2012-11-04 11:54:35
A balance of cell life and death is essential for health
Although we generally do not like to admit it, death is inherent to life. One cannot be conceived without the other. The game of life and death, in fact, happens every day, every hour, every minute in our bodies, and its correct balance is essential to enjoy good health.
To date, three types of cell death have been described that occur by different molecular mechanisms. These are autophagy, apoptosis and necrosis. Autophagy, as its name suggests, is a form of self-destruction by self-digestion. In the absence of adequate nutrients, perhaps in an attempt to survive, the cell destroys its own components, digesting them in special vesicles called lysosomes. It is the equivalent of us, induced by hunger, eating some part of our bodies, but in the end dying anyway. It’s horrible, but cells don’t have feelings.
Apoptosis is a cell death that is triggered by certain stimuli, among which, for example, damage to DNA can be mentioned. If the cell detects that the damage cannot be repaired, it triggers a molecular suicide process, which can also be produced by a variety of external factors. Among these factors is virus infection. Infected cells are induced to commit suicide by immune cells, which prevents the virus from reproducing inside them and allowing it to continue infecting other healthy cells.
Necrosis is a less sophisticated type of death than the previous ones, and is produced by the irreparable rupture of the cell membrane, which leads to the loss of proteins, ions, etc. from the cytoplasm to the external environment and the consequent disorganization or arrest of the processes that maintain life. Necrosis can occur, for example, if we give ourselves a strong blow that damages some of our cells.
FAGOPTOSIS
Recently, a new cell death process has been described that, unlike the previous ones, does not depend on mechanisms of the cell itself. This process leads to death by ingestion and digestion by “eating cells,” called phagocytes, which is why it has been called phagoptosis.
The process of cellular ingestion and digestion, called phagocytosis, has been known since the end of the 19th century. Phagocytosis is essential in the fight against bacterial infections, since these are mainly eliminated by their ingestion and digestion by the phagocytic cells of the immune system, mainly the so-called macrophages and neutrophils.
Until recently, it was thought that phagocytosis was limited to antibacterial fighting and that the body’s cells could not be phagocytosed under normal conditions. However, this idea has proven false. Today we know that all cells are at risk of being eaten.
In fact, whether a cell is eaten or not depends on molecular signals that it presents on its surface. In this sense, there are two types of signals: “eat me” signals and “don’t eat me” signals. “Eat me” signals consist of molecules on the surface of the cell that signal to macrophages, the main phagocytic cells, that the cell is unhealthy. These signals appear when the cell cannot generate enough energy to maintain life processes.
DO NOT EAT ME
But in addition to the “eat me” signals we have the “don’t-eat-me” signals. These signals are made up of molecules also located on the cell surface that indicate to macrophages that the cell is in good health. A very important “don’t eat me” signal is generated by a molecule located on the surface of red blood cells. Two million red blood cells are produced every second in our bodies. After 120 days of life, old red blood cells must be eliminated by phagocytosis at the same speed of two million per second, which maintains the necessary balance. Phagocytosis is induced by the loss of the “don’t-eat-me” molecule in old red blood cells, allowing them to be phagocytosed and digested by macrophages.
Therefore, whether a cell is phagocytosed or not depends on the correct balance of forces between the “eat me” signals and the “don’t eat me” signals. If this balance is broken, it can cause severe illnesses. For example, inadequate phagocytosis of healthy blood cells generates a disease called Hemophagocytosis.
Surprisingly, it has also been proven that inappropriate phagocytosis of neurons is possible. These cells, of which we always have less than we would like, can sometimes be phagocytosed by the so-called glial cells of the brain. Incorrect neuronal phagocytosis has been proven to be involved in the development of neurodegenerative diseases, such as Alzheimer’s or Parkinson’s.
Another disease in which incorrect phagocytosis can play an important role is cancer, in this case not due to an increase in it, but due to its inhibition. It has been proven that most tumor cells show high concentrations of the “don’t eat me” molecules of red blood cells on their surface, which inhibits their phagocytosis. In laboratory animals, it has been possible to stimulate the phagocytosis of tumor cells by blocking said “don’t-eat-me” molecule, which has resulted in less tumor growth.
Every day, science continues to produce new knowledge, often surprising and unsuspected, which always allows us to imagine its use to improve the life and health of everyone.
WORKS BY JORGE LABORDA.
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