| dc.description.abstract | Cdc42 is a member of the Rho family of small GTPases and functions as a molecular switch regulating multiple cellular processes. We determined whether Cdc42 is involved in lymphatic development via generating two Cdc42 knockout mouse models. Our results demonstrated that endothelial cell (EC)-specific deletion of Cdc42 caused embryonic lethality with severe edema. Furthermore, both EC-specific and lymphatic EC (LEC)-specific knockout mice exhibited impaired lymphatic vessel sprouting while the lumen size of lymphatic vessels significantly increased. Deletion of Cdc42 impaired the maturation of mesenteric collecting lymphatic vessels and interfered with the maturation of lymphatic valves (LVs). Furthermore, Cdc42 knockout led to disorganized lymphatic endothelial junctions, in which the distribution of ZO-1 (encoded by the Tjp1 gene and also known as tight junction protein-1) was disorganized and discontinuous. We then generated a novel EC-specific Tjp1 knockout mouse model in which vascular and lymphatic development was compromised. The defective lymphatic sprouting displayed in TJP1-deficient animals was similar to defects noted in the Cdc42 knockout mouse, indicating that ZO-1 may function in the Cdc42 signaling axis to regulate lymphatic development.
Focal adhesion kinase (FAK), a non-receptor tyrosine kinase, is a central point of convergence to regulate multiple signaling pathways. We generated both EC- and LEC- specific knockout mice to determine the functions of FAK in lymphangiogenesis. Deletion of FAK in ECs led to aberrantly formed lymph sacs. Also, EC-specific FAK knockout in ECs compromised the sprouting lymphangiogenesis in multiple organs such as the skin and the diaphragm. LEC-specific knockout of FAK induced defective sprouting lymphangiogenesis in the dermal lymphatic vasculature. Meanwhile, the inactivation of FAK interfered with the development of mesenteric lymphatic vasculature, indicated by aberrant enlargement and less mature LVs. Deletion of FAK led to blood-filled lymphatic vessels, indicating the misconnection between the blood and lymphatic vasculatures. In vitro studies revealed that knockdown of FAK in cultured human dermal lymphatic endothelial cells (HDLECs) decreased phosphorylation of Erk and Akt.
In summary, our findings highlight the importance of multiple molecules, including Cdc42, ZO-1, and FAK, in lymphatic development. | |
