Platelets exploit fibrillar adhesions to assemble fibronectin matrix revealing new force-regulated thrombus remodeling mechanisms

Upon vascular injury, platelets are crucial for thrombus formation and contraction, but do they directly initiate early tissue repair processes? Using 3D super-resolution microscopy, micropost traction force microscopy, and specific integrin or myosin IIa inhibitors, we discovered here that platelets form fibrillar adhesions. They assemble fibronectin nanofibrils using αIIbβ3 (CD41/CD61, GPIIb-IIIa) rather than α5β1 integrins, in contrast to fibroblasts. Highly contractile platelets in contact with thrombus proteins (fibronectin, fibrin) pull fibronectin fibrils along their apical membrane, whereas platelets on basement membrane proteins (collagen IV, laminin) are less contractile generating less stretched planar meshworks beneath themselves. As probed by vinculin-decorated talin unfolding, platelets on fibronectin generate similar traction forces in apical fibrillar adhesions as fibroblasts do. These are novel mechanobiology mechanisms by which platelets spearhead the fibrillogenesis of the first ECM, including its 2D versus 3D network architectures depending on their ECM environment, and thereby pave the way for cell infiltration.