Low-intensity pulsed ultrasound inhibits RANKL-induced osteoclast formation via modulating ERK-c-Fos-NFATc1 signaling cascades.

Low-intensity pulsed ultrasound (LIPUS), which is a noninvasive form of mechanical energy, has been utilized as a clinical therapy for bone fracture healing. However, the mechanism how LIPUS affects osteoclast formation and osteoclast activity, has not been fully detailed. Here we found that LIPUS inhibited RANKL-induced osteoclast differentiation in vitro, characterized by decreased number and area of tartrate-resistant acid phosphatase (TRAP) positive cells. Moreover, the expression levels of osteoclast-specific gene were also suppressed by LIPUS treatment. Interestingly, F-actin staining and resorption pit assay showed that LIPUS did not affect the bone resorptive activity of mature osteoclasts. Mechanistically, LIPUS achieved these inhibitory effects by disrupting the phosphorylation of ERK and subsequent activation of the osteoclastic transcription factors, c-Fos and NFATc1. Collectively, our results demonstrated that LIPUS effectively suppresses osteoclast differentiation and osteoclast-specific gene expression through the inhibition of ERK-c-Fos-NFATC1 cascades.