Nerve growth factor regulates human choroidal, but not retinal, endothelial cell migration and proliferation

Gambogic amide inhibits angiogenesis by suppressing VEGF/VEGFR2 in endothelial cells in a TrkA-independent manner

CONTEXT

Gambogic amide (GA-amide) is a non-peptide molecule that has high affinity for tropomyosin receptor kinase A (TrkA) and possesses robust neurotrophic activity, but its effect on angiogenesis is unclear.

OBJECTIVE

The study investigates the antiangiogenic effect of GA-amide on endothelial cells (ECs).

MATERIALS AND METHODS

The viability of endothelial cells (ECs) treated with 0.1, 0.15, 0.2, 0.3, 0.4, and 0.5 μM GA-amide for 48 h was detected by MTS assay. Wound healing and angiogenesis assays were performed on cells treated with 0.2 μM GA-amide. Chicken eggs at day 7 post-fertilization were divided into the dimethyl sulfoxide (DMSO), bevacizumab (40 μg), and GA-amide (18.8 and 62.8 ng) groups to assess the antiangiogenic effect for 3 days. mRNA and protein expression in cells treated with 0.1, 0.2, 0.4, 0.8, and 1.2 μM GA-amide for 6 h was detected by qRT-PCR and Western blots, respectively.

RESULTS

GA-amide inhibited HUVEC (IC₅₀ = 0.1269 μM) and NhEC (IC₅₀ = 0.1740 μM) proliferation, induced cell apoptosis, and inhibited the migration and angiogenesis at a relatively safe dose (0.2 μM) in vitro. GA-amide reduced the number of capillaries from 56 ± 14.67 (DMSO) to 20.3 ± 5.12 (62.8 ng) in chick chorioallantoic membrane (CAM) assay. However, inactivation of TrkA couldn't reverse the antiangiogenic effect of GA-amide. Moreover, GA-amide suppressed the expression of VEGF and VEGFR2, and decreased activation of the AKT/mTOR and PLCγ/Erk1/2 pathways.

CONCLUSIONS

Considering the antiangiogenic effect of GA-amide, it might be developed as a useful agent for use in clinical combination therapies.

Do Neurotrophins Connect Neurological Disorders and Heart Diseases?

Neurotrophins (NTs) are one of the most characterized neurotrophic factor family members and consist of four members in mammals. Growing evidence suggests that there is a complex inter- and bi-directional relationship between central nervous system (CNS) disorders and cardiac dysfunction, so-called "brain-heart axis". Recent studies suggest that CNS disorders, including neurodegenerative diseases, stroke, and depression, affect cardiovascular function via various mechanisms, such as hypothalamic-pituitary-adrenal axis augmentation. Although this brain-heart axis has been well studied in humans and mice, the involvement of NT signaling in the axis has not been fully investigated. In the first half of this review, we emphasize the importance of NTs not only in the nervous system, but also in the cardiovascular system from the embryonic stage to the adult state. In the second half, we discuss the involvement of NTs in the pathogenesis of cardiovascular diseases, and then examine whether an alteration in NTs could serve as the mediator between neurological disorders and heart dysfunction. The further investigation we propose herein could contribute to finding direct evidence for the involvement of NTs in the axis and new treatment for cardiovascular diseases.

TGFβ-Neurotrophin Interactions in Heart, Retina, and Brain

Ischemic insults to the heart and brain, i.e., myocardial and cerebral infarction, respectively, are amongst the leading causes of death worldwide. While there are therapeutic options to allow reperfusion of ischemic myocardial and brain tissue by reopening obstructed vessels, mitigating primary tissue damage, post-infarction inflammation and tissue remodeling can lead to secondary tissue damage. Similarly, ischemia in retinal tissue is the driving force in the progression of neovascular eye diseases such as diabetic retinopathy (DR) and age-related macular degeneration (AMD), which eventually lead to functional blindness, if left untreated. Intriguingly, the easily observable retinal blood vessels can be used as a window to the heart and brain to allow judgement of microvascular damages in diseases such as diabetes or hypertension. The complex neuronal and endocrine interactions between heart, retina and brain have also been appreciated in myocardial infarction, ischemic stroke, and retinal diseases. To describe the intimate relationship between the individual tissues, we use the terms heart-brain and brain-retina axis in this review and focus on the role of transforming growth factor β (TGFβ) and neurotrophins in regulation of these axes under physiologic and pathologic conditions. Moreover, we particularly discuss their roles in inflammation and repair following ischemic/neovascular insults. As there is evidence that TGFβ signaling has the potential to regulate expression of neurotrophins, it is tempting to speculate, and is discussed here, that cross-talk between TGFβ and neurotrophin signaling protects cells from harmful and/or damaging events in the heart, retina, and brain.

The pleiotropic molecule NGF regulates the in vitro properties of fibroblasts, keratinocytes, and endothelial cells: implications for wound healing

Nerve growth factor (NGF) is recognized as a pleiotropic molecule, exerting a variety of biological effects on different cell types and pathophysiological conditions, and its role in tissue wound healing has been recently highlighted. However, the preferential cellular target of NGF is still elusive in the complex cellular and molecular cross talk that accompanies wound healing. Thus, to explore possible NGF cellular targets in skin wound healing, we investigated the in vitro NGF responsiveness of keratinocytes (cell line HEKa), fibroblasts (cell line BJ), and endothelial cells (cell line HUVEC), also in the presence of adverse microenvironmental conditions, e.g., hyperglycemia. The main results are summarized as follows: 1) NGF stimulates keratinocyte proliferation and HUVEC proliferation and angiogenesis in a dose-dependent manner although it has no effect on fibroblast proliferation; 2) NGF stimulates keratinocyte but not fibroblast migration in the wound healing assay; and 3) NGF completely reverts the proliferation impairment of keratinocytes and the angiogenesis impairment of HUVECs induced by high d-glucose concentration in the culture medium. These results contribute to better understanding possible targets for the therapeutic use of NGF in skin repair.

Nerve growth factor regulates endothelial cell survival and pathological retinal angiogenesis

The mechanism underlying vasoproliferative retinopathies like retinopathy of prematurity (ROP) is hypoxia-triggered neovascularisation. Nerve growth factor (NGF), a neurotrophin supporting survival and differentiation of neuronal cells may also regulate endothelial cell functions. Here we studied the role of NGF in pathological retinal angiogenesis in the course of the ROP mouse model. Topical application of NGF enhanced while intraocular injections of anti-NGF neutralizing antibody reduced pathological retinal vascularization in mice subjected to the ROP model. The pro-angiogenic effect of NGF in the retina was mediated by inhibition of retinal endothelial cell apoptosis. In vitro, NGF decreased the intrinsic (mitochondria-dependent) apoptosis in hypoxia-treated human retinal microvascular endothelial cells and preserved the mitochondrial membrane potential. The anti-apoptotic effect of NGF was associated with increased BCL2 and reduced BAX, as well as with enhanced ERK and AKT phosphorylation, and was abolished by inhibition of the AKT pathway. Our findings reveal an anti-apoptotic role of NGF in the hypoxic retinal endothelium, which is involved in promoting pathological retinal vascularization, thereby pointing to NGF as a potential target for proliferative retinopathies.

NGF protects endothelial cells from indomethacin-induced injury through activation of mitochondria and upregulation of IGF-1

BACKGROUND/AIMS

Endothelial cells (ECs) lining blood vessels are critical for delivery of oxygen and nutrients to all tissues and organs and play a crucial role in the regeneration of blood vessel following tissue injury. ECs are also major targets of injury by a variety of noxious factors [e.g., ethanol and nonsteroidal anti-inflammatory drugs (NSAIDs) such as aspirin, indomethacin, diclofenac], especially in gastric mucosa that has direct exposure to these agents. In this study, we investigated whether nerve growth factor (NGF) can protect gastric microvascular ECs (GECs) from injury by indomethacin (INDO) and the mechanisms involved.

METHODS

GECs were isolated from rat gastric mucosa and pre-treated with either vehicle or NGF (100ng/ml) for 30min to 4h followed by treatment with vehicle or 0.25mM INDO for 4h.

STUDIES

1) cell viability using Calcein AM live cell tracking dye, 2) mitochondrial structure and function using MitoTracker, molecular probe that stains mitochondria in live cells in a manner dependent on mitochondrial membrane potential (MMP), 3) in vitro angiogenesis - endothelial tube formation on Matrigel, 4) expression and subcellular localization of NGF receptor, TrkA, and 5) expression of IGF-1 protein.

RESULTS

Treatment with INDO reduced GEC viability and in vitro angiogenesis and induced mitochondrial injury and MMP depolarization. NGF pre-treatment protected GECs from INDO-induced injury preventing both INDO-induced MMP depolarization and reduced in vitro angiogenesis. The NGF high affinity receptor, TrkA, was localized in GECs to both cell membrane and mitochondria. NGF treatment of GECs also resulted in increased IGF-1 protein expression.

CONCLUSIONS

1) NGF protects GECs against IND-induced injury. 2) Mitochondria are major targets of both INDO-induced injury and NGF afforded protection of GECs. 3) TrkA expression in the mitochondria of GECs indicates that the protection afforded by NGF is partly mediated by its direct action on mitochondria. 4) NGF prevents MMP depolarization and increases expression of IGF-1 protein in GECs. These studies indicate that NGF may play a protective role against injury to GECs; and, that maintenance of mitochondrial structure and function is one of the mechanisms.

A Critical Analysis of the Available In Vitro and Ex Vivo Methods to Study Retinal Angiogenesis

Angiogenesis is a biological process with a central role in retinal diseases. The choice of the ideal method to study angiogenesis, particularly in the retina, remains a problem. Angiogenesis can be assessed through in vitro and in vivo studies. In spite of inherent limitations, in vitro studies are faster, easier to perform and quantify, and typically less expensive and allow the study of isolated angiogenesis steps. We performed a systematic review of PubMed searching for original articles that applied in vitro or ex vivo angiogenic retinal assays until May 2017, presenting the available assays and discussing their applicability, advantages, and disadvantages. Most of the studies evaluated migration, proliferation, and tube formation of endothelial cells in response to inhibitory or stimulatory compounds. Other aspects of angiogenesis were studied by assessing cell permeability, adhesion, or apoptosis, as well as by implementing organotypic models of the retina. Emphasis is placed on how the methods are applied and how they can contribute to retinal angiogenesis comprehension. We also discuss how to choose the best cell culture to implement these methods. When applied together, in vitro and ex vivo studies constitute a powerful tool to improve retinal angiogenesis knowledge. This review provides support for researchers to better select the most suitable protocols in this field.

Nerve Growth Factor Promotes Angiogenesis and Skeletal Muscle Fiber Remodeling in a Murine Model of Hindlimb Ischemia

Background:

Therapeutic angiogenesis has been shown to promote blood vessel growth and improve tissue perfusion. Nerve growth factor (NGF) has been reported to play an important role in both physiological and pathological angiogenesis. This study aimed to investigate the effects of NGF on angiogenesis and skeletal muscle fiber remodeling in a murine model of hindlimb ischemia and study the relationship between NGF and vascular endothelial growth factor (VEGF) in angiogenesis.

Methods:

Twenty-four mice were randomly allocated to normal control group (n = 6), blank control group (n = 6), VEGF gene transfection group (n = 6), and NGF gene transfection group (n = 6). The model of left hindlimb ischemia model was established by ligating the femoral artery. VEGF₁₆₅ plasmid (125 μg) and NGF plasmid (125 μg) was injected into the ischemic gastrocnemius of mice from VEGF group and NGF group, respectively. Left hindlimb function and ischemic damage were assessed with terminal points at 21^th day postischemia induction. The gastrocnemius of four groups was tested by hematoxylin-eosin staining, proliferating cell nuclear antigen and CD34 immunohistochemistry staining, and myosin ATPase staining. NGF and VEGF protein expression was detected by enzyme-linked immunosorbent assay.

Results:

On the 21^th day after surgery, the functional assessment score and skeletal muscle atrophy degree of VEGF group and NGF group were significantly lower than those of normal control group and blank control group. The endothelial cell proliferation index and the capillary density of VEGF group and NGF group were significantly increased compared with normal control group and blank control group (P < 0.05). The NGF and VEGF protein expression of NGF group showed a significant rise when compared with blank control group (P < 0.05). Similarly, the VEGF protein expression of VEGF group was significantly higher than that of blank control group (P < 0.05), but there was no significant difference of the NGF protein expression between VEGF group and blank control group (P > 0.05). The type I skeletal muscle fiber proportion in gastrocnemius of NGF group and VEGF group was significantly higher than that of blank control group (P < 0.05).

Conclusions:

NGF transfection can promote NGF and VEGF protein expression which not only can induce angiogenesis but also induce type I muscle fiber expression in ischemic limbs.

Nerve growth factor is critical requirement for in vitro angiogenesis in gastric endothelial cells

Angiogenesis is critical for the healing of gastric mucosal injury and is considered to be primarily regulated by vascular endothelial growth factor (VEGF), the fundamental proangiogenic factor. The role of nerve growth factor (NGF) in gastric angiogenesis is unknown. We examined the expression of NGF and its TrkA receptor in endothelial cells (ECs) isolated from gastric mucosa of rats (GMECs), the effect of NGF treatment on in vitro angiogenesis in GMECs, and, the mechanisms underlying NGF's proangiogenic actions. Isolated GMECs from Fisher rats were treated with vehicle, NGF (10-1,000 ng/ml), VEGF (20 ng/ml), or NGF+VEGF. To determine whether and to what extent NGF is critical for angiogenesis in GMECs, we silenced NGF expression using specific siRNA and examined in vitro angiogenesis with and without treatment with exogenous NGF and/or VEGF. Treatment of GMECs with NGF significantly increased in vitro angiogenesis similar to that seen in GMECs treated with VEGF. Silencing of NGF in GMECs abolished angiogenesis, and this effect was reversed only by exogenous NGF but not VEGF, which indicates a direct proangiogenic action of NGF on GMECs that is, at least in part, distinct and independent of VEGF. NGF's proangiogenic action on GMECs was mediated via PI3-K/Akt signaling. This study showed for the first time that gastric mucosal ECs express NGF and its receptor TrkA and that NGF is critical for angiogenesis in these cells.

Silencing p75(NTR) prevents proNGF-induced endothelial cell death and development of acellular capillaries in rat retina

Accumulation of the nerve growth factor precursor (proNGF) and its receptor p75(NTR) have been associated with several neurodegenerative diseases in both brain and retina. However, whether proNGF contributes to microvascular degeneration remain unexplored. This study seeks to investigate the mechanism by which proNGF/p75(NTR) induce endothelial cell (EC) death and development of acellular capillaries, a surrogate marker of retinal ischemia. Stable overexpression of the cleavage-resistant proNGF and molecular silencing of p75(NTR) were utilized in human retinal EC and rat retinas in vivo. Stable overexpression of proNGF decreased NGF levels and induced retinal vascular cell death evident by 1.9-fold increase in acellular capillaries and activation of JNK and cleaved-PARP that were mitigated by p75(NTR)shRNA. In vitro, overexpression of proNGF did not alter TNF-α level, reduced NGF, however induced EC apoptosis evident by activation of JNK and p38 MAPK, cleaved-PARP. Silencing p75(NTR) using siRNA restored expression of NGF and TrkA activation and prevented EC apoptosis. Treatment of EC with human-mutant proNGF induced apoptosis that coincided with marked protein interaction and nuclear translocation of p75(NTR) and the neurotrophin receptor interacting factor. These effects were abolished by a selective p75(NTR) antagonist. Therefore, targeting p75(NTR) represents a potential therapeutic strategy for diseases associated with aberrant expression of proNGF.

Novel approaches for treating diabetic retinopathy based on recent pathogenic evidence

Diabetic retinopathy remains as a leading cause of blindness in developed countries. Current treatments target late stages of DR when vision has already been significantly affected. A better understanding of the pathogenesis of DR would permit the development of more efficient preventional/interventional strategies against early stages of DR. In this article a critical review of the state of the art of this issue is provided along with a discussion of problems which have yet to be overcome. Neuroprotection as a new approach for the treatment of the early stages of DR has been particularly emphasized. The development and progression of DR is not homogeneous and, apart from blood glucose levels and blood pressure, it depends on genetic factors which remain to be elucidated. In addition, the role of the pathogenic pathways is not the same in all patients. All these factors should be taken into account in the near future when an individualized oriented treatment for DR could become feasible. The new techniques in retinal imaging acquisition, the identification of useful circulating biomarkers and the individualized analysis of biological samples could facilitate the development of early and personalized therapy in the setting of DR. Finally, it should be noted that only a coordinated action among ophthalmologists, diabetologists, basic researchers, experts in pharmaco-economics and health care providers addressed to the design of rational strategies targeting prevention and the early stages of DR will be effective in reducing the burden and improving the clinical outcome of this devastating complication of diabetes.

Expression of thrombospondin-1 modulates the angioinflammatory phenotype of choroidal endothelial cells

The choroidal circulation plays a central role in maintaining the health of outer retina and photoreceptor function. Alterations in this circulation contribute to pathogenesis of many eye diseases including exudative age-related macular degeneration. Unfortunately, very little is known about the choroidal circulation and its molecular and cellular regulation. This has been further hampered by the lack of methods for routine culturing of choroidal endothelial cells (ChEC), especially from wild type and transgenic mice. Here we describe a method for isolation and culturing of mouse ChEC. We show that expression of thrombospondin-1 (TSP1), an endogenous inhibitor of angiogenesis and inflammation, has a significant impact on phenotype of ChEC. ChEC from TSP1-deficient (TSP1-/-) mice were less proliferative and more apoptotic, less migratory and less adherent, and failed to undergo capillary morphogenesis in Matrigel. However, re-expression of TSP1 was sufficient to restore TSP1-/- ChEC migration and capillary morphogenesis. TSP1-/- ChEC expressed increased levels of TSP2, phosphorylated endothelial nitric oxide synthase (NOS) and inducible NOS (iNOS), a marker of inflammation, which was associated with significantly higher level of NO and oxidative stress in these cells. Wild type and TSP1-/- ChEC produced similar levels of VEGF, although TSP1-/- ChEC exhibited increased levels of VEGF-R1 and pSTAT3. Other signaling pathways including Src, Akt, and MAPKs were not dramatically affected by the lack of TSP1. Together our results demonstrate an important autocrine role for TSP1 in regulation of ChEC phenotype.

Interrelationships between the Retinal Neuroglia and Vasculature in Diabetes

For years, diabetic retinopathy has been defined based on vascular lesions, and neural abnormalities were not regarded as important. This review summarizes evidence that the neural retina has important effects on the retinal vasculature under normal conditions, and the interaction between the retinal neuroglial cells and vascular function is altered in diabetes. Importantly, new evidence raises a possibility that abnormalities within retinal neuroglial cells (notably photoreceptors) might actually be causing or initiating the vascular disease in diabetic retinopathy.

Peripheral changes in endometriosis-associated pain

BACKGROUND

Pain remains the cardinal symptom of endometriosis. However, to date, the underlying mechanisms are still only poorly understood. Increasing evidence points towards a close interaction between peripheral nerves, the peritoneal environment and the central nervous system in pain generation and processing. Recently, studies demonstrating nerve fibres and neurotrophic and angiogenic factors in endometriotic lesions and their vicinity have led to increased interest in peripheral changes in endometriosis-associated pain. This review focuses on the origin and function of these nerves and factors as well as possible peripheral mechanisms that may contribute to the generation and modulation of pain in women with endometriosis.

METHODS

We conducted a systematic search using several databases (PubMed, MEDLINE, EMBASE and CINAHL) of publications from January 1977 to October 2013 to evaluate the possible roles of the peripheral nervous system in endometriosis pathophysiology and how it can contribute to endometriosis-associated pain.

RESULTS

Endometriotic lesions and peritoneal fluid from women with endometriosis had pronounced neuroangiogenic properties with increased expression of new nerve fibres, a shift in the distribution of sensory and autonomic fibres in some locations, and up-regulation of several neurotrophins. In women suffering from deep infiltrating endometriosis and bowel endometriosis, in which the anatomical distribution of lesions is generally more closely related to pelvic pain symptoms, endometriotic lesions and surrounding tissues present higher nerve fibre densities compared with peritoneal lesions and endometriomas. More data are needed to fully confirm a direct correlation between fibre density in these locations and the amount of perceived pain. A better correlation between the presence of nerve fibres and pain symptoms seems to exist for eutopic endometrium. However, this appears not to be exclusive to endometriosis. No correlation between elevated neurotrophin levels and pain severity appears to exist, suggesting the involvement of other mediators in the modulation of pain.

CONCLUSIONS

The increased expression of neurotrophic factors and nerve fibres in endometriotic lesions, eutopic endometrium and the peritoneum imply a role of such peripheral changes in the pathogenesis of endometriosis-associated pain. However, a clear link between these findings and pain in patients with endometriosis has so far not been demonstrated.

Anti-cancer effect of HS-345, a new tropomyosin-related kinase A inhibitor, on human pancreatic cancer

Tropomyosin-related kinase A (TrkA) is emerging as an important player in carcinogenic progression. TrkA overexpression, which is associated with cell growth, proliferation, survival, and invasion, has been observed in pancreatic cancer. We therefore synthesized HS-345, a novel TrkA inhibitor, and evaluated its anti-cancer effect and underlying mechanism of action in pancreatic cancer. In this study, HS-345 effectively inhibited the growth and proliferation in three pancreatic cancer cell lines (PANC-1, MIA PaCa-2, and BxPC-3). Activation of the TrkA/Akt signal cascade was also inhibited by HS-345 treatment in a dose-dependent manner. The pro-apoptotic effect of HS-345 was evidenced by increased levels of cleaved caspase-3 and cleaved PARP, and decrease of Bcl/Bax expression via mitochondria membrane potential, as well as elevated numbers of TUNEL-positive apoptotic cells. HS-345 was additionally found to exert anti-angiogenic effect by decreasing the expression of HIF-1α and VEGF, major factors of angiogenesis, which were also demonstrated by the suppression of tube formation and migration of VEGF-treated human umbilical vein endothelial cells along with inhibition of blood vessel formation by HS-345 in a Matrigel plug assay with mice. Results of our investigation show that HS-345 inhibited the TrkA/Akt signaling pathway resulting in cell growth/angiogenesis inhibition and apoptosis induction. Based on our data, we suggest that HS-345 is a potential candidate for treating pancreatic cancer.

Nerve growth factor-mediated vascular endothelial growth factor expression of astrocyte in retinal vascular development

The angiogenic aspect of neurotrophins and their receptors rather than the neuroscientific aspect has been focused. However, their role in retinal vascular development is underdiscovered. The purpose of this study is to understand the role of neurotrophin receptors in retinal vascular development and the mechanisms of their action. To identify the expression of tropomyosin receptor kinase receptor (Trk) in developing retina, tissues of 4, 8, 12, 16 and 26 day-old mice were prepared for experiments. Immunohistochemistry and immunofluorescence double staining against glial fibrillary acidic protein and type IV collagen were performed. TrkA was expressed mainly along the vessel structure in inner part of retina, especially in retinal astrocyte. In cultured primary astrocyte, recombinant nerve growth factor (NGF) was used to activate TrkA. NGF induced the phosphorylation of TrkA, and it also enhanced the level of activated Akt and vascular endothelial growth factor (VEGF) mRNA. Inhibition of phosphoinositide 3-kinase (PI3K) reversed the NGF-induced activation of these two molecules. This study demonstrated that TrkA activation on NGF leads to VEGF elevation by PI3K-Akt pathway and therefore suggested that TrkA could be a stimulator of retinal vascular development.

Role of the retinal vascular endothelial cell in ocular disease

Retinal endothelial cells line the arborizing microvasculature that supplies and drains the neural retina. The anatomical and physiological characteristics of these endothelial cells are consistent with nutritional requirements and protection of a tissue critical to vision. On the one hand, the endothelium must ensure the supply of oxygen and other nutrients to the metabolically active retina, and allow access to circulating cells that maintain the vasculature or survey the retina for the presence of potential pathogens. On the other hand, the endothelium contributes to the blood-retinal barrier that protects the retina by excluding circulating molecular toxins, microorganisms, and pro-inflammatory leukocytes. Features required to fulfill these functions may also predispose to disease processes, such as retinal vascular leakage and neovascularization, and trafficking of microbes and inflammatory cells. Thus, the retinal endothelial cell is a key participant in retinal ischemic vasculopathies that include diabetic retinopathy and retinopathy of prematurity, and retinal inflammation or infection, as occurs in posterior uveitis. Using gene expression and proteomic profiling, it has been possible to explore the molecular phenotype of the human retinal endothelial cell and contribute to understanding of the pathogenesis of these diseases. In addition to providing support for the involvement of well-characterized endothelial molecules, profiling has the power to identify new players in retinal pathologies. Findings may have implications for the design of new biological therapies. Additional progress in this field is anticipated as other technologies, including epigenetic profiling methods, whole transcriptome shotgun sequencing, and metabolomics, are used to study the human retinal endothelial cell.

Evidence of synergistic/additive effects of sildenafil and erythropoietin in enhancing survival and migration of hypoxic endothelial cells

Endothelial cell dysfunction is a common event to several pathologies including pulmonary hypertension, which is often associated with hypoxia. As the endothelium plays an essential role in regulating the dynamic interaction between pulmonary vasodilatation and vasoconstriction, this cell type is fundamental in the development of vascular remodeling and increased vascular resistance. We investigated the protective effects of sildenafil, a phosphodiesterase type 5 inhibitor, given in combination with erythropoietin (Epo), as it has been demonstrated that both drugs have antiapoptotic effects on several cell types. Specifically, we examined the viability and angiogenic properties of rat pulmonary artery endothelial cells upon exposure to either 21% or 1% oxygen, in presence of sildenafil (1 and 100 nM) and Epo (5 and 20 U/ml) alone or in combination (1 nM and 20 U/ml). Cell proliferation and viability were analyzed by Trypan blue staining, MTT assay, and Annexin V/propidium iodide stainings. In all assays, the ability of the combination treatment in improving cell viability was superior to that of either drug alone. The angiogenic properties were studied using a migration and a 3D collagen assay, and the results revealed increases in the migration potential of endothelial cells as well as the ability to form tube-like structures in response to sildenafil and the combination treatment. We therefore conclude that both drugs exert protective effects on endothelial cells on hypoxia and that sildenafil enhances the migratory and angiogenic properties, especially in hypoxic conditions. Furthermore, we present evidence of possible additive or synergistic effects of both drugs.

Mechanisms and targets of angiogenesis and nerve growth in osteoarthritis

During osteoarthritis (OA), angiogenesis is increased in the synovium, osteophytes and menisci and leads to ossification in osteophytes and the deep layers of articular cartilage. Angiogenic and antiangiogenic factors might both be upregulated in the osteoarthritic joint; however, vascular growth predominates, and the articular cartilage loses its resistance to vascularization. In addition, blood vessel growth is increased at--and disrupts--the osteochondral junction. Angiogenesis in this location is dependent on the creation of channels from subchondral bone spaces into noncalcified articular cartilage. Inflammation drives synovial angiogenesis through macrophage activation. Blood vessel and nerve growth are linked by common pathways that involve the release of proangiogenic factors, such as vascular endothelial growth factor, β-nerve growth factor and neuropeptides. Proangiogenic factors might also stimulate nerve growth, and molecules produced by vascular cells could both stimulate and guide nerve growth. As sensory nerves grow along new blood vessels in osteoarthritic joints, they eventually penetrate noncalcified articular cartilage, osteophytes and the inner regions of menisci. Angiogenesis could, therefore, contribute to structural damage and pain in OA and provide potential targets for new treatments.

Cellular and physiological mechanisms underlying blood flow regulation in the retina and choroid in health and disease

We review the cellular and physiological mechanisms responsible for the regulation of blood flow in the retina and choroid in health and disease. Due to the intrinsic light sensitivity of the retina and the direct visual accessibility of fundus blood vessels, the eye offers unique opportunities for the non-invasive investigation of mechanisms of blood flow regulation. The ability of the retinal vasculature to regulate its blood flow is contrasted with the far more restricted ability of the choroidal circulation to regulate its blood flow by virtue of the absence of glial cells, the markedly reduced pericyte ensheathment of the choroidal vasculature, and the lack of intermediate filaments in choroidal pericytes. We review the cellular and molecular components of the neurovascular unit in the retina and choroid, techniques for monitoring retinal and choroidal blood flow, responses of the retinal and choroidal circulation to light stimulation, the role of capillaries, astrocytes and pericytes in regulating blood flow, putative signaling mechanisms mediating neurovascular coupling in the retina, and changes that occur in the retinal and choroidal circulation during diabetic retinopathy, age-related macular degeneration, glaucoma, and Alzheimer's disease. We close by discussing issues that remain to be explored.

Nerve growth factor promotes endothelial progenitor cell-mediated angiogenic responses

PURPOSE

In response to ischemia, retinal neuronal cells express nerve growth factor (NGF), which can be proangiogenic. Endothelial progenitor cells (EPCs) can participate with the resident vasculature to promote angiogenesis. We postulated that NGF may stimulate CD34⁺ EPCs to convert to an angiogenic phenotype.

METHODS

Human CD34⁺ cells and human retinal endothelial cells (HRECs) were used to examine the effect of NGF on key steps associated with neovascularization. CD34⁺ cells and HRECs were stimulated with NGF (1 to 4 pM) for 24, 48, and 72 hours. Cell migration was measured using a modified Boyden chamber assay. Expression of the receptor for the cytokine stromal derived growth factor 1 (SDF-1), CXCR-4, was assessed by flow cytometry. In vitro angiogenesis was tested using a three-dimensional (3D) extracellular matrix with HRECs/CD34⁺ cell cocultures. NGF receptor activation was assessed by western analysis.

RESULTS

NGF promoted proliferation of CD34⁺ cells but not HRECs. Pretreatment of CD34⁺ cells with NGF increased CXCR-4 expression in CD34⁺ cells, resulting in enhanced migration to SDF-1 (P < 0.0001). The enhanced tubule-forming effect of NGF in HRECs was further potentiated by coculture with NGF-pretreated CD34⁺ cells (P < 0.01). The beneficial effect of NGF was blocked (P < 0.0001) by the ERK inhibitor PD98059. In both CD34⁺ and HRECs, NGF increased phosphorylation of neurotrophic tyrosine kinase receptor type 1 (TrkA) receptor by ERK1 activation (P < 0.01).

CONCLUSIONS

Our in vitro results suggest that NGF released from ischemic nerves in vivo may contribute to the "angiogenic switch" by stimulating the angiogenic behavior of CD34⁺ cells while minimally affecting resident retinal endothelial cells.

Topical administration of adrenergic receptor pharmaceutics and nerve growth factor

Topical application of nerve growth factor (NGF) and adrenergic receptor pharmaceutics are currently in use for corneal ulcers and glaucoma. A recent interest in the neuroprotective abilities of NGF has led to a renewed interest in NGF as a therapeutic for retinal and choroidal diseases. NGF can promote cell proliferation through actions of the TrkA receptor or promote apoptosis through receptor p75^NTR. This understanding has led to novel interest in the role of NGF for diseases of the posterior eye. The role of β-adrenergic receptor agonists and antagonists for treatments of glaucoma, diabetic retinopathy, and their potential mechanisms of action, are still under investigation. This review discusses the current knowledge and applications of topical NGF and adrenergic receptor drugs for ocular disease.

Nerve growth factor promotes breast cancer angiogenesis by activating multiple pathways

Background

Although several anti-angiogenic therapies have been approved in the treatment of cancer, the survival benefits of such therapies are relatively modest. Discovering new molecules and/or better understating signaling pathways of angiogenesis is therefore essential for therapeutic improvements. The objective of the present study was to determine the involvement of nerve growth factor (NGF) in breast cancer angiogenesis and the underlying molecular mechanisms.

Results

We showed that both recombinant NGF and NGF produced by breast cancer cells stimulated angiogenesis in Matrigel plugs in immunodeficient mice. NGF strongly increased invasion, cord formation and the monolayer permeability of endothelial cells. Moreover, NGF-stimulated invasion was under the control of its tyrosine kinase receptor (TrkA) and downstream signaling pathways such as PI3K and ERK, leading to the activation of matrix metalloprotease 2 and nitric oxide synthase. Interestingly, NGF increased the secretion of VEGF in both endothelial and breast cancer cells. Inhibition of VEGF, with a neutralizing antibody, reduced about half of NGF-induced endothelial cell invasion and angiogenesis in vivo.

Conclusions

Our findings provided direct evidence that NGF could be an important stimulator for breast cancer angiogenesis. Thus, NGF, as well as the activated signaling pathways, should be regarded as potential new targets for anti-angiogenic therapy against breast cancer.

The promotion of endothelial progenitor cells recruitment by nerve growth factors in tissue-engineered blood vessels

Endothelial progenitor cells (EPCs) mobilization and homing are critical to the development of an anti-thrombosis and anti-stenosis tissue-engineered blood vessel. The growth and activation of blood vessels are supported by nerves. We investigated whether nerve growth factors (NGF) can promote EPCs mobilization and endothelialization of tissue-engineered blood vessels. In vitro, NGF promoted EPCs to form more colonies, stimulated human EPCs to differentiate into endothelial cells, and significantly enhanced EPCs migration. Flow cytometric analysis revealed that NGF treatment increased the number of EPCs in the peripheral circulation of C57BL/6 mice. Furthermore, the treatment of human EPCs with NGF facilitated their homing into wire-injured carotid arteries after injection into mice. Decellularized rat blood vessel matrix was incubated with EDC cross-linked collagen and bound to NGF protein using the bifunctional coupling agent N-succinmidyl3-(2-pyridyldit-hio) propionate (SPDP). The NGF-bound tissue-engineered blood vessel was implanted into rat carotid artery for 1 week and 1 month. NGF-bound blood vessels possessed significantly higher levels of endothelialization and patency than controls did. These results demonstrated that NGF can markedly increase EPCs mobilization and homing to vascular grafts. Neurotrophic factors such as NGF have a therapeutic potential for the construction of tissue-engineered blood vessels in vivo.

Correlation between NGF/TrkA and microvascular density in human pterygium

Pterygium is a surface ocular lesion that is associated with chronic UV exposure. The primary effect is a solar actinic elastosis within the stroma. All the other changes are secondary. Pterygium is characterized by proliferation, inflammatory infiltrates, fibrosis, angiogenesis and extracellular matrix breakdown. The aim of this study was to correlate microvascular density and nerve growth factor (NGF)/NGF-receptor transmembrane tyrosine kinase (TrkA) expression in endothelial cells in human pterygium. Specimens of human pterygium obtained from 30 patients who had undergone surgical excision and of 10 normal bulbar conjunctiva were investigated immunohistochemically by using anti-CD31, anti-NGF and anti-TrkA antibodies. Results showed that endothelial cells in human pterygium are immunoreactive to both NGF and its receptor TrkA, and that this immunoreactivity is correlated to microvascular density. The results of this study suggest that an autocrine loop between NGF and its receptor TrkA is activated in pterygium and that it is involved in the angiogenic response taking place in this pathological condition. These data are in accord with recent evidences, which have clearly established that NGF plays a role as an angiogenic factor in several pathological conditions. Understanding the mechanism of angiogenesis in pterygium provides a basis for a rational approach to the development of anti-angiogenic therapy in patients affected by this disease.

Nerve growth factor and its receptors TrkA and p75 are upregulated in the brain of mdx dystrophic mouse

Increased angiogenesis and an altered blood-brain barrier have been reported in the brain of dystrophin-deficient mdx mouse, an experimental model of Duchenne muscular dystrophy. To further elucidate the mechanisms underlying angiogenesis in Duchenne muscular dystrophy, in this study we evaluated whether nerve growth factor (NGF) and nerve growth factor receptors (NGFRs) are involved, then correlated NGF-NGFRs expression with vascular endothelial growth factor (VEGF) and its receptor-2 (VEGFR-2) content and matrix metalloproteinases-2 and -9 (MMP-2 and -9) activity, by confocal laser microscopy and immunohistochemistry. Results showed that neurons, astrocytes and ependymal cells were strongly labeled by NGF in mdx brain, expressing NGFRs on glial and endothelial cells. In controls, NGF faintly labeled neurons and astrocytes, whereas endothelial cells were negative for NGFRs. Immunogold electron microscopy demonstrated NGFR gold particles on endothelial cells in mdx brain, while in controls few particles were recognizable only on glial end feet. Western blotting and real time polymerase chain reaction (RT-PCR) demonstrated a higher expression of NGF and NGFR mRNA and protein in mdx brain as compared to controls, and increase of VEGF-VEGFR-2 and active MMP-2 and -9 content. Overall, these data suggest that in the brain of mdx mice, an upregulation of the NGF-NGFRs system might be involved directly, or indirectly through the activation of VEGF-VEGFR-2 and MMP-2 and -9, in the angiogenic response taking place in this pathological condition.

Cardiovascular actions of neurotrophins

Neurotrophins were christened in consideration of their actions on the nervous system and, for a long time, they were the exclusive interest of neuroscientists. However, more recently, this family of proteins has been shown to possess essential cardiovascular functions. During cardiovascular development, neurotrophins and their receptors are essential factors in the formation of the heart and critical regulator of vascular development. Postnatally, neurotrophins control the survival of endothelial cells, vascular smooth muscle cells, and cardiomyocytes and regulate angiogenesis and vasculogenesis, by autocrine and paracrine mechanisms. Recent studies suggest the capacity of neurotrophins, via their tropomyosin-kinase receptors, to promote therapeutic neovascularization in animal models of hindlimb ischemia. Conversely, the neurotrophin low-affinity p75(NTR) receptor induces apoptosis of endothelial cells and vascular smooth muscle cells and impairs angiogenesis. Finally, nerve growth factor looks particularly promising in treating microvascular complications of diabetes or reducing cardiomyocyte apoptosis in the infarcted heart. These seminal discoveries have fuelled basic and translational research and thus opened a new field of investigation in cardiovascular medicine and therapeutics. Here, we review recent progress on the molecular signaling and roles played by neurotrophins in cardiovascular development, function, and pathology, and we discuss therapeutic potential of strategies based on neurotrophin manipulation.

Nerve growth factor beta/pro-nerve growth factor and their receptors in normal human oral mucosa

Nerve growth factor beta (NGF-beta) and its precursor proNGF are important for the differentiation and survival of neurons and dermal keratinocytes. The aim of this study was to determine the role that NGF might play in the differentiation and wound healing of oral mucosa. Cultured normal human oral mucosal keratinocytes expressed mRNA for NGF-beta/proNGF and for their receptors TrkA and p75(NTR). Lysates from cultured oral mucosal keratinocytes did not contain detectable amounts of mature 14-kDa NGF-beta but did contain several NGF proforms with molecular weights between 32 and 114 kDa. Culture medium from oral mucosal keratinocytes contained 75 kDa proNGF. The addition of NGF-beta significantly enhanced the proliferation of oral mucosal keratinocyte cultures and in vitro scratch closure. Immunostaining of biopsies from normal oral mucosa showed the presence of proNGF in all epithelial layers. NGF staining was observed in the granular and upper spinous cell layers. TrkA immunoreactivity was detected in basal and parabasal cells, with weak to moderate staining in spinous and granular cell layers. p75(NTR) staining was seen in basal cell layers. These findings indicate that NGF-beta/proNGF have mitogenic and motogenic effects on oral mucosal keratinocytes and therefore may aid in the healing of oral wounds. Differential expression of NGF and NGF receptors throughout the epithelium suggests a role in epithelial differentiation.

Nerve growth factor induces endothelial cell invasion and cord formation by promoting matrix metalloproteinase-2 expression through the phosphatidylinositol 3-kinase/Akt signaling pathway and AP-2 transcription factor

Nerve growth factor (NGF) is a well characterized neurotrophic agonist in the nervous system that triggers angiogenesis. In this study, we investigated the signaling mechanisms involved in NGF-induced angiogenesis. NGF stimulated endothelial cell invasion and cord formation on Matrigel in vitro but had marginal effect on proliferation and migration of these cells. NGF stimulated matrix metalloproteinase (MMP)-2 mRNA expression and protein secretion in human umbilical vein endothelial cells. Using synthetic and endogenous inhibitors of MMP-2 and MMP-2 small interfering RNA suppressed NGF-induced invasion and cord formation. We demonstrated that NGF-induced MMP-2 secretion, invasion, and cord formation are regulated via activation of the NGF receptor, TrkA, phosphatidylinositol 3-kinase (PI3K), and Akt using various pharmacological inhibitors. Specifically, NGF enhanced TrkA phosphorylation, PI3K activity, and Akt phosphorylation. Introduction of NGF-neutralizing antibodies, dominant-negative Akt, or wild-type PTEN effectively inhibited NGF-induced MMP-2 secretion and cord formation. Deletion and site-directed mutagenesis analysis of the MMP-2 promoter demonstrated that the AP-2-binding site is critical for NGF-induced MMP-2 promoter activity. NGF increased the DNA binding activity of AP-2, which was suppressed by inhibitors of TrkA and PI3K. Furthermore, transfection of AP-2 small interfering RNA effectively blocked NGF-induced MMP-2 secretion and cord formation. Finally, NGF promoted neovessel formation in Matrigel plugs in vivo, which was significantly inhibited by K252a and LY294002, but it failed to promote angiogenesis using MMP-2 knock-out mice. Our data collectively suggest that NGF stimulates endothelial cell invasion and cord formation by augmenting MMP-2 via the PI3K/Akt signaling pathway and AP-2 transcription factor, which may be responsible for triggering angiogenesis.

Nerve growth factor as an angiogenic factor

Nerve growth factor (NGF), a neurotrophin that plays a crucial role in promoting neurotrophic and neurotropic effects in sympathetic neurons, has recently been identified as a novel angiogenic molecule, which exerts a variety of effects in the cardiovascular system and on endothelial cells. In fact, NGF may contribute to maintenance, survival, and function of endothelial cells by autocrine and/or paracrine mechanisms. This review summarizes the involvement of NGF in the regulation of angiogenesis in both normal and pathological conditions.

Heterotypic RPE-choroidal endothelial cell contact increases choroidal endothelial cell transmigration via PI 3-kinase and Rac1

Age-related macular degeneration (AMD) is the major cause of non-preventable blindness. Severe forms of AMD involve breaching of the retinal pigment epithelial (RPE) barrier by underlying choroidal endothelial cells (CECs), followed by migration into, and subsequent neovascularization of the neurosensory retina. However, little is known about the interactions between RPE and CECs and the signaling events leading to CEC transmigration. While soluble chemotactic factors secreted from RPE can contribute to inappropriate CEC transmigration, other unidentified stimuli may play an additional role. Using a coculture model that maintains the natural structural orientation of CECs to the basal aspect of RPE, we show that "contact" with RPE and/or RPE extracellular matrix increases CEC transmigration of the RPE barrier. From a biochemical standpoint, contact between CECs and RPE results in an increase in the activity of the GTPase Rac1 within the CECs; this increase is dependent on upstream activation of PI 3-K and Akt1. To confirm a link between these signaling molecules and increased CEC transmigration, we performed transmigration assays while inhibiting both PI 3-K and Rac1 activity, and observed that both decreased CEC transmigration. We hypothesize that contact between CECs and RPE stimulates a signaling pathway involving PI 3-K, Akt1, and Rac1 that facilitates CEC transmigration across the RPE barrier, an important step in the development of neovascular AMD.

Nerve growth factor (NGF) promotes angiogenesis in the quail chorioallantoic membrane

Angiogenesis, the formation of new blood vessels, is tightly regulated by growth factors, such as vascular endothelial growth factor (VEGF) and fibroblast growth factor (FGF). The authors hypothesize that nerve growth factor (NGF), a well known neurotrophin, may play a direct angiogenic role. To test this hypothesis, the authors measured the effects of NGF on the natural vascularization of the quail chorioallantoic membrane (CAM). The angiogenic effect of NGF was compared to that of human recombinant VEGF165 (rhVEGF) and basic FGF (rhbFGF). In comparison to phosphate-buffered saline-treated controls, NGFs from different biological sources (mouse, viper, and cobra) increased the rate of angiogenesis in a dose-dependent fashion from 0.5 to 5 microg. For quantitative morphometry, grayscale images of the blood vessels end points of the CAM arteries were binarized for visualization and skeletonized for quantization by fractal analysis. In mouse NGF-treated embryos the fractal dimension (Df), indicative of arterial vessel length and density, increased to 1.266 +/- 0.021 compared to 1.131 +/- 0.018 (p < .001) for control embryos. This effect was similar to that of 0.5 microg rhVEGF (1.290 +/- 0.021, p < .001) and 1.5 microg rhbFGF (1.264 +/- 0.028, p < .001). The mouse NGF-induced angiogenic effect was blocked by 1 microM K252a (1.149 +/- 0.018, p < .001), an antagonist of the NGF/trkA receptor, but not by 1 microM SU-5416 (1.263 +/- 0.029, p < .001), the VEGF/Flk1 receptor antagonist, indicating a direct, selective angiogenic effect of NGF via quail embryo trkA receptor activation. These results confirm previous observations that NGF has angiogenic activity and suggest that this neurotrophin may also play an important role in the cardiovascular system, besides its well-known effects in the nervous system. The angiogenic properties of NGF may be beneficial in engineering new blood vessels and for developing novel antiangiogenesis therapies for cancer.

Promotion of functioning of human periodontal ligament cells and human endothelial cells by nerve growth factor

BACKGROUND

We have previously shown that cultured human periodontal ligament (HPL) cells produce nerve growth factor (NGF) and express mRNA of tyrosine kinase receptor (trkA), a high-affinity receptor of NGF. These findings suggest that NGF modulates the differentiation and proliferation of the periodontal ligament cells by paracrine and autocrine functions in vivo. Endothelial cells also express NGF and trkA. Therefore, NGF may regulate functions of periodontal ligament cells and endothelial cells during periodontal tissue regeneration.

METHODS

Effects of NGF on expressions of bone/cementum-related proteins (osteocalcin [OC], bone sialoprotein [BSP], bone morphogenetic protein [BMP-7], core binding factor alpha [Cbfa-1], and type I collagen), calcification in HPL cells, and proliferation and mRNA expression of vascular endothelial growth factor (VEGF), an endothelial cell mitogen, in human microvascular endothelial cells (HMVECs) were examined.

RESULTS

NGF elevated mRNA levels of OC, BSP, BMP-7, Cbfa-1, and type I collagen and enhanced mineral deposition in cultures of HPL cells. Furthermore, NGF stimulated mRNA expressions of VEGF-A and VEGF-B and cell proliferation in HMVEC.

CONCLUSION

These findings suggest that the functional regulation of periodontal ligament cells and endothelial cells by NGF might result in the acceleration of periodontal tissue regeneration in vivo.

Endothelial cell proliferation in the choriocapillaris during human retinal differentiation

BACKGROUND

Differentiation patterns of the neural retina and its retinal vasculature are not well matched. The foveal region differentiates first, however the central retina is not vascularised until late in gestation. The authors explored the hypothesis that higher rates of endothelial cell proliferation in the choriocapillaris of the central retina might compensate for the slow growth of central retinal vessels, providing supplementary nutrients to the region during the early stages of neuronal maturation.

METHODS

Frozen sections of five human fetal eyes (14-18.5 weeks' gestation), were examined for Ki-67 and CD34 immunoreactivity using confocal microscopy. Measurements of choriocapillaris area and the number of proliferating choroidal endothelial cells were used to calculate the rate of choroidal endothelial proliferation at five different chorioretinal locations.

RESULTS

The choriocapillaris area is consistently greater in the foveal region than at other locations and increases progressively with age. A higher rate of endothelial cell proliferation was found in parts of the choriocapillaris associated with the undifferentiated (proliferating) neural retina, compared with the differentiated, central region.

CONCLUSION

The findings suggest that mechanisms regulating proliferation and growth of the choroidal vasculature are independent of differentiation in the neural retina, and are thus profoundly different from mechanisms that regulate formation of the retinal vasculature.

Nerve growth factor-induced migration of endothelial cells

Nerve growth factor (NGF) is a well known neurotropic and neurotrophic agonist in the nervous system, which recently was shown to also induce angiogenic effects in endothelial cells (ECs). To measure NGF effects on the migration of cultured ECs, an important step in neoangiogenesis, we optimized an omnidirectional migration assay using human aortic endothelial cells (HAECs) and validated the assay with human recombinant basic fibroblast growth factor (rhbFGF) and human recombinant vascular endothelial growth factor (rhVEGF). The potencies of nerve growth factor purified from various species (viper, mouse, and recombinant human) to stimulate HAEC migration was similar to that of VEGF and basic fibroblast growth factor (bFGF) (EC50 of approximately 0.5 ng/ml). Recombinant human bFGF was significantly more efficacious than either viper NGF or rhVEGF, both of which stimulated HAEC migration by approximately 30% over basal spontaneous migration. NGF-mediated stimulation of HAEC migration was completely blocked by the NGF/TrkA receptor antagonist K252a [(8R*,9S*,11S*)-(/)-9-hydroxy-9-methoxycarbonyl-8-methyl-2,3,9,10-tetrahydro-8,11-epoxy-1H,-8H,11H-2,7b,11a-triazadibenzo(a,g)cycloocta(c,d,e)trindene-1-one] (30 nM) but not by the VEGF/Flk receptor antagonist SU-5416 [3-[(2,4-dimethylpyrrol-5-yl) methylidenyl]-indolin-2-one] (250 nM), indicating a direct effect of NGF via TrkA receptor activation on HAEC migration. Viper NGF stimulation of HAEC migration was additively increased by either rhVEGF or rhbFGF, suggesting a potentiating interaction between their tyrosine kinase receptor signaling pathways. Viper NGF represents a novel pharmacological tool to investigate possible TrkA receptor subtypes in endothelial cells. The ability of NGF to stimulate migration of HAEC cells in vitro implies that this factor may play an important role in the cardiovascular system besides its well known effects in the nervous system.

Nerve growth factor activates aorta endothelial cells causing PI3K/Akt- and ERK-dependent migration

Nerve growth factor (NGF) is a well-known neurotrophin. We determined whether NGF can activate endothelial cell migration and signalling that underlie angiogenic processes. We showed that aorta endothelial cells express mRNA for both the receptor tyrosine kinase TrkA and the p75 neurotrophin receptor (p75NTR) that associates with TrkA when signalling occurs. Pig aortic endothelial cells migrated when exposed to an NGF gradient, due to the simultaneous activation of the phosphatidylinositol 3-kinase and extracellular signal-regulated kinase signalling pathways. Furthermore, morphological changes were found in migrating cells: they appear with elongated structures with a smaller cell volume than control cells. Our data show that NGF is an activator of endothelial cells and suggest that NGF plays a role in mediating angiogenesis.