IN-VITRO STRUCTURAL AND FUNCTIONAL-RELATIONSHIPS BETWEEN PREOSTEOCLASTIC AND BONE ENDOTHELIAL-CELLS - A JUXTACRINE MODEL FOR MIGRATION AND ADHESION OF OSTEOCLAST PRECURSORS

The role of vascularization in the process of bone resorption has not been clarified. The interactions between vascular endothelium and oste oclast progenitors were analyzed using clonal cell lines of bone-deriv ed endothelial and preosteoclastic cells. Insulin-like growth factor I is a major chemotactic stimulator of preosteoclastic cell migration m ediated by bone endothelial cells. Osteoclast precursors rapidly adher ed to bone endothelial monolayers. This phenomenon appeared to be cell -specific and mediated through the binding of vitronectin and fibronec tin receptors to fibronectin. In addition, direct contact with bone en dothelial cells induced osteoclast progenitors to differentiate into m ore mature elements, with the tendency to cluster together to form lar ge multinucleated cells. These findings demonstrated specific in vitro interactions between bone endothelial cells and osteoclast progenitor s, offering a new model for understanding the molecular mechanisms whi ch direct the processes of osteoclast recruitment and ontogeny. (C) 19 95 Wiley-Liss, Inc.