RESUMO
Immunoglobulin (Ig) isotype diversification by class switch recombination (CSR) is an essential process for mounting a protective humoral immune response. Ig CSR deficiencies in humans can result from an intrinsic B cell defect; however, most of these deficiencies are still molecularly undefined and diagnosed as common variable immunodeficiency (CVID). Here, we show that extracellular adenosine critically contributes to CSR in human naive and IgM memory B cells. In these cells, coordinate stimulation of B cell receptor and toll-like receptors results in the release of ATP stored in Ca(2+)-sensitive secretory vesicles. Plasma membrane ectonucleoside triphosphate diphosphohydrolase 1 CD39 and ecto-5'-nucleotidase CD73 hydrolyze ATP to adenosine, which induces CSR in B cells in an autonomous fashion. Notably, CVID patients with impaired class-switched antibody responses are selectively deficient in CD73 expression in B cells, suggesting that CD73-dependent adenosine generation contributes to the pathogenesis of this disease.
Assuntos
5'-Nucleotidase/imunologia , Trifosfato de Adenosina/imunologia , Formação de Anticorpos/imunologia , Linfócitos B/imunologia , Switching de Imunoglobulina/imunologia , 5'-Nucleotidase/genética , 5'-Nucleotidase/metabolismo , Trifosfato de Adenosina/genética , Trifosfato de Adenosina/metabolismo , Animais , Formação de Anticorpos/genética , Antígenos CD/imunologia , Antígenos CD/metabolismo , Apirase/imunologia , Apirase/metabolismo , Subpopulações de Linfócitos B/citologia , Subpopulações de Linfócitos B/imunologia , Linfócitos B/citologia , Linfócitos B/metabolismo , Imunodeficiência de Variável Comum/genética , Imunodeficiência de Variável Comum/imunologia , Imunodeficiência de Variável Comum/metabolismo , Humanos , Camundongos , Camundongos Transgênicos , Recombinação GenéticaRESUMO
TCR signal strength instructs αß versus γδ lineage decision in immature T cells. Increased signal strength of γδTCR with respect to pre-TCR results in induction of the γδ differentiation program. Extracellular ATP evokes physiological responses through purinergic P2 receptors expressed in the plasma membrane of virtually all cell types. In peripheral T cells, ATP released upon TCR stimulation enhances MAPK activation through P2X receptors. We investigated whether extracellular ATP and P2X receptors signaling tuned TCR signaling at the αß/γδ lineage bifurcation checkpoint. We show that P2X7 expression was selectively increased in immature γδ(+)CD25(+) cells. These cells were much more competent to release ATP than pre-TCR-expressing cells following TCR stimulation and Ca(2+) influx. Genetic ablation as well as pharmacological antagonism of P2X7 resulted in impaired ERK phosphorylation, reduction of early growth response (Egr) transcripts induction, and diversion of γδTCR-expressing thymocytes toward the αß lineage fate. The impairment of the ERK-Egr-inhibitor of differentiation 3 (Id3) signaling pathway in γδ cells from p2rx7(-/-) mice resulted in increased representation of the Id3-independent NK1.1-expressing γδ T cell subset in the periphery. Our results indicate that ATP release and P2X7 signaling upon γδTCR expression in immature thymocytes constitutes an important costimulus in T cell lineage choice through the ERK-Egr-Id3 signaling pathway and contributes to shaping the peripheral γδ T cell compartment.
Assuntos
Receptores de Antígenos de Linfócitos T gama-delta/biossíntese , Receptores Purinérgicos P2X7/fisiologia , Subpopulações de Linfócitos T/imunologia , Subpopulações de Linfócitos T/metabolismo , Trifosfato de Adenosina/metabolismo , Trifosfato de Adenosina/fisiologia , Animais , Linhagem da Célula/genética , Linhagem da Célula/imunologia , Células Cultivadas , Técnicas de Cocultura , Camundongos , Camundongos Endogâmicos BALB C , Camundongos Endogâmicos C57BL , Camundongos Knockout , Receptores de Antígenos de Linfócitos T gama-delta/antagonistas & inibidores , Receptores de Antígenos de Linfócitos T gama-delta/genética , Receptores Purinérgicos P2X7/deficiência , Receptores Purinérgicos P2X7/genética , Transdução de Sinais/imunologia , Subpopulações de Linfócitos T/citologiaRESUMO
BACKGROUND INFORMATION: ATP is the main transmitter stored and released from astrocytes under physiological and pathological conditions. Morphological and functional evidence suggest that besides secretory granules, secretory lysosomes release ATP. However, the molecular mechanisms involved in astrocytic lysosome fusion remain still unknown. RESULTS: In the present study, we identify tetanus neurotoxin-insensitive vesicle-associated membrane protein (TI-VAMP, also called VAMP7) as the vesicular SNARE which mediates secretory lysosome exocytosis, contributing to release of both ATP and cathepsin B from glial cells. We also demonstrate that fusion of secretory lysosomes is triggered by slow and locally restricted calcium elevations, distinct from calcium spikes which induce the fusion of glutamate-containing clear vesicles. Downregulation of TI-VAMP/VAMP7 expression inhibited the fusion of ATP-storing vesicles and ATP-mediated calcium wave propagation. TI-VAMP/VAMP7 downregulation also significantly reduced secretion of cathepsin B from glioma. CONCLUSIONS: Given that sustained ATP release from glia upon injury greatly contributes to secondary brain damage and cathepsin B plays a critical role in glioma dissemination, TI-VAMP silencing can represent a novel strategy to control lysosome fusion in pathological conditions.
Assuntos
Trifosfato de Adenosina/metabolismo , Astrócitos/metabolismo , Cálcio/metabolismo , Catepsina B/metabolismo , Lisossomos/metabolismo , Proteínas R-SNARE/metabolismo , Animais , Astrócitos/citologia , Córtex Cerebral/citologia , Córtex Cerebral/embriologia , Córtex Cerebral/metabolismo , Regulação para Baixo , Embrião de Mamíferos , Exocitose , Glioma/metabolismo , Glioma/patologia , Hipocampo/citologia , Hipocampo/embriologia , Hipocampo/metabolismo , Humanos , Fusão de Membrana , Neuroglia/citologia , Neuroglia/metabolismo , Cultura Primária de Células , Ligação Proteica , Proteínas R-SNARE/antagonistas & inibidores , Proteínas R-SNARE/genética , RNA Interferente Pequeno/genética , Ratos , Transdução de Sinais , TransfecçãoRESUMO
Extracellular nucleotides are pleiotropic regulators of mammalian cell function. Adenosine triphosphate (ATP) released from CD4(+) helper T cells upon stimulation of the T cell receptor (TCR) contributes in an autocrine manner to the activation of mitogen-activated protein kinase (MAPK) signaling through purinergic P2X receptors. Increased expression of p2rx7, which encodes the purinergic receptor P2X7, is part of the transcriptional signature of immunosuppressive CD4(+)CD25(+) regulatory T cells (T(regs)). Here, we show that the activation of P2X7 by ATP inhibits the suppressive potential and stability of T(regs). The inflammatory cytokine interleukin-6 (IL-6) increased ATP synthesis and P2X7-mediated signaling in T(regs), which induced their conversion to IL-17-secreting T helper 17 (T(H)17) effector cells in vivo. Moreover, pharmacological antagonism of P2X receptors promoted the cell-autonomous conversion of naïve CD4(+) T cells into T(regs) after TCR stimulation. Thus, ATP acts as an autocrine factor that integrates stimuli from the microenvironment and cellular energetics to tune the developmental and immunosuppressive program of the T cell in adaptive immune responses.
Assuntos
Trifosfato de Adenosina/fisiologia , Receptores Purinérgicos P2/metabolismo , Linfócitos T Reguladores/imunologia , Humanos , Linfócitos T Reguladores/metabolismoRESUMO
The regulation of filopodia plays a crucial role during neuronal development and synaptogenesis. Axonal filopodia, which are known to originate presynaptic specializations, are regulated in response to neurotrophic factors. The structural components of filopodia are actin filaments, whose dynamics and organization are controlled by ensembles of actin-binding proteins. How neurotrophic factors regulate these latter proteins remains, however, poorly defined. Here, using a combination of mouse genetic, biochemical, and cell biological assays, we show that genetic removal of Eps8, an actin-binding and regulatory protein enriched in the growth cones and developing processes of neurons, significantly augments the number and density of vasodilator-stimulated phosphoprotein (VASP)-dependent axonal filopodia. The reintroduction of Eps8 wild type (WT), but not an Eps8 capping-defective mutant, into primary hippocampal neurons restored axonal filopodia to WT levels. We further show that the actin barbed-end capping activity of Eps8 is inhibited by brain-derived neurotrophic factor (BDNF) treatment through MAPK-dependent phosphorylation of Eps8 residues S624 and T628. Additionally, an Eps8 mutant, impaired in the MAPK target sites (S624A/T628A), displays increased association to actin-rich structures, is resistant to BDNF-mediated release from microfilaments, and inhibits BDNF-induced filopodia. The opposite is observed for a phosphomimetic Eps8 (S624E/T628E) mutant. Thus, collectively, our data identify Eps8 as a critical capping protein in the regulation of axonal filopodia and delineate a molecular pathway by which BDNF, through MAPK-dependent phosphorylation of Eps8, stimulates axonal filopodia formation, a process with crucial impacts on neuronal development and synapse formation.
Assuntos
Proteínas Adaptadoras de Transdução de Sinal/metabolismo , Fator Neurotrófico Derivado do Encéfalo/farmacologia , Proteínas do Citoesqueleto/metabolismo , Neurônios/efeitos dos fármacos , Pseudópodes/fisiologia , Actinas/metabolismo , Proteínas Adaptadoras de Transdução de Sinal/genética , Animais , Axônios/metabolismo , Axônios/fisiologia , Linhagem Celular , Células Cultivadas , Proteínas do Citoesqueleto/genética , Feminino , Proteínas de Fluorescência Verde/genética , Proteínas de Fluorescência Verde/metabolismo , Hipocampo/citologia , Humanos , Masculino , Camundongos , Camundongos Endogâmicos C57BL , Camundongos Knockout , Microscopia de Fluorescência , Proteínas Quinases Ativadas por Mitógeno/metabolismo , Neurônios/citologia , Neurônios/metabolismo , Fosforilação/efeitos dos fármacos , Pseudópodes/efeitos dos fármacos , Pseudópodes/metabolismo , Interferência de RNA , Ratos , TransfecçãoRESUMO
T cell receptor (TCR) stimulation results in the influx of Ca(2+), which is buffered by mitochondria and promotes adenosine triphosphate (ATP) synthesis. We found that ATP released from activated T cells through pannexin-1 hemichannels activated purinergic P2X receptors (P2XRs) to sustain mitogen-activated protein kinase (MAPK) signaling. P2XR antagonists, such as oxidized ATP (oATP), blunted MAPK activation in stimulated T cells, but did not affect the nuclear translocation of the transcription factor nuclear factor of activated T cells, thus promoting T cell anergy. In vivo administration of oATP blocked the onset of diabetes mediated by anti-islet TCR transgenic T cells and impaired the development of colitogenic T cells in inflammatory bowel disease. Thus, pharmacological inhibition of ATP release and signaling could be beneficial in treating T cell-mediated inflammatory diseases.
Assuntos
Trifosfato de Adenosina/biossíntese , Conexinas/metabolismo , AMP Cíclico/metabolismo , Proteínas do Tecido Nervoso/metabolismo , Receptores Purinérgicos P2/fisiologia , Linfócitos T/fisiologia , Transporte Ativo do Núcleo Celular , Trifosfato de Adenosina/análogos & derivados , Trifosfato de Adenosina/farmacologia , Animais , Comunicação Autócrina , Cálcio/metabolismo , Núcleo Celular/metabolismo , Proliferação de Células/efeitos dos fármacos , Inflamação/imunologia , Inflamação/metabolismo , Interleucina-2/biossíntese , Ativação Linfocitária , Sistema de Sinalização das MAP Quinases/fisiologia , Camundongos , Camundongos Knockout , Camundongos Mutantes , Antagonistas do Receptor Purinérgico P2 , Transdução de Sinais , Linfócitos T/imunologiaRESUMO
Regulation of brain-derived neurotrophic factor (BDNF) secretion plays a critical role in long-term potentiation (LTP). It is generally thought that the supply for this secretion is newly synthesized BDNF targeted to the synapse. Here we provide evidence that hippocampal neurons additionally recycle BDNF for activity-dependent secretion. Exogenously applied BDNF is internalized by cultured neurons and rapidly becomes available for activity-dependent secretion, which is controlled by the same mechanisms that regulate the secretion of newly synthesized BDNF. Moreover, BDNF recycling replaced the new synthesis pathway in mediating the maintenance of LTP in hippocampal slices: the late phase LTP, which is abolished by protein synthesis inhibition, was rescued in slices preincubated with BDNF. Thus, endocytosed BDNF is fed back to the activity-dependent releasable pool required for LTP maintenance.
Assuntos
Fator Neurotrófico Derivado do Encéfalo/metabolismo , Hipocampo/metabolismo , Potenciação de Longa Duração/fisiologia , Animais , Anisomicina/farmacologia , Fator Neurotrófico Derivado do Encéfalo/farmacologia , Células Cultivadas , Endocitose , Hipocampo/efeitos dos fármacos , Técnicas In Vitro , Potenciação de Longa Duração/efeitos dos fármacos , Masculino , Microscopia Eletrônica , Neurônios/efeitos dos fármacos , Neurônios/metabolismo , Inibidores da Síntese de Proteínas/farmacologia , Ratos , Ratos Sprague-Dawley , Receptor trkB/metabolismoRESUMO
Regulated expression of positive and negative regulatory factors controls the extent and duration of T cell adaptive immune response preserving the organism's integrity. Calreticulin (CRT) is a major Ca2+ buffering chaperone in the lumen of the endoplasmic reticulum. Here we investigated the impact of CRT deficiency on T cell function in immunodeficient mice reconstituted with fetal liver crt-/- hemopoietic progenitors. These chimeric mice displayed severe immunopathological traits, which correlated with a lower threshold of T cell receptor (TCR) activation and exaggerated peripheral T cell response to antigen with enhanced secretion of inflammatory cytokines. In crt-/- T cells TCR stimulation induced pulsatile cytosolic elevations of Ca2+ concentration and protracted accumulation of nuclear factor of activated T cells in the nucleus as well as sustained activation of the mitogen-activated protein kinase pathways. These observations support the hypothesis that CRT-dependent shaping of Ca2+ signaling critically contributes to the modulation of the T cell adaptive immune response.
Assuntos
Calreticulina/fisiologia , Ativação Linfocitária , Linfócitos T/imunologia , Linfócitos T/metabolismo , Animais , Calreticulina/deficiência , Calreticulina/genética , Diferenciação Celular/genética , Diferenciação Celular/imunologia , Células Cultivadas , Anergia Clonal/genética , Anergia Clonal/imunologia , Feminino , Memória Imunológica/genética , Fígado/imunologia , Fígado/patologia , Ativação Linfocitária/genética , Camundongos , Camundongos Endogâmicos BALB C , Camundongos Endogâmicos C57BL , Camundongos Knockout , Camundongos Transgênicos , Quimera por Radiação/imunologia , Transdução de Sinais/genética , Transdução de Sinais/imunologia , Linfócitos T Reguladores/imunologia , Timo/imunologia , Timo/metabolismo , Timo/patologiaRESUMO
The SNARE-dependent exocytosis of glutamate-containing vesicles in astrocytes is increasingly viewed as an important signal at the basis of the astrocyte-to-neurone communication system in the brain. Here we provide further insights into the molecular features and dynamics of vesicles in cultured astrocytes. We found that immunoisolated synaptobrevin2 vesicles are clear vesicles quite heterogenous in size and contain the vesicular glutamate transporter v-Glut-2. Moreover, they are immunopositive for synaptotagmin IV, for AMPA receptor subunits GluR2,3 and, to a lesser extent, for GluR1. We also provide direct evidence for the functional expression of v-Glut-2 in astrocytes and demonstrate that synaptobrevin2-positive vesicles can specifically take up (3H)L-glutamate via a bafilomycin-sensitive mechanism. Finally, by time lapse confocal microscopy, we show that a subpopulation of vesicles (tagged with a synaptobrevin2-EGFP chimera) is highly mobile and can fuse with the plasma membrane, preferentially at the level of the astrocyte processes, in a Ca2+-dependent manner. These latter observations, together with the evidence reported here for the expression of functional v-Glut-2 in synaptobrevin2-positive vesicles, provide a molecular basis for regulated exocytosis in astrocyte.
Assuntos
Astrócitos/fisiologia , Vesículas Citoplasmáticas/fisiologia , Exocitose/fisiologia , Proteína 2 Associada à Membrana da Vesícula/genética , Proteína 2 Associada à Membrana da Vesícula/metabolismo , Animais , Astrócitos/ultraestrutura , Cálcio/metabolismo , Vesículas Citoplasmáticas/ultraestrutura , Ácido Glutâmico/metabolismo , Proteínas de Fluorescência Verde/genética , Fusão de Membrana/fisiologia , Microscopia Confocal , Microscopia Eletrônica , Ratos , Ratos WistarRESUMO
ATP has been indicated as a primary factor in microglial response to brain injury and inflammation. By acting on different purinergic receptors 2, ATP is known to induce chemotaxis and stimulate the release of several cytokines from these cells. The activation of purinergic receptors 2 in microglia can be triggered either by ATP deriving from dying cells, at sites of brain injury or by ATP released from astrocytes, in the absence of cell damage. By the use of a biochemical approach integrated with video microscopy experiments, we investigated the functional consequences triggered in microglia by ATP released from mechanically stimulated astrocytes, in mixed glial cocultures. Astrocyte-derived ATP induced in nearby microglia the formation and the shedding of membrane vesicles. Vesicle formation was inhibited by the ATP-degrading enzyme apyrase or by P2X(7)R antagonists. Isolation of shed vesicles, followed by IL-1beta evaluation by a specific ELISA revealed the presence of the cytokine inside the vesicular organelles and its subsequent efflux into the extracellular medium. IL-1beta efflux from shed vesicles was enhanced by ATP stimulation and inhibited by pretreatment with the P2X(7) antagonist oxidized ATP, thus indicating a crucial involvement of the pore-forming P2X(7)R in the release of the cytokine. Our data identify astrocyte-derived ATP as the endogenous factor responsible for microvesicle shedding in microglia and reveal the mechanisms by which astrocyte-derived ATP triggers IL-1beta release from these cells.
Assuntos
Trifosfato de Adenosina/fisiologia , Astrócitos/fisiologia , Membrana Celular/metabolismo , Interleucina-1/metabolismo , Proteínas de Membrana/metabolismo , Microglia/metabolismo , Vesículas Secretórias/metabolismo , Trifosfato de Adenosina/farmacologia , Animais , Linhagem Celular , Membrana Celular/efeitos dos fármacos , Técnicas de Cocultura , Hipocampo/citologia , Camundongos , Microglia/citologia , Microglia/efeitos dos fármacos , Microscopia de Fluorescência , Microscopia de Vídeo , Processamento de Proteína Pós-Traducional , Ratos , Receptores Purinérgicos P2/fisiologia , Receptores Purinérgicos P2X7 , Vesículas Secretórias/efeitos dos fármacosRESUMO
AMPA-type glutamate receptors play a key role in mediating postsynaptic responses of excitatory neurotransmitters. It is now well accepted that AMPA receptors are also present at the presynapse, where they are thought to modulate neurotransmitter release. However, the mechanisms through which they control synaptic vesicle traffic have remained elusive. We used cultured hippocampal neurons and growth cone particles prepared from fetal rat brain to investigate the functional role of presynaptic AMPA receptors. We show here that stimulation of presynaptic AMPA receptors induces activation of mitogen-activated protein kinase (MAPK) through a nonreceptor tyrosine kinase-dependent and Na+/Ca2+-independent mechanism. This pathway is activated predominantly in axonal growth cones compared with the somatodendritic compartment. After stimulation of presynaptic AMPA receptors, synapsin I is phosphorylated at MAPK-specific sites. These events are paralleled by a prominent increase in evoked synaptic vesicle recycling that is blocked by the specific MAPK inhibitor 2-(2-amino-3-methoxyphenyl)-4H-1-benzopyran-4-one. Similarly, in synaptosomes isolated from adult brain, AMPA stimulation induces MAPK activation and phosphorylation of synapsin I at MAPK-dependent sites and enhances significantly synaptic vesicle recycling. These results reveal a novel pathway for activation of presynaptic MAPK and suggest a role of this pathway in the regulation of short-term presynaptic plasticity.
Assuntos
Sistema de Sinalização das MAP Quinases , Neurônios/fisiologia , Receptores de AMPA/fisiologia , Ácido alfa-Amino-3-hidroxi-5-metil-4-isoxazol Propiônico/farmacologia , Animais , Células Cultivadas/efeitos dos fármacos , Células Cultivadas/fisiologia , Citoesqueleto/ultraestrutura , Ativação Enzimática/efeitos dos fármacos , Exocitose/efeitos dos fármacos , Exocitose/fisiologia , Cones de Crescimento/fisiologia , Hipocampo/citologia , Hipocampo/embriologia , Sistema de Sinalização das MAP Quinases/efeitos dos fármacos , Plasticidade Neuronal , Neurônios/química , Neurônios/ultraestrutura , Fosforilação , Terminações Pré-Sinápticas , Processamento de Proteína Pós-Traducional , Ratos , Receptores de AMPA/agonistas , Receptores Pré-Sinápticos , Frações Subcelulares/metabolismo , Sinapsinas/metabolismo , Vesículas Sinápticas/fisiologia , Sinaptossomos/fisiologiaRESUMO
AMPA receptor ion channels are of paramount importance for postsynaptic excitation. Several reports demonstrate that AMPA receptors are present in the presynaptic compartment and point to a role of these receptors in the modulation of presynaptic function. We discuss here the possibility that not only ion influx through the receptor, but also biochemical cascades, activated by ligand binding and independent from ion flux, might contribute to AMPA mediated presynaptic modulation.
Assuntos
Canais Iônicos/fisiologia , Terminações Pré-Sinápticas/metabolismo , Receptores de AMPA/metabolismo , Animais , Ácido Glutâmico/metabolismo , Humanos , Ligantes , Modelos Biológicos , Receptores de Glutamato/metabolismo , Transdução de Sinais , Transmissão Sináptica , Ácido alfa-Amino-3-hidroxi-5-metil-4-isoxazol Propiônico/metabolismoRESUMO
Over the past decade, evidence has accumulated indicating that, during development, the construction of synapses--the sites of communication between neurons--might rely on the utilization of preassembled sets of synaptic proteins, which have already accumulated in the axon and are highly mobile, before getting recruited to the sites of contact with the postsynaptic neuron. In this review, we discuss evidence from most recent publications pointing to the existence of active vesicle traffic and turnover in developing neurons, which lead to the construction of new synaptic sites.
Assuntos
Neurônios/citologia , Neurônios/fisiologia , Terminações Pré-Sinápticas/fisiologia , Vesículas Sinápticas/fisiologia , Animais , Transporte Biológico , Membrana Celular/metabolismo , Neurotransmissores/metabolismoRESUMO
Although vascular endothelial growth factor (VEGF) has been described as a potent angiogenic stimulus, its application in therapy remains difficult: blood vessels formed by exposure to VEGF tend to be malformed and leaky. In nature, the principal form of VEGF possesses a binding site for ECM components that maintain it in the immobilized state until released by local cellular enzymatic activity. In this study, we present an engineered variant form of VEGF, alpha2PI1-8-VEGF121, that mimics this concept of matrix-binding and cell-mediated release by local cell-associated enzymatic activity, working in the surgically-relevant biological matrix fibrin. We show that matrix-conjugated alpha2PI1-8-VEGF121 is protected from clearance, contrary to native VEGF121 mixed into fibrin, which was completely released as a passive diffusive burst. Grafting studies on the embryonic chicken chorioallantoic membrane (CAM) and in adult mice were performed to assess and compare the quantity and quality of neovasculature induced in response to fibrin implants formulated with matrix-bound alpha2PI1-8-VEGF121 or native diffusible VEGF121. Our CAM measurements demonstrated that cell-demanded release of alpha2PI1-8-VEGF121 increases the formation of new arterial and venous branches, whereas exposure to passively released wild-type VEGF121 primarily induced chaotic changes within the capillary plexus. Specifically, our analyses at several levels, from endothelial cell morphology and endothelial interactions with periendothelial cells, to vessel branching and network organization, revealed that alpha2PI1-8-VEGF121 induces vessel formation more potently than native VEGF121 and that those vessels possess more normal morphologies at the light microscopic and ultrastructural level. Permeability studies in mice validated that vessels induced by alpha2PI1-8-VEGF121 do not leak. In conclusion, cell-demanded release of engineered VEGF121 from fibrin implants may present a therapeutically safe and practical modality to induce local angiogenesis.
Assuntos
Fibrina/metabolismo , Neovascularização Fisiológica/efeitos dos fármacos , Fator A de Crescimento do Endotélio Vascular/metabolismo , Alantoide/irrigação sanguínea , Alantoide/efeitos dos fármacos , Sequência de Aminoácidos , Animais , Sítios de Ligação , Permeabilidade Capilar/efeitos dos fármacos , Embrião de Galinha , Córion/irrigação sanguínea , Córion/efeitos dos fármacos , Difusão , Implantes de Medicamento , Células Endoteliais/efeitos dos fármacos , Células Endoteliais/ultraestrutura , Endotélio Vascular/citologia , Proteínas da Matriz Extracelular/análise , Fibrina/administração & dosagem , Géis , Humanos , Camundongos , Morfogênese/efeitos dos fármacos , Cadeias Pesadas de Miosina , Miosina não Muscular Tipo IIB , Fragmentos de Peptídeos/química , Fragmentos de Peptídeos/genética , Fragmentos de Peptídeos/metabolismo , Engenharia de Proteínas , Estrutura Terciária de Proteína , Receptor TIE-2/análise , Proteínas Recombinantes de Fusão/química , Proteínas Recombinantes de Fusão/metabolismo , Fator A de Crescimento do Endotélio Vascular/química , Fator A de Crescimento do Endotélio Vascular/genética , Receptor 2 de Fatores de Crescimento do Endotélio Vascular/análise , alfa 2-Antiplasmina/química , alfa 2-Antiplasmina/genéticaRESUMO
Recently, a new system of astrocyte-neurone glutamatergic signalling has been identified. It is started in astrocytes by ectocellular, CD38-catalysed conversion of NAD(+) to the calcium mobilizer cyclic ADP-ribose (cADPR). This is then pumped by CD38 itself into the cytosol where the resulting free intracellular Ca(2+) concentration [Ca(2+)](i) transients elicit an increased release of glutamate, which can induce an enhanced Ca(2+) response in neighbouring neurones. Here, we demonstrate that co-culture of either cortical or hippocampal astrocytes with neurones results in a significant overexpression of astrocyte CD38 both on the plasma membrane and intracellularly. The causal role of neurone-released glutamate in inducing overexpression of astrocyte CD38 is demonstrated by two observations: first, in the absence of neurones, induction of CD38 in pure astrocyte cultures can be obtained with glutamate and second, it can be prevented in co-cultures by glutamate receptor antagonists. The neuronal glutamate-mediated effect of neurones on astrocyte CD38 expression is paralleled by increased intracellular cADPR and [Ca(2+)](i) levels, both findings indicating functionality of overexpressed CD38. These results reveal a new neurone-to-astrocyte glutamatergic signalling based on the CD38/cADPR system, which affects the [Ca(2+)](i) in both cell types, adding further complexity to the bi-directional patterns of communication between astrocytes and neurones.
Assuntos
ADP-Ribosil Ciclase/biossíntese , Antígenos CD/biossíntese , Astrócitos/metabolismo , Ácido Glutâmico/metabolismo , Neurônios/metabolismo , ADP-Ribosil Ciclase 1 , Animais , Astrócitos/citologia , Astrócitos/efeitos dos fármacos , Cálcio/metabolismo , Células Cultivadas , Técnicas de Cocultura , ADP-Ribose Cíclica/metabolismo , Antagonistas de Aminoácidos Excitatórios/farmacologia , Ácido Glutâmico/farmacologia , Líquido Intracelular/metabolismo , Glicoproteínas de Membrana , N-Glicosil Hidrolases/metabolismo , Neurônios/citologia , RatosRESUMO
SNAP-25 is a component of the SNARE complex implicated in synaptic vesicle exocytosis. In this study, we demonstrate that hippocampal GABAergic synapses, both in culture and in brain, lack SNAP-25 and are resistant to the action of botulinum toxins type A and E, which cleave this SNARE protein. Relative to glutamatergic neurons, which express SNAP-25, GABAergic cells were characterized by a higher calcium responsiveness to depolarization. Exogenous expression of SNAP-25 in GABAergic interneurons lowered calcium responsiveness, and SNAP-25 silencing in glutamatergic neurons increased calcium elevations evoked by depolarization. Expression of SNAP-25(1-197) but not of SNAP-25(1-180) inhibited calcium responsiveness, pointing to the involvement of the 180-197 residues in the observed function. These data indicate that SNAP-25 is crucial for the regulation of intracellular calcium dynamics and, possibly, of network excitability. SNAP-25 is therefore a multifunctional protein that participates in exocytotic function both at the mechanistic and at the regulatory level.
Assuntos
Sinalização do Cálcio/fisiologia , Ácido Glutâmico/metabolismo , Proteínas de Membrana/metabolismo , Proteínas do Tecido Nervoso/metabolismo , Neurônios/metabolismo , Terminações Pré-Sinápticas/metabolismo , Ácido gama-Aminobutírico/metabolismo , Potenciais de Ação/efeitos dos fármacos , Potenciais de Ação/fisiologia , Sequência de Aminoácidos/fisiologia , Animais , Toxinas Botulínicas/farmacologia , Toxinas Botulínicas Tipo A/farmacologia , Cálcio/metabolismo , Sinalização do Cálcio/efeitos dos fármacos , Células Cultivadas , Exocitose/efeitos dos fármacos , Exocitose/fisiologia , Feto , Hipocampo/metabolismo , Hipocampo/ultraestrutura , Imuno-Histoquímica , Inibição Neural/efeitos dos fármacos , Inibição Neural/fisiologia , Terminações Pré-Sinápticas/efeitos dos fármacos , Terminações Pré-Sinápticas/ultraestrutura , Ratos , Ratos Sprague-Dawley , Transmissão Sináptica/efeitos dos fármacos , Transmissão Sináptica/fisiologia , Vesículas Sinápticas/efeitos dos fármacos , Vesículas Sinápticas/metabolismo , Proteína 25 Associada a SinaptossomaRESUMO
In recent years, a role for AMPA receptors as modulators of presynaptic functions has emerged. We have investigated the presence of AMPA receptor subunits and the possible dynamic control of their surface exposure at the presynaptic membrane. We demonstrate that the AMPA receptor subunits GluR1 and GluR2 are expressed and organized in functional receptors in axonal growth cones of hippocampal neurons. AMPA receptors are actively internalized upon activation and recruited to the surface upon depolarization. Pretreatment of cultures with botulinum toxin E or tetanus toxin prevents the receptor insertion into the plasma membrane, whereas treatment with alpha-latrotoxin enhances the surface exposure of GluR2, both in growth cones of cultured neurons and in brain synaptosomes. Purification of small synaptic vesicles through controlled-pore glass chromatography, revealed that both GluR2 and GluR1, but not the GluR2 interacting protein GRIP, copurify with synaptic vesicles. These data indicate that, at steady state, a major pool of AMPA receptor subunits reside in synaptic vesicle membranes and can be recruited to the presynaptic membrane as functional receptors in response to depolarization.
Assuntos
Cones de Crescimento/metabolismo , Receptores de AMPA/metabolismo , Membranas Sinápticas/metabolismo , Animais , Anticorpos/metabolismo , Toxinas Botulínicas/farmacologia , Cálcio/metabolismo , Fracionamento Celular , Células Cultivadas , Agonistas de Aminoácidos Excitatórios/farmacologia , Corantes Fluorescentes/metabolismo , Cones de Crescimento/efeitos dos fármacos , Hipocampo/citologia , Hipocampo/metabolismo , Proteínas de Membrana/metabolismo , Subunidades Proteicas/metabolismo , Transporte Proteico , Proteínas R-SNARE , Ratos , Venenos de Aranha/farmacologia , Vesículas Sinápticas/química , Vesículas Sinápticas/metabolismo , Toxina Tetânica/farmacologia , Ácido alfa-Amino-3-hidroxi-5-metil-4-isoxazol Propiônico/farmacologiaRESUMO
Glutamine and alanine are important precursors for the synthesis of glutamate. Provided to neurons by neighboring astrocytes, these amino acids are internalized by classical system A amino acid carriers. In particular, System A transporter (SAT1) is a highly efficient glutamine transporter, whereas SAT2 exhibits broad specificity for neutral amino acids with a preference for alanine. We investigated the localization and the functional relevance of SAT1 and SAT2 in primary cultures of hippocampal neurons. Both carriers have been expressed since early developmental stages and are uniformly distributed throughout all neuronal processes. However, whereas SAT1 is present in axonal growth cones and can be detected at later developmental stages at the sites of synaptic contacts, SAT2 does not appear to be significantly expressed in these compartments. The non-metabolizable amino acid analogue alpha-(methylamino)-isobutyric acid, a competitive inhibitor of system A carriers, significantly reduced miniature excitatory postsynaptic current amplitude in neurons growing on top of astrocytes, being ineffective in pure neuronal cultures. alpha-(Methylamino)-isobutyric acid did not alter neuronal responsitivity to glutamate, thus excluding a postsynaptic effect. These data indicate that system A carriers are expressed with a different subcellular distribution in hippocampal neurons and play a crucial role in controlling the astrocyte-mediated supply of glutamatergic neurons with neurotransmitter precursors.