Prothrombinase components can accelerate tissue plasminogen activator-catalyzed plasminogen activation

Area of Science:

• Biochemistry
• Hemostasis and Thrombosis
• Molecular Biology

Background:

• Prothrombinase, comprising factor Xa (FXa) and factor Va (FVa), is central to the coagulation cascade.
• Tissue plasminogen activator (tPA) initiates fibrinolysis by activating plasminogen (Pg) to plasmin (Pn).
• The interplay between coagulation and fibrinolysis is crucial for hemostasis.

Purpose of the Study:

• To investigate the role of FXa and FVa as modulators of tPA-mediated Glu- and Lys-plasminogen activation.
• To elucidate the mechanisms and dependencies of FXa and FVa on plasminogen activation.
• To quantify the interactions between plasminogen and prothrombinase components.

Main Methods:

• Enzymatic assays were used to measure plasminogen activation by tPA in the presence of FXa and FVa.
• Surface plasmon resonance or similar techniques were employed to quantify binding affinities (Kd) between components.
• Experiments were conducted under varying conditions, including the presence of Ca2+, phospholipids, and plasmin-pretreated FVa.

Main Results:

• Both FXa and FVa significantly accelerated tPA activity, enhancing Lys-Pg activation up to 60-fold and Glu-Pg activation over 150-fold.
• FVa's cofactor activity required prior activation by plasmin, whereas FXa exhibited endogenous fibrinolytic cofactor activity.
• Plasminogen binding affinity to FVa increased significantly (approximately 100-fold) upon FVa pretreatment with plasmin.

Conclusions:

• FXa and FVa act as potent positive modulators of tPA-driven plasminogen activation, linking coagulation and fibrinolysis.
• The fibrinolytic cofactor activity of FVa is dependent on plasmin activation and Ca2+/phospholipid interactions.
• These findings suggest a mechanism for localized and coordinated plasmin generation at procoagulant surfaces.