Mitochondrial calcium uniporter b deletion inhibits platelet function and reduces susceptibility to arterial thrombosis

Abstract

Background: Mitochondrial calcium uniporter b (MCUb) is a negative regulator of the mitochondrial calcium uniporter (MCU) and is known to limit mitochondrial calcium ion (Ca2+) uptake. The role of MCUb in platelet function remains unclear. Objectives: Utilizing MCUb−/− mice, we examined the role of MCUb in regulating platelet function and thrombosis. Methods: Platelet activation was evaluated in agonist-induced standardized in vitro assays. Susceptibility to arterial thrombosis was evaluated in FeCl3 injury–induced carotid artery and laser injury–induced mesenteric artery thrombosis models. The glycolytic proton efflux rate and oxygen consumption rate were measured to evaluate aerobic glycolysis. Results: Upon stimulation, MCUb−/− platelets exhibited reduced cytoplasmic Ca2+ responses concomitant with increased mitochondrial Ca2+ uptake. MCUb−/− platelets displayed reduced agonist-induced platelet aggregation and spreading on fibrinogen and decreased α and dense-granule secretion and clot retraction. MCUb−/− mice were less susceptible to arterial thrombosis in FeCl3 injury–induced carotid and laser injury–induced mesenteric thrombosis models with unaltered tail bleeding time. In adoptive transfer experiments, thrombocytopenic hIL-4Rα/GPIbα-transgenic mice transfused with MCUb−/− platelets were less susceptible to FeCl3 injury-induced carotid thrombosis compared with hIL-4Rα/GPIbα-Tg mice transfused with wild type platelets, suggesting a platelet-specific role of MCUb in thrombosis. MCUb−/− stimulated platelets exhibited reduced glucose uptake, decreased glycolytic rate, and lowered pyruvate dehydrogenase phosphorylation, suggesting that mitochondrial Ca2+ mediates bioenergetic changes in platelets. Conclusion: Our findings suggest that mitochondrial Ca2+ signaling and glucose oxidation are functionally linked in activated platelets and reveal a novel role of MCUb in platelet activation and arterial thrombosis.