Ras Pathways on Prox1 and Lymphangiogenesis: Insights for Therapeutics

Calcitonin gene-related peptide and intermedin induce phosphorylation of p44/42 MAPK in primary human lymphatic endothelial cells in vitro

Calcitonin gene-related peptide (CGRP) and adrenomedullin 2/intermedin (AM2/IMD) play important roles in several pathologies, including cardiovascular disease, migraine and cancer. The efficacy of drugs targeting CGRP signalling axis for the treatment of migraine patients is sometimes offset by side effects (e.g. inflammation and microvascular complications, including aberrant neovascularisation in the skin). Recent studies using animal models implicate CGRP in lymphangiogenesis and lymphatic vessel function. However, whether CGRP or AM2/IMD can act directly on lymphatic endothelial cells is unknown. Here, we found that CGRP and AM2/IMD induced p44/42 MAPK phosphorylation in a time- and dose-dependent manner in primary human dermal lymphatic endothelial cells (HDLEC) in vitro, and thus directly affected these cells. These new findings reveal CGRP and AM2/IMD as novel regulators of LEC biology and warrant further investigation of their roles in the context of pathologies associated with lymphatic function in the skin and other organs, and therapies targeting CGRP signalling axis.

Lymphatic endothelial cell-specific NRAS p.Q61R mutant embryos show abnormal lymphatic vessel morphogenesis

Generalized lymphatic anomaly (GLA) and kaposiform lymphangiomatosis (KLA) are rare congenital disorders that arise through anomalous embryogenesis of the lymphatic system. A somatic activating NRAS p.Q61R variant has been recently detected in GLA and KLA tissues, suggesting that the NRAS p.Q61R variant plays an important role in the development of these diseases. To address this role, we studied the effect of the NRAS p.Q61R variant in lymphatic endothelial cells (LECs) on the structure of the lymphatics during embryonic and postnatal lymphangiogenesis applying inducible, LEC-specific NRAS p.Q61R variant in mice. Lox-stop-Lox NrasQ61R mice were crossed with Prox1-CreERT2 mice expressing tamoxifen-inducible Cre recombinase specifically in LECs. Whole-mount immunostaining of embryonic back skin using an antibody against the LEC surface marker VEGFR3 showed considerably greater lymphatic vessel width in LEC-specific NRAS p.Q61R mutant embryos than in littermate controls. These mutant embryos also showed a significant reduction in the number of lymphatic vessel branches. Furthermore, immunofluorescence staining of whole-mount embryonic back skin using an antibody against the LEC-specific nuclear marker Prox1 showed a large increase in the number of LECs in LEC-specific NRAS p.Q61R mutants. In contrast, postnatal induction of the NRAS p.Q61R variant in LECs did not cause abnormal lymphatic vessel morphogenesis. These results suggest that the NRAS p.Q61R variant in LECs plays a role in development of lymphatic anomalies. While this model does not directly reflect the human pathology of GLA and KLA, there are overlapping features, suggesting that further study of this model may help in studying GLA and KLA mechanisms.

Targeting lymphatic function in cardiovascular-kidney-metabolic syndrome: preclinical methods to analyze lymphatic function and therapeutic opportunities

The lymphatic vascular system spans nearly every organ in the body and serves as an important network that maintains fluid, metabolite, and immune cell homeostasis. Recently, there has been a growing interest in the role of lymphatic biology in chronic disorders outside the realm of lymphatic abnormalities, lymphedema, or oncology, such as cardiovascular-kidney-metabolic syndrome (CKM). We propose that enhancing lymphatic function pharmacologically may be a novel and effective way to improve quality of life in patients with CKM syndrome by engaging multiple pathologies at once throughout the body. Several promising therapeutic targets that enhance lymphatic function have already been reported and may have clinical benefit. However, much remains unclear of the discreet ways the lymphatic vasculature interacts with CKM pathogenesis, and translation of these therapeutic targets to clinical development is challenging. Thus, the field must improve characterization of lymphatic function in preclinical mouse models of CKM syndrome to better understand molecular mechanisms of disease and uncover effective therapies.

Quantification of Lymphangiogenesis in the Murine Lymphedema Tail Model Using Intravital Microscopy

Background: Lymphedema is chronic limb swelling resulting from lymphatic dysfunction. It affects an estimated five million Americans. There is no cure for this disease. Assessing lymphatic growth is essential in developing novel therapeutics. Intravital microscopy (IVM) is a powerful imaging tool for investigating various biological processes in live animals. Tissue nanotransfection technology (TNT) facilitates a direct, transcutaneous nonviral vector gene delivery using a chip with nanochannel poration in a rapid (<100 ms) focused electric field. TNT was used in this study to deliver the genetic cargo in the murine tail lymphedema to assess the lymphangiogenesis. The purpose of this study is to experimentally evaluate the applicability of IVM to visualize and quantify lymphatics in the live mice model. Methods and Results: The murine tail model of lymphedema was utilized. TNT was applied to the murine tail (day 0) directly at the surgical site with genetic cargo loaded into the TNT reservoir: TNTpCMV6 group receives pCMV6 (expression vector backbone alone) (n = 6); TNTProx1 group receives pCMV6-Prox1 (n = 6). Lymphatic vessels (fluorescein isothiocyanate [FITC]-dextran stained) and lymphatic branch points (indicating lymphangiogenesis) were analyzed with the confocal/multiphoton microscope. The experimental group TNTProx1 exhibited reduced postsurgical tail lymphedema and increased lymphatic distribution compared to TNTpCMV6 group. More lymphatic branching points (>3-fold) were observed at the TNT site in TNTProx1 group. Conclusions: This study demonstrates a novel, powerful imaging tool for investigating lymphatic vessels in live murine tail model of lymphedema. IVM can be utilized for functional assessment of lymphatics and visualization of lymphangiogenesis following gene-based therapy.

Knockdown of PROX1 promotes milk fatty acid synthesis by targeting PPARGC1A in dairy goat mammary gland

Goat milk is rich in various fatty acids that are beneficial to human health. Chromatin immunoprecipitation followed by sequencing (ChIP-seq) and RNA-seq analyses of goat mammary glands at different lactation stages revealed a novel lactation regulatory factor, Prospero homeobox 1 (PROX1). However, the mechanism whereby PROX1 regulates lipid metabolism in dairy goats remains unclear. We found that PROX1 exhibits the highest expression level during peak lactation period. PROX1 knockdown enhanced the expression of genes related to de novo fatty acid synthesis (e.g., SREBP1 and FASN) and triacylglycerol (TAG) synthesis (e.g., DGAT1 and GPAM) in goat mammary epithelial cells (GMECs). Consistently, intracellular TAG and lipid droplet contents were significantly increased in PROX1 knockdown cells and reduced in PROX1 overexpression cells, and we observed similar results in PROX1 knockout mice. Following PROX1 overexpression, RNA-seq showed a significant upregulation of peroxisome proliferator-activated receptor gamma coactivator-1 alpha (PPARGC1A) expression. Further, PPARGC1A knockdown attenuated the inhibitory effects of PROX1 on TAG contents and lipid-droplet formation in GMECs. Moreover, we found that PROX1 promoted PPARGC1A transcription via the PROX1 binding sites (PBSs) located in the PPARGC1A promoter. These results suggest a novel target for manipulating the goat milk-fat composition and improving the quality of goat milk.

Advances in lymphatic metastasis of non-small cell lung cancer

Lung cancer is a deeply malignant tumor with high incidence and mortality. Despite the rapid development of diagnosis and treatment technology, abundant patients with lung cancer are still inevitably faced with recurrence and metastasis, contributing to death. Lymphatic metastasis is the first step of distant metastasis and an important prognostic indicator of non-small cell lung cancer. Tumor-induced lymphangiogenesis is involved in the construction of the tumor microenvironment, except promoting malignant proliferation and metastasis of tumor cells, it also plays a crucial role in individual response to treatment, especially immunotherapy. Thus, this article reviews the current research status of lymphatic metastasis in non-small cell lung cancer, in order to provide some insights for the basic research and clinical and translational application in this field.

Hypocalcaemic tetany linked to vitamin D deficiency and hypomagnesemia in primary intestinal lymphangiectasia: a literature review

Primary intestinal lymphangiectasia (PIL) is a rare disorder in children causing protein-losing enteropathy. Vitamin D deficiency and hypomagnesemia contributed to the tetany. The literature review reflects the importance of screening for these deficiencies and regular serum magnesium monitoring in PIL cases with neuromuscular or ionic abnormalities.

Topical tissue nanotransfection of Prox1 is effective in the prophylactic management of lymphedema

Lymphedema is chronic limb swelling resulting from lymphatic dysfunction. There is no cure for the disease. Clinically, a preventive surgical approach called immediate lymphatic reconstruction (ILR) has gained traction. Experimental gene-based therapeutic approaches (e.g., using viral vectors) have had limited translational applicability. Tissue nanotransfection (TNT) technology uses a direct, transcutaneous nonviral vector, gene delivery using a chip with nanochannel poration in response to a rapid (<100 ms) focused electric field. The purpose of this study was to experimentally prevent lymphedema using focal delivery of a specific gene Prox1 (a master regulator of lymphangiogenesis). TNT was applied to the previously optimized lymphedematous mice tail (day 0) directly at the surgical site with genetic cargo loaded into the TNT reservoir: group I (sham) was given pCMV6 (expression vector backbone alone) and group II was treated with pCMV6-Prox1. Group II mice had decreased tail volume (47.8%) compared to sham and greater lymphatic clearance on lymphangiography. Immunohistochemistry showed greater lymphatic vessel density and RNA sequencing exhibited reduced inflammatory markers in group II compared to group I. Prox1 prophylactically delivered using TNT to the surgical site on the day of injury decreased the manifestations of lymphedema in the murine tail model compared to control.

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

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

Dysregulation of Lymphatic Endothelial VEGFR3 Signaling in Disease

Vascular endothelial growth factor (VEGF) receptor 3 (VEGFR3), a receptor tyrosine kinase encoded by the FLT4 gene, plays a significant role in the morphogenesis and maintenance of lymphatic vessels. Under both normal and pathologic conditions, VEGF-C and VEGF-D bind VEGFR3 on the surface of lymphatic endothelial cells (LECs) and induce lymphatic proliferation, migration, and survival by activating intracellular PI3K-Akt and MAPK-ERK signaling pathways. Impaired lymphatic function and VEGFR3 signaling has been linked with a myriad of commonly encountered clinical conditions. This review provides a brief overview of intracellular VEGFR3 signaling in LECs and explores examples of dysregulated VEGFR3 signaling in various disease states, including (1) lymphedema, (2) tumor growth and metastasis, (3) obesity and metabolic syndrome, (4) organ transplant rejection, and (5) autoimmune disorders. A more complete understanding of the molecular mechanisms underlying the lymphatic pathology of each disease will allow for the development of novel strategies to treat these chronic and often debilitating illnesses.

Temporospatial inhibition of Erk signaling is required for lymphatic valve formation

Intraluminal lymphatic valves (LVs) and lymphovenous valves (LVVs) are critical to ensure the unidirectional flow of lymphatic fluid. Morphological abnormalities in these valves always cause lymph or blood reflux, and result in lymphedema. However, the underlying molecular mechanism of valve development remains poorly understood. We here report the implication of Efnb2-Ephb4-Rasa1 regulated Erk signaling axis in lymphatic valve development with identification of two new valve structures. Dynamic monitoring of phospho-Erk activity indicated that Erk signaling is spatiotemporally inhibited in some lymphatic endothelial cells (LECs) during the valve cell specification. Inhibition of Erk signaling via simultaneous depletion of zygotic erk1 and erk2 or treatment with MEK inhibitor selumetinib causes lymphatic vessel hypoplasia and lymphatic valve hyperplasia, suggesting opposite roles of Erk signaling during these two processes. ephb4b mutants, efnb2a;efnb2b or rasa1a;rasa1b double mutants all have defective LVs and LVVs and exhibit blood reflux into lymphatic vessels with an edema phenotype. Importantly, the valve defects in ephb4b or rasa1a;rasa1b mutants are mitigated with high-level gata2 expression in the presence of MEK inhibitors. Therefore, Efnb2-Ephb4 signaling acts to suppress Erk activation in valve-forming cells to promote valve specification upstream of Rasa1. Not only do our findings reveal a molecular mechanism of lymphatic valve formation, but also provide a basis for the treatment of lymphatic disorders.

Localized Prox1 Regulates Aortic Valve Endothelial Cell Diversity and Extracellular Matrix Stratification in Mice

BACKGROUND

Specialized valve endothelial cell (VEC) populations are localized oriented to blood flow in developing aortic and mitral valves, but their roles in valve development and disease are unknown. In the aortic valve (AoV), a population of VECs on the fibrosa side expresses the transcription factor Prox1 together with genes found in lymphatic ECs. In this study, we examine Prox1's role in regulating a lymphatic-like gene network and promoting VEC diversity required for the development of the stratified trilaminar extracellular matrix (ECM) of murine AoV leaflets.

METHODS

To determine whether disruption of Prox1 localization affects heart valve development, we generated mice (NFATc1enCre Prox1 gain-of-function) in which Prox1 is overexpressed on the ventricularis side of the AoV beginning in embryonic development. To identify potential targets of Prox1, we performed cleavage under targets and release using nuclease on wild-type and NFATc1enCre Prox1 gain-of-function AoVs with validation by colocalization in vivo using RNA in situ hybridization in NFATc1enCre Prox1 gain-of-function AoVs. Natural induction of Prox1 and target gene expression was evaluated in myxomatous AoVs in a mouse model of Marfan syndrome (Fbn1C1039G/+).

RESULTS

The overexpression of Prox1 is sufficient to cause enlargement of AoVs by postnatal day (P)0, as well as a decrease in ventricularis-specific gene expression and disorganized interstitial ECM layers at P7. We identified potential targets of Prox1 known to play roles in lymphatic ECs including Flt1, Efnb2, Egfl7, and Cx37. Ectopic Prox1 colocalized with induced Flt1, Efnb2, and Cx37 expression in NFATc1enCre Prox1 gain-of-function AoVs. Moreover, in Marfan syndrome myxomatous AoVs, endogenous Prox1, and its identified targets, were ectopically induced in ventricularis side VECs.

CONCLUSIONS

Our results support a role for Prox1 in localized lymphatic-like gene expression on the fibrosa side of the AoV. Furthermore, localized VEC specialization is required for development of the stratified trilaminar ECM critical for AoV function and is dysregulated in congenitally malformed valves.

Lymphatic vasculature in the central nervous system

The central nervous system (CNS) is considered as an immune privilege organ, based on experiments in the mid 20th century showing that the brain fails to mount an efficient immune response against an allogeneic graft. This suggests that in addition to the presence of the blood-brain barrier (BBB), the apparent absence of classical lymphatic vasculature in the CNS parenchyma limits the capacity for an immune response. Although this view is partially overturned by the recent discovery of the lymphatic-like hybrid vessels in the Schlemm's canal in the eye and the lymphatic vasculature in the outmost layer of the meninges, the existence of lymphatic vessels in the CNS parenchyma has not been reported. Two potential mechanisms by which lymphatic vasculature may arise in the organs are: 1) sprouting and invasion of lymphatic vessels from the surrounding tissues into the parenchyma and 2) differentiation of blood endothelial cells into lymphatic endothelial cells in the parenchyma. Considering these mechanisms, we here discuss what causes the dearth of lymphatic vessels specifically in the CNS parenchyma.

A Novel Lymphangiogenesis-Related Gene Signature can Predict Prognosis and Immunosuppressive Microenvironment in Patients with Clear Cell Renal Cell Carcinoma

Background: Lymphangiogenesis represents a key event in the progression and metastasis of patients with clear cell renal cell carcinoma (ccRCC). Nevertheless, the prognostic value of lymphangiogenesis-related genes (LRGs) in ccRCC patients remains unknown. Method: Differential analyses were performed to identify differentially expressed LRGs between normal and tumor tissues. A univariate Cox analysis was performed to identify differently expressed LRGs associated with overall survival (OS). LASSO and multivariate Cox analyses were performed to construct and optimize the LRG signature. To further explore the molecular characterization of the LRG signature, a functional enrichment analysis, immune signature, somatic mutations, and drug sensitivity were assessed. Immunohistochemistry (IHC) and immunofluorescence staining were performed to validate the relationship between lymphangiogenesis and immunity using our ccRCC samples. Results: Four candidate genes (IL4, CSF2, PROX1, and TEK) were eventually available to construct the LRG signature in the training set. Patients in the high-risk group had a shorter survival than those in the low-risk group. The LRG signature was an independent prognostic factor of OS. These results were confirmed in the validation group. The LRG signature was correlated with immunosuppressive cell infiltration, T cell exhaustion markers, somatic mutations, and drug sensitivity. The IHC and immunofluorescence staining results confirmed the correlation between lymphangiogenesis and CD163⁺ macrophages, exhausted CD8⁺PD-1⁺, and CD8⁺ LAG3⁺ T cells. Conclusion: A novel prognostic signature based on LRGs could provide insight into the prognostic evaluation and treatment of ccRCC patients.

Hydrogen Sulfide Attenuates Lymphedema Via the Induction of Lymphangiogenesis Through a PI3K/Akt‐Dependent Mechanism

Background

Accumulating evidence suggests that hydrogen sulfide ( H 2 S ), an endogenously produced gaseous molecule, plays a critical role in the regulation of cardiovascular homeostasis. However, little is known about its role in lymphangiogenesis. Thus, the current study aimed to investigate the involvement of H 2 S in lymphatic vessel growth and lymphedema resolution using a murine model and assess the underlying mechanisms.

Methods and Results

A murine model of tail lymphedema was created both in wild‐type mice and cystathionine γ‐lyase–knockout mice, to evaluate lymphedema up to 28 days after lymphatic ablation. Cystathionine γ‐lyase–knockout mice had greater tail diameters than wild‐type mice, and this phenomenon was associated with the inhibition of reparative lymphangiogenesis at the site of lymphatic ablation. In contrast, the administration of an H 2 S donor, diallyl trisulfide, ameliorated lymphedema by inducing the formation of a considerable number of lymphatic vessels at the injured sites in the tails. In vitro experiments using human lymphatic endothelial cells revealed that diallyl trisulfide promoted their proliferation and differentiation into tube‐like structures by enhancing Akt (protein kinase B) phosphorylation in a concentration‐dependent manner. The blockade of Akt activation negated the diallyl trisulfide–induced prolymphangiogenic responses in lymphatic endothelial cells. Furthermore, the effects of diallyl trisulfide treatment on lymphangiogenesis in the tail lymphedema model were also negated by the inhibition of phosphoinositide 3'‐kinase (P13K)/Akt signaling.

Conclusions

H 2 S promotes reparative lymphatic vessel growth and ameliorates secondary lymphedema, at least in part, through the activation of the Akt pathway in lymphatic endothelial cells. As such, H 2 S donors could be used as therapeutics against refractory secondary lymphedema.

Lymphatic endothelial sphingosine 1-phosphate receptor 1 enhances macrophage clearance via lymphatic system following myocardial infarction

Lymphatic endothelial cell homeostasis plays important roles in normal physiological cardiac functions, and its dysfunction significantly influences pathological cardiac remodeling after myocardial infarction (MI). Our results revealed that sphingosine 1-phosphate receptor 1 (S1pr1) expression in cardiac lymphatic endothelial cells (LECs) was sharply changed after MI. It has been shown that S1pr1 tightly controlled LEC functions and homeostasis. We thus hypothesized that lymphatic endothelial S1pr1 might be involved in post-MI cardiac remodeling. We generated LEC-conditional S1pr1 transgenic mice, in which S1pr1 expression was reduced in cardiac LECs. We performed the left anterior descending coronary artery (LAD) ligation operation to induce MI in these mice. Cardiac functions and remodeling were examined by echocardiography analysis and serial histological analysis. Meanwhile, we performed adoptive cell transfer experiments to monitor macrophage trafficking in post-MI myocardium and their draining lymphatic system. Furthermore, in vitro cell culture experiments and mechanism studies were undertaken to uncover the molecular mechanism by which LEC-S1pr1 regulated cardiac inflammation and remodeling after MI. Our results showed that S1pr1 expression significantly decreased in cardiac LECs after MI. Our in vivo experiments showed that the reduced expression of LEC-S1pr1 deteriorated cardiac function and worsened pathological cardiac remodeling after MI. Our further results demonstrated that the reduced expression of LEC-S1pr1 did not influence macrophage infiltration in an early inflammatory phase of MI, but significantly affected macrophages clearance in the later phase of MI via afferent cardiac lymphatics, and thus influenced inflammatory responses and cardiac outcome after MI. Further study showed that S1P/S1pr1 activated ERK signaling pathway and enhanced CCL2 expression, which promoted macrophage trafficking in a paracrine manner. This study reveals that cardiac lymphatic endothelial cells tightly control macrophage trafficking via lymphatic vessels in injured hearts via S1P/S1pr1/ERK/CCL2 pathway and thus regulate post-MI immune modulation and heart repair. This study highlights the importance of cardiac lymphatic vessel system in orchestrating post-MI immune responses and cardiac remodeling by regulating macrophage transit in injured hearts. Our finding implies that a feasible modulation of S1pr1 signaling in LECs might provide a promising target to resolve excessive inflammation and to ameliorate adverse cardiac remodeling after MI.

Low Efficacy of Genetic Tests for the Diagnosis of Primary Lymphedema Prompts Novel Insights into the Underlying Molecular Pathways

Lymphedema is a chronic inflammatory disorder caused by ineffective fluid uptake by the lymphatic system, with effects mainly on the lower limbs. Lymphedema is either primary, when caused by genetic mutations, or secondary, when it follows injury, infection, or surgery. In this study, we aim to assess to what extent the current genetic tests detect genetic variants of lymphedema, and to identify the major molecular pathways that underlie this rather unknown disease. We recruited 147 individuals with a clinical diagnosis of primary lymphedema and used established genetic tests on their blood or saliva specimens. Only 11 of these were positive, while other probands were either negative (63) or inconclusive (73). The low efficacy of such tests calls for greater insight into the underlying mechanisms to increase accuracy. For this purpose, we built a molecular pathways diagram based on a literature analysis (OMIM, Kegg, PubMed, Scopus) of candidate and diagnostic genes. The PI3K/AKT and the RAS/MAPK pathways emerged as primary candidates responsible for lymphedema diagnosis, while the Rho/ROCK pathway appeared less critical. The results of this study suggest the most important pathways involved in the pathogenesis of lymphedema, and outline the most promising diagnostic and candidate genes to diagnose this disease.

Lymphangiogenesis requires Ang2/Tie/PI3K signaling for VEGFR3 cell surface expression

Vascular endothelial growth factor C (VEGF-C) induces lymphangiogenesis via VEGF receptor 3 (VEGFR3), which is encoded by the most frequently mutated gene in human primary lymphedema. Angiopoietins (Angs) and their Tie receptors regulate lymphatic vessel development, and mutations of the ANGPT2 gene were recently found in human primary lymphedema. However, the mechanistic basis of Ang2 activity in lymphangiogenesis is not fully understood. Here, we used gene deletion, blocking Abs, transgene induction, and gene transfer to study how Ang2, its Tie2 receptor, and Tie1 regulate lymphatic vessels. We discovered that VEGF-C–induced Ang2 secretion from lymphatic endothelial cells (LECs) was involved in full Akt activation downstream of phosphoinositide 3 kinase (PI3K). Neonatal deletion of genes encoding the Tie receptors or Ang2 in LECs, or administration of an Ang2-blocking Ab decreased VEGFR3 presentation on LECs and inhibited lymphangiogenesis. A similar effect was observed in LECs upon deletion of the PI3K catalytic p110α subunit or with small-molecule inhibition of a constitutively active PI3K located downstream of Ang2. Deletion of Tie receptors or blockade of Ang2 decreased VEGF-C–induced lymphangiogenesis also in adult mice. Our results reveal an important crosstalk between the VEGF-C and Ang signaling pathways and suggest new avenues for therapeutic manipulation of lymphangiogenesis by targeting Ang2/Tie/PI3K signaling.

Anti-Angiogenetic and Anti-Lymphangiogenic Effects of a Novel 2-Aminobenzimidazole Derivative, MFB

Background and Purpose

Benzimidazoles have attracted much attention over the last few decades due to their broad-spectrum pharmacological properties. Increasing evidence is showing the potential use of benzimidazoles as anti-angiogenic agents, although the mechanisms that impact angiogenesis remain to be fully defined. In this study, we aim to investigate the anti-angiogenic mechanisms of MFB, a novel 2-aminobenzimidazole derivative, to develop a novel angiogenesis inhibitor.

Experimental Approach

MTT, BrdU, migration and invasion assays, and immunoblotting were employed to examine MFB’s effects on vascular endothelial growth factor (VEGF)-induced endothelial cell proliferation, migration, invasion, as well as signaling molecules activation. The anti-angiogenic effects of MFB were analyzed by tube formation, aorta ring sprouting, and matrigel plug assays. We also used a mouse model of lung metastasis to determine the MFB’s anti-metastatic effects.

Key Results

MFB suppressed cell proliferation, migration, invasion, and endothelial tube formation of VEGF-A-stimulated human umbilical vascular endothelial cells (HUVECs) or VEGF-C-stimulated lymphatic endothelial cells (LECs). MFB suppressed VEGF-A and VEGF-C signaling in HUVECs or LECs. In addition, MFB reduced VEGF-A- or tumor cells-induced neovascularization in vivo. MFB also diminished B16F10 melanoma lung metastasis. The molecular docking results further showed that MFB may bind to VEGFR-2 rather than VEGF-A with high affinity.

Conclusions and Implications

These observations indicated that MFB may target VEGF/VEGFR signaling to suppress angiogenesis and lymphangiogenesis. It also supports the role of MFB as a potential lead in developing novel agents for the treatment of angiogenesis- or lymphangiogenesis-associated diseases and cancer.

Reactive Oxygen Species in Regulating Lymphangiogenesis and Lymphatic Function

The lymphatic system is pivotal for immunosurveillance and the maintenance of tissue homeostasis. Lymphangiogenesis, the formation of new lymphatic vessels from pre-existing vessels, has both physiological and pathological roles. Recent advances in the molecular mechanisms regulating lymphangiogenesis have opened a new area of research on reparative lymphangiogenesis for the treatment of various pathological disorders comprising neurological disorders, cardiac repair, autoimmune disease, obesity, atherosclerosis, etc. Reactive oxygen species (ROS) produced by the various cell types serve as signaling molecules in several cellular mechanisms and regulate various aspects of growth-factor-mediated responses, including lymphangiogenesis. The ROS, including superoxide anion, hydrogen peroxide, and nitric oxide, play both beneficial and detrimental roles depending upon their levels and cellular microenvironment. Low ROS levels are essential for lymphangiogenesis. On the contrary, oxidative stress due to enhanced ROS generation and/or reduced levels of antioxidants suppresses lymphangiogenesis via promoting lymphatic endothelial cell apoptosis and death. In this review article, we provide an overview of types and sources of ROS, discuss the role of ROS in governing lymphangiogenesis and lymphatic function, and summarize the role of lymphatics in various diseases.

Adipose tissue-derived microvascular fragments promote lymphangiogenesis in a murine lymphedema model

Chronic lymphedema after cancer treatment is common and there is still no cure for this disease. We herein investigated the lymphangiogenic capacity of adipose tissue-derived microvascular fragments (MVF), which contain stem cells and lymphatic vessel fragments. Secondary lymphedema was induced in the hindlimbs of C57BL/6J mice. Green fluorescence protein (GFP)+ MVF were isolated from transgenic C57BL/6Tg (CAG-EGFP)1Osb/J mice, suspended in collagen hydrogel, and injected in the lymphadenectomy defect of wild-type animals. This crossover model allowed the detection of MVF-derived blood and lymphatic vessels after transplantation. The MVF group was compared with animals receiving collagen hydrogel only or a sham intervention. Lymphangiogenic effects were analyzed using volumetry, magnetic resonance (MR) lymphography, histology, and immunohistochemistry. MVF injection resulted in reduced hindlimb volumes when compared to non-treated controls. MR lymphography revealed lymphatic regeneration with reduced dermal backflow after MVF treatment. Finally, MVF transplantation promoted popliteal angiogenesis and lymphangiogenesis associated with a significantly increased microvessel and lymphatic vessel density. These findings indicate that MVF transplantation represents a promising approach to induce therapeutic lymphangiogenesis.

Crosstalk Between microRNAs and the Pathological Features of Secondary Lymphedema

Secondary lymphedema is characterized by lymphatic fluid retention and subsequent tissue swelling in one or both limbs that can lead to decreased quality of life. It often arises after loss, obstruction, or blockage of lymphatic vessels due to multifactorial modalities, such as lymphatic insults after surgery, immune system dysfunction, deposition of fat that compresses the lymphatic capillaries, fibrosis, and inflammation. Although secondary lymphedema is often associated with breast cancer, the condition can occur in patients with any type of cancer that requires lymphadenectomy such as gynecological, genitourinary, or head and neck cancers. MicroRNAs demonstrate pivotal roles in regulating gene expression in biological processes such as lymphangiogenesis, angiogenesis, modulation of the immune system, and oxidative stress. MicroRNA profiling has led to the discovery of the molecular mechanisms involved in the pathophysiology of auto-immune, inflammation-related, and metabolic diseases. Although the role of microRNAs in regulating secondary lymphedema is yet to be elucidated, the crosstalk between microRNAs and molecular factors involved in the pathological features of lymphedema, such as skin fibrosis, inflammation, immune dysregulation, and aberrant lipid metabolism have been demonstrated in several studies. MicroRNAs have the potential to serve as biomarkers for diseases and elucidation of their roles in lymphedema can provide a better understanding or new insights of the mechanisms underlying this debilitating condition.

Conjunctival lymphangiectasia in a pediatric patient with neurofibromatosis type 1

Conjunctival lymphangiectasia, a rare condition characterized by dilated lymphatic channels in the bulbar conjunctiva, generally develops as a consequence of a local lymphatic scarring or distal mechanical outflow obstruction following surgery, radiotherapy, neoplastic disease, or other disease processes. The actual cause often remains unknown. We report a case of a unilateral conjunctival lymphangiectasia in a 7-year-old girl with neurofibromatosis type 1 (NF-1) and discuss a possible association between the two entities.

Quantitative 3-dimensional imaging and tissue cytometry reveals lymphatic expansion in acute kidney injury

The lymphatic system plays an integral role in physiology and has recently been identified as a key player in disease progression. Tissue injury stimulates lymphatic expansion, or lymphangiogenesis (LA), though its precise role in disease processes remains unclear. LA is associated with inflammation, which is a key component of acute kidney injury (AKI), for which there are no approved therapies. While LA research has gained traction in the last decade, there exists a significant lack of understanding of this process in the kidney. Though innovative studies have elucidated markers and models with which to study LA, the field is still evolving with ways to visualize lymphatics in vivo. Prospero-related homeobox-1 (Prox-1) is the master regulator of LA and determines lymphatic cell fate through its action on vascular endothelial growth factor receptor expression. Here, we investigate the consequences of AKI on the abundance and distribution of lymphatic endothelial cells using Prox1-tdTomato reporter mice (ProxTom) coupled with large-scale three-dimensional quantitative imaging and tissue cytometry (3DTC). Using these technologies, we describe the spatial dynamics of lymphatic vasculature in quiescence and post-AKI. We also describe the use of lymphatic vessel endothelial hyaluronan receptor-1 (LYVE-1) as a marker of lymphatic vessels using 3DTC in the absence of the ProxTom reporter mice as an alternative approach. The use of 3DTC for lymphatic research presents a new avenue with which to study the origin and distribution of renal lymphatic vessels. These findings will enhance our understanding of renal lymphatic function during injury and could inform the development of novel therapeutics for intervention in AKI.

A novel role of Hippo-Yap/TAZ signaling pathway in lymphatic vascular development

The lymphatic vasculature plays important role in regulating fluid homeostasis, intestinal lipid absorption, and immune surveillance in humans. Malfunction of lymphatic vasculature leads to several human diseases. Understanding the fundamental mechanism in lymphatic vascular development not only expand our knowledge, but also provide a new therapeutic insight. Recently, Hippo-YAP/TAZ signaling pathway, a key mechanism of organ size and tissue homeostasis, has emerged as a critical player that regulate lymphatic specification, sprouting, and maturation. In this review, we discuss the mechanistic regulation and pathophysiological significant of Hippo pathway in lymphatic vascular development.

Sirtuin 3 deficiency aggravates angiotensin II-induced hypertensive cardiac injury by the impairment of lymphangiogenesis

Lymphangiogenesis is possibly capable of attenuating hypertension‐induced cardiac injury. Sirtuin 3 (SIRT3) is an effective mitochondrial deacetylase that has the potential to modulate this process; however, its role in hypertension‐induced cardiac lymphangiogenesis to date has not been investigated. Our experiments were performed on 8‐week‐old wild‐type (WT), SIRT3 knockout (SIRT3‐KO) and SIRT3 overexpression (SIRT3‐LV) mice infused with angiotensin II (Ang II) (1000 ng/kg per minute) or saline for 28 days. After Ang II infusion, SIRT3‐KO mice developed a more severe cardiac remodelling, less lymphatic capillaries and lower expression of lymphatic marker when compared to wild‐type mice. In comparison, SIRT3‐LV restored lymphangiogenesis and attenuated cardiac injury. Furthermore, lymphatic endothelial cells (LECs) exposed to Ang II in vitro exhibited decreased migration and proliferation. Silencing SIRT3 induced functional decrease in LECs, while SIRT3 overexpression LECs facilitated. Moreover, SIRT3 may up‐regulate lymphangiogenesis by affecting vascular endothelial growth factor receptor 3 (VEGFR3) and ERK pathway. These findings suggest that SIRT3 could promote lymphangiogenesis and attenuate hypertensive cardiac injury.