Fractalkine/CX3CL1 engages different neuroprotective responses upon selective glutamate receptor overactivation.

Clotilde Lauro,Giuseppina Chece,Flavia Trettel,Ida De Costanzo,Eleonora Di Paolo,Myriam Catalano,Cristina Limatola

doi:10.3389/fncel.2014.00472

Abstract

Neuronal death induced by overactivation of N-methyl-d-aspartate receptors (NMDARs) is implicated in the pathophysiology of many neurodegenerative diseases such as stroke, epilepsy and traumatic brain injury. This toxic effect is mainly mediated by NR2B-containing extrasynaptic NMDARs, while NR2A-containing synaptic NMDARs contribute to cell survival, suggesting the possibility of therapeutic approaches targeting specific receptor subunits. We report that fractalkine/CX3CL1 protects hippocampal neurons from NMDA-induced cell death with a mechanism requiring the adenosine receptors type 2A (A2AR). This is different from CX3CL1-induced protection from glutamate (Glu)-induced cell death, that fully depends on A1R and requires in part A3R. We show that CX3CL1 neuroprotection against NMDA excitotoxicity involves D-serine, a co-agonist of NR2A/NMDAR, resulting in cyclic AMP-dependent transcription factor cyclic-AMP response element-binding protein (CREB) phosphorylation.

Highlights

Neuroprotection is a complex procedure aimed at preservation of neuronal structure and function upon toxic insults
MATERIALS Recombinant human CX3CL1 was from Calbiochem/Merck (Nottingham, UK); D-serine was from Ascent Scientific (Bristol, UK); rabbit anti-phospho TrkB (Tyr 515) was from Abcam (Cambridge, UK), rabbit anti-phospo cyclic-AMP response element-binding protein (CREB) (Ser 133) and rabbit anti-PARP were from Cell Signaling (Danvers, Ma, USA); secondary antibodies were from DAKO (Milan, Italy); culture media were from Invitrogen Life Technologies (San Giuliano Milanese, Italy); 3-[4,5-Dimethylthiazol-2-yl]-2,5diphenyltetrazolium bromide (MTT), in vitro Toxicology Assay Kit Lactic Dehydrogenase based (LDH assay), catalase, D-amino acid oxidase (DAAO), poly-L-lysine, rabbit anti-actin antibody and all the other reagents were from Sigma-Aldrich (Milan, Italy)
N-methyl-d-aspartate receptors (NMDARs) stimulation may induce neuronal death (Choi, 1987; Choi et al, 1988; Tymianski et al, 1993) or protection, through preconditioning (Grabb and Choi, 1999; Navon et al, 2012). This apparently dicothomic behavior of NMDARs has been in part ascribed to their synaptic or extrasynaptic localization (Ikonomidou and Turski, 2002; Hardingham, 2006; Hetman and Kharebava, 2006), corresponding to different subunit composition (Hardingham et al, 2002; Chen et al, 2008)

Summary

Introduction

Neuroprotection is a complex procedure aimed at preservation of neuronal structure and function upon toxic insults. Low levels of Glu activate NMDARs in preconditioning experiments (Liu et al, 2009), resulting protective against a subsequent stronger insult. This is achieved through multifactorial mechanisms involving the rapid adaptation of the voltage-dependent Ca2+ channels (Shimazaki et al, 1998), the release of brain derived neurotropic factor (BDNF; Blondeau et al, 2001), the activation of phosphatidylinositol 3-kinase (PI3K)/Akt/glycogen synthase kinase 3-beta signaling (Hetman and Xia, 2000; Papadia et al, 2005; Soriano et al, 2006), extracellular signal-regulated kinase (ERK 1/2), the inactivation of c-Jun N-terminal kinase (JNK) and cyclic-AMP response element-binding protein (CREB; Navon et al, 2012). Since it is known that CX3CL1 is able to counteract excitotoxic damage (Deiva et al, 2004; Limatola et al, 2005) in the present paper we investigated the effects of Frontiers in Cellular Neuroscience www.frontiersin.org

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