Deletions in CCM2 are a common cause of cerebral cavernous malformations

Updates in Genetic Testing for Head and Neck Vascular Anomalies

Vascular anomalies include benign or malignant tumors or benign malformations of the arteries, veins, capillaries, or lymphatic vasculature. The genetic etiology of the lesion is essential to define the lesion and can help navigate choice of therapy. . In the United States, about 1.2% of the population has a vascular anomaly, which may be underestimating the true prevalence as genetic testing for these conditions continues to evolve.

Pathophysiology of Slow-Flow Vascular Malformations: Current Understanding and Unanswered Questions

Background

Slow-flow vascular malformations include venous, lymphatic, and lymphaticovenous malformations. Recent studies have linked genetic variants hyperactivating either the PI3K/AKT/mTOR and/or RAS/RAF/MAPK signaling pathways with slow-flow vascular malformation development, leading to the use of pharmacotherapies such as sirolimus and alpelisib. It is important that clinicians understand basic and translational research advances in slow-flow vascular malformations.

Methods

A literature review of basic science publications in slow-flow vascular malformations was performed on Pubmed, using search terms "venous malformation," "lymphatic malformation," "lymphaticovenous malformation," "genetic variant," "genetic mutation," "endothelial cells," and "animal model." Relevant publications were reviewed and summarized.

Results

The study of patient tissues and the use of primary pathogenic endothelial cells from vascular malformations shed light on their pathological behaviors, such as endothelial cell hyperproliferation and disruptions in vessel architecture. The use of xenograft and transgenic animal models confirmed the pathogenicity of genetic variants and allowed for preclinical testing of potential therapies. These discoveries underscore the importance of basic and translational research in understanding the pathophysiology of vascular malformations, which will allow for the development of improved biologically targeted treatments.

Conclusion

Despite basic and translation advances, a cure for slow-flow vascular malformations remains elusive. Many questions remain unanswered, including how genotype variants result in phenotypes, and genotype-phenotype heterogeneity. Continued research into venous and lymphatic malformation pathobiology is critical in understanding the mechanisms by which genetic variants contribute to vascular malformation phenotypic features.

The First Potentially Causal Genetic Variant Documented in a Polish Woman with Multiple Cavernous Malformations of the Brain

Cerebral cavernous malformations (CCMs) are relatively common in the central nervous system. They occur in two forms, sporadic and familial (FCCMs). Three genes are recognized to be associated with FCCM, including CCM1, CCM2, and CCM3, the latter also called PDCD10. In this article, we describe a single-nucleotide variant in the PDCD10 gene in a 23-year-old Polish female with CCM. The NM_007217.4 (PDCD10): c.395+1G>A variant destroys the canonical splice donor site following exon 6. This is the first reported genetically characterized case of CCM (FCCM) in Poland.

Large-scale detection and characterization of interchromosomal rearrangements in normozoospermic bulls using massive genotype and phenotype data sets

In this paper, we developed a highly sensitive approach to detect interchromosomal rearrangements in cattle by searching for abnormal linkage disequilibrium patterns between markers located on different chromosomes in large paternal half-sib families genotyped as part of routine genomic evaluations. We screened 5571 families of artificial insemination sires from 15 breeds and revealed 13 putative interchromosomal rearrangements, 12 of which were validated by cytogenetic analysis and long-read sequencing. These consisted of one Robertsonian fusion, 10 reciprocal translocations, and the first case of insertional translocation reported in cattle. Taking advantage of the wealth of data available in cattle, we performed a series of complementary analyses to define the exact nature of these rearrangements, investigate their origins, and search for factors that may have favored their occurrence. We also evaluated the risks to the livestock industry and showed significant negative effects on several traits in the sires and in their balanced or aneuploid progeny compared with wild-type controls. Thus, we present the most comprehensive and thorough screen for interchromosomal rearrangements compatible with normal spermatogenesis in livestock species. This approach is readily applicable to any population that benefits from large genotype data sets, and will have direct applications in animal breeding. Finally, it also offers interesting prospects for basic research by allowing the detection of smaller and rarer types of chromosomal rearrangements than GTG banding, which are interesting models for studying gene regulation and the organization of genome structure.

Clinicoradiologic data of familial cerebral cavernous malformation with age-related disease burden

OBJECTIVE

Familial cerebral cavernous malformation (FCCM) is an autosomal dominant disease induced by loss-of-function mutations in three CCM genes, KRIT1, CCM2, and PDCD10. However, previous studies paid little attention to analyzing the radiologic features and age-related disease burden according to the genes. Therefore, we retrospectively reviewed the genetic tests of our center's clinical FCCM patients.

METHOD

This study investigated clinical FCCM patients with multiple lesions or a family history of CCMs who underwent the FCCM gene (KRTI1, CCM2, and PDCD10) panel test. The clinical, genetic, and radiologic features were analyzed.

RESULT

Among the patients (n = 34) undergoing the FCCM gene test, twenty-seven patients had CCM confirmed by brain MRI, and twenty-one patients were considered to have FCCM (cohort 1). In cohort 1, thirteen patients had mutations in the FCCM gene, but eight did not. Cohort 2 comprised cohort 1 and four family members with the same mutation as the probands. Six novel variants in CCM genes were detected (KRIT1 c.22_26del, c.815dup, c.1094_1098del, c.1147-2A>G, c.2124dup, and PDCD10 c.150 + 1dup). Cohort 1 demonstrated that brainstem lesions were mostly associated with the mutation detection in CCM genes (brainstem, lateral temporal, and parietal lesions vs. lateral temporal and parietal lesions, AUC 0.928 vs. 0.779, P = 0.0389). The radiologic severity worsened according to age in the KRIT1 group compared with the Mutation not detected group (correlation coefficient 0.75 (P < 0.001) versus 0.53 (P = 0.004)).

CONCLUSION

The brainstem lesion could be the radiologic marker for FCCM with the mutation detected. The age-related disease burden regarding FCCM according to genetic information was demonstrated.

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.

Natural history of familial cerebral cavernous malformation syndrome in children: a multicenter cohort study

PURPOSE

There is limited data concerning neuroimaging findings and longitudinal evaluation of familial cerebral cavernous malformations (FCCM) in children. Our aim was to study the natural history of pediatric FCCM, with an emphasis on symptomatic hemorrhagic events and associated clinical and imaging risk factors.

METHODS

We retrospectively reviewed all children diagnosed with FCCM in four tertiary pediatric hospitals between January 2010 and March 2022. Subjects with first available brain MRI and [Formula: see text] 3 months of clinical follow-up were included. Neuroimaging studies were reviewed, and clinical data collected. Annual symptomatic hemorrhage risk rates and cumulative risks were calculated using survival analysis and predictors of symptomatic hemorrhagic identified using regression analysis.

RESULTS

Forty-one children (53.7% males) were included, of whom 15 (36.3%) presenting with symptomatic hemorrhage. Seven symptomatic hemorrhages occurred during 140.5 person-years of follow-up, yielding a 5-year annual hemorrhage rate of 5.0% per person-year. The 1-, 2-, and 5-year cumulative risks of symptomatic hemorrhage were 7.3%, 14.6%, and 17.1%, respectively. The latter was higher in children with prior symptomatic hemorrhage (33.3%), CCM2 genotype (33.3%), and positive family history (20.7%). Number of brainstem (adjusted hazard ratio [HR] = 1.37, P = 0.005) and posterior fossa (adjusted HR = 1.64, P = 0.004) CCM at first brain MRI were significant independent predictors of prospective symptomatic hemorrhage.

CONCLUSION

The 5-year annual and cumulative symptomatic hemorrhagic risk in our pediatric FCCM cohort equals the overall risk described in children and adults with all types of CCM. Imaging features at first brain MRI may help to predict potential symptomatic hemorrhage at 5-year follow-up.

Cas9-Mediated Nanopore Sequencing Enables Precise Characterization of Structural Variants in CCM Genes

Deletions in the CCM1, CCM2, and CCM3 genes are a common cause of familial cerebral cavernous malformations (CCMs). In current molecular genetic laboratories, targeted next-generation sequencing or multiplex ligation-dependent probe amplification are mostly used to identify copy number variants (CNVs). However, both techniques are limited in their ability to specify the breakpoints of CNVs and identify complex structural variants (SVs). To overcome these constraints, we established a targeted Cas9-mediated nanopore sequencing approach for CNV detection with single nucleotide resolution. Using a MinION device, we achieved complete coverage for the CCM genes and determined the exact size of CNVs in positive controls. Long-read sequencing for a CCM1 and CCM2 CNV revealed that the adjacent ANKIB1 and NACAD genes were also partially or completely deleted. In addition, an interchromosomal insertion and an inversion in CCM2 were reliably re-identified by long-read sequencing. The refinement of CNV breakpoints by long-read sequencing enabled fast and inexpensive PCR-based variant confirmation, which is highly desirable to reduce costs in subsequent family analyses. In conclusion, Cas9-mediated nanopore sequencing is a cost-effective and flexible tool for molecular genetic diagnostics which can be easily adapted to various target regions.

Genetic genealogy uncovers a founder deletion mutation in the cerebral cavernous malformations 2 gene

Cerebral cavernous malformations (CCM) are vascular malformations consisting of collections of enlarged capillaries occurring in the brain or spinal cord. These vascular malformations can occur sporadically or susceptibility to develop these can be inherited as an autosomal dominant trait due to mutation in one of three genes. Over a decade ago, we described a 77.6 Kb germline deletion spanning exons 2-10 in the CCM2 gene found in multiple affected individuals from seemingly unrelated families. Segregation analysis using linked, microsatellite markers indicated that this deletion may have arisen at least twice independently. In the ensuing decades, many more CCM patients have been identified with this deletion. In this present study we examined 27 reportedly unrelated affected individuals with this deletion. To investigate the origin of the deletion at base pair level resolution, we sequenced approximately 10 Kb upstream and downstream from the recombination junction on the deleted allele. All patients showed the identical SNP haplotype across this combined 20 Kb interval. In parallel, genealogical records have traced 11 of these individuals to five separate pedigrees dating as far back as the 1600-1700s. These haplotype and genealogical data suggest that these families and the remaining "unrelated" samples converge on a common ancestor due to a founder mutation occurring centuries ago on the North American continent. We also note that another gene, NACAD, is included in this deletion. Although patient self-reporting does not indicate an apparent phenotypic consequence for heterozygous deletion of NACAD, further investigation is warranted for these patients.

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.

Cerebral Cavernous Malformation: Immune and Inflammatory Perspectives

Cerebral cavernous malformation (CCM) is a type of vascular anomaly that arises due to the dyshomeostasis of brain capillary networks. In the past two decades, many advances have been made in this research field. Notably, as a more reasonable current view, the CCM lesions should be attributed to the results of a great number of additional events related to the homeostasis disorder of the endothelial cell. Indeed, one of the most fascinating concerns in the research field is the inflammatory perturbation in the immune microenvironment, which would affect the disease progression as well as the patients’ outcomes. In this work, we focused on this topic, and underlined the immune-related factors’ contribution to the CCM pathologic progression.

In-silico analysis of nonsynonymous genomic variants within CCM2 gene reaffirm the existence of dual cores within typical PTB domain

Purpose

The objective of this study is to validate the existence of dual cores within the typical phosphotyrosine binding (PTB) domain and to identify potentially damaging and pathogenic nonsynonymous coding single nuclear polymorphisms (nsSNPs) in the canonical PTB domain of the CCM2 gene that causes cerebral cavernous malformations (CCMs).

Methods

The nsSNPs within the coding sequence for PTB domain of human CCM2 gene, retrieved from exclusive database searches, were analyzed for their functional and structural impact using a series of bioinformatic tools. The effects of mutations on the tertiary structure of the PTB domain in human CCM2 protein were predicted to examine the effect of nsSNPs on the tertiary structure of PTB Cores.

Results

Our mutation analysis, through alignment of protein structures between wildtype CCM2 and mutant, predicted that the structural impacts of pathogenic nsSNPs is biophysically limited to only the spatially adjacent substituted amino acid site with minimal structural influence on the adjacent core of the PTB domain, suggesting both cores are independently functional and essential for proper CCM2 PTB function.

Conclusion

Utilizing a combination of protein conservation and structure-based analysis, we analyzed the structural effects of inherited pathogenic mutations within the CCM2 PTB domain. Our results predicted that the pathogenic amino acid substitutions lead to only subtle changes locally, confined to the surrounding tertiary structure of the PTB core within which it resides, while no structural disturbance to the neighboring PTB core was observed, reaffirming the presence of independently functional dual cores in the CCM2 typical PTB domain.

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The pathogenic amino acid mutants lead to subtle structural changes in the PTB core.

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No structural disturbance to the neighboring PTB core was observed.

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Data reaffirm the presence of dual functional cores in the CCM2 PTB domain.

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More new genetic variants leading to CCM pathogenesis were suggested.

Compendium of causative genes and their encoded proteins for common monogenic disorders

A compendium is presented of inherited monogenic disorders that have a prevalence of >1:20,000 in the human population, along with their causative genes and encoded proteins. "Simple" monogenic diseases are those for which the clinical features are caused by mutations impacting a single gene, usually in a manner that alters the sequence of the encoded protein. Of course, for a given "monogenic disorder", there is sometimes more than one potential disease gene, mutations in any one of which is sufficient to cause phenotypes of that disorder. Disease-causing mutations for monogenic disorders are usually passed on from generation to generation in a Mendelian fashion, and originate from spontaneous (de novo) germline founder mutations. In the past monogenic disorders have often been written off as targets for drug discovery because they sometimes are assumed to be rare disorders, for which the meager projected financial payoff of drug discovery and development has discouraged investment. However, not all monogenic diseases are rare. Here, we report that that currently available data identifies 72 disorders with a prevalence of at least 1 in 20,000 humans. For each, we tabulate the gene(s) for which mutations cause the spectrum of phenotypes associated with that disorder. We also identify the gene and protein that most commonly causes each disease. 34 of these disorders are caused exclusively by mutations in only a single gene and encoded protein.

Assessing the association of common genetic variants in EPHB4 and RASA1 with phenotype severity in familial cerebral cavernous malformation

Background

To investigate whether common variants in EPHB4 and RASA1 are associated with cerebral cavernous malformation (CCM) disease severity phenotypes, including intracranial hemorrhage (ICH), total and large lesion counts.

Methods

Familial CCM cases enrolled in the Brain Vascular Malformation Consortium were included (n = 338). Total lesions and large lesions (≥5 mm) were counted on MRI; clinical history of ICH at enrollment was assessed by medical records. Samples were genotyped on the Affymetrix Axiom Genome‐Wide LAT1 Human Array. We tested the association of seven common variants (three in EPHB4 and four in RASA1) using multivariable logistic regression for ICH (odds ratio, OR) and multivariable linear regression for total and large lesion counts (proportional increase, PI), adjusting for age, sex, and three principal components. Significance was based on Bonferroni adjustment for multiple comparisons (0.05/7 variants = 0.007).

Results

EPHB4 variants were not significantly associated with CCM severity phenotypes. One RASA1 intronic variant (rs72783711 A>C) was significantly associated with ICH (OR = 1.82, 95% CI = 1.21–2.37, p = 0.004) and nominally associated with large lesion count (PI = 1.17, 95% CI = 1.03–1.32, p = 0.02).

Conclusion

A common RASA1 variant may be associated with ICH and large lesion count in familial CCM. EPHB4 variants were not associated with any of the three CCM severity phenotypes.

Cerebral Cavernous Malformation: From Mechanism to Therapy

Cerebral cavernous malformations are acquired vascular anomalies that constitute a common cause of central nervous system hemorrhage and stroke. The past 2 decades have seen a remarkable increase in our understanding of the pathogenesis of this vascular disease. This new knowledge spans genetic causes of sporadic and familial forms of the disease, molecular signaling changes in vascular endothelial cells that underlie the disease, unexpectedly strong environmental effects on disease pathogenesis, and drivers of disease end points such as hemorrhage. These novel insights are the integrated product of human clinical studies, human genetic studies, studies in mouse and zebrafish genetic models, and basic molecular and cellular studies. This review addresses the genetic and molecular underpinnings of cerebral cavernous malformation disease, the mechanisms that lead to lesion hemorrhage, and emerging biomarkers and therapies for clinical treatment of cerebral cavernous malformation disease. It may also serve as an example for how focused basic and clinical investigation and emerging technologies can rapidly unravel a complex disease mechanism.

Systemic and CNS manifestations of inherited cerebrovascular malformations

Cerebrovascular malformations occur in both sporadic and inherited patterns. This paper reviews imaging and clinical features of cerebrovascular malformations with a genetic basis. Genetic diseases such as familial cerebral cavernous malformations and hereditary hemorrhagic telangiectasia often have manifestations in bone, skin, eyes, and visceral organs, which should be recognized. Genetic and molecular mechanisms underlying the inherited disorders are becoming better understood, and treatments are likely to follow. An interaction between the intestinal microbiome and formation of cerebral cavernous malformations has emerged, with possible treatment implications. Two-hit mechanisms are involved in these disorders, and additional triggering mechanisms are part of the development of malformations. Hereditary hemorrhagic telangiectasia encompasses a variety of vascular malformations, with widely varying risks, and a more recently recognized association with cortical malformations. Somatic mutations are implicated in the genesis of some sporadic malformations, which means that discoveries related to inherited disorders may aid treatment of sporadic cases. This paper summarizes the current state of knowledge of these conditions, salient features regarding mechanisms of development, and treatment prospects.

A Novel CCM2 Gene Mutation Associated With Cerebral Cavernous Malformation

Cerebral cavernous malformations (CCMs) are the second most prevalent type of vascular malformation within the central nervous system. CCMs occur in two forms—sporadic and familial—the latter of which has an autosomal dominant mode of inheritance with incomplete penetrance and variable clinical expressivity. There are three genes considered to be associated with CCMs,—CCM1, which codes for KRIT1 protein; CCM2, which codes for MGC4607 protein; and CCM3, which codes for PDCD10 protein. To date, more than 74 gene mutations of CCM2 have been reported, and ~45% are deletion mutations. In this article, we disclose a novel CCM2 genetic variant (c.755delC, p.S252fs^*40X) identified in a Chinese family to enrich the database of CCM2 genotypes.

Novel Pathogenic Variants in a Cassette Exon of CCM2 in Patients With Cerebral Cavernous Malformations

Autosomal dominant cerebral cavernous malformation (CCM) represents a genetic disorder with a high mutation detection rate given that stringent inclusion criteria are used and copy number variation analyses are part of the diagnostic workflow. Pathogenic variants in either CCM1 (KRIT1), CCM2 or CCM3 (PDCD10) can be identified in 87–98% of CCM families with at least two affected individuals. However, the interpretation of novel sequence variants in the 5′-region of CCM2 remains challenging as there are various alternatively spliced transcripts and different transcription start sites. Comprehensive genetic and clinical data of CCM2 patients with variants in cassette exons that are either skipped or included into alternative CCM2 transcripts in the splicing process can significantly facilitate clinical variant interpretation. We here report novel pathogenic CCM2 variants in exon 3 and the adjacent donor splice site, describe the natural history of CCM disease in mutation carriers and provide further evidence for the classification of the amino acids encoded by the nucleotides of this cassette exon as a critical region within CCM2. Finally, we illustrate the advantage of a combined single nucleotide and copy number variation detection approach in NGS-based CCM1/CCM2/CCM3 gene panel analyses which can significantly reduce diagnostic turnaround time.

Phenotypic characterization of murine models of cerebral cavernous malformations

Cerebral cavernous malformations (CCMs) are clusters of dilated capillaries that affect around 0.5% of the population. CCMs exist in two forms, sporadic and familial. Mutations in three documented genes, KRIT1(CCM1), CCM2, and PDCD10(CCM3), cause the autosomal dominant form of the disease, and somatic mutations in these same genes underlie lesion development in the brain. Murine models with constitutive or induced loss of respective genes have been applied to study disease pathobiology and therapeutic manipulations. We aimed to analyze the phenotypic characteristic of two main groups of models, the chronic heterozygous models with sensitizers promoting genetic instability, and the acute neonatal induced homozygous knockout model. Acute model mice harbored a higher lesion burden than chronic models, more localized in the hindbrain, and largely lacking iron deposition and inflammatory cell infiltrate. The chronic model mice showed a lower lesion burden localized throughout the brain, with significantly greater perilesional iron deposition, immune B- and T-cell infiltration, and less frequent junctional protein immunopositive endothelial cells. Lesional endothelial cells in both models expressed similar phosphorylated myosin light chain immunopositivity indicating Rho-associated protein kinase activity. These data suggest that acute models are better suited to study the initial formation of the lesion, while the chronic models better reflect lesion maturation, hemorrhage, and inflammatory response, relevant pathobiologic features of the human disease.

A Novel CCM1/KRIT1 Heterozygous Nonsense Mutation (c.1864C>T) Associated with Familial Cerebral Cavernous Malformation: a Genetic Insight from an 8-Year Continuous Observational Study

Cerebral cavernous malformation (CCM) is a congenital vascular abnormality that predominantly affects the central nervous system, but that sometimes encroaches other vital tissues, including the retina, skin, and even liver. The familial form of CCM (FCCM) is considered to be an autosomal dominant disease with incomplete penetrance and variable expression, which is often attributed to mutations in three genes: CCM1, CCM2, and CCM3. We screened a Chinese family diagnosed with FCCM by using Sanger sequencing. A 29-year-old male proband with cutaneous angiomas was pathologically diagnosed but presented with an atypical form of CCM as revealed by magnetic resonance imaging (MRI) findings, prompting further clinical evaluation and genetic analyses of him and his immediate family. We performed continuous observation over an 8-year period using MRI gradient echo imaging and susceptibility-weighted imaging of these individuals. Sanger sequencing of the CCM1, CCM2, and CCM3 genes identified a novel heterozygous nonsense nucleotide transition (c.1864C>T; p.Gln622X) in exon 17 of the CCM1/KRIT1 gene; this mutation was predicted to cause a premature stop codon (TAG) at nucleotides 1864 to 1866 to generate a truncated Krev interaction trapped 1 (Krit1) protein of 621 amino acids. During this long-term observational study, one of the enrolled family members with neurological deficits progressed to a stage indicative of brain surgery. This study provides a new CCM gene mutation profile, which highlights the significance of genetic counseling for individuals suspected of having this condition.

Genome-Wide Sequencing Reveals MicroRNAs Downregulated in Cerebral Cavernous Malformations

Cerebral cavernous malformations (CCM) are vascular lesions associated with loss-of-function mutations in one of the three genes encoding KRIT1 (CCM1), CCM2, and PDCD10. Recent understanding of the molecular mechanisms that lead to CCM development is limited. The role of microRNAs (miRNAs) has been demonstrated in vascular pathologies resulting in loss of tight junction proteins, increased vascular permeability and endothelial cell dysfunction. Since the relevance of miRNAs in CCM pathophysiology has not been elucidated, the primary aim of the study was to identify the miRNA-mRNA expression network associated with CCM. Using small RNA sequencing, we identified a total of 764 matured miRNAs expressed in CCM patients compared to the healthy brains. The expression of the selected miRNAs was validated by qRT-PCR, and the results were found to be consistent with the sequencing data. Upon application of additional statistical stringency, five miRNAs (let-7b-5p, miR-361-5p, miR-370-3p, miR-181a-2-3p, and miR-95-3p) were prioritized to be top CCM-relevant miRNAs. Further in silico analyses revealed that the prioritized miRNAs have a direct functional relation with mRNAs, such as MIB1, HIF1A, PDCD10, TJP1, OCLN, HES1, MAPK1, VEGFA, EGFL7, NF1, and ENG, which are previously characterized as key regulators of CCM pathology. To date, this is the first study to investigate the role of miRNAs in CCM pathology. By employing cutting edge molecular and in silico analyses on clinical samples, the current study reports global miRNA expression changes in CCM patients and provides a rich source of data set to understand detailed molecular machinery involved in CCM pathophysiology.

The pathobiology of vascular malformations: insights from human and model organism genetics

Vascular malformations may arise in any of the vascular beds present in the human body. These lesions vary in location, type, and clinical severity of the phenotype. In recent years, the genetic basis of several vascular malformations has been elucidated. This review will consider how the identification of the genetic factors contributing to different vascular malformations, with subsequent functional studies in animal models, has provided a better understanding of these factors that maintain vascular integrity in vascular beds, as well as their role in the pathogenesis of vascular malformations. Copyright © 2016 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

CCM3/SERPINI1 bidirectional promoter variants in patients with cerebral cavernous malformations: a molecular and functional study

BACKGROUND

Cerebral cavernous malformations (CCMs) are vascular anomalies of the nervous system mostly located in the brain presenting sporadically or familial. Causes of familial forms are mutations in CCM1 (Krit1), CCM2 (MGC4607) and CCM3 (PDCD10) genes. Sporadic forms with no affected relative most often have only one lesion and no germ line mutations. However, a number of sporadic cases with multiple lesions have been reported and are indeed genetic cases with a de novo mutation or a mutation inherited from an asymptomatic parent.

METHODS

Here, we performed an analysis of regulatory region of CCM genes in 60 sporadic patients, negative for mutations in coding region and intron-exon boundaries and large deletion/duplications in CCM genes by direct sequencing and MLPA. Among 5 variants identified in 851-bp region shared by CCM3 and SERPINI1 genes and acting as asymmetric bidirectional promoter, two polymorphisms c.-639 T > C/rs9853967 and c.-591 T > C/rs11714980 were selected. A case-control study was performed to analyze their possible relationships with sporadic CCMs. Promoter haplotypes activities on CCM3/SERPINI1 genes expression were tested by dual-luciferase assay.

RESULTS

No variants were identified in CCM1 and CCM2 regulatory regions. In CCM3/SERPINI1 asymmetric bidirectional promoter 5 variants, 2 of them unknown and 3 corresponding to polymorphisms c.-639 T > C/rs9853967, c.-591 T > C/rs11714980 and c.-359G > A/rs9834676 were detected. While rs9853967 and rs11714980 polymorphisms fall in a critical regulatory fragment outside the minimal promoter in intergenic region, other variants had no effects on transcription factor binding according to RegRNA tool. Case-control study performed on 60 patients and 350 healthy controls showed frequencies of the mutated alleles significantly higher in the control group than in patients. Furthermore, the functional assay showed a significant reduction of CCM3 expression for C-C haplotype even more than for T-C and C-T haplotypes. In SERPINI1 direction, the reduction was not statistically significant.

CONCLUSIONS

Our data indicated that rs9853967 and rs11714980 polymorphisms could be associated with a protective role in CCM disease.

Identification of a Novel Deletion Mutation (c.1780delG) and a Novel Splice-Site Mutation (c.1412-1G>A) in the CCM1/KRIT1 Gene Associated with Familial Cerebral Cavernous Malformation in the Chinese Population

Cerebral cavernous malformation (CCM) is a congenital vascular anomaly predominantly located within the central nervous system. Its familial forms (familial cerebral cavernous malformation (FCCM)), inherited in an autosomal dominant manner with incomplete penetrance, are attributed to mutations in CCM1/KRIT1, CCM2/MGC4607, and CCM3/PDCD10 genes. To date, little is known about the genetic alterations leading to FCCM in the Chinese population. We aimed to investigate the genetic defect of FCCM by DNA sequencing in Chinese families. This study enrolled five Chinese families with FCCM. All index cases underwent surgical treatment and were diagnosed with CCM by pathology; their relatives were diagnosed based on radiological and/or pathological evidence. Genomic DNA was extracted from peripheral blood and amplified using polymerase chain reaction (PCR) for DNA sequencing. The five families comprised a total of 21 affected individuals: 12 of these were symptomatic, and 9 were asymptomatic. Sequence analyses in the index patients disclosed three heterozygous loss-of-function mutations in the CCM1/KRIT1 gene in three families, respectively: a novel deletion mutation (c.1780delG; p.Ala594HisfsX67) in exon 16, a novel splice-site mutation (c.1412-1G>A) in the splice acceptor site in intron 13, and a previously described 4-bp deletion (c.1197_1200delCAAA; p.Gln401ThrfsX10) in exon 12. All of these mutations are predicted to cause a premature termination codon to generate a truncated Krev interaction trapped 1 (Krit1) protein. These mutations segregated in affected relatives. Our findings provided new CCM1 gene mutation profiles, which help to elucidate the pathogenesis of FCCM and will be of great significance in genetic counseling.

Endothelial Cells Lining Sporadic Cerebral Cavernous Malformation Cavernomas Undergo Endothelial-to-Mesenchymal Transition

BACKGROUND AND PURPOSE

Cerebral cavernous malformation (CCM) is characterized by multiple lumen vascular malformations in the central nervous system that can cause neurological symptoms and brain hemorrhages. About 20% of CCM patients have an inherited form of the disease with ubiquitous loss-of-function mutation in any one of 3 genes CCM1, CCM2, and CCM3. The rest of patients develop sporadic vascular lesions histologically similar to those of the inherited form and likely mediated by a biallelic acquired mutation of CCM genes in the brain vasculature. However, the molecular phenotypic features of endothelial cells in CCM lesions in sporadic patients are still poorly described. This information is crucial for a targeted therapy.

METHODS

We used immunofluorescence microscopy and immunohistochemistry to analyze the expression of endothelial-to-mesenchymal transition markers in the cavernoma of sporadic CCM patients in parallel with human familial cavernoma as a reference control.

RESULTS

We report here that endothelial cells, a cell type critically involved in CCM development, undergo endothelial-to-mesenchymal transition in the lesions of sporadic patients. This switch in endothelial phenotype has been described only in genetic CCM patients and in murine models of the disease. In addition, TGF-β/p-Smad- and β-catenin-dependent signaling pathways seem activated in sporadic cavernomas as in familial ones.

CONCLUSIONS

Our findings support the use of common therapeutic strategies for both sporadic and genetic CCM malformations.

Genetics of cerebral cavernous malformations: current status and future prospects

Cerebral cavernous malformations (CCM) are vascular lesions which affect up to 0.5% of the general population, predisposing to headaches, seizures, cerebral hemorrhages and focal neurological deficits. CCM occurs in both sporadic and familial forms; familial cases follow an autosomal-dominant mode of inheritance and are caused by mutations in CCM1 (KRIT1), CCM2 (MGC4607), or CCM3 (PDCD10). Somatic mutations within the three CCM genes have been identified in CCM lesions from both sporadic and familial patients. We reviewed articles published in PubMed in English prior to March 2015 and provide an update on CCM mutations and the screening strategies used to identify them. Further, we summarize the specific clinical features related to CCM genotypes. As 5% to 15% of familial CCM cases remain genetically unexplained, we also discuss future approaches to expand understanding of the genetic architecture of CCM. Finally, we discuss possible genetic modifiers of CCM disease severity and progression. Understanding the genetic architecture of CCM is essential for an earlier diagnosis of the disease, predictive testing of at-risk patients, and design of targeted medical therapies of which there are currently none available.

Molecular diagnosis in cerebral cavernous malformations

INTRODUCTION

Cerebral cavernous malformations (CCMs; OMIM 116860) are enlarged vascular cavities without intervening brain parenchyma whose estimated prevalence in the general population is between 0.1% and 0.5%. Familial CCM is an autosomal dominant disease with incomplete clinical and radiological penetrance. Three genes have been linked to development of the lesions: CCM1/KRIT1, CCM2/MGC4607, and CCM3/PDCD10.

DEVELOPMENT

The aetiological mutation is not detected in a large percentage of cases and new approaches are therefore needed. The aim of this review is to analyse current molecular techniques and the possible mutations or variations which can be detected in a molecular genetics or molecular biology laboratory. Likewise, we will analyse other alternatives that may help detect mutations in those patients showing negative results.

CONCLUSIONS

A molecular diagnosis of cerebral cavernous malformations should provide at least the copy number variation and sequencing of CCM genes. In addition, appropriate genetic counselling is a crucial source of information and support for patients and their relatives.

Structural Insights into the Molecular Recognition between Cerebral Cavernous Malformation 2 and Mitogen-Activated Protein Kinase Kinase Kinase 3

Cerebral cavernous malformation 2 (CCM2) functions as an adaptor protein implicated in various biological processes. By interacting with the mitogen-activated protein kinase MEKK3, CCM2 either mediates the activation of MEKK3 signaling in response to osmotic stress or negatively regulates MEKK3 signaling, which is important for normal cardiovascular development. However, the molecular basis governing CCM2-MEKK3 interaction is largely unknown. Here we report the crystal structure of the CCM2 C-terminal part (CCM2ct) containing both the five-helix domain (CCM2cts) and the following C-terminal tail. The end of the C-terminal tail forms an isolated helix, which interacts intramolecularly with CCM2cts. By biochemical studies we identified the N-terminal amphiphilic helix of MEKK3 (MEKK3-nhelix) as the essential structural element for CCM2ct binding. We further determined the crystal structure of CCM2cts-MEKK3-nhelix complex, in which MEKK3-nhelix binds to the same site of CCM2cts for CCM2ct intramolecular interaction. These findings build a structural framework for understanding CCM2ct-MEKK3 molecular recognition.

Strategy for identifying repurposed drugs for the treatment of cerebral cavernous malformation

BACKGROUND

Cerebral cavernous malformation (CCM) is a hemorrhagic stroke disease affecting up to 0.5% of North Americans that has no approved nonsurgical treatment. A subset of patients have a hereditary form of the disease due primarily to loss-of-function mutations in KRIT1, CCM2, or PDCD10. We sought to identify known drugs that could be repurposed to treat CCM.

METHODS AND RESULTS

We developed an unbiased screening platform based on both cellular and animal models of loss of function of CCM2. Our discovery strategy consisted of 4 steps: an automated immunofluorescence and machine-learning-based primary screen of structural phenotypes in human endothelial cells deficient in CCM2, a secondary screen of functional changes in endothelial stability in these same cells, a rapid in vivo tertiary screen of dermal microvascular leak in mice lacking endothelial Ccm2, and finally a quaternary screen of CCM lesion burden in these same mice. We screened 2100 known drugs and bioactive compounds and identified 2 candidates, cholecalciferol (vitamin D3) and tempol (a scavenger of superoxide), for further study. Each drug decreased lesion burden in a mouse model of CCM vascular disease by ≈50%.

CONCLUSIONS

By identifying known drugs as potential therapeutics for CCM, we have decreased the time, cost, and risk of bringing treatments to patients. Each drug also prompts additional exploration of biomarkers of CCM disease. We further suggest that the structure-function screening platform presented here may be adapted and scaled to facilitate drug discovery for diverse loss-of-function genetic vascular disease.

The structure of the ternary complex of Krev interaction trapped 1 (KRIT1) bound to both the Rap1 GTPase and the heart of glass (HEG1) cytoplasmic tail

Loss of function mutation in Krev interaction trapped 1 (KRIT1) causes autosomal dominant familial cerebral cavernous malformations and disrupts cardiovascular development. The biological function of KRIT1 requires that its FERM (band 4.1, ezrin, radixin, moesin) domain physically interact with both the small GTPase Rap1 and the cytoplasmic tail of the Heart of glass (HEG1) membrane anchor. In this study, we show that the KRIT1 FERM domain can bind both Rap1 and HEG1 simultaneously, and we solved the crystal structure of the KRIT1-Rap1-HEG1 ternary complex. Rap1 binds on the surface of the F1 and F2 subdomains, in an interaction that leaves its Switch II region accessible to other potential effectors. HEG1 binds in a hydrophobic pocket at the KRIT1 F1 and F3 interface, and there is no overlap with the Rap1-binding site. Indeed, the affinity of KRIT1 or the KRIT1-Rap1 complex for HEG1 is comparable (Kd = 1.2 and 0.96 μm, respectively) showing that there is no competition between the two sites. Furthermore, analysis of this structure revealed a specific ionic interaction between the F2 lobe of KRIT1 and Rap1 that could explain the remarkable Rap1 specificity of KRIT1. This structural insight enabled design of KRIT1(K570I), a mutant that binds Rap1 with 8-fold lower affinity and exhibits increased binding to HRas. These data show that HEG1 can recruit the Rap1-KRIT complex to the plasma membrane where Rap1's Switch II region remains accessible and reveals an important determinant of KRIT1's specificity for Rap1.

CCM molecular screening in a diagnosis context: novel unclassified variants leading to abnormal splicing and importance of large deletions

Loss of function mutations in CCM1/KRIT1, CCM2/MGC4607, and CCM3/PDCD10 gene are identified in about 95 % of familial cases of cerebral cavernous malformations and 2/3 of sporadic cases with multiple lesions. In this study, 279 consecutive index patients referred for either genetic counseling or for diagnosis of cerebral hemorrhage of unknown etiology were analyzed for the three cerebral cavernous malformations (CCM) genes by direct sequencing and quantitative studies, to characterize in more detail the mutation spectrum associated with cerebral cavernous malformations and to optimize CCM gene screening. Analysis of the cDNA was performed when possible to detect the consequences of the genomic variations. A pathogenic mutation was identified in 122 patients. CCM1 was mutated in 80 patients (65 %), CCM2 in 23 (19 %), and CCM3 in 19 (16 %). One hundred patients harbored a loss of function point mutation (82 %) and 22 had a large deletion (18 %). Novel unclassified variants were detected in the patients among whom six led to a splicing defect. The causality of three missense variants that did not modify the splicing could not be established. These findings expand the CCM mutation spectrum and highlight the importance of screening the three CCM genes with both direct sequencing and a quantitative method. In addition, six new unclassified variants were shown to be deleterious because they led to a splicing defect. This underlines the necessity of the cDNA analysis when an unknown variant is detected.

A founder mutation in the Ashkenazi Jewish population affecting messenger RNA splicing of the CCM2 gene causes cerebral cavernous malformations

PURPOSE

Cerebral cavernous malformations can occur sporadically or are caused by mutations in one of three identified genes. Cerebral cavernous malformations often remain clinically silent until a mutation carrier suffers a stroke or seizure. Presymptomatic genetic testing has been valuable to follow and manage cerebral cavernous malformation mutation carriers. During routine diagnostic testing, we identified a two base pair change in seven unrelated people of Ashkenazi Jewish heritage. Because of the location of the variant beyond the invariant splice donor sequence, the change was reported as a variant of unknown significance. In this study, we determined whether this change was a disease-causing mutation and whether it represents a founder mutation in the Ashkenazi Jewish population.

METHODS

Transcripts arising from the normal and mutant alleles were examined by reverse transcription-polymerase chain reaction from affected and unaffected Ashkenazi Jewish cerebral cavernous malformation family members. A synthetic splicing system using a chimeric exon was used to visualize the effects of the change on splice donor site utilization.

RESULTS

The two base pair change in CCM2, c.30 + 5_6delinsTT, segregated with affected status in the study families. Reverse transcription-polymerase chain reaction revealed loss of the transcript allele that was in phase with the mutation. The two base pair change, when tested in an in vitro synthetic splicing system, altered splice donor site utilization. Resequencing of the genomic region proximal and distal to the CCM2 gene mutation revealed a common single-nucleotide polymorphism haplotype in affected individuals.

CONCLUSIONS

The two base pair change in CCM2, c.30 + 5_6delinsTT, disrupted proper splice donor utilization leading to a degraded transcript. Single nucleotide polymorphism haplotype analysis demonstrated that this mutation was due to a founder in the Ashkenazi Jewish population. These data have the potential to simplify genetic testing for cerebral cavernous malformation in the Ashkenazi Jewish population.

Cerebral cavernous malformations: from genes to proteins to disease

Over the past half century molecular biology has led to great advances in our understanding of angio- and vasculogenesis and in the treatment of malformations resulting from these processes gone awry. Given their sporadic and familial distribution, their developmental and pathological link to capillary telangiectasias, and their observed chromosomal abnormalities, cerebral cavernous malformations (CCMs) are regarded as akin to cancerous growths. Although the exact pathological mechanisms involved in the formation of CCMs are still not well understood, the identification of 3 genetic loci has begun to shed light on key developmental pathways involved in CCM pathogenesis. Cavernous malformations can occur sporadically or in an autosomal dominant fashion. Familial forms of CCMs have been attributed to mutations at 3 different loci implicated in regulating important processes such as proliferation and differentiation of angiogenic precursors and members of the apoptotic machinery. These processes are important for the generation, maintenance, and pruning of every vessel in the body. In this review the authors highlight the latest discoveries pertaining to the molecular genetics of CCMs, highlighting potential new therapeutic targets for the treatment of these lesions.

An Alu repeat-mediated genomic GCNT2 deletion underlies congenital cataracts and adult i blood group

We performed homozygosity mapping in a consanguineous Pakistani family segregating autosomal-recessive congenital cataracts and identified linkage to a 3.03 Mb locus on chromosome 6p24 containing the GCNT2 gene. GCNT2 encodes glucosaminyl (N-acetyl) transferase 2, an enzyme responsible for the formation of the blood group I antigen. Rare biallelic GCNT2 mutations have been shown to cause the association of congenital cataracts and the adult i blood group, making GCNT2 the prime candidate gene for the observed phenotype. Indeed, we identified a homozygous deletion segregating with cataracts that encompasses exons 1B, 1C, 2 and 3 of GCNT2. Long-range polymerase chain reaction and breakpoint sequencing revealed that affected individuals in this and in a second, apparently unrelated Pakistani family segregating congenital cataracts are homozygous for the same 93 kb deletion. The deletion is flanked by Alu repeats of the AluS family on both sides and microsatellite genotyping suggested that its occurrence in the two families was the product of recurrent Alu-Alu repeat-mediated nonhomologous recombinations or an old founder effect. Subsequently, we showed that cataract-affected individuals in both families have the adult i blood group, whereas unaffected individuals have blood group I as the vast majority of the population. Because the GCNT2 locus is rich in Short INterspersed Elements (SINE repeats) and thus likely prone to genomic rearrangements, microdeletions or microduplications at this locus might cause a larger than currently anticipated fraction of apparently isolated autosomal-recessive cataracts.

Cerebral cavernous malformations as a disease of vascular permeability: from bench to bedside with caution

Tremendous insight into the molecular and genetic pathogenesis of cerebral cavernous malformations (CCMs) has been gained over the past 2 decades. This includes the identification of 3 distinct genes involved in familial CCMs. Still, a number of unanswered questions regarding the process from gene mutation to vascular malformation remain. It is becoming more evident that the disruption of interendothelial junctions and ensuing vascular hyperpermeability play a principal role. The purpose of this review is to summarize the current understanding of CCM genes, associated proteins, and functional pathways. Promising molecular and genetic therapies targeted at identified molecular aberrations are discussed as well.

Evaluating strategies for the treatment of cerebral cavernous malformations

Cerebral cavernous malformations are common vascular lesions of the central nervous system that predispose to seizures, focal neurological deficits, and potentially fatal hemorrhagic stroke. Human genetic studies have identified 3 genes associated with the disease, and biochemical studies of these proteins have identified interaction partners and possible signaling pathways. A recurring theme dominating the recent scientific literature is the causal link between mutations in the 3 cerebral cavernous malformation genes and hyperactivation of the small GTP exchange protein, RhoA, and the efficacy of reducing this hyperactivation using inexpensive and well-studied medicines, statins. Familial cerebral cavernous malformation offers a unique opportunity to use a personalized genomic medicine approach to identify a subset of patients prone to intracerebral hemorrhage that may benefit from a pharmacological therapy, where presently only neurosurgical options are available.

Advances in the biology of cerebral cavernous malformations

OBJECT

To provide a review of current, high-impact scientific findings pertaining to the biology of cerebral cavernous malformations (CCMs).

METHODS

A comprehensive literature review was conducted using PubMed to examine the current literature regarding the molecular biology and pathophysiology of CCMs.

RESULTS

In this literature review, a comprehensive approach is taken to review the current scientific status of CCMs. This includes discussion of molecular biology and animal models, ultrastructure and angioarchitectural features and immunological methods and hypotheses.

CONCLUSIONS

Studies examining the molecular biology of CCMs have shown that genes involved in angiogenesis, blood-brain barrier formation, cell size regulation, vascular permeability and apoptosis play critical roles in the ontogeny of this disease. In vivo work suggests the likelihood of a "two-hit mechanism" resulting in somatic mosaicism and biallelic loss of angiogenic genes. The etiological effects of angioarchitecture and immune response within these lesions further complicate the pathophysiology. Future treatment endeavors will necessitate exploitation of the multiple facets of CCM formation to maximize success at CCM prevention or obliteration.

Mutation analysis of CCM1, CCM2 and CCM3 genes in a cohort of Italian patients with cerebral cavernous malformation

Cerebral cavernous malformations (CCMs) are vascular lesions of the CNS characterized by abnormally enlarged capillary cavities. CCMs can occur as sporadic or familial autosomal dominant form. Familial cases are associated with mutations in CCM1[K-Rev interaction trapped 1 (KRIT1)], CCM2 (MGC4607) and CCM3 (PDCD10) genes. In this study, a three-gene mutation screening was performed by direct exon sequencing, in a cohort of 95 Italian patients either sporadic or familial, as well as on their at-risk relatives. Sixteen mutations in 16 unrelated CCM patients were identified,nine mutations are novel: c.413T > C; c.601C > T; c.846 + 2T > G; c.1254delA; c.1255-4delGTA; c.1682-1683 delTA in CCM1; c.48A > G; c.82-83dupAG in CCM2; and c.395 + 1G > A in CCM3 genes [corrected].The samples, negative to direct exon sequencing, were investigated by MLPA to search for intragenic deletions or duplications. One deletion in CCM1 exon 18 was detected in a sporadic patient. Among familial cases 67% had a mutation in CCM1, 5.5% in CCM2, and 5.5% in CCM3, whereas in the remaining 22% no mutations were detected, suggesting the existence of either undetectable mutations or other CCM genes. This study represents the first extensive research program for a comprehensive molecular screening of the three known genes in an Italian cohort of CCM patients and their at-risk relatives.

Small deletion at the 7q21.2 locus in a CCM family detected by real-time quantitative PCR

Cerebral cavernous malformations (CCMs) represent a common autosomal dominant disorder that predisposes patients to haemorrhagic strokes and focal neurological signs. About 56% of the hereditary forms of CCMs have been so far associated with mutations in the KRIT1 (Krev Interaction Trapped 1) gene, located at 7q21.2 (CCM1 locus). We described the complete loss of 7q21.2 locus encompassing the KRIT1 gene and 4 flanking genes in a CCM family by using a dense set of 12 microsatellite markers. The complete loss of the maternal copy of KRIT1 gene region was confirmed by Real-Time Quantitative Polymerase Chain Reaction (RT-QPCR) and the same approach was used for expression analysis. Additional RT-QPCR analysis showed the extension of the deletion, for a total of 700 kb, to the adjacent downstream and upstream-located genes, MTERF, AKAP9, CYP51A1, as well as a partial loss of the ANKIB1 gene. Here we report the molecular characterization of an interstitial small genomic deletion of the 7q21.2 region in a CCMs affected family, encompassing the KRIT1 gene. Our findings confirm the loss of function mechanism for the already known CCM1 locus, without any evident involvement of the other deleted genes. Moreover, our investigations highlight the usefulness of the RT-QPCR to the molecular characterization of the breakpoints genomic deletions and to the identification of internal deleted genes involved in the human genetic diseases.

Cerebral cavernous malformations proteins inhibit Rho kinase to stabilize vascular integrity

Endothelial cell–cell junctions regulate vascular permeability, vasculogenesis, and angiogenesis. Familial cerebral cavernous malformations (CCMs) in humans result from mutations of CCM2 (malcavernin, OSM, MGC4607), PDCD10 (CCM3), or KRIT1 (CCM1), a Rap1 effector which stabilizes endothelial cell–cell junctions. Homozygous loss of KRIT1 or CCM2 produces lethal vascular phenotypes in mice and zebrafish. We report that the physical interaction of KRIT1 and CCM2 proteins is required for endothelial cell–cell junctional localization, and lack of either protein destabilizes barrier function by sustaining activity of RhoA and its effector Rho kinase (ROCK). Protein haploinsufficient Krit1^+/− or Ccm2^+/− mouse endothelial cells manifested increased monolayer permeability in vitro, and both Krit1^+/− and Ccm2^+/− mice exhibited increased vascular leak in vivo, reversible by fasudil, a ROCK inhibitor. Furthermore, we show that ROCK hyperactivity occurs in sporadic and familial human CCM endothelium as judged by increased phosphorylation of myosin light chain. These data establish that KRIT1–CCM2 interaction regulates vascular barrier function by suppressing Rho/ROCK signaling and that this pathway is dysregulated in human CCM endothelium, and they suggest that fasudil could ameliorate both CCM disease and vascular leak.

Recent insights into cerebral cavernous malformations: a complex jigsaw puzzle under construction

Cerebral cavernous malformations (CCM) are common vascular malformations with an unpredictable risk of hemorrhage, the consequences of which range from headache to stroke or death. Three genes, CCM1, CCM2 and CCM3, have been linked to the disease. The encoded CCM proteins interact with each other within a large protein complex. Within the past 2 years, a plethora of new data has emerged on the signaling pathways in which CCM proteins are involved. CCM proteins regulate diverse aspects of endothelial cell morphogenesis and blood vessel stability such as cell-cell junctions, cell shape and polarity, or cell adhesion to the extracellular matrix. Although fascinating, a global picture is hard to depict because little is known about how these pathways coordinate to orchestrate angiogenesis. Here we present what is known about the structural domain organization of CCM proteins, their association as a ternary complex and their subcellular localization. Numerous CCM partners have been identified using two-hybrid screens, genetic analyses or proteomic studies. We focus on the best-characterized partners and review data on the signaling pathways they regulate as a step towards a better understanding of the etiology of CCM disease.

Recent insights into cerebral cavernous malformations: the molecular genetics of CCM

Cerebral cavernous malformations (CCM) are vascular lesions which can occur as a sporadic (80% of the cases) or familial autosomal dominant form (20%). Three CCM genes have been identified: CCM1/KRIT1, CCM2/MGC4607 and CCM3/PDCD10. Almost 80% of CCM patients affected with a genetic form of the disease harbor a heterozygous germline mutation in one of these three genes. Recent work has shown that a two-hit mechanism is involved in CCM pathogenesis which is caused by a complete loss of any of the three CCM proteins within endothelial cells lining the cavernous capillary cavities. These data were an important step towards the elucidation of the mechanisms of this condition.

Cerebral cavernous malformations: somatic mutations in vascular endothelial cells

OBJECTIVE

Germline mutations in 3 genes have been found in familial cases of cerebral cavernous malformations (CCMs). We previously discovered somatic and germline truncating mutations in the KRIT1 gene, supporting the "2-hit" mechanism of CCM lesion formation in a single lesion. The purpose of this study was to screen for somatic, nonheritable mutations in 3 more lesions from different patients and identify the cell type(s) in which somatic mutations occur.

METHODS

Somatic mutations were sought in DNA from 3 surgically excised, fresh-frozen CCM lesions by cloning and screening polymerase chain reaction products generated from KRIT1 or PDCD10 coding regions. Laser capture microdissection was used on isolated endothelial and nonendothelial cells to determine whether somatic mutations were found in endothelial cells.

RESULTS

CCM lesions harbor somatic and germline KRIT1 mutations on different chromosomes and are therefore biallelic. Both mutations are predicted to truncate the protein. The KRIT1 somatic mutations (novel c.1800delG mutation and previously identified 34 nucleotide deletion) in CCMs from 2 different patients were found only in the vascular endothelial cells lining caverns. No obvious somatic mutations were identified in the 2 other lesions; however, the results were inconclusive, possibly owing to the technical limitations or the fact that these specimens had a small proportion of vascular endothelial cells lining pristine caverns.

CONCLUSION

The "2-hit" mechanism occurs in vascular endothelial cells lining CCM caverns from 2 patients with somatic and Hispanic-American KRIT1 germline mutations. Methods for somatic mutation detection should focus on vascular endothelial cells lining pristine caverns.

Control of cell adhesion dynamics by Rap1 signaling

Individual cells in their particular environments adhere to the extracellular matrix (ECM) and their neighbours via integrin-containing and cadherin-containing complexes, respectively. The dynamics of these interactions regulate the formation and maintenance of complex tissues. An expanding body of evidence accentuates the role of the small Rap1 GTPase and its associated signaling network in many of these processes. In this review we will discuss more recently revealed roles of Rap1 signaling by primarily focusing on functions of the Rap1 effectors RIAM, KRIT-1/CCM1 and AF-6/Afadin in junctional regulation of the vascular system and in epithelial cells. Furthermore, we will describe novel findings on the Rap activator PDZ-GEF in the regulation of cell-cell adhesion between epithelial cells and within a stem cell niche.

Molecular screening test in familial forms of cerebral cavernous malformation: the impact of the Multiplex Ligation-dependent Probe Amplification approach

Object The purpose of this study was to underline the effectiveness of molecular analysis in cerebral cavernous angioma, with special attention to the familial forms. Methods Multiplex Ligation-dependent Probe Amplification analysis integrates the consecutive sequence analysis of the 3 genes (Krit1/CCM1, MGC4607/CCM2, and PDCD10/CCM3) known to be responsible for cerebral cavernous malformation lesions. Results The Multiplex Ligation-dependent Probe Amplification analysis revealed a new mutation, a heterozygous exon 9/10 deletion of Krit1, in the proband and in all affected family members. Conclusions The identification of the molecular defect allows physicians to screen family members at risk and to identify affected individuals before the onset of clinical symptoms caused by the presence of lesions.