title: Low sirtuin 1 levels in human osteoarthritis subchondral osteoblasts lead to abnormal sclerostin expression which decreases Wnt/β-catenin activity.
abstract: BACKGROUND
  Wnt/β-catenin (cWnt) signaling plays a key role in osteogenesis by promoting the differentiation and mineralization of osteoblasts, activities altered in human osteoarthritic subchondral osteoblast (OA Ob). Sclerostin (SOST) has been shown to alter cWnt signaling. Sirtuin 1 (SIRT1) acts as a novel bone regulator and represses SOST levels in Ob. However the role of SIRT1 and SOST in OA Ob remains unknown. Herein, we explored the role played by SIRT1 and SOST on the abnormal mineralization and cWnt signaling in OA Ob.
  
  
  METHODS
  Primary human normal and OA Ob were prepared from tibial plateaus. SOST levels were evaluated by immunohistochemistry, the expression and production of genes by qRT-PCR and WB analysis. Their inhibitions were performed using siRNA. cWnt signaling was measured by the TOPflash TCF/lef luciferase reporter assay. Mineralization was determined by alizarin red staining.
  
  
  RESULTS
  SOST levels were significantly increased in OA Ob compared to normal and were linked with elevated TGF-β1 levels in these cells. SIRT1 expression was significantly reduced in OA Ob compared to normal yet not modified by TGF-β1. Specific inhibition of SIRT1 increased TGF-β1 and SOST expressions in OA Ob, while stimulating SIRT1 activity with β-Nicotinamide mononucleotide reduced the expression of TGF-β1 and SOST, and increased mineralization in OA Ob. Resveratrol also reduced SOST expression in OA Ob. Reduced cWnt signaling, β-catenin levels, and mineralization in OA Ob were all corrected via reducing SOST expression.
  
  
  CONCLUSIONS
  These data indicate that high level of SOST is responsible, in part, for the reduced cWnt and mineralization of human OA Ob, which in turn is linked with abnormal SIRT1 levels in these pathological cells.
authors.affiliation: Unité de recherche en arthrose, Centre de Recherche du Centre Hospitalier de l'Université de Montréal (CRCHUM), Hôpital Notre-Dame, Montréal, Québec H2L 4M1, Canada.
authors.forename: Élie
authors.initials: É
authors.lastname: Abed
authors.affiliation: Unité de recherche en arthrose, Centre de Recherche du Centre Hospitalier de l'Université de Montréal (CRCHUM), Hôpital Notre-Dame, Montréal, Québec H2L 4M1, Canada.
authors.forename: Denis
authors.initials: D
authors.lastname: Couchourel
authors.affiliation: Unité de recherche en arthrose, Centre de Recherche du Centre Hospitalier de l'Université de Montréal (CRCHUM), Hôpital Notre-Dame, Montréal, Québec H2L 4M1, Canada.
authors.forename: Aline
authors.initials: A
authors.lastname: Delalandre
authors.affiliation: Unité de recherche en arthrose, Centre de Recherche du Centre Hospitalier de l'Université de Montréal (CRCHUM), Hôpital Notre-Dame, Montréal, Québec H2L 4M1, Canada.
authors.forename: Nicholas
authors.initials: N
authors.lastname: Duval
authors.affiliation: Unité de recherche en arthrose, Centre de Recherche du Centre Hospitalier de l'Université de Montréal (CRCHUM), Hôpital Notre-Dame, Montréal, Québec H2L 4M1, Canada.
authors.forename: Jean-Pierre
authors.initials: JP
authors.lastname: Pelletier
authors.affiliation: Unité de recherche en arthrose, Centre de Recherche du Centre Hospitalier de l'Université de Montréal (CRCHUM), Hôpital Notre-Dame, Montréal, Québec H2L 4M1, Canada.
authors.forename: Johanne
authors.initials: J
authors.lastname: Martel-Pelletier
authors.affiliation: Unité de recherche en arthrose, Centre de Recherche du Centre Hospitalier de l'Université de Montréal (CRCHUM), Hôpital Notre-Dame, Montréal, Québec H2L 4M1, Canada. Electronic address: daniel.lajeunesse@umontreal.ca.
authors.forename: Daniel
authors.initials: D
authors.lastname: Lajeunesse
mesh_terms: D048868:Adaptor Proteins, Signal Transducing; D000368:Aged; D000818:Animals; D019485:Bone Morphogenetic Proteins / Q000096:biosynthesis / Q000235:genetics* / Q000378:metabolism; D002113:Calcification, Physiologic / Q000187:drug effects / Q000235:genetics; D002478:Cells, Cultured; D005260:Female; D005819:Genetic Markers / Q000235:genetics*; D006801:Humans; D008297:Male; D051379:Mice; D008875:Middle Aged; D010003:Osteoarthritis / Q000235:genetics* / Q000473:pathology*; D010006:Osteoblasts / Q000378:metabolism* / Q000473:pathology*; D010641:Phenotype; D056564:Sirtuin 1 / Q000378:metabolism*; D053773:Transforming Growth Factor beta1 / Q000494:pharmacology; D060449:Wnt Signaling Pathway / Q000187:drug effects / Q000235:genetics
chemical_list: D048868:Adaptor Proteins, Signal Transducing; D019485:Bone Morphogenetic Proteins; D005819:Genetic Markers; C422903:SOST protein, human; D053773:Transforming Growth Factor beta1; D056564:Sirtuin 1
keywords: Osteoarthritis; Sclerostin; Sirtuins; Subchondral bone; Wnt signaling