Mitochondrial sodium/calcium exchanger NCLX regulates glycolysis in astrocytes, impacting on cognitive performance

Abstract

Intracellular Ca 2+ concentrations are strictly controlled by plasma membrane transporters, the endoplasmic reticulum, and mitochondria, in which Ca 2+ uptake is mediated by the mitochondrial calcium uniporter complex (MCUc), while efflux occurs mainly through the mitochondrial Na + /Ca 2+ exchanger (NCLX). RNAseq database repository searches led us to identify the Nclx transcript as highly enriched in astrocytes when compared with neurons. To assess the role of NCLX in mouse primary culture astrocytes, we inhibited its function both pharmacologically or genetically. This resulted in re-shaping of cytosolic Ca 2+ signaling and a metabolic shift that increased glycolytic flux and lactate secretion in a Ca 2+ -dependent manner. Interestingly, in vivo genetic deletion of NCLX in hippocampal astrocytes improved cognitive performance in behavioral tasks, whereas hippocampal neuron-specific deletion of NCLX impaired cognitive performance. These results unveil a role for NCLX as a novel modulator of astrocytic glucose metabolism, impacting on cognition.

Mitochondrial Sodium/Calcium Exchanger (NCLX) Regulates Basal and Starvation-Induced Autophagy Through Calcium Signaling

“…This was evidenced in our model by slower decay (increased half-life) after an ATP-induced Ca 2+ peak in siMCU cells ( Figure 1K ). Conversely, inhibition of mitochondrial Ca 2+ efflux can lead to accumulation of Ca 2+ in mitochondria, and thus faster reduction in cytoplasmic Ca 2+ , which was indeed observed with NCLX inhibition in this work and others [26,28]. Interestingly, siMCU and CGP did not change the Ca 2+ peak after ATP stimulation, while siNCLX resulted in a significant reduction of peak intensity ( Figure 1J ).…”

“…After the identification of the NCLX gene in 2010 [24], several studies uncovered important functions of this transporter in a myriad of biological contexts. For example, inhibition of NCLX was shown to regulate insulin secretion, cardiomyocyte automaticity, and lactate and glutamate secretion in astrocytes, all by shaping Ca 2+ signals [25][26][27][28]. Nonetheless, the participation of NCLX in autophagy regulation has not yet been investigated.…”

Mitochondrial sodium/calcium exchanger (NCLX) regulates basal and starvation‐induced autophagy through calcium signaling

“…Indeed, decreased cytoplasmic Ca 2+ levels due to NCLX inhibition have been observed in studies. 8,12 Consistently, siN-CLX cells presented decreased Ca 2+ release after ATP stimulus (Figure S5A). 9,11,53,54 In KD cells, the half-life decay was strikingly higher (Figure S5A), indicating that other Ca 2+ clearance pathways are strongly affected by decreased NCLX expression, and further linking reduced NCLX activity to impaired cytoplasmic Ca 2+ signals.…”

“…In addition to the accumulation of Ca 2+ in the mitochondrial matrix, decreased Ca 2+ release into the cytosol is a direct downstream effect of NCLX inhibition. 8,12 Together with the ER and plasma membrane, mitochondrial Ca 2+ uptake is responsible for Ca 2+ clearance from the cytosol during signaling events. 4 Interestingly, early steps of autophagy activation during starvation were shown to be regulated by Ca 2+ signaling.…”

“…Prior effects of NCLX in the literature have been mechanistically associated with changes in intra-or extramitochondrial Ca 2+ , [8][9][10][11][12][13][14][15] both of which are plausible mechanisms capable of modulating autophagic activity. In mitochondria, controlled increases in Ca 2+ concentrations are known to promote oxidative phosphorylation, as long as they are within a specific "Goldilocks" concentration range.…”