In Vivo Evidence for a Lactate Gradient from Astrocytes to Neurons

Metabolic reprogramming of astrocytes: Emerging roles of lactate

Lactate serves as a key energy metabolite in the central nervous system, facilitating essential brain functions, including energy supply, signaling, and epigenetic modulation. Moreover, it links epigenetic modifications with metabolic reprogramming. Nonetheless, the specific mechanisms and roles of this connection in astrocytes remain unclear. Therefore, this review aims to explore the role and specific mechanisms of lactate in the metabolic reprogramming of astrocytes in the central nervous system. The close relationship between epigenetic modifications and metabolic reprogramming was discussed. Therapeutic strategies for targeting metabolic reprogramming in astrocytes in the central nervous system were also outlined to guide future research in central nervous system diseases. In the nervous system, lactate plays an essential role. However, its mechanism of action as a bridge between metabolic reprogramming and epigenetic modifications in the nervous system requires future investigation. The involvement of lactate in epigenetic modifications is currently a hot research topic, especially in lactylation modification, a key determinant in this process. Lactate also indirectly regulates various epigenetic modifications, such as N6-methyladenosine, acetylation, ubiquitination, and phosphorylation modifications, which are closely linked to several neurological disorders. In addition, exploring the clinical applications and potential therapeutic strategies of lactic acid provides new insights for future neurological disease treatments.

Mesenchymal stem cell transplantation ameliorates inflammation in spinal cord injury by inhibiting lactylation-related genes

BACKGROUND

The immune microenvironment significantly influences neural regeneration in spinal cord injury (SCI). Lactate activates central nervous system (CNS) glial cells, prompting the secretion of proinflammatory cytokines and triggering an inflammatory response. Mesenchymal stem cells (MSCs) make a promising future for SCI therapy due to their immune regulation and anti-inflammatory properties. However, it is unclear whether MSCs inhibit inflammatory responses in the SCI microenvironment through lactylation regulation. This study aimed to identify lactylation-related genes (LRGs) in SCI and investigate their role in immune cell infiltration and MSC-mediated inflammation reduction.

METHODS

Transcription datasets of SCI patients were acquired from Gene Expression Omnibus (GEO). Differentially expressed genes (DEGs) underwent functional enrichment analysis, and CIBERSORT assessed immune cell infiltration in SCI. Crucial lactylation-related differentially expressed genes (LRDEGs) associated with SCI were identified via machine learning. The association between LRDEGs and inflammatory response in SCI mediated by immune cell infiltration was confirmed using Gene Ontology (GO), and Kyoto Encyclopedia of Genes and Genomes (KEGG). Rats with subacute thoracic SCI were transplanted with hUC-MSCs, and transcriptome analyses were conducted on their spinal cords and retrieved hUC-MSCs, respectively.

RESULTS

The study identified 808 DEGs and 13 differentially infiltrated immune cell types in SCI patients compared to healthy controls. Multiple inflammatory response-related signaling pathways were activated in SCI. Seven LRDEGs, including LSP1, XRCC4, HSDL2, HNRNPH1, RPL14, IKZF1, and TP53, were recognized as key regulators. These genes are linked to immune cell infiltration and inflammatory responses in SCI. In SCI rats, the increased expression of LRDEGs and inflammatory cytokines were observed, which were significantly reduced after hUC-MSC transplantation. Differences in LRDEG expression patterns, enriched functions, and pathways between two SCI subtypes were statistically significant.

CONCLUSIONS

LRDEGs are involved in immune cell-mediated inflammatory response in SCI, and hUC-MSC transplantation reduces LRDEGs expression and inflammation response in the SCI microenvironment.

Astrocytic GLUT1 deletion in adult mice enhances glucose metabolism and resilience to stroke

Brain activity relies on a steady supply of blood glucose. Astrocytes express glucose transporter 1 (GLUT1), considered their primary route for glucose uptake to sustain metabolic and antioxidant support for neurons. While GLUT1 deficiency causes severe developmental impairments, its role in adult astrocytes remains unclear. Here, we show that astrocytes and neurons tolerate the inducible, astrocyte-specific deletion of GLUT1 in adulthood. Sensorimotor and memory functions remain intact in male GLUT1 cKO mice, indicating that GLUT1 loss does not impair behavior. Despite GLUT1 loss, two-photon glucose sensor imaging reveals that astrocytes maintain normal resting glucose levels but exhibit a more than two-fold increase in glucose consumption, indicating enhanced metabolic activity. Notably, male GLUT1 cKO mice display reduced infarct volumes following stroke, suggesting a neuroprotective effect of increased astrocytic glucose metabolism. Our findings reveal metabolic adaptability in astrocytes, ensuring glucose uptake and neuronal support despite the absence of their primary transporter.

A multiscale electro-metabolic model of a rat neocortical circuit reveals the impact of ageing on central cortical layers

The high energetic demands of the brain arise primarily from neuronal activity. Neurons consume substantial energy to transmit information as electrical signals and maintain their resting membrane potential. These energetic requirements are met by the neuro-glial-vascular (NGV) ensemble, which generates energy in a coupled metabolic process. In ageing, metabolic function becomes impaired, producing less energy and, consequently, the system is unable to sustain the neuronal energetic needs. We propose a multiscale model of electro-metabolic coupling in a reconstructed rat neocortex. This combines an electro-morphologically reconstructed electrophysiological model with a detailed NGV metabolic model. Our results demonstrate that the large-scale model effectively captures electro-metabolic processes at the circuit level, highlighting the importance of heterogeneity within the circuit, where energetic demands vary according to neuronal characteristics. Finally, in metabolic ageing, our model indicates that the middle cortical layers are particularly vulnerable to energy impairment.

Apolipoprotein E in Alzheimer's disease: molecular insights and therapeutic opportunities

Apolipoprotein E (APOE- gene; apoE- protein) is the strongest genetic modulator of late-onset Alzheimer's disease (AD), with its three major isoforms conferring risk for disease ε2 < ε3 < ε4. Emerging protective gene variants, such as APOE Christchurch and the COLBOS variant of REELIN, an alternative target of certain apoE receptors, offer novel insights into resilience against AD. In recent years, the role of apoE has been shown to extend beyond its primary function in lipid transport, influencing multiple biological processes, including amyloid-β (Aβ) aggregation, tau pathology, neuroinflammation, autophagy, cerebrovascular integrity and protection from lipid peroxidation and the resulting ferroptotic cell death. While the detrimental influence of apoE ε4 on these and other processes has been well described, the molecular mechanisms underpinning this disadvantage require further enunciation, particularly to realize therapeutic opportunities related to apoE. This review explores the multifaceted roles of apoE in AD pathogenesis, emphasizing recent discoveries and translational approaches to target apoE-mediated pathways. These findings underscore the potential for apoE-based therapeutic strategies to prevent or mitigate AD in genetically at-risk populations.

Lactate shuttling links histone lactylation to adult hippocampal neurogenesis in mice

Lactate has emerged as a central metabolic fuel and an important signaling molecule. Its availability participates in various brain functions. Although lactate homeostasis is vital for adult hippocampal neurogenesis and cognition, it is still unknown how shuttles lactate across the plasma membrane of neural stem cells (NSCs) to control their activity and neurogenic potential. In this study, we show that monocarboxylate transporter (MCT)1 and MCT2, respectively, control efflux and influx of lactate in the murine NSCs, thereby maintaining intracellular lactate homeostasis. Mechanistically, lactate shuttling links histone lactylation to govern NSC proliferation through MDM2-p53 signaling pathway. Notably, genetic ablation of MCT2 from NSCs or pharmacological inhibition of MDM2-P53 interaction prevents voluntary running-induced NSC proliferation in the murine adult hippocampus. Taken together, our findings demonstrate that lactate shuttling controls histone lactylation, which acts as a nexus for controlling adult hippocampal neurogenesis.

From energy metabolism to mood regulation: The rise of lactate as a therapeutic target

BACKGROUND

Disruption of cerebral energy metabolism is increasingly recognized as a key factor in the pathophysiology of mood disorders. Lactate, beyond its role as a metabolic byproduct, is now understood to be a critical player in brain energy homeostasis and a modulator of neuronal function. Recent advances in understanding lactate shuttling between astrocytes and neurons have opened new avenues for exploring its multifaceted roles in mood regulation. Exercise, known to modulate brain lactate levels, further underscores the potential of lactate as a therapeutic target in mood disorders.

AIM OF REVIEW

This review delves into the alterations in cerebral lactate associated with mood disorders, emphasizing their implications for brain energy dynamics and signaling pathways. Additionally, we discuss the therapeutic potential of lactate in mood disorders, particularly through its capacity to remodel cerebral function. We conclude by assessing the promise of exercise-induced lactate production as a novel strategy for mood disorder treatment.

KEY SCIENTIFIC CONCEPTS OF THE REVIEW

Alterations in brain lactate may contribute to the pathogenesis of mood disorders. In several studies, lactate is not only a substrate for brain energy metabolism, but also a molecule that triggers signaling cascades. Specifically, lactate is involved in the regulation of neurogenesis, neuroplasticity, endothelial cell function, and microglia lysosomal acidification, therefore improving mood disorders. Meanwhile, exercise as a low-risk intervention strategy can improve mood disorders through lactate regulation. Thus, the evidence from this review supports that lactate could be a potential therapeutic target for mood disorder, contributing to a deeper understanding of mood disorder pathogenesis and intervention.

Insulin acts on astrocytes to shift their substrate preference to fatty acids

It is increasingly recognized that brain can β-oxidize fatty acids for use as an energy substrate. However, mechanism(s) by which neural cells switch their preference from glucose to fatty acids are not fully elucidated. Here we provide evidence that insulin acts directly on astrocytes to promote the uptake of glucose and fatty acids while modifying their substrate preference through a sequential shift in the expression of genes associated with fatty acid uptake, synthesis, transport, and metabolism. Under these conditions, fatty acids are converted into TCA cycle intermediates to satisfy astrocyte energy demands, allowing pyruvate derived from glucose to be directed toward the production of lactate; a preferred fuel for neurons. This shift in astrocyte energy substrate preference is required for insulin to enhance long-term potentiation in the Schaffer collateral. These findings establish a homeostatic mechanism where insulin promotes LTP by switching the energy substrate preference of astrocytes to fatty acids.

Fueling Brain Inhibition: Integrating GABAergic Neurotransmission and Energy Metabolism

Despite decades of research in brain energy metabolism and to what extent different cell types utilize distinct substrates for their energy metabolism, this topic remains a vibrant area of neuroscience research. In this review, we focus on the substrates utilized by the inhibitory GABAergic neurons, which has been less explored than glutamatergic neurons. First, we discuss how GABAergic neurons may utilize both glucose, lactate, or ketone bodies under different functional conditions, and provide some preliminary data suggesting that unlike glutamatergic neurons, GABAergic neurons work well when substrate supply is restricted to lactate. We end by discussing the role of GABAergic neuron energy metabolism in pathologies where failure of inhibitory function play a central role, namely epilepsy, hepatic encephalopathy, and Alzheimer's disease.

Lactylation in Glioblastoma: A Novel Epigenetic Modifier Bridging Epigenetic Plasticity and Metabolic Reprogramming

Glioblastoma, the most common and aggressive primary malignant brain tumor, is characterized by a high rate of recurrence, disability, and lethality. Therefore, there is a pressing need to develop more effective prognostic biomarkers and treatment approaches for glioblastoma. Lactylation, an emerging form of protein post-translational modification, has been closely associated with lactate, a metabolite of glycolysis. Since the initial identification of lactylation sites in core histones in 2019, accumulating evidence has shown the critical role that lactylation plays in glioblastoma development, assessment of poor clinical prognosis, and immunosuppression, which provides a fresh angle for investigating the connection between metabolic reprogramming and epigenetic plasticity in glioblastoma cells. The objective of this paper is to present an overview of the metabolic and epigenetic roles of lactylation in the expanding field of glioblastoma research and explore the practical value of developing novel treatment plans combining targeted therapy and immunotherapy.

Monitoring Acidification Preceding Aβ Deposition in Alzheimer's Disease

Amyloid beta (Aβ) is the primary early biomarker of Alzheimer's disease (AD), and since an acidic environment promotes Aβ aggregation, acidification plays a crucial role in AD progression. In this study, a novel acid-responsive near-infrared (NIR) fluorescent probe alongside multiple molecular biology techniques to investigate the temporal relationship between acidification and Aβ deposition, as well as the underlying mechanisms of acidification is employed. By monitoring 2- to 11-month-old APP/PS1 mice and wild-type (WT) mice, it is detected significant fluorescence signal in APP/PS1 mice beginning at 3 months preceding Aβ deposition at 5 months, and peaking at 5 months, followed by cognitive deficits at 8 months. Additionally, elevated monocarboxylate transporter 4 (MCT4) protein expression in 3-month-old APP/PS1 mice indicated disruption of astrocyte-neuron lactate shuttle (ANLS) homeostasis. Overall, this findings first demonstrate that acidification precedes Aβ deposition, peaks at the onset of Aβ deposition, and diminishes thereafter, with early acidification likely driven by the disruption of ANLS.

Metabolic reprogramming: a new option for the treatment of spinal cord injury

Spinal cord injuries impose a notably economic burden on society, mainly because of the severe after-effects they cause. Despite the ongoing development of various therapies for spinal cord injuries, their effectiveness remains unsatisfactory. However, a deeper understanding of metabolism has opened up a new therapeutic opportunity in the form of metabolic reprogramming. In this review, we explore the metabolic changes that occur during spinal cord injuries, their consequences, and the therapeutic tools available for metabolic reprogramming. Normal spinal cord metabolism is characterized by independent cellular metabolism and intercellular metabolic coupling. However, spinal cord injury results in metabolic disorders that include disturbances in glucose metabolism, lipid metabolism, and mitochondrial dysfunction. These metabolic disturbances lead to corresponding pathological changes, including the failure of axonal regeneration, the accumulation of scarring, and the activation of microglia. To rescue spinal cord injury at the metabolic level, potential metabolic reprogramming approaches have emerged, including replenishing metabolic substrates, reconstituting metabolic couplings, and targeting mitochondrial therapies to alter cell fate. The available evidence suggests that metabolic reprogramming holds great promise as a next-generation approach for the treatment of spinal cord injury. To further advance the metabolic treatment of the spinal cord injury, future efforts should focus on a deeper understanding of neurometabolism, the development of more advanced metabolomics technologies, and the design of highly effective metabolic interventions.

Neuroprotective mechanisms of exercise and the importance of fitness for healthy brain ageing

Ageing is a scientifically fascinating and complex biological occurrence characterised by morphological and functional changes due to accumulated molecular and cellular damage impairing tissue and organ function. Ageing is often accompanied by cognitive decline but is also the biggest known risk factor for Alzheimer's disease, the most common form of dementia. Emerging evidence suggests that sedentary and unhealthy lifestyles accelerate brain ageing, while regular physical activity, high cardiorespiratory fitness (CRF), or a combination of both, can mitigate cognitive impairment and reduce dementia risk. The purpose of this Review is to explore the neuroprotective mechanisms of endurance exercise and highlight the importance of CRF in promoting healthy brain ageing. Key findings show how CRF mediates the neuroprotective effects of exercise via mechanisms such as improved cerebral blood flow, reduced inflammation, and enhanced neuroplasticity. We summarise evidence supporting the integration of endurance exercise that enhances CRF into public health initiatives as a preventive measure against age-related cognitive decline. Additionally, we address important challenges such as lack of long-term studies with harmonised study designs across preclinical and clinical settings, employing carefully controlled and repeatable exercise protocols, and outline directions for future research.

Lactate: Beyond a mere fuel in the epileptic brain

Epilepsy, a prevalent neurological disorder characterized by spontaneous recurrent seizures, significantly impacts physiological and cognitive functions. Emerging evidence suggests a crucial role for metabolic factors, particularly lactate, in epilepsy. We discuss the applicability of the astrocyte-neuron lactate shuttle (ANLS) model during acute seizure events and examine lactate's metabolic adaptation in epilepsy progression. Additionally, the roles of lactate metabolism in microglia and oligodendrocytes are considered, aiming to supplement our understanding of neuro-glial metabolic interactions as extensions of the ANLS model. Additionally, lactate modulates neuronal excitability via its interaction with hydroxycarboxylic acid receptor 1 (HCAR1), alongside additional mechanisms involving acid-sensing ion channels (ASICs) and ATP-sensitive potassium (KATP) channels, which contribute as secondary modulatory pathways. In conclusion, we propose that lactate functions as more than a mere fuel source in the epileptic brain, offering potential insights into new therapeutic targets for seizure control.

Energetic diversity in retinal ganglion cells is modulated by neuronal activity and correlates with resilience to degeneration

Neuronal function requires high energy expenditure that is likely customized to meet specific signaling demands. However, little is known about diversity of metabolic homeostasis among divergently-functioning types of neurons. To this end, we examined retinal ganglion cells (RGCs), a population of closely related, yet electrophysiologically distinct excitatory projection neurons. Using in vivo 2-photon imaging to measure ATP with single cell resolution, we identified differential homeostatic energy maintenance in the RGC population that correspond to distinct RGC types. In the presence of circuit activity, the most active RGC type (Alpha RGCs), had lower homeostatic ATP levels than other types and exhibited the greatest magnitude of ATP decline when ATP synthesis was inhibited. By simultaneously manipulating circuit activity and mitochondrial function, we found that while oxidative phosphorylation was required to meet ATP demands during circuit activity, it was expendable to maintain resting ATP levels. We also examined ATP signatures associated with survival and injury response after axotomy and report a correlation between low homeostatic ATP and increased survival. In addition, we observed transient ATP increases in RGCs following axon injury. Together, these findings identify diversity of energy handling capabilities of dynamically active neurons with implications for neuronal resilience.

Causal interaction of metabolic oscillations in monolayers of Hela cervical cancer cells: emergence of complex networks

A novel global cooperative phenomenon was observed in monolayers of HeLa cervical cancer cells that exhibited glycolytic oscillations but did not exhibit synchronisation or partial synchronisation. The analysis of causality of the oscillations between cell pairs in the cell-monolayer sheet revealed a hidden causal interaction network. Furthermore, the network exhibits characteristics of a broad-scale network. This suggests that key cells perform a hub-like function in the network and that the population of HeLa cells forms metabolically connected functional network rather than randomly connected one. Unlike previous work that focused on the synchronisation of glycolytic oscillations in the HeLa cells, the present study analysed the causality between the oscillating cells by Convergent Cross Mapping (CCM), which is based on the phase-space reconstruction of time-series data and is used to find causality in weakly coupled components of nonlinear dynamical systems. We believe that the framework proposed in this study is useful for investigating the hidden state of a group of cells and can accelerate studies on cellular metabolic phenomena including metabolic oscillations in [Formula: see text] cells within islets of Langerhans. It would also be applicable to systems of weakly coupled oscillators that may include hidden cooperative phenomena.

Knocking down the neuronal lactate transporter MCT2 in the arcuate nucleus of female rats increases food intake and body weight

In the arcuate nucleus of the hypothalamus, tanycyte-neuron interactions regulate glucose homeostasis and feeding behavior. Previously, we reported that monocarboxylate transporters (MCT) 1 and 4 are localized in tanycytes, whereas MCT2 is present in arcuate nucleus neurons, including orexigenic and anorexigenic neurons (POMC). MCT1 and MCT4 inhibition impacts feeding behavior, suggesting that monocarboxylate transfer between tanycytes and neurons influences food intake. Electrophysiological studies have shown that POMC neurons respond to lactate through transport and indirect signaling using astrocytic hydroxycarboxylic acid receptor 1. To investigate the role of MCT2 further, we generated MCT2 knockdown rats and analyzed their feeding behavior. Female Sprague-Dawley rats received bilateral injections in the arcuate nucleus with an adeno-associated virus (AAV) carrying a specific short hairpin RNA to inhibit MCT2 expression, thereby generating neuronal MCT2 knockdown rats. Knockdown efficiency in rat hypothalamic tissue was assessed using real-time PCR, Western Blot, and immunohistochemistry. The acute effect on feeding behavior was evaluated following 24 h of fasting, followed by 24 h of refeeding. In MCT2-knockdown rats, we observed additional inhibition of MCT1, suggesting a potential glial response to increased parenchymal lactate levels. Both macrostructure and microstructure of feeding were evaluated in MCT2-knockdown rats and compared to control AAV-injected rats. MCT2 knockdown led to a significant increase in macrostructural parameters, such as food intake and body weight. These findings underscore the importance of lactate transfer as a mechanism in tanycyte-neuron communication mediated by monocarboxylates.

Astrocyte neuronal metabolic coupling in the anterior cingulate cortex of mice with inflammatory pain

Chronic pain is a major global concern, with at least 1 in 5 people suffering from chronic pain worldwide. Mounting evidence indicates that neuroplasticity of the anterior cingulate cortex (ACC) is a critical step in the development of chronic pain. Previously, we found that chronic pain and fear learning are both associated with enhanced neuronal excitability and cause similar neuroplasticity-related gene expression changes in the ACC of male mice. However, neuroplasticity, imposes large metabolic demands. In the brain, neurons have the highest energy needs and interact with astrocytes, which extract glucose from blood, mobilize glycogen, and release lactate in response to neuronal activity. Here, we use chronic and continuous inflammatory pain models in female and male mice to investigate the involvement of astrocyte-neuronal lactate shuttling (ANLS) in the ACC of female and male mice experiencing inflammatory pain. We found that ANLS in the mouse ACC promotes the development of chronic inflammatory pain, and expresses sex specific patterns of activation. Specifically, whereas both male and female mice show similar levels of chronic pain hypersensitivity, only male mice show sustained increases in lactate levels. Accordingly, chronic pain alters the expression levels of proteins involved in lactate metabolism and shuttling in a sexually dimorphic manner. We found that disrupting astrocyte-neuronal lactate shuttling in the ACC prior to inflammatory injury prevents the development of pain hypersensitivity in female and male mice, but only reduces temporary pain in male mice. Furthermore, using a transgenic mouse model (itga1-null mice) that displays a naturally occurring form of spontaneous osteoarthritis (OA), a painful inflammatory pain condition, we found that whereas both female and male mice develop OA, only male mice show increases in mechanisms involved in astrocyte-neuronal lactate shuttling. Our findings thus indicate that there are sex differences in astrocyte-neuronal metabolic coupling in the mouse ACC during chronic pain development.

Astrocyte involvement in metabolic regulation and disease

Astrocytes, the predominant glial cell type in the mammalian brain, influence a wide variety of brain parameters including neuronal energy metabolism. Exciting recent studies have shown that obesity and diabetes can impact on astrocyte function. We review evidence that dysregulation of astrocytic lipid metabolism and glucose sensing contributes to dysregulation of whole-body energy balance, thermoregulation, and insulin sensitivity. In addition, we consider the overlooked topic of the sex-specific roles of astrocytes and their response to hormonal fluctuations that provide insights into sex differences in metabolic regulation. Finally, we provide an update on potential ways to manipulate astrocyte function, including genetic targeting, optogenetic and chemogenetic techniques, transplantation, and tailored exosome-based therapies, which may lead to improved treatments for metabolic disease.

Dynamics of Neuronal and Astrocytic Energy Molecules in Epilepsy

The dynamics of energy molecules in the mouse brain during metabolic challenges induced by epileptic seizures were examined. A transgenic mouse line expressing a fluorescence resonance energy transfer (FRET)-based adenosine triphosphate (ATP) sensor, selectively expressed in the cytosol of neurons, was used. An optical fiber was inserted into the hippocampus, and changes in cytosolic ATP concentration were estimated using the fiber photometry method. To induce epileptic neuronal hyperactivity, a train of electrical stimuli was delivered to a bipolar electrode placed alongside the optical fiber. Although maintaining a steady cytosolic ATP concentration is crucial for cell survival, a single episode of epileptic neuronal hyperactivity drastically reduced neuronal ATP levels. Interestingly, the magnitude of ATP reduction did not increase with the exacerbation of epilepsy, but rather decreased. This suggests that the primary consumption of ATP during epileptic neuronal hyperactivity may not be solely directed toward restoring the Na+ and K+ ionic imbalance caused by action potential bursts. Cytosolic ATP concentration reflects the balance between supply and consumption. To investigate the metabolic flux leading to neuronal ATP production, a new FRET-based pyruvate sensor was developed and selectively expressed in the cytosol of astrocytes in transgenic mice. Upon epileptic neuronal hyperactivity, an increase in astrocytic pyruvate concentration was observed. Changes in the supply of energy molecules, such as glucose and oxygen, due to blood vessel constriction or dilation, as well as metabolic alterations in astrocyte function, may contribute to cytosolic ATP dynamics in neurons.

Application and Mechanism of Action of a Ketogenic Diet in Antiepileptic Therapy

Epilepsy is a chronic neurological disorder caused by abnormal discharges of neurons in the brain, which seriously affects the quality of life of patients. Although there are various drug treatments available, many epilepsy patients still experience seizures with the effect of drugs and develop refractory epilepsy. The ketogenic diet can treat drug-refractory epilepsy by regulating the body's metabolism and can enhance the quality of life by improving their cognition, behavior, and sleep quality. However, there is no unified conclusion on the mechanism through which the ketogenic diet plays a therapeutic role in epilepsy. This article provides a review of the possible mechanisms of how the ketogenic diet exerts a protective effect on epilepsy.

Paradoxical mTORC1-Dependent microRNA-mediated Translation Repression in the Nucleus Accumbens of Mice Consuming Alcohol Attenuates Glycolysis

mTORC1 promotes protein translation, learning and memory, and neuroadaptations that underlie alcohol use and abuse. We report that activation of mTORC1 in the nucleus accumbens (NAc) of mice consuming alcohol promotes the translation of microRNA (miR) machinery components and the upregulation of microRNAs (miRs) expression including miR-34a-5p. In parallel, we detected a paradoxical mTORC1-dependent repression of translation of transcripts including Aldolase A, an essential glycolytic enzyme. We found that miR-34a-5p in the NAc targets Aldolase A for translation repression and promotes alcohol intake. Our data further suggest that glycolysis is inhibited in the NAc manifesting in an mTORC1-dependent attenuation of L-lactate, the end product of glycolysis. Finally, we show that systemic administration of L-lactate attenuates mouse excessive alcohol intake. Our data suggest that alcohol promotes paradoxical actions of mTORC1 on translation and glycolysis which in turn drive excessive alcohol use.

Ecological Trait Differences Are Associated with Gene Expression in the Primary Visual Cortex of Primates

Primate species differ drastically from most other mammals in how they visually perceive their environments, which is particularly important for foraging, predator avoidance, and detection of social cues.

BACKGROUND/OBJECTIVES

Although it is well established that primates display diversity in color vision and various ecological specializations, it is not understood how visual system characteristics and ecological adaptations may be associated with gene expression levels within the primary visual cortex (V1).

METHODS

We performed RNA-Seq on V1 tissue samples from 28 individuals, representing 13 species of primates, including hominoids, cercopithecoids, and platyrrhines. We explored trait-dependent differential expression (DE) by contrasting species with differing visual system phenotypes and ecological traits.

RESULTS

Between 4-25% of genes were determined to be differentially expressed in primates that varied in type of color vision (trichromatic or polymorphic di/trichromatic), habitat use (arboreal or terrestrial), group size (large or small), and primary diet (frugivorous, folivorous, or omnivorous).

CONCLUSIONS

Interestingly, our DE analyses revealed that humans and chimpanzees showed the most marked differences between any two species, even though they are only separated by 6-8 million years of independent evolution. These results show a combination of species-specific and trait-dependent differences in the evolution of gene expression in the primate visual cortex.

Therapeutic Efficacy of a Synthetic Brain-Targeted H2S Donor Cross-Linked Nanomicelle in Autism Spectrum Disorder Rats through Aerobic Glycolysis

Autism spectrum disorder (ASD) is characterized by cognitive inflexibility and social deficits, with a notably limited range of brain-targeted medications, particularly in the field of nanomedicine. Herein, we introduce the brain-targeted H2S donor cross-linked nanomicelle, named mannose-PEG600-lipoic acid (Man-LA). Man-LA demonstrates enhanced stability and precise brain delivery by interacting with glucose transporter 1 (GLUT1) in astrocytes, facilitating a gradual release of H2S that is modulated by glutathione (GSH). In vivo, studies suggest that Man-LA alleviates symptoms of ASD, correlating with increased expression of aerobic glycolysis enzymes, elevated lactate production, and higher H2S levels, while preventing damage to hippocampal neurons. In vitro, Man-LA tightly binds to aldehyde dehydrogenase family 3 member B1 (Aldh3b1) in astrocytes, upregulating its expression. This interaction promotes aerobic glycolysis and enhances lactate production. These findings suggest a connection between ASD deficits and the dysregulation of astrocytic aerobic glycolysis, underscoring the role of H2S. Identifying the Aldh3b1 gene within aerobic glycolysis pathways provides a promising target for ASD treatment.

Cognitive disorders: Potential astrocyte-based mechanism

Cognitive disorders are a common clinical manifestation, including a deterioration in the patient's memory ability, attention, executive power, language, and other functions. The contributing factors of cognitive disorders are numerous and diverse in nature, including organic diseases and other mental disorders. Neurodegenerative diseases are a common type of organic disease related to the pathology of neuronal death and disruption of glial cell balance, ultimately accompanied with cognitive impairment. Thus, cognitive disorder frequently serves as an extremely critical indicator of neurodegenerative disorders. Cognitive impairments negatively affect patients' daily lives. However, our understanding of the precise pathogenic pathways of cognitive defects remains incomplete. The most prevalent kind of glial cells in the central nervous system are called astrocytes. They have a unique significance in cerebral function because of their wide range of functions in maintaining homeostasis in the central nervous system, regulating synaptic plasticity, and so on. Dysfunction of astrocytes is intimately linked to cognitive disorders, and we are attempting to understand this phenomenon predominantly from those perspectives: neuroinflammation, astrocytic senescence, connexin, Ca2 + signaling, mitochondrial dysfunction, and the glymphatic system.

Genetically Encoded Metabolic Sensors to Study Retina Metabolism

Dysfunctional retinal metabolism has been shown to contribute to retinal diseases such as age-related macular degeneration (AMD), diabetic retinopathy (DR) and inherited retinal degeneration (IRD). Data indicates that metabolism in the retina is complex and involves intricate interactions between cell types, including the exchange of metabolites between photoreceptors and retinal pigment epithelium (RPE) cells. To understand these interactions on a single cell level, cell-type specific expression of genetically encoded metabolic sensors can be used to reach a spatial and temporal resolution that is superior to other techniques. These sensors comprise a metabolite binding site and a fluorescent reporter protein. The binding of the metabolite leads to changes in the emission of the fluorophore which can be detected by specialized microscopy. The usage of such sensors together with other techniques in the normal and diseased retina will not only help to resolve metabolic interactions between cells and fluxes of metabolites but also enhance our understanding of pathophysiological changes in the retina.

Neuroglia and brain energy metabolism

The glial control of energy homeostasis is of crucial importance for health and disease. Astrocytes in particular play a major role in controlling the equilibrium among adenosine 5'-triphosphate (ATP), adenosine 5'-diphosphate (ADP), adenosine 5'-monophosphate (AMP), and adenosine. Any energy crisis leads to a drop in ATP, and the resulting increase in adenosine is an evolutionary ancient mechanism to suppress energy-consuming activities. The maintenance of brain energy homeostasis, in turn, requires the availability of energy sources, such as glucose and ketones. Astrocytes have assumed an important role in enabling efficient energy utilization by neurons. In addition, neurons are under the metabolic control of astrocytes through regulation of glutamate and GABA levels. The intricate interplay between glial brain energy metabolism and brain function can be best understood once the homeostatic system of energy metabolism is brought out of control. This has best been studied within the context of epilepsy where metabolic treatments provide unprecedented opportunities for the control of seizures that are refractory to conventional antiseizure medications. This chapter will discuss astroglial energy metabolism in the healthy brain and will use epilepsy as a model condition in which glial brain energy homeostasis is disrupted. We will conclude with an outlook on how those principles can be applied to other conditions such as Alzheimer disease.

Metabolic Dysfunction in Parkinson's Disease: Unraveling the Glucose-Lipid Connection

Despite many years of research into the complex neurobiology of Parkinson's disease, the precise aetiology cannot be pinpointed down to one causative agent but rather a multitude of mechanisms. Current treatment options can alleviate symptomsbut only slightly slow down the progression and not cure the disease and its underlying causes. Factors that play a role in causing the debilitating neurodegenerative psycho-motoric symptoms include genetic alterations, oxidative stress, neuroinflammation, general inflammation, neurotoxins, iron toxicity, environmental influences, and mitochondrial dysfunction. Recent findings suggest that the characteristic abnormal protein aggregation of alpha-synuclein and destruction of substantia nigra neurons might be due to mitochondrial dysfunction related to disturbances in lipid and glucose metabolism along with insulin resistance. The latter mechanism of action might be mediated by insulin receptor substrate docking to proteins that are involved in neuronal survival and signaling related to cell destruction. The increased risk of developing Type 2 Diabetes Mellitus endorses a connection between metabolic dysfunction and neurodegeneration. Here, we explore and highlight the potential role of glycolipid cellular insults in the pathophysiology of the disorder, opening up new promising avenues for the treatment of PD. Thus, antidiabetic drugs may be employed as neuromodulators to hinder the progression of the disorder.

Visualizing metabolic regulation using metabolic biosensors during sea urchin embryogenesis

Growing evidence suggests that metabolic regulation directly influences cellular function and development and thus may be more dynamic than previously expected. In vivo and in real-time analysis of metabolite activities during development is crucial to test this idea directly. In this study, we employ two metabolic biosensors to track the dynamics of pyruvate and oxidative phosphorylation (Oxphos) during the early embryogenesis of the sea urchin. A pyruvate sensor, PyronicSF, shows the signal enrichment on the mitotic apparatus, which is consistent with the localization patterns of the corresponding enzyme, pyruvate kinase (PKM). The addition of pyruvate increases the PyronicSF signal, while PKM knockdown decreases its signal, responding to the pyruvate level in the cell. Similarly, a ratio-metric sensor, Grx-roGFP, that reads the redox potential of the cell responds to DTT and H2O2, the known reducer and inducer of Oxphos. These observations suggest that these metabolic biosensors faithfully reflect the metabolic status in the cell during embryogenesis. The time-lapse imaging of these biosensors suggests that pyruvate and Oxphos levels change both spatially and temporarily during embryonic development. Pyruvate level is increased first in micromeres compared to other blastomeres at the 16-cell stage and remains high in ectoderm while decreasing in endomesoderm during gastrulation. In contrast, the Oxphos signal first decreases in micromeres at the 16-cell stage, while it increases in the endomesoderm during gastrulation, showing the opposite trend of the pyruvate signal. These results suggest that metabolic regulation is indeed both temporally and spatially dynamic during embryogenesis, and these biosensors are a valuable tool to monitor metabolic activities in real-time in developing embryos.

Lactate metabolism and histone lactylation in the central nervous system disorders: impacts and molecular mechanisms

Brain takes up approximately 20% of the total body oxygen and glucose consumption due to its relatively high energy demand. Glucose is one of the major sources to generate ATP, the process of which can be realized via glycolysis, oxidative phosphorylation, pentose phosphate pathways and others. Lactate serves as a hub molecule amid these metabolic pathways, as it may function as product of glycolysis, substrate of a variety of enzymes and signal molecule. Thus, the roles of lactate in central nervous system (CNS) diseases need to be comprehensively elucidated. Histone lactylation is a novel lactate-dependent epigenetic modification that plays an important role in immune regulation and maintaining homeostasis. However, there's still a lack of studies unveiling the functions of histone lactylation in the CNS. In this review, we first comprehensively reviewed the roles lactate plays in the CNS under both physiological and pathological conditions. Subsequently, we've further discussed the functions of histone lactylation in various neurological diseases. Furthermore, future perspectives regarding histone lactylation and its therapeutic potentials in stroke are also elucidated, which may possess potential clinical applications.

The Warburg Effect: Is it Always an Enemy?

The Warburg effect, also known as 'aerobic' glycolysis, describes the preference of cancer cells to favor glycolysis over oxidative phosphorylation for energy (adenosine triphosphate-ATP) production, despite having high amounts of oxygen and fully active mitochondria, a phenomenon first identified by Otto Warburg. This metabolic pathway is traditionally viewed as a hallmark of cancer, supporting rapid growth and proliferation by supplying energy and biosynthetic precursors. However, emerging research indicates that the Warburg effect is not just a strategy for cancer cells to proliferate at higher rates compared to normal cells; thus, it should not be considered an 'enemy' since it also plays complex roles in normal cellular functions and/or under stress conditions, prompting a reconsideration of its purely detrimental characterization. Moreover, this review highlights that distinguishing glycolysis as 'aerobic' and 'anaerobic' should not exist, as lactate is likely the final product of glycolysis, regardless of the presence of oxygen. Finally, this review explores the nuanced contributions of the Warburg effect beyond oncology, including its regulatory roles in various cellular environments and the potential effects on systemic physiological processes. By expanding our understanding of these mechanisms, we can uncover novel therapeutic strategies that target metabolic reprogramming, offering new avenues for treating cancer and other diseases characterized by metabolic dysregulation. This comprehensive reevaluation not only challenges traditional views but also enhances our understanding of cellular metabolism's adaptability and its implications in health and disease.

LDHB-deficient brain exhibits resistance to ischemic neuronal cell death due to increased vasodilation

Ischemic stroke triggers a cascade of metabolic and inflammatory events leading to neuronal death, particularly in the hippocampus. Here, we investigate the role of lactate metabolism in ischemic resistance using LDHB-deficient mice, which exhibit impaired lactate utilization. Contrary to expectations of severe neuronal damage due to metabolic defects, LDHB-deficient mice displayed significantly increased neuronal survival following ischemic insult. Magnetic resonance spectroscopy revealed elevated lactate levels in LDHB-deficient brains, which correlated with enhanced vasodilation of the posterior communicating artery (PComA) and increased extracellular PGE2 levels. These findings suggest that elevated lactate inhibits PGE2 reabsorption, promoting vasodilation and neuronal protection. Our results highlight lactate's potential role in neuroprotection and its therapeutic promise for ischemic stroke.

Elucidating the spatiotemporal dynamics of glucose metabolism with genetically encoded fluorescent biosensors

Glucose metabolism has been well understood for many years, but some intriguing questions remain regarding the subcellular distribution, transport, and functions of glycolytic metabolites. To address these issues, a living cell metabolic monitoring technology with high spatiotemporal resolution is needed. Genetically encoded fluorescent sensors can achieve specific, sensitive, and spatiotemporally resolved metabolic monitoring in living cells and in vivo, and dozens of glucose metabolite sensors have been developed recently. Here, we highlight the importance of tracking specific intermediate metabolites of glycolysis and glycolytic flux measurements, monitoring the spatiotemporal dynamics, and quantifying metabolite abundance. We then describe the working principles of fluorescent protein sensors and summarize the existing biosensors and their application in understanding glucose metabolism. Finally, we analyze the remaining challenges in developing high-quality biosensors and the huge potential of biosensor-based metabolic monitoring at multiple spatiotemporal scales.

Dynamic Real-Time Biosensing Enabled Biorhythm Tracking for Psychiatric Disorders

This review article explores the transformative potential of dynamic, real-time biosensing in biorhythm tracking for psychiatric disorders. Psychiatric diseases, characterized by a complex, heterogeneous, and multifactorial pathophysiology, pose challenges in both diagnosis and treatment. Common denominators in the pathophysiology of psychiatric diseases include disruptions in the stress response, sleep-wake cycle, energy metabolism, and immune response: all of these are characterized by a strong biorhythmic regulation (e.g., circadian), leading to dynamic changes in the levels of biomarkers involved. Technological and practical limitations have hindered the analysis of such dynamic processes to date. The integration of biosensors marks a paradigm shift in psychiatric research. These advanced technologies enable multiplex, non-invasive, and near-continuous analysis of biorhythmic biomarkers in real time, overcoming the constraints of conventional approaches. Focusing on the regulation of the stress response, sleep/wake cycle, energy metabolism, and immune response, biosensing allows for a deeper understanding of the heterogeneous and multifactorial pathophysiology of psychiatric diseases. The potential applications of nanobiosensing in biorhythm tracking, however, extend beyond observation. Continuous monitoring of biomarkers can provide a foundation for personalized medicine in Psychiatry, and allow for the transition from syndromal diagnostic entities to pathophysiology-based psychiatric diagnoses. This evolution promises enhanced disease tracking, early relapse prediction, and tailored disease management and treatment strategies. As non-invasive biosensing continues to advance, its integration into biorhythm tracking holds promise not only to unravel the intricate etiology of psychiatric disorders but also for ushering in a new era of precision medicine, ultimately improving the outcomes and quality of life for individuals grappling with these challenging conditions.

Astrocytic GLUT1 reduction paradoxically improves central and peripheral glucose homeostasis

Astrocytes are considered an essential source of blood-borne glucose or its metabolites to neurons. Nonetheless, the necessity of the main astrocyte glucose transporter, i.e., GLUT1, for brain glucose metabolism has not been defined. Unexpectedly, we found that brain glucose metabolism was paradoxically augmented in mice with astrocytic GLUT1 reduction (GLUT1ΔGFAP mice). These mice also exhibited improved peripheral glucose metabolism especially in obesity, rendering them metabolically healthier. Mechanistically, we observed that GLUT1-deficient astrocytes exhibited increased insulin receptor-dependent ATP release, and that both astrocyte insulin signaling and brain purinergic signaling are essential for improved brain function and systemic glucose metabolism. Collectively, we demonstrate that astrocytic GLUT1 is central to the regulation of brain energetics, yet its depletion triggers a reprogramming of brain metabolism sufficient to sustain energy requirements, peripheral glucose homeostasis, and cognitive function.

Brain Metabolism in Health and Neurodegeneration: The Interplay Among Neurons and Astrocytes

The regulation of energy in the brain has garnered substantial attention in recent years due to its significant implications in various disorders and aging. The brain's energy metabolism is a dynamic and tightly regulated network that balances energy demand and supply by engaging complementary molecular pathways. The crosstalk among these pathways enables the system to switch its preferred fuel source based on substrate availability, activity levels, and cell state-related factors such as redox balance. Brain energy production relies on multi-cellular cooperation and is continuously supplied by fuel from the blood due to limited internal energy stores. Astrocytes, which interface with neurons and blood vessels, play a crucial role in coordinating the brain's metabolic activity, and their dysfunction can have detrimental effects on brain health. This review characterizes the major energy substrates (glucose, lactate, glycogen, ketones and lipids) in astrocyte metabolism and their role in brain health, focusing on recent developments in the field.

Inhibition of the mitochondrial pyruvate carrier in astrocytes reduces amyloid and tau accumulation in the 3xTgAD mouse model of Alzheimer's disease

Alzheimer's Disease (AD) is characterized by an accumulation of pathologic amyloid-beta (Aβ) and Tau proteins, neuroinflammation, metabolic changes and neuronal death. Reactive astrocytes participate in these pathophysiological processes by releasing pro-inflammatory molecules and recruiting the immune system, which further reinforces inflammation and contributes to neuronal death. Besides these neurotoxic effects, astrocytes can protect neurons by providing them with high amounts of lactate as energy fuel. Astrocytes rely on aerobic glycolysis to generate lactate by reducing pyruvate, the end product of glycolysis, through lactate dehydrogenase. Consequently, limited amounts of pyruvate enter astrocytic mitochondria through the Mitochondrial Pyruvate Carrier (MPC) to be oxidized. The MPC is a heterodimer composed of two subunits MPC1 and MPC2, the function of which in astrocytes has been poorly investigated. Here, we analyzed the role of the MPC in the pathogeny of AD, knowing that a reduction in overall glucose metabolism has been associated with a drop in cognitive performances and an accumulation of Aβ and Tau. We generated 3xTgAD mice in which MPC1 was knocked-out in astrocytes specifically and focused our study on the biochemical hallmarks of the disease, mainly Aβ and neurofibrillary tangle production. We show that inhibition of the MPC before the onset of the disease significantly reduces the quantity of Aβ and Tau aggregates in the brain of 3xTgAD mice, suggesting that acting on astrocytic glucose metabolism early on could hinder the progression of the disease.

The Cerebrovascular Side of Plasticity: Microvascular Architecture across Health and Neurodegenerative and Vascular Diseases

The delivery of nutrients to the brain is provided by a 600 km network of capillaries and microvessels. Indeed, the brain is highly energy demanding and, among a total amount of 100 billion neurons, each neuron is located just 10-20 μm from a capillary. This vascular network also forms part of the blood-brain barrier (BBB), which maintains the brain's stable environment by regulating chemical balance, immune cell transport, and blocking toxins. Typically, brain microvascular endothelial cells (BMECs) have low turnover, indicating a stable cerebrovascular structure. However, this structure can adapt significantly due to development, aging, injury, or disease. Temporary neural activity changes are managed by the expansion or contraction of arterioles and capillaries. Hypoxia leads to significant remodeling of the cerebrovascular architecture and pathological changes have been documented in aging and in vascular and neurodegenerative conditions. These changes often involve BMEC proliferation and the remodeling of capillary segments, often linked with local neuronal changes and cognitive function. Cerebrovascular plasticity, especially in arterioles, capillaries, and venules, varies over different time scales in development, health, aging, and diseases. Rapid changes in cerebral blood flow (CBF) occur within seconds due to increased neural activity. Prolonged changes in vascular structure, influenced by consistent environmental factors, take weeks. Development and aging bring changes over months to years, with aging-associated plasticity often improved by exercise. Injuries cause rapid damage but can be repaired over weeks to months, while neurodegenerative diseases cause slow, varied changes over months to years. In addition, if animal models may provide useful and dynamic in vivo information about vascular plasticity, humans are more complex to investigate and the hypothesis of glymphatic system together with Magnetic Resonance Imaging (MRI) techniques could provide useful clues in the future.

Astrocytes modulate brain phosphate homeostasis via polarized distribution of phosphate uptake transporter PiT2 and exporter XPR1

Aberrant inorganic phosphate (Pi) homeostasis causes brain calcification and aggravates neurodegeneration, but the underlying mechanism remains unclear. Here, we found that primary familial brain calcification (PFBC)-associated Pi transporter genes Pit2 and Xpr1 were highly expressed in astrocytes, with importer PiT2 distributed over the entire astrocyte processes and exporter XPR1 localized to astrocyte end-feet on blood vessels. This polarized PiT2 and XPR1 distribution endowed astrocyte with Pi transport capacity competent for brain Pi homeostasis, which was disrupted in mice with astrocyte-specific knockout (KO) of either Pit2 or Xpr1. Moreover, we found that Pi uptake by PiT2, and its facilitation by PFBC-associated galactosidase MYORG, were required for the high Pi transport capacity of astrocytes. Finally, brain calcification was suppressed by astrocyte-specific PiT2 re-expression in Pit2-KO mice. Thus, astrocyte-mediated Pi transport is pivotal for brain Pi homeostasis, and elevating astrocytic Pi transporter function represents a potential therapeutic strategy for reducing brain calcification.

The Astrocyte: Metabolic Hub of the Brain

Astrocytic metabolism has taken center stage. Interposed between the neuron and the vasculature, astrocytes exert control over the fluxes of energy and building blocks required for neuronal activity and plasticity. They are also key to local detoxification and waste recycling. Whereas neurons are metabolically rigid, astrocytes can switch between different metabolic profiles according to local demand and the nutritional state of the organism. Their metabolic state even seems to be instructive for peripheral nutrient mobilization and has been implicated in information processing and behavior. Here, we summarize recent progress in our understanding of astrocytic metabolism and its effects on metabolic homeostasis and cognition.

Pyruvate dehydrogenase complex E1 subunit α crotonylation modulates cocaine-associated memory through hippocampal neuron activation

Neuronal activation is required for the formation of drug-associated memory, which is critical for the development, persistence, and relapse of drug addiction. Nevertheless, the metabolic mechanisms underlying energy production for neuronal activation remain poorly understood. In the study, a large-scale proteomics analysis of lysine crotonylation (Kcr), a type of protein posttranslational modification (PTM), reveals that cocaine promoted protein Kcr in the hippocampal dorsal dentate gyrus (dDG). We find that Kcr is predominantly discovered in a few enzymes critical for mitochondrial energy metabolism; in particular, pyruvate dehydrogenase (PDH) complex E1 subunit α (PDHA1) is crotonylated at the lysine 39 (K39) residue through P300 catalysis. Crotonylated PDHA1 promotes pyruvate metabolism by activating PDH to increase ATP production, thus providing energy for hippocampal neuronal activation and promoting cocaine-associated memory recall. Our findings identify Kcr of PDHA1 as a PTM that promotes pyruvate metabolism to enhance neuronal activity for cocaine-associated memory.

Cell-specific expression of key mitochondrial enzymes limits OXPHOS in astrocytes of the adult human neocortex and hippocampal formation

The astrocyte-to-neuron lactate shuttle model entails that, upon glutamatergic neurotransmission, glycolytically derived pyruvate in astrocytes is mainly converted to lactate instead of being entirely catabolized in mitochondria. The mechanism of this metabolic rewiring and its occurrence in human brain are unclear. Here by using immunohistochemistry (4 brains) and imaging mass cytometry (8 brains) we show that astrocytes of the adult human neocortex and hippocampal formation express barely detectable amounts of mitochondrial proteins critical for performing oxidative phosphorylation (OXPHOS). These data are corroborated by queries of transcriptomes (107 brains) of neuronal versus non-neuronal cells fetched from the Allen Institute for Brain Science for genes coding for a much larger repertoire of entities contributing to OXPHOS, showing that human non-neuronal elements barely expressed mRNAs coding for such proteins. With less OXPHOS, human brain astrocytes are thus bound to produce more lactate to avoid interruption of glycolysis.

Restoring hippocampal glucose metabolism rescues cognition across Alzheimer's disease pathologies

Impaired cerebral glucose metabolism is a pathologic feature of Alzheimer's disease (AD), with recent proteomic studies highlighting disrupted glial metabolism in AD. We report that inhibition of indoleamine-2,3-dioxygenase 1 (IDO1), which metabolizes tryptophan to kynurenine (KYN), rescues hippocampal memory function in mouse preclinical models of AD by restoring astrocyte metabolism. Activation of astrocytic IDO1 by amyloid β and tau oligomers increases KYN and suppresses glycolysis in an aryl hydrocarbon receptor-dependent manner. In amyloid and tau models, IDO1 inhibition improves hippocampal glucose metabolism and rescues hippocampal long-term potentiation in a monocarboxylate transporter-dependent manner. In astrocytic and neuronal cocultures from AD subjects, IDO1 inhibition improved astrocytic production of lactate and uptake by neurons. Thus, IDO1 inhibitors presently developed for cancer might be repurposed for treatment of AD.

Large field-of-view metabolic profiling of murine brain tissue following morphine incubation using label-free multiphoton microscopy

BACKGROUND

Although the effects on neural activation and glucose consumption caused by opiates such as morphine are known, the metabolic machinery underlying opioid use and misuse is not fully explored. Multiphoton microscopy (MPM) techniques have been developed for optical imaging at high spatial resolution. Despite the increased use of MPM for neural imaging, the use of intrinsic optical contrast has seen minimal use in neuroscience.

NEW METHOD

We present a label-free, multimodal microscopy technique for metabolic profiling of murine brain tissue following incubation with morphine sulfate (MSO4). We evaluate two- and three-photon excited autofluorescence, and second and third harmonic generation to determine meaningful intrinsic contrast mechanisms in brain tissue using simultaneous label-free, autofluorescence multi-harmonic (SLAM) microscopy.

RESULTS

Regional differences quantified in the cortex, caudate, and thalamus of the brain demonstrate region-specific changes to metabolic profiles measured from FAD intensity, along with brain-wide quantification. While the overall intensity of FAD signal significantly decreased after morphine incubation, this metabolic molecule accumulated near the nucleus accumbens.

COMPARISON WITH EXISTING METHODS

Histopathology requires tissue fixation and staining to determine cell type and morphology, lacking information about cellular metabolism. Tools such as fMRI or PET imaging have been widely used, but lack cellular resolution. SLAM microscopy obviates the need for tissue preparation, permitting immediate use and imaging of tissue with subcellular resolution in its native environment.

CONCLUSIONS

This study demonstrates the utility of SLAM microscopy for label-free investigations of neural metabolism, especially the intensity changes in FAD autofluorescence and structural morphology from third-harmonic generation.

Adenosine signalling to astrocytes coordinates brain metabolism and function

Brain computation performed by billions of nerve cells relies on a sufficient and uninterrupted nutrient and oxygen supply1,2. Astrocytes, the ubiquitous glial neighbours of neurons, govern brain glucose uptake and metabolism3,4, but the exact mechanisms of metabolic coupling between neurons and astrocytes that ensure on-demand support of neuronal energy needs are not fully understood5,6. Here we show, using experimental in vitro and in vivo animal models, that neuronal activity-dependent metabolic activation of astrocytes is mediated by neuromodulator adenosine acting on astrocytic A2B receptors. Stimulation of A2B receptors recruits the canonical cyclic adenosine 3',5'-monophosphate-protein kinase A signalling pathway, leading to rapid activation of astrocyte glucose metabolism and the release of lactate, which supplements the extracellular pool of readily available energy substrates. Experimental mouse models involving conditional deletion of the gene encoding A2B receptors in astrocytes showed that adenosine-mediated metabolic signalling is essential for maintaining synaptic function, especially under conditions of high energy demand or reduced energy supply. Knockdown of A2B receptor expression in astrocytes led to a major reprogramming of brain energy metabolism, prevented synaptic plasticity in the hippocampus, severely impaired recognition memory and disrupted sleep. These data identify the adenosine A2B receptor as an astrocytic sensor of neuronal activity and show that cAMP signalling in astrocytes tunes brain energy metabolism to support its fundamental functions such as sleep and memory.

Downregulated expression of lactate dehydrogenase in adult oligodendrocytes and its implication for the transfer of glycolysis products to axons

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.

Lactate-carried Mitochondrial Energy Overflow

We addressed the question of mitochondrial lactate metabolism using genetically-encoded sensors. The organelle was found to contain a dynamic lactate pool that leads to dose- and time-dependent protein lactylation. In neurons, mitochondrial lactate reported blood lactate levels with high fidelity. The exchange of lactate across the inner mitochondrial membrane was found to be mediated by a high affinity H+-coupled transport system involving the mitochondrial pyruvate carrier MPC. Assessment of electron transport chain activity and determination of lactate flux showed that mitochondria are tonic lactate producers, a phenomenon driven by energization and stimulated by hypoxia. We conclude that an overflow mechanism caps the redox level of mitochondria, while saving energy in the form of lactate.

Astrocytic metabolic control of orexinergic activity in the lateral hypothalamus regulates sleep and wake architecture

Neuronal activity undergoes significant changes during vigilance states, accompanied by an accommodation of energy demands. While the astrocyte-neuron lactate shuttle has shown that lactate is the primary energy substrate for sustaining neuronal activity in multiple brain regions, its role in regulating sleep/wake architecture is not fully understood. Here we investigated the involvement of astrocytic lactate supply in maintaining consolidated wakefulness by downregulating, in a cell-specific manner, the expression of monocarboxylate transporters (MCTs) in the lateral hypothalamus of transgenic mice. Our results demonstrate that reduced expression of MCT4 in astrocytes disrupts lactate supply to wake-promoting orexin neurons, impairing wakefulness stability. Additionally, we show that MCT2-mediated lactate uptake is necessary for maintaining tonic firing of orexin neurons and stabilizing wakefulness. Our findings provide both in vivo and in vitro evidence supporting the role of astrocyte-to-orexinergic neuron lactate shuttle in regulating proper sleep/wake stability.

The Multiple Roles of Lactate in the Skeletal Muscle

Believed for a long time to be merely a waste product of cell metabolism, lactate is now considered a molecule with several roles, having metabolic and signalling functions together with a new, recently discovered role as an epigenetic modulator. Lactate produced by the skeletal muscle during physical exercise is conducted to the liver, which uses the metabolite as a gluconeogenic precursor, thus generating the well-known "Cori cycle". Moreover, the presence of lactate in the mitochondria associated with the lactate oxidation complex has become increasingly clear over the years. The signalling role of lactate occurs through binding with the GPR81 receptor, which triggers the typical signalling cascade of the G-protein-coupled receptors. Recently, it has been demonstrated that lactate regulates chromatin state and gene transcription by binding to histones. This review aims to describe the different roles of lactate in skeletal muscle, in both healthy and pathological conditions, and to highlight how lactate can influence muscle regeneration by acting directly on satellite cells.

Orchestrating Stress Responses in Multiple Sclerosis: A Role for Astrocytic IFNγ Signaling

Multiple sclerosis (MS) is an inflammatory and neurodegenerative disease that is characterized by the infiltration of peripheral immune cells into the central nervous system (CNS), secretion of inflammatory factors, demyelination, and axonal degeneration. Inflammatory mediators such as cytokines alter cellular function and activate resident CNS cells, including astrocytes. Notably, interferon (IFN)γ is a prominent pleiotropic cytokine involved in MS that contributes to disease pathogenesis. Astrocytes are dynamic cells that respond to changes in the cellular microenvironment and are highly responsive to many cytokines, including IFNγ. Throughout the course of MS, intrinsic cell stress is initiated in response to inflammation, which can impact the pathology. It is known that cell stress is pronounced during MS; however, the specific mechanisms relating IFNγ signaling to cell stress responses in astrocytes are still under investigation. This review will highlight the current literature regarding the impact of IFNγ signaling alone and in combination with other immune mediators on astrocyte synthesis of free oxygen radicals and cell death, and cover what is understood regarding astrocytic mitochondrial dysfunction and endoplasmic reticulum stress.