ABSTRACT

Objective: Interleukin-17 (IL-17), produced by T helper (Th)-17 cells, is a potent regulator of bone homeostasis. Osteoblasts are key cells that orchestrate inflammatory bone destruction and bone remodeling. This study examines the effect of different concentrations of IL-17 on osteogenesis and receptor activator of nuclear factor-kappa B ligand (RANKL) expression of primary osteoblasts.

Methods: First, the growth of primary osteoblasts was evaluated. Second, we assessed the effects of IL-17 on the level of autophagy and the related Janus activated kinase 2 (JAK2) and downstream signal transducer and activator of transcription 3 (STAT3) signaling pathway. Next, osteogenic activity in different concentrations of IL-17 was tested. Finally, the specific JAK2/STAT3 signaling pathway inhibitor AG490 and autophagy inhibitor 3-MA were used to investigate the involvement of this pathway and autophagy in IL-17-induced regulation of RANKL expression.

Results: Initially, we found that IL-17 treatment promoted growth of osteoblasts in a time- and dose-dependent manner. Next, we showed that low levels of IL-17 promoted autophagy activity, whereas the opposite was observed at high levels of IL-17. Moreover, high levels of IL-17 activated the JAK2/STAT3 signaling pathway, although this effect was reversed by upregulation of autophagy. Furthermore, our findings indicated that high concentrations of IL-17 promoted the differentiation, calcification, and RANKL expression of murine osteoblasts via activation of the JAK2/STAT3 pathway. Importantly, downregulation of autophagy at high IL-17 concentrations further enhanced RANKL expression via suppressing the JAK2/STAT3 cascade.

Conclusion: Overall, our findings demonstrate, for the first time, that IL-17 modulates RANKL expression of osteoblasts through an autophagy–JAK2-STAT3 signaling pathway, thus affecting bone metabolism.

摘要

目的：白细胞介素17（IL-17）由T辅助（Th）-17细胞产生，是一种有效的骨稳态调节剂。成骨细胞是协调炎症性骨破坏和骨重塑的关键细胞。本研究考察了不同浓度的 IL-17 对原代成骨细胞成骨和核因子-κB 配体 (RANKL) 受体激活剂表达的影响。

方法：首先，评估原代成骨细胞的生长情况。其次，我们评估了 IL-17 对自噬水平和相关的 Janus 活化激酶 2 (JAK2) 以及下游信号转导和转录激活因子 3 (STAT3) 信号通路的影响。接下来，测试了不同浓度的 IL-17 的成骨活性。最后，使用特异性 JAK2/STAT3 信号通路抑制剂 AG490 和自噬抑制剂 3-MA 来研究该通路和自噬在 IL-17 诱导的 RANKL 表达调节中的作用。

结果：最初，我们发现 IL-17 治疗以时间和剂量依赖性方式促进成骨细胞的生长。接下来，我们发现低水平的 IL-17 促进了自噬活性，而在高水平的 IL-17 中观察到相反的情况。此外，高水平的 IL-17 激活了 JAK2/STAT3 信号通路，尽管这种作用被自噬上调所逆转。此外，我们的研究结果表明，高浓度的 IL-17 通过激活 JAK2/STAT3 通路促进小鼠成骨细胞的分化、钙化和 RANKL 表达。重要的是，在高 IL-17 浓度下自噬的下调通过抑制 JAK2/STAT3 级联进一步增强了 RANKL 的表达。

结论：总体而言，我们的研究结果首次表明，IL-17 通过自噬-JAK2-STAT3 信号通路调节成骨细胞的 RANKL 表达，从而影响骨代谢。