Neuropilin-1 is required for endothelial cell adhesion to soluble vascular endothelial growth factor receptor 1.

Neuropilin-1 (NRP-1) is a semaphorin receptor involved in neuron guidance, and a co-receptor for selected isoforms of the vascular endothelial growth factor (VEGF) family. NRP-1 binding to several VEGF-A isoforms promotes growth factor interaction with VEGF receptor (VEGFR)-2, increasing receptor phosphorylation. Additionally, NRP-1 directly interacts with VEGFR-1, but this interaction competes with NRP-1 binding to VEGF-A165 and does not enhance VEGFR-1 activation. In this work, we investigated in detail the role of NRP-1 interaction with the soluble isoform of VEGFR-1 (sVEGFR-1) in angiogenesis. sVEGFR-1 acts both as a decoy receptor for VEGFs and as an extracellular matrix protein directly binding to α5ß1 integrin on endothelial cells. By combining cell adhesion assays and surface plasmon resonance experiments on purified proteins, we found that sVEGFR-1/NRP-1 interaction is required both for α5ß1 integrin binding to sVEGFR-1 and for endothelial cell adhesion to a sVEGFR-1-containing matrix. We also found that a previously reported anti-angiogenic peptide (Flt2-11 ), which maps in the second VEGFR-1 Ig-like domain, specifically binds NRP-1 and inhibits NRP-1/sVEGFR-1 interaction, a process that likely contributes to its anti-angiogenic activity. In view of potential translational applications, we developed a five-residue-long peptide, derived from Flt2-11 , which has the same ability as the parent Flt2-11 peptide to inhibit cell adhesion to, and migration towards, sVEGFR-1. Therefore, the Flt2-5 peptide represents a potential anti-angiogenic compound per se, as well as an attractive lead for the development of novel angiogenesis inhibitors acting with a different mechanism with respect to currently used therapeutics, which interfere with VEGF-A165 binding.

Monozygotic twins discordant for recessive dystrophic epidermolysis bullosa phenotype highlight the role of TGF-ß signalling in modifying disease severity.

Recessive dystrophic epidermolysis bullosa (RDEB) is a genodermatosis characterized by fragile skin forming blisters that heal invariably with scars. It is due to mutations in the COL7A1 gene encoding type VII collagen, the major component of anchoring fibrils connecting the cutaneous basement membrane to the dermis. Identical COL7A1 mutations often result in inter- and intra-familial disease variability, suggesting that additional modifiers contribute to RDEB course. Here, we studied a monozygotic twin pair with RDEB presenting markedly different phenotypic manifestations, while expressing similar amounts of collagen VII. Genome-wide expression analysis in twins' fibroblasts showed differential expression of genes associated with TGF-ß pathway inhibition. In particular, decorin, a skin matrix component with anti-fibrotic properties, was found to be more expressed in the less affected twin. Accordingly, fibroblasts from the more affected sibling manifested a profibrotic and contractile phenotype characterized by enhanced α-smooth muscle actin and plasminogen activator inhibitor 1 expression, collagen I release and collagen lattice contraction. These cells also produced increased amounts of proinflammatory cytokines interleukin 6 and monocyte chemoattractant protein-1. Both TGF-ß canonical (Smads) and non-canonical (MAPKs) pathways were basally more activated in the fibroblasts of the more affected twin. The profibrotic behaviour of these fibroblasts was suppressed by decorin delivery to cells. Our data show that the amount of type VII collagen is not the only determinant of RDEB clinical severity, and indicate an involvement of TGF-ß pathways in modulating disease variability. Moreover, our findings identify decorin as a possible anti-fibrotic/inflammatory agent for RDEB therapeutic intervention.

Endothelial cell adhesion to soluble vascular endothelial growth factor receptor-1 triggers a cell dynamic and angiogenic phenotype.

The aim of this study was to identify the molecular signals produced in human endothelial cells (ECs) by the interaction of α5ß1 integrin with soluble vascular endothelial growth factor receptor-1 (sVEGFR-1) present in the extracellular matrix. We generated a gene expression profile of ECs adhering to sVEGFR-1 or to fibronectin, the classic extracellular matrix ligand for α5ß1 integrin or in a nonadhering condition. Several biological pathways were differently modulated, 3 protein kinase C substrates [adducin, myristoylated alanine-rich protein kinase C substrate (MARCKS), and radixin] were differently expressed and phosphorylated when cells adhering to sVEGFR-1 were compared with those adhering to fibronectin. Rac1 activation and Gα13 protein involvement through the interaction with radixin were also detected after attachment to sVEGFR-1, and these responses depended on active VEGFR-2 signaling. On sVEGFR-1, ECs exhibited a motile phenotype that was consistent with the abundant presence of MARCKS, a stabilizer of dynamic adhesions. Moreover, ECs silenced for radixin expression no longer responded to the proangiogenic VEGFR-1-derived peptide 12. We propose that the presence of sVEGFR-1 in the EC microenvironment directs α5ß1 integrin signaling to generate a dynamic, motile phenotype. Our findings also provide new insights into the mechanism of action of proangiogenic peptide 12, relevant to a therapeutic perspective.

PNA as a potential modulator of COL7A1 gene expression in dominant dystrophic epidermolysis bullosa: a physico-chemical study.

Dominant diseases are single gene disorders occurring in the heterozygous state. The mutated allele exerts a dominant effect because it produces an abnormal polypeptide that interferes with the function of the normal allele product. Peptide Nucleic Acids (PNAs) offer a route for a potential therapy for dominant diseases by selectively silencing the allele carrying the dominant mutation. Here, we have synthesized and studied the properties of a 15-mer PNA fully complementary to the site of the c.5272-38T>A sequence variation, which identifies a recurrent mutant COL7A1 allele causing dominant dystrophic epidermolysis bullosa (DDEB), a mendelian disease characterized by skin blistering. The PNA was conjugated with four lysine residues at the C-terminus and a fluorescent probe at the N-terminus. Physico-chemical results proved the formation of a stable, selective PNA/mutant-DNA heteroduplex in vitro. Intriguingly, when transfected into normal human fibroblasts, the PNA correctly localized in the cell nucleus. Our results open new therapeutic possibilities for patients with DDEB.

Photoreceptor avascular privilege is shielded by soluble VEGF receptor-1.

Optimal phototransduction requires separation of the avascular photoreceptor layer from the adjacent vascularized inner retina and choroid. Breakdown of peri-photoreceptor vascular demarcation leads to retinal angiomatous proliferation or choroidal neovascularization, two variants of vascular invasion of the photoreceptor layer in age-related macular degeneration (AMD), the leading cause of irreversible blindness in industrialized nations. Here we show that sFLT-1, an endogenous inhibitor of vascular endothelial growth factor A (VEGF-A), is synthesized by photoreceptors and retinal pigment epithelium (RPE), and is decreased in human AMD. Suppression of sFLT-1 by antibodies, adeno-associated virus-mediated RNA interference, or Cre/lox-mediated gene ablation either in the photoreceptor layer or RPE frees VEGF-A and abolishes photoreceptor avascularity. These findings help explain the vascular zoning of the retina, which is critical for vision, and advance two transgenic murine models of AMD with spontaneous vascular invasion early in life. DOI:http://dx.doi.org/10.7554/eLife.00324.001.

Skin equivalents: a tool for the discovery and validation of pharmacodynamic biomarkers.

In the development of targeted oncology drugs, it is important to assess drug effectiveness in individual patients. We evaluated the possibility of reproducing in an ex-vivo system the biological effects observed in vitro and in vivo by the combined administration of two chemotherapeutic drugs, gemcitabine and a small inhibitor of Wee1. We found that modulation of both CDC2 phosphorylation and of a previously-identified gene signature was detectable in human skin equivalents obtained with primary keratinocytes from three individuals. Therefore, we suggest that human skin equivalents could represent a promising tool for the identification and validation of novel pharmacodynamic biomarkers.

Sirtinol treatment reduces inflammation in human dermal microvascular endothelial cells.

Histone deacetylases (HDAC) are key enzymes in the epigenetic control of gene expression. Recently, inhibitors of class I and class II HDAC have been successfully employed for the treatment of different inflammatory diseases such as rheumatoid arthritis, colitis, airway inflammation and asthma. So far, little is known so far about a similar therapeutic effect of inhibitors specifically directed against sirtuins, the class III HDAC. In this study, we investigated the expression and localization of endogenous sirtuins in primary human dermal microvascular endothelial cells (HDMEC), a cell type playing a key role in the development and maintenance of skin inflammation. We then examined the biological activity of sirtinol, a specific sirtuin inhibitor, in HDMEC response to pro-inflammatory cytokines. We found that, even though sirtinol treatment alone affected only long-term cell proliferation, it diminishes HDMEC inflammatory responses to tumor necrosis factor (TNF)α and interleukin (IL)-1ß. In fact, sirtinol significantly reduced membrane expression of adhesion molecules in TNFã- or IL-1ß-stimulated cells, as well as the amount of CXCL10 and CCL2 released by HDMEC following TNFα treatment. Notably, sirtinol drastically decreased monocyte adhesion on activated HDMEC. Using selective inhibitors for Sirt1 and Sirt2, we showed a predominant involvement of Sirt1 inhibition in the modulation of adhesion molecule expression and monocyte adhesion on activated HDMEC. Finally, we demonstrated the in vivo expression of Sirt1 in the dermal vessels of normal and psoriatic skin. Altogether, these findings indicated that sirtuins may represent a promising therapeutic target for the treatment of inflammatory skin diseases characterized by a prominent microvessel involvement.

Inhibition of endothelial cell migration and angiogenesis by a vascular endothelial growth factor receptor-1 derived peptide.

Vascular endothelial growth factor receptor-1 (VEGFR-1) exists in two isoforms: a membrane-bound isoform (mVEGFR-1) and a soluble one (sVEGFR-1). mVEGFR-1 is involved in endothelial cell migration and survival supported by VEGF-A and placenta growth factor (PlGF), whereas the biologic function of sVEGFR-1 has not been fully elucidated. We previously reported that sVEGFR-1 induces endothelial cell motility and promotes endothelial cell adhesion. In this study, we tested a set of VEGFR-1-derived peptides for their ability to interfere with endothelial cell migration. Peptide B3 was found to specifically inhibit cell migration induced by sVEGFR-1 and by mVEGFR-1-specific ligands. Moreover, peptide B3 markedly hampered angiogenesis in vitro and in vivo and was found to interfere with VEGFR-1 homodimerisation. Altogether, these data demonstrate that peptide B3 might be a useful tool for the specific inhibition of VEGFR-1 function and might represent a basis for the development of new anti-angiogenic compounds.

A proangiogenic peptide derived from vascular endothelial growth factor receptor-1 acts through alpha5beta1 integrin.

Vascular endothelial growth factor receptor-1 (VEGFR-1) is a tyrosine kinase receptor for growth factors of the VEGF family. Endothelial cells express a membrane-bound and a soluble variant of this protein, the latter being mainly considered as a negative regulator of VEGF-A signaling. We previously reported that the soluble form is deposited in the extracellular matrix produced by endothelial cells in culture and is able to promote cell adhesion and migration through binding to alpha5beta1 integrin. In this study, we demonstrate that the Ig-like domain II of VEGFR-1, which contains the binding determinants for the growth factors, is involved in the interaction with alpha5beta1 integrin. To identify domain regions involved in integrin binding, we designed 12 peptides putatively mimicking the domain II surface and tested their ability to inhibit alpha5beta1-mediated endothelial cell adhesion to soluble VEGFR-1 and directly support cell adhesion. One peptide endowed with both these properties was identified and shown to inhibit endothelial cell migration toward soluble VEGFR-1 as well. This peptide directly binds alpha5beta1 integrin, but not VEGF-A, inducing endothelial cell tubule formation in vitro and neoangiogenesis in vivo. Alanine scanning mutagenesis of the peptide defined which residues were responsible for its biologic activity and integrin binding.

Corneal avascularity is due to soluble VEGF receptor-1.

Corneal avascularity-the absence of blood vessels in the cornea-is required for optical clarity and optimal vision, and has led to the cornea being widely used for validating pro- and anti-angiogenic therapeutic strategies for many disorders. But the molecular underpinnings of the avascular phenotype have until now remained obscure and are all the more remarkable given the presence in the cornea of vascular endothelial growth factor (VEGF)-A, a potent stimulator of angiogenesis, and the proximity of the cornea to vascularized tissues. Here we show that the cornea expresses soluble VEGF receptor-1 (sVEGFR-1; also known as sflt-1) and that suppression of this endogenous VEGF-A trap by neutralizing antibodies, RNA interference or Cre-lox-mediated gene disruption abolishes corneal avascularity in mice. The spontaneously vascularized corneas of corn1 and Pax6+/- mice and Pax6+/- patients with aniridia are deficient in sflt-1, and recombinant sflt-1 administration restores corneal avascularity in corn1 and Pax6+/- mice. Manatees, the only known creatures uniformly to have vascularized corneas, do not express sflt-1, whereas the avascular corneas of dugongs, also members of the order Sirenia, elephants, the closest extant terrestrial phylogenetic relatives of manatees, and other marine mammals (dolphins and whales) contain sflt-1, indicating that it has a crucial, evolutionarily conserved role. The recognition that sflt-1 is essential for preserving the avascular ambit of the cornea can rationally guide its use as a platform for angiogenic modulators, supports its use in treating neovascular diseases, and might provide insight into the immunological privilege of the cornea.

Increased melanoma growth and metastasis spreading in mice overexpressing placenta growth factor.

Placenta growth factor (PlGF), a member of the vascular endothelial growth factor family, plays an important role in adult pathological angiogenesis. To further investigate PlGF functions in tumor growth and metastasis formation, we used transgenic mice overexpressing PlGF in the skin under the control of the keratin 14 promoter. These animals showed a hypervascularized phenotype of the skin and increased levels of circulating PlGF with respect to their wild-type littermates. Transgenic mice and controls were inoculated intradermally with B16-BL6 melanoma cells. The tumor growth rate was fivefold increased in transgenic animals compared to wild-type mice, in the presence of a similar percentage of tumor necrotic tissue. Tumor vessel area was increased in transgenic mice as compared to controls. Augmented mobilization of endothelial and hematopoietic stem cells from the bone marrow was observed in transgenic animals, possibly contributing to tumor vascularization. The number and size of pulmonary metastases were significantly higher in transgenic mice compared to wild-type littermates. Finally, PlGF promoted tumor cell invasion of the extracellular matrix and increased the activity of selected matrix metalloproteinases. These findings indicate that PlGF, in addition to enhancing tumor angiogenesis and favoring tumor growth, may directly influence melanoma dissemination.

Vascular endothelial growth factor-C expression correlates with lymph node localization of human melanoma metastases.

BACKGROUND: Melanoma metastasizes by different mechanisms comprising direct invasion of the surrounding tissue and spreading via the lymphatic or vascular system. Despite their clinical relevance, the molecular mechanisms that guide the route of spreading and localization of the metastases in different tissues are not well known. Recent studies in different tumor types have shown that vascular endothelial growth factor-C (VEGF-C), which displays a high specificity for lymphatic endothelium, is involved in tumor-induced lymphangiogenesis and lymphatic metastatic spread. The authors studied the expression of VEGF-C in cultured human melanoma cells derived from cutaneous and lymph node metastases as well as in metastatic melanoma tissue specimens to assess a possible involvement of this growth factor in lymph node localization of melanoma metastases. METHODS: VEGF-C expression was evaluated in vitro on human melanoma cell lines established from cutaneous and lymph node metastasis specimens by reverse transcriptase-polymerase chain reaction, Northern blot analysis, and immunofluorescence analysis. Immunohistochemical analysis of 42 tissue specimens of melanoma metastases and 10 tissue specimens of primary skin melanomas was also performed. RESULTS: Preferential expression of VEGF-C was detected in lymph node-derived tumor cell lines at both the mRNA and protein levels. The association between VEGF-C production and lymph node localization of metastases was confirmed by the in vivo analysis. In addition, analysis of 10 patients, from whom specimens of both the primary skin melanoma and melanoma metastases were available, indicated a correlation between VEGF-C expression in the primary tumor and lymph node localization of metastases. CONCLUSIONS: The findings of the current study demonstrate that VEGF-C expression is correlated with localization of melanoma metastases in the lymph nodes and suggest that VEGF-C expression in primary skin melanoma may be predictive of lymph node metastatic dissemination.

Vascular endothelial growth factor receptor-1 is deposited in the extracellular matrix by endothelial cells and is a ligand for the alpha 5 beta 1 integrin.

Vascular endothelial growth factor receptor-1 (VEGFR-1) is a tyrosine kinase receptor for several growth factors of the VEGF family. Endothelial cells express a membrane-spanning form of VEGFR-1 and secrete a soluble variant of the receptor comprising only the extracellular region. The role of this variant has not yet been completely defined. In this study, we report that the secreted VEGFR-1 is present within the extracellular matrix deposited by endothelial cells in culture, suggesting a possible involvement in endothelial cell adhesion and migration. In adhesion assays, VEGFR-1 extracellular region specifically promoted endothelial cell attachment. VEGFR-1-mediated cell adhesion was divalent cation-dependent, and inhibited by antibodies directed against the alpha 5 beta 1 integrin. Moreover, VEGFR-1 promoted endothelial cell migration, and this effect was inhibited by anti-alpha 5 beta 1 antibodies. Direct binding of VEGFR-1 to the alpha 5 beta 1 integrin was also detected. Finally, binding to VEGFR-1 initiated endothelial cell spreading. Altogether these results indicate that the soluble VEGFR-1 secreted by endothelial cells becomes a matrix-associated protein that is able to interact with the alpha 5 beta 1 integrin, suggesting a new role of VEGFR-1 in angiogenesis, in addition to growth factor binding.

Evidence for differential S100 gene over-expression in psoriatic patients from genetically heterogeneous pedigrees.

Psoriasis is an inflammatory skin disorder characterised by keratinocyte hyper-proliferation and altered differentiation. To date, linkage analyses have identified at least seven distinct disease susceptibility regions (PSORS1-7). The PSORS4 locus was mapped by our group to chromosome 1q21, within the Epidermal Differentiation Complex. This cluster contains 13 genes encoding S100 calcium-binding proteins, some of which ( S100A7, S100A8 and S100A9) are known to be up-regulated in individual patient keratinocytes. In this study, we analysed S100 gene expression in psoriatic individuals from families characterised by linkage studies. We first selected individuals from two large pedigrees, one of which was linked to the 1q21 locus, whereas the other was unlinked to that region. We studied the expression of 12 S100 genes, by semi-quantitative RT-PCR and Northern blot. These analyses demonstrated up-regulation of S100A8, S100A9 and, to a lesser extent, S100A7 and S100A12, only in the 1q21 linked family. We subsequently analysed S100A7, S100A8, S100 A9 and S100 A12 in three additional samples and were able to confirm S100A8/ S100A9-specific over-expression in 1q-linked pedigrees. Thus, our data provide preliminary evidence for a locus-specific molecular mechanism underlying psoriasis susceptibility.