Angiogenesis, angiogenic factor expression and hematological malignancies

Solid tumor growth consists of an avascular and a subsequent vascular phase. Several studies have now shown that, as in solid tumors, angiogenesis also plays a critical role in the progression of hematological malignancies. Monoclonal gammopathy of undetermined significance (MGUS) and non-active to active multiple myeloma (MM) progress when plasma cells induce angiogenesis and this in turn promotes progression. The increased bone marrow neovascularization, increased angiogenic and proteolytic potential of plasma cells may explain the frequent occurrence of extramedullary localization in MM. As observed in active MM, enhanced bone marrow neovascularization is apparent in acute untreated lymphoblastic leukemia. In B-cell non-Hodgkin's lymphomas, angiogenesis is significantly enhanced in relation to progression. Angiostatic molecules, such as thalidomide, could also be considered for the clinical management of hematological tumors.

GABA immunoreactivity in the human cerebellar cortex: a light and electron microscopical study

The distribution of gamma-aminobutyric acid (GABA) in surgical samples of human cerebellar cortex was studied by light and electron microscope immunocytochemistry using a polyclonal antibody generated in rabbit against GABA coupled to bovine serum albumin with glutaraldehyde. Observations by light microscopy revealed immunostained neuronal bodies and processes as well as axon terminals in all layers of the cerebellar cortex. Perikarya of stellate, basket and Golgi neurons showed evident GABA immunoreactivity. In contrast, perikarya of Purkinje neurons appeared to be negative or weakly positive. Immunoreactive tracts of longitudinally- or obliquely-sectioned neuronal processes and punctate elements, corresponding to axon terminals or cross-sectioned neuronal processes, showed a layer-specific pattern of distribution and were seen on the surface of neuronal bodies, in the neuropil and at microvessel walls. Electron microscope observations mainly focussed on the analysis of GABA-labelled axon terminals and of their relationships with neurons and microvessels. GABA-labelled terminals contained gold particles associated with pleomorphic vesicles and mitochondria and established symmetric synapses with neuronal bodies and dendrites in all cortex layers. GABA-labelled terminals associated with capillaries were seen to contact the perivascular glial processes, basal lamina and endothelial cells and to establish synapses with subendothelial unlabelled axons.

Angiogenic activity of leptin in the chick embryo chorioallantoic membrane is in part mediated by endogenous fibroblast growth factor-2

Recently, it has been demonstrated that leptin, the product of the ob gene, playing a key role in the regulation of body weight, is angiogenic in vitro and in vivo. In this study we investigated the angiogenic potential of human leptin in vivo by using the chick embryo chorioallantoic membrane (CAM) assay, with the aim to establish whether this angiogenic activity is partly dependent on endogenous fibroblast growth factor-2 (FGF-2), which is normally expressed during CAM development. Results showed that leptin is able to stimulate angiogenesis and that the angiogenic response is similar to that obtained with FGF-2. The stimulating property of leptin is specific, as the application of anti-leptin antibodies onto the CAM significantly inhibits the angiogenic response. Moreover, this angiogenic activity is in part due to the activation of endogenous FGF-2. The application of anti-FGF-2 antibodies reduces the angiogenic response to leptin by 40%. Our study confirms that leptin is angiogenic in vivo and suggests that, at least in the chick CAM, its activity is in part mediated by the activation of endogenous FGF-2.

Developmental effects of lead acetate on the chick embryo metanephros

The developmental effects of lead acetate were studied in the chick embryo metanephros, the third renal rudiment that acquires morphological characteristics of functioning kidney already during the prenatal life. Lead exposure was obtained by applying a lead acetate solution on the chick embryo chorioallantoic membrane at the days 9, 10 and 11 of incubation. Quantitative evaluation of the lead concentration assessed by furnace atomic absorption spectrophotometry at the days 14 and 21 of incubation demonstrated metal presence both in the chorioallantoic membrane (CAM) and in metanephros (MN). The lead concentration was higher in CAM than in MN; the metal amount was similar in the CAM of 14 and 21 day embryos, but significantly higher in the 14day embryo MN than in the 21 day embryo MN. Morphological observations on metanephros tissue of control and lead-treated embryos were performed under light, electron transmission and electron scanning microscopes. Peculiar attention was devoted to the expression of the junctional protein connexin 43, the major component of the gap junctions in the renal cells. The results indicated that lead treatment does not intervene in the general differentiation of the metanephric nephrons. The lead is reabsorbed by the proximal tubule cells that are engulfed by endocytotic vacuoles and metal deposits and show long term degenerative changes. Expression of Cx43 protein and ultrastructure of gap junctions between proximal tubule cells appeared to be unchanged. The morphological aspects of the MN corpuscles and tubules agree with the suggestion of a lead cytotoxic effect but do not corroborate, at least in this experimental model, the view of primary damage exerted by lead on the gap junctions of the renal epithelial cells.

Cell-mediated delivery of fibroblast growth factor-2 and vascular endothelial growth factor onto the chick chorioallantoic membrane: endothelial fenestration and angiogenesis

Fibroblast growth factor-2 (FGF2) and vascular endothelial growth factor (VEGF) exert their angiogenic activity by interacting with endothelial cells in a distinct manner. In this study, we investigated the morphological features of endothelial cells of the chick embryo chorioallantoic membrane (CAM) microvasculature after stimulation with FGF2 or VEGF. In order to provide a continuous delivery of the growth factor, we utilized a recently developed gelatin sponge/CAM assay in which a limited number of FGF2- or VEGF-transfected cells were adsorbed onto gelatin sponges and applied on the top of the CAM on day 8 of development. Their angiogenic activity was compared to that exerted by a single bolus of the corresponding growth factor. All the angiogenic stimuli induced a comparable vasoproliferative response, as demonstrated by the appearance of similar numbers of immature blood vessels within the sponge on day 12. No angiogenic response was observed in CAMs implanted with the corresponding parental cell lines or vehicle. Electron microscopy demonstrated that VEGF-overexpressing cells modified the phenotype of the endothelium of the blood vessels at the boundary between the implant and the surrounding CAM mesenchyme. The endothelial lining of 30% of these vessels showed segmental attenuations, was frequently interrupted and became fenestrated, mimicking what is observed in tumor vasculature. In contrast, the vessels consisted of continuous endothelium sealed by tight junctions in all the other experimental conditions. These results indicate that FGF2 and VEGF interact with endothelial cells of the CAM in a distinct manner. Both growth factors induce a potent angiogenic response, but only VEGF delivered in a continuous manner by its transfectants can modify the phenotype of the otherwise quiescent endothelium of CAM blood microvessels. The gelatin sponge/CAM assay may constitute a new model to study the mechanisms leading to endothelial fenestration in tumor growth.

Glial cells and blood-brain barrier in the human cerebral cortex

The spatial relationship established between glial cells and microvasculature in the human cerebral cortex was analysed on peritumoral tissue of the parietal lobe removed during surgery. Observations performed by light microscope immunocytochemistry demonstrated that processes of astrocytes, strongly immunoreactive to both glial fibrillary acidic protein and S-100 protein, form sheaths to the capillaries, and that isolated cells positive to the oligodendrocyte marker 2',3'-cyclic nucleotide 3'-phosphodiesterase are detectable in perivascular areas. Morphometrical analysis by transmission electron microscopy showed that 80% of the vascular endothelium-pericyte layer is invested by small endfeet of astrocyte processes. This study demonstrates that either astrocyte bodies or oligodendrocytes as well as microgliocytes may substitute the astrocytic endfeet adhering to the capillary basement lamina.

Vascular endothelial growth factor and vascular endothelial growth factor receptor-2 expression in the chick embryo area vasculosa

Vascular endothelial growth factor is an angiogenic factor in vivo and in vitro that plays a crucial role in the control of blood vessel development and in pathological angiogenesis. The vascularized extraembryonic membranes of the chick embryo include the area vasculosa and the chorioallantoic membrane. In this study, we investigated the expression of vascular endothelial growth factor and of its receptor-2, specifically expressed by the endothelial cells, in the chick area vasculosa at days 6, 10 and 14 of incubation. Our results indicate that, in all the three developmental stages examined, vascular endothelial growth factor is clearly expressed in the endodermal cells immediately adjacent to the mesodermal endothelial cells which, in turn, expressed vascular endothelial growth factor receptor-2. These observations suggest that during the development of the vascular system, endodermal cells, expressing vascular endothelial growth factor, initiate angiogenesis by stimulating directly mesodermal cells, which express vascular endothelial growth factor receptor-2. Moreover, our data demonstrate that vascular endothelial growth factor receptor-2 expression is also maintained by endothelial cells in the later stages of development, until day 14 of incubation. In accord with other literature data, this suggests that vascular endothelial growth factor is required not only for proliferation, but also for the survival of endothelial cells.

Role of aquaporin-4 water channel in the development and integrity of the blood-brain barrier

In this study, we have investigated the expression of aquaporin 4 during blood-brain barrier development in the optic tectum of chick embryos and newly hatched chicks, by means of western-blot, reverse transcriptase-polymerase chain reaction, immunohistochemistry, and freeze-fracture and high-resolution immunogold electron microscopy. In the optic tecta of day-14 embryos, western blot analysis revealed an approx. 30 kDa band, immunoreactive for aquaporin-4, which was increased in day-20 embryos and in chicks. Semi-quantitative reverse transcriptase chain reaction experiments showed that there was already a high level of aquaporin-4 mRNA in day-9 embryos as well as in the subsequent stages and in newly hatched chicks. Immunohistochemically, reactivity for aquaporin-4 was detected in the optic tectum of day-14 embryos; similar results were obtained in telencephalon and cerebellum. Ultrastructurally, the microvessels of the tectum showed immunoreactivity for aquaporin-4 on the astroglial endfeet, which discontinuously surrounded endothelial cells joined by immature tight junctions. In the tectum, telencephalon and cerebellum of 20-day embryos and chicks, aquaporin-4 strongly labeled the ependymal cells and the subpial glial membranes, as well as the bodies and processes of astroglial cells. A continuous aquaporin-4 staining was found around the microvessel endothelial cells, which were sealed off from one another by extensive tight junctions. A complete astrocytic sheath, labeled by anti-aquaporin-4 gold particles, enveloped the endothelium-pericyte layer. Orthogonal arrays of particles were observed on fractured astrocytic membranes, starting from embryonic day 14 when the aquaporin-4 immunogold staining revealed clusters of gold particles, often forming square or rectangular clusters. The results showed that aquaporin-4 expression and organization of the intramembrane particles in orthogonal arrays followed the same temporal sequence. Finally, the lipopolysaccharide, a substance that induces blood-brain barrier distruption, determines a remarkable reduction in aquaporin-4 labeling, expressed by a few aquaporin-4 gold particles attached on swollen perivascular glial membranes. All these data show that aquaporin-4 expression occurs in the chick embryonic brain, in parallel with maturation and functioning of the blood-brain barrier and suggest that there is a close relationship between water transport regulation and brain development.

Coordinate immunoreactivity to vascular endothelial growth factor receptor-2 and its ligand suggests a paracrine regulation during the development of the vascular system in the chick embryo bursa of Fabricius

The bursa of Fabricius is a lymphoid organ of the chick which plays an important role in the development of the immune system. The role of angiogenic factors in the development of the vascular system of this organ has been poorly investigated. Vascular endothelial growth factor (VEGF) is a major regulator of endothelial cell proliferation, angiogenesis and vascular permeability, and its activities are mediated by two receptors, VEGFR-1 and VEGFR-2. In this study we have investigated by immunohistochemistry the VEGF and VEGFR-2 immunoreactivity in developing bursa of Fabricius. Starting from day 10 of incubation, the endodermal epithelium reacts with VEGF and gives rise to the lymphoid follicles, while the vascular endothelium reacts with VEGFR-2. These data support the view that VEGF acts as a paracrine stimulator of angiogenesis in the avian embryo and confirm the requirement of the endodermal layer for the normal formation of blood vessels by mesodermal cells.

Cholinergic nerve fibres associated with the microvessels of the human cerebral cortex: a study based on monoclonal immunocytochemistry for choline acetyltrasferase

The distribution of cholinergic nerve fibres associated with the microvasculature of the human parietal cerebral cortex was investigated by immunocytochemistry, employing monoclonal antibodies against choline acetyl-transferase, the acetylcholine-synthesizing enzyme. The results revealed strongly immunoreactive nerve fibres in the tunica adventitia of arterioles penetrating the superficial cortical layers from the pial vasculature. Networks of stained nerve fibres were seen within the tunica muscularis of the radially directed arterioles that cross the intermediate and deep cortical laminae, and of their transverse and recurrent branches. Tiny positive nerve fibres were also seen around the cortex capillaries, some reaching the endothelial cells. The morphological data support the involvement of acetylcholine in microvasculature local regulation, possibly with a differentiated role in the arterioles and capillaries.

Postnatal vasculogenesis

It is generally accepted that vasculogenesis is limited to early embryogenesis and is believed not to occur in adult, whereas angiogenesis occurs in both the developing embryo and postnatal life. However, the distinction between them is not absolute, because both require endothelial cell proliferation and migration and three-dimensional reorganization of newly formed blood vessels, nor are they mutually exclusive, inasmuch as angioblasts can be incorporated into expanding pre-existing blood vessels. Recent observations indicate that vasculogenesis may not be restricted to early embryogenesis, but may also have a physiological role or contribute to the pathology of vascular diseases in adults. The major evidence in favor of this new view comes from: (i) demonstration of the presence of circulating endothelial cells and endothelial precursor cells; (ii) newly described mechanisms of blood vessel formation in tumor growth. The potential biomedical applications of endothelial precursor cells and the new opportunities for the development of new forms of tumor-targeted treatments are discussed.

Aquaporin-4 deficiency in skeletal muscle and brain of dystrophic mdx mice

We report a detailed study of AQP4 expression in the neuromuscular system of mdx mice. Immunocytochemical analysis performed by double immunostaining revealed that mdx mice manifest a progressive reduction in AQP4 at the sarcolemmal level of skeletal muscle fast fibers and that type IIB fibers are the first to manifest this reduction in AQP4 expression. No labeling was observed in the cytoplasm of muscle fibers, indicating that the reduction in sarcolemma staining is not associated with an intracellular compartmentalization of mistargeted protein. By Western blot and RT-PCR analysis, we found that whereas the total content of AQP4 protein decreased (by 90% in adult mdx mice), mRNA levels for AQP4 remained unchanged. A similar age-related reduction in AQP4 expression was found in brain astrocytic end-feet surrounding capillaries of mdx mice. Morphometric analysis performed after immunogold electron microscopy indicated a reduction of approximately 85% in gold particles (32+/-2/microm vs. 4.7+/-0.61/microm). Western blot experiments conducted using membrane fractions from brain cortex revealed a strong reduction (of 70%) in AQP4 protein in adult mdx mice, and RT-PCR experiments demonstrated that the reduction was not at transcription level. More interesting was the finding that AQP4 reduction was associated with swelling of astrocytic perivascular processes whose ultrastructural modifications are commonly indicated as an important and early event in the development of brain edema. No apparent reduction in AQP4 was found in mdx stomach and kidney. Our data provide evidence that dystrophin deficiency in mdx mice leads to disturbances in AQP4 assembly in the plasma membrane of fast skeletal muscle fibers and brain astrocytic end-feet, suggesting that changes in the osmotic equilibrium of the neuromuscular apparatus may be involved in the pathology of muscular dystrophy.

Immunogold cytochemistry of the blood-brain barrier glucose transporter GLUT1 and endogenous albumin in the developing human brain

The blood-brain barrier (BBB) glucose transporter, GLUT1, was detected by immunogold electron microscopy on the microvascular compartment of the human foetus telencephalon at the 12th and 18th weeks of gestation. By computerized morphometry, the cellular and subcellular localization of the immunosignal for GLUT1 was quantitatively evaluated. The study showed that the glucose transporter is strongly expressed by endothelial cells while a very low signal is detected on vascular pericytes. The GLUT1 antigenic sites are preferentially associated to the ablumenal and junctional plasma membranes of the endothelial cells and tend to increase significantly with age. A parallel study carried out by the endogenous serum protein albumin demonstrated that already at the 12th week the endothelial routes are hindered to the protein as happens at the blood-endothelium interface of mature brain. The results demonstrate that in the human foetus the brain microvessels express BBB-specific functional activities early.

Immunolocalization of glutamic acid decarboxylase in postmortem human cerebellar cortex. A light microscopy study

The distribution of glutamic acid decarboxylase (GAD), the gamma-aminobutyric acid (GABA) synthesizing enzyme, was examined in the postmortem human cerebellar cortex by immunocytochemistry. The results, obtained on nervous tissues taken at autopsy and fixed within 24-36 h after death, enabled the authors to precisely reveal the topographical distribution of GAD-containing neurons and axon terminals in the human cerebellar cortex. Labeled neurons, corresponding to different neuronal cytotypes of the cerebellar cortex, showed a diffuse cytoplasmic immunoreactivity in both bodies and processes. Labeled axon terminals appeared as immunoreactive puncta. The use of immunocytochemistry in the detection of GAD in the postmortem human brain greatly increases the possibility of carrying out morphological studies on the GABAergic system, both in normal and in pathological conditions.

Glutamic acid decarboxylase-positive neuronal cell bodies and terminals in the human cerebellar cortex

The distribution of gamma-aminobutyric acid (GABA) in the human cerebellar cortex was studied using immunohistochemistry for glutamic acid decarboxylase (GAD), the enzyme that catalyses GABA synthesis. Observations by light microscopy revealed, in all layers of the cerebellar cortex, strong, punctate positivity for GAD, related to putative GABAergic nerve terminals, as well as a diffuse cytoplasmic immunoreactivity within neuronal cell bodies. GAD-positive nerve terminals were found in close relationship with the walls of the cerebellar cortex microvessels. Observations by electron microscopy revealed positive nerve terminals in contact with the astrocyte perivascular sheath of capillaries. GAD immunoreactivity was also detected within astroglial perivascular endfeet and endothelial cells. The findings provide further insights into the GABAergic synapses of the circuitry of the human cerebellar cortex. The detection of 'vascular' GAD immunoreactivities suggests that GABAergic mechanisms may regulate cerebellar microvessel function.

An experimental study in the chick embryo chorioallantoic membrane of the anti-angiogenic activity of cyclosporine in rheumatoid arthritis versus osteoarthritis

OBJECTIVE AND DESIGN

Angiogenesis plays an important role in the pathogenesis of rheumatoid arthritis (RA) and correlates with clinical score, synovial hyperplasia and infiltration of inflammatory cells. Many of the available treatments for RA have been shown to possess some degree of anti-angiogenic activity. Here, we studied the effect of cyclosporine, which exerts anti-angiogenic activity in vitro and in vivo [1] on angiogenesis induced in vivo in the chick embryo chorioallantoic membrane (CAM) by synovial RA and osteoarthritis (OA) tissues.

MATERIAL AND METHODS

Wet synovial biopsies from 10 RA and 6 OA patients were treated with vehicle alone or with cyclosporine and implanted on the CAM at day 8 of incubation. On day 12, CAM tissues were assessed for the extent of angiogenesis and mononuclear cell infiltration.

RESULTS

Cyclosporine inhibited angiogenesis and reduced the number of mononuclear cells in the CAM extracellular matrix only in RA implants.

CONCLUSIONS

These data provide further evidence for a central role of new-formed blood vessels in RA. Moreover, cyclosporine on account of both its immunosuppressive and its anti-angiogenic activity can be proposed for the treatment of RA.

The chick embryo chorioallantoic membrane as a model for in vivo research on anti-angiogenesis

Anti-angiogenesis, i.e. inhibition of blood vessel growth, is being investigated as a way to prevent the growth of tumors and other angiogenesis-dependent diseases. Pharmacological inhibition interferes with the angiogenic cascade or the immature neovasculature with synthetic or semi-synthetic substances, endogenous inhibitors or biological antagonists. The chick embryo chorioallantoic membrane (CAM) is an extraembryonic membrane commonly used in vivo to study both new vessel formation and its inhibition in response to tissues, cells, or soluble factors. Angiogenesis or anti-angiogenesis is evaluated quantitatively or semiquantitatively. The fields of application of CAM in the study of anti-angiogenesis, including our personal experience, are illustrated in this paper.

Aquaporin-4-containing astrocytes sustain a temperature- and mercury-insensitive swelling in vitro

In order to understand the molecular mechanism underlying astroglial swelling, we studied primary astrocyte cultures from newborn mouse and analyzed them for expression of functional water channels. Immunocytochemical analysis of mouse brain confirms the presence of AQP4 location in astrocytic endfeet with a polarized pattern, as found in rat. Using Southern blot PCR and Western blot analysis, we demonstrate that primary astrocyte cultures from mouse express the AQP4 water channel at both the RNA and protein levels. Two polypeptides, of 30 kDa and 32 kDa, were identified in the astrocytes. Densitometric analysis demonstrates that the 32-kDa form represents 25% of the total AQP4 protein. Moreover, immunofluorescence experiments show strong surface membrane expression of AQP4 protein in cultured cells, even though the polarity of the expression is not maintained. Furthermore, functional studies indicate that cultured astrocytes manifest rapid and temperature-independent volume changes in response to osmotic gradients, in agreement with a channel-mediated water transport. Water movement was found to be HgCl(2) insensitive, suggesting AQP4 and AQP7 as putative water channels. Using Western blot and PCR experiments, we exclude the presence of AQP7 in astrocytes, indicating that only AQP4 is responsible for the rapid water movement. Altogether, the results indicate that primary astrocyte cultures are a valid cell model for further investigation of the molecular mechanism of water movement in the brain and its physiological regulation.

Inhibition of protein kinase C counteracts TNFalpha-induced intercellular adhesion molecule 1 expression and fluid phase endocytosis on brain microvascular endothelial cells

TNFalpha (100 U/ml, 24 h) upregulated intercellular adhesion molecule 1 (ICAM1) expression and fluid phase endocytosis (FPE) of horseradish peroxidase on brain microvascular endothelial cell (BMEC) culture. The protein kinase C (PKC) inhibitor staurosporin (0. 5-10 nM) antagonized ICAM1 expression and FPE due to TNFalpha, whereas the protein kinase A inhibitor H89 (0.5-10 nM) did not. These findings indicate that a PKC-dependent mechanism may affect TNFalpha signalling on different barrier properties of BMECs.

Interferon beta-1a prevents the effects of lipopolysaccharide on embryonic brain microvessels

By means of light and electron microscopy we have studied the effect of interferon beta-1a (IFNbeta-1a) in the optic tecta of 20-day-old chick embryos under normal conditions and after exposure to lipopolysaccharide (LPS) which mimics the blood-brain barrier (BBB) disruption in meningoencephalitis. Optic tecta were examined for: (i) ultrastructure by means of transmission electron microscopy; (ii) the immunohistochemical localization of HT7 antigen, a specific marker of differentiation of the brain microvessels; (iii) the brain microvessel permeability, by means of horseradish peroxidase (HRP) tracer; (iv) the expression of microvessel glycoconjugates, by means of lectin histochemistry, using Ricinus communis agglutinin-I (RCA-I), specific for beta-D-galactosyl moieties and Wheat Germ agglutinin (WGA) specific for sialyl and N-acetylglucosaminyl moieties. A morphometric evaluation of brain microvessel permeability and of glycoconjugate expression was also performed. In control- and in IFNbeta-1a-treated embryos, HRP was confined to the vessel lumina which were sealed by the interendothelial tight junctions. RCA-I binding sites were recognizable both in the basal membranes and in the tight junctions, while WGA sites were present on the luminal side of the endothelial cells. HRP was blocked in the vessels lumina by the interendothelial tight junctions. After LPS treatment, HRP showed an extravascular localization and the labeling of microvessels by anti-HT7 antibodies disappeared. RCA-I binding was only found ultrastructurally and appeared as irregularly clustered gold particles, in the cleft of damaged tight junctions, but were no longer detectable in the endothelial basement membranes. After pretreatment of LPS-treated embryos with IFNbeta-1a, the vessel permeability to HRP strongly decreased and the vessels showed the normal pattern of HT7 protein and of the RCA-I binding sites. These results indicate that the changes induced by LPS in the endothelial cells are prevented by IFNbeta-1a.

Angiogenesis and mast cell density with tryptase activity increase simultaneously with pathological progression in B-cell non-Hodgkin's lymphomas

Node biopsies of 16 benign lymphadenopathies and 72 B-cell non-Hodgkin's lymphomas (B-NHLs) were investigated for counts of microvessels, total metachromatic mast cells (MCs) and MCs expressing tryptase, an angiogenesis-inducing molecule. Counts were higher in B-NHLs. When grouped according to the Working Formulation (WF) malignancy grades, they were significantly higher in low-grade B-NHLs vs. lymphadenopathies and intermediate-grade vs. low-grade tumors and there was a further increase in the high-grade tumors. A high correlation was demonstrated in all groups of tissues between microvessel counts and both total metachromatic and tryptase-reactive MCs. These results suggest that angiogenesis in B-NHLs increases with their progression, and that MCs cooperate in its induction via the tryptase contained in their secretory granules.

Hematopoiesis and angiogenesis: a link between two apparently independent processes

In early ontogeny, hematopoiesis is closely associated with angiogenesis. This article reviews recent studies on the role of angiogenic factors that regulate the proliferation and differentiation of endothelial cells in promoting hematopoietic cell growth and studies on the ability of hematopoietic cytokines to affect several endothelial cell functions. The findings in all these studies support the hypothesis formulated at the beginning of this century that a common ancestral cell, the hemangioblast, gives rise to cells of both the endothelial and the hematopoietic lineages.

In vivo angiogenic activity of urokinase: role of endogenous fibroblast growth factor-2

In vitro experimental evidences suggest that the proteolytic degradation of the extracellular matrix (ECM) by activation of the urokinase-type plasminogen activator (uPA)/plasmin system may affect growth factor activity and bioavailability. However, no direct in vivo observations were available to support this hypothesis. Here we demonstrate that endothelial GM 7373 cells overexpressing human uPA (uPA-R5 cells) cause the release of (125)I-labeled fibroblast growth factor-2 (FGF2) from endothelial ECM in a plasmin-dependent manner. Accordingly, uPA-R5 cells are angiogenic in vivo when applied on the top of the chorioallantoic membrane (CAM) of the chick embryo. In contrast, mock-transfected Neo2 cells are unable to release ECM-bound (125)I-FGF2 and are poorly angiogenic. Neovascularization elicited by uPA-R5 cells is significantly reduced by neutralizing anti-FGF2 antibodies to values similar to those observed in Neo2 cell-treated CAMs. Accordingly, purified human uPA stimulates neovascularization of the CAM in the absence of an inflammatory response. The angiogenic activity of uPA is significantly inhibited by neutralizing anti-FGF2 antibodies or by pretreatment with phenylmethylsulfonyl fluoride. The non-catalytic, receptor-binding amino-terminal fragment of uPA is instead non angiogenic. Taken together, the data indicate that uPA is able to induce angiogenesis in vivo via a plasmin-dependent degradation of ECM that causes the mobilization of stored endogenous FGF2.

Alterations of blood vessel development by endothelial cells overexpressing fibroblast growth factor-2

A close relationship exists between angiogenesis and the formation of vascular lesions. The development of the vascular system in the chick embryo chorioallantoic membrane (CAM) may thus represent a model to study the effects of the deregulation of endothelial cell behaviour. Alterations of the developing vascular tree of the CAM were observed after exposure to murine aortic endothelial (MAE) cells overexpressing human fibroblast growth factor-2 (FGF2) cDNA (pZipFGF2 MAE cells), or to their conditioned medium (CM). pZipFGF2 MAE cells injected into the allantoic sac or applied on to the CAM of day 8-9 chick embryos induce neovascularization and the appearance of haemangioma-like lesions. This activity was not prevented by anti-FGF2 antibodies. The CM from pZipFGF2 MAE cells was also active when adsorbed into a gelatin sponge and applied on to the CAM, both in the absence and in the presence of anti-FGF2 antibodies. No effects on vessel development were exerted by parental MAE cells, FGF2-transfected NIH 3T3 fibroblasts, or their conditioned media. In vitro, pZipFGF2 MAE cell CM caused parental MAE cells to invade fibrin gels and to undergo morphogenesis on Matrigel. This activity was not mimicked by recombinant FGF2 nor affected by anti-FGF2 antibodies, and depended on a M (r) approximately 45 000 heat-labile heparin-binding factor. Size exclusion chromatography of pZipFGF2 MAE cell CM demonstrated that the in vitro activity co-purified with an in vivo angiogenic capacity. Thus, FGF2 overexpression in mouse endothelial cells induces the production of an angiogenic activity distinct from FGF2, which may contribute to the genesis of angioproliferative lesions.

Localization of factor VIII-related antigen in the endothelium of the chick embryo chorioallantoic membrane

In this study, by using a polyclonal antibody against factor VIII-related antigen (FVIII-RA), we have examined the expression of FVIII-RA in the blood and lymphatic vessels of the chick embryo chorioallantoic membrane (CAM). The antibody marked the endothelium of blood and lymphatic vessels starting from day 8 of incubation and the cytoplasm of the allantoic epithelial cells. The application of this antibody may be useful for quantifying neovascularization in response to various angiogenic stimuli applied to the CAM.