Acute exposure to lead acetate activates microglia and induces subsequent bystander neuronal death via caspase-3 activation Kanhaiya Lal Kumawat a,b , Deepak Kumar Kaushik a , Praveen Goswami b,c , Anirban Basu a, * a National Brain Research Centre, Manesar, Haryana 122051, India b Dr. K.N. Modi University, Newai, Rajasthan 304021, India c Poddar International College, Jaipur 302020, India 1. Introduction Lead (Pb) is a toxic environmental agent with debilitating effects on human health. Lead toxicity is one of the major occupational hazards such as in mining, automotive and paint industries. It accounts for most of the cases of pediatric heavy metal poisoning as it is shown to interfere with the development of the nervous system resulting in permanent learning and behav- ioral disorders (Chen et al., 2007; Yuan et al., 2006). In addition, lead exposure has also shown to be associated with neurodegen- erative disorders which has multitude of intracellular targets, thereby contributing to several pathogenic processes, which may be typical of such disorders such as mitochondrial dysfunction, oxidative stress, as well as brain inflammation. It has been shown that exposure to lead and mercury early in development can precondition the brain for developing neurodegenerative condi- tions later in life and heavy metals can exert adverse effects through acute neurotoxicity or through slow accumulation during prolonged periods (Monnet-Tschudi et al., 2006). Brain is one of the major target organs where severe neurological complications may arise after exposure to this heavy metal. Lead is shown to damage the nervous system microvascu- lature extensively (Garcia-Arenas et al., 1999). In their study, Garcia-arenas et al. have shown that lead exposure increases the production of inducible nitric oxide synthase (iNOS) in capillaries of the central nervous system (CNS) (Garcia-Arenas et al., 1999). However the findings of this study was in stark contrast to recent observations which suggested that inflammation may play a trivial role in lead mediated toxicity (Songdej et al., 2010). Numerous studies on lead neurotoxicity have indicated this metal to be a dangerous toxin, particularly during the developmental stages of higher organisms. This phenomenon is accompanied by death of neuronal cells and may be connected with inflammatory events owing to the production of a wide range of cytokines and chemokines (Kasten-Jolly et al., 2011). Prolonged exposure to Pb has also been examined in immature rats to investigate its NeuroToxicology 41 (2014) 143–153 A R T I C L E I N F O Article history: Received 16 August 2013 Received in revised form 20 January 2014 Accepted 4 February 2014 Available online 14 February 2014 Keywords: Microglia Lead COX-2 Apoptosis Central nervous system NF-kB A B S T R A C T Lead is one of the major pollutants of environment and is highly toxic to the functioning of central nervous system (CNS). The chronic exposure of this heavy metal is debilitating to the functional behavior of an organism. Studies have shown that acute exposure to Pb can lead to glial activation and secretion of cyto-chemokines in both in vitro and in vivo models. However, the cellular source of secretion of these cyto-chemokines remains to be identified. Microglia are monocytes of the brain, and are primary source of cytokine secretion in the CNS. We hypothesized that microglia exposed to Pb can secrete cyto- chemokines, thereby resulting in subsequent neuronal death. Our studies show that stimulation of BV-2 mouse microglia with 10 m; dose of Pb resulted in up-regulation of extracellular signal-regulated kinase (ERK) and protein kinase B (Akt) pathways, along with activation of an important transcription factor, nuclear factor-kB (NF-kB). Further, we found that the levels of tumor necrosis factor-a (TNF-a), interleukin-6 (IL-6) and monocyte chemoattractant protein-1 (MCP-1), and cyclooxygenase-2 (COX-2) pro-inflammatory enzyme were increased in response to Pb exposure. Furthermore, treatment with conditioned media from Pb treated BV-2 cells lead to neuronal death in neuroblastoma cells, which potentially involved the activation of caspase-3 enzyme. In all, the current study brings forth critical involvement of microglial activation in mediating the neurotoxicity associated with lead exposure. ß 2014 Elsevier Inc. All rights reserved. * Corresponding author at: National Brain Research Centre, Near NSG Campus, Manesar, Gurgaon 122051, Haryana, India. Tel.: +91 124 2845225. E-mail addresses: kanhaiya81@gmail.com (K.L. Kumawat), deepakkaushiik@gmail.com (D.K. Kaushik), drpraveen.goswami@gmail.com (P. Goswami), anirban@nbrc.ac.in (A. Basu). Contents lists available at ScienceDirect NeuroToxicology http://dx.doi.org/10.1016/j.neuro.2014.02.002 0161-813X/ß 2014 Elsevier Inc. All rights reserved.