Profiling of Human Milk miRNA

Breastmilk has been recently identified as a rich source of miRNA with potential regulatory functions in the infant. We compared the miRNA content of breastmilk with that of circulating blood in lactating women, with the aim to shed light into the potential functions of these milk molecules and their origin. Breastmilk and blood samples were collected from 10 mothers in month 2 of lactation. miRNA was analyzed from the cellular and lipid fraction of breastmilk as well as maternal peripheral blood mononucleated cells (PBMCs) and plasma using the TaqMan OpenArray system for 770 different human miRNAs. The total miRNA content of breastmilk and blood was high, particularly in the breastmilk cellular fraction and PBMCs. More than 293 miRNA species were detected in breastmilk cells, 233 in the breastmilk lipids, 169 in blood plasma and 345 in PBMCs. Single correlation analysis showed that within milk cells, milk lipids, and PBMCs, miRNA expression levels were similar among participants. In plasma, marked inter‐individual variation in single miRNA species was observed. Cluster analysis indicated that the miRNA profiles of breastmilk cells and lipids grouped together; however, differences were seen between PBMCs and plasma, with the latter showing the most variable miRNA composition. This study confirms the rich miRNA nature of human breastmilk. Our comparisons between blood and milk miRNA suggest that a proportion of milk miRNA may be derived from the maternal bloodstream, whilst some may originate from the breast epithelium. Given the recently identified stability and function of food‐derived miRNA in regulating mammalian genes, we propose that breastmilk is a rich source of miRNA, which may contribute to early infant development.