Reassessment of Exosome Composition

AUTHORS

Jeppesen DKDennis K , Fenix AMAidan M , Franklin JLJeffrey L , Higginbotham JNJames N , Zhang QQin , Zimmerman LJLisa J , Liebler DCDaniel C , Ping JJie , Liu QQi , Evans RRachel , Fissell WHWilliam H , Patton JGJames G , Rome LHLeonard H , Burnette DTDylan T , Coffey RJRobert J . Cell. 2019 4 4; 177(2). 428-445.e18

PMID: 30951670[PubMed].

ABSTRACT

The heterogeneity of small extracellular vesicles and presence of non-vesicular extracellular matter have led to debate about contents and functional properties of exosomes. Here, we employ high-resolution density gradient fractionation and direct immunoaffinity capture to precisely characterize the RNA, DNA, and protein constituents of exosomes and other non-vesicle material. Extracellular RNA, RNA-binding proteins, and other cellular proteins are differentially expressed in exosomes and non-vesicle compartments. Argonaute 1-4, glycolytic enzymes, and cytoskeletal proteins were not detected in exosomes. We identify annexin A1 as a specific marker for microvesicles that are shed directly from the plasma membrane. We further show that small extracellular vesicles are not vehicles of active DNA release. Instead, we propose a new model for active secretion of extracellular DNA through an autophagy- and multivesicular-endosome-dependent but exosome-independent mechanism. This study demonstrates the need for a reassessment of exosome composition and offers a framework for a clearer understanding of extracellular vesicle heterogeneity.