Glutamate Receptor Expression Research Articles

GluR2 can Drive Neuroinflammation and Cognitive Impairments Following Peripherally Repeated Lipopolysaccharide Exposures.

Neuroinflammation is being increasingly recognized as a vital factor in the development of various neurological and neuropsychiatric diseases. Lipopolysaccharides (LPS), an outer membrane component of gram-negative bacteria, can trigger innate immune responses, resulting in neuroinflammation and subsequent cognitive deficits. The expression of glutamate receptors (GluRs) on glial cells can induce glial activation. Therefore, we hypothesized that repeated LPS exposure can increase GluR levels, promoting microglial activation and ultimately affecting synaptic plasticity and cognitive function. In this study, C57/BL6 mice were repeatedly exposed to LPS to construct a neuroinflammation animal model. The levels of GluRs, inflammatory cytokines, ionized calcium-binding adaptor molecule 1, postsynaptic density protein 95, synaptophysin 38, NMDA receptor 2A, and NMDA receptor 2B (GluN2B) were measured in the hippocampi. Furthermore, dendritic spine density in the CA1 hippocampal region was determined. Repeated LPS exposure induced cognitive impairments and microglial activation and increased GluR1 and GluR2 levels. This was accompanied by a significant decrease in GluN2B expression and dendritic spine density in the hippocampi. However, CFM-2, an α-amino-3- hydroxy-5-methyl-4-isoxazolepropionate receptor antagonist, reversed these anomalies. Furthermore, minocycline, a microglial inhibitor, reversed these anomalies and downregulated GluR2 but not GluR1 expression. In summary, we demonstrated that GluR2 plays an essential role in microglia-induced neuroinflammation, resulting in synaptic plasticity and cognitive impairment induced by repeated exposure to LPS.

Is autism a PIN1 deficiency syndrome? A proposed etiological role for glyphosate.

Autism is a neurodevelopmental disorder, the prevalence of which has increased dramatically in the United States over the past two decades. It is characterized by stereotyped behaviors and impairments in social interaction and communication. In this paper, we present evidence that autism can be viewed as a PIN1 deficiency syndrome. Peptidyl-prolyl cis/trans isomerase, NIMA-Interacting 1 (PIN1) is a peptidyl-prolyl cis/trans isomerase, and it has widespread influences in biological organisms. Broadly speaking, PIN1 deficiency is linked to many neurodegenerative diseases, whereas PIN1 over-expression is linked to cancer. Death-associated protein kinase 1 (DAPK1) strongly inhibits PIN1, and the hormone melatonin inhibits DAPK1. Melatonin deficiency is strongly linked to autism. It has recently been shown that glyphosate exposure to rats inhibits melatonin synthesis as a result of increased glutamate release from glial cells and increased expression of metabotropic glutamate receptors. Glyphosate's inhibition of melatonin leads to a reduction in PIN1 availability in neurons. In this paper, we show that PIN1 deficiency can explain many of the unique morphological features of autism, including increased dendritic spine density, missing or thin corpus callosum, and reduced bone density. We show how PIN1 deficiency disrupts the functioning of powerful high-level signaling molecules, such as nuclear factor erythroid 2-related factor 2 (NRF2) and p53. Dysregulation of both of these proteins has been linked to autism. Severe depletion of glutathione in the brain resulting from chronic exposure to oxidative stressors and extracellular glutamate leads to oxidation of the cysteine residue in PIN1, inactivating the protein and further contributing to PIN1 deficiency. Impaired autophagy leads to increased sensitivity of neurons to ferroptosis. It is imperative that further research be conducted to experimentally validate whether the mechanisms described here take place in response to chronic glyphosate exposure and whether this ultimately leads to autism.

A glutamatergic biomarker panel enables differentiating Grade 4 gliomas/astrocytomas from brain metastases.

The differentiation of high-grade glioma and brain tumors of an extracranial origin is eminent for the decision on subsequent treatment regimens. While in high-grade glioma, a surgical resection of the tumor mass is a fundamental part of current standard regimens, in brain metastasis, the burden of the primary tumor must be considered. However, without a cancer history, the differentiation remains challenging in the imaging. Hence, biopsies are common that may help to identify the tumor origin. An additional tool to support the differentiation may be of great help. For this purpose, we aimed to identify a biomarker panel based on the expression analysis of a small sample of tissue to support the pathological analysis of surgery resection specimens. Given that an aberrant glutamate signaling was identified to drive glioblastoma progression, we focused on glutamate receptors and key players of glutamate homeostasis. Based on surgically resected samples from 55 brain tumors, the expression of ionotropic and metabotropic glutamate receptors and key players of glutamate homeostasis were analyzed by RT-PCR. Subsequently, a receiver operating characteristic (ROC) analysis was performed to identify genes whose expression levels may be associated with either glioblastoma or brain metastasis. Out of a total of 29 glutamatergic genes analyzed, nine genes presented a significantly different expression level between high-grade gliomas and brain metastases. Of those, seven were identified as potential biomarker candidates including genes encoding for AMPA receptors GRIA1, GRIA2, kainate receptors GRIK1 and GRIK4, metabotropic receptor GRM3, transaminase BCAT1 and the glutamine synthetase (encoded by GLUL). Overall, the biomarker panel achieved an accuracy of 88% (95% CI: 87.1, 90.8) in predicting the tumor entity. Gene expression data, however, could not discriminate between patients with seizures from those without. We have identified a panel of seven genes whose expression may serve as a biomarker panel to discriminate glioblastomas and brain metastases at the molecular level. After further validation, our biomarker signatures could be of great use in the decision making on subsequent treatment regimens after diagnosis.

An antagonist-based two-photon fluorogenic probe for imaging metabotropic glutamate receptor 5 in neuronal cells

The expression of metabotropic glutamate receptor 5 (mGluR5) is subject to developmental regulation and undergoes significant changes in neuropsychiatric disorders and diseases. Visualizing mGluR5 by fluorescence imaging is a highly desired innovative technology for biomedical applications. Nevertheless, there are substantial problems with the chemical probes that are presently accessible. In this study, we have successfully developed a two-photon fluorogenic probe, mGlu-5-TP, based on the structure of mGluR5 antagonist 6-methyl-2-(phenylethynyl)pyridine (MPEP). Due to this antagonist-based probe selectively recognizes mGluR5, high expression of mGluR5 on living SH-SY5Y human neuroblastoma cells has been detected during intracellular inflammation triggered by lipopolysaccharides (LPS). Of particular significance, the probe can be employed along with two-photon fluorescence microscopy to enable real-time visualization of the mGluR5 in Aβ fiber-treated neuronal cells, thereby establishing a connection to the progression of Alzheimer's disease (AD). These results revealed that the probe can be a valuable imaging tool for studying mGluR5-related diseases in the nervous system.

Circulatory levels of dopamine and glutamate and assessment of gene expression of dopamine and glutamate receptors in patients with schizophrenia. A case control study

Circulatory levels of dopamine and glutamate and assessment of gene expression of dopamine and glutamate receptors in patients with schizophrenia. A case control study

The SNX17-Retriever endosomal recycling pathway is a key regulator of synaptic function and plasticity in hippocampal neurons

The insertion and removal of integral membrane proteins is a key mechanism for the regulation of synaptic function. Once surface proteins are internalized, they can either be routed to lysosomes for degradation or can be recycled back to the cell surface. Two recycling protein complexes - the SNX27-Retromer complex and the recently discovered SNX17-Retriever complex - are the main drivers in recycling internalized cargoes in non-neuronal cells. In neurons, the SNX27-Retromer pathway has been shown to regulate surface expression of AMPA-type glutamate receptors (AMPARs) during long-term potentiation (LTP), but almost nothing is known regarding the role of the SNX17-Retriever pathway at synapses. Here, using cultured hippocampal neurons, we demonstrate that the SNX17-Retriever pathway localizes to both synaptic and extra-synaptic sites and that RNAi-mediated disruption of this pathway leads to the functional and structural loss of excitatory synapses. Moreover, we find that synaptic stimulation leads to the recruitment of SNX17 to synaptic sites in a manner that depends on Ca2+ influx through NMDARs, activation of CaMKII, and Retriever complex binding. Knockdown of either SNX17 or the Retriever subunit DSCR3 prevents structural plasticity of dendritic spines during LTP. Finally, this loss of structural plasticity is associated with altered traffcking of the cell adhesion molecule β1 Integrin, which is a SNX17 cargo in non-neuronal cells and as we show, in neurons as well. Additionally, SNX17-Retriever is shown to not play a role in AMPAR recycling. Preliminary studies suggest that SNX27 and SNX17 sort distinct cargos in neurons, suggesting that these two recycling pathways each play important, but unique, roles at synaptic sites. National Institute of Neurological Disorders and Stroke (NINDS) of the National Institutes of Health (NIH) under award numbers R01-NS129198 to L.S. Weisman and M.A. Sutton, R01-NS099340 and R01- NS064015 to L.S. Weisman, R01-NS097498 to M.A. Sutton, and R21-NS125449, and R01-NS116008 to S. Iwase, by the National Institute of Mental Health (NIMH) of the NIH under award number R21-MH127485 to S. Iwase. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Mechanisms Underlying Long-Term Facilitation in the Carotid Body

Glutamate and γ-aminobutyric acid (GABA) are major modulators of excitatory and inhibitory transmission in the mammalian brain. Glutamate transmission is critical for neural plasticity, learning and memory, whereas GABA plays a fundamental role in regulating neuronal excitability and facilitating the generation of neural oscillations. Our data indicates that both glutamate and GABA are released in the carotid body (CB) to modulates its response to hypoxia. Objectives: We set out to investigate whether repeated stimulation with glutamate and GABA induces lasting effects on CB afferent discharge. Hypothesis: We hypothesised that glutamate/GABA mediates long-term facilitation (LTF) of CB afferent activity. Methods: We mined high-throughput RNA sequence data and used immunohistochemistry to map components underlying neuroplasticity in the CB in Wistar and Spontaneously-hypertensive rats (SHR). CSN discharge was measured as a functional readout of CB function from an ex vivo arterially perfused carotid artery-CB preparation. Data: We catalogue the expression of glutamate receptors (R) and transporters in the rat and mouse CB. We found N-methyl-D-aspartic acid receptor (NMDAR), α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPAR) and transporters to be localised to the CB chemosensory cells. Targeted administration of 15 mM glutamate activated the carotid sinus nerve ( p=0.003). Repetitive [5 times, 2-minute duration, 5-minute intervals] application of 15 mM glutamate evoked LTF of CB afferent discharge as demonstrated by both a 12-fold increase in basal firing frequency (0.78 ± 0.37 vs 1232 ± 596 spikes 1s−1; p = 0.004) over 60 minutes ( p = 0.004) and amplification of the evoked response to chemical hypoxia (CN−; 1.23 μmol bolus) by 2-fold ( p = 0.009). The stimulation paradigm was specific as neither application of glutamate, 5 times for 1-minute at 5-minute intervals, nor a single glutamate exposure evoked LTF. In contrast, repeated application of 15mM GABA [3 times for 1-minute at 5-minute intervals] evoked long-term depression (LTD) of CB afferent activity as seen by a reduced basal discharge from 10.5 to 3.5 spikes 1s−1 ( p = 0.0004) and a 2-fold suppression of the response to chemical hypoxia ( p = 3.71 x 10−5). Summary of the data: Repetitive exposure to glutamate using a specific protocol increased basal discharge of CB afferent output akin to LTF and caused sensitisation of evoked responses to CN−. Repeated exposures of GABA depressed the CB basal discharge akin to LTD. A statement of the conclusions: It is conceivable that processes such as LTP and LTD operate in the CB to modulate the set point of peripheral chemoreceptor sensitivity and its state-dependent tonicity; the role of LTP in peripheral chemoreflex sensitisation in disease remains to be determined. Research was supported by the Health Research Council of New Zealand and the Sidney Taylor Trust. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Limb-Clasping Response in NMDA Receptor Palmitoylation-Deficient Mice.

Proper regulation of N-methyl-D-aspartate-type glutamate receptor (NMDA receptor) expression is responsible for excitatory synaptic functions in the mammalian brain. NMDA receptor dysfunction can cause various neuropsychiatric disorders and neurodegenerative diseases. Posttranslational protein S-palmitoylation, the covalent attachment of palmitic acid to intracellular cysteine residues via thioester bonds, occurs in the carboxyl terminus of GluN2B, which is the major regulatory NMDA receptor subunit. Mutations of three palmitoylatable cysteine residues in the membrane-proximal cluster of GluN2B to non-palmitoylatable serine (3CS) lead to the dephosphorylation of GluN2B Tyr1472 in the hippocampus and cerebral cortex, inducing a reduction in the surface expression of GluN2B-containig NMDA receptors. Furthermore, adult GluN2B 3CS homozygous mice demonstrated a definite clasping response without abnormalities in the gross brain structure, other neurological reflexes, or expression levels of synaptic proteins in the cerebrum. This behavioral disorder, observed in the GluN2B 3CS knock-in mice, indicated that complex higher brain functions are coordinated through the palmitoylation-dependent regulation of NMDA receptors in excitatory synapses.

Repeated Morphine Exposure Alters Temporoamonic-CA1 Synaptic Plasticity in Male Rat Hippocampus

In this study, the electrophysiological and biochemical consequences of repeated exposure to morphine in male rats on glutamatergic synaptic transmission, synaptic plasticity, the expression of GABA receptors and glutamate receptors at the temporoammonic-CA1 synapse along the longitudinal axis of the hippocampus (dorsal, intermediate, ventral, DH, IH, VH, respectively) were investigated. Slice electrophysiological methods, qRT-PCR, and western blotting techniques were used to characterize synaptic plasticity properties. We showed that repeated morphine exposure (RME) reduced excitatory synaptic transmission and ability for long-term potentiation (LTP) in the VH as well as eliminated the dorsoventral difference in paired-pulse responses. A decreased expression of NR2B subunit in the VH and an increased expression GABAA receptor of α1 and α5 subunits in the DH were observed following RME. Furthermore, RME did not affect the expression of NR2A, AMPA receptor subunits, and γ2GABAA and GABAB receptors in either segment of the hippocampus. In sum, the impact of morphine may differ depending on the region of the hippocampus studied. A distinct change in the short- and long-term synaptic plasticity along the hippocampus long axis due to repeated morphine exposure, partially mediated by a change in the expression profile of glutamatergic receptor subunits. These findings can be useful in further understanding the cellular mechanism underlying deficits in information storage and, more generally, cognitive processes resulting from chronic opioid abuse.

Isradipine, an L-type calcium channel blocker, attenuates cocaine effects in mice by reducing central glutamate release

Substance abuse disorder is a chronic condition for which pharmacological treatment options remain limited. L-type calcium channels (LTCC) have been implicated in drug-related plasticity and behavior. Specifically, dopaminergic neurons in the mesocorticolimbic pathway express Cav1.2 and Cav1.3 channels, which may regulate dopaminergic activity associated with reward behavior. Therefore, this study aimed to investigate the hypothesis that pre-administration of the LTCC blocker, isradipine can mitigate the effects of cocaine by modulating central glutamatergic transmission. For that, we administered isradipine at varying concentrations (1, 7.5, and 15 μg/μL) via intracerebroventricular injection in male Swiss mice. This pretreatment was carried out prior to subjecting animals to behavioral assessments to evaluate cocaine-induced locomotor sensitization and conditioned place preference (CPP). The results revealed that isradipine administered at a concentration of 1 μg/μL effectively attenuated both the sensitization and CPP induced by cocaine (15 mg/kg, via i. p.). Moreover, mice treated with 1 μg/μL of isradipine showed decreased presynaptic levels of glutamate and calcium in the cortex and hippocampus as compared to control mice following cocaine exposure. Notably, the gene expression of ionotropic glutamate receptors, AMPA, and NMDA, remained unchanged, as did the expression of Cav1.2 and Cav1.3 channels. Importantly, these findings suggest that LTCC blockage may inhibit behavioral responses to cocaine, most likely by decreasing glutamatergic input in areas related to addiction.

Effect of antipsychotic drugs on group II metabotropic glutamate receptor expression and epigenetic control in postmortem brains of schizophrenia subjects

Antipsychotic-induced low availability of group II metabotropic glutamate receptors (including mGlu2R and mGlu3R) in brains of schizophrenia patients may explain the limited efficacy of mGlu2/3R ligands in clinical trials. Studies evaluating mGlu2/3R levels in well-designed, large postmortem brain cohorts are needed to address this issue. Postmortem samples from the dorsolateral prefrontal cortex of 96 schizophrenia subjects and matched controls were collected. Toxicological analyses identified cases who were (AP+) or were not (AP-) receiving antipsychotic treatment near the time of death. Protein and mRNA levels of mGlu2R and mGlu3R, as well as GRM2 and GRM3 promoter-attached histone posttranslational modifications, were quantified. Experimental animal models were used to compare with data obtained in human tissues. Compared to matched controls, schizophrenia cortical samples had lower mGlu2R protein amounts, regardless of antipsychotic medication. Downregulation of mGlu3R was observed in AP- schizophrenia subjects only. Greater predicted occupancy values of dopamine D2 and serotonin 5HT2A receptors correlated with higher density of mGlu3R, but not mGlu2R. Clozapine treatment and maternal immune activation in rodents mimicked the mGlu2R, but not mGlu3R regulation observed in schizophrenia brains. mGlu2R and mGlu3R mRNA levels, and the epigenetic control mechanisms did not parallel the alterations at the protein level, and in some groups correlated inversely. Insufficient cortical availability of mGlu2R and mGlu3R may be associated with schizophrenia. Antipsychotic treatment may normalize mGlu3R, but not mGlu2R protein levels. A model in which epigenetic feedback mechanisms controlling mGlu3R expression are activated to counterbalance mGluR loss of function is described.

Metabotropic glutamate receptor 5 promotes blood-brain barrier recovery after traumatic brain injury

Blood-brain barrier (BBB) impairment and glutamate release are two pathophysiological features of traumatic brain injury (TBI), contributing to secondary brain damage and neuroinflammation. However, our knowledge of BBB integrity damage and dysfunction are still limited due to the diverse and fluctuating expression of glutamate receptors after trauma. Here, we confirmed the downregulation of metabotropic glutamate receptor 5 (mGluR5) on microvascular endothelial cell within the acute phase of TBI, and the recovered mGluR5 levels on BBB was positively associated with blood perfusion and neurological recovery. In whole body mGluR5-knockout mice, BBB dysfunction and neurological deficiency were exacerbated after TBI compared with wild type mice. In terms of mechanism, the amino acid sequence 201–259 of cytoskeletal protein Alpha-actinin-1 (ACTN1) interacted with mGluR5, facilitating mGluR5 translocation from cytoplasmic compartment to plasma membrane in endothelial cells. Activation of plasma membrane mGluR5 triggers the PLC/PKCμ/c-Jun signaling pathway, leading to increased expression of the tight junction-actin cytoskeleton connecting protein zonula occludens-1 (ZO-1). Our findings uncover a novel mechanism mediated by membrane and cytoplasmic mGluR5 in endothelial cell integrity maintenance and repair, providing the potential therapeutic target for TBI treatment targeting at mGluR5 and mGluR5/ACTN1 complex in BBB.

5-HT2A Receptor Knockout Mice Show Sex-Dependent Differences following Acute Noribogaine Administration.

Noribogaine (noribo) is the primary metabolite from ibogaine, an atypical psychedelic alkaloid isolated from the root bark of the African shrub Tabernanthe iboga. The main objective of this study was to test the hypothesis that molecular, electrophysiological, and behavioral responses of noribo are mediated by the 5-HT2A receptor (5-HT2AR) in mice. In that regard, we used male and female, 5-HT2AR knockout (KO) and wild type (WT) mice injected with a single noribo dose (10 or 40 mg/kg; i.p.). After 30 min., locomotor activity was recorded followed by mRNA measurements by qPCR (immediate early genes; IEG, glutamate receptors, and 5-HT2AR levels) and electrophysiology recordings of layer V pyramidal neurons from the medial prefrontal cortex. Noribo 40 decreased locomotion in male, but not female WT. Sex and genotype differences were observed for IEG and glutamate receptor expression. Expression of 5-HT2AR mRNA increased in the mPFC of WT mice following Noribo 10 (males) or Noribo 40 (females). Patch-clamp recordings showed that Noribo 40 reduced the NMDA-mediated postsynaptic current density in mPFC pyramidal neurons only in male WT mice, but no effects were found for either KO males or females. Our results highlight that noribo produces sexually dimorphic effects while the genetic removal of 5HT2AR blunted noribo-mediated responses to NMDA synaptic transmission.

Analysis of Surface Expression of NMDAR Subunits in Primary Hippocampal Neurons.

The expression and activity of ionotropic glutamate receptors control signal transduction at the excitatory synapses in the CNS. The NMDAR comprises two obligatory GluN1 subunits and two GluN2 or GluN3 subunits in different combinations. Each GluN subunit consists of four domains: the extracellular amino-terminal and agonist-binding domains, the transmembrane domain, and the intracellular C-terminal domain (CTD). The CTD interaction with various classes of intracellular proteins is critical for trafficking and synaptic localization of NMDARs. Amino acid mutations or the inclusion of premature stop codons in the CTD could contribute to the emergence of neurodevelopmental and neuropsychiatric disorders. Here, we describe the method of preparing primary hippocampal neurons and lentiviral particles expressing GluN subunits that can be used as a model to study cell surface expression and synaptic localization of NMDARs. We also show a simple method of fluorescence immunostaining of eGFP-tagged GluN2 subunits and subsequent microscopy technique and image analysis to study the effects of disease-associated mutations in the CTDs of GluN2A and GluN2B subunits.

Deletion of transcription factor Satb1 leads to disturbance in mice behavior through changes in the expression of genes-regulators of the excitive component of neurotransmission

The transcription factor Satb1 exhibits widespread expression in multiple tissues and different regions of the brain. Notable levels of expression are observed in the neocortex, the nucleus of the diagonal band, the amygdala, and the tegmental area. In the ventral midbrain, Satb1-positive neurons are only found in a small portion of the substantia nigra, the ventral tegmental area, and the retrorubral field, and none were detected in the inferior colliculus. The transcription factor Satb1 is highly expressed in interneurons labeled as SST+, CR+, and NPY+, but not VIP+ interneurons. In mice with the Satb1 mutation, incomplete eye opening and a constriction reflex were observed. Behavioral tests revealed that mice lacking Satb1 exhibited deficits in motor coordination, characterized by reduced mobility on flat bars and decreased grip strength on metal wires. In addition, these mice exhibited elevated levels of motor activity in novel environments and heightened anxiety in the light-dark test. Satb1-deficient males demonstrated proficiency in passive avoidance tests, while their female counterparts exhibited no significant difference in entrance time to the dark compartment between the reproduction and learning stages, indicating an impairment in the process of conditioned response formation. To investigate the expression patterns of genes encoding vital protein kinases and proteins associated with neurotransmission, we extracted total RNA from the cerebral cortex of adult males with an incomplete deletion of Satb1. Real-time PCR analysis was conducted, which revealed a higher expression level of the pik3ca, pik3cb, and pic3cg genes responsible for phosphoinositide-3-kinase isoforms in Satb1-deficient mice compared to wild-type mice. The expression levels of genes encoding protein kinase C (Prkce and Prkcg) as well as Ca2+/calmodulin-dependent protein kinase II (Camk2) were lower in comparison to wild-type mice. Satb1-deficient mice displayed notably higher expression levels of genes encoding NMDA receptor subunits (Grin1, Grin2a, and Grin2b), whereas the expression of Gria1 (encoding the Glua2 subunit of AMPA receptors responsible for Ca2+ receptor conductance) decreased. The influence on excitatory glutamate receptor expression can cause hyperexcitability in animals, particularly when inhibitory neurotransmission is suppressed due to decreased Gabra1 and Gad65/67 expression encoding the GABA(A) receptor and glutamate decarboxylase. In addition, the levels of expression for the Calb1, Calb2, and Pvalb genes responsible for encoding the calcium-binding proteins calbindin, calretinin, and parvalbumin decreased in comparison to the wild-type mice. Thus, a correlation was found between behavioral disturbances and expression of genes that encode proteins related to brain development and neurotransmission after deleting the Satb1 transcription factor. Satb1-deleted mice exhibited hyperexcitation and impaired motor activity due to impaired gene expression.

Development of Potent and Selective Negative Allosteric Modulators of the Metabotropic Glutamate Receptor 2 for the Potential Treatment of Alzheimer’s Disease

AbstractBackgroundThe metabotropic glutamate receptor 2 (mGluR2) is a group II mGluR that binds glutamate and utilizes Gi/o signaling within the central nervous system (CNS) to modulate synaptic transmission and neuronal excitation.1 The alteration of basal glutamate signaling has been implicated in a variety of neurodegenerative diseases including Alzheimer’s disease (AD).2 mGluR2 has been found to be overexpressed in the hippocampal neurons of AD patients and receptor overactivation has been shown to induce plaque formation in in vitro AD models.3, 4 Thus, the utilization of a mGluR2 negative allosteric modulator (NAM) may prevent neurodegeneration. The utility of mGluR2 NAMs for neurodegenerative diseases remains unclear due to the lack of mGluR selectivity of historical compounds.1. Niswender, C.M. and P.J. Conn, Metabotropic glutamate receptors: physiology, pharmacology, and disease. Annual review of pharmacology and toxicology, 2010. 50: p. 295‐322.2. Li, S.H., K.S. Abd‐Elrahman, and S.S.G. Ferguson, Targeting mGluR2/3 for treatment of neurodegenerative and neuropsychiatric diseases. Pharmacology & Therapeutics, 2022. 239: p. 108275.3. Lee, H.‐g., et al., Aberrant expression of metabotropic glutamate receptor 2 in the vulnerable neurons of Alzheimer’s disease. Acta Neuropathologica, 2004. 107(4): p. 365‐371.4. Caraci, F., et al., Targeting group II metabotropic glutamate (mGlu) receptors for the treatment of psychosis associated with Alzheimer’s disease: selective activation of mGlu2 receptors amplifies beta‐amyloid toxicity in cultured neurons, whereas dual activation of mGlu2 and mGlu3 receptors is neuroprotective. Mol Pharmacol, 2011. 79(3): p. 618‐26.MethodNovel mGluR2 NAMs were synthesized using an iterative library synthetic approach to improve potency, selectivity, and provide an overall sufficient drug metabolism/pharmacokinetics (DMPK) profile. Compound potency (IC50) and selectivity were evaluated in an in vitro GIRK cell‐based T1 flux assay expressing mGluR2 or mGluR3 receptors. Lead compounds were tested in in vitro plasma protein binding assays and rat in vitro and in vivo clearance values were obtained.ResultThe successful discovery and development of a potent and selective mGluR2 NAM as an in vivo tool compound to elucidate the biological effects associated with mGluR2 antagonism was achieved.ConclusionmGluR2 NAMs may be useful therapeutic agents for the potential treatment of AD and other neurodegenerative diseases.

Doxorubicin impairs cognitive function by upregulating AMPAR and NMDAR subunit expression and increasing neuroinflammation, oxidative stress, and apoptosis in the brain

Introduction: The anticancer drug doxorubicin (DOX) is used for various malignancies. However, it also causes cognitive impairment in cancer survivors. In order to determine the mechanisms underlying the acute effects of DOX, we assessed the mRNA and protein expression of glutamate receptors and proteins involved in cognitive function and apoptosis.Methods: Fear-conditioning memory tests were performed in rats after a single intraperitoneal injection of DOX (25 mg/kg) to evaluate short-term memory function. Rat brain samples were collected, and GluA1 mRNA and protein expression; NR2A and NR2B mRNA expression; and COX-2, NF-kB, TNF-α, and MDA, Bax, and caspase-3 levels were assessed via reverse transcription polymerase chain reaction and enzyme-linked immunosorbent assays.Results: We observed a decreased number of entries in Y-maze, decreased exploration time to the novel object in the novel object recognition (NOR), and decreased freezing time in the fear-conditioning memory tests in DOX-treated rats relative to those in control rats, demonstrating cognitive impairment. GluA1, NR2B, and NR2A expression and MDA, NF-κB, Bax, COX-2, TNF-α, and caspase-3 levels in the brain were significantly elevated in DOX-treated rats.Conclusion: DOX induced cognitive impairment in the rats via neuronal toxicity by upregulating AMPAR and NMDAR expression and increasing neuroinflammation, oxidative stress, and apoptosis in the brain.

Comparative transcriptome analysis reveals growth and molecular pathway of body color regulation in turbot (Scophthalmus maximus) exposed to different light spectrum

Fish body color changes play vital roles in adapting to ecological light environment and influencing market value. However, the initial mechanisms governing the changes remain unknown. Here, we scrutinized the impact of light spectrum on turbot (Scophthalmus maximus) body coloration, exposing them to red, blue, and full light spectra from embryo to 90 days post hatch. Transcriptome and quantitative real-time PCR (qRT-PCR) analyses were employed to elucidate underlying biological processes. The results showed that red light induced dimorphism in turbot juvenile skin pigmentation: some exhibited black coloration (Red_Black_Surface, R_B_S), while others displayed lighter skin (Red_White_Bottom, R_W_B), with red light leading to reduced skin lightness (L*) and body weight, particularly in R_B_S group. Transcriptomic and qRT-PCR analyses showcased upregulated gene expressions related to melanin synthesis in R_B_S individuals, notably tyrosinase (tyr), tyrosinase-related protein 1 (tyrp1), and dopachrome tautomerase (dct), alongside solute carrier family 24 member 5 (slc24a5) and oculocutaneous albinism type II (oca2) as pivotal regulators. Nervous system emerged as a critical mediator in spectral environment-driven color regulation. N-methyl d-aspartate (NMDA) glutamate receptor, and calcium signaling pathway emerged as pivotal links intertwining spectral conditions, neural signal transduction, and color regulation. The individual differences in NMDA glutamate receptor expression and subsequent neural excitability seemed responsible for dichromatic body coloration in red light-expose juveniles. This study provides new insights into the comprehending of fish adaptation to environment and methods for fish body color regulation and could potentially help enhance the economic benefit of fish farming industry.

THU495 Glutamate Metabolic Enzymes GLUD1/2 And GPX4 Are Associated with Tumor Size In Black Women With Invasive Lobular Breast Cancer

Abstract Disclosure: T. Young: None. T.C. Abalum: None. N. Hodgins: None. S. Persaud: None. A.I. Fernandez: None. A.O. Olukoya: None. A.M. Rozeboom: None. R.B. Riggins: None. Background and Objective: Invasive Lobular Breast Cancer (ILC) is a special histologic type of breast cancer with unique genetic and biological features. ILC may be less dependent on glucose metabolism than the more common histologic type, invasive ductal breast cancer (IDC), instead relying more on lipid and amino acid metabolism. Our lab has previously published that expression of metabotropic glutamate receptors is increased in more rapidly growing and therapy-resistant cell line models of ILC. We hypothesized that increased expression of glutamate transporters and regulatory enzymes is associated with poor prognostic features. Methods and Analysis: We used multispectral immunohistochemical staining to measure the expression of four functionally related proteins: CD98, GLUD1/2, GPX4, and SLC7A11 in a cohort of 72 women with ILC (23.5% Black, 64.7% White, 11.8% Other). The cohort was in a two-fold redundant tissue microarray (TMA) format comprised of primary tumors collected by the Georgetown University Histopathology and Tissue Shared Resource. SLC7A11 and CD98 form a heterodimer that exports glutamate from, and imports cystine to, the cell. GLUD1/2 are two isoenzymes that convert glutamate into α-ketoglutarate to replenish the TCA cycle, or recycle ammonia to support amino acid synthesis. GPX4 is an enzyme that protects cells from lipid peroxidation-induced death. We compared expression of these proteins with clinical, pathological, and demographic variables (overall survival, hormone receptor expression, tumor size, race, age) using t test/ANOVA, Kaplan-Meier survival analysis, and linear regression. Results: In the 68 evaluable cases, the percentage of ILC tumor cells stained positive for GLUD1/2 and GPX4 was significantly higher than for CD98 or SLC7A11 (P<0.001), so further analyses focused on these. Women with a combination of high (above median) GLUD1/2+ (>49%) and GPX4+ (>54%) expression had a trend toward decreased survival (Hazard Ratio, HR 3.53, P=0.159). GPX4, GLUD1/2, and estrogen receptor (ER) expression were associated with tumor size in the entire cohort (R2 = 0.124, P = 0.041), but this relationship was markedly stronger in Black women (R2 = 0.487, P = 0.040). In univariate analyses, GLUD1/2 (R2 = 0.43, P<0.01) and GPX4 (R2 = 0.27, P<0.05) expression were each associated with tumor size in Black women, but not in the entire cohort. GPX4 expression and tumor size were both significantly higher (P<0.05) in Black women over 60 years of age, compared to those under 60. Conclusion: GLUD1/2 and GPX4 expression may be prognostic in ILC, as our results show that tumor size increases with higher expression of these proteins (especially among Black women). Limitations of this study include small sample size and lack of an independent cohort for validation. Future studies will include analysis of these proteins in a TMA comprised of tissue from women with IDC. Presentation: Thursday, June 15, 2023

Effect of Suanzaoren Decoction on expression of ionotropic glutamate receptors and synaptic plasticity in hippocampus of anxiety rats

This study investigated the effect of Suanzaoren Decoction on the expression of N-methyl-D-aspartate receptors(NMDAR) and α-amino-3-hydroxy-5-methyl-4-isoxazole-propionic acid receptors(AMPAR) in the hippocampus and synaptic plasticity in rats with conditioned fear-induced anxiety. The effect of Suanzaoren Decoction on rat behaviors were evaluated through open field experiment, elevated plus maze experiment, and light/dark box experiment. Enzyme-linked immunosorbent assay(ELISA) was used to measure the levels of glutamate(Glu) and γ-aminobutyric acid(GABA) in the rat hippocampus. Real-time fluorescence quantitative PCR(qRT-PCR) and Western blot were employed to assess the gene and protein expression of ionotropic glutamate receptors in the hippocampal region. Transmission electron microscopy was utilized to observe the changes in the ultrastructure of synaptic neurons in the hippocampal region. Long-term potentiation(LTP) detection technique was employed to record the changes in population spike(PS) amplitude in the hippocampal region of mice in each group. The behavioral results showed that compared with the model group, the Suanzaoren Decoction group effectively increased the number of entries into open arms, time spent in open arms, percentage of time spent in open arms out of total movement time, number of entries into open arms out of total entries into both arms(P<0.01), and significantly increased the time spent in the light box and the number of shuttle crossings(P<0.01). There was an increasing trend in the number of grid crossings, entries into the center grid, and time spent in the center grid, indicating a significant anxiolytic effect. ELISA results showed that compared with the model group, the Suanzaoren Decoction group exhibited significantly reduced levels of Glu, Glu/GABA ratio(P<0.01), and significantly increased levels of GABA(P<0.01) in the rat hippocampus. Furthermore, Suanzaoren Decoction significantly decreased the gene and protein expression of NMDAR(GluN2B and GluN2A) and AMPAR(GluA1 and GluA2) compared with the model group. Transmission electron microscopy results demonstrated improvements in synapses, neuronal cells, and organelles in the hippocampal region of the Suanzaoren Decoction group compared with the model group. LTP detection results showed a significant increase in the PS amplitude changes in the hippocampal region of Suanzaoren Decoction group from 5 to 35 min compared with the model group(P<0.05, P<0.01). In conclusion, Suanzaoren Decoction exhibits significant anxiolytic effects, which may be attributed to the reduction in NMDAR and AMPAR expression levels and the improvement of synaptic plasticity.