Somatic variants of MAP3K3 are sufficient to cause cerebral and spinal cord cavernous malformations

Targeted Therapies for Slow-Flow Vascular Malformations

Advances in genetic sequencing technologies have enabled the identification of key activating somatic variants in cellular signalling pathways involved in the pathogenesis of vascular malformations. Given that these genetic variants are also implicated in the pathogenesis of several cancers, the repurposing of targeted therapies developed in oncology has been increasingly investigated for treating vascular malformations. This review provides an update on the current evidence for targeted therapies in slow-flow vascular malformations, particularly in the context of gain-of-function variants in the PI3K/AKT/mTOR pathway.

Map3k3 I441M Knock-In Mouse Model of Cerebral Cavernous Malformations

BACKGROUND

Cerebral cavernous malformations (CCMs) refer to vascular dysplasia primarily found in the brain, affecting ≈0.5% of the population. A somatic Map3k3I441M mutation has been found in ≈40% of patients with sporadic CCMs, which were typically accompanied by somatic gain-of-function mutations in PIK3CA. Although mouse models of adeno-associated virus-BR1-mediated mutant overexpression have been reported, these models have limitations in representing clinical specimens of CCMs, which typically harbor single allele mutation in Map3k3. A Map3k3I441M knock-in murine model of CCMs has not yet been established.

METHODS

The Map3k3I441M knock-in mice were crossed with Cdh5-creERT2 mice to induce mutant gene expression specifically in endothelial cells. Subsequently, Map3k3I441M mice were bred with Ptenfl/fl mice to generate Map3k3I441M; Ptenfl/fl mice. In both murine models, CCM lesions were examined using magnetic resonance imaging, while single-cell RNA sequencing and immunostaining were utilized to investigate the pathomechanism of the mutation. Finally, we administered an mTOR (mechanistic target of rapamycin) inhibitor to explore its therapeutic effect on lesions of both murine models.

RESULTS

Both endothelial Map3k3I441M mutant juvenile mice and Map3k3I441M; Ptenfl/fl mice developed abnormal lesions with human CCM characteristics. In Map3k3I441M mice, the mutant promoted endothelial apoptosis, while activation of the PI3K (phosphatidylinositol 3-kinase) pathway was able to activate the downstream AKT (protein kinase B)/mTOR/p-S6 (phosphorylated S6 ribosomal protein) pathway and upregulate VEGFA (vascular endothelial growth factor A) expression, counteracting apoptosis, and facilitating lesion progression. The activation of PI3K signaling is required for Map3k3I441M to generate CCM-like lesions in adult mice. Finally, we demonstrated that rapamycin effectively inhibited the formation of lesions in the Map3k3I441M mice and Map3k3I441M; Ptenfl/fl mice.

CONCLUSIONS

Map3k3I441M heterozygous is sufficient to induce lesions in juvenile mice, while the additional activation of PI3K signaling is required for the effective formation of CCMs at the adult stage. The Map3k3I441M murine model provides a preclinical model for further mechanistic and therapeutic studies of CCMs.

Cerebral Cavernous Malformation: From Genetics to Pharmacotherapy

INTRODUCTION

Cerebral cavernous malformation (CCM) is a type of cerebrovascular abnormality in the central nervous system linked to both germline and somatic genetic mutations. Recent preclinical and clinical studies have shown that various drugs can effectively reduce the burden of CCM lesions. Despite significant progress, the mechanisms driving CCM remain incompletely understood, and to date, no drugs have been developed that can cure or prevent CCM. This review aims to explore the genetic mutations, molecular mechanisms, and pharmacological interventions related to CCM.

METHODS

Literatures on the genetic mechanisms and pharmacological treatments of CCM can be searched in PubMed and Web of Science.

RESULTS

Germline and somatic mutations mediate the onset and development of CCM through several molecular pathways. Medications such as statins, fasudil, rapamycin, and propranolol can alleviate CCM symptoms or hinder its progression by specifically modulating the corresponding targets.

CONCLUSIONS

Understanding the molecular mechanisms underlying CCM offers potential for targeted therapies. Further research into novel mutations and treatment strategies is essential for improving patient outcomes.

Cerebral vascular malformations: pathogenesis and therapy

Cerebral vascular malformations (CVMs), particularly cerebral cavernous malformations and cerebral arteriovenous malformations, pose significant neurological challenges due to their complex etiologies and clinical implications. Traditionally viewed as congenital conditions with structural abnormalities, CVMs have been treated primarily through resection, embolization, and stereotactic radiosurgery. While these approaches offer some efficacy, they often pose risks to neurological integrity due to their invasive nature. Advances in next-generation sequencing, particularly high-depth whole-exome sequencing and bioinformatics, have facilitated the identification of gene variants from neurosurgically resected CVMs samples. These advancements have deepened our understanding of CVM pathogenesis. Somatic mutations in key mechanistic pathways have been identified as causative factors, leading to a paradigm shift in CVM treatment. Additionally, recent progress in noninvasive and minimally invasive techniques, including gene imaging genomics, liquid biopsy, or endovascular biopsies (endovascular sampling of blood vessel lumens), has enabled the identification of gene variants associated with CVMs. These methods, in conjunction with clinical data, offer potential for early detection, dynamic monitoring, and targeted therapies that could be used as monotherapy or adjuncts to surgery. This review highlights advancements in CVM pathogenesis and precision therapies, outlining the future potential of precision medicine in CVM management.

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.

Force-mediated recruitment and reprogramming of healthy endothelial cells drive vascular lesion growth

Force-driven cellular interactions are crucial for cancer cell invasion but remain underexplored in vascular abnormalities. Cerebral cavernous malformations (CCM), a vascular abnormality characterized by leaky vessels, involves CCM mutant cells recruiting wild-type endothelial cells to form and expand mosaic lesions. The mechanisms behind this recruitment remain poorly understood. Here, we use an in-vitro model of angiogenic invasion with traction force microscopy to reveal that hyper-angiogenic Ccm2-silenced endothelial cells enhance angiogenic invasion of neighboring wild-type cells through force and extracellular matrix-guided mechanisms. We demonstrate that mechanically hyperactive CCM2-silenced tips guide wild-type cells by transmitting pulling forces and by creating paths in the matrix, in a ROCKs-dependent manner. This is associated with reinforcement of β1 integrin and actin cytoskeleton in wild-type cells. Further, wild-type cells are reprogrammed into stalk cells and activate matrisome and DNA replication programs, thereby initiating proliferation. Our findings reveal how CCM2 mutants hijack wild-type cell functions to fuel lesion growth, providing insight into the etiology of vascular malformations. By integrating biophysical and molecular techniques, we offer tools for studying cell mechanics in tissue heterogeneity and disease progression.

Mapping cell diversity in human sporadic cerebral cavernous malformations

BACKGROUND

Cerebral cavernous malformation (CCM) is a low-flow, bleeding-prone vascular disease that can cause cerebral hemorrhage, seizure and neurological deficits. Its inheritance mode includes sporadic or autosomal dominant inheritance with incomplete penetrance, namely sporadic CCM (SCCM) and familial CCM. SCCM is featured by single lesion and single affection in a family. Among CCM patients especially SCCM, the pathogenesis of the corresponding phenotypes and pathological features or candidate genes have not been fully elucidated yet.

METHODS

Here, we performed in-depth single-cell RNA sequencing (scRNA-Seq) and bulk assay for transposase-accessible chromatin sequencing (ATAC-Seq) in SCCM and control patients. Further validation was conducted for the gene of interest using qPCR and RNA in situ hybridization (RNA FISH) techniques to provide further atlas and evidence for SCCM generative process.

RESULTS

We identified six cell types in the SCCM and control vessels and found that the expression of NEK1, RNPC3, FBRSL1, IQGAP2, MCUB, AP3B1, ESCO1, MYO9B and PVT1 were up-regulated in SCCM tissues. Among the six cell types, we found that compared with control conditions, PVT1 showed a rising peak which followed the pseudo-time axis in endothelial cell clusters of SCCM samples, while showed an increasing trend in smooth muscle cell clusters of SCCM samples. Further experiments indicated that, compared with the control vessels, PVT1 exhibited significantly elevated expression in SCCM samples.

CONCLUSION

In SCCM conditions, We found that in the process of development from control to lesion conditions, PVT1 showed a rising peak in endothelial cells and showed an increasing trend in smooth muscle cells at the same time. Overall, there was a significantly elevated expression of NEK1, RNPC3, FBRSL1, IQGAP2, MCUB, AP3B1, ESCO1, MYO9B and PVT1 in SCCM specimens compared to control samples.

Endothelial Myosin IIA Is Required for the Maintenance of Blood-Brain Barrier Integrity

Brain endothelial cells (ECs) are essential elements of the blood-brain barrier (BBB), maintaining its integrity through both paracellular junctions and transcellular transport systems. Myosin IIA, a multifunctional protein, plays a significant role in various cellular processes, including cytoskeletal maintenance, cell division, and signal transduction. While Myosin IIA has been implicated in bleeding and ischemic stroke, its role in regulating BBB integrity under physiological conditions remains unclear. In this study, we investigated the impact of Myosin IIA deficiency on BBB integrity using intravenous tracer injections and models of epilepsy. Flow cytometry, Western blot, and real-time PCR were employed to isolate brain cells and assess changes in protein and mRNA levels. Additionally, immunofluorescence staining and electron microscopy were used to explore alterations in protein expression and the structure of BBB. Our results demonstrate that endothelial Myosin IIA deficiency increased BBB permeability and exacerbated symptoms in BBB-related diseases. Mechanistically, we found that Myosin IIA modulates β-catenin transcription and protein interactions. The overexpression of β-catenin in brain endothelial Myosin IIA deficiency mice improved BBB integrity and reduced disease severity. This study establishes Myosin IIA as a critical regulator of BBB integrity and suggests new therapeutic targets for vascular diseases.

Astrocytic LRP1 enables mitochondria transfer to neurons and mitigates brain ischemic stroke by suppressing ARF1 lactylation

Low-density lipoprotein receptor-related protein-1 (LRP1) is an endocytic/signaling cell-surface receptor that regulates diverse cellular functions, including cell survival, differentiation, and proliferation. LRP1 has been previously implicated in the pathogenesis of neurodegenerative disorders, but there are inconsistencies in its functions. Therefore, whether and how LRP1 maintains brain homeostasis remains to be clarified. Here, we report that astrocytic LRP1 promotes astrocyte-to-neuron mitochondria transfer by reducing lactate production and ADP-ribosylation factor 1 (ARF1) lactylation. In astrocytes, LRP1 suppressed glucose uptake, glycolysis, and lactate production, leading to reduced lactylation of ARF1. Suppression of astrocytic LRP1 reduced mitochondria transfer into damaged neurons and worsened ischemia-reperfusion injury in a mouse model of ischemic stroke. Furthermore, we examined lactate levels in human patients with stroke. Cerebrospinal fluid (CSF) lactate was elevated in stroke patients and inversely correlated with astrocytic mitochondria. These findings reveal a protective role of LRP1 in brain ischemic stroke by enabling mitochondria-mediated astrocyte-neuron crosstalk.

Somatic BrafV600E mutation in the cerebral endothelium induces brain arteriovenous malformations

Current treatments of brain arteriovenous malformation (BAVM) are associated with considerable risks and at times incomplete efficacy. Therefore, a clinically consistent animal model of BAVM is urgently needed to investigate its underlying biological mechanisms and develop innovative treatment strategies. Notably, existing mouse models have limited utility due to heterogenous and untypical phenotypes of AVM lesions. Here we developed a novel mouse model of sporadic BAVM that is consistent with clinical manifestations in humans. Mice with BrafV600E mutations in brain ECs developed BAVM closely resembled that of human lesions. This strategy successfully induced BAVMs in mice across different age groups and within various brain regions. Pathological features of BAVM were primarily dilated blood vessels with reduced vascular wall stability, accompanied by spontaneous hemorrhage and neuroinflammation. Single-cell sequencing revealed differentially expressed genes that were related to the cytoskeleton, cell motility, and intercellular junctions. Early administration of Dabrafenib was found to be effective in slowing the progression of BAVMs; however, its efficacy in treating established BAVM lesions remained uncertain. Taken together, our proposed approach successfully induced BAVM that closely resembled human BAVM lesions in mice, rendering the model suitable for investigating the pathogenesis of BAVM and assessing potential therapeutic strategies.

Shear stress and pathophysiological PI3K involvement in vascular malformations

Molecular characterization of vascular anomalies has revealed that affected endothelial cells (ECs) harbor gain-of-function (GOF) mutations in the gene encoding the catalytic α subunit of PI3Kα (PIK3CA). These PIK3CA mutations are known to cause solid cancers when occurring in other tissues. PIK3CA-related vascular anomalies, or "PIKopathies," range from simple, i.e., restricted to a particular form of malformation, to complex, i.e., presenting with a range of hyperplasia phenotypes, including the PIK3CA-related overgrowth spectrum. Interestingly, development of PIKopathies is affected by fluid shear stress (FSS), a physiological stimulus caused by blood or lymph flow. These findings implicate PI3K in mediating physiological EC responses to FSS conditions characteristic of lymphatic and capillary vessel beds. Consistent with this hypothesis, increased PI3K signaling also contributes to cerebral cavernous malformations, a vascular disorder that affects low-perfused brain venous capillaries. Because the GOF activity of PI3K and its signaling partners are excellent drug targets, understanding PIK3CA's role in the development of vascular anomalies may inform therapeutic strategies to normalize EC responses in the diseased state. This Review focuses on PIK3CA's role in mediating EC responses to FSS and discusses current understanding of PIK3CA dysregulation in a range of vascular anomalies that particularly affect low-perfused regions of the vasculature. We also discuss recent surprising findings linking increased PI3K signaling to fast-flow arteriovenous malformations in hereditary hemorrhagic telangiectasias.

Discovery and Characterization of Ephrin B2 and EphB4 Dysregulation and Novel Mutations in Cerebral Cavernous Malformations: In Vitro and Patient-Derived Evidence of Ephrin-Mediated Endothelial Cell Pathophysiology

Intracranial vascular malformations manifest on a continuum ranging from predominantly arterial to predominantly venous in pathology. Cerebral cavernous malformations (CCMs) are capillary malformations that exist at the midpoint of this continuum. The axon guidance factor Ephrin B2 and its receptor EphB4 are critical regulators of vasculogenesis in the developing central nervous system. Ephrin B2/EphB4 dysregulation has been implicated in the pathogenesis of arterial-derived arteriovenous malformations and vein-based vein of Galen malformations. Increasing evidence supports the hypothesis that aberrant Ephrin B2/EphB4 signaling may contribute to developing vascular malformations, but their role in CCMs remains largely uncharacterized. Evidence of Ephrin dysregulation in CCMs would be important to establish a common link in the pathogenic spectrum of EphrinB2/Ephb4 dysregulation. By studying patient-derived primary CCM endothelial cells (CCMECs), we established that CCMECs are functionally distinct from healthy endothelial cell controls; CCMECs demonstrated altered patterns of migration, motility, and impaired tube formation. In addition to the altered phenotype, the CCMECs also displayed an increased ratio of EphrinB2/EphB4 compared to the healthy endothelial control cells. Furthermore, whole exome sequencing identified mutations in both EphrinB2 and EphB4 in the CCMECs. These findings identify functional alterations in the EphrinB2/EphB4 ratio as a feature linking pathophysiology across the spectrum of arterial, capillary, and venous structural malformations in the central nervous system while revealing a putative therapeutic target.

Understanding the pathogenesis of brain arteriovenous malformation: genetic variations, epigenetics, signaling pathways, and immune inflammation

Brain arteriovenous malformation (BAVM) is a rare but serious cerebrovascular disease whose pathogenesis has not been fully elucidated. Studies have found that epigenetic regulation, genetic variation and their signaling pathways, immune inflammation, may be the cause of BAVM the main reason. This review comprehensively analyzes the key pathways and inflammatory factors related to BAVMs, and explores their interplay with epigenetic regulation and genetics. Studies have found that epigenetic regulation such as DNA methylation, non-coding RNAs and m6A RNA modification can regulate endothelial cell proliferation, apoptosis, migration and damage repair of vascular malformations through different target gene pathways. Gene defects such as KRAS, ACVRL1 and EPHB4 lead to a disordered vascular environment, which may promote abnormal proliferation of blood vessels through ERK, NOTCH, mTOR, Wnt and other pathways. PDGF-B and PDGFR-β were responsible for the recruitment of vascular adventitial cells and smooth muscle cells in the extracellular matrix environment of blood vessels, and played an important role in the pathological process of BAVM. Recent single-cell sequencing data revealed the diversity of various cell types within BAVM, as well as the heterogeneous expression of vascular-associated antigens, while neutrophils, macrophages and cytokines such as IL-6, IL-1, TNF-α, and IL-17A in BAVM tissue were significantly increased. Currently, there are no specific drugs targeting BAVMs, and biomarkers for BAVM formation, bleeding, and recurrence are lacking clinically. Therefore, further studies on molecular biological mechanisms will help to gain insight into the pathogenesis of BAVM and develop potential therapeutic strategies.