Crosslinking of CD44 on human osteoblastic cells upregulates ICAM-1 and VCAM-1.

Cell adhesion of osteoblasts and osteoclastic precursors of hematopoietic origin is a prerequisite for osteoclast maturation. We have investigated the relevance of osteoblast-matrix binding and regulation of adhesion molecules to this process. Human osteoblastic cells highly expressed CD44, a major receptor for hyaluronan present in the surrounding bone matrix. Crosslinking of CD44 on osteoblastic cells with specific antibodies augmented the expression of intercellular adhesion molecule (ICAM)-1 and vascular cell adhesion molecule (VCAM)-1. Hyaluronan, the major ligand of CD44, also up-regulated ICAM-1 expression. Stimulation of CD44 on osteoblastic cells amplified their adhesion to monocytic cells through ICAM-1 and VCAM-1. These results suggest that such crosstalk among distinct adhesion molecules may be relevant to bone metabolism, including osteoclastogenesis.