Article

Developmental timing of CCM2 loss influences cerebral cavernous malformations in mice

Institut National de la Santé et de la Recherche Médicale, UMR-S 740, 75010 Paris, France.
Journal of Experimental Medicine (Impact Factor: 12.52). 08/2011; 208(9):1835-47. DOI: 10.1084/jem.20110571
Source: PubMed

ABSTRACT

Cerebral cavernous malformations (CCM) are vascular malformations of the central nervous system (CNS) that lead to cerebral hemorrhages. Familial CCM occurs as an autosomal dominant condition caused by loss-of-function mutations in one of the three CCM genes. Constitutive or tissue-specific ablation of any of the Ccm genes in mice previously established the crucial role of Ccm gene expression in endothelial cells for proper angiogenesis. However, embryonic lethality precluded the development of relevant CCM mouse models. Here, we show that endothelial-specific Ccm2 deletion at postnatal day 1 (P1) in mice results in vascular lesions mimicking human CCM lesions. Consistent with CCM1/3 involvement in the same human disease, deletion of Ccm1/3 at P1 in mice results in similar CCM lesions. The lesions are located in the cerebellum and the retina, two organs undergoing intense postnatal angiogenesis. Despite a pan-endothelial Ccm2 deletion, CCM lesions are restricted to the venous bed. Notably, the consequences of Ccm2 loss depend on the developmental timing of Ccm2 ablation. This work provides a highly penetrant and relevant CCM mouse model.

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Available from: Ralf H Adams, Aug 11, 2015
    • "Similarly to patients, in murine models the vascular phenotype can be faithfully reproduced by endothelium-specific loss-offunction mutations of anyone of these three Ccm genes (Liebner et al, 2008; Boulday et al, 2011; Chan et al, 2011; McDonald et al, 2011; Maddaluno et al, 2013; Mleynek et al, 2014). CCM tripartite cytoplasmic complex controls barrier functions both by inhibiting the small GTPase RhoA (Whitehead et al, 2009; Borikova et al, 2010; Stockton et al, 2010) and by acting as an effector of the small GTPase Ras-related protein 1 (Rap1) at the cell-to-cell adherens junctions (AJ) in the endothelium (Beraud- Dufour et al, 2007; Glading et al, 2007; Glading & Ginsberg, 2010; Fisher & Boggon, 2013). "
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    ABSTRACT: Cerebral cavernous malformations (CCMs) are vascular malformations located within the central nervous system often resulting in cerebral hemorrhage. Pharmacological treatment is needed, since current therapy is limited to neurosurgery. Familial CCM is caused by loss-of-function mutations in any of Ccm1, Ccm2, and Ccm3 genes. CCM cavernomas are lined by endothelial cells (ECs) undergoing endothelial-to-mesenchymal transition (EndMT). This switch in phenotype is due to the activation of the transforming growth factor beta/bone morphogenetic protein (TGFβ/BMP) signaling. However, the mechanism linking Ccm gene inactivation and TGFβ/BMP-dependent EndMT remains undefined. Here, we report that Ccm1 ablation leads to the activation of a MEKK3-MEK5-ERK5-MEF2 signaling axis that induces a strong increase in Kruppel-like factor 4 (KLF4) in ECs in vivo. KLF4 transcriptional activity is responsible for the EndMT occurring in CCM1-null ECs. KLF4 promotes TGFβ/BMP signaling through the production of BMP6. Importantly, in endothelial-specific Ccm1 and Klf4 double knockout mice, we observe a strong reduction in the development of CCM and mouse mortality. Our data unveil KLF4 as a therapeutic target for CCM.
    No preview · Article · Nov 2015 · EMBO Molecular Medicine
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    • "To study the contribution of autophagy to CCM pathogenesis, we investigated whether KRIT1 down-regulation would lead to the impairment of autophagy in endothelial cell lines. Endothelial-specific KRIT1 knockout (KO) in mice produced lesions that were identical to the CCM malformations observed in humans (Boulday et al, 2011; Maddaluno et al, 2013). We used KRIT1-KO lung endothelial cells derived from KRIT1 fl/fl mice treated with Tat-Cre recombinase (Maddaluno et al, 2013). "
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    ABSTRACT: Cerebral cavernous malformation (CCM) is a major cerebrovascular disease affecting approximately 0.3-0.5% of the population and is characterized by enlarged and leaky capillaries that predispose to seizures, focal neurological deficits, and fatal intracerebral hemorrhages. Cerebral cavernous malformation is a genetic disease that may arise sporadically or be inherited as an autosomal dominant condition with incomplete penetrance and variable expressivity. Causative loss-of-function mutations have been identified in three genes, KRIT1 (CCM1), CCM2 (MGC4607), and PDCD10 (CCM3), which occur in both sporadic and familial forms. Autophagy is a bulk degradation process that maintains intracellular homeostasis and that plays essential quality control functions within the cell. Indeed, several studies have identified the association between dysregulated autophagy and different human diseases. Here, we show that the ablation of the KRIT1 gene strongly suppresses autophagy, leading to the aberrant accumulation of the autophagy adaptor p62/SQSTM1, defective quality control systems, and increased intracellular stress. KRIT1 loss-of-function activates the mTOR-ULK1 pathway, which is a master regulator of autophagy, and treatment with mTOR inhibitors rescues some of the mole-cular and cellular phenotypes associated with CCM. Insufficient autophagy is also evident in CCM2-silenced human endothelial cells and in both cells and tissues from an endothelial-specific CCM3-knockout mouse model, as well as in human CCM lesions. Furthermore, defective autophagy is highly correlated to endothelial-to-mesenchymal transition, a crucial event that contributes to CCM progression. Taken together, our data point to a key role for defective autophagy in CCM disease pathogenesis, thus providing a novel framework for the development of new pharmacological strategies to prevent or reverse adverse clinical outcomes of CCM lesions.
    Full-text · Article · Sep 2015 · EMBO Molecular Medicine
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    ABSTRACT: Vascular integrity is characterized by a tight control of permeability to cells and solutes and by resistance to blood flow. In several pathologies including tumor angiogenesis, vascular malformations, hemorrhagic stroke and others, there is the need to stabilize the vessels and prevent undesired bleeding or edema. Here, we discuss the current knowledge on the role of endothelial cell-to-cell adherens junctions in maintaining vascular integrity. The identification of several components of adherens junctions in endothelial cells helped understanding of the complex role of these structures not only in maintaining cell-to-cell adhesion but also in transferring intracellular signals. Vascular endothelial (VE)-cadherin, an endothelial-specific adhesion protein at adherens junctions, was found to interact with several signaling partners that induce contact inhibition of growth, decrease in permeability, tight junction organization and others. Changes in VE-cadherin levels in vivo may significantly affect vascular permeability, and induce uncontrolled growth and vascular fragility. In the past years, the research on angiogenesis was mostly directed to the definition of the mechanisms able to modulate vascular growth. We now understand that in many pathological conditions we do not simply need to increase or inhibit vascularization but we also need to develop tools able to stabilize organ perfusion and to avoid hemorrhages or edema.
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