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Biomedical subjects

W Risau

Publications and source records attributed to W Risau.

At least 127 records · Page 7Linked to original sources
PubMed1990

Development of the blood-brain barrier.

The microenvironment of the CNS is important for neuronal function, and the blood-brain barrier is involved in its maintenance. The barrier is present in a complex cellular system at the level of the tight junctions between endothelial cells. The unique properties of the endothelial cells in the CNS compared with those present in other organs are not predetermined by brain-specific endothelial precursors but are induced by the neural environment during the development of the vascular system. Astrocytes that tightly appose endfeet onto the abluminal side of brain capillaries seem to be important for the induction and maintenance of the endothelial barrier.

Animals↗
PubMed1990

Angiogenic growth factors.

Angiogenesis, the formation of new blood vessels, plays a central role in a variety of physiological and pathological processes such as embryonic development, wound healing and tumor growth. It is a complex, multi-step process that involves the migration and proliferation of capillary endothelial cells. Several factors that stimulate the proliferation of endothelial cells in vitro have been shown to induce angiogenesis in vivo. Among these angiogenic growth factors are wide-spectrum multifunctional mitogens (e.g. the fibroblast growth factors) and the recently identified factors with distinct specificity for vascular endothelial cells (e.g. the platelet-derived endothelial cell growth factor). Another group of factors apparently induce angiogenesis indirectly (e.g. transforming growth factor-beta) by stimulating target cells to release angiogenic factors or by other mechanisms. The differential expression, release and activation of these factors might regulate angiogenesis under various physiological and pathological conditions.

Angiogenesis Inducing Agents↗
PubMed1990

Immune function of the blood-brain barrier: incomplete presentation of protein (auto-)antigens by rat brain microvascular endothelium in vitro.

The endothelial blood-brain barrier (BBB) has a critical role in controlling lymphocyte traffic into the central nervous system (CNS), both in physiological immunosurveillance, and in its pathological aberrations. The intercellular signals that possibly could induce lymphocytes to cross the BBB include immunogenic presentation of protein (auto-)antigens by BBB endothelia to circulating T lymphocytes. This concept has raised much, though controversial, attention. We approached this problem by analyzing in vitro immunospecific interactions between clonal rat T lymphocyte lines with syngeneic, stringently purified endothelial monolayer cultures from adult brain micro-vessels. The rat brain endothelia (RBE) were established from rat brain capillaries using double collagenase digestion, density gradient fractionation and selective cytolysis of contaminating pericytes by anti-Thy 1.1 antibodies and complement. Incubation with interferon-gamma in most of the brain-derived endothelial cells induced Ia-antigens in the cytoplasm and on the cell surface in some of the cells. Before the treatment, the cells were completely Ia-negative. Pericytes were unresponsive to IFN-gamma treatment. When confronted with syngeneic T cell lines specific for protein (auto-)antigens (e.g., ovalbumin and myelin basic protein, MBP), RBE were completely unable to induce antigen-specific proliferation of syngeneic T lymphocytes irrespective of pretreatment with IFN-gamma and of cell density. RBE were inert towards the T cells, and did not suppress T cell activation induced by other "professional" antigen presenting cells (APC) such as thymus-derived dendritic cells or macrophages. IFN-gamma-treated RBE were, however, susceptible to immunospecific T cell killing. They were lysed by MBP-specific T cells in the presence of the specific antigen or Con A. Antigen dependent lysis was restricted by the appropriate (MHC) class II product. We conclude that the interaction of brain endothelial cells with encephalitogenic T lymphocytes may involve recognition of antigen in the molecular context of relevant MHC products, but that this interaction per se is insufficient to initiate the full T cell activation program.

Animals↗
PubMed1990

In situ detection of basic fibroblast growth factor by highly specific antibodies.

Basic fibroblast growth factor (bFGF) is thought to be of major importance for fibrosis and angiogenesis. Despite intensive studies dealing with the biochemistry and multiple biologic effects of bFGF, the cellular distribution is virtually unknown. Therefore, using the indirect immunoperoxidase technique, we examined the effect of bFGF on a large pattern of normal, inflammatory, and tumorous human tissues. Staining was performed on cryostat sections with a highly specific affinity-purified antiserum. In normal tissues, especially those of the thymus and placenta, mainly dendritic cells contained the growth factor. High levels of bFGF were also detected in basal cells and gland epithelial cells of skin biopsies. A conspicuous expression was observed in chronic inflammatory tissues corresponding to a generally pronounced proliferation of fibroblasts and endothelial cells in these situations. Tumors revealed a very heterogenous staining pattern. In some lesions, bFGF was predominantly present in infiltrating and endothelial cells. In several, neoplasms tumor cells exhibited an intensive staining. In some, especially vascular tumors, bFGF could not be detected. From the staining results it is concluded that angiogenesis is not simply controlled by the presence of bFGF but is mediated by a balance of several angiogenic inducers and inhibitors.

Blood Cells↗
PubMed1989

Endothelioma cells expressing the polyoma middle T oncogene induce hemangiomas by host cell recruitment.

Mouse endothelioma cells expressing the polyoma middle T oncogene induced hemangiomas in a variety of species such as mice, rats, chicks, and quails. In embryos and newborn mice the hemangiomas expanded within 10-18 hr of injection, disrupting the vasculature and causing the death of the animal. In contrast, the hemangiomas formed a stable structure reminiscent of benign human hemangiomas in adult mice within 5 days. Analysis of the cells comprising the hemangioma revealed that over 95% of the endothelial cells were host derived. No induction of host cell proliferation was detected, and no endothelial mitogens were secreted by the endothelioma cells in vitro. The maintenance of the hemangioma appeared to require the continuous presence of endothelioma cells. The results indicate that these endothelioma cells act as a potent stimulating agent in the rapid formation of hemangiomas by recruiting nonproliferating host endothelial cells.

Animals↗
PubMed1989

Expression of synthetic genes encoding bovine and human basic fibroblast growth factors (bFGFs) in Escherichia coli.

Synthetic genes encoding bovine and human basic fibroblast growth factors (bFGFs) were assembled and cloned using established Escherichia coli expression plasmids. Transformed E. coli cells were able to synthesize either a fusion protein, comprising the first seven amino acids of beta-galactosidase, a linker fragment and bovine FGF, or genomic human bFGF. The two growth factors were purified from E. coli lysates by cation exchange and heparin-Sepharose affinity chromatography. The purified recombinant proteins were biologically active as monitored by their mitogenic activity for bovine aortic endothelial cells and their angiogenic capacity in the rabbit cornea.

Amino Acid Sequence↗
PubMed1989

Role of growth factors in the formation of blood vessels.

The turnover of endothelial cells in the normal human adult male is very low, on the order of years. However, in a number of mainly pathological conditions endothelial cells rapidly proliferate, thereby giving rise to new blood vessels (a process called angiogenesis). Angiogenesis-inducing factors have been purified from normal and tumor tissues. Some of these factors are growth or chemotactic factors for endothelial cells. Others have no effect in vitro and are thought to act via indirect mechanisms. Growth and chemotactic factors are also secreted by endothelial cells themselves and may be involved in the development of the vascular wall. In addition they might play a role in atherosclerosis.

Angiogenesis Inducing Agents↗
PubMed1988

Cultured, AIDS-related Kaposi's sarcoma cells express endothelial cell markers and are weakly malignant in vitro.

Up to 30% of patients with acquired immunodeficiency syndrome (AIDS) suffer from Kaposi's sarcoma (AIDS-KS). The histogenesis and neoplastic nature of this tumor is still controversial. We have established cell cultures of KS biopsies from 7 patients with AIDS. All donors were seropositive for the human immunodeficiency virus I (HIV-I), cytomegalovirus (CMV) and hepatitis B virus (HBV). The tumors were histologically shown to be KS. Cell cultures derived from these tumors all expressed the endothelial cell marker BMA 120 antigen. Most of these cultures were positive for acetylated low-density lipoprotein (acLDL) uptake and alkaline phosphatase (AP) expression, and negative for factor-VIII-related antigen (FVIII-RAg). The staining pattern was heterogeneous with respect to number of endothelial cell markers expressed in each culture. We conclude from subcloning experiments that the cultured cells cease to express acLDL receptor and AP, but not the antigen detected by the monoclonal antibody (MAb) BMA 120. The cells grew well in culture up to 50 passages and showed a fibroblast-like morphology. Assays performed to investigate their degree of malignancy revealed a significantly increased passage number under reduced serum conditions as compared to normal fibroblasts but no tumor formation in nude mice. Neither HIV, HBV nor CMV sequences were found in any of the cell lines tested. We conclude that AIDS-KS is an endothelial-cell-derived neoplasm of low malignancy and that HIV, HBV and CMV are not directly involved in its genesis.

Acquired Immunodeficiency Syndrome↗
PubMed1988

Endothelial cell growth factors in embryonic and adult chick brain are related to human acidic fibroblast growth factor.

We have investigated the nature of endothelial cell growth factors in 14-day embryonic and adult chick brain extracts. Mitogenic activity was isolated by a combination of cation-exchange, heparin-Sepharose affinity, and reverse-phase HPLC. Two major mitogenic fractions eluted from heparin-Sepharose at 0.8-1.3 M and 1.5-2 M. Biologically active proteins eluting at 0.8-1.3 M NaCl, after purification to homogeneity from embryonic and adult brain, were found to possess the same amino-terminal sequence as human acidic fibroblast growth factor (aFGF). The notion that the isolated mitogens represent chick aFGF is further supported by the findings that their affinity for heparin and their retention behavior in highly resolutive HPLC are indistinguishable from those of genuine aFGF. Mitogenic activities eluting at 1.5-2 M NaCl were also present in embryonic and adult brain, but in quantities insufficient for preliminary characterization. The high specific mitogenic activity for endothelial cells, high affinity for heparin and cross-reactivity with antibodies against bovine basic FGF (bFGF) suggest a relationship of those materials with basic FGF. Our data also suggest that the sequence of aFGF is highly conserved among vertebrates. While angiogenesis occurs predominantly in the embryonic brain, the absence of notable differences in the contents of the potent angiogenic factors aFGF and bFGF in embryonic versus adult chick brain is interesting.

Amino Acid Sequence↗
PubMed1988

Changes in the vascular extracellular matrix during embryonic vasculogenesis and angiogenesis.

We have previously characterized monoclonal antibodies against chick brain cells. One of them (14-2B2) brightly stained all capillaries in frozen sections of chick brain. Here we show that this antibody is directed against chick fibronectin. Using this antibody and polyclonal antibodies against laminin, we have studied the development of the vascular extracellular matrix. Vasculogenesis, the development of capillaries from in situ differentiating endothelial cells, was studied in yolk sac blood islands and intraembryonic dorsal aorta. Blood islands produced high levels of fibronectin but not laminin. Early intraembryonic capillaries all expressed fibronectin but little if any laminin. The dorsal aorta of a 6-day-old chick embryo has several layers of fibronectin-producing cells, but is devoid of laminin. Laminin expression commenced at Day 8 and by Day 10 an adult-like distribution was found in the aortic vascular wall. Angiogenesis, the formation of capillaries from preexisting vessels, was studied during brain development. Capillary sprouts invading the neuroectoderm at Embryonic Day 4 migrated in a fibronectin-rich matrix devoid of laminin. Ultrastructural immunolocalization demonstrated the presence of fibronectin exclusively on the abluminal site of the endothelial cells. Beginning on Day 6, laminin codistributed with fibronectin in brain capillaries. We conclude that immature capillaries migrate and proliferate in a fibronectin-rich extracellular matrix, which is subsequently remodeled acquiring basement membrane-like characteristics. We suggest that laminin expression is an early indication of vascular maturation.

Animals↗
PubMed1988

Preferential expression of a 130,000-Da cell surface protein by vascular wall cells in vitro and in vivo.

Monoclonal antibodies have been raised against cell surface proteins of cultured bovine retinal pericytes. One antibody was selected, designated PC4, which preferentially stained primary cultures of bovine pericytes and smooth muscle cells, but not endothelial cells and fibroblasts. In freshly plated cells a homogeneous cell surface staining was observed, whereas in well-spread cells the antigen was concentrated at cell attachment sites. The antigen remained at these sites after spontaneous detachment of the cells. PC4 monoclonal antibodies reacted with a major protein of 130,000 Da and two minor antigens of 75,000 and 70,000 Da in immunoblots of extracts from cultured pericytes and smooth muscle cells and from fibroblasts cultured for an extended period of time. In frozen sections of bovine tissues the antigen was found in the vascular wall. There was no staining of skeletal muscle cells or duodenal smooth muscle cells, indicating that the antigen may be a specific component of the vascular wall.

Animals↗
PubMed1988

Vasculogenesis and angiogenesis in embryonic-stem-cell-derived embryoid bodies.

Embryonic stem cells (ESC) have been established previously from the inner cell mass cells of mouse blastocysts. In suspension culture, they spontaneously differentiate to blood-island-containing cystic embryoid bodies (CEB). The development of blood vessels from in situ differentiating endothelial cells of blood islands, a process which we call vasculogenesis, was induced by injecting ESC into the peritoneal cavity of syngeneic mice. In the peritoneum, fusion of blood islands and formation of an in vivo-like primary capillary plexus occurred. Transplantation of ESC and ESC-derived complex and cystic embryoid bodies (ESC-CEB) onto the quail chorioallantoic membrane (CAM) induced an angiogenic response, which was directed by nonyolk sac endoderm structures. Neither yolk sac endoderm from ESC-CEB nor normal mouse yolk sac tissue induced angiogenesis on the quail CAM. Extracts from ESC-CEB stimulated the proliferation of capillary endothelial cells in vitro. Mitogenic activity increase during in vitro culture and differentiation of ESC. Almost all growth factor activity was associated with the cells. The ESC-CEB derived endothelial cell growth factor bound to heparin-sepharose. The identification of acidic fibroblast growth factor (FGF)in heparin-sepharose-purified material was accomplished by immunoblot experiments involving antibodies against acidic and basic FGF. We conclude that vasculogenesis, the development of blood vessels from in situ differentiating endothelial cells, and angiogenesis, the sprouting of capillaries from preexisting vessels are very early events during embryogenesis which can be studied using ESC differentiating in vitro. Our results suggest that vasculogenesis and angiogenesis are differently regulated.

Animals↗
PubMed1987

Tumor necrosis factor type alpha, a potent inhibitor of endothelial cell growth in vitro, is angiogenic in vivo.

Tumor necrosis factor type alpha (TNF-alpha) inhibits endothelial cell proliferation in vitro. Basal cell growth (in the absence of exogenously added growth factor) and fibroblast growth factor (FGF)-stimulated cell proliferation are inhibited in a dose-dependent manner from 0.1 to 10 ng/ml with half-maximal inhibition occurring at 0.5-1.0 ng of TNF-alpha per ml. Bovine aortic and brain capillary endothelial and smooth muscle cells are similarly affected. TNF-alpha is a noncompetitive antagonist of FGF-stimulated cell proliferation. Its action on endothelial cells is reversible and noncytotoxic. Surprisingly, TNF-alpha does not seem to inhibit endothelial cell proliferation in vivo. In the rabbit cornea, even a high dose of TNF-alpha (10 micrograms) does not suppress angiogenesis induced by basic FGF. On the contrary, in this model system TNF-alpha stimulates neovascularization. The inflammatory response that is seen in the cornea after TNF-alpha implantation suggests that the angiogenic properties of this agent may be a consequence of leukocyte infiltration.

Animals↗
PubMed1987

Polarized secretion of a platelet-derived growth factor-like chemotactic factor by endothelial cells in vitro.

Cultured bovine aortic endothelial cells secrete a potent migration-stimulating factor for vascular smooth muscle cells (SMCs) and adventitial fibroblasts. Vascular pericytes are 20-fold less responsive, and endothelial cells themselves do not respond at all. Checkerboard analysis of SMC migration in a micro-chemotaxis chamber assay shows that the factor is chemotactic. Chemotactic activity for SMCs and adventitial fibroblasts is specifically inhibited by antibodies against platelet-derived growth factor. Endothelial cells cultured on nitrocellulose filters secrete the platelet-derived growth factor-like factor almost exclusively into the basal compartment. We suggest that this factor plays an important role in the recruitment of vascular wall cells during the morphogenesis of blood vessels and pathological conditions, such as atherosclerosis.

Animals↗
PubMed1987

Regression of blood vessels precedes cartilage differentiation during chick limb development.

We have previously investigated distinct areas of vascular regression in the developing vascular system of the chick limb bud. Avascular areas appear in a characteristic spatial and temporal pattern, and are correlated with the position of developing cartilage. In the present study, we examined limb-bud sections which had been double labeled for endothelial cells and developing cartilage in order to determine the relationship between the appearance of cartilage and the disappearance of capillaries. Endothelial cells, which specifically take up acetylated low-density lipoprotein (acLDL), were labeled by intravenously injecting fluorescent acLDL (DiIacLDL) into chick embryos at Hamburger and Hamilton stages 26-30. Avascular zones, which correspond to the developing digits, were clearly visible within the fluorescently labeled distal vasculature. The same sections were labeled with monoclonal antibodies specific for cartilage. We found that progressing avascularity in the digital regions was followed by increased staining for cartilage antigens in the same areas. Zones of avascularity always developed earlier than morphologically and immunologically detectable cartilage in all planes of section and were always larger than the areas of cartilage. These results demonstrate that blood vessels disappear in predictable areas prior to the overt differentiation of cartilage.

Animals↗
PubMed1987

[Endothelium, angiogenesis and metastasis].

The turnover of endothelium in a normal adult male is very low. Angiogenesis, the formation of new blood vessels, involves a high turnover of endothelial cells. It takes place during embryogenesis, ovulation and many pathological conditions, e.g. tumor growth. Soluble polypeptide growth factors for endothelial cells have been biochemically characterized. They are able to induce angiogenesis in vivo. Inhibitors of angiogenesis can inhibit tumor vascularization and the growth of solid tumors in mice. Tumor metastasis involves the migration of malignant tumor cells through endothelial cells. The organ and tissue specificity of these and other invasive migrations through vascular endothelium may be related to the heterogeneity and organ specificity of endothelial cells.

Animals↗
PubMed1986

Brain induces the expression of an early cell surface marker for blood-brain barrier-specific endothelium.

Capillaries derived from the perineural vascular plexus invade brain tissue early in embryonic development. Considerably later they differentiate into blood-brain barrier (BBB)-forming blood vessels. In the chick, the BBB as defined by impermeability for the protein horseradish peroxidase develops around embryonic day 13. We have previously found that brain endothelial cells start to express a number of proteins at around the same time, suggesting that these proteins play a role in BBB function. Here we describe a 74 kd protein defined by the monoclonal antibody HT7 that is expressed on the surface of chick embryonic blood cells and brain endothelial but on no other endothelial cells. This protein is not detectable on early embryonic brain endothelium, but is expressed by these cells on embryonic day 10. It is absent in choroid plexus endothelial cells which represent permeable fenestrated endothelial cells. The antigen is expressed on choroid plexus epithelium which is the site of the blood-cerebrospinal fluid barrier. Since it is also found in basolateral membranes of kidney tubules, it may be involved in specific carrier mechanisms. Embryonic mouse brain tissue transplanted on the chick chorio-allantoic membrane induces the expression of this antigen on endothelial cells derived from the chorio-allantois. Brain tissue can therefore induce in endothelial cells in vivo the expression of a molecule characteristic of brain endothelium.

Animals↗