The heptapeptide LSARLAF mediates platelet activation through phospholipase Cgamma2 independently of glycoprotein IIb-IIIa

Identification of key genes and immune infiltration in peripheral blood biomarker analysis of delayed cerebral ischemia: Valproic acid as a potential therapeutic drug

BACKGROUND

Delayed cerebral ischemia (DCI) is a common and serious complication of subarachnoid hemorrhage (SAH). Its pathogenesis is not fully understood. Here, we developed a predictive model based on peripheral blood biomarkers and validated the model using several bioinformatic multi-analysis methods.

METHODS

Six datasets were obtained from the GEO database. Characteristic genes were screened using weighted correlation network analysis (WGCNA) and differentially expressed genes. Three machine learning algorithms, elastic networks-LASSO, support vector machines (SVM-RFE) and random forests (RF), were also used to construct diagnostic prediction models for key genes. To further evaluate the performance and predictive value of the diagnostic models, nomogram model were constructed, and the clinical value of the models was assessed using Decision Curve Analysis (DCA), Area Under the Check Curve (AUC), Clinical Impact Curve (CIC), and validated in the mouse single-cell RNA-seq dataset. Mendelian randomization(MR) analysis explored the causal relationship between SAH and stroke, and the intermediate influencing factors. We validated this by retrospectively analyzing the qPCR levels of the most relevant genes in SAH and SAH-DCI patients. This experiment demonstrated a statistically significant difference between SAH and SAH-DCI and normal group controls. Finally, potential small molecule compounds interacting with the selected features were screened from the Comparative Toxicogenomics Database (CTD).

RESULTS

The fGSEA results showed that activation of Toll-like receptor signaling and leukocyte transendothelial cell migration pathways were positively correlated with the DCI phenotype, whereas cytokine signaling pathways and natural killer cell-mediated cytotoxicity were negatively correlated. Consensus feature selection of DEG genes using WGCNA and three machine learning algorithms resulted in the identification of six genes (SPOCK2, TRRAP, CIB1, BCL11B, PDZD8 and LAT), which were used to predict DCI diagnosis with high accuracy. Three external datasets and the mouse single-cell dataset showed high accuracy of the diagnostic model, in addition to high performance and predictive value of the diagnostic model in DCA and CIC. MR analysis looked at stroke after SAH independent of SAH, but associated with multiple intermediate factors including Hypertensive diseases, Total triglycerides levels in medium HDL and Platelet count. qPCR confirmed that significant differences in DCI signature genes were observed between the SAH and SAH-DCI groups. Finally, valproic acid became a potential therapeutic agent for DCI based on the results of target prediction and molecular docking of the characterized genes.

CONCLUSION

This diagnostic model can identify SAH patients at high risk for DCI and may provide potential mechanisms and therapeutic targets for DCI. Valproic acid may be an important future drug for the treatment of DCI.

Interleukin-17 (IL-17) triggers systemic inflammation, peripheral vascular dysfunction, and related prothrombotic state in a mouse model of Alzheimer's disease

Alzheimer's disease (AD) is one of the most prevalent forms of neurodegenerative disorders. Previously, we have shown that in vivo administration of an IL-17 neutralizing antibody (IL-17Ab) rescues amyloid-β-induced neuro-inflammation and memory impairment, demonstrating the pivotal role of IL-17 in AD-derived cognitive deficit. Recently, AD has been recognized as a more intriguing pathology affecting vascular networks and platelet function. However, not much is known about peripheral vascular inflammation and how pro-inflammatory circulating cells/mediators could affect peripheral vessels' function. This study aimed to evaluate whether IL-17Ab treatment could also impact peripheral AD features, such as systemic inflammation, peripheral vascular dysfunction, and related pro-thrombotic state in a non-genetic mouse model of AD. Mice were injected intracerebroventricularly with Aβ_1-42 peptide (3 μg/3 μl). To evaluate the systemic/peripheral protective profile of IL-17Ab, we used an intranasal administration of IL-17Ab (1 μg/10 μl) at 5, 12, and 19 days after Aβ_1-42 injection. Circulating Th17/Treg cells and related cyto-chemokines, haematological parameters, vascular/endothelial reactivity, platelets and coagulation function in mice were evaluated. IL-17Ab treatment ameliorates the systemic/peripheral inflammation, immunological perturbance, vascular/endothelial impairment and pro-thrombotic state, suggesting a key role for this cytokine in fostering inflammatory processes that characterize the multifaced aspects of AD.

Disulfide Bonds as Regulators of Integrin Function in Thrombosis and Hemostasis

SIGNIFICANCE

Disulfide bonds are generally viewed as structure-stabilizing elements in proteins, but some display an alternative functional role as redox switches. Functional disulfide bonds have recently emerged as important regulators of integrin function in thrombosis and hemostasis.

RECENT ADVANCES

Functional disulfide bonds were identified in the β subunit of the major platelet integrin αIIbβ3 and in other integrins involved in thrombus formation that is, αvβ3 and α2β1. Most of these functional bonds are located in the four epidermal growth factor-like domains of the integrins. Redox agents such as glutathione and nitric oxide and enzymatic thiol isomerase activity were shown to regulate the function of these integrins by disulfide bond reduction and thiol/disulfide exchange.

CRITICAL ISSUES

Increasing evidence suggests that thiol isomerases such as protein disulfide isomerase (PDI) and Erp57 directly bind to the β3 subunit of αIIbβ3 and αvβ3 and regulate their function during thrombus formation. αIIbβ3 also exhibits an endogenous thiol isomerase activity. The specific functional disulfide bonds identified in the β3 subunit might be the targets for both exogenous and endogenous thiol isomerase activity.

FUTURE DIRECTIONS

Targeting redox sites of integrins or redox agents and enzymes that regulate their function can provide a useful tool for development of anti-thrombotic therapy. Hence, inhibitors of PDI are currently studied for this purpose.

Inhibition of αIIbβ3 Ligand Binding by an αIIb Peptide that Clasps the Hybrid Domain to the βI Domain of β3

Agonist-stimulated platelet activation triggers conformational changes of integrin αIIbβ3, allowing fibrinogen binding and platelet aggregation. We have previously shown that an octapeptide, ^p1YMESRADR⁸, corresponding to amino acids 313–320 of the β-ribbon extending from the β-propeller domain of αIIb, acts as a potent inhibitor of platelet aggregation. Here we have performed in silico modelling analysis of the interaction of this peptide with αIIbβ3 in its bent and closed (not swing-out) conformation and show that the peptide is able to act as a substitute for the β-ribbon by forming a clasp restraining the β3 hybrid and βI domains in a closed conformation. The involvement of species-specific residues of the β3 hybrid domain (E356 and K384) and the β1 domain (E297) as well as an intrapeptide bond (^pE315-^pR317) were confirmed as important for this interaction by mutagenesis studies of αIIbβ3 expressed in CHO cells and native or substituted peptide inhibitory studies on platelet functions. Furthermore, NMR data corroborate the above results. Our findings provide insight into the important functional role of the αIIb β-ribbon in preventing integrin αIIbβ3 head piece opening, and highlight a potential new therapeutic approach to prevent integrin ligand binding.

Activation of glycoprotein VI (GPVI) and C-type lectin-like receptor-2 (CLEC-2) underlies platelet activation by diesel exhaust particles and other charged/hydrophobic ligands

Platelets are activated by a range of stimuli that share little or no resemblance in structure to each other or to recognized ligands, including diesel exhaust particles (DEP), small peptides [4N1-1, Champs (computed helical anti-membrane proteins), LSARLAF (Leu-Ser-Ala-Arg-Leu-Ala-Phe)], proteins (histones) and large polysaccharides (fucoidan, dextran sulfate). This miscellaneous group stimulate aggregation of human and mouse platelets through the glycoprotein VI (GPVI)-FcR γ-chain complex and/or C-type lectin-like receptor-2 (CLEC-2) as shown using platelets from mice deficient in either or both of these receptors. In addition, all of these ligands stimulate tyrosine phosphorylation in GPVI/CLEC-2-double-deficient platelets, indicating that they bind to additional surface receptors, although only in the case of dextran sulfate does this lead to activation. DEP, fucoidan and dextran sulfate, but not the other agonists, activate GPVI and CLEC-2 in transfected cell lines as shown using a sensitive reporter assay confirming a direct interaction with the two receptors. We conclude that this miscellaneous group of ligands bind to multiple proteins on the cell surface including GPVI and/or CLEC-2, inducing activation. These results have pathophysiological significance in a variety of conditions that involve exposure to activating charged/hydrophobic agents.

Peptide LSARLAF induces integrin β3 dependent outside-in signaling in platelets

INTRODUCTION

Peptide LSARLAF (LSA) can bind and activate integrin αIIbβ3 in the absence of 'inside-out' signal. The active αIIbβ3 mediates 'outside-in' signaling that elicits platelet aggregation, granule secretion and TxA2 production. Here we identify the membrane glycoproteins which mediate LSA-induced platelet activation other than αIIbβ3, and determine the roles of Src, PLCγ2, FcRγ-chain, and SLP-76 in LSA-induced platelet activation.

METHOD

Ligand-receptor binding assay was performed to study the effect of peptide LSA or its control peptide FRALASL (FRA) on integrins binding to their ligands. Spreading of CHO cells expressing αIIbβ3 or αVβ3 on immobilized fibrinogen was measured in the presence of LSA or FRA. Washed β3, Src, FcRγ-chain, LAT and SLP-76 deficient platelets aggregation and secretion were tested in response to LSA.

RESULTS

Ligand-receptor binding assay indicated that LSA promoted the binding of multiple ligands to αIIbβ3 or αVβ3. LSA also enhanced CHO cells with αIIbβ3 or αVβ3 expression spreading on immobilized fibrinogen. β3 deficient platelets failed to aggregate and secrete in response to LSA. The phosphorylation of PLCγ2 and Syk was also β3 dependent. Src, FcRγ-chain, LAT and SLP-76 deficient platelets did not aggregate, secrete ATP or produce TxA2 in response to LSA.

CONCLUSION

LSA-induced platelet activation is β3 dependent, and signaling molecules Src, FcRγ-chain, SLP-76 and LAT play crucial roles in LSA-induced β3 mediated signaling.

Molecular basis of platelet activation by an alphaIIbbeta3-CHAMPS peptide

BACKGROUND

A novel method, known as computed helical anti-membrane protein (CHAMP), for the design of peptides that bind with high affinity and selectivity to transmembrane helices was recently described and illustrated using peptides that bind alphaIIb- and alphav-integrin subunits, which induce selective activation of integrins alphaIIbbeta3 and alphavbeta3, respectively.

OBJECTIVES

In the present study, we have investigated the ability of an alphaIIb-CHAMPS peptide (termed integrin-activatory-peptide or IAP) to stimulate protein tyrosine phosphorylation and aggregation in human and mouse platelets.

METHODS

The ability of IAP to stimulate platelet aggregation and dense granule secretion was measured in washed preparations of human and mouse platelets. Samples were taken for measurement of tyrosine phosphorylation.

RESULTS

IAP stimulates robust tyrosine phosphorylation of the tyrosine kinase Syk and the FcR gamma-chain, but only weak phosphorylation of PLCgamma2. Aggregation to low but not high concentrations of IAP is reduced in the presence of the Src kinase inhibitor, PP1, or by inhibitors of the two feedback agonists, ADP and thromboxane A(2) (TxA(2)) suggesting that activation is reinforced by Src kinase-driven release of ADP and TxA(2). Unexpectedly, aggregation by IAP is only partially inhibited in human and mouse platelets deficient in integrin alphaIIbbeta3. Further, IAP induces partial aggregation of formaldehyde-fixed platelets.

CONCLUSIONS

The present study demonstrates that the alphaIIb-CHAMPS peptide induces platelet activation through integrin alphaIIbbeta3-dependent and independent pathways with the former mediating tyrosine phosphorylation of FcR gamma-chain and Syk. The use of the alphaIIb-CHAMPS peptide to study integrin alphaIIbbeta3 function is compromised by non-integrin-mediated effects.

MyosinIIa contractility is required for maintenance of platelet structure during spreading on collagen and contributes to thrombus stability

BACKGROUND

MyosinIIs are adenosine triphosphate-driven molecular motors that form part of a cell's contractile machinery. They are activated by phosphorylation of their light chains, by either activation of myosin light chain (MLC) kinase or inhibition of MLC phosphatase via Rho kinase (ROCK). MyosinIIa phosphorylation underlies platelet rounding and stress fiber formation.

OBJECTIVE

To identify the functional significance of myosinIIa in platelet spreading and thrombus formation on collagen using inhibitors of ROCK (Y27632) and myosinII (blebbistatin).

RESULTS

Stress fiber formation on collagen is inhibited by both Y27632 and blebbistatin. A substantial proportion of spread platelets generate internal holes or splits on collagen, presumably because of a reduction in contractile strength. Platelet integrity, however, is maintained. In an in vitro model, thrombus embolization on collagen is increased in the presence of Y27632 and blebbistatin at intermediate shear, leading to a reduction in platelet aggregate growth. Moreover, Y27632 causes a marked reduction in thrombus formation in an in vivo laser-injury model.

CONCLUSIONS

MyosinIIa contractility is required for maintenance of platelet structure during spreading on collagen and contributes to thrombus stability.

Platelet receptor recognition and cross-talk in collagen-induced activation of platelets

Comprehensive mapping of protein-binding sites within human collagen III has allowed the recognition motifs for integrin alpha(2)beta(1) and VWF A3 domain to be identified. Glycoprotein VI-binding sites are understood, although less well defined. This information, together with recent developments in understanding collagen fiber architecture, and crystal structures of the receptor collagen-binding domains, allows a coherent model for the interaction of collagen with the platelet surface to be developed. This complements our understanding of the orchestration of receptor presentation by membrane microdomains, such that the polyvalent collagen surface may stabilize signaling complexes within the heterogeneous receptor composition of the lipid raft. The ensuing interactions lead to the convergence of signals from each of the adhesive receptors, mediated by FcR gamma-chain and/or FcgammaRIIa, leading to concerted and co-operative platelet activation. Each receptor has a shear-dependent role, VWF/GpIb essential at high shear, and alpha(2)beta(1) at low and intermediate shear, whilst GpVI provides core signals that contribute to enhanced integrin affinity, tighter binding to collagen and consequent platelet activation.

Vav family proteins are required for optimal regulation of PLCgamma2 by integrin alphaIIbbeta3

Vav proteins belong to the family of guanine-nucleotide-exchange factors for the Rho/Rac family of small G-proteins. In addition, they serve as important adapter proteins for the activation of PLCgamma (phospholipase Cgamma) isoforms by ITAM (immunoreceptor tyrosine-based activation motif) receptors, including the platelet collagen receptor GPVI (glycoprotein VI). Vav proteins are also regulated downstream of integrins, including the major platelet integrin alphaIIbbeta3, which has recently been shown to regulate PLCgamma2. In the present study, we have investigated the role of Vav family proteins in filopodia and lamellipodia formation on fibrinogen using platelets deficient in Vav1 and Vav3. Wild-type mouse platelets undergo a limited degree of spreading on fibrinogen, characterized by the formation of numerous filopodia and limited lamellipodia structures. Platelets deficient in Vav1 and Vav3 exhibit reduced filopodia and lamellipodia formation during spreading on fibrinogen. This is accompanied by reduced alphaIIbbeta3-mediated PLCgamma2 tyrosine phosphorylation and reduced Ca(2+) mobilization. In contrast, the G-protein agonist thrombin stimulates full spreading of control and Vav1/3-deficient platelets. Consistent with this, stimulation of F-actin (filamentous actin) formation and Rac activation by thrombin is not altered in Vav-deficient cells. These results demonstrate that Vav1 and Vav3 are required for optimal spreading and regulation of PLCgamma2 by integrin alphaIIbbeta3, but that their requirement is by-passed upon G-protein receptor activation.

Lipid rafts are required in Galpha(i) signaling downstream of the P2Y12 receptor during ADP-mediated platelet activation

ADP is important in propagating hemostasis upon its secretion from activated platelets in response to other agonists. Lipid rafts are microdomains within the plasma membrane that are rich in cholesterol and sphingolipids, and have been implicated in the stimulatory mechanisms of platelet agonists. We sought to determine the importance of lipid rafts in ADP-mediated platelet activation via the G protein-coupled P2Y1 and P2Y12 receptors using lipid raft disruption by cholesterol depletion with methyl-beta-cyclodextrin. Stimulation of cholesterol-depleted platelets with ADP resulted in a reduction in the extent of aggregation but no difference in the extent of shape change or intracellular calcium release. Furthermore, repletion of cholesterol to previously depleted membranes restored ADP-mediated platelet aggregation. In addition, P2Y12-mediated inhibition of cAMP formation was significantly decreased upon cholesterol depletion from platelets. Stimulation of cholesterol-depleted platelets with agonists that depend upon Galpha(i) activation for full activation displayed significant loss of aggregation and secretion, but showed restoration when simultaneously stimulated with the Galpha(z)-coupled agonist epinephrine. Finally, Galpha(i) preferentially localizes to lipid rafts as determined by sucrose density centrifugation. We conclude that Galpha(i) signaling downstream of P2Y12 activation, but not Galpha(q) or Galpha(z) signaling downstream of P2Y1 or alpha2A activation, respectively, has a requirement for lipid rafts that is necessary for its function in ADP-mediated platelet activation.