Isobavachin alleviates hyperuricemia-induced bone loss by GPR35-NLRP3 signal

GPR35, a member of the G protein-coupled receptor (GPCR) family, promotes osteogenic differentiation and ameliorates inflammation when its expression is enhanced. However, its role in bone homeostasis under hyperuricemia (HUA) conditions remains unexplored, and effective clinical agents for managing osteoporosis comorbid with HUA are scarce. This study aimed to investigate the osteoprotective potential of the GPR35 agonist isobavachin (IBC) against HUA-induced bone loss, focusing on its mechanism involving NOD-like receptor thermal protein domain associated protein 3 (NLRP3) inflammasome modulation.

Bone tissue markers of bone homeostasis and inflammatory infiltration were evaluated in patients with hyperuricemia. To delineate the relationship of HUA, bone homeostasis, and GPR35, osteoblasts (OB) and osteoclasts (OC) were treated with high concentrations of soluble uric acid, in conjunction with label-free cellular assays. The mechanisms underlying the effects of the GPR35 agonist IBC were investigated using molecular docking, in vitro cell culture with IBC treatment, and siRNA-mediated gene silencing. Furthermore, hyperuricemic model mice were established in C57BL/6 J mice to corroborate the bone loss induced by HUA and evaluate the osteoprotective efficacy of IBC.

Analysis of bone tissue from HUA patients revealed increased activity of both OB and OC, along with inflammatory cell infiltration. Consistently, in vitro experiments demonstrated that exposure to high concentrations of soluble uric acid specifically and significantly impaired OB differentiation and mineralization. This inhibitory effect was closely associated with NLRP3 inflammasome activation. Furthermore, high concentrations of soluble uric acid treatment modulated GPR35 expression levels in cultured cells. Critically, the GPR35 agonist IBC activated GPR35 and promoted osteogenic effects. Mechanistically, GPR35 knockdown experiments confirmed that IBC exerted its bone-promoting actions primarily via the GPR35-NLRP3 signaling axis. Importantly, these findings were corroborated in a chronic hyperuricemia mouse model, where IBC treatment effectively attenuated HUA-induced bone loss compared to the standard antihyperuricemic agent allopurinol.

Our findings demonstrate that GPR35 activation protects OB from HUA-induced bone loss. The GPR35 agonist IBC enhances osteogenic differentiation by modulating the GPR35-NLRP3 signaling axis, effectively attenuating bone loss in HUA. These results identify IBC as a promising novel therapeutic candidate for managing HUA-associated osteoporosis.