FUNCTIONS OF THE M-CSF RECEPTOR ON OSTEOCLASTS

Macrophage colony-stimulating factor (M-CSF) receptor has been previou sly reported to be present in osteoclasts both at mRNA and protein lev els, However, the biochemical interactions between M-CSF and its recep tor on osteoclasts are less well characterized than in mononuclear pha gocytes. In this study, we show that (1) I-125-labeled M-CSF ligand sp ecifically binds to the M-CSF receptor on osteoclasts by autoradiograp hy; (2) binding of M-CSF to the receptor stimulates protein tyrosine p hosphorylation in osteoclasts by immunostaining; (3) oxygen-derived fr ee radicals produced by calvarial osteoclasts are increased by M-CSF s timulation (1.37 +/- 0.08, n = 10, p < 0.01); and (4) bone resorption in calvarial explants is enhanced by M-CSF (1.153 +/- 0.09, n = 10, p < 0.001), Thus, our data provide multiple lines of evidences that mous e calvarial osteoclasts are activated by M-CSF, These data suggest tha t under the conditions present in the calvarial model, M-CSF activates osteoclastic bone resorption.