A Key Role for the Integrin α2β1 in Experimental and Developmental Angiogenesis

The α2β1 integrin receptor plays a key role in angiogenesis. Here we investigated the effects of small molecule inhibitors (SMIs) designed to disrupt integrin α2 I or β1 I-like domain function on angiogenesis. In unchallenged endothelial cells, fibrillar collagen induced robust capillary morphogenesis. In contrast, tube formation was significantly reduced by SMI496, a β1 I-like domain inhibitor and by function-blocking anti-α2β1 but not -α1β1 antibodies. Endothelial cells bound fluorescein-labeled collagen I fibrils, an interaction specifically inhibited by SMI496. Moreover, SMI496 caused cell retraction and cytoskeletal collapse of endothelial cells as well as delayed endothelial cell wound healing. SMI activities were examined in vivo by supplementing the growth medium of zebrafish embryos expressing green fluorescent protein under the control of the vascular endothelial growth factor receptor-2 promoter. SMI496, but not a control compound, interfered with angiogenesis in vivo by reversibly inhibiting sprouting from the axial vessels. We further characterized zebrafish α2 integrin and discovered that this integrin is highly conserved, especially the I domain. Notably, a similar vascular phenotype was induced by morpholino-mediated knockdown of the integrin α2 subunit. By live videomicroscopy, we confirmed that the vessels were largely nonfunctional in the absence of α2β1 integrin. Collectively, our results provide strong biochemical and genetic evidence of a central role for α2β1 integrin in experimental and developmental angiogenesis.