The last decade has seen a sharp increase in the number of scientific publications describing physiological and pathological functions of extracellular vesicles (EVs), a collective term covering various subtypes of cell-released, membranous structures, called exosomes, microvesicles, microparticles, ectosomes, oncosomes, apoptotic bodies, and many other names. However, specific issues arise when working with these entities, whose size and amount often make them difficult to obtain as relatively pure preparations, and to characterize properly. The International Society for Extracellular Vesicles (ISEV) proposed Minimal Information for Studies of Extracellular Vesicles (“MISEV”) guidelines for the field in 2014. We now update these “MISEV2014” guidelines based on evolution of the collective knowledge in the last four years. An important point to consider is that ascribing a specific function to EVs in general, or to subtypes of EVs, requires reporting of specific information beyond mere description of function in a crude, potentially contaminated, and heterogeneous preparation. For example, claims that exosomes are endowed with exquisite and specific activities remain difficult to support experimentally, given our still limited knowledge of their specific molecular machineries of biogenesis and release, as compared with other biophysically similar EVs. The MISEV2018 guidelines include tables and outlines of suggested protocols and steps to follow to document specific EV-associated functional activities. Finally, a checklist is provided with summaries of key points.

MicroRNAs (miRs) are important posttranscriptional regulators of gene expression. Besides their well‐characterized inhibitory effects on mRNA stability and translation, miRs can also activate gene expression. In this study, we identified a novel noncanonical function of miR‐574‐5p. We found that miR‐574‐5p acts as an RNA decoy to CUG RNA‐binding protein 1 (CUGBP1) and antagonizes its function. MiR‐574‐5p induces microsomal prostaglandin E synthase‐1 (mPGES‐1) expression by preventing CUGBP1 binding to its 3′UTR, leading to an enhanced alternative splicing and generation of an mPGES‐1 3′UTR isoform, increased mPGES‐1 protein expression, PGE2 formation, and tumor growth in vivo. miR‐574‐5p–induced tumor growth in mice could be completely inhibited with the mPGES‐1 inhibitor OIL Moreover, miR‐574‐5p is induced by IL‐1β and is strongly overexpressed in human nonsmall cell lung cancer where high mPGES‐1 expression correlates with a low survival rate. The discovered function of miR‐574‐5p as a CUGBP1 decoy opens up new therapeutic opportunities. It might serve as a stratification marker to select lung tumor patients who respond to the pharmacological inhibition of PGE2 formation.—Saul, M. J., Baumann, I., Bruno, A., Emmerich, A. C., Wellstein, J., Ottinger, S. M., Contursi, A., Dovizio, M., Donnini, S., Tacconelli, S., Raouf, J., Idborg, H., Stein, S., Korotkova, M., Savai, R., Terzuoli, E., Sala, G., Seeger, W., Jakobsson, P.‐J., Patrignani, P., Suess, B., Steinhilber, D. miR‐574‐5p as RNA decoy for CUGBP1 stimulates human lung tumor growth by mPGES‐1 induction. FASEB J. 33, 6933–6947 (2019). http://www.fasebj.org

Rheumatoid arthritis (RA) is a chronic autoimmune disease characterized by synovial inflammation and joint destruction. Cell-derived small extracellular vesicles (sEV) mediate cell-to-cell communication in the synovial microenvironment by carrying microRNAs (miRs), a class of small non-coding RNAs. Herein, we report that sEV from synovial fluid promote osteoclast differentiation which is attributed to high levels of extracellular miR-574-5p. Moreover, we demonstrate for the first time that enhanced osteoclast maturation is mediated by Toll-like receptor (TLR) 7/8 signaling which is activated by miR-574-5p binding. This is a novel mechanism by which sEV and miRs contribute to RA pathogenesis and indicate that pharmacological inhibition of extracellular miR-574-5p might offer new therapeutic strategies to protect osteoclast-mediated bone destruction in RA.

Intercellular communication plays an essential role in lung cancer (LC). One of the major players in cell‐cell‐communication is small extracellular vesicles (sEV). SEV trigger various biological responses by transporting cellular cargo to target cells. One essential sEV component are microRNAs (miRs), whose transport has recently attracted increasing research interest. We report that prostaglandin E 2 (PGE 2 ), a key inflammatory lipid mediator, specifically induces the sorting of miR‐574‐5p in sEV of A549 and 2106T cells. We found that sEV‐derived miR‐574‐5p activates Toll‐like receptors (TLR) 7/8, thereby decreasing PGE 2 ‐levels. In contrast, intracellular miR‐574‐5p induces PGE 2 ‐biosynthesis. Consequently, the combination of intracellular and sEV‐derived miR‐574‐5p controls PGE 2 ‐levels via a feedback loop. This was only observed in adeno‐ but not in squamous cell carcinoma, indicating a cell‐specific response to sEV‐derived miRs, which might be due to unique tetraspanin compositions. Hence, we describe a novel function of miR‐574‐5p unique to adenocarcinoma. Intracellular miR‐574‐5p induces PGE 2 and thus the secretion of sEV‐derived miR‐574‐5p, which in turn decreases PGE 2 ‐biosynthesis in recipient cells.