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The Journal of Biological Chemistry May 2024Synapse formation depends on the coordinated expression and regulation of scaffold proteins. The JNK family kinases play a role in scaffold protein regulation, but the...
Synapse formation depends on the coordinated expression and regulation of scaffold proteins. The JNK family kinases play a role in scaffold protein regulation, but the nature of this functional interaction in dendritic spines requires further investigation. Here, using a combination of biochemical methods and live-cell imaging strategies, we show that the dynamics of the synaptic scaffold molecule SAP102 are negatively regulated by JNK inhibition, that SAP102 is a direct phosphorylation target of JNK3, and that SAP102 regulation by JNK is restricted to neurons that harbor mature synapses. We further demonstrate that SAP102 and JNK3 cooperate in the regulated trafficking of kainate receptors to the cell membrane. Specifically, we observe that SAP102, JNK3, and the kainate receptor subunit GluK2 exhibit overlapping expression at synaptic sites and that modulating JNK activity influences the surface expression of the kainate receptor subunit GluK2 in a neuronal context. We also show that SAP102 participates in this process in a JNK-dependent fashion. In summary, our data support a model in which JNK-mediated regulation of SAP102 influences the dynamic trafficking of kainate receptors to postsynaptic sites, and thus shed light on common pathophysiological mechanisms underlying the cognitive developmental defects associated with diverse mutations.
Topics: Animals; Humans; Rats; Cell Membrane; Dendritic Spines; GluK2 Kainate Receptor; Hippocampus; Intracellular Signaling Peptides and Proteins; Membrane Proteins; Mitogen-Activated Protein Kinase 10; Neurons; Neuropeptides; Phosphorylation; Protein Transport; Receptors, Kainic Acid; Synapses; Cells, Cultured
PubMed: 38582451
DOI: 10.1016/j.jbc.2024.107263 -
Frontiers in Neuroanatomy 2024The brain contains thousands of millions of synapses, exhibiting diverse structural, molecular, and functional characteristics. However, synapses can be classified into...
The brain contains thousands of millions of synapses, exhibiting diverse structural, molecular, and functional characteristics. However, synapses can be classified into two primary morphological types: Gray's type I and type II, corresponding to Colonnier's asymmetric (AS) and symmetric (SS) synapses, respectively. AS and SS have a thick and thin postsynaptic density, respectively. In the cerebral cortex, since most AS are excitatory (glutamatergic), and SS are inhibitory (GABAergic), determining the distribution, size, density, and proportion of the two major cortical types of synapses is critical, not only to better understand synaptic organization in terms of connectivity, but also from a functional perspective. However, several technical challenges complicate the study of synapses. Potassium ferrocyanide has been utilized in recent volume electron microscope studies to enhance electron density in cellular membranes. However, identifying synaptic junctions, especially SS, becomes more challenging as the postsynaptic densities become thinner with increasing concentrations of potassium ferrocyanide. Here we describe a protocol employing Focused Ion Beam Milling and Scanning Electron Microscopy for studying brain tissue. The focus is on the unequivocal identification of AS and SS types. To validate SS observed using this protocol as GABAergic, experiments with immunocytochemistry for the vesicular GABA transporter were conducted on fixed mouse brain tissue sections. This material was processed with different concentrations of potassium ferrocyanide, aiming to determine its optimal concentration. We demonstrate that using a low concentration of potassium ferrocyanide (0.1%) improves membrane visualization while allowing unequivocal identification of synapses as AS or SS.
PubMed: 38645671
DOI: 10.3389/fnana.2024.1348032 -
Neuroscience Jan 2024GluA1-containing α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptors (AMPARs) inserted into postsynaptic membranes are key to the process of long-term...
OBJECTIVE
GluA1-containing α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptors (AMPARs) inserted into postsynaptic membranes are key to the process of long-term potentiation (LTP). Some evidence has shown that 4.1N plays a critical role in the membrane trafficking of AMPARs. However, the underlying mechanism behind this is still unclear. We investigated the role of 4.1N-mediated membrane trafficking of AMPARs during theta-burst stimulation long-term potentiation (TBS-LTP), to illustrate the molecular mechanism behind LTP.
METHODS
LTP was induced by TBS in rat hippocampal CA1 neuron. Tat-GluA1 (MPR), which disrupts the association of 4.1N-GluA1, and autocamtide-2-inhibitory peptide, myristoylated (Myr-AIP), a CaMKII antagonist, were used to explore the role of 4.1N in the AMPARs trafficking during TBS-induced LTP. Immunoprecipitation (IP) and immunoblotting (IB)were used to detect protein expression, phosphorylation, and the interaction of p-CaMKII-4.1N-GluA1.
RESULTS
We found that Myr-AIP attenuated increases of p-CaMKII (T286), p-GluA1 (ser831), and 4.1N phosphorylation after TBS-LTP, and decreased the association of p-CaMKII-4.1N-GluA1, along with the expression of GluA1, at postsynaptic densities during TBS-LTP. We also designed interfering peptides to disrupt the interaction between 4.1N and GluA1, which showed that Tat-GluA1 (MPR) or Myr-AIP inhibited TBS-LTP and attenuated increases of GluA1 at postsynaptic sites, while Tat-GluA1 (MPR) or Myr-AIP had no effects on miniature excitatory postsynaptic currents (mEPSCs) in non-stimulated hippocampal CA1 neurons.
CONCLUSION
Active CaMKII enhanced the phosphorylation of 4.1N and facilitated the association of p-CaMKII with 4.1N-GluA1, which in turn resulted in GluA1 trafficking during TBS-LTP. The association of 4.1N-GluA1 is required for LTP, but not for basal synaptic transmission.
Topics: Animals; Rats; Calcium-Calmodulin-Dependent Protein Kinase Type 2; Hippocampus; Long-Term Potentiation; Phosphorylation; Receptors, AMPA; Synapses
PubMed: 37993087
DOI: 10.1016/j.neuroscience.2023.11.016 -
PloS One 2024Although behavioural defensive responses have been recorded several times in both laboratory and natural habitats, their neural mechanisms have seldom been investigated....
Although behavioural defensive responses have been recorded several times in both laboratory and natural habitats, their neural mechanisms have seldom been investigated. To explore how chemical, water-borne cues are conveyed to the forebrain and instruct behavioural responses in anuran larvae, we conditioned newly hatched agile frog tadpoles using predator olfactory cues, specifically either native odonate larvae or alien crayfish kairomones. We expected chronic treatments to influence the basal neuronal activity of the tadpoles' mitral cells and alter their sensory neuronal connections, thereby impacting information processing. Subsequently, these neurons were acutely perfused, and their responses were compared with the defensive behaviour of tadpoles previously conditioned and exposed to the same cues. Tadpoles conditioned with odonate cues differed in both passive and active cell properties compared to those exposed to water (controls) or crayfish cues. The observed upregulation of membrane conductance and increase in both the number of active synapses and receptor density at the postsynaptic site are believed to have enhanced their responsiveness to external stimuli. Odonate cues also affected the resting membrane potential and firing rate of mitral cells during electrophysiological patch-clamp recordings, suggesting a rearrangement of the repertoire of voltage-dependent conductances expressed in cell membranes. These recorded neural changes may modulate the induction of an action potential and transmission of information. Furthermore, the recording of neural activity indicated that the lack of defensive responses towards non-native predators is due to the non-recognition of their olfactory cues.
Topics: Animals; Larva; Predatory Behavior; Cues; Anura; Olfactory Receptor Neurons; Astacoidea
PubMed: 38696517
DOI: 10.1371/journal.pone.0302728 -
BioRxiv : the Preprint Server For... Oct 2023In a chemical synapse, information flow occurs via the release of neurotransmitters from a presynaptic neuron that triggers an Action potential (AP) in the postsynaptic...
In a chemical synapse, information flow occurs via the release of neurotransmitters from a presynaptic neuron that triggers an Action potential (AP) in the postsynaptic neuron. At its core, this occurs via the postsynaptic membrane potential integrating neurotransmitter-induced synaptic currents, and AP generation occurs when potential reaches a critical threshold. This manuscript investigates feedback implementation via an autapse, where the axon from the postsynaptic neuron forms an inhibitory synapse onto itself. Using a stochastic model of neuronal synaptic transmission, we formulate AP generation as a first-passage time problem and derive expressions for both the mean and noise of AP-firing times. Our analytical results supported by stochastic simulations identify parameter regimes where autaptic feedback transmission enhances the precision of AP firing times consistent with experimental data. These noise attenuating regimes are intuitively based on two orthogonal mechanisms - either expanding the time window to integrate noisy upstream signals; or by linearizing the mean voltage increase over time. Interestingly, we find regimes for noise amplification that specifically occur when the inhibitory synapse has a low probability of release for synaptic vesicles. In summary, this work explores feedback modulation of the stochastic dynamics of autaptic neurotransmission and reveals its function of creating more regular AP firing patterns.
PubMed: 37873216
DOI: 10.1101/2023.10.06.561207 -
Proceedings of the National Academy of... May 2024The muscle-type nicotinic acetylcholine receptor is a transmitter-gated ion channel residing in the plasma membrane of electrocytes and striated muscle cells. It is...
The muscle-type nicotinic acetylcholine receptor is a transmitter-gated ion channel residing in the plasma membrane of electrocytes and striated muscle cells. It is present predominantly at synaptic junctions, where it effects rapid depolarization of the postsynaptic membrane in response to acetylcholine released into the synaptic cleft. Previously, cryo-EM of intact membrane from revealed that the lipid bilayer surrounding the junctional receptor has a uniquely asymmetric and ordered structure, due to a high concentration of cholesterol. It is now shown that this special lipid environment influences the transmembrane (TM) folding of the protein. All five submembrane MX helices of the membrane-intact junctional receptor align parallel to the surface of the cholesterol-ordered lipids in the inner leaflet of the bilayer; also, the TM helices in the outer leaflet are splayed apart. However in the structure obtained from the same protein after extraction and incorporation in nanodiscs, the MX helices do not align to a planar surface, and the TM helices arrange compactly in the outer leaflet. Realignment of the MX helices of the nanodisc-solved structure to a planar surface converts their adjoining TM helices into an obligatory splayed configuration, characteristic of the junctional receptor. Thus, the form of the receptor sustained by the special lipid environment of the synaptic junction is the one that mediates fast synaptic transmission; whereas, the nanodisc-embedded protein may be like the extrajunctional form, existing in a disordered lipid environment.
Topics: Receptors, Nicotinic; Lipid Bilayers; Animals; Torpedo; Cryoelectron Microscopy; Cholesterol; Cell Membrane; Protein Folding; Models, Molecular
PubMed: 38683987
DOI: 10.1073/pnas.2319913121 -
IScience Mar 2024Transcranial direct current stimulation (tDCS) induces subcellular compartmental-dependent polarization, maximal in the distal portions of axons and dendrites. Using a...
Transcranial direct current stimulation (tDCS) induces subcellular compartmental-dependent polarization, maximal in the distal portions of axons and dendrites. Using a morphologically realistic neuron model, we simulated tDCS-induced membrane polarization of the apical dendrite. Thus, we investigated the differential dendritic effects of anodal and cathodal tDCS on membrane potential polarization along the dendritic structure and its subsequent effects on dendritic membrane resistance, excitatory postsynaptic potential amplitude, backpropagating action potential amplitude, input/output relations, and long-term synaptic plasticity. We further showed that the effects of anodal and cathodal tDCS on the backpropagating action potential were asymmetric, and explained this asymmetry. Additionally, we showed that the effects on input/output relations were rather weak and limited to the low-mid range of stimulation frequencies, and that synaptic plasticity effects were mostly limited to the distal portion of the dendrite. Thus, we demonstrated how tDCS modifies dendritic physiology due to the dendrite's unique morphology and composition of voltage-gated ion channels.
PubMed: 38433894
DOI: 10.1016/j.isci.2024.109230 -
Medicine Apr 2024Cerebral palsy (CP) is the most common disabling disease in children, and motor dysfunction is the core symptom of CP. Although relevant risk factors have been found to... (Observational Study)
Observational Study
Cerebral palsy (CP) is the most common disabling disease in children, and motor dysfunction is the core symptom of CP. Although relevant risk factors have been found to be closely associated with CP: congenital malformations, multiple gestation, prematurity, intrauterine inflammation and infection, birth asphyxia, thrombophilia, and perinatal stroke. Its important pathophysiological mechanism is amniotic fluid infection and intraamniotic inflammation leading to fetal developing brain damage, which may last for many years. However, the molecular mechanism of CP is still not well explained. This study aimed to use bioinformatics to identify key biomarker-related signaling pathways in CP. The expression profile of children with CP was selected from the Gene Expression Comprehensive Database, and the CP disease gene data set was obtained from GeneCards. A protein-protein interaction network was established and functional enrichment analysis was performed using Gene Ontology and Kyoto Encyclopedia of Genes and Genomes databases. A total of 144 differential key intersection genes and 10 hub genes were identified through molecular biology. Gene Ontology functional enrichment analysis results show that differentially expressed genes are mainly concentrated in biological processes, such as immune response and neurogenesis. The cellular components involved mainly include axons, postsynaptic membranes, etc, and their molecular functions mainly involve proteoglycan binding, collagen binding, etc. Kyoto Encyclopedia of Genes and Genomes analysis shows that the intersection genes are mainly in signaling pathways related to the immune system, inflammatory response, and nervous system, such as Th17 cell differentiation, Toll-like receptor signaling pathway, tumor necrosis factor signaling pathway, NF-κB signaling pathway, axon guidance, PI3K-Akt signaling pathway, HIF-1 signaling pathway, gap junction, etc. Jak-STAT signaling pathway, mTOR signaling pathway, and related hub genes regulate immune cells and inflammatory factors and play an important role in the development and progression of CP.
Topics: Child; Female; Pregnancy; Humans; Cerebral Palsy; Phosphatidylinositol 3-Kinases; Biomarkers; Brain Injuries; Computational Biology; Inflammation
PubMed: 38640267
DOI: 10.1097/MD.0000000000037828 -
Frontiers in Cellular Neuroscience 2023In presynaptic terminals 4 types of endocytosis, kiss-and-run, clathrin-mediated, bulk and ultrafast endocytosis have been reported to maintain repetitive exocytosis of...
In presynaptic terminals 4 types of endocytosis, kiss-and-run, clathrin-mediated, bulk and ultrafast endocytosis have been reported to maintain repetitive exocytosis of neurotransmitter. However, detailed characteristics and relative contribution of each type of endocytosis still need to be determined. Our previous live-cell imaging study demonstrated individual exocytosis events of synaptic vesicle within an active-zone-like membrane (AZLM) formed on glass using synaptophysin tagged with a pH-sensitive fluorescent protein. On the other hand, individual endocytosis events of postsynaptic receptors were recorded with a rapid extracellular pH exchange method. Combining these methods, here we live-cell imaged endocytosed synaptophysin with total internal reflection fluorescence microscopy in rat hippocampal culture preparations. Clathrin-dependent and -independent endocytosis, which was seemingly bulk endocytosis, occurred within several seconds after electrical stimulation at multiple locations around AZLM at room temperature, with the locations varying trial to trial. The contribution of clathrin-independent endocytosis was more prominent when the number of stimulation pulses was large. The skewness of synaptophysin distribution in intracellular vesicles became smaller after addition of a clathrin inhibitor, which suggests that clathrin-dependent endocytosis concentrates synaptophysin. Ultrafast endocytosis was evident immediately after stimulation only at near physiological temperature and was the predominant endocytosis when the number of stimulation pulses was small.
PubMed: 37927445
DOI: 10.3389/fncel.2023.1277729 -
Proceedings of the National Academy of... Apr 2024Stable matching of neurotransmitters with their receptors is fundamental to synapse function and reliable communication in neural circuits. Presynaptic neurotransmitters...
Stable matching of neurotransmitters with their receptors is fundamental to synapse function and reliable communication in neural circuits. Presynaptic neurotransmitters regulate the stabilization of postsynaptic transmitter receptors. Whether postsynaptic receptors regulate stabilization of presynaptic transmitters has received less attention. Here, we show that blockade of endogenous postsynaptic acetylcholine receptors (AChR) at the neuromuscular junction destabilizes the cholinergic phenotype in motor neurons and stabilizes an earlier, developmentally transient glutamatergic phenotype. Further, expression of exogenous postsynaptic gamma-aminobutyric acid type A receptors (GABA receptors) in muscle cells stabilizes an earlier, developmentally transient GABAergic motor neuron phenotype. Both AChR and GABA receptors are linked to presynaptic neurons through transsynaptic bridges. Knockdown of specific components of these transsynaptic bridges prevents stabilization of the cholinergic or GABAergic phenotypes. Bidirectional communication can enforce a match between transmitter and receptor and ensure the fidelity of synaptic transmission. Our findings suggest a potential role of dysfunctional transmitter receptors in neurological disorders that involve the loss of the presynaptic transmitter.
Topics: Synapses; Receptors, Cholinergic; Synaptic Transmission; Motor Neurons; Receptors, GABA-A; gamma-Aminobutyric Acid; Neurotransmitter Agents; Cholinergic Agents; Receptors, Presynaptic
PubMed: 38568976
DOI: 10.1073/pnas.2318041121