Microautophagy
From Wikipedia, the free encyclopedia
Microautophagy is one of the three common forms of autophagic pathway, but unlike macroautophagy and chaperone-mediated autophagy, it is mediated—in mammals by lysosomal action or in plants and fungi by vacuolar action—by direct engulfment of the cytoplasmic cargo. Cytoplasmic material is trapped in the lysosome/vacuole by a random process of membrane invagination.
The microautophagic pathway is especially important for survival of cells under conditions of starvation, nitrogen deprivation, or after treatment with rapamycin. Generally a non-selective process, there are three special cases of a selective microautophagic pathway: micropexophagy, piecemeal microautophagy of the nucleus, and micromitophagy, all which are activated only under a specific conditions.[1]
Microautophagy together with macroautophagy is necessary for nutrient recycling under starvation. Microautophagy due to degradation of lipids incorporated into vesicles regulates the composition of lysosomal/vacuolar membrane.[1] Microautophagic pathway functions also as one of the mechanism of glycogen delivery into the lysosomes.[2] This autophagic pathway engulfs multivesicular bodies formed after endocytosis therefore it plays role in membrane proteins turnover.[3] Microautophagy is also connected with organellar size maintenance, composition of biological membranes, cell survival under nitrogen restriction, and the transition pathway from starvation-induced growth arrest to logarithmic growth.[1]