Mechanotransduction activates canonical Wnt/β-catenin signaling to promote lymphatic vascular patterning and the development of lymphatic and lymphovenous valves

Abstract

Lymphatic vasculature regulates fluid homeostasis by returning interstitial fluid to blood circulation. Lymphatic endothelial cells (LECs) are the building blocks of the entire lymphatic vasculature. LECs originate as a homogeneous population of cells predominantly from the embryonic veins and undergo stepwise morphogenesis to become the lymphatic capillaries, collecting vessels or valves. The molecular mechanisms underlying the morphogenesis of the lymphatic vasculature remain to be fully understood. Here we show that canonical Wnt/β-catenin signaling is necessary for lymphatic vascular morphogenesis. Lymphatic vascular-specific ablation of β-catenin in mice prevents the formation of lymphatic and lymphovenous valves. Additionally, lymphatic vessel patterning is defective in these mice, with abnormal recruitment of mural cells. We found that oscillatory shear stress (OSS), which promotes lymphatic vessel maturation, triggers Wnt/β-catenin signaling in LECs. In turn, Wnt/β-catenin signaling controls the expression of several molecules, including the lymphedema-associated transcription factor FOXC2. Importantly, FOXC2 completely rescues the lymphatic vessel patterning defects in mice lacking β-catenin. Thus, our work reveals that mechanical stimulation is a critical regulator of lymphatic vascular development via activation of Wnt/β-catenin signaling and, in turn, FOXC2.

Lymphatic Vessel Network Structure and Physiology

“…Intriguingly, Wnt5b was recently found to induce LEC specification through β-catenin signaling in the zebrafish (765). On the other hand, β-catenin signaling is not critical for the specification of LEC progenitors during mouse embryonic development, but is essential for lymphatic vascular morphogenesis (174). …”

“…In cultured LEC, β-catenin was shown to be necessary for the upregulation of the valve formation genes Foxc2 and Gata2 in response to oscillatory shear stress. Therefore, β-catenin signaling is a critical regulator of valve formation (174). In addition, Ephb4 is not only important for collecting lymphatic vessel valve formation but also critical for lymphovenous valve formation.…”

“…However, little is known about how each of these molecules contributes to lymphatic permeability regulation. Interestingly, mice with a lymphatic-specific deletion of β-catenin have severe defects in the formation of lymphatic valves and are embryonic lethal, providing another potential link between defects in valve formation and permeability regulation (174). …”

<b>Fine structure of human thoracic duct as revealed by light and scanning electron micr</b><b>oscopy </b>

“…Meanwhile, the area of the valves and their vicinity showed elongated or rhomboidal endothelial cells contacted tightly with each other, it being different from endothelial mode of the lymphangions, and moreover, the long axial directions of the cells on the valve tips were perpendicular to those on the valvular bases. The present findings, therefore, afford a precise configuration and array of the endothelial cells in the thoracic duct valve territory in which molecular insights into lymphatic valve development have been recently described (2,3). This unique organization of the endothelial cells on the valves is presumed to avail for structural endurance for mechanical stress by propulsive lymph transport between distal and proximal lymphangions.…”

Effect of fluid shear stress on in vitro cultured ureteric bud cells

“…It is possible that FSS could have triggered these signaling pathways in UB cells and led to the enrichment of tip cell population. In this regard, it is of interest to note that FSS has been shown to trigger Wnt/β-catenin signaling in lymphatic endothelial cells, 33 while Wnt/β-catenin signaling is known to be essential in maintaining UB cells in a precursor state 34 . FSS has also been shown to activate mTOR-dependent pathway in kidney tubules, 35 while mTOR pathway is known to maintain Ret expression in UB tip cells 31 .…”