title: Rac1 mediates load-driven attenuation of mRNA expression of nerve growth factor beta in cartilage and chondrocytes.
abstract: OBJECTIVE
  To determine effect of gentle loads applied to the knee on mRNA expression of nerve growth factor, particularly, the active beta subunit (NGFβ) in cartilage and chondrocyte.
  
  
  METHODS
  Cyclic compressive loads in vivo and fluid flow in vitro were used to determine the mRNA levels. Alteration of Rac1 GTPase as well as effect of salubrinal, a specific inhibitor of eIF2α phosphatase was assessed using fluorescence resonance energy transfer (FRET)-based Rac1 biosensor.
  
  
  RESULTS
  Knee loading at 1 N reduced mRNA levels of NGFβ and its low affinity receptor, p75 in cartilage and subchondral bone. In cartilage, knee loading at 1 N reduced the phosphorylation level of p38 MAPK (p38-p) and activity of Rac1 GTPase. Consistent with in vivo results, fluid flow at 5 and 10 dyn/cm(2) reduced mRNA levels of NGFβ and p75 in C28/I2 human chondrocytes. SB203580, which decreases p38-p, reduced the mRNA levels of NGFβ and p75. Silencing Rac1 by siRNA decreased the levels of p38-p and NGFβ mRNA but not p75. Furthermore, administration of salubrinal reduced FRET-based activity of Rac1 as well as the mRNA levels of NGFβ and p75.
  
  
  CONCLUSIONS
  These results provide evidence that mechanical stimulation and salubrinal may attenuate pain perception-linked NGFβ signaling through Rac1-mediated p38 MAPK.
authors.affiliation: Department of Biomedical Engineering, Indiana University-Purdue University Indianapolis, 723 West Michigan Street, Indianapolis, IN 46202, USA. shimjoon@iupui.edu
authors.forename: J W
authors.initials: JW
authors.lastname: Shim
authors.forename: K
authors.initials: K
authors.lastname: Hamamura
authors.forename: A
authors.initials: A
authors.lastname: Chen
authors.forename: Q
authors.initials: Q
authors.lastname: Wan
authors.forename: S
authors.initials: S
authors.lastname: Na
authors.forename: H
authors.initials: H
authors.lastname: Yokota
mesh_terms: D000818:Animals; D015153:Blotting, Western; D002356:Cartilage / Q000378:metabolism*; D002478:Cells, Cultured; D019902:Chondrocytes / Q000378:metabolism*; D005260:Female; D031541:Fluorescence Resonance Energy Transfer; D005786:Gene Expression Regulation; D006801:Humans; D051379:Mice; D008810:Mice, Inbred C57BL; D020932:Nerve Growth Factor / Q000096:biosynthesis*; D012333:RNA, Messenger / Q000378:metabolism; D060888:Real-Time Polymerase Chain Reaction; D015398:Signal Transduction / Q000502:physiology*; D013314:Stress, Mechanical; D016474:Weight-Bearing / Q000502:physiology*; D048051:p38 Mitogen-Activated Protein Kinases / Q000378:metabolism; D020830:rac1 GTP-Binding Protein / Q000378:metabolism*
chemical_list: D012333:RNA, Messenger; D020932:Nerve Growth Factor; D048051:p38 Mitogen-Activated Protein Kinases; D020830:rac1 GTP-Binding Protein