Endothelial proliferation, neoangiogenesis, and potential de novo generation of cerebrovascular malformations

MiR-25-3p regulates pulmonary arteriovenous malformation after Glenn procedure in patients with univentricular heart via the PHLPP2-HIF-1α axis

The detailed mechanism of pulmonary arteriovenous malformations after Glenn surgery (G-PAVMs) in cyanotic congenital heart disease (CHD) remains unclear. Microarray in situ hybridization was performed to assess the miRNA (miRNA) profiles of serum from pediatric patients (0-6 years of age) with G-PAVMs and after the Fontan procedure without G-PAVMs. In addition, we investigated the tube formation, migration, and proliferation of human lung microvascular endothelial cells (HMVEC-L) transfected with miR-25-3p mimic, miR-25-3p inhibitor, or PHLPP2 small interfering RNA, and examined HIF-1α/VEGF-A signaling after hypoxic stimulation. Serum miRNAs that showed ≥ 2-fold higher levels in patients with G-PAVMs than in other patients were selected. MiR-25-3p was significantly upregulated in the pulmonary artery sera of the post-Glenn group than in the post-Fontan group. We identified PHLPP2 as a direct target of miR-25-3p. PHLPP2 expression was significantly decreased in HMVEC-L transfected with miR-25-3p mimic compared to the control cells. HIF-1α and VEGF-A expression levels were increased in HMVEC-L transfected with miR-25-3p mimic compared to the control cells in a PHLPP2/Akt/mTOR signaling-dependent manner after hypoxic stimulation. MiR-25-3p promoted HMVEC-L angiogenesis, proliferation, and migration under hypoxic conditions. MiR-25-3p in the pulmonary arteries may contribute to G-PAVM development.

CRISPR/CasRx suppresses KRAS-induced brain arteriovenous malformation developed in postnatal brain endothelial cells in mice

Brain arteriovenous malformations (bAVMs) are anomalies forming vascular tangles connecting the arteries and veins, which cause hemorrhagic stroke in young adults. Current surgical approaches are highly invasive, and alternative therapeutic methods are warranted. Recent genetic studies identified KRAS mutations in endothelial cells of bAVMs; however, the underlying process leading to malformation in the postnatal stage remains unknown. Here we established a mouse model of bAVM developing during the early postnatal stage. Among 4 methods tested, mutant KRAS specifically introduced in brain endothelial cells by brain endothelial cell-directed adeno-associated virus (AAV) and endothelial cell-specific Cdh5-CreERT2 mice successfully induced bAVMs in the postnatal period. Mutant KRAS led to the development of multiple vascular tangles and hemorrhage in the brain with increased MAPK/ERK signaling and growth in endothelial cells. Three-dimensional analyses in cleared tissue revealed dilated vascular networks connecting arteries and veins, similar to human bAVMs. Single-cell RNA-Seq revealed dysregulated gene expressions in endothelial cells and multiple cell types involved in the pathological process. Finally, we employed CRISPR/CasRx to knock down mutant KRAS expression, which efficiently suppressed bAVM development. The present model reveals pathological processes that lead to postnatal bAVMs and demonstrates the efficacy of therapeutic strategies with CRISPR/CasRx.

Single-cell and bulk RNA-seq unveils the immune infiltration landscape associated with cuproptosis in cerebral cavernous malformations

BACKGROUND

Cerebral cavernous malformations (CCMs) are vascular abnormalities associated with deregulated angiogenesis. Their pathogenesis and optimal treatment remain unclear. This study aims to investigate the molecular signatures of cuproptosis, a newly identified type of cell death, associated with CCMs development.

METHODS

Bulk RNA sequencing (RNA-seq) from 15 CCM and 6 control samples were performed with consensus clustering and clustered to two subtypes based on expression levels of cuproptosis-related genes (CRGs). Differentially expressed genes and immune infiltration between subtypes were then identified. Machine learning algorithms including the least absolute shrinkage and selection operator and random forest were employed to screen for hub genes for CCMs associated with cuproptosis. Furthermore, Pathway enrichment and correlation analysis were used to explore the functions of hub genes and their association with immune phenotypes in CCMs. An external dataset was then employed for validation. Finally, employing the Cellchat algorithm on a single-cell RNA-seq dataset, we explored potential mechanisms underlying the participation of these hub genes in cell-cell communication in CCMs.

RESULTS

Our study revealed two distinct CCM subtypes with differential pattern of CRG expression and immune infiltration. Three hub genes (BTBD10, PFDN4, and CEMIP) were identified and validated, which may significantly associate with CCM pathogenesis. These genes were found to be significantly upregulated in CCM endothelial cells (ECs) and were validated through immunofluorescence and western blot analysis. Single-cell RNA-seq analysis revealed the cellular co-expression patterns of these hub genes, particularly highlighting the high expression of BTBD10 and PFDN4 in ECs. Additionally, a significant co-localization was also observed between BTBD10 and the pivotal cuproptosis gene FDX1 in Mki67+ tip cells, indicating the crucial role of cuproptosis for angiogenesis in CCMs. The study also explored the cell-cell communication between subcluster of ECs expressing these hub genes and immune cells, particularly M2 macrophages, suggesting a role for these interactions in CCM pathogenesis.

CONCLUSION

This study identifies molecular signatures linking cuproptosis to CCMs pathogenesis. Three hub genes-PFDN4, CEMIP, and BTBD10-may influence disease progression by modulating immunity. Further research is needed to understand their precise disease mechanisms and evaluate their potential as biomarkers or therapeutic targets for CCMs.

Nicotinic Acid-Mediated Modulation of Metastasis-Associated Protein 1 Methylation and Inflammation in Brain Arteriovenous Malformation

We explored metastasis-associated protein 1 (MTA1) promoter methylation in the development of brain arteriovenous malformation (BAVM). The clinical data of 148 sex- and age-matched BAVMs and controls were collected, and the MTA1 DNA methylation in peripheral white blood cells (WBC) was assessed by bisulfite pyrosequencing. Among them, 18 pairs of case-control samples were used for WBC mRNA detection, 32 pairs were used for WBC MTA1 protein measurement, and 50 pairs were used for plasma inflammatory factor analysis. Lipopolysaccharide (LPS) treatment was used to induce an inflammatory injury cell model of human brain microvascular endothelial cells (BMECS). 5-Aza-2'-deoxycytidine (5-AZA), nicotinic acid (NA), and MTA1 siRNAs were used in functional experiments to examine BMECS behaviors. RT-qPCR, Western blot, and ELISA or cytometric bead arrays were used to measure the expression levels of MTA1, cytokines, and signaling pathway proteins in human blood or BMECS. The degree of MTA1 promoter methylation was reduced in BAVM compared with the control group and was inversely proportional to MTA1 expression. Plasma ApoA concentrations in BAVM patients were significantly lower than those in controls and correlated positively with MTA1 promoter methylation and negatively with MTA1 expression. The expression of cytokine was markedly higher in BAVM than in controls. Cell experiments showed that 5-AZA decreased the methylation level of MTA1 and increased the expression of MTA1 protein. LPS treatment significantly increased cytokine concentrations (p < 0.05). NA and MTA1 silencing could effectively reverse the LPS-mediated increase in IL-6 and TNF-α expression through the NF-κB pathway. Our study indicated that NA may regulate MTA1 expression by affecting promoter DNA methylation, improve vascular inflammation through the NF-κB pathway, and alleviate the pathological development of BAVM.

The angio-architectural features of brain arteriovenous malformations: is it possible to predict the probability of rupture?

BACKGROUND

Hemorrhage is the most devastating complication of brain arteriovenous malformations (bAVMs), and to date, there is still concern about the needing for treatment in case of unruptured and asymptomatic bAVM. In fact, the morbidity and mortality of treatments may exceed that of the AVM's natural history. None of the classifications and scores for bAVM allows to predict the risk of bleeding. In this study, we aimed to identify the angio-architectural characteristics of brain AVMs associated with bleeding.

METHODS

We retrospectively evaluated all consecutive patients diagnosed with cerebral AVMs, between January 2010 and December 2019 from our prospective bAVM database. Univariate and multivariate logistic regression analysis were used to evaluate relationships between angio-architectural features of ruptured and unruptured bAVMs.

RESULTS

Of the 143 retrieved bAVMs, 65 were unruptured and 78 were ruptured. The univariate logistic regression analysis demonstrated statistically significant differences into angio-architectural features of unruptured and ruptured bAVMs. The multivariate logistic regression analysis fitted well (p =.113) with a good discrimination capacity (ROC = 0.83) of three independent angio-architectural features mainly related to bleeding in bAVMs: a smaller diameter of the nidus (p < .001), the absence of venous drainage alterations (p = .047), of the presence of prenidal aneurysms (p = .005).

CONCLUSIONS

In our study, several features resulted related to an increased probability of rupture for bAVMs, among which the more relevant were a small diameter of the nidus, the absence of venous drainage alterations, and the presence of prenidal aneurysms.

Molecular and genetic mechanisms in brain arteriovenous malformations: new insights and future perspectives

Brain arteriovenous malformations (bAVMs) are rare vascular lesions made of shunts between cerebral arteries and veins without the interposition of a capillary bed. The majority of bAVMs are asymptomatic, but some may be revealed by seizures and potentially life-threatening brain hemorrhage. The management of unruptured bAVMs remains a matter of debate. Significant progress in the understanding of their pathogenesis has been made during the last decade, particularly using genome sequencing and biomolecular analysis. Herein, we comprehensively review the recent molecular and genetic advances in the study of bAVMs that not only allow a better understanding of the genesis and growth of bAVMs, but also open new insights in medical treatment perspectives.

Emerging pathogenic mechanisms in human brain arteriovenous malformations: a contemporary review in the multiomics era

A variety of pathogenic mechanisms have been described in the formation, maturation, and rupture of brain arteriovenous malformations (bAVMs). While the understanding of bAVMs has largely been formulated based on animal models of rare hereditary diseases in which AVMs form, a new era of “omics” has permitted large-scale examinations of contributory genetic variations in human sporadic bAVMs. New findings regarding the pathogenesis of bAVMs implicate changes to endothelial and mural cells that result in increased angiogenesis, proinflammatory recruitment, and breakdown of vascular barrier properties that may result in hemorrhage; a greater diversity of cell populations that compose the bAVM microenvironment may also be implicated and complicate traditional models. Genomic sequencing of human bAVMs has uncovered inherited, de novo, and somatic activating mutations, such as KRAS, which contribute to the pathogenesis of bAVMs. New droplet-based, single-cell sequencing technologies have generated atlases of cell-specific molecular derangements. Herein, the authors review emerging genomic and transcriptomic findings underlying pathologic cell transformations in bAVMs derived from human tissues. The application of multiple sequencing modalities to bAVM tissues is a natural next step for researchers, although the potential therapeutic benefits or clinical applications remain unknown.

Prolonged culturing of iPSC-derived brain endothelial-like cells is associated with quiescence, downregulation of glycolysis, and resistance to disruption by an Alzheimer’s brain milieu

Background

Human induced pluripotent stem cell (hiPSC)-derived brain endothelial-like cells (iBECs) are a robust, scalable, and translatable model of the human blood–brain barrier (BBB). Prior works have shown that high transendothelial electrical resistance (TEER) persists in iBECs for at least 2 weeks, emphasizing the utility of the model for longer term studies. However, most studies evaluate iBECs within the first few days of subculture, and little is known about their proliferative state, which could influence their functions. In this study, we characterized iBEC proliferative state in relation to key BBB properties at early (2 days) and late (9 days) post-subculture time points.

Methods

hiPSCs were differentiated into iBECs using fully defined, serum-free medium. The proportion of proliferating cells was determined by BrdU assays. We evaluated TEER, expression of glycolysis enzymes and tight and adherens junction proteins (TJP and AJP), and glucose transporter-1 (GLUT1) function by immunoblotting, immunofluorescence, and quantifying radiolabeled tracer permeabilities. We also compared barrier disruption in response to TNF-α and conditioned medium (CM) from hiPSC-derived neurons harboring the Alzheimer’s disease (AD)-causing Swedish mutation (APPSwe/+).

Results

A significant decline in iBEC proliferation over time in culture was accompanied by adoption of a more quiescent endothelial metabolic state, indicated by downregulation of glycolysis-related proteins and upregulation GLUT1. Interestingly, upregulation of GLUT1 was associated with reduced glucose transport rates in more quiescent iBECs. We also found significant decreases in claudin-5 (CLDN5) and vascular endothelial-cadherin (VE-Cad) and a trend toward a decrease in platelet endothelial cell adhesion molecule-1 (PECAM-1), whereas zona occludens-1 (ZO-1) increased and occludin (OCLN) remained unchanged. Despite differences in TJP and AJP expression, there was no difference in mean TEER on day 2 vs. day 9. TNF-α induced disruption irrespective of iBEC proliferative state. Conversely, APPSwe/+ CM disrupted only proliferating iBEC monolayers.

Conclusion

iBECs can be used to study responses to disease-relevant stimuli in proliferating vs. more quiescent endothelial cell states, which may provide insight into BBB vulnerabilities in contexts of development, brain injury, and neurodegenerative disease.

'De Novo' Brain AVMs-Hypotheses for Development and a Systematic Review of Reported Cases

Background and Objectives: Brain arteriovenous malformations AVMs have been consistently regarded as congenital malformations of the cerebral vasculature. However, recent case reports describing "de novo AVMs" have sparked a growing debate on the nature of these lesions. Materials and Methods: We have performed a systematic review of the literature concerning de novo AVMs utilizing the PubMed and Google Academic databases. Termes used in the search were "AVM," "arteriovenous," "de novo," and "acquired," in all possible combinations. Results: 53 articles including a total of 58 patients harboring allegedly acquired AVMs were identified by researching the literature. Of these, 32 were male (55.17%), and 25 were female (43.10%). Mean age at de novo AVM diagnosis was 27.833 years (standard deviation (SD) of 21.215 years and a 95% confidence interval (CI) of 22.3 to 33.3). Most de novo AVMs were managed via microsurgical resection (20 out of 58, 34.48%), followed by radiosurgery and conservative treatment for 11 patients (18.97%) each, endovascular embolization combined with resection for five patients (8.62%), and embolization alone for three (5.17%), the remaining eight cases (13.79%) having an unspecified therapy. Conclusions: Increasing evidence suggests that some of the AVMs discovered develop some time after birth. We are still a long way from finally elucidating their true nature, though there is reason to believe that they can also appear after birth. Thus, we reason that the de novo AVMs are the result of a 'second hit' of a variable type, such as a previous intracranial hemorrhage or vascular pathology. The congenital or acquired characteristic of AVMs may have a tremendous impact on prognosis, risk of hemorrhage, and short and long-term management.

Somatic Mosaicism in the Pathogenesis of de novo Cerebral Arteriovenous Malformations: A Paradigm Shift Implicating the RAS-MAPK Signaling Cascade

Cerebral arteriovenous malformations (AVMs) are leading causes of lesional hemorrhagic stroke in both the pediatric and young adult population, with sporadic AVMs accounting for the majority of cases. Recent evidence has identified somatic mosaicism in key proximal components of the RAS-MAPK signaling cascade within endothelial cells collected from human sporadic cerebral AVMs, with early preclinical models supporting a potential causal role for these mutations in the pathogenesis of these malformations. Germline mutations that predispose to deregulation of the RAS-MAPK signaling axis have also been identified in hereditary vascular malformation syndromes, highlighting the key role of this signaling axis in global AVM development. Herein, we review the most recent genomic and preclinical evidence implicating somatic mosaicism in the RAS-MAPK signaling pathway in the pathogenesis of sporadic cerebral AVMs. Also, we review evidence for RAS-MAPK dysregulation in hereditary vascular malformation syndromes and present a hypothesis suggesting that this pathway is central for the development of both sporadic and syndrome-associated AVMs. Finally, we examine the clinical implications of these recent discoveries and highlight potential therapeutic targets within this signaling pathway.

Cerebral Arteriovenous Malformations in Pediatric Patients with Hereditary Hemorrhagic Telangiectasia: Re-evaluating Appearance, Bleeding Risk, and Treatment Necessity in a Selective Meta-analysis

Pediatric patients suffering from cerebral nidal arteriovenous malformations are a unique population due to the rare occurrence of the disease. Diagnosis of hereditary hemorrhagic telangiectasia (HHT) in children is a rare event and mainly restricted to coincidental detection from screening of possibly afflicted family members. In patients with HHT, it is well known that the incidence of cerebral vascular malformations (CVMs) is higher than expected when compared with the nonafflicted population. Even though CVMs comprise a variety of different distinct anatomical and radiographic entities (e.g., capillary telangiectasia, nidal arteriovenous malformation [AVM], cavernous malformation, dural or pial as well as mixed fistula, and vein of Galen malformation), they are mostly summarized and analyzed all in one category due to the low number of individual cases identified in single centers. Nevertheless, the best treatment algorithm will likely vary significantly between different CVMs as does the clinical presentation and the natural course of the CVM. It is therefore the objective of this article to focus on nidal AVMs in pediatric patients suffering from HHT. To this end, we performed a systematic selective literature research to estimate incidence, clinical and radiological appearance, as well as classification according to established grading system, and to evaluate the necessity of treatment of these lesions in light of their respective outcomes. Our line of arguments explains why we recommend to follow these lesions expectantly and suggest to keep pediatric patients under surveillance with sequential scans until they reach adulthood.

Risk Factors for Early Brain AVM Rupture: Cohort Study of Pediatric and Adult Patients

BACKGROUND AND PURPOSE

Whether architectural characteristics of ruptured brain AVMs vary across the life span is unknown. We aimed to identify angioarchitectural features associated with brain AVMs ruptured early in life.

MATERIALS AND METHODS

Patients with ruptured brain AVMs referred to 2 distinct academic centers between 2000 and 2018 were pooled and retrospectively analyzed. Imaging was retrospectively reviewed for angioarchitectural characteristics, including nidus size, location, Spetzler-Martin grade, venous drainage, and arterial or nidal aneurysm. Angioarchitecture variations across age groups were analyzed using uni- and multivariable models; then cohorts were pooled and analyzed using Kaplan-Meier and Cox models to determine factors associated with earlier rupture.

RESULTS

Among 320 included patients, 122 children (mean age, 9.8 ± 3.8 years) and 198 adults (mean age, 43.3 ± 15.7 years) were analyzed. Pediatric brain AVMs were more frequently deeply located (56.3% versus 21.2%, P < .001), with a larger nidus (24.2  versus 18.9 mm, P = .002), were less frequently nidal (15.9% versus 23.5%, P = .03) and arterial aneurysms (2.7% versus 17.9%, P < .001), and had similar drainage patterns or Spetzler-Martin grades. In the fully adjusted Cox model, supratentorial, deep brain AVM locations (adjusted relative risk, 1.19; 95% CI, 1.01-1.41; P = .03 and adjusted relative risk, 1.43; 95% CI, 1.22-1.67; P < .001, respectively) and exclusively deep venous drainage (adjusted relative risk, 1.46, 95% CI, 1.21-1.76; P < .001) were associated with earlier rupture, whereas arterial or nidal aneurysms were associated with rupture later in life.

CONCLUSIONS

The angioarchitecture of ruptured brain AVMs significantly varies across the life span. These distinct features may help to guide treatment decisions for patients with unruptured AVMs.

The impact of preradiosurgery embolization on intracranial arteriovenous malformations: a matched cohort analysis based on de novo lesion volume

OBJECTIVE

The benefits and risks of pre-stereotactic radiosurgery (SRS) embolization have been reported in different studies. The goal of this study was to compare the long-term outcome of arteriovenous malformations (AVMs) treated with and without pre-SRS embolization.

METHODS

A database including 1159 patients with AVMs who underwent SRS was reviewed. The embolized group was selected by including AVMs with pre-SRS embolization, maximal diameter > 30 mm, and estimated volume > 8 ml. The nonembolized group was defined as AVMs treated by SRS alone with matched de novo nidus volume. Outcomes including incidences of favorable clinical outcome (obliteration without hemorrhage, cyst formation, worsening, or new seizures), obliteration, adverse effects, and angioarchitectural complexity were evaluated.

RESULTS

The study cohort comprised 17 patients in the embolized group (median AVM volume 17.0 ml) and 35 patients in the nonembolized group (median AVM volume 13.1 ml). The rates of obliteration (embolized cohort: 33%, 44%, and 56%; nonembolized cohort: 32%, 47%, and 47% at 4, 6, and 10 years, respectively) and favorable outcome were comparable between the 2 groups. However, the embolized group had a significantly higher incidence of repeat SRS (41% vs 23%, p = 0.012) and total procedures (median number of procedures 4 vs 1, p < 0.001), even with a significantly higher margin dose delivered at the first SRS (23 Gy vs 17 Gy, p < 0.001). The median angioarchitectural complexity score was reduced from 7 to 5 after embolization. Collateral flow and neovascularization were more frequently observed in the embolized nonobliterated AVMs.

CONCLUSIONS

Both embolization plus SRS and SRS alone were effective therapies for moderately large (8-39 ml) AVMs. Even with a significantly higher prescription dose at the time of initial SRS, the embolized group still required more procedures to reach final obliteration. The presence of collateral flow and neovascularization could be risk factors for a failure to obliterate following treatment.

Evidence for endothelial-to-mesenchymal transition in human brain arteriovenous malformations

BACKGROUND

Brain arteriovenous malformations (AVMs) are rare, potentially devastating cerebrovascular lesions that can occur in both children and adults. AVMs are largely sporadic and the basic disease biology remains unclear, limiting advances in both detection and treatment. This study aimed to investigate human brain AVMs for endothelial-to-mesenchymal transition (EndMT), a process recently implicated in cerebral cavernous malformations (CCMs).

METHODS

We used 29 paraffin-embedded and 13 fresh/frozen human brain AVM samples to profile expression of panels of EndMT-associated proteins and RNAs. CCMs, a cerebrovascular disease also characterized by abnormal vasculature, were used as a primary comparison, given that EndMT specifically contributes to CCM disease biology. AVM-derived cell lines were isolated from three fresh, surgical AVM samples and characterized by protein expression.

RESULTS

We observed high collagen deposition, high PAI-1 expression, and expression of EndMT-associated transcription factors such as KLF4, SNAI1, and SNAI2 and mesenchymal-associated markers such as VIM, ACTA2, and S100A4. SMAD-dependent TGF-β signaling was not strongly activated in AVMs and this pathway may be only partially involved in mediating EndMT. Using serum-free culture conditions, we isolated myofibroblast-like cell populations from AVMs that expressed a unique range of proteins associated with mature cell types and with EndMT. Conditioned medium from these cells led to increased proliferation of HUVECs and SMCs.

CONCLUSIONS

Collectively, our results suggest a role for EndMT in AVM disease. This may lead to new avenues for disease models to further our understanding of disease mechanisms, and to the development of improved diagnostics and therapeutics.

Symptomatic developmental venous anomalies

Cerebral developmental venous anomalies (DVAs) are variations of venous vascular anatomy related to an underdevelopment of either the superficial or deep venous emissary system, resulting in a dilated transmedullary vein fed by multiple smaller venous radicles responsible for drainage of normal brain parenchyma. While typically benign and found incidentally on imaging studies, DVAs can rarely be symptomatic. The radiographic appearance of DVAs, as well as their symptomatic manifestations, is diverse. Herein, we will discuss the pathophysiology of symptomatic DVAs while providing illustrative case examples depicting each of their pathogenic mechanisms.

Effect of elevation of vascular endothelial growth factor level on exacerbation of hemorrhage in mouse brain arteriovenous malformation

OBJECTIVE

A high level of vascular endothelial growth factor (VEGF) has been implicated in brain arteriovenous malformation (bAVM) bleeding and rupture. However, direct evidence is missing. In this study the authors used a mouse bAVM model to test the hypothesis that elevation of focal VEGF levels in bAVMs exacerbates the severity of bAVM hemorrhage.

METHODS

Brain AVMs were induced in adult mice in which activin receptor-like kinase 1 (Alk1, a gene that causes AVM) gene exons 4-6 were floxed by intrabasal ganglia injection of an adenoviral vector expressing Cre recombinase to induce Alk1 mutation and an adeno-associated viral vector expressing human VEGF (AAV-VEGF) to induce angiogenesis. Two doses of AAV-VEGF (5 × 109 [high] or 2 × 109 [low]) viral genomes were used. In addition, the common carotid artery and external jugular vein were anastomosed in a group of mice treated with low-dose AAV-VEGF 6 weeks after the model induction to induce cerebral venous hypertension (VH), because VH increases the VEGF level in the brain. Brain samples were collected 8 weeks after the model induction. Hemorrhages in the bAVM lesions were quantified on brain sections stained with Prussian blue, which detects iron deposition. VEGF levels were quantified in bAVM tissue by enzyme-linked immunosorbent assay.

RESULTS

Compared to mice injected with a low dose of AAV-VEGF, the mice injected with a high dose had higher levels of VEGF (p = 0.003) and larger Prussian blue-positive areas in the bAVM lesion at 8 or 9 weeks after model induction (p = 0.002). VH increased bAVM hemorrhage in the low-dose AAV-VEGF group. The overall mortality in the high-dose AAV-VEGF group was 26.7%, whereas no mouse died in the low-dose AAV-VEGF group without VH. In contrast, VH caused a mortality of 50% in the low-dose AAV-VEGF group.

CONCLUSIONS

Using mouse bAVM models, the authors provided direct evidence that elevation of the VEGF level increases bAVM hemorrhage and mouse mortality.

Emerging Pharmacologic Targets in Cerebral Cavernous Malformation and Potential Strategies to Alter the Natural History of a Difficult Disease: A Review

Importance

Cerebral cavernous malformations (CCMs) are vascular lesions of the brain that may lead to hemorrhage, seizures, and neurologic deficits. Most are linked to loss-of-function mutations in 1 of 3 genes, namely CCM1 (originally called KRIT1), CCM2 (MGC4607), or CCM3 (PDCD10), that can either occur as sporadic events or are inherited in an autosomal dominant pattern with incomplete penetrance. Familial forms originate from germline mutations, often have multiple intracranial lesions that grow in size and number over time, and cause an earlier and more severe presentation. Despite active preclinical research on a few pharmacologic agents, clinical translation has been slow. Open surgery and, in some cases, stereotactic radiosurgery remain the only effective treatments, but these options are limited by lesion accessibility and are associated with nonnegligible rates of morbidity and mortality.

Observations

We discuss the limits of CCM management and introduce findings from in vitro and in vivo studies that provide insight into CCM pathogenesis and indicate molecular mechanisms as potential therapeutic targets. These studies report dysregulated cellular pathways shared between CCM, cardiovascular diseases, and cancer. They also suggest the potential effectiveness of proper drug repurposing in association with, or as an alternative to, targeted interventions.

Conclusions and Relevance

We propose methods to exploit specific molecular pathways to design patient-tailored therapeutic approaches in CCM, with the aim to alter its natural progression. In this scenario, the lack of effective pharmacologic options remains a critical barrier that poses an unfulfilled and urgent medical need.

RNA-Sequencing Highlights Inflammation and Impaired Integrity of the Vascular Wall in Brain Arteriovenous Malformations

Background and Purpose—

Interventional treatment of unruptured brain arteriovenous malformations (BAVMs) has become increasingly controversial. Because medical therapy is still lacking, we aimed to obtain insight into the disease mechanisms implicated in BAVMs and to identify potential targets for medical treatment to prevent rupture of a BAVM.

Methods—

We used next-generation RNA sequencing to identify differential expression on a transcriptome-wide level comparing tissue samples of 12 BAVMs to 16 intracranial control arteries. We identified differentially expressed genes by negative binominal generalized log-linear regression (false discovery rate corrected P <0.05). We selected 10 genes for validation using droplet digital polymerase chain reaction. We performed functional pathway analysis accounting for potential gene-length bias, to establish enhancement of biological pathways involved in BAVMs. We further assessed which Gene Ontology terms were enriched.

Results—

We found 736 upregulated genes in BAVMs including genes implicated in the cytoskeletal machinery and cell-migration and genes encoding for inflammatory cytokines and secretory products of neutrophils and macrophages. Furthermore, we found 498 genes downregulated including genes implicated in extracellular matrix composition, the binary angiopoietin-TIE system, and TGF (transforming growth factor)-β signaling. We confirmed the differential expression of top 10 ranked genes. Functional pathway analysis showed enrichment of the protein digestion and absorption pathway (false discovery rate-adjusted P =1.70×10 −2 ). We identified 47 enriched Gene Ontology terms (false discovery rate-adjusted P <0.05) implicated in cytoskeleton network, cell-migration, endoplasmic reticulum, transmembrane transport, and extracellular matrix composition.

Conclusions—

Our genome-wide RNA-sequencing study points to involvement of inflammatory mediators, loss of cerebrovascular quiescence, and impaired integrity of the vascular wall in the pathophysiology of BAVMs. Our study may lend support to potential receptivity of BAVMs to medical therapeutics, including those promoting vessel maturation, and anti-inflammatory and immune-modifying drugs.

CCM1/KRIT1 mutation in monozygotic twins of a polyzygotic triplet birth: genetic, clinical and radiological characteristics

Cerebral cavernous malformations are focal vascular lesions of the brain, occurring sporadically or as an autosomal dominant familial form. The genetic background influences not only the clinical course but also patients' consultation and the indication to treat. We here present the rare case of monozygotic male twins of a polyzygotic triplet birth, carrying a CCM1 mutation, inherited from the mother. Both twins showed an identical site and size of a large frontobasal lesion. The genetic segregation and the clinical course in affected family members are presented and discussed.

Defective vascular signaling & prospective therapeutic targets in brain arteriovenous malformations

The neurovascular unit is composed of endothelial cells, vascular smooth muscle cells, pericytes, astrocytes and neurons. Through tightly regulated multi-directional cell signaling, the neurovascular unit is responsible for the numerous functionalities of the cerebrovasculature - including the regulation of molecular and cellular transport across the blood-brain barrier, angiogenesis, blood flow responses to brain activation and neuroinflammation. Historically, the study of the brain vasculature focused on endothelial cells; however, recent work has demonstrated that pericytes and vascular smooth muscle cells - collectively known as mural cells - play critical roles in many of these functions. Given this emerging data, a more complete mechanistic understanding of the cellular basis of brain vascular malformations is needed. In this review, we examine the integrated functions and signaling within the neurovascular unit necessary for normal cerebrovascular structure and function. We then describe the role of aberrant cell signaling within the neurovascular unit in brain arteriovenous malformations and identify how these pathways may be targeted therapeutically to eradicate or stabilize these lesions.

Co-expression of tissue factor and IL-6 in immature endothelial cells of cerebral cavernous malformations

Cerebral cavernous malformations (CCMs) are congenital abnormal clusters of capillaries that are prone to leaking and thought to result from a disorder of endothelial cells. The underlying pathology of CCM is not fully understood. We analyzed the expression of tissue factor (TF) and interleukin-6 (IL-6) in CCMs to determine the association of TF and IL-6 with clinical and pathological findings. Thirteen cases of operative specimens of sporadic CCMs were included in this study. The expression of messenger RNA of TF and IL-6 was assayed and the association with clinical factors was investigated. Then, the distribution of TF and IL-6 was examined with immunofluorescence. The mRNA expression of TF of CCMs was significantly higher than that of the control (p=0.017), and was correlated with the number of hemorrhage appearances (p=0.190, ρ=0.62). The mRNA expression level of IL-6 was significantly correlated with the mRNA expression level of TF (p=0.034, ρ=0.58). Examination of immunostained sections indicated that TF⁺ cells were also positive for IL-6, and distributed around normal endothelial cells. Moreover, the TF⁺/IL-6⁺ cells expressed CD31 and VEGFR2. The expressions of IL-6 and TF were correlated, and both were present in the same immature endothelial cells. TF is elevated in CCM and might mediate progressive events. These factors may play a prognostic role in CCM.

Pathology of cavernous malformations

Cavernous malformations (CMs) are low-pressure angiographically occult lesions, composed of blood-filled sinusoidal locules known as "caverns." Although these lesions were once believed to be congenital in nature, there is compelling evidence to support de novo formation of CMs as well. They can occur as sporadic lesions or be inherited in an autosomal-dominant phenotype in familial forms of the disease. The pathophysiology of CMs is commonly believed to be due to abnormal vascular pathology. Three genes, CCM1, CCM2, and CCM3, have been extensively studied for their role in vascular pathology, resulting in abnormal angiogenesis and compromising the structural integrity of vessel endothelial cell. The expression of growth factors has been researched to gain insight into the dynamic behavior of CM lesions. Gross and microscopic images are utilized in this chapter to illustrate the pathologic findings of these lesions. Ultrastructural analysis demonstrates the aberrations in CM endothelial cells and structural integrity that may provide better understanding into how and why these lesions have a propensity to hemorrhage.

Multiple cerebral arterio-venous malformations: impact of multiplicity and hemodynamics on treatment strategies

BACKGROUND

Multiple AVMs are exceptionally rare lesions and only a few larger series have been published, including other vascular pathologies, such as arterio-venous fistulae (AVF) or patients with hereditary syndromes. Our study presents clinical, angiographic, and therapeutic characteristics of patients harboring sporadic multiple AVMs.

METHODS

Basic demographic data, vascular architecture, clinical presentation, treatment strategies, and treatment outcome were analyzed retrospectively from patients with cerebral AVMs treated in our department between 1990 and 2015.

RESULTS

Six out of 539 patients (1.1 %) harbored 15 multiple and distinct cerebral lesions. Nidus size was predominantly small, consequently determining a Spetzler-Martin grade °I-°II (three-tier grading system). In three patients, AVMs shared a proximal feeding artery supply, whereas each AVM displayed its own venous drainage. Five of six patients (83 %) presented with hemorrhage. Four patients received therapy of the AVMs with complete elimination in 3/4 patients (75 %) and 8/9 treated AVMs (89 %). All patients with treatment of the AVM showed good-to-excellent recovery (n = 4, mRS ≤ 2).

CONCLUSIONS

Multiple cerebral AVMs are complex vascular lesions. The multiplicity of hemodynamic and malformation-related variables influence treatment strategy and sequence. Thus, awareness of these parameters (of various malformations before and during treatment) is important. The high number of hemorrhagic events in the present series might justify a more aggressive treatment of multiple AVMs than previously thought.

Systemic Expression of Vascular Endothelial Growth Factor in Patients with Cerebral Cavernous Malformation Treated by Stereotactic Radiosurgery

OBJECTIVE

Increased expression of angiogenic factors, such as vascular endothelial growth factor (VEGF), is associated with the pathogenesis of cerebral cavernous malformations (CCMs). The purpose of this study was to investigate plasma levels of VEGF in normal subjects and in patients with CCM and to evaluate change in these levels following stereotactic radiosurgery (SRS).

METHODS

Peripheral venous blood was collected from 6 patients with CCM before SRS using Gamma Knife and at the 1 week, 1 month, 3month, and 6 month follow-up visits. Plasma VEGF levels were measured using commercially available enzyme-linked immunosorbent assay kits. Peripheral blood samples were obtained from 10 healthy volunteers as controls.

RESULTS

Mean plasma VEGF level of 41.9 pg/mL (range, 11.7-114.9 pg/mL) in patients with CCM at baseline was higher than that of the healthy controls (29.3 pg/mL, range, 9.2-64.3 pg/mL), without significant differences between CCM patients and controls (p=0.828). Plasma VEGF level following SRS dropped to 24.6 pg/mL after 1 week, and decreased to 18.5 pg/mL after 1 month, then increased to 24.3 pg/mL after 3 months, and 32.6 pg/mL after 6 months. Two patients suffering from rebleeding after SRS showed a higher level of VEGF at 6 months after SRS than their pretreatment level.

CONCLUSION

Plasma VEGF levels in patients with CCM were elevated over controls at baseline, and decreased from baseline to 1 month after SRS and increased further for up to 6 months. Theses results indicated that anti-angiogenic effect of SRS might play a role in the treatment of CCMs.

Optic chiasmal cavernous angioma: A rare suprasellar vascular malformation

Background:

Suprasellar cavernous malformation in the optic pathway is not commonly encountered. To date, there are only few reports present in the literature.

Case Description:

The authors report a rare case of suprasellar optic pathway cavernous malformation in a 33-year-old female who presented with progressive visual loss. Her imaging revealed a large heterogeneous, hyperintense, hemorrhagic right suprasellar extra-axial complex cystic structure, causing mass effect on the adjacent hypothalamus and third ventricle displacing these structures. Gross total resection of the lesion was achieved utilizing a right frontal craniotomy approach. Histopathological examination confirmed the diagnosis of suprasellar chiasmal cavernous malformation.

Conclusion:

Although visual pathway cavernous malformation is a rare event, it should be included in the differential diagnosis of lesions occurring suprasellarly in the visual pathway and hypothalamus.

Biological relevance of tissue factor and IL-6 in arteriovenous malformations

Arteriovenous malformations (AVMs) are congenital abnormal vessels that shunt blood directly from the arterial to the venous system without a capillary bed. The underlying pathology of AVMs is not fully understood. The objective of the study was to determine the association between the expression patterns of tissue factor (TF) and interleukin-6 (IL-6) in AVMs with clinical and pathological findings. Eighteen cases of sporadic AVM with operative specimens were included in this study. The expression of messenger RNA (mRNA) of TF and IL-6 was assayed, and association with clinical factors was investigated. The distribution of TF and IL-6 was examined with immunofluorescence. The mRNA expression of TF was significantly higher in AVM specimens than in control tissues (P = 0.002) and significantly higher in the symptomatic group than in the asymptomatic group (P = 0.037). The mRNA expression of IL-6 was likewise significantly higher in AVM specimens than in control tissues (P = 0.038). Examination of immunostained sections indicated that TF⁺ cells were also positive for IL-6 and were distributed around normal endothelial cells and pericytes. Moreover, TF⁺/IL-6⁺ cells also expressed CD31, vascular endothelial growth factor receptor 2 (VEGFR2), and platelet-derived growth factor receptor beta (PDGFR-beta). These results suggest that TF is elevated in AVMs and that it mediates symptomatic events. IL-6 is associated with the angiogenic activity of TF, and both are present in the same abnormal endothelial cells and pericytes. These factors may have interactive effects and may serve in a prognostic role for AVMs.

Surgical management of symptomatic brain stem cavernoma in a developing country: technical difficulties and outcome

Brain stem cavernomas (BSCs) are angiographically occult vascular malformations in an intricate location. Surgical excision of symptomatic BSCs represents a neurosurgical challenge especially in developing countries. We reviewed the clinical data and surgical outcome of 24 consecutive cases surgically treated for brain stem cavernoma at the Neurosurgery Department, Alexandria University, between 2006 and 2014. All patients were followed up for at least 12 months after surgery and the mean follow-up period was 45 months. All patients suffered from at least two clinically significant hemorrhagic episodes before surgery. There were 10 males and 14 females. The mean age was 34 years (range 12 to 58 years). Fourteen cases had pontine cavernomas, 7 cases had midbrain cavernomas, and in 3 cases, the lesion was found in the medulla oblongata. The most commonly used approach in this series was the midline suboccipital approach with or without telovelar exposure (9 cases). There was a single postoperative mortality in this series due to pneumonia. Fourteen cases (58.3 %) showed initial worsening of their preoperative neurological status, most of which was transient and only three patients had permanent new deficits and one case had a permanent worsening of her preoperatively existing hemiparesis. There was neither immediate nor long-term rebleeding in any of our cases. In spite of the significant associated risks, surgery for BSCs in properly selected patients can have favorable outcomes in most cases. Surgery markedly improves the risk of rebleeding and should be considered in patients with accessible lesions.

Therapeutic management of cerebral arteriovenous malformations: a review

The therapeutic management of cerebral arteriovenous malformations has undergone significant change over the past 40 years. Embolization, radiosurgery, advanced imaging modalities, neuropsychological testing and advances in surgical technique has both significantly improved our ability to treat patients, as well as confounding the landscape as to what constitutes best medical practice. Variability in natural history provides additional challenges in that it is challenging to determine an accurate estimate of the risk of hemorrhage, morbidity and mortality. It is clear that the complexity of the treatment of these lesions demands a multidisciplinary approach. The need for a team of neurosurgeons, interventional and diagnostic neuroradiologists, neurologists, radiation oncologists and neuropsychologists will improve outcomes and aid in determining best therapy for patients.

Unique double recurrence of cerebral arteriovenous malformation

Surgically treated patients with arteriovenous malformations (AVMs) are considered cured when the postoperative angiogram proves complete resection. However, despite no residual nidus or early draining vein on postoperative angiogram, rare instances of AVM recurrence have been reported in adults. In this paper, the authors present a case of a 24-year-old woman with asymptomatic double recurrence of her cerebral AVM after angiographically proven complete resection. To the authors' knowledge, this patient represents the first case with double de novo asymptomatic recurrence of Spetzler-Martin grade I AVM. Also, she represents the first case with unique AVM criteria in each recurrence.

Pathological response of cavernous malformations following radiosurgery

OBJECT

Stereotactic radiosurgery (SRS) is a therapeutic option for repeatedly hemorrhagic cavernous malformations (CMs) located in areas deemed to be high risk for resection. During the latency period of 2 or more years after SRS, recurrent hemorrhage remains a persistent risk until the obliterative process has finished. The pathological response to SRS has been studied in relatively few patients. The authors of the present study aimed to gain insight into the effect of SRS on CM and to propose possible mechanisms leading to recurrent hemorrhages following SRS.

METHODS

During a 13-year interval between 2001 and 2013, bleeding recurred in 9 patients with CMs that had been treated using Gamma Knife surgery at the authors' institution. Microsurgical removal was subsequently performed in 5 of these patients, who had recurrent hemorrhages between 4 months and 7 years after SRS. Specimens from 4 patients were available for analysis and used for this report.

RESULTS

Histopathological analysis demonstrated that vascular sclerosis develops as early as 4 months after SRS. In the samples from 2 to 7 years after SRS, sclerotic vessels were prominent, but there were also vessels with incomplete sclerosis as well as some foci of neovascularization.

CONCLUSIONS

Recurrent bleeding after SRS for CM could be related to incomplete sclerosis of the vessels, but neovascularization may also play a role.

Biology of cerebral arteriovenous malformations with a focus on inflammation

Cerebral arteriovenous malformations (AVMs) entail a significant risk of intracerebral hemorrhage owing to the direct shunting of arterial blood into the venous vasculature without the dissipation of the arterial blood pressure. The mechanisms involved in the growth, progression and rupture of AVMs are not clearly understood, but a number of studies point to inflammation as a major contributor to their pathogenesis. The upregulation of proinflammatory cytokines induces the overexpression of cell adhesion molecules in AVM endothelial cells, resulting in enhanced recruitment of leukocytes. The increased leukocyte-derived release of metalloproteinase-9 is known to damage AVM walls and lead to rupture. Inflammation is also involved in altering the AVM angioarchitecture via the upregulation of angiogenic factors that affect endothelial cell proliferation, migration and apoptosis. The effects of inflammation on AVM pathogenesis are potentiated by certain single-nucleotide polymorphisms in the genes of proinflammatory cytokines, increasing their protein levels in the AVM tissue. Furthermore, studies on metalloproteinase-9 inhibitors and on the involvement of Notch signaling in AVMs provide promising data for a potential basis for pharmacological treatment of AVMs. Potential therapeutic targets and areas requiring further investigation are highlighted.

Human brain arteriovenous malformations express lymphatic-associated genes

Objective

Brain arteriovenous malformations (AVMs) are devastating, hemorrhage-prone, cerebrovascular lesions characterized by well-defined feeding arteries, draining vein(s) and the absence of a capillary bed. The endothelial cells (ECs) that comprise AVMs exhibit a loss of arterial and venous specification. Given the role of the transcription factor COUP-TFII in vascular development, EC specification, and pathological angiogenesis, we examined human AVM tissue to determine if COUP-FTII may have a role in AVM disease biology.

Methods

We examined 40 human brain AVMs by immunohistochemistry (IHC) and qRT-PCR for the expression of COUP-TFII as well as other genes involved in venous and lymphatic development, maintenance, and signaling. We also examined proliferation and EC tube formation with human umbilical ECs (HUVEC) following COUP-TFII overexpression.

Results

We report that AVMs expressed COUP-TFII, SOX18, PROX1, NFATC1, FOXC2, TBX1, LYVE1, Podoplanin, and vascular endothelial growth factor (VEGF)-C, contained Ki67-positive cells and heterogeneously expressed genes involved in Hedgehog, Notch, Wnt, and VEGF signaling pathways. Overexpression of COUP-TFII alone in vitro resulted in increased EC proliferation and dilated tubes in an EC tube formation assay in HUVEC.

Interpretation

This suggests AVM ECs are further losing their arterial/venous specificity and acquiring a partial lymphatic molecular phenotype. There was significant correlation of gene expression with presence of clinical edema and acute hemorrhage. While the precise role of these genes in the formation, stabilization, growth and risk of hemorrhage of AVMs remains unclear, these findings have potentially important implications for patient management and treatment choice, and opens new avenues for future work on AVM disease mechanisms.

Symptomatic de novo arteriovenous malformation in an adult: Case report and review of the literature

BACKGROUND

Cerebral arteriovenous malformations (AVMs) have been long thought to be a congenital anomaly of vasculogenesis in which arteries and veins form direct connections forming a vascular nidus without an intervening capillary bed or neural tissue. Scattered case reports have described that AVMs may form de novo suggesting they can become an acquired lesion.

CASE DESCRIPTION

The current case report describes a patient who presented with new-onset seizures with an initial negative magnetic resonance imaging (MRI) of the brain and subsequently developed an AVM on a MRI 9 years later.

CONCLUSION

This case joins a small, but growing body of literature that challenges the notion that all AVMs are congenital.

Factors Determining the Clinical Complications of Radiosurgery for AVM

Purpose:

To identify the predictors of symptomatic post-radiation T2 signal change in patients with arteriovenous malformations (AVM) treated with radiosurgery.

Materials and Methods:

The charts of 211 consecutive patients with arteriovenous malformations treated with either gamma knife radisurgery or linear accelerator radiosurgery between 2000-2009 were retrospectively reviewed. 168 patients had a minimum of 12 months of clinical and radiologic follow-up following the procedure and complete dosage data. Pretreatment characteristics and dosimetric variables were analyzed to identify predictors of adverse radiation effects.

Results:

141 patients had no clinical symptomatic complications. 21 patients had global or focal neurological deficits attributed to symptomatic edema. Variables associated with development of symptomatic edema included a non-hemorrhagic symptomatic presentation compared to presentation with hemorrhage, p=0.001; OR (95%CI) = 6.26 (1.99, 19.69); the presence of venous rerouting compared to the lack of venous rerouting, p=0.031; OR (95% CI) = 3.25 (1.20, 8.80); radiosurgery with GKS compared to linear accelerator radiosurgery p = 0.012; OR (95% CI) = 4.58 (1.28, 16.32); and the presence of more than one draining vein compared to a single draining vein p = 0.032; OR (95% CI) = 2.82 (1.06, 7.50).

Conclusions:

We postulated that the higher maximal doses used with gamma knife radiosurgery may be responsible for the greater number of adverse radiation effects with this modality compared to linear accelerator radiosurgery. We found that AVMs with greater venous complexity and therefore instability resulted in more adverse treatment outcomes, suggesting that AVM angioarchitecture should be considered when making treatment decisions.

Zebrafish models of cerebrovascular disease

Perturbations in cerebral blood flow and abnormalities in blood vessel structure are the hallmarks of cerebrovascular disease. While there are many genetic and environmental factors that affect these entities through a heterogeneous group of disease processes, the ultimate final pathologic insult in humans is defined as a stroke, or damage to brain parenchyma. In the case of ischemic stroke, blood fails to reach its target destination whereas in hemorrhagic stroke, extravasation of blood occurs outside of the blood vessel lumen, resulting in direct damage to brain parenchyma. As these acute events can be neurologically devastating, if not fatal, development of novel therapeutics are urgently needed. The zebrafish (Danio rerio) is an attractive model for the study of cerebrovascular disease because of its morphological and physiological similarity to human cerebral vasculature, its ability to be genetically manipulated, and its fecundity allowing for large-scale, phenotype-based screens.

Brain vascular lesions: a clinicopathologic, immunohistochemistry, and ultrastructural approach

Brain vascular malformations are relatively common lesions that cause serious neurologic disability or death in a significant proportion of individuals bearing them. The purpose of this study was to analyze the clinicopathologic and immunohistochemistry these lesions, looking for common antibodies expressed such as CD31, CD34, CD15, factor VIII, nestin, vimentin, vascular endothelial grow factor (VEGF), vascular endothelial grow factor receptor-2 (VEGF-R2), glial fibrillar acidic protien (GFAP), and fibroblastic grow factor β (β-FGF) and ultrastructure in endothelial cells as well as in vessel walls. Fifty cases of vascular lesions were included in this study: 29 (58%) of them were arteriovenous malformations and 21 (52%) were brain cavernomas. Twenty-six (52%) patients were women and 24 (48%) men. The age range was from 13 to 68 years (mean age, 35.86 ± 15.19 years). The size of the lesions ranged between 1 and 8 cm (3 ± 1.65 cm), and parieto-occipital lesions had a bigger size. Evolution time varied from 1 month to 1 year (mean, 7.5 months). There was a significant statistical correlation between age and sex (P = -035), rupture of lesion (P = .015), brain hemorrhage (P = .033), necrosis (P = .011), hemosiderin deposit (P = .042), VEGF (P = .015), and VEGFR (P = .037), as well as localization of rupture (P = .017), loss of consciousness (P = .000), visual deficit (P = .026), hyaline vessels (P = .000), and CD31 (.009). Interactions between endothelial cells and mural cells (pericytes and vascular smooth muscle cells) in blood vessel walls have recently come into focus as central processes in the regulation of vascular formation, stabilization, remodeling, and function in brain vascular lesions. However, the molecular mechanisms that underlie the formation and growth of brain arteriovenous malformations are still poorly understood.

A xenograft animal model of human arteriovenous malformations

Background

Arteriovenous malformations (AVMs) are a type of high-flow vascular malformations that most commonly occurs in the head and neck. They are present at birth but are usually clinically asymptomatic until later in life. The pathogenesis of AVMs remains unclear and therapeutic approaches to AVMs are unsatisfied. In order to provide a tool for studying the pathogenesis and therapies of this disease, we established and studied a xenograft animal model of human AVMs.

Methods

Fresh human AVMs specimens harvested from 4 patients were sectioned (5x5x5 mm) and xenografted subcutaneously in 5 immunologically naïve nude mice (Athymic Nude-Foxn1^nu). Each mouse had four pieces specimens in four quadrants along the back. The grafts were observed weekly for volume, color and texture. The grafts were harvested at every 30 days intervals for histologic examination. All grafts (n = 20) were sectioned and stained for hematoxylin and eosin (H&E). Comparative pathologic evaluation of the grafts and native AVMs were performed by two blinded pathologists. Immunohistochemical examination of human-specific nuclear antigen, vascular endothelial growth factor receptor-2 (VEGFR-2) and Ki-67 was performed.

Results

Clinical characteristics and pathologic diagnosis of native human derived AVMs were confirmed. 85% (n = 17) of AVM xenografts survived although the sizes decreased after implantation. Histological examination demonstrated numerous small and medium-size vessels and revealed structural characteristics matching the native AVMs tissue.76.5% (n = 13) of the surviving xenografts were positive for Ki-67 and human-specific nuclear antigen suggesting survival of the human derived tissue, 52.9% (n = 9) were positive for VEGFR-2.

Conclusions

This preliminary xenograft animal model suggests that AVMs can survive in the nude mouse. The presence of human-specific nuclear antigen, VEGFR-2, and Ki-67 demonstrates the stability of native tissue qualities within the xenografts.

Endothelial signaling and the molecular basis of arteriovenous malformation

Arteriovenous malformations occur when abnormalities of vascular patterning result in the flow of blood from arteries to veins without an intervening capillary bed. Recent work has revealed the importance of the Notch and TGF-β signaling pathways in vascular patterning. Specifically, Notch signaling has an increasingly apparent role in arterial specification and suppression of branching, whereas TGF-β is implicated in vascular smooth muscle development and remodeling under angiogenic stimuli. These physiologic roles, consequently, have implicated both pathways in the pathogenesis of arteriovenous malformation. In this review, we summarize the studies of endothelial signaling that contribute to arteriovenous malformation and the roles of genes implicated in their pathogenesis. We further discuss how endothelial signaling may contribute to vascular smooth muscle development and how knowledge of signaling pathways may provide us targets for medical therapy in these vascular lesions.

Magnetic Resonance Evolution of De Novo Formation of a Cavernoma in a Thrombosed Developmental Venous Anomaly

BACKGROUND AND IMPORTANCE:

Mechanisms that lead to de novo formations of nonfamilial-type cavernomas are not well understood. One of the interesting hypotheses is the causative relationship between developmental venous anomaly (DVA) and cavernoma formation. We report a unique case in which serial imaging demonstrated the evolution of de novo formation of a cavernoma in association with a thrombosed DVA. A detailed review of the causal hypothesis between a DVA and cavernoma is also provided.

CLINICAL PRESENTATION:

We report a 37-year-old female patient in whom a cavernoma-like lesion arose 1 year after the progressive thrombosis of a medullary (or caput medusa) vein of a DVA. The presence of an acute angulation in the draining vein may have prompted an intrinsic outflow restriction. Possible worsening of venous disequilibrium led to subsequent thrombus progression, venous congestion, and occlusion of the vein with venous dilation and signs of stasis on follow-up magnetic resonance imaging. Finally, this developed into a lobulated lesion with salt-and-pepper appearance at the converging region of medullary tributaries, which typified the classic features of a cavernoma.

CONCLUSION:

Compared with other published cases of de novo cavernoma formation in relation to a DVA, our case, for the first time, allows us to witness the temporal evolution from a thrombosed DVA to the birth of a cavernoma around it. This supports the hypothesis that the cavernoma can be an acquired disease that arises from a DVA.

Combined blockade of AKT/mTOR pathway inhibits growth of human hemangioma via downregulation of proliferating cell nuclear antigen

Protein kinase B (AKT)/mammalian target of rapamycin (mTOR) signaling pathway plays a crucial role in the tumorigenesis and progression of multiple tumors, and has been shown to be important therapeutic targets for cancer. The present study aimed to explore the role and molecular mechanisms of AKT/mTOR pathway in human hemangioma (HA). Twenty-five cases of human HA tissues were collected. The expression of AKT, mTOR and proliferating cell nuclear antigen (PCNA) proteins was evaluated using semi-quantitative immunohistochemistry in biopsy samples in different phases of HA. AKT/mTOR pathway was blocked by recombinant small hairpin RNA adenovirus vector rAd5-AKT+mTOR (rAd5-Am), used for infecting proliferating phase HA-derived endothelial cells (HDEC). The expression of AKT, mTOR and PCNA was detected by Real-time PCR and Western blot assays. Cell proliferative activities were determined by MTT assay, and cell cycle distribution and apoptosis were analyzed by flow cytometry. As a consequence, the expression of AKT, mTOR and PCNA was significantly increased in proliferative phase HA, while that was decreased in involutive phase. Combined blockade of AKT/mTOR pathway by rAd5-Am diminished cell proliferative activities, and induced cell apoptosis and cycle arrest with the decreased expression of AKT, mTOR and PCNA in proliferative phase HDEC. In conclusion, the activity of AKT/mTOR pathway was increased in proliferative phase HA, while it was decreased in involutive phase. Combined blockade of AKT/mTOR pathway might suppress cell proliferation via down-regulation of PCNA expression, and induce apoptosis and cycle arrest in proliferative phase HDEC, suggesting that AKT/mTOR pathway might represent the important therapeutic targets for human HA.

Two-hit mechanism in cerebral cavernous malformation? A case of monozygotic twins with a CCM1/KRIT1 germline mutation

Cerebral cavernous malformations are focal vascular abnormalities that show recurrent intralesional microhemorrhage and may cause focal deficits or seizures in affected patients. These lesions occur in both sporadic and inherited autosomal dominant form. Germline mutations in three different genes have been identified yet. One explanation for the unpredictable individual clinical course with wide variability of the number of developing cerebral cavernous malformations (CCMs) and their rate of progression within CCM families is thought to be based upon a "two-hit" mechanism. However, the direct influence of a heterozygous underlying germline mutation in combination with secondary somatic mutations on a patient's individual clinical course is hard to investigate in vivo. In this context, we present a rare and interesting case of monozygotic twins heterozygous for the CCM1 germline mutation c.730-1G>A and discuss their similar age and type of disease manifestation and their beginning divergent clinical course.

An early venous abnormality: a potential cause of arteriovenous malformation recurrence

In adults, complete surgical resection of arteriovenous malformations (AVMs) is generally curative. Recurrence of AVMs is extremely rare and most often delayed over many years. The authors report the case of a man in his 20s with rapid AVM recurrence and dual blood supply from the dura and intracerebral vessels. Early recurrence of the AVM allowed documentation of the early events associated with this recurrence. This was evidenced by the first appearance of an early vein without any signs of abnormal vasculature, suggesting that abnormality of the venous drainage system might be an inciting event in the recurrence and perhaps genesis of AVMs.

Recurrence of "cured" dural arteriovenous fistulas after Onyx embolization

Endovascular embolization with Onyx has been increasingly used to treat intracranial and spinal dural arteriovenous fistulas (DAVFs). Several case series have been published in recent years reporting high DAVF cure rates with this technique. Although it is seldom reported, DAVF recurrence may occur despite initial "cure." The authors present 3 separate cases of a recurrent DAVF after successful transarterial Onyx embolization. Despite adequate Onyx penetration into the fistula and draining vein, these cases demonstrate that DAVF recanalization may reappear with filling from previous or newly recruited arterial feeders. Other published reports of DAVF recurrence are examined, and potential contributory factors are discussed. These cases highlight the need for awareness of this possible phenomenon and suggest that follow-up angiography should be considered in patients treated with catheter embolization.