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Cell Death & Disease Apr 2024Abnormal intraneuronal accumulation of soluble and insoluble α-synuclein (α-Syn) is one of the main pathological hallmarks of synucleinopathies, such as Parkinson's...
Abnormal intraneuronal accumulation of soluble and insoluble α-synuclein (α-Syn) is one of the main pathological hallmarks of synucleinopathies, such as Parkinson's disease (PD). It has been well documented that the reversible liquid-liquid phase separation of α-Syn can modulate synaptic vesicle condensates at the presynaptic terminals. However, α-Syn can also form liquid-like droplets that may convert into amyloid-enriched hydrogels or fibrillar polymorphs under stressful conditions. To advance our understanding on the mechanisms underlying α-Syn phase transition, we employed a series of unbiased proteomic analyses and found that actin and actin regulators are part of the α-Syn interactome. We focused on Neural Wiskott-Aldrich syndrome protein (N-WASP) because of its association with a rare early-onset familial form of PD. In cultured cells, we demonstrate that N-WASP undergoes phase separation and can be recruited to synapsin 1 liquid-like droplets, whereas it is excluded from α-Syn/synapsin 1 condensates. Consistently, we provide evidence that wsp-1/WASL loss of function alters the number and dynamics of α-Syn inclusions in the nematode Caenorhabditis elegans. Together, our findings indicate that N-WASP expression may create permissive conditions that promote α-Syn condensates and their potentially deleterious conversion into toxic species.
Topics: alpha-Synuclein; Animals; Humans; Caenorhabditis elegans; Wiskott-Aldrich Syndrome Protein, Neuronal; Actins; Parkinson Disease; Synapsins; Caenorhabditis elegans Proteins
PubMed: 38693139
DOI: 10.1038/s41419-024-06686-7 -
ENeuro May 2024Glutamatergic mossy cells (MCs) mediate associational and commissural connectivity, exhibiting significant heterogeneity along the septotemporal axis of the mouse... (Comparative Study)
Comparative Study
Glutamatergic mossy cells (MCs) mediate associational and commissural connectivity, exhibiting significant heterogeneity along the septotemporal axis of the mouse dentate gyrus (DG). However, it remains unclear whether the neuronal features of MCs are conserved across mammals. This study compares the neuroanatomy of MCs in the DG of mice and monkeys. The MC marker, calretinin, distinguishes two subpopulations: septal and temporal. Dual-colored fluorescence labeling is utilized to compare the axonal projection patterns of these subpopulations. In both mice and monkeys, septal and temporal MCs project axons across the longitudinal axis of the ipsilateral DG, indicating conserved associational projections. However, unlike in mice, no MC subpopulations in monkeys make commissural projections to the contralateral DG. In monkeys, temporal MCs send associational fibers exclusively to the inner molecular layer, while septal MCs give rise to wide axonal projections spanning multiple molecular layers, akin to equivalent MC subpopulations in mice. Despite conserved septotemporal heterogeneity, interspecies differences are observed in the topological organization of septal MCs, particularly in the relative axonal density in each molecular layer along the septotemporal axis of the DG. In summary, this comparative analysis sheds light on both conserved and divergent features of MCs in the DG of mice and monkeys. These findings have implications for understanding functional differentiation along the septotemporal axis of the DG and contribute to our knowledge of the anatomical evolution of the DG circuit in mammals.
Topics: Animals; Axons; Male; Dentate Gyrus; Calbindin 2; Mice, Inbred C57BL; Mossy Fibers, Hippocampal; Mice; Species Specificity; Female
PubMed: 38688719
DOI: 10.1523/ENEURO.0151-24.2024 -
American Journal of Physiology. Cell... Jun 2024The authors' previous research has shown the pivotal roles of cyclin-dependent kinase 5 (CDK5) and its regulatory protein p35 in nerve growth factor (NGF)-induced...
The authors' previous research has shown the pivotal roles of cyclin-dependent kinase 5 (CDK5) and its regulatory protein p35 in nerve growth factor (NGF)-induced differentiation of sympathetic neurons in PC12 cells. During the process of differentiation, neurons are susceptible to environmental influences, including the effects of drugs. Metformin is commonly used in the treatment of diabetes and its associated symptoms, particularly in diabetic neuropathy, which is characterized by dysregulation of the sympathetic neurons. However, the impacts of metformin on sympathetic neuronal differentiation remain unknown. In this study, we investigated the impact of metformin on NGF-induced sympathetic neuronal differentiation using rat pheochromocytoma PC12 cells as a model. We examined the regulation of TrkA-p35/CDK5 signaling in NGF-induced PC12 differentiation. Our results demonstrate that metformin reduces NGF-induced PC12 differentiation by inactivating the TrkA receptor, subsequently inhibiting ERK and EGR1. Inhibition of this cascade ultimately leads to the downregulation of p35/CDK5 in PC12 cells. Furthermore, metformin inhibits the activation of the presynaptic protein Synapsin-I, a substrate of CDK5, in PC12 differentiation. In addition, metformin alters axonal and synaptic bouton formation by inhibiting p35 at both the axons and axon terminals in fully differentiated PC12 cells. In summary, our study elucidates that metformin inhibits sympathetic neuronal differentiation in PC12 cells by disrupting TrkA/ERK/EGR1 and p35/CDK5 signaling. This research contributes to uncovering a novel signaling mechanism in drug response during sympathetic neuronal differentiation, enhancing our understanding of the intricate molecular processes governing this critical aspect of neurodevelopment. This study unveils a novel mechanism influenced by metformin during sympathetic neuronal differentiation. By elucidating its inhibitory effects from the nerve growth factor (NGF) receptor, TrkA, to the p35/CDK5 signaling pathways, we advance our understanding of metformin's mechanisms of action and emphasize its potential significance in the context of drug responses during sympathetic neuronal differentiation.
Topics: Animals; Metformin; Rats; PC12 Cells; Cyclin-Dependent Kinase 5; Nerve Growth Factor; Receptor, trkA; Neurons; Cell Differentiation; Signal Transduction; Neurogenesis; Early Growth Response Protein 1; Nerve Tissue Proteins; Phosphotransferases
PubMed: 38682237
DOI: 10.1152/ajpcell.00121.2024 -
BioRxiv : the Preprint Server For... Apr 2024Neurotransmitters are released from synaptic vesicles with remarkable precision in response to presynaptic Ca influx but exhibit significant heterogeneity in exocytosis...
Neurotransmitters are released from synaptic vesicles with remarkable precision in response to presynaptic Ca influx but exhibit significant heterogeneity in exocytosis timing and efficacy based on the recent history of activity. This heterogeneity is critical for information transfer in the brain, yet its molecular basis remains poorly understood. Here, we employ a biochemically-defined fusion assay under physiologically-relevant conditions to delineate the minimal protein machinery sufficient to account for different modes of Ca-triggered vesicle fusion and short-term facilitation. We find that Synaptotagmin-1, Synaptotagmin-7, and Complexin, synergistically restrain SNARE complex assembly, thus preserving vesicles in a stably docked state at rest. Upon Ca activation, Synaptotagmin-1 induces rapid vesicle fusion, while Synaptotagmin-7 mediates delayed fusion. Competitive binding of Synaptotagmin-1 and Synaptotagmin-7 to the same SNAREs, coupled with differential rates of Ca-triggered fusion clamp reversal, govern the kinetics of vesicular fusion. Under conditions mimicking sustained neuronal activity, the Synaptotagmin-7 fusion clamp is destabilized by the elevated basal Ca concentration, thereby enhancing the synchronous component of fusion. These findings provide a direct demonstration that a small set of proteins is sufficient to account for how nerve terminals adapt and regulate the Ca-evoked neurotransmitter exocytosis process to support their specialized functions in the nervous system.
PubMed: 38659918
DOI: 10.1101/2024.04.15.589559 -
The Journal of Neuroscience : the... Jun 2024Vertebrate vision begins with light absorption by rod and cone photoreceptors, which transmit signals from their synaptic terminals to second-order neurons: bipolar and...
Vertebrate vision begins with light absorption by rod and cone photoreceptors, which transmit signals from their synaptic terminals to second-order neurons: bipolar and horizontal cells. In mouse rods, there is a single presynaptic ribbon-type active zone at which the release of glutamate occurs tonically in the dark. This tonic glutamatergic signaling requires continuous exo- and endocytosis of synaptic vesicles. At conventional synapses, endocytosis commonly requires dynamins: GTPases encoded by three genes (), which perform membrane scission. Disrupting endocytosis by dynamin deletions impairs transmission at conventional synapses, but the impact of disrupting endocytosis and the role(s) of specific dynamin isoforms at rod ribbon synapses are understood incompletely. Here, we used cell-specific knock-outs (KOs) of the neuron-specific and to investigate the functional roles of dynamin isoforms in rod photoreceptors in mice of either sex. Analysis of synaptic protein expression, synapse ultrastructure, and retinal function via electroretinograms (ERGs) showed that dynamins 1 and 3 act redundantly and are essential for supporting the structural and functional integrity of rod ribbon synapses. Single KO showed no phenotype, and single KO only modestly reduced synaptic vesicle density without affecting vesicle size and overall synapse integrity, whereas double KO impaired vesicle endocytosis profoundly, causing enlarged vesicles, reduced vesicle density, reduced ERG responses, synaptic terminal degeneration, and disassembly and degeneration of postsynaptic processes. Concurrently, cone function remained intact. These results show the fundamental redundancy of dynamins 1 and 3 in regulating the structure and function of rod ribbon synapses.
Topics: Animals; Retinal Rod Photoreceptor Cells; Mice; Synapses; Male; Female; Electroretinography; Dynamin I; Dynamin III; Mice, Knockout; Mice, Inbred C57BL
PubMed: 38641407
DOI: 10.1523/JNEUROSCI.1379-23.2024 -
Cureus Mar 2024In the field of general anesthesia, magnesium sulfate (MgSO4) has become a valuable adjunct because it provides a range of benefits that enhance and optimize... (Review)
Review
In the field of general anesthesia, magnesium sulfate (MgSO4) has become a valuable adjunct because it provides a range of benefits that enhance and optimize conventional aesthetic procedures. This review highlights the various intra-anesthetic benefits of MgSO4 while examining its complex function in the treatment using anesthesia. Magnesium inhibits the release of acetylcholine at the motor endplate and blocks calcium channels at presynaptic nerve terminals. This reduces the amplitude of endplate potential and the excitability of muscle fibers, which increases the potency of a neuromuscular blockade by nondepolarizing neuromuscular blockers. This activity may lessen the need for primary muscle relaxants. Moreover, its capacity to potentially reduce the total amount of main aesthetic agents needed emphasizes its function in maximizing anesthesia dosage, ensuring sufficient depth while perhaps potentially reducing adverse effects linked with increased dosages. MgSO4's adaptable qualities present a viable path for improving anesthetic outcomes, possibly improving patient safety and improving surgical results.
PubMed: 38633961
DOI: 10.7759/cureus.56348 -
The Journal of Physiology Apr 2024We used whole-cell patch clamp to estimate the stationary voltage dependence of persistent sodium-current density (i) in rat hippocampal mossy fibre boutons. Cox's...
We used whole-cell patch clamp to estimate the stationary voltage dependence of persistent sodium-current density (i) in rat hippocampal mossy fibre boutons. Cox's method for correcting space-clamp errors was extended to the case of an isopotential compartment with attached neurites. The method was applied to voltage-ramp experiments, in which i is assumed to gate instantaneously. The raw estimates of i led to predicted clamp currents that were at variance with observation, hence an algorithm was devised to improve these estimates. Optionally, the method also allows an estimate of the membrane specific capacitance, although values of the axial resistivity and seal resistance must be provided. Assuming that membrane specific capacitance and axial resistivity were constant, we conclude that seal resistance continued to fall after adding TTX to the bath. This might have been attributable to a further deterioration of the seal after baseline rather than an unlikely effect of TTX. There was an increase in the membrane specific resistance in TTX. The reason for this is unknown, but it meant that i could not be determined by simple subtraction. Attempts to account for i with a Hodgkin-Huxley model of the transient sodium conductance met with mixed results. One thing to emerge was the importance of voltage shifts. Also, a large variability in previously reported values of transient sodium conductance in mossy fibre boutons made comparisons with our results difficult. Various other possible sources of error are discussed. Simulations suggest a role for i in modulating the axonal attenuation of EPSPs. KEY POINTS: We used whole-cell patch clamp to estimate the stationary voltage dependence of persistent sodium-current density (i) in rat hippocampal mossy fibre boutons, using a KCl-based internal (pipette) solution and correcting for the liquid junction potential (2 mV). Space-clamp errors and deterioration of the patch-clamp seal during the experiment were corrected for by compartmental modelling. Attempts to account for i in terms of the transient sodium conductance met with mixed results. One possibility is that the transient sodium conductance is higher in mossy fibre boutons than in the axon shaft. The analysis illustrates the need to account for various voltage shifts (Donnan potentials, liquid junction potentials and, possibly, other voltage shifts). Simulations suggest a role for i in modulating the axonal attenuation of excitatory postsynaptic potentials, hence analog signalling by dentate granule cells.
Topics: Rats; Animals; Mossy Fibers, Hippocampal; Sodium; Presynaptic Terminals
PubMed: 38594842
DOI: 10.1113/JP284657 -
BioRxiv : the Preprint Server For... Mar 2024Cochlear outer hair cells (OHCs) are electromotile and are implicated in mechanisms of amplification of responses to sound that enhance sound sensitivity and frequency...
Cochlear outer hair cells (OHCs) are electromotile and are implicated in mechanisms of amplification of responses to sound that enhance sound sensitivity and frequency tuning. They send information to the brain through glutamatergic synapses onto a small subpopulation of neurons of the ascending auditory nerve, the type II spiral ganglion neurons (SGNs). The OHC synapses onto type II SGNs are sparse and weak, suggesting that type II SGNs respond primarily to loud and possibly damaging levels of sound. OHCs also receive innervation from the brain through the medial olivocochlear (MOC) efferent neurons. MOC neurons are cholinergic yet exert an inhibitory effect on auditory function as they are coupled to alpha9/alpha10 nicotinic acetylcholine receptors (nAChRs) on OHCs, which leads to calcium influx that gates SK potassium channels. The net hyperpolarization exerted by this efferent synapse reduces OHC activity-evoked electromotility and is implicated in cochlear gain control, protection against acoustic trauma, and attention. MOC neurons also label for markers of gamma-aminobutyric acid (GABA) and GABA synthesis. GABA autoreceptor (GABAR) activation by GABA released from MOC terminals has been demonstrated to reduce ACh release, confirming important negative feedback roles for GABA. However, the full complement of GABAergic activity in the cochlea is not currently understood, including the mechanisms that regulate GABA release from MOC axon terminals, whether GABA diffuses from MOC axon terminals to other postsynaptic cells, and the location and function of GABA receptors (GABARs). Previous electron microscopy studies suggest that MOC neurons form contacts onto several other cell types in the cochlea, but whether these contacts form functional synapses, and what neurotransmitters are employed, are unknown. Here we use immunohistochemistry, optical neurotransmitter imaging and patch-clamp electrophysiology from hair cells, afferent dendrites, and efferent axons to demonstrate that in addition to presynaptic GABAR autoreceptor activation, MOC efferent axon terminals release GABA onto type II SGN afferent dendrites with postsynaptic activity mediated by GABARs. This synapse may have multiple roles including developmental regulation of cochlear innervation, fine tuning of OHC activity, or providing feedback to the brain about MOC and OHC activity.
PubMed: 38586043
DOI: 10.1101/2024.03.28.587185 -
BioRxiv : the Preprint Server For... Mar 2024Although glucagon-like peptide 1 (GLP-1) is known to regulate feeding, the central mechanisms contributing to this function remain enigmatic. Here, we aim to test the...
OBJECTIVE
Although glucagon-like peptide 1 (GLP-1) is known to regulate feeding, the central mechanisms contributing to this function remain enigmatic. Here, we aim to test the role of neurons expressing GLP-1 receptors (GLP-1R) in the dorsolateral septum (dLS; dLS ) and their downstream projections on food intake and determine the relationship with feeding regulation.
METHODS
Using chemogenetic manipulations, we assessed how activation or inhibition of dLS neurons affected food intake in mice. Then, we used channelrhodopsin-assisted circuit mapping, chemogenetics, and electrophysiological recordings to identify and assess the role of the pathway from dLS neurons to the lateral hypothalamic area (LHA) in regulating food intake.
RESULTS
Chemogenetic inhibition of dLS neurons increases food intake. LHA is a major downstream target of dLS neurons. The dLS →LHA projections are GABAergic, and chemogenetic inhibition of this pathway also promotes food intake. While chemogenetic activation of dLS →LHA projections modestly decreases food intake, optogenetic stimulation of the dLS →LHA projection terminals in the LHA rapidly suppressed feeding behavior. Finally, we demonstrate that the GLP-1R agonist, Exendin 4 enhances dLS →LHA GABA release.
CONCLUSIONS
Together, these results demonstrate that dLS-GLP-1R neurons and the inhibitory pathway to LHA can regulate feeding behavior, which might serve as a potential therapeutic target for the treatment of eating disorders or obesity.
HIGHLIGHTS
Chemogenetic inhibition of dLS neurons boosts food intake in mice dLS neuron activation does not alter feeding, likely by collateral inhibition dLS neurons project to LHA and release GABA Activation of dLS →LHA axonal terminals suppresses food intake GLP-1R agonism enhances dLS →LHA GABA release via a presynaptic mechanism.
PubMed: 38585874
DOI: 10.1101/2024.03.26.586855 -
The Journal of Cell Biology Jun 2024Disruption of synapse assembly and maturation leads to a broad spectrum of neurodevelopmental disorders. Presynaptic proteins are largely synthesized in the soma, where... (Review)
Review
Disruption of synapse assembly and maturation leads to a broad spectrum of neurodevelopmental disorders. Presynaptic proteins are largely synthesized in the soma, where they are packaged into precursor vesicles and transported into distal axons to ensure precise assembly and maintenance of presynapses. Due to their morphological features, neurons face challenges in the delivery of presynaptic cargos to nascent boutons. Thus, targeted axonal transport is vital to build functional synapses. A growing number of mutations in genes encoding the transport machinery have been linked to neurodevelopmental disorders. Emerging lines of evidence have started to uncover presynaptic mechanisms underlying axonal transport defects, thus broadening the view of neurodevelopmental disorders beyond postsynaptic mechanisms. In this review, we discuss presynaptic perspectives of neurodevelopmental disorders by focusing on impaired axonal transport and disturbed assembly and maintenance of presynapses. We also discuss potential strategies for restoring axonal transport as an early therapeutic intervention.
Topics: Humans; Axonal Transport; Axons; Cell Body; Mutation; Neurodevelopmental Disorders; Presynaptic Terminals
PubMed: 38568173
DOI: 10.1083/jcb.202401145