Effects of Moderate Intensity Static Magnetic Fields on Osteoclastic Differentiation

Objectives: We recently demonstrated that static magnetic fields (SMFs) stimulate osteoblast differentiation, but the effects of SMFs on osteoclastogenesis are still poorly understood. This study focused on the suppressive effects of SMFs on receptor activator of nuclear factor κB (NF-κB) ligand (RANKL)-induced osteoclastogenesis and bone resorption.
Methods: Mouse bone marrow-derived macrophages (BMMs) were used as osteoclast precursor cells. Direct and indirect effects of SMFs on osteoclastogenesis were evaluated by tartrate-resistant acid phosphatase (TRAP) staining and bone resorption assay. Signaling pathways were assessed by western blotting and immunocytochemistry.

Results: Direct exposure to SMFs inhibited the RANKL-induced formation of multinucleated osteoclasts, TRAP activity, and bone resorption in mouse bone marrow-derived macrophages (BMMs). Conditioned medium from osteoblasts treated with SMFs also inhibited osteoclast differentiation as well as bone resorption. RANKL-induced expression of osteoclast-specific transcription factors such as c-Fos and NFATc1 was markedly downregulated by SMFs. In addition, SMFs inhibited the activation by RANKL of Akt, glycogen synthase kinase 3β (GSK3β), ERK and c-jun N-terminal protein kinase (JNK), mitogen-activated protein kinase (MAPK), and nuclear factor-κB (NF-κB).

Conclusions: These findings provide the first evidence that SMF-mediated attenuation of these RANKL-induced pathways contributes to direct and indirect inhibition of osteoclast formation and bone resorption. SMFs could be developed as therapeutic agent against periprosthetic or peri-implant osteolysis, and osteolytic diseases such as osteoporosis and rheumatoid arthritis.