Figure 3.

The life of an exosome. The exosomes originate from endocytosis and form early-sorting endosomes. Exosome biogenesis relies on both ESCRT-dependent and ESCRT-independent pathways to sort cargos and form MVBs by budding inward. Some MVBs deliver cargo molecules to lysosomes for degradation and recycling. Some fuse with the plasma membrane to release ILVs, which play a role in intercellular communication in the form of exosomes. Other MVBs fuse with autophagosomes to form amphisomes, which can fuse with lysosomes for degradation, as well as with the plasma membrane to secrete exosomes; the process of exosome generation is regulated by a variety of factors. Tetraspanin 6 (Tspan6) promotes lysosomal degradation and exosome secretion through the recruitment of syntenin, and proteins such as SNEAR and Rab11, Rab27A/B, and Rab35 promote fusion of MVBs with the plasma membrane to release exosomes. There are several exosome–recipient cell interaction modes. Exosomes can be uptaken and internalized by recipient cells through various endocytosis pathways and deliver bioactive substances to the receptor cells. Exosome membrane proteins can also bind to target cell membrane proteins. Exosomes activate intracellular signaling pathways in the target cell by binding to the recipient cell via the adhesion molecules they carry. Direct membrane fusion is another mechanism for the internalization of exosomes. (By Figdraw. Hangzhou, Duotai. Technology Co., Ltd., Hangzhou 310000, China).