AUTHOR=Davis Michael J. , Zawieja Scott D. , Yang Ying 

TITLE=Developmental progression of lymphatic valve morphology and function

JOURNAL=Frontiers in Cell and Developmental Biology

VOLUME=Volume 12 - 2024

YEAR=2024

URL=https://www.frontiersin.org/journals/cell-and-developmental-biology/articles/10.3389/fcell.2024.1331291

DOI=10.3389/fcell.2024.1331291

ISSN=2296-634X

ABSTRACT=Introduc�on. The bicuspid valves found in collec�ng lympha�c vessels and some veins are essen�al for maintaining the unidirec�onal flow that is important for both lympha�c and venous func�on. Under an adverse pressure gradient, the two valve leaflets �ghtly overlap to prevent backflow. Valves are proposed to share 4 main stages of development, based on images obtained from randomly orientated valves in fixed mouse embryos (Bazigou et al., 2009;Sabine et al., 2012), with the best structural views obtained from larger, venous valves (Bazigou et al., 2011). It is not known at what stage lympha�c valves (LVs) become func�onal (e.g., able to oppose backflow), although a requirement for stage 4 is presumed.To gain insight into this sequence of events for LVs, we took advantage of Prox1CreER T2 ;Foxo1 f/f mice and Foxc2CreER T2 ;Foxo1 f/f mouse models, in which dele�on of the valve repressor factor Foxo1 promotes the development of new LVs in adult lympha�c vessels. Both strains also contained a Prox1eGFP reporter for imaging. Mesenteric collec�ng lympha�c vessels were dissected, cannulated, and pressurized for ex vivo tests of valve func�on. LVs at various stages (1-4 and intermediate) were iden�fied in mul�-valve segments, which were subsequently shortened to perform tests of back leak on single valves. The GFP signal was then imaged at high magnifica�on on a confocal microscope. Z-stack reconstruc�ons allowed 1:1 comparisons of LV morphology with quan�ta�ve measurement of back leak.Results. As expected, LVs from stages 1-3 were completely leaky. Stage 4 valves were generally not leaky. A high percentage of valves at an intermediate stage (3.5), in which there was inser�on of a second commissure but without proper luminal alignment, effec�vely resisted back leak in the face of elevated ou�low pressure. Discussion. Our findings represent the first 3D images of developing lympha�c valves and indicate that valves become competent between stages 3 and 4 of development.