MiR-acle milk: Profiling milk-derived microRNAs using molecular barcoding technology for understanding their potential role in gastrointestinal function

Xuejing (Ivy) Men, Grasslands Research Centre, Tennent Drive, Palmerston North, New Zealand

X. Men1,2,4, M.J. McCann1,3, A. Thompson2,4, and N. Roy1,2,3,4
1. Food Nutrition & Health Team, Food & Bio-based Products, AgResearch Limited, Palmerston North, New Zealand;
2. Riddet Institute, Massey University, Palmerston North, New Zealand;
3. Gravida: National Centre for Growth and Development, Auckland, New Zealand;
4. Massey Institute of Food Science and Technology, Massey University, Palmerston North, New Zealand.

Milk is a complex fluid that provides nutrition and aids postnatal development for infants, while also contributing to our overall health as we age. Recent evidence has identified a class of small non-coding RNAs stably expressed in milk, called microRNA (miRNA). These miRNAs function at the post-transcriptional level to influence protein translation by binding to the complementary region of mRNA and repressing translation or promoting degradation of the mRNA.

MiRNAs have been shown to be key regulators of gene expression networks and are implicated in several biological processes associated with our health. Therefore, milk-derived miRNAs may represent another mechanism by which milk influences key biological processes. There is evidence suggesting that milk-derived miRNA encapsulated in exosomes can survive digestion and be absorbed, so we hypothesise that: (1) miRNA within milk exosomes are quantifiable by the novel digital molecular barcoding technology (NanoString technologies nCounter® system), and (2) direct quantification of miRNA enables a more appropriate understanding of the role of miRNA in gastrointestinal function.

A preliminary study with crude lysate and exosomal RNA was completed to develop a method for direct quantification of miRNA in breast milk using the NanoString technologies nCounter® system. The results showed that the column-based exosomal miRNA extraction is the most suitable method for future miRNA profiling studies, especially with low sample volume. Amongst the top 10 most abundant exosomal miRNAs identified, 5 of them were also reported as the most highly expressed miRNAs in another study using small RNA sequencing, and 3 were described as the most highly expressed miRNAs in lipid fraction of the breast milk.

Human milk miRNA profiles differ considerably between individuals, suggesting that they may be influenced by maternal health, and there may also be differences in miRNA composition and abundance. Therefore, future studies will require accurate and direct counting of miRNA in order to appropriately account for the inter-individual differences when exploring the miRNA-mediated health benefits of milk.

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