Introduction
The term “extracellular vesicles” (EVs) is relatively new in the field of science. The rising attention to EVs was attributable to their potential value as circulating biomarkers for cancer. An increasing amount of research into the roles of extracellular vesicles released by many cell types has led to a significant increase in this knowledge in recent years. We summarized the information from different sources in this EVs 101.
What are the EVs and what is their role?
EVs are a generic term for lipid-bound vesicles secreted by cells into the extracellular space, acting as carriers of proteins, metabolites, lipids, and nucleic acids. They are mainly classified into exosomes, ectosomes/ microvesicles (MVs), and apoptotic extracellular vesicles (Apo-EVs).
EVs have just lately been recognized to play a crucial and evolutionary conserved role in cell-to-cell communication. They transport proteins, metabolites, lipids, and nucleic acids to target cells as part of their biological roles. The substances carried by EVs can influence physiological and pathological processes. Researchers are looking at the possibility of applying this characteristic in the treatment of cancer by delivering the drugs, ncRNAs, and peptides to targeted cancer cells. Moreover, they have the ability to control how cancer cells grow (proliferation), move (migration), die (apoptosis), and clean out damaged components (autophagy).
What is the difference between Exosomes, MVs, and Apo-EVs?
Exosomes and MVs are both released by healthy cells for the purpose of intercellular communication; however, there are several key distinctions between the two, including their size, the membrane of origin, and protein contents. Exosomes are originated from the endosomal pathway and MVs are released through plasma membrane budding.
Apo-EVs (or bigger Apo-EVs, also known as apoptotic bodies) are generated in a variety of sizes by apoptotic cells. They are often greater in size than other EVs, with the primary role of facilitating phagocytosis. [Phagocytosis is the biological process through which bacteria, foreign substances, and apoptotic cells are ingested and eliminated.]
Apo-EVs contain nuclear fractions and cell organelles with information and substances from dying cells. They were once considered garbage bags until they were recently found to convey useful materials to healthy recipient cells.
Do all cells produce EVs?
During apoptosis, cells have long been recognized to release vesicles into the extracellular environment. However, it was only relatively recently discovered that healthy cells also release vesicles into the extracellular environment. [Apoptosis: the process of programmed cell death]
EVs are produced by nearly all of the cell types that make up the human body. These cell types include but are not limited to immune cells, endothelial cells, red blood cells, erythrocytes, liver cells, and epithelial cells.
Can EVs serve as a good biomarker?
EVs have maximum potential as the target of liquid biopsies as they can be detected in almost all types of body fluids such as blood, urine, saliva, breast milk, and ascites. EVs can be isolated from all biofluids for this purpose and contain a tremendous number of molecules that can be used as target biomarkers. To discover reliable biomarkers for detecting cancer at an early stage, an ideal biomarker should be highly specific for a primary tumor type and be reproducibly detectable at premetastatic stages using non-invasive techniques
EVs have been found to circulate through many different body fluids including blood and urine. Due to the resemblance of EVs composition with the parental cell, circulating EVs have raised considerable interest as a source for the discovery of biomarkers.
Signatures of miRNAs represent a recently identified biomarker family that is characteristic of tumor type and developmental origin. MiRNAs have been already associated with EVs, and hence, circulating tumor-derived EVs are being analyzed to search for specific miRNA signatures.
Publication about Small Extracellular Vesicles (sEVs)
By the end of 2022, a new paper on extracellular vesicles and RNA transfection complexes was published by Dr. Li’s node. Using the untargeted lipidomics method on samples that were incredibly diluted was difficult, but the findings were stunning. Check this open-access article, “Contaminating transfection complexes can masquerade as small extracellular vesicles and impair their delivery of RNA” for more information!
Endosomal membranes often bud inward to create multivesicular bodies which can eventually be excreted into the extracellular space as small EVs (sEV) with a range in size from 50 to 150 nm. The ability of sEVs to carry RNA into the cytoplasm of target cells is one of their functions that has drawn the most attention. These investigations are frequently carried out by transfecting RNAs into cells that produce sEV in order to purify and research sEV delivery of RNA.
Once absorbed by cells, transfection complexes and other delivery vehicles concentrate in late endosomes where sEV are generated. Hence, more than 50% of transfection complexes or delivery vehicles supplied to cells are exocytosed back into the extracellular space. One of the significant findings is that transfection complexes, like lipid-based RNAiMax, may commonly contaminate sEV preparations. This could explain certain reports of sEV-mediated delivery of nucleic acids. It appears that transfection of cells affected the capacity of sEVs to transmit stably-expressed siRNAs, as this process also can modify sEVs and limit research into their endogenous capacity to deliver RNA to target cells.
Summarized by Juan Darius and Adriana Zardini Buzatto
References
McCann J, et al. Contaminating transfection complexes can masquerade as small extracellular vesicles and impair their delivery of RNA. J Extracell Vesicles. 2022 Oct;11(10):e12220.
Ibrahim SA &Khan YS. Histology, Extracellular Vesicles. 2022 Aug 8. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2022 Jan.
Zhang X, et al. The Biology and Function of Extracellular Vesicles in Cancer Development. Front Cell Dev Biol. 2021 Nov 5;9:777441.
Kalluri R & LeBleu VS. The Biology, Function, and Biomedical Applications of Exosomes. Science. 2020 Feb 7;367(6478):eaau6977
Battistelli M & Falcieri E. Apoptotic Bodies: Particular Extracellular Vesicles Involved in Intercellular Communication. Biology (Basel). 2020 Jan 20;9(1):21.
Doyle LM & Wang MZ. Overview of Extracellular Vesicles, Their Origin, Composition, Purpose, and Methods for Exosome Isolation and Analysis. Cells. 2019 Jul 15;8(7):727.
van Niel G, D’Angelo G, and Raposo G. Shedding Light on the Cell Biology of Extracellular Vesicles. Nat Rev Mol Cell Biol. 2018 Apr;19(4):213-228.
Lynch C, Panagopoulou M, and Gregory CD. Extracellular Vesicles Arising from Apoptotic Cells in Tumors: Roles in Cancer Pathogenesis and Potential Clinical Applications. Front Immunol. 2017 Sep 22;8:1174.
Zaborowski MP, et al. Extracellular Vesicles: Composition, Biological Relevance, and Methods of Study. Bioscience. 2015 Aug 1;65(8):783-797
Yáñez-Mó M, et al. Biological Properties of Extracellular Vesicles and Their Physiological Functions. J Extracell Vesicles. 2015 May 14;4:27066.
