Pulsed electromagnetic fields stimulate osteogenic differentiation and maturation of osteoblasts by upregulating the expression of BMPRII localized at the base of primary cilium

Abstract

Pulsed electromagnetic fields (PEMFs) have been considered as a potential candidate for the prevention and treatment of osteoporosis, however, the mechanism of its action is still elusive. We have previously reported that 50Hz 0.6mT PEMFs stimulate osteoblastic differentiation and mineralization in a primary cilium- dependent manner, but did not know the reason. In the current study, we found that the PEMFs promoted osteogenic differentiation and maturation of rat calvarial osteoblasts (ROBs) by activating bone morphogenetic protein BMP-Smad1/5/8 signaling on the condition that primary cilia were normal. Further studies revealed that BMPRII, the primary binding receptor of BMP ligand, was readily and strongly upregulated by PEMF treatment and localized at the bases of primary cilia. Abrogation of primary cilia with small interfering RNA sequence targeting IFT88 abolished the PEMF-induced upregulation of BMPRII and its ciliary localization. Knockdown of BMPRII expression level with RNA interference had no effects on primary cilia but significantly decreased the promoting effect of PEMFs on osteoblastic differentiation and maturation. These results indicated that PEMFs stimulate osteogenic differentiation and maturation of osteoblast by primary cilium-mediated upregulation of BMPRII expression and subsequently activation of BMP-Smad1/5/8 signaling, and that BMPRII is the key component linking primary cilium and BMP-Smad1/5/8 pathway. This study has thus revealed the molecular mechanism for the osteogenic effect of PEMFs.

Pulsed Electromagnetic Field Regulates MicroRNA 21 Expression to Activate TGF-β Signaling in Human Bone Marrow Stromal Cells to Enhance Osteoblast Differentiation

“…The results show that the PEMF-stimulated Smad2 activation in differentiated osteoblasts (day 23) was blocked when cells were pretreated with pan-TGF- β antibody (Figure 4(c)). Since a recent paper has described a different PEMF signal as acting through the BMP pathway on rat calvarial osteoblasts [18], we examined whether Smad1/5/8 was phosphorylated in response to the Cervical-Stim signal in hBMSCs (Figure 4(d)). We were unable to observe any stimulation of this pathway, in contrast to the activation of the Smad2 pathway, even though the strong positive control, TGF- β 2, slightly stimulated Smad1/5/8 phosphorylation, as has been observed by others [19, 20].…”

“…The TGF- β /BMP signaling effect may be complex and highly time- and space-specific during skeletal development and bone formation. Very recently, Xie et al [18] have described a different PEMF signal as operating through the BMP receptor on the primary cilium of rat calvarial osteoblasts in culture. Our accumulated data do not indicate that the BMP pathway is involved in the signaling mechanism of either Spinal-Stim or Cervical-Stim but we cannot rule out that it may have a role if investigated further.…”

Cilia-dependent GLI processing in neural crest cells is required for tongue development

“…The cilium has previous been associated with transduction of several pathways including Wnt (Corbit et al, 2008; McDermott et al, 2010; Tran et al, 2014), PDGF (Clement et al, 2013; Schneider et al, 2010; Schneider et al, 2005; Schneider et al, 2009), FGF (Hong and Dawid, 2009; Neugebauer et al, 2009; Tabler et al, 2013) and BMP (Xie et al, 2016). Of these pathway, however; the strongest association has been with the Hh pathway (Briscoe and Therond, 2013).…”

Microgravity induces inhibition of osteoblastic differentiation and mineralization through abrogating primary cilia

“…Since a variety of receptors, ion channels and transporter proteins have been localized to the cilium 20, 21 , its role as a mechanosensor has been established. Primary cilium will change its orientation in response to mechanical stimuli and trigger biochemical and transcriptional changes.…”