Sphingosine-1-phosphate regulates platelet fibrinogen binding via sphingosine-1-phosphate receptor type 4

Sphingosine-1-phosphate (S1P) is a bioactive signaling sphingolipid secreted by platelets during activation. Platelets express distinct S1P receptors on their surface, and a comprehensive understanding of their effects is yet to be achieved.

Here, we describe the regulation of fibrinogen binding in activated platelets via S1P receptor type 4 (S1PR₄).

Thrombus formation and platelet function on an S1PR4-deficient (S1pr₄^-/-) background were assessed in an ex vivo flow chamber setting and by rotational thromboelastometry. In vivo coagulation was studied in a murine model of polymicrobial abdominal sepsis. Fibrinogen binding was assessed by flow cytometry in the murine and human systems.

In the colon ascendens stent peritonitis model, an increased incidence of disseminated intravascular coagulation was observed in S1pr₄^-/- mice. Murine platelets from S1pr₄^-/- mice showed excessive fibrinogen binding and disorganized thrombus formation compared with wild-type platelets. Rotational thromboelastometry confirmed these results, showing a reduced clotting time and an increased clot size in S1pr₄^-/- mice. Flow cytometry analysis of glycoprotein IIb/IIIa expression indicated an increased low-to-high-affinity switch for increased fibrinogen binding in S1pr₄^-/- platelets. Analysis of human platelets using a specific antagonist showed that S1PR₄ signaling impacted fibrinogen binding.

These findings strongly suggest that S1P signaling via S1PR₄ acts as a negative regulator of fibrinogen binding in activated platelets.