Macrophage tolerance to MyD88-dependent TLR agonists is mediated by LPS-/R848-induced miR-146a (IRM12P.649)

Abstract Toll like receptors (TLRs) TLRs facilitate the recognition of pathogens by immune cells and the initiation of the immune response, leading to the production of proinflammatory mediators. Production of proinflammatory mediators by innate immune cells such as macrophages is tightly regulated to facilitate pathogen clearance while limiting adverse impact on host tissue. Exposure to TLR ligands induces a state of temporary refractoriness to a subsequent exposure of a TLR ligand, a phenomenon referred to as ‘tolerance’. This study sought to evaluate the mechanistic regulation of TLR4 and TLR7/8 ligand induced tolerance to other TLRs by miR-146a. Using THP-1 macrophages as well as human M1 and M2 macrophages, we demonstrate that priming with a TLR4 agonist (LPS) or a TLR7/8 agonist (R848) induce tolerance to a panel of TLR ligands in macrophages, leading to the impaired production of a variety of cytokines and chemokines. We also demonstrate that overexpression of miR-146a is sufficient to mimic LPS- or R848-induced hyporesponsiveness. Conversely, the knockdown of miR-146a leads to LPS- or R848-induced TLR hyperresponsiveness. Furthermore, we demonstrate that while miR-146a dampens cytokine production following a primary stimulus with MyD88-dependent, but not MyD88- independent TLR pathways. Collectively, these data provide comprehensive evidence of the central role of miR-146a in TLR signaling tolerance to plasma membrane as well as endosomal TLR ligands in human macrophages.