title: Effects of cyclic tension stress on the apoptosis of osteoclastsin vitro.
abstract: The aim of the present study was to investigate the effect of cyclic tension stress on osteoclast apoptosisin vitrousing murine RAW264.7 cells treated with receptor activator of nuclear factor-κB. Using the EF3200 mechanical testing instrument with BioDynamic bioreactor system, cultured osteoclasts which were seeded in a silicone rubber membrane load carrier, were loaded with periodic cyclic stretch microstrain. The induced osteoclasts were subjected to 0, 5, 10 and 15% stretch microstrain for 1 h daily for three days. The number of tartrate-resistant acid phosphatase-positive osteoclasts and the resorption area were assessed. Osteoclast apoptosis was detected by the Annexin V-fluorescein isothiocyanate (FITC)/propidium iodide binding assay. The mRNA expression of Bcl-2, Bax, caspase-3 and cytochromecwas detected following force loading using reverse transcription-quantitative polymerase chain reaction (RT-qPCR) analysis. Compared with the cells under no cyclic tension stress, the number of osteoclasts and the resorption area were increased in the cells under 10 and 15% stretch microstrain. The Annexin V binding assay showed that the early apoptosis rate of the 5, 10 and 15% stretch microstrain groups was decreased compared with that of the control group. RT-qPCR results showed that the Bcl-2/Bax ratio was significantly increased in the cells subjected to 5, 10 and 15% stretch microstrain compared with that in the control cells (P<0.05), while the expression of cytochromecin the 10 and 15% stretch microstrain groups was decreased significantly (P<0.05). No significant difference was observed between the cytochromecexpression of the 5% stretch microstrain group and that of the control group (P>0.05). The expression of caspase-3 in the 5, 10 and 15% stretch microstrain groups was decreased significantly compared with that in the control group (P<0.05). These data suggest that cyclic tension stress can inhibit apoptosis in osteoclasts, possibly by increasing the Bcl-2/Bax ratio, inhibiting the activity of caspase-3 and downregulating the expression of cytochromec.
authors.affiliation: Institute of Orthopedics, Tianjin Hospital, Tianjin 300211, P.R. China.
authors.forename: Fengbo
authors.initials: F
authors.lastname: Li
authors.affiliation: Institute of Orthopedics, Tianjin Hospital, Tianjin 300211, P.R. China.
authors.forename: Xiaolei
authors.initials: X
authors.lastname: Sun
authors.affiliation: Institute of Orthopedics, Tianjin Hospital, Tianjin 300211, P.R. China.
authors.forename: Bin
authors.initials: B
authors.lastname: Zhao
authors.affiliation: Institute of Orthopedics, Tianjin Hospital, Tianjin 300211, P.R. China.
authors.forename: Jianxiong
authors.initials: J
authors.lastname: Ma
authors.affiliation: Institute of Orthopedics, Tianjin Hospital, Tianjin 300211, P.R. China.
authors.forename: Yang
authors.initials: Y
authors.lastname: Zhang
authors.affiliation: Institute of Orthopedics, Tianjin Hospital, Tianjin 300211, P.R. China.
authors.forename: Shuang
authors.initials: S
authors.lastname: Li
authors.affiliation: Institute of Orthopedics, Tianjin Hospital, Tianjin 300211, P.R. China.
authors.forename: Yanjun
authors.initials: Y
authors.lastname: Li
authors.affiliation: Institute of Orthopedics, Tianjin Hospital, Tianjin 300211, P.R. China.
authors.forename: Xinlong
authors.initials: X
authors.lastname: Ma
keywords: RAW264.7; apoptosis; cyclic tension stress; mitochondria; osteoclast; tartrate-resistant acid phosphatase