Abstract 9237: An Adaptor Protein Afadin Regulates Lymphatic Vessel Development by Modulating RhoA Activation

Abstract

Afadin is an intracellular binding partner of nectins, the cell-cell adhesion molecules; it plays important roles in the formation of cell-cell junctions. Afadin knockout mice show early embryonic lethality, therefore little is known about the function of afadin in organ development. To elucidate the role of afadin in the vascular system in vivo, we generated endothelial cell-specific afadin-null mice by the Cre-LoxP system. These afadin conditional knockout (cKO) mice were almost embryonically lethal as a result of severe subcutaneous edema. Defects in the lymphatic vessels of the skin were observed, although the abnormality in the blood vessels was not detected. We also found that severe disruption of the VE-cadherin-mediated cell-cell junctions occurred only in lymphatic endothelial cells, but not in blood endothelial cells. Since depletion of afadin did not affect the ability of differentiation and proliferation of lymphatic endothelial cells, the disruption of cell-cell junctions in the lymphatic vessels is considered to be the primary reason to cause the embryonic lethality in afadin cKO mice. We further investigated the molecular mechanism by which the phenotype in afadin cKO was specifically observed in the lymphatic vessels in the in vitro assays using blood and lymphatic microvascular endothelial cells (BMVECs and LMVECs). Knockdown of afadin caused the elongated shapes and cell-cell junction disruption in LMVECs, but not BMVECs. In afadin-knockdown LMVECs, enhanced F-actin bundles were formed at the cell periphery and the activation of RhoA was strongly increased in comparison with afadin-knockdown BMVECs. Given that the excessive RhoA activation can induce the force to shrink the cells, these results indicate that afadin has different effects on blood and lymphatic endothelial cells by controlling the activation of RhoA, which critically regulates the development of mouse embryos.