Glutamine Supplementation Ameliorates Chronic Stress-induced Reductions in Glutamate and Glutamine Transporters in the Mouse Prefrontal Cortex

Glutamine transporter SLC38A3 promotes breast cancer metastasis via Gsk3β/β-catenin/EMT pathway

Breast cancer is the leading cancer-related cause of death in women. Here we show that solute carrier family 38-member 3 (SLC38A3) is overexpressed in breast cancer, particularly in triple-negative breast cancer (TNBC) cells and tissues. Our study reveals that SLC38A3 regulates cellular glutamine, glutamate, asparagine, aspartate, alanine, and glutathione (GSH) levels in breast cancer cells. Our data demonstrate that SLC38A3 enhances cell viability, cell migration and invasion in vitro, and promotes tumor growth and metastasis in vivo, while reducing apoptosis and oxidative stress. Mechanistically, we show that SLC38A3 suppresses the activity of glycogen synthase kinase 3-β (Gsk3β), a negative regulator of β-catenin, and increases protein levels of β-catenin, leading to the upregulation of epithelial-to-mesenchymal-transition (EMT)-inducing transcription factors and EMT markers in breast cancer. In summary, we show that SLC38A3 is overexpressed in breast cancer and promotes breast cancer metastasis via the GSK3β/β-catenin/EMT pathway, presenting a novel therapeutic target to explore for breast cancer.

The Role of Glutamine Homeostasis in Emotional and Cognitive Functions

Glutamine (Gln), a non-essential amino acid, is synthesized de novo by glutamine synthetase (GS) in various organs. In the brain, GS is exclusively expressed in astrocytes under normal physiological conditions, producing Gln that takes part in glutamatergic neurotransmission through the glutamate (Glu)-Gln cycle. Because the Glu-Gln cycle and glutamatergic neurotransmission play a pivotal role in normal brain activity, maintaining Gln homeostasis in the brain is crucial. Recent findings indicated that a neuronal Gln deficiency in the medial prefrontal cortex in rodents led to depressive behaviors and mild cognitive impairment along with lower glutamatergic neurotransmission. In addition, exogenous Gln supplementation has been tested for its ability to overcome neuronal Gln deficiency and reverse abnormal behaviors induced by chronic immobilization stress (CIS). Although evidence is accumulating as to how Gln supplementation contributes to normalizing glutamatergic neurotransmission and the Glu-Gln cycle, there are few reviews on this. In this review, we summarize recent evidence demonstrating that Gln supplementation ameliorates CIS-induced deleterious changes, including an imbalance of the Glu-Gln cycle, suggesting that Gln homeostasis is important for emotional and cognitive functions. This is the first review of detailed mechanistic studies on the effects of Gln supplementation on emotional and cognitive functions.

Diet's Impact on Post-Traumatic Brain Injury Depression: Exploring Neurodegeneration, Chronic Blood-Brain Barrier Destruction, and Glutamate Neurotoxicity Mechanisms

Traumatic brain injury (TBI) has a profound impact on cognitive and mental functioning, leading to lifelong impairment and significantly diminishing the quality of life for affected individuals. A healthy blood-brain barrier (BBB) plays a crucial role in guarding the brain against elevated levels of blood glutamate, making its permeability a vital aspect of glutamate regulation within the brain. Studies have shown the efficacy of reducing excess glutamate in the brain as a treatment for post-TBI depression, anxiety, and aggression. The purpose of this article is to evaluate the involvement of dietary glutamate in the development of depression after TBI. We performed a literature search to examine the effects of diets abundant in glutamate, which are common in Asian populations, when compared to diets low in glutamate, which are prevalent in Europe and America. We specifically explored these effects in the context of chronic BBB damage after TBI, which may initiate neurodegeneration and subsequently have an impact on depression through the mechanism of chronic glutamate neurotoxicity. A glutamate-rich diet leads to increased blood glutamate levels when contrasted with a glutamate-poor diet. Within the context of chronic BBB disruption, elevated blood glutamate levels translate to heightened brain glutamate concentrations, thereby intensifying neurodegeneration due to glutamate neurotoxicity.

A Three-Way Interaction of Sex, PER2 rs56013859 Polymorphism, and Family Maltreatment in Depressive Symptoms in Adolescents

The prevalence of depressive symptoms in adolescents is 12-18% and is twice as frequent in females. Sleep problems and thoughts of death are depressive symptoms or co-occurrent phenomena. Family maltreatment is a risk factor for later depressive symptoms and the period circadian regulator (PER) has been studied in relation to neurotransmitters, adaptation to stress, and winter depression. The purpose of this work was to study the relation of the three-way interactions of sex, PER2 rs56013859, and family maltreatment in relation to core depressive symptoms, sleep complaints, and thoughts of death and suicide in self-reports from a cohort of Swedish adolescents in 2012, 2015, and 2018. Cross-sectional and longitudinal analyses with linear and logistic regressions were used to study the relationships to the three outcomes. The three-way interaction was related to core depressive symptoms at both baseline and six years later. In contrast, the model did not show any relation to the other dependent variables. At 13-15 years, a sex-related differential expression was observed: females with the minor allele C:C/C:T exposed to family maltreatment showed higher levels of core depressive symptoms. Six years later, the trend was inverted among carriers of minor alleles.

The SLC38A5/SNAT5 amino acid transporter: from pathophysiology to pro-cancer roles in the tumor microenvironment

SLC38A5/SNAT5 is a system N transporter that can mediate net inward or outward transmembrane fluxes of neutral amino acids coupled with Na+ (symport) and H+ (antiport). Its preferential substrates are not only amino acids with side chains containing amide (glutamine and asparagine) or imidazole (histidine) groups, but also serine, glycine, and alanine are transported by the carrier. Expressed in the pancreas, intestinal tract, brain, liver, bone marrow, and placenta, it is regulated at mRNA and protein levels by mTORC1 and WNT/β-catenin pathways, and it is sensitive to pH, nutritional stress, inflammation, and hypoxia. SNAT5 expression has been found to be altered in pathological conditions such as chronic inflammatory diseases, gestational complications, chronic metabolic acidosis, and malnutrition. Growing experimental evidence shows that SNAT5 is overexpressed in several types of cancer cells. Moreover, recently published results indicate that SNAT5 expression in stromal cells can support the metabolic exchanges occurring in the tumor microenvironment of asparagine-auxotroph tumors. We review the functional role of the SNAT5 transporter in pathophysiology and propose that, due to its peculiar operational and regulatory features, SNAT5 may play important pro-cancer roles when expressed either in neoplastic or in stromal cells of glutamine-auxotroph tumors.NEW & NOTEWORTHY The transporter SLC38A5/SNAT5 provides net influx or efflux of glutamine, asparagine, and serine. These amino acids are of particular metabolic relevance in several conditions. Changes in transporter expression or activity have been described in selected types of human cancers, where SNAT5 can mediate amino acid exchanges between tumor and stromal cells, thus providing a potential therapeutic target. This is the first review that recapitulates the characteristics and roles of the transporter in physiology and pathology.

Glutamine ameliorates Bungarus multicinctus venom-induced lung and heart injury through HSP70: NF-κB p65 and P53/PUMA signaling pathways involved

Background

Bungarus multicinctus is one of the most dangerous venomous snakes prone to cardiopulmonary damage with extremely high mortality. In our previous work, we found that glutamine (Gln) and glutamine synthetase (GS) in pig serum were significantly reduced after Bungarus multicinctus bite. In the present study, to explore whether there is a link between the pathogenesis of cardiopulmonary injury and Gln metabolic changes induced by Bungarus multicinctus venom. We investigated the effect of Gln supplementation on the lung and heart function after snakebite.

Methods

We supplemented different concentrations of Gln to mice that were envenomated by Bungarus multicinctus to observe the biological behavior, survival rate, hematological and pathological changes. Gln was supplemented immediately or one hour after the venom injection, and then changes in Gln metabolism were analyzed. Subsequently, to further explore the protective mechanism of glutamine on tissue damage, we measured the expression of heat-shock protein70 (HSP70), NF-κB P65, P53/PUMA by western blotting and real-time polymerase in the lung and heart.

Results

Gln supplementation delayed the envenoming symptoms, reduced mortality, and alleviated the histopathological changes in the heart and lung of mice bitten by Bungarus multicinctus. Additionally, Gln increased the activity of glutamine synthetase (GS), glutamate dehydrogenase (GDH) and glutaminase (GLS) in serum. It also balanced the transporter SLC7A11 expression in heart and lung tissues. Bungarus multicinctus venom induced the NF-κB nuclear translocation in the lung, while the HO-1 expression was suppressed. At the same time, venom activated the P53/PUMA signaling pathway and the BAX expression in the heart. Gln treatment reversed the above phenomenon and increased HSP70 expression.

Conclusion

Gln alleviated the glutamine metabolism disorder and cardiopulmonary damage caused by Bungarus multicinctus venom. It may protect lungs and heart against venom by promoting the expression of HSP70, inhibiting the activation of NF-κB and P53/PUMA, thereby delaying the process of snake venom and reducing mortality. The present results indicate that Gln could be a potential treatment for Bungarus multicinctus bite.

Glutamine Supplementation Preserves Glutamatergic Neuronal Activity in the Infralimbic Cortex, Which Delays the Onset of Mild Cognitive Impairment in 3×Tg-AD Female Mice

It was recently found that glutamine (Gln) supplementation activates glutamatergic neurotransmission and prevents chronic-stress-induced mild cognitive impairment (MCI). In this study, we evaluated the effects of Gln on glutamatergic activity in the medial prefrontal cortex and the onset of cognitive impairment in a triple-transgenic Alzheimer's disease mouse model (3×Tg-AD). Female 3×Tg-AD mice were fed a normal diet (3×Tg) or a Gln-supplemented diet (3×Tg+Gln) from 2 to 6 months of age. Glutamatergic neuronal activity was analyzed at 6 months, and cognitive function was examined at 2, 4, and 6 months. 3×Tg mice exhibited a decrease in glutamatergic neurotransmission in the infralimbic cortex, but 3×Tg+Gln mice did not. The 3×Tg group showed MCI at 6 months of age, but the 3×Tg+Gln group did not. The expressions of amyloid peptide, inducible nitric oxide synthase, and IBA-1 were not elevated in the infralimbic cortex in the 3×Tg+Gln group. Therefore, a Gln-supplemented diet could delay the onset of MCI even in a mouse model predisposed to cognitive impairment and dementia through genetic modification.

Long-term exposure changes the environmentally relevant bis(2-ethylhexyl) phthalate to be a neuro-hazardous substance disrupting neural homeostasis in emotional and cognitive functions

Bis(2-ethylhexyl) phthalate (DEHP) is the most used member of the phthalate class of compounds. Extensive use of this plasticizer allows daily exposure to humans via various routes. A positive relationship between DEHP exposure and neurobehavioral disorders is suspected. But, there are insufficient data on the harmfulness of neurobehavioral disorders caused by DEHP exposure, particularly at daily exposure levels. In this study, we assessed the consequences of daily DEHP ingestion (2 and 20 mg/kg diets) in male mice for at least 100 days and examined its effects on neuronal functions associated with neurobehavioral disorders, such as depression and cognitive decline. We found the marked depressive behaviors and reduced learning and memory function in the DEHP-ingestion groups, and that biomarkers related to chronic stress were increased in plasma and brain tissues. Long-term DEHP ingestion induced collapse of glutamate (Glu) and glutamine (Gln) homeostasis as a result of disruption of the Glu-Gln cycle in the medial prefrontal cortex and hippocampus. The reduced glutamatergic neurotransmission activity caused by DEHP ingestion was demonstrated using an electrophysiological method. This study revealed that long-term exposure to DEHP is hazardous and can cause neurobehavioral disorders, even at daily exposure levels.

Prophylactic Efficacy of Riluzole against Anxiety- and Depressive-Like Behaviors in Two Rodent Stress Models

Introduction

Chronic stress-related illnesses such as major depressive disorder and post-traumatic stress disorder share symptomatology, including anxiety, anhedonia, and helplessness. Across disorders, neurotoxic dysregulated glutamate (Glu) signaling may underlie symptom emergence. Current first-line antidepressant drugs, which do not directly target Glu signaling, fail to provide adequate benefit for many patients and are associated with high relapse rates. Riluzole modulates glutamatergic neurotransmission by increasing metabolic cycling and modulating signal transduction. Clinical studies exploring riluzole's efficacy in stress-related disorders have provided varied results. However, the utility of riluzole for treating specific symptom dimensions or as a prophylactic treatment has not been comprehensively assessed.

Methods

We investigated whether chronic prophylactic riluzole (∼12-15 mg/kg/day p.o.) could prevent the emergence of behavioral deficits induced by unpredictable chronic mild stress (UCMS) in mice. We assessed (i) anxiety-like behavior using the elevated-plus maze, open-field test, and novelty-suppressed feeding, (ii) mixed anxiety/anhedonia-like behavior in the novelty-induced hypophagia test, and (iii) anhedonia-like behavior using the sucrose consumption test. Z-scoring summarized changes across tests measuring similar dimensions. In a separate learned helplessness (LH) cohort, we investigated whether chronic prophylactic riluzole treatment could block the development of helplessness-like behavior.

Results

UCMS induced an elevation in anhedonia-like behavior and overall behavioral emotionality that was blocked by prophylactic riluzole. In the LH cohort, prophylactic riluzole blocked the development of helplessness-like behavior.

Discussion/Conclusion

This study supports the utility of riluzole as a prophylactic medication for preventing anhedonia and helplessness symptoms associated with stress-related disorders.

Long-Term Hyperglycemia Causes Depressive Behaviors in Mice with Hypoactive Glutamatergic Activity in the Medial Prefrontal Cortex, Which Is Not Reversed by Insulin Treatment

The etiology of hyperglycemic-induced depressive behaviors is unclear. We hypothesized that long-term hyperglycemia may induce long-lasting disturbances in glutamatergic signaling and neural damages, causing depressive behaviors. To prove our hypothesis, a C57BL/6N mouse model of hyperglycemia was maintained for 4 weeks (equivalent to approximately 3 years in humans), after which insulin treatment was administered for an additional 4 weeks to normalize hyperglycemia-induced changes. Hyperglycemic mice showed depressive-like behaviors. Glutamatergic neurons and glial cells in the medial prefrontal cortex (mPFC) were affected by hyperglycemia. Insulin treatment improved blood glucose, water intake, and food intake to normoglycemic levels, but did not improve depressive-like behaviors. Glutamatergic signaling decreased with long-term hyperglycemia and did not normalize with insulin-induced normoglycemia. Importantly, hyperglycemia-induced changes in the mPFC were almost not reversed by the 4-week insulin treatment. In particular, levels of insulin receptor beta subunit (IRβ), IRS-1, vesicular glutamate transporter 1, glutamine transporter SNAT2, phosphate-activated glutaminase, and GLUT-3 were not changed by insulin. Nitration and the dephosphorylation of IRβ in the PFC also did not improve with insulin treatment. Therefore, our results suggest that hypoactive glutamatergic activity in the mPFC is involved in diabetic-associated depressive behaviors, and it is difficult to cure with glycemic regulation alone.

Isoflavone-Enriched Soybean Leaves (Glycine Max) Alleviate Cognitive Impairment Induced by Ovariectomy and Modulate PI3K/Akt Signaling in the Hippocampus of C57BL6 Mice

(1) Background: The estrogen decline during perimenopause can induce various disorders, including cognitive impairment. Phytoestrogens, such as isoflavones, lignans, and coumestans, have been tried as a popular alternative to avoid the side effects of conventional hormone replacement therapy, but their exact mechanisms and risk are not fully elucidated. In this study, we investigated the effects of isoflavone-enriched soybean leaves (IESLs) on the cognitive impairment induced by ovariectomy in female mice. (2) Methods: Ovariectomy was performed at 9 weeks of age to mimic menopausal women, and the behavior tests for cognition were conducted 15 weeks after the first administration. IESLs were administered for 18 weeks. (3) Results: The present study showed the effects of IESLs on the cognitive function in the OVX (ovariectomized) mice. Ovariectomy markedly increased the body weight and fat accumulation in the liver and perirenal fat, but IESL treatment significantly inhibited them. In the behavioral tests, ovariectomy impaired cognitive functions, but administration of IESLs restored it. In addition, in the OVX mice, administration of IESLs restored decreased estrogen receptor (ER) β and PI3K/Akt expression in the hippocampus. (4) Conclusions: The positive effects of IESLs on cognitive functions may be closely related to the ER-mediated PI3/Akt signaling pathway in the hippocampus.

Effects of Branched-Chain Amino Acids on Skeletal Muscle, Glycemic Control, and Neuropsychological Performance in Elderly Persons with Type 2 Diabetes Mellitus: An Exploratory Randomized Controlled Trial

Although branched-chain amino acids (BCAA) are known to stimulate myofibrillar protein synthesis and affect insulin signaling and kynurenine metabolism (the latter being a metabolite of tryptophan associated with depression and dementia), the effects of BCAA supplementation on type 2 diabetes (T2D) are not clear. Therefore, a 24-week, prospective randomized open blinded-endpoint trial was conducted to evaluate the effects of supplementation of 8 g of BCAA or 7.5 g of soy protein on skeletal muscle and glycemic control as well as adverse events in elderly individuals with T2D. Thirty-six participants were randomly assigned to the BCAA group (n = 21) and the soy protein group (n = 15). Skeletal muscle mass and HbA1c, which were primary endpoints, did not change over time or differ between groups. However, knee extension muscle strength was significantly increased in the soy protein group and showed a tendency to increase in the BCAA group. Homeostasis model assessment for insulin resistance did not significantly change during the trial. Depressive symptoms were significantly improved in the BCAA group but the difference between groups was not significant. Results suggested that BCAA supplementation may not affect skeletal muscle mass and glycemic control and may improve depressive symptoms in elderly individuals with T2D.

Alterations in Astrocytic Regulation of Excitation and Inhibition by Stress Exposure and in Severe Psychopathology

Dysregulation of excitatory and inhibitory signaling is commonly observed in major psychiatric disorders, including schizophrenia, depression, and bipolar disorder, and is often targeted by psychological and pharmacological treatment methods. The balance of excitation and inhibition is highly sensitive to severe psychological stress, one of the strongest risk factors for psychiatric disorders. The role of astrocytes in regulating excitatory and inhibitory signaling is now widely recognized; however, the specific involvement of astrocytes in the context of psychiatric disorders with a history of significant stress exposure remains unclear. In this review, we summarize how astrocytes regulate the balance of excitation and inhibition in the context of stress exposure and severe psychopathology, with a focus on the PFC, a brain area highly implicated in psychopathology. We first focus on preclinical models to demonstrate that the duration of stress (particularly acute vs chronic stress) is key to shaping astrocyte function and downstream behavior. We then provide a hypothesis for how astrocytes are involved in stress-associated cortical signaling imbalance, discuss how this directly contributes to phenotypes of psychopathologies, and provide suggestions for future research. We highlight that astrocytes are a key target to understand and treat the dysregulation of cortical signaling associated with stress-related psychiatric disorders.

Metabotropic Glutamate Receptor 5 in Amygdala Target Neurons Regulates Susceptibility to Chronic Social Stress

BACKGROUND

Metabotropic glutamate receptor 5 (mGluR5) has been implicated in stress-related psychiatric disorders, particularly major depressive disorder. Although growing evidence supports the proresilient role of mGluR5 in corticolimbic circuitry in the depressive-like behaviors following chronic stress exposure, the underlying neural mechanisms, including circuits and molecules, remain unknown.

METHODS

We measured the c-Fos expression and probability of neurotransmitter release in and from basolateral amygdala (BLA) neurons projecting to the medial prefrontal cortex (mPFC) and to the ventral hippocampus (vHPC) after chronic social defeat stress. The role of BLA projections in depressive-like behaviors was assessed using optogenetic manipulations, and the underlying molecular mechanisms of mGluR5 and downstream signaling were investigated by Western blotting, viral-mediated gene transfer, and pharmacological manipulations.

RESULTS

Chronic social defeat stress disrupted neural activity and glutamatergic transmission in both BLA projections. Optogenetic activation of BLA projections reversed the detrimental effects of chronic social defeat stress on depressive-like behaviors and mGluR5 expression in the mPFC and vHPC. Conversely, inhibition of BLA projections of mice undergoing subthreshold social defeat stress induced a susceptible phenotype and mGluR5 reduction. These two BLA circuits appeared to act in an independent way. We demonstrate that mGluR5 overexpression in the mPFC or vHPC was proresilient while the mGluR5 knockdown was prosusceptible and that the proresilient effects of mGluR5 are mediated through distinctive downstream signaling pathways in the mPFC and vHPC.

CONCLUSIONS

These findings identify mGluR5 in the mPFC and vHPC that receive BLA inputs as a critical mediator of stress resilience, highlighting circuit-specific signaling for depressive-like behaviors.

Ingestion of Bis(2-ethylhexyl) phthalate (DEHP) during adolescence causes depressive-like behaviors through hypoactive glutamatergic signaling in the medial prefrontal cortex

Over the past decades, the production and use of hazardous chemicals has increased worldwide, and the incidence of neurological diseases is increasing proportionately. Among these chemicals, Bis(2-ethylhexyl) phthalate (DEHP) is the most common member of the phthalate family used as a plasticizer. The present study assessed the consequences of daily DEHP ingestion and its effects on brain functions related to depressive-like behaviors. Adolescent C57BL/6 male mice ingested different concentrations of DEHP in their diet (2, 20, and 200 mg/kg of diet), and behavioral changes in anxiety, despair, anhedonia, and sociality were investigated. DEHP exposure evoked depressive-like behaviors in a dose-dependent manner for each symptom. The levels of corticosterone and reactive oxygen species/reactive nitrogen species increased in DEHP-exposed groups, suggesting chronic stress-like responses. In the medial prefrontal cortex (mPFC), glutamate and glutamine were decreased, and glutamine synthetase showed lower activity compared to the control group, suggesting imbalanced glutamatergic signaling. Measuring the spontaneous excitatory postsynaptic current of glutamatergic neurons, we found that DEHP ingestion resulted in hypoactive glutamatergic signaling in the mPFC.

Beyond the GFAP-Astrocyte Protein Markers in the Brain

The idea of central nervous system as one-man band favoring neurons is long gone. Now we all are aware that neurons and neuroglia are team players and constant communication between those various cell types is essential to maintain functional efficiency and a quick response to danger. Here, we summarize and discuss known and new markers of astroglial multiple functions, their natural heterogeneity, cellular interactions, aging and disease-induced dysfunctions. This review is focused on newly reported facts regarding astrocytes, which are beyond the old stereotypes. We present an up-to-date list of marker proteins used to identify a broad spectrum of astroglial phenotypes related to the various physiological and pathological nervous system conditions. The aim of this review is to help choose markers that are well-tailored for specific needs of further experimental studies, precisely recognizing differential glial phenotypes, or for diagnostic purposes. We hope it will help to categorize the functional and structural diversity of the astroglial population and ease a clear readout of future experimental results.

Glutamate and depression: Reflecting a deepening knowledge of the gut and brain effects of a ubiquitous molecule

The versatility of glutamate as the brain’s foremost excitatory neurotransmitter and modulator of neurotransmission and function is considered common knowledge. Years of research have continued to uncover glutamate’s effects and roles in several neurological and neuropsychiatric disorders, including depression. It had been considered that a deeper understanding of the roles of glutamate in depression might open a new door to understanding the pathological basis of the disorder, improve the approach to patient management, and lead to the development of newer drugs that may benefit more patients. This review examines our current understanding of the roles of endogenous and exogenous sources of glutamate and the glutamatergic system in the aetiology, progression and management of depression. It also examines the relationships that link the gut-brain axis, glutamate and depression; as it emphasizes how the gut-brain axis could impact depression pathogenesis and management via changes in glutamate homeostasis. Finally, we consider what the likely future of glutamate-based therapies and glutamate-based therapeutic manipulations in depression are, and if with them, we are now on the final chapter of understanding the neurochemical milieu of depressive disorders.

Ceftriaxone regulates glutamate production and vesicular assembly in presynaptic terminals through GLT-1 in APP/PS1 mice

Perturbations in the glutamate-glutamine cycle and glutamate release from presynaptic terminals have been involved in the development of cognitive deficits in Alzheimer's disease (AD) patients and mouse models. Glutamate transporter-1 (GLT-1) removes glutamate from the synaptic cleft and transports it into astrocytes, where it is used as substrate for the glutamate-glutamine cycle. Ceftriaxone has been reported to improve cognitive deficits in AD mice by increasing GLT-1 expression, glutamate transformation to glutamine, and glutamine efflux from astrocytes. However, the impact of ceftriaxone on glutamine metabolism in neurons is unknown. The present study aimed to investigate whether ceftriaxone regulated the production and vesicular assembly of glutamate in the presynaptic terminals of neurons and to determine GLT-1 involvement in this process. We used the amyloid precursor protein (APP)/presenilin-1 (PS1) AD mouse model and GLT-1 knockdown APP/PS1 (GLT-1^+/-/APP/PS1) mice. The expression levels of sodium-coupled neutral amino-acid transporter 1 (SNAT1) and vesicular glutamate transporters 1 and 2 (VGLUT1/2) were analyzed by immunofluorescence and immunohistochemistry staining as well as by Western blotting. Glutaminase activity was assayed by fluorometry. Ceftriaxone treatment significantly increased SNAT1 expression and glutaminase activity in neurons in APP/PS1 mice. Similarly, VGLUT1/2 levels were increased in the presynaptic terminals of APP/PS1 mice treated with ceftriaxone. The deletion of one GLT-1 allele in APP/PS1 mice prevented the ceftriaxone-induced upregulation of SNAT1 and VGLUT1/2 expression, indicating that GLT-1 played an important role in ceftriaxone effect. Based on the role of SNAT1, glutaminase, and VGLUT1/2 in the glutamate-glutamine cycle in neurons, the present results suggested that ceftriaxone improved the production and vesicular assembly of glutamate as a neurotransmitter in presynaptic terminals by acting on GLT-1 in APP/PS1 mice.

Glutamine Supplementation Prevents Chronic Stress-Induced Mild Cognitive Impairment

We recently reported that glutamine (Gln) supplementation protected glutamatergic neurotransmission from the harmful effects of chronic stress. Altered glutamatergic neurotransmission is one of the main causes of cognitive disorders. However, the cognitive enhancer function of Gln has not been clearly demonstrated thus far. Here, we evaluated whether and how Gln supplementation actually affects chronic stress-induced cognitive impairment. Using a chronic immobilization stress (CIS) mouse model, we confirmed that chronic stress induced mild cognitive impairment (MCI) and neuronal damage in the hippocampus. In contrast, Gln-supplemented mice did not show evidence of MCI. To investigate possible underlying mechanisms, we confirmed that CIS increased plasma corticosterone levels as well as brain and plasma levels of reactive oxygen/nitrogen species. CIS also increased levels of inducible nitric oxide synthase and NADPH oxidase subunits (p47^phox and p67^phox) in both the prefrontal cortex and CA1 region of the hippocampus. CIS decreased the number of synaptic puncta in the prefrontal cortex and hippocampus, but these effects were inhibited by Gln supplementation. Taken together, the present results suggest that Gln is an effective agent against chronic stress-induced MCI.