Influence of Maternal Diet and Lactation Time on the Exosomal miRNA Cargo in Breast Milk

The importance of breastfeeding for maternal and infant health is widely accepted. In this sense, the presence of macro and micronutrients in human milk ensures proper and safe infant nutrition, along with multiple bioactive molecules that modulate the newborn's immunity. Usually packaged within exosomes, miRNAs circulating in milk are bioavailable to breastfed infants. Their role in infant development is poorly understood, mainly because the miRNA cargo of human milk has not been fully elucidated to date. The objective of this study is to assess the presence of eleven miRNAs (miR-148a-3p, miR-29b-3p, miR-125b-5p, miR-200c-3p, let-7f-5p, let-7b-5p, let-7a-5p, miR-92a, miR-181a-3p, miR-30a-5p and miR-155-5p) in breast milk exosomes and determine the impact of lactation time and maternal factors on their levels. Samples were collected from a cohort of 59 Spanish mothers, ranging from 1 to 59 months of lactation. MiRNAs were analyzed using reverse transcription and qPCR. Lactation time showed a significant and noteworthy downregulation for miR-148a-3p, miR-200c-3p and miR-125b-5p and hsa-let-7a-5p. The levels of miRNAs were correlated with the levels of some fatty acids such as arachidonic acid and DHA. Also, a positive correlation between Se and arachidonic acid levels in breast milk was found, linked with upregulated miR-125b. The results of this work demonstrate that miRNA levels are dynamic, probably with the aim of adapting to the specific needs of the infant.