title: Effect of fluid flow-induced shear stress on osteoclast formation induced by osteocyte.
abstract: OBJECTIVE
  To study the role of osteocyte in bone remodeling due to mechanical loading in vitro.
  
  
  METHODS
  MLO-Y4 osteocyte-like cells were exposed to fluid flow-induced shear stress(12dyn/cm(2))for 0, 1, 2, 4, 6, 12, and 24 hours. Osteocyte exposed to shear stress at different time points were used in co-culture system for 9 days, and then the cells were stained with tartrate-resistant acid phosphatase on the 9(th) day and the amount of positively stained osteoclasts were counted and compared. The expressions of osteoprotegerin (OPG) and receptor activator of nuclear factor-kappa (RANKL) were detected by semi-quantitative reverse transcription polymerase chain reaction (semi-quantitative RT-PCR).
  
  
  RESULTS
  Compared with bone cells without stimulation with fluid flow-induced shear stress, the amount of osteocytes significantly decreased at all time points after the application of fluid flow-induced shear stress (all P<0.05). The OPG expression at mRNA levels was significantly up-regulated in the first 12 hours (P<0.001), the RANKL mRNA expression was significantly down-regulated in the first 4 hours (P<0.05), and the RANKL/OPG ratio significantly decreased within 12 hours (P<0.01). However, all these indicators showed no significant difference at 24 hours when compared with the pre-stimulation level.
  
  
  CONCLUSIONS
  Osteocytes may act as mechanosensors that are able to inhibit bone resorption after mechanical loading; however, such effect shows certain adaptation ability to shear stress as time goes.
authors: Department of Stomatology, PUMC Hospital, CAMS and PUMC, Beijing 100730, China.
authors: Liang
authors: L
authors: Cui
authors: Xiao-tong
authors: XT
authors: Li
authors: Ding
authors: D
authors: Zhang
mesh_terms: D000818:Animals; D002454:Cell Differentiation; D002478:Cells, Cultured; D018920:Coculture Techniques; D008297:Male; D051379:Mice; D010010:Osteoclasts / Q000166:cytology*; D010011:Osteocytes / Q000166:cytology*; D053244:Osteoprotegerin / Q000378:metabolism; D053245:RANK Ligand / Q000378:metabolism; D013314:Stress, Mechanical
chemical_list: D053244:Osteoprotegerin; D053245:RANK Ligand; C506031:Tnfrsf11b protein, mouse; C505689:Tnfsf11 protein, mouse