VEGF-A stimulation of leukocyte adhesion to colonic microvascular endothelium: implications for inflammatory bowel disease

Neutralizing anti-vascular endothelial growth factor (VEGF) antibody reduces severity of experimental ulcerative colitis in rats: direct evidence for the pathogenic role of VEGF

In ulcerative colitis (UC), an increased expression of vascular endothelial growth factor (VEGF) correlates with disease activity, but a causal relationship is unknown. We tested the hypothesis that VEGF plays a mechanistic role in the pathogenesis of experimental UC and that VEGF neutralization may exert therapeutic effect. UC was induced in Sprague-Dawley rats by 6% iodoacetamide given intracolonically. Neutralizing anti-VEGF antibody (50 microg/rat), nonspecific IgG, or saline (0.1 ml/rat) was injected intramuscularly on the 3rd and 5th days after iodoacetamide enema. Rats were euthanized on the 7th day. We examined the extent of macroscopic, histologic, and clinical features of colitis and colonic vascular permeability. Colonic VEGF mRNA and protein expressions increased as early as 0.5 h after iodoacetamide enema and remained elevated in the active phase of colitis. Treatment with anti-VEGF antibody markedly improved the clinical and morphologic features of UC. Colonic lesion area was significantly reduced from 370 +/- 140 or 311 +/- 170 mm(2) in saline- or IgG-treated groups to 122 +/- 57 mm(2) in the anti-VEGF-group (p < 0.05). Increased colonic vascular permeability was decreased by the anti-VEGF antibody (p < 0.05) and the Src inhibitor PP1 [pyrazolopyrimidine, 4-amino-5-(4-methylphenyl)-7-(t-butyl)pyrazolo[3,4-d]-pyrimidine] (p < 0.01). The number of acute and chronic inflammatory cells in the lesion area was significantly reduced in anti-VEGF-treated rats. In the anti-VEGF-treated group, mucosal levels of VEGF, platelet-derived growth factor, and basic fibroblast growth factor were also reduced.

IN CONCLUSION

1) Neutralizing anti-VEGF antibody significantly ameliorates experimental UC in rats in part by reducing excessive vascular permeability and decreasing inflammatory cells infiltration; and 2) VEGF seems to mediate increased colonic vascular permeability in experimental UC via the Src-dependent mechanism.

VEGF-A links angiogenesis and inflammation in inflammatory bowel disease pathogenesis

BACKGROUND & AIMS

Vascular endothelial growth factor A (VEGF-A) mediates angiogenesis and might also have a role in inflammation and immunity. We examined whether VEGF-A signaling has a role in inflammatory bowel disease (IBD).

METHODS

Expression levels of VEGF-A, and its receptors VEGFR-1 and VEGFR-2, were examined in samples from patients with IBD and compared with those of controls. The capacity of VEGF-A to induce angiogenesis was tested in human intestinal microvascular endothelial cells using cell-migration and matrigel tubule-formation assays. Levels of vascular cellular adhesion molecule-1 and intercellular adhesion molecule were measured by flow cytometry to determine induction of inflammation; neutrophil adhesion was also assayed. Expression patterns were determined in tissues from mice with dextran sulfate sodium (DSS)-induced colitis; the effects of VEGF-A overexpression and blockade were assessed in these mice by adenoviral transfer of VEGF-A and soluble VEGFR-1. Intestinal angiogenesis was measured by quantitative CD31 staining and leukocyte adhesion in vivo by intravital microscopy.

RESULTS

Levels of VEGF-A and VEGFR-2 increased in samples from patients with IBD and colitic mice. VEGF-A induced angiogenesis of human intestinal microvascular endothelial cells in vitro as well as an inflammatory phenotype and adherence of neutrophils to intestinal endothelium. Overexpression of VEGF-A in mice with DSS-induced colitis worsened their condition, whereas overexpression of soluble VEGFR-1 had the opposite effect. Furthermore, overexpression of VEGF-A increased mucosal angiogenesis and stimulated leukocyte adhesion in vivo.

CONCLUSIONS

VEGF-A appears to be a novel mediator of IBD by promoting intestinal angiogenesis and inflammation. Agents that block VEGF-A signaling might reduce intestinal inflammation in patients with IBD.

Upregulation of vascular endothelial growth factor isoform VEGF-164 and receptors (VEGFR-2, Npn-1, and Npn-2) in rats with cyclophosphamide-induced cystitis

Regulation of the VEGF-VEGF receptor system was examined in the urinary bladder after acute (2-48 h) and chronic (10 days) cyclophosphamide (CYP)-induced cystitis. ELISAs demonstrated significant (P < or = 0.01) upregulation of VEGF in whole urinary bladder with acute and chronic CYP-induced cystitis; however, the magnitude of increase was greater after acute (2-4 h) cystitis. Immunohistochemistry for VEGF immunoreactivity revealed a significant (P < or = 0.05) increase in VEGF immunoreactivity in the urothelium, suburothelial vasculature, and detrusor smooth muscle with acute (4 and 48 h) CYP treatment. RT-PCR identified the isoform VEGF-164, the VEGF receptor VEGFR-2, and the VEGF co-receptors neuropilin (Npn)-1 and Npn-2 in the urinary bladder. Quantitative PCR demonstrated upregulation of VEGF-164 transcript with acute and chronic CYP-induced cystitis, but VEGFR-2, Npn-1, and Npn-2 transcripts were upregulated (P < or = 0.01) in whole bladder only with chronic CYP-induced cystitis. Additional studies demonstrated regulation of VEGF transcript expression in the urinary bladder by nerve growth factor (NGF) in a novel line of NGF-overexpressing mice. These studies demonstrated that urinary bladder inflammation and NGF regulate the VEGF-VEGF receptor system in the urinary bladder. Functional role(s) for the VEGF-VEGF receptor system in urinary bladder inflammation remain to be determined.

Multiple pathogenic roles of microvasculature in inflammatory bowel disease: a Jack of all trades

The etiology of Crohn's disease and ulcerative colitis, the two major forms of inflammatory bowel disease (IBD), is still largely unknown. However, it is now clear that the abnormalities underlying pathogenesis of intestinal inflammation are not restricted to those mediated by classic immune cells but also involve nonimmune cells. In particular, advances in vascular biology have outlined a central and multifaceted pathogenic role for the microcirculation in the initiation and perpetuation of IBD. The microcirculation and its endothelial lining play a crucial role in mucosal immune homeostasis through tight regulation of the nature and magnitude of leukocyte migration from the intravascular to the interstitial space. Chronically inflamed IBD microvessels display significant alterations in microvascular physiology and function compared with vessels from healthy and uninvolved IBD intestine. The investigation into human IBD has demonstrated how endothelial activation present in chronically inflamed IBD microvessels results in a functional phenotype that also includes leakiness, chemokine and cytokine expression, procoagulant activity, and angiogenesis. This review contemplates the newly uncovered contribution of intestinal microcirculation to pathogenesis and maintenance of chronic intestinal inflammation. In particular, we assess the multiple roles of the microvascular endothelium in innate immunity, leukocyte recruitment, coagulation and perfusion, and immune-driven angiogenesis in IBD.

Multiple pathogenic roles of microvasculature in inflammatory bowel disease: a Jack of all trades

The etiology of Crohn's disease and ulcerative colitis, the two major forms of inflammatory bowel disease (IBD), is still largely unknown. However, it is now clear that the abnormalities underlying pathogenesis of intestinal inflammation are not restricted to those mediated by classic immune cells but also involve nonimmune cells. In particular, advances in vascular biology have outlined a central and multifaceted pathogenic role for the microcirculation in the initiation and perpetuation of IBD. The microcirculation and its endothelial lining play a crucial role in mucosal immune homeostasis through tight regulation of the nature and magnitude of leukocyte migration from the intravascular to the interstitial space. Chronically inflamed IBD microvessels display significant alterations in microvascular physiology and function compared with vessels from healthy and uninvolved IBD intestine. The investigation into human IBD has demonstrated how endothelial activation present in chronically inflamed IBD microvessels results in a functional phenotype that also includes leakiness, chemokine and cytokine expression, procoagulant activity, and angiogenesis. This review contemplates the newly uncovered contribution of intestinal microcirculation to pathogenesis and maintenance of chronic intestinal inflammation. In particular, we assess the multiple roles of the microvascular endothelium in innate immunity, leukocyte recruitment, coagulation and perfusion, and immune-driven angiogenesis in IBD.

Regulation of galectin-3 function in mucosal fibroblasts: potential role in mucosal inflammation

Recently we identified galectin-3 (gal-3), which is secreted by colonic epithelial cells (CEC), to be a strong activator of colonic lamina propria fibroblasts (CLPF). Modulation of CLPF function may play a role during stricture and fistula formation in inflammatory bowel disease (IBD). Therefore, we investigated further the expression of gal-3 and effects on CLPF. The aim of this study is to perform a direct comparison of gal-3 between tissue from healthy controls and from patients with either Crohn's disease (CD) or ulcerative colitis (UC). CEC, CLPF and intestinal macrophages (IMAC) were isolated from control and IBD colonic tissue. Interleukin-8 secretion as a readout of CLPF activation was quantified by enzyme-linked immunosorbent assay. Gal-3 in cell cultures and tissue samples was evaluated by Western blot, immunofluorescence and immunohistochemistry. CLPF-migration was assayed in the 48-well modified Boyden chamber. Gal-3 expression was found in all segments of the colon. In the terminal ileum, less gal-3 was found compared with the colon. Immunohistochemistry and immunofluorescence revealed a homogenous distribution of gal-3 in CEC and IMAC of control mucosa and UC. However, significantly less gal-3 was found in IMAC from CD patients. In CD fistulae and stenoses, gal-3 expression was reduced significantly and barely detectable. In co-incubation studies lactose reduced significantly the CLPF-stimulatory potential of gal-3, indicating that the C-terminal domain of gal-3 is responsible for CLPF activation. Gal-3 stimulated CLPF migration in CLPF derived from fistulae. In conclusion, gal-3 expression is down-regulated in CD-fistulae and stenoses as well as in IMAC in CD patients. Gal-3 induces migration of CLPF derived from fistulae. Its role for stricture and fistula formation warrants further investigation.

Lack of thrombospondin-1 increases angiogenesis in a model of chronic inflammatory bowel disease

BACKGROUND AND AIMS

Vascular abnormalities and expression of pro-angiogenic factors are observed in inflammatory bowel diseases (IBD). In this study, the role of thrombospondin-1 (TSP-1), an antiangiogenic protein, was analyzed using the dextran sulfate sodium (DSS) model for IBD.

MATERIALS AND METHODS

Wild-type (WT) and thrombospondin-1-deficient (TSP-1(-/-)) mice were subjected to four cycles (7 days) of DSS. Basic fibroblast growth factor (bFGF), vascular endothelial growth factor (VEGF), transforming growth factor beta 1 (TGFbeta-1), and pro-apoptotic proteins such as Fas and its ligand (FasL) were determined by enzyme-linked immunosorbent assay. Double immunohistochemistry for cluster of differential 31 (CD31) and panendothelial cell antigen-32 antibodies was performed for detecting blood vessels. The terminal deoxynucleotidyl transferase-mediated dUTP nick end-labeling assay was also performed for identifying apoptotic cells. Inflammation, dysplasia, microvascular density (MVD), apoptotic indices (AI), protein 53 (p53), and beta-catenin expression were determined.

RESULTS

VEGF and bFGF protein levels and MVD were higher in the TSP-1(-/-) mice (p = 0.0312, p = 0.0246, and p = 0.0085, respectively). AI in the endothelial cells (EC) and FasL levels were significantly lower in TSP-1(-/-) compared to WT mice (p = 0.0042 and p = 0.0362, respectively). Dysplasia was detected in 66% of TSP-1(-/-) mice compared to 14% in WT mice. Hscores of ss-catenin and areas overexpressing p53 were higher in TSP-1(-/-) mice (p = 0.0002 and p = 0.0339, respectively).

CONCLUSION

TSP-1 may decrease angiogenesis by reducing the levels of pro-angiogenic factors and inducing apoptosis in EC through the Fas or FasL pathway. These findings, along with the increased overexpression of p53 and beta-catenin in TSP-1(-/-) mice, underline its role in carcinogenesis.

Stromal cell-derived factor-1/CXCL12 stimulates chemorepulsion of NOD/LtJ T-cell adhesion to islet microvascular endothelium

OBJECTIVE

Diabetogenic T-cell recruitment into pancreatic islets facilitates beta-cell destruction during autoimmune diabetes, yet specific mechanisms governing this process are poorly understood. The chemokine stromal cell-derived factor-1 (SDF-1) controls T-cell recruitment, and genetic polymorphisms of SDF-1 are associated with early development of type 1 diabetes.

RESEARCH DESIGN AND METHODS

Here, we examined the role of SDF-1 regulation of diabetogenic T-cell adhesion to islet microvascular endothelium. Islet microvascular endothelial cell monolayers were activated with tumor necrosis factor-alpha (TNF-alpha), subsequently coated with varying concentrations of SDF-1 (1-100 ng/ml), and assayed for T-cell/endothelial cell interactions under physiological flow conditions.

RESULTS

TNF-alpha significantly increased NOD/LtJ T-cell adhesion, which was completely blocked by SDF-1 in a dose-dependent manner, revealing a novel chemorepulsive effect. Conversely, SDF-1 enhanced C57BL/6J T-cell adhesion to TNF-alpha-activated islet endothelium, demonstrating that SDF-1 augments normal T-cell adhesion. SDF-1 chemorepulsion of NOD/LtJ T-cell adhesion was completely reversed by blocking G(i)alpha-protein-coupled receptor activity with pertussis toxin. CXCR4 protein expression was significantly decreased in NOD/LtJ T-cells, and inhibition of CXCR4 activity significantly reversed SDF-1 chemorepulsive effects. Interestingly, SDF-1 treatment significantly abolished T-cell resistance to shear-mediated detachment without altering adhesion molecule expression, thus demonstrating decreased integrin affinity and avidity.

CONCLUSIONS

In this study, we have identified a previously unknown novel function of SDF-1 in negatively regulating NOD/LtJ diabetogenic T-cell adhesion, which may be important in regulating diabetogenic T-cell recruitment into islets.

Up-regulation of intestinal vascular endothelial growth factor by Afa/Dr diffusely adhering Escherichia coli

BACKGROUND

Angiogenesis has been recently described as a novel component of inflammatory bowel disease pathogenesis. The level of vascular endothelial growth factor (VEGF) has been found increased in Crohn's disease and ulcerative colitis mucosa. To question whether a pro-inflammatory Escherichia coli could regulate the expression of VEGF in human intestinal epithelial cells, we examine the response of cultured human colonic T84 cells to infection by E. coli strain C1845 that belongs to the typical Afa/Dr diffusely adhering E. coli family (Afa/Dr DAEC).

METHODOLOGY

VEGF mRNA expression was examined by Northern blotting and q-PCR. VEGF protein levels were assayed by ELISA and its bioactivity was analysed in endothelial cells. The bacterial factor involved in VEGF induction was identified using recombinant E. coli expressing Dr adhesin, purified Dr adhesin and lipopolysaccharide. The signaling pathway activated for the up-regulation of VEGF was identified using a blocking monoclonal anti-DAF antibody, Western blot analysis and specific pharmacological inhibitors.

PRINCIPAL FINDINGS

C1845 bacteria induce the production of VEGF protein which is bioactive. VEGF is induced by adhering C1845 in both a time- and bacteria concentration-dependent manner. This phenomenon is not cell line dependent since we reproduced this observation in intestinal LS174, Caco2/TC7 and INT407 cells. Up-regulation of VEGF production requires: (1) the interaction of the bacterial F1845 adhesin with the brush border-associated decay accelerating factor (DAF, CD55) acting as a bacterial receptor, and (2) the activation of a Src protein kinase upstream of the activation of the Erk and Akt signaling pathways.

CONCLUSIONS

Results demonstrate that a Afa/Dr DAEC strain induces an adhesin-dependent activation of DAF signaling that leads to the up-regulation of bioactive VEGF in cultured human intestinal cells. Thus, these results suggest a link between an entero-adherent, pro-inflammatory E. coli strain and angiogenesis which appeared recently as a novel component of IBD pathogenesis.

Neutrophil depletion decreases VEGF-induced focal angiogenesis in the mature mouse brain

To explore the role of neutrophil-derived matrix metalloproteinases (MMPs) during angiogenesis in the brain, we hypothesized that transient neutrophil depletion attenuates the angiogenic response to focal hyperstimulation with vascular endothelial growth factor (VEGF). Brain focal angiogenesis was achieved using an adeno-associated virus delivered VEGF (AAV-VEGF) gene transfer in the mature mouse. Four groups of mice underwent AAV vector injection in the brain parenchyma: (1) AAV-LacZ; (2) AAV-VEGF; (3) AAV-VEGF plus anti-polymorphonuclear (PMN) antibody; and (4) AAV-VEGF plus serum. Animals in groups 3 and 4 underwent 4 days of PMN antibody or serum treatment before transfection; treatment was sustained for an additional 14 days. Anti-PMN treatment decreased circulating neutrophils to 9% of baseline (P<0.001). Microvessels in the AAV-VEGF-group increased 25% compared with the AAV-lacZ-transduced group (256+/-15 versus 208+/-16; P<0.05). Anti-PMN treatment attenuated the increase to 10% compared with control serum treatment (234+/-16 versus 255+/-22; P<0.05). Similarly, compared with control serum treatment, anti-PMN treatment also reduced MMP-9 by 50% (2+/-0.9 versus 4+/-1.4; P<0.05) and MPO expression by 25% (2+/-0.8 versus 3+/-0.9; P<0.05); MMP-9 activity correlated with MPO expression (R(2)=0.8, P<0.05). Our study demonstrated that transient depletion of neutrophils suppressed VEGF-induced angiogenesis, indicating that circulating neutrophils contribute to VEGF-induced focal angiogenesis. In addition, brain MMP-9 activity was attenuated after neutrophil depletion, suggesting that neutrophil is an important source of MMP-9.

Pathogenic angiogenesis in IBD and experimental colitis: new ideas and therapeutic avenues

Angiogenesis is now understood to play a major role in the pathology of chronic inflammatory diseases and is indicated to exacerbate disease pathology. Recent evidence shows that angiogenesis is crucial during inflammatory bowel disease (IBD) and in experimental models of colitis. Examination of the relationship between angiogenesis and inflammation in experimental colitis shows that initiating factors for these responses simultaneously increase as disease progresses and correlate in magnitude. Recent studies show that inhibition of the inflammatory response attenuates angiogenesis to a similar degree and, importantly, that inhibition of angiogenesis does the same to inflammation. Recent data provide evidence that differential regulation of the angiogenic mediators involved in IBD-associated chronic inflammation is the root of this pathological angiogenesis. Many factors are involved in this phenomenon, including growth factors/cytokines, chemokines, adhesion molecules, integrins, matrix-associated molecules, and signaling targets. These factors are produced by various vascular, inflammatory, and immune cell types that are involved in IBD pathology. Moreover, recent studies provide evidence that antiangiogenic therapy is a novel and effective approach for IBD treatment. Here we review the role of pathological angiogenesis during IBD and experimental colitis and discuss the therapeutic avenues this recent knowledge has revealed.

Inflammation and the mucosal microcirculation in inflammatory bowel disease: the ebb and flow

PURPOSE OF REVIEW

Inflammatory bowel disease pathogenesis involves the interplay of multiple biological factors, among which nonimmune cells, including the endothelium, represent a crucial component of disease pathogenesis.

RECENT FINDINGS

Endothelial cells play a key role in chronic inflammation through multiple and disparate activities. The mucosal microvasculature in inflammatory bowel disease is dysfunctional, overexpresses inflammatory molecules and undergoes intense angiogenesis, failing to exert its physiological antiinflammatory and anticoagulant activities.

SUMMARY

The mucosal microcirculation is abnormal in inflammatory bowel disease and represents a novel component of disease pathogenesis; targeting the various abnormalities of the inflammatory bowel disease microcirculation may lead to new forms of therapeutic intervention.

Inflammatory bowel disease: cause and immunobiology

Crohn's disease and ulcerative colitis are idiopathic inflammatory bowel disorders. In this paper, we discuss how environmental factors (eg, geography, cigarette smoking, sanitation and hygiene), infectious microbes, ethnic origin, genetic susceptibility, and a dysregulated immune system can result in mucosal inflammation. After describing the symbiotic interaction of the commensal microbiota with the host, oral tolerance, epithelial barrier function, antigen recognition, and immunoregulation by the innate and adaptive immune system, we examine the initiating and perpetuating events of mucosal inflammation. We pay special attention to pattern-recognition receptors, such as toll-like receptors and nucleotide-binding-oligomerisation-domains (NOD), NOD-like receptors and their mutual interaction on epithelial cells and antigen-presenting cells. We also discuss the important role of dendritic cells in directing tolerance and immunity by modulation of subpopulations of effector T cells, regulatory T cells, Th17 cells, natural killer T cells, natural killer cells, and monocyte-macrophages in mucosal inflammation. Implications for novel therapies, which are discussed in detail in the second paper in this Series, are covered briefly.

Therapeutic and prophylactic thalidomide in TNBS-induced colitis: Synergistic effects on TNF-α, IL-12 and VEGF production

AIM: To evaluated the therapeutic and prophylactic effect of thalidomide on 2, 4, 6-trinitrobenzene sulfonic acid (TNBS)-induced colitis. Thalidomide has been reported to downregulate the expression of tumor necrosis factor α (TNF-α), IL-12, and vascular endothelial growth factor (VEGF), hallmarks of intestinal inflammation in Crohn’s disease (CD).

METHODS: Male Wistar rats were divided in five groups of ten animals each. Four groups received a rectal infusion of TNBS in ethanol. The first group was sacrificed 7 d after colitis induction. The second and third groups received either thalidomide or placebo by gavage and were sacrificed at 14 d. The fourth group received thalidomide 6 h before TNBS administration, and was sacrificed 7 d after induction. The fifth group acted as the control group and colitis was not induced. Histological inflammatory scores of the colon were performed and lamina propria CD4+ T cells, macrophages, and VEGF+ cells were detected by immunohistochemistry. TNF-α and IL-12 were quantified in the supernatant of organ cultures by ELISA.

RESULTS: Significant reduction in the inflammatory score and in the percentage of VEGF+ cells was observed in the group treated with thalidomide compared with animals not treated with thalidomide. Both TNF-α and IL-12 levels were significantly reduced among TNBS induced colitis animals treated with thalidomide compared with animals that did not receive thalidomide. TNF-α levels were also significantly reduced among the animals receiving thalidomide prophylaxis compared with untreated animals with TNBS-induced colitis. Intestinal levels of TNF-α and IL-12 were significantly correlated with the inflammatory score and the number of VEGF+ cells.

CONCLUSION: Thalidomide significantly attenuates TNBS-induced colitis by inhibiting the intestinal production of TNF-α, IL-12, and VEGF. This effect may support the use of thalidomide as an alternate approach in selected patients with CD.

Regulation of endothelial glutathione by ICAM-1 governs VEGF-A-mediated eNOS activity and angiogenesis

Previous studies suggest that inflammatory cell adhesion molecules may modulate endothelial cell migration and angiogenesis through unknown mechanisms. Using a combination of in vitro and in vivo approaches, herein we reveal a novel redox-sensitive mechanism by which ICAM-1 modulates endothelial GSH that controls VEGF-A-induced eNOS activity, endothelial chemotaxis, and angiogenesis. In vivo disk angiogenesis assays showed attenuated VEGF-A-mediated angiogenesis in ICAM-1(-/-) mice. Moreover, VEGF-A-dependent chemotaxis, eNOS phosphorylation, and nitric oxide production were impaired in ICAM-1(-/-) mouse aortic endothelial cells (MAEC) compared to WT MAEC. Decreasing intracellular GSH in ICAM-1(-/-) MAEC to levels observed in WT MAEC with 150 microM buthionine sulfoximine restored VEGF-A responses. Conversely, GSH supplementation of WT MAEC with 5 mM glutathione ethyl ester mimicked defects observed in ICAM-1(-/-) cells. Deficient angiogenic responses in ICAM-1(-/-) cells were associated with increased expression of the lipid phosphatase PTEN, consistent with antagonism of signaling pathways leading to eNOS activation. PTEN expression was also sensitive to GSH status, decreasing or increasing in proportion to intracellular GSH concentrations. These data suggest a novel role for ICAM-1 in modulating VEGF-A-induced angiogenesis and eNOS activity through regulation of PTEN expression via modulation of intracellular GSH status.

Differential angiogenic regulation of experimental colitis

Inflammatory bowel diseases (IBDs) are chronic inflammatory disorders of the intestinal tract with unknown multifactorial etiology that, among other things, result in alteration and dysfunction of the intestinal microvasculature. Clinical observations of increased colon microvascular density during IBD have been made. However, there have been no reports investigating the physiological or pathological importance of angiogenic stimulation during the development of intestinal inflammation. Here we report that the dextran sodium sulfate and CD4+CD45RBhigh T-cell transfer models of colitis stimulate angiogenesis that results in increased blood vessel density concomitant with increased histopathology, suggesting that the neovasculature contributes to tissue damage during colitis. We also show that leukocyte infiltration is an obligatory requirement for the stimulation of angiogenesis. The angiogenic response during experimental colitis was differentially regulated in that the production of various angiogenic mediators was diverse between the two models with only a small group of molecules being similarly controlled. Importantly, treatment with the anti-angiogenic agent thalidomide or ATN-161 significantly reduced angiogenic activity and associated tissue histopathology during experimental colitis. Our findings identify a direct pathological link between angiogenesis and the development of experimental colitis, representing a novel therapeutic target for IBD.

[Vascular development in inflammatory bowel disease]

There are 4 major concepts in vascular development: vasculogenesis (formation of blood vessels from angioblasts), angiogenesis (formation of vascular sprouts from preexisting vessels), arteriogenesis (thickening and development of vessels) and lymphangiogenesis (formation of lymphatic vessels). In the last decade, these concepts, especially angiogenesis and lymphangiogenesis, have acquired major importance due to their role in tumoral growth and metastatic dissemination. Moreover, the activity of various diseases that involve chronic inflammation, such as asthma, psoriasis and rheumatoid arthritis, has been associated with vascular development. Several growth factors and cytokines are involved in this process and consequently investigation into these elements, both in peripheral blood and their expression in affected tissues, could elucidate the role of vascular development in diseases whose pathogenesis involves chronic inflammation, such as inflammatory bowel disease. The presence of distinct molecules involved in vascular development processes, such as vascular endothelial growth factor (VEGF), basic fibroblastic growth factor and placental growth factor, among others, has been studied in both ulcerative colitis and Crohn's disease, although not extensively. It has been suggested that the phenomena of vasculogenesis, angiogenesis and lymphangiogenesis play a critical, although not exclusive, role in the inflammation that characterizes inflammatory bowel disease. In general, the results obtained to date suggest that new vascular formation is involved in the pathogenesis of these diseases.

Expression of VEGFR-2 on HaCaT cells is regulated by VEGF and plays an active role in mediating VEGF induced effects

Vascular endothelial growth factor (VEGF) and its receptor VEGFR-2 play important roles in mitogenesis and chemotaxis of endothelial cells. In normal human skin, VEGF is expressed and secreted by epidermal keratinocytes. Emerging data suggest that keratinocyte-derived VEGF targets other cell types besides the dermal endothelial cells. We have recently showed that keratinocytes from human normal skin expressed all five known VEGF receptors and co-receptors (neuropilin 1 and 2). To define the functional significance of VEGFR-2 in epidermis, we examined its role in a keratinocyte cell line, HaCaT cells, in response to VEGF treatment. Expression of VEGFR-2 on HaCaT cells was confirmed at both RNA and protein levels and was regulated by VEGF165 treatment. Treatment of HaCaT cells with VEGF165 induced tyrosine-autophosphorylation of VEGFR-2 and phosphorylation of PLC-gamma and p44/42 MAPK in a time-dependent manner. Preincubation with a neutralizing antibody for VEGFR-2 (MAB3571) completely abrogated these phosphorylation effects. Furthermore, VEGF165 stimulated proliferation and migration of HaCaT cells, and this effect was significantly blocked by a pretreatment with MAB3571. Neutralizing VEGFR-2 in HaCaT cells increased cell adhesion during culture. Our results suggest that VEGFR-2 expressed on HaCaT cells plays a crucial role in VEGF-mediated regulation of cell activity.