Abstract 539: Collateral Formation Is Regulated by Vascular Endothelial Growth Factor-A and a Disintegrin and Metalloprotease Family Members 10 and 17

The density of native (pre-existing) collaterals varies widely and is a significant determinant of variation in severity of ischemic stroke, myocardial infarction and peripheral artery disease. However, little is known about mechanisms responsible for formation of the collateral circulation in healthy tissues. We previously found that variation in VEGF expression causes differences in collateral density of newborn and adult mice. Herein, we sought to determine mechanisms of collaterogenesis in the embryo and the role of VEGF in this process. Pial collaterals formed between embryonic day (E) 13.5 and 14.5 as sprout-like extensions from distal-most arterioles of the cerebral artery trees that increased in number up until birth. Global VEGF-A overexpressing mice ( Vegf hi/+ ) formed more_and Vegf lo/+ formed fewer_collaterals during embryogenesis, in association with differences in vascular patterning. Conditional global reduction of VEGF or FLK1 (VEGFR2) during collaterogenesis significantly reduced collateral formation, compared to wildtype littermates, without affecting vascular patterning. Endothelial-specific reduction of VEGF had no effect on collaterogenesis. Endothelial-specific reduction of a disintegrin-and-metalloprotease-domain-10 (ADAM10) and inhibition of γ-secretase increased collateral formation, consistent with their roles in VEGF-induced Notch1 activation and suppression of “pro-sprouting” signals. Endothelial-specific reduction of ADAM17 reduced collateral formation, consistent with its roles in endothelial cell migration and embryonic vascular stability, but not in activation of ligand-bound Notch1. These effects of ADAM 10/17 reduction persisted into adulthood. Conclusions: Formation of pial collaterals occurs during a narrow developmental window, requires paracrine VEGF-signaling, and is shaped by mechanisms associated with sprouting angiogenesis.