Cell death in heart failure

Programmed Cell Death: Complex Regulatory Networks in Cardiovascular Disease

Abnormalities in programmed cell death (PCD) signaling cascades can be observed in the development and progression of various cardiovascular diseases, such as apoptosis, necrosis, pyroptosis, ferroptosis, and cell death associated with autophagy. Aberrant activation of PCD pathways is a common feature leading to excessive cardiac remodeling and heart failure, involved in the pathogenesis of various cardiovascular diseases. Conversely, timely activation of PCD remodels cardiac structure and function after injury in a spatially or temporally restricted manner and corrects cardiac development similarly. As many cardiovascular diseases exhibit abnormalities in PCD pathways, drugs that can inhibit or modulate PCD may be critical in future therapeutic strategies. In this review, we briefly describe the process of various types of PCD and their roles in the occurrence and development of cardiovascular diseases. We also discuss the interplay between different cell death signaling cascades and summarize pharmaceutical agents targeting key players in cell death signaling pathways that have progressed to clinical trials. Ultimately a better understanding of PCD involved in cardiovascular diseases may lead to new avenues for therapy.

Positron Emission Tomography Techniques to Measure Active Inflammation, Fibrosis and Angiogenesis: Potential for Non-invasive Imaging of Hypertensive Heart Failure

Heart failure, which is responsible for a high number of deaths worldwide, can develop due to chronic hypertension. Heart failure can involve and progress through several different pathways, including: fibrosis, inflammation, and angiogenesis. Early and specific detection of changes in the myocardium during the transition to heart failure can be made via the use of molecular imaging techniques, including positron emission tomography (PET). Traditional cardiovascular PET techniques, such as myocardial perfusion imaging and sympathetic innervation imaging, have been established at the clinical level but are often lacking in pathway and target specificity that is important for assessment of heart failure. Therefore, there is a need to identify new PET imaging markers of inflammation, fibrosis and angiogenesis that could aid diagnosis, staging and treatment of hypertensive heart failure. This review will provide an overview of key mechanisms underlying hypertensive heart failure and will present the latest developments in PET probes for detection of cardiovascular inflammation, fibrosis and angiogenesis. Currently, selective PET probes for detection of angiogenesis remain elusive but promising PET probes for specific targeting of inflammation and fibrosis are rapidly progressing into clinical use.

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.

Egr-1 is involved in coronary microembolization-induced myocardial injury via Bim/Beclin-1 pathway-mediated autophagy inhibition and apoptosis activation

Coronary microembolization (CME) substantially reduces the clinical benefits of myocardial reperfusion therapy. Autophagy and apoptosis participate in the pathophysiological processes of almost all cardiovascular diseases, including CME-induced myocardial injury, but the precise underlying mechanisms remain unclear. In the present study, we observed that Egr-1 expression was substantially increased after CME modeling. Inhibition of Egr-1 expression through the targeted delivery of rAAV9-Egr-1-shRNA improved cardiac function and reduced myocardial injury. The microinfarct size was also significantly smaller in the Egr-1 inhibitor group than in the CME group. These benefits were partially reversed by the autophagy inhibitor 3-MA. As shown in our previous study, autophagy in the myocardium was impaired after CME. Inhibition of Egr-1 expression in vivo restored the autophagy flux and reduced myocardial apoptosis, at least partially, by inhibiting the Egr-1/Bim/Beclin-1 pathway, as evidenced by the results of the western blot, RT-qPCR, and TUNEL staining. At the same time, TEM showed a dramatic increase in the number of typical autophagic vacuoles in the Egr-1 inhibitor group compared to the CME group. Based on these findings, the Egr-1/Bim/Beclin-1 pathway may be involved in CME-induced myocardial injury by regulating myocardial autophagy and apoptosis, and this pathway represents a potential therapeutic target in CME.

Thrombospondins: A Role in Cardiovascular Disease

Thrombospondins (TSPs) represent extracellular matrix (ECM) proteins belonging to the TSP family that comprises five members. All TSPs have a complex multidomain structure that permits the interaction with various partners including other ECM proteins, cytokines, receptors, growth factors, etc. Among TSPs, TSP1, TSP2, and TSP4 are the most studied and functionally tested. TSP1 possesses anti-angiogenic activity and is able to activate transforming growth factor (TGF)-β, a potent profibrotic and anti-inflammatory factor. Both TSP2 and TSP4 are implicated in the control of ECM composition in hypertrophic hearts. TSP1, TSP2, and TSP4 also influence cardiac remodeling by affecting collagen production, activity of matrix metalloproteinases and TGF-β signaling, myofibroblast differentiation, cardiomyocyte apoptosis, and stretch-mediated enhancement of myocardial contraction. The development and evaluation of TSP-deficient animal models provided an option to assess the contribution of TSPs to cardiovascular pathology such as (myocardial infarction) MI, cardiac hypertrophy, heart failure, atherosclerosis, and aortic valve stenosis. Targeting of TSPs has a significant therapeutic value for treatment of cardiovascular disease. The activation of cardiac TSP signaling in stress and pressure overload may be therefore beneficial.

Sterile Inflammation and Degradation Systems in Heart Failure

In most patients with chronic heart failure (HF), levels of circulating cytokines are elevated and the elevated cytokine levels correlate with the severity of HF and prognosis. Various stresses induce subcellular component abnormalities, such as mitochondrial damage. Damaged mitochondria induce accumulation of reactive oxygen species and apoptogenic proteins, and subcellular inflammation. The vicious cycle of subcellular component abnormalities, inflammatory cell infiltration and neurohumoral activation induces cardiomyocyte injury and death, and cardiac fibrosis, resulting in cardiac dysfunction and HF. Quality control mechanisms at both the protein and organelle levels, such as elimination of apoptogenic proteins and damaged mitochondria, maintain cellular homeostasis. An imbalance between protein synthesis and degradation is likely to result in cellular dysfunction and disease. Three major protein degradation systems have been identified, namely the cysteine protease system, autophagy, and the ubiquitin proteasome system. Autophagy was initially believed to be a non-selective process. However, recent studies have described the process of selective mitochondrial autophagy, known as mitophagy. Elimination of damaged mitochondria by autophagy is important for maintenance of cellular homeostasis. DNA and RNA degradation systems also play a critical role in regulating inflammation and maintaining cellular homeostasis mediated by damaged DNA clearance and post-transcriptional regulation, respectively. This review discusses some recent advances in understanding the role of sterile inflammation and degradation systems in HF.

Role of cell death in the progression of heart failure

All multicellular organisms develop during evolution the highly regulated and interconnected pathways of cell death. This complex network contributes to the pathogenesis of various cardiovascular disorders including ischemia/reperfusion injury, myocardial infarction, heart failure, dysrhythmias and atherosclerosis. Chronic cardiac remodeling response and transition to overt HF have been associated with modestly increased apoptosis, although the actual burden of chronic cell loss attributable to apoptosis is not clear. Central mediators of cardiomyocyte survival and death are the mitochondrial organelles. Based on its morphological characteristics, cell death can be classified into three major types: apoptosis, necrosis and autophagy. Recently, a new pathway of regulated necrosis, necroptosis, has also been reported in the failing heart. The mitochondrial (intrinsic) and the death-receptor-mediated (extrinsic) converge at mitochondria inducing release of mitochondrial apoptogens to initiate the caspase cascade and eventually degradation of the doomed cardiomyocyte. Activation of death receptors can initiate not only extrinsic apoptotic pathway, but also necrosis. On the other hand, autophagy, which is characterized by the massive formation of lysosomal-derived vesicles, containing degenerating cytoplasmic contents, is primarily a survival response to nutrient deprivation, and a selective form of autophagy, mitophagy, is also a protective mechanism that allows to eliminate damaged mitochondria and thereby to attenuate mitochondria-mediated apoptosis and necrosis in the myocardium. Further insight into the molecular mechanisms underlying cell death will increase the efficiency and repertoire of therapeutic interventions available in cardiovascular disease.

Nutritional leucine supplementation attenuates cardiac failure in tumour-bearing cachectic animals

BACKGROUND

The condition known as cachexia presents in most patients with malignant tumours, leading to a poor quality of life and premature death. Although the cancer-cachexia state primarily affects skeletal muscle, possible damage in the cardiac muscle remains to be better characterized and elucidated. Leucine, which is a branched chain amino acid, is very useful for preserving lean body mass. Thus, this amino acid has been studied as a coadjuvant therapy in cachectic cancer patients, but whether this treatment attenuates the effects of cachexia and improves cardiac function remains poorly understood. Therefore, using an experimental cancer-cachexia model, we evaluated whether leucine supplementation ameliorates cachexia in the heart.

METHODS

Male Wistar rats were fed either a leucine-rich or a normoprotein diet and implanted or not with subcutaneous Walker-256 carcinoma. During the cachectic stage (approximately 21 days after tumour implantation), when the tumour mass was greater than 10% of body weight, the rats were subjected to an electrocardiogram analysis to evaluate the heart rate, QT-c, and T wave amplitude. The myocardial tissues were assayed for proteolytic enzymes (chymotrypsin, alkaline phosphatase, cathepsin, and calpain), cardiomyopathy biomarkers (myeloperoxidase, tissue inhibitor of metalloproteinases, and total plasminogen activator inhibitor 1), and caspase-8, -9, -3, and -7 activity.

RESULTS

Both groups of tumour-bearing rats, especially the untreated group, had electrocardiography alterations that were suggestive of ischemia, dilated cardiomyopathy, and sudden death risk. Additionally, the rats in the untreated tumour-bearing group but not their leucine-supplemented littermates exhibited remarkable increases in chymotrypsin activity and all three heart failure biomarkers analysed, including an increase in caspase-3 and -7 activity.

CONCLUSIONS

Our data suggest that a leucine-rich diet could modulate heart damage, cardiomyocyte proteolysis, and apoptosis driven by cancer-cachexia. Further studies must be conducted to elucidate leucine's mechanisms of action, which potentially includes the modulation of the heart's inflammatory process.

Involvement of PINK1/Parkin-mediated mitophagy in AGE-induced cardiomyocyte aging

CONTEXT AND OBJECTIVES

Advanced glycation end products (AGEs) can induce senescence in cardiomyocytes. However, its underlying molecular mechanisms remain unknown.

METHODS

Neonatal rat cardiomyocytes were incubated with AGEs, and cellular senescence was evaluated by senescence-associated beta-galactosidase (SA-β-gal) activity and aging-associated p16 expression. In addition, mitophagic activity was evaluated by measuring the expression of the PINK1, Parkin, LC3 and p62 proteins. The mitophagy inhibitor cyclosporine A (CsA) or PINK1 siRNAs was then administered to cardiomyocytes to study the role of mitophagy in AGE-induced aging.

RESULTS

A significantly increased number of SA-β-gal positive cells and increased p16 protein levels were observed in cardiomyocytes treated with AGEs. Moreover, AGEs significantly increased the protein levels of PINK1 and Parkin as well as the LC3-II/LC3-I ratio, which occurred in a dose-dependent manner. However, the expression of p62 decreased significantly in the AGE group compared to the control. Surprisingly, both CsA and the knockdown of PINK1 by small-interfering RNA (siRNA) significantly decreased the LC3-II/LC3-I ratio and the PINK1 and Parkin protein levels in AGE-treated cardiomyocytes. Moreover, CsA treatment or knockdown of PINK1 expression attenuated the increased number of SA-β-gal positive cells and the upregulated p16 level in cardiomyocytes induced by AGEs.

CONCLUSIONS

PINK1/Parkin-mediated mitophagy is involved in the process of cardiomyocyte senescence induced by AGEs, and a reduction in mitophagic activity might be a promising approach to block the senescent state in cardiomyocytes.

Pathways of cardiac toxicity: comparison between chemotherapeutic drugs doxorubicin and mitoxantrone

Anthracyclines, e.g., doxorubicin (DOX), and anthracenediones, e.g., mitoxantrone (MTX), are drugs used in the chemotherapy of several cancer types, including solid and non-solid malignancies such as breast cancer, leukemia, lymphomas, and sarcomas. Although they are effective in tumor therapy, treatment with these two drugs may lead to side effects such as arrhythmia and heart failure. At the same clinically equivalent dose, MTX causes slightly reduced cardiotoxicity compared with DOX. These drugs interact with iron to generate reactive oxygen species (ROS), target topoisomerase 2 (Top2), and impair mitochondria. These are some of the mechanisms through which these drugs induce late cardiomyopathy. In this review, we compare the cardiotoxicities of these two chemotherapeutic drugs, DOX and MTX. As described here, even though they share similarities in their modes of toxicant action, DOX and MTX seem to differ in a key aspect. DOX is a more redox-interfering drug, while MTX induces energy imbalance. In addition, DOX toxicity can be explained by underlying mechanisms that include targeting of Top2 beta, mitochondrial impairment, and increases in ROS generation. These modes of action have not yet been demonstrated for MTX, and this knowledge gap needs to be filled.

Effects of short-chain acyl-CoA dehydrogenase on cardiomyocyte apoptosis

Short-chain acyl-CoA dehydrogenase (SCAD), a key enzyme of fatty acid β-oxidation, plays an important role in cardiac hypertrophy. However, its effect on the cardiomyocyte apoptosis remains unknown. We aimed to determine the role of SCAD in tert-butyl hydroperoxide (tBHP)-induced cardiomyocyte apoptosis. The mRNA and protein expression of SCAD were significantly down-regulated in the cardiomyocyte apoptosis model. Inhibition of SCAD with siRNA-1186 significantly decreased SCAD expression, enzyme activity and ATP content, but obviously increased the content of free fatty acids. Meanwhile, SCAD siRNA treatment triggered the same apoptosis as cardiomyocytes treated with tBHP, such as the increase in cell apoptotic rate, the activation of caspase3 and the decrease in the Bcl-2/Bax ratio, which showed that SCAD may play an important role in primary cardiomyocyte apoptosis. The changes of phosphonate AMP-activated protein kinase α (p-AMPKα) and Peroxisome proliferator-activated receptor α (PPARα) in cardiomyocyte apoptosis were consistent with that of SCAD. Furthermore, PPARα activator fenofibrate and AMPKα activator AICAR treatment significantly increased the expression of SCAD and inhibited cardiomyocyte apoptosis. In conclusion, for the first time our findings directly demonstrated that SCAD may be as a new target to prevent cardiomyocyte apoptosis through the AMPK/PPARα/SCAD signal pathways.

Effects of hydrogen sulfide on myocardial fibrosis and PI3K/AKT1-regulated autophagy in diabetic rats

Myocardial fibrosis is the predominant pathological characteristic of diabetic myocardial damage. Previous studies have indicated that hydrogen sulfide (H2S) has beneficial effects in the treatment of various cardiovascular diseases. However, there is little research investigating the effect of H2S on myocardial fibrosis in diabetes. The present study aimed to investigate the effects of H2S on the progression of myocardial fibrosis induced by diabetes. Diabetes was induced in rats by intraperitoneal injection of streptozotocin. Sodium hydrosulfide (NaHS) was used as an exogenous donor of H2S. After 8 weeks, expression levels of cystathionine-γ-lyase were determined by western blot analysis and morphological changes in the myocardium were assessed by hematoxylin and eosin staining and Masson staining. The hydroxyproline content and fibrosis markers were determined by a basic hydrolysis method and western blot analysis, respectively. Autophagosomes were observed under transmission electron microscopy. Expression levels of autophagy-associated proteins and their upstream signaling molecules were also evaluated by western blotting. The results of the current study indicated that diabetes induced marked myocardial fibrosis, enhanced myocardial autophagy and suppressed the phosphatidylinositol-4,5-bisphosphate 3-kinase/RAC-α serine/threonine-protein kinase (PI3K/AKT1) signaling pathway. By contrast, following treatment with NaHS, myocardial fibrosis was ameliorated, myocardial autophagy was decreased and the PI3K/AKT1 pathway suppression was reversed. The results of the present study demonstrated that the protective effect of H2S against diabetes-induced myocardial fibrosis may be associated with the attenuation of autophagy via the upregulation of the PI3K/AKT1 signaling pathway.

Inactivation of INK4a and ARF induces myocardial proliferation and improves cardiac repair following ischemia‑reperfusion

The growth of the heart during mammalian embryonic development is primarily dependent on an increase in the number of cardiomyocytes (CM). However, shortly following birth, CMs cease proliferating and further growth of the myocardium is achieved via hypertrophic expansion of the existing CM population. The cyclin-dependent kinase inhibitor 2A (Cdkn2a) locus encodes overlapping genes for two tumor suppressor proteins, p16INK4a and p19 alternative reading frame (ARF). To determine whether decreased Cdkn2a gene expression results in improved cardiac regeneration in vitro and in vivo following cardiac injury, the proliferation of CMs isolated from Cdkn2a knockout (KO) and wild‑type (WT) mice in vitro and in vivo were evaluated following generation of ischemia reperfusion (IR) injury. The KO mice demonstrated enhanced CM proliferation not only in vitro, but also in vivo. Furthermore, heart function was improved and scar size was decreased in the KO mice compared with that of the WT mice. The results also indicated that microRNA (miR)‑1 and miR‑195 expression levels associated with cell proliferation were reduced following IR injury in KO mice compared with those of WT mice. These results suggested that the inactivation of INK4a and ARF stimulated CM proliferation and promoted cardiac repair.

Hydrogen sulfide improves left ventricular function in smoking rats via regulation of apoptosis and autophagy

The present study was designed to investigate the protective effects of hydrogen sulfide (H2S) against cigarette smoking-induced left ventricular dysfunction in rats. Left ventricular structure and function were assessed using two-dimensional echocardiography. Cardiomyocyte apoptosis was determined by Annexin V/PI and terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling staining. Cardiac autophagy was evaluated by detection of autophagy-related protein expression and observation of autophagosomes. Our results indicated that administration of NaHS (a donor of H2S) could protect against smoking-induced left ventricular systolic dysfunction. H2S was found to exert anti-apoptotic effects in the myocardium of smoking rats by inhibiting JNK and P38 mitogen-activated protein kinases pathways and activating PI3K/Akt signaling. Moreover, H2S could also reduce smoking-induced autophagic cell death via regulation of AMPK/mTOR signaling pathway. In conclusion, our study demonstrates that H2S can improve left ventricular systolic function in smoking rats via regulation of apoptosis and autophagy.

Caspase-1 transcripts in failing human heart after mechanical unloading

BACKGROUND

Caspase (Casp)-1 has been indicated as a molecular target capable of preventing the progression of cardiovascular diseases, including heart failure (HF), due to its central role in promoting inflammation and cardiomyocyte loss. The aim of this study was to assess whether Left Ventricular Assist Device (LVAD) implantation modifies the inflammatory and apoptotic profile in the heart through the modulation of Casp-1 expression level.

METHODS

Cardiac tissue was collected from end-stage HF patients before LVAD implant (pre-LVAD group, n=22) and at LVAD removal (post-LVAD, n=6), and from stable HF patients on medical therapy without prior circulatory support (HTx, n=7) at heart transplantation, as control. The cardiac expression of Casp-1, of its inhibitors caspase recruitment domain (CARD) only protein (COP) and CARD family, member 18 (ICEBERG), was evaluated by real-time PCR in the three groups of patients.

RESULTS

Casp-1 was increased in the pre-LVAD group compared to HTx (p=0.006), while on the contrary the ICEBERG level was significantly decreased in pre-LVAD with respect to HTx patients (p<0.001); no difference in COP expression level was found.

CONCLUSIONS

This study describes a specific pattern of the Casp-1 system associated with inflammation and apoptosis markers in patients who require LVAD insertion. The inflammation could be the key process regulating, in a negative loop, Casp-1 signaling and its down-stream effects, apoptosis included.

Advanced glycation endproducts trigger autophagy in cadiomyocyte via RAGE/PI3K/AKT/mTOR pathway

Methods

Rat neonate cardiomyocytes were cultured and treated with AGEs at different concentration. Two classic autophagy markers, microtubule-associated protein 1 light chain 3 (LC3) and Beclin-1, were detected by western blot assay. The inhibition of RAGE and phosphatidylinositol 3-phosphate kinase (PI3K)/Akt/mTOR pathway were applied to cells, respectively.

Results

AGEs administration enhanced the expression of Beclin-1 and LC3 II in cardiomyocytes, increased the number of autophagic vacuoles and impaired the cell viability in dose-dependant manners. Also, AGEs inhibited the PI3K/Akt/mTOR pathway via RAGE. Inhibition of RAGE with RAGE antibody reduced expression of Beclin-1 and LC3 II/I and inhibited the cellular autophagy, accompanied by the reactivation of PI3K/Akt/mTOR pathway in cultured cells. Notably, the presence of inhibition of PI3K/Akt/mTOR pathway abolished the protective effect of RAGE inhibition on cardiomyocytes.

Conclusion

This study provides evidence that AGEs induces cardiomyocyte autophagy by, at least in part, inhibiting the PI3K/Akt/mTOR pathway via RAGE.

Previous studies showed that the accumulation of advanced glycation end products (AGEs) induce cardiomyocyte apoptoisis, leading to heart dysfunction. However, the effect of AGEs on another cell death pathway, autophagy, in cardiomyocytes remains unknown.

Mitochondria in heart failure: the emerging role of mitochondrial dynamics

Over the past decade, mitochondria have emerged as critical integrators of energy production, generation of reactive oxygen species (ROS), multiple cell death, and signaling pathways in the constantly beating heart. Clarification of the molecular mechanisms, underlying mitochondrial ROS generation and ROS-induced cell death pathways, associated with cardiovascular diseases, by itself remains an important aim; more recently, mitochondrial dynamics has emerged as an important active mechanism to maintain normal mitochondria number and morphology, both are necessary to preserve cardiomyocytes integrity. The two opposing processes, division (fission) and fusion, determine the cell type-specific mitochondrial morphology, the intracellular distribution and activity. The tightly controlled balance between fusion and fission is of particular importance in the high energy demanding cells, such as cardiomyocytes, skeletal muscles, and neuronal cells. A shift toward fission will lead to mitochondrial fragmentation, observed in quiescent cells, while a shift toward fusion will result in the formation of large mitochondrial networks, found in metabolically active cardiomyocytes. Defects in mitochondrial dynamics have been associated with various human disorders, including heart failure, ischemia reperfusion injury, diabetes, and aging. Despite significant progress in our understanding of the molecular mechanisms of mitochondrial function in the heart, further focused research is needed to translate this knowledge into the development of new therapies for various ailments.

Mechanisms of Ghrelin anti-heart failure: inhibition of Ang II-induced cardiomyocyte apoptosis by down-regulating AT1R expression

Background

Ghrelin is a novel growth hormone–releasing peptide administered to treat chronic heart failure (CHF). However, the underlying mechanism of its protective effects against heart failure (HF) remains unclear.

Methods and Results

A total of 68 patients with CHF and 20 healthy individuals were included. The serum levels of Angiotensin II (Ang II) and ghrelin were measured using ELISA. The results showed that Ang II and ghrelin were both significantly increased in CHF patients and that the ghrelin levels were significantly positively correlated with Ang II. The left anterior descending coronary artery was ligated to establish a rat model of CHF, and cultured cardiomyocytes from neonatal rats were stimulated with Ang II to explore the role of ghrelin in CHF. The results showed that ghrelin inhibited cardiomyocyte apoptosis both in vivo and in vitro. Furthermore, caspase-3 expression was examined, and the results revealed that Ang II induces cardiomyocyte apoptosis through the caspase-3 pathway, whereas ghrelin inhibits this action. Lastly, to further elucidate the mechanism by which ghrelin inhibits Ang II action, the expression of the AT1 and AT2 receptors was evaluated; the results showed that Ang II up-regulates the AT1 and AT2 receptors in cardiomyocytes, whereas ghrelin inhibits AT1 receptor up-regulation but does not affect AT2 receptor expression.

Conclusions

These data suggest that the serum levels of ghrelin are significantly positively correlated with Ang II in CHF patients and that ghrelin can inhibit Ang II-induced cardiomyocyte apoptosis by down-regulating AT1R, thereby playing a role in preventing HF.

Cardiac alpha1-adrenergic receptors: novel aspects of expression, signaling mechanisms, physiologic function, and clinical importance

Adrenergic receptors (AR) are G-protein-coupled receptors (GPCRs) that have a crucial role in cardiac physiology in health and disease. Alpha1-ARs signal through Gαq, and signaling through Gq, for example, by endothelin and angiotensin receptors, is thought to be detrimental to the heart. In contrast, cardiac alpha1-ARs mediate important protective and adaptive functions in the heart, although alpha1-ARs are only a minor fraction of total cardiac ARs. Cardiac alpha1-ARs activate pleiotropic downstream signaling to prevent pathologic remodeling in heart failure. Mechanisms defined in animal and cell models include activation of adaptive hypertrophy, prevention of cardiac myocyte death, augmentation of contractility, and induction of ischemic preconditioning. Surprisingly, at the molecular level, alpha1-ARs localize to and signal at the nucleus in cardiac myocytes, and, unlike most GPCRs, activate "inside-out" signaling to cause cardioprotection. Contrary to past opinion, human cardiac alpha1-AR expression is similar to that in the mouse, where alpha1-AR effects are seen most convincingly in knockout models. Human clinical studies show that alpha1-blockade worsens heart failure in hypertension and does not improve outcomes in heart failure, implying a cardioprotective role for human alpha1-ARs. In summary, these findings identify novel functional and mechanistic aspects of cardiac alpha1-AR function and suggest that activation of cardiac alpha1-AR might be a viable therapeutic strategy in heart failure.

Myocardial structure, function and ischaemic tolerance in a rodent model of obesity with insulin resistance

Obesity and its comorbidities (dyslipidaemia, insulin resistance and hypertension) that together constitute the metabolic syndrome are all risk factors for ischaemic heart disease. Although obesity has been reported to be an independent risk factor for congestive heart failure, whether obesity-induced heart failure develops in the absence of increased afterload (induced by hypertension) is not clear. We have previously shown that obesity with insulin resistance decreases myocardial tolerance to ischaemia-reperfusion, but the mechanism for this decreased tolerance remains unclear. We hypothesize that obesity with insulin resistance induces adverse cardiac remodelling and pump dysfunction, as well as adverse changes in myocardial prosurvival reperfusion injury salvage kinase (RISK) pathway signalling to reduce myocardial tolerance to ischaemia-reperfusion. Wistar rats were fed an obesogenic (obese group) or a standard rat chow diet (control group) for 32 weeks. Echocardiography was performed over the 32 weeks before isolated Langendorff-perfused hearts were subjected to 40 min coronary artery ligation followed by reperfusion, and functional recovery (rate-pressure product), infarct size and RISK pathway function were assessed (Western blot analysis). Obesity with insulin resistance increased myocardial lipid accumulation but had no effect on in vivo or ex vivo left ventricular structure/function. Hearts from obese rats had lower reperfusion rate-pressure products (13115 ± 562 beats min(-1) mmHg for obese rats versus 17781 ± 1109 beats min(-1) mmHg for control rats, P < 0.05) and larger infarcts (36.3 ± 5.6% of area at risk in obese rats versus 14.1 ± 2.8% of area at risk in control rats, P < 0.01) compared with control hearts. These changes were associated with reductions in RISK pathway function, with 30-50 and 40-60% reductions in Akt and glycogen synthase kinase 3 beta (GSK-3β) expression and phosphorylation, respectively, in obese rat hearts compared with control hearts. Total endothelial nitric oxide synthase expression was reduced by 25% in obese rats. We conclude that obesity with insulin resistance had no effect on basal cardiac structure or function but decreased myocardial tolerance to ischaemia-reperfusion. This reduction in ischaemic tolerance was likely to be due to compromised RISK pathway function in obese, insulin-resistant animals.

FoxO1 is crucial for sustaining cardiomyocyte metabolism and cell survival

Diabetic cardiomyopathy is a term used to describe cardiac muscle damage-induced heart failure. Multiple structural and biochemical reasons have been suggested to induce this disorder. The most prominent feature of the diabetic myocardium is attenuated insulin signalling that reduces survival kinases (Akt), potentially switching on protein targets like FoxOs, initiators of cell death. FoxO1, a prominent member of the forkhead box family and subfamily O of transcription factors and produced from the FKHR gene, is involved in regulating metabolism, cell proliferation, oxidative stress response, immune homeostasis, pluripotency in embryonic stem cells, and cell death. In this review we describe distinctive functions of FoxOs, specifically FoxO1 under conditions of nutrient excess, insulin resistance and diabetes, and its manipulation to restore metabolic equilibrium to limit cardiac damage due to cell death. Because FoxO1 helps cardiac tissue to combat a variety of stress stimuli, it could be a major determinant in regulating diabetic cardiomyopathy. In this regard, we highlight studies from our group and others who illustrate how cardiac tissue-specific FoxO1 deletion protects the heart against cardiomyopathy and how its down-regulation in endothelial tissue could prevent against atherosclerotic plaques. In addition, we also describe studies that show FoxO1's beneficial qualities by highlighting their role in inducing anti-oxidant, autophagic, and anti-apoptotic genes under stress conditions of ischaemia-reperfusion and myocardial infarction. Thus, the aforementioned FoxO1 traits could be useful in curbing cardiac tissue-specific impairment of function following diabetes.

Functional screening identifies miRNAs inducing cardiac regeneration

In mammals, enlargement of the heart during embryonic development is primarily dependent on the increase in cardiomyocyte numbers. Shortly after birth, however, cardiomyocytes stop proliferating and further growth of the myocardium occurs through hypertrophic enlargement of the existing myocytes. As a consequence of the minimal renewal of cardiomyocytes during adult life, repair of cardiac damage through myocardial regeneration is very limited. Here we show that the exogenous administration of selected microRNAs (miRNAs) markedly stimulates cardiomyocyte proliferation and promotes cardiac repair. We performed a high-content microscopy, high-throughput functional screening for human miRNAs that promoted neonatal cardiomyocyte proliferation using a whole-genome miRNA library. Forty miRNAs strongly increased both DNA synthesis and cytokinesis in neonatal mouse and rat cardiomyocytes. Two of these miRNAs (hsa-miR-590 and hsa-miR-199a) were further selected for testing and were shown to promote cell cycle re-entry of adult cardiomyocytes ex vivo and to promote cardiomyocyte proliferation in both neonatal and adult animals. After myocardial infarction in mice, these miRNAs stimulated marked cardiac regeneration and almost complete recovery of cardiac functional parameters. The miRNAs identified hold great promise for the treatment of cardiac pathologies consequent to cardiomyocyte loss.

Role of apoptosis in disease

Since the initial description of apoptosis, a number of different forms of cell death have been described. In this review we will focus on classic caspase-dependent apoptosis and its variations that contribute to diseases. Over fifty years of research have clarified molecular mechanisms involved in apoptotic signaling as well and shown that alterations of these pathways lead to human diseases. Indeed both reduced and increased apoptosis can result in pathology. More recently these findings have led to the development of therapeutic approaches based on regulation of apoptosis, some of which are in clinical trials or have entered medical practice.

Regulation of PUMA induced by mechanical stress in rat cardiomyocytes

Background

PUMA (p53-up-regulated modulator of apoptosis), an apoptosis regulated gene, increased during endoplasmic reticulum stress. However, the expression of PUMA in cardiomyocytes under mechanical stress is little known. We aimed to investigate the regulation mechanism of PUMA expression and apoptosis induced by mechanical stress in cardiomyocytes.

Methods

Aorta-caval (AV) shunt was performed in adult Wistar rats to induce volume overload. Rat neonatal cardiomyocytes were stretched by vacuum to 20% of maximum elongation at 60 cycles/min.

Results

PUMA protein and mRNA were up-regulated in the shunt group as compared with sham group. The increased PUMA protein expression and apoptosis induced by shunt was reversed by treatment with atorvastatin at 30 mg/kg/ day orally for 7 days. TUNEL assay showed that treatment with atorvastatin inhibited the apoptosis induced by volume overload. Cyclic stretch significantly enhanced PUMA protein and gene expression. Addition of c-jun N-terminal kinase (JNK) inhibitor SP600125, JNK small interfering RNA (siRNA) and interferon-γ (INF-γ) antibody 30 min before stretch reduced the induction of PUMA protein. Gel shift assay demonstrated that stretch increased the DNA binding activity of interferon regulatory factor-1. Stretch increased, while PUMA-Mut plasmid, SP600125 and INF-γ antibody abolished the PUMA promoter activity induced by stretch. PUMA mediated apoptosis induced by stretch was reversed by PUMA siRNA and atorvastatin.

Conclusions

Mechanical stress enhanced apoptosis and PUMA expression in cardiomyocytes. Treatment with atorvastatin reversed both PUMA expression and apoptosis induced by mechanical stress in cardiomyocytes.

Clair DK. p53 Regulates oxidative stress-mediated retrograde signaling: a novel mechanism for chemotherapy-induced cardiac injury

The side effects of cancer therapy on normal tissues limit the success of therapy. Generation of reactive oxygen species (ROS) has been implicated for numerous chemotherapeutic agents including doxorubicin (DOX), a potent cancer chemotherapeutic drug. The production of ROS by DOX has been linked to DNA damage, nuclear translocation of p53, and mitochondrial injury; however, the causal relationship and molecular mechanisms underlying these events are unknown. The present study used wild-type (WT) and p53 homozygous knock-out (p53^−/−) mice to investigate the role of p53 in the crosstalk between mitochondria and nucleus. Injecting mice with DOX (20 mg/kg) causes oxidative stress in cardiac tissue as demonstrated by immunogold analysis of the levels of 4-hydroxy-2′-nonenal (4HNE)-adducted protein, a lipid peroxidation product bound to proteins. 4HNE levels increased in both nuclei and mitochondria of WT DOX-treated mice but only in nuclei of DOX-treated p53^(−/−) mice, implicating a critical role for p53 in causing DOX-induced oxidative stress in mitochondria. The stress-activated protein c-Jun amino-terminal kinase (JNKs) was activated in response to increased 4HNE in WT mice but not p53^(−/−) mice receiving DOX treatment, as determined by co-immunoprecipitation of HNE and pJNK. The activation of JNK in DOX treated WT mice was accompanied by Bcl-2 dissociation from Beclin in mitochondria and induction of type II cell death (autophagic cell death), as evidenced by an increase in LC3-I/LC-3-II ratio and γ-H2AX, a biomarker for DNA damage. The absence of p53 significantly reduces mitochondrial injury, assessed by quantitative morphology, and decline in cardiac function, assessed by left ventricular ejection fraction and fraction shortening. These results demonstrate that p53 plays a critical role in DOX-induced cardiac toxicity, in part, by the induction of oxidative stress mediated retrograde signaling.

Reduced ACTC1 expression might play a role in the onset of congenital heart disease by inducing cardiomyocyte apoptosis

BACKGROUND

The Cardiac α actin 1 gene (ACTC1) has been related to familial atrial septal defects. This study was set to explore a potential role of this gene in the formation of sporadic congenital heart disease (CHD).

METHODS AND RESULTS

Assessment of cardiac tissue samples from 33 patients with sporadic CHD (gestational age (GA) 18 weeks-49 months) with real-time RT-PCR, Western blotting and immunohistochemistry has revealed a markedly decreased ACTC1 expression in the majority of samples (78.8%) compared with autopsied normal heart tissue from aged-matched subjects (GA 17 weeks-36 months). Also, as shown by terminal deoxynucleotidyl transferase-mediated dUTP nick end-labeling (TUNEL) assay, the proportion of apoptotic cardiomyocytes in samples featuring down-regulated ACTC1 expression (Group 1) was significantly greater than those with normal expression (Group 2) and the controls (P<0.01). The proportion of apoptotic cells strongly correlated with the expression of ACTC1 (r=-0.918, P<0.01). A study of 2 essential genes involved in apoptosis, Caspase-3 and Bcl-2, confirmed that the former has significantly increased expression, whilst the latter has decreased expression in Group 1 than in the other groups (P<0.01). Transfection of a small interfering RNA targeting, Actc1 (Actc1-siRNA), to a cardiomyocyte cell line, H9C2, also detected more apoptotic cells.

CONCLUSIONS

Reduced ACTC1 expression might play a role in the onset of CHD through induction of cardiomyocyte apoptosis.

Increasing cardiac contractility after myocardial infarction exacerbates cardiac injury and pump dysfunction

RATIONALE

Myocardial infarction (MI) leads to heart failure (HF) and premature death. The respective roles of myocyte death and depressed myocyte contractility in the induction of HF after MI have not been clearly defined and are the focus of this study.

OBJECTIVES

We developed a mouse model in which we could prevent depressed myocyte contractility after MI and used it to test the idea that preventing depression of myocyte Ca(2+)-handling defects could avert post-MI cardiac pump dysfunction.

METHODS AND RESULTS

MI was produced in mice with inducible, cardiac-specific expression of the β2a subunit of the L-type Ca(2+) channel. Myocyte and cardiac function were compared in control and β2a animals before and after MI. β2a myocytes had increased Ca(2+) current; sarcoplasmic reticulum Ca(2+) load, contraction and Ca(2+) transients (versus controls), and β2a hearts had increased performance before MI. After MI, cardiac function decreased. However, ventricular dilation, myocyte hypertrophy and death, and depressed cardiac pump function were greater in β2a versus control hearts after MI. β2a animals also had poorer survival after MI. Myocytes isolated from β2a hearts after MI did not develop depressed Ca(2+) handling, and Ca(2+) current, contractions, and Ca(2+) transients were still above control levels (before MI).

CONCLUSIONS

Maintaining myocyte contractility after MI, by increasing Ca(2+) influx, depresses rather than improves cardiac pump function after MI by reducing myocyte number.

Molecular imaging targets of cardiac remodeling

Left ventricular (LV) remodeling is a major determinant of the clinical course and outcome of systolic heart failure (HF). Activation of neurohormonal and inflammatory cytokine pathways and their effects on intracellular signal transduction cascades through stimulation of membrane-bound receptors mediate LV remodeling. Although major advances have been made in clinical management of HF through large randomized trials, its prognosis remains poor. Interindividual differences, often genetically based, are increasingly recognized as important determinants of LV remodeling. Identification of the influence of these individual factors on the clinical course of HF has stimulated a search for specific pathophysiologic mechanisms that operate at the individual level and can be targeted directly. This article summarizes the current application of molecular imaging techniques to the understanding of the cellular and molecular mechanisms involved in LV remodeling in an attempt to provide the tools necessary for personalized, truly "evidence-based" assessment, serial evaluation, and monitoring of HF.

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).