Neurocentre Magendie



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4 publication(s) depuis Décembre 2010:

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Cortical GABAergic synapses exhibit a high degree of molecular, anatomical and functional heterogeneity of their neurons of origins, presynaptic mechanisms, receptors, and scaffolding proteins. GABA transporters (GATs) have an important role in regulating GABA levels; among them, GAT-1 and GAT-3 play a prominent role in modulating tonic and phasic GABAAR-mediated inhibition. We asked whether GAT-1 and GAT-3 contribute to generating heterogeneity by studying their ultrastructural localization at cortical symmetric synapses using pre- and post-embedding electron microcopy. GAT-1 and GAT-3 staining at symmetric synapses showed that in some cases the transporters were localized exclusively over axon terminals; in others they were in both axon terminals and perisynaptic astrocytic processes; and in some others GAT-1 and GAT-3 were in perisynaptic astrocytic processes only. Moreover, we showed that the organizational pattern of GAT-1, but not of GAT-3, exhibits a certain degree of specificity related to the post-synaptic target of GABAergic synapses. These findings show that symmetric synapses expressing GAT-1 or GAT-3 are heterogeneous, and indicate that plasma membrane transporters can contribute to synaptic heterogeneity.

25/12/2013 | Brain Struct Funct   IF 5.8
A quantitative analysis of cellular and synaptic localization of GAT-1 and GAT-3 in rat neocortex.
Melone M, Ciappelloni S, Conti F

High-affinity plasma membrane GABA transporters GAT-1 and GAT-3 contribute to the modulation of GABA-mediated inhibition in adult mammalian cerebral cortex. How GATs regulate inhibition in neocortical circuits remains however poorly understood for the lack of information on key localizational features. In this study, we used quantitative pre- and post-embedding electron microscopy to define the distribution of GAT-1 and GAT-3 in elements contributing to synapses and to unveil their ultrastructural organization at adult cortical GABAergic synapses. GAT-1 and GAT-3 were found in both neuronal and astrocytic processes: GAT-1 was prevalently segregated in neuronal elements and in profiles contributing to synapses, whereas GAT-3 was mostly expressed in astrocytes and did not exhibit a preferential distribution in elements contributing to synapses. Analysis of the ultrastructural distribution of GAT-1 and GAT-3 in the plasma membrane of axon terminals and perisynaptic astrocytic processes of symmetric synapses in relation to the active zone revealed that GAT-1 was more concentrated in restricted perisynaptic and extrasynaptic regions, whereas GAT-3 was prominent in extrasynaptic areas. These studies provide a basis for understanding the role GAT-1 and GAT-3 play in the modulation of GABA-mediated phasic and tonic inhibition in cerebral cortex.

2011 | Front Cell Neurosci   IF 4.6
A Role for GAT-1 in Presynaptic GABA Homeostasis?
Conti F, Melone M, Fattorini G, Bragina L, Ciappelloni S

In monoamine-releasing terminals, neurotransmitter transporters - in addition to terminating synaptic transmission by clearing released transmitters from the extracellular space - are the primary mechanism for replenishing transmitter stores and thus regulate presynaptic homeostasis. Here, we analyze whether GAT-1, the main plasma membrane GABA transporter, plays a similar role in GABAergic terminals. Re-examination of existing literature and recent data gathered in our laboratory show that GABA homeostasis in GABAergic terminals is dominated by the activity of the GABA synthesizing enzyme and that GAT-1-mediated GABA transport contributes to cytosolic GABA levels. However, analysis of GAT-1 KO, besides demonstrating the effects of reduced clearance, reveals the existence of changes compatible with an impaired presynaptic function, as miniature IPSCs frequency is reduced by one-third and glutamic acid decarboxylases and phosphate-activated glutaminase levels are significantly up-regulated. Although the changes observed are less robust than those reported in mice with impaired dopamine, noradrenaline, and serotonin plasma membrane transporters, they suggest that in GABAergic terminals GAT-1 impacts on presynaptic GABA homeostasis, and may contribute to the activity-dependent regulation of inhibitory efficacy.

23/12/2010 | Blood   IF 11.8
The prolyl isomerase Pin1 acts as a novel molecular switch for TNF-alpha-induced priming of the NADPH oxidase in human neutrophils.
Boussetta T, Gougerot-Pocidalo MA, Hayem G, Ciappelloni S, Raad H, Arabi Derkawi R, Bournier O, Kroviarski Y, Zhou XZ, Malter JS, Lu PK, Bartegi A, Dang PM, El-Benna J

Neutrophils play a key role in host defense by releasing reactive oxygen species (ROS). However, excessive ROS production by neutrophil nicotinamide adenine dinucleotide phosphate (NADPH) oxidase can damage bystander tissues, thereby contributing to inflammatory diseases. Tumor necrosis factor-alpha (TNF-alpha), a major mediator of inflammation, does not activate NADPH oxidase but induces a state of hyperresponsiveness to subsequent stimuli, an action known as priming. The molecular mechanisms by which TNF-alpha primes the NADPH oxidase are unknown. Here we show that Pin1, a unique cis-trans prolyl isomerase, is a previously unrecognized regulator of TNF-alpha-induced NADPH oxidase hyperactivation. We first showed that Pin1 is expressed in neutrophil cytosol and that its activity is markedly enhanced by TNF-alpha. Inhibition of Pin1 activity with juglone or with a specific peptide inhibitor abrogated TNF-alpha-induced priming of neutrophil ROS production induced by N-formyl-methionyl-leucyl-phenylalanine peptide (fMLF). TNF-alpha enhanced fMLF-induced Pin1 and p47phox translocation to the membranes and juglone inhibited this process. Pin1 binds to p47phox via phosphorylated Ser345, thereby inducing conformational changes that facilitate p47phox phosphorylation on other sites by protein kinase C. These findings indicate that Pin1 is critical for TNF-alpha-induced priming of NADPH oxidase and for excessive ROS production. Pin1 inhibition could potentially represent a novel anti-inflammatory strategy.