Regulation of lymphatic vascular morphogenesis: Implications for pathological (tumor) lymphangiogenesis

In Vitro, In Vivo, and In Silico Models of Lymphangiogenesis in Solid Malignancies

Simple Summary

Lymphangiogenesis is the formation of new lymphatic vessels in physiological conditions but has also been found to be associated with pathologies. For example, it has been proven to be involved in cancer progression and metastatic dissemination through the body. Thus, it became a key element to study in the management of this widespread disease. To date, the study of lymphangiogenesis takes place at the biological (in vitro and in vivo) and computational (in silico) levels. The association of these complementary fields combined with imaging techniques constitutes a real toolbox in pathological lymphangiogenesis understanding.

Abstract

Lymphangiogenesis (LA) is the formation of new lymphatic vessels by lymphatic endothelial cells (LECs) sprouting from pre-existing lymphatic vessels. It is increasingly recognized as being involved in many diseases, such as in cancer and secondary lymphedema, which most often results from cancer treatments. For some cancers, excessive LA is associated with cancer progression and metastatic dissemination to the lymph nodes (LNs) through lymphatic vessels. The study of LA through in vitro, in vivo, and, more recently, in silico models is of paramount importance in providing novel insights and identifying the key molecular actors in the biological dysregulation of this process under pathological conditions. In this review, the different biological (in vitro and in vivo) models of LA, especially in a cancer context, are explained and discussed, highlighting their principal modeled features as well as their advantages and drawbacks. Imaging techniques of the lymphatics, complementary or even essential to in vivo models, are also clarified and allow the establishment of the link with computational approaches. In silico models are introduced, theoretically described, and illustrated with examples specific to the lymphatic system and the LA. Together, these models constitute a toolbox allowing the LA research to be brought to the next level.

Molecular Mechanisms Controlling Lymphatic Endothelial Junction Integrity

The lymphatic system is essential for lipid absorption/transport from the digestive system, maintenance of tissue fluid and protein homeostasis, and immune surveillance. Despite recent progress toward understanding the cellular and molecular mechanisms underlying the formation of the lymphatic vascular system, the nature of lymphatic vessel abnormalities and disease in humans is complex and poorly understood. The mature lymphatic vasculature forms a hierarchical network in which lymphatic endothelial cells (LECs) are joined by functionally specialized cell-cell junctions to maintain the integrity of lymphatic vessels. Blind-ended and highly permeable lymphatic capillaries drain interstitial fluid via discontinuous, button-like LEC junctions, whereas collecting lymphatic vessels, surrounded by intact basement membranes and lymphatic smooth muscle cells, have continuous, zipper-like LEC junctions to transport lymph to the blood circulatory system without leakage. In this review, we discuss the recent advances in our understanding of the mechanisms by which lymphatic button- and zipper-like junctions play critical roles in lymphatic permeability and function in a tissue- and organ-specific manner, including lacteals of the small intestine. We also provide current knowledge related to key pathways and factors such as VEGF and RhoA/ROCK signaling that control lymphatic endothelial cell junctional integrity.

Cancer treatment in the lymphatic system: A prospective targeting employing nanostructured systems

Cancer related to lymphangiogenesis has gained a great deal of attention in recent decades ever since specific markers of this intriguing system were discovered. Unlike the blood system, the lymphatic system has unique features that can advance cancer in future metastasis, or, conversely, can provide an opportunity to prevent or treat this disease that affects people worldwide. The aim of this review is to show the recent research of cancer treatment associated with the lymphatic system, considered one of the main gateways for disseminating metastatic cells to distant organs. Nanostructured systems based on theranostics and immunotherapies can offer several options for this complex disease. Precision targeting and accumulation of nanomaterials into the tumor sites and their elimination, or targeting the specific immune defense cells to promote optimal regression of cancer cells are highlighted in this paper. Moreover, therapies based on nanostructured systems through lymphatic systems may reduce the side effects and toxicity, avoid first pass hepatic metabolism, and improve patient recovery. We emphasize the general understanding of the association between the immune and lymphatic systems, their interaction with tumor cells, the mechanisms involved and the recent developments in several nanotechnology treatments related to this disease.

Substance P Promotes the Progression of Endometrial Adenocarcinoma

OBJECTIVES

It has been demonstrated that substance P (SP) promotes while neurokinin-1 receptor (NK-1R) antagonist inhibits the proliferation of several human cancer cells. Currently, it is still unknown whether such actions exist in human endometrial carcinoma. This study aimed to explore the role of SP/NK-1R signaling in the progression of endometrial adenocarcinoma.

MATERIALS AND METHODS

The expression levels of SP and NK-1R in endometrial adenocarcinoma tissues and Ishikawa cell line were detected by real-time quantitative PCR and Western blot analysis. The effects of SP on Ishikawa cells proliferation and invasion were analyzed using MTT assay and transwell matrigel invasion assay, respectively. The expression levels of matrix metalloproteinase 9 (MMP-9) and vascular endothelial growth factor C (VEGF-C) in Ishikawa cells after administration of SP were detected by real-time quantitative RCR and Western blot analysis.

RESULTS

The expression levels of SP and NK-1R were significantly higher in endometrial adenocarcinoma tissues and Ishikawa cells than in normal endometrium. Substance P significantly enhanced the proliferation and invasion of Ishikawa cells. In addition, SP induced the expression of MMP-9 and VEGF-C in Ishikawa cells, whereas NK-1R antagonist inhibited these effects.

CONCLUSIONS

Substance P plays an important role in the development of endometrial carcinoma by inducing the expression of MMP-9 and VEGF-C and promoting cancer cell proliferation and metastasis, which can be blocked by NK-1R antagonist.

Lymphangiogenesis guidance by paracrine and pericellular factors

This review by Vaahtomeri et al. discusses the mechanisms by which the lymphatic vasculature network is formed, remodeled, and adapted to physiological and pathological challenges. It describes how the lymphatic vasculature network is controlled by an intricate balance of growth factors and biomechanical cues.

Lymphatic vessels are important for tissue fluid homeostasis, lipid absorption, and immune cell trafficking and are involved in the pathogenesis of several human diseases. The mechanisms by which the lymphatic vasculature network is formed, remodeled, and adapted to physiological and pathological challenges are controlled by an intricate balance of growth factor and biomechanical cues. These transduce signals for the readjustment of gene expression and lymphatic endothelial migration, proliferation, and differentiation. In this review, we describe several of these cues and how they are integrated for the generation of functional lymphatic vessel networks.

Bone Marrow Derived Mesenchymal Stem Cells Involve in the Lymphangiogenesis of Lung Cancer and Jinfukang Inhibits the Involvement In Vivo

Lymphangiogenesis plays an important role in cancer metastasis. Bone marrow-derived mesenchymal stem cells (BMMSCs) migrate to the site of tumorigenesis and in turn promote the metastasis. However, whether BMMSCs involve in the lymphangiogenesis of lung cancer is unclear. Jinfukang has clinically been used for the treatment of non small cell lung cancer (NSCLC) in China. In this study, to investigate the involvement of BMMSCs in lymphangiogenesis in lung cancer, and evaluate the inhibitory effect of Jinfukang on the lymphangiogenesis, chimeric mice were prepared by transplanting bone marrow from green fluorescent protein (GFP) transgenic mice (C57BL/6-EGFP) into irradiated C57BL/6 mice. Then, the chimeric mice were injected subcutaneously with freshly prepared Lewis lung carcinoma cell suspension to make lung tumor model, and the model mice were further orally administrated with Jinfukang once per day for 3 weeks. Four weeks after the bone marrow transplantation, GFP-positive cells primarily existed in bone marrow of acceptor mice, and three more weeks after, Lewis lung carcinoma cells formed a tumor mass in chimeric mice. Observation of GFP-positive cells revealed that BMMSCs transferred into the lung tumor. Immunofluorescent analyses of lymphatic vessel endothelial hyaluronan receptor-1 (LYVE-1), a lymphatic endothelium marker, demonstrated a part of lymphatic endothelial cells in lung cancer were derived from BMMSCs, and those lymphatic endothelial cells contributed to the lung tumor lymphangiogenesis. Furthermore, Jinfukang treatment resulted in a significant reduction of the average weight of the tumor mass in chimeric mice, and displayed a significant lower number of LYVE-1 positive cells. The present results suggest that BMMSCs transfer to tumor, differentiate into lymphatic endothelial cells, and involve in the lymphangiogenesis in lung cancer of mice. Jinfukang inhibits the lung tumor mass via suppression of the BMMSCs transformation and lung tumor lymphangiogenesis. Our findings might provide the potential for the cancer therapies.

Regulation of lymphangiogenesis in the diaphragm by macrophages and VEGFR-3 signaling

Lymphatic vessels play important roles in fluid drainage and in immune responses, as well as in pathological processes including cancer progression and inflammation. While the molecular regulation of the earliest lymphatic vessel differentiation and development has been investigated in much detail, less is known about the control and timing of lymphatic vessel maturation in different organs, which often occurs postnatally. We investigated the time course of lymphatic vessel development on the pleural side of the diaphragmatic muscle in mice, the so-called submesothelial initial diaphragmatic lymphatic plexus. We found that this lymphatic network develops largely after birth and that it can serve as a reliable and easily quantifiable model to study physiological lymphangiogenesis in vivo. Lymphangiogenic growth in this tissue was highly dependent on vascular endothelial growth factor receptor (VEGFR)-3 signaling, whereas VEGFR-1 and -2 signaling was dispensable. During diaphragm development, macrophages appeared first in a linearly arranged pattern, followed by ingrowth of lymphatic vessels along these patterned lines. Surprisingly, ablation of macrophages in colony-stimulating factor-1 receptor (Csf1r)-deficient mice and by treatment with a CSF-1R-blocking antibody did not inhibit the general lymphatic vessel development in the diaphragm but specifically promoted branch formation of lymphatic sprouts. In agreement with these findings, incubation of cultured lymphatic endothelial cells with conditioned medium from P7 diaphragmatic macrophages significantly reduced LEC sprouting. These results indicate that the postnatal diaphragm provides a suitable model for studies of physiological lymphangiogenic growth and maturation, and for the identification of modulators of lymphatic vessel growth.

The effects of sonic hedgehog signaling pathway components on non-small-cell lung cancer progression and clinical outcome

Background

Researchers in recent studies have reported that the sonic hedgehog (Shh) signaling pathway plays a crucial role during tumorigenesis, angiogenesis and cellular differentiation. We investigated the clinical and pathological significances of the Shh pathway and of its lymphangiogenic components in non-small-cell lung cancer (NSCLC), namely, Shh, glioma-associated oncogene homolog zinc finger protein 1 (Gli1), lymphatic vessel endothelial hyaluronan receptor 1 (LYVE-1) and vascular endothelial growth factor D (VEGF-D).

Methods

The expression of Shh, Gli1, LYVE-1 and VEGF-D in primary NSCLC tissue from 40 patients was examined using immunohistochemical assays, and relationships between expression and clinicopathological data, such as age, gender, histology, tumor size, nodal stage, visceral pleural invasion, lymphatic thromboembolism, recurrence and overall survival were investigated.

Results

Of the 40 specimens examined, 25 (62.5%), 20 (50.0%), 11 (27.5%) and 20 (50.0%) were positive for Shh, Gli1, LYVE-1 or VEGF-D expression, respectively. The expression of Gli1 and LYVE-1 were significantly associated (P = 0.011), and Shh and LYVE-1 expression was related to visceral pleural invasion and lymphatic thromboembolism, respectively (P < 0.05). Shh expression levels compared on survival curves were statistically significant in univariate logrank analysis (P = 0.020). However, other clinicopathological factors did not reveal any statistical significance in univariate and multivariate analyses.

Conclusions

To our knowledge, this the first report of the relationship between components of the Shh signaling pathway and prognosis in NSCLC. The expression of Shh, Gli1 and LYVE-1 was found to be associated with clinicopathological factors and survival. Thus, the overexpression of the Shh signaling pathway could serve as a predictor of malignant behavior, including lymphangiogenesis, in NSCLC.

Lymphatic collecting vessel maturation and valve morphogenesis

The lymphatic vasculature plays an essential role in the maintenance of tissue interstitial fluid balance and in the immune response. After capture of fluids, proteins and antigens by lymphatic capillaries, lymphatic collecting vessels ensure lymph transport. An important component to avoid lymph backflow and to allow a unidirectional flow is the presence of intraluminal valves. Defects in the function of collecting vessels lead to lymphedema. Several important factors and signaling pathways involved in lymphatic collecting vessel maturation and valve morphogenesis have now been discovered. The present review summarizes the current knowledge about the key steps of lymphatic collecting vessel development and maturation and focuses on the regulatory mechanisms involved in lymphatic valve formation.

Emerging Role of Sphingosine-1-phosphate in Inflammation, Cancer, and Lymphangiogenesis

The main function of the lymphatic system is to control and maintain fluid homeostasis, lipid transport, and immune cell trafficking. In recent years, the pathological roles of lymphangiogenesis, the generation of new lymphatic vessels from preexisting ones, in inflammatory diseases and cancer progression are beginning to be elucidated. Sphingosine-1-phosphate (S1P), a bioactive lipid, mediates multiple cellular events, such as cell proliferation, differentiation, and trafficking, and is now known as an important mediator of inflammation and cancer. In this review, we will discuss recent findings showing the emerging role of S1P in lymphangiogenesis, in inflammation, and in cancer.

Murine Notch1 is required for lymphatic vascular morphogenesis during development

BACKGROUND

The transmembrane receptor Notch1 is a critical regulator of arterial differentiation and blood vessel sprouting. Recent evidence shows that functional blockade of Notch1 and its ligand, Dll4, leads to postnatal lymphatic defects in mice. However, the precise role of the Notch signaling pathway in lymphatic vessel development has yet to be defined. Here we show the developmental role of Notch1 in lymphatic vascular morphogenesis by analyzing lymphatic endothelial cell (LEC)-specific conditional Notch1 knockout mice crossed with an inducible Prox1CreER(T2) driver.

RESULTS

LEC-specific Notch1 mutant embryos exhibited enlarged lymphatic vessels. The phenotype of lymphatic overgrowth accords with increased LEC sprouting from the lymph sacs and increased filopodia formation. Furthermore, cell death was significantly reduced in Notch1-mutant LECs, whereas proliferation was increased. RNA-seq analysis revealed that expression of cytokine/chemokine signaling molecules was upregulated in Notch1-mutant LECs isolated from E15.5 dorsal skin, whereas VEGFR3, VEGFR2, VEGFC, and Gja4 (Connexin 37) were downregulated.

CONCLUSIONS

The lymphatic phenotype of LEC-specific conditional Notch1 mouse mutants indicates that Notch activity in LECs controls lymphatic sprouting and growth during development. These results provide evidence that similar to postnatal and pathological lymphatic vessel formation, the Notch signaling pathway plays a role in inhibiting developmental lymphangiogenesis.

Hypoxia induces VEGF-C expression in metastatic tumor cells via a HIF-1α-independent translation-mediated mechanism

Various tumors metastasize via lymph vessels and lymph nodes to distant organs. Even though tumors are hypoxic, the mechanisms of how hypoxia regulates lymphangiogenesis remain poorly characterized. Here, we show that hypoxia reduced vascular endothelial growth factor C (VEGF-C) transcription and cap-dependent translation via the upregulation of hypophosphorylated 4E-binding protein 1 (4E-BP1). However, initiation of VEGF-C translation was induced by hypoxia through an internal ribosome entry site (IRES)-dependent mechanism. IRES-dependent VEGF-C translation was independent of hypoxia-inducible factor 1α (HIF-1α) signaling. Notably, the VEGF-C IRES activity was higher in metastasizing tumor cells in lymph nodes than in primary tumors, most likely because lymph vessels in these lymph nodes were severely hypoxic. Overall, this transcription-independent but translation-dependent upregulation of VEGF-C in hypoxia stimulates lymphangiogenesis in tumors and lymph nodes and may contribute to lymphatic metastasis.

Clinical disorders of primary malfunctioning of the lymphatic system

Primary lymphedema is defined as lymphedema caused by dysplasia of the lymph vessels. This complex group of diseases is discussed in detail from a clinical perspective. A review of the epidemiology and classification of lymphedema on the backdrop of its clinical presentation reveals weaknesses of the present classification system, which, however, is the basis for the choice of optimal patient care. Non-syndrome and syndrome types of primary lymphedema are presented in detail and related molecular findings are summarized.

Molecular mechanisms and imaging of lymphatic metastasis

In many types of cancer, tumors metastasize through the lymphatic system to draining lymph nodes. These sentinel lymph nodes have gained increased attention as a prognostic indicator for the severity of the disease, leading to the sentinel lymph node mapping and biopsy procedure to be accepted as standard-of-care for breast cancer and melanoma. However, many limitations exist with this procedure resulting in high false negative rates. In this review we highlight the new advances in the understanding of the molecular mechanisms of lymphangiogenesis and tumor metastasis that may lead to improved strategies in the detection of the sentinel lymph nodes and therapeutic interventions to prevent further tumor spread. In addition, advances in imaging technology are allowing new approaches for anatomical mapping of lymphatic drainage patterns and molecular imaging strategies that may improve detection of metastatic tumor cells within sentinel lymph nodes.