Apoptosis

Lore & Background

Apoptosis is a highly regulated form of programmed cell death that occurs in multicellular organisms and some single-celled eukaryotes like yeast. The process is characterized by a distinct sequence of morphological changes: the cell shrinks, its membrane develops blebs, the nucleus fragments, and chromatin condenses. Internally, the cell’s DNA is fragmented and messenger RNA decays. These events culminate in the cell breaking apart into small, membrane-bound fragments called apoptotic bodies. Unlike necrosis, which results from acute injury and spills cellular contents, apoptosis produces these tidy fragments that are quickly engulfed and removed by phagocytes, preventing damage to neighboring cells. The process is irreversible once initiated and is therefore tightly controlled. It can be triggered through two main pathways: the intrinsic pathway, where the cell senses internal stress and self-destructs, and the extrinsic pathway, where signals from other cells instruct it to die. Both pathways activate a family of proteases called caspases; initiator caspases first activate executioner caspases, which then indiscriminately degrade proteins to kill the cell. In the human body, apoptosis is a constant, massive event: an average adult loses 50 to 70 billion cells daily, while a child between 8 and 14 years loses 20 to 30 billion cells each day. This process is essential for normal development, such as the separation of fingers and toes in an embryo, where genetically determined apoptosis removes cells between the digits. Defects in apoptosis are linked to disease: excessive apoptosis leads to atrophy, while insufficient apoptosis can result in uncontrolled cell proliferation, as seen in cancer. Key molecular players include Fas receptors and caspases, which promote apoptosis, and certain Bcl-2 family proteins, which inhibit it. The term itself was reintroduced in 1972 by researchers John Kerr, Alastair Currie, and Andrew Wyllie, following a suggestion by Greek professor James Cormack. In Greek, “apoptosis” means the “falling off” of petals or leaves, and Hippocrates used it to describe the falling off of bones, while Galen applied it to the dropping of scabs. The discovery of the BCL2 gene in 1988, which encodes a protein that inhibits cell death, helped link apoptosis to human disease, particularly cancer. The 2002 Nobel Prize in Medicine was awarded to Sydn

Reader's Guide

Apoptosis is a fundamental biological process that removes unwanted or damaged cells in a controlled manner, preventing inflammation and maintaining tissue homeostasis. The average adult human loses 50 to 70 billion cells each day to apoptosis, while a child between 8 and 14 years old loses 20 to 30 billion cells daily. The process is initiated through either the intrinsic pathway (triggered by cell stress) or the extrinsic pathway (triggered by signals from other cells), both of which activate caspases that degrade proteins and kill the cell. Defects in apoptosis can lead to disease: excessive apoptosis causes atrophy, while insufficient apoptosis results in uncontrolled cell proliferation, such as cancer. The discovery of genes controlling apoptosis in the nematode C. Robert Horvitz, and John Sulston. The term 'apoptosis' comes from Greek, meaning 'falling off' of leaves from a tree, and was reintroduced for medical use by James Cormack.

Did You Know?

• The average adult human loses 50 to 70 billion cells each day to apoptosis.
• Apoptosis produces cell fragments called apoptotic bodies that phagocytes engulf and remove before cell contents can damage surrounding cells.
• The term 'apoptosis' was coined by John Kerr, Alastair Currie, and Andrew Wyllie in 1972, with James Cormack suggesting the Greek etymology.