RESUMO
Dysfunction of the proteins regulating synaptic function can cause synaptic plasticity imbalance that underlies neurological disorders such as intellectual disability. A study found that four distinct mutations within BRAG1, an Arf-GEF synaptic protein, each led to X-chromosome-linked intellectual disability (XLID). Although the physiological functions of BRAG1 are poorly understood, each of these mutations reduces BRAG1's Arf-GEF activity. Here we show that BRAG1 is required for the activity-dependent removal of AMPA receptors in rat hippocampal pyramidal neurons. Moreover, we show that BRAG1 bidirectionally regulates synaptic transmission. On one hand, BRAG1 is required for the maintenance of synaptic transmission. On the other hand, BRAG1 expression enhances synaptic transmission, independently of BRAG1 Arf-GEF activity or neuronal activity, but dependently on its C-terminus interactions. This study demonstrates a dual role of BRAG1 in synaptic function and highlights the functional relevance of reduced BRAG1 Arf-GEF activity as seen in the XLID-associated human mutations.
Assuntos
Fatores de Troca do Nucleotídeo Guanina/metabolismo , Depressão Sináptica de Longo Prazo , Transmissão Sináptica , Sequência de Aminoácidos , Fatores de Troca do Nucleotídeo Guanina/química , Células HEK293 , Humanos , Receptores de AMPA/metabolismoRESUMO
The NMDA-type glutamate receptor (NMDAR) is essential for synaptogenesis, synaptic plasticity, and higher cognitive function. Emerging evidence indicates that NMDAR Ca(2+) permeability is under the control of cAMP/protein kinase A (PKA) signaling. Whereas the functional impact of PKA on NMDAR-dependent Ca(2+) signaling is well established, the molecular target remains unknown. Here we identify serine residue 1166 (Ser1166) in the carboxy-terminal tail of the NMDAR subunit GluN2B to be a direct molecular and functional target of PKA phosphorylation critical to NMDAR-dependent Ca(2+) permeation and Ca(2+) signaling in spines. Activation of ß-adrenergic and D1/D5-dopamine receptors induces Ser1166 phosphorylation. Loss of this single phosphorylation site abolishes PKA-dependent potentiation of NMDAR Ca(2+) permeation, synaptic currents, and Ca(2+) rises in dendritic spines. We further show that adverse experience in the form of forced swim, but not exposure to fox urine, elicits striking phosphorylation of Ser1166 in vivo, indicating differential impact of different forms of stress. Our data identify a novel molecular and functional target of PKA essential to NMDAR-mediated Ca(2+) signaling at synapses and regulated by the emotional response to stress.
Assuntos
Sinalização do Cálcio/fisiologia , Proteínas Quinases Dependentes de AMP Cíclico/metabolismo , Espinhas Dendríticas/metabolismo , Receptores de N-Metil-D-Aspartato/metabolismo , Serina/metabolismo , Sinapses/fisiologia , Animais , Animais Recém-Nascidos , Células Cultivadas , Proteínas Quinases Dependentes de AMP Cíclico/genética , Espinhas Dendríticas/genética , Raposas , Células HEK293 , Hipocampo/metabolismo , Humanos , Inibição Neural/fisiologia , Fosforilação/fisiologia , Ratos Sprague-Dawley , Receptores de N-Metil-D-Aspartato/genética , Receptores de N-Metil-D-Aspartato/fisiologia , Serina/genética , Estresse Psicológico/genética , Estresse Psicológico/metabolismoRESUMO
The first family identified as having a nonsyndromic intellectual disability was mapped in 1988. Here we show that a mutation of IQSEC2, encoding a guanine nucleotide exchange factor for the ADP-ribosylation factor family of small GTPases, caused this disorder. In addition to MRX1, IQSEC2 mutations were identified in three other families with X-linked intellectual disability. This discovery was made possible by systematic and unbiased X chromosome exome resequencing.
Assuntos
Fatores de Troca do Nucleotídeo Guanina/genética , Deficiência Intelectual Ligada ao Cromossomo X/genética , Mutação , Cromossomos Humanos X , Feminino , Humanos , Masculino , LinhagemRESUMO
The postsynaptic density (PSD) at excitatory synapses is a dynamic complex of glutamatergic receptors and associated proteins that governs synaptic structure and coordinates signal transduction. In this study, we report that BRAG1, a putative guanine nucleotide exchange factor for the Arf family of GTP-binding proteins, is a major component of the PSD. BRAG1 was identified in a 190 kDa band in the PSD fraction with the use of mass spectrometry coupled to searching of a protein sequence database. BRAG1 expression is abundant in the adult rat forebrain, and it is strongly enriched in the PSD fraction compared to forebrain homogenate and synaptosomes. Immunocytochemical localization of BRAG1 in dissociated hippocampal neurons shows that it forms discrete clusters that colocalize with the postsynaptic marker PSD-95 at sites along dendrites. BRAG1 contains a Sec7 domain, a domain that catalyzes exchange of GDP for GTP on the Arf family of small GTP-binding proteins. In their GTP-bound active state, Arfs regulate trafficking of vesicles and cytoskeletal structure. We demonstrate that the Sec7 domain of BRAG1 promotes binding of GTP to Arf in vitro. These data suggest that BRAG1 may modulate the functions of Arfs at synaptic sites.