Endothelial cell guidance and vascular patterning during retina developmental angiogenesis

The process of angiogenesis is critical for the normal development of higher level organisms. However, relatively little is known about the mechanisms that participate in endothelial cell guidance during formation of characteristic adult vascular patterns. Endothelial cell guidance was studied using a post-natal mouse retina model of developmental vascularization. During formation of the superficial vascular plexus, vessels migrate across a pre-existing astrocytic template. Immunohistochemical, global gene expression, and functional studies determined that endothelial cells are guided along the underlying astrocytic template using filopodia interactions and specific R-cadherin mediated cell-cell adhesions. R-cadherin expression was also found to be correlated both temporally and spatially with formation of the deep vascular plexuses. Blocking R-cadherin mediated adhesion during formation of both the superficial and deep vascular plexuses, either by function blocking antibodies or novel R-cadherin specific peptide antagonists, resulted in dramatic disruption of the normal vascular patterns. Targeting of endothelial progenitor cells to the developing retinal vasculature was also disrupted by blocking R-cadherin mediated adhesion. Binding of the very low density lipoprotein receptor (VLDLR) to its extracellular matrix ligand reelin was also found to be important for normal retina vascular development. Mice deficient in reelin (reeler) or VLDLR ( vldlr−/−) were characterized by numerous vascular sprouts extended within the photoreceptor layer, similar to the extra deep vessels observed by blocking R-cadherin mediated adhesion. Work in this dissertation describes novel in vivo mechanisms of endothelial cell guidance and vascular patterning. In addition, described parallels between neuronal guidance and endothelial cell guidance during retina development suggest a new paradigm for studying developmental vascular patterning.