title: Functional redundancy of MyD88-dependent signaling pathways in a murine model of histidyl-transfer RNA synthetase-induced myositis.
abstract: We have previously shown that i.m. administration of bacterially expressed murine histidyl-tRNA synthetase (HRS) triggers florid muscle inflammation (relative to appropriate control proteins) in various congenic strains of mice. Because severe disease develops even in the absence of adaptive immune responses to HRS, we sought to identify innate immune signaling components contributing to our model of HRS-induced myositis. In vitro stimulation assays demonstrated HRS-mediated activation of HEK293 cells transfected with either TLR2 or TLR4, revealing an excitatory capacity exceeding that of other bacterially expressed fusion proteins. Corresponding to this apparent functional redundancy of TLR signaling pathways, HRS immunization of B6.TLR2(-/-) and B6.TLR4(-/-) single-knockout mice yielded significant lymphocytic infiltration of muscle tissue comparable to that produced in C57BL/6 wild-type mice. In contrast, concomitant elimination of TLR2 and TLR4 signaling in B6.TLR2(-/-).TLR4(-/-) double-knockout mice markedly reduced the severity of HRS-induced muscle inflammation. Complementary subfragment analysis demonstrated that aa 60-90 of HRS were absolutely required for in vitro as well as in vivo signaling via these MyD88-dependent TLR pathways--effects mediated, in part, through preferential binding of exogenous ligands capable of activating specific TLRs. Collectively, these experiments indicate that multiple MyD88-dependent signaling cascades contribute to this model of HRS-induced myositis, underscoring the antigenic versatility of HRS and confirming the importance of innate immunity in this system.
authors.affiliation: Division of Rheumatology, Department of Medicine, University of Miami Miller School of Medicine, Miami, FL 33136, USA.
authors.forename: Irina
authors.initials: I
authors.lastname: Fernandez
authors.forename: Lisa
authors.initials: L
authors.lastname: Harlow
authors.forename: Yunjuan
authors.initials: Y
authors.lastname: Zang
authors.forename: Ru
authors.initials: R
authors.lastname: Liu-Bryan
authors.forename: William M
authors.initials: WM
authors.lastname: Ridgway
authors.forename: Paula R
authors.initials: PR
authors.lastname: Clemens
authors.forename: Dana P
authors.initials: DP
authors.lastname: Ascherman
mesh_terms: D000818:Animals; D001324:Autoantigens / Q000737:chemistry / Q000276:immunology / Q000633:toxicity*; D004075:Diglycerides / Q000378:metabolism; D004731:Endotoxins / Q000378:metabolism; D005260:Female; D024243:HMGB1 Protein / Q000378:metabolism; D006643:Histidine-tRNA Ligase / Q000737:chemistry / Q000276:immunology / Q000633:toxicity*; D007113:Immunity, Innate; D007114:Immunization; D016056:Immunodominant Epitopes / Q000737:chemistry / Q000276:immunology / Q000633:toxicity; D008024:Ligands; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D053594:Myeloid Differentiation Factor 88 / Q000172:deficiency / Q000502:physiology*; D020721:Nervous System Autoimmune Disease, Experimental / Q000209:etiology / Q000503:physiopathology*; D009842:Oligopeptides / Q000378:metabolism; D010446:Peptide Fragments / Q000276:immunology / Q000633:toxicity; D011485:Protein Binding; D011993:Recombinant Fusion Proteins / Q000276:immunology / Q000633:toxicity; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology*; D051195:Toll-Like Receptor 2 / Q000172:deficiency / Q000187:drug effects / Q000502:physiology*; D051197:Toll-Like Receptor 4 / Q000172:deficiency / Q000187:drug effects / Q000502:physiology*
chemical_list: D001324:Autoantigens; D004075:Diglycerides; D004731:Endotoxins; C460864:FSL-1 lipoprotein, synthetic; D024243:HMGB1 Protein; C585491:HMGB1 protein, human; D016056:Immunodominant Epitopes; D008024:Ligands; C507780:Myd88 protein, mouse; D053594:Myeloid Differentiation Factor 88; D009842:Oligopeptides; D010446:Peptide Fragments; D011993:Recombinant Fusion Proteins; C493486:Tlr2 protein, mouse; C493487:Tlr4 protein, mouse; D051195:Toll-Like Receptor 2; D051197:Toll-Like Receptor 4; C044101:endotoxin, Escherichia coli; D006643:Histidine-tRNA Ligase