Human milk exosomes provide a natural means of genetic material transfer to infants; however, the effect of gastric/pancreatic digestion milk exosomes stability and their microRNA content is largely unknown.
University of California, Davis researchers took a simulated gastric/pancreatic digestion protocol to perform in vitro digestion of milk exosomes, explore intestinal epithelial uptake, and further elucidate microRNA responses to digestion at early-, mid-, -late lactation by massive parallel sequencing. Both undigested and digested exosomes enter human intestinal crypt-like cells (HIEC), with evidence of nuclear localization. They identified 288 mature microRNAs from all 24 exosome samples, and an additional 610 at low abundance. A large number of synapse development- and immune-related microRNAs were identified. hsa-miR-22-3p was the most abundant miR, and the top 15 microRNAs contributed ∼11% of the sequencing reads. Upon digestion, the overall microRNA abundance in human milk exosomes was stable.
Human milk exosomes largely protects proteins contained in them during
in vitro gastric/pancreatic digestion
A. Proteins (5μg/lane) from exosomes were digested with pepsin at pH 2.0 and pH 4.0 followed by pancreatin digestion (see details in Methods), subjected to SDS-PAGE, and stained with 0.25% Coomassie brilliant Blue R-250. B. Antibody array membrane showing the presence/absence of tested proteins in both undigested human milk exosomes (upper panel) and paired exosomes digested at pH 4.0 (lower panel). Black dots on the pre-printed spots indicate presence of the tested protein. Positive control (+ctrl), positive for HRP detection as claimed by the manufacturer; negative control (-ctrl), GM130. C. Representative confocal images of the localiza tion of digested human milk exosomes following incubation with HIEC cells for indicated time periods. Cells were viewed at 60 ✕ magnification. Green (Alexa Fluor 488), exosome; red (Topro3-iodide), nuclei.
These results for the first time reveal the survivability and complexity of human milk exosome microRNAs upon simulated gastric/pancreatic digestion, and the dynamics during lactation stages. The results suggest a previously underexplored area of infant response to genetic material in human milk exosomes.