Effect of maternal stress during lactation on microRNA-125b-5p expression in breast milk and on the neonatal...

microRNA-125b-5p (miR-125b) is abundant in breast milk. However, the physiological role of milk-derived miR-125b in infant development is unknown. Although maternal stress during lactation is well known to change the lipid and protein content of milk, the effect of stress on miR-125b expression in breast milk has never been examined. The objective of this study was to evaluate the correlation between maternal stress and miR-125b expression in the milk, and to investigate the effect of changes in miR-125b expression caused by maternal stress during lactation on intestinal barrier function and zonula occludens-1 (ZO-1) protein levels in infants.

Healthy Japanese nursing women were enrolled in this study. Psychological stress was assessed using the Profile of Mood State 2nd-Adult short (POMS2). miR-125b expression in breast milk was determined using quantitative real-time polymerase chain reaction. Levels of the tight junction protein ZO-1 and P53, which is a direct target of miR-125b, in the ileum of neonatal mice breastfed by stressed nursing mice were assessed using western blotting. To investigate the effect of miR-125b on the intestinal barrier function, the levels of ZO-1 and transepithelial electrical resistance in human intestinal epithelial Caco-2 cells with lentivirus-mediated miR-125b overexpression were evaluated.

A significant negative correlation was observed between miR-125b expression in breast milk and total mood disturbance (TMD) score. Each negative mood scale (anger-hostility, confusion-bewilderment, depression-dejection, fatigue-inertia, and tension-anxiety) on the TMD subscale was significantly negatively correlated with miR-125b expression in breast milk. In contrast, the positive mood scale vigor-activity on the TMD subscale was significantly positively correlated with miR-125b expression in breast milk. Additionally, a positive mood scale friendliness exhibited a significant positive correlation with miR-125b expression in breast milk. The miR-125b levels in mammary tissues of stressed maternal mice were significantly lower than those in control maternal mice. The miR-125b levels in pups nursed by stressed mothers (stressed pups) were significantly lower than those in pups nursed by control mothers (control pups). Additionally, P53 protein levels were significantly higher in stressed pups than in control pups. A marked increase in transepithelial electrical resistance was observed in miR-125b-overexpressing cells compared with that in control cells. ZO-1 protein levels in miR-125b-overexpressing Caco-2 cells were significantly higher than those in control cells. Additionally, p53 levels in miR-125b-overexpressing Caco-2 cells were significantly lower than those in control cells.

Stress during lactation may decrease miR-125b expression in breast milk. Additionally, stress-induced suppression of miR-125b expression in breast milk may inhibit intestinal barrier function and ZO-1 levels in infants, and this inhibition may be related to an increase in P53 levels in the intestinal tissue. The study findings should benefit breastfeeding mothers, their families, and perinatal healthcare professionals.