Deletion of mitochondrial calcium uniporter incompletely inhibits calcium uptake and induction of the permeability transition pore in brain mitochondria

Abstract

Ca influx into mitochondria is mediated by the mitochondrial calcium uniporter (MCU), whose identity was recently revealed as a 40-kDa protein that along with other proteins forms the mitochondrial Ca uptake machinery. The MCU is a Ca-conducting channel spanning the inner mitochondrial membrane. Here, deletion of the MCU completely inhibited Ca uptake in liver, heart, and skeletal muscle mitochondria. However, in brain nonsynaptic and synaptic mitochondria from neuronal somata/glial cells and nerve terminals, respectively, the MCU deletion slowed, but did not completely block, Ca uptake. Under resting conditions, brain MCU-KO mitochondria remained polarized, and in brain MCU-KO mitochondria, the electrophoretic Ca ionophore ETH129 significantly accelerated Ca uptake. The residual Ca uptake in brain MCU-KO mitochondria was insensitive to inhibitors of mitochondrial Na/Ca exchanger and ryanodine receptor (CGP37157 and dantrolene, respectively), but was blocked by the MCU inhibitor Ru360. Respiration of WT and MCU-KO brain mitochondria was similar except that for mitochondria that oxidized pyruvate and malate, Ca more strongly inhibited respiration in WT than in MCU-KO mitochondria. Of note, the MCU deletion significantly attenuated but did not completely prevent induction of the permeability transition pore (PTP) in brain mitochondria. Expression level of cyclophilin D and ATP content in mitochondria, two factors that modulate PTP induction, were unaffected by MCU-KO, whereas ADP was lower in MCU-KO than in WT brain mitochondria. Our results suggest the presence of an MCU-independent Ca uptake pathway in brain mitochondria that mediates residual Ca influx and induction of PTP in a fraction of the mitochondrial population.

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

“…Consistent with this result, we found that both WT and mcu -/- cones have a population of mitochondrial clusters which still appear to take up Ca 2+ even in the presence of the MCU inhibitor Ru360, and the characteristics of this population match those of the responding mitochondria in mcu -/- cones. This is similar to what has been observed in non-synaptic brain mitochondria isolated from Mcu -/- mice, in which uptake of Ca 2+ into mitochondria was not blocked but instead occurred at a slower rate compared to controls 20 . Taken together, these results suggest that that neuronal tissue like retina and brain may have an alternative mitochondrial Ca 2+ uptake pathway with different response kinetics and Ca 2+ uptake capacity.…”

“…MCU has been widely thought to be the sole route of Ca 2+ entry into mitochondria in eukaryotes, as loss of MCU completely inhibits mitochondrial Ca 2+ uptake in skeletal muscle, liver, heart, brown adipose tissue, and a wide variety of cell lines 15 – 19 . Despite this, it is possible that certain specialized cell types might not rely solely on MCU for mitochondrial Ca 2+ uptake, since it also has been observed that brain mitochondria lacking MCU expression do not have a complete loss of mitochondrial Ca 2+ uptake 20 . Thus, the role that MCU plays in vertebrate photoreceptors remains an open question.…”

Mechanisms of malignancy in glioblastoma cells are linked to mitochondrial Ca2+ uniporter upregulation and higher intracellular Ca2+ levels

“…Mitochondria accumulate large amounts of Ca 2+ and contribute to the maintenance of a low resting [Ca 2+ ] i (Foskett and Philipson, 2015): if [Ca 2+ ] i exceeds a threshold in the micromolar range, cells trigger metabolic pathways leading to cell death (Liu et al, 2015). Ca 2+ influx into mitochondria is mediated by mitochondrial Ca 2+ uniporter (MCU), and genetic ablation of Mcu decreases mitochondrial Ca 2+ uptake (Hamilton et al, 2018), while persistent MCU activity enhances mitochondrial Ca 2+ uptake (Dong et al, 2017). It has been proposed that cancer stem cells share several properties of adult neural stem cells, in particular altered Ca 2+ regulation (Leclerc et al, 2016).…”

The Effects of a Combination of Ion Channel Inhibitors in Female Rats Following Repeated Mild Traumatic Brain Injury

“…However, the activation of Na + /K + -ATPase rapidly reduces intracellular energy stores and causes neurons to produce more energy in a quick but inefficient way, namely, glycolysis [ 13 ]. Concurrently, oxidative metabolism is disrupted to overproduce reactive oxygen and nitrogen species (ROS and RNS, respectively) [ 12 , 14 ] and increase mitochondrial permeability [ 15 , 16 , 17 ], leading to further loss of neurons and associated functions. Therefore, ion channels are a candidate target for therapeutic intervention.…”