Mechanistic studies on human fibrinogen polymorphisms that influence blood clot formation and lysis

The blood clot is composed of a mesh of fibrin fibres with cellular elements embedded in this network. The structure of the fibrin clot can determine predisposition to atherothrombotic conditions, as compact clots composed of thin fibres and small pores are associated with premature and more severe cardiovascular disease. Both genetic and environmental effects can cause qualitative and quantitative changes in procoagulant and anti-fibrinolytic proteins, altering fibrin clot formation, structure and lysis. Three hypothesese were tested in this work: Firstly, the BβArg448Lys fibrinogen variant affects clot structural and functional properties in T2DM patients. Secondly, α2-AP is the protein responsible for the differences in lysis of recombinant BβArg448Lys fibrinogen variants in the plasma environment. And lastly, I proposed the AαTrp334Cys/Asn335Tyr changes in the Birmingham II patient are responsible for her clinical presentation. Accordingly, the aims of this work were to identify any additional effect of BβArg448Lys on fibrin network in type 2 diabetes, study the mechanisms behind the effects of the BβArg448Lys mutation on fibrin clot structural and functional properties, and finally, investigate the effect of fibrinogen AαTrp334Cys/Asn335Tyr on clot structure and lysis and abnormal patient phenotype. Compact clots with resistance to fibrinolysis were detected in carriers of Bβ448Lys variant of fibrinogen with diabetes. A direct role of the polymorphism in the changes observed with plasma clots was identified, and this may add to an already increased level of vascular risk in women with diabetes. In a recombinant system, differences in lysis between BβArg448Lys variants were attributable to the interplay between porosity of the clot, the fibrin-α2-AP interaction and plasmin generation. Finally, we confirm the AαTrp334Cys/Asn335Tryr substitutions in the fibrinogen BII patient are responsible for a clinical presentation of bleeding and thrombosis, providing mechanistic explanations for this patient phenotype. In summary, I extensively investigated the interplay between the fibrinogen molecule, fibrin clot structure, fibrinolysis and the environment and made a number of novel observations. Data generated has shed light on the mechanisms of increased thrombosis risk in patients with compact clots made of thin fibres, through genetic or environmental influence, which in turn will help to develop effective treatment strategies to reduce ischemic events in high risk patients.