Researchers from the Johns Hopkins University School of Medicine, propose a model for characterizing exosome size distributions based on dynamic scaling of domain growth on the limiting membrane of multivesicular bodies in the established exosome biogenesis pathway. The scaling exponent in this model captures the asymmetry of exosome size distributions, which are notably right-skewed to larger vesicles independent of the minimum detectable vesicle size. Analyses of exosome size distributions obtained by cryo-TEM imaging and nanoparticle tracking (NTA) show, respectively, that the scaling exponent is sensitive to the state of the cell source for exosomes in cell culture supernatants, and can distinguish exosome size distributions in serum samples taken from cancer patients relative to those from healthy donors. Finally, the researchers comment on mechanistic differences between our dynamic scaling model and random fragmentation models used to describe size distributions of synthetic vesicles.
Probability distribution, p(D), of exosome diameters measured by NTA for exosomes isolated from serum samples taken from a patient diagnosed with early-stage squamous cell carcinoma (SCC-EX1) and a healthy donor (HS-EX3). Open circles are the NTA data; solid lines are calculated using the probability density distribution function eq. 8 with scaling exponents and average exosome diameters given in Table 2. Number fractions are shifted up (SCC-EX1) and down (HS-EX3) by a factor of 10 for visual clarity.