Mild Hypoxia Accelerates Cerebral Cavernous Malformation Disease Through CX3CR1-CX3CL1 Signaling

BACKGROUND

Heterogeneity in the severity of cerebral cavernous malformations (CCMs) disease, including brain bleedings and thrombosis that cause neurological disabilities in patients, suggests that environmental, genetic, or biological factors act as disease modifiers. Still, the underlying mechanisms are not entirely understood. Here, we report that mild hypoxia accelerates CCM disease by promoting angiogenesis, neuroinflammation, and vascular thrombosis in the brains of CCM mouse models.

METHODS

We used genetic studies, RNA sequencing, spatial transcriptome, micro-computed tomography, fluorescence-activated cell sorting, multiplex immunofluorescence, coculture studies, and imaging techniques to reveal that sustained mild hypoxia via the CX3CR1-CX3CL1 signaling pathway influences cell-specific neuroinflammatory interactions, contributing to heterogeneity in CCM severity.

RESULTS

Histological and expression profiles of CCM neurovascular lesions (Slco1c1-iCreERT2;Pdcd10fl/fl; Pdcd10BECKO) in male and female mice found that sustained mild hypoxia (12% O2, 7 days) accelerates CCM disease. Our findings indicate that a small reduction in oxygen levels can significantly increase angiogenesis, neuroinflammation, and thrombosis in CCM disease by enhancing the interactions between endothelium, astrocytes, and immune cells. Our study indicates that the interactions between CX3CR1 and CX3CL1 are crucial in the maturation of CCM lesions and propensity to CCM immunothrombosis. In particular, this pathway regulates the recruitment and activation of microglia and other immune cells in CCM lesions, which leads to lesion growth and thrombosis. We found that human CX3CR1 variants are linked to lower lesion burden in familial CCMs, proving it is a genetic modifier in human disease and a potential marker for aggressiveness. Moreover, monoclonal blocking antibody against CX3CL1 or reducing 1 copy of the Cx3cr1 gene significantly reduces hypoxia-induced CCM immunothrombosis.

CONCLUSIONS

Our study reveals that interactions between CX3CR1 and CX3CL1 can modify CCM neuropathology when lesions are accelerated by environmental hypoxia. Moreover, a hypoxic environment or hypoxia signaling caused by CCM disease influences the balance between neuroinflammation and neuroprotection mediated by CX3CR1-CX3CL1 signaling. These results establish CX3CR1 as a genetic marker for patient stratification and a potential predictor of CCM aggressiveness.

Transcriptomic signatures of individual cell types in cerebral cavernous malformation

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

Single-nucleus DNA sequencing reveals hidden somatic loss-of-heterozygosity in Cerebral Cavernous Malformations

Cerebral Cavernous Malformations (CCMs) are vascular malformations of the central nervous system which can lead to moderate to severe neurological phenotypes in patients. A majority of CCM lesions are driven by a cancer-like three-hit mutational mechanism, including a somatic, activating mutation in the oncogene PIK3CA, as well as biallelic loss-of-function mutations in a CCM gene. However, standard sequencing approaches often fail to yield a full complement of pathogenic mutations in many CCMs. We suggest this reality reflects the limited sensitivity to identify low-frequency variants and the presence of mutations undetectable with bulk short-read sequencing. Here we report a single-nucleus DNA-sequencing approach that leverages the underlying biology of CCMs to identify lesions with somatic loss-of-heterozygosity, a class of such hidden mutations. We identify an alternative genetic mechanism for CCM pathogenesis and establish a method that can be repurposed to investigate the genetic underpinning of other disorders with multiple somatic mutations.

mTORC1 Inhibitor Rapamycin Inhibits Growth of Cerebral Cavernous Malformation in Adult Mice

BACKGROUND

Cerebral cavernous malformations (CCMs) are vascular malformations that frequently cause stroke. CCMs arise due to loss of function in one of the genes that encode the CCM complex, a negative regulator of MEKK3-KLF2/4 signaling in vascular endothelial cells. Gain-of-function mutations in PIK3CA (encoding the enzymatic subunit of the PI3K (phosphoinositide 3-kinase) pathway associated with cell growth) synergize with CCM gene loss-of-function to generate rapidly growing lesions.

METHODS

We recently developed a model of CCM formation that closely reproduces key events in human CCM formation through inducible CCM loss-of-function and PIK3CA gain-of-function in mature mice. In the present study, we use this model to test the ability of rapamycin, a clinically approved inhibitor of the PI3K effector mTORC1, to treat rapidly growing CCMs.

RESULTS

We show that both intraperitoneal and oral administration of rapamycin arrests CCM growth, reduces perilesional iron deposition, and improves vascular perfusion within CCMs.

CONCLUSIONS

Our findings further establish this adult CCM model as a valuable preclinical model and support clinical testing of rapamycin to treat rapidly growing human CCMs.

Inflammatory Mechanisms in a Neurovascular Disease: Cerebral Cavernous Malformation

Cerebral cavernous malformation (CCM) is a common cerebrovascular malformation causing intracranial hemorrhage, seizures, and focal neurologic deficits. A unique CCM lesional inflammatory microenvironment has been shown to influence the clinical course of the disease. This review addresses the inflammatory cell infiltrate in the CCM lesion and the role of a defined antigen-driven immune response in pathogenicity. We summarize immune mechanisms associated with the loss of the CCM gene and disease progression, including the potential role of immunothrombosis. We also review evidence of circulating inflammatory biomarkers associated with CCM disease and its clinical activity. We articulate future directions for this research, including the role of individual cell type contributions to the immune response in CCM, single cell transcriptomics of inflammatory cells, biomarker development, and therapeutic implications. The concepts are applicable for developing diagnostic and treatment strategies for CCM and for studying other neurovascular diseases.

Circulating Plasma miRNA Homologs in Mice and Humans Reflect Familial Cerebral Cavernous Malformation Disease

Patients with familial cerebral cavernous malformation (CCM) inherit germline loss of function mutations and are susceptible to progressive development of brain lesions and neurological sequelae during their lifetime. To date, no homologous circulating molecules have been identified that can reflect the presence of germ line pathogenetic CCM mutations, either in animal models or patients. We hypothesize that homologous differentially expressed (DE) plasma miRNAs can reflect the CCM germline mutation in preclinical murine models and patients. Herein, homologous DE plasma miRNAs with mechanistic putative gene targets within the transcriptome of preclinical and human CCM lesions were identified. Several of these gene targets were additionally found to be associated with CCM-enriched pathways identified using the Kyoto Encyclopedia of Genes and Genomes. DE miRNAs were also identified in familial-CCM patients who developed new brain lesions within the year following blood sample collection. The miRNome results were then validated in an independent cohort of human subjects with real-time-qPCR quantification, a technique facilitating plasma assays. Finally, a Bayesian-informed machine learning approach showed that a combination of plasma levels of miRNAs and circulating proteins improves the association with familial-CCM disease in human subjects to 95% accuracy. These findings act as an important proof of concept for the future development of translatable circulating biomarkers to be tested in preclinical studies and human trials aimed at monitoring and restoring gene function in CCM and other diseases.

Plasma metabolites with mechanistic and clinical links to the neurovascular disease cavernous angioma

BACKGROUND

Cavernous angiomas (CAs) affect 0.5% of the population, predisposing to serious neurologic sequelae from brain bleeding. A leaky gut epithelium associated with a permissive gut microbiome, was identified in patients who develop CAs, favoring lipid polysaccharide producing bacterial species. Micro-ribonucleic acids along with plasma levels of proteins reflecting angiogenesis and inflammation were also previously correlated with CA and CA with symptomatic hemorrhage.

METHODS

The plasma metabolome of CA patients and CA patients with symptomatic hemorrhage was assessed using liquid-chromatography mass spectrometry. Differential metabolites were identified using partial least squares-discriminant analysis (p < 0.05, FDR corrected). Interactions between these metabolites and the previously established CA transcriptome, microbiome, and differential proteins were queried for mechanistic relevance. Differential metabolites in CA patients with symptomatic hemorrhage were then validated in an independent, propensity matched cohort. A machine learning-implemented, Bayesian approach was used to integrate proteins, micro-RNAs and metabolites to develop a diagnostic model for CA patients with symptomatic hemorrhage.

RESULTS

Here we identify plasma metabolites, including cholic acid and hypoxanthine distinguishing CA patients, while arachidonic and linoleic acids distinguish those with symptomatic hemorrhage. Plasma metabolites are linked to the permissive microbiome genes, and to previously implicated disease mechanisms. The metabolites distinguishing CA with symptomatic hemorrhage are validated in an independent propensity-matched cohort, and their integration, along with levels of circulating miRNAs, enhance the performance of plasma protein biomarkers (up to 85% sensitivity and 80% specificity).

CONCLUSIONS

Plasma metabolites reflect CAs and their hemorrhagic activity. A model of their multiomic integration is applicable to other pathologies.

Abstract TMP15: Transcriptomic Signatures Of Individual Cell Types In Cavernous Angioma

Introduction: Cavernous Angiomas (CAs) are vascular malformations characterized by clusters of blood-filled capillary spaces lined by “leaky” endothelium. While mutations in endothelial cells have long been recognized as necessary for lesion genesis, there is evidence of inflammation, response to hypoxia, and non-endothelial autonomous cell effects driving pathogenesis. Disrupted gene expression in the CA neurovascular unit (NVU) has been described but the contribution of each cell type has not been previously investigated.

Methods: Six CA and four control brain samples were collected and frozen during surgical resection. The endothelial cells, pericytes, and neuroglia (astrocytes and neurons) were sorted, and the RNA was extracted and sequenced. The differentially expressed genes (DEGs) were identified ( p <0.05, FDR corrected) for each cell type. Enrichment pathway analyses were performed through Ingenuity Pathway Analyses (IPA, Qiagen; p <0.05, FDR corrected), Gene Ontology (GO; p <0.1, FDR corrected) and Kyoto Encyclopedia of Genes and Genomes (KEGG; p <0.1, FDR corrected).

Results: In endothelial cells, 362 DEGs were identified contributing to 54 enriched IPA pathways. In addition, 484 DEGs were found in pericytes and 50 IPA pathways were identified. The common functions between these two cell types were related to angiogenesis, extracellular matrix organization, cell adhesion, and platelet activation, while the function related to response to hypoxia was only shown in pericytes. Finally, 242 DEGs and 52 IPA pathways were identified in neuroglia cells. The associated pathway functions were related to inflammatory response and cell adhesion. The IPA results were further confirmed by the GO term and KEGG pathway analyses.

Conclusion: We confirm that disrupted genes related to angiogenesis, blood-brain barrier integrity, cell adhesion and platelet activation in the CA lesion involve endothelial cells and pericytes primarily. Pericytes are particularly associated with disrupted genes related to response to hypoxia, while neuroglia is associated with greater gene disruptions related to inflammation. These results motivate novel mechanistic hypotheses regarding non-endothelial cell contributions to lesion pathobiology.

Abstract TMP18: Multiplexed Histopathological Characterization Of Cerebral Microbleeds In The Aging Brain

Background: Cerebral microbleeds (CMBs) are manifestations of age-related microangiopathies associated with an increased risk of hemorrhagic stroke and cognitive decline. The pathophysiology of this age-related breakdown of the neurovascular unit remain unclear. Understanding CMB cellular architecture is needed for gene, pathway, and mechanism analyses, to pave the way for biomarker and therapeutic development. Herein, we aim to systematically describe histopathological changes in the CMB lesional milieu.

Methods: Eight CMBs, along with contralateral non-lesional tissue, were identified by gross appearance at autopsy by a neuropathologist. Samples were first stained with H&E, then Prussian blue for non-heme iron, to localize the lesion. This was followed by multiplex fluorescence staining of β-amyloid and individual cell types including astrocytes (GFAP + ), macrophages (CD163 + /Iba1 + ), microglia (CD163 - /Iba1 + ), B-cells (CD20 + ), T-cells (CD3 + ), and endothelium (CD31 + ). The cell types within the lesional milieu, defined as 200μm from the periphery of the CMB, were quantified using QuPath. Astrocyte and microglia morphology were assessed via fluorescence imaging.

Results: One CMB contained dilated capillaries, 2 contained lipohyalinized arterioles, and 4 contained dystrophic arterioles due to amyloid angiopathy. Astrocytes and macrophages showed higher normalized cell counts in all CMB tissues compared with controls ( p<0.005 and p<0.05 , respectively). Astrocytes in 7 of 8 CMB milieux showed reactive morphological changes, including larger cell bodies with peripheral nuclei. Microglia had higher normalized cell counts in 4 CMB tissues, with senescence-associated amoeboid, as well as ramified, reactive morphologies. The lesional milieu also showed higher counts of B-cells in 7 CMB tissues and T-cells in 3 CMB tissues when compared with controls.

Conclusions: We provide the first description of the cellular architecture of the CMB and the associated lesional milieu. Despite heterogeneity of disrupted vasculature, there are common features of glial reactive changes and inflammation in CMBs. These results offer a basis for additional study of the CMB transcriptome and individual roles of respective cell types in CMB pathology.

Abstract 123: In Vivo Permeability Of The Aging Brain With Cerebral Microbleeds

Introduction: Age-related cerebral microbleeds (CMBs) are vascular changes associated with an increased risk of intracerebral hemorrhage (ICH) and neurocognitive decline. CMBs share a strikingly similar appearance on MRI to cerebral cavernous malformations (CCMs), which are leaky capillary lesions predisposing patients to brain bleeding. Our team had previously shown increased vascular permeability in CCM and in the brain of older subjects, with common circulating biomarkers of angiogenesis and inflammation. We examine here whether vascular permeability is greater in the aging brain harboring CBMs.

Methods: Dynamic Contrast-Enhanced Quantitative Perfusion (DCEQP) MRI, which assesses vascular permeability, was acquired for 7 patients with CMBs (>50 years old), 10 old (>50 years old), and 9 young (18-30 years old) healthy subjects without CMBs. Cases with active brain disease, stroke or seizure in the prior year were excluded. DCEQP scans were co-registered onto their respective T1-weighted images, normalized using the Desikan-Killiany atlas, and finally segmented into white and gray matter within frontal, temporal, parietal, and occipital lobes. The mean permeability was calculated within each segmented area, and values were compared between the 3 groups of interest.

Results: Increased permeability was observed within the frontal white and gray matter as well as the parietal gray matter of patients with CMBs compared to age matched old healthy controls (both: p<0.05). In addition, greater background brain permeability was also observed in old healthy controls compared to young healthy controls, in the occipital white matter, as well as the white and gray matter in the temporal and parietal lobes (all: p<0.05).

Conclusion: We confirm that the human brain exhibits increased vascular permeability with aging, and this is more pronounced in brains harboring CMBs. This may provide insight into the pathogenesis of CMBs, potentially reflecting end stage age-related failure of the blood brain barrier, associated with frank bleeding. These results offer a starting point for the development of diagnostic and prognostic imaging biomarkers of CMBs, which can help stratify patients at higher risk of future ICH and cognitive decline.

Abstract WP17: Plasma Proteins In Correlation With Lesional Iron Content And Permeability Imaging In Clinical Trial Of Cavernous Angioma With Symptomatic Hemorrhage

Background: Increases in mean lesional iron content (≥6%) measurement by QSM and vascular permeability (≥40%) assessed by DCEQP MRI have been associated with new bleeding, and are used as monitoring biomarkers in NINDS funded 1st clinical trial of pharmacotherapy (clinicaltrials.gov NCT02603328) in cavernous angiomas with symptomatic hemorrhage (CASH). Plasma protein levels previously associated with CASH in diagnostic and prognostic contexts have never been compared to lesional QSM and DCEQP in the same subjects.

Methods: Plasma samples and MRI sequences were simultaneously acquired during 1 year-epochs of prospective follow-up of CASH patients. Plasma levels of 16 proteins were assayed by ELISA and correlated with lesional QSM and DCEQP during the same epochs. Univariate correlations were followed by multivariate analyses combining multiple protein levels to minimize Akaike Information Criterion (AIC) and increase R 2 . Accuracy (AUC on receiver operating curves) and sum of squared error (SSE) are reported for associations achieving statistical significance with FDR correction.

Results: None of the proteins individually correlated with QSM/DCEQP (continuous or categorical). Relative change of angiopoietin2, and absolute change of the combination (endoglin+IL1B+IL16) had the highest accuracy (AUC 78.7%, SD 0.062 and 98.4%, SD 0.013 respectively) for lesional QSM increase ≥6%. Relative change of endoglin+IL1B, and absolute change of angiopoetin2+endoglin+thromobomodulin+VEGF, had the highest accuracy (AUC 64.6%, SD 0.057 and 93.2%, SD 0.040 respectively) for lesional DCEQP increase ≥40%. Relative change in angiopoetin1 had the lowest SSE (8.87) with QSM change as a continuous variable, and relative change in lipopolysaccharide binding protein had the lowest SSE (469.06) with DCEQP change as continuous variable.

Conclusion: Circulating proteins reflect changes in lesional iron content and permeability in CASH during prospective follow-up. Results are a proof of concept that blood tests could replace more complex and costly imaging biomarkers in the monitoring of hemorrhage in cavernous angiomas. Additional mechanistic plasma molecules (miRNAs and metabolites) may further enhance the accuracy of these monitoring biomarkers.

β1 integrin monoclonal antibody treatment ameliorates cerebral cavernous malformations

β1 integrins are important in blood vessel formation and function, finely tuning the adhesion of endothelial cells to each other and to the extracellular matrix. The role of integrins in the vascular disease, cerebral cavernous malformation (CCM) has yet to be explored in vivo. Endothelial loss of the gene KRIT1 leads to brain microvascular defects, resulting in debilitating and often fatal consequences. We tested administration of a monoclonal antibody that enforces the active β1 integrin conformation, (clone 9EG7), on a murine neonatal CCM mouse model, Krit1flox/flox ;Pdgfb-iCreERT2 (Krit1ECKO ), and on KRIT1-silenced human umbilical vein endothelial cells (HUVECs). In addition, endothelial deletion of the master regulator of integrin activation, Talin 1 (Tln1), in Krit1ECKO mice was performed to assess the effect of completely blocking endothelial integrin activation on CCM. Treatment with 9EG7 reduced lesion burden in the Krit1ECKO model and was accompanied by a strong reduction in the phosphorylation of the ROCK substrate, myosin light chain (pMLC), in both retina and brain endothelial cells. Treatment of KRIT1-silenced HUVECs with 9EG7 in vitro stabilized cell-cell junctions. Overnight treatment of HUVECs with 9EG7 resulted in significantly reduced total surface expression of β1 integrin, which was associated with reduced pMLC levels, supporting our in vivo findings. Genetic blockade of integrin activation by Tln1ECKO enhanced bleeding and did not reduce CCM lesion burden in Krit1ECKO mice. In sum, targeting β1 integrin with an activated-specific antibody reduces acute murine CCM lesion development, which we found to be associated with suppression of endothelial ROCK activity.

Developmental venous anomalies are a genetic primer for cerebral cavernous malformations

Cerebral cavernous malformations (CCM) are a neurovascular anomaly that may occur sporadically, or be inherited due to autosomal dominant mutations in KRIT1 , CCM2 , or PDCD10 . Individual lesions are caused by somatic mutations which have been identified in KRIT1, CCM2, PDCD10, MAP3K3, and PIK3CA . However, the interactions between mutations, and their relative contributions to sporadic versus familial cases remain unclear. We show that mutations in KRIT1, CCM2, PDCD10, and MAP3K3 are mutually exclusive, but may co-occur with mutations in PIK3CA. We also find that MAP3K3 mutations may cause sporadic, but not familial CCM. Furthermore, we find identical PIK3CA mutations in CCMs and adjacent developmental venous anomalies (DVA), a common vascular malformation frequently found in the vicinity of sporadic CCMs. However, somatic mutations in MAP3K3 are found only in the CCM. This suggests that sporadic CCMs are derived from cells of the DVA which have acquired an additional mutation in MAP3K3 .

Abstract TMP9: Novel Single-cell Isolation From Cerebral Cavernous Angioma Specimens For Transcriptomic Studies

Introduction: Cavernous angiomas (CAs) are common neurovascular lesions predisposing patients to seizures and hemorrhagic stroke. Recent evidence shows non-endothelial cell autonomous effects contribute to CA pathogenesis within the dysfunctional neurovascular units (NVUs), consisting of endothelial cells, pericytes, astrocytes, and microglia. Herein, we developed a single-cell isolation protocol to study the transcriptome of each of these cell populations.

Method: CAs and control brain tissue were frozen in optimal cutting temperature compound immediately after surgical resection. Tissue was enzymatically digested with Collagenase Type IV and DNase I. The cell suspension was then filtered, washed, and pelleted. Cell debris and myelin were removed using 25% Percoll. A multispectral LED light was used for 30 minutes to reduce background autofluorescence. Cells were stained with a CD31, CD45, CD13, P2RY12, CD49f, GLAST, CD24 and CD90 antibody cocktail. Size, granularity, and antibody-specific gating were set to sort each cell population using the BD FACSymphony S6 Cell Sorter. After isolation, RNA was extracted for each cell population, and the quality was assessed. Cell-specific genes including VWF (endothelial cells), ACTA2 (pericytes ), AQP4 (astrocytes ) and IBA-1 (microglia ), as well as GAPDH were assessed with real-time qPCR (rt-qPCR) for validation.

Results: Endothelial cells (CD31 + , CD13 - , CD45 - , CD49f - , GLAST - ), pericytes (CD13 + , CD31 - , CD45 - , CD49f - , GLAST - ), astrocytes (CD49f + , GLAST + ) and microglia (P2RY12 + , CD45 + , CD31 - , CD13 - , CD49f - , GLAST - ) were individually isolated from both 5 CA lesions and 5 control brain tissue using FACS sorting. RNA quantity ranged from 31 to 83 pg/μl, with RNA Integrity Number ranging from 1 to 8.7. Each cell population within the CA lesion was validated by showing differential expression of cell-specific genes.

Conclusion: We have shown, for the first-time, feasibility of individual cell type isolation from frozen, surgically excised CA lesions. The RNA quantity and quality of each cell population was suitable for the establishment of cell-specific transcriptome libraries. These will help clarify individual cell type contributions to CA pathogenesis.

Abstract TMP1: Multi-omic Biomarker Development In A Mendelian Neurovascular Disease, Cavernous Angioma

Introduction: Cavernous Angioma (CA) is a hemorrhagic neurovascular disease characterized by either a familial form with autosomal dominant germline mutations in one of three CCM genes or a sporadic form with somatic mutations of the same genes. Circulating proteins have been previously investigated as possible diagnostic and prognostic biomarkers of disease activity, with up to 86% and 88% sensitivity and specificity, respectively. We hypothesize that differentially expressed (DE) plasma microRNAs and metabolites in CA patients can be integrated with plasma proteins to increase the sensitivity and specificity of circulating CA biomarkers.

Methods: Mechanistically relevant homologous DE miRNAs were identified between familial CA patients and preclinical murine models and validated in an independent cohort of patients using real time qPCR. In conjunction, DE metabolites were determined in CA patients using liquid-chromatography mass spectrometry. The interactions of these metabolites with the previously established CA transcriptome, proteome, and microbiome were queried to assess for mechanistic relevance. Optimal diagnostic models of proteins, DE miRNAs, and DE metabolites alone were next established. Plasma metabolites and miRNAs were then separately integrated with protein, using a machine learning-implemented, Bayesian approach to develop diagnostic CA biomarkers.

Results: The optimal diagnostic biomarker model with only DE miRNAs performed at up to 68%, while proteins and metabolites achieved up to 68%, and 82% accuracy respectively. The optimal combination for proteins with miRNAs improved the diagnostic association of familial-CA disease to up to 94.7% sensitivity and 100% specificity. Integrating metabolites and proteins improved the diagnosis of CA disease and its clinical manifestations to 100% sensitivity and 100% specificity.

Conclusion: Combining plasma proteins with miRNAs or metabolites can improve diagnostic accuracy of CA disease and its disease characteristics above any single molecular modality alone. Future studies should incorporate proteins, miRNAs, and metabolites to further increase diagnostic accuracy, and validate these in a larger cohort with control for demographic and disease features.

Perfusion and permeability as diagnostic biomarkers of cavernous angioma with symptomatic hemorrhage

Cavernous angiomas with symptomatic hemorrhage (CASH) have a high risk of rebleeding, and hence an accurate diagnosis is needed. With blood flow and vascular leak as established mechanisms, we analyzed perfusion and permeability derivations of dynamic contrast-enhanced quantitative perfusion (DCEQP) MRI in 745 lesions of 205 consecutive patients. Thirteen respective derivations of lesional perfusion and permeability were compared between lesions that bled within a year prior to imaging (N = 86), versus non-CASH (N = 659) using machine learning and univariate analyses. Based on logistic regression and minimizing the Bayesian information criterion (BIC), the best diagnostic biomarker of CASH within the prior year included brainstem lesion location, sporadic genotype, perfusion skewness, and high-perfusion cluster area (BIC = 414.9, sensitivity = 74%, specificity = 87%). Adding a diagnostic plasma protein biomarker enhanced sensitivity to 100% and specificity to 85%. A slightly modified derivation achieved similar accuracy (BIC = 321.6, sensitivity = 80%, specificity = 82%) in the cohort where CASH occurred 3-12 months prior to imaging after signs of hemorrhage would have disappeared on conventional MRI sequences. Adding the same plasma biomarker enhanced sensitivity to 100% and specificity to 87%. Lesional blood flow on DCEQP may distinguish CASH after hemorrhagic signs on conventional MRI have disappeared and are enhanced in combination with a plasma biomarker.

Perfusion and Permeability MRI Predicts Future Cavernous Angioma Hemorrhage and Growth

BACKGROUND

Cerebral cavernous angioma (CA) is a capillary vasculopathy affecting more than a million Americans with a small fraction of cases demonstrating lesional bleed or growth with major clinical sequelae. Perfusion and permeability are fundamental features of CA pathophysiology, but their role as prognostic biomarkers is unclear.

PURPOSE

To investigate whether perfusion or permeability lesional descriptors derived from dynamic contrast-enhanced quantitative perfusion (DCEQP) magnetic resonance imaging (MRI) can predict subsequent lesional bleed/growth in the year following imaging.

STUDY TYPE

Single-site case-controlled study.

SUBJECTS

Two hundred and five consecutively enrolled patients (63.4% female).

FIELD STRENGTH/SEQUENCE

Three-Tesla/T₁ -mapping with contrast-enhanced dynamic two-dimensional (2D) spoiled gradient recalled acquisition (SPGR) sequences.

ASSESSMENT

Prognostic associations with bleed/growth (present or absent) in the following year were assessed in 745 CA lesions evaluated by DCEQP in the 205 patients in relation to lesional descriptors calculated from permeability and perfusion maps. A subgroup of 30 cases also underwent peripheral blood collection at the time of DCEQP scans and assays of plasma levels of soluble CD14, IL-1β, VEGF, and soluble ROBO4 proteins, whose weighted combination had been previously reported in association with future CA bleeding.

STATISTICAL TESTS

Mann-Whitney U-test for univariate analyses. Logistic regression models minimizing the Bayesian information criterion (BIC), testing sensitivity and specificity (receiver operating characteristic curves) of weighted combinations of parameters.

RESULTS

The best prognostic biomarker for lesional bleed or growth included brainstem lesion location, mean lesional permeability, and low-value perfusion cluster mean (BIC = 201.5, sensitivity = 77%, specificity = 72%, P < 0.05). Adding a previously published prognostic plasma protein biomarker improved the performance of the imaging model (sensitivity = 100%, specificity = 88%, P < 0.05).

DATA CONCLUSION

A combination of MRI-based descriptors reflecting higher lesional permeability and lower perfusion cluster may potentially predict future bleed/growth in CAs. The sensitivity and specificity of the prognostic imaging biomarker can be enhanced when combined with brainstem lesion location and a plasma protein biomarker of CA hemorrhage.

LEVEL OF EVIDENCE

2 TECHNICAL EFFICACY: Stage 5.

Astrocytes propel neurovascular dysfunction during cerebral cavernous malformation lesion formation

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

PIK3CA and CCM mutations fuel cavernomas through a cancer-like mechanism

Vascular malformations are thought to be monogenic disorders that result in dysregulated growth of blood vessels. In the brain, cerebral cavernous malformations (CCMs) arise owing to inactivation of the endothelial CCM protein complex, which is required to dampen the activity of the kinase MEKK31-4. Environmental factors can explain differences in the natural history of CCMs between individuals5, but why single CCMs often exhibit sudden, rapid growth, culminating in strokes or seizures, is unknown. Here we show that growth of CCMs requires increased signalling through the phosphatidylinositol-3-kinase (PI3K)-mTOR pathway as well as loss of function of the CCM complex. We identify somatic gain-of-function mutations in PIK3CA and loss-of-function mutations in the CCM complex in the same cells in a majority of human CCMs. Using mouse models, we show that growth of CCMs requires both PI3K gain of function and CCM loss of function in endothelial cells, and that both CCM loss of function and increased expression of the transcription factor KLF4 (a downstream effector of MEKK3) augment mTOR signalling in endothelial cells. Consistent with these findings, the mTORC1 inhibitor rapamycin effectively blocks the formation of CCMs in mouse models. We establish a three-hit mechanism analogous to cancer, in which aggressive vascular malformations arise through the loss of vascular 'suppressor genes' that constrain vessel growth and gain of a vascular 'oncogene' that stimulates excess vessel growth. These findings suggest that aggressive CCMs could be treated using clinically approved mTORC1 inhibitors.

Abortive intussusceptive angiogenesis causes multi-cavernous vascular malformations

Mosaic inactivation of CCM2 in humans causes cerebral cavernous malformations (CCMs) containing adjacent dilated blood-filled multi-cavernous lesions. We used CRISPR-Cas9 mutagenesis to induce mosaic inactivation of zebrafish ccm2 resulting in a novel lethal multi-cavernous lesion in the embryonic caudal venous plexus (CVP) caused by obstruction of blood flow by intraluminal pillars. These pillars mimic those that mediate intussusceptive angiogenesis; however, in contrast to the normal process, the pillars failed to fuse to split the pre-existing vessel in two. Abortive intussusceptive angiogenesis stemmed from mosaic inactivation of ccm2 leading to patchy klf2a overexpression and resultant aberrant flow signaling. Surviving adult fish manifested histologically typical hemorrhagic CCM. Formation of mammalian CCM requires the flow-regulated transcription factor KLF2; fish CCM and the embryonic CVP lesion failed to form in klf2a null fish indicating a common pathogenesis with the mammalian lesion. These studies describe a zebrafish CCM model and establish a mechanism that can explain the formation of characteristic multi-cavernous lesions.

A Roadmap for Developing Plasma Diagnostic and Prognostic Biomarkers of Cerebral Cavernous Angioma With Symptomatic Hemorrhage (CASH)

BACKGROUND

Cerebral cavernous angioma (CA) is a capillary microangiopathy predisposing more than a million Americans to premature risk of brain hemorrhage. CA with recent symptomatic hemorrhage (SH), most likely to re-bleed with serious clinical sequelae, is the primary focus of therapeutic development. Signaling aberrations in CA include proliferative dysangiogenesis, blood-brain barrier hyperpermeability, inflammatory/immune processes, and anticoagulant vascular domain. Plasma levels of molecules reflecting these mechanisms and measures of vascular permeability and iron deposition on magnetic resonance imaging are biomarkers that have been correlated with CA hemorrhage.

OBJECTIVE

To optimize these biomarkers to accurately diagnose cavernous angioma with symptomatic hemorrhage (CASH), prognosticate the risk of future SH, and monitor cases after a bleed and in response to therapy.

METHODS

Additional candidate biomarkers, emerging from ongoing mechanistic and differential transcriptome studies, would further enhance the sensitivity and specificity of diagnosis and prediction of CASH. Integrative combinations of levels of plasma proteins and characteristic micro-ribonucleic acids may further strengthen biomarker associations. We will deploy advanced statistical and machine learning approaches for the integration of novel candidate biomarkers, rejecting noncorrelated candidates, and determining the best clustering and weighing of combined biomarker contributions.

EXPECTED OUTCOMES

With the expertise of leading CA researchers, this project anticipates the development of future blood tests for the diagnosis and prediction of CASH to clinically advance towards precision medicine.

DISCUSSION

The project tests a novel integrational approach of biomarker development in a mechanistically defined cerebrovascular disease with a relevant context of use, with an approach applicable to other neurological diseases with similar pathobiologic features.

Cerebral cavernous malformations are driven by ADAMTS5 proteolysis of versican

Cerebral cavernous malformations (CCMs) form following loss of the CCM protein complex in brain endothelial cells due to increased endothelial MEKK3 signaling and KLF2/4 transcription factor expression, but the downstream events that drive lesion formation remain undefined. Recent studies have revealed that CCM lesions expand by incorporating neighboring wild-type endothelial cells, indicative of a cell nonautonomous mechanism. Here we find that endothelial loss of ADAMTS5 reduced CCM formation in the neonatal mouse model. Conversely, endothelial gain of ADAMTS5 conferred early lesion genesis in the absence of increased KLF2/4 expression and synergized with KRIT1 loss of function to create large malformations. Lowering versican expression reduced CCM burden, indicating that versican is the relevant ADAMTS5 substrate and that lesion formation requires proteolysis but not loss of this extracellular matrix protein. These findings identify endothelial secretion of ADAMTS5 and cleavage of versican as downstream mechanisms of CCM pathogenesis and provide a basis for the participation of wild-type endothelial cells in lesion formation.

Abstract P737: Human Homologs Of Differentially Expressed Plasma MicroRNAs In Preclinical Murine Models Target Fundamental Mechanisms Of Cerebral Cavernous Malformation

Introduction: There is a current need for sensitive and specific biomarkers of Cerebral Cavernous Malformation (CCM) that can be readily translated from preclinical to human models to accurately diagnose and monitor disease states and response to novel therapeutics. MiRNAs are small non-coding RNAs that influence gene expression and whose levels can be affected by disease states. We hypothesize that there are human homologs of differentially expressed (DE) miRNA in the plasma of CCM murine models that can be identified in CCM patients. We further hypothesize that these miRNAs have gene targets within previously published CCM transcriptomes, mechanistically linking them to CCM disease.

Methods: Plasma miRNAs from homozygous and heterozygous Ccm1 and Ccm3 mice, as well as their respective wild type controls were sequenced and analyzed. Putative gene targets of DE miRNAs [p<0.05, false discovery rate (FDR) corrected] were queried in previously published mouse CCM transcriptomes. The human homologs of the DE miRNAs in the plasma of Ccm1 and Ccm3 mouse models were identified and assessed in the plasma of healthy controls (n=13), CCM1 (n=11), and CCM3 (n=11) patients using RT-qPCR.

Results: 5 miRNAs in homozygous and 10 in heterozygous for Ccm1 , while 45 in homozygous and 2 in heterozygous for Ccm3 were DE in the plasma of mouse models (p<0.05, FDR corrected), had gene targets within CCM mouse transcriptomes, and have a human homolog. Preliminary results show mmu-miR-375-3p as DE in both Ccm1 +/- and Ccm3 -/- mice. RT-qPCR assays show that plasma relative quantification values of the human homolog hsa-miR-375-3p were higher in CCM3 than in CCM1 patients ( p <0.001) and in healthy controls ( p <0.05).

Conclusion: DE plasma miRNAs identified in mouse models with human homologs and putative gene targets mechanistically implicated in CCM disease may be used as candidate biomarkers for specific clinical contexts.

Abstract P36: Lesional Perfusion and Permeability Are Diagnostic and Prognostic Biomarkers of Cavernous Angioma With Symptomatic Hemorrhage

Introduction: Diagnosis of cavernous angioma with symptomatic hemorrhage (CASH) requires MRI evidence of lesional bleeding associated directly with attributable symptoms. However, hemorrhagic signs of CASH may become clinically silent on conventional MRI after 3 months. As CASH is likely to rebleed for several years, accurate diagnosis of CASH that bled more than 3 months prior is needed.

Hypothesis: Perfusion and permeability derivations of dynamic contrast-enhanced quantitative perfusion (DCEQP) MRI can diagnose CASH and predict bleeding/growth in CAs.

Methods: CAs of 205 consecutively enrolled patients scanned with DCEQP during clinical visits were classified as CASH that bled 3 - 12 months prior (N = 55) versus non-CASH (N = 658) or CA with (N = 23) versus without (N = 721) bleeding/growth within a year after MRI. Demographics and 13 perfusion and 13 permeability derivations of DCEQP were assessed via machine learning and univariate analyses. Logistic regression models ln ( P / 1 - P ) = Σ (β i x i ) + β 0 were selected as the best diagnostic and prognostic biomarkers by minimizing the Bayesian information criterion (BIC).

Results: The best diagnostic biomarker of CASH that bled 3 - 12 months prior (BIC = 321.6, Figure A) showed 80% sensitivity and 82% specificity. Permeability derivations did not add diagnostic efficacy when combined with perfusion. The best prognostic biomarker of bleeding/growth (BIC = 201.5, Figure B) showed 77% sensitivity and 72% specificity.

Conclusion: Perfusion imaging may diagnose CASH even after hemorrhagic signs disappear on conventional MRI. A combination of permeability and perfusion derivations may help predict bleeding/growth in CAs.

Propranolol inhibits cavernous vascular malformations by β1 adrenergic receptor antagonism in animal models

Propranolol, a pleiotropic β-adrenergic blocker, has been anecdotally reported to reduce cerebral cavernous malformations (CCMs) in humans. However, propranolol has not been rigorously evaluated in animal models, nor has its mechanism of action in CCM been defined. We report that propranolol or its S(-) enantiomer dramatically reduced embryonic venous cavernomas in ccm2 mosaic zebrafish, whereas R-(+)-propranolol, lacking β antagonism, had no effect. Silencing of the β1, but not β2, adrenergic receptor mimicked the beneficial effects of propranolol in a zebrafish CCM model, as did the β1-selective antagonist metoprolol. Thus, propranolol ameliorated cavernous malformations by β1 adrenergic antagonism in zebrafish. Oral propranolol significantly reduced lesion burden in 2 chronic murine models of the exceptionally aggressive Pdcd10/Ccm3 form of CCM. Propranolol or other β1-selective antagonists may be beneficial in CCM disease.

Antibodies in cerebral cavernous malformations react with cytoskeleton autoantigens in the lesional milieu

Previous studies have reported robust inflammatory cell infiltration, synthesis of IgG, B-cell clonal expansion, deposition of immune complexes and complement within cerebral cavernous malformation (CCM) lesions. B-cell depletion has also been shown to reduce the maturation of CCM in murine models. We hypothesize that antigen(s) within the lesional milieu perpetuate the pathogenetic immune responses in CCMs. This study aims to identify those putative antigen(s) using monoclonal antibodies (mAbs) derived from plasma cells found in surgically removed human CCM lesions. We produced human mAbs from laser capture micro-dissected plasma cells from four CCM patients, and also germline-reverted versions. CCM mAbs were assayed using immunofluorescence on central nervous system (CNS) tissues and immunocytochemistry on human primary cell lines. Antigen characterization was performed using a combination of confocal microscopy, immunoprecipitation and mass spectrometry. Affinity was determined by enzyme-linked immunosorbent assay, and specificity by multi-color confocal microscopy and quantitative co-localization. CCM mAbs bound CNS tissue, especially endothelial cells and astrocytes. Non-muscle myosin heavy chain IIA (NMMHCIIA), vimentin and tubulin are three cytoskeleton proteins that were commonly targeted. Selection of cytoskeleton proteins by plasma cells was supported by a high frequency of immunoglobulin variable region somatic hypermutations, high affinity and selectivity of mAbs in their affinity matured forms, and profoundly reduced affinity and selectivity in the germline reverted forms. Antibodies produced by plasma cells in CCM lesions commonly target cytoplasmic and cytoskeletal autoantigens including NMMHCIIA, vimentin and tubulin that are abundant in endothelial cells and astrocytes. Binding to, and selection on autoantigen(s) in the lesional milieu likely perpetuates the pathogenetic immune response in CCMs. Blocking this in situ autoimmune response may yield a novel treatment for CCM.

Novel Murine Models of Cerebral Cavernous Malformations

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

Common transcriptome, plasma molecules, and imaging signatures in the aging brain and a Mendelian neurovascular disease, cerebral cavernous malformation

Brain senescence is associated with impaired endothelial barrier function, angiogenic and inflammatory activity, and propensity to brain hemorrhage. The same pathological changes occur in cerebral cavernous malformations (CCM), a genetic neurovascular anomaly. We hypothesized common transcriptomic and plasma cytokine signatures in the aging brain and CCM. We identified 320 genes [fold change ≥1.5; p < 0.05; false discovery rate (FDR) corrected] commonly dysregulated in the aging brain and CCM. Ontology and pathway analyses of the common differentially expressed genes were related to inflammation and extracellular matrix organization. Plasma levels of C-reactive protein and angiopoietin-2 were significantly greater in older compared to younger healthy non-CCM subjects and were also greater in CCM (Sporadic and Familial) subjects regardless of age (all: p < 0.05; FDR corrected). Plasma levels of vascular endothelial growth factor were significantly greater in older compared to younger subjects, in both healthy non-CCM and Sporadic-CCM groups (all: p_adj < 0.05). Plasma levels of vascular endothelial growth factor were also significantly greater in Familial-CCM cases with germ line mutations regardless of age (all: p_adj < 0.05) compared to both healthy non-CCM and Sporadic-CCM subjects. Brain white matter vascular permeability assessed by MRI followed the same pattern as vascular endothelial growth factor across all groups. In addition, quantitative susceptibility mapping of brain white matter, a measure of iron deposition, was increased in older compared to younger healthy non-CCM subjects. Genetic aberrations, plasma molecules, and imaging biomarkers in a well characterized Mendelian neurovascular disease may also be applicable in the aging brain. Graphical abstract.

Abstract TMP115: Common Transcriptomic and Biomarker Signatures in the Aging Brain and in Mendelian Neurovascular Disease, Cerebral Cavernous Malformation

Background: Cellular senescence is associated with gene expression dysregulation affecting endothelial barrier function as well as angiogenic and inflammatory processes. These pathological changes occur in cerebral cavernous malformations (CCMs), a neurovascular anomaly predisposing patients to hemorrhagic stroke. We hypothesize common transcriptomic and biomarker signatures between the aging brain and CCMs.

Method: Brain specific genes dysregulate in Younger (age < 30) and Older (age > 50) human brain parenchyma were identified using the Genotype-Tissue Expression database, and compared with differential transcriptome in microdissected neurovascular units of human CCM lesions. Brain white matter vascular permeability in areas devoid of lesions was measured in non-CCM (23 Younger, 27 Older), Sporadic-CCM (S-CCM) (26 Younger, 37 Older) and Familial-CCM (F-CCM) (41 Younger, 17 Older) using dynamic contrast-enhanced quantitative perfusion MRI. Plasma levels of 6 proteins with reported roles in CCMs were quantified, including VEGF, angiopoietin (ANG 1 & 2), CRP, thrombospondin 2 (THBS 2), and endoglin (ENG). All reported correlations were significant at P< 0.05, FDR corrected.

Result: We identified 320 genes (absolute fold change≥1.5) commonly dysregulated in aging brain and CCM, related to inflammation and extracellular matrix organization pathways. Brain permeability was greater in Older non-CCM and S-CCM compared to Younger subjects. Brain permeability was higher in Younger F-CCM harboring germ line CCM mutations, than in both Younger non-CCM (p<0.001) and S-CCM (p<0.05) lacking those mutations. No difference was observed in Younger or Older F-CCM and Older S-CCM or controls. Plasma levels of VEGF, ANG-2 and CRP were greater in both Older non-CCM and S-CCM compared to Younger. No difference was found in Older or Younger F-CCM. No differences were observed in THBS2, ENG and ANG1.

Conclusion: There are common transcriptomic, and brain permeability and plasma biomarker signatures in the aging brain and CCM, suggesting common dysregulated pathways. Biomarkers and potential therapies identified in a well characterized Mendelian neurovascular disease may be applicable to mitigate the same mechanistic aberrations in the aging brain.

Abstract TMP120: Autoantigen(s) Trigger a Robust Immune Response in Cerebral Cavernous Malformations

Introduction: Previous studies have reported robust inflammatory cell infiltration, selective synthesis of IgG, B-cell clonal expansion, and deposition of immune complexes and complement within Cerebral Cavernous Malformation (CCM) lesions. Furthermore,B-cell depletion has been shown to reduce the maturation of CCM in murine models. We hypothesize that specific autoantigen(s) within the lesional milieu trigger the pathogenetic immune responses in CCMs. This study aims to identify those putative autoantigen(s) using recombinant antibodies (rAbs) derived from plasma cells found in surgical human CCM lesions.

Methods: CD138 + plasma cells were laser captured from fresh frozen surgically resected human CCM lesions. Clonally expanded immunoglobulin heavy- and light-chain variable region pairs were cloned into IgG expression vectors and expressed as monoclonal antibodies. Purified rAbs were assayed by immunofluorescence with CCM lesion tissue and normal brain tissue sections. rAbs assayed by immunocytochemistry with human primary cell line were used to further define the staining pattern. The cell lysates were immunoprecipitated with rAb, after protein purification by SDS-PAGE, and analyzed by Mass spectrometry.

Results: In normal brain tissue, rAbs stained endothelial cells with limited staining of glial cells. In CCM lesional tissue, rAbs stained endothelial cells, glial cells as well as structures in the acellular matrix adjacent to caverns. In cultured Human Brain Microvascular Endothelial Cells (HBMECs) and Human Astrocytes (HAs), rAbs co-localized with cytoplasmic components. After HBMEC and HA cell lysates were immunoprecipitated with rAb, a Coomassie Stain detected bands of approximately 50 kDa.

Conclusions: Our results suggest that autoantigen(s) in human CCM lesions are cytoplasmic components present in lesional tissue as well as in normal brain tissue. Molecular level identification of the triggering antigen is still ongoing by mass spectrometry. Identification of the autoantigen(s) in the lesional milieu might explain the propensity of lesion development from leaky endothelium in the neuroglial parenchyma. Characterization of the autoantigen triggers will open new venues for therapy or vaccine in this disease.

Distinct cellular roles for PDCD10 define a gut-brain axis in cerebral cavernous malformation

Cerebral cavernous malformation (CCM) is a genetic, cerebrovascular disease. Familial CCM is caused by genetic mutations in KRIT1, CCM2, or PDCD10 Disease onset is earlier and more severe in individuals with PDCD10 mutations. Recent studies have shown that lesions arise from excess mitogen-activated protein kinase kinase kinase 3 (MEKK3) signaling downstream of Toll-like receptor 4 (TLR4) stimulation by lipopolysaccharide derived from the gut microbiome. These findings suggest a gut-brain CCM disease axis but fail to define it or explain the poor prognosis of patients with PDCD10 mutations. Here, we demonstrate that the gut barrier is a primary determinant of CCM disease course, independent of microbiome configuration, that explains the increased severity of CCM disease associated with PDCD10 deficiency. Chemical disruption of the gut barrier with dextran sulfate sodium augments CCM formation in a mouse model, as does genetic loss of Pdcd10, but not Krit1, in gut epithelial cells. Loss of gut epithelial Pdcd10 results in disruption of the colonic mucosal barrier. Accordingly, loss of Mucin-2 or exposure to dietary emulsifiers that reduce the mucus barrier increases CCM burden analogous to loss of Pdcd10 in the gut epithelium. Last, we show that treatment with dexamethasone potently inhibits CCM formation in mice because of the combined effect of action at both brain endothelial cells and gut epithelial cells. These studies define a gut-brain disease axis in an experimental model of CCM in which a single gene is required for two critical components: gut epithelial function and brain endothelial signaling.

Rho Kinase Inhibition Blunts Lesion Development and Hemorrhage in Murine Models of Aggressive Pdcd10/Ccm3 Disease

Background and Purpose- Previously, murine models Krit1 ^+/- Msh2 ^{-/ -} and Ccm2 ^{+/ -} Trp53 ^{-/ -} showed a reduction or no effect on cerebral cavernous malformation (CCM) burden and favorable effects on lesional hemorrhage by the robust Rock (Rho-associated protein kinase) inhibitor fasudil and by simvastatin (a weak pleiotropic inhibitor of Rock). Herein, we concurrently investigated treatment of the more aggressive Pdcd10/Ccm3 model with fasudil, simvastatin, and higher dose atorvastatin to determined effectiveness of Rock inhibition. Methods- The murine models, Pdcd10 ^{+/ -} Trp53 ^{-/ -} and Pdcd10 ^{+/ -} Msh2 ^{-/ -}, were contemporaneously treated from weaning to 5 months of age with fasudil (100 mg/kg per day in drinking water, n=9), simvastatin (40 mg/kg per day in chow, n=11), atorvastatin (80 mg/kg per day in chow, n=10), or with placebo (n=16). We assessed CCM volume in mouse brains by microcomputed tomography. Lesion burden was calculated as lesion volume normalized to total brain volume. We analyzed chronic hemorrhage in CCM lesions by quantitative intensity of Perls staining in brain sections. Results- The Pdcd10 ^{+/ -} Trp53 ^{-/ -} /Msh2 ^{-/ -} models showed a mean CCM lesion burden per mouse reduction from 0.0091 in placebos to 0.0042 ( P=0.027) by fasudil, and to 0.0047 ( P=0.025) by atorvastatin treatment, but was not changed significantly by simvastatin. Hemorrhage intensity per brain was commensurately decreased by Rock inhibition. Conclusions- These results support the exploration of proof of concept effect of high-dose atorvastatin on human CCM disease for potential therapeutic testing.

A Brain-Targeted Orally Available ROCK2 Inhibitor Benefits Mild and Aggressive Cavernous Angioma Disease

Cavernous angioma (CA) is a vascular pathology caused by loss of function in one of the 3 CA genes (CCM1, CCM2, and CCM3) that result in rho kinase (ROCK) activation. We investigated a novel ROCK2 selective inhibitor for the ability to reduce brain lesion formation, growth, and maturation. We used genetic methods to explore the use of a ROCK2-selective kinase inhibitor to reduce growth and hemorrhage of CAs. The role of ROCK2 in CA was investigated by crossing Rock1 or Rock2 hemizygous mice with Ccm1 or Ccm3 hemizygous mice, and we found reduced lesions in the Rock2 hemizygous mice. A ROCK2-selective inhibitor, BA-1049 was used to investigate efficacy in reducing CA lesions after oral administration to Ccm1^+/- and Ccm3^+/- mice that were bred into a mutator background. After assessing the dose range effective to target brain endothelial cells in an ischemic brain model, Ccm1^+/- and Ccm3^+/- transgenic mice were treated for 3 (Ccm3^+/-) or 4 months (Ccm1^+/-), concurrently, randomized to receive one of three doses of BA-1049 in drinking water, or placebo. Lesion volumes were assessed by micro-computed tomography. BA-1049 reduced activation of ROCK2 in Ccm3^+/-Trp53^-/- lesions. Ccm1^+/-Msh2^-/- (n=68) and Ccm3^+/-Trp53^-/- (n=71) mice treated with BA-1049 or placebo showed a significant dose-dependent reduction in lesion volume after treatment with BA-1049, and a reduction in hemorrhage (iron deposition) near lesions at all doses. These translational studies show that BA-1049 is a promising therapeutic agent for the treatment of CA, a disease with no current treatment except surgical removal of the brain lesions.

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

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

Biomarkers of cavernous angioma with symptomatic hemorrhage

BACKGROUNDCerebral cavernous angiomas (CAs) with a symptomatic hemorrhage (CASH) have a high risk of recurrent hemorrhage and serious morbidity.METHODSEighteen plasma molecules with mechanistic roles in CA pathobiology were investigated in 114 patients and 12 healthy subjects. The diagnostic biomarker of a CASH in the prior year was derived as that minimizing the Akaike information criterion and validated using machine learning, and was compared with the prognostic CASH biomarker predicting bleeding in the subsequent year. Biomarkers were longitudinally followed in a subset of cases. The biomarkers were queried in the lesional neurovascular unit (NVU) transcriptome and in plasma miRNAs from CASH and non-CASH patients.RESULTSThe diagnostic CASH biomarker included a weighted combination of soluble CD14 (sCD14), VEGF, C-reactive protein (CRP), and IL-10 distinguishing CASH patients with 76% sensitivity and 80% specificity (P = 0.0003). The prognostic CASH biomarker (sCD14, VEGF, IL-1β, and sROBO-4) was confirmed to predict a bleed in the subsequent year with 83% sensitivity and 93% specificity (P = 0.001). Genes associated with diagnostic and prognostic CASH biomarkers were differentially expressed in CASH lesional NVUs. Thirteen plasma miRNAs were differentially expressed between CASH and non-CASH patients.CONCLUSIONShared and unique biomarkers of recent symptomatic hemorrhage and of future bleeding in CA are mechanistically linked to lesional transcriptome and miRNA. The biomarkers may be applied for risk stratification in clinical trials and developed as a tool in clinical practice.FUNDINGNIH, William and Judith Davis Fund in Neurovascular Surgery Research, Be Brave for Life Foundation, Safadi Translational Fellowship, Pritzker School of Medicine, and Sigrid Jusélius Foundation.

Phenotypic characterization of murine models of cerebral cavernous malformations

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

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

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

Abstract TMP106: Intestinal Barrier Leakage Exacerbates Cerebral Cavernous Malformation Development in Murine Models

Introduction: A serendipitous discovery demonstrating a greater cerebral cavernous malformation (CCM) burden within a murine CCM disease model housed in an unclean vivarium than in a cleaner facility led to the observation of intestinal microbiome involvement in CCM development through lipopolysaccharide from gram negative bacteria. Hence we investigated the effect on CCM development in CCM models by genetic or chemical disruption of the intestinal barrier.

Hypothesis: Intestinal barrier disruption increases CCM burden in CCM murine models.

Methods: Acute iBECre; Ccm3 fl/fl mice were bred to be deficient ( Muc2 +/- , Muc2 -/- ) in the mucin 2 gene with CCM assessment at P21. CCM burden was assessed in the following 3 chronic models at 5 months of age. The murine model Ccm3 +/- housed in an unclean vivarium was treated with 1% p80 emulsifier starting at 21 days of age (n=22) or with placebo (n=16). Less CCM penetrant Ccm1 +/- mice housed in a clean facility were contemporaneously treated with 2% dextran sodium sulfate (DSS) starting at 21 days of age (n=22) or with placebo (n=17). More CCM penetrant Ccm1 +/- Msh2 -/- mice housed in an unclean vivarium were treated with 0.5% DSS starting at 2 months of age (n=11) or with placebo (n=6). We assessed CCM volume in brains by micro-computed tomography.

Results: Mean CCM volume in acute Ccm3 -/- models doubled from 1.8 mm 3 with no Muc2 loss (n=11) to 4.7 mm 3 with homozygotic Muc2 loss (p<0.001, n=10) with an increasing trend to 2.6 mm 3 with heterozygotic Muc2 loss (p=0.07, n=15). Mean CCM volume/brain volume (X 10 6 ) per mouse doubled from 10.7 in placebos to 24.4 (p=0.01) by emulsifier treatment in the Ccm3 +/- chronic model and significantly increased from 0.1 in placebos to 9.2 (p<0.001) by 2% DSS treatment in the Ccm1 +/- model, with an increasing trend from 11.0 in placebos to 15.2 (p=0.086) by 0.5% DSS treatment in the Ccm1 +/- Msh2 -/- model.

Conclusion: CCM lesion development was enhanced by intestinal barrier disruption in 4 CCM models, regardless of the method used (genetic or chemical), time of onset, murine genotype or vivarium cleanliness status. Ongoing investigations include an early onset studies in the unclean vivarium with the Ccm1 +/- Msh2 -/- mice receiving 0.5% DSS and the Ccm3 +/- mice receiving 2% DSS.

Abstract 63: Plasma Biomarkers of Cavernous Angioma With Symptomatic Hemorrhage (CASH)

Introduction: Cerebral cavernous angiomas with a documented symptomatic hemorrhage (CASH) are associated with an exceptionally high risk of recurrent hemorrhage and serious morbidity. It is unclear if peripheral blood plasma biomarkers implicated in disease biology can differentiate CASH, and whether the same or different biomarkers can distinguish cases who would rebleed.

Methods: Eighteen plasma molecules with postulated mechanistic roles in this disease were quantified in 114 patients and 12 healthy subjects. The best biomarker combination differentiating CASH in the prior year (+/- 30 days) was derived by minimizing the Akaike Information Criterion (AIC), and was validated using statistical and machine-learning simulations. This was compared to the biomarker predicting bleeding in the subsequent year (+/- 30 days), and both explanatory and predictive biomarkers were followed longitudinally in a subset of cases.

Results: Nine plasma molecules had significantly different levels expressed in CASH patients (p<0·05, FDR corrected). The best biomarker (AIC=75·9) included a weighted combination of 4 of these (sCD-14, VEGF, CRP, and IL-10), and distinguished CASH patients with 76% sensitivity and 80% specificity (p=0·0003). A weighed combination of two of these compounds (sCD14 and VEGF) and two others (IL-1β and sROBO-4) predicted which patients would bleed in the subsequent year with 83% sensitivity and 93% specificity (p=0·001). The CASH biomarker increased in recovering patients (p=0·01), while the predictive biomarker decreased after a bleed (p=0·01). No significant change over time was observed in stable subjects in either biomarker.

Conclusions: Our results suggest shared and unique biomarkers of recent symptomatic hemorrhage and of future bleeding in cavernous angiomas. This may be applied for risk stratification in clinical trials, and potentially developed as a tool in clinical practice.

The cerebral cavernous malformation disease causing gene KRIT1 participates in intestinal epithelial barrier maintenance and regulation

Epithelial barrier maintenance and regulation requires an intact perijunctional actomyosin ring underneath the cell-cell junctions. By searching for known factors affecting the actin cytoskeleton, we identified Krev interaction trapped protein 1 (KRIT1) as a major regulator for epithelial barrier function through multiple mechanisms. KRIT1 is expressed in both small intestinal and colonic epithelium, and KRIT1 knockdown in differentiated Caco-2 intestinal epithelium decreases epithelial barrier function and increases cation selectivity. KRIT1 knockdown abolished Rho-associated protein kinase-induced and myosin II motor inhibitor-induced barrier loss by limiting both small and large molecule permeability but did not affect myosin light chain kinase-induced increases in epithelial barrier function. These data suggest that KRIT1 participates in Rho-associated protein kinase- and myosin II motor-dependent (but not myosin light chain kinase-dependent) epithelial barrier regulation. KRIT1 knockdown exacerbated low-dose TNF-induced barrier loss, along with increased cleaved caspase-3 production. Both events are blocked by pan-caspase inhibition, indicating that KRIT1 regulates TNF-induced barrier loss through limiting epithelial apoptosis. These data indicate that KRIT1 controls epithelial barrier maintenance and regulation through multiple pathways, suggesting that KRIT1 mutation in cerebral cavernous malformation disease may alter epithelial function and affect human health.-Wang, Y., Li, Y., Zou, J., Polster, S. P., Lightle, R., Moore, T., Dimaano, M., He, T.-C., Weber, C. R., Awad, I. A., Shen, L. The cerebral cavernous malformation disease causing gene KRIT1 participates in intestinal epithelial barrier maintenance and regulation.

Abstract 64: Novel and Known Genes Elucidated in Cerebral Cavernous Malformation Through Comparative Transcriptomic Analysis of Multiple Model Species and Human Microdissected Lesional Endothelial Cells

Cerebral cavernous malformations (CCMs) are vascular brain lesions predisposing 0.5% of the population to a lifetime risk of hemorrhagic stroke and seizures. The disease is associated to a mutation in one of the three CCM genes ( CCM1, CCM2 and CCM3 ). CCM pathogenesis has been shown to be endothelial autonomous, linked to angiogenic, adhesion, and inflammatory processes.

Using RNA-Seq, we profiled the transcriptomes of lesional endothelial cells (ECs) extracted from 5 human CCMs. We also profiled the more common Ccm1, and the exceptionally aggressive Ccm3 genotypes in mouse brain microvascular endothelial cells (BMECs) and C. elegans . We first identified differently expressed genes (DEGs), gene ontology (GO) functions, and gene networks for each model separately. We then cross-compared the models and genotypes to identify the important and conserved genes likely contributing to pathogenesis of CCM disease.

Nine hundred-fifteen DEGs in human microdissected lesional ECs, 1932 in Ccm1 ECKO and 524 in Ccm3 ECKO BMECs, as well as 1643 in ccm1 C. elegans and 1581 in ccm3 C. elegans were identified (p<0.05, FDR corrected, fold change≥1.2). FAT1 was commonly identified in the 5 models, while 7 other DEGs were common between human lesional ECs, mouse BMEC Ccm1 ECKO and ccm1 C. elegans: GNAO1 , SPARCL1 , PLXDC2 , PLCD3 , PDGFRA , FAXC , and UNC13A . Seventy-one DEGs were only identified in Ccm1 models, these genes were related to DNA repair, angiogenesis, microtubule functions and magnesium ion binding. Eleven DEGs were only found in Ccm3 models, and were related to rRNA processing, ribosome biogenesis and structural constituent, protein targeting to endoplasmic reticulum, protein intracellular targeting, and vesicle transportation to a cell membrane.

We provide a comprehensive transcriptome library of CCM disease across species and genotypes. The results will be useful for validating putative mechanistic targets and biomarkers in this disease. For the first time, we also report fundamental transcriptomic differences between Ccm1 and Ccm3 genotypes, potentially explaining differences in CCM disease severity. Our results confirm several previously reported mechanisms, and suggest multiple novel gene candidates to be investigated in CCM pathogenesis.

Plasma Biomarkers of Inflammation and Angiogenesis Predict Cerebral Cavernous Malformation Symptomatic Hemorrhage or Lesional Growth

RATIONALE

The clinical course of cerebral cavernous malformations is highly unpredictable, with few cross-sectional studies correlating proinflammatory genotypes and plasma biomarkers with prior disease severity.

OBJECTIVE

We hypothesize that a panel of 24 candidate plasma biomarkers, with a reported role in the physiopathology of cerebral cavernous malformations, may predict subsequent clinically relevant disease activity.

METHODS AND RESULTS

Plasma biomarkers were assessed in nonfasting peripheral venous blood collected from consecutive cerebral cavernous malformation subjects followed for 1 year after initial sample collection. A first cohort (N=49) was used to define the best model of biomarker level combinations to predict a subsequent symptomatic lesional hemorrhagic expansion within a year after the blood sample. We generated the receiver operating characteristic curves and area under the curve for each biomarker individually and each weighted linear combination of relevant biomarkers. The best model to predict lesional activity was selected as that minimizing the Akaike information criterion. In this cohort, 11 subjects experienced symptomatic lesional hemorrhagic expansion (5 bleeds and 10 lesional growths) within a year after the blood draw. Subjects had lower soluble CD14 (cluster of differentiation 14; P=0.05), IL (interleukin)-6 (P=0.04), and VEGF (vascular endothelial growth factor; P=0.0003) levels along with higher plasma levels of IL-1β (P=0.008) and soluble ROBO4 (roundabout guidance receptor 4; P=0.03). Among the 31 weighted linear combinations of these 5 biomarkers, the best model (with the lowest Akaike information criterion value, 25.3) was the weighted linear combination including soluble CD14, IL-1β, VEGF, and soluble ROBO4, predicting a symptomatic hemorrhagic expansion with a sensitivity of 86% and specificity of 88% (area under the curve, 0.90; P<0.0001). We then validated our best model in the second sequential independent cohort (N=28).

CONCLUSIONS

This is the first study reporting a predictive association between plasma biomarkers and subsequent cerebral cavernous malformation disease clinical activity. This may be applied in clinical prognostication and stratification of cases in clinical trials.

Abstract 75: Plasma Biomarkers of Inflammation and Angiogenesis Predict Cerebral Cavernous Malformation Symptomatic Hemorrhage or Lesional Growth

Introduction: The clinical course of cerebral cavernous malformations (CCMs) is highly unpredictable, with a limited number of cross sectional studies correlating pro-inflammatory genotypes and plasma biomarkers with prior disease severity. We hereby hypothesize that a panel of plasma biomarkers, with reported role in the physiopathology of CCM, may predict subsequent clinically relevant disease activity.

Methods: This was a single-site prospective observational cohort study, without planned intervention. Non-fasting peripheral venous blood samples from 55 patients (25 with sporadic and 30 with familial CCM) were collected. Twenty-four plasma biomarkers were quantified and analyzed regarding their predictive association with the occurrence of a symptomatic hemorrhage or lesional growth within a year following the blood sample. We generated the receiver operating characteristic (ROC) curves and area under curves (AUC) for each biomarker individually and for each weighted linear combination of relevant biomarkers. The best model to predict lesional activity was selected as that minimizing the Akaike Information Criterion (AIC), representing parsimonious model offering the best fit to the data with the fewest number of predictors.

Results: Eleven patients experienced lesional activity events (5 symptomatic bleeds and 10 lesional growths) within a year after the blood draw. These patients had lower levels of CD14 (p=0.05), IL6 (p=0.04), ROBO4 (p=0.03) and VEGF (p=0.0003), along with higher IL1β (p=0.008) plasma levels. Among the 35 weighted linear combinations of these 5 biomarkers, the best model (with the lowest AIC value=25.3), was the combination including CD14, IL1β, VEGF and ROBO4, predicting a symptomatic bleed or lesional growth with a sensitivity of 86% and specificity of 88% (AUC=0.90, p<0.0001).

Conclusion: This is the first study reporting a predictive association between plasma biomarkers and subsequent CCM disease clinical activity. This may be applied in clinical prognostication, and in the stratification of cases in clinical trials.

Endothelial TLR4 and the microbiome drive cerebral cavernous malformations

Cerebral cavernous malformations (CCMs) are a cause of stroke and seizure for which no effective medical therapies yet exist. CCMs arise from the loss of an adaptor complex that negatively regulates MEKK3-KLF2/4 signalling in brain endothelial cells, but upstream activators of this disease pathway have yet to be identified. Here we identify endothelial Toll-like receptor 4 (TLR4) and the gut microbiome as critical stimulants of CCM formation. Activation of TLR4 by Gram-negative bacteria or lipopolysaccharide accelerates CCM formation, and genetic or pharmacologic blockade of TLR4 signalling prevents CCM formation in mice. Polymorphisms that increase expression of the TLR4 gene or the gene encoding its co-receptor CD14 are associated with higher CCM lesion burden in humans. Germ-free mice are protected from CCM formation, and a single course of antibiotics permanently alters CCM susceptibility in mice. These studies identify unexpected roles for the microbiome and innate immune signalling in the pathogenesis of a cerebrovascular disease, as well as strategies for its treatment.

Abstract 121: Transcriptome Profiling of Laser-Capture Microdissected Endothelial Cells From Human Cerebral Cavernous Malformations

Introduction: Cerebral cavernous malformations (CCMs) are common lesions causing stroke and epilepsy. Mechanistic studies in cultured endothelial cells (ECs) and in murine models have correlated CCM gene loss with signaling aberrations related to MEKK3-KLF2/4, Rho/ROCK and angiogenesis activity, and disruption of junctional proteins and EC-mesenchymal transition. Other studies demonstrated a robust antigen driven clonally expanded B-cell immune response, and pathogenetic B-T cell interactions. We hypothesized that the transcriptome of endothelial ECs from human CCM lesions reflects these postulated mechanisms.

Methods: Resected human CCMs were harvested at the time of surgical resection, snap frozen, embedded in OCT and stored at -80 °C. Normal brain tissue was acquired at autopsy from patients free of neurological disease. Five human CCMs and 3 normal brain tissues were included in the study. ECs from CCMs and normal capillaries were collected using laser-captured microdissection. RNA was extracted using the TRIzol protocol. RNA libraries, generated using low-input strand specific RNA-Seq kit (Clontech), were multiplexed and sequenced with 50 basepair (bp) single end reads (SR 50 bp), and mapped using STAR v2.4.0g1 alignment. Differentially expressed (DE) genes between CCM and normal ECs were identified with DESeq2. QIAGEN’s Ingenuity® was used to conduct functional enrichment analysis on the DE genes, defining canonical pathways associated with DE genes.

Results: There were 774 DE genes ( P <0.05; Fold-change>4). Most significant enriched canonical pathways were inflammation related (the highest enriched were signaling in T-helper cells, complement system and leukocyte extravasation signaling). Other pathways related to extracellular matrix and actin signaling (Rac, Paxillin, actin cytoskeleton and integrin signaling), angiogenesis, MMPs and the coagulation cascade.

Conclusion: Differential transciptome analysis is feasible in CCM ECs in situ. It validates previously postulated disease mechanisms, and identifies other candidates for future study. This approach can categorize disease-related gene activity in lesions with different genotypes, clinical severity, and therapeutic interventions.

Abstract 126: Phenotypic Features of Murine Models of Cerebral Cavernous Malformations

Introduction: Cerebral cavernous malformations (CCM) are hemorrhagic lesions causing stroke and epilepsy. They develop with loss of function of three known genes in endothelial cells (ECs). Mice heterozygous for Ccm 1, 2 or 3 genes develop CCMs stochastically during life (“chronic models”), especially when bred in a background predisposing to somatic mutations ( p53 or Msh2 loss) . CCM lesions can also be generated in the developing hindbrain and retinas by Cre-recombinase induced homozygous loss of Ccm 1, 2, or 3 genes in the immediate postnatal period (“acute models”). We hypothesized that the CCM lesions which develop in the various models reflect different phenotypic features of the human disease.

Methods: Eight murine models of CCM were used in this study and defined as being chronic ( Ccm1 +/- Msh2 -/- , Ccm3 +/- and Ccm3 +/- Trp53 -/- ) or acute ( Pdgfb iCreERT2 Ccm1 fl/fl , Pdgfb iCreERT2 Ccm3 fl/fl and Cdh5 CreERT2 Ccm1 fl/fl ). Volumetric lesion burden was assessed using micro-CT after adjusting for total brain volume. Other phenotypic markers were assessed including the prevalence of ECs with Rho-associated protein kinase (ROCK) activity, and quantitation of B and T cells infiltration and non-heme iron deposition in the CCM lesions.

Results: The acute neonatal models showed higher adjusted volume lesion burden than the paired chronic model (p=0.013). CCM EC ROCK activity was similar in the acute and chronic models. Background brain EC ROCK activity in chronic models was higher than that in acute model (p=0.012). CCM lesions in chronic models (16 lesions/13 mice) had higher integrated iron intensity per lesion area compared to the acute lesions (12 lesions/9 mice) (p=0.03). Chronic lesions had a higher number of B cells (p=0.005), more T cells (p=0.04) per lesion area, and more combined lymphocytes (p=0.002) per lesion area compared to the acute model.

Conclusion: The acute model harbored a significantly higher lesion burden making them suitable for studying lesion genesis mechanisms. The chronic model however is more suited to study the role of inflammation and iron deposition in CCM, hallmark features of clinically relevant CCM lesions in man.