title: Linked decreases in liver kinase B1 and AMP-activated protein kinase activity modulate matrix catabolic responses to biomechanical injury in chondrocytes.
abstract: BACKGROUND
  AMP-activated protein kinase (AMPK) maintains cultured chondrocyte matrix homeostasis in response to inflammatory cytokines. AMPK activity is decreased in human knee osteoarthritis (OA) chondrocytes. Liver kinase B1 (LKB1) is one of the upstream activators of AMPK. Hence, we examined the relationship between LKB1 and AMPK activity in OA and aging cartilages, and in chondrocytes subjected to inflammatory cytokine treatment and biomechanical compression injury, and performed translational studies of AMPK pharmacologic activation.
  
  
  METHODS
  We assessed activity (phosphorylation) of LKB1 and AMPKα in mouse knee OA cartilage, in aging mouse cartilage (6 to 24 months), and in chondrocytes after mechanical injury by dynamic compression, via immunohistochemistry or western blot. We knocked down LKB1 by siRNA transfection. Nitric oxide, matrix metalloproteinase (MMP)-3, and MMP-13 release were measured by Griess reaction and ELISA, respectively.
  
  
  RESULTS
  Knockdown of LKB1 attenuated chondrocyte AMPK activity, and increased nitric oxide, MMP-3 and MMP-13 release (P <0.05) in response to IL-1β and TNFα. Both LKB1 and AMPK activity were decreased in mouse knee OA and aged knee cartilage, and in bovine chondrocytes after biomechanical injury. Pretreatment of bovine chondrocytes with AMPK activators AICAR and A-769662 inhibited both AMPKα dephosphorylation and catabolic responses after biomechanical injury.
  
  
  CONCLUSIONS
  LKB1 is required for chondrocyte AMPK activity, thereby inhibiting matrix catabolic responses to inflammatory cytokines. Concurrent loss of LKB1 and AMPK activity in articular chondrocytes is associated with OA, aging and biomechanical injury. Conversely, pharmacologic AMPK activation attenuates catabolic responses to biomechanical injury, suggesting a potentially novel approach to inhibit OA development and progression.
authors.forename: Freyr
authors.initials: F
authors.lastname: Petursson
authors.forename: Matt
authors.initials: M
authors.lastname: Husa
authors.forename: Ron
authors.initials: R
authors.lastname: June
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: D000091162:AMP-Activated Protein Kinase Kinases; D055372:AMP-Activated Protein Kinases / Q000378:metabolism*; D000818:Animals; D001169:Arthritis, Experimental / Q000378:metabolism; D015153:Blotting, Western; D002358:Cartilage, Articular / Q000378:metabolism; D002417:Cattle; D019902:Chondrocytes / Q000378:metabolism*; D004797:Enzyme-Linked Immunosorbent Assay; D055785:Gene Knockdown Techniques; D006801:Humans; D007150:Immunohistochemistry; D051379:Mice; D008810:Mice, Inbred C57BL; D010003:Osteoarthritis / Q000378:metabolism*; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism*; D034741:RNA, Small Interfering; D020133:Reverse Transcriptase Polymerase Chain Reaction; D013314:Stress, Mechanical; D014162:Transfection
chemical_list: D034741:RNA, Small Interfering; D017346:Protein Serine-Threonine Kinases; C109790:STK11 protein, human; C491654:Stk11 protein, mouse; D000091162:AMP-Activated Protein Kinase Kinases; D055372:AMP-Activated Protein Kinases