title: Characterization of the Inflammatory Properties of Actively Released HMGB1 in Juvenile Idiopathic Arthritis.
abstract: OBJECTIVE
  Pathogenic effects of the endogenous inflammatory mediator high mobility group box protein 1 (HMGB1) have been described in several inflammatory diseases. Recent reports have underlined the importance of post-translational modifications (PTMs) in determination of HMGB1 function and release mechanisms. We investigated the occurrence of PTMs of HMGB1 obtained from synovial fluid (SF) of juvenile idiopathic arthritis (JIA) patients.
  
  
  RESULTS
  Analyses of 17 JIA patients confirmed high HMGB1 levels in SF. Liquid chromatography tandem mass-spectrometry (LC-MS/MS) analyses of PTMs revealed that total HMGB1 levels were not associated with increased lactate dehydrogenase activity but strongly correlated with nuclear location sequence 2 (NLS2) hyperacetylation, indicating active release of HMGB1. The correlation between total HMGB1 levels and NLS2 hypoacetylation suggests additional, acetylation-independent release mechanisms. Monomethylation of lysine 43 (K43), a proposed neutrophil-specific PTM, was strongly associated with high HMGB1 levels, implying that neutrophils are a source of released HMGB1. Analysis of cysteine redox isoforms, fully reduced HMGB1, disulfide HMGB1, and oxidized HMGB1, revealed that HMGB1 acts as both a chemotactic and a cytokine-inducing mediator. These properties were associated with actively released HMGB1.
  
  
  METHODS
  This is the first report that characterizes HMGB1-specific PTMs during a chronic inflammatory condition.
  
  
  CONCLUSIONS
  HMGB1 in SF from JIA patients is actively released through both acetylation-dependent and -nondependent manners. The presence of various functional HMGB1 redox isoforms confirms the complexity of their pathogenic role during chronic inflammation. Defining HMGB1 release pathways and redox isoforms is critical for the understanding of the contribution of HMGB1 during inflammatory processes.
authors.affiliation: 1 Department of Medicine, Rheumatology Unit, Karolinska Institutet , Stockholm, Sweden .
authors.forename: Peter
authors.initials: P
authors.lastname: Lundbäck
authors.affiliation: 2 Department of Clinical Neuroscience, Center for Molecular Medicine, Karolinska Institutet , Stockholm, Sweden .
authors.forename: Pernilla
authors.initials: P
authors.lastname: Stridh
authors.affiliation: 3 Department of Women's and Children's Health, Paediatric Unit, Karolinska Institutet , Stockholm, Sweden .
authors.forename: Lena
authors.initials: L
authors.lastname: Klevenvall
authors.affiliation: 4 MRC Centre for Drug Safety Science, Department of Molecular and Clinical Pharmacology, Liverpool University , Liverpool, United Kingdom .
authors.forename: Rosalind E
authors.initials: RE
authors.lastname: Jenkins
authors.affiliation: 1 Department of Medicine, Rheumatology Unit, Karolinska Institutet , Stockholm, Sweden .
authors.forename: Marie
authors.initials: M
authors.lastname: Fischer
authors.affiliation: 3 Department of Women's and Children's Health, Paediatric Unit, Karolinska Institutet , Stockholm, Sweden .
authors.forename: Erik
authors.initials: E
authors.lastname: Sundberg
authors.affiliation: 3 Department of Women's and Children's Health, Paediatric Unit, Karolinska Institutet , Stockholm, Sweden .
authors.forename: Ulf
authors.initials: U
authors.lastname: Andersson
authors.affiliation: 4 MRC Centre for Drug Safety Science, Department of Molecular and Clinical Pharmacology, Liverpool University , Liverpool, United Kingdom .
authors.forename: Daniel J
authors.initials: DJ
authors.lastname: Antoine
authors.affiliation: 1 Department of Medicine, Rheumatology Unit, Karolinska Institutet , Stockholm, Sweden .
authors.forename: Helena Erlandsson
authors.initials: HE
authors.lastname: Harris
mesh_terms: D000293:Adolescent; D001171:Arthritis, Juvenile / Q000378:metabolism*; D002648:Child; D002675:Child, Preschool; D024243:HMGB1 Protein / Q000378:metabolism*; D006801:Humans; D007249:Inflammation / Q000378:metabolism*
chemical_list: D024243:HMGB1 Protein; C585491:HMGB1 protein, human