title: A20 suppresses canonical Smad-dependent fibroblast activation: novel function for an endogenous inflammatory modulator.
abstract: The ubiquitin-editing cytosolic enzyme A20, the major negative regulator of toll-like receptor (TLR)-mediated cellular inflammatory responses, has tight genetic linkage with systemic sclerosis (SSc). Because recent studies implicate endogenous ligand-driven TLR signaling in SSc pathogenesis, we sought to investigate the regulation, role and mechanism of action of A20 in skin fibroblasts.
  
  
  
  A20 expression and the effects of forced A20 expression or siRNA-mediated A20 knockdown on fibrotic responses induced by transforming growth factor-ß (TGF-ß) were evaluated was evaluated in explanted human skin fibroblasts. Additionally, A20 regulation by TGF-ß, and by adiponectin, a pleiotropic adipokine with anti-fibrotic activity, was evaluated.
  
  
  
  In normal fibroblasts, TGF-ß induced sustained downregulation of A20, and abrogated its TLR4-dependent induction. Forced expression of A20 aborted the stimulation of collagen gene expression and myofibroblast transformation induced by TGF-ß, and disrupted canonical Smad signaling and Smad-dependent transcriptional responses. Conversely, siRNA-mediated knockdown of A20 enhanced the amplitude of fibrotic responses elicited by TGF-ß. Adiponectin, previously shown to block TLR-dependent fibrotic responses, elicited rapid and sustained increase in A20 accumulation in fibroblasts.
  
  
  
  These results identify the ubiquitin-editing enzyme A20 as a novel endogenous mechanism for negative regulation of fibrotic response intensity. Systemic sclerosis-associated genetic variants of A20 that cause impaired A20 expression or function, combined with direct suppression of A20 by TGF-ß within the fibrotic milieu, might play a significant functional role in persistence of fibrotic responses, while pharmacological augmentation of A20 inhibitory pathway activity might represent a novel therapeutic strategy.
authors.affiliation: Department of Medicine, Division of Rheumatology, Northwestern University Feinberg School of Medicine, McGaw M230, 240 E Huron Street, Chicago, IL, 60611, USA. s-bhattacharyya@northwestern.edu.
authors.forename: Swati
authors.initials: S
authors.lastname: Bhattacharyya
authors.affiliation: Department of Medicine, Division of Rheumatology, Northwestern University Feinberg School of Medicine, McGaw M230, 240 E Huron Street, Chicago, IL, 60611, USA.
authors.forename: Wenxia
authors.initials: W
authors.lastname: Wang
authors.affiliation: Department of Dermatology, Northwestern University Feinberg School of Medicine, GALTER 676 N St Clair St Suite 1600 CH HNMH, Chicago, IL, 60611, USA.
authors.forename: Lauren Van Duyn
authors.initials: LV
authors.lastname: Graham
authors.affiliation: Department of Medicine, Division of Rheumatology, Northwestern University Feinberg School of Medicine, McGaw M230, 240 E Huron Street, Chicago, IL, 60611, USA. j-varga@northwestern.edu.
authors.forename: John
authors.initials: J
authors.lastname: Varga
mesh_terms: D015153:Blotting, Western; D002478:Cells, Cultured; D005347:Fibroblasts / Q000378:metabolism* / Q000473:pathology; D005355:Fibrosis / Q000378:metabolism / Q000473:pathology; D005455:Fluorescent Antibody Technique; D055785:Gene Knockdown Techniques; D006801:Humans; D018613:Microscopy, Confocal; D016133:Polymerase Chain Reaction; D012595:Scleroderma, Systemic / Q000378:metabolism* / Q000473:pathology; D015398:Signal Transduction / Q000502:physiology; D012867:Skin / Q000378:metabolism / Q000473:pathology; D051785:Smad Proteins / Q000378:metabolism*; D016212:Transforming Growth Factor beta / Q000378:metabolism; D000072598:Tumor Necrosis Factor alpha-Induced Protein 3 / Q000378:metabolism*
chemical_list: D051785:Smad Proteins; D016212:Transforming Growth Factor beta; C076529:TNFAIP3 protein, human; D000072598:Tumor Necrosis Factor alpha-Induced Protein 3
keywords: A20; Fibrosis; IL-6; LPS; Systemic sclerosis; TGF-ß; TLR4; TNFAIP3; Type I collagen; adiponectin