osteoclast precursors and through stromal cells Regulation of osteoclast development by Notch signaling directed to

Abstract Osteoclasts are derived from hematopoietic precursor cells belonging to the monocyte/macrophage lineage. Orthoclase development has been reported to be regulated by several molecules such as macrophage colony-stimulating factor (M-CSF), receptor activator of NF-B ligand (RANKL), and a decoy receptor of RANKL, osteoprotegerin (OPG). Recently it was demonstrated that the Notch signaling regulates myeloid differentiation and antagonizes cell fate determination, however, the effect of Notch signaling on the osteoclast lineage has not been reported yet. In this study, we examined the effect of signaling via Notch receptors on the differentiation into osteoclasts by using cells from the bone marrow, spleen, and peritoneal cavity, and a cloned macrophage-like cell line. The osteoclastogenesis was inhibited by an immobilized Notch ligand, Delta-1.The osteoclastogenesis of dish-adherent bone marrow cells, which were pre-cultured with M-CSF and expressed both Mac-1 and M-CSF receptor, c-Fms was efficiently inhibited.The immobilized Delta-1 also down-regulated the surface c-Fms expression, while the c-Fms gene expression was not changed. Genes for Notch receptors and Notch ligands are expressed in not only hematopoietic cells but also stromal cells which support osteoclast development. Constitutively active Notch1-transfected stromal cells showed increased expression of RANKL and OPG genes, and strong inhibition of M-CSF gene expression, resulting in reduction of their ability to support osteoclast development. Taken together, these findings indicate that Notch signaling affects both osteoclast precursors and stromal cells and thereby negatively regulates osteoclastogenesis. (231 words) From bloodjournal.hematologylibrary.org by guest on June 12, 2013. For personal use only.