Somatic activating mutations in Pik3ca cause sporadic venous malformations in mice and humans

Dysfunctional mechanotransduction regulates the progression of PIK3CA-driven vascular malformations

Somatic activating mutations in PIK3CA are common drivers of vascular and lymphatic malformations. Despite common biophysical signatures of tissues susceptible to lesion formation, including compliant extracellular matrix and low rates of perfusion, lesions vary in clinical presentation from localized cystic dilatation to diffuse and infiltrative vascular dysplasia. The mechanisms driving the differences in disease severity and variability in clinical presentation and the role of the biophysical microenvironment in potentiating progression are poorly understood. Here, we investigate the role of hemodynamic forces and the biophysical microenvironment in the pathophysiology of vascular malformations (VMs), and we identify hemodynamic shear stress and defective endothelial cell mechanotransduction as key regulators of lesion progression. We found that constitutive PI3K activation impaired flow-mediated endothelial cell alignment and barrier function. We show that defective shear stress sensing in PIK3CAE542K endothelial cells is associated with reduced myosin light chain phosphorylation, junctional instability, and defective recruitment of vinculin to cell-cell junctions. Using three dimensional (3D) microfluidic models of the vasculature, we demonstrate that PIK3CAE542K microvessels apply reduced traction forces and are unaffected by flow interruption. We further found that draining transmural flow resulted in increased sprouting and invasion responses in PIK3CAE542K microvessels. Mechanistically, constitutive PI3K activation decreased cellular and nuclear elasticity resulting in defective cellular tensional homeostasis in endothelial cells which may underlie vascular dilation, tissue hyperplasia, and hypersprouting in PIK3CA-driven venous and lymphatic malformations. Together, these results suggest that defective nuclear mechanics, impaired cellular mechanotransduction, and maladaptive hemodynamic responses contribute to the development and progression of PIK3CA-driven vascular malformations.

Microfluidic vessel-on-chip platform for investigation of cellular defects in venous malformations and responses to various shear stress and flow conditions

A novel microfluidic platform was designed to study the cellular architecture of endothelial cells (ECs) in an environment replicating the 3D organization and flow of blood vessels. In particular, the platform was constructed to investigate EC defects in slow-flow venous malformations (VMs) under varying shear stress and flow conditions. The platform featured a standard microtiter plate footprint containing 32 microfluidic units capable of replicating wall shear stress (WSS) in normal veins and enabling precise control of shear stress and flow directionality without the need for complex pumping systems. Using genetically engineered human umbilical vein endothelial cells (HUVECs) and induced pluripotent stem cell (iPSC)-derived ECs (iECs) to express the recurrent TIE2L914F VM mutation we assessed responses on EC orientation and area, actin organization, and Golgi polarization to uni- and bidirectional flow and varying WSS. Comparison of control and TIE2L914F expressing ECs showed differential cellular responses to flow and WSS in terms of cell shape elongation, orientation of F-actin, and Golgi polarization, indicating altered mechanosensory or mechanotransduction signaling pathways in the presence of the VM causative mutation. The data also revealed significant differences in how the primary and iPSC-derived iECs responded to flow. As a conclusion, the developed microfluidic platform allowed simulation of multiple flow conditions in a scalable and pumpless format. The design made it a desirable tool for studying different EC types as well as cellular changes in vascular disease. The platform should offer new opportunities for biomechanical research by providing a controlled environment to analyze the flow-dependent mechanosensory pathways in ECs.

A new hereditary PROS1 gene mutation caused isolated cortical venous thrombosis

BACKGROUND

Protein S deficiency is a rare inherited disease. We report the case of a young man who unexpectedly developed isolated cortical vein thrombosis (ICoVT) associated with a novel PROS1 mutation.

METHODS

Clinical symptoms were recorded, and physical examinations conducted. Comprehensive laboratory tests included routine coagulation function tests, protein C activity, and antithrombin III levels. Advanced imaging techniques, such as magnetic resonance imaging (MRI), magnetic resonance venography (MRV), and computed tomography angiography (CTA) were employed. We also performed genetic analysis on the patient and his parents.

RESULTS

The patient presented with headaches and paroxysmal convulsions without identifiable triggers. Physical examinations and routine coagulation tests were generally normal, except for a markedly reduced protein S activity at 21.2 %. MRI scans revealed right parietal cerebral hemorrhage and thickening of the cortical vein, characterized by high T1-weighted Imaging and low T2-weighted Imaging and Fluid-Attenuated Inversion Recovery signals. CTA and Doppler ultrasound of the lower limbs showed no abnormalities. Family history revealed that his father had suffered from multiple venous thromboses. Genetic testing identified a missense mutation (c.1912G>T p.Gly638Cys) in both the patient and his father, along with a duplication of approximately 403.6 kb on chromosome 3q26.32-33 in the patient.

CONCLUSIONS

This case highlights a novel PROS1 missense mutation and its significant role in development of cortical venous thrombosis. It provides a new insight into the genetic basis of autosomal dominant thrombophilia associated with protein S deficiency (THPH5).

PPP2R5D-Related Neurodevelopmental Disorder and Multiple Haemangiomas: A Novel Phenotypic Trait?

BACKGROUND

Houge-Janssens syndrome 1 is a condition with onset in early childhood caused by heterozygous pathogenic variants in the PPP2R5D gene, which encodes a B56 regulatory subunit of the serine/threonine protein phosphatase 2A (PP2A). There is evidence that the PP2A-PPP2R5D complex is involved in regulating the phosphatidylinositol 3-kinase (PI3K)/AKT signalling pathway, which is crucial for several cellular processes, including the pathogenesis and progression of haemangiomas.

CASE PRESENTATION

We report the first PPP2R5D-related neurodevelopmental disorder case from Sardinia, a child with transient hypoglycaemia, facial dysmorphisms, and multiple haemangiomas. Whole Exome Sequencing analysis confirmed the clinical suspicion, detecting the presence of the de novo missense variant c.592G>A in the PPP2R5D gene.

CONCLUSIONS

Haemangiomas have never been linked to the syndromic phenotype of the PPP2R5D-associated disorder. The close correlation between the PP2A enzyme and the PI3K/AKT signalling pathway suggests the possible correlation between its dysfunction and activation of haemangiogenesis. Our report highlights a possible link between the PPP2R5D-related disorder and altered angiogenesis, characterizing diffuse haemangiomas as a possible novel phenotypic trait of this condition.

Alk1/Endoglin signaling restricts vein cell size increases in response to hemodynamic cues

Hemodynamic cues are thought to control blood vessel hierarchy through a shear stress set point, where flow increases lead to blood vessel diameter expansion, while decreases in blood flow cause blood vessel narrowing. Aberrations in blood vessel diameter control can cause congenital arteriovenous malformations (AVMs). We show in zebrafish embryos that while arteries behave according to the shear stress set point model, veins do not. This behavior is dependent on distinct arterial and venous endothelial cell (EC) shapes and sizes. We show that arterial ECs enlarge more strongly when experiencing higher flow, as compared to vein cells. Through the generation of chimeric embryos, we discover that this behavior of vein cells depends on the bone morphogenetic protein (BMP) pathway components Endoglin and Alk1. Endoglin (eng) or alk1 (acvrl1) mutant vein cells enlarge when in normal hemodynamic environments, while we do not observe a phenotype in either acvrl1 or eng mutant ECs in arteries. We further show that an increase in vein diameters initiates AVMs in eng mutants, secondarily leading to higher flow to arteries. These enlarge in response to higher flow through increasing arterial EC sizes, fueling the AVM. This study thus reveals a mechanism through which BMP signaling limits vein EC size increases in response to flow and provides a framework for our understanding of how a small number of mutant vein cells via flow-mediated secondary effects on wildtype arterial ECs can precipitate larger AVMs in disease conditions, such as hereditary hemorrhagic telangiectasia (HHT).

Dysfunctional mechanotransduction regulates the progression of PIK3CA-driven vascular malformations

Somatic activating mutations in PIK3CA are common drivers of vascular and lymphatic malformations. Despite common biophysical signatures of tissues susceptible to lesion formation, including compliant extracellular matrix and low rates of perfusion, lesions vary in clinical presentation from localized cystic dilatation to diffuse and infiltrative vascular dysplasia. The mechanisms driving the differences in disease severity and variability in clinical presentation and the role of the biophysical microenvironment in potentiating progression are poorly understood. Here, we investigate the role of hemodynamic forces and the biophysical microenvironment in the pathophysiology of vascular malformations, and we identify hemodynamic shear stress and defective endothelial cell mechanotransduction as key regulators of lesion progression. We found that constitutive PI3K activation impaired flow-mediated endothelial cell alignment and barrier function. We show that defective shear stress sensing in PIK3CA E542K endothelial cells is associated with reduced myosin light chain phosphorylation, junctional instability, and defective recruitment of vinculin to cell-cell junctions. Using 3D microfluidic models of the vasculature, we demonstrate that PIK3CA E542K microvessels apply reduced traction forces and are unaffected by flow interruption. We further found that draining transmural flow resulted in increased sprouting and invasion responses in PIK3CA E542K microvessels. Mechanistically, constitutive PI3K activation decreased cellular and nuclear elasticity resulting in defective cellular tensional homeostasis in endothelial cells which may underlie vascular dilation, tissue hyperplasia, and hypersprouting in PIK3CA-driven venous and lymphatic malformations. Together, these results suggest that defective nuclear mechanics, impaired cellular mechanotransduction, and maladaptive hemodynamic responses contribute to the development and progression of PIK3CA-driven vascular malformations.

Bleomycin induces endothelial cell pyroptosis and regulates fibrosis by activating the NLRP3/caspase-1/GSDMD pathway: a possible mechanism contributing to the sclerotherapy of venous malformations

Venous malformations (VMs) are slow-flow vascular anomalies that pose significant health challenges. Bleomycin (BLM) is frequently used in Sclerotherapy for VMs, but its mechanism, particularly through pyroptosis, remains poorly understood. This study explores the role of BLM-induced endothelial cell pyroptosis in VMs sclerotherapy and its regulatory effects on fibrosis via the NLRP3/caspase-1/GSDMD pathway. Using a combination of TUNEL staining, Western blotting, and immunohistochemistry, we investigated the effects of BLM on VMs and endothelial cells in vitro. Pyroptosis and fibrosis were quantified, and the involvement of the NLRP3/caspase-1/GSDMD pathway was assessed. BLM treatment significantly increased pyroptosis and fibrosis in VMs tissues and cultured endothelial cells. Activation of the NLRP3/caspase-1/GSDMD pathway was crucial for these effects, which could be mitigated by pathway inhibition. BLM regulates fibrosis and induces pyroptosis through the NLRP3/caspase-1/GSDMD pathway in VMs. Understanding this mechanism could enhance the effectiveness and safety of Sclerotherapy in clinical settings.

Targeted treatments for vascular malformations: current state of the art

Vascular malformations, which arise from anomalies in angiogenesis, encompass capillary, lymphatic, venous, arteriovenous, and mixed malformations, each affecting specific vessel types. Historically, therapeutic options such as sclerotherapy and surgery have shown limited efficacy in complicated malformations. Most vascular malformations stem from hereditary or somatic mutations akin to oncogenic alterations, activating the PI3K-AKT-mTOR, RAS-MAPK-ERK, and G-protein coupled receptor pathways. Recognizing the parallels with oncogenic mutations, we emphasize the potential of targeted molecular inhibitors in the treatment of vascular malformations by repurposing anticancer drugs. This review delves into the recent development and future use of such agents for the management of slow- and fast-flow vascular malformations, including in more specific situations, such as prenatal treatment and the management of associated coagulopathies.

Organismal metabolism regulates the expansion of oncogenic PIK3CA mutant clones in normal esophagus

Oncogenic PIK3CA mutations generate large clones in aging human esophagus. Here we investigate the behavior of Pik3ca mutant clones in the normal esophageal epithelium of transgenic mice. Expression of a heterozygous Pik3caH1047R mutation drives clonal expansion by tilting cell fate toward proliferation. CRISPR screening and inhibitor treatment of primary esophageal keratinocytes confirmed the PI3K-mTOR pathway increased mutant cell competitive fitness. The antidiabetic drug metformin reduced mutant cell advantage in vivo and in vitro. Conversely, metabolic conditions such as type 1 diabetes or diet-induced obesity enhanced the competitive fitness of Pik3caH1047R cells. Consistently, we found a higher density of PIK3CA gain-of-function mutations in the esophagus of individuals with high body mass index compared with those with normal weight. We conclude that the metabolic environment selectively influences the evolution of the normal epithelial mutational landscape. Clinically feasible interventions to even out signaling imbalances between wild-type and mutant cells may limit the expansion of oncogenic mutants in normal tissues.

GNA14 and GNAQ somatic mutations cause spinal and intracranial extra-axial cavernous hemangiomas

Extra-axial cavernous hemangiomas (ECHs) are complex vascular lesions mainly found in the spine and cavernous sinus. Their removal poses significant risk due to their vascularity and diffuse nature, and their genetic underpinnings remain incompletely understood. Our approach involved genetic analyses on 31 tissue samples of ECHs employing whole-exome sequencing and targeted deep sequencing. We explored downstream signaling pathways, gene expression changes, and resultant phenotypic shifts induced by these mutations, both in vitro and in vivo. In our cohort, 77.4% of samples had somatic missense variants in GNA14, GNAQ, or GJA4. Transcriptomic analysis highlighted significant pathway upregulation, with the GNAQ c.626A>G (p.Gln209Arg) mutation elevating PI3K-AKT-mTOR and angiogenesis-related pathways, while GNA14 c.614A>T (p.Gln205Leu) mutation led to MAPK and angiogenesis-related pathway upregulation. Using a mouse xenograft model, we observed enlarged vessels from these mutations. Additionally, we initiated rapamycin treatment in a 14-year-old individual harboring the GNAQ c.626A>G (p.Gln209Arg) variant, resulting in gradual regression of cutaneous cavernous hemangiomas and improved motor strength, with minimal side effects. Understanding these mutations and their pathways provides a foundation for developing therapies for ECHs resistant to current therapies. Indeed, the administration of rapamycin in an individual within this study highlights the promise of targeted treatments in treating these complex lesions.

Genetic mutations and phenotype characteristics in peripheral vascular malformations: A systematic review

Vascular malformations (VMs) are clinically diverse with regard to the vessel type, anatomical location, tissue involvement and size. Consequently, symptoms and disease impact differ significantly. Diverse causative mutations in more and more genes are discovered and play a major role in the development of VMs. However, the relationship between the underlying causative mutations and the highly variable phenotype of VMs is not yet fully understood. In this systematic review, we aimed to provide an overview of known causative mutations in genes in VMs and discuss associations between the causative mutations and clinical phenotypes. PubMed and EMBASE libraries were systematically searched on November 9th, 2022 for randomized controlled trials and observational studies reporting causative mutations in at least five patients with peripheral venous, lymphatic, arteriovenous and combined malformations. Study quality was assessed with the Newcastle-Ottawa Scale. Data were extracted on patient and VM characteristics, molecular sequencing method and results of molecular analysis. In total, 5667 articles were found of which 69 studies were included, reporting molecular analysis in a total of 4261 patients and 1686 (40%) patients with peripheral VMs a causative mutation was detected. In conclusion, this systematic review provides a comprehensive overview of causative germline and somatic mutations in various genes and associated phenotypes in peripheral VMs. With these findings, we attempt to better understand how the underlying causative mutations in various genes contribute to the highly variable clinical characteristics of VMs. Our study shows that some causative mutations lead to a uniform phenotype, while other causal variants lead to more varying phenotypes. By contrast, distinct causative mutations may lead to similar phenotypes and result in almost indistinguishable VMs. VMs are currently classified based on clinical and histopathology features, however, the findings of this systematic review suggest a larger role for genotype in current diagnostics and classification.

Targeted therapy for capillary-venous malformations

Sporadic venous malformations are genetic conditions primarily caused by somatic gain-of-function mutation of PIK3CA or TEK, an endothelial transmembrane receptor signaling through PIK3CA. Venous malformations are associated with pain, bleedings, thrombosis, pulmonary embolism, esthetic deformities and, in severe cases, life-threatening situations. No authorized medical treatment exists for patients with venous malformations. Here, we created a genetic mouse model of PIK3CA-related capillary venous malformations that replicates patient phenotypes. We showed that these malformations only partially signal through AKT proteins. We compared the efficacy of different drugs, including rapamycin, a mTORC1 inhibitor, miransertib, an AKT inhibitor and alpelisib, a PI3Kα inhibitor at improving the lesions seen in the mouse model. We demonstrated the effectiveness of alpelisib in preventing vascular malformations' occurrence, improving the already established ones, and prolonging survival. Considering these findings, we were authorized to treat 25 patients with alpelisib, including 7 children displaying PIK3CA (n = 16) or TEK (n = 9)-related capillary venous malformations resistant to usual therapies including sirolimus, debulking surgical procedures or percutaneous sclerotherapies. We assessed the volume of vascular malformations using magnetic resonance imaging (MRI) for each patient. Alpelisib demonstrated improvement in all 25 patients. Vascular malformations previously considered intractable were reduced and clinical symptoms were attenuated. MRI showed a decrease of 33.4% and 27.8% in the median volume of PIK3CA and TEK malformations respectively, over 6 months on alpelisib. In conclusion, this study supports PI3Kα inhibition as a promising therapeutic strategy in patients with PIK3CA or TEK-related capillary venous malformations.

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.

Progressive vascular tumor in infant: A case report and literature review of PIK3CA vascular malformation

PURPOSE

Vascular anomalies are classified as either vascular tumors or vascular malformations. Vascular malformations can be difficult to diagnose and treat in the pediatric population and can masquerade as malignant processes. Understanding the genetics behind vascular malformations can lead to identification of specific mutations which can be treated with targeted immunotherapy.

METHODS

Our case presents a pediatric patient with progressively enlarging vascular malformation despite multiple surgical resections and systemic medical treatments who underwent genetic evaluation and was found to have PIK3CA mutation.

RESULTS

After identification of PIK3CA mutation, our patient was successfully treated with the p110ɑ-specific inhibitor, alpelisib, with both shrinkage of malformation on follow-up imaging as well as gains in her developmental milestones.

CONCLUSION

Progressive vascular malformations in the pediatric population can be hard to diagnose and treat and are thought to arise from somatic mutations. Our case highlights a patient with progressive malformation despite multiple surgical resections who was successfully treated with targeted immunotherapy after proper identification of genetic mutation.

Lymphatic malformations: mechanistic insights and evolving therapeutic frontiers

The lymphatic vascular system is gaining recognition for its multifaceted role and broad pathological significance. Once perceived as a mere conduit for interstitial fluid and immune cell transport, recent research has unveiled its active involvement in critical physiological processes and common diseases, including inflammation, autoimmune diseases, and atherosclerosis. Consequently, abnormal development or functionality of lymphatic vessels can result in serious health complications. Here, we discuss lymphatic malformations (LMs), which are localized lesions that manifest as fluid-filled cysts or extensive infiltrative lymphatic vessel overgrowth, often associated with debilitating, even life-threatening, consequences. Genetic causes of LMs have been uncovered, and several promising drug-based therapies are currently under investigation and will be discussed.

Comprehensive phenotypic and genomic characterization of venous malformations

Venous malformations (VMs) are the most common vascular malformations. TEK and PIK3CA are the causal genes of VMs, and may be involved in the PI3K/AKT pathway. However, the downstream mechanisms underlying the TEK or PIK3CA mutations in VMs are not completely understood. This study aimed to identify a possible association between genetic mutations and clinicopathological features. A retrospective clinical, pathological, and genetic study of 114 patients with VMs was performed. TEK, PIK3CA, and combined TEK/PIK3CA mutations were identified in 49 (43%), 13 (11.4%), and 2 (1.75%) patients, respectively. TEK-mutant VMs more commonly occurred in younger patients than TEK and PIK3CA mutation-negative VMs (other-mutant VMs), and showed more frequent skin involvement and no lymphocytic aggregates. No significant differences were observed in sex, location of occurrence, malformed vessel size, vessel density, or thickness of the vascular smooth muscle among the VM genotypes. Immunohistochemical analysis revealed that the expression levels of phosphorylated AKT (p-AKT) were higher in the TEK-mutant VMs than those in PIK3CA-mutant and other-mutant VMs. The expression levels of p-mTOR and its downstream effectors were higher in all the VM genotypes than those in normal vessels. Spatial transcriptomics revealed that the genes involved in "blood vessel development", "positive regulation of cell migration", and "extracellular matrix organization" were up-regulated in a TEK-mutant VM. Significant genotype-phenotype correlations in clinical and pathological features were observed among the VM genotypes, indicating gene-specific effects. Detailed analysis of gene-specific effects in VMs may offer insights into the underlying molecular pathways and implications for targeted therapies.

Pathophysiology of Slow-Flow Vascular Malformations: Current Understanding and Unanswered Questions

Background

Slow-flow vascular malformations include venous, lymphatic, and lymphaticovenous malformations. Recent studies have linked genetic variants hyperactivating either the PI3K/AKT/mTOR and/or RAS/RAF/MAPK signaling pathways with slow-flow vascular malformation development, leading to the use of pharmacotherapies such as sirolimus and alpelisib. It is important that clinicians understand basic and translational research advances in slow-flow vascular malformations.

Methods

A literature review of basic science publications in slow-flow vascular malformations was performed on Pubmed, using search terms "venous malformation," "lymphatic malformation," "lymphaticovenous malformation," "genetic variant," "genetic mutation," "endothelial cells," and "animal model." Relevant publications were reviewed and summarized.

Results

The study of patient tissues and the use of primary pathogenic endothelial cells from vascular malformations shed light on their pathological behaviors, such as endothelial cell hyperproliferation and disruptions in vessel architecture. The use of xenograft and transgenic animal models confirmed the pathogenicity of genetic variants and allowed for preclinical testing of potential therapies. These discoveries underscore the importance of basic and translational research in understanding the pathophysiology of vascular malformations, which will allow for the development of improved biologically targeted treatments.

Conclusion

Despite basic and translation advances, a cure for slow-flow vascular malformations remains elusive. Many questions remain unanswered, including how genotype variants result in phenotypes, and genotype-phenotype heterogeneity. Continued research into venous and lymphatic malformation pathobiology is critical in understanding the mechanisms by which genetic variants contribute to vascular malformation phenotypic features.

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

Cerebral cavernous malformations (CCMs) and spinal cord cavernous malformations (SCCMs) are common vascular abnormalities of the CNS that can lead to seizure, haemorrhage and other neurological deficits. Approximately 85% of patients present with sporadic (versus congenital) CCMs. Somatic mutations in MAP3K3 and PIK3CA were recently reported in patients with sporadic CCM, yet it remains unknown whether MAP3K3 mutation is sufficient to induce CCMs. Here we analysed whole-exome sequencing data for patients with CCM and found that ∼40% of them have a single, specific MAP3K3 mutation [c.1323C>G (p.Ile441Met)] but not any other known mutations in CCM-related genes. We developed a mouse model of CCM with MAP3K3I441M uniquely expressed in the endothelium of the CNS. We detected pathological phenotypes similar to those found in patients with MAP3K3I441M. The combination of in vivo imaging and genetic labelling revealed that CCMs were initiated with endothelial expansion followed by disruption of the blood-brain barrier. Experiments with our MAP3K3I441M mouse model demonstrated that CCM can be alleviated by treatment with rapamycin, the mTOR inhibitor. CCM pathogenesis has usually been attributed to acquisition of two or three distinct genetic mutations involving the genes CCM1/2/3 and/or PIK3CA. However, our results demonstrate that a single genetic hit is sufficient to cause CCMs.

Whole mount of adult ear skin as a model to study vascular malformations

BACKGROUND

Genetic analysis in human patients has linked mutations in PIK3CA, the catalytic subunit of PI-3'Kinase, to sporadic incidences of vascular malformations.

METHODS

We have developed a mouse model with inducible and endothelial-specific expression of PIK3CAH1047R , resulting in the development of vascular malformations. Systemic induction of this mutation in adult mice results in rapid lethality, limiting our ability to track and study these lesions; therefore, we developed a topical and local induction protocol using the active metabolite of tamoxifen, 4OH-T, on the ear skin of adults.

RESULTS

This approach allows us to successfully model the human disease in a mature and established vascular bed and track the development of vascular malformations. To validate the utility of this model, we applied a topical rapamycin ointment, as rapamycin is therapeutically beneficial to patients in clinical trials. We found that the induced ear lesions showed significant attenuation after treatment, which was easily quantified.

CONCLUSIONS

These data collectively provide evidence of a new model to study vascular malformations in adult tissues, which should be particularly useful in environments lacking specialized small-animal imaging facilities.

Contemporary management of extracranial vascular malformations

Vascular malformations are congenital vascular anomalies that originate because of disorganized angiogenesis, most commonly from spontaneous somatic genetic mutations. The modern management of vascular malformations requires a multidisciplinary team that offers patients the gamut of medical, surgical, and percutaneous treatment options with supportive care. This manuscript discusses the standard and contemporary management strategies surrounding extracranial vascular malformations and overgrowth syndromes.

Role of UDP-glucose ceramide glucosyltransferase in venous malformation

Venous malformation (VM) results from the abnormal growth of the vasculature; however, the detailed molecular mechanism remains unclear. As a glycosyltransferase, UDP-glucose ceramide glucosyltransferase (UGCG) is localized to the Golgi body and is a key enzyme in the first step of glycosphingolipid synthesis. Here, we aimed to explore the relationship between UGCG and the development of VM. First, investigations using RT-qPCR and Western blotting on the diseased vasculature of VM patients and normal vascular tissues revealed that UGCG expression was markedly elevated in the diseased vessels. Subsequently, immunofluorescence assay showed that UGCG was co-localized with CD31, an endothelial cell marker, in tissues from patients with VM and healthy subjects. Then, we established TIE2-L914F-mutant human umbilical vein endothelial cells (HUVECs) by lentivirus transfection. Next, Western blotting revealed that UGCG expression was considerably higher in HUVECs^TIE2-L914F. In addition, we established a UGCG-overexpressing HUVECs line by plasmid transfection. With the CCK8 cell proliferation experiment, wound healing assay, and tube formation assay, we found that UGCG could promote the proliferation, migration, and tube formation activity of HUVECs, whereas the inhibition of UGCG could inhibit the proliferation, migration, and tube formation activity of HUVECs^TIE2-L914F. Finally, Western blotting revealed that UGCG regulates the AKT/mTOR pathway in HUVECs. These data demonstrated that UGCG can affect the activity of vascular endothelial cells and regulate the AKT/mTOR signaling pathway; this is a potential mechanism underlying VM pathogenesis.

Profiling PIK3CA variants in disorders of somatic mosaicism

Purpose

Variants in PIK3CA (encoding p110α; the catalytic subunit of PI3K) characterize some disorders of somatic mosaicism (DoSM) conditions with clinical features, including sporadic overgrowth and vascular malformations. Here, we profile PIK3CA variants in DoSM.

Methods

We applied a next-generation, sequencing-based, laboratory-developed test, using an average coverage of approximately 2000× for up to 37 genes associated with DoSM, on a cohort of 1197 patients with DoSM referred for clinical genomics services between 2013 and 2022.

Results

We identified clinically reportable variants in 747 (62.4%) individuals in this cohort. Notably, 371 clinically reportable variants in PIK3CA were identified in 368 patients, constituting approximately 49.2% of all patients with reportable findings. Variants in the C2 domain of p110α are enriched in DoSM (this cohort) compared with those of cancer (Catalogue of Somatic Mutations in Cancer [COSMIC] database), highlighting the role of the C2 domain in driving uncontrolled cell proliferation in DoSM. Furthermore, we report 17 novel variants in PIK3CA that are not previously reported in DoSM and describe clinical presentation correlation for 4 novel variants.

Conclusion

Our findings from the largest single-center cohort of patients with DoSM expand the spectrum of variants in PIK3CA and shed light on the less-studied role of the C2 domain in the pathogenesis of DoSM.

Beyond PI3Ks: targeting phosphoinositide kinases in disease

Lipid phosphoinositides are master regulators of almost all aspects of a cell's life and death and are generated by the tightly regulated activity of phosphoinositide kinases. Although extensive efforts have focused on drugging class I phosphoinositide 3-kinases (PI3Ks), recent years have revealed opportunities for targeting almost all phosphoinositide kinases in human diseases, including cancer, immunodeficiencies, viral infection and neurodegenerative disease. This has led to widespread efforts in the clinical development of potent and selective inhibitors of phosphoinositide kinases. This Review summarizes our current understanding of the molecular basis for the involvement of phosphoinositide kinases in disease and assesses the preclinical and clinical development of phosphoinositide kinase inhibitors.

Familial CCM Genes Might Not Be Main Drivers for Pathogenesis of Sporadic CCMs-Genetic Similarity between Cancers and Vascular Malformations

Cerebral cavernous malformations (CCMs) are abnormally dilated intracranial capillaries that form cerebrovascular lesions with a high risk of hemorrhagic stroke. Recently, several somatic "activating" gain-of-function (GOF) point mutations in PIK3CA (phosphatidylinositol-4, 5-bisphosphate 3-kinase catalytic subunit p110α) were discovered as a dominant mutation in the lesions of sporadic forms of cerebral cavernous malformation (sCCM), raising the possibility that CCMs, like other types of vascular malformations, fall in the PIK3CA-related overgrowth spectrum (PROS). However, this possibility has been challenged with different interpretations. In this review, we will continue our efforts to expound the phenomenon of the coexistence of gain-of-function (GOF) point mutations in the PIK3CA gene and loss-of-function (LOF) mutations in CCM genes in the CCM lesions of sCCM and try to delineate the relationship between mutagenic events with CCM lesions in a temporospatial manner. Since GOF PIK3CA point mutations have been well studied in reproductive cancers, especially breast cancer as a driver oncogene, we will perform a comparative meta-analysis for GOF PIK3CA point mutations in an attempt to demonstrate the genetic similarities shared by both cancers and vascular anomalies.

Immune-interacting lymphatic endothelial subtype at capillary terminals drives lymphatic malformation

Oncogenic mutations in PIK3CA, encoding p110α-PI3K, are a common cause of venous and lymphatic malformations. Vessel type-specific disease pathogenesis is poorly understood, hampering development of efficient therapies. Here, we reveal a new immune-interacting subtype of Ptx3-positive dermal lymphatic capillary endothelial cells (iLECs) that recruit pro-lymphangiogenic macrophages to promote progressive lymphatic overgrowth. Mouse model of Pik3caH1047R-driven vascular malformations showed that proliferation was induced in both venous and lymphatic ECs but sustained selectively in LECs of advanced lesions. Single-cell transcriptomics identified the iLEC population, residing at lymphatic capillary terminals of normal vasculature, that was expanded in Pik3caH1047R mice. Expression of pro-inflammatory genes, including monocyte/macrophage chemokine Ccl2, in Pik3caH1047R-iLECs was associated with recruitment of VEGF-C-producing macrophages. Macrophage depletion, CCL2 blockade, or anti-inflammatory COX-2 inhibition limited Pik3caH1047R-driven lymphangiogenesis. Thus, targeting the paracrine crosstalk involving iLECs and macrophages provides a new therapeutic opportunity for lymphatic malformations. Identification of iLECs further indicates that peripheral lymphatic vessels not only respond to but also actively orchestrate inflammatory processes.

Genetics of brain arteriovenous malformations and cerebral cavernous malformations

Cerebrovascular malformations comprise abnormal development of cerebral vasculature. They can result in hemorrhagic stroke due to rupture of lesions as well as seizures and neurological defects. The most common forms of cerebrovascular malformations are brain arteriovenous malformations (bAVMs) and cerebral cavernous malformations (CCMs). They occur in both sporadic and inherited forms. Rapidly evolving molecular genetic methodologies have helped to identify causative or associated genes involved in genesis of bAVMs and CCMs. In this review, we highlight the current knowledge regarding the genetic basis of these malformations.

Review of diagnosis, differential diagnosis, and management of retroperitoneal lymphangioma

Lymphatic malformation (LM) is the currently preferred term for what was previously known as lymphangioma. Retroperitoneal LMs are extremely rare, benign, cystic masses that arise from lymphatic vessels. They can be challenging to diagnose because they resemble other retroperitoneal cystic tumors. The development of treatment strategies for rare diseases, including retroperitoneal LM, requires the acquisition of new knowledge to enhance our understanding of the disease progression. Therefore, we present an update regarding fundamental and advanced issues associated with retroperitoneal LM. This review describes the epidemiology, histopathology, biomedicine, clinical manifestations, radiological features, differential diagnosis, and management of this lesion.

Microphysiological model of PIK3CA-driven vascular malformations reveals a role of dysregulated Rac1 and mTORC1/2 in lesion formation

Somatic activating mutations of PIK3CA are associated with development of vascular malformations (VMs). Here, we describe a microfluidic model of PIK3CA-driven VMs consisting of human umbilical vein endothelial cells expressing PIK3CA activating mutations embedded in three-dimensional hydrogels. We observed enlarged, irregular vessel phenotypes and the formation of cyst-like structures consistent with clinical signatures and not previously observed in cell culture models. Pathologic morphologies occurred concomitant with up-regulation of Rac1/p21-activated kinase (PAK), mitogen-activated protein kinase cascades (MEK/ERK), and mammalian target of rapamycin (mTORC1/2) signaling networks. We observed differential effects between alpelisib, a PIK3CA inhibitor, and rapamycin, an mTORC1 inhibitor, in mitigating matrix degradation and network topology. While both were effective in preventing vessel enlargement, rapamycin failed to reduce MEK/ERK and mTORC2 activity and resulted in hyperbranching, while inhibiting PAK, MEK1/2, and mTORC1/2 mitigates abnormal growth and vascular dilation. Collectively, these findings demonstrate an in vitro platform for VMs and establish a role of dysregulated Rac1/PAK and mTORC1/2 signaling in PIK3CA-driven VMs.

Vascular malformations: An overview of their molecular pathways, detection of mutational profiles and subsequent targets for drug therapy

Vascular malformations are anomalies in vascular development that portend a significant risk of hemorrhage, morbidity and mortality. Conventional treatments with surgery, radiosurgery and/or endovascular approaches are often insufficient for cure, thereby presenting an ongoing challenge for physicians and their patients. In the last two decades, we have learned that each type of vascular malformation harbors inherited germline and somatic mutations in two well-known cellular pathways that are also implicated in cancer biology: the PI3K/AKT/mTOR and RAS/RAF/MEK pathways. This knowledge has led to recent efforts in: (1) identifying reliable mechanisms to detect a patient's mutational burden in a minimally-invasive manner, and then (2) understand how cancer drugs that target these mutations can be repurposed for vascular malformation care. The idea of precision medicine for vascular pathologies is growing in potential and will be critical in expanding the clinician's therapeutic armamentarium.

Localized heterochrony integrates overgrowth potential of oncogenic clones

Somatic mutations occur frequently and can arise during embryogenesis, resulting in the formation of a patchwork of mutant clones. Such mosaicism has been implicated in a broad range of developmental anomalies; however, their etiology is poorly understood. Patients carrying a common somatic oncogenic mutation in either PIK3CA or AKT1 can present with disproportionally large digits or limbs. How mutant clones, carrying an oncogenic mutation that often drives unchecked proliferation, can lead to controlled and coordinated overgrowth is unknown. We use zebrafish to explore the growth dynamics of oncogenic clones during development. Here, in a subset of clones, we observed a local increase in proportion of the fin skeleton closely resembling overgrowth phenotypes in patients. We unravel the cellular and developmental mechanisms of these overgrowths, and pinpoint the cell type and timing of clonal expansion. Coordinated overgrowth is associated with rapid clone expansion during early pre-chondrogenic phase of bone development, inducing a heterochronic shift that drives the change in bone size. Our study details how development integrates and translates growth potential of oncogenic clones, thereby shaping the phenotypic consequences of somatic mutations.

PIK3CA gain-of-function mutation in adipose tissue induces metabolic reprogramming with Warburg-like effect and severe endocrine disruption

PIK3CA-related overgrowth syndrome (PROS) is a genetic disorder caused by somatic mosaic gain-of-function mutations of PIK3CA. Clinical presentation of patients is diverse and associated with endocrine disruption. Adipose tissue is frequently involved, but its role in disease development and progression has not been elucidated. Here, we created a mouse model of PIK3CA-related adipose tissue overgrowth that recapitulates patient phenotype. We demonstrate that PIK3CA mutation leads to GLUT4 membrane accumulation with a negative feedback loop on insulin secretion, a burst of liver IGFBP1 synthesis with IGF-1 sequestration, and low circulating levels. Mouse phenotype was mainly driven through AKT2. We also observed that PIK3CA mutation induces metabolic reprogramming with Warburg-like effect and protein and lipid synthesis, hallmarks of cancer cells, in vitro, in vivo, and in patients. We lastly show that alpelisib is efficient at preventing and improving PIK3CA-adipose tissue overgrowth and reversing metabolomic anomalies in both animal models and patients.

A clinicopathological reappraisal of orbital vascular malformations and distinctive GJA4 mutation in cavernous venous malformations

Vascular anomalies are common orbital lesions, while variations in previous nomenclature might hamper robust characterization of their clinicopathological and genetic features. We reviewed and reclassified 92 orbital vascular lesions by the modified International Society for the Study of Vascular Anomalies (ISSVA) classification with reappraising clinicopathological parameters of 4 main types of vascular malformations, including orbital venous malformation 1 (OVM1, cavernous venous malformation), OVM2 (varix), OVM3 (infiltrating venous malformation), and arteriovenous malformation (AVM). GJA4, BRAF, and KRAS mutations were assessed by Sanger sequencing. There were 90 cases of vascular malformations, consisting of 60 OVM1 (67%), 13 AVM (14%), 8 OVM2 (9%), 8 OVM3 (9%), and 1 lymphatic-venous malformation (1%). The prevailing OVM1, histologically characterized by well-delineated borders and a uniform cavernous growth pattern, predominantly occurred in intraconal space (57%, P = .019) with an older median age (49 years) and female predilection (73%). OVM2, OVM3, and AVM exhibited differences in the distributions of patients' ages and lesion locations. Sizes of lesions were significantly correlated with periorbital and intraconal/extraconal locations (P < .001). OVM1 had the lowest rate of residual and recurrent diseases (3%). GJA4 mutations were identified in 75% (44/59) of OVM1 but not in OVM2/3 and AVM. No BRAF or KRAS mutations were detected. In conclusion, the modified ISSVA scheme enables meaningful classification of orbital vascular malformations by highlighting the molecular correlation between the distinct clinicopathological features and specific GJA4 mutation in OVM1, which implies OVM1 as a unique variant of venous malformation genetically akin to cutaneous and hepatic counterparts.

Cardiac venous malformation concurrent with multiple hepatic venous malformations: A case report

A 50-year-old woman who had previously undergone right radical mastectomy presented with chest tightness and shortness of breath after physical activities. A cardiac mass and multiple hepatic lesions were successively detected. We first performed hepatic puncture biopsy. Histopathologic examination confirmed that the multiple hepatic lesions were venous malformations. Based on the imaging findings and previous reports in the literature, we boldly speculated that the cardiac mass was also a venous malformation. The cardiac venous malformation was successfully resected, and the postoperative pathology confirmed our suspicion.

Multiple congenital malformations arise from somatic mosaicism for constitutively active Pik3ca signaling

Recurrent missense mutations of the PIK3CA oncogene are among the most frequent drivers of human cancers. These often lead to constitutive activation of its product p110α, a phosphatidylinositol 3-kinase (PI3K) catalytic subunit. In addition to causing a broad range of cancers, the H1047R mutation is also found in affected tissues of a distinct set of congenital tumors and malformations. Collectively termed PIK3CA-related disorders (PRDs), these lead to overgrowth of brain, adipose, connective and musculoskeletal tissues and/or blood and lymphatic vessel components. Vascular malformations are frequently observed in PRD, due to cell-autonomous activation of PI3K signaling within endothelial cells. These, like most muscle, connective tissue and bone, are derived from the embryonic mesoderm. However, important organ systems affected in PRDs are neuroectodermal derivatives. To further examine their development, we drove the most common post-zygotic activating mutation of Pik3ca in neural crest and related embryonic lineages. Outcomes included macrocephaly, cleft secondary palate and more subtle skull anomalies. Surprisingly, Pik3ca-mutant subpopulations of neural crest origin were also associated with widespread cephalic vascular anomalies. Mesectodermal neural crest is a major source of non-endothelial connective tissue in the head, but not the body. To examine the response of vascular connective tissues of the body to constitutive Pik3ca activity during development, we expressed the mutation by way of an Egr2 (Krox20) Cre driver. Lineage tracing led us to observe new lineages that had normally once expressed Krox20 and that may be co-opted in pathogenesis, including vascular pericytes and perimysial fibroblasts. Finally, Schwann cell precursors having transcribed either Krox20 or Sox10 and induced to express constitutively active PI3K were associated with vascular and other tumors. These murine phenotypes may aid discovery of new candidate human PRDs affecting craniofacial and vascular smooth muscle development as well as the reciprocal paracrine signaling mechanisms leading to tissue overgrowth.

A histological study of vascular wall resident stem cells in venous malformations

Vascular wall resident stem cells (VW-SCs) play a key role in vascular formation and remodeling under both physiological and pathological situations. They not only serve as a reservoir to supply all types of vascular cells needed, but also regulate vascular homeostasis by paracrine effects. Venous malformations (VMs) are common congenital vascular malformations which are just characterized by the deficient quantity and abnormal function of vascular cells. However, the existence and role of VW-SCs in VMs is still unclear at present. In this study, the level and distribution of VW-SCs in 22 specimens of VMs were measured by immunochemistry, double-labeling immunofluorescence, and qPCR, followed by the Spearman rank correlation test. We found that both the protein and mRNA expression levels of CD34, vWF, VEGFR2, CD44, CD90, and CD105 were significantly downregulated in VMs compared with that in normal venules. VW-SCs were sporadically distributed or even absent within and outside the endothelium of VMs. The expression of the VW-SC-related markers was positively correlated with the density of both endothelial cells and perivascular cells. All those results and established evidence indicated that VW-SCs were more sporadically distributed with fewer amounts in VMs, which possibly contributing to the deficiency of vascular cells in VMs.

When, where and which PIK3CA mutations are pathogenic in congenital disorders

PIK3CA encodes the class I PI3Kα isoform and is frequently mutated in cancer. Activating mutations in PIK3CA also cause a range of congenital disorders featuring asymmetric tissue overgrowth, known as the PIK3CA-related overgrowth spectrum (PROS), with frequent vascular involvement. In PROS, PIK3CA mutations arise postzygotically, during embryonic development, leading to a mosaic body pattern distribution resulting in a variety of phenotypic features. A clear skewed pattern of overgrowth favoring some mesoderm-derived and ectoderm-derived tissues is observed but not understood. Here, we summarize our current knowledge of the determinants of PIK3CA-related pathogenesis in PROS, including intrinsic factors such as cell lineage susceptibility and PIK3CA variant bias, and extrinsic factors, which refers to environmental modifiers. We also include a section on PIK3CA-related vascular malformations given that the vasculature is frequently affected in PROS. Increasing our biological understanding of PIK3CA mutations in PROS will contribute toward unraveling the onset and progression of these conditions and ultimately impact on their treatment. Given that PIK3CA mutations are similar in PROS and cancer, deeper insights into one will also inform about the other.

How we approach genetics in the diagnosis and management of vascular anomalies

Vascular anomalies are a heterogeneous group of disorders that are currently classified based on their clinical and histological characteristics. Over the past decade, there have been significant advances in molecular genetics that have led to identification of genetic alterations associated with vascular tumors, vascular malformations, and syndromes. Here, we describe known genetic alterations in vascular anomalies, discuss when and how to test, and examine how identification of causative genetic mutations provides for better management of these disorders through improved understanding of their pathogenesis and increasing use of targeted therapeutic agents in order to achieve better outcomes for our patients.

Genomic landscape of lymphatic malformations: a case series and response to the PI3Kα inhibitor alpelisib in an N-of-1 clinical trial

Background

Lymphatic malformations (LMs) often pose treatment challenges due to a large size or a critical location that could lead to disfigurement, and there are no standardized treatment approaches for either refractory or unresectable cases.

Methods

We examined the genomic landscape of a patient cohort of LMs (n = 30 cases) that underwent comprehensive genomic profiling using a large-panel next-generation sequencing assay. Immunohistochemical analyses were completed in parallel.

Results

These LMs had low mutational burden with hotspot PIK3CA mutations (n = 20) and NRAS (n = 5) mutations being most frequent, and mutually exclusive. All LM cases with Kaposi sarcoma-like (kaposiform) histology had NRAS mutations. One index patient presented with subacute abdominal pain and was diagnosed with a large retroperitoneal LM harboring a somatic PIK3CA gain-of-function mutation (H1047R). The patient achieved a rapid and durable radiologic complete response, as defined in RECIST1.1, to the PI3Kα inhibitor alpelisib within the context of a personalized N-of-1 clinical trial (NCT03941782). In translational correlative studies, canonical PI3Kα pathway activation was confirmed by immunohistochemistry and human LM-derived lymphatic endothelial cells carrying an allele with an activating mutation at the same locus were sensitive to alpelisib treatment in vitro, which was demonstrated by a concentration-dependent drop in measurable impedance, an assessment of cell status.

Conclusions

Our findings establish that LM patients with conventional or kaposiform histology have distinct, yet targetable, driver mutations.

Funding

R.P. and W.A. are supported by awards from the Levy-Longenbaugh Fund. S.G. is supported by awards from the Hugs for Brady Foundation. This work has been funded in part by the NCI Cancer Center Support Grants (CCSG; P30) to the University of Arizona Cancer Center (CA023074), the University of New Mexico Comprehensive Cancer Center (CA118100), and the Rutgers Cancer Institute of New Jersey (CA072720). B.K.M. was supported by National Science Foundation via Graduate Research Fellowship DGE-1143953.

Clinical trial number

NCT03941782.

The onset of PI3K-related vascular malformations occurs during angiogenesis and is prevented by the AKT inhibitor miransertib

Low‐flow vascular malformations are congenital overgrowths composed of abnormal blood vessels potentially causing pain, bleeding and obstruction of different organs. These diseases are caused by oncogenic mutations in the endothelium, which result in overactivation of the PI3K/AKT pathway. Lack of robust in vivo preclinical data has prevented the development and translation into clinical trials of specific molecular therapies for these diseases. Here, we demonstrate that the Pik3ca^H1047R activating mutation in endothelial cells triggers a transcriptome rewiring that leads to enhanced cell proliferation. We describe a new reproducible preclinical in vivo model of PI3K‐driven vascular malformations using the postnatal mouse retina. We show that active angiogenesis is required for the pathogenesis of vascular malformations caused by activating Pik3ca mutations. Using this model, we demonstrate that the AKT inhibitor miransertib both prevents and induces the regression of PI3K‐driven vascular malformations. We confirmed the efficacy of miransertib in isolated human endothelial cells with genotypes spanning most of human low‐flow vascular malformations.

Zebrafish mutants in vegfab can affect endothelial cell proliferation without altering ERK phosphorylation and are phenocopied by loss of PI3K signaling

The formation of appropriately patterned blood vessel networks requires endothelial cell migration and proliferation. Signaling through the Vascular Endothelial Growth Factor A (VEGFA) pathway is instrumental in coordinating these processes. mRNA splicing generates short (diffusible) and long (extracellular matrix bound) Vegfa isoforms. The differences between these isoforms in controlling cellular functions are not understood. In zebrafish, vegfaa generates short and long isoforms, while vegfab only generates long isoforms. We found that mutations in vegfaa had an impact on endothelial cell (EC) migration and proliferation. Surprisingly, mutations in vegfab more strongly affected EC proliferation in distinct blood vessels, such as intersegmental blood vessels in the zebrafish trunk and central arteries in the head. Analysis of downstream signaling pathways revealed no change in MAPK (ERK) activation, while inhibiting PI3 kinase signaling phenocopied vegfab mutant phenotypes in affected blood vessels. Together, these results suggest that extracellular matrix bound Vegfa might act through PI3K signaling to control EC proliferation in a distinct set of blood vessels during angiogenesis.

Cerebral cavernous malformations do not fall in the spectrum of PIK3CA-related overgrowth

Somatic gain-of-function (GOF) mutations in phosphatidylinositol-4, 5-bisphosphate 3-kinase catalytic subunit alpha (PIK3CA), the catalytic subunit of phosphoinositide 3-kinase (PI3K), have been recently discovered in cerebral cavernous malformations (CCMs), raising the possibility that the activation of PI3K pathways is a possible universal regulator of vascular morphogenesis. However, there have been contradicting data presented among various groups and studies. To enhance the current understanding of vascular anomalies, it is essential to explore this possible relationship between altered PI3K signalling pathways and its influence on the pathogenesis of CCMs. GOF PIK3CA-mutants have been linked to overgrowth syndromes, allowing this group of disorders, resulting from somatic activating mutations in PIK3CA, to be collectively named as PIK3CA-related overgrowth spectrum disorders. This paper reviews and attempts to conceptualise the relationships and differences among clinical presentations, genotypic and phenotypic correlations and possible coexistence of PIK3CA and CCM mutations/phenotypes in CCM lesions. Finally, we present a model reflecting our hypothetical understanding of CCM pathogenesis based on a systematic review and conceptualisation of data obtained from other studies.

ISSVA Classification of Vascular Anomalies and Molecular Biology

Vascular anomalies include various diseases, which are classified into two types according to the International Society for the Study of Vascular Anomalies (ISSVA) classification: vascular tumors with proliferative changes of endothelial cells, and vascular malformations primarily consisting of structural vascular abnormalities. The most recent ISSVA classifications, published in 2018, detail the causative genes involved in many lesions. Here, we summarize the latest findings on genetic abnormalities, with the presentation of the molecular pathology of vascular anomalies.

Translational medicine in hereditary hemorrhagic telangiectasia

Scientific community have gained lots of new insights in the genetic and biochemical background of different conditions, rare diseases included, settling the basis for preclinical models that are helping to identify new biomarkers and therapeutic targets. Translational Medicine (TM) is an interdisciplinary area of biomedicine with an essential role in bench-to-bedside transition enhancement, generating a circular flow of knowledge transference between research environment and clinical setting, always centered in patient needs. Here, we present different tools used in TM and an overview of what is being done related to hereditary hemorrhagic telangiectasia (HHT), as a disease's model. This work is focused on how this combination of basic and clinical research impacts in HHT patient's daily clinical management and also looking into the future. Further randomized clinical trials with HHT patients should assess the findings of this bench-to-bedside transition. The benefits of this basic and clinical research combination, may not only be important for HHT patients but for patients with other vascular diseases sharing angiogenic disturbances.

Case Report of Fibro-Adipose Vascular Anomaly (FAVA) with Activating Somatic PIK3CA Mutation

Fibro-adipose vascular anomaly (FAVA) is a recently described complex and painful benign lesion found in young adults and the pediatric population composed of intramuscular vascular, fibrous, and adipose tissues. A previous report has identified the presence of somatic mosaic mutations in the gene for the catalytic subunit of phosphatidylinositol 3-kinase (PIK3CA) in cases of FAVA. Herein, we present a case of FAVA found in a 23-year-old male patient who presented with chronic wrist pain associated with a mass, and we identified an associated somatic activating mutation (H1047R) in PIK3CA. We briefly review the relevant literature surrounding the identification and histology of FAVA, the known mutational spectrum, downstream signaling pathways, and relevant treatment modalities. Our case highlights the association between FAVA and somatic mosaic activating PIK3CA mutations.

Endothelial GNAQ p.R183Q Increases ANGPT2 (Angiopoietin-2) and Drives Formation of Enlarged Blood Vessels

OBJECTIVE

Capillary malformation (CM) occurs sporadically and is associated with Sturge-Weber syndrome. The somatic mosaic mutation in GNAQ (c.548G>A, p.R183Q) is enriched in endothelial cells (ECs) in skin CM and Sturge-Weber syndrome brain CM. Our goal was to investigate how the mutant Gαq (G-protein αq subunit) alters EC signaling and disrupts capillary morphogenesis. Approach and Results: We used lentiviral constructs to express p.R183Q or wild-type GNAQ in normal human endothelial colony forming cells (EC-R183Q and EC-WT, respectively). EC-R183Q constitutively activated PLC (phospholipase C) β3, a downstream effector of Gαq. Activated PLCβ3 was also detected in human CM tissue sections. Bulk RNA sequencing analyses of mutant versus wild-type EC indicated constitutive activation of PKC (protein kinase C), NF-κB (nuclear factor kappa B) and calcineurin signaling in EC-R183Q. Increased expression of downstream targets in these pathways, ANGPT2 (angiopoietin-2) and DSCR (Down syndrome critical region protein) 1.4 were confirmed by quantitative PCR and immunostaining of human CM tissue sections. The Gαq inhibitor YM-254890 as well as siRNA targeted to PLCβ3 reduced mRNA expression levels of these targets in EC-R183Q while the pan-PKC inhibitor AEB071 reduced ANGPT2 but not DSCR1.4. EC-R183Q formed enlarged blood vessels in mice, reminiscent of those found in human CM. shRNA knockdown of ANGPT2 in EC-R183Q normalized the enlarged vessels to sizes comparable those formed by EC-WT.

CONCLUSIONS

Gαq-R183Q, when expressed in ECs, establishes constitutively active PLCβ3 signaling that leads to increased ANGPT2 and a proangiogenic, proinflammatory phenotype. EC-R183Q are sufficient to form enlarged CM-like vessels in mice, and suppression of ANGPT2 prevents the enlargement. Our study provides the first evidence that endothelial Gαq-R183Q is causative for CM and identifies ANGPT2 as a contributor to CM vascular phenotype.

Treatment strategies for mosaic overgrowth syndromes of the PI3K-AKT-mTOR pathway

INTRODUCTION OR BACKGROUND

Mosaic overgrowth syndromes (OS) are a proteiform ensemble of rare diseases displaying asymmetric overgrowth involving any tissue type, with degrees of severity ranging from isolated malformation to life-threatening conditions such as pulmonary embolism. Despite discordant clinical presentations, all those syndromes share common genetic anomalies: somatic mutations of genes involved in cell growth and proliferation. The PI3K-AKT-mTOR signaling pathway is one of the most prominent regulators of cell homeostasis, and somatic oncogenic mutations affecting this pathway are responsible for mosaic OS. This review aims to describe the clinical and molecular characteristics of the main OS involving the PI3K-AKT-mTOR pathway, along with the treatments available or under development.

SOURCES OF DATA

This review summarizes available data regarding OS in scientific articles published in peer-reviewed journals.

AREAS OF AGREEMENT

OS care requires a multidisciplinary approach relying on clinical and radiological follow-up along with symptomatic treatment. However, no specific treatment has yet shown efficacy in randomized control trials.

AREAS OF CONTROVERSY

Clinical classifications of OS led to frequent misdiagnosis. Moreover, targeted therapies directed at causal mutated proteins are developing in OSs through cancer drugs repositioning, but the evidence of efficacy and tolerance is still lacking for most of them.

GROWING POINTS

The genetic landscape of OS is constantly widening and molecular classifications tend to increase the accuracy of diagnosis, opening opportunities for targeted therapies.

AREAS TIMELY FOR DEVELOPING RESEARCH

OS are a dynamic, expanding field of research. Studies focusing on the identification of genetic anomalies and their pharmacological inhibition are needed.

Lateralized and Segmental Overgrowth in Children

Congenital disorders of lateralized or segmental overgrowth (LO) are heterogeneous conditions with increased tissue growth in a body region. LO can affect every region, be localized or extensive, involve one or several embryonic tissues, showing variable severity, from mild forms with minor body asymmetry to severe ones with progressive tissue growth and related relevant complications. Recently, next-generation sequencing approaches have increased the knowledge on the molecular defects in LO, allowing classifying them based on the deranged cellular signaling pathway. LO is caused by either genetic or epigenetic somatic anomalies affecting cell proliferation. Most LOs are classifiable in the Beckwith-Wiedemann spectrum (BWSp), PI3KCA/AKT-related overgrowth spectrum (PROS/AROS), mosaic RASopathies, PTEN Hamartoma Tumor Syndrome, mosaic activating variants in angiogenesis pathways, and isolated LO (ILO). These disorders overlap over common phenotypes, making their appraisal and distinction challenging. The latter is crucial, as specific management strategies are key: some LO is associated with increased cancer risk making imperative tumor screening since childhood. Interestingly, some LO shares molecular mechanisms with cancer: recent advances in tumor biological pathway druggability and growth downregulation offer new avenues for the treatment of the most severe and complicated LO.

Identification of ACTA2 as a Key Contributor to Venous Malformation

Objectives: Proteomics and high connotation functional gene screening (HCS) were used to screen key functional genes that play important roles in the pathogenesis of venous malformation. Furthermore, this study was conducted to analyze and explore their possible functions, establish a gene mutation zebrafish model, and perform a preliminary study to explore their possible pathogenic mechanisms in venous malformation.

Methods: Pathological and normal tissues from patients with disseminated venous malformation were selected for Tandem Mass Tag (TMT) proteomics analysis to identify proteins that were differentially expressed. Based on bioinformatics analysis, 20 proteins with significant differential expression were selected for HCS to find key driver genes and characterize the expression of these genes in patients with venous malformations. In vitro experiments were then performed using human microvascular endothelial cells (HMEC-1). A gene mutant zebrafish model was also constructed for in vivo experiments to explore gene functions and pathogenic mechanisms.

Results: The TMT results showed a total of 71 proteins that were differentially expressed as required, with five of them upregulated and 66 downregulated. Based on bioinformatics and proteomics results, five highly expressed genes and 15 poorly expressed genes were selected for functional screening by RNAi technology. HCS screening identified ACTA2 as the driver gene. Quantitative polymerase chain reaction (qPCR) and western blot were used to detect the expression of ACTA2 in the pathological tissues of patients with venous malformations and in control tissues, and the experimental results showed a significantly lower expression of ACTA2 in venous malformation tissues (P < 0.05). Cell assays on the human microvascular endothelial cells (HMEC-1) model showed that cell proliferation, migration, invasion, and angiogenic ability were all significantly increased in the ACTA2 over-expression group (P < 0.05), and that overexpression of ACTA2 could improve the inhibitory effect on vascular endothelial cell proliferation. We constructed an ACTA2-knockdown zebrafish model and found that the knockdown of ACTA2 resulted in defective vascular development, disruption of vascular integrity, and malformation of micro vein development in zebrafish. Further qPCR assays revealed that the knockdown of ACTA2 inhibited the Dll4/notch1 signaling pathway, Ephrin-B2 signaling pathway, and vascular integrity-related molecules and activated the Hedgehog signaling pathway.

Conclusion: This study revealed that ACTA2 deficiency is an important factor in the pathogenesis of venous malformation, resulting in the disruption of vascular integrity and malformed vascular development. ACTA2 can be used as a potential biomarker for the treatment and prognosis of venous malformations.

Downregulation of microRNA-21 contributes to decreased collagen expression in venous malformations via transforming growth factor-β/Smad3/microRNA-21 signaling feedback loop

OBJECTIVE

Venous malformations (VMs) are the most frequent vascular malformations and are characterized by dilated and tortuous veins with a dysregulated vascular extracellular matrix. The purpose of the present study was to investigate the potential involvement of microRNA-21 (miR-21), a multifunctional microRNA tightly associated with extracellular matrix regulation, in the pathogenesis of VMs.

METHODS

The expression of miR-21, collagen I, III, and IV, transforming growth factor-β (TGF-β), and Smad3 (mothers against decapentaplegic homolog 3) was evaluated in VMs and normal skin tissue using in situ hybridization, immunohistochemistry, Masson trichrome staining, and real-time polymerase chain reaction. Human umbilical vein endothelial cells (HUVECs) were used to explore the underlying mechanisms.

RESULTS

miR-21 expression was markedly decreased in the VM specimens compared with normal skin, in parallel with downregulation of collagen I, III, and IV and the TGF-β/Smad3 pathway in VMs. Moreover, our data demonstrated that miR-21 positively regulated the expression of collagens in HUVECs and showed a positive association with the TGF-β/Smad3 pathway in the VM tissues. In addition, miR-21 was found to mediate TGF-β-induced upregulation of collagens in HUVECs. Our data have indicated that miR-21 and the TGF-β/Smad3 pathway could form a positive feedback loop to synergistically regulate endothelial collagen synthesis. In addition, TGF-β/Smad3/miR-21 feedback loop signaling was upregulated in bleomycin-treated HUVECs and VM specimens, which was accompanied by increased collagen deposition.

CONCLUSIONS

To the best of our knowledge, the present study has, for the first time, revealed downregulation of miR-21 in VMs, which might contribute to decreased collagen expression via the TGF-β/Smad3/miR-21 signaling feedback loop. These findings provide new information on the pathogenesis of VMs and might facilitate the development of new therapies for VMs.

Somatic PIK3CA Mutations in Sporadic Cerebral Cavernous Malformations

BACKGROUND

Cerebral cavernous malformations (CCMs) are common sporadic and inherited vascular malformations of the central nervous system. Although familial CCMs are linked to loss-of-function mutations in KRIT1 (CCM1), CCM2, or PDCD10 (CCM3), the genetic cause of sporadic CCMs, representing 80% of cases, remains incompletely understood.

METHODS

We developed two mouse models harboring mutations identified in human meningiomas with the use of the prostaglandin D2 synthase (PGDS) promoter. We performed targeted DNA sequencing of surgically resected CCMs from patients and confirmed our findings by droplet digital polymerase-chain-reaction analysis.

RESULTS

We found that in mice expressing one of two common genetic drivers of meningioma - Pik3ca ^H1047R or AKT1 ^E17K - in PGDS-positive cells, a spectrum of typical CCMs develops (in 22% and 11% of the mice, respectively) instead of meningiomas, which prompted us to analyze tissue samples from sporadic CCMs from 88 patients. We detected somatic activating PIK3CA and AKT1 mutations in 39% and 1%, respectively, of lesion tissue from the patients. Only 10% of lesions harbored mutations in the CCM genes. We analyzed lesions induced by the activating mutations Pik3ca ^H1074R and AKT1 ^E17K in mice and identified the PGDS-expressing pericyte as the probable cell of origin.

CONCLUSIONS

In tissue samples from sporadic CCMs, mutations in PIK3CA were represented to a greater extent than mutations in any other gene. The contribution of somatic mutations in the genes that cause familial CCMs was comparatively small. (Funded by the Fondation ARC pour la Recherche contre le Cancer and others.).