Synapse-associated Protein Research Articles

A Two-state Model for the Diffusion of the A2A Adenosine Receptor in Hippocampal Neurons: AGONIST-INDUCED SWITCH TO SLOW MOBILITY IS MODIFIED BY SYNAPSE-ASSOCIATED PROTEIN 102 (SAP102)

The A2A receptor is a class A/rhodopsin-like G protein-coupled receptor. Coupling to its cognate protein, Gs, occurs via restricted collision coupling and is contingent on the presence of cholesterol. Agonist activation slows diffusion of the A2A adenosine receptor in the lipid bilayer. We explored the contribution of the hydrophobic core and of the extended C terminus by examining diffusion of quantum dot-labeled receptor variants in dissociated hippocampal neurons. Single particle tracking of the A2A receptor(1-311), which lacks the last 101 residues, revealed that agonist-induced confinement was abolished and that the agonist-induced decrease in diffusivity was reduced substantially. A fragment comprising the SH3 domain and the guanylate kinase domain of synapse-associated protein 102 (SAP102) was identified as a candidate interactor that bound to the A2A receptor C terminus. Complex formation between the A2A receptor and SAP102 was verified by coimmunoprecipitation and by tracking its impact on receptor diffusion. An analysis of all trajectories by a hidden Markov model was consistent with two diffusion states where agonist activation reduced the transition between the two states and, thus, promoted the accumulation of the A2A receptor in the compartment with slow mobility. Overexpression of SAP102 precluded the access of the A2A receptor to a compartment with restricted mobility. In contrast, a mutated A2A receptor (with (383)DVELL(387) replaced by RVRAA) was insensitive to the action of SAP102. These observations show that the hydrophobic core per se does not fully account for the agonist-promoted change in mobility of the A2A receptor. The extended carboxyl terminus allows for regulatory input by scaffolding molecules such as SAP102.

Effects of curcumin on chronic, unpredictable, mild, stress-induced depressive-like behaviour and structural plasticity in the lateral amygdala of rats

Depression is a neuropsychiatric disease associated with wide ranging disruptions in neuronal plasticity throughout the brain. Curcumin, a natural polyphenolic compound of curcuma loga, has been demonstrated to be effective in the treatment of depressive-like disorders. The present study aimed to investigate the mechanisms underlying the antidepressant-like effects of curcumin in a rat model of chronic, unpredictable, mild, stress (CUMS) -induced depression. The results showed that CUMS produced depressive-like behaviours in rats, which were associated with ultra-structural changes in neurons within the lateral amygdala (LA). In addition, the expression of synapse-associated proteins such as brain-derived neurotrophic factor (BDNF), PSD-95 and synaptophysin were significantly decreased in the LA of CUMS-treated rats. Chronic administration of curcumin (40 mg/kg, i.p. 6 wk) before stress exposure significantly prevented these neuronal and biochemical alterations induced by CUMS, and suppressed depressive-like behaviours, suggesting that this neuronal dysregulation may be related to the depressive-like behaviours caused by CUMS. Together with our previous results, the current findings demonstrate that curcumin exhibits neuroprotection and antidepressant-like effects in the CUMS-induced depression model. Furthermore, this antidepressant-like action of curcumin appears to be mediated by modulating synapse-associated proteins within the LA. These findings provide new insights into the underlying mechanisms leading to neural dysfunction in depression and reveal the therapeutic potential for curcumin use in clinical trials.

Abstract 19102: Cardiac Specific Ablation of SAP97 Alters Normal Excitability of the Murine Heart

Synapse-associated protein 97 (SAP97) is a scaffolding protein and is the archetypical MAGUK. In vitro studies suggest that SAP97 regulates expression of cardiac Na and K channels, and may be important for cardiac excitation. OBJECTIVES: To generate a model for inducible, targeted SAP97 ablation, and to investigate arrhythmia susceptibility and the underlying cellular/molecular mechanisms. Methods: SAP97 targeted deletion was generated using the Cre-Lox system. Animals were subjected to biochemistry, electrophysiology, echo- and electrocardiographic analyses. Results: Western blot analyses demonstrated SAP97 ablation was specific to the myocardium. Test animals showed several ECG abnormalities; including changes in P waves, premature atrial contractions, and prolongations in ST and QT intervals. ST interval averaged (ms) 22.3±2.53 (heterozygote) compared to 15.9±0.98 (control; p=0.03). ST prolongation was more pronounced (34.8±2.22 ms) in homozygote than in heterozygote mice; p< 0.001. Similarly, QT interval was much longer in homozygote than in heterozygote animals, both of which were longer than control values (p<0.001; n=13-15 in each group). In isolated ventricular cells, action potential duration at 80% repolarization; (APD80) were significantly longer in test animals compared to controls. Thus, control APD80 (ms) was 11.6±2.38 versus 47.19±11.27 in heterozygote animals (p=0.012). APD prolongation was more severe in homozygote animals. Early after depolarizations were more prevalent in test mice, compared to control. Data in cells isolated from control and homozygote mouse hearts showed significant changes in INa, ITO and IK1 current densities following SAP97 ablation. Control densities of ITO and IK1 were (pA/pF) 43.68±3.91 (+60mV) and -18.13±0.95 (-120mV) and were 19.96±2.48 and -12.38±0.64 after SAP97 ablation. In contrast, INa density was upregulated, averaging (pA/pF) -32.52±4.60 (-50mV) in control and -47.53±4.47 after SAP97 ablation. Conclusion: SAP97 is important for normal functionality of cardiac ion channels in the murine myocardium, and its ablation predisposes to arrhythmogenicity. Our model of targeted SAP97 ablation is important for understanding the role of SAP97 in cardiac excitation.

P.1.j.022 A dopamine D1 agonist improved ketamineinduced spatial working memory dysfunction in common marmosets

Using the RNA arbitrarily-primed PCR and the competitive RT-PCR, we have isolated the neocortical transcripts that are upregulated and unchanged in the adult and infant rats, respectively, after a systemic injection of an N-methyl-d-aspartate (NMDA) receptor antagonist phencyclidine (PCP), and found them identical to the synapse-associated protein-97 (SAP97) gene mRNAs. The upregulation of the SAP97 transcripts in the adult neocortex after the acute PCP injection was mimicked by another NMDA antagonist, dizocilpine, but not by the indirect dopamine agonists, methamphetamine and cocaine, a selective D1 receptor antagonist SCH23390, a D2 receptor-preferring antagonist haloperidol and a GABAergic anesthetic pentobarbital. Moreover, the pretreatment with a typical antipsychotic haloperidol failed to antagonize the increased neocortical SAP97 gene expression by PCP. These findings suggest that SAP97 might be involved in the molecular basis of the development-dependent onset of the non-dopaminergic symptoms seen in schizophrenia and the schizophrenia-like psychosis induced by NMDA receptor blocking.

Identification and Structural Characterization of Interneurons of the Drosophila Brain by Monoclonal Antibodies of the Würzburg Hybridoma Library

Several novel synaptic proteins have been identified by monoclonal antibodies (mAbs) of the Würzburg hybridoma library generated against homogenized Drosophila brains, e.g. cysteine string protein, synapse-associated protein of 47 kDa, and Bruchpilot. However, at present no routine technique exists to identify the antigens of mAbs of our library that label only a small number of cells in the brain. Yet these antibodies can be used to reproducibly label and thereby identify these cells by immunohistochemical staining. Here we describe the staining patterns in the Drosophila brain for ten mAbs of the Würzburg hybridoma library. Besides revealing the neuroanatomical structure and distribution of ten different sets of cells we compare the staining patterns with those of antibodies against known antigens and GFP expression patterns driven by selected Gal4 lines employing regulatory sequences of neuronal genes. We present examples where our antibodies apparently stain the same cells in different Gal4 lines suggesting that the corresponding regulatory sequences can be exploited by the split-Gal4 technique for transgene expression exclusively in these cells. The detection of Gal4 expression in cells labeled by mAbs may also help in the identification of the antigens recognized by the antibodies which then in addition to their value for neuroanatomy will represent important tools for the characterization of the antigens. Implications and future strategies for the identification of the antigens are discussed.

Synaptic State-Dependent Functional Interplay between Postsynaptic Density-95 and Synapse-Associated Protein 102

Activity-dependent regulation of AMPA receptor (AMPAR)-mediated synaptic transmission is the basis for establishing differences in synaptic weights among individual synapses during developmental and experience-dependent synaptic plasticity. Synaptic signaling scaffolds of the Discs large (DLG)-membrane-associated guanylate kinase (MAGUK) protein family regulate these processes by tethering signaling proteins to receptor complexes. Using a molecular replacement strategy with RNAi-mediated knockdown in rat and mouse hippocampal organotypic slice cultures, a postsynaptic density-95 (PSD-95) knock-out mouse line and electrophysiological analysis, our current study identified a functional interplay between two paralogs, PSD-95 and synapse-associated protein 102 (SAP102) to regulate synaptic AMPARs. During synaptic development, the SAP102 protein levels normally plateau but double if PSD-95 expression is prevented during synaptogenesis. For an autonomous function of PSD-95 in regulating synaptic AMPARs, in addition to the previously demonstrated N-terminal multimerization and the first two PDZ (PSD-95, Dlg1, zona occludens-1) domains, the PDZ3 and guanylate kinase domains were required. The Src homology 3 domain was dispensable for the PSD-95-autonomous regulation of basal synaptic transmission. However, it mediated the functional interaction with SAP102 of PSD-95 mutants to enhance AMPARs. These results depict a protein domain-based multifunctional aspect of PSD-95 in regulating excitatory synaptic transmission and unveil a novel form of domain-based interplay between signaling scaffolds of the DLG-MAGUK family.

Synapse-Associated Protein 97 Regulates the Membrane Properties of Fast-Spiking Parvalbumin Interneurons in the Visual Cortex

Fast-spiking parvalbumin (PV)-positive interneurons in layers 2/3 of the visual cortex regulate gain control and tuning of visual processing. Synapse-associated protein 97 (SAP97) belongs to a family of proteins that have been implicated in regulating glutamatergic synaptic transmission at pyramidal-to-pyramidal connections in the nervous system. For PV interneurons in mouse visual cortex, the expression of SAP97 is developmentally regulated, being expressed in almost all juvenile but only a fraction, ~40%, of adult PV interneurons. Using whole-cell patch-clamping, single-cell RT-PCR to assay endogenous expression of SAP97 and exogenous expression of SAP97, we investigated the functional significance of SAP97 in PV interneurons in layers 2/3 of the visual cortex. PV interneurons expressing SAP97, either endogenously or via exogenous expression, showed distinct membrane properties from those not expressing SAP97. This included an overall decrease in membrane excitability, as indexed by a decrease in membrane resistance and an increase in the stimulus threshold for the first action potential firing. Additionally, SAP97-expressing PV interneurons fired action potentials more frequently and, at moderate stimulus intensities, showed irregular or stuttering firing patterns. Furthermore, SAP97-expressing PV interneurons showed increased glutamatergic input and more extensive dendritic branching when compared with non-expressing PV interneurons. These differences in membrane and synaptic properties would significantly alter how PV interneurons expressing SAP97 compared with those not expressing SAP97 would function in local networks. Thus, our results indicate that the scaffolding protein SAP97 is a critical molecular factor regulating the input-output relationships of cortical PV interneurons.

Modulation of 5-Lipoxygenase in Proteotoxicity and Alzheimer's Disease

The accumulation of intracellular β amyloid (Aβ) may be one of the factors leading to neuronal cell death in Alzheimer's disease (AD). Using a pyrazole called CNB-001, which was selected for its ability to reduce intracellular Aβ, we show that the activation of the eIF2α/ATF4 arm of the unfolded protein response is sufficient to degrade aggregated intracellular Aβ. CNB-001 is a potent inhibitor of 5-lipoxygenase (5-LOX), decreases 5-LOX expression, and increases proteasome activity. 5-LOX inhibition induces eIF2α and PERK (protein kinase R-like extracellular signal-regulated kinase) phosphorylation, and HSP90 and ATF4 levels. When fed to AD transgenic mice, CNB-001 also increases eIF2α phosphorylation and HSP90 and ATF4 levels, and limits the accumulation of soluble Aβ and ubiquitinated aggregated proteins. Finally, CNB-001 maintains the expression of synapse-associated proteins and improves memory. Therefore, 5-LOX metabolism is a key element in the promotion of endoplasmic reticulum dysfunction, and its inhibition under conditions of stress is sufficient to reduce proteotoxicity both in vivo and in vitro.

Altered Pancreatic Islet Function and Morphology in Mice Lacking the Beta-Cell Surface Protein Neuroligin-2

Neuroligin-2 is a transmembrane, cell-surface protein originally identified as an inhibitory synapse-associated protein in the central nervous system. Neuroligin-2 is also present on the pancreatic beta-cell surface, and there it engages in transcellular interactions that drive functional maturation of the insulin secretory machinery; these are necessary for normal insulin secretion. The effects of neuroligin-2 deficiency on brain and neuronal function and morphology and on behavior and coordination have been extensively characterized using neuroligin-2 knockout mice. The effects of absent neuroligin-2 expression on islet development and function, however, are unknown. Here, to help test whether neuroligin-2 is necessary for normal islet development, we characterized islet morphology in mice lacking neuroligin-2. To test whether–as predicted by our earlier co-culture studies–absence of neuroligin-2 impairs beta cell function, we compared glucose-stimulated insulin secretion by islets from mutant and wild-type mice. Our results show that while islets from neuroligin-2-deficient mice do not to appear to differ architecturally from wild-type islets, they are smaller, fewer in number, and contain beta cells with lower insulin content. Evaluation of transcript levels suggests that upregulation of neuroligin-1 helps compensate for loss of neuroligin-2. Surprisingly, under both basal and stimulating glucose levels, isolated islets from the knockout mice secreted more of their intracellular insulin content. Rat islets with shRNA-mediated neuroligin-2 knockdown also exhibited increased insulin secretion. Neurexin transcript levels were lower in the knockout mice and, consistent with our prior finding that neurexin is a key constituent of the insulin granule docking machinery, insulin granule docking was reduced. These results indicate that neuroligin-2 is not necessary for the formation of pancreatic islets but that neuroligin-2 influences islet size and number. Neuroligin-2–perhaps through its effects on the expression and/or activity of its binding partner neurexin–promotes insulin granule docking, a known constraint on insulin secretion.

Double deletion of melanocortin 4 receptors and SAPAP3 corrects compulsive behavior and obesity in mice

Compulsive behavior is a debilitating clinical feature of many forms of neuropsychiatric disease, including Tourette syndrome, obsessive-compulsive spectrum disorders, eating disorders, and autism. Although several studies link striatal dysfunction to compulsivity, the pathophysiology remains poorly understood. Here, we show that both constitutive and induced genetic deletion of the gene encoding the melanocortin 4 receptor (MC4R), as well as pharmacologic inhibition of MC4R signaling, normalize compulsive grooming and striatal electrophysiologic impairments in synapse-associated protein 90/postsynaptic density protein 95-associated protein 3 (SAPAP3)-null mice, a model of human obsessive-compulsive disorder. Unexpectedly, genetic deletion of SAPAP3 restores normal weight and metabolic features of MC4R-null mice, a model of human obesity. Our findings offer insights into the pathophysiology and treatment of both compulsive behavior and eating disorders.

Adenylyl Cyclase Anchoring by a Kinase Anchor Protein AKAP5 (AKAP79/150) Is Important for Postsynaptic β-Adrenergic Signaling

Recent evidence indicates that the A kinase anchor protein AKAP5 (AKAP79/150) interacts not only with PKA but also with various adenylyl cyclase (AC) isoforms. However, the physiological relevance of AC-AKAP5 binding is largely unexplored. We now show that postsynaptic targeting of AC by AKAP5 is important for phosphorylation of the AMPA-type glutamate receptor subunit GluA1 on Ser-845 by PKA and for synaptic plasticity. Phosphorylation of GluA1 on Ser-845 is strongly reduced (by 70%) under basal conditions in AKAP5 KO mice but not at all in D36 mice, in which the PKA binding site of AKAP5 (i.e. the C-terminal 36 residues) has been deleted without affecting AC association with GluA1. The increase in Ser-845 phosphorylation upon β-adrenergic stimulation is much more severely impaired in AKAP5 KO than in D36 mice. In parallel, long term potentiation induced by a 5-Hz/180-s tetanus, which mimics the endogenous θ-rhythm and depends on β-adrenergic stimulation, is only modestly affected in acute forebrain slices from D36 mice but completely abrogated in AKAP5 KO mice. Accordingly, anchoring of not only PKA but also AC by AKAP5 is important for regulation of postsynaptic functions and specifically AMPA receptor activity.

Early degeneration of photoreceptor synapse inCcl2/Cx3cr1-deficient mice onCrb1rd8background

Photoreceptor ribbon synapse releases glutamate to postsynaptic targets. The synaptic ribbon may play multiple roles in ribbon synapse development, synaptic vesicle recycling, and synaptic transmission. Age-related macular degeneration (AMD) patients appear to have fewer or no detectable synaptic ribbons as well as abnormal swelling in the photoreceptor terminals in the macula. However, reports on changes of photoreceptor synapses in AMD are scarce and photoreceptor type and quantity affected in early AMD is still unclear. Here, we employed multiple anatomical techniques to investigate these questions in Ccl2⁻/⁻/Cx3cr1⁻/⁻ mouse on Crb1(rd8) background (DKO rd8) at one month of age. We found that approximately 17% of photoreceptors over the focal lesion were lost. Immunostaining for synapse-associated proteins (CtBP2, synaptophysin, and vesicular glutamate transporter 1) showed significantly reduced expression and ectopic localization. Cone opsins demonstrated dramatic reduction in expression (S-opsins) and extensive mislocalization (M-opsins). Quantitative ultrastructural analysis confirmed a significant decrease in the number of cone terminals and nuclei, numerous vacuoles in remaining cone terminals, reduction in the number of synaptic ribbons in photoreceptor terminals, and ectopic rod ribbon synapses. In addition, glutamate receptor immunoreactivity on aberrant sprouting of rod bipolar cells and horizontal cells were identified at the ectopic synapses. These results indicate that synaptic alterations occur at the early stages of disease and cones are likely more susceptible to damage caused by DKO rd8 mutation. They provide a new insight into potential mechanism of vision function lost due to synaptic degeneration before cell death in the early stages of AMD.

Endocytosis of synaptic ADAM10 in neuronal plasticity and Alzheimer’s disease

A disintegrin and metalloproteinase 10 (ADAM10), a disintegrin and metalloproteinase that resides in the postsynaptic densities (PSDs) of excitatory synapses, has previously been shown to limit β-amyloid peptide (Aβ) formation in Alzheimer's disease (AD). ADAM10 also plays a critical role in regulating functional membrane proteins at the synapse. Using human hippocampal homogenates, we found that ADAM10 removal from the plasma membrane was mediated by clathrin-dependent endocytosis. Additionally, we identified the clathrin adaptor AP2 as an interacting partner of a previously uncharacterized atypical binding motif in the ADAM10 C-terminal domain. This domain was required for ADAM10 endocytosis and modulation of its plasma membrane levels. We found that the ADAM10/AP2 association was increased in the hippocampi of AD patients compared with healthy controls. Long-term potentiation (LTP) in hippocampal neuronal cultures induced ADAM10 endocytosis through AP2 association and decreased surface ADAM10 levels and activity. Conversely, long-term depression (LTD) promoted ADAM10 synaptic membrane insertion and stimulated its activity. ADAM10 interaction with the synapse-associated protein-97 (SAP97) was necessary for LTD-induced ADAM10 trafficking and required for LTD maintenance and LTD-induced changes in spine morphogenesis. These data identify and characterize a mechanism controlling ADAM10 localization and activity at excitatory synapses that is relevant to AD pathogenesis.

The enigma of B cell memory: the scaffolding protein synapse-associated protein 97 is required for enhanced activation signaling through isotype-switched IgG memory B cell receptors (P1124)

Abstract The acquired immunological memory was probably first described by the Greek historian Thucydides who observed during a plague in Athens in 430 BCE that “the same man was never attacked twice”. Now 2442 years later, the mechanisms by which the IgG-BCRs function to enhance B cell responses are not completely understood. We showed earlier that the membrane proximal region of the mIgG1 cytoplasmic tail is necessary and sufficient to dramatically enhance the initiation of BCR signaling. We identified that the conserved cytoplasmic tail of the IgG BCR, which contains a putative PDZ-binding motif, associated with SAP97, a PDZ domain containing scaffolding molecule that is involved in controlling receptor density and signal strength at neuronal synapses. SAP97 accumulated and bound to IgG BCRs in the immunological synapses (IS) that formed in response to B cell engagement with antigen. Knocking down SAP97 in IgG+ B cells or mutating the putative PDZ-binding motif on mIgG impaired formation of the IS, initiation of IgG BCR signaling, and downstream activation of the mitogen-activated protein kinase p38. Our subsequent studies showed that SAP97 binding protein, ERM family member ezrin, actively involved in the burst-enhanced memory B cell activation through isotype-switched IgG memory B Cell Receptors. Thus, our studies propose that SAP97 serves as a scaffold protein stabilizing the antigen-driven formation of IgG BCR oligomers and facilitating assembly of the BCR signalosome.

Role of SAP97 Protein in the Regulation of Corticotropin-releasing Factor Receptor 1 Endocytosis and Extracellular Signal-regulated Kinase 1/2 Signaling

The corticotropin-releasing factor (CRF) receptor 1 (CRFR1) is a target for the treatment of psychiatric diseases such as depression, schizophrenia, anxiety disorder, and bipolar disorder. The carboxyl-terminal tail of the CRFR1 terminates in a PDZ-binding motif that provides a potential site for the interaction of PSD-95/Discs Large/Zona Occludens 1 (PDZ) domain-containing proteins. In this study, we found that CRFR1 interacts with synapse-associated protein 97 (SAP97; also known as DLG1) by co-immunoprecipitation in human embryonic 293 (HEK 293) cells and cortical brain lysates and that this interaction is dependent upon an intact PDZ-binding motif at the end of the CRFR1 carboxyl-terminal tail. Similarly, we demonstrated that SAP97 is recruited to the plasma membrane in HEK 293 cells expressing CRFR1 and that mutation of the CRFR1 PDZ-binding motif results in the redistribution of SAP97 into the cytoplasm. Overexpression of SAP97 antagonized agonist-stimulated CRFR1 internalization, whereas single hairpin (shRNA) knockdown of endogenous SAP97 in HEK 293 cells resulted in increased agonist-stimulated CRFR1 endocytosis. CRFR1 was internalized as a complex with SAP97 resulting in the redistribution of SAP97 to endocytic vesicles. Overexpression or shRNA knockdown of SAP97 did not significantly affect CRFR1-mediated cAMP formation, but SAP97 knockdown did significantly attenuate CRFR1-stimulated ERK1/2 phosphorylation in a PDZ interaction-independent manner. Taken together, our studies show that SAP97 interactions with CRFR1 attenuate CRFR1 endocytosis and that SAP97 is involved in coupling G protein-coupled receptors to the activation of the ERK1/2 signaling pathway.

Inhibition of Spontaneous Recovery of Fear by mGluR5 after Prolonged Extinction Training

Fear behavior is vital for survival and involves learning contingent associations of non-threatening cues with aversive stimuli. In contrast, excessive levels of fear can be maladaptive and lead to anxiety disorders. Generally, extensive sessions of extinction training correlates with reduced spontaneous recovery. The molecular mechanisms underlying the long-term inhibition of fear recovery following repeated extinction training are not fully understood. Here we show that in rats, prolonged extinction training causes greater reduction in both fear-potentiated startle and spontaneous recovery. This effect was specifically blocked by metabotropic glutamate receptor 5 (mGluR5), but not by mGluR1 antagonists and by a protein synthesis inhibitor. Similar inhibition of memory recovery following prolonged extinction training was also observed in mice. In agreement with the instrumental role of mGluR5 in the prolonged inhibition of fear recovery, we found that FMR1−/− mice which exhibit enhanced mGluR5-mediated signaling exhibit lower spontaneous recovery of fear after extinction training than wild-type littermates. At the molecular level, we discovered that prolonged extinction training reversed the fear conditioning-induced increase in surface expression of GluR1, AMPA/NMDA ratio, postsynaptic density-95 (PSD-95) and synapse-associated protein-97 (SAP97). Accordingly, delivery of Tat-GluR23Y, a synthetic peptide that blocks AMPA receptor endocytosis, inhibited prolonged extinction training-induced inhibition of fear recovery. Together, our results demonstrate that prolonged extinction training results in the mGluR5-dependent long-term inhibition of fear recovery. This effect may involve the degradation of original memory and may explain the beneficial effects of prolonged exposure therapy for the treatment of phobias.

Altered expression of genes for Kir ion channels in dilated cardiomyopathy

Dilated cardiomyopathy (DCM) is a multifactorial disease characterized by left ventricular dilation that is associated with systolic dysfunction and increased action potential duration. The Kir2.x K⁺ channels (encoded by KCNJ genes) regulate the inward rectifier current (IK1) contributing to the final repolarization in cardiac muscle. Here, we describe the transitions in the gene expression profiles of 4 KCNJ genes from healthy or dilated cardiomyopathic human hearts. In the healthy adult ventricles, KCNJ2, KCNJ12, and KCNJ4 (Kir2.1-2.3, respectively) genes were expressed at high levels, while expression of the KCNJ14 (Kir2.4) gene was low. In DCM ventricles, the levels of Kir2.1 and Kir2.3 were upregulated, but those of Kir2.2 channels were downregulated. Additionally, the expression of the DLG1 gene coding for the synapse-associated protein 97 (SAP97) anchoring molecule exhibited a 2-fold decline with increasing age in normal hearts, and it was robustly downregulated in young DCM patients. These adaptations could offer a new aspect for the explanation of the generally observed physiological and molecular alterations found in DCM.

GluA1 promotes the activity‐dependent development of motor circuitry in the developing segmental spinal cord

The neuronal dendritic tree is a key determinant of how neurons receive, compute, and transmit information. During early postnatal life, synaptic activity promotes dendrite elaboration. Spinal motor neurons utilize GluA1-containing AMPA (2-amino-3-(3-hydroxy-5-methyl-isoxazol-4-yl) propanoic acid) receptors (AMPA-R) to control this process. This form of developmental dendrite growth can occur independently of N-methyl-d-aspartate receptors (NMDA-R). This review focuses on the mechanism by which the GluA1 subunit of AMPA-R transforms synaptic activity into dendrite growth, and describes the essential role of the GluA1 binding partner SAP97 (synapse-associated protein of 97 kDa molecular weight) in this process. This work defines a new mechanism of activity-dependent development, which might be harnessed to stimulate the recovery of function following insult to the central nervous system.

Effects of antipsychotic drugs on the expression of synaptic proteins and dendritic outgrowth in hippocampal neuronal cultures

Recent evidence has suggested that atypical antipsychotic drugs regulate synaptic plasticity. We investigated whether some atypical antipsychotic drugs (olanzapine, aripiprazole, quetiapine, and ziprasidone) altered the expression of synapse-associated proteins in rat hippocampal neuronal cultures under toxic conditions induced by B27 deprivation. A typical antipsychotic, haloperidol, was used for comparison. We measured changes in the expression of various synaptic proteins including postsynaptic density protein-95 (PSD-95), brain-derived neurotrophic factor (BDNF), and synaptophysin (SYP). Then we examined whether these drugs affected the dendritic morphology of hippocampal neurons. We found that olanzapine, aripiprazole, and quetiapine, but not haloperidol, significantly hindered the B27 deprivation-induced decrease in the levels of these synaptic proteins. Ziprasidone did not affect PSD-95 or BDNF levels, but significantly increased the levels of SYP under B27 deprivation conditions. Moreover, olanzapine and aripiprazole individually significantly increased the levels of PSD-95 and BDNF, respectively, even under normal conditions, whereas haloperidol decreased the levels of PSD-95. These drugs increased the total outgrowth of hippocampal dendrites via PI3K signaling, whereas haloperidol had no effect in this regard. Together, these results suggest that the up-regulation of synaptic proteins and dendritic outgrowth may represent key effects of some atypical antipsychotic drugs but that haloperidol may be associated with distinct actions.

Circuit-Selective Striatal Synaptic Dysfunction in the Sapap3 Knockout Mouse Model of Obsessive-Compulsive Disorder

Synapse-associated protein 90/postsynaptic density protein 95-associated protein 3 (SAPAP3) is an excitatory postsynaptic protein implicated in the pathogenesis of obsessive-compulsive behaviors. In mice, genetic deletion of Sapap3 causes obsessive-compulsive disorder (OCD)-like behaviors that are rescued by striatal expression of Sapap3, demonstrating the importance of striatal neurotransmission for the OCD-like behaviors. In the striatum, there are two main excitatory synaptic circuits, corticostriatal and thalamostriatal. Neurotransmission defects in either or both of these circuits could potentially contribute to the OCD-like behaviors of Sapap3 knockout (KO) mice. Previously, we reported that Sapap3 deletion reduces corticostriatal alpha-amino-3-hydroxy-5-methyl-4-isoxazole-propionic acid-type glutamate receptor-mediated synaptic transmission. Whole-cell electrophysiological recording techniques in acute brain slices were used to measure synaptic transmission in the corticostriatal and thalamostriatal circuits of Sapap3 KO mice and littermate control animals. Transgenic fluorescent reporters identified striatopallidal and striatonigral projection neurons. SAPAP isoforms at corticostriatal and thalamostriatal synapses were detected using immunostaining techniques. In contrast to corticostriatal synapses, thalamostriatal synaptic activity is unaffected by Sapap3 deletion. At the molecular level, we find that another SAPAP family member, SAPAP4, is present at thalamostriatal, but not corticostriatal, synapses. This finding provides a molecular rationale for the functional divergence we observe between thalamic and cortical striatal circuits in Sapap3 KO mice. These findings define the circuit-level neurotransmission defects in a genetic mouse model for OCD-related behaviors, focusing attention on the corticostriatal circuit for mediating the behavioral abnormalities. Our results also provide the first evidence that SAPAP isoforms may be localized to synapses according to circuit-selective principles.