Minimum essential medium alpha medium (α-MEM), RPMI 1640 medium, Dulbecco’s modified Eagle’s medium (DMEM)/F-12 phenol red-free medium (1:1), fetal bovine serum (FBS), antibiotic-antimycotic mixture (100×), phosphate-buffered saline (PBS), and 0.25% trypsin-EDTA (1×) were purchased from Gibco BRL Co. (Grand Island, NY). Dimethyl sulfoxide (DMSO), LPS, and 3-(4,5 dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) were obtained from Sigma-Aldrich (St Louis, MO). Recombinant mouse soluble RANK ligand (sRANKL) was purchased from Koma Biotech (Seoul, Republic of Korea). Recombinant mouse macrophage colony-stimulating factor (M-CSF) was purchased from R&D System (Minneapolis, MN). EETC was provided by COSMAX Inc. R&I Center (Seongnam City, Republic of Korea).