Psoralen promotes the expression of cyclin D1 in chondrocytes via the Wnt/β-catenin signaling pathway

Psoralen (PSO), the active ingredient of Fructus Psoraleae (FP) the dried ripe fruit of Psoralea corylifolia L., has been commonly used in traditional Chinese medicine (TCM) for the treatment of osteoarthritis (OA). We found that PSO activates cartilaginous cellular functions of rat chondrocytes in vitro. However, the effect of PSO on chondrocyte proliferation and the precise mechanisms involved remain to be elucidated. We investigated the effects of PSO on chondrocytes isolated from Sprague-Dawley (SD) rats and evaluated involvement of the Wnt/β-catenin signaling pathway. The viability of chondrocytes treated with PSO was increased in a dose- and time-dependent manner, as assessed by MTT assay. We found that the gene expression and protein levels of Wnt-4, Frizzled-2, β-catenin and cyclin D1 in the PSO-treated chondrocytes were significantly upregulated, while the gene expression and protein level of glycogen synthase kinase-3β (GSK-3β) were downregulated, compared with the untreated chondrocytes. By immunofluorescence, we also found that PSO induced β-catenin nuclear translocation. Importantly, the expression of β-catenin and cyclin D1 was partly inhibited by Dickkopf-1 (DKK-1), an inhibitor of the Wnt/β-catenin signaling pathway. Additionally, Col-II expression in chondrocytes was increased after treatment with PSO. Taken together, these results indicate that PSO promotes chondrocyte proliferation by activating the Wnt/β-catenin signaling pathway, and it may play an important role in the treatment of OA.