Characterizing single extracellular vesicles by droplet barcode sequencing for protein analysis

Extracellular Vesicles
/References

Small extracellular vesicles (sEVs) have in recent years evolved as a source of biomarkers for disease diagnosis and therapeutic follow up. sEV samples derived from multicellular organisms exhibit a high heterogeneous repertoire of vesicles which current methods based on ensemble measurements cannot capture. In this work we present droplet barcode sequencing for protein analysis (DBS-Pro) to profile surface proteins on individual sEVs, facilitating identification of sEV-subtypes within and between samples. The method allows for analysis of multiple proteins through use of DNA barcoded affinity reagents and sequencing as readout. High throughput single vesicle profiling is enabled through compartmentalization of individual sEVs in emulsion droplets followed by droplet barcoding through PCR. In this proof-of-concept study we demonstrate that DBS-Pro allows for analysis of single sEVs, with a mixing rate below 2%. A total of over 120,000 individual sEVs obtained from a NSCLC cell line and from malignant pleural effusion (MPE) fluid of NSCLC patients have been analyzed based on their surface proteins. We also show that the method enables single vesicle surface protein profiling and by extension characterization of sEV-subtypes, which is essential to identify the cellular origin of vesicles in heterogenous samples.

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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.

2023
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