High-dose PMA with RANKL and MCSF induces THP‑1 cell differentiation into human functional osteoclasts in vitro.

Osteoclasts are large multinuclear cells, which serve role in erosive bone disease. However, it is not possible to separate osteoclasts from cortical bone in order to culture the cells for further experiments. Therefore, a human osteoclast model is required to investigate the underlying mechanism of bone destruction. The most commonly‑used osteoclast model is the RAW264.7 cell line, a murine mononuclear macrophage cell line; however, there exists no reliable osteoclast model using a human cell line. The aim of the present study was to establish a functional osteoclast model using the THP‑1 cell line. Suspended THP‑1 cells were stimulated for 2 days with 5 or 100 ng/ml phorbol‑12 myristate‑13 acetate (PMA) in order to induce the cells to differentiate into adherent macrophages. A 10‑day stimulation with 50 ng/ml receptor activator of nuclear factor κ‑B ligand (RANKL) and macrophage colony‑stimulating factor (MCSF) was performed in order to induce macrophage differentiation into osteoclasts. Treatment with high‑dose PMA with RANKL and MCSF enabled the THP‑1 cells to form tartrate‑resistant acid phosphatase‑positive osteoclasts, which were able absorb bone in a bone resorption test. Treatment with low‑dose PMA with RANKL and MCSF failed to induce THP‑1 cell differentiation into osteoclasts. PMA alone, or a combination of RANKL and MCSF alone, is insufficient to stimulate THP‑1 cell differentiation into osteoclasts. In the present study, a reliable human osteoclast model was established using the THP‑1 cell line. This osteoclast model may provide a useful tool for further studies.