Fig. 2
From: Physiological and pathological consequences of exosomes at the blood–brain-barrier interface
The molecular machinery of Exo biogenesis. Newly generated early endosomes are produced via cell membrane invagination to support the intracellular transmission of uptaken Exos. In the next step, early endosomes mature into later Exos and eventually MVBs. Along with these changes, the invagination of the endosomal membrane into the lumen leads to the formation of several ILVs, known as Exos after secretion into the ECM. The participation of ESCRT independent mechanisms and/or ESCRT complex (ESCRT-0, -I, -II, and -III) with several tetraspanin types is mandatory for the sequestration of new cargo into the ILVs. By engaging the SNARE system and several GTPases, MVBs are directly fused with the cell membrane to release their contents. Exos have nano-sized bi-lipid layer structures with specific molecular identities. ESCRT: endosomal sorting complex transport; MHC: major histocompatibility complex; MVB: multi-vesicular body; Rab: Ras-associated binding proteins. Reprinted with permission [29], Copyright 2021. Frontiers in Cell and Developmental Biology