“The weight of cells which we kill off every year is equivalent to the weight of our body.” Nicole Le Douarin
Indeed, every living cell contains a genetic code for its programmed death which, if it is initiated, causes, with the utmost discretion, the cell’s departure. This furtive death is referred to by the term “apoptosis” (in Greek, this refers to falling leaves).
Cells which die by apoptosis begin by cutting contact from neighboring cells, then undergo major internal modifications: the content of their nucleus fragments itself while their cytoplasm is divided into small pieces: apoptotic bodies, quickly absorbed by neighboring cells. Death by apoptosis is thus quick and generally does not cause any inflammation or scarring. This is why it has gone unnoticed for so long.
The decision to activate or repress apoptosis is controlled by certain genes, as well as being under the influence of mitochondria; they participate by discharging part of their contents into the cytoplasm: an enzyme, Cytochrome C, and a factor, AIF (Apoptosis Inducing Factor).
Apoptosis is an essential element for the proper functioning of organisms, and in particular of homeostasis. Entire regions of our organism undergo rapid regeneration: our skin, the inner lining of our intestines and our blood, for example. The remains of dead cells are reused to build new tissue. We thus constantly fuel our bodies with part of ourselves.
The regulation of cellular life and death is therefore crucial for the functional balance of our organism. It is part of the “social” life of the cells which form it. These discoveries have allowed us to understand the mechanisms responsible for a number of diseases. We now know for example tat that acute liver failure, caused by viruses or alcohol, is due to the large-scale death of liver cells.
Apoptosis and Cancer
The abnormal blocking of programmed cell death constitutes a decisive step in the transformation of a cell into a cancerous cell. By disrupting the proliferation signaling pathways in their favor, cancerous cells can benefit from a dual advantage: ample proliferation and improved resistance to cell death. Protein p53 is able to induce apoptosis in cells with too many abnormalities or too much stress. Consequently the inactivation of p53 gives cancerous cells a powerful advantage for survival. Other proteins which initiate apoptosis are inactivated or their expression diminished in cancerous cells in order to increase their ability to survive the stress and damage which they are constantly undergoing.