MicroRNA-146a promotes mycobacterial survival in macrophages through suppressing nitric oxide production.

Miao Li,Yimin Fang,Xiaomin Lai,Xi Huang,Minhao Wu,Gucheng Zeng,Kun Yang,Yi Wang,Meiyu Li,Jinli Wang,Sitang Gong

doi:10.1038/srep23351

Abstract

Macrophages play a crucial role in host innate anti-mycobacterial defense, which is tightly regulated by multiple factors, including microRNAs. Our previous study showed that a panel of microRNAs was markedly up-regulated in macrophages upon mycobacterial infection. Here, we investigated the biological function of miR-146a during mycobacterial infection. miR-146a expression was induced both in vitro and in vivo after Mycobacterium bovis BCG infection. The inducible miR-146a could suppress the inducible nitric oxide (NO) synthase (iNOS) expression and NO generation, thus promoting mycobacterial survival in macrophages. Inhibition of endogenous miR-146a increased NO production and mycobacterial clearance. Moreover, miR-146a attenuated the activation of nuclear factor κB and mitogen-activated protein kinases signaling pathways during BCG infection, which in turn repressed iNOS expression. Mechanistically, miR-146a directly targeted tumor necrosis factor (TNF) receptor-associated factor 6 (TRAF6) at post-transcriptional level. Silencing TRAF6 decreased iNOS expression and NO production in BCG-infected macrophages, while overexpression of TRAF6 reversed miR-146a-mediated inhibition of NO production and clearance of mycobacteria. Therefore, we demonstrated a novel role of miR-146a in the modulation of host defense against mycobacterial infection by repressing NO production via targeting TRAF6, which may provide a promising therapeutic target for tuberculosis.

Highlights

Macrophages play a crucial role in host innate anti-mycobacterial defense, which is tightly regulated by multiple factors, including microRNAs
The present study reveals a novel role of miR-146a in regulating inducible nitric oxide synthase (iNOS) expression and nitric oxide (NO) production in macrophages upon M. bovis BCG infection
Our data show that miR-146a impairs nuclear factor kappa B (NF-κ B), JNK and p38 MAPKs signaling activation by targeting TRAF6, resulting in an inhibition of NO production and BCG killing

Summary

Introduction

Macrophages play a crucial role in host innate anti-mycobacterial defense, which is tightly regulated by multiple factors, including microRNAs. Inhibition of iNOS in human alveolar macrophages from TB patients abolishes the macrophage-mediated anti-mycobacterial activity in vitro[20] These studies establish a critical role of iNOS-mediated NO production in host defense against MTB. Pro-inflammatory cytokines and interferons are prototypical inducers of iNOS15 These factors trigger NF-κ B, MAPK or signal transducer and activator transcription 1 (STAT1) pathways, which initiate the transcription of iNOS gene in macrophages[16,21]. In patients with active TB, miR-582-5p is up-regulated and reduces MTB-induced apoptosis of monocytes by targeting FOXO128 It remains unclear whether mycobacteria-triggered miRNAs regulate NO-mediated bacterial clearance

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Conclusion