Kif15 deficiency contributes to depression-like behavior in mice.

Neuropsychiatric disorders have a high incidence worldwide. Kinesins, a family of microtubule-based molecular motor proteins, play essential roles in intracellular and axonal transport. Variants of kinesins have been found to be related to many diseases, including neurodevelopmental/neurodegenerative disorders. Kinesin-12 (also known as Kif15) was previously found to affect the frequency of both directional microtubule transports. However, whether Kif15 deficiency impacts mood in mice is yet to be investigated. In this study, we used the CRISPR/Cas9 method to obtain Kif15-/- mice. In behavioral tests, Kif15-/- female mice exhibited prominent depressive characteristics. Further studies showed that the expression of BDNF was significantly decreased in the frontal cortex, corpus callosum, and hippocampus of Kif15-/- mice, along with the upregulation of Interleukin-6 and Interleukin-1ß in the corpus callosum. In addition, the expression patterns of AnkG were notably changed in the developing brain of Kif15-/- mice. Based on our previous studies, we suggested that this appearance of altered AnkG was due to the maladjustment of the microtubule patterns induced by Kif15 deficiency. The distribution of PSD95 in neurites notably decreased after cultured neurons treated with the Kif15 inhibitor, but total PSD95 protein level was not impacted, which revealed that Kif15 may contribute to PSD95 transportation. This study suggested that Kif15 may serve as a potential target for future depression studies.

[Effect of Xiaoxuming Decoction on synaptic plasticity following acute cerebral ischemia-reperfusion in rats].

This study aims to explore the effect of Xiaoxuming Decoction on synaptic plasticity in rats with acute cerebral ischemia-reperfusion. A rat model of cerebral ischemia-reperfusion injury was established by middle cerebral artery occlusion(MCAO). Rats were randomly assigned into a sham group, a MCAO group, and a Xiaoxuming Decoction(60 g·kg~(-1)·d~(-1)) group. The Longa score was rated to assess the neurological function of rats with cerebral ischemia for 1.5 h and reperfusion for 24 h. The 2,3,5-triphenyltetrazolium chloride(TTC) staining and hematoxylin-eosin(HE) staining were employed to observe the cerebral infarction and the pathological changes of brain tissue after cerebral ischemia, respectively. Transmission electron microscopy was employed to detect the structural changes of neurons and synapses in the ischemic penumbra, and immunofluorescence, Western blot to determine the expression of synaptophysin(SYN), neuronal nuclei(NEUN), and postsynaptic density 95(PSD95) in the ischemic penumbra. The experimental results showed that the modeling increased the Longa score and led to cerebral infarction after 24 h of ischemia-reperfusion. Compared with the model group, Xiaoxuming Decoction intervention significantly decreased the Longa score and reduced the formation of cerebral infarction area. The modeling led to the shrinking and vacuolar changes of nuclei in the brain tissue, disordered cell arrangement, and severe cortical ischemia-reperfusion injury, while the pathological damage in the Xiaoxuming Decoction group was mild. The modeling blurred the synaptic boundaries and broadened the synaptic gap, while such changes were recovered in the Xiaoxuming Decoction group. The modeling decreased the fluorescence intensity of NEUN and SYN, while the intensity in Xiaoxuming Decoction group was significantly higher than that in the model group. The expression of SYN and PSD95 in the ischemic penumbra was down-regulated in the model group, while such down-regulation can be alleviated by Xiaoxuming Decoction. In summary, Xiaoxuming Decoction may improve the synaptic plasticity of ischemic penumbra during acute cerebral ischemia-reperfusion by up-regulating the expression of SYN and PSD95.

LOTUS suppresses amyloid ß-induced dendritic spine elimination through the blockade of amyloid ß binding to PirB.

BACKGROUND: Alzheimer's disease (AD) is the most common neurodegenerative disease worldwide but has no effective treatment. Amyloid beta (Aß) protein, a primary risk factor for AD, accumulates and aggregates in the brain of patients with AD. Paired immunoglobulin-like receptor B (PirB) has been identified as a receptor of Aß and Aß-PirB molecular interactions that cause synapse elimination and synaptic dysfunction. PirB deletion has been shown to suppress Aß-induced synaptic dysfunction and behavioral deficits in AD model mice, implying that PirB mediates Aß-induced AD pathology. Therefore, inhibiting the Aß-PirB molecular interaction could be a successful approach for combating AD pathology. We previously showed that lateral olfactory tract usher substance (LOTUS) is an endogenous antagonist of type1 Nogo receptor and PirB and that LOTUS overexpression promotes neuronal regeneration following damage to the central nervous system, including spinal cord injury and ischemic stroke. Therefore, in this study, we investigated whether LOTUS inhibits Aß-PirB interaction and Aß-induced dendritic spine elimination. METHODS: The inhibitory role of LOTUS against Aß-PirB (or leukocyte immunoglobulin-like receptor subfamily B member 2: LilrB2) binding was assessed using a ligand-receptor binding assay in Cos7 cells overexpressing PirB and/or LOTUS. We assessed whether LOTUS inhibits Aß-induced intracellular alterations and synaptotoxicity using immunoblots and spine imaging in a primary cultured hippocampal neuron. RESULTS: We found that LOTUS inhibits the binding of Aß to PirB overexpressed in Cos7 cells. In addition, we found that Aß-induced dephosphorylation of cofilin and Aß-induced decrease in post-synaptic density-95 expression were suppressed in cultured hippocampal neurons from LOTUS-overexpressing transgenic (LOTUS-tg) mice compared with that in wild-type mice. Moreover, primary cultured hippocampal neurons from LOTUS-tg mice improved the Aß-induced decrease in dendritic spine density. Finally, we studied whether human LOTUS protein inhibits Aß binding to LilrB2, a human homolog of PirB, and found that human LOTUS inhibited the binding of Aß to LilrB2 in a similar manner. CONCLUSIONS: This study implied that LOTUS improved Aß-induced synapse elimination by suppressing Aß-PirB interaction in rodents and inhibited Aß-LilrB2 interaction in humans. Our findings revealed that LOTUS may be a promising therapeutic agent in counteracting Aß-induced AD pathologies.

An Overview of the Main Genetic, Epigenetic and Environmental Factors Involved in Autism Spectrum Disorder Focusing on Synaptic Activity.

Autism spectrum disorder (ASD) is a neurodevelopmental disorder that affects social interaction and communication, with restricted interests, activity and behaviors. ASD is highly familial, indicating that genetic background strongly contributes to the development of this condition. However, only a fraction of the total number of genes thought to be associated with the condition have been discovered. Moreover, other factors may play an important role in ASD onset. In fact, it has been shown that parental conditions and in utero and perinatal factors may contribute to ASD etiology. More recently, epigenetic changes, including DNA methylation and micro RNA alterations, have been associated with ASD and proposed as potential biomarkers. This review aims to provide a summary of the literature regarding ASD candidate genes, mainly focusing on synapse formation and functionality and relevant epigenetic and environmental aspects acting in concert to determine ASD onset.

Alterations in CA1 hippocampal synapses in a mouse model of fragile X syndrome.

Fragile X Syndrome (FXS) is the major cause of inherited mental retardation and the leading genetic cause of Autism spectrum disorders. FXS is caused by mutations in the Fragile X Mental Retardation 1 (Fmr1) gene, which results in transcriptional silencing of Fragile X Mental Retardation Protein (FMRP). To elucidate cellular mechanisms involved in the pathogenesis of FXS, we compared dendritic spines in the hippocampal CA1 region of adult wild-type (WT) and Fmr1 knockout (Fmr1-KO) mice. Using diolistic labeling, confocal microscopy, and three-dimensional electron microscopy, we show a significant increase in the diameter of secondary dendrites, an increase in dendritic spine density, and a decrease in mature dendritic spines in adult Fmr1-KO mice. While WT and Fmr1-KO mice had the same mean density of spines, the variance in spine density was three times greater in Fmr1-KO mice. Reduced astrocyte participation in the tripartite synapse and less mature post-synaptic densities were also found in Fmr1-KO mice. We investigated whether the increase in synaptic spine density was associated with altered synaptic pruning during development. Our data are consistent with reduced microglia-mediated synaptic pruning in the CA1 region of Fmr1-KO hippocampi when compared with WT littermates at postnatal day 21, which is the peak period of synaptic pruning in the mouse hippocampus. Collectively, these results support abnormal synaptogenesis and synaptic remodeling in mice deficient in FMRP. Deficits in the maturation and distribution of synaptic spines on dendrites of CA1 hippocampal neurons may play a role in the intellectual disabilities associated with FXS.

The catalytic function of the gephyrin-binding protein IQSEC3 regulates neurotransmitter-specific matching of pre- and post-synaptic structures in primary hippocampal cultures.

In dissociated neuronal cultures the absence of spatial and temporal cues causes the emergence of mismatched synapses, where post-synaptic proteins of GABAergic synapses are in part apposed to glutamatergic pre-synaptic terminals and vice versa. This mismatch offers an opportunity to study the mechanisms that regulate correct apposition of pre- and post-synaptic elements. We report here that the IQ motif and Sec7 domain-containing protein 3 (IQSEC3; BRAG3; synArfGEF) specifically regulates the mislocalization of GABAergic post-synaptic density (PSD) proteins. Over-expression of IQSEC3 constructs harboring mutations that ablate Sec7 domain or IQ motif function revealed that IQSEC3 catalytic activity is involved in the control of apposition between the GABAergic PSD and glutamatergic terminals. Neurons co-expressing eGFP-gephyrin with IQSEC3 Sec7 mutant displayed a drastically increased fraction of mismatched eGFP-gephyrin clusters compared to other IQSEC3 constructs. Along with eGFP-gephyrin, endogenous GABAA receptor cluster mismatching was increased by IQSEC3 Sec7 mutant over-expression. Conversely, GFP-PSD-95 clusters were unaffected by over-expression of any IQSEC3 construct. The GABAergic PSD mismatch phenotype was recapitulated by Arf6 dominant-negative mutant over-expression, suggesting that Arf6 activation by IQSEC3 is an essential step in this pathway. In addition, we provide biochemical evidence to confirm gephyrin/IQSEC3 interaction near the IQSEC3 IQ motif, which in turn binds calmodulin at low Ca2+ concentrations. Taken together, our findings identify a post-synaptic protein which specifically regulates correct apposition of the GABAergic PSD to pre-synaptic terminals.

Protein components of post-synaptic density lattice, a backbone structure for type I excitatory synapses.

It is essential to study the molecular architecture of post-synaptic density (PSD) to understand the molecular mechanism underlying the dynamic nature of PSD, one of the bases of synaptic plasticity. A well-known model for the architecture of PSD of type I excitatory synapses basically comprises of several scaffolding proteins (scaffold protein model). On the contrary, 'PSD lattice' observed through electron microscopy has been considered a basic backbone of type I PSDs. However, major constituents of the PSD lattice and the relationship between the PSD lattice and the scaffold protein model, remain unknown. We purified a PSD lattice fraction from the synaptic plasma membrane of rat forebrain. Protein components of the PSD lattice were examined through immuno-gold negative staining electron microscopy. The results indicated that tubulin, actin, α-internexin, and Ca2+ /calmodulin-dependent kinase II are major constituents of the PSD lattice, whereas scaffold proteins such as PSD-95, SAP102, GKAP, Shank1, and Homer, were rather minor components. A similar structure was also purified from the synaptic plasma membrane of forebrains from 7-day-old rats. On the basis of this study, we propose a 'PSD lattice-based dynamic nanocolumn' model for PSD molecular architecture, in which the scaffold protein model and the PSD lattice model are combined and an idea of dynamic nanocolumn PSD subdomain is also included. In the model, cytoskeletal proteins, in particular, tubulin, actin, and α-internexin, may play major roles in the construction of the PSD backbone and provide linker sites for various PSD scaffold protein complexes/subdomains.

Structural basis for PDZ domain interactions in the post-synaptic density scaffolding protein Shank3.

The Shank proteins are crucial scaffolding elements of the post-synaptic density (PSD). One of the best-characterized domains in Shank is the PDZ domain, which binds to C-terminal segments of several other PSD proteins. We carried out a detailed structural analysis of Shank3 PDZ domain-peptide complexes, to understand determinants of binding affinity towards different ligand proteins. Ligand peptides from four different proteins were cocrystallized with the Shank3 PDZ domain, and binding affinities were determined calorimetrically. In addition to conserved class I interactions between the first and third C-terminal peptide residue and Shank3, side chain interactions of other residues in the peptide with the PDZ domain are important factors in defining affinity. Structural conservation suggests that the binding specificities of the PDZ domains from different Shanks are similar. Two conserved buried water molecules in PDZ domains may affect correct local folding of ligand recognition determinants. The solution structure of a tandem Shank3 construct containing the SH3 and PDZ domains showed that the two domains are close to each other, which could be of relevance, when recognizing and binding full target proteins. The SH3 domain did not affect the affinity of the PDZ domain towards short target peptides, and the schizophrenia-linked Shank3 mutation R536W in the linker between the domains had no effect on the structure or peptide interactions of the Shank3 SH3-PDZ unit. Our data show the spatial arrangement of two adjacent Shank domains and pinpoint affinity determinants for short PDZ domain ligands with limited sequence homology.

Examining the potential clinical value of curcumin in the prevention and diagnosis of Alzheimer's disease.

Curcumin derived from turmeric is well documented for its anti-carcinogenic, antioxidant and anti-inflammatory properties. Recent studies show that curcumin also possesses neuroprotective and cognitive-enhancing properties that may help delay or prevent neurodegenerative diseases, including Alzheimer's disease (AD). Currently, clinical diagnosis of AD is onerous, and it is primarily based on the exclusion of other causes of dementia. In addition, phase III clinical trials of potential treatments have mostly failed, leaving disease-modifying interventions elusive. AD can be characterised neuropathologically by the deposition of extracellular ß amyloid (Aß) plaques and intracellular accumulation of tau-containing neurofibrillary tangles. Disruptions in Aß metabolism/clearance contribute to AD pathogenesis. In vitro studies have shown that Aß metabolism is altered by curcumin, and animal studies report that curcumin may influence brain function and the development of dementia, because of its antioxidant and anti-inflammatory properties, as well as its ability to influence Aß metabolism. However, clinical studies of curcumin have revealed limited effects to date, most likely because of curcumin's relatively low solubility and bioavailability, and because of selection of cohorts with diagnosed AD, in whom there is already major neuropathology. However, the fresh approach of targeting early AD pathology (by treating healthy, pre-clinical and mild cognitive impairment-stage cohorts) combined with new curcumin formulations that increase bioavailability is renewing optimism concerning curcumin-based therapy. The aim of this paper is to review the current evidence supporting an association between curcumin and modulation of AD pathology, including in vitro and in vivo studies. We also review the use of curcumin in emerging retinal imaging technology, as a fluorochrome for AD diagnostics.

Lambda-cyhalothrin disrupts the up-regulation effect of 17ß-estradiol on post-synaptic density 95 protein expression via estrogen receptor α-dependent Akt pathway.

Lambda-cyhalothrin (LCT), one of the type II pyrethroids, has been widely used throughout the world. The estrogenic effect of LCT to increase cell proliferation has been well established. However, whether the estrogenic effect of LCT will influence neurodevelopment has not been investigated. In addition, 17ß-Estradiol (E2) plays a crucial role in neurodevelopment and induces an increase in synaptic proteins. The post-synaptic density 95 (PSD95) protein, which is involved in the development of the structure and function of new spines and localized with estrogen receptor α (ERα) at the post-synaptic density (PSD), was detected in our study by using hippocampal neuron cell line HT22. We found that LCT up-regulated PSD95 and ERα expression, estrogen receptor (ER) antagonist ICI182,780 and phosphatidylinositol-4; 5-bisphosphate 3-kinase (PI3K) inhibitor LY294,002 blocked this effect. In addition, LCT disrupted the promotion effect of E2 on PSD95. To investigate whether the observed changes are caused by ERα-dependent signaling activation, we next detected the effects of LCT on the ERα-mediated PI3K-Protein kinase B (PKB/Akt)-eukaryotic initiation factor (eIF) 4E-binding protein 1 (4E-BP1) pathway. There existed an activation of Akt and the downstream factor 4E-BP1 after LCT treatment. In addition, LCT could disrupt the activation effect of E2 on the Akt pathway. However, no changes in cAMP response element-binding protein (CREB) activation and PSD95 messenger ribonucleic acid (mRNA) were observed. Our findings demonstrated that LCT could increase the PSD95 protein level via the ERα-dependent Akt pathway, and LCT might disrupt the up-regulation effect of E2 on PSD95 protein expression via this signaling pathway.

An intracellular domain with a novel sequence regulates cell surface expression and synaptic clustering of leucine-rich repeat transmembrane proteins in hippocampal neurons.

Leucine-rich repeat transmembrane proteins (LRRTMs) are single-spanning transmembrane proteins that belong to the family of synaptically localized adhesion molecules that play various roles in the formation, maturation, and function of synapses. LRRTMs are highly localized in the post-synaptic density; however, the mechanisms and significance of LRRTM synaptic clustering remain unclear. Here, we focus on the intracellular domain of LRRTMs and investigate its role in cell surface expression and synaptic clustering. The deletion of 55-56 residues in the cytoplasmic tail caused significantly reduced synaptic clustering of LRRTM1-4 in rat hippocampal neurons, whereas it simultaneously resulted in augmented LRRTM1-2 cell surface expression. A series of deletions and further single amino acid substitutions in the intracellular domain of LRRTM2 demonstrated that a previously uncharacterized sequence at the region of -16 to -13 from the C-terminus was responsible for efficient synaptic clustering and proper cell surface trafficking of LRRTMs. Furthermore, the clustering-deficient LRRTM2 mutant lost the ability to promote the accumulation of post-synaptic density protein-95 (PSD-95). These results suggest that trafficking to the cell surface and synaptic clustering of LRRTMs are regulated by a specific mechanism through this novel sequence in the intracellular domain that underlies post-synaptic molecular assembly and maturation. Leucine-rich repeat transmembrane proteins (LRRTMs) are synaptic cell adhesion molecules promoting synapse formation. LRRTMs are highly localized in the postsynaptic density. We report amino acid sequence YxxC in the intracellular domain of LRRTMs is responsible for the postsynaptic localization of LRRTMs. This novel amino acid sequence of LRRTMs facilitates synapse maturation. We propose this regulated synaptic clustering of LRRTMs by the intracellular domain presents a novel molecular mechanism of synapse maturation.

Effects of corticosterone and amyloid-beta on proteins essential for synaptic function: implications for depression and Alzheimer's disease.

The relationship between Alzheimer's disease (AD) and depression has been well established in terms of epidemiological and clinical observations. Depression has been considered to be both a symptom and risk factor of AD. Several genetic and neurobiological mechanisms have been described to underlie these two disorders. Despite the accumulating knowledge on this topic, the precise neuropathological mechanisms remain to be elucidated. In this study, we propose that synaptic degeneration plays an important role in the disease progression of depression and AD. Using primary culture of hippocampal neurons treated with oligomeric Aß and corticosterone as model agents for AD and depression, respectively, we found significant changes in the pre-synaptic vesicle proteins synaptophysin and synaptotagmin. We further investigated whether the observed protein changes affected synaptic functions. By using FM(®)4-64 fluorescent probe, we showed that synaptic functions were compromised in treated neurons. Our findings led us to investigate the involvement of protein degradation mechanisms in mediating the observed synaptic protein abnormalities, namely, the ubiquitin-proteasome system and autophagy. We found up-regulation of ubiquitin-mediated protein degradation, and the preferential signaling for the autophagic-lysosomal degradation pathway. Lastly, we investigated the neuroprotective role of different classes of antidepressants. Our findings demonstrated that the antidepressants Imipramine and Escitalopram were able to rescue the observed synaptic protein damage. In conclusion, our study shows that synaptic degeneration is an important common denominator underlying depression and AD, and alleviation of this pathology by antidepressants may be therapeutically beneficial.

EFA6A, a guanine nucleotide exchange factor for Arf6, interacts with sorting nexin-1 and regulates neurite outgrowth.

The membrane trafficking and actin cytoskeleton remodeling mediated by ADP ribosylation factor 6 (Arf6) are functionally linked to various neuronal processes including neurite formation and maintenance, neurotransmitter release, and receptor internalization. EFA6A is an Arf6-specific guanine nucleotide exchange factor that is abundantly expressed in the brain. In this study, we identified sorting nexin-1 (SNX1), a retromer component that is implicated in endosomal sorting and trafficking, as a novel interacting partner for EFA6A by yeast two-hybrid screening. The interaction was mediated by the C-terminal region of EFA6A and a BAR domain of SNX1, and further confirmed by pull-down assay and immunoprecipitation from mouse brain lysates. In situ hybridization analysis demonstrated the widespread expression of SNX1 in the mouse brain, which overlapped with the expression of EFA6A in the forebrain. Immunofluorescent analysis revealed the partial colocalization of EFA6A and SNX1 in the dendritic fields of the hippocampus. Immunoelectron microscopic analysis revealed the overlapping subcellular localization of EFA6A and SNX1 at the post-synaptic density and endosomes in dendritic spines. In Neuro-2a neuroblastoma cells, expression of either EFA6A or SNX1 induced neurite outgrowth, which was further enhanced by co-expression of EFA6A and SNX1. The present findings suggest a novel mechanism by which EFA6A regulates Arf6-mediated neurite formation through the interaction with SNX1.

Detergent-dependent separation of postsynaptic density, membrane rafts and other subsynaptic structures from the synaptic plasma membrane of rat forebrain.

We systematically investigated the purification process of post-synaptic density (PSD) and post-synaptic membrane rafts (PSRs) from the rat forebrain synaptic plasma membranes by examining the components and the structures of the materials obtained after the treatment of synaptic plasma membranes with TX-100, n-octyl ß-d-glucoside (OG) or 3-([3-cholamidopropyl]dimethylammonio)-2-hydroxy-1-propanesulfonate (CHAPSO). These three detergents exhibited distinct separation profiles for the synaptic subdomains. Type I and type II PSD proteins displayed mutually exclusive distribution. After TX-100 treatment, type I PSD was recovered in two fractions: a pellet and an insoluble fraction 8, which contained partially broken PSD-PSR complexes. Conventional PSD was suggested to be a mixture of these two PSD pools and did not contain type II PSD. An association of type I PSD with PSRs was identified in the TX-100 treatment, and those with type II PSD in the OG and CHAPSO treatments. An association of GABA receptors with gephyrin was easily dissociated. OG at a high concentration solubilized the type I PSD proteins. CHAPSO treatment resulted in a variety of distinct fractions, which contained certain novel structures. Two different pools of GluA, either PSD or possibly raft-associated, were identified in the OG and CHAPSO treatments. These results are useful in advancing our understanding of the structural organization of synapses at the molecular level. We systematically investigated the purification process of post-synaptic density (PSD) and synaptic membrane rafts by examining the structures obtained after treatment of the SPMs with TX-100, n-octyl ß-d-glucoside or CHAPSO. Differential distribution of type I and type II PSD, synaptic membrane rafts, and other novel subdomains in the SPM give clues to understand the structural organization of synapses at the molecular level.

The multi-PDZ domain protein-1 (MUPP-1) expression regulates cellular levels of the PALS-1/PATJ polarity complex.

MUPP-1 (multi-PDZ domain protein-1) and PATJ (PALS-1-associated tight junction protein) proteins are closely related scaffold proteins and bind to many common interactors including PALS-1 (protein associated with Lin seven) a member of the Crumbs complex. Our goal is to understand how MUPP-1 and PATJ and their interaction with PALS-1 are regulated in the same cells. We have shown that in MCF10A cells there are at least two different and co-existing complexes, PALS-1/MUPP-1 and PALS-1/PATJ. Surprisingly, MUPP-1 levels inversely correlated with PATJ protein levels by acting on the stabilization of the PATJ/PALS-1 complex. Upon MUPP-1 depletion, the increased amounts of PATJ are in part localized at the migrating front of MCF10A cells and are able to recruit more PAR3 (partition defective 3). All together these data indicate that a precise balance between MUPP-1 and PATJ is achieved in epithelial cells by regulating their association with PALS-1.

Loss of the E3 ubiquitin ligase TRIM67 alters the post-synaptic density proteome.

The E3 ubiquitin ligase TRIM67 is enriched in the central nervous system and is required for proper neuronal development. Previously we demonstrated TRIM67 coordinates with the closely related E3 ubiquitin ligase TRIM9 to regulate cytoskeletal dynamics downstream of the netrin-1 during axon guidance and axon branching in early neuronal morphogenesis. Interestingly, loss of Trim67 impacts cognitive flexibility in a spatial learning and memory task. Despite this behavioral phenotype, it was previously uninvestigated if TRIM67 was involved in synapse formation or function. Here we demonstrate TRIM67 localizes to the post-synaptic density (PSD) within dendritic spines. Furthermore, we show that loss of Trim67 significantly changes the PSD proteome, including changes in the regulation of the actin and microtubule cytoskeletons. Collectively, our data propose a synaptic role for TRIM67.

The mGluR5-mediated Arc activation protects against experimental traumatic brain injury in rats.

INTRODUCTION: Traumatic brain injury (TBI) is a complex pathophysiological process, and increasing attention has been paid to the important role of post-synaptic density (PSD) proteins, such as glutamate receptors. Our previous study showed that a PSD protein Arc/Arg3.1 (Arc) regulates endoplasmic reticulum (ER) stress and neuronal necroptosis in traumatic injury in vitro. AIM: In this study, we investigated the expression, regulation and biological function of Arc in both in vivo and in vitro experimental TBI models. RESULTS: Traumatic neuronal injury (TNI) induced a temporal upregulation of Arc in cortical neurons, while TBI resulted in sustained increase in Arc expression up to 24 h in rats. The increased expression of Arc was mediated by the activity of metabotropic glutamate receptor 5 (mGluR5), but not dependent on the intracellular calcium (Ca2+) release. By using inhibitors and antagonists, we found that TNI regulates Arc expression via Gq protein and protein turnover. In addition, overexpression of Arc protects against TBI-induced neuronal injury and motor dysfunction both in vivo and in vitro, whereas the long-term cognitive function was not altered. To determine the role of Arc in mGluR5-induced protection, lentivirus-mediated short hairpin RNA (shRNA) transfection was performed to knockdown Arc expression. The mGluR5 agonist (RS)-2-chloro-5-hydroxyphenylglycine (CHPG)-induced protection against TBI was partially prevented by Arc knockdown. Furthermore, the CHPG-induced attenuation of Ca2+ influx after TNI was dependent on Arc activation and followed regulation of AMPAR subunits. The results of Co-IP and Ca2+ imaging showed that the Arc-Homer1 interaction contributes to the CHPG-induced regulation of intracellular Ca2+ release. CONCLUSION: In summary, the present data indicate that the mGluR5-mediated Arc activation is a protective mechanism that attenuates neurotoxicity following TBI through the regulation of intracellular Ca2+ hemostasis. The AMPAR-associated Ca2+ influx and ER Ca2+ release induced by Homer1-IP3R pathway might be involved in this protection.

BAI1 localizes AMPA receptors at the cochlear afferent post-synaptic density and is essential for hearing.

Type I spiral ganglion neurons (SGNs) convey sound information to the central auditory pathway by forming synapses with inner hair cells (IHCs) in the mammalian cochlea. The molecular mechanisms regulating the formation of the post-synaptic density (PSD) in the SGN afferent terminals are still unclear. Here, we demonstrate that brain-specific angiogenesis inhibitor 1 (BAI1) is required for the clustering of AMPA receptors GluR2-4 (glutamate receptors 2-4) at the PSD. Adult Bai1-deficient mice have functional IHCs but fail to transmit information to the SGNs, leading to highly raised hearing thresholds. Despite the almost complete absence of AMPA receptor subunits, the SGN fibers innervating the IHCs do not degenerate. Furthermore, we show that AMPA receptors are still expressed in the cochlea of Bai1-deficient mice, highlighting a role for BAI1 in trafficking or anchoring GluR2-4 to the PSDs. These findings identify molecular and functional mechanisms required for sound encoding at cochlear ribbon synapses.

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.

Mitigation of synaptic and memory impairments via F-actin stabilization in Alzheimer's disease.

BACKGROUND: Synaptic dysfunction, characterized by synapse loss and structural alterations, emerges as a prominent correlate of cognitive decline in Alzheimer's disease (AD). Actin cytoskeleton, which serves as the structural backbone of synaptic architecture, is observed to be lost from synapses in AD. Actin cytoskeleton loss compromises synaptic integrity, affecting glutamatergic receptor levels, neurotransmission, and synaptic strength. Understanding these molecular changes is crucial for developing interventions targeting synaptic dysfunction, potentially mitigating cognitive decline in AD. METHODS: In this study, we investigated the synaptic actin interactome using mass spectrometry in a mouse model of AD, APP/PS1. Our objective was to explore how alterations in synaptic actin dynamics, particularly the interaction between PSD-95 and actin, contribute to synaptic and cognitive impairment in AD. To assess the impact of restoring F-actin levels on synaptic and cognitive functions in APP/PS1 mice, we administered F-actin stabilizing agent, jasplakinolide. Behavioral deficits in the mice were evaluated using the contextual fear conditioning paradigm. We utilized primary neuronal cultures to study the synaptic levels of AMPA and NMDA receptors and the dynamics of PSD-95 actin association. Furthermore, we analyzed postmortem brain tissue samples from subjects with no cognitive impairment (NCI), mild cognitive impairment (MCI), and Alzheimer's dementia (AD) to determine the association between PSD-95 and actin. RESULTS: We found a significant reduction in PSD-95-actin association in synaptosomes from middle-aged APP/PS1 mice compared to wild-type (WT) mice. Treatment with jasplakinolide, an actin stabilizer, reversed deficits in memory recall, restored PSD-95-actin association, and increased synaptic F-actin levels in APP/PS1 mice. Additionally, actin stabilization led to elevated synaptic levels of AMPA and NMDA receptors, enhanced dendritic spine density, suggesting improved neurotransmission and synaptic strength in primary cortical neurons from APP/PS1 mice. Furthermore, analysis of postmortem human tissue with NCI, MCI and AD subjects revealed disrupted PSD-95-actin interactions, underscoring the clinical relevance of our preclinical studies. CONCLUSION: Our study elucidates disrupted PSD-95 actin interactions across different models, highlighting potential therapeutic targets for AD. Stabilizing F-actin restores synaptic integrity and ameliorates cognitive deficits in APP/PS1 mice, suggesting that targeting synaptic actin regulation could be a promising therapeutic strategy to mitigate cognitive decline in AD.