A New Functional Role of the Fibrinogen RGD Motif as the Molecular Switch That Selectively Triggers Integrin αIIbβ3-dependent RhoA Activation during Cell Spreading

Material matters: exploring the interplay between natural biomaterials and host immune system

Biomaterials are widely used for various medical purposes, for instance, implants, tissue engineering, medical devices, and drug delivery systems. Natural biomaterials can be obtained from proteins, carbohydrates, and cell-specific sources. However, when these biomaterials are introduced into the body, they trigger an immune response which may lead to rejection and failure of the implanted device or tissue. The immune system recognizes natural biomaterials as foreign substances and triggers the activation of several immune cells, for instance, macrophages, dendritic cells, and T cells. These cells release pro-inflammatory cytokines and chemokines, which recruit other immune cells to the implantation site. The activation of the immune system can lead to an inflammatory response, which can be beneficial or detrimental, depending on the type of natural biomaterial and the extent of the immune response. These biomaterials can also influence the immune response by modulating the behavior of immune cells. For example, biomaterials with specific surface properties, such as charge and hydrophobicity, can affect the activation and differentiation of immune cells. Additionally, biomaterials can be engineered to release immunomodulatory factors, such as anti-inflammatory cytokines, to promote a tolerogenic immune response. In conclusion, the interaction between biomaterials and the body's immune system is an intricate procedure with potential consequences for the effectiveness of therapeutics and medical devices. A better understanding of this interplay can help to design biomaterials that promote favorable immune responses and minimize adverse reactions.

Soluble endoglin reduces thrombus formation and platelet aggregation via interaction with αIIbβ3 integrin

BACKGROUND

The circulating form of human endoglin (sEng) is a cleavage product of membrane-bound endoglin present on endothelial cells. Because sEng encompasses an RGD motif involved in integrin binding, we hypothesized that sEng would be able to bind integrin αIIbβ3, thereby compromising platelet binding to fibrinogen and thrombus stability.

METHODS

In vitro human platelet aggregation, thrombus retraction, and secretion-competition assays were performed in the presence of sEng. Surface plasmon resonance (SPR) binding and computational (docking) analyses were carried out to evaluate protein-protein interactions. A transgenic mouse overexpressing human sEng (hsEng+) was used to measure bleeding/rebleeding, prothrombin time (PT), blood stream, and embolus formation after FeCl3-induced injury of the carotid artery.

RESULTS

Under flow conditions, supplementation of human whole blood with sEng led to a smaller thrombus size. sEng inhibited platelet aggregation and thrombus retraction, interfering with fibrinogen binding, but did not affect platelet activation. SPR binding studies demonstrated that the specific interaction between αIIbβ3 and sEng and molecular modeling showed a good fitting between αIIbβ3 and sEng structures involving the endoglin RGD motif, suggesting the possible formation of a highly stable αIIbβ3/sEng. hsEng+ mice showed increased bleeding time and number of rebleedings compared to wild-type mice. No differences in PT were denoted between genotypes. After FeCl3 injury, the number of released emboli in hsEng+ mice was higher and the occlusion was slower compared to controls.

CONCLUSIONS

Our results demonstrate that sEng interferes with thrombus formation and stabilization, likely via its binding to platelet αIIbβ3, suggesting its involvement in primary hemostasis control.

Intravenous Hemostats: Foundation, Targeting, and Controlled-Release

Uncontrollable blood loss is the greatest cause of mortality in prehospital patients and the main source of disability and death in hospital care. Compared with external hemostats, intravenous hemostats are more appropriate for preventing and treating uncontrolled bleeding in vivo and large bleeding on the body surface. This Review initially establishes intravenous hemostats' response basis, including the coagulation mechanism, fibrinolytic pathway, and protein corona. Second, the study of advancement of intravenous hemostat targeting was expanded from two perspectives, cellular hemostatic agents and synthetic hemostatic agents. Meanwhile, after discussing the progress of controlled-release intravenous hemostats with platelets as the stimuli, this Review offers insight into the possibility of controlled-release intravenous hemostats with microenvironment as the stimuli, combining the studies of controlled-release targeted thrombolysis.

Neonatal Fibrin Scaffolds Promote Enhanced Cell Adhesion, Migration, and Wound Healing In Vivo Compared to Adult Fibrin Scaffolds

INTRODUCTION

Fibrin scaffolds are often utilized to treat chronic wounds. The monomer fibrinogen used to create such scaffolds is typically derived from adult human or porcine plasma. However, our previous studies have identified extensive differences in fibrin network properties between adults and neonates, including higher fiber alignment in neonatal networks. Wound healing outcomes have been linked to fibrin matrix structure, including fiber alignment, which can affect the binding and migration of cells. We hypothesized that fibrin scaffolds derived from neonatal fibrin would enhance wound healing outcomes compared to adult fibrin scaffolds.

METHODS

Fibrin scaffolds were formed from purified adult or neonatal fibrinogen and thrombin then structural analysis was conducted via confocal microscopy. Human neonatal dermal fibroblast attachment, migration, and morphology on fibrin scaffolds were assessed. A murine full thickness injury model was used to compare healing in vivo in the presence of neonatal fibrin, adult fibrin, or saline.

RESULTS

Distinct fibrin architectures were observed between adult and neonatal scaffolds. Significantly higher fibroblast attachment and migration was observed on neonatal scaffolds compared to adults. Cell morphology on neonatal scaffolds exhibited higher spreading compared to adult scaffolds. In vivo significantly smaller wound areas and greater epidermal thickness were observed when wounds were treated with neonatal fibrin compared to adult fibrin or a saline control.

CONCLUSIONS

Distinctions in neonatal and adult fibrin scaffold properties influence cellular behavior and wound healing. These studies indicate that fibrin scaffolds sourced from neonatal plasma could improve healing outcomes compared to scaffolds sourced from adult plasma.

SpTGase plays an important role in the hemolymph clotting in mud crab (Scylla paramamosain)

Transglutaminase (TGase) is important in blood coagulation, a conserved immunological defense mechanism among invertebrates. This study is the first report of the TGase in mud crab (Scylla paramamosain) (SpTGase) with a 2304 bp ORF encoding 767 amino acids (molecular weight 85.88 kDa). SpTGase is acidic, hydrophilic, stable and thermostable, containing three transglutaminase domains, one TGase/protease-like homolog domain (TGc), one integrin-binding motif (Arg²⁷⁰, Gly²⁷¹, Asp²⁷²) and three catalytic sites (Cys³³³, His⁴⁰¹, Asp⁴²⁴) within the TGc. Neither a signal peptide nor a transmembrane domain was found, and the random coil is dominant in the secondary structure of SpTGase. Phylogenetic analysis revealed a close relation between SpTGase to its homolog EsTGase 1 from Chinese mitten crab (Eriocheir sinensis). Expression of SpTGase was investigated using qRT-PCR (1) in eight tissues from healthy mud crabs, with the highest expression in hemocytes, and (2) in response to various immune challenges (Vibrio parahaemolyticus, lipopolysaccharide (LPS) or Poly I:C infection), revealing a major up-regulation in hemocytes, skin, and hepatopancreas during the 96-h post injection. The recombinant SpTGase showed a capacity of agglutination activities on both Gram-negative bacteria and yeast. SpTGase was found to directly interact with another important blood coagulation component clip domain serine protease (SpcSP). Moreover, knockdown of SpTGase resulted in a decreased expression of both clotting protein precursor (SppreCP) and SpcSP and an increase of duration time in the blood coagulation. Taken together, the findings of this study suggest SpTGase play an important role in the hemolymph clotting in mud crab S. paramamosain.

Micromolar concentrations of citalopram or escitalopram inhibit glycoprotein VI-mediated and integrin αIIbβ3-mediated signaling in human platelets

Collagen and convulxin induce platelet aggregation through glycoprotein VI (GPVI)-FcRγ-Syk signaling pathway. In addition, fibrinogen induces platelet activation through integrin αIIbβ3-FcγRIIa-Syk signaling pathway. We previously reported that high concentrations of selective serotonin reuptake inhibitors (SSRI) reduce platelet aggregation induced by collagen. We further investigated the effects of SSRI on GPVI- and αIIbβ3-mediated signaling pathway. Citalopram and escitalopram, two relatively pure SSRI, were used in this study. Both citalopram and escitalopram concentration-dependently inhibited convulxin-induced platelet aggregation, serotonin (5-HT) release and the activation of αIIbβ3. 5-HT concentration in washed platelets was unchanged after short-term treatment with citalopram. The additional 5-HT failed to fully rescue the inhibitory effect of citalopram on convulxin-induced aggregation. Convulxin-induced phosphorylation of Syk, LAT, and Akt was inhibited by citalopram and escitalopram. Citalopram inhibited the interaction between FcRγ and Syk, whereas the phosphorylation of FcRγ in response to convulxin remained unaltered. Further, citalopram inhibited the increase of the interaction between serotonin transporter and Syk induced by convulxin. In the presence of Mn²⁺, escitalopram inhibited the formation of lamellipodia on immobilized fibrinogen. Escitalopram did not influence the binding of fibrinogen to platelets. It inhibited the phosphorylation of Syk and PAK triggered by the adhesion on fibrinogen. Our data demonstrate that micromolar concentrations of citalopram and escitalopram inhibit GPVI- and αIIbβ3-mediated platelet functions. The mechanism of the inhibitory effect of citalopram or escitalopram is not the influence on the activation of GPVI or the interaction between fibrinogen and αIIbβ3, but the interaction between Syk and its upstream molecules.

GRGDS-functionalized chitosan nanoparticles as a potential intravenous hemostat for traumatic hemorrhage control in an animal model

Hemostats, which are used for immediate intervention during internal hemorrhage in order to reduce resulting mortality and morbidity, are relatively rare. Here, we describe novel intravenous nanoparticles (CPG-NPs-2000) with chitosan succinate (CSS) as cores, polyethylene glycol (PEG-2000) as spacers and a glycine-arginine-glycine-aspartic acid-serine (GRGDS) peptide as targeted, active hemostatic motifs. CPG-NPs-2000 displayed significant hemostatic efficacy, compared to the saline control, CSS nanoparticles, and tranexamic acid in liver trauma rat models. Further studies have demonstrated that CPG-NPs-2000 are effectively cleared from organs and blood, within 2 and 48 h, respectively. In addition, administration of CPG-NPs-2000 does not affect clotting function under normal physiological conditions, indicating their potential safety in vivo. CPG-NPs-2000 exhibit excellent thermal stability, good solubility, and redistribution ability, in addition to being low cost. These characteristics indicate that CPG-NPs-2000 may have strong potential as effective intravenous hemostats for treating severe internal bleeding.

Biomimetic Architectures for Peripheral Nerve Repair: A Review of Biofabrication Strategies

Biofabrication techniques have endeavored to improve the regeneration of the peripheral nervous system (PNS), but nothing has surpassed the performance of current clinical practices. However, these current approaches have intrinsic limitations that compromise patient care. The "gold standard" autograft provides the best outcomes but requires suitable donor material, while implantable hollow nerve guide conduits (NGCs) can only repair small nerve defects. This review places emphasis on approaches that create structural cues within a hollow NGC lumen in order to match or exceed the regenerative performance of the autograft. An overview of the PNS and nerve regeneration is provided. This is followed by an assessment of reported devices, divided into three major categories: isotropic hydrogel fillers, acting as unstructured interluminal support for regenerating nerves; fibrous interluminal fillers, presenting neurites with topographical guidance within the lumen; and patterned interluminal scaffolds, providing 3D support for nerve growth via structures that mimic native PNS tissue. Also presented is a critical framework to evaluate the impact of reported outcomes. While a universal and versatile nerve repair strategy remains elusive, outlined here is a roadmap of past, present, and emerging fabrication techniques to inform and motivate new developments in the field of peripheral nerve regeneration.

Topical application of palmitoyl-RGD reduces human facial wrinkle formation in Korean women

Maintaining a youthful appearance is a common desire among the aging population. Loss of elasticity and dermal density constitutes major causes of wrinkle formation during skin aging. In particular, periorbital wrinkles comprise the critical assessment point of skin aging. To address these issues, cosmetic industries have been making increasing efforts to develop efficient agents against wrinkle formation. Arg-Gly-Asp (RGD) is a tripeptide sequence used for surface coating because of its integrin-binding property. However, its pharmacological properties on skin have not yet been studied. Here, we synthesize the novel palmitoyl-Arg-Gly-Asp (Palm-RGD) and investigate its effects on periorbital wrinkle formation by clinical and in vitro studies. We observed that Palm-RGD cream application for 12 weeks decreased global photodamage and skin roughness (R1, R2, R3, and Ra) scores without causing skin irritation. In addition, topical application of Palm-RGD cream time-dependently increased skin elasticity and dermal density. An in vitro study using human dermal fibroblasts (HDFs) demonstrated increased type I procollagen production by Palm-RGD treatment. Furthermore, Palm-RGD suppressed MMP-1 expression in HDFs. Our results demonstrate that Palm-RGD has protective effects against wrinkle formation, likely through the activation of collagen expression and the protection against collagen degradation. Therefore, Palm-RGD could be used as a potential agent for the prevention of wrinkle formation consequent to aging.

The role of protein disulfide isomerase in the post-ligation phase of β3 integrin-dependent cell adhesion

INTRODUCTION

Protein disulfide isomerase (PDI) catalyzes disulfide bond exchange. It is crucial for integrin-mediated platelet adhesion and aggregation and disulfide bond exchange is necessary for αIIbβ3 and αvβ3 activation. However, the role of disulfide bond exchange and PDI in the post-ligation phase of αIIbβ3 and αvβ3 mediated cell adhesion has yet to be determined.

METHODS

To investigate a possible such role, we expressed wild type (WT) human αIIb and either WT human β3, or β3 harboring single or double cysteine to serine substitutions disrupting Cys473-Cys503 or Cys523-Cys544 bonds, in baby hamster kidney (BHK) cells, leading to expression of both human αIIbβ3 and a chimeric hamster/human αvβ3. Adhesion to fibrinogen-coated wells was studied in the presence or absence of bacitracin, a PDI inhibitor, with and without an αvβ3 blocker.

RESULTS

Flow cytometry showed WT and mutant αIIbβ3 expression in BHK cells and indicated that mutated αIIbβ3 receptors were constitutively active while WT αIIbβ3 was inactive. Both αIIbβ3 and αvβ3 integrins, WT and mutants, mediated adhesion to fibrinogen as shown by reduced but still substantial adhesion following treatment with the αvβ3 blocker. Mutated αIIbβ3 integrins disrupted in the Cys523-Cys544 bond still depended on PDI for adhesion as shown by the inhibitory effect of bacitracin in the presence of the αvβ3 blocker. Mutated integrins disrupted in the Cys473-Cys503 bond showed a similar trend.

CONCLUSIONS

PDI-mediated disulfide bond exchange plays a pivotal role in the post-ligation phase of αIIbβ3-mediated adhesion to fibrinogen, while this step in αvβ3-mediated adhesion is independent of disulfide exchange.

Synthetic Strategies for Engineering Intravenous Hemostats

While there are currently many well-established topical hemostatic agents for field administration, there are still limited tools to staunch bleeding at less accessible injury sites. Current clinical methods to restore hemostasis after large volume blood loss include platelet and clotting factor transfusion, which have respective drawbacks of short shelf life and risk of viral transmission. Therefore, synthetic hemostatic agents that can be delivered intravenously and encourage stable clot formation after localizing to sites of vascular injury are particularly appealing. In the past three decades, platelet substitutes have been prepared using drug delivery vehicles such as liposomes and PLGA nanoparticles that have been modified to mimic platelet properties. Additionally, structural considerations such as particle size, shape, and flexibility have been addressed in a number of reports. Since platelets are the first responders after vascular injury, platelet substitutes represent an important class of intravenous hemostats under development. More recently, materials affecting fibrin formation have been introduced to induce faster or more stable blood clot formation through fibrin cross-linking. Fibrin represents a major structural component in the final blood clot, and a fibrin-based hemostatic mechanism acting downstream of initial platelet plug formation may be a safer alternative to platelets to avoid undesired thrombotic activity. This Review explores intravenous hemostats under development and strategies to optimize their clotting activity.

Integrin-directed modulation of macrophage responses to biomaterials

Macrophages are the primary mediator of chronic inflammatory responses to implanted biomaterials, in cases when the material is either in particulate or bulk form. Chronic inflammation limits the performance and functional life of numerous implanted medical devices, and modulating macrophage interactions with biomaterials to mitigate this response would be beneficial. The integrin family of cell surface receptors mediates cell adhesion through binding to adhesive proteins nonspecifically adsorbed onto biomaterial surfaces. In this work, the roles of integrin Mac-1 (αMβ2) and RGD-binding integrins were investigated using model systems for both particulate and bulk biomaterials. Specifically, the macrophage functions of phagocytosis and inflammatory cytokine secretion in response to a model particulate material, polystyrene microparticles were investigated. Opsonizing proteins modulated microparticle uptake, and integrin Mac-1 and RGD-binding integrins were found to control microparticle uptake in an opsonin-dependent manner. The presence of adsorbed endotoxin did not affect microparticle uptake levels, but was required for the production of inflammatory cytokines in response to microparticles. Furthermore, it was demonstrated that integrin Mac-1 and RGD-binding integrins influence the in vivo foreign body response to a bulk biomaterial, subcutaneously implanted polyethylene terephthalate. A thinner foreign body capsule was formed when integrin Mac-1 was absent (~30% thinner) or when RGD-binding integrins were blocked by controlled release of a blocking peptide (~45% thinner). These findings indicate integrin Mac-1 and RGD-binding integrins are involved and may serve as therapeutic targets to mitigate macrophage inflammatory responses to both particulate and bulk biomaterials.

Angiopoietin-like 4 confers resistance to hypoxia/serum deprivation-induced apoptosis through PI3K/Akt and ERK1/2 signaling pathways in mesenchymal stem cells

Angiopoietin-like 4 (ANGPTL4) is a potential anti-apoptotic agent for various cells. We examined the protective effect of ANGPTL4 on hypoxia/serum deprivation (SD)-induced apoptosis of MSCs, as well as the possible mechanisms. MSCs were obtained from rat bone marrow and cultured in vitro. Apoptosis was induced by hypoxia/SD for up to 24 hr, and assessed by flow cytometry and TUNEL assay. Expression levels of Akt, ERK1/2, focal adhesion kinase (FAK), Src, Bcl-2, Bax, cytochrome C and cleaved caspase-3 were detected by Western blotting. Integrin β1 mRNA was detected by qRT-PCR. Mitochondrial membrane potential was assayed using a membrane-permeable dye. Hypoxia/SD-induced apoptosis was significantly attenuated by recombinant rat ANGPTL4 in a concentration dependent manner. Moreover, ANGPTL4 decreased the hypoxia/SD-induced caspase-3 cleavage and the cytochrome C release, but increased the Bcl-2/Bax ratio and the mitochondrial membrane potential. Decreased expression of integrin β1, the ANGPTL4 receptor was observed during hypoxia/SD conditions, however, such decrease was reversed by ANGPTL4. In addition, ANGPTL4 induced integrin β1-associated FAK and Src phosphorylation, which was blocked by anti-integrin β1 antibody. ANGPTL4 also reversed the hypoxia/SD-induced decrease of Akt and ERK 1/2 phosphorylation, and the effect of ANGPTL4 was abolished by inhibitors of either integrins, ERK1/2, or phosphatidylinositol 3-kinase (PI3K). Blocking integrinβ1, Akt or ERK largely attenuated anti-apoptotic effect of ANGPTL4. ANGPTL4 protects MSCs from hypoxia/SD-induced apoptosis by interacting with integrins to stimulate FAK complex, leading to downstream ERK1/2 and PI3K/Akt signaling pathways and mimicking the pathway in which MSCs contact with the extracellular matrix.

Converting stem cells to dendritic cells by agonist antibodies from unbiased morphogenic selections

When combinatorial antibody libraries are rendered infectious for eukaryotic cells, the integrated antibody genotype and cellular phenotype become permanently linked and each cell becomes a selection system unto itself. These systems should be ideal for the identification of proteins and pathways that regulate differentiation so long as selection systems can be devised. Here we use a selection system based on the ability of secreted antibodies to alter the morphology of colonies expressing them when grown in soft agar. Importantly, this approach is different from all previous studies in that it used a pure discovery format where unbiased libraries that were not preselected against any known protein were used as probes. As such, the strategy is analogous to classical forward genetic approaches except that it operates directly at the protein level. This approach led to the identification of integrin-binding agonist antibodies that efficiently converted human stem cells to dendritic cells.

Platelet responses to dynamic biomaterial surfaces with different poly(ethylene glycol) and polyrotaxane molecular architectures constructed on gold substrates

Four different dynamic biomaterial surfaces with different molecular architectures were prepared using two hydrophilic polymers: poly(ethylene glycol) and polyrotaxanes containing α-cyclodextrin. Either one or both terminals of the poly(ethylene glycol) or polyrotaxanes were immobilized onto a gold substrate via Au-S bonds, resulting in poly(ethylene glycol)-graft, polyrotaxanes-graft, poly(ethylene glycol)-loop, and polyrotaxanes-loop structures. Human platelet adhesion was suppressed more effectively on the graft surfaces than on the loop surfaces for both poly(ethylene glycol) and polyrotaxanes due to the high mobility of graft polymer chains with a free terminal. Moreover, the platelets adhered to the polyrotaxane surfaces much less than the poly(ethylene glycol) surfaces, possibly because of the mobile nature of the α-cyclodextrin molecules that were threaded on the poly(ethylene glycol) chain. Actin filament assembly in adherent platelets was also greatly prevented on the poly(ethylene glycol)/polyrotaxanes-graft surfaces in comparison with the corresponding loop surfaces. A clear correlation between the numbers and areas of adherent platelets on these surfaces suggests that platelet adhesion and activation were dominated by the platelet GPIIb/IIIa-adsorbed fibrinogen interaction. These results indicate that both of the different modes of dynamic features, sliding/rotation of α-cyclodextrin and polymer chain mobility, effectively suppressed platelet adhesion in spite of the similar hydrophilicity. This research affords a novel chemical strategy for designing hemocompatibile biomaterial surfaces.

Effect of substrate stiffness on pulmonary fibroblast activation by TGF-β

Peptide crosslinkers containing the sequence C-X-CG (X represents various adhesive peptides) were incorporated into poly(ethylene glycol) (PEG) hydrogel networks with different mechanical properties. Pulmonary fibroblasts (PFs) exhibit increased adhesion to rigid hydrogels modified with X=RGDS, DGEA and IKVAV (0.5 and/or 5 mM) compared with a scrambled control (X=HRPNS). PFs exhibit increased adhesion to softer hydrogels when X=DGEA at low (0.5 mM) peptide concentration. PFs seeded onto hydrogels modified with X=RGDS produce alpha-smooth muscle actin (α-SMA), a myofibroblast marker, and form an extensive cytoskeleton with focal adhesions. Decreasing substrate stiffness (achieved through hydrolytic degradation) results in down-regulation of α-SMA expression by PFs. Substrate stiffness increases the sensitivity of PFs to exogenously applied transforming growth factor beta (TGF-β1); PFs on the most rigid gels (E=900 kPa) express α-SMA when treated with low concentrations of TGF-β1 (1 ng ml(-1)), while those on less rigid gels (E=20-60 kPa) do not. These results demonstrate the importance of both mechanical and chemical cues in studying pulmonary fibroblast activation, and establish PEG hydrogels as a viable material for further study of IPF etiology.

The endocytic adaptor protein Disabled-2 is required for cellular uptake of fibrinogen

Endocytosis is pivotal for uptake of fibrinogen from plasma into megakaryocytes and platelet α-granules. Due to the complex adaptor and cargo contents in endocytic vehicles, the underlying mechanism of fibrinogen uptake is not yet completely elucidated. In this study, we investigated whether the endocytic adaptor protein Disabled-2 (DAB2) mediates fibrinogen uptake in an adaptor-specific manner. By employing primary megakaryocytes and megakaryocytic differentiating human leukemic K562 cells as the study models, we found that fibrinogen uptake is associated with the expression of integrin αIIbβ3 and DAB2 and is mediated through clathrin-dependent manner. Accordingly, constitutive and inducible knockdown of DAB2 by small interfering RNA reduced fibrinogen uptake for 53.2 ± 9.8% and 59.0 ± 10.7%, respectively. Culturing the cells in hypertonic solution or in the presence of clathrin inhibitor chlorpromazine abrogated clathrin-dependent endocytosis and diminished the uptake of fibrinogen. Consistent with these findings, 72.2 ± 0.2% of cellular DAB2 was colocalized with clathrin, whereas 56.4±4.1% and 54.6 ± 2.0% of the internalized fibrinogen were colocalized with clathrin and DAB2, respectively. To delineate whether DAB2 mediates fibrinogen uptake in an adaptor-specific manner, K562 stable cell lines with knockdown of the adaptor protein-2 (AP-2) or double knockdown of AP-2/DAB2 were established. The AP-2 knockdown cells elicited normal fibrinogen uptake activity but the uptake of collagen was diminished. In addition, collagen uptake was further reduced in DAB2/AP-2 knockdown cells. These findings thereby define an adaptor-specific mechanism in the control of fibrinogen uptake and implicate that DAB2 is the key adaptor in the clathrin-associated endocytic complexes to mediate fibrinogen internalization.

Identification and cloning of a transglutaminase from giant freshwater prawn, Macrobrachium rosenbergii, and its transcription during pathogen infection and moulting

Complementary (c)DNA encoding transglutaminase (TG) messenger (m)RNA of the giant freshwater prawn, Macrobrachium rosenbergii, was cloned from haemocytes by a reverse-transcription polymerase chain reaction (RT-PCR) and rapid amplification of cDNA ends (RACE) using oligonucleotide primers based on the TG sequence of the horseshoe crab, Tachypleus tridentatus; tiger shrimp, Penaeus monodon; kuruma shrimp, Marsupenaeus japonicus; and crayfish, Pacifastacus leniusculus. The 2722-bp cDNA contained an open reading frame (ORF) of 2334 bp, a 72-bp 5'-untranslated region (UTR), and a 316-bp 3'-UTR containing a stop codon and a poly A tail. The molecular mass of the deduced amino acid (aa) sequence (778 aa) was 86.67 kDa with an estimated pI of 5.4. The M. rosenbergii TG (abbreviated MrTG, accession no.: JF309296) contains a typical transglutaminase-like homologue, two putative integrin-binding motifs (RGD), ten glycosylation sites, and four calcium-binding sites; a catalytic triad is present as in arthropod TGs. Sequence comparison and a phylogenetic analysis revealed that shrimp TG can be separated into three subgroups, penaeid TG1, freshwater crustacean TG2 and marine crustacean TG2, and MrTG was more closely related to TG2 than to TG1. MrTG mRNA and TG activities were detected in all tested tissues of M. rosenbergii, with MrTG mainly being synthesised by haemocytes. There was a negative correlation between clotting time of haemolymph, and MrTG expression and TG activity of haemocytes in prawn injected with Lactococcus garvieae. The pattern of MrTG mRNA expression and TG activity in haemocytes exhibited a contrary tendency with clotting time of haemolymph during the moult stages. Those results indicate that cloned MrTG is involved in the defence response, and is probably the major functional TG for haemolymph coagulation in M. rosenbergii.

Effects of down-regulation of integrin-beta1 expression on migration and hepatic metastasis of human colon carcinoma

Organ-specific tumor cell adhesion to extracellular matrix (ECM) components and cell migration into host organs often involve integrin-mediated cellular processes. Direct integrin-mediated cell adhesion to ECM components in the space of Disse appears to be required for the successful liver metastatic formation of colon cancer. In the present study, human colon cancer HT-29 cells were transfected by liposome with integrin-beta1 antisense oligodeoxynucleotide (ASODN). The integrin-beta1 gene expression in HT-29 cells was significantly down-regulated. The migration of HT-29 cells was assayed using transwell cell culture chambers in vitro. The number of migrating HT-29 cells in experimental group was far less than that in control group (P<0.05). The models of hepatic metastasis in nude mice were established by the intrasplenic injection of transfected HT-29 cells. Thirty days later, the nude mice were killed and the average number of hepatic metastases (4.00+/-0.93 per mouse), average volume (10.10+/-6.50 mm3 per mouse), average weight (0.0440+/-0.0008 g per mouse) in experimental group were remarkably reduced as compared with those in control group (P<0.05). Integrin-beta1 expression in the hepatic metastasis was studied by immunohistochemistry (SP). Positive cell percentage of hepatic metastases in experimental group was markedly decreased as compared with that in control group (P<0.05). It was concluded that integrin-beta1 may take part in hepatic metastasis, and down-regulation of integrin-beta1 expression may play a key role in decreasing migration and hepatic metastasis of human colon carcinoma cells (HT-29).

Conformational behavior of fibrinogen on topographically modified polymer surfaces

The influence of topographical surface features at the submicron scale on the structural changes in the surface-adsorbed fibrinogen was investigated on poly(lactic-co-glycolic-acid) (PLGA) films. Attenuated total reflection-Fourier transform infrared spectroscopy (ATR-FTIR) was employed in this study for the induced conformational change of fibrinogen over various adsorption times, while the adsorption kinetics of fibrinogen was quantified by the enzyme linked immunosorbent assay (ELISA). When a PLGA surface is modified topographically, the adsorbed fibrinogen undergoes less conformational change when compared to adsorption on the pristine PLGA surface. The extent of conformational change is related to platelet adhesion. Reduced thrombogenicity was demonstrated by the higher ratios of alpha-helix to beta-turn and beta-sheet to beta-turn structures on the topographic PLGA film, which suggests that topographical manipulation of surfaces is a viable approach to influence the thrombogenicity of surfaces.

Reactive oxygen species inhibit adhesion of mesenchymal stem cells implanted into ischemic myocardium via interference of focal adhesion complex

The integrity of transplanted mesenchymal stem cells (MSCs) for cardiac regeneration is dependent on cell-cell or cell-matrix adhesion, which is inhibited by reactive oxygen species (ROS) generated in ischemic surroundings after myocardial infarction. Intracellular ROS play a key role in the regulation of cell adhesion, migration, and proliferation. This study was designed to investigate the role of ROS on MSC adhesion. In H(2)O(2) treated MSCs, adhesion and spreading were inhibited and detachment was increased in a dose-dependent manner, and these effects were significantly rescued by co-treatment with the free radical scavenger, N-acetyl-L-cysteine (NAC, 1 mM). A similar pattern was observed on plates coated with different matrices such as fibronectin and cardiogel. Hydrogen peroxide treatment resulted in a marked decrease in the level of focal adhesion-related molecules, such as phospho-FAK and p-Src in MSCs. We also observed a significant decrease in the integrin-related adhesion molecules, alpha V and beta1, in H(2)O(2) treated MSCs. When injected into infarcted hearts, the adhesion of MSCs co-injected with NAC to the border region was significantly improved. Consequently, we observed that fibrosis and infarct size were reduced in MSC and NAC-injected rat hearts compared to in MSC-only injected hearts. These results indicate that ROS inhibit cellular adhesion of engrafted MSCs and provide evidence that the elimination of ROS might be a novel strategy for improving the survival of engrafted MSCs.

The platelet integrin alphaIIbbeta3 binds to the RGD and AGD motifs in fibrinogen

Fibrinogen (Fbg) mediates platelet aggregation by binding the alphaIIbbeta3 integrin receptor, but the interaction of the receptor with peptide motifs of Fbg remains unresolved. This paper describes the use of self-assembled monolayers (SAMs) to study the adhesion of alphaIIbbeta3-transfected CHO cells to the GRGDS and HHLGGAKQAGDV motifs within Fbg. Cells adhered to and spread on monolayers presenting either peptide. Cell adhesion could be inhibited by either soluble peptide, demonstrating that the peptides bind competitively to the integrin. A peptide array was used to show that AGD was the minimal binding sequence in HHLGGAKQAGDV and that the receptor recognizes ligands of the form GXGDSC, where X is a hydrophobic or basic residue. This work revises our understanding of the alphaIIbbeta3 specificity and also suggests a new class of antithrombotic agents.

Lnk regulates integrin alphaIIbbeta3 outside-in signaling in mouse platelets, leading to stabilization of thrombus development in vivo

The nature of the in vivo cellular events underlying thrombus formation mediated by platelet activation remains unclear because of the absence of a modality for analysis. Lymphocyte adaptor protein (Lnk; also known as Sh2b3) is an adaptor protein that inhibits thrombopoietin-mediated signaling, and as a result, megakaryocyte and platelet counts are elevated in Lnk-/- mice. Here we describe an unanticipated role for Lnk in stabilizing thrombus formation and clarify the activities of Lnk in platelets transduced through integrin alphaIIbbeta3-mediated outside-in signaling. We equalized platelet counts in wild-type and Lnk-/- mice by using genetic depletion of Lnk and BM transplantation. Using FeCl3- or laser-induced injury and in vivo imaging that enabled observation of single platelet behavior and the multiple steps in thrombus formation, we determined that Lnk is an essential contributor to the stabilization of developing thrombi within vessels. Lnk-/- platelets exhibited a reduced ability to fully spread on fibrinogen and mediate clot retraction, reduced tyrosine phosphorylation of the beta3 integrin subunit, and reduced binding of Fyn to integrin alphaIIbbeta3. These results provide new insight into the mechanism of alphaIIbbeta3-based outside-in signaling, which appears to be coordinated in platelets by Lnk, Fyn, and integrins. Outside-in signaling modulators could represent new therapeutic targets for the prevention of cardiovascular events.

Overexpression of the partially activated alpha(IIb)beta3D723H integrin salt bridge mutant downregulates RhoA activity and induces microtubule-dependent proplatelet-like extensions in Chinese hamster ovary cells

BACKGROUND

We have recently reported a novel mutation in the beta3 subunit of the platelet fibrinogen receptor (alpha(IIb)beta3D723H) identified in a patient with dominantly inherited macrothrombocytopenia, and we have shown that this mutation promotes a new phenotype in Chinese hamster ovary (CHO) cells, characterized by fibrinogen-dependent, microtubule-driven proplatelet-like cell extensions.

RESULTS

Here we demonstrate that the partially activated alpha(IIb)beta3D723H or alpha(IIb)beta3D723A salt bridge mutants, but not fully activated alpha(IIb)beta3 mutants, cause this phenotype. Time-lapse videomicroscopy clearly differentiated these stable microtubule-driven and nocodazole-sensitive extensions from common dynamic actin-driven pseudopodia. In addition, overexpression of a mitochondrial marker confirmed their functional role in organelle transport. Comparative immunofluorescence analysis of the subcellular localization of alpha(IIb)beta3, the focal adhesion proteins talin or vinculin and actin revealed a similar membrane labeling of CHO cell extensions and CD34+-derived megakaryocyte proplatelets. Mutant alpha(IIb)beta3D723H signaling was independent of Src, protein kinase C or phosphoinositide 3-kinase, but correlated with decreased RhoA activity as compared with wild-type alpha(IIb)beta3 signaling, reminiscent of integrin signaling during neurite outgrowth. Accordingly, overexpression of constitutively active RhoA in CHO alpha(IIb)beta3D723H cells prevented protrusion formation on fibrinogen. Most interestingly, RhoA/ROCK inhibition was necessary, but not sufficient, and integrin activity was additionally required to induce CHO cell extension formation.

CONCLUSIONS

CHO alpha(IIb)beta3D723H cell protrusions and megakaryocyte proplatelets, like neuronal cell neurites, result from a common integrin-dependent signaling pathway, promoting strongly decreased RhoA activity and leading to microtubule-driven formation of cytoplasmic extensions.

Strain matrix-dependently dissociates gut epithelial spreading and motility

BACKGROUND

Repetitive deformation enhances intestinal epithelial migration across tissue fibronectin (tFN) via Src but inhibits migration across collagen. Since cell spreading generally precedes motility, we compared the effects of cyclic strain on Caco-2 spreading and migration on tFN, collagen-I, and plasma fibronectin (pFN), and investigated the role of Src in deformation-influenced spreading and migration.

MATERIALS AND METHODS

Human Caco-2 intestinal epithelial cells on tFN, collagen-I or pFN were subjected to an average 10% strain at 10 cycles/min for 2 h. Src was inhibited with 10muM PP2 or Src was reduced with siRNA. Parallel studies assessed deformation effects on monolayer wound closure.

RESULTS

Deformation, Src-inhibition or reduction each inhibited spreading on tFN but Src-inhibition or reduction prevented further inhibition of spreading by deformation without preventing further inhibition of motility. Deformation did not alter spreading on collagen-I or pFN, but inhibited wound closure.

CONCLUSIONS

Although cell spreading generally precedes and parallels motility, repetitive deformation regulates motility independently of spreading. Since deformation activates Src, the ability of Src blockade to mimic strain-associated inhibition of spreading on tFN suggests that this effect occurs by a separate mechanism that may also require basal Src activity. Further delineation of the mechanisms by which strain disparately modulates spreading and motility may permit acceleration of mucosal healing by targeted interventions to separately promote spreading and epithelial motility.

Salvicine inactivates beta 1 integrin and inhibits adhesion of MDA-MB-435 cells to fibronectin via reactive oxygen species signaling

Integrin-mediated adhesion to the extracellular matrix plays a fundamental role in tumor metastasis. Salvicine, a novel diterpenoid quinone compound identified as a nonintercalative topoisomerase II poison, possesses a broad range of antitumor and antimetastatic activity. Here, the mechanism underlying the antimetastatic capacity of salvicine was investigated by exploring the effect of salvicine on integrin-mediated cell adhesion. Salvicine inhibited the adhesion of human breast cancer MDA-MB-435 cells to fibronectin and collagen without affecting nonspecific adhesion to poly-l-lysine. The fibronectin-dependent formation of focal adhesions and actin stress fibers was also inhibited by salvicine, leading to a rounded cell morphology. Furthermore, salvicine down-regulated beta(1) integrin ligand affinity, clustering and signaling via dephosphorylation of focal adhesion kinase and paxillin. Conversely, salvicine induced extracellular signal-regulated kinase (ERK) and p38 mitogen-activated protein kinase (MAPK) phosphorylation. The effect of salvicine on beta(1) integrin function and cell adhesion was reversed by U0126 and SB203580, inhibitors of MAPK/ERK kinase 1/2 and p38 MAPK, respectively. Salvicine also induced the production of reactive oxygen species (ROS) that was reversed by ROS scavenger N-acetyl-l-cysteine. N-acetyl-l-cysteine additionally reversed the salvicine-induced activation of ERK and p38 MAPK, thereby maintaining functional beta(1) integrin activity and restoring cell adhesion and spreading. Together, this study reveals that salvicine activates ERK and p38 MAPK by triggering the generation of ROS, which in turn inhibits beta(1) integrin ligand affinity. These findings contribute to a better understanding of the antimetastatic activity of salvicine and shed new light on the complex roles of ROS and downstream signaling molecules, particularly p38 MAPK, in the regulation of integrin function and cell adhesion.

A nonsynonymous SNP in the ITGB3 gene disrupts the conserved membrane-proximal cytoplasmic salt bridge in the alphaIIbbeta3 integrin and cosegregates dominantly with abnormal proplatelet formation and macrothrombocytopenia

We report a 3-generation pedigree with 5 individuals affected with a dominantly inherited macrothrombocytopenia. All 5 carry 2 nonsynonymous mutations resulting in a D723H mutation in the beta3 integrin and a P53L mutation in glycoprotein (GP) Ibalpha. We show that GPIbalpha-L53 is phenotypically silent, being also present in 3 unaffected pedigree members and in 7 of 1639 healthy controls. The beta3-H723 causes constitutive, albeit partial, activation of the alphaIIbbeta3 complex by disruption of the highly conserved cytoplasmic salt bridge with arginine 995 in the alphaIIb integrin as evidenced by increased PAC-1 but not fibrinogen binding to the patients' resting platelets. This was confirmed in CHO alphaIIbbeta3-H723 transfectants, which also exhibited increased PAC-1 binding, increased adhesion to von Willebrand factor (VWF) in static conditions and to fibrinogen under shear stress. Crucially, we show that in the presence of fibrinogen, alphaIIbbeta3-H723, but not wild-type alphaIIbbeta3, generates a signal that leads to the formation of proplatelet-like protrusions in transfected CHO cells. Abnormal proplatelet formation was confirmed in the propositus's CD34+ stem cell-derived megakaryocytes. We conclude that the constitutive activation of the alphaIIbbeta3-H723 receptor causes abnormal proplatelet formation, leading to incorrect sizing of platelets and the thrombocytopenia observed in the pedigree.

Ligand density dramatically affects integrin alpha IIb beta 3-mediated platelet signaling and spreading

The impact of ligand density on integrin-mediated cell adhesion and outside-in signaling is not well understood. Using total internal reflection fluorescent microscopy, conformation-specific antibodies, and Ca(2+) flux measurements, we found that the surface density of fibrinogen affects alpha II b beta 3-mediated platelet signaling, adhesion, and spreading. Adhesion to fibrinogen immobilized at low density leads to rapid increases in cytosolic Ca(2+) and sequential formation of filopodia and lamellipodia. In contrast, adhesion to high-density fibrinogen results in transient or no increases in Ca(2+) and simultaneous formation of filopodia and lamellipodia. alpha II b beta 3 receptors at the basal surface of platelets engage fibrinogen in a ringlike pattern at the cell edges under both conditions. This engagement is, however, more dynamic and easily reversed on high-density fibrinogen. Src and Rac activity and actin polymerization are important for adhesion to low-density fibrinogen, whereas PKC/PI3 kinases contribute to platelet spreading on high-density fibrinogen. We conclude that 2 fundamentally different signaling mechanisms can be initiated by a single integrin receptor interacting with the same ligand when it is immobilized at different densities.

[Platelet--vessel wall interactions]

The vascular endothelium is a thromboresistant surface, allowing the free flowing of blood cell elements. Platelets are predominantly involved in the rapid response to a vascular lesion, exposing the underlying thrombogenic subendothelium and leading to initiation of thrombus formation. Thrombus growth requires on the one hand, the recruitment of circulating platelets to the luminal side of the thrombus and on the other hand, the assembly of the proteins of the blood coagulation cascade on the platelet catalytic surface leading to thrombin formation. High shear forces are necessary for the dual role of von Willebrand factor (VWF) in the initiation of platelet thrombus formation and in its growth and stabilization. In hemodynamic conditions, platelet adhesion depends on the interaction between VWF and the platelet receptor glycoprotein Ib (GPIb). This interaction is the only one able to resist to the high shear rates that prevail in arterioles, the microcirculation or stenosed arteries. Thereafter, the interaction between VWF and the alphaIIbbeta3 integrin allows the definitive arrest of platelets and induces thrombus formation. Thus, high shear forces by themselves are able to induce platelet activation/aggregation, without added exogenous agonist. VWF is synthesised by endothelial cells as a series of multimers of different sizes. The multimers with the highest molecular weight, the so-called ultra-large multimers, are strongly thrombogenic by their increased ability to bind platelet GPIb and to induce the formation of circulating aggregates. These ultra-large multimers are normally cleaved by the ADAMTS13 metalloprotease into smaller multimers which are also less thrombogenic. The in vivo proteolysis of VWF by ADAMTS13 depends on the high shear rates, which increase the opening of multimers anchored to the endothelial cell layer and the exposure of the cleavage site of VWF by ADAMTS13. An ADAMTS13 deficiency thus likely would result in the accumulation of ultra-large multimers on the endothelial surface, which retains platelets on the activated endothelium and results in micro-thrombi formation, as seen in thrombotic thrombocytopenic purpura. Platelet-VWF interactions are also involved in inflammation. Activation of endothelial cells induces the release of VWF from the Weibel-Palade bodies as well as the surface expression of VWF and P-selectin. These molecules allow leukocyte and platelet rolling on endothelial cells, and expression of E-selectin, VCAM-1 and other adhesion molecules. Recently, it has been shown that activated platelets allow transient activation of intact, non stimulated endothelial cells, thus increasing the inflammation process. VWF and platelet P-selectin have been shown to be essential to this process. Thus, platelet--vessel wall interactions are involved in thrombosis and inflammation essentially via VWF.

Fibrinogen adsorption, platelet adhesion and activation on mixed hydroxyl-/methyl-terminated self-assembled monolayers

The effect of surface wettability on fibrinogen adsorption, platelet adhesion and platelet activation was investigated using self-assembled monolayers (SAMs) containing different ratios of longer chain methyl- and shorter chain hydroxyl-terminated alkanethiols (C15CH3 vs. C11OH) on gold. Protein adsorption studies were performed using radiolabeled human fibrinogen (HFG). Platelet adhesion and activation studies with and without pre-adsorbed fibrinogen, albumin and plasma were assessed using scanning electron microscopy (SEM) and a glutaraldehyde-induced fluorescence technique (GIFT). Results demonstrated a linear decrease of HFG adsorption with the increase of OH groups on the monolayer (increase of the hydrophilicity). Platelet adhesion and activation also decrease with increase of hydrophilicity of surface. Concerning SAMs pre-immersed in proteins, fibrinogen adsorption was related with high platelet adhesion and activation. The passivant effect of albumin on platelet adhesion and activation was only demonstrated on SAMs contained C11OH. When all the blood proteins are present (plasma) platelet adhesion was almost absent on SAMs with 65% and 100% C11OH. This could be explained by the higher albumin affinity of the SAMs with 65% C11OH and the lower total protein adsorption associated with SAMs with 100% C11OH.

A novel functional role for the highly conserved alpha-subunit KVGFFKR motif distinct from integrin alphaIIbbeta3 activation processes

BACKGROUND

The highly conserved integrin alpha-subunit membrane-proximal motif KVGFFKR plays a decisive role in modulating the activation of integrin alphaIIbbeta3. Previously, we have shown that a platelet permeable palmityl (pal)-peptide with this seven amino acid sequence can directly activate alphaIIbbeta3 leading to platelet aggregation.

OBJECTIVES

To investigate further the role of the KVGFFKR motif in integrin alphaIIbbeta3 function.

METHODS

We used two sequence-specific complementary model systems, palmityl pal-peptides in platelets, and mutant alphaIIbbeta3-expressing Chinese Hamster Ovary (CHO) cell lines.

RESULTS

In platelets we show that the two phenylalanine amino acids in pal-KVGFFKR (pal-FF) peptide are critical for stimulating platelet aggregation. Pal-FF peptide treatment of platelets also gives rise to a tyrosine phosphorylation signal despite the presence of inhibitors of fibrinogen binding. In CHO cells, a double alanine substitution, alphaIIb(F992A, F993A)beta3, induces constitutive integrin activation but prevents actin stress fiber formation upon adhesion to fibrinogen, suggesting that alphaIIbbeta3-mediated cytoskeletal reorganization is also dependent on F992 and F993. This further highlights a critical role for the two phenylalanine residues in both of these alphaIIbbeta3-mediated processes.

CONCLUSION

In addition to regulating integrin alphaIIbbeta3 activation state, the KVGFFKR motif also influences cytoskeletal reorganization. This activity is critically determined by F992 and F993 within the seven amino acid sequence.

Biochemical characterization and cloning of transglutaminases responsible for hemolymph clotting in Penaeus monodon and Marsupenaeus japonicus

To investigate the shrimp blood clotting enzyme, a transglutaminase in the hemocytes of Penaeus monodon (abbreviated as TGH) was purified. TGH is an abundant homodimeric cytosolic protein with 84.2 kDa subunits. It clotted shrimp plasma and incorporated fluorescent dansylcadaverine into succinyl casein upon activation by CaCl(2) in vitro. IC(50) for the activation was 3 mM, which is below the shrimp plasma Ca(2+) level. Showing similar properties as other type II transglutaminase, TGH was particularly unstable after activation. MALDI-TOF/TOF mass-analyses of tryptic peptides of P. monodon TGH confirmed its identity to STG I (AY074924) previously cloned. A possible allele of the other isozyme STG II (AY771615) has also been cloned from the P. monodon cDNA and designated as PmTG. The predicted PmTG protein sequence is 58% similar to that of STG I and 99.2% to that of STG II. Likewise, a novel enzyme Mj-TGH was purified and cloned from Marsupenaeus japonicus hemocytes. Results of sequence alignment and phylogenetic analyses of these transglutaminases suggest that STG I and Mj-TGH are 83% identical and orthologous to each other, while PmTG/STG II and a previously cloned M. japonicus transglutaminase (AB162767) are their paralogs. Protein of the latter two could not be isolated, their regulated expression was discussed.

RGD, the Rho’d to cell spreading

Some RGD-type integrins rely on a synergistic site in addition to the canonical RGD site for ligand binding. However, the precise involvement of each of these recognition sites during cell adhesion is still unclear. Here we review recent investigations on integrin alphaIIbbeta3-mediated cell adhesion to immobilized fibrinogen providing evidence that the fibrinogen synergy gamma(400-411) sequence by itself promotes cell attachment by initiating alphaIIbbeta3 clustering and recruitment of intracellular proteins to focal complexes, while the RGD motif subsequently acts as a molecular switch on the beta3 subunit to induce a conformational change necessary for RhoA activation and full cell spreading.

CHO cells expressing the high affinity alpha(IIb)beta3 T562N integrin demonstrate enhanced adhesion under shear

BACKGROUND

Alpha(IIb)beta3-mediated platelet adhesive interactions in the vasculature, which are dependent on the functional state of this receptor, may be sensitive to shear forces.

OBJECTIVES

To evaluate the influence of the alpha(IIb)beta3 affinity state on cell attachment under flow, we compared Chinese hamster ovary cells expressing the low affinity alpha(IIb)beta3 wild-type (wt) receptor to those expressing the high affinity alpha(IIb)beta3 T562N receptor.

MATERIALS AND METHODS

We designed a real-time videomicroscopy adhesion assay for von Willebrand factor (VWF) or fibrinogen under flow conditions.

RESULTS

At 50 s(-1), alpha(IIb)beta3 T562N supported higher cell adhesion to fibrinogen (63.3 +/- 2.9 cells/field) than alpha(IIb)beta3 wt (38.7 +/- 2.4 cells/field, P < 0.0001). At 100 s(-1), alpha(IIb)beta3 T562N mediated cell adhesion (40.5 +/- 3.8 cells/field), while alpha(IIb)beta3 wt did not (5.3 +/- 1.4 cells/field, P < 0.001), allowing to discriminate the efficiency of each receptor. Similar findings were observed for adhesion to VWF. Complete inhibition of cell adhesion to fibrinogen was achieved with 800 microM fibrinogen gamma-chain dodecapeptide [HHLGGAKQAGDV (H12)], while Arg-Gly-Asp-Ser (RGDS) peptide (10-1000 microM) induced a dose-dependent cell detachment. These results suggest that the H12 motif allows initial attachment, in contrast to the RGDS site, which strengthens the stability of adhesion. Interestingly, compared with wt, a 10-fold lower concentration of RGDS was required to reach a similar reduction of cell adhesion mediated by alpha(IIb)beta3 T562N.

CONCLUSIONS

Our data show that alpha(IIb)beta3 activation is associated with a stabilization of integrin binding to fibrinogen or VWF under shear.