RESUMO
Phosphatase and tensin homolog deleted on chromosome ten (PTEN) is an important regulator of phosphatidylinositol-(3,4,5,)-trisphosphate signalling, which controls cell growth and differentiation. However, PTEN is also highly expressed in the adult brain, in which it can be found in dendritic spines in hippocampus and other brain regions. Here, we have investigated specific functions of PTEN in the regulation of synaptic function in excitatory hippocampal synapses. We found that NMDA receptor activation triggers a PDZ-dependent association between PTEN and the synaptic scaffolding molecule PSD-95. This association is accompanied by PTEN localization at the postsynaptic density and anchoring within the spine. On the other hand, enhancement of PTEN lipid phosphatase activity is able to drive depression of AMPA receptor-mediated synaptic responses. This activity is specifically required for NMDA receptor-dependent long-term depression (LTD), but not for LTP or metabotropic glutamate receptor-dependent LTD. Therefore, these results reveal PTEN as a regulated signalling molecule at the synapse, which is recruited to the postsynaptic membrane upon NMDA receptor activation, and is required for the modulation of synaptic activity during plasticity.
Assuntos
Depressão Sináptica de Longo Prazo , PTEN Fosfo-Hidrolase/metabolismo , Receptores de N-Metil-D-Aspartato/metabolismo , Sinapses/metabolismo , Animais , Proteína 4 Homóloga a Disks-Large , Hipocampo/metabolismo , Peptídeos e Proteínas de Sinalização Intracelular/metabolismo , Proteínas de Membrana/metabolismo , Domínios PDZ , PTEN Fosfo-Hidrolase/análise , Ratos , Receptores de AMPA/metabolismo , Coluna Vertebral/ultraestrutura , Transmissão SinápticaRESUMO
Endosomal membrane trafficking in dendritic spines is important for proper synaptic function and plasticity. However, little is known about the molecular identity and functional compartmentalization of the membrane trafficking machinery operating at the postsynaptic terminal. Here we report that the transport of AMPA-type glutamate receptors into synapses occurs in two discrete steps, and we identify the specific endosomal functions that control this process during long-term potentiation. We found that Rab11-dependent endosomes translocate AMPA receptors from the dendritic shaft into spines. Subsequently, an additional endosomal trafficking step, controlled by Rab8, drives receptor insertion into the synaptic membrane. Separate from this receptor delivery route, we show that Rab4 mediates a constitutive endosomal recycling within the spine. This Rab4-dependent cycling is critical for maintaining spine size but does not influence receptor transport. Therefore, our data reveal a highly compartmentalized endosomal network within the spine and identify the molecular components and functional organization of the membrane organelles that mediate AMPA receptor synaptic delivery during plasticity.
Assuntos
Endossomos/metabolismo , Potenciação de Longa Duração/fisiologia , Neurônios/fisiologia , Receptores de AMPA/metabolismo , Membranas Sinápticas/metabolismo , Análise de Variância , Animais , Proteína Quinase Tipo 2 Dependente de Cálcio-Calmodulina/genética , Proteína Quinase Tipo 2 Dependente de Cálcio-Calmodulina/metabolismo , Dendritos/metabolismo , Estimulação Elétrica/métodos , Ginecomastia , Hipocampo/citologia , Hipocampo/metabolismo , Técnicas In Vitro , Potenciação de Longa Duração/genética , Potenciação de Longa Duração/efeitos da radiação , Proteínas Luminescentes/genética , Proteínas Luminescentes/metabolismo , Neurônios/citologia , Técnicas de Patch-Clamp/métodos , Transporte Proteico/fisiologia , Ratos , Receptores de Glutamato/genética , Receptores de Glutamato/metabolismo , Transformação Genética , Proteínas rab de Ligação ao GTP/metabolismoRESUMO
Despite their low abundance, phosphoinositides are critical regulators of intracellular signaling and membrane compartmentalization. However, little is known of phosphoinositide function at the postsynaptic membrane. Here we show that continuous synthesis and availability of phosphatidylinositol-(3,4,5)-trisphosphate (PIP(3)) at the postsynaptic terminal is necessary for sustaining synaptic function in rat hippocampal neurons. This requirement was specific for synaptic, but not extrasynaptic, AMPA receptors, nor for NMDA receptors. PIP(3) downregulation impaired PSD-95 accumulation in spines. Concomitantly, AMPA receptors became more mobile and migrated from the postsynaptic density toward the perisynaptic membrane within the spine, leading to synaptic depression. Notably, these effects were only revealed after prolonged inhibition of PIP(3) synthesis or by direct quenching of this phosphoinositide at the postsynaptic cell. Therefore, we conclude that a slow, but constant, turnover of PIP(3) at synapses is required for maintaining AMPA receptor clustering and synaptic strength under basal conditions.