Mitochondrial calcium uniporter Mcu controls excitotoxicity and is transcriptionally repressed by neuroprotective nuclear calcium signals

Abstract

The recent identification of the mitochondrial Ca2+ uniporter gene (Mcu/Ccdc109a) has enabled us to address its role, and that of mitochondrial Ca2+ uptake, in neuronal excitotoxicity. Here we show that exogenously expressed Mcu is mitochondrially localized and increases mitochondrial Ca2+ levels following NMDA receptor activation, leading to increased mitochondrial membrane depolarization and excitotoxic cell death. Knockdown of endogenous Mcu expression reduces NMDA-induced increases in mitochondrial Ca2+, resulting in lower levels of mitochondrial depolarization and resistance to excitotoxicity. Mcu is subject to dynamic regulation as part of an activity-dependent adaptive mechanism that limits mitochondrial Ca2+ overload when cytoplasmic Ca2+ levels are high. Specifically, synaptic activity transcriptionally represses Mcu, via a mechanism involving the nuclear Ca2+ and CaM kinase-mediated induction of Npas4, resulting in the inhibition of NMDA receptor-induced mitochondrial Ca2+ uptake and preventing excitotoxic death. This establishes Mcu and the pathways regulating its expression as important determinants of excitotoxicity, which may represent therapeutic targets for excitotoxic disorders.

Inhibition of N-Methyl-d-aspartate-induced Retinal Neuronal Death by Polyarginine Peptides Is Linked to the Attenuation of Stress-induced Hyperpolarization of the Inner Mitochondrial Membrane Potential

“…Supporting this conclusion, it has been reported that Tat does not induce internalization of the NMDA NR2B subunit and the sodium calcium exchanger (NCX) proteins, whereas the neuroprotective peptide Tat-CBD3, a 15-amino acid peptide from CRMP2 fused to Tat, attenuated NMDAR activity and protected neurons against glutamate-induced Ca 2ϩ dysregulation (52). As mitochondria are key players in signaling neuronal death (35,53,54), and with biotin-C-R(7) peptide localizing to mitochondria (Fig. 10, b-d) and structures within the retina resembling mitochondria (Fig.…”

“…Another possible target for C-R(7) to interfere with NMDAR-induced calcium influx into the mitochondria would be the mitochondrial calcium uniporter (Mcu). Recent studies established the role of Mcu in coupling NMDA receptor stimulation to neuronal excitotoxicity (35), where calcium entry through Mcu mediates mPTP opening. Thus C-R(7) could act similarly to the hexava-FIGURE 11.…”

“…r, for ease of comparison of all the treatment conditions, area II (1-2 mm from the optic nerve head) was chosen to evaluate neuroprotection (quantification of the number of retinas/treatment condition in graphs q and r are listed following each treatment condition described in legends a-o above). Error bars S.E., * indicates a significant difference from NMDA-treated retina, p Ͻ 0.001. grammed cell death pathways (32,35,36). Using the mitochondrion-specific probe MitoSOX, which becomes fluorescently activated by the generation of superoxide resulting from mitochondrial oxidative stress, we examined retinas exposed to 20 nmol of NMDA alone, C-s-s-C-R(7)/NMDA, or PBS-sham 2 h following intravitreal injection.…”

Mitochondrial dynamics in neuronal injury, development and plasticity

“…Mitochondrial fission is thought to sensitize neurons to insults, such as oxidative stress and excitotoxicity, because the subsequent decrease in the ability of the fragmented mitochondria to produce ATP ultimately impairs their capability to detoxify excess ROS and sequester or extrude intracellular Ca 2+ . In support of this, knockdown of MCU prevents NMDA-mediated excitotoxicity induced mitochondrial depolarization and improves neuron survival (Qiu et al, 2013). Similarly, promotion of mitochondrial elongation prior to injury through inhibition of Drp1 could improve neuronal survival as it increases mitochondrial membrane potential and, in turn, bioenergetic capacity, helping neurons weather an ischemic energy crisis (Fig.…”

Mitochondrial calcium homeostasis: Implications for neurovascular and neurometabolic coupling

“…Additionally, mCU expression can also be repressed in a nuclear Ca 2þ -dependent manner leading to protective effects against NMDA-receptor dependent excitotoxicity. 63 mCU and mCUb activities are regulated by additional subunits MICU1, MICU2, MCUR1, and EMRE. 64 Hence mCU channel population numbers and their regulatory subunit configurations that efficiently conduct Ca 2þ and other isoforms that do not conduct Ca 2þ during cellular activity may become important factors determining the diversity of mitochondrial function in different brain regions during normal and pathological states 59 ( Figure 2).…”