Current technical approaches to brain energy metabolism

Abstract

Neuroscience is a technology-driven discipline and brain energy metabolism is no exception. Once satisfied with mapping metabolic pathways at organ level, we are now looking to learn what it is exactly that metabolic enzymes and transporters do and when, where do they reside, how are they regulated, and how do they relate to the specific functions of neurons, glial cells, and their subcellular domains and organelles, in different areas of the brain. Moreover, we aim to quantify the fluxes of metabolites within and between cells. Energy metabolism is not just a necessity for proper cell function and viability but plays specific roles in higher brain functions such as memory processing and behavior, whose mechanisms need to be understood at all hierarchical levels, from isolated proteins to whole subjects, in both health and disease. To this aim, the field takes advantage of diverse disciplines including anatomy, histology, physiology, biochemistry, bioenergetics, cellular biology, molecular biology, developmental biology, neurology, and mathematical modeling. This article presents a well-referenced synopsis of the technical side of brain energy metabolism research. Detail and jargon are avoided whenever possible and emphasis is given to comparative strengths, limitations, and weaknesses, information that is often not available in regular articles.

A highly responsive pyruvate sensor reveals pathway-regulatory role of the mitochondrial pyruvate carrier MPC

“…A new approach to mitochondrial function Mitochondria are the chief ATP producers of eukaryotic cells and also a principal site for the generation of building blocks for macromolecular synthesis. The speeds of these catabolic and anabolic pathways are assessed by diverse techniques 30 of complementary strengths and weaknesses. For catabolism, respirometry is the standard technique since the days of Otto Warburg.…”

“…A protocol to approach flux was devised based on the idea that acute inhibition of mitochondrial pyruvate entry at the MPC should cause a progressive fall in mitochondrial pyruvate as it is consumed by PDH and PC. Analogous methods have been applied successfully to the measurement of whole cell glucose, lactate and pyruvate consumptions in various cell types 9,29,30 .…”

GSEA of mouse and human mitochondriomes reveals fatty acid oxidation in astrocytes

“…A drawback of our study is that it is mainly based on data from transcriptomic studies, and hence it may not precisely reflect metabolic fluxes (Chubukov et al, ). Nevertheless transcriptomic studies have previously led to the identification of metabolic pathways (Corominas et al, ; Hu, Gu, Sun, Bai, & Wang, ) and they are a sound approach to address brain metabolism in humans (Barros et al, ). Moreover, genomic‐based models have been extensively used to study metabolic networks (Duarte et al, ) and to simulate metabolic‐based phenotypes of cancer cells (Gruetter, Seaquist, & Ugurbil, ; Lewis & Abdel‐Haleem, ; Lewis et al, ).…”

FRET‐based imaging of intracellular ATP in organotypic brain slices

“…In the last years, a large toolbox of genetically‐encoded nanosensors for metabolite imaging were developed, among them different sensors for ATP (Barros et al, ; Nakano, Imamura, Nagai, & Noji, ; Rajendran et al, ; Tantama et al, ; Yaginuma et al, ). Ateam, the sensor employed in the present study, exists in several variants, which exhibit different binding affinities to ATP ranging from several µM to 3.3 mM (Imamura et al, ).…”

“…While there is a wealth of experimental evidence supporting this so‐called astrocyte‐neuron lactate shuttle, there is an ongoing debate about its relevance (Bak & Walls, ; Barros & Weber, ), indicating that many aspects of neuron‐glia interaction and metabolic relationships between astrocytes and neurons are still not understood in detail. This is partly due to the lack of appropriate tools in the past, circumventing a dynamic determination of activity‐related changes in energy metabolites in brain tissue with (sub‐) cellular resolution (Barros et al, ). The recent development of suitable genetically encoded fluorescence sensors for metabolites such as ATP, glucose, lactate, or pyruvate (San Martin et al, ; Tantama, Hung, & Yellen, ) has provided first exciting new insights into cellular metabolism in cells in primary culture (Bittner et al, ; Tantama, Martinez‐Francois, Mongeon, & Yellen, ; Winkler et al, ), in isolated white matter tracts (Trevisiol et al ), brain tissue slices (Fernandez‐Moncada et al, ; Köhler et al, ), as well as in vivo (Mächler et al, ).…”