Diphtheria toxin-induced autophagic cardiomyocyte death plays a pathogenic role in mouse model of heart failure

Presence of fetal microchimerisms in the heart and effect on cardiac repair

Multiple complex biological processes take place during pregnancy, including the migration of fetal cells to maternal circulation and their subsequent engraftment in maternal tissues, where they form microchimerisms. Fetal microchimerisms have been identified in several tissues; nevertheless, their functional role remains largely unknown. Different reports suggest these cells contribute to tissue repair and modulate the immune response, but they have also been associated with pre-eclampsia and tumor formation. In the maternal heart, cells of fetal origin can contribute to different cell lineages after myocardial infarction. However, the functional role of these cells and their effect on cardiac function and repair are unknown. In this work, we found that microchimerisms of fetal origin are present in the maternal circulation and graft in the heart. To determine their functional role, WT female mice were crossed with male mice expressing the diphtheria toxin (DT) receptor. Mothers were treated with DT to eliminate microchimerisms and the response to myocardial infarction was investigated. We found that removal of microchimerisms improved cardiac contraction in postpartum and post-infarction model females compared to untreated mice, where DT administration had no significant effects. These results suggest that microchimerisms play a detrimental role in the mother following myocardial infarction.

Autophagy in Heart Failure: Insights into Mechanisms and Therapeutic Implications

Autophagy, a dynamic and complex process responsible for the clearance of damaged cellular components, plays a crucial role in maintaining myocardial homeostasis. In the context of heart failure, autophagy has been recognized as a response mechanism aimed at counteracting pathogenic processes and promoting cellular health. Its relevance has been underscored not only in various animal models, but also in the human heart. Extensive research efforts have been dedicated to understanding the significance of autophagy and unravelling its complex molecular mechanisms. This review aims to consolidate the current knowledge of the involvement of autophagy during the progression of heart failure. Specifically, we provide a comprehensive overview of published data on the impact of autophagy deregulation achieved by genetic modifications or by pharmacological interventions in ischemic and non-ischemic models of heart failure. Furthermore, we delve into the intricate molecular mechanisms through which autophagy regulates crucial cellular processes within the three predominant cell populations of the heart: cardiomyocytes, cardiac fibroblasts, and endothelial cells. Finally, we emphasize the need for future research to unravel the therapeutic potential associated with targeting autophagy in the management of heart failure.

Autophagy, innate immunity, and cardiac disease

Autophagy is an evolutionarily conserved mechanism of cell adaptation to metabolic and environmental stress. It mediates the disposal of protein aggregates and dysfunctional organelles, although non-conventional features have recently emerged to broadly extend the pathophysiological relevance of autophagy. In baseline conditions, basal autophagy critically regulates cardiac homeostasis to preserve structural and functional integrity and protect against cell damage and genomic instability occurring with aging. Moreover, autophagy is stimulated by multiple cardiac injuries and contributes to mechanisms of response and remodeling following ischemia, pressure overload, and metabolic stress. Besides cardiac cells, autophagy orchestrates the maturation of neutrophils and other immune cells, influencing their function. In this review, we will discuss the evidence supporting the role of autophagy in cardiac homeostasis, aging, and cardioimmunological response to cardiac injury. Finally, we highlight possible translational perspectives of modulating autophagy for therapeutic purposes to improve the care of patients with acute and chronic cardiac disease.

The multifaceted nature of endogenous cardiac regeneration

Since the first evidence of cardiac regeneration was observed, almost 50 years ago, more studies have highlighted the endogenous regenerative abilities of several models following cardiac injury. In particular, analysis of cardiac regeneration in zebrafish and neonatal mice has uncovered numerous mechanisms involved in the regenerative process. It is now apparent that cardiac regeneration is not simply achieved by inducing cardiomyocytes to proliferate but requires a multifaceted response involving numerous different cell types, signaling pathways and mechanisms which must all work in harmony in order for regeneration to occur. In this review we will endeavor to highlight a variety of processes that have been identifed as being essential for cardiac regeneration.

Dissection of the autophagic route in oocytes from atretic follicles

BACKGROUND INFORMATION

Autophagy is a conserved process that functions as a cytoprotective mechanism; it may function as a cell death process called programmed cell death type II. There is considerable evidence for the presence of autophagic cell death during oocyte elimination in prepubertal rats. However, the mechanisms involved in this process have not been deciphered.

RESULTS

Our observations revealed autophagic cell death in oocytes with increased labeling of the autophagic proteins Beclin 1, light chain 3 A (LC3 A), and lysosomal-associated membrane protein 1 (Lamp1). Furthermore, mTOR and phosphorylated (p)-mTOR (S2448) proteins were significantly decreased in oocytes with increased levels of autophagic proteins, indicating autophagic activation. Moreover, phosphorylated protein kinase B (p-AKT) was not expressed by oocytes, but mitogen-activated protein kinase/extracellular signalregulated kinase (MAPK/ERK) signaling was observed. Additionally, selective and elevated mitochondrial degradation was identified in altered oocytes.

CONCLUSIONS

All these results suggest that mTOR downregulation, which promotes autophagy, could be mediated by low energy levels and sustained starvation involving the phosphoinositide 3-kinase (PI3K)/AKT/mTOR and MAPK/ERK pathways.

SIGNIFICANCE

In this work, we analyzed the manner in which autophagy is carried out in oocytes undergoing autophagic cell death by studying the behavior of proteins involved in different steps of the autophagic pathway.

Urinary FABP1 is a biomarker for impaired proximal tubular protein reabsorption and is synergistically enhanced by concurrent liver injury

Urinary fatty acid binding protein 1 (FABP1, also known as liver‐type FABP) has been implicated as a biomarker of acute kidney injury (AKI) in humans. However, the precise biological mechanisms underlying its elevation remain elusive. Here, we show that urinary FABP1 primarily reflects impaired protein reabsorption in proximal tubule epithelial cells (PTECs). Bilateral nephrectomy resulted in a marked increase in serum FABP1 levels, suggesting that the kidney is an essential organ for removing serum FABP1. Injected recombinant FABP1 was filtered through the glomeruli and robustly reabsorbed via the apical membrane of PTECs. Urinary FABP1 was significantly elevated in mice devoid of megalin, a giant endocytic receptor for protein reabsorption. Elevation of urinary FABP1 was also observed in patients with Dent disease, a rare genetic disease characterized by defective megalin function in PTECs. Urinary FABP1 levels were exponentially increased following acetaminophen overdose, with both nephrotoxicity and hepatotoxicity observed. FABP1‐deficient mice with liver‐specific overexpression of FABP1 showed a massive increase in urinary FABP1 levels upon acetaminophen injection, indicating that urinary FABP1 is liver‐derived. Lastly, we employed transgenic mice expressing diphtheria toxin receptor (DT‐R) either in a hepatocyte‐ or in a PTEC‐specific manner, or both. Upon administration of diphtheria toxin (DT), massive excretion of urinary FABP1 was induced in mice with both kidney and liver injury, while mice with either injury type showed marginal excretion. Collectively, our data demonstrated that intact PTECs have a considerable capacity to reabsorb liver‐derived FABP1 through a megalin‐mediated mechanism. Thus, urinary FABP1, which is synergistically enhanced by concurrent liver injury, is a biomarker for impaired protein reabsorption in AKI. These findings address the use of urinary FABP1 as a biomarker of histologically injured PTECs that secrete FABP1 into primary urine, and suggest the use of this biomarker to simultaneously monitor impaired tubular reabsorption and liver function. © 2021 The Authors. The Journal of Pathology published by John Wiley & Sons, Ltd. on behalf of The Pathological Society of Great Britain and Ireland.

Induction of autophagy has protective roles in imatinib-induced cardiotoxicity

Cardiotoxicity is one of the severe adverse effects of chemotherapeutic agents. Imatinib was previously reported to induce cardiotoxicity. Autophagy is an intracellular bulk protein and organelle degradation process, but its roles in cardiac diseases are unclear. We examined whether imatinib induces cardiomyocyte autophagy, and the role of autophagy in imatinib-induced cardiotoxicity using in vitro and in vivo experiments. In in vitro experiments, neonatal rat cardiomyocytes were treated with imatinib (1, 5, or 10 μM; 6 h). Myocyte autophagy was assessed by microtubule-associated protein light chain (LC) 3-II, beclin 1, mature cathepsin D, and acridine orange-stained mature autolysosome expression. Imatinib increased their expression, suggesting that it induced autophagy. Consequently, imatinib altered the production of mitochondria-derived reactive oxygen species (ROS) and loss of mitochondrial membrane potential, which were assessed by the fluorescent indicator MitoSOX and JC-1, respectively, leading to cardiomyocyte apoptosis. 3-methyl-adenine (3MA), an autophagic inhibitor, exacerbated imatinib-induced apoptosis by 30 %. In in vivo experiments, C57BL/6 mice were treated with imatinib (50 and 200 mg/kg/day) for 5 weeks in the presence or absence of 3MA. Echocardiographic measurement revealed that imatinib (200 mg) caused dilatation of the left ventricle (LV) and reduced LV fractional shortening. Apoptosis and LC3-II expression in cardiac tissue were increased by imatinib. Co-treatment with 3MA and imatinib further impaired imatinib-induced cardiac apoptosis and LV dysfunction. This study suggests that imatinib induces cardiomyocyte apoptosis, leading to cardiac dysfunction. Imatinib increases cardiomyocyte autophagy as a consequence of apoptosis and autophagy has a pro-survival role in imatinib-induced cardiac impairment.

Ferroptosis Is a Potential Novel Diagnostic and Therapeutic Target for Patients With Cardiomyopathy

Cardiomyocyte death is a fundamental progress in cardiomyopathy. However, the mechanism of triggering the death of myocardial cells remains unclear. Ferroptosis, which is the nonapoptotic, iron-dependent, and peroxidation-driven programmed cell death pathway, that is abundant and readily accessible, was not discovered until recently with a pharmacological approach. New researches have demonstrated the close relationship between ferroptosis and the development of many cardiovascular diseases, and several ferroptosis inhibitors, iron chelators, and small antioxidant molecules can relieve myocardial injury by blocking the ferroptosis pathways. Notably, ferroptosis is gradually being considered as an important cell death mechanism in the animal models with multiple cardiomyopathies. In this review, we will discuss the mechanism of ferroptosis and the important role of ferroptosis in cardiomyopathy with a special emphasis on the value of ferroptosis as a potential novel diagnostic and therapeutic target for patients suffering from cardiomyopathy in the future.

Fat-1 transgenic mice rich in endogenous omega-3 fatty acids are protected from lipopolysaccharide-induced cardiac dysfunction

Aims

Cardiac malfunctions developing in result of sepsis are hard to treat so they eventually contribute to the increased mortality. Previous reports indicated for therapeutic potential of exogenous ω‐3 polyunsaturated fatty acids (PUFA) in sepsis, but potential benefits of this compound on the malfunctional heart have not been explored yet. In the present study, we investigated whether the constantly elevated levels of endogenous ω‐3 PUFA in transgenic fat‐1 mice would alleviate the lipopolysaccharide (LPS)‐induced cardiac failure and death.

Methods and results

After both wild type (WT) and transgenic fat‐1 mice were challenged with LPS, a Kaplan–Meier curve and echocardiography were performed to evaluate the survival rates and cardiac function. Proteomics analysis, RT‐PCR, western blotting, immune‐histochemistry, and transmission electron microscopy were further performed to investigate the underlying mechanisms. Results showed that transgenic fat‐1 mice exhibited the significantly lower mortality after LPS challenge as compared with their WT counterparts (30% vs. 42.5%, P < 0.05). LPS injection consistently impaired the left ventricular contractile function and caused the cardiac injury in the wild type mice, but not significantly affected the fat‐1 mice (P < 0.05). Proteomic analyses, ELISA, and immunohistochemistry further revealed that myocardium of the LPS‐challenged fat‐1 mice demonstrated the significantly lower levels of pro‐inflammatory markers and ROS than WT mice. Meaningfully, the LPS‐treated fat‐1 mice also demonstrated a significantly higher levels of LC3 II/I and Atg7 expressions than the LPS‐treated WT mice (P < 0.05), as well as displayed a selectively increased levels of peroxisome proliferator‐activated receptor (PPAR) γ and sirtuin (Sirt)‐1 expression, associated with a parallel decrease in NFκB activation.

Conclusions

The fat‐1 mice were protected from the detrimental LPS‐induced inflammation and oxidative stress, and exhibited enhancement of the autophagic flux activities, associating with the increased Sirt‐1 and PPARγ signals.

A Genetic Cardiomyocyte Ablation Model for the Study of Heart Regeneration in Zebrafish

Adult zebrafish possess an elevated cardiac regenerative capacity as compared with adult mammals. In the past two decades, zebrafish have provided a key model system for studying the cellular and molecular mechanisms of innate heart regeneration. The ease of genetic manipulation in zebrafish has enabled the establishment of a genetic ablation injury model in which over 60% of cardiomyocytes can be depleted, eliciting signs of heart failure. After this severe injury, adult zebrafish efficiently regenerate lost cardiomyocytes and reverse heart failure. In this chapter, we describe the methods for inducing genetic cardiomyocyte ablation in adult zebrafish, assessing cardiomyocyte proliferation, and histologically analyzing regeneration after injury.

Myocardial Infarction Techniques in Adult Mice

The discovery of endogenous regenerative potential of the heart in zebrafish and neonatal mice has shifted the cardiac regenerative field towards the utilization of intrinsic regenerative mechanisms in the mammalian heart. The goal of these studies is to understand, and eventually apply, the neonatal regenerative mechanisms into adulthood. To facilitate these studies, the last two decades have seen advancements in the development of injury models in adult mice representative of the diversity of cardiac diseases. Here, we provide an overview for a selection of the most common cardiac ischemic injury models and describe a set of methods used to accurately analyze and quantify cardiac outcomes. Importantly, a comprehensive understanding of cardiac regeneration and repair requires a combination of multiple functional, histological, and molecular analyses.

p38δ genetic ablation protects female mice from anthracycline cardiotoxicity

The efficacy of an anthracycline antibiotic doxorubicin (DOX) as a chemotherapeutic agent is limited by dose-dependent cardiotoxicity. DOX is associated with activation of intracellular stress signaling pathways including p38 MAPKs. While previous studies have implicated p38 MAPK signaling in DOX-induced cardiac injury, the roles of the individual p38 isoforms, specifically, of the alternative isoforms p38γ and p38δ, remain uncharacterized. We aimed to determine the potential cardioprotective effects of p38γ and p38δ genetic deletion in mice subjected to acute DOX treatment. Male and female wild-type (WT), p38γ-/-, p38δ-/-, and p38γ-/-δ-/- mice were injected with 30 mg/kg DOX and their survival was tracked for 10 days. During this period, cardiac function was assessed by echocardiography and electrocardiography and fibrosis by Picro Sirius Red staining. Immunoblotting was performed to assess the expression of signaling proteins and markers linked to autophagy. Significantly improved survival was observed in p38δ-/- female mice post-DOX relative to WT females, but not in p38γ-/- or p38γ-/-δ-/- male or female mice. The improved survival in DOX-treated p38δ-/- females was associated with decreased fibrosis, increased cardiac output and LV diameter relative to DOX-treated WT females, and similar to saline-treated controls. Structural and echocardiographic parameters were either unchanged or worsened in all other groups. Increased autophagy, as suggested by increased LC3-II level, and decreased mammalian target of rapamycin activation was also observed in DOX-treated p38δ-/- females. p38δ plays a crucial role in promoting DOX-induced cardiotoxicity in female mice by inhibiting autophagy. Therefore, p38δ targeting could be a potential cardioprotective strategy in anthracycline chemotherapy.NEW & NOTEWORTHY This study for the first time identifies the sex-specific roles of the alternative p38γ and p38δ MAPK isoforms in promoting doxorubicin (DOX) cardiotoxicity. We show that p38δ and p38γ/δ systemic deletion was cardioprotective in female but not in male mice. Cardiac structure and function were preserved in DOX-treated p38δ-/- females and autophagy marker was increased.

Cholesterol induced autophagy via IRE1/JNK pathway promotes autophagic cell death in heart tissue

BACKGROUND

Cardiovascular diseases (CVDs), with highest mortality and morbidity rates, are the major cause of death in the world. Due to the limited information on heart tissue changes, mediated by hypercholesterolemia, we planned to investigate molecular mechanisms of endoplasmic reticulum (ER) stress and related cell death in high cholesterol fed rabbit model and possible beneficial effects of α-tocopherol.

METHODS

Molecular changes in rabbit heart tissue and cultured cardiomyocytes (H9c2 cells) were measured by western blotting, qRT-PCR, immunflouresence and flow cytometry experiments. Histological modifications were assessed by light and electron microscopes, while degradation of mitochondria was quantified through confocal microscope.

RESULTS

Feeding rabbits 2% cholesterol diet for 8 weeks and treatment of cultured cardiomyocytes with 10 μg/mL cholesterol for 3 h induced excessive autophagic activity via IRE1/JNK pathway. While no change in ER-associated degradation (ERAD) and apoptotic cell death were determined, electron and confocal microscopy analyses in cholesterol supplemented rabbits revealed significant parameters of autophagic cell death, including cytoplasmic autophagosomes, autolysosomes and organelle loss in juxtanuclear area as well as mitochondria engulfment by autophagosome. Either inhibition of ER stress or JNK in cultured cardiomyocytes or α-tocopherol supplementation in rabbits could counteract the effects of cholesterol.

CONCLUSION

Our findings underline the essential role of hypercholesterolemia in stimulating IRE1/JNK branch of ER stress response which then leads to autophagic cell death in heart tissue. Results also showed α-tocopherol as a promising regulator of autophagic cell death in cardiomyocytes.

High-mobility group AT-hook 1 promotes cardiac dysfunction in diabetic cardiomyopathy via autophagy inhibition

High-mobility group AT-hook1 (HMGA1, formerly HMG-I/Y), an architectural transcription factor, participates in a number of biological processes. However, its effect on cardiac remodeling (refer to cardiac inflammation, apoptosis and dysfunction) in diabetic cardiomyopathy remains largely indistinct. In this study, we found that HMGA1 was upregulated in diabetic mouse hearts and high-glucose-stimulated cardiomyocytes. Overexpression of HMGA1 accelerated high-glucose-induced cardiomyocyte inflammation and apoptosis, while HMGA1 knockdown relieved inflammation and apoptosis in cardiomyocytes in response to high glucose. Overexpression of HMGA1 in mice heart by adeno-associated virus 9 (AAV9) delivery system deteriorated the inflammatory response, increased apoptosis and accelerated cardiac dysfunction in streptozotocin-induced diabetic mouse model. Knockdown of HMGA1 by AAV9-shHMGA1 in vivo ameliorated cardiac remodeling in diabetic mice. Mechanistically, we found that HMGA1 inhibited the formation rather than the degradation of autophagy by regulating P27/CDK2/mTOR signaling. CDK2 knockdown or P27 overexpression blurred HMGA1 overexpression-induced deteriorating effects in vitro. P27 overexpression in mice heart counteracted HMGA1 overexpression-induced increased cardiac remodeling in diabetic mice. The luciferase reporter experiment confirmed that the regulatory effect of HMGA1 on P27 was mediated by miR-222. In addition, a miR-222 antagomir counteracted HMGA1 overexpression-induced deteriorating effects in vitro. Taken together, our data indicate that HMGA1 aggravates diabetic cardiomyopathy by directly regulating miR-222 promoter activity, which inhibits P27/mTOR-induced autophagy.

Differentially expressed autophagy-related genes are potential prognostic and diagnostic biomarkers in clear-cell renal cell carcinoma

We examined the role of differentially expressed autophagy-related genes (DEARGs) in clear cell Renal Cell Carcinoma (ccRCC) using high-throughput RNA-seq data from The Cancer Genome Atlas (TCGA). Cox regression analyses showed that 5 DEARGs (PRKCQ, BID, BAG1, BIRC5, and ATG16L2) correlated with overall survival (OS) and 4 DEARGs (EIF4EBP1, BAG1, ATG9B, and BIRC5) correlated with disease-free survival (DFS) in ccRCC patients. Multivariate Cox regression analysis using the OS and DFS prognostic risk models showed that expression of the nine DEARGs accurately and independently predicted the risk of disease recurrence or progression in ccRCC patients (area under curve or AUC values > 0.70; all p < 0.05). Moreover, the DEARGs accurately distinguished healthy individuals from ccRCC patients based on receiver operated characteristic (ROC) analyses (area under curve or AUC values > 0.60), suggesting their potential as diagnostic biomarkers for ccRCC. The expression of DEARGs also correlated with the drug sensitivity of ccRCC cell lines. The ccRCC cell lines were significantly sensitive to Sepantronium bromide, a drug that targets BIRC5. This makes BIRC5 a potential therapeutic target for ccRCC. Our study thus demonstrates that DEARGs are potential diagnostic and prognostic biomarkers and therapeutic targets in ccRCC.

A Comprehensive Review of Autophagy and Its Various Roles in Infectious, Non-Infectious, and Lifestyle Diseases: Current Knowledge and Prospects for Disease Prevention, Novel Drug Design, and Therapy

Autophagy (self-eating) is a conserved cellular degradation process that plays important roles in maintaining homeostasis and preventing nutritional, metabolic, and infection-mediated stresses. Autophagy dysfunction can have various pathological consequences, including tumor progression, pathogen hyper-virulence, and neurodegeneration. This review describes the mechanisms of autophagy and its associations with other cell death mechanisms, including apoptosis, necrosis, necroptosis, and autosis. Autophagy has both positive and negative roles in infection, cancer, neural development, metabolism, cardiovascular health, immunity, and iron homeostasis. Genetic defects in autophagy can have pathological consequences, such as static childhood encephalopathy with neurodegeneration in adulthood, Crohn's disease, hereditary spastic paraparesis, Danon disease, X-linked myopathy with excessive autophagy, and sporadic inclusion body myositis. Further studies on the process of autophagy in different microbial infections could help to design and develop novel therapeutic strategies against important pathogenic microbes. This review on the progress and prospects of autophagy research describes various activators and suppressors, which could be used to design novel intervention strategies against numerous diseases and develop therapeutic drugs to protect human and animal health.

Rab9-dependent autophagy is required for the IGF-IIR triggering mitophagy to eliminate damaged mitochondria

Mitochondria dysfunction is the major characteristic of mitophagy, which is essential in mitochondrial quality control. However, excessive mitophagy contributes to cell death in a number of diseases, including ischemic stroke and hepatotoxicity. Insulin-like growth factor II (IGF-II) and its receptor (IGF-IIR) play vital roles in the development of heart failure during hypertension. We found that IGF-II triggers IGF-IIR receptor activation, causing mitochondria dysfunction, resulting in mitophagy, and cardiomyocyte cell death. These results indicated that IGF-IIR activation triggers mitochondria fragmentation, leading to autophagosome formation, and loss of mitochondria content. These results are associated with Parkin-dependent mitophagy. Additionally, autophagic proteins Atg5, and Atg7 deficiency did not suppress IGF-IIR-induced mitophagy. However, Rab9 knockdown reduced mitophagy and maintained mitochondrial function. These constitutive mitophagies through IGF-IIR activation trigger mitochondria loss and mitochondrial ROS accumulation for cardiomyocyte viability decrease. Together, our results indicate that IGF-IIR predominantly induces mitophagy through the Rab9-dependent alternative autophagy.

Glucosyltransferase Activity of Clostridium difficile Toxin B Triggers Autophagy-mediated Cell Growth Arrest

Autophagy is a bulk cell-degradation process that occurs through the lysosomal machinery, and many reports have shown that it participates in microbial pathogenicity. However, the role of autophagy in Clostridium difficile infection (CDI), the leading cause of antibiotics-associated diarrhea, pseudomembranous colitis and even death in severe cases, is not clear. Here we report that the major virulent factor toxin B (TcdB) of Clostridium difficile elicits a strong autophagy response in host cells through its glucosyltransferase activity. Using a variety of autophagy-deficient cell lines, i.e. HeLa/ATG7^−/−, MEF/atg7^−/−, MEF/tsc2^−/−, we demonstrate that toxin-triggered autophagy inhibits host cell proliferation, which contributes to TcdB-caused cytopathic biological effects. We further show that both the PI3K complex and mTOR pathway play important roles in this autophagy induction process and consequent cytopathic event. Although the glucosyltransferase activity of TcdB is responsible for inducing both cell rounding and autophagy, there is no evidence suggesting the causal relationship between these two events. Taken together, our data demonstrate for the first time that the glucosyltransferase enzymatic activity of a pathogenic bacteria is responsible for host autophagy induction and the following cell growth arrest, providing a new paradigm for the role of autophagy in host defense mechanisms upon pathogenic infection.

Standard Immunohistochemical Assays to Assess Autophagy in Mammalian Tissue

Autophagy is a highly conserved lysosomal degradation pathway with major impact on diverse human pathologies. Despite the development of different methodologies to detect autophagy both in vitro and in vivo, monitoring autophagy in tissue via immunohistochemical techniques is hampered due to the lack of biomarkers. Immunohistochemical detection of a punctate pattern of ATG8/MAP1LC3 proteins is currently the most frequently used approach to detect autophagy in situ, but it depends on a highly sensitive detection method and is prone to misinterpretation. Moreover, reliable MAP1LC3 immunohistochemical staining requires correct tissue processing and high-quality, isoform-specific antibodies. Immunohistochemical analysis of other autophagy-related protein targets such as SQSTM1, ubiquitin, ATG5 or lysosomal proteins is not recommended as marker for autophagic activity in tissue for multiple reasons including aspecific labeling of cellular structures and a lack of differential protein expression during autophagy initiation. To better understand the role of autophagy in human disease, novel biomarkers for visualization of the autophagic process with standard histology techniques are urgently needed.

Genetic cell ablation

Targeted cell ablation has proven to be a valuable approach to study in vivo cell functions during organogenesis, tissue homeostasis, and regeneration. Over the last two decades, various approaches have been developed to refine the control of cell ablation. In this review, we give an overview of the distinct genetic tools available for targeted cell ablation, with a particular emphasis on their respective specificity.

Z-disc transcriptional coupling, sarcomeroptosis and mechanoptosis [corrected]

Cardiovascular diseases are the leading cause of morbidity and mortality worldwide. Heart failure, which contributes significantly to the incidence and prevalence of cardiovascular-related diseases, can be the result of a myriad of diverse aetiologies including viral infections, coronary heart disease and genetic abnormalities—just to name a few. Interestingly, almost every type of heart failure is characterized by the loss of cardiac myocytes, either via necrosis, apoptosis or autophagy. While the former for a long time mainly has been characterized by passive loss of cells and only the latter two have been regarded as active processes, a new view is now emerging, whereby all three forms of cell death are regarded as different types of programmed cell death which can be induced via different stimuli and pathways, most of which are probably not well understood (Kung et al., Circulation Research 108(8):1017–1036, 2011). Here, we focus on the sarcomeric Z-disc, Z-disc transcriptional coupling and its role in pro-survival pathways as well as in striated muscle specific forms of cell death (sarcomeroptosis) and mechanically induced apoptosis or mechanoptosis.

The interplay between autophagy and apoptosis in the diabetic heart

Diabetic cardiomyopathy is characterized by ventricular dysfunction that occurs in diabetic patients independent of coronary artery disease, hypertension, and any other cardiovascular diseases. Diabetic cardiomyopathy has become a major cause of diabetes-related mortality. Thus, an urgent need exists to clarify the mechanism of pathogenesis. Emerging evidence demonstrates that diabetes induces cardiomyocyte apoptosis and suppresses cardiac autophagy, indicating that the interplay between the autophagy and apoptotic cell death pathways is important in the pathogenesis of diabetic cardiomyopathy. This review highlights recent advances in the crosstalk between autophagy and apoptosis and its importance in the development of diabetic cardiomyopathy. This article is part of a Special Issue entitled "Protein Quality Control, the Ubiquitin Proteasome System, and Autophagy".

Attenuating heat-induced cellular autophagy, apoptosis and damage in H9c2 cardiomyocytes by pre-inducing HSP70 with heat shock preconditioning

PURPOSE

We sought to assess whether heat-induced autophagy, apoptosis and cell damage in H9c2 cells can be affected by pre-inducing HSP70 (heat shock protein 70).

MATERIALS AND METHODS

Cell viability was determined using 3-(4,5-dimethyl-thiazol-2-yl)-2,5-diphenyl tetrazolium bromide staining and a lactate dehydrogenase assay. Apoptosis was evidenced using both flow cytometry and counting caspase-3 positive cells, whereas autophagy was evidenced by the increased LC3-II expression and lysosomal activity.

RESULTS

The viability of H9c2 cells was temperature-dependently (40-44 °C) and time-dependently (90-180 min) significantly (p < 0.05) reduced by severe heat, which caused cell damage, apoptosis and autophagy. Heat-induced cell injury could be attenuated by pretreatment with 3-methylademine (an autophagy inhibitor) or Z-DEVD-FMK (a caspase-3 inhibitor). Neither apoptosis nor autophagy over the levels found in normothermic controls was induced in heat-shock preconditioned controls (no subsequent heat injury). The beneficial effects of mild heat preconditioning (preventing heat-induced cell damage, apoptosis and autophagy) were significantly attenuated by inhibiting HSP70 overexpression with triptolide (Tripterygium wilfordii) pretreatment.

CONCLUSION

We conclude that pre-inducing HSP70 attenuates heat-stimulated cell autophagy, apoptosis and damage in the heart. However, this requires in vivo confirmation.

Therapeutic targeting of autophagy in disease: biology and pharmacology

Autophagy, a process of self-digestion of the cytoplasm and organelles through which cellular components are recycled for reuse or energy production, is an evolutionarily conserved response to metabolic stress found in eukaryotes from yeast to mammals. It is noteworthy that autophagy is also associated with various pathophysiologic conditions in which this cellular process plays either a cytoprotective or cytopathic role in response to a variety of stresses such as metabolic, inflammatory, neurodegenerative, and therapeutic stress. It is now generally believed that modulating the activity of autophagy through targeting specific regulatory molecules in the autophagy machinery may impact disease processes, thus autophagy may represent a new pharmacologic target for drug development and therapeutic intervention of various human disorders. Induction or inhibition of autophagy using small molecule compounds has shown promise in the treatment of diseases such as cancer. Depending on context, induction or suppression of autophagy may exert therapeutic effects via promoting either cell survival or death, two major events targeted by therapies for various disorders. A better understanding of the biology of autophagy and the pharmacology of autophagy modulators has the potential for facilitating the development of autophagy-based therapeutic interventions for several human diseases.

Biochemistry of cardiomyopathy in the mitochondrial disease Friedreich's ataxia

FRDA (Friedreich's ataxia) is a debilitating mitochondrial disorder leading to neural and cardiac degeneration, which is caused by a mutation in the frataxin gene that leads to decreased frataxin expression. The most common cause of death in FRDA patients is heart failure, although it is not known how the deficiency in frataxin potentiates the observed cardiomyopathy. The major proposed biochemical mechanisms for disease pathogenesis and the origins of heart failure in FRDA involve metabolic perturbations caused by decreased frataxin expression. Additionally, recent data suggest that low frataxin expression in heart muscle of conditional frataxin knockout mice activates an integrated stress response that contributes to and/or exacerbates cardiac hypertrophy and the loss of cardiomyocytes. The elucidation of these potential mechanisms will lead to a more comprehensive understanding of the pathogenesis of FRDA, and will contribute to the development of better treatments and therapeutics.

Role of mitochondrial dysfunction and altered autophagy in cardiovascular aging and disease: from mechanisms to therapeutics

Advanced age is associated with a disproportionate prevalence of cardiovascular disease (CVD). Intrinsic alterations in the heart and the vasculature occurring over the life course render the cardiovascular system more vulnerable to various stressors in late life, ultimately favoring the development of CVD. Several lines of evidence indicate mitochondrial dysfunction as a major contributor to cardiovascular senescence. Besides being less bioenergetically efficient, damaged mitochondria also produce increased amounts of reactive oxygen species, with detrimental structural and functional consequences for the cardiovascular system. The age-related accumulation of dysfunctional mitochondrial likely results from the combination of impaired clearance of damaged organelles by autophagy and inadequate replenishment of the cellular mitochondrial pool by mitochondriogenesis. In this review, we summarize the current knowledge about relevant mechanisms and consequences of age-related mitochondrial decay and alterations in mitochondrial quality control in the cardiovascular system. The involvement of mitochondrial dysfunction in the pathogenesis of cardiovascular conditions especially prevalent in late life and the emerging connections with neurodegeneration are also illustrated. Special emphasis is placed on recent discoveries on the role played by alterations in mitochondrial dynamics (fusion and fission), mitophagy, and their interconnections in the context of age-related CVD and endothelial dysfunction. Finally, we discuss pharmacological interventions targeting mitochondrial dysfunction to delay cardiovascular aging and manage CVD.

Diminished autophagy limits cardiac injury in mouse models of type 1 diabetes

Cardiac autophagy is inhibited in type 1 diabetes. However, it remains unknown if the reduced autophagy contributes to the pathogenesis of diabetic cardiomyopathy. We addressed this question using mouse models with gain- and loss-of-autophagy. Autophagic flux was inhibited in diabetic hearts when measured at multiple time points after diabetes induction by streptozotocin as assessed by protein levels of microtubule-associated protein light chain 3 form 2 (LC3-II) or GFP-LC3 puncta in the absence and presence of the lysosome inhibitor bafilomycin A1. Autophagy in diabetic hearts was further reduced in beclin 1- or Atg16-deficient mice but was restored partially or completely by overexpression of beclin 1 to different levels. Surprisingly, diabetes-induced cardiac damage was substantially attenuated in beclin 1- and Atg16-deficient mice as shown by improved cardiac function as well as reduced levels of oxidative stress, interstitial fibrosis, and myocyte apoptosis. In contrast, diabetic cardiac damage was dose-dependently exacerbated by beclin 1 overexpression. The cardioprotective effects of autophagy deficiency were reproduced in OVE26 diabetic mice. These effects were associated with partially restored mitophagy and increased expression and mitochondrial localization of Rab9, an essential regulator of a non-canonical alternative autophagic pathway. Together, these findings demonstrate that the diminished autophagy is an adaptive response that limits cardiac dysfunction in type 1 diabetes, presumably through up-regulation of alternative autophagy and mitophagy.

Hypothermia may attenuate ischemia/reperfusion-induced cardiomyocyte death by reducing autophagy

OBJECTIVE

We sought to assess the effect of therapeutic hypothermia on the autophagy that occurred in ischemia-reperfused (IR) H9c2 cardiomyocytes.

METHODS

In control studies, the H9c2 cells at a density of 1 × 10(5) per culture dish in six-well plate were exposed to normoxic culture medium at 37 °C for 12h. All assays contained appropriate controls and were performed in triplicate and repeated on three separately initiated cultures. In hypothermia-treated group, the ischemic and hypoxic cells were maintained in a 32 °C incubation. The trypan blue exclusion method was used to assess the cell viability. Autophagy was evaluated by determining both the microtubule-associated protein 1 light chain 3 [LC3] levels and punctuate distribution of the autophagic vesicle associated form [LC3-II].

RESULTS

The results were mean ± standard error of mean of triplicates. The viable cell percentage for control group, IR group, and IR group treated with hypothermia at the start of ischemia, or reperfusion were 100% ± 9%, 20% ± 1%, 32% ± 3%, and 41% ± 3%, respectively. The cell death in I/R H9c2 cells was positively associated with increased LC3 levels and punctuate distribution of (LC3-II). Mild hypothermia adopted at the start of ischemia or reperfusion significantly reduced both the cell death and the autophagy in H9c2 cells.

CONCLUSION

Our data indicate that in H9c2, IR stimulates cell autophagy and causes cell death, which can be attenuated by mild hypothermia. Our results, if further confirmed in vivo, may have important clinical implications during IR injury.

Sex differences at cellular level: "cells have a sex"

Different pathways involved in the complex machinery implicated in determining cell fate have been investigated in the recent years. Different forms of cell death have been described: apart from the "classical" form of death known as necrosis, a well characterized traumatic injury of the cell, several additional forms of cell death have been identified. Among these, apoptosis has been characterized in detail. These studies stem from the implication that the apoptotic process plays a key role in a plethora of human pathologies, including cardiovascular diseases. In fact, defects in the mechanisms of cell death, i.e., both an increase or a decrease of apoptosis, have been associated with the pathogenesis of vessel and myocardial diseases. Some new insights also derived from the study of autophagy, a less characterized form of cell damage mainly associated with cell survival strategies but that also leads, as final event, to the death of the cell. Interestingly, very recently, a gender difference has been found in this respect: cells from males and females can behave differently. In fact, they seem to display several different features, including those determining their fate. These gender cytology differences are briefly described here. The study of this gender disparity is of great relevance in cardiovascular disease pathogenesis and pharmacology. The comprehension of the gender-related mechanisms of cell demise can in fact disclose new scenarios in preclinical and clinical management of cardiovascular diseases.

Zebrafish cardiac injury and regeneration models: a noninvasive and invasive in vivo model of cardiac regeneration

Despite current treatment regimens, heart failure still remains one of the leading causes of morbidity and mortality in the world due to failure to adequately replace lost ventricular myocardium from ischemia-induced infarct. Although adult mammalian ventricular cardiomyocytes have a limited capacity to divide, this proliferation is insufficient to overcome the significant loss of myocardium from ventricular injury. However, lower vertebrates, such as the zebrafish and newt, have the remarkable capacity to fully regenerate their hearts after severe injury. Thus, there is great interest in studying these animal model systems to discover new regenerative approaches that might be applied to injured mammalian hearts. To this end, the zebrafish has been utilized more recently to gain additional mechanistic insight into cardiac regeneration because of its genetic tractability. Here, we describe two cardiac injury methods, a mechanical and a genetic injury model, for studying cardiac regeneration in the zebrafish.

Immunohistochemical analysis of macroautophagy: recommendations and limitations

Transmission electron microscopy (TEM) is an indispensable standard method to monitor macroautophagy in tissue samples. Because TEM is time consuming and not suitable for daily routine, many groups try to identify macroautophagy in tissue by conventional immunohistochemistry. The aim of the present study was to evaluate whether immunohistochemical assessment of macroautophagy-related marker proteins such as LC3, ATG5, CTSD/cathepsin D, BECN1/Beclin 1 or SQSTM1/p62 is feasible and autophagy-specific. For this purpose, livers from starved mice were used as a model because hepatocytes are highly sensitive to autophagy induction. ATG7-deficient mouse livers served as negative control. Our findings indicate that unambiguous immunodetection of LC3 in paraffin-embedded tissue specimens was hampered due to low in situ levels of this protein. Maximum sensitivity could only be obtained using high-quality, isoform-specific antibodies, such as antibody 5F10, in combination with Envision+ signal amplification. Moreover, LC3 stains were optimal in neutral-buffered formalin-fixed tissue, immersed in citrate buffer during antigen retrieval. However, even when using this methodology, LC3 monitoring required overexpression of the protein, e.g., in GFP-LC3 transgenic mice. This was not only the case for the liver but also for other organs including heart, skeletal muscle, kidney and gut. Immunohistochemical detection of the autophagy-related proteins ATG5, CTSD or BECN1 is not recommendable for monitoring autophagy, due to lack of differential gene expression or doubtful specificity. SQSTM1 accumulated in autophagy-deficient liver, thus it is not a useful marker for tissue with autophagic activity. We conclude that TEM remains an indispensable technique for in situ evaluation of macroautophagy, particularly in clinical samples for which genetic manipulation or other in vitro techniques are not feasible.

RETRACTED: Cardiac-specific overexpression of catalase attenuates lipopolysaccharide-induced myocardial contractile dysfunction: Role of autophagy

This article has been retracted: please see Elsevier Policy on Article Withdrawal (http://www.elsevier.com/locate/withdrawalpolicy). This article has been retracted at the request of the Editor-in-Chief. After an institutional investigation into the work of Dr. Jun Ren, University of Wyoming subsequently conducted an examination of other selected publications of Dr. Ren's under the direction of the HHS Office of Research Integrity. Based on the findings of this examination, the University of Wyoming recommended this article be retracted due to concerns regarding data irregularities inconsistent with published conclusions. Specifically, University of Wyoming found evidence of data irregularities and image reuse in Figure 2 that significantly affect the results and conclusions reported in the manuscript.

Cardiac aging: from molecular mechanisms to significance in human health and disease

Cardiovascular diseases (CVDs) are the major causes of death in the western world. The incidence of cardiovascular disease as well as the rate of cardiovascular mortality and morbidity increase exponentially in the elderly population, suggesting that age per se is a major risk factor of CVDs. The physiologic changes of human cardiac aging mainly include left ventricular hypertrophy, diastolic dysfunction, valvular degeneration, increased cardiac fibrosis, increased prevalence of atrial fibrillation, and decreased maximal exercise capacity. Many of these changes are closely recapitulated in animal models commonly used in an aging study, including rodents, flies, and monkeys. The application of genetically modified aged mice has provided direct evidence of several critical molecular mechanisms involved in cardiac aging, such as mitochondrial oxidative stress, insulin/insulin-like growth factor/PI3K pathway, adrenergic and renin angiotensin II signaling, and nutrient signaling pathways. This article also reviews the central role of mitochondrial oxidative stress in CVDs and the plausible mechanisms underlying the progression toward heart failure in the susceptible aging hearts. Finally, the understanding of the molecular mechanisms of cardiac aging may support the potential clinical application of several "anti-aging" strategies that treat CVDs and improve healthy cardiac aging.

Contribution of impaired mitochondrial autophagy to cardiac aging: mechanisms and therapeutic opportunities

The prevalence of cardiovascular disease increases with advancing age. Although long-term exposure to cardiovascular risk factors plays a major role in the etiopathogenesis of cardiovascular disease, intrinsic cardiac aging enhances the susceptibility to developing heart pathologies in late life. The progressive decline of cardiomyocyte mitochondrial function is considered a major mechanism underlying heart senescence. Damaged mitochondria not only produce less ATP but also generate increased amounts of reactive oxygen species and display a greater propensity to trigger apoptosis. Given the postmitotic nature of cardiomyocytes, the efficient removal of dysfunctional mitochondria is critical for the maintenance of cell homeostasis, because damaged organelles cannot be diluted by cell proliferation. The only known mechanism whereby mitochondria are turned over is through macroautophagy. The efficiency of this process declines with advancing age, which may play a critical role in heart senescence and age-related cardiovascular disease. The present review illustrates the putative mechanisms whereby alterations in the autophagic removal of damaged mitochondria intervene in the process of cardiac aging and in the pathogenesis of specific heart diseases that are especially prevalent in late life (eg, left ventricular hypertrophy, ischemic heart disease, heart failure, and diabetic cardiomyopathy). Interventions proposed to counteract cardiac aging through improvements in macroautophagy (eg, calorie restriction and calorie restriction mimetics) are also presented.

Resveratrol attenuates doxorubicin-induced cardiomyocyte death via inhibition of p70 S6 kinase 1-mediated autophagy

Resveratrol is a plant-derived polyphenol that can attenuate the cardiotoxic effects of doxorubicin (DOX), a powerful antibiotic widely used in cancer chemotherapy. However, the underlying protective mechanisms of resveratrol remain elusive. Here, we show that resveratrol inhibited DOX-induced autophagy and cardiomyocyte death, and autophagy suppression is an important mechanism that mediates the ability of resveratrol to protect against DOX cardiotoxicity. Indeed, resveratrol, 3-methyladenine (3-MA), and a short hairpin RNA directed against autophagy gene beclin 1 (shBCN1) each was able to attenuate DOX-induced autophagy and cardiomyocyte death, but resveratrol did not provide additional protection in the presence of 3-MA or shBCN1. In contrast, up-regulation of autophagy by beclin 1 overexpression not only exacerbated DOX cardiotoxicity but also abolished the protective effects of resveratrol. Intriguingly, p70 S6 kinase 1 (S6K1) was activated by DOX, which was prevented by resveratrol. Knocking down S6K1 with small interfering RNA diminished DOX-induced autophagy and cardiotoxicity, but resveratrol failed to exert an additive effect. In addition, S6K1 overexpression impaired the ability of resveratrol to antagonize DOX-induced autophagy and cardiomyocyte death. Taken together, our data indicate that the protective effect of resveratrol against DOX cardiotoxicity largely depends on its ability to suppress DOX-induced autophagy via the inhibition of S6K1.

On the role of autophagy in human diseases: a gender perspective

Cytopathological features of cells from males and females, i.e. XX and XY isolated cells, have been demonstrated to represent a key variable in the mechanism underlying gender disparity in human diseases. Major insights came from the studies of gender differences in cell fate, e.g. in apoptotic susceptibility. We report here some novel insights recently emerged from literature that are referred as to a cytoprotection mechanism by which cells recycle cytoplasm and dispose of excess or defective organelles, i.e. autophagy. Autophagy and related genes have first been identified in yeast. Orthologue genes have subsequently been found in other organisms, including human beings. This stimulated the research in the field and, thanks to the use of molecular genetics and cell biology in different model systems, autophagy gained the attention of several research groups operating to analyse the pathogenetic mechanisms of human diseases. It remains unclear, however, whether autophagy can exert a protective effect or instead contribute to the pathogenesis of important human diseases. On the basis of the growing importance of sex/gender as key determinant of human pathology and of the known differences between males and females in the onset, progression, drug susceptibility and outcome of a plethora of diseases, the idea that autophagy could represent key and critical factor should be taken into account. In the review, we summarize our current knowledge about the role of autophagy in some paradigmatic human diseases (cancer, neurodegenerative, autoimmune, cardiovascular) and the role of ‘cell sex’ differences in this context.

The regenerative capacity of zebrafish reverses cardiac failure caused by genetic cardiomyocyte depletion

Natural models of heart regeneration in lower vertebrates such as zebrafish are based on invasive surgeries causing mechanical injuries that are limited in size. Here, we created a genetic cell ablation model in zebrafish that facilitates inducible destruction of a high percentage of cardiomyocytes. Cell-specific depletion of over 60% of the ventricular myocardium triggered signs of cardiac failure that were not observed after partial ventricular resection, including reduced animal exercise tolerance and sudden death in the setting of stressors. Massive myocardial loss activated robust cellular and molecular responses by endocardial, immune, epicardial and vascular cells. Destroyed cardiomyocytes fully regenerated within several days, restoring cardiac anatomy, physiology and performance. Regenerated muscle originated from spared cardiomyocytes that acquired ultrastructural and electrophysiological characteristics of de-differentiation and underwent vigorous proliferation. Our study indicates that genetic depletion of cardiomyocytes, even at levels so extreme as to elicit signs of cardiac failure, can be reversed by natural regenerative capacity in lower vertebrates such as zebrafish.

Role of autophagy in heart failure associated with aging

Heart failure is a progressive disease, leading to reduced quality of life and premature death. Adverse ventricular remodeling involves changes in the balance between cardiomyocyte protein synthesis and degradation, forcing these myocytes in equilibrium between life and death. In this context, autophagy has been recognized to play a role in the pathophysiology of heart failure. At basal levels, autophagy performs housekeeping functions, maintaining cardiomyocyte function and ventricular mass. Autophagy also occurs in the failing human heart, and upregulation has been reported in animal models of pressure overload-induced heart failure. Although the factors that determine whether autophagy will be protective or detrimental are not well known, the level and duration of autophagy seem important. Autophagy may antagonize ventricular hypertrophy by increasing protein degradation, which decreases tissue mass. However, the rate of protective autophagy declines with age. The inability to remove damaged structures results in the progressive accumulation of 'garbage', including abnormal intracellular proteins aggregates and undigested materials such as lipofuscin. Eventually, the progress of these changes results in enhanced oxidative stress, decreased ATP production, collapse of the cellular catabolic machinery, and cell death. By contrast, in load-induced heart failure, the extent of autophagic flux can rise to maladaptive levels. Excessive autophagy induction leads to autophagic cell death and loss of cardiomyocytes and may contribute to the worsening of heart failure. Accordingly, the development of therapies that up-regulate the repair qualities of the autophagic process and down-regulate the cell death aspects would be of great value in the treatment of heart failure.

A differential autophagic response to hyperglycemia in the developing murine embryo

Autophagy is critical to the process of development because mouse models have shown that lack of autophagy leads to developmental arrest during the pre-implantation stage of embryogenesis. The process of autophagy is regulated through signaling pathways, which respond to the cellular environment. Therefore, any alteration in the environment may lead to the dysregulation of the autophagic process potentially resulting in cell death. Using both in vitro and in vivo models to study autophagy in the pre-implantation murine embryo, we observed that the cells respond to environmental stressors (i.e. hyperglycemic environment) by increasing activation of autophagy in a differential pattern within the embryo. This upregulation is accompanied by an increase in apoptosis, which appears to plateau at high concentrations of glucose. The activation of the autophagic pathway was further confirmed by an increase in GAPDH activity in both in vivo and in vitro hyperglycemic models, which has been linked to autophagy through the activation of the Atg12 gene. Furthermore, this increase in autophagy in response to a hyperglycemic environment was observed as early as the oocyte stage. In conclusion, in this study, we provided evidence for a differential response of elevated activation of autophagy in embryos and oocytes exposed to a hyperglycemic environment.

Propofol protects the autophagic cell death induced by the ischemia/reperfusion injury in rats

Autophagy has been implicated in cardiac cell death during ischemia/reperfusion (I/R). In this study we investigated how propofol, an antioxidant widely used for anesthesia, affects the autophagic cell death induced by the myocardial I/R injury. The infarction size in the myocardium was dramatically reduced in rats treated with propofol during I/R compared with untreated rats. A large number of autophagic vacuoles were observed in the cardiomyocytes of I/R-injured rats but rarely in I/R-injured rats treated with propofol. While LC3-II formation, an autophagy marker, was up-regulated in the I/R-injured myocardium, it was significantly down-regulated in the myocardial tissues of I/R-injured and propofol-treated rats. Moreover, propofol inhibited the I/R-induced expression of Beclin-1, and it accelerated phosphorylation of mTOR during I/R and Beclin-1/Bcl-2 interaction in cells, which indicates that it facilitates the inhibitory pathway of autophagy. These data suggest that propofol protects the autophagic cell death induced by the myocardial I/R injury.

Cardiomyocyte autophagy: remodeling, repairing, and reconstructing the heart

Autophagy is an evolutionarily conserved catabolic pathway of lysosome-dependent turnover of damaged proteins and organelles. When nutrients are in short supply, bulk removal of cytoplasmic components by autophagy replenishes depleted energy stores, a process critical for maintaining cellular homeostasis. However, prolonged activation of autophagic pathways can result in cell death. Longstanding evidence has linked the stimulation of lysosomal pathways to pathologic cardiac remodeling and a number of cardiac diseases, including heart failure and ischemia. Only recently, however, has work begun to parse cytoprotective autophagy from autophagy that contributes to disease pathogenesis. Current thinking suggests that the effects of autophagy exist on a continuum, with the eliciting triggers, the duration and amplitude of autophagic flux, and possibly the targeted intra-cellular cargo as critical determinants of the end result. Deciphering how autophagy participates in basal homeostasis of the heart, in aging, and in disease pathogenesis may uncover novel insights with clinical relevance in the treatment of heart disease.

Double transgenic mice crossed GFP-LC3 transgenic mice with alphaMyHC-mCherry-LC3 transgenic mice are a new and useful tool to examine the role of autophagy in the heart

BACKGROUND

The involvement of autophagy in heart disease has been reported. Transgenic mice expressing GFP-LC3 have been a useful tool in detecting autophagosomes systemically. It is difficult to differentiate increased formation of autophagosomes from decreased clearance of autophagosomes in the heart using GFP-LC3 mice.

METHODS AND RESULTS

We generated transgenic mice expressing mCherry-LC3 under alphaMyHC promoter and crossed the mice with transgenic mice expressing GFP-LC3. The deference of resistance to acidic conditions between GFP and mCherry overcame the limitation.

CONCLUSIONS

This method is an innovative approach to examine the role of autophagy and to analyze autophagosome maturation in cardiomyocytes. (Circ J 2010; 74: 203 - 206).

Transcription factor GATA4 inhibits doxorubicin-induced autophagy and cardiomyocyte death

Doxorubicin (DOX) is a potent anti-tumor drug known to cause heart failure. The transcription factor GATA4 antagonizes DOX-induced cardiotoxicity. However, the protective mechanism remains obscure. Autophagy is the primary cellular pathway for lysosomal degradation of long-lived proteins and organelles, and its activation could be either protective or detrimental depending on specific pathophysiological conditions. Here we investigated the ability of GATA4 to inhibit autophagy as a potential mechanism underlying its protection against DOX toxicity in cultured neonatal rat cardiomyocytes. DOX markedly increased autophagic flux in cardiomyocytes as indicated by the difference in protein levels of LC3-II (microtubule-associated protein light chain 3 form 2) or numbers of autophagic vacuoles in the absence and presence of the lysosomal inhibitor bafilomycin A1. DOX-induced cardiomyocyte death determined by multiple assays was aggravated by a drug or genetic approach that activates autophagy, but it was attenuated by manipulations that inhibit autophagy, suggesting that autophagy contributes to DOX cardiotoxicity. DOX treatment depleted GATA4 protein levels, which predisposed cardiomyocytes to DOX toxicity. Indeed, GATA4 gene silencing triggered autophagy that rendered DOX more toxic, whereas GATA4 overexpression inhibited DOX-induced autophagy, reducing cardiomyocyte death. Mechanistically, GATA4 up-regulated gene expression of the survival factor Bcl2 and suppressed DOX-induced activation of autophagy-related genes, which may likely be responsible for the anti-apoptotic and anti-autophagic effects of GATA4. Together, these findings suggest that activation of autophagy mediates DOX cardiotoxicity, and preservation of GATA4 attenuates DOX cardiotoxicity by inhibiting autophagy through modulation of the expression of Bcl2 and autophagy-related genes.

Targeted injury of type II alveolar epithelial cells induces pulmonary fibrosis

RATIONALE

Ineffective repair of a damaged alveolar epithelium has been postulated to cause pulmonary fibrosis. In support of this theory, epithelial cell abnormalities, including hyperplasia, apoptosis, and persistent denudation of the alveolar basement membrane, are found in the lungs of humans with idiopathic pulmonary fibrosis and in animal models of fibrotic lung disease. Furthermore, mutations in genes that affect regenerative capacity or that cause injury/apoptosis of type II alveolar epithelial cells have been identified in familial forms of pulmonary fibrosis. Although these findings are compelling, there are no studies that demonstrate a direct role for the alveolar epithelium or, more specifically, type II cells in the scarring process.

OBJECTIVES

To determine if a targeted injury to type II cells would result in pulmonary fibrosis.

METHODS

A transgenic mouse was generated to express the human diphtheria toxin receptor on type II alveolar epithelial cells. Diphtheria toxin was administered to these animals to specifically target the type II epithelium for injury. Lung fibrosis was assessed by histology and hydroxyproline measurement.

MEASUREMENTS AND MAIN RESULTS

Transgenic mice treated with diphtheria toxin developed an approximately twofold increase in their lung hydroxyproline content on Days 21 and 28 after diphtheria toxin treatment. The fibrosis developed in conjunction with type II cell injury. Histological evaluation revealed diffuse collagen deposition with patchy areas of more confluent scarring and associated alveolar contraction.

CONCLUSIONS

The development of lung fibrosis in the setting of type II cell injury in our model provides evidence for a causal link between the epithelial defects seen in idiopathic pulmonary fibrosis and the corresponding areas of scarring.

The ubiquitin-proteasome system in cardiac proteinopathy: a quality control perspective

Protein quality control (PQC) depends on elegant collaboration between molecular chaperones and targeted proteolysis in the cell. The latter is primarily carried out by the ubiquitin-proteasome system, but recent advances in this area of research suggest a supplementary role for the autophagy-lysosomal pathway in PQC-related proteolysis. The (patho)physiological significance of PQC in the heart is best illustrated in cardiac proteinopathy, which belongs to a family of cardiac diseases caused by expression of aggregation-prone proteins in cardiomyocytes. Cardiac proteasome functional insufficiency (PFI) is best studied in desmin-related cardiomyopathy, a bona fide cardiac proteinopathy. Emerging evidence suggests that many common forms of cardiomyopathy may belong to proteinopathy. This review focuses on examining current evidence, as it relates to the hypothesis that PFI impairs PQC in cardiomyocytes and contributes to the progression of cardiac proteinopathies to heart failure.