Skimmianine Attenuates Osteoclast Activity by Suppressing ERp57-Driven Calcium Oscillations/Calcineurin/Nfatc1 Signalling in Postmenopausal Osteoporosis.

Postmenopausal osteoporosis is primarily attributed to the hyperactivation of osteoclast-induced bone resorption. The differentiation and function of osteoclasts rely on the regulation of calcium oscillations/calcineurin/nuclear factor of activated T cells (Nfat) pathway. Therefore, the development of natural compounds that aim at the crucial regulator of the aforementioned pathway is essential for the suppression of osteoclastogenesis and its clinical application. Skimmianine (Ski), a furoquinoline alkaloid extracted from the Zanthoxylum genus, is known for its anti-inflammatory properties. Yet, its exact role in osteoclast differentiation and function remains largely undefined. Herein, we evaluate the impact of Ski on osteoclastogenesis and elucidate the molecular mechanism involved. We conducted network pharmacology and molecule structure-based pharmacokinetics analyses on Ski, followed by experimental validations on osteoclastogenesis in vitro and ovariectomy (OVX) mice model in vivo. The network pharmacology results indicated Ski's therapeutic effects predominantly influence the calcium signalling pathway by controlling cytosolic calcium concentration in response to bone resorption during osteoporosis. Pharmacokinetic analyses revealed Ski's excellent oral bioavailability. Furthermore, experimental validations revealed that Ski inhibited the formation of multinucleated osteoclasts in a concentration-dependent manner without affecting cell viability, while impeding osteoclast-related gene expression. The underlying mechanism involved the Ski-induced downregulation of calcineurin/Nfatc1 expression through modulation of ERp57-driven calcium oscillations. Micro-CT results confirmed that Ski treatment substantially curbed the progression of osteoporosis by mitigating bone loss. In conclusion, our findings indicated that Ski suppressed osteoclast formation by suppressing ERp57-driven calcium oscillations/calcineurin/Nfatc1 signalling, thus establishing Ski as a promising therapeutic alternative for osteoporosis.