Physical exosome:exosome interactions

Abstract

Exosomes are extracellular nanovesicles that mediate a number of cellular processes, including intracellular signalling. There are many published examples of exosome-exosome dimers; however, their relevance has not been explored. Here, we propose that cells release exosomes to physically interact with incoming exosomes, forming dimers that we hypothesize attenuate incoming exosome-mediated signalling. We discuss experiments to test this hypothesis and potential relevance in health and disease.

Keywords: exosome; hypothesis; physical interaction; signalling; zeta potential.

Figure 1

Effect of the ionic strength of two different vehicles, on the size of exosomes. Normal Trabecular Meshwork (NTM)‐derived exosome size distribution depends on the vehicle, as it was different for exosomes suspended in artificial aqueous humour (AAH; pH 7.2, IS = 0.153) and for exosomes suspended in 0.02 M phosphate buffer (PBS; pH 7.2, IS = 0.025) The size of NTM‐derived exosomes was measured with NanoSight5000 for exosomes (at the same concentration) suspended in PBS or artificial AH. An increase in exosome size was detected when the exosomes were suspended in the PBS relative to the same exosomes suspended in the artificial AH.

Figure 2

Representative physical exosome:exosome interaction by TEM analysis. Typically, exosomes isolated from conditioned media of cells appear as round vesicles of heterogeneous sizes, ranging from 30 to 150 nm. Physical exosome:exosome interactions lead to changes in exosome shape. (A) Non‐Pigmented Cilliary Epithelium (NPCE): Upon interaction, the round single exosomes become more flattened, with relatively a contact area between the interacting exosomes. (B) TM‐123: On the right side, three flattened exosome:exosome interactions can be observed (▲); non‐interacting exosomes are presented (*). Non‐pigmented ciliary epithelium cell and TM‐123‐derived exosomes were extracted by ultracentrifugation, suspended in 0.1 M PBS, pH 7.2. Picture A and B was generated by TEM.

Figure 3

Representative graph of nanoparticle tracking analysis (NTA) analysis of Trabecular Meshwork (TM) exosomes. Normal trabecular meshwork cell‐derived exosomes were extracted. The arrow indicates possible couple forming exosomes following extraction, storing and dilution for size analysis. The amount of exosomes couple is estimated <5%.

Figure 4

ImageStream analysis of physical exosome:exosome interactions. (A) DID (red)‐stained NPCE‐derived exosome and DIO (green)‐stained NTM‐derived exosome were mixed in vitro in a 1:1 number ratio in PBS pH = 7.2, ionic strength = 0.06 at room temperature and analysed with ImageStream. (A) Physical exosome:exosome interaction of DID‐stained NPCE‐derived exosomes (B) DIO‐stained TM‐derived exosomes demonstrate proximity without physical exosome:exosome interaction(C) Physical exosome:exosome interaction between NPCE‐ and TM‐derived exosomes(C1&C2).