期刊名称：Proceedings of the National Academy of Sciences
印刷版ISSN：0027-8424
电子版ISSN：1091-6490
出版年度：2021
卷号：118
期号：37
DOI：10.1073/pnas.2105004118
语种：English
出版社：The National Academy of Sciences of the United States of America
摘要：Significance
Platelet activation induces reorganization of the cell and the formation of cellular protrusions, pseudopodia. These processes are accompanied by remodeling of the actin cytoskeleton and the activation of platelet integrins, which mediate strong adhesion to the extracellular matrix. In this work, we analyzed the actin polarity and integrin architecture in pseudopodia. A nonuniform polarity of actin filaments in pseudopodia indicates that these protrusions may be involved in contractile acto-myosin forces. Heterogeneity in integrin conformation was found, while solely a bent integrin structure was resolved, ∼50 to 70 nm above the support.
During activation the platelet cytoskeleton is reorganized, inducing adhesion to the extracellular matrix and cell spreading. These processes are critical for wound healing and clot formation. Initially, this task relies on the formation of strong cellular–extracellular matrix interactions, exposed in subendothelial lesions. Despite the medical relevance of these processes, there is a lack of high-resolution structural information on the platelet cytoskeleton controlling cell spreading and adhesion. Here, we present in situ structural analysis of membrane receptors and the underlying cytoskeleton in platelet protrusions by applying cryoelectron tomography to intact platelets. We utilized three-dimensional averaging procedures to study receptors at the plasma membrane. Analysis of substrate interaction-free receptors yielded one main structural class resolved to 26 Å, resembling the α
IIbβ
3 integrin folded conformation. Furthermore, structural analysis of the actin network in pseudopodia indicates a nonuniform polarity of filaments. This organization would allow generation of the contractile forces required for integrin-mediated cell adhesion.
