Cerebral cavernous malformation (CCM) is a vascular dysplasia, mainly localized within the brain and affecting up to 0.5% of the human population. CCM lesions are formed by enlarged and irregular blood vessels that often result in cerebral haemorrhages. CCM is caused by loss-of-function mutations in one of three genes, namely CCM1 (also known as KRIT1), CCM2 (OSM) and CCM3 (PDCD10), and occurs in both sporadic and familial forms. Recent studies have investigated the cause of vascular dysplasia and fragility in CCM, but the in vivo functions of this ternary complex remain unclear. Postnatal deletion of any of the three Ccm genes in mouse endothelium results in a severe phenotype, characterized by multiple brain vascular malformations that are markedly similar to human CCM lesions. Endothelial-to-mesenchymal transition (EndMT) has been described in different pathologies, and it is defined as the acquisition of mesenchymal- and stem-cell-like characteristics by the endothelium. Here we show that endothelial-specific disruption of the Ccm1 gene in mice induces EndMT, which contributes to the development of vascular malformations. EndMT in CCM1-ablated endothelial cells is mediated by the upregulation of endogenous BMP6 that, in turn, activates the transforming growth factor-β (TGF-β) and bone morphogenetic protein (BMP) signalling pathway. Inhibitors of the TGF-β and BMP pathway prevent EndMT both in vitro and in vivo and reduce the number and size of vascular lesions in CCM1-deficient mice. Thus, increased TGF-β and BMP signalling, and the consequent EndMT of CCM1-null endothelial cells, are crucial events in the onset and progression of CCM disease. These studies offer novel therapeutic opportunities for this severe, and so far incurable, pathology.

During heart development endocardial cells within the atrio-ventricular (AV) region undergo TGFβ-dependent epithelial-mesenchymal transformation (EMT) and invade the underlying cardiac jelly. This process gives rise to the endocardial cushions from which AV valves and part of the septum originate. In this paper we show that in mouse embryos and in AV explants TGFβ induction of endocardial EMT is strongly inhibited in mice deficient for endothelial β-catenin, leading to a lack of heart cushion formation. Using a Wnt-signaling reporter mouse strain, we demonstrated in vivo and ex vivo that EMT in heart cushion is accompanied by activation of β-catenin/TCF/Lef transcriptional activity. In cultured endothelial cells, TGFβ2 induces α-smooth muscle actin (αSMA) expression. This process was strongly reduced in β-catenin null cells, although TGFβ2 induced smad phosphorylation was unchanged. These data demonstrate an involvement of β-catenin/TCF/Lef transcriptional activity in heart cushion formation, and suggest an interaction between TGFβ and Wnt-signaling pathways in the induction of endothelial-mesenchymal transformation.

We investigated the clinical significance of a vascular growth pattern of hepatocellular carcinoma (HCC), the vessels that encapsulate tumor clusters (VETC), previously linked to HCC metastatic dissemination. VETC was assessed in a large multi‐institutional cohort of 541 resected HCCs from Italy, Korea and Japan, and matched against a full spectrum of clinical and pathological variables. The VETC phenotype (defined as ≥ 55% tumor area by CD34 immunostaining) was easily reproducible and reliably detectable in whole sections and small‐sized tissues of tissue microarray. VETC HCCs represented 18.9% of the whole series, the lowest proportion occurring in the cohort with smallest tumors (8.7%, Japanese series). VETC was significantly associated with several clinical and pathological features such as high alfa‐fetoprotein (AFP) level, tumor size greater than 5 cm, poor differentiation, macrotrabecular pattern, less compact pattern, less inflammatory infiltrates, and frequent microvascular invasion. VETC was associated with early recurrence (hazard ratio [HR]: 1.52 [1.06‐2.19], P = 0.023), disease‐free survival (HR: 1.66 [1.21‐2.27], P = 0.002), and overall survival (HR: 2.26 [1.37‐3.72], P = 0.001) at multivariable analysis. VETC affected the survival in HCC patients stratified for etiology (hepatitis C virus/hepatitis B virus), vascular invasion, and specific molecular phenotypes (β‐catenin/GS+). This distinct vascular pattern was enriched in the recently reported macrotrabecular massive HCC subtype, which was seen in 7.8% (42 of 541) of patients and associated with high AFP levels and poor differentiation. Conclusion: The VETC pattern was found to be easily detectable in a consistent fraction of HCC and a powerful pathological finding affecting survival. This study suggests that the heterogeneous pattern of angiogenesis is involved in HCC behavior.

SummaryLittle is known about the molecular mechanisms that regulate the organization of vascular lumen. In this paper we show that lumen formation correlates with endothelial polarization. Adherens junctions (AJs) and VE-cadherin (VEC, encoded by CDH5) are required for endothelial apicobasal polarity in vitro and during embryonic development. Silencing of CDH5 gene expression leads to abrogation of endothelial polarity accompanied by strong alterations in lumenal structure. VEC co-distributes with members of the Par polarity complex (Par3 and PKCz) and is needed for activation of PKCz. CCM1 is encoded by the CCM1 gene, which is mutated in 60% of patients affected by cerebral cavernous malformation (CCM). The protein interacts with VEC and directs AJ organization and AJ association with the polarity complex, both in cell-culture models and in human CCM1 lesions. Both VEC and CCM1 control Rap1 concentration at cell-cell junctions. We propose that VEC, CCM1 and Rap1 form a signaling complex. In the absence of any of these proteins, AJs are dismantled, cell polarity is lost and vascular lumenal structure is severely altered.