Loss of cerebral cavernous malformation 3 (Ccm3) in neuroglia leads to CCM and vascular pathology

Transcriptomic signatures of individual cell types in cerebral cavernous malformation

Cerebral cavernous malformation (CCM) is a hemorrhagic neurovascular disease with no currently available therapeutics. Prior evidence suggests that different cell types may play a role in CCM pathogenesis. The contribution of each cell type to the dysfunctional cellular crosstalk remains unclear. Herein, RNA-seq was performed on fluorescence-activated cell sorted endothelial cells (ECs), pericytes, and neuroglia from CCM lesions and non-lesional brain tissue controls. Differentially Expressed Gene (DEG), pathway and Ligand-Receptor (LR) analyses were performed to characterize the dysfunctional genes of respective cell types within CCMs. Common DEGs among all three cell types were related to inflammation and endothelial-to-mesenchymal transition (EndMT). DEG and pathway analyses supported a role of lesional ECs in dysregulated angiogenesis and increased permeability. VEGFA was particularly upregulated in pericytes. Further pathway and LR analyses identified vascular endothelial growth factor A/ vascular endothelial growth factor receptor 2 signaling in lesional ECs and pericytes that would result in increased angiogenesis. Moreover, lesional pericytes and neuroglia predominantly showed DEGs and pathways mediating the immune response. Further analyses of cell specific gene alterations in CCM endorsed potential contribution to EndMT, coagulation, and a hypoxic microenvironment. Taken together, these findings motivate mechanistic hypotheses regarding non-endothelial contributions to lesion pathobiology and may lead to novel therapeutic targets. Video Abstract.

Programmed cell death 10 increased blood-brain barrier permeability through HMGB1/TLR4 mediated downregulation of endothelial ZO-1 in glioblastoma

Dysfunction of blood brain barrier (BBB) contributes to the development of peritumoral edema (PTE) and GBM progression. Programmed cell death 10 (PDCD10) exerts various influence on cancers, especially in glioblastoma (GBM). We previously found that PDCD10 expression was positively correlated with PTE extent in GBM. Thus, the present study aims to investigate the emerging role of PDCD10 in regulating BBB permeability in GBM. Here we found that in vitro indirect co-culture of ECs with Pdcd10-overexpressed GL261 cells resulted in a significant increase of FITC-Dextran (MW, 4000) leakage by reducing endothelial zonula occluden-1 (ZO-1) and Claudin-5 expression in ECs respectively. Overexpression of Pdcd10 in GBM cells (GL261) triggered an increase of soluble high mobility group box 1 (HMGB1) release, which in turn activated endothelial toll like receptor 4 (TLR4) and downstream NF-κB, Erk1/2 and Akt signaling in ECs through a paracrine manner. Moreover, Pdcd10-overexpressed GL261 cells facilitated a formation of abnormal vasculature and increased the BBB permeability in vivo. Our present study demonstrates that upregulation of PDCD10 in GBM triggered HMGB1/TLR4 signaling in ECs and significantly decreased endothelial ZO-1 expression, which in turn dominantly increased BBB permeability and contributed to tumor progression in GBM.

Endothelial Differentiation of CCM1 Knockout iPSCs Triggers the Establishment of a Specific Gene Expression Signature

Cerebral cavernous malformation (CCM) is a neurovascular disease that can lead to seizures and stroke-like symptoms. The familial form is caused by a heterozygous germline mutation in either the CCM1, CCM2, or CCM3 gene. While the importance of a second-hit mechanism in CCM development is well established, it is still unclear whether it immediately triggers CCM development or whether additional external factors are required. We here used RNA sequencing to study differential gene expression in CCM1 knockout induced pluripotent stem cells (CCM1^-/- iPSCs), early mesoderm progenitor cells (eMPCs), and endothelial-like cells (ECs). Notably, CRISPR/Cas9-mediated inactivation of CCM1 led to hardly any gene expression differences in iPSCs and eMPCs. However, after differentiation into ECs, we found the significant deregulation of signaling pathways well known to be involved in CCM pathogenesis. These data suggest that a microenvironment of proangiogenic cytokines and growth factors can trigger the establishment of a characteristic gene expression signature upon CCM1 inactivation. Consequently, CCM1^-/- precursor cells may exist that remain silent until entering the endothelial lineage. Collectively, not only downstream consequences of CCM1 ablation but also supporting factors must be addressed in CCM therapy development.

KRIT1-mediated regulation of neutrophil adhesion and motility

Loss of Krev interaction-trapped-1 (KRIT1) expression leads to the development of cerebral cavernous malformations (CCM), a disease in which abnormal blood vessel formation compromises the structure and function of the blood-brain barrier. The role of KRIT1 in regulating endothelial function is well-established. However, several studies have suggested that KRIT1 could also play a role in regulating nonendothelial cell types and, in particular, immune cells. In this study, we generated a mouse model with neutrophil-specific deletion of KRIT1 in order to investigate the effect of KRIT1 deficiency on neutrophil function. Neutrophils isolated from adult Ly6Gtm2621(cre)Arte Krit1flox/flox mice had a reduced ability to attach and spread on the extracellular matrix protein fibronectin and exhibited a subsequent increase in migration. However, adhesion to and migration on ICAM-1 was unchanged. In addition, we used a monomeric, fluorescently-labelled fragment of fibronectin to show that integrin activation is reduced in the absence of KRIT1 expression, though β1 integrin expression appears unchanged. Finally, neutrophil migration in response to lipopolysaccharide-induced inflammation in the lung was decreased, as shown by reduced cell number and myeloperoxidase activity in lavage samples from Krit1PMNKO mice. Altogether, we show that KRIT1 regulates neutrophil adhesion and migration, likely through regulation of integrin activation, which can lead to altered inflammatory responses in vivo.

The Dual Role of PDCD10 in Cancers: A Promising Therapeutic Target

Programmed cell death 10 (PDCD10) was initially considered as a protein associated with apoptosis. However, recent studies showed that PDCD10 is actually an adaptor protein. By interacting with multiple molecules, PDCD10 participates in various physiological processes, such as cell survival, migration, cell differentiation, vesicle trafficking, cellular senescence, neurovascular development, and gonadogenesis. Moreover, over the past few decades, accumulating evidence has demonstrated that the aberrant expression or mutation of PDCD10 is extremely common in various pathological processes, especially in cancers. The dysfunction of PDCD10 has been strongly implicated in oncogenesis and tumor progression. However, the updated data seem to indicate that PDCD10 has a dual role (either pro- or anti-tumor effects) in various cancer types, depending on cell/tissue specificity with different cellular interactors. In this review, we aimed to summarize the knowledge of the dual role of PDCD10 in cancers with a special focus on its cellular function and potential molecular mechanism. With these efforts, we hoped to provide new insight into the future development and application of PDCD10 as a clinical therapeutic target in cancers.

Dysregulated Hemostasis and Immunothrombosis in Cerebral Cavernous Malformations

Cerebral cavernous malformation (CCM) is a neurovascular disease that affects 0.5% of the general population. For a long time, CCM research focused on genetic mutations, endothelial junctions and proliferation, but recently, transcriptome and proteome studies have revealed that the hemostatic system and neuroinflammation play a crucial role in the development and severity of cavernomas, with some of these publications coming from our group. The aim of this review is to give an overview of the latest molecular insights into the interaction between CCM-deficient endothelial cells with blood components and the neurovascular unit. Specifically, we underscore how endothelial dysfunction can result in dysregulated hemostasis, bleeding, hypoxia and neurological symptoms. We conducted a thorough review of the literature and found a field that is increasingly poised to regard CCM as a hemostatic disease, which may have implications for therapy.

Contact-dependent signaling triggers tumor-like proliferation of CCM3 knockout endothelial cells in co-culture with wild-type cells

Cerebral cavernous malformations (CCM) are low-flow vascular lesions prone to cause severe hemorrhage-associated neurological complications. Pathogenic germline variants in CCM1, CCM2, or CCM3 can be identified in nearly 100% of CCM patients with a positive family history. In line with the concept that tumor-like mechanisms are involved in CCM formation and growth, we here demonstrate an abnormally increased proliferation rate of CCM3-deficient endothelial cells in co-culture with wild-type cells and in mosaic human iPSC-derived vascular organoids. The observation that NSC59984, an anticancer drug, blocked the abnormal proliferation of mutant endothelial cells further supports this intriguing concept. Fluorescence-activated cell sorting and RNA sequencing revealed that co-culture induces upregulation of proangiogenic chemokine genes in wild-type endothelial cells. Furthermore, genes known to be significantly downregulated in CCM3^−/− endothelial cell mono-cultures were upregulated back to normal levels in co-culture with wild-type cells. These results support the hypothesis that wild-type ECs facilitate the formation of a niche that promotes abnormal proliferation of mutant ECs. Thus, targeting the cancer-like features of CCMs is a promising new direction for drug development.

Cerebral Cavernous Malformation Pathogenesis: Investigating Lesion Formation and Progression with Animal Models

Cerebral cavernous malformation (CCM) is a cerebromicrovascular disease that affects up to 0.5% of the population. Vessel dilation, decreased endothelial cell-cell contact, and loss of junctional complexes lead to loss of brain endothelial barrier integrity and hemorrhagic lesion formation. Leakage of hemorrhagic lesions results in patient symptoms and complications, including seizures, epilepsy, focal headaches, and hemorrhagic stroke. CCMs are classified as sporadic (sCCM) or familial (fCCM), associated with loss-of-function mutations in KRIT1/CCM1, CCM2, and PDCD10/CCM3. Identifying the CCM proteins has thrust the field forward by (1) revealing cellular processes and signaling pathways underlying fCCM pathogenesis, and (2) facilitating the development of animal models to study CCM protein function. CCM animal models range from various murine models to zebrafish models, with each model providing unique insights into CCM lesion development and progression. Additionally, these animal models serve as preclinical models to study therapeutic options for CCM treatment. This review briefly summarizes CCM disease pathology and the molecular functions of the CCM proteins, followed by an in-depth discussion of animal models used to study CCM pathogenesis and developing therapeutics.

GCKIII (Germinal Center Kinase III) Kinases STK24 and STK25 (Serine/Threonine Kinase 24 and 25) Inhibit Cavernoma Development

BACKGROUND

Cavernous cerebral malformations can arise because of mutations in the CCM1, CCM2, or CCM3 genes, and lack of Cdc42 has also been reported to induce these malformations in mice. However, the role of the CCM3 (cerebral cavernous malformation 3)-associated kinases in cavernoma development is not known, and we, therefore, have investigated their role in the process.

METHODS

We used a combination of an in vivo approach, using mice genetically modified to be deficient in the CCM3-associated kinases STK24 and STK25 (serine/threonine kinases 24 and 25), and the in vitro model of human endothelial cells in which expression of STK24 and STK25 was inhibited by RNA interference.

RESULTS

Mice deficient for both Stk24 and Stk25, but not for either of them individually, developed aggressive vascular lesions with the characteristics of cavernomas at an early age. Stk25 deficiency also gave rise to vascular anomalies in the context of Stk24 heterozygosity. Human endothelial cells deficient for both kinases phenocopied several of the consequences of CCM3 loss, and single STK25 deficiency also induced KLF2 expression, Golgi dispersion, altered distribution of β-catenin, and appearance of stress fibers.

CONCLUSIONS

The CCM3-associated kinases STK24 and STK25 play a major role in the inhibition of cavernoma development.

CCM3 Loss-Induced Lymphatic Defect Is Mediated by the Augmented VEGFR3-ERK1/2 Signaling

OBJECTIVE

Cerebral cavernous malformations (CCMs) can happen anywhere in the body, although they most commonly produce symptoms in the brain. The role of CCM genes in other vascular beds outside the brain and retina is not well-examined, although the 3 CCM-associated genes (CCM1, CCM2, and CCM3) are ubiquitously expressed in all tissues. We aimed to determine the role of CCM gene in lymphatics. Approach and Results: Mice with an inducible pan-endothelial cell (EC) or lymphatic EC deletion of Ccm3 (Pdcd10ECKO or Pdcd10LECKO) exhibit dilated lymphatic capillaries and collecting vessels with abnormal valve structure. Morphological alterations were correlated with lymphatic dysfunction in Pdcd10LECKO mice as determined by Evans blue dye and fluorescein isothiocyanate(FITC)-dextran transport assays. Pdcd10LECKO lymphatics had increased VEGFR3 (vascular endothelial growth factor receptor-3)-ERK1/2 (extracellular signal-regulated kinase 1/2) signaling with lymphatic hyperplasia. Mechanistic studies suggested that VEGFR3 is primarily regulated at a transcriptional level in Ccm3-deficient lymphatic ECs, in an NF-κB (nuclear factor κB)-dependent manner. CCM3 binds to importin alpha 2/KPNA2 (karyopherin subunit alpha 2), and a CCM3 deletion releases KPNA2 to activate NF-κB P65 by facilitating its nuclear translocation and P65-dependent VEGFR3 transcription. Moreover, increased VEGFR3 in lymphatic EC preferentially activates ERK1/2 signaling, which is critical for lymphatic EC proliferation. Importantly, inhibition of VEGFR3 or ERK1/2 rescued the lymphatic defects in structure and function.

CONCLUSIONS

Our data demonstrate that CCM3 deletion augments the VEGFR3-ERK1/2 signaling in lymphatic EC that drives lymphatic hyperplasia and malformation and warrant further investigation on the potential clinical relevance of lymphatic dysfunction in patients with CCM.

The multifaceted PDCD10/CCM3 gene

The programmed cell death 10 (PDCD10) gene was originally identified as an apoptosis-related gene, although it is now usually known as CCM3, as the third causative gene of cerebral cavernous malformation (CCM). CCM is a neurovascular disease that is characterized by vascular malformations and is associated with headaches, seizures, focal neurological deficits, and cerebral hemorrhage. The PDCD10/CCM3 protein has multiple subcellular localizations and interacts with several multi-protein complexes and signaling pathways. Thus PDCD10/CCM3 governs many cellular functions, which include cell-to-cell junctions and cytoskeleton organization, cell proliferation and apoptosis, and exocytosis and angiogenesis. Given its central role in the maintenance of homeostasis of the cell, dysregulation of PDCD10/CCM3 can result in a wide range of altered cell functions. This can lead to severe diseases, including CCM, cognitive disability, and several types of cancers. Here, we review the multifaceted roles of PDCD10/CCM3 in physiology and pathology, with a focus on its functions beyond CCM.

Somatic PIK3CA Mutations in Sporadic Cerebral Cavernous Malformations

BACKGROUND

Cerebral cavernous malformations (CCMs) are common sporadic and inherited vascular malformations of the central nervous system. Although familial CCMs are linked to loss-of-function mutations in KRIT1 (CCM1), CCM2, or PDCD10 (CCM3), the genetic cause of sporadic CCMs, representing 80% of cases, remains incompletely understood.

METHODS

We developed two mouse models harboring mutations identified in human meningiomas with the use of the prostaglandin D2 synthase (PGDS) promoter. We performed targeted DNA sequencing of surgically resected CCMs from patients and confirmed our findings by droplet digital polymerase-chain-reaction analysis.

RESULTS

We found that in mice expressing one of two common genetic drivers of meningioma - Pik3ca ^H1047R or AKT1 ^E17K - in PGDS-positive cells, a spectrum of typical CCMs develops (in 22% and 11% of the mice, respectively) instead of meningiomas, which prompted us to analyze tissue samples from sporadic CCMs from 88 patients. We detected somatic activating PIK3CA and AKT1 mutations in 39% and 1%, respectively, of lesion tissue from the patients. Only 10% of lesions harbored mutations in the CCM genes. We analyzed lesions induced by the activating mutations Pik3ca ^H1074R and AKT1 ^E17K in mice and identified the PGDS-expressing pericyte as the probable cell of origin.

CONCLUSIONS

In tissue samples from sporadic CCMs, mutations in PIK3CA were represented to a greater extent than mutations in any other gene. The contribution of somatic mutations in the genes that cause familial CCMs was comparatively small. (Funded by the Fondation ARC pour la Recherche contre le Cancer and others.).

Astrocytes propel neurovascular dysfunction during cerebral cavernous malformation lesion formation

Cerebral cavernous malformations (CCMs) are common neurovascular lesions caused by loss-of-function mutations in 1 of 3 genes, including KRIT1 (CCM1), CCM2, and PDCD10 (CCM3), and generally regarded as an endothelial cell-autonomous disease. Here we reported that proliferative astrocytes played a critical role in CCM pathogenesis by serving as a major source of VEGF during CCM lesion formation. An increase in astrocyte VEGF synthesis is driven by endothelial nitric oxide (NO) generated as a consequence of KLF2- and KLF4-dependent elevation of eNOS in CCM endothelium. The increased brain endothelial production of NO stabilized HIF-1α in astrocytes, resulting in increased VEGF production and expression of a "hypoxic" program under normoxic conditions. We showed that the upregulation of cyclooxygenase-2 (COX-2), a direct HIF-1α target gene and a known component of the hypoxic program, contributed to the development of CCM lesions because the administration of a COX-2 inhibitor significantly prevented the progression of CCM lesions. Thus, non-cell-autonomous crosstalk between CCM endothelium and astrocytes propels vascular lesion development, and components of the hypoxic program represent potential therapeutic targets for CCMs.

Using Zebrafish to Elucidate Glial-Vascular Interactions During CNS Development

An emerging area of interest in Neuroscience is the cellular relationship between glia and blood vessels, as many of the presumptive support roles of glia require an association with the vasculature. These interactions are best studied in vivo and great strides have been made using mice to longitudinally image glial-vascular interactions. However, these methods are cumbersome for developmental studies, which could benefit from a more accessible system. Zebrafish (Danio rerio) are genetically tractable vertebrates, and given their translucency, are readily amenable for daily live imaging studies. We set out to examine whether zebrafish glia have conserved traits with mammalian glia regarding their ability to interact with and maintain the developing brain vasculature. We utilized transgenic zebrafish strains in which oligodendrocyte transcription factor 2 (olig2) and glial fibrillary acidic protein (gfap) identify different glial populations in the zebrafish brain and document their corresponding relationship with brain blood vessels. Our results demonstrate that olig2+ and gfap+ zebrafish glia have distinct lineages and each interact with brain vessels as previously observed in mouse brain. Additionally, we manipulated these relationships through pharmacological and genetic approaches to distinguish the roles of these cell types during blood vessel development. olig2+ glia use blood vessels as a pathway during their migration and Wnt signaling inhibition decreases their single-cell vessel co-option. By contrast, the ablation of gfap+ glia at the beginning of CNS angiogenesis impairs vessel development through a reduction in Vascular endothelial growth factor (Vegf), supporting a role for gfap+ glia during new brain vessel formation in zebrafish. This data suggests that zebrafish glia, akin to mammalian glia, have different lineages that show diverse interactions with blood vessels, and are a suitable model for elucidating glial-vascular relationships during vertebrate brain development.

Pdcd10-Stk24/25 complex controls kidney water reabsorption by regulating Aqp2 membrane targeting

PDCD10, also known as CCM3, is a gene found to be associated with the human disease cerebral cavernous malformations (CCMs). PDCD10 forms a complex with GCKIII kinases including STK24, STK25, and MST4. Studies in C. elegans and Drosophila have shown a pivotal role of the PDCD10-GCKIII complex in maintaining epithelial integrity. Here, we found that mice deficient of Pdcd10 or Stk24/25 in the kidney tubules developed polyuria and displayed increased water consumption. Although the expression levels of aquaporin genes were not decreased, the levels of total and phosphorylated aquaporin 2 (Aqp2) protein in the apical membrane of tubular epithelial cells were decreased in Pdcd10- and Stk24/25-deficient mice. This loss of Aqp2 was associated with increased expression and membrane targeting of Ezrin and phosphorylated Ezrin, Radixin, Moesin (p-ERM) proteins and impaired intracellular vesicle trafficking. Treatment with Erlotinib, a tyrosine kinase inhibitor promoting exocytosis and inhibiting endocytosis, normalized the expression level and membrane abundance of Aqp2 protein, and partially rescued the water reabsorption defect observed in the Pdcd10-deficient mice. Our current study identified the PDCD10-STK-ERM signaling pathway as a potentially novel pathway required for water balance control by regulating vesicle trafficking and protein abundance of AQP2 in the kidneys.

Programmed Cell Death 10 Mediated CXCL2-CXCR2 Signaling in Regulating Tumor-Associated Microglia/Macrophages Recruitment in Glioblastoma

Background

Programmed cell death 10 (PDCD10) plays a crucial role in regulating tumor phenotyping, especially in glioblastoma (GBM). Glioma-associated microglia/macrophages (GAMs) in tumor pathological microenvironment contribute to GBM progression. We previously found that the infiltration of GAMs was associated with PDCD10 expression in GBM patients. The present study aims to further explore the regulation of PDCD10 on GAMs in GBM.

Methods

Overexpression of PDCD10 in human- and murine-GBM cells was established by lentiviral transduction. Cell behaviors and polarization of primary microglia, microglia- and macrophage-like cells were investigated through indirect co-culture with GBM cells in vitro respectively. The PDCD10-induced release of chemokines was identified by a chemokine protein array. The cross-talk between GBM and microglia as well as macrophages was further studied using selective antagonist SB225002. Finally, an orthotopic homograft mouse model was employed to verify the results of in vitro experiments.

Results

Indirect co-culture with PDCD10-overexpressed GBM cells promoted proliferation and migration of microglia- and macrophage-like cells, and stimulated pro-tumorigenic polarization of primary microglia, microglia- and macrophage-like cells. Pdcd10-upregulated GBM cells triggered a nearly 6-fold increase of CXC motif chemokine ligand 2 (CXCL2) release, which in turn activated CXC chemokine receptor 2 (CXCR2) and downstream Erk1/2 and Akt signaling in primary microglia, microglia- and macrophage-like cells. The blockage of CXCR2 signaling with specific inhibitor (SB225002) abolished microglia- and macrophage-like cell migration induced by PDCD10-upregulated GBM cells. Moreover, Pdcd10-upregulated GL261 cells promoted GAMs recruitment and tumor growth in vivo.

Conclusion

Our study demonstrates that overexpression of PDCD10 in GBM recruits and activates microglia/macrophages, which in turn promotes tumor progression. CXCL2-CXCR2 signaling mediated by PDCD10 is potentially involved in the crosstalk between GBM cells and GAMs.

Inhibition of the HEG1-KRIT1 interaction increases KLF4 and KLF2 expression in endothelial cells

The transmembrane protein heart of glass1 (HEG1) directly binds to and recruits Krev interaction trapped protein 1 (KRIT1) to endothelial junctions to form the HEG1-KRIT1 protein complex that establishes and maintains junctional integrity. Genetic inactivation or knockdown of endothelial HEG1 or KRIT1 leads to the upregulation of transcription factors Krüppel-like factors 4 and 2 (KLF4 and KLF2), which are implicated in endothelial vascular homeostasis; however, the effect of acute inhibition of the HEG1-KRIT1 interaction remains incompletely understood. Here, we report a high-throughput screening assay and molecular design of a small-molecule HEG1-KRIT1 inhibitor to uncover acute changes in signaling pathways downstream of the HEG1-KRIT1 protein complex disruption. The small-molecule HEG1-KRIT1 inhibitor 2 (HKi2) was demonstrated to be a bona fide inhibitor of the interaction between HEG1 and KRIT1 proteins, by competing orthosterically with HEG1 through covalent reversible interactions with the FERM (4.1, ezrin, radixin, and moesin) domain of KRIT1. The crystal structure of HKi2 bound to KRIT1 FERM revealed that it occupies the same binding pocket on KRIT1 as the HEG1 cytoplasmic tail. In human endothelial cells (ECs), acute inhibition of the HEG1-KRIT1 interaction by HKi2 increased KLF4 and KLF2 mRNA and protein levels, whereas a structurally similar inactive compound failed to do so. In zebrafish, HKi2 induced expression of klf2a in arterial and venous endothelium. Furthermore, genome-wide RNA transcriptome analysis of HKi2-treated ECs under static conditions revealed that, in addition to elevating KLF4 and KLF2 expression, inhibition of the HEG1-KRIT1 interaction mimics many of the transcriptional effects of laminar blood flow. Furthermore, HKi2-treated ECs also triggered Akt signaling in a phosphoinositide 3-kinase (PI3K)-dependent manner, as blocking PI3K activity blunted the Akt phosphorylation induced by HKi2. Finally, using an in vitro colocalization assay, we show that HKi6, an improved derivative of HKi2 with higher affinity for KRIT1, significantly impedes recruitment of KRIT1 to mitochondria-localized HEG1 in CHO cells, indicating a direct inhibition of the HEG1-KRIT1 interaction. Thus, our results demonstrate that early events of the acute inhibition of HEG1-KRIT1 interaction with HKi small-molecule inhibitors lead to: (i) elevated KLF4 and KLF2 gene expression; and (ii) increased Akt phosphorylation. Thus, HKi's provide new pharmacologic tools to study acute inhibition of the HEG1-KRIT1 protein complex and may provide insights to dissect early signaling events that regulate vascular homeostasis.

Mouse models of vascular development and disease

PURPOSE OF REVIEW

The use of genetic models has facilitated the study of the origins and mechanisms of vascular disease. Mouse models have been developed to specifically target endothelial cell populations, with the goal of pinpointing when and where causative mutations wreck their devastating effects. Together, these approaches have propelled the development of therapies by providing an in-vivo platform to evaluate diagnoses and treatment options. This review summarizes the most widely used mouse models that have facilitated the study of vascular disease, with a focus on mouse models of vascular malformations and the road ahead.

RECENT FINDINGS

Over the past 3 decades, the vascular biology scientific community has been steadily generating a powerful toolkit of useful mouse lines that can be used to tightly regulate gene ablation, or to express transgenic genes, in the murine endothelium. Some of these models inducibly (constitutively) alter gene expression across all endothelial cells, or within distinct subsets, by expressing either Cre recombinase (or inducible versions such as CreERT), or the tetracycline controlled transactivator protein tTA (or rtTA). This now relatively standard technology has been used to gain cutting edge insights into vascular disorders, by allowing in-vivo modeling of key molecular pathways identified as dysregulated across the vast spectrum of vascular anomalies, malformations and dysplasias. However, as sequencing of human patient samples expands, the number of interesting candidate molecular culprits keeps increasing. Consequently, there is now a pressing need to create new genetic mouse models to test hypotheses and to query mechanisms underlying vascular disease.

SUMMARY

The current review assesses the collection of mouse driver lines that have been instrumental is identifying genes required for blood vessel formation, remodeling, maintenance/quiescence and disease. In addition, the usefulness of these driver lines is underscored here by cataloguing mouse lines developed to experimentally assess the role of key candidate genes in vascular malformations. Despite this solid and steady progress, numerous new candidate vascular malformation genes have recently been identified for which no mouse model yet exists.

CTCFL expression is associated with cerebral vascular abnormalities

CTCFL is expressed in testis, oocytes and embryonic stem cells, and is aberrantly expressed in malignant cells, and is classified as a cancer-testis gene. We have previously shown by using a tetracycline-inducible Ctcfl transgene that inappropriate expression of Ctcfl negatively impacts fetal development and causes early postnatal lethality in the mouse. The affected pups displayed severe vascular abnormalities and localized hemorrhages in the brain evocative of cerebral cavernous malformations (CCM) and arteriovenous malformations (AVM) in humans. Thus, we aim to analyze; a) the presence of CCM-related proteins CCM1/KRIT1, CCM2/malcavernin and CCM3/PDCD10 in Ctcfl transgenic animals and, b) whether there is CTCFL expression in human CCM and AVM tissues. Ctcfl transgenic animals exhibited increased CD31 expression in vascular areas of the dermis and periadnexal regions but no difference was observed for vWF and α-SMA expressions. CCM-related proteins CCM1/KRIT1, CCM2/malcavernin and CCM3/PDCD10 were aberrantly expressed in coronal sections of the head in transgenic animals. We also observed CTCFL expression in human CCMs and AVMs. The induced expression of CTCFL resulting in vascular brain malformations in mice combined with the presence of CTCFL in human vascular malformations provide new insights into the role of this gene in vascular development in humans.

Bidimentional In Vitro Angiogenic Assays to Study CCM Pathogenesis: Endothelial Cell Proliferation and Migration

Cerebral cavernous malformation (CCM) is a cerebrovascular disorder of proven genetic origin characterized by abnormally dilated and leaky capillaries occurring mainly in the central nervous system, with a prevalence of 0.3-0.5% in the general population. Genetic studies have identified three genes associated to CCMs: KRIT1 (CCM1), MGC4607 (CCM2), and PDCD10 (CCM3), which account for about 50%, 20%, and 10% of the cases, respectively. The great advances in the knowledge of the physiopathological functions of CCM genes, such as their involvement in the angiogenic process, have allowed to propose distinct putative therapeutic compounds, which showed to be effective at least in limiting some pathological phenotypes in cellular and animal models of the disease. However, despite numerous efforts, targeted pharmacological therapies that improve the outcome of CCM disease are currently lacking.Here we describe simply and low-cost assays as in vitro endothelial cell proliferation and migration assays that can be used to better understand the role of CCM genes on endothelial cell functions and to screen potential new compounds for CCM therapy.

From Genes and Mechanisms to Molecular-Targeted Therapies: The Long Climb to the Cure of Cerebral Cavernous Malformation (CCM) Disease

Cerebral cavernous malformation (CCM) is a rare cerebrovascular disorder of genetic origin consisting of closely clustered, abnormally dilated and leaky capillaries (CCM lesions), which occur predominantly in the central nervous system. CCM lesions can be single or multiple and may result in severe clinical symptoms, including focal neurological deficits, seizures, and intracerebral hemorrhage. Early human genetic studies demonstrated that CCM disease is linked to three chromosomal loci and can be inherited as autosomal dominant condition with incomplete penetrance and highly variable expressivity, eventually leading to the identification of three disease genes, CCM1/KRIT1, CCM2, and CCM3/PDCD10, which encode for structurally unrelated intracellular proteins that lack catalytic domains. Biochemical, molecular, and cellular studies then showed that these proteins are involved in endothelial cell-cell junction and blood-brain barrier stability maintenance through the regulation of major cellular structures and mechanisms, including endothelial cell-cell and cell-matrix adhesion, actin cytoskeleton dynamics, autophagy, and endothelial-to-mesenchymal transition, suggesting that they act as pleiotropic regulators of cellular homeostasis, and opening novel therapeutic perspectives. Indeed, accumulated evidence in cellular and animal models has eventually revealed that the emerged pleiotropic functions of CCM proteins are mainly due to their ability to modulate redox-sensitive pathways and mechanisms involved in adaptive responses to oxidative stress and inflammation, thus contributing to the preservation of cellular homeostasis and stress defenses.In this introductory review, we present a general overview of 20 years of amazing progress in the identification of genetic culprits and molecular mechanisms underlying CCM disease pathogenesis, and the development of targeted therapeutic strategies.

Signalling through cerebral cavernous malformation protein networks

Cerebral cavernous malformations (CCMs) are neurovascular abnormalities characterized by thin, leaky blood vessels resulting in lesions that predispose to haemorrhages, stroke, epilepsy and focal neurological deficits. CCMs arise due to loss-of-function mutations in genes encoding one of three CCM complex proteins, KRIT1, CCM2 or CCM3. These widely expressed, multi-functional adaptor proteins can assemble into a CCM protein complex and (either alone or in complex) modulate signalling pathways that influence cell adhesion, cell contractility, cytoskeletal reorganization and gene expression. Recent advances, including analysis of the structures and interactions of CCM proteins, have allowed substantial progress towards understanding the molecular bases for CCM protein function and how their disruption leads to disease. Here, we review current knowledge of CCM protein signalling with a focus on three pathways which have generated the most interest—the RhoA–ROCK, MEKK3–MEK5–ERK5–KLF2/4 and cell junctional signalling pathways—but also consider ICAP1-β1 integrin and cdc42 signalling. We discuss emerging links between these pathways and the processes that drive disease pathology and highlight important open questions—key among them is the role of subcellular localization in the control of CCM protein activity.

The interaction of lead exposure and CCM3 defect plays an important role in regulating angiogenesis through eNOS/NO pathway

In this study, we aimed to explore the role of nitric oxide (NO) in regulating angiogenesis in cerebral cavernous malformations 3 gene (CCM3)-deficient mice exposed to lead during vascular development; further, we aimed to identify and study the potential mechanism involved as well. Angiogenesis was detected by whole mount immunofluorescent staining of retinal vessels in WT and CCM3^+/- mice. Brain microvascular endothelial cells (BMECs) isolated from WT and CCM3^+/- mice, primary HUVECs, and immortalized HUVECs (imHUVECs) (CCM3^+/+ and CCM3^-/-) were used and treated with lead acetate (PbAc). RT-PCR and Western blotting were used to detect the mRNA and protein expression of iNOS, eNOS, and VEGF genes. The results showed that both lead exposure and CCM3 gene deficiency adversely affected endothelial cell function, causing abnormal angiogenesis and vascular remodeling. The mRNA expression of eNOS and iNOS was significantly different in WT and CCM3^+/- BMECs (0.04 ± 0.001 vs. 0.016 ± 0.002; 0.26 ± 0.002 vs. 0.306 ± 0.002, respectively), and the expression of eNOS and iNOS in imHUVECs (CCM3^+/+ and CCM3^-/-) also increased after PbAc exposure. In conclusion, CCM3 gene-deficient mice were more susceptible to abnormal vascular development after low-level lead exposure, probably due to the release of NO.

Early-Onset Familial Alzheimer Disease Variant PSEN2 N141I Heterozygosity is Associated with Altered Microglia Phenotype

BACKGROUND

Early-onset familial Alzheimer disease (EOFAD) is caused by heterozygous variants in the presenilin 1 (PSEN1), presenilin 2 (PSEN2), and APP genes. Decades after their discovery, the mechanisms by which these genes cause Alzheimer's disease (AD) or promote AD progression are not fully understood. While it is established that presenilin (PS) enzymatic activity produces amyloid-β (Aβ), PSs also regulate numerous other cellular functions, some of which intersect with known pathogenic drivers of neurodegeneration. Accumulating evidence suggests that microglia, resident innate immune cells in the central nervous system, play a key role in AD neurodegeneration.

OBJECTIVE

Previous work has identified a regulatory role for PS2 in microglia. We hypothesized that PSEN2 variants lead to dysregulated microglia, which could further contribute to disease acceleration. To mimic the genotype of EOFAD patients, we created a transgenic mouse expressing PSEN2 N141I on a mouse background expressing one wildtype PS2 and two PS1 alleles.

RESULTS

Microglial expression of PSEN2 N141I resulted in impaired γ-secretase activity as well as exaggerated inflammatory cytokine release, NFκB activity, and Aβ internalization. In vivo, PS2 N141I mice showed enhanced IL-6 and TREM2 expression in brain as well as reduced branch number and length, an indication of "activated" morphology, in the absence of inflammatory stimuli. LPS intraperitoneal injection resulted in higher inflammatory gene expression in PS2 N141I mouse brain relative to controls.

CONCLUSION

Our findings demonstrate that PSEN2 N141I heterozygosity is associated with disrupted innate immune homeostasis, suggesting EOFAD variants may promote disease progression through non-neuronal cells beyond canonical dysregulated Aβ production.

Novel Murine Models of Cerebral Cavernous Malformations

Cerebral cavernous malformations (CCMs) are ectatic capillary-venous malformations that develop in approximately 0.5% of the population. Patients with CCMs may develop headaches, focal neurologic deficits, seizures, and hemorrhages. While symptomatic CCMs, depending upon the anatomic location, can be surgically removed, there is currently no pharmaceutical therapy to treat CCMs. Several mouse models have been developed to better understand CCM pathogenesis and test therapeutics. The most common mouse models induce a large CCM burden that is anatomically restricted to the cerebellum and contributes to lethality in the early days of life. These inducible models thus have a relatively short period for drug administration. We developed an inducible CCM3 mouse model that develops CCMs after weaning and provides a longer period for potential therapeutic intervention. Using this new model, three recently proposed CCM therapies, fasudil, tempol, vitamin D₃, and a combination of the three drugs, failed to substantially reduce CCM formation when treatment was administered for 5 weeks, from postnatal day 21 (P21) to P56. We next restricted Ccm3 deletion to the brain vasculature and provided greater time (121 days) for CCMs to develop chronic hemorrhage, recapitulating the human lesions. We also developed the first model of acute CCM hemorrhage by injecting mice harboring CCMs with lipopolysaccharide. These efficient models will enable future drug studies to more precisely target clinically relevant features of CCM disease: CCM formation, chronic hemorrhage, and acute hemorrhage.

Mural Cell-Specific Deletion of Cerebral Cavernous Malformation 3 in the Brain Induces Cerebral Cavernous Malformations

OBJECTIVE

Cerebral cavernous malformations (CCM), consisting of dilated capillary channels formed by a single layer of endothelial cells lacking surrounding mural cells. It is unclear why CCM lesions are primarily confined to brain vasculature, although the 3 CCM-associated genes (CCM1, CCM2, and CCM3) are ubiquitously expressed in all tissues. We aimed to determine the role of CCM gene in brain mural cell in CCM pathogenesis. Approach and Results: SM22α-Cre was used to drive a specific deletion of Ccm3 in mural cells, including pericytes and smooth muscle cells (Ccm3smKO). Ccm3smKO mice developed CCM lesions in the brain with onset at neonatal stages. One-third of Ccm3smKO mice survived upto 6 weeks of age, exhibiting seizures, and severe brain hemorrhage. The early CCM lesions in Ccm3smKO neonates were loosely wrapped by mural cells, and adult Ccm3smKO mice had clustered and enlarged capillary channels (caverns) formed by a single layer of endothelium lacking mural cell coverage. Importantly, CCM lesions throughout the entire brain in Ccm3smKO mice, which more accurately mimicked human disease than the current endothelial cell-specific CCM3 deletion models. Mechanistically, CCM3 loss in brain pericytes dramatically increased paxillin stability and focal adhesion formation, enhancing ITG-β1 (integrin β1) activity and extracellular matrix adhesion but reducing cell migration and endothelial cell-pericyte associations. Moreover, CCM3-wild type, but not a paxillin-binding defective mutant, rescued the phenotypes in CCM3-deficient pericytes.

CONCLUSIONS

Our data demonstrate for the first time that deletion of a CCM gene in the brain mural cell induces CCM pathogenesis.

KRIT1 loss-mediated upregulation of NOX1 in stromal cells promotes paracrine pro-angiogenic responses

Cerebral cavernous malformation (CCM) is a cerebrovascular disorder of proven genetic origin characterized by abnormally dilated and leaky capillaries occurring mainly in the central nervous system, with a prevalence of 0.3-0.5% in the general population. Genetic studies have identified causative mutations in three genes, CCM1/KRIT1, CCM2 and CCM3, which are involved in the maintenance of vascular homeostasis. However, distinct studies in animal models have clearly shown that CCM gene mutations alone are not sufficient to cause CCM disease, but require additional contributing factors, including stochastic events of increased oxidative stress and inflammation. Consistently, previous studies have shown that up-regulation of NADPH oxidase-mediated production of reactive oxygen species (ROS) in KRIT1 deficient endothelium contributes to the loss of microvessel barrier function. In this study, we demonstrate that KRIT1 loss-of-function in stromal cells, such as fibroblasts, causes the up-regulation of NADPH oxidase isoform 1 (NOX1) and the activation of inflammatory pathways, which in turn promote an enhanced production of proangiogenic factors, including vascular endothelial growth factor (VEGF) and prostaglandin E2 (PGE2). Furthermore and importantly, we show that conditioned media from KRIT1 null fibroblasts induce proliferation, migration, matrix metalloproteinase 2 (MMP2) activation and VE-cadherin redistribution in wild type human endothelial cells. Taken together, our results demonstrate that KRIT1 loss-of-function in stromal cells affects the surrounding microenvironment through a NOX1-mediated induction and release of angiogenic factors that are able to promote paracrine proangiogenic responses in human endothelial cells, thus pointing to a novel role for endothelial cell-nonautonomous effects of KRIT1 mutations in CCM pathogenesis, and opening new perspectives for disease prevention and treatment.

MiR-107 overexpression attenuates neurotoxicity induced by 6-hydroxydopamine both in vitro and in vivo

Alzheimer's disease (AD), the most common form of dementia, is a neurodegenerative disease characterized by neuronal atrophy in various brain regions. The expression of miR-107 is down-regulated in AD patients and target genes of miR-107 have been shown to directly involved in AD. In this study, we aimed to investigate the potential neuroprotective effects of miR-107. We first assessed brain activity in health controls and patients with AD. Then we examined miR-107 expression in SH-SY5Y and PC12 cells treated with 6-hydroxydopamine (6-OHDA), and investigated its function in cytotoxicity induced by 6-OHDA. We predicted a potential miR-107 target and assessed its role in miR-107 mediated effects and explored the intracellular signaling pathways downstream of miR-107. Finally, we assessed the function of miR-107 in the mouse model insulted by 6-OHDA. We found that 6-OHDA suppressed miR-107 expression and miR-107 played neuroprotective effects against 6-OHDA mediated cytotoxicity. We showed that miR-107 targeted programmed cell death 10 (PDCD10). MiR-107 suppressed PDCD10 expression and exogenous expression of PDCD10 inhibited miR-107 mediated neuroprotection. Additionally, we found that Notch signal pathway was downstream of miR-107/PDCD10. Finally, we found that 6-OHDA treatment suppressed miR-107 in mice and restoration of miR-107 alleviated motor disorder in the mouse model. Our study shows that miR-107 plays important neuroprotective roles against neurotoxicity both in vitro and in vivo by inhibiting PDCD10. Our findings confirm that miR-107 may be involved in AD pathogenesis and may be a therapeutic target for the treatment of AD-related impairments.

Cerebral Cavernous Malformations Develop Through Clonal Expansion of Mutant Endothelial Cells

RATIONALE

Vascular malformations arise in vessels throughout the entire body. Causative genetic mutations have been identified for many of these diseases; however, little is known about the mutant cell lineage within these malformations.

OBJECTIVE

We utilize an inducible mouse model of cerebral cavernous malformations (CCMs) coupled with a multicolor fluorescent reporter to visualize the contribution of mutant endothelial cells (ECs) to the malformation.

METHODS AND RESULTS

We combined a Ccm3 mouse model with the confetti fluorescent reporter to simultaneously delete Ccm3 and label the mutant EC with 1 of 4 possible colors. We acquired Z-series confocal images from serial brain sections and created 3-dimensional reconstructions of entire CCMs to visualize mutant ECs during CCM development. We observed a pronounced pattern of CCMs lined with mutant ECs labeled with a single confetti color (n=42). The close 3-dimensional distribution, as determined by the nearest neighbor analysis, of the clonally dominant ECs within the CCM was statistically different than the background confetti labeling of ECs in non-CCM control brain slices as well as a computer simulation ( P<0.001). Many of the small (<100 μm diameter) CCMs consisted, almost exclusively, of the clonally dominant mutant ECs labeled with the same confetti color, whereas the large (>100 μm diameter) CCMs contained both the clonally dominant mutant cells and wild-type ECs. We propose of model of CCM development in which an EC acquires a second somatic mutation, undergoes clonal expansion to initiate CCM formation, and then incorporates neighboring wild-type ECs to increase the size of the malformation.

CONCLUSIONS

This is the first study to visualize, with single-cell resolution, the clonal expansion of mutant ECs within CCMs. The incorporation of wild-type ECs into the growing malformation presents another series of cellular events whose elucidation would enhance our understanding of CCMs and may provide novel therapeutic opportunities.

Transcriptome clarifies mechanisms of lesion genesis versus progression in models of Ccm3 cerebral cavernous malformations

Cerebral cavernous malformations (CCMs) are dilated capillaries causing epilepsy and stroke. Inheritance of a heterozygous mutation in CCM3/PDCD10 is responsible for the most aggressive familial form of the disease. Here we studied the differences and commonalities between the transcriptomes of microdissected lesional neurovascular units (NVUs) from acute and chronic in vivo Ccm3/Pdcd10ECKO mice, and cultured brain microvascular endothelial cells (BMECs) Ccm3/Pdcd10ECKO.We identified 2409 differentially expressed genes (DEGs) in acute and 2962 in chronic in vivo NVUs compared to microdissected brain capillaries, as well as 121 in in vitro BMECs with and without Ccm3/Pdcd10 loss (fold change ≥ |2.0|; p < 0.05, false discovery rate corrected). A functional clustered dendrogram generated using the Euclidean distance showed that the DEGs identified only in acute in vivo NVUs were clustered in cellular proliferation gene ontology functions. The DEGs only identified in chronic in vivo NVUs were clustered in inflammation and immune response, permeability, and adhesion functions. In addition, 1225 DEGs were only identified in the in vivo NVUs but not in vitro BMECs, and these clustered within neuronal and glial functions. One miRNA mmu-miR-3472a was differentially expressed (FC = - 5.98; p = 0.07, FDR corrected) in the serum of Ccm3/Pdcd10+/- when compared to wild type mice, and this was functionally related as a putative target to Cand2 (cullin associated and neddylation dissociated 2), a DEG in acute and chronic lesional NVUs and in vitro BMECs. Our results suggest that the acute model is characterized by cell proliferation, while the chronic model showed inflammatory, adhesion and permeability processes. In addition, we highlight the importance of extra-endothelial structures in CCM disease, and potential role of circulating miRNAs as biomarkers of disease, interacting with DEGs. The extensive DEGs library of each model will serve as a validation tool for potential mechanistic, biomarker, and therapeutic targets.

Cavernous angiomas: deconstructing a neurosurgical disease

Cavernous angioma (CA) is also known as cavernoma, cavernous hemangioma, and cerebral cavernous malformation (CCM) (National Library of Medicine Medical Subject heading unique ID D006392). In its sporadic form, CA occurs as a solitary hemorrhagic vascular lesion or as clustered lesions associated with a developmental venous anomaly. In its autosomal dominant familial form (Online Mendelian Inheritance in Man #116860), CA is caused by a heterozygous germline loss-of-function mutation in one of three genes-CCM1/KRIT1, CCM2/Malcavernin, and CCM3/PDCD10-causing multifocal lesions throughout the brain and spinal cord.In this paper, the authors review the cardinal features of CA's disease pathology and clinical radiological features. They summarize key aspects of CA's natural history and broad elements of evidence-based management guidelines, including surgery. The authors also discuss evidence of similar genetic defects in sporadic and familial lesions, consequences of CCM gene loss in different tissues at various stages of development, and implications regarding the pathobiology of CAs.The concept of CA with symptomatic hemorrhage (CASH) is presented as well as its relevance to clinical care and research in the field. Pathobiological mechanisms related to CA include inflammation and immune-mediated processes, angiogenesis and vascular permeability, microbiome driven factors, and lesional anticoagulant domains. These mechanisms have motivated the development of imaging and plasma biomarkers of relevant disease behavior and promising therapeutic targets.The spectrum of discoveries about CA and their implications endorse CA as a paradigm for deconstructing a neurosurgical disease.

CCM3 and cerebral cavernous malformation disease

Cerebral cavernous malformations (CCMs) are vascular lesions characterised by enlarged and irregular structure of small blood vessels in the brain, which can result in increased risk of stroke, focal neurological defects and seizures. Three different genes, CCM1/Krev/Rap1 Interacting Trapped 1, CCM2/MGC4607 and CCM3/PDCD10, are associated with the CCMs’ progression, and mutations in one of three CCM genes cause CCM disease. These three CCM proteins have similar function in maintaining the normal structure of small blood vessels. However, CCM3 mutation results in a more severe form of the disease which may suggest that CCM3 has unique biological function in the vasculature. The current review focuses on the signalling pathways mediated by CCM3 in regulating endothelial cell junction, proliferation, migration and permeability. These findings may offer potential therapeutic strategies for the treatment of CCMs.

Comprehensive transcriptome analysis of cerebral cavernous malformation across multiple species and genotypes

The purpose of this study was to determine important genes, functions, and networks contributing to the pathobiology of cerebral cavernous malformation (CCM) from transcriptomic analyses across 3 species and 2 disease genotypes. Sequencing of RNA from laser microdissected neurovascular units of 5 human surgically resected CCM lesions, mouse brain microvascular endothelial cells, Caenorhabditis elegans with induced Ccm gene loss, and their respective controls provided differentially expressed genes (DEGs). DEGs from mouse and C. elegans were annotated into human homologous genes. Cross-comparisons of DEGs between species and genotypes, as well as network and gene ontology (GO) enrichment analyses, were performed. Among hundreds of DEGs identified in each model, common genes and 1 GO term (GO:0051656, establishment of organelle localization) were commonly identified across the different species and genotypes. In addition, 24 GO functions were present in 4 of 5 models and were related to cell-to-cell adhesion, neutrophil-mediated immunity, ion transmembrane transporter activity, and responses to oxidative stress. We have provided a comprehensive transcriptome library of CCM disease across species and for the first time to our knowledge in Ccm1/Krit1 versus Ccm3/Pdcd10 genotypes. We have provided examples of how results can be used in hypothesis generation or mechanistic confirmatory studies.

Cerebrovascular disorders associated with genetic lesions

Cerebrovascular disorders are underlain by perturbations in cerebral blood flow and abnormalities in blood vessel structure. Here, we provide an overview of the current knowledge of select cerebrovascular disorders that are associated with genetic lesions and connect genomic findings with analyses aiming to elucidate the cellular and molecular mechanisms of disease pathogenesis. We argue that a mechanistic understanding of genetic (familial) forms of cerebrovascular disease is a prerequisite for the development of rational therapeutic approaches, and has wider implications for treatment of sporadic (non-familial) forms, which are usually more common.

The STRIPAK complex components FAM40A and FAM40B regulate endothelial cell contractility via ROCKs

BACKGROUND

Endothelial cells provide a barrier between blood and tissues, which is regulated to allow molecules and cells in out of tissues. Patients with cerebral cavernous malformations (CCM) have dilated leaky blood vessels, especially in the central nervous system. A subset of these patients has loss-of-function mutations in CCM3. CCM3 is part of the STRIPAK protein complex that includes the little-characterized proteins FAM40A and FAM40B.

RESULTS

We show here that FAM40A and FAM40B can interact with CCM3. Knockdown of CCM3, FAM40A or FAM40B in endothelial cells by RNAi causes an increase in stress fibers and a reduction in loop formation in an in vitro angiogenesis assay, which can be reverted by inhibiting the Rho-regulated ROCK kinases. FAM40B depletion also increases endothelial permeability.

CONCLUSIONS

These results demonstrate the importance of the FAM40 proteins for endothelial cell physiology, and suggest that they act as part of the CCM3-containing STRIPAK complex.

Recent advances in cerebral cavernous malformation research

Cerebral cavernous malformations (CCM) are manifested by microvascular lesions characterized by leaky endothelial cells with minimal intervening parenchyma predominantly in the central nervous system predisposed to hemorrhagic stroke, resulting in focal neurological defects. Till date, three proteins are implicated in this condition: CCM1 (KRIT1), CCM2 (MGC4607), and CCM3 (PDCD10). These multi-domain proteins form a protein complex via CCM2 that function as a docking site for the CCM signaling complex, which modulates many signaling pathways. Defects in the formation of this signaling complex have been shown to affect a wide range of cellular processes including cell-cell contact stability, vascular angiogenesis, oxidative damage protection and multiple biogenic events. In this review we provide an update on recent advances in structure and function of these CCM proteins, especially focusing on the signaling cascades involved in CCM pathogenesis and the resultant CCM cellular phenotypes in the past decade.

Connexin 43 gap junctions contribute to brain endothelial barrier hyperpermeability in familial cerebral cavernous malformations type III by modulating tight junction structure

Familial cerebral cavernous malformations type III (fCCM3) is a disease of the cerebrovascular system caused by loss-of-function mutations in ccm3 that result in dilated capillary beds that are susceptible to hemorrhage. Before hemorrhage, fCCM3 lesions are characterized by a hyperpermeable blood-brain barrier (BBB), the key pathologic feature of fCCM3. We demonstrate that connexin 43 (Cx43), a gap junction (GJ) protein that is incorporated into the BBB junction complex, is up-regulated in lesions of a murine model of fCCM3. Small interfering RNA-mediated ccm3 knockdown (CCM3KD) in brain endothelial cells in vitro increased Cx43 protein expression, GJ plaque size, GJ intracellular communication (GJIC), and barrier permeability. CCM3KD hyperpermeability was rescued by GAP27, a peptide gap junction and hemichannel inhibitor of Cx43 GJIC. Tight junction (TJ) protein, zonula occludens 1 (ZO-1), accumulated at Cx43 GJs in CCM3KD cells and displayed fragmented staining at TJs. The GAP27-mediated inhibition of Cx43 GJs in CCM3KD cells restored ZO-1 to TJ structures and reduced plaque accumulation at Cx43 GJs. The TJ protein, Claudin-5, was also fragmented at TJs in CCM3KD cells, and GAP27 treatment lengthened TJ-associated fragments and increased Claudin 5-Claudin 5 transinteraction. Overall, we demonstrate that Cx43 GJs are aberrantly increased in fCCM3 and regulate barrier permeability by a TJ-dependent mechanism.-Johnson, A. M., Roach, J. P., Hu, A., Stamatovic, S. M., Zochowski, M. R., Keep, R. F., Andjelkovic, A. V. Connexin 43 gap junctions contribute to brain endothelial barrier hyperpermeability in familial cerebral cavernous malformations type III by modulating tight junction structure.

Arsenic exposure assists ccm3 genetic polymorphism in elevating blood pressure

Epidemiologic study has suggested that arsenic exposure is positively related to increased blood pressure. However, the underlying mechanism concerning interaction between genetic polymorphisms and arsenic exposure remains unclear. In present study, within 395 Chinese, the effects of interaction between arsenic exposure and CCM3 gene polymorphisms on elevation of blood pressure were probed by multiple Logistic regression models after adjusting for confounding factors. Firstly, we found that serum arsenic was positively associated with blood pressure, cholesterol, glucose and C-reactive protein. Then, adjusted for confounding factors of age, gender, smoking, alcohol consumption, BMI and degree of education, arsenic exposure incurred the hazard of increased systolic pressure and diastolic pressure, with odds ratios (ORs) being 1.725 and 1.425, respectively. Distinctly, we found that interactions between rs3804610^* rs9818496, rs6784267^*rs9818496, and rs3804610^* rs6784267 variant genotype can increase significantly risks of SBP. Additionally, interactions between rs9818496, rs3804610 and rs6784267 genotypic variantions and arsenic exposure boosted the hazard of increased systolic pressure, with ORs being 1.496, 1.496 and 1.312. In conclusion, our fingdings suggest that As exposure of population can assist CCM3 polymorphism in elevating SBP.

EphB4 forward signalling mediates angiogenesis caused by CCM3/PDCD10-ablation

CCM3, also named as PDCD10, is a ubiquitous protein expressed in nearly all tissues and in various types of cells. It is essential for vascular development and post-natal vessel maturation. Loss-of-function mutation of CCM3 predisposes for the familial form of cerebral cavernous malformation (CCM). We have previously shown that knock-down of CCM3 stimulated endothelial angiogenesis via impairing DLL4-Notch signalling; moreover, loss of endothelial CCM3 stimulated tumour angiogenesis and promoted tumour growth. The present study was designed to further elucidate the inside signalling pathway involved in CCM3-ablation-mediated angiogenesis. Here we report for the first time that silencing endothelial CCM3 led to a significant up-regulation of EphB4 mRNA and protein expression and to an increased kinase activity of EphB4, concomitantly accompanied by an activation of Erk1/2, which was reversed by treatment with the specific EphB4 kinase inhibitor NVP-BHG712 (NVP), indicating that silencing CCM3 activates EphB4 kinase forward signalling. Furthermore, treatment with NVP rescued the hyper-angiogenic phenotype induced by knock-down of endothelial CCM3 in vitro and in vivo. Additional study demonstrated that the activation of EphB4 forward signalling in endothelial cells under basal condition and after CCM3-silence was modulated by DLL4/Notch signalling, relying EphB4 at downstream of DLL4/Notch signalling. We conclude that angiogenesis induced by CCM3-silence is mediated by the activation of EphB4 forward signalling. The identified endothelial signalling pathway of CCM3-DLL4/Notch-EphB4-Erk1/2 may provide an insight into mechanism of CCM3-ablation-mediated angiogenesis and could potentially contribute to novel therapeutic concepts for disrupting aberrant angiogenesis in CCM and in hyper-vascularized tumours.

Combined HMG-COA reductase and prenylation inhibition in treatment of CCM

Cerebral cavernous malformations (CCMs) are common vascular anomalies that develop in the central nervous system and, more rarely, the retina. The lesions can cause headache, seizures, focal neurological deficits, and hemorrhagic stroke. Symptomatic lesions are treated according to their presentation; however, targeted pharmacological therapies that improve the outcome of CCM disease are currently lacking. We performed a high-throughput screen to identify Food and Drug Administration-approved drugs or other bioactive compounds that could effectively suppress hyperproliferation of mouse brain primary astrocytes deficient for CCM3. We demonstrate that fluvastatin, an inhibitor of 3-hydroxy-3-methyl-glutaryl (HMG)-CoA reductase and the N-bisphosphonate zoledronic acid monohydrate, an inhibitor of protein prenylation, act synergistically to reverse outcomes of CCM3 loss in cultured mouse primary astrocytes and in Drosophila glial cells in vivo. Further, the two drugs effectively attenuate neural and vascular deficits in chronic and acute mouse models of CCM3 loss in vivo, significantly reducing lesion burden and extending longevity. Sustained inhibition of the mevalonate pathway represents a potential pharmacological treatment option and suggests advantages of combination therapy for CCM disease.

Oxidative stress and inflammation in cerebral cavernous malformation disease pathogenesis: Two sides of the same coin

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CCM proteins play pleiotropic roles in various redox-sensitive signaling pathways.

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CCM proteins modulate the crosstalk between redox signaling and autophagy that govern cell homeostasis and stress responses.

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Oxidative stress and inflammation are emerging as key focal determinants of CCM lesion formation, progression and severity.

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The pleiotropic functions of CCM proteins may prevent vascular dysfunctions triggered by local oxidative stress and inflammatory events.

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The distinct therapeutic compounds proposed so far for CCM disease share the ability to modulate redox signaling and autophagy.

Cerebral Cavernous Malformation (CCM) is a vascular disease of proven genetic origin, which may arise sporadically or is inherited as an autosomal dominant condition with incomplete penetrance and highly variable expressivity. CCM lesions exhibit a range of different phenotypes, including wide inter-individual differences in lesion number, size, and susceptibility to intracerebral hemorrhage (ICH). Lesions may remain asymptomatic or result in pathological conditions of various type and severity at any age, with symptoms ranging from recurrent headaches to severe neurological deficits, seizures, and stroke. To date there are no direct therapeutic approaches for CCM disease besides the surgical removal of accessible lesions. Novel pharmacological strategies are particularly needed to limit disease progression and severity and prevent de novo formation of CCM lesions in susceptible individuals.

Useful insights into innovative approaches for CCM disease prevention and treatment are emerging from a growing understanding of the biological functions of the three known CCM proteins, CCM1/KRIT1, CCM2 and CCM3/PDCD10. In particular, accumulating evidence indicates that these proteins play major roles in distinct signaling pathways, including those involved in cellular responses to oxidative stress, inflammation and angiogenesis, pointing to pathophysiological mechanisms whereby the function of CCM proteins may be relevant in preventing vascular dysfunctions triggered by these events. Indeed, emerging findings demonstrate that the pleiotropic roles of CCM proteins reflect their critical capacity to modulate the fine-tuned crosstalk between redox signaling and autophagy that govern cell homeostasis and stress responses, providing a novel mechanistic scenario that reconciles both the multiple signaling pathways linked to CCM proteins and the distinct therapeutic approaches proposed so far. In addition, recent studies in CCM patient cohorts suggest that genetic susceptibility factors related to differences in vascular sensitivity to oxidative stress and inflammation contribute to inter-individual differences in CCM disease susceptibility and severity.

This review discusses recent progress into the understanding of the molecular basis and mechanisms of CCM disease pathogenesis, with specific emphasis on the potential contribution of altered cell responses to oxidative stress and inflammatory events occurring locally in the microvascular environment, and consequent implications for the development of novel, safe, and effective preventive and therapeutic strategies.

Genomic landscape of intracranial meningiomas

Meningiomas are the most common primary intracranial neoplasms in adults. Current histopathological grading schemes do not consistently predict their natural history. Classic cytogenetic studies have disclosed a progressive course of chromosomal aberrations, especially in high-grade meningiomas. Furthermore, the recent application of unbiased next-generation sequencing approaches has implicated several novel genes whose mutations underlie a substantial percentage of meningiomas. These insights may serve to craft a molecular taxonomy for meningiomas and highlight putative therapeutic targets in a new era of rational biology-informed precision medicine.

Micro-computed tomography in murine models of cerebral cavernous malformations as a paradigm for brain disease

BACKGROUND

Cerebral cavernous malformations (CCMs) are hemorrhagic brain lesions, where murine models allow major mechanistic discoveries, ushering genetic manipulations and preclinical assessment of therapies. Histology for lesion counting and morphometry is essential yet tedious and time consuming. We herein describe the application and validations of X-ray micro-computed tomography (micro-CT), a non-destructive technique allowing three-dimensional CCM lesion count and volumetric measurements, in transgenic murine brains.

NEW METHOD

We hereby describe a new contrast soaking technique not previously applied to murine models of CCM disease. Volumetric segmentation and image processing paradigm allowed for histologic correlations and quantitative validations not previously reported with the micro-CT technique in brain vascular disease.

RESULTS

Twenty-two hyper-dense areas on micro-CT images, identified as CCM lesions, were matched by histology. The inter-rater reliability analysis showed strong consistency in the CCM lesion identification and staging (K=0.89, p<0.0001) between the two techniques. Micro-CT revealed a 29% greater CCM lesion detection efficiency, and 80% improved time efficiency.

COMPARISON WITH EXISTING METHOD

Serial integrated lesional area by histology showed a strong positive correlation with micro-CT estimated volume (r(2)=0.84, p<0.0001).

CONCLUSIONS

Micro-CT allows high throughput assessment of lesion count and volume in pre-clinical murine models of CCM. This approach complements histology with improved accuracy and efficiency, and can be applied for lesion burden assessment in other brain diseases.

B-Cell Depletion Reduces the Maturation of Cerebral Cavernous Malformations in Murine Models

Cerebral cavernous malformations (CCMs) are relatively common vascular malformations, characterized by increased Rho kinase (ROCK) activity, vascular hyper-permeability and the presence of blood degradation products including non-heme iron. Previous studies revealed robust inflammatory cell infiltration, selective synthesis of IgG, in situ antigen driven B-cell clonal expansion, and deposition of immune complexes and complement proteins within CCM lesions. We aimed to evaluate the impact of suppressing the immune response on the formation and maturation of CCM lesions, as well as lesional iron deposition and ROCK activity. Two murine models of heterozygous Ccm3 (Pdcd10), which spontaneously develop CCM lesions with severe and milder phenotypes, were either untreated or received anti-mouse BR3 to deplete B cells. Brains from anti-mouse BR3-treated mice exhibited significantly fewer mature CCM lesions and smaller lesions compared to untreated mice. B cell depletion halted the progression of lesions into mature stage 2 lesions but did not prevent their genesis. Non-heme iron deposition and ROCK activity was decreased in lesions of B cell depleted mice. This represents the first report of the therapeutic benefit of B-cell depletion in the development and progression of CCMs, and provides a proof of principle that B cells play a critical role in CCM lesion genesis and maturation. These findings add biologics to the list of potential therapeutic agents for CCM disease. Future studies would characterize the putative antigenic trigger and further define the mechanism of immune response in the lesions.

PDCD10 (CCM3) regulates brain endothelial barrier integrity in cerebral cavernous malformation type 3: role of CCM3-ERK1/2-cortactin cross-talk

Impairment of brain endothelial barrier integrity is critical for cerebral cavernous malformation (CCM) lesion development. The current study investigates changes in tight junction (TJ) complex organization when PDCD10 (CCM3) is mutated/depleted in human brain endothelial cells. Analysis of lesions with CCM3 mutation and brain endothelial cells transfected with CCM3 siRNA (CCM3-knockdown) showed little or no increase in TJ transmembrane and scaffolding proteins mRNA expression, but proteins levels were generally decreased. CCM3-knockdown cells had a redistribution of claudin-5 and occludin from the membrane to the cytosol with no alterations in protein turnover but with diminished protein-protein interactions with ZO-1 and ZO-1 interaction with the actin cytoskeleton. The most profound effect of CCM3 mutation/depletion was on an actin-binding protein, cortactin. CCM3 depletion caused cortactin Ser-phosphorylation, dissociation from ZO-1 and actin, redistribution to the cytosol and degradation. This affected cortical actin ring organization, TJ complex stability and consequently barrier integrity, with constant hyperpermeability to inulin. A potential link between CCM3 depletion and altered cortactin was tonic activation of MAP kinase ERK1/2. ERK1/2 inhibition increased cortactin expression and incorporation into the TJ complex and improved barrier integrity. This study highlights the potential role of CCM3 in regulating TJ complex organization and brain endothelial barrier permeability.

Downregulation of programmed cell death 10 is associated with tumor cell proliferation, hyperangiogenesis and peritumoral edema in human glioblastoma

Background

Neovascularization and peritumoral edema are hallmarks of glioblastoma (GBM). Programmed cell death 10 (PDCD10) plays a pivotal role in regulating apoptosis, neoangiogenesis and vessel permeability and is implicated in certain tumor signaling pathways. However, little is known about PDCD10 in GBM. We aimed to investigate the expression pattern of PDCD10 and to identify the association of its expression with some molecular and clinical parameters in human GBM.

Methods

mRNA and protein expression of PDCD10 were examined respectively by real-time RT-PCR and Western blotting in GBM (n = 27), astrocytoma grade II (n = 13) and control (n = 11). The protein level of p-Akt and GFAP was detected by Western blot. Double-imunofluorecent staining was performed to reveal the cellular expression profile of PDCD10. Brain edema and microvascular density (MVD) were respectively analyzed based on pre-operative MRI and after laminin immnostaining. MGMT promoter methylation was detected by methylation specific PCR.

Results

mRNA and protein levels of PDCD10 were significantly downregulated in GBM, concomitantly accompanied by the activation of Akt. PDCD10 immunoreactivity was absent in proliferating tumor cells, endothelial cells and GFAP-positive cells, but exclusively present in the hypoxic pseudopalisading cells which underwent apoptosis. Moreover, loss of PDCD10 was associated with a higher MVD and a more severe peritumoral edema but not with MGMT promoter methylation in GBM.

Conclusion

We report for the first time that PDCD10 expression is downregulated in GBM, which is associated with the activation of Akt signaling protein. PDCD10 is potentially implicated in tumor proliferation and apoptosis, hyperangiogenesis and peritumoral edema in GBM.

Loss of endothelial programmed cell death 10 activates glioblastoma cells and promotes tumor growth

BACKGROUND

Neo-angiogenesis is a hallmark of glioblastoma (GBM) and is sustained by autocrine and paracrine interactions between neoplastic and nonneoplastic cells. Programmed cell death 10 (PDCD10) is ubiquitously expressed in nearly all tissues and plays crucial roles in regulating angiogenesis and apoptosis. We recently discovered the absence of PDCD10 expression in the tumor vessels of GBM patients. This raised the hypothesis that loss of endothelial PDCD10 affected GBM cell phenotyping and tumor progression.

METHODS

Endothelial PDCD10 was silenced by siRNA and lentiviral shRNA. The tumor cell phenotype was studied in direct and indirect co-culture of endothelial cells (ECs) with U87 or LN229. Angiogenic protein array was performed in the media of PDCD10-silenced ECs. Tumor angiogenesis and tumor growth were investigated in a human GBM xenograft mouse model.

RESULTS

Endothelial silence of PDCD10 significantly stimulated tumor cell proliferation, migration, adhesion, and invasion and inhibited apoptosis in co-cultures. Stable knockdown of endothelial PDCD10 increased microvessel density and the formation of a functional vascular network, leading to a 4-fold larger tumor mass in mice. Intriguingly, endothelial deletion of PDCD10 increased (≥2-fold) the release of 20 of 55 tested proangiogenic factors including VEGF, which in turn activated Erk1/2 and Akt in GBM cells.

CONCLUSIONS

For the first time, we provide evidence that loss of endothelial PDCD10 activates GBM cells and promotes tumor growth, most likely via a paracrine mechanism. PDCD10 shows a tumor-suppressor-like function in the cross talk between ECs and tumor cells and is potentially implicated in GBM progression.

The cerebral cavernous malformation 3 gene is necessary for senescence induction

Mutations in cerebral cavernous malformation 3 gene are known to result in development of vascular malformations and have recently been proposed to also give rise to meningiomas. We report in this study that lack of CCM3 unexpectedly impairs the senescence response of cells, and this is related to the inability of CCM3-deficient cells to induce the C/EBPβ transcription factor and implement the senescence-associated secretory phenotype. Induction of C/EBPβ and cytokines is also impaired in the absence of CCM3 in response to cytokines in nonsenescent cells, pointing to it being a primary defect and not secondary to impaired senescence. CCM3-deficient cells also have a defect in autophagy at late passages of culture, and this defect is also not dependent on impaired senescence, as it is evident in immortal cells after nutrient starvation. Further, these two defects may be related, as enforcing autophagy in CCM3-deficient late passage cells increases C/EBPβ cytokine expression. These results broaden our knowledge on the mechanisms by which CCM3 deficiency results in disease and open new avenues of research into both CCM3 and senescence biology.