Stress-stimulated volitional coping competencies and depression in multiple sclerosis.

OBJECTIVE: The present study examined the relationship between volitional modes of coping (self-regulation, volitional inhibition, and self-control) and depression in individuals with multiple sclerosis. METHODS: A cross-sectional study of 121 participants aged 22-60 years with clinically defined MS who were consecutively admitted to a neurological rehabilitation center during a 23-month period. Correlation analyses and hierarchical regressions were conducted to evaluate the predictive value of volitional competencies (Volitional Components Questionnaire, short form, VCQ-S) on depression (Centre for Epidemiologic Studies Depression Scale, CES-D), while controlling for demographic (age, gender, and education) and certain clinical variables (Expanded Disability Status Scale, EDSS; disease duration; and Modified Fatigue Impact Scale, MFIS). RESULTS: Hierarchical regression analyses of depression revealed a model in which 68% of the variance in the CES-D was explained by daily stress situations (VCQ-S), self-regulation (VCQ-S), fatigue (MFIS), and education. However, when the analysis included only participants who had scored above the cut-off of the CES-D (n=42), the VCQ-S factor volitional inhibition seemed to play a more relevant part in depression. In particular, the VCQ-S scales stimulation of self-access, stimulation of volitional inhibition, self-motivation, and emotional perseverance/state orientation after failure appear to be valuable predictors on CES-D. CONCLUSIONS: The results suggest that personality-accentuated volitional coping competencies elicited by daily stressful situations could be a relevant factor for depressive mood states in individuals with MS. However, to clarify the exact relationships of this rather circular framework, longitudinal study designs with objective measurements and a stronger focus on MS-specific stressors are needed.

[Autocrine stimulation of receptor-tyrosine kinases (RTK) in human tumor cell lines in vitro: therapeutic implications]. / Die autokrine Stimulation von Rezeptor-Tyrosinkinasen in humanen Tumorzelllinien. Eine in vitro studie und deren therapeutische Bedeutung.

AIMS: The VEGF/VEGFR system is known to play an important role in the development of new blood vessels during tumor formation. There is evidence that VEGFRs are not only present on endothelial cells but also on tumor cells. Since VEGF is able to induce proliferation and migration via VEGFR-2 we have studied the expression of VEGFRs and related receptor tyrosine kinases (RTKs) in different tumor cell lines and the effect of growth factor stimulation. METHODS: RTK expression was investigated in 5 different human tumor cell lines on protein and mRNA levels. Tumor cell lines were exposed to growth factors such as VEGF and the phosphorylation of downstream molecules involved in proliferation, migration and apoptosis were assessed. Under comparable conditions proliferation and migration essays were performed. Endogenous production of VEGF and PDGF by the tumor cells was measured by ELISA of cell culture supernatants. RESULTS: Most tested cell lines expressed all known VEGFR's, PDGFR-beta on protein and mRNA levels to a varying extent. 3 out of 5 cell lines could be stimulated after addition of VEGF reflected by an increased phosphorylation of MAPK, AKT/PKB and to a lesser extent of p38. This was underlined by an increased cell number and reduced number of apoptotic cells. After stimulation with PDGF-BB a stronger induction of MAPK and AKT/PKB phosphorylation than for VEGF could be seen. In contrast, no effect on tumor cell migration was detectable in all examined cell lines. The investigation of cell culture supernatants revealed that most cell lines do not produce VEGF or PDGF. CONCLUSIONS: Tumor cell lines express RTKs and the receptor is stimulable after addition of growth factors such as VEGF. Thus, secretion of groth factors in the tumor microenvironment is not only able to stimulate proliferation and survival of endothelial cells but also tumor cells themselve. One cell line displayed high levels of endogenous VEGF which could explain the lack of an increased cell number after addition of VEGF. It remains obscure why another cell line could not be stimulated although receptors were present at the cellular surface. Further investigations should prove that RTK's could be influenced by therapeutic drugs in order to suppress cell proliferation and migration and induce apoptosis in tumor cell lines.

Functions of the VEGF/VEGF receptor system in the vascular system.

The vascular endothelial growth factor (VEGF)/VEGF receptor system plays a central regulatory role in physiological and pathological angiogenesis. During embryogenesis, the VEGF/VEGF receptor system is critically involved in the formation of the vascular system by regulating both the growth and the survival of blood vessels. In the vasculature of the adult organism, the high-affinity signaling VEGF receptor-2 (VEGFR-2) is downregulated but is reinduced during transient phases of physiological angiogenesis. Moreover, a variety of pathological conditions are associated with the upregulation of VEGF and the VEGF receptors. VEGF stimulates angiogenesis and the survival of endothelial cells in tumors, thereby enabling tumor expansion and metastasis. VEGF is also upregulated in ischemic diseases, such as coronary heart disease or stroke, and is thought to stimulate the--often insufficient--compensatory formation of blood vessels. The implication of VEGF in these pathological processes has opened up promising new therapeutic strategies. In malignancies, attempts are made to inhibit VEGF-mediated signaling and angiogenesis. In ischemic disease, the exogenous application of VEGF may enhance the formation of collaterals. However, considering the complexity of the regulatory pathways involved in the formation of new blood vessels under physiological conditions, a treatment relying on VEGF as the sole angiogenic factor may be insufficient, and the combination with other factors may improve the functionality of newly formed blood vessels and the efficacy of therapeutic angiogenesis.

Tumor endothelium-specific transgene expression directed by vascular endothelial growth factor receptor-2 (Flk-1) promoter/enhancer sequences.

The receptor tyrosine kinase Flk-1 plays a pivotal role in the development of the vascular system and in the vascularization of a wide variety of tumors. We have investigated the activity of cis-acting sequences of the murine Flk-1 gene in the tumor endothelium of experimental tumor models in vivo. B16 melanoma, BFS-1 fibrosarcoma, and polyoma middle T-induced mammary adenocarcinoma were grown in transgenic mice that express the LacZ reporter gene under the control of a 939-bp Flk-1 promoter fragment and an enhancer element located in a 2.3-kb fragment of the first intron. In all experimental tumor models examined, strong endothelium-specific reporter gene expression was observed while being absent from most blood vessels in normal adult tissue. The expression patterns of the LacZ reporter gene correlate well between established tumors grown in Flk1-LacZ transgenic mice and tumors grown in Flk-1+/LacZ knock-in mice that express the LacZ reporter gene from the endogenous Flk-1 locus. The endothelium-specific activity of the Flk-1 promoter/enhancer sequences in three different experimental tumor models demonstrates that the regulatory sequences that mediate the up-regulation of Flk-1 in the tumor endothelium are contained in the Flk-1 promoter/enhancer sequences used, and that these elements function relatively independently of the tumor type. The Flk-1 promoter/enhancer sequences should allow the analysis of the signaling pathways that lead to the up-regulation of Flk-1 in the tumor endothelium and to specifically target therapeutic genes to the endothelium of tumors for antiangiogenic tumor therapy.

De novo expression of vascular endothelial growth factor in human pancreatic cancer: evidence for an autocrine mitogenic loop.

BACKGROUND & AIMS: The role of vascular endothelial growth factor (VEGF) and its receptors in tumor angiogenesis has been well established. We analyzed the expression pattern and biologic significance of VEGF and its receptors in human pancreatic cancer. METHODS: VEGF, KDR/flk-1, and flt-1 expression were examined by immunohistochemistry, in situ hybridization, reverse-transcription polymerase chain reaction, enzyme-linked immunosorbent assay, and receptor phosphorylation. VEGF-stimulated mitogenesis was investigated by mitogen-activated protein kinase (MAPK) phosphorylation, transactivation of a c-fos promoter reporter construct, DNA synthesis assays, and stable transfection of a dominant-negative flk-1 complementary DNA (cDNA) construct. RESULTS: Compared with normal pancreas and chronic pancreatitis, VEGF and its receptors were overexpressed in pancreatic cancer. KDR and flt-1 were detected not only in endothelial cells but also in tumor cells. VEGF expression was observed in all human pancreatic tumor cell lines examined, and the KDR/flk-1 and flt-1 receptor was detected in 2 cell lines. VEGF treatment results in phosphorylation of MAPKs, transactivation of a c-fos promoter construct, and growth stimulation in KDR/flk-1-expressing cell lines, which could be blocked by VEGF antagonists. Furthermore, stable transfection of a dominant-negative flk-1 cDNA significantly inhibited tumor cell growth. CONCLUSIONS: These results not only support the important role of the VEGF/VEGF receptor system in pancreatic tumor biology but also suggest the existence of an autocrine/paracrine mitogenic loop for pancreatic cancer cells.

Role of SCL/Tal-1, GATA, and ets transcription factor binding sites for the regulation of flk-1 expression during murine vascular development.

The receptor tyrosine kinase Flk-1 is essential for embryonic blood vessel development and for tumor angiogenesis. To identify upstream transcriptional regulators of Flk-1, the gene regulatory elements that mediate endothelium-specific expression in mouse embryos were characterized. By mutational analysis, binding sites for SCL/Tal-1, GATA, and Ets transcription factors located in the Flk-1 enhancer were identified as critical elements for the endothelium-specific Flk-1 gene expression in transgenic mice. c-Ets1, a transcription factor that is coexpressed with Flk-1 during embryonic development and tumor angiogenesis, activated the Flk-1 promoter via 2 binding sites. One of these sites was required for Flk-1 promoter function in the embryonic vasculature. These results provide the first evidence that SCL/Tal-1, GATA, and Ets transcription factors act upstream of Flk-1 in a combinatorial fashion to determine embryonic blood vessel formation and are key regulators not only of the hematopoietic program, but also of vascular development.

Angiogenesis in embryonic development--a review.

Recent studies, particularly of genetically altered mice, have greatly improved our understanding of the molecular basis underlying the development of the vascular system. Endothelial signalling systems, such as the vascular endothelial growth factor (VEGF)/VEGF receptor system and the angiopoietin/Tie2 system, were identified as central regulators of embryonic angiogenesis. The complex interactions between these and other endothelial signalling systems are beginning to emerge. Placenta (2000), 21, Supplement A, Trophoblast Research, 14, S11-S15.

Identification of vascular endothelial growth factor (VEGF) receptor-2 (Flk-1) promoter/enhancer sequences sufficient for angioblast and endothelial cell-specific transcription in transgenic mice.

The vascular endothelial growth factor (VEGF) receptor-2 (Flk-1) is the first endothelial receptor tyrosine kinase to be expressed in angioblast precursors, and its function is essential for the differentiation of endothelial cells and hematopoietic precursors. We have identified cis-acting regulatory elements of the murine Flk-1 gene that mediate endothelium-specific expression of a LacZ reporter gene in transgenic mice. Sequences within the 5'-flanking region of the Flk-1 gene, in combination with sequences located in the first intron, specifically targeted transgene expression to angioblasts and endothelial cells of transgenic mice. The intronic regulatory sequences functioned as an autonomous endothelium-specific enhancer. Sequences of the 5'-flanking region contributed to a strong, uniform, and reproducible transgene expression and were stimulated by the transcription factor HIF-2alpha. The Flk-1 gene regulatory elements described in this study should allow the elucidation of the molecular mechanisms involved in endothelial cell differentiation and angiogenesis.

Differential downregulation of vascular endothelial growth factor by dexamethasone in normoxic and hypoxic rat glioma cells.

Vascular endothelial growth factor/vascular permeability factor (VEGF/VPF) is a mitogen and chemotactic factor for endothelial cells in vitro and an angiogenesis and vascular permeability factor in vivo. Due to its properties, VEGF is a candidate for both angiogenesis and vascular permeability/oedema induction which typically occur in glioblastomas. In this study we test the hypothesis that the antioedema effect of dexamethasone is mediated by downregulation of VEGF or VEGF receptor expression. VEGF mRNA and protein levels of two rat glioma cells lines, C6 and GS-9L, were determined after incubation with dexamethasone under normoxic and hypoxic conditions. In normoxic C6 and GS9L cells, we observed 50-60% downregulation of VEGF mRNA by dexamethasone (P=0.015 and P=0. 01, respectively). This effect was dependent on glucocorticoid-receptor (GR) function. The inhibitory effect of dexamethasone on VEGF gene expression by tumour cells was markedly reduced by hypoxia which suggests that the upregulation of VEGF driven by hypoxia overcomes the effect of the dexamethasone. Dexamethasone did not alter VEGFR-2 mRNA levels in human umbilical endothelial cells. In a subcutaneous glioma tumour model, we observed only a 15% decrease in VEGF mRNA expression in dexamethasone treated animals (n = 12) compared with controls animals (P = 0.24). We conclude that dexamethasone may decrease brain tumour-associated oedema by reduction of VEGF expression in tumour cells. However, the highly reduced activity on hypoxic tumour cells suggests that dexamethasone efficacy may be limited by hypoxia in rapidly growing tumours.

Upregulation of vascular endothelial growth factor in severe chronic brain hypoxia of the rat.

The vascular endothelial growth factor (VEGF) has been shown to be upregulated in acute hypoxia. Although an increase in blood vessel number has been described in severe chronic brain hypoxia, it is unclear whether VEGF is upregulated in this condition. We therefore investigated male inbred Wistar rats, which were exposed for 9 to 13 weeks to decreasing amounts of oxygen, down to 7% O2 (15%: 15 days; 12%, 10%, respectively; 8%: 1 day, 3 weeks, respectively; 7%: 4 weeks). The expression of VEGF was studied by Northern analysis and in situ hybridization in frozen sections of cerebral cortex, hippocampus and cerebellum in six chronic hypoxic and two control rats. We found a marked upregulation of VEGF mRNA in all brain regions investigated, being strongest in cerebral cortex and cerebellum. Our results suggest a potential role of VEGF for vascular growth and vascular permeability observed in chronic cerebral hypoxia.

Vascular endothelial growth factor induces endothelial fenestrations in vitro.

Vascular endothelial growth factor (VEGF) is an important regulator of vasculogenesis, angiogenesis, and vascular permeability. In contrast to its transient expression during the formation of new blood vessels, VEGF and its receptors are continuously and highly expressed in some adult tissues, such as the kidney glomerulus and choroid plexus. This suggests that VEGF produced by the epithelial cells of these tissues might be involved in the induction or maintenance of fenestrations in adjacent endothelial cells expressing the VEGF receptors. Here we describe a defined in vitro culture system where fenestrae formation was induced in adrenal cortex capillary endothelial cells by VEGF, but not by fibroblast growth factor. A strong induction of endothelial fenestrations was observed in cocultures of endothelial cells with choroid plexus epithelial cells, or mammary epithelial cells stably transfected with cDNAs for VEGF 120 or 164, but not with untransfected cells. These results demonstrate that, in these cocultures, VEGF is sufficient to induce fenestrations in vitro. Identical results were achieved when the epithelial cells were replaced by an epithelial-derived basal lamina-type extracellular matrix, but not with collagen alone. In this defined system, VEGF-mediated induction of fenestrae was always accompanied by an increase in the number of fused diaphragmed caveolae-like vesicles. Caveolae, but not fenestrae, were labeled with a caveolin-1-specific antibody both in vivo and in vitro. VEGF stimulation led to VEGF receptor tyrosine phosphorylation, but no change in the distribution, phosphorylation, or protein level of caveolin-1 was observed. We conclude that VEGF in the presence of a basal lamina-type extracellular matrix specifically induces fenestrations in endothelial cells. This defined in vitro system will allow further study of the signaling mechanisms involved in fenestrae formation, modification of caveolae, and vascular permeability.

Upregulation of the vascular endothelial growth factor/vascular endothelial growth factor receptor system in experimental background diabetic retinopathy of the rat.

Vascular endothelial growth factor (VEGF) is a major contributor to retinal neovascularization. The possible participation of VEGF and its high-affinity tyrosine kinase receptors, flk-1 and flt-1, in early background diabetic retinopathy was studied in the streptozotocin-induced diabetic rat model of experimental retinopathy using in situ hybridization, blotting techniques, and immunohistochemistry. Diabetic retinopathy was assessed by quantitative morphometry of retinal digest preparations. The number of acellular capillaries increased 2.7-fold in diabetic animals with diabetes' duration of 6 months compared with nondiabetic controls. VEGF expression was not detectable by in situ hybridization in nondiabetic rats but was highly increased in the ganglion cell layer and in the inner and outer nuclear layers of retinas from diabetic animals. VEGF protein was extractable only from diabetic retinas, and a strong immunolabeling was detected in vascular and perivascular structures. Increased flk-1 and flt-1 mRNA levels were also found in the ganglion cell and both nuclear layers of diabetic samples only. Dot blot and Western blot analyses confirmed the increase in flk-1 mRNA and protein in diabetic retinas. Also, flk-1 immunoreactivity was associated with vascular and nonvascular structures of the inner retinas from diabetic animals. These data obtained from a rodent model in which retinal neovascularization does not occur support the concept that the VEGF/VEGF receptor system is upregulated in early diabetic retinopathy.

Thrombopoietin stimulates VEGF release from c-Mpl-expressing cell lines and haematopoietic progenitors.

Vascular endothelial growth factor (VEGF) production was analysed in megakaryocytic cell lines and CD34+ haematopoietic progenitors following treatment with thrombopoietin (TPO). In CMK cells TPO caused a time- and dose-dependent increase in the levels of VEGF released into the medium. A similar effect was observed in UT-7/mpl cells transfected with the TPO receptor c-Mpl, but not in parental UT-7 cells. In CD34+ haematopoietic progenitor cell cultures TPO stimulated VEGF mRNA expression and VEGF protein release. Production of VEGF in CD34+ cultures increased with TPO-induced megakaryocytic differentiation, but not with erythroid or myelomonocytic differentiation induced respectively by erythropoietin and granulocyte-macrophage colony-stimulating factor. These results demonstrate that TPO stimulates VEGF release in c-Mpl-expressing cells and suggest that this process is an integral feature of the megakaryocytic differentiation programme.

VEGF gene transfer reduces intimal thickening via increased production of nitric oxide in carotid arteries.

Thickening of the arterial intima and smooth muscle cell (SMC) proliferation remain major problems after vascular surgery and other types of vascular manipulations. We studied the effect of endothelial cell (EC)-specific vascular endothelial growth factor (VEGF) gene transfer on the thickening of the intima using a silicone collar inserted around carotid arteries that acted both as the agent that caused intimal SMC growth and as a reservoir for the transfected gene. The model preserved EC integrity and permitted direct extravascular gene transfer without any intravascular manipulation. Compared to beta-galactosidase (lacZ)-transfected control arteries, plasmid/liposome-mediated VEGF gene transfer significantly reduced intimal thickening 1 week after the gene transfer. Administration to the experimental animals of the nitric oxide (NO) synthase inhibitor L-NAME abolished the difference in intimal thickening between VEGF and lacZ-transfected arteries. Furthermore, VEGF caused NO release from cultured human umbilical vein EC. It is concluded that extravascular VEGF gene transfer attenuates intimal growth and could be useful for the prevention of intimal thickening during vascular surgery. Our results further suggest that VEGF may reduce SMC proliferation via a mechanism that involves VEGF-induced NO production from the endothelium.

Up-regulation of flk-1/vascular endothelial growth factor receptor 2 by its ligand in a cerebral slice culture system.

Vascular endothelial growth factor (VEGF) and its tyrosine kinase receptors VEGFR-1 (flt-1) and VEGFR-2 (flk-1/KDR) are key mediators of physiological and pathological angiogenesis. They are expressed in most tissues during embryonic development but are down-regulated in the adult, when angiogenesis ceases. Up-regulation of VEGFR-2 and of VEGF are observed in many pathological conditions under which angiogenesis is reinduced. A major regulator of VEGF expression is hypoxia. Although the temporal expression pattern of VEGFR-2 parallels VEGF expression to a high extent, little is known about its regulation. Here, we show that VEGFR-2 is highly expressed in early postnatal mouse brain but is down-regulated commencing at postnatal day 15 (P15) of mouse brain development and is hardly detectable in P30 mouse brain. Using P30 mouse brain slices, we observed that hypoxia up-regulates VEGFR-2 in the slices but not in human umbilical vein endothelial cells, suggesting the presence of a hypoxia-inducible factor in the murine neuroectoderm that up-regulates VEGFR-2. To identify the factors involved, normoxic P30 cerebral slices were cultured with growth factors that are either hypoxia-inducible (e.g., PDGF-BB, erythropoietin, and VEGF) and/or are known to act on endothelial cells (e.g., PDGF-BB, VEGF, and PIGF). Exogenously added recombinant VEGF led to an up-regulation of VEGFR-2 expression, which could be inhibited by preincubation with a neutralizing anti-VEGF antibody. Addition of PDGF-BB, PIGF, and erythropoietin had no effect on VEGFR-2 expression. Our results suggest a differential but synergistic regulation by hypoxia of VEGF and VEGFR-2: a direct induction of VEGF that subsequently up-regulates VEGFR-2 in endothelial cells. This autoenhancing system may represent an important mechanism of tumor angiogenesis.

Up-regulation of vascular endothelial growth factor expression in a rat glioma is conferred by two distinct hypoxia-driven mechanisms.

Up-regulation of vascular endothelial growth factor (VEGF) expression is a major event leading to neovascularization in malignant gliomas. Hypoxia is believed to be the crucial environmental stimulus for this up-regulation. To critically assess this hypothesis, we asked whether the mechanisms defined previously for hypoxia-induced VEGF expression in vitro are similarly involved and sufficient for up-regulation of VEGF gene expression in vivo, using a lacZ reporter gene under the control of VEGF regulatory sequences in an experimental glioma model. Inclusion of the binding site for hypoxia-inducible factor 1 (HIF 1) in the 5' regulatory sequences used in the hybrid gene produced weak beta-galactosidase staining in a special tumor cell subtype, the so-called perinecrotic palisading (PNP) cells that flank necrotic regions within the tumor. Deletion of the HIF 1 binding site abolished reporter gene expression in the PNP cells, indicating that transcriptional activation of VEGF expression in gliomas is mediated by HIF 1. Inclusion of 3' untranslated sequences from the VEGF gene in the reporter constructs resulted in an increased beta-galactosidase staining in the PNP cells, suggesting that mRNA stabilization also contributes to VEGF up-regulation in glioblastoma cells growing as solid tumors. Combination of the 5' flanking region including the HIF 1 site along with 3' untranslated sequences produced increased levels of beta-galactosidase expression in PNP cells. EF 5 immunostaining for regions of low oxygen partial pressure covered the same PNP cells that were stained for beta-galactosidase. Collectively, the data provide experimental evidence that VEGF gene expression is activated in a distinct tumor cell subpopulation, the perinecrotic palisading cells of gliomas, by two distinct hypoxia-driven regulatory mechanisms.

Angiogenesis in embryos and ischemic diseases.

Angiogenic growth factors and their endothelial receptors are thought to function as major regulators of blood vessel formation. Vascular endothelial growth factor (VEGF) and its receptors, Flt-1 (VEGFR-1) and Flk-1 (VEGFR-2), as well as Angiopoietin-1 and its receptor, Tie-2, represent key signal transduction systems involved in the regulation of embryonic vascular development. The expression of these molecules correlates with phases of blood vessel formation during embryogenesis. Inactivation of any of the genes encoding these molecules in mouse embryos results in defective vascular development and embryonic lethality around mid-gestation. In addition, the VEGF signal transduction system has been implicated in the regulation of pathological blood vessel growth during certain angiogenesis-dependent diseases that are often associated with tissue ischemia, such as proliferative retinopathy or solid tumor growth. This hypothesis is substantiated by experiments, in which the inhibition of VEGF signal transduction resulted in the the inhibition of neovascularization in these diseases. Thus, the VEGF signal transduction system represents a useful target for an anti-angiogenic therapy.