title: Shear stress modulates macrophage-induced urokinase plasminogen activator expression in human chondrocytes.
abstract: BACKGROUND
  Synovial macrophages, which can release proinflammatory factors, are responsible for the upregulation of cartilage-breakdown proteases and play critical roles in cartilage degradation during the progression of osteoarthritis (OA). In addition, shear stress exerts multifunctional effects on chondrocytes by inducing the synthesis of catabolic or anabolic genes. However, the interplay of macrophages, chondrocytes, and shear stress during the regulation of cartilage function remains poorly understood. We investigated the mechanisms underlying the modulation of human chondrocyte urokinase plasminogen activator (uPA) expression by macrophages and shear stress.
  
  
  METHODS
  Human chondrocytes were stimulated by peripheral blood-macrophage- conditioned medium (PB-MCM), or exposure of chondrocytes cultured in PB-MCM to different levels of shear stress (2 to 20 dyn/cm2). Real-time polymerase chain reaction was used to analyze uPA gene expression. Inhibitors and small interfering RNA were used to investigate the mechanism for the effects of PB-MCM and shear stress in chondrocytes.
  
  
  RESULTS
  Stimulation of human chondrocytes with PB-MCM was found to induce uPA expression. We demonstrated that activation of the JNK and Akt pathways and NF-κB are critical for PB-MCM-induced uPA expression. Blocking assays by using IL-1ra further demonstrated that IL-1β in PB-MCM is the major mediator of uPA expression in chondrocytes. PB-MCM-treated chondrocytes subjected to a lower level of shear stress showed inhibition of MCM-induced JNK and Akt phosphorylation, NF-κB activation, and uPA expression. The PB-MCM-induced uPA expression was suppressed by AMP-activated protein kinase (AMPK) agonist. The inhibitor or siRNA for AMPK abolished the shear-mediated inhibition of uPA expression.
  
  
  CONCLUSIONS
  These data support the hypothesis that uPA upregulation stimulated by macrophages may play an active role in the onset of OA and in the shear-stress protection against this induction.
authors.forename: Chih-Chang
authors.initials: CC
authors.lastname: Yeh
authors.forename: Shun-Fu
authors.initials: SF
authors.lastname: Chang
authors.forename: Ting-Ying
authors.initials: TY
authors.lastname: Huang
authors.forename: Hsin-I
authors.initials: HI
authors.lastname: Chang
authors.forename: Hsing-Chun
authors.initials: HC
authors.lastname: Kuo
authors.forename: Yi-Chien
authors.initials: YC
authors.lastname: Wu
authors.forename: Ching-Hsiang
authors.initials: CH
authors.lastname: Hsieh
authors.forename: Chung-Sheng
authors.initials: CS
authors.lastname: Shi
authors.forename: Cheng-Nan
authors.initials: CN
authors.lastname: Chen
mesh_terms: D015153:Blotting, Western; D002358:Cartilage, Articular / Q000378:metabolism; D002478:Cells, Cultured; D019902:Chondrocytes / Q000378:metabolism*; D047369:Chromatin Immunoprecipitation; D017077:Culture Media, Conditioned / Q000494:pharmacology; D004797:Enzyme-Linked Immunosorbent Assay; D006801:Humans; D008264:Macrophages / Q000378:metabolism*; D010003:Osteoarthritis / Q000378:metabolism; D034741:RNA, Small Interfering; D060888:Real-Time Polymerase Chain Reaction; D015398:Signal Transduction / Q000502:physiology; D013314:Stress, Mechanical; D014162:Transfection; D015854:Up-Regulation; D014568:Urokinase-Type Plasminogen Activator / Q000096:biosynthesis*
chemical_list: D017077:Culture Media, Conditioned; D034741:RNA, Small Interfering; D014568:Urokinase-Type Plasminogen Activator