title: Morphological characterization of intra-articular HMGB1 expression during the course of collagen-induced arthritis.
abstract: High-mobility group chromosomal box protein 1 (HMGB1) is a structural nuclear protein that promotes inflammation when present extracellularly. Aberrant, extracellular HMGB1 expression has been demonstrated in human and experimental synovitis. The aim of the present study was to elucidate the temporal and spatial expression of HMGB1 compared to that of the central mediators tumor necrosis factor (TNF) and interleukin-1-beta (IL-1beta) during the course of collagen-induced arthritis. Thus, Dark Agouti rats were immunized with homologous type II collagen and synovial tissue specimens were obtained at various time points prior to and during the course of clinical arthritis. Local cytokine responses were assessed by immunohistochemistry and by in situ hybridization. We demonstrate a distinct nuclear expression of HMGB1 at early disease-preceding time points. Preceding clinical onset by a few days, cytoplasmic HMGB1 expression was evident in synoviocytes within the non-proliferative lining layer. Pronounced cytoplasmic and additional extracellular HMGB1 expression coincided with the progression of clinical disease. In advanced arthritis, the number of cells with cytoplasmic HMGB1 expression was quantitatively comparable to that of cells expressing TNF and IL-1beta. Interestingly, although HMGB1 was abundantly expressed throughout the inflamed synovium at a protein level, upregulation of HMGB1 mRNA was restricted mainly to areas of cartilage and bone destruction. In conclusion, these new findings implicate a role for HMGB1 in both inducing and perpetuating inflammatory events of significant importance in the destructive processes in chronic arthritis.
authors.affiliation: Department of Woman and Child Health, Karolinska Institutet, Astrid Lindgren Children's Hospital, SE-171 76 Stockholm, Sweden. Karin.Palmblad@ki.se
authors.forename: Karin
authors.initials: K
authors.lastname: Palmblad
authors.forename: Erik
authors.initials: E
authors.lastname: Sundberg
authors.forename: Margarita
authors.initials: M
authors.lastname: Diez
authors.forename: Riikka
authors.initials: R
authors.lastname: Söderling
authors.forename: Ann-Charlotte
authors.initials: AC
authors.lastname: Aveberger
authors.forename: Ulf
authors.initials: U
authors.lastname: Andersson
authors.forename: Helena Erlandsson
authors.initials: HE
authors.lastname: Harris
mesh_terms: D000818:Animals; D001169:Arthritis, Experimental / Q000378:metabolism*; D002467:Cell Nucleus / Q000378:metabolism; D003094:Collagen / Q000633:toxicity; D003593:Cytoplasm / Q000378:metabolism; D005455:Fluorescent Antibody Technique; D024243:HMGB1 Protein; D006609:High Mobility Group Proteins / Q000096:biosynthesis*; D007150:Immunohistochemistry; D017403:In Situ Hybridization; D007249:Inflammation / Q000378:metabolism*; D053583:Interleukin-1beta / Q000096:biosynthesis; D008297:Male; D012333:RNA, Messenger / Q000032:analysis; D051381:Rats; D012097:Repressor Proteins / Q000096:biosynthesis*; D013583:Synovial Membrane / Q000378:metabolism*; D013997:Time Factors; D014409:Tumor Necrosis Factor-alpha / Q000096:biosynthesis
chemical_list: D024243:HMGB1 Protein; C104200:Hbp1 protein, rat; D006609:High Mobility Group Proteins; D053583:Interleukin-1beta; D012333:RNA, Messenger; D012097:Repressor Proteins; D014409:Tumor Necrosis Factor-alpha; D003094:Collagen