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HUMAN OSTEOBLAST DIFFERENTIATION IS EXPEDITED IN CULTURE IN A MAGNETIC FIELD.  L. Yuge¹, T. Kumagai¹, I. Hide¹, S. Hiyama², M. Kanno¹, Y. Kumei³, S. Takeda⁴,  Y. Ikuta¹,  M. Sugiyama¹, and  K. Kataoka^{1  1}Faculty of Medicine, Hiroshima University, Hiroshima, Japan.  ²Faculty of Dentistry, Hiroshima University, Hiroshima, Japan.  ³Faculty of Dentistry, Tokyo Medical and Dental University, Tokyo, Japan. ⁴Dept. of Molecular Genetics, National Institute of Neuroscience, Tokyo, Japan 

We developed a new cell stimulation method in which magnetic microparticles (MPs) were introduced into the cytoplasm of cultured human osteoblasts and the cells were cultured in a magnetic field.  We examined the differentiation of osteoblasts with respect to MAPK-cascade, osteogenesis and morphology including histological detection of minerals.  After exposure to the magnetic field, the cells containing MPs became larger and were elongated along the axis of the magnetic pole. The expression of bone specific regulatory factors such as osteopontin, bone sialoprotein (BSP) and osteocalcine, and formation of hydroxyapatite crystals were seen earlier and more frequently in this group of osteoblasts than in the other groups (cells alone without magnetic field, cells containing MPs but without magnetic field, and cells alone with magnetic field).  The differences were statistically significant at p<0.001 by analysis of variance on a day-by-day basis.  P38 activity was increased (increasing phosphorylation activity) in this environment, whereas MAPK/ERK and SAPK/JNK phosphate activity were not changed in any group.  The precisely quantitative and stable stimulus induced by a magnetic field developed in the present study offers a new approach to elucidate the entire process of osteoblast differentiation to form hydroxyapatite crystals.

(Supported by Japan Space Forum form NASDA, Space Utilization Research from ISAS, the Ministry of Education, JPTA, and the Magnetic Health Science Foundation.)