The detection of miRNAs in human milk led to two hypotheses to explain their existence; one proposes their use as a nutrient source and the other suggests they serve as functional molecules that retain their ability to influence gene expression. To date, we still know little about the miRNA expression profile of human milk or the pattern of expression over time after birth. In order to characterize the distribution of miRNA in human milk, Raymond and colleagues conducted a longitudinal study using samples from healthy women. The results of their study are published in the January 2022 issue of The Journal of Nutrition.
Breast milk samples from 44 French mothers that had delivered at term were collected on days 17, 60, and 90 after delivery. Quantification of miRNAs was performed using HTG EdgeSeq miRNA whole transcriptome assays. Caco-2 human intestinal cells were used to explore the functional relevance of two miRNAs identified as having a dynamic expression profile over time.
There were 35 miRNA that maintained a high and stable expression profile over the sampling time frame. A dynamic expression profile was identified for 11 miRNAs, and of those, miR-3126 and miR-3814 were used to treat Caco-2 cells in order to determine their influence on gene expression and alterations within relevant biological pathways. Observations from these analyses led the authors to conclude that there is a potential functional relevance to miRNA content of human milk as there were some longitudinal dynamics in their expression. Furthermore, they suggested their data support the hypothesis that miRNA present in human breast milk retain a signaling role in the neonate.
In a commentary, Hirschi stated the analytical approach used by Raymond and colleagues was robust in nature and that the 635 miRNAs found at all 3 time points were consistent with previously reported miRNA, which further validated their analyses. Hirschi does raise the question of whether the miRNA identified as having a dynamic expression pattern were able to survive digestion, and thus have a functional impact on gene expression in the neonate, as packaging of the molecules may dictate whether they are digested or not. Hirschi concludes the work of Raymond demonstrates there are potentially relevant changes in miRNA in human milk and that much more work needs to be done to determine their impact on neonatal development and health.
Frederic Raymond, Gregory Lefebvre, Lorane Texari, Solenn Pruvost, Sylviane Metairon, Geoffrey Cottenet, Alix Zollinger, Bogdan Mateescu, Claude Billeaud, Jean-Charles Picaud, Irma Silva-Zolezzi, Patrick Descombes, Nabil Bosco, Longitudinal Human Milk miRNA Composition over the First 3 mo of Lactation in a Cohort of Healthy Mothers Delivering Term Infants, The Journal of Nutrition, Volume 152, Issue 1, January 2022, Pages 94–106, https://doi.org/10.1093/jn/nxab282.
Kendal D Hirschi, Milking miRNAs for All Their Worth, The Journal of Nutrition, Volume 152, Issue 1, January 2022, Pages 1–2, https://doi.org/10.1093/jn/nxab326.
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