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

TLDR

Exosomes are nanovesicles released by virtually all cells that transfer protein, lipid, and RNA cargo between cells, yet their uptake efficiency, routes, and subcellular fate remain poorly understood. Exosomes are recruited to the cell body by surfing along filopodia and by filopodial grabbing and pulling motions to reach endocytic hot spots, after which they travel within endocytic vesicles to scan the endoplasmic reticulum before being sorted into lysosomes. Uptake of exosomes saturates with dose and time, achieving nearly 100 % transduction efficiency at picomolar concentrations, and the data reveal a virus‑like host‑cell interaction and novel subcellular cargo delivery routes.

Abstract

Exosomes are nanovesicles released by virtually all cells, which act as intercellular messengers by transfer of protein, lipid, and RNA cargo. Their quantitative efficiency, routes of cell uptake, and subcellular fate within recipient cells remain elusive. We quantitatively characterize exosome cell uptake, which saturates with dose and time and reaches near 100% transduction efficiency at picomolar concentrations. Highly reminiscent of pathogenic bacteria and viruses, exosomes are recruited as single vesicles to the cell body by surfing on filopodia as well as filopodia grabbing and pulling motions to reach endocytic hot spots at the filopodial base. After internalization, exosomes shuttle within endocytic vesicles to scan the endoplasmic reticulum before being sorted into the lysosome as their final intracellular destination. Our data quantify and explain the efficiency of exosome internalization by recipient cells, establish a new parallel between exosome and virus host cell interaction, and suggest unanticipated routes of subcellular cargo delivery.