Molecular Genetic Dissection of Fenestrated Vascular Development in the Choroid Plexus

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PROJECT SUMMARY/ABSTRACT Cerebrovascular diseases remain a leading cause of serious long-term disability. Many of these diseases originate, at least in part, from genetic defects that impact the development and maturation of blood vessels in the central nervous system (CNS) and meninges. Despite substantial progress in our understanding of CNS angiogenesis and barriergenesis, our knowledge of the highly permeable, or fenestrated, microvasculature formed in the choroid plexus (CP) and circumventricular organs remains limited. The overall goal of this proposal is to fill this gap in scientific knowledge by understanding the molecular genetic mechanisms of fenestrated brain vascular development, specifically focusing on the CP. We recently found that CP vascularization in zebrafish requires a unique angiogenic mechanism whereby zebrafish vascular endothelial growth factor (Vegf) orthologs, specifically Vegfab and Vegfc, play a functionally redundant role. Surprisingly, this mechanism is specific to CP vascularization, since the neighboring non-fenestrated brain vasculature is not affected in the vegfab;vegfc double mutants. These results led us to formulate a paradigm-shifting hypothesis that fenestrated CP and non-fenestrated brain vascular development requires distinct sets of the Vegf/Vegfr codes and signaling. Given the critical roles for Vegfs in diverse pathophysiological processes and also the fact that no molecular cue that drives CP vascularization has been reported in any vertebrate species, the results of this study will have a significant positive impact on the fields of CP physiology and vascular biology beyond CP vascularization. Our further genetic, pharmacological, and expression data propose a model in which paracrine Vegfab from CP epithelial cells and autocrine Vegfc from the endothelium together controls CP vascularization via PI3K and ERK signaling pathways. The following two Specific Aims are proposed to test our hypotheses. Aim 1 will test the hypothesis that fenestrated CP and non-fenestrated brain vascular development requires distinct Vegf/Vegfr codes and signaling. Aim 2 will test the hypothesis that the spatiotemporal coordination of paracrine Vegfab from CP epithelial cells and autocrine Vegfc from the endothelium together drives fenestrated CP vascular development. We will pursue these aims by combining novel zebrafish molecular genetic tools with advanced imaging technologies and genetic mosaic analyses. The proposed work is an innovative molecular genetics study in this field because it exploits various strengths of the zebrafish model to overcome technical limitations and address the following fundamental processes: 1) the cellular and molecular basis of fenestrated CP vascular development; and 2) the developmental mechanisms behind the formation of heterogeneous brain vascular networks. Mechanistic information gleaned from this work will shed new light on potential molecular pathways involved in the pathogenesis of CP vascular malformations and also help to design therapeutics for preventing or treating CNS vascular diseases.