SynGAP-MUPP1-CaMKII Synaptic Complexes Regulate p38 MAP Kinase Activity and NMDA Receptor- Dependent Synaptic AMPA Receptor Potentiation

Structural and Intermolecular Associations Between Connexin36 and Protein Components of the Adherens Junction-Neuronal Gap Junction Complex

Intimate structural and functional relationships between gap junctions and adherens junctions have been demonstrated in peripheral tissues, but have not been thoroughly examined in the central nervous system, where adherens junctions are often found in close proximity to neuronal gap junctions. Here, we used immunofluorescence approaches to document the localization of various protein components of adherens junctions in relation to those that we have previously reported to occur at electrical synapses formed by neuronal gap junctions composed of connexin36 (Cx36). The adherens junction constituents N-cadherin and nectin-1 were frequently found to localize near or overlap with Cx36-containing gap junctions in several brain regions examined. This was also true of the adherens junction-associated proteins α-catenin and β-catenin, as well as the proteins zonula occludens-1 and AF6 (aka, afadin) that were reported constituents of both adherens junctions and gap junctions. The deployment of the protein constituents of these junctions was especially striking at somatic contacts between primary afferent neurons in the mesencephalic trigeminal nucleus (MesV), where the structural components of adherens junctions appeared to be maintained in connexin36 null mice. These results support emerging views concerning the multi-molecular composition of electrical synapses and raise possibilities for various structural and functional protein-protein interactions at what now can be considered the adherens junction-neuronal gap junction complex. Further, the results point to intracellular signaling pathways that could potentially contribute to the assembly, maintenance and turnover of this complex, as well as to the dynamic nature of neuronal communication at electrical synapses.

Phosphorylation of synaptic GTPase-activating protein (synGAP) by polo-like kinase (Plk2) alters the ratio of its GAP activity toward HRas, Rap1 and Rap2 GTPases

SynGAP is a Ras and Rap GTPase-activating protein (GAP) found in high concentration in the postsynaptic density (PSD) fraction from mammalian forebrain where it binds to PDZ domains of PSD-95. Phosphorylation of pure recombinant synGAP by Ca²⁺/calmodulin-dependent protein kinase II (CaMKII) shifts the balance of synGAP's GAP activity toward inactivation of Rap1; whereas phosphorylation by cyclin-dependent kinase 5 (CDK5) has the opposite effect, shifting the balance toward inactivation of HRas. These shifts in balance contribute to regulation of the numbers of surface AMPA receptors, which rise during synaptic potentiation (CaMKII) and fall during synaptic scaling (CDK5). Polo-like kinase 2 (Plk2/SNK), like CDK5, contributes to synaptic scaling. These two kinases act in concert to reduce the number of surface AMPA receptors following elevated neuronal activity by tagging spine-associated RapGAP protein (SPAR) for degradation, thus raising the level of activated Rap. Here we show that Plk2 also phosphorylates and regulates synGAP. Phosphorylation of synGAP by Plk2 stimulates its GAP activity toward HRas by 65%, and toward Rap1 by 16%. Simultaneous phosphorylation of synGAP by Plk2 and CDK5 at distinct sites produces an additive increase in GAP activity toward HRas (∼230%) and a smaller, non-additive increase in activity toward Rap1 (∼15%). Dual phosphorylation also produces an increase in GAP activity toward Rap2 (∼40-50%), an effect not produced by either kinase alone. As we previously observed for CDK5, addition of Ca²⁺/CaM causes a substrate-directed doubling of the rate and stoichiometry of phosphorylation of synGAP by Plk2, targeting residues also phosphorylated by CaMKII. In summary, phosphorylation by Plk2, like CDK5, shifts the ratio of GAP activity of synGAP to produce a greater decrease in active Ras than in active Rap, which would produce a shift toward a decrease in the number of surface AMPA receptors in neuronal dendrites.

PI3K/Akt/GSK3β induced CREB activation ameliorates arsenic mediated alterations in NMDA receptors and associated signaling in rat hippocampus: Neuroprotective role of curcumin

Protective efficacy of curcumin in arsenic induced NMDA receptor dysfunctions and PI3K/Akt/ GSK3β signalling in hippocampus has been investigated in vivo and in vitro. Exposure to sodium arsenite (in vivo - 20 mg/kg, body weight p.o. for 28 days; in vitro - 10 μM for 24 h) and curcumin (in vivo - 100 mg/kg body weight p.o. for 28 days; in vitro - 20 μM for 24 h) was carried out alone or simultaneously. Treatment with curcumin ameliorated sodium arsenite induced alterations in the levels of NMDA receptors, its receptor subunits and synaptic proteins - pCaMKIIα, PSD-95 and SynGAP both in vivo and in vitro. Decreased levels of BDNF, pAkt, pERK1/2, pGSK3β and pCREB on sodium arsenite exposure were also protected by curcumin. Curcumin was found to decrease sodium arsenite induced changes in hippocampus by modulating PI3K/Akt/GSK3β neuronal survival pathway, known to regulate various cellular events. Treatment of hippocampal cultures with pharmacological inhibitors for ERK1/2, GSK3β and Akt individually inhibited levels of CREB and proteins associated with PI3K/Akt/GSK3β pathway. Simultaneous treatment with curcumin was found to improve sodium arsenite induced learning and memory deficits in rats assessed by water maze and Y-maze. The results provide evidence that curcumin exercises its neuroprotective effect involving PI3K/Akt pathway which may affect NMDA receptors and downstream signalling through TrKβ and BDNF in arsenic induced cognitive deficits in hippocampus.

Dendritic spine actin cytoskeleton in autism spectrum disorder

Dendritic spines are small actin-rich protrusions from neuronal dendrites that form the postsynaptic part of most excitatory synapses. Changes in the shape and size of dendritic spines correlate with the functional changes in excitatory synapses and are heavily dependent on the remodeling of the underlying actin cytoskeleton. Recent evidence implicates synapses at dendritic spines as important substrates of pathogenesis in neuropsychiatric disorders, including autism spectrum disorder (ASD). Although synaptic perturbations are not the only alterations relevant for these diseases, understanding the molecular underpinnings of the spine and synapse pathology may provide insight into their etiologies and could reveal new drug targets. In this review, we will discuss recent findings of defective actin regulation in dendritic spines associated with ASD.

MPDZ promotes DLL4-induced Notch signaling during angiogenesis

Angiogenesis is coordinated by VEGF and Notch signaling. DLL4-induced Notch signaling inhibits tip cell formation and vessel branching. To ensure proper Notch signaling, receptors and ligands are clustered at adherens junctions. However, little is known about factors that control Notch activity by influencing the cellular localization of Notch ligands. Here, we show that the multiple PDZ domain protein (MPDZ) enhances Notch signaling activity. MPDZ physically interacts with the intracellular carboxyterminus of DLL1 and DLL4 and enables their interaction with the adherens junction protein Nectin-2. Inactivation of the MPDZ gene leads to impaired Notch signaling activity and increased blood vessel sprouting in cellular models and the embryonic mouse hindbrain. Tumor angiogenesis was enhanced upon endothelial-specific inactivation of MPDZ leading to an excessively branched and poorly functional vessel network resulting in tumor hypoxia. As such, we identified MPDZ as a novel modulator of Notch signaling by controlling ligand recruitment to adherens junctions.

Junctional adhesion molecule-A: functional diversity through molecular promiscuity

Cell adhesion molecules (CAMs) of the immunoglobulin superfamily (IgSF) regulate important processes such as cell proliferation, differentiation and morphogenesis. This activity is primarily due to their ability to initiate intracellular signaling cascades at cell-cell contact sites. Junctional adhesion molecule-A (JAM-A) is an IgSF-CAM with a short cytoplasmic tail that has no catalytic activity. Nevertheless, JAM-A is involved in a variety of biological processes. The functional diversity of JAM-A resides to a large part in a C-terminal PDZ domain binding motif which directly interacts with nine different PDZ domain-containing proteins. The molecular promiscuity of its PDZ domain motif allows JAM-A to recruit protein scaffolds to specific sites of cell-cell adhesion and to assemble signaling complexes at those sites. Here, we review the molecular characteristics of JAM-A, including its dimerization, its interaction with scaffolding proteins, and the phosphorylation of its cytoplasmic domain, and we describe how these characteristics translate into diverse biological activities.

PTENα Modulates CaMKII Signaling and Controls Contextual Fear Memory and Spatial Learning

PTEN (phosphatase and tensin homology deleted on chromosome 10) has multiple functions, and recent studies have shown that the PTEN family has isoforms. The roles of these PTEN family members in biologic activities warrant specific evaluation. Here, we show that PTENα maintains CaMKII in a state that is competent to induce long-term potentiation (LTP) with resultant regulation of contextual fear memory and spatial learning. PTENα binds to CaMKII with its distinctive N terminus and resets CaMKII to an activatable state by dephosphorylating it at sites T305/306. Loss of PTENα impedes the interaction of CaMKII and NR2B, leading to defects in hippocampal LTP, fear-conditioned memory, and spatial learning. Restoration of PTENα in the hippocampus of PTENα-deficient mice rescues learning deficits through regulation of CaMKII. CaMKII mutations in dementia patients inhibit CaMKII activity and result in disruption of PTENα-CaMKII-NR2B signaling. We propose that CaMKII is a target of PTENα phosphatase and that PTENα is an essential element in the molecular regulation of neural activity.

Species-conserved SYNGAP1 phenotypes associated with neurodevelopmental disorders

SYNGAP1 loss-of-function variants are causally associated with intellectual disability, severe epilepsy, autism spectrum disorder and schizophrenia. While there are hundreds of genetic risk factors for neurodevelopmental disorders (NDDs), this gene is somewhat unique because of the frequency and penetrance of loss-of-function variants found in patients combined with the range of brain disorders associated with SYNGAP1 pathogenicity. These clinical findings indicate that SYNGAP1 regulates fundamental neurodevelopmental processes that are necessary for brain development. Here, we describe four phenotypic domains that are controlled by Syngap1 expression across vertebrate species. Two domains, the maturation of cognitive functions and maintenance of excitatory-inhibitory balance, are defined exclusively through a review of the current literature. Two additional domains are defined by integrating the current literature with new data indicating that SYNGAP1/Syngap1 regulates innate survival behaviors and brain structure. These four phenotypic domains are commonly disrupted in NDDs, suggesting that a deeper understanding of developmental Syngap1 functions will be generalizable to other NDDs of known or unknown etiology. Therefore, we discuss the known molecular and cellular functions of Syngap1 and consider how these functions may contribute to the emergence of disease-relevant phenotypes. Finally, we identify major unexplored areas of Syngap1 neurobiology and discuss how a deeper understanding of this gene may uncover general principles of NDD pathobiology.

The first international conference on SYNGAP1-related brain disorders: a stakeholder meeting of families, researchers, clinicians, and regulators

BACKGROUND

Pathologic mutations in SYNGAP1 cause a genetically defined form of intellectual disability (ID) with comorbid epilepsy and autistic features. While only recently discovered, pathogenicity of this gene is a relatively frequent genetic cause of classically undefined developmental delay that progresses to ID with commonly occurring comorbidities.

MAIN BODY

A meeting of 150 people was held that included affected individuals and their caregivers, clinicians that treat this and related brain disorders, neuroscientists that study SYNGAP1 biology or the function of related genes, and representatives from government agencies that fund science and approve new medical treatments. The meeting focused on developing a consensus among all stakeholders as to how best to achieve a more fundamental and profound understanding of SYNGAP1 biology and its role in human disease.

SHORT CONCLUSION

From all of these proceedings, several areas of consensus emerged. The clinicians and geneticists agreed that the prevalence of epilepsy and sensory processing impairments in SYNGAP1-related brain disorders approached 100%. The neurobiologists agreed that more basic research is needed to better understand the molecular and cellular functions of the Syngap1 gene, which will lead to targets for therapeutic intervention. Finally, everyone agreed that there is a pressing need to form a robust patient registry as an initial step toward a prospective natural history study of patients with pathogenic SYNGAP1 variants.

The polarity protein Angiomotin p130 controls dendritic spine maturation

Wigerius et al. identify the polarity protein AMOT-130 as vital for dendritic spine morphogenesis. They show that reduced Lats1 kinase activity in the neonatal brain is required for the recruitment of AMOT-130 to postsynaptic compartments to stabilize dendritic spines.

The actin cytoskeleton is essential for the structural changes in dendritic spines that lead to the formation of new synapses. Although the molecular mechanisms underlying spine formation are well characterized, the events that drive spine maturation during development are largely unknown. In this study, we demonstrate that Angiomotin (AMOT-130) is necessary for spine stabilization. AMOT-130 is enriched in mature dendritic spines and functions to stabilize the actin cytoskeleton by coupling F-actin to postsynaptic protein scaffolds. These functions of AMOT are transiently restricted during postnatal development by phosphorylation imposed by the kinase Lats1. Our study proposes that AMOT-130 is essential for normal spine morphogenesis and identifies Lats1 as an upstream regulator in this process. Moreover, our findings may link AMOT-130 loss and the related spine defects to neurological disorders.

Tau exacerbates excitotoxic brain damage in an animal model of stroke

Neuronal excitotoxicity induced by aberrant excitation of glutamatergic receptors contributes to brain damage in stroke. Here we show that tau-deficient (tau^−/−) mice are profoundly protected from excitotoxic brain damage and neurological deficits following experimental stroke, using a middle cerebral artery occlusion with reperfusion model. Mechanistically, we show that this protection is due to site-specific inhibition of glutamate-induced and Ras/ERK-mediated toxicity by accumulation of Ras-inhibiting SynGAP1, which resides in a post-synaptic complex with tau. Accordingly, reducing SynGAP1 levels in tau^−/− mice abolished the protection from pharmacologically induced excitotoxicity and middle cerebral artery occlusion-induced brain damage. Conversely, over-expression of SynGAP1 prevented excitotoxic ERK activation in wild-type neurons. Our findings suggest that tau mediates excitotoxic Ras/ERK signaling by controlling post-synaptic compartmentalization of SynGAP1.

Excitotoxicity contributes to neuronal injury following stroke. Here the authors show that tau promotes excitotoxicity by a post-synaptic mechanism, involving site-specific control of ERK activation, in a mouse model of stroke.

A RasGAP, DAB2IP, regulates lipid droplet homeostasis by serving as GAP toward RAB40C

Lipid droplet (LD) homeostasis involves activities of various RAB small GTPases. Recently, we found RAB40C was one of the RAB proteins regulating LD homeostasis. RAB40C contains a unique SOCS domain that is required for clustering of LDs. However, its precise functional role in LD homeostasis and mechanism of regulation remain largely unknown. In this study, we observed over-accumulation of LDs in cells with RAB40C deleted by Crispr-Cas9 editing. RAB40C appeared to reduce LD accumulation after long term incubation of cells with oleic acid (24 hours). Unexpectedly, we found that Ras GTPase activating protein (GAP), DAB2IP, bound to RAB40C mainly via its GAP domain and could serve as RAB40C GAP. Studies involving overexpression of DAB2IP and its GAP defective mutant and siRNA depletion of DAB2IP all confirmed that DAB2IP negatively regulated the effect of RAB40C on LD homeostasis. These results provide a novel perspective on the regulation of RAB40C and implicate various signalling pathways regulated by DAB2IP, which may play a role in LD homeostasis via RAB40C.

Synaptic GAP and GEF Complexes Cluster Proteins Essential for GTP Signaling

GTPase-activating proteins (GAPs) and guanine exchange factors (GEFs) play essential roles in regulating the activity of small GTPases. Several GAPs and GEFs have been shown to be present at the postsynaptic density (PSD) within excitatory glutamatergic neurons and regulate the activity of glutamate receptors. However, it is not known how synaptic GAP and GEF proteins are organized within the PSD signaling machinery, if they have overlapping interaction networks, or if they associate with proteins implicated in contributing to psychiatric disease. Here, we determine the interactomes of three interacting GAP/GEF proteins at the PSD, including the RasGAP Syngap1, the ArfGAP Agap2, and the RhoGEF Kalirin, which includes a total of 280 interactions. We describe the functional properties of each interactome and show that these GAP/GEF proteins are highly associated with and cluster other proteins directly involved in GTPase signaling mechanisms. We also utilize Agap2 as an example of GAP/GEFs localized within multiple neuronal compartments and determine an additional 110 interactions involving Agap2 outside of the PSD. Functional analysis of PSD and non-PSD interactomes illustrates both common and unique functions of Agap2 determined by its subcellular location. Furthermore, we also show that these GAPs/GEFs associate with several proteins involved in psychiatric disease.

Anchoring high concentrations of SynGAP at postsynaptic densities via liquid-liquid phase separation

SynGAP, encoded by SYNGAP1, is a Ras/Rap GTPase activator specifically expressed in the nervous systems. SynGAP is one of the most abundant proteins in the postsynaptic densities (PSDs) of excitatory synapses and acts as a critical synaptic activity brake by tuning down synaptic GTPase activities. Mutations of SYNGAP1 have been frequently linked to brain disorders including intellectual disability, autisms, and seizure. SynGAP has been shown to undergo fast dispersions from synapses in response to stimulations, a strategy that neurons use to control the specific activities of the enzyme within the tiny, semi-open compartments in dendritic spines. However, the mechanism governing the activity-dependent synaptic localization modulations of SynGAP is poorly understood. It has been shown recently that SynGAP α1, via specifically binding to PSD-95, can undergo liquid-liquid phase separation forming membraneless, condensed protein-rich sub-compartments. This phase transition-mediated, PSD-95-dependent synaptic enrichment of SynGAP α1 not only suggests a dynamic anchoring mechanism of the protein within the PSD, but also implies a new model for the PSD formation in living neurons.

The Kv1-associated molecules TAG-1 and Caspr2 are selectively targeted to the axon initial segment in hippocampal neurons

Caspr2 and TAG-1 (also known as CNTNAP2 and CNTN2, respectively) are cell adhesion molecules (CAMs) associated with the voltage-gated potassium channels Kv1.1 and Kv1.2 (also known as KCNA1 and KCNA2, respectively) at regions controlling axonal excitability, namely, the axon initial segment (AIS) and juxtaparanodes of myelinated axons. The distribution of Kv1 at juxtaparanodes requires axo-glial contacts mediated by Caspr2 and TAG-1. In the present study, we found that TAG-1 strongly colocalizes with Kv1.2 at the AIS of cultured hippocampal neurons, whereas Caspr2 is uniformly expressed along the axolemma. Live-cell imaging revealed that Caspr2 and TAG-1 are sorted together in axonal transport vesicles. Therefore, their differential distribution may result from diffusion and trapping mechanisms induced by selective partnerships. By using deletion constructs, we identified two molecular determinants of Caspr2 that regulate its axonal positioning. First, the LNG2-EGF1 modules in the ectodomain of Caspr2, which are involved in its axonal distribution. Deletion of these modules promotes AIS localization and association with TAG-1. Second, the cytoplasmic PDZ-binding site of Caspr2, which could elicit AIS enrichment and recruitment of the membrane-associated guanylate kinase (MAGuK) protein MPP2. Hence, the selective distribution of Caspr2 and TAG-1 may be regulated, allowing them to modulate the strategic function of the Kv1 complex along axons.

Rho GTPase-activating proteins: Regulators of Rho GTPase activity in neuronal development and CNS diseases

The Rho family of small GTPases was considered as molecular switches in regulating multiple cellular events, including cytoskeleton reorganization. The Rho GTPase-activating proteins (RhoGAPs) are one of the major families of Rho GTPase regulators. RhoGAPs were initially considered negative mediators of Rho signaling pathways via their GAP domain. Recent studies have demonstrated that RhoGAPs also regulate numerous aspects of neuronal development and are related to various neurodegenerative diseases in GAP-dependent and GAP-independent manners. Moreover, RhoGAPs are regulated through various mechanisms, such as phosphorylation. To date, approximately 70 RhoGAPs have been identified; however, only a small portion has been thoroughly investigated. Thus, the characterization of important RhoGAPs in the central nervous system is crucial to understand their spatiotemporal role during different stages of neuronal development. In this review, we summarize the current knowledge of RhoGAPs in the brain with an emphasis on their molecular function, regulation mechanism and disease implications in the central nervous system.

Biochemistry and neuroscience: the twain need to meet

Neuroscience has come to mean the study of electrophysiology of neurons and synapses, micro and macro-scale neuroanatomy, and the functional organization of brain areas. The molecular axis of the field, as reflected in textbooks, often includes only descriptions of the structure and function of individual channels and receptor proteins, and the extracellular signals that guide development and repair. Studies of cytosolic 'molecular machines', large assemblies of proteins that orchestrate regulation of neuronal functions, have been neglected. However, a complete understanding of brain function that will enable new strategies for treatment of the most intractable neural disorders will require that in vitro biochemical studies of molecular machines be reintegrated into the field of neuroscience.

Rational design of an orthogonal noncovalent interaction system at the MUPP1 PDZ11 complex interface with CaMKIIα-derived peptides in human fertilization

An orthogonal noncovalent interaction (ONI) system between a native hydrogen bond and a designed halogen bond across the complex interface of the MUPP1 PDZ11 domain with the CaMKIIαsia[Asn-1Phe] peptide mutant is introduced using a structure-based rational approach.

A Subset of Autism-Associated Genes Regulate the Structural Stability of Neurons

Autism spectrum disorder (ASD) comprises a range of neurological conditions that affect individuals’ ability to communicate and interact with others. People with ASD often exhibit marked qualitative difficulties in social interaction, communication, and behavior. Alterations in neurite arborization and dendritic spine morphology, including size, shape, and number, are hallmarks of almost all neurological conditions, including ASD. As experimental evidence emerges in recent years, it becomes clear that although there is broad heterogeneity of identified autism risk genes, many of them converge into similar cellular pathways, including those regulating neurite outgrowth, synapse formation and spine stability, and synaptic plasticity. These mechanisms together regulate the structural stability of neurons and are vulnerable targets in ASD. In this review, we discuss the current understanding of those autism risk genes that affect the structural connectivity of neurons. We sub-categorize them into (1) cytoskeletal regulators, e.g., motors and small RhoGTPase regulators; (2) adhesion molecules, e.g., cadherins, NCAM, and neurexin superfamily; (3) cell surface receptors, e.g., glutamatergic receptors and receptor tyrosine kinases; (4) signaling molecules, e.g., protein kinases and phosphatases; and (5) synaptic proteins, e.g., vesicle and scaffolding proteins. Although the roles of some of these genes in maintaining neuronal structural stability are well studied, how mutations contribute to the autism phenotype is still largely unknown. Investigating whether and how the neuronal structure and function are affected when these genes are mutated will provide insights toward developing effective interventions aimed at improving the lives of people with autism and their families.

The effects of intra-hippocampal L-thyroxine infusion on long-term potentiation and long-term depression: A possible role for the αvβ3 integrin receptor

Although the effects of long-term experimental dysthyroidism on long-term potentiation (LTP) and long-term depression (LTD) have been documented, the relationship between LTP/LTD and acute administration of L-thyroxine (T4) has not been described. Here, we investigated the effects of intra-hippocampal administration of T4 on synaptic plasticity in the dentate gyrus of the hippocampal formation. After a 15-minute baseline recording, LTP and LTD were induced by application of high- and low-frequency stimulation protocols, respectively. Infusions of saline or T4 and tetraiodothyroacetic acid (tetrac), a T4 analog that inhibits binding of iodothyronines to the integrin αvβ3 receptor, either alone or together, were made during the stimulation protocols. The averages of the excitatory postsynaptic potential (EPSP) slopes and population spike (PS) amplitudes, between 55 to 60 minutes, were used as a measure of the LTP/LTD magnitude and were analyzed by two-way univariate ANOVA with T4 and tetrac as between-subjects factors. The input-output curves of the infusion groups were comparable to each other, as shown by the non significant interaction observed between stimulus intensity and infused drug. The magnitude of the LTP in T4-infused rats was significantly lower as compared to saline-infused rats. Both the PS amplitude and the EPSP slope were depressed more markedly with T4 infusion than with saline, tetrac, and T4 + tetrac infusion. Data of this study provide in vivo evidence that T4 can promote LTD over LTP via the integrin αvβ3 receptor, and that the effect of endogenous T4 on this receptor can be suppressed by tetrac in the hippocampus. © 2016 Wiley Periodicals, Inc.

Molecular Mechanisms of Stress-Induced Increases in Fear Memory Consolidation within the Amygdala

Stress can significantly impact brain function and increase the risk for developing various psychiatric disorders. Many of the brain regions that are implicated in psychiatric disorders and are vulnerable to the effects of stress are also involved in mediating emotional learning. Emotional learning has been a subject of intense investigation for the past 30 years, with the vast majority of studies focusing on the amygdala and its role in associative fear learning. However, the mechanisms by which stress affects the amygdala and amygdala-dependent fear memories remain unclear. Here we review the literature on the enhancing effects of acute and chronic stress on the acquisition and/or consolidation of a fear memory, as measured by auditory Pavlovian fear conditioning, and discuss potential mechanisms by which these changes occur in the amygdala. We hypothesize that stress-mediated activation of glucocorticoid receptors (GR) and norepinephrine release within the amygdala leads to the mobilization of α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptors to the synapse, which underlies stress-induced increases in fear memory. We discuss the implications of this hypothesis for evaluating the effects of stress on extinction and for developing treatments for anxiety disorders. Understanding how stress-induced changes in glucocorticoid and norepinephrine signaling might converge to affect emotional learning by increasing the trafficking of AMPA receptors and enhancing amygdala excitability is a promising area for future research.

The dark side of opioids in pain management: basic science explains clinical observation

Although there is no doubt about opioids' ability to relieve pain in the short term, it is not always clear why longer-term analgesic efficacy seems to be impaired. Tolerance and hyperalgesia have been suggested as mechanisms for opioid analgesic deterioration. But could there also be an effect of opioids on pain itself?

Introduction:

In the past 2 decades, opioids have been used increasingly for the treatment of persistent pain, and doses have tended to creep up. As basic science elucidates mechanisms of pain and analgesia, the cross talk between central pain and opioid actions becomes clearer.

Objectives:

We aimed to examine the published literature on basic science explaining pronociceptive opioid actions, and apply this knowledge to clinical observation.

Methods:

We reviewed the existing literature on the pronociceptive actions of opioids, both preclinical and clinical studies.

Results:

Basic science provides a rationale for the clinical observation that opioids sometimes increase rather than decrease pain. Central sensitization (hyperalgesia) underlies pain chronification, but can also be produced by high dose and high potency opioids. Many of the same mechanisms account for both central pain and opioid hyperalgesia.

Conclusion:

Newly revealed basic mechanisms suggest possible avenues for drug development and new drug therapies that could alter pain sensitization through endogenous and exogenous opioid mechanisms. Recent changes in practice such as the introduction of titration-to-effect for opioids have resulted in higher doses used in the clinic setting than ever seen previously. New basic science knowledge hints that these newer dosing practices may need to be reexamined. When pain worsens in a patient taking opioids, can we be assured that this is not because of the opioids, and can we alter this negative effect of opioids through different dosing strategies or new drug intervention?

Wip1 phosphatase modulates both long-term potentiation and long-term depression through the dephosphorylation of CaMKII

Synaptic plasticity is an important mechanism that underlies learning and cognition. Protein phosphorylation by kinases and dephosphorylation by phosphatases play critical roles in the activity-dependent alteration of synaptic plasticity. In this study, we report that Wip1, a protein phosphatase, is essential for long-term potentiation (LTP) and long-term depression (LTD) processes. Wip1-deletion suppresses LTP and enhances LTD in the hippocampus CA1 area. Wip1 deficiency-induced aberrant elevation of CaMKII T286/287 and T305 phosphorylation underlies these dysfunctions. Moreover, we showed that Wip1 modulates CaMKII dephosphorylation. Wip1(-/-) mice exhibit abnormal GluR1 membrane expression, which could be reversed by the application of a CaMKII inhibitor, indicating that Wip1/CaMKII signaling is crucial for synaptic plasticity. Together, our results demonstrate that Wip1 phosphatase plays a vital role in regulating hippocampal synaptic plasticity by modulating the phosphorylation of CaMKII.

The multiple PDZ domain protein Mpdz/MUPP1 regulates opioid tolerance and opioid-induced hyperalgesia

BACKGROUND

Opioids are a mainstay for the treatment of chronic pain. Unfortunately, therapy-limiting maladaptations such as loss of treatment effect (tolerance), and paradoxical opioid-induced hyperalgesia (OIH) can occur. The objective of this study was to identify genes responsible for opioid tolerance and OIH.

RESULTS

These studies used a well-established model of ascending morphine administration to induce tolerance, OIH and other opioid maladaptations in 23 strains of inbred mice. Genome-wide computational genetic mapping was then applied to the data in combination with a false discovery rate filter. Transgenic mice, gene expression experiments and immunoprecipitation assays were used to confirm the functional roles of the most strongly linked gene. The behavioral data processed using computational genetic mapping and false discovery rate filtering provided several strongly linked biologically plausible gene associations. The strongest of these was the highly polymorphic Mpdz gene coding for the post-synaptic scaffolding protein Mpdz/MUPP1. Heterozygous Mpdz +/- mice displayed reduced opioid tolerance and OIH. Mpdz gene expression and Mpdz/MUPP1 protein levels were lower in the spinal cords of low-adapting 129S1/Svlm mice than in high-adapting C57BL/6 mice. Morphine did not alter Mpdz expression levels. In addition, association of Mpdz/MUPP1 with its known binding partner CaMKII did not differ between these high- and low-adapting strains.

CONCLUSIONS

The degrees of maladaptive changes in response to repeated administration of morphine vary greatly across inbred strains of mice. Variants of the multiple PDZ domain gene Mpdz may contribute to the observed inter-strain variability in tolerance and OIH by virtue of changes in the level of their expression.

Analysis of rare copy number variation in absence epilepsies

OBJECTIVE

To identify shared genes and pathways between common absence epilepsy (AE) subtypes (childhood absence epilepsy [CAE], juvenile absence epilepsy [JAE], and unclassified absence epilepsy [UAE]) that may indicate common mechanisms for absence seizure generation and potentially a diagnostic continuum.

METHODS

We used high-density single-nucleotide polymorphism arrays to analyze genome-wide rare copy number variation (CNV) in a cohort of 144 children with AEs (95 CAE, 26 UAE, and 23 JAE).

RESULTS

We identified CNVs that are known risk factors for AE in 4 patients, including 3x 15q11.2 deletion. We also expanded the phenotype at 4 regions more commonly identified in other neurodevelopmental disorders: 1p36.33 duplication, 1q21.1 deletion, 22q11.2 duplication, and Xp22.31 deletion and duplication. Fifteen patients (10.5%) were found to carry rare CNVs that disrupt genes associated with neuronal development and function (8 CAE, 2 JAE, and 5 UAE). Four categories of protein are each disrupted by several CNVs: (1) synaptic vesicle membrane or vesicle endocytosis, (2) synaptic cell adhesion, (3) synapse organization and motility via actin, and (4) gap junctions. CNVs within these categories are shared across the AE subtypes.

CONCLUSIONS

Our results have reinforced the complex and heterogeneous nature of the AEs and their potential for shared genetic mechanisms and have highlighted several pathways that may be important in epileptogenesis of absence seizures.

Genetic and neurodevelopmental spectrum of SYNGAP1-associated intellectual disability and epilepsy

OBJECTIVE

We aimed to delineate the neurodevelopmental spectrum associated with SYNGAP1 mutations and to investigate genotype-phenotype correlations.

METHODS

We sequenced the exome or screened the exons of SYNGAP1 in a total of 251 patients with neurodevelopmental disorders. Molecular and clinical data from patients with SYNGAP1 mutations from other centres were also collected, focusing on developmental aspects and the associated epilepsy phenotype. A review of SYNGAP1 mutations published in the literature was also performed.

RESULTS

We describe 17 unrelated affected individuals carrying 13 different novel loss-of-function SYNGAP1 mutations. Developmental delay was the first manifestation of SYNGAP1-related encephalopathy; intellectual disability became progressively obvious and was associated with autistic behaviours in eight patients. Hypotonia and unstable gait were frequent associated neurological features. With the exception of one patient who experienced a single seizure, all patients had epilepsy, characterised by falls or head drops due to atonic or myoclonic seizures, (myoclonic) absences and/or eyelid myoclonia. Triggers of seizures were frequent (n=7). Seizures were pharmacoresistant in half of the patients. The severity of the epilepsy did not correlate with the presence of autistic features or with the severity of cognitive impairment. Mutations were distributed throughout the gene, but spared spliced 3' and 5' exons. Seizures in patients with mutations in exons 4-5 were more pharmacoresponsive than in patients with mutations in exons 8-15.

CONCLUSIONS

SYNGAP1 encephalopathy is characterised by early neurodevelopmental delay typically preceding the onset of a relatively recognisable epilepsy comprising generalised seizures (absences, myoclonic jerks) and frequent triggers.

SYNGAP1: Mind the Gap

A cardinal feature of early stages of human brain development centers on the sensory, cognitive, and emotional experiences that shape neuronal-circuit formation and refinement. Consequently, alterations in these processes account for many psychiatric and neurodevelopmental disorders. Neurodevelopment disorders affect 3-4% of the world population. The impact of these disorders presents a major challenge to clinicians, geneticists, and neuroscientists. Mutations that cause neurodevelopmental disorders are commonly found in genes encoding proteins that regulate synaptic function. Investigation of the underlying mechanisms using gain or loss of function approaches has revealed alterations in dendritic spine structure, function, and plasticity, consequently modulating the neuronal circuit formation and thereby raising the possibility of neurodevelopmental disorders resulting from synaptopathies. One such gene, SYNGAP1 (Synaptic Ras-GTPase-activating protein) has been shown to cause Intellectual Disability (ID) with comorbid Autism Spectrum Disorder (ASD) and epilepsy in children. SYNGAP1 is a negative regulator of Ras, Rap and of AMPA receptor trafficking to the postsynaptic membrane, thereby regulating not only synaptic plasticity, but also neuronal homeostasis. Recent studies on the neurophysiology of SYNGAP1, using Syngap1 mouse models, have provided deeper insights into how downstream signaling proteins and synaptic plasticity are regulated by SYNGAP1. This knowledge has led to a better understanding of the function of SYNGAP1 and suggests a potential target during critical period of development when the brain is more susceptible to therapeutic intervention.

Overexpression of αCaMKII impairs behavioral flexibility and NMDAR-dependent long-term depression in the medial prefrontal cortex

The medial prefrontal cortex (mPFC) participates in the behavioral flexibility. As a major downstream molecule in the NMDA receptor signaling, alpha-Ca(2+)/calmodulin-dependent protein kinase II (αCaMKII) is crucial for hippocampal long-term potentiation (LTP) and hippocampus-related memory. However, the role of αCaMKII in mPFC-related behavioral flexibility and mPFC synaptic plasticity remains elusive. In the present study, using chemical-genetic approaches to temporally up-regulate αCaMKII activity, we found that αCaMKII-F89G transgenic mice exhibited impaired behavioral flexibility in Y-water maze arm reversal task. Notably, in vitro electrophysiological analysis showed normal basal synaptic transmission, LTP and depotentiation, but selectively impaired NMDAR-dependent long-term depression (LTD) in the mPFC of αCaMKII-F89G transgenic mice. In accordance with the deficit in NMDAR-dependent LTD, αCaMKII-F89G transgenic mice exhibited impaired AMPAR internalization during NMDAR-dependent chemical LTD expression in the mPFC. Furthermore, the above deficits in behavioral flexibility, NMDAR-dependent LTD and AMPAR internalization could all be reversed by 1-naphthylmethyl (NM)-PP1, a specific inhibitor of exogenous αCaMKII-F89G activity. Taken together, our results for the first time indicate that αCaMKII overexpression in the forebrain impairs behavioral flexibility and NMDAR-dependent LTD in the mPFC, and supports the notion that there is a close relationship between NMDAR-dependent LTD and behavioral flexibility.

Wnt-related SynGAP1 is a neuroprotective factor of glutamatergic synapses against Aβ oligomers

Wnt-5a is a synaptogenic factor that modulates glutamatergic synapses and generates neuroprotection against Aβ oligomers. It is known that Wnt-5a plays a key role in the adult nervous system and synaptic plasticity. Emerging evidence indicates that miRNAs are actively involved in the regulation of synaptic plasticity. Recently, we showed that Wnt-5a is able to control the expression of several miRNAs including miR-101b, which has been extensively studied in carcinogenesis. However, its role in brain is just beginning to be explored. That is why we aim to study the relationship between Wnt-5a and miRNAs in glutamatergic synapses. We performed in silico analysis which predicted that miR-101b may inhibit the expression of synaptic GTPase-Activating Protein (SynGAP1), a Ras GTPase-activating protein critical for the development of cognition and proper synaptic function. Through overexpression of miR-101b, we showed that miR-101b is able to regulate the expression of SynGAP1 in an hippocampal cell line. Moreover and consistent with a decrease of miR-101b, Wnt-5a enhances SynGAP expression in cultured hippocampal neurons. Additionally, Wnt-5a increases the activity of SynGAP in a time-dependent manner, with a similar kinetic to CaMKII phosphorylation. This also, correlates with a modulation in the SynGAP clusters density. On the other hand, Aβ oligomers permanently decrease the number of SynGAP clusters. Interestingly, when neurons are co-incubated with Wnt-5a and Aβ oligomers, we do not observe the detrimental effect of Aβ oligomers, indicating that, Wnt-5a protects neurons from the synaptic failure triggered by Aβ oligomers. Overall, our findings suggest that SynGAP1 is part of the signaling pathways induced by Wnt-5a. Therefore, possibility exists that SynGAP is involved in the synaptic protection against Aβ oligomers.

Rapid dispersion of SynGAP from synaptic spines triggers AMPA receptor insertion and spine enlargement during LTP

SynGAP is a Ras-GTPase activating protein highly enriched at excitatory synapses in the brain. Previous studies have shown that CaMKII and the RAS-ERK pathway are critical for several forms of synaptic plasticity including LTP. NMDA receptor-dependent calcium influx has been shown to regulate the RAS-ERK pathway and downstream events that result in AMPA receptor synaptic accumulation, spine enlargement, and synaptic strengthening during LTP. However, the cellular mechanisms whereby calcium influx and CaMKII control Ras activity remain elusive. Using live-imaging techniques, we have found that SynGAP is rapidly dispersed from spines upon LTP induction in hippocampal neurons, and this dispersion depends on phosphorylation of SynGAP by CaMKII. Moreover, the degree of acute dispersion predicts the maintenance of spine enlargement. Thus, the synaptic dispersion of SynGAP by CaMKII phosphorylation during LTP represents a key signaling component that transduces CaMKII activity to small G protein-mediated spine enlargement, AMPA receptor synaptic incorporation, and synaptic potentiation.

Strain Differences in Presynaptic Function: PROTEOMICS, ULTRASTRUCTURE, AND PHYSIOLOGY OF HIPPOCAMPAL SYNAPSES IN DBA/2J AND C57Bl/6J MICE

The inbred strains C57BL/6J and DBA/2J (DBA) display striking differences in a number of behavioral tasks depending on hippocampal function, such as contextual memory. Historically, this has been explained through differences in postsynaptic protein expression underlying synaptic transmission and plasticity. We measured the synaptic hippocampal protein content (iTRAQ (Isobaric Tags for Relative and Absolute Quantitation) and mass spectrometry), CA1 synapse ultrastructural morphology, and synaptic functioning in adult C57BL/6J and DBA mice. DBA mice showed a prominent decrease in the Ras-GAP calcium-sensing protein RASAL1. Furthermore, expression of several presynaptic markers involved in exocytosis, such as syntaxin (Stx1b), Ras-related proteins (Rab3a/c), and rabphilin (Rph3a), was reduced. Ultrastructural analysis of CA1 hippocampal synapses showed a significantly lower number of synaptic vesicles and presynaptic cluster size in DBA mice, without changes in postsynaptic density or active zone. In line with this compromised presynaptic morphological and molecular phenotype in DBA mice, we found significantly lower paired-pulse facilitation and enhanced short term depression of glutamatergic synapses, indicating a difference in transmitter release and/or refilling mechanisms. Taken together, our data suggest that in addition to strain-specific postsynaptic differences, the change in dynamic properties of presynaptic transmitter release may underlie compromised synaptic processing related to cognitive functioning in DBA mice.

Structural mechanisms of plexin signaling

Signaling through plexin, the major cell surface receptor for semaphorin, plays critical roles in regulating processes such as neuronal axon guidance, angiogenesis and immune response. Plexin is normally kept inactive in the absence of semaphorin. Upon binding of semaphorin to the extracellular region, plexin is activated and transduces signal to the inside of the cell through its cytoplasmic region. The GTPase Activating Protein (GAP) domain in the plexin cytoplasmic region mediates the major intracellular signaling pathway. The substrate specificity and regulation mechanisms of the GAP domain have only been revealed recently. Many intracellular proteins serve as either upstream regulators or downstream transducers by directly interacting with plexin. The mechanisms of action for some of these proteins also start to emerge from recent studies. We review here these advances in the mechanistic understanding of plexin intracellular signaling from a structural perspective.

Novel MPDZ/MUPP1 transgenic and knockdown models confirm Mpdz's role in ethanol withdrawal and support its role in voluntary ethanol consumption

Association studies implicate multiple PDZ domain protein (MPDZ/MUPP1) sequence and/or expression in risk for alcoholism in humans and ethanol withdrawal (EW) in mice, but confirmation has been hindered by the dearth of targeted genetic models. We report the creation of transgenic (MPDZ-TG) and knockout heterozygote (Mpdz(+/-) ) mice, with increased (2.9-fold) and decreased (53%) target expression, respectively. Both models differ in EW compared with wild-type littermates (P ≤ 0.03), providing compelling evidence for an inverse relationship between Mpdz expression and EW severity. Additionally, ethanol consumption is reduced up to 18% (P = 0.006) in Mpdz(+/-) , providing the first evidence implicating Mpdz in ethanol self-administration.

Phosphorylation of synaptic GTPase-activating protein (synGAP) by Ca2+/calmodulin-dependent protein kinase II (CaMKII) and cyclin-dependent kinase 5 (CDK5) alters the ratio of its GAP activity toward Ras and Rap GTPases

synGAP is a neuron-specific Ras and Rap GTPase-activating protein (GAP) found in high concentrations in the postsynaptic density (PSD) fraction from the mammalian forebrain. We have previously shown that, in situ in the PSD fraction or in recombinant form in Sf9 cell membranes, synGAP is phosphorylated by Ca(2+)/calmodulin-dependent protein kinase II (CaMKII), another prominent component of the PSD. Here, we show that recombinant synGAP (r-synGAP), lacking 102 residues at the N terminus, can be purified in soluble form and is phosphorylated by cyclin-dependent kinase 5 (CDK5) as well as by CaMKII. Phosphorylation of r-synGAP by CaMKII increases its HRas GAP activity by 25% and its Rap1 GAP activity by 76%. Conversely, phosphorylation by CDK5 increases r-synGAP's HRas GAP activity by 98% and its Rap1 GAP activity by 20%. Thus, phosphorylation by both kinases increases synGAP activity; CaMKII shifts the relative GAP activity toward inactivation of Rap1, and CDK5 shifts the relative activity toward inactivation of HRas. GAP activity toward Rap2 is not altered by phosphorylation by either kinase. CDK5 phosphorylates synGAP primarily at two sites, Ser-773 and Ser-802. Phosphorylation at Ser-773 inhibits r-synGAP activity, and phosphorylation at Ser-802 increases it. However, the net effect of concurrent phosphorylation of both sites, Ser-773 and Ser-802, is an increase in GAP activity. synGAP is phosphorylated at Ser-773 and Ser-802 in the PSD fraction, and its phosphorylation by CDK5 and CaMKII is differentially regulated by activation of NMDA-type glutamate receptors in cultured neurons.

Plk2 Raps up Ras to subdue synapses

We recently identified the activity-inducible protein kinase Plk2 as a novel overseer of the balance between Ras and Rap small GTPases. Plk2 achieves a profound level of regulatory control by interacting with and phosphorylating at least four Ras and Rap guanine nucleotide exchange factors (GEFs) and GTPase activating proteins (GAPs). Combined, these actions result in synergistic suppression of Ras and hyperstimulation of Rap signaling. Perturbation of Plk2 function abolished homeostatic adaptation of synapses to enhanced activity and impaired behavioral adaptation in various learning tasks, indicating that this regulation was critical for maintaining appropriate Ras/Rap levels. These studies provide insights into the highly cooperative nature of Ras and Rap regulation in neurons. However, different GEF and GAP substrates of Plk2 also controlled specific aspects of dendritic spine morphology, illustrating the ability of individual GAPs/GEFs to assemble microdomains of Ras and Rap signaling that respond to different stimuli and couple to distinct output pathways.

Mpdz expression in the caudolateral substantia nigra pars reticulata is crucially involved in alcohol withdrawal

Association studies implicate the multiple PDZ domain protein (MUPP1/MPDZ) gene in risk for alcoholism in humans and alcohol withdrawal in mice. Although manipulation of the Mpdz gene by homologous recombination and bacterial artificial chromosome transgenesis has suggested that its expression affects alcohol withdrawal risk, the potential confounding effects of linked genes and developmental compensation currently limit interpretation. Here, using RNA interference (RNAi), we directly test the impact of Mpdz expression on alcohol withdrawal severity and provide brain regional mechanistic information. Lentiviral-mediated delivery of Mpdz short hairpin RNA (shRNA) to the caudolateral substantia nigra pars reticulata (clSNr) significantly reduces Mpdz expression and exacerbates alcohol withdrawal convulsions compared with control mice that delivered a scrambled shRNA. Neither baseline nor pentylenetetrazol-enhanced convulsions differed between Mpdz shRNA and control animals, indicating Mpdz expression in the clSNr does not generally affect seizure susceptibility. To our knowledge, these represent the first in vivo Mpdz RNAi analyses, and provide the first direct evidence that Mpdz expression impacts behavior. Our results confirm that Mpdz is a quantitative trait gene for alcohol withdrawal and demonstrate that its expression in the clSNr is crucially involved in risk for alcohol withdrawal.

Reciprocal signaling between translational control pathways and synaptic proteins in autism spectrum disorders

Autism spectrum disorder (ASD) is a heterogeneous group of heritable neurodevelopmental disorders. Symptoms of ASD, which include deficits in social interaction skills, impaired communication ability, and ritualistic-like repetitive behaviors, appear in early childhood and continue throughout life. Genetic studies have revealed at least two clusters of genes frequently associated with ASD and intellectual disability: those encoding proteins involved in translational control and those encoding proteins involved in synaptic function. We hypothesize that mutations occurring in these two clusters of genes interfere with interconnected downstream signaling pathways in neuronal cells to cause ASD symptomatology. In this review, we discuss the monogenic forms of ASD caused by mutations in genes encoding for proteins that regulate translation and synaptic function. Specifically, we describe the function of these proteins, the intracellular signaling pathways that they regulate, and the current mouse models used to characterize the synaptic and behavioral features associated with their mutation. Finally, we summarize recent studies that have established a connection between mRNA translation and synaptic function in models of ASD and propose that dysregulation of one has a detrimental impact on the other.

Evolution of the Ras-like small GTPases and their regulators

Small GTPases are molecular switches at the hub of many signaling pathways and the expansion of this protein family is interwoven with the origin of unique eukaryotic cell features. We have previously reported on the evolution of CDC25 Homology Domain containing proteins, which act as guanine nucleotide exchange factors (GEFs) for Ras-like proteins. We now report on the evolution of both the Ras-like small GTPases as well as the GTPase activating proteins (GAPs) for Ras-like small GTPases. We performed an in depth phylogenetic analysis in 64 genomes of diverse eukaryotic species. These analyses revealed that multiple ancestral Ras-like GTPases and GAPs were already present in the Last Eukaryotic Common Ancestor (LECA), compatible with the presence of RasGEFs in LECA . Furthermore, we endeavor to reconstruct in which order the different Ras-like GTPases diverged from each other. We identified striking differences between the expansion of the various types of Ras-like GTPases and their respective GAPs and GEFs. Altogether, our analysis forms an extensive evolutionary framework for Ras-like signaling pathways and provides specific predictions for molecular biologists and biochemists.

Inhibition of p38 mitogen-activated protein kinase activation in the rostral anterior cingulate cortex attenuates pain-related negative emotion in rats

The emotional components of pain are far less studied than the sensory components. Previous studies have indicated that the rostral anterior cingulate cortex (rACC) is implicated in the affective response to noxious stimuli. Activation of p38 mitogen-activated protein kinase (MAPK) in the spinal cord has been documented to play an important role in diverse kinds of pathological pain states. We used formalin-induced conditioned place aversion (F-CPA) in rats, an animal model believed to reflect the emotional response to pain, to investigate the involvement of p38 MAPK in the rACC after the induction of affective pain. Intraplantar formalin injection produced a significant activation of p38 MAPK, as well as mitogen-activated kinase kinase (MKK) 3 and MKK6, its upstream activators, in the bilateral rACC. p38 MAPK was elevated in both NeuN-positive neurons and Iba1-positive microglia in the rACC, but not GFAP-positive cells. Blocking p38 MAPK activation in the bilateral rACC using its specific inhibitor SB203580 or SB239063 dose-dependently suppressed the formation of F-CPA. Inhibiting p38 MAPK activation did not affect formalin-induced two-phase spontaneous nociceptive response and low intensity electric foot-shock induced CPA. The present study demonstrated that p38 MAPK signaling pathway in the rACC contributes to pain-related negative emotion. Thus, a new pharmacological strategy targeted at the p38 MAPK cascade may be useful in treating pain-related emotional disorders.

The human plasma membrane peripherome: visualization and analysis of interactions

A major part of membrane function is conducted by proteins, both integral and peripheral. Peripheral membrane proteins temporarily adhere to biological membranes, either to the lipid bilayer or to integral membrane proteins with noncovalent interactions. The aim of this study was to construct and analyze the interactions of the human plasma membrane peripheral proteins (peripherome hereinafter). For this purpose, we collected a dataset of peripheral proteins of the human plasma membrane. We also collected a dataset of experimentally verified interactions for these proteins. The interaction network created from this dataset has been visualized using Cytoscape. We grouped the proteins based on their subcellular location and clustered them using the MCL algorithm in order to detect functional modules. Moreover, functional and graph theory based analyses have been performed to assess biological features of the network. Interaction data with drug molecules show that ~10% of peripheral membrane proteins are targets for approved drugs, suggesting their potential implications in disease. In conclusion, we reveal novel features and properties regarding the protein-protein interaction network created by peripheral proteins of the human plasma membrane.

Genetics and genomics of alcohol sensitivity

Alcohol abuse and alcoholism incur a heavy socioeconomic cost in many countries. Both genetic and environmental factors contribute to variation in the inebriating effects of alcohol and alcohol addiction among individuals within and across populations. From a genetics perspective, alcohol sensitivity is a quantitative trait determined by the cumulative effects of multiple segregating genes and their interactions with the environment. This review summarizes insights from model organisms as well as human populations that represent our current understanding of the genetic and genomic underpinnings that govern alcohol metabolism and the sedative and addictive effects of alcohol on the nervous system.

Neuronal cell-surface protein neurexin 1 interaction with multi-PDZ domain protein MUPP1

Location of membrane proteins is often stabilized by PDZ domain-containing scaffolding proteins. Using the yeast two-hybrid screening, we found that neurexin 1 interacted with multi-PDZ domain protein 1 (MUPP1) through PDZ domain. Neurexin 2 and 3 also interacted with MUPP1. MUPP1 and neurexin 1 were co-localized in cultured cells. These results suggest a novel mechanism for localizing neurexin 1 to synaptic sites.

Neurofibromin is the major ras inactivator in dendritic spines

In dendritic spines, Ras plays a critical role in synaptic plasticity but its regulation mechanism is not fully understood. Here, using a fluorescence resonance energy transfer/fluorescence lifetime imaging microscopy-based Ras imaging technique in combination with 2-photon glutamate uncaging, we show that neurofibromin, in which loss-of-function mutations cause Neurofibromatosis Type 1 (NF1), contributes to the majority (∼90%) of Ras inactivation in dendritic spines of pyramidal neurons in the CA1 region of the rat hippocampus. Loss of neurofibromin causes sustained Ras activation in spines, which leads to impairment of spine structural plasticity and loss of spines in an activity-dependent manner. Therefore, deregulation of postsynaptic Ras signaling may explain, at least in part, learning disabilities associated with NF1.

Current view on the functional regulation of the neuronal K(+)-Cl(-) cotransporter KCC2

In the mammalian central nervous system (CNS), the inhibitory strength of chloride (Cl(-))-permeable GABAA and glycine receptors (GABAAR and GlyR) depends on the intracellular Cl(-) concentration ([Cl(-)]i). Lowering [Cl(-)]i enhances inhibition, whereas raising [Cl(-)]i facilitates neuronal activity. A neuron's basal level of [Cl(-)]i, as well as its Cl(-) extrusion capacity, is critically dependent on the activity of the electroneutral K(+)-Cl(-) cotransporter KCC2, a member of the SLC12 cation-Cl(-) cotransporter (CCC) family. KCC2 deficiency compromises neuronal migration, formation and the maturation of GABAergic and glutamatergic synaptic connections, and results in network hyperexcitability and seizure activity. Several neurological disorders including multiple epilepsy subtypes, neuropathic pain, and schizophrenia, as well as various insults such as trauma and ischemia, are associated with significant decreases in the Cl(-) extrusion capacity of KCC2 that result in increases of [Cl(-)]i and the subsequent hyperexcitability of neuronal networks. Accordingly, identifying the key upstream molecular mediators governing the functional regulation of KCC2, and modifying these signaling pathways with small molecules, might constitute a novel neurotherapeutic strategy for multiple diseases. Here, we discuss recent advances in the understanding of the mechanisms regulating KCC2 activity, and of the role these mechanisms play in neuronal Cl(-) homeostasis and GABAergic neurotransmission. As KCC2 mediates electroneutral transport, the experimental recording of its activity constitutes an important research challenge; we therefore also, provide an overview of the different methodological approaches utilized to monitor function of KCC2 in both physiological and pathological conditions.