Glutamate Transport Decreases Mitochondrial pH and Modulates Oxidative Metabolism in Astrocytes

Azarias, Guillaume; Perreten, Hélène; Lengacher, Sylvain; Poburko, Damon; Demaurex, Nicolas; Magistretti, Pierre J.; Chatton, Jean–Yves

doi:10.1523/jneurosci.4378-10.2011

Cited by 97 publications

(99 citation statements)

References 47 publications

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“…BCECF and mitoSypHer were calibrated by exposing the cultures to different pH in the presence of 10 μg/mL nigericin and 20 μg/mL gramicidin in an intracellular buffer. The permeabilization procedure shifted the mitoSypHer signal, and therefore baseline mitochondrial pH was assumed to be 7.6 (34). For mitochondrial membrane potential imaging the cultures were loaded with the fluorescent dye TMRM for 30 min at 37°C.…”

Section: Methodsmentioning

confidence: 99%

“…The uptake of pyruvate by mitochondria is mediated by the H + -coupled MPC (36,37), and therefore the reduction of the transmitochondrial pH gradient by NH + 4 provides a parsimonious explanation for the reduced uptake of pyruvate. There is increasing evidence that mitochondrial pH plays important physiological and pathological roles (43); for example, a recent study in astrocytes showed that glutamate inhibited oxygen consumption, a phenomenon ascribed to cytosolic acidification leading to mitochondrial acidification (34).…”

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confidence: 99%

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NH4+ triggers the release of astrocytic lactate via mitochondrial pyruvate shunting

Lerchundi

Fernández‐Moncada

Contreras-Baeza

et al. 2015

Proc. Natl. Acad. Sci. U.S.A.

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Neural activity is accompanied by a transient mismatch between local glucose and oxygen metabolism, a phenomenon of physiological and pathophysiological importance termed aerobic glycolysis. Previous studies have proposed glutamate and K + as the neuronal signals that trigger aerobic glycolysis in astrocytes. Here we used a panel of genetically encoded FRET sensors in vitro and in vivo to investigate the participation of NH + 4 , a by-product of catabolism that is also released by active neurons. Astrocytes in mixed cortical cultures responded to physiological levels of NH + 4 with an acute rise in cytosolic lactate followed by lactate release into the extracellular space, as detected by a lactate-sniffer. An acute increase in astrocytic lactate was also observed in acute hippocampal slices exposed to NH + 4 and in the somatosensory cortex of anesthetized mice in response to i.v. NH + 4 . Unexpectedly, NH + 4 had no effect on astrocytic glucose consumption. Parallel measurements showed simultaneous cytosolic pyruvate accumulation and NADH depletion, suggesting the involvement of mitochondria. An inhibitor-stop technique confirmed a strong inhibition of mitochondrial pyruvate uptake that can be explained by mitochondrial matrix acidification. These results show that physiological NH + 4 diverts the flux of pyruvate from mitochondria to lactate production and release. Considering that NH + 4 is produced stoichiometrically with glutamate during excitatory neurotransmission, we propose that NH + 4 behaves as an intercellular signal and that pyruvate shunting contributes to aerobic lactate production by astrocytes.B rain tissue is almost exclusively energized by the oxidation of glucose. However, during neuronal activation, there is a larger increase in local glucose consumption relative to oxygen consumption (1). As this mismatch occurs in the presence of normal or augmented oxygen levels, it has been termed aerobic glycolysis, paralleling the signal detected by functional magnetic resonance imaging (2). Aerobic glycolysis and its associated lactate surge are causally linked to diverse functions of the brain in health and disease (3-10). Two signals are known to trigger aerobic glycolysis in brain tissue: glutamate and K + , which are released by active neurons and stimulate glycolysis in astrocytes (11,12).Neurons produce as much NH + 4 as they produce glutamate, both molecules being stoichiometrically linked in the glutamateglutamine cycle (13). Brain tissue NH + 4 increases within seconds of neural activation (14-16) and is quickly released to the interstitium (17, 18) to be captured by astrocytes through K + channels and transporters (19). It is well established that chronic exposure to pathological levels of NH + 4 such as those observed during liver failure has a major impact on brain metabolism, but it is not known whether this molecule may affect energy metabolism at physiological levels, particularly within the time scale of synaptic transmission. A previous study showed a reversible rise in brain tissue la...

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Section: Methodsmentioning

confidence: 99%

mentioning

confidence: 99%

NH4+ triggers the release of astrocytic lactate via mitochondrial pyruvate shunting

Lerchundi

Fernández‐Moncada

Contreras-Baeza

et al. 2015

Proc. Natl. Acad. Sci. U.S.A.

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“…Increased electrical activity along with larger cytoplasmic and mitochondrial Ca 2 þ loads during mCU enhancement would help stimulate mitochondrial dehydrogenases, 2,3 higher reduction rate of NAD þ , increased lactate-pyruvate ratio, and higher aerobic glycolysis due to increased glial clearance of neurotransmitters. 59 Hence, strong neuronal (and glial) metabolic response may contribute to continuously enhance CBF while saturating BOLD. These results qualitatively support enhanced resting state spontaneous and evoked activity-dependent increase in oxidative demand and quantitatively support the recruitment of a larger network of neural populations (both neuronal and glial) during mCU enhancement.…”

Section: Ru360 Has Been Shown To Permeate Cells In Vitromentioning

confidence: 99%

Mitochondrial Calcium Uptake Capacity Modulates Neocortical Excitability

Sanganahalli

Hermán

Hyder

et al. 2013

J Cereb Blood Flow Metab

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Local calcium (Ca 2 þ ) changes regulate central nervous system metabolism and communication integrated by subcellular processes including mitochondrial Ca 2 þ uptake. Mitochondria take up Ca 2 þ through the calcium uniporter (mCU) aided by cytoplasmic microdomains of high Ca 2 þ . Known only in vitro, the in vivo impact of mCU activity may reveal Ca 2 þ -mediated roles of mitochondria in brain signaling and metabolism. From in vitro studies of mitochondrial Ca 2 þ sequestration and cycling in various cell types of the central nervous system, we evaluated ranges of spontaneous and activity-induced Ca 2 þ distributions in multiple subcellular compartments in vivo. We hypothesized that inhibiting (or enhancing) mCU activity would attenuate (or augment) cortical neuronal activity as well as activity-induced hemodynamic responses in an overall cytoplasmic and mitochondrial Ca 2 þ -dependent manner. Spontaneous and sensory-evoked cortical activities were measured by extracellular electrophysiology complemented with dynamic mapping of blood oxygen level dependence and cerebral blood flow. Calcium uniporter activity was inhibited and enhanced pharmacologically, and its impact on the multimodal measures were analyzed in an integrated manner. Ru360, an mCU inhibitor, reduced all stimulus-evoked responses, whereas Kaempferol, an mCU enhancer, augmented all evoked responses. Collectively, the results confirm aforementioned hypotheses and support the Ca 2 þ uptake-mediated integrative role of in vivo mitochondria on neocortical activity.

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“…By monitoring the effect of NO in real time, we were able to observe that the stimulation of glucose consumption is immediate, leading to intracellular glucose depletion and lactate accumulation. The immediate translation of mitochondrial inhibition into glycolysis stimulation is not trivial, as it was not observed after acute mitochondrial matrix acidification by glutamate (28,29) or by NH 4 ϩ (18). The effect was dose-dependent and could be detected at 100 nM NO.…”

Section: Discussionmentioning

confidence: 99%

Nanomolar nitric oxide concentrations quickly and reversibly modulate astrocytic energy metabolism

Martín

Arce-Molina

Galaz

et al. 2017

Journal of Biological Chemistry

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Nitric oxide (NO) is an intercellular messenger involved in multiple bodily functions. Prolonged NO exposure irreversibly inhibits respiration by covalent modification of mitochondrial cytochrome oxidase, a phenomenon of pathological relevance. However, the speed and potency of NO's metabolic effects at physiological concentrations are incompletely characterized. To this end, we set out to investigate the metabolic effects of NO in cultured astrocytes from mice by taking advantage of the high spatiotemporal resolution afforded by genetically encoded Förster resonance energy transfer (FRET) nanosensors. NO exposure resulted in immediate and reversible intracellular glucose depletion and lactate accumulation. Consistent with cytochrome oxidase involvement, the glycolytic effect was enhanced at a low oxygen level and became irreversible at a high NO concentration or after prolonged exposure. Measurements of both glycolytic rate and mitochondrial pyruvate consumption revealed significant effects even at nanomolar NO concentrations. We conclude that NO can modulate astrocytic energy metabolism in the short term, reversibly, and at concentrations known to be released by endothelial cells under physiological conditions. These findings suggest that NO modulates the size of the astrocytic lactate reservoir involved in neuronal fueling and signaling.In brain tissue and retina, NO contributes to both vasodilation and vasoconstriction (1, 2). The vasoactive effects of NO are mediated by the enzymes guanylate cyclase, cytochrome P450 epoxygenase, and -hydroxylase, which sense different NO concentrations. Guanylate cyclase is stimulated in the picomolar to low nanomolar range, whereas cytochrome P450 enzymes are inhibited at tens to hundreds of nanomolar NO (1, 3). However, there is more to NO than vasodilation. Endothelial cells express both endothelial NO synthase (eNOS) 3 and inducible NO synthase (iNOS) (4) resulting in NO production strong enough to sustain up to 70 nM extracellular NO in response to shear stress (5), to reach cells millimeters away in bicameral cultures (6), or to permeate across layers of astrocytes and myelin toward axons in vivo (7). A fourth well characterized molecular target of NO is mitochondrial cytochrome oxidase (EC 1.9.3.1), whose sensitivity to NO is similar to that of cytochrome P450 (8, 9). As inhibition of cytochrome oxidase reduces local oxygen consumption, endothelial NO has been proposed to extend the effective zone of oxygenation away from the vessel (10). A role for NO-dependent mitochondrial inhibition in brain tissue was suggested upon the observation that NO inhibits astrocytic respiration, resulting in stimulated glycolysis and lactate production (11, 12). Conceivably, inhibition of cytochrome oxidase may not only play a tonic distributive role but may also participate in activity-dependent neurometabolic coupling (13). However, there are aspects that need further exploring, notably the speed and potency of the metabolic effects in the face of actual NO concentrations found under...

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Glutamate Transport Decreases Mitochondrial pH and Modulates Oxidative Metabolism in Astrocytes

Cited by 97 publications

References 47 publications

NH4+ triggers the release of astrocytic lactate via mitochondrial pyruvate shunting

NH4+ triggers the release of astrocytic lactate via mitochondrial pyruvate shunting

Mitochondrial Calcium Uptake Capacity Modulates Neocortical Excitability

Nanomolar nitric oxide concentrations quickly and reversibly modulate astrocytic energy metabolism

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