Biomedical subjects

Richard L Huganir

Publications and source records attributed to Richard L Huganir.

At least 19 recordsLinked to original sources

PubMed2006

Synapse-specific regulation of AMPA receptor function by PSD-95.

PSD-95 is a major protein found in virtually all mature excitatory glutamatergic synapses in the brain. Here, we have addressed the role of PSD-95 in controlling glutamatergic synapse function by generating and characterizing a PSD-95 KO mouse. We found that the alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA)subtype of glutamate receptor (AMPAR)-mediated synaptic transmission was reduced in these mice. Two-photon (2P) uncaging of MNI-glutamate onto individual spines suggested that the decrease in AMPAR function in the PSD-95 KO mouse stems from an increase in the proportion of "silent" synapses i.e., synapses containing N-methyl-d-aspartate (NMDA) receptors (NMDARs) but no AMPARs. Unexpectedly, the silent synapses in the KO mouse were located onto morphologically mature spines. We also observed that a significant population of synapses appeared unaffected by PSD-95 gene deletion, suggesting that the functional role of PSD-95 displays synapse-specificity. In addition, we report that the decay of NMDAR-mediated current was slower in KO mice: The contribution of NR2B subunit containing receptors to the NMDAR-mediated synaptic current was greater in KO mice. The greater occurrence of silent synapses might be related to the greater magnitude of potentiation after long-term potentiation induction observed in these mice. Together, these results suggest a synapse-specific role for PSD-95 in controlling synaptic function that is independent of spine morphology.

Animals↗

PubMed2006

Arc/Arg3.1 interacts with the endocytic machinery to regulate AMPA receptor trafficking.

Arc/Arg3.1 is an immediate-early gene whose mRNA is rapidly transcribed and targeted to dendrites of neurons as they engage in information processing and storage. Moreover, Arc/Arg3.1 is known to be required for durable forms of synaptic plasticity and learning. Despite these intriguing links to plasticity, Arc/Arg3.1's molecular function remains enigmatic. Here, we demonstrate that Arc/Arg3.1 protein interacts with dynamin and specific isoforms of endophilin to enhance receptor endocytosis. Arc/Arg3.1 selectively modulates trafficking of AMPA-type glutamate receptors (AMPARs) in neurons by accelerating endocytosis and reducing surface expression. The Arc/Arg3.1-endocytosis pathway appears to regulate basal AMPAR levels since Arc/Arg3.1 KO neurons exhibit markedly reduced endocytosis and increased steady-state surface levels. These findings reveal a novel molecular pathway that is regulated by Arc/Arg3.1 and likely contributes to late-phase synaptic plasticity and memory consolidation.

Acyltransferases↗

PubMed2006

Arc/Arg3.1 mediates homeostatic synaptic scaling of AMPA receptors.

Homeostatic plasticity may compensate for Hebbian forms of synaptic plasticity, such as long-term potentiation (LTP) and depression (LTD), by scaling neuronal output without changing the relative strength of individual synapses. This delicate balance between neuronal output and distributed synaptic weight may be necessary for maintaining efficient encoding of information across neuronal networks. Here, we demonstrate that Arc/Arg3.1, an immediate-early gene (IEG) that is rapidly induced by neuronal activity associated with information encoding in the brain, mediates homeostatic synaptic scaling of AMPA type glutamate receptors (AMPARs) via its ability to activate a novel and selective AMPAR endocytic pathway. High levels of Arc/Arg3.1 block the homeostatic increases in AMPAR function induced by chronic neuronal inactivity. Conversely, loss of Arc/Arg3.1 results in increased AMPAR function and abolishes homeostatic scaling of AMPARs. These observations, together with evidence that Arc/Arg3.1 is required for memory consolidation, reveal the importance of Arc/Arg3.1's dynamic expression as it exerts continuous and precise control over synaptic strength and cellular excitability.

Anesthetics, Local↗

PubMed2006

Amyotrophic lateral sclerosis 2-deficiency leads to neuronal degeneration in amyotrophic lateral sclerosis through altered AMPA receptor trafficking.

Amyotrophic lateral sclerosis (ALS), the most common adult-onset motor neuron disease is caused by a selective loss of motor neurons. One form of juvenile onset autosomal recessive ALS (ALS2) has been linked to the loss of function of the ALS2 gene. The pathogenic mechanism of ALS2-deficiency, however, remains unclear. To further understand the function of alsin that is encoded by the full-length ALS2 gene, we screened proteins interacting with alsin. Here, we report that alsin interacted with glutamate receptor interacting protein 1 (GRIP1) both in vitro and in vivo, and colocalized with GRIP1 in neurons. In support of the physiological interaction between alsin and GRIP1, the subcellular distribution of GRIP1 was altered in ALS2(-/-) spinal motor neurons, which correlates with a significant reduction of AMPA-type glutamate receptor subunit 2 (GluR2) at the synaptic/cell surface of ALS2(-/-) neurons. The decrease of calcium-impermeable GluR2-containing AMPA receptors at the cell/synaptic surface rendered ALS2(-/-) neurons more susceptible to glutamate receptor-mediated neurotoxicity. Our findings reveal a novel function of alsin in AMPA receptor trafficking and provide a novel pathogenic link between ALS2-deficiency and motor neuron degeneration, suggesting a protective role of alsin in maintaining the survival of motor neurons.

Adaptor Proteins, Signal Transducing↗

PubMed2006

Synaptic incorporation of AMPA receptors during LTP is controlled by a PKC phosphorylation site on GluR1.

Incorporation of GluR1-containing AMPA receptors into synapses is essential to several forms of neural plasticity, including long-term potentiation (LTP). Numerous signaling pathways that trigger this process have been identified, but the direct modifications of GluR1 that control its incorporation into synapses are unclear. Here, we show that phosphorylation of GluR1 by PKC at a highly conserved serine 818 residue is increased during LTP and critical for LTP expression. GluR1 is phosphorylated by PKC at this site in vitro and in vivo. In addition, acute phosphorylation at GluR1 S818 by PKC, as well as a phosphomimetic mutation, promotes GluR1 synaptic incorporation. Conversely, preventing GluR1 S818 phosphorylation reduces LTP and blocks PKC-driven synaptic incorporation of GluR1. We conclude that the phosphorylation of GluR1 S818 by PKC is a critical event in the plasticity-driven synaptic incorporation of AMPA receptors.

Animals↗

PubMed2006

Protein interacting with C-kinase 1/protein kinase Calpha-mediated endocytosis converts netrin-1-mediated repulsion to attraction.

In vertebrates, the receptor families deleted in colorectal cancer (DCC) and UNC5 mediate responses to the bifunctional guidance cue netrin-1. DCC mediates attraction, whereas a complex of DCC and UNC5 mediates repulsion. Thus, a primary determinant of the responsiveness of an axon to netrin-1 is the presence or absence of UNC5 family members on the cell surface. Currently, little is known about the role of receptor trafficking in regulating neuronal responses to netrin-1. We show that protein interacting with C-kinase 1 (PICK1) recruits activated protein kinase Calpha (PKCalpha) to MycUNC5A at the plasma membrane, stimulating its endocytosis. We identify two PKCalpha phosphorylation sites at serines 408 and 587, as well as dileucine internalization motifs, which are required for this endocytosis. We find that PKCalpha-stimulated internalization of UNC5A alters the functional response of developing hippocampal axons to netrin-1, preventing UNC5A-mediated growth cone collapse and converting netrin-1-stimulated chemorepulsion to attraction. To address whether this conversion in axonal response occurs in neurons expressing endogenous levels of UNC5, we show that mouse cerebellar granule axons exhibit chemorepulsion in a netrin-1 gradient and that this chemorepulsion is converted to chemoattraction after PKCalpha activation. We demonstrate that this repulsion depends on UNC5A because Unc5a-/- axons are not repelled and show this conversion depends on PICK1 because PICK1-/- axons are not converted to chemoattraction after PKCalpha activation. Together, these data provide a potential mechanism to explain how developing neurons alter their responsiveness to netrin-1 at intermediate choice points as they navigate to their targets.

Animals↗

PubMed2006

Targeted in vivo mutations of the AMPA receptor subunit GluR2 and its interacting protein PICK1 eliminate cerebellar long-term depression.

Cerebellar long-term depression (LTD) is a major form of synaptic plasticity that is thought to be critical for certain types of motor learning. Phosphorylation of the AMPA receptor subunit GluR2 on serine-880 as well as interaction of GluR2 with PICK1 have been suggested to contribute to the endocytic removal of postsynaptic AMPA receptors during LTD. Here, we show that targeted mutation of PICK1, the GluR2 C-terminal PDZ ligand, or the GluR2 PKC phosphorylation site eliminates cerebellar LTD in mice. LTD can be rescued in cerebellar cultures from mice lacking PICK1 by transfection of wild-type PICK1 but not by a PDZ mutant or a BAR domain mutant deficient in lipid binding, indicating the importance of these domains in PICK1 function. These results demonstrate that PICK1-GluR2 PDZ-based interactions and GluR2 phosphorylation are required for LTD expression in the cerebellum.

Age Factors↗

PubMed2006

SynGAP regulates synaptic strength and mitogen-activated protein kinases in cultured neurons.

Silent synapses, or excitatory synapses that lack functional alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptors (AMPARs), are thought to be critical for regulation of neuronal circuits and synaptic plasticity. Here, we report that SynGAP, an excitatory synapse-specific RasGAP, regulates AMPAR trafficking, silent synapse number, and excitatory synaptic transmission in hippocampal and cortical cultured neurons. Overexpression of SynGAP in neurons results in a remarkable depression of AMPAR-mediated miniature excitatory postsynaptic currents, a significant reduction in synaptic AMPAR surface expression, and a decrease in the insertion of AMPARs into the plasma membrane. This change is specific for AMPARs because no change is observed in synaptic NMDA receptor expression or total synapse density. In contrast to these results, synaptic transmission is increased in neurons from SynGAP knockout mice as well as in neuronal cultures treated with SynGAP small interfering RNA. In addition, activation of the extracellular signal-regulated kinase, ERK, is significantly decreased in SynGAP-overexpressing neurons, whereas P38 mitogen-activated protein kinase (MAPK) signaling is potentiated. Furthermore, ERK activation is up-regulated in neurons from SynGAP knockout mice, whereas P38 MAPK function is depressed. Taken together, these data suggest that SynGAP plays a critical role in the regulation of neuronal MAPK signaling, AMPAR membrane trafficking, and excitatory synaptic transmission.

Animals↗

PubMed2006

Regulation of AMPA receptor trafficking by N-cadherin.

Dendritic spines are dynamically regulated, both morphologically and functionally, by neuronal activity. Morphological changes are mediated by a variety of synaptic proteins, whereas functional changes can be dramatically modulated by the regulation of alpha-amino-3-hydroxy-5-methylisoxazole-4-propionate (AMPA) receptor trafficking. Although these two forms of plasticity appear to be highly coordinated, the connections between them are not fully understood. In this study the synaptic cell adhesion molecule N-cadherin was found to associate with AMPA receptors and regulate AMPA receptor trafficking in neurons. N-cadherin and beta-catenin formed a protein complex with AMPA receptors in vivo, and this association was regulated by extracellular Ca2+. In addition, these proteins co-clustered at synapses in cultured neurons. In heterologous cells and in cultured neurons, overexpression of wild-type N-cadherin specifically increased the surface expression level of the AMPA receptor subunit glutamate receptor 1 (GluR1) and this effect was reversed by a dominant-negative form of N-cadherin. Finally, GluR1 increased the surface expression of N-cadherin in heterologous cells. Importantly, recent studies suggest that N-cadherin and beta-catenin play key roles in structural plasticity in neurons. Therefore, our data suggest that the association of N-cadherin with AMPA receptors may serve as a biochemical link between structural and functional plasticity of synapses.

Animals↗

PubMed2006

Regulation of thalamocortical patterning and synaptic maturation by NeuroD2.

During cortical development, both activity-dependent and genetically determined mechanisms are required to establish proper neuronal connectivity. While activity-dependent transcription may link the two processes, specific transcription factors that mediate such a process have not been identified. We identified the basic helix-loop-helix (bHLH) transcription factor Neurogenic Differentiation 2 (NeuroD2) in a screen for calcium-regulated transcription factors and report that it is required for the proper development of thalamocortical connections. In neuroD2 null mice, thalamocortical axon terminals fail to segregate in the somatosensory cortex, and the postsynaptic barrel organization is disrupted. Additionally, synaptic transmission is defective at thalamocortical synapses in neuroD2 null mice. Total excitatory synaptic currents are reduced in layer IV in the knockouts, and the relative contribution of AMPA and NMDA receptor-mediated currents to evoked responses is decreased. These observations indicate that NeuroD2 plays a critical role in regulating synaptic maturation and the patterning of thalamocortical connections.

2-Amino-5-phosphonovalerate↗

PubMed2005

Activity-dependent dendritic spine structural plasticity is regulated by small GTPase Rap1 and its target AF-6.

Activity-dependent remodeling of dendritic spines is essential for neural circuit development and synaptic plasticity, but the mechanisms that coordinate synaptic structural and functional plasticity are not well understood. Here we investigate the signaling pathways that enable excitatory synapses to undergo activity-dependent structural modifications. We report that activation of NMDA receptors in cultured cortical neurons induces spine morphogenesis and activation of the small GTPase Rap1. Rap1 bimodally regulates spine morphology: activated Rap1 recruits the PDZ domain-containing protein AF-6 to the plasma membrane and induces spine neck elongation, while inactive Rap1 dissociates AF-6 from the membrane and induces spine enlargement. Rap1 also regulates spine content of AMPA receptors: thin spines induced by Rap1 activation have reduced GluR1-containing AMPA receptor content, while large spines induced by Rap1 inactivation are rich in AMPA receptors. These results identify a signaling pathway that regulates activity-dependent synaptic structural plasticity and coordinates it with functional plasticity.

2-Amino-5-phosphonovalerate↗

PubMed2005

Bipolar I disorder and schizophrenia: a 440-single-nucleotide polymorphism screen of 64 candidate genes among Ashkenazi Jewish case-parent trios.

Bipolar, schizophrenia, and schizoaffective disorders are common, highly heritable psychiatric disorders, for which familial coaggregation, as well as epidemiological and genetic evidence, suggests overlapping etiologies. No definitive susceptibility genes have yet been identified for any of these disorders. Genetic heterogeneity, combined with phenotypic imprecision and poor marker coverage, has contributed to the difficulty in defining risk variants. We focused on families of Ashkenazi Jewish descent, to reduce genetic heterogeneity, and, as a precursor to genomewide association studies, we undertook a single-nucleotide polymorphism (SNP) genotyping screen of 64 candidate genes (440 SNPs) chosen on the basis of previous linkage or of association and/or biological relevance. We genotyped an average of 6.9 SNPs per gene, with an average density of 1 SNP per 11.9 kb in 323 bipolar I disorder and 274 schizophrenia or schizoaffective Ashkenazi case-parent trios. Using single-SNP and haplotype-based transmission/disequilibrium tests, we ranked genes on the basis of strength of association (P<.01). Six genes (DAO, GRM3, GRM4, GRIN2B, IL2RB, and TUBA8) met this criterion for bipolar I disorder; only DAO has been previously associated with bipolar disorder. Six genes (RGS4, SCA1, GRM4, DPYSL2, NOS1, and GRID1) met this criterion for schizophrenia or schizoaffective disorder; five replicate previous associations, and one, GRID1, shows a novel association with schizophrenia. In addition, six genes (DPYSL2, DTNBP1, G30/G72, GRID1, GRM4, and NOS1) showed overlapping suggestive evidence of association in both disorders. These results may help to prioritize candidate genes for future study from among the many suspected/proposed for schizophrenia and bipolar disorders. They provide further support for shared genetic susceptibility between these two disorders that involve glutamate-signaling pathways.

Adolescent↗

PubMed2005

Ribosomal S6 kinase 2 interacts with and phosphorylates PDZ domain-containing proteins and regulates AMPA receptor transmission.

Extracellular signal-regulated kinase (ERK) signaling is important for neuronal synaptic plasticity. We report here that the protein kinase ribosomal S6 kinase (RSK)2, a downstream target of ERK, uses a C-terminal motif to bind several PDZ domain proteins in heterologous systems and in vivo. Different RSK isoforms display distinct specificities in their interactions with PDZ domain proteins. Mutation of the RSK2 PDZ ligand does not inhibit RSK2 activation in intact cells or phosphorylation of peptide substrates by RSK2 in vitro but greatly reduces RSK2 phosphorylation of PDZ domain proteins of the Shank family in heterologous cells. In primary neurons, NMDA receptor (NMDA-R) activation leads to ERK and RSK2 activation and RSK-dependent phosphorylation of transfected Shank3. RSK2-PDZ domain interactions are functionally important for synaptic transmission because neurons expressing kinase-dead RSK2 display a dramatic reduction in frequency of AMPA-type glutamate receptor-mediated miniature excitatory postsynaptic currents, an effect dependent on the PDZ ligand. These results suggest that binding of RSK2 to PDZ domain proteins and phosphorylation of these proteins or their binding partners regulates excitatory synaptic transmission.

Adaptor Proteins, Signal Transducing↗

PubMed2005

Differential regulation of AMPA receptor subunit trafficking by palmitoylation of two distinct sites.

Modification of AMPA receptor function is a major mechanism for the regulation of synaptic transmission and underlies several forms of synaptic plasticity. Post-translational palmitoylation is a reversible modification that regulates localization of many proteins. Here, we report that palmitoylation of the AMPA receptor regulates receptor trafficking. All AMPA receptor subunits are palmitoylated on two cysteine residues in their transmembrane domain (TMD) 2 and in their C-terminal region. Palmitoylation on TMD 2 is upregulated by the palmitoyl acyl transferase GODZ and leads to an accumulation of the receptor in the Golgi and a reduction of receptor surface expression. C-terminal palmitoylation decreases interaction of the AMPA receptor with the 4.1N protein and regulates AMPA- and NMDA-induced AMPA receptor internalization. Moreover, depalmitoylation of the receptor is regulated by activation of glutamate receptors. These data suggest that regulated palmitoylation of AMPA receptor subunits modulates receptor trafficking and may be important for synaptic plasticity.

Amino Acid Sequence↗

PubMed2005

GRIP1 in GABAergic synapses.

The glutamate receptor-interacting protein GRIP1 is present in glutamatergic synapses and interacts with the GluR2/3/4c subunits of the AMPA receptors. This interaction plays important roles in trafficking, synaptic targeting, and recycling of AMPA receptors as well as in the plasticity of glutamatergic synapses. Although GRIP1 has been shown to be present at GABAergic synapses in cultured neurons, the use of EM (electron microscopy) immunocytochemistry in the intact brain has failed to convincingly reveal the presence of GRIP1 in GABAergic synapses. Therefore, most studies on GRIP1 have focused on glutamatergic synapses. By using mild tissue fixation and embedding in EM, we show that in the intact brain the 7-PDZ domain GRIP1a/b is present not only in glutamatergic synapses but also in GABAergic synapses. In GABAergic synapses GRIP1a/b localizes both at the presynaptic terminals and postsynaptically, being frequently localized on the synaptic membranes or the synaptic junctional complex. Considerably higher density of GRIP1a/b is found in the presynaptic GABAergic terminals than in the glutamatergic terminals, while the density of GRIP1a/b in the postsynaptic complex is similar in both types of synapses. The results also show that the 7-PDZ and the shorter 4-PDZ domain splice forms of GRIP1 (GRIP1c 4-7) frequently colocalize with each other in individual GABAergic and glutamatergic synapses. The results suggest that GRIP1 splice forms might play important roles in brain GABAergic synapses.

Animals↗

PubMed2005

S-nitrosylation of N-ethylmaleimide sensitive factor mediates surface expression of AMPA receptors.

Postsynaptic AMPA receptor (AMPAR) trafficking mediates some forms of synaptic plasticity that are modulated by NMDA receptor (NMDAR) activation and N-ethylmaleimide sensitive factor (NSF). We report that NSF is physiologically S-nitrosylated by endogenous, neuronally derived nitric oxide (NO). S-nitrosylation of NSF augments its binding to the AMPAR GluR2 subunit. Surface insertion of GluR2 in response to activation of synaptic NMDARs requires endogenous NO, acting selectively upon the binding of NSF to GluR2. Thus, AMPAR recycling elicited by NMDA neurotransmission is mediated by a cascade involving NMDA activation of neuronal NO synthase to form NO, leading to S-nitrosylation of NSF which is thereby activated, enabling it to bind to GluR2 and promote the receptor's surface expression.

Adenylyl Imidodiphosphate↗

PubMed2005

Secreted semaphorins modulate synaptic transmission in the adult hippocampus.

Modulation of synaptic activity is critical for neural circuit function and behavior. The semaphorins are a large, phylogenetically conserved protein family with important roles in neural development. However, semaphorin function in the adult brain has yet to be determined. Here, we show that the coreceptors for secreted semaphorins, the neuropilins, are found at synapses and localize to molecular layers of the adult mouse hippocampus and accessory olfactory cortex. Moreover, application of the secreted semaphorin Sema3F to acute hippocampal slices modulates both the frequency and amplitude of miniature EPSCs in granule cells of the dentate gyrus and pyramidal neurons of CA1. Finally, we show that mice lacking Sema3F are prone to seizures. These results suggest a novel role for semaphorins as synaptic modulators and illustrate the diverse repertoire of these guidance cues in both the formation and function of neural circuits.

Age Factors↗

PubMed2005

Calcium-permeable AMPA receptor plasticity is mediated by subunit-specific interactions with PICK1 and NSF.

A recently described form of synaptic plasticity results in dynamic changes in the calcium permeability of synaptic AMPA receptors. Since the AMPA receptor GluR2 subunit confers calcium permeability, this plasticity is thought to occur through the dynamic exchange of synaptic GluR2-lacking and GluR2-containing receptors. To investigate the molecular mechanisms underlying this calcium-permeable AMPA receptor plasticity (CARP), we examined whether AMPA receptor exchange was mediated by subunit-specific protein-protein interactions. We found that two GluR2-interacting proteins, the PDZ domain-containing Protein interacting with C kinase (PICK1) and N-ethylmaleimide sensitive fusion protein (NSF), are specifically required for CARP. Furthermore, PICK1, but not NSF, regulates the formation of extrasynaptic plasma membrane pools of GluR2-containing receptors that may be laterally mobilized into synapses during CARP. These results demonstrate that PICK1 and NSF dynamically regulate the synaptic delivery of GluR2-containing receptors during CARP and thus regulate the calcium permeability of AMPA receptors at excitatory synapses.

Animals↗