Inhibitory Effects of Rhaponticin on Osteoclast Formation and Resorption by Targeting RANKL-Induced NFATc1 and ROS Activity

Jianbo He; Kai Chen; Tiancheng Deng; Jiewei Xie; Kunjing Zhong; Jinbo Yuan; Ziyi Wang; Zhifeng Xiao; Ronghe Gu; Delong Chen; Xiaojuan Li; Dingkun Lin; Jiake Xu

doi:10.3389/fphar.2021.645140

Inhibitory Effects of Rhaponticin on Osteoclast Formation and Resorption by Targeting RANKL-Induced NFATc1 and ROS Activity

Front Pharmacol. 2021 Sep 23:12:645140. doi: 10.3389/fphar.2021.645140. eCollection 2021.

Authors

Jianbo He^{1

2}, Kai Chen², Tiancheng Deng¹, Jiewei Xie¹, Kunjing Zhong¹, Jinbo Yuan², Ziyi Wang², Zhifeng Xiao¹, Ronghe Gu^{2

3}, Delong Chen⁴, Xiaojuan Li⁵, Dingkun Lin¹, Jiake Xu²

Affiliations

¹ The Second Affiliated Hospital of Guangzhou University of Chinese Medicine, Guangdong Provincial Hospital of Chinese Medicine, Guangzhou, China.
² School of Biomedical Sciences, University of Western Australia, Perth, WA, Australia.
³ Department of Orthopedics, First People's Hospital of Nanning, Fifth Affiliated Hospital of Guangxi Medical University, Nanning, China.
⁴ The First Affiliated Hospital of Guangzhou University of Chinese Medicine, Guangzhou, China.
⁵ Formula-Pattern Research Center, School of Traditional Chinese Medicine, Jinan University, Guangzhou, China.

Abstract

The extravagant osteoclast formation and resorption is the main cause of osteoporosis. Inhibiting the hyperactive osteoclastic resorption is considered as an efficient treatment for osteoporosis. Rhaponticin (RH) is a small molecule that has been reported to possess anti-inflammatory, anti-allergic, anti-fibrotic, and anti-diabetic activities. However, the influence of RH on osteoclasts differentiation and function is still unclear. To this end, an array of assays including receptor activator of nuclear factor kappa-Β (NF-κB) ligand (RANKL) induced osteoclastogenesis, tartrate-resistant acidic phosphatase (TRAcP) staining, immunofluorescence, and hydroxyapatite resorption were performed in this study. It was found that RH had significant anti-catabolic effects by inhibiting osteoclastogenesis and bone resorption without cytotoxicity. Mechanistically, the expression of NADPH oxidase 1 (Nox1) was found to be suppressed and antioxidant enzymes including catalase, superoxide dismutase 2 (SOD-2), and heme oxygenase-1(HO-1) were enhanced following RH treatment, suggesting RH exhibited antioxidant activity by reducing the generation of reactive oxygen species (ROS) as well as enhancing the depletion of ROS. In addition, MAPKs, NF-κB, and intracellular Ca²⁺ oscillation pathways were significantly inhibited by RH. These changes led to the deactivation of osteoclast master transcriptional factor-nuclear factor of activated T cells 1 (NFATc1), as examined by qPCR and Western blot assay, which led to the decreased expression of downstream integrin β3, c-Fos, cathepsin K, and Atp6v0d2. These results suggested that RH could effectively suppress RANKL-regulated osteoclast formation and bone resorption. Therefore, we propose that RH can represent a novel natural small molecule for the treatment of osteoporosis by inhibiting excessive osteoclast activity.

Keywords: NFATc1; ROS; bone; osteoclast; rhaponticin.

Grants and funding

This study was supported in part by the Australian National Health and Medical Research Council (NHMRC, Nos. 1107828, 1127156, 1163933), National Natural Science Foundation of China Youth Fund (No. 81904091) and Fundamental Research Funds for the Central Universities (No. 21619307).