RASA1 maintains the lymphatic vasculature in a quiescent functional state in mice

Abstract

RASA1 (also known as p120 RasGAP) is a Ras GTPase-activating protein that functions as a regulator of blood vessel growth in adult mice and humans. In humans, RASA1 mutations cause capillary malformation-arteriovenous malformation (CM-AVM); whether it also functions as a regulator of the lymphatic vasculature is unknown. We investigated this issue using mice in which Rasa1 could be inducibly deleted by administration of tamoxifen. Systemic loss of RASA1 resulted in a lymphatic vessel disorder characterized by extensive lymphatic vessel hyperplasia and leakage and early lethality caused by chylothorax (lymphatic fluid accumulation in the pleural cavity). Lymphatic vessel hyperplasia was a consequence of increased proliferation of lymphatic endothelial cells (LECs) and was also observed in mice in which induced deletion of Rasa1 was restricted to LECs. RASA1-deficient LECs showed evidence of constitutive activation of Ras in situ. Furthermore, in isolated RASA1-deficient LECs, activation of the Ras signaling pathway was prolonged and cellular proliferation was enhanced after ligand binding to different growth factor receptors, including VEGFR-3. Blockade of VEGFR-3 was sufficient to inhibit the development of lymphatic vessel hyperplasia after loss of RASA1 in vivo. These findings reveal a role for RASA1 as a physiological negative regulator of LEC growth that maintains the lymphatic vasculature in a quiescent functional state through its ability to inhibit Ras signal transduction initiated through LEC-expressed growth factor receptors such as VEGFR-3.

Vegfc acts through ERK to induce sprouting and differentiation of trunk lymphatic progenitors

“…Mice lacking both Spred1 and Spred2, or deficient in the RasGAP Rasa1, all of which are negative regulators of the MEK/ERK signaling cascade, display increased numbers of lymphatic endothelial cells (Lapinski et al, 2012;Taniguchi et al, 2007). Moreover, lymphatic endothelial cells in these mice exhibit ectopic ERK signaling and abnormal lymphatic function.…”

Unbiased RNAi screen for hepcidin regulators links hepcidin suppression to proliferative Ras/RAF and nutrient-dependent mTOR signaling

“…We further analyzed iron-related parameters in inducible knockout mice for the Ras suppressor Rasa1, a mouse model that develops a lymphatic vessel disorder. 51 We show that systemic disruption of Rasa1 expression, including liver and spleen tissues (supplemental Figure 6), for 6 weeks reduces liver hepcidin mRNA expression. Consistently, we observe a tendency for an increase of plasma iron and a decrease of spleen iron levels ( Figure 5G), whereas liver iron levels are not significantly changed between wildtype and Rasa1 knockout mice (data not shown).…”

Endothelial ERK signaling controls lymphatic fate specification

“…Binding of VEGF-C to VEGFR3 leads to activation of PI3K/AKT and RAF1/MEK/ERK signaling pathways, with the former playing a critical role in regulation of LEC migration (20,21). The role of ERK is suggested in studies demonstrating excessive LEC differentiation, subcutaneous hemorrhage, edema, and the presence of dilated lymphatic vessels in mice with deletions of the negative regulators of ERK signaling Spred1, Spred2, and Rasa1 (22,23). Nevertheless, the role of ERK signaling in lymphatic development and its mechanism of action have not been established.…”