Tumor-like proliferation of CCM3 knockout endothelial cells: insights from semaxinib treatment and transcriptome profiling of co-cultures.

Cerebral cavernous malformations (CCMs) are vascular lesions associated with severe neurological complications. Increasing evidence suggests that cancer-like mechanisms, like an abnormal expansion of CCM3 knockout (KO) endothelial cells (ECs) in co-culture with wild-type (WT) cells, contribute to lesion formation. Yet, the underlying processes remain poorly understood. Here, we employed a human induced pluripotent stem cell (iPSC)-derived EC co-culture model to screen a cytokine inhibitor library for modulators of this tumor-like behavior. We identified the known VEGFR2 inhibitor semaxinib which selectively suppressed proliferation of WT ECs in co-culture, but not in monoculture. In contrast, CCM3 KO cells maintained their abnormal expansion under semaxinib treatment which was unaffected by modulation of extracellular VEGFA levels. RNA-seq profiling revealed distinct transcriptional responses to semaxinib including extracellular matrix remodeling, stress signaling, and overexpression of growth factors and receptors in CCM3 KO cells, which may contribute to their survival advantage. These findings advance our understanding of the complex interplay between WT and KO cells in CCM pathogenesis and demonstrate that the proliferative advantage of CCM3-deficient cells is not solely driven by CCM3 loss. Finally, our iPSC-based EC co-culture assay provides a scalable platform to study KO/WT interactions and may accelerate the identification of effective therapeutic strategies for CCM disease.