title: Effects of high frequency loading on RANKL and OPG mRNA expression in ST-2 murine stromal cells.
abstract: BACKGROUND
  Oscillatory fluid flow (OFF)-induced shear stress leads to positive bone remodeling through pro-formative and anti-resorptive effects on bone cells. In this study, the effects of high frequency OFF on expression of receptor activator of NF-kappaB ligand (RANKL) and osteoprotegerin (OPG), two important regulators of osteoclast differentiation, were investigated.
  
  
  METHODS
  Cells were exposed to 1 Pa peak shear stress using three loading frequencies (1, 10, and 20 Hz) widely employed in cell, animal, and clinical studies of bone remodeling. Two separate experiments were performed where either the total number of cycles (3600 cycles) or the total loading time (60 min) was kept constant. Real-time RT-PCR was used to quantify mRNA levels of RANKL, OPG.
  
  
  RESULTS
  3600 cycles of OFF at 1 Hz and 10 Hz loading decreased RANKL/OPG ratio. Interestingly, these results were due to different mechanisms where at 1 Hz the decrease was due to an increase in OPG mRNA, whereas at 10 Hz the decrease was due to a decrease in RANKL mRNA.
  
  
  CONCLUSIONS
  Although high frequency OFF does not appear to further enhance the decrease in the RANKL/OPG ratio, these results suggest a potential to differentially control the change in either RANKL or OPG mRNA expression by applying different loading frequencies.
authors.affiliation: Department of Biomedical Engineering, Yonsei University, Gangwon Do, Korea. chihyun@yonsei.ac.kr
authors.forename: Chi Hyun
authors.initials: CH
authors.lastname: Kim
authors.forename: Kyung Hwan
authors.initials: KH
authors.lastname: Kim
authors.forename: Christopher R
authors.initials: CR
authors.lastname: Jacobs
mesh_terms: D000818:Animals; D002478:Cells, Cultured; D005786:Gene Expression Regulation / Q000502:physiology; D051379:Mice; D053244:Osteoprotegerin / Q000096:biosynthesis* / Q000235:genetics; D053245:RANK Ligand / Q000096:biosynthesis* / Q000235:genetics; D012333:RNA, Messenger / Q000096:biosynthesis*; D011846:Radio Waves; D017154:Stromal Cells / Q000378:metabolism
chemical_list: D053244:Osteoprotegerin; D053245:RANK Ligand; D012333:RNA, Messenger; C506031:Tnfrsf11b protein, mouse