Human Breastmilk miRNAs, Diversity and Potentials for Preventive Strategy in Nutritional Therapy

The endogenous miRNAs of breast milk are the products of more than 1,000 nonprotein-coding genes, giving rise to mature small regulatory molecules of 19–25 nucleotides. They are incorporated in macromolecular complexes, loaded on Argonaut proteins, sequestrated in exosomes, lipid complexes, or present in exfoliated cells of epithelial, endothelial, or immune origins. Their expression is dependent on the stage of lactation, however their detection depends on progress in RNA sequencing and the reappraisal of small RNAs definition. Some miRNAs from plants are detected in breast milk, opening the possibility of stimulation of immune cells of the allergic repertoire. Each miRNA harbors a seeding sequence, which targets mRNAs, gene promoters, or long noncoding RNAs. Their activities depend on their bioavailability. Efficient doses of miRNAs are estimated at roughly 100 molecules in the cytoplasm of target cells from in vitro and in vivo experiments. Each miRNA is included in networks of stimulation/inhibition/sequestration driving the expression of cellular phenotypes. Three types of stress applied during lactation to manipulate miRNA supply, have been explored on the rodent offspring: foster mother, cafeteria diet, early weaning. The review present the main mature miRNAs described across current mothers’ cohorts, their bioavailability in experimental models, and the studies assessing the potentials of miR-26 or miR-320 miRNA families to alter offspring phenotype.