Mutations in FOXC2 Are Strongly Associated With Primary Valve Failure in Veins of the Lower Limb

Lymphatic System Development and Function

PURPOSE OF REVIEW

This review delves into recent advancements in understanding generalized and organ-specific lymphatic development. It emphasizes the distinct characteristics and critical anomalies that can impair lymphatic function. By exploring developmental mechanisms, the review seeks to illuminate the profound impact of lymphatic malformations on overall health and disease progression.

RECENT FINDINGS

The introduction of genome sequencing, single-cell transcriptomic analysis, and advanced imaging technologies has significantly enhanced our ability to identify and characterize developmental defects within the lymphatic system. As a result, a wide range of lymphatic anomalies have been uncovered, spanning from congenital abnormalities present at birth to conditions that can become life-threatening in adulthood. Additionally, recent research highlights the heterogeneity of lymphatics, revealing organ-specific developmental pathways, unique molecular markers, and specialized physiological functions specific to each organ. A deeper understanding of the unique characteristics of lymphatic cell populations in an organ-specific context is essential for guiding future research into lymphatic disease processes. An integrated approach to translational research could revolutionize personalized medicine, where treatments are precisely tailored to individual lymphatic profiles, enhancing effectiveness and minimizing side effects.

Vicious Circle With Venous Hypertension, Irregular Flow, Pathological Venous Wall Remodeling, and Valve Destruction in Chronic Venous Disease: A Review

Substantial advances occurred in phlebological practice in the last two decades. With the use of modern diagnostic equipment, the patients' venous hemodynamics can be examined in detail in everyday practice. Application of venous segments for arterial bypasses motivated studies on the effect of hemodynamic load on the venous wall. New animal models have been developed to study hemodynamic effects on the venous system. In vivo and in vitro studies revealed cellular phase transitions of venous endothelial, smooth muscle, and fibroblastic cells and changes in connective tissue composition, under hemodynamic load and at different locations of the chronically diseased venous system. This review is an attempt to integrate our knowledge from epidemiology, paleoanthropology and anthropology, clinical and experimental hemodynamic studies, histology, cell physiology, cell pathology, and molecular biology on the complex pathomechanism of this frequent disease. Our conclusion is that the disease is initiated by limited genetic adaptation of mankind not to bipedalism but to bipedalism in the unmoving standing or sitting position. In the course of the disease several pathologic vicious circles emerge, sustained venous hypertension inducing cellular phase transitions, chronic wall inflammation, apoptosis of cells, pathologic dilation, and valvular damage which, in turn, further aggravate the venous hypertension.

Pathophysiology and Genetic Associations of Varicose Veins: A Narrative Review

Varicose veins (VVs) have a high prevalence worldwide and have become a major medical burden. Their pathophysiology involves a complex interplay of inflammation and tissue remodeling, and current treatment is limited by its impact on the pathophysiological mechanisms. In addition, despite clear environmental factors, family history is an important risk factor, suggesting a genetic component to the risk of developing VVs. Our understanding of the pathogenesis of these diseases has benefited greatly from the expansion of population genetic studies, from pioneering family studies to large genome-wide association studies; we now find multiple risk loci for each venous disease. This review considers the pathophysiology of VVs, highlighting the current state of genetic knowledge. We also propose future directions for research.

The intricate cellular ecosystem of human peripheral veins as revealed by single-cell transcriptomic analysis

The venous system has been historically understudied despite its critical roles in blood distribution, heart function, and systemic immunity. This study dissects the microanatomy of upper arm veins at the single cell level, and how it relates to wall structure, remodeling processes, and inflammatory responses to injury. We applied single-cell RNA sequencing to 4 non-diseased human veins (3 basilic, 1 cephalic) obtained from organ donors, followed by bioinformatic and histological analyses. Unsupervised clustering of 20,006 cells revealed a complex ecosystem of endothelial cell (EC) types, smooth muscle cell (SMCs) and pericytes, various types of fibroblasts, and immune cell populations. The venous endothelium showed significant upregulation of cell adhesion genes, with arteriovenous zonation EC phenotypes highlighting the heterogeneity of vasa vasorum (VV) microvessels. Venous SMCs had atypical contractile phenotypes and showed widespread localization in the intima and media. MYH11+DESlo SMCs were transcriptionally associated with negative regulation of contraction and pro-inflammatory gene expression. MYH11+DEShi SMCs showed significant upregulation of extracellular matrix genes and pro-migratory mediators. Venous fibroblasts ranging from secretory to myofibroblastic phenotypes were 4X more abundant than SMCs and widely distributed throughout the wall. Fibroblast-derived angiopoietin-like factors were identified as versatile signaling hubs to regulate angiogenesis and SMC proliferation. An abundant monocyte/macrophage population was detected and confirmed by histology, including pro-inflammatory and homeostatic phenotypes, with cell counts positively correlated with age. Ligand-receptor interactome networks identified the venous endothelium in the main lumen and the VV as a niche for monocyte recruitment and infiltration. This study underscores the transcriptional uniqueness of venous cells and their relevance for vascular inflammation and remodeling processes. Findings from this study may be relevant for molecular investigations of upper arm veins used for vascular access creation, where single-cell analyses of cell composition and phenotypes are currently lacking.

Lymphatic contractile dysfunction in mouse models of Cantú Syndrome with KATP channel gain-of-function

Cantú Syndrome (CS) is an autosomal dominant disorder caused by gain-of-function (GoF) mutations in the Kir6.1 and SUR2 subunits of KATP channels. KATP overactivity results in a chronic reduction in arterial tone and hypotension, leading to other systemic cardiovascular complications. However, the underlying mechanism of lymphedema, developed by >50% of CS patients, is unknown. We investigated whether lymphatic contractile dysfunction occurs in mice expressing CS mutations in Kir6.1 (Kir6.1[V65M]) or SUR2 (SUR2[A478V], SUR2[R1154Q]). Pressure myograph tests of contractile function of popliteal lymphatic vessels over the physiological pressure range revealed significantly impaired contractile strength and reduced frequency of spontaneous contractions at all pressures in heterozygous Kir6.1[V65M] vessels, compared to control littermates. Contractile dysfunction of intact popliteal lymphatics in vivo was confirmed using near-infrared fluorescence microscopy. Homozygous SUR2[A478V] vessels exhibited profound contractile dysfunction ex vivo, but heterozygous SUR2[A478V] vessels showed essentially normal contractile function. However, further investigation of vessels from all three GoF mouse strains revealed significant disruption in contraction wave entrainment, decreased conduction speed and distance, multiple pacemaker sites, and reversing wave direction. Tests of 2-valve lymphatic vessels forced to pump against an adverse pressure gradient revealed that all CS-associated genotypes were essentially incapable of pumping under an imposed outflow load. Our results show that varying degrees of lymphatic contractile dysfunction occur in proportion to the degree of molecular GoF in Kir6.1 or SUR2. This is the first example of lymphatic contractile dysfunction caused by a smooth muscle ion channel mutation and potentially explains the susceptibility of CS patients to lymphedema.

Molecular Determinants of Chronic Venous Disease: A Comprehensive Review

Chronic Venous Disease (CVD) refers to several pathological and hemodynamic alterations of the veins of lower limbs causing a wide range of symptoms and signs with a high prevalence in the general population and with disabling consequences in the most severe forms. The etiology and pathophysiology of CVD is complex and multifactorial, involving genetic, proteomic, and cellular mechanisms that result in changes to the venous structure and functions. Expressions of several genes associated with angiogenesis, vascular development, and the regulation of veins are responsible for the susceptibility to CVD. Current evidence shows that several extracellular matrix alterations (ECM) could be identified and in some cases pharmacologically targeted. This review shows the most up to date information on molecular determinants of CVD in order to provide a complete overview of the current knowledge on this topic. In particular, the article explores the genetic influence, the hormonal influence, ECM imbalance, and histopathology of CVD and the role of endothelial dysfunction in CVD.

A vascular smooth muscle-specific integrin-α8 Cre mouse for lymphatic contraction studies that allows male-female comparisons and avoids visceral myopathy

Introduction: The widely-used, tamoxifen-inducible, smooth muscle (SM)-specific Cre, Myh11-CreERT2 , suffers from two disadvantages: 1) it is carried on the Y-chromosome and thus only effective for gene deletion in male mice, and 2) it recombines in both vascular and non-vascular SM, potentially leading to unwanted or confounding gastrointestinal phenotypes. Here, we tested the effectiveness of a new, SM-specific Cre, based on the integrin α8 promoter (Itga8-CreERT2 ), that has been recently developed and characterized, to assess the effects of Cav1.2 deletion on mouse lymphatic SM function. Methods: Cav1.2 (the L-type voltage-gated calcium channel) is essential for lymphatic pacemaking and contraction and its deletion using either Myh11-CreERT2 or Itga8-CreERT2 abolished spontaneous lymphatic contractions. Mouse lymphatic contractile function was assessed using two ex vivo methods. Results: Myh11-CreERT2 ; Cav1.2 f/f mice died of gastrointestinal obstruction within 20 days of the first tamoxifen injection, preceded by several days of progressively poor health, with symptoms including weight loss, poor grooming, hunched posture, and reduced overall activity. In contrast, Itga8-CreERT2 ; Cav1.2 f/f mice survived for >80 days after induction and were in normal health until the time of sacrifice for experimental studies. Cav1.2 deletion was equally effective in male and female mice. Discussion: Our results demonstrate that Itga8-CreER T2 can be used to effectively delete genes in lymphatic smooth muscle while avoiding potentially lethal visceral myopathy and allowing comparative studies of lymphatic contractile function in both male and female mice.

Mechanical forces in lymphatic vessel development: Focus on transcriptional regulation

The lymphatic system is crucial for the maintenance of interstitial fluid and protein homeostasis. It has important roles in collecting excess plasma and interstitial fluid leaked from blood vessels, lipid absorption and transportation in the digestive system, and immune surveillance and response. The development of lymphatic vessels begins during fetal life as lymphatic endothelial progenitor cells first differentiate into lymphatic endothelial cells (LECs) by expressing the master lymphatic vascular regulator, prospero-related homeobox 1 (PROX1). The lymphatic vasculature forms a hierarchical network that consists of blind-ended and unidirectional vessels. Although much progress has been made in the elucidation of the cellular and molecular mechanisms underlying the formation of the lymphatic vascular system, the causes of lymphatic vessel abnormalities and disease are poorly understood and complicated; specifically, the mechanistic basis for transcriptional dysregulation in lymphatic vessel development remains largely unclear. In this review, we discuss the recent advances in our understanding of the molecular and cellular mechanisms of lymphatic vascular development, including LEC differentiation, lymphangiogenesis, and valve formation, and the significance of mechanical forces in lymphatic vessels, with a focus on transcriptional regulation. We also summarize the current knowledge on epigenetic mechanisms of lymphatic gene expression.

Global impact and contributing factors in varicose vein disease development

Varicose veins are convoluted, expanded, and stretched subcutaneous veins of the lower leg and are the most frequently reported medical condition. This condition has a higher prevalence in Western and developed countries. Inadequacy of the valves results in reflux of blood in the veins of the lower leg. The present study aims to describe the epidemiology and contributing factors (risk factors and pathological factors) in the development of varicose veins disease. PubMed/Medline, Science Direct, Google Scholar, SciFinder, Scopus, and Web of Science databases were explored to include potential research and review articles. Finally, 65 articles were considered appropriate to include in the study. Pain, swelling, heaviness, and tingling of the lower limbs are the most common sign and symptoms caused by varicose veins while in some individuals it is asymptomatic. The Prevalence of varicose veins varies geographically. Currently, it is reported that globally about 2%–73% of the population is affected by varicose veins while the prevalence rate in Pakistan is 16%–20%. Different risk factors associated with the advancement of varicose veins are age, gender, occupation, pregnancy, family history, smoking, BMI and obesity, exercise, genetic factor, and current lifestyle. In varicose veins, some contributory elements may also play an important role in the disease development, incorporating constant venous wall aggravation, hereditary variation, and persistent venous hypertension. This condition has now turned into a curable issue that was previously viewed broadly as less important for treatment, determining the individual’s satisfaction. Moreover, the mechanisms behind the risk factors involve diet, physical work, and hormonal contribution. These are more likely to be explored.

A Single-Cell Survey of Cellular Heterogeneity in Human Great Saphenous Veins

Background: The great saphenous vein (GSV) is the most commonly used conduit for coronary arterial bypass graft. However, the status of the GSV, including metabolic dysfunction such as diabetes mellitus (DM) complication, is strongly associated with vein graft failure (VGF). To date, the molecular mechanism underlying VGF remains elusive. Detailed characterization of the cellular components and corresponding expression regulation in GSVs would be of great importance for clinical decision making to reduce VGF. Methods: To this end, we performed single-cell RNA sequencing to delineate cellular heterogeneity in three human GSV samples. Results: Scrutinization of cellular composition and expression revealed cell diversity in human GSVs, particularly endothelial cells (ECs). Our results unraveled that functional adaptation drove great expression differences between venous ECs and valvular ECs. For instance, cell surface receptor ACKR1 demarcated venous Ecs, whereas ACRK3/ACKR4 were exclusively expressed by valvular ECs. Differential gene expression analysis suggested that genes highly expressed in venous ECs were mainly involved in vasculature development and regulation of leukocyte adhesion, whereas valvular ECs have more pronounced expression of genes participating in extracellular matrix organization, ossification and platelet degranulation. Of note, pseudo-time trajectory analysis provided in silico evidence indicating that venous ECs, valvular ECs and lymphatic vessels were developmentally connected. Further, valvular ECs might be an importance source for lymphatic vessel differentiation in adults. Additionally, we found a venous EC subset highly expressing IL6, which might be associated with undesirable prognosis. Meanwhile, we identified a population of ANGPTL7+ fibroblasts (FBs), which may be profibrotic and involved in insulin resistance in human GSVs. Additionally, our data suggest that immune cells only accounted for a small fraction, most of which were macrophages. By assessing the intertwined remodeling in metabolic dysfunction that potentially increases the gene expression regulatory network in mural cells and leukocytes, we found that transcription factor KLF9 likely operated a proinflammatory program, inducing the transcription of metallothionein proteins in two mural cell subsets and proinflammatory immune cells. Lastly, cellular communication analysis revealed that proinflammatory signaling, including TRAIL, PVR, CSF and GDF, were uniquely activated in patients with metabolic dysfunction. Conclusions: Our results identified critical cell-specific responses and cellular interactions in GSVs. Beyond serving as a repertoire, this work illustrates multifactorial likelihood of VGF.

Retrograde Lymph Flow in the Lymphatic Vessels in Limb Lymphedema

OBJECTIVE

Retrograde movement of lymph due to damaged and/or incompetent valves in the lymphatic vessels has been considered a pathological feature of lymphedema. This study aimed to determine the prevalence of retrograde lymph flow and the characteristics of patients with this condition using indocyanine green (ICG) lymphography.

METHODS

An audit of 679 patients with upper or lower limb swelling who underwent ICG lymphography was undertaken over a 4-year period. Harvey's technique was applied to identify retrograde flow in the lymph collecting vessel during ICG lymphography. The characteristics of patients with retrograde lymph flow were recorded.

RESULTS

Twenty-one patients (3.7%, lower limb: n=19, upper limb: n=2) were identified as having retrograde flow in lymph collecting vessels out of 566 confirmed lymphedema patients (lower limb: n=275, upper limb: n=291). Of the two patients with upper limb lymphedema, one had a short segment of retrograde lymph flow in the forearm. The other patient with upper limb lymphedema and one patient with lower limb lymphedema were previously diagnosed with Lymphedema-Distichiasis Syndrome. Of the remaining 18 patients with lower limb lymphedema and retrograde lymph flow, nine had initiating insect bites with lymphangitis and three had palpable benign enlarged inguinal lymph nodes evident prior to lower limb swelling onset. None had cancer-related lower limb lymphedema.

CONCLUSIONS

Retrograde lymph flow with valve incompetence in the lymph collecting vessels was a rare finding in upper limb lymphedema and a relatively uncommon in lower limb lymphedema, contradicting conventional understanding of pathological changes in lymphedema. ICG lymphography identified anticipated retrograde lymph flow in two patients with Lymphedema-Distichiasis. In the remaining patients, retrograde lymph flow may have resulted from toxic or asymptomatic lymphangitis but no association with secondary cancer-related lymphedema. These findings have implication for conservative management as well as lymphovenous anastomosis surgery where both ends of a transected lymph collecting vessel would be potential targets for anastomoses.

Genome-wide association analysis and replication in 810,625 individuals with varicose veins

Varicose veins affect one-third of Western society, with a significant subset of patients developing venous ulceration, costing $14.9 billion annually in the USA. Current management consists of either compression stockings, or surgical ablation for more advanced disease. Most varicose veins patients report a positive family history, and heritability is ~17%. We describe the largest two-stage genome-wide association study of varicose veins in 401,656 individuals from UK Biobank, and replication in 408,969 individuals from 23andMe (total 135,514 cases and 675,111 controls). Forty-nine signals at 46 susceptibility loci were discovered. We map 237 genes to these loci, several of which are biologically plausible and tractable to therapeutic targeting. Pathway analysis identified enrichment in extracellular matrix biology, inflammation, (lymph)angiogenesis, vascular smooth muscle cell migration, and apoptosis. Using a polygenic risk score (PRS) derived in an independent cohort, we demonstrate its predictive utility and correlation with varicose veins surgery.

A genome-wide association study for varicose veins

Background

The aim was to compare the genetic information of varicose vein patients with that of a healthy population attempting to identify certain significant genetic associations.

Method

Patients’ clinical characteristics and demographics were collected, and their genetic samples were examined. The results were compared to the genetic information of one thousand sex-matched healthy controls from Taiwan Biobank database. The Clinical-Etiology-Anatomy-Pathophysiology classification was applied for further subgroup analysis.

Results

After comparison of genetic information of ninety-six patients to that of healthy controls, two significant single nucleotide polymorphisms (SNPs) were identified. One was in DPYSL2 gene, and the other was in VSTM2L gene. A further comparison between C2-3 patient subgroup and C4-6 subgroup identified another four significant SNPs, which were located in ZNF664-FAM101A, PHF2, ACOT11, and TOM1L1 genes.

Conclusion

Our preliminary result identified six significant SNPs located in six different genes. All of them and their genetic products may warrant further investigations.

Post-Transcriptional Regulation of Molecular Determinants during Cardiogenesis

Cardiovascular development is initiated soon after gastrulation as bilateral precardiac mesoderm is progressively symmetrically determined at both sides of the developing embryo. The precardiac mesoderm subsequently fused at the embryonic midline constituting an embryonic linear heart tube. As development progress, the embryonic heart displays the first sign of left-right asymmetric morphology by the invariably rightward looping of the initial heart tube and prospective embryonic ventricular and atrial chambers emerged. As cardiac development progresses, the atrial and ventricular chambers enlarged and distinct left and right compartments emerge as consequence of the formation of the interatrial and interventricular septa, respectively. The last steps of cardiac morphogenesis are represented by the completion of atrial and ventricular septation, resulting in the configuration of a double circuitry with distinct systemic and pulmonary chambers, each of them with distinct inlets and outlets connections. Over the last decade, our understanding of the contribution of multiple growth factor signaling cascades such as Tgf-beta, Bmp and Wnt signaling as well as of transcriptional regulators to cardiac morphogenesis have greatly enlarged. Recently, a novel layer of complexity has emerged with the discovery of non-coding RNAs, particularly microRNAs and lncRNAs. Herein, we provide a state-of-the-art review of the contribution of non-coding RNAs during cardiac development. microRNAs and lncRNAs have been reported to functional modulate all stages of cardiac morphogenesis, spanning from lateral plate mesoderm formation to outflow tract septation, by modulating major growth factor signaling pathways as well as those transcriptional regulators involved in cardiac development.

Varicose Veins and Chronic Venous Disease

Chronic venous disease is a worldwide problem associated with significant morbidity and is expected to increase in prevalence as the current population ages. This is a comprehensive review of the anatomy, pathophysiology, genomics, clinical classification, and treatment modalities of chronic venous disease.

Development and physiological functions of the lymphatic system: insights from human genetic studies of primary lymphedema

Primary lymphedema is a long-term (chronic) condition characterized by tissue lymph retention and swelling that can affect any part of the body, although it usually develops in the arms or legs. Due to the relevant contribution of the lymphatic system to human physiology, while this review mainly focuses on the clinical and physiological aspects related to the regulation of fluid homeostasis and edema, clinicians need to know that the impact of lymphatic dysfunction with a genetic origin can be wide ranging. Lymphatic dysfunction can affect immune function so leading to infection; it can influence cancer development and spread, and it can determine fat transport so impacting on nutrition and obesity. Genetic studies and the development of imaging techniques for the assessment of lymphatic function have enabled the recognition of primary lymphedema as a heterogenic condition in terms of genetic causes and disease mechanisms. In this review, the known biological functions of several genes crucial to the development and function of the lymphatic system are used as a basis for understanding normal lymphatic biology. The disease conditions originating from mutations in these genes are discussed together with a detailed clinical description of the phenotype and the up-to-date knowledge in terms of disease mechanisms acquired from in vitro and in vivo research models.

Mutations in EPHB4 cause human venous valve aplasia

Venous valve (VV) failure causes chronic venous insufficiency, but the molecular regulation of valve development is poorly understood. A primary lymphatic anomaly, caused by mutations in the receptor tyrosine kinase EPHB4, was recently described, with these patients also presenting with venous insufficiency. Whether the venous anomalies are the result of an effect on VVs is not known. VV formation requires complex "organization" of valve-forming endothelial cells, including their reorientation perpendicular to the direction of blood flow. Using quantitative ultrasound, we identified substantial VV aplasia and deep venous reflux in patients with mutations in EPHB4. We used a GFP reporter in mice to study expression of its ligand, ephrinB2, and analyzed developmental phenotypes after conditional deletion of floxed Ephb4 and Efnb2 alleles. EphB4 and ephrinB2 expression patterns were dynamically regulated around organizing valve-forming cells. Efnb2 deletion disrupted the normal endothelial expression patterns of the gap junction proteins connexin37 and connexin43 (both required for normal valve development) around reorientating valve-forming cells and produced deficient valve-forming cell elongation, reorientation, polarity, and proliferation. Ephb4 was also required for valve-forming cell organization and subsequent growth of the valve leaflets. These results uncover a potentially novel cause of primary human VV aplasia.

PIEZO1-gene gain-of-function mutations with lower limb lymphedema onset in an adult: Clinical, scintigraphic, and noncontrast magnetic resonance lymphography findings

Primary lymphedema, a rare disease, has a genetic cause in ~40% of patients. Recently, loss-of-function mutations in PIEZO1, which encodes the mechanotransducer protein PIEZO1, were described as causing primary lymphedema, when gain-of-function PIEZO1 mutations were attributed to dehydrated hereditary stomatocytosis type-1 (DHS), a dominant red cell hemolytic disorder, with ~20% of patients having perinatal edema. Lymphedema was diagnosed in a 36-year-old man from a three-generation DHS family, with a PIEZO1-allele harboring 3 missense mutations in cis. Four affected family members had severe fetal and neonatal edema, most severe in the proband, whose generalized edema with prevailing ascites resolved after 8 months. Our patient's intermittent lower limb-lymphedema episodes during hot periods appeared at puberty; they became persistent and bilateral at age 32. Clinical Stemmer's sign confirmed lymphedema. Lower leg lymphoscintigraphy showed substantial dermal backflow in both calves, predominantly on the right. Noncontrast magnetic resonance lymphography showed bilateral lower limb lymphedema, dilated dysplastic lymphatic iliac, and inguinal trunks. Exome-sequencing analysis identified no additional pathogenic variation in primary lymphedema-associated genes. This is the first description of well-documented lymphedema in an adult with PIEZO1-DHS. The pathophysiology of PIEZO1-associated primary lymphedema is poorly understood. Whether it infers overlapping phenotypes or different mechanisms of gain- and loss-of-function PIEZO1 mutations deserves further investigation.

MicroRNA‑199a‑5p regulates FOXC2 to control human vascular smooth muscle cell phenotypic switch

Varicose veins are among the most common disorders of the vascular system; however, the pathogenesis of varicose veins remains unclear. The present study aimed to investigate the roles of microRNA (miR)‑199a‑5p in varicose veins and in the phenotypic transition of vascular smooth muscle cells (VSMCs). Bioinformatics analysis confirmed that miR‑199a‑5p had target sites on the forkhead box C2 (FOXC2) 3'‑untranslated region. Reverse transcription‑quantitative PCR (RT‑qPCR) and western blotting were used to detect the expression levels of miR‑199a‑5p and FOXC2 in varicose vein and normal great saphenous vein tissues. Cell Counting Kit‑8 and Transwell migration assays were performed to validate the effects of miR‑199a‑5p on VSMCs. Contractile markers, such as smooth muscle 22α, calponin, smooth muscle actin and myosin heavy chain 11 were used to detect phenotypic transition. RT‑qPCR revealed that miR‑199a‑5p was downregulated in varicose veins compared with expression in normal great saphenous veins, whereas FOXC2 was upregulated in varicose veins. In addition, biomarkers of the VSMC contractile phenotype were downregulated in varicose veins. Overexpression of miR‑199a‑5p by mimics suppressed VSMC proliferation and migration, whereas depletion of miR‑199a‑5p enhanced VSMC proliferation and migration. Notably, the effects caused by miR‑199a‑5p could be reversed by FOXC2 overexpression. Dual luciferase reporter analysis confirmed that FOXC2 was a target of miR‑199a‑5p. In conclusion, miR‑199a‑5p may be a novel regulator of phenotypic switching in VSMCs by targeting FOXC2 during varicose vein formation.

Biochemical and mechanical signals in the lymphatic vasculature

Lymphatic vasculature is an integral part of the cardiovascular system where it maintains interstitial fluid balance. Additionally, lymphatic vasculature regulates lipid assimilation and inflammatory response. Lymphatic vasculature is composed of lymphatic capillaries, collecting lymphatic vessels and valves that function in synergy to absorb and transport fluid against gravitational and pressure gradients. Defects in lymphatic vessels or valves leads to fluid accumulation in tissues (lymphedema), chylous ascites, chylothorax, metabolic disorders and inflammation. The past three decades of research has identified numerous molecules that are necessary for the stepwise development of lymphatic vasculature. However, approaches to treat lymphatic disorders are still limited to massages and compression bandages. Hence, better understanding of the mechanisms that regulate lymphatic vascular development and function is urgently needed to develop efficient therapies. Recent research has linked mechanical signals such as shear stress and matrix stiffness with biochemical pathways that regulate lymphatic vessel growth, patterning and maturation and valve formation. The goal of this review article is to highlight these innovative developments and speculate on unanswered questions.

Epidemiology and Genetics of Venous Thromboembolism and Chronic Venous Disease

Venous disease is a term that broadly covers both venous thromboembolic disease and chronic venous disease. The basic pathophysiology of venous thromboembolism and chronic venous disease differ as venous thromboembolism results from an imbalance of hemostasis and thrombosis while chronic venous disease occurs in the setting of tissue damage because of prolonged venous hypertension. Both diseases are common and account for significant mortality and morbidity, respectively, and collectively make up a large health care burden. Despite both diseases having well-characterized environmental components, it has been known for decades that family history is an important risk factor, implicating a genetic element to a patient's risk. Our understanding of the pathogenesis of these diseases has greatly benefited from an expansion of population genetic studies from pioneering familial studies to large genome-wide association studies; we now have multiple risk loci for each venous disease. In this review, we will highlight the current state of knowledge on the epidemiology and genetics of venous thromboembolism and chronic venous disease and directions for future research.

Mechanisms of Lower Extremity Vein Dysfunction in Chronic Venous Disease and Implications in Management of Varicose Veins

Chronic venous disease (CVD) is a common venous disorder of the lower extremities. CVD can be manifested as varicose veins (VVs), with dilated and tortuous veins, dysfunctional valves and venous reflux. If not adequately treated, VVs could progress to chronic venous insufficiency (CVI) and lead to venous leg ulcer (VLU). Predisposing familial and genetic factors have been implicated in CVD. Additional environmental, behavioral and dietary factors including sedentary lifestyle and obesity may also contribute to CVD. Alterations in the mRNA expression, protein levels and proteolytic activity of matrix metalloproteinases (MMPs) have been detected in VVs and VLU. MMP expression/activity can be modulated by venous hydrostatic pressure, hypoxia, tissue metabolites, and inflammation. MMPs in turn increase proteolysis of different protein substrates in the extracellular matrix particularly collagen and elastin, leading to weakening of the vein wall. MMPs could also promote venous dilation by increasing the release of endothelium-derived vasodilators and activating potassium channels, leading to smooth muscle hyperpolarization and relaxation. Depending on VVs severity, management usually includes compression stockings, sclerotherapy and surgical removal. Venotonics have also been promoted to decrease the progression of VVs. Sulodexide has also shown benefits in VLU and CVI, and recent data suggest that it could improve venous smooth muscle contraction. Other lines of treatment including induction of endogenous tissue inhibitors of metalloproteinases (TIMPs) and administration of exogenous synthetic inhibitors of MMPs are being explored, and could provide alternative strategies in the treatment of CVD.

Cell lineage- and expression-based inference of the roles of forkhead box transcription factor Foxc2 in craniofacial development

BACKGROUND

Foxc2 is a member of the winged helix/forkhead (Fox) box family of transcription factors. Loss of function of Foxc2 causes craniofacial abnormalities such as cleft palate and deformed cranial base, but its role during craniofacial development remains to be elucidated.

RESULTS

The contributions of Foxc2-positive and its descendant cells to the craniofacial structure at E18.5 were examined using a tamoxifen-inducible Cre driver mouse (Foxc2-CreERT2) crossed with the R26R-LacZ reporter mouse. Foxc2 expression at E8.5 is restricted to the cranial mesenchyme, contributing to specific components including the cranial base, sensory capsule, tongue, upper incisor, and middle ear. Expression at E10.5 was still positively regulated in most of those regions. In situ hybridization analysis of Foxc2 and its closely related gene, Foxc1, revealed that expression domains of these genes largely overlap in the cephalic mesenchyme. Meanwhile, the tongue expressed Foxc2 but not Foxc1, and its development was affected by the neural crest-specific deletion of Foxc2 in mice (Wnt1-Cre; Foxc2^fl/fl ).

CONCLUSIONS

Foxc2 is expressed in cranial mesenchyme that contributes to specific craniofacial tissue components from an early stage, and it seems to be involved in their development in cooperation with Foxc1. Foxc2 also has its own role in tongue development.

Hemodynamics mediated epigenetic regulators in the pathogenesis of vascular diseases

Endothelium of blood vessels is continuously exposed to various hemodynamic forces. Flow-mediated epigenetic plasticity regulates vascular endothelial function. Recent studies have highlighted the significant role of mechanosensing-related epigenetics in localized endothelial dysfunction and the regional susceptibility for lesions in vascular diseases. In this article, we review the epigenetic mechanisms such as DNA de/methylation, histone modifications, as well as non-coding RNAs in promoting endothelial dysfunction in major arterial and venous diseases, consequent to hemodynamic alterations. We also discuss the current challenges and future prospects for the use of mechanoepigenetic mediators as biomarkers of early stages of vascular diseases and dysregulated mechanosensing-related epigenetic regulators as therapeutic targets in various vascular diseases.

Lymphatic Valves and Lymph Flow in Cancer-Related Lymphedema

Lymphedema is a complex disease caused by the accumulation of fluid in the tissues resulting from a dysfunctional or damaged lymphatic vasculature. In developed countries, lymphedema most commonly occurs as a result of cancer treatment. Initially, impaired lymph flow causes edema, but over time this results in inflammation, fibrotic and fatty tissue deposition, limited mobility, and bacterial infections that can lead to sepsis. While chronically impaired lymph flow is generally believed to be the instigating factor, little is known about what pathophysiological changes occur in the lymphatic vessels to inhibit lymph flow. Lymphatic vessels not only regulate lymph flow through a variety of physiologic mechanisms, but also respond to lymph flow itself. One of the fascinating ways that lymphatic vessels respond to flow is by growing bicuspid valves that close to prevent the backward movement of lymph. However, lymphatic valves have not been investigated in cancer-related lymphedema patients, even though the mutations that cause congenital lymphedema regulate genes involved in valve development. Here, we review current knowledge of the regulation of lymphatic function and development by lymph flow, including newly identified genetic regulators of lymphatic valves, and provide evidence for lymphatic valve involvement in cancer-related lymphedema.

Hemodynamic regulation of perivalvular endothelial gene expression prevents deep venous thrombosis

Deep venous thrombosis (DVT) and secondary pulmonary embolism cause approximately 100,000 deaths per year in the United States. Physical immobility is the most significant risk factor for DVT, but a molecular and cellular basis for this link has not been defined. We found that the endothelial cells surrounding the venous valve, where DVTs originate, express high levels of FOXC2 and PROX1, transcription factors known to be activated by oscillatory shear stress. The perivalvular venous endothelial cells exhibited a powerful antithrombotic phenotype characterized by low levels of the prothrombotic proteins vWF, P-selectin, and ICAM1 and high levels of the antithrombotic proteins thrombomodulin (THBD), endothelial protein C receptor (EPCR), and tissue factor pathway inhibitor (TFPI). The perivalvular antithrombotic phenotype was lost following genetic deletion of FOXC2 or femoral artery ligation to reduce venous flow in mice, and at the site of origin of human DVT associated with fatal pulmonary embolism. Oscillatory blood flow was detected at perivalvular sites in human veins following muscular activity, but not in the immobile state or after activation of an intermittent compression device designed to prevent DVT. These findings support a mechanism of DVT pathogenesis in which loss of muscular activity results in loss of oscillatory shear-dependent transcriptional and antithrombotic phenotypes in perivalvular venous endothelial cells, and suggest that prevention of DVT and pulmonary embolism may be improved by mechanical devices specifically designed to restore perivalvular oscillatory flow.

Shear stimulation of FOXC1 and FOXC2 differentially regulates cytoskeletal activity during lymphatic valve maturation

Mutations in the transcription factor FOXC2 are predominately associated with lymphedema. Herein, we demonstrate a key role for related factor FOXC1, in addition to FOXC2, in regulating cytoskeletal activity in lymphatic valves. FOXC1 is induced by laminar, but not oscillatory, shear and inducible, endothelial-specific deletion impaired postnatal lymphatic valve maturation in mice. However, deletion of Foxc2 induced valve degeneration, which is exacerbated in Foxc1; Foxc2 mutants. FOXC1 knockdown (KD) in human lymphatic endothelial cells increased focal adhesions and actin stress fibers whereas FOXC2-KD increased focal adherens and disrupted cell junctions, mediated by increased ROCK activation. ROCK inhibition rescued cytoskeletal or junctional integrity changes induced by inactivation of FOXC1 and FOXC2 invitro and vivo respectively, but only ameliorated valve degeneration in Foxc2 mutants. These results identify both FOXC1 and FOXC2 as mediators of mechanotransduction in the postnatal lymphatic vasculature and posit cytoskeletal signaling as a therapeutic target in lymphatic pathologies.

Human venous valve disease caused by mutations in FOXC2 and GJC2

Venous valves (VVs) prevent venous hypertension and ulceration. We report that FOXC2 and GJC2 mutations are associated with reduced VV number and length. In mice, early VV formation is marked by elongation and reorientation ("organization") of Prox1hi endothelial cells by postnatal day 0. The expression of the transcription factors Foxc2 and Nfatc1 and the gap junction proteins Gjc2, Gja1, and Gja4 were temporospatially regulated during this process. Foxc2 and Nfatc1 were coexpressed at P0, and combined Foxc2 deletion with calcineurin-Nfat inhibition disrupted early Prox1hi endothelial organization, suggesting cooperative Foxc2-Nfatc1 patterning of these events. Genetic deletion of Gjc2, Gja4, or Gja1 also disrupted early VV Prox1hi endothelial organization at postnatal day 0, and this likely underlies the VV defects seen in patients with GJC2 mutations. Knockout of Gja4 or Gjc2 resulted in reduced proliferation of Prox1hi valve-forming cells. At later stages of blood flow, Foxc2 and calcineurin-Nfat signaling are each required for growth of the valve leaflets, whereas Foxc2 is not required for VV maintenance.

The Concept of Chronic Edema-A Neglected Public Health Issue and an International Response: The LIMPRINT Study

Lymphedema has always been a neglected global health care problem. A central requirement for the development of any chronic disease is the clear use of public health definitions that can be used internationally to define populations. The term "lymphedema" has historically been defined as either primary, resulting from failure of lymphatic development, or secondary, following damage to the lymphatics (e.g., cancer treatment, injury, or filariasis). Attempts to integrate causes of edema arising from damage to the venous system or the effects of gravity, immobility, and systemic disease have rarely been integrated. More recently, the prominent role of the lymphatics in tissue fluid homeostasis in all forms of chronic edema has been recognized. These advances led to the development of the term: "Chronic edema: a broad term used to describe edema, which has been present for more than three months." It can be considered an umbrella term that includes not only conventional "lymphedema" but also chronic swelling, which may have a more complex cause. This definition has been adapted in the international epidemiology study (LIMPRINT) that identified people throughout the health and social care systems in participating countries. Clearer definitions will allow for examination of this important public health problem that is likely to escalate given the projections of an aging population with multiple comorbidities. It will be possible to define both the hidden mortality and morbidity associated with complications, such as cellulitis and the impact on health-related quality of life. This evidence is urgently required to lobby for increased resource and effective health care in an increasingly competitive health care arena in which more established conditions have greater priority and funding.

A Primer on a Comprehensive Genetic Approach to Vascular Anomalies

The field of vascular anomalies has grown tremendously in the last few decades with the identification of key molecular pathways and genetic mutations that drive the formation and progression of vascular anomalies. Understanding these pathways is critical for the classification of vascular anomalies, patient care, and development of novel therapeutics. The goal of this review is to provide a basic understanding of the classification of vascular anomalies and knowledge of their underlying molecular pathways. Here we provide an organizational framework for phenotype/genotype correlation and subsequent development of a diagnostic and treatment roadmap. With the increasing importance of genetics in the diagnosis and treatment of vascular anomalies, we highlight the importance of clinical geneticists as part of a comprehensive multidisciplinary vascular anomalies team.

FOXC2-AS1 regulates phenotypic transition, proliferation and migration of human great saphenous vein smooth muscle cells

Objectives

In varicose veins, vascular smooth muscle cells (VSMCs) often shows phenotypic transition and abnormal proliferation and migration. Evidence suggests the FOXC2–Notch pathway may be involved in the pathogenesis of varicose veins. Here, this study aimed to explore the role of long non-coding RNA FOXC2-AS1 (FOXC2 antisense RNA 1) in phenotypic transition, proliferation, and migration of varicose vein-derived VSMCs and to explore whether the FOXC2-Notch pathway was involved in this process.

Methods

The effect of FOXC2-AS1 on the proliferation and migration of human great saphenous vein smooth muscle cells (SV-SMCs) was analyzed using MTT assay and Transwell migration assay, respectively. The levels of contractile marker SM22α and synthetic marker osteopontin were measured by immunohistochemistry and Western blot to assess the phenotypic transition.

Results

The human varicose veins showed thickened intima, media and adventitia layers, increased synthetic VSMCs, as well as upregulated FOXC2-AS1 and FOXC2 expression. In vitro assays showed that FOXC2-AS1 overexpression promoted phenotypic transition, proliferation, and migration of SV-SMCs. However, the effect of FOXC2-AS1 overexpression could be abrogated by both FOXC2 silencing and the Notch signaling inhibitor FLI-06. Furthermore, FOXC2-AS1 overexpression activated the Notch pathway by upregulating FOXC2.

Conclusion

FOXC2-AS1 overexpression promotes phenotypic transition, proliferation, and migration of SV-SMCs, at least partially, by activating the FOXC2-Notch pathway.

Lymphatic Vessel Network Structure and Physiology

The lymphatic system is comprised of a network of vessels interrelated with lymphoid tissue, which has the holistic function to maintain the local physiologic environment for every cell in all tissues of the body. The lymphatic system maintains extracellular fluid homeostasis favorable for optimal tissue function, removing substances that arise due to metabolism or cell death, and optimizing immunity against bacteria, viruses, parasites, and other antigens. This article provides a comprehensive review of important findings over the past century along with recent advances in the understanding of the anatomy and physiology of lymphatic vessels, including tissue/organ specificity, development, mechanisms of lymph formation and transport, lymphangiogenesis, and the roles of lymphatics in disease. © 2019 American Physiological Society. Compr Physiol 9:207-299, 2019.

Global Expression Profiling Identifies a Novel Hyaluronan Synthases 2 Gene in the Pathogenesis of Lower Extremity Varicose Veins

Lower extremities varicose veins (VV) are among the most easily recognized venous abnormalities. The genetic mechanism of VV is largely unknown. In this study, we sought to explore the global expressional change of VV and identify novel genes that might play a role in VV. We used next-generation ribonucleic acid (RNA) sequence (RNA seq) technology to study the global messenger RNA expressional change in the venous samples of five diseased and five control patients. We identified several differentially expressed genes, which were further confirmed by conventional reverse transcription polymerase chain reaction (RT-PCR). Using these significant genes we performed in silico pathway analyses and found distinct transcriptional networks, such as angiogenesis, cell adhesion, vascular injury, and carbohydrate metabolisms that might be involved in the mechanism of VV. Among these significant genes, we also found hyaluronan synthases 2 gene (HAS2) played a pivotal role and governed all these pathways. We further confirmed that HAS2 expression was decreased in the venous samples of patients with VV. Finally, we used a zebrafish model with fluorescence emitting vasculature and red blood cells to see the morphological changes of the venous system and blood flow. We found that HAS2 knockdown in zebrafish resulted in dilated venous structural with static venous flow. HAS2 may modulate the transcriptional networks of angiogenesis, cell adhesion, vascular injury, and carbohydrate metabolisms in venous tissues and downregulation of HAS2 may underlie the mechanism of VV.

Mechanisms of Connexin-Related Lymphedema

RATIONALE

Mutations in GJC2 and GJA1, encoding Cxs (connexins) 47 and 43, respectively, are linked to lymphedema, but the underlying mechanisms are unknown. Because efficient lymph transport relies on the coordinated contractions of lymphatic muscle cells (LMCs) and their electrical coupling through Cxs, Cx-related lymphedema is proposed to result from dyssynchronous contractions of lymphatic vessels.

OBJECTIVE

To determine which Cx isoforms in LMCs and lymphatic endothelial cells are required for the entrainment of lymphatic contraction waves and efficient lymph transport.

METHODS AND RESULTS

We developed novel methods to quantify the spatiotemporal entrainment of lymphatic contraction waves and used optogenetic techniques to analyze calcium signaling within and between the LMC and the lymphatic endothelial cell layers. Genetic deletion of the major lymphatic endothelial cell Cxs (Cx43, Cx47, or Cx37) revealed that none were necessary for the synchronization of the global calcium events that triggered propagating contraction waves. We identified Cx45 in human and mouse LMCs as the critical Cx mediating the conduction of pacemaking signals and entrained contractions. Smooth muscle-specific Cx45 deficiency resulted in 10- to 18-fold reduction in conduction speed, partial-to-severe loss of contractile coordination, and impaired lymph pump function ex vivo and in vivo. Cx45 deficiency resulted in profound inhibition of lymph transport in vivo, but only under an imposed gravitational load.

CONCLUSIONS

Our results (1) identify Cx45 as the Cx isoform mediating the entrainment of the contraction waves in LMCs; (2) show that major endothelial Cxs are dispensable for the entrainment of contractions; (3) reveal a lack of coupling between lymphatic endothelial cells and LMCs, in contrast to arterioles; (4) point to lymphatic valve defects, rather than contraction dyssynchrony, as the mechanism underlying GJC2- or GJA1-related lymphedema; and (5) show that a gravitational load exacerbates lymphatic contractile defects in the intact mouse hindlimb, which is likely critical for the development of lymphedema in the adult mouse.

Intraluminal valves: development, function and disease

The circulatory system consists of the heart, blood vessels and lymphatic vessels, which function in parallel to provide nutrients and remove waste from the body. Vascular function depends on valves, which regulate unidirectional fluid flow against gravitational and pressure gradients. Severe valve disorders can cause mortality and some are associated with severe morbidity. Although cardiac valve defects can be treated by valve replacement surgery, no treatment is currently available for valve disorders of the veins and lymphatics. Thus, a better understanding of valves, their development and the progression of valve disease is warranted. In the past decade, molecules that are important for vascular function in humans have been identified, with mouse studies also providing new insights into valve formation and function. Intriguing similarities have recently emerged between the different types of valves concerning their molecular identity, architecture and development. Shear stress generated by fluid flow has also been shown to regulate endothelial cell identity in valves. Here, we review our current understanding of valve development with an emphasis on its mechanobiology and significance to human health, and highlight unanswered questions and translational opportunities.

[Lower extremity varicose veins in childhood and at a young age: Mechanism of development and specific features]

In Russia more than 125,000 patients with various venous diseases, lower extremity varicose veins (LEVV) being predominant, were annually operated on. In recent years, there has been a trend toward younger patients with signs of LEVV. Screening studies have revealed the signs of the disease in 10-15% of high-school children. The high prevalence of LEVV as a whole and its younger onset in recent decades cause more attention to an investigation of the relationship between the development of varicose veins, in childhood and adolescence in particular, and genomic changes. Patients with varicose veins have been noted to have a genetically reduced capacity for contraction of the smooth muscle cells of the vein walls, their remodeling due to the increased synthesis of matrix Gla protein, overproduction of TGF-β1, a matrix metalloproteinase inhibitor, hyperhomocysteinemia, and mutations in the genes encoding the synthesis of thrombomodulin. Varicose vein transformation is considered to be a minor phenomenon of undifferentiated connective tissue dysplasia (UCTD) leading to failure of their walls due to abnormalities in the fibrous structures and extracellular matrix. Confirmation of the role of UCTD in the development of varicose veins will be able to provide an individual approach to treating patients and to choosing adequate postoperative therapy aimed at preventing a disease recurrence.

Apolipoprotein A-I Modulates Atherosclerosis Through Lymphatic Vessel-Dependent Mechanisms in Mice

Background

Subcutaneously injected lipid‐free apoA‐I (apolipoprotein A‐I) reduces accumulation of lipid and immune cells within the aortic root of hypercholesterolemic mice without increasing high‐density lipoprotein–cholesterol concentrations. Lymphatic vessels are now recognized as prerequisite players in the modulation of cholesterol removal from the artery wall in experimental conditions of plaque regression, and particular attention has been brought to the role of the collecting lymphatic vessels in early atherosclerosis‐related lymphatic dysfunction. In the present study, we address whether and how preservation of collecting lymphatic function contributes to the protective effect of apoA‐I.

Methods and Results

Atherosclerotic Ldlr^−/− mice treated with low‐dose lipid‐free apoA‐I showed enhanced lymphatic transport and abrogated collecting lymphatic vessel permeability in atherosclerotic Ldlr^−/− mice when compared with albumin‐control mice. Treatment of human lymphatic endothelial cells with apoA‐I increased the adhesion of human platelets on lymphatic endothelial cells, in a bridge‐like manner, a mechanism that could strengthen endothelial cell–cell junctions and limit atherosclerosis‐associated collecting lymphatic vessel dysfunction. Experiments performed with blood platelets isolated from apoA‐I‐treated Ldlr^−/− mice revealed that apoA‐I decreased ex vivo platelet aggregation. This suggests that in vivo apoA‐I treatment limits platelet thrombotic potential in blood while maintaining the platelet activity needed to sustain adequate lymphatic function.

Conclusions

Altogether, we bring forward a new pleiotropic role for apoA‐I in lymphatic function and unveil new potential therapeutic targets for the prevention and treatment of atherosclerosis.

A Novel Mutation in the FOXC2 Gene: A Heterozygous Insertion of Adenosine (c.867insA) in a Family with Lymphoedema of Lower Limbs without Distichiasis

Background

Primary lymphoedema is a rare genetic disorder characterized by swelling of different parts of the body and highly heterogenic clinical presentation. Mutations in several causative genes characterize specific forms of the disease. FOXC2 mutations are associated with lymphoedema of lower extremities, usually distichiasis and late onset.

Patients and methods

Subjects from three generations of a family with lymphoedema of lower limbs without distichiasis were searched for mutations in the FOXC2 gene.

Results

All affected family members with lymphoedema of lower limbs without distichiasis, and still asymptomatic six years old girl from the same family, carried the same previously unreported insertion of adenosine (c.867insA) in FOXC2.

Conclusions

Identification of a novel mutation in the FOXC2 gene in affected family members of three generations with lymphoedema of lower limbs without distichiasis, highlights the high phenotypic variability caused by FOXC2 mutations.

[Primary lymphedema in childhood]

Lymphedema results from impaired lymphatic transport with increased limb volume and is divided into primary and secondary forms. In children, primary lymphedema is the most frequent, with a sporadic, rarely familial form or associated with complex malformative or genetic disorders. Diagnosis of lymphedema is mainly clinical and lymphoscintigraphy is useful to assess the lymphatic function of both limbs precisely. The main differential diagnosis is overgrowth syndrome. Erysipelas (cellulitis) is the main complication, but psychological or functional discomfort may occur throughout the course of lymphedema. Lymphedema management is based on multilayer low-stretch bandage, skin care, and eventually manual lymph drainage. The objective of treatment is to reduce lymphedema volume and then stabilize it. Multilayer low-stretch bandage and elastic compression are the cornerstone of treatment. Parent's motivation, including self-management, is required to ensure the child's compliance and improve quality of life.

Smooth muscle cells of human veins show an increased response to injury at valve sites

OBJECTIVE

Venous valves are essential but are prone to injury, thrombosis, and fibrosis. We compared the behavior and gene expression of smooth muscle cells (SMCs) in the valve sinus vs nonvalve sites to elucidate biologic differences associated with vein valves.

METHODS

Tissue explants of fresh human saphenous veins were prepared, and the migration of SMCs from explants of valve sinus vs nonvalve sinus areas was measured. Proliferation and death of SMCs were determined by staining for Ki67 and terminal deoxynucleotidyl transferase dUTP nick end labeling. Proliferation and migration of passaged valve vs nonvalve SMCs were determined by cell counts and using microchemotaxis chambers. Global gene expression in valve vs nonvalve intima-media was determined by RNA sequencing.

RESULTS

Valve SMCs demonstrated greater proliferation in tissue explants compared with nonvalve SMCs (19.3% ± 5.4% vs 6.8% ± 2.0% Ki67-positive nuclei at 4 days, respectively; mean ± standard error of the mean, five veins; P < .05). This was also true for migration (18.2 ± 2.7 vs 7.5 ± 3.0 migrated SMCs/explant at 6 days, respectively; 24 veins, 15 explants/vein; P < .0001). Cell death was not different (39.6% ± 16.1% vs 41.5% ± 16.0% terminal deoxynucleotidyl transferase dUTP nick end labeling-positive cells, respectively, at 4 days, five veins). Cultured valve SMCs also proliferated faster than nonvalve SMCs in response to platelet-derived growth factor subunit BB (2.9 ± 0.2-fold vs 2.1 ± 0.2-fold of control, respectively; P < .001; n = 5 pairs of cells). This was also true for migration (6.5 ± 1.2-fold vs 4.4 ± 0.8-fold of control, respectively; P < .001; n = 7 pairs of cells). Blockade of fibroblast growth factor 2 (FGF2) inhibited the increased responses of valve SMCs but had no effect on nonvalve SMCs. Exogenous FGF2 increased migration of valve but not of nonvalve SMCs. Unlike in the isolated, cultured cells, blockade of FGF2 in the tissue explants did not block migration of valve or nonvalve SMCs from the explants. Thirty-seven genes were differentially expressed by valve compared with nonvalve intimal-medial tissue (11 veins). Peptide-mediated inhibition of SEMA3A, one of the differentially expressed genes, increased the number of migrated SMCs of valve but not of nonvalve explants.

CONCLUSIONS

Valve compared with nonvalve SMCs have greater rates of migration and proliferation, which may in part explain the propensity for pathologic lesion formation in valves. Whereas FGF2 mediates these effects in cultured SMCs, the mediators of these stimulatory effects in the valve wall tissue remain unclear but may be among the differentially expressed genes discovered in this study. One of these genes, SEMA3A, mediates a valve-specific inhibitory effect on the injury response of valve SMCs.

In silico analysis of single nucleotide polymorphisms (SNPs) in human FOXC2 gene

Introduction: Lymphedema is abnormal accumulation of interstitial fluid, due to inefficient uptake and reduced flow, leading to swelling and disability, mostly in the extremities. Hereditary lymphedema usually occurs as an autosomal dominant trait with allelic heterogeneity.  Methods: We identified single nucleotide polymorphisms (SNPs) in the FOXC2 gene using dbSNP, analyzed their effect on the resulting protein using VEP and Biomart, modelled the resulting protein using Project HOPE, identified gene - gene interactions using GeneMANIA and predicted miRNAs affected and the resulting effects of SNPs in the 5' and 3' regions using PolymiRTS.  Results: We identified 448 SNPs - 429 were nsSNPs and 44 SNPs were in the 5' and 3' UTRs. In total, 2 SNPs have deleterious effects on the resulting protein, and a 3D model confirmed those effects. The gene - gene interaction network showed the involvement of FOXC2 protein in the development of the lymphatic system. hsa-miR-6886-5p, hsa-miRS-6886-5p , hsa-miR-6720-3p, which were affected by the SNPs rs201118690, rs6413505, rs201914560, respectively, were the most important miRNAs affected, due to their high conservation score.  Conclusions: rs121909106 and rs121909107 were predicted to have the most harmful effects, while hsa-miR-6886-5p, hsa-miR-6886-5p and hsa-miR-6720-3p were predicted to be the most important miRNAs affected. Computational biology tools have advantages and disadvantages, and the results they provide are predictions that require confirmation.

In silico analysis of single nucleotide polymorphisms (SNPs) in human FOXC2 gene

Introduction: Lymphedema is an abnormal accumulation of interstitial fluid, due to inefficient uptake and reduced flow, leading to swelling and disability, mostly in the extremities. Hereditary lymphedema usually occurs as an autosomal dominant trait with allelic heterogeneity. Methods: We identified single nucleotide polymorphisms (SNPs) in the FOXC2 gene using dbSNP, analyzed their effect on the resulting protein using VEP and Biomart, modelled the resulting protein using Project HOPE, identified gene - gene interactions using GeneMANIA and predicted miRNAs affected and the resulting effects of SNPs in the 5' and 3' regions using PolymiRTS. Results: We identified 473 SNPs - 429 were nsSNPs and 44 SNPs were in the 5' and 3' UTRs. In total, 2 SNPs - rs121909106 and rs121909107 - have deleterious effects on the resulting protein, and a 3D model confirmed those effects. The gene - gene interaction network showed the involvement of FOXC2 protein in the development of the lymphatic system. hsa-miR-6886-5p, hsa-miRS-6886-5p, hsa-miR-6720-3p, which were affected by the SNPs rs201118690, rs6413505, rs201914560, respectively, were the most important miRNAs affected, due to their high conservation score. Conclusions: rs121909106 and rs121909107 were predicted to have the most harmful effects, while hsa-miR-6886-5p, hsa-miR-6886-5p and hsa-miR-6720-3p were predicted to be the most important miRNAs affected. Computational biology tools have advantages and disadvantages, and the results they provide are predictions that require confirmation using methods such as functional studies.

New diagnostic modalities in the evaluation of lymphedema

OBJECTIVE

Currently, lymphedema (LED) is typically diagnosed clinically on the basis of a patient's history and characteristic physical findings. Whereas the diagnosis of LED is sometimes confirmed by lymphoscintigraphy (LSG), the technique is limited in both its ability to identify disease and to guide therapy. Recent advancements provide opportunities for new imaging techniques not only to assist in the diagnosis of LED, based on anatomic changes, but also to assess contractile function and to guide therapeutic intervention. The purpose of this contribution was to review these imaging techniques.

METHODS

Literature for each technique is reviewed and discussed, and the evidence for each of these new diagnostic techniques was assessed on several criteria to determine if each could (1) establish whether disease is present, (2) determine the severity of the disease process, (3) define the pathophysiologic mechanism of the disease process, (4) demonstrate whether intervention is possible as well as what type, and (5) objectively grade the response to therapy.

RESULTS

LSG is currently the standard test to confirm LED. Duplex ultrasound (DUS) is a simple, readily available noninvasive test that can identify LED by specific tissue characteristics as well as the response to therapy. Magnetic resonance imaging and computed tomography scans similarly demonstrate the alterations in epidermal and subcutaneous tissue, but the latter can also detect obstructing neoplasms as a cause of secondary LED. Moreover, magnetic resonance lymphangiography details lymphatic vessels and nodes and their function. Newer fluorescence imaging techniques provide opportunities to image lymphatic anatomy and function. Visible microlymphangiography by fluorescein sodium is limited by tissue light absorption to imaging depths of 200 μm. Near-infrared fluorescence lymphatic imaging, a newer test using intradermal injection of indocyanine green, can penetrate several centimeters of tissue and can visualize the initial and conducting lymphatics, the lymph node basins, and the active function of lymphangions (the key module) in exquisite detail.

CONCLUSIONS

The availability and the noninvasive nature of DUS should make this modality the first choice for establishing the diagnosis of LED based on tissue changes. Further studies comparing DUS with LSG, however, are needed. The costs of magnetic resonance imaging and computed tomography limit their adoption as a means to regularly assess the lymphatics. Whereas lymphatic truncal anatomy and transit times can be delineated by the older technique of LSG, near-infrared fluorescence lymphatic imaging is rapid, highly sensitive, and repeatable and provides exquisite detail for lymphatic vessel anatomy and function of the lymphangions as well as the response to therapy.

Foxc2CreERT2 knock-in mice mark stage-specific Foxc2-expressing cells during mouse organogenesis

Foxc2, a member of the winged helix transcription factor family, is essential for eye, calvarial bone, cardiovascular and kidney development in mice. Nevertheless, how Foxc2-expressing cells and their descendent cells contribute to the development of these tissues and organs has not been elucidated. Here, we generated a Foxc2 knock-in (Foxc2^CreERT2 ) mouse, in which administration of estrogen receptor antagonist tamoxifen induces nuclear translocation of Cre recombinase in Foxc2-expressing cells. By crossing with ROSA-LacZ reporter mice (Foxc2^CreERT2 ; R26R), the fate of Foxc2 positive (Foxc2⁺ ) cells was analyzed through LacZ staining at various embryonic stages. We found Foxc2⁺ cell descendants in the supraoccipital and exoccipital bone in E18.5 embryos, when tamoxifen was administered at embryonic day (E) 8.5. Furthermore, Foxc2⁺ descendant cranial neural crest cells at E8-10 were restricted to the corneal mesenchyme, while Foxc2⁺ cell derived cardiac neural crest cells at E6-12 were found in the aorta, pulmonary trunk and valves, and endocardial cushions. Foxc2⁺ cell descendant contributions to the glomerular podocytes in the kidney were also observed following E6.5 tamoxifen treatment. Our results are consistent with previous reports of Foxc2 expression during early embryogenesis and the Foxc2^CreERT2 mouse provides a tool to investigate spatiotemporal roles of Foxc2 and contributions of Foxc2⁺ expressing cells during mouse embryogenesis.