MOLECULAR ASPECTS OF BONE FORMATION INDUCED BY MECHANICAL STRESS

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Calvaria of SD rats were removed out and parietal bones were dissected and washed of soft tissue. Pin holes were made at the top of bones and sterilized clips were set into the holes to make 0.7g of outerward force. Those bones were incubated in alphaMEM for 1,3,7 days and upto 2 weeks and expression of mRNA of bone related proteins, such as Osteopontin (OPN), Osteonectin (ON), Osteocalcin (OC) and Bone Morphogenetic Protein 4 (BMP-4), were investigated by the mathods of RT-PCR and in situ hybridization (ISH). On normal condition, ON and OC were expressed by mature osteoblasts a djacent to minerized bone and ON were also expressed by proliferating osteoblasts toward the suture. Those ON and OC positive cells were also positive for Alkaline phosphatase. After the force was laod, OPN were expressed by immature osteoblasts in proliferating suture zone and by osteocytes embedded in mineralized matrix. There was no OPN signal in resting osteoblasts around the mature bone. BMP-4 were detected by RT-PCR just after the load and during the early phase of mineralization, however, no histological signal was found in ISH.Further study is under investigation including the modification of ISH methodlogy for OPN.