Autophagy (自噬)

Autophagy is a conserved cellular degradation and recycling process in the lysosome. In mammalian cells, there are three primary types of autophagy: microautophagy, macroautophagy, and chaperone-mediated autophagy (CMA). Microphagy captures cargoes by means of invaginations or protrusions of the lysosomal membrane directly, CMA uses chaperones to identify cargo proteins and then unfolds and transfers them into the lysosomal, while macroautophagy sequesters cargo by autophagosomes-de novo synthesized of double-membrane vesicles-and subsequently transport it to the lysosome.

Macroautophagy is the best studied and it occurs at a low level constitutively and can also be further induced under stress conditions, such as nutrient or energy starvation with a salient feature of autophagy protein degradation. Stress-induced macrophagy plays an important role in protein catabolism with another key protein degradation pathway, the ubiquitin–proteasome system (UPS).

As the study progressed, autophagy gains its importance under basal, nutrient-rich conditions, and is now recognized as a critical housekeeping pathway in catabolism of diverse cellular constituents, such as protein aggregates (aggrephagy), lipid droplets (lipophagy), iron complex (Ferritinophagy) and carbohydrate. Except for macromolecules, autophagy can also target several organelles and structures, such as mitochondria (mitophagy), peroxisome (pexophagy), endoplasmic reticulum (reticulophagy or ER-phagy), ribosome (ribophagy), spermatozoon-inherited organelles following fertilization (allophagy), secretory granules within pancreatic cells (zymophagy) and intracellular pathogens (xenophagy).

Autophagy and its dysfunction are associated with a variety of human pathologies, including ageing, cancer, neurodegenerative disease, heart disease and metabolic diseases, such as diabetes. Plenty of drugs and natural products are involved in autophagy modulation through multiple signaling pathways. Small molecules that can regulate autophagy seem to have great potential to intervene such diseases in animal models or clinical courses.