title: Enhanced susceptibility to lipopolysaccharide-induced arthritis and endotoxin shock in interleukin-32 alpha transgenic mice through induction of tumor necrosis factor alpha.
abstract: BACKGROUND
  The present study assessed the potential functions of interleukin (IL)-32α on inflammatory arthritis and endotoxin shock models using IL-32α transgenic (Tg) mice. The potential signaling pathway for the IL-32-tumor necrosis factor (TNF)α axis was analyzed in vitro.
  
  
  METHODS
  IL-32α Tg mice were generated under control of a ubiquitous promoter. Two disease models were used to examine in vivo effects of overexpressed IL-32α: Toll-like receptor (TLR) ligand-induced arthritis developed using a single injection of lipopolysaccharide (LPS) or zymosan into the knee joints; and endotoxin shock induced with intraperitoneal injection of LPS and D-galactosamine. TNFα antagonist etanercept was administered simultaneously with LPS in some mice. Using RAW264.7 cells, in vitro effects of exogenous IL-32α on TNFα, IL-6 or macrophage inflammatory protein 2 (MIP-2) production were assessed with or without inhibitors for nuclear factor kappa B (NFκB) or mitogen-activated protein kinase (MAPK).
  
  
  RESULTS
  Single injection of LPS, but not zymosan, resulted in development of severe synovitis with substantial articular cartilage degradation in knees of the Tg mice. The expression of TNFα mRNA in inflamed synovia was highly upregulated in the LPS-injected Tg mice. Moreover, the Tg mice were more susceptive to endotoxin-induced lethality than the wild-type control mice 48 hours after LPS challenge; but blockade of TNFα by etanercept protected from endotoxin lethality. In cultured bone marrow cells derived from the Tg mice, overexpressed IL-32α accelerated production of TNFα upon stimulation with LPS. Of note, exogenously added IL-32α alone stimulated RAW264.7 cells to express TNFα, IL-6, and MIP-2 mRNAs. Particularly, IL-32α -induced TNFα, but not IL-6 or MIP-2, was inhibited by dehydroxymethylepoxyquinomicin (DHMEQ) and U0126, which are specific inhibitors of nuclear factor kappa B (NFκB) and extracellular signal regulated kinase1/2 (ERK1/2), respectively.
  
  
  CONCLUSIONS
  These results show that IL-32α contributed to the development of inflammatory arthritis and endotoxin lethality. Stimulation of TLR signaling with LPS appeared indispensable for activating the IL-32α-TNFα axis in vivo. However, IL-32α alone induced TNFα production in RAW264.7 cells through phosphorylation of inhibitor kappa B (IκB) and ERK1/2 MAPK. Further studies on the potential involvement of IL-32α-TNFα axis will be beneficial in better understanding the pathology of autoimmune-related arthritis and infectious immunity.
authors.affiliation: Department of Orthopaedic Surgery, Keio University, 35 Shinanomachi, Shinjuku, Tokyo 160-8582, Japan.
authors.forename: Masanori
authors.initials: M
authors.lastname: Nakayama
authors.forename: Yasuo
authors.initials: Y
authors.lastname: Niki
authors.forename: Toshiki
authors.initials: T
authors.lastname: Kawasaki
authors.forename: Yuki
authors.initials: Y
authors.lastname: Takeda
authors.forename: Keisuke
authors.initials: K
authors.lastname: Horiuchi
authors.forename: Aya
authors.initials: A
authors.lastname: Sasaki
authors.forename: Yasunori
authors.initials: Y
authors.lastname: Okada
authors.forename: Kazuo
authors.initials: K
authors.lastname: Umezawa
authors.forename: Hiroyasu
authors.initials: H
authors.lastname: Ikegami
authors.forename: Yoshiaki
authors.initials: Y
authors.lastname: Toyama
authors.forename: Takeshi
authors.initials: T
authors.lastname: Miyamoto
mesh_terms: D000818:Animals; D001169:Arthritis, Experimental / Q000235:genetics / Q000378:metabolism* / Q000473:pathology; D006801:Humans; D015151:Immunoblotting; D007378:Interleukins / Q000235:genetics / Q000378:metabolism*; D008070:Lipopolysaccharides / Q000276:immunology; D051379:Mice; D008810:Mice, Inbred C57BL; D008822:Mice, Transgenic; D060888:Real-Time Polymerase Chain Reaction; D012772:Shock, Septic / Q000235:genetics / Q000378:metabolism* / Q000473:pathology; D015398:Signal Transduction / Q000502:physiology*; D014409:Tumor Necrosis Factor-alpha / Q000096:biosynthesis*
chemical_list: D007378:Interleukins; D008070:Lipopolysaccharides; D014409:Tumor Necrosis Factor-alpha; C569037:interleukin-32, mouse