The NMDA receptor regulates integrin activation, ATP release and arterial thrombosis through store-operated Ca(2+) entry in platelets

INTRODUCTION: Platelet activation and thrombus formation is crucial for hemostasis, but also trigger arterial thrombosis. Calcium mobilization plays an important role in platelet activation, because many cellular processes depend on the level of intracellular Ca(2+) ([Ca(2+)](i)), such as integrin activation, degranulation, cytoskeletal reorganization. Different modulators of Ca(2+) signaling have been implied, such as STIM1, Orai1, CyPA, SGK1, etc. Also, the N-methyl-D-aspartate receptor (NMDAR) was identified to contribute to Ca(2+) signaling in platelets. However, the role of the NMDAR in thrombus formation is not well defined. METHODS: In vitro and in vivo analysis of platelet-specific NMDAR knock-out mice. RESULTS: In this study, we analyzed Grin1(fl/fl)-Pf4-Cre(+) mice with a platelet-specific knock-out of the essential GluN1 subunit of the NMDAR. We found reduced store-operated Ca(2+) entry (SOCE), but unaltered store release in GluN1-deficient platelets. Defective SOCE resulted in reduced Src and PKC substrate phosphorylation following stimulation of glycoprotein (GP)VI or the thrombin receptor PAR4 followed by decreased integrin activation but unaltered degranulation. Consequently, thrombus formation on collagen under flow conditions was reduced ex vivo, and Grin1(fl/fl)-Pf4-Cre(+) mice were protected against arterial thrombosis. Results from human platelets treated with the NMDAR antagonist MK-801 revealed a crucial role of the NMDAR in integrin activation and Ca(2+) homeostasis in human platelets as well. CONCLUSION: NMDAR signaling is important for SOCE in platelets and contributes to platelet activation and arterial thrombosis. Thus, the NMDAR represents a novel target for anti-platelet therapy in cardiovascular disease (CVD).