Pulsed electromagnetic fields promote osteoblast mineralization and maturation needing the existence of primary cilia

• The effects of 50 Hz pulsed electromagnetic fields on rat osteoblasts were studied.
• The proliferation of osteoblasts was stimulated with the optimal effect at 0.6 mT.
• Osteoblastic differentiation was also enhanced with the optimal effect at 0.6 mT.
• Enhancing effects were abrogated when primary cilia of osteoblasts were inhibited.
• Primary cilia are indispensable for the osteogenic effect of electromagnetic fields.

Although pulsed electromagnetic fields (PEMFs) have been approved as a therapy for osteoporosis, action mechanisms and optimal parameters are elusive. To determine the optimal intensity, exposure effects of 50 Hz PEMFs of 0.6–3.6 mT (0.6 interval at 90 min/day) were investigated on proliferation and osteogenic differentiation of cultured calvarial osteoblasts. All intensity groups stimulated proliferation significantly with the highest effect at 0.6 mT. The 0.6 mT group also obtained the optimal osteogenic effect as demonstrated by the highest ALP activity, ALP+ CFU-f colony formation, nodule mineralization, and expression of COL-1 and BMP-2. To verify our hypothesis that the primary cilia are the cellular sensors for PEMFs, osteoblasts were also transfected with IFT88 siRNA or scrambled control, and osteogenesis-promoting effects of 0.6 mT PEMFs were found abrogated when primary cilia were inhibited by IFT88 siRNA. Thus primary cilia of osteoblasts play an indispensable role in mediating PEMF osteogenic effect in vitro.