Corylin ameliorates diabetic osteoporosis by inhibiting inflammation via targeting RAG1

Diabetic osteoporosis (DOP), a severe complication of diabetes mellitus, arises primarily from hyperglycemia-induced chronic inflammation and remains challenging to treat. Corylin, a flavonoid isolated from Psoralea corylifolia l., has been reported to possess anti-inflammatory properties; however, its therapeutic potential for DOP remains unknown.

This study aimed to determine the therapeutic potential of corylin on DOP and to elucidate its underlying mechanisms preliminarily.

The effects of corylin on lipopolysaccharide-induced inflammatory responses in macrophages, as well as its impacts on the anti-osteoblastic and pro-osteoclastic abilities of activated macrophages, were assessed by quantitative real-time PCR analysis and cytochemical staining. In vivo, the effects of corylin in a streptozotocin-induced DOP mouse model were evaluated using microcomputed tomography, biomechanical testing, immunohistochemistry, and immunofluorescence. Molecular docking analysis was employed to identify potential targets of corylin. Surface plasmon resonance experiments were performed to validate the docking-predicted corylin-target interactions and to quantify binding affinity and kinetics. Subsequently, the roles of the potential target in the regulatory effects of corylin on osteogenesis, osteoclastogenesis, and inflammation were evaluated by using small interfering RNA in bone marrow mesenchymal stem cells, bone marrow macrophages, and RAW264.7 cells, as well as by using recombinant adeno-associated virus in mice.

In vitro, corylin not only enhanced osteoblast differentiation and suppressed osteoclast formation, but also reduced the secretion of pro-inflammatory cytokines in lipopolysaccharide-activated macrophages, thereby impairing their anti-osteoblastic and pro-osteoclastic activities. Consistently, in vivo studies demonstrated that intragastric administration of corylin significantly improved bone mass and microarchitecture in streptozotocin-induced DOP mice by promoting bone formation, inhibiting bone resorption, and alleviating local and systemic inflammation. Mechanistically, these beneficial effects depended on recombination-activating gene 1 (RAG1), as RAG1 knockdown abolished corylin's effects on bone metabolism and inflammation, both in vitro and in vivo.

This study provides the first evidence of corylin's efficacy in a diabetic osteoporosis model and identifies RAG1 as its direct binding target, highlighting a previously unrecognized role of RAG1 in regulating bone metabolism and inflammation.