Impaired expression of the mitochondrial calcium uniporter suppresses mast cell degranulation
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Calcium ion (Ca2+) uptake into the mitochondrial matrix influences ATP production, Ca2+ homeostasis, and apoptosis regulation. Ca2+ uptake across the ion-impermeable inner mitochondrial membrane is mediated by the mitochondrial Ca2+ uniporter (MCU) complex. The MCU complex forms a pore structure composed of several proteins. MCU is a Ca2+-selective channel in the inner-mitochondrial membrane that allows electrophoretic Ca2+ entry into the matrix. Mitochondrial Ca2+ uptake 1 (MICU1) functions as a Ca2+-sensing regulator of the MCU complex. Previously, by microscopic analysis at the single-cell level, we found that during mast cell activation, mitochondria capture cytosolic Ca2+ in two steps. Consequently, mitochondrial Ca2+ uptake likely plays a role in cellular function through cytosolic Ca2+ buffering. Here, we investigate the role of MCU and MICU1 in mitochondrial Ca2+ uptake and mast cell degranulation using MCU- and MICU1-knockdown (KD) mast cells. Whereas MCU- and MICU1-KD mast cells show normal proliferation rates and mitochondrial membrane potential, they exhibit slow and reduced cytosolic and mitochondrial Ca2+ elevation after antigen stimulation. Moreover, β-hexosaminidase release induced by antigen was significantly suppressed in MCU-KD cells but not MICU1-KD cells. This suggests that both MCU and MICU1 are involved in mitochondrial Ca2+ uptake in mast cells, while MCU plays a role in mast cell degranulation.
KeywordsCalcium Degranulation Mast cell MCU Mitochondria
This research was supported, in part, by the Ministry of Education, Culture, Sports, and Technology of Japan (grant nos. 26440083 to T.F.; and 24590060 to M.N.).
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