Effect of TNF-α on Wnt signaling in nucleus pulposus cells. (A-B) Cells transfected with the Topflash reporter plasmid (A) or the Fopflash plasmid (B) together with the pGL4.74 plasmid were treated with different concentrations of TNF-α for 6 to 12 h. (C) Nucleus pulposus cells were transfected with the Topflash reporter plasmid or the Fopflash reporter plasmid and increasing concentrations of the Sclerostin (SOST) plasmids (100 to 500 ng) or empty backbone plasmids. (D) SOST mRNA expression after exposure of nucleus pulposus cells to TNF-α (10 ng/mL) for 24 h, as assessed by real-time PCR. *P <0.05 indicates significant differences between groups. Error bars represent the SD. n.s., not significant.