In multicellular organisms, homeostasis is maintained through a balance between cell proliferation and cell death. Although much is known about the control of cell proliferation, less is known about the control of cell death. Physiologic cell death occurs primarily through an evolutionarily conserved form of cell suicide termed apoptosis. The decision of a cell to undergo apoptosis can be influenced by a wide variety of regulatory stimuli. Recent evidence suggests that alterations in cell survival contribute to the pathogenesis of a number of human diseases, including cancer, viral infections, autoimmune diseases, neurodegenerative disorders, and AIDS (acquired immunodeficiency syndrome). Treatments designed to specifically alter the apoptotic threshold may have the potential to change the natural progression of some of these diseases.

https://science.sciencemag.org/content/sci/267/5203/1456.full.pdf

Apoptosis in the pathogenesis and treatment of disease

Background Loss of myocytes is an important mechanism in the development of cardiac failure of either ischemic or nonischemic origin. However, whether programmed cell death (apoptosis) is implicated in the terminal stages of heart failure is not known. We therefore studied the magnitude of myocyte apoptosis in patients with intractable congestive heart failure. Methods Myocardial samples were obtained from the hearts of 36 patients who underwent cardiac transplantation and from the hearts of 3 patients who died soon after myocardial infarction. Samples from 11 normal hearts were used as controls. Apoptosis was evaluated histochemically, biochemically, and by a combination of histochemical analysis and confocal microscopy. The expression of two proto-oncogenes that influence apoptosis, BCL2 and BAX, was also determined. Results Heart failure was characterized morphologically by a 232-fold increase in myocyte apoptosis and biochemically by DNA laddering (an indicator of apoptosis). The histochemical demonst...

Apoptosis in the Failing Human Heart

Swynghedauw, Bernard. Molecular Mechanisms of Myocardial Remodeling. Physiol. Rev. 79: 215–262, 1999. — “Remodeling” implies changes that result in rearrangement of normally existing structures. Th...

Molecular Mechanisms of Myocardial Remodeling

Background Heart failure can result from a variety of causes, including ischemic, hypertensive, toxic, and inflammatory heart disease. However, the cellular mechanisms responsible for the progressive deterioration of myocardial function observed in heart failure remain unclear and may result from apoptosis (programmed cell death). Methods We examined seven explanted hearts obtained during cardiac transplantation for evidence of apoptosis. All seven patients had severe chronic heart failure: four had idiopathic dilated cardiomyopathy, and three had ischemic cardiomyopathy. DNA fragmentation (an indicator of apoptosis) was identified histochemically by in situ end-labeling as well as by agarose-gel electrophoresis of end-labeled DNA. Myocardial tissues obtained from four patients who had had a myocardial infarction one to two days previously were used as positive controls, and heart tissues obtained from four persons who died in motor vehicle accidents were used as negative controls for the end-labeling stu...

https://www.nejm.org/doi/pdf/10.1056/NEJM199610173351603

Apoptosis in Myocytes in End-Stage Heart Failure

Apoptosis is characterised by a series of typical morphological features, such as shrinkage of the cell, fragmentation into membrane-bound apoptotic bodies and rapid phagocytosis by neighbouring cells. This paper reviews the current knowledge on the molecular mechanisms of apoptosis as they relate to the morphologic hallmarks and their implications for the detection of apoptosis in cardiac tissue. Activation of cysteine proteases called caspases plays a major role in the execution of apoptosis. These proteases selectively cleave vital cellular substrates, which results in apoptotic morphology and internucleosomal fragmentation of DNA by selectively activated DNases. In response to several pro-apoptotic signals, mitochondria release caspase activating factors, that initiate an escalating caspase cascade and commit the cell to die. Members of the Bcl-2 oncoprotein family control mitochondrial events and are able to prevent, or induce, both apoptotic and non-apoptotic types of cell death. This suggests that different types of cell death share common mechanisms in the early phases, whereas activation of caspases determines the phenotype of cell death. Detection of apoptotic cells in tissue samples currently relies on the TUNEL assay. TUNEL-positive cardiomyocytes show morphological features of apoptosis and the typical ladder pattern in DNA electrophoresis. Thus, provided that the staining protocol is carefully standardised, this quantitative methodology provides reproducible results of the occurrence of cardiomyocyte apoptosis in cardiac samples. Recently, potentially more specific assays based on analysis of DNA fragmentation or demonstration of caspase activation have been developed. Applicability of these assays to demonstrate cardiomyocyte apoptosis should be tested.

Morphologic and biochemical hallmarks of apoptosis.

The most effective way to limit myocardial ischemic necrosis is reperfusion, but reperfusion itself may result in tissue injury, which has been difficult to separate from ischemic injury. This report identifies elements of apoptosis (programmed cell death) in myocytes as a response to reperfusion but not ischemia. The hallmark of apoptosis, nucleosomal ladders of DNA fragments (approximately 200 base pairs), was detected in ischemic/reperfused rabbit myocardial tissue but not in normal or ischemic-only rabbit hearts. Granulocytopenia did not prevent nucleosomal DNA cleavage. In situ nick end labeling demonstrated DNA fragmentation predominantly in myocytes. The pattern of nuclear chromatin condensation was distinctly different in reperfused than in persistently ischemic tissue by transmission electron microscopy. Apoptosis may be a specific feature of reperfusion injury in cardiac myocytes, leading to late cell death.

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Katharine O. Burleson

Papers

Reperfusion injury induces apoptosis in rabbit cardiomyocytes.