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 6

Differential requirement of integrin-α9 and ephrin-B2 for the maintenance of venous and lymphatic valves.

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Differential requirement of integrin-α9 and ephrin-B2 for the maintenanc...
(A–F) SEM images of venous valves of adult control and Itga9 and Efnb2 mutant mice (3 valves per genotype) after oral administration of tamoxifen for 2 weeks. (B, D, and F) Higher-magnification views of the boxed regions in A, C, and E, respectively. Arrows denote valve leaflets. (G–L) Immunofluorescence of ears of control Prox1-CreERT2 (G and H), Itga9lx/lx;Prox1-CreERT2 (I and J) and Efnb2lx/lx;Prox1-CreERT2 (K and L) adult mice (n = 3 per genotype) using antibodies against PECAM-1 (green) and podoplanin (red). Arrows denote valves. (H, J, and L) Higher-magnification views of boxed regions in G, I, and K, respectively. (M and N) Immunofluorescence of ears of control Prox1-CreERT2 (M) and Itga9lx/lx;Prox1-CreERT2 (N) adult mice after oral administration of tamoxifen for 2 weeks, using antibodies against PECAM-1 (red) and integrin-α9 (green). Note the reduced expression of integrin-α9 in the Itga9 mutants. (O) Number of lymphatic valves in the ear skin of adult control and Itga9 and Efnb2 mutant mice. Data represent mean ± SD valves in 0.5-mm2 dermal area (n = 3 per genotype, 2 random areas per mouse). **P = 0.005, ***P < 0.001, t test. Scale bars: 500 μm (A, C, and E); 50 μm (B, D, F, G, I, and K); 20 μm (H, J, L, M, and N).