Functional factor XIII-A is exposed on the stimulated platelet surface

Area of Science:

• Hematology
• Biochemistry
• Molecular Biology

Background:

• Factor XIII (FXIII) is crucial for stabilizing blood clots (thrombi) by cross-linking fibrin.
• Cellular FXIII (FXIII-A) is abundant in platelets, but its extracellular role is not well understood.
• Platelet activation and its role in hemostasis are complex processes.

Purpose of the Study:

• To investigate the extracellular function of platelet-derived FXIII-A.
• To determine if platelet FXIII-A contributes to thrombus stabilization against fibrinolysis.
• To elucidate the mechanism by which platelet FXIII-A exerts its antifibrinolytic effect.

Main Methods:

• Utilized Chandler model thrombi formed from FXIII-depleted plasma.
• Assessed thrombus stabilization using transglutaminase-dependent assays.
• Employed fluorescence confocal microscopy and flow cytometry to detect FXIII-A localization.
• Used neutralizing antibodies against α2-antiplasmin (α2AP) to probe functional dependence.

Main Results:

• Platelets stabilized FXIII-depleted thrombi in a transglutaminase-dependent manner.
• Platelet FXIII-A activity was found on activated platelet membranes and was α2AP-dependent.
• FXIII-A exposure on activated platelets increased with thrombin and collagen stimulation.
• Platelet FXIII-A demonstrated antifibrinolytic function by cross-linking α2AP to fibrin.

Conclusions:

• Platelet FXIII-A plays a significant antifibrinolytic role by being exposed on activated platelet membranes.
• This exposed FXIII-A stabilizes thrombi by cross-linking α2AP to fibrin, enhancing clot resistance to lysis.
• The findings reveal a novel extracellular function for platelet FXIII-A in hemostasis.