Evidence that αC region is origin of low modulus, high extensibility, and strain stiffening in fibrin fibers

Fibrin clot structure and function: a role in the pathophysiology of arterial and venous thromboembolic diseases

The formation of fibrin clots that are relatively resistant to lysis represents the final step in blood coagulation. We discuss the genetic and environmental regulators of fibrin structure in relation to thrombotic disease. In addition, we discuss the implications of fibrin structure for treatment of thrombosis. Fibrin clots composed of compact, highly branched networks with thin fibers are resistant to lysis. Altered fibrin structure has consistently been reported in patients with several diseases complicated by thromboembolic events, including patients with acute or prior myocardial infarction, ischemic stroke, and venous thromboembolism. Relatives of patients with myocardial infarction or venous thromboembolism display similar fibrin abnormalities. Low-dose aspirin, statins, lowering of homocysteine, better diabetes control, smoking cessation, and suppression of inflammatory response increase clot permeability and susceptibility to lysis. Growing evidence indicates that abnormal fibrin properties represent a novel risk factor for arterial and venous thrombotic events, particularly of unknown etiology in young and middle-aged patients.

Protein unfolding accounts for the unusual mechanical behavior of fibrin networks

We describe the mechanical behavior of isotropic fibrin networks at the macroscopic scale in terms of the nanoscale force response of fibrin molecules that are its basic building blocks. We show that the remarkable extensibility and compressibility of fibrin networks have their origins in the unfolding of fibrin molecules. The force-stretch behavior of a single fibrin fiber is described using a two-state model in which the fiber has a linear force-stretch relation in the folded phase and behaves like a worm-like-chain in the unfolded phase. The nanoscale force-stretch response is connected to the macro-scale stress-stretch response by means of the eight-chain model. This model is able to capture the macroscopic response of a fibrin network in uniaxial tension and appears remarkably simple given the molecular complexity. We use the eight-chain model to explain why fibrin networks have negative compressibility and Poisson's ratio greater than 1 due to unfolding of fibrin molecules.

Molecular mechanisms affecting fibrin structure and stability

Fibrin structure and stability have been linked to many thrombotic diseases, including venous thromboembolism. Analysis of the molecular mechanisms that affect fibrin structure and stability became possible when the crystal structure of fibrinogen was solved. Biochemical studies of natural and recombinant variant fibrinogens have examined the interactions that mediate the conversion of soluble fibrinogen to the insoluble fibrin network. These studies identified intermolecular interactions that control fibrin structure, although some critical events remain ambiguous. Studies show that fibrin structure modulates the enzymatic lysis of the fibrin network, so the molecular mechanisms that control structure also control stability. Studies show that the mechanical stability of the fibrin clot depends on the properties of the fibrin monomer, leading investigators to explore the molecular basis of the monomer's mechanical properties. The work summarized here provides insights that might allow the development of pharmaceuticals and treatments to modulate fibrin structure and stability in vivo and thereby prevent or limit thrombotic disease.