The first view of the physical mechanism of how a blood clot contracts at the level of individual platelets is giving researchers from the Perelman School of Medicine at the University of Pennsylvania a new look at a natural process that is part of blood clotting. A team led by John W. Weisel, PhD, a professor of Cell and Developmental Biology, describes in Nature Communications how specialized proteins in platelets cause clots to shrink in size.

To learn how a clot contracts, the Penn team imaged clots (networks of fibrin fibers and blood platelets) using an imaging technique called confocal light microscopy. The natural process of clot contraction is necessary for the body to effectively stem bleeding, reduce the size of otherwise obstructive clots, and promote wound healing.

The physical mechanism of platelet-driven clot contraction they observed is already informing new ways to think about diagnosing and treating conditions such as ischemic stroke, deep vein thrombosis, and heart attacks. In all of these conditions, clots are located where they should not be and block blood flow to critical parts of the body. Evidence from a study published earlier this year from the Weisel lab suggests that platelets in people with these diseases are less effective at clot contraction, thereby contributing to clots being more obstructive.

“Under normal circumstances, blood clot contraction plays an important role in preventing bleeding by making a better seal, since the cells become tightly packed as the spaces between them are eliminated,” Weisel said. “In this study, we unwrapped and quantified clot contraction in single platelets.” The team quantified the structural details of how contracting platelets cause clots to shrink, accompanied by dramatic structural alterations of the platelet-fibrin meshwork.

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