Metabolic differences in hippocampal ‘Rett’ neurons revealed by ATP imaging

Key points Employing quantitative Na+‐imaging and Förster resonance energy transfer‐based imaging with ATeam1.03YEMK (ATeam), we studied the relation between activity‐induced Na+ influx and intracellular ATP in CA1 pyramidal neurons of the mouse hippocampus. Calibration of ATeam in situ enabled a quantitative estimate of changes in intracellular ATP concentrations. Different paradigms of stimulation that induced global Na+ influx into the entire neuron resulted in decreases in [ATP] in the range of 0.1–0.6 mm in somata and dendrites, while Na+ influx that was locally restricted to parts of dendrites did not evoke a detectable change in dendritic [ATP]. Our data suggest that global Na+ transients require global cellular activation of the Na+/K+‐ATPase resulting in a consumption of ATP that transiently overrides its production. For recovery from locally restricted Na+ influx, ATP production as well as fast intracellular diffusion of ATP and Na+ might prevent a local drop in [ATP]. Abstract Excitatory neuronal activity results in the influx of Na+ through voltage‐ and ligand‐gated channels. Recovery from accompanying increases in intracellular Na+ concentrations ([Na+]i) is mainly mediated by the Na+/K+‐ATPase (NKA) and is one of the major energy‐consuming processes in the brain. Here, we analysed the relation between different patterns of activity‐induced [Na+]i signalling and ATP in mouse hippocampal CA1 pyramidal neurons by Na+ imaging with sodium‐binding benzofurane isophthalate (SBFI) and employing the genetically encoded nanosensor ATeam1.03YEMK (ATeam). In situ calibrations demonstrated a sigmoidal dependence of the ATeam Förster resonance energy transfer ratio on the intracellular ATP concentration ([ATP]i) with an apparent KD of 2.6 mm, indicating its suitability for [ATP]i measurement. Induction of recurrent network activity resulted in global [Na+]i oscillations with amplitudes of ∼10 mm, encompassing somata and dendrites. These were accompanied by a steady decline in [ATP]i by 0.3–0.4 mm in both compartments. Global [Na+]i transients, induced by afferent fibre stimulation or bath application of glutamate, caused delayed, transient decreases in [ATP]i as well. Brief focal glutamate application that evoked transient local Na+ influx into a dendrite, however, did not result in a measurable reduction in [ATP]i. Our results suggest that ATP consumption by the NKA following global [Na+]i transients temporarily overrides its availability, causing a decrease in [ATP]i. Locally restricted Na+ transients, however, do not result in detectable changes in local [ATP]i, suggesting that ATP production, together with rapid intracellular diffusion of both ATP and Na+ from and to unstimulated neighbouring regions, counteracts a local energy shortage under these conditions.

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“…; Toloe et al . ; Pathak et al . ), data derived from calibrations were fit linearly for [ATP] between 1 and 3 m m ( R 2 = 0.76) (Fig.…”

Section: Resultsmentioning

confidence: 99%

“…This is somewhat lower as reported before based on estimates of [ATP] using the sensor ATeam1.03 (Toloe et al . ). A reduction in this range might alter the conductance of K ATP channels, resulting in a dampening of neuronal excitability, thereby executing an anti‐convulsant effect (Proks & Ashcroft, ; Mollajew et al .…”

Section: Discussionmentioning

confidence: 97%

Relation between activity‐induced intracellular sodium transients and ATP dynamics in mouse hippocampal neurons

Gerkau

Lerchundi

Nelson

et al. 2019

The Journal of Physiology

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“…Rett patients show an increased incidence of epileptic seizures (Hagberg et al, 1983; Steffenburg et al, 2001) and increased neuronal excitability is also evident in MeCP2-deficient mice (Medrihan et al, 2008; Fischer et al, 2009; Calfa et al, 2011; McLeod et al, 2013; Toloe et al, 2014). Since the Trolox-mediated decrease in fEPSP/fiber-volley ratio in Mecp2 - /y slices confirms successful dampening of neuronal hyperexcitability, we also tested for potential anticonvulsive effects of this free radical scavenger.…”

Section: Resultsmentioning

confidence: 99%

The free radical scavenger Trolox dampens neuronal hyperexcitability, reinstates synaptic plasticity, and improves hypoxia tolerance in a mouse model of Rett syndrome

Janc

Müller

2014

Front. Cell. Neurosci.

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Rett syndrome (RS) causes severe cognitive impairment, loss of speech, epilepsy, and breathing disturbances with intermittent hypoxia. Also mitochondria are affected; a subunit of respiratory complex III is dysregulated, the inner mitochondrial membrane is leaking protons, and brain ATP levels seem reduced. Our recent assessment of mitochondrial function in MeCP2 (methyl-CpG-binding protein 2)-deficient mouse (Mecp2-/y) hippocampus confirmed early metabolic alterations, an increased oxidative burden, and a more vulnerable cellular redox balance. As these changes may contribute to the manifestation of symptoms and disease progression, we now evaluated whether free radical scavengers are capable of improving neuronal and mitochondrial function in RS. Acute hippocampal slices of adult mice were incubated with the vitamin E derivative Trolox for 3–5 h. In Mecp2-/y slices this treatment dampened neuronal hyperexcitability, improved synaptic short-term plasticity, and fully restored synaptic long-term potentiation (LTP). Furthermore, Trolox specifically attenuated the increased hypoxia susceptibility of Mecp2-/y slices. Also, the anticonvulsive effects of Trolox were assessed, but the severity of 4-aminopyridine provoked seizure-like discharges was not significantly affected. Adverse side effects of Trolox on mitochondria can be excluded, but clear indications for an improvement of mitochondrial function were not found. Since several ion-channels and neurotransmitter receptors are redox modulated, the mitochondrial alterations and the associated oxidative burden may contribute to the neuronal dysfunction in RS. We confirmed in Mecp2-/y hippocampus that Trolox dampens neuronal hyperexcitability, reinstates synaptic plasticity, and improves the hypoxia tolerance. Therefore, radical scavengers are promising compounds for the treatment of neuronal dysfunction in RS and deserve further detailed evaluation.

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“…It has been suggested that local differences of ATP consumption by Na + /K + -ATPase lead to ATP microdomains close to the cell membrane with low ATP concentrations (Haller et al, 2001; Toloe et al, 2014). Contrarily, ATP diffusion is reported to be very fast not allowing formation of ATP microdomains (Barros et al, 2013).…”

Section: Discussionmentioning

confidence: 99%

Monitoring ATP dynamics in electrically active white matter tracts

Trevisiol

Saab

Winkler

et al. 2017

eLife

126

168

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In several neurodegenerative diseases and myelin disorders, the degeneration profiles of myelinated axons are compatible with underlying energy deficits. However, it is presently impossible to measure selectively axonal ATP levels in the electrically active nervous system. We combined transgenic expression of an ATP-sensor in neurons of mice with confocal FRET imaging and electrophysiological recordings of acutely isolated optic nerves. This allowed us to monitor dynamic changes and activity-dependent axonal ATP homeostasis at the cellular level and in real time. We find that changes in ATP levels correlate well with compound action potentials. However, this correlation is disrupted when metabolism of lactate is inhibited, suggesting that axonal glycolysis products are not sufficient to maintain mitochondrial energy metabolism of electrically active axons. The combined monitoring of cellular ATP and electrical activity is a novel tool to study neuronal and glial energy metabolism in normal physiology and in models of neurodegenerative disorders.DOI: http://dx.doi.org/10.7554/eLife.24241.001

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Metabolic differences in hippocampal ‘Rett’ neurons revealed by ATP imaging

Cited by 50 publications

References 58 publications

Relation between activity‐induced intracellular sodium transients and ATP dynamics in mouse hippocampal neurons

Relation between activity‐induced intracellular sodium transients and ATP dynamics in mouse hippocampal neurons

The free radical scavenger Trolox dampens neuronal hyperexcitability, reinstates synaptic plasticity, and improves hypoxia tolerance in a mouse model of Rett syndrome

Monitoring ATP dynamics in electrically active white matter tracts

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