Human milk exosomes and their microRNAs survive digestion

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.

Liao Y, Du X, Li J, Lönnerdal B. (2017) Human milk exosomes and their microRNAs survive digestion in vitro and are taken up by human intestinal cells. Mol Nutr Food Res [Epub ahead of print]. [abstract]

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