Modeling lymphangiogenesis in a three-dimensional culture system

Decorin suppresses tumor lymphangiogenesis: A mechanism to curtail cancer progression

The complex interplay between malignant cells and the cellular and molecular components of the tumor stroma is a key aspect of cancer growth and development. These tumor-host interactions are often affected by soluble bioactive molecules such as proteoglycans. Decorin, an archetypical small leucine-rich proteoglycan primarily expressed by stromal cells, affects cancer growth in its soluble form by interacting with several receptor tyrosine kinases (RTK). Overall, decorin leads to a context-dependent and protracted cessation of oncogenic RTK activity by attenuating their ability to drive a prosurvival program and to sustain a proangiogenic network. Through an unbiased transcriptomic analysis using deep RNAseq, we identified that decorin down-regulated a cluster of tumor-associated genes involved in lymphatic vessel (LV) development when systemically delivered to mice harboring breast carcinoma allografts. We found that Lyve1 and Podoplanin, two established markers of LVs, were markedly suppressed at both the mRNA and protein levels, and this suppression correlated with a significant reduction in tumor LVs. We further identified that soluble decorin, but not its homologous proteoglycan biglycan, inhibited LV sprouting in an ex vivo 3D model of lymphangiogenesis. Mechanistically, we found that decorin interacted with vascular endothelial growth factor receptor 3 (VEGFR3), the main lymphatic RTK, and its activity was required for the decorin-mediated block of lymphangiogenesis. Finally, we identified that Lyve1 was in part degraded via decorin-evoked autophagy in a nutrient- and energy-independent manner. These findings implicate decorin as a biological factor with antilymphangiogenic activity and provide a potential therapeutic agent for curtailing breast cancer growth and metastasis.

A human initial lymphatic chip reveals distinct mechanisms of primary lymphatic valve dysfunction in acute and chronic inflammation

Interstitial fluid uptake and retention by lymphatic vessels (LVs) play a role in maintaining interstitial fluid homeostasis. While it is well-established that intraluminal lymphatic valves in the collecting LVs prevent fluid backflow (secondary lymphatic valves), a separate valve system in the initial LVs that only permits interstitial fluid influx into the LVs, preventing fluid leakage back to the interstitium (primary lymphatic valves), remains incompletely understood. Although lymphatic dysfunction is commonly observed in inflammation and autoimmune diseases, how the primary lymphatic valves are affected by acute and chronic inflammation has scarcely been explored and even less so using in vitro lymphatic models. Here, we developed a human initial lymphatic vessel chip where interstitial fluid pressure and luminal fluid pressure are controlled to examine primary lymph valve function. In normal conditions, lymphatic drainage (fluid uptake) and permeability (fluid leakage) in engineered LVs were maintained high and low, respectively, which was consistent with our understanding of healthy primary lymph valves. Next, we examined the effects of acute and chronic inflammation. Under the acute inflammation condition with a TNF-α treatment (2 hours), degradation of fibrillin and impeded lymphatic drainage were observed, which were reversed by treatment with anti-inflammatory dexamethasone. Surprisingly, the chronic inflammation condition (repeated TNF-α treatments during 48 hours) deposited fibrillin to compensate for the fibrillin loss, showing no change in lymphatic drainage. Instead, the chronic inflammation condition led to cell death and disruption of lymphatic endothelial cell-cell junctions, increasing lymphatic permeability and fluid leakage. Our human lymphatic model shows two distinct mechanisms by which primary lymphatic valve dysfunction occurs in acute and chronic inflammation.

A 3D biomimetic model of lymphatics reveals cell-cell junction tightening and lymphedema via a cytokine-induced ROCK2/JAM-A complex

Impaired lymphatic drainage and lymphedema are major morbidities whose mechanisms have remained obscure. To study lymphatic drainage and its impairment, we engineered a microfluidic culture model of lymphatic vessels draining interstitial fluid. This lymphatic drainage-on-chip revealed that inflammatory cytokines that are known to disrupt blood vessel junctions instead tightened lymphatic cell-cell junctions and impeded lymphatic drainage. This opposing response was further demonstrated when inhibition of rho-associated protein kinase (ROCK) was found to normalize fluid drainage under cytokine challenge by simultaneously loosening lymphatic junctions and tightening blood vessel junctions. Studies also revealed a previously undescribed shift in ROCK isoforms in lymphatic endothelial cells, wherein a ROCK2/junctional adhesion molecule-A (JAM-A) complex emerges that is responsible for the cytokine-induced lymphatic junction zippering. To validate these in vitro findings, we further demonstrated in a genetic mouse model that lymphatic-specific knockout of ROCK2 reversed lymphedema in vivo. These studies provide a unique platform to generate interstitial fluid pressure and measure the drainage of interstitial fluid into lymphatics and reveal a previously unappreciated ROCK2-mediated mechanism in regulating lymphatic drainage.

Decorin suppresses tumor lymphangiogenesis: A mechanism to curtail cancer progression

The complex interplay between malignant cells and the cellular and molecular components of the tumor stroma is a key aspect of cancer growth and development. These tumor-host interactions are often affected by soluble bioactive molecules such as proteoglycans. Decorin, an archetypical small leucine-rich proteoglycan primarily expressed by stromal cells, affects cancer growth in its soluble form by interacting with several receptor tyrosine kinases (RTK). Overall, decorin leads to a context-dependent and protracted cessation of oncogenic RTK activity by attenuating their ability to drive a pro-survival program and to sustain a pro-angiogenic network. Through an unbiased transcriptomic analysis using deep RNAseq, we discovered that decorin downregulated a cluster of tumor-associated genes involved in lymphatic vessel development when systemically delivered to mice harboring breast carcinoma allografts. We found that Lyve1 and Podoplanin, two established markers of lymphatic vessels, were markedly suppressed at both the mRNA and protein levels and this suppression correlated with a significant reduction in tumor lymphatic vessels. We further discovered that soluble decorin, but not its homologous proteoglycan biglycan, inhibited lymphatic vessel sprouting in an ex vivo 3D model of lymphangiogenesis. Mechanistically, we found that decorin interacted with VEGFR3, the main lymphatic RTK, and its activity was required for the decorin-mediated block of lymphangiogenesis. Finally, we discovered that Lyve1 was in part degraded via decorin-evoked autophagy in a nutrient- and energy-independent manner. These findings implicate decorin as a new biological factor with anti-lymphangiogenic activity and provide a potential therapeutic agent for curtailing breast cancer growth and metastasis.

A 3D Human Lymphatic Vessel-on-Chip Reveals the Roles of Interstitial Flow and VEGF-A/C for Lymphatic Sprouting and Discontinuous Junction Formation

Introduction

Lymphatic vessels (LVs) maintain fluid homeostasis by draining excess interstitial fluid, which is accomplished by two distinct LVs: initial LVs and collecting LVs. The interstitial fluid is first drained into the initial LVs through permeable "button-like" lymphatic endothelial cell (LEC) junctions. Next, the drained fluid ("lymph") transports to lymph nodes through the collecting LVs with less permeable "zipper-like" junctions that minimize loss of lymph. Despite the significance of LEC junctions in lymphatic drainage and transport, it remains unclear how luminal or interstitial flow affects LEC junctions in vascular endothelial growth factors A and C (VEGF-A and VEGF-C) conditions. Moreover, it remains unclear how these flow and growth factor conditions impact lymphatic sprouting.

Methods

We developed a 3D human lymphatic vessel-on-chip that can generate four different flow conditions (no flow, luminal flow, interstitial flow, both luminal and interstitial flow) to allow an engineered, rudimentary LV to experience those flows and respond to them in VEGF-A/C.

Results

We examined LEC junction discontinuities, lymphatic sprouting, LEC junction thicknesses, and cell contractility-dependent vessel diameters in the four different flow conditions in VEGF-A/C. We discovered that interstitial flow in VEGF-C generates discontinuous LEC junctions that may be similar to the button-like junctions with no lymphatic sprouting. However, interstitial flow or both luminal and interstitial flow stimulated lymphatic sprouting in VEGF-A, maintaining zipper-like LEC junctions. LEC junction thickness and cell contractility-dependent vessel diameters were not changed by those conditions.

Conclusions

In this study, we provide an engineered lymphatic vessel platform that can generate four different flow regimes and reveal the roles of interstitial flow and VEGF-A/C for lymphatic sprouting and discontinuous junction formation.

Supplementary Information

The online version contains supplementary material available at 10.1007/s12195-023-00780-0.

In Vitro Models of Blood and Lymphatic Vessels-Connecting Tissues and Immunity

Blood and lymphatic vessels are regulators of physiological processes, including oxygenation and fluid transport. Both vessels are ubiquitous throughout the body and are critical for sustaining tissue homeostasis. The complexity of each vessel's processes has limited the understanding of exactly how the vessels maintain their functions. Both vessels have been shown to be involved in the pathogenesis of many diseases, including cancer metastasis, and it is crucial to probe further specific mechanisms involved. In vitro models are developed to better understand blood and lymphatic physiological functions and their mechanisms. In this review, blood and lymphatic in vitro model systems, including 2D and 3D designs made using Transwells, microfluidic devices, organoid cultures, and various other methods, are described. Models studying endothelial cell-extracellular matrix interactions, endothelial barrier properties, transendothelial transport and cell migration, lymph/angiogenesis, vascular inflammation, and endothelial-cancer cell interactions are particularly focused. While the field has made significant progress in modeling and understanding lymphatic and blood vasculature, more models that include coculture of multiple cell types, complex extracellular matrix, and 3D morphologies, particularly for models mimicking disease states, will help further the understanding of the role of blood and lymphatic vasculature in health and disease.

Modeling lymphangiogenesis: Pairing in vitro and in vivo metrics

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

In Vitro Comparison of Lymphangiogenic Potential of Hypoxia Preconditioned Serum (HPS) and Platelet-Rich Plasma (PRP)

Strategies for therapeutic lymphangiogenesis are gradually directed toward the use of growth factor preparations. In particular, blood-derived growth factor products, including Hypoxia Preconditioned Serum (HPS) and Platelet-rich Plasma (PRP), are both clinically employed for accelerating tissue repair and have received considerable attention in the field of regenerative medicine research. In this study, a comparative analysis of HPS and PRP was conducted to explore their lymphangiogenic potential. We found higher pro-lymphangiogenic growth factor concentrations of VEGF-C, PDGF-BB, and bFGF in HPS in comparison to normal serum (NS) and PRP. The proliferation and migration of lymphatic endothelial cells (LECs) were promoted considerably with both HPS and PRP, but the strongest effect was achieved with HPS-40% dilution. Tube formation of LECs showed the highest number of tubes, branching points, greater tube length, and cell-covered area with HPS-10%. Finally, the effects were double-validated using an ex vivo lymphatic ring assay, in which the highest number of sprouts and the greatest sprout length were achieved with HPS-10%. Our findings demonstrate the superior lymphangiogenic potential of a new generation blood-derived secretome obtained by hypoxic preconditioning of peripheral blood cells-a method that offers a novel alternative to PRP.

Enhancement of Lymphangiogenesis by Human Mesenchymal Stem Cell Sheet

Preparation of human mesenchymal stem cell (hMSC) suspension for lymphedema treatment relies on conventional enzymatic digestion methods, which severely disrupts cell-cell and cell-extracellular matrix (ECM) connections, and drastically impairs cell retention and engraftment after transplantation. The objective of the present study is to evaluate the ability of hMSC-secreted ECM to augment lymphangiogenesis by using an in vitro coculturing model of hMSC sheets with lymphatic endothelial cells (LECs) and an in vivo mouse tail lymphedema model. Results demonstrate that the hMSC-secreted ECM augments the formation of lymphatic capillary-like structure by a factor of 1.2-3.6 relative to the hMSC control group, by serving as a prolymphangiogenic growth factor reservoir and facilitating cell regenerative activities. hMSC-derived ECM enhances MMP-2 mediated matrix remodeling, increases the synthesis of collagen IV and laminin, and promotes lymphatic microvessel-like structure formation. The injection of rat MSC sheet fragments into a mouse tail lymphedema model confirms the benefits of the hMSC-derived ECM by stimulating lymphangiogenesis and wound closure.

A Challenge for Engineering Biomimetic Microvascular Models: How do we Incorporate the Physiology?

The gap between in vitro and in vivo assays has inspired biomimetic model development. Tissue engineered models that attempt to mimic the complexity of microvascular networks have emerged as tools for investigating cell-cell and cell-environment interactions that may be not easily viewed in vivo. A key challenge in model development, however, is determining how to recreate the multi-cell/system functional complexity of a real network environment that integrates endothelial cells, smooth muscle cells, vascular pericytes, lymphatics, nerves, fluid flow, extracellular matrix, and inflammatory cells. The objective of this mini-review is to overview the recent evolution of popular biomimetic modeling approaches for investigating microvascular dynamics. A specific focus will highlight the engineering design requirements needed to match physiological function and the potential for top-down tissue culture methods that maintain complexity. Overall, examples of physiological validation, basic science discoveries, and therapeutic evaluation studies will emphasize the value of tissue culture models and biomimetic model development approaches that fill the gap between in vitro and in vivo assays and guide how vascular biologists and physiologists might think about the microcirculation.

Synthetic hydrogels engineered to promote collecting lymphatic vessel sprouting

The lymphatic vasculature is an essential component of the body's circulation providing a network of vessels to return fluid and proteins from the tissue space to the blood, to facilitate immune ce-ll and antigen transport to lymph nodes, and to take up dietary lipid from the intestine. The development of biomaterial-based strategies to facilitate the growth of lymphatics either for regenerative purposes or as model system to study lymphatic biology is still in its nascent stages. In particular, platforms that encourage the sprouting and formation of lymphatic networks from collecting vessels are particularly underdeveloped. Through implementation of a modular, poly(ethylene glycol) (PEG)-based hydrogel, we explored the independent contributions of matrix elasticity, degradability, and adhesive peptide presentation on sprouting of implanted segments of rat lymphatic collecting vessels. An engineered hydrogel with 680 Pa elasticity, 2.0 mM RGD adhesive peptide, and full susceptibility to protease degradability produced the highest levels of sprouting relative to other physicochemical matrix properties. This engineered hydrogel was then utilized as a scaffold to facilitate the implantation of a donor vessel that functionally grafted into the host vasculature. This hydrogel provides a promising platform for facilitating lymphangiogenesis in vivo or as a means to understand the cellular mechanisms involved in the sprout process during collecting lymphatic vessel collateralization.

The role of albumin and the extracellular matrix on the pathophysiology of oedema formation in severe malnutrition

BACKGROUND

While fluid flows in a steady state from plasma, through interstitium, and into the lymph compartment, altered fluid distribution and oedema can result from abnormal Starling's forces, increased endothelial permeability or impaired lymphatic drainage. The mechanism of oedema formation, especially the primary role of hypoalbuminaemia, remains controversial. Here, we explored the roles of albumin and albumin-independent mechanisms in oedema formation among children with severe malnutrition (SM).

METHODS

We performed secondary analysis of data obtained from two independent clinical trials in Malawi and Kenya (NCT02246296 and NCT00934492). We then used an unconventional strategy of comparing children with kwashiorkor and marasmus by matching (discovery cohort, n = 144) and normalising (validation cohort, n = 98, 2 time points) for serum albumin. Untargeted proteomics was used in the discovery cohort to determine plausible albumin-independent mechanisms associated with oedema, which was validated using enzyme-linked immunosorbent assay and multiplex assays in the validation cohort.

FINDINGS

We demonstrated that low serum albumin is necessary but not sufficient to develop oedema in SM. We further found that markers of extracellular matrix (ECM) degradation rather than markers of EG degradation distinguished oedematous and non-oedematous children with SM.

INTERPRETATION

Our results show that oedema formation has both albumin-dependent and independent mechanisms. ECM integrity appears to have a greater role in oedema formation than EG shedding in SM.

FUNDING

Research Foundation Flanders (FWO), Thrasher Foundation (15122 and 9403), VLIR-UOS-Ghent University Global Minds Fund, Bill & Melinda Gates Foundation (OPP1131320), MRC/DfID/Wellcome Trust Global Health Trials Scheme (MR/M007367/1), Canadian Institutes of Health Research (156307), Wellcome Trust (WT083579MA).

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

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.

Lymphatic Tissue and Organ Engineering for In Vitro Modeling and In Vivo Regeneration

The lymphatic system has an important role in maintaining fluid homeostasis and transporting immune cells and biomolecules, such as dietary fat, metabolic products, and antigens in different organs and tissues. Therefore, impaired lymphatic vessel function and/or lymphatic vessel deficiency can lead to numerous human diseases. The discovery of lymphatic endothelial markers and prolymphangiogenic growth factors, along with a growing number of in vitro and in vivo models and technologies has expedited research in lymphatic tissue and organ engineering, advancing therapeutic strategies. In this article, we describe lymphatic tissue and organ engineering in two- and three-dimensional culture systems and recently developed microfluidics and organ-on-a-chip systems in vitro. Next, we discuss advances in lymphatic tissue and organ engineering in vivo, focusing on biomaterial and scaffold engineering and their applications for lymphatic vessels and lymphoid organ regeneration. Last, we provide expert perspective and prospects in the field of lymphatic tissue engineering.

Cardiac macrophage subsets differentially regulate lymphatic network remodeling during pressure overload

The lymphatic network of mammalian heart is an important regulator of interstitial fluid compartment and immune cell trafficking. We observed a remodeling of the cardiac lymphatic vessels and a reduced lymphatic efficiency during heart hypertrophy and failure induced by transverse aortic constriction. The lymphatic endothelial cell number of the failing hearts was positively correlated with cardiac function and with a subset of cardiac macrophages. This macrophage population distinguished by LYVE-1 (Lymphatic vessel endothelial hyaluronic acid receptor-1) and by resident macrophage gene expression signature, appeared not replenished by CCR2 mediated monocyte infiltration during pressure overload. Isolation of macrophage subpopulations showed that the LYVE-1 positive subset sustained in vitro and in vivo lymphangiogenesis through the expression of pro-lymphangiogenic factors. In contrast, the LYVE-1 negative macrophage subset strongly expressed MMP12 and decreased the endothelial LYVE-1 receptors in lymphatic endothelial cells, a feature of cardiac lymphatic remodeling in failing hearts. The treatment of mice with a CCR2 antagonist during pressure overload modified the proportion of macrophage subsets within the pathological heart and preserved lymphatic network from remodeling. This study reports unknown and differential functions of macrophage subpopulations in the regulation of cardiac lymphatic during pathological hypertrophy and may constitute a key mechanism underlying the progression of heart failure.

Wnt Signaling Regulates the Lymphatic Endothelial Transdifferentiation of Adipose-Derived Stromal Cells In Vitro

Lymphedema is a chronic, progressive disease that causes pain as well as heavy economic burdens to patients. Reconstruction of the impaired lymphatic system is the key to treat lymphedema. Currently, there is no cure, but mesenchymal stromal cells show promising potential for lymphatic endothelial regeneration. Adipose-derived stromal cells (ADSCs) have been proved to support lymphangiogenesis both in vivo and in vitro. However, the mechanism in vascular endothelial growth factor C-induced (VEGF-C-induced) lymphatic endothelial transdifferentiation of ADSCs remains unknown. In this study, we show a novel link between the Wingless and int-1 (Wnt) pathway and the lymphatic endothelial differentiation process. We used LiCl to activate Wnt and DKK-1 to inhibit Wnt. Compared with the Wnt inhibition group and the control groups, the Wnt activation group produced more lymphatic endothelial cell (LEC)-related mRNA and proteins. Besides, Wnt-activated ADSCs formed longer tubes in two-dimensional culture and promoted the growth of lymphatic vessels in a three-dimensional transwell ADSC-LEC co-culture system. Our results demonstrated that activation of Wnt during the lymphatic endothelial transdifferentiation of ADSCs would enhance the efficacy of VEGF-C treatment. We anticipate our assay to expand our knowledge of Wnt in cell transdifferentiation and lay a foundation for future efforts to explore a novel and effective ADSC-based therapy for lymphedema.

Prostaglandin E2 Receptor 4 (EP4) as a Therapeutic Target to Impede Breast Cancer-Associated Angiogenesis and Lymphangiogenesis

The formation of new blood (angiogenesis) and lymphatic (lymphangiogenesis) vessels are major events associated with most epithelial malignancies, including breast cancer. Angiogenesis is essential for cancer cell survival. Lymphangiogenesis is critical in maintaining tumoral interstitial fluid balance and importing tumor-facilitatory immune cells. Both vascular routes also serve as conduits for cancer metastasis. Intratumoral hypoxia promotes both events by stimulating multiple angiogenic/lymphangiogenic growth factors. Studies on tumor-associated lymphangiogenesis and its exploitation for therapy have received less attention from the research community than those on angiogenesis. Inflammation is a key mediator of both processes, hijacked by many cancers by the aberrant expression of the inflammation-associated enzyme cyclo-oxygenase (COX)-2. In this review, we focus on breast cancer and showed that COX-2 is a major promoter of both events, primarily resulting from the activation of prostaglandin (PG) E receptor EP4 on tumor cells, tumor-infiltrating immune cells, and endothelial cells; and the induction of oncogenic microRNAs. The COX-2/EP4 pathway also promotes additional events in breast cancer progression, such as cancer cell migration, invasion, and the stimulation of stem-like cells. Based on a combination of studies using multiple breast cancer models, we show that EP4 antagonists hold a major promise in breast cancer therapy in combination with other modalities including immune check-point inhibitors.

The β1-integrin plays a key role in LEC invasion in an optimized 3-D collagen matrix model

Lymphangiogenesis, or formation of new lymphatic vessels, is a tightly regulated process that is controlled by growth factor signaling and biomechanical cues. Lymphatic endothelial cells (LECs) undergo remodeling, migration, and proliferation to invade the surrounding extracellular matrix (ECM) during both physiological and pathological lymphangiogenesis. This study optimized conditions for an in vitro three-dimensional (3-D) collagen-based model that induced LEC invasion and recapitulated physiological formation of lymphatic capillaries with lumens. Invasion of LECs was enhanced in the presence of sphingosine 1-phosphate (S1P). Effects of various known lymphangiogenic factors, vascular endothelial growth factor (VEGF)-A, basic fibroblast growth factor (bFGF), interleukin (IL)-8, and hepatocyte growth factor (HGF), were tested on LEC sprout formation synergistically with VEGF-C. Several of these growth factors significantly enhanced LEC invasion, and synergistic effects of some of these further enhanced the sprouting density and lumen volume. To determine the contribution of specific ECM components, we analyzed the expression of different integrin subunits. Basal expressions of the integrin α₅- and integrin β₁-subunits were high in LECs. The addition of fibronectin, which mediates cellular responses through these integrins, enhanced LEC sprouting density and sprout length dose-dependently. siRNA-mediated knockdown of the integrin β₁-subunit suppressed LEC invasion and also inhibited VEGF receptor (VEGFR)3 and ERK activation. Furthermore, exposing LECs to the inflammatory mediator lipopolysaccharide (LPS) inhibited sprouting. This optimized model for LEC invasion includes S1P, VEGF-C, and fibronectin within a 3-D collagen matrix, along with VEGF-C, VEGF-A, bFGF, and HGF in the culture medium, and provides a useful tool to investigate the functional effect of various lymphangiogenic factors and inhibitors.

Biomaterial Based Strategies for Engineering New Lymphatic Vasculature

The lymphatic system is essential for tissue regeneration and repair due to its pivotal role in resolving inflammation, immune cell surveillance, lipid transport, and maintaining tissue homeostasis. Loss of functional lymphatic vasculature is directly implicated in a variety of diseases, including lymphedema, obesity, and the progression of cardiovascular diseases. Strategies that stimulate the formation of new lymphatic vessels (lymphangiogenesis) could provide an appealing new approach to reverse the progression of these diseases. However, lymphangiogenesis is relatively understudied and stimulating therapeutic lymphangiogenesis faces challenges in precise control of lymphatic vessel formation. Biomaterial delivery systems could be used to unleash the therapeutic potential of lymphangiogenesis for a variety of tissue regenerative applications due to their ability to achieve precise spatial and temporal control of multiple therapeutics, direct tissue regeneration, and improve the survival of delivered cells. In this review, the authors begin by introducing therapeutic lymphangiogenesis as a target for tissue regeneration, then an overview of lymphatic vasculature will be presented followed by a description of the mechanisms responsible for promoting new lymphatic vessels. Importantly, this work will review and discuss current biomaterial applications for stimulating lymphangiogenesis. Finally, challenges and future directions for utilizing biomaterials for lymphangiogenic based treatments are considered.

Quantification of Angiogenesis and Lymphangiogenesis in the Dual ex vivo Aortic and Thoracic Duct Assay

Abstract: Background

Lymphatic vessel formation (lymphangiogenesis) plays important roles in cancer metastasis, organ rejection, and lymphedema, but the underlying molecular events remain unclear. Furthermore, despite significant overlap in the molecular families involved in angiogenesis and lymphangiogenesis, little is known about the crosstalk between these processes. The ex vivo aortic ring assay and lymphatic ring assay have enabled detailed studies of vessel sprouting, but harvesting and imaging clear thoracic duct samples remain challenging. Here we present a modified ex vivo dual aortic ring and thoracic duct assay using tissues from dual fluorescence reporter Prox1-GFP/Flt1-DsRed (PGFD) mice, which permit simultaneous visualization of blood and lymphatic endothelial cells.

Objective

To characterize the concurrent sprouting of intrinsically fluorescent blood and lymphatic vessels from harvested aorta and thoracic duct samples.

Methods

Dual aorta and thoracic duct specimens were harvested from PGFD mice, grown in six types of endothelial cell growth media (one control, five that each lack a specific growth factor), and visualized by confocal fluorescence microscopy. Linear mixed models were used to compare the extent of vessel growth and sprouting over a 28-day period.

Results

Angiogenesis occurred prior to lymphangiogenesis in our assay. The control medium generally induced superior growth of both vessel types compared with the different modified media formulations. The greatest decrease in lymphangiogenesis was observed in vascular endothelial growth factor-C (VEGF-C)-devoid medium, suggesting the importance of VEGF-C in lymphangiogenesis.

Conclusion

The modified ex vivo dual aortic ring and thoracic duct assay represents a powerful tool for studying angiogenesis and lymphangiogenesis in concert.

Lymphatic-to-blood vessel transition in adult microvascular networks: A discovery made possible by a top-down approach to biomimetic model development

OBJECTIVE

Emerging areas of vascular biology focus on lymphatic/blood vessel mispatterning and the regulation of endothelial cell identity. However, a fundamental question remains unanswered: Can lymphatic vessels become blood vessels in adult tissues? Leveraging a novel tissue culture model, the objective of this study was to track lymphatic endothelial cell fate over the time course of adult microvascular network remodeling.

METHODS

Cultured adult Wistar rat mesenteric tissues were labeled with BSI-lectin and time-lapse images were captured over five days of serum-stimulated remodeling. Additionally, rat mesenteric tissues on day 0 and day 3 and 5 post-culture were labeled for PECAM + LYVE-1 or PECAM + podoplanin.

RESULTS

Cultured networks were characterized by increases in blood capillary sprouting, lymphatic sprouting, and the number of lymphatic/blood vessel connections. Comparison of images from the same network regions identified incorporation of lymphatic vessels into blood vessels. Mosaic lymphatic/blood vessels contained lymphatic marker positive and negative endothelial cells.

CONCLUSIONS

Our results reveal the ability for lymphatic vessels to transition into blood vessels in adult microvascular networks and discover a new paradigm for investigating lymphatic/blood endothelial cell dynamics during microvascular remodeling.

Encapsulation of echinomycin in cyclodextrin inclusion complexes into liposomes: in vitro anti-proliferative and anti-invasive activity in glioblastoma

Echinomycin, a DNA bis-intercalator peptide, belongs to the family of quinoxaline antibiotics. Echinomycin exhibits potent antitumor and antimicrobial activity. However, it is highly water insoluble and suffers from low bioavailability and unwanted side effects. Therefore, developing new formulations and delivery systems that can enhance echinomycin solubility and therapeutic potency is needed for further clinical application. In this study, echinomycin has been complexed into the hydrophobic cavity of γ-cyclodextrin (γCD) then encapsulated into PEGylated liposomes. The anti-proliferative and anti-invasive effect has been evaluated against U-87 MG glioblastoma cells. Echinomycin-in-γCD inclusion complexes have been characterized by phase solubility assay, TLC, and 1H-NMR. The echinomycin-in-γCD inclusion complexes have been loaded into liposomes using a thin film hydration method to end up with echinomycin-in-γCD-in-liposomes. Drug-loaded liposomes were able to inhibit cell proliferation with IC50 of 1.0 nM. Moreover, echinomycin-in-γCD-in-liposomes were found to inhibit the invasion of U-87 MG cells using the spheroid gel invasion assay. In conclusion, the current work describes for the first time γCD-echinomycin complexes and their encapsulation into PEGylated liposomes.

Human organotypic lymphatic vessel model elucidates microenvironment-dependent signaling and barrier function

The lymphatic system is an active player in the pathogenesis of several human diseases, including lymphedema and cancer. Relevant models are needed to advance our understanding of lymphatic biology in disease progression to improve therapy and patient outcomes. Currently, there are few 3D in vitro lymphatic models that can recapitulate the physiological structure, function, and interactions of lymphatic vessels in normal and diseased microenvironments. Here, we developed a 3D microscale lymphatic vessel (μLYMPH) system for generating human lymphatic vessels with physiological tubular structure and function. Consistent with characteristics of lymphatic vessels in vivo, the endothelium of cultured vessels was leaky with an average permeability of 1.38 × 10^-5 ± 0.29 × 10^-5 cm/s as compared to 0.68 × 10^-5 ± 0.13 × 10^-5 cm/s for blood vessels. This leakiness also resulted in higher uptake of solute by the lymphatic vessels under interstitial flow, demonstrating recapitulation of their natural draining function. The vessels secreted appropriate growth factors and inflammatory mediators. Our system identified the follistatin/activin axis as a novel pathway in lymphatic vessel maintenance and inflammation. Moreover, the μLYMPH system provided a platform for examining crosstalk between lymphatic vessels and tumor microenvironmental components, such as breast cancer-associated fibroblasts (CAFs). In co-culture with CAFs, vessel barrier function was significantly impaired by CAF-secreted IL-6, a possible pro-metastatic mechanism of lymphatic metastasis. Targeted blocking of the IL-6/IL-6R signaling pathway with an IL-6 neutralizing antibody fully rescued the vessels, demonstrating the potential of our system for screening therapeutic targets. These results collectively demonstrate the μLYMPH system as a powerful model for advancing lymphatic biology in health and disease.

Application of microscale culture technologies for studying lymphatic vessel biology

Immense progress in microscale engineering technologies has significantly expanded the capabilities of in vitro cell culture systems for reconstituting physiological microenvironments that are mediated by biomolecular gradients, fluid transport, and mechanical forces. Here, we examine the innovative approaches based on microfabricated vessels for studying lymphatic biology. To help understand the necessary design requirements for microfluidic models, we first summarize lymphatic vessel structure and function. Next, we provide an overview of the molecular and biomechanical mediators of lymphatic vessel function. Then we discuss the past achievements and new opportunities for microfluidic culture models to a broad range of applications pertaining to lymphatic vessel physiology. We emphasize the unique attributes of microfluidic systems that enable the recapitulation of multiple physicochemical cues in vitro for studying lymphatic pathophysiology. Current challenges and future outlooks of microscale technology for studying lymphatics are also discussed. Collectively, we make the assertion that further progress in the development of microscale models will continue to enrich our mechanistic understanding of lymphatic biology and physiology to help realize the promise of the lymphatic vasculature as a therapeutic target for a broad spectrum of diseases.

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.

Roles of prostaglandins in tumor-associated lymphangiogenesis with special reference to breast cancer

Lymphangiogenesis (formation of new lymphatic vessels), unlike angiogenesis, has been a lesser-focused field in cancer biology, because of earlier controversy regarding whether lymphatic metastasis occurs via pre-existing or newly formed lymphatics. Recent evidence reveals that peri-tumoral or intra-tumoral lymphangiogenesis is a precursor for lymphatic metastasis in most carcinomas and melanomas. Two major lymphangiogenic factors, vascular endothelial growth factor (VEGF)-C and VEGF-D, are produced by cancer cells or immune cells such as macrophages in the tumor-stroma to promote sprouting of lymphatics from lymphatic endothelial cells (LEC) or LEC precursors (LECP) by binding to their primary (high affinity) receptor VEGF-R3 or secondary receptors VEGF-R2, neuropilin (NRP)2 and α9/β1 integrin. Many other growth factors/receptors such as VEGF-A/VEGF-R2, fibroblast growth factor (FGF)2/FGF-R, platelet-derived growth factor (PDGF)/PDGF-R, hepatocyte growth factor (HGF)/C-Met, angiopoietins (Ang)1, 2/Tie2, and chemokines/ chemokine receptors (CCL21/CCR7, CCL12/CCR4) can also stimulate LEC sprouting directly or indirectly. This review deals with the roles of prostaglandins (PG), in particular PGE2, in cancer-associated lymphangiogenesis, with special emphasis on breast cancer. We show that cyclooxygenase (COX)-2 expression by breast cancer cells or tumor stroma leading to high PGE2 levels in the tumor milieu promotes lymphangiogenesis and lymphatic metastases, resulting from binding of PGE2 to PGE receptors (EP, in particular EP4) on multiple cell types: tumor cells, tumor-infiltrating immune cells, and LEC. EP4 activation on cancer cells and macrophages upregulated VEGF-C/D production to stimulate LEC sprouting. Furthermore, ligation of EP4 with PGE2 on cancer or host cells can initiate a new cascade of molecular events leading to cross-talk between cancer cells and LEC, facilitating lymphangiogenesis and lympho-vascular transport of cancer cells. We make a case for EP4 as a potential therapeutic target for breast cancer.

Fluorescent reporter transgenic mice for in vivo live imaging of angiogenesis and lymphangiogenesis

The study of lymphangiogenesis is an emerging science that has revealed the lymphatic system as a central player in many pathological conditions including cancer metastasis, lymphedema, and organ graft rejection. A thorough understanding of the mechanisms of lymphatic growth will play a key role in the development of therapeutic strategies against these conditions. Despite the known potential of this field, the study of lymphatics has historically lagged behind that of hemangiogenesis. Until recently, significant strides in lymphatic studies were impeded by a lack of lymphatic-specific markers and suitable experimental models compared to those of the more immediately visible blood vasculature. Lymphangiogenesis has also been shown to be a key phenomenon in developmental biological processes, such as cell proliferation, guided migration, differentiation, and cell-to-cell communication, making lymphatic-specific visualization techniques highly desirable and desperately needed. Imaging modalities including immunohistochemistry and in situ hybridization are limited by the need to sacrifice animal models for tissue harvesting at every experimental time point. Moreover, the processes of mounting and staining harvested tissues may introduce artifacts that can confound results. These traditional methods for investigating lymphatic and blood vasculature are associated with several problems including animal variability (e.g., between mice) when replicating lymphatic growth environments and the cost concerns of prolonged, labor-intensive studies, all of which complicate the study of dynamic lymphatic processes. With the discovery of lymphatic-specific markers, researchers have been able to develop several lymphatic and blood vessel-specific, promoter-driven, fluorescent-reporter transgenic mice for visualization of lymphatics in vivo and in vitro. For instance, GFP, mOrange, tdTomato, and other fluorescent proteins can be expressed under control of a lymphatic-specific marker like Prospero-related homeobox 1 (Prox1), which is a highly conserved transcription factor for determining embryonic organogenesis in vertebrates that is implicated in lymphangiogenesis as well as several human cancers. Importantly, Prox1-null mouse embryos develop without lymphatic vessels. In human adults, Prox1 maintains lymphatic endothelial cells and upregulates proteins associated with lymphangiogenesis (e.g., VEGFR-3) and downregulates angiogenesis-associated gene expression (e.g., STAT6). To visualize lymphatic development in the context of angiogenesis, dual fluorescent-transgenic reporters, like Prox1-GFP/Flt1-DsRed mice, have been bred to characterize lymphatic and blood vessels simultaneously in vivo. In this review, we discuss the trends in lymphatic visualization and the potential usage of transgenic breeds in hemangiogenesis and lymphangiogenesis research to understand spatial and temporal correlations between vascular development and pathological progression.

Integrin binding site within the gC1q domain orchestrates EMILIN-1-induced lymphangiogenesis

Lymphatic vessels (LVs) play a pivotal role in the control of tissue homeostasis and also have emerged as important regulators of immunity, inflammation and tumor metastasis. EMILIN-1 is the first ECM protein identified as a structural modulator of the growth and maintenance of LV; accordingly, Emilin1^-/- mice display lymphatic morphological alterations leading to functional defects as mild lymphedema, leakage and compromised lymph drainage. Many EMILIN-1 functions are exerted by the binding of its gC1q domain with the E933 residue of α4 and α9β1 integrins. To investigate the specific regulatory role of this domain on lymphangiogenesis, we generated a transgenic mouse model expressing an E933A-mutated EMILIN-1 (E1-E933A), unable to interact with α4 or α9 integrin. The mutant resulted in abnormal LV architecture with dense, tortuous and irregular networks; moreover, the number of anchoring filaments was reduced and collector valves had aberrant narrowed structures. E933A mutation also affected lymphatic function in lymphangiography assays and made the transgenic mice more prone to lymph node metastases. The finding that the gC1q/integrin interaction is crucial for a correct lymphangiogenesis response was confirmed and reinforced by functional in vitro tubulogenesis assays. In addition, ex vivo thoracic-duct ring assays revealed that E1-E933A-derived lymphatic endothelial cells had a severe reduction in sprouting capacity and were unable to organize into capillary-like structures. All these data provide evidence that the novel "regulatory structural" role of EMILIN-1 in the lymphangiogenic process is played by the integrin binding site within its gC1q domain.

Targeting corneal inflammation by gene therapy: Emerging strategies for keratitis

Inflammation is the underlying process of several diseases within the eye, specifically in the cornea. Current treatment options for corneal inflammation or keratitis, and related neovascularization, are restricted by limited efficacy, adverse effects, and short duration of action. Gene therapy has shown great potential for the treatment of diseases affecting the ocular surface, and major efforts are being targeted to inflammatory mediators and neovascularization, in order to develop potential treatments for corneal inflammation. Gene therapy to treat ocular disorders is still starting, and current therapies are primarily experimental, with most human clinical trials still in research state, although some of them have already shown encouraging results. In this review, we focus on the progress and challenges of gene therapy to treat corneal inflammation. After introducing the inflammation process, we present the main nucleic acid delivery systems, including viral and non-viral vectors, and the most studied strategies to address the therapy: control of neovascularization and regulation of pro- and anti-inflammatory cytokines.

Cooperative Effects of Vascular Angiogenesis and Lymphangiogenesis

In this study, we modeled lymphangiogenesis and vascular angiogenesis in a microdevice using a tissue engineering approach. Lymphatic vessels (LV) and blood vessels (BV) were fabricated by sacrificial molding with seeding human lymphatic endothelial cells and human umbilical vein endothelial cells into molded microchannels (600 μm diameter). During subsequent perfusion culture, lymphangiogenesis and vascular angiogenesis were induced by addition of phorbol 12-myristate 13-acetate (PMA) and VEGF-C or VEGF-A characterized by podoplanin and Prox-1 expression. The lymphatic capillaries formed button-like junctions treated with dexamethasone. To test the potential for screening anti-angiogenic (vascular and lymphatic) factors, antagonists of VEGF were introduced. We found that an inhibitor of VEGF-R3 did not completely suppress lymphatic angiogenesis with BVs present, although lymphatic angiogenesis was selectively prevented by addition of a VEGF-R3 inhibitor without BVs. To probe the mechanism of action, we focus on matrix metalloproteinase (MMP) secretion by vascular endothelial cells and lymphatic endothelial cells under monoculture or co-culture conditions. We found that vascular angiogenesis facilitated lymphangiogenesis via remodeling of the local microenvironment by the increased secretion of MMP, mainly by endothelial cells. Applications of this model include a drug screening assay for corneal disease and models for tumorigenesis including lymphatic angiogenesis and vascular angiogenesis.

Isolation of Human Skin Lymphatic Endothelial Cells and 3D Reconstruction of the Lymphatic Vasculature In Vitro

Studies of lymphangiogenesis and lymphatic endothelial biology in vitro require pure cultures of lymphatic endothelial cells and 3D vascular constructs, which closely resemble native human lymphatic vasculature. We describe a method for the isolation of human dermal microvascular lymphatic endothelial cells and generation of a 3D lymphatic capillary network. The lymphatic vascular construct is generated by coculturing primary lymphatic endothelial cells and fibroblasts in their native matrix, without the use of synthetic scaffolds or exogenous factors. The tissue is stable over many weeks and accurately recapitulates features of human dermal lymphatic microvasculature.

TGFβ counteracts LYVE-1-mediated induction of lymphangiogenesis by small hyaluronan oligosaccharides

During tissue injury, inflammation, and tumor growth, enhanced production and degradation of the extracellular matrix glycosaminoglycan hyaluronan (HA) can lead to the accumulation of small HA (sHA) oligosaccharides. We have previously reported that accumulation of sHA in colorectal tumors correlates with lymphatic invasion and lymph node metastasis, and therefore, investigated here are the effects of sHA on the lymphatic endothelium. Using cultured primary lymphatic endothelial cells (LECs) and ex vivo and in vivo lymphangiogenesis assays, we found that in contrast to high-molecular-weight HA (HMW-HA), sHA of 4-25 disaccharides in length can promote the proliferation of LECs and lymphangiogenesis in a manner that is dependent on their size and concentration. At pathophysiologically relevant concentrations found in tumor interstitial fluid, sHA is pro-proliferative, acts synergistically with VEGF-C and FGF-2, and stimulates the outgrowth of lymphatic capillaries in ex vivo lymphangiogenesis assays. In vivo, intradermally injected sHA acts together with VEGF-C to increase lymphatic vessel density. Higher concentrations of sHA were found to induce expression of the anti-lymphangiogenic cytokine TGFβ in LECs, which serves to counter-regulate sHA-induced LEC proliferation and lymphangiogenesis. Using appropriate knockout mice and blocking antibodies, we found that the effects of sHA are mediated by the sialylated form of the lymphatic HA receptor LYVE-1, but not by CD44 or TLR-4. These data are consistent with the notion that accumulation of sHA in tumors may contribute to tumor-induced lymphangiogenesis, leading to increased dissemination to regional lymph nodes. KEY MESSAGES : sHA promotes lymphangiogenesis primarily through increased LEC proliferation sHA induces proliferation in a narrow concentration window due to upregulated TGFβ Smaller HA oligosaccharides more potently induce proliferation than larger ones VEGF-C and FGF-2-induced LEC proliferation and lymphangiogenesis is augmented by sHA Sialylated LYVE-1, but not CD44 or TLR-4, mediate the effects of sHA on LEC.

GABRA3 promotes lymphatic metastasis in lung adenocarcinoma by mediating upregulation of matrix metalloproteinases

Tumor metastasis is the main reason for the poor prognosis of lung cancer patients. The GABAA receptor subunit GABR_A3 is reportedly upregulated in lung cancer. Herein, we show that high GABR_A3 protein expression in lung adenocarcinoma correlated positively with disease stage, lymphatic metastasis status and poor patient survival. In addition, GABR_A3 induced MMP-2 and MMP-9 expression through activation of the JNK/AP-1 signaling pathway, which enhanced lymphatic metastasis by lung adenocarcinoma both in vitro and in vivo. These results indicate that GABR_A3 promotes lymph node metastasis and may thus be an effective therapeutic target for anticancer treatment.

Blockade of MMP-2 and MMP-9 inhibits corneal lymphangiogenesis

PURPOSE

To investigate the roles of a selective MMP-2 and -9 inhibitor (SB-3CT) in corneal inflammatory lymphangiogenesis.

METHODS

The expression of MMP-2 and -9 in the cornea after suture inplacement, treated with SB-3CT or negative control, was detected by real-time polymerase chain reaction (PCR). Inflammatory corneal neovascularization (NV) was induced by corneal suture placement. Mice were treated with SB-3CT eye drops (twice daily for 1 week, 5 μL per drop; 50, 100, or 200 μM). The outgrowth of blood and lymphatic vessels, and macrophage recruitment were analyzed by immunofluorescence assay. The expressions of vascular endothelial growth factor-C (VEGF-C) and its receptor VEGFR-3 were tested by real-time PCR.

RESULTS

MMP-2 and -9 expression were suppressed significantly by treatment with SB-3CT. The data demonstrated, for the first time, that SB-3CT strongly reduced corneal lymphangiogenesis and macrophage infiltration during inflammation. Furthermore, expressions of VEGF-C and its receptor VEGFR-3 were significantly inhibited by SB-3CT during corneal lymphangiogenesis.

CONCLUSIONS

These novel findings indicated that blockade of MMP-2 and -9 could inhibit lymphangiogenesis. Further investigation of this factor may provide novel therapies for transplant rejection and other lymphatic disorders.

Targeting VEGFR-3/-2 signaling pathways with AD0157: a potential strategy against tumor-associated lymphangiogenesis and lymphatic metastases

Background

Lymphatic metastasis is one of the leading causes of death in patients with different types of cancer and is the main prognostic factor for the disease survival. The formation of new lymphatic vessels (lymphangiogenesis) in primary tumors facilitates tumor cell dissemination to regional lymph nodes and correlates with distant metastases. Lymphangiogenesis has thus emerged as a suitable therapeutic target to block metastases, but no anti-lymphangiogenic compounds have been approved for clinical use to date. Therefore, new or improved therapies blocking lymphatic metastases are urgently required.

Methods

We established murine breast tumors to assess the effect of AD0157 on tumor growth, lymphangiogenesis, and lymphatic dissemination. Then, a battery of in vivo (mouse corneal neovascularization and ear sponges), ex vivo (mouse lymphatic rings and rat mesentery explants), and in vitro (proliferation, tubulogenesis, wound-healing, Boyden chambers, and spheroids) assays was used to give insight into the lymphangiogenic steps affected by AD0157. Finally, we investigated the molecular pathways controlled by this drug.

Results

AD0157 was found to inhibit the growth of human breast cancer xenografts in mice, to strongly reduce tumor-associated lymphangiogenesis and to block metastatic dissemination to both lymph nodes and distant organs. The high anti-lymphangiogenic potency of AD0157 was further supported by its inhibitory activity at low micromolar range in two in vivo pathological models and in two ex vivo assays. In addition, AD0157 inhibited lymphatic endothelial cell proliferation, migration and invasion, cellular sprouting, and tube formation. Mechanistically, this compound induced apoptosis in lymphatic endothelial cells and decreased VEGFR-3/-2, ERK1/2, and Akt phosphorylations.

Conclusions

These findings demonstrate the suitability of AD0157 to suppress tumor-associated lymphangiogenesis. Beyond discovering a new potent anti-lymphangiogenic drug that is worth considering in future clinical settings, our study supports the interest of designing anti-lymphangiogenic therapies to avoid distant metastatic processes.

Electronic supplementary material

The online version of this article (doi:10.1186/s13045-017-0484-1) contains supplementary material, which is available to authorized users.

A Mathematical Model of Lymphangiogenesis in a Zebrafish Embryo

The lymphatic system of a vertebrate is important in health and diseases. We propose a novel mathematical model to elucidate the lymphangiogenic processes in zebrafish embryos. Specifically, we are interested in the period when lymphatic endothelial cells (LECs) exit the posterior cardinal vein and migrate to the horizontal myoseptum of a zebrafish embryo. We wonder whether vascular endothelial growth factor C (VEGFC) is a morphogen and a chemotactic factor for these LECs. The model considers the interstitial flow driving convection, the reactive transport of VEGFC, and the changing dynamics of the extracellular matrix in the embryo. Simulations of the model illustrate that VEGFC behaves very differently in diffusion and convection-dominant scenarios. In the former case, it must bind to the matrix to establish a functional morphogen gradient. In the latter case, the opposite is true and the pressure field is the key determinant of what VEGFC may do to the LECs. Degradation of collagen I, a matrix component, by matrix metallopeptidase 2 controls the spatiotemporal dynamics of VEGFC. It controls whether diffusion or convection is dominant in the embryo; it can create channels of abundant VEGFC and scarce collagen I to facilitate lymphangiogenesis; when collagen I is insufficient, VEGFC cannot influence the LECs at all. We predict that VEGFC is a morphogen for the migrating LECs, but it is not a chemotactic factor for them.

Effects of fatty acid synthase inhibitors on lymphatic vessels: an in vitro and in vivo study in a melanoma model

Fatty acid synthase (FASN) is responsible for the endogenous production of fatty acids from acetyl-CoA and malonyl-CoA. Its overexpression is associated with poor prognosis in human cancers including melanomas. Our group has previously shown that the inhibition of FASN with orlistat reduces spontaneous lymphatic metastasis in experimental B16-F10 melanomas, which is a consequence, at least in part, of the reduction of proliferation and induction of apoptosis. Here, we sought to investigate the effects of pharmacological FASN inhibition on lymphatic vessels by using cell culture and mouse models. The effects of FASN inhibitors cerulenin and orlistat on the proliferation, apoptosis, and migration of human lymphatic endothelial cells (HDLEC) were evaluated with in vitro models. The lymphatic outgrowth was evaluated by using a murine ex vivo assay. B16-F10 melanomas and surgical wounds were produced in the ears of C57Bl/6 and Balb-C mice, respectively, and their peripheral lymphatic vessels evaluated by fluorescent microlymphangiography. The secretion of vascular endothelial growth factor C and D (VEGF-C and -D) by melanoma cells was evaluated by ELISA and conditioned media used to study in vitro lymphangiogenesis. Here, we show that cerulenin and orlistat decrease the viability, proliferation, and migration of HDLEC cells. The volume of lymph node metastases from B16-F10 experimental melanomas was reduced by 39% in orlistat-treated animals as well as the expression of VEGF-C in these tissues. In addition, lymphatic vessels from orlistat-treated mice drained more efficiently the injected FITC-dextran. Orlistat and cerulenin reduced VEGF-C secretion and, increase production of VEGF-D by B16-F10 and SK-Mel-25 melanoma cells. Finally, reduced lymphatic cell extensions, were observed following the treatment with conditioned medium from cerulenin- and orlistat-treated B16-F10 cells. Altogether, our results show that FASN inhibitors have anti-metastatic effects by acting on lymphatic endothelium and melanoma cells regardless the increase of lymphatic permeability promoted by orlistat.

Quantitative evaluation of single cell spread on collagen matrices

Cells change their morphology as a response to environmental cues. The quantitative evaluation of single cell spread on extracellular matrices, such as type I collagen, is a key tool in cancer research. Inherent to the manual scoring of cellular spread is inter-observer but also intra-observer variation. To overcome these problems, we have developed the Morphology Analysis Software (MAS). MAS scores phase-contrast images of cells on native type I collagen gels and identifies whether a cell has a spread or round morphology using a combination of four unique parameters: the presence of a cellular extension, the cell area, the cell eccentricity and cell circularity. The MAS software scores are equivalent to the average score of five independent observers but MAS is faster, more objective and standardized. A functional screening assay using six cytokines identified TGFα as a stimulator of HCT8/E11 and SK-BR-3 single cell spreading on top of type I collagen gels. This change in morphology correlates with increased migration potential as evidenced by xCELLigence migration assays and are counteracted by EGFR signaling pathway inhibitors. This underscores the use of morphology classification on a population of unlabeled cells as read-out of an important cancer cell property and the potential for the MAS software in drug screening strategies.

Tumor-associated macrophages induce capillary morphogenesis of lymphatic endothelial cells derived from human gastric cancer

Tumor lymphangiogenesis is a major prognostic indicator of gastric cancer. Tumor‐induced inflammation has been shown to attract tumor‐associated macrophages that affect lymphangiogenesis. However, detailed mechanisms of macrophage‐induced lymphangiogenesis have not been elucidated. Here, we evaluated the interaction between tumor‐associated macrophages and lymphatic endothelial cells (LECs) derived from lymph nodes (LNs) of human gastric cancer. Lymphatic endothelial cells were directly or indirectly cocultured with macrophages from healthy human blood, with or without the supernatant of the gastric cancer cell line, OCUM‐12. We analyzed the effect of cancer pretreated macrophages and of macrophages from metastatic LNs of gastric cancer on LECs. We observed morphological changes of LECs in coculture and assessed the gene expression of possible lymphangiogenic molecules of macrophages and LECs after contact coculture, and of cancer pretreated macrophages, by quantitative RT‐PCR. Specimens of metastatic LN of gastric cancer were immunofluorescently stained. We found that tubulogenesis of LECs was observed only in the contact coculture model. OCUM‐12 cells promoted macrophage‐induced tubulogenesis of LECs. Relative gene expression of MMP and adhesion molecules was significantly upregulated in both capillary‐forming LECs and cocultured macrophages. Cancer pretreated macrophages upregulated lymphangiogenic factors including inflammatory cytokines, MMPs, adhesion molecules, and vascular endothelial growth factor‐C. Blocking of intercellular adhesion molecule‐1 and macrophage activation suppressed tubulogenesis of LECs. Immunohistochemistry showed macrophages localized around lymphatic vessels. Our results suggested that interaction between LECs and macrophages may be an important initial step of tumor lymphangiogenesis developing LN metastasis. Understanding of its mechanisms could be useful for future therapeutics of gastric cancer.

Novel application assigned to toluquinol: inhibition of lymphangiogenesis by interfering with VEGF-C/VEGFR-3 signalling pathway

BACKGROUND AND PURPOSE

Lymphangiogenesis is an important biological process associated with the pathogenesis of several diseases, including metastatic dissemination, graft rejection, lymphoedema and other inflammatory disorders. The development of new drugs that block lymphangiogenesis has become a promising therapeutic strategy. In this study, we investigated the ability of toluquinol, a 2-methyl-hydroquinone isolated from the culture broth of the marine fungus Penicillium sp. HL-85-ALS5-R004, to inhibit lymphangiogenesis in vitro, ex vivo and in vivo.

EXPERIMENTAL APPROACH

We used human lymphatic endothelial cells (LECs) to analyse the effect of toluquinol in 2D and 3D in vitro cultures and in the ex vivo mouse lymphatic ring assay. For in vivo approaches, the transgenic Fli1:eGFPy1 zebrafish, mouse ear sponges and cornea models were used. Western blotting and apoptosis analyses were carried out to search for drug targets.

KEY RESULTS

Toluquinol inhibited LEC proliferation, migration, tubulogenesis and sprouting of new lymphatic vessels. Furthermore, toluquinol induced apoptosis of LECs after 14 h of treatment in vitro, blocked the development of the thoracic duct in zebrafish and reduced the VEGF-C-induced lymphatic vessel formation and corneal neovascularization in mice. Mechanistically, we demonstrated that this drug attenuates VEGF-C-induced VEGFR-3 phosphorylation in a dose-dependent manner and suppresses the phosphorylation of Akt and ERK1/2.

CONCLUSIONS AND IMPLICATIONS

Based on these findings, we propose toluquinol as a new candidate with pharmacological potential for the treatment of lymphangiogenesis-related pathologies. Notably, its ability to suppress corneal neovascularization paves the way for applications in vascular ocular pathologies.

Quantitative Assessment of Mouse Mammary Gland Morphology Using Automated Digital Image Processing and TEB Detection

The assessment of rodent mammary gland morphology is largely used to study the molecular mechanisms driving breast development and to analyze the impact of various endocrine disruptors with putative pathological implications. In this work, we propose a methodology relying on fully automated digital image analysis methods including image processing and quantification of the whole ductal tree and of the terminal end buds as well. It allows to accurately and objectively measure both growth parameters and fine morphological glandular structures. Mammary gland elongation was characterized by 2 parameters: the length and the epithelial area of the ductal tree. Ductal tree fine structures were characterized by: 1) branch end-point density, 2) branching density, and 3) branch length distribution. The proposed methodology was compared with quantification methods classically used in the literature. This procedure can be transposed to several software and thus largely used by scientists studying rodent mammary gland morphology.

Heterochromatin Protein 1 Alpha (HP1α: CBX5) is a Key Regulator in Differentiation of Endothelial Progenitor Cells to Endothelial Cells

As the ability to control the differentiation of endothelial stem/progenitor cells (EPCs) into vascular endothelial cell lineages could be useful for promoting neovascularization, it is important to obtain a deeper understanding of the epigenetic mechanisms that regulate EPC differentiation and neovascularization. Heterochromatin protein 1α (HP1α) is known to be involved in the epigenetic regulation of gene silencing. However, recent reports demonstrate that HP1α can also activate gene expression during cell differentiation. In this study, microarray analysis revealed that HP1α expression was induced during EPC differentiation and is associated with the expression of outgrowing endothelial cell (OEC)-specific protein markers. To explore the role of HP1α in the differentiation of EPCs to OECs, its expression was knocked-down or over-expressed in differentiating EPCs. Overexpression of HP1α promoted the differentiation and angiogenic activity of EPCs in vitro and in vivo, whereas knockdown of HP1α led to a defect in OEC migration, tube formation, and angiogenic sprouting activity. Gene expression profiling showed increased expression of angiogenic genes, including NOTCH1, cadherin-5, and angiopoietin-like-2, and decreased expression of progenitor cell marker genes, including CD133, CXCR4, and C-KIT, in HP1α-overexpressing EPCs. Also, increased HP1α at an early stage of EPC differentiation may regulate angiogenic gene transcription by interacting with chromatin that modifies epigenetic factors such as the methyl-CpG binding domain, Polycomb group ring finger 2, and DNA methyltransferases. Our findings demonstrate, for the first time, that HP1α plays an important role in the differentiation and angiogenic function of EPCs by regulating endothelial gene expression. Stem Cells 2015;33:1512-1522.

Cell-based approach for 3D reconstruction of lymphatic capillaries in vitro reveals distinct functions of HGF and VEGF-C in lymphangiogenesis

Regeneration of lymphatic vessels is important for treatment of various disorders of lymphatic system and for restoration of lymphatic function after surgery. We have developed a method for generating a human 3D lymphatic vascular construct. In this system, human lymphatic endothelial cells, co-cultured with fibroblasts, spontaneously organized into a stable 3D lymphatic capillary network without the use of any exogenous factors. In vitro-generated lymphatic capillaries exhibited the major molecular and ultra-structural features of native, human lymphatic microvasculature: branches in the three dimensions, wide lumen, blind ends, overlapping borders, adherens and tight junctions, anchoring filaments, lack of mural cells, and poorly developed basement membrane. Furthermore, we show that fibroblast-derived VEGF-C and HGF cooperate in the formation of lymphatic vasculature by activating ERK1/2 signaling, and demonstrate distinct functions of HGF/c-Met and VEGF-C/VEGFR-3 in lymphangiogenesis. This lymphatic vascular construct is expected to facilitate studies of lymphangiogenesis in vitro and it holds promise as a strategy for regeneration of lymphatic vessels and treatment of lymphatic disorders in various conditions.

Three-dimensional biomimetic model to reconstitute sprouting lymphangiogenesis in vitro

Formation of new lymphatic vessels, termed lymphangiogenesis, is central for diverse biological processes during development, inflammation and tumor metastasis. However, reliable in vitro model is still under demand for detailed elucidation of how sprouting lymphangiogenesis is initiated and coordinated. Here, we describe a microfluidic platform optimized for close reconstitution of lymphangiogenesis, achieved by on-chip integration of salient constituents of lymphatic microenvironment found in vivo. With flexible and precise control over the factors that include biochemical cues, interstitial flow (IF), and endothelial-stromal interactions, we found that orchestrated efforts of multiple environmental factors are necessary for robust lymphatic sprouting in 3D extracellular matrix. Especially, we demonstrate that IF serves as a central regulatory cue which defines lymphangiogenic responses and phenotypes of lymphatic endothelial cells. When synergized with pro-lymphangiogenic factors, IF significantly augmented initiation and outgrowth of lymphatic sprouts toward upstream of the flow while suppressing downstream-directed sprouting. In an appropriate synergism, lymphatic sprouts exhibited structural, molecular signatures and cellular phenotypes that closely approximate sprouting lymphatic neovessels in vivo, and precisely reflected the modulatory effects of pro- and anti-lymphangiogenic stimuli. Our study not only reveals critical but unappreciated role of mechanical cue that regulates lymphangiogenic sprouting, but also provides a novel biomimetic model that may leverage further biological studies as well as phenotypic drug screening.

VEGF-C induces lymphangiogenesis and angiogenesis in the rat mesentery culture model

OBJECTIVE

Lymphatic and blood microvascular systems are critical for tissue function. Insights into the coordination of both systems can be gained by investigating the relationships between lymphangiogenesis and angiogenesis. Recently, our laboratory established the rat mesentery culture model as a novel tool to investigate multicellular interactions during angiogenesis in an intact microvascular network scenario. The objective of this study was to determine whether the rat mesentery culture model can be used to study lymphangiogenesis.

METHODS

Mesenteric tissue windows were harvested from adult male Wistar rats and cultured for three or five days in either serum-free MEM or MEM supplemented with VEGF-C. Tissues were immunolabeled for PECAM and LYVE-1 to identify blood and lymphatic endothelial cells, respectively. Tissues selected randomly from those containing vascular networks were quantified for angiogenesis and lymphangiogenesis.

RESULTS

VEGF-C treatment resulted in an increase in the density of blood vessel sprouting compared to controls by day 3. By day 5, lymphatic sprouting was increased compared to controls.

CONCLUSIONS

These results are consistent with in vivo findings that lymphangiogenesis lags angiogenesis after chronic stimulation and establish a tool for investigating the interrelationships between lymphangiogenesis and angiogenesis in a multisystem microvascular environment.

Inhibition of TGFBIp expression reduces lymphangiogenesis and tumor metastasis

Transforming growth factor-β-induced protein (TGFBIp) is an extracellular matrix protein that has a role in a wide range of pathological conditions. However, the role of TGFBIp signaling in lymphangiogenesis is poorly understood. The purpose of this study was therefore to analyze the effects of TGFBIp on lymphangiogenesis and determine whether TGFBIp-related lymphangiogenesis is important for the metastasis of tumor cells. TGFBIp increased adhesion, migration, and morphologic differentiation of human lymphatic endothelial cells (LECs), consistent with an increase in lymphatic vessel sprouting in a three-dimensional lymphatic ring assay. TGFBIp also induced phosphorylation of intracellular signaling molecules SRC, FAK, AKT, JNK and ERK. TGFBIp-induced lymphatic vessel sprouting was inhibited by addition of anti-integrin β3 antibody and pharmacologic inhibitors of FAK, AKT, JNK or ERK. TGFBIp increased both CCL21 expression in LECs, a chemokine that actively recruits tumor cells expressing the cognate chemokine receptors to lymphatic vessels and LEC permeability by inducing the dissociation of VE-cadherin junctions between LECs via the activation of SRC signaling. In vivo, inhibition of TGFBIp expression in SW620 cancer cells dramatically reduced tumor lymphangiogenesis and metastasis. Collectively, our findings demonstrate that TGFBIp is a lymphangiogenic factor contributing to tumor dissemination and represents a potential target to inhibit metastasis.