UC San Diego

Cerebral Cavernous Malformations (CCM) are central nervous system vascular anomalies that arise primarily due to loss-of-function mutations in KRIT1, CCM2, or PDCD10 (CCM3). CCM are characterized by endothelial dysfunction and the loss of endothelial junctions, leading to grossly-dilated blood vessels and increased vascular permeability. Previous studies demonstrate that CCM are hypersensitive to angiogenesis due to the loss of an anti-angiogenic checkpoint and increased VEGF signaling. Here, we report that loss of PDCD10 in brain endothelial cells causes upregulation of eNOS in CCM lesions. Furthermore, elevated eNOS expression results in increased secretion of NO, an important intercellular messenger in the CNS responsible for vascular remodeling and angiogenesis. To analyze the effect of upregulated eNOS and release of NO during CCM, we prepared co-culture studies using purified astrocytes and mouse brain microvascular endothelial cells (BMEC) harboring inactivated Pdcd10 (Pdcd10ECKO). Increased levels of eNOS in Pdcd10ECKO BMEC induced upregulation of astrocyte-derived Vegfa. The increase in astrocyte-derived Vegfa mRNA was specific to the upregulation of eNOS because genetic inactivation of one copy of the Nos3 gene in Pdcd10ECKO BMEC was sufficient to prevent Vegfa upregulation in astrocytes. Moreover, upregulation of eNOS in Pdcd10ECKO BMEC was correlated with HIF-1 protein stabilization in astrocytes during co-culture studies. These studies identify that increased expression of eNOS during CCM may lead to augmented levels of NO capable of stabilizing HIF-1 protein and inducing astrocyte-derived VEGF. Therefore, we propose the possibility that CCM lesion formation and progression can be exacerbated by the non-cell-autonomous release of VEGF from perivascular astrocytes.