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Molecular and Cellular Neurosciences Mar 2024The EphB receptor tyrosine kinase family participates in intricate signaling pathways that orchestrate neural networks, guide neuronal axon development, and modulate...
BACKGROUND
The EphB receptor tyrosine kinase family participates in intricate signaling pathways that orchestrate neural networks, guide neuronal axon development, and modulate synaptic plasticity through interactions with surface-bound ephrinB ligands. Additionally, Kalirin, a Rho guanine nucleotide exchange factor, is notably expressed in the postsynaptic membrane of excitatory neurons and plays a role in synaptic morphogenesis. This study postulates that Kalirin may act as a downstream effector of EphB3 in epilepsy. This investigation focuses on understanding the link between EphB3 and epilepsy.
MATERIALS AND METHODS
Chronic seizure models using LiCl-pilocarpine (LiCl/Pilo) and pentylenetetrazol were developed in rats. Neuronal excitability was gauged through whole-cell patch clamp recordings on rat hippocampal slices. Real-time PCR determined Kalirin's mRNA expression, and Western blotting was employed to quantify EphB3 and Kalirin protein levels. Moreover, dendritic spine density in epileptic rats was evaluated using Golgi staining.
RESULTS
Modulation of EphB3 functionality influenced acute seizure severity, latency duration, and frequency of spontaneous recurrent seizures. Golgi staining disclosed an EphB3-driven alteration in dendritic spine density within the hippocampus of epileptic rats, underscoring its pivotal role in the reconfiguration of hippocampal neural circuits. Furthermore, our data propose Kalirin as a prospective downstream mediator of the EphB3 receptor.
CONCLUSIONS
Our findings elucidate that EphB3 impacts the action potential dynamics in isolated rat hippocampal slices and alters dendritic spine density in the inner molecular layer of epileptic rat hippocampi, likely through Kalirin-mediated pathways. This hints at EphB3's significant role in shaping excitatory circuit loops and recurrent seizure activity via Kalirin.
Topics: Rats; Animals; Rats, Sprague-Dawley; Prospective Studies; Neurons; Epilepsy; Seizures
PubMed: 38143048
DOI: 10.1016/j.mcn.2023.103915 -
Nature Communications Dec 2023How aging affects cells of the human brain active milieu remains largely unknown. Here, we analyze astrocytes and neurons in the neocortical tissue of younger (22-50...
How aging affects cells of the human brain active milieu remains largely unknown. Here, we analyze astrocytes and neurons in the neocortical tissue of younger (22-50 years) and older (51-72 years) adults. Aging decreases the amount of reduced mitochondrial cytochromes in astrocytes but not neurons. The protein-to-lipid ratio decreases in astrocytes and increases in neurons. Aged astrocytes show morphological atrophy quantified by the decreased length of branches, decreased volume fraction of leaflets, and shrinkage of the anatomical domain. Atrophy correlates with the loss of gap junction coupling between astrocytes and increased input resistance. Aging is accompanied by the upregulation of glial fibrillary acidic protein (GFAP) and downregulation of membrane-cytoskeleton linker ezrin associated with leaflets. No significant changes in neuronal excitability or spontaneous inhibitory postsynaptic signaling is observed. Thus, brain aging is associated with the impaired morphological presence and mitochondrial malfunction of cortical astrocytes, but not neurons.
Topics: Humans; Aged; Astrocytes; Cerebral Cortex; Neurons; Aging; Glial Fibrillary Acidic Protein; Atrophy
PubMed: 38104196
DOI: 10.1038/s41467-023-44192-0 -
Cell Reports Dec 2023Catecholamine signaling is thought to modulate cognition in an inverted-U relationship, but the mechanisms are unclear. We measured norepinephrine and dopamine release,...
Catecholamine signaling is thought to modulate cognition in an inverted-U relationship, but the mechanisms are unclear. We measured norepinephrine and dopamine release, postsynaptic calcium responses, and interactions between tonic and phasic firing modes under various stimuli and conditions. High tonic activity in vivo depleted catecholamine stores, desensitized postsynaptic responses, and decreased phasic transmission. Together, these findings provide a more complete understanding of the inverted-U relationship, offering insights into psychiatric disorders and neurodegenerative diseases with impaired catecholamine signaling.
Topics: Humans; Catecholamines; Locus Coeruleus; Norepinephrine; Dopamine; Signal Transduction
PubMed: 38100349
DOI: 10.1016/j.celrep.2023.113566 -
Biochemical Society Transactions Dec 2023The PDZ and LIM domain (PDLIM) proteins are associated with the actin cytoskeleton and have conserved in roles in metazoan actin organisation and function. They... (Review)
Review
The PDZ and LIM domain (PDLIM) proteins are associated with the actin cytoskeleton and have conserved in roles in metazoan actin organisation and function. They primarily function as scaffolds linking various proteins to actin and its binding partner α-actinin via two conserved domains; an N-terminal postsynaptic density 95, discs large and zonula occludens-1 (PDZ) domain, and either single or multiple C-terminal LIN-11, Isl-1 and MEC-3 (LIM) domains in the actinin-associated LIM protein (ALP)- and Enigma-related proteins, respectively. While their role in actin organisation, such as in stress fibres or in the Z-disc of muscle fibres is well known, emerging evidence also suggests a role in actin-dependent membrane trafficking in the endosomal system. This is mediated by a recently identified interaction with the sorting nexin 17 (SNX17) protein, an adaptor for the trafficking complex Commander which is itself intimately linked to actin-directed formation of endosomal recycling domains. In this review we focus on the currently understood structural basis for PDLIM function. The PDZ domains mediate direct binding to distinct classes of PDZ-binding motifs (PDZbms), including α-actinin and other actin-associated proteins, and a highly specific interaction with the type III PDZbm such as the one found in the C-terminus of SNX17. The structures of the LIM domains are less well characterised and how they engage with their ligands is completely unknown. Despite the lack of experimental structural data, we find that recently developed machine learning-based structure prediction methods provide insights into their potential interactions and provide a template for further studies of their molecular functions.
Topics: Animals; Actins; Actinin; PDZ Domains; Actin Cytoskeleton; LIM Domain Proteins; Protein Binding
PubMed: 38095060
DOI: 10.1042/BST20220804 -
Molecular and Cellular Neurosciences Mar 2024The exocyst protein complex is important for targeted vesicle fusion in a variety of cell types, however, its function in neurons is still not entirely known. We found...
The exocyst protein complex is important for targeted vesicle fusion in a variety of cell types, however, its function in neurons is still not entirely known. We found that presynaptic knockdown (KD) of the exocyst component sec15 by transgenic RNAi expression caused a number of unexpected morphological and physiological defects in the synapse. These include the development of active zones (AZ) devoid of essential presynaptic proteins, an increase in the branching of the presynaptic arbor, the appearance of satellite boutons, and a decrease in the amplitude of stimulated postsynaptic currents as well as a decrease in the frequency of spontaneous synaptic vesicle release. We also found the release of extracellular vesicles from the presynaptic neuron was greatly diminished in the Sec15 KDs. These effects were mimicked by presynaptic knockdown of Rab11, a protein known to interact with the exocyst. sec15 RNAi expression caused an increase in phosphorylated Mothers against decapentaplegic (pMad) in the presynaptic terminal, an indication of enhanced bone morphogenic protein (BMP) signaling. Some morphological phenotypes caused by Sec15 knockdown were reduced by attenuation of BMP signaling through knockdown of wishful thinking (Wit), while other phenotypes were unaffected. Individual knockdown of multiple proteins of the exocyst complex also displayed a morphological phenotype similar to Sec15 KD. We conclude that Sec15, functioning as part of the exocyst complex, is critically important for proper formation and function of neuronal synapses. We propose a model in which Sec15 is involved in the trafficking of vesicles from the recycling endosome to the cell membrane as well as possibly trafficking extracellular vesicles for presynaptic release and these processes are necessary for the correct structure and function of the synapse.
Topics: Animals; Drosophila; Drosophila Proteins; Animals, Genetically Modified; Synapses; Neurons; Vesicular Transport Proteins
PubMed: 38086519
DOI: 10.1016/j.mcn.2023.103914 -
Neurobiology of Stress Jan 2024Glucocorticoids are primary stress hormones that exert neuronal effects via both genomic and non-genomic signaling pathways. However, their rapid non-genomic effects and...
Glucocorticoids are primary stress hormones that exert neuronal effects via both genomic and non-genomic signaling pathways. However, their rapid non-genomic effects and underlying mechanisms on neural activities remain elusive. In the present study, we investigated the rapid non-genomic effect of glucocorticoids on Kv2.2 channels in cultured HEK293 cells and acute brain slices including cortical pyramidal neurons and calyx-type synapses in the brain stem. We found that cortisol, the endogenous glucocorticoids, rapidly increased Kv2.2 currents by increasing the single-channel open probability in Kv2.2-expressing HEK293 cells through activation of the membrane-associated glucocorticoid receptor. Bovine serum albumin-conjugated dexamethasone, a membrane-impermeable agonist of the glucocorticoid receptor, could mimic the effect of cortisol on Kv2.2 channels. The cortisol-increased Kv2.2 currents were induced by activation of the extracellular signal-regulated protein kinase (ERK) 1/2 kinase, which could be inhibited by U0126, an antagonist of the ERK signaling pathway. In layer 2 cortical pyramidal neurons and the calyx of Held synapses, cortisol suppressed the action potential firing frequency during depolarization and reduced the successful rate upon high-frequency stimulation by activating Kv2.2 channels. We further examined the postsynaptic responses and found that cortisol did not affect the mEPSC and evoked EPSC, but increased the activity-dependent synaptic depression induced by a high-frequency stimulus train. In conclusion, glucocorticoids can rapidly activate Kv2.2 channels through membrane-associated glucocorticoid receptors via the ERK1/2 signaling pathway, suppress presynaptic action potential firing, and inhibit synaptic transmission and plasticity. This may be a universal mechanism of the glucocorticoid-induced non-genomic effects in the central nervous system.
PubMed: 38075025
DOI: 10.1016/j.ynstr.2023.100593 -
Cell Death Discovery Dec 2023Synaptotoxic Aβ oligomers are thought to play a major role in the early pathology of Alzheimer´s disease (AD). However, the molecular mechanisms involved in...
Synaptotoxic Aβ oligomers are thought to play a major role in the early pathology of Alzheimer´s disease (AD). However, the molecular mechanisms involved in Aβ-induced synaptic dysfunction and synapse damage remain largely unclear. Previously, Aβ synaptotoxicity has been reported to be enhanced by increased levels of a C-terminal fragment of the synaptic adhesion molecule N-cadherin that is generated by proteolytic shedding of the extracellular domains [1]. To address the molecular mechanisms involved in this process, we have now studied the functional synaptic changes induced by C-terminal fragments (CTF1) of synaptic adhesion proteins. We used synaptophysin-pHluorin (SypHy) fluorescence imaging to monitor synaptic vesicle exo- and endocytosis in cultures of mouse cortical neurons. We increased the levels of C-terminal fragments of synaptic adhesion proteins by pharmacologically inhibiting γ-secretase, which further degrades CTF1 fragments. We found that this intervention caused a delay in synaptic vesicle endocytosis. A similar effect was induced by overexpression of N-cadherin CTF1, but not by overexpression of Neurexin3β CTF1. Based on these observations, we further studied whether directly modulating synaptic vesicle endocytosis enhances Aβ synaptotoxicity. We pharmacologically induced a delayed synaptic vesicle endocytosis by a low concentration of the endocytosis inhibitor dynasore. This treatment enhanced synaptoxicity of Aβ oligomers as indicated by a reduced frequency of miniature postsynaptic currents. In conclusion, we propose that delayed endocytosis results in prolonged exposure of synaptic vesicle membranes to the extracellular space, thus enabling enhanced vesicle membrane binding of Aβ oligomers. This might in turn promote the endocytic uptake of toxic Aβ oligomers and might thus play an important role in intracellular Aβ-mediated synaptotoxicity in AD.
PubMed: 38062019
DOI: 10.1038/s41420-023-01739-w -
Neuropsychiatric Disease and Treatment 2023The terminal complement C5 inhibitor ravulizumab was engineered from the humanized monoclonal antibody eculizumab to have an extended half-life and duration of action.... (Review)
Review
The terminal complement C5 inhibitor ravulizumab was engineered from the humanized monoclonal antibody eculizumab to have an extended half-life and duration of action. It binds to human terminal complement protein C5, inhibiting its cleavage into C5a and C5b, thus preventing the cascade of events that lead to architectural destruction of the postsynaptic neuromuscular junction membrane by the membrane attack complex, and consequent muscle weakness in patients with anti-acetylcholine receptor (AChR) antibody-positive generalized myasthenia gravis (gMG). The 26-week randomized, placebo-controlled period (RCP) of the phase 3 CHAMPION MG study demonstrated the rapid efficacy of ravulizumab in reducing MG symptoms. Weight-based dosing of ravulizumab every 8 weeks provided sustained efficacy, in terms of patient-reported (Myasthenia Gravis-Activities of Daily Living) and clinician-reported (Quantitative Myasthenia Gravis) endpoints in patients with anti-AChR antibody-positive gMG. Pharmacokinetic and pharmacodynamic analyses showed therapeutic serum ravulizumab concentrations (>175 µg/mL) were achieved immediately after the first dose and were maintained throughout 26 weeks, irrespective of patient body weight; inhibition of serum free C5 was immediate, complete (<0.5 μg/mL), and sustained in all patients. Interim results from the open-label extension (OLE) showed that after 60 weeks, efficacy was maintained in patients continuing on ravulizumab. Rapid and sustained improvements in efficacy, similar to those seen in patients initiating ravulizumab in the RCP, were observed after initiation of ravulizumab treatment in patients who switched from placebo in the RCP to ravulizumab in the OLE. The findings from the RCP and OLE support ravulizumab's favorable safety profile. In conclusion, ravulizumab has a simple weight-based administration and long dosing interval. Its targeted mechanism of action without generalized immunosuppression is reflected in its rapid onset of symptom improvement, sustained efficacy and good safety profile in the treatment of patients with anti-AChR antibody-positive gMG.
PubMed: 38059203
DOI: 10.2147/NDT.S374694 -
BioRxiv : the Preprint Server For... Nov 2023Rapid delivery of glutamate receptors to the postsynaptic membrane via vesicle fusion is a central component of synaptic plasticity. However, it is unknown how this...
Rapid delivery of glutamate receptors to the postsynaptic membrane via vesicle fusion is a central component of synaptic plasticity. However, it is unknown how this process supports specific neural computations during behavior. To bridge this gap, we combined conditional genetic deletion of a component of the postsynaptic membrane fusion machinery, Syntaxin3 (Stx3), in hippocampal CA1 neurons of mice with population calcium imaging. This approach revealed that Stx3 is necessary for forming the neural dynamics that support novelty processing, spatial reward memory and offline memory consolidation. In contrast, CA1 Stx3 was dispensable for maintaining aspects of the neural code that exist presynaptic to CA1 such as representations of context and space. Thus, manipulating postsynaptic membrane fusion identified computations that specifically require synaptic restructuring via membrane trafficking in CA1 and distinguished them from neural representation that could be inherited from upstream brain regions or learned through other mechanisms.
PubMed: 38045362
DOI: 10.1101/2023.11.20.567978 -
Nature Communications Dec 2023Ketamine produces rapid antidepressant effects at sub-anesthetic dosage through early and sustained activation of α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid...
Ketamine produces rapid antidepressant effects at sub-anesthetic dosage through early and sustained activation of α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptors (AMPARs), however, the exact molecular mechanism still remains unclear. Transmembrane AMPAR regulatory protein-γ8 (TARP-γ8) is identified as one of AMPAR auxiliary subunits, which controls assemblies, surface trafficking and gating of AMPARs. Here, we show that ketamine rescues both depressive-like behaviors and the decreased AMPARs-mediated neurotransmission by recruitment of TARP-γ8 at the postsynaptic sites in the ventral hippocampus of stressed male mice. Furthermore, the rapid antidepressant effects of ketamine are abolished by selective blockade of TARP-γ8-containing AMPAR or uncoupling of TARP-γ8 from PSD-95. Overexpression of TARP-γ8 reverses chronic stress-induced depressive-like behaviors and attenuation of AMPARs-mediated neurotransmission. Conversely, knockdown of TARP-γ8 in excitatory neurons prevents the rapid antidepressant effects of ketamine.
Topics: Mice; Animals; Male; Ketamine; Receptors, AMPA; Neurons; Membrane Proteins; Antidepressive Agents
PubMed: 38042894
DOI: 10.1038/s41467-023-42780-8