The mouse cornea micropocket angiogenesis assay

Akt1-dependent expression of angiopoietin 1 and 2 in vascular smooth muscle cells leads to vascular stabilization

Retinal angiogenesis was delayed in VSMC-specific Akt1-deficient mice (Akt1^∆SMC) but not in Akt2^∆SMC mice. The proliferation of ECs, recruitment of pericytes, and coverage of VSMCs to the endothelium were defective in Akt1^∆SMC. The silencing of Akt1 in VSMCs led to the downregulation of angiopoietin 1 (Ang1) and the upregulation of Ang2. The activation of Notch3 in VSMCs was significantly reduced in the retinas of Akt1^∆SMC mice. Silencing Akt1 suppressed the activation of Notch3. Moreover, the silencing of Notch3 downregulated Ang1, whereas the overexpression of Notch3 intracellular domain (NICD3) enhanced Ang1 expression. The nuclear localization and transcriptional activity of yes-associated protein (YAP) were affected by the expression level of Akt1. Silencing YAP downregulated Ang2 expression, whereas overexpression of YAP showed the opposite results. Ang1 antibody and Ang2 suppressed endothelial sprouting of wild-type aortic tissues, whereas the Ang2 antibody and Ang1 facilitated the endothelial sprouting of aortic tissues from Akt1^∆SMC mice. Finally, severe hemorrhage was observed in Akt1^∆SMC mice, which was further facilitated under streptozotocin (STZ)-induced diabetic conditions. Therefore, the Akt1-Notch3/YAP-Ang1/2 signaling cascade in VSMCs might play an essential role in the paracrine regulation of endothelial function.

Capillary morphogenesis gene 2 (CMG2) mediates growth factor-induced angiogenesis by regulating endothelial cell chemotaxis

Anthrax protective antigen (PA) is a potent inhibitor of pathological angiogenesis with an unknown mechanism. In anthrax intoxication, PA interacts with capillary morphogenesis gene 2 (CMG2) and tumor endothelial marker 8 (TEM8). Here, we show that CMG2 mediates the antiangiogenic effects of PA and is required for growth-factor-induced chemotaxis. Using specific inhibitors of CMG2 and TEM8 interaction with natural ligand, as well as mice with the CMG2 or TEM8 transmembrane and intracellular domains disrupted, we demonstrate that inhibiting CMG2, but not TEM8 reduces growth-factor-induced angiogenesis in the cornea. Furthermore, the antiangiogenic effect of PA was abolished when the CMG2, but not the TEM8, gene was disrupted. Binding experiments demonstrated a broad ligand specificity for CMG2 among extracellular matrix (ECM) proteins. Ex vivo experiments demonstrated that CMG2 (but not TEM8) is required for PA activity in human dermal microvascular endothelial cell (HMVEC-d) network formation assays. Remarkably, blocking CMG2-ligand binding with PA or CRISPR knockout abolishes endothelial cell chemotaxis but not chemokinesis in microfluidic migration assays. These effects are phenocopied by Rho inhibition. Because CMG2 mediates the chemotactic response of endothelial cells to peptide growth factors in an ECM-dependent fashion, CMG2 is well-placed to integrate growth factor and ECM signals. Thus, CMG2 targeting is a novel way to inhibit angiogenesis.

Targeting HIF-1α by newly synthesized Indolephenoxyacetamide (IPA) analogs to induce anti-angiogenesis-mediated solid tumor suppression

BACKGROUND

Hypoxic microenvironment is a common feature of solid tumors, which leads to the promotion of cancer. The transcription factor, HIF-1α, expressed under hypoxic conditions stimulates tumor angiogenesis, favoring HIF-1α as a promising anticancer agent. On the other hand, synthetic Indolephenoxyacetamide derivatives are known for their pharmacological potentiality. With this background here, we have synthesized, characterized, and validated the new IPA (8a-n) analogs for anti-tumor activity.

METHODS

The new series of IPA (8a-n) were synthesized through a multi-step reaction sequence and characterized based on the different spectroscopic analysis FT-IR, ¹H, ¹³C NMR, mass spectra, and elemental analyses. Cell-based screening of IPA (8a-n) was assessed by MTT assay. Anti-angiogenic efficacy of IPA (8k) validated through CAM, Rat corneal, tube formation and migration assay. The underlying molecular mechanism is validated through zymogram and IB studies. The in vivo anti-tumor activity was measured in the DLA solid tumor model.

RESULTS

Screening for anti-proliferative studies inferred, IPA (8k) is a lead molecule with an IC₅₀ value of _˜5 μM. Anti-angiogenic assays revealed the angiopreventive activity through inhibition of HIF-1α and modulation downstream regulatory genes, VEGF, MMPs, and P53. The results are confirmative in an in vivo solid tumor model.

CONCLUSION

The IPA (8k) is a potent anti-proliferative molecule with anti-angiogenic activity and specifically targets HIF1α, thereby modulates its downstream regulatory genes both in vitro and in vivo. The study provides scope for new target-specific drug development against HIF-1α for the treatment of solid tumors.

Studying Angiogenesis in the Rabbit Corneal Pocket Assay

The rabbit corneal micropocket assay uses the avascular cornea as a substrate to study angiogenesis in vivo. The continuous monitoring of neovascular growth in the same animal allows for the evaluation of drugs acting as suppressors or stimulators of angiogenesis. Through the use of standardized slow-release pellets, a predictable angiogenic response can be quantified over the course of 1-2 weeks. Uniform slow-release pellets are prepared by mixing purified angiogenic growth factors such as basic fibroblast growth factor (FGF) or vascular endothelial growth factor (VEGF) and a synthetic polymer to allow for their slow release. A micropocket is surgically created in the cornea thickness under anesthesia and in sterile conditions. The angiogenesis stimulus (growth factor but also tissue fragment or cell suspension) is placed into the pocket in order to induce vascular outgrowth from the limbal capillaries where vessels are preexisting. On the following days, the neovascular development and progression are measured and qualified using a slit lamp, as well as the concomitant vascular phenotype or inflammatory features. The results of the assay allow to assess the ability of potential therapeutic molecules to modulate angiogenesis in vivo, both when released locally or given by ocular formulations or through systemic treatment. In this chapter the experimental details of the avascular rabbit cornea assay, the technical challenges, advantages, and limitations are discussed.

Cartilage type IIB procollagen NH₂-propeptide, PIIBNP, inhibits angiogenesis

<abstract> <p>Cartilage tissue is avascular and resistant to tumor invasion, but the basis for these properties is still unclear. Here we report that the NH₂-propeptide of type IIB procollagen (PIIBNP), a product of collagen biosynthesis, is capable of inhibiting angiogenesis both <italic>in vitro</italic> and <italic>in vivo</italic>. PIIBNP inhibits tube formation in human umbilical vein cells (HUVEC), inhibits endogenous endothelial cell outgrowth in mouse aortic ring angiogenesis bioassay and is anti-angiogenic in the mouse cornea angiogenesis assay. As α_Vß₃ and α_Vß₅ integrins are expressed primarily in endothelial cells, cancer cells and osteoclasts, but not in normal chondrocytes and PIIBNP binds to cell surface integrin α_Vß₃ and αVß₅, we propose that natural occurring PIIBNP protects cartilage by targeting endothelial cells during chondrogenesis, thus inhibiting angiogenesis, and rendering the tissue avascular.</p> </abstract>

An Overview of In Vitro, In Vivo, and Computational Techniques for Cancer-Associated Angiogenesis Studies

Angiogenesis is a crucial area in scientific research because it involves many important physiological and pathological processes. Indeed, angiogenesis is critical for normal physiological processes, including wound healing and embryonic development, as well as being a component of many disorders, such as rheumatoid arthritis, obesity, and diabetic retinopathies. Investigations of angiogenic mechanisms require assays that can activate the critical steps of angiogenesis as well as provide a tool for assessing the efficacy of therapeutic agents. Thus, angiogenesis assays are key tools for studying the mechanisms of angiogenesis and identifying the potential therapeutic strategies to modulate neovascularization. However, the regulation of angiogenesis is highly complex and not fully understood. Difficulties in assessing the regulators of angiogenic response have necessitated the development of an alternative approach. In this paper, we review the standard models for the study of tumor angiogenesis on the macroscopic scale that include in vitro, in vivo, and computational models. We also highlight the differences in several modeling approaches and describe key advances in understanding the computational models that contributed to the knowledge base of the field.

Low dose amiodarone reduces tumor growth and angiogenesis

Amiodarone is an anti-arrhythmic drug that was approved by the US Food and Drug Administration (FDA) in 1985. Pre-clinical studies suggest that Amiodarone induces cytotoxicity in several types of cancer cells, thus making it a potential candidate for use as an anti-cancer treatment. However, it is also known to cause a variety of severe side effects. We hypothesized that in addition to the cytotoxic effects observed in cancer cells Amiodarone also has an indirect effect on angiogensis, a key factor in the tumor microenvironment. In this study, we examined Amiodarone's effects on a murine tumor model comprised of U-87 MG glioblastoma multiforme (GBM) cells, known to form highly vascularized tumors. We performed several in vitro assays using tumor and endothelial cells, along with in vivo assays utilizing three murine models. Low dose Amiodarone markedly reduced the size of GBM xenograft tumors and displayed a strong anti-angiogenic effect, suggesting dual cancer fighting properties. Our findings lay the ground for further research of Amiodarone as a possible clinical agent that, used in safe doses, maintains its dual properties while averting the drug's harmful side effects.

Pharmacological Potential of Small Molecules for Treating Corneal Neovascularization

Under healthy conditions, the cornea is an avascular structure which allows for transparency and optimal visual acuity. Its avascular nature is maintained by a balance of proangiogenic and antiangiogenic factors. An imbalance of these factors can result in abnormal blood vessel proliferation into the cornea. This corneal neovascularization (CoNV) can stem from a variety of insults including hypoxia and ocular surface inflammation caused by trauma, infection, chemical burns, and immunological diseases. CoNV threatens corneal transparency, resulting in permanent vision loss. Mainstay treatments of CoNV have partial efficacy and associated side effects, revealing the need for novel treatments. Numerous natural products and synthetic small molecules have shown potential in preclinical studies in vivo as antiangiogenic therapies for CoNV. Such small molecules include synthetic inhibitors of the vascular endothelial growth factor (VEGF) receptor and other tyrosine kinases, plus repurposed antimicrobials, as well as natural source-derived flavonoid and non-flavonoid phytochemicals, immunosuppressants, vitamins, and histone deacetylase inhibitors. They induce antiangiogenic and anti-inflammatory effects through inhibition of VEGF, NF-κB, and other growth factor receptor pathways. Here, we review the potential of small molecules, both synthetics and natural products, targeting these and other molecular mechanisms, as antiangiogenic agents in the treatment of CoNV.

Pericyte Bridges in Homeostasis and Hyperglycemia

Diabetic retinopathy is a potentially blinding eye disease that threatens the vision of one-ninth of patients with diabetes. Progression of the disease has long been attributed to an initial dropout of pericytes that enwrap the retinal microvasculature. Revealed through retinal vascular digests, a subsequent increase in basement membrane bridges was also observed. Using cell-specific markers, we demonstrate that pericytes rather than endothelial cells colocalize with these bridges. We show that the density of bridges transiently increases with elevation of Ang-2, PDGF-BB, and blood glucose; is rapidly reversed on a timescale of days; and is often associated with a pericyte cell body located off vessel. Cell-specific knockout of KLF4 in pericytes fully replicates this phenotype. In vivo imaging of limbal vessels demonstrates pericyte migration off vessel, with rapid pericyte filopodial-like process formation between adjacent vessels. Accounting for off-vessel and on-vessel pericytes, we observed no pericyte loss relative to nondiabetic control retina. These findings reveal the possibility that pericyte perturbations in location and process formation may play a role in the development of pathological vascular remodeling in diabetic retinopathy.

Inhibition of EZH2 alleviates angiogenesis in a model of corneal neovascularization by blocking FoxO3a-mediated oxidative stress

Enhancer of zeste homolog 2 (EZH2), a well-known methyltransferase, mediates histone H3 lysine 27 trimethylation (H3K27me3) and plays a vital role in ophthalmological disease. However, its role in corneal neovascularization (CoNV) remains unclear. In vitro and in vivo models were assessed in hypoxia-stimulated angiogenesis and in a mouse model of alkali burn-induced CoNV. Human umbilical vein endothelial cells (HUVECs) were cultured under hypoxic conditions and different reoxygenation times to identify the molecular mechanisms involved in this process. In this study, we found that EZH2 was positively related to corneal alkali burn-induced injury. Inhibition of EZH2 with 3-Deazaneplanocin A (DZNeP) alleviated corneal injury, including oxidative stress and neovascularization in vivo. Similarly, inhibition of EZH2 with either DZNeP or small interfering RNA (siRNA) exerted an inhibitory effect on hypoxia/reoxygenation (H/R)-induced oxidative stress and angiogenesis in HUVECs. Moreover, our study revealed that ablation of reactive oxygen species (ROS) with N-acetyl-cysteine suppressed angiogenesis in HUVECs exposed to H/R stimulation. Furthermore, Forkhead-box protein O3a (FoxO3a), which was positively associated with ROS production and angiogenesis, was elevated during H/R. This effect could be reversed through the suppression of the transcription activity of EZH2 with DZNeP or siRNA. In addition, the PI3K/Akt pathway, which is the upstream of FoxO3a, was activated in both DZNeP-treated mice and EZH2-inhibited HUVECs. Collectively, our results demonstrated that the inhibition of EZH2 alleviated corneal angiogenesis by inhibiting FoxO3a-dependent ROS production through the PI3K/Akt signaling pathway. These findings indicate that EZH2 may be a valuable therapeutic target for CoNV.

3D Extracellular Matrix Mimics: Fundamental Concepts and Role of Materials Chemistry to Influence Stem Cell Fate

Synthetic 3D extracellular matrices (ECMs) find application in cell studies, regenerative medicine, and drug discovery. While cells cultured in a monolayer may exhibit unnatural behavior and develop very different phenotypes and genotypes than in vivo, great efforts in materials chemistry have been devoted to reproducing in vitro behavior in in vivo cell microenvironments. This requires fine-tuning the biochemical and structural actors in synthetic ECMs. This review will present the fundamentals of the ECM, cover the chemical and structural features of the scaffolds used to generate ECM mimics, discuss the nature of the signaling biomolecules required and exploited to generate bioresponsive cell microenvironments able to induce a specific cell fate, and highlight the synthetic strategies involved in creating functional 3D ECM mimics.

Co-delivery of metformin and levofloxacin hydrochloride using biodegradable thermosensitive hydrogel for the treatment of corneal neovascularization

Corneal neovascularization (CNV) is one of the major causes of severe disorders in ocular surface. Subconjunctival administration provides a localized and effective delivery of anti-angiogenic agents to inhibit neovascularization. In the present study, the ABA triblock copolymer of poly(D,L-lactic-co-glycolic acid)-block-poly(ethylene glycol)-block-poly(D,L-lactic-co-glycolic acid) (PLGA-PEG-PLGA) was used as a sustained drug delivery carrier for metformin (MET) and levofloxacin hydrochloride (LFH). Both drugs and PLGA-PEG-PLGA copolymers could be easily dissolved in water at low or room temperature and the mixed solution could form a drug-loaded thermosensitive hydrogel in terms of body temperature response. The in vitro release investigation displayed a sustained release of MET and LFH from the formulation for one month. The in vivo efficacy of subconjunctival injection of the MET + LFH loaded thermosensitive hydrogel in inhibiting CNV was evaluated on a mouse model of corneal alkali burn. Compared with the single administration of MET or LFH loaded thermosensitive hydrogel, the MET + LFH loaded thermosensitive hydrogel remarkably inhibited the formation of CNV. The sustained release of MET and an antibiotic (LFH) provides synergistic therapeutic outcome. As a result, the co-delivery of MET and LFH using PLGA-PEG-PLGA thermosensitive hydrogel by subconjunctival injection has great potential for ocular anti-angiogenic therapy.

Efficacy of a new automated method for quantification of corneal neovascularisation

BACKGROUND/AIMS

To evaluate the efficacy of a new automated method for quantification of corneal neovascularisation (NV).

METHODS

An in-house software for automated measurement of corneal NV was developed. Anterior segment photographs (ASPs) of 81 consecutive patients with corneal NV were analysed using our newly developed software. Manual measurements were performed by three independent examiners using ImageJ software V.1.48 (National Institute of Health, Bethesda, Maryland, USA). Interobserver reliability of the automated and manual methods, and correlations between the results of both methods were evaluated.

RESULTS

The automated method showed a strong interexaminer reliability (intraclass correlation coefficient (ICC)=0.994), which was slightly better than the manual method (ICC=0.958). A significant correlation was found between the results of both methods (p<0.001 for all three examiners). The time spent for analysis of each ASP was significantly reduced in the automated method compared with the manual method (p<0.001 for all three examiners).

CONCLUSIONS

Our newly developed automated method for quantification of corneal NV was more reproducible and time-saving compared with the manual method. Our method can be useful for diagnosis and monitoring diseases causing corneal NV.

Angiogenesis in Gynecological Cancers: Role of Neurotrophins

Angiogenesis, or generation of new blood vessels from other pre-existing, is a key process to maintain the supply of nutrients and oxygen in tissues. Unfortunately, this process is exacerbated in pathologies such as retinopathies and cancers with high angiogenesis as ovarian cancer. Angiogenesis is regulated by multiple systems including growth factors and neurotrophins. One of the most studied angiogenic growth factors is the vascular endothelial growth factor (VEGF), which is overexpressed in several cancers. It has been recently described that neurotrophins could regulate angiogenesis through direct and indirect mechanisms. Neurotrophins are a family of proteins that include nerve growth factor (NGF), brain-derived growth factor (BDNF), and neurotrophins 3 and 4/5 (NT 3, NT 4/5). These molecules and their high affinity receptors (TRKs) regulate the development, maintenance, and plasticity of the nervous system. Furthermore, it was recently described that they display essential functions in non-neuronal tissues, such as reproductive organs among others. Studies have shown that several types of cancer overexpress neurotrophins such as NGF and BDNF, which might contribute to tumor progression and angiogenesis. Besides, in recent years the FDA has approved the use of pharmacologic inhibitors of pan-TRK receptors in patients with TRKs fusion-positive cancers. In this review, we discuss the mechanisms by which neurotrophins stimulate tumor progression and angiogenesis, with emphasis on gynecological cancers.

Cucurbita argyrosperma Seed Extracts Attenuate Angiogenesis in a Corneal Chemical Burn Model

Severe corneal inflammation produces opacity or even perforation, scarring, and angiogenesis, resulting in blindness. In this study, we used the cornea to examine the effect of new anti-angiogenic chemopreventive agents. We researched the anti-angiogenic effect of two extracts, methanol (Met) and hexane (Hex), from the seed of Cucurbita argyrosperma, on inflamed corneas. The corneas of Wistar rats were alkali-injured and treated intragastrically for seven successive days. We evaluated: opacity score, corneal neovascularization (CNV) area, re-epithelialization percentage, and histological changes. Also, we assessed the inflammatory (cyclooxigenase-2, nuclear factor-kappaB, and interleukin-1β) and angiogenic (vascular endothelial growth factor A, VEGF-A; -receptor 1, VEGFR1; and -receptor 2, VEGFR2) markers. Levels of Cox-2, Il-1β, and Vegf-a mRNA were also determined. After treatment, we observed a reduction in corneal edema, with lower opacity scores and cell infiltration compared to untreated rats. Treatment also accelerated wound healing and decreased the CNV area. The staining of inflammatory and angiogenic factors was significantly decreased and related to a down-expression of Cox-2, Il-1β, and Vegf. These results suggest that intake of C. argyrosperma seed has the potential to attenuate the angiogenesis secondary to inflammation in corneal chemical damage.

Modelling of endothelial cell migration and angiogenesis in microfluidic cell culture systems

Tumour-induced angiogenesis is a complex biological process that involves growth of new blood vessels within the tumour microenvironment and is an important target for cancer therapies. Significant efforts have been undertaken to develop theoretical models as well as in vitro experimental models to study angiogenesis in a highly controllable and accessible manner. Various mathematical models have been developed to study angiogenesis, but these have mostly been applied to in vivo assays. Recently, microfluidic cell culture systems have emerged as useful and powerful tools for studying cell migration and angiogenesis processes, but thus far, mathematical angiogenesis models have not yet been applied to microfluidic geometries. Integrating mathematical and computational modelling with microfluidic-based assays has potential to enable greater control over experimental parameters, provide new insights into fundamental angiogenesis processes and assist in accelerating design and optimization of operating conditions. Here, we describe the development and application of a combined mathematical and computational modelling approach tailored specifically for microfluidic cell culture systems. The objective was to allow optimization of the engineering design of microfluidic systems, where the model may be used to test the impact of various geometric parameters on cell migration and angiogenesis processes, and assist in identifying optimal device dimensions to achieve desired readouts. We employed two separate continuum mathematical models that treated cell density, vessel length density and vascular endothelial growth factor (VEGF) concentration as continuous average variables, and we implemented these models numerically using finite difference discretization and a Method of Lines approach. We examined the average response of cells to VEGF gradients inside our microfluidic device, including the time-dependent changes in cell density and vessel density, and how they were affected by changes in device geometries including the migration port width and length. Our study demonstrated that mathematical modelling can be integrated with microfluidics to offer new perspectives on emerging problems in biomicrofluidics and cancer biology.

Chemerin promotes angiogenesis in vivo

Chemerin acts as a chemotactic factor for leukocyte populations expressing the G protein-coupled receptor CMKLR1 (ChemR23). It is also an adipocytokine involved in obesity and metabolic syndromes. Previous studies have demonstrated that chemerin promotes angiogenesis in vitro, although the precise mechanism has not been elucidated. In this study, we have investigated whether chemerin regulates angiogenic processes and validated the associated mechanisms. In this study, chemerin stimulated angiogenesis in mice, which was demonstrated using Matrigel plug implantation assay, mouse corneal models of angiogenesis, and ex vivo rat aortic ring assay. To explore the mechanisms by which chemerin induced angiogenesis, we examined the effects of chemerin in human umbilical vein endothelium cells (HUVECs). Chemerin stimulated the differentiation of HUVECs into capillary-like structures, promoted the proliferation of HUVECs, and functioned as a chemoattractant in migration assays. Chemerin induced the phosphorylation of Akt and p42/44 extracellular signal-regulated kinase (ERK) in HUVECs and chemerin promotes angiogenesis via Akt and ERK. SiRNA against the chemerin receptor CMKLR1 but not that against another chemerin receptor, CCRL2, completely inhibited the chemerin-induced migration and angiogenesis of HUVECs, which indicates that chemerin promotes the migration and angiogenic activities of HUVECs mainly through CMKLR1.

Self-implantable double-layered micro-drug-reservoirs for efficient and controlled ocular drug delivery

Eye diseases and injuries impose a significant clinical problem worldwide. Safe and effective ocular drug delivery is, however, challenging due to the presence of ocular barriers. Here we report a strategy using an eye patch equipped with an array of detachable microneedles. These microneedles can penetrate the ocular surface tissue, and serve as implanted micro-reservoirs for controlled drug delivery. The biphasic drug release kinetics enabled by the double-layered micro-reservoirs largely enhances therapeutic efficacy. Using corneal neovascularization as the disease model, we show that delivery of an anti-angiogenic monoclonal antibody (DC101) by such eye patch produces ~90% reduction of neovascular area. Furthermore, quick release of an anti-inflammatory compound (diclofenac) followed by a sustained release of DC101 provides synergistic therapeutic outcome. The eye patch application is easy and minimally invasive to ensure good patient compliance. Such intraocular drug delivery strategy promises effective home-based treatment of many eye diseases.

Treatment for eye injuries and diseases is most efficient when delivered directly into the eye. Here, the authors developed a patient-friendly eye patch equipped with an array of detachable microneedles, through which drugs can be delivered through the cornea for an extended period of time.

Epsin deficiency promotes lymphangiogenesis through regulation of VEGFR3 degradation in diabetes

Impaired lymphangiogenesis is a complication of chronic complex diseases, including diabetes. VEGF-C/VEGFR3 signaling promotes lymphangiogenesis, but how this pathway is affected in diabetes remains poorly understood. We previously demonstrated that loss of epsins 1 and 2 in lymphatic endothelial cells (LECs) prevented VEGF-C-induced VEGFR3 from endocytosis and degradation. Here, we report that diabetes attenuated VEGF-C-induced lymphangiogenesis in corneal micropocket and Matrigel plug assays in WT mice but not in mice with inducible lymphatic-specific deficiency of epsins 1 and 2 (LEC-iDKO). Consistently, LECs isolated from diabetic LEC-iDKO mice elevated in vitro proliferation, migration, and tube formation in response to VEGF-C over diabetic WT mice. Mechanistically, ROS produced in diabetes induced c-Src-dependent but VEGF-C-independent VEGFR3 phosphorylation, and upregulated epsins through the activation of transcription factor AP-1. Augmented epsins bound to and promoted degradation of newly synthesized VEGFR3 in the Golgi, resulting in reduced availability of VEGFR3 at the cell surface. Preclinically, the loss of lymphatic-specific epsins alleviated insufficient lymphangiogenesis and accelerated the resolution of tail edema in diabetic mice. Collectively, our studies indicate that inhibiting expression of epsins in diabetes protects VEGFR3 against degradation and ameliorates diabetes-triggered inhibition of lymphangiogenesis, thereby providing a novel potential therapeutic strategy to treat diabetic complications.

Consensus guidelines for the use and interpretation of angiogenesis assays

The formation of new blood vessels, or angiogenesis, is a complex process that plays important roles in growth and development, tissue and organ regeneration, as well as numerous pathological conditions. Angiogenesis undergoes multiple discrete steps that can be individually evaluated and quantified by a large number of bioassays. These independent assessments hold advantages but also have limitations. This article describes in vivo, ex vivo, and in vitro bioassays that are available for the evaluation of angiogenesis and highlights critical aspects that are relevant for their execution and proper interpretation. As such, this collaborative work is the first edition of consensus guidelines on angiogenesis bioassays to serve for current and future reference.

Endothelial smoothened-dependent hedgehog signaling is not required for sonic hedgehog induced angiogenesis or ischemic tissue repair

Sonic Hedgehog (Shh) signaling induces neovascularization and angiogenesis. It is not known whether the hedgehog signaling pathway in endothelial cells is essential to angiogenesis. Smoothened (Smo) transduces hedgehog signaling across the cell membrane. This study assessed whether endothelial Smoothened-dependent Shh signaling is required for Shh-mediated angiogenesis and ischemic tissue repair. Endothelial-specific smoothened knockout mice, eSmo^Null were created using Cre-lox recombination system. eSmo^Null mice had no observable phenotype at baseline and showed normal cardiac function. Smoothened in CD31+ cells isolated from eSmo^Null hearts was significantly reduced compared to CD31+ cells from eSmo^WT littermate control hearts. Fluorescence immunostaining of eSmo^Null heart sections showed Smo expression in endothelial cells was abolished. The hind-limb ischemia (HLI) model was used to assess the response to ischemic injury. Perfusion ratio, limb motor function, and limb necrosis were not significantly different after HLI between eSmo^Null mice and eSmo^WT. Capillary densities in the ischemic limb in eSmo^Null mice were also similar to eSmo^WT at 4 weeks after HLI. Next, response to exogenous Shh was assessed in the corneal angiogenesis model. There was no significant difference in corneal angiogenesis induced by administration of Shh pellets between eSmo^WT and eSmo^Null mice. Furthermore, in vitro experiments demonstrated that direct Shh had limited effects on endothelial cell proliferation and migration. However, conditioned media from Shh-treated fibroblasts had a more potent effect on endothelial cell proliferation and migration than non-treated conditioned media. Furthermore, Shh treatment of fibroblasts dramatically stimulated angiogenic growth factor expression, including PDGF-B, VEGF-A, HGF and IGF. PDGF-B was the most upregulated and may contribute to the large neo-vessels associated with Shh-induced angiogenesis. Taken together, these data demonstrate that Shh signaling via Smoothened in endothelial cells is not required for angiogenesis and ischemic tissue repair. Shh signaling via stromal cells likely mediates its angiogenic effects.

A 3D in vitro pericyte-supported microvessel model: visualisation and quantitative characterisation of multistep angiogenesis

Angiogenesis, which refers to the formation of new blood vessels from already existing vessels, is a promising therapeutic target and a complex multistep process involving many different factors. Pericytes (PCs) are attracting attention as they are considered to make significant contributions to the maturation and stabilisation of newly formed vessels, although not much is known about the precise mechanisms involved. Since there is no single specific marker for pericytes, in vivo models may complicate PC identification and the study of PCs in angiogenesis would benefit from in vitro models recapitulating the interactions between PCs and endothelial cells (ECs) in a three-dimensional (3D) configuration. In this study, a 3D in vitro co-culture microvessel model incorporating ECs and PCs was constructed by bottom-up tissue engineering. Angiogenesis was induced in the manner of sprout formation by the addition of a vascular endothelial cell growth factor. It was found that the incorporation of PCs prevented expansion of the parent vessel diameter and enhanced sprout formation and elongation. Physical interactions between ECs and PCs were visualised by immunostaining and it disclosed that PCs covered the EC monolayer from its basal side in the parent vessel as well as angiogenic sprouts. Furthermore, the microvessels were visualized in 3D by using a non-invasive optical coherence tomography (OCT) imaging system and sprout features were quantitatively assessed. It revealed that the sprouts in EC-PC co-culture vessels were longer and tighter than those in EC mono-culture vessels. The combination of the microvessel model and the OCT system analysis can be useful for the visualisation and demonstration of the multistep process of angiogenesis, which incorporates PCs.

Semaphorin3A induces nerve regeneration in the adult cornea-a switch from its repulsive role in development

The peripheral sensory nerves that innervate the cornea can be easily damaged by trauma, surgery, infection or diabetes. Several growth factors and axon guidance molecules, such as Semaphorin3A (Sema3A) are upregulated upon cornea injury. Nerves can regenerate after injury but do not recover their original density and patterning. Sema3A is a well known axon guidance and growth cone repellent protein during development, however its role in adult cornea nerve regeneration remains undetermined. Here we investigated the neuro-regenerative potential of Sema3A on adult peripheral nervous system neurons such as those that innervate the cornea. First, we examined the gene expression profile of the Semaphorin class 3 family members and found that all are expressed in the cornea. However, upon cornea injury there is a fast increase in Sema3A expression. We then corroborated that Sema3A totally abolished the growth promoting effect of nerve growth factor (NGF) on embryonic neurons and observed signs of growth cone collapse and axonal retraction after 30 min of Sema3A addition. However, in adult isolated trigeminal ganglia or dorsal root ganglia neurons, Sema3A did not inhibited the NGF-induced neuronal growth. Furthermore, adult neurons treated with Sema3A alone produced similar neuronal growth to cells treated with NGF and the length of the neurites and branching was comparable between both treatments. These effects were replicated in vivo, where thy1-YFP neurofluorescent mice subjected to cornea epithelium debridement and receiving intrastromal pellet implantation containing Sema3A showed increased corneal nerve regeneration than those receiving pellets with vehicle. In adult PNS neurons, Sema3A is a potent inducer of neuronal growth in vitro and cornea nerve regeneration in vivo. Our data indicates a functional switch for the role of Sema3A in PNS neurons where the well-described repulsive role during development changes to a growth promoting effect during adulthood. The high expression of Sema3A in the normal and injured adult corneas could be related to its role as a growth factor.

A mathematical model of tumour angiogenesis: growth, regression and regrowth

Cancerous tumours have the ability to recruit new blood vessels through a process called angiogenesis. By stimulating vascular growth, tumours get connected to the circulatory system, receive nutrients and open a way to colonize distant organs. Tumour-induced vascular networks become unstable in the absence of tumour angiogenic factors (TAFs). They may undergo alternating stages of growth, regression and regrowth. Following a phase-field methodology, we propose a model of tumour angiogenesis that reproduces the aforementioned features and highlights the importance of vascular regression and regrowth. In contrast with previous theories which focus on vessel remodelling due to the absence of flow, we model an alternative regression mechanism based on the dependency of tumour-induced vascular networks on TAFs. The model captures capillaries at full scale, the plastic dynamics of tumour-induced vessel networks at long time scales, and shows the key role played by filopodia during angiogenesis. The predictions of our model are in agreement with in vivo experiments and may prove useful for the design of antiangiogenic therapies.

Deformability-based microfluidic separation of pancreatic islets from exocrine acinar tissue for transplant applications

The long-term management of type-1 diabetes (T1D) is currently achieved through lifelong exogenous insulin injections. Although there is no cure for T1D, transplantation of pancreatic islets of Langerhans has the potential to restore normal endocrine function versus the morbidity of hypoglycemic unawareness that is commonly associated with sudden death among fragile diabetics. However, since endocrine islet tissues form a small proportion of the pancreas, sufficient islet numbers can be reached only by combining islets from multiple organ donors and the transplant plug contains significantly high levels of exocrine acinar tissue, thereby exacerbating immune responses. Hence, lifelong administration of immunosuppressants is required after transplantation, which can stress islet cells. The density gradient method that is currently used to separate islets from acinar tissue causes islets to be sparsely distributed over the centrifuged bins, so that the transplant sample obtained by combining multiple bins also contains significant acinar tissue levels. We show that in comparison to the significant size and density overlaps between the islet and acinar tissue populations post-organ digestion, their deformability overlaps are minimal. This feature is utilized to design a microfluidic separation strategy, wherein tangential flows enable selective deformation of acinar populations towards the bifurcating waste stream and sequential switching of hydrodynamic resistance enables the collection of rigid islets. Using 25 bifurcating daughter channels, a throughput of ∼300 islets per hour per device is obtained for enabling islet enrichment from relatively dilute starting levels to purity levels that meet the transplant criteria, as well as to further enhance islet purity from samples following density gradient enrichment. Based on confirmation of viability and functionality of the microfluidic-isolated islets using insulin secretion analysis and an angiogenesis assay, we envision utilizing this strategy to generate small-volume transplant plugs with high islet purity and significantly reduced acinar levels for minimizing immune responses after transplantation.

Cathepsin B-mediated CD18 shedding regulates leukocyte recruitment from angiogenic vessels

Cathepsin B (CtsB) contributes to atherosclerosis and cancer progression by processing the extracellular matrix and promoting angiogenesis. Although CtsB was reported to promote and reduce angiogenesis, there is no mechanistic explanation that reconciles this apparent discrepancy. CtsB cleaves CD18 from the surface of immune cells, but its contribution to angiogenesis has not been studied. We developed an in vivo technique for visualization of immune cell transmigration from corneal vessels toward implanted cytokines. Wild-type (WT) leukocytes extravasated from limbal vessels, angiogenic stalks, and growing tip vessels and migrated toward the cytokines, indicating immune competence of angiogenic vessels. Compared to WT leukocytes, CtsB^-/- leukocytes accumulated in a higher number in angiogenic vessels, but extravasated less toward the implanted cytokine. The accumulated CtsB^-/- leukocytes in angiogenic vessels expressed more CD18. CD18^-/- leukocytes extravasated later than WT leukocytes. However, once extravasated, CD18^-/- leukocytes transmigrated more rapidly than their WT counterparts. These results suggest that, although CD18 facilitates efficient extravasation, outside of the vessel CD18 interaction with the extracellular matrix, it reduced transmigration velocity. Our results reveal an unexpected role for CtsB in leukocyte extravasation and transmigration, which advances our understanding of the complex contribution of CtsB to angiogenesis.-Nakao, S., Zandi, S., Sun, D., Hafezi-Moghadam, A. Cathepsin B-mediated CD18 shedding regulates leukocyte recruitment from angiogenic vessels.

Dynamic, heterogeneous endothelial Tie2 expression and capillary blood flow during microvascular remodeling

Microvascular endothelial cell heterogeneity and its relationship to hemodynamics remains poorly understood due to a lack of sufficient methods to examine these parameters in vivo at high resolution throughout an angiogenic network. The availability of surrogate markers for functional vascular proteins, such as green fluorescent protein, enables expression in individual cells to be followed over time using confocal microscopy, while photoacoustic microscopy enables dynamic measurement of blood flow across the network with capillary-level resolution. We combined these two non-invasive imaging modalities in order to spatially and temporally analyze biochemical and biomechanical drivers of angiogenesis in murine corneal neovessels. By stimulating corneal angiogenesis with an alkali burn in Tie2-GFP fluorescent-reporter mice, we evaluated how onset of blood flow and surgically-altered blood flow affects Tie2-GFP expression. Our study establishes a novel platform for analyzing heterogeneous blood flow and fluorescent reporter protein expression across a dynamic microvascular network in an adult mammal.

Animal models of ocular angiogenesis: from development to pathologies

Pathological angiogenesis in the eye is an important feature in the pathophysiology of many vision-threatening diseases, including retinopathy of prematurity, diabetic retinopathy, and age-related macular degeneration, as well as corneal diseases with abnormal angiogenesis. Development of reproducible and reliable animal models of ocular angiogenesis has advanced our understanding of both the normal development and the pathobiology of ocular neovascularization. These models have also proven to be valuable experimental tools with which to easily evaluate potential antiangiogenic therapies beyond eye research. This review summarizes the current available animal models of ocular angiogenesis. Models of retinal and choroidal angiogenesis, including oxygen-induced retinopathy, laser-induced choroidal neovascularization, and transgenic mouse models with deficient or spontaneous retinal/choroidal neovascularization, as well as models with induced corneal angiogenesis, are widely used to investigate the molecular and cellular basis of angiogenic mechanisms. Theoretical concepts and experimental protocols of these models are outlined, as well as their advantages and potential limitations, which may help researchers choose the most suitable models for their investigative work.-Liu, C.-H., Wang, Z., Sun, Y., Chen, J. Animal models of ocular angiogenesis: from development to pathologies.

A novel strategy to enhance angiogenesis in vivo using the small VEGF-binding peptide PR1P

Therapeutic angiogenesis is an experimental frontier in vascular biology that seeks to deliver angiogenic growth factors to ischemic or injured tissues to promote targeted formation of new blood vessels as an alternative approach to surgical revascularization procedures. Vascular endothelial growth factor (VEGF) is a potent angiogenic signal protein that is locally upregulated at sites of tissue injury. However, therapies aimed at increasing VEGF levels experimentally by injecting VEGF gene or protein failed to improve outcomes in human trials in part due to its short half-life and systemic toxicity. We recently designed a novel 12-amino acid peptide (PR1P) whose sequence was derived from an extracellular VEGF-binding domain of the pro-angiogenic glycoprotein prominin-1. In this study, we characterized the molecular binding properties of this novel potential therapeutic for targeted angiogenesis and provided the foundation for its use as an angiogenic molecule that can potentiate endogenous VEGF. We showed that PR1P bound VEGF directly and enhanced VEGF binding to endothelial cells and to VEGF receptors VEGFR2 and neuropilin-1. PR1P increased angiogenesis in the murine corneal micropocket assay when combined with VEGF, but had no activity without added VEGF. In addition, PR1P also enhanced angiogenesis in murine choroidal neovascularization and wound-healing models and augmented reperfusion in a murine hind-limb ischemia model. Together our data suggest that PR1P enhanced angiogenesis by potentiating the activity of endogenous VEGF. In so doing, this novel therapy takes advantage of endogenous VEGF gradients generated in injured tissues and may improve the efficacy of and avoid systemic toxicity seen with previous VEGF therapies.

Engineered ligand-based VEGFR antagonists with increased receptor binding affinity more effectively inhibit angiogenesis

Pathologic angiogenesis is mediated by the coordinated action of the vascular endothelial growth factor (VEGF)/vascular endothelial growth factor receptor 2 (VEGFR2) signaling axis, along with crosstalk contributed by other receptors, notably α_vβ₃ integrin. We build on earlier work demonstrating that point mutations can be introduced into the homodimeric VEGF ligand to convert it into an antagonist through disruption of binding to one copy of VEGFR2. This inhibitor has limited potency, however, due to loss of avidity effects from bivalent VEGFR2 binding. Here, we used yeast surface display to engineer a variant with VEGFR2 binding affinity approximately 40‐fold higher than the parental antagonist, and 14‐fold higher than the natural bivalent VEGF ligand. Increased VEGFR2 binding affinity correlated with the ability to more effectively inhibit VEGF‐mediated signaling, both in vitro and in vivo, as measured using VEGFR2 phosphorylation and Matrigel implantation assays. High affinity mutations found in this variant were then incorporated into a dual‐specific antagonist that we previously designed to simultaneously bind to and inhibit VEGFR2 and α_vβ₃ integrin. The resulting dual‐specific protein bound to human and murine endothelial cells with relative affinities of 120 ± 10 pM and 360 ± 50 pM, respectively, which is at least 30‐fold tighter than wild‐type VEGF (3.8 ± 0.5 nM). Finally, we demonstrated that this engineered high‐affinity dual‐specific protein could inhibit angiogenesis in a murine corneal neovascularization model. Taken together, these data indicate that protein engineering strategies can be combined to generate unique antiangiogenic candidates for further clinical development.

Comparison of Topical Low-Molecular-Weight Heparin-Taurocholate and Bevacizumab for Treatment and Prevention of Corneal Neovascularization

PURPOSE

To compare the therapeutic and preventive effects of topically administered 7-taurocholic acid-conjugated low-molecular-weight heparin (LHT7) and bevacizumab in experimentally induced corneal neovascularization (CoNV).

METHODS

CoNV was induced using sutures in the right eyes of 24 mice. To investigate the therapeutic effects, CoNV was allowed to develop for 1 week before treatment. To ascertain the preventive effects, the treatments were applied immediately after the suture. In each experiment, 12 eyes were divided into 3 groups and treated topically using bevacizumab (bevacizumab group), LHT7 (LHT7 group), and normal saline (control group). The treatments were instilled 3 times daily for 2 weeks. The CoNV area was measured before instillation and after 1 and 2 weeks after instillation.

RESULTS

In the investigation of therapeutic effects, the CoNV area had decreased significantly 1 week after treatment in the bevacizumab group (1.58-0.75 mm; P = 0.036) and LHT7 group (1.38-0.74 mm; P = 0.018). Two weeks after treatment, the CoNV area was significantly smaller in the bevacizumab groups (0.60 mm; P = 0.005) and LHT7 group (0.64 mm; P = 0.015) than in the control group (1.68 mm), but the bevacizumab group did not differ significantly from the LHT7 group. In the experiment addressing the preventive effects, CoNV was less developed in the bevacizumab group (0.70 mm; P = 0.003) and LHT7 group (0.54 mm; P = 0.003) than in the control group (1.75 mm), and the CoNV area was smaller in the LHT7 group than in the bevacizumab group (P = 0.021).

CONCLUSIONS

The effects of LHT7 on CoNV regression are comparable to those of bevacizumab. Topical administration of LHT7 prevents CoNV more effectively than bevacizumab.

Anti-tumoral, anti-angiogenic and anti-metastatic efficacy of a tetravalent bispecific antibody (TAvi6) targeting VEGF-A and angiopoietin-2

Vascular endothelial growth factor (VEGF)-A blockade has been validated clinically as a treatment for human cancers. Angiopoietin-2 (Ang-2) is a key regulator of blood vessel remodeling and maturation. In tumors, Ang-2 is up-regulated and an unfavorable prognostic factor. Recent data demonstrated that Ang-2 inhibition mediates anti-tumoral effects. We generated a tetravalent bispecific antibody (Ang-2-VEGF-TAvi6) targeting VEGF-A with 2 arms based on bevacizumab (Avastin®), and targeting Ang-2 with 2 arms based on a novel anti-Ang-2 antibody (LC06). The two Ang-2-targeting single-chain variable fragments are disulfide-stabilized and fused to the C-terminus of the heavy chain of bevacizumab. Treatment with Ang-2-VEGF-A-TAvi6 led to a complete abrogation of angiogenesis in the cornea micropocket assay. Metastatic spread and tumor growth of subcutaneous, orthotopic and anti-VEGF-A resistant tumors were also efficiently inhibited. These data further establish Ang-2-VEGF bispecific antibodies as a promising anti-angiogenic, anti-metastatic and anti-tumor agent for the treatment of cancer.

BP-1T, an antiangiogenic benzophenone-thiazole pharmacophore, counteracts HIF-1 signalling through p53/MDM2-mediated HIF-1α proteasomal degradation

Hypoxia is a feature of all solid tumours, contributing to tumour progression. Activation of HIF-1α plays a critical role in promoting tumour angiogenesis and metastasis. Since its expression is positively correlated with poor prognosis for cancer patients, HIF-1α is one of the most convincing anticancer targets. BP-1T is a novel antiproliferative agent with promising antiangiogenic effects. In the present study, the molecular mechanism underlying cytotoxic/antiangiogenic effects of BP-1T on tumour/non-tumour angiogenesis was evaluated. Evidences show that BP-1T exhibits potent cytotoxicity with prolonged activity and effectively regressed neovessel formation both in reliable non-tumour and tumour angiogenic models. The expression of CoCl₂-induced HIF-1α was inhibited by BP-1T in various p53 (WT)-expressing cancer cells, including A549, MCF-7 and DLA, but not in mutant p53-expressing SCC-9 cells. Mechanistically, BP-1T mediates the HIF-1α proteasomal degradation by activating p53/MDM2 pathway and thereby downregulated HIF-1α-dependent angiogenic genes such as VEGF-A, Flt-1, MMP-2 and MMP-9 under hypoxic condition of in vitro and in vivo solid tumour, eventually leading to abolition of migration and invasion. Based on these observations, we conclude that BP-1T acts on HIF-1α degradation through p53/MDM2 proteasome pathway.

An integrated approach to quantitative modelling in angiogenesis research

Angiogenesis, the process by which new vessels form from existing ones, plays an important role in many developmental processes and pathological conditions. We study angiogenesis in the context of a highly controllable experimental environment: the cornea micropocket assay. Using a multidisciplinary approach that combines experiments, image processing and analysis, and mathematical modelling, we aim to provide mechanistic insight into the action of two angiogenic factors, vascular endothelial growth factor A (VEGF-A) and basic fibroblast growth factor (bFGF). We use image analysis techniques to extract quantitative data, which are both spatially and temporally resolved, from experimental images, and we develop a mathematical model, in which the corneal vasculature evolves in response to both VEGF-A and bFGF. The experimental data are used for model parametrization, while the mathematical model is used to assess the utility of the cornea micropocket assay and to characterize proposed synergies between VEGF-A and bFGF.

Pathological lymphangiogenesis is modulated by galectin-8-dependent crosstalk between podoplanin and integrin-associated VEGFR-3

Lymphangiogenesis plays a pivotal role in diverse pathological conditions. Here, we demonstrate that a carbohydrate-binding protein, galectin-8, promotes pathological lymphangiogenesis. Galectin-8 is markedly upregulated in inflamed human and mouse corneas, and galectin-8 inhibitors reduce inflammatory lymphangiogenesis. In the mouse model of corneal allogeneic transplantation, galectin-8-induced lymphangiogenesis is associated with an increased rate of corneal graft rejection. Further, in the murine model of herpes simplex virus keratitis, corneal pathology and lymphangiogenesis are ameliorated in Lgals8(-/-) mice. Mechanistically, VEGF-C-induced lymphangiogenesis is significantly reduced in the Lgals8(-/-) and Pdpn(-/-) mice; likewise, galectin-8-induced lymphangiogenesis is reduced in Pdpn(-/-) mice. Interestingly, knockdown of VEGFR-3 does not affect galectin-8-mediated lymphatic endothelial cell (LEC) sprouting. Instead, inhibiting integrins α1β1 and α5β1 curtails both galectin-8- and VEGF-C-mediated LEC sprouting. Together, this study uncovers a unique molecular mechanism of lymphangiogenesis in which galectin-8-dependent crosstalk among VEGF-C, podoplanin and integrin pathways plays a key role.

PKN3 is the major regulator of angiogenesis and tumor metastasis in mice

PKN, a conserved family member related to PKC, was the first protein kinase identified as a target of the small GTPase Rho. PKN is involved in various functions including cytoskeletal arrangement and cell adhesion. Furthermore, the enrichment of PKN3 mRNA in some cancer cell lines as well as its requirement in malignant prostate cell growth suggested its involvement in oncogenesis. Despite intensive research efforts, physiological as well as pathological roles of PKN3 in vivo remain elusive. Here, we generated mice with a targeted deletion of PKN3. The PKN3 knockout (KO) mice are viable and develop normally. However, the absence of PKN3 had an impact on angiogenesis as evidenced by marked suppressions of micro-vessel sprouting in ex vivo aortic ring assay and in vivo corneal pocket assay. Furthermore, the PKN3 KO mice exhibited an impaired lung metastasis of melanoma cells when administered from the tail vein. Importantly, PKN3 knock-down by small interfering RNA (siRNA) induced a glycosylation defect of cell-surface glycoproteins, including ICAM-1, integrin β1 and integrin α5 in HUVECs. Our data provide the first in vivo genetic demonstration that PKN3 plays critical roles in angiogenesis and tumor metastasis, and that defective maturation of cell surface glycoproteins might underlie these phenotypes.

The Rabbit Corneal Pocket Assay

The rabbit corneal micropocket angiogenesis assay uses the avascular cornea as a substrate canvas to study angiogenesis in vivo. Through the use of standardized slow-release pellets, a predictable angiogenic response is generated over the course of 1-2 weeks and then quantified. Uniform slow-release pellets are prepared by mixing purified angiogenic growth factors such as basic fibroblast growth factor or vascular endothelial growth factor and a synthetic polymer to allow slow release. A micropocket is surgically created in the rabbit cornea under anesthesia and a pellet implanted. On the days later, the angiogenic response is measured and qualified using a slit lamp, as well as the concomitant vascular phenotype or inflammatory features. The results of the assay are used to assess the ability of potential therapeutic molecules to modulate angiogenesis in vivo, both when released locally or given by ocular formulations or through systemic treatment. In this chapter, the experimental details of the rabbit cornea assay and technical implementations to the original protocol are described.

Neuropilin-2 contributes to LPS-induced corneal inflammatory lymphangiogenesis

Neuropilin-2 (NP2), a high-affinity kinase-deficient co-receptor for vascular endothelial growth factor (VEGF)-C, is involved in embryonic vessel development, tumor growth, tumor lymphangiogenesis and metastasis. However, the pathological role of NP2 in other disorders, particularly under inflammatory lymphangiogenic conditions, remains largely unknown. In this study, we investigated the role of NP2 in inflammation-induced lymphangiogenesis in vivo using a lipopolysaccharide (LPS)-induced corneal neovascularization mouse model and in vitro using a macrophage-mouse lymphatic endothelial cell (mLEC) co-culture system. In the mouse model of LPS-induced inflammatory corneal neovascularization, NP2 and VEGFR-3 expression were rapidly up-regulated after LPS stimulation, and microRNA-mediated knockdown of NP2 significantly inhibited the up-regulation of VEGFR-3. Moreover, NP2 knockdown specifically inhibited the increase in the number of corneal lymphatic vessels but did not influence the increase in the number of blood vessels or macrophage recruitment induced by LPS. In a macrophage-LEC co-culture system, LPS up-regulated VEGFR-3 expression and induced mLEC migration and proliferation, and NP2 knockdown inhibited the up-regulation of VEGFR-3 expression and mLEC migration but not proliferation. Taken together, these results suggested that NP2 might be involved in the regulation of lymphangiogenesis via the regulation of VEGFR-3 expression during corneal inflammation. Therefore, NP2-targeted therapy might be a promising strategy for selective inhibition of inflammatory lymphangiogenesis in corneal inflammatory diseases, transplant immunology and oncology.

Ocular surgical models for immune and angiogenic responses

Corneal transplantation serves as a reproducible and simple surgical model to study mechanisms regulating immunity and angiogenesis. The simplicity of the model allows for systematic analysis of different mechanisms involved in immune and angiogenic privilege and their failures. This protocol describes how to induce neovessels and inflammation in an actively regulated avascular and immune-privileged site. This involves placing intra-stromal corneal sutures for two weeks, disrupting the privileges, and performing corneal transplantation subsequently. Privileged and non-privileged recipient responses to donor cornea can be compared to identify key immunological mechanisms that underlie angiogenesis and graft rejection. This protocol can also be adapted to the growing repertoire of genetic models available in the mouse, and is a valuable tool to elucidate molecular mechanisms mediating acceptance or failure of corneal graft. The model could be used to assess the potential of therapeutic molecules to enhance graft survival in vivo.

Isolation of microvascular endothelial cells from cadaveric corneal limbus

Limbal microvascular endothelial cells (L-MVEC) contribute to formation of the corneal-limbal stem cell niche and to neovascularization of diseased and injuries corneas. Nevertheless, despite these important roles in corneal health and disease, few attempts have been made to isolate L-MVEC with the view to studying their biology in vitro. We therefore explored the feasibility of generating primary cultures of L-MVEC from cadaveric human tissue. We commenced our study by evaluating growth conditions (MesenCult-XF system) that have been previously found to be associated with expression of the endothelial cell surface marker thrombomodulin/CD141, in crude cultures established from collagenase-digests of limbal stroma. The potential presence of L-MVEC in these cultures was examined by flow cytometry using a more specific marker for vascular endothelial cells, CD31/PECAM-1. These studies demonstrated that the presence of CD141 in crude cultures established using the MesenCult-XF system is unrelated to L-MVEC. Thus we subsequently explored the use of magnetic assisted cell sorting (MACS) for CD31 as a tool for generating cultures of L-MVEC, in conjunction with more traditional endothelial cell growth conditions. These conditions consisted of gelatin-coated tissue culture plastic and MCDB-131 medium supplemented with foetal bovine serum (10% v/v), D-glucose (10 mg/mL), epidermal growth factor (10 ng/mL), heparin (50 μg/mL), hydrocortisone (1 μg/mL) and basic fibroblast growth factor (10 ng/mL). Our studies revealed that use of endothelial growth conditions are insufficient to generate significant numbers of L-MVEC in primary cultures established from cadaveric corneal stroma. Nevertheless, through use of positive-MACS selection for CD31 we were able to routinely observe L-MVEC in cultures derived from collagenase-digests of limbal stroma. The presence of L-MVEC in these cultures was confirmed by immunostaining for von Willebrand factor (vWF) and by ingestion of acetylated low-density lipoprotein. Moreover, the vWF(+) cells formed aligned cell-to-cell 'trains' when grown on Geltrex™. The purity of L-MVEC cultures was found to be unrelated to tissue donor age (32-80 years) or duration in eye bank corneal preservation medium prior to use (3-10 days in Optisol) (using multiple regression test). Optimal purity of L-MVEC cultures was achieved through use of two rounds of positive-MACS selection for CD31 (mean ± s.e.m, 65.0 ± 20.8%; p < 0.05). We propose that human L-MVEC cultures generated through these techniques, in conjunction with other cell types, will provide a useful tool for exploring the mechanisms of blood vessel cell growth in vitro.

Melanocyte pigmentation inversely correlates with MCP-1 production and angiogenesis-inducing potential

The incidence of certain angiogenesis-dependent diseases is higher in Caucasians than in African Americans. Angiogenesis is amplified in wound healing and cornea models in albino C57 mice compared with black C57 mice. Moreover, mouse and human melanocytes with low pigmentation stimulate endothelial cell (EC) proliferation and migration in vitro more than melanocytes with high pigmentation. This effect is due, in part, to the secretion of an angiogenic protein called fibromodulin (FMOD) from lowly pigmented melanocytes. Herein, we expand upon the mechanism contributing to increased angiogenesis in lighter skin and report that monocyte chemotactic protein-1 (MCP-1) is secreted by nonpigmented mouse melanocytes by 5- to 10-fold more than pigmented melanocytes. MCP-1 protein stimulates EC proliferation and migration in vitro and angiogenesis in vivo. Mechanistic studies determine that FMOD is upstream of MCP-1 and promotes its secretion from both melanocytes and activated ECs via stimulation of NF-κB activity. Mice injected with FMOD-neutralizing antibodies show 2.3-fold decreased levels of circulating MCP-1. Human studies confirmed that, on average, Caucasians have 2-fold higher serum levels of MCP-1 than African Americans. Taken together, this study implicates the FMOD/MCP-1 pathway in the regulation of angiogenesis by local melanocytes and suggests that melanogenic activity may protect against aberrant angiogenic diseases.

VEGF-B selectively regenerates injured peripheral neurons and restores sensory and trophic functions

VEGF-B primarily provides neuroprotection and improves survival in CNS-derived neurons. However, its actions on the peripheral nervous system have been less characterized. We examined whether VEGF-B mediates peripheral nerve repair. We found that VEGF-B induced extensive neurite growth and branching in trigeminal ganglia neurons in a manner that required selective activation of transmembrane receptors and was distinct from VEGF-A-induced neuronal growth. VEGF-B-induced neurite elongation required PI3K and Notch signaling. In vivo, VEGF-B is required for normal nerve regeneration: mice lacking VEGF-B showed impaired nerve repair with concomitant impaired trophic function. VEGF-B treatment increased nerve regeneration, sensation recovery, and trophic functions of injured corneal peripheral nerves in VEGF-B-deficient and wild-type animals, without affecting uninjured nerves. These selective effects of VEGF-B on injured nerves and its lack of angiogenic activity makes VEGF-B a suitable therapeutic target to treat nerve injury.

The corneal micropocket assay: a model of angiogenesis in the mouse eye

The mouse corneal micropocket assay is a robust and quantitative in vivo assay for evaluating angiogenesis. By using standardized slow-release pellets containing specific growth factors that trigger blood vessel growth throughout the naturally avascular cornea, angiogenesis can be measured and quantified. In this assay the angiogenic response is generated over the course of several days, depending on the type and dose of growth factor used. The induction of neovascularization is commonly triggered by either basic fibroblast growth factor (bFGF) or vascular endothelial growth factor (VEGF). By combining these growth factors with sucralfate and hydron (poly-HEMA (poly(2-hydroxyethyl methacrylate))) and casting the mixture into pellets, they can be surgically implanted in the mouse eye. These uniform pellets slowly-release the growth factors over five or six days (bFGF or VEGF respectively) enabling sufficient angiogenic response required for vessel area quantification using a slit lamp. This assay can be used for different applications, including the evaluation of angiogenic modulator drugs or treatments as well as comparison between different genetic backgrounds affecting angiogenesis. A skilled investigator after practicing this assay can implant a pellet in less than 5 min per eye.

Glycobiology of ocular angiogenesis

Ocular neovascularization can affect almost all the tissues of the eye: the cornea, the iris, the retina, and the choroid. Pathological neovascularization is the underlying cause of vision loss in common ocular conditions such as diabetic retinopathy, retinopathy of prematurity and age-related macular neovascularization. Glycosylation is the most common covalent posttranslational modification of proteins in mammalian cells. A growing body of evidence demonstrates that glycosylation influences the process of angiogenesis and impacts activation, proliferation, and migration of endothelial cells as well as the interaction of angiogenic endothelial cells with other cell types necessary to form blood vessels. Recent studies have provided evidence that members of the galectin class of β-galactoside-binding proteins modulate angiogenesis by novel carbohydrate-based recognition systems involving interactions between glycans of angiogenic cell surface receptors and galectins. This review discusses the significance of glycosylation and the role of galectins in the pathogenesis of ocular neovascularization.

Sema3A maintains corneal avascularity during development by inhibiting Vegf induced angioblast migration

Corneal avascularity is important for optical clarity and normal vision. However, the molecular mechanisms that prevent angioblast migration and vascularization of the developing cornea are not clear. Previously we showed that periocular angioblasts and forming ocular blood vessels avoid the presumptive cornea despite dynamic ingression of neural crest cells. In the current study, we investigate the role of Semaphorin3A (Sema3A), a cell guidance chemorepellent, on angioblast migration and corneal avascularity during development. We show that Sema3A, Vegf, and Nrp1 are expressed in the anterior eye during cornea development. Sema3A mRNA transcripts are expressed at significantly higher levels than Vegf in the lens that is positioned adjacent to the presumptive cornea. Blockade of Sema3A signaling via lens removal or injection of a synthetic Sema3A inhibitor causes ectopic migration of angioblasts into the cornea and results in its subsequent vascularization. In addition, using bead implantation, we demonstrate that exogenous Sema3A protein inhibits Vegf-induced vascularization of the cornea. In agreement with these findings, loss of Sema/Nrp1 signaling in Nrp1(Sema-) mutant mice results in ectopic angioblasts and vascularization of the embryonic mouse corneas. Altogether, our results reveal Sema3A signaling as an important cue during the establishment of corneal avascularity in both chick and mouse embryos. Our study introduces cornea development as a new model for studying the mechanisms involved in vascular patterning during embryogenesis and it also provides new insights into therapeutic potential for Sema3A in neovascular diseases.

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.