title: Metabolic activation stimulates acid production in synovial fibroblasts.
abstract: OBJECTIVE
  In rheumatoid arthritis (RA), synovial fibroblasts express proteases such as collagenases or cathepsins and inflammatory cytokines at elevated levels and so contribute to the inflammatory degradation process. Extracellular matrix degradation and cathepsin activity is dependent upon the presence of an acidic milieu. We examined whether activated synovial fibroblasts secrete acidic components.
  
  
  METHODS
  Synovial fibroblasts were isolated and immortalized to study the mechanisms of metabolic activation. Naïve and immortalized fibroblasts were activated with different cytokines. The responses were investigated by immunoblot to detect Egr-1 and by a cytosensor microphysiometer analysis to evaluate acid secretion. Basic gene expression patterns were investigated in naïve and immortalized cells by RT-PCR analysis.
  
  
  RESULTS
  We found RA synovial fibroblasts respond to different cytokines associated with the pathomechanisms of RA including interleukin 1, basic fibroblast growth factor, platelet derived growth factor, and tumor necrosis factor-alpha, with metabolic activation and enhanced secretion of acidic components. In addition, naive and SV40 TAg immortalized fibroblasts rapidly release acidic components after stimulation with phorbol ester or ionomycin as well.
  
  
  CONCLUSIONS
  Activated synovial fibroblasts not only express inflammatory cytokines and matrix degrading proteases that are associated with the pathomechanisms of RA, but upon stimulation may release acidic components that lower pH and consequently enhance cathepsin activity and collagen solubilization.
authors.affiliation: Institute of Applied Physics, University of Munich, Germany.
authors.forename: W J
authors.initials: WJ
authors.lastname: Parak
authors.forename: S
authors.initials: S
authors.lastname: Dannöhl
authors.forename: M
authors.initials: M
authors.lastname: George
authors.forename: M K
authors.initials: MK
authors.lastname: Schuler
authors.forename: J
authors.initials: J
authors.lastname: Schaumburger
authors.forename: H E
authors.initials: HE
authors.lastname: Gaub
authors.forename: O
authors.initials: O
authors.lastname: Müller
authors.forename: W K
authors.initials: WK
authors.lastname: Aicher
mesh_terms: D001172:Arthritis, Rheumatoid / Q000378:metabolism* / Q000473:pathology; D001711:Biotransformation; D002461:Cell Line, Transformed; D016207:Cytokines / Q000494:pharmacology; D017931:DNA Primers / Q000737:chemistry; D004268:DNA-Binding Proteins / Q000096:biosynthesis; D051766:Early Growth Response Protein 1; D005347:Fibroblasts / Q000187:drug effects / Q000378:metabolism* / Q000473:pathology; D006801:Humans; D006863:Hydrogen-Ion Concentration; D017874:Immediate-Early Proteins / Q000096:biosynthesis; D011199:Potentiometry / Q000295:instrumentation; D011522:Protons; D020133:Reverse Transcriptase Polymerase Chain Reaction; D013583:Synovial Membrane / Q000187:drug effects / Q000378:metabolism* / Q000473:pathology; D014157:Transcription Factors / Q000096:biosynthesis
chemical_list: D016207:Cytokines; D017931:DNA Primers; D004268:DNA-Binding Proteins; C497325:EGR1 protein, human; D051766:Early Growth Response Protein 1; D017874:Immediate-Early Proteins; D011522:Protons; D014157:Transcription Factors