title: Acid-sensing ion channel 3 decreases phosphorylation of extracellular signal-regulated kinases and induces synoviocyte cell death by increasing intracellular calcium.
abstract: BACKGROUND
  Acid-sensing ion channel 3 (ASIC3) is expressed in synoviocytes, activated by decreases in pH, and reduces inflammation in animal models of inflammatory arthritis. The purpose of the current study was to characterize potential mechanisms underlying the control of inflammation by ASIC3 in fibroblast-like synoviocytes (FLS).
  
  
  METHODS
  Experiments were performed in cultured FLS from wild-type (WT) and ASIC3-/- mice, ASIC1-/- mice, and people with rheumatoid arthritis. We assessed the effects of acidic pH with and without interleukin-1β on FLS and the role of ASICs in modulating intracellular calcium [Ca(2+)](i), mitogen activated kinase (MAP kinase) expression, and cell death. [Ca(2+)](i) was assessed by fluorescent calcium imaging, MAP kinases were measured by Western Blots; ASIC, cytokine and protease mRNA expression were measured by quantitative PCR and cell death was measured with a LIVE/DEAD assay.
  
  
  RESULTS
  Acidic pH increased [Ca(2+)](i) and decreased p-ERK expression in WT FLS; these effects were significantly smaller in ASIC3-/- FLS and were prevented by blockade of [Ca(2+)]i. Blockade of protein phosphatase 2A (PP2A) prevented the pH-induced decreases in p-ERK. In WT FLS, IL-1β increases ASIC3 mRNA, and when combined with acidic pH enhances [Ca(2+)](i), p-ERK, IL-6 and metalloprotienase mRNA, and cell death. Inhibitors of [Ca(2+)](i) and ERK prevented cell death induced by pH 6.0 in combination with IL-1β in WT FLS.
  
  
  CONCLUSIONS
  Decreased pH activates ASIC3 resulting in increased [Ca(2+)](i), and decreased p-ERK. Under inflammatory conditions, acidic pH results in enhanced [Ca(2+)](i) and phosphorylation of extracellular signal-regulated kinase that leads to cell death. Thus, activation of ASIC3 on FLS by acidic pH from an inflamed joint could limit synovial proliferation resulting in reduced accumulation of inflammatory mediators and subsequent joint damage.
authors.forename: Weiyi
authors.initials: W
authors.lastname: Gong
authors.forename: Sandra J
authors.initials: SJ
authors.lastname: Kolker
authors.forename: Yuriy
authors.initials: Y
authors.lastname: Usachev
authors.forename: Roxanne Y
authors.initials: RY
authors.lastname: Walder
authors.forename: David L
authors.initials: DL
authors.lastname: Boyle
authors.forename: Gary S
authors.initials: GS
authors.lastname: Firestein
authors.forename: Kathleen A
authors.initials: KA
authors.lastname: Sluka
mesh_terms: D062565:Acid Sensing Ion Channels / Q000235:genetics / Q000378:metabolism*; D000818:Animals; D001172:Arthritis, Rheumatoid / Q000378:metabolism / Q000473:pathology; D015153:Blotting, Western; D002118:Calcium / Q000378:metabolism*; D016923:Cell Death / Q000187:drug effects; D002478:Cells, Cultured; D048049:Extracellular Signal-Regulated MAP Kinases / Q000235:genetics / Q000378:metabolism*; D015870:Gene Expression / Q000187:drug effects; D006801:Humans; D006863:Hydrogen-Ion Concentration; D053583:Interleukin-1beta / Q000494:pharmacology; D015850:Interleukin-6 / Q000235:genetics / Q000378:metabolism; D042541:Intracellular Space / Q000187:drug effects / Q000378:metabolism; D008297:Male; D020782:Matrix Metalloproteinases / Q000235:genetics / Q000378:metabolism; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D010766:Phosphorylation; D020133:Reverse Transcriptase Polymerase Chain Reaction; D013583:Synovial Membrane / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*
chemical_list: C508378:ASIC3 protein, mouse; D062565:Acid Sensing Ion Channels; D053583:Interleukin-1beta; D015850:Interleukin-6; D048049:Extracellular Signal-Regulated MAP Kinases; D020782:Matrix Metalloproteinases; D002118:Calcium