Exosomes surf on filopodia to enter cells at endocytic hot spots, traffic within endosomes, and are targeted to the ER

Abstract

Heusermann et al. use a single-vesicle dye-tracing analysis in live cells showing that exosomes enter cells as intact vesicles, primarily at filopodia-active regions, and sort into endocytic vesicle circuits that are targeted to scan the ER before being directed to lysosomes.

Therapeutic and diagnostic applications of extracellular vesicles

“…Unfortunately, the EVs used in this study were not able to escape the endolysosomal degradation pathway and hence failed to functionally deliver the siRNA in contrast to anionic fusogenic liposomes that were equally loaded with chol-siRNA. Moreover, the endogenously present miRNAs were not able to silence their respective target proteins which is in accordance with recent reports describing that (1) even the most abundant miRNAs found in EVs are secreted at a (low) ratio of 1 molecule per 100 vesicles [46,177] and (2) internalized EVs are typically trafficked toward the lysosomes [140,178]. Although this particular combination of EVs and recipient cells did not lead to successful EV-mediated drug delivery [176], it does not invalidate the concept of EVs as drug carriers as their interaction with cells might be highly specific.…”

“…tetraspanins, integrins, proteoglycans and lectins) as comprehensively reviewed by Mulcahy et al [139]. These interactions, possibly preceded by surfing onto filopodia according to recent observations [140], mostly lead to cell uptake via one of the common endocytosis pathways (i.e. clathrin-and caveolin-dependent endocytosis, lipid raft-mediated endocytosis, macropinocytosis or phagocytosis) [105,139].…”

“…As the interaction of EVs with cells likely involves multivalent ligand-receptor binding, it is reasonable to assume that they finally are trafficked to lysosomes for degradation [140]. Hence, delivery of drugs into the cell cytoplasm will require a mechanism that allows the EV cargo to escape the endolysosomal compartment.…”

Extracellular microRNAs as messengers in the central and peripheral nervous system

“…In synaptosome preparations, internalized microRNAs were recruited to RISC where they were functionally active [48]. Alternatively, internalized exosomes may be targeted to the lysosome for degradation [97,100]. Uptake via invagination of the plasma membrane, or macropinocytosis, has been observed in microglia [102] and a cancer cell line [98].…”

“…Imaging showed filopodia, highly dynamic protrusions of the cell and hotspots for endocytosis, attracting EV localization and supporting their uptake into the cell by surfing, grabbing and pulling within minutes of EV addition [100]. Exosomes incorporated via endocytosis are detected within endosomes [97,[99][100][101] and thought to be transferred to the endoplasmatic reticulum, a centre for translation and mRNA silencing by microRNAs, where they may release their cargo [100]. In synaptosome preparations, internalized microRNAs were recruited to RISC where they were functionally active [48].…”