Exploration of bovine milk exosomal microRNAs during Streptococcus uberis induced mastitis. Bos taurus

Milk is an indispensable source of infant nutrition in all mammals, made up of complex constituents needed for infant nourishment and immunity. Comparison of miRNA profiles between infected and non-infected/control Holstein cattle could provide important information on the differences in composition of milk at the level of miRNA, if any, and broaden our perspective and understanding of the effect of pathology on cellular compositions and functions. In the present study we therefore analyzed the expression profiles of bovine milk exosomal miRNAs during S. uberis infection and identified 328 known miRNAs and 82 high-confidence miRNA candidates by deep sequencing. The top 10 miRNAs in both control and infected replicates accounted for approximately 80% of total counts, which were predicted to target 605 genes using two computational approaches. In addition, 15 significantly differentially expressed miRNAs were identified between control and infected replicates during S. uberis infection, and a total of 1,852 unique genes were predicted to be targeted by these miRNAs. Ingenuity Canonical Pathways and Diseases and Biological Function analyses using IPA indicated that the identified miRNAs targets mainly enriched in regulating the innate and adaptive immune responses in newborns, as well as infant growth and development. The characterization of these miRNAs could contribute to a better understanding of the molecular mechanisms involved in lactation physiology and milk imparted immune function in the dairy cattle. Overall design: Three exosomal small RNA libraries were constructed from S. uberis infected bovine breast milk at 2 days post-infection (dpi), and correspondingly three libraries from bovine milk prior to infection were used as controls. They were named control (1, 2 and 3) and infection (1, 2 and 3), respectively.