Identification of ILK as a critical regulator of VEGFR3 signalling and lymphatic vascular growth

Epidermal growth factor-like domain 7 drives brain lymphatic endothelial cell development through integrin αvβ3

In zebrafish, brain lymphatic endothelial cells (BLECs) are essential for meningeal angiogenesis and cerebrovascular regeneration. Although epidermal growth factor-like domain 7 (Egfl7) has been reported to act as a pro-angiogenic factor, its roles in lymphangiogenesis remain unclear. Here, we show that Egfl7 is expressed in both blood and lymphatic endothelial cells. We generate an egfl7 cq180 mutant with a 13-bp-deletion in exon 3 leading to reduced expression of Egfl7. The egfl7 cq180 mutant zebrafish exhibit defective formation of BLEC bilateral loop-like structures, although trunk and facial lymphatic development remains unaffected. Moreover, while the egfl7 cq180 mutant displays normal BLEC lineage specification, the migration and proliferation of these cells are impaired. Additionally, we identify integrin αvβ3 as the receptor for Egfl7. αvβ3 is expressed in the CVP and sprouting BLECs, and blocking this integrin inhibits the formation of BLEC bilateral loop-like structures. Thus, this study identifies a role for Egfl7 in BLEC development that is mediated through the integrin αvβ3.

The Alzheimer's disease-linked protease BACE2 cleaves VEGFR3 and modulates its signaling

The β-secretase β-site APP cleaving enzyme (BACE1) is a central drug target for Alzheimer's disease. Clinically tested, BACE1-directed inhibitors also block the homologous protease BACE2. Yet little is known about physiological BACE2 substrates and functions in vivo. Here, we identify BACE2 as the protease shedding the lymphangiogenic vascular endothelial growth factor receptor 3 (VEGFR3). Inactivation of BACE2, but not BACE1, inhibited shedding of VEGFR3 from primary human lymphatic endothelial cells (LECs) and reduced release of the shed, soluble VEGFR3 (sVEGFR3) ectodomain into the blood of mice, nonhuman primates, and humans. Functionally, BACE2 inactivation increased full-length VEGFR3 and enhanced VEGFR3 signaling in LECs and also in vivo in zebrafish, where enhanced migration of LECs was observed. Thus, this study identifies BACE2 as a modulator of lymphangiogenic VEGFR3 signaling and demonstrates the utility of sVEGFR3 as a pharmacodynamic plasma marker for BACE2 activity in vivo, a prerequisite for developing BACE1-selective inhibitors for safer prevention of Alzheimer's disease.

Halofuginone-guided nano-local therapy: Nano-thermosensitive hydrogels for postoperative metastatic canine mammary carcinoma with scar removal

In female dogs, the highest morbidity and mortality rates cancer are the result of mammary adenocarcinoma, which presents with metastases in the lung. Other than early surgical removal, however, no special methods are available to treat mammary adenocarcinoma. Because human breast cancer and canine mammary carcinoma share clinical characteristics and heterogeneity, the canine model is a suitable spontaneous tumor model for breast cancer in humans. In this study, the physical swelling method was used to prepare halofuginone-loaded D-α-tocopherol polyethylene glycol 1000 succinate (TPGS) polymer micelles nano-thermosensitive hydrogels (HTPM-gel). Furthermore, HTPM-gel was investigated via characterization, morphology, properties such as swelling experiment and in vitro release with reflecting its splendid nature. Moreover, HTPM-gel was further examined its capability to anti-proliferation, anti-migration, and anti-invasion. Ultimately, HTPM-gel was investigated for its in vivo anticancer activity in the post-operative metastatic and angiogenic canine mammary carcinoma. HTPM-gel presented spherical under transmission electron microscope (TEM) and represented grid structure under scanning electron microscope (SEM), with hydrodynamic diameter (HD) of 20.25 ± 2.5 nm and zeta potential (ZP) of 15.10 ± 1.82 mV. Additionally, HTPM-gel own excellent properties comprised of pH-dependent swelling behavior, sustained release behavior. To impede the migration, invasion, and proliferation of CMT-U27 cells, we tested the efficacy of HTPM-gel. Evaluation of in vivo anti-tumor efficacy demonstrates HTPM-gel exhibit a splendid anti-metastasis and anti-angiogenic ability, with exhibiting ideal biocompatibility. Notably, HTPM-gel also inhibited the scar formation in the healing process after surgery. In summary, HTPM-gel exhibited anti-metastasis and anti-angiogenic and scar repair features. According to the results of this study, HTPM-gel has encouraging clinical potential to treat tumors with multifunctional hydrogel.

HIF-1A as a prognostic biomarker related to invasion, migration and immunosuppression of cervical cancer

Background

The incidence of cervical cancer ranks second among malignant tumors in women, exerting a significant impact on their quality of life and overall well-being. The hypoxic microenvironment plays a pivotal role in the initiation and progression of tumorigenesis. The present study aims to investigate the fundamental genes and pathways associated with the hypoxia-inducible factor (HIF-1A) in cervical cancer, aiming to identify potential downstream targets for diagnostic and therapeutic purposes.

Methods

We obtained dataset GSE63514 from the Comprehensive Gene Expression Database (GEO). The dataset comprised of 24 patients in the normal group and 28 patients in the tumor group. Gene set difference analysis (GSVA) and gene set enrichment analysis (GSEA) were used to identify the genes related to HIF-1A expression and the specific signaling pathways involved.The association between HIF-1A and tumor immune infiltration was examined in the TCGA dataset. The WGCAN network was constructed to identify key genes within the blue module, and subsequent gene ontology (GO) function and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analyses were conducted to determine the pathways and functional annotations associated with HIF-1A. The protein interaction network of the HIF-1A gene was obtained from the STRING database and visualized using Cytoscape in the meantime.The function of HIF-1A and its related gene expression were verified in vivo.

Results

HIF-1A was a risk factor in both univariate and multivariate Cox regression analysis of cervical cancer patients. A total of 344 genes significantly correlated with the expression of HIF-1A were identified through correlation analysis, and the genes exhibiting the strongest correlation were obtained. The major signaling pathways involved in HIF-1A encompass TNF-α/NF-κB, PI3K/AKT/MTOR, TGF-β, JAK-STAT, and various other signaling cascades. Reinforced by qRT-PCR, we identified Integrin beta-1 (ITGB1), C-C motif chemokine ligand 2 (CCL2), striatin 3 (STRN3), and endothelin-1 (EDN1) as pivotal downstream genes influenced by HIF-1A. HIF-1A is associated with immune infiltration of natural killer (NK) cells, mast cells, CD4+T cells, M0 macrophages, neutrophils, follicular helper T cells, CD8+T cells, and regulatory T cells (Treg). HIF-1A is associated with sensitivity to chemotherapy drugs. The identification of the HIF-1A pathway and its function primarily focuses on cytoplasmic translation, aerobic respiration, cellular respiration, oxidative phosphorylation, thermogenesis, among others. The results of in vivo experiments have confirmed that HIF-1A plays a crucial role in promoting the migration and invasion of cervical cancer cells. Moreover, the overexpression of HIF-1A led to an upregulation in the expressions of ITGB1, CCL2, STRN3, and EDN1.

Conclusions

The role of HIF-1A in cervical cancer was determined through a combination of bioinformatics analysis and experimental validation. The genes potentially implicated in the tumorigenesis mechanism of HIF-1A were identified. These findings has the potential to enhance our comprehension of the progression of cervical cancer and offer promising therapeutic targets for its clinical management.

Understanding the development, pathogenesis, and injury response of meningeal lymphatic networks through the use of animal models

Meningeal lymphatic vessels (MLVs) help maintain central nervous system (CNS) homeostasis via their ability to facilitate macromolecule waste clearance and neuroimmune trafficking. Although these vessels were overlooked for centuries, they have now been characterized in humans, non-human primates, and rodents. Recent studies in mice have explored the stereotyped growth and expansion of MLVs in dura mater, the various transcriptional, signaling, and environmental factors regulating their development and long-term maintenance, and the pathological changes these vessels undergo in injury, disease, or with aging. Key insights gained from these studies have also been leveraged to develop therapeutic approaches that help augment or restore MLV functions to improve brain health and cognition. Here, we review fundamental processes that control the development of peripheral lymphatic networks and how these might apply to the growth and expansion of MLVs in their unique meningeal environment. We also emphasize key findings in injury and disease models that may reveal additional insights into the plasticity of these vessels throughout the lifespan. Finally, we highlight unanswered questions and future areas of study that can further reveal the exciting therapeutic potential of meningeal lymphatics.

In situ forming oxygen/ROS-responsive niche-like hydrogel enabling gelation-triggered chemotherapy and inhibition of metastasis

Though the development of the diverse hypoxia-activated prodrugs (HAPs) has made great progresses in the last several decades, current cancer therapy based on HAPs still suffers many obstacles, e.g., poor therapeutic outcome owing to hard deep reaching to hypoxic region, and the occurrence of metastasis due to hypoxia. Inspired by engineered niches, a novel functional chitosan polymer (CS-FTP) is synthesized for construction of a hydrogel-based bio-niche (CS-FTP-gel) in aiming at remodeling tumor hypoxic microenvironment. The CS-FTP polymers are crosslinked to form a niche-like hydrogel via enzyme-mediated oxygen-consumable dimerization after injected into tumor, in which a HAP (i.e., AQ4N) could be physically encapsulated, resulting in enhanced tumor hypoxia to facilitate AQ4N-AQ4 toxic transformation for maximizing efficacy of chemotherapy. Furthermore, Pazopanib (PAZ) conjugated onto the CS backbone via ROS-sensitive linker undergoes a stimuli-responsive release behavior to promote antiangiogenesis for tumor starvation, eventually contributing to the inhibition of lung metastasis and synergistic action with AQ4N-based chemotherapy for an orthotopic 4T1 breast tumor model. This study provides a promising strategy for hypoxia-based chemotherapy and demonstrates an encouraging clinical potential for multifunctional hydrogel applicable for antitumor treatment.

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CS-FTP shows enzyme-mediated hypoxia-inducible gelation and reactive oxygen species (ROS)-responsive drug release.

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CS-FTP gel formed intratumorally can be used as a bio-niche to enhance tumor hypoxic microenvironment.

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In vivo PET/CT directly monitors the tumor hypoxia changes and confirm the ability of CS-FTP to enhance tumor hypoxia.

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Oxygen-consumable gelation of ROS-responsive CS-FTP triggers chemotherapy and starvation therapy for antimetastasis.

Current Status of Lymphangiogenesis: Molecular Mechanism, Immune Tolerance, and Application Prospect

The lymphatic system is a channel for fluid transport and cell migration, but it has always been controversial in promoting and suppressing cancer. VEGFC/VEGFR3 signaling has long been recognized as a major molecular driver of lymphangiogenesis. However, many studies have shown that the neural network of lymphatic signaling is complex. Lymphatic vessels have been found to play an essential role in the immune regulation of tumor metastasis and cardiac repair. This review describes the effects of lipid metabolism, extracellular vesicles, and flow shear forces on lymphangiogenesis. Moreover, the pro-tumor immune tolerance function of lymphatic vessels is discussed, and the tasks of meningeal lymphatic vessels and cardiac lymphatic vessels in diseases are further discussed. Finally, the value of conversion therapy targeting the lymphatic system is introduced from the perspective of immunotherapy and pro-lymphatic biomaterials for lymphangiogenesis.

From lymphatic endothelial cell migration to formation of tubular lymphatic vascular network

During development, lymphatic endothelial cell (LEC) progenitors differentiate from venous endothelial cells only in limited regions of the body. Thus, LEC migration and subsequent tube formation are essential processes for the development of tubular lymphatic vascular network throughout the body. In this review, we discuss chemotactic factors, LEC-extracellular matrix interactions and planar cell polarity regulating LEC migration and formation of tubular lymphatic vessels. Insights into molecular mechanisms underlying these processes will help in understanding not only physiological lymphatic vascular development but lymphangiogenesis associated with pathological conditions such as tumors and inflammation.

Fetal nuchal edema and developmental anomalies caused by gene mutations in mice

Fetal nuchal edema, a subcutaneous accumulation of extracellular fluid in the fetal neck, is detected as increased nuchal translucency (NT) by ultrasonography in the first trimester of pregnancy. It has been demonstrated that increased NT is associated with chromosomal anomalies and genetic syndromes accompanied with fetal malformations such as defective lymphatic vascular development, cardiac anomalies, anemia, and a wide range of other fetal anomalies. However, in many clinical cases of increased NT, causative genes, pathogenesis and prognosis have not been elucidated in humans. On the other hand, a large number of gene mutations have been reported to induce fetal nuchal edema in mouse models. Here, we review the relationship between the gene mutants causing fetal nuchal edema with defective lymphatic vascular development, cardiac anomalies, anemia and blood vascular endothelial barrier anomalies in mice. Moreover, we discuss how studies using gene mutant mouse models will be useful in developing diagnostic method and predicting prognosis.

siRNA high throughput screening identifies regulators of chloropicrin and hydrogen fluoride injury in human corneal epithelial cell models

Corneal injuries induced by various toxicants result in similar clinical presentations such as corneal opacity and neovascularization. Many studies suggest that several weeks post-exposure a convergence of the molecular mechanisms drives these progressive pathologies. However, chemical agents vary in toxicological properties, and early molecular responses are anticipated to be somewhat dissimilar for different toxicants. We chose 3120 targets from the Dharmacon Human Druggable genome to screen for chloropicrin (CP) and hydrogen fluoride (HF) corneal injury as we hypothesized that targets identified in vitro may be effective as therapeutic targets in future studies. Human immortalized corneal epithelial cells (SV40-HCEC) were used for screening. Cell viability and IL-8 were analyzed to down-select hits into validation studies, where multiplex cytokine analysis and high content analysis were performed to understand toxicant effect and target function. Some endpoints were also evaluated in a second human immortalized corneal epithelial cell line, TCEpi. Over 20 targets entered validation studies for CP and HF; of these, only three targets were shared: NR3C1, RELA, and KMT5A. These findings suggest that early molecular responses to different toxicants may be somewhat distinctive and present dissimilar targets for possible early intervention.

Charge Reversal Polypyrrole Nanocomplex-Mediated Gene Delivery and Photothermal Therapy for Effectively Treating Papillary Thyroid Cancer and Inhibiting Lymphatic Metastasis

As a traditional treatment for papillary thyroid cancer (PTC), surgical resection of diseased tissues often brings lots of inconveniences to patients, and the tumor recurrence and metastasis are difficult to avoid. Herein, we developed a gene and photothermal combined therapy nanosystem based on a polypyrrole (Ppy)-poly(ethylene imine)-siILK nanocomplex (PPR_ILK) to achieve minimally invasive ablation and lymphatic metastasis inhibition in PTC simultaneously. In this system, gelatin-stabilized Ppy mainly acted as a photothermal- and photoacoustic (PA)-responsive nanomaterial and contributed to its well-behaved photosensitivity in the near-infrared region. Moreover, gelatin-stabilized Ppy possessed a charge reversal function, facilitating the tight conjunction of siILK gene at physiological pH (7.35-7.45) and its automatic release into acidic lysosomes (pH 4.0-5.5); the proton sponge effect generated during this process further facilitated the escape of siILK from lysosomes to the cytoplasm and played its role in inhibiting PTC proliferation and lymphatic metastasis. With the guidance of fluorescence and PA bimodal imaging, gene delivery and Ppy location in tumor regions could be clearly observed. As a result, tumors were completely eradicated by photothermal therapy, and the recurrences and metastases were obviously restrained by siILK.

Integrin-linked kinase (ILK): the known vs. the unknown and perspectives

Integrin-linked kinase (ILK) is a multifunctional molecular actor in cell-matrix interactions, cell adhesion, and anchorage-dependent cell growth. It combines functions of a signal transductor and a scaffold protein through its interaction with integrins, then facilitating further protein recruitment within the ILK-PINCH-Parvin complex. ILK is involved in crucial cellular processes including proliferation, survival, differentiation, migration, invasion, and angiogenesis, which reflects on systemic changes in the kidney, heart, muscle, skin, and vascular system, also during the embryonal development. Dysfunction of ILK underlies the pathogenesis of various diseases, including the pro-oncogenic activity in tumorigenesis. ILK localizes mostly to the cell membrane and remains an important component of focal adhesion. We do know much about ILK but a lot still remains either uncovered or unclear. Although it was initially classified as a serine/threonine-protein kinase, its catalytical activity is now questioned due to structural and functional issues, leaving the exact molecular mechanism of signal transduction by ILK unsolved. While it is known that the three isoforms of ILK vary in length, the presence of crucial domains, and modification sites, most of the research tends to focus on the main isoform of this protein while the issue of functional differences of ILK2 and ILK3 still awaits clarification. The activity of ILK is regulated on the transcriptional, protein, and post-transcriptional levels. The crucial role of phosphorylation and ubiquitylation has been investigated, but the functions of the vast majority of modifications are still unknown. In the light of all those open issues, here we present an extensive literature survey covering a wide spectrum of latest findings as well as a past-to-present view on controversies regarding ILK, finishing with pointing out some open questions to be resolved by further research.

The role of lymphangiogenesis in cardiovascular diseases and heart transplantation

Cardiac lymphangiogenesis plays an important physiological role in the regulation of interstitial fluid homeostasis, inflammatory, and immune responses. Impaired or excessive cardiac lymphatic remodeling and insufficient lymph drainage have been implicated in several cardiovascular diseases including atherosclerosis and myocardial infarction (MI). Although the molecular mechanisms underlying the regulation of functional lymphatics are not fully understood, the interplay between lymphangiogenesis and immune regulation has recently been explored in relation to the initiation and development of these diseases. In this field, experimental therapeutic strategies targeting lymphangiogenesis have shown promise by reducing myocardial inflammation, edema and fibrosis, and improving cardiac function. On the other hand, however, whether lymphangiogenesis is beneficial or detrimental to cardiac transplant survival remains controversial. In the light of recent evidence, cardiac lymphangiogenesis, a thriving and challenging field has been summarized and discussed, which may improve our knowledge in the pathogenesis of cardiovascular diseases and transplant biology.

The Role of Lymphangiogenesis in Coronary Atherosclerosis

Lymphatic circulation, a one-way channel system independent of blood circulation, collects interstitial fluid in a blind-end way. Existing widely in various organs and tissues, lymphatic vessels play important roles in maintaining tissue fluid homeostasis, regulating immune function, and promoting lipid transport. Recent studies have shown clear evidence that lymphangiogenesis has a strong mutual effect on coronary atherosclerosis (AS). In this study, we focus on this topic, especially in the aspects of relevant ligand/receptor, inflammation, and adipose metabolism. For the moment, however, the role of lymphangiogenesis and remodeling in coronary AS still remains controversial. The studies of our group and accumulating published evidence show that the pathological remodeling of lymphatic vessels in coronary AS may have a negative effect, but normal functional lymphangiogenesis is probably beneficial to the regression of coronary AS. Thus, the conclusion of this review is that lymphatic vessel function rather than its quantity determines its influence in AS, which needs more evidence to support.

Lymphatics in the broken heart

Cardiac lymphatics have emerged as a therapeutic target in cardiovascular diseases to limit myocardial edema and inflammation, notably after myocardial infarction (MI). While most experimental therapeutic approaches have focused on vascular endothelial growth factor C (VEGF-C) delivery, it remains uncertain to what degree the beneficial cardiac effects are related to lymphatic expansion in the heart. In this issue of the JCI, Keller, Lim, et al. reexamined the acute functional impact of endogenous cardiac lymphangiogenesis in the infarct zone after MI in mice. Their data, obtained by elegant comparisons of several complementary genetic mouse models, indicate that infarct expansion and left ventricular dilation and function after MI are unaffected by infarct lymphangiogenesis. This Commentary places the results into the context of previous findings. We believe these data will help further advance the research field of cardiac lymphatics to guide better clinical translation and benefit patients with ischemic heart disease.

Insights Into Unveiling a Potential Role of Tertiary Lymphoid Structures in Metastasis

Tertiary lymphoid structures (TLSs) develop in non-lymphatic tissue in chronic inflammation and cancer. TLS can mature to lymph node (LN) like structures with germinal centers and associated vasculature. TLS neogenesis in cancer is highly varied and tissue dependent. The role of TLS in adaptive antitumor immunity is of great interest. However, data also show that TLS can play a role in cancer metastasis. The importance of lymphatics in cancer distant metastasis is clear yet the precise detail of how various immunosurveillance mechanisms interplay within TLS and/or draining LN is still under investigation. As part of the tumor lymphatics, TLS vasculature can provide alternative routes for the establishment of the pre-metastatic niche and cancer dissemination. The nature of the cytokine and chemokine signature at the heart of TLS induction can be key in determining the success of antitumor immunity or in promoting cancer invasiveness. Understanding the biochemical and biomechanical factors underlying TLS formation and the resulting impact on the primary tumor will be key in deciphering cancer metastasis and in the development of the next generation of cancer immunotherapeutics.

Discovery, Synthesis, and Evaluation of Highly Selective Vascular Endothelial Growth Factor Receptor 3 (VEGFR3) Inhibitor for the Potential Treatment of Metastatic Triple-Negative Breast Cancer

We herein report the identification, structural optimization, and structure-activity relationship of thieno[2,3-d]pyrimidine derivatives as a novel kind of selective vascular endothelial growth factor receptor 3 (VEGFR3) inhibitors. N-(4-Chloro-3-(trifluoromethyl)phenyl)-4-(6-(4-(4-methylpiperazin-1-yl)phenyl)thieno[2,3-d]pyrimidin-4-yl)piperazine-1-carboxamide (38k) was the most potent VEGFR3 inhibitor (IC50 = 110.4 nM) among developed compounds. Compared with VEGFR1 and VEGFR2, VEGFR3 was approximately 100 times more selective. Here, compound 38k significantly inhibited proliferation and migration of VEGF-C-induced human dermal lymphatic endothelial cells (HDLEC), MDA-MB-231, and MDA-MB-436 cells by inactivating the VEGFR3 signaling pathway. Additionally, 38k induced cell apoptosis and a prolonged G1/S-phase in MDA-MB-231 and MDA-MB-436 cells. It also presented acceptable pharmacokinetic characteristics in Sprague-Dawley (SD) rats with an oral bioavailability of 30.9%. In the xenograft model in vivo, 38k effectively inhibited breast cancer growth by suppressing the VEGFR3 signaling pathway. 38k pronouncedly resisted the formation of pulmonary metastatic nodules in mice. Collectively, 38k may be a promising therapeutic agent of metastatic breast cancer.

Genetic blockade of lymphangiogenesis does not impair cardiac function after myocardial infarction

In recent decades, treatments for myocardial infarction (MI), such as stem and progenitor cell therapy, have attracted considerable scientific and clinical attention but failed to improve patient outcomes. These efforts indicate that more rigorous mechanistic and functional testing of potential MI therapies is required. Recent studies have suggested that augmenting post-MI lymphatic growth via VEGF-C administration improves cardiac function. However, the mechanisms underlying this proposed therapeutic approach remain vague and untested. To more rigorously test the role of lymphatic vessel growth after MI, we examined the post-MI cardiac function of mice in which lymphangiogenesis had been blocked genetically by pan-endothelial or lymphatic endothelial loss of the lymphangiogenic receptor VEGFR3 or global loss of the VEGF-C and VEGF-D ligands. The results obtained using all three genetic approaches were highly concordant and demonstrated that loss of lymphatic vessel growth did not impair left ventricular ejection fraction two weeks after MI in mice. We observed a trend toward excess fluid in the infarcted region of the left ventricle, but immune cell infiltration and clearance were unchanged with loss of expanded lymphatics. These studies refute the hypothesis that lymphangiogenesis contributes significantly to cardiac function after MI, and suggest that any effect of exogenous VEGF-C is likely to be mediated by non-lymphangiogenic mechanisms.

Biochemical and mechanical signals in the lymphatic vasculature

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

Homeostatic maintenance of the lymphatic vasculature

The lymphatic vasculature is emerging as a multifaceted regulator of tissue homeostasis and regeneration. Lymphatic vessels drain fluid, macromolecules, and immune cells from peripheral tissues to lymph nodes (LNs) and the systemic circulation. Their recently uncovered functions extend beyond drainage and include direct modulation of adaptive immunity and paracrine regulation of organ growth. The developmental mechanisms controlling lymphatic vessel growth have been described with increasing precision. It is less clear how the essential functional features of lymphatic vessels are established and maintained. We discuss the mechanisms that maintain lymphatic vessel integrity in adult tissues and control vessel repair and regeneration. This knowledge is crucial for understanding the pathological vessel changes that contribute to disease, and provides an opportunity for therapy development.

Regulation of VEGFR Signalling in Lymphatic Vascular Development and Disease: An Update

The importance of lymphatic vessels in a myriad of human diseases is rapidly gaining recognition; lymphatic vessel dysfunction is a feature of disorders including congenital lymphatic anomalies, primary lymphoedema and obesity, while improved lymphatic vessel function increases the efficacy of immunotherapy for cancer and neurological disease and promotes cardiac repair following myocardial infarction. Understanding how the growth and function of lymphatic vessels is precisely regulated therefore stands to inform the development of novel therapeutics applicable to a wide range of human diseases. Lymphatic vascular development is initiated during embryogenesis following establishment of the major blood vessels and the onset of blood flow. Lymphatic endothelial progenitor cells arise from a combination of venous and non-venous sources to generate the initial lymphatic vascular structures in the vertebrate embryo, which are then further ramified and remodelled to elaborate an extensive lymphatic vascular network. Signalling mediated via vascular endothelial growth factor (VEGF) family members and vascular endothelial growth factor receptor (VEGFR) tyrosine kinases is crucial for development of both the blood and lymphatic vascular networks, though distinct components are utilised to different degrees in each vascular compartment. Although much is known about the regulation of VEGFA/VEGFR2 signalling in the blood vasculature, less is understood regarding the mechanisms by which VEGFC/VEGFD/VEGFR3 signalling is regulated during lymphatic vascular development. This review will focus on recent advances in our understanding of the cellular and molecular mechanisms regulating VEGFA-, VEGFC- and VEGFD-mediated signalling via VEGFRs which are important for driving the construction of lymphatic vessels during development and disease.

The physiological and pathological functions of VEGFR3 in cardiac and lymphatic development and related diseases

Vascular endothelial growth factor receptors (VEGFRs) are part of the evolutionarily conserved VEGF signalling pathways that regulate the development and maintenance of the body's cardiovascular and lymphovascular systems. VEGFR3, encoded by the FLT4 gene, has an indispensable and well-characterized function in development and establishment of the lymphatic system. Autosomal dominant VEGFR3 mutations, that prevent the receptor functioning as a homodimer, cause one of the major forms of hereditary primary lymphoedema; Milroy disease. Recently, we and others have shown that FLT4 variants, distinct to those observed in Milroy disease cases, predispose individuals to Tetralogy of Fallot, the most common cyanotic congenital heart disease, demonstrating a novel function for VEGFR3 in early cardiac development. Here, we examine the familiar and emerging roles of VEGFR3 in the development of both lymphovascular and cardiovascular systems, respectively, compare how distinct genetic variants in FLT4 lead to two disparate human conditions, and highlight the research still required to fully understand this multifaceted receptor.

Severe Ovarian Hyperstimulation Syndrome in a Woman With Breast Cancer Under Letrozole Triggered With GnRH Agonist: A Case Report and Review of the Literature

We report a rare case of ovarian hyperstimulation syndrome (OHSS) in a 28-year-old woman with breast cancer and with a history of polycystic ovary syndrome (PCOS) despite treatment with letrozole and gonadotropin-releasing hormone agonist (GnRH-a) triggering in a GnRH antagonist (GnRH-ant) protocol without the administration of any human chorionic gonadotropin (hCG) for luteal-phase support. The patient, who underwent controlled ovarian syndrome (COS)-oocyte cryopreservation before chemotherapy, required hospitalization. Complete recovery was achieved after treatment with volume expanders, human albumin, and cabergoline. Based on our case and literature review, it is possible to establish that estradiol (E₂) modulation with letrozole and GnRH-a triggering does not eliminate the risk of OHSS. Furthermore, it is advisable to postpone GnRH-a depot to minimize the risk of OHSS after the suspension of letrozole, following menstruation or at least 7–8 days after triggering. It would be desirable to identify high-risk patients, also on a genetic basis, in order to avoid delays in oncologic treatments that could strongly impact life expectancy.

A Potential Role for Integrin-Linked Kinase in Colorectal Cancer Growth and Progression via Regulating Senescence and Immunity

Integrin-linked kinase (ILK) has been implicated as a molecular driver and mediator in both inflammation and tumorigenesis of the colon. ILK functions as an adaptor and mediator protein linking the extracellular matrix with downstream signaling pathways. ILK is broadly expressed in many human tissues and cells. It is also overexpressed in many cancers, including colorectal cancer (CRC). Inflammation, as evidenced by inflammatory bowel disease (IBD), is one of the highest risk factors for initiating CRC. This has led to the hypothesis that targeting ILK therapeutically could have potential in CRC, as it regulates different cellular processes associated with CRC development and progression as well as inflammation in the colon. A number of studies have indicated an ILK function in senescence, a cellular process that arrests the cell cycle while maintaining active metabolism and transcription. Senescent cells produce different secretions collectively known as the senescence-associated secretory phenotype (SASP). The SASP secretions influence infiltration of different immune cells, either positively for clearing senescent cells or negatively for promoting tumor growth, reflecting the dual role of senescence in cancer. However, a role for ILK in senescence and immunity in CRC remains to be determined. In this review, we discuss the possible role for ILK in senescence and immunity, paying particular attention to the relevance of ILK in CRC. We also examine how activating Toll-like receptors (TLRs) and their agonists in CRC could trigger immune responses against cancer, as a combination therapy with ILK inhibition.

When form meets function: the cells and signals that shape the lymphatic vasculature during development

The lymphatic vasculature is an integral component of the cardiovascular system. It is essential to maintain tissue fluid homeostasis, direct immune cell trafficking and absorb dietary lipids from the digestive tract. Major advances in our understanding of the genetic and cellular events important for constructing the lymphatic vasculature during development have recently been made. These include the identification of novel sources of lymphatic endothelial progenitor cells, the recognition of lymphatic endothelial cell specialisation and heterogeneity, and discovery of novel genes and signalling pathways underpinning developmental lymphangiogenesis. Here, we review these advances and discuss how they inform our understanding of lymphatic network formation, function and dysfunction.

Mechanosensation and Mechanotransduction by Lymphatic Endothelial Cells Act as Important Regulators of Lymphatic Development and Function

Our understanding of the function and development of the lymphatic system is expanding rapidly due to the identification of specific molecular markers and the availability of novel genetic approaches. In connection, it has been demonstrated that mechanical forces contribute to the endothelial cell fate commitment and play a critical role in influencing lymphatic endothelial cell shape and alignment by promoting sprouting, development, maturation of the lymphatic network, and coordinating lymphatic valve morphogenesis and the stabilization of lymphatic valves. However, the mechanosignaling and mechanotransduction pathways involved in these processes are poorly understood. Here, we provide an overview of the impact of mechanical forces on lymphatics and summarize the current understanding of the molecular mechanisms involved in the mechanosensation and mechanotransduction by lymphatic endothelial cells. We also discuss how these mechanosensitive pathways affect endothelial cell fate and regulate lymphatic development and function. A better understanding of these mechanisms may provide a deeper insight into the pathophysiology of various diseases associated with impaired lymphatic function, such as lymphedema and may eventually lead to the discovery of novel therapeutic targets for these conditions.

Role of Cardiac Lymphatics in Myocardial Edema and Fibrosis: JACC Review Topic of the Week

The cardiac lymphatic network plays a key role in regulation of myocardial extracellular volume and immune cell homeostasis. In different pathological conditions cardiac lymphatics undergo significant remodeling, with insufficient lymphatic function and/or lymphangiogenesis leading to fluid accumulation and development of edema. Additionally, by modulating the reuptake of tissue-infiltrating immune cells, lymphatics regulate immune responses. Available evidence suggests that both edema and inadequate immune response resolution may contribute to extracellular matrix remodeling and interstitial myocardial fibrosis. Interestingly, stimulation of lymphangiogenesis has been shown to improve cardiac function and reduce the progression of myocardial fibrosis during heart failure development after myocardial infarction. This review goes through the available clinical and experimental data supporting a role for cardiac lymphatics in cardiac disease, focusing on the current evidence linking poor cardiac lymphatic transport to the fibrogenic process and discussing potential avenues for novel biomarkers and therapeutic targets to limit cardiac fibrosis and dysfunction.

Rare genetic variants suggest dysregulation of signaling pathways in low- and high-risk patients developing severe ovarian hyperstimulation syndrome

PURPOSE

To investigate if rare gene variants in women with severe ovarian hyperstimulation syndrome (OHSS) provide clues to the mechanisms involved in the syndrome.

METHODS

Among participants in a prospective randomized study (Toftager et al. 2016), six women with predicted low and six women with predicted high risk of OHSS developing severe OHSS (grades 4 and 5, Golan classification) were selected. In the same cohort, six plus six matched controls developing no signs of OHSS (Golan grade 0) were selected. Whole-exome sequencing was performed. Analysis using a predefined in silico OHSS gene panel, variant filtering, and pathway analyses was done.

RESULTS

We found no convincing monogenetic association with the development of OHSS using the in silico gene panel. Pathway analysis of OHSS variant lists showed substantial overlap in highly enriched top pathways (p value range p < 0.0001 and p > 9.8E-17) between the low- and high-risk group developing severe OHSS, i.e., "the integrin-linked kinase (ILK) signaling pathway" and the "axonal guidance signaling pathway," both being connected to vasoactive endothelial growth factor (VEGF) and endothelial function.

CONCLUSION

Rare variants in OHSS cases with two distinct risk profiles enrich the same signaling pathways linked to VEGF and endothelial function. Clarification of the mechanism as well as potentially defining genetic predisposition of the high vascular permeability is important for future targeted treatment and prevention of OHSS; the potential roles of ILK signaling and the axonal guidance signaling need to be validated by functional studies.

Adipose-derived stem cell therapy shows promising results for secondary lymphedema

Lymphedema is mainly identified by progressive soft tissue swelling in impaired lymphatic system. Secondary lymphedema attributed to cancer therapy, parasite infection, and trauma remains a serious global disease. Patients with lymphedema suffer swelling, pain, and fatigue, with the dysfunction of the deformed extremities reducing the quality of life and increasing the risk of infection and lymphangiosarcoma. Adipose-derived stem cells (ADSCs) possess prominent regenerative potential to differentiate into multilineage cells, and produce various lymphangiogenic factors, making ADSC therapy a promising approach for lymphedema. The development of lymphedema consists of local inflammation, the fibrosis of lymphatic vessels, and the deposition of adipose fat. Existing animal models do not mimic the chronic inflammation environment, therefore suitable models are required in further studies. Some signal pathways and molecular mechanisms in physiological and pathological lymphagiogenesis remain unclear. In previous animal and human trials, ADSC therapy reduced edema in varying degrees. A larger number of trials with larger samples and longer follow-up periods are required to verify the efficiency and feasibility of ADSC therapy. ADSCs are of easy availability and immune exemption, making them a candidate for lymphedema treatment. Whether ADSCs enhance malignant characteristics or trigger the malignant change deserves further exploration and study before ADSC therapy can be made widely available.

Biological functions of lymphatic vessels

The general functions of lymphatic vessels in fluid transport and immunosurveillance are well recognized. However, accumulating evidence indicates that lymphatic vessels play active and versatile roles in a tissue- and organ-specific manner during homeostasis and in multiple disease processes. This Review discusses recent advances to understand previously unidentified functions of adult mammalian lymphatic vessels, including immunosurveillance and immunomodulation upon pathogen invasion, transport of dietary fat, drainage of cerebrospinal fluid and aqueous humor, possible contributions toward neurodegenerative and neuroinflammatory diseases, and response to anticancer therapies.

Cell Fate Determination of Lymphatic Endothelial Cells

The lymphatic vasculature, along with the blood vasculature, is a vascular system in our body that plays important functions in fluid homeostasis, dietary fat uptake, and immune responses. Defects in the lymphatic system are associated with various diseases such as lymphedema, atherosclerosis, fibrosis, obesity, and inflammation. The first step in lymphangiogenesis is determining the cell fate of lymphatic endothelial cells. Several genes involved in this commitment step have been identified using animal models, including genetically modified mice. This review provides an overview of these genes in the mammalian system and related human diseases.

Assessing functional status of cardiac lymphatics: From macroscopic imaging to molecular profiling

Here we describe various techniques for visualization of the lymphatic vasculature, particularly in the heart. Addressing macro-, microscopic, and molecular levels of lymphatic organization, we give examples of how to explore the roles of specific antigens/markers expressed in lymphatic vessels and their extracellular matrix as structural and functional elements involved in various biological functions of lymphatics. Some obstacles and technical challenges related to lymphatic visualization are also discussed.

RhoJ Regulates α5β1 Integrin Trafficking to Control Fibronectin Remodeling during Angiogenesis

Rho guanosine triphosphatases (GTPases) are master regulators of cell shape and cell movement [1]. The archetypal family members RhoA, Rac1, and Cdc42 arose early in eukaryotic evolution and coordinate a diverse range of cell morphologies and migrations. Evolution of the vertebrates was paralleled by expansion of this family through gene duplication. Emergence of an adaptive immune system and more complex neural systems presented new roles for Rho GTPases, filled by new family members. Cdc42 underwent gene duplication to produce two related proteins-RhoQ and RhoJ [2]. RhoQ is active in neural dynamics; however, RhoJ is highly expressed in endothelial cells under control of the endothelial-specific promoter ERG [3, 4]. RhoJ is required for angiogenesis [5, 6] and has multiple roles in this process [7, 8]. We recently demonstrated that RhoJ regulates the endosomal trafficking of podocalyxin during angiogenesis to control lumen formation [9]. Here, we use vesicle purification and proteomic analysis to identify the endothelial targets of RhoJ-mediated trafficking. We identify α5β1 integrin as a major RhoJ cargo and show that RhoJ regulates the intracellular trafficking of active α5β1 integrin in endothelial cells to repress fibronectin fibrillogenesis. Accordingly, mice lacking RhoJ show deregulated deposition of fibronectin around vessels during developmental angiogenesis. Intriguingly, we show that RhoJ acts in opposition to Cdc42 in this process through competition for a shared partner, PAK3. These studies identify a critical role for RhoJ in matrix remodeling during blood vessel formation and demonstrate a functional interrelationship between RhoJ and its evolutionary parent.

Phomaketide A Inhibits Lymphangiogenesis in Human Lymphatic Endothelial Cells

Lymphangiogenesis is an important biological process associated with cancer metastasis. The development of new drugs that block lymphangiogenesis represents a promising therapeutic strategy. Marine fungus-derived compound phomaketide A, isolated from the fermented broth of Phoma sp. NTOU4195, has been reported to exhibit anti-angiogenic and anti-inflammatory effects. However, its anti-lymphangiogenic activity has not been clarified to date. In this study, we showed that phomaketide A inhibited cell growth, migration, and tube formation of lymphatic endothelial cells (LECs) without an evidence of cytotoxicity. Mechanistic investigations revealed that phomaketide A reduced LECs-induced lymphangiogenesis via vascular endothelial growth factor receptor-3 (VEGFR-3), protein kinase Cδ (PKCδ), and endothelial nitric oxide synthase (eNOS) signalings. Furthermore, human proteome array analysis indicated that phomaketide A significantly enhanced the protein levels of various protease inhibitors, including cystatin A, serpin B6, tissue factor pathway inhibitor (TFPI), and tissue inhibitor matrix metalloproteinase 1 (TIMP-1). Importantly, phomaketide A impeded tumor growth and lymphangiogenesis by decreasing the expression of LYVE-1, a specific marker for lymphatic vessels, in tumor xenograft animal model. These results suggest that phomaketide A may impair lymphangiogenesis by suppressing VEGFR-3, PKCδ, and eNOS signaling cascades, while simultaneously activating protease inhibitors in human LECs. We document for the first time that phomaketide A inhibits lymphangiogenesis both in vitro and in vivo, which suggests that this natural product could potentially treat cancer metastasis.