MicroRNA expression profiles of bovine milk exosomes in response to Staphylococcus aureus infection. Bos taurus

Milk is an essential source of nutrients to all mammalian offspring, and is rich in a wide variety of immunological components. Recently reported miRNAs that are present in breast milk and are selectively packaged into the exosomes, a type of membrane vesicles, secreted by most cell types. These exosomal miRNAs could be actively delivered into recipient cells, and play a key role in the regulation of innate and adaptive immunity. In the present study we analyzed the lactation-related miRNA expression profiles in bovine milk exosomes at 2 days post-infection with Staphylococcus aureus (S. aureus) using a deep sequencing. Analyzing over 76.44 million sequencing reads, a total of 720 miRNAs including 303 high-confident miRNA candidates were identified by two different approaches. The top 10 highly expressed miRNAs accounted for approximately 80% of all aligned reads, with the remaining miRNAs showing much lower expression. Bta-miR-101, -142-5p, -183, -2285g-3p, -223 and -99a-5p were significantly differentially regulated in S. aureus infected milk compared to their uninfected controls. Target prediction of the differently expressed miRNAs revealed 219 potential target candidates, and 22 unique target genes identified by David Gene Ontology analysis were significantly related to host immune processes and inflammation. This new knowledge of milk miRNA expression in response to S. aureus infection significantly provides new and comprehensive information on milk miRNA composition in general as well as changes occurring during an infection. Overall design: Four exosomal small RNA libraries were constructed from S. aureus infected bovine breast milk at 2 days post-infection (dpi), and correspondingly four libraries from bovine milk prior to infection were used as controls. They were named control (1, 2, 3 and 4) and infection (1, 2, 3 and 4), respectively.