title: Salivary mucins induce a Toll-like receptor 4-mediated pro-inflammatory response in human submandibular salivary cells: are mucins involved in Sjögren's syndrome?
abstract: OBJECTIVE
  A hallmark characteristic of SS patients is the ectopic presence of the mucins MUC5B and MUC7 in the extracellular matrix of salivary glands that have lost apical-basolateral acinar-cell polarity. This study aims to determine whether exogenous salivary mucins induce gene expression of pro-inflammatory cytokines, as well as to evaluate whether the Toll-like receptor-4 (TLR4) pathway is involved in this response.
  
  
  METHODS
  Differentiated human submandibular gland (HSG) cells were stimulated with mucins or oligosaccharide residues at different concentrations and for different periods of time. The expression of pro-inflammatory cytokines and their receptors was determined by semi-quantitative real time PCR (sqPCR). TLR4-mediated responses induced by mucin were evaluated with the Toll-IL-1 receptor domain containing adaptor protein (TIRAP) inhibitory peptide or using anti-hTLR4 blocking antibody. TLR4-receptor expression was also determined in SS patients, controls and HSG cells.
  
  
  RESULTS
  Mucins induced a significant increase in CXCL8, TNF-α, IFN-α, IFN-β, IL-6 and IL-1β, but not B cell activating factor (BAFF). Cytokine induction was mediated by TLR4, as shown using TIRAP or using anti-hTLR4 antibody. Sugar residues present in MUC5B, such as sulpho-Lewis (SO3-3Galβ1-3GlcNAc), also induced cytokines. Unexpectedly, mucins induced MUC5B, but not MUC7 expression.
  
  
  CONCLUSIONS
  Salivary mucins were recognized by TLR4 in epithelial cells initiating a pro-inflammatory response that could attract inflammatory cells to amplify and perpetuate inflammation and thereby contribute to the development of a chronic state characteristic of SS. The ectopic localization of MUC5B and MUC7 in the salivary gland extracellular matrix from SS patients and the current results reveal the importance of salivary epithelial cells in innate immunity, as well as in SS pathogenesis.
authors: Programa de Biología Celular y Molecular, Instituto de Ciencias Biomédicas, Facultad de Medicina, Universidad de Chile.
authors: María-José
authors: MJ
authors: Barrera
authors: Departamento de Reumatología, Clínica INDISA, Santiago, Chile.
authors: Sergio
authors: S
authors: Aguilera
authors: Academic Centre for Dentistry Amsterdam, Section Periodontology and Oral Biochemistry, Amsterdam, The Netherlands.
authors: Enno
authors: E
authors: Veerman
authors: Programa de Biología Celular y Molecular, Instituto de Ciencias Biomédicas, Facultad de Medicina, Universidad de Chile, Center for Molecular Studies of the Cell, Advanced Center for Chronic Diseases.
authors: Andrew F G
authors: AF
authors: Quest
authors: Programa de Inmunología, Instituto de Ciencias Biomédicas, Facultad de Medicina, Universidad de Chile and.
authors: David
authors: D
authors: Díaz-Jiménez
authors: Programa de Biología Celular y Molecular, Instituto de Ciencias Biomédicas, Facultad de Medicina, Universidad de Chile.
authors: Ulises
authors: U
authors: Urzúa
authors: Programa de Biología Celular y Molecular, Instituto de Ciencias Biomédicas, Facultad de Medicina, Universidad de Chile.
authors: Juan
authors: J
authors: Cortés
authors: Departamento de Patología Oral, Facultad de Odontología, Universidad Mayor, Santiago, Chile.
authors: Sergio
authors: S
authors: González
authors: Programa de Biología Celular y Molecular, Instituto de Ciencias Biomédicas, Facultad de Medicina, Universidad de Chile.
authors: Isabel
authors: I
authors: Castro
authors: Departamento de Patología Oral, Facultad de Odontología, Universidad Mayor, Santiago, Chile.
authors: Claudio
authors: C
authors: Molina
authors: Programa de Biología Celular y Molecular, Instituto de Ciencias Biomédicas, Facultad de Medicina, Universidad de Chile.
authors: Verónica
authors: V
authors: Bahamondes
authors: Programa de Biología Celular y Molecular, Instituto de Ciencias Biomédicas, Facultad de Medicina, Universidad de Chile.
authors: Cecilia
authors: C
authors: Leyton
authors: Programa de Inmunología, Instituto de Ciencias Biomédicas, Facultad de Medicina, Universidad de Chile and.
authors: Marcela A
authors: MA
authors: Hermoso
authors: Programa de Biología Celular y Molecular, Instituto de Ciencias Biomédicas, Facultad de Medicina, Universidad de Chile, jgonzale@med.uchile.cl.
authors: María-Julieta
authors: MJ
authors: González
mesh_terms: D000328:Adult; D016022:Case-Control Studies; D002478:Cells, Cultured; D016207:Cytokines / Q000378:metabolism*; D004305:Dose-Response Relationship, Drug; D005109:Extracellular Matrix / Q000378:metabolism; D005260:Female; D006801:Humans; D007113:Immunity, Innate / Q000502:physiology; D007249:Inflammation / Q000378:metabolism*; D008297:Male; D008875:Middle Aged; D055257:Mucin-5B / Q000378:metabolism; D009077:Mucins / Q000378:metabolism / Q000494:pharmacology*; D012471:Salivary Proteins and Peptides / Q000378:metabolism; D015398:Signal Transduction / Q000502:physiology; D012859:Sjogren's Syndrome / Q000378:metabolism* / Q000473:pathology; D013363:Submandibular Gland / Q000187:drug effects* / Q000378:metabolism* / Q000473:pathology; D013997:Time Factors; D051197:Toll-Like Receptor 4 / Q000378:metabolism*
chemical_list: D016207:Cytokines; C524578:MUC5B protein, human; C083238:MUC7 protein, human; D055257:Mucin-5B; D009077:Mucins; D012471:Salivary Proteins and Peptides; C495345:TLR4 protein, human; D051197:Toll-Like Receptor 4
keywords: Sjögren’s syndrome; TLR4; cytokines; human salivary cells; inflammation; salivary mucins