Mitochondrial Calcium Uniporter (MCU) deficiency reveals an alternate path for Ca2+ uptake in photoreceptor mitochondria

Abstract Rods and cones use intracellular Ca2+ to regulate many functions, including phototransduction and neurotransmission. The Mitochondrial Calcium Uniporter (MCU) complex is thought to be the primary pathway for Ca2+ entry into mitochondria in eukaryotes. We investigate the hypothesis that mitochondrial Ca2+ uptake via MCU influences phototransduction and energy metabolism in photoreceptors using a mcu-/- zebrafish and a rod photoreceptor-specific Mcu-/- mouse. Using genetically encoded Ca2+ sensors to directly examine Ca2+ uptake in zebrafish cone mitochondria, we found that loss of MCU reduces but does not eliminate mitochondrial Ca2+ uptake. Loss of MCU does not lead to photoreceptor degeneration, mildly affects mitochondrial metabolism, and does not alter physiological responses to light, even in the absence of the Na+/Ca2+, K+ exchanger. Our results reveal that MCU is dispensable for vertebrate photoreceptor function, consistent with its low expression and the presence of an alternative pathway for Ca2+ uptake into photoreceptor mitochondria.

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Small Interfering RNA Targeting Mitochondrial Calcium Uniporter Improves Cardiomyocyte Cell Viability in Hypoxia/Reoxygenation Injury by Reducing Calcium Overload

Oxidative Medicine and Cellular Longevity ◽

10.1155/2017/5750897 ◽

2017 ◽

Vol 2017 ◽

pp. 1-13 ◽

Cited By ~ 22

Author(s):

Yuriana Oropeza-Almazán ◽

Eduardo Vázquez-Garza ◽

Héctor Chapoy-Villanueva ◽

Guillermo Torre-Amione ◽

Gerardo García-Rivas

Keyword(s):

Underlying Mechanism ◽

Mitochondrial Calcium ◽

Mitochondrial Calcium Uniporter ◽

Calcium Uniporter ◽

Rna Targeting ◽

Intracellular Ca ◽

Pore Opening ◽

Reoxygenation Injury ◽

Interfering Rna ◽

Hypoxia Reoxygenation

Intracellular Ca2+mishandling is an underlying mechanism in hypoxia/reoxygenation (H/R) injury that results in mitochondrial dysfunction and cardiomyocytes death. These events are mediated by mitochondrial Ca2+(mCa2+) overload that is facilitated by the mitochondrial calcium uniporter (MCU) channel. Along this line, we evaluated the effect of siRNA-targeting MCU in cardiomyocytes subjected to H/R injury. First, cardiomyocytes treated with siRNA demonstrated a reduction of MCU expression by 67%, which resulted in significant decrease in mitochondrial Ca2+transport. siRNA treated cardiomyocytes showed decreased mitochondrial permeability pore opening and oxidative stress trigger by Ca2+overload. Furthermore, after H/R injury MCU silencing decreased necrosis and apoptosis levels by 30% and 50%, respectively, and resulted in reduction in caspases 3/7, 9, and 8 activity. Our findings are consistent with previous conclusions that demonstrate that MCU activity is partly responsible for cellular injury induced by H/R and support the concept of utilizing siRNA-targeting MCU as a potential therapeutic strategy.

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Proteolytic control of the mitochondrial calcium uniporter complex

Proceedings of the National Academy of Sciences ◽

10.1073/pnas.1702938114 ◽

2017 ◽

Vol 114 (17) ◽

pp. 4388-4393 ◽

Cited By ~ 39

Author(s):

Chen-Wei Tsai ◽

Yujiao Wu ◽

Ping-Chieh Pao ◽

Charles B. Phillips ◽

Carole Williams ◽

...

Keyword(s):

Cell Death ◽

Complex Formation ◽

Membrane Protein ◽

Atp Hydrolysis ◽

Neuromuscular Disorders ◽

Mitochondrial Calcium ◽

Dynamic Nature ◽

Mitochondrial Calcium Uniporter ◽

Calcium Uniporter ◽

Intracellular Ca

The mitochondrial calcium uniporter is a Ca2+-activated Ca2+ channel complex mediating mitochondrial Ca2+ uptake, a process crucial for Ca2+ signaling, bioenergetics, and cell death. The uniporter is composed of the pore-forming MCU protein, the gatekeeping MICU1 and MICU2 subunits, and EMRE, a single-pass membrane protein that links MCU and MICU1 together. As a bridging subunit required for channel function, EMRE could paradoxically inhibit uniporter complex formation if expressed in excess. Here, we show that mitochondrial mAAA proteases AFG3L2 and SPG7 rapidly degrade unassembled EMRE using the energy of ATP hydrolysis. Once EMRE is incorporated into the complex, its turnover is inhibited >15-fold. Protease-resistant EMRE mutants produce uniporter subcomplexes that induce constitutive Ca2+ leakage into mitochondria, a condition linked to debilitating neuromuscular disorders in humans. The results highlight the dynamic nature of uniporter subunit assembly, which must be tightly regulated to ensure proper mitochondrial responses to intracellular Ca2+ signals.

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