Autophagy: fasting to be healthy

Abstract

Autophagy is an intracellular degradation system that delivers cytoplasmic constituents to the lysosome. Despite its simplicity, recent progress has demonstrated that autophagy plays a wide variety of physiological and pathophysiological roles, which are sometimes complex. Autophagy consists of several sequential steps²sequestration, transport to lysosomes, degradation, and utilization of degradation products²and each step may exert different function. This process is quite distinct from endocytosis-mediated lysosomal degradation of extracellular and plasma membrane proteins. There are three types of autophagy²macroautophagy, microautophagy, and chaperone-mediated autophagy²and the term ³autophagy´ usually indicates macroautophagy unless otherwise specified. Autophagy is mediated by a unique organelle called the autophagosome. As autophagosomes engulf a portion of cytoplasm, autophagy is generally thought to be a nonselective degradation system. This feature is in marked contrast to the ubiquitin±proteasome system, which specifically recognizes only ubiquitinated proteins for proteasomal degradation. It is therefore reasonable to assume that the ubiquitin±proteasome system has numerous specific functions because it can selectively degrade thousands of substrates.