Bone Abstracts

The osteocyte most likely plays a role in bone remodeling by instructing osteoclasts to remove bone at specific sites. This entire process includes recruitment, proliferation and differentiation of osteoclast precursors. And osteocytes are responsible for detecting and responding to mechanical strain and may send signal to other cells. Therefore, to determine the role for osteocytes and mechanical strain in bone remodeling, we examined the effect of steady or pulsatile shear stress of osteocytes on osteoclast precursor migration and proliferation. We used the MLO-Y4 cells as in vitro model for osteocytes, RAW 264.7 cells as osteoclast precursors. 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/cm² or steady fluid flow (SFF) using Flexcell Streamer system. Y4 CM was collected during 24 h cultures after fluid flow experiment (1st – 24 h Y4 CM) or after collecting 1st – 24 h Y4 CM (2nd – 24 h Y4 CM). We did proliferation assay of RAW 264.7 cells with control media or 10% Y4-CM at specific time. The migration of RAW 264.7 cells was assayed using transwells with control media or Y4-CM. MLO-Y4-CM increased osteoclast precursor proliferation and migration. And the increase of RAW 264.7 cell migration induced by MLO-Y4 cells was partially blocked by M-CSF antibody. After MLO-Y4 cells were exposed to SFF, 1st – 24 h Y4 CM had no effect on RAW 264.7 cell proliferation and migration but, 2nd – 24 h Y4 CM decreased RAW 267.4 cell migration compared to control CM (Y4-CM without strain). After MLO-Y4 cells were exposed to PFF, 1st – 24 h Y4 CM decreased RAW 264.7 cell migration and proliferation to control CM. These results suggest that osteocytes can regulate the bone remodeling by communication with osteoclast precursors and that mechanical strain may inhibit the bone resorption which is induced by osteocytes.