Abstract 3169: Reduced PDGFR-beta Expression After Regional Alk1 Deletion and VEGF Stimulation in the Brain is Associated with Reduced Mural Cell Coverage
Background and Purpose: About 2% of brain arteriovenous malformations (bAVM) are attributable to Hereditary Hemorrhagic Telangectasia (HHT). Previously we created a bAVM model in the adult mouse using regional Alk1 (the causal gene in HHT2) deletion and VEGF stimulation, and reported that the dysplastic vessels in this model have less smooth muscle cell coverage than the normal cerebrovasculature. We hypothesized that VEGF stimulation in the setting of Alk1 loss-of-function leads to impaired mural cell coverage through reduction of platelet-derived growth factor receptor (PDGFR) signaling, and is associated with impaired cerebrovascular integrity.
Methods: Brain AVM formation was induced by injection of 2X107 PFU adenoviral vector expressing cre-recombinase (AdCre) and 2X109 genome copies of adeno-associated viral vector (AAV) expressing VEGF (AAV-VEGF) into the basal ganglia of Alk1-floxed mice (loxP sites flanking Exons 4-6). The brain samples were collected 8 weeks after vector injection. Intra-parenchymal hemorrhage, microglial/macrophage counts, Alk1 and PDGFR/PDGFB protein expression were evaluated using Prussian blue staining, Iba1 staining and Western blot.
Results: We found a 66±27% reduction in Alk1 protein expression around the injection site of the AdCre and AAV-VEGF-treated group compared with the control vector treated group (p=0.002, ANOVA). Fresh red blood cells (RBCs) were detected in the extravascular space in the Alk1-deficient brain parenchyma (Ad-Cre-treated Alk1-floxed mice), with ≈10-fold increase of Prussian blue coverage area compared to the brain with intact Alk1 gene (Ad-GFP-treated Alk1-floxed mice; p=0.016, rank sum test; or AdCre-treated wild-type mice, p=0.010, rank sum test) after VEGF stimulation. The area of Prussian blue coverage was positively correlated with the number of Iba1+ cells (R2=0.39, p<0.05). Alk1 deletion resulted in a 26±10% reduction of PDGFR-beta expression compared to controls (p<0.001; ANOVA) after VEGF stimulation. However, Alk1 deletion did not affect the level of one of the PDGFR-beta ligands, PDGF-B.
Conclusions: These results indicate an important role for Alk1 in maintaining cerebrovascular integrity as shown by its effect on pericyte function through interaction with PDGFR-beta signaling. Alk1 deletion plus VEGF stimulation reduced vessel wall integrity that was associated with an inflammatory response. Altered pericyte-endothelial cell interaction may play a causal role in the pathogenesis of human bAVM, possibly involving a local inflammatory response associated with RBC extravasation.
- © 2012 by American Heart Association, Inc.