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Inhibition of PPP1R15A alleviates osteoporosis via suppressing RANKL-induced osteoclastogenesis

Acta Pharmacologica Sinica volume 45, pages 790–802 (2024)Cite this article

Abstract

Osteoporosis results from overactivation of osteoclasts. There are currently few drug options for treatment of this disease. Since the successful development of allosteric inhibitors, phosphatases have become attractive therapeutic targets. Protein phosphatase 1, regulatory subunit 15 A (PPP1R15A), is a stress-responsive protein, which promotes the UPR (unfolded protein response) and restores protein homeostasis. In this study we investigated the role of PPP1R15A in osteoporosis and osteoclastogenesis. Ovariectomy (OVX)-induced osteoporosis mouse model was established, osteoporosis was evaluated in the left femurs using micro-CT. RANKL-stimulated osteoclastogenesis was used as in vitro models. We showed that PPP1R15A expression was markedly increased in BMMs derived from OVX mice and during RANKL-induced osteoclastogenesis in vitro. Knockdown of PPP1R15A or application of Sephin1 (a PPP1R15A allosteric inhibitor in a phase II clinical trial) significantly inhibited osteoclastogenesis in vitro. Sephin1 (0.78, 3.125 and 12.5 μM) dose-dependently mitigated the changes in NF-κB, MAPK, and c-FOS and the subsequent nuclear factor of activated T cells 1 (NFATc1) translocation in RANKL-stimulated BMMs. Both Sephin1 and PPP1R15A knockdown increased the phosphorylated form of eukaryotic initiation factor 2α (eIF2α); knockdown of eIF2α reduced the inhibitory effects of Sephin1 on NFATc1-luc transcription and osteoclast formation. Furthermore, Sephin1 or PPP1R15A knockdown suppressed osteoclastogenesis in CD14+ monocytes from osteoporosis patients. In OVX mice, injection of Sephin1 (4, 8 mg/kg, i.p.) every two days for 6 weeks significantly inhibited bone loss, and restored bone destruction and decreased TRAP-positive cells. This study has identified PPP1R15A as a novel target for osteoclast differentiation, and genetic inhibition or allosteric inhibitors of PPP1R15A, such as Sephin1, can be used to treat osteoporosis.

This study revealed that PPP1R15A expression was increased in osteoporosis in both human and mice. Inhibition of PPP1R15A by specific knockdown or an allosteric inhibitor Sephin1 mitigated murine osteoclast formation in vitro and attenuated ovariectomy-induced osteoporosis in vivo. PPP1R15A inhibition also suppressed pathogenic osteoclastogenesis in CD14+ monocytes from osteoporosis patients. These results identify PPP1R15A as a novel regulator of osteoclastogenesis and a valuable therapeutic target for osteoporosis.

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Fig. 1: PPP1R15A is increased in osteoclastogenesis, and inhibition of PPP1R15A suppresses RANKL-induced osteoclast formation in mice.
Fig. 2: Allosteric inhibition of PPP1R15A reduces RANKL-induced F-actin ring formation and osteoclastic bone resorption.
Fig. 3: Allosteric inhibition of PPP1R15A blocks NF-κB and MAPK signaling pathways induced by RANKL.
Fig. 4: Allosteric inhibition of PPP1R15A suppresses NFATc1 activity induced by RANKL.
Fig. 5: The suppressive effect of PPP1R15A inhibitors on osteoclastogenesis is reduced after eIF2α interference.
Fig. 6: A PPP1R15A allosteric inhibitor alleviates ovariectomy-induced osteoporosis in vivo.
Fig. 7: Targeted inhibition of PPP1R15A represses osteoclast differentiation and bone resorption in monocytes from osteoporosis patients.

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Acknowledgements

This work was supported by the National Natural Science Foundation of China (82173825, 81773740, and 81972064) and the Science and Technology Plan Project of Guangzhou City (201804010027).

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  1. These authors contributed equally: Zong-bao Ding, Yan Chen, Yu-rong Zheng

Authors and Affiliations

  1. Laboratory of Anti-inflammatory and Immunomodulatory Pharmacology, Innovation Program of Drug Research on Inflammatory and Immune Diseases, NMPA Key Laboratory for Research and Evaluation of Drug Metabolism & Guangdong Provincial Key Laboratory of New Drug Screening, School of Pharmaceutical Sciences, Southern Medical University, Guangzhou, 510515, China

    Zong-bao Ding, Yan Chen, Yi-yuan Wang, Wen-de Deng, Jie-huang Zheng, Qin Yang, Zi-ye Chen, Li-hong Li & Xiao-juan Li

  2. Department of Bioengineering, Zhuhai Campus of Zunyi Medical University, Zhuhai, 519041, China

    Zong-bao Ding

  3. Division of Spine Surgery, Department of Orthopedics, Nanfang Hospital, Southern Medical University, Guangzhou, 510515, China

    Yu-rong Zheng & Hui Jiang

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Contributions

This study was designed by ZBD, YC, XJL, and conducted by ZBD, YC, YRZ, YYW, QY, JHZ, WDD, ZYC, and LHL. The manuscript was written by ZBD and YC, and revised by HJ and XJL.

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Correspondence to Hui Jiang or Xiao-juan Li.

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Ding, Zb., Chen, Y., Zheng, Yr. et al. Inhibition of PPP1R15A alleviates osteoporosis via suppressing RANKL-induced osteoclastogenesis. Acta Pharmacol Sin 45, 790–802 (2024). https://doi.org/10.1038/s41401-023-01209-0

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