Bone Abstracts

There are several evidences that osteocyte plays a critical role in bone remodeling. Healthy or apoptotic osteocytes can send signals to other bone surface cells like osteoblasts, osteoclasts, osteoclast precursors and bone lining cells through their networking in canaliculi. Therefore, to determine the role for osteocytes in bone remodeling, we examined the effect of healthy and apoptotic osteocytes on osteoblasts proliferation and recruitment. In addition, the effects of mechanical strain through osteocyte on bone remodeling were examined using fluid flow system. We used the MLO-Y4 cells as in vitro model for osteocytes, and 2T3 cells as osteoblasts. For induction of MLO-Y4 cell apoptosis, MLO-Y4 cells were treated with 100 μM etoposide for 6 h and apoptosis was determined with increase of casapase-3 activity and ratio of trypan blue straining cells. For fluid flow experiments, MLO-Y4 cells were exposed to 2 h of fluid flow at 2, 4, 8, 16 dynes/cm² using Flexcell Streamer^TM system. Healthy, apoptotic and shear stress-exposed MLO-Y4 cells conditioned medium (Y4-CM) was collected after 24 h culture. We did proliferation assay 2T3 cells with Y4-CM at specific time. The migration of 2T3 cells was assayed using transwells with control media or Y4-CM. Healthy Y4-CM decreased 2T3 cell proliferation and migration. However apoptotic Y4-CM increased the proliferation of 2T3 cells compared to control Y4-CM. Apoptotic Y4-CM had no effect on migration of 2T3 cell. After MLO-Y4 cells were exposed to fluid flow, Y4-CM after application of high magnitude of stress (8, 16 dynes/cm²), decreased the migration of 2T3 cells. These results suggest that the osteocytes responding to apoptosis and mechanical strain might modulate the bone formation by changing the signals to osteoblasts.