During nutrient starvation, increased levels of autophagy lead to the breakdown of non-vital components and the release of nutrients, ensuring that vital processes can continue. Mutant yeast cells that have a reduced autophagic capability rapidly perish in nutrition-deficient conditions.
A gene known as ''Atg7'' has been implicated in nutrient-mediated autophagy, as mice studies have shown that starvation-induced autophagy was impaired in ''Atg7''-deficient mice.
Autophagy plays a role in the destruction of some bacteria within the cell. Intracellular pathogens such as ''Mycobacterium tuberculosis'' persist within cells and block the normal actions taken by the cell to rid itself of it. Stimulating autophagy in infected cells overcomes the block and helps to rid the cell of pathogens.
In addition to "simple" breakdown of pathogens, it has also been shown that at least in some cell types (plasmacytoid dendritic cells) autophagy play a role in detection of virus by the so-called pattern recognition receptors (PRR), which are part of the innate immune system.
The virus (Vesicular stomatitis virus) is believed to be taken up by the autophagosome from the cytosol and translocated to the endosomes where detection takes place by a member of the PRRs called toll-like receptor 7, detecting single-stranded RNA.
Following activation of the toll-like receptor, intracellular signalling cascades are initiated, leading to induction of interferon, among other anti-viral cytokines.
A subset of viruses and bacteria subvert the autophagic pathway to promote their own replication. (http://www.plosbiology.org/article/info:doi/10.1371/journal.pbio.0030156)
Autophagy degrades damaged organelles, cell membranes and proteins, and the failure of autophagy is thought to be one of the main reasons for the accumulation of cell damage and aging.
Programmed cell death
It has been proposed that autophagy resulting in the total destruction of the cell is one of several types of programmed cell death; yet, no conclusive evidence exists for such a process. Nevertheless, observations that cells possessing autophagic features in areas undergoing programmed cell death have led to the coining of the phrase ''autophagic cell death'' (also known as ''cytoplasmic cell death'' or ''type II cell death'').
Studies of the metamorphosis of insects have shown cells undergoing a form of programmed cell death that appears distinct from other forms; these have been proposed as examples of autophagic cell death.
It is not known whether autophagic activity in dying cells actually causes cell death or whether it simply occurs as a process alongside it. In many neurological diseases, in certain neuronal cell death pathways and after neuronal injury, there are increased numbers of ''autophagosomes''.
A causative relationship between autophagy and cell death has not been established. It is unclear whether the increase in autophagosomes indicates an increase in autophagic activity or decreased autophagosome-lysosome fusion.
Certain diets utilize a form of autophagia. The Atkins Diet relies heavily on ketosis as a method of reducing body fat, which, in itself, could be considered a form of cellular autophagia.
This article is licensed under the Creative Commons Attribution-ShareAlike License.
It uses material from the Wikipedia article on
All material adapted used from Wikipedia is available under the terms of the
Creative Commons Attribution-ShareAlike License.
Wikipedia® itself is a registered trademark of the Wikimedia Foundation, Inc.