Glucose metabolism and astrocyte-neuron interactions in the neonatal brain

Effect of recurrent severe insulin-induced hypoglycemia on the cognitive function and brain oxidative status in the rats

BACKGROUND

Episodes of recurrent or severe hypoglycemia can occur in patients with diabetes mellitus, insulinoma, neonatal hypoglycemia, and medication errors. However, little is known about the short-term and long-term effects of repeated episodes of acute severe hypoglycemia on the brain, particularly in relation to hippocampal damage and cognitive dysfunction.

METHODS

Thirty-six wistar rats were randomly assigned to either the experimental or control group. The rats were exposed to severe hypoglycemia, and assessments were conducted to evaluate oxidative stress in brain tissue, cognitive function using the Morris water maze test, as well as histopathology and immunohistochemistry studies. The clinical and histopathological evaluations were conducted in the short-term and long-term.

RESULTS

The mortality rate attributed to hypoglycemia was 34%, occurring either during hypoglycemia or within 24 h after induction. Out of the 14 rats monitored for 7 to 90 days following severe/recurrent hypoglycemia, all exhibited clinical symptoms, which mostly resolved within three days after the last hypoglycemic episode, except for three rats. Despite the decrease in catalase activity in the brain, the total antioxidant capacity following severe insulin-induced hypoglycemia increased. The histopathology findings revealed that the severity of the hippocampal damage was higher compared to the brain cortex 90 days after hypoglycemia. Memory impairments with neuron loss particularly pronounced in the dentate gyrus region of the hippocampus were observed in the rats with severe hypoglycemia. Additionally, there was an increase in reactive astrocytes indicated by GFAP immunoreactivity in the brain cortex and hippocampus.

CONCLUSION

Recurrent episodes of severe hypoglycemia can lead to high mortality rates, memory impairments, and severe histopathological changes in the brain. While many histopathological and clinical changes improved after three months, it seems that the vulnerability of the hippocampus and the development of sustained changes in the hippocampus were greater and more severe compared to the brain cortex following severe and recurrent hypoglycemia. Furthermore, it does not appear that oxidative stress plays a central role in neuronal damage following severe insulin-induced hypoglycemia. Further research is necessary to assess the consequences of repeated hypoglycemic episodes on sustained damage across various brain regions.

A tribute to Leif Hertz: The historical context of his pioneering studies of the roles of astrocytes in brain energy metabolism, neurotransmission, cognitive functions, and pharmacology identifies important, unresolved topics for future studies

Leif Hertz, M.D., D.Sc. (honōris causā) (1930-2018), was one of the original and noteworthy participants in the International Conference on Brain Energy Metabolism (ICBEM) series since its inception in 1993. The biennial ICBEM conferences are organized by neuroscientists interested in energetics and metabolism underlying neural functions; they have had a high impact on conceptual and experimental advances in these fields and on promoting collaborative interactions among neuroscientists. Leif made major contributions to ICBEM discussions and understanding of metabolic and signaling characteristics of astrocytes and their roles in brain function. His studies ranged from uptake of K+ from extracellular fluid and its stimulation of astrocytic respiration, identification, and regulation of enzymes specifically or preferentially expressed in astrocytes in the glutamate-glutamine cycle of excitatory neurotransmission, a requirement for astrocytic glycogenolysis for fueling K+ uptake, involvement of glycogen in memory consolidation in the chick, and pharmacology of astrocytes. This tribute to Leif Hertz highlights his major discoveries, the high impact of his work on astrocyte-neuron interactions, and his unparalleled influence on understanding the cellular basis of brain energy metabolism. His work over six decades has helped integrate the roles of astrocytes into neurotransmission where oxidative and glycogenolytic metabolism during neurotransmitter glutamate turnover are key aspects of astrocytic energetics. Leif recognized that brain astrocytic metabolism is greatly underestimated unless the volume fraction of astrocytes is taken into account. Adjustment for pathway rates expressed per gram tissue for volume fraction indicates that astrocytes have much higher oxidative rates than neurons and astrocytic glycogen concentrations and glycogenolytic rates during sensory stimulation in vivo are similar to those in resting and exercising muscle, respectively. These novel insights are typical of Leif's astute contributions to the energy metabolism field, and his publications have identified unresolved topics that provide the neuroscience community with challenges and opportunities for future research.

Metabolic dynamics in astrocytes and microglia during post-natal development and their implications for autism spectrum disorders

Autism Spectrum Disorder (ASD) is a complex neurodevelopmental condition characterized by elusive underlying mechanisms. Recent attention has focused on the involvement of astrocytes and microglia in ASD pathology. These glial cells play pivotal roles in maintaining neuronal homeostasis, including the regulation of metabolism. Emerging evidence suggests a potential association between ASD and inborn errors of metabolism. Therefore, gaining a comprehensive understanding of the functions of microglia and astrocytes in ASD is crucial for the development of effective therapeutic interventions. This review aims to provide a summary of the metabolism of astrocytes and microglia during post-natal development and the evidence of disrupted metabolic pathways in ASD, with particular emphasis on those potentially important for the regulation of neuronal post-natal maturation by astrocytes and microglia.

Neuron-Astrocyte Interactions: A Human Perspective

This chapter explores the intricate interactions between neurons and astrocytes within the nervous system with a particular emphasis on studies conducted in human tissue or with human cells. We specifically explore how neuron-astrocyte interactions relate to processes of cellular development, morphology, migration, synapse formation, and metabolism. These findings enrich our understanding of basic neurobiology and how disruptions in these processes are relevant to human diseases.The study of human neuron-astrocyte interactions is made possible because of transformative in vitro advancements that have facilitated the generation and sustained culture of human neural cells. In addition, the rise of techniques like sequencing at single-cell resolution has enabled the exploration of numerous human cell atlases and their comparisons to other animal model systems. Thus, the innovations outlined in this chapter illuminate the convergence and divergence of neuron-astrocyte interactions across species. As technologies progress, continually more sophisticated in vitro systems will increasingly reflect in vivo environments and deepen our command of neuron-glial interactions in human biology.

Hexosamine biosynthetic pathway and O-GlcNAc cycling of glucose metabolism in brain function and disease

Impaired brain glucose metabolism is considered a hallmark of brain dysfunction and neurodegeneration. Disruption of the hexosamine biosynthetic pathway (HBP) and subsequent O-linked N-acetylglucosamine (O-GlcNAc) cycling has been identified as an emerging link between altered glucose metabolism and defects in the brain. Myriads of cytosolic and nuclear proteins in the nervous system are modified at serine or threonine residues with a single N-acetylglucosamine (O-GlcNAc) molecule by O-GlcNAc transferase (OGT), which can be removed by β-N-acetylglucosaminidase (O-GlcNAcase, OGA). Homeostatic regulation of O-GlcNAc cycling is important for the maintenance of normal brain activity. Although significant evidence linking dysregulated HBP metabolism and aberrant O-GlcNAc cycling to induction or progression of neuronal diseases has been obtained, the issue of whether altered O-GlcNAcylation is causal in brain pathogenesis remains uncertain. Elucidation of the specific functions and regulatory mechanisms of individual O-GlcNAcylated neuronal proteins in both normal and diseased states may facilitate the identification of novel therapeutic targets for various neuronal disorders. The information presented in this review highlights the importance of HBP/O-GlcNAcylation in the neuronal system and summarizes the roles and potential mechanisms of O-GlcNAcylated neuronal proteins in maintaining normal brain function and initiation and progression of neurological diseases.

Intracellular spatiotemporal metabolism in connection to target engagement

The metabolism in eukaryotic cells is a highly ordered system involving various cellular compartments, which fluctuates based on physiological rhythms. Organelles, as the smallest independent sub-cell unit, are important contributors to cell metabolism and drug metabolism, collectively designated intracellular metabolism. However, disruption of intracellular spatiotemporal metabolism can lead to disease development and progression, as well as drug treatment interference. In this review, we systematically discuss spatiotemporal metabolism in cells and cell subpopulations. In particular, we focused on metabolism compartmentalization and physiological rhythms, including the variation and regulation of metabolic enzymes, metabolic pathways, and metabolites. Additionally, the intricate relationship among intracellular spatiotemporal metabolism, metabolism-related diseases, and drug therapy/toxicity has been discussed. Finally, approaches and strategies for intracellular spatiotemporal metabolism analysis and potential target identification are introduced, along with examples of potential new drug design based on this.

Integrative Analysis of Proteome-wide Association Studies and Functional Enrichment Analysis to Identify Genes and Chemicals Associated with Alcohol Dependence

OBJECTIVES

Alcohol dependence accounts for a large proportion of the global burden of disease and disability. This study aims to investigate the candidate genes and chemicals associated with alcohol dependence.

METHODS

Using data from published alcohol dependence genome-wide association studies, we first conducted a proteome-wide association study of alcohol dependence by integrating alcohol dependence genome-wide association studies with 2 human brain reference proteomes of dorsolateral prefrontal cortex from the Religious Order Study and Rush Memory and Aging Project and the Banner Sun Health Research Institute. Then, based on the identified genes in proteome-wide association study, we conducted functional enrichment analysis and chemical-related functional enrichment analysis to detect the related Gene Ontology terms and chemicals.

RESULTS

Proteome-wide association study identified several potential candidate genes for alcohol dependence, such as GOT2 (P = 7.59 × 10-6) and C3orf33 (P = 5.00 × 10-3). Furthermore, functional enrichment analysis identified multiple candidate Gene Ontology terms associated with alcohol dependence, such as glyoxylate metabolic process (adjusted P = 2.99 × 10-6) and oxoglutarate metabolic process (adjusted P = 9.95 × 10-6). Chemical-related functional enrichment analysis detected several alcohol dependence-related candidate chemicals, such as pitavastatin (P = 2.00 × 10-4), cannabinoids (P = 4.00 × 10-4), 11-nor-Δ(9)-tetrahydrocannabinol-9-carboxylic acid (P = 4.00 × 10-4), and gabapentin (P = 2.00 × 10-3).

CONCLUSIONS

Our study reports multiple candidate genes and chemicals associated with alcohol dependence, providing novel clues for understanding the biological mechanism of alcohol dependence.

Gestational exposure to bisphenol A induces region-specific changes in brain metabolomic fingerprints in sheep

Fetal brain development depends on maternofetal thyroid function. In rodents and sheep, perinatal BPA exposure is associated with maternal and/or fetal thyroid disruption and alterations in central nervous system development as demonstrated by metabolic modulations in the encephala of mice. We hypothesized that a gestational exposure to a low dose of BPA affects maternofetal thyroid function and fetal brain development in a region-specific manner. Pregnant ewes, a relevant model for human thyroid and brain development, were exposed to BPA (5 µg/kg bw/d, sc). The thyroid status of ewes during gestation and term fetuses at delivery was monitored. Fetal brain development was assessed by metabolic fingerprints at birth in 10 areas followed by metabolic network-based analysis. BPA treatment was associated with a significant time-dependent decrease in maternal TT4 serum concentrations. For 8 fetal brain regions, statistical models allowed discriminating BPA-treated from control lambs. Metabolic network computational analysis revealed that prenatal exposure to BPA modulated several metabolic pathways, in particular excitatory and inhibitory amino-acid, cholinergic, energy and lipid homeostasis pathways. These pathways might contribute to BPA-related neurobehavioral and cognitive disorders. Discrimination was particularly clear for the dorsal hippocampus, the cerebellar vermis, the dorsal hypothalamus, the caudate nucleus and the lateral part of the frontal cortex. Compared with previous results in rodents, the use of a larger animal model allowed to examine specific brain areas, and generate evidence of the distinct region-specific effects of fetal BPA exposure on the brain metabolome. These modifications occur concomitantly to subtle maternal thyroid function alteration. The functional link between such moderate thyroid changes and fetal brain metabolomic fingerprints remains to be determined as well as the potential implication of other modes of action triggered by BPA such as estrogenic ones. Our results pave the ways for new scientific strategies aiming at linking environmental endocrine disruption and altered neurodevelopment.

Lactylation may be a Novel Posttranslational Modification in Inflammation in Neonatal Hypoxic-Ischemic Encephalopathy

Perinatal hypoxia-ischemia remains the most common cause of acute neonatal brain injury and is associated with a high death rate and long-term neurological abnormalities such as memory and cognitive deficits and dyskinesia. Hypoxia-ischemia triggers an inflammatory cascade in the brain that is amplified by the activation of immune cells and the influx of peripheral immune cells into the brain parenchyma in response to cellular injury. Thus, acute cerebral hypoxic-ischemic inflammation is a major contributor to the pathogenesis of newborn hypoxic-ischemic brain injury. Lactate is a glycolysis end product that can regulate inflammation through histone lactylation, a unique posttranslational modification that was identified in recent studies. The purpose of this review is to outline the recent improvements in our understanding of microglia-mediated hypoxic-ischemic inflammation and to further discuss how histone lactylation regulates inflammation by affecting macrophage activation. These findings may suggest that epigenetic reprogramming-associated lactate input is linked to disease outcomes such as acute neonatal brain injury pathogenesis and the therapeutic effects of drugs and other strategies in relieving neonatal hypoxic-ischemic brain injury. Therefore, improving our knowledge of the reciprocal relationships between histone lactylation and inflammation could lead to the development of new immunomodulatory therapies for brain damage in newborns.

Reprogramming of Rat Fibroblasts into Induced Neurons by Small-Molecule Compounds In Vitro and In Vivo

Cell replacement is a promising approach for neurodegenerative disease treatment. Somatic cells such as fibroblasts can be induced to differentiate into neurons by specific transcription factors; however, the potential of viral vectors used for reprogramming to integrate into the genome raises concerns about the potential clinical applications of this approach. Here, we directly reprogrammed rat embryonic skin fibroblasts into induced neurons (iNs) via six small-molecule compounds (SMs) (VPA, CHIR99021, forskolin, Y-27632, Repsox, and P7C3-A20). iNs exhibit typical neuronal morphology, and immunofluorescence showed that more than 96% of the iNs expressed the early neuronal marker class III beta-tubulin (TUJ1) and that more than 91% of iNs expressed the mature neuronal marker neuron-specific enolase (NSE) after 10 days of reprogramming. Quantitative real-time polymerase chain reaction also showed that most iNs expressed the dopaminergic neuron marker tyrosine hydroxylase, the neural marker Nur correlation factor 1, the (γ-aminobutyric acid, GABA) GABAergic neuronal marker GABA, and the cholinergic neuron marker choline acetyltransferase. In addition, we found that cell proliferation decreased during reprogramming and that protein synthesis increased initially and then decreased. SMs were mixed with hydrogels, and the hydrogels were implanted subcutaneously into the backs of rats. After 7 days, the TUJ1 and NSE proteins were expressed in surrounding tissues, indicating that SMs caused reprogramming in vivo. In summary, rat skin fibroblasts can be efficiently reprogrammed into iNs by SMs in vitro and in vivo.

Preventive Effect of Limosilactobacillus fermentum SCHY34 on Lead Acetate-Induced Neurological Damage in SD Rats

Lead poisoning caused by lead pollution seriously affects people's health. Lactic acid bacteria has been shown to be useful for biological scavenging of lead. In this experiment, Sprague-Dawley (SD) rats were treated with 200 mg/L of lead acetate solution daily to induce chronic lead poisoning, and oral Limosilactobacillus fermentum (L. fermentum) SCHY34 to study its mitigation effects and mechanisms on rat neurotoxicity. The L. fermentum SCHY34 showed competent results on in vitro survival rate and the lead ion adsorption rate. Animal experiments showed that L. fermentum SCHY34 maintained the morphology of rat liver, kidney, and hippocampi, reduced the accumulation of lead in the blood, liver, kidney, and brain tissue. Further, L. fermentum SCHY34 alleviated the lead-induced decline in spatial memory and response capacity of SD rats, and also regulated the secretion of neurotransmitters and related enzyme activities in the brain tissue of rats, such as glutamate (Glu), monoamine oxidase (MAO), acetylcholinesterase (AchE), cyclic adenosine monophosphate (cAMP), and adenylate cyclase (AC). In addition, the expression of genes related to cognitive capacity, antioxidation, and anti-apoptotic in rat brain tissues were increased L. fermentum SCHY34 treatment, such as brain-derived neurotrophic factor (BDNF), c-fos, c-jun, superoxide dismutase (SOD)1/2, Nuclear factor erythroid 2-related factor 2 (Nrf2), and B-cell lymphoma 2 (Bcl-2), and so on. L. fermentum SCHY34 showed a great biological scavenging and potential effect on alleviating the toxicity of lead ions.

Effect of Anesthetics on Functional Connectivity of Developing Brain

The potential anesthetic neurotoxicity on the neonate is an important focus of research investigation in the field of pediatric anesthesiology. It is essential to understand how these anesthetics may affect the development and growth of neonatal immature and vulnerable brains. Functional magnetic resonance imaging (fMRI) has suggested that using anesthetics result in reduced functional connectivity may consider as core sequence for the neurotoxicity and neurodegenerative changes in the developed brain. Anesthetics either directly impact the primary structures and functions of the brain or indirectly alter the hemodynamic parameters that contribute to cerebral blood flow (CBF) in neonatal patients. We hypothesis that anesthetic agents may either decrease the brain functional connectivity in neonatal patients or animals, which was observed by fMRI. This review will summarize the effect and mechanism of anesthesia on the rapid growth and development infant and neonate brain with fMRI through functional connectivity. It is possible to provide the new mechanism of neuronal injury induced by anesthetics and objective imaging evidence in animal developing brain.

Switching to the cyclic pentose phosphate pathway powers the oxidative burst in activated neutrophils

Neutrophils are cells at the frontline of innate immunity that can quickly activate effector functions to eliminate pathogens upon stimulation. However, little is known about the metabolic adaptations that power these functions. Here we show rapid metabolic alterations in neutrophils upon activation, particularly drastic reconfiguration around the pentose phosphate pathway, which is specifically and quantitatively coupled to an oxidative burst. During this oxidative burst, neutrophils switch from glycolysis-dominant metabolism to a unique metabolic mode termed 'pentose cycle', where all glucose-6-phosphate is diverted into oxidative pentose phosphate pathway and net flux through upper glycolysis is reversed to allow substantial recycling of pentose phosphates. This reconfiguration maximizes NADPH yield to fuel superoxide production via NADPH oxidase. Disruptions of pentose cycle greatly suppress oxidative burst, the release of neutrophil extracellular traps and pathogen killing by neutrophils. Together, these results demonstrate the remarkable metabolic flexibility of neutrophils, which is essential for their functions as the first responders in innate immunity.

Effect of environmental enrichment on behavioral and morphological outcomes following neonatal hypoxia-ischemia in rodent models: A systematic review and meta-analysis

Neonatal hypoxia-ischemia (HI) is a major cause of mortality and morbidity in newborns and, despite recent advances in neonatal intensive care, there is no definitive treatment for this pathology. Once preclinical studies have shown that environmental enrichment (EE) seems to be a promising therapy for children with HI, the present study conducts a systematic review and meta-analysis of articles with EE in HI rodent models focusing on neurodevelopmental reflexes, motor and cognitive function as well as brain damage. The protocol was registered a priori at PROSPERO. The search was conducted in PubMed, Embase and PsycINFO databases, resulting in the inclusion of 22 articles. Interestingly, EE showed a beneficial impact on neurodevelopmental reflexes (SMD= -0.73, CI= [-0.98; -0.47], p< 0.001, I²= 0.0%), motor function (SMD= -0.55, CI= [-0.81; -0.28], p< 0.001, I²= 62.6%), cognitive function (SMD= -0.93, CI= [-1.14; -0.72], p< 0.001, I²= 27.8%) and brain damage (SMD= -0.80, CI= [-1.03; -0.58], p< 0.001, I²= 10.7%). The main factors that potentiate EE positive effects were enhanced study quality, earlier age at injury as well as earlier start and longer duration of EE exposure. Overall, EE was able to counteract the behavioral and histological damage induced by the lesion, being a promising therapeutic strategy for HI.

Menopause and development of Alzheimer's disease: Roles of neural glucose metabolism and Wnt signaling

Late onset Alzheimer´s disease (AD) is a neurodegenerative disease with gender differences in its onset and progression, being the prevalence predominant in women and at an earlier age than in men. The pathophysiology of the menopausal condition has been associated to this dementia, playing major roles regarding both endocrine and glucose metabolism changes, amongst other mechanisms. In the current review we address the role of estrogen deficiency in the processes involved in the development of AD, including amyloid precursor protein (APP) processing to form senile plaques, Tau phosphorylation forming neurofibrillary tangles, Wnt signaling and AD neuropathology, the role of glucose brain metabolism, Wnt signaling and glucose transport in the brain, and our research contribution to these topics.

Neuroprotective Effects of Deproteinized Calf Serum in Ischemic Stroke

Deproteinized calf serum (DCS) may have neuroprotective effects after ischemic stroke. The aim of this study is to investigate whether and how the DCS inhibits neuronal injury following cerebral ischemia. Rats were subjected to 2 h transient middle cerebral artery occlusion (MCAO). One dose of 0.125 mg/gbw DCS was given immediately after reperfusion. Neurological deficit and infarct volume at 24 h post-MCAO in DCS-treated rats were lower than those in vehicle-treated rats (p < 0.0005). In cultured neurons model, cell viability was decreased, and apoptosis was increased by oxygen-glucose deprivation/reperfusion (OGD/R) (p < 0.0005). These effects of OGD/R were attenuated by 0.4 μg/μl DCS (p < 0.05) that were validated by CCK8 cell viability assay, phycoerythrin–Annexin V Apoptosis Detection assay, and TUNEL assay. Furthermore, the increase of intracellular ROS level in cultured neurons was suppressed by DCS (p < 0.05). Compared with cells subjected to OGD/R, the expression level of Bax protein decreased, and bcl-2 protein increased after DSC treatment (p < 0.05). Overall, the neuroprotective effects of DCS following cerebral ischemia may in part be due to decreased ROS production and inhibition of apoptosis.

Metabolic dysregulation in bronchopulmonary dysplasia: Implications for identification of biomarkers and therapeutic approaches

Bronchopulmonary dysplasia (BPD) is a common chronic lung disease in premature infants. Accumulating evidence shows that dysregulated metabolism of glucose, lipids and amino acids are observed in premature infants. Animal and cell studies demonstrate that abnormal metabolism of these substrates results in apoptosis, inflammation, reduced migration, abnormal proliferation or senescence in response to hyperoxic exposure, and that rectifying metabolic dysfunction attenuates neonatal hyperoxia-induced alveolar simplification and vascular dysgenesis in the lung. BPD is often associated with several comorbidities, including pulmonary hypertension and neurodevelopmental abnormalities, which significantly increase the morbidity and mortality of this disease. Here, we discuss recent progress on dysregulated metabolism of glucose, lipids and amino acids in premature infants with BPD and in related in vivo and in vitro models. These findings suggest that metabolic dysregulation may serve as a biomarker of BPD and plays important roles in the pathogenesis of this disease. We also highlight that targeting metabolic pathways could be employed in the prevention and treatment of BPD.

Stanniocalcin-1 Protected Astrocytes from Hypoxic Damage Through the AMPK Pathway

Our previous studies revealed that the expression of stanniocalcin-1 (STC1) in astrocytes increased under hypoxic conditions. However, the role of STC1 in hypoxic astrocytes is not well understood. In this work, we first showed the increased expression of STC1 in astrocyte cell line and astrocytes in the brain tissues of mice after exposure to hypoxia. Then, we found that knockdown of STC1 inhibited cell viability and increased apoptosis. These effects were mediated by decreasing the levels of SIRT3, UCP2, and glycolytic genes and increasing the levels of ROS. Further studies suggested that STC1 silencing promoted oxidative stress and suppressed glycolysis by downregulating AMPKα1. Moreover, HIF-1α knockdown in hypoxic astrocytes led to decreased expression of STC1 and AMPKα1, indicating that the expression of STC1 was regulated by HIF-1α. In conclusion, our study showed that HIF-1α-induced STC1 could protect astrocytes from hypoxic damage by regulating glycolysis and redox homeostasis in an AMPKα1-dependent manner.

Energy metabolism in childhood neurodevelopmental disorders

Whereas energy function in the aging brain and their related neurodegenerative diseases has been explored in some detail, there is limited knowledge about molecular mechanisms and brain networks of energy metabolism during infancy and childhood. In this review we describe current insights on physiological brain energetics at prenatal and neonatal stages, and in childhood. We then describe the main groups of inborn errors of energy metabolism affecting the brain. Of note, scarce basic neuroscience research in this field limits the opportunity for these disorders to provide paradigms of energy utilization during neurodevelopment. Finally, we report energy metabolism disturbances in well-known non-metabolic neurodevelopmental disorders. As energy metabolism is a fundamental biological function, brain energy utilization is likely altered in most neuropediatric diseases. Precise knowledge on mechanisms of brain energy disturbance will open the possibility of metabolic modulation therapies regardless of disease etiology.

Self-Regulation of Cerebral Metabolism and Its Neuroprotective Effect After Hypoxic-Ischemic Injury: Evidence From 1H-MRS

¹H-MRS technology can be used to non-invasively detect the content of cerebral metabolites, to assess the severity of hypoxic-ischemic (HI) injury, and to predict the recovery of compromised neurological function. However, changes to the cerebral self-regulation process after HI are still unclear. This study investigated the changes in cerebral metabolites and the potential relationship with the number of neurons and neural stem/progenitor cells (NSPC) using ¹H-MRS, and finally clarifies the self-regulation of cerebral metabolism and neuroprotection after HI injury. Newborn Yorkshire pigs (28 males, 1.0–1.5 kg) aged 3–5 days were used for the HI model in this study. The pigs were randomly divided into the HI group (n = 24) and the control group (n = 4), then the experimental group was subdivided according to different recovery time after HI into the following groups: 0–2 h (n = 4), 2–6 h (n = 4), 6–12 h (n = 4), 12–24 h (n = 4), 24–48 h (n = 4), and 48–72 h (n = 4). Following the HI timepoints, ¹H-MRS scans were performed and processed using LCModel software, and brain tissue was immunohistochemically stained for Nestin and NeuN. Immunofluorescence staining of creatine phosphokinase-BB (CK-BB), N-acetylaspartylglutamate synthetase (NAAGS), glutamate carboxypeptidase II (GCP-II), glutamate-cysteine ligase catalytic subunit (GCLC), glutathione synthase (GS), and excitatory amino acid carrier 1 (EAAC1) was then performed. The ¹H-MRS results showed that cerebral N-acetylaspartylglutamate (NAAG), glutathione (GSH), and creatine (Cr) content reached their peaks at 12–24 h, which was consistent with the recovery time of hippocampal NSPCs and neurons, indicating a potential neuroprotective effect of NAAG, GSH, and Cr after HI injury.

Metabolism of [1,6-13 C]glucose in the cerebellum of 18-day-old rats: Comparison with cerebral metabolism

There is little information on metabolism in developing cerebellum despite the known importance of this region in cognition and motor tasks. Ex vivo ¹ H- and ¹³ C-NMR spectroscopy were used to determine metabolism during late postnatal development in cerebellum and cerebrum from 18-day-old rat pups after intraperitoneal (i.p.) injection of [1,6-¹³ C]glucose. The concentration of several metabolites in cerebellum was distinctly different than cerebrum; alanine, glutamine, creatine and myo-inositol were higher in cerebellum than cerebrum, the concentrations of lactate, GABA, aspartate and N-acetylaspartate (NAA) were lower in cerebellum than in cerebrum, and levels of glutamate, succinate, choline and taurine were similar in both brain regions. The incorporation of label from the metabolism of [1,6-¹³ C]glucose into most isotopomers of glutamate (GLU), glutamine (GLN), GABA and aspartate was lower in cerebellum than in cerebrum. Incorporation of label into the C2 position of lactate via the pyruvate recycling pathway was found in both brain regions. The ratio of newly synthesized GLN/GLU was significantly higher in cerebellum than in cerebrum indicating relatively active metabolism via glutamine synthetase in cerebellar astrocytes at postnatal day 18. This is the first study to determine metabolism in the cerebellum and cerebrum of male and female rat brain.

Single-cell transcriptome profiling reveals vascular endothelial cell heterogeneity in human skin

Vascular endothelial cells (ECs) are increasingly recognized as active players in intercellular crosstalk more than passive linings of a conduit for nutrition delivery. Yet, their functional roles and heterogeneity in skin remain uncharacterized. We have used single-cell RNA sequencing (scRNA-seq) as a profiling strategy to investigate the tissue-specific features and intra-tissue heterogeneity in dermal ECs at single-cell level.

Methods: Skin tissues collected from 10 donors were subjected to scRNA-seq. Human dermal EC atlas of over 23,000 single-cell transcriptomes was obtained and further analyzed. Arteriovenous markers discovered in scRNA-seq were validated in human skin samples via immunofluorescence. To illustrate tissue-specific characteristics of dermal ECs, ECs from other human tissues were extracted from previously reported data and compared with our transcriptomic data.

Results: In comparison with ECs from other human tissues, dermal ECs possess unique characteristics in metabolism, cytokine signaling, chemotaxis, and cell adhesions. Within dermal ECs, 5 major subtypes were identified, which varied in molecular signatures and biological activities. Metabolic transcriptome analysis revealed a preference for oxidative phosphorylation in arteriole ECs when compared to capillary and venule ECs. Capillary ECs abundantly expressed HLA-II molecules, suggesting its immune-surveillance role. Post-capillary venule ECs, with high levels of adhesion molecules, were equipped with the capacity in immune cell arrest, adhesion, and infiltration.

Conclusion: Our study provides a comprehensive characterization of EC features and heterogeneity in human dermis and sets the stage for future research in identifying disease-specific alterations of dermal ECs in various dermatoses.

Astrocyte responses to nanomaterials: Functional changes, pathological changes and potential applications

Astrocytes are responsible for regulating and optimizing the functional environment of neurons in the brain and can reduce the adverse impacts of external factors by protecting neurons. However, excessive astrocyte activation upon stimulation may alter their initial protective effect and actually lead to aggravation of injury. Similar to the dual effects of astrocytes in the response to injury within the central nervous system (CNS), nanomaterials (NMs) can have either toxic or beneficial effects on astrocytes, serving to promote injury or inhibit tumors. As the important physiological functions of astrocytes have been gradually revealed, the effects of NMs on astrocytes and the underlying mechanisms have become a new frontier in nanomedicine and neuroscience. This review summarizes the in vitro and in vivo findings regarding the effects of various NMs on astrocytes, focusing on functional alterations and pathological processes in astrocytes, as well as the possible underlying mechanisms. We also emphasize the importance of co-culture models in studying the interaction between NMs and cells of the CNS. Finally, we discuss NMs that have shown promise for application in astrocyte-related diseases and propose some challenges and suggestions for further investigations, with the aim of providing guidance for the widespread application of NMs in the CNS.

Intraoperative dextrose rate during exploratory laparotomies in neonates and the incidence of postoperative hyperglycemia: A retrospective observational study

INTRODUCTION

Compared with the older pediatric population, neonates have greater perioperative morbidity and mortality. Difficulty with glucose regulation may be a contributing modifiable risk factor during perioperative anesthetic management. To mitigate the risk of hyperglycemia in neonates, some providers empirically halve the preoperative rate of dextrose-containing infusions during surgery.

AIM

To assess the association between halving the preoperative maintenance dextrose rate and postoperative euglycemia in neonatal intensive care unit patients undergoing exploratory laparotomies.

METHODS

Neonatal intensive care unit patients who underwent exploratory laparotomy under general anesthesia from 1/1/2014 to 11/21/2019 were included in this analysis. Hyperglycemia and hypoglycemia were defined as >150 mg/dL and <46 mg/dL. A calculated dextrose ratio was utilized to categorize patients into full and half intraoperative dextrose rate cohorts. Univariate analyses were performed with Fisher's exact test, the Wilcoxon rank sum test, or Spearman's correlation. Multivariable analyses with regression models were conducted after graphical evaluation of a predetermined set of independent variables.

RESULTS

107 patients were included in the full dextrose rate cohort and 96 patients in the half dextrose rate cohort with postoperative hyperglycemia occurring in 47 and 28 patients, respectively. On univariate analysis, halving the preoperative dextrose rate was associated with decreased postoperative hyperglycemia (odds ratio: 0.53; 95% CI: 0.28-0.98, P = 0.041). This association continued in the regression model (adjusted odds ratio: 0.49; 95% CI: 0.25-0.80, P = 0.008) after controlling for preoperative dextrose rate, preoperative serum glucose, preoperative pH, surgical duration, postmenstrual age at surgery, and the presence of necrotizing enterocolitis. Only one patient was hypoglycemic postoperatively, and they were in the full dextrose cohort.

CONCLUSION

Halving of preoperative dextrose rates intraoperatively during exploratory laparotomy in neonatal intensive care unit patients was associated with a decreased risk of postoperative hyperglycemia without substantially increasing the occurrence of postoperative hypoglycemia. The practice of halving preoperative dextrose rates may be an effective empirical approach for intraoperative glucose management in the high-risk neonatal population when blood glucose monitoring is challenging.

Neuroprotective role of lactate in rat neonatal hypoxia-ischemia

Hypoxic-ischemic (HI) encephalopathy remains a major cause of perinatal mortality and chronic disability in newborns worldwide (1-6 for 1000 births). The only current clinical treatment is hypothermia, which is efficient for less than 60% of babies. Mainly considered as a waste product in the past, lactate, in addition to glucose, is increasingly admitted as a supplementary fuel for neurons and, more recently, as a signaling molecule in the brain. Our aim was to investigate the neuroprotective effect of lactate in a neonatal (seven day old) rat model of hypoxia-ischemia. Pups received intra-peritoneal injection(s) of lactate (40 μmol). Size and apparent diffusion coefficients of brain lesions were assessed by magnetic resonance diffusion-weighted imaging. Oxiblot analyses and long-term behavioral studies were also conducted. A single lactate injection induced a 30% reduction in brain lesion volume, indicating a rapid and efficient neuroprotective effect. When oxamate, a lactate dehydrogenase inhibitor, was co-injected with lactate, the neuroprotection was completely abolished, highlighting the role of lactate metabolism in this protection. After three lactate injections (one per day), pups presented the smallest brain lesion volume and a complete recovery of neurological reflexes, sensorimotor capacities and long-term memory, demonstrating that lactate administration is a promising therapy for neonatal HI insult.

Differential Age-Dependent Mitochondrial Dysfunction, Oxidative Stress, and Apoptosis Induced by Neonatal Hypoxia-Ischemia in the Immature Rat Brain

Neonatal hypoxia-ischemia (HI) is among the main causes of mortality and morbidity in newborns. Experimental studies show that the immature rat brain is less susceptible to HI injury, suggesting that changes that occur during the first days of life drastically alter its susceptibility. Among the main developmental changes observed is the mitochondrial function, namely, the tricarboxylic acid (TCA) cycle and respiratory complex (RC) activities. Therefore, in the present study, we investigated the influence of neonatal HI on mitochondrial functions, redox homeostasis, and cell damage at different postnatal ages in the hippocampus of neonate rats. For this purpose, animals were divided into four groups: sham postnatal day 3 (ShP3), HIP3, ShP11, and HIP11. We initially observed increased apoptosis in the HIP11 group only, indicating a higher susceptibility of these animals to brain injury. Mitochondrial damage, as determined by flow cytometry showing mitochondrial swelling and loss of mitochondrial membrane potential, was also demonstrated only in the HIP11 group. This was consistent with the decreased mitochondrial oxygen consumption, reduced TCA cycle enzymes, and RC activities and induction of oxidative stress in this group of animals. Considering that HIP3 and the sham animals showed no alteration of mitochondrial functions, redox homeostasis, and showed no apoptosis, our data suggest an age-dependent vulnerability of the hippocampus to hypoxia-ischemia. The present results highlight age-dependent metabolic differences in the brain of neonate rats submitted to HI indicating that different treatments might be needed for HI newborns with different gestational ages.

Metabolomic profiling reveals a differential role for hippocampal glutathione reductase in infantile memory formation

The metabolic mechanisms underlying the formation of early-life episodic memories remain poorly characterized. Here, we assessed the metabolomic profile of the rat hippocampus at different developmental ages both at baseline and following episodic learning. We report that the hippocampal metabolome significantly changes over developmental ages and that learning regulates differential arrays of metabolites according to age. The infant hippocampus had the largest number of significant changes following learning, with downregulation of 54 metabolites. Of those, a large proportion was associated with the glutathione-mediated cellular defenses against oxidative stress. Further biochemical, molecular, and behavioral assessments revealed that infantile learning evokes a rapid and persistent increase in the activity of neuronal glutathione reductase, the enzyme that regenerates reduced glutathione from its oxidized form. Inhibition of glutathione reductase selectively impaired long-term memory formation in infant but not in juvenile and adult rats, confirming its age-specific role. Thus, metabolomic profiling revealed that the hippocampal glutathione-mediated antioxidant pathway is differentially required for the formation of infantile memory.

Improving glucose metabolism in the auditory cortex delays the aging of auditory function of guinea pig

The glucose homeostasis is essential for brain function, and energy deficiency is a key feature of brain aging. We investigated whether improving glucose metabolism in the auditory cortex can delay the aging of auditory function of guinea pigs with age-related hearing loss (ARHL) by d-galactose. Auditory function was assessed by auditory brainstem response (ABR), glucose metabolism was detected by micro PET/CT, and the proteome were identified in auditory cortex by two-dimensional electrophoresis and matrix assisted laser desorption/ionization mass spectrometry. Glucose metabolism decreased in the auditory cortex of d-galactose group, and improving glucose metabolism can delay the aging of auditory function by upregulating seven metabolism-related proteins including ATP synthase subunit beta, triosephosphate isomerase, creatine kinase U-type, pyruvate dehydrogenase E1 component subunit beta, alpha-enolase, phosphoglycerate kinase, and tubulin beta-2A chain. These results suggest that the decrease of glucose metabolism in the auditory cortex may be an important role in the aging of auditory function, and improving glucose metabolism in the auditory cortex can delay the aging of auditory function of guinea pig with ARHL induced by d-galactose.

The Role of Ketone Bodies in Improving Neurological Function and Efficiency

: Neurological coordination is essential for performing biological and mechanical activities achieved by the cooperation of biomolecules such as carbohydrates, lipids, and proteins. It plays an important role in energy production, which can be fascinatingly improved by ketone bodies. Ketone bodies are small, water-soluble lipid molecules by shifting the glycolytic phase KBs directly enters into the tricarboxylic acid cycle for ATP synthesis. It leads to the production of much more energy levels than a single molecule of glucose. Therefore, it could have a profound effect on neuro-metabolism as well as bioenergetics of ATP production. These neuro-enhancement properties are useful for epilepsy, Alzheimer's, and several neurocognitive disorders treatment. Interestingly, the cancer cells cannot use it for efficiently energy production results in decreasing cancer cells viability. This review summarized ketone bodies generation, related imperative effects on normal cells, and more importantly its application in various neurological disorders treatment by rising neuronal functions.

Differential glucose and beta-hydroxybutyrate metabolism confers an intrinsic neuroprotection to the immature brain in a rat model of neonatal hypoxia ischemia

Neonatal hypoxia ischemia (HI) is the main cause of newborn mortality and morbidity. Preclinical studies have shown that the immature rat brain is more resilient to HI injury, suggesting innate mechanisms of neuroprotection. During neonatal period brain metabolism experience changes that might greatly affect the outcome of HI injury. Therefore, the aim of the present study was to investigate how changes in brain metabolism interfere with HI outcome in different stages of CNS development. For this purpose, animals were divided into 6 groups: HIP3, HIP7 and HIP11 (HI performed at postnatal days 3, 7 and 11, respectively), and their respective shams. In vivo [¹⁸F]FDG micro positron emission tomography (microPET) imaging was performed 24 and 72 h after HI, as well as ex-vivo assessments of glucose and beta-hydroxybutyrate (BHB) oxidation. At adulthood behavioral tests and histology were performed. Behavioral and histological analysis showed greater impairments in HIP11 animals, while HIP3 rats were not affected. Changes in [¹⁸F]FDG metabolism were found only in the lesion area of HIP11, where a substantial hypometabolism was detected. Furthermore, [¹⁸F]FDG hypometabolism predicted impaired cognition and worst histological outcomes at adulthood. Finally, substrate oxidation assessments showed that glucose oxidation remained unaltered and higher level of BHB oxidation found in P3 animals, suggesting a more resilient metabolism. Overall, present results show [¹⁸F]FDG microPET predicts long-term injury outcome and suggests that higher BHB utilization is one of the mechanisms that confer the intrinsic neuroprotection to the immature brain and should be explored as a therapeutic target for treatment of HI.

Zona incerta projection neurons and GABAergic and GLP-1 mechanisms in the nucleus accumbens are involved in the control of gastric function and food intake

OBJECTIVE

Our aim was to explore the effect of γ-aminobutyric acid (GABA) signaling in the nucleus accumbens (NAc) on promoting gastric function and food intake through glucagon-like peptide 1 (GLP-1)-sensitive gastric distension (GD) neurons under the regulatory control of the zona incerta (ZI).

METHODS

GABA neuronal projections were traced using retrograde tracing following fluorescence immunohistochemistry. An extracellular electrophysiological recording method was used to observe the firing of neurons in the NAc. HPLC was used to quantify the GABA and glutamate levels in the NAc after electrical stimulation of the ZI. Gastric functions including gastric motility and secretion, as well as food intake, were measured after the administration of different concentrations of GABA in the NAc or electrical stimulation of the ZI.

RESULTS

Some of the GABA-positive neurons arising from the ZI projected to the NAc. Some GABA-A receptor (GABA-AR)-immunoreactive neurons in the NAc were also positive for GLP-1 receptor (GLP-1R) immunoreactivity. The firing of most GLP-1-sensitive GD neurons was decreased by GABA infusion in the NAc. Intra-NAc GABA administration also promoted gastric function and food intake. The responses induced by GABA were partially blocked by the GABA-AR antagonist bicuculline (BIC) and weakened by the GLP-1R antagonist exendin 9-39 (Ex9). Electrical stimulation of the ZI changed the firing patterns of most GLP-1-sensitive GD neurons in the NAc and promoted gastric function and food intake. Furthermore, these excitatory effects induced by electrical stimulation of the ZI were weakened by preadministration of BIC in the NAc.

CONCLUSION

Retrograde tracing and immunohistochemical staining showed a GABAergic pathway from the ZI to the NAc. GABAergic and GLP-1 mechanisms in the NAc are involved in the control of gastric function and food intake. In addition, the interaction (direct or indirect) between the ZI and these NAc mechanisms is involved in the control of gastric function and food intake.

Identifying risk effectors involved in neonatal hypoglycemia occurrence

Hypoglycemia is a common metabolic condition in neonatal period, but severe and persistent hypoglycemia can cause neurological damage and brain injury. The aim of the present study was to analyze the risk factors of neonatal hypoglycemia in clinic. A total of 135 neonatal hypoglycemia infants and 135 healthy infants were included in the present study. The differences in birth weight between neonatal hypoglycemia group and healthy control group were analyzed via t test. The associations between neonatal blood sugar level and relevant characteristic factors were explored using χ2 test. Binary logistic regression analysis was used to analyze risk factors related to the incidence of neonatal hypoglycemia. The results showed that the average birth weight was matched in neonatal hypoglycemia group and healthy control group. Neonatal blood sugar level of the infants was significantly associated with born term, birth weight, feed, gestational diabetes mellitus (GDM) and hypothermia (all P<0.05). Besides, logistic regression analysis showed that babies' born term (odds ratio (OR) = 2.715, 95% confidence interval (95% CI): 1.311-5.625), birth weight (OR = 1.910, 95% CI: 1.234-2.955), improper feeding (OR = 3.165, 95% CI: 1.295-7.736) and mother's GDM (OR = 2.184, 95% CI: 1.153-4.134) were high risk factors for neonatal hypoglycemia. The incidence of hypoglycemia in infants was significantly associated with various clinical factors. And monitoring these risk factors is one of important measures to reduce long-term neurological damage caused by neonatal hypoglycemia.

Birth weight related blood concentrations of the neurotransmission amino acids glutamine plus glutamate, phenylalanine and tyrosine in full-term breastfed infants perinatally

Background The amino acids glutamine plus glutamate, phenylalanine and tyrosine are implicated in neurotransmission. We aimed to evaluate these amino acid blood concentrations in full-term breastfed infants with different birth weight (BW) perinatally. Methods Breastfed full-term infants (n = 6000, males 3000, females 3000) BW 2000-4000 g were divided into four equal groups. Both males and females Groups A, 2000-2500 g, B 2500-3000 g, C 3000-3500 g, D 3500-4000 g. Blood samples on Guthrie cards, were taken on the 3rd day of life and quantified via a liquid chromatography tandem mass spectrometry (LC-MS/MS) method. Results Glutamine plus glutamate mean values were found to be statistically significantly different between males vs. females in all the studied groups. The highest values were determined in both males and females in group D. Statistically significantly higher values of phenylalanine appeared in group D vs. other groups. Tyrosine mean values were calculated to be statistically significantly different in both sexes in group A compared to other groups. Conclusions Differences of glutamine plus glutamate, phenylalanine and tyrosine levels among full-term newborns with different BW are presented for the first time in the literature. Newborns with BW 3000-4000 g are benefited by having higher concentrations of the mentioned neurotransmission related amino acids. Neonatal screening reference values for these amino acids in relation to BW could be established, not only for preterm and low BW infants but also for full-term newborns with BW >3000 g.

Hypothalamic Fatty Acids and Ketone Bodies Sensing and Role of FAT/CD36 in the Regulation of Food Intake

The obesity and type-2 diabetes epidemic is escalating and represents one of the costliest biomedical challenges confronting modern society. Moreover, the increasing consumption of high fat food is often correlated with an increase in body mass index. In people predisposed to be obese or already obese, the impaired ability of the brain to monitor and respond to alterations in fatty acid (FA) metabolism is increasingly recognized as playing a role in the pathophysiological development of these disorders. The brain senses and regulates metabolism using highly specialized nutrient-sensing neurons located mainly in the hypothalamus. The same neurons are able to detect variation in the extracellular levels of glucose, FA and ketone bodies as a way to monitor nutrient availability and to alter its own activity. In addition, glial cells such as astrocytes create major connections to neurons and form a tight relationship to closely regulate nutrient uptake and metabolism. This review will examine the different pathways by which neurons are able to detect free fatty acids (FFA) to alter its activity and how high fat diet (HFD)-astrocytes induced ketone bodies production interplays with neuronal FA sensing. The role of HFD-induced inflammation and how FA modulate the reward system will also be investigated here.

Ketone Bodies in Neurological Diseases: Focus on Neuroprotection and Underlying Mechanisms

There is growing evidence that ketone bodies, which are derived from fatty acid oxidation and usually produced in fasting state or on high-fat diets have broad neuroprotective effects. Although the mechanisms underlying the neuroprotective effects of ketone bodies have not yet been fully elucidated, studies in recent years provided abundant shreds of evidence that ketone bodies exert neuroprotective effects through possible mechanisms of anti-oxidative stress, maintaining energy supply, modulating the activity of deacetylation and inflammatory responses. Based on the neuroprotective effects, the ketogenic diet has been used in the treatment of several neurological diseases such as refractory epilepsy, Parkinson's disease, Alzheimer's disease, and traumatic brain injury. The ketogenic diet has great potential clinically, which should be further explored in future studies. It is necessary to specify the roles of components in ketone bodies and their therapeutic targets and related pathways to optimize the strategy and efficacy of ketogenic diet therapy in the future.

Equine Neonatal Encephalopathy: Facts, Evidence, and Opinions

Neonatal encephalopathy (NE) and neonatal maladjustment syndrome (NMS) are terms used for newborn foals that develop noninfectious neurologic signs in the immediate postpartum period. Cerebral ischemia, hypoxia, and inflammation leading to neuronal and glial dysfunction and excitotoxicity are considered key mechanisms behind NE/NMS. Attention has been placed on endocrine and paracrine factors that alter brain cell function. Abnormal steroid concentrations (progestogens, neurosteroids) have been measured in critically ill and NE foals. In addition to supportive treatment, antimicrobials should be considered. Controversies regarding the pathophysiology, diagnosis, and treatment of NE and NMS will remain until controlled mechanistic and therapeutic studies are conducted.

How Early Can a Seizure Happen? Pathophysiological Considerations of Extremely Premature Infant Brain Development

Seizures in neonates represent a neurologic emergency requiring prompt recognition, determination of etiology, and treatment. Yet, the definition and identification of neonatal seizures remain challenging and controversial, in part due to the unique physiology of brain development at this life stage. These issues are compounded when considering seizures in premature infants, in whom the complexities of brain development may engender different clinical and electrographic seizure features at different points in neuronal maturation. In extremely premature infants (< 28 weeks gestational age), seizure pathophysiology has not been explored in detail. This review discusses the physiological and structural development of the brain in this developmental window, focusing on factors that may lead to seizures and their consequences at this early time point. We hypothesize that the clinical and electrographic phenomenology of seizures in extremely preterm infants reflects the specific pathophysiology of brain development in that age window.

Transient Improvement of Cerebellar Oligodendroglial Development in a Neonatal Hyperoxia Model by PDGFA Treatment

In preterm infants, the changes from fetal life to ex-utero conditions often coincide with reduced growth and white matter damage of the cerebellum. The premature increase in arterial oxygen tension caused by preterm birth may dysregulate cerebellar development. In a hyperoxia rat model of white matter damage to mimic a steep increase in oxygen levels by 24 h exposure to 80% O2 from postnatal day 6 (P6) to day 7, we analyzed growth factor (GF) synthesis of cerebellar astrocytes. Determination of GF production was performed in astrocytes after Magnetic-activated cell sorting (MACS) isolation from cerebelli after hyperoxia exposure ex vivo, and also in astroglial cultures. Oligodendrocyte progenitor cell (OPC) function was analyzed in cerebellar OPCs isolated by MACS after hyperoxia. Administration of PDGFA from P6 to P11, during hyperoxia and during 4 days recovery, was finally tested for protection of oligodendroglia and myelination. As a result, expression of the GFs Pdgfa, Fgf2, and Bdnf was diminished in cerebellar astrocytes in vitro and in vivo. Gene expression of Olig1, Olig2, Sox9, Sox10, and Cnp was reduced in OPCs in vivo. Nasal PDGFA application improved oligodendroglial proliferation after hyperoxia at P7. However, this treatment effect vanished until P9. Impaired MBP expression after hyperoxia was attenuated by PDGFA treatment until P11, but not beyond when PDGFA supply was stopped. In this study on neonatal cerebellar injury, it is documented for the first time that improvement of oligodendroglial proliferation and of myelination can be achieved by PDGFA treatment. However, the treatment benefit is not maintained long term.

Insufficient glutamine synthetase activity during synaptogenesis causes spatial memory impairment in adult mice

Glutamatergic synapses constitute a major excitatory neurotransmission system and are regulated by glutamate/glutamine (Gln) cycling between neurons and astrocytes. Gln synthetase (GS) produced by astrocytes plays an important role in maintaining the cycle. However, the significance of GS during synaptogenesis has not been clarified. GS activity and expression significantly increase from postnatal day (PD) 7 to 21, and GS is expressed prior to glial fibrillary acidic protein (GFAP) and is more abundant than GFAP throughout synaptogenesis. These observations suggest that GS plays an important role in synaptogenesis. We investigated this by inhibiting GS activity in neonatal mice and assessed the consequences in adult animals. Lower expression levels of GS and GFAP were found in the CA3 region of the hippocampus but not in the CA1 region. Moreover, synaptic puncta and glutamatergic neurotransmission were also decreased in CA3. Behaviorally, mice with inhibited GS during synaptogenesis showed spatial memory-related impairment as adults. These results suggest that postnatal GS activity is important for glutamatergic synapse development in CA3.

Fundamentals of CNS energy metabolism and alterations in lysosomal storage diseases

The brain has a very high requirement for energy. Adult brain relies on glucose as an energy substrate, whereas developing brain can utilize alternative substrates as well as glucose for energy and for the biosynthesis of lipids and proteins required for brain development. Metabolism provides the energy required to support all cellular functions and brain development and building blocks for macromolecules. Lysosomes are organelles involved in breakdown of biological compounds including proteins and complex lipids in the body and brain. Recent studies suggest that lysosomal dysfunction can damage neurons and/or alter neurotransmitter homeostasis. Several studies also implicate mitochondrial dysfunction in the pathophysiology of brain damage in lysosomal storage diseases. This manuscript provides a brief review of energy metabolism and the key pathways involved in metabolism in brain. Roles of lysosomes related to metabolism and neurotransmission are discussed, and evidence for mitochondrial dysfunction in several lysosomal storage diseases is presented. This article is part of the Special Issue "Lysosomal Storage Disorders".

Energy Demands of Early Life Drive a Disease Tolerant Phenotype and Dictate Outcome in Neonatal Bacterial Sepsis

Bacterial sepsis is one of the leading causes of death in newborns. In the face of growing antibiotic resistance, it is crucial to understand the pathology behind the disease in order to develop effective interventions. Neonatal susceptibility to sepsis can no longer be attributed to simple immune immaturity in the face of mounting evidence that the neonatal immune system is tightly regulated and well controlled. The neonatal immune response is consistent with a "disease tolerance" defense strategy (minimizing harm from immunopathology) whereas adults tend toward a "disease resistance" strategy (minimizing harm from pathogens). One major advantage of disease tolerance is that is less energetically demanding than disease resistance, consistent with the energetic limitations of early life. Immune effector cells enacting disease resistance responses switch to aerobic glycolysis upon TLR stimulation and require steady glycolytic flux to maintain the inflammatory phenotype. Rapid and intense upregulation of glucose uptake by immune cells necessitates an increased reliance on fatty acid metabolism to (a) fuel vital tissue function and (b) produce immunoregulatory intermediates which help control the magnitude of inflammation. Increasing disease resistance requires more energy: while adults have fat and protein stores to catabolize, neonates must reallocate resources away from critical growth and development. This understanding of sepsis pathology helps to explain many of the differences between neonatal and adult immune responses. Taking into account the central role of metabolism in the host response to infection and the severe metabolic demands of early life, it emerges that the striking clinical susceptibility to bacterial infection of the newborn is at its core a problem of metabolism. The evidence supporting this novel hypothesis, which has profound implications for interventions, is presented in this review.

Astrocyte glycogen and lactate: New insights into learning and memory mechanisms

Memory, the ability to retain learned information, is necessary for survival. Thus far, molecular and cellular investigations of memory formation and storage have mainly focused on neuronal mechanisms. In addition to neurons, however, the brain comprises other types of cells and systems, including glia and vasculature. Accordingly, recent experimental work has begun to ask questions about the roles of non-neuronal cells in memory formation. These studies provide evidence that all types of glial cells (astrocytes, oligodendrocytes, and microglia) make important contributions to the processing of encoded information and storing memories. In this review, we summarize and discuss recent findings on the critical role of astrocytes as providers of energy for the long-lasting neuronal changes that are necessary for long-term memory formation. We focus on three main findings: first, the role of glucose metabolism and the learning- and activity-dependent metabolic coupling between astrocytes and neurons in the service of long-term memory formation; second, the role of astrocytic glucose metabolism in arousal, a state that contributes to the formation of very long-lasting and detailed memories; and finally, in light of the high energy demands of the brain during early development, we will discuss the possible role of astrocytic and neuronal glucose metabolisms in the formation of early-life memories. We conclude by proposing future directions and discussing the implications of these findings for brain health and disease. Astrocyte glycogenolysis and lactate play a critical role in memory formation. Emotionally salient experiences form strong memories by recruiting astrocytic β2 adrenergic receptors and astrocyte-generated lactate. Glycogenolysis and astrocyte-neuron metabolic coupling may also play critical roles in memory formation during development, when the energy requirements of brain metabolism are at their peak.

Evolution of Energy Related Metabolites in Plasma from Newborns with Hypoxic-Ischemic Encephalopathy during Hypothermia Treatment

Therapeutic hypothermia (TH) initiated within 6 h from birth is the most effective therapeutic approach for moderate to severe hypoxic-ischemic encephalopathy (HIE). However, underlying mechanisms and effects on the human metabolism are not yet fully understood. This work aims at studying the evolution of several energy related key metabolites in newborns with HIE undergoing TH employing gas chromatography - mass spectrometry. The method was validated following stringent FDA requirements and applied to 194 samples from a subgroup of newborns with HIE (N = 61) enrolled in a multicenter clinical trial (HYPOTOP) for the determination of lactate, pyruvate, ketone bodies and several Krebs cycle metabolites at different sampling time points. The analysis of plasma samples from newborns with HIE revealed a decrease of lactate, pyruvate and β-hydroxybutyrate concentrations, whereas rising malate concentrations were observed. In healthy control newborns (N = 19) significantly lower levels of pyruvate and lactate were found in comparison to age-matched newborns with HIE undergoing TH, whereas acetoacetate and β-hydroxybutyrate levels were clearly increased. Access to a validated analytical method and a controlled cohort of newborns with HIE undergoing hypothermia treatment for the first time allowed the in-depth study of the evolution of key metabolites of metabolic junctions in this special population.

NMR Metabolomics for Stem Cell type discrimination

Cell metabolism is a key determinant factor for the pluripotency and fate commitment of Stem Cells (SCs) during development, ageing, pathological onset and progression. We derived and cultured selected subpopulations of rodent fetal, postnatal, adult Neural SCs (NSCs) and postnatal glial progenitors, Olfactory Ensheathing Cells (OECs), respectively from the subventricular zone (SVZ) and the olfactory bulb (OB). Cell lysates were analyzed by proton Nuclear Magnetic Resonance (¹H-NMR) spectroscopy leading to metabolites identification and quantitation. Subsequent multivariate analysis of NMR data by Principal Component Analysis (PCA), and Partial Least Square Discriminant Analysis (PLS-DA) allowed data reduction and cluster analysis. This strategy ensures the definition of specific features in the metabolic content of phenotypically similar SCs sharing a common developmental origin. The metabolic fingerprints for selective metabolites or for the whole spectra demonstrated enhanced peculiarities among cell types. The key result of our work is a neat divergence between OECs and the remaining NSC cells. We also show that statistically significant differences for selective metabolites characterizes NSCs of different ages. Finally, the retrived metabolome in cell cultures correlates to the physiological SC features, thus allowing an integrated bioengineering approach for biologic fingerprints able to dissect the (neural) SC molecular specificities.

Developmental regulation and localization of carnitine palmitoyltransferases (CPTs) in rat brain

While the brain's high energy demands are largely met by glucose, brain is also equipped with the ability to oxidize fatty acids for energy and metabolism. The brain expresses the carnitine palmitoyltransferases (CPTs) that mediate carnitine-dependent entry of long-chain acyl-CoAs into the mitochondrial matrix for β-oxidation - CPT1a and CPT2 located on the outer and inner mitochondrial membranes, respectively. Their developmental profile, regional distribution and activity as well as cell type expression remain unknown. We determined that brain CPT1a RNA and total protein expression were unchanged throughout post-natal development (PND0, PND7, PND14, PND21 and PND50); however, CPT2 RNA peaked at PND 21 and remained unchanged through PND50 in all regions studied (cortex, hippocampus, midbrain, and cerebellum). Both long-chain acyl CoA dehydrogenase and medium acyl-CoA dehydrogenase showed a similar developmental profile to CPT2. Acylcarnitines, generated as a result of CPT1a activity, significantly increased with age and peaked at PND21 in all brain regions, concurrent with the increased expression of enzymes involved in mitochondrial β-oxidation. The CPT system is highly enriched in vivo in hippocampus and cerebellum, relative to cortex and midbrain, and is exclusively present in astrocytes and neural progenitor cells, while absent in neurons, microglia, and oligodendrocytes. Using radiolabeled oleate, we demonstrate regional differences in brain fatty acid oxidation that may be blocked by the irreversible CPT1a inhibitor etomoxir. This study contributes to the field of knowledge in brain cell-specific metabolic pathways, which are important for understanding normal brain development and aging, as well as pathophysiology of neurological diseases. Read the Editorial Comment for this article on page 347.

Brain glucose metabolism: Role of Wnt signaling in the metabolic impairment in Alzheimer's disease

The brain is an organ that has a high demand for glucose. In the brain, glucose is predominantly used in energy production, with almost 70% of the energy used by neurons. The importance of the energy requirement in neurons is clearly demonstrated by the fact that all neurodegenerative disorders exhibit a critical metabolic impairment that includes decreased glucose uptake/utilization and decreased mitochondrial activity, with a consequent diminution in ATP production. In fact, in Alzheimer's disease, the measurement of the general metabolic rate of the brain has been reported to be an accurate tool for diagnosis. Additionally, the administration of metabolic activators such as insulin/glucagon-like peptide 1 can improve memory/learning performance. Despite the importance of energy metabolism in the brain, little is known about the cellular pathways involved in the regulation of this process. Several reports postulate a role for Wnt signaling as a general metabolic regulator. Thus, in the present review, we discuss the antecedents that support the relationship between Wnt signaling and energy metabolism in the Alzheimer's disease.

ARALAR/AGC1 deficiency, a neurodevelopmental disorder with severe impairment of neuronal mitochondrial respiration, does not produce a primary increase in brain lactate

ARALAR/AGC1 (aspartate-glutamate mitochondrial carrier 1) is an important component of the NADH malate-aspartate shuttle (MAS). AGC1-deficiency is a rare disease causing global cerebral hypomyelination, developmental arrest, hypotonia, and epilepsy (OMIM ID #612949); the aralar-KO mouse recapitulates the major findings in humans. This study was aimed at understanding the impact of ARALAR-deficiency in brain lactate levels as a biomarker. We report that lactate was equally abundant in wild-type and aralar-KO mouse brain in vivo at postnatal day 17. We find that lactate production upon mitochondrial blockade depends on up-regulation of lactate formation in astrocytes rather than in neurons. However, ARALAR-deficiency decreased cell respiration in neurons, not astrocytes, which maintained unchanged respiration and lactate production. As the primary site of ARALAR-deficiency is neuronal, this explains the lack of accumulation of brain lactate in ARALAR-deficiency in humans and mice. On the other hand, we find that the cytosolic and mitochondrial components of the glycerol phosphate shuttle are present in astrocytes with similar activities. This suggests that glycerol phosphate shuttle is the main NADH shuttle in astrocytes and explains the absence of effects of ARALAR-deficiency in these cells.