Vascular Endothelial Cadherin-Expressing Cells Involved in Both Developmental and Adult Neovascularization.

Vessel formation, including vasculogenesis and angiogenesis, is thought to be directly mediated by adhesive molecules between vascular endothelial cells and adjacent cells. Vascular endothelial cadherin (VE-cadherin, CD144) is a adhesive molecule exclusively expressed in adherens junctions of cultured endothelial cells. VE-cadherin transcripts have been detected at first in mesodermal cells. However, no work has focused on which cell type expresses VE-cadherin during vessel formation and after vessel stabilization. To monitor VE-cadherin in vivo, we generated transgenic mice expressing a VE-cadherin promoter-driven Cre (VE-cad-Cre). By crossing VE-cad-Cre with loxP-based EGFP reporter mice (CAG-CAT-EGFP) and LacZ reporter mice (cAct-XstopX-LacZ), we obtained two double transgenic mice; one expressing EGFP (VE/EG) another expressing LacZ (VE/Z) dependently upon Cre driven by VE-cadherin promoter. Both reporter expression was increased in developing vasculature during embryogenesis, while it was decreased in postnatal vessel maturation. Intriguingly, LacZ reporter was found in the budding cells and lining cells of the dorsal aorta in the aorta-gonad-mesonephros region, suggesting that VE-cadherin-expressing cells belongs to hemangioblasts. Consistently, although VE-cadherin and its mRNA was detected in vasculature by immunohistochemistry and in situ hybridization, respectively, during embryogenesis, it was not detected in maturated vessels. These results indicated that VE-cadherin promoter activity reflects the endogeneous VE-cadherin expression and that VE-cadherin promoter is activated during developmental vasculogenesis and angiogenesis. To test whether the VE-cadherin promoter is re-activated in postnatal neovascularization, we used two models; a VEGF-induced cornea angiogenesis model and a myocardial ischemia model. VEGF implanted in the VE/EG eyes promoted the neovascularization visualized by EGFP expression. Myocardial ischemia in which the coronary artery was banded triggered the VE-cadherin promoter, thereby inducing reporter expression in vascular cells (endothelial cells and mural cells) of undamaged region and in infiltrated cells of damaged region. Furthermore, by flow cytometric analyses, we confirmed that myocardial ischemia re-activated the VE-cadherin promoter of both bone marrow cells and peripheral blood cells, as indicated by the remarkable increase of EGFP-positive cells. These data show that the VE-cadherin promoter is re-activated in pre-existing vascular cells and infiltrated cells during adult neovascularization. Collectively, VE-cadherin-expressing cells participates in both developmental and postnatal vasulogenesis and angiogenesis.