Quantitative proteomics identifies the core proteome of exosomes with syntenin-1 as the highest abundant protein and a putative universal biomarker

Extracellular Vesicles

Exosomes are extracellular vesicles derived from the endosomal compartment that are potentially involved in intercellular communication. Here, we found that frequently used biomarkers of exosomes are heterogeneous, and do not exhibit universal utility across different cell types. To uncover ubiquitous and abundant proteins, we used an unbiased and quantitative proteomic approach based on super-stable isotope labeling with amino acids in cell culture (super-SILAC), coupled to high-resolution mass spectrometry. In total, 1,212 proteins were quantified in the proteome of exosomes, irrespective of the cellular source or isolation method. A cohort of 22 proteins was universally enriched. Fifteen proteins were consistently depleted in the proteome of exosomes compared to cells. Among the enriched proteins, we identified biogenesis-related proteins, GTPases and membrane proteins, such as CD47 and ITGB1. The cohort of depleted proteins in exosomes was predominantly composed of nuclear proteins. We identified syntenin-1 as a consistently abundant protein in exosomes from different cellular origins. Syntenin-1 is also present in exosomes across different species and biofluids, highlighting its potential use as a putative universal biomarker of exosomes. Our study provides a comprehensive quantitative atlas of core proteins ubiquitous to exosomes that can serve as a resource for the scientific community.

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Recent Publications

Cigarette smoke (CS) represents one of the most relevant environmental risk factors for several chronic pathologies. Tissue damage caused by CS exposure is mediated, at least in part, by oxidative stress induced by its toxic and pro-oxidant components. Evidence demonstrates that extracellular vesicles (EVs) released by various cell types exposed to CS extract (CSE) are characterized by altered biochemical cargo and gained pathological properties. In the present study, we evaluated the content of oxidized proteins and phospholipid fatty acid profiles of EVs released by human bronchial epithelial BEAS-2B cells treated with CSE. This specific molecular characterization has hitherto not been performed. After confirmation that CSE reduces viability of BEAS-2B cells and elevates intracellular ROS levels, in a dose-dependent manner, we demonstrated that 24 h exposure at 1% CSE, a concentration that only slight modifies cell viability but increases ROS levels, was able to increase carbonylated protein levels in cells and released EVs. The release of oxidatively modified proteins via EVs might represent a mechanism used by cells to remove toxic proteins in order to avoid their intracellular overloading. Moreover, 1% CSE induced only few changes in the fatty acid asset in BEAS-2B cell membrane phospholipids, whereas several rearrangements were observed in EVs released by CSE-treated cells. The impact of changes in acyl chain composition of CSE-EVs accounted for the increased saturation levels of phospholipids, a membrane parameter that might influence EV stability, uptake and, at least in part, EV-mediated biological effects. The present in vitro study adds new information concerning the biochemical composition of CSE-related EVs, useful to predict their biological effects on target cells. Furthermore, the information regarding the presence of oxidized proteins and the specific membrane features of CSE-related EVs can be useful to define the utilization of circulating EVs as marker for diagnosing of CS-induced lung damage and/or CS-related diseases.

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