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KMID : 0848120080330040179
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International Journal of Oral Biology
2008 Volume.33 No. 4 p.179 ~ p.186
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The Effects of Mechanical Strain on Bone Cell Proliferation and Recruitment Induced by Osteocytes
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Ko Seong-Hee
Lee Jiy-Hye
Kim So-Hee
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Abstract
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Several lines of evidence suggest that osteocytes play a critical role in bone remodeling. Both healthy and apoptotic
osteocytes can send signals to other bone surface cells such as osteoblasts, osteoclasts, osteoclast precursors, and bone lining cells through canalicular networks. Osteocytes responding to mechanical strain may also send signals to
other cells. To determine the role for osteocytes and mechanical strain in bone remodeling, we examined the effects of fluid flow shear stress on osteoclast precursor cell and osteoblast proliferation and recruitment induced by osteocytes. In addition, the effects of fluid flow shear stress on osteocyte M-CSF, RANKL, and OPG mRNA expression were also examined. MLO-Y4 cells were used as an in vitro model for osteocytes, RAW 264.7 cells and MOCP-5 cells as
osteoclast precursors, and 2T3 cells as osteoblasts. MLO-Y4 cells conditioned medium (Y4-CM) was collected after 24h
culture. For fluid flow experiments, MLO-Y4 cells were exposed to 2 h of pulsatile fluid flow (PFF) at 2, 4, 8, 16 0.6 dynes/cm 2 using the Flexcell Streamer TM system. For proliferation assays, MOCP-5, RAW 264.7, and 2T3 cells
were cultured with control media or 10 - 100 % Y4 CM. Cells were cultured for 3 d, and then cells were counted. RAW 264.7 and 2T3 cell migration was assayed using transwells with control media or 10 - 100 % Y4-CM. MCSF, RANKL and OPG in MLO-Y4 mRNA expression was determined by semiquantitative RT-PCR. Y4-CM increased osteoclast precursor proliferation and migration, but decreased 2T3 cell proliferation and migration. CM from MLO-Y4 cells exposed to PFF caused decreased RAW 267.4 cell proliferation and migration and 2T3 migration compared to control Y4-CM. However, Y4-CM from cells exposed to PFF had no effect on 2T3 osteoblastic cell proliferation. PFF decreased RNAKL mRNA and
increased OPG mRNA in MLO-Y4 cells compared to control (without PFF). PFF had no effect on M-CSF mRNA expression in MLO-Y4 cells. These results suggest that osteocytes can regulate bone remodeling by communication with osteoclast precursors and osteoblasts and that osteocytes can communicate mechanical signals to other cells.
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KEYWORD
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Mechanical strain, Osteocyte, Proliferation of osteoblast and osteoclast precursors, Migration of osteoblast and osteoclast precursors
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