Exosomes (EXs) are a major type of extracellular vesicles released by cells highly conserved from microorganisms to mammals. 1 Their size ranges from 20 to 150 nm in diameter. About 50 years ago, they were initially considered cellular "waste." In the early 1980s, EXs were recognized as distinct entities. Later in 1987, the term "exosome" was coined for these membrane particles. Over the past decades, increasing evidence shows that EXs can cross the blood-brain barrier (BBB) and serve cell-to-cell communicators via conveying their carried biological cargoes (nuclear acids, proteins, and lipids). 2,3 In the central nervous system (CNS), EXs are released from virtually all brain cells, including neurons, astrocytes, microglia, and endothelial cells., 4,5 and exchange molecule messages related to neuronal function and neurotransmission in the brain via the reciprocal communication between brain cells.Given the capability of EXs to reach body compartments and connect origin cells with target cells, EXs have a promising potential to be used in clinical applications. Indeed, a large body of preclinical studies has shown the implication and therapeutic potential of EXs in CNS diseases. Here, we review the current state of the knowledge of EXs, the roles and applications of EXs as a viable pathological biomarker, and EX-based therapy for CNS diseases.
| OVERVIE W OF E X S
| EX biogenesis, isolation, and contentsEX generation is initiated by a process that involves double invagination of the plasma membrane and the formation of intracellular multivesicular bodies (MVBs). The MVBs contain intraluminal vesicles that are secreted as EXs via exocytosis and MVB fusion to the plasma membrane. 6,7 Although the exact biogenesis mechanism has not been fully delineated, multiple molecules including Ras-related