Osteopontin function in pathology: Lessons from osteopontin-deficient mice

Osteopontin (OPN) is a soluble secreted phosphoprotein that binds with high affinity to several different integrins. While numerous activities have be en ascribed to OPN in vitro, and several in vivo functions have been sugges ted for the molecule, including much attention focused recently on OPN in d ifferent pathologies, the actual role that the protein plays in mammalian p hysiology remains conjectural. Analysis of recently developed strains of mi ce lacking OPN because of a targeted disruption of its gene promises to pro vide important information on this issue. Here, we review the data implicat ing OPN as functioning in a variety of pathologic conditions as well as the initial results generated with the OPN knockout mice, with particular focu s on the question of whether OPN has a protective or a damaging effect in d ifferent pathologies. These data will be important to the definition of how OPN contributes to mammalian physiology and pathophysiology.