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Increased expression of glutaminase and glutamine synthetase mRNA in the thalamus in schizophrenia

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Abstract

Numerous molecules enable the handling of glutamate that is destined for neurotransmitter release, including transporters, receptors and glutamatergic enzymes. Previous work in our lab has shown altered levels of transcript expression of excitatory amino acid transporters and a vesicular glutamate transporter in the thalamus in schizophrenia. These changes suggest that molecules that facilitate the release and reuptake of glutamate may be abnormal in schizophrenia. In this study we determined the levels of expression of phosphate activated glutaminase (PAG), which converts glutamine to glutamate, and glutamine synthetase (GS), which converts glutamate to glutamine, with the hypothesis that thalamic PAG and GS transcript expression is altered in schizophrenia. We investigated expression of PAG and GS mRNA using in situ hybridization in six different thalamic nuclei (anterior, dorsomedial, centromedial, ventral anterior, ventral and reticular) from 13 persons with schizophrenia and 8 comparison subjects and found that transcripts for PAG and GS were significantly increased in schizophrenia. Increased PAG and GS transcripts suggest enhanced glutamatergic neurotransmission in the thalamus and its efferent targets in schizophrenia.
... Systemic mutations of the GS gene have been associated with brain malformations, seizures, multiorgan failure, and early death (22,23). Studies have further suggested that acquired GS deficiencies in discrete areas of the brain might play a causative role in various neurological disorders and psychiatric conditions including Alzheimer's disease, hepatic encephalopathy, suicide/depression schizophrenia, and epilepsy (24)(25)(26)(27)(28)(29)(30)(31)(32). The goal of this review is to discuss the significance of GS in the pathogenesis of focal epilepsies, particularly mesial temporal lobe epilepsy (MTLE), which is one of the most common types of medication-refractory epilepsies in humans (26,(32)(33)(34)(35). ...
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The enzyme glutamine synthetase (GS), also referred to as glutamate ammonia ligase, is abundant in astrocytes and catalyzes the conversion of ammonia and glutamate to glutamine. Deficiency or dysfunction of astrocytic GS in discrete brain regions have been associated with several types of epilepsy, including medically-intractable mesial temporal lobe epilepsy (MTLE), neocortical epilepsies, and glioblastoma-associated epilepsy. Moreover, experimental inhibition or deletion of GS in the entorhinal-hippocampal territory of laboratory animals causes an MTLE-like syndrome characterized by spontaneous, recurrent hippocampal-onset seizures, loss of hippocampal neurons, and in some cases comorbid depressive-like features. The goal of this review is to summarize and discuss the possible roles of astroglial GS in the pathogenesis of epilepsy.
... Consistent with this, a microarray analysis reported a reduction of GS mRNA in the PFC of suicidal cases with SCZ (Kim et al., 2007). The observation that increased GS mRNA was also present in the thalamus of patients with SCZ in subregions that are connected to the DLPFC and show enhanced expression of ALDH1L1 (Bruneau et al., 2005) further supports our observation. One exception is the reduced GS expression that was reported in an older SCZ study (Burbaeva et al., 2003). ...
Article
Background: Patients with schizophrenia (SCZ) run a lifelong risk of suicide. Alterations in glia activities in the prefrontal cortex (PFC) have been reported in relation to suicide in patients with SCZ. While immune processes in the CNS have been related to the susceptibility and course of SCZ, there are hardly any direct comparisons between individuals with SCZ, both those who died of natural causes and those that committed suicide, and healthy controls. Materials and methods: We compared mRNA expression using real time qPCR of 16 glia-related genes in the dorsal lateral prefrontal cortex (DLPFC) and the anterior cingulate cortex (ACC) between 35 patients with SCZ (7 suicide completers and 28 patients who died of natural causes) and 34 well-matched controls without psychiatric or neurological diseases. Results: We found an increased expression of the astrocytic gene aldehyde dehydrogenase-1 family member L1 (ALDH1L1) mRNA, a marker involved in dopaminergic activity, in SCZ versus controls. Excluding individuals with SCZ that committed suicide resulted in an elevated expression in the DLPFC of both ALDH1L1 and glutamine synthetase (GS) genes in patients with SCZ, compared to suicide completers and non-psychiatric controls. Regarding microglia genes: in the ACC, homeostatic markers such as chemokine (C-X3-C motif) ligand 1 (CX3CR1) mRNA expression was increased in SCZ without suicide as compared to suicide completers, while no change was found when compared to controls. Another, purinergic receptor 12 (P2RY12) mRNA was exclusively elevated in the ACC of suicide completers, compared to either other group. Triggering receptor expressed on myeloid cells 2 (TREM2) expression, which maintains microglial metabolism, was reduced in non-suicide patients with SCZ, compared to suicide victims and control subjects. Conclusions: Differential changes are found in astrocyte and microglia genes in the PFC subregions in relation to SCZ and suicide, indicating possible disturbances of glia homeostasis in these conditions.
... Research has also reported various genetic mutations that may affect excitatory-inhibitory processes in schizophrenia, including those seen in autism (e.g., CNTNAP2, SHANK3, neurexin 1), as well as disruption to the glutamate-GABA metabolism enzymes glutaminase and glutamine synthetase (Bruneau et al., 2005). 1H-MRS studies have relatively consistently shown increased glutamate, glutamine and Glx across brain regions, which have been associated with negative symptoms (for a review, see Foss-Feig et al., 2017). ...
Article
Several lines of evidence identify aberrant excitatory-inhibitory neural processes across autism and schizophrenia spectrum disorders, particularly within the psychosocial domain. Such neural processes include increased excitatory glutamate and reduced inhibitory GABA concentrations, which may affect auditory pre-attentive processing as indexed by the mismatch negativity (MMN); thus, an excitation-inhibition imbalance might lead to aberrant MMN, which might in turn drive the relationship between the MMN and psychosocial difficulties. This research has the potential to enhance the neurochemical understanding of the relationship between electrophysiology (MMN) and behavioural/clinical measures (psychosocial difficulties). Thirty-eight adults (18 male, 18-40 years) completed the Schizotypal Personality Questionnaire (SPQ) and Autism-Spectrum Quotient (AQ). Glutamate and GABA concentrations in bilateral superior temporal cortex (STC) were quantified using proton magnetic resonance spectroscopy (1H-MRS) while auditory MMN to a duration deviant was measured with magnetoencephalography. Spearman correlations probed the relationships between STC glutamate/GABA ratios, MMN amplitude and latency, and AQ and SPQ dimensions. Mediation effects of glutamate/GABA ratios on the relationship between MMN and AQ-SPQ dimensions were probed using causal mediation analysis. Only SPQ-interpersonal and AQ-communication were significantly correlated with right hemisphere glutamate/GABA ratios and MMN latency (ps < 0.05), which were themselves correlated (p = .035). Two mediation models were investigated, with right MMN latency as predictor and SPQ-interpersonal and AQ-communication as outcome variables. Right STC glutamate/GABA ratios significantly mediated the relationship between MMN latency and SPQ-interpersonal scores, but only partially mediated the relationship between MMN latency and AQ-communication scores. These findings support the growing body of literature pointing toward an excitation-inhibition imbalance that is central to psychosocial functioning across multi-dimensional spectrum disorders, such as autism and schizophrenia, and provides neurochemical indicators of the processes that underlie psychosocial dysfunction.
... GS recycles the neurotransmitter glutamate (Rose et al., 2013), as neurons are incapable of de novo synthesis of glutamate. Given the important role of glial GS in several metabolic pathways, such as the glutamate-glutamine-cycle and metabolism of ammonia (Rose et al., 2013), it is no surprise that alterations in GS expression are associated with several neurological disorders including depression, schizophrenia, epilepsy, Parkinson's, and Alzheimer's disease (Bruneau et al., 2005;Gruenbaum et al., 2015;Hensley et al., 1995;Kalkman, 2011;Kulijewicz-Nawrot et al., 2013;Rose et al., 2013;Yu et al., 2012). ...
Article
Even though lithium is widely used as treatment for mood disorders, the exact mechanisms of lithium in the brain remain unknown. A potential mechanism affects the downstream target of the Wnt/β-catenin signaling pathway, specifically glutamine synthetase (GS). Here, we investigate the effect of lithium on GS-promoter activity in the brain. Over seven days, B6C3H-Glultm(T2A-LacZ) mice that carry LacZ as a reporter gene fused to the GS-promotor received either daily intraperitoneal injections of lithium carbonate (25 mg/kg) or NaCl, or no treatment. Following histochemical staining of β-galactosidase relative GS-promotor activity was measured by analyzing the intensity of the staining. Furthermore cell counts were conducted. GS-promotor activity was significantly decreased in female compared to male mice. Treatment group differences were only found in male hippocampi, with increased activity after NaCl treatment compared to both the lithium treatment and no treatment. Lithium treatment increased the overall number of cells in the CA1 region in males. Daily injections of NaCl might have been sufficient to induce stress-related GS-promotor activity changes in male mice; however, lithium was able to reverse the effect. Taken together, the current study indicates that lithium acts to prevent stress, rather affecting general GS-promoter activity.
... http://dx.doi.org/10.1101/728204 doi: bioRxiv preprint first posted online Aug. 7, 2019; metabolism enzymes glutaminase and glutamine synthetase (Bruneau et al., 2005). 1H-MRS 470 studies have relatively consistently shown increased glutamate, glutamine and Glx across 471 brain regions, which have been associated with negative symptoms (for a review, see Foss-472 however the MMN was recorded fronto-centrally (Kompus et al., 2015). ...
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Several lines of evidence identify aberrant excitatory-inhibitory neural processes across autism and schizophrenia spectrum disorders, particularly within the psychosocial domain. Such neural processes include increased excitatory glutamate and reduced inhibitory GABA concentrations, which may affect auditory pre-attentive processing as indexed by the mismatch negativity (MMN); thus, an excitation-inhibition imbalance might lead to aberrant MMN, which might in turn drive the relationship between the MMN and psychosocial difficulties. This research has the potential to enhance the neurochemical understanding of the relationship between electrophysiology (MMN) and behavioural/clinical measures (psychosocial difficulties). Thirty-eight adults (18 male, 18-40 years) completed the Schizotypal Personality Questionnaire (SPQ) and Autism-Spectrum Quotient (AQ). Glutamate and GABA concentrations in bilateral superior temporal cortex (STC) were quantified using proton magnetic resonance spectroscopy (1H-MRS) while auditory MMN to a duration deviant was measured with magnetoencephalography. Spearman correlations probed the relationships between STC glutamate/GABA ratios, MMN amplitude and latency, and AQ and SPQ dimensions. Mediation effects of glutamate/GABA ratios on the relationship between MMN and AQ-SPQ dimensions were probed using causal mediation analysis. Only SPQ-interpersonal and AQ-communication were significantly correlated with right hemisphere glutamate/GABA ratios and MMN latency ( p s<.05), which were themselves correlated ( p =.038). Two mediation models were investigated, with right MMN latency as predictor and SPQ-interpersonal and AQ-communication as outcome variables. Right STC glutamate/GABA ratios significantly mediated the relationship between MMN latency and SPQ-interpersonal scores (ß=86.6, p =.033), but only partially mediated the relationship between MMN latency and AQ-communication scores (ß=21.0, p =.093). These findings support the growing body of literature pointing toward an excitation-inhibition imbalance that is central to psychosocial functioning across multi-dimensional spectrum disorders, such as autism and schizophrenia, and provides neurochemical indicators of the processes that underlie psychosocial dysfunction.
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Chapter
Schizophrenia is a neuropsychiatric disease with 1% worldwide prevalence and characterized by a deep distortion in thought and perception, cognitive dysfunction, and social behavioral deficits. After the discovery of the antipsychotic effects of chlorpromazine, a large body of evidence pointed out to the neurotransmission misbalance as the main factor in the development of this pathology. Nowadays, it is known that schizophrenia is related to a pluri-factorial etiopathogenesis where gene factors, neuroinflammation, and brain microenvironment’s alterations are taken into account as well. In this sense, glial cells (oligodendrocytes, astrocytes, and microglial cells) are essential pieces in brain microenvironment with crucial roles in synaptic establishment and function, neuroinflammation, and metabolic and ion homeostasis, among others. Currently, glial cells are the target of numerous researches on the race to puzzle out the schizophrenia etiopathology.
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Astrocytes are morphologically and functionally heterogeneous cell population. Most studies are focused on changes in glia during the development of neurodegenerative diseases, however, the heterogeneity of cells in the physiological state and normal aging is also of great interest for understanding neuron-glial interactions. The aim of this study was to investigate regionally heterogeneous expression of two commonly used astrocytic markers: glial fibrillary acid protein (GFAP) and glutamine synthetase (GS) in vitro. Astrocytes isolated from the brainstem are divided into two populations: GFAP- and GFAP +, the latter is characterized by increased expression compared to cortical and hippocampal astrocytes. With respect to GS expression, astrocytes from the cerebral cortex show a significantly higher level of GS compared to astrocytes from the hippocampus and brainstem. Moreover, there is a positive correlation between GFAP and GS expression. Thus, our data indicate that astrocytes from the cerebral cortex, hippocampus and brainstem are heterogeneous with respect to GFAP and GS expression.
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Schizophrenia is a chronic disease characterized by the impairment of mental functions with a marked social dysfunction. A quantitative proteomic approach using iTRAQ labeling and SRM, applied to the characterization of mitochondria (MIT), crude nuclear fraction (NUC) and cytoplasm (CYT), can allow the observation of dynamic changes in cell compartments providing valuable insights concerning schizophrenia physiopathology. Mass spectrometry analyses of the orbitofrontal cortex from 12 schizophrenia patients and 8 healthy controls identified 655 protein groups in MIT fraction, 1500 in NUC and 1591 in CYT. We found 166 groups of proteins dysregulated among all enriched cellular fractions. Through the quantitative proteomic analysis, we detect as the main biological pathways those related to calcium and glutamate imbalance, cell signaling disruption of CREB activation, axon guidance and proteins involved in the activation of NF-kB signaling along with the increase of complement proteins C3. Based on our data analysis, we suggest the activation of NF-kB as a possible pathway that links the deregulation of glutamate, calcium, apoptosis and the activation of the immune system in schizophrenia patients. All MS data are available in the ProteomeXchange Repository under the identifier PXD014284 and PXD014350.
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Reductions of 40% in total cell number and 25% in volume of the mediodorsal thalamic nucleus were recently reported in an unbiased neurostereological study of neuroleptic-treated schizophrenic patients. In order to investigate whether these results might be secondary to many years of treatment with neuroleptic drugs, eight brains from schizophrenics never treated with neuroleptics and eight controls were studied using the unbiased Cavalieri volume estimator. To compare left-right differences in this region, twelve neuroleptic-treated schizophrenics and eleven control cases were compared. The brains used for the left-right comparison study and five of 20 used for comparison of treated and untreated brain volumes have been used in an earlier study. The mediodorsal thalamus volume was reduced by 31% in untreated schizophrenics and by 22% in neuroleptic-treated schizophrenics. No differences were found in mean total volume of the left and right mediodorsal thalamus in brains from controls nor from schizophrenics. A major difference exists with respect to time of fixation in controls (12 years) and untreated schizophrenics (39 years) that makes shrinkage differences a possible confounding variable. The results suggest that the consistent reduction in number of neurons in the mediodorsal thalamic nucleus are not secondary to prolonged treatment with neuroleptic drugs and that asymmetry in this specific brain region is not a feature of the schizophrenia-afflicted brain.
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Schizophrenia has been hypothesized to be caused by a hypofunction of glutamatergic neurons. Findings of reduced concentrations of glutamate in the cerebrospinal fluid of patients with schizophrenia and the ability of glutamate-receptor antagonists to cause psychotic symptoms lend support to this hypothesis. N-acetylaspartylglutamate (NAAG), a neuropeptide that is highly concentrated in glutamatergic neurons, antagonizes the effects of glutamate at N-methyl-D-aspartate receptors. Moreover, NAAG is cleaved to glutamate and N-acetylaspartate by a specific peptidase, N-acetyl-alpha-linked acidic dipeptidase (NAALADase). To test the glutamatergic hypothesis of schizophrenia, we studied the NAAG-related glutamatergic variables in postmortem brains from patients with schizophrenia, neuroleptic-treated controls, and normal individuals, with particular emphasis on the prefrontal cortex and hippocampus. Different regions of frozen brain tissue from three different groups (patients with schizophrenia, neuroleptic-treated controls, and normal controls) were assayed to determine levels of NAAG, N-acetylaspartate, NAALADase, and several amino acids, including aspartate and glutamate. Our study demonstrates alterations in brain levels of aspartate, glutamate, and NAAG and in NAALADase activity. Levels of NAAG were increased and NAALADase activity and glutamate levels were decreased in the schizophrenic brains. Notably, the changes in NAAG level and NAALADase activity in schizophrenic brains were more selective than those for aspartate and glutamate. In neuroleptic-treated control brains, levels of aspartate, glutamate, and glycine were found to be increased. The changes in levels of aspartate, glutamate, NAAG, and NAALADase are prominent in the prefrontal and hippocampal regions, where previous neuropathological studies of schizophrenic brains demonstrate consistent changes. These findings support the hypothesis that schizophrenia results from a hypofunction of certain glutamatergic neuronal systems. They also suggest that the therapeutic efficacy of neuroleptics may be related to increased glutamatergic activity.
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