Bruceine D suppressed osteoclast formation via STAT3/NF-κB/NFATc1 signaling and protected postmenopausal osteoporosis.

Postmenopausal osteoporosis is characterized by excessive osteoclast-mediated bone resorption driven by estrogen deficiency. Bruceine D (BD) has been demonstrated anti-inflammatory activity through modulation of STAT3 and NF-κB signaling. This study aimed to investigate the effects of BD on osteoclastogenesis and its therapeutic potential in osteoporosis. In vitro, BMMs were stimulated with RANKL in the presence or absence of BD. Osteoclast formation was assessed by TRAP staining, while gene and protein expression were analyzed using qRT-PCR and western blotting. Cytoskeletal organization and bone resorption activity were evaluated. In vivo, an ovariectomy (OVX)-induced osteoporosis model was established to assess the protective effects of BD. Our results demonstrated that BD significantly inhibited RANKL-induced osteoclast differentiation in a dose-dependent manner without cytotoxic effects at effective concentrations. BD suppressed the formation of multinucleated osteoclasts, reduced expression of osteoclast-specific genes, and impaired podosome formation and bone resorption activity. Mechanistically, BD attenuated the activation of STAT3 and NF-κB signaling pathways without affecting MAPKs and AKT signaling, leading to downregulation of key transcription factor NFATc1. In vivo, BD treatment markedly alleviated trabecular bone loss in OVX mice, as indicated by improved bone microarchitecture parameters. In conclusion, BD suppresses osteoclastogenesis and protects against estrogen deficiency-induced bone loss by inhibiting the STAT3/NF-κB/NFATc1 signaling axis.