Notch signaling functions in lymphatic valve formation

Abstract

Collecting lymphatic ducts contain intraluminal valves that prevent backflow. In mice, lymphatic valve morphogenesis begins at embryonic day 15.5 (E15.5). In the mesentery, Prox1 expression is high in valve-forming lymphatic endothelial cells, whereas cells of the lymphatic ducts express lower levels of Prox1. Integrin α9, fibronectin EIIIA, Foxc2, calcineurin and the gap junction protein Cx37 are required for lymphatic valve formation. We show that Notch1 is expressed throughout the developing mesenteric lymphatic vessels at E16.5, and that, by E18.5, Notch1 expression becomes highly enriched in the lymphatic valve endothelial cells. Using a Notch reporter mouse, Notch activity was detected in lymphatic valves at E17.5 and E18.5. The role of Notch in lymphatic valve morphogenesis was studied using a conditional lymphatic endothelial cell driver either to delete Notch1 or to express a dominant-negative Mastermind-like (DNMAML) transgene. Deletion of Notch1 led to an expansion of Prox1high cells, a defect in Prox1high cell reorientation and a decrease in integrin α9 expression at sites of valve formation. Expression of DNMAML, which blocks all Notch signaling, resulted in a more severe phenotype characterized by a decrease in valves, failure of Prox1high cells to cluster, and rounding of the nuclei and decreased fibronectin-EIIIA expression in the Prox1high cells found at valve sites. In human dermal lymphatic endothelial cells, activation of Notch1 or Notch4 induced integrin α9, fibronectin EIIIA and Cx37 expression. We conclude that Notch signaling is required for proper lymphatic valve formation and regulates integrin α9 and fibronectin EIIIA expression during valve morphogenesis.

Foxc1 and Foxc2 deletion causes abnormal lymphangiogenesis and correlates with ERK hyperactivation

“…hi LECs clustered and reoriented in littermate control mice by at least 45° at E18.5, as described previously (22,44,46) (Supplemental Figure 7, B and E). In contrast, the clustering and reorientation of PROX1…”

Leukotriene B 4 antagonism ameliorates experimental lymphedema

“…8A), as shown in previous studies (26,27,30). With lymphatic abrogation, Notch1 LECKO mice developed lymphedema accompanied by hypersprouting and enlarged, dysfunctional lymphatic vessels that were unable to take up FITC-dextran (Fig.…”

Lymphatic Vessel Network Structure and Physiology

“…Notch1 also plays a role in lymphatic valve development by regulating the key factors of valve formation, Cx37, Itga9 , and fibronectin ( FNEIIIA ). Lymphatic endothelial-specific loss of Notch signaling resulted in defective valve formation and decreased FNEIIIA and Itga9 expression (739). Taken together, these data demonstrated that oscillatory shear stress, junction proteins, and ECM proteins play critical roles in valve formation.…”