RASA1 functions in EPHB4 signaling pathway to suppress endothelial mTORC1 activity

Abstract

Vascular malformations are linked to mutations in RAS p21 protein activator 1 (RASA1, also known as p120RasGAP); however, due to the global expression of this gene, it is unclear how these mutations specifically affect the vasculature. Here, we tested the hypothesis that RASA1 performs a critical effector function downstream of the endothelial receptor EPHB4. In zebrafish models, we found that either RASA1 or EPHB4 deficiency induced strikingly similar abnormalities in blood vessel formation and function. Expression of WT EPHB4 receptor or engineered receptors with altered RASA1 binding revealed that the ability of EPHB4 to recruit RASA1 is required to restore blood flow in EPHB4-deficient animals. Analysis of EPHB4-deficient zebrafish tissue lysates revealed that mTORC1 is robustly overactivated, and pharmacological inhibition of mTORC1 in these animals rescued both vessel structure and function. Furthermore, overexpression of mTORC1 in endothelial cells exacerbated vascular phenotypes in animals with reduced EPHB4 or RASA1, suggesting a functional EPHB4/ RASA1/mTORC1 signaling axis in endothelial cells. Tissue samples from patients with arteriovenous malformations displayed strong endothelial phospho-S6 staining, indicating increased mTORC1 activity. These results indicate that deregulation of EPHB4/RASA1/mTORC1 signaling in endothelial cells promotes vascular malformation and suggest that mTORC1 inhibitors, many of which are approved for the treatment of certain cancers, should be further explored as a potential strategy to treat patients with vascular malformations.

Endothelial Mitogen-Activated Protein Kinase Kinase Kinase Kinase 4 Is Critical for Lymphatic Vascular Development and Function

“…Few mouse models display lymphatic dysfunction and chyle leakage, and these mice genetically map out a signaling pathway that is critical for lymphatic development and function, including gain or loss of Vegf-c or Vegfr3 (28,29), loss or mutation of Ephrinb2 (30) or Ephb4 (31) and Rasa1 (10,32), or gain of function of Ras and Erk (22,33,34). Furthermore, the similarity of the phenotypes of these animal models and mice lacking endothelial Map4k4 strongly suggested that Map4k4 functions within this signaling pathway.…”

Identification of functional networks associated with cell death in the retina of OXYS rats during the development of retinopathy

“…36 In addition, the Rasa1 gene is a known negative regulator of the Ras pathway via enhancement of activity of the GAP proteins (GTPase-activating proteins). 37 The strain of mice deficient in Rasa1 is characterized by the death of neuronal cells, disorganization of blood vessels, and high embryonic mortality. 38 The most substantial changes in the expression of genes involved in the processes of regulation of cellular death were uncovered here in the retina of 3-month-old OXYS rats.…”

Constitutively active Notch4 receptor elicits brain arteriovenous malformations through enlargement of capillary-like vessels

“…Genetic deletion of each of these genes has revealed that they are required for normal vascular development and prevention of AVM formation (6)(7)(8). Mutations in SMAD4, RASA1, and PTEN have also been linked to AVMs in humans (9,10), and mutations in Rasa1 lead to AV shunting in zebrafish (11).…”