Macrophage colony-stimulating factor suppresses osteoblast formation

We provide the first evidence that the bone marrow-derived cytokine, macrop hage colony-stimulating factor (M-CSF), inhibits the formation of bone-form ing osteoblasts, We examined both osteoclast and osteoblast formation in pr imary rat bone marrow cultures. As expected, M-CSF together with osteoprote gerin ligand (OPGL) markedly accelerated osteoclastogenesis, In contrast, t reatment with M-CSF alone yielded no osteoclasts at any time. The most stri king and novel observation was that M-CSF with or without OPGL dramatically suppressed osteoblast formation. In separate experiments, estradiol marked ly suppressed osteoclast formation in the M-CSF/OPGL-treated cultures indep endently of osteoblasts, Consistent with this was the expression of estroge n receptor-alpha (ER alpha) and ERP mRNA in osteoclast precursors. We there fore conclude that in addition to the well-known action of M-CSF to modulat e osteoclastogenesis, this cytokine may also regulate osteoblast formation. (C) 2001 Academic Press.