Programmed Cell Death

Programmed cell death, sometimes known as apoptosis, is when an unwanted cell deliberately commits suicide in a multicellular organism. This often comes from the advantages to be obtained from an organism's life cycle, not as a result of acute tissue injury.

In evolutionary terms, it has long been thought that bacteria had been originally incorporated as endosymbionts, living inside larger eukaryotic cells. The theory was championed by Lynn Margulis in 1967 and much of the evidence is based on the fact that mitochondria have their own DNA. There had also been studies of programmed cell deaths in plant tissue, with Jannecke Balk and Christopher J. Leaver of the Department of Plant Sciences at the University of Oxford undertaking research into the mitochondrial genome of the cells of sunflowers; and other work on the programmed cell death in slime mold. It was not long before researchers came to see elements of the work conducted into programmed cell death as being potentially important in medical research into diseases facing humans. From the early 20th century, embryologists had become familiar with the process of programmed cell death with embryos sacrificing some of their cells in order to create what is to be the final form of the organism. In 1972, research by John F. R. Kerr, Andrew H. Wyllie, and Alastair Currie recognized this broader significance in healthcare, and used the term apoptosis, derived from the Greek for “falling off,” in a similar manner to trees shedding their leaves in the fall.

Their research showed that programmed cell death in humans is a normal physiological process that is used to offset cell proliferation. It can result from both internal and external stimuli, with a cell shriveling and then pulling away from other cells. A formation like a bubble then appears on the surface of the cell, and the chromosomal DNA and protein in the nucleus of the cell condenses. Soon afterward, the cell either breaks into small pieces, is consumed by other cells, or is entirely engulfed by “scavenger cells.” This happens regularly for women during the menstrual cycle with cells lining the uterine wall undergoing “programmed death.”

Some of the major work in the field of programmed cell death is in the use of genes to regulate tissue or organ development, and thus, the possible ability of human bodies, after suitable treatment, to program the death of cells that are not healthy, especially those that form cancerous tumors. Furthermore, it is believed that the concept of programmed cell death is how the human immunodeficiency virus (HIV) virus is involved in programming the “deaths” of the healthy white blood cells known as T lymphocytes. The research in the field of gene regulation resulted in the South African-born biologist Sydney Brenner, the British biologist John E. Sulston, and the American biologist H. Robert Horvitz sharing the Nobel Prize for Physiology or Medicine in 2002.