Guizhi Shaoyao Zhimu granules attenuate bone destruction in mice with collagen-induced arthritis by promoting mitophagy of osteoclast precursors to inhibit osteoclastogenesis

Guizhi Shaoyao Zhimu decoction, a traditional Chinese medicine formula used empirically for the treatment of rheumatoid arthritis (RA), has been shown to alleviate bone destruction in rats with collagen-induced arthritis (CIA).The aim of this study is to characterize the effects of Guizhi Shaoyao Zhimu granules (GSZGs) on bone destruction in RA and the underlying mechanism.A CIA arthritis model using DBA/1 mice. The animals were divided into a normal group; CIA model group; low, medium, and high-dose GSZG groups (3, 6, and 9 g/kg/day); and a methotrexate group (1.14 mg/kg/w). In vitro, a cytokine induced osteoclastogenesis model was established.After 28 days of treatment, the paw volume was measured, bone destruction was examined by micro-CT, and the generation of osteoclasts in bone tissue was evaluated via tartrate-resistant acid phosphatase (TRAP) staining. Furthermore, the inhibitory effect and underlying mechanism of action of GSZG on RANKL-induced osteoclastogenesis were investigated in vitro.The in vivo analyses demonstrated that the paw volume and degree of bone erosion of mice in the medium- and high-dose GSZG groups were significantly decreased compared to the CIA model group. In addition, GSZG treatment suppressed the excessive generation of osteoclasts in the bone tissue of CIA mice. In vitro, GSZG inhibited RANKL-induced osteoclastogenesis and osteoclast-mediated bone resorption. Specifically, it only inhibited the generation of osteoclast precursors (OCPs); it had no significant effect on the fusion of OCPs or maturation of osteoclasts. Finally, we showed that the inhibitory effect of GSZG on osteoclastogenesis was related to the promotion of PTEN-induced kinase protein 1 (PINK1)/Parkin pathway-mediated mitophagy of osteoclast precursors, which was verified using a PINK1 knockdown small interfering RNA in OCPs.These findings indicate that GSZG is a candidate for the treatment of bone destruction in RA and provide a more detailed elucidation of the mechanism of GSZG anti-RA bone erosion, i.e., inhibition of the ROS/NF-κB axis through the PINK1/Parkin-mediated mitochondrial autophagic pathway to inhibit osteoclast precursor production, compared to the published literature.