RESUMEN
AIMS: Cardiomyocyte apoptosis is known to occur in infarct border zones, where cardiomyocyte dedifferentiation, as seen in hibernating myocardium, can also be observed. The aim of the study is to determine whether dedifferentiated cardiomyocytes represent a population of cells stably surviving or undergoing apoptosis. METHODS AND RESULTS: Microinfarctions were induced in sheep (n=8) by intracoronary injection of polymer macrobeads. The sheep were killed when cardiac function was gradually decreased (ejection fraction 37+/-6%, mean+/-SEM), but not earlier than 6 weeks after embolization. Transmural biopsies were taken from embolized and remote areas, based on flow measurements with positron emission tomography. Cells were classified as dedifferentiated when sarcomere content was depleted by >10% and glycogen content increased. Apoptosis was detected using the Tdt-mediated nick-end labelling (TUNEL) method and activated caspase-3 immunolabelling. Dedifferentiated cardiomyocytes were identified by morphology and by immunohistochemical evaluation of dedifferentiation related expression patterns of desmin, titin, cardiotin and alpha-smooth muscle actin. Cardiomyocyte apoptosis was detected in both the infarction border zones and remote areas. Dedifferentiated cardiomyocytes accounted for up to 30% of the cells in embolized areas and were almost exclusively non-apoptotic. CONCLUSION: In embolization induced microinfarcted tissue, dedifferentiated cardiomyocytes are preferentially spared to undergo apoptosis. It is hypothesized that dedifferentiated cardiomyocytes and apoptotic cardiomyocytes represent two different cell populations. The dedifferentiated cells can be considered as stable surviving cells.
Asunto(s)
Infarto del Miocardio/patología , Aturdimiento Miocárdico/patología , Miocardio/patología , Actinas/metabolismo , Animales , Apoptosis , Caspasa 3 , Caspasas/metabolismo , Supervivencia Celular , Fragmentación del ADN , Precursores Enzimáticos , Femenino , Fluorodesoxiglucosa F18 , Corazón/diagnóstico por imagen , Etiquetado Corte-Fin in Situ , Infarto del Miocardio/metabolismo , Aturdimiento Miocárdico/metabolismo , Miocardio/metabolismo , Radiofármacos , Ovinos , Tomografía Computarizada de EmisiónRESUMEN
Our current knowledge of the pathophysiology of chronic hibernating myocardium is mainly based on results from clinical studies, because of the absence of appropriate and validated animal models. These clinical observations have given rise to two major controversies: the role of reduced blood flow and that of histological changes in the hibernating segments. In this review, these two subjects will be briefly discussed, and put into the perspective of findings emerging from recently developed animal models.
Asunto(s)
Aturdimiento Miocárdico/fisiopatología , Animales , Velocidad del Flujo Sanguíneo/fisiología , Enfermedad Crónica , HumanosRESUMEN
OBJECTIVES: Little is known about the causal factors which induce the typical structural changes accompanying cardiomyocyte dedifferentiation in vivo such as in chronic hibernating myocardium. For identifying important factors involved in cardiomyocyte dedifferentiation, as seen in chronic hibernation, an in vitro model mimicking those morphological changes, would be extremely helpful. METHODS: Adult rabbit cardiomyocytes were co-cultured with cardiac fibroblasts. The typical changes induced by this culturing paradigm were investigated using morphometry, electron microscopy and immunocytochemical analysis of several structural proteins, which were used as dedifferentiation markers, i.e., titin, desmin, cardiotin and alpha-smooth muscle actin. RESULTS: Close apposition of fibroblasts with adult rabbit cardiomyocytes induced hibernation-like dedifferentiation, similar to the typical changes seen in chronic hibernation in vivo. Both changes in ultrastructure and in the protein expression pattern of dedifferentiation markers as seen in chronic hibernating myocardium were seen in the co-cultured cardiomyocytes. CONCLUSION: Hibernation-like changes can be induced by co-culturing adult rabbit cardiomyocytes with fibroblasts. This cellular model can be a valuable tool in identifying and characterizing the pathways involved in the dedifferentiation phenotype in vivo, and already suggests that many of the structural changes accompanying dedifferentiation are not per se dependent on a decreased oxygen availability.
Asunto(s)
Aturdimiento Miocárdico/patología , Miocardio/patología , Actinas/análisis , Animales , Diferenciación Celular , Tamaño de la Célula , Técnicas de Cocultivo/métodos , Fibroblastos/patología , Microscopía Electrónica , Microscopía de Contraste de Fase , Mitocondrias Cardíacas/ultraestructura , Modelos Animales , Miocardio/química , Conejos , Sarcómeros/ultraestructuraRESUMEN
Substantial evidence has accumulated that apoptosis, sometimes called "programmed cell death," is important in several cardiac diseases. Although most researchers focus on apoptosis in the hope that by understanding its mechanisms one can block this form of cell death, little attention has been given to programmed cell survival.
Asunto(s)
Apoptosis/fisiología , Insuficiencia Cardíaca/patología , Fibras Musculares Esqueléticas/patología , Aturdimiento Miocárdico/patología , Miocardio/patología , Animales , Supervivencia Celular/fisiología , HumanosRESUMEN
The aim of this study was to evaluate the relationship between flow/metabolism, histology and functional follow-up in a sheep model of subacute myocardial infarction. In eight juvenile sheep, a myocardial infarction was induced by intracoronary injection of macrobeads. Left ventricular function was evaluated using echocardiography. 2-[18F]fluoro-2-deoxy-D-glucose (18F-FDG)/nitrogen-13-labelled ammonia (13NH3) positron emission tomography (PET) was performed at 6 weeks and 16 weeks after embolization. In five sheep, a dynamic carbon-11 acetate study was performed. In each animal, two regions of interest were defined on the polar map, corresponding to the embolized and the non-embolized region. After the final measurements, the hearts were processed for histological evaluation. PET revealed a moderately decreased flow and oxidative metabolism in the embolized region at 6 weeks, without significant changes at follow-up. At 6 weeks, 18F-FDG uptake in the embolized area was more severely decreased as compared to the flow index in the embolized area (P < 0.05). At 16 weeks, 18F-FDG metabolism had significantly recovered (P < 0.05). Serial echocardiography showed a persistent decrease in global and regional left ventricular function. Histology revealed a mix of micro-infarcted and viable tissue in the embolized region. In this model of subacute myocardial infarction, a PET "reversed mismatch" pattern was observed, with partial recovery of 18F-FDG uptake at follow-up. The histological counterpart of this PET pattern appears to be patchy necrosis.
Asunto(s)
Infarto del Miocardio/diagnóstico por imagen , Enfermedad Aguda , Animales , Circulación Coronaria/fisiología , Ecocardiografía , Femenino , Fluorodesoxiglucosa F18 , Corazón/diagnóstico por imagen , Procesamiento de Imagen Asistido por Computador , Infarto del Miocardio/metabolismo , Infarto del Miocardio/fisiopatología , Miocardio/metabolismo , Radiofármacos , Ovinos , Tomografía Computarizada de Emisión , Función Ventricular IzquierdaRESUMEN
It has been suggested that Ca(2+)content of atrial cardiomyocytes is increased at the onset of atrial fibrillation (AF). Whether this phenomenon is transient is currently unknown. Therefore, in this study the time-related changes in Ca(2+)location in atrial myocytes from goats with chronic AF have been investigated. The distribution of calcium was assessed with the electron microscope using the cytochemical phosphate-pyroantimonate and oxalate-pyroantimonate methods in atrial biopsies from goats in sinus rhythm and goats with 1-16 weeks of burst-pacing-induced AF. In atrial myocytes from control goats in sinus rhythm, a normal Ca(2+)distribution was observed, with regular deposits along the sarcolemma (an average of 3.4 deposits per microm at a regular distance). The number of sarcolemma-bound Ca(2+)deposits substantially increased after 1 and 2 weeks of atrial fibrillation. After this period the amount of Ca(2+)precipitate decreased at 4 and 8 weeks, and became below control level at 16 weeks. A similar time-related redistribution of Ca(2+)occurred in mitochondria. Whereas mitochondria from control goats displayed very few Ca(2+)deposits (average 4.0 deposits per micro m(2)), their number markedly increased after 1 and 2 weeks of atrial fibrillation, which indicates cellular Ca(2+)overload. From 4 weeks, Ca(2+)deposits reached control levels and were below control level after 16 weeks of atrial fibrillation (2.5 deposits per microm(2)). Our findings are consistent with the previously observed Ca(2+)overload early after the onset of atrial fibrillation. The present study shows that this overload persists for at least 2 weeks, after which the cardiomyocytes apparently adapt to a new Ca(2+)homeostasis, thereby avoiding Ca(2+)overload. This protection against Ca(2+)overload co-occurs with dedifferentiation like cellular remodeling.
Asunto(s)
Fibrilación Atrial/metabolismo , Calcio/metabolismo , Atrios Cardíacos/metabolismo , Animales , Fibrilación Atrial/patología , Femenino , Cabras , Atrios Cardíacos/patología , Atrios Cardíacos/ultraestructura , Factores de TiempoRESUMEN
Is the 'smart heart' smart enough? Since the introduction of the term 'hibernating myocardium', this has been referred to as the 'smart heart', however more recently several publications have suggested that cell death accompanies the hibernation process, so that revascularisation of patients with hibernating myocardium should be performed without delay. Other data, however, point to cellular dedifferentiation instead of cellular degeneration, which means that cardiac hibernation is an adaptive mechanism capable of preserving the myocardial viability for a prolonged period. In an attempt to find an answer to the above-mentioned question, this review summarises and discusses the findings in this field, also giving attention to possible explanations for the discrepant findings.
Asunto(s)
Apoptosis , Corazón/fisiopatología , Aturdimiento Miocárdico/fisiopatología , Animales , Enfermedad Crónica , Modelos Animales de Enfermedad , Humanos , Proyectos de InvestigaciónRESUMEN
OBJECTIVE: Similar structural changes in the myocardium can be observed in chronic hibernating myocardium and in myocardium taken from hearts suffering chronic atrial fibrillation. We investigated whether or not these changes are indicative of apoptosis. METHODS: Myocardial biopsies from 28 strictly selected patients with chronic hibernating myocardium and heart samples from 13 goats with pacing-induced chronic atrial fibrillation were used. Special attention was paid to processing the tissues immediately (fixation/freezing) in order to prevent artificial degenerative changes, thereby excluding false positive identification of apoptosis. Infarcted areas or infarcted border zones were excluded from our study. Apoptosis was detected with light and electron microscopy and terminal deoxynucleotidyl transferase nick end-labelling. Immunohistochemistry was used for detecting Bcl-2, P53 and PCNA-proteins associated with apoptosis/DNA damage. RESULTS: The results obtained for chronic hibernating left ventricular myocardium were similar to those for chronic fibrillating atrial myocardium. No apoptotic nuclei, as characterised by extensive chromatin clumping, could be observed in normal or dedifferentiated cardiomyocytes under the electron microscope. The end-labelling assay did not reveal any cardiomyocytes with damaged DNA. Nor could we find any evidence of substantial expression of Bcl-2, P53 or PCNA, a result indicative of the absence of apoptotic threat or DNA damage. CONCLUSION: Cardiomyocyte dedifferentiation, but not extensive degeneration through apoptosis, can be observed in chronic hibernating myocardium and chronic fibrillating atrium. Dedifferentiation may be the best way to survive prolonged exposure to the unfavourable conditions imposed by increased wall stress, a relative lowered oxygen environment, or both.
Asunto(s)
Apoptosis , Fibrilación Atrial/patología , Aturdimiento Miocárdico/patología , Miocardio/patología , Animales , Fibrilación Atrial/metabolismo , Biomarcadores/análisis , Femenino , Cabras , Humanos , Inmunohistoquímica , Etiquetado Corte-Fin in Situ , Microscopía Electrónica , Aturdimiento Miocárdico/metabolismo , Miocardio/química , Antígeno Nuclear de Célula en Proliferación/análisis , Proteínas Proto-Oncogénicas c-bcl-2/análisis , Proteína p53 Supresora de Tumor/análisisRESUMEN
Left ventricular biopsies from 21 patients with clinically diagnosed chronic hibernating myocardium (CHM) were examined by light- and electron microscopy. A mean of 27% of cardiomyocytes were structurally altered and were characterized as hibernating, because of reduced amount of myofibrils and increased glycogen content. Electron microscopy of these cells showed reduction of T-tubules and numerous small mitochondria, but few changes associated with degeneration, acute ischemia or apoptosis. The structural changes found in CHM are reminiscent of dedifferentiation rather than degeneration. The expression patterns of some structural proteins show resemblance with those in embryonic cardiomyocytes. Histochemically, mitochondrial NADH-oxidase and proton translocating ATPase activities were absent, whereas cytochrome c activity was present. Intracellular calcium distribution indicated normally bound sarcolemmal calcium and absence of excess mitochondrial calcium accumulation. Nuclear chromatin ranged from normal to dispersed with only a few nuclei that were clumped. These results suggest that cardiomyocytes from human CHM hearts are structurally altered, but viable, and lack morphologic and cytochemical characteristics suggestive of apoptosis or acute ischemia.