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.
Highlights
The recent identification of the mitochondrial Ca2 þ uniporter gene (Mcu/Ccdc109a) has enabled us to address its role, and that of mitochondrial Ca2 þ uptake, in neuronal excitotoxicity
We employed immunofluorescence and biochemical fractionation approaches to show that mitochondrial calcium uniporter (Mcu) fused to the fluorescent proteins eGFP or tDimer localized to neuronal mitochondria, consistent with its known subcellular distribution (Fig. 1b, Supplementary Fig. S1b and data not shown)
Our overarching aim was to investigate the effect of manipulating Mcu expression on responses of forebrain neurons to NMDA treatment, focusing on mitochondrial and cytoplasmic Ca2 þ increases, mitochondrial depolarization, and cell death
Summary
The gene product encoding the uniporter channel (Mcu) was identified as the ubiquitously expressed gene previously known as Ccdc109a18,19, which acts in concert with regulatory proteins such as Micu[1] and Mcur[1] to mediate potential-driven mitochondrial Ca2 þ uptake[20,21]. This finding allows selective approaches involving exogenous Mcu expression and knockdown to be employed to determine the role of mitochondrial Ca2 þ uptake in all aspects of cellular physiology and pathology
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