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Sharon - Symposium Antioxidant and Redox Regulation of...

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Symposium: Antioxidant and Redox Regulation of Cellular Signaling Apoptosis and exercise SHARON PHANEUF and CHRISTIAAN LEEUWENBURGH Biochemistry of Aging Laboratory, Center for Exercise Science, College of Health and Human Performance, University of Florida, Gainesville, FL 32611 ABSTRACT PHANEUF, S., and C. LEEUWENBURGH. Apoptosis and exercise. Med. Sci. Sports Exerc. , Vol. 33, No. 3, 2001, pp. 393–396. This brief review will discuss an exciting new area in exercise science, namely the role of apoptosis or programmed cell death in exercise. Apoptotic cell death differs morphologically and biochemically from necrotic cell death, although both appear to occur after exercise. Accelerated apoptosis has been documented to occur in a variety of disease states, such as AIDS and Alzheimer’s disease, as well as in the aging heart. In striking contrast, failure to activate this genetically regulated cell death may result in cancer and certain viral infections. We will discuss factors that may activate apoptosis during and after exercise and the importance of cell turnover after exercise. We will also discuss differences in apoptosis between lymphocyte and skeletal muscle cells. We speculate that exercise- induced apoptosis is a normal regulatory process that serves to remove certain damaged cells without a pronounced inflammatory response, thus ensuring optimal body function. A poptosis is a highly regulated form of cell death that is characterized by specific morphological, bio- chemical, and molecular events (29). It is essential for the normal development of multicellular organisms (11) and is involved in cell turnover in healthy adult tissues (8). Apoptosis also plays a critical role in removing unwanted and potentially dangerous cells, such as tumor cells (32) and cells infected by viruses (31). Disorders such as cancer, AIDS, Alzheimer’s disease, and rheumatoid arthritis are thought to be, at least partially, a result of aberrant regula- tion of apoptosis (11). Recently, apoptosis has gained the interest of many exercise scientists because, in addition to necrotic cell death, evidence indicates that apoptotic cell death also occurs with exercise. There are distinctive differences between necrotic and apoptotic cell death that can be observed and measured. Necrosis occurs when a cell suffers lethal injury and is characterized by swelling, rupturing of the cell, and inflam- mation. This type of injury is typically seen with eccentric exercise and is characterized by delayed-onset muscle sore- ness (8). Apoptosis, however, is a normal, genetically con- trolled event characterized by cell shrinkage, membrane blebbing, and chromatin condensation. Additionally, activa- tion of endogenous endonucleases and caspases (ICE-like proteases named after interleukin-1 b converting enzyme) results in irreversible DNA fragmentation along with frag- mentation of the cell into membrane-bound apoptotic bod- ies. These apoptotic bodies are subsequently phagocytosed by surrounding cells or macrophages (15,30). An often-used
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