Low-magnitude mechanical vibration regulates expression of osteogenic proteins in ovariectomized rats

The present study aimed to investigate the impact of low-magnitude and high-frequency mechanical vibration with various lengths of resting period incorporated between loading cycles on the expression of osteogenesis-related proteins in a rat model of osteoporosis.

The rats in the mechanical loading groups received low-magnitude and high-frequency vibration (35 Hz and acceleration of 0.25 g, 15 min/day) for 8 weeks. Bilateral humeral heads and femoral heads were then isolated, and protein levels of bone morphogenetic protein 2 (BMP-2), extracellular signal-regulated kinase 1/2 (ERK1/2), phosphorylated ERK1/2 (p-ERK1/2), runt-related transcription factor 2 (Runx2) and osteocalcin (OCN) were determined by Western blotting.

Increased levels of BMP-2, Runx2 and OCN were observed in rats receiving mechanical vibration. Total ERK1/2 protein remained unchanged, whereas the level of activated ERK1/2 (p-ERK1/2) increased after mechanical vibration. Vibration with incorporated resting period, regardless of length, was more effective in inducing expression of these osteogenic proteins, and the vibration with 7-day resting period had the most profound impact.

Signals from low-magnitude and high-frequency mechanical vibration upregulated the expression of BMP-2 and Runx2, activated the ERK1/2 signaling pathway, and consequently led to increased expression of OCN. The anabolic effect of mechanical stimulation was enhanced with incorporation of resting period between loadings, and the one with 7-day resting period exhibited the strongest effect among all. Our results could provide a reference for development of mechanical stimulation as a non-pharmacological intervention for osteoporosis.