Experimental models to study lymphatic and blood vascular metastasis

Prox1-GFP/Flt1-DsRed transgenic mice: an animal model for simultaneous live imaging of angiogenesis and lymphangiogenesis

The roles of angiogenesis in development, health, and disease have been studied extensively; however, the studies related to lymphatic system are limited due to the difficulty in observing colorless lymphatic vessels. But recently, with the improved technique, the relative importance of the lymphatic system is just being revealed. We bred transgenic mice in which lymphatic endothelial cells express GFP (Prox1-GFP) with mice in which vascular endothelial cells express DsRed (Flt1-DsRed) to generate Prox1-GFP/Flt1-DsRed (PGFD) mice. The inherent fluorescence of blood and lymphatic vessels allows for direct visualization of blood and lymphatic vessels in various organs via confocal and two-photon microscopy and the formation, branching, and regression of both vessel types in the same live mouse cornea throughout an experimental time course. PGFD mice were bred with CDh5CreERT2 and VEGFR2lox knockout mice to examine specific knockouts. These studies showed a novel role for vascular endothelial cell VEGFR2 in regulating VEGFC-induced corneal lymphangiogenesis. Conditional deletion of vascular endothelial VEGFR2 abolished VEGFA- and VEGFC-induced corneal lymphangiogenesis. These results demonstrate the potential use of the PGFD mouse as a powerful animal model for studying angiogenesis and lymphangiogenesis.

Modeling pre-metastatic lymphvascular niche in the mouse ear sponge assay

Lymphangiogenesis, the formation of new lymphatic vessels, occurs in primary tumors and in draining lymph nodes leading to pre-metastatic niche formation. Reliable in vivo models are becoming instrumental for investigating alterations occurring in lymph nodes before tumor cell arrival. In this study, we demonstrate that B16F10 melanoma cell encapsulation in a biomaterial, and implantation in the mouse ear, prevents their rapid lymphatic spread observed when cells are directly injected in the ear. Vascular remodeling in lymph nodes was detected two weeks after sponge implantation, while their colonization by tumor cells occurred two weeks later. In this model, a huge lymphangiogenic response was induced in primary tumors and in pre-metastatic and metastatic lymph nodes. In control lymph nodes, lymphatic vessels were confined to the cortex. In contrast, an enlargement and expansion of lymphatic vessels towards paracortical and medullar areas occurred in pre-metastatic lymph nodes. We designed an original computerized-assisted quantification method to examine the lymphatic vessel structure and the spatial distribution. This new reliable and accurate model is suitable for in vivo studies of lymphangiogenesis, holds promise for unraveling the mechanisms underlying lymphatic metastases and pre-metastatic niche formation in lymph nodes, and will provide new tools for drug testing.

Intravital Imaging Reveals Dynamics of Lymphangiogenesis and Valvulogenesis

Lymphatic research signifies a field of rapid progression in recent years. Though lymphatic dysfunction has been found in a myriad of disorders, to date, few effective treatments are available for lymphatic diseases. It is therefore urgent to develop new experimental approaches and therapeutic protocols. The cornea offers an ideal site for lymphatic research due to its transparent nature, accessible location, and lymphatic-free but -inducible features. Moreover, we have recently discovered that corneal lymphatic vessels develop luminal valves as lymphangiogenesis proceeds. This tissue thus provides an optimal tool to study both lymphangiogenesis and valvulogenesis upon a pathological insult. In this paper, we show that the modified Prox-1-GFP mice carrying wildtype C57BL/6 background provide a valuable tool for intravital imaging of corneal lymphatic vessels and valves and can be used to study pathological lymphangiogenesis induced by various insults. Further, we demonstrate the multifaceted dynamics of lymphangiogenesis and valvulogenesis associated with transplantation, from the initiation to regression phases, and report several novel and critical phenomena and mechanisms that cannot be detected by conventional ex vivo approaches. Further investigation holds the great potential for divulging new mechanisms and therapeutic strategies for lymphangiogenesis and lymphangiogenesis-related diseases at various stages and inside or outside the eye.

Walking the Line: A Fibronectin Fiber-Guided Assay to Probe Early Steps of (Lymph)angiogenesis

Angiogenesis and lymphangiogenesis are highly complex morphogenetic processes, central to many physiological and pathological conditions, including development, cancer metastasis, inflammation and wound healing. While it is described that extracellular matrix (ECM) fibers are involved in the spatiotemporal regulation of angiogenesis, current angiogenesis assays are not specifically designed to dissect and quantify the underlying molecular mechanisms of how the fibrillar nature of ECM regulates vessel sprouting. Even less is known about the role of the fibrillar ECM during the early stages of lymphangiogenesis. To address such questions, we introduced here an in vitro (lymph)angiogenesis assay, where we used microbeads coated with endothelial cells as simple sprouting sources and deposited them on single Fn fibers used as substrates to mimic fibrillar ECM. The fibers were deposited on a transparent substrate, suitable for live microscopic observation of the ensuing cell outgrowth events at the single cell level. Our proof-of-concept studies revealed that fibrillar Fn, compared to Fn-coated surfaces, provides far stronger sprouting and guidance cues to endothelial cells, independent of the tested mechanical strains of the Fn fibers. Additionally, we found that VEGF-A, but not VEGF-C, stimulates the collective outgrowth of lymphatic endothelial cells (LEC), while the collective outgrowth of blood vascular endothelial cells (HUVEC) was prominent even in the absence of these angiogenic factors. In addition to the findings presented here, the modularity of our assay allows for the use of different ECM or synthetic fibers as substrates, as well as of other cell types, thus expanding the range of applications in vascular biology and beyond.

Corneal lymphatic valve formation in relation to lymphangiogenesis

PURPOSE

We have recently provided evidence showing that luminal lymphatic valves are formed right after the onset of corneal inflammatory lymphangiogenesis (LG). The purpose of this study was to further characterize the long-term time course, spatial distribution, directional orientation, and functional implications of the valve formation in relation to corneal LG.

METHODS

Corneal LG was induced in normal adult BALB/c mice by a modified suture placement model with equal distribution in the nasal and temporal side. Whole-mount corneas were harvested every 2 weeks for up to 8 weeks post suturing for immunofluorescent microscopic assays. Quantitative analysis on both lymphatic vessels and valves was performed by using National Institutes of Health ImageJ software. Corneal lymphatic live imaging was performed to show functional drainage of the valves.

RESULTS

Lymphatic vessel invasion areas at 4, 6, and 8 weeks were significantly less than the peak at 2 weeks post corneal suturing. In contrast, the ratio of lymphatic valves to vessel invasion area was at its lowest at 2 weeks with a peak approximately at 6 weeks post suturing. Lymphatic valves were more localized in the nasal quadrant at all time points studied, and most of the well-formed valves were directionally oriented toward the limbus. The lymphatic valves function to guide lymphatic drainage outside the cornea.

CONCLUSIONS

This study presents new insights into corneal lymphatic valve formation and function in inflammatory LG. Further investigation on lymphatic valves may provide novel strategies to interfere with lymphatic maturation and function and to treat lymphatic-related disorders.

Protective effects of matrix metalloproteinase-12 following corneal injury

Corneal scarring due to injury is a leading cause of blindness worldwide and results from dysregulated inflammation and angiogenesis during wound healing. Here we demonstrate that the extracellular matrix metalloproteinase MMP12 (macrophage metalloelastase) is an important regulator of these repair processes. Chemical injury resulted in higher expression of the fibrotic markers α-smooth muscle actin and type I collagen, and increased levels of angiogenesis in corneas of Mmp12(-/-) mice compared with corneas of wild-type mice. In vivo, we observed altered immune cell dynamics in Mmp12(-/-) corneas by confocal imaging. We determined that the altered dynamics were the result of an altered inflammatory response, with delayed neutrophil infiltration during the first day and excessive macrophage infiltration 6 days later, mediated by altered expression levels of chemokines CXCL1 and CCL2, respectively. Corneal repair returned to normal upon inhibition of these chemokines. Taken together, these data show that MMP12 has a protective effect on corneal fibrosis during wound repair through regulation of immune cell infiltration and angiogenesis.

[Proteome profiling for the identification of lung cancer signatures]

在新近蛋白质组学的发展中，对疾病蛋白质组的综合和深入研究已成为重要议题。已有研究报道了在包括肺癌在内的不同疾病中发现的一些生物标志物，有一些在肺癌诊断和预测中有潜在价值。然而，它们很少作为器官特异性生物标志物以充分比较不同肿瘤类别的模型。本文评价了最近发表的一项在不同基因工程小鼠模型中进行比较蛋白质组的研究，并阐明已发现标志物在人肺癌诊断中的有效性及应用。

Proteome profiling for the identification of lung cancer signatures

Comprehensive and in-depth discovery of the disease proteome is an important issue in recent proteomics developments. Previous studies have shown a number of biomarkers discovered in various diseases, including lung cancer. Some of them are potentially useful in lung cancer diagnostics and prognostics. However, few of them can act as organ-specific biomarkers to extensively compare multiple cancer models. This article evaluates a recently published study employing comparative proteomics on multiple genetically engineered mouse models and sheds light on the usefulness and application of the discovered marker panel for human lung cancer diagnostics.

Conjunctival lymphatic response to corneal inflammation in mice

Due to its unique characteristics, the cornea has been widely used for vascular research. However, it has never been studied whether lymphatic vessels in the conjunctiva, its neighboring tissue, are affected by corneal lymphangiogenesis (LG). The purpose of this study was to investigate whether the distribution pattern of conjunctival lymphatic vessels changes during LG using a standardized two-suture placement model. Our data from immunofluorescent microscopic studies demonstrate, for the first time, that conjunctival lymphatic vessels were more distributed in the nasal side under both normal and inflamed conditions. Additionally, under the inflamed condition, conjunctival lymphatic vessels showed a higher density and more branching points, indicating that LG occurs in the conjunctiva in response to corneal inflammation. This study not only provides novel insights into lymphatic events in the ocular surface but also offers new guidelines for developing therapeutic strategies to treat lymphatic diseases at related sites.

Increased lymphangiogenesis and hemangiogenesis in infant cornea

BACKGROUND

Corneal lymphangiogenesis (LG) and hemangiogenesis (HG) accompany many diseases after inflammatory, infectious, traumatic or chemical insults. They also contribute to transplant rejection. It is known that corneal transplants in infants or children have a higher rejection rate than in adults. However, it has never been studied whether infant corneas differ from adult corneas in inflammatory LG, HG, or both, which is the focus of this study.

METHODS AND RESULTS

Corneal inflammatory LG and HG were induced by a standard suture placement model in C57BL/6 mice of 3 weeks and 8 weeks of age, respectively. Corneal LG, HG, and macrophage infiltration were assessed by immunofluorescent microscopic studies using specific antibodies against CD31 (a panendothelial cell marker), LYVE-1 (a lymphatic marker), and F4/80 (a macrophage marker). Blood vessels were also examined by ophthalmic slit-lamp microscopic assays in vivo. Digital images were analyzed by NIH Image J software. It was found, for the first time, that infant corneas exhibited a higher level of LG, HG, and macrophage infiltration during inflammation. Infant lymphatic and blood vessels demonstrated greater density and invasion area but similar branching points. Additionally, infant lymphatic vessels were also of larger diameter.

CONCLUSIONS

Infant and adult corneas differ greatly in their inflammatory responses of LG, HG, and macrophage infiltration. These novel findings will shed some light on our understanding of the LG and HG processes, as well as the development of new therapeutic protocols for corneal diseases, particularly, in infants or children, where an early restoration of sight is critically important in preventing amblyopia or permanent vision loss.

Combined blockade of VEGFR-3 and VLA-1 markedly promotes high-risk corneal transplant survival

PURPOSE. High-risk corneal transplantation refers to grafting performed on inflamed and highly vascularized host beds. It represents a clinical dilemma because the rejection rate can be as high as 90%, irrespective of current treatment modalities. This study was conducted to investigate whether combined blockade of VEGFR-3 (vascular endothelial growth factor receptor-3) and VLA-1 (very late antigen-1) promotes high-risk transplant survival and how it correlates with corneal lymphangiogenesis and hemangiogenesis before and after transplantation. METHODS. High-risk corneal transplantation was performed between normal C57BL/6 (donor) and inflamed BALB/c (recipient) mice. The recipients were randomized to receive intraperitoneal injections of VEGFR-3 and VLA-1-neutralizing antibodies or their controls twice a week for up to 8 weeks after transplantation. Corneal grafts were evaluated by ophthalmic slit-lamp biomicroscopy and analyzed by Kaplan-Meier survival curve. Additionally, whole-mount corneas before and after transplantation were examined by immunofluorescent microscopic assays, and the correlation between lymphatic or blood vessel distribution and transplant outcome was analyzed. RESULTS. The combined blockade markedly promotes 90% survival of high-risk transplants. This strategy specifically modified host beds by selective inhibition of lymphangiogenesis but not hemangiogenesis. A strong correlation was also identified between high-risk transplant rejection and severe lymphatic invasion reaching the donor-graft border. CONCLUSIONS. These novel findings not only provide a new and potentially powerful strategy to promote high-risk transplant survival, they also confirm a critical role of high-degree lymphangiogenesis in mediating high-risk transplant rejection. Results from this study may also shed new light on our understanding and management of other lymphatic- and immune-related diseases in general.

Novel characterization of lymphatic valve formation during corneal inflammation

Lymphatic research has progressed rapidly in recent years. Though lymphatic dysfunction has been found in a wide array of disorders from transplant rejection to cancer metastasis, to date, there is still little effective treatment for lymphatic diseases. The cornea offers an optimal site for lymphatic research due to its accessible location, transparent nature, and lymphatic-free but inducible features. However, it still remains unknown whether lymphatic valves exist in newly formed lymphatic vessels in the cornea, and how this relates to an inflammatory response. In this study, we provide the first evidence showing that lymphatic valves were formed in mouse cornea during suture-induced inflammation with the up-regulation of integrin alpha 9. The number of corneal valves increased with the progression of inflammatory lymphangiogenesis. Moreover, we have detected lymphatic valves at various developmental stages, from incomplete to more developed ones. In addition to defining the average diameter of lymphatic vessels equipped with lymphatic valves, we also report that lymphatic valves were more often located near the branching points. Taken together, these novel findings not only provide new insights into corneal lymphatic formation and maturation, but also identify a new model for future investigation on lymphatic valve formation and possibly therapeutic intervention.