Mirella Belleri

Cutting Edge: Extracellular High Mobility Group Box-1 Protein Is a Proangiogenic Cytokine

The chromosomal high mobility group box-1 (HMGB1) protein acts as a proinflammatory cytokine when released in the extracellular environment by necrotic and inflammatory cells. In the present study, we show that HMGB1 exerts proangiogenic effects by inducing MAPK ERK1/2 activation, cell proliferation, and chemotaxis in endothelial cells of different origin. Accordingly, HMGB1 stimulates membrane ruffling and repair of a mechanically wounded endothelial cell monolayer and causes endothelial cell sprouting in a three-dimensional fibrin gel. In keeping with its in vitro properties, HMGB1 stimulates neovascularization when applied in vivo on the top of the chicken embryo chorioallantoic membrane whose blood vessels express the HMGB1 receptor for advanced glycation end products (RAGE). Accordingly, RAGE blockade by neutralizing Abs inhibits HMGB1-induced neovascularization in vivo and endothelial cell proliferation and membrane ruffling in vitro. Taken together, the data identify HMGB1/RAGE interaction as a potent proangiogenic stimulus.

Generation of Biologically Active Angiostatin Kringle 1–3 by Activated Human Neutrophils

The contribution of polymorphonuclear neutrophils (PMN) to host defense and natural immunity extends well beyond their traditional role as professional phagocytes. In this study, we demonstrate that upon stimulation with proinflammatory stimuli, human PMN release enzymatic activities that, in vitro, generate bioactive angiostatin fragments from purified plasminogen. We also provide evidence that these angiostatin-like fragments, comprising kringle domain 1 to kringle domain 3 (kringle 1–3) of plasminogen, are generated as a byproduct of the selective proteolytic activity of neutrophil-secreted elastase. Remarkably, affinity-purified angiostatin kringle 1–3 fragments generated by neutrophils inhibited basic fibroblast growth factor plus vascular endothelial growth factor-induced endothelial cell proliferation in vitro, and both vascular endothelial growth factor-induced angiogenesis in the matrigel plug assay and fibroblast growth factor-induced angiogenesis in the chick embryo chorioallantoic membrane assay, in vivo. These results represent the first demonstration that biologically active angiostatin-like fragments can be generated by inflammatory human neutrophils. Because angiostatin is a potent inhibitor of angiogenesis, tumor growth, and metastasis, the data suggest that activated PMN not only act as potent effectors of inflammation, but might also play a critical role in the inhibition of angiogenesis in inflammatory diseases and tumors, by generation of a potent anti-angiogenic molecule.

Basic fibroblast growth factor overexpression in endothelial cells: an autocrine mechanism for angiogenesis and angioproliferative diseases

Basic fibroblast growth factor (bFGF) is expressed in vascular endothelium during tumor neovascularization and angioproliferative diseases. The ultimate significance of this observation is poorly understood. We have investigated the biological consequences of endothelial cell activation by endogenous bFGF in a mouse aortic endothelial cell line stably transfected with a retroviral expression vector harboring a human bFGF cDNA. Selected clones expressing M(r) 24,000, M(r) 22,000, and/or M(r) 18,000 bFGF isoforms were characterized by a transformed morphology and an increased saturation density. bFGF transfectants showed invasive behavior and sprouting activity in three-dimensional fibrin gels and formed a complex network of branching cord-like structures connecting foci of infiltrating cells when seeded on laminin-rich basement membrane matrix (Matrigel). The invasive and morphogenetic behavior was prevented by anti-bFGF antibody, revealing the autocrine modality of the process. The biological consequences of this autocrine activation were investigated in vivo. bFGF-transfected cells gave rise to highly vascularized lesions resembling Kaposis sarcoma when injected in nude mice and induced angiogenesis in avascular rabbit cornea. When injected into the allantoic sac of the chick embryo, they caused an increase in vascular density and formation of hemangiomas in the chorioallantoic membrane. In conclusion, bFGF-overexpressing endothelial cells acquired an angiogenic phenotype and recruit quiescent endothelium originating angioproliferative lesions in vivo. These findings demonstrate that bFGF overexpression exerts an autocrine role for endothelial cells and support the notion that tumor neovascularization and angioproliferative diseases can be triggered by stimuli that induce vascular endothelium to produce its own autocrine factor(s).

The natural compound n-butylidenephthalide derived from the volatile oil of Radix Angelica sinensis inhibits angiogenesis in vitro and in vivo.

Radix Angelica sinensis is a Chinese medicinal herb that has been used extensively in the East for the treatment of cardiovascular diseases (CVDs). Angiogenesis plays an important role in the pathogenesis of CVDs. We hypothesized that Radix A. sinensis may contain angiogenesis modulators. In the current study, we investigated the effects of a volatile oil of Radix A. sinensis (VOAS) and n-butylidenephthalide (BP), one of the bioactive components in VOAS, on angiogenesis in vitro and in vivo. The results suggested that VOAS exerted anti-angiogenic effects by inhibiting human umbilical vein endothelial cell proliferation, migration and capillary-like tube formation on Matrigel. BP was also shown to be anti-angiogenic and its mechanisms were through inhibition of cell cycle progression and induction of apoptosis. Western blotting analysis indicated that the anti-angiogenic actions of BP were associated with the activation of p38 and ERK 1/2 but not SAPK/JNK and Akt signaling pathways. Further investigations showed that BP inhibited endothelial sprouting in an ex vivo mouse aortic ring model and was a potent inhibitor of the development of zebrafish subintestinal vessels in vivo. Our data using the volatile oil contrast with previous findings, which showed an aqueous extract of Radix A. sinensis was pro-angiogenic. This highlights the importance of identifying pro- and anti-angiogenic substances in Radix A. sinensis, not only for the development of novel angiogenesis modulators for the treatment of CVDs, but also to ensure the proper use of Radix A. sinensis as a nutraceutical.

Paracrine and autocrine effects of fibroblast growth factor-4 in endothelial cells.

Recombinant Fibroblast Growth Factor-4 (FGF4) and FGF2 induce extracellular signal-regulated kinase-1/2 activation and DNA synthesis in murine aortic endothelial (MAE) cells. These cells co-express the IIIc/Ig-3 loops and the novel glycosaminoglycan-modified IIIc/Ig-2 loops isoforms of FGF receptor-2 (FGFR2). The affinity of FGF4/FGFR2 interaction is 20–30 times lower than that of FGF2 and is enhanced by heparin. Overexpression of FGF2 or FGF4 cDNA in MAE cells results in a transformed phenotype and increased proliferative capacity, more evident for FGF2 than FGF4 transfectants. Both transfectants induce angiogenesis when applied on the top of the chick embryo chorioallantoic membrane. However, in contrast with FGF2-transfected cells, FGF4 transfectants show a limited capacity to growth under anchorage-independent conditions and lack the ability to invade 3D fibrin gel and to undergo morphogenesis in vitro. Also, they fail to induce hemangiomas when injected into the allantoic sac of the chick embryo. In conclusion, although exogenous FGF2 and FGF4 exert a similar response in MAE cells, significant differences are observed in the biological behavior of FGF4 versus FGF2 transfectants, indicating that the expression of the various members of the FGF family can differently affect the behavior of endothelial cells and, possibly, of other cell types, including tumor cells.

A pro-inflammatory signature mediates FGF2-induced angiogenesis

Fibroblast growth factor‐2 (FGF2) is a potent angiogenic growth factor. Here, gene expression profiling of FGF2‐stimulated microvascular endothelial cells revealed, together with a prominent pro‐angiogenic profile, a pro‐inflammatory signature characterized by the up‐regulation of pro‐inflammatory cytokine/chemokines and their receptors, endothelial cell adhesion molecules and members of the eicosanoid pathway. Real‐time quantitative PCR demonstrated early induction of most of the FGF2‐induced, inflammation‐related genes. Accordingly, chick embryo chorioallantoic membrane (CAM) and murine Matrigel plug angiogenesis assays demonstrated a significant monocyte/macrophage infiltrate in the areas of FGF2‐driven neovascularization. Similar results were obtained when the conditioned medium (CM) of FGF2‐stimulated endothelial cells was delivered onto the CAM, suggesting that FGF2‐upregulated chemoattractants mediate the inflammatory response. Importantly, FGF2‐triggered new blood vessel formation was significantly reduced in phosphatidylinositol 3‐kinase‐γ null mice exhibiting defective leucocyte migration or in clodronate liposome‐treated, macrophage‐depleted mice. Furthermore, the viral pan‐chemokine antagonist M3 inhibited the angiogenic and inflammatory responses induced by the CM of FGF2‐stimulated endothelial cells and impaired FGF2‐driven neovascularization in the CAM assay. These findings point to inflammatory chemokines as early mediators of FGF2‐driven angiogenesis and indicate a non‐redundant role for inflammatory cells in the neovascularization process elicited by the growth factor.

Long Pentraxin 3/Tumor Necrosis Factor-Stimulated Gene-6 Interaction A Biological Rheostat for Fibroblast Growth Factor 2–Mediated Angiogenesis

Objective— Angiogenesis is regulated by the balance between pro- and antiangiogenic factors and by extracellular matrix protein interactions. Fibroblast growth factor 2 (FGF2) is a major proangiogenic inducer inhibited by the interaction with the soluble pattern recognition receptor long pentraxin 3 (PTX3). PTX3 is locally coexpressed with its ligand TSG-6, a secreted glycoprotein that cooperates with PTX3 in extracellular matrix assembly. Here, we characterized the effect of TSG-6 on PTX3/FGF2 interaction and FGF2-mediated angiogenesis.nnMethods and Results— Solid phase binding and surface plasmon resonance assays show that TSG-6 and FGF2 bind the PTX3 N-terminal domain with similar affinity. Accordingly, TSG-6 prevents FGF2/PTX3 interaction and suppresses the inhibition exerted by PTX3 on heparan sulfate proteoglycan/FGF2/FGF receptor complex formation and on FGF2-dependent angiogenesis in vitro and in vivo. Also, endogenous PTX3 exerts an inhibitory effect on vascularization induced by FGF2 in a murine subcutaneous Matrigel plug assay, the inhibition being abolished in Ptx3 -null mice or by TSG-6 treatment in wild-type animals.nnConclusion— TSG-6 reverts the inhibitory effects exerted by PTX3 on FGF2-mediated angiogenesis through competition of FGF2/PTX3 interaction. This may provide a novel mechanism to control angiogenesis in those pathological settings characterized by the coexpression of TSG-6 and PTX3, in which the relative levels of these proteins may fine-tune the angiogenic activity of FGF2.Objective—Angiogenesis is regulated by the balance between pro- and antiangiogenic factors and by extracellular matrix protein interactions. Fibroblast growth factor 2 (FGF2) is a major proangiogenic inducer inhibited by the interaction with the soluble pattern recognition receptor long pentraxin 3 (PTX3). PTX3 is locally coexpressed with its ligand tumor necrosis factor-stimulated gene-6 (TSG-6), a secreted glycoprotein that cooperates with PTX3 in extracellular matrix assembly. Here, we characterized the effect of TSG-6 on PTX3/FGF2 interaction and FGF2-mediated angiogenesis. Methods and Results—Solid phase binding and surface plasmon resonance assays show that TSG-6 and FGF2 bind the PTX3 N-terminal domain with similar affinity. Accordingly, TSG-6 prevents FGF2/PTX3 interaction and suppresses the inhibition exerted by PTX3 on heparan sulfate proteoglycan/FGF2/FGF receptor complex formation and on FGF2-dependent angiogenesis in vitro and in vivo. Also, endogenous PTX3 exerts an inhibitory effect on vascularization induced by FGF2 in a murine subcutaneous Matrigel plug assay, the inhibition being abolished in Ptx3-null mice or by TSG-6 treatment in wild-type animals. Conclusion—TSG-6 reverts the inhibitory effects exerted by PTX3 on FGF2-mediated angiogenesis through competition of FGF2/PTX3 interaction. This may provide a novel mechanism to control angiogenesis in those pathological settings characterized by the coexpression of TSG-6 and PTX3, in which the relative levels of these proteins may fine-tune the angiogenic activity of FGF2.

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

A close relationship exists between angiogenesis and the formation of vascular lesions. The development of the vascular system in the chick embryo chorioallantoic membrane (CAM) may thus represent a model to study the effects of the deregulation of endothelial cell behaviour. Alterations of the developing vascular tree of the CAM were observed after exposure to murine aortic endothelial (MAE) cells overexpressing human fibroblast growth factor‐2 (FGF2) cDNA (pZipFGF2 MAE cells), or to their conditioned medium (CM). pZipFGF2 MAE cells injected into the allantoic sac or applied on to the CAM of day 8–9 chick embryos induce neovascularization and the appearance of haemangioma‐like lesions. This activity was not prevented by anti‐FGF2 antibodies. The CM from pZipFGF2 MAE cells was also active when adsorbed into a gelatin sponge and applied on to the CAM, both in the absence and in the presence of anti‐FGF2 antibodies. No effects on vessel development were exerted by parental MAE cells, FGF2‐transfected NIH 3T3 fibroblasts, or their conditioned media. In vitro, pZipFGF2 MAE cell CM caused parental MAE cells to invade fibrin gels and to undergo morphogenesis on Matrigel. This activity was not mimicked by recombinant FGF2 nor affected by anti‐FGF2 antibodies, and depended on a M r∼45u2009000 heat‐labile heparin‐binding factor. Size exclusion chromatography of pZipFGF2 MAE cell CM demonstrated that the in vitro activity co‐purified with an in vivo angiogenic capacity. Thus, FGF2 overexpression in mouse endothelial cells induces the production of an angiogenic activity distinct from FGF2, which may contribute to the genesis of angioproliferative lesions. Copyright

The COOH-Terminal Peptide of Platelet Factor-4 Variant (CXCL4L1/PF-4var47-70) Strongly Inhibits Angiogenesis and Suppresses B16 Melanoma Growth In vivo

Chemokines influence tumor growth directly or indirectly via both angiogenesis and tumor-leukocyte interactions. Platelet factor-4 (CXCL4/PF-4), which is released from α-granules of activated platelets, is the first described angiostatic chemokine. Recently, it was found that the variant of CXCL4/PF-4 (CXCL4L1/PF-4var) could exert a more pronounced angiostatic and antitumoral effect than CXCL4/PF-4. However, the molecular mechanisms of the angiostatic activities of the PF-4 forms remain partially elusive. Here, we studied the biological properties of the chemically synthesized COOH-terminal peptides of CXCL4/PF-4 (CXCL4/PF-447-70) and CXCL4L1/PF-4var (CXCL4L1/PF-4var47-70). Both PF-4 peptides lacked monocyte and lymphocyte chemotactic activity but equally well inhibited (25 nmol/L) endothelial cell motility and proliferation in the presence of a single stimulus (i.e., exogenous recombinant fibroblast growth factor-2). In contrast, when assayed in more complex angiogenesis test systems characterized by the presence of multiple mediators, including in vitro wound-healing (2.5 nmol/L versus 12.5 nmol/L), Matrigel (60 nmol/L versus 300 nmol/L), and chorioallantoic membrane assays, CXCL4L1/PF-4var47-70 was found to be significantly (5-fold) more angiostatic than CXCL4/PF-447-70. In addition, low (7 μg total) doses of intratumoral CXCL4L1/PF-4var47-70 inhibited B16 melanoma growth in mice more extensively than CXCL4/PF-447-70. This antitumoral activity was predominantly mediated through inhibition of angiogenesis (without affecting blood vessel stability) and induction of apoptosis, as evidenced by immunohistochemical and fluorescent staining of B16 tumor tissue. In conclusion, CXCL4L1/PF-4var47-70 is a potent antitumoral and antiangiogenic peptide. These results may represent the basis for the design of CXCL4L1/PF-4var COOH-terminal–derived peptidomimetic anticancer drugs. Mol Cancer Res; 8(3); 322–34

Antiangiogenic Activity of Semisynthetic Biotechnological Heparins. Low-Molecular-Weight-Sulfated Escherichia coli K5 Polysaccharide Derivatives as Fibroblast Growth Factor Antagonists

Objective— Low-molecular-weight heparin (LMWH) exerts antitumor activity in clinical trials. The K5 polysaccharide from Escherichia coli has the same structure as the heparin precursor. Chemical and enzymatic modifications of K5 polysaccharide lead to the production of biotechnological heparin-like compounds. We investigated the fibroblast growth factor-2 (FGF2) antagonist and antiangiogenic activity of a series of LMW N,O-sulfated K5 derivatives. Methods and Results— Surface plasmon resonance analysis showed that LMW-K5 derivatives bind FGF2, thus inhibiting its interaction with heparin immobilized to a BIAcore sensor chip. Interaction of FGF2 with tyrosine-kinase receptors (FGFRs), heparan sulfate proteoglycans (HSPGs), and αvβ3 integrin is required for biological response in endothelial cells. Similar to LMWH, LMW-K5 derivatives abrogate the formation of HSPG/FGF2/FGFR ternary complexes by preventing FGF2-mediated attachment of FGFR1-overexpressing cells to HSPG-bearing cells and inhibit FGF2-mediated endothelial cell proliferation. However, LMW-K5 derivatives, but not LMWH, also inhibit FGF2/αvβ3 integrin interaction and consequent FGF2-mediated endothelial cell sprouting in vitro and angiogenesis in vivo in the chick embryo chorioallantoic membrane. Conclusions— LMW N,O-sulfated K5 derivatives affect both HSPG/FGF2/FGFR and FGF2/αvβ3 interactions and are endowed with FGF2 antagonist and antiangiogenic activity. These compounds may provide the basis for the design of novel LMW heparin-like angiostatic compounds.