Cell-to-Cell Adhesion via Intercellular Adhesion Molecule-1 and Leukocyte Function-Associated Antigen-1 Pathway Is Involved in 1 alpha ,25(OH) sub(2)D sub(3), PTH and IL-1 alpha -Induced Osteoclast Differentiation and Bone Resorption

Cell-to-cell interaction is required for the differentiation of osteoclast precursors as well as for osteoclast function. The present study was undertaken to determine whether 1,25 dihydroxyvitamin D sub(3) (1,25D), PTH, IL-1 alpha and PGE sub(2) depend on cell-to-cell interactions through the intercellular adhesion molecule (ICAM)-1/leukocyte function-associated antigen (LFA)-1 pathway in osteoclast formation and bone resorption. We found that mouse osteoblasts expressed ICAM-1 and that the expression was increased by treatment with PTH, IL-1 alpha or 1,25D, but not by PGE sub(2). In resorption assays measuring either super(45)Ca release from bone organ cultures or pit formation in bone cell cultures, 1,25D-, PTH- and IL-1 alpha -stimulated resorption was inhibited by anti-ICAM-1 monoclonal antibody (mAb) and/or anti-LFA-1 mAb, while basal and PGE sub(2)-stimulated bone resorbing activities were not affected by these mAbs. Furthermore, in a mouse bone marrow culture system, stimulation of osteoclast-like (OCL) cell formation by 1,25D (10 nM), PTH (10 ng/ml) or IL-1 alpha (10 ng/ml) was inhibited by the addition of anti-ICAM-1 mAb and/or anti-LFA-1 mAb. In a coculture system of murine spleen cells and osteoblasts, the ICAM-1/LFA-1 interaction was also involved in 1,25D-, PTH- and IL-1 alpha -stimulated TRAP-positive MNC formation. However, anti-ICAM-1 mAb and anti-LFA-1 mAb did not alter either 1,25D- or PTH-stimulated receptor activator of NF- Kappa B ligand (RANKL) mRNA transcription in bone marrow cultures. Taken together, we here propose that ICAM-1-mediated cell-to-cell adhesion of osteoblasts and osteoclast precursors is involved in RANKL-dependent osteoclast maturation stimulated by 1,25D, PTH, and IL-1 alpha .