological, or mechanical treatments against ischemia-reperfusion injury, as well as subsequent adverse outcomes by modulation of subcellular signaling mechanisms (especially mitochondrial function). We also review emerging translational clinical trials and the subsistent clinical comorbidities that need to be overcome to make these trials applicable in clinical medicine.

Tuning flux: autophagy as a target of heart disease therapy

PURPOSE OF REVIEW

Despite maximum medical and mechanical support therapy, heart failure remains a relentlessly progressive disorder with substantial morbidity and mortality. Autophagy, an evolutionarily conserved process of cellular cannibalization, has been implicated in virtually all forms of cardiovascular disease. Indeed, its role is context dependent, antagonizing or promoting disease depending on the circumstance. Here, we review current understanding of the role of autophagy in the pathogenesis of heart failure and explore this pathway as a target of therapeutic intervention.

RECENT FINDINGS

In preclinical models of heart disease, cardiomyocyte autophagic flux is activated; indeed, its role in disease pathogenesis is the subject of intense investigation to define mechanism. Similarly, in failing human heart of a variety of etiologies, cardiomyocyte autophagic activity is upregulated, and therapy, such as with mechanical support systems, elicits declines in autophagy activity. However, when suppression of autophagy is complete, rapid and catastrophic cell death occurs, consistent with a model in which basal autophagic flux is required for proteostasis. Thus, a narrow zone of 'optimal' autophagy seems to exist. The challenge moving forward is to tune the stress-triggered autophagic response within that 'sweet spot' range for therapeutic benefit.

SUMMARY

Whereas we have known for some years of the participation of lysosomal mechanisms in heart disease, it is only recently that upstream mechanisms (autophagy) are being explored. The challenge for the future is to dissect the underlying circuitry and titrate the response into an optimal, proteostasis-promoting range in hopes of mitigating the ever-expanding epidemic of heart failure.

Autophagy as a therapeutic target in cardiovascular disease

The epidemic of heart failure continues apace, and development of novel therapies with clinical efficacy has lagged. Now, important insights into the molecular circuitry of cardiovascular autophagy have raised the prospect that this cellular pathway of protein quality control may be a target of clinical relevance. Whereas basal levels of autophagy are required for cell survival, excessive levels - or perhaps distinct forms of autophagic flux - contribute to disease pathogenesis. Our challenge will be to distinguish mechanisms that drive adaptive versus maladaptive autophagy and to manipulate those pathways for therapeutic gain. Recent evidence suggests this may be possible. Here, we review the fundamental biology of autophagy and its role in a variety of forms of cardiovascular disease. We discuss ways in which this evolutionarily conserved catabolic mechanism can be manipulated, discuss studies presently underway in heart disease, and provide our perspective on where this exciting field may lead in the future. This article is part of a special issue entitled ''Key Signaling Molecules in Hypertrophy and Heart Failure.''

Preconditioning involves selective mitophagy mediated by Parkin and p62/SQSTM1

Autophagy-dependent mitochondrial turnover in response to cellular stress is necessary for maintaining cellular homeostasis. However, the mechanisms that govern the selective targeting of damaged mitochondria are poorly understood. Parkin, an E3 ubiquitin ligase, has been shown to be essential for the selective clearance of damaged mitochondria. Parkin is expressed in the heart, yet its function has not been investigated in the context of cardioprotection. We previously reported that autophagy is required for cardioprotection by ischemic preconditioning (IPC). In the present study, we used simulated ischemia (sI) in vitro and IPC of hearts to investigate the role of Parkin in mediating cardioprotection ex vivo and in vivo. In HL-1 cells, sI induced Parkin translocation to mitochondria and mitochondrial elimination. IPC induced Parkin translocation to mitochondria in Langendorff-perfused rat hearts and in vivo in mice subjected to regional IPC. Mitochondrial depolarization with an uncoupling agent similarly induced Parkin translocation to mitochondria in cells and Langendorff-perfused rat hearts. Mitochondrial loss was blunted in Atg5-deficient cells, revealing the requirement for autophagy in mitochondrial elimination. Consistent with previous reports indicating a role for p62/SQSTM1 in mitophagy, we found that depletion of p62 attenuated mitophagy and exacerbated cell death in HL-1 cardiomyocytes subjected to sI. While wild type mice showed p62 translocation to mitochondria and an increase in ubiquitination, Parkin knockout mice exhibited attenuated IPC-induced p62 translocation to the mitochondria. Importantly, ablation of Parkin in mice abolished the cardioprotective effects of IPC. These results reveal for the first time the crucial role of Parkin and mitophagy in cardioprotection.

Mitochondrial turnover in the heart

Mitochondrial quality control is increasingly recognized as an essential element in maintaining optimally functioning tissues. Mitochondrial quality control depends upon a balance between biogenesis and autophagic destruction. Mitochondrial dynamics (fusion and fission) allows for the redistribution of mitochondrial components. We speculate that this permits sorting of highly functional components into one end of a mitochondrion, while damaged components are segregated at the other end, to be jettisoned by asymmetric fission followed by selective mitophagy. Ischemic preconditioning requires autophagy/mitophagy, resulting in selective elimination of damaged mitochondria, leaving behind a population of robust mitochondria with a higher threshold for opening of the mitochondrial permeability transition pore. In this review we will consider the factors that regulate mitochondrial biogenesis and destruction, the machinery involved in both processes, and the biomedical consequences associated with altered mitochondrial turnover. This article is part of a Special Issue entitled: Mitochondria and Cardioprotection.

Profound cardioprotection with chloramphenicol succinate in the swine model of myocardial ischemia-reperfusion injury

BACKGROUND

Emerging evidence suggests that "adaptive" induction of autophagy (the cellular process responsible for the degradation and recycling of proteins and organelles) may confer a cardioprotective phenotype and represent a novel strategy to limit ischemia-reperfusion injury. Our aim was to test this paradigm in a clinically relevant, large animal model of acute myocardial infarction.

METHODS AND RESULTS

Anesthetized pigs underwent 45 minutes of coronary artery occlusion and 3 hours of reperfusion. In the first component of the study, pigs received chloramphenicol succinate (CAPS) (an agent that purportedly upregulates autophagy; 20 mg/kg) or saline at 10 minutes before ischemia. Infarct size was delineated by tetrazolium staining and expressed as a % of the at-risk myocardium. In separate animals, myocardial samples were harvested at baseline and 10 minutes following CAPS treatment and assayed (by immunoblotting) for 2 proteins involved in autophagosome formation: Beclin-1 and microtubule-associated protein light chain 3-II. To investigate whether the efficacy of CAPS was maintained with "delayed" treatment, additional pigs received CAPS (20 mg/kg) at 30 minutes after occlusion. Expression of Beclin-1 and microtubule-associated protein light chain 3-II, as well as infarct size, were assessed at end-reperfusion. CAPS was cardioprotective: infarct size was 25±5 and 41±4%, respectively, in the CAPS-pretreated and CAPS-delayed treatment groups versus 56±5% in saline controls (P<0.01 and P<0.05 versus control). Moreover, administration of CAPS was associated with increased expression of both proteins.

CONCLUSIONS

Our results demonstrate attenuation of ischemia-reperfusion injury with CAPS and are consistent with the concept that induction of autophagy may provide a novel strategy to confer cardioprotection.

Autophagy and protein aggregation after brain ischemia

Autophagy is the main degradation pathway responsible for eliminating abnormal protein aggregates and damaged organelles prevalent in neurons after transient cerebral ischemia. This study investigated whether accumulation of protein aggregate-associated organelles in post-ischemic neurons is a consequence of changes in autophagy. Electron microscopic analysis indicated that both autophagosomes and autolysosomes are significantly up-regulated in hippocampal CA1 and DG neurons after ischemia. The microtubule-associated protein light chain 3 (LC3)-II conjugate, a marker for autophagosomes assessed by western blotting, was up-regulated in post-ischemic brain tissues. Confocal microscopy showed that LC3 isoforms were located in living post-ischemic neurons. Treatment with chloriquine resulted in accumulation of LC3-II in sham-operated rats, but did not further change the LC3-II levels in post-ischemic brain tissues. The results indicate that at least part of the accumulation of protein aggregate-associated organelles seen following ischemia is likely to be because of failure of the autophagy pathway. The resulting protein aggregation on subcellular organelle membranes could lead to multiple organelle damage and to delayed neuronal death after transient cerebral ischemia.

Autophagy induced by ischemic preconditioning is essential for cardioprotection

Based on growing evidence linking autophagy to preconditioning, we tested the hypothesis that autophagy is necessary for cardioprotection conferred by ischemic preconditioning (IPC). We induced IPC with three cycles of 5 min regional ischemia alternating with 5 min reperfusion and assessed the induction of autophagy in mCherry-LC3 transgenic mice by imaging of fluorescent autophagosomes in cryosections. We found a rapid and significant increase in the number of autophagosomes in the risk zone of the preconditioned hearts. In Langendorff-perfused hearts subjected to an IPC protocol of 3 x 5 min ischemia, we also observed an increase in autophagy within 10 min, as assessed by Western blotting for p62 and cadaverine dye binding. To establish the role of autophagy in IPC cardioprotection, we inhibited autophagy with Tat-ATG5(K130R), a dominant negative mutation of the autophagy protein Atg5. Cardioprotection by IPC was reduced in rat hearts perfused with recombinant Tat-ATG5(K130R). To extend the potential significance of autophagy in cardioprotection, we also assessed three structurally unrelated cardioprotective agents--UTP, diazoxide, and ranolazine--for their ability to induce autophagy in HL-1 cells. We found that all three agents induced autophagy; inhibition of autophagy abolished their protective effect. Taken together, these findings establish autophagy as an end-effector in ischemic and pharmacologic preconditioning.

Autophagy: definition, molecular machinery, and potential role in myocardial ischemia-reperfusion injury

Autophagy is the endogenous, tightly regulated cellular "housekeeping" process responsible for the degradation of damaged and dysfunctional cellular organelles and protein aggregates. There is a growing consensus that autophagy is upregulated in the setting of myocardial ischemia-reperfusion. Moreover, emerging data suggest that autophagy may serve as an adaptive process and confer increased resistance to ischemia-reperfusion injury. Our aims in this review are to (1) provide a brief synopsis of process of autophagy (including an overview of the key molecular mediators of this catabolic process and its relationship with other cardiac signaling pathways) and (2) most importantly, summarize the current evidence for versus against the intriguing concept of autophagy-mediated cardioprotection.

Oxidative stress and autophagy in cardiac disease, neurological disorders, aging and cancer

Autophagy is a catalytic process of the bulk degradation of long-lived cellular components, ultimately resulting in lysosomal digestion within mature cytoplasmic compartments known as autophagolysosomes. Autophagy serves many functions in the cell, including maintaining cellular homeostasis, a means of cell survival during stress (e.g., nutrient deprivation or starvation) or conversely as a mechanism for cell death. Increased reactive oxygen species (ROS) production and the resulting oxidative cell stress that occurs in many disease states has been shown to induce autophagy. The following review focuses on the roles that autophagy plays in response to the ROS generated in several diseases.