Monday, March 06, 2006

What is the relationship between cancer and aging? (part 1)

Life is possible because the millions of cells that compose our bodies agree to perform their roles. They do what they have to do at the precise place, and only at the right moment. Some important tasks that have to be precisely regulated are:

  • Cell division: If a cell divides when it is not required, it may form an imbalance, leading to physical problems (as with solid tumours), metabolic changes (as in cachexia), or functional disturbances (as in leukaemias).
  • Cell migration: If a cell migrates to a place where it should not be, it is almost guaranteed that there will appear disturbances similar to the ones produced by uncontrolled cell division. Moreover, cells that fail to control both cell division and migration usually lead to metastatic tumours.
  • Cell differentiation: If a cell changes its differentiation when it should not do it, it will not perform its intended function. Besides its lack of functionality, its new physiological state may itself lead to further problems.

As we live, some of our cells divide, while others perform their tasks in a non dividing state. Both groups of cells, dividing and not dividing, are exposed to aggressions through their life. Some examples of these damaging influences are exogenous toxins, reactive molecules generated by the body metabolism, and cosmic rays. Our body has many protective systems to cope with these attacks. However, as powerful as those systems are, in some cases a cell does not fully revert to its original state. Those altered cells are a potential security risk for the body. If the damages are located in processes that control any of the tasks indicated above, the cell is getting closer to a malignant state. There are two ways to stop this dangerous progression: cell senescence and apoptosis. Cell senescence makes a cell unable to divide, protecting the organism from cancer. Apoptosis induces the cell to commit suicide, protecting the organism from what may happen if the cell stays alive.

As we age, more and more cells enter apoptosis to protect the organism, and more and more cells get senescent. Senescent cells are less functional than normal cells, and do not contribute to the pool of dividing progenitors. The tissues have less and less cells that work at peak efficiency, so the function degrades progressively. The regeneration capacity decreases with age. Our defences decrease with age. In the end, any random strike can blow us away.

Cancer cells are cells that escape controls. Senescent cells are cells that do not escape controls, but who are not healthy enough to divide and work as young cells. The only way to have a long and healthy life is to have good repair systems to keep every cell in good condition for as long as possible, and to have good premalignant cell removal systems (apoptosis and senescence).


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