High shear dependent von Willebrand factor self-assembly fostered by platelet interaction and controlled by ADAMTS13

The paradigm of activation induced platelet aggregation has recently been refuted under blood flow conditions with shear rates exceeding 20,000s(-1). These lead to reversible rolling platelet aggregates, which were dependent on the presence of immobilized and soluble von Willebrand factor.

In vitro experiments using direct fluorescence video-microscopy were performed in wall parallel and stagnation point flow chambers with shear rates raised from 20,000 to 50,000s(-1). Washed blood cell suspension containing recombinant von Willebrand factor (rVWF) was perfused over rVWF or collagen coated surfaces.

Here we show for the first time with the visualization of rVWF that not only colloid and polymer, i.e. platelets and VWF, form a composite, but that VWF itself is capable of entirely reversible self-assembly. On a collagen surface the platelet-VWF-conglomerates did not roll but VWF nets bound permanently to the collagen fibers and captured and immobilized platelets from the flow. Lowering the shear rate below the threshold of 20,000s(-1) no longer dissolved these deposits. Ultralarge multimer containing rVWF was most effective compared to normal sized rVWF. The presence of ADAMTS13 limited rolling aggregate and platelet-VWF-conglomerate formation to a time window of 7-8minutes. Changing wall parallel flow to stagnation point flow halved the required shear rate threshold.

We conclude that flow dynamics can trigger reversible von Willebrand factor self-assembly and platelet-VWF-conglomerate accrual, which are regulated by ADAMTS13 to a time span needed by coagulation to stabilize it, e.g. in case of vessel injury.