Myocyte loss in chronic heart failure

Cell Cycle and Senescence Regulation by Podocyte Histone Deacetylase 1 and 2

SIGNIFICANCE STATEMENT

The loss of integrity of the glomerular filtration barrier results in proteinuria that is often attributed to podocyte loss. Yet how damaged podocytes are lost remains unknown. Germline loss of murine podocyte-associated Hdac1 and Hdac2 ( Hdac1/2 ) results in proteinuria and collapsing glomerulopathy due to sustained double-stranded DNA damage. Hdac1/2 deletion induces loss of podocyte quiescence, cell cycle entry, arrest in G1, and podocyte senescence, observed both in vivo and in vitro . Through the senescence secretory associated phenotype, podocytes secrete proteins that contribute to their detachment. These results solidify the role of HDACs in cell cycle regulation and senescence, providing important clues in our understanding of how podocytes are lost following injury.

BACKGROUND

Intact expression of podocyte histone deacetylases (HDAC) during development is essential for maintaining a normal glomerular filtration barrier because of its role in modulating DNA damage and preventing premature senescence.

METHODS

Germline podocyte-specific Hdac1 and 2 ( Hdac1 / 2 ) double-knockout mice were generated to examine the importance of these enzymes during development.

RESULTS

Podocyte-specific loss of Hdac1 / 2 in mice resulted in severe proteinuria, kidney failure, and collapsing glomerulopathy. Hdac1 / 2 -deprived podocytes exhibited classic characteristics of senescence, such as senescence-associated β-galactosidase activity and lipofuscin aggregates. In addition, DNA damage, likely caused by epigenetic alterations such as open chromatin conformation, not only resulted in podocyte cell-cycle entry as shown in vivo by Ki67 expression and by FUCCI-2aR mice, but also in p21-mediated cell-cycle arrest. Through the senescence secretory associated phenotype, the damaged podocytes secreted proinflammatory cytokines, growth factors, and matrix metalloproteinases, resulting in subsequent podocyte detachment and loss, evidenced by senescent podocytes in urine.

CONCLUSIONS

Hdac1 / 2 plays an essential role during development. Loss of these genes in double knockout mice leads to sustained DNA damage and podocyte senescence and loss.

Prematurity and Pulmonary Vein Stenosis: The Role of Parenchymal Lung Disease and Pulmonary Vascular Disease

Pulmonary vein stenosis (PVS) has emerged as a critical problem in premature infants with persistent respiratory diseases, particularly bronchopulmonary dysplasia (BPD). As a parenchymal lung disease, BPD also influences vascular development with associated pulmonary hypertension recognized as an important comorbidity of both BPD and PVS. PVS is commonly detected later in infancy, suggesting additional postnatal factors that contribute to disease development, progression, and severity. The same processes that result in BPD, some of which are inflammatory-mediated, may also contribute to the postnatal development of PVS. Although both PVS and BPD are recognized as diseases of inflammation, the link between them is less well-described. In this review, we explore the relationship between parenchymal lung diseases, BPD, and PVS, with a specific focus on the epidemiology, clinical presentation, risk factors, and plausible biological mechanisms in premature infants. We offer an algorithm for early detection and prevention and provide suggestions for research priorities.

Microscopic Findings in the Cardiac Muscle of Stranded Extreme Deep-Diving Cuvier's Beaked Whales (Ziphius cavirostris)

Considerable information has been gained over the last few decades on several disease processes afflicting free-ranging cetaceans from a pathologist's point of view. Nonetheless, there is still a dearth of studies on the hearts of these species. For this reason, we aimed to improve our understanding of cardiac histological lesions occurring in free-ranging stranded cetaceans and, more specifically, in deep-diving Cuvier's beaked whales. The primary cardiac lesions that have been described include vascular changes, such as congestion, edema, hemorrhage, leukocytosis, and intravascular coagulation; acute degenerative changes, which consist of contraction band necrosis, wavy fibers, cytoplasmic hypereosinophilia, and perinuclear vacuolization; infiltration of inflammatory cells; and finally, the presence and/or deposition of different substances, such as interstitial myoglobin globules, lipofuscin pigment, polysaccharide complexes, and intra- and/or extravascular gas emboli and vessel dilation. This study advances our current knowledge about the histopathological findings in the cardiac muscle of cetaceans, and more specifically, of Cuvier's beaked whales.

Molecular Perspectives of Mitochondrial Adaptations and Their Role in Cardiac Proteostasis

Mitochondria are the key to properly functioning energy generation in the metabolically demanding cardiomyocytes and thus essential to healthy heart contractility on a beat-to-beat basis. Mitochondria being the central organelle for cellular metabolism and signaling in the heart, its dysfunction leads to cardiovascular disease. The healthy mitochondrial functioning critical to maintaining cardiomyocyte viability and contractility is accomplished by adaptive changes in the dynamics, biogenesis, and degradation of the mitochondria to ensure cellular proteostasis. Recent compelling evidence suggests that the classical protein quality control system in cardiomyocytes is also under constant mitochondrial control, either directly or indirectly. Impairment of cytosolic protein quality control may affect the position of the mitochondria in relation to other organelles, as well as mitochondrial morphology and function, and could also activate mitochondrial proteostasis. Despite a growing interest in the mitochondrial quality control system, very little information is available about the molecular function of mitochondria in cardiac proteostasis. In this review, we bring together current understanding of the adaptations and role of the mitochondria in cardiac proteostasis and describe the adaptive/maladaptive changes observed in the mitochondrial network required to maintain proteomic integrity. We also highlight the key mitochondrial signaling pathways activated in response to proteotoxic stress as a cellular mechanism to protect the heart from proteotoxicity. A deeper understanding of the molecular mechanisms of mitochondrial adaptations and their role in cardiac proteostasis will help to develop future therapeutics to protect the heart from cardiovascular diseases.

Agents that Modulate Peritoneal Membrane Structure and Function

Extensive experience with chronic peritoneal dialysis has identified a series of functional and anatomical pathologic changes in the peritoneal membrane thought to be the result of repeated insults from bioincompatible solutions. Laboratory and clinical findings from recent investigations often conflict and are difficult to interpret due to variations in methodologies, animal models, study designs, and data analyses. The principal pathophysiologic mechanisms identified thus far are oxidative stress, inflammation, and their consequences. Many substances used to neutralize the action of these insults, prevent formation of toxic compounds, or directly alter solute and water transport to improve peritoneal membrane performance have been studied. We herein review the most promising of these substances or those that deserve attention because their use has contributed to better understanding of peritoneal pathophysiology. Most peritoneal solution additives have proved useless due to their toxicity and undesirable effects, ineffectiveness, or manufacturing limitations. A few substances deserve more attention, particularly those capable of restoring negatively charged membrane sites, those that somehow improve permselectivity, scavengers of oxidants, and advanced glycation end-product inhibitors and breakers. Recent publications on clinical experience with neutral pH, low glucose degradation product (GDP) peritoneal solutions, although few and preliminary, are most encouraging. The virtual elimination of GDPs in these novel solutions will probably preclude the need for GDP scavengers and inhibitors. Nonetheless, there is room for further significant improvement in solution biocompatibility and for compounds that may restore peritoneal function.

Gender Difference in Damage-Mediated Signaling Contributes to Pulmonary Arterial Hypertension

Aims: Pulmonary arterial hypertension (PAH) is a progressive lethal disease with a known gender dimorphism. Female patients are more susceptible to PAH, whereas male patients have a lower survival rate. Initial pulmonary vascular damage plays an important role in PAH pathogenesis. Therefore, this study aimed at investigating the role of gender in activation of apoptosis/necrosis-mediated signaling pathways in PAH. Results: The media collected from pulmonary artery endothelial cells (PAECs) that died by necrosis or apoptosis were used to treat naive PAECs. Necrotic cell death stimulated phosphorylation of toll-like receptor 4, accumulation of interleukin 1 beta, and expression of E-selectin in a redox-dependent manner; apoptosis did not induce any of these effects. In the animal model of severe PAH, the necrotic marker, high mobility group box 1 (HMGB1), was visualized in the pulmonary vascular wall of male but not female rats. This vascular necrosis was associated with male-specific redox changes in plasma, activation of the same inflammatory signaling pathway seen in response to necrosis in vitro, and an increased endothelial-leukocyte adhesion in small pulmonary arteries. In PAH patients, gender-specific changes in redox homeostasis correlated with the prognostic marker, B-type natriuretic peptide. Males had also shown elevated circulating levels of HMGB1 and pro-inflammatory changes. Innovation: This study discovered the role of gender in the initiation of damage-associated signaling in PAH and highlights the importance of the gender-specific approach in PAH therapy. Conclusion: In PAH, the necrotic cell death is augmented in male patients compared with female patients. Factors released from necrotic cells could alter redox homeostasis and stimulate inflammatory signaling pathways.

Myocardial lipofuscin accumulation in ageing and sudden cardiac death

Lipofuscin is an intracellular aggregate of highly oxidized proteins that cannot be digested in the ubiquitin-proteasome system and accumulate mainly in lysosomes, especially in aged cells and pathological conditions. However, no systematic study has evaluated the cardiac accumulation of lipofuscin during human ageing and sudden cardiac death (SCD). Age estimation in unidentified bodies and postmortem SCD diagnosis are important themes in forensics. Thus, we aimed to elucidate their correlations with myocardial lipofuscin accumulation. We collected 76 cardiac samples from autopsy patients aged 20–97 years. After histopathological examination, myocardial lipofuscin was measured using its autofluorescence. Lipofuscin accumulated mainly in the perinuclear zone, and its accumulation rate positively correlated with chronological ageing (r = 0.82). Meanwhile, no significant change in lipofuscin level was observed with different causes of death, including SCD. There was also no significant change in lipofuscin level in relation to body mass index, serum brain natriuretic peptide level, or heart weight. Moreover, we performed LC3 and p62 immunoblotting to evaluate autophagic activity, and no change was observed in ageing. Therefore, lipofuscin accumulation more directly reflects chronological ageing rather than human cardiac pathology. Our study reveals the stability and utility of cardiac lipofuscin measurement for age estimation during autopsy.

Glucocorticoids, antenatal corticosteroid therapy and fetal heart maturation

Glucocorticoids are essential in mammals to mature fetal organs and tissues in order to survive after birth. Hence, antenatal glucocorticoid treatment (termed antenatal corticosteroid therapy) can be life-saving in preterm babies and is commonly used in women at risk of preterm birth. While the effects of glucocorticoids on lung maturation have been well described, the effects on the fetal heart remain less clear. Experiments in mice have shown that endogenous glucocorticoid action is required to mature the fetal heart. However, whether the potent synthetic glucocorticoids used in antenatal corticosteroid therapy have similar maturational effects on the fetal heart is less clear. Moreover, antenatal corticosteroid therapy may increase the risk of cardiovascular disease in adulthood. Here, we present a narrative review of the evidence relating to the effects of antenatal glucocorticoid action on the fetal heart and discuss the implications for antenatal corticosteroid therapy.

Increased risk of congestive heart failure in patients with acetaminophen poisoning: A nationwide cohort study

Acetaminophen poisoning increases cytochrome P450 2E1 expression and reactive oxygen species production, which may lead to maladaptive myocardial remodeling and congestive heart failure (CHF). We conducted a nationwide cohort study to investigate the incidence and risk of CHF in patients with acetaminophen poisoning. We identified a cohort of adult patients with newly diagnosed acetaminophen poisoning in the inpatient claims of the Taiwan National Health Insurance Research Database for the 1998-2011 period. A comparison cohort was frequency matched at a 4:1 ratio for sex, age and index year. All patients were followed up until the occurrence of CHF, withdrawal from the National Health Insurance program, or December 31, 2011. Cox proportional hazards models were employed to calculate the risk of CHF in the acetaminophen poisoning cohort compared with the comparison cohort, and the hazard ratios with 95% confidence intervals are presented. A total of 3546 and 14 184 patients with and without acetaminophen poisoning were followed up for a total of 25 856 and 102 119 person-years, respectively. The overall incidence of CHF was higher in the acetaminophen poisoning cohort than in the comparison cohort (8.12 vs. 5.19 per 10 000 person-years). After adjustment for covariates, the acetaminophen poisoning cohort exhibited a 1.59-fold higher risk of CHF (adjusted hazard ratio = 1.59; 95% confidence interval = 1.43-1.75) than did the comparison cohort. Patients with acetaminophen poisoning exhibited a significantly higher risk of CHF compared with the comparison cohort. Clinicians should follow up heart function in patients with acetaminophen poisoning.

Identification of cardioprotective agents from traditional Chinese medicine against oxidative damage

Reactive oxygen species are damaging to cardiomyocytes. H9c2 cardiomyocytes are commonly used to study the cellular mechanisms and signal transduction in cardiomyocytes, and to evaluate the cardioprotective effects of drugs following oxidative damage. The present study developed a robust, automated high throughput screening (HTS) assay to identify cardioprotective agents from a traditional Chinese medicine (TCM) library using a H₂O₂-induced oxidative damage model in H9c2 cells. Using this HTS format, several hits were identified as cardioprotective by detecting changes to cell viability using the cell counting kit (CCK)-8 assay. Two TCM extracts, KY-0520 and KY-0538, were further investigated. The results of the present study demonstrated that treatment of oxidatively damaged cells with KY-0520 or KY-0538 markedly increased the cell viability and superoxide dismutase activity, decreased lactate dehydrogenase activity and malondialdehyde levels, and inhibited early growth response-1 (Egr-1) protein expression. The present study also demonstrated that KY-0520 or KY-0538 treatment protected H9c2 cells from H₂O₂-induced apoptosis by altering the Bcl-2/Bax protein expression ratio, and decreasing the levels of cleaved caspase-3. In addition, KY-0520 and KY-0538 reduced the phosphorylation of ERK1/2 and p38-MAPK proteins, and inhibited the translocation of Egr-1 from the cytoplasm to nucleus in H₂O₂-treated H9c2 cells. These findings suggested that oxidatively damaged H9c2 cells can be used for the identification of cardioprotective agents that reduce oxidative stress by measuring cell viabilities using CCK-8 in an HTS format. The underlying mechanism of the cardioprotective activities of KY-0520 and KY-0538 may be attributed to their antioxidative activity, regulation of Egr-1 and apoptosis-associated proteins, and the inhibition of ERK1/2, p38-MAPK and Egr-1 signaling pathways.

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.

Left ventricular remodeling with exercise in hypertension

We investigated how exercise training superimposed on chronic hypertension impacted left ventricular remodeling. Cardiomyocyte hypertrophy, apoptosis, and proliferation in hearts from female spontaneously hypertensive rats (SHRs) were examined. Four-month-old SHR animals were placed into a sedentary group (SHR-SED; n = 18) or a treadmill running group (SHR-TRD, 20 m/min, 1 h/day, 5 days/wk, 12 wk; n = 18). Age-matched, sedentary Wistar Kyoto (WKY) rats were controls (n = 18). Heart weight was greater in SHR-TRD vs. both WKY (P < 0.01) and SHR-SED (P < 0.05). Morphometric-derived left ventricular anterior, posterior, and septal wall thickness were increased in SHR-SED relative to WKY and augmented in SHR-TRD. Cardiomyocyte surface area, length, and width were increased in SHR-SED relative to WKY and further increased in SHR-TRD. Calcineurin abundance was increased in SHR-SED vs. WKY (P < 0.001) and attenuated in SHR-TRD relative to SHR-SED (P < 0.05). Protein abundance and mRNA of Akt was not different among groups. The rate of apoptosis was increased in SHR-SED relative to WKY and mitigated in SHR-TRD. The abundance of Ki-67(+) cells across groups was not statistically different across groups. The abundance of cardiac progenitor cells (c-Kit(+) cells) was increased in SHR-TRD relative to WKY. These data suggest that exercise training superimposed on hypertension augmented cardiomyocyte hypertrophy, despite attenuating calcineurin abundance. Exercise training also mitigated apoptosis in hypertension and showed a tendency to enhance the abundance of cardiac progenitor cells, resulting in a more favorable cardiomyocyte number in the exercise-trained hypertensive heart.

Nonmyofilament-associated troponin T fragments induce apoptosis

Troponin T (TnT) is a striated muscle-specific protein and an abundant component of the myofilaments. Nonmyofilament-associated TnT is rapidly degraded in myocytes, implying an importance in the maintenance of the cellular environment. However, if the level of nonmyofilament-associated TnT or TnT fragments exceeds the degradation capacity, it may cause cytotoxicity. To investigate this hypothesis, we constructed bicistronic vectors to express different portions of TnT polypeptide chain, together with nonfusion green fluorescent protein as a tracer for the transfection. Cytotoxicity of the TnT fragments was studied through forced expression in C(2)C(12) myoblasts and human embryonic kidney-293 nonmuscle cells and examination of the viability of the transfected cells. The results demonstrated that, in the absence of myofilaments, the conserved COOH-terminal and middle fragments of TnT were highly effective on inducing cell death via apoptosis, whereas the NH(2)-terminal variable region was not. As combined effects, nonmyofilament-associated intact cardiac TnT and a COOH-terminal truncated slow TnT fragment found in Amish nemaline myopathy exhibited intermediate cytotoxicity. A particular significance of this finding is that peak releases of TnT or TnT fragments from decomposition of a large number of myofibrils in acute myocardial infarction may breach the cellular protection of proteolytic degradation and result in apoptosis as a potential cause for the loss of cardiomyocytes.

Mitochondrial centrality in heart failure

A number of observations have shown that mitochondria are at the center of the pathophysiology of the failing heart and mitochondrial-based oxidative stress (OS), myocardial apoptosis, and cardiac bioenergetic dysfunction are implicated in the progression of heart failure (HF), as shown by both clinical studies and animal models. In this manuscript, we review the body of evidence that multiple defects in mitochondria are central and primary to HF progression. In addition, novel approaches to therapeutic targeting of mitochondrial bioenergetic, biogenic, and signaling abnormalities that can impact HF are discussed.

Myocardial apoptosis associated with the expression of proinflammatory cytokines during the course of myocardial infarction

To clarify the role of myocardial apoptosis associated with the expression of proinflammatory cytokines in human myocardial infarction (MI), we have analyzed the expression of apoptosis positive for single-stranded DNA (ss-DNA) antibody, tumor necrosis factor (TNF)-alpha, and interleukin (IL)-8 in 147 samples of infarcted myocardial tissue from 65 patients. ss-DNA-positive apoptotic nuclei were found mainly in cardiomyocytes in the border zones and granulation tissue cells in the infarct foci. The ss-DNA index (SI) of cardiomyocytes (average 0.13%) peaked at stage II (established myocardial necrosis), the value being significantly higher than at stages III (macrophage infiltration), IV (granulation formation), and V (scar formation) (P<0.05), whereas the SI of granulation tissue (average 0.08%) at stages III, IV, and V showed no significant differences between the three stages. These results suggest that cardiomyocyte apoptosis in the border zone is responsible for cellular loss in the acute stage of MI, whereas granulation tissue apoptosis may not be involved in the process of ventricular remodeling. TNF-alpha was expressed in cardiomyocytes in the border zones of infarct foci, but no significant positive correlation was found between SI and TNF-alpha index in cardiomyocytes (r=0.08, P = 0.37), suggesting that TNF-alpha does not serve as a direct trigger of cardiomyocyte apoptosis in vivo. The number of IL-8-positive cells peaked at stage II, and IL-8-myeloperoxidase-double-positive neutrophils were frequently detected, indicating that infiltrating neutrophils are the predominant source of IL-8 in the infarcted myocardium. These results suggest that, in human MI, TNF-alpha produced by cardiomyocytes does not play a critical role in their apoptosis, and that IL-8 produced by neutrophils is responsible for the subsequent accumulation and activation of neutrophils, thus increasing the degree of myocardial damage.

Oxygen, oxidative stress, hypoxia, and heart failure

A constant supply of oxygen is indispensable for cardiac viability and function. However, the role of oxygen and oxygen-associated processes in the heart is complex, and they and can be either beneficial or contribute to cardiac dysfunction and death. As oxygen is a major determinant of cardiac gene expression, and a critical participant in the formation of ROS and numerous other cellular processes, consideration of its role in the heart is essential in understanding the pathogenesis of cardiac dysfunction.

Oxygen, oxidative stress, hypoxia, and heart failure

A constant supply of oxygen is indispensable for cardiac viability and function. However, the role of oxygen and oxygen-associated processes in the heart is complex, and they and can be either beneficial or contribute to cardiac dysfunction and death. As oxygen is a major determinant of cardiac gene expression, and a critical participant in the formation of ROS and numerous other cellular processes, consideration of its role in the heart is essential in understanding the pathogenesis of cardiac dysfunction.

Balanced expression of mitochondrial apoptosis regulatory proteins correlates with long-term survival of cardiac allografts

Abnormal regulation of apoptosis is observed in ischemic injury and may contribute to the pathogenesis of atherosclerosis. However, its role in cardiac allograft vasculopathy (CAV), the fundamental lesion of chronic rejection (CR) in heart transplantation, remains uncertain. To clarify this issue, apoptosis was quantitated in myocardium and coronary arteries from 5 cardiac allograft donors (NL) and explanted hearts of 24 patients with ischemic cardiomyopathy (IsCM) and 15 patients with CR. Tissue samples were analyzed via end-labeling fragmented DNA [via deoxynucleotidyl transferase-mediated dUTP nick end-labeling (TUNEL)] and immunoblotting for activated caspase-3 and -9. Myocyte apoptosis assessed by TUNEL was similarly increased over NL (0.21%) in both the CR (0.88%; P < 0.01) and IsCM (0.88%; P < 0.01) groups. Activated caspase-9 levels were significantly higher in CR (14.7%) compared with IsCM (6.9%; P < 0.01) and NL (0%) groups, whereas activated caspase-3 levels were similarly elevated in both CR and IsCM (7.8 and 6.5% vs. 0% in NL; P < 0.01 and P < 0.05) groups. Expression of myocardial Bcl-2 and Bax was increased in CR compared with both NL (Bax, 4.3-fold; P < 0.01; Bcl-2, 5.9-fold; P < 0.01) and IsCM (IsCM: Bax, 2.2-fold; P < 0.05; Bcl-2, 3.2-fold; P < 0.01) groups. The rate of apoptosis and the Bcl-2/Bax ratio independently correlated to graft survival in CR (activation of caspase-9: r = 0.87; P < 0.01; Bcl-2/Bax: r = 0.57; P = 0.05). Compared with native atherosclerosis, coronary arteries with CAV showed more medial apoptosis (7.8-fold; P < 0.01) and higher Bcl-2 levels (5.1-fold; P < 0.01) with lower Bax levels (threefold; P < 0.05) in the intima. These results indicate that abnormal Bcl-2 and Bax expression in myocardium and coronary arteries of cardiac allografts with CR is distinct from that in IsCM and suggest that balancing Bcl-2 to Bax in transplanted hearts promotes long-term graft survival.

Cyclical mechanical stretch-induced apoptosis in myocytes from young rats but necrosis in myocytes from old rats

Mechanical load as stimulus for apoptosis and necrosis could be responsible for the loss of cardiomyocytes. Ventricular myocytes from young (3 mo) and old (14-24 mo) rats underwent cyclical mechanical stretch (CMS; 5% elongation, 1 Hz) for 24 h. Spontaneous apoptosis was in myocytes from young rats 0.33 +/- 0.12% and from old rats 1.05 +/- 0.35% [Tdt-mediated dUTP nick-end labeling (TUNEL) assay]; associated with a decrease of Bcl-2. CMS increased the apoptosis to 0.58 +/- 0.18% in myocytes from young rats. Western blot analysis showed that CMS reduced Bcl-2 and increased p53 (young rats). Bax was not changed by CMS. These were confirmed by cytochrome c release (31 +/- 13%) and by the enrichment of cytosolic nucleosomes (11 +/- 8%). CMS did not influence the apoptosis in myocytes from old rats (TUNEL assay, Bcl-2, Bax, or p53). CMS did not cause necrosis in myocytes from young rats. CMS increased the number of necrotic cells by showing the cell membrane rupture in myocytes from old rats (50 +/- 13% 5-hexadecanoylaminofluorescein-positive and 38 +/- 6% propidium iodide-positive cells) as well as by measuring the lactate dehydrogenase release. The results suggest that CMS-induced apoptosis in myocytes of young rats but necrosis in myocytes from old rats, which could be attributed to more stress sensitivity of cells from old rats.

Right ventricular dilatation after left ventricular acute myocardial infarction is predictive of extremely high peri-infarctual apoptosis at postmortem examination in humans

BACKGROUND

Cardiac remodelling after acute myocardial infarction (AMI) is characterised by molecular and cellular mechanisms involving both left and right ventricles, and biventricular failure identifies patients with an extremely unfavourable prognosis.

AIMS

To assess whether a link exists between increased myocardial apoptotic rates (AR) at sites of recent infarction and patterns of unfavourable cardiac remodelling, such as biventricular enlargement after left ventricular (LV) infarction.

METHODS

Twelve patients with recent AMI involving the LV and not the right ventricle (RV) and with permanent infarct related artery occlusion were selected at necropsy. Gross pathological characteristics, such as LV and RV dilatation, and AR at site of infarction were assessed. Potential false positive results (DNA synthesis and RNA splicing) were excluded from the cell count.

RESULTS

RV enlargement, defined as a tricuspidal ring greater than 120 mm, was found in five cases and was associated with LV dilatation. These patients showed significantly higher AR than the others. When the subjects were divided into three groups according to progressive cardiac remodelling (absence of cardiac dilatation, isolated LV dilatation, and biventricular enlargement), the last group had significantly higher ARs than the other two groups, showing that myocardiocyte apoptosis is increased in more unfavourable forms of cardiac remodelling.

CONCLUSION

Patients with severely unfavourable cardiac remodelling, such as biventricular enlargement, have extremely high myocardiocyte apoptosis at necropsy, even late after LV myocardial infarction, supporting the role of myocardiocyte loss in determining post-infarction adverse remodelling.

Targeting ischemic cardiac dysfunction through gene transfer

Ischemic cardiac injury is a complication of atherosclerosis, which remains a major contributor to morbidity and mortality throughout much of the world. Previous studies have documented apoptotic cardiomyocyte death in this setting; however, its functional contribution remains incompletely defined. We briefly review general mechanisms of apoptosis and then present evidence from interventional studies that suggests apoptotic cell death may indeed play an important role in the pathogenesis of ischemic injury. In some instances, the signaling pathways controlling both cardiomyocyte survival and function appear to converge, suggesting these pathways may represent particularly attractive targets for therapeutic intervention in ischemic heart disease. In this context, gene transfer provides both a powerful experimental tool for validating such targets for intervention, as well as an approach to therapy.

Hypoxia-induced cleavage of caspase-3 and DFF45/ICAD in human failed cardiomyocytes

It has been proposed that the hemodynamic deterioration associated with heart failure (HF) may be due in part to ongoing loss of viable cardiac myocytes through apoptosis. Hypoxia has been shown to promote apoptosis in normal cardiomyocytes. Adaptation and maladaptations inherent to heart failure can modify the susceptibility of cells to different stress factors. We hypothesized that HF modifies the threshold of cardiomyocytes to hypoxia-induced apoptosis. Cardiomyocytes were isolated from 18 human hearts explanted at the time of cardiac transplantation due to either ischemic cardiomyopathy (ICM) (n = 9) or idiopathic dilated cardiomyopathy (IDC) (n = 9). Tissue from five normal donor hearts (NL) for whom no suitable recipient was available was used as control. Cardiomyocytes were incubated for 3 h under normoxic (95% air-5% CO(2)) or hypoxic (95% N(2)-5% CO(2)) conditions. Expression of caspase-3 and DNA fragmentation factor-45 (DFF45)/inhibitor of caspase-3-activated DNase (ICAD) was detected by Western blot analysis. Three hours of hypoxia did not affect the expression of these proteins in NL cardiomyocytes. In contrast, hypoxia led to cleavage of caspase-3 and DFF45/ICAD both in ICM and IDC. In conclusion, failing cardiomyocytes exhibit increased susceptibility to hypoxia-induced apoptosis.

Losing heart: the role of apoptosis in heart disease--a novel therapeutic target?

Cardiovascular disease is a leading cause of death worldwide. In recent years it has emerged that loss of myocardial cells may be a major pathogenic factor. Cell death can occur in a destructive, uncontrolled manner via necrosis or by a highly regulated programmed cell suicide mechanism termed apoptosis. As cell death in conditions such as heart failure and myocardial infarction does not always follow a typically apoptotic pathway, it remains to be established whether it occurs by apoptosis, necrosis, or a novel uncharacterized mechanism combining aspects of both types of cell death. Apoptotic pathways have been well studied in nonmyocytes and it is thought that similar pathways exist in cardiomyocytes. These pathways include death initiated by ligation of membrane-bound death receptors or death initiated by release of cytochrome c from mitochondria. Increasing evidence supports the existence of these pathways and their regulators in the heart. These regulators include inhibitors of caspases, which are the key enzymes of apoptosis, the Bcl-2 family of proteins, growth factors, stress proteins, calcium, and oxidants. It is hoped that a better understanding of the pathways of apoptosis and their regulation may yield novel therapeutic targets for cardiovascular disease.

Load-dependent induction of apoptosis in multicellular myocardial preparations

Increased mechanical load has been proposed as an inductor of apoptosis, but it is unknown whether this can occur in the range of pre- and afterloads that prevail in the beating heart. We investigated apoptosis in cultured rabbit multicellular myocardial preparations over several days. Muscles contracted in absence of pre- and afterload (unloaded isotonic), in absence of preload but in presence of afterload (unloaded isometric), or in presence of both (loaded isometric). After up to 48 h of continuous contractions, apoptosis was assessed by TdT-mediated nick-end labeling (TUNEL) assay and DNA ladder analysis. In muscles that contracted loaded isometric, apoptosis was detected after 6-24 h. After 48 h, apoptosis was most prominent in this group, reflected by a high level of DNA ladder intensity (DLI; 27.8 +/- 11.5), whereas Bcl-xL (on RNA level) was significantly downregulated, and Fas remained unchanged. In unloaded isometric preparations, apoptosis was significantly less (6.9 +/- 5.9 DLI) and very similar to those contracting unloaded isotonic (6.1 +/- 5.1 DLI). We conclude that load-dependent apoptosis can occur at sarcomere lengths achievable in vivo and may mainly result from increased preload.

Gene therapy and pharmaceutical modulation of apoptosis

Apoptosis is detectable in cardiovascular disease in various forms. Although the methods to detect apoptosis need improvement, and its magnitude is not known clearly, there is sufficient evidence to postulate that it might be important in progression of disease. Clinicians now have some specific compounds that can be used to modulate apoptosis. The preliminary data suggest that we can modulate apoptosis in animal models and that this is associated with obvious benefits in terms of tissue salvage and possibly improved function. There are no human data as yet. Many questions must be addresses before undertaking human studies. Despite these shortcomings, there is a tremendous potential for apoptotic modulation in preventing or ameliorating cardiovascular disease in the near future.

Cellular events linked to cardiac remodeling in heart failure: targets for pharmacologic intervention

Over the past decade, there has been a paradigm shift in the understanding of heart failure pathophysiology. Heart failure is no longer conceptualized as a hemodynamic disorder resulting from changes in renal and hormonal function. Rather, the syndrome of heart failure is more complex and is characterized by abnormal myocyte growth, proliferation of cells in the extracellular matrix, and myocyte cell loss (apoptosis)--all of which culminate in significant structural remodeling of the heart and loss of ventricular function. The loss of ventricle function is preceded by an initiating event such as myocardial infarction, which leads to changes in cell function, activation of specific neurohormones and peptides, which in turn are linked to the remodeling of the ventricle, and progression of heart failure. This article discusses how changes in myocyte and nonmyocyte structure may contribute to the progression of heart failure. Insight into these mechanisms will provide a better understanding of newer pharmacologic approaches in the treatment of heart failure.

The role of apoptosis in vascular disease

Normal arteries are characterized by a low turnover of endothelial (EC) and smooth muscle cells (SMC). Different mechanisms protect the EC and SMC against apoptosis in the normal artery. In hypertension, SMC replication is increased but this is not counterbalanced by increased apoptosis, resulting in thickening of the media of arteries and arterioles. The significance of apoptosis in atherosclerosis depends on the stage of the plaque, localization and the cell types involved. Both macrophages and SMC undergo apoptosis in atherosclerotic plaques. Apoptosis of macrophages is mainly present in regions showing signs of DNA synthesis/repair. SMC apoptosis is mainly present in less cellular regions and is not associated with DNA synthesis/repair. Even in the early stages of atherosclerosis SMC become susceptible to apoptosis since they increase different pro-apoptotic factors. Moreover, recent data indicate that SMC may be killed by activated macrophages. The loss of the SMC can be detrimental for plaque stability since most of the interstitial collagen fibres, which are important for the tensile strength of the fibrous cap, are produced by SMC. Apoptosis of macrophages could be beneficial for plaque stability if apoptotic bodies were removed. Apoptotic cells that are not scavenged in the plaque activate thrombin, which could further induce intraplaque thrombosis. It can be concluded that apoptosis in primary atherosclerosis is detrimental since it could lead to plaque rupture and thrombosis. Recent data of our group indicate that apoptosis decreased after lipid lowering which could be important in the understanding of the cell biology of plaque stabilization.