A Key Role for the Integrin alpha 2 beta 1 in Experimental and Developmental Angiogenesis

The alpha 2 beta 1 integrin receptor plays a key role in angiogenesis. Here we investigated the effects of small molecule inhibitors (SMIs) designed to disrupt integrin alpha 2 I or 131 I-like domain function on angiogenesis. in unchallenged endothelial cells, fibrillar collagen induced robust capillary morphogenesis. In contrast, tube formation was significantly reduced by SM1496, a beta 1 I-like domain inhibitor and by function-blocking anti-alpha 2 beta 1 but not -alpha 1 beta 1 antibodies. Endothelial cells bound fluorescein-labeled collagen I fibrils, an interaction specifically inhibited by SM1496. Moreover, SM1496 caused cell retraction and cytoskeletal collapse of endothelial cells as well as delayed endothelial cell wound heating. 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. SM1496, but not a control compound, interfered with angiogenesis in vivo by reversibly inhibiting sprouting from the axial vessels. We further characterized zebrafish alpha 2 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 alpha 2 subunit. By live videomicroscopy, we confirmed that the vessels were largely nonfunctional in the absence of alpha 2 beta 1 integrin. Collectively, our results provide strong biochemical and genetic evidence of a central role for alpha 2 beta 1 integrin in experimental and developmental angiogenesis. (Am J Pathol 2009, 175:1138-1347; DOI: 10.2353/ajpath.2009.090234)