Cerebral cavernous malformation (CCM) is a disease of the central nervous system causing hemorrhage-prone multiple lumen vascular malformations and very severe neurological consequences. At present, the only recommended treatment of CCM is surgical. Because surgery is often not applicable, pharmacological treatment would be highly desirable. We describe here a murine model of the disease that develops after endothelial-cell-selective ablation of the CCM3 gene. We report an early, cell-autonomous, Wnt-receptor-independent stimulation of β-catenin transcription activity in CCM3-deficient endothelial cells both in vitro and in vivo and a triggering of a β-catenin-driven transcription program that leads to endothelial-tomesenchymal transition. TGF-β/BMP signaling is then required for the progression of the disease. We also found that the anti-inflammatory drugs sulindac sulfide and sulindac sulfone, which attenuate β-catenin transcription activity, reduce vascular malformations in endothelial CCM3-deficient mice. This study opens previously unidentified perspectives for an effective pharmacological therapy of intracranial vascular cavernomas.cerebral cavernous malformation | endothelial cells | β-catenin | sulindac metabolites | vascular pathology T he vascular malformations that characterize the disease known as cerebral cavernous malformation (CCM) are concentrated in the central nervous system, and they typically show multiple lumens and vascular leakage (1). These abnormalities can result in severe neurological symptoms, including hemorrhagic stroke (2), and, to date, the only possible therapy is surgery (3). In humans, loss-of-function mutations in any one of three independent genes known as cerebral cavernous malformation 1, 2, and 3 (CCM1, CCM2, and CCM3) are the cause of the genetic form of CCM (4). Similarly, in murine models, the vascular phenotype can be reproduced by endothelium-specific loss-of-function mutations of any one of these three CCM-linked genes (5-7).We have recently reported (7) that TGF-β/BMP signaling is activated after ablation of CCM1, CCM2, or CCM3 and induces endothelial-to-mesenchymal transition (EndMT) that plays a crucial role in the development of vascular malformations. Nevertheless, the sequence of signaling responses elicited by ablation of CCM genes still remains to be defined. Inhibitors of the TGF-β/BMP-signaling pathways reduce the number and size of the malformations, but not completely (7), suggesting that other signaling pathways may be implicated.The Wnt/β-catenin pathway, in synergy with TGF-β signaling (8), is responsible for the EndMT switch of endothelial cells giving rise to the heart cushion in the embryo. In addition, the knockdown of CCM1 and CCM3 expression in cultured aortic and artery endothelial cells promotes β-catenin signaling (9, 10), although no direct link with the in vivo model of the disease has been made. Activation of canonical Wnt/β-catenin signaling is critical for brain vascularization and acquisition, by the microvasculature, of blood-brain barr...