Abstract 116: Increased Collagen I/Collagen III Ratio is Associated With Hemorrhage in Brain Arteriovenous Malformations in Human and Mouse

Abstract

Background and purpose: Brain arteriovenous malformation (bAVM) is an important risk factor for hemorrhagic stroke in young adults, but the underlying mechanisms are unclear. Increase of Col I/Col III ratio enhances vessel wall stiffness and renders vessel less resistant to changes of blood flow and pressure. Hypothesis: Col I/Col III ratio is increased in bAVM vessels, which is associated with bAVM hemorrhage. Method: Human bAVMs were collected from HHT and sporadic bAVM patients. Temporal lobe specimens from epilepsy patients were used as controls. Three mouse models were used: 1) PdgfbicreER; Alk1 f/f ; 2) PdgfbicreER; Eng f/f ; 3) Alk 1 f/f . Mice in models 1 and 2 have Pdgfb promoter driving, tamoxifen (TM) inducible cre expression in endothelial cells (ECs). BAVMs were induced by intra-brain injection of AAV-VEGF to induce angiogenesis and i.p. injection of TM to delete Alk1 or Eng in ECs. In model 3, bAVMs were by intra-brain injection of AAV-VEGF and an adenoviral vector expressing Cre to delete Alk1 gene focally. Colony stimulating factor receptor inhibitor (PLX5622) was given to Alk1 f/f mice 8 week after model induction when bAVMs have fully developed to transiently deplete microglia. Vascular Col I and Col III levels were analyzed by immunostaining using anti- CD31 and anti-Col I or Col II antibodies. Brain AVM bleeding was detected by Prussian blue staining, and RNA-Sequencing used to study gene profiles. Results: Col I and Col III levels and the Col I/Col III ratio were higher in the vessels of human HHT and sporadic bAVM than controls. Col I/Col III ratio was higher in ruptured than unruptured sporadic bAVM. RNA-seq data shown that Col I and Co III mRNA levels were higher in Eng deficient bAVMs than normal brain angiogenic regions. Col I and Col III levels were higher on Alk1 and Eng deficient bAVMs compared to normal vessels. Col I/Col III ratio was also increased in the Alk1 deficient bAVMs. Depletion of microglia by PLX5622 reduced Col I and Col III levels and reduced microhemorrhage of Alk1 deficient bAVMs. Conclusion: Col I, Col III and Col I/Col III ratio are increased on human and mouse bAVM vessels, which is associated with bAVM hemorrhage. Depletion of microglia reduces Col I and Col III and hemorrhage in bAVMs in mice.