Integrins α_vβ₃ and α_vβ₅ mediate VSMC migration and are elevated during neointima formation in the rat aorta

Abstract

Neointima formation involves tissue expression of matrix proteins and growth factors. The role of α_vβ₃, but not α_vβ₅ integrin in vascular cells has been sufficiently investigated. The aim of the present study was to determine and compare the function of α_vβ₃ and α_vβ₅ integrins in rat aortic (RASMC) and human coronary vascular smooth muscle cells (HCSMC) and to characterize their expression accompanying neointima formation in vivo. RASMC and HCSMC express α_vβ₃ and α_vβ₅ integrin subunits. The α_vβ₅ integrin predominantly mediated adhesion of RASMCs to vitronectin and spreading on vitronectin via RGD-binding sequences. In contrast, the α_vβ₃ integrin did not contribute to the adhesion and spreading on fibronectin, vitronectin, gelatin or collagen I coated layers. PDGF-directed migration through gelatin coated membranes involved both α_vβ₃ and α_vβ₅ integrins. Selective blocking antibodies for α_vβ₃ and α_vβ₅ inhibited migration of RASMC and HCSMC by more than 60% (p < 0.01). Integrin expression was studied in vivo in thoracic aorta of Sprague Dawley rats before and after balloon injury. In situ hybridization demonstrated low signals for α_vβ₃ and β₅ mRNA in uninjuried aorta, which increased significantly at 14 days, localized predominantly in the neointima. Northern analysis of aorta after 14 days of injury also demonstrated an upregulation of α_vβ₃ and β₅ mRNA compared to uninjured aorta. Consistent with the increase in message levels, increased inegrin protein expression was seen in the neointima after 7 and 14 days. This study provides evidence that α_vβ₃ and α_vβ₅ are elevated during neointima formation in the rat and indicates a novel role for α_vβ₅ participating in mechanisms regulating smooth muscle cell migration.