Mechanical vibration inhibits osteoclast formation by reducing DC-STAMP receptor expression in osteoclast precursor cells

- Mechanical vibration directly inhibits osteoclast formation from mouse macrophage cell line RAW264.7 cells.
- Mechanical vibration down-regulates DC-STAMP gene expression and protein production but does not affect P2X7R gene expression in RAW264.7 cells.
- The vibration induced reduction of osteoclast formation is mediated by DC-STAMP, but not by P2X7 purinergic receptor.

It is well known that physical inactivity leads to loss of muscle mass, but it also causes bone loss. Mechanistically, osteoclastogenesis and bone resorption have recently been shown to be regulated by vibration. However, the underlying mechanism behind the inhibition of osteoclast formation is yet unknown. Therefore, we investigated whether mechanical vibration of osteoclast precursor cells affects osteoclast formation by the involvement of fusion-related molecules such as dendritic cell-specific transmembrane protein (DC-STAMP) and P2X7 receptor (P2X7R).RAW264.7 (a murine osteoclastic-like cell line) cells were treated with 20 ng/ml receptor activator of NF-κB ligand (RANKL). For 3 consecutive days, the cells were subjected to 1 h of mechanical vibration with 20 μm displacement at a frequency of 4 Hz and compared to the control cells that were treated under the same condition but without the vibration. After 5 days of culture, osteoclast formation was determined. Gene expression of DC-STAMP and P2X7R by RAW264.7 cells was determined after 1 h of mechanical vibration, while protein production of the DC-STAMP was determined after 6 h of postincubation after vibration.As a result, mechanical vibration of RAW264.7 cells inhibited the formation of osteoclasts. Vibration down-regulated DC-STAMP gene expression by 1.6-fold in the presence of RANKL and by 1.4-fold in the absence of RANKL. Additionally, DC-STAMP protein production was also down-regulated by 1.4-fold in the presence of RANKL and by 1.2-fold in the absence of RANKL in RAW264.7 cells in response to mechanical vibration. However, vibration did not affect P2X7R gene expression. Mouse anti-DC-STAMP antibody inhibited osteoclast formation in the absence of vibration.Our results suggest that mechanical vibration of osteoclast precursor cells reduces DC-STAMP expression in osteoclast precursor cells leading to the inhibition of osteoclast formation.