title: TGF-β is a potent inducer of Nerve Growth Factor in articular cartilage via the ALK5-Smad2/3 pathway. Potential role in OA related pain?
abstract: OBJECTIVE
  Pain is the main problem for patients with osteoarthritis (OA). Pain is linked to inflammation, but in OA a subset of patients suffers from pain without inflammation, indicating an alternative source of pain. Nerve Growth Factor (NGF) inhibition is very efficient in blocking pain during OA, but the source of NGF is unclear. We hypothesize that damaged cartilage in OA releases Transforming Growth Factor-β (TGF-β), which in turn stimulates chondrocytes to produce NGF.
  
  
  METHODS
  Murine and human chondrocyte cell lines, primary bovine and human chondrocytes, and cartilage explants from bovine metacarpal joints and human OA joints were stimulated with TGF-β1 and/or Interleukin-1 (IL-1)β. We analyzed NGF expression on mRNA level with QPCR and stained human OA cartilage for NGF immunohistochemically. Cultures were additionally pre-incubated with inhibitors for TAK1, Smad2/3 or Smad1/5/8 signaling to identify the TGF-β pathway inducing NGF.
  
  
  RESULTS
  NGF expression was consistently induced in higher levels by TGF-β than IL-1 in all of our experiments: murine, bovine and human origin, in cell lines, primary chondrocytes and explants cultures. TAK1 inhibition consistently reduced TGF-β-induced NGF whereas it fully blocked IL-1β-induced NGF expression. In contrast, ALK5-Smad2/3 inhibition fully blocked TGF-β-induced NGF expression. Despite the large variation in basal NGF in human OA samples (mRNA and histology), TGF-β exposure led to a consistent high level of NGF induction.
  
  
  CONCLUSIONS
  We show for the first time that TGF-β induces NGF expression in chondrocytes, in a ALK5-Smad2/3 dependent manner. This reveals a potential alternative non-inflammatory source of pain in OA.
authors.affiliation: Radboud University Medical Centre, Experimental Rheumatology, Geert Grooteplein 26-28, 6500 HB Nijmegen, The Netherlands. Electronic address: Esmeralda.blaneydavidson@radboudumc.nl.
authors.forename: E N
authors.initials: EN
authors.lastname: Blaney Davidson
authors.affiliation: Radboud University Medical Centre, Experimental Rheumatology, Geert Grooteplein 26-28, 6500 HB Nijmegen, The Netherlands. Electronic address: Arjan.vancaam@radboucumc.nl.
authors.forename: A P M
authors.initials: AP
authors.lastname: van Caam
authors.affiliation: Radboud University Medical Centre, Experimental Rheumatology, Geert Grooteplein 26-28, 6500 HB Nijmegen, The Netherlands. Electronic address: elly.vitters@radboudumc.nl.
authors.forename: E L
authors.initials: EL
authors.lastname: Vitters
authors.affiliation: Radboud University Medical Centre, Experimental Rheumatology, Geert Grooteplein 26-28, 6500 HB Nijmegen, The Netherlands. Electronic address: miranda.bennink@radboudumc.nl.
authors.forename: M B
authors.initials: MB
authors.lastname: Bennink
authors.affiliation: Radboud University Medical Centre, Experimental Rheumatology, Geert Grooteplein 26-28, 6500 HB Nijmegen, The Netherlands. Electronic address: eva.thijssen@radboudumc.nl.
authors.forename: E
authors.initials: E
authors.lastname: Thijssen
authors.affiliation: Radboud University Medical Centre, Experimental Rheumatology, Geert Grooteplein 26-28, 6500 HB Nijmegen, The Netherlands. Electronic address: wim.vandenberg@radboudumc.nl.
authors.forename: W B
authors.initials: WB
authors.lastname: van den Berg
authors.affiliation: Radboud University Medical Centre, Experimental Rheumatology, Geert Grooteplein 26-28, 6500 HB Nijmegen, The Netherlands. Electronic address: marije.koenders@radboudumc.nl.
authors.forename: M I
authors.initials: MI
authors.lastname: Koenders
authors.affiliation: Radboud University Medical Centre, Experimental Rheumatology, Geert Grooteplein 26-28, 6500 HB Nijmegen, The Netherlands. Electronic address: peter.vanlent@radboudumc.nl.
authors.forename: P L E M
authors.initials: PL
authors.lastname: van Lent
authors.affiliation: Radboud University Medical Centre, Experimental Rheumatology, Geert Grooteplein 26-28, 6500 HB Nijmegen, The Netherlands. Electronic address: Fons.vandeloo@radboudumc.nl.
authors.forename: F A J
authors.initials: FA
authors.lastname: van de Loo
authors.affiliation: Radboud University Medical Centre, Experimental Rheumatology, Geert Grooteplein 26-28, 6500 HB Nijmegen, The Netherlands. Electronic address: peter.vanderkraan@radboudumc.nl.
authors.forename: P M
authors.initials: PM
authors.lastname: van der Kraan
mesh_terms: D000818:Animals; D002358:Cartilage, Articular / Q000187:drug effects* / Q000378:metabolism; D002417:Cattle; D002460:Cell Line; D019902:Chondrocytes / Q000187:drug effects* / Q000378:metabolism; D006801:Humans; D053583:Interleukin-1beta / Q000494:pharmacology*; D051379:Mice; D020932:Nerve Growth Factor / Q000187:drug effects* / Q000235:genetics / Q000378:metabolism; D010003:Osteoarthritis / Q000150:complications / Q000235:genetics / Q000378:metabolism*; D010146:Pain / Q000209:etiology / Q000235:genetics / Q000378:metabolism*; D017346:Protein Serine-Threonine Kinases / Q000187:drug effects / Q000235:genetics / Q000378:metabolism; D012333:RNA, Messenger / Q000378:metabolism*; D060888:Real-Time Polymerase Chain Reaction; D000077293:Receptor, Transforming Growth Factor-beta Type I; D018125:Receptors, Transforming Growth Factor beta / Q000187:drug effects / Q000235:genetics / Q000378:metabolism; D015398:Signal Transduction; D051899:Smad2 Protein / Q000187:drug effects / Q000235:genetics / Q000378:metabolism; D051900:Smad3 Protein / Q000187:drug effects / Q000235:genetics / Q000378:metabolism; D053773:Transforming Growth Factor beta1 / Q000494:pharmacology*
chemical_list: D053583:Interleukin-1beta; D012333:RNA, Messenger; D018125:Receptors, Transforming Growth Factor beta; D051899:Smad2 Protein; D051900:Smad3 Protein; D053773:Transforming Growth Factor beta1; D020932:Nerve Growth Factor; D017346:Protein Serine-Threonine Kinases; D000077293:Receptor, Transforming Growth Factor-beta Type I; C000625841:TGFBR1 protein, human; C000625842:Tgfbr1 protein, mouse
keywords: Cartilage; NGF; Pain; Smad; TGF-β