Endothelial cell culture from human cerebral cavernous malformations

Simplex cerebral cavernous malformations with MAP3K3 mutation have distinct clinical characteristics

Objectives

To investigate the clinical characteristics of cerebral cavernous malformations (CCMs) with MAP3K3 somatic mutation.

Methods

We performed a retrospective review of our CCMs database between May 2017 and December 2019. The patients with simplex CCMs identified to harbor a MAP3K3 or CCM gene somatic mutation were included. Clinical characteristics were recorded. Univariate and multivariate logistic analyses were used to assess the risk factors associated with hemorrhage events of CCMs. To explore the underlying mechanism, we transfected MEKK3-I441M-overexpressing and CCM2-knockdown lentiviruses into human umbilical vein endothelial cells (HUVECs) and investigated thrombomodulin (TM) and tight junctions (TJs) protein expression by western blotting and immunofluorescence. Finally, immunohistochemistry was used to validate TM and TJs protein expression in surgical samples.

Results

Fifty simplex CCMs patients were included, comprising 38 MAP3K3 mutations and 12 CCM gene mutations. Nine (23.7%) patients with MAP3K3 mutations and 11(91.7%) patients with CCM gene mutations exhibited overt hemorrhage, respectively. Multivariate logistic analyses revealed that MAP3K3 mutation was associated with a lower risk of hemorrhage events. In the vitro experiments, ZO-1 expression was not reduced in MEKK3-I441M-overexpressing HUVECs compared with wild type, whereas it was significantly decreased in CCM2-knockdown HUVECs compared with control. In the MEKK3-I441M-overexpressing HUVECs, TM expression was increased, and the NF-κB pathway was significantly activated. After treatment with an NF-κB signaling inhibitor, TM expression was further upregulated. Meanwhile, TM expression was increased, but the NF-κB pathway was not activated in CCM2-knockdown HUVECs. Accordingly, immunohistochemistry showed that ZO-1 expression in the MAP3K3-mutant samples was significantly higher than that in the CCM-mutant samples. TM expression in the MAP3K3-mutant lesions was significantly lower than that in the CCM-mutant samples.

Conclusion

Simplex CCMs with MAP3K3 mutation occasionally present with overt hemorrhage, which is associated with the biological function of MAP3K3 mutation.

Nanocellulose for peripheral nerve regeneration in rabbits using citric acid as crosslinker with chitosan and freeze/thawed PVA

This work investigates peripheral nerve regeneration using membranes consisting of pure chitosan (CHI), which was further blended with nanofibrillated cellulose, with citric acid as crosslinker, with posterior addition of polyvinyl alcohol, with subsequent freeze thawing. Nanocellulose improves the mechanical and thermal resistance, as well as flexibility of the film, which is ideal for the surgical procedure. The hydrogel presented a slow rate of swelling, which is adequate for cell and drug delivery. A series ofin vitrotests revealed to be non-toxic for neuronal Schwann cell from the peripheral nervous system of Rattus norvegicus, while there was a slight increase in toxicity if crosslink is performed-freeze-thaw. Thein vivoresults, using rabbits with a 5 mm gap nerve defect, revealed that even though pure CHI was able to regenerate the nerve, it did not present functional recovery with only the deep pain attribute being regenerated. When autologous implant was used jointly with the biomaterial membrane, as a covering agent, it revealed a functional recovery within 15 d when cellulose and the hydrogel were introduced, which was attributed to the film charge interaction that may help influence the neuronal axons growth into correct locations. Thus, indicating that this system presents ideal regeneration as nerve conduits.

Procedure for the Isolation of Endothelial Cells from Human Cerebral Arteriovenous Malformation (cAVM) Tissues

In this study, we successfully established a stable method for the isolation of endothelial cells (ECs) from human cerebral arteriovenous malformation (cAVM) tissues. Despite human cAVM tissues having a minor population of ECs, they play an important role in the manifestation and development of cAVM as well as in hemorrhagic stroke and thrombogenesis. To characterize and understand the biology of ECs in human cAVM (cAVM-ECs), methods for the isolation and purification of these cells are necessary. We have developed this method to reliably obtain pure populations of ECs from cAVMs. To obtain pure cell populations, cAVM tissues were mechanically and enzymatically digested and the resulting single cAVM-ECs suspensions were then labeled with antibodies of specific cell antigens and selected by flow cytometry. Purified ECs were detected using specific makers of ECs by immunostaining and used to study different cellular mechanisms. Compared to the different methods of isolating ECs from tissues, we could isolate ECs from cAVMs confidently, and the numbers of cAVM-ECs harvested were almost similar to the amounts present in vessel components. In addition to optimizing the protocol for isolation of ECs from human cAVM tissues, the protocol could also be applied to isolate ECs from other human neurovascular-diseased tissues. Depending on the tissues, the whole procedure could be completed in about 20 days.

In vitro characteristics of endothelial cells prepared from human cerebral arteriovenous malformation lesions using a novel method

BACKGROUND AND PURPOSE

The cerebral arteriovenous malformation (cAVM) is a usual and continually unaware reason of heamorrhage and seizure. It contains of feeder arteries, drain veins and abnormal vessel nets. However, pathologic mechanisms of the development of cAVM are unknown. The purpose of this study was to explore a novel protocol to isolate, culture and passage endothelial cells (ECs) from human cAVM lesions.

METHODS

We developed a protocol for isolating and growing ECs from eight patients with cAVM. The tissues were microsurgically removed from cAVM lesion and were digested by 0.25% Trypsin-EDTA, and cultured in ECM medium. ECs were selected by FACS and confirmed their EC origin by immunocytochemistry of the basic expression patterns of CD31 and CD34. LDL-uptake and capillary tube formation were used to determine their functional features.

RESULTS

The isolated cAVM-ECs exhibited contact inhibition of growth and appearance of rounded cobblestone. cAVM-ECs were CD31- and CD34-positive. In functional assays, cAVM-ECs were able to uptake LDL and form capillary tubes. cAVM-ECs from younger patients proliferated faster than that from elders, and cAVM-ECs were less stable than normal artery ECs. In addition, cAVM-ECs appeared to more easily transform into mesenchymal cells than normal artery ECs.

CONCLUSION

Using the protocol, isolated cAVM-ECs are stably established, and retain their endothelial phenotypes. These cAVM-ECs may provide a biological tool to examine molecular phenotypes and mechanisms responsible for human cAVM.

Systems biology and proteomic analysis of cerebral cavernous malformation

Cerebral cavernous malformations (CCM) are vascular anomalies caused by mutations in genes encoding KRIT1, OSM and PDCD10 proteins causing hemorrhagic stroke. We examine proteomic change of loss of CCM gene expression. Using human umbilical vein endothelial cells, label-free differential protein expression analysis with multidimensional liquid chromatography/tandem mass spectrometry was applied to three CCM protein knockdown cell lines and two control cell lines: ProteomeXchange identifier PXD000362. Principle component and cluster analyses were used to examine the differentially expressed proteins associated with CCM. The results from the five cell lines revealed 290 and 192 differentially expressed proteins (p < 0.005 and p < 0.001, respectively). Most commonly affected proteins were cytoskeleton-associated proteins, in particular myosin-9. Canonical genetic pathway analysis suggests that CCM may be a result of defective cell-cell interaction through dysregulation of cytoskeletal associated proteins.

CONCLUSION

The work explores signaling pathways that may elucidate early detection and novel therapy for CCM.

Isolation and characterization of endothelial cells from intramuscular hemangioma

BACKGROUND

Intramuscular hemangiomas (IMHs) are benign vascular tumors of deep soft tissue characterized by endothelial cell (EC) proliferation. The purpose of this study was to isolate ECs from IMH, characterize their angiogenic phenotype and functional characteristics, and search for a possible signaling pathway related to IMH development.

METHODS

EC Isolation from IMH was performed by digestion, filtration, washing, incubation, and purification in sequence. Tie2 expression was compared between ECs from IMH and controls using reverse transcriptase polymerase chain reaction (RT-PCR). Cell invasion and proliferation assays were used to analyze functional responses of ECs to angiopoietin 1 (Ang1) and vascular endothelial growth factor (VEGF). Expression of downstream targets was analyzed using Western blot analysis.

RESULTS

Isolated ECs showed typical cobblestone appearance under light microscopy and formed capillary-like tubular structures using Matrigel tube-forming assay. RT-PCR of isolated ECs from six patients showed increased expression of Tie2 and VEGF receptor 1 (VEGFR1) compared with control ECs. Tie2 activation by Ang1 compared with VEGFR1 by VEGF resulted in increased EC migration and proliferation. Western blot analysis showed increased Tie2 expression in hemangioma samples compared with normal ECs. Phosphorylated Akt and phosphorylated forkhead box O1 (FOXO1) expression was observed in hemangioma samples only.

CONCLUSION

EC isolation from IMH could be a useful tool for further research. These results suggest that increased Tie2 expression, via Akt-FOXO1 pathway activation, may play an important role in IMH pathogenesis.

Temporal expression analysis of angiogenesis-related genes in brain development

Background

The current knowledge on molecular pathogenesis of cerebral vascular malformations (CVM), which are believed to arise during development, is very limited. To unravel the molecular mechanisms involved in CVMs, a detailed understanding of the brain vascular development at molecular level is crucial. In this study, we aimed to explore the temporal and comparative expression profile of angiogenesis-related genes in the establishment of brain vasculature.

Methods

Expression of a total of 113 angiogenesis-related genes during murine brain development has been analyzed using low-density array systems designed for angiogenesis-related genes. Bai1 (brain specific angiogenesis inhibitor-1), a recently identified novel anti-angiogenic gene, has been selected for further characterization.

Results

We found that 62 out of 113 analyzed genes have expression in brain development at varying levels. Nineteen of these were differentially expressed between embryonic and postnatal stages (>1.5 fold). Bai1 is strongly expressed on growing blood vessels of cerebral cortex and hippocampus, partially expressed in the lateral regions of striatum, but mostly absent on the thalamus.

Conclusion

By showing the comparative expression analysis of angiogenesis-related genes throughout brain development, the data presented here will be a crucial addition to further functional studies on cerebrovascular research.

In vitro characterization of the angiogenic phenotype and genotype of the endothelia derived from sporadic cerebral cavernous malformations

BACKGROUND

Cerebral cavernous malformation (CCM) is mainly a disorder of endothelial cells. Although the endothelial function of CCM genes has been characterized in familial CCMs, little attention has been paid to the pathological alterations of the endothelium in sporadic CCMs.

OBJECTIVE

We assumed that the endothelia derived from sporadic CCMs present genotypic and/or phenotypic alterations and exhibit unique responses to the pathogenic stimuli.

METHODS

Endothelial cells were prepared from fresh operative specimens of sporadic CCMs with a single lesion (CCM-ECs, n = 20). The expression of VEGF and its receptors and CCM1-3 genes were detected by real-time reverse transcriptase polymerase chain reaction (RT-PCR). Endothelial cell proliferation, migration, sprouting, and tube formation were compared between CCM-ECs and control endothelial cells after different angiogenic stimuli and after silencing CCM1.

RESULTS

RT-PCR revealed a highly activated VEGF system in CCM-ECs without significant alteration in CCM1-3 gene expression. Accordingly, CCM-ECs exhibited great growth potential under normal culture conditions and a significantly high proliferation activity in response to various angiogenic stimuli including hypoxia, fetal calf serum, and vascular endothelial growth factor treatment. A considerably higher mobility, spontaneous sprouting and extensive tube-branching were exclusively detected in CCM-ECs. In comparison with control endothelia, CCM-EC resisted apoptotic stimuli and showed distinct responses to activating angiogenesis after silencing CCM1.

CONCLUSION

Distinct genotypic and phenotypic features occur in CCM-EC independently from the deficiency in CCM1-3 gene expression. The distinct responses of CCM-EC to different pathogenic stimuli suggest that CCM-EC is a valuable in vitro model for further study of CCMs.

Differential angiogenesis function of CCM2 and CCM3 in cerebral cavernous malformations

Object

Loss-of-function mutations in CCM genes are frequently detected in familial cerebral cavernous malformations (CCMs). However, the current functional studies of the CCM genes in vitro have been performed mostly in commercially purchased normal cell lines and the results appeared discrepant. The fact that the cerebral vascular defects are rarely observed in CCM gene-deficient animals suggests the requirement of additional pathological background for the formation of vascular lesions. Consistent with these data, the authors assumed that silencing CCM genes in the endothelium derived from CCMs (CCM-ECs) serves as a unique and valuable model for investigating the function of the CCM genes in the pathogenesis of CCMs. To this end, the authors investigated the role and signaling of CCM2 and CCM3 in the key steps of angiogenesis using CCM-ECs.

Methods

Endothelial cells (ECs) derived from CCMs were isolated, purified, and cultured from the fresh operative specimens of sporadic CCMs (31 cases). The CCM2 and CCM3 genes were silenced by the specific short interfering RNAs in CCM-ECs and in control cultures (human brain microvascular ECs and human umbilical vein ECs). The efficiency of gene silencing was proven by real-time reverse transcriptase polymerase chain reaction. Cell proliferation and apoptosis, migration, tube formation, and the expression of phosphor-p38, phosphor-Akt, and phosphor-extracellular signal-regulated kinase–1 and 2 (ERK1/2) were analyzed under CCM2 and CCM3 silenced conditions in CCM-ECs.

Results

The CCM3 silencing significantly promoted proliferation and reduced apoptosis in all 3 types of endothelium, but accelerated cell migration exclusively in CCM-ECs. Interestingly, CCM2 siRNA influenced neither cell proliferation nor migration. Silencing of CCM3, and to a lesser extent CCM2, stimulated the growth and extension of sprouts selectively in CCM-ECs. Loss of CCM2 or CCM3 did not significantly influence the formation of the tubelike structure. However, the maintenance of tube stability was largely impaired by CCM2, but not CCM3, silencing. Western blot analysis revealed that CCM2 and CCM3 silencing commonly activated p38, Akt, and ERK1/2 in CCM-ECs.

Conclusions

The unique response of CCM-ECs to CCM2 or CCM3 siRNA indicates that silencing CCM genes in CCM-ECs is valuable for further studies on the pathogenesis of CCMs. Using this model system, the authors demonstrate a distinct role of CCM2 and CCM3 in modulating the different processes of angiogenesis. The stimulation of endothelial proliferation, migration, and massively growing and branching angiogenic sprouts after CCM3 silencing may potentially contribute to the formation of enriched capillary-like immature vessels in CCM lesions. The severe impairment of the tube integrity by CCM2, but not CCM3, silencing is associated with the different intracranial hemorrhage rate observed from CCM2 and CCM3 mutation carriers. The activation of p38, ERK1/2, and Akt signal proteins in CCM2- or CCM3-silenced CCM-ECs suggests a possible involvement of these common pathways in the pathogenesis of CCMs. However, the specific signaling mediating the distinct function of CCM genes in the pathogenesis of CCMs needs to be further elucidated.

Ultrastructural characteristics of peripheral arteriovenous and venous angiodysplasias

Comparative histological and electron microscopic study of arteriovenous and venous angiodysplasias revealed specific features of their structure, presumably reflecting differences in their morphogenesis. Specific ultrastructural characteristics of angiodysplasias are modified shape of endotheliocytes, impaired structure of the basal membrane, and reduced count of pericytes.

Inhibition of angiogenesis induced by cerebral arteriovenous malformations using Gamma Knife irradiation

Object

The authors studied the effect of Gamma Knife irradiation on angiogenesis induced by cerebral arteriovenous malformation (AVM) tissues implanted in the corneas of rats.

Methods

Ten AVM specimens obtained from tissue resections performed at Marmara University between 1998 and 2004 were used. A uniform amount of tissue was implanted into the micropocket between the two epithelial layers of the cornea. Gamma Knife irradiation was applied with dose prescriptions of 15 or 30 Gy to one cornea at 100% iso-dose. Dosing was adjusted so that the implanted cornea of one eye received 1.5 Gy when 15 Gy was applied to the other cornea. Similarly, one cornea received 3 Gy when 30 Gy was applied to the other cornea. Angiogenic activity was graded daily by biomicroscopic observations. Forty-eight other rats were used for microvessel counting and vascularendothelial growth factor (VEGF) staining portions of the experiment. Micropieces of the specimens were again used for corneal implantation. Rats from each group were killed on Days 5, 10, 15, and 20, and four corneas from each group were examined.

Gamma Knife irradiation dose dependently decreased AVM-induced neovascularization in the rat cornea as determined by biomicroscopic grading of angiogenesis, microvessel count, and VEGF expression.

Conclusions

The results suggest that Gamma Knife irradiation inhibits angiogenesis induced by AVM tissue in the cornea angiogenesis model. The data are not directly related to understanding how Gamma Knife irradiation occludes existing AVM vasculature, but to understanding why properly treated AVMs do not recur and do not show neovascularization after Gamma Knife irradiation.

Cavernous malformations of the orbit: a distinct entity? A review of own experiences

We collected data to provide evidence that orbital cavernous malformations (CMs) are histopathologically, neuroradiologically, and clinically different from cerebral CMs and may represent a distinct entity. In this study, the main clinical, histopathological and radiological characteristics of 19 patients (11 females and eight males, mean age 49.1 years) with orbital CMs out of a series of 376 orbital tumors are analyzed and compared with 107 cases with cerebral CMs treated in the same period. Decrease of visual acuity and painless progressive proptosis were the main clinical signs observed in 17 patients (89%). Complete microsurgical excision of lesions via individualized approaches was obtained in all cases. Follow-up examinations were obtained after a mean of 3.1 years (11 months to 7 years) and yielded complete recovery in 14 patients, while five remained clinically unchanged. Based on clinicopathological and neuroradiological studies of these 19 patients with orbital and 107 patients with cerebral CMs treated in the same period, we found evidence that orbital CMs have specific features to distinguish them from cerebral CMs. Orbital CMs, in contrast to the cerebral CMs, showed non-degenerated well-developed vessel walls and were covered by a hard and compact capsule. Clinical symptoms are characterized by the growth of orbital CMs due to intraluminal thrombosis and subsequent recanalization of cavernous vessels; there were no signs of hemorrhage. We found evidence to suggest that orbital CMs represent a distinct clinicopathologic and neuroradiologic entity.

Expression of integrins in cerebral arteriovenous and cavernous malformations

OBJECTIVE

To assess and compare levels and patterns of expression for integrins alphavbeta1, alphavbeta3, and alphavbeta5 in arteriovenous malformations (AVMs) and cavernous malformations (CCMs) of the brain.

MATERIALS AND METHODS

Specimens from 10 AVM and 10 CCM lesions were selected from 112 patients with AVMs and 97 patients with CCMs who were treated microsurgically in the Department of Neurosurgery, Marmara University, Istanbul, Turkey. Sections were immunohistochemically stained with antibodies for integrins alphavbeta1, alphavbeta3, and alphavbeta5. Separate histological layers of the vascular wall were evaluated, and levels of expression were graded using a four-tier system.

RESULTS

Integrin alphavbeta1 was more strongly expressed in AVMs than in CCMs. This difference was most pronounced in the endothelium and subendothelium/media. Integrin alphavbeta3 was more strongly expressed in CCM endothelium than in AVM endothelium (average grades, 0.9 and 0.4, respectively). All 10 of the CCM lesions expressed integrin alphavbeta5 in the endothelium, whereas only five of the AVMs showed minimal expression of this molecule in the endothelium.

CONCLUSION

Current scientific understanding of the roles integrins play in angiogenesis is far from complete. The levels and patterns of expression for these molecules in the histological layers of the vascular walls of AVMs and CCMs provide some clues about the complex biological activities of integrins in these lesions. If one accepts the premise that immunohistochemistry has its inherent methodological problems, integrins alphavbeta1, alphavbeta3, and alphavbeta5 are expressed in AVMs and CCMs in different ways that may be linked to stages of angiogenic maturation. Integrin alphavbeta1 is expressed more strongly in endothelium and subendothelium/media of AVMs than in the corresponding layers of CCMs. Integrins alphavbeta3 and alphavbeta5 are expressed more strongly in CCM endothelium than in AVM endothelium. In addition, integrin alphavbeta5 staining was stronger in CCM subendothelium than AVM subendothelium/media.

Isolation and culture of microvascular endothelial cells from gliomas of different WHO grades

Gliomas are the most common intrinsic brain tumors. The degree of vascularization corresponds to malignancy and is related to prognosis. In order to retrieve information about tumor behavior in situ, the use of primary tissue material for experiments is advantageous. With increasing evidence for the importance of microenvironment and vascularization in tumor biology, we concentrated on the isolation of endothelial cells (EC) from primary tumor material to investigate the role of endothelium within tumor tissue. We developed a method for isolation and purification of tumor-derived endothelial cells. EC were isolated and cultivated from normal brain using tissue digestion and Percoll density gradient centrifugation resulting in a <95% of EC culture. For isolation of EC from gliomas of different malignancy grades a combination of tissue digestion, Percoll gradient centrifugation and magnetic bead sorting by anti-CD31, -VE-Cadherin and -CD 105 was employed. This approach provided a purity of <98%. Cells were classified and characterized by testing expression of CD105, CD31, VE-Cadherin, vWF, UEA-1 and measuring DiI-Ac-LDL-uptake. To exclude contamination, staining and negative selection with anti-SMA, -GFAP, and -CD68 was performed. Tumors were histopathologically diagnosed according to WHO classification. We isolated EC from normal brain (NBEC, n = 11), low-grade gliomas WHO II (LGEC, n = 22), and high-grade gliomas WHO III & IV (HGEC, n = 11). There were no clear differences in EC morphology between the different tumor grades. However, a significantly higher proliferation rate of HGEC compared to LGEC was observed as well as distinctive antigen expression. Already in early passages isolated EC showed a rapid change in antigen expression indicating a phenotypic shift under culture conditions. We could establish a protocol for reliable and reproducible isolation and culture of EC from gliomas with different WHO grading. In first phenotypical and functional analyses, NBEC, LGEC and HGEC show remarkable differences. EC from all tumors could be grown in culture. However, passage related changes of EC phenotype demand very early passages to work with.

Characterization of the Integrin αvβ3 in Arteriovenous Malformations and Cavernous Malformations

BACKGROUND

Alpha V beta 3 (alphavbeta3) is an integrin specifically expressed on the endothelial cells of central nervous system (CNS) neoplasms. However, no data exist on the expression of alphavbeta3 in vascular malformations of the CNS. In this study, we investigate the expression of alphavbeta3 in arteriovenous malformations (AVMs) and cavernous malformations (CMs).

METHOD

Frozen samples of AVMs from 12 patients and CMs from 5 patients were obtained intraoperatively. Once the final pathology had been confirmed, immunohistochemistry was performed using an antibody to the integrin alphavbeta3. The alphavbeta3 expression pattern was graded according to the percentage of positively staining vessels.

RESULTS

Ten of 12 AVMs demonstrated alphavbeta3 immunopositivity. Six of these 10 AVMs had moderate or strong staining. Most notably, 5 of the 6 moderate or strongly staining AVMs came from patients 22 years of age or younger. Four of these 6 AVMs had previously been embolized. None of the cavernous malformations demonstrated alphavbeta3 immunopositivity.

DISCUSSION

alphavbeta3 may contribute to the formation of AVMs in younger patients. alphavbeta3 may also provide a potential therapeutic target. The lack of alphavbeta3 expression in cavernous malformations, despite their high vascular densities, suggests that the pathophysiology of their formation differs from that of AVMs.

Giant infiltrative cavernous malformation: clinical presentation, intervention, and genetic analysis: case report

OBJECTIVE AND IMPORTANCE

Cavernous malformations can present in children with a sporadic course of repeated hemorrhage and enlargement, but they are rarely aggressive, infiltrative, or multilobar. We present the case of a young boy with a complex cavernous malformation that evolved during the course of a decade to encompass the majority of his right cerebral hemisphere.

CLINICAL PRESENTATION

A 16-month-old boy presented with seizures, and radiographic studies demonstrated a large cavernous malformation in his right frontal pole. During the next 10 years, his seizures became intractable, and he developed progressive left hand weakness and atrophy. His malformation infiltrated his entire right frontal lobe as well as portions of his right parietal lobe, temporal lobe, and deep gray matter structures.

INTERVENTION

The patient underwent right hemicraniotomy and near total resection of the lesion. Pathological analysis revealed dilated, thin-walled vessels separated by small amounts of intervening astrogliotic brain consistent with cavernous malformation. The patient recovered to his baseline neurological condition and has had no seizure or hemorrhage since his operation. Genetic testing did not reveal mutations in either the CCM1 (KRIT1) or CCM2 (malcavernin) genes.

CONCLUSION

This case may represent an atypical variant of cavernous malformation best termed giant infiltrative cavernous malformation. Despite its unusual size, multilobar location, and aggressive infiltration, it can be managed effectively with standard surgical resection.

Gene microarray analysis of human brain arteriovenous malformations

OBJECTIVE

Human brain arteriovenous malformations (BAVMs) display abnormal expression of various angiogenesis-related genes and their products. We examined gene expression patterns in BAVMs by the gene microarray technique.

METHODS

We analyzed BAVM and control brain samples obtained by temporal lobectomy for medically intractable seizure by Affymetrix Human Gene Set U95Av2 (Affymetrix, Inc., Santa Clara, CA). The gene microarray data were compared with new and previously published data that used conventional molecular biology techniques.

RESULTS

We analyzed six BAVM and five control brain samples. From 12,625 gene probes assayed, 1781 gene probes showed differential expression between BAVMs and controls. BAVM samples had a gene expression pattern that was distinct from those of control brain samples. Increased messenger ribonucleic acid expression of vascular endothelial growth factor A was accompanied by increased expression of its protein product. A majority of the gene data was in agreement with previously published data. The gene microarray data generated a new testable hypothesis regarding integrin, and we found increased expression of integrin alphavbeta3 protein in BAVMs.

CONCLUSION

The gene expression pattern of BAVMs was distinct from those of control brain samples. We verified the gene microarray data by demonstrating that increased gene expression levels for angiogenesis-related molecules were accompanied by increased levels of their protein product expression. The gene microarray technique may be a useful tool to study multiple pathways simultaneously in BAVM specimens.

Processing and presentation of the islet autoantigen GAD by vascular endothelial cells promotes transmigration of autoreactive T-cells

Type 1 diabetes is characterized by T-cell infiltration of the islets of Langerhans and abundant HLA class II molecule expression on islet endothelial cells (ECs). The specificity of infiltrating T-cells for islet autoantigens has been amply demonstrated in animal models, and is implicit in human diabetes, but the processes regulating endothelial transmigration of islet autoantigen-specific T-cells into islets are not known. We examined the ability of ECs expressing HLA class II molecules to process and present the islet autoantigen GAD65 and examined the effects of presentation on transmigration of GAD65-specific T-cells. Primary cultures of human vascular ECs expressing the DRB1*0401 (VEC1) and DRB1*0301 (VEC2) genotypes were established and de novo expression of HLA class II molecules induced with interferon-gamma. Under these conditions, VEC1 efficiently processed and presented whole GAD65 to the HLA-DR4-restricted murine T-cell hybridoma T33.1 that recognizes the 274-286 epitope of GAD65. Using a transwell system, we examined the effect of GAD65 presentation on migration of GAD65-specific T-cells across EC monolayers. Migration of T33.1 hybridoma cells and of the human T-cell clone, PM1#11 (recognizes GAD65 epitope 339-352 presented by HLA-DR3) across VEC1 and VEC2, respectively, were greatly enhanced in the presence of GAD65, commencing more rapidly and achieving a higher peak migration at 3 h. Migrated PM1#11 cells retained full proliferative capacity. These results support the hypothesis that presentation of autoantigens by islet endothelium in vivo could promote transmigration of circulating islet autoantigen-specific T-cells primed in regional lymph nodes against islet autoantigens.

Differential gene expression in human cerebrovascular malformations

OBJECTIVE

We sought to identify genes with differential expression in cerebral cavernous malformations (CCMs), arteriovenous malformations (AVMs), and control superficial temporal arteries (STAs) and to confirm differential expression of genes previously implicated in the pathobiology of these lesions.

METHODS

Total ribonucleic acid was isolated from four CCM, four AVM, and three STA surgical specimens and used to quantify lesion-specific messenger ribonucleic acid expression levels on human gene arrays. Data were analyzed with the use of two separate methodologies: gene discovery and confirmation analysis.

RESULTS

The gene discovery method identified 42 genes that were significantly up-regulated and 36 genes that were significantly down-regulated in CCMs as compared with AVMs and STAs (P = 0.006). Similarly, 48 genes were significantly up-regulated and 59 genes were significantly down-regulated in AVMs as compared with CCMs and STAs (P = 0.006). The confirmation analysis showed significant differential expression (P < 0.05) in 11 of 15 genes (angiogenesis factors, receptors, and structural proteins) that previously had been reported to be expressed differentially in CCMs and AVMs in immunohistochemical analysis.

CONCLUSION

We identify numerous genes that are differentially expressed in CCMs and AVMs and correlate expression with the immunohistochemistry of genes implicated in cerebrovascular malformations. In future efforts, we will aim to confirm candidate genes specifically related to the pathobiology of cerebrovascular malformations and determine their biological systems and mechanistic relevance.

Effect of a single high-dose gamma irradiation on cultured cells in human cerebral arteriovenous malformation

Object. The purpose of this study was to analyze the effect of single high-dose gamma irradiation at a cellular biological level on tissue cultures obtained in patients who underwent surgery for cerebral arteriovenous malformation (AVM).

Methods. The cell proliferation indices and changes in activation of p53, p21Waf-1, and mdm-2 were determined. Additionally, immunohistochemical investigations for vimentin, desmin, α—smooth muscle actin (α-SMA), glial fibrillary acidic protein, Factor VIII—related antigen (F-VIII), cytokeratin, S100, and transforming growth factor—β (TGFβ) were performed on cultured AVM cells after a single high-dose irradiation. Normal human brain microvessel endothelial (HBE) cells and aortic smooth muscle cells served as controls.

The proliferation index decreased on the 5th day after irradiation and remained depressed over the observation period in the irradiated AVM cultures. The p53, p21Waf-1, and mdm-2 messenger RNA measurements showed considerable elevation both in AVM cultures and HBE cells after 15-Gy irradiation, which indicated apoptosis. Immunohistochemistry revealed strong vimentin positivity in the nonirradiated cultures, which gradually decreased in the irradiated cultures. Transforming growth factor—β positivity was demonstrated in the irradiated specimens, indicating transformation of fibroblastic cells into activated myofibroblastic elements. This transformation was confirmed by demonstrating elevated SMA expression as well in the radiation-treated fibroblasts.

Conclusions. The presence of TGFβ and α-SMA activity in the irradiated AVM cells suggests that along with the genetically confirmed apoptotic activity, fibroblast transformation into myofibroblasts might be one of the mechanisms leading to shrinkage and obliteration of AVMs after single high-dose gamma irradiation.

Epidemiology and natural history of arteriovenous malformations

The epidemiology and natural history of cerebral arteriovenous malformations (AVMs) remains incompletely elucidated. Several factors are responsible. With regard to the incidence and prevalence of AVMs, the results of prior studies have suffered because of the retrospective design, the use of nonspecific ICD-9 codes, and a focus on small genetically isolated populations. Recent data from the New York Islands AVM Hemorrhage Study, an ongoing, prospective, population-based survey determining the incidence of AVM-related hemorrhage and the associated rates of morbidity and mortality in a zip code–defined population of 10 million people, suggests that the AVM detection rate is 1.21/100,000 person-years (95% confidence interval [CI] 1.02–1.42) and the incidence of AVM-hemorrhage is 0.42/100,000 person-years (95% CI 0.32–0.55). Contemporaneous data from the Northern Manhattan Stroke Study, a prospective, longitudinal population-based study of nearly 150,000 patients in which the focus is to define the incidence of stroke, suggest the crude incidence for first-ever AVM-related hemorrhage to be 0.55/100,000 person-years (95% CI 0.11–1.61). Efforts are ongoing to study the natural history of both ruptured and unruptured AVMs in these datasets to examine the relevance of prior studies of patients selected for conservative follow up in Finland. In addition, data are being gathered to determine whether risk factors for future hemorrhage, which have previously been established in small case series, are valid when applied to whole populations. Together, these data should help inform therapeutic decisionmaking.

Vascular smooth muscle cell differentiation in human cerebral vascular malformations

OBJECTIVE

The pathogenesis of central nervous system vascular malformations likely involves the abnormal assembly, differentiation of vascular smooth muscle cells (VSMC), or both in association with dysmorphic vessel wall. We hypothesize that intracranial arteriovenous malformations (AVMs) and cerebral cavernous malformations (CCMs) exhibit distinct patterns of expression of molecular markers of differentiation and maturity of VSMCs. We further speculate that the unique VSMC phenotype in the different lesions is not necessarily maintained in cell culture.

METHODS

Paraffin-embedded sections of five AVMs, CCMs, and control brain tissues were stained immunohistochemically with antibodies to alpha-smooth muscle actin (alpha-SMA), myosin heavy chain, and smoothelin, a novel marker for contractile VSMC phenotype. Large (> or =100 microm) and small (<100 microm) vessels were counted and assessed for immunoexpression of each protein, then categorized according to expression of one or more of these markers. Cultured nonendothelial cells isolated from four other excised AVM and CCM lesions were assessed for immunoexpression of the same antibodies.

RESULTS

Alpha-SMA was universally expressed in all vessels in AVMs and in control brains. It was expressed in the subendothelial layer of 97% of large caverns and 85% of small caverns and in scattered intercavernous connective tissue fibrocytes in CCMs. Myosin heavy chain was expressed in the majority of brain and AVM vessels, except for normal veins, and in the subendothelial layer of more than half of the caverns in CCMs. Smoothelin expression was less prevalent in large vessels in AVMs than in control brains and was not found in any caverns in CCMs (large vessels in control brains, 40.9%; AVMs, 21.9%; CCMs, 0%; P < 0.0001). Cultured AVM and CCM nonendothelial cells expressed alpha-SMA, but myosin heavy chain was expressed weakly in cells from only one CCM. Smoothelin was negative in all cells.

CONCLUSION

We describe vessels with various stages of VSMC differentiation in AVMs and CCMs. The subendothelial layer of CCMs commonly expresses alpha-SMA and less commonly expresses myosin heavy chain. Expression of smoothelin was less prevalent in large AVM vessels than in normal brain, which may reflect the loss of contractile property associated with hemodynamic stress. It is difficult to evaluate VSMC differentiation in culture because of phenotypic change.

Expression of endothelial cell angiogenesis receptors in human cerebrovascular malformations

OBJECTIVE

To further understand the role of angiogenic growth factors in the development of cerebral cavernous malformations (CCMs) and arteriovenous malformations (AVMs), we investigated endothelial cell (EC) expression of receptors for vascular endothelial growth factor (VEGF) and angiopoietin systems in patients with surgically resected lesions.

METHODS

Paraffin-embedded sections of five AVMs, CCMs, and normal control brain tissue samples were stained immunohistochemically with antibodies to von Willebrand factor and CD31 (to characterize ECs) and angiogenesis growth factor receptors Flt-1 (VEGF-R1), Flk-1 (VEGF-R2), Tie-1, and Tie-2. We counted large and small vessels in each specimen, assessed each specimen's immunoexpression of each antigen, and analyzed differences between CCMs, AVMs, and the normal control brain tissue samples.

RESULTS

The ECs of CCMs, AVMs, and normal control brain tissue samples expressed the von Willebrand factor uniformly, but the ECs of CCMs were largely negative for CD31 (P < 0.05). Flk-1, Flt-1, and Tie-2 were not expressed in the control brain tissue samples. The proportion of immunopositive vessels to VEGF receptors Flk-1 and Flt-1 was significantly greater in AVMs and CCMs than in the control brain tissue samples (P < 0.05). Tie-2 in AVMs and CCMs was expressed in a higher percentage of immunopositive vessels than in the control brain tissue samples, but the difference was not statistically significant. Tie-1 was expressed in rare vessels of all lesion types and control brain tissue samples.

CONCLUSION

ECs of CCMs do not seem to express CD31 to the same extent that AVMs and normal brain tissue do. AVMs and CCMs show greater expression of VEGF receptors, but not of angiopoietin receptors, than normal brain tissue does.

Ultrastructural pathological features of cerebrovascular malformations: a preliminary report

OBJECTIVE

Although cerebrovascular malformations have been characterized histologically, a systematic examination of such lesions by transmission electron microscopy has not been previously published. In this preliminary study, we describe the ultrastructural pathological features of cerebral arteriovenous malformations (AVMs) and cavernous malformations (CMs).

METHODS

Using transmission electron microscopy, we examined three CMs and three AVMs microsurgically harvested from patients, for conventional indications. Normal control cerebral tissue was obtained from two patients undergoing surgery for epilepsy. Specific attention was directed at components of the vascular wall, endothelial cell (EC) morphology, intercellular tight junctions, and the subendothelial layer.

RESULTS

In embolized AVM vessels, ECs were disrupted, with preservation of the underlying subendothelial vessel wall. Nidal vessel walls of AVMs showed disorganized collagen bundles. In CM specimens, ECs lined attenuated cavern walls that were composed of an amorphous material lacking organized collagen. Peripheral to the CMs, capillaries were often surrounded by rings of hemosiderin. Tight junctions between ECs were present in AVMs and control specimens, but substantial inter-EC gaps were found in CMs. Subendothelial smooth muscle cells were present in AVM and control specimens, but they were sparse or poorly characterized in CMs.

CONCLUSION

Surgically resected vascular malformations demonstrate abnormal ultrastructural pathological features. The preoperative embolization of AVMs results in EC denudation, with preservation of vessel wall structural integrity. The thin walls of CMs, lacking significant subendothelial support, along with the rarity of intact tight junctions between ECs, may contribute to the known propensity of CMs for recurrent microhemorrhage.

New concepts in adult brain arteriovenous malformations

Brain arteriovenous malformations are currently attracting increasing attention among clinicians as modern brain imaging techniques facilitate both diagnostic and follow-up evaluation. Their frequent presentation in young individuals, at times with flagrant clinical effects caused by cerebral hemorrhages or seizure disorders, keeps clinicians alert to any improvement in treatment strategies. Recent technical advances in surgical, endovascular, and radiation therapy add to the constantly accumulating data on clinical features, natural course, and treatment outcome in adult arteriovenous malformation patients. This review focuses on new concepts in arteriovenous malformation etiology, classification, treatment, and study approaches.