The precise organization of the complex set of synaptic proteins at the nanometer scale is crucial for synaptic transmission. At the heart of this nanoscale architecture lies the nanocolumn. This aligns presynaptic neurotransmitter release with a high local density of postsynaptic receptor channels, thereby optimizing synaptic strength. Although synapses exhibit diverse protein compositions and nanoscale organizations, the role of structural diversity in the notable differences observed in synaptic physiology remains poorly understood. In this review we examine the current literature on the molecular mechanisms underlying the formation and maintenance of nanocolumns, as well as their role in modulating various aspects of synaptic transmission. We also discuss how the reorganization of nanocolumns contributes to functional dynamics in both synaptic plasticity and pathology.

Autism spectrum disorder (ASD) is a neurodevelopmental disorder characterized by deficits in social communication and limited behavior. Despite the association of numerous synaptic gene mutations with ASD, the presence of behavioral abnormalities in mice expressing autism-associated R617W mutation in synaptic adhesion protein neuroligin-3 (NL3) has not been established. This work focuses on establishing a mouse model of ASD caused by NL3 R617W missense mutation (NL3R617W) and characterizing and profiling the molecular as well as behavioral features of the animal model.

The expression and distribution of NL3R617W mutant protein in the 293T cell membrane and intracellular NL3 was detected by using immunofluorescence approach. Meanwhile, synaptic markers (Synapsin I, vesicular glutamate transporter (VGluT) I and vesicular γ-aminobutyric acid transporter (VGAT)) and synapse number were detected with a confocal fluorescence microscope. Thereafter, the effect on NL3R617W was verified. The expression of synaptic proteins, postsynaptic density protein-95 (PSD95) and Src homology domain and multiple ankyrin repeat domains protein 3 (SHANK3), was verified by Western blot. The interaction between NL3 and neurexin 1 (NRXN1) was studied by means of co-immunoprecipitation. The behavior of autistic mice induced by NL3R617W mutation was examined using the Morris water maze and the Y maze. NL3R617W mutant mice were assessed in the open field, and three-chamber test was conducted to assess and observe the presence of hyperactivity, repetitive behavior, friendliness, and social novelty.

The results indicated that the NL3 mutation could influence the interaction between NL3 and NRXN1, and inhibit the expression of VGluT I. Nevertheless, NL3 mutation would not influence the expression of NL3 on cell membrane, the intracellular distribution of NL3, or the endoplasmic reticulum retention. The outcomes of animal studies demonstrated that the ASD mice with NL3R617W exhibited a significant decrease in the capacity for spatial memory and exploration, as well as the expression levels of the postsynaptic scaffolding proteins, PSD95 and SHANK3 (p < 0.05). The number of excitatory synapses in hippocampal cornu ammonis (CA)1 and CA3 and the sensory cortex was also significantly reduced (p < 0.01). Compared to the control mice, the NL3R617W mutant mice were less active in the open field (p < 0.001), a finding consistent with the three-chamber test result showing reduced degree of activity. Furthermore, compared to the control mice, the NL3R617W mutant animals spent less time with stranger mice (p < 0.05).

NL3R617W mutation may inhibit the expression of postsynaptic scaffolding proteins by influencing the interaction with NRXN1, thus inhibiting synapse formation and reducing the number of excitatory synapses.

Depression, a widespread psychiatric disorder, is characterized by a diverse array of symptoms such as melancholic mood and anhedonia, imposing a significant burden on both society and individuals. Despite extensive research into the neurobiological foundations of depression, a complete understanding of its complex mechanisms is yet to be attained, and targeted therapeutic interventions remain under development. Synaptic homeostasis, a compensatory feedback mechanism, involves neurons adjusting synaptic strength by regulating pre- or postsynaptic processes. Recent advancements in depression research reveal a crucial association between the disorder and disruptions in synaptic homeostasis within neural regions and circuits pivotal for emotional and cognitive functions. This paper explores the mechanisms governing synaptic homeostasis in depression, focusing on the role of ion channels, the regulation of presynaptic neurotransmitter release, synaptic scaling processes, and essential signaling molecules. By mapping new pathways in the study of synaptic homeostasis as it pertains to depression, this research aims to provide valuable insights for identifying novel therapeutic targets for more effective antidepressant treatments.

Alzheimer's disease (AD) progresses as a continuum, from preclinical stages to late-stage cognitive decline, yet the molecular mechanisms driving this progression remain poorly understood. Here, we provide a systems-level map of protein-protein interaction (PPI) network dysfunction across the AD spectrum and uncover epichaperomes-stable scaffolding platforms formed by chaperones and co-factors-as central drivers of this process. Using over 100 human brain specimens, mouse models, and human neurons, we show that epichaperomes emerge early, even in preclinical AD, and progressively disrupt multiple PPI networks critical for synaptic function and neuroplasticity. Glutamatergic neurons, essential for learning and memory, exhibit heightened vulnerability, with their dysfunction driven by protein sequestration into epichaperome scaffolds, independent of changes in protein expression. Notably, pharmacological disruption of epichaperomes with PU-AD restores PPI network integrity and reverses synaptic and cognitive deficits, directly linking epichaperome-driven network dysfunction to AD pathology. These findings establish epichaperomes as key mediators of molecular collapse in AD and identify network-centric intervention strategies as a promising avenue for disease-modifying therapies.

Actin, a ubiquitous and highly conserved cytoskeletal protein, plays a pivotal role in various cellular functions such as structural support, facilitating cell motility, and contributing to the dynamic processes of synaptic function. Apart from its established role in inducing morphological changes, recent developments in the field indicate an active involvement of actin in modulating both the structure and function of pre- and postsynaptic terminals. Within the presynapse, it is involved in the organization and trafficking of synaptic vesicles, contributing to neurotransmitter release. In the postsynapse, actin dynamically modulates dendritic spines, influencing the postsynaptic density organization and anchoring of neurotransmitter receptors. In addition, the dynamic interplay of actin at the synapse underscores its essential role in regulating neural communication. This review strives to offer a comprehensive overview of the recent advancements in understanding the multifaceted role of the actin cytoskeleton in synaptic functions. By emphasizing its aberrant regulation, we aim to provide valuable insights into the underlying mechanisms of Alzheimer's disease pathophysiology.

SYNGAP1 is a key Ras-GAP protein enriched at excitatory synapses, with mutations causing intellectual disability and epilepsy in humans. Recent studies have revealed that in addition to its role as a negative regulator of G-protein signaling through its GAP enzymatic activity, SYNGAP1 plays an important structural role through its interaction with post-synaptic density proteins. Here, we reveal that intrinsic excitability deficits and seizure phenotypes in heterozygous Syngap1 knockout (KO) mice are differentially dependent on Syngap1 GAP activity. Cortical excitatory neurons in heterozygous KO mice displayed reduced intrinsic excitability, including lower input resistance, and increased rheobase, a phenotype recapitulated in GAP-deficient Syngap1 mutants. However, seizure severity and susceptibility to pentylenetetrazol (PTZ)-induced seizures were significantly elevated in heterozygous KO mice but unaffected in GAP-deficient mutants, implicating the structural rather than enzymatic role of Syngap1 in seizure regulation. These findings highlight the complex interplay between SYNGAP1 structural and catalytic functions in neuronal physiology and disease.

Synaptic proteins are essential for neuronal development, synaptic transmission, and synaptic plasticity. The postsynaptic density (PSD) is a membrane-associated structure at excitatory synapses, which is composed of a huge protein complex. To understand the interactions and functions of PSD proteins, researchers have employed a variety of imaging and biochemical approaches including sophisticated mass spectrometry. However, the field is lacking a systematic comparison of different experimental conditions and how they might influence the study of the PSD interactome isolated from various tissue preparations. To evaluate the efficiency of several common solubilization conditions, we isolated receptors, scaffolding proteins, and adhesion molecules from brain tissue or primary cultured neurons or human forebrain neurons differentiated from induced pluripotent stem cells (iPSCs). We observed some striking differences in solubility. We found that N-methyl-d-aspartate receptors (NMDARs) and PSD-95 are relatively insoluble in brain tissue, cultured neurons, and human forebrain neurons compared to α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic receptors (AMPARs) or SAP102. In general, synaptic proteins were more soluble in primary neuronal cultures and human forebrain neurons compared to brain tissue. Interestingly, NMDARs are relatively insoluble in HEK293T cells suggesting that insolubility does not directly represent the synaptic fraction but rather it is related to a detergent-insoluble fraction such as lipid rafts. Surprisingly, truncation of the intracellular carboxyl-terminal tail (C-tail) of NMDAR subunits increased NMDAR solubility in HEK293T cells. Our findings show that detergent, pH, and temperature are important for protein preparations to study PSD protein complexes, and NMDAR solubility is regulated by its C-tail, thus providing a technical guide to study synaptic interactomes and subcellular localization of synaptic proteins.

RNA-binding proteins (RBPs) play central roles in post-transcriptional gene regulation. However, the function of RBP in retinal progenitor cell differentiation and synaptic signal transmission are largely unexplored. Previously we have shown that Elavl2 regulates amacrine cell (AC) differentiation during retinogenesis, by directly binding to Nr4a2 and Barhl2. Elavl2 is expressed in early neuronal progenitors to mature neurons, and Elavl4 expression begins slightly later, during cortical neuron development as a paralog. Here, Retinal-specific Elavl2 and Elavl4 double knockout mice were made to further explore the role of Elavl2 and Elavl4 in retinal development and signal transduction. We disclose that Elavl4 binds to Satb1 to regulate Neurod1, then promoting retinal progenitor and amacrine cells differentiation. We were also surprised to find that Elavl2 interacted with GABAB receptors at the RNA and protein levels. In conclusion, Elavl2 and Elavl4 regulate amacrine cells differentiation through different pathways, leading to decreased scotopic vision. Our findings reveal the roles of Elavl2 and Elavl4 in retinal amacrine cells differentiation in modulating visual functions.

Despite the substantial contribution of disruptions in GABAergic inhibitory neurotransmission to the etiology of psychiatric, neurodevelopmental, and neurodegenerative disorders, surprisingly few drugs targeting the GABAergic system are currently available, partly due to insufficient understanding of circuit-specific GABAergic synapse biology. In addition to GABA receptors, GABAergic synapses contain an elaborate organizational protein machinery that regulates the properties of synaptic transmission. Until recently, this machinery remained largely unexplored, but key methodological advances have now led to the identification of a wealth of new GABAergic organizer proteins. Notably, many of these proteins appear to function only at specific subsets of GABAergic synapses, creating a diversity of organizer complexes that may serve as circuit-specific targets for pharmacotherapies. The present review aims to summarize the methodological developments that underlie this newfound knowledge and provide a current overview of synapse-specific GABAergic organizer complexes, as well as outlining future avenues and challenges in translating this knowledge into clinical applications.

SYNGAP1 is a major regulator of synaptic plasticity through its interaction with synaptic scaffold proteins and modulation of Ras and Rap GTPase signaling pathways. SYNGAP1 mutations in humans are often associated with intellectual disability, epilepsy, and autism spectrum disorder. Syngap1 heterozygous loss-of-function results in impaired LTP, premature maturation of dendritic spines, learning disabilities and seizures in mice. More recently, SYNGAP1 was shown to influence cortical neurogenesis and the proliferation of progenitors in human organoids. Here, we show that the absence or haploinsufficiency of Syngap1 does not influence the properties of neocortical progenitors and their cellular output in mice. This discrepancy highlights potential species-specific or methodological differences and raises important questions about the broader applicability of SYNGAP1's role in neurogenesis.

Rare diseases affect one in ten people but only a small fraction of these diseases have an FDA-approved treatment. Haploinsufficiency, caused by a dominant loss-of-function mutation, is a unique rare disease group because patients have one normal allele of the affected gene. This makes rare haploinsufficiency diseases promising candidates for drug development by increasing expression of the normal gene allele, decreasing the target protein degradation and enhancing the target protein function. This review summarizes recent progresses and approaches used in the translational research of therapeutics to treat haploinsufficiency diseases including gene therapy, nucleotide-based therapeutics and small-molecule drug development. We hope that these drug development strategies will accelerate therapeutic development to treat haploinsufficiency diseases.

The circadian clock controls various physiological processes, including synaptic function and neuronal activity, affecting the functioning of the entire organism. Light is an important external factor regulating the day-night cycle. This study examined the effects of the circadian clock and light on synaptic plasticity, and explored how locomotor activity contributes to these processes. We analyzed synaptic protein expression and excitatory synapse density in the somatosensory cortex of mice from four groups exposed to different lighting conditions (LD 12:12, DD, LD 16:8, and LL). Locomotor activity was assessed through individual wheel-running monitoring. To explore daily and circadian changes in synaptic proteins, we performed double-immunofluorescence labeling and laser scanning confocal microscopy imaging, targeting three pairs of presynaptic and postsynaptic proteins (Synaptophysin 1/PSD95, Piccolo/Homer 1, Neurexins/PICK1). Excitatory synapse density was evaluated by co-labeling presynaptic and postsynaptic markers. Our results demonstrated that all the analyzed synaptic proteins exhibited circadian regulation modulated by light. Under constant light conditions, only Piccolo and Homer 1 showed rhythmicity. Locomotor activity was also associated with the circadian clock's effects on synaptic proteins, showing a stronger connection to changes in postsynaptic protein levels. Excitatory synapse density peaked during the day/subjective day and exhibited an inverse relationship with locomotor activity. Continued light exposure disrupted cyclic changes in synapse density but kept it consistently elevated. These findings underscore the crucial roles of light and locomotor activity in regulating synaptic plasticity.

Neurodevelopmental disorders (NDDs) are a group of conditions affecting brain development, with variable degrees of severity and heterogeneous clinical features. They include intellectual disability (ID), autism spectrum disorder (ASD), attention-deficit/hyperactivity disorder (ADHD), often coexisting with epilepsy, extra-neurological comorbidities, and multisystemic involvement. In recent years, next-generation sequencing (NGS) technologies allowed the identification of several gene pathogenic variants etiologically related to these disorders in a large cohort of affected children. These genes encode proteins involved in synaptic homeostasis, such as SNARE proteins, implicated in calcium-triggered pre-synaptic release of neurotransmitters, or channel subunit proteins, such as post-synaptic ionotropic glutamate receptors involved in the brain's fast excitatory neurotransmission. In this narrative review, we dissected emerged molecular mechanisms related to NDDs and epilepsy due to defects in pre- and post-synaptic transmission. We focused on the most recently discovered SNAREopathies and AMPA-related synaptopathies.

The phosphorylation state of PSD-95 at Serine 295 (Ser295) is important for the regulation of synaptic plasticity. Although the activation of NMDA receptors (NMDARs), which initiates an intracellular calcium signaling cascade, decreases phosphorylated Ser295 (pS295) of PSD-95, the molecular mechanisms are not fully understood. We found that the calcium-activated protein phosphatase PP2B dephosphorylated pS295 not only in basal conditions but also in NMDAR-activated conditions in cultured neurons. The biochemical assay also revealed the dephosphorylation of pS295 by PP2B, consistently supporting the results obtained using neurons. The newly identified calcium signaling cascade "Ca2+-PP2B-PSD-95 axis" would play an important role in the molecular mechanism for NMDA receptor-dependent plasticity.

Epilepsy is a chronic neurological disorder characterized by recurrent seizures. Despite various treatment approaches, a significant number of patients continue to experience uncontrolled seizures, leading to refractory epilepsy. The emergence of novel anti-epileptic drugs, such as perampanel (PER), has provided promising options for effective epilepsy treatment. However, the specific mechanisms underlying the therapeutic effects of PER remain unclear. This study aimed to investigate the intrinsic molecular regulatory mechanisms involved in the downregulation of GluA2, a key subunit of α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptors, following epileptic seizures. Primary mouse hippocampal neurons were cultured and subjected to an epilepsy cell model. The expression levels of GluA2 and autophagy-related proteins were assessed using Western blotting and real-time fluorescent quantitative PCR. Immunofluorescence and immunohistochemistry techniques were employed to investigate the nuclear translocation of CREB-regulated transcriptional coactivator 1 (CRTC1). Additionally, status epilepticus animal models were established to further validate the findings. The epilepsy cell model exhibited a significant decrease in GluA2 expression, accompanied by elevated levels of autophagy-related proteins. Immunofluorescence analysis revealed the nuclear translocation of CRTC1, which correlated with the expression of autophagy-related genes. Treatment with an autophagy inhibitor reversed the decreased expression of GluA2 in the epilepsy cell model. Furthermore, the calcium/calmodulin-dependent protein phosphatase inhibitor FK506 and CaN overexpression affected the dephosphorylation and nuclear translocation of CRTC1, consequently influencing GluA2 expression. Animal model results further supported the involvement of these molecular mechanisms in epilepsy. Our findings suggest that the downregulation of GluA2 following epileptic seizures involves the activation of autophagy and the regulation of CRTC1 nuclear translocation. These intrinsic molecular regulatory mechanisms provide potential targets for developing novel therapeutic strategies to alleviate refractory epilepsy and preserve cognitive functions in patients.

Brain connectivity arises from interactions across biophysical scales, ranging from molecular to cellular to anatomical to network level. To date, there has been little progress toward integrated analysis across these scales. To bridge this gap, from a unique cohort of 98 individuals, we collected antemortem neuroimaging and genetic data, as well as postmortem dendritic spine morphometric, proteomic and gene expression data from the superior frontal and inferior temporal gyri. Through the integration of the molecular and dendritic spine morphology data, we identified hundreds of proteins that explain interindividual differences in functional connectivity and structural covariation. These proteins are enriched for synaptic structures and functions, energy metabolism and RNA processing. By integrating data at the genetic, molecular, subcellular and tissue levels, we link specific biochemical changes at synapses to connectivity between brain regions. These results demonstrate the feasibility of integrating data from vastly different biophysical scales to provide a more comprehensive understanding of brain connectivity.

The recent advances in high throughput sequencing technology have drastically changed the practice of medical diagnosis, allowing for rapid identification of hundreds of genes causing human diseases. This unprecedented progress has made clear that most forms of intellectual disability that affect more than 3% of individuals worldwide are monogenic diseases. Strikingly, a substantial fraction of the mendelian forms of intellectual disability is associated with genes related to the ubiquitin-proteasome system, a highly conserved pathway made up of approximately 1200 genes involved in the regulation of protein homeostasis. Within this group is currently emerging a new class of neurodevelopmental disorders specifically caused by proteasome pathogenic variants which we propose to designate "neurodevelopmental proteasomopathies". Besides cognitive impairment, these diseases are typically associated with a series of syndromic clinical manifestations, among which facial dysmorphism, motor delay, and failure to thrive are the most prominent ones. While recent efforts have been made to uncover the effects exerted by proteasome variants on cell and tissue landscapes, the molecular pathogenesis of neurodevelopmental proteasomopathies remains ill-defined. In this review, we discuss the cellular changes typically induced by genomic alterations in proteasome genes and explore their relevance as biomarkers for the diagnosis, management, and potential treatment of these new rare disease entities.

Robust structural and functional plasticity occurs at excitatory synapses in the motor cortex in response to learning. It is well established that local spinogenesis and the subsequent maintenance of newly formed spines are crucial for motor learning. However, despite local synaptic inhibition being essential for shaping excitatory synaptic input, less is known about the structural rearrangement of inhibitory synapses following learning. In this study, we co-expressed the structural marker tdTomato and a mEmerald-tagged intrabody against gephyrin to visualize inhibitory synapses in layer 2/3 cortical neurons of wild-type CD1 mice. We found that a 1-day accelerated rotarod paradigm induced robust motor learning in male and female adult CD1 mice. Histological analyses revealed a significant increase in the surface area of gephyrin puncta in neurons within the motor cortex but not in the somatosensory cortex upon motor learning. Furthermore, this learning-induced reorganization of inhibitory synapses only occurred in dendritic shafts and not in the spines. These data suggest that learning induces experience-dependent remodelling of existing inhibitory synapses to fine-tune intrinsic plasticity and input-specific modulation of excitatory connections in the motor cortex.

Human-specific genes are potential drivers of brain evolution. Among them, SRGAP2C has contributed to the emergence of features characterizing human cortical synapses, including their extended period of maturation. SRGAP2C inhibits its ancestral copy, the postsynaptic protein SRGAP2A, but the synaptic molecular pathways differentially regulated in humans by SRGAP2 proteins remain largely unknown. Here, we identify CTNND2, a protein implicated in severe intellectual disability (ID) in Cri-du-Chat syndrome, as a major partner of SRGAP2. We demonstrate that CTNND2 slows synaptic maturation and promotes neuronal integrity. During postnatal development, CTNND2 moderates neuronal excitation and excitability. In adults, it supports synapse maintenance. While CTNND2 deficiency is deleterious and results in synaptic loss of SYNGAP1, another major ID-associated protein, the human-specific protein SRGAP2C, enhances CTNND2 synaptic accumulation in human neurons. Our findings suggest that CTNND2 regulation by SRGAP2C contributes to synaptic neoteny in humans and link human-specific and ID genes at the synapse.

PICK1 plays a crucial role in mammalian spermatogenesis. Here, we integrated single-molecule long-read and short-read sequencing to comprehensively examine PICK1 expression patterns in adult Baoshan pig (BS) testes. We identified the most important transcript ENSSSCT00000000120 of PICK1, obtaining its full-length coding sequence (CDS) spanning 1254 bp. Gene structure analysis located PICK1 on pig chromosome 5 with 14 exons. Protein structure analysis reflected that PICK1 consisted of 417 amino acids containing two conserved domains, PDZ and BAR_PICK1. Phylogenetic analysis underscored the evolutionary conservation and homology of PICK1 across different mammalian species. Evaluation of protein interaction network, KEGG, and GO pathways implied that interacted with 50 proteins, predominantly involved in glutamatergic synapses, amphetamine addiction, neuroactive ligand-receptor interactions, dopaminergic synapses, and synaptic vesicle recycling, and PICK1 exhibited significant correlation with DLG4 and TBC1D20. Functional annotation identified that PICK1 was involved in 9 GOs, including seven cellular components and two molecular functions. ceRNA network analysis suggested BS PICK1 was regulated by seven miRNA targets. Moreover, qPCR expression analysis across 15 tissues highlighted that PICK1 was highly expressed in the bulbourethral gland and testis. Subcellular localization analysis in ST (Swine Tesits) cells demonstrated that PICK1 significantly localized within the cytoplasm. Overall, our findings shed new light on PICK1's role in BS reproduction, providing a foundation for further functional studies of PICK1.

Palmitoylation, a lipid-based posttranslational protein modification, plays a crucial role in regulating various aspects of neuronal function through altering protein membrane-targeting, stabilities, and protein-protein interaction profiles. Disruption of palmitoylation has recently garnered attention as disease mechanism in neurodegeneration. Many proteins implicated in neurodegenerative diseases and associated neuronal dysfunction, including but not limited to amyloid precursor protein, β-secretase (BACE1), postsynaptic density protein 95, Fyn, synaptotagmin-11, mutant huntingtin, and mutant superoxide dismutase 1, undergo palmitoylation, and recent evidence suggests that altered palmitoylation contributes to the pathological characteristics of these proteins and associated disruption of cellular processes. In addition, dysfunction of enzymes that catalyze palmitoylation and depalmitoylation has been connected to the development of neurological disorders. This review highlights some of the latest advances in our understanding of palmitoylation regulation in neurodegenerative diseases and explores potential therapeutic implications.

Alzheimer's disease (AD), a multifactorial disease, is characterized by the accumulation of neurofibrillary tangles (NFTs) and amyloid beta (Aβ) plaques. AD is triggered via several factors like alteration in cytoskeletal proteins, a mutation in presenilin 1 (PSEN1), presenilin 2 (PSEN2), amyloid precursor protein (APP), and post-translational modifications (PTMs) in the cytoskeletal elements. Owing to the major structural and functional role of cytoskeletal elements, like the organization of axon initial segmentation, dendritic spines, synaptic regulation, and delivery of cargo at the synapse; modulation of these elements plays an important role in AD pathogenesis; like Tau is a microtubule-associated protein that stabilizes the microtubules, and it also causes inhibition of nucleo-cytoplasmic transportation by disrupting the integrity of nuclear pore complex. One of the major cytoskeletal elements, actin and its dynamics, regulate the dendritic spine structure and functions; impairments have been documented towards learning and memory defects. The second major constituent of these cytoskeletal elements, microtubules, are necessary for the delivery of the cargo, like ion channels and receptors at the synaptic membranes, whereas actin-binding protein, i.e., Cofilin's activation form rod-like structures, is involved in the formation of paired helical filaments (PHFs) observed in AD. Also, the glial cells rely on their cytoskeleton to maintain synaptic functionality. Thus, making cytoskeletal elements and their regulation in synaptic structure and function as an important aspect to be focused for better management and targeting AD pathology. This review advocates exploring phytochemicals and Ayurvedic plant extracts against AD by elucidating their neuroprotective mechanisms involving cytoskeletal modulation and enhancing synaptic plasticity. However, challenges include their limited bioavailability due to the poor solubility and the limited potential to cross the blood-brain barrier (BBB), emphasizing the need for targeted strategies to improve therapeutic efficacy.

The hippocampus is crucial for acquiring and retrieving episodic and contextual memories. In previous studies, the inactivation of dentate gyrus (DG) neurons by chemogenetic- and optogenetic-mediated hyperpolarization led to opposing conclusions about DG's role in memory retrieval. One study used Designer Receptors Exclusively Activated by Designer Drugs (DREADD)-mediated clozapine N-oxide (CNO)-induced hyperpolarization and reported that the previously formed memory was erased, thus concluding that denate gyrus is needed for memory maintenance. The other study used optogenetic with halorhodopsin induced hyperpolarization and reported and dentate gyrus is needed for memory retrieval. We hypothesized that this apparent discrepancy could be due to the length of hyperpolarization in previous studies; minutes by optogenetics and several hours by DREADD/CNO. Since hyperpolarization interferes with anterograde and retrograde neuronal signaling, it is possible that the memory engram in the dentate gyrus and the entorhinal to hippocampus trisynaptic circuit was erased by long-term, but not with short-term hyperpolarization. We developed and applied an advanced chemogenetic technology to selectively silence synaptic output by blocking neurotransmitter release without hyperpolarizing DG neurons to explore this apparent discrepancy. We performed in vivo electrophysiology during trace eyeblink in a rabbit model of associative learning. Our work shows that the DG output is required for memory retrieval. Based on previous and recent findings, we propose that the actively functional anterograde and retrograde neuronal signaling is necessary to preserve synaptic memory engrams along the entorhinal cortex to the hippocampal trisynaptic circuit.

Cholesterol homeostasis in neurons is critical for synapse formation and maintenance. Neurons with impaired cholesterol uptake undergo progressive synapse loss and eventual degeneration. To investigate the molecular mechanisms of neuronal cholesterol homeostasis and its role during synapse development, we studied motor neurons of Caenorhabditis elegans because these neurons rely on dietary cholesterol. Combining lipidomic analysis, we discovered that NCR-1, a lysosomal cholesterol transporter, promotes cholesterol absorption and synapse development. Loss of ncr-1 causes smaller synapses, and low cholesterol exacerbates the deficits. Moreover, NCR-1 deficiency hinders the increase in synapses under high cholesterol. Unexpectedly, NCR-2, the NCR-1 homolog, increases the use of cholesterol and sphingomyelins and impedes synapse formation. NCR-2 deficiency causes an increase in synapses regardless of cholesterol concentration. Inhibiting the degradation or synthesis of sphingomyelins can induce or suppress the synaptic phenotypes in ncr-2 mutants. Our findings indicate that neuronal cholesterol homeostasis is differentially controlled by two lysosomal cholesterol transporters and highlight the importance of neuronal cholesterol homeostasis in synapse development.

Hydrogels find widespread applications in biomedicine because of their outstanding biocompatibility, biodegradability, and tunable material properties. Hydrogels can be chemically functionalized or reinforced to respond to physical or chemical stimulation, which opens up new possibilities in the emerging field of intelligent bioelectronics. Here, the state-of-the-art in functional hydrogel-based transistors and memristors is reviewed as potential artificial synapses. Within these systems, hydrogels can serve as semisolid dielectric electrolytes in transistors and as switching layers in memristors. These synaptic devices with volatile and non-volatile resistive switching show good adaptability to external stimuli for short-term and long-term synaptic memory effects, some of which are integrated into synaptic arrays as artificial neurons; although, there are discrepancies in switching performance and efficacy. By comparing different hydrogels and their respective properties, an outlook is provided on a new range of biocompatible, environment-friendly, and sustainable neuromorphic hardware. How potential energy-efficient information storage and processing can be achieved using artificial neural networks with brain-inspired architecture for neuromorphic computing is described. The development of hydrogel-based artificial synapses can significantly impact the fields of neuromorphic bionics, biometrics, and biosensing.

The melanocortin-4 receptor (MC4R) is a G protein-coupled receptor (GPCR) that is expressed in several brain locations encompassing the hypothalamus and the brainstem, where the receptor controls several body functions, including metabolism. In a well-defined pathway to decrease appetite, hypothalamic proopiomelanocortin (POMC) neurons localized in the arcuate nucleus (Arc) project to MC4R neurons in the paraventricular nuclei (PVN) to release the natural MC4R agonist α-melanocyte-stimulating hormone (α-MSH). Arc neurons also project excitatory glutamatergic fibers to the MC4R neurons in the PVN for a fast synaptic transmission to regulate a satiety pathway potentiated by α-MSH. By using super-resolution microscopy, we found that in hypothalamic neurons in a primary culture, postsynaptic density protein 95 (PSD95) colocalizes with GluN1, a subunit of the ionotropic N-methyl-D-aspartate receptor (NMDAR). Thus, hypothalamic neurons form excitatory postsynaptic specializations. To study the MC4R distribution at these sites, tagged HA-MC4R under the synapsin promoter was expressed in neurons by adeno-associated virus (AAV) gene transduction. HA-MC4R immunofluorescence peaked at the center and in proximity to the PSD95- and NMDAR-expressing sites. These data provide morphological evidence that MC4R localizes together with glutamate receptors at postsynaptic and peri-postsynaptic sites.

The spatial distribution of proteins and their arrangement within the cellular ultrastructure regulates the opening of α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptors in response to glutamate release at the synapse. Fluorescence microscopy imaging revealed that the postsynaptic density (PSD) and scaffolding proteins in the presynaptic active zone (AZ) align across the synapse to form a trans-synaptic "nanocolumn," but the relation to synaptic vesicle release sites is uncertain. Here, we employ focused-ion beam (FIB) milling and cryoelectron tomography to image synapses under near-native conditions. Improved image contrast, enabled by FIB milling, allows simultaneous visualization of supramolecular nanoclusters within the AZ and PSD and synaptic vesicles. Surprisingly, membrane-proximal synaptic vesicles, which fuse to release glutamate, are not preferentially aligned with AZ or PSD nanoclusters. These synaptic vesicles are linked to the membrane by peripheral protein densities, often consistent in size and shape with Munc13, as well as globular densities bridging the synaptic vesicle and plasma membrane, consistent with prefusion complexes of SNAREs, synaptotagmins, and complexin. Monte Carlo simulations of synaptic transmission events using biorealistic models guided by our tomograms predict that clustering AMPARs within PSD nanoclusters increases the variability of the postsynaptic response but not its average amplitude. Together, our data support a model in which synaptic strength is tuned at the level of single vesicles by the spatial relationship between scaffolding nanoclusters and single synaptic vesicle fusion sites.

The bidirectional long-distance transport of organelles is crucial for cell body-synapse communication. However, the mechanisms by which this transport is modulated for synapse formation, maintenance, and plasticity are not fully understood. Here, we demonstrate through quantitative analyses that maintaining sensory neuron-motor neuron synapses in the Aplysia gill-siphon withdrawal reflex is linked to a sustained reduction in the retrograde transport of lysosomal vesicles in sensory neurons. Interestingly, while mitochondrial transport in the anterograde direction increases within 12 hours of synapse formation, the reduction in lysosomal vesicle retrograde transport appears three days after synapse formation. Moreover, we find that formation of new synapses during learning induced by neuromodulatory neurotransmitter serotonin further reduces lysosomal vesicle transport within 24 hours, whereas mitochondrial transport increases in the anterograde direction within one hour of exposure. Pharmacological inhibition of several signaling pathways pinpoints PKA as a key regulator of retrograde transport of lysosomal vesicles during synapse maintenance. These results demonstrate that synapse formation leads to organelle-specific and direction specific enduring changes in long-distance transport, offering insights into the mechanisms underlying synapse maintenance and plasticity.

Cortical networks exhibit complex stimulus-response patterns that are based on specific recurrent interactions between neurons. For example, the balance between excitatory and inhibitory currents has been identified as a central component of cortical computations. However, it remains unclear how the required synaptic connectivity can emerge in developing circuits where synapses between excitatory and inhibitory neurons are simultaneously plastic. Using theory and modeling, we propose that a wide range of cortical response properties can arise from a single plasticity paradigm that acts simultaneously at all excitatory and inhibitory connections-Hebbian learning that is stabilized by the synapse-type-specific competition for a limited supply of synaptic resources. In plastic recurrent circuits, this competition enables the formation and decorrelation of inhibition-balanced receptive fields. Networks develop an assembly structure with stronger synaptic connections between similarly tuned excitatory and inhibitory neurons and exhibit response normalization and orientation-specific center-surround suppression, reflecting the stimulus statistics during training. These results demonstrate how neurons can self-organize into functional networks and suggest an essential role for synapse-type-specific competitive learning in the development of cortical circuits.

Latrophilin-1 (Lphn1, aka CIRL1 and CL1; gene symbol Adgrl1) is an adhesion GPCR that has been implicated in excitatory synaptic transmission as a candidate receptor for α-latrotoxin. Here we analyzed conditional knock-in/knock-out mice for Lphn1 that contain an extracellular myc epitope tag. Mice of both sexes were used in all experiments. Surprisingly, we found that Lphn1 is localized in cultured neurons to synaptic nanoclusters that are present in both excitatory and inhibitory synapses. Conditional deletion of Lphn1 in cultured neurons failed to elicit a detectable impairment in excitatory synapses but produced a decrease in inhibitory synapse numbers and synaptic transmission that was most pronounced for synapses close to the neuronal soma. No changes in axonal or dendritic outgrowth or branching were observed. Our data indicate that Lphn1 is among the few postsynaptic adhesion molecules that are present in both excitatory and inhibitory synapses and that Lphn1 by itself is not essential for excitatory synaptic transmission but is required for some inhibitory synaptic connections.

Autism spectrum disorder (ASD) is a developmental disorder with a rising prevalence and unknown etiology presenting with deficits in cognition and abnormal behavior. We hypothesized that the investigation of the synaptic component of prefrontal cortex may provide proteomic signatures that may identify the biological underpinnings of cognitive deficits in childhood ASD. Subcellular fractions of synaptosomes from prefrontal cortices of age-, brain area-, and postmortem-interval-matched samples from children and adults with idiopathic ASD vs. controls were subjected to HPLC-tandem mass spectrometry. Analysis of data revealed the enrichment of ASD risk genes that participate in slow maturation of the postsynaptic density (PSD) structure and function during early brain development. Proteomic analysis revealed down regulation of PSD-related proteins including AMPA and NMDA receptors, GRM3, DLG4, olfactomedins, Shank1-3, Homer1, CaMK2α, NRXN1, NLGN2, Drebrin1, ARHGAP32, and Dock9 in children with autism (FDR-adjusted P < 0.05). In contrast, PSD-related alterations were less severe or unchanged in adult individuals with ASD. Network analyses revealed glutamate receptor abnormalities. Overall, the proteomic data support the concept that idiopathic autism is a synaptopathy involving PSD-related ASD risk genes. Interruption in evolutionarily conserved slow maturation of the PSD complex in prefrontal cortex may lead to the development of ASD in a susceptible individual.

NMDA receptors are Ca2+-permeable ligand-gated ion channels that mediate fast excitatory transmission in the central nervous system. NMDA receptors regulate the proliferation and differentiation of neural progenitor cells and also play critical roles in neural plasticity, memory, and learning. In addition to their physiological role, NMDA receptors are also involved in glutamate-mediated excitotoxicity, which results from excessive glutamate stimulation, leading to Ca2+ overload, and ultimately to neuronal death. Thus, NMDA receptor-mediated excitotoxicity has been linked to several neurodegenerative diseases such as Alzheimer's, Parkinson's, Huntington's, dementia, and stroke. Interestingly, in addition to its effects on cell death, aberrant expression or activation of NMDA receptors is also involved in pathological cellular proliferation, and is implicated in the invasion and proliferation of various types of cancer. These disorders are thought to be related to the contribution of NMDA receptors to cell proliferation and cell death through cell cycle modulation. This review aims to discuss the evidence implicating NMDA receptor activity in cell cycle regulation and the link between aberrant NMDA receptor activity and the development of neurodegenerative diseases and cancer due to cell cycle dysregulation. The information presented here will provide insights into the signaling pathways and the contribution of NMDA receptors to these diseases, and suggests that NMDA receptors are promising targets for the prevention and treatment of these diseases, which are leading causes of death and disability worldwide.

Alzheimer's disease remains an issue of great controversy due to its pathology. It is characterized by cognitive impairments and neuropsychiatric symptoms. The FDA approved medications for this disease, can only mitigate the symptoms. One reason for the lack of effective medications is the inaccessibility of the brain which is encompassed by the blood-brain barrier, making intranasal (IN) route of administration potentially advantageous. Male Wistar rats underwent stereotaxic surgery to induce an Alzheimer's disease model via intracerebroventricular (ICV) streptozotocin injection, and Carbamylated Erythropoietin-Fc (CEPO-FC), a derivative of Erythropoietin without its harmful characteristics, was administered intranasally for ten consecutive days. Cognition performance for memory and attention was assessed using the Novel Object Recognition Test and the Object-Based Attention Test respectively. Depression like behavior was evaluated using the Forced Swim Test. Western blotting was done on the extracted hippocampus to quantify STIM proteins. Calbindin, PSD-95, Neuroplastin, Synaptophysin and GAP-43 genes were assessed by Realtime PCR. Behavioral tests demonstrated that IN CEPO-FC could halt cognition deficits and molecular investigations showed that, STIM proteins were decreased in Alzheimer's model, and increased after IN CEPO-FC treatment. Calbindin and PSD-95 were downregulated in our disease model and upregulated when treated with IN CEPO-FC. While Neuroplastin, and GAP-43 expressions remained unchanged. This study suggests that IN CEPO-FC in low doses could be promising for improving cognition and synaptic plasticity deficits in Alzheimer's disease and since IN route of administration is a convenient way, choosing IN CEPO-FC for clinical trial might worth consideration. See also the graphical abstract(Fig. 1).

Encystment is a natural process that involves cyst formation, and at least some species of tardigrades can form cysts. However, the encystment process and cyst structure among tardigrades are still poorly understood. Despite some aspects of the encysted animals' systems organisation being examined in the past, the morphology and structure of the nervous system have never been thoroughly investigated. This study covers anatomical, histological and morphological details and proposes physiological aspects of the nervous system in encysted Thulinius ruffoi up to 11 months duration in encystment. This is the first record of the nervous system organisation in a species belonging to the family Doryphoribiidae. The cyst formation results in morphological changes in the nervous system. It comprises central and peripheral elements, which may be observable even after many months since the cyst formation. Based on the nervous system's organisation in cysts, there is no sign that histolysis is a part of encystment.

The postsynaptic density protein of excitatory neurons PSD-95 is encoded by discs large MAGUK scaffold protein 4 (DLG4), de novo pathogenic variants of which lead to DLG4-related synaptopathy. The major clinical features are developmental delay, intellectual disability (ID), hypotonia, sleep disturbances, movement disorders, and epilepsy. Even though epilepsy is present in 50% of the individuals, it has not been investigated in detail. We describe here the phenotypic spectrum of epilepsy and associated comorbidities in patients with DLG4-related synaptopathy.

We included 35 individuals with a DLG4 variant and epilepsy as part of a multicenter study. The DLG4 variants were detected by the referring laboratories. The degree of ID, hypotonia, developmental delay, and motor disturbances were evaluated by the referring clinician. Data on awake and sleep electroencephalography (EEG) and/or video-polygraphy and brain magnetic resonance imaging were collected. Antiseizure medication response was retrospectively assessed by the referring clinician.

A large variety of seizure types was reported, although focal seizures were the most common. Encephalopathy related to status epilepticus during slow-wave sleep (ESES)/developmental epileptic encephalopathy with spike-wave activation during sleep (DEE-SWAS) was diagnosed in >25% of the individuals. All but one individual presented with neurodevelopmental delay. Regression in verbal and/or motor domains was observed in all individuals who suffered from ESES/DEE-SWAS, as well as some who did not. We could not identify a clear genotype-phenotype relationship even between individuals with the same DLG4 variants.

Our study shows that a subgroup of individuals with DLG4-related synaptopathy have DEE, and approximately one fourth of them have ESES/DEE-SWAS. Our study confirms DEE as part of the DLG4-related phenotypic spectrum. Occurrence of ESES/DEE-SWAS in DLG4-related synaptopathy requires proper investigation with sleep EEG.

Angelica Sinensis Radix (ASR) is a commonly used Chinese medicine known for its effects on tonifying blood, promoting blood circulation, and alleviating pain associated with menstrual regulation. Additionally, it has been used in the treatment of vascular cognitive impairment (VCI). The primary pharmacodynamic agent within ASR is volatile oil of Angelica Sinensis Radix (VOASR), which has demonstrated efficacy in combating cognitive impairment, although its mechanism remains unclear.

This study aimed to elucidate the potential molecular mechanisms underlying VOASR's improvement of cognitive function in cerebral ischemic mice.

A model of cerebral ischemic mice was established through unilateral common carotid artery occlusion (UCCAO) surgery, followed by intervention with VOASR. Cognitive function was assessed using the Morris water maze (MWM) test, while RT-qPCR was utilized to measure the differential expression of miR-301a-3p in the hippocampus. To evaluate cognitive function and hippocampal protein differences, wild-type mice and miR-301a-3p knockout mice were subjected to the MWM test and iTRAQ protein profiling. The relationship between miR-301a-3p and potential target genes was validated through a Dual-Luciferase Reporter experiment. RT-qPCR and Western blot were employed to determine the differential expression of Ppp2ca and synaptic plasticity-related proteins in the mouse hippocampus.

Intervention with VOASR significantly improved cognitive impairment in cerebral ischemic mice and reduced the expression of miR-301a-3p in the hippocampus. Our findings suggest that miR-301a-3p may regulate cognitive function by targeting Ppp2ca. Furthermore, VOASR intervention led to an increase in the expression of Ppp2ca and synaptic plasticity-related proteins.

Our study indicates that VOASR may be involved in regulating cognitive function by inhibiting miR-301a-3p, consequently increasing the expression of Ppp2ca and synaptic plasticity proteins. These results provide a new target and direction for the treatment of cognitive dysfunction.

Ubiquitin modifications alter protein function and stability, thereby regulating cell homeostasis and viability, particularly under stress. Ischemic stroke induces protein ubiquitination at the ischemic periphery, wherein cells remain viable, however the identity of ubiquitinated proteins is unknown. Here, we employed a proteomics approach to identify these proteins in mice undergoing ischemic stroke. The data are available in a searchable web interface ( https://hochrainerlab.shinyapps.io/StrokeUbiOmics/ ). We detected increased ubiquitination of 198 proteins, many of which localize to the postsynaptic density (PSD) of glutamatergic neurons. Among these were proteins essential for maintaining PSD architecture, such as PSD95, as well as NMDA and AMPA receptor subunits. The largest enzymatic group at the PSD with elevated post-ischemic ubiquitination were kinases, such as CaMKII, PKC, Cdk5, and Pyk2, whose aberrant activities are well-known to contribute to post-ischemic neuronal death. Concurrent phospho-proteomics revealed altered PSD-associated phosphorylation patterns, indicative of modified kinase activities following stroke. PSD-located CaMKII, PKC, and Cdk5 activities were decreased while Pyk2 activity was increased after stroke. Removal of ubiquitin restored kinase activities to pre-stroke levels, identifying ubiquitination as the responsible molecular mechanism for post-ischemic kinase regulation. These findings unveil a previously unrecognized role of ubiquitination in the regulation of essential kinases involved in ischemic injury.