Academic literature on the topic 'GFOGER Peptide'

AbstractExposed subendothelial collagen acts as a substrate for platelet adhesion and thrombus formation after vascular injury. Synthetic collagen-derived triple-helical peptides, designated collagen-related peptide (CRP), GFOGER, and VWF-III, can specifically engage the platelet collagen receptors, glycoprotein VI and integrin α2β1, and plasma von Willebrand factor (VWF), respectively. Hitherto, the role of these 3 collagen-binding axes has been studied indirectly. Use of these uniform peptide substrates, rather than collagen fibers, provides independent control of each axis. Here, we use confocal imaging and novel image analysis techniques to investigate the effects of receptor-ligand engagement on platelet binding and activation during thrombus formation under flow conditions. At low shear (100s−1 and 300s−1), both GFOGER and CRP are required for thrombus formation. At 1000s−1, a combination of either CRP or GFOGER with VWF-III induces comparable thrombus formation, and VWF-III increases thrombus deposition at all shear rates, being indispensable at 3000s−1. A combination of CRP and VWF-III is sufficient to support extensive platelet deposition at 3000s−1, with slight additional effect of GFOGER. Measurement of thrombus height after specific receptor blockade or use of altered proportions of peptides indicates a signaling rather than adhesive role for glycoprotein VI, and primarily adhesive roles for both α2β1 and the VWF axis.

SummaryCalreticulin is an abundant protein in the endoplasmic reticulum of most cells. In this study, flow cytometry and immunoprecipitation from surface-biotinylated platelets each provided direct evidence that calreticulin is also expressed on the surface of human platelets. Anti-calreticulin antibodies caused platelet activation, inducing Fc RIIa-independent platelet aggregation. In addition, these antibodies inhibited platelet adhesion to the integrin α2β1-specific ligands, GFOGER-GPP and monomeric collagen I, and to the glycoprotein VI-specific ligand, CRP. Inhibition of platelet adhesion to these ligands was independent of integrin αIIbβ3. In resting platelets, calreticulin was shown to interact with integrin α2β1 and glycoprotein VI. Together, these data demonstrate that surface calreticulin is associated with collagen receptors on the platelet surface, where it may play a role in the modulation of the platelet-collagen interaction.Abbreviations: BSA: bovine serum albumin; cC1qR: complement component 1q receptor; CRP: collagen-related peptide; DTSSP: 3,3’-dithiobis (sulfosuccinimidyl propionate); ER: endoplasmic reticulum; GFOGER-GPP: GPC[GPP]5GFOGER[GPP]5GPC; GpVI: glycoprotein VI; HRP: horseradish peroxidase; PDI: protein disulfide isomerase.

Abstract Abstract 2207 Multimerin 1 (MMRN1) is a large, homopolymeric adhesive protein stored in platelets and endothelium that binds to activated platelets, endothelial cells and the extracellular matrix after agonist stimulation. MMRN1 supports platelet adhesion by von Willebrand factor (VWF) dependent and independent mechanisms, and also increases platelet adhesion to Horm collagen. Mice deficient in Mmrn1/Snca (α-synuclein) showed defective platelet adhesion to collagen in vitro and in vivo which was corrected by MMRN1. The ability of MMRN1 to support platelet adhesion in vivo and enhance platelet adhesion to collagen ex vivo, led us to explore the molecular basis of MMRN1 interactions with collagen. Solid phase binding assays were used to test MMRN1 binding to human fibril forming collagen (types I, II, III and V) and to types IV and VI collagen. Binding assays were also used to map the MMRN1 binding sites on collagen using collagen peptide toolkits III and II (which has significant similarity to type I collagen). Static adhesion assays were used to test selected collagen peptides for platelet adhesion. Platelet adhesion assays at high shear rates 1500s−1, were used to test the adhesion of washed platelets from normal and VWF-deficient subjects to type I collagen pre-treated or in fluid phase with: BSA (negative control), MMRN1, VWF or their combination. Human collagens types I, II, III and VI (p-values <0.001) but not types IV or V (p-values = 0.84 and 0.09, respectively) supported MMRN1 binding. Peptide toolkits binding studies indicated that MMRN1 bound to a single site on collagen III (peptide III-38) and to two sites on collagen II, with peptide II-9 showing much stronger binding than peptide II-44. Like the VWF binding peptide III-23 (which did not overlap the MMRN1 binding site), peptide III-38 supported platelet adhesion in combination with GFOGER, the peptide with high affinity for platelet α2β1. The possibility that MMRN1 binds to collagen at sites distinct from VWF was supported by the observations that pre-treatment of collagen I matrices, with the combination of MMRN1 and VWF, increased platelet adhesion more than MMRN1 or VWF alone (p-values< 0.001). Moreover, adhesion deficit of VWF-deficient platelets on collagen type I matrix pre-treated with a combination of MMRN1 and VWF was corrected by adding fluid phase VWF but not MMRN1 (p-values < 0.0001). Taken together, our data indicates that MMRN1 binds to different forms of human collagen that support platelet adhesion. As MMRN1 binds to sites on collagen distinct from VWF or integrin α2β1, it may be important for maximizing platelet adhesion at sites of vascular injury. Disclosures: No relevant conflicts of interest to declare.

Abstract Integrin α2β1–mediated adhesion of human platelets to monomeric type I collagen or to the GFOGER peptide caused a time-dependent activation of PI3K and Akt phosphorylation. This process was abrogated by pharmacologic inhibition of PI3Kβ, but not of PI3Kγ or PI3Kα. Moreover, Akt phosphorylation was undetectable in murine platelets expressing a kinase-dead mutant of PI3Kβ (PI3KβKD), but occurred normally in PI3KγKD platelets. Integrin α2β1 failed to stimulate PI3Kβ in platelets from phospholipase Cγ2 (PLCγ2)–knockout mice, and we found that intracellular Ca2+ linked PLCγ2 to PI3Kβ activation. Integrin α2β1 also caused a time-dependent stimulation of the focal kinase Pyk2 downstream of PLCγ2 and intracellular Ca2+. Whereas activation of Pyk2 occurred normally in PI3KβKD platelets, stimulation of PI3Kβ was strongly reduced in Pyk2-knockout mice. Neither Pyk2 nor PI3Kβ was required for α2β1–mediated adhesion and spreading. However, activation of Rap1b and inside-out stimulation of integrin αIIbβ3 were reduced after inhibition of PI3Kβ and were significantly impaired in Pyk2-deficient platelets. Finally, both PI3Kβ and Pyk2 significantly contributed to thrombus formation under flow. These results demonstrate that Pyk2 regulates PI3Kβ downstream of integrin α2β1, and document a novel role for Pyk2 and PI3Kβ in integrin α2β1 promoted inside-out activation of integrin αIIbβ3 and thrombus formation.

Abstract The platelet glycoproteins (GPs) Ib, integrin α2β1, and GPVI are considered central to thrombus formation. Recently, their relative importance has been re-evaluated based on data from murine knockout models. To examine their relationship during human thrombus formation on collagen type I fibers at high shear (1000 s–1), we tested a novel antibody against GPVI, an immunoglobulin single-chain variable fragment, 10B12, together with specific antagonists for GPIbα (12G1 Fab2) and α2β1 (6F1 mAb or GFOGER-GPP peptide). GPVI was found to be crucial for aggregate formation, Ca2+ signaling, and phosphatidylserine (PS) exposure, but not for primary adhesion, even with more than 97% receptor blockade. Inhibiting α2β1 revealed its involvement in regulating Ca2+ signaling, PS exposure, and aggregate size. Both GPIbα and α2β1 contributed to primary adhesion, showing overlapping function. The coinhibition of receptors revealed synergism in thrombus formation: the coinhibition of adenosine diphosphate (ADP) receptors with collagen receptors further decreased adhesion and aggregation, and, crucially, the complete eradication of thrombus formation required the coinhibition of GPVI with either GPIbα or α2β1. In summary, human platelet deposition on collagen depends on the concerted interplay of several receptors: GPIb in synergy with α2β1 mediating primary adhesion, reinforced by activation through GPVI, which further regulates the thrombus formation.

ABSTRACT The bacterial twin arginine translocation (Tat) pathway translocates across the cytoplasmic membrane folded proteins which, in most cases, contain a tightly bound cofactor. Specific amino-terminal signal peptides that exhibit a conserved amino acid consensus motif, S/T-R-R-X-F-L-K, direct these proteins to the Tat translocon. The glucose-fructose oxidoreductase (GFOR) ofZymomonas mobilis is a periplasmic enzyme with tightly bound NADP as a cofactor. It is synthesized as a cytoplasmic precursor with an amino-terminal signal peptide that shows all of the characteristics of a typical twin arginine signal peptide. However, GFOR is not exported to the periplasm when expressed in the heterologous host Escherichia coli, and enzymatically active pre-GFOR is found in the cytoplasm. A precise replacement of the pre-GFOR signal peptide by an authentic E. coli Tat signal peptide, which is derived from pre-trimethylamine N-oxide (TMAO) reductase (TorA), allowed export of GFOR, together with its bound cofactor, to the E. coli periplasm. This export was inhibited by carbonyl cyanide m-chlorophenylhydrazone, but not by sodium azide, and was blocked in E. coli tatC andtatAE mutant strains, showing that membrane translocation of the TorA-GFOR fusion protein occurred via the Tat pathway and not via the Sec pathway. Furthermore, tight cofactor binding (and therefore correct folding) was found to be a prerequisite for proper translocation of the fusion protein. These results strongly suggest that Tat signal peptides are not universally recognized by different Tat translocases, implying that the signal peptides of Tat-dependent precursor proteins are optimally adapted only to their cognate export apparatus. Such a situation is in marked contrast to the situation that is known to exist for Sec-dependent protein translocation.

Abstract Platelets tether to collagen in the subendothelial matrix that is exposed by vascular damage. Collagen is a particularly important matrix component in this context, not only because it is a substrate for platelet adhesion, but because it is an agonist for platelet aggregation and secretion as well. There are two platelet collagen receptors, the immunoglobulin gene superfamily member GPVI and the integrin α2Β1. Both are involved in adhesion to exposed collagen and generate downstream activating signals. α2Β1 is widely expressed and has been implicated in hemostasis and thrombosis, as well as cancer metastasis, wound healing, and angiogenesis. In mice, α2Β1 deficiency results in decreased ex vivo platelet aggregation, but normal bleeding times. In mouse tumor models, α2Β1 blockade reduces both metastasis and angiogenesis. Humans lacking α2Β1 have a mild bleeding diathesis. Given this background, α2Β1 appears to be an appropriate target for the development of small-molecule inhibitors to serve as relatively safe anti-platelet and anti-tumor agents, either acting alone or in synergy with other anti-platelet or anti-tumor agents. We have developed two classes of small-molecule α2Β1 inhibitors. The first class is targeted against the collagen binding site located on the α2 I-domain and was designed using molecular modeling to superimpose a dipeptide scaffold onto the published crystal structure of the I-domain bound to a collagen-mimetic peptide (GFOGER). These molecules block recombinant human I-domain binding to immobilized collagen type I with IC50s as low as 10 μM. Although the molecules inhibit platelet adhesion to collagen only at higher concentrations, they readily inhibit melanoma cell adhesion to collagen mimetics. It is also noteworthy that the molecules induce platelet protein phosphorylation and potentiate platelet aggregation induced by other platelet agonists, both of which can be prevented by pre-incubating platelets with monoclonal antibodies directed against the α2 I-domain, but not against GPVI. The second class of molecules was derived from proline-substituted 2,3-diaminopropionic acids and is directed against the Β1 I-like domain, an allosteric site that regulates ligand binding. These molecules are potent inhibitors of platelet adhesion to immobilized soluble collagen type I with IC50s of 10–50 nM and inhibit the adhesion of melanoma cells to collagen mimetics with IC50s of 250–350 nM. These molecules do not inhibit platelet aggregation, nor do they inhibit I-domain binding to immobilized collagen type I, behavior consistent with binding to the Β1 I-like domain. In a murine model of ferric-chloride induced carotid thrombosis, the molecules synergize with aspirin to prevent arterial thrombosis. In summary, we have developed two classes of small molecule inhibitors that impair the interaction of collagen with the integrin α2Β1. Although both classes of inhibitors bind to α2Β1, their effects on its function are substantially different, indicating that there are multiple potential strategies for inhibiting integrin function pharmacologically. Further development of these inhibitors may lead to agents that will be clinically useful in the treatment of thrombosis and cancer.

Les maladies cardiovasculaires (MCV) sont classées en tête de liste parmi les principales causes de décès dans le monde. La calcification de la paroi vasculaire entraîne diverses conséquences cardiovasculaires critiques et explique les taux de mortalité élevés chez les patients atteints de nombreuses maladies comme le diabète, l'athérosclérose et la maladie rénale chronique (IRC). VC est un processus actif avec des caractéristiques de la physiologie osseuse et il est régulé par des processus inductifs et inhibiteurs multifactoriels. Au cours du processus de calcification, les cellules musculaires lisses vasculaires (VSMC) subissent un processus ostéogénique actif pour devenir des cellules de type ostéoblaste et libérer des populations hétérogènes de Vésicules Extracellulaires (EV). Les VE agissent comme des foyers de nucléation pour la cristallisation grâce à leur interaction avec le collagène de type 1 (Col1) via les intégrines et leur teneur en protéines procalcifiantes soutient fortement la progression de la calcification. Parce que ces deux mécanismes sont cruciaux pour le développement de la VC, ils représentent finalement deux cibles thérapeutiques pour la régression de la VC. Notre objectif principal était d'identifier de nouvelles molécules naturelles ou synthétisées chimiquement pouvant inhiber la VC. Nous avons démontré la capacité d'un acide oligogalacturonique spécifique (DP8), extrait de graines de lin, à inhiber la calcification induite par Pi in vitro et ex vivo en diminuant l'expression des marqueurs ostéogéniques, masquant une répétition consensus des acides aminés trouvée dans Col1 (séquence: GFOGER) , et empêchant ainsi les VE de se lier. Nous avons également synthétisé chimiquement un peptide GFOGER et vérifié sa capacité à inhiber la calcification. Semblable à DP8, le peptide GFOGER a été capable d'inhiber la calcification induite par Pi in vitro et ex vivo en régulant à la baisse l'expression des marqueurs ostéogéniques et en modifiant la teneur en protéines des EV dérivés des VSMC. Par conséquent, nos travaux suggèrent deux nouvelles approches thérapeutiques pour la prévention de la CV
Cardiovascular diseases (CVDs) are classified on top of the list among different death leading causes in the world. Calcification of the vessel wall leads to various critical cardiovascular consequences and accounts for high mortality rates in patients with many diseases like diabetes, atherosclerosis and chronic kidney disease (CKD). VC is an active process with features of bone physiology and it is regulated by multifactorial inductive and inhibitory processes. During the calcification process, Vascular Smooth Muscle Cells (VSMCs) undergo active osteogenic process to become osteoblast-like cells and release heterogeneous populations of Extracellular Vesicles (EVs). EVs act as nucleating foci for crystallization through their interaction with type 1 collagen (Col1) via integrins and their procalcifying protein content strongly supports calcification progression. Because these two mechanisms are crucial for the development of VC, they eventually represent two therapeutic targets for VC regression. Our primary objective was to identify new natural or chemically synthesized molecules that can inhibit VC. We demonstrated the ability of a specific oligogalacturonic acid (DP8), extracted from flax seeds, to inhibit in vitro and ex-vivo Pi-induced calcification by diminishing osteogenic markers expression, masking a consensus amino acid repeat found in Col1 (sequence: GFOGER), and thus preventing EVs from binding. Also we chemically synthesized a GFOGER peptide and checked its ability to inhibit calcification. Similar to DP8, GFOGER peptide was able to inhibit in vitro and ex-vivo Pi-induced calcification by downregulating osteogenic markers expression and through modifying the protein content of VSMCs derived EVs. Therefore, our work suggests two novel therapeutic approaches for the prevention of VC