Identification and Characterization of Endothelial Glycoprotein Ib Using Viper Venom Proteins Modulating Cell Adhesion

Collagen scaffolds functionalized with triple-helical peptides support 3D HUVEC culture

Porous biomaterials which provide a structural and biological support for cells have immense potential in tissue engineering and cell-based therapies for tissue repair. Collagen biomaterials that can host endothelial cells represent promising tools for the vascularization of engineered tissues. Three-dimensional collagen scaffolds possessing controlled architecture and mechanical stiffness are obtained through freeze–drying of collagen suspensions, followed by chemical cross-linking which maintains their stability. However, cross-linking scaffolds renders their biological activity suboptimal for many cell types, including human umbilical vein endothelial cells (HUVECs), by inhibiting cell–collagen interactions. Here, we have improved crucial HUVEC interactions with such cross-linked collagen biomaterials by covalently coupling combinations of triple-helical peptides (THPs). These are ligands for collagen-binding cell-surface receptors (integrins or discoidin domain receptors) or secreted proteins (SPARC and von Willebrand factor). THPs enhanced HUVEC adhesion, spreading and proliferation on 2D collagen films. THPs grafted to 3D-cross-linked collagen scaffolds promoted cell survival over seven days. This study demonstrates that THP-functionalized collagen scaffolds are promising candidates for hosting endothelial cells with potential for the production of vascularized engineered tissues in regenerative medicine applications.

Selective Tropism of Dengue Virus for Human Glycoprotein Ib

Since the hemorrhage in severe dengue seems to be primarily related to the defect of the platelet, the possibility that dengue virus (DENV) is selectively tropic for one of its surface receptors was investigated. Flow cytometric data of DENV-infected megakaryocytic cell line superficially expressing human glycoprotein Ib (CD42b) and glycoprotein IIb/IIIa (CD41 and CD41a) were analyzed by our custom-written software in MATLAB. In two-dimensional analyses, intracellular DENV was detected in CD42b+, CD41+ and CD41a+ cells. In three-dimensional analyses, the DENV was exclusively detected in CD42b+ cells but not in CD42b- cells regardless of the other expressions. In single-cell virus-protein analyses, the amount of DENV was directly correlated with those of CD42b at the Pearson correlation coefficient of 0.9. Moreover, RT- PCR and apoptosis assays showed that DENV was able to replicate itself and release its new progeny from the infected CD42b+ cells and eventually killed those cells. These results provide evidence for the involvement of CD42b in DENV infection.

Acurhagin-C, an ECD disintegrin, inhibits integrin alphavbeta3-mediated human endothelial cell functions by inducing apoptosis via caspase-3 activation

BACKGROUND AND PURPOSE

Acurhagin, a member of versatile metalloproteinase disintegrins from Agkistrodon acutus venom, has been identified as a platelet aggregation inhibitor, previously. Here, acurhagin-C, the C-terminal Glu-Cys-Asp (ECD)-containing fragment of acurhagin, was evaluated for its biological activities and potential applications in anti-angiogenic therapy.

EXPERIMENTAL APPROACH

Human umbilical vein endothelial cells (HUVECs) were treated with acurhagin-C to assay effects on viability, apoptosis, adhesion, migration, invasion, proliferation and angiogenesis. The recognition site and signalling involved for the interactions of acurhagin-C with HUVEC were determined using flow cytometric, electrophoresis and immunoblotting analyses.

KEY RESULTS

Acurhagin-C decreased viability and induced apoptosis in HUVEC. It also dose-dependently inhibited HUVEC adhesion to immobilized extracellular matrices fibronectin, collagen I and vitronectin with respective IC(50) values of approximately 0.6, 0.3 and 0.1 microM. Acurhagin-C prevented migration and invasion of HUVEC through vitronectin- and Matrigel-coated barriers respectively. Furthermore, acurhagin-C attenuated fibroblast growth factor-2-primed angiogenesis both in vitro and in vivo, and specifically blocked the binding of anti-alphavbeta3 monoclonal antibody 23C6 to HUVEC in an ECD-dependent manner. However, purified alphavbeta3 also dose-dependently bound to immobilized acurhagin and acurhagin-C with a saturable pattern. Interference with integrin alphavbeta3-mediated functions and promotion of caspase-3 activation by acurhagin-C affected morphology of HUVEC and induced apoptosis.

CONCLUSIONS AND IMPLICATIONS

Acurhagin-C elicited endothelial anoikis via disruption of alphavbeta3/focal adhesion kinase/phosphatidylinositol 3-kinase/Akt survival cascade and subsequent initiation of the procaspase-3 apoptotic signalling pathway.

Antithrombotic effects of naturally derived products on coagulation and platelet function

To date, there have been few systematic studies of the antiplatelet and/or anticoagulant effects of natural products. According to the Natural Medicines Comprehensive Database, approximately 180 dietary supplements have the potential to interact with warfarin, and more than 120 may interact with aspirin, clopidogrel, and dipyridamole. These include anise and dong quai (anticoagulant effects); omega 3-fatty acids in fish oil, ajoene in garlic, ginger, ginko, and vitamin E (antiplatelet properties); fucus (heparin-like activity); danshen (antithrombin III-like activity and anticoagulant bioavailability); and St. John's Wort and American Ginseng (interference with drug metabolism). Other supplements, such as high doses of vitamin E (vitamin K antagonist activity), alfalfa (high-vitamin K content), and coenzyme Q10 (vitamin K-like activity), may affect blood clotting, which is dependent on vitamin K. Studies are needed to understand the role of various dietary supplements in thrombosis and their interactions with standard anticoagulants and antiplatelet drugs.

Up-regulation of integrin beta3 expression in porcine vascular endothelial cells cultured in vitro by classical swine fever virus

Classical swine fever (CSF) caused by virulent strains of classical swine fever virus (CSFV) is a haemorrhagic disease of pigs, characterized by disseminated intravascular coagulation, thrombocytopenia and immunosuppression. The cell adhesion molecule, integrin beta3, plays a central role in maintaining and regulating vascular permeability. In view of the haemorrhagic pathology of the disease, the effect of CSFV infection on integrin beta3 expression was investigated using the swine umbilical vein endothelial cell (SUVEC) line, in conjunction with quantitative PCR and Western blotting techniques. Following infection, the expression levels of integrin beta3 were significantly up-regulated along with corresponding transcription levels. The infected endothelial cells adhered onto immobilized extracellular matrix (ECM) with more extensive spreading than that of the control, and such interaction was strongly inhibited by an anti-integrin beta3 monoclonal antibody (mAb). This study revealed the up-regulation of integrin beta3 in vascular endothelial cells by CSFV infection, and cell adhesion molecules of this kind possibly play an important role in the changes of haemostatic balance in haemorrhagic pathology of CSF.

The endothelial glycocalyx: composition, functions, and visualization

This review aims at presenting state-of-the-art knowledge on the composition and functions of the endothelial glycocalyx. The endothelial glycocalyx is a network of membrane-bound proteoglycans and glycoproteins, covering the endothelium luminally. Both endothelium- and plasma-derived soluble molecules integrate into this mesh. Over the past decade, insight has been gained into the role of the glycocalyx in vascular physiology and pathology, including mechanotransduction, hemostasis, signaling, and blood cell–vessel wall interactions. The contribution of the glycocalyx to diabetes, ischemia/reperfusion, and atherosclerosis is also reviewed. Experimental data from the micro- and macrocirculation alludes at a vasculoprotective role for the glycocalyx. Assessing this possible role of the endothelial glycocalyx requires reliable visualization of this delicate layer, which is a great challenge. An overview is given of the various ways in which the endothelial glycocalyx has been visualized up to now, including first data from two-photon microscopic imaging.

Platelets adhere to and translocate on von Willebrand factor presented by endothelium in stimulated veins

With the use of intravital microscopy, a new type of platelet–endothelial interaction in mouse mesenteric venules at low shear (80-100 seconds−1) is described. Stimulation of these vessels with calcium ionophore A23187, a known secretagogue of Weibel-Palade bodies, induced immediate platelet adhesion (within 15 seconds) and translocation without the formation of aggregates. This stop-and-go process reached a maximum in approximately 1 minute, when approximately 25 000 platelets adhered/mm2·s, and then adhesion progressively decreased. This adhesion process was dependent on von Willebrand factor (vWF) and independent of P-selectin. Immunohistologic analysis showed that the venules were not denuded withA23187 treatment, suggesting that platelets adhered to vWF secreted on the luminal face of the endothelial cells. Histamine treatment induced a similar adhesion phenomenon. Platelet adhesion was not abolished in β3-deficient mice or when the platelets were treated with inhibitory antibodies to PECAM-1 or PSGL-1, indicating that these molecules are not required for platelet–endothelium interaction at low shear. The adhesion was mediated by platelet glycoprotein Ibα (GPIbα) because the adhesion of murine platelets expressing exclusively the human GPIbα could be prevented by a pretreatment with mocarhagin, a snake venom protease that cleaves human GPIbα. The results indicate that vWF released from Weibel-Palade bodies can dramatically increase the concentration of platelets along the vessel wall through an interaction with GPIbα. It is proposed that this process may rapidly recruit platelets to sites of injury or inflammation in veins.

Platelets adhere to and translocate on von Willebrand factor presented by endothelium in stimulated veins

With the use of intravital microscopy, a new type of platelet–endothelial interaction in mouse mesenteric venules at low shear (80-100 seconds−1) is described. Stimulation of these vessels with calcium ionophore A23187, a known secretagogue of Weibel-Palade bodies, induced immediate platelet adhesion (within 15 seconds) and translocation without the formation of aggregates. This stop-and-go process reached a maximum in approximately 1 minute, when approximately 25 000 platelets adhered/mm2·s, and then adhesion progressively decreased. This adhesion process was dependent on von Willebrand factor (vWF) and independent of P-selectin. Immunohistologic analysis showed that the venules were not denuded withA23187 treatment, suggesting that platelets adhered to vWF secreted on the luminal face of the endothelial cells. Histamine treatment induced a similar adhesion phenomenon. Platelet adhesion was not abolished in β3-deficient mice or when the platelets were treated with inhibitory antibodies to PECAM-1 or PSGL-1, indicating that these molecules are not required for platelet–endothelium interaction at low shear. The adhesion was mediated by platelet glycoprotein Ibα (GPIbα) because the adhesion of murine platelets expressing exclusively the human GPIbα could be prevented by a pretreatment with mocarhagin, a snake venom protease that cleaves human GPIbα. The results indicate that vWF released from Weibel-Palade bodies can dramatically increase the concentration of platelets along the vessel wall through an interaction with GPIbα. It is proposed that this process may rapidly recruit platelets to sites of injury or inflammation in veins.

Inhibitory effects of MLDG-containing heterodimeric disintegrins reveal distinct structural requirements for interaction of the integrin alpha 9beta 1 with VCAM-1, tenascin-C, and osteopontin

The integrin alpha9beta1 is expressed on epithelial cells, smooth muscle cells, skeletal muscle, and neutrophils and recognizes at least three distinct ligands: vascular cell adhesion molecule 1 (VCAM-1), tenascin-C, and osteopontin. The alpha9 subunit is structurally similar to the integrin alpha4 subunit, and alpha9beta1 and alpha4beta1 both recognize VCAM-1 as a ligand. We therefore examined whether the disintegrin EC3, which we have recently shown specifically inhibits the binding of alpha4 integrins to ligands, would also be a functional inhibitor of alpha9beta1. EC3 and a novel heterodimeric disintegrin that we identified, EC6, both were potent inhibitors of alpha9beta1-mediated adhesion to VCAM-1 and of neutrophil migration across tumor necrosis factor-activated endothelial cells. A peptide containing a novel MLDG motif shared by both of these disintegrins also inhibited alpha9beta1- and alpha4beta1-mediated adhesion to VCAM-1. Surprisingly though, concentrations of EC3 that completely inhibited adhesion of alpha9-transfected cells to VCAM-1 had little or no effect on adhesion to either of the other alpha9beta1 ligands, osteopontin and tenascin-C. Furthermore, peptides AEIDGIEL and SVVYGLR, which we have previously shown inhibit binding of alpha9beta1-expressing cells to tenascin-C and osteopontin, respectively, had no effect on adhesion to VCAM-1. These data suggest that there are structurally distinct requirements for interactions of the alpha9beta1 integrin with VCAM-1 and the extracellular matrix ligands osteopontin and tenascin-C.

Agkistin, a snake venom-derived glycoprotein Ib antagonist, disrupts von Willebrand factor-endothelial cell interaction and inhibits angiogenesis

Glycoprotein (GP) Ib, an adhesion receptor expressed on both platelets and endothelial cells, mediates the binding of von Willebrand factor (vWF). Platelet GPIb plays an important role in platelet adhesion and activation, whereas the interaction of vWF and endothelial GPIb is not fully understood. We report here that agkistin, a snake venom protein, selectively blocks the interaction of vWF with human endothelial GPIb and inhibits angiogenesis in vivo. Agkistin specifically blocked human umbilical vein endothelial cell (HUVEC) adhesion to immobilized vWF in a concentration-dependent manner. Fluorescein isothiocyanate (FITC)-conjugated agkistin bound to HUVECs in a saturable manner. AP1, a monoclonal antibody (mAb) raised against GPIb, specifically inhibited the binding of FITC-conjugated agkistin to HUVECs in a dose-dependent manner, but other anti-integrin mAbs raised against alpha(v)beta(3), alpha(2)beta(1), and alpha(5)beta(1) did not affect this binding reaction. However, neither agkistin (2 microgram/ml) nor AP1 (40 microgram/ml) apparently reduced HUVEC viability. Both agkistin and AP1 exhibited a profound anti-angiogenic effect in vivo when assayed by using the 10-day-old embryo chick chorioallantoic membrane model. These results suggest endothelial GPIb plays a role in spontaneous angiogenesis in vivo, and the anti-angiogenic effect of agkistin may be because of disruption of the interaction of endogenous vWF with endothelial GPIb.

Glycoprotein Ibalpha can mediate endothelial cell migration on von Willebrand factor-containing substrata

We have previously shown that, in addition to the vitronectin receptor (VNR, alpha(v)beta(3)), the GP Ib complex can participate in endothelial cell (EC) attachment to von Willebrand Factor (vWF) (D. A. Beacham, M. S. Cruz, and R. I. Handin, 1995, Thromb. Haemostas. 73, 309-317; D. A. Beacham, L.-P. Tran, and S. S. Shapiro, 1997, Blood 89, 4071-4077). In this study we have investigated the functional roles of these vWF receptors in the migration of untreated and TNFalpha-treated EC on vWF, a mixture of vWF and type I collagen, and on vitronectin (VN). In agreement with previous studies (D. I. Leavesley, M. A. Schwartz, M. Rosenfeld, and D. A. Cheresh, 1993, J. Cell Biol. 121, 163-170), the migration of untreated and TNFalpha-treated EC on VN was dependent entirely on the VNR. Migration of untreated EC on vWF was inhibited 10-15% by recombinant vWF-A1, the GP Ibalpha-binding domain on vWF which abrogates the platelet GP Ibalpha-vWF interaction. In contrast, migration of TNFalpha-treated EC on vWF was inhibited 50-60% by vWF-A1 or the anti-GP Ibalpha mAb AS-7 but only 20% by the anti-VNR mAb LM609. On a mixed vWF-collagen substratum, vWF-A1 inhibited untreated EC migration by 45%, and TNFalpha-treated EC migration by 75%. The possible role of EC proliferation was eliminated, since hydroxyurea completely inhibited EC proliferation without reducing migration significantly. The anti-GP Ibalpha mAb Ib1 inhibited EC migration by 50%, but reduced proliferation by only 15%. Taken together, our data demonstrate that EC migration on vWF-containing substrata involves the GP Ib complex as well as the VNR and raises the possibility that the VNR and GP Ib act cooperatively in supporting EC migration.