The mitochondrial calcium uniporter regulates procoagulant platelet formation

Background: Procoagulant platelets comprise a phenotypically distinct subpopulation of activated platelets with high-level phosphatidylserine externalization. When initiated by co-stimulation with thrombin and a glycoprotein VI (GPVI) agonist, the transition to the procoagulant phenotype is mediated by extracellular calcium entry and mitochondrial permeability transition pore (mPTP) formation. Objectives: The intracellular mechanisms coordinating these distinct cytoplasmic and mitochondrial processes remain unclear. The mitochondrial calcium uniporter (MCU) protein is a central component of the transmembrane ion channel that allows the passage of Ca2+ from the cytosol into the mitochondrial matrix. Here we investigate the role of the MCU in the regulation of procoagulant platelet formation. Results: Procoagulant platelet formation was directly correlated with pre-stimulatory mitochondrial transmembrane potential, a key determinant of calcium flux from the cytoplasm to the mitochondria. The role of MCU in the regulation of procoagulant platelet formation was investigated using MCU null platelets. Procoagulant platelet formation in MCU null platelets was significantly decreased coincident with decreased mPTP formation. In contrast, neither granule release nor initial integrin activation was altered in response to stimulation. In the genomic absence of MCU, developmental induction of an alternative intracellular pathway partially rescued procoagulant platelet formation. Conclusion: These results identify a key role for the mitochondrial calcium uptake channel in the regulation of mPTP-mediated procoagulant platelet formation and suggest a novel pharmacologic target for procoagulantplatelet-related pathologies.