miR-21a-5p regulates gualynate-binding protein 5 and IL-10 expression in macrophages affecting host control of Brucella abortus infection. Mus musculus strain:C57BL/6

Brucella abortus is a Gram-negative intracellular bacterium that causes a worldwide zoonosis termed brucellosis, which is characterized as a debilitating infection with serious clinical manifestations leading to severe complications. In spite of great advances in studies involving host-B. abortus interactions, there are many gaps related to B. abortus modulation of the host immune response through regulatory mechanisms. Here, we deep sequenced small RNAs from bone marrow-derived macrophages infected or not with B. abortus, identifying that several miRNAs were up- and down-regulated during infection. We validated 4 up-regulated and 5 dow-nregulated miRNAs in vitro in macrophages and in spleens from infected mice at 1, 3 or 6 days post-infection when compared to non-infected animals. Among these miRNAs, mmu-miR-181a-5p (up-regulated) or mmu-miR-21a-5p (down-regulated) were selected for further analysis. First, we determined that changes in the expression of both miRNAs induced by infection were dependent on the adaptor molecule MyD88. Further, evaluating putative targets of mmu-miR-181a-5p, we demonstrated this miRNA negatively regulates TNF-alpha expression following Brucella infection. In contrast, miR-21a-5p targets included a negative regulator of IL-10, PDCD4, and several guanylate-binding proteins (GBP). As a result, during infection miR-21a-5p led to up-regulation of IL-10 expression and down-regulation of GBP5 in macrophages infected with Brucella. Since GBP5 and IL-10 are important molecules involved in host control of Brucella infection, we decided to investigate the role of mmu-miR-21a-5p in bacterial replication in macrophages. mmu-miR-21a-5p mimic enhances bacterial growth whereas miRNA inhibitor reduced Brucella load in macrophages. Taken together, the results indicate that down-regulation of mmu-miR-21a-5p induced by infection increases GBP5 levels and decreases IL-10 expression thus contributing to bacterial control in host cells.