title: Peroxisome proliferator-activated receptor γ coactivator 1α and FoxO3A mediate chondroprotection by AMP-activated protein kinase.
abstract: OBJECTIVE
  AMP-activated protein kinase (AMPK) inhibits chondrocyte procatabolic responses to inflammation and biomechanical injury. This study was undertaken to test the hypothesis that peroxisome proliferator-activated receptor γ coactivator 1α (PGC-1α) and FoxO3A, 2 major AMPK downstream targets, mediate the chondroprotective effect of AMPK activation.
  
  
  METHODS
  We assessed the activity of AMPKα (threonine 172 phosphorylation) and the expression of PGC-1α and FoxO3A in human chondrocytes and AMPKα1- or AMPKα2-knockout mouse chondrocytes by Western blotting, and in mouse knee cartilage by immunohistochemistry. We also knocked down or overexpressed PGC-1α and FoxO3A by small interfering RNA or plasmid DNA transfection, respectively. We assessed mitochondrial superoxide generation using MitoSOX Red.
  
  
  RESULTS
  Expression of PGC-1α and FoxO3A was enhanced by pharmacologic AMPK activator A-769662 but impaired in AMPKα1(-/-) or AMPKα2(-/-) mouse chondrocytes. Reduced expression of PGC-1α and FoxO3A was observed in mouse knee instability-induced osteoarthritis (OA) cartilage and in aged C57BL/6 mouse knee cartilage. Knockdown of PGC-1α and FoxO3A enhanced, but limited the ability of A-769662 to inhibit, phosphorylation of p65 NF-κB (Ser(536) ) and procatabolic responses induced by inflammatory cytokines. Forced expression of PGC-1α and FoxO3A induced increased expression of superoxide dismutase 2 (SOD2) and catalase, but A-769662 failed to increase the expression of SOD2 and catalase in either PGC-1α- or FoxO3A-knockdown chondrocytes. Last, menadione-induced superoxide generation was inhibited by AMPK pharmacologic activators and by overexpression of PGC-1α or FoxO3A.
  
  
  CONCLUSIONS
  PGC-1α and FoxO3A limit oxidative stress and at least partially mediate the capacity of AMPK activity to block procatabolic responses in chondrocytes, and therefore have the potential to inhibit the progression of cartilage damage in OA.
authors.affiliation: VA San Diego Medical Center and University of California, San Diego.
authors.forename: Xianling
authors.initials: X
authors.lastname: Zhao
authors.forename: Freyr
authors.initials: F
authors.lastname: Petursson
authors.forename: Benoit
authors.initials: B
authors.lastname: Viollet
authors.forename: Martin
authors.initials: M
authors.lastname: Lotz
authors.forename: Robert
authors.initials: R
authors.lastname: Terkeltaub
authors.forename: Ru
authors.initials: R
authors.lastname: Liu-Bryan
mesh_terms: D055372:AMP-Activated Protein Kinases / Q000172:deficiency / Q000235:genetics / Q000378:metabolism*; D000375:Aging / Q000378:metabolism; D000818:Animals; D002374:Catalase / Q000378:metabolism; D002478:Cells, Cultured; D019902:Chondrocytes / Q000187:drug effects / Q000378:metabolism* / Q000473:pathology*; D004195:Disease Models, Animal; D000071316:Forkhead Box Protein O3; D051858:Forkhead Transcription Factors / Q000172:deficiency / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D008592:Menisci, Tibial / Q000601:surgery; D051379:Mice; D008810:Mice, Inbred C57BL; D010003:Osteoarthritis / Q000209:etiology / Q000378:metabolism / Q000473:pathology; D018384:Oxidative Stress / Q000502:physiology; D000071248:Peroxisome Proliferator-Activated Receptor Gamma Coactivator 1-alpha; D034741:RNA, Small Interfering / Q000494:pharmacology; D013482:Superoxide Dismutase / Q000378:metabolism; D014157:Transcription Factors / Q000172:deficiency / Q000235:genetics / Q000378:metabolism*; D014162:Transfection; D000099156:Superoxide Dismutase 2
chemical_list: D055372:AMP-Activated Protein Kinases; D002374:Catalase; D000071316:Forkhead Box Protein O3; D051858:Forkhead Transcription Factors; D000071248:Peroxisome Proliferator-Activated Receptor Gamma Coactivator 1-alpha; D034741:RNA, Small Interfering; D013482:Superoxide Dismutase; D014157:Transcription Factors; D000099156:Superoxide Dismutase 2; C499517:FOXO3 protein, human; C474033:FoxO3 protein, mouse; C486497:PPARGC1A protein, human; C485290:Ppargc1a protein, mouse; C548179:Prkaa1 protein, mouse; C534978:Prkaa2 protein, mouse