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

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.