![]() ![]() In some cases it’s the type of stimuli and/or the degree of stimuli that determines if cells die by apoptosis or necrosis. There is also the issue of distinguishing apoptosis from necrosis, two processes that can occur independently, sequentially, as well as simultaneously ( Hirsch, 1997 Zeiss, 2003). Other cells have a default death pathway that must be blocked by a survival factor such as a hormone or growth factor. Some cells express Fas or TNF receptors that can lead to apoptosis via ligand binding and protein cross-linking. Some hormones, such as corticosteroids, may lead to apoptotic death in some cells (e.g., thymocytes) although other cells are unaffected or even stimulated. Irradiation or drugs used for cancer chemotherapy results in DNA damage in some cells, which can lead to apoptotic death through a p53-dependent pathway. Although there are a wide variety of stimuli and conditions, both physiological and pathological, that can trigger apoptosis, not all cells will necessarily die in response to the same stimulus. ![]() Apoptosis also occurs as a defense mechanism such as in immune reactions or when cells are damaged by disease or noxious agents ( Norbury and Hickson, 2001). However, it is important to note that other forms of programmed cell death have been described and other forms of programmed cell death may yet be discovered ( Formigli et al., 2000 Sperandio et al., 2000 Debnath et al., 2005).Īpoptosis occurs normally during development and aging and as a homeostatic mechanism to maintain cell populations in tissues. Apoptosis has since been recognized and accepted as a distinctive and important mode of “programmed” cell death, which involves the genetically determined elimination of cells. In this organism 1090 somatic cells are generated in the formation of the adult worm, of which 131 of these cells undergo apoptosis or “programmed cell death.” These 131 cells die at particular points during the development process, which is essentially invariant between worms, demonstrating the remarkable accuracy and control in this system. Our understanding of the mechanisms involved in the process of apoptosis in mammalian cells transpired from the investigation of programmed cell death that occurs during the development of the nematode Caenorhabditis elegans ( Horvitz, 1999). The term apoptosis (a-po-toe-sis) was first used in a now-classic paper by Kerr, Wyllie, and Currie in 1972 to describe a morphologically distinct form of cell death, although certain components of the apoptosis concept had been explicitly described many years previously ( Kerr et al., 1972 Paweletz, 2001 Kerr, 2002). The goal of this review is to provide a general overview of current knowledge on the process of apoptosis including morphology, biochemistry, the role of apoptosis in health and disease, detection methods, as well as a discussion of potential alternative forms of apoptosis. Although many of the key apoptotic proteins have been identified, the molecular mechanisms of action or inaction of these proteins remain to be elucidated. To that end, the field of apoptosis research has been moving forward at an alarmingly rapid rate. Therefore, research continues to focus on the elucidation and analysis of the cell cycle machinery and signaling pathways that control cell cycle arrest and apoptosis. The ability to modulate the life or death of a cell is recognized for its immense therapeutic potential. ![]() Inappropriate apoptosis (either too little or too much) is a factor in many human conditions including neurodegenerative diseases, ischemic damage, autoimmune disorders and many types of cancer. Apoptosis is considered a vital component of various processes including normal cell turnover, proper development and functioning of the immune system, hormone-dependent atrophy, embryonic development and chemical-induced cell death. The process of programmed cell death, or apoptosis, is generally characterized by distinct morphological characteristics and energy-dependent biochemical mechanisms. ![]()
0 Comments
Leave a Reply. |
Details
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |