Linkage of Metabolic Defects to Activated PIK3CA Alleles in Endothelial Cells Derived from Lymphatic Malformation

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.

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.

The role of key biomarkers in lymphatic malformation: An updated review

The lymphatic system, crucial for tissue fluid balance and immune surveillance, can be severely impacted by disorders that hinder its activities. Lymphatic malformations (LMs) are caused by fluid accumulation in tissues owing to defects in lymphatic channel formation, the obstruction of lymphatic vessels or injury to lymphatic tissues. Somatic mutations, varying in symptoms based on lesions' location and size, provide insights into their molecular pathogenesis by identifying LMs' genetic causes. In this review, we collected the most recent findings about the role of genetic and inflammatory biomarkers in LMs that control the formation of these malformations. A thorough evaluation of the literature from 2000 to the present was conducted using the PubMed and Google Scholar databases. Although it is obvious that the vascular endothelial growth factor receptor 3 mutation accounts for a significant proportion of LM patients, several mutations in other genes thought to be linked to LM have also been discovered. Also, inflammatory mediators like interleukin-6, interleukin-8, tumor necrosis factor-alpha and mammalian target of rapamycin are the most commonly associated biomarkers with LM. Understanding the mutations and genes expression responsible for the abnormalities in lymphatic endothelial cells could lead to novel therapeutic strategies based on molecular pathways.

Hyperactive KRAS/MAPK signaling disrupts normal lymphatic vessel architecture and function

Complex lymphatic anomalies (CLAs) are sporadically occurring diseases caused by the maldevelopment of lymphatic vessels. We and others recently reported that somatic activating mutations in KRAS can cause CLAs. However, the mechanisms by which activating KRAS mutations cause CLAs are poorly understood. Here, we show that KRASG12D expression in lymphatic endothelial cells (LECs) during embryonic development impairs the formation of lymphovenous valves and causes the enlargement of lymphatic vessels. We demonstrate that KRASG12D expression in primary human LECs induces cell spindling, proliferation, and migration. It also increases AKT and ERK1/2 phosphorylation and decreases the expression of genes that regulate the maturation of lymphatic vessels. We show that MEK1/2 inhibition with the FDA-approved drug trametinib suppresses KRASG12D-induced morphological changes, proliferation, and migration. Trametinib also decreases ERK1/2 phosphorylation and increases the expression of genes that regulate the maturation of lymphatic vessels. We also show that trametinib and Cre-mediated expression of a dominant-negative form of MEK1 (Map2k1 K97M) suppresses KRASG12D-induced lymphatic vessel hyperplasia in embryos. Last, we demonstrate that conditional knockout of wild-type Kras in LECs does not affect the formation or function of lymphatic vessels. Together, our data indicate that KRAS/MAPK signaling must be tightly regulated during embryonic development for the proper development of lymphatic vessels and further support the testing of MEK1/2 inhibitors for treating CLAs.

Somatic activating BRAF variants cause isolated lymphatic malformations

Somatic activating variants in PIK3CA, the gene that encodes the p110α catalytic subunit of phosphatidylinositol 3-kinase (PI3K), have been previously detected in ∼80% of lymphatic malformations (LMs).^1,2 We report the presence of somatic activating variants in BRAF in individuals with LMs that do not possess pathogenic PIK3CA variants. The BRAF substitution p.Val600Glu (c.1799T>A), one of the most common driver mutations in cancer, was detected in multiple individuals with LMs. Histology revealed abnormal lymphatic channels with immunopositivity for BRAF^V600E in endothelial cells that was otherwise indistinguishable from PIK3CA-positive LM. The finding that BRAF variants contribute to low-flow LMs increases the complexity of prior models associating low-flow vascular malformations (LM and venous malformations) with mutations in the PI3K-AKT-MTOR and high-flow vascular malformations (arteriovenous malformations) with mutations in the RAS-mitogen-activated protein kinase (MAPK) pathway.³ In addition, this work highlights the importance of genetic diagnosis prior to initiating medical therapy as more studies examine therapeutics for individuals with vascular malformations.

Oral lymphatic malformations: A multicenter study of 208 cases and literature review

BACKGROUND

To evaluate the frequency and analyze demographic and clinical characteristics of individuals with a histopathological diagnosis of oral lymphatic malformations (OLMs).

METHODS

A multicenter study was performed, collecting biopsy record data from a consortium of Brazilian Oral and Maxillofacial Pathology Centers. A review was also conducted to compare this data with cases already available in the literature.

RESULTS

This study retrieved 208 cases of OLM in the multicenter study and 1035 cases in the literature review. In both, OLMs affected male and female individuals equally, with the most affected site being the tongue. Individuals ≥60 years of age were uncommonly affected. Symptomatic and larger lesions were more commonly reported in the literature review.

CONCLUSIONS

This study comprises the largest sample of OLMs to date. OLMs are rare conditions, without sex predilection. The elderly proved to be less frequently affected, and the tongue is the most commonly affected site.

Assessment of PI3K/AKT and MAPK/ERK pathways activation in oral lymphatic malformations

OBJECTIVE

Lymphatic malformations are characterized by the overgrowth of lymphatic vessels during development. Activation of PI3K/AKT and MAPK/ERK signaling pathways occur in isolated lymphatic malformation and in those associated with syndromes such as CLOVES and Klippel-Trenaunay. We aimed to assess the activation of these pathways in sporadic oral lymphatic malformations.

STUDY DESIGN

A convenience sample of 14 formalin-fixed paraffin-embedded samples of oral lymphatic malformations underwent immunohistochemical reactions for the phosphorylated forms of AKT1 (pAKT-Ser473) and ERK1/2 (pERK1/2-Thr202/Tyr204), which are markers of PI3K/AKT and MAPK/ERK pathways activation, respectively.

RESULTS

Positive staining for pAKT1 and pERK1/2 was observed in the endothelial cells in all samples of oral lymphatic malformations evaluated.

CONCLUSIONS

Our results suggest that activation of PI3K/AKT and MAPK/ERK signaling pathways participates in the pathogenesis of oral lymphatic malformations.

Recent Progress in Lymphangioma

Lymphangioma is a common type of congenital vascular disease in children with a broad spectrum of clinical manifestations. The current classification of lymphangioma by International Society for the Study of Vascular Anomalies is largely based on the clinical manifestations and complications and is not sufficient for selection of therapeutic strategies and prognosis prediction. The clinical management and outcome of lymphangioma largely depend on the clinical classification and the location of the disease, ranging from spontaneous regression with no treatment to severe sequelae even with comprehensive treatment. Recently, rapid progression has been made toward elucidating the molecular pathology of lymphangioma and the development of treatments. Several signaling pathways have been revealed to be involved in the progression and development of lymphangioma, and specific inhibitors targeting these pathways have been investigated for clinical applications and clinical trials. Some drugs already currently in clinical use for other diseases were found to be effective for lymphangioma, although the mechanisms underlying the anti-tumor effects remain unclear. Molecular classification based on molecular pathology and investigation of the molecular mechanisms of current clinical drugs is the next step toward developing more effective individualized treatment of children with lymphangioma with reduced side effects.

Pyruvate Kinase M2 Mediates Glycolysis in the Lymphatic Endothelial Cells and Promotes the Progression of Lymphatic Malformations

Metabolism plays a pivotal role in the formation of the lymphatic vasculature. Pyruvate kinase M2 (PKM2) is typically a metabolic marker of proliferating cells and maintains the growth of vascular endothelial cells. In this study, the potential status of PKM2 in lymphatic endothelial cells and the pathogenesis of lymphatic malformations (LMs) was investigated. The glycolysis index, including glucose uptake, ATP, and lactate production, stayed at a relatively high level in human dermal lymphatic endothelial cells (HDLECs) compared with human umbilical vein endothelial cells, whereas the inhibition of PKM2 by shikonin or PKM2 knockdown significantly suppressed glycolysis, migration, tubular formation, and invasion of HDLECs. Moreover, compared with lymphatic vessels in healthy skin, lymphatic vessels of LMs expressed PKM2 highly, and this expression correlated with infection of LMs. Meanwhile, the overexpression of PKM2 in HDLECs strengthened the proliferation, migration, tubular formation, and invasion of HDLECs. The findings from further experiments in a rat LM model support that targeting PKM2 by shikonin significantly impedes the progression of LMs, even in an infected LM rat model. Taken together, these results indicate that PKM2 plays a pivotal role in the activation of LECs and promotes the progression of LMs, whereas the inhibition of PKM2 can effectively suppress the pathogenesis of LM lesions in the rat model.

Cell-free DNA as a diagnostic analyte for molecular diagnosis of vascular malformations

Purpose:

Vascular malformations (VM) are primarily caused by somatic activating pathogenic variants in oncogenes. Targeted pharmacotherapies are emerging but require molecular diagnosis. Since variants are currently only detected in malformation tissue, patients may be ineligible for clinical trials prior to surgery. We hypothesized that cell-free DNA (cfDNA) could provide molecular diagnoses for patients with isolated VM.

Methods:

cfDNA was isolated from plasma or cyst fluid from patients with arteriovenous malformations (AVM), venous malformations (VeM), or lymphatic malformations (LM), and assayed for known pathogenic variants using droplet digital PCR (ddPCR). Cyst fluid cfDNA from an independent cohort of LM patients was prospectively screened for variants using a multiplex ddPCR assay.

Results:

Variants were detected in plasma cfDNA in patients with AVM (2/8) and VeM (1/3). Variants were detected in cyst fluid cfDNA (7/7) but not plasma (0/26) in LM patients. Prospective testing of cyst fluid cfDNA with multiplex ddPCR identified variants in LM patients who had never undergone surgery (4/5).

Conclusion:

Variants were detected in plasma from AVM and VeM patients, and in cyst fluid from patients with LM. These data support investigation of cfDNA-based molecular diagnostics for VM patients which may provide opportunities to initiate targeted pharmacotherapies without prior surgery.

Genotype correlates with clinical severity in PIK3CA-associated lymphatic malformations

Lymphatic malformations (LMs) are congenital, nonneoplastic vascular malformations associated with postzygotic activating PIK3CA mutations. The mutation spectrum within LMs is narrow, with the majority having 1 of 3 hotspot mutations. Despite this relative genetic homogeneity, clinical presentations differ dramatically. We used molecular inversion probes and droplet digital polymerase chain reaction to perform deep, targeted sequencing of PIK3CA in 271 affected and unaffected tissue samples from 81 individuals with isolated LMs and retrospectively collected clinical data. Pathogenic PIK3CA mutations were identified in affected LM tissue in 64 individuals (79%) with isolated LMs, with variant allele fractions (VAFs) ranging from 0.1% to 13%. Initial analyses revealed no correlation between VAF and phenotype variables. Recognizing that different mutations activate PI3K to varying degrees, we developed a metric, the genotype-adjusted VAF (GVAF), to account for differences in mutation strength, and found significantly higher GVAFs in LMs with more severe clinical characteristics including orofacial location or microcystic structure. In addition to providing insight into LM pathogenesis, we believe GVAF may have broad applicability for genotype-phenotype analyses in mosaic disorders.

Cellular and molecular mechanisms of PIK3CA-related vascular anomalies

The phosphoinositide 3-kinase (PI3K) pathway is a major mediator of growth factor signaling, cell proliferation and metabolism. Somatic gain-of-function mutations in PIK3CA, the catalytic subunit of PI3K, have recently been discovered in a number of vascular anomalies. The timing and origin of these mutations remain unclear although they are believed to occur during embryogenesis. The cellular origin of these lesions likely involves endothelial cells or an early endothelial cell lineage. This review will cover the diseases and syndromes associated with PIK3CA mutations and discuss the cellular origin, pathways and mechanisms. Activating PIK3CA 'hot spot' mutations have long been associated with a multitude of cancers allowing the development of targeted pharmacological inhibitors that are FDA-approved or in clinical trials. Current and future therapeutic approaches for PIK3CA-related vascular anomalies are discussed.

Gene Expression Differences in Pediatric Lymphatic Malformations: Size Really Matters

Lymphatic malformations (LMs) are congenital vascular anomalies characterized by dilated and cystic lymphatic channels. They are subdivided into macrocystic and microcystic lesions based upon the predominant size of the cysts involved. However, significant differences in clinical characteristics, treatment outcomes, and prognosis between macrocytic and microcytic disease suggest variation in underlying biologic and genetic influences. Indirect differential expression analysis revealed that 426 genes are significantly different (p < 0.01) in a small sample of LM subtypes. Functional analyses on the differentially expressed gene sets showed that microcystic LM gene expression favors a prooncogenic profile with upregulation of MYC target genes and cell cycle proteins, whereas macrocystic expression demonstrates hypoxic events that lead to angiogenesis and cell proliferation. Therefore, microcystic and macrocystic LMs, although histologically and physiologically similar, may occur under the influence of vastly different biological pathways and mechanisms of action.

Expression of Embryonic Stem Cell Markers in Microcystic Lymphatic Malformation

Aim: To investigate the expression of embryonic stem cell (ESC) markers in microcystic lymphatic malformation (mLM). Methods and Results: Cervicofacial mLM tissue samples from nine patients underwent 3,3'-diaminobenzidine (DAB) immunohistochemical (IHC) staining for ESC markers octamer-binding protein 4 (OCT4), homeobox protein NANOG, sex determining region Y-box 2 (SOX2), Krupple-like factor (KLF4), and proto-oncogene c-MYC. Transcriptional activation of these ESC markers was investigated using real-time polymerase chain reaction (RT-qPCR) and colorimetric in situ hybridization (CISH) on four and five of these mLM tissue samples, respectively. Immunofluorescence (IF) IHC staining was performed on three of these mLM tissue samples to investigate localization of these ESC markers. DAB and IF IHC staining demonstrated the expression of OCT4, SOX2, NANOG, KLF4, and c-MYC on the endothelium of lesional vessels with abundant expression of c-MYC and SOX2, which was also present on the cells within the stroma, in all nine mLM tissue samples. RT-qPCR and CISH confirmed transcriptional activation of all these ESC markers investigated. Conclusions: These findings suggest the presence of a primitive population on the endothelium of lesional vessels and the surrounding stroma in mLM. The abundant expression of the progenitor-associated markers SOX2 and c-MYC suggests that the majority are of progenitor phenotype with a small number of ESC-like cells.

Overexpression of TAF1L Promotes Cell Proliferation, Migration and Invasion in Esophageal Squamous Cell Carcinoma

Currently, it reported that TAF1L gene mutation is found in a number of carcinomas, but its pathophysiological function has not been well studied. We focused on investigating expressive levels of TAF1L gene and protein in esophageal squamous cell carcinoma (ESCC) with two tissue microarrays, forty fresh paired ESCC and paracancer samples using immunohistochemistry, real-time PCR or Western blot in this study. Furthermore, we executed TAF1L silence with siRNA in ESCC cell lines to evaluate effects of TAF1L expression on cell proliferation, migration and invasion of ESCC via CCK-8, wound healing and transwell chamber assays. Moreover, key proteins related to ESCC development were also analyzed by Western blot. Results from this study showed that the expression of TAF1L mRNA and protein in ESCC tissues were significantly higher than that in matched paracancer tissues. However, its abnormal expression was not associated with other clinic features, such as the age, gender and pathological grade, except of TNM-N stage. Furthermore, the proliferation, migration and invasion of ESCC cells were inhibited after TAF1L gene silencing. As a consequence, the expression of c-Myc and phosphorylated Akt in esophageal squamous cell line after TAF1L-siRNA treatment were inversely decreased, while p53 was increased significantly, compared those to control group. Taken together, the results from this study suggest that TAF1L gene might be served as an oncogene, and its overexpression could accelerate to the tumorigenesis of ESCC via promoting the malignant cell proliferation and tumor metastasis.

Proliferative Cells From Kaposiform Lymphangiomatosis Lesions Resemble Mesenchyme Stem Cell-like Pericytes Defective in Vessel Formation

Kaposiform lymphangiomatosis (KLA) is a vascular anomaly featuring lymphatic expansion. It has no known cause, no effective treatment, and is associated with high morbidity. Proliferative cells from 3 KLA patient lesions were characterized relative to adiopose-derived mesenchyme stem cells (ADSCs) and cells derived from a patient with the related disease kaposiform hemangioendothelioma (KHE). KLA cells variably expressed markers of mesenchyme stem cells (CD73, CD90, CD105, CD146) and lacked endothelial cell markers (CD31, CD34) as determined by flow cytometry. They expressed markers of vascular pericytes (neural/glial antigen 2, alpha-smooth muscle actin, platelet-derived growth factor-beta receptor, and CXCL12) as determined by quantitative reverse transcription polymerase chain reaction. Lesion cells transcribed vascular markers VEGFC and VEGFD, as well as VCAM-1, the latter of which was confirmed by flow cytometry, consistent with angiogenic MSC-like pericytes. Furthermore, conditioned medium from each was shown to promote the proliferation of growth factor-starved lymphatic endothelial cells. Unlike kaposiform hemangioendothelioma-derived MSC-like pericytes and ADSCs, KLA isolates were defective in support of vascular network formation in co-cultures with either vascular or lymphatic endothelial cells. Genetic analysis by whole exome sequencing revealed novel variant alleles in 2 populations of KLA cells (BAD, TSC1) that may bear on aberrant pericyte growth and function.

PIK3CA mutations are specifically localized to lymphatic endothelial cells of lymphatic malformations

Lymphatic malformations (LM) are characterized by the overgrowth of lymphatic vessels during pre- and postnatal development. Macrocystic, microcystic and combined forms of LM are known. The cysts are lined by lymphatic endothelial cells (LECs). Resection and sclerotherapy are the most common treatment methods. Recent studies performed on LM specimens in the United States of America have identified activating mutations in the phosphatidylinositol-4,5-bisphosphate 3-kinase catalytic subunit alpha (PIK3CA) gene in LM. However, whole tissue but not isolated cell types were studied. Here, we studied LM tissues resected at the University Hospitals Freiburg and Regensburg, Germany. We isolated LECs and fibroblasts separately, and sequenced the commonly affected exons 8, 10, and 21 of the PIK3CA gene. We confirm typical monoallelic mutations in 4 out of 6 LM-derived LEC lines, and describe two new mutations i.) in exon 10 (c.1636C>A; p.Gln546Lys), and ii.) a 3bp in-frame deletion of GAA (Glu109del). LM-derived fibroblasts did not possess such mutations, showing cell-type specificity of the gene defect. High activity of the PIK3CA—AKT- mTOR pathway was demonstrated by hyperphosphorylation of AKT-Ser473 in all LM-derived LECs (including the ones with newly identified mutations), as compared to normal LECs. Additionally, hyperphosphorylation of ERK was seen in all LM-derived LECs, except for the one with Glu109del. In vitro, the small molecule kinase inhibitors Buparlisib/BKM-120, Wortmannin, and Ly294002, (all inhibitors of PIK3CA), CAL-101 (inhibitor of PIK3CD), MK-2206 (AKT inhibitor), Sorafenib (multiple kinases inhibitor), and rapamycin (mTOR inhibitor) significantly blocked proliferation of LM-derived LECs in a concentration-dependent manner, but also blocked proliferation of normal LECs. However, MK-2206 appeared to be more specific for mutated LECs, except in case of Glu109 deletion. In sum, children that are, or will be, treated with kinase inhibitors must be monitored closely.

Medical Management of Vascular Anomalies

PURPOSE OF REVIEW

This chapter will summarize the most recent literature regarding the current state of medical treatment for vascular anomalies.

RECENT FINDINGS

Research into the biology of these anomalies has strengthened our understanding of each anomaly and has helped to pave the way for more tailored treatment options involving molecular and/or genetic targets.

SUMMARY

While there is still a role for surgical intervention, medical therapies that target the etiology of vascular anomalies may represent an alternative or adjunctive approach in the management of these lesions.