OC 16.3 - Differential Modulation of Platelet Adhesion and Aggregation by von Willebrand Factor as a New Therapeutic Strategy against Arterial Thrombosis

Sunday, June 25, 2023

11:15 – 11:30 ET

Room: 510

Session Available As: On-Demand

Presenting Author(s)

Yunfeng Chen, PhD

Assistant Professor
The University of Texas Medical Branch
Galveston, Texas, United States

Co-Author(s)

BS

Brian Savage

Staff Scientist
The Scripps Research Institute
La Jolla, California, United States
JR

James Roberts

Research Assistant
The Scripps Research Institute
La Jolla, California, United States
JO

Jennifer Orje

Research Technician
The Scripps Research Institute
La Jolla, California, United States
SK

Sachiko Kanaji

Staff Scientist
The Scripps Research Institute
La Jolla, California, United States
TK

Taisuke Kanaji

Institute Investigator
The Scripps Research Institute
La Jolla, California, United States
AZ

Alessandro Zarpellon

Research Associate
The Scripps Research Institute
La Jolla, California, United States
ZR

Zaverio Ruggeri

Professor
The Scripps Research Institute
La Jolla, California, United States

Background: Platelets bind to surface immobilized von Willebrand factor (VWF) for adhesion, and interact with soluble VWF to achieve aggregation, both contributing to arterial thrombosis. However, how VWF functions in different forms are regulated is unclear.

Aims: We aim to understand whether different VWF forms bind to platelets differentially, and how they respectively regulate hemostasis and thrombosis.

Methods: Surface plasmon resonance and force spectroscopy were respectively used to measure the binding kinetics of soluble and immobilized VWF. Platelet aggregation and adhesion under shear flow were assessed using a flow chamber assay. FeCl3-induced thrombosis assay and tail bleeding assay were performed to evaluate thrombosis and hemostasis in vivo.

Results: Guided by biophysical principles, we created a mutation R636/K642/643A in VWF A1 domain (M13) (Fig. 1A), which reduced the binding of soluble VWF but enhanced that of immobilized VWF (Fig. 1B, 3D vs. 2D affinity). Correspondingly, M13 VWF was deficient in mediating shear-induced platelet aggregation (Fig. 1C), but became stronger in supporting platelet adhesion (Fig. 1D). An VWF antibody named NMC4 was found to partially mirror M13's effects, which eliminated the formation of large platelet aggregates in shear flow while maintaining a considerable level of platelet adhesion at low doses (Fig. 1E,F). By testing NMC4 in mice expressing human GPIbα and VWFA1, we showed that NMC4 also had a stronger inhibitory effect on arterial thrombosis than on hemostasis, preventing arterial occlusion without causing excessive bleeding under the dose range of 0.625-1.25 µg per 25 g animal weight (Fig. 1G,H).

Conclusion(s): Our results indicated that soluble VWF primarily mediates platelet aggregation while immobilized VWF primarily mediates platelet adhesion, which are respectively more important to arterial thrombosis and hemostasis. Therefore, selectively inhibiting soluble VWF-platelet binding may prevent arterial occlusion without compromising hemostasis, which should serve as a novel strategy to treat arterial thrombosis safely and effectively.

Learning Objectives:

Differentiate VWF functions in mediating platelet adhesion and platelet aggregation.
Articulate the principle of how to design VWFA1 mutations to selectively inhibit its function in mediating platelet aggregation but not its function in mediating platelet adhesion.
Develop an understanding that selectively inhibiting platelet aggregation but not platelet adhesion might be a novel startegy to safely and effectively prevent arterial thrombosis.