Adenosine A1 Receptors and Microglial Cells Mediate CX3CL1-Induced Protection of Hippocampal Neurons Against Glu-Induced Death

Istituto Pasteur, Fondazione Cenci Bolognetti, Rome, Italy.
Neuropsychopharmacology: official publication of the American College of Neuropsychopharmacology (Impact Factor: 7.05). 03/2010; 35(7):1550-9. DOI: 10.1038/npp.2010.26
Source: PubMed

ABSTRACT Fractalkine/CX3CL1 is a neuron-associated chemokine, which modulates microglia-induced neurotoxicity activating the specific and unique receptor CX3CR1. CX3CL1/CX3CR1 interaction modulates the release of cytokines from microglia, reducing the level of tumor necrosis factor-alpha, interleukin-1-beta, and nitric oxide and induces the production of neurotrophic substances, both in vivo and in vitro. We have recently shown that blocking adenosine A(1) receptors (A(1)R) with the specific antagonist 1,3-dipropyl-8-cyclopentylxanthine (DPCPX) abolishes CX3CL1-mediated rescue of neuronal excitotoxic death and that CX3CL1 induces the release of adenosine from microglia. In this study, we show that the presence of extracellular adenosine is mandatory for the neurotrophic effect of CX3CL1 as reducing adenosine levels in hippocampal cultures, by adenosine deaminase treatment, strongly impairs CX3CL1-mediated neuroprotection. Furthermore, we confirm the predominant role of microglia in mediating the neuronal effects of CX3CL1, because the selective depletion of microglia from hippocampal cultures treated with clodronate-filled liposomes causes the complete loss of effect of CX3CL1. We also show that hippocampal neurons obtained from A(1)R(-/-) mice are not protected by CX3CL1 whereas A(2A)R(-/-) neurons are. The requirement of functional A(1)R for neuroprotection is not unique for CX3CL1 as A(1)R(-/-) hippocampal neurons are not rescued from Glu-induced cell death by other neurotrophins such as brain-derived neurotrophic factor and erythropoietin, which are fully active on wt neurons.

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    • "One way to further understand how inflammation and other seizure-induced brain pathologies are related is to study single potential signaling pathways between microglia and neurons. Various inflammatory mediators which are known to regulate microglial activation (Cardona et al., 2006; D'Haese et al., 2012), have also been implicated in adult neurogenesis and synaptic transmission (Butovsky et al., 2006; Lauro et al., 2010; Scianni et al., 2013). Fractalkine is an inflammatory chemokine secreted by neurons and astrocytes. "
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    ABSTRACT: Temporal lobe seizures lead to an acute inflammatory response in the brain primarily characterized by activation of parenchymal microglial cells. Simultaneously, degeneration of pyramidal cells and interneurons is evident together with a seizure-induced increase in the production of new neurons within the dentate gyrus of the hippocampus. We have previously shown a negative correlation between the acute seizure-induced inflammation and the survival of newborn hippocampal neurons. Here, we aimed to evaluate the role of the fractalkine-CX3CR1 pathway for these acute events. Fractalkine is a chemokine expressed by both neurons and glia, while its receptor, CX3CR1 is primarily expressed on microglia. Electrically-induced partial status epilepticus (SE) was induced in adult rats through stereotaxically implanted electrodes in the hippocampus. Recombinant rat fractalkine or CX3CR1 antibody was infused intraventricularly during one week post-SE. A significant increase in the expression of CX3CR1, but not fractalkine, was observed in the dentate gyrus at one week. CX3CR1 antibody treatment resulted in a reduction in microglial activation, neurodegeneration, as well as neuroblast production. In contrast, fractalkine treatment had only minor effects. This study provides evidence for a role of the fractalkine-CX3CR1 signaling pathway in seizure-induced microglial activation and suggests that neuroblast production following seizures may partly occur as a result of microglial activation. Copyright © 2014 The Authors. Published by Elsevier Inc. All rights reserved.
    Neurobiology of Disease 11/2014; 74. DOI:10.1016/j.nbd.2014.11.009 · 5.08 Impact Factor
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    • "Catalano et al. (2013), in fact, demonstrated that CX3CL1, acting on microglia, induced the production and release of soluble factors that exerted their effects on astrocytes, inducing the functional up regulation and the increased expression of the excitatory amino acid transporter GLT-1. As already reported in in vitro and in vivo systems (Lauro et al., 2010; Cipriani et al., 2011), this cross-talk requires the “permissive” presence of adenosine, specifically acting on astrocyte A1R (Catalano et al., 2013). These data demonstrated for the first time a role for astrocytes in mediating the neuroprotection induced by CX3CL1/CX3CR1 signaling between microglia and neurons. "
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    ABSTRACT: Since the initial cloning of fractalkine/CX3CL1, it was proposed that the only known member of the CX3C or δ subfamily of chemotactic cytokines could play some significant role in the nervous system, due to its high expression on neurons. The pivotal description of the localization of the unique CX3CL1 receptor, CX3CR1, on microglial cells, firmed up by the generation of cx3cr1(GFP/GFP) mice, opened the road to the hypothesis of some specific key interactions between microglia and neurons mediated by this pair. This expectation has been indeed supported by recent exciting evidence indicating that CX3CL1-mediated microglia-neuron interaction modulates basic physiological activities during development, adulthood and aging, including: synaptic pruning; promoting survival of neurons and neural precursors; modulating synaptic transmission and plasticity; enhancing synapse and network maturation; and facilitating the establishment of neuropathic pain circuits. Beyond playing such fascinating roles in physiological conditions, CX3CL1 signaling has been implicated in different neuropathologies. Early papers demonstrated that the levels of CX3CL1 may be modulated by various toxic stimuli in vitro and that CX3CL1 signaling is positively or negatively regulated in EAE and MS, in HIV infection and LPS challenge, in epilepsy, in brain tumors, and in other neuropathologies. In this review we focus on the experimental evidence of CX3CL1 involvement in neuroprotection and survey the common molecular and cellular mechanisms described in different brain diseases.
    Frontiers in Cellular Neuroscience 08/2014; 8:229. DOI:10.3389/fncel.2014.00229 · 4.29 Impact Factor
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    • "Overall, previous studies indicate a predominantly inhibitory role for CX3CL1, perhaps as a component of neuroprotective synaptic scaling mechanisms necessary for hippocampal memory-associated synaptic plasticity processes (Bertollini et al., 2006; Turrigiano, 2008; Piccinin et al., 2010). Consistent with this hypothesis, ADAM17-mediated increase in soluble CX3CL1 is observed in multiple settings of glutamatergic neurotransmission where the chemokine is suggested to perform a neuroprotective function (Chapman et al., 2000; Tsou et al., 2001; Erichsen et al., 2003; Limatola et al., 2005; Ragozzino et al., 2006; Lauro et al., 2010; Pabon et al., 2011). At levels reached during inflammatory conditions, CX3CL1 signaling has previously been associated with activation of pro-survival and anti-apoptotic pathways through phosphorylation of molecules such as Akt, as well as activation of MAP kinases such as p-38 and Erk1/2 (p44/42; Maciejewski-Lenoir et al., 1999; Meucci et al., 2000; Cambien et al., 2001; Deiva et al., 2004; Klosowska et al., 2009; Lyons et al., 2009). "
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    ABSTRACT: Several cytokines and chemokines are now known to play normal physiological roles in the brain where they act as key regulators of communication between neurons, glia and microglia. In particular, cytokines and chemokines can affect cardinal cellular and molecular processes of hippocampal-dependent long-term memory consolidation including synaptic plasticity, synaptic scaling and neurogenesis. The chemokine, CX3CL1 (fractalkine), has been shown to modulate synaptic transmission and long-term potentiation (LTP) in the CA1 pyramidal cell layer of the hippocampus. Here, we confirm widespread expression of CX3CL1 on mature neurons in the adult rat hippocampus. We report an up-regulation in CX3CL1 protein expression in the CA1, CA3 and dentate gyrus of the rat hippocampus 2 h after spatial learning in the water maze task. Moreover, the same temporal increase in CX3CL1 was evident following long-term potentiation-inducing theta-burst stimulation in the dentate gyrus. At physiologically relevant concentrations, CX3CL1 inhibited LTP maintenance in the dentate gyrus. This attenuation in dentate LTP was lost in the presence of GABAA receptor/chloride channel antagonism. CX3CL1 also had opposing actions on glutamate-mediated rise in intracellular calcium in hippocampal organotypic slice cultures in the presence and absence of GABAA receptor/chloride channel blockade. Using primary dissociated hippocampal cultures, we established that CX3CL1 reduces glutamate-mediated intracellular calcium rises in both neurons and glia in a dose dependent manner. In conclusion, CX3CL1 is up-regulated in the hippocampus during a brief temporal window following spatial learning the purpose of which may be to regulate glutamate-mediated neurotransmission tone. Our data supports a possible role for this chemokine in the protective plasticity process of synaptic scaling.
    Frontiers in Cellular Neuroscience 07/2014; 8(233). DOI:10.3389/fncel.2014.00233 · 4.29 Impact Factor
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