Genes regulating lymphangiogenesis control venous valve formation and maintenance in mice
Eleni Bazigou, … , Nigel A. Brown, Taija Makinen
Eleni Bazigou, … , Nigel A. Brown, Taija Makinen
Published July 18, 2011
Citation Information: J Clin Invest. 2011;121(8):2984-2992. https://doi.org/10.1172/JCI58050.
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Research Article Vascular biology

Genes regulating lymphangiogenesis control venous valve formation and maintenance in mice

Abstract

Chronic venous disease and venous hypertension are common consequences of valve insufficiency, yet the molecular mechanisms regulating the formation and maintenance of venous valves have not been studied. Here, we provide what we believe to be the first description of venous valve morphogenesis and identify signaling pathways required for the process. The initial stages of valve development were found to involve induction of ephrin-B2, a key marker of arterial identity, by venous endothelial cells. Intriguingly, developing and mature venous valves also expressed a repertoire of proteins, including prospero-related homeobox 1 (Prox1), Vegfr3, and integrin-α9, previously characterized as specific and critical regulators of lymphangiogenesis. Using global and venous valve–selective knockout mice, we further demonstrate the requirement of ephrin-B2 and integrin-α9 signaling for the development and maintenance of venous valves. Our findings therefore identified molecular regulators of venous valve development and maintenance and highlighted the involvement of common morphogenetic processes and signaling pathways in controlling valve formation in veins and lymphatic vessels. Unexpectedly, we found that venous valve endothelial cells closely resemble lymphatic (valve) endothelia at the molecular level, suggesting plasticity in the ability of a terminally differentiated endothelial cell to take on a different phenotypic identity.

Authors

Eleni Bazigou, Oliver T.A. Lyons, Alberto Smith, Graham E. Venn, Celia Cope, Nigel A. Brown, Taija Makinen

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Figure 2

Development of venous valves.

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Development of venous valves. (A) Visualization of valve development by ...
(A) Visualization of valve development by X-gal staining in Tie2lacZ reporter mice and SEM imaging of veins that were opened with a longitudinal incision. 5 developmental stages were discerned: stage 0, rounding up of endothelial cells at the sites of developing valves; stage 1, valve endothelial cell alignment perpendicular to the longitudinal axis of the vessel; stage 2, formation of a circular shelf; stage 3, formation of the first commissure; stage 4, formation of the second commissure. Venous valve formation through these stages are shown in schematic form below, with the developing leaflets shown in blue. For stage 4 valve, only 1 of the leaflets is clearly visible. (B) Distribution of stage 0–stage 4 valves in mice of different ages (E18 to P42, n = 89, 143 valves; >P42, n = 12). Boxes denote interquartile range; lines within boxes denote median; whiskers denote range. Extreme outliers were excluded. (C) Percent stage 0–stage 4 valves at the indicated ages. (D) SEM images of resin cast of a stage 3 valve. Shown are 2 images from opposite sides of the same valve to demonstrate the single commissure stage in an adult mouse. Asterisks mark the entrance of a tributary. (E) SEM image of resin cast of a stage 4 valve (representative of 10 valves at various anatomical positions). Scale bars: 250 μm (A, photographs); 50 μm (A, SEM images); 200 μm (D and E).