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Ultrasound Accelerated Differentiation of Cultured Human Osteoblasts.   Chika Umeda1, Yumi Kawahara2, Atsuko Okubo1, Teruyuki Kajiume1, Hideki Moriyama1, Katsuko Kataoka2, Louis Yuge1. (1Graduate School of Health Sciences, 2Graduate School of Biomedical Sciences, Hiroshima University, Japan)

   An ultrasound therapy is recently used in treatment of bone atrophy and osteoporosis.  However, cellular responses to ultrasound have not been elucidated.   We examined the effects of ultrasound in differentiation of cultured osteoblasts.   A normal human osteoblast (NHOst) cell system was used.   The cells were seeded in polymeric membrane culture dishes, the bottom of which is thin enough to transmit ultrasound stimulus (day 0).   In group US, ultrasound stimulus was administered through the thin silicon pad to the bottom of the culture dish.   The set condition of the stimulus was 0.2 W/cm2 and 1 MHz.   The osteoblasts were exposed ultrasound for 3 min on day 1, 3 and 5.   For control, the cells were seeded and cultured in the same culture condition but without ultrasound stimulation (group C).   We studied morphological characteristics of the cells and expression of Cbfa1 and osteocalcin by RT-PCR and western blot analysis.   In group US, the formation of bone nodules and appearance of alkaline phosphatase activities were accelerated.   The expression levels of Cbfa1 (a transcription factor) and osteocalcin (bone specific regulatory factor) were increased, and calcification were seen earlier and more frequently in group US than in group C.   The osteoblast differentiation is accelerated by ultrasound stimulus.   Moreover, it is suggested by these results that ultrasound stimulus facilitates the switch-on of osteoblast differentiation.   Therapeutic ultrasound stimulation has been considered to enhance the bone formation.   This study proved the effect in osteoblast culture system, and this system would contribute to clarify precise mechanism of osteoblast differentiation.