Establishment and characterization of macrophage-like cell lines expressing osteoclast-specific markers.

Osteoclasts differentiate from hematopoietic precursors of the monocyte/macrophage lineage to mononuclear preosteoclasts and multinuclear mature osteoclasts. In the present study, we report on the establishment of macrophage like cell lines from mouse bone marrow by coculturing bone marrow cells with mouse chondrocytes. Isolated clones (MLC-6 and MLC-7 cells) expressed fully differentiated osteoclast markers, such as calcitonin receptors, vitronectin receptors, tartrate-resistant acid phosphatase and vacuolar H+ -ATPase, in the absence of osteoclast differentiation factor/osteoprotegerin ligand/RANKL/TRANCE, which was essential for osteoclast differentiation. Most clones also maintained expression of a macrophage-associated protein, namely non-specific esterase. Both MLC-6 and MLC-7 cells released cathepsin K into the culture medium. Both clones resolved dentine slices when cocultured with the osteoblast cell line ST2. The cloned cell lines are considered to be useful tools in the study of osteoclast differentiation.