Human milk exosomes and their microRNAs survive digestion in vitro and are taken up by human intestinal cells

Scope: 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. Methods and results: We 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. We 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 microRNA, and the top 15 microRNAs contributed similar to 11% of the sequencing reads. Upon digestion, the overall microRNA abundance in human milk exosomes was stable. Conclusion: Our 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.