Dynamic process of apoptosis in adult rat cardiomyocytes analyzed using 48-hour videomicroscopy and electron microscopy: beating and rate are associated with the apoptotic process

Advances in small-molecule fluorescent probes for the study of apoptosis

Apoptosis, as type I cell death, is an active death process strictly controlled by multiple genes, and plays a significant role in regulating various activities. Mounting research indicates that the unique modality of cell apoptosis is directly or indirectly related to different diseases including cancer, autoimmune diseases, viral diseases, neurodegenerative diseases, etc. However, the underlying mechanisms of cell apoptosis are complicated and not fully clarified yet, possibly due to the lack of effective chemical tools for the nondestructive and real-time visualization of apoptosis in complex biological systems. In the past 15 years, various small-molecule fluorescent probes (SMFPs) for imaging apoptosis in vitro and in vivo have attracted broad interest in related disease diagnostics and therapeutics. In this review, we aim to highlight the recent developments of SMFPs based on enzyme activity, plasma membranes, reactive oxygen species, reactive sulfur species, microenvironments and others during cell apoptosis. In particular, we generalize the mechanisms commonly used to design SMFPs for studying apoptosis. In addition, we discuss the limitations of reported probes, and emphasize the potential challenges and prospects in the future. We believe that this review will provide a comprehensive summary and challenging direction for the development of SMFPs in apoptosis related fields.

A liver digital twin for in silico testing of cellular and inter-cellular mechanisms in regeneration after drug-induced damage

This communication presents a mathematical mechanism-based model of the regenerating liver after drug-induced pericentral lobule damage resolving tissue microarchitecture. The consequence of alternative hypotheses about the interplay of different cell types on regeneration was simulated. Regeneration dynamics has been quantified by the size of the damage-induced dead cell area, the hepatocyte density and the spatial-temporal profile of the different cell types. We use deviations of observed trajectories from the simulated system to identify branching points, at which the systems behavior cannot be explained by the underlying set of hypotheses anymore. Our procedure reflects a successful strategy for generating a fully digital liver twin that, among others, permits to test perturbations from the molecular up to the tissue scale. The model simulations are complementing current knowledge on liver regeneration by identifying gaps in mechanistic relationships and guiding the system toward the most informative (lacking) parameters that can be experimentally addressed.

Targeted Antitumor Mechanism of C-PC/CMC-CD55sp Nanospheres in HeLa Cervical Cancer Cells

In vitro studies had shown that C-Phycocyanin (C-PC) inhibited cervical cancer HeLa cells growth. We constructed C-PC/CMC-CD55sp nanospheres using C-PC, Carboxymethyl Chitosan (CMC), and CD55 ligand peptide (CD55sp) to allow for targeted antitumor effects against HeLa cells in vitro and in vivo. The characteristics of the nanospheres were determined using FTIR, electron microscopy, and laser particle size analysis. Flow cytometry, laser confocal microscopy and small animal imaging system showed the targeting of C-PC/CMC-CD55sp nanospheres on HeLa cells. Subsequently, the proliferation and apoptosis were analyzed by Cell Counting Kit-8 (CCK-8), flow cytometry, TUNEL assay and electron microscopy. The expression of the apoptosis-related protein was determined using western blot. The stainings of Hematoxylin and Eosin (HE) were employed to evaluate the cell condition of tumor tissue sections. The cytokines in the blood in tumor-bearing nude mice was determined using ELISA. These results showed that C-PC/CMC-CD55sp nanospheres were successfully constructed and targeted HeLa cells. The constructed nanospheres were more effective than C-PC alone in inhibiting the proliferation and inducing apoptosis in HeLa cells. We also found that C-PC/CMC-CD55sp nanospheres had a significant inhibitory effect on the expression of antiapoptotic protein Bcl-2 and a promotion on the transformation of caspase 3 to cleaved caspase 3. C-PC/CMC-CD55sp nanospheres played an important role in tumor suppression, reduced the expression TGF-β, and increased IL-6 and TNF-α. This study demonstrates that the constructed new C-PC/CMC-CD55sp nanospheres exerted targeted antitumor effects in vivo and in vitro which provided a novel idea for application of C-PC, and provided experimental basis for comprehensive targeted treatment of tumors.

A study on screening and antitumor effect of CD55-specific ligand peptide in cervical cancer cells

Background

To improve the targeting ability of antitumor drugs, we identified the antigens with high expression on the surface of tumor cells associated with tumor escape, such as the complement regulatory protein CD55 molecule, which is also known as the decay accelerating factor. In this study, phage display technology was used to screen and identify CD55-specific ligand peptide (CD55sp) bound to CD55 molecule on the surface of cervical cancer HeLa cells. We then explored the role of this peptide in inhibiting the growth of cervical cancer cells in vitro. Our characterization of CD55sp will provide implication for tumor target therapy.

Methods

The phage bound to the surface of HeLa cells were isolated by phage display technology. Positive phage clones were identified by ELISA. Phage was then amplified and determined by agarose gel electrophoresis after monoclonal DNA extraction. DNA sequencing and bioinformatical analysis were conducted to obtain specific ligand peptides. Flow cytometry and immunofluorescence were used to measure the expression of CD55 molecule on the surface of tumor and normal cells. Subsequently, the effects of CD55sp on the proliferation and apoptosis of HeLa and SiHa cells were determined by Cell Counting Kit-8 (CCK-8), flow cytometry, and TUNEL assay, respectively. The morphology of apoptotic cells was examined by electron microscope. The distribution of Cleaved caspase-3 was detected by immunofluorescence. The expression of bcl-2 and Cleaved caspase-3 were determined by Western blot.

Results

The results showed that the peptide (QVNGLGERSQQM) can bind to the CD55 molecule on the surface of cervical cancer HeLa and SiHa cells as a ligand peptide. It can also effectively inhibit the proliferation of cervical cancer cells and induce cell apoptosis.

Conclusion

This study demonstrates that CD55sp screened by phage display technology plays a strong antitumor role.

Recombinant Atrial Natriuretic Peptide Prevents Aberrant Ca2+ Leakage through the Ryanodine Receptor by Suppressing Mitochondrial Reactive Oxygen Species Production Induced by Isoproterenol in Failing Cardiomyocytes

Catecholamines induce intracellular reactive oxygen species (ROS), thus enhancing diastolic Ca²⁺ leakage through the ryanodine receptor during heart failure (HF). However, little is known regarding the effect of atrial natriuretic peptide (ANP) on ROS generation and Ca²⁺ handling in failing cardiomyocytes. The aim of the present study was to clarify the mechanism by which an exogenous ANP exerts cardioprotective effects during HF. Cardiomyocytes were isolated from the left ventricles of a canine tachycardia-induced HF model and sham-operated vehicle controls. The degree of mitochondrial oxidized DNA was evaluated by double immunohistochemical (IHC) staining using an anti-VDAC antibody for the mitochondria and an anti-8-hydroxy-2′-deoxyguanosine antibody for oxidized DNA. The effect of ANP on ROS was investigated using 2,7-dichlorofluorescin diacetate, diastolic Ca²⁺ sparks assessed by confocal microscopy using Fluo 4-AM, and the survival rate of myocytes after 48 h. The double IHC study revealed that isoproterenol (ISO) markedly increased oxidized DNA in the mitochondria in HF and that the ISO-induced DNA damage was markedly inhibited by the co-presence of ANP. ROS production and Ca²⁺ spark frequency (CaSF) were increased in HF compared to normal controls, and were further increased in the presence of ISO. Notably, ANP significantly suppressed both ISO-induced ROS and CaSF without changing sarcoplasmic reticulum Ca²⁺ content in HF (p<0.01, respectively). The survival rate after 48 h in HF was significantly decreased in the presence of ISO compared with baseline (p<0.01), whereas it was significantly improved by the co-presence of ANP (p<0.01). Together, our results suggest that ANP strongly suppresses ISO-induced mitochondrial ROS generation, which might correct aberrant diastolic Ca²⁺ sparks, eventually contributing to the improvement of cardiomyocyte survival in HF.

Cardiomyocytes induce macrophage receptor shedding to suppress phagocytosis

BACKGROUND

Mobilization of the innate immune response to clear and metabolize necrotic and apoptotic cardiomyocytes is a prerequisite to heart repair after cardiac injury. Suboptimal kinetics of dying myocyte clearance leads to secondary necrosis, and in the case of the heart, increased potential for collateral loss of neighboring non-regenerative myocytes. Despite the importance of myocyte phagocytic clearance during heart repair, surprisingly little is known about its underlying cell and molecular biology.

OBJECTIVE

To determine if phagocytic receptor MERTK is expressed in human hearts and to elucidate key sequential steps and phagocytosis efficiency of dying adult cardiomyocytes, by macrophages.

RESULTS

In infarcted human hearts, expression profiles of the phagocytic receptor MER-tyrosine kinase (MERTK) mimicked that found in experimental ischemic mouse hearts. Electron micrographs of myocardium identified MERTK signal along macrophage phagocytic cups and Mertk-/- macrophages contained reduced digested myocyte debris after myocardial infarction. Ex vivo co-culture of primary macrophages and adult cardiomyocyte apoptotic bodies revealed reduced engulfment relative to resident cardiac fibroblasts. Inefficient clearance was not due to the larger size of myocyte apoptotic bodies, nor were other key steps preceding the formation of phagocytic synapses significantly affected; this included macrophage chemotaxis and direct binding of phagocytes to myocytes. Instead, suppressed phagocytosis was directly associated with myocyte-induced inactivation of MERTK, which was partially rescued by genetic deletion of a MERTK proteolytic susceptibility site.

CONCLUSION

Utilizing an ex vivo co-cultivation approach to model key cellular and molecular events found in vivo during infarction, cardiomyocyte phagocytosis was found to be inefficient, in part due to myocyte-induced shedding of macrophage MERTK. These findings warrant future studies to identify other cofactors of macrophage-cardiomyocyte cross-talk that contribute to cardiac pathophysiology.

Unique mode of cell death in freshly isolated adult rat ventricular cardiomyocytes exposed to hydrogen peroxide

To address whether adult rat ventricular cardiomyocytes (ARVCs) exposed to oxidant stress die via apoptosis (secondarily by necrosis) or primarily by necrosis, we exposed ARVCs to hydrogen peroxide (H2O2; 0.1-100 microM) for up to 24 h and then compared them with isoproterenol-induced apoptotic and Triton X-induced necrotic controls. Cellular shrinkage preceded plasma membrane disruption, reflected by trypan blue uptake in ARVCs exposed to lower concentrations of H2O2 (<1 microM; an apoptotic pattern), but the order was reversed in cells exposed to higher concentrations of H2O2 (>1 microM; a necrotic pattern). DNA fragmentation, caspase-3 activation, mitochondrial membrane potential preservation, and ATP preservation were all apparent in ARVCs treated with low H2O2 (0.5 microM), but not in those treated with high H2O2 (10 microM). In addition, electron microscopy revealed unique morphology in H2O2-treated ARVCs; i.e., the nuclei had a homogeneous ground glass-like appearance that was never accompanied by chromatin condensation. Apparently, high concentrations of H2O2 caused primary necrosis in ARVCs, whereas low concentrations induced biochemically comparable apoptosis, although the latter did not satisfy the morphological criteria of apoptosis. These findings caution against the use of oxidant stress, H2O2 in particular, as an inducer of apoptosis in ARVCs.

Morphological and biochemical characterization of basal and starvation-induced autophagy in isolated adult rat cardiomyocytes

Autophagy is simultaneously a mode of programmed cell death and an important physiological process for cell survival, but its pathophysiological significance in cardiac myocytes remains largely unknown. We induced autophagy in isolated adult rat ventricular cardiomyocytes (ARVCs) by incubating them in glucose-free, mannitol-supplemented medium for up to 4 days. Ultrastructurally, intracellular vacuoles containing degenerated subcellular organelles (e.g., mitochondria) were markedly apparent in the glucose-starved cells. Microtubule-associated protein-1 light chain 3 was significantly upregulated among the glucose-starved ARVCs than among the controls. After 4 days, glucose-starved ARVCs showed a significantly worse survival rate (19+/-5.2%) than the controls (55+/-8.3%, P<0.005). Most dead ARVCs in both groups showed features of necrosis, and the rate of apoptosis did not differ between the groups. Two inhibitors of autophagy, 3-methyladenine (3-MA) and leupeptin, significantly and dose-dependently reduced the viability of both control and glucose-starved ARVCs and caused specific morphological alterations; 3-MA reduced autophagic findings, whereas leupeptin greatly increased the numbers and the sizes of vacuoles that contained incompletely digested organelles. The knockdown of the autophagy-related genes with small interfering RNA also reduced the glucose-starved ARVCs viability, but rapamycin, an autophagy enhancer, improved it. Reductions in the ATP content of ARVCs caused by glucose depletion were exacerbated by the inhibitors while attenuated by rapamycin, suggesting that autophagy inhibition might accelerate energy depletion, leading to necrosis. Taken together, our findings suggest that autophagy in cardiomyocytes reflects a prosurvival, compensatory response to stress and that autophagic cardiomyocyte death represents an unsuccessful outcome due to necrosis.

Caspases in myocardial infarction

The discovery of apoptosis sheds a new light on the role of cell death in myocardial infarction and other cardiovascular diseases. There is mounting evidence that apoptosis plays an important role at multiple points in the evolution of myocardial infarction, and comprises not only cardiomyocytes but also inflammatory cells, as well as cells of granulation tissue and fibrous tissue. It appears that apoptosis contributes to cardiomyocyte loss in the border zone and in remote myocardium in the early phase, as well as months after myocardial infarction, thus playing a role in remodeling and development of heart failure after myocardial infarction. Apoptosis, being a highly regulated process, is a potential target for therapeutic intervention. Caspases are the key effector molecules in apoptosis, and are therefore a particularly attractive target for pharmacological modulation of apoptosis. Although several potential therapeutic agents have been tested in animal models of ischemia/reperfusion heart injury with some success, nearly none of the specific antiapoptotic agents have reached the stage of clinical research.

Morphological aspects of apoptosis in heart diseases

It has been suggested that apoptosis may be responsible for a significant amount of cardiomyocyte death during acute myocardial infarction as well as for a progressive loss of surviving cells in failing hearts. Typical apoptosis can indeed be induced in cardiomyocytes at the experimental conditions. In actual heart diseases, in contrast, there is very little direct morphological evidence of apoptosis in cardiomyocytes occurring at any stage of myocardial infarction and heart failure, despite the availability of much indirect evidence that includes detection of DNA fragmentation and apoptosis-related factors. For that reason, the potential efficacy of therapeutic intervention to prevent apoptosis remains controversial. This review will survey available data from both animals and humans to critically assess the role of cardiomyocyte apoptosis during myocardial infarction and its relevance to myocardial remodeling and during progression to heart failure. Also considered will be nonmyocyte interstitial cells, which have received less attention than myocytes despite definitive evidence of their apoptosis in the infarcted heart and recent studies suggesting that blockade of apoptosis among these cells mitigates postinfarction cardiac remodeling and heart failure. We conclude from our survey that there are many hurdles to surmount before regulation of apoptosis can be clinically applied in the treatment of myocardial infarction and heart failure.

Granulocyte Colony-Stimulating Factor Mediates Cardioprotection Against Ischemia/Reperfusion Injury via Phosphatidylinositol-3-Kinase/Akt Pathway in Canine Hearts

PURPOSE

Recent studies suggest that G-CSF prevents cardiac remodeling following myocardial infarction (MI) likely through regeneration of the myocardium and coronary vessels. However, it remains unclear whether G-CSF administered at the onset of reperfusion prevents ischemia/reperfusion injury in the acute phase. We investigated acute effects of G-CSF on myocardial infarct size and the incidence of lethal arrhythmia and evaluated the involvement of the phosphatidylinositol-3 kinase (PI3K) in the in vivo canine models.

METHODS

In open-chest dogs, left anterior descending coronary artery (LAD) was occluded for 90 minutes followed by 6 hours of reperfusion. We intravenously administered G-CSF (0.33 micro/kg/min) for 30 minutes from the onset of reperfusion. Wortmannin, a PI3K inhibitor, was selectively administered into the LAD after the onset of reperfusion.

RESULTS

G-CSF significantly (p<0.05) reduced myocardial infarct size (38.7+/-4.3% to 15.7+/-5.3%) and the incidence of ventricular fibrillation during reperfusion periods (50% to 0%) compared with the control. G-CSF enhanced Akt phospholylation in ischemic canine myocardium. Wortmannin blunted both the infarct size-limiting and anti-arrhythmic effects of G-CSF. G-CSF did not change myeloperoxidase activity, a marker of neutrophil accumulation, in the infarcted myocardium.

CONCLUSION

An intravenous administration of G-CSF at the onset of reperfusion attenuates ischemia/reperfusion injury through PI3K/Akt pathway in the in vivo model. G-CSF administration can be a promising candidate for the adjunctive therapy for patients with acute myocardial infarction.

Autophagic cardiomyocyte death in cardiomyopathic hamsters and its prevention by granulocyte colony-stimulating factor

In UM-X7.1 hamster model of human dilated cardiomyopathy, heart failure progressively develops and causes 50% mortality by 30 weeks of age. Through ultrastructural analysis, we found that many cardiomyocytes of this model contain typical autophagic vacuoles including degraded mitochondria, glycogen granules, and myelin-like figures. In addition, ubiquitin, cathepsin D, and Rab7 were overexpressed as determined by immunoassays. Importantly, most cardiomyocytes with leaky plasma membranes were positive for cathepsin D, suggesting a direct link between autophagic degeneration and cell death. Meanwhile, cardiomyocyte apoptosis appeared insignificant. Granulocyte colony-stimulating factor (10 microg/kg/day), injected 5 days/week from 15 to 30 weeks of age, improved survival among 30-week-old hamsters (100% versus 53% in the untreated hamsters, P < 0.0001); ventricular function and remodeling, increased cardiomyocyte size, and reduced myocardial fibrosis followed by a dramatic reduction in the autophagic findings were also seen. Granulocyte colony-stimulating factor also down-regulated tumor necrosis factor-alpha and increased activities of Akt signal transducer and activator of transcription-3, and matrix metalloproteinases. However, there was no clear evidence of transdifferentiation from bone marrow cells into cardiomyocytes. In conclusion, autophagic death is important for cardiomyocyte loss in the cardiomyopathic hamster, and the beneficial effect of granulocyte colony-stimulating factor acts mainly via an anti-autophagic mechanism rather than anti-apo-ptosis or regeneration.

Apoptosis at a distance: Remote activation of caspase-3 occurs early after myocardial infarction

OBJECTIVE

After an acute myocardial infarction, the viable myocardium remote from the infarct zone is subjected to ventricular remodeling. Besides hypertrophy, processes of apoptosis may contribute to these remodeling processes. Reports on apoptosis in this area have been doubted because they were mainly based on in-situ nick-end DNA labeling (TUNEL) measurements, with questionable specifity. Moreover, the time course of initiation of these processes has not been characterized. Therefore the goals of this study were to (1) reliably determine if in the remote area of the infarcted heart apoptosis may be initiated using highly specific biochemical markers and (2) evaluate the time course of such an activation.

METHODS

A well-defined model, regional myocardial infarction induced by ligation of the left anterior coronary artery in rats in vivo, was used. Heart and lung wet weights, the left ventricular end-diastolic pressure (LVEDP), and the serum level of the atrial natriuretic propeptide (proANP) were determined from 1 day up to 4 weeks as indicators of developing heart failure. In transmural biopsies from the non-ischemic left ventricular wall of the infarcted heart, the activation of caspase-3, the bcl-2/bax ratio (Western blot analysis), and the DNA laddering (LM-PCR) were determined.

RESULTS

Although heart- and lung weights did not increase before 1 week after infarction, proANP levels were elevated already 1 day after myocardial infarction suggesting early sub-clinical heart failure. The activity of caspase-3 increased significantly to 160+/- 20% compared to sham operated controls as early as 1 day after ligation and remained elevated over the entire time course. In parallel, the bcl-2/bax ratio shifted toward the pro-apoptotic bax. Moreover, these clear and specific biochemical indicators of apoptosis in the remote area of the infarcted heart were paralleled by the fragmentation of genomic DNA.

CONCLUSION

These data demonstrate that apoptotic markers are activated in the surviving zone of the heart remote from the infarct area as early as 1 day after myocardial infarction with persistence for up to 4 weeks. This activation coincides with early markers of heart failure. The exact regulation of this apoptotic process remains to be elucidated.

Synchronous progression of calcium transient-dependent beating and sarcomere destruction in apoptotic adult cardiomyocytes

During early apoptosis, adult cardiomyocytes show unusual beating, suggesting possible participation of abnormal Ca(2+) transients in initiation of apoptotic processes in this cell type. Simultaneously with the beating, these cells show dynamic structural alteration resulting from cytoskeletal disintegration that is quite rapid. Because of the specialized structure and extensive cytoskeleton of cardiomyocytes, we hypothesized that its degradation in so short a time would require a particularly efficient mechanism. To better understand this mechanism, we used serial video microscopy to observe beta-adrenergic stimulation-induced apoptosis in isolated adult rat cardiomyocytes while simultaneously recording intracellular Ca(2+) concentration and cell length. Trains of Ca(2+) transients and corresponding rhythmic contractions and relaxations (beating) were observed in apoptotic cells. Frequencies of Ca(2+) transients and beating gradually increased with time and were accompanied by cellular shrinkage. As the cells shrank, amplitudes of Ca(2+) transients declined and diastolic intracellular Ca(2+) concentration increased until the transients were lost. Beating and progression of apoptosis were significantly inhibited by antagonists against the L-type Ca(2+) channel (nifedipine), ryanodine receptor (ryanodine), inositol 1,4,5-trisphosphate receptor (heparin), sarco(endo)plasmic Ca(2+)-ATPase (thapsigargin), and Na(+)/Ca(2+) exchanger (KB-R7943). Electron-microscopic examination of beating cardiomyocytes revealed progressive breakdown of Z disks. Immunohistochemical analysis and Western blot confirmed that disappearance of Z disk constituent proteins (alpha-actinin, desmin, and tropomyosin) preceded degradation of other cytoskeletal proteins. It thus appears that, in adult cardiomyocyte apoptosis, Ca(2+) transients mediate apoptotic beating and efficient sarcomere destruction initiated by Z disk breakdown.

Ultrastructural changes in endothelium during apoptosis indicate low microembolic potential

BACKGROUND

Apoptotic endothelium has been suggested to have microthrombotic and microembolic potential. While some describe pro-coagulant activities and platelet binding, others demonstrate maintained fibrinolytic protein and anti-platelet aggregatory activity. Canalicular fragmentation is unique to apoptotic endothelium and is suggested to facilitate size reduction of apoptotic cells to reduce microembolic potential. Despite the potential importance of apoptotic microemboli, there are no reports characterizing changes in cell size and shape during endothelial apoptosis.

METHODS

Here, we describe transmission and scanning electron microscopic studies of apoptotic endothelium and compare changes seen with apoptotic HL-60 cells incapable of canalicular fragmentation.

RESULTS

We demonstrate reduced endothelial size (p<0.05) with progressive apoptosis relative to apoptotic HL-60 cells. Mechanical stress accelerated size reduction of apoptotic endothelium(P< 0.01) but did not affect the size of apoptotic HL-60 cells. Mechanical stress also increased circularity in apoptotic endothelium (p<0.01), suggested to facilitate passage through small vessels. Earlier work indicated that canaliculi form through plasma membrane invagination, but we report fusion of small vesicles contributing to canalicular growth, while canaliculi fuse to form large vacuoles and also dilate at late stages of apoptosis.

CONCLUSIONS

These observations are consistent with the suggestion that endothelium is adapted to minimize microembolic potential and that canalicular fragmentation contributes to this.

Apoptosis and oncosis in acute coronary syndromes: assessment and implications

The rational design of therapeutic interventions for protection of ischemic myocardium from ultimate death requires an understanding of the mechanistic basis of cardiomyocyte (CM) cell death, its timing and the tools for its quantification. Until recently, CM cell death following ischemia and/or reperfusion was considered to involve necrosis or 'accidental cell death' from very early on. Collective evidence over the past decade indicates that early CM cell death after myocardial ischemia and post-ischemic reperfusion involves apoptosis with cell shrinkage and drop-out, and/or oncosis with cell swelling followed by necrosis. This paradigm shift suggests that different approaches for cardioprotection are required. Oncologists, pathologists, anatomists and basic scientists who have studied apoptosis over the last three decades separated physiological apoptosis from inappropriate apoptosis in pathological states. Until recently, cardiologists resisted the concepts of CM apoptosis and regeneration. Cumulative evidence indicating that apoptosis in the heart may occur in different cell types, spread from one cell type to another, and occur in bursts, may have profound implications for therapies aimed at protection of ischemic myocardium by targeting CM apoptosis in acute coronary syndromes. This review focuses on a critique of the methods used for the assessment of CM apoptosis and the implications of CM apoptosis in acute coronary syndromes.

Role of apoptosis in remodeling after myocardial infarction

The magnitude of an acute myocardial infarction (MI; i.e., number of dead cardiomyocytes) is the most critical determinant of subsequent left ventricular remodeling and heart failure. Also affecting the post-infarction disease process, however, are events occurring during the subacute and chronic stages of the infarction, including late cardiomyocyte death, cardiomyocyte hypertrophy, fibrosis, and expression of various cytokines. Additionally, it has been suggested that apoptosis may be responsible for a significant amount of cardiomyocyte death during the acute ischemic stage, as well as for a progressive loss of surviving cells during the subacute and chronic stages. However, there is very little direct morphological evidence of apoptosis occurring at any stage of MI, despite the availability of much indirect evidence that includes detection of DNA fragmentation and apoptosis-related factors. For that reason, the potential efficacy of therapeutic intervention to prevent apoptosis remains controversial. This review will survey available data from both animals and humans to critically assess the role of cardiomyocyte apoptosis during MI and its relevance to myocardial remodeling and heart failure. Also considered will be nonmyocyte interstitial cells, which have received less attention than myocytes despite definitive evidence of their apoptosis in the infarcted heart and recent studies suggesting that blockade of apoptosis among these cells mitigates post-infarction cardiac remodeling and heart failure. We conclude from our survey that there are many hurdles to surmount before regulation of apoptosis can be clinically applied in the treatment of MI and other heart diseases.

Prolonged endoplasmic reticulum stress in hypertrophic and failing heart after aortic constriction: possible contribution of endoplasmic reticulum stress to cardiac myocyte apoptosis

BACKGROUND

The endoplasmic reticulum (ER) is recognized as an organelle that participates in folding secretory and membrane proteins. The ER responds to stress by upregulating ER chaperones, but prolonged and/or excess ER stress leads to apoptosis. However, the potential role of ER stress in pathophysiological hearts remains unclear.

METHODS AND RESULTS

Mice were subjected to transverse aortic constriction (TAC) or sham operation. Echocardiographic analysis demonstrated that mice 1 and 4 weeks after TAC had cardiac hypertrophy and failure, respectively. Cardiac expression of ER chaperones was significantly increased 1 and 4 weeks after TAC, indicating that pressure overload by TAC induced prolonged ER stress. In addition, the number of terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling (TUNEL)-positive cells increased, and caspase-3 was cleaved in failing hearts. The antagonism of angiotensin II type 1 receptor prevented upregulation of ER chaperones and apoptosis in failing hearts. On the other hand, angiotensin II upregulated ER chaperones and induced apoptosis in cultured adult rat cardiac myocytes. We also investigated possible signaling pathways for ER-initiated apoptosis. The CHOP- (a transcription factor induced by ER stress), but not JNK- or caspase-12-, dependent pathway was activated in failing hearts by TAC. Pharmacological ER stress inducers upregulated ER chaperones and induced apoptosis in cultured cardiac myocytes. Finally, mRNA levels of ER chaperones were markedly increased in failing hearts of patients with elevated brain natriuretic peptide levels.

CONCLUSIONS

These findings suggest that pressure overload by TAC induces prolonged ER stress, which may contribute to cardiac myocyte apoptosis during progression from cardiac hypertrophy to failure.

Cytotoxic lymphocytes and cardiac electrophysiology

It is widely recognized that immune effector mechanisms contribute to cardiac dysfunction in major cardiac pathologies, such as myocarditis and the consequent dilated cardiomyopathy, Chagas' disease and heart transplant rejection. Of the wealth of immune mechanisms known to affect cardiac function, this review will deal with the adverse effects caused by cytotoxic T lymphocytes (CTL, CD4(+) and CD8(+) T lymphocytes), which participate in a broad range of heart pathologies. The interaction between cytotoxic lymphocytes and their target cells can set off two different effector mechanisms: (1) The perforin/granzymes, and (2) The Fas/FasL. In this review, I will discuss these mechanisms, and present experimental evidence showing that both can adversely affect cardiac myocytes in vitro, in a way that can contribute to a decline in the overall cardiac function.

Sensitivity to apoptosis signal, clearance rate, and ultrastructure of fas ligand-induced apoptosis in in vivo adult cardiac cells

BACKGROUND

Sensitivity to apoptotic signals, the clearance rate of apoptosis, and the apoptotic ultrastructure have not been studied in cells of the in vivo adult heart.

METHODS AND RESULTS

To minimize the systemic influence, soluble Fas ligand was injected directly into in vivo rat hearts and livers (as the control) at concentrations of 0, 0.5, 2, and 5 microg/mL (groups C, F0.5, F2, and F5). Apoptotic cardiomyocytes and apoptotic noncardiomyocytes of the heart were identified with similar incidences only in F5. Their incidences peaked at 12 hours after injection (2.0+/-0.09% in cardiomyocytes) and diminished markedly 24 hours later. Caspase-3 was activated only in F5. Boc-Asp-fmk, a pancaspase inhibitor, inhibited apoptosis, suggesting that the apoptosis sensitivity was regulated upstream of caspase-3. Apoptotic noncardiomyocytes showed typical ultrastructure. In addition to the typical ultrastructure, such as cellular shrinkage, chromatin condensation, and apoptotic bodies, however, apoptotic cardiomyocytes showed unique features: doughnut-like, but not half-moon- or crescent-like, chromatin condensation; frequent plasma membrane rupture even during the early stage; condensed mitochondria with wrinkled cristae inside; the appearance of cytoplasmic lipid-like droplets; and myofibrillar derangement. In the livers, typical apoptosis was induced in hepatocytes and nonhepatocytes of the liver even in the F0.5 group, which were cleared 24 hours later.

CONCLUSIONS

Compared with liver cells, cardiomyocytes as well as noncardiomyocytes of the heart are more resistant against the apoptotic signal, but the clearance is similarly rapid (within 24 hours). The ultrastructure of apoptotic cardiomyocytes is unique. These findings provide new insights into the dynamics of cell death in the heart.

Apoptosis in myocardial infarction

Apoptosis, one of the major forms of cell death, has been implicated in different cardiovascular diseases. In this paper we review many of the different studies that have been performed to address the occurrence of apoptotic cell death associated with myocardial infarction. A definitive differentiation between apoptosis and other forms of cell death is still needed, mainly because of differences and limitations of the methods used for detection. In myocardial infarction apoptosis has been reported at acute stages of evolution in the ischemic area as well as in remote zones. In the ischemic area it might be a determinant of the final size of the infarct and it seems to depend on the presence of post-ischemic reperfusion. However, the incidence of apoptosis reported until now varies widely. In the myocardium remote from the ischemic area it might be associated with the progression towards heart failure. At present, the role and significance of apoptosis in myocardial infarction is rather inconclusive. Further studies are needed to solve methodological uncertainties and clarify the mechanisms involved in the process of cell death, which is particularly important as a basis for therapeutic interventions.