Abstract
The number and diameter of native collaterals in tissues of healthy mice vary widely, resulting in large differences in tissue injury in occlusive diseases. Recent studies suggest similar variation may exist in humans. Collateral variation in mice is determined by genetic background-dependent differences in embryonic collateral formation, by variation in maturation of the nascent collaterals, and by environmental factors such as aging that cause collateral rarefaction in the adult. Recently, formation of the collateral circulation in the brain was found to involve a unique VEGF-A-dependent "arteriolar" angiogenic sprouting-like mechanism. Elsewhere, chloride intracellular protein 4 (CLIC4) was implicated but not investigated directly, prompting the present study. Deletion of Clic4 had no effect on embryonic collaterogenesis. However, during collateral maturation from embryonic day 18.5 to postnatal day 7, reduced mural cell investment was observed and excessive pruning of collaterals occurred. Growth in collateral diameter was reduced. This resulted in 50% fewer collaterals of smaller diameter in the adult and thus larger infarct volume after middle cerebral artery occlusion. During collateral maturation, CLIC4 deficiency resulted in reduced expression of Vegfr2, Vegfr1, Vegfc, and mural cell markers, but not notch-pathway genes. Overexpression of VEGF-A in Clic4(-/-) mice had no effect on collaterogenesis, but rescued the above defects in collateral maturation by preventing mural cell loss and collateral pruning, thus restoring collateral number and diameter and reducing stroke severity in the adult. CLIC4 is not required for collaterogenesis but is essential for perinatal maturation of nascent collaterals through a mechanism that supports VEGF signaling.