Shear-induced fibronectin fibrillogenesis: Differential mechanisms under high and low shear stress conditions

Fibrillogenesis of plasma fibronectin (FN) can be triggered by shear stress, even in the absence of cells. While high shear stress is known to promote FN fibril formation, recent evidence suggests that low shear conditions also contribute to FN assembly. It is likely that distinct molecular mechanisms govern fibril formation under different flow regimes. In this study, we investigated FN fibril formation under high shear (2000-5000 s^-1) and low shear (50 s^-1) conditions which correspond to 7-17.5 Pa and 0.175 Pa, respectively. Morphological analysis showed that high shear rapidly induced thick, interconnected fibrils, whereas low shear led to the gradual formation of thin, sparse fibrils. Molecular dynamic simulations indicated that shear stress alone did not unfold FN in suspension; however, surface-adsorbed FN enabled shear-driven interaction with soluble FN. Under low shear, fibrillogenesis proceeded via slow FN accumulation and weak intermolecular binding, while high shear promoted strong domain-domain interactions. Molecular docking identified top-ranked trans-binding interfaces between FNI1-5 and FNIII1-3 regions, stabilized by salt bridges (e.g., Glu92-Arg694) and hydrogen bonds involving residues such as Lys149-Gly713 and Tyr265-Ser864. These interdomain interactions provide a structural basis for shear-induced fibril assembly.