The transcription factor Prox1 is a marker for lymphatic endothelial cells in normal and diseased human tissues

Mesothelial Cells Exhibit Characteristics of Perivascular Cells in an In Vitro Angiogenesis Assay

Mesothelial cells have been shown to have remarkable plasticity towards mesenchymal cell types during development and in disease situations. Here, we have characterized the potential of mesothelial cells to undergo changes toward perivascular cells using an in vitro angiogenesis assay. We demonstrate that GFP-labeled mesothelial cells (GFP-MCs) aligned closely and specifically with endothelial networks formed when human dermal microvascular endothelial cells (HDMECs) were cultured in the presence of VEGF-A165 on normal human dermal fibroblasts (NHDFs) for a 7-day period. The co-culture with GFP-MCs had a positive effect on branch point formation indicating that the cells supported endothelial tube formation. We interrogated the molecular response of the GFP-MCs to the angiogenic co-culture by qRT-PCR and found that the pericyte marker Ng2 was upregulated when the cells were co-cultured with HDMECs on NHDFs, indicating a change towards a perivascular phenotype. When GFP-MCs were cultured on the NHDF feeder layer, they upregulated the epithelial-mesenchymal transition marker Zeb1 and lost their circularity while increasing their size, indicating a change to a more migratory cell type. We analyzed the pericyte-like behavior of the GFP-MCs in a 3D cardiac microtissue (spheroid) with cardiomyocytes, cardiac fibroblasts and cardiac endothelial cells where the mesothelial cells showed alignment with the endothelial cells. These results indicate that mesothelial cells have the potential to adopt a perivascular phenotype and associate with endothelial cells to potentially support angiogenesis.

The emerging roles of long noncoding RNAs in lymphatic vascular development and disease

Recent advances in RNA sequencing technologies helped uncover what was once uncharted territory in the human genome-the complex and versatile world of long noncoding RNAs (lncRNAs). Previously thought of as merely transcriptional "noise", lncRNAs have now emerged as essential regulators of gene expression networks controlling development, homeostasis and disease progression. The regulatory functions of lncRNAs are broad and diverse, and the underlying molecular mechanisms are highly variable, acting at the transcriptional, post-transcriptional, translational, and post-translational levels. In recent years, evidence has accumulated to support the important role of lncRNAs in the development and functioning of the lymphatic vasculature and associated pathological processes such as tumor-induced lymphangiogenesis and cancer metastasis. In this review, we summarize the current knowledge on the role of lncRNAs in regulating the key genes and pathways involved in lymphatic vascular development and disease. Furthermore, we discuss the potential of lncRNAs as novel therapeutic targets and outline possible strategies for the development of lncRNA-based therapeutics to treat diseases of the lymphatic system.

Three-Dimensional Histological Characterization of the Placental Vasculature Using Light Sheet Microscopy

The placenta is the first embryonic organ, representing the connection between the embryo and the mother, and is therefore necessary for the embryo's growth and survival. To meet the ever-growing need for nutrient and gas exchange, the maternal spiral arteries undergo extensive remodeling, thus increasing the uteroplacental blood flow by 16-fold. However, the insufficient remodeling of the spiral arteries can lead to severe pregnancy-associated disorders, including but not limited to pre-eclampsia. Insufficient endovascular trophoblast invasion plays a key role in the manifestation of pre-eclampsia; however, the underlying processes are complex and still unknown. Classical histopathology is based on two-dimensional section microscopy, which lacks a volumetric representation of the vascular remodeling process. To further characterize the uteroplacental vascularization, a detailed, non-destructive, and subcellular visualization is beneficial. In this study, we use light sheet microscopy for optical sectioning, thus establishing a method to obtain a three-dimensional visualization of the vascular system in the placenta. By introducing a volumetric visualization method of the placenta, we could establish a powerful tool to deeply investigate the heterogeneity of the spiral arteries during the remodeling process, evaluate the state-of-the-art treatment options, effects on vascularization, and, ultimately, reveal new insights into the underlying pathology of pre-eclampsia.

Modeling lymphangiogenesis: Pairing in vitro and in vivo metrics

Lymphangiogenesis is the mechanism by which the lymphatic system develops and expands new vessels facilitating fluid drainage and immune cell trafficking. Models to study lymphangiogenesis are necessary for a better understanding of the underlying mechanisms and to identify or test new therapeutic agents that target lymphangiogenesis. Across the lymphatic literature, multiple models have been developed to study lymphangiogenesis in vitro and in vivo. In vitro, lymphangiogenesis can be modeled with varying complexity, from monolayers to hydrogels to explants, with common metrics for characterizing proliferation, migration, and sprouting of lymphatic endothelial cells (LECs) and vessels. In comparison, in vivo models of lymphangiogenesis often use genetically modified zebrafish and mice, with in situ mouse models in the ear, cornea, hind leg, and tail. In vivo metrics, such as activation of LECs, number of new lymphatic vessels, and sprouting, mirror those most used in vitro, with the addition of lymphatic vessel hyperplasia and drainage. The impacts of lymphangiogenesis vary by context of tissue and pathology. Therapeutic targeting of lymphangiogenesis can have paradoxical effects depending on the pathology including lymphedema, cancer, organ transplant, and inflammation. In this review, we describe and compare lymphangiogenic outcomes and metrics between in vitro and in vivo studies, specifically reviewing only those publications in which both testing formats are used. We find that in vitro studies correlate well with in vivo in wound healing and development, but not in the reproductive tract or the complex tumor microenvironment. Considerations for improving in vitro models are to increase complexity with perfusable microfluidic devices, co-cultures with tissue-specific support cells, the inclusion of fluid flow, and pairing in vitro models of differing complexities. We believe that these changes would strengthen the correlation between in vitro and in vivo outcomes, giving more insight into lymphangiogenesis in healthy and pathological states.

Imaging peripheral lymphatic dysfunction in chronic conditions

The lymphatics play important roles in chronic diseases/conditions that comprise the bulk of healthcare worldwide. Yet the ability to routinely image and diagnose lymphatic dysfunction, using commonly available clinical imaging modalities, has been lacking and as a result, the development of effective treatment strategies suffers. Nearly two decades ago, investigational near-infrared fluorescence lymphatic imaging and ICG lymphography were developed as routine diagnostic for clinically evaluating, quantifying, and treating lymphatic dysfunction in cancer-related and primary lymphedema, chronic venous disease, and more recently, autoimmune and neurodegenerative disorders. In this review, we provide an overview of what these non-invasive technologies have taught us about lymphatic (dys) function and anatomy in human studies and in corollary animal studies of human disease. We summarize by commenting on new impactful clinical frontiers in lymphatic science that remain to be facilitated by imaging.

Triptolide inhibits the progression of Glioblastoma U251 cells via targeting PROX1

Background

Glioblastoma multiforme (GBM) is the most lethal brain cancer in adults, characterized by rapid growth, extensive invasiveness, and poor prognosis, and there is still a lack of effective treatments. Here, we aimed to explore the role of triptolide (TPL), purified from Tripterygium wilfordii Hook F, on glioblastoma cell growth, apoptosis, proliferation, migration and invasion, as well as potential underlying mechanisms.

Methods

The publicly available clinical data of Brain Lower Grade Glioma (LGG) from The Cancer Genome Atlas (TCGA) had been screened to observe PROX1 expression. The Kaplan-Meier analysis was used to analyze the relationship between PROX1 expression and GBM prognosis. CCK8, cell cycle, EDU, apoptosis, wound healing, and transwell assays were performed to detect the effects of TPL on glioblastoma U251 cell viability, cell cycle, proliferation, apoptosis, migration and invasion, respectively. Further, a soft agar colony assay was used to calculate the growth of glioblastoma cells. The qRT-PCR and western blot were conducted to quantify PROX1 mRNA and protein levels. The transcriptional regulation of TPL was detected by Dual luciferase reporter assay.

Results

We found that TPL inhibited glioblastoma cell viability, proliferation, cell cycle, migration and invasion, but enhanced apoptosis in a dose-dependent manner. The expression of cell cycle inhibitor, P21, and pro-apoptosis factor, Bax was increased, while invasion-related factors MMP2 and MMP9 were silenced after TPL treatments. Mechanistically, TPL showed transcriptional inhibition of PROX1 appearance. Moreover, ectopic expression of PROX1 partially rescued the effects of TPL on glioblastoma cell viability, proliferation, apoptosis, migration and invasion, and on the expression of cell function-related genes.

Conclusion

This study verified that TPL inhibited the progression of glioblastoma cells by transcriptionally depressing the expression of PROX1.

Platelets and (Lymph)angiogenesis

The formation of new blood and lymphatic vessels is essential for both the development of multicellular organisms and (patho)physiological processes like wound repair and tumor growth. In the 1990s, circulating blood platelets were first postulated to regulate tumor angiogenesis by interacting with the endothelium and releasing angiogenic regulators from specialized α granules. Since then, many studies have validated the contributions of platelets to tumor angiogenesis, while uncovering novel roles for platelets in other angiogenic processes like wound resolution and retinal vascular disease. Although the majority of (lymph)angiogenesis occurs during development, platelets appear necessary for lymphatic but not vascular growth, implying their particular importance in pathological cases of adult angiogenesis. Future work is required to determine whether drugs targeting platelet production or function offer a clinically relevant tool to limit detrimental angiogenesis.

Lymph node lymphatic endothelial cells as multifaceted gatekeepers in the immune system

Single-cell technologies have recently allowed the identification of multiple lymphatic endothelial cell (LEC) subsets in subcapsular, paracortical, medullary, and other lymph node (LN) sinus systems in mice and humans. New analyses show that LECs serve key immunological functions in the LN stroma during immune responses. We discuss the roles of different LEC types in guiding leukocyte and cancer cell trafficking to and from the LN parenchyma, in capturing microbes, and in transporting, presenting, and storing lymph-borne antigens in distinct types of lymphatic sinuses. We underscore specific adaptations of human LECs and raise unanswered questions concerning LEC functions in human disease. Despite our limited understanding of human lymphatics - hampering clinical translation in inflammation and metastasis - we support the potential of LN LECs as putative targets for boosting/inhibiting immunoreactivity.

Single-Cell RNA Transcriptomics Reveals the State of Hepatic Lymphatic Endothelial Cells in Hepatitis B Virus-Related Acute-on-Chronic Liver Failure

Acute-on-chronic liver failure (ACLF) is an acutely decompensated cirrhosis syndrome with high short-term mortality. Very little is known about the relationship between the lymphatic system and ACLF. We explored the role of hepatic lymphatic vessels (LVs) and lymphatic endothelial cells (LyECs) in ACLF using human liver samples with the help of single-cell RNA-sequencing (scRNA-seq) technology. Here, ACLF exhibited more severe liver injury and inflammation than cirrhosis, as indicated by significant increases in plasma levels of alanine/aspartate aminotransferases and total bilirubin. Compared with cirrhosis cases, the number of intrahepatic LVs was decreased significantly in ACLF patients. ScRNA-seq revealed that many monocyte/macrophages infiltrated into the liver of ACLF cases. Meanwhile, scRNA-seq revealed a group of apoptotic and dysfunctional LyECs, which were the result of secreted phosphoprotein 1 (SPP1) released from infiltrating monocyte/macrophages. In vitro, SPP1 increased the proportion of dead LyECs significantly and impaired the ability of tube formation of LyECs in a dose- and time-dependent manner. In conclusion, ACLF is associated with less LV and LyEC dysfunction, at least in part mediated by SPP1 released from infiltrating monocyte/macrophages. Hepatic LVs and LyECs can be a novel therapeutic strategy for ACLF.

Detection of Lymphatic Vessels in Dental Pulp

Simple Summary

Our studies and results suggest a moderate correlation between pulp inflammation and the formation of new vessels, including lymphatic vessels. In view of the above, it can be concluded that as inflammation increases, the size of the vascular bed that enables circulation of body fluids, blood, and lymph increases as well. However, microscopic and immunohistochemical studies did not conclusively demonstrate if these vessels form systems within the pulp that facilitate drainage of the tooth cavity.

Abstract

The literature lacks conclusive evidence that lymphatic vessels can form in the dental pulp. Lymphangiogenesis is believed to occur in an inflamed pulp. If one defines lymphangiogenesis as the development of lymphatic vessels from already existing ones, such a mechanism is possible only when lymphatic vessels are present in healthy teeth. This paper aims to identify lymphatic vessels in the dental pulp using microscopic and immunohistochemical methods under physiological and pathological conditions. The tissue material consisted of human teeth intended for extraction. Our studies and results suggest a moderate correlation between pulp inflammation and the formation of new vessels, including lymphatic vessels.

Smad3 regulates smooth muscle cell fate and mediates adverse remodeling and calcification of the atherosclerotic plaque

Atherosclerotic plaques consist mostly of smooth muscle cells (SMC), and genes that influence SMC phenotype can modulate coronary artery disease (CAD) risk. Allelic variation at 15q22.33 has been identified by genome-wide association studies to modify the risk of CAD and is associated with the expression of SMAD3 in SMC. However, the mechanism by which this gene modifies CAD risk remains poorly understood. Here we show that SMC-specific deletion of Smad3 in a murine atherosclerosis model resulted in greater plaque burden, more outward remodelling and increased vascular calcification. Single-cell transcriptomic analyses revealed that loss of Smad3 altered SMC transition cell state toward two fates: a SMC phenotype that governs both vascular remodelling and recruitment of inflammatory cells, as well as a chondromyocyte fate. Together, the findings reveal that Smad3 expression in SMC inhibits the emergence of specific SMC phenotypic transition cells that mediate adverse plaque features, including outward remodelling, monocyte recruitment, and vascular calcification.

Lymphatic Endothelial Markers and Tumor Lymphangiogenesis Assessment in Human Breast Cancer

Metastasis via lymphatic vessels or blood vessels is the leading cause of death for breast cancer, and lymphangiogenesis and angiogenesis are critical prerequisites for the tumor invasion–metastasis cascade. The research progress for tumor lymphangiogenesis has tended to lag behind that for angiogenesis due to the lack of specific markers. With the discovery of lymphatic endothelial cell (LEC) markers, growing evidence demonstrates that the LEC plays an active role in lymphatic formation and remodeling, tumor cell growth, invasion and intravasation, tumor–microenvironment remodeling, and antitumor immunity. However, some studies have drawn controversial conclusions due to the variation in the LEC markers and lymphangiogenesis assessments used. In this study, we review recent findings on tumor lymphangiogenesis, the most commonly used LEC markers, and parameters for lymphangiogenesis assessments, such as the lymphatic vessel density and lymphatic vessel invasion in human breast cancer. An in-depth understanding of tumor lymphangiogenesis and LEC markers can help to illustrate the mechanisms and distinct roles of lymphangiogenesis in breast cancer progression, which will help in exploring novel potential predictive biomarkers and therapeutic targets for breast cancer.

Review on the Lymphatic Vessels in the Dental Pulp

Simple Summary

It is debatable whether lymphatic vessels exist in the dental pulp. Most researchers confirm their presence; however, the lymphatic system in the dental pulp is much less developed compared to other tissues of the body. Lymphangiogenesis occurs in the dental pulp with inflammatory changes as a response to inflammatory stimuli acting on the tooth. If lymphangiogenesis is defined as the development of lymphatic vessels from already existing ones, such a mechanism is possible only when lymphatic vessels are present in healthy teeth. Research papers have not conclusively proved whether lymphatic vessels can form in the dental pulp. The use of an immunohistochemical examination can very likely prove the presence of a lymphatic system in dental tissues. However, the evaluation of the lymphatic system of the teeth is problematic because it is quite difficult to clearly distinguish lymphatic vessels from small blood vessels.

Abstract

Despite many studies, opinions on the lymphatic system of the teeth are still incompatible. Studies using light and electron microscopy and directly using methods such as a radioisotope (radionuclide) scan and interstitial fluid pressure measurement reported incomplete results. Immunohistochemistry (IHC) plays the main role in investigating presence of the lymphatic system in dental tissues. This method uses labeled antibodies against antigens typical of lymphatic vessels. The use of appropriate staining enables the detection of antigen-antibody reaction products using a light (optical), electron or fluorescence microscope. However, these studies do not show the system of vessels, their histologic structure under physiological conditions and inflammation as well as the lymphangiogenesis process in the dental pulp. Unfortunately, there is a lack of studies associating the presence of lymphatic vessels in the dental pulp with local lymphatic nodes or large vessels outside the tooth. In the scientific and research environment, the evaluation of the lymphatic system of the teeth is problematic because it is quite difficult to clearly distinguish lymphatic vessels from small blood vessels. Despite many indications of the presence of lymphatic vessels in the pulp chamber, this problem remains open and needs further research.

Primary head and neck tumour-derived fibroblasts promote lymphangiogenesis in a lymphatic organotypic co-culture model

BACKGROUND

In head and neck cancer, intratumour lymphatic density and tumour lymphangiogenesis have been correlated with lymphatic metastasis, making lymphangiogenesis a promising therapeutic target. However, inter-patient tumour heterogeneity makes it challenging to predict tumour progression and lymph node metastasis. Understanding the lymphangiogenic-promoting factors leading to metastasis (e.g., tumour-derived fibroblasts or TDF), would help develop strategies to improve patient outcomes.

METHODS

A microfluidic in vitro model of a tubular lymphatic vessel was co-cultured with primary TDF from head and neck cancer patients to evaluate the effect of TDF on lymphangiogenesis. We assessed the length and number of lymphangiogenic sprouts and vessel permeability via microscopy and image analysis. Finally, we characterised lymphatic vessel conditioning by TDF via RT-qPCR.

FINDINGS

Lymphatic vessels were conditioned by the TDF in a patient-specific manner. Specifically, the presence of TDF induced sprouting, altered vessel permeability, and increased the expression of pro-lymphangiogenic genes. Gene expression and functional responses in the fibroblast-conditioned lymphatic vessels were consistent with the patient tumour stage and lymph node status. IGF-1, upregulated among patients, was targeted to validate our personalised medicine approach. Interestingly, IGF-1 blockade was not effective across different patients.

INTERPRETATION

The use of lymphatic organotypic models incorporating head and neck TDF provides insight into the pathways leading to lymphangiogenesis in each patient. This model provided a platform to test anti-angiogenic therapeutics and inform of their effectiveness for individual patients.

FUNDING

NIH R33CA225281. Wisconsin Head and Neck SPORE NIH P50DE026787. NIH R01AI34749.

FOXC2 Autoregulates Its Expression in the Pulmonary Endothelium After Endotoxin Stimulation in a Histone Acetylation-Dependent Manner

The innate immune response of pulmonary endothelial cells (EC) to lipopolysaccharide (LPS) induces Forkhead box protein C2 (FOXC2) activation through Toll Like Receptor 4 (TLR4). The mechanisms by which FOXC2 expression is regulated in lung EC under LPS stimulation remain unclear. We postulated that FOXC2 regulates its own expression in sepsis, and its transcriptional autoregulation directs lymphatic EC cell-fate decision. Bioinformatic analysis identified potential FOXC2 binding sites in the FOXC2 promoter. In human lung EC, we verified using chromatin immunoprecipitation (ChIP) and luciferase assays that FOXC2 bound to its own promoter and stimulated its expression after LPS stimulation. Chemical inhibition of histone acetylation by garcinol repressed LPS-induced histone acetylation in the FOXC2 promoter region, and disrupted LPS-mediated FOXC2 binding and transcriptional activation. CRISPR/dCas9/gRNA directed against FOXC2-binding-element (FBE) suppressed LPS-stimulated FOXC2 binding and autoregulation by blocking FBEs in the FOXC2 promoter, and repressed expression of lymphatic EC markers. In a neonatal mouse model of sterile sepsis, LPS-induced FOXC2 binding to FBE and FOXC2 expression in lung EC was attenuated with garcinol treatment. These data reveal a new mechanism of LPS-induced histone acetylation-dependent FOXC2 autoregulation.

Transcriptome Analysis of Hypoxic Lymphatic Endothelial Cells Indicates Their Potential to Contribute to Extracellular Matrix Rearrangement

Lymphedema (LE) affects millions of people worldwide. It is a chronic progressive disease with massive development of fibrosclerosis when untreated. There is no pharmacological treatment of lymphedema. The disease is associated with swelling of the interstitium of the affected organ, mostly arm or leg, impressive development of adipose tissue, fibrosis and sclerosis with accumulation of huge amounts of collagen, and Papillomatosis cutis. Malnutrition and reduced oxygenation of the affected tissues is a hallmark of lymphedema. Here, we investigated if the hypoxia of lymphatic endothelial cells (LECs) might contribute to fibrosis. We applied RNASeq and qPCR to study the concordant changes of the exome of three human foreskin-derived LEC isolates after 4 days of hypoxia (1% O₂) vs. normoxia (21% O₂). Of the approximately 16,000 genes expressed in LECs, 162 (1%) were up- or down-regulated by hypoxia. Of these, 21 genes have important functions in the production or modification of the extracellular matrix (ECM). In addition to the down-regulation of elastin, we found up-regulation of druggable enzymes and regulators such as the long non-coding RNA H19, inter-alpha-trypsin inhibitor heavy chain family member 5 (ITIH5), lysyl-oxidase (LOX), prolyl 4-hydroxylase subunit alpha 1 (P4HA1), procollagen-lysine 2-oxoglutarate 5-dioxygenase 2 (PLOD2), and others that are discussed in the paper. Initial lymphatics do not produce a continuous basement membrane; however, our study shows that hypoxic LECs have an unexpectedly high ability to alter the ECM.

Transient Expression of Lymphatic Markers in Retrobulbar Intraconal Orbital Vasculature During Fetal Development

Purpose

The aim of this study is to investigate the presence of orbital lymphatic vessels during fetal and neonatal development and in adults using a panel of lymphatic markers.

Methods

This was a retrospective observational case series. For analyzing lymphatic vessels, we used formalin-fixed paraffin-embedded enucleated eyes from 25 human fetuses between 13 and 24 weeks of gestation and postnatal eyes from 15 children and 5 adults. Immunohistochemical analysis of lymphatic vessels was performed for the markers: lymphatic vessel endothelial hyaluronic acid receptor-1 (LYVE-1), podoplanin (D2-40), Prospero-related homeobox gene-1 (Prox-1), pan-endothelial marker CD31, and blood vessel endothelium specific CD34.

Results

Vasculature showing endothelial expression of LYVE-1, D2-40, Prox-1, and CD31 in combination with absence or weak expression of CD34, as would be expected for lymphatic vessels, was seen in 11 of 25 fetuses in an age range from 14 weeks to 23 weeks of gestation (44%). This lymphatic vascular staining pattern was also observed in 4 of 15 liveborn children (27%), all within 1 month of age, of which two were born prematurely at 32 and 34 weeks of gestation. Interestingly, an incomplete lymphatic staining pattern was observed in another 4 fetuses and two liveborn children of 4 months and 7 years old. No expression of lymphatic markers was observed in adult orbital vasculature.

Conclusions

No retrobulbar intraorbital lymphatic vessels were observed in adults, however, we did observe transient expression of lymphatic markers in retrobulbar intraconal orbital vasculature during fetal and early neonatal development. The orbit may, therefore, be proposed to possess a full range of lymphatic plasticity.

Oxidized Low-Density Lipoprotein Drives Dysfunction of the Liver Lymphatic System

BACKGROUND AND AIMS

As the incidence of nonalcoholic steatohepatitis (NASH) continues to rise, understanding how normal liver functions are affected during disease is required before developing novel therapeutics which could reduce morbidity and mortality. However, very little is understood about how the transport of proteins and cells from the liver by the lymphatic vasculature is affected by inflammatory mediators or during disease.

METHODS

To answer these questions, we utilized a well-validated mouse model of NASH and exposure to highly oxidized low density lipoprotein (oxLDL). In addition to single cell sequencing, multiplexed immunofluorescence and metabolomic analysis of liver lymphatic endothelial cells (LEC)s we evaluated lymphatic permeability and transport both in vitro and in vivo.

RESULTS

Confirming similarities between human and mouse liver lymphatic vasculature in NASH, we found that the lymphatic vasculature expands as disease progresses and results in the downregulation of genes important to lymphatic identity and function. We also demonstrate, in mice with NASH, that fluorescein isothiocyanate (FITC) dextran does not accumulate in the liver draining lymph node upon intrahepatic injection, a defect that was rescued with therapeutic administration of the lymphatic growth factor, recombinant vascular endothelial growth factor C (rVEGFC). Similarly, exposure to oxLDL reduced the amount of FITC-dextran in the portal draining lymph node and through an LEC monolayer. We provide evidence that the mechanism by which oxLDL impacts lymphatic permeability is via a reduction in Prox1 expression which decreases lymphatic specific gene expression, impedes LEC metabolism and reorganizes the highly permeable lymphatic cell-cell junctions which are a defining feature of lymphatic capillaries.

CONCLUSIONS

We identify oxLDL as a major contributor to decreased lymphatic permeability in the liver, a change which is consistent with decreased protein homeostasis and increased inflammation during chronic liver disease.

Two rare PROX1 variants in patients with lymphedema

Background

The PROX1 gene is specifically expressed in a subpopulation of endothelial cells that, by budding and sprouting, give rise to the lymphatic system. It also plays a critical role in neurogenesis and during development of many organs, such as the eye lens, liver, and pancreas.

Methods

We used next‐generation sequencing (NGS) to sequence the DNA of a cohort of 246 Italian patients with lymphatic malformations. We first investigated 29 known disease‐causing genes: 235 of 246 patients tested negative and were then retested for a group of candidate genes, including PROX1, selected from a database of mouse models. The aim of the study was to define these patients’ genotypes and explore the role of the candidate gene PROX1 in lymphedema.

Results

Two of 235 probands were found to carry rare heterozygous missense variants in PROX1. In silico analysis of these variants—p.(Leu590His) and p.(Gly106Asp)—indicates that the overall protein structure was altered by changes in interactions between nearby residues, leading to functional protein defects.

Conclusions

Our results suggest that PROX1 is a new candidate gene for predisposition to lymphedema.

Meningeal Lymphatics: From Anatomy to Central Nervous System Immune Surveillance

At steady state, the CNS parenchyma has few to no lymphocytes and less potent Ag-presentation capability compared with other organs. However, the meninges surrounding the CNS host diverse populations of immune cells that influence how CNS-related immune responses develop. Interstitial and cerebrospinal fluid produced in the CNS is continuously drained, and recent advances have emphasized that this process is largely taking place through the lymphatic system. To what extent this fluid process mobilizes CNS-derived Ags toward meningeal immune cells and subsequently the peripheral immune system through the lymphatic vessel network is a question of significant clinical importance for autoimmunity, tumor immunology, and infectious disease. Recent advances in understanding the role of meningeal lymphatics as a communicator between the brain and peripheral immunity are discussed in this review.

Absence of lymphatic vessels in term placenta

Background

There has been debate about the existence of lymphatic vessels in placenta. Lymphatic endothelial cell (LEC) markers such as LYVE-1 and podoplanin/D2–40 have been found, although PROX1 has not been detected. The most reliable marker for LECs is the double staining for CD31 and PROX1, which has not been performed yet.

Methods

We studied three term placentas and dissected them into three areas: i.) basal plate area, ii.) intermediate area, and iii.) chorionic plate area. We used immunofluorescence single and double staining with antibodies against CD31, PROX1, LYVE-1, VEGFR-3, D2–40/PDPN, CD34, CCBE-1, and vimentin, as well as nested PCR, qPCR, Western blot and transmission electron microscopy (TEM).

Results

At TEM level we observed structures that have previously mistakenly been interpreted as lymphatics, however, we did not find any CD31/PROX1 double-positive cells in placenta. Absence of PROX1 was also noted by nested PCR, qPCR and Western blot. Also, LEC marker VEGFR-3 was expressed only in a small number of scattered leukocytes but was absent from vessels. The LEC marker D2–40/PDPN was expressed in most stromal cells, and the LEC marker LYVE-1 was found in a considerable number of stromal cells, but not in endothelial cells, which were positive for CD31, CD34, CCBE-1 and vimentin. Additionally, vimentin was found in stromal cells.

Conclusions

Our studies clearly show absence of lymphatics in term placenta. We also show that the functional area of the mother’s endometrium is not penetrated by lymphatics in term pregnancy.

Structural and functional conservation of non-lumenized lymphatic endothelial cells in the mammalian leptomeninges

The vertebrate CNS is surrounded by the meninges, a protective barrier comprised of the outer dura mater and the inner leptomeninges, which includes the arachnoid and pial layers. While the dura mater contains lymphatic vessels, no conventional lymphatics have been found within the brain or leptomeninges. However, non-lumenized cells called Brain/Mural Lymphatic Endothelial Cells or Fluorescent Granule Perithelial cells (muLECs/BLECs/FGPs) that share a developmental program and gene expression with peripheral lymphatic vessels have been described in the meninges of zebrafish. Here we identify a structurally and functionally similar cell type in the mammalian leptomeninges that we name Leptomeningeal Lymphatic Endothelial Cells (LLEC). As in zebrafish, LLECs express multiple lymphatic markers, containing very large, spherical inclusions, and develop independently from the meningeal macrophage lineage. Mouse LLECs also internalize macromolecules from the cerebrospinal fluid, including Amyloid-β, the toxic driver of Alzheimer's disease progression. Finally, we identify morphologically similar cells co-expressing LLEC markers in human post-mortem leptomeninges. Given that LLECs share molecular, morphological, and functional characteristics with both lymphatics and macrophages, we propose they represent a novel, evolutionary conserved cell type with potential roles in homeostasis and immune organization of the meninges.

Bradykinin signaling regulates solute permeability and cellular junction organization in lymphatic endothelial cells

OBJECTIVE

Determine the effect of bradykinin on solute permeability and cellular junctional proteins in human dermis microvascular endothelial cells.

METHODS

Cells were characterized by immunofluorescence and fluorescence-activated cell sorting. Macromolecular transport of dextran and albumin was monitored. Junctional protein expression and phosphorylation were determined by immunoblot analyses. Intracellular calcium and cAMP levels were evaluated. Target gene expression at mRNA and protein levels was determined.

RESULTS

Human dermis microvascular endothelial cells comprised 97% lymphatic endothelial cells. Bradykinin increased the permeability to dextran in a concentration-dependent manner, while reduced the permeability to albumin. Bradykinin treatment down-regulated VE-cadherin expression and affected its phosphorylation status at Tyr731. It also down-regulated claudin-5 expression at the transcriptional level through bradykinin-2-receptor signaling. An increase in the intracellular calcium levels and a reduction in the cAMP concentration were associated effects. Finally, bradykinin induced the up-regulation of vascular endothelial growth factor-C protein which was found increased in BK-induced human dermis microvascular endothelial cells culture supernates.

CONCLUSIONS

Human dermis microvascular endothelial cells represent a model of lymphatic endothelial cells, in which bradykinin-2-receptor is expressed. Bradykinin-induced bradykinin-2-receptor signaling through intracellular calcium mobilization and reduction in cAMP levels, triggered changes in solute permeability and cellular junction expression. It further up-regulated vascular endothelial growth factors-C protein expression, which is a key modulator of lymphatic vessels function and lymphangiogenesis.

Transplanted spleen stromal cells with osteogenic potential support ectopic myelopoiesis

Spleen stromal lines which support in vitro hematopoiesis are investigated for their lineage origin and hematopoietic support function in vivo. Marker expression and gene profiling identify a lineage relationship with mesenchymal stem cells and perivascular reticular cells described recently in bone marrow. Stromal lines commonly express Cxcl12, Pdgfra and Pdgfr typical of bone marrow derived perivascular reticular cells but reflect a unique cell type in terms of other gene and marker expression. Their classification as osteoprogenitors is confirmed through ability to undergo osteogenic, but not adipogenic or chondrogenic differentiation. Some stromal lines were shown to form ectopic niches for HSCs following engraftment under the kidney capsule of NOD/SCID mice. The presence of myeloid cells and a higher representation of a specific dendritic-like cell type over other myeloid cells within grafts was consistent with previous in vitro evidence of hematopoietic support capacity. These studies reinforce the role of perivascular/perisinusoidal reticular cells in hematopoiesis and implicate such cells as niches for hematopoiesis in spleen.

A novel role of HIF-1α/PROX-1/LYVE-1 axis on tissue regeneration after renal ischaemia/reperfusion in mice

Context: Renal ischaemia reperfusion (I/R) is a common clinical condition with a high morbidity and mortality rate. To date, I/R-induced renal injury remains an ineffective treatment. Objective: We hypothesis that angiogenesis and lymphangiogenesis markers, prospero homeobox-1 (PROX-1) and lymphatic endothelial hyaluronan receptor-1 (LYVE-1), are critical during I/R. Material and methods: Kunming mice were subjected to I/R and observed for the following eight consecutive days. Pathology analysis and protein distribution were detected by H&E staining, immunohistochemistry and immunofluorescence confocal analysis. Results: After I/R treatment, renal pathology was changed. HIF-1α was induced in the early stage and colocalisation with PROX-1 mainly in the renal tubular region, whereas PROX-1 and LYVE-1 were colocalised in the glomerulus of the endothelial region. Conclusions: In this study, we revealed HIF-1α/PROX-1/LVYE-1 axis dynamic changes in different regions after I/R and demonstrated for the first time it activates during I/R repair.

Absence of Intraocular Lymphatic Vessels in Uveal Melanomas with Extrascleral Growth

The aim of this study was to investigate the presence of intraocular lymphatic vessels in patients with uveal melanomas and extrascleral extension using a panel of lymphatic markers. The following immunohistochemical markers were analyzed: lymphatic vessel endothelial hyaluronic acid receptor-1 (LYVE-1), podoplanin (D2-40), prospero-related homeobox gene-1 (Prox-1), pan-endothelial marker cluster of differentiation 31 (CD31), and blood vessel endothelium-specific CD34. Lymphatic vessels were defined as a combination of staining of the following positive markers: LYVE-1, D2-40, Prox-1, and CD31; and no staining of the negative marker CD34. In total, 456 patients were enucleated; 16 of the 46 uveal melanomas with extrascleral extension were contained in stored paraffin tissue. Two samples of the 16 uveal melanomas showed focal positive intraocular vascular staining for LYVE-1 and co-expression of CD31 and CD34. Due to the lack of Prox-1 and D2-40, and positive expression of CD34, these cannot be classified as lymphatic vessels. In one case recruitment of an extraocular, intratumoral lymphatic vascular structure was observed in the periphery of the subconjunctival extrascleral extension. Intraocular lymphatic vessels are absent in uveal melanomas with extrascleral extension; however, we provide proof for recruitment of intratumoral lymphatics by uveal melanomas with extraocular extension from subconjunctival lymphatics that may explain the rare cases of regional lymphatic spread. A panel of antibodies is necessary to detect lymphatic vessels with high specificity.

Functions and Regeneration of Mature Cardiac Lymphatic Vessels in Atherosclerosis, Myocardial Infarction, and Heart Failure

Cardiac lymphatic vessels play a vital role in maintaining cardiac homeostasis both under physiological and pathological conditions. Clearer illustration of the anatomy of cardiac lymphatics has been achieved by fluorescence exhibition comparing to dye injection. Besides, identification of specific lymphatic markers in recent decades paves the way for researches in development and regeneration of cardiac lymphatics, such as VEGF-C/VEGFR-3, EphB4/ephrin-B2, Prox-1, Podoplanin, and Lyve-1. Knocking out each of these markers in mice model also reveals the signaling pathways instructing the formation of cardiac lymphatics. In the major cardiovascular disease series of atherosclerosis, myocardial infarction (MI), and heart failure, cardiac lymphatics regulate the transportation of extravasated proteins and lipids, inflammatory and immune responses, as well as fluid balance. Elementary intervention methods, such as lymphatic factor protein injection VEGF-C, are applied in murine MI models to restore or enhance functions of lymphatic vessels, achieving improvements in cardiac function. Also, data from our laboratory showed that intramyocardial EphB4 injection also improved lymphatic regeneration in mouse MI model. Therefore, we believe that enhancing functions and regeneration of mature cardiac lymphatic vessels in cardiovascular diseases is of great potential therapeutic meaning in the future.

Development of the pulmonary pleura with special reference to the lung surface morphology: a study using human fetuses

In and after the third trimester, the lung surface is likely to become smooth to facilitate respiratory movements. However, there are no detailed descriptions as to when and how the lung surface becomes regular. According to our observations of 33 fetuses at 9–16 weeks of gestation (crown-rump length [CRL], 39–125 mm), the lung surface, especially its lateral (costal) surface, was comparatively rough due to rapid branching and outward growing of bronchioli at the pseudoglandular phase of lung development. The pulmonary pleura was thin and, beneath the surface mesothelium, no or little mesenchymal tissue was detectable. Veins and lymphatic vessels reached the lung surface until 9 weeks and 16 weeks, respectively. In contrast, in 8 fetuses at 26–34 weeks of gestation (CRL, 210–290 mm), the lung surface was almost smooth because, instead of bronchioli, the developing alveoli faced the external surfaces of the lung. Moreover, the submesothelial tissue became thick due to large numbers of dilated veins connected to deep intersegmental veins. CD34-positive, multilayered fibrous tissue was also evident beneath the mesothelium in these stages. The submesothelial tissue was much thicker at the basal and mediastinal surfaces compared to apical and costal surfaces. Overall, rather than by a mechanical stress from the thoracic wall and diaphragm, a smooth lung surface seemed to be established largely by the thick submesothelial tissue including veins and lymphatic vessels until 26 weeks.

Utilizing lymphatic cell markers to visualize human lymphatic abnormalities

In vivo visualization of the human lymphatic system is limited by the mode of delivery of tracing agents, depth of field and size of the area examined, and specificity of the cell markers used to distinguish lymphatic endothelium from the blood vessels and the surrounding tissues. These limitations are particularly problematic when imaging human lymphatic abnormalities. First, limited understanding of the lymphatic disease aetiology exists with respect to genetic causes and phenotypic presentations. Second, the ability of a tracer to reach the entire lymphatic network within the diseased tissue is suboptimal. Third, what is known about the expression of lymphatic endothelial cell (LEC) markers, such as podoplanin, lymphatic vessel endothelial hyaluronan receptor, Drosophila melanogaster homeobox gene prospero-1 and vascular endothelial growth factor receptor-3 in rodent lymphatic vessels and healthy human LECs may not necessarily apply in human lymphatic disease settings. The aim of this review is to highlight challenges in visualizing lymphatic vessels in human lymphatic abnormalities with respect to distribution patterns of the cellular markers currently employed to visualize abnormal human lymphatic vessels in experimental settings. Allowing for these limitations within new diagnostic visualization technologies is likely to improve our ability to image human lymphatic diseases.

Angiogenesis revisited from a metabolic perspective: role and therapeutic implications of endothelial cell metabolism

Endothelial cell (EC) metabolism has lately emerged as a novel and promising therapeutic target to block vascular dysregulation associated with diseases like cancer and blinding eye disease. Glycolysis, fatty acid oxidation (FAO) and, more recently, glutamine/asparagine metabolism emerged as key regulators of EC metabolism, able to impact angiogenesis in health and disease. ECs are highly glycolytic as they require ATP and biomass for vessel sprouting. Notably, a regulator of the glycolytic pathway, 6-phosphofructo-2-kinase/fructose-2,6-bisphosphatase 3, controls vessel sprouting during the angiogenic switch and its inhibition in tumour ECs leads to vessel normalization, thereby reducing metastasis and ameliorating chemotherapy. Moreover, FAO promotes EC proliferation through DNA synthesis, and plays an essential role in lymphangiogenesis via epigenetic regulation of histone acetylation. Pathological angiogenesis was decreased upon blockade of carnitine palmitoyltransferase 1, a regulator of FAO in ECs. More recently, metabolism of glutamine, in conjunction with asparagine, was reported to maintain EC sprouting through TCA anaplerosis, redox homeostasis, mTOR activation and endoplasmic stress control. Inactivation or blockade of glutaminase 1, which hydrolyses glutamine into ammonia and glutamate, impairs angiogenesis in health and disease, while silencing of asparagine synthetase reduces vessel sprouting in vitro. In this review, we summarize recent insights into EC metabolism and discuss therapeutic implications of targeting EC metabolism.

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

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

Comparison of lymphangiogenesis, lymphatic invasion, and axillary lymph node metastasis in breast carcinoma

Context

Lymphangiogenesis correlates with poor prognosis in Invasive Ductal Carcinoma (IDC) breast. D2-40 antibody, a specific marker for lymphatic endothelium, differentiates lymphatic from vascular endothelium. Therefore, the aims of this study were to estimate lymphangiogenesis using D2-40 antibody and correlate with lymphatic invasion (LI) and axillary lymph node (LN) status and compare lymphatic mean vessel density (LMVD) with Tumor (T) and Node (N) stages and grade of tumor.

Methods and Material

The study was conducted on fifty consecutive cases of IDC breast who underwent modified radical mastectomy (MRM) from Jan 2009 to March 2011. Hematoxylin-eosin sections and Immunohistochemistry (IHC) slides were studied along with their LN status. LMVD was counted after D2-40 immunostaining (100x magnification) in three hot spots in peritumoral areas and averaged. LI as opposed to vascular invasion (BVI), and LN status for all cases were assessed.

Statistical Analysis

Statistical analysis was done using SPSS software (version 14.0 for Windows). Pearson's correlations, χ² tests and Mann-Whitney U test were used.

Results

Lymphangiogenesis varied from 0 to 58 with mean LMVD of 11. Of 50 cases, five showed no lymphatic vessels in peritumoral areas; of these five, three had positive LNs. 21/50 cases had LI. No statistical significant association was seen between lymphangiogenesis and LI. 34/50 cases had positive LNs. Mean LMVD was higher in patients with N2/N3 stage as compared to N0/N1 stage and was statistically significant (P = 0.013).

Conclusions

D2-40 is specific marker for lymphatic endothelium. LI and lymphangiogenesis, as opposed to BVI, are better prognostic indicators in IDC breast.

Fucoidan inhibits lymphangiogenesis by downregulating the expression of VEGFR3 and PROX1 in human lymphatic endothelial cells

Lymphangiogenesis is one of the promoters of tumor lymphatic metastasis. Fucoidan which is a fucose-enriched sulfated polysaccharide has effect on various pharmacological activities including anti-metastasis activity. However, the inhibitory effect of fucoidan on lymphangiogenesis remains unclear. Here, fucoidan extracted from U. pinnatifida sporophylls suppressed HLECs proliferation, migration and tube-like structure formation, and had inhibitory effect of tumor-induced lymphangiogenesis in vitro. Additionally, we found that fucoidan had a dose-dependent depressive effect on the expressions of PROX1, vascular endothelial growth factor receptor 3 (VEGFR3), NF-κB, phospho-PI3K and phospho-Akt in HLECs. Moreover, anti-lymphangiogenesis effect of fucoidan was assessed by using mouse tumor model. In summary, fucoidan inhibit tumor lymphangiogenesis and lymphatic metastasis by suppressing the NF-κB/PI3K/Akt signaling pathway through reduced levels of PROX1 and VEGFR3.

Visualization and Tools for Analysis of Zebrafish Lymphatic Development

The accessibility and optical transparency of the zebrafish embryo offers a unique platform for live-imaging of developmental lymphangiogenesis. Transgenic lines labelling lymphatic progenitors and vessels enable researchers to visualize cellular processes and ask how they contribute to lymphatic development in genetic models. Furthermore, validated immunofluorescence staining for key signaling and cell fate markers (phosphorylated Erk and Prox1) allow single cell resolution studies of lymphatic differentiation. Here, we describe in detail how zebrafish embryos and larvae can be mounted for high resolution, staged imaging of lymphatic networks, how lymphangiogenesis can be reliably quantified and how immunofluorescence can reveal lymphatic signaling and differentiation. These methods offer researchers the opportunity to experimentally dissect developmental lymphangiogenesis with outstanding resolution.

Comparison and functional characterisation of peripheral blood mononuclear cells isolated from filarial lymphoedema and endemic normals of a South Indian population

OBJECTIVE

The underlying problem in lymphatic filariasis is irreversible swelling of the limbs (lymphoedema), which is a unique feature of lymphatic insufficiency. It is still unclear whether the natural ability of lymphatics to form functional lymphatic vasculature is achieved or attenuated in the lymphoedemal pathology. Clinical studies have clearly shown that circulating lymphatic progenitors (CLPs), a subset of bone marrow-derived mononuclear cells (PBMCs), contribute to post-natal lymph vasculogenesis. CLP-based revascularisation could be a promising strategy to bypass the endothelial disruption and damage incurred by the filarial parasites. Thus our aim was to compare and characterise the functional prowess of PBMCs in physiological and lymphoedemal pathology.

METHODS

PBMCs were isolated from venous blood sample from drug-naive endemic normals (EN) and drug-deprived filarial lymphoedema (FL) individuals using density gradient centrifugation. Adhesion, transwell migration and in vitro matrigel assays were employed to characterise the lymphvasculogenic potential of PBMCs. CLPs were phenotypically characterised using flow cytometry; expression levels of lymphatic markers and inflammatory cytokines were quantified using qRT-PCR and ELISA, respectively.

RESULTS

PBMCs from FL group display poor adherence to fibronectin (P = 0.040), reduced migration towards SDF-1α (P = 0.035), impaired tubular network (P = 0.004) and branching point (P = 0.048) formation. The PBMC mRNA expression of VEGFR3 (P = 0.039) and podoplanin (P = 0.050) was elevated, whereas integrin α9 (P = 0.046) was inhibited in FL individuals; additionally, the surface expression of CD34 (P = 0.048) was significantly reduced in the FL group compared to the EN group.

CONCLUSION

PBMCs from filarial lymphoedema show defective and dysregulated lymphvasculogenic function compared to endemic normals.

Lymphatic Endothelial Cells Produce M-CSF, Causing Massive Bone Loss in Mice

Gorham-Stout disease (GSD) is a rare bone disorder characterized by aggressive osteolysis associated with lymphatic vessel invasion within bone marrow cavities. The etiology of GSD is not known, and there is no effective therapy or animal model for the disease. Here, we investigated if lymphatic endothelial cells (LECs) affect osteoclasts (OCs) to cause a GSD osteolytic phenotype in mice. We examined the effect of a mouse LEC line on osteoclastogenesis in co-cultures. LECs significantly increased receptor activator of NF-κB ligand (RANKL)-mediated OC formation and bone resorption. LECs expressed high levels of macrophage colony-stimulating factor (M-CSF), but not RANKL, interleukin-6 (IL-6), and tumor necrosis factor (TNF). LEC-mediated OC formation and bone resorption were blocked by an M-CSF neutralizing antibody or Ki20227, an inhibitor of the M-CSF receptor, c-Fms. We injected LECs into the tibias of wild-type (WT) mice and observed massive osteolysis on X-ray and micro-CT scans. Histology showed that LEC-injected tibias had significant trabecular and cortical bone loss and increased OC numbers. M-CSF protein levels were significantly higher in serum and bone marrow plasma of mice given intra-tibial LEC injections. Immunofluorescence staining showed extensive replacement of bone and marrow by podoplanin+ LECs. Treatment of LEC-injected mice with Ki20227 significantly decreased tibial bone destruction. In addition, lymphatic vessels in a GSD bone sample were stained positively for M-CSF. Thus, LECs cause bone destruction in vivo in mice by secreting M-CSF, which promotes OC formation and activation. Blocking M-CSF signaling may represent a new therapeutic approach for treatment of patients with GSD. Furthermore, tibial injection of LECs is a useful mouse model to study GSD. © 2017 American Society for Bone and Mineral Research.

Characterisation of Development and Electrophysiological Mechanisms Underlying Rhythmicity of the Avian Lymph Heart

Despite significant advances in tissue engineering such as the use of scaffolds, bioreactors and pluripotent stem cells, effective cardiac tissue engineering for therapeutic purposes has remained a largely intractable challenge. For this area to capitalise on such advances, a novel approach may be to unravel the physiological mechanisms underlying the development of tissues that exhibit rhythmic contraction yet do not originate from the cardiac lineage. Considerable attention has been focused on the physiology of the avian lymph heart, a discrete organ with skeletal muscle origins yet which displays pacemaker properties normally only found in the heart. A functional lymph heart is essential for avian survival and growth in ovo. The histological nature of the lymph heart is similar to skeletal muscle although molecular and bioelectrical characterisation during development to assess mechanisms that contribute towards lymph heart contractile rhythmicity have not been undertaken. A better understanding of these processes may provide exploitable insights for therapeutic rhythmically contractile tissue engineering approaches in this area of significant unmet clinical need. Here, using molecular and electrophysiological approaches, we describe the molecular development of the lymph heart to understand how this skeletal muscle becomes fully functional during discrete in ovo stages of development. Our results show that the lymph heart does not follow the normal transitional programme of myogenesis as documented in most skeletal muscle, but instead develops through a concurrent programme of precursor expansion, commitment to myogenesis and functional differentiation which offers a mechanistic explanation for its rapid development. Extracellular electrophysiological field potential recordings revealed that the peak-to-peak amplitude of electrically evoked local field potentials elicited from isolated lymph heart were significantly reduced by treatment with carbachol; an effect that could be fully reversed by atropine. Moreover, nifedipine and cyclopiazonic acid both significantly reduced peak-to-peak local field potential amplitude. Optical recordings of lymph heart showed that the organ’s rhythmicity can be blocked by the HCN channel blocker, ZD7288; an effect also associated with a significant reduction in peak-to-peak local field potential amplitude. Additionally, we also show that isoforms of HCN channels are expressed in avian lymph heart. These results demonstrate that cholinergic signalling and L-type Ca²⁺ channels are important in excitation and contraction coupling, while HCN channels contribute to maintenance of lymph heart rhythmicity.

A Huge Cystic Retroperitoneal Lymphangioma Presenting with Back Pain

Retroperitoneal lymphangioma is a rare location and type of benign abdominal tumors. The clinical presentation of this rare disease is nonspecific, ranging from abdominal distention to sepsis. Here we present a 73-year-old female patient with 3-month history of back pain. USG and CT revealed a huge cystic mass which was surgically excised and appeared to be lymphangioma on histopathology.

Morphological and Molecular Characterization of Human Dermal Lymphatic Collectors

Millions of patients suffer from lymphedema worldwide. Supporting the contractility of lymphatic collectors is an attractive target for pharmacological therapy of lymphedema. However, lymphatics have mostly been studied in animals, while the cellular and molecular characteristics of human lymphatic collectors are largely unknown. We studied epifascial lymphatic collectors of the thigh, which were isolated for autologous transplantations. Our immunohistological studies identify additional markers for LECs (vimentin, CCBE1). We show and confirm differences between initial and collecting lymphatics concerning the markers ESAM1, D2-40 and LYVE-1. Our transmission electron microscopic studies reveal two types of smooth muscle cells (SMCs) in the media of the collectors with dark and light cytoplasm. We observed vasa vasorum in the media of the largest collectors, as well as interstitial Cajal-like cells, which are highly ramified cells with long processes, caveolae, and lacking a basal lamina. They are in close contact with SMCs, which possess multiple caveolae at the contact sites. Immunohistologically we identified such cells with antibodies against vimentin and PDGFRα, but not CD34 and cKIT. With Next Generation Sequencing we searched for highly expressed genes in the media of lymphatic collectors, and found therapeutic targets, suitable for acceleration of lymphatic contractility, such as neuropeptide Y receptors 1, and 5; tachykinin receptors 1, and 2; purinergic receptors P2RX1, and 6, P2RY12, 13, and 14; 5-hydroxytryptamine receptors HTR2B, and 3C; and adrenoceptors α2A,B,C. Our studies represent the first comprehensive characterization of human epifascial lymphatic collectors, as a prerequisite for diagnosis and therapy.

The Hepatic Lymphatic Vascular System: Structure, Function, Markers, and Lymphangiogenesis

The lymphatic vascular system has been minimally explored in the liver despite its essential functions including maintenance of tissue fluid homeostasis. The discovery of specific markers for lymphatic endothelial cells has advanced the study of lymphatics by methods including imaging, cell isolation, and transgenic animal models and has resulted in rapid progress in lymphatic vascular research during the last decade. These studies have yielded concrete evidence that lymphatic vessel dysfunction plays an important role in the pathogenesis of many diseases. This article reviews the current knowledge of the structure, function, and markers of the hepatic lymphatic vascular system as well as factors associated with hepatic lymphangiogenesis and compares liver lymphatics with those in other tissues.

Building the drains: the lymphatic vasculature in health and disease

The lymphatic vasculature is comprised of a network of endothelial vessels found in close proximity to but separated from the blood vasculature. An essential tissue component of all vertebrates, lymphatics are responsible for the maintenance of fluid homeostasis, dissemination of immune cells, and lipid reabsorption under healthy conditions. When lymphatic vessels are impaired due to invasive surgery, genetic disorders, or parasitic infections, severe fluid build-up accumulates in the affected tissues causing a condition known as lymphedema. Malignant tumors can also directly activate lymphangiogenesis and use these vessels to promote the spread of metastatic cells. Although their first description goes back to the times of Hippocrates, with subsequent anatomical characterization at the beginning of the 20th-century, the lack of identifying molecular markers and tools to visualize these translucent vessels meant that investigation of lymphatic vessels fell well behind research of blood vessels. However, after years under the shadow of the blood vasculature, recent advances in imaging technologies and new genetic and molecular tools have accelerated the pace of research on lymphatic vessel development. These new tools have facilitated both work in classical mammalian models and the emergence of new powerful vertebrate models like zebrafish, quickly driving the field of lymphatic development back into the spotlight. In this review, we summarize the highlights of recent research on the development and function of the lymphatic vascular network in health and disease. WIREs Dev Biol 2016, 5:689-710. doi: 10.1002/wdev.246 For further resources related to this article, please visit the WIREs website.

Integration of CD45-positive leukocytes into newly forming lymphatics of adult mice

The embryonic origin of lymphatic endothelial cells (LECs) has been a matter of controversy since more than a century. However, recent studies in mice have supported the concept that embryonic lymphangiogenesis is a complex process consisting of growth of lymphatics from specific venous segments as well as the integration of lymphangioblasts into the lymphatic networks. Similarly, the mechanisms of adult lymphangiogenesis are poorly understood and have rarely been studied. We have recently shown that endothelial progenitor cells isolated from the lung of adult mice have the capacity to form both blood vessels and lymphatics when grafted with Matrigel plugs into the skin of syngeneic mice. Here, we followed up on these experiments and studied the behavior of host leukocytes during lymphangiogenesis in the Matrigel plugs. We observed a striking co-localization of CD45(+) leukocytes with the developing lymphatics. Numerous CD45(+) cells expressed the LEC marker podoplanin and were obviously integrated into the lining of lymphatic capillaries. This indicates that, similar to inflammation-induced lymphangiogenesis in man, circulating CD45(+) cells of adult mice are capable of initiating lymphangiogenesis and of adopting a lymphvasculogenic cellular differentiation program. The data are discussed in the context of embryonic and inflammation-induced lymphangiogenesis.

CXCL12/CXCR4 axis regulates neovascularization and lymphangiogenesis in sutured corneas in mice

The present study aimed to determine the plausible functional role of chemokine (C-X-C motif) ligand 12 (CXCL12)/chemokine (C-X-C motif) receptor 4 (CXCR4) in inflammatory corneal hemangiogenesis and lymphangiogenesis in vivo. Corneal hemangiogenesis and lymphangiogenesis were induced by placing an 11-0 nylon suture in an intrastromal position. The expression levels of the vascular endothelial growth factor (VEGF) family, CXCL12 and CXCR4 in the corneas were investigated in the corneas using reverse transcription-quantitative polymerase chain reaction and immunohistochemistry. Corneal hemangiogenic and lymphangiogenic responses were assessed by immunofluorescence using specific antibodies against cluster of differentiation 31 and lymphatic vessel endothelial hyaluronan receptor-1. Subconjunctival injection of AMD3100 to the sutured corneas was also performed. CXCL12/CXCR4 mRNA and protein expression levels increased markedly in suture-induced corneal neovascularization (CNV) and decreased with AMD3100 treatment. Hemangiogenesis and lymphangiogenesis were captured in images using immunofluorescence and were shown to be markedly increased with suture placement and reduced with AMD3100 treatment. VEGF-A/VEGFR-1 and VEGF-C/VEGFR-3 mRNA expression levels were upregulated in the suture placement and control groups, whereas the expression levels of all the factors were downregulated in the AMD3100 treatment group. The results from the present study demonstrated that CXCL12/CXCR4 interactions regulate hemangiogenesis and lymphangiogenesis in suture-induced CNV. AMD3100 may be a novel therapeutic target for the prevention of blindness.