Identification and characterization of differentially expressed exosomal microRNAs in bovine milk infected with Staphylococcus aureus

BACKGROUND: MicroRNAs (miRNAs) in milk-derived exosomes may reflect pathophysiological changes caused by mastitis. This study profiled miRNAs in exosomes from both normal milk and mastitic milk infected by Staphylococcus aureus (S. aureus). The potential targets for differentially expressed (DE) miRNAs were predicted and the target genes for bta-miR-378 and bta-miR-185 were also validated. RESULTS: Total RNA from milk exosomes was collected from healthy cows (n = 3, the control group) and S. aureus infected cows (n = 6, the SA group). Two hundred ninety miRNAs (221 known and 69 novel ones) were identified. Among them, 22 known and 15 novel miRNAs were differentially expressed. Target genes of DE miRNAs were significantly enriched in intracellular protein transport, endoplasmic reticulum and identical protein binding. The expression of two miRNAs (bta-miR-378 and bta-miR-185) with high read counts and log(2) fold changes (> 3.5) was significantly higher in mastitic milk infected with S. aureus. One target gene (VAT1L) of bta-miR-378 and five target genes (DYRK1B, MLLT3, HP1BP3, NPR2 and PGM1) of bta-miR-185 were validated. CONCLUSION: DE miRNAs in exosomes from normal and S. aureus infected milk were identified. The predicted targets for two DE miRNAs (bta-miR-378 and bta-miR-185) were further validated. The linkage between the validated target genes and diseases suggested that we should pay particular attention to exosome miRNAs from mastitic milk in terms of milk safety.