Autophagy refers to the process in cells with which they degrade and use their own ingredients. This ranges from misfolded proteins to whole cell organelles. A related process is the phagocytosis, a form of endocytosis to be absorbed and utilized in the substances from outside the cell.
The Japanese scientist Yoshinori Ōsumi was awarded the 2016 Nobel Prize in Physiology or Medicine for his discoveries in the field. The autophagy was first described in 1962 by Keith R. Porter and his student Thomas Ashford. The reduction and reuse of cellular constituents in the lysosome was described in 1963. The word autophagy is derived from the Greek words automatic and phagy meaning the food. Autophagy is a normal physiological treatment in the organism that is responsible for the destruction of the cells in the body.
It maintains homeostasis or normal operation by protein degradation and turnover of organelles destroyed for new cell formation cells. The Cellular stress is caused when there is deprivation of nutrients and/or growth factors. So Autophagy can provide a source of elementary particles and alternates of intracellular substrates that can generate energy to allow the continued survival of the cells.
Autophagy also kills the cells under certain conditions. These are form of programmed cell death (PCD) and are called autophagic cell death. Programmed cell death is commonly called apoptosis. Autophagy is defined nonapoptotic a programmed death of cells with different pathways and mediators of apoptosis.
Autophagy mainly maintains a balance between the production of cellular components and starts harmful or useless organelle and other cellular components. There are some important routes that include degrading proteasome which includes the subdivision of most short-lived protein.
Autophagy allows cells to survive the stress from the external environment such as nutrient deprivation, and also allows them to resist the domestic efforts as capitalization of organelles and harmful pathogen or infectious organism invasion. Autophagy is seen in all eukaryotic systems including fungi, plants, slime mold, nematodes, fruit flies and insects, rodents (laboratory mice and rats), humans.
In insects, the process used to convert the larval tissue in the adult form . Here, during the pupation the fabric melted and rearranged to the adult animal.
There are two signals that trigger this process: Lack of nutrients leads to the degradation of non-essential cellular constituents. Thus on vital processes are still energized. Oversupply of nutrients can trigger autophagy. Then new organelles are formed with the energy surplus and old reused.
Autophagy may also cause the death of cells. It is part of programmed cell death (apoptosis, autophagic cell death). It thus regulates the growth of multicellular organisms and colonies (yeast). Autophagy also allows the intracellular degradation by viruses , bacteria or foreign proteins which have entered the cell. It is used with cutting operations and the immune response , because then the carried antigen presentation via MHC I and II.