Selective triggering of platelet apoptosis, platelet activation or both

Anucleate platelets perform two fundamental processes, activation and apoptosis. We elaborated an approach for selective and concurrent stimulation of platelet apoptosis and/or activation, processes important in haemostasis and platelet clearance. Human platelets were treated with BH3 mimetic ABT-737, thrombin, calcium ionophore A23187 and matched diluents. Apoptosis was determined as mitochondrial inner membrane potential (m) depolarization and activation as P-selectin exposure. At optimal treatment conditions (90180min, 37 degrees C), ABT-737 predominantly induced apoptosis, when 7781% platelets undergo only m depolarization. The ABT-737 impact on m depolarization is strongly time- and temperature-dependent, and much higher at 37 degrees C than at room temperature. In contrast, when platelets were treated with thrombin for 1590min at either temperature, activation-only was predominantly (7985%) induced, whereas A23187 triggers both apoptosis and activation (7381%) when platelets were treated for 1560min at 37 degrees C or 1590min at room temperature. These data demonstrate that, depending on the triggering stimulus, platelets predominantly undergo m depolarization-only, P-selectin exposure-only, or both responses, indicating that platelet apoptosis and activation are different phenomena driven by different mechanisms. The described model provides a basis for studying differential pharmacological manipulation of platelet apoptosis and activation and their role in haemostasis, thrombosis and platelet clearance.