Estrogen receptor mediates simvastatin-stimulated osteogenic effects in bone marrow mesenchymal stem cells

Simvastatin, an HMG-CoA reductase inhibitor, is known to promote osteogenic differentiation. However, the mechanism underlying simvastatin-induced osteogenesis is not well understood. In this study, we hypothesize that the estrogen receptor (ER) mediates simvastatin-induced osteogenic differentiation. ER antagonists and siRNA were used to determine the involvement of the ER in simvastatin-induced osteogenesis in mouse bone marrow mesenchymal stem cells (D1 cells). Osteogenesis was evaluated by mRNA expression, protein level/activity of osteogenic markers, and mineralization. The estrogen response element (ERE) promoter activity and the ER-simvastatin binding affinity were examined. Our results showed that the simvastatin-induced osteogenic effects were decreased by treatment with ERα antagonists and ERα siRNA but not by an antagonist specific for the G protein-coupled estrogen receptor (GPER-1). The simvastatin-induced osteogenic effects were further increased by E2 treatment and were reversed by ERα antagonists or siRNA treatment. Luciferase reporter gene assays demonstrated that simvastatin increase ERα-dependent transcriptional activity that was suppressed by ERα antagonists. Furthermore, the ERα-simvastatin binding assay showed that IC50 value of simvastatin is 7.85 μM and that of E2 is 32.8 nM, indicating that simvastatin is a weak ligand for ERα. These results suggest that simvastatin-stimulated osteogenesis is mediated by ERα but not GPER-1. Moreover, this is the first report to demonstrate that simvastatin acts as an ERα ligand and a co-activator to enhance ERα-dependent transcriptional activity and thus promotes osteogenesis. These results indicate that simvastatin-induced osteogenesis is mediated via an ERα-dependent pathway.