Angiogenic switching in cerebral cavernous malformations driven by MAP3K3-PIK3CA synergy

Cerebral cavernous malformations are common vascular anomalies in the CNS that predispose individuals to seizures and haemorrhagic stroke. Familial forms are linked to germline loss-of-function mutations in CCM1-3, and sporadic lesions frequently harbour somatic gain-of-function mutations in MAP3K3 and PIK3CA. However, the mechanisms by which these somatic mutations drive lesion development remain incompletely understood, and no medical therapies are currently available. Here, we investigated the cooperative effects of MAP3K3I441M and PIK3CAH1047R mutations using transgenic neonatal and adult mouse models, supported by histology, micro-CT, bulk and single-cell RNA sequencing, and samples of human cerebral cavernous malformations. MAP3K3 I441M activated inflammatory and angiogenic transcriptional programmes in brain endothelial cells, whereas PIK3CAH1047R enhanced cell cycle and DNA replication pathways. Notably, MAP3K3I441M and PIK3CAH1047R double mutations synergistically amplified PI3K-AKT-mTOR signalling, inducing an 'angiogenic switch' reminiscent of tumour neovascularization. This interaction promoted endothelial angiogenesis and lesion development in mouse brains. Transcriptomic analyses of human cerebral cavernous malformations confirmed enrichment of angiogenesis-related gene signatures in double-mutation-related lesions. Treatment with the PI3Kα-selective inhibitor alpelisib suppressed lesion formation and reversed pro-angiogenic signalling in both mouse models and patient-derived cerebral cavernous malformation organoids. These findings uncover a convergent mechanism involving MAPK and PI3K pathway activation in the pathogenesis of cerebral cavernous malformations and demonstrate that PI3Kα inhibition might offer a viable therapeutic strategy for a disease that currently lacks effective pharmacological treatment.