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061. EphrinB2:EphB4 ratio is impaired in human cerebral cavernous malformations and contributes to pathologic alteration of endothelial phenotype

Authors: Julie Sesen

Introduction:
Cerebral cavernous malformations (CCM) are slow-flow low-pressure vascular lesions that can be sporadic or familial and exhibit aberrant endothelial function. Axon guidance factors (AGFs)—specifically EphrinB2 and EphB4—are major regulators of vascular development in the central nervous system. Dysregulation of EphrinB2 and EphB4 has been implicated in the development of related cerebrovascular diseases, atypical angiogenesis, and anomalous endothelial-to-mesenchymal transition, in which endothelial-specific behavior is lost. We hypothesize that dysregulation of the EphrinB2/EphB4 ratio is contributory to the pathogenesis of CCM through impaired endothelial cell function.Methods: Patient-derived endothelial cells (ECs) were established from surgically resected CCMs to investigate the potential dysregulation of EphrinB2 and EphB4. CCM ECs phenotypes were evaluated via western blot and tube formation assays and compared to control ECs. Surgical specimens were analyzed by immunohistochemistry.
Results:
Human primary CCM ECs exhibit decreased expression of the endothelial cell marker CD31 and increased expression of the smooth muscle cell-marker ?SMA, relative to control ECs. Functionally, CCM ECs displayed disorganized tube formation versus controls. EphB4 expression is decreased, and EphrinB2 is increased in CCM ECs compared to normal ECs in vitro. Immunostaining of patient operative specimens validated this trend, revealing increased EphrinB2 and decreased EphB4 expression in CCM compared to normal brain.
Conclusion:
These findings reveal that CCMs have altered regulation of EphrinB2 and EphB4, which increases our understanding of how AGFs influence CCM development. The dysregulation of EphrinB2:EphB4 ratio is important as it offers a mechanism that helps to explain the pathogenesis of abnormal vessel formation in CCM. These findings have clinical implications, both diagnostically (as Ephrin levels are quantifiable with non-invasive testing, such as urine), and therapeutically (as potential druggable targets on the cell surface).