RESUMO
Glycogen synthase kinase-3 (GSK3) is an important signalling protein in the brain and modulates different forms of synaptic plasticity. Neuronal functions of GSK3 are typically attributed to one of its two isoforms, GSK3ß, simply because of its prevalent expression in the brain. Consequently, the importance of isoform-specific functions of GSK3 in synaptic plasticity has not been fully explored. We now directly address this question for NMDA receptor-dependent long-term depression (LTD) in the hippocampus. Here, we specifically target the GSK3 isoforms with shRNA knock-down in mouse hippocampus and with novel isoform-selective drugs to dissect their roles in LTD. Using electrophysiological and live imaging approaches, we find that GSK3α, but not GSK3ß, is required for LTD. The specific engagement of GSK3α occurs via its transient anchoring in dendritic spines during LTD induction. We find that the major GSK3 substrate, the microtubule-binding protein tau, is required for this spine anchoring of GSK3α and mediates GSK3α-induced LTD. These results link GSK3α and tau in a common mechanism for synaptic depression and rule out a major role for GSK3ß in this process.
Assuntos
Glicogênio Sintase Quinase 3 beta/metabolismo , Quinase 3 da Glicogênio Sintase/metabolismo , Hipocampo/metabolismo , Receptores de N-Metil-D-Aspartato/metabolismo , Proteínas tau/metabolismo , Animais , Camundongos , Plasticidade Neuronal/fisiologia , Neurônios/metabolismo , Isoformas de Proteínas/metabolismoRESUMO
Long-term synaptic plasticity is typically associated with morphological changes in synaptic connections. However, the molecular mechanisms coupling functional and structural aspects of synaptic plasticity are still poorly defined. The catalytic activity of type I phosphoinositide-3-kinase (PI3K) is required for specific forms of synaptic plasticity, such as NMDA receptor-dependent long-term potentiation (LTP) and mGluR-dependent long-term depression (LTD). On the other hand, PI3K signaling has been linked to neuronal growth and synapse formation. Consequently, PI3Ks are promising candidates to coordinate changes in synaptic strength with structural remodeling of synapses. To investigate this issue, we targeted individual regulatory subunits of type I PI3Ks in hippocampal neurons and employed a combination of electrophysiological, biochemical and imaging techniques to assess their role in synaptic plasticity. We found that a particular regulatory isoform, p85α, is selectively required for LTP. This specificity is based on its BH domain, which engages the small GTPases Rac1 and Cdc42, critical regulators of the actin cytoskeleton. Moreover, cofilin, a key regulator of actin dynamics that accumulates in dendritic spines after LTP induction, failed to do so in the absence of p85α or when its BH domain was overexpressed as a dominant negative construct. Finally, in agreement with this convergence on actin regulatory mechanisms, the presence of p85α in the PI3K complex determined the extent of actin polymerization in dendritic spines during LTP. Therefore, this study reveals a molecular mechanism linking structural and functional synaptic plasticity through the coordinate action of PI3K catalytic activity and a specific isoform of the regulatory subunits.
Assuntos
Fatores de Despolimerização de Actina , Actinas , Espinhas Dendríticas , Hipocampo , Potenciação de Longa Duração , Animais , Espinhas Dendríticas/metabolismo , Potenciação de Longa Duração/fisiologia , Actinas/metabolismo , Hipocampo/metabolismo , Hipocampo/citologia , Fatores de Despolimerização de Actina/metabolismo , Ratos , Proteínas rac1 de Ligação ao GTP/metabolismo , Sinapses/metabolismo , Polimerização , Proteína cdc42 de Ligação ao GTP/metabolismo , Plasticidade Neuronal/fisiologia , Fosfatidilinositol 3-Quinases/metabolismo , Classe Ia de Fosfatidilinositol 3-Quinase/metabolismo , Classe Ia de Fosfatidilinositol 3-Quinase/genética , Neurônios/metabolismo , Transdução de Sinais , Camundongos , Células CultivadasRESUMO
The mitochondrial ATP synthase emerges as key hub of cellular functions controlling the production of ATP, cellular signaling, and fate. It is regulated by the ATPase inhibitory factor 1 (IF1), which is highly abundant in neurons. Herein, we ablated or overexpressed IF1 in mouse neurons to show that IF1 dose defines the fraction of active/inactive enzyme in vivo, thereby controlling mitochondrial function and the production of mitochondrial reactive oxygen species (mtROS). Transcriptomic, proteomic, and metabolomic analyses indicate that IF1 dose regulates mitochondrial metabolism, synaptic function, and cognition. Ablation of IF1 impairs memory, whereas synaptic transmission and learning are enhanced by IF1 overexpression. Mechanistically, quenching the IF1-mediated increase in mtROS production in mice overexpressing IF1 reduces the increased synaptic transmission and obliterates the learning advantage afforded by the higher IF1 content. Overall, IF1 plays a key role in neuronal function by regulating the fraction of ATP synthase responsible for mitohormetic mtROS signaling.
Assuntos
Mitocôndrias/metabolismo , ATPases Mitocondriais Próton-Translocadoras/metabolismo , Proteínas/metabolismo , Trifosfato de Adenosina/metabolismo , Animais , Encéfalo/metabolismo , Linhagem Celular , Hipocampo/metabolismo , Camundongos , Camundongos Endogâmicos C57BL , ATPases Mitocondriais Próton-Translocadoras/fisiologia , Cultura Primária de Células , Proteínas/fisiologia , Espécies Reativas de Oxigênio/metabolismo , Transdução de Sinais , Proteína Inibidora de ATPaseRESUMO
Nuclear Cyclin D1 (Ccnd1) is a main regulator of cell cycle progression and cell proliferation. Interestingly, Ccnd1 moves to the cytoplasm at the onset of differentiation in neuronal precursors. However, cytoplasmic functions and targets of Ccnd1 in post-mitotic neurons are unknown. Here we identify the α4 subunit of gamma-aminobutyric acid (GABA) type A receptors (GABAARs) as an interactor and target of Ccnd1-Cdk4. Ccnd1 binds to an intracellular loop in α4 and, together with Cdk4, phosphorylates the α4 subunit at threonine 423 and serine 431. These modifications upregulate α4 surface levels, increasing the response of α4-containing GABAARs, measured in whole-cell patch-clamp recordings. In agreement with this role of Ccnd1-Cdk4 in neuronal signalling, inhibition of Cdk4 or expression of the non-phosphorylatable α4 decreases synaptic and extra-synaptic currents in the hippocampus of newborn rats. Moreover, according to α4 functions in synaptic pruning, CCND1 knockout mice display an altered pattern of dendritic spines that is rescued by the phosphomimetic α4. Overall, our findings molecularly link Ccnd1-Cdk4 to GABAARs activity in the central nervous system and highlight a novel role for this G1 cyclin in neuronal signalling.
Assuntos
Ciclina D1 , Quinase 4 Dependente de Ciclina , Receptores de GABA-A , Animais , Camundongos , Ratos , Ciclina D1/genética , Ácido gama-Aminobutírico , Camundongos Knockout , Neurônios , Fosforilação , Receptores de GABA-A/genética , Quinase 4 Dependente de Ciclina/genéticaRESUMO
Increasing evidence from animal and epidemiological studies indicates that perinatal exposure to pesticides cause developmental neurotoxicity and may increase the risk for psychiatric disorders such as autism and intellectual disability. However, the underlying pathogenic mechanisms remain largely elusive. This work was aimed at testing the hypothesis that developmental exposure to different classes of pesticides hijacks intracellular neuronal signaling contributing to synaptic and behavioral alterations associated with neurodevelopmental disorders (NDD). Low concentrations of organochlorine (dieldrin, endosulfan, and chlordane) and organophosphate (chlorpyrifos and its oxon metabolite) pesticides were chronically dosed ex vivo (organotypic rat hippocampal slices) or in vivo (perinatal exposure in rats), and then biochemical, electrophysiological, behavioral, and proteomic studies were performed. All the pesticides tested caused prolonged activation of MAPK/ERK pathway in a concentration-dependent manner. Additionally, some of them impaired metabotropic glutamate receptor-dependent long-term depression (mGluR-LTD). In the case of the pesticide chlordane, the effect was attributed to chronic modulation of MAPK/ERK signaling. These synaptic alterations were reproduced following developmental in vivo exposure to chlordane and chlorpyrifos-oxon, and were also associated with prototypical behavioral phenotypes of NDD, including impaired motor development, increased anxiety, and social and memory deficits. Lastly, proteomic analysis revealed that these pesticides differentially regulate the expression of proteins in the hippocampus with pivotal roles in brain development and synaptic signaling, some of which are associated with NDD. Based on these results, we propose a novel mechanism of synaptic dysfunction, involving chronic overactivation of MAPK and impaired mGluR-LTD, shared by different pesticides which may have important implications for NDD.
Assuntos
Clorpirifos , Transtornos do Neurodesenvolvimento , Praguicidas , Humanos , Feminino , Gravidez , Ratos , Animais , Praguicidas/toxicidade , Clorpirifos/toxicidade , Clorpirifos/metabolismo , Clordano/metabolismo , Clordano/farmacologia , Proteômica , Hipocampo/metabolismo , Plasticidade Neuronal , Transtornos do Neurodesenvolvimento/induzido quimicamente , Transtornos do Neurodesenvolvimento/metabolismoRESUMO
It is well--established that Rab11-dependent recycling endosomes drive the activity-dependent delivery of AMPA receptors (AMPARs) into synapses during long-term potentiation (LTP). Nevertheless, the molecular basis for this specialized function of recycling endosomes is still unknown. Here, we have investigated RAB11FIP2 (FIP2 hereafter) as a potential effector of Rab11-dependent trafficking during LTP in rat hippocampal slices. Surprisingly, we found that FIP2 operates independently from Rab11 proteins, and acts as a negative regulator of AMPAR synaptic trafficking. Under basal conditions, FIP2 associates with AMPARs at immobile compartments, separately from recycling endosomes. Using shRNA-mediated knockdown, we found that FIP2 prevents GluA1 (encoded by the Gria1 gene) AMPARs from reaching the surface of dendritic spines in the absence of neuronal stimulation. Upon induction of LTP, FIP2 is rapidly mobilized, dissociates from AMPARs and undergoes dephosphorylation. Interestingly, this dissociation of the FIP2-AMPAR complex, together with FIP2 dephosphorylation, is required for LTP, but the interaction between FIP2 and Rab11 proteins is not. Based on these results, we propose a retention-release mechanism, where FIP2 acts as a gate that restricts the trafficking of AMPARs, until LTP induction triggers their release and allows synaptic delivery.
Assuntos
Proteínas de Transporte/metabolismo , Espinhas Dendríticas/metabolismo , Potenciação de Longa Duração/fisiologia , Proteínas de Membrana/metabolismo , Receptores de AMPA/metabolismo , Sinapses/metabolismo , Animais , Proteínas de Transporte/genética , Endossomos/metabolismo , Feminino , Hipocampo/metabolismo , Masculino , Proteínas de Membrana/genética , Ratos , Ratos Wistar , Receptores de AMPA/genéticaRESUMO
BACKGROUND: The complex pathophysiology of Alzheimer's disease (AD) hampers the development of effective treatments. Attempts to prevent neurodegeneration in AD have failed so far, highlighting the need for further clarification of the underlying cellular and molecular mechanisms. Neuroinflammation seems to play a crucial role in disease progression, although its specific contribution to AD pathogenesis remains elusive. We have previously shown that the modulation of the endocannabinoid system (ECS) renders beneficial effects in a context of amyloidosis, which triggers neuroinflammation. In the 5xFAD model, the genetic inactivation of the enzyme that degrades anandamide (AEA), the fatty acid amide hydrolase (FAAH), was associated with a significant amelioration of the memory deficit. METHODS: In this work, we use electrophysiology, flow cytometry and molecular analysis to evaluate the cellular and molecular mechanisms underlying the improvement associated to the increased endocannabinoid tone in the 5xFAD mouse- model. RESULTS: We demonstrate that the chronic enhancement of the endocannabinoid tone rescues hippocampal synaptic plasticity in the 5xFAD mouse model. At the CA3-CA1 synapse, both basal synaptic transmission and long-term potentiation (LTP) of synaptic transmission are normalized upon FAAH genetic inactivation, in a CB1 receptor (CB1R)- and TRPV1 receptor-independent manner. Dendritic spine density in CA1 pyramidal neurons, which is notably decreased in 6-month-old 5xFAD animals, is also restored. Importantly, we reveal that the expression of microglial factors linked to phagocytic activity, such as TREM2 and CTSD, and other factors related to amyloid beta clearance and involved in neuron-glia crosstalk, such as complement component C3 and complement receptor C3AR, are specifically upregulated in 5xFAD/FAAH-/- animals. CONCLUSION: In summary, our findings support the therapeutic potential of modulating, rather than suppressing, neuroinflammation in Alzheimer's disease. In our model, the long-term enhancement of the endocannabinoid tone triggered augmented microglial activation and amyloid beta phagocytosis, and a consequent reversal in the neuronal phenotype associated to the disease.
Assuntos
Doença de Alzheimer/metabolismo , Amidoidrolases/deficiência , Peptídeos beta-Amiloides/metabolismo , Plasticidade Neuronal/fisiologia , Transmissão Sináptica/fisiologia , Doença de Alzheimer/patologia , Animais , Modelos Animais de Doenças , Humanos , Camundongos , Camundongos Endogâmicos C57BL , Camundongos Knockout , Fagocitose/fisiologiaRESUMO
NPC is a neurodegenerative disorder characterized by cholesterol accumulation in endolysosomal compartments. It is caused by mutations in the gene encoding NPC1, an endolysosomal protein mediating intracellular cholesterol trafficking. Cognitive and psychiatric alterations are hallmarks in NPC patients pointing to synaptic defects. However, the role of NPC1 in synapses has not been explored. We show that NPC1 is present in the postsynaptic compartment and is locally translated during LTP. A mutation in a region of the NPC1 gene commonly altered in NPC patients reduces NPC1 levels at synapses due to enhanced NPC1 protein degradation. This leads to shorter postsynaptic densities, increased synaptic cholesterol and impaired LTP in NPC1nmf164 mice with cognitive deficits. NPC1 mediates cholesterol mobilization and enables surface delivery of CYP46A1 and GluA1 receptors necessary for LTP, which is defective in NPC1nmf164 mice. Pharmacological activation of CYP46A1 normalizes synaptic levels of cholesterol, LTP and cognitive abilities, and extends life span of NPC1nmf164 mice. Our results unveil NPC1 as a regulator of cholesterol dynamics in synapses contributing to synaptic plasticity, and provide a potential therapeutic strategy for NPC patients.
Assuntos
Colesterol 24-Hidroxilase/metabolismo , Colesterol/metabolismo , Peptídeos e Proteínas de Sinalização Intracelular/genética , Peptídeos e Proteínas de Sinalização Intracelular/metabolismo , Potenciação de Longa Duração , Doença de Niemann-Pick Tipo C/genética , Doença de Niemann-Pick Tipo C/metabolismo , Animais , Modelos Animais de Doenças , Humanos , Imuno-Histoquímica , Camundongos , Camundongos Knockout , Modelos Biológicos , Proteína C1 de Niemann-Pick , Biossíntese de Proteínas , Receptores de AMPA/metabolismo , Sinapses/metabolismoRESUMO
Phosphatase and tensin homolog on chromosome 10 (PTEN) is a tumor suppressor and autism-associated gene that exerts an important influence over neuronal structure and function during development. In addition, it participates in synaptic plasticity processes in adulthood. As an attempt to assess synaptic and developmental mechanisms by which PTEN can modulate cognitive function, we studied the consequences of 2 different genetic manipulations in mice: presence of additional genomic copies of the Pten gene (Ptentg) and knock-in of a truncated Pten gene lacking its PDZ motif (Pten-ΔPDZ), which is required for interaction with synaptic proteins. Ptentg mice exhibit substantial microcephaly, structural hypoconnectivity, enhanced synaptic depression at cortico-amygdala synapses, reduced anxiety, and intensified social interactions. In contrast, Pten-ΔPDZ mice have a much more restricted phenotype, with normal synaptic connectivity, but impaired synaptic depression at cortico-amygdala synapses and virtually abolished social interactions. These results suggest that synaptic actions of PTEN in the amygdala contribute to specific behavioral traits, such as sociability. Also, PTEN appears to function as a bidirectional rheostat in the amygdala: reduction in PTEN activity at synapses is associated with less sociability, whereas enhanced PTEN activity accompanies hypersocial behavior.
Assuntos
Tonsila do Cerebelo/fisiologia , Córtex Cerebral/fisiologia , Plasticidade Neuronal , PTEN Fosfo-Hidrolase/fisiologia , Comportamento Social , Tonsila do Cerebelo/ultraestrutura , Animais , Feminino , Hipocampo/fisiologia , Masculino , Memória/fisiologia , Camundongos Transgênicos , Sinapses/fisiologia , Sinapses/ultraestruturaRESUMO
Tau is a microtubule-associated neuronal protein found mainly in axons. However, its presence in dendrites and dendritic spines is particularly relevant due to its involvement in synaptic plasticity and neurodegeneration. Here, we show that Tau plays a novel in vivo role in the morphological and synaptic maturation of newborn hippocampal granule neurons under basal conditions. Furthermore, we reveal that Tau is involved in the selective cell death of immature granule neurons caused by acute stress. Also, Tau deficiency protects newborn neurons from the stress-induced dendritic atrophy and loss of postsynaptic densities (PSDs). Strikingly, we also demonstrate that Tau regulates the increase in newborn neuron survival triggered by environmental enrichment (EE). Moreover, newborn granule neurons from Tau(-/-) mice did not show any stimulatory effect of EE on dendritic development or on PSD generation. Thus, our data demonstrate that Tau(-/-) mice show impairments in the maturation of newborn granule neurons under basal conditions and that they are insensitive to the modulation of adult hippocampal neurogenesis exerted by both stimulatory and detrimental stimuli.
Assuntos
Hipocampo/citologia , Hipocampo/fisiologia , Neurogênese , Proteínas tau/metabolismo , Animais , Camundongos , Camundongos KnockoutRESUMO
The regulated transport of AMPA-type glutamate receptors (AMPARs) to the synaptic membrane is a key mechanism to determine the strength of excitatory synaptic transmission in the brain. In this work, we uncovered a new role for the microtubule-associated protein MAP1B in modulating access of AMPARs to the postsynaptic membrane. Using mice and rats of either sex, we show that MAP1B light chain (LC) accumulates in the somatodendritic compartment of hippocampal neurons, where it forms immobile complexes on microtubules that limit vesicular transport. These complexes restrict AMPAR dendritic mobility, leading to the intracellular trapping of receptors and impairing their access to the dendritic surface and spines. Accordingly, increasing MAP1B-LC expression depresses AMPAR-mediated synaptic transmission. This effect is specific for the GluA2 subunit of the AMPAR and requires glutamate receptor interacting protein 1 (GRIP1) interaction with MAP1B-LC. Therefore, MAP1B-LC represents an alternative link between GRIP1-AMPARs and microtubules that does not result in productive transport, but rather limits AMPAR availability for synaptic insertion, with a direct impact on synaptic transmission.SIGNIFICANCE STATEMENT The ability of neurons to modify their synaptic connections, known as synaptic plasticity, is accepted as the cellular basis for learning and memory. One mechanism for synaptic plasticity is the regulated addition and removal of AMPA-type glutamate receptors (AMPARs) at excitatory synapses. In this study, we found that a microtubule-associated protein, MAP1B light chain (MAP1B-LC), participates in this process. MAP1B-LC forms immobile complexes along dendrites. These complexes limit intracellular vesicular trafficking and trap AMPARs inside the dendritic shaft. In this manner, MAP1B restricts the access of AMPARs to dendritic spines and the postsynaptic membrane, contributing to downregulating synaptic transmission.
Assuntos
Proteínas Associadas aos Microtúbulos/fisiologia , Receptores de AMPA/fisiologia , Sinapses/fisiologia , Transmissão Sináptica/genética , Proteínas Adaptadoras de Transdução de Sinal/metabolismo , Animais , Dendritos/efeitos dos fármacos , Espinhas Dendríticas/fisiologia , Feminino , Hipocampo/citologia , Hipocampo/metabolismo , Masculino , Camundongos , Proteínas Associadas aos Microtúbulos/biossíntese , Proteínas Associadas aos Microtúbulos/genética , Proteínas do Tecido Nervoso/metabolismo , Neurônios/metabolismo , Ratos , Ratos Wistar , Receptores de AMPA/metabolismoRESUMO
Hippocampal synaptic plasticity involves both membrane trafficking events and intracellular signaling, but how these are coordinated is far from clear. The endosomal transport of glutamate receptors in and out of the postsynaptic membrane responds to multiple signaling cascades triggered by synaptic activity. In this work, we have identified adaptor protein containing a plekstrin homology domain, phosphotyrosine-binding domain and leucine zipper motif 1 (APPL1) as a crucial element linking trafficking and signaling during synaptic plasticity. We show that APPL1 knockdown specifically impairs PI3K-dependent forms of synaptic plasticity, such as long-term potentiation (LTP) and metabotropic-glutamate-receptor-dependent long-term depression (mGluR-LTD). Indeed, we demonstrate that APPL1 is required for the activation of the phosphatidylinositol triphosphate (PIP3) pathway in response to LTP induction. This requirement can be bypassed by membrane localization of PI3K and is related to phosphoinositide binding. Interestingly, inhibitors of PDK1 (also known as PDPK1) and Akt have no effect on LTP expression. Therefore, we conclude that APPL1 gates PI3K activation at the plasma membrane upon LTP induction, which is then relayed by downstream PIP3 effectors that are different from PDK1 and Akt.
Assuntos
Proteínas Adaptadoras de Transdução de Sinal/química , Proteínas Adaptadoras de Transdução de Sinal/metabolismo , Potenciação de Longa Duração , Proteínas do Tecido Nervoso/química , Proteínas do Tecido Nervoso/metabolismo , Animais , Espinhas Dendríticas/metabolismo , Ativação Enzimática , Hipocampo/citologia , Fosfatidilinositol 3-Quinases/metabolismo , Domínios Proteicos , Proteínas Serina-Treonina Quinases , Proteínas Proto-Oncogênicas c-akt/metabolismo , Piruvato Desidrogenase Quinase de Transferência de Acetil , RNA Interferente Pequeno/metabolismo , Ratos Wistar , Transdução de Sinais , Sinapses/metabolismo , Transmissão SinápticaRESUMO
The microtubule-associated protein 1B (MAP1B) plays critical roles in neurite growth and synapse maturation during brain development. This protein is well expressed in the adult brain. However, its function in mature neurons remains unknown. We have used a genetically modified mouse model and shRNA techniques to assess the role of MAP1B at established synapses, bypassing MAP1B functions during neuronal development. Under these conditions, we found that MAP1B deficiency alters synaptic plasticity by specifically impairing long-term depression (LTD) expression. Interestingly, this is due to a failure to trigger AMPA receptor endocytosis and spine shrinkage during LTD. These defects are accompanied by an impaired targeting of the Rac1 activator Tiam1 at synaptic compartments. Accordingly, LTD and AMPA receptor endocytosis are restored in MAP1B-deficient neurons by providing additional Rac1. Therefore, these results indicate that the MAP1B-Tiam1-Rac1 relay is essential for spine structural plasticity and removal of AMPA receptors from synapses during LTD. This work highlights the importance of MAPs as signalling hubs controlling the actin cytoskeleton and receptor trafficking during plasticity in mature neurons.
Assuntos
Endocitose/fisiologia , Depressão Sináptica de Longo Prazo/fisiologia , Proteínas Associadas aos Microtúbulos/metabolismo , Plasticidade Neuronal/fisiologia , Receptores de AMPA/metabolismo , Sinapses/fisiologia , Animais , Fatores de Troca do Nucleotídeo Guanina/metabolismo , Hipocampo/citologia , Camundongos , Camundongos Transgênicos , Microscopia de Fluorescência , Proteínas Associadas aos Microtúbulos/deficiência , Neuropeptídeos , Técnicas de Patch-Clamp , RNA Interferente Pequeno/genética , Coluna Vertebral/citologia , Estatísticas não Paramétricas , Proteína 1 Indutora de Invasão e Metástase de Linfoma de Células T , Proteínas rac1 de Ligação ao GTPRESUMO
Ghrelin is a peptide mainly produced by the stomach and released into circulation, affecting energy balance and growth hormone release. These effects are guided largely by the expression of the ghrelin receptor growth hormone secretagogue type 1a (GHS-R1a) in the hypothalamus and pituitary. However, GHS-R1a is expressed in other brain regions, including the hippocampus, where its activation enhances memory retention. Herein we explore the molecular mechanism underlying the action of ghrelin on hippocampal-dependent memory. Our data show that GHS-R1a is localized in the vicinity of hippocampal excitatory synapses, and that its activation increases delivery of α-amino-3-hydroxy-5-methyl-4-isoxazole propionic-type receptors (AMPARs) to synapses, producing functional modifications at excitatory synapses. Moreover, GHS-R1a activation enhances two different paradigms of long-term potentiation in the hippocampus, activates the phosphatidylinositol 3-kinase, and increases GluA1 AMPAR subunit and stargazin phosphorylation. We propose that GHS-R1a activation in the hippocampus enhances excitatory synaptic transmission and synaptic plasticity by regulating AMPAR trafficking. Our study provides insights into mechanisms that may mediate the cognition-enhancing effect of ghrelin, and suggests a possible link between the regulation of energy metabolism and learning.
Assuntos
Regulação da Expressão Gênica , Grelina/fisiologia , Hipocampo/metabolismo , Receptores de AMPA/metabolismo , Sinapses/fisiologia , Animais , Eletrofisiologia , Metabolismo Energético , Grelina/metabolismo , Aprendizagem , Potenciação de Longa Duração/fisiologia , Memória , Peptídeos/química , Fosforilação , Ratos , Transdução de Sinais , Transmissão SinápticaRESUMO
Glutamate excitotoxicity is caused by sustained activation of neuronal NMDA receptors causing a large Ca(2+) and Na(+) influx, activation of poly(ADP ribose) polymerase-1 (PARP-1), and delayed Ca(2+) deregulation. Mitochondria undergo early changes in membrane potential during excitotoxicity, but their precise role in these events is still controversial. Using primary cortical neurons derived from mice, we show that NMDA exposure results in a rapid fall in mitochondrial ATP in neurons deficient in SCaMC-3/Slc25a23, a Ca(2+)-regulated mitochondrial ATP-Mg/Pi carrier. This fall is associated with blunted increases in respiration and a delayed decrease in cytosolic ATP levels, which are prevented by PARP-1 inhibitors or by SCaMC-3 activity promoting adenine nucleotide uptake into mitochondria. SCaMC-3 KO neurons show an earlier delayed Ca(2+) deregulation, and SCaMC-3-deficient mitochondria incubated with ADP or ATP-Mg had reduced Ca(2+) retention capacity, suggesting a failure to maintain matrix adenine nucleotides as a cause for premature delayed Ca(2+) deregulation. SCaMC-3 KO neurons have higher vulnerability to in vitro excitotoxicity, and SCaMC-3 KO mice are more susceptible to kainate-induced seizures, showing that early PARP-1-dependent fall in mitochondrial ATP levels, counteracted by SCaMC-3, is an early step in the excitotoxic cascade.
Assuntos
Trifosfato de Adenosina/metabolismo , Antiporters/metabolismo , Proteínas Mitocondriais/metabolismo , Neurônios/metabolismo , Poli(ADP-Ribose) Polimerases/metabolismo , Potenciais de Ação , Animais , Antiporters/genética , Cálcio/metabolismo , Respiração Celular , Células Cultivadas , Córtex Cerebral/citologia , Camundongos , Camundongos Endogâmicos C57BL , Mitocôndrias/metabolismo , Proteínas Mitocondriais/genética , N-Metilaspartato/farmacologia , Neurônios/efeitos dos fármacos , Neurônios/fisiologia , Poli(ADP-Ribose) Polimerase-1 , Inibidores de Poli(ADP-Ribose) Polimerases , Convulsões/metabolismoRESUMO
Post-traumatic stress disorder (PTSD) occurs after exposure to traumatic situations and it is characterized by cognitive deficits that include impaired explicit memory. The neurobiological bases of such PTSD-associated memory alterations are yet to be elucidated and no satisfactory treatment for them exists. To address this issue, we first studied whether a single exposure of young adult rats (60 days) to immobilization on boards (IMO), a putative model of PTSD, produces long-term behavioral effects (2-8 days) similar to those found in PTSD patients. Subsequently, we investigated whether the administration of the TrkB agonist 7,8-dihydroxyflavone (DHF) 8 h after stress (therapeutic window) ameliorated the PTSD-like effect of IMO and the associated changes in synaptic plasticity. A single IMO exposure induced a spatial memory impairment similar to that found in other animal models of PTSD or in PTSD patients. IMO also increased spine density and long-term potentiation (LTP) in the CA3-CA1 pathway. Significantly, DHF reverted both spatial memory impairment and the increase in LTP, while it produced no effect in the controls. These data provide novel insights into the possible neurobiological substrate for explicit memory impairment in PTSD patients, supporting the idea that the activation of the BDNF/TrkB pathway fulfils a protective role after severe stress. Administration of DHF in the aftermath of a traumatic experience might be relevant to prevent its long-term consequences. © 2016 Wiley Periodicals, Inc.
Assuntos
Flavonas/farmacologia , Potenciação de Longa Duração/efeitos dos fármacos , Transtornos da Memória/prevenção & controle , Psicotrópicos/farmacologia , Receptor trkB/agonistas , Transtornos de Estresse Pós-Traumáticos/tratamento farmacológico , Animais , Região CA1 Hipocampal/efeitos dos fármacos , Região CA1 Hipocampal/patologia , Região CA1 Hipocampal/fisiopatologia , Região CA3 Hipocampal/efeitos dos fármacos , Região CA3 Hipocampal/patologia , Região CA3 Hipocampal/fisiopatologia , Espinhas Dendríticas/efeitos dos fármacos , Espinhas Dendríticas/patologia , Espinhas Dendríticas/fisiologia , Modelos Animais de Doenças , Potenciação de Longa Duração/fisiologia , Masculino , Transtornos da Memória/etiologia , Transtornos da Memória/patologia , Transtornos da Memória/fisiopatologia , Distribuição Aleatória , Ratos , Ratos Sprague-Dawley , Receptor trkB/metabolismo , Restrição Física , Memória Espacial/efeitos dos fármacos , Memória Espacial/fisiologia , Transtornos de Estresse Pós-Traumáticos/complicações , Transtornos de Estresse Pós-Traumáticos/patologia , Transtornos de Estresse Pós-Traumáticos/fisiopatologia , Estresse Psicológico/complicações , Estresse Psicológico/tratamento farmacológico , Estresse Psicológico/patologia , Estresse Psicológico/fisiopatologia , Técnicas de Cultura de TecidosRESUMO
Phosphoinositide 3-kinase (PI3K) and PTEN have been shown to participate in synaptic plasticity during long-term potentiation (LTP) and long-term depression (LTD), respectively. Nevertheless, the dynamics of phosphatidylinositol-(3,4,5)-trisphosphate (PIP3) and the regulation of its synthesis and degradation at synaptic compartments is far from clear. Here, we have used fluorescence resonance energy transfer (FRET) imaging to monitor changes in PIP3 levels in dendritic spines from CA1 hippocampal neurons under basal conditions and upon induction of NMDA receptor (NMDAR)-dependent LTD and LTP. We found that PIP3 undergoes constant turnover in dendritic spines. Contrary to expectations, both LTD and LTP induction trigger an increase in PIP3 synthesis, which requires NMDARs and PI3K activity. Using biochemical methods, the upregulation of PIP3 levels during LTP was estimated to be twofold. However, in the case of LTD, PTEN activity counteracts the increase in PIP3 synthesis, resulting in no net change in PIP3 levels. Therefore, both LTP and LTD signaling converge towards PIP3 upregulation, but PTEN acts as an LTD-selective switch that determines the outcome of PIP3 accumulation.
Assuntos
Espinhas Dendríticas/metabolismo , Depressão Sináptica de Longo Prazo , PTEN Fosfo-Hidrolase/metabolismo , Fosfatos de Fosfatidilinositol/metabolismo , Receptores de N-Metil-D-Aspartato/metabolismo , Regulação para Cima , Animais , Transferência Ressonante de Energia de Fluorescência , Potenciação de Longa Duração , PTEN Fosfo-Hidrolase/antagonistas & inibidores , Fosfatidilinositol 3-Quinases/metabolismo , Ratos , Transdução de Sinais/efeitos dos fármacosRESUMO
Cell adhesion molecules and downstream growth factor-dependent signaling are critical for brain development and synaptic plasticity, and they have been linked to cognitive function in adult animals. We have previously developed a mimetic peptide (FGL) from the neural cell adhesion molecule (NCAM) that enhances spatial learning and memory in rats. We have now investigated the cellular and molecular basis of this cognitive enhancement, using biochemical, morphological, electrophysiological, and behavioral analyses. We have found that FGL triggers a long-lasting enhancement of synaptic transmission in hippocampal CA1 neurons. This effect is mediated by a facilitated synaptic delivery of AMPA receptors, which is accompanied by enhanced NMDA receptor-dependent long-term potentiation (LTP). Both LTP and cognitive enhancement are mediated by an initial PKC activation, which is followed by persistent CaMKII activation. These results provide a mechanistic link between facilitation of AMPA receptor synaptic delivery and improved hippocampal-dependent learning, induced by a pharmacological cognitive enhancer.
Assuntos
Cognição/fisiologia , Hipocampo/citologia , Potenciação de Longa Duração/efeitos dos fármacos , Moléculas de Adesão de Célula Nervosa/farmacologia , Neurônios/efeitos dos fármacos , Receptores de AMPA/metabolismo , Transmissão Sináptica/efeitos dos fármacos , Análise de Variância , Animais , Western Blotting , Proteína Quinase Tipo 2 Dependente de Cálcio-Calmodulina/metabolismo , Ensaio de Imunoadsorção Enzimática , Hipocampo/fisiologia , Potenciação de Longa Duração/fisiologia , Masculino , Aprendizagem em Labirinto/efeitos dos fármacos , Microscopia Eletrônica , Microscopia de Fluorescência , Neurônios/fisiologia , Técnicas de Patch-Clamp , Fosforilação , Proteína Quinase C/metabolismo , Ratos , Ratos Wistar , Receptor Tipo 1 de Fator de Crescimento de Fibroblastos/metabolismo , Transdução de Sinais/efeitos dos fármacos , Transdução de Sinais/fisiologia , Transmissão Sináptica/fisiologiaRESUMO
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.