DEVELOPMENT OF OSTEOCLASTS FROM EMBRYONIC STEM-CELLS THROUGH A PATHWAY THAT IS C-FMS BUT NOT C-KIT DEPENDENT

Osteoclasts are hematopoietic cells essential for bone resorption, To study the derivation of these interesting cells, we developed a stepwi se culture system where stromal cells promote embryonic stem (ES) cell s to differentiate into mature osteoclasts. Three phases to this diffe rentiation process include (1) induction of hematopoiesis, along with the generation of osteoclast precursors, (2) expansion of these precur sors, and (3) terminal differentiation into mature osteoclasts in the presence of 1 alpha, 25-dihydroxyvitamine D-3. Although the transition of ES cells to the hematopoietic lineage was not blocked by an antibo dy to c-fms, later phases were dependent on a signaling through this t ransmembrane receptor as indicated by the finding that anti-c-fms-trea tment of cells in the second and third phases reduced the number of os teoclasts produced by 75% and more than 99%, respectively, Blockade of signaling through another tyrosine kinase-type receptor, c-kit did no t affect any stages of osteoclastogenesis, although generation of othe r hemopoietic lineages was reduced to less than 10% of untreated. When small numbers of ES cells were directly cultured under conditions tha t promote osteoclast differentiation, tartrate-resistant acid phosphat ase-positive multinucleated cells were observed at the edge but not in side of colonies, This suggests that some types of cell-cell interacti ons may inhibit development of mature osteoclasts. The culture system developed here provides an important tool for osteoclast biology, (C) 1997 by The American Society of Hematology.