Mechanistic bases of vessel diameter regulation by Plexind1 - Resubmission

PROJECT SUMMARY Blood vessels must be properly shaped and placed and have a hierarchical organization with characteristic and distinct calibers to perform their vital circulatory function. In particular, vascular caliber is the primary determinant of blood flow properties. Thus, abnormalities in luminal morphometry disrupt blood circulation and decrease cardiovascular health. We found that Semaphorin-Plexind1 (Sema-Plxnd1) signaling, known for its role in guiding the anatomical patterning of the vasculature, plays a novel blood flow-dependent role in determining the caliber of the axial midline vessels (the major artery and vein of the body). Our aims are as follows. (1) To define the signaling pathways and cellular mechanisms by which Plxnd1, its Sema3 ligands, and blood flow regulate the caliber of these vessels. (2) To define the structural bases of Plxnd1-dependent vessel caliber sizing and the role of Semas and flow forces as modulators of Plxnd1 expression, apicobasal targeting, and flow mechanosensing activity. We will use zebrafish as our primary model system to exploit its unique experimental advantages for studying vascular development, function, and signaling in vivo. We will also perform experiments with mice to determine if the receptor's novel role is conserved in mammals. Finally, to further illuminate how Sema ligands and circulatory forces modulate Plexin-D1 expression, localization, and function, we will perform studies with human endothelial cell systems under tunable flow conditions.