Brucella Omp25 Upregulates miR-155, miR-21-5p, and miR-23b to Inhibit Interleukin-12 Production via Modulation of Programmed Death-1 Signaling in Human Monocyte/Macrophages

Abstract

<i>Brucella</i> spp. infection results in compromised Type1 (Th1) cellular immune response. Several reports have described an immunomodulatory function for <i>Brucella</i> major outer membrane protein Omp25. However, the mechanism by which Omp25 modulates macrophage dysfunction has not been defined. Herein, we reported that Omp25-deficient mutant of <i>Brucella suis</i> exhibited an enhanced ability to induce interleukin (IL)-12 whereas ectopic expression of Omp25 protein inhibited TLR agonists-induced IL-12 p70 production through suppression of both IL-12 p40 and p35 subunit expression in THP-1 cells. In addition, Omp25 significantly upregulated miR-155, -23b and -21-5p, as well as the immunomodulator molecule programmed death-1 (PD-1) in monocyte/macrophages. The upregulation of miR-155 and -23b correlated temporally with decreased TAB2 levels, IκB phosphorylation and IL-12 p40 levels by targeting TAB2 and <i>il12B</i> 3' untranslated region (UTR), respectively, while miR-21-5p increase directly led to the reduction of lipopolysaccharide (LPS)/R848-induced IL-12 p35 protein by targeting <i>il12A</i> 3'UTR. Consistent with this finding, reduction of miR-155 and -23b attenuated the inhibitory effects of Omp25 on LPS/R848-induced IL-12 p40 expression at both transcriptional and posttranscriptional levels, while reduction of miR-21-5p attenuated the inhibitory effects of Omp25 on LPS/R848-induced IL-12 p35 expression at the posttranscriptional level, together significantly enhanced IL-12 p70 production upon LPS/R848 stimulation. We also found that blocking PD-1 signaling decreased the expression of miR-155, -23b and -21-5p induced by Omp25 and enhanced IL-12 production in monocyte/macrophages. Altogether, these data demonstrate that <i>Brucella</i> Omp25 induces miR-155, -23b and -21-5p to negatively regulate IL-12 production at both transcriptional and posttranscriptional levels <i>via</i> regulation of PD-1 signaling, which provides an entirely new mechanism underlying monocyte/macrophages dysfunction during <i>Brucella</i> spp. infection.