Extracellular Vesicles
Extracellular vesicles (EVs; including classical-exosomes, non-classical-exosomes, microvesicles, large oncosomes, apoptotic bodies, apoptotic vesicles, autophagic extracellular vesicles, amphisomes and ARRMs) are membrane vesicles of 40-1000 nm that are released into the extracellular milieu and body fluids from most cell types, including red blood cells, platelets, lymphocytes, dendritic cells, endothelial cells and tumor cells. These vesicles are classified into 2 types according to their secretory mechanism. Thus, classical-exosomes are formed in multivesicular endosomes, whereas microvesicles originate by direct budding from the plasma membrane. Although classical-exosome components vary by their originating cell type, a certain set of molecules appears likely to be shared, regardless of their origin. These molecules include the tetraspanin proteins (CD9, CD63 and CD81) that are thought to be essential components of the biogenesis mechanism of classical-exosomes. CD9, CD63 and CD81 to isolate and characterize the purity of classical-exosome preparations.
Exosome
Exosomes are membrane-enclosed vesicles of 30 to 100 nm containing proteins and nucleic acids and are secreted by various cells. By gaining access to the circulation, they may transmit signals to cells at distant locations. It has been observed that intercellular communication via exosomes is associated with antigen presentation, apoptosis, inflammation, tumor progression and malignant transformation. It is expected that exosomes will be important in various fields, such as in the development of drug delivery systems.
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Over the past decade, exosomes have been the focus of intense interest as microRNA (miRNA) carriers, disease biomarkers, and potential therapeutic drug delivery vehicles. Despite the importance of exosomes, their isolation and characterization are still considered major scientific challenges, especially when translating to the demands of the clinic. Classically, exosomes and other EVs have been purified by ultracentrifugation. Technical challenges, time and cost have led to a proliferation of alternative purification approaches such as Tangential Flow Filtration (TFF), Size Exclusion Chromatography (SEC), immunoaffinity and chemical precipitation
Biogenesis and Components of EVs
A. Microvesicle (MV) biogenesis comprises several steps, including plasma membrane reorganization, redistribution of phospholipids, outward repositioning of phosphatidylserine, disassembly of the cytoskeleton network, and actomyosin basal abscission. B. Exosome biogenesis starts inward of the plasma membrane to form early endosomes. Intraluminal vesicles (ILVs) are formed, and the endosomes mature to multivesicular bodies (MVBs). MVBs fuse with the plasma membrane to release ILVs into the extracellular space, where they are then referred to as exosomes. Alternatively, the MVBs can fuse with lysosomes, resulting in the degradation of ILVs. C. EVs can contain nucleic acids (DNA and/or RNA), membrane anchored-proteins, cytosolic proteins, and lipids; these contents can vary depending on the releasing cell types and their conditions. (Source: Yokoi and T. Ochiya; 2021)
