Citrullinated fibrinogen forms densely packed clots with decreased permeability

Area of Science:

• Biochemistry
• Biophysics
• Hematology

Background:

• Fibrin forms the scaffold of thrombi and is citrullinated by peptidyl arginine deiminase 4 (PAD4).
• Citrullinated fibrinogen (citFg) is found in human plasma and murine thrombi, reducing clot lysability and mechanical resistance.

Purpose of the Study:

• To investigate how fibrinogen citrullination impacts the structural organization of fibrin clots.
• To elucidate the structural basis for altered mechanical properties and lysis resistance in citrullinated fibrin.

Main Methods:

• Fibrinogen was citrullinated using PAD4 and then clotted with thrombin.
• Structural analysis employed scanning electron microscopy (SEM), atomic force microscopy (AFM), laser scanning microscopy (LSM), and small-angle X-ray scattering (SAXS).
• Clot porosity was assessed via permeability measurements.

Main Results:

• SEM revealed decreased median fiber diameter with increasing citFg fraction; AFM showed unchanged fiber width/length ratio.
• SAXS and LSM indicated denser fibrin clots with increased fiber density.
• Permeability decreased over 3-fold, signifying significantly reduced porosity.
• SAXS confirmed largely preserved longitudinal fibrin monomer assembly periodicity.

Conclusions:

• Citrullinated fibrin clots exhibit thinner fibers, denser packing, and lower porosity.
• These structural alterations provide a framework for understanding the mechanical fragility and enhanced lysis resistance of citrullinated fibrin.
• The findings offer insights into the role of fibrin citrullination in thrombosis and hemostasis.