AKT hyper-phosphorylation associated with PI3K mutations in lymphatic endothelial cells from a patient with lymphatic malformation

Changes in cell morphology and function induced by the NRAS Q61R mutation in lymphatic endothelial cells

Recently, a low-level somatic mutation in the NRAS gene (c.182 A > G, Q61R) was identified in various specimens from patients with kaposiform lymphangiomatosis. However, it is unknown how these low-frequency mutated cells can affect the characterization and surrounding environment of their lesions. To understand the pathogenesis and association of these gene abnormalities, we established NRASQ61R mutated lymphatic endothelial cells transfected with lentivirus vector and undertook morphological and functional characterization, protein expression profiling, and metabolome analysis. NRASQ61R human dermal lymphatic endothelial cells showed poor tube formation, a low proliferation rate, and high migration ability, with an increase in the ratio of mutated cells. An analysis of signaling pathways showed inactivation of the PIK3/AKT/mTOR pathway and hyperactivation of the RAS/MAPK/ERK pathway, which was improved by MAPK kinase (MEK) inhibitor treatment. This study shows the theoretical circumstances induced in vitro by NRASQ61R-mutated cells in the affected lesions of kaposiform lymphangiomatosis patients.

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.

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.

Sirolimus treatment for intractable lymphatic anomalies: an open-label, single-arm, multicenter, prospective trial

Introduction

Intractable lymphatic anomalies (LAs) include cystic lymphatic malformation (LM; macrocystic, microcystic, or mixed), generalized lymphatic anomaly, and Gorham-Stout disease. LAs can present with severe symptoms and poor prognosis. Thus, prospective studies for treatments are warranted. We conducted a prospective clinical trial of sirolimus for intractable LAs.

Methods

This was an open-label, single-arm, multicenter, prospective trial involving five institutions in Japan. All patients with LAs received oral sirolimus once daily, and the dose was adjusted to ensure that the trough concentration remained within 5-15 ng/mL. We prospectively assessed the drug response (response rate for radiological volumetric change in target lesion), performance state, change in respiratory function, visceral impairment (pleural effusion, ascites, bleeding, pain), laboratory examination data, quality of life (QOL), and safety at 12, 24, and 52 weeks of administration.

Results

Eleven patients with LAs (9 generalized lymphatic anomaly, 1 cystic LM, 1 Gorham-Stout disease) were treated with sirolimus, of whom 6 (54.5%; 95% confidence interval: 23.4-83.3%) demonstrated a partial response on radiological examination at 52 weeks of administration. No patients achieved a complete response. At 12 and 24 weeks of administration, 8 patients (72.7%) already showed a partial response. However, patients with stable disease showed minor or no reduction after 12 weeks. Adverse events, such as stomatitis, acneiform dermatitis, diarrhea, and fever, were common with sirolimus. Sirolimus was safe and tolerable.

Conclusion

Sirolimus can reduce the lymphatic tissue volume in LAs and may lead to improvements in clinical symptoms and QOL.

Lymphatic vessel: origin, heterogeneity, biological functions, and therapeutic targets

Lymphatic vessels, comprising the secondary circulatory system in human body, play a multifaceted role in maintaining homeostasis among various tissues and organs. They are tasked with a serious of responsibilities, including the regulation of lymph absorption and transport, the orchestration of immune surveillance and responses. Lymphatic vessel development undergoes a series of sophisticated regulatory signaling pathways governing heterogeneous-origin cell populations stepwise to assemble into the highly specialized lymphatic vessel networks. Lymphangiogenesis, as defined by new lymphatic vessels sprouting from preexisting lymphatic vessels/embryonic veins, is the main developmental mechanism underlying the formation and expansion of lymphatic vessel networks in an embryo. However, abnormal lymphangiogenesis could be observed in many pathological conditions and has a close relationship with the development and progression of various diseases. Mechanistic studies have revealed a set of lymphangiogenic factors and cascades that may serve as the potential targets for regulating abnormal lymphangiogenesis, to further modulate the progression of diseases. Actually, an increasing number of clinical trials have demonstrated the promising interventions and showed the feasibility of currently available treatments for future clinical translation. Targeting lymphangiogenic promoters or inhibitors not only directly regulates abnormal lymphangiogenesis, but improves the efficacy of diverse treatments. In conclusion, we present a comprehensive overview of lymphatic vessel development and physiological functions, and describe the critical involvement of abnormal lymphangiogenesis in multiple diseases. Moreover, we summarize the targeting therapeutic values of abnormal lymphangiogenesis, providing novel perspectives for treatment strategy of multiple human diseases.

Edema and lymphatic clearance: molecular mechanisms and ongoing challenges

Resolution of edema remains a significant clinical challenge. Conditions such as traumatic shock, sepsis, or diabetes often involve microvascular hyperpermeability, which leads to tissue and organ dysfunction. Lymphatic insufficiency due to genetic causes, surgical removal of lymph nodes, or infections, leads to varying degrees of tissue swelling that impair mobility and immune defenses. Treatment options are limited to management of edema as there are no specific therapeutics that have demonstrated significant success for ameliorating microvascular leakage or impaired lymphatic function. This review examines current knowledge about the physiological, cellular, and molecular mechanisms that control microvascular permeability and lymphatic clearance, the respective processes for interstitial fluid formation and removal. Clinical conditions featuring edema, along with potential future directions are discussed.

Targeted next-generation sequencing for detection of PIK3CA mutations in archival tissues from patients with Klippel-Trenaunay syndrome in an Asian population : List the full names and institutional addresses for all authors

BACKGROUND

Klippel-Trenaunay syndrome (KTS) is a rare slow-flow combined vascular malformation with limb hypertrophy. KTS is thought to lie on the PIK3CA-related overgrowth spectrum, but reports are limited. PIK3CA encodes p110α, a catalytic subunit of phosphatidylinositol 3-kinase (PI3K) that plays an essential role in the PI3K/AKT/mammalian target of rapamycin (mTOR) signaling pathway. We aimed to demonstrate the clinical utility of targeted next-generation sequencing (NGS) in identifying PIK3CA mosaicism in archival formalin-fixed paraffin-embedded (FFPE) tissues from patients with KTS.

RESULTS

Participants were 9 female and 5 male patients with KTS diagnosed as capillaro-venous malformation (CVM) or capillaro-lymphatico-venous malformation (CLVM). Median age at resection was 14 years (range, 5-57 years). Median archival period before DNA extraction from FFPE tissues was 5.4 years (range, 3-7 years). NGS-based sequencing of PIK3CA achieved an amplicon mean coverage of 119,000x. PIK3CA missense mutations were found in 12 of 14 patients (85.7%; 6/8 CVM and 6/6 CLVM), with 8 patients showing the hotspot variants E542K, E545K, H1047R, and H1047L. The non-hotspot PIK3CA variants C420R, Q546K, and Q546R were identified in 4 patients. Overall, the mean variant allele frequency for identified PIK3CA variants was 6.9% (range, 1.6-17.4%). All patients with geographic capillary malformation, histopathological lymphatic malformation or macrodactyly of the foot had PIK3CA variants. No genotype-phenotype association between hotspot and non-hotspot PIK3CA variants was found. Histologically, the vessels and adipose tissues of the lesions showed phosphorylation of the proteins in the PI3K/AKT/mTOR signaling pathway, including p-AKT, p-mTOR, and p-4EBP1.

CONCLUSIONS

The PI3K/AKT/mTOR pathway in mesenchymal tissues was activated in patients with KTS. Amplicon-based targeted NGS could identify low-level mosaicism from low-input DNA extracted from FFPE tissues, potentially providing a diagnostic option for personalized medicine with inhibitors of the PI3K/AKT/mTOR signaling pathway.

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.

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.

Laparoscopy for evaluating mesenteric lymphangiomatosis: A case report

Background

Lymphangiomatosis is an extremely rare disease with potential soft tissue, bone, and spleen involvement, which can be characterized by lymphangioma. Only a few cases of colon and mesenteric lymphangiomatosis have been reported. We report a case presenting with fatigue, periumbilical pain, and intermittent bloody stools. This patient underwent a series of examinations. Exploratory laparoscopy, in particular, yielded very valuable images and videos for this disease, which can provide evidence for the diagnosis of this disease.

Case summary

The current patient had fatigue, periumbilical pain, and intermittent bloody stools. Colonoscopy indicated numerous variable-sized hyaline cysts in the colon. Submucosal puncture was performed during colonoscopy. The patient was readmitted to the hospital due to periumbilical pain. B-ultrasound and abdominal CT showed multiple hypoechoic nodules in the mesenteric area. Exploratory laparoscopy was performed, and histopathology revealed that D2-40 was positive. Based on auxiliary examination and laparoscopic biopsy, surgeons and pathologists reached the diagnosis of mesenteric lymphangiomatosis.

Conclusion

Clinicians need to comprehensively improve their knowledge of lymphangiomatosis, and the combination of clinical symptoms, histological characteristics, and colonoscopy biopsy findings should be considered to improve lymphangiomatosis diagnosis, thereby reducing misdiagnosis.

Core tip

Colon and mesenteric lymphangiomatosis is an extremely uncommon benign condition of unknown etiology and pathogenesis in adult patients. We report a case of mesenteric lymphangiomatosis in a 37-year-old woman who presented with fatigue, periumbilical pain, and intermittent bloody stools, as well as lesions in the kidney, spleen, and bones. This case provides new insights into the diagnosis and treatment of this disease.

Osteopathy in Complex Lymphatic Anomalies

Complex Lymphatic Anomalies (CLA) are lymphatic malformations with idiopathic bone and soft tissue involvement. The extent of the abnormal lymphatic presentation and boney invasion varies between subtypes of CLA. The etiology of these diseases has proven to be extremely elusive due to their rarity and irregular progression. In this review, we compiled literature on each of the four primary CLA subtypes and discuss their clinical presentation, lymphatic invasion, osseous profile, and regulatory pathways associated with abnormal bone loss caused by the lymphatic invasion. We highlight key proliferation and differentiation pathways shared between lymphatics and bone and how these systems may interact with each other to stimulate lymphangiogenesis and cause bone loss.

Topical sirolimus solution for lingual microcystic lymphatic malformations in children and adults (TOPGUN): study protocol for a multicenter, randomized, assessor-blinded, controlled, stepped-wedge clinical trial

Background

Lingual microcystic lymphatic malformations (LMLMs) are rare congenital vascular malformations presenting as clusters of cysts filled with lymph fluid or blood. Even small well-limited lesions can be responsible for a heavy burden, inducing pain, aesthetic prejudice, or oozing, bleeding, infections. The natural history of LMLMs is progressive worsening punctuated by acute flares. Therapeutic options include surgery, laser excision, and radiofrequency ablation but all are potentially detrimental and expose to local relapse. Therefore, the management frequently relies on a “watchful waiting” approach. In complicated LMLMs, treatment with oral sirolimus, a mammalian target of rapamycin (mTOR) inhibitor, is often used. Topical applications of sirolimus on the buccal mucosae have been reported in other oral diseases with good tolerance and none to slight detectable blood sirolimus concentrations. We aim to evaluate the efficacy and safety of a 1 mg/mL sirolimus solution applied once daily on LMLM of any stage in children and adults after 4, 8, 12, 16, 20, and 24 weeks of treatment compared to usual care (no treatment).

Methods

This is a randomized, multicentric study using an individually randomized stepped-wedge design over 24 weeks to evaluate topical application of a 1 mg/mL sirolimus solution once daily, on LMLM, versus usual care (no treatment), the control condition. Participants begin with an observational period and later switch to the intervention at a randomized time (week 0, 4, 8, or 12). Visits occur every 4 weeks, either in the study center or by teleconsulting. The primary outcome will be the evaluation of global severity of the LMLM on monthly standardized photographs by 3 independent blinded experts using the physical global assessment (PGA) 0 to 5 scale. Secondary outcomes will include lesion size measurement and quality of life assessment, investigator, and patient-assessed global disease and specific symptoms (oozing, bleeding, sialorrhea, eating impairment, taste modification, aesthetic impairment, pain, and global discomfort) assessment. A biological monitoring will be performed including residual blood sirolimus concentration and usual laboratory parameters.

Discussion

Given the disappointing state of current treatment options in LMLMs, topical sirolimus could become firstline therapy in treating LMLMs if its efficacy and safety were to be demonstrated.

Trial registration

ClinicalTrials.gov NCT04128722. Registered on 24 September 2019.

EudraCT: EUCTR2019-001530-33-FR

Sponsor (University Hospital Center of Tours – CHRU Tours): DR190041-TOPGUN

French regulatory authorities: ID RCB: 2019-001530-33

Supplementary Information

The online version contains supplementary material available at 10.1186/s13063-022-06365-y.

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.

Combination mTOR and SHP2 inhibitor treatment of lymphatic malformation endothelial cells

Mammalian target of rapamycin (mTOR) inhibitors are clinically effective at treating some complex lymphatic malformations (LM). The mTOR inhibitor rapamycin blocks the phosphoinositide 3-kinase (PI3K) pathway, which is commonly mutated in this condition. Although rapamycin is effective at controlling symptoms of LM, treatment courses are long, not all LMs respond to treatment, and many patients relapse after treatment has stopped. Concurrent rat sarcoma virus (RAS) pathway abnormalities have been identified in LM, which may limit the effectiveness of rapamycin. Protein tyrosine phosphatase-2 (SHP2) controls the RAS pathway upstream, and SHP2 inhibitors are being investigated for treatment of various tumors. The objective of this study was to determine the impact of SHP2 inhibition in combination with rapamycin on LM growth in vitro. Using primary patient cells isolated from a surgically resected LM, we found that combination treatment with rapamycin and the SHP2 inhibitor SHP099 caused a synergistic reduction in cell growth, migration and lymphangiogenesis. These results suggest that combination treatment targeting the PI3K and RAS signaling pathways may result in effective treatment of LMs of the head and neck.

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.

The Genetics of Vascular Birthmarks

One in ten infants are born with a vascular birthmark each year. Some vascular birthmarks, such as infantile hemangiomas, are common, while vascular malformations, such as capillary, lymphatic, venous, and arteriovenous malformations, are less so. Diagnosing uncommon vascular birthmarks can be challenging, given the phenotypic heterogeneity and overlap amongst these lesions. Both sporadic and germline variants have been detected in various genes associated with vascular birthmarks. Identification of these genetic variants offers insight into both diagnosis and underlying molecular pathways and can be fundamental in the discovery of novel therapeutic approaches. The PIK3/AKT/mTOR and RAS/MEK/ERK signaling pathways, which mediate cell growth and angiogenesis, are activated secondary to genetic variations in vascular malformations. Somatic variants in TEK (TIE2) and PIK3CA cause venous malformations. Variants in PIK3CA also cause lymphatic malformations as well as a number of overgrowth syndromes associated with vascular anomalies. Variants in GNAQ and GNA11 have been identified in both so-called "congenital" hemangiomas and capillary malformations. RASA1 and EPHB4 variants are associated with capillary malformation-arteriovenous malformation syndrome. This review discusses the genetics of vascular birthmarks including the various phenotypes, genetic variants, pathogenesis, associated syndromes, and new diagnostic techniques.

Introduction of Mutant GNAQ into Endothelial Cells Induces a Vascular Malformation Phenotype with Therapeutic Response to Imatinib

Simple Summary

Mutations in GNAQ underlie vascular malformations, including Sturge-Weber disease. In order to develop novel therapies for lesions with mutant GNAQ, we introduced mutant GNAQ into MS1 endothelial cells. Mutant GNAQ conferred a novel phenotype of progressive vascular malformations in mice. Chromatin analysis revealed upregulation of C-Kit in the vascular endothelial cells, and we found C-Kit to be highly expressed in Sturge-Weber disease. Given that imatinib is an FDA approved multikinase inhibitor that blocks C-Kit, we evaluated it in our mouse model, and showed that imatinib had activity against these vascular malformations. Repurposing imatinib should be evaluated in clinical trials, including Sturge-Weber disease.

Abstract

GNAQ is mutated in vascular and melanocytic lesions, including vascular malformations and nevi. No in vivo model of GNAQ activation in endothelial cells has previously been described. We introduce mutant GNAQ into a murine endothelial cell line, MS1. The resultant transduced cells exhibit a novel phenotype in vivo, with extensive vasoformative endothelial cells forming aberrant lumens similar to those seen in vascular malformations. ATAC-seq analysis reveals activation of c-Kit in the novel vascular malformations. We demonstrate that c-Kit is expressed in authentic human Sturge–Weber vascular malformations, indicating a novel druggable target for Sturge–Weber syndrome. Since c-Kit is targeted by the FDA-approved drug imatinib, we tested the ability of imatinib on the phenotype of the vascular malformations in vivo. Imatinib treated vascular malformations are significantly smaller and have decreased supporting stromal cells surrounding the lumen. Imatinib may be useful in the treatment of human vascular malformations that express c-Kit, including Sturge–Weber syndrome.

Lymphatic Endothelial Cell Defects in Congenital Cardiac Patients With Postoperative Chylothorax

Objectives

Chylothorax following cardiac surgery for congenital cardiac anomalies is a complication associated with severe morbidities and mortality. We hypothesize that there are intrinsic defects in the lymphatics of congenital cardiac patients.

Methods

Postsurgical chylothorax lymphatic endothelial cells (pcLECs) (n = 10) were isolated from the chylous fluid from congenital cardiac defect patients, and characterized by fluorescent-activated cell sorting, immunofluorescent staining, and quantitative RT-PCR. Results were compared to normal human dermal lymphatic endothelial cells (HdLECs). pcLECs (n = 3) and HdLECs were xenografted into immunocompromised mice. Implants and postoperative chylothorax patient's pulmonary tissues were characterized by immunostaining for lymphatic endothelial proteins.

Results

pcLECs expressed endothelial markers VECADHERIN, CD31, VEGFR2, lymphatic endothelial markers PROX1, podoplanin, VEGFR3, and progenitor endothelial markers CD90 and CD146. However, pcLECs had key differences relative to HdLECs, including altered expression and mislocalization of junctional proteins (VECADHERIN and CD31), and essential endothelial proteins, VEGFR2, VEGFR3, and PROX1. When xenografted in mice, pcLECs formed dilated lymphatic channels with poor cell-cell association. Similar to congenital lymphatic anomalies, the pulmonary lymphatics were dilated in a patient who developed postoperative chylothorax after cardiac surgery.

Conclusions

Recent studies have shown that some postoperative chylothoraces in congenital cardiac anomalies are associated with anatomical lymphatic defects. We found that pcLECs have defects in expression and localization of proteins necessary to maintain lymphatic specification and function. This pcLEC phenotype is similar to that observed in lymphatic endothelial cells from congenital lymphatic anomalies. Co-existence of lymphatic anomalies should be considered as a feature of congenital cardiac anomalies.

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.

Refractory Head and Neck Lymphatic Malformation in Infants Treated With Sirolimus: A Case Series

Background

Extensive and complex head and neck lymphatic malformations (LMs) are challenging to manage through traditional therapy. The purpose of this retrospective study was to assess the efficacy and safety of sirolimus in infants with refractory head and neck LMs.

Methods

Sirolimus was administered orally on a continuous dosing schedule. Patients were seen every month for the first three months and then subsequently every three months. The primary endpoints were safety and efficacy based on clinical and radiological evaluations.

Results

Eight patients, refractory to standard care, were enrolled and received sirolimus continuously. After 12 months of follow-up, the response and safety to medication was evaluated: all patients experienced reductions in LMs bulk, ranging from modest to significant. Some minor adverse effects were reported: mouth sores, eczema, gastrointestinal reaction, dyslipidemia, and neutropenia.

Conclusion

Sirolimus was efficient in children with refractory head and neck LMs and was well tolerated.

Lymphatic Malformations: Genetics, Mechanisms and Therapeutic Strategies

Lymphatic vessels maintain tissue fluid homeostasis by returning to blood circulation interstitial fluid that has extravasated from the blood capillaries. They provide a trafficking route for cells of the immune system, thus critically contributing to immune surveillance. Developmental or functional defects in the lymphatic vessels, their obstruction or damage, lead to accumulation of fluid in tissues, resulting in lymphedema. Here we discuss developmental lymphatic anomalies called lymphatic malformations and complex lymphatic anomalies that manifest as localized or multifocal lesions of the lymphatic vasculature, respectively. They are rare diseases that are caused mostly by somatic mutations and can present with variable symptoms based upon the size and location of the lesions composed of fluid-filled cisterns or channels. Substantial progress has been made recently in understanding the molecular basis of their pathogenesis through the identification of their genetic causes, combined with the elucidation of the underlying mechanisms in animal disease models and patient-derived lymphatic endothelial cells. Most of the solitary somatic mutations that cause lymphatic malformations and complex lymphatic anomalies occur in genes that encode components of oncogenic growth factor signal transduction pathways. This has led to successful repurposing of some targeted cancer therapeutics to the treatment of lymphatic malformations and complex lymphatic anomalies. Apart from the mutations that act as lymphatic endothelial cell-autonomous drivers of these anomalies, current evidence points to superimposed paracrine mechanisms that critically contribute to disease pathogenesis and thus provide additional targets for therapeutic intervention. Here, we review these advances and discuss new treatment strategies that are based on the recently identified molecular pathways.

Non-hotspot PIK3CA mutations are more frequent in CLOVES than in common or combined lymphatic malformations

Background

Theragnostic management, treatment according to precise pathological molecular targets, requests to unravel patients’ genotypes. We used targeted next-generation sequencing (NGS) or digital droplet polymerase chain reaction (ddPCR) to screen for somatic PIK3CA mutations on DNA extracted from resected lesional tissue or lymphatic endothelial cells (LECs) isolated from lesions. Our cohort (n = 143) was composed of unrelated patients suffering from a common lymphatic malformation (LM), a combined lymphatic malformation [lymphatico-venous malformation (LVM), capillaro-lymphatic malformation (CLM), capillaro-lymphatico-venous malformation (CLVM)], or a syndrome [CLVM with hypertrophy (Klippel-Trenaunay-Weber syndrome, KTS), congenital lipomatous overgrowth-vascular malformations-epidermal nevi -syndrome (CLOVES), unclassified PIK3CA-related overgrowth syndrome (PROS) or unclassified vascular (lymphatic) anomaly syndrome (UVA)].

Results

We identified a somatic PIK3CA mutation in resected lesions of 108 out of 143 patients (75.5%). The frequency of the variant allele ranged from 0.54 to 25.33% in tissues, and up to 47% in isolated endothelial cells. We detected a statistically significant difference in the distribution of mutations between patients with common and combined LM compared to the syndromes, but not with KTS. Moreover, the variant allele frequency was higher in the syndromes.

Conclusions

Most patients with an common or combined lymphatic malformation with or without overgrowth harbour a somatic PIK3CA mutation. However, in about a quarter of patients, no such mutation was detected, suggesting the existence of (an)other cause(s). We detected a hotspot mutation more frequently in common and combined LMs compared to syndromic cases (CLOVES and PROS). Diagnostic genotyping should thus not be limited to PIK3CA hotspot mutations. Moreover, the higher mutant allele frequency in syndromes suggests a wider distribution in patients’ tissues, facilitating detection. Clinical trials have demonstrated efficacy of Sirolimus and Alpelisib in treating patients with an LM or PROS. Genotyping might lead to an increase in efficacy, as treatments could be more targeted, and responses could vary depending on presence and type of PIK3CA-mutation.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13023-021-01898-y.

Vascular anomalies of the head and neck: diagnosis and treatment

Vascular malformations and vascular tumors comprise the two specific subsets of vascular anomalies that arise as a result of disorganized angiogenesis and neoplasm, respectively. Malformations are separate entities from vascular tumors (e.g., hemangiomas) and are recognized by the International Society for the Study of Vascular Anomalies (ISSVA) as such. Vascular malformations are classified into four main groups: simple, combined, anomalies of major vessels, and those associated with other vascular anomalies. Vascular tumors are neoplastic growths of blood vessels and are morphologically and molecularly distinct from malformations but can arise in the head and neck and have syndromic association. Head and neck vascular anomalies are not uncommon in the pediatric population and require special care in the workup, diagnostic imaging and clinical care. The purpose of this manuscript is to discuss the diagnosis and management of the most common intracranial and extracranial vascular malformations and tumors in the head and neck in children and adolescents.

A somatic mutation in PIK3CD unravels a novel candidate gene for lymphatic malformation

Background

Lymphatic malformations (LMs) are benign congenital malformations that stem from the abnormal development of the lymphatic vessels during early embryogenesis. Somatic PIK3CA gene mutations are conventional cause leading to LMs. Both macrocystic and microcystic LMs arise due to lymphatic endothelial cell-autonomous defects, depending on the time in development at which PIK3CA gene mutation occurs. Recent study finds a PIK3CA mutation in 79% of LMs. However, discovering new genetic events in this disease is crucial to identify the molecular mechanism of the pathogenesis and further develop new targeted therapies.

Results

Here, we initially performed whole-exome sequencing in six children with LMs to find a new causal gene. Somatic mutations in PIK3CA (c.1633G > A [p. E545K] and PIK3CD (c.1997T > C [p.L666P]) were discovered in two different individuals. In vitro functional studies were conducted to demonstrate the pathogenicity of the novel mutation c.1997T > C in PIK3CD. We found that L666P promoted the cell proliferation and migration of human umbilical vein endothelial cells (HUVECs) and induced hyperactivation of the mTOR pathway. These findings indicate that the PIK3CD mutation affects downstream signalling in endothelial cells, which may impair normal lymphangiogenesis.

Conclusions

This study reveals a novel candidate gene associated with the development of LMs, which is consistent with previous researches. These findings in our study may offer a novel gene target for developing therapies, which acts in tight interaction with the previously known PIK3CA.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13023-021-01782-9.

Molecular mechanisms detected in yak lung tissue via transcriptome-wide analysis provide insights into adaptation to high altitudes

Due to their long-term colonization of and widespread distribution in plateau environments, yaks can serve as an ideal natural animal model for the adaptive evolution of other plateau species, including humans. Some studies reported that the lung and heart are two key organs that show adaptive transcriptional changes in response to high altitudes, and most of the genes that show differential expression in lung tissue across different altitudes display nonlinear regulation. To explore the molecular mechanisms that are activated in yak lung tissue in response to hypoxia, the mRNAs, lncRNAs and miRNAs of lung tissue from 9 yaks living at three different altitudes (3400 m, 4200 m and 5000 m), with three repetitions per altitude, were sequenced. Two Zaosheng cattle from 1500 m were selected as low-altitude control. A total of 21,764 mRNAs, 14,168 lncRNAs and 1209 miRNAs (305 known and 904 novel miRNAs) were identified. In a comparison of yaks and cattle, 4975 mRNAs, 3326 lncRNAs and 75 miRNAs were differentially expressed. A total of 756 mRNAs, 346 lncRNAs and 83 miRNAs were found to be differentially expressed among yaks living at three different altitudes (fold change ≥ 2 and P-value < 0.05). The differentially expressed genes between yaks and cattle were functionally enriched in long-chain fatty acid metabolic process and protein processing, while the differentially expressed genes among yaks living at three different altitudes were enriched in immune response and the cell cycle. Furthermore, competing endogenous RNA (ceRNA) networks were investigated to illustrate the roles of ceRNAs in this process, the result was also support the GO and KEGG analysis. The present research provides important genomic insights for discovering the mechanisms that are activated in response to hypoxia in yak lung tissue.

Role of receptor tyrosine kinases mediated signal transduction pathways in tumor growth and angiogenesis-New insight and futuristic vision

In the past two decades, significant progress has been made in the past two decades towards the understanding of the basic mechanisms underlying cancer growth and angiogenesis. In this context, receptor tyrosine kinases (RTKs) play a pivotal role in cell proliferation, differentiation, growth, motility, invasion, and angiogenesis, all of which contribute to tumor growth and progression. Mutations in RTKs lead to abnormal signal transductions in several pathways such as Ras-Raf, MEK-MAPK, PI3K-AKT and mTOR pathways, affecting a wide range of biological functions including cell proliferation, survival, migration and vascular permeability. Increasing evidence demonstrates that multiple kinases are involved in angiogenesis including RTKs such as vascular endothelial growth factor, platelet derived growth factor, epidermal growth factor, insulin-like growth factor-1, macrophage colony-stimulating factor, nerve growth factor, fibroblast growth factor, Hepatocyte Growth factor, Tie 1 & 2, Tek, Flt-3, Flt-4 and Eph receptors. Overactivation of RTKs and its downstream regulation is implicated in tumor initiation and angiogenesis, representing one of the hallmarks of cancer. This review discusses the role of RTKs, PI3K, and mTOR, their involvement, and their implication in pro-oncogenic cellular processes and angiogenesis with effective approaches and newly approved drugs to inhibit their unrestrained action.

Oxidatively Modified LDL Suppresses Lymphangiogenesis via CD36 Signaling

Arterial accumulation of plasma-derived LDL and its subsequent oxidation contributes to atherosclerosis. Lymphatic vessel (LV)-mediated removal of arterial cholesterol has been shown to reduce atherosclerotic lesion formation. However, the precise mechanisms that regulate LV density and function in atherosclerotic vessels remain to be identified. The aim of this study was to investigate the role of native LDL (nLDL) and oxidized LDL (oxLDL) in modulating lymphangiogenesis and underlying molecular mechanisms. Western blotting and immunostaining experiments demonstrated increased oxLDL expression in human atherosclerotic arteries. Furthermore, elevated oxLDL levels were detected in the adventitial layer, where LV are primarily present. Treatment of human lymphatic endothelial cells (LEC) with oxLDL inhibited in vitro tube formation, while nLDL stimulated it. Similar results were observed with Matrigel plug assay in vivo. CD36 deletion in mice and its siRNA-mediated knockdown in LEC prevented oxLDL-induced inhibition of lymphangiogenesis. In addition, oxLDL via CD36 receptor suppressed cell cycle, downregulated AKT and eNOS expression, and increased levels of p27 in LEC. Collectively, these results indicate that oxLDL inhibits lymphangiogenesis via CD36-mediated regulation of AKT/eNOS pathway and cell cycle. These findings suggest that therapeutic blockade of LEC CD36 may promote arterial lymphangiogenesis, leading to increased cholesterol removal from the arterial wall and reduced atherosclerosis.

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.

Effectiveness of sirolimus in the treatment of complex lymphatic malformations: Single center report of 56 cases

BACKGROUND

Lymphatic malformations are common congenital vascular lesions. Neither surgical resection nor other surgical treatments have been found to be effective for invasive cases. Recent research has suggested that sirolimus is effective in treating complex lymphatic malformations (LMs). We aimed to evaluate the effectiveness and safety of oral sirolimus for children living with LMs in our hospital.

METHODS

Fifty-six cases of complex LMs treated with sirolimus were collected from Shanghai Children's Medical Centre between June 2016 and March 2019. All cases were confirmed either by pathology (44) or enhanced MRI (12). Following informed consent, sirolimus 0.8 mg/m² bid was administered orally to participants and maintained at a trough concentration of 10-15 ng/ml. Children's ages at diagnosis were neonate to 16 years (mean 44.3 months). All children were followed up for 5 to 30 months, with a mean of 16.8 months.

RESULTS

During the follow-up period, blood, liver and kidney function as well as disseminated intravascular coagulation was regularly reviewed in all 56 children. Enhanced MRI was regularly performed to evaluate therapeutic effects. Total effective rate (complete response or partial response) of LMs was 89.3% (50/56). No serious adverse reactions were found.

CONCLUSION

This study suggests that sirolimus is effective and tolerable for decreasing lesions in children with complex LMs, leading to fewer and more tolerable side effects. There is no need to pursue an excision rate to reduce unnecessary operative complications since adjuvant sirolimus therapy modifies the complex LMs clinical appearance and alleviates their symptoms.

TYPE OF STUDY

Clinical research.

LEVEL OF EVIDENCE

Level IV.

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.

A novel method for isolating lymphatic endothelial cells from lymphatic malformations and detecting PIK3CA somatic mutation in these isolated cells

PURPOSE

Tissue disaggregation and the cell sorting technique by surface markers has played an important role in isolating lymphatic endothelial cells (LECs) from lymphatic malformation (LM). However, this technique may have the drawback of impurities or result in isolation failure because it is dependent on surface marker expressions, the heterogeneity of which has been found in the lymphatic system. We developed a novel method for isolating LM-LECs without using whole tissue disaggregation.

METHODS

Seven LM surgical specimens were collected from seven patients with LMs. LM-LECs were detached from the LM cyst wall by "lumen digestion" and irrigating the cystic cavity with trypsin, and maintained in culture.

RESULTS

The cells formed a monolayer with a cobblestone-like appearance. Immunohistochemistry and quantitative RT-PCR of these cells revealed high expression of lymphatic-specific genes, confirming their identity as LM-LECs. The whole-exome sequencing and PIK3CA sequencing of these cells revealed somatic mutations in PIK3CA in all cases.

CONCLUSIONS

We established a novel technique for isolating LM-LECs from LM tissue by "lumen digestion" without whole-tissue disaggregation. The limited incorporation of non-LM LECs in the isolate in our method could make it an important tool for investigating the heterogeneity of gene expression as well as mutations in LM-LECs.

Fibro-adipose vascular anomaly (FAVA): three case reports with an emphasis on the mammalian target of rapamycin (mTOR) pathway

BACKGROUND

Fibro-adipose vascular anomaly (FAVA) is a new entity of vascular anomalies with somatic and mosaic gain-of-function mutations of the phosphatidylinositol-4, 5-bisphosphate 3-kinase catalytic subunit alpha (PIK3CA). PIK3CA mutation excessively activates mammalian target of rapamycin (mTOR) pathway, which promotes angiogenesis and lymphangiogenesis. Histologically, FAVA is composed of intramuscular fibrous and adipose tissues with venous malformation (VM). Although sirolimus known as a mTOR inhibitor has good response to FAVA, expression pattern of the mTOR pathway was still unclear. Herein, we immunohistochemically investigated three novel FAVA patients with an emphasis on the mTOR pathway (p-S6K1, p-4EBP1 and p-AKT).

CASE PRESENTATION

Case 1: A 10-year-old female had complained of pain in the left thigh since she was 6-year-old. Under the clinical diagnosis of VM, she underwent surgical resection for the lesion. Case 2: A 29-year-old female patient had complained of discomfort and mild pain in the left shoulder since she was 18-year-old. After childbirth, she had severe ongoing pain and contracture of the shoulder. Under clinical diagnosis of VM, surgical resection was performed. Case 3: A 53-year-old female had complained of pain and knee restriction after surgical treatment of a knee tumor at the age of 31. Under the clinical diagnosis of atypical lipomatous tumor or high grade liposarcoma, surgical resection was performed. Histologically, all three patients presented with characteristic features of fibrous and adipose tissues with abnormal vessels within the skeletal muscle, leading to diagnosis of FAVA. Although VM has been reported as an important finding in FAVA, immunohistological findings demonstrated that abnormal vessels comprised complex of VM and lymphatic malformation (LM) in all cases. Furthermore, besides vascular malformation, abnormal fibrous and adipose tissues of FAVA expressed mTOR pathway components.

CONCLUSIONS

We presented three new cases of FAVA. Histological and immunohistochemical analyses revealed that VM and LM complex was an important finding in FAVA, and that the mTOR pathway components were expressed in abnormal fibrous tissue, adipose tissue and vascular malformation. These findings suggested that FAVA might be a mesenchymal malformation caused by PI3K/AKT/mTOR pathway.

Emerging importance of molecular pathogenesis of vascular malformations in clinical practice and classifications

Vascular malformations occur during early vascular development resulting in abnormally formed vessels that can manifest as arterial, venous, capillary or lymphatic lesions, or in combination, and include local tissue overdevelopment. Vascular malformations are largely caused by sporadic somatic gene mutations. This article aims to review and discuss current molecular signaling pathways and therapeutic targets for vascular malformations and to classify vascular malformations according to the molecular pathways involved. A literature review was performed using Embase and Medline. Different MeSH terms were combined for the search strategy, with the aim of encompassing all studies describing the classification, pathogenesis, and treatment of vascular malformations. Major pathways involved in the pathogenesis of vascular malformations are vascular endothelial growth factor (VEGF), Ras/Raf/MEK/ERK, angiopoietin-TIE2, transforming growth factor beta (TGF-β), and PI3K/AKT/mTOR. These pathways are involved in controlling cellular growth, apoptosis, differentiation, and proliferation, and play a central role in endothelial cell signaling and angiogenesis. Many vascular malformations share similar aberrant molecular signaling pathways with cancers and inflammatory disorders. Therefore, selective anticancer agents and immunosuppressants may be beneficial in treating vascular malformations of specific mutations. The current classification systems of vascular malformations, including the International Society of the Study of Vascular Anomalies (ISSVA) classification, are primarily observational and clinical, and are not based on the molecular pathways involved in the pathogenesis of the condition. Several molecular pathways with potential therapeutic targets have been demonstrated to contribute to the development of various vascular anomalies. Classifying vascular malformations based on their molecular pathogenesis may improve treatment by determining the underlying nature of the condition and their potential therapeutic target.

Blockade of VEGF-C signaling inhibits lymphatic malformations driven by oncogenic PIK3CA mutation

Lymphatic malformations (LMs) are debilitating vascular anomalies presenting with large cysts (macrocystic) or lesions that infiltrate tissues (microcystic). Cellular mechanisms underlying LM pathology are poorly understood. Here we show that the somatic PIK3CA^H1047R mutation, resulting in constitutive activation of the p110α PI3K, underlies both macrocystic and microcystic LMs in human. Using a mouse model of PIK3CA^H1047R-driven LM, we demonstrate that both types of malformations arise due to lymphatic endothelial cell (LEC)-autonomous defects, with the developmental timing of p110α activation determining the LM subtype. In the postnatal vasculature, PIK3CA^H1047R promotes LEC migration and lymphatic hypersprouting, leading to microcystic LMs that grow progressively in a vascular endothelial growth factor C (VEGF-C)-dependent manner. Combined inhibition of VEGF-C and the PI3K downstream target mTOR using Rapamycin, but neither treatment alone, promotes regression of lesions. The best therapeutic outcome for LM is thus achieved by co-inhibition of the upstream VEGF-C/VEGFR3 and the downstream PI3K/mTOR pathways.

Lymphatic malformation (LM) is a debilitating often incurable vascular disease. Using a mouse model of LM driven by a disease-causative PIK3CA mutation, the authors show that vascular growth is dependent on the upstream lymphangiogenic VEGF-C signalling, permitting effective therapeutic intervention.

The molecular pathophysiology of vascular anomalies: Genomic research

Vascular anomalies are congenital localized abnormalities that result from improper development and maintenance of the vasculature. The lesions of vascular anomalies vary in location, type, and clinical severity of the phenotype, and the current treatment options are often unsatisfactory. Most vascular anomalies are sporadic, but patterns of inheritance have been noted in some cases, making genetic analysis relevant. Developments in the field of genomics, including next-generation sequencing, have provided novel insights into the genetic and molecular pathophysiological mechanisms underlying vascular anomalies. These insights may pave the way for new approaches to molecular diagnosis and potential disease-specific therapies. This article provides an introduction to genetic testing for vascular anomalies and presents a brief summary of the etiology and genetics of vascular anomalies.

Tuberous sclerosis complex presenting as primary intestinal lymphangiectasia: A case report

BACKGROUND

Primary intestinal lymphangiectasia (PIL) is a rare congenital protein-losing enteropathy caused by dysplasia of the small intestinal lymphatics. The cause of the disease is unknown. Through a literature review, we found that PIL and tuberous sclerosis complex (TSC) have some common symptoms and molecular pathways.

CASE SUMMARY

Here, we present the case of a patient with a three-year history of primary intestinal lymphangiectasia. The patient most recently visited the hospital with abdominal distension and swelling of the left leg. His mother told us that she was diagnosed with TSC one year previously, which alerted us because the patient had multiple regions of pigmentation. To evaluate the condition of the child and make a definite diagnosis, multiple imaging examinations were performed, as was TSC gene analysis. The results met the diagnostic criteria for TSC. The patient was discharged after symptomatic treatment. Through a review of the literature, it can be seen that changes at the molecular gene level of TSC can lead to abnormal lymphatic vessels.

CONCLUSION

In summary, when patients with hypomelanotic macules or enamel hypoplasia are diagnosed with PIL, TSC gene screening may be important for further diagnosis.

Constitutively active PIK3CA mutations are expressed by lymphatic and vascular endothelial cells in capillary lymphatic venous malformation

Capillary lymphatic venous malformations (CLVM) are complex vascular anomalies characterized by aberrant and enlarged lymphatic and blood vessels. CLVM appear during fetal development and enlarge after birth, causing life-long complications such as coagulopathy, pulmonary embolism, chronic pain, and disfigurement. Treatment includes surgical debulking, amputation, and recurrent sclerotherapy. Somatic, mosaic mutations in the 110-kD catalytic α-subunit of phosphoinositide-3-kinase (PIK3CA) gene have been previously identified in affected tissues from CLVM patients; however, the cell population harboring the mutation is still unknown. In this study, we hypothesized that endothelial cells (EC) carry the PIK3CA mutations and play a major role in the cellular origin of CLVM. We isolated EC from the lesions of seven patients with CLVM and identified PIK3CA hotspot mutations. The CLVM EC exhibited constitutive phosphorylation of the PI3K effector AKT as well as hyperproliferation and increased resistance to cell death compared to normal EC. Inhibitors of PIK3CA (BYL719) and AKT (ARQ092) attenuated the proliferation of CLVM EC in a dose-dependent manner. A xenograft model of CLVM was developed by injecting patient-derived EC into the flanks of immunocompromised mice. CLVM EC formed lesions with enlarged lymphatic and vascular channels, recapitulating the patient histology. EC subpopulations were further obtained by both immunomagnetic separation into lymphatic EC (LEC) and vascular EC (VEC) and generation of clonal populations. By sequencing these subpopulations, we determined that both LEC and VEC from the same patient express the PIK3CA mutation, exhibit increased AKT activation and can form lymphatic or vascular lesions in mouse.

Lymphatics in bone arise from pre-existing lymphatics

Bones do not normally have lymphatics. However, individuals with generalized lymphatic anomaly (GLA) or Gorham-Stout disease (GSD) develop ectopic lymphatics in bone. Despite growing interest in the development of tissue-specific lymphatics, the cellular origin of bone lymphatic endothelial cells (bLECs) is not known and the development of bone lymphatics has not been fully characterized. Here, we describe the development of bone lymphatics in mouse models of GLA and GSD. Through lineage-tracing experiments, we show that bLECs arise from pre-existing Prox1-positive LECs. We show that bone lymphatics develop in a stepwise manner where regional lymphatics grow, breach the periosteum and then invade bone. We also show that the development of bone lymphatics is impaired in mice that lack osteoclasts. Last, we show that rapamycin can suppress the growth of bone lymphatics in our models of GLA and GSD. In summary, we show that bLECs can arise from pre-existing LECs and that rapamycin can prevent the growth of bone lymphatics.

Analysis of mTOR pathway expression in lymphatic malformation and related diseases

The mammalian target of rapamycin (mTOR) inhibitor sirolimus is an effective treatment for difficult-to-treat lymphatic anomalies. However, little is known about the expression of mTOR pathway components in lymphatic anomalies. Here we investigated the expression pattern of mTOR pathway components and their phosphorylated forms (mTOR, p-mTOR, 4EBP1, p-4EBP1, S6K1 and p-S6K1) in normal lymphatic vessels and lymphatic anomalies using immunohistochemistry. We studied 18 patients of lymphatic anomalies, including lymphatic malformation (LM, n = 14), Kaposiform lymphangiomatosis (KLA, n = 2) and Kaposiform hemangioendothelioma (KHE, n = 2). Normal lymphatic vessels expressed 4EBP1, S6K1 and p-S6K1, but not p-4EBP1, mTOR or p-mTOR. The mTOR was detected in all lymphatic anomalies, whereas its activation form p-mTOR was detected in half cases of KLA and KHE but not in LM. All lymphatic anomalies expressed S6K1 and its activated form p-S6K1. The expression of 4EBP1 was also found in all lymphatic anomalies, but its activation was detected in approximately half of them. The activation of mTOR was seen in tumor (KLA and KHE) but not in malformation (LM), whereas the activation of S6K1 and 4EBP1 was seen in all and half of lymphatic anomalies, respectively.

Successful treatment of diffuse pulmonary lymphangiomatosis with sirolimus

Diffuse pulmonary lymphangiomatosis (DPL) is a rare disease characterized by uncontrolled proliferation of anastomosing lymphatic channels in the lungs, pleura and mediastinum. Several palliative treatment options have been suggested for this condition, such as surgical interventions, radiotherapy and systemic medications. However, the existing treatment modalities yield inconsistent results, and their use is often limited by toxic side effects. The aim of this case report is to demonstrate the diagnostic challenges of a rare disease and improvement in the condition of a DPL patient treated with sirolimus. A 27-year-old man presented to the pulmonologist with exertional dyspnea, chronic cough and intermittent hemoptysis. Upon medical investigation, a chest computed tomography (CT) scan revealed soft tissue masses infiltrating the mediastinum and bilateral interlobular septal thickening. A surgical biopsy was performed, and pathological tissue analysis showed findings consistent with the diagnosis of DPL. Treatment with sirolimus was initiated, maintaining trough concentrations between 10 and 15 ng/ml. At 21 months of treatment, the patient reported reduced symptoms of cough and dyspnea. A CT scan showed decreased interstitial thickening and reduced infiltrations in the mediastinum. Moreover, pulmonary function tests revealed a significant increase in FEV1 and FVC. The authors believe this is the first article reporting pulmonary function improvement in an adult DPL patient treated with sirolimus. Therefore, sirolimus therapy should be considered for DPL patients as it may be effective in improving their condition and preventing disease progression.

Isolation of Stem Cells, Endothelial Cells and Pericytes from Human Infantile Hemangioma

Infantile hemangioma (IH) is a vascular tumor noted for its excessive blood vessel formation during infancy, glucose-transporter-1 (GLUT1)-positive staining of the blood vessels, and its slow spontaneous involution over several years in early childhood. For most children, IH poses no serious threat because it will eventually involute, but a subset can destroy facial structures and impair vision, breathing and feeding. To unravel the molecular mechanism(s) driving IH-specific vascular overgrowth, which to date remains elusive, investigators have studied IH histopathology, the cellular constituents and mRNA expression. Hemangioma endothelial cells (HemEC) were first isolated from surgically removed IH specimens in 1982 by Mulliken and colleagues ( Mulliken et al., 1982 ). Hemangioma stem cells (HemSC) were isolated in 2008, hemangioma pericytes in 2013 and GLUT1-positive HemEC in 2015. Indeed, as we describe here, it is possible to isolate HemSC, GLUT1-positive HemEC, GLUT1-negative HemEC and HemPericytes from a single proliferating IH tissue specimen. This is accomplished by sequential selection using antibodies against specific cell surface markers: anti-CD133 to select HemSC, anti-GLUT1 and anti-CD31 to select HemECs and anti-PDGFRβ to select HemPericytes. IH-derived cells proliferate well in culture and can be used for in vitro and in vivo vasculogenesis and angiogenesis assays.

Ponatinib Combined With Rapamycin Causes Regression of Murine Venous Malformation

Objective- Venous malformations (VMs) arise from developmental defects of the vasculature and are characterized by massively enlarged and tortuous venous channels. VMs grow commensurately leading to deformity, obstruction of vital structures, bleeding, and pain. Most VMs are associated with the activating mutation L914F in the endothelial cell (EC) tyrosine kinase receptor TIE2. Therapeutic options for VM are limited and ineffective while therapy with the mammalian target of rapamycin inhibitor rapamycin shows moderate efficacy. Here, we investigated novel therapeutic targets promoting VM regression. Approach and Results- We performed an unbiased screen of Food and Drug Administration-approved drugs in human umbilical vein ECs expressing the TIE2-L914F mutation (HUVEC-TIE2-L914F). Three ABL (Abelson) kinase inhibitors prevented cell proliferation of HUVEC-TIE2-L914F. Moreover, c-ABL, common target of these inhibitors, was highly phosphorylated in HUVEC-TIE2-L914F and VM patient-derived ECs with activating TIE2 mutations. Knockdown of c-ABL/ARG in HUVEC-TIE2-L914F reduced cell proliferation and vascularity of murine VM. Combination treatment with the ABL kinase inhibitor ponatinib and rapamycin caused VM regression in a xenograft model based on injection of HUVEC-TIE2-L914F. A reduced dose of this drug combination was effective in this VM murine model with minimal side effects. The drug combination was antiproliferative, enhanced cell apoptosis and vascular channel regression both in vivo and in a 3-dimensional fibrin gel assay. Conclusions- This is the first report of a combination therapy with ponatinib and rapamycin promoting regression of VM. Mechanistically, the drug combination enhanced AKT inhibition compared with single drug treatment and reduced PLCγ (phospholipase C) and ERK (extracellular signal-regulated kinase) activity.

Paracrine Effects of Adipose-Derived Stem Cells Promote Lymphangiogenesis in Irradiated Lymphatic Endothelial Cells

BACKGROUND

There is currently no reliable treatment for secondary lymphedema caused by lymph node dissection or radiotherapy; however, stem cell-based regenerative medicine is emerging as a promising remedy for such complications. The purpose of this study was to examine the effects of adipose-derived stem cells on lymphangiogenesis involving human dermal lymphatic endothelial cells exposed to ionizing radiation.

METHODS

Proliferation, migration, and tube formation were analyzed in human dermal lymphatic endothelial cells that were co-cultured with adipose-derived stem cells or cultured in adipose-derived stem cell-conditioned medium. The levels of lymphangiogenic factors secreted from adipose-derived stem cells were analyzed by enzyme-linked immunosorbent assays and Western blotting.

RESULTS

Co-culturing with adipose-derived stem cells and the use of adipose-derived stem cell-conditioned medium both significantly promoted proliferation, migration, and tube formation in nonirradiated human dermal lymphatic endothelial cells. The authors also found that irradiated adipose-derived stem cells had similar alleviative effects on irradiated human dermal lymphatic endothelial cells. Enzyme-linked immunosorbent assays and Western blotting analysis revealed that irradiating adipose-derived stem cells increased their secretion of basic fibroblast growth factor in a dose-dependent manner, whereas it caused no detectable change in their secretion of vascular endothelial growth factor A or C, or hepatocyte growth factor.

CONCLUSIONS

These results demonstrated that factors secreted by adipose-derived stem cells contribute to the promotion of lymphangiogenesis in irradiated human dermal lymphatic endothelial cells. The authors' findings also suggest that radiation potentiates the paracrine effects of adipose-derived stem cells by stimulating basic fibroblast growth factor protein expression.