Characterization of the global bovine microRNAome of peripheral blood mononuclear cells isolated from Mycobacterium bovis exposed cattle

Accurate diagnostics are urgently needed for bovine TB - an economically devastating disease posing a re-emerging threat to veterinary and public health worldwide. MicroRNAs, post-transcriptional gene regulators involved in a range of biological processes and immunological pathways, have emerged as promising diagnostic biomarkers for numerous diseases. In human TB, microRNAs have been widely studied, but not much is currently known about their role in bovine TB. This study aimed to investigate the diagnostic potential of microRNAs in bTB through comprehensive analysis of their expression profiles in disparate states of M. bovis exposure. We used RNA-sequencing to characterize the global microRNAome of peripheral blood mononuclear cells from cattle that were either unvaccinated, BCG-vaccinated, unprotected or protected. A total of 468 microRNAs were detected across all samples, none of which were uniquely expressed in any group. Significant differential expression was observed for bta-miR-6122-3p, bta-miR-3533 and bta-miR29b in various comparisons. Subsequent target analysis of bta-miR-29b, a candidate biomarker in human tuberculosis, revealed that several genes (ACVR2A, PIK3R1, TBX21, TGFBR1 and TGFBR2) involved in a number of relevant T-cell and immune signaling pathways, were amongst the predicted targets. Overall, this study provides evidence that microRNAs could be promising novel biomarkers for bovine TB diagnostics.