Figure 1.

The process of exosome formation. Firstly, the cytoplasmic membrane invaginates, wrapping the extracellular components and cytosolic proteins together to form early-sorting endosomes (ESEs). The formation of ESEs consists of two pathways: clathrin-mediated endocytosis (CME) and clathrin-independent endocytosis (CIE). CME is mediated by a variety of molecules, including clathrin proteins, constriction, and release processes, and eventually, clathrin proteins are shed to form ESEs. CIE takes two forms: the caveola-dependent endocytosis pathway, where plasma membranes are trapped in lipid rafts rich in molecules such as GPI-anchored proteins, cholesterol, and other molecules to form ESEs under the guidance of caveolins and flotillin, and the Arf6-dependent endocytosis pathway, where Arf6 activates phosphatidylinositol kinase PI5K to produce plasma membrane phosphatidylinositol PI(4,5)P₂, which in turn drives endocytosis by recruiting microfilament assemblies to form ESEs. Then, the ESEs produced through different pathways, with the involvement of proteins such as Rab5 to form late-sorting endosomes (LSEs), and late endosomal membranes bud inward to form intracellular multivesicular bodies (MVBs), which contain many intraluminal vesicles (future exosomes), and eventually MVBs fuse with the cell plasma membrane to release exosomes outside. (By Figdraw. Hangzhou, Duotai. Technology Co., Ltd., Hangzhou 310000, China).