Altered mRNA Editing and Expression of Ionotropic Glutamate Receptors after Kainic Acid Exposure in Cyclooxygenase-2 Deficient Mice Luca Caracciolo1,2, Alessandro Barbon 2 , Sara Palumbo 1 , Cristina Mora2, Christopher D. Toscano 1 , Francesca Bosetti1*¤, Sergio Barlati2 1 Molecular Neuroscience Unit, Brain Physiology and Metabolism Section, National Institute on Aging, National Institutes of Health, Bethesda, Maryland, United States of America, 2 Division of Biology and Genetics, Department of Biomedical Sciences and Biotechnologies and National Institute of Neuroscience, University of Brescia, Brescia, Italy Abstract Kainic acid (KA) binds to the AMPA/KA receptors and induces seizures that result in inflammation, oxidative damage and neuronal death. We previously showed that cyclooxygenase-2 deficient (COX-22/2) mice are more vulnerable to KA-induced excitotoxicity. Here, we investigated whether the increased susceptibility of COX-22/2 mice to KA is associated with altered mRNA expression and editing of glutamate receptors. The expression of AMPA GluR2, GluR3 and KA GluR6 was increased in vehicle-injected COX-22/2 mice compared to wild type (WT) mice in hippocampus and cortex, whereas gene expression of NMDA receptors was decreased. KA treatment decreased the expression of AMPA, KA and NMDA receptors in the hippocampus, with a significant effect in COX-22/2 mice. Furthermore, we analyzed RNA editing levels and found that the level of GluR3 R/G editing site was selectively increased in the hippocampus and decreased in the cortex in COX-22/2 compared with WT mice. After KA, GluR4 R/G editing site, flip form, was increased in the hippocampus of COX-22/2 mice. Treatment of WT mice with the COX-2 inhibitor celecoxib for two weeks decreased the expression of AMPA/KA and NMDAR subunits after KA, as observed in COX-22/2 mice. After KA exposure, COX-22/2 mice showed increased mRNA expression of markers of inflammation and oxidative stress, such as cytokines (TNF-a, IL-1b and IL-6), inducible nitric oxide synthase (iNOS), microglia (CD11b) and astrocyte (GFAP). Thus, COX-2 gene deletion can exacerbate the inflammatory response to KA. We suggest that COX-2 plays a role in attenuating glutamate excitotoxicity by modulating RNA editing of AMPA/KA and mRNA expression of all ionotropic glutamate receptor subunits and, in turn, neuronal excitability. These changes may contribute to the increased vulnerability of COX-22/2 mice to KA. The overstimulation of glutamate receptors as a consequence of COX-2 gene deletion suggests a functional coupling between COX-2 and the glutamatergic system. Citation: Caracciolo L, Barbon A, Palumbo S, Mora C, Toscano CD, et al. (2011) Altered mRNA Editing and Expression of Ionotropic Glutamate Receptors after Kainic Acid Exposure in Cyclooxygenase-2 Deficient Mice. PLoS ONE 6(5): e19398. doi:10.1371/journal.pone.0019398 Editor: Jialin Charles Zheng, University of Nebraska Medical Center, United States of America Received December 3, 2010; Accepted April 4, 2011; Published May 12, 2011 This is an open-access article, free of all copyright, and may be freely reproduced, distributed, transmitted, modified, built upon, or otherwise used by anyone for any lawful purpose. The work is made available under the Creative Commons CC0 public domain dedication. Funding: This work was entirely supported by the Intramural Research Program of the National Institute on Aging, National Institutes of Health. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. Competing Interests: The authors have declared that no competing interests exist. * E-mail: frances@mail.nih.gov ¤ Current address: National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, Maryland, United States of America Introduction Cyclooxygenases (COX-1 and COX-2) convert arachidonic acid to bioactive prostaglandins (PG) and tromboxanes (TX), which have been implicated in important physiological functions [1,2], as well as in the pathophysiology of several neurological and neurodegenerative diseases, such as stroke, epilepsy, and Alzhei- mer’s disease [3]. Although COX-2 is typically inducible, in the central nervous system (CNS) both COX-1 and COX-2 are constitutively expressed and COX-2 is mainly detected in the perinuclear, dendritic and axonal domains of neurons, particularly in cortex, hippocampus, amygdala and dorsal horn of the spinal cord [4,5]. We have previously demonstrated that COX-2 deficient (COX- 22/2), but not COX-12/2 mice, are more susceptible to kainic- acid (KA)-induced seizure intensity and neuronal damage [6]. KA, the prototypic excitoxin, binds to the alpha-amino-propionic-acid/ kainate (AMPA/KA) and N-methyl-D-aspartic acid (NMDA) receptors (AMPAR, KAR and NMDAR), which are subtypes of the ionotropic glutamate receptors (iGluRs) in the brain [7], inducing seizures that result in inflammation, oxidative damage and neuronal death. These processes have been implicated in neurological, neurodegenerative, and psychiatric diseases [6,8,9, 10,11,12,13,14,15]. Activation of AMPA/KA and NMDA receptors elicits a number of cellular events, including the increase in intracellular Ca2+, production of ROS, and other biochemical events leading to neuronal cell death [16,17,18,19,20]. In recent years, neurode- generation caused by systemic injection of KA has been widely used to investigate mechanisms of excitotoxicity mediated by excitatory neurotransmitter agonists and possible pharmacological neuroprotective interventions [6,21]. AMPA/KA and NMDA glutamate receptors play a major role in excitatory synaptic transmission and plasticity. Their channel PLoS ONE | www.plosone.org 1 May 2011 | Volume 6 | Issue 5 | e19398