Glycoprotein VI/Fc receptor gamma chain-independent tyrosine phosphorylation and activation of murine platelets by collagen

Mechanism of platelet activation and potential therapeutic effects of natural drugs

BACKGROUND

Cardiovascular disease is one of the most concerning chronic diseases in the world. Many studies have shown that platelet overactivation is a very important factor in the occurrence and development of cardiovascular diseases. At present, the widely used antiplatelet drugs have some defects, such as drug resistance and adverse reactions.

PURPOSE

The purpose of this article is to summarize the main mechanisms and pathways of platelet activation, the main targets of antiplatelet aggregation, and the antiplatelet aggregation components of natural drugs and their mechanisms of action to provide new research ideas for the development and application of antiplatelet drugs.

STUDY DESIGN AND METHODS

In this review, we systematically searched the PubMed, Google Scholar, Web of Science, and CNKI databases and selected studies based on predefined eligibility criteria. We then assessed their quality and extracted data.

RESULTS

ADP, AA, THR, AF, collagen, SDF-1α, and Ca²⁺ can induce platelet aggregation and trigger thrombosis. Natural drugs have a good inhibitory effect on platelet activation. More than 50 kinds of natural drugs and over 120 kinds of chemical compounds, including flavonoids, alkaloids, saponins, terpenoids, coumarins, and organic acids, have significantly inhibited platelet activation activity. The MAPK pathway, cGMP-PKG pathway, cAMP-PKA pathway, PI3K-AKT pathway, PTK pathway, PLC pathway, and AA pathway are the main mechanisms and pathways of platelet activation.

CONCLUSION

Natural drugs and their active ingredients have shown good activity and application prospects in anti-platelet aggregation. We hope that this review provides new research ideas for the development and application of antiplatelet drugs.

Tyrosine-phosphorylation of the scaffold protein ADAP and its role in T cell signaling

INTRODUCTION

The Adhesion and Degranulation promoting Adaptor Protein (ADAP) is phosphorylated upon T cell activation and acts as a scaffold for the formation of a signaling complex that integrates molecular interactions between T cell or chemokine receptors, the actin cytoskeleton, and integrin-mediated cellular adhesion and migration.

AREAS COVERED

This article reviews current knowledge of the functions of the adapter protein ADAP in T cell signaling with a focus on the role of individual phosphotyrosine (pY) motifs for SH2 domain mediated interactions. The data presented was obtained from literature searches (PubMed) as well as the authors own research on the topic. Expert commentary: ADAP can be regarded as a paradigmatic example of how tyrosine phosphorylation sites serve as dynamic interaction hubs. Molecular crowding at unstructured and redundant sites (pY595, pY651) is contrasted by more specific interactions enabled by the three-dimensional environment of a particular phosphotyrosine motif (pY571).

A role for adhesion and degranulation-promoting adapter protein in collagen-induced platelet activation mediated via integrin α(2) β(1)

BACKGROUND

Collagen-induced platelet activation is a key step in the development of arterial thrombosis via its interaction with the receptors glycoprotein (GP)VI and integrin α(2) β(1) . Adhesion and degranulation-promoting adapter protein (ADAP) regulates α(IIb) β(3) in platelets and α(L) β(2) in T cells, and is phosphorylated in GPVI-deficient platelets activated by collagen.

OBJECTIVES

To determine whether ADAP plays a role in collagen-induced platelet activation and in the regulation and function of α(2) β(1).

METHODS

Using ADAP(-/-) mice and synthetic collagen peptides, we investigated the role of ADAP in platelet aggregation, adhesion, spreading, thromboxane synthesis, and tyrosine phosphorylation.

RESULTS AND CONCLUSIONS

Platelet aggregation and phosphorylation of phospholipase Cγ2 induced by collagen were attenuated in ADAP(-/-) platelets. However, aggregation and signaling induced by collagen-related peptide (CRP), a GPVI-selective agonist, were largely unaffected. Platelet adhesion to CRP was also unaffected by ADAP deficiency. Adhesion to the α(2) β(1) -selective ligand GFOGER and to a peptide (III-04), which supports adhesion that is dependent on both GPVI and α(2) β(1), was reduced in ADAP(-/-) platelets. An impedance-based label-free detection technique, which measures adhesion and spreading of platelets, indicated that, in the absence of ADAP, spreading on GFOGER was also reduced. This was confirmed with non-fluorescent differential-interference contrast microscopy, which revealed reduced filpodia formation in ADAP(-/-) platelets adherent to GFOGER. This indicates that ADAP plays a role in mediating platelet activation via the collagen-binding integrin α(2) β(1). In addition, we found that ADAP(-/-) mice, which are mildly thrombocytopenic, have enlarged spleens as compared with wild-type animals. This may reflect increased removal of platelets from the circulation.

Modulation of experimental autoimmune encephalomyelitis by VLA-2 blockade

Multiple sclerosis (MS) is an inflammatory demyelinating disease of the central nervous system (CNS). Adhesion molecules play important roles in cell-cell and cell-extracellular matrix (ECM) interactions in inflammation. Blocking the interaction between inflammatory cells and vascular endothelia can prevent cell entry into tissues and harmful inflammatory responses, that is, autoimmunity, but could also limit immunosurveillance by anti-viral T cells in sites of infection or latency. Development of progressive multifocal leukoencephalopathy in patients treated with antibody against very late antigen (VLA)-4 prompted us to explore an alternative therapeutic approach. We used an antibody against the integrin alpha2, VLA-2, that interacts with ECM, not vascular endothelium. SJL/J mice were sensitized with myelin proteolipid protein (PLP)(139-151) peptide to induce experimental autoimmune encephalomyelitis (EAE), an animal model for MS. Treatment of mice with VLA-2 antibody suppressed clinical signs and CNS inflammation of EAE, when antibody was given immediately after disease onset. In contrast, VLA-4 or VLA-2 antibody treatment of mice during the priming or remission phase of EAE had minor effects on the disease's clinical course. No differences were found in lymphoproliferative responses to PLP(139-151) among treatment groups. Data suggest that blocking cell-ECM interactions can be an alternative therapy for MS.

GPVI and integrin alphaIIb beta3 signaling in platelets

This review summarizes recent developments in our understanding of the molecular basis of platelet activation by two distinct types of surface receptor, the immunoglobulin GPVI, and the integrin alphaIIb beta3 (also known as GPIIbIIIa). These two classes of receptor signal through similar yet distinct tyrosine kinase-based signaling cascades leading to activation of phospholipase C gamma2. The significance of these signaling cascades in platelet adhesion and platelet aggregation at arterial rates of shear is discussed.

GPVI and alpha2beta1 play independent critical roles during platelet adhesion and aggregate formation to collagen under flow

The roles of the 2 major platelet-collagen receptors, glycoprotein VI (GPVI) and integrin alpha2beta1, have been intensely investigated using a variety of methods over the past decade. In the present study, we have used pharmacologic and genetic approaches to study human and mouse platelet adhesion to collagen under flow conditions. Our studies demonstrate that both GPVI and integrin alpha2beta1 play significant roles for platelet adhesion to collagen under flow and that the loss of both receptors completely ablates this response. Intracellular signaling mediated by the cytoplasmic adaptor Src homology 2 domain-containing leukocyte protein of 76 kDa (SLP-76) but not by the transmembrane adaptor linker for activation of T cells (LAT) is critical for platelet adhesion to collagen under flow. In addition, reduced GPVI receptor density results in severe defects in platelet adhesion to collagen under flow. Defective adhesion to collagen under flow is associated with prolonged tail-bleeding times in mice lacking one or both collagen receptors. These studies establish platelet-collagen responses under physiologic flow as the consequence of a close partnership between 2 structurally distinct receptors and suggest that both receptors play significant hemostatic roles in vivo.

Adhesion of human and mouse platelets to collagen under shear: a unifying model

There is presently confusion as to the roles of alpha2beta1 and GPVI in supporting platelet adhesion and aggregate formation on collagen at intermediate/high shear. Recent studies have reported essential, partial, or dispensable roles for either receptor in supporting these events, and the possibility that there may be fundamental differences between their roles in human and mouse platelets has been proposed. Further, the recent recognition that Src family tyrosine kinases contribute to signaling by alpha2beta1 and other adhesive receptors, in addition to GPVI, has added to this debate. The present study compares the roles of alpha2beta1, GPVI, and Src-dependent kinases in supporting adhesion and aggregation in human and mouse platelets in whole blood using blocking antibodies, mutant mice, and a novel inhibitor of Src kinases, PD0173952, which is effective in plasma. The results demonstrate that the fundamental processes of adhesion and aggregate formation are conserved in mice and human platelets and that two mechanisms of stable adhesion and activation on collagen exist. These can be distinguished by the contributions of GPVI and alpha2beta1, with GPVI-mediated platelet activation either preceding or following integrin-mediated adhesion. The relative contribution of each pathway depends on environmental conditions and may also reflect platelet heterogeneity. These observations form the basis of a unifying two-state model of platelet adhesion and aggregate formation on collagen that is conserved between human and mouse platelets.