title: Mechanistic role of microRNA-146a in endotoxin-induced differential cross-regulation of TLR signaling.
abstract: Human TLRs are critical sensors for microbial components leading to the production of proinflammatory cytokines that are controlled by various mechanisms. Monocytes pretreated with LPS exhibit a state of hyporesponsiveness, referred to as cross-tolerance, to both homologous and heterologous ligands, which play a broader role in innate immunity. To date, LPS-induced cross-tolerance has not been examined regarding microRNA expression kinetics. In this study, THP-1 monocytes treated with various inflammatory ligands showed a continuous amplification of microRNA (miR)-146a over 24 h that is inversely correlated to TNF-α production. In contrast, inhibition of miR-146a showed a reciprocal effect. Thus, the characteristic upregulation of miR-146a in LPS-exposed THP-1 monocytes was studied for cross-tolerance. Strikingly, in LPS-tolerized THP-1 monocytes, only miR-146a showed a continuous overexpression, suggesting its crucial role in cross-tolerance. Similarly, peptidoglycan-primed THP-1 cells showed homologous tolerance associated with miR-146a upregulation. Subsequently, interchangeable differential cross-regulation was observed among non-LPS ligands. TLR2 and TLR5 ligands showed both homologous and heterologous tolerance correlated to miR-146a overexpression. More importantly, inflammatory responses to TLR4, TLR2, and TLR5 ligands were reduced due to knockdown of miR-146a targets IL-1R-associated kinase 1 or TNFR-associated factor 6, suggesting the regulatory effect of miR-146a on these TLRs signaling. Transfection of miR-146a into THP-1 cells caused reduction of TNF-α production, mimicking LPS-induced cross-tolerance. Aside from individual ligands, a whole bacterial challenge in LPS-primed THP-1 monocytes was accompanied by less TNF-α production, which is conversely correlated to miR-146a expression. Our studies have thus demonstrated that miR-146a plays a crucial role for in vitro monocytic cell-based endotoxin-induced cross-tolerance.
authors.affiliation: Department of Oral Biology, University of Florida, Gainesville, FL 32610, USA.
authors.forename: Md A
authors.initials: MA
authors.lastname: Nahid
authors.forename: Minoru
authors.initials: M
authors.lastname: Satoh
authors.forename: Edward K L
authors.initials: EK
authors.lastname: Chan
mesh_terms: D000818:Animals; D016866:Bacteroidaceae Infections / Q000276:immunology / Q000378:metabolism; D045744:Cell Line, Tumor; D016207:Cytokines / Q000037:antagonists & inhibitors / Q000096:biosynthesis; D004927:Escherichia coli Infections / Q000276:immunology / Q000378:metabolism; D005260:Female; D006801:Humans; D007108:Immune Tolerance; D007113:Immunity, Innate; D018836:Inflammation Mediators / Q000037:antagonists & inhibitors / Q000378:metabolism; D008024:Ligands; D008070:Lipopolysaccharides / Q000633:toxicity*; D051379:Mice; D008810:Mice, Inbred C57BL; D035683:MicroRNAs / Q000037:antagonists & inhibitors / Q000096:biosynthesis / Q000502:physiology*; D009000:Monocytes / Q000276:immunology / Q000378:metabolism; D015398:Signal Transduction / Q000276:immunology*; D013203:Staphylococcal Infections / Q000276:immunology / Q000378:metabolism; D051193:Toll-Like Receptors / Q000378:metabolism* / Q000502:physiology
chemical_list: D016207:Cytokines; D018836:Inflammation Mediators; D008024:Ligands; D008070:Lipopolysaccharides; C542542:MIRN146 microRNA, human; D035683:MicroRNAs; D051193:Toll-Like Receptors