Augmented endothelial exocytosis of angiopoietin-2 resulting from CCM3-deficiency contributes to the progression of cerebral cavernous malformation

Cerebral cavernous malformations (CCMs) are vascular malformations that affect the central nervous system and result in cerebral hemorrhage, seizure and stroke. CCM arises from loss-of-function mutations in one of three genes: CCM1, CCM2 and CCM3 (PDCD10). CCM3 mutations in human often result in a more severe form of the disease, and CCM3 knockout mice show severe phenotypes with yet-to-be defined mechanisms. We have recently reported that CCM3 regulates UNC13 family-mediated exocytosis. Here we investigate endothelial cells (EC) exocytosis in CCM disease progression. We find that CCM3 suppresses UNC13B/VAMP3-dependent exocytosis of angiopoietin-2 (ANGPT2) in brain endothelial cells. CCM3 ablation in EC augments exocytosis and secretion of ANGPT2, correlating with destabilized EC junctions, enlarged lumen formation, and endothelial cell-pericyte dissociations. UNC13B deficiency that blunts ANGPT2 secretion from EC or an ANGPT2 neutralization antibody normalizes the defects caused by CCM3 deficiency. More importantly, ANGPT2 neutralization antibody treatment or UNC13B deficiency blunts the CCM lesion phenotypes, including disruption of EC junctions, vessel dilation and pericyte dissociation, in the brains and retinas caused by endothelial cell-specific CCM3 inactivation. Our study reveals that enhanced secretion of ANGPT2 in endothelial cells contributes to the progression of the CCM disease, providing a novel therapeutic approach to treat this devastating pathology.