ERβ induces the differentiation of cultured osteoblasts by both Wnt/β-catenin signaling pathway and estrogen signaling pathways

Although 17 beta-estradial (E2) is known to stimulate bone formation, the underlying mechanisms are not fully understood. Recent studies have implicated the Wnt/beta-catenin pathway as a major signaling cascade in bone biology. The interactions between Wnt/beta-catenin signaling pathway and estrogen signaling pathways have been reported in many tissues. In this study, E2 significantly increased the expression of beta-catenin by inducing phosphorylations of GsK3 beta at serine 9. ER beta siRNAs were transfected into MC3T3-81 cells and revealed that ER beta involved E2-induced osteoblasts proliferation and differentiation via Wnt/beta-catenin signaling. The osteoblast differentiation genes (BGP, ALP and OPN) and proliferation related gene (cyclin D1) expression were significantly induced by E2-mediated ER beta. Furthermore immunofluorescence and immunoprecipitation analysis demonstrated that E2 induced the accumulation of beta-catenin protein in the nucleus which leads to interaction with T-cell-specific transcription factor/lymphoid enhancer binding factor (TCF/LEF) transcription factors. Taken together, these findings suggest that E2 promotes osteoblastic proliferation and differentiation by inducing proliferation-related and differentiation-related gene expression via ER beta/GSK-3 beta-dependent Wnt/beta-catenin signaling pathway. Our findings provide novel insights into the mechanisms of action of E2 in osteoblastogenesis. (C) 2015 Elsevier Inc. All rights reserved.