Do Tumor-Suppressors Promote Ageing? - Page 2© David Olle
Page 2
Jun 1, 2003
The relationship of apoptosis and cell senescence to ageing
Apoptosis is essential for the maintenance of renewable tissues in adults, such as skin, muscle and bone. The process eliminates damaged and dysfunctional cells before they can become cancerous. The replacement of cells lost in renewable tissues is dependent upon the presence and activity of stem cells. Stem cells are undifferentiated precursor cells that give rise to replacement cells. Stem cells can become depleted in adult tissues if there has been a lot of demand for replacement cells. When there is considerable unrestored cell loss, the tissue can exhibit loss of function characteristic of ageing. Tyner and colleagues at the Baylor College of Medicine have demonstrated this phenomenon experimentally. Mice with a hyperactive p53 gene developed far fewer tumors than developed in their normal counterparts, but had a 20% reduced lifespan. The mutant mice appeared normal until one year of age and then rapidly developed the physical appearances characteristic of ageing. Senescent cells do not divide, and gradually deteriorate, frequently resulting in the secretion of degradative enzymes, cytokines and growth factors. These changes contribute to ageing by actively disrupting the integrity, function and homeostasis (steady-state condition) of the tissues where they accumulate. Paradoxically, these changes can eventually give rise to the development of cancer. References 1. Campisi, J. Cancer and Ageing: Rival Demons? Nature Reviews Cancer, Vol. 3, No. 5, pp. 339-349 (May 2003) 2. Tyner, S. et. al. P53 Mutant Mice that Display Early Ageing-Associated Phenotypes. Nature, Vol 415, pp.45-53 (2002)
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