Knockdown of Abr suppresses osteoclast formation, the resorption area, and osteoclast-marker gene expression. A Knockdown efficiency of Abr was evaluated by measuring the mRNA levels. Cells were transfected with control or Abr-specific siRNA (720 ng/μL) in the presence of RANKL (100 ng/mL) for 1–3 days. *P < 0.05; **P < 0.01; compared with the control cells. B TRAP staining of control and Abr-knockdown osteoclasts. Control and Abr-depleted RAW-D cells were stimulated with RANKL (100 ng/mL) for 3 days. The cells were fixed and stained for TRAP. Scale bar, 50 μm. C. The number of TRAP-positive multinucleated cells (MNCs) in control and Abr-knockdown cells was counted on the indicated day. **P < 0.01, compared with control cells. D Bone resorption area of control and Abr-knockdown osteoclasts. RAW-D cells were seeded onto Osteo Assay Stripwell Plates with RANKL (500 ng/mL) for 10 days. Photographs of the bone resorption area of each osteoclast are shown. Scale bar, 50 μm. E The resorption area was determined using Image J software. The data are represented as mean ± SD of values from three independent experiments. *P < 0.05, compared with control cells. F Control and Abr-knockdown RAW-D cells were cultured with RANKL (100 ng/mL) for 1–3 days. After the isolation of mRNA, RT-PCR was performed. *P < 0.05, compared with control cells. G Western blot analysis of Abr-knockdown RAW-D cells that were cultured with RANKL (100 ng/mL) for 1–3 days. The cultured cells were harvested on the indicated day and lysates were subjected to western blot analysis with specific antibodies, such as NFATc1, Src, Cathepsin K, Vinclin, LIMK, RhoA and GAPDH (control)