SUMMARY
RAS signaling has been implicated in a wide spectrum of processes central to normal development and
disease. Human mutations in RASA1 (a GAP negative regulator of RAS) are associated with capillary
malformation-arteriovenous malformations (CM-AVM). These comprise a group of non-cancerous vascular
lesions characterized by hyperproliferative endothelial cells that form abnormal and fragile blood vessels. CM-
AVMs are underdiagnosed, but when identified in the clinic are often responsible for seizures, internal
hemorrhage, and/or stroke.
Germline mutations affecting one RASA1 allele alone are insufficient to give rise to vascular anomalies. For
pathologic malformations to arise, additional somatic mutations are necessary. Open questions in the field
include: 1) What are the secondary hits that trigger malformations in the context of RASA1 haploinsufficiency
and, 2) How do the additional altered genes collaborate with RASA1 mutations to facilitate the emergence of
abnormal vessels? Answers to these questions are needed to develop pharmacological interventions and to
develop strategies to restore vascular homeostasis. Here we will use novel mouse models that reproduce AVMs
in several organs to study the biological consequences of RASA1 loss. Preliminary experiments revealed that
RASA1 is a critical regulator of endothelial cell-cell junctions and vascular integrity. In addition, we found that
RASA1-haploinsufficiency in mice provides a sensitized genetic platform that can be used to interrogate the
effect of potential second-hit targets. Genetic combinatorial effects can be tested, followed, and studied in a
highly tractable murine ear assay. Based on our preliminary data, we hypothesize that RASA1
haploinsufficiency alters junctional complexes, and sensitizes endothelial cells to the emergence of vascular
malformations. Two aims were developed to test this hypothesis: (1) To identify partners that synergize with
RASA1 haploinsufficiency to promote the emergence of vascular malformations and, (2) To elucidate molecular
targets that act downstream of RASA1 to promote junctional complex integrity and resist emergence of vascular
anomalies. Mechanistic experiments will be performed with human cells and several mouse models. In addition,
we will extend validation to human lesions through retrospective analysis of donor tissue. Clarifying the
contribution of RASA1 to vascular homeostasis could offer an unprecedented opportunity for intervention by
identifying the key players in this debilitating condition. In addition, understanding cooperating genes will
improve screening protocols and benefit patients harboring RASA1 mutations who live with an elevated lifetime
risk of complications from AVMs. The proposed studies will be directly applicable to the clinical setting of RAS-
related malformations, as they will broaden our understanding of the disease and potentially aid in stratifying
patients toward specific management paradigms.