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Exosomes in Cancer Disease, Progression, and Drug Resistance
Published in Vladimir Torchilin, Handbook of Materials for Nanomedicine, 2020
Taraka Sai Pavan Grandhi, Rajeshwar Nitiyanandan, Kaushal Rege
Tetraspanins (CD63, CD9, CD81, and CD82) are integral membrane protein components that are highly enriched in exosomes. They organize into tetraspanin-enriched domains by interacting with lipids, other cytosolic and transmembrane proteins [33, 38]. Cytoplasmic and transmembrane protein interactome of tetraspanins is considered another major source of protein loading into the exosomes [33]. Sphingosine and fatty acid containing ceramides have been shown to be essential in exosome biogenesis [39]. It is well known that ceramides can induce stable and spontaneous curvature in lipid bilayer membranes (liposomes), and play an essential role in inward budding of late endosomal limiting membrane for ILV generation [39]. Kajimoto et al. [34] showed that continuous metabolization of ceramide into sphingosine 1-phosphate (S1P) activates inhibitory G protein-coupled S1P receptors, essential for successful cargo sorting into ILVs in HeLa cells; S1P signaling was shown to play a role in the sorting of the tetraspanin CD63 protein into exosomes [34].
Advances of engineered extracellular vesicles-based therapeutics strategy
Published in Science and Technology of Advanced Materials, 2022
Hiroaki Komuro, Shakhlo Aminova, Katherine Lauro, Masako Harada
Since all types of cells secrete EVs, their recovery has been reported in all bodily fluids [20], including blood [21], urine [22], saliva [23], breast milk [24], semen [25], bronchoalveolar lavage fluid [26], synovial fluid [27], cerebrospinal fluid [28], and amniotic fluid [29]. EVs are broadly classified into three types: exosomes, microvesicles, and apoptotic bodies (Figure 1). The classification of EV can be associated with their biogenesis. Exosomes (50–150 nm) derive from the inward budding of the endosomal compartment, multivesicular bodies (MVBs). Upon fusion with the cell membrane, exosomes are released to the extracellular space and mediate intercellular communication by transferring bioactive molecules such as RNAs, proteins, and lipids between cells in living organisms [30]. Tetraspanins belong to a cell surface protein family with four transmembrane domains required for intraluminal vesicle formation [31]. CD9, CD63, and CD81 are tetraspanin proteins found enriched in exosomes and often used as EV surface markers [12]. Microvesicles (100–1000 nm), on the other hand, are secreted directly from the plasma membrane. Microvesicles are not as well studied or defined as the other EV types, resulting in more broad characteristics. Apoptotic bodies (100–5000 nm) are produced from apoptotic cells when they undergo programmed cell death. Numerous studies illustrate the heterogeneity of these EVs and missing pieces of information left uncovered, implicating the change in descriptions in the future [12]. For example, there is no defined method or unique maker to separate one EV type from another. A report suggested that 100,000 g ultracentrifugation (UC) co-isolates two EV subtypes defined by specific proteins [32], proposing the importance of considering heterogeneity and diversity among EV types in the study design. Furthermore, some EV subtypes are named after the cell from which they are secreted, such as cardiosome (cardiovascular-origin) and oncosome (oncology-origin) [33–36], though ISEV strongly suggests that the generic term EV be widely adopted [37]. Moreover, the guidelines published by ISEV in 2018 recommend referring to small EVs (sEVs) (<100 nm or <200 nm) or >200 nm as medium/large EVs (m/lEVs) EVs based on their physical characteristic, size and density [12]. This article will adhere to the term ‘EV’ in place of exosome or the names used in the original literature to avoid terminology ambiguity.