Aberrant methylation events in arteriovenous malformation of the brain

Introduction: Arteriovenous malformation of the brain (bAVM) is a vascular condition affecting brain arterioles. It most likely arises due to an impaired expression of vascular differentiation markers that leads failed capillary bed development and, then, to the arteriolar-to-venule direct shunt. In this context, EFNB2 and ephrin-B4 seem to drive arteriovenous differentiation. Although several pathways have been linked to disease development, knowledge on the molecular basis of this phenotype is still very limited.

Methods: Methylome analysis was performed in endothelial cells purified from bAVM in order to identify aberrant methylation patterns in genes controlling vascular development and endothelial cell/vascular smooth muscle cell (VSMC) cross-talk. Human cerebral microvascular endothelial cells (HCMECs) were used as the control. The results were validated by quantitative methylation-specific PCR and quantitative real-time PCR.

Results: Both CpG- and CHG-aberrant methylation events were identified in bAVM endothelial cells. Most differentially methylated loci included noncoding RNA genes. Genes already known to be linked to bAVM development were identified. Interestingly, we focused our attention on the EPHB1 gene, not yet linked to bAVM onset. Likewise, other differentially methylated genes included transcription factors expressed in VSMCs that regulate the expression of genes involved in endothelial cell differentiation.

Conclusion: Our data allow to identify aberrant methylation events occurring in bAVM endothelial cells when compared to HCMECs. Notably, these genes are clustered in pathways related to vascular homeostasis, as well as to VSMC-- endothelial cell crosstalk, suggesting that an impairment of this interaction plays a prominent role in the loss of vascular differentiation in bAVM phenotypes.