The objective of this proposal is to elucidate the molecular and biophysical mechanisms that regulate platelet adhesion to disrupted vessel wall at sites of injury. The focus is the interaction of the platelet glycoprotein Ib (GPIb) with plasma protein von Willebrand factor (VWF) that is bound to collagen on subendothelial extracellular matrix. The GPIb-VWF interaction mediates the initial step of the multistep adhesion and signaling cascade, which includes platelet tethering to and rolling (or translocating) on disrupted vascular surfaces. Regulation of this initial adhesion process is crucial: Insufficient adhesion cannot stop bleeding to maintain hemostasis. Excessive adhesion results in thrombosis. Our hypothesis is that initial platelet adhesion is regulated by the interplay of biophysical parameters of the blood flow with specific kinetic and mechanical properties of the GPIb-VWF interaction. Mutations in GPIb and VWF, such as those naturally occurring in patients with various types of von Willebrand diseases (VWD), alter these kinetic and mechanical properties as well as their regulation by biophysical parameters, thereby changing platelet adhesion and resulting in thrombotic or bleeding disorders. Using combined experimental, computational, and theoretical approaches, this hypothesis will be tested in three integrated specific aims: 1) Quantify the regulation of GPIb-VWF interaction by biophysical parameters, 2) Determine the regulation of GPIb-VWF interaction by structural variations, and 3) Investigate GPIb-VWF interaction by molecular dynamics simulations. This integrated and systematic study will clarify how the kinetic and mechanical properties of GPIb-VWF interaction fulfill the biophysical requirements for platelets to adhere to blood vessel wall in the mechanically stressful environment of the circulation. Decoding how molecular structure determines these properties and their regulation by biophysical parameters will provide key insights into vascular physiology and pathology. As a result, the data may offer new therapeutic approaches to inhibiting pathological platelet adhesion during thrombosis and/or intervention to the bleeding disorder. We propose to elucidate the biophysical mechanisms that regulate the molecular interaction of the platelet glycoprotein Ib (GPIb) with protein von Willebrand factor, which mediates platelet adhesion to disrupted vessel wall at sites of injury. This regulation is crucial because insufficient adhesion cannot stop bleeding to maintain hemostasis but excessive adhesion results in thrombosis. The data may offer new therapeutic approaches to inhibiting pathological platelet adhesion during thrombosis and/or intervention to the bleeding disorder von Willebrand diseases.

National Institute of Health (NIH)
National Heart, Lung, and Blood Institute (NHLBI)
Research Project (R01)
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Modeling and Analysis of Biological Systems Study Section (MABS)
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Kindzelski, Andrei L
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Georgia Institute of Technology
Engineering (All Types)
Schools of Engineering
United States
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Liu, Baoyu; Chen, Wei; Zhu, Cheng (2015) Molecular force spectroscopy on cells. Annu Rev Phys Chem 66:427-51
Ju, Lining; Chen, Yunfeng; Zhou, Fangyuan et al. (2015) Von Willebrand factor-A1 domain binds platelet glycoprotein Ib? in multiple states with distinctive force-dependent dissociation kinetics. Thromb Res 136:606-12
Chen, Yunfeng; Liu, Baoyu; Ju, Lining et al. (2015) Fluorescence Biomembrane Force Probe: Concurrent Quantitation of Receptor-ligand Kinetics and Binding-induced Intracellular Signaling on a Single Cell. J Vis Exp :e52975
Ju, Lining; Lou, Jizhong; Chen, Yunfeng et al. (2015) Force-Induced Unfolding of Leucine-Rich Repeats of Glycoprotein Ib? Strengthens Ligand Interaction. Biophys J 109:1781-4
Zhu, Cheng (2014) Mechanochemitry: a molecular biomechanics view of mechanosensing. Ann Biomed Eng 42:388-404
Lee, Cho-yin; Lou, Jizhong; Wen, Kuo-kuang et al. (2013) Actin depolymerization under force is governed by lysine 113:glutamic acid 195-mediated catch-slip bonds. Proc Natl Acad Sci U S A 110:5022-7
Ju, Lining; Wang, Yijie Dylan; Hung, Ying et al. (2013) An HMM-based algorithm for evaluating rates of receptor-ligand binding kinetics from thermal fluctuation data. Bioinformatics 29:1511-8
Ju, Lining; Dong, Jing-fei; Cruz, Miguel A et al. (2013) The N-terminal flanking region of the A1 domain regulates the force-dependent binding of von Willebrand factor to platelet glycoprotein Ib?. J Biol Chem 288:32289-301
Zarnitsyna, Veronika I; Zhu, Cheng (2011) Adhesion frequency assay for in situ kinetics analysis of cross-junctional molecular interactions at the cell-cell interface. J Vis Exp :e3519
Coburn, L A; Damaraju, V S; Dozic, S et al. (2011) GPIbýý-vWF rolling under shear stress shows differences between type 2B and 2M von Willebrand disease. Biophys J 100:304-12

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