The platelet receptor for von Willebrand factor (VWF), the glycoprotein (GP) Ib-IX-V complex (GPIb-IX), is vital for initial platelet adhesion to injured blood vessel wall, especially under shear stress. VWF binding to GPIb-IX also initiates signaling resulting in the activation of the platelet integrin aIIbb3, which mediates stable platelet adhesio, platelet aggregation, and thrombus formation. In the current funding periods, we have made significant progress in understanding the signaling mechanisms that regulates the receptor function of GPIb and VWF-induced GPIb signaling leading to platelet activation. In particular, we have demonstrated an important role for Rac1 in mediating VWF/GPIb-IX-mediated early signaling. We also demonstrated an unexpected role of a potential downstream Rac1 effector, LIM kinase 1 (LIMK1) in selectively stimulating GPIb- IX-dependent thromboxane (TX) A2 synthesis and signal amplification. GPIb-IX also interacts with thrombin, and is important in low dose thrombin-induced platelet activation. However, it is unclear whether GPIb-IX serves facilitate more efficient thrombin cleavage of protease-activated receptors (PAR), or GPIb signaling promote thrombin-induced platelet activation. Based on our preliminary data, we hypothesize that the Rac1- and LIMK1-mediated GPIb-IX signaling pathways promotes PAR-dependent platelet response to low dose thrombin.
In Aim 1 of this competitive renewal application, we will investigate the role of GPIb-IX signaling in promoting thrombin-induced platelet activation and the Rac1 and LIMK1 signaling pathways that mediates VWF- and thrombin-induced GPIb-IX signaling. Activated platelets play an important role in facilitating coagulation, mainly by providing externalized phosphotidylserine (PS). However, under currently accepted assay conditions, even extremely high concentrations of physiological platelet agonists collagen and thrombin only induce a small fraction of platelets to externalize PS, the reason for this paradox remains unclear. We show that under the shear force relevant to normal blood flow, platelets do not express procoagulant activity (although the extremely high shear stress may induce platelet procoagulant MP release that requires GPIb-IX- VWF interaction). However, physiological levels of shear stress are required for agonists to efficiently induce PS externalization and MP release from platelets. Importantly, we discovered that Rac1 plays a critical role in shear-dependent platelet PS externalization and MP release induced by GPIb-independent platelet agonists. Thus, we hypothesize that activation of platelet procoagulant function requires shear force-induced signaling in which Rac1 plays an important role. Therefore, in Aim 2, we will investigate the role of shear force, Rac1 and GPIb-IX signaling in the activation of platelet procoagulant function. These study should facilitate our understanding how low concentrations of agonists thrombin or initial platelet adhesion will elicit strong platele response leading to not only platelet thrombus formation but also clotting at the site of vascular injury, and help develop new inhibitor for treating thrombotic diseases.

Public Health Relevance

A receptor molecule on the surface of blood platelets, named glycoprotein Ib-IX (GPIb- IX), mediates adhesion of blood platelets to blood vessel wall, and is important in preventing excessive bleeding when blood vessels are injured. This molecule is also important in thrombosis that is clotting in the blood vessels causing heart attack and stroke. This research project is to study how glycoprotein Ib-IX initiates platelet adhesion and clotting. We will also investigate how this molecule transmit signal to the inside of platelets t stimulate platelet in the formation of clots when blood vessels are injured, and how platelets participates in the clotting by releasing small membrane vesicles that facilitates clotting in bloo flow. The findings of this study will be useful in developing anti-clotting agents in in treating hart attack, stroke and sepsis etc.

Agency
National Institute of Health (NIH)
Type
Research Project (R01)
Project #
2R01HL062350-14
Application #
8786806
Study Section
Special Emphasis Panel (ZRG1)
Program Officer
Kindzelski, Andrei L
Project Start
Project End
Budget Start
Budget End
Support Year
14
Fiscal Year
2014
Total Cost
Indirect Cost
Name
University of Illinois at Chicago
Department
Pharmacology
Type
Schools of Medicine
DUNS #
City
Chicago
State
IL
Country
United States
Zip Code
60612
Li, Jing; Kim, Kyungho; Hahm, Eunsil et al. (2014) Neutrophil AKT2 regulates heterotypic cell-cell interactions during vascular inflammation. J Clin Invest 124:1483-96
Rusu, Luiza; Andreeva, Alexandra; Visintine, David J et al. (2014) G protein-dependent basal and evoked endothelial cell vWF secretion. Blood 123:442-50
Yin, Hong; Stojanovic-Terpo, Aleksandra; Xu, Weidong et al. (2013) Role for platelet glycoprotein Ib-IX and effects of its inhibition in endotoxemia-induced thrombosis, thrombocytopenia, and mortality. Arterioscler Thromb Vasc Biol 33:2529-37
Shen, Bo; Zhao, Xiaojuan; O'Brien, Kelly A et al. (2013) A directional switch of integrin signalling and a new anti-thrombotic strategy. Nature 503:131-5
Estevez, Brian; Stojanovic-Terpo, Aleksandra; Delaney, M Keegan et al. (2013) LIM kinase-1 selectively promotes glycoprotein Ib-IX-mediated TXA2 synthesis, platelet activation, and thrombosis. Blood 121:4586-94
O'Brien, Kelly A; Stojanovic-Terpo, Aleksandra; Hay, Nissim et al. (2011) An important role for Akt3 in platelet activation and thrombosis. Blood 118:4215-23
Zhang, Guoying; Xiang, Binggang; Dong, Anping et al. (2011) Biphasic roles for soluble guanylyl cyclase (sGC) in platelet activation. Blood 118:3670-9
Li, Zhenyu; Delaney, M Keegan; O'Brien, Kelly A et al. (2010) Signaling during platelet adhesion and activation. Arterioscler Thromb Vasc Biol 30:2341-9
Gong, Haixia; Shen, Bo; Flevaris, Panagiotis et al. (2010) G protein subunit Galpha13 binds to integrin alphaIIbbeta3 and mediates integrin "outside-in" signaling. Science 327:340-3
Li, Zhenyu; Zhang, Guoying; Liu, Junling et al. (2010) An important role of the SRC family kinase Lyn in stimulating platelet granule secretion. J Biol Chem 285:12559-70

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