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

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-a, interleukin-1-b, 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 À/À mice are not protected by CX3CL1 whereas A 2A R À/À neurons are. The requirement of functional A 1 R for neuroprotection is not unique for CX3CL1 as A 1 R À/À 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.

CXCL16 Orchestrates Adenosine A3Receptor and MCP-1/CCL2 Activity to Protect Neurons from Excitotoxic Cell Death in the CNS

“…We decided to investigate the possible role of CXCL16 in protecting neurons from cell death following Glu-excitotoxic insult (100 M, 30 min). In this experimental condition Glu induces specific neuronal cell death without affecting glial cells (Chen et al, 2000;Lauro et al, 2010). When CXCL16 was administrated during Glu challenge, neuronal cell death was reduced in a concentrationdependent way, as shown in Figure 3A (n ϭ 5-9; p Ͻ 0.05).…”

“…was removed and stored for later usage; neurons were washed and stimulated with Glu (100 M, 30 min) in modified Locke's buffer (without MgCl 2 plus 1 M glycine to stimulate all types of Glu receptors) in the presence or in the absence of CXCL16, hCX 3 CL1, or hCCL2 (100 nM) (Peprotech). Under these experimental conditions, only neurons die (Chen et al, 2000;Lauro et al, 2010). After treatment, cells were reincubated in the original c.m.…”

“…croglia, as determined with ␤-tubulin III, glial fibrillary acidic protein (GFAP), and isolectin IB 4 staining (Lauro et al, 2010).…”

“…We have previously shown that another transmembrane chemokine, CX 3 CL1, induces protection of hippocampal neurons from Glu-induced excitotoxicity with a mechanism mediated by microglia (Lauro et al, 2008(Lauro et al, , 2010). Since we found that CXCR6 is functionally expressed on microglia (see Fig.…”

Microglia in Health and Disease

“…One particularly lucid series of experiments showed that neuronal fractalkine elicited adenosine release from microglia, activating survival pathways in excitotoxicity-challenged neurons via adenosine A1 receptors (Lauro et al 2008(Lauro et al , 2010. Initial findings in vitro were extended in vivo to a permanent focal ischemia model (Cipriani et al 2011) and were enriched by showing that fractalkine signaling also supported glutamate uptake by astrocytes (Catalano et al 2013).…”