Spatiotemporal Imaging of Cellular Energy Metabolism with Genetically-Encoded Fluorescent Sensors in Brain

Abstract

The brain has very high energy requirements and consumes 20% of the oxygen and 25% of the glucose in the human body. Therefore, the molecular mechanism underlying how the brain metabolizes substances to support neural activity is a fundamental issue for neuroscience studies. A well-known model in the brain, the astrocyte-neuron lactate shuttle, postulates that glucose uptake and glycolytic activity are enhanced in astrocytes upon neuronal activation and that astrocytes transport lactate into neurons to fulfill their energy requirements. Current evidence for this hypothesis has yet to reach a clear consensus, and new concepts beyond the shuttle hypothesis are emerging. The discrepancy is largely attributed to the lack of a critical method for real-time monitoring of metabolic dynamics at cellular resolution. Recent advances in fluorescent protein-based sensors allow the generation of a sensitive, specific, real-time readout of subcellular metabolites and fill the current technological gap. Here, we summarize the development of genetically encoded metabolite sensors and their applications in assessing cell metabolism in living cells and in vivo, and we believe that these tools will help to address the issue of elucidating neural energy metabolism.

A Dual Nanosensor Approach to Determine the Cytosolic Concentration of ATP in Astrocytes

“…It adds an option to the toolbox for quantifying changes in cellular metabolite concentrations from fluorescence changes, which is particularly useful if determination of R max is difficult or impeded since the dual sensor approach is independent of this parameter. Finally, this method is not only applicable to metabolic nanosensors, but also for other sensors reporting, e.g., pH or the concentration of ions or second messengers (San Martin et al, 2014;Zhang et al, 2018;Bischof et al, 2019;Depaoli et al, 2019).…”

Quantitative sub-cellular acyl-CoA analysis reveals distinct nuclear regulation

“…Quantification of compartmentalized metabolite pools has been previously approached by several methods. Genetically encoded fluorescent metabolite sensors can be targeted to specific compartments, and have been applied to a limited set of metabolites, including nicotinamide adenine dinucleotides (NAD+, NADH), adenosine triphosphate (ATP), glucose, glutamine, lactate, pyruvate, S-adenosyl methionine (SAM) and guanosine triphosphate (GTP) (Jaffrey, 2018; Okumoto et al, 2012; Zhang et al, 2018). However, these methods have technical limitations in that they require highly engineered experimental settings, and probes generally do not allow simultaneous monitoring of multiple metabolite species.…”

Altered Energy Metabolism During Early Optic Nerve Crush Injury: Implications of Warburg-Like Aerobic Glycolysis in Facilitating Retinal Ganglion Cell Survival

“…This discrepancy may be explained by differences between in vitro and in vivo conditions. In vivo, neurons are supported by the surrounding environment, particularly relying on astrocytes to provide lactate and pyruvate for oxidative phosphorylation [48][49][50]. Energetic support from activated astrocytes to neurons is important during early neurodegeneration and periods of increased energy demand [51][52][53], while isolated cultured neurons are typically cultured in 25 mmol/L glucose, a hyperglycemic environment that may disturb glucose b Fig.…”