title: Reciprocal regulation by hypoxia-inducible factor-2α and the NAMPT-NAD(+)-SIRT axis in articular chondrocytes is involved in osteoarthritis.
abstract: OBJECTIVE
  Hypoxia-inducible factor-2α (HIF-2α) transcriptionally upregulates Nampt in articular chondrocytes. NAMPT, which exhibits nicotinamide phosphoribosyltransferase activity, in turn causes osteoarthritis (OA) in mice by stimulating the expression of matrix-degrading enzymes. Here, we sought to elucidate whether HIF-2α activates the NAMPT-NAD(+)-SIRT axis in chondrocytes and thereby contributes to the pathogenesis of OA.
  
  
  METHODS
  Assays of NAD levels, SIRT activity, reporter gene activity, mRNA, and protein levels were conducted in primary cultured mouse articular chondrocytes. Experimental OA in mice was induced by intra-articular (IA) injection of adenovirus expressing HIF-2α (Ad-Epas1) or NAMPT (Ad-Nampt). The functions of SIRT in OA were examined by IA co-injection of SIRT inhibitors or adenovirus expressing individual SIRT isoforms or shRNA targeting specific SIRT isoforms.
  
  
  RESULTS
  HIF-2α activated the NAMPT-NAD(+)-SIRT axis in chondrocytes by upregulating NAMPT, which stimulated NAD(+) synthesis and thereby activated SIRT family members. The activated NAMPT-SIRT pathway, in turn, promoted HIF-2α protein stability by negatively regulating its hydroxylation and 26S proteasome-mediated degradation, resulting in increased HIF-2α transcriptional activity. Among SIRT family members (SIRT1-7), SIRT2 and SIRT4 were positively associated with HIF-2α stability and transcriptional activity in chondrocytes. This reciprocal regulation was required for the expression of catabolic matrix metalloproteinases (MMP3, MMP12, and MMP13) and OA cartilage destruction caused by IA injection of Ad-Epas1 Ad-Nampt.
  
  
  CONCLUSIONS
  The reciprocal regulation of HIF-2α and the NAMPT-NAD(+)-SIRT axis in articular chondrocytes is involved in OA cartilage destruction caused by HIF-2α or NAMPT.
authors.affiliation: School of Life Sciences, Gwangju Institute of Science and Technology, Gwangju 500-712, South Korea.
authors.forename: H
authors.initials: H
authors.lastname: Oh
authors.affiliation: School of Life Sciences, Gwangju Institute of Science and Technology, Gwangju 500-712, South Korea.
authors.forename: J-S
authors.initials: JS
authors.lastname: Kwak
authors.affiliation: School of Life Sciences, Gwangju Institute of Science and Technology, Gwangju 500-712, South Korea.
authors.forename: S
authors.initials: S
authors.lastname: Yang
authors.affiliation: School of Life Sciences, Gwangju Institute of Science and Technology, Gwangju 500-712, South Korea.
authors.forename: M-K
authors.initials: MK
authors.lastname: Gong
authors.affiliation: School of Life Sciences, Gwangju Institute of Science and Technology, Gwangju 500-712, South Korea; Department of Biological Sciences, Seoul National University, Seoul 151-747, South Korea.
authors.forename: J-H
authors.initials: JH
authors.lastname: Kim
authors.affiliation: School of Life Sciences, Gwangju Institute of Science and Technology, Gwangju 500-712, South Korea.
authors.forename: J
authors.initials: J
authors.lastname: Rhee
authors.affiliation: School of Life Sciences, Gwangju Institute of Science and Technology, Gwangju 500-712, South Korea.
authors.forename: S K
authors.initials: SK
authors.lastname: Kim
authors.affiliation: School of Life Sciences, Gwangju Institute of Science and Technology, Gwangju 500-712, South Korea.
authors.forename: H-E
authors.initials: HE
authors.lastname: Kim
authors.affiliation: School of Life Sciences, Gwangju Institute of Science and Technology, Gwangju 500-712, South Korea; Research Center for Biomineralization Disorders and Dental Science Research Institute, School of Dentistry, Chonnam National University, Gwangju 500-757, South Korea.
authors.forename: J-H
authors.initials: JH
authors.lastname: Ryu
authors.affiliation: School of Life Sciences, Gwangju Institute of Science and Technology, Gwangju 500-712, South Korea. Electronic address: jschun@gist.ac.kr.
authors.forename: J-S
authors.initials: JS
authors.lastname: Chun
mesh_terms: D000818:Animals; D001169:Arthritis, Experimental / Q000235:genetics* / Q000378:metabolism; D051792:Basic Helix-Loop-Helix Proteins / Q000235:genetics* / Q000378:metabolism; D015153:Blotting, Western; D002358:Cartilage, Articular / Q000378:metabolism*; D019902:Chondrocytes / Q000378:metabolism*; D016207:Cytokines / Q000235:genetics* / Q000378:metabolism; D047468:Immunoprecipitation; D053508:Matrix Metalloproteinase 12 / Q000235:genetics / Q000378:metabolism; D053509:Matrix Metalloproteinase 13 / Q000235:genetics / Q000378:metabolism; D019278:Matrix Metalloproteinase 3 / Q000235:genetics / Q000378:metabolism; D051379:Mice; D009243:NAD / Q000378:metabolism*; D054409:Nicotinamide Phosphoribosyltransferase / Q000235:genetics* / Q000378:metabolism; D020370:Osteoarthritis, Knee / Q000235:genetics* / Q000378:metabolism; D012333:RNA, Messenger / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D056564:Sirtuin 1 / Q000235:genetics* / Q000378:metabolism; D056565:Sirtuin 2 / Q000235:genetics* / Q000378:metabolism; D037761:Sirtuins / Q000235:genetics / Q000378:metabolism; D015854:Up-Regulation; D000099162:Endothelial PAS Domain-Containing Protein 1
chemical_list: D051792:Basic Helix-Loop-Helix Proteins; D016207:Cytokines; D053508:Matrix Metalloproteinase 12; D053509:Matrix Metalloproteinase 13; D019278:Matrix Metalloproteinase 3; D009243:NAD; D054409:Nicotinamide Phosphoribosyltransferase; D012333:RNA, Messenger; D056564:Sirtuin 1; D056565:Sirtuin 2; D037761:Sirtuins; D000099162:Endothelial PAS Domain-Containing Protein 1; C495867:nicotinamide phosphoribosyltransferase, mouse; C507081:Mmp13 protein, mouse; C511769:Mmp3 protein, mouse; C000602031:matrix metallopeptidase 12, mouse; C470545:Sirt1 protein, mouse; C418743:Sirt2 protein, mouse
keywords: Chondrocytes; Hypoxia-inducible factor (HIF); NAD(+) biosynthesis; Osteoarthritis; Sirtuin