Platelet aggregation requires caspases, but is not apoptosis

Abstract

Apoptosis utilizes three groups of proteins: death receptors, the Bcl-2 family, and caspases. Recent observations indicate that platelets contain caspases. However, the role of caspases in platelet function remains unclear. We have demonstrated in a rodent model, that there is a decrease in aggregation when platelets were treated in vitro with zVAD-fmk, a broad spectrum caspase inhibitor. There is limited research on specific caspases in platelet activation. The aim of this study was to investigate if inhibition of caspase-3, -8, or -9, attenuates ADP-induced platelet aggregation compared to aggregation with ADP alone (control). Using blood from Sprague-Dawley rats, we found that ex-vivo pre-treatment with IETD-fmk, an inhibitor specific for caspase 8, significantly attenuated platelet aggregation in ADP stimulated platelets, (Control 82.3 ± 3.9 % vs. IETD-fmk 63.8 ± 4.9 %, p ≤ 0.03). LEHD-fmk (specific for caspase 9) also significantly attenuated platelet aggregation, but to a lesser degree (LEHD-fmk 69.3 ± 4.1 %, p ≤ 0.03). DEVD-fmk, an inhibitor of caspase 3, did not significantly decrease aggregation (74.6 ± 4.0 %) when compared to control. These data suggest that caspases may play a role in platelet activation. Since the main apoptosis effector caspase (caspase 3) did not inhibit platelet aggregation, the idea that caspases work in an apoptotic-like manner in platelets is less than clear. It is clear, however, that at minimum, caspases-8 and-9 are involved in portions of platelet activation. This novel finding may lead to the development of improved agents to limit pathologic platelet activation. Supported by T32NRO7958, NIH HLB 58859, NIH NR005208.