title: Chronic Toll-like receptor 4 stimulation in skin induces inflammation, macrophage activation, transforming growth factor beta signature gene expression, and fibrosis.
abstract: BACKGROUND
  The crucial role of innate immunity in the pathogenesis of systemic sclerosis (SSc) is well established, and in the past few years the hypothesis that Toll-like receptor 4 (TLR4) activation induced by endogenous ligands is involved in fibrogenesis has been supported by several studies on skin, liver, and kidney fibrosis. These findings suggest that TLR4 activation can enhance transforming growth factor beta (TGF-β) signaling, providing a potential mechanism for TLR4/Myeloid differentiation factor 88 (MyD88)-dependent fibrosis.
  
  
  METHODS
  The expression of TLR4, CD14 and MD2 genes was analyzed by real-time polymerase chain reaction from skin biopsies of 24 patients with diffuse cutaneous SSc. In order to investigate the effects of the chronic skin exposure to endotoxin (Lipopolysaccharide (LPS)) in vivo we examined the expression of inflammation, TGF-β signaling and cellular markers genes by nanostring. We also identified cellular subsets by immunohistochemistry and flow cytometry.
  
  
  RESULTS
  We found that TLR4 and its co-receptors, MD2 and CD14, are over-expressed in lesional skin from patients with diffuse cutaneous SSc, and correlate significantly with progressive or regressive skin disease as assessed by the Delta Modified Rodnan Skin Score. In vivo, a model of chronic dermal LPS exposure showed overexpression of proinflammatory chemokines, recruitment and activation of macrophages, and upregulation of TGF-β signature genes.
  
  
  CONCLUSIONS
  We delineated the role of MyD88 as necessary for the induction not only for the early phase of inflammation, but also for pro-fibrotic gene expression via activation of macrophages. Chronic LPS exposure might be a model of early stage of SSc when inflammation and macrophage activation are important pathological features of the disease, supporting a role for innate immune activation in SSc skin fibrosis.
authors.forename: Giuseppina
authors.initials: G
authors.lastname: Stifano
authors.forename: Alsya J
authors.initials: AJ
authors.lastname: Affandi
authors.forename: Allison L
authors.initials: AL
authors.lastname: Mathes
authors.forename: Lisa M
authors.initials: LM
authors.lastname: Rice
authors.forename: Sashidhar
authors.initials: S
authors.lastname: Nakerakanti
authors.forename: Banafsheh
authors.initials: B
authors.lastname: Nazari
authors.forename: Jungeun
authors.initials: J
authors.lastname: Lee
authors.forename: Romy B
authors.initials: RB
authors.lastname: Christmann
authors.forename: Robert
authors.initials: R
authors.lastname: Lafyatis
mesh_terms: D000818:Animals; D005355:Fibrosis / Q000276:immunology / Q000473:pathology; D005434:Flow Cytometry; D006801:Humans; D007150:Immunohistochemistry; D007249:Inflammation / Q000276:immunology* / Q000473:pathology; D008262:Macrophage Activation / Q000276:immunology*; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D053594:Myeloid Differentiation Factor 88; D060888:Real-Time Polymerase Chain Reaction; D012595:Scleroderma, Systemic / Q000276:immunology* / Q000473:pathology*; D012867:Skin / Q000276:immunology / Q000473:pathology; D051197:Toll-Like Receptor 4 / Q000276:immunology*; D059467:Transcriptome; D016212:Transforming Growth Factor beta / Q000096:biosynthesis*
chemical_list: D053594:Myeloid Differentiation Factor 88; C495345:TLR4 protein, human; C493487:Tlr4 protein, mouse; D051197:Toll-Like Receptor 4; D016212:Transforming Growth Factor beta