RANKL expression of primary osteoblasts is enhanced by an IL-17-mediated JAK2/STAT3 pathway through autophagy suppression

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.

KEYWORDS:

• IL-17
• primary osteoblasts
• autophagy
• RANKL
• JAK2/STAT3 pathway

Disclosure statement

The authors have no conflicts of interest to report.

Ethical approval

The Ethics Committee of the Second Affiliated Hospital of Zhejiang University School of Medicine on Animal Care approved the procedures for the entire study. The approval number of animal ethics committee of Second Affiliated Hospital of Zhejiang University School of Medicine is 2017-052.

Additional information

Funding

This work was supported by the National Natural Science Foundation of China [grant numbers 81771072, 81800972], the Science and Technology Department of Zhejiang Province [grant number 2019C03027], and Zhejiang Provincial Basic Public Welfare Project [grant number LGF18H140003].