Macrophage colony-stimulating factor (M-CSF) induces migration in osteoclasts in vitro

It has recently been shown that M-CSF is essential for osteoclast formation and survival. Paradoxically, the cytokine inhibits bone resorption by isolated osteoclasts. This implies that it may stimulate some function in osteoclasts not directly related to the bone resorptive process itself. We now report that M-CSF stimulates migration in isolated rat osteoclasts. This was achieved predominantly by a 3-8-fold increase in the proportion of osteoclasts demonstrating migration, combined with an increase in the area of substrate covered (43-96%) by each migrating cell. This action of M-CSF on migration is the inverse of its effect on resorption, wherein it has been previously found to reduce the proportion of osteoclasts that resorb bone and suggests that migration and resorption might represent alternative states of osteoclast behaviour. The results also suggest that osteoblast-derived M-CSF might play a role in the induction and regulation of localisation of these cells in bone.