What is Apoptosis? And Why it is important? Give Some Examples

We explain what apoptosis is, what function it has and what its phases are. In addition, neuronal apoptosis and differences with necrosis.

1. What is apoptosis?

Apoptosis is the mechanism of cell self-destruction that allows the body to control the development and growth of cells to rule out those with abnormalities or dangerous defects. This process of programmed cell death operates through genetically controlled cell signals and has an important preventive function in the body .

This process can occur in the body in two ways:

• Negative induction : By isolating the cell destined to die, that is, removing growth factors, losing some type of suppressive activity or cutting off its contact with the cells that surround it.
• Positive induction : By activating proteins or other organic compounds that trigger cell death, or even the reception of conflicting signals by the cell marked to die.

In both cases, apoptosis occurs in orderly and methodical , non-chaotic, following strict guidelines of cellular suicide, and leaving the immune system to deal with the “remains” of the removed cells.

It is, then, a natural process that is part of the mechanisms of protection and renewal of the organism . It usually does not represent significant damage to any cellular system, since, if necessary, young cells of the same type as those removed are occurring at the same rate.

2. Apoptosis function

Apoptosis is a vital planning role of the organism, which fulfills the following functions:

• Get rid of abnormal cells  that have been born atrophied, that have abnormalities or that have been infected with viruses or have suffered damage to their DNA .
• Eliminate some old and defective cells and replace them with new cells that fulfill the same function, keeping the body healthy. This is particularly important in the case of the body’s defense cells, which can develop the tendency to attack healthy tissues by mistake.
• Proceed with the formation of the organism during key stages of its development, such as various embryonic stages in which the tissue must be lost or separated. Thus, for example, the fingers are formed, which are initially joined by a membrane: the cells of the latter must be programmed to die and separate each member. It is also what happens with the uterine endometrium during menstruation.

3. Phases of apoptosis

Apoptosis has two recognizable phases, which are:

• Decision phase . The apoptosis process begins with the reception by the determined cells of a death signal, that is, an instruction for suicide. Then she must “decide” if she survives or begins the processes of death. For this, mitochondria are fundamental organelles: they generate multiproteic complexes that release intramitochondrial content such as cytochrome C, certain hormones of the caspases family and other apoptosis triggers.
• Implementation phase . Once the cell has “decided” to die, a process of degradation of chromatin proteins begins inside, starting everything secreted in the previous phase by mitochondria. This implies a series of ordered biochemical reactions , which culminate with a cellular autolysis, that is, with the cell disintegrating itself, and leaving behind molecular residues that the immune system will take over.

4. Apoptosis and necrosis

Apoptosis and necrosis should not be confused. The first is a natural, healthy and orderly process. On the contrary, necrosis is a case of unscheduled and unwanted cell death

The fundamental difference is that necrosis is a chaotic, accidental and irreversible process , in which the cells of some tissue begin to die massively.

Necrosis can occur due to various causes : uncontrolled bacterial infections , interruption of blood flow to certain tissues (vascular accidents) or the action of toxins such as poisons, lethal substances or high-level ionizing radiation.

It is also common when a person’s limbs have been exposed to too intense cold. These cases often lead to amputation, since necrosis spreads through the body and can cause a general septic reaction (generalized infection).

5. Neuronal apoptosis

Nervous system and brain cells , called neurons , also go through the natural apoptosis process , in which old neurons are supplanted by young women. However, the generation of this type of cells in the body is much slower and more sporadic than the rest of the body’s ordinary cells.

Consequently, over time, our nervous system deteriorates , causing loss of brain efficiency, late nervous reaction or even loss of certain functions, as is very evident in advanced old age. In fact, many mental ailments that usually afflict people in old age, such as senile dementia, depend on this process.

There are other pathologies, such as epilepsy or Alzheimer’s disease, in which this process is combined with a malfunction of the glial cells, responsible for absorbing and discarding the remains of dead neurons, preventing them from causing problems.

Thus, in these diseases, waste accumulates and interferes with the regular functioning of the brain, causing the loss of brain mass or leaving scars and lesions that contribute to the perpetuation of the problem.

Scientific experimentation currently devotes great efforts to apoptosis, foreseeing the eventual cure of these and other related ailments, such as cancer.

6. Apoptosis and cancer

Various internal or external causes can cause the appearance of defective cells, usually carrying a damaged DNA. The cell attempts to repair the damage caused by the damaged DNA or, if impossible, sentences itself to programmed death . Thus, the organism prevents defective cells from reproducing, spreading genetic failure.

In the event that the planned mechanisms fail, the same immune system can exert pressure to force the cell to perform apoptosis. If the process is successful, the proliferation of possible cancer cells is prevented, for example.

The problem is that many precancerous cells do not respond to internal or external apoptosis signals , thus proceeding to divide without control and generate tumors, masses of crazed cells reproducing without stopping.

For this reason, many current studies on carcinogenic matter focus on the understanding of why cancer cells block their natural apoptosis functions. A possible cure would be to intervene externally to restart the process , without the need to apply invasive and highly destructive therapies such as radiotherapy or chemotherapy.