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Archives of Biochemistry and Biophysics Nov 2023Membrane cholesterol oxidation is a hallmark of redox and metabolic imbalance, and it may accompany neurodegenerative disorders. Using microelectrode recordings of...
Membrane cholesterol oxidation is a hallmark of redox and metabolic imbalance, and it may accompany neurodegenerative disorders. Using microelectrode recordings of postsynaptic responses as well as fluorescent dyes for monitoring synaptic vesicle cycling and membrane properties, the action of enzymatic cholesterol oxidation on neuromuscular transmission was studied in the mice diaphragms. Cholesterol oxidase (ChO) at low concentration disturbed lipid-ordering specifically in the synaptic membranes, but it did not change markedly spontaneous exocytosis and evoked release in response to single stimuli. At low external Ca conditions, analysis of single exocytotic events revealed a decrease in minimal synaptic delay and the probability of exocytosis upon plasmalemmal cholesterol oxidation. At moderate- and high-frequency activity, ChO treatment enhanced both neurotransmitter and FM-dye release. Furthermore, it precluded a change in exocytotic mode from full-fusion to kiss-and-run during high-frequency stimulation. Accumulation of extracellular acetylcholine (without stimulation) dependent on vesamicol-sensitive transporters was suppressed by ChO. The effects of plasmalemmal cholesterol oxidation on both neurotransmitter/dye release at intense activity and external acetylcholine levels were reversed when synaptic vesicle membranes were also exposed to ChO (i.e., the enzyme treatment was combined with induction of exo-endocytotic cycling). Thus, we suggest that plasmalemmal cholesterol oxidation affects exocytotic machinery functioning, enhances synaptic vesicle recruitment to the exocytosis and decreases extracellular neurotransmitter levels at rest, whereas ChO acting on synaptic vesicle membranes suppresses the participation of the vesicles in the subsequent exocytosis and increases the neurotransmitter leakage. The mechanisms underlying ChO action can be related to the lipid raft disruption.
Topics: Mice; Animals; Cholesterol Oxidase; Acetylcholine; Synaptic Transmission; Neuromuscular Junction; Cholesterol; Neurotransmitter Agents
PubMed: 37955112
DOI: 10.1016/j.abb.2023.109803 -
Trends in Neurosciences Mar 2020Synaptic transmission and plasticity are shaped by the dynamic reorganization of signaling molecules within pre- and postsynaptic compartments. The nanoscale... (Review)
Review
Synaptic transmission and plasticity are shaped by the dynamic reorganization of signaling molecules within pre- and postsynaptic compartments. The nanoscale organization of key effector molecules has been revealed by single-particle trajectory (SPT) methods. Interestingly, this nanoscale organization is highly heterogeneous. For example, presynaptic voltage-gated calcium channels (VGCCs) and postsynaptic ligand-gated ion channels such as AMPA receptors (AMPARs) are organized into so-called nanodomains where individual molecules are only transiently trapped. These pre- and postsynaptic nanodomains are characterized by a high density of molecules but differ in their molecular organization and stability within the synaptic membrane. We review the main properties of these nanodomains, as well as the methods developed to extract parameters from SPT experiments. We discuss how such molecular dynamics influences synaptic transmission. The nanoscale organization of active synapses opens new insights into the dynamics and turnover of molecules as well as casting light on their contributions to signal transfer between individual neurons.
Topics: Humans; Neuronal Plasticity; Neurons; Receptors, AMPA; Synapses; Synaptic Transmission
PubMed: 32101710
DOI: 10.1016/j.tins.2020.01.005 -
Frontiers in Computational Neuroscience 2022The neuroscientific field benefits from the conjoint evolution of experimental and computational techniques, allowing for the reconstruction and simulation of complex... (Review)
Review
The neuroscientific field benefits from the conjoint evolution of experimental and computational techniques, allowing for the reconstruction and simulation of complex models of neurons and synapses. Chemical synapses are characterized by presynaptic vesicle cycling, neurotransmitter diffusion, and postsynaptic receptor activation, which eventually lead to postsynaptic currents and subsequent membrane potential changes. These mechanisms have been accurately modeled for different synapses and receptor types (AMPA, NMDA, and GABA) of the cerebellar cortical network, allowing simulation of their impact on computation. Of special relevance is short-term synaptic plasticity, which generates spatiotemporal filtering in local microcircuits and controls burst transmission and information flow through the network. Here, we present how data-driven computational models recapitulate the properties of neurotransmission at cerebellar synapses. The simulation of microcircuit models is starting to reveal how diverse synaptic mechanisms shape the spatiotemporal profiles of circuit activity and computation.
PubMed: 36387305
DOI: 10.3389/fncom.2022.1006989 -
Molecular Neurobiology Sep 2022The ER (endoplasmic reticulum) is a Ca reservoir and the unique protein-synthesizing machinery which is distributed throughout the neuron and composed of multiple... (Review)
Review
The ER (endoplasmic reticulum) is a Ca reservoir and the unique protein-synthesizing machinery which is distributed throughout the neuron and composed of multiple different structural domains. One such domain is called EMC (endoplasmic reticulum membrane protein complex), pleiotropic nature in cellular functions. The ER/EMC position inside the neurons unmasks its contribution to synaptic plasticity via regulating various cellular processes from protein synthesis to Ca signaling. Since presynaptic Ca channels and postsynaptic ionotropic receptors are organized into the nanodomains, thus ER can be a crucial player in establishing TMNCs (transsynaptic molecular nanocolumns) to shape efficient neural communications. This review hypothesized that ER is not only involved in stress-mediated neurodegeneration but also axon regrowth, remyelination, neurotransmitter switching, information processing, and regulation of pre- and post-synaptic functions. Thus ER might not only be a protein-synthesizing and quality control machinery but also orchestrates plasticity of plasticity (metaplasticity) within the neuron to execute higher-order brain functions and neural repair.
Topics: Endoplasmic Reticulum; Neuronal Plasticity; Neurons; Proteostasis; Signal Transduction
PubMed: 35739409
DOI: 10.1007/s12035-022-02916-1 -
Current Opinion in Neurobiology Aug 2022Neuronal morphogenesis is guided by outside-in signals and inside-out mechanisms, which require spatiotemporal precision. How the intracellular mechanisms of neuronal... (Review)
Review
Neuronal morphogenesis is guided by outside-in signals and inside-out mechanisms, which require spatiotemporal precision. How the intracellular mechanisms of neuronal morphogenesis are spatiotemporally controlled is not well understood. Septins comprise a unique GTPase module, which consists of complexes with differential localizations and functions. Septins demarcate distinct membrane domains in neural precursor cells, orienting the axis of cell division and the sites of neurite formation. By controlling the localization of membrane and cytoskeletal proteins, septins promote axon-dendrite formation and polarity. Furthermore, septins modulate vesicle exocytosis at pre-synaptic terminals, and stabilize dendritic spines and post-synaptic densities in a phospho-regulatable manner. We posit that neuronal septins are topologically and functionally specialized for the spatiotemporal regulation of neuronal morphogenesis and plasticity.
Topics: Morphogenesis; Neural Stem Cells; Neurogenesis; Neurons; Septins
PubMed: 35609489
DOI: 10.1016/j.conb.2022.102557 -
Frontiers in Molecular Neuroscience 2021Regulated delivery of AMPA receptors (AMPARs) to the postsynaptic membrane is an essential step in synaptic strength modification, and in particular, long-term...
Regulated delivery of AMPA receptors (AMPARs) to the postsynaptic membrane is an essential step in synaptic strength modification, and in particular, long-term potentiation (LTP). While LTP has been extensively studied using electrophysiology and light microscopy, several questions regarding the molecular mechanisms of AMPAR delivery trafficking vesicles remain outstanding, including the gross molecular make up of AMPAR trafficking organelles and identification and location of calcium sensors required for SNARE complex-dependent membrane fusion of such trafficking vesicles with the plasma membrane. Here, we isolated AMPA-containing vesicles (ACVs) from whole mouse brains immunoisolation and characterized them using immunoelectron microscopy, immunoblotting, and liquid chromatography-tandem mass spectrometry (LC-MS/MS). We identified several proteins on ACVs that were previously found to play a role in AMPAR trafficking, including synaptobrevin-2, Rabs, the SM protein Munc18-1, the calcium-sensor synaptotagmin-1, as well as several new candidates, including synaptophysin and synaptogyrin on ACV membranes. Additionally, we identified two populations of ACVs based on size and molecular composition: small-diameter, synaptobrevin-2- and GluA1-containing ACVs, and larger transferrin- receptor-, GluA1-, GluA2-, and GluA3-containing ACVs. The small-diameter population of ACVs may represent a fusion-capable population of vesicles due to the presence of synaptobrevin-2. Because the fusion of ACVs may be a requisite of LTP, this population could represent trafficking vesicles related to LTP.
PubMed: 34720876
DOI: 10.3389/fnmol.2021.754631 -
Developmental Cell Oct 2020Formation of biomolecular condensates that are not enclosed by membranes via liquid-liquid phase separation (LLPS) is a general strategy that cells adopt to organize... (Review)
Review
Formation of biomolecular condensates that are not enclosed by membranes via liquid-liquid phase separation (LLPS) is a general strategy that cells adopt to organize membraneless subcellular compartments for diverse functions. Neurons are highly polarized with elaborate branching and functional compartmentalization of their neurites, thus, raising additional demand for the proper subcellular localization of both membraneless and membrane-based organelles. Recent studies have provided evidence that several protein assemblies involved in the establishment of neuronal stem cell (NSC) polarity and in the asymmetric division of NSCs form distinct molecular condensates via LLPS. In synapses of adult neurons, molecular apparatuses controlling presynaptic neurotransmitter release and postsynaptic signaling transmission are also likely formed via LLPS. These molecular condensates, though not enclosed by lipid bilayers, directly associate with plasma membranes or membrane-based organelles, indicating that direct communication between membraneless and membrane-based organelles is a common theme in neurons and other types of cells.
Topics: Animals; Cell Communication; Humans; Neurogenesis; Neurons; Organelles; Synapses; Synaptic Transmission
PubMed: 32726576
DOI: 10.1016/j.devcel.2020.06.012 -
Protein Science : a Publication of the... Nov 2021Chemical synaptic transmission represents the most sophisticated dynamic process and is highly regulated with optimized neurotransmitter balance. Imbalanced transmitters...
Chemical synaptic transmission represents the most sophisticated dynamic process and is highly regulated with optimized neurotransmitter balance. Imbalanced transmitters can lead to transmission impairments, for example, intracellular zinc accumulation is a hallmark of degenerating neurons. However, the underlying mechanisms remain elusive. Postsynaptic density protein-95 (PSD-95) is a primary postsynaptic membrane-associated protein and the major scaffolding component in the excitatory postsynaptic densities, which performs substantial functions in synaptic development and maturation. Its membrane association induced by palmitoylation contributes largely to its regulatory functions at postsynaptic sites. Unlike other structural domains in PSD-95, the N-terminal region (PSD-95NT) is flexible and interacts with various targets, which modulates its palmitoylation of two cysteines (C3/C5) and glutamate receptor distributions in postsynaptic densities. PSD-95NT contains a putative zinc-binding motif (C2H2) with undiscovered functions. This study is the first effort to investigate the interaction between Zn and PSD-95NT. The NMR titration of N-labeled PSD-95NT by ZnCl was performed and demonstrated Zn binds to PSD-95NT with a binding affinity (K ) in the micromolar range. The zinc binding was confirmed by fluorescence and mutagenesis assays, indicating two cysteines and two histidines (H24, H28) are critical residues for the binding. These results suggested the concentration-dependent zinc binding is likely to influence PSD-95 palmitoylation since the binding site overlaps the palmitoylation sites, which was verified by the mimic PSD-95 palmitoyl modification and intact cell palmitoylation assays. This study reveals zinc as a novel modulator for PSD-95 postsynaptic membrane association by chelating its N-terminal region, indicative of its importance in postsynaptic signaling.
Topics: Amino Acid Motifs; Chelating Agents; Disks Large Homolog 4 Protein; HEK293 Cells; Humans; Lipoylation; Protein Domains; Zinc
PubMed: 34538002
DOI: 10.1002/pro.4187 -
Neuropharmacology Sep 2021Glutamate is by far the most abundant neurotransmitter used by excitatory synapses in the vertebrate central nervous system. Once released into the synaptic cleft, it... (Review)
Review
Glutamate is by far the most abundant neurotransmitter used by excitatory synapses in the vertebrate central nervous system. Once released into the synaptic cleft, it depolarises the postsynaptic membrane and activates downstream signalling pathways resulting in the propagation of the excitatory signal. Initial depolarisation is primarily mediated by α-amino-3-hydroxy-5-methyl-4-isoxazolepropionate (AMPA) receptors. These ion channels are the first ones to be activated by released glutamate and their kinetics, dynamics and abundance on the postsynaptic membrane defines the strength of the postsynaptic response. This review focuses on native AMPA receptors and synaptic environment they inhabit and considers structural and functional properties of the receptors obtained in heterologous systems in the light of spatial and temporal constraints of the synapse. This article is part of the special Issue on 'Glutamate Receptors - AMPA receptors'.
Topics: Animals; Glutamic Acid; Humans; Receptors, AMPA; Synapses; Synaptic Membranes; Synaptic Transmission; Time Factors
PubMed: 34271021
DOI: 10.1016/j.neuropharm.2021.108711 -
Neuroscience Letters Oct 2019At vertebrate motor endplates, the conversion of nerve impulses into muscle contraction is initiated by binding of acetylcholine to its nicotinic receptor (nAChR) at the... (Review)
Review
At vertebrate motor endplates, the conversion of nerve impulses into muscle contraction is initiated by binding of acetylcholine to its nicotinic receptor (nAChR) at the postsynapse. Efficiency and safety of this process are dependent on proper localization, density, and molecular composition of the receptors. To warrant this, intricate machineries regulating the turnover of nAChR are in place. They control and execute the processes of i) expression, ii) delivery to the postsynaptic membrane, iii) clustering at the plasma membrane, iv) endocytic retrieval, v) activity-dependent recycling, and vi) degradation of nAChR. Concentrating on aspects iv-vi, this review addresses the current status of techniques, concepts, and open questions on endocytosis, recycling, and degradation of nAChR. A picture is emerging, that shows connections between executing machineries and their regulators. The first group includes the actin cytoskeleton, myosin motor proteins, Rab G-proteins, and the autophagic cascade. The second group features protein kinases A and C, Cdk5, and CaMKII as well as other components like the E3-ligase MuRF1 and the membrane shaping regulator, SH3GLB1. Recent studies have started to shed light onto nerve inputs that appear to master the tuning of the postsynaptic protein trafficking apparatus and the expression of critical components for nAChR turnover.
Topics: Animals; Endocytosis; Humans; Motor Endplate; Receptors, Nicotinic
PubMed: 31421156
DOI: 10.1016/j.neulet.2019.134434