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Anna Figueroa, Nicole R. Congrove, Sara Ann Sillik, Doraid Tarek Sadideen, Torsten Falk, Catherine Bowes Rickman, Brian S McKay; Exosome uptake is selective but not species or tissue-specific. Invest. Ophthalmol. Vis. Sci. 2018;59(9):3993.
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© ARVO (1962-2015); The Authors (2016-present)
Exosomes are small extracellular vesicles, 40-130 nm in diameter, that are released by most cells and potentially function in multiple cellular processes. Exosomes carry miRNA, mRNA, proteins, and bioactive lipids that are thought to be delivered as cargo to downstream cells and could influence the disease process in AMD through RPE-retina interaction. However, for exosomes to be functional in inter-tissue communication, delivery of cargo must be selective. Here we explore exosome binding and uptake by testing exosomes isolated from a variety of sources including in situ RPE.
We developed a mix-and-match paradigm with a variety of cell types from different species. We isolated the exosomes by differential ultracentrifugation, labeled the exosomes and viewed them by fluorescence microscopy. To test exosome binding and uptake, we added 5,000 – 10,000 labeled exosomes per cell and examined cells up to 24 hours later. In addition, to test if exosome uptake can be blocked, exosomes were introduced to cells chilled to -4°C to inhibit active cellular uptake. We extended our study by using apical specific RPE exosomes obtained in situ from eye cups and tested these exosomes with primary RPE and retinal explants.
Unexpectedly, in 6 experiments our mix-and-match paradigm demonstrated no species or cell-type specificity. In addition, we observed that exosomes were trapped on the cell surface at cold temperatures, suggesting they bound a receptor. In the primary tissue paradigm through 9 experiments, apical RPE exosomes were selectively taken up by less than 10% of RPE or retinal cells. Interestingly, uptake was independent as each experiment illustrated cells heavily loaded with exosomes, next to cells with no uptake. Similarly, at -4°C exosomes were only trapped on a minority of cells. Despite the observed lack of specificity between different species and cell-types in the mix-and-match experiments, there is clear evidence of selectivity within cell populations.
Our data show for the first-time that exosome communication may cross species and cell-type boundaries. However, we also show that exosome uptake in primary tissue is very selective. We hypothesize that cell selectivity is based on differential expression of a cell-surface exosome receptor, and we are evaluating the possibility of a “shared” cell-surface exosome-receptor across cells, and conserved broadly across species.
This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.
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