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Single-cell imaging tools for brain energy metabolism: a review.

San Martín A, Sotelo-Hitschfeld T, Lerchundi R, Fernández-Moncada I, Ceballo S, Valdebenito R, Baeza-Lehnert F, Alegría K, Contreras-Baeza Y, Garrido-Gerter P, Romero-Gómez I, Barros LF - Neurophotonics (2014)

Bottom Line: We argue that metabolism needs to be approached both in vitro and in vivo, and that it does not just exist as a low-level platform but is also a relevant player in information processing.In recent years, genetically encoded fluorescent nanosensors have been introduced to measure glucose, glutamate, ATP, NADH, lactate, and pyruvate in mammalian cells.Reporting relative metabolite levels, absolute concentrations, and metabolic fluxes, these sensors are instrumental for the discovery of new molecular mechanisms.

View Article: PubMed Central - PubMed

Affiliation: Centro de Estudios Científicos , Arturo Prat 514, Valdivia, 5110466, Chile ; Universidad Austral de Chile , Valdivia, Chile.

ABSTRACT
Neurophotonics comes to light at a time in which advances in microscopy and improved calcium reporters are paving the way toward high-resolution functional mapping of the brain. This review relates to a parallel revolution in metabolism. We argue that metabolism needs to be approached both in vitro and in vivo, and that it does not just exist as a low-level platform but is also a relevant player in information processing. In recent years, genetically encoded fluorescent nanosensors have been introduced to measure glucose, glutamate, ATP, NADH, lactate, and pyruvate in mammalian cells. Reporting relative metabolite levels, absolute concentrations, and metabolic fluxes, these sensors are instrumental for the discovery of new molecular mechanisms. Sensors continue to be developed, which together with a continued improvement in protein expression strategies and new imaging technologies, herald an exciting era of high-resolution characterization of metabolism in the brain and other organs.

No MeSH data available.


Organization of metabolism. The living organism is represented as a hierarchical stack of modular systems. Interactions at any level are stronger than at higher levels, which is the basis for dissectability. In this example regarding metabolism, the enzyme hexokinase (represented by a blue oval) is shown to be constituted by amino acids (black ovals). In the next level up, hexokinase associates with other enzymes and cofactors to constitute the glycolytic machinery (green oval). Further up the organizational ladder, the glycolytic machinery associates with organelles and other structures to form an astrocyte (yellow oval), which in turn interacts with neurons and vessels to shape the neurogliovascular unit (orange oval) [after J. G. Miller’s generalized living system13].
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f1: Organization of metabolism. The living organism is represented as a hierarchical stack of modular systems. Interactions at any level are stronger than at higher levels, which is the basis for dissectability. In this example regarding metabolism, the enzyme hexokinase (represented by a blue oval) is shown to be constituted by amino acids (black ovals). In the next level up, hexokinase associates with other enzymes and cofactors to constitute the glycolytic machinery (green oval). Further up the organizational ladder, the glycolytic machinery associates with organelles and other structures to form an astrocyte (yellow oval), which in turn interacts with neurons and vessels to shape the neurogliovascular unit (orange oval) [after J. G. Miller’s generalized living system13].

Mentions: Metabolism is the sum of the chemical processes that occur in living organisms. Defined in a broader way, it also includes the transport of the chemicals between membrane compartments. Metabolism is hierarchically ordered, spanning multiple spatial and temporal scales, and is modular, hence accessible to reductionist investigation13 (Fig. 1). The modular nature of metabolism is explained by a progressive weakening of interactions as distances become larger. Molecular processes are dominated by strong, short-range forces, and are relatively insensitive to the weaker, long-range forces that determine the structure of cells and tissues. Thus, microscopic properties of enzymes, such as substrate specificity, withstanding harsh extraction and purification procedures, are what proved fundamental for the mapping of the metabolic network during the first half of the 20th century. At the next level of organization, enzymes associate with other proteins and lipids, interactions that are important for regulation. Except for the inner workings of mitochondria, which are readily purified and studied by respirometry, the subcellular level of metabolic organization is virtually uncharted territory. For instance, there is evidence of physical interaction and functional cross-talk between the glycolytic machinery and the ATPase, the great energy spender, but the nature of the interaction does not seem to be energetic.14 What are the mechanisms that match energy production to energy consumption? The enzymes of glycolysis are expressed in stoichiometric proportions.15 Is this finding related to their possible association in functional modules? Hexokinase, the first enzyme of glycolysis, is bound to mitochondria and also to the co-transporter.16,17 Are these interactions part of the machinery matching glycolysis to mitochondrial respiration? Mitochondrial metabolism is sensitive to calcium signals.18–20 What are the relative roles of energy status, redox status, substrate supply, and calcium-signaling in the control of mitochondrial flux? Are mitochondria fueled by pyruvate or by lactate?21 How can glycogen be mobilized without generating a traffic jam at phosphofructokinase? These are the kinds of questions that need to be tackled at the subcellular level.


Single-cell imaging tools for brain energy metabolism: a review.

San Martín A, Sotelo-Hitschfeld T, Lerchundi R, Fernández-Moncada I, Ceballo S, Valdebenito R, Baeza-Lehnert F, Alegría K, Contreras-Baeza Y, Garrido-Gerter P, Romero-Gómez I, Barros LF - Neurophotonics (2014)

Organization of metabolism. The living organism is represented as a hierarchical stack of modular systems. Interactions at any level are stronger than at higher levels, which is the basis for dissectability. In this example regarding metabolism, the enzyme hexokinase (represented by a blue oval) is shown to be constituted by amino acids (black ovals). In the next level up, hexokinase associates with other enzymes and cofactors to constitute the glycolytic machinery (green oval). Further up the organizational ladder, the glycolytic machinery associates with organelles and other structures to form an astrocyte (yellow oval), which in turn interacts with neurons and vessels to shape the neurogliovascular unit (orange oval) [after J. G. Miller’s generalized living system13].
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC4478754&req=5

f1: Organization of metabolism. The living organism is represented as a hierarchical stack of modular systems. Interactions at any level are stronger than at higher levels, which is the basis for dissectability. In this example regarding metabolism, the enzyme hexokinase (represented by a blue oval) is shown to be constituted by amino acids (black ovals). In the next level up, hexokinase associates with other enzymes and cofactors to constitute the glycolytic machinery (green oval). Further up the organizational ladder, the glycolytic machinery associates with organelles and other structures to form an astrocyte (yellow oval), which in turn interacts with neurons and vessels to shape the neurogliovascular unit (orange oval) [after J. G. Miller’s generalized living system13].
Mentions: Metabolism is the sum of the chemical processes that occur in living organisms. Defined in a broader way, it also includes the transport of the chemicals between membrane compartments. Metabolism is hierarchically ordered, spanning multiple spatial and temporal scales, and is modular, hence accessible to reductionist investigation13 (Fig. 1). The modular nature of metabolism is explained by a progressive weakening of interactions as distances become larger. Molecular processes are dominated by strong, short-range forces, and are relatively insensitive to the weaker, long-range forces that determine the structure of cells and tissues. Thus, microscopic properties of enzymes, such as substrate specificity, withstanding harsh extraction and purification procedures, are what proved fundamental for the mapping of the metabolic network during the first half of the 20th century. At the next level of organization, enzymes associate with other proteins and lipids, interactions that are important for regulation. Except for the inner workings of mitochondria, which are readily purified and studied by respirometry, the subcellular level of metabolic organization is virtually uncharted territory. For instance, there is evidence of physical interaction and functional cross-talk between the glycolytic machinery and the ATPase, the great energy spender, but the nature of the interaction does not seem to be energetic.14 What are the mechanisms that match energy production to energy consumption? The enzymes of glycolysis are expressed in stoichiometric proportions.15 Is this finding related to their possible association in functional modules? Hexokinase, the first enzyme of glycolysis, is bound to mitochondria and also to the co-transporter.16,17 Are these interactions part of the machinery matching glycolysis to mitochondrial respiration? Mitochondrial metabolism is sensitive to calcium signals.18–20 What are the relative roles of energy status, redox status, substrate supply, and calcium-signaling in the control of mitochondrial flux? Are mitochondria fueled by pyruvate or by lactate?21 How can glycogen be mobilized without generating a traffic jam at phosphofructokinase? These are the kinds of questions that need to be tackled at the subcellular level.

Bottom Line: We argue that metabolism needs to be approached both in vitro and in vivo, and that it does not just exist as a low-level platform but is also a relevant player in information processing.In recent years, genetically encoded fluorescent nanosensors have been introduced to measure glucose, glutamate, ATP, NADH, lactate, and pyruvate in mammalian cells.Reporting relative metabolite levels, absolute concentrations, and metabolic fluxes, these sensors are instrumental for the discovery of new molecular mechanisms.

View Article: PubMed Central - PubMed

Affiliation: Centro de Estudios Científicos , Arturo Prat 514, Valdivia, 5110466, Chile ; Universidad Austral de Chile , Valdivia, Chile.

ABSTRACT
Neurophotonics comes to light at a time in which advances in microscopy and improved calcium reporters are paving the way toward high-resolution functional mapping of the brain. This review relates to a parallel revolution in metabolism. We argue that metabolism needs to be approached both in vitro and in vivo, and that it does not just exist as a low-level platform but is also a relevant player in information processing. In recent years, genetically encoded fluorescent nanosensors have been introduced to measure glucose, glutamate, ATP, NADH, lactate, and pyruvate in mammalian cells. Reporting relative metabolite levels, absolute concentrations, and metabolic fluxes, these sensors are instrumental for the discovery of new molecular mechanisms. Sensors continue to be developed, which together with a continued improvement in protein expression strategies and new imaging technologies, herald an exciting era of high-resolution characterization of metabolism in the brain and other organs.

No MeSH data available.