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Glutamine synthetase (GS) is the enzyme responsible for the biosynthesis of glutamine, providing the only source of endogenous glutamine necessary for several critical metabolic and developmental pathways. GS deficiency, caused by pathogenic variants in the glutamate-ammonia ligase (GLUL) gene, is a rare autosomal recessive inborn error of metabolism characterized by systemic glutamine deficiency, persistent moderate hyperammonemia, and clinically devastating seizures and multi-organ failure shortly after birth. The four cases reported thus far were caused by homozygous GLUL missense variants. We report a case of GS deficiency caused by homozygous GLUL gene deletion, diagnosed prenatally and likely representing the most severe end of the spectrum. We expand the known phenotype of this rare condition with novel dysmorphic, radiographic and neuropathologic features identified on post-mortem examination. The biallelic deletion identified in this case also included the RNASEL gene and was associated with immune dysfunction in the fetus. This case demonstrates that total absence of the GLUL gene in humans is viable beyond the embryonic period, despite the early embryonic lethality found in GLUL animal models., (© 2020 John Wiley & Sons A/S . Published by John Wiley & Sons Ltd.)

The cellular, molecular, and metabolic mechanisms that underlie the development of mesial temporal lobe epilepsy are incompletely understood. Here we review the role of astrocytes in epilepsy development (a.k.a. epileptogenesis), particularly astrocyte pathologies related to: aquaporin 4, the inwardly rectifying potassium channel Kir4.1, monocarboxylate transporters MCT1 and MCT2, excitatory amino acid transporters EAAT1 and EAAT2, and glutamine synthetase. We propose that inhibition, dysfunction or loss of astrocytic glutamine synthetase is an important causative factor for some epilepsies, particularly mesial temporal lobe epilepsy and glioblastoma-associated epilepsy. We postulate that the regulatory mechanisms of glutamine synthetase as well as the downstream effects of glutamine synthetase dysfunction, represent attractive, new targets for antiepileptogenic interventions. Currently, no antiepileptogenic therapies are available for human use. The discovery of such interventions is important as it will fundamentally change the way we approach epilepsy by preventing the disease from ever becoming manifest after an epileptogenic insult to the brain., (© 2019 Wiley Periodicals, Inc.)

Streptomyces coelicolor is a Gram-positive soil bacterium with a high metabolic and adaptive potential that is able to utilize a variety of nitrogen sources. However, little is known about the utilization of the alternative nitrogen source ethanolamine. Our study revealed that S. coelicolor can utilize ethanolamine as a sole nitrogen or carbon ( N / C ) source, although it grows poorly on this nitrogen source due to the absence of a specific ethanolamine permease. Heterologous expression of a putative ethanolamine permease (SPRI_5940) from Streptomyces pristinaespiralis positively influenced the biomass accumulation of the overexpression strain grown in defined medium with ethanolamine. In this study, we demonstrated that a glutamine synthetase-like protein, GlnA4 (SCO1613), is involved in the initial metabolic step of a novel ethanolamine utilization pathway in S. coelicolor M145. GlnA4 acts as a gamma-glutamylethanolamide synthetase. Transcriptional analysis revealed that expression of glnA4 was induced by ethanolamine and repressed in the presence of ammonium. Regulation of glnA4 is governed by the transcriptional repressor EpuRI (SCO1614). The ΔglnA4 mutant strain was unable to grow on defined liquid Evans medium supplemented with ethanolamine. High-performance liquid chromatography (HPLC) analysis demonstrated that strain ΔglnA4 is unable to utilize ethanolamine. GlnA4-catalyzed glutamylation of ethanolamine was confirmed in an enzymatic in vitro assay, and the GlnA4 reaction product, gamma-glutamylethanolamide, was detected by HPLC/electrospray ionization-mass spectrometry (HPLC/ESI-MS). In this work, the first step of ethanolamine utilization in S. coelicolor M145 was elucidated, and a putative ethanolamine utilization pathway was deduced based on the sequence similarity and genomic localization of homologous genes. IMPORTANCE Until now, knowledge of the utilization of ethanolamine in Streptomyces was limited. Our work represents the first attempt to reveal a novel ethanolamine utilization pathway in the actinobacterial model organism S. coelicolor through the characterization of the key enzyme gamma-glutamylethanolamide synthetase GlnA4, which is absolutely required for growth in the presence of ethanolamine. The novel ethanolamine utilization pathway is dissimilar to the currently known ethanolamine utilization pathway, which occurs in metabolome. The novel ethanolamine utilization pathway does not result in the production of toxic by-products (such as acetaldehyde); thus, it is not encapsulated. We believe that this contribution is a milestone in understanding the ecology of Streptomyces and the utilization of alternative nitrogen sources. Our report provides new insight into bacterial primary metabolism, which remains complex and partially unexplored., (Copyright © 2019 Krysenko et al.)

Mutations in the human GLUL gene, which encodes the enzyme glutamine synthetase (GS), may cause congenital glutamine synthetase deficiency. The disease was first described in 2005 and only three patients have been reported to date. We report a fourth patient suffering from congenital GS deficiency who was found to have some distinctive clinical findings. The patient was a 30-month-old girl who was referred to us due to developmental delay and seizures which began at 5 months of age. She was seizure free for 5 months with valproic acid and vigabatrin. At presentation, she was found to have microcephaly and hypotonia. Her plasma glutamine concentration was near normal and she had mild hyperammonemia. Cranial magnetic resonance imaging (MRI) showed mild changes. Whole exome sequencing (WES) revealed a homozygous c.121C > T (p.R41C) (p.Arg41Cys) pathogenic variant of the GLUL gene. The diagnosis of this patient underlines the importance of careful evaluation of patients with borderline low glutamine levels. Treatment was begun with L-glutamine and nicotinamide and biochemical improvements have been observed at 6 months of follow-up. The outcome of this patient may provide important data about the effectiveness of glutamine and nicotinamide treatment in patients with congenital GS deficiency., Competing Interests: None., (Georg Thieme Verlag KG Stuttgart · New York.)

Glutamate-ammonia ligase (glutamine synthetase; Glul) is enriched in astrocytes and serves as the primary enzyme for ammonia detoxification and glutamate inactivation in the brain. Loss of astroglial Glul is reported in hippocampi of epileptic patients, but the mechanism by which Glul deficiency might cause disease remains elusive. Here we created a novel mouse model by selectively deleting Glul in the hippocampus and neocortex. The Glul deficient mice were born without any apparent malformations and behaved unremarkably until postnatal week three. There were reductions in tissue levels of aspartate, glutamate, glutamine and GABA and in mRNA encoding glutamate receptor subunits GRIA1 and GRIN2A as well as in the glutamate transporter proteins EAAT1 and EAAT2. Adult Glul-deficient mice developed progressive neurodegeneration and spontaneous seizures which increased in frequency with age. Importantly, progressive astrogliosis occurred before neurodegeneration and was first noted in astrocytes along cerebral blood vessels. The responses to CO 2 -provocation were attenuated at four weeks of age and dilated microvessels were observed histologically in sclerotic areas of cKO. Thus, the abnormal glutamate metabolism observed in this model appeared to cause epilepsy by first inducing gliopathy and disrupting the neurovascular coupling., (Copyright © 2018. Published by Elsevier Ltd.)

Glutamine synthetase, encoded by the gene GLUL, is an enzyme that converts glutamate and ammonia to glutamine. It is expressed by endothelial cells, but surprisingly shows negligible glutamine-synthesizing activity in these cells at physiological glutamine levels. Here we show in mice that genetic deletion of Glul in endothelial cells impairs vessel sprouting during vascular development, whereas pharmacological blockade of glutamine synthetase suppresses angiogenesis in ocular and inflammatory skin disease while only minimally affecting healthy adult quiescent endothelial cells. This relies on the inhibition of endothelial cell migration but not proliferation. Mechanistically we show that in human umbilical vein endothelial cells GLUL knockdown reduces membrane localization and activation of the GTPase RHOJ while activating other Rho GTPases and Rho kinase, thereby inducing actin stress fibres and impeding endothelial cell motility. Inhibition of Rho kinase rescues the defect in endothelial cell migration that is induced by GLUL knockdown. Notably, glutamine synthetase palmitoylates itself and interacts with RHOJ to sustain RHOJ palmitoylation, membrane localization and activation. These findings reveal that, in addition to the known formation of glutamine, the enzyme glutamine synthetase shows unknown activity in endothelial cell migration during pathological angiogenesis through RHOJ palmitoylation.

Previously, it was inferred that a high glutamine synthetase (GS) activity in human embryonic kidney (HEK) 293E cells results in elevated resistance to methionine sulfoximine (MSX) and consequently hampers GS-mediated gene amplification and selection by MSX. To overcome this MSX resistance in HEK293E cells, a GS-knockout HEK293E cell line was generated using the CRISPR/Cas9 system to target the endogenous human GS gene. The GS-knockout in the HEK293E cell line (RK8) was confirmed by Western blot analysis of GS and by observation of glutamine-dependent growth. Unlike the wild type HEK293E cells, the RK8 cells were successfully used as host cells to generate a recombinant HEK293E cell line (rHEK293E) producing a monoclonal antibody (mAb). When the RK8 cells were transfected with the GS expression vector containing the mAb gene, rHEK293E cells producing the mAb could be selected in the absence as well as in the presence of MSX. The gene copies and mRNA expression levels of the mAb in rHEK293E cells were also quantified using qRT-PCR. Taken together, the GS-knockout HEK293E cell line can be used as host cells to generate stable rHEK293E cells producing a mAb through GS-mediated gene selection in the absence as well as in the presence of MSX., (© 2018 Wiley Periodicals, Inc.)

In cells derived from several types of cancer, a transcriptional program drives high consumption of glutamine (Gln), which is used for anaplerosis, leading to a metabolic addiction for the amino acid. Low or absent expression of Glutamine Synthetase (GS), the only enzyme that catalyzes de novo Gln synthesis, has been considered a marker of Gln-addicted cancers. In this study, two human cell lines derived from brain tumors with oligodendroglioma features, HOG and Hs683, have been shown to be GS-negative. Viability of both lines depends from extracellular Gln with EC 50 of 0.175 ± 0.056 mM (Hs683) and 0.086 ± 0.043 mM (HOG), thus suggesting that small amounts of extracellular Gln are sufficient for OD cell growth. Gln starvation does not significantly affect the cell content of anaplerotic substrates, which, consistently, are not able to rescue cell growth, but causes hindrance of the Wnt/β-catenin pathway and protein synthesis attenuation, which is mitigated by transient GS expression. Gln transport inhibitors cause partial depletion of intracellular Gln and cell growth inhibition, but do not lower cell viability. Therefore, GS-negative human oligodendroglioma cells are Gln-auxotrophic but do not use the amino acid for anaplerosis and, hence, are not Gln addicted, exhibiting only limited Gln requirements for survival and growth., Competing Interests: The authors declare no conflict of interest.

Glutamine-synthetase (GS), the glutamine-synthesizing enzyme from glutamate, controls important events, including the release of inflammatory mediators, mammalian target of rapamycin (mTOR) activation, and autophagy. However, its role in macrophages remains elusive. We report that pharmacologic inhibition of GS skews M2-polarized macrophages toward the M1-like phenotype, characterized by reduced intracellular glutamine and increased succinate with enhanced glucose flux through glycolysis, which could be partly related to HIF1α activation. As a result of these metabolic changes and HIF1α accumulation, GS-inhibited macrophages display an increased capacity to induce T cell recruitment, reduced T cell suppressive potential, and an impaired ability to foster endothelial cell branching or cancer cell motility. Genetic deletion of macrophagic GS in tumor-bearing mice promotes tumor vessel pruning, vascular normalization, accumulation of cytotoxic T cells, and metastasis inhibition. These data identify GS activity as mediator of the proangiogenic, immunosuppressive, and pro-metastatic function of M2-like macrophages and highlight the possibility of targeting this enzyme in the treatment of cancer metastasis., (Copyright © 2017 The Author(s). Published by Elsevier Inc. All rights reserved.)

Dietary protein restriction has multiple benefits in kidney disease. Because protein intake is a major determinant of endogenous acid production, it is important that net acid excretion changes in parallel during changes in dietary protein intake. Dietary protein restriction decreases endogenous acid production and decreases urinary ammonia excretion, a major component of net acid excretion. Glutamine synthetase (GS) catalyzes the reaction of [Formula: see text] and glutamate, which regenerates the essential amino acid glutamine and decreases net ammonia generation. Because renal proximal tubule GS expression increases during dietary protein restriction, this could contribute to the decreased ammonia excretion. The purpose of the current study was to determine the role of proximal tubule GS in the renal response to protein restriction. We generated mice with proximal tubule-specific GS deletion (PT-GS-KO) using Cre-loxP techniques. Cre-negative (Control) and PT-GS-KO mice in metabolic cages were provided 20% protein diet for 2 days and were then changed to low-protein (6%) diet for the next 7 days. Additional PT-GS-KO mice were maintained on 20% protein diet. Dietary protein restriction caused a rapid decrease in urinary ammonia excretion in both genotypes, but PT-GS-KO blunted this adaptive response significantly. This occurred despite no significant genotype-dependent differences in urinary pH or in serum electrolytes. There were no significant differences between Control and PT-GS-KO mice in expression of multiple other proteins involved in renal ammonia handling. We conclude that proximal tubule GS expression is necessary for the appropriate decrease in ammonia excretion during dietary protein restriction.

Genetic defects in ammonia metabolism can produce irreversible damage of the developing CNS causing an impairment of cognitive and motor functions. We investigated alterations in behavior, synaptic plasticity and gene expression in the hippocampus and dorsal striatum of transgenic mice with systemic hyperammonemia resulting from conditional knockout of hepatic glutamine synthetase (LGS-ko). These mice showed reduced exploratory activity and delayed habituation to a novel environment. Field potential recordings from LGS-ko brain slices revealed significantly reduced magnitude of electrically-induced long-term potentiation (LTP) in both CA3-CA1 hippocampal and corticostriatal synaptic transmission. Corticostriatal but not hippocampal slices from LGS-ko brains demonstrated also significant alterations in long-lasting effects evoked by pharmacological activation of glutamate receptors. Real-time RT-PCR revealed distinct patterns of dysregulated gene expression in the hippocampus and striatum of LGS-ko mice: LGS-ko hippocampus showed significantly modified expression of mRNAs for mGluR1, GluN2B subunit of NMDAR, and A1 adenosine receptors while altered expression of mRNAs for D1 dopamine receptors, the M1 cholinoreceptor and the acetylcholine-synthetizing enzyme choline-acetyltransferase was observed in LGS-ko striatum. Thus, inborn systemic hyperammonemia resulted in significant deficits in novelty acquisition and disturbed synaptic plasticity in corticostriatal and hippocampal pathways involved in learning and goal-directed behavior.

Glutamine synthetase (GS) catalyzes ATP-dependent ligation of ammonia and glutamate to glutamine. Two mutations of human GS (R324C and R341C) were connected to congenital glutamine deficiency with severe brain malformations resulting in neonatal death. Another GS mutation (R324S) was identified in a neurologically compromised patient. However, the molecular mechanisms underlying the impairment of GS activity by these mutations have remained elusive. Molecular dynamics simulations, free energy calculations, and rigidity analyses suggest that all three mutations influence the first step of GS catalytic cycle. The R324S and R324C mutations deteriorate GS catalytic activity due to loss of direct interactions with ATP. As to R324S, indirect, water-mediated interactions reduce this effect, which may explain the suggested higher GS residual activity. The R341C mutation weakens ATP binding by destabilizing the interacting residue R340 in the apo state of GS. Additionally, the mutation is predicted to result in a significant destabilization of helix H8, which should negatively affect glutamate binding. This prediction was tested in HEK293 cells overexpressing GS by dot-blot analysis: Structural stability of H8 was impaired through mutation of amino acids interacting with R341, as indicated by a loss of masking of an epitope in the glutamate binding pocket for a monoclonal anti-GS antibody by L-methionine-S-sulfoximine; in contrast, cells transfected with wild type GS showed the masking. Our analyses reveal complex molecular effects underlying impaired GS catalytic activity in three clinically relevant mutants. Our findings could stimulate the development of ATP binding-enhancing molecules by which the R324S mutant can be repaired extrinsically.

Astrocytes play crucial roles in maintaining brain homeostasis and in orchestrating neural development, all through tightly coordinated steps that cooperate to maintain the balance needed for normal development. Here, we review the alterations in astrocyte functions that contribute to a variety of developmental neurometabolic disorders and provide additional data on the predominant role of astrocyte dysfunction in the neurometabolic neurodegenerative disease glutaric acidemia type I. Finally, we describe some of the therapeutical approaches directed to neurometabolic diseases and discuss if astrocytes can be possible therapeutic targets for treating these disorders.

Glutamine synthetase (GS) deficiency is an ultra-rare inborn error of amino acid metabolism that has been described in only three patients so far. The disease is characterized by neonatal onset of severe encephalopathy, low levels of glutamine in blood and cerebrospinal fluid, chronic moderate hyperammonemia, and an overall poor prognosis in the absence of an effective treatment. Recently, enteral glutamine supplementation was shown to be a safe and effective therapy for this disease but there are no data available on the long-term effects of this intervention. The amino acid glutamine, severely lacking in this disorder, is central to many metabolic pathways in the human organism and is involved in the synthesis of nicotinamide adenine dinucleotide (NAD(+)) starting from tryptophan or niacin as nicotinate, but not nicotinamide. Using fibroblasts, leukocytes, and immortalized peripheral blood stem cells (PBSC) from a patient carrying a GLUL gene point mutation associated with impaired GS activity, we tested whether glutamine deficiency in this patient results in NAD(+) depletion and whether it can be rescued by supplementation with glutamine, nicotinamide or nicotinate. The present study shows that congenital GS deficiency is associated with NAD(+) depletion in fibroblasts, leukocytes and PBSC, which may contribute to the severe clinical phenotype of the disease. Furthermore, it shows that NAD(+) depletion can be rescued by nicotinamide supplementation in fibroblasts and leukocytes, which may open up potential therapeutic options for the treatment of this disorder.

The prevalence of depression and suicide is increased in patients with mesial temporal lobe epilepsy (MTLE); however, the underlying mechanism remains unknown. Anhedonia, a core symptom of depression that is predictive of suicide, is common in patients with MTLE. Glutamine synthetase, an astrocytic enzyme that metabolizes glutamate and ammonia to glutamine, is reduced in the amygdala in patients with epilepsy and depression and in suicide victims. Here, we sought to develop a novel model of anhedonia in MTLE by testing the hypothesis that deficiency in glutamine synthetase in the central nucleus of the amygdala (CeA) leads to epilepsy and comorbid anhedonia. Nineteen male Sprague-Dawley rats were implanted with an osmotic pump infusing either the glutamine synthetase inhibitor methionine sulfoximine [MSO (n=12)] or phosphate buffered saline [PBS (n=7)] into the right CeA. Seizure activity was monitored by video-intracranial electroencephalogram (EEG) recordings for 21days after the onset of MSO infusion. Sucrose preference, a measure of anhedonia, was assessed after 21days. Methionine sulfoximine-infused rats exhibited recurrent seizures during the monitoring period and showed decreased sucrose preference over days when compared with PBS-infused rats (p<0.01). Water consumption did not differ between the PBS-treated group and the MSO-treated group. Neurons were lost in the CeA, but not the medial amygdala, lateral amygdala, basolateral amygdala, or the hilus of the dentate gyrus, in the MSO-treated rats. The results suggest that decreased glutamine synthetase activity in the CeA is a possible common cause of anhedonia and seizures in TLE. We propose that the MSO CeA model can be used for mechanistic studies that will lead to the development and testing of novel drugs to prevent seizures, depression, and suicide in patients with TLE., (Copyright © 2015 Elsevier Inc. All rights reserved.)

It is well established that the plastidic isoform of glutamine synthetase (GS2) is the enzyme in charge of photorespiratory ammonium reassimilation in plants. The metabolic events associated to photorespiratory NH4(+) accumulation were analyzed in a Lotus japonicus photorespiratory mutant lacking GS2. The mutant plants accumulated high levels of NH4(+) when photorespiration was active, followed by a sudden drop in the levels of this compound. In this paper it was examined the possible existence of enzymatic pathways alternative to GS2 that could account for this decline in the photorespiratory ammonium. Induction of genes encoding for cytosolic glutamine synthetase (GS1), glutamate dehydrogenase (GDH) and asparagine synthetase (ASN) was observed in the mutant in correspondence with the diminishment of NH4(+). Measurements of gene expression, polypeptide levels, enzyme activity and metabolite levels were carried out in leaf samples from WT and mutant plants after different periods of time under active photorespiratory conditions. In the case of asparagine synthetase it was not possible to determine enzyme activity and polypeptide content; however, an increased asparagine content in parallel with the induction of ASN gene expression was detected in the mutant plants. This increase in asparagine levels took place concomitantly with an increase in glutamine due to the induction of cytosolic GS1 in the mutant, thus revealing a major role of cytosolic GS1 in the reassimilation and detoxification of photorespiratory NH4(+) when the plastidic GS2 isoform is lacking. Moreover, a diminishment in glutamate levels was observed, that may be explained by the induction of NAD(H)-dependent GDH activity.

Epilepsy is a family of brain disorders with a largely unknown etiology and high percentage of pharmacoresistance. The clinical manifestations of epilepsy are seizures, which originate from aberrant neuronal synchronization and hyperexcitability. Reactive astrocytosis, a hallmark of the epileptic tissue, develops into loss-of-function of glutamine synthetase, impairment of glutamate-glutamine cycle and increase in extracellular and astrocytic glutamate concentration. Here, we argue that chronically elevated intracellular glutamate level in astrocytes is instrumental to alterations in the metabolism of glycogen and leads to the synthesis of polyglucosans. Unaccessibility of glycogen-degrading enzymes to these insoluble molecules compromises the glycogenolysis-dependent reuptake of extracellular K(+) by astrocytes, thereby leading to increased extracellular K(+) and associated membrane depolarization. Based on current knowledge, we propose that the deterioration in structural homogeneity of glycogen particles is relevant to disruption of brain K(+) homeostasis and increased susceptibility to seizures in epilepsy.

In this study, we focused on the effect of glutamine synthetase (GSI) activity in Mesorhizobium loti on the symbiosis between the host plant, Lotus japonicus, and the bacteroids. We used a signature-tagged mutant of M. loti (STM30) with a transposon inserted into the GSI (mll0343) gene. The L. japonicus plants inoculated with STM30 had significantly more nodules, and the occurrence of senesced nodules was much higher than in plants inoculated with the wild-type. The acetylene reduction activity (ARA) per nodule inoculated with STM30 was lowered compared to the control. Also, the concentration of chlorophyll, glutamine, and asparagine in leaves of STM30-infected plants was found to be reduced. Taken together, these data demonstrate that a GSI deficiency in M. loti differentially affects legume-rhizobia symbiosis by modifying nodule development and metabolic processes., (Copyright © 2013 Elsevier GmbH. All rights reserved.)

Glutamine synthetase (GS) is ubiquitously expressed in mammalian organisms and is a key enzyme in nitrogen metabolism. It is the only known enzyme capable of synthesising glutamine, an amino acid with many critical roles in the human organism. A defect in GLUL, encoding for GS, leads to congenital systemic glutamine deficiency and has been described in three patients with epileptic encephalopathy. There is no established treatment for this condition.Here, we describe a therapeutic trial consisting of enteral and parenteral glutamine supplementation in a four year old patient with GS deficiency. The patient received increasing doses of glutamine up to 1020 mg/kg/day. The effect of this glutamine supplementation was monitored clinically, biochemically, and by studies of the electroencephalogram (EEG) as well as by brain magnetic resonance imaging and spectroscopy.Treatment was well tolerated and clinical monitoring showed improved alertness. Concentrations of plasma glutamine normalized while levels in cerebrospinal fluid increased but remained below the lower reference range. The EEG showed clear improvement and spectroscopy revealed increasing concentrations of glutamine and glutamate in brain tissue. Concomitantly, there was no worsening of pre-existing chronic hyperammonemia.In conclusion, supplementation of glutamine is a safe therapeutic option for inherited GS deficiency since it corrects the peripheral biochemical phenotype and partially also improves the central biochemical phenotype. There was some clinical improvement but the patient had a long standing severe encephalopathy. Earlier supplementation with glutamine might have prevented some of the neuronal damage.

Glutamine deficiency with hyperammonemia due to an inherited defect of glutamine synthetase (GS) was found in a 2 year old patient. He presented neonatal seizures and developed chronic encephalopathy. Thus, GS deficiency leads to severe neurological disease but is not always early lethal., (Copyright © 2011 Elsevier Inc. All rights reserved.)

The role of plastidic glutamine synthetase (GS2) in proline biosynthesis and drought stress responses in Lotus japonicus was investigated using the GS2 mutant, Ljgln2-2. Wild-type (WT) and mutant plants were submitted to different lengths of time of water and nutrient solution deprivation. Several biochemical markers were measured and the transcriptional response to drought was determined by both quantitative real-time polymerase chain reaction and transcriptomics. The Ljgln2-2 mutant exhibited normal sensitivity to mild water deprivation, but physiological, biochemical and massive transcriptional differences were detected in the mutant, which compromised recovery (rehydration) following re-watering after severe drought stress. Proline accumulation during drought was substantially lower in mutant than in WT plants, and significant differences in the pattern of expression of the genes involved in proline metabolism were observed. Transcriptomic analysis revealed that about three times as many genes were regulated in response to drought in Ljgln2-2 plants compared with WT. The transcriptomic and accompanying biochemical data indicate that the Ljgln2-2 mutant is subject to more intense cellular stress than WT during drought. The results presented here implicate plastidic GS2 in proline production during stress and provide interesting insights into the function of proline in response to drought., (© The Authors (2010). Journal compilation © New Phytologist Trust (2010).)

Lowering the culture temperature is often useful to improve the production of many recombinant proteins in Chinese hamster ovary (CHO) cells. Batch cultivation of GS-CHO cells expressing TNFR-Fc antibody was therefore carried out at 30, 33.5 and 37 degrees C. TNFR-Fc productivity, q(TNFR-Fc), increased as culture temperature decreased; and the maximum q(TNFR-Fc) was 20 mg/(10(9) cells.day) at 30 degrees C which was three times that at 37 degrees C. Increasing the viable cell density (VCD) to above 2.2 x 10(6) cells/ml, however, decreased the q(TNFR-Fc) at 30 degrees C, which was due to a reduction in transcription of the TNFR-Fc gene. Taken together, lowering temperature can improve q(TNFR-Fc) but the negative effect of increasing VCD compromises this effect. Further process development addressing the issue of cell density-dependent TNFR-Fc productivity is therefore needed.

Glutamine synthetase (GS) is a key enzyme in the "glutamine-glutamate cycle" between astrocytes and neurons, but its function in vivo was thus far tested only pharmacologically. Crossing GS(fl/lacZ) or GS(fl/fl) mice with hGFAP-Cre mice resulted in prenatal excision of the GS(fl) allele in astrocytes. "GS-KO/A" mice were born without malformations, did not suffer from seizures, had a suckling reflex, and did drink immediately after birth, but then gradually failed to feed and died on postnatal day 3. Artificial feeding relieved hypoglycemia and prolonged life, identifying starvation as the immediate cause of death. Neuronal morphology and brain energy levels did not differ from controls. Within control brains, amino acid concentrations varied in a coordinate way by postnatal day 2, implying an integrated metabolic network had developed. GS deficiency caused a 14-fold decline in cortical glutamine and a sevenfold decline in cortical alanine concentration, but the rising glutamate levels were unaffected and glycine was twofold increased. Only these amino acids were uncoupled from the metabolic network. Cortical ammonia levels increased only 1.6-fold, probably reflecting reduced glutaminolysis in neurons and detoxification of ammonia to glycine. These findings identify the dramatic decrease in (cortical) glutamine concentration as the primary cause of brain dysfunction in GS-KO/A mice. The temporal dissociation between GS(fl) elimination and death, and the reciprocal changes in the cortical concentration of glutamine and alanine in GS-deficient and control neonates indicate that the phenotype of GS deficiency in the brain emerges coincidentally with the neonatal activation of the glutamine-glutamate and the associated alanine-lactate cycles., ((c) 2010 Wiley-Liss, Inc.)

An excess of extracellular glutamate in the hippocampus has been linked to the generation of recurrent seizures and brain pathology in patients with medically intractable mesial temporal lobe epilepsy (MTLE). However, the mechanism which results in glutamate excess in MTLE remains unknown. We recently reported that the glutamate-metabolizing enzyme glutamine synthetase is deficient in the hippocampus in patients with MTLE, and we postulated that this deficiency is critically involved in the pathophysiology of the disease. To further explore the role of glutamine synthetase in MTLE we created a novel animal model of hippocampal glutamine synthetase deficiency by continuous (approximately 28 days) microinfusion of methionine sulfoximine (MSO: 0.625 to 2.5 microg/h) unilaterally into the hippocampus in rats. This treatment led to a deficiency in hippocampal glutamine synthetase activity by 82-97% versus saline. The majority (>95%) of the MSO-treated animals exhibited recurrent seizures that continued for several weeks. Some of the MSO-treated animals exhibited neuropathological features that were similar to mesial temporal sclerosis, such as hippocampal atrophy and patterned loss of hippocampal neurons. However, many MSO-treated animals displayed only minimal injury to the hippocampus, with no clear evidence of mesial temporal sclerosis. These findings support the hypothesis that a deficiency in hippocampal glutamine synthetase causes recurrent seizures, even in the absence of classical mesial temporal sclerosis, and that restoration of glutamine synthetase may represent a novel approach to therapeutic intervention in this disease.

This paper focuses on the three areas in this field in which there have been advances in amino acid and organic acid metabolism. These are the description of glutamine synthetase deficiency, the elucidation of the mechanism of pyridoxine-dependent convulsions, and a hypothesis to explain the neurological complications of some organic acidaemias.

Glutamine synthetase (GS) is ubiquitously expressed in human tissues, being involved in ammonia detoxification and interorgan nitrogen flux. Inherited systemic deficiency of glutamine based on a defect of glutamine synthetase was recently described in two newborns with an early fatal course of disease. Glutamine was largely absent in their serum, urine and cerebrospinal fluid. Each of the patients had a homozygous mutation in the glutamine synthetase gene and enzymatic investigations confirmed that these mutations lead to a severely reduced glutamine synthetase activity. From the observation in the first patients with congenital glutamine synthetase deficiency, brain malformation can be expected as one of the leading signs. In addition, other organ systems are probably involved as observed in one of the index patients who suffered from severe enteropathy and necrolytic erythema of the skin. Deficiency of GS has to be added to the list of inherited metabolic disorders as a rare example of a defect in the biosynthesis of an amino acid.

Glutamine synthetase plays a major role in ammonia detoxification, interorgan nitrogen flux, acid-base homeostasis, and cell signaling. We report on two unrelated newborns who had congenital human glutamine synthetase deficiency with severe brain malformations resulting in multiorgan failure and neonatal death. Glutamine was largely absent from their serum, urine, and cerebrospinal fluid. Each infant had a homozygous mutation in the glutamine synthetase gene (R324C and R341C). Studies that used immortalized lymphocytes expressing R324C glutamine synthetase (R324C-GS) and COS7 cells expressing R341C-GS suggest that these mutations are associated with reduced glutamine synthetase activity., (Copyright 2005 Massachusetts Medical Society.)

We report a 48-year-old man presenting with refractory hyperammonemia after orthotopic liver transplantation. On investigation he was found to have acquired hepatic glutamine synthetase deficiency, a rare condition that occurs after organ transplantations. The patient was started on continuous venovenous hemofiltration treatment, but the hyperammonemia did not respond. The patient was then subjected to molecular adsorption recirculation system (MARS) therapy and the ammonia level gradually improved with successive treatments. In conclusion, the response was unlikely due to the hemofiltration component of MARS alone but more probably due to the removal of putative albumin-bound toxin by the adsorption circuit that had ameliorated the internal milieu of the graft and reversed the enzyme deficiency.

Background: Increased levels of glutamate have been reported in the epileptogenic hippocampus of patients with temporal lobe epilepsy (TLE). This sustained increase, which may contribute to the initiation and propagation of seizure activity, indicates impaired clearance of glutamate released by neurons. Glutamate is predominantly cleared by glial cells through the excitatory amino acid transporter 2 (EAAT2) and its subsequent conversion to glutamine by the glial enzyme glutamine synthetase (GS)., Methods: The authors examined the hippocampal distribution of GS, EAAT2, and glial fibrillary acidic protein (GFAP) by immunohistochemistry in TLE patients with (HS group) and without hippocampal sclerosis (non-HS group), and in autopsy controls. In hippocampal homogenates the authors measured relative protein amounts by immunoblotting and GS enzyme activity., Results: In the autopsy control and non-HS group GS immunoreactivity (IR) was predominantly found in glia in the neuropil of the subiculum, of the pyramidal cell layer of all CA fields, and in the supragranular layer of the dentate gyrus. In the HS group, GS and EAAT2 IR were markedly reduced in subfields showing neuron loss (CA1 and CA4), whereas GFAP IR was increased. The reduction in GS IR in the HS group was confirmed by immunoblotting and paralleled by decreased GS enzyme activity., Conclusions: Glial glutamine synthetase is downregulated in the hippocampal sclerosis (HS) hippocampus of temporal lobe epilepsy (TLE) patients in areas with severe neuron loss. This downregulation appears to be pathology-related, rather than seizure-related, and may be part of the mechanism underlying impaired glutamate clearance found in the hippocampus of TLE patients with HS.

Background: High extracellular glutamate concentrations have been identified as a likely trigger of epileptic seizures in mesial temporal lobe epilepsy (MTLE), but the underlying mechanism remains unclear. We investigated whether a deficiency in glutamine synthetase, a key enzyme in catabolism of extracellular glutamate in the brain, could explain the perturbed glutamate homoeostasis in MTLE., Methods: The anteromedial temporal lobe is the focus of the seizures in MTLE, and surgical resection of this structure, including the hippocampus, leads to resolution of seizures in many cases. By means of immunohistochemistry, western blotting, and functional enzyme assays, we assessed the distribution, quantity, and activity of glutamine synthetase in the MTLE hippocampus., Findings: In western blots, the expression of glutamine synthetase in the hippocampus was 40% lower in MTLE than in non-MTLE samples (median 44 [IQR 30-58] vs 69 [56-87]% of maximum concentration in standard curve; p=0.043; n=8 and n=6, respectively). The enzyme activity was lower by 38% in MTLE vs non-MTLE (mean 0.0060 [SD 0.0031] vs 0.0097 [0.0042] U/mg protein; p=0.045; n=6 and n=9, respectively). Loss of glutamine synthetase was particularly pronounced in areas of the MTLE hippocampus with astroglial proliferation, even though astrocytes normally have high content of the enzyme. Quantitative immunoblotting showed no significant change in the amount of EAAT2, the predominant glial glutamate transporter in the hippocampus., Interpretation: A deficiency in glutamine synthetase in astrocytes is a possible molecular basis for extracellular glutamate accumulation and seizure generation in MTLE. Further studies are needed to define the cause, but the loss of glutamine synthetase may provide a new focus for therapeutic interventions in MTLE.

Huntington's disease (HD) is a late-onset neurodegenerative disease for which the mutation is CAG/polyglutamine repeat expansion. The R6 mouse lines expressing the HD mutation develop a movement disorder that is preceded by the formation of neuronal polyglutamine aggregates. The phenotype is likely caused by a widespread neuronal dysfunction, whereas neuronal cell death occurs late and is very selective. We show that a decreased mRNA level of the major astroglial glutamate transporter (GLT1) in the striatum and cortex of these mice is accompanied by a concomitant decrease in glutamate uptake. In contrast, the expression of the glutamate transporters, GLAST and EAAC1, remain unchanged. The mRNA level of the astroglial enzyme glutamine synthetase is also decreased. These changes in expression occur prior to any evidence of neurodegeneration and suggest that a defect in astrocytic glutamate uptake may contribute to the phenotype and neuronal cell death in HD., (Copyright 2001 Academic Press.)

The role of the Ntr system in Herbaspirillum seropedicae was determined via ntrB and ntrC mutants. Three phenotypes were identified in these mutants: Nif(-), deficiency in growth using nitrate, and low glutamine synthetase (GS) activity. All phenotypes were restored by the plasmid pKRT1 containing the intact glnA, ntrB and ntrC genes of H. seropedicae. The promoter region of glnA was subcloned into a beta-galactosidase fusion vector and the results suggested that NtrC positively regulates the glnA promoter in response to low nitrogen. The H. seropedicae ntrC and ntrB mutant strains showed a deficiency of adenylylation/deadenylylation of GS, indicating that NtrC and NtrB are involved in both transcription and activity control of GS in this organism.

Background: A case of fatal hyperammonemia complicating orthotopic lung transplantation was previously reported., Objective: To describe the incidence, clinical features, and treatment of hyperammonemia associated with orthotopic lung transplantation., Design: Retrospective cohort analysis., Setting: Academic medical center and lung transplantation center in Philadelphia, Pennsylvania., Patients: 145 sequential adult patients who underwent orthotopic lung transplantation., Measurements: Plasma ammonium levels., Results: Six of the 145 patients who had had orthotopic lung transplantation developed hyperammonemia, all within the first 26 days after transplantation. The 30-day post-transplantation mortality rate was 67% for patients with hyperammonemia compared with 17% for those without hyperammonemia (P = 0.01). Development of major gastrointestinal complications (P = 0.03), use of total parenteral nutrition (P < 0.001), and lung transplantation for primary pulmonary hypertension (P = 0.045) were associated with hyperammonemia., Conclusions: Hyperammonemia is a potentially fatal event occurring after orthotopic lung transplantation. It is associated with high nitrogen load, concurrent medical stressors, primary pulmonary hypertension, and hepatic glutamine synthetase deficiency.

Background: The cause of severe acquired hyperammonemia, an uncommon but often fatal complication of organ transplantation and chemotherapy for cancer, is obscure., Objective: To test the hypothesis that liver glutamine synthetase deficiency may explain hyperammonemia in patients who have had organ transplantation or are receiving chemotherapy., Design: Case report., Patients: Two patients who had fatal hyperammonemia after orthotopic lung transplantation., Measurements: Liver tissue was analyzed to determine the activities of two urea cycle enzymes and glutamine synthetase. Western blot assays for hepatic glutamine synthetase were performed to determine whether glutamine synthetase deficiency resulted from reduced enzyme levels., Results: Activities of carbamoyl phosphate synthetase I and ornithine carbamoyltransferase in the liver were normal. The activity of hepatic glutamine synthetase was markedly reduced (in patient 1, 12% of the mean value in controls; in patient 2, 28% of the mean value in controls), and a concomitant reduction in the amount of glutamine synthetase protein was observed., Conclusion: Hyperammonemia after transplantation was associated with hepatic glutamine synthetase deficiency in two patients, but the causal relation between these two conditions must be further studied.

A barley leaf cDNA library has been screened with two oligonucleotide probes designed to hybridize to conserved sequences in glutamine synthetase (GS) genes from higher plants. Two GS cDNA clones were identified as hybridizing strongly to one or both probes. The larger clone (pcHvGS6) contained a 1.6 kb insert which was shown by primer extension analysis to be an almost full-length cDNA. Both clones were more closely related to cDNAs for the chloroplast form of GS (GS2) from pea and Phaseolus vulgaris than to cDNAs for the cytosolic form (GS1). A sequence identical to an N-terminal sequence determined from a purified preparation of the mature GS2 polypeptide (NH2-XLGPETTGVIQRMQQ) was found in the pcHvGS6-encoded polypeptide at residues 46-61, indicating a pre-sequence of at least 45 amino acids. The pre-sequence has only limited sequence homology to the pre-sequences of pea and P. vulgaris GS2 subunits, but is similarly rich in basic residues and possesses some of the structural features common to the targeting sequences of other chloroplast proteins. The molecular lesions responsible for the GS2-deficient phenotypes of eight photorespiratory mutants of barley were investigated using a gene-specific probe from pcHvGS6 to assay for GS2 mRNA, and an anti-GS antiserum to assay for GS2 protein. Three classes of mutants were identified: class I, in which absence of cross-reacting material was correlated with low or undetectable levels of GS2 mRNA; class II, which had normal or increased levels of GS2 mRNA but very little GS2 protein; and class III, which had significant amounts of GS2 protein but little or no GS2 activity.

1. Seizure prone (SP)-gerbils (Meriones unguiculatus) tested repeatedly in an open field exhibited habituation of seizures after one or two trials and subsequently showed more ambulatory activity than non-seizure prone (NSP) individuals. 2. A subset of 5 SP and 5 NSP animals were killed and portions of each cerebral hemisphere, the cerebellum and the brainstem medulla were analysed for glutamine synthetase (GS). 3. GFAP immunohistochemistry was used on forebrain sections to assay astrocyte density. 4. It was found by MANOVA, PCA and regression analyses that seizures and ambulatory activity were related to a deficiency in cerebral GS. 5. Rearing behaviour was related to medullary brainstem and cerebellar GS concentrations. 6. The decreased GS of the seizure-prone gerbils was not apparently associated with a deficiency of astrocytes, perhaps the reverse. 7. The results are discussed in relation to glial-neuronal interactions modulating arousal and the propensity for seizures.

Neurospora crassa wild-type is almost unable to grow on glutamine as sole nitrogen and carbon source but a GDH-; GS +/- double mutant strain, lacking NADP-dependent glutamate dehydrogenase and partially lacking glutamine synthetase did grow. Under these conditions, the double mutant had a higher chemical energy content than the wild-type. Enzyme assays and labelling experiments with glutamine indicated that in the double mutant glutamine was degraded to ammonium and to carbon skeletons by glutamate synthase, the catabolic (NADH-dependent) glutamate dehydrogenase and the glutamine transaminase-omega-amidase pathway.