Academic literature on the topic 'Glutamatergic post-synaptic pathway'

Electrophysiological and pharmacological techniques were used to study glutamatergic signalling in the parasitic nematode, Ascaris suum. Glutamate or kainate injections into whole worms produced a paralysed quasi-static posture similar to the waveform in behaving worms. The DE2 motorneuron class is a primary target. Several glutamatergic substances produced pronounced conductance increases and depolarization in DE2; domoate and kainate were the most potent agonists tested. Glutamate responses and spontaneous excitatory post-synaptic potentials in DE2 were reversibly blocked in sodium-free saline. DE2 sensitivity to exogenous glutamate was sustained during block of synaptic transmission suggesting that glutamatergic receptors are located on DE2 neurons. The glutamate-induced response was localized to the DE2 dendrite, coincident with the synapses responsible for spontaneous potentials in DE2. Steady-state potentials reached during glutamate superfusion were similar to the reversal potentials for both the spontaneous post-synaptic potentials and glutamate, also suggesting that these potentials may be glutamatergic. Non-N-methyl-D-aspartate receptor antagonists partially blocked spontaneous DE2 excitatory potentials and responses elicited by exogenous glutamate and kainate. This glutamatergic pathway may play a role in nematode locomotory behaviour and account for the paralysing anthelmintic action of excitatory amino acid analogues like kainate and domoate.

Abstract Major depressive disorder (MDD) has been linked to changes in function and activity of the hippocampus, one of the central limbic regions involved in regulation of emotions and mood. The exact cellular and molecular mechanisms underlying hippocampal plasticity in response to stress are yet to be fully characterized. In this study, we examined the genetic profile of micro-dissected subfields of post-mortem hippocampus from subjects diagnosed with MDD and comparison subjects matched for sex, race and age. Gene expression profiles of the dentate gyrus and CA1 were assessed by 48K human HEEBO whole genome microarrays and a subgroup of identified genes was confirmed by real-time polymerase chain reaction (qPCR). Pathway analysis revealed altered expression of several gene families, including cytoskeletal proteins involved in rearrangement of neuronal processes. Based on this and evidence of hippocampal neuronal atrophy in MDD, we focused on the expression of cytoskeletal, synaptic and glutamate receptor genes. Our findings demonstrate significant dysregulation of synaptic function/structure related genes SNAP25, DLG2 (SAP93), and MAP1A, and 2-amino-3-(5-methyl-3-oxo-1,2-oxazol-4-yl)propanoic acid receptor subunit genes GLUR1 and GLUR3. Several of these human target genes were similarly dysregulated in a rat model of chronic unpredictable stress and the effects reversed by antidepressant treatment. Together, these studies provide new evidence that disruption of synaptic and glutamatergic signalling pathways contribute to the pathophysiology underlying MDD and provide interesting targets for novel therapeutic interventions.

To investigate the changes in the expression of specific genes that occur during the acute-to-chronic post-stroke phase, we identified differentially expressed genes (DEGs) between naive cortical tissues and peri-infarct tissues at 1, 4, and 8 weeks after photothrombotic stroke. The profiles of DEGs were subjected to the Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway and gene ontology analyses, followed by string analysis of the protein–protein interactions (PPI) of the products of these genes. We found 3771, 536, and 533 DEGs at 1, 4, and 8 weeks after stroke, respectively. A marked decrease in biological–process categories, such as brain development and memory, and a decrease in neurotransmitter synaptic and signaling pathways were observed 1 week after stroke. The PPI analysis showed the downregulation of Dlg4, Bdnf, Gria1, Rhoa, Mapk8, and glutamatergic receptors. An increase in biological–process categories, including cell population proliferation, cell adhesion, and inflammatory responses, was detected at 4 and 8 weeks post-stroke. The KEGG pathways of complement and coagulation cascades, phagosomes, antigen processing, and antigen presentation were also altered. CD44, C1, Fcgr2b, Spp1, and Cd74 occupied a prominent position in network analyses. These time-dependent changes in gene profiles reveal the unique pathophysiological characteristics of stroke and suggest new therapeutic targets for this disease.

Regulation of excitatory to inhibitory signaling balance is essential to nervous system health and is maintained by numerous enzyme systems that modulate the activity, localization, and abundance of synaptic proteins. SUMOylation is a key post-translational regulator of protein function in diverse cells, including neurons. There, its role in regulating synaptic transmission through pre- and postsynaptic effects has been shown primarily at glutamatergic central nervous system synapses, where the sole SUMO-conjugating enzyme Ubc9 is a critical player. However, whether Ubc9 functions globally at other synapses, including inhibitory synapses, has not been explored. Here, we investigated the role of UBC-9 and the SUMOylation pathway in controlling the balance of excitatory cholinergic and inhibitory GABAergic signaling required for muscle contraction in Caenorhabditis elegans. We found inhibition or overexpression of UBC-9 in neurons modestly increased muscle excitation. Similar and even stronger phenotypes were seen with UBC-9 overexpression specifically in GABAergic neurons, but not in cholinergic neurons. These effects correlated with accumulation of synaptic vesicle-associated proteins at GABAergic presynapses, where UBC-9 and the C. elegans SUMO ortholog SMO-1 localized, and with defects in GABA-dependent behaviors. Experiments involving expression of catalytically inactive UBC-9 [UBC-9(C93S)], as well as co-expression of UBC-9 and SMO-1, suggested wild type UBC-9 overexpressed alone may act via substrate sequestration in the absence of sufficient free SUMO, underscoring the importance of tightly regulated SUMO enzyme function. Similar effects on muscle excitation, GABAergic signaling, and synaptic vesicle localization occurred with overexpression of the SUMO activating enzyme subunit AOS-1. Together, these data support a model in which UBC-9 and the SUMOylation system act at presynaptic sites in inhibitory motor neurons to control synaptic signaling balance in C. elegans. Future studies will be important to define UBC-9 targets at this synapse, as well as mechanisms by which UBC-9 and the SUMO pathway are regulated.

Noonan syndrome (NS) and NS with multiple lentigines (NSML) cognitive dysfunction are linked to SH2 domain-containing protein tyrosine phosphatase-2 (SHP2) gain-of-function (GoF) and loss-of-function (LoF), respectively. In Drosophila disease models, we find both SHP2 mutations from human patients and corkscrew (csw) homolog LoF/GoF elevate glutamatergic transmission. Cell-targeted RNAi and neurotransmitter release analyses reveal a presynaptic requirement. Consistently, all mutants exhibit reduced synaptic depression during high-frequency stimulation. Both LoF and GoF mutants also show impaired synaptic plasticity, including reduced facilitation, augmentation, and post-tetanic potentiation. NS/NSML diseases are characterized by elevated MAPK/ERK signaling, and drugs suppressing this signaling restore normal neurotransmission in mutants. Fragile X syndrome (FXS) is likewise characterized by elevated MAPK/ERK signaling. Fragile X Mental Retardation Protein (FMRP) binds csw mRNA and neuronal Csw protein is elevated in Drosophila fragile X mental retardation 1 (dfmr1) nulls. Moreover, phosphorylated ERK (pERK) is increased in dfmr1 and csw null presynaptic boutons. We find presynaptic pERK activation in response to stimulation is reduced in dfmr1 and csw nulls. Trans-heterozygous csw/+; dfmr1/+ recapitulate elevated presynaptic pERK activation and function, showing FMRP and Csw/SHP2 act within the same signaling pathway. Thus, a FMRP and SHP2 MAPK/ERK regulative mechanism controls basal and activity-dependent neurotransmission strength.

AbstractBackgroundLumateperone is a first-in-class agent in development for schizophrenia that acts synergistically through serotonergic, dopaminergic and glutamatergic systems. Lumateperone is a potent 5-HT2A antagonist, a mesolimbic/mesocortical dopamine phosphoprotein modulator (DPPM) with pre-synaptic partial agonist and post-synaptic antagonist activity at D2, a glutamate GluN2B receptor phosphoprotein modulator with D1-dependent enhancement of both NMDA and AMPA currents via the mTOR protein pathway and an inhibitor of serotonin reuptake.MethodsLumateperone was evaluated in 3 controlled clinical trials to evaluate efficacy in patients with acute schizophrenia. The primary endpoint was change from baseline on the PANSS total score compared to placebo. In Study ‘005, 335 patients were randomized to receive ITI-007 60mg or 120mg , risperidone 4mg (active control) or placebo QAM for 4weeks. In Study ‘301, 450 patients were randomized to receive ITI-007 60mg or 40mg , or placebo QAM for 4weeks. In Study ‘302, 696 patients were randomized to receive ITI-007 60mg or 20mg , risperidone 4mg (active control) or placebo QAM for 6weeks. Also, an open-label safety switching study was conducted in which 302 patients with stable schizophrenia were switched from standard-of-care (SOC) antipsychotics and treated for 6weeks with lumateperone QPM and then switched back to SOC.ResultsIn Studies ‘005 and ‘301, lumateperone (60mg ITI-007) met the primary endpoint with statistically significant superior efficacy over placebo at Day 28. In Study ‘302, neither dose of lumateperone separated from placebo on the primary endpoint; a high placebo response was observed in this study. Across all 3 efficacy trials, lumateperone improved symptoms of schizophrenia with the same trajectory and same magnitude of improvement from baseline to endpoint on the PANSS total score.Lumateperone was well-tolerated with a favorable safety profile in all studies. In the two studies with risperidone included as an active control, lumateperone was statistically significantly better than risperidone on key safety and tolerability measures. In the open-label safety switching study statistically significant improvements from SOC were observed in body weight, cardiometabolic and endocrine parameters worsened again when switched back to SOC medication. In this study, symptoms of schizophrenia generally remained stable or improved. Greater improvements were observed in subgroups of patients with elevated symptomatology (comorbid symptoms of depression and those with prominent negative symptoms).DiscussionLumateperone represents a novel approach to the treatment of schizophrenia with a favorable safety profile in clinical trials. The lack of cardiometabolic and motor safety issues presents a safety profile differentiated from standard-of-care antipsychotic therapy.Funding Acknowledgements: Intra-Cellular Therapies, Inc.

Abstract Background Evidence from clinical and preclinical studies has led to the hypothesis that impaired glutamatergic transmission and NMDA receptor hypofunction play an important role in cognitive impairment associated with schizophrenia (CIAS). Second messenger pathways depending on cAMP and/or cGMP are key regulators of glutamatergic transmission and NMDA receptor related pathways. Therefore, the specific cyclic nucleotide phosphodiesterases (PDEs) PDE2 and PDE9, expressed in cognition relevant brain regions such as cortex and hippocampus, are putative targets for cognition enhancement in neuropsychiatric disorders (Dorner-Ciossek et al., 2017; Zhang et al., 2017). In fact, it has previously been shown that either PDE2 or PDE9 inhibition increases synaptic plasticity, as determined by hippocampal long-term potentiation (LTP), and improves memory performance in animal cognition tasks. However, the exact sub-cellular localization of PDE2 and PDE9 enzymes in neurons is not fully established. Thus, in the present study, co-localization studies of PDE2 and PDE9 with pre- and post-synaptic markers were performed by double immunofluorescence staining. Moreover, the PDE2 inhibitor PF-05180999 (Helal et al., 2018) was characterized regarding enhancement of hippocampal LTP and further investigated in combination with the PDE9 inhibitor Bay 73–6691 (Wunder et al., 2005) for potential synergistic effects on LTP. Methods Brains of adult rats were fixed with formalin and sliced for double immunofluorescence staining of PDE2 or PDE9 enzymes with pre-/post-synaptic markers. Analysis of staining was performed by confocal microscopy. Effects of the PDE2 inhibitor PF-05180999 alone and in combination with the PDE9 inhibitor Bay 73–6691 on synaptic plasticity were evaluated in rat hippocampal slices by using a protein-synthesis independent early LTP paradigm. Results Double immunofluorescence analysis revealed co-localization of PDE2 predominantly with pre-synaptic, but not post-synaptic, markers and mainly in glutamatergic neurons. In contrast, PDE9 showed co-localization with post-synaptic markers. Inhibition of PDE2 by PF-05180999 led to a concentration-dependent enhancement of early LTP. Combination of PF-05180999 with a subthreshold concentration of the PDE9 inhibitor Bay 73–6691 caused a transformation from early LTP into protein-synthesis dependent late LTP. Discussion Immunofluorescence staining suggests that PDE2 is localized pre-synaptically in glutamatergic neurons. This might indicate an involvement of PDE2 in neurotransmitter release via regulating cGMP/cAMP levels at pre-synaptic terminals, whereas PDE9 is located post-synaptically presumably involved in the NMDA receptor signaling cascade via regulation of cGMP. Corroborating previous findings, PDE2 inhibition improves synaptic plasticity as shown by enhanced LTP. Moreover, for the first time, we could show that the combination of a PDE2 with a PDE9 inhibitor acts synergistically on improvement of synaptic plasticity as demonstrated by the shift from early into late LTP, which is considered to be a crucial mechanism for memory formation. References

Although acetylcholine is the major neurotransmitter operating at the skeletal neuromuscular junction of many invertebrates and of vertebrates, glutamate participates in modulating cholinergic transmission and plastic changes in the last. Presynaptic terminals of neuromuscular junctions contain and release glutamate that contribute to the regulation of synaptic neurotransmission through its interaction with pre- and post-synaptic receptors activating downstream signaling pathways that tune synaptic efficacy and plasticity. During vertebrate development, the chemical nature of the neurotransmitter at the vertebrate neuromuscular junction can be experimentally shifted from acetylcholine to other mediators (including glutamate) through the modulation of calcium dynamics in motoneurons and, when the neurotransmitter changes, the muscle fiber expresses and assembles new receptors to match the nature of the new mediator. Finally, in adult rodents, by diverting descending spinal glutamatergic axons to a denervated muscle, a functional reinnervation can be achieved with the formation of new neuromuscular junctions that use glutamate as neurotransmitter and express ionotropic glutamate receptors and other markers of central glutamatergic synapses. Here, we summarize the past and recent experimental evidences in support of a role of glutamate as a mediator at the synapse between the motor nerve ending and the skeletal muscle fiber, focusing on the molecules and signaling pathways that are present and activated by glutamate at the vertebrate neuromuscular junction.

Glioblastoma (GB) is the most aggressive, lethal and frequent primary brain tumor. It originates from glial cells and is characterized by rapid expansion through infiltration. GB cells interact with the microenvironment and healthy surrounding tissues, mostly neurons and vessels. GB cells project tumor microtubes (TMs) contact with neurons, and exchange signaling molecules related to Wingless/WNT, JNK, Insulin or Neuroligin-3 pathways. This cell to cell communication promotes GB expansion and neurodegeneration. Moreover, healthy neurons form glutamatergic functional synapses with GB cells which facilitate GB expansion and premature death in mouse GB xerograph models. Targeting signaling and synaptic components of GB progression may become a suitable strategy against glioblastoma. In a Drosophila GB model, we have determined the post-synaptic nature of GB cells with respect to neurons, and the contribution of post-synaptic genes expressed in GB cells to tumor progression. In addition, we document the presence of intratumoral synapses between GB cells, and the functional contribution of pre-synaptic genes to GB calcium dependent activity and expansion. Finally, we explore the relevance of synaptic genes in GB cells to the lifespan reduction caused by GB advance. Our results indicate that both presynaptic and postsynaptic proteins play a role in GB progression and lethality.

Schizophrenia is a chronic debilitating mental illness. In many aspects, the neuropathology of schizophrenia is closely associated with neuroinflammation, especially microglial activation. Microglial hyperactivity, which is characterized by the predominant release of proinflammatory cytokines serves as the basis of the neuroinflammation hypothesis in schizophrenia. The enhanced inflammatory induce neuronal susceptibility to oxidative stress and trigger, glutamatergic synaptic dysregulation, especially in the mesolimbic and mesocortical pathways. Many in vitro studies, in vivo animal evidence, post-mortem examinations, neuroimaging evaluations with Positron Emission Tomography (PET), anti-inflammatory and antipsychotic use converge upon the central role of microglial activation and proinflammatory cytokines as common of features schizophrenia.

Thyroid hormones (TH), namely thyroxine (T4) and 3,5,3’-triiodothyronine (T3), are crucial regulators of multiple growth processes and control systems of energy metabolism. T4 and T3 undergo a complex metabolism in vivo, by several enzymes encompassing deiodinases, amine transferases, amine oxidases, decarboxylases and several classes of conjugating enzymes, particularly sulfotransferases and UDP-glucuronosyltransferases. T4 or T3 metabolites can produce significant functional effects when administered via interaction either with Thyroid Hormone Receptor (TR), or with other receptors. They are considered as chemical messengers further enriching TH signaling, and have become known as “novel thyroid hormones” or “active thyroid hormones metabolites”. These novel hormones include: T2; Thyronamines (TAMs), mostly 3-iodothyronamine (T1AM) and non-iodinated thyronamine (T0AM); thyroacetic acids, mostly 3,5,3’,5’-thyroacetic acid (TA4), 3,5,3’-thyroacetic acid (TA3), and 3-thyroacetic acid (TA1). Recently, it emerged that 3-iodothyronamine (T1AM), a derivative of decarboxylation and deiodination of thyroid hormones, has pro-learning and anti-amnestic effects, modulates pain threshold, sleep pattern and food intake. It also counteracts beta-amyloid toxicity in mice. Glutamatergic neurotransmission, the major excitatory system in the brain, plays a key role in regulating neuroplasticity, learning and memory, and it is often compromised in neurological disorders. T1AM reduced availability might results in some disorders associated with thyroid hormones. T1AM binds to the trace amine-associated receptor 1 (TAAR1) a G-protein coupled receptor with a putative role in neurotransmission. In the present work, firstly we characterized the gene expression profile of two different brain cell lines and then we evaluated the effects of T1AM on the expression of proteins involved in the glutamatergic postsynaptic pathway. A hybrid line of cancer cells of mouse neuroblastoma and rat glioma (NG 108-15) and a human glioblastoma cell line (U-87 MG) were used. We first characterized the in vitro model by analyzing gene expression of several proteins involved in the glutamatergic postsynaptic cascade by real time PCR (RT-PCR), and cellular uptake and metabolism of T1AM by HPLC coupled to mass spectrometry (HPLC MS-MS). The cell lines were then treated with T1AM, ranging from 0.1 to 10 μM, alone or in combination with 10 µM resveratrol (RSV) and/or 10 µM amyloid β peptide (25-35). Cell viability, glucose consumption, protein expression, cAMP production and calcium concentration in cell lysates were assessed. Our results indicated that both cell lines expressed receptors implicated in glutamatergic pathway, namely AMPA, NMDA and EphB2, but only U-87 MG cells expressed TAAR1 and they took up T1AM which was catabolized to TA1 and might be used as biochemical model to study its post synaptic signaling cascade. At micromolar concentration T1AM had a slightly but significant cytotoxic effect, that is completely blunted if incubated with RSV and it was able to induce different post-translational modification in neuronal cell lines. T1AM reduced glucose consumption and decreased intracellular calcium concentration in NG 108-15 cell line, while increased cAMP concentration, albeit at different doses. At pharmacological concentrations, the major effect highlighted in both cell lines was an increase in the phosphorylation of proteins involved in the glutamatergic postsynaptic signaling. In the NG 108-15 cells an increase in phosphorylation of ERK extracellular signal-regulated kinases (ERKs) (pERK/ total ERK) and CaMKII Ca-calmodulin-dependent protein kinase (CaMK) II (pCaMKII/total CaMKII). In U-87 MG cells, T1AM induced the phosphorylation of the transcriptional factor cAMP response element-binding protein (CREB) and increase the expression of cFOS. Expression or post-translational modifications of other proteins were not affected. We then extend investigation on the effects of 3-iodothyroacetic acid TA1, a catabolite of T1AM and of thyroid hormone, on brain cell lines focusing on the glutamatergic postsynaptic pathway that we explored by infusion with T1AM, assuming that TA1 may either strengthen T1AM effects or exert parallel actions, especially in brain tissue. First, we assessed uptake and metabolism of TA1. Cell lines were treated with TA1 for 24h, at concentration ranging from 0.1 to 10 μM. Uptake, cell viability, cAMP production and protein expression were assessed. TA1 was taken up by cells, even though only a slight reduction in medium concentration was recorded upon 24h of incubation. Cell viability was significantly increased by TA1 10 µM in U-87 MG cell line, while NG 108-15 cells were unaffected. Western blot analysis indicated that, upon infusion of pharmacological doses of TA1, neither the expression of Sirtuin 1, (p=NS) nor the post-translational modifications of ERK (pERK/total ERK, p=NS) were affected in U-87 MG. Instead TA1 induced the phosphorylation of the transcriptional factor cAMP response element-binding protein (CREB) (pCREB/total). In NG 108-15 cell line, preliminary analysis on protein expression and post-translational modification after TA1 infusion, indicated that no modifications of ERK (pERK/total ERK) were occurred. In conclusion our results indicated that NG 108-15 and U-87 MG cells express receptors implicated in the glutamatergic system and, at pharmacological concentrations, T1AM can affect glutamatergic signaling. Therefore, our preliminary results suggest that, in our experimental models, TA1 does not seem to mimic T1AM effects.