Modulation of bovine microvascular endothelial cell proteolytic properties by inhibitors of angiogenesis

Curcumin inhibits angiogenesis by up-regulation of microRNA-1275 and microRNA-1246: a promising therapy for treatment of corneal neovascularization

OBJECTIVE

Curcumin (capable of inhibiting angiogenic growth of human umbilical vein endothelial cells [HUVECs]), can be employed in vitro as a model of pathogenesis of corneal neovascularization (CRNV). The aim of this study was to explore regulatory mechanisms of microRNA (miR) levels after curcumin treatment.

MATERIALS AND METHODS

Expression profiles of miRs in curcumin-treated HUVECs were investigated by miR microassay. Specific mimics and inhibitors of miR-1275 or miR-1246 were transfected into HUVECs. Then, their target genes, vascular endothelial growth factor B (VEGFB) and nuclear transcription factor kappa B acting protein (NKAP) were detected by quantitative real-time PCR, Western blotting assay or immunofluorescence assay. Cell proliferation and cell cycle parameters were measured with the help of CCK-8 assay and flow cytometry.

RESULTS

MiR-1275 and miR-1246 expression levels were up-regulated by curcumin. Administration of the specific mimics and inhibitors of the two miRs led to significant changes in expression of VEGFB and NKAP as well as the indicators related to angiogenesis. Anti-angiogenic effect of curcumin depended on expression patterns of the two miRs in that inhibition of either miR interfered with the effect of curcumin. Furthermore, overexpression of NKAP interrupted effects of curcumin on the cells.

CONCLUSION

Collectively, our findings demonstrate that curcumin inhibited HUVEC proliferation by up-regulation of miR-1275 and miR-1246.

Domain 2 of uPAR regulates single-chain urokinase-mediated angiogenesis through β1-integrin and VEGFR2

How single-chain urokinase (ScuPA) mediates angiogenesis is incompletely understood. ScuPA (≥4 nM) induces phosphorylated (p)ERK1/2 (MAPK44 and MAPK42) and pAkt (Ser(473)) in umbilical vein and dermal microvascular endothelial cells. Activation of pERK1/2 by ScuPA is blocked by PD-98059 or U-0126, and pAkt (Ser(473)) activation is inhibited by wortmannin or LY-294002. ScuPA (32 nM) or protease-inhibited two-chain urokinase stimulates pERK1/2 to the same extent, indicating that signaling is not dependent on enzymatic activity. ScuPA induces pERK1/2, but not pAkt (Ser(473)), in SIN1(-/-) cells, indicating that the two pathways are not identical. Peptides from domain 2 of the urokinase plasminogen activator receptor (uPAR) or domain 5 of high-molecular-weight kininogen compete with ScuPA for the induction of pERK1/2 and pAkt (Ser(473)). A peptide of the integrin-binding site on uPAR, a β1-integrin peptide that binds uPAR, antibody 6S6 to β1-integrin, tyrosine kinase inhibitors AG-1478 or PP3, and small interfering RNA knockdown of VEFG receptor 2, but not HER1-HER4, blocked ScuPA-induced pERK1/2 and pAkt (Ser(473)). ScuPA-induced endothelial cell proliferation was blocked by inhibitors of pERK1/2 and pAkt (Ser(473)), antibody 6S6, and uPAR or kininogen peptides. ScuPA initiated aortic sprouts and Matrigel plug angiogenesis in normal, but not uPAR-deficient, mouse aortae or mice, respectively, but these were blocked by PD-98059, LY-294002, AG-1478, or cleaved high-molecular-weight kininogen. In summary, this investigation indicates a novel, a nonproteolytic signaling pathway initiated by zymogen ScuPA and mediated by domain 2 of uPAR, β1-integrins, and VEGF receptor 2 leading to angiogenesis. Kininogens or peptides from it downregulate this pathway.

Importance of vascular endothelial growth factor (VEGF) in ovarian physiology of mammals

Ovarian folliculogenesis in mammals is a complex process. Several compounds have been tested during in vitro culture of follicular cells for a better understanding of the mechanisms and factors related to ovarian folliculogenesis in mammals. From these compounds, vascular endothelial growth factor (VEGF) can be highlighted, as it is strongly associated with angiogenesis and, in recent years, its presence in ovarian cells has been investigated extensively. Previous studies have shown that the presence of VEGF protein, as well as mRNA expression of its receptor 2 (VEGFR-2) increases during follicular development. Therefore, it is likely that the interaction between VEGF and VEGFR-2 is crucial to promote follicular development. However, few studies on the influence of this factor on follicular development have been reported. This review addresses aspects related to the structural characterization and mechanism of action of VEGF and its receptors, and their biological importance in the ovary of mammals.

A2E, a component of lipofuscin, is pro-angiogenic in vivo

A recent study in vitro demonstrated that a major lipofuscin component, A2E, serves as a retinoic acid receptor ligand. The current study investigated the effects of A2E on retinal pigment epithelial (RPE) cells in vivo and was performed to extend the understanding of the effects of A2E. Firstly, subretinal injection of A2E was performed and 3 weeks after the injection, and it was demonstrated that subretinal injection of A2E induced RPE cell death, and concomitant upregulation of vascular endothelial growth factor (VEGF) in the RPE and choroid. The upregulation of VEGF was attenuated by an RARalpha antagonist. Next we performed laser photocoagulation in mice that accumulated A2E either after subretinal injection, by Ccl2 gene knockout or by aging demonstrated that mice that accumulated A2E in the RPE, which showed higher rates of choroidal neobascularization (CNV) formation after weak laser injury than the controls and the formation of CNV was inhibited by an RARalpha antagonist in all models tested. The data suggest that A2E accumulation induces RPE cell death, and concomitant increase of VEGF. Accumulation of A2E alone is not sufficient to induce CNV in vivo, but induces the expression of VEGF in RPE and choroid. The mice that accumulated A2E in RPE cells are vulnerable to CNV development via RAR activation, at least in part.

A2E, a pigment of the lipofuscin of retinal pigment epithelial cells, is an endogenous ligand for retinoic acid receptor

Lipofuscin contains fluorophores, which represent a biomarker for cellular aging. Although it remains unsubstantiated clinically, experimental results support that the accumulation of lipofuscin is related to an increased risk of choroidal neovascularization due to age-related macular degeneration, a leading cause of legal blindness. Here, we report that a major lipofuscin component, A2E, activates the retinoic acid receptor (RAR). In vitro experiments using luciferase reporter assay, competitional binding assay, analysis of target genes, and chromatin immunoprecipitation (ChIP) assay strongly suggest that A2E is a bona fide ligand for RAR and induces sustained activation of RAR target genes. A2E-induced vascular endothelial growth factor (VEGF) expression in a human retinal pigment epithelial cell line (ARPE-19) and RAR antagonist blocked the up-regulation of VEGF. The conditioned medium of A2E-treated ARPE-19 cells induced tube formation in human umbilical vascular endothelial cells, which was blocked by the RAR antagonist and anti-VEGF antibody. These results suggest that A2E accumulation results in the phenotypic alteration of retinal pigment epithelial cells, predisposing the environment to choroidal neovascularization development. This is mediated through the agonistic function of A2E, at least in part. The results of this study provide a novel potential therapeutic target for this incurable condition.

Nonclassic Endogenous Novel Regulators of Angiogenesis

Angiogenesis, the process through which new blood vessels arise from preexisting ones, is regulated by several "classic" factors, among which the most studied are vascular endothelial growth factor (VEGF) and fibroblast growth factor-2 (FGF-2). In recent years, investigations showed that, in addition to the classic factors, numerous endogenous peptides play a relevant regulatory role in angiogenesis. Such regulatory peptides, each of which exerts well-known specific biological activities, are present, along with their receptors, in the blood vessels and may take part in the control of the "angiogenic switch." An in vivo and in vitro proangiogenic effect has been demonstrated for erythropoietin, angiotensin II (ANG-II), endothelins (ETs), adrenomedullin (AM), proadrenomedullin N-terminal 20 peptide (PAMP), urotensin-II, leptin, adiponectin, resistin, neuropeptide-Y, vasoactive intestinal peptide (VIP), pituitary adenylate cyclase-activating polypeptide (PACAP), and substance P. There is evidence that the angiogenic action of some of these peptides is at least partly mediated by their stimulating effect on VEGF (ANG-II, ETs, PAMP, resistin, VIP and PACAP) and/or FGF-2 systems (PAMP and leptin). AM raises the expression of VEGF in endothelial cells, but VEGF blockade does not affect the proangiogenic action of AM. Other endogenous peptides have been reported to exert an in vivo and in vitro antiangiogenic action. These include somatostatin and natriuretic peptides, which suppress the VEGF system, and ghrelin, that antagonizes FGF-2 effects. Investigations on "nonclassic" regulators of angiogenesis could open new perspectives in the therapy of diseases coupled to dysregulation of angiogenesis.

All-trans retinoic acid induces in vitro angiogenesis via retinoic acid receptor: possible involvement of paracrine effects of endogenous vascular endothelial growth factor signaling

A natural retinoid all-trans retinoic acid (ATRA) regulates a variety of important cellular functions via retinoic acid receptor (RAR). ATRA has therapeutically been used against various malignancies including acute promyelocytic leukemia. Recently ATRA has also been recognized to be beneficial against atherosclerotic vascular disorders. However, its effects on angiogenesis remain controversial. We therefore examined ATRA effects on in vitro angiogenesis in terms of capillary-like tube formation using human umbilical vein endothelial cells (HUVECs)/normal human dermal fibroblast (NHDF) coculture. ATRA as well as RAR agonist Am80 significantly induced capillary-like tube formation. The ATRA-induced tube formation was inhibited by coincubation with RAR antagonist LE540/LE135. HUVEC proliferation, but not its migration, was also induced by ATRA. The ATRA-induced tube formation was completely abolished by coincubation with vascular endothelial growth factor (VEGF) neutralizing antibody or with VEGF receptor (VEGFR)-2 (KDR) neutralizing antibody, but not VEGFR-1 (Flt-1) neutralizing antibody. ATRA and Am80 induced VEGF secretion in the coculture as well as VEGF secretion/mRNA expression in NHDFs. Transcription activity of human VEGF gene promoter in NHDFs was stimulated by ATRA, which was augmented by RAR overexpression. ATRA also induced VDGFR-2/KDR mRNA expression in HUVECs. Moreover, ATRA-induced secretion of hepatocyte growth factor as well as angiopoietin-2 in the coculture. Taken together, ATRA may have induced angiogenesis via RAR mainly by stimulation of HUVEC proliferation and enhancement of endogenous VEGF signaling and in part by induction of hepatocyte growth factor and angiopoietin-2 production. Retinoids may therefore be potential candidates for therapeutic angiogenesis against ischemic vascular disorders.

Endogenous inhibitors of angiogenesis

Angiogenesis, the formation of new blood vessels, is required for many pathologic processes, including invasive tumor growth as well as physiologic organ/tissue maintenance. Angiogenesis during development and adulthood is likely regulated by a balance between endogenous proangiogenic and antiangiogenic factors. It is speculated that tumor growth requires disruption of such balance; thus, the angiogenic switch must be turned "on" for cancer progression. If the angiogenic switch needs to be turned on to facilitate the tumor growth, the question remains as to what the physiologic status of this switch is in the adult human body; is it "off," with inhibitors outweighing the stimulators, or maintained at a fine "balance," keeping the proangiogenic properties of many factors at a delicate "activity" balance with endogenous inhibitors of angiogenesis. The physiologic status of this balance is important to understand as it might determine an individual's predisposition to turn the switch on during pathologic events dependent on angiogenesis. Conceivably, if the physiologic angiogenesis balance in human population exists somewhere between off and even balance, an individual's capacity and rate to turn the switch on might reflect their normal physiologic angiogenic status. In this regard, although extensive knowledge has been gained in our understanding of endogenous growth factors that stimulate angiogenesis, the activities associated with endogenous inhibitors are poorly understood. In this review, we will present an overview of the knowledge gained in studies related to the identification and characterization of 27 different endogenous inhibitors of angiogenesis.

Retinoic acid decreases nitric oxide production in endothelial cells: a role of phosphorylation of endothelial nitric oxide synthase at Ser(1179)

The effects of retinoic acid (RA) on nitric oxide (NO) production are controversial. Furthermore, it has never been studied whether these effects are mediated by direct modulation of phosphorylation of endothelial nitric oxide synthase (eNOS). Using bovine aortic endothelial cells, we found that all-trans RA (atRA) dose- and time-dependently decreased NO production without alteration in eNOS expression. This decrease was accompanied by reduction in eNOS-Ser(1179) phosphorylation. However, atRA did not alter the phosphorylation of eNOS-Ser(116) or eNOS-Thr(497). Concurrently, atRA also decreased the expressions of vascular endothelial growth factor (VEGF) and its receptor KDR/Flk-1, and Akt phosphorylation. Co-treatment with troglitazone, an activator of VEGF expression, reversed the atRA-induced reductions in eNOS-Ser(1179) phosphorylation and NO production, with concomitant restoration in VEGF expression. Direct treatment with VEGF also reversed these inhibitory effects, suggesting an important role for VEGF. Nonetheless, the RARalpha antagonist Ro 41-5253 did not block all the inhibitory effects of atRA, indicating that these inhibitory effects are not mediated by the RA response element (RARE). Thus, atRA decreases eNOS-Ser(1179) phosphorylation through a mechanism that depends on VEGF-KDR/Flk-1-mediated Akt phosphorylation but is independent of RARE, leading to reduction in NO production.

Increased Vascularization Predicts Favorable Outcome in Follicular Lymphoma

Purpose: In malignant lymphoma, angiogenesis has been associated with adverse outcome or more aggressive clinical behavior. This correlation has been established in groups of patients with a large heterogeneity regarding lymphoma subtypes and treatment regimens. The aim of this study is to investigate the significance of vascularization in patients with follicular lymphoma receiving uniform first-line treatment.

Experimental Design: We assessed microvessel density (MVD) in pretreatment lymph node biopsies of 46 previously untreated patients with follicular lymphoma using anti-CD34 immunohistochemical staining and interactive quantification. In a selection of cases, vascular endothelial growth factor (VEGF)-RNA in situ hybridization was done. Patients were treated with cyclophosphamide-vincristine-prednisone induction chemotherapy combined with IFN-α2b. Thirty-six patients responded and received IFN-α as maintenance therapy.

Results: MVD ranged from 10 to 70 per measurement field of 0.19 mm2 (median, 38). Median progression-free survival was 47 months in patients with MVD in the highest tertile and only 13 months in patients with lower MVD. Overall survival in patients with low vessel density was 59 months. In patients with high vessel density, median overall survival was not reached. Multivariate analysis indicated that MVD was independently associated with overall survival. There was a lack of correlation between VEGF-RNA expression and vessel density.

Conclusion: This study shows that in follicular lymphoma increased vascularization is associated with improved clinical outcome. Furthermore, VEGF-A expression seems not to be involved in follicular lymphoma angiogenesis.

Role of TGF-β1 and JNK signaling in capillary tube patterning

The transforming growth factor (TGF) family of secretory polypeptides comprises signaling proteins involved in numerous physiological processes, including vascular development and vessel wall integrity. Both pro- and anti-angiogenic effects of TGF-β1 have also been documented. To study the intracellular mechanisms involved in capillary tube morphogenesis, endothelial cell aggregates were cultured in a fibrin matrix. It was found that the pattern of capillary tubes formed in a fibrin matrix was altered in response to TGF-β1 treatment such that the capillary-like structures displayed a bipolarized pattern. In contrast, in untreated control and fibroblast growth factor-2-treated cells, the pattern of capillary tubes formed was random. TGF-β1 also downregulated urokinase-type plasminogen activator (uPA) activity while upregulating PA inhibitor (PAI)-1 and thrombospondin (TSP)1 gene expression. To investigate the signaling cascade mediating the phenotypic changes observed, pharmacological inhibitors of p38 MAPK, Sp1 transcription factor, c-Jun NH2-terminal kinase (JNK), and the cytokine TNF-α were used. The p38 MAPK inhibitor SB203580 reversed the TGF-β1-dependent inhibition of uPA activity but not its morphogenetic effect. In contrast, the DNA intercalator WP631 and TNF-α counteracted the TGF-β1-induced morphogenetic effect while the JNK inhibitor SP600125 effectively inhibited capillary tube formation. These results indicate that the TGF-β1-induced capillary tube pattern is independent of the p38 MAPK-activated PAI-1 and TSP1 expression, but the mechanism involves Sp1-dependent transcriptional regulation. The results also raise the possibility that the JNK pathway, which controls convergent extension in Xenopus, may be involved in vessel wall patterning in mammalian systems.

Inhibited angiogenesis in aging: a role for TIMP-2

Factors responsible for age-associated impairment of angiogenesis are poorly understood. We observed that in aged mice, new fibrovascular tissue within subcutaneous polyvinyl alcohol sponges expressed more tissue inhibitor of metalloproteinases (TIMP)-2 than did corresponding tissue from young mice. In complementary studies in vitro, we utilized young and aged human microvascular endothelial cell lines (hmEC36 and hmEC90, respectively) and compared their morphogenetic capacity within three-dimensional collagen. HmEC90 exhibited poor formation of tubular, capillary-like structures in vitro, diminished expression of active matrix metalloproteinase (MMP)-2, and similar or lesser amounts of MT1-MMP relative to hmEC36. Correspondingly, the MMP inhibitor GM6001 decreased tubulogenesis by hmEC36 to levels observed for hmEC90. In vitro, hmEC90 expressed similar quantities of TIMP-1, but more TIMP-2 than did hmEC36. Accordingly, purified TIMP-2 inhibited tubulogenesis by hmEC36. Collectively, our studies indicate that elevated levels of TIMP-2 modulate decreased angiogenesis in aged tissues, most likely via TIMP-2-mediated inhibition of MMP-2 and MT1-MMP.

Angiopoietin/Tek interactions regulate mmp-9 expression and retinal neovascularization

The objective of the study was to determine the role of the angiopoietins in the regulation of gelatinase expression during angiogenesis, and whether inhibition of the angiopoietin/Tek interaction in vivo can suppress the extent of retinal neovascularization. Retinal microvascular endothelial cells were treated with angiopoietins and examined for the production of gelatinases. The effects of inhibiting angiopoietin binding to the Tie-2 receptor was studied in newborn mice with experimentally induced retinal neovascularization. Animals were treated with an ip injection of the Tie-2 antagonist, muTek delta Fc, while oxygen-exposed mice treated with similar concentrations of murine IgG were used as controls. The effect of muTek delta Fc on the gelatinase expression in the retina was examined by real-time RT-PCR analysis. The stimulation of cultured retinal endothelial cells with Ang-1 and -2 resulted in the increased expression of matrix metalloproteinase (MMP)-9. Ang-2 expression was up-regulated in experimental animals during the period of angiogenesis and was the greatest on Day 17 (the time of maximal angiogenic response). Histologic analysis of mice treated with the Tie-2 antagonist, muTek delta Fc, showed significant (87%; p = 0.001) inhibition of retinal neovascularization, and the response was dose-dependent. In vitro binding data support the fact that both Ang-1 and Ang-2 bind with high avidity to muTek delta Fc. The RT-PCR analysis of the retinas of the Tek-treated animals showed a similar (80%; p = 0.001) inhibition of the MMP-9 expression, which correlated with the decrease in angiogenesis. The up-regulation of gelatinases in microvascular endothelial cells by Ang-2 may be an important early response during the development of retinal neovascularization. Inhibition of the binding activity of the angiopoietins in vivo suppressed retinal neovascularization concomitant with a reduction in the expression of MMP-9.

Angiogenesis and anti-angiogenesis in hematological malignancies

Although it is well established that the growth of solid tumors requires vigorous neovascularization, it has been assumed that leukemias and other hematological malignancies do not depend on angiogenesis. However, the role of angiogenesis in growth and survival of neoplastic cells of the hematopoietic system has recently been recognized, and provides a rationale for novel therapeutic approaches to hematological malignancy. This review summarizes the literature concerning the relationship between angiogenesis and disease progression of several hematological malignancies. It is becoming increasingly evident that agents that interfere with blood vessel formation also block tumor progression, and, accordingly, antiangiogenic therapy has gained much interest as a potential adjunct to conventional therapy of many hematological malignancies. Recent successful applications of antiangiogenic agents that interfere or block the progression of hematological malignancies are evaluated in light of recent demonstrations of potent angiogenic activity of several hematopoietic growth factors. A novel finding regarding the role of angiogenesis in hematological malignancies, which accounts for many clinical observations as well as the apparent independence of these tumors on marrow vascularity, is presented. The information presented in this review will facilitate the design of future clinical trials using antiangiogenic agents for the treatment of hematological malignancies and will provide a basis for the design of experiments undertaken to define the mechanisms involved, mechanisms that may shed new light on the pathology of hematological malignancies.

Vascular endothelial growth factor (VEGF) is expressed by neoplastic Hodgkin-Reed-Sternberg cells in Hodgkin's disease

Vascular endothelial growth factor (VEGF) is involved in tumour angiogenesis, an important process for the growth and metastatic potential of solid tumours. Numerous studies have demonstrated up-regulation of VEGF at both mRNA and protein level in various tumours and a correlation with advanced stage and prognosis has been demonstrated in some cases. Limited information exists about its role in lymphoid malignancies and in particular, Hodgkin's disease. The present study examined the immunohistochemical expression of VEGF using the monoclonal antibody VG1 in a series of 61 cases of Hodgkin's disease, including both classical Hodgkin's disease and the nodular lymphocyte predominance variant, and correlated these results with microvessel density, using an anti-CD31 monoclonal antibody. In 41 cases (70.6%) of classical Hodgkin's disease and one of the three cases of nodular lymphocyte predominance Hodgkin's disease, the neoplastic Reed-Sternberg and Hodgkin cells expressed VEGF. The staining observed was cytoplasmic, either diffuse or with a focal paranuclear distribution. Macrophages were always positive, while reactive lymphocytes showed occasional positivity. A variable amount of strong extracellular staining was also observed in the tissue stroma and intravascular plasma staining was prominent. There was no statistically significant relationship between VEGF expression and the subtype of Hodgkin's disease or microvessel density. In vitro studies using the Reed-Sternberg cell lines L428 and KM-H2 were also performed in both normoxia and hypoxia and VEGF protein production was assessed by flow cytometry (FACS), immunoassay of cell culture supernatant, and RT-PCR. Analysis by FACS demonstrated a subset of cells in both cell lines reacting with VG1 and analysis of secreted VEGF (pg/ml per 1x10(6) cells) in cell culture supernatant confirmed the normoxic production in both cell lines and significant hypoxic induction (p<0.005). Additionally, both cell lines expressed VEGF mRNA, as demonstrated using the RT-PCR method. In conclusion, neoplastic cells express VEGF in Hodgkin's disease, as is the case in solid tumours, and this expression may be induced by hypoxia. The presence of VEGF in reactive macrophages and in the extracellular matrix might facilitate tumour progression.

Granulomatous and suppurative dermatitis at interferon alfa injection sites: report of 2 cases

It has previously been reported that interferon alfa injection sites may develop pyoderma gangrenosum, interface dermatitis, vasculitis, or, more commonly, ulcers characterized by intravascular thrombi and a mixed inflammatory cell infiltrate. We describe 2 patients in whom granulomatous and suppurative dermatitis developed at interferon alfa injection sites. These cases extend the spectrum of interferon alfa injection site reactions. The histologic and clinical similarities of these cases with pyoderma gangrenosum and cutaneous Crohn's disease are explored.

Retinoic acids repress the expression of ETS-1 in endothelial cells

The transcription factor ETS-1 expressed in endothelial cells (ECs) regulates angiogenesis by inducing MMP-1, MMP-3, MMP-9, u-PA and integrin beta3 in endothelial cells (ECs). Here, we examined whether antiangiogenic retinoic acids affect the expression of ETS-1 in ECs. The expression of ets-1 mRNA was up-regulated in sparse to subconfluent ECs and down-regulated in confluent ECs. When confluent ECs were stimulated with basic fibroblast growth factor (bFGF), ets-1 mRNA was induced. All-trans retinoic acid (ATRA) as well as 9-cis retinoic acid reduced the augmented expression of ets-1 mRNA in both subconfluent ECs and bFGF-treated confluent ECs. This inhibitory effect of ATRA was dose dependent and was evident at a concentration as low as 10(-7) M. ATRA did not alter the stability of ets-1 mRNA. Moreover, promoter analysis indicated that ATRA repressed the expression of ets-1 mRNA at transcriptional level. As a result, ATRA reduced the binding of ETS-1 protein to the ETS binding motif. These results indicate that the anti-angiogenic effect of retinoic acids is mediated at least in part by the transcriptional repression of ets-1 mRNA in ECs.

Retinoids induce fibroblast growth factor-2 production in endothelial cells via retinoic acid receptor alpha activation and stimulate angiogenesis in vitro and in vivo

The effect of retinoic acid (RA) on endothelial cells is still controversial and was examined in the present study. In bovine aortic endothelial cells (BAECs), all-trans RA (ATRA) and 9-cis RA (9CRA), but not 13-cis RA (13CRA), induced fibroblast growth factor-2 (FGF-2) production and exhibited a biphasic dose-dependent effect to enhance BAEC proliferation and differentiation into tubular structures on reconstituted basement membrane proteins (Matrigel); both processes were inhibited by FGF-2-neutralizing antibody. The pan RA receptor (RAR)-selective ligand (E)-4-[2-(5,5,8,8,-tetramethyl-5,6,7,8-tetrahydro-2-naphtalenyl)-1-propenyl] benzoic acid and the RARalpha-selective ligand 4-[1-(3,5,5,8,8-pentamethyl-5,6,7,8-tetrahydro-2-naphtyl)-ethenyl] benzoic acid stimulated the production of FGF-2, whereas the addition of the RARalpha-antagonist RO 41-5253 inhibited this effect. In BAECs, the forced expression of RARalpha, but not RARbeta or RARgamma, enhanced FGF-2 production, whereas the RARalpha-dominant negative, Delta403, blocked this effect. Furthermore, RARalpha overexpression directly stimulated BAEC differentiation on Matrigel and potentiated the effects of ATRA in this assay. Finally, ATRA-treated BAECs coinjected with Matrigel subcutaneously in mice induced neovascularization within the Matrigel plug, and ATRA also enhanced angiogenesis in the chicken chorioallantoic membrane assay. In conclusion, RA can stimulate endothelial cell proliferation and differentiation in vitro via enhanced RARalpha-dependent FGF-2 production, and it can also induce angiogenesis in vivo. The full text of this article is available at http://www.circresaha.org.

Avascular necrosis of the femoral head in chronic myeloid leukemia patients treated with interferon-alpha: a synergistic correlation?

BACKGROUND

The objectives of this study were to describe cases of avascular necrosis of the femoral head (ANFH) observed in chronic myeloid leukemia (CML) patients who were treated with interferon-alpha and to review the literature.

METHODS

The authors undertook a case review of the M. D. Anderson experience with ANFH occurring in CML patients who were managed with interferon-alpha-based therapy. MEDLINE (from 1966 to November 1999) and CancerLit (from 1983 to November 1999) searches were conducted to identify cases of avascular necrosis (AVN) associated with either CML or interferon-alpha.

RESULTS

Three patients with ANFH were identified from the authors' experience. No common features related to the disease or therapy were seen among them, except for the presence of thrombocytosis and loss of response. A literature review revealed seven cases of ANFH associated with CML with or without interferon-alpha-based therapy. ANFH was not reported in association with interferon-alpha use for indications other than the treatment of patients with CML.

CONCLUSIONS

ANFH may be the result of an interaction between CML and interferon-alpha therapy. ANFH that occurs in patients with CML who are treated with interferon-alpha should be recognized for treatment implications. Thrombocytosis with consequent microvascular thrombi and avascular necrosis manifesting in susceptible vascular or weight-bearing areas (e.g., the femoral head) may be an associated finding along with loss of response to interferon-alpha therapy.

New concepts in fibrinolysis and angiogenesis

Angiogenesis, the process by which new blood vessels form from preexisting vasculature, underlies a number of biologic processes including embryologic development, inflammation, wound healing, hypoxic retinal vascular proliferation, tumor growth, and atherosclerosis. The fibrinolytic system represents a cascade of serine protease activation events that culminate in the generation of plasmin. Although in-vitro studies suggest several possible roles that plasmin might play in angiogenesis, angiogenesis and fibrinolytic activity do not always correlate in in-vivo systems. During cutaneous and corneal wound healing, for example, angiogenesis proceeds normally in plasminogen-deficient animals. Similarly, the growth of most neoplasms is unimpaired in the absence of plasminogen. On the other hand, hypoxia-driven vascular proliferation may require plasmin-like activity, and angiogenesis within the atherosclerotic plaque seems to be associated with increased expression of fibrinolytic proteins. Recently, several nonplasmin fibrinolysins that may support the invasive phenotype of endothelial cells under specific circumstances have been identified. Thus, the contribution of individual fibrinolysins appears to be context-specific, just as the profile of endothelial cell gene expression depends upon the surrounding tissue milieu.

Retinoic acid selectively inhibits the vascular permeabilizing effect of VPF/VEGF, an early step in the angiogenic cascade

All-trans-retinoic acid (RA) and other retinoids modulate cell growth and differentiation, generally favoring terminal cell differentiation and inhibiting carcinogenesis. Retinoids are also reported to inhibit angiogenesis and endothelial cell migration, actions that are also anti-carcinogenic. Vascular permeability factor/vascular endothelial growth factor (VPF/VEGF) is a multifunctional cytokine secreted by many tumors. It renders microvessels hyperpermeable to plasma and stimulates endothelial cell migration and division. To investigate further the mechanisms by which RA inhibits angiogenesis, we evaluated the effects of RA on VPF/VEGF-induced angiogenesis and microvascular permeability. RA selectively inhibited the angiogenic response induced by VPF/VEGF, but not that induced by fibroblast growth factor-2 (FGF-2), in the CAM assay. RA and two of its isomers also inhibited the vascular permeabilizing effect of VPF/VEGF but not that induced by histamine. The vascular permeabilization induced by VPF/VEGF and blocked by RA takes place within 1-15 min, too short a time frame for RA to act by modulating transcription through classic retinoid receptors. RA also inhibited VPF/VEGF-induced phosphorylation of PLC-gamma and synthesis of cGMP but actually increased VPF/VEGF binding to cultured endothelial cells. Taken together, these findings indicate that RA selectively blocks VPF/VEGF-induced microvascular permeability and angiogenesis and also identify VPF/VEGF as a major target of RA action. The selectivity of RA's action suggests that other, RA-independent pathways must exist for the angiogenesis induced by FGF-2 and the vascular permeabilizing effect of histamine.

TNP-470 and recombinant human interferon-alpha2a inhibit angiogenesis synergistically

The hypothesis that the combination of two known antiangiogenic agents TNP-470 and interferon (IFN)-alpha exerts synergistic effects has been investigated in vitro and in vivo. In vitro, TNP-470 and recombinant human IFN-alpha2a (rhIFN-alpha2a) resulted in a dose-dependent inhibition of proliferation of human umbilical vein endothelial cells (HUVECs) and EA.hy926 endothelial cells. Compared with the two agents used singly at their lowest or ineffective doses, combined treatment with the same doses inhibited more intensely in the absence of cytotoxicity and displayed similar behaviour on cell chemotaxis and capillary morphogenesis on Matrigel. However, the secretion of matrix metalloproteinase 2 (MMP-2) and MMP-9 was not influenced by the two agents, either alone or in combination, even when they were applied at their lowest efficacious doses or at higher cytotoxic doses. Experiments in vivo with the chick embryo chorioallantoic membrane (CAM)-sponge assay revealed the same dose-dependent inhibition and synergy. As the basic fibroblast growth factor (bFGF)-induced angiogenesis in the CAM-sponge model was strongly inhibited by the combined treatment, TNP-470 and rhIFN-alpha2a would appear to exert antiangiogenesis synergistically, perhaps by interfering with the bFGF-mediated pathway.

Modulation of endothelial cell proliferation by retinoid x receptor agonists

One feature that contraindicates the wide therapeutic use of natural retinoids is their adverse effects during systemic use and the lack of receptor selectivity. In contrast, synthetic retinoids are distinguishable from each other on the basis of their partial or exclusive preference in binding and activation of selective retinoid receptors. We examined the inhibitory activities of natural and synthetic retinoids for their ability to reverse basic fibroblast growth factor-induced endothelial cell proliferation. Both the naturally occurring retinoids at nanomolar concentrations reversed basic fibroblast growth factor-induced endothelial cell proliferation. Among the synthetic retinoids tested, retinoic acid receptor/retinoid x receptor pan-agonist AGN 191659 [(E)-5-[2-(5,6,7, 8-tetrahydro-3, 5,5,8,8-pentamethyl-2-naphtyl) propen-1-yl]-2-thiophenecarboxylic acid] and retinoid x receptor pan-agonist AGN 191701 [(E)-2-[2-(5,6,7,8-tetrahydro-3, 5,5,8, 8-pentamethyl-2-naphthyl) propen-1-yl]-4-thiophenecarboxylic acid] at nanomolar concentrations reversed the basic fibroblast growth factor-induced endothelial cell proliferation. Since none of the retinoic acid receptor agonists tested had any effect, the inhibitory effect of AGN 191659 could be attributed to its retinoid x receptor receptor activity. These results suggest that retinoid x receptor agonists may be more selective anti-angiogenic agents due to their ability to inhibit endothelial cell proliferation.

Hormone-activated nuclear receptors inhibit the stimulation of the JNK and ERK signalling pathways in endothelial cells

Glucocorticoid hormones, retinoids, and vitamin D3 display anti-angiogenic activity in tumor-bearing animals. However, despite their in vivo effect on the tumor vasculature little is known about their mechanism of action. Here we show that the synthetic glucocorticoid dexamethasone (Dex) and retinoic acid (RA) inhibit the activation of c-Jun N-terminal kinase (JNK) and extracellular-regulated kinase (ERK) signalling pathways by the pro-angiogenic agents tumor necrosis factor and vascular endothelial growth factor in endothelial cells. In contrast, Dex and RA failed to inhibit the activation of the p38 mitogen-activated protein kinase cascade. As a number of pro-angiogenic factors activate AP-1 transcription factor via the JNK and ERK pathways, our results suggest that the antagonism with AP-1 may underlie at least partially the anti-angiogenic effect of glucocorticoids and retinoids.

Angiostatic activity of steroids in the chick embryo CAM and rabbit cornea models of neovascularization

Ocular neovascular diseases represent a major cause of blindness in the world. Angiostatic steroids are a unique class of compounds which inhibit the formation of new blood vessels in various models, including ocular models of angiogenesis. In search of potent new anti-angiogenic agents for the treatment of ocular neovascular disease, a large group of steroids were evaluated for angiostatic activity in the chick embryo CAM model. Angiostatic activity was found among all steroid classes included in the study. There was a good correlation between the angiostatic efficacies of 15 diverse steroids tested in the chick CAM and in the rabbit LPS-induced corneal pocket models of neovascularization (r=0.76, p=0.01). These studies show that potent angiostatic steroids inhibit neovascularization in two different animal models, suggesting a common mechanism of action. Glucocorticoid therapy is sometimes associated with ocular side effects. Two of the most potent angiostatic steroids, AL-3789 and AL-4940, were evaluated for glucocorticoid-mediated antiinflammatory activity in the in vitro U937 cell model of LPS-induced IL-1 induction and found to be devoid of glucocorticoid activity. Angiostatic steroids which lack glucocorticoid activity should be attractive drug candidates for treating ocular neovascular disease.

Angiostatin inhibits endothelial and melanoma cellular invasion by blocking matrix-enhanced plasminogen activation

Angiostatin, a kringle-containing fragment of plasminogen, is a potent inhibitor of angiogenesis. The mechanism(s) responsible for the anti-angiogenic properties of angiostatin are unknown. We now report that human angiostatin blocks plasmin(ogen)-enhanced in vitro invasion of tissue plasminogen activator (t-PA)-producing endothelial and melanoma cells. Kinetic analyses demonstrated that angiostatin functions as a non-competitive inhibitor of extracellular-matrix (ECM)-enhanced, t-PA-catalysed plasminogen activation, with a Ki of 0.9+/-0.03 microM. This mechanism suggests that t-PA has a binding site for the inhibitor angiostatin, as well as for its substrate plasminogen that, when occupied, prevents ternary complex formation between t-PA, plasminogen and matrix protein. Direct binding experiments confirmed that angiostatin bound to t-PA with an apparent Kd [Kd(app)] of 6.7+/-0.7 nM, but did not bind with high affinity to ECM proteins. Together, these data suggest that angiostatin in the cellular micro-environment can inhibit matrix-enhanced plasminogen activation, resulting in reduced invasive activity, and suggest a biochemical mechanism whereby angiostatin-mediated regulation of plasmin formation could influence cellular migration and invasion.

Endothelial cell integrin alpha5beta1 expression is modulated by cytokines and during migration in vitro

Alterations in endothelial cell-extracellular matrix interactions are central to the process of angiogenesis. We have investigated the effect of wound-induced two-dimensional migration, basic fibroblast growth factor (bFGF), transforming growth factor-beta1 (TGF-beta1) and leukemia inhibitory factor (LIF) on expression of the alpha5beta1 integrin in endothelial cells. In multiple-wounded monolayers of bovine microvascular endothelial (BME) cells, an increase in mRNA and total protein for both alpha5 and beta1 subunits was observed, and this could be correlated with a reduction in cell density but not proliferation, both of which are induced following wounding. Although as previously reported, the alpha5 subunit was increased when cells were exposed to TGF-beta1 alone, co-addition of bFGF and TGF-beta1 resulted in a striking synergistic induction of alpha5, with no significant changes in the expression of beta1. In contrast, the alpha5 subunit was decreased by LIF in bovine aortic endothelial but not in BME cells. These findings suggest that quantitative alterations in alpha5 and beta1 integrin subunit expression modulate the adhesive and migratory properties of endothelial cells during angiogenesis.

Angiogenesis: possibilities for therapeutic interventions

Vascular proliferation normally occurs only during embryonic development, the female reproductive cycle and wound healing. Various pathological conditions such as diabetic retinopathy are characterized by persistent, uncontrolled angiogenesis. At the other hand, impaired development of new blood vessels has been found to be related with myocardial infarction. A series of anti-angiogenic drugs are currently included in experimental cancer treatment, whereas the failure of ulcers to heal may be limited by increased angiogenesis upon administration of growth factors. In the present review control mechanisms of the vasculature are summarized and therapeutic approaches discussed.

Effect of Steroid Hormones and Retinoids on the Formation of Capillary-Like Tubular Structures of Human Microvascular Endothelial Cells in Fibrin Matrices Is Related to Urokinase Expression

Angiogenesis, the formation of new capillary blood vessels, is a feature of a variety of pathological processes. To study the effects of a specific group of hormones (all ligands of the steroid/retinoid/thyroid hormone receptor superfamily) on the angiogenic process in humans, we have used a model system in which human microvascular endothelial cells from foreskin (hMVEC) are cultured on top of a human fibrin matrix in the presence of basic fibroblast growth factor and tumor necrosis factor-α. This model mimics the in vivo situation where fibrin appears to be a common component of the matrix present at sites of chronic inflammation and tumor stroma. Our results show that testosterone and dexamethasone are strong inhibitors and all-trans retinoic acid (at-RA) and 9-cis retinoic acid (9-cis RA) are potent stimulators of the formation of capillary-like tubular structures. These effects are mediated by their respective nuclear hormone receptors as demonstrated by the use of specific synthetic receptor agonists and antagonists. 17β-estradiol, progesterone, and 1,25-dihydroxyvitamin D3 did not affect or only weakly affected in vitro angiogenesis, which may be related to the lack of significant nuclear receptor expression. Although hMVEC express both thyroid hormone receptors α and β, no effect of thyroid hormone on tube formation was found. The effects of testosterone, dexamethasone,at-RA, and 9-cis RA on tube formation were accompanied by parallel changes in urokinase-type plasminogen activator (u-PA) expression, at both mRNA and antigen levels. Exogenous suppletion of the medium with single chain u-PA enhances tube formation in our in vitro model, whereas quenching of u-PA activity (but not of tissue-type plasminogen activator activity) or of u-PA binding to u-PA receptor by specific antibodies suppressed basal and retinoid-stimulated tube formation. Moreover, addition of scu-PA to testosterone- or dexamethasone-treated hMVEC restored the suppressed angiogenic activity for a substantial part. Aprotinin, an inhibitor of plasmin activity, completely inhibited tube formation, indicating that the proteolytic properties of the u-PA/u-PA receptor complex are crucial in this process. Our results show that steroid hormones (testosterone and dexamethasone) and retinoids have strong, but opposite effects on tube formation in a human in vitro model reflecting pathological angiogenesis in the presence of fibrin and inflammatory mediators. These effects can be explained by hormone-receptor–mediated changes in u-PA expression, resulting in enhanced local proteolytic capacity of the u-PA/u-PA receptor complex.

© 1998 by The American Society of Hematology.

Effect of Steroid Hormones and Retinoids on the Formation of Capillary-Like Tubular Structures of Human Microvascular Endothelial Cells in Fibrin Matrices Is Related to Urokinase Expression

Angiogenesis, the formation of new capillary blood vessels, is a feature of a variety of pathological processes. To study the effects of a specific group of hormones (all ligands of the steroid/retinoid/thyroid hormone receptor superfamily) on the angiogenic process in humans, we have used a model system in which human microvascular endothelial cells from foreskin (hMVEC) are cultured on top of a human fibrin matrix in the presence of basic fibroblast growth factor and tumor necrosis factor-α. This model mimics the in vivo situation where fibrin appears to be a common component of the matrix present at sites of chronic inflammation and tumor stroma. Our results show that testosterone and dexamethasone are strong inhibitors and all-trans retinoic acid (at-RA) and 9-cis retinoic acid (9-cis RA) are potent stimulators of the formation of capillary-like tubular structures. These effects are mediated by their respective nuclear hormone receptors as demonstrated by the use of specific synthetic receptor agonists and antagonists. 17β-estradiol, progesterone, and 1,25-dihydroxyvitamin D3 did not affect or only weakly affected in vitro angiogenesis, which may be related to the lack of significant nuclear receptor expression. Although hMVEC express both thyroid hormone receptors α and β, no effect of thyroid hormone on tube formation was found. The effects of testosterone, dexamethasone,at-RA, and 9-cis RA on tube formation were accompanied by parallel changes in urokinase-type plasminogen activator (u-PA) expression, at both mRNA and antigen levels. Exogenous suppletion of the medium with single chain u-PA enhances tube formation in our in vitro model, whereas quenching of u-PA activity (but not of tissue-type plasminogen activator activity) or of u-PA binding to u-PA receptor by specific antibodies suppressed basal and retinoid-stimulated tube formation. Moreover, addition of scu-PA to testosterone- or dexamethasone-treated hMVEC restored the suppressed angiogenic activity for a substantial part. Aprotinin, an inhibitor of plasmin activity, completely inhibited tube formation, indicating that the proteolytic properties of the u-PA/u-PA receptor complex are crucial in this process. Our results show that steroid hormones (testosterone and dexamethasone) and retinoids have strong, but opposite effects on tube formation in a human in vitro model reflecting pathological angiogenesis in the presence of fibrin and inflammatory mediators. These effects can be explained by hormone-receptor–mediated changes in u-PA expression, resulting in enhanced local proteolytic capacity of the u-PA/u-PA receptor complex.

© 1998 by The American Society of Hematology.

The proteasome is involved in angiogenesis

The proteasome is a recently identified intracellular protease whose catalytic active site is a threonine residue and has been shown to play key roles in a variety of important intracellular events, including cell cycle progression, the antigen-presenting pathway, and apoptosis. However, its biological significance in multicellular organisms is still largely unknown because of lack of experimental systems for its study. Here we verified potential involvement of the proteasome in angiogenesis using lactacystin, a specific proteasome inhibitor. Lactacystin treatment resulted in almost complete prevention of in vivo neovascularization in the developing chick embryo chorioallantoic membrane. It also inhibited vascular endothelial tube formation on Matrigel, a model for in vitro angiogenesis, in a concentration-dependent fashion. Moreover, it prevented production of plasminogen activator, an important protease responsible for induction of angiogenesis, by endothelial cells, which correlated well with its suppression of intracellular proteasome activity. Our studies suggest that the proteasome operates in the process of angiogenesis, a phenomenon essential in important physiological and pathological settings.

Gene Polymorphisms for PAI-1 Are Associated with the Angiographic Extent of Coronary Artery Disease

Localized regulation of fibrinolytic protein gene expression is associated with the histologic extent of atherosclerosis. This regulation may be dependent on the presence of certain fibrinolytic protein gene polymorphisms. The relationship between the plasminogen activator inhibitor (PAI)-1 Hin dIII and the tissue plasminogen activator (t-PA) EcoR1 gene polymorphisms and the extent of coronary artery disease (CAD) were investigated in 49 Caucasian patients with symptomatic CAD. There was a strong association between PAI-1, but not t-PA, gene polymorphisms and the extent of CAD detected by coronary angiography. Patients homozygous for the presence or absence of the PAI-1 HindIII (1/1, 2/2 PAI-1) gene polymorphisms had a significantly greater extent of CAD (number of diseased vessels) than patients with the respective heterozygous forms (vs. 1/2 PAI-1, P&< = 0.05). Stepwise ordinal multiple regression analysis of classic CAD risk factors and fibrinolytic protein genotypes indicated that only the PAI-1 genotypes were predictive of the extent of angiographic CAD (P = 0.019). Analysis of variance between classic risk factors and fibrinolytic protein genotypes identified an association between t-PA genotypes and a history of prior infarction or stroke. Fibrinolytic gene polymorphisms for PAI-1 are associated with the extent of CAD in symptomatic patients and with certain risk factors for coronary atherosclerosis.

Positive and negative regulation of angiogenesis: from cell biology to the clinic

Virtually every subspecialty in medicine in one way or another deals with angiogenesis-associated physiological or pathological processes and, without exception, every organ system in the body has many diseases in which angiogenesis is an important component. This in itself makes the study of angiogenesis mandatory, in both basic science and clinical settings. Yet the study of angiogenesis does not require this justification. As a biological process it is extraordinarily rich, touching on virtually every aspect of modern cell biology, making it almost impossible for molecular biologists, biochemists and morphologists to ignore. Considerable therapeutic benefit can now be obtained through positive or negative manipulation of the angiogenic process, and this is due in large part to the rapid transfer to the clinical setting of knowledge acquired through a cell biological approach.

Basic fibroblast growth factor is a morphogenic modulator in kidney vessel development

During kidney organogenesis the development of renal vessels must be synchronized with the maturation of nephrons and the collecting duct system. Several reports showed that hormones and mitogenic peptides as basic fibroblast growth factor (bFGF) or vascular endothelial growth factor (VEGF) are involved in this regulatory process. It is a known fact that bFGF receptors are expressed by differentiating tubular epithelium and mesenchyme, but little information is available about the function of bFGF in kidney organogenesis. The role of bFGF during kidney development was investigated using an organotypic culture system and immunohistological techniques. Renal cortex explants were prepared from the kidneys of neonatal rabbits with a microsurgical method, retaining the natural tissue composition. The explants were cultured serum free under continuous medium perfusion. Our results indicate a new and unexpected role of bFGF during the differentiation process. When bFGF alone was applied, vessels could no longer be detected. The inhibitory influence of bFGF could be overcome by addition of VEGF or hormones such as retinoic acid and aldosterone/vitamin D3. The combination of these factors with bFGF resulted in the expression of small vessel-like structures. We conclude that bFGF has a morphogenic rather than a mitogenic function during kidney vessel development.

Loss of a consensus heparin binding site by alternative splicing of latent transforming growth factor-beta binding protein-1

Latent transforming growth factor-beta binding protein-1 (LTBP-1), plays an important role in controlling localisation and activation of transforming growth factor-beta (TGF-beta). We show that alternative splicing generates a form of mRNA which lacks bases 1277-1435 (termed LTBP-1delta53). The 53 amino acids encoded by these bases include the eighth cysteine of the first cysteine repeat and a consensus heparin binding sequence. Sequencing of genomic clones showed that alternative splicing resulted from the use of an intra-exonic 3' splice acceptor site. The loss of the heparin binding site implies that LTBP-1delta53 will bind to the extracellular matrix less efficiently than LTBP-1.

Isolation and characterization of the circulating form of human endostatin

Recently, fragments of extracellular proteins, including endostatin, were defined as a novel group of angiogenesis inhibitors. In this study, human plasma equivalent hemofiltrate was used as a source for the purification of high molecular weight peptides (10-20 kDa), and the isolation and identification of circulating human endostatin are described. The purification of this C-terminal fragment of collagen alpha1(XVIII) was guided by MALDI-MS and the exact molecular mass determined by ESI-MS was found to be 18 494 Da. N-terminal sequencing revealed the identity of this putative angiogenesis inhibitor and its close relation to mouse endostatin. The cysteine residues 1-3 and 2-4 in the molecule are linked by disulfide bridges. In vitro biological characterization of the native protein demonstrated no anti-proliferative activity on different endothelial cell types. These data indicate that human endostatin, which is a putative angiogenesis inhibitor, is present in the circulation.

Is avascular necrosis of the femoral head the result of inhibition of angiogenesis?

An hypothesis is offered here that the pathogenesis of avascular necrosis (AVN) of the femoral head is based on the inhibition of angiogenesis. Well-established facts supporting this hypothesis are: 1, the lesion of AVN is vascular obliteration often leading to infarction; 2, glucocorticoids, which are a risk factor for AVN, are inhibitors of angiogenesis; 3, interferons, which are now being used in the treatment of multiple sclerosis, hepatitis, leukemias, and hemangiomas are inhibitors of angiogenesis, and other endogenously produced cytokines are also inhibitors; 4, constituents of cartilage are inhibitors of angiogenesis, explaining the subchondral location of AVN; 5, angiography of the femoral head indicates the need for continual renewal of its blood supply, shows the inhibition of revascularization by steroids, and suggests that the stress of weight bearing makes the femoral head particularly vulnerable. This hypothesis has implications for the therapeutic use of inhibitors of angiogenesis.

Transcriptional activation by p53 of the human type IV collagenase (gelatinase A or matrix metalloproteinase 2) promoter

p53, a tumor suppressor and a transcription factor, has been shown to transcriptionally activate the expression of a number of important genes involved in the regulation of cell growth, DNA damage, angiogenesis, and apoptosis. In a computer search for other potential p53 target genes, we identified a perfect p53 binding site in the promoter of the human type IV collagenase (also called 72-kDa gelatinase or matrix metalloproteinase 2 [MMP-2]) gene. This p53 binding site was found to specifically bind to p53 protein in a gel shift assay. Transcription assays with luciferase reporters driven by the promoter or enhancer of the type IV collagenase gene revealed that (i) activation of the promoter activity is p53 binding site dependent in p53-positive cells but not in p53-negative cells and (ii) wild-type p53, but not p53 mutants commonly found in human cancers, transactivates luciferase expression driven by the type IV collagenase promoter as well as by a p53 site-containing enhancer element in the promoter. Significantly, expression of the endogenous type IV collagenase is also under the control of p53. Treatment of U2-OS cells, a wild-type p53-containing osteogenic sarcoma line, with a common p53 inducer, etoposide, induced p53 DNA binding and transactivation activities in a time-dependent manner. Induction of type IV collagenase expression followed the p53 activation pattern. No induction of type IV collagenase expression can be detected under the same experimental conditions in p53-negative Saos-2 cells. All these in vitro and in vivo assays strongly suggest that the type IV collagenase gene is a p53 target gene and that its expression is subject to p53 regulation. Our finding links p53 to a member of the MMP genes, a family of genes implicated in trophoblast implantation, wound healing, angiogenesis, arthritis, and tumor cell invasion. p53 may regulate these processes by upregulating expression of type IV collagenase.

Lumen formation and other angiogenic activities of cultured capillary endothelial cells are inhibited by thrombospondin-1

The large secreted glycoprotein thrombospondin-1 is a potent inhibitor of neovascularization in vivo. In order to better understand its mechanism of action, we have determined the full range of deficits thrombospondin can impose on cultured capillary endothelial cells. Exogenously added thrombospondin-1 blocked the ability of these cells to organize into cords. It blocked the migration of endothelial cells and vascular smooth muscle cells, but not that of fibroblasts, neutrophils, or keratinocytes, demonstrating specificity. Conversely, when the endogenous thrombospondin-1 produced by the endothelial cells was inactivated using antibodies that can neutralize its inhibition of neovascularization in vivo, migration toward basic fibroblast growth factor and cord formation were stimulated, and sparsely plated cells developed cylindrical cavities. These cavities formed by vesicle fusion, extended the depth of the cell, and appeared to be incipient lumens, staining positively for the luminal marker angiotensin converting enzyme. Antiangiogenic levels of thrombospondin-1 had no measurable effect on the overall level of activity of soluble gelatinases or on urokinase plasminogen activator produced by activated endothelial cells. Coupled with previously published data, these results demonstrate thrombospondin-1 is a multifaceted inhibitor able to block the entire program of dedifferentiation and redifferentiation essential to the formation of new vessels. They also support the contention that the endogenously produced protein contributes to the quiescence of the normal vasculature.

Manipulating angiogenesis. From basic science to the bedside

Considerable progress has been made recently in understanding the molecular mechanisms of angiogenesis, which like most other biological processes is the result of subtle and often complex interactions between molecules that have regulatory (eg, cytokines and their receptors) and effector (eg, extracellular matrix, integrins, and proteases) functions. The title of this review was chosen to reflect a recent trend in which knowledge acquired through a molecular/cell biological approach is being rapidly transferred to the clinical setting. As a result, by manipulating angiogenesis either positively or negatively, considerable therapeutic benefit can now be envisaged in physiological and pathological settings in which neovascularization is a prominent component.

Differential expression of the urokinase receptor (CD87) in arthritic and normal synovial tissues

AIM

To determine whether the urokinase plasminogen activator receptor (u-PAR; CD87) exhibits a possible pathogenic role in rheumatoid and osteoarthritis.

METHODS

A semiquantitative, indirect immunoperoxidase histochemical analysis was performed on frozen synovial tissue sections. The recently characterised monoclonal antibody 10G7 recognising transfectants bearing u-PAR was used. Synovial tissue was obtained from 10 patients with rheumatoid arthritis, 10 patients with osteoarthritis, and four normal subjects.

RESULTS

u-PAR was expressed on 70-90% of synovial tissue lining cells and subsynovial, interstitial macrophages from the arthritis patients, but only on a few myeloid cells from the normal subjects. It was also present on more endothelial cells from the rheumatoid and osteoarthritis patients, than from normal synovial tissue.

CONCLUSIONS

Plasminogen activators are important in joint destruction underlying arthritis. The up-regulated expression of u-PAR in diseased versus normal synovial tissue suggests a role for this antigen in the inflammatory and angiogenic mechanisms underlying rheumatoid and osteoarthritis.

Transforming growth factor-beta: vasculogenesis, angiogenesis, and vessel wall integrity

Genetic studies have recently revealed a role for transforming growth factor-beta-1 (TGF-beta 1) and its receptors (TGF-beta Rs I and II as well as endoglin) in embryonic vascular assembly and in the establishment and maintenance of vessel wall integrity. The purpose of this review is threefold: first, to reassess previous studies on TGF-beta and endothelium in the light of these recent findings; second, to describe some of the well-established as well as controversial issues concerning TGF-beta and its regulatory role in angiogenesis; and third, to explore the notion of "context' with respect to TGF-beta and endothelial cell function. Although the focus of this review will be on the endothelium, other vascular wall cells are also likely to be important in the pathogenesis of the vascular lesions revealed by genetic studies.

Role of fibrin and plasminogen activators in repair-associated angiogenesis: in vitro studies with human endothelial cells

Angiogenesis, the formation of new blood vessels from existing ones, plays a central role in development and in a number of pathological conditions. Tissue repair-associated angiogenesis usually involves cell invasion into a fibrin structure and the presence of inflammatory cells. In this chapter the role of plasminogen activators in the dissolution of fibrin and the invasion of endothelial cells into a fibrin matrix is described. Tissue-type plasminogen activator is stored in endothelial cells and can be released acutely into the vessel lumen upon stimulation of the endothelium to activate fibrinolysis and to prevent fibrin deposition. At the basolateral side of the cell, urokinase-type plasminogen activator (uPA) bound to a specific cellular receptor is involved in the proteolytic modulation of matrix proteins and cell-matrix interaction. The cytokine tumor necrosis factor-alpha (TNF-alpha) cooperates with the angiogenic factors basic fibroblast growth factor (bFGF) and vascular endothelial growth factor (VEGF) in inducing human microvascular endothelial cells in vitro to invade a three dimensional fibrin matrix and to form capillary-like tubular structures. The formation of these capillary-like tubules requires cell-bound uPA activity.

Synergistic stimulation of gamma-glutamyl transpeptidase and alkaline phosphatase activities by retinoic acid and astroglial factors in immortalized rat brain microvessel endothelial cells

The immortalized rat brain microvessel endothelial cell line RBE4 was used to investigate the in vitro regulation of two blood-brain barrier specific enzymes, gamma-glutamyl transpeptidase (GTP) and alkaline phosphatase (ALP). The effects of bFGF, astroglial factors, and retinoic acid (a cell differentiation agent) on GTP and ALP activities were separately or simultaneously studied in order to define optimal culture conditions for induction of these two specific enzymes of the blood-brain barrier. In the present study, a phenotypically distinct subpopulation of endothelial cells has been shown to develop from confluent cobblestone monolayers of RBE4 immortalized cerebral endothelial cells. These distinct cells were present within multicellular aggregates and specifically exhibited GTP and ALP activities. Addition of bFGF, astroglial factors, or retinoic acid induced the formation of these three-dimensional structures and in consequence an increase in GTP and ALP activities. For retinoic acid and astroglial factors, this increase could also be explained by the stimulation of either GTP or ALP expression in the phenotypically distinct positive cells associated with aggregates. Simultaneous treatment with retinoic acid and astroglial factors had a synergistic effect on GTP and ALP expression and thus may allow these distinct cells to evolve toward a more differentiated state. Since such results were also obtained with physiological concentrations of retinoic acid, we suggest that addition of this agent might contribute to greater differentiation of cells in in vitro blood-brain barrier models where endothelial cells are cocultured with astrocytes.

Localization of matrix metalloproteinase MMP-2 to the surface of invasive cells by interaction with integrin alpha v beta 3

SUMMARY

Cellular invasion depends on cooperation between adhesive and proteolytic mechanisms. Evidence is provided that the matrix metalloproteinase MMP-2 can be localized in a proteolytically active form on the surface of invasive cells, based on its ability to bind directly integrin alpha v beta 3. MMP-2 and alpha v beta 3 were specifically colocalized on angiogenic blood vessels and melanoma cells in vivo. Expression of alpha v beta 3 on cultured melanoma cells enabled their binding to MMP-2 in a proteolytically active form, facilitating cell-mediated collagen degradation. In vitro, these proteins formed an SDS-stable complex that depended on the noncatalytic C-terminus of MMP-2, since a truncation mutant lost the ability to bind alpha v beta 3. These findings define a single cell-surface receptor that regulates both matrix degradation and motility, thereby facilitating directed cellular invasion.