MicroRNAs as novel bioactive components of human breastmilk

Abstract

MicroRNAs are short, non-coding oligonucleotides that regulate gene expression at the post-transcriptional level. These small molecules participate in the control of various cellular processes and signalling pathways. Since 2010 microRNAs have been recognized as a new bioactive component of breastmilk, which is an exceptionally rich source of these oligonucleotides. In infants fed with breastmilk, microRNAs are involved in the growth and proper development as well as maturation of the immune system. It has been demonstrated that microRNAs are resistant to harsh conditions during in vitro digestion in simulated gastrointestinal tract of a newborn and, therefore, may be absorbed by the intestinal cells. Protection against RNase activity and low pH is provided by exosomes, which are carriers of microRNAs in skim milk or by fat globules and milk cells. It has been reported that, in contrast to human milk, infant formulas contain only a few microRNAs, which have been derived from other organisms, such as cow or soy. It may be presumed that supplementing infant formulas with microRNAs identical with those which occur naturally in breastmilk may constitute a new way of designing artificial substitutes for human breastmilk.