Fibrinogen αC-subregions critically contribute blood clot fibre growth, mechanical stability and resistance to fibrinolysis

Abstract

Fibrinogen is essential for blood coagulation. The C-terminus of the fibrinogen α-chain (αC-region) is composed of an αC-domain and αC-connector. Two recombinant fibrinogen variants (α390 and α220) were produced to investigate the role of subregions in modulating clot stability and resistance to lysis. The α390 variant, truncated before the αC-domain, produced clots with a denser structure and thinner fibres. In contrast, the α220 variant, truncated at the start of the αC-connector, produced clots that were porous with short stunted fibres and visible fibre ends. These clots were mechanically weak and susceptible to lysis. Our data demonstrate differential effects for the αC-subregions in fibrin polymerisation, clot mechanical strength, and fibrinolytic susceptibility. Furthermore, we demonstrate that the αC-subregions are key for promoting longitudinal fibre growth. Together, these findings highlight critical functions of the αC-subregions in relation to clot structure and stability, with future implications for development of novel therapeutics for thrombosis.

Why fibrin biomechanical properties matter for hemostasis and thrombosis

“…However, bulk measurements show that fibers are not completely straight but straightened by up to 25% shear strain of the whole clot, and fibers only start to align in the direction of stress above 25% shear strain. 54,57 Fibers appear less straight on electron microscopy images than confocal microscopy 29 and fibers appear less straight in uncrosslinked clots. 30 Strain stiffening is a typical behavior of filamentous biological polymers 58 and involves complex interplay of entropic and enthalpic elasticity: low strain mechanical behavior is dominated by entropic behavior, when thermal undulations are pulled out decreasing the degree of disorder, the entropy, 58 while enthalpic behavior dominates at high strains when the filament backbone is stretched leading to actual bonds being pulled, thus increasing enthalpy, the internal energy.…”

“…21 A recent study from our lab found that the absence of the αC-domain (α390 truncation) leads to thinner, highly branched fibers resulting in reduced clot firmness, whereas abolishing the complete αC-region including the globular domain and the connector region (α220 truncation) impairs longitudinal growth of protofibrils and results in clots with even lower firmness and a highly abnormal network structure with stunted fibers and a severely reduced resistance to fibrinolysis. 29 Thus, besides the kinetic effect on fibrin assembly and lateral aggregation, the αC-region has important roles in clot formation including longitudinal fibrin fiber growth and clot stability.…”