Jiexi Liao

BME Ph.D. Thesis Defense

Date: 07/16/2020

Time: 11:00 AM ET

BlueJeans link: https://gatech.bluejeans.com/232841791

Meeting ID: 232 841 791

Thesis committee:

Cheng Zhu, PhD (Advisor)

Brian Petrich, PhD (Emory University)

Shaun Jackson, PhD (University of Sydney)

Shuichi Takayama, PhD

Manu Platt, PhD 

Title: Regulation of platelet integrin mechanobiology by talin 

Abstract: Platelets are reactive to mechanical forces in disturbed blood flow caused by vessel branching, stenosis, and interventional medical devices, leading to life-threatening clots composed of platelet aggregates. How forces drive platelet aggregation on the molecular level is incompletely understood. Integrins, particularly the platelet-specific αIIbβ3 (GPIIbIIIa), mediate the gradient shear-induced platelet aggregation not in their fully activated but intermediate state. Since integrins need the cytoplasmic adaptor molecule, talin, for activation and cytoskeletal linkage, elucidating talin’s role is critical to understand this process. 

Using stenosis-modeling microfluidics and mouse models that perturb specific interactions in the Rap-1-talin-integrin axis, we first demonstrated that talin indeed regulates platelet aggregation in disturbed flow and proposed the mechanism that aggregate buildup is achieved by membrane-recruited talin providing cytoskeletal linkage to the integrins. To gain mechanistic insights on the molecular level, we used single-cell force spectroscopy to characterize the two-dimensional kinetics of integrin-ligand binding with talin perturbations. We found that talin, a mechanosensor itself, is particularly important for force-mediated integrin binding without prior inside-out activation. The formation of catch bond (force prolonged bond lifetime) between the fibrinogen ligand and β3 integrin may be crucial for platelet aggregation in disturbed flow. Lastly, we extended the platelet mechanobiology study to investigate a disease that bears a pathology independent of cardiovascular aberration but is known to dysregulate platelets: diabetes. Using the stenosis microfluidics to screen patients’ blood, we preliminarily concluded that type I diabetes could amplify platelet aggregation by promoting more integrins to the intermediate state, but many other factors including racial heritage could cause large variance in patient samples’ responses.

Overall, we identified talin’s critical role in gradient shear-induced platelet aggregation. The biophysics studies offered a clearer understanding of how integrins finely tune their kinetics in response to mechanical cues. Our results showed anti-thrombotic potential of specific talin and Rap1 blockade and could inform design of novel therapeutics that address the mechanosensitivity of integrins.