Abstract TMP3: Overexpression of Alk1 in Brain Endothelial Cells Alleviates the Severity of Brain Arteriovenous Malformations in Alk1 Mutant Mice

Abstract

Background and purpose: Brain arteriovenous malformation (bAVM) can cause life threatening intra-cranial hemorrhage. Currently, there is no effective medical therapy available to treat bAVM patients. Mutation of activin receptor-like kinase 1 ( Alk1 also called ACVRL1 ) causes a familiar form of bAVM. Genetically overexpression of Alk1 in endothelial cells (ECs) recurs the phenotype of Alk1 deficient mice. We hypothesize that transduction of Alk1 gene into brain ECs using an adeno associated viral vector (AAV) may lead to cure of bAVM in Alk1 mutant mice. Methods: To identify a AAV capsid that can transduce brain ECs after intravenous (i.v.) delivery, several engineered AAV capsids were screened. A single-stranded CBA promoter driven tdTomato transgene was packaged in these capsids and delivered i.v. to wild-type mice. Tissues were collected 4 weeks later. After identifying a capsid, cc84, that can transduce brain ECs effectively after i.v. deliver, we package CMV-Alk1 transgene into AAV.cc84. Brain AVMs were induced on PdgfbiCre; Alk1 f/f mice through intra-brain injection of AAV1-VEGF followed by intraperitoneal injection of 1.25 mg/25g tamoxifen two weeks later. AAV.cc84-Alk1 was delivered to PdgfbiCre; Alk1 f/f mice through i.v. injection at the time of tamoxifen treatment Histological analyses were used to analyze viral transduction in the brain and liver, vessel density, and abnormal vessels in the brain and liver inflammation. Liver and kidney function were analyzed by colorimetric assays for Alkaline Phosphatase Activity (ALP), Alanine Transaminase Activity ALT), and Creatinine levels (Cr). Results: After i.v. injection, AAV-cc84 transduced a high percentage of brain ECs and a few hepatocytes. AAV.cc84-Alk1 treatment reduced vessel density (p=0.008), abnormal vessels (p=0.034), mouse mortality rates (20% vs 60% respectively) compared to the AAV.cc84-RFP (control vector) treated PdgfbiCre; Alk1 f/f mice. The levels of ALP, ALT and Cr were similar between AAV injected and uninjected mice. Conclusion: AAV.cc84 mediated EC overexpression of Alk1 reduced bAVM severity in Alk1 deficient mice indicating that AAV.cc84 is a promising gene therapy vector to treat bAVMs.