Very little is known about miRNAs found in breastmilk cells, which also reflect the cells of the lactating mammary epithelium. Our hypothesis is that breastmilk cells are richer in miRNA compared to other milk fractions, such as skim milk. Further, the effects of milk removal by the infant on milk cell miRNA content and/or composition have not been investigated. Breastmilk cells conserved higher miRNA content than previously published lipid and skim fractions of breastmilk as well as other known sources of miRNA in humans. Specifically, 1,467 known mature miRNAs were identified and a further 1996 novel miRNAs, of which 89 were highly expressed. As previously shown, post-feed milk contained more cells than pre-feed milk, and the same was observed for miRNA content. However, no statistically significant difference was found in the expression of the total known and novel miRNAs between pre- and post-feed milk (p=0.76), although 27 known miRNAs and 1 novel miRNA were higher expressed in post-feed milk. As expected, samples richer in viable cells contained more known miRNAs (p = 0.01). Functional analysis of the top 10 most highly expressed known miRNAs showed that they may be potentially involved in crucial roles for the infant, including body fluid balance, thirst, appetite, immune responses, and development. In conclusion, breastmilk is highly rich in miRNA which may play important functions in the breastfed infant and the lactating breast. Milk removal by the infant can influence the total miRNA content of breastmilk, similar to its cell and fat content, but the miRNA composition remains constant
Overall design: Freshly expressed breastmilk samples were collected from 10 mothers on month 2 of lactation. Total RNA and miRNA content were quantified in pre- and post-feed samples from each mother. Next generation sequencing using illumina HiSeq 2000 was performed on 20 samples (one sample pre-feed and one sample post-feed from each mother) to profile mature miRNAs in the breastmilk cellular fraction. Filtered (clean) reads were aligned to the latest version of miRBase 21.0. Also, mireap software was used to predict novel miRNAs. Linear mixed effect models and ANOVA were used to compare miRNA expression levels between samples.
Less...