MFG‐E8 Regulates Vascular Smooth Muscle Cell Migration Through Dose‐Dependent Mediation of Actin Polymerization

Abstract

Background Migration of vascular smooth muscle cells (VSMCs) is the main contributor to neointimal formation. The Arp2/3 (actin‐related proteins 2 and 3) complex activates actin polymerization and is involved in lamellipodia formation during VSMC migration. Milk fat globule‐epidermal growth factor 8 (MFG‐E8) is a glycoprotein expressed in VSMCs. We hypothesized that MFG‐E8 regulates VSMC migration through modulation of Arp2/3‐mediated actin polymerization. Methods and Results To determine whether MFG‐E8 is essential for VSMC migration, a model of neointimal hyperplasia was induced in the common carotid artery of wild‐type and MFG‐E8 knockout mice, and the extent of neointimal formation was evaluated. Genetic deletion of MFG‐E8 in mice attenuated injury‐induced neointimal hyperplasia. Cultured VSMCs deficient in MFG‐E8 exhibited decreased cell migration. Immunofluorescence and immunoblotting revealed decreased Arp2 but not Arp3 expression in the common carotid arteries and VSMCs deficient in MFG‐E8. Exogenous administration of recombinant MFG‐E8 biphasically and dose‐dependently regulated the cultured VSMCs. At a low concentration, MFG‐E8 upregulated Arp2 expression. By contrast, MFG‐E8 at a high concentration reduced the Arp2 level and significantly attenuated actin assembly. Arp2 upregulation mediated by low‐dose MFG‐E8 was abolished by treating cultured VSMCs with β1 integrin function‐blocking antibody and Rac1 inhibitors. Moreover, treatment of the artery with a high dose of recombinant MFG‐E8 diminished injury‐induced neointimal hyperplasia and reduced VSMC migration. Conclusions MFG‐E8 plays a critical role in VSMC migration through dose‐dependent regulation of Arp2‐mediated actin polymerization. These findings suggest that high doses of MFG‐E8 may have therapeutic potential for treating vascular occlusive diseases.