ABSTRACT: Purpose: The goal of this study is to explore the role of miRNAs in dairy cow response to E. coli and S. aureus, mastitis causing pathogens, is not well understood. Results: The global expression of miRNAs in bovine mammary epithelial cells (MAC-T cells) challenged with heat-inactivated Staphylococcus aureus (S. aureus) or Escherichia coli (E. coli) bacteria (treatments: 6, 12, 24 and 48 hr) and without challenge (control: 0, 6, 12, 24 and 48 hr) was profiled using next-generation-sequencing. A total of 231 known bovine miRNAs were identified with more than 10 counts per million (CPM) in at least one of 13 libraries and 5 miRNAs including bta-miR-21-5p, miR-27b, miR-22-3p, miR-184 and let-7f represented more than 50% of the total reads of known bovine miRNAs. One hundred and fifty novel miRNAs were identified and half of them belong to the bta-miR-2284 family. Seventeen miRNAs were significantly (P<0.05) differentially regulated by the presence of pathogens. E. coli initiated an earlier regulation of miRNAs (6 miRNAs differentially regulated within the first 6 hrs post challenge as compared to one for S. aureus) while S. aureus presented a delayed response. Five differentially expressed miRNAs (Bta-miR184, miR-24-3p, miR-148, miR-486 and bta-let-7a-5p) were unique to E. coli while four (bta-miR-2339, miR-499, miR-23a and miR-99b) were unique to S. aureus. In addition, our study revealed a temporal differential regulation of five miRNAs (bta-miR-193a-3p, miR-423-5p, miR-30b-5p, miR-29c and miR-un116) in unchallenged cells. Target gene predictions of pathogen differentially expressed miRNAs indicate a significant enrichment in gene ontology functional categories in development/cellular processes, biological regulation as well as cell growth and death. Furthermore, target genes were significantly enriched in several KEGG (Kyoto encyclopedia of genes and genomes) pathways of the immune system, signal transduction, cellular process, nervous system, development and pathways in human diseases, especially cancer. Conclusion: Using next-generation sequencing, our study identified 150 novel bovine miRNAs and revealed a pathogen directed differential regulation of miRNAs in MAC-T cells with roles in immunity and development. E. coli elicited an earlier differential regulation of miRNAs as opposed to a delayed regulation by S. aureus. Furthermore, target gene prediction showed significant enrichments for functions in different biological and cellular processes as well as KEGG pathways in immunity, development and human diseases. Our study provides a further confirmation of the involvement of mammary epithelia cells in contributing to the immune response to infecting pathogens and suggests the potential of miRNAs to serve as biomarkers for diagnosis of mastitis and development of control measures.
