Functional overlap and cooperativity among αv and β1 integrin subfamilies during skin angiogenesis

Abstract

Angiogenesis requires endothelial cell survival and proliferation, which depend upon cytokine stimulation together with integrin-mediated cell adhesion to extracellular matrix; however, the question of which specific integrins are the best targets for suppressing neovascularization is controversial and unresolved. Therefore, we designed experiments to compare contributions of individual integrins from both the αv and β1 integrin subfamilies. With immobilized antibodies, we determined that adhesion through integrins α1β1, α2β1, αvβ3, and αvβ5 each individually supported dermal microvascular endothelial cell survival. Also, substratum coated with collagen I (which binds α1β1 and α2β1) and vitronectin (which binds αvβ3 and αvβ5) each supported survival. Importantly, substratum coated with combinations of collagen I and vitronectin were most effective at promoting survival, and survival on three-dimensional collagen I gels was strongly enhanced by vitronectin. Vascular endothelial growth factor activation of the p44/p42 mitogen-activated protein kinase pathway, which is required for angiogenesis, was supported by adhesion through either α1β1, α2β1, αvβ3, or αvβ5, and pharmacologic inhibition of this pathway blocked proliferation and suppressed survival. Therefore, these studies establish that the α1β1, α2β1 αvβ3, and αvβ5 integrins each support dermal microvascular endothelial cell viability, and that each collaborate with vascular endothelial growth factor to support robust activation of the mitogen-activated protein kinase pathway which mediates both proliferation and survival. Moreover, survival is supported most significantly by extracellular matrices, which engage all of these integrins in combination. Consistent with important complementary and overlapping functions, combined antagonism of these integrins provided superior inhibition of angiogenesis in skin, indicating that multiplicity of integrin involvement should be considered in designing strategies for controlling neovascularization.