VE-Cadherin Is Required for Cardiac Lymphatic Maintenance and Signaling.

Background: The adherens protein VE-cadherin has diverse roles in organ-specific lymphatic vessels. However, its physiological role in cardiac lymphatics and its interaction with lymphangiogenic factors, has not been fully explored. We sought to determine the spatio-temporal functions of VE-cadherin in cardiac lymphatics and mechanistically elucidate how VE-cadherin loss influences pro-lymphangiogenic signaling pathways, such as adrenomedullin (AM) and VEGF-C/VEGFR3 signaling. Methods: Cdh5flox/flox;Prox1CreERT2 mice were used to delete VE-cadherin in lymphatic endothelial cells (LECs) across life stages, including embryonic, postnatal and adult. Lymphatic architecture and function was characterized utilizing immunostaining and functional lymphangiography. To evaluate the impact of temporal and functional regression of cardiac lymphatics in Cdh5flox/flox;Prox1CreERT2 mice, left anterior descending artery ligation was performed and cardiac function and repair after myocardial infarction was evaluated by echocardiography and histology. Cellular effects of VE-cadherin deletion on lymphatic signaling pathways were assessed by knock-down of VE-cadherin in cultured LECs. Results: Embryonic deletion of VE-cadherin produced edematous embryos with dilated cardiac lymphatics with significantly altered vessel tip morphology. Postnatal deletion of VE-cadherin caused complete disassembly of cardiac lymphatics. Adult deletion caused a temporal regression of the quiescent epicardial lymphatic network which correlated with significant dermal and cardiac lymphatic dysfunction, as measured by fluorescent and quantum dot lymphangiography, respectively. Surprisingly, despite regression of cardiac lymphatics, Cdh5flox/flox;Prox1CreERT2 mice exhibited preserved cardiac function, both at baseline and following myocardial infarction, compared to control mice. Mechanistically, loss of VE-cadherin leads to aberrant cellular internalization of VEGFR3, precluding the ability of VEGFR3 to be either canonically activated by VEGF-C or non-canonically transactivated by AM signaling, impairing downstream processes such as cellular proliferation. Conclusions: VE-cadherin is an essential scaffolding protein to maintain pro-lymphangiogenic signaling nodes at the plasma membrane, which are required for the development and adult maintenance of cardiac lymphatics, but not for cardiac function basally or after injury.