Notch3 Signaling Mediates Heterotypic Cell Interactions During Blood Vessel Formation

Abstract

Blood vessel formation is essential for embryogenesis, wound healing, menstruation, and pregnancy [1, 2]. While much emphasis has been placed on understanding the initial event of endothelial-tube formation, relatively little attention has been paid to the interactions of endothelial cells and the surrounding mural cells (pericytes, smooth muscle cells and fibroblasts). Increasing evidence suggests that the communication of endothelial cells and mural cells is crucial for the assembly, subsequent maturation, and stabilization of blood vessels [3-5]. Abnormal interactions between these two cell types have been implicated in many pathological conditions, including tumor angiogenesis, diabetic microangiopathy, tissue calcification and stroke. However, the molecules mediating the heterotypic interaction are still largely unknown. Our previous studies have shown that in a three-dimensional (3-D) angiogenesis assay, mural cells enhance blood vessel formation and directly interact with endothelial cells [6]. During this process, Notch3 is one gene that is strongly induced in mural cells upon coculture with endothelial cells [6]. Notch3, the causative gene of the neurovascular disorder CADASIL [7], belongs to an evolutionarily conserved family of transmembrane receptors that are known to govern cell fate determination in diverse cell types [8]. Given that Notch receptors and ligands are expressed on both endothelial and mural cells and - 2 - Notch3 is upregulated in mural cells by coculturing with endothelial cells, it is reasonable to assume that the Notch3 receptor might regulate the association of endothelial and mural cells through receptor-ligand interaction during blood vessel formation. The goal of my thesis is to investigate how Notch3 gene expression is regulated in mural cells by endothelial cells and whether the Notch3 receptor is involved in the communication between endothelial and mural cells during blood vessel formation. To achieve these goals, three aims were proposed: Specific Aim 1: To define how Notch3 expression in mural cells is upregulated by endothelial cells. Specific Aim 2: To determine if endothelial cell-induced Notch3 expression is critical for mural cell differentiation. Specific Aim 3: To determine whether Notch3 expression in mural cells modulates blood vessel formation under both physiological and pathological conditions.