Abstract
OBJECTIVE: To explore the mechanism by which simvastatin (SIM) regulates osteoclast apoptosis. METHODS: Murine macrophage RAW264.7 cells were divided into 5 groups, namely group A (control group), group B (sRANKL+ M-CSF), group C (SIM+sRANKL+M-CSF), group D (VIVIT peptide+sRANKL+ M-CSF), and group E (SIM+VIVIT peptide+sRANKL+M-CSF). WST-1 assay was used to assess the effects of simvastatin on the proliferation activity of the osteoclasts, and flow cytometry was performed to analyze the effects of SIM and VIVIVIT peptide (a NFATc1 pathway inhibitor) on apoptosis of the osteoclasts. The translocation of NFATc1 into the nucleus was investigated using immunofluorescence assay, and Western blotting was employed to assess the effect of SIM on the phosphorylation of NFATc1 in the nucleus. RESULTS: WST-1 assay showed that SIM (1×10(-6) mol/L) treatment for 24 and 48 h significantly inhibited the proliferation of the osteoclasts (P=0.039 and 0.022, respectively). Compared with the control group, the SIM-treated osteoclasts exhibited significantly reduced cell percentage in G0/G1 phase (P=0.041) and increased cells in sub-G1 phase (P=0.028) with obvious cell apoptosis. DAPI staining and flow cytometry showed that both SIM and VIVIVIT peptide alone significantly promoted osteoclast apoptosis (P=0.002 and 0.015, respectively), and their combination produced a similar pro-apoptosis effect (P=0.08). Immunofluorescence and Western blotting showed that SIM significantly inhibited the intranuclear translocation of NFATc1 and the phosphorylation of NFATc1 pathway protein (P=0.013). CONCLUSIONS: SIM promotes osteoclast apoptosis through NFATc1 signaling pathway.