Molecular architecture of postsynaptic Interactomes

Multifaceted roles of DLG3/SAP102 in neurophysiology, neurological disorders and tumorigenesis

DLG3, also known as Synapse-associated protein 102 (SAP102), is essential for the organization and plasticity of excitatory synapses within the central nervous system (CNS). It plays a critical role in clustering and moving key components necessary for learning and memory processes. Mutations in the DLG3 gene, which result in truncated SAP102 proteins, have been associated with a range of neurological disorders, including X-linked intellectual disability (XLID), autism spectrum disorders (ASD), and schizophrenia, all of which can disrupt synaptic structure and cognitive functions. Abnormal SAP102 expression has also been linked to various psychiatric and neurodegenerative conditions, such as bipolar disorder, major depression, and Alzheimer's disease. Recent studies suggest that SAP102 influences cancer development and metastasis by regulating multiple signaling pathways, including the PI3K/AKT axis and the Hippo pathway. Moreover, SAP102 has been demonstrated to regulate tumor-induced bone pain through activating NMDA receptors. These findings highlight SAP102 as a promising therapeutic target for both neurological disorders and cancer. Therefore, further investigation into the regulatory roles of SAP102 in neural development and disease may lead to novel therapeutic approaches for treating synaptic disorders and managing cancer progression.

Genome-wide association study identifies DRAM1 associated with Tourette syndrome in Taiwan

BACKGROUND

Tourette syndrome (TS) is a neurodevelopmental disorder characterized by motor and vocal tics. Several susceptibility loci associated with TS have been identified previously in populations of European descent using genome-wide association studies (GWAS). However, the exact pathogenic mechanism underlying TS is unknown; additionally, the results of previous GWAS for TS were based on Western populations, which may not translate to other populations. Therefore, we conducted a GWAS in Taiwanese patients with TS and chronic tic disorders (CTDs), with an aim to elucidate the genetic basis and potential risk factors for TS in this population.

METHODS

GWAS was performed on a Taiwanese TS/CTDs cohort with a sample size of 1007 patients with TS and 25,522 ancestry-matched controls. Additionally, polygenic risk score was calculated and assessed.

RESULTS

Genome-wide significant locus, rs12313062 (p = 1.43 × 10-8) and other 9 single nucleotide polymorphisms, were identified in chromosomes 12q23.2, associated with DRAM1 and was a novel susceptibility locus identified in TS/CTDs group. DRAM1, a lysosomal transmembrane protein regulated by p53, modulates autophagy and apoptosis, with potential implications for neuropsychiatric conditions associated with autophagy disruption.

CONCLUSIONS

This study conducted the first GWAS for TS in a Taiwanese population, identifying a significant locus on chromosome 12q23.2 associated with DRAM1. These findings provide novel insights into the neurobiology of TS and potential directions for future research in this area.

A trans-synaptic IgLON adhesion molecular complex directly contacts and clusters a nicotinic receptor

The localization and clustering of neurotransmitter receptors at appropriate postsynaptic sites is a key step in the control of synaptic transmission. Here, we identify a novel paradigm for the synaptic localization of an ionotropic acetylcholine receptor (AChR) based on the direct interaction of its extracellular domain with a cell adhesion molecule of the IgLON family. Our results show that RIG-5 and ZIG-8, which encode the sole IgLONs in C. elegans, are tethered in the pre- and postsynaptic membranes, respectively, and interact in vivo through their first immunoglobulin-like (Ig) domains. In addition, ZIG-8 traps ACR-16 via a direct cis- interaction between the ZIG-8 Ig2 domain and the base of the large extracellular AChR domain. Such mechanism has never been reported, but all these molecules are conserved during evolution. Similar interactions may directly couple Ig superfamily adhesion molecules and members of the large family of Cys-loop ionotropic receptors, including AChRs, in the mammalian nervous system, and may be relevant in the context of IgLON-associated brain diseases.

Perinatal stress modulates glutamatergic functional connectivity: A post-synaptic density immediate early gene-based network analysis

Early life stress may induce synaptic changes within brain regions associated with behavioral disorders. Here, we investigated glutamatergic functional connectivity by a postsynaptic density immediate-early gene-based network analysis. Pregnant female Sprague-Dawley rats were randomly divided into two experimental groups: one exposed to stress sessions and the other serving as a stress-free control group. Homer1 expression was evaluated by in situ hybridization technique in eighty-eight brain regions of interest of male rat offspring. Differences between the perinatal stress exposed group (PRS) (n = 5) and the control group (CTR) (n = 5) were assessed by performing the Student's t-test via SPSS 28.0.1.0 with Bonferroni correction. Additionally, all possible pairwise Spearman's correlations were computed as well as correlation matrices and networks for each experimental group were generated via RStudio and Cytoscape. Perinatal stress exposure was associated with Homer1a reduction in several cortical, thalamic, and striatal regions. Furthermore, it was found to affect functional connectivity between: the lateral septal nucleus, the central medial thalamic nucleus, the anterior part of the paraventricular thalamic nucleus, and both retrosplenial granular b cortex and hippocampal regions; the orbitofrontal cortex, amygdaloid nuclei, and hippocampal regions; and lastly, among regions involved in limbic system. Finally, the PRS networks showed a significant reduction in multiple connections for the ventrolateral part of the anteroventral thalamic nucleus after perinatal stress exposure, as well as a decrease in the centrality of ventral anterior thalamic and amygdaloid nuclei suggestive of putative reduced cortical control over these regions. Within the present preclinical setting, perinatal stress exposure is a modifier of glutamatergic early gene-based functional connectivity in neuronal circuits involved in behaviors relevant to model neurodevelopmental disorders.

The NMDA receptor modulator zelquistinel durably relieves behavioral deficits in three mouse models of autism spectrum disorder

Autism spectrum disorders (ASD) are complex neurodevelopmental disorders characterized by deficient social communication and interaction together with restricted, stereotyped behaviors. Currently approved treatments relieve comorbidities rather than core symptoms. Since excitation/inhibition balance and synaptic plasticity are disrupted in ASD, molecules targeting excitatory synaptic transmission appear as highly promising candidates to treat this pathology. Among glutamatergic receptors, the NMDA receptor has received particular attention through the last decade to develop novel allosteric modulators. Here, we show that positive NMDA receptor modulation by zelquistinel, a spirocyclic β-lactam platform chemical, relieves core symptoms in two genetic and one environmental mouse models of ASD. A single oral dose of zelquistinel rescued, in a dose-response manner, social deficits and stereotypic behavior in Shank3Δex13-16-/- mice while chronic intraperitoneal administration promoted a long-lasting relief of such autistic-like features in these mice. Subchronic oral mid-dose zelquistinel treatment demonstrated durable effects in Shank3Δex13-16-/-, Fmr1-/- and in utero valproate-exposed mice. Carry-over effects were best maintained in the Fmr1 null mouse model, with social parameters being still fully recovered two weeks after treatment withdrawal. Among recently developed NMDA receptor subunit modulators, zelquistinel displays a promising therapeutic potential to relieve core symptoms in ASD patients, with oral bioavailability and long-lasting effects boding well for clinical applications. Efficacy in three mouse models with different etiologies supports high translational value. Further, this compound represents an innovative pharmacological tool to investigate plasticity mechanisms underlying behavioral deficits in animal models of ASD.

Mutations in the postsynaptic density signaling hub TNIK disrupt PSD signaling in human models of neurodevelopmental disorders

A large number of synaptic proteins have been recurrently associated with complex brain disorders. One of these proteins, the Traf and Nck interacting kinase (TNIK), is a postsynaptic density (PSD) signaling hub, with many variants reported in neurodevelopmental disorder (NDD) and psychiatric disease. While rodent models of TNIK dysfunction have abnormal spontaneous synaptic activity and cognitive impairment, the role of mutations found in patients with TNIK protein deficiency and TNIK protein kinase activity during early stages of neuronal and synapse development has not been characterized. Here, using hiPSC-derived excitatory neurons, we show that TNIK mutations dysregulate neuronal activity in human immature synapses. Moreover, the lack of TNIK protein kinase activity impairs MAPK signaling and protein phosphorylation in structural components of the PSD. We show that the TNIK interactome is enriched in NDD risk factors and TNIK lack of function disrupts signaling networks and protein interactors associated with NDD that only partially overlap to mature mouse synapses, suggesting a differential role of TNIK in immature synapsis in NDD.

FAM81A is a postsynaptic protein that regulates the condensation of postsynaptic proteins via liquid-liquid phase separation

Proteome analyses of the postsynaptic density (PSD), a proteinaceous specialization beneath the postsynaptic membrane of excitatory synapses, have identified several thousands of proteins. While proteins with predictable functions have been well studied, functionally uncharacterized proteins are mostly overlooked. In this study, we conducted a comprehensive meta-analysis of 35 PSD proteome datasets, encompassing a total of 5,869 proteins. Employing a ranking methodology, we identified 97 proteins that remain inadequately characterized. From this selection, we focused our detailed analysis on the highest-ranked protein, FAM81A. FAM81A interacts with PSD proteins, including PSD-95, SynGAP, and NMDA receptors, and promotes liquid-liquid phase separation of those proteins in cultured cells or in vitro. Down-regulation of FAM81A in cultured neurons causes a decrease in the size of PSD-95 puncta and the frequency of neuronal firing. Our findings suggest that FAM81A plays a crucial role in facilitating the interaction and assembly of proteins within the PSD, and its presence is important for maintaining normal synaptic function. Additionally, our methodology underscores the necessity for further characterization of numerous synaptic proteins that still lack comprehensive understanding.

Advancements in the study of synaptic plasticity and mitochondrial autophagy relationship

Synapses serve as the points of communication between neurons, consisting primarily of three components: the presynaptic membrane, synaptic cleft, and postsynaptic membrane. They transmit signals through the release and reception of neurotransmitters. Synaptic plasticity, the ability of synapses to undergo structural and functional changes, is influenced by proteins such as growth-associated proteins, synaptic vesicle proteins, postsynaptic density proteins, and neurotrophic growth factors. Furthermore, maintaining synaptic plasticity consumes more than half of the brain's energy, with a significant portion of this energy originating from ATP generated through mitochondrial energy metabolism. Consequently, the quantity, distribution, transport, and function of mitochondria impact the stability of brain energy metabolism, thereby participating in the regulation of fundamental processes in synaptic plasticity, including neuronal differentiation, neurite outgrowth, synapse formation, and neurotransmitter release. This article provides a comprehensive overview of the proteins associated with presynaptic plasticity, postsynaptic plasticity, and common factors between the two, as well as the relationship between mitochondrial energy metabolism and synaptic plasticity.

A Systematic Compilation of Human SH3 Domains: A Versatile Superfamily in Cellular Signaling

SRC homology 3 (SH3) domains are fundamental modules that enable the assembly of protein complexes through physical interactions with a pool of proline-rich/noncanonical motifs from partner proteins. They are widely studied modular building blocks across all five kingdoms of life and viruses, mediating various biological processes. The SH3 domains are also implicated in the development of human diseases, such as cancer, leukemia, osteoporosis, Alzheimer's disease, and various infections. A database search of the human proteome reveals the existence of 298 SH3 domains in 221 SH3 domain-containing proteins (SH3DCPs), ranging from 13 to 720 kilodaltons. A phylogenetic analysis of human SH3DCPs based on their multi-domain architecture seems to be the most practical way to classify them functionally, with regard to various physiological pathways. This review further summarizes the achievements made in the classification of SH3 domain functions, their binding specificity, and their significance for various diseases when exploiting SH3 protein modular interactions as drug targets.

Postsynaptic Proteins at Excitatory Synapses in the Brain—Relationship with Depressive Disorders

Depressive disorders (DDs) are an increasingly common health problem that affects all age groups. DDs pathogenesis is multifactorial. However, it was proven that stress is one of the most important environmental factors contributing to the development of these conditions. In recent years, there has been growing interest in the role of the glutamatergic system in the context of pharmacotherapy of DDs. Thus, it has become increasingly important to explore the functioning of excitatory synapses in pathogenesis and pharmacological treatment of psychiatric disorders (including DDs). This knowledge may lead to the description of new mechanisms of depression and indicate new potential targets for the pharmacotherapy of illness. An excitatory synapse is a highly complex and very dynamic structure, containing a vast number of proteins. This review aimed to discuss in detail the role of the key postsynaptic proteins (e.g., NMDAR, AMPAR, mGluR5, PSD-95, Homer, NOS etc.) in the excitatory synapse and to systematize the knowledge about changes that occur in the clinical course of depression and after antidepressant treatment. In addition, a discussion on the potential use of ligands and/or modulators of postsynaptic proteins at the excitatory synapse has been presented.

The Homer1 family of proteins at the crossroad of dopamine-glutamate signaling: An emerging molecular "Lego" in the pathophysiology of psychiatric disorders. A systematic review and translational insight

Once considered only scaffolding proteins at glutamatergic postsynaptic density (PSD), Homer1 proteins are increasingly emerging as multimodal adaptors that integrate different signal transduction pathways within PSD, involved in motor and cognitive functions, with putative implications in psychiatric disorders. Regulation of type I metabotropic glutamate receptor trafficking, modulation of calcium signaling, tuning of long-term potentiation, organization of dendritic spines' growth, as well as meta- and homeostatic plasticity control are only a few of the multiple endocellular and synaptic functions that have been linked to Homer1. Findings from preclinical studies, as well as genetic studies conducted in humans, suggest that both constitutive (Homer1b/c) and inducible (Homer1a) isoforms of Homer1 play a role in the neurobiology of several psychiatric disorders, including psychosis, mood disorders, neurodevelopmental disorders, and addiction. On this background, Homer1 has been proposed as a putative novel target in psychopharmacological treatments. The aim of this review is to summarize and systematize the growing body of evidence on Homer proteins, highlighting the role of Homer1 in the pathophysiology and therapy of mental diseases.

Expression analyses of Cep152, a responsible gene product for autosomal recessive primary microcephaly, during mouse brain development

Centrosomal protein 152 (Cep152) regulates centriole duplication as a molecular scaffold during the cell cycle. Its gene abnormalities are responsible for autosomal recessive primary microcephaly 9 (MCPH9) and Seckel syndrome. In this study, we prepared an antibody against mouse Cep152, anti-Cep152, and performed expression analyses focusing on mouse brain development. Western blotting analyses revealed that Cep152 with a molecular mass of ~150 kDa was expressed strongly at embryonic day (E) 13 and then gradually decreased during the brain development process. Instead, protein bands of ~80 kDa and ~60 kDa came to be recognized after postnatal day (P)15 and P30, respectively. In immunohistochemical analyses, Cep152 was enriched in the centrosome of neuronal progenitors in the ventricular zone at E14, whereas it was diffusely distributed mainly in the cytoplasm of cortical neurons at P18. In developing cerebellum at P7, Cep152 was localized at the centrosome in the external granular layer, where neurogenesis takes place. Notably, biochemical analysis revealed that Cep152 was also present in the post-synaptic density fraction. Subsequent immunofluorescent analyses showed co-localization of Cep152 with excitatory synaptic markers, PSD-95 and synaptophysin, but not with an inhibitory synaptic marker gephyrin in differentiated primary cultured hippocampal neurons. The obtained results suggest that Cep152 takes part not only in neurogenesis during corticogenesis but also in the regulation of synaptic function in differentiated neurons.

Targeted NMDA Receptor Interventions for Autism: Developmentally Determined Expression of GluN2B and GluN2A-Containing Receptors and Balanced Allosteric Modulatory Approaches

Various ASD risk alleles have been associated with impairment of NMDA receptor activation (i.e., NMDA Receptor Hypofunction) and/or disturbance of the careful balance between activation mediated by GluN2B-subtype and GluN2A-subtype-containing NMDA receptors. Importantly, although these various risk alleles affect NMDA receptor activation through different mechanisms, they share the pathogenic consequences of causing disturbance of highly regulated NMDA receptor activation. Disturbances of NMDA receptor activation due to sequence variants, protein termination variants and copy number variants are often cell-specific and regionally selective. Thus, translational therapeutic NMDA receptor agonist interventions, which may require chronic administration, must have specificity, selectivity and facilitate NMDA receptor activation in a manner that is physiologic (i.e., mimicking that of endogenously released glutamate and glycine/D-serine released in response to salient and relevant socio-cognitive provocations within discrete neural circuits). Importantly, knockout mice with absent expression and mice with haploinsufficient expression of the deleterious genes often serve as good models to test the potential efficacy of promising pharmacotherapeutic strategies. The Review considers diverse examples of “illness” genes, their pathogenic effects on NMDA receptor activation and, when available, results of studies of impaired sociability in mouse models, including “proof of principle/proof of concept” experiments exploring NMDA receptor agonist interventions and the development of promising positive allosteric modulators (PAMs), which serve as support and models for developing an inventory of PAMs and negative allosteric modulators (NAMs) for translational therapeutic intervention. Conceivably, selective PAMs and NAMs either alone or in combination will be administered to patients guided by their genotype in order to potentiate and/or restore disrupted balance between activation mediated by GluN2B-subtype and GluN2A-subtype containing NMDA receptors.

Structural properties and peptide ligand binding of the capsid homology domains of human Arc

The activity-regulated cytoskeleton-associated protein (Arc) is important for synaptic plasticity and the normal function of the brain. Arc interacts with neuronal postsynaptic proteins, but the mechanistic details of its function have not been fully established. The C-terminal domain of Arc consists of tandem domains, termed the N- and C-lobe. The N-lobe harbours a peptide binding site, able to bind multiple targets. By measuring the affinity of human Arc towards various peptides from stargazin and guanylate kinase-associated protein (GKAP), we have refined its specificity determinants. We found two sites in the GKAP repeat region that bind to Arc and confirmed these interactions by X-ray crystallography. Phosphorylation of the stargazin peptide did not affect binding affinity but caused changes in thermodynamic parameters. Comparison of the crystal structures of three high-resolution human Arc-peptide complexes identifies three conserved C-H…π interactions at the binding cavity, explaining the sequence specificity of short linear motif binding by Arc. We further characterise central residues of the Arc lobe fold, show the effects of peptide binding on protein dynamics, and identify acyl carrier proteins as structures similar to the Arc lobes. We hypothesise that Arc may affect protein-protein interactions and phase separation at the postsynaptic density, affecting protein turnover and re-modelling of the synapse. The present data on Arc structure and ligand binding will help in further deciphering these processes.