Epithelial Cells Secrete Interferon-γ Which Suppresses Expression of Receptor Activator of Nuclear Factor Kappa-B Ligand in Human Mandibular Osteoblast-Like Cells

Intermittent compressive force induces human mandibular-derived osteoblast differentiation via WNT/β-catenin signaling

Mechanical force induces an efflux of ATP that regulates osteoblast differentiation. However, the effect of mechanical force-induced ATP efflux on WNT/β-catenin signaling remains unclarified. The aim of this study was to investigate the effect of intermittent compressive force (ICF) and ICF-induced extracellular ATP on osteoblast differentiation via WNT/β-catenin signaling in human mandibular-derived osteoblast precursors (hMOBPs). The hMOBPs were subjected to ICF (1.5 g/cm² , 0.3 Hz) for 20 h. To investigate the role of ATP, Apyrase (0.5 units/mL), an enzyme that hydrolyzes ATP, was added 30 min before ICF was applied. The extracellular ATP levels were measured immediately after ICF was removed. The mRNA expression of osteogenic related genes, including WNT was evaluated via quantitative real time polymerase chain reaction. In vitro mineralization was determined by Alizarin Red S staining. The localization of β-catenin was detected using immunofluorescence staining and lentiviral-TOP-dGFP reporter assay. The results demonstrated that ICF increased ATP efflux and in vitro mineralization by hMOBPs. In addition, OSX, ALP, and WNT3A mRNA expression and β-catenin nuclear translocation increased when ICF was applied. The upregulation of these genes was reduced by Apyrase, suggesting the role of ICF-induced ATP on osteoblast differentiation. Notably, ICF altered the mRNA expression of purinergic 2X receptors (P2XRs). A P2X1R antagonist (NF449) downregulated ICF-induced WNT3A, OSX, and ALP mRNA expression. Moreover, when 25 μM α, β-meATP, a P2X1R agonist, was added, WNT3A, and OSX expression increased. In conclusion, our results demonstrate that ICF-induced ATP enhanced hMOBP differentiation. This enhancement was associated with WNT/β-catenin signaling and P2X1R activation.

Purinergic 2X7 receptor activation regulates WNT signaling in human mandibular-derived osteoblasts

OBJECTIVE

Purinergic 2X7 receptor (P2X7R) activation modulates in vitro mineralization by primary rat and human osteoblasts. However, the detailed mechanism of how P2X7R activation affects primary human osteoblasts remains unclear. The aim of this study was to investigate the effect of P2X7R activation on human mandibular-derived osteoblast (hMOB) differentiation.

DESIGN

Primary human osteoblasts were obtained from non-pathologic mandibular bone from healthy patients. The hMOBs were cultured in osteogenic medium with or without 0.5-5μM 2'(3')-O-(4-benzoyl) benzoyl-ATP (BzATP), a selective P2X7R agonist. The mRNA expression of osteogenic differentiation markers and WNT-signaling molecules was investigated by quantitative real time polymerase chain reaction. In vitro mineral deposition was determined by Alizarin Red S staining. Transfection of small interfering RNA was performed to confirm the effect of P2X7R activation. WNT/β-catenin signaling was detected by immunofluorescence staining for β-catenin.

RESULTS

BzATP inhibited osteogenic medium-induced RUNX2 and OSX mRNA expression in hMOBs. Moreover, BzATP significantly retarded in vitro mineralization. These findings indicated that BzATP/P2X7R activation inhibited hMOB differentiation. Interestingly, reduced WNT3A mRNA expression and blockage of osteogenic medium-induced β-catenin nuclear translocation were also found. These data suggested that WNT signaling might be a target of P2X7R-regulated osteogenic differentiation. Furthermore, when recombinant human WNT3A was added to the BzATP-treated group, it rescued the reduced RUNX2 and OSX expression, and in vitro mineralization.

CONCLUSION

Our results demonstrate that P2X7R activation by BzATP inhibits hMOB differentiation. This inhibitory effect was associated with inhibition of the WNT/β-catenin signaling pathway.