Abstract DP171: Balancing EphrinB2:EphB4 Ratio Alleviates the Severity of Brain Arteriovenous Malformation

Background and Purpose: Arteriovenous malformations (AVMs) are abnormal connections of vessels that shunt blood directly from arteries into the veins without any capillary bed. Vessels in the brain AVMs, have reduced mural cells and are prone to rupture, resulting in intracranial hemorrhage. EphrinB2/EphB4 signaling maintains vascular integrity. It has been indicated that the ratio of EphrinB2 to EphB4 is critical for normal angiogenesis, which is reduced in cerebral AVMs. Hypothesis: Reduction of EphrinB2 in endothelial cells (ECs) enhances the severity of brain AVMs. Balancing the EphrinB2/EphB4 ratio reduces the severity of brain AVMs. Methods: BAVMs were induced by Eng deletion in adult Eng -floxed mice ( Eng f/f ) globally or in ECs using a rosa promoter driving ( Rosa-creER ) or a platelet-derived growth factor b promoter driving ( Pdgfb- icreER) estrogen inducible cre. Brain angiogenesis was induced by the injection of AAV-VEGF into the brain. Pdgfb- icreER was also used to delete EphrinB2 together with Eng in the endothelial cells (ECs) in mice with both EphrinB2 and Eng gene floxed. Pre-clustered Ephrin B2-Fc was delivered intraperitoneally to RosaCreER ; Eng f/f mice and Pdgfb-icreER:Eng f/f mice twice per week for 2 weeks, starting 6 weeks after AVM induction. The brains were taken 8 weeks after AVM induction to study vessel density, dysplasia vessels, mural cell coverage, microhemorrhage, and gene expression profile. Results: Co-deletion of EphrinB2 with Eng in ECs increased the dysplasia index, the penetrance of bAVM phenotype from 46% ( Eng EC deletion alone) to 100%, and smooth muscular negative vessels. RNAseq data showed that EphB4 gene expression is increased in bAVMs of global and EC Eng deleted mice compared to the wild-type mice, suggesting an imbalance of the EphrinB2/EphB4 ratio in bAVMs. EphrinB2-Fc treatment reduced vessel density and dysplasia vessels; increased vascular pericyte and smooth muscle cell coverage; decreased microhemorrhage in bAVMs of mice with global or EC Eng deletion. IgG-fc staining showed that the intraperitoneal injected EphrinB2-Fc entered the bAVM region. RNAseq results showed that EphrinB2-Fc treatment reduced the expression of pro-angiogenic and pro-inflammatory genes. Conclusion: Co-deletion of EphrinB2 with Eng in ECs enhances bAVM severity. Balancing the EphrinB2/EphB4 ratio by EphrinB2-Fc treatment reduced bAVM severity through reducing angiogenesis and inflammation.