Identification of signaling mechanisms controlling the development of organ-specific vascular networks
Date of Award
Doctor of Philosophy (PhD)
Cellular and Molecular Physiology
Blood vessels form highly branched networks that extend throughout the entire body. Endothelial cells forming the inner lining of blood vessels are responsible for vascular growth and physiological function, in that they control the exchange of gases, nutrients and immune cells between blood and tissues and respond to injury by mounting an appropriate repair response. While considered a homogenous cell population, endothelial cells display heterogeneity in structure and function and in health and disease. This structural and functional variability enables endothelial cells to adapt to their microenvironment and perform different roles in each organ. Various organotypic vascular beds have been identified in every organ to carry out critical tissue-specific functions. Despite recent identification of differentially expressed marker genes, how endothelial cells adapt to the microenvironment and develop heterogeneity among different organs remains incompletely understood. My thesis project explored signaling pathways that regulate formation of retinal, intestinal and renal vasculature, with a specific focus on Slit-Robo signaling and glomerular capillaries. The kidney functions to remove metabolic wastes from the blood while keeping proteins and other nutrients in the circulation. The heterogeneous renal endothelium lining the arterial and venous trees and three distinct capillary beds are required to make up a functional renal vasculature. Among them, the glomerular capillary loop is a highly specialized vasculature that continuously filters blood. Disruption of glomerular vascular development or maintenance contributes to the pathogenesis of renal diseases. Nevertheless, the signaling events regulating the development of glomerular vasculature remain incompletely understood. Here, we discovered a novel role of Slit2-Robo signaling in glomerular vascularization. Slit2 is a secreted polypeptide that binds to transmembrane Robo receptors and regulates axon guidance as well as ureteric bud branching and angiogenesis. For this study, we performed Slit2-alkaline phosphatase binding assay on kidney cryosections from mice with or without tamoxifen-inducible Slit2 or Robo1&2 deletions. Immunohistological, electron microscopy and functional intravenous dye perfusion analysis were used to characterize the phenotype. The results showed that only the glomerular endothelium, but no other renal endothelial compartment, responded to Slit2 in the developing kidney vasculature. Postnatally induced Slit2 gene deletion or a Slit2 ligand trap inhibited vascularization of developing glomeruli, leading to defective glomerular perfusion and abnormal podocyte differentiation, as well as to reduced numbers of functional nephrons. Mechanistically, reduced proliferation and decreased migration of glomerular endothelial cells contributed to the glomerular capillary defects. Global and endothelial-specific Robo deletion showed that both endothelial and epithelial Robo receptors contributed to glomerular vascularization. In summary, we discovered a novel role of Slit2-Robo signaling in glomerular vascularization. Our study provides new insights into the signaling pathways involved in glomerular vascular development and identifies Slit2 as a potential tool to enhance glomerular angiogenesis.
Li, Jinyu, "Identification of signaling mechanisms controlling the development of organ-specific vascular networks" (2021). Yale Graduate School of Arts and Sciences Dissertations. 366.