lncRNA NORAD is consistently detected in breastmilk exosomes and its expression is downregulated in mothers of preterm infants.

Breast milk is the ideal food for infants and undoubtedly has immediate and long­term benefits. Breast milk contains extracellular vesicles (EVs) i.e., exosomes secreted by maternal breast cells. Exosomes carry genetic material, such as long non­coding RNAs (lncRNAs), which possibly participate in cell­to­cell communications, as they are known to regulate critical gene pathways. The aim of the present study was to screen human breastmilk exosomes for their lncRNA cargo and to examine exosomal lncRNA levels associated with milk obtained from mothers that gave birth at term or prematurely (<37 weeks of gestation). Samples were collected at 3 weeks postpartum from 20 healthy, breastfeeding mothers; 10 mothers had given birth at full­term and 10 mothers preterm. Exosomal RNA was extracted from all samples and the expression of 88 distinct lncRNAs was determined using reverse transcription­quantitative PCR. A total of 13 lncRNAs were detected in ≥85% of the samples, while 31 were detected in ≥50% of the samples. Differential expression analysis of the lncRNAs between the two groups revealed ≥2­fold differences, with generally higher lncRNA concentrations found in the milk of the mothers that gave birth at term compared with those that gave birth preterm. Among these, the non­coding RNA activated at DNA damage (NORAD) was prominently detected in both groups, and its expression was significantly downregulated in the breast milk exosomes of mothers who delivered preterm. On the whole, the present study demonstrates that breast milk lncRNAs may be important factors of normal early human development. Collectively, the presence of lncRNAs in human breast milk may explain the consistent inability of researchers to fully 'humanize' animal milk.