Cerebral cavernous malformations: from molecular pathogenesis to genetic counselling and clinical management

Contribution of Endothelial-to-Mesenchymal Transition to the Pathogenesis of Human Cerebral and Orbital Cavernous Malformations

BACKGROUND

The analysis of gene-targeted mouse mutants has demonstrated that endothelial-to-mesenchymal transition (EndMT) is crucial to the onset and progression of cerebral cavernous malformations (CMs). It has also been shown that Notch and ephrin/Eph signaling are involved in EndMT. However, their roles in the pathogenesis of human intracranial CMs remain unclear.

OBJECTIVE

To elucidate the contribution of EndMT, the Notch pathway, and ephrin-B2/EphB4 signaling to the pathogenesis of human intracranial CMs.

METHODS

Eight human intracranial CMs (5 cerebral and 3 orbital CMs) were immunohistochemically investigated.

RESULTS

CD31 (an endothelial marker) and EndMT markers, such as α-smooth muscle actin (a mesenchymal marker) and CD44 (a mesenchymal stem cell marker), were expressed in the endothelial layer of vascular sinusoids in all cases, suggesting that endothelial cells (ECs) have acquired mesenchymal and stem-cell-like characteristics and undergone EndMT in all cerebral and orbital CMs. EndMT was observed in about 70% and 35% of ECs in cerebral and orbital CMs, respectively. In all cases, Notch3 was expressed in the endothelial layer, indicating that ECs of vascular sinusoids have acquired mesenchymal features. In all cases, both ephrin-B2 and EphB4 were detected in the endothelial layer, suggesting that ECs of vascular sinusoids are immature or malformed cells and have both arterial and venous characteristics.

CONCLUSION

EndMT plays a critical role in the pathogenesis of human cerebral and orbital CMs. Modulating EndMT is expected to be a new therapeutic strategy for cerebral and orbital CMs.

Awad I, Dahlem K, Flemming K, Hart B, Kim H, Jusue-Torres I, Kondziolka D, Lee C, Morrison L, Rigamonti D, Rebeiz T, Tournier-Lasserve E, Waggoner D, Whitehead K. Synopsis of Guidelines for the Clinical Management of Cerebral Cavernous Malformations: Consensus Recommendations Based on Systematic Literature Review by the Angioma Alliance Scientific Advisory Board Clinical Experts Panel

BACKGROUND

Despite many publications about cerebral cavernous malformations (CCMs), controversy remains regarding diagnostic and management strategies.

OBJECTIVE

To develop guidelines for CCM management.

METHODS

The Angioma Alliance ( www.angioma.org ), the patient support group in the United States advocating on behalf of patients and research in CCM, convened a multidisciplinary writing group comprising expert CCM clinicians to help summarize the existing literature related to the clinical care of CCM, focusing on 5 topics: (1) epidemiology and natural history, (2) genetic testing and counseling, (3) diagnostic criteria and radiology standards, (4) neurosurgical considerations, and (5) neurological considerations. The group reviewed literature, rated evidence, developed recommendations, and established consensus, controversies, and knowledge gaps according to a prespecified protocol.

RESULTS

Of 1270 publications published between January 1, 1983 and September 31, 2014, we selected 98 based on methodological criteria, and identified 38 additional recent or relevant publications. Topic authors used these publications to summarize current knowledge and arrive at 23 consensus management recommendations, which we rated by class (size of effect) and level (estimate of certainty) according to the American Heart Association/American Stroke Association criteria. No recommendation was level A (because of the absence of randomized controlled trials), 11 (48%) were level B, and 12 (52%) were level C. Recommendations were class I in 8 (35%), class II in 10 (43%), and class III in 5 (22%).

CONCLUSION

Current evidence supports recommendations for the management of CCM, but their generally low levels and classes mandate further research to better inform clinical practice and update these recommendations. The complete recommendations document, including the criteria for selecting reference citations, a more detailed justification of the respective recommendations, and a summary of controversies and knowledge gaps, was similarly peer reviewed and is available on line www.angioma.org/CCMGuidelines .

Review of familial cerebral cavernous malformations and report of seven additional families

Cerebral cavernous malformations are vascular anomalies of the central nervous system characterized by clusters of enlarged, leaky capillaries. They are caused by loss-of-function mutations in KRIT1, CCM2, or PDCD10. The proteins encoded by these genes are involved in four partially interconnected signaling pathways that control angiogenesis and endothelial permeability. Cerebral cavernous malformations can occur sporadically, or as a familial autosomal dominant disorder (FCCM) with incomplete clinical and neuroradiological penetrance and great inter-individual variability. Although the clinical course is unpredictable, symptoms typically present during adult life and include headaches, focal neurological deficits, seizures, and potentially fatal stroke. In addition to neural lesions, extraneural cavernous malformations have been described in familial disease in several tissues, in particular the skin. We here present seven novel FCCM families with neurologic and cutaneous lesions. We review histopathological and clinical features and provide an update on the pathophysiology of cerebral cavernous malformations and associated cutaneous vascular lesions. © 2016 Wiley Periodicals, Inc.

Familial Multiple Cavernous Malformation Syndrome: MR Features in This Uncommon but Silent Threat

Cerebral cavernous malformations (CCM) are vascular malformations in the brain and spinal cord. The familial form of cerebral cavernous malformation (FCCM) is uncommon. This autosomal dominant pathology mostly presents with seizures and focal neurological symptoms. Many persons affected by FCCM remain asymptomatic. However, acute hemorrhages may appear over time.

MRI demonstrates multiple focal regions of susceptibility induced signal loss, well seen on gradient-echo sequences (GRE) or even better on susceptibility-weighted imaging (SWI). The presence of a single CCM – especially in young persons – without history of FCCM does not exclude this diagnosis.

Some clinicians also advise an MRI of the spinal cord at the time of diagnosis to serve as a baseline and a control MRI of the brain every one to two years. MRI is certainly indicated in individuals with obvious new neurologic symptoms.

Symptomatic siblings should also undergo an MRI of the brain to determine presence, size, and location of the lesions. Even in asymptomatic siblings, a screening MRI may be considered, as there may be an increased risk of hemorrhage, spontaneous or due to the use of certain medications; the knowledge of the presence and the type of these lesions are important. Surgical removal of a CCM may be justified to prevent a life-threatening hemorrhage. Control MRI may reveal the postoperative outcome.

Nogo-B receptor deficiency causes cerebral vasculature defects during embryonic development in mice

Nogo-B receptor (NgBR) was identified as a receptor specific for Nogo-B. Our previous work has shown that Nogo-B and its receptor (NgBR) are essential for chemotaxis and morphogenesis of endothelial cells in vitro and intersomitic vessel formation via Akt pathway in zebrafish. Here, we further demonstrated the roles of NgBR in regulating vasculature development in mouse embryo and primitive blood vessel formation in embryoid body culture systems, respectively. Our results showed that NgBR homozygous knockout mice are embryonically lethal at E7.5 or earlier, and Tie2Cre-mediated endothelial cell-specific NgBR knockout (NgBR ecKO) mice die at E11.5 and have severe blood vessel assembly defects in embryo. In addition, mutant embryos exhibit dilation of cerebral blood vessel, resulting in thin-walled endothelial caverns. The similar vascular defects also were detected in Cdh5(PAC)-CreERT2 NgBR inducible ecKO mice. Murine NgBR gene-targeting embryonic stem cells (ESC) were generated by homologous recombination approaches. Homozygous knockout of NgBR in ESC results in cell apoptosis. Heterozygous knockout of NgBR does not affect ESC cell survival, but reduces the formation and branching of primitive blood vessels in embryoid body culture systems. Mechanistically, NgBR knockdown not only decreases both Nogo-B and VEGF-stimulated endothelial cell migration by abolishing Akt phosphorylation, but also decreases the expression of CCM1 and CCM2 proteins. Furthermore, we performed immunofluorescence (IF) staining of NgBR in human cerebral cavernous malformation patient tissue sections. The quantitative analysis results showed that NgBR expression levels in CD31 positive endothelial cells is significantly decreased in patient tissue sections. These results suggest that NgBR may be one of important genes coordinating the cerebral vasculature development.

Cerebral cavernous malformations associated to meningioma: High penetrance in a novel family mutated in the PDCD10 gene

Multiple familial meningiomas occur in rare genetic syndromes, particularly neurofibromatosis type 2. The association of meningiomas and cerebral cavernous malformations (CCMs) has been reported in few patients in the medical literature. The purpose of our study is to corroborate a preferential association of CCMs and multiple meningiomas in subjects harbouring mutations in the PDCD10 gene (also known as CCM3). Three members of an Italian family affected by seizures underwent conventional brain Magnetic Resonance Imaging (MRI) with gadolinium contrast agent including gradient echo (GRE) imaging. The three CCM-causative genes were sequenced by Sanger method. Literature data reporting patients with coexistence of CCMs and meningiomas were reviewed. MRI demonstrated dural-based meningioma-like lesions associated to multiple parenchymal CCMs in all affected individuals. A disease-causative mutation in the PDCD10 gene (p.Gln112PhefsX13) was identified. Based on neuroradiological and molecular data as well as on literature review, we outline a consistent association between PDCD10 mutations and a syndrome of CCMs with multiple meningiomas. This condition should be considered in the differential diagnosis of multiple/familial meningioma syndromes. In case of multiple/familial meningioma the use of appropriate MRI technique may include GRE and/or susceptibility-weighted imaging (SWI) to rule out CCM. By contrast, proper post-gadolinium scans may aid defining dural lesions in CCM patients and are indicated in PDCD10-mutated individuals.

Detection of Novel Mutation in Ccm3 Causes Familial Cerebral Cavernous Malformations

Cerebral cavernous malformations are vascular lesions that usually involve brain micro-vessels. They can occur both in a sporadic form and familial one. Causes of familial forms are mutations at three loci: CCM1/KRIT1, CCM2/MGC4607, and CCM3/PDCD10. Here, we describe a novel CCM3 missense mutation (c.422T>G) detected in two Greek brothers showing multiple lesions at magnetic resonance imaging; to date, only the youngest is symptomatic. Bioinformatics tools showed this novel variant causes a loss of function in Pdcd10 protein due to its localization in the eighth helix and, particularly, affects Leu141, a highly conserved amino acid. Roles of Pdcd10 in angiogenesis regulation and its association with early development of cerebral cavernous malformations were also considered.

Focal defects in single-celled tubes mutant for Cerebral cavernous malformation 3, GCKIII, or NSF2

Tubes of differing cellular architecture connect into networks. In the Drosophila tracheal system, two tube types connect within single cells (terminal cells); however, the genes that mediate this interconnection are unknown. Here we characterize two genes that are essential for this process: lotus, required for maintaining a connection between the tubes, and wheezy, required to prevent local tube dilation. We find that lotus encodes N-ethylmaleimide sensitive factor 2 (NSF2), whereas wheezy encodes Germinal center kinase III (GCKIII). GCKIIIs are effectors of Cerebral cavernous malformation 3 (CCM3), a protein mutated in vascular disease. Depletion of Ccm3 by RNA interference phenocopies wheezy; thus, CCM3 and GCKIII, which prevent capillary dilation in humans, prevent tube dilation in Drosophila trachea. Ectopic junctional and apical proteins are present in wheezy terminal cells, and we show that tube dilation is suppressed by reduction of NSF2, of the apical determinant Crumbs, or of septate junction protein Varicose.

Antithrombotic therapy and bleeding risk in a prospective cohort study of patients with cerebral cavernous malformations

BACKGROUND AND PURPOSE

Cerebral cavernous malformations (CCMs) are one of the most frequently diagnosed vascular malformations of the brain and constitute a potential source of intracranial hemorrhage. In CCM patients suffering ischemic stroke or heart disease, the use of anticoagulants or antiplatelet therapy is generally avoided by fear of hemorrhagic complications, but no systematic studies exist to support this hypothesis.

METHODS

We prospectively followed-up consecutive patients with a diagnosis of one or more CCMs in a prospective database since 2008. Retrospective data collection was used for patients with a diagnostic event or imaging studies done before first assessment. Symptomatic hemorrhage and other focal neurological events during prospective follow-up were defined according to the current guidelines of the Angioma Alliance Scientific Advisory board.

RESULTS

A total of 87 patients were prospectively enrolled in our cohort [50 women (57%), mean age 44.8 years (SD±17.6), mean follow-up 3.9 years], harboring a total of 738 CCMs. Fifty-five patients (63%) had a single CCM, and 32 patients (37%) had multiple CCMs. Longitudinal follow-up included 16 (18%) patients receiving long-term antithrombotic therapy by antiplatelet treatment (n=11) or oral anticoagulants (n=5). During 5536 lesion-years of observation, none of the patients under antithrombotic therapy experienced CCM hemorrhage on follow-up.

CONCLUSIONS

Our observational data suggest that long-term antithrombotic treatment by antiplatelet drugs or warfarin does not increase the frequency of CCM-related hemorrhage. Patients harboring single or multiple CCMs suffering ischemic stroke or heart disease should not be withheld antithrombotic therapy.