What is Apoptosis?

We read a lot in scientific journals about apoptosis and its implications in disease treatment but what exactly does it mean and what is its significance.

We'll try and explain.

Apoptosis

Apoptosis is programmed cell death. It is a normal process in the development and health of multicellular organisms. 

During apoptosis cells die in a controlled and regulated fashion. This is distinct from necrosis in which uncontrolled cell death leads to lysis of cells, inflammatory responses and, potentially, to serious health problems. 

Apoptosis, by contrast, is a process in which cells play an active role in their own death (which is why apoptosis is often referred to as cell suicide).

Cells will receive chemical specific signals instructing the cells to undergo apoptosis and a number of distinctive changes occur in the cell. A family of proteins known as caspases are typically activated in the early stages of apoptosis. These proteins breakdown or cleave key cellular components that are required for normal cellular function including structural proteins in the cytoskeleton and nuclear proteins such as DNA repair enzymes. The caspases can also activate other degradative enzymes such as DNases, which begin to cleave the DNA in the nucleus.

So why is it important?

The combination of apoptosis and cell proliferation is responsible for shaping tissues and organs in developing embryos. For example the apoptosis of cells located in-between the toes allows for their separation.

What is its implication in disease?

Apoptosis is an important process of the immune system. T lymphocytes are cells of the immune system and destroy infected cells in the body. Any ineffective or self-reactive T-cells are tested by the systems in the body and are removed through the induction of apoptosis.

"Cancer is a disease that is often characterized by too little apoptosis"

Cancer cells can have mutations that have permitted them to ignore normal cellular signals regulating their growth. 

"Under normal circumstances damaged cells will undergo apoptosis"

Cancer cells mutations have, however, prevented their cells from undergoing normal processes like apoptosis. There is no check on the cellular proliferation and so the disease can progress to the formation of tumors.  Understanding how apoptosis is regulated in cancer is therefore of major interest in the development of treatments for this disease.

Other diseases have too much apoptosis going on.  In the neurodegenerative diseases Parkinson's and Alzheimer's apoptosis can account for much of the cell death and the progressive loss of neurons.

In the progression of many auto-immune diseases apotosis is said to be key too. Rheumatoid arthritis is characterised by excessive proliferation of synovial cells and is thought to be due, in part, to the resistance of these cells to apoptotic stimuli.

Sources: St George's, University of London , Principals of Cellular and Molecular Immunology (Austyn & Wood)