YAP and TAZ maintain PROX1 expression in the developing lymphatic and lymphovenous valves in response to VEGF-C signaling

Abstract

Lymphatic vasculature is an integral part of digestive, immune and circulatory systems. The homeobox transcription factor PROX1 is necessary for the development of lymphatic vessels, lymphatic valves (LVs) and lymphovenous valves (LVVs). We and others previously reported a feedback loop between PROX1 and Vascular Endothelial Growth Factor-C (VEGF-C) signaling. PROX1 promotes the expression of the VEGF-C receptor VEGFR3 in lymphatic endothelial cells (LECs). In turn, VEGF-C signaling maintains PROX1 expression in LECs. However, the mechanisms of PROX1/VEGF-C feedback loop remain poorly understood. Whether VEGF-C signaling is necessary for LV and LVV development is also unknown. Here, we report for the first time that VEGF-C signaling is necessary for valve morphogenesis. We have also discovered that the transcriptional co-activators YAP and TAZ are required to maintain PROX1 expression in LVs and LVVs in response to VEGF-C signaling. Deletion of Yap and Taz in the lymphatic vasculature of mouse embryos did not affect the formation of LVs or LVVs, but resulted in the degeneration of these structures. Our results have identified VEGF-C/YAP/TAZ as a critical molecular pathway in valve development.

Mechanosensation and Mechanotransduction by Lymphatic Endothelial Cells Act as Important Regulators of Lymphatic Development and Function

“…Flow-generated mechanical forces and molecular factors that are involved in lymphatic valve formation, such as FOXC2, GATA2, PROX1, integrin α9, connexin 37, and Wnt/ß-catenin signaling, were shown to contribute to LVV morphogenesis [ 124 , 138 , 140 , 141 , 142 ]. The role of YAP/TAZ signaling in the development and maintenance of LVVs is also suggested by a recent study [ 134 ].…”

“…Numerous molecules and pathways, such as ephrin B2 [ 117 ] and B4 [ 120 ], angiopoietin 2 [ 121 ], integrin α9 [ 24 ], transcription factor nuclear factor of activated T cells 1 (NFATc1) [ 25 , 71 ], connexin 37 and 43 [ 71 , 122 ], bone morphogenetic protein (BMP-9) [ 123 ], mechanically induced Wnt/ß-catenin signaling [ 124 ], RAS p21 protein activator 1 (RASA1) [ 125 ], VEGFR-3 signaling [ 126 , 127 ] FAT4 [ 72 , 128 ], platelet endothelial cell adhesion molecule (PECAM) [ 129 ], vascular endothelial cadherin (VE-cadherin) [ 130 ], neuropilins, semaphorins, and plexins, [ 131 , 132 ] have been revealed to contribute to the development of the intraluminal lymphatic vessel valves. Recent data suggest that yes-associated protein (YAP)/transcriptional coactivator with PDZ-binding motif (TAZ) signaling might be critical for the maturation and maintenance of lymphatic valves [ 133 , 134 ]. Transcription factors GATA2 [ 135 ], FOXC2 [ 25 , 136 ], and PROX1 [ 71 ] were identified as key molecular factors of the lymphatic valve development, and their expression is also critical for the maintenance of these structures [ 137 , 138 , 139 ].…”

“…Recent studies suggest the possible role of YAP/TAZ signaling in flow-dependent regulation of gene transcription in LECs. Transcription factor TAZ is expressed in lymphatic valve forming LECs [ 133 , 134 , 137 ], and in vitro data suggest that 4 dynes/cm 2 , ¼ Hz OSS enhances the nuclear translocation of YAP and TAZ, which is necessary for their function in regulating gene transcription [ 137 ]. Some investigators in their in vitro and in vivo experiments found that VEGF-C signaling is also capable of inducing the YAP/TAZ pathway that in turn enhances the expression of PROX1 [ 134 ].…”

“…Transcription factor TAZ is expressed in lymphatic valve forming LECs [ 133 , 134 , 137 ], and in vitro data suggest that 4 dynes/cm 2 , ¼ Hz OSS enhances the nuclear translocation of YAP and TAZ, which is necessary for their function in regulating gene transcription [ 137 ]. Some investigators in their in vitro and in vivo experiments found that VEGF-C signaling is also capable of inducing the YAP/TAZ pathway that in turn enhances the expression of PROX1 [ 134 ]. However, other researchers reported that YAP/TAZ signaling is negatively regulated by the VEGF-C–VEGFR-3 pathway and represses PROX1 expression [ 133 ].…”

Vascular endothelial cell specification in health and disease

“…Similar to early LEC specification from progenitor cells, VEGF-C signaling plays an important role in the upregulation of PROX1 in the cells located in the valve-forming region [213]. VEGF-C-VEGFR3 signaling promotes the upregulation of PROX1 in valve-forming LECs through the activation of the transcriptional co-activators YAP and TAZ [213]. However, the mechanisms by which VEGF-C signaling promotes valve formation in restricted localized areas within the lymphatic vasculature remains unknown.…”