br Conflicts of interest br Author contributions
Conflicts of interest
Acknowledgements This work was supported by the University of Brescia (ex 60%) and Siderurgica Leonessa research funds to AF. RR was supported by Associazione Italiana per la Ricerca sul Cancro - AIRC (MFAG 18459 grant). We are grateful to Umberto Veronesi Foundation for granting FMa with Post-doctoral Fellowship year-2018 Award. We acknowledge Luigi Poliani and Manuela Cominelli for assistance in tumor samples inclusion.
Introduction Atrazine (6-chloro-N-ethyl-N′-(1-methylethyl)-1,3,5-triazine-2,4-diamine, ATR) is a form of chlorotriazine herbicide, which has been extensively utilized world-wide. ATR is able to selectively kill a variety of weeds, functioning by disrupting the electron transport chain in the chloroplast, thereby inhibiting photosynthesis (Eldridge et al., 1999). Due to the widespread application of ATR, it is considered an environmental contaminant. It has been detected in both the notch signaling and groundwater, and is even detectable in food and drinking water (Meffe and de Bustamante, 2014, Gammon et al., 2005, Wang et al., 2012). Of particular concern, persistent ATR and its metabolites have also been found in human bodies (Bouvier et al., 2006). Despite its prevalence, the deleterious effects of ATR exposure on humans are still unclear. Epidemiological studies have demonstrated that exposure to ATR may impact reproductive and developmental processes (Jowa and Howd, 2011). Furthermore, a large number of animal studies have indicated that ATR can have adverse effects on the endocrine, reproductive and developing central nervous systems (CNS) (Abarikwu et al., 2010, Foradori et al., 2011, Bardullas et al., 2011). In addition, numerous studies using both behavioral and biochemical methods have suggested that ATR may act as a dopaminergic system toxin (Bardullas et al., 2011, Rodríguez et al., 2013). Recently, neurobehavioral studies have found that ATR may also affect hippocampus-dependent learning and memory in rodents. Bardullas et al. showed that male SD rats exposed to ATR at a dose of 10 mg/kg BW displayed more errors in a learning and memory task (Bardullas et al., 2011). Similar findings were also observed in a Y-maze spontaneous alternation test amongst male Wistar rats exposed to ATR at a dose of 300 mg/kg BW for 7 days (Kale et al., 2018). Additionally, Lin et al. found that male C57BL/6 mice exposed to 25 mg/kg BW of ATR for 10 days showed diminished performance in a novel object recognition (NOR) task (Lin et al., 2013). Despite ATR having been proven to affect hippocampus-dependent learning and memory functions, especially during development, the underlying mechanisms remain poorly understood. The hippocampus plays a critical role in learning and memory. In particular, hippocampal synaptic plasticity is crucial for the conversion of short-term information into long-term memories (Waltereit and Weller, 2003). Activation of the mitogen activated protein kinase (MAPK) signaling pathway, whose members include the extracellular signal-regulated kinase 1/2 (ERK1/2), has been shown to be a key molecular mechanism underlying hippocampal synaptic plasticity (Selcher et al., 1999). In order to initiate synaptic plasticity, ERK1/2 must first be phosphorylated by mitogen-activated protein kinase 1/2 (MEK1/2), after which it exerts a cascade of effects by phosphorylating the cAMP response element-binding protein (CREB) (Grewal et al., 2000). Phosphorylated CREB (p-CREB) mediates the induction of several immediate early genes (IEGs), which regulate hippocampal synaptic plasticity (Treisman, 1996). Interestingly, recent studies have demonstrated that exposure to ATR may affect ERK1/2 and its downstream signaling pathway elements in the Leydig and granulosa cells of rats (Fa et al., 2013, Karmaus and Zacharewski, 2015, Pogrmic-Majkic et al., 2016).
Materials and methods