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Osteopontin and β3 Integrin Are Coordinately Expressed in Regenerating Endothelium In Vivo and Stimulate Arg-Gly-Asp–Dependent Endothelial Migration In Vitro

Osteopontin is an Arg-Gly-Asp (RGD)–containing acidic glycoprotein postulated to mediate cellular adhesion and migration in a growing number of normal and pathological conditions through interaction with integrin molecules. In this report, we have investigated the potential contributions of osteopontin and one of its receptors, the αvβ3 integrin, to endothelial regenerative processes by using both in vivo and in vitro models. In vivo, uninjured rat arterial endothelium had undetectable levels of osteopontin and β3-integrin mRNA by in situ hybridization. After balloon catheter denudation, osteopontin mRNA levels correlated temporally and spatially with active endothelial proliferation and migration, with the highest levels observed at the wound edge between 8 hours and 2 weeks after injury, declining to uninjured levels at 6 weeks, when regeneration was complete. Osteopontin protein levels, as determined by immunocytochemistry, paralleled the time course of mRNA expression. Likewise, β3-integrin mRNA and protein levels were substantially elevated in regenerating endothelial cells but were not detectable in uninjured or healed endothelium. In vitro, rat smooth muscle cell–derived and bacterial expressed mouse recombinant osteopontins both stimulated the adhesion and directed migration of bovine aortic endothelial cells through interactions with the αvβ3 receptor. Structural mutants of osteopontin confirmed the importance of the RGD domain for both adhesion and migration of endothelial cells through αvβ3. These data suggest important roles for osteopontin and β3 integrin in regenerating endothelium.