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Oligodendrocytes and astrocytes are metabolically coupled to neuronal compartments. Pyruvate and lactate can shuttle between glial cells and axons via monocarboxylate transporters. However, lactate can only be synthesized or used in metabolic reactions with the help of lactate dehydrogenase (LDH), a tetramer of LDHA and LDHB subunits in varying compositions. Here we show that mice with a cell type-specific disruption of both Ldha and Ldhb genes in oligodendrocytes lack a pathological phenotype that would be indicative of oligodendroglial dysfunctions or lack of axonal metabolic support. Indeed, when combining immunohistochemical, electron microscopical, and in situ hybridization analyses in adult mice, we found that the vast majority of mature oligodendrocytes lack detectable expression of LDH. Even in neurodegenerative disease models and in mice under metabolic stress LDH was not increased. In contrast, at early development and in the remyelinating brain, LDHA was readily detectable in immature oligodendrocytes. Interestingly, by immunoelectron microscopy LDHA was particularly enriched at gap junctions formed between adjacent astrocytes and at junctions between astrocytes and oligodendrocytes. Our data suggest that oligodendrocytes metabolize lactate during development and remyelination. In contrast, for metabolic support of axons mature oligodendrocytes may export their own glycolysis products as pyruvate rather than lactate. Lacking LDH, these oligodendrocytes can also "funnel" lactate through their "myelinic" channels between gap junction-coupled astrocytes and axons without metabolizing it. We suggest a working model, in which the unequal cellular distribution of LDH in white matter tracts facilitates a rapid and efficient transport of glycolysis products among glial and axonal compartments., (© 2024 The Authors. GLIA published by Wiley Periodicals LLC.)

Astrocytes are a heterogeneous population of glial cells in the brain, which adapt their properties to the requirements of the local environment. Two major groups of astrocytes are protoplasmic astrocytes residing in gray matter as well as fibrous astrocytes of white matter. Here, we compared the energy metabolism of astrocytes in the cortex and corpus callosum as representative gray matter and white matter regions, in acute brain slices taking advantage of genetically encoded fluorescent nanosensors for the NADH/NAD + redox ratio and for ATP. Astrocytes of the corpus callosum presented a more reduced basal NADH/NAD + redox ratio, and a lower cytosolic concentration of ATP compared to cortical astrocytes. In cortical astrocytes, the neurotransmitter glutamate and increased extracellular concentrations of K + , typical correlates of neuronal activity, induced a more reduced NADH/NAD + redox ratio. While application of glutamate decreased [ATP], K + as well as the combination of glutamate and K + resulted in an increase of ATP levels. Strikingly, a very similar regulation of metabolism by K + and glutamate was observed in astrocytes in the corpus callosum. Finally, strong intrinsic neuronal activity provoked by application of bicuculline and withdrawal of Mg 2+ caused a shift of the NADH/NAD + redox ratio to a more reduced state as well as a slight reduction of [ATP] in gray and white matter astrocytes. In summary, the metabolism of astrocytes in cortex and corpus callosum shows distinct basal properties, but qualitatively similar responses to neuronal activity, probably reflecting the different environment and requirements of these brain regions., (© 2022 The Authors. GLIA published by Wiley Periodicals LLC.)

Studies over the past two decades have demonstrated that astrocytes are tightly associated with neurons and play pivotal roles in neural circuit development, operation, and adaptation in health and disease. Nevertheless, precisely how astrocytes integrate diverse neuronal signals, modulate neural circuit structure and function at multiple temporal and spatial scales, and influence animal behavior or disease through aberrant excitation and molecular output remains unclear. This Perspective discusses how new and state-of-the-art approaches, including fluorescence indicators, opto- and chemogenetic actuators, genetic targeting tools, quantitative behavioral assays, and computational methods, might help resolve these longstanding questions. It also addresses complicating factors in interpreting astrocytes' role in neural circuit regulation and animal behavior, such as their heterogeneity, metabolism, and inter-glial communication. Research on these questions should provide a deeper mechanistic understanding of astrocyte-neuron assemblies' role in neural circuit function, complex behaviors, and disease., (© 2022 The Authors. GLIA published by Wiley Periodicals LLC.)

Astrocytes are a glial cell type, which is indispensable for brain energy metabolism. Within cells, the NADH/NAD + redox state is a crucial node in metabolism connecting catabolic pathways to oxidative phosphorylation and ATP production in mitochondria. To characterize the dynamics of the intracellular NADH/NAD + redox state in cortical astrocytes Peredox, a genetically encoded sensor for the NADH/NAD + redox state, was expressed in cultured cortical astrocytes as well as in cortical astrocytes in acutely isolated brain slices. Calibration of the sensor in cultured astrocytes revealed a mean basal cytosolic NADH/NAD + redox ratio of about 0.01; however, with a broad distribution and heterogeneity in the cell population, which was mirrored by a heterogeneous basal cellular concentration of lactate. Inhibition of glucose uptake decreased the NADH/NAD + redox state while inhibition of lactate dehydrogenase or of lactate release resulted in an increase in the NADH/NAD + redox ratio. Furthermore, the NADH/NAD + redox state was regulated by the extracellular concentration of K + , and application of the neurotransmitters ATP or glutamate increased the NADH/NAD + redox state dependent on purinergic receptors and glutamate uptake, respectively. This regulation by K + , ATP, and glutamate involved NBCe1 mediated sodium-bicarbonate transport. These results demonstrate that the NADH/NAD + redox state in astrocytes is a metabolic node regulated by neuronal signals reflecting physiological activity, most likely contributing to adjust astrocytic metabolism to energy demand of the brain., (© 2018 Wiley Periodicals, Inc.)

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., (© 2017 Wiley Periodicals, Inc.)

Nervous tissue is characterized by a tight structural association between glial cells and neurons. It is well known that glial cells support neuronal functions, but their role under pathologic conditions is less well understood. Here, we addressed this question in vivo using an experimental model of retinal ischemia and transgenic mice for glia-specific inhibition of soluble N-ethylmaleimide-sensitive factor attachment protein receptor (SNARE)-dependent exocytosis. Transgene expression reduced glutamate, but not ATP release from single Müller cells, impaired glial volume regulation under normal conditions and reduced neuronal dysfunction and death in the inner retina during the early stages of ischemia. Our study reveals that the SNARE-dependent exocytosis in glial cells contributes to neurotoxicity during ischemia in vivo and suggests glial exocytosis as a target for therapeutic approaches., (© 2017 The Authors GLIA Published by Wiley Periodicals, Inc.)

In the mammalian brain, the subcortical white matter comprises long-range axonal projections and their associated glial cells. Here, astrocytes and oligodendrocytes serve specific functions during development and throughout adult life, when they meet the metabolic needs of long fiber tracts. Within a short period of time, oligodendrocytes generate large amount of lipids, such as cholesterol, and membrane proteins for building the myelin sheaths. After myelination has been completed, a remaining function of glial metabolism is the energetic support of axonal transport and impulse propagation. Astrocytes can support axonal energy metabolism under low glucose conditions by the degradation of stored glycogen. Recently it has been recognized that the ability of glycolytic oligodendrocytes to deliver pyruvate and lactate is critical for axonal functions in vivo. In this review, we discuss the specific demands of oligodendrocytes during myelination and potential routes of metabolites between glial cells and myelinated axons. As examples, four specific metabolites are highlighted (cholesterol, glycogen, lactate, and N-acetyl-aspartate) that contribute to the specific functions of white matter glia. Regulatory processes are discussed that could be involved in coordinating metabolic adaptations and in providing feedback information about metabolic states., (© 2014 Wiley Periodicals, Inc.)

Astrocytes operate in close spatial relationship to other cells including neurons. Structural interaction is controlled by a dynamic interplay between actin-based cell motility and contact formation via cell-cell and cell-extracellular matrix adhesions. A central player in the control of cell adhesion is the cytoskeletal adaptor protein Vinculin. Incorporation of Vinculin affects mechanical properties and turnover of cell adhesion sites. To study the in vivo function of Vinculin in astrocytes, a mouse line with astrocyte specific and inducible deletion of vinculin was generated. Deletion of vinculin decreased the expression of the glial acidic fibrillary protein (GFAP) in Bergmann glial cells in the cerebellum. In addition, localization of GFAP to Bergmann glial endfeet was disturbed, indicating a role for vinculin in controlling its expression and localization. In contrast, vimentin expression, morphology, activation state and polarity of the targeted cells as well as the localization of the extracellular matrix protein laminin was not compromised. Furthermore, stab wound lesions were performed in the cerebellar cortex. In both wildtype and vinculin knockout mice GFAP expression was upregulated in Bergmann glial cells of the lesioned area with no differences observed between genotypes in expression and localization of GFAP. These results propose a selective requirement for vinculin in cellular events related to cell adhesion in vivo. As in vitro data suggested a major role for vinculin in the control of the cytoskeletal connection affecting mechanical stability and cell motility, our data add a note of caution to the extrapolation of in vitro data to in vivo function., (Copyright © 2013 Wiley Periodicals, Inc.)

To understand the pathomechanisms of spinal cord injuries will be a prerequisite to develop efficient therapies. By investigating acute lesions of spinal cord white matter in anesthetized mice with fluorescently labeled microglia and axons using in vivo two-photon laser-scanning microscopy (2P-LSM), we identified the messenger nitric oxide (NO) as a modulator of injury-activated microglia. Local tissue damages evoked by high-power laser pulses provoked an immediate attraction of microglial processes. Spinal superfusion with NO synthase and guanylate cyclase inhibitors blocked these extensions. Furthermore, local injection of the NO-donor spermine NONOate (SPNO) or the NO-dependent second messenger cGMP induced efficient migration of microglial cells toward the injection site. High-tissue levels of NO, achieved by uniform superfusion with SPNO and mimicking extended tissue damage, resulted in a fast conversion of the microglial shape from ramified to ameboid indicating cellular activation. When the spinal white matter was preconditioned by increased, ambient ATP (known as a microglial chemoattractant) levels, the attraction of microglial processes to local NO release was augmented, whereas it was abolished at low levels of tissue ATP. Because both signaling molecules, NO and ATP, mediate acute microglial reactions, coordinated pharmacological targeting of NO and purinergic pathways will be an effective mean to influence the innate immune processes after spinal cord injury., (Copyright 2010 Wiley-Liss, Inc.)

Inducible gene modification using the Cre/loxP system provides a valuable tool for the analysis of gene function in the active animal. GFAP-Cre transgenic mice have been developed to achieve gene recombination in astrocytes, the most abundant cells of the central nervous system, with pivotal roles during brain function and pathology. Unfortunately, these mice displayed neuronal recombination as well, since the GFAP promoter is also active in embryonic radial glia, which possess a substantial neurogenic potential. To enable the temporal control of gene deletions in astrocytes only, we generated a transgenic mouse with expression of CreERT2, a fusion protein of the DNA recombinase Cre and a mutated ligand-binding domain of the estrogen receptor, under the control of the human GFAP promoter. In offspring originating from crossbreedings of GFAP-CreERT2-transgenic mice with various Cre-sensitive reporter mice, consecutive intraperitoneal injections of tamoxifen induced genomic recombination selectively in astrocytes of almost all brain regions. In Bergmann glia, which represent the main astroglial cell population of the cerebellum, virtually all cells showed successful gene recombination. When adult mice received cortical stab wound lesions, simultaneously given tamoxifen induced substantial recombination in reactive glia adjacent to the site of injury. These transgenic GFAP-CreERT2 mice will allow the functional analysis of loxP-modified genes in astroglia of the postnatal and adult brain., (Copyright 2005 Wiley-Liss, Inc.)