Extracellular Sulfatase Regulation of BMP-7 and FGF-2 Signaling in Human Articular Chondrocytes

We performed a new set of experiments to confirm findings reported in our previous publication regarding the role of Sulf-1 and Sulf-2 in regulating BMP-7 and FGF-2 signaling in human articular chondrocytes. Using primary chondrocytes from five independent human donors, we examined the effects of Sulf knockdown on Smad1/5 and Erk1/2 phosphorylation. Sulf-1 and Sulf-2 knockdown consistently reduced BMP-7-induced Smad1/5 phosphorylation and enhanced FGF-2-induced Erk1/2 phosphorylation. Although the magnitude of Erk1/2 activation was somewhat lower than originally reported, the direction and statistical significance of the effects were preserved. These results confirm the original conclusions and support the role of Sulfs as dual regulators of BMP-7 and FGF-2 signaling pathways in human chondrocytes.