title: Toll-like Receptor 9 Signaling Is Augmented in Systemic Sclerosis and Elicits Transforming Growth Factor β-Dependent Fibroblast Activation.
abstract: Although transforming growth factor β (TGFβ) is recognized as being a key trigger of fibroblast activation in systemic sclerosis (SSc), prominent innate immunity suggests that additional pathways contribute to disease persistence. Toll-like receptor 9 (TLR9) is implicated in autoimmunity and fibrosis; however, the expression, mechanism of action, and pathogenic role of TLR9 signaling in SSc remain uncharacterized. The aim of this study was to explore the expression, activity, and potential pathogenic role of TLR9 in the context of skin fibrosis in SSc and in mouse models of experimental fibrosis.
  
  
  
  Expression and localization of TLR9 were evaluated in SSc skin biopsy specimens and explanted skin fibroblasts. Fibrotic responses elicited by type A CpG oligonucleotide and mitochondrial DNA (mtDNA) were examined in human skin fibroblasts by a combination of real-time quantitative polymerase chain reaction, Western blot analysis, transient transfection, immunofluorescence microscopy, and functional assays. Expression of TLR9 was examined in 2 distinct mouse models of experimental fibrosis.
  
  
  
  Skin biopsy specimens obtained from 2 independent cohorts of SSc patients showed up-regulation of TLR9, and myofibroblasts were the major cellular source. Moreover, SSc skin biopsy specimens showed evidence of TLR9 pathway activation. CpG induced robust TLR9-dependent fibrotic responses in explanted normal fibroblasts that could be blocked by bortezomib and were mediated through the action of endogenous TGFβ. Mice with experimental fibrosis showed a time-dependent increase in TLR9 localized primarily to myofibroblasts in the dermis.
  
  
  
  In isolated fibroblasts, TLR9 elicits fibrotic responses mediated via endogenous TGFβ. In patients with SSc, mtDNA and other damage-associated TLR9 ligands in the skin might trigger localized activation of TLR9 signaling, TGFβ production, and consequent fibroblast activation. Disrupting this fibrotic process with inhibitors targeting TLR9 or its downstream signaling pathways might therefore represent a novel approach to SSc therapy.
authors.affiliation: Northwestern University Feinberg School of Medicine, Chicago, Illinois.
authors.forename: Feng
authors.initials: F
authors.lastname: Fang
authors.affiliation: Northwestern University Feinberg School of Medicine, Chicago, Illinois.
authors.forename: Roberta Goncalves
authors.initials: RG
authors.lastname: Marangoni
authors.affiliation: China Pharmaceutical University, Nanjing, China.
authors.forename: Xingchun
authors.initials: X
authors.lastname: Zhou
authors.affiliation: China Pharmaceutical University, Nanjing, China.
authors.forename: Yang
authors.initials: Y
authors.lastname: Yang
authors.affiliation: China Pharmaceutical University, Nanjing, China.
authors.forename: Boping
authors.initials: B
authors.lastname: Ye
authors.affiliation: Northwestern University Feinberg School of Medicine, Chicago, Illinois.
authors.forename: Anna
authors.initials: A
authors.lastname: Shangguang
authors.affiliation: University of Illinois at Chicago, Chicago, Illinois.
authors.forename: Wenyi
authors.initials: W
authors.lastname: Qin
authors.affiliation: Northwestern University Feinberg School of Medicine, Chicago, Illinois.
authors.forename: Wenxia
authors.initials: W
authors.lastname: Wang
authors.affiliation: Northwestern University Feinberg School of Medicine, Chicago, Illinois.
authors.forename: Swati
authors.initials: S
authors.lastname: Bhattacharyya
authors.affiliation: Northwestern University Feinberg School of Medicine, Chicago, Illinois.
authors.forename: Jun
authors.initials: J
authors.lastname: Wei
authors.affiliation: Northwestern University Feinberg School of Medicine, Chicago, Illinois.
authors.forename: Warren G
authors.initials: WG
authors.lastname: Tourtellotte
authors.affiliation: Northwestern University Feinberg School of Medicine, Chicago, Illinois.
authors.forename: John
authors.initials: J
authors.lastname: Varga
mesh_terms: D000818:Animals; D002478:Cells, Cultured; D005260:Female; D005347:Fibroblasts / Q000502:physiology*; D005355:Fibrosis / Q000209:etiology; D051379:Mice; D008810:Mice, Inbred C57BL; D012595:Scleroderma, Systemic / Q000150:complications / Q000276:immunology*; D015398:Signal Transduction; D012867:Skin / Q000473:pathology; D051217:Toll-Like Receptor 9 / Q000502:physiology*; D016212:Transforming Growth Factor beta / Q000502:physiology*
chemical_list: D051217:Toll-Like Receptor 9; D016212:Transforming Growth Factor beta