Negative regulation of Toll-like receptor 4 signaling by IL-10-dependent microRNA-146b

Toll-like receptors (TLRs) play key roles in detecting pathogens and initiating inflammatory responses that, subsequently, prime specific adaptive responses. Several mechanisms control TLR activity to avoid excessive inflammation and consequent immunopathology, including the anti-inflammatory cytokine IL-10. Recently, several TLR-respon- sive microRNAs (miRs) have also been proposed as potential regu- lators of this signaling pathway, but their functional role during the inflammatory response still is incompletely understood. In this study, we report that, after LPS engagement, monocytes up-regulate miR- 146b via an IL-10–mediated STAT3-dependent loop. We show evi- dence that miR-146b modulates the TLR4 signaling pathway by direct targeting of multiple elements, including the LPS receptor TLR4 and the key adaptor/signaling proteins myeloid differentiation primary re- sponse (MyD88), interleukin-1 receptor-associated kinase 1 (IRAK-1), and TNF receptor-associated factor 6 (TRAF6). Furthermore, we demonstrate that the enforced expression of miR-146b in human monocytes led to a significant reduction in the LPS-dependent pro- duction of several proinflammatory cytokines and chemokines, in- cluding IL-6, TNF-α, IL-8, CCL3, CCL2, CCL7, and CXCL10. Our results thus identify miR-146b as an IL-10–responsive miR with an anti-in- flammatory activity based on multiple targeting of components of the TLR4 pathway in monocytes and candidate miR-146b as a mo- lecular effector of the IL-10 anti-inflammatory activity.