Presence of osteoclast precursors in colonies cloned in the presence of hematopoietic colony-stimulating factors

Objective. Osteoclasts are derived from hematopoietic stem cells, but the r elationship between osteoclast precursors (OCPs) and hematopoietic colony-f orming cells (CFCs) has not yet been clarified, Although osteoclasts share certain cell surface markers and growth factor requirements with their macr ophage and monocyte cell lineages, osteoclasts are a different lineage with regard to the requirement for signaling via c-Kit, To investigate whether CFCs are able to differentiate into osteoclasts, we performed in vitro stud ies of osteoclastogenesis, Materials and Methods, We performed progenitor assays in the presence of he matopoietic colon-stimulating factors, Primary colonies were plucked and ex amined for their potential to differentiate into osteoclasts, Results. We found that osteoclasts are present in colonies elicited by macr ophage colony-stimulating factor (M-CSF) and receptor activator of nuclear factor kB ligand (RANKL) in semisolid cultures. Moreover, a part of the cel ls composing the colonies elicited by granulocyte-macrophage colony-stimula ting factor (GM-CSF) or M-CSF alone possessed the potential to differentiat e into osteoclasts. These OCPs in the colonies were enriched in the c-Fms() large-sized cell fraction and had a foamy cell morphology. like mature ma crophages. A small number of cells in M-CSF-promoted and GM-CSF-promoted co lonies formed secondary colonies in the semisolid medium containing these f actors, The frequency of OCPs in these secondary colonies elicited by M-CSF was 10 times higher than that elicited by GM-CSF. Conclusion. Multiple origins of OCPs that differentiate into mature osteocl asts are proposed based on the observation that osteoclasts could be genera ted from OCPs that emerged from CFCs induced under different conditions or developmental stages, (C) 2001 international Society for Experimental Hemat ology. Published by Elsevier Science Inc.