Researchers from the University of California, Davis set out to investigate the ability of preterm milk exosomes to survive gastric/pancreatic digestion, internalization by intestinal epithelia, and the microRNAs (miRNAs) contents.
At average infant age 1 week 6 days, milk was collected from mothers who delivered preterm and term infants (n = 10). Milk was exposed to conditions simulating infant gut digestion. Exosomes were isolated and lysed, and the exposed miRNAs were sequenced. Preterm milk exosomes survive in vitro digestion, and can be taken up by intestinal epithelia. 330 miRNAs were identified as preterm milk exosome miRNAs, and in vitro digestion does not have a pronounced effect on their expression. The abundant miRNAs in preterm milk exosomes were similar to those from term milk. 21 low abundance miRNAs were specifically expressed in preterm milk exosomes compared to early term milk in the current study and what we previously found in mature term milk.
These results for the first time reveal the survivability of preterm milk exosomes following simulated gastric/pancreatic digestion. The researchers demonstrate the richness of miRNAs content in these exosomes. The results improve our knowledge of preterm milk biology and the molecular basis by which exosome miRNAs may uniquely affect preterm infants during early development
Characterization and uptake of preterm milk exosome
A. E xperimental flow of the study. * refers to Liao et al. 2017  . ** indicates that comparison were performed between the three datasets. B. Proteins (5 μ g/lane) from exosomes wer e digested with pepsin at acidic pH (pH 4.0 for term milk exosome s , and pH 4.5 for preterm milk exosome s ), followed by pancreatin digestion (see details in Methods), subjected to SDS – PAGE, an d stained with 0.25% Coomassie B rilliant Blue R – 250. C. Proteins from term and preterm hum an milk exosome s were r esolved by SDS – PAGE and analyzed by western blot. Ramos cell lysate w as used as a control for CD54 and l actoferrin western blots (top and middle panel) ; Caco – 2 cell lysate was used as control in the GM130 western blot (bottom panel) . D. Representative confocal images of the localization of digested human milk exosomes following incubation with HIEC cells. Cells were viewed at 60 ✕ magnification. Green (Alexa Fluor 488), exosome; red (Topro3 – iodide), nuclei. Scale bar, 20 μm .