A next generation sequencing approach to profiling the host miRNA response to a bovine mastitis pathogen

Substantial evidence is now beginning to emerge that miRNAs, short, non-coding RNAs, which post-transcriptionally regulate gene expression, play a key role in the regulation of innate and adaptive immunity in humans and mice. Little is currently known, however, regarding the importance miRNAs in regulating the host response to infection in agriculturally important animals, such as cattle. Mastitis is an inflammatory disease of the mammary gland caused either by infection or physical damage, which is associated with substantial economic losses. In this study, we report a next generation sequencing approach to profile the expression of bovine miRNAs in primary bovine mammary epithelial (BMEs) cells challenged with a bovine mastitis pathogen, Streptococcus uberis (0140J). Computational analysis has been undertaken on 450 million raw sequence reads and revealed that 20% of known bovine miRNAs are expressed in BMEs. Furthermore, 22 miRNAs were found to be differentially expressed over the 6 hour time-course. We have completed miRNA target prediction analysis and found that the target genes of down-regulated miRNAs are enriched for having a role in innate immunity, and pathways associated with target genes of up-regulated miRNA correspond to previously reported mastitis-relevant pathways. In addition, we report 21 potentially novel bovine miRNAs that have not previously been described, two of which have close human orthologs. This study provides new insight into the regulation of miRNAs in the host response to infection at an unprecedented level in any species.