Integrin-α9 Is Required for Fibronectin Matrix Assembly during Lymphatic Valve Morphogenesis

Abstract

SummaryDysfunction of lymphatic valves underlies human lymphedema, yet the process of valve morphogenesis is poorly understood. Here, we show that during embryogenesis lymphatic valve leaflet formation is initiated by upregulation of integrin-α9 expression and deposition of its ligand, fibronectin-EIIIA (FN-EIIIA), in the extracellular matrix. Endothelial cell specific deletion of Itga9 (encoding integrin-α9) in mouse embryos results in the development of rudimentary valve leaflets, characterized by disorganized FN matrix, short cusps and retrograde lymphatic flow. Similar morphological and functional defects are observed in mice lacking the EIIIA domain of FN. Mechanistically, we demonstrate that in primary human lymphatic endothelial cells the integrin-α9-EIIIA interaction directly regulates FN fibril assembly, which is essential for the formation of the extracellular matrix core of valve leaflets. Our findings reveal an important role for integrin-α9 signaling during lymphatic valve morphogenesis and implicate it as a candidate gene for primary lymphedema caused by valve defects.

Integrin α9 on lymphatic endothelial cells regulates lymphocyte egress

“…1C). It was shown that the interaction of FN-EDA with its receptor α9β1 plays a role in the development of lymphatic valves, although both FN-EDA and TN-C were colocalized in developing lymphatic valves (15). We found that blockade of α9 did not cause defects of lymphatic flow (Fig.…”

“…Factors, including vascular endothelial growth factor receptor 3 (VEGFR3), lymphatic vessel endothelial hyaluronan receptor 1 (LYVE-1), transcription factor prox-1, and integrins, regulate lymphatic vessel growth and development (9)(10)(11)(12)(13). Among the integrins, α9 integrin (α9 hereafter) is critical for the development of lymphatic valves (14,15). Furthermore, prox-1-induced lymphatic endothelial differentiation is mediated at least in part through α9 (10).…”

Role of Lymphatic Vessels in Tumor Immunity: Passive Conduits or Active Participants?

“…These capillaries drain into precollecting and collecting vessels that have continuous, "zipper-like" interendothelial junctions [30] and are surrounded by smooth muscle. Collecting vessels are organized into contractile segments called lymphangions, separated by bileaflet valves, that create the driving force for unidirectional lymph propulsion [30,31,[34][35][36]. Collecting lymphatic vessels that carry lymph to and from the lymph nodes are referred to as afferent and efferent lymphatic vessels, respectively.…”

Molecular Regulation of Lymphangiogenesis in Development and Tumor Microenvironment

“…Recent studies using genetic mouse models have revealed that several genes play important roles in lymphatic valve development. Defects with lymphatic valve formation have been shown in mice upon suppression of calcineurin/NFATc1 signaling (Norrmen et al 2009), or with genetic deletion / mutation of the following genes, including Foxc2 (Petrova et al 2004), Ephrinb2 (Makinen et al 2005), Itga9 and Fn-EIIIA (Bazigou et al 2009), Pik3r1 (Mouta-Bellum et al 2009) and Akt1 . Mice deficient in Cx37 (connexin-37), a downstream target of FOXC2, were recently shown to display abnormal valve formation (Kanady et al 2011;Sabine et al 2012).…”

“…Lymphatic valves are semilunar structures and the valve leaflet is composed of an extracellular matrix core covered by LECs on both sides (Bazigou et al 2009). Recent studies using genetic mouse models have revealed that several genes play important roles in lymphatic valve development.…”