title: Identification of a Novel Toll-like Receptor 7 Endogenous Ligand in Rheumatoid Arthritis Synovial Fluid That Can Provoke Arthritic Joint Inflammation.
abstract: Levels of Toll-like receptor 7 (TLR-7) are elevated in rheumatoid arthritis (RA), but the impact on RA is unknown because the endogenous ligand for TLR-7 has not been identified. The aim of this study was to identify a TLR-7 endogenous ligand and to determine its role in the pathogenesis of RA.
  
  
  
  The presence of an endogenous TLR-7 ligand, microRNA let-7b (miR-let-7b), was examined by real-time polymerase chain reaction (PCR) analysis. Using RA knockdown cells, TLR-7-knockout mice, or antagonist, the specificity of miR-let-7b as a potential ligand for TLR-7 was tested. The mechanism by which ligation of miR-let-7b to TLR-7 promotes disease was investigated in RA myeloid cells by real-time PCR, enzyme-linked immunosorbent assay, and fluorescence-activated cell sorting. We also established the effect of ectopic miR-let-7b expression on arthritic joint inflammation.
  
  
  
  We found that a TLR-7 endogenous ligand resides mainly in RA synovial fluid macrophages. The GU-rich domain in miR-let-7b was found to be essential for TLR-7 ligation, since miR-147, the positive control for GU, was able to stimulate TLR-7+ myeloid cells, whereas miR-124, the negative, non-GU, control, was not. We demonstrated that miR-let-7b or exosomes containing miR-let-7b could transform the RA and/or mouse naive or antiinflammatory macrophages into inflammatory M1 macrophages via TLR-7 ligation. Consistently, we showed that miR-let-7b provokes arthritis by remodeling naive myeloid cells into M1 macrophages via TLR-7 ligation, since joint swelling and M1 macrophages are absent in TLR-7-deficient mice.
  
  
  
  The results of this study underscore the importance of miR-let-7b ligation to TLR-7 in the joint during the effector phase of RA.
authors.affiliation: Jesse Brown VA Medical Center and University of Illinois at Chicago.
authors.forename: Seung-Jae
authors.initials: SJ
authors.lastname: Kim
authors.affiliation: Jesse Brown VA Medical Center and University of Illinois at Chicago.
authors.forename: Zhenlong
authors.initials: Z
authors.lastname: Chen
authors.affiliation: Jesse Brown VA Medical Center and University of Illinois at Chicago.
authors.forename: Abdul B
authors.initials: AB
authors.lastname: Essani
authors.affiliation: Jesse Brown VA Medical Center and University of Illinois at Chicago.
authors.forename: Hatem A
authors.initials: HA
authors.lastname: Elshabrawy
authors.affiliation: Midwestern University, Chicago College of Osteopathic Medicine, Downers Grove, Illinois.
authors.forename: Michael V
authors.initials: MV
authors.lastname: Volin
authors.affiliation: University of Illinois at Chicago.
authors.forename: Suncica
authors.initials: S
authors.lastname: Volkov
authors.affiliation: Jesse Brown VA Medical Center and University of Illinois at Chicago.
authors.forename: William
authors.initials: W
authors.lastname: Swedler
authors.affiliation: Jesse Brown VA Medical Center and University of Illinois at Chicago.
authors.forename: Shiva
authors.initials: S
authors.lastname: Arami
authors.affiliation: University of Illinois at Chicago.
authors.forename: Nadera
authors.initials: N
authors.lastname: Sweiss
authors.affiliation: Jesse Brown VA Medical Center and University of Illinois at Chicago.
authors.forename: Shiva
authors.initials: S
authors.lastname: Shahrara
mesh_terms: D000818:Animals; D001169:Arthritis, Experimental / Q000276:immunology*; D001172:Arthritis, Rheumatoid / Q000276:immunology*; D015153:Blotting, Western; D001854:Bone Marrow Cells / Q000187:drug effects / Q000276:immunology; D016207:Cytokines / Q000235:genetics / Q000276:immunology; D004797:Enzyme-Linked Immunosorbent Assay; D005434:Flow Cytometry; D055785:Gene Knockdown Techniques; D006801:Humans; D008264:Macrophages / Q000276:immunology*; D008562:Membrane Glycoproteins / Q000235:genetics / Q000276:immunology*; D018345:Mice, Knockout; D035683:MicroRNAs / Q000235:genetics / Q000276:immunology*; D022423:Myeloid Cells / Q000276:immunology*; D011804:Quinolines / Q000494:pharmacology; D012333:RNA, Messenger / Q000378:metabolism; D060888:Real-Time Polymerase Chain Reaction; D020133:Reverse Transcriptase Polymerase Chain Reaction; D013582:Synovial Fluid / Q000276:immunology*; D051199:Toll-Like Receptor 7 / Q000037:antagonists & inhibitors / Q000235:genetics / Q000276:immunology*
chemical_list: D016207:Cytokines; D008562:Membrane Glycoproteins; D035683:MicroRNAs; D011804:Quinolines; D012333:RNA, Messenger; D051199:Toll-Like Receptor 7; C557465:1-(2-methylpropyl)-1H-imidazo(4,5-c)quinolin 4-amine; C549242:MIRN7-1 microRNA, human; C495348:TLR7 protein, human; C477038:Tlr7 protein, mouse