Toward correlating structure and mechanics of platelets

Abstract

The primary physiological function of blood platelets is to seal vascular lesions after injury and form hemostatic thrombi in order to prevent blood loss. This task relies on the formation of strong cellular-extracellular matrix interactions in the subendothelial lesions. The cytoskeleton of a platelet is key to all of its functions: its ability to spread, adhere and contract. Despite the medical significance of platelets, there is still no high-resolution structural information of their cytoskeleton. Here, we discuss and present 3-dimensional (3D) structural analysis of intact platelets by using cryoelectron tomography (cryo-ET) and atomic force microscopy (AFM). Cryo-ET provides in situ structural analysis and AFM gives stiffness maps of the platelets. In the future, combining highresolution structural and mechanical techniques will bring new understanding of how structural changes modulate platelet stiffness during activation and adhesion.

Glycoprotein Ib clustering in platelets can be inhibited by α-linolenic acid as revealed by cryo-electron tomography

“…High resolution imaging of the GpIb receptors at the plasma membrane of intact platelets was conducted using cryo-electron tomography 27 (cryo-ET, Figure which is in agreement with the difference in abundance of the two receptors in platelets 28 .…”

Quantifying single‐platelet biomechanics: An outsider’s guide to biophysical methods and recent advances

“…Since the subcortical architecture of actin cytoskeleton influences elastic modulus of cells, the observed increased stiffness at platelet edges is a result of shorter, densely packed, and homogeneous distribution actin filaments . These observations were recently confirmed by Sorrentino et al, who investigated the mechanical stiffness of thrombin‐activated single platelets spreading on fibrinogen surface by force‐volume mapping by acquiring force‐distance curves in x‐y plane (Figure B‐D) revealing Young’s modulus of platelet granulomere to be 32 kPa, and the peripheral regions showed higher stiffness of ~224 kPa.…”

“…I G U R E 3 A, Schematic representation of a typical rectangular cantilever with a pyramidal sharp tip used for AFM and the equation for determination of cantilever spring constant k based on beam theory; C, 3D topography (height) and D, Young's modulus E of a single platelet spreading on fibrinogen passivated surface obtained by force-volume imaging by acquiring force-distance curves in x-y plane. (B, C, and D adapted and modified from Sorrentino et al44 ) E, Schematic diagram of single platelet force spectroscopy using flat cantilever to assess biomechanical forces generated during single platelet adhesion at the tip of the cantilever. Single platelet firmly adhering on the lower side of a collagen-coated tipless cantilever (fplatelet labeled with plasma membrane dye DiI and imaged with confocal florescence microscopy) lowered along the z-axis (Step 1) and allowed to approach and contact briefly with collagen coated substrate (Step 2) to facilitate adhesion.…”

Lipid rafts are essential for release of phosphatidylserine-exposing extracellular vesicles from platelets

“…The molecular mechanisms that control PS-exposing EV release in platelets are poorly understood, especially when considered in comparison to our detailed knowledge of other platelet effector processes, such as integrin α IIb β 3 activation or granule secretion 44 – 47 . A rise in [Ca 2+ ] i leads to calpain activation and cleavage of cytoskeletal proteins, such as talin 7 , 28 , 29 .…”