Secreted phospholipase A 2 group IIA is a neurotoxin released by stimulated human glial cells Erika B. Villanueva a , Jonathan P. Little a , Gérard Lambeau b , Andis Klegeris a, ⁎ a Laboratory of Cellular and Molecular Pharmacology, Department of Biology, University of British Columbia Okanagan, Kelowna, BC, Canada b Institut de Pharmacologie Moléculaire et Cellulaire, UMR7275, Centre National de la Recherche Scientifique, Université de Nice-Sophia-Antipolis, Valbonne, France abstract article info Article history: Received 18 August 2011 Revised 20 February 2012 Accepted 21 February 2012 Available online 3 March 2012 Keywords: Neuroinflammation Microglia Astrocytes Alzheimer's disease Neurodegeneration Neuroprotection Neuroinflammation, which is one of the hallmarks of neurodegenerative disorders such as Alzheimer's dis- ease, involves secretion of pro-inflammatory mediators by activated glial cells. Secreted phospholipase A 2 group IIA (sPLA 2 IIA) has been implicated as an inflammatory mediator contributing to various peripheral in- flammatory conditions; however, little is known about the role this enzyme plays in neuroinflammation. Human microglia-like promonocytic THP-1 cells and human primary astrocytes were used to study sPLA 2 IIA expression, secretion and function. Production of sPLA 2 IIA by these cells was induced in response to stimula- tion by pro-inflammatory mediators at both mRNA and protein levels. Removal of sPLA 2 IIA from stimulated human microglia-like cell and astrocyte supernatants by immunosorbent caused significant reduction of their toxicity towards SH-SY5Y neuroblastoma cells. Both sPLA 2 IIA specific and non-specific PLA 2 inhibitors exhibited no anti-cytotoxic or neuroprotective effects, suggesting that sPLA 2 IIA cytotoxicity is mediated by a non-enzymatic mechanism. The data obtained indicate that sPLA 2 IIA may contribute to the pathogenesis of neurodegenerative diseases involving neuroinflammation. Agents inhibiting the non-enzymatic actions of sPLA 2 IIA could be used to slow down progression of neurodegenerative processes that are driven by inflammation. © 2012 Elsevier Inc. All rights reserved. Introduction Glia, particularly microglia and astrocytes, provide neurons with vital nutrients and protection, and are essential for defense against pathological events that may occur in the central nervous system (Aloisi, 2001; Maragakis and Rothstein, 2006; Parpura and Haydon, 2000; Rock et al., 2004). Activated glial cells release pro-inflammatory mediators that trigger the activation and proliferation of other glial cells (Aloisi, 2001; Hashioka et al., 2009). Several studies have sug- gested that microglia and astrocytes respond to pathological substances that are present in Alzheimer's disease (AD) and Parkinson's disease, as well as to neuronal cell death (Maragakis and Rothstein, 2006; Nakajima and Kohsaka, 2001; Streit et al., 2004; Wang et al., 2005). Dur- ing such neuroinflammatory responses, glial cells release substances that can cause substantial neuronal death, including reactive oxygen and nitrogen species (Coyle and Puttfarcken, 1993), and toxins such as lysozymes and proteases (Block et al., 2007; Klegeris and McGeer, 2000, 2005). Because neurons depend on glial cells for survival, it has been theorized that the imbalance in glial cell secretion of neurotoxic and neurotrophic substances could exacerbate neurodegenerative diseases (Aschner et al., 1999; Block and Hong, 2007; Parpura and Haydon, 2000). Phospholipases A 2 (PLA 2 ) convert cell membrane glyceropho- spholipids into arachidonic acid, which in turn is a substrate for cyclooxygenases and lipoxygenases (Farooqui and Horrocks, 2006). Studies on phospholipases have shown that secreted PLA 2 , specifi- cally group IIA (sPLA 2 IIA, EC 3.1.1.4), plays a regulatory role in monocyte-induced inflammation (Ibeas et al., 2009; Saegusa et al., 2008). sPLA 2 IIA can be present in body fluids, such as human synovial fluid in rheumatoid arthritis (Bidgood et al., 2000; Jamal et al., 1998; Masuda et al., 2005), and may mediate inflammation in various inflammatory diseases including atherosclerosis (Divchev and Schieffer, 2008; Ghesquiere et al., 2005; Piek and de Winter, 2003). Thus far, it has been shown that sPLA 2 IIA, sPLA 2 group X (sPLA 2 X) and sPLA 2 group V are the most prominent groups of sPLA 2 in inflam- matory events (Lambeau and Gelb, 2008). Microglia represent the mononuclear phagocyte system in the brain. We hypothesized that Molecular and Cellular Neuroscience 49 (2012) 430–438 Abbreviations: AD, Alzheimer's disease; BPPA, 5-(4-benzyloxyphenyl)-4S-(7-phenyl- heptanoylamino) pentanoic acid; ConA, concanavalin A; DMDA, 7,7-dimethyl-5,8-eicosa- dienoic acid; DMEM-F12, Dulbecco's modified Eagle medium nutrient mixture F-12 Ham; DMSO, dimethyl sulfoxide; FBS, fetal bovine serum; IFN-γ, interferon-gamma; LDH, lactate dehydrogenase; LPS, lipopolysaccharide; mAb, monoclonal antibody; MAFP, methyl arachi- donyl fluorophosphonate; MTT, 3-(4,5-dimethylthiazol-2-yl) 2,5-diphenyltetrazolium bromide; OPHAO, 4-[(1-oxo-7-phenylheptyl)amino]-(4R)-octanoic acid; PBS, phosphate- buffered saline; PGPM, 1-hexadecanoyl-2-(1-pyrenedecanoyl)-sn-glycero-3-phospho- methanol; PLA 2 , phospholipase A 2 ; sPLA 2 IIA, secreted PLA 2 group IIA; sPLA 2 X, sPLA 2 group X; rsPLA 2 IIA, recombinant sPLA 2 IIA. ⁎ Corresponding author at: Department of Biology, University of British Columbia Okanagan, 3333 University Way, Kelowna, BC, Canada V1V 1V7. Fax: + 1 250 807 8830. E-mail address: andis.klegeris@ubc.ca (A. Klegeris). 1044-7431/$ – see front matter © 2012 Elsevier Inc. All rights reserved. doi:10.1016/j.mcn.2012.02.006 Contents lists available at SciVerse ScienceDirect Molecular and Cellular Neuroscience journal homepage: www.elsevier.com/locate/ymcne