Sprifermin is a human recombinant fibroblast growth factor 18 (rhFGF18) in clinical development for knee osteoarthritis. Previously, we demonstrated that sprifermin exerts an anabolic effect on chondrocytes in 3D culture with cyclic but not permanent exposure. Here, we hypothesized that permanent exposure to sprifermin de-sensitizes the cells. To test this, a combination of Western-blot and cell staining methods was used. We demonstrate that sprifermin is transiently internalized in chondrocytes along with a transient increase in ERK1/2 activation. We also show that sprifermin is intracellularly degraded, probably together with its receptor FGFR3, thus preventing further stimulation. However, incubation without sprifermin re-sensitizes the cells. Finally, we show that sprifermin endocytosis is clathrin- and dynamin-independent and that receptor activation is not necessary for sprifermin's endocytosis. In this study, we link the role of endocytosis to the cell response and elucidate for the first time a de-sensitization phenomenon to a FGF.

Sprifermin是人类重组纤维母细胞生长因子18（rhFGF18），在膝关节骨关节炎的临床开发中。以前，我们证明了sprifermin对3D培养中的软骨细胞具有合成代谢作用，但具有周期性但非永久性暴露。在这里，我们假设永久暴露于sprifermin会使细胞失去敏感性。为了测试这一点，结合了蛋白质印迹和细胞染色方法。我们证明，sprifermin瞬时内在软骨细胞内，以及ERK1 / 2激活的瞬时增加。我们还显示，Sprifermin可能与其受体FGFR3一起在细胞内降解，从而阻止了进一步的刺激。但是，不使用Sprifermin进行孵育会使细胞重新敏感。最后，我们显示，Sprifermin的内吞作用与网格蛋白和动力蛋白无关，并且受体的激活对于Sprifermin的内吞作用不是必需的。在这项研究中，我们将胞吞作用与细胞反应联系在一起，并首次阐明了对FGF的脱敏现象。