Gene regulation by dietary microRNAs.

MicroRNAs (miRNAs) silence genes through destabilizing mRNA or preventing translation of mRNA, thereby playing an essential role in gene silencing. Traditionally, miRNAs have been considered endogenous regulators of genes, i.e., miRNAs synthesized by an organism regulate the genes in that organism. Recently, that dogma has been challenged in studies suggesting that food-borne miRNAs are bioavailable and affect gene expression in mice and humans. While the evidence in support of this theory may be considered weak for miRNAs that originate in plants, there is compelling evidence to suggest that humans use bovine miRNAs in cow's milk and avian miRNAs in chicken eggs for gene regulation. Importantly, evidence also suggests that mice fed a miRNA-depleted diet cannot compensate for dietary depletion by increased endogenous synthesis. Bioinformatics predictions implicate bovine miRNAs in the regulation of genes that play roles in human health and development. Current challenges in this area of research include that some miRNAs are unable to establish a cause-and-effect between miRNA depletion and disease in miRNA knockout mice, and sequence similarities and identities for bovine and human miRNAs render it difficult to distinguish between exogenous and endogenous miRNAs. Based on what is currently known about dietary miRNAs, the body of evidence appears to be sufficient to consider milk miRNA bioactive compounds in foods, and to increase research activities in this field.