VE‐cadherin Controls Mechanotransduction Signaling in Embryonic and Postnatal Lymphatic Valves
Authors: Scallan Joshua Paul , Yang Ying , Cha Boksik , Angulo Mariana Burgos , Srinivasan Sathish 
Published: June 2021

Lymphatic valve dysfunction is a major risk factor for developing lymphedema. The formation and lifelong maintenance of intraluminal valves in lymphatic collecting vessels is critically dependent on shear forces exerted on the lymphatic endothelium by low magnitude oscillatory fluid flow. Oscillatory flow stimulates the expression of the transcription factors controlling valve development (e.g. Gata2, Foxc2, Prox1), but the mechanism of how fluid shear on the cell membrane is sensed by proteins located in the cell nucleus remains unknown. While the adherens junction protein, VE‐cadherin, is a crucial part of the mechanotransduction cascade in blood vessels, its function has not been investigated in lymphatic endothelium. To test whether VE‐cadherin controls lymphatic valve development by transducing fluid shear stress into intracellular signals, we generated a conditional ‘floxed’ VE‐cadherin allele and crossed it with a lymphatic‐specific and tamoxifen‐inducible Cre strain (Prox1CreERT2). An additional Prox1‐ GFP reporter strain was included to enable visualization of the lymphatic vasculature for counting valves and morphologic analysis. Inactivation of the VE‐cadherin gene during embryonic development resulted in the complete absence of lymphatic valves in the mesentery. Additionally, the lymphovenous valves connecting the primitive thoracic duct and subclavian vein were completely absent. Postnatal deletion of VE‐cadherin on the first day of life (P1) caused a 75% reduction in the total valve number in the mesentery at day P8 (743±14 vs 173±4, n=3), and a 90% reduction at day P14 (1083±49 vs 115±9, n=3), demonstrating that VE‐cadherin signaling is constitutively required for maintaining the presence of lymphatic valve structures. To confirm the role of fluid flow in VE‐cadherin signaling, human dermal lymphatic endothelial cells (LEC) were cultured in the absence and presence of oscillatory shear stress (OSS), both with and without knockdown of VE‐cadherin. Exposure to OSS significantly increased the transcription of FOXC2, GATA2, KLF4, and Cx37 in control LECs, and this was prevented upon knockdown of VE‐cadherin. To determine the signaling events downstream of VE‐cadherin, we investigated whether the transcriptionally active VE‐cadherin binding partner, β‐catenin, was capable of rescuing the lymphatic valve regression. LEC treated with a chemical inhibitor of the β‐catenin destruction complex (BIO; a GSK3β antagonist) restored the response of FOXC2 and GATA2 to OSS. Similarly, overexpression of a stable β‐catenin mutant in vivo led to a 45% increase in the total number of mesenteric valves at P14 compared to VE‐cadherin knockouts. In conclusion, these results demonstrate a novel, required role for VE‐cadherin in lymphatic valve formation and maintenance in response to oscillatory shear stress. Further, VE‐cadherin activates β‐catenin signaling to stimulate the nuclear transcription factors responsible for valve development.Support or Funding InformationSupported by NIH R00HL124142, R01HL131652, & R01HL133216.This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.