Abstract 529: A Chloride Intracellular Channel-4 (Clic4) and VEGF-A Signaling Pathway Regulates Maturation of the Collateral Circulation

The density of native (pre-existing) cerebral collaterals in healthy tissues varies widely and is a major determinant of the wide variation in infarct volume in ischemic stroke. Collateral number in adults has been shown to be dependent on 3 processes: formation in the embryo, maturation in the perinate (i.e. slight pruning, increase in diameterand muralization) and maintenance thereafter. However, the mechanisms underlying these processes are not well understood. We previously found that collaterogenesis is led by a unique “arteriolar” angiogenic sprouting-like mechanism involving the VEGF-Notch signaling pathway. We also observed that mice lacking chloride intracellular protein 4 (Clic4), a protein which appears to reside upstream of VEGF-A in hypoxia-induced signaling, had fewer pial collaterals on postnatal day (P)1 that underwent greater pruning by P21, to yield lower collateral number and more severe stroke in adults. Therefore, herein we hypothesized that Clic4 is required for both formation and maturation of the collateral circulation. Wildtype and Clic4 -/- mice formed similar numbers of collaterals through embryonic day (E)18.5. Thus, collaterogenesis does not require Clic4. However, perinatal pruning was strongly augmented in Clic4 -/- mice, resulting in reduced collateral number and larger infarct volume in adults after MCA occlusion. Pial diameter was also reduced, consistent with our previous findings. Overexpression of VEGF-A in Clic4 -/- mice by crossing them to Vegf hi/+ mice did not affect collaterogenesis but inhibited the excessive perinatal pruning, resulting in adults with the abundant collaterals and small infarct volume seen in wildtype mice. We conclude that Clic4 is not required for embryonic collaterogenesis but is essential for perinatal stabilization of nascent collaterals through a mechanism involving VEGF signaling.