Differential association of postsynaptic signaling protein complexes in striatum and hippocampus

Excitation-transcription coupling, neuronal gene expression and synaptic plasticity

Excitation-transcription coupling (E-TC) links synaptic and cellular activity to nuclear gene transcription. It is generally accepted that E-TC makes a crucial contribution to learning and memory through its role in underpinning long-lasting synaptic enhancement in late-phase long-term potentiation and has more recently been linked to late-phase long-term depression: both processes require de novo gene transcription, mRNA translation and protein synthesis. E-TC begins with the activation of glutamate-gated N-methyl-D-aspartate-type receptors and voltage-gated L-type Ca2+ channels at the membrane and culminates in the activation of transcription factors in the nucleus. These receptors and ion channels mediate E-TC through mechanisms that include long-range signalling from the synapse to the nucleus and local interactions within dendritic spines, among other possibilities. Growing experimental evidence links these E-TC mechanisms to late-phase long-term potentiation and learning and memory. These advances in our understanding of the molecular mechanisms of E-TC mean that future efforts can focus on understanding its mesoscale functions and how it regulates neuronal network activity and behaviour in physiological and pathological conditions.

Spinophilin-dependent regulation of GluN2B-containing NMDAR-dependent calcium influx, GluN2B surface expression, and cleaved caspase expression

N-methyl-d-aspartate receptors (NMDARs) are calcium-permeable ion channels that are ubiquitously expressed within the glutamatergic postsynaptic density. Phosphorylation of NMDAR subunits defines receptor conductance and surface localization, two alterations that can modulate overall channel activity. Modulation of NMDAR phosphorylation by kinases and phosphatases regulates the amount of calcium entering the cell and subsequent activation of calcium-dependent processes. The dendritic spine enriched protein, spinophilin, is the major synaptic protein phosphatase 1 (PP1) targeting protein. Depending on the substrate, spinophilin can act as either a PP1 targeting protein, to permit substrate dephosphorylation, or a PP1 inhibitory protein, to enhance substrate phosphorylation. Spinophilin limits NMDAR function in a PP1-dependent manner. Specifically, we have previously shown that spinophilin sequesters PP1 away from the GluN2B subunit of the NMDAR, which results in increased phosphorylation of Ser-1284 on GluN2B. However, how spinophilin modifies NMDAR function is unclear. Herein, we utilize a Neuro2A cell line to detail that Ser-1284 phosphorylation increases calcium influx via GluN2B-containing NMDARs. Moreover, overexpression of spinophilin decreases GluN2B-containing NMDAR activity by decreasing its surface expression, an effect that is independent of Ser-1284 phosphorylation. In hippocampal neurons isolated from spinophilin knockout animals, there is an increase in cleaved caspase-3 levels, a marker of calcium-associated apoptosis, compared with wildtype mice. Taken together, our data demonstrate that spinophilin regulates GluN2B containing NMDAR phosphorylation, channel function, and trafficking and that loss of spinophilin enhances neuronal cleaved caspase-3 expression.

Dephosphorylation of neural wiring protein shootin1 by PP1 phosphatase regulates netrin-1-induced axon guidance

Axon pathfinding is an essential step in neuronal network formation. Shootin1a is a clutch-linker molecule that is mechanically involved in axon outgrowth and guidance. It was previously shown that concentration gradients of axon guidance molecule netrin-1 in the extracellular environment elicit asymmetrically localized Pak1 kinase-mediated phosphorylation of shootin1a within axonal growth cones, which is higher on the netrin-1 source side. This asymmetric phosphorylation promotes shootin1a-mediated local actin-adhesion coupling within growth cones, thereby generating directional forces for turning the growth cone toward the netrin-1 source. However, how the spatial differences in netrin-1 concentration are transduced into the asymmetrically localized signaling within growth cones remains unclear. Moreover, the protein phosphatases that dephosphorylate shootin1a remain unidentified. Here, we report that protein phosphatase-1 (PP1) dephosphorylates shootin1a in growth cones. We found that PP1 overexpression abolished the netrin-1-induced asymmetric localization of phosphorylated-shootin1a as well as axon turning. In addition, we show PP1 inhibition reversed the asymmetrically localized shootin1a phosphorylation within growth cones under netrin-1 gradient, thereby changing the netrin-1-induced growth cone turning from attraction to repulsion. These data indicate that PP1-mediated shootin1a dephosphorylation plays a key role in organizing asymmetrically-localized phosphorylated shootin1a within growth cones, which regulates netrin-1-induced axon guidance.

Inhibition of endoplasmic reticulum stress reverses synaptic plasticity deficits in striatum of DYT1 dystonia mice

Background and objective: Striatal plasticity alterations caused by endoplasmic reticulum (ER) stress is supposed to be critically involved in the mechanism of DYT1 dystonia. In the current study, we expanded this research field by investigating the critical role of ER stress underlying synaptic plasticity impairment imposed by mutant heterozygous Tor1a^+/- in a DYT1 dystonia mouse model.

Methods: Heterozygous Tor1a^+/- mouse model for DYT1 dystonia was established. Wild-type (Tor1a^+/+, N=10) and mutant (Tor1a^+/-, N=10) mice from post-natal day P25 to P35 were randomly distributed to experimental and control groups. Patch-clamp and current-clamp recordings of SPNs were conducted with intracellular electrodes for electrophysiological analyses. Striatal changes of the direct and indirect pathways were investigated via immunofluorescence. Golgi-Cox staining was conducted to observe spine morphology of SPNs. To quantify postsynaptic signaling proteins in striatum, RNA-Seq, qRT-PCR and WB were performed in striatal tissues.

Results: Long-term depression (LTD) was failed to be induced, while long-term potentiation (LTP) was further strengthened in striatal spiny projection neurons (SPNs) from the Tor1a^+/- DYT1 dystonia mice. Spine morphology analyses revealed a significant increase of both number of mushroom type spines and spine width in Tor1a^+/- SPNs. In addition, increased AMPA receptor function and the reduction of NMDA/AMPA ratio in the postsynaptic of Tor1a^+/- SPNs was observed, along with increased ER stress protein levels in striatum of Tor1a^+/- DYT1 dystonia mice. Notably, ER stress inhibitors, tauroursodeoxycholic acid (TUDCA), could rescue LTD as well as AMPA currents.

Conclusion: The current study illustrated the role of ER stress in mediating structural and functional plasticity alterations in Tor1a^+/- SPNs. Inhibition of the ER stress by TUDCA is beneficial in reversing the deficits at the cellular and molecular levels. Remedy of dystonia associated neurological and motor functional impairment by ER stress inhibitors could be a recommendable therapeutic agent in clinical practice.

Regulation of the NMDA receptor by its cytoplasmic domains: (How) is the tail wagging the dog?

Excitatory neurotransmission mediated by N-methyl-d-aspartate receptors (NMDARs) is critical for synapse development, function, and plasticity in the brain. NMDARs are tetra-heteromeric cation-channels that mediate synaptic transmission and plasticity. Extensive human studies show the existence of genetic variants in NMDAR subunits genes (GRIN genes) that are associated with neurodevelopmental and neuropsychiatric disorders, including autism spectrum disorders (ASD), epilepsy (EP), intellectual disability (ID), attention deficit hyperactivity disorder (ADHD), and schizophrenia (SCZ). NMDAR subunits have a unique modular architecture with four semiautonomous domains. Here we focus on the carboxyl terminal domain (CTD), also known as the intracellular C-tail, which varies in length among the glutamate receptor subunits and is the most diverse domain in terms of amino acid sequence. The CTD shows no sequence homology to any known proteins but encodes short docking motifs for intracellular binding proteins and covalent modifications. Our review will discuss the many important functions of the CTD in regulating NMDA membrane and synaptic targeting, stabilization, degradation targeting, allosteric modulation and metabotropic signaling of the receptor. This article is part of the special issue on 'Glutamate Receptors - NMDA Receptors'.

Regulation of Synaptic Transmission and Plasticity by Protein Phosphatase 1

Protein phosphatases, by counteracting protein kinases, regulate the reversible phosphorylation of many substrates involved in synaptic plasticity, a cellular model for learning and memory. A prominent phosphatase regulating synaptic plasticity and neurologic disorders is the serine/threonine protein phosphatase 1 (PP1). PP1 has three isoforms (α, β, and γ, encoded by three different genes), which are regulated by a vast number of interacting subunits that define their enzymatic substrate specificity. In this review, we discuss evidence showing that PP1 regulates synaptic transmission and plasticity, as well as presenting novel models of PP1 regulation suggested by recent experimental evidence. We also outline the required targeting of PP1 by neurabin and spinophilin to achieve substrate specificity at the synapse to regulate AMPAR and NMDAR function. We then highlight the role of inhibitor-2 in regulating PP1 function in plasticity, including its positive regulation of PP1 function in vivo in memory formation. We also discuss the distinct function of the three PP1 isoforms in synaptic plasticity and brain function, as well as briefly discuss the role of inhibitory phosphorylation of PP1, which has received recent emphasis in the regulation of PP1 activity in neurons.

The pathophysiological mechanism of ischemic stroke after hypobaric hypoxia simulation at high altitude

Tibet is an area in China with a high incidence of stroke, typically attributed to hypobaric hypoxia. The present study aimed to observe the neuronal injury of ischemic stroke after hypobaric hypoxia and explore the mechanism by which N-methyl-D-aspartate receptor (NMDAR) and its downstream pathways are involved. This study employed a hypobaric chamber to imitate high altitude at 4000 m. After hypoxia, the middle cerebral artery occlusion (MCAO) model was used to mimic ischemic stroke. Behavioral tests and measurements of infarct area were used to observe neuronal injuries. The expression of NMDAR, Ca²⁺/calmodulin-dependent protein kinase II (CaMKII) and phosphorylated CaMKII (Threonine 286) (P-CaMKII) was tested by western blot, and hematological tests were used to count the number of red blood cells (RBCs) and hemoglobin. Compared with the plain+MCAO group, the neurological deficit scores and infarct area of rats in the 4000 m + MCAO group were all decreased, and the protein expression of NMDAR, CaMKII and P-CaMKII was reduced. Compared with the plain group, the numbers of RBCs, hemoglobin and hematocrit were increased in the 4000 m group; compared with the 4000 m groups, the three indexes were increased in the 4000 m + MCAO groups. The neuronal injuries after hypoxia were not more serious than those in rats enduring ischemia and reperfusion in plain. The underlying mechanisms were related to the decreased expression of NMDAR and CaMKII; furthermore, the increased numbers of RBCs and hemoglobin may be crucial mechanisms for the incidence and development of ischemic stroke at high altitude.

NMDAR-Activated PP1 Dephosphorylates GluN2B to Modulate NMDAR Synaptic Content

In mature neurons, postsynaptic N-methyl-D-aspartate receptors (NMDARs) are segregated into two populations, synaptic and extrasynaptic, which differ in localization, function, and associated intracellular cascades. These two pools are connected via lateral diffusion, and receptor exchange between them modulates synaptic NMDAR content. Here, we identify the phosphorylation of the PDZ-ligand of the GluN2B subunit of NMDARs (at S1480) as a critical determinant in dynamically controlling NMDAR synaptic content. We find that phosphorylation of GluN2B at S1480 maintains NMDARs at extrasynaptic membranes as part of a protein complex containing protein phosphatase 1 (PP1). Global activation of NMDARs leads to the activation of PP1, which mediates dephosphorylation of GluN2B at S1480 to promote an increase in synaptic NMDAR content. Thus, PP1-mediated dephosphorylation of the GluN2B PDZ-ligand modulates the synaptic expression of NMDARs in mature neurons in an activity-dependent manner, a process with profound consequences for synaptic and structural plasticity, metaplasticity, and synaptic neurotransmission.

The dynamic regulation of synaptically expressed NMDA receptors (NMDARs) is essential for synaptic function. Here, Chiu et al. describe a mechanism controlling this process in mature neurons by showing that increases in NMDAR synaptic content are driven by PP1-mediated dephosphorylation of extrasynaptic NMDARs within their GluN2B PDZ-ligands.

Enduring alterations in hippocampal astrocytesynaptic proximity following adolescent alcohol exposure: reversal by gabapentin

Adolescent alcohol abuse is a substantive public health problem that has been the subject of intensive study in recent years. Despite reports of a wide range of effects of adolescent intermittent ethanol (AIE) exposure on brain and behavior, little is known about the mechanisms that may underlie those effects, and even less about treatments that might reverse them. Recent studies from our laboratory have indicated that AIE produced enduring changes in astrocyte function and synaptic activity in the hippocampal formation, suggesting the possibility of an alteration in astrocyte-neuronal connectivity and function. We utilized astrocyte-specific, membrane restricted viral labeling paired with immunohistochemistry to perform confocal single cell astrocyte imaging, three-dimensional reconstruction, and quantification of astrocyte morphology in hippocampal area CA1 from adult rats after AIE. Additionally, we assessed the colocalization of astrocyte plasma membrane labeling with immunoreactivity for AMPA-(α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid) glutamate receptor 1, an AMPA receptor subunit and established neuronal marker of excitatory synapses, as a metric of astrocyte-synapse proximity. AIE significantly reduced the colocalization of the astrocyte plasma membrane with synaptic marker puncta in adulthood. This is striking in that it suggests not only an alteration of the physical association of astrocytes with synapses by AIE, but one that lasts into adulthood - well after the termination of alcohol exposure. Perhaps even more notable, the AIE-induced reduction of astrocyte-synapse interaction was reversed by sub-chronic treatment with the clinically used agent, gabapentin (Neurontin), in adulthood. This suggests that a medication in common clinical use may have the potential to reverse some of the enduring effects of adolescent alcohol exposure on brain function. All animal experiments conducted were approved by the Duke University Institutional Animal Care and Use Committee (Protocol Registry Number A159-18-07) on July 27, 2018.

Spinophilin regulates phosphorylation and interactions of the GluN2B subunit of the N-methyl-d-aspartate receptor

N-methyl-d-Aspartate receptors (NMDARs) are abundant postsynaptic proteins that are critical for normal synaptic communication. NMDAR channel function is regulated by multiple properties, including phosphorylation. Inhibition of protein phosphatase 1 (PP1) in hippocampal neurons increases NMDAR activity, an effect abrogated by loss of spinophilin, the major PP1-targeting protein in the postsynaptic density. However, how spinophilin regulates PP1-dependent NMDAR function is unclear. We hypothesize that spinophilin regulates PP1 binding to the NMDAR to alter NMDAR phosphorylation. Our data demonstrate that spinophilin interacts with the GluN2B subunit of the NMDAR. In human embryonic kidney 293 FT cells, activation and/or overexpression of protein kinase A increased the association between spinophilin and the GluN2B subunit of the NMDAR. Functionally, we found that spinophilin overexpression decreased PP1 binding to the GluN2B subunit of the NMDAR and attenuated the PP1-dependent dephosphorylation of GluN2B at Ser-1284. Moreover, in P28 hippocampal lysates isolated from spinophilin KO compared to WT mice, there was increased binding of GluN2B to PP1, decreased phosphorylation of GluN2B at Ser-1284, and altered GluN2B protein interactions with postsynaptic density-enriched proteins. Together, our data demonstrate that spinophilin decreases PP1 binding to GluN2B and concomitantly enhances the phosphorylation of GluN2B at Ser-1284. The putative consequences of these spinophilin-dependent alterations in GluN2B phosphorylation and interactions on synaptic GluN2B localization and function are discussed. Open Science: This manuscript was awarded with the Open Materials Badge For more information see: https://cos.io/our-services/open-science-badges/.

Proteomic Analysis of the Spinophilin Interactome in Rodent Striatum Following Psychostimulant Sensitization

Glutamatergic projections from the cortex and dopaminergic projections from the substantia nigra or ventral tegmental area synapse on dendritic spines of specific GABAergic medium spiny neurons (MSNs) in the striatum. Direct pathway MSNs (dMSNs) are positively coupled to protein kinase A (PKA) signaling and activation of these neurons enhance specific motor programs whereas indirect pathway MSNs (iMSNs) are negatively coupled to PKA and inhibit competing motor programs. An imbalance in the activity of these two programs is observed following increased dopamine signaling associated with exposure to psychostimulant drugs of abuse. Alterations in MSN signaling are mediated by changes in MSN protein post-translational modifications, including phosphorylation. Whereas direct changes in specific kinases, such as PKA, regulate different effects observed in the two MSN populations, alterations in the specific activity of serine/threonine phosphatases, such as protein phosphatase 1 (PP1) are less well known. This lack of knowledge is due, in part, to unknown, cell-specific changes in PP1 targeting proteins. Spinophilin is the major PP1-targeting protein in striatal postsynaptic densities. Using proteomics and immunoblotting approaches along with a novel transgenic mouse expressing hemagglutainin (HA)-tagged spinophilin in dMSNs and iMSNs, we have uncovered cell-specific regulation of the spinophilin interactome following a sensitizing regimen of amphetamine. These data suggest regulation of spinophilin interactions in specific MSN cell types and may give novel insight into putative cell-specific, phosphatase-dependent signaling pathways associated with psychostimulants.

Characterisation of spinophilin immunoreactivity in postmortem human brain homogenates

Spinophilin is a multifunctional scaffold protein that regulates the formation and function of dendritic spines and plays a role in neuronal migration. The distinct roles of spinophilin depend on its localization and the direct interaction with other proteins, which may target spinophilin to specific locations within the cell. Several studies suggest a role of spinophilin in the pathophysiology of neurological or psychiatric diseases. However, the majority have been performed in animals or cultured cells. Thus, the aim of the present study was to characterise the regional and subcellular expression of spinophilin immunoreactivity by western blot in postmortem human brain. Two specific immunoreactive bands for spinophilin were observed: an intense band migrating at around 120kDa, which seems to correspond to the apparent molecular weight of spinophilin described by other authors, and a less intense band of around 95kDa. This second form seems to be a proteolysis or cleavage product of the ~120kDa spinophilin. Interestingly, the subcellular distribution of both bands was different. In membrane fraction, the ~120kDa spinophilin band was the most abundant, whereas in cytosol it was the ~95kDa form. Furthermore, a different regional distribution for ~120kDa spinophilin band was observed, with the highest expression in prefrontal cortex, followed by hippocampus and cerebellum, and the lowest in caudate nucleus. Altogether, these results constitute a useful reference for future studies of spinophilin in pathological and non-pathological human brain tissues.

Distinct Roles of Protein Phosphatase 1 Bound on Neurabin and Spinophilin and Its Regulation in AMPA Receptor Trafficking and LTD Induction

Protein phosphatase-1 (PP1) constrains learning and memory formation in part through its effects on the induction threshold of long-term potentiation (LTP) and depression (LTD). LTD induction requires both the enzymatic activity of PP1 and its proper anchoring to synaptic spines. We have shown previously that neurabin, a major synaptic scaffolding protein, targets PP1 to synapses for LTD induction. Here, we show that PP1 bound on spinophilin, a close homolog of neurabin and another major synaptic PP1 anchoring protein, does not play a role in LTD induction, which suggests that neurabin plays a privileged role in nanodomain targeting of PP1 in LTD induction. We found that protein kinase A can significantly weaken the neurabin-PP1 interaction in neurons via phosphorylation of neurabin at serine 461, a phosphorylation site adjacent to the PP1-binding motif that is not conserved in spinophilin. Finally, we found that a neurabin mutation (S461E), which mimics phosphorylation, blocked AMPA receptor endocytosis and LTD induction. The results indicate the critical importance of nanodomain targeting of PP1 within synaptic spines and its regulation in LTD induction.

Role of the endogenous cannabinoid receptor 1 in brain injury induced by chronic intermittent hypoxia in rats

PURPOSE

This study investigated the effect of rimonabant, a cannabinoid receptor type 1 antagonist, on calcium/calmodulin- dependent protein kinase II and cannabinoid receptor type 1 in chronic intermittent hypoxia.

MATERIALS AND METHODS

Healthy male rats were divided into control group, intermittent hypoxia group for 4 or 6 weeks, hypoxic intervention group that received rimonabant (1 mg/kg/d) before exposure to hypoxia for 4 or 6 weeks (n = 10/group). Morphological changes and expressions of the two indexes in the cerebral hippocampus cells were determined by haematoxylin-eosin staining and immunohistochemistry, respectively.

RESULTS

In the intermittent hypoxia group at 4 weeks, the hippocampal cells were damaged with sparse cytoplasm and unclear boundaries, which are even worse at 6 weeks. In contrast, the hippocampal cells of the hypoxic intervention group were neatly arranged at 4 weeks. At 6 weeks, cells were larger with scarce cytoplasm and nuclear changes indicative of cell death. Calcium/calmodulin-dependent protein kinase II and cannabinoid receptor type 1 expression in the cerebral hippocampus was elevated in the intermittent hypoxia group at 4 weeks with even greater at 6 weeks. Cannabinoid receptor type 1 expression was reduced in the hypoxic intervention group compared to the intermittent hypoxia group. Correlation analysis revealed significant positive correlation of them in the intermittent hypoxia group.

CONCLUSIONS

Chronic intermittent hypoxia induced structural damage in the hippocampus and increased cannabinoid receptor type 1 and calcium/calmodulin-dependent protein kinase II expression, which may mediate cognitive impairment associated with chronic intermittent hypoxia. Rimonabant had a protective effect against chronic intermittent hypoxia.

Mechanisms and Consequences of Dopamine Depletion-Induced Attenuation of the Spinophilin/Neurofilament Medium Interaction

Signaling changes that occur in the striatum following the loss of dopamine neurons in the Parkinson disease (PD) are poorly understood. While increases in the activity of kinases and decreases in the activity of phosphatases have been observed, the specific consequences of these changes are less well understood. Phosphatases, such as protein phosphatase 1 (PP1), are highly promiscuous and obtain substrate selectivity via targeting proteins. Spinophilin is the major PP1-targeting protein enriched in the postsynaptic density of striatal dendritic spines. Spinophilin association with PP1 is increased concurrent with decreases in PP1 activity in an animal model of PD. Using proteomic-based approaches, we observed dopamine depletion-induced decreases in spinophilin binding to multiple protein classes in the striatum. Specifically, there was a decrease in the association of spinophilin with neurofilament medium (NF-M) in dopamine-depleted striatum. Using a heterologous cell line, we determined that spinophilin binding to NF-M required overexpression of the catalytic subunit of protein kinase A and was decreased by cyclin-dependent protein kinase 5. Functionally, we demonstrate that spinophilin can decrease NF-M phosphorylation. Our data determine mechanisms that regulate, and putative consequences of, pathological changes in the association of spinophilin with NF-M that are observed in animal models of PD.

Chronic intermittent alcohol disrupts the GluN2B-associated proteome and specifically regulates group I mGlu receptor-dependent long-term depression

N-Methyl-d-aspartate receptors (NMDARs) are major targets of both acute and chronic alcohol, as well as regulators of plasticity in a number of brain regions. Aberrant plasticity may contribute to the treatment resistance and high relapse rates observed in alcoholics. Recent work suggests that chronic alcohol treatment preferentially modulates both the expression and subcellular localization of NMDARs containing the GluN2B subunit. Signaling through synaptic and extrasynaptic GluN2B-NMDARs has already been implicated in the pathophysiology of various other neurological disorders. NMDARs interact with a large number of proteins at the glutamate synapse, and a better understanding of how alcohol modulates this proteome is needed. We employed a discovery-based proteomic approach in subcellular fractions of hippocampal tissue from chronic intermittent alcohol (CIE)-exposed C57Bl/6J mice to gain insight into alcohol-induced changes in GluN2B signaling complexes. Protein enrichment analyses revealed changes in the association of post-synaptic proteins, including scaffolding, glutamate receptor and PDZ-domain binding proteins with GluN2B. In particular, GluN2B interaction with metabotropic glutamate (mGlu)1/5 receptor-dependent long-term depression (LTD)-associated proteins such as Arc and Homer 1 was increased, while GluA2 was decreased. Accordingly, we found a lack of mGlu1/5 -induced LTD while α1 -adrenergic receptor-induced LTD remained intact in hippocampal CA1 following CIE. These data suggest that CIE specifically disrupts mGlu1/5 -LTD, representing a possible connection between NMDAR and mGlu receptor signaling. These studies not only demonstrate a new way in which alcohol can modulate plasticity in the hippocampus but also emphasize the utility of this discovery-based proteomic approach to generate new hypotheses regarding alcohol-related mechanisms.

A Novel Human CAMK2A Mutation Disrupts Dendritic Morphology and Synaptic Transmission, and Causes ASD-Related Behaviors

Characterizing the functional impact of novel mutations linked to autism spectrum disorder (ASD) provides a deeper mechanistic understanding of the underlying pathophysiological mechanisms. Here we show that a de novo Glu183 to Val (E183V) mutation in the CaMKIIα catalytic domain, identified in a proband diagnosed with ASD, decreases both CaMKIIα substrate phosphorylation and regulatory autophosphorylation, and that the mutated kinase acts in a dominant-negative manner to reduce CaMKIIα-WT autophosphorylation. The E183V mutation also reduces CaMKIIα binding to established ASD-linked proteins, such as Shank3 and subunits of l-type calcium channels and NMDA receptors, and increases CaMKIIα turnover in intact cells. In cultured neurons, the E183V mutation reduces CaMKIIα targeting to dendritic spines. Moreover, neuronal expression of CaMKIIα-E183V increases dendritic arborization and decreases both dendritic spine density and excitatory synaptic transmission. Mice with a knock-in CaMKIIα-E183V mutation have lower total forebrain CaMKIIα levels, with reduced targeting to synaptic subcellular fractions. The CaMKIIα-E183V mice also display aberrant behavioral phenotypes, including hyperactivity, social interaction deficits, and increased repetitive behaviors. Together, these data suggest that CaMKIIα plays a previously unappreciated role in ASD-related synaptic and behavioral phenotypes.SIGNIFICANCE STATEMENT Many autism spectrum disorder (ASD)-linked mutations disrupt the function of synaptic proteins, but no single gene accounts for >1% of total ASD cases. The molecular networks and mechanisms that couple the primary deficits caused by these individual mutations to core behavioral symptoms of ASD remain poorly understood. Here, we provide the first characterization of a mutation in the gene encoding CaMKIIα linked to a specific neuropsychiatric disorder. Our findings demonstrate that this ASD-linked de novo CAMK2A mutation disrupts multiple CaMKII functions, induces synaptic deficits, and causes ASD-related behavioral alterations, providing novel insights into the synaptic mechanisms contributing to ASD.

Changes in the Adult GluN2B Associated Proteome following Adolescent Intermittent Ethanol Exposure

Adolescent alcohol use is the strongest predictor for alcohol use disorders. In rodents, adolescents have distinct responses to acute ethanol, and prolonged alcohol exposure during adolescence can maintain these phenotypes into adulthood. One brain region that is particularly sensitive to the effects of both acute and chronic ethanol exposure is the hippocampus. Adolescent intermittent ethanol exposure (AIE) produces long lasting changes in hippocampal synaptic plasticity and dendritic morphology, as well as in the susceptibility to acute ethanol-induced spatial memory impairment. Given the pattern of changes in hippocampal structure and function, one potential target for these effects is the ethanol sensitive GluN2B subunit of the NMDA receptor, which is known to be involved in synaptic plasticity and dendritic morphology. Thus we sought to determine if there were persistent changes in hippocampal GluN2B signaling cascades following AIE. We employed a previously validated GluN2B-targeted proteomic strategy that was used to identify novel signaling mechanisms altered by chronic ethanol exposure in the adult hippocampus. We collected adult hippocampal tissue (P70) from rats that had been given 2 weeks of AIE from P30-45. Tissue extracts were fractionated into synaptic and non-synaptic pools, immuno-precipitated for GluN2B, and then analyzed using proteomic methods. We detected a large number of proteins associated with GluN2B. AIE produced significant changes in the association of many proteins with GluN2B in both synaptic and non-synaptic fractions. Intriguingly the number of proteins changed in the non-synaptic fraction was double that found in the synaptic fraction. Some of these proteins include those involved in glutamate signaling cytoskeleton rearrangement, calcium signaling, and plasticity. Disruptions in these pathways may contribute to the persistent cellular and behavioral changes found in the adult hippocampus following AIE. Further, the robust change in non-synaptic proteins suggests that AIE may prime this signaling pathway for future ethanol exposures in adulthood.

microRNAs Modulate Spatial Memory in the Hippocampus and in the Ventral Striatum in a Region-Specific Manner

MicroRNAs are endogenous, noncoding RNAs crucial for the post-transcriptional regulation of gene expression. Their role in spatial memory formation, however, is poorly explored. In this study, we analyzed learning-induced microRNA expression in the hippocampus and in the ventral striatum. Among miRNAs specifically downregulated by spatial training, we focused on the hippocampus-specific miR-324-5p and the ventral striatum-specific miR-24. In vivo overexpression of the two miRNAs demonstrated that miR-324-5p is able to impair memory if administered in the hippocampus but not in the ventral striatum, while the opposite is true for miR-24. Overall, these findings demonstrate a causal relationship between miRNA expression changes and spatial memory formation. Furthermore, they provide support for a regional dissociation in the post-transcriptional processes underlying spatial memory in the two brain structures analyzed.

Differential CaMKII regulation by voltage-gated calcium channels in the striatum

Calcium signaling regulates synaptic plasticity and many other functions in striatal medium spiny neurons to modulate basal ganglia function. Ca(2+)/calmodulin-dependent protein kinase II (CaMKII) is a major calcium-dependent signaling protein that couples calcium entry to diverse cellular changes. CaMKII activation results in autophosphorylation at Thr286 and sustained calcium-independent CaMKII activity after calcium signals dissipate. However, little is known about the mechanisms regulating striatal CaMKII. To address this, mouse brain slices were treated with pharmacological modulators of calcium channels and punches of dorsal striatum were immunoblotted for CaMKII Thr286 autophosphorylation as an index of CaMKII activation. KCl depolarization increased levels of CaMKII autophosphorylation ~2-fold; this increase was blocked by an LTCC antagonist and was mimicked by treatment with pharmacological LTCC activators. The chelation of extracellular calcium robustly decreased basal CaMKII autophosphorylation within 5min and increased levels of total CaMKII in cytosolic fractions, in addition to decreasing the phosphorylation of CaMKII sites in the GluN2B subunit of NMDA receptors and the GluA1 subunit of AMPA receptors. We also found that the maintenance of basal levels of CaMKII autophosphorylation requires low-voltage gated T-type calcium channels, but not LTCCs or R-type calcium channels. Our findings indicate that CaMKII activity is dynamically regulated by multiple calcium channels in the striatum thus coupling calcium entry to key downstream substrates.

Quantitative proteomics analysis of CaMKII phosphorylation and the CaMKII interactome in the mouse forebrain

Ca(2+)/calmodulin-dependent protein kinase IIα (CaMKIIα) autophosphorylation at Thr286 and Thr305/Thr306 regulates kinase activity and modulates subcellular targeting and is critical for normal synaptic plasticity and learning and memory. Here, a mass spectrometry-based approach was used to identify Ca(2+)-dependent and -independent in vitro autophosphorylation sites in recombinant CaMKIIα and CaMKIIβ. CaMKII holoenzymes were then immunoprecipitated from subcellular fractions of forebrains isolated from either wild-type (WT) mice or mice with a Thr286 to Ala knock-in mutation of CaMKIIα (T286A-KI mice) and analyzed using the same approach in order to characterize in vivo phosphorylation sites in both CaMKII isoforms and identify CaMKII-associated proteins (CaMKAPs). A total of six and seven autophosphorylation sites in CaMKIIα and CaMKIIβ, respectively, were detected in WT mice. Thr286-phosphorylated CaMKIIα and Thr287-phosphorylated CaMKIIβ were selectively enriched in WT Triton-insoluble (synaptic) fractions compared to Triton-soluble (membrane) and cytosolic fractions. In contrast, Thr306-phosphorylated CaMKIIα and Ser315- and Thr320/Thr321-phosphorylated CaMKIIβ were selectively enriched in WT cytosolic fractions. The T286A-KI mutation significantly reduced levels of phosphorylation of CaMKIIα at Ser275 across all subcellular fractions and of cytosolic CaMKIIβ at Ser315 and Thr320/Thr321. Significantly more CaMKAPs coprecipitated with WT CaMKII holoenzymes in the synaptic fraction compared to that in the membrane fraction, with functions including scaffolding, microtubule organization, actin organization, ribosomal function, vesicle trafficking, and others. The T286A-KI mutation altered the interactions of multiple CaMKAPs with CaMKII, including several proteins linked to autism spectrum disorders. These data identify CaMKII isoform phosphorylation sites and a network of synaptic protein interactions that are sensitive to the abrogation of Thr286 autophosphorylation of CaMKIIα, likely contributing to the diverse synaptic and behavioral deficits of T286A-KI mice.

In vivo amphetamine action is contingent on αCaMKII

Addiction to psychostimulants (ie, amphetamines and cocaine) imposes a major socioeconomic burden. Prevention and treatment represent unmet medical needs, which may be addressed, if the mechanisms underlying psychostimulant action are understood. Cocaine acts as a blocker at the transporters for dopamine (DAT), serotonin (SERT), and norepinephrine (NET), but amphetamines are substrates that do not only block the uptake of monoamines but also induce substrate efflux by promoting reverse transport. Reverse transport has been a focus of research for decades but its mechanistic basis still remains enigmatic. Recently, transporter-interacting proteins were found to regulate amphetamine-triggered reverse transport: calmodulin kinase IIα (αCaMKII) is a prominent example, because it binds the carboxyl terminus of DAT, phosphorylates its amino terminus, and supports amphetamine-induced substrate efflux in vitro. Here, we investigated whether, in vivo, the action of amphetamine was contingent on the presence of αCaMKII by recording the behavioral and neurochemical effects of amphetamine. Measurement of dopamine efflux in the dorsal striatum by microdialysis revealed that amphetamine induced less dopamine efflux in mice lacking αCaMKII. Consistent with this observation, the acute locomotor responses to amphetamine were also significantly blunted in αCaMKII-deficient mice. In addition, while the rewarding properties of amphetamine were preserved in αCaMKII-deficient mice, their behavioral sensitization to amphetamine was markedly reduced. Our findings demonstrate that amphetamine requires the presence of αCaMKII to elicit a full-fledged effect on DAT in vivo: αCaMKII does not only support acute amphetamine-induced dopamine efflux but is also important in shaping the chronic response to amphetamine.

Gastrodin ameliorates Parkinson's disease by downregulating connexin 43

Gastrodin, the predominant constituent of a Chinese herbal medicine, has been utilized in the prevention of Parkinson's disease (PD); however, its mechanism of action remains unknown. Astrocytes are involved in PD and are proposed to be coupled with gap junction connexin 43 (Cx43). To evaluate the effects of gastrodin on PD, the effect of gastrodin on Cx43 in astrocytes and in a PD model were observed. Different doses of gastrodin were added to the astrocyte culture medium or injected into the rotenone model of PD. The relative expression of Cx43 was determined by qPCR and western blot analysis, while gap junctional intercellular communication (GJIC) was quantified using fluorescence recovery after photobleaching (FRAP). The phosphorylated Cx43 was significantly inhibited by gastrodin and the quantity of GJIC was significantly downregulated compared with that of the control cells (P<0.05). In addition, in the rat model of PD induced by rotenone, phosphorylated Cx43 was selectively enhanced in the striatal and hippocampal regions. The enhanced activity was inhibited significantly by gastrodin treatment (P<0.01). Gastrodin results in the prevention of PD by reducing the expression of Cx43 and inhibiting the phosphorylation of Cx43; therefore, it may offer a potential therapeutic alternative for patients with PD.

Metabolic regulation of CaMKII protein and caspases in Xenopus laevis egg extracts

The metabolism of the Xenopus laevis egg provides a cell survival signal. We found previously that increased carbon flux from glucose-6-phosphate (G6P) through the pentose phosphate pathway in egg extracts maintains NADPH levels and calcium/calmodulin regulated protein kinase II (CaMKII) activity to phosphorylate caspase 2 and suppress cell death pathways. Here we show that the addition of G6P to oocyte extracts inhibits the dephosphorylation/inactivation of CaMKII bound to caspase 2 by protein phosphatase 1. Thus, G6P sustains the phosphorylation of caspase 2 by CaMKII at Ser-135, preventing the induction of caspase 2-mediated apoptotic pathways. These findings expand our understanding of oocyte biology and clarify mechanisms underlying the metabolic regulation of CaMKII and apoptosis. Furthermore, these findings suggest novel approaches to disrupt the suppressive effects of the abnormal metabolism on cell death pathways.