Abstract 5295: Impaired Tube Formation and Endothelial Barrier Function in a Mouse Model of Human Vascular Malformation
INTRODUCTION: Cerebral cavernous malformation (CCM) is a common vascular dysplasia that affects both systemic and CNS blood vessels. Heterozygous loss of function mutations in osmosensing scaffold for MEKK3 (OSM) cause CCM. We hypothesized that OSM would be essential for vascular morphogenesis and development in an endothelial autonomous manner. To investigate this hypothesis we studied mice with two distinct mutations in Osm - a gene trap mutation, and a tissue specific (Cre-Lox) conditional mutation. We use siRNA to study the role of OSM in vitro, and translate our observations from homozygous mutants and cell culture to revisit vascular physiology in heterozygous mice, the genotype equivalent of human CCM.
RESULTS: Mice with homozygous mutations in Osm show growth arrest by embryonic day 9.5, and die by day 11.5. We show that targeted disruption of Osm in mice results in failed lumen formation and early embryonic death through an endothelial cell autonomous mechanism. The first essential angiogenic event, the formation of the first branchial arch artery is impaired in homozygous mutants. We used siRNA to inhibit expression of OSM in umbilical artery (HUVEC) and microvascular (HMVEC) endothelial cells. We demonstrate that OSM regulates endothelial cytoskeletal architecture, cell-cell interactions and lumen formation. These findings suggest activation of the small GTPase RhoA. We observe increased active (GTP bound) RhoA in OSM depleted HMVECs. Our observations in homozygous mutant embryos, and endothelial cell culture led us to revisit mice with heterozygous mutations in Osm. These mice are viable and fertile, and do not develop cavernous malformations like human CCM patients (their genotype equivalents). We hypothesized that subtle abnormalities of endothelial cell-cell interaction would be present in these mice, and demonstrate impaired endothelial barrier function when stimulated as compared to wild type littermates. This increased vascular permeability can be reversed by inhibition of Rho in vivo.
CONCLUSIONS: OSM is essential for endothelial cell-cell interactions and normal barrier function. Impaired endothelial interactions may be a common mechanism underlying vascular malformations.
This research has received full or partial funding support from the American Heart Association, AHA Western States Affiliate (California, Nevada & Utah).