Genetic Modulation of HSPA1A Accelerates Kindling Progression and Exerts Pro-convulsant Effects Eva-Lotta von Ru¨ den, ay Fabio Wolf, ay Michael Keck, a Fabio Gualtieri, a Marta Nowakowska, a Michael Oglesbee b and Heidrun Potschka a * a Institute of Pharmacology, Toxicology, and Pharmacy, Ludwig-Maximilians-University, Munich, Germany b Department of Veterinary Biosciences, The Ohio State University, OH, USA Abstract—Strong evidence exists that Toll-like receptor (TLR)-mediated effects on microglia functional states can promote ictogenesis and epileptogenesis. So far, research has focused on the role of high-mobility group box protein 1 as an activator of TLRs. However, the development of targeting strategies might need to consider a role of additional receptor ligands. Considering the fact that heat shock protein A1 (hsp70) has been confirmed as a TLR 2 and 4 ligand, we have explored the consequences of its overexpression in a mouse kindling paradigm. The genetic modulation enhanced seizure susceptibility with lowered seizure thresholds prior to kindling. In contrast to wildtype (WT) mice, HSPA1A transgenic (TG) mice exhibited generalized seizures very early during the kindling paradigm. Along with an increased seizure severity, seizure duration proved to be prolonged in TG mice during this phase. Toward the end of the stimulation phase seizure parameters of WT mice reached comparable levels. However, a difference between genotypes was still evident when comparing seizure parameters during the post- kindling threshold determination. Surprisingly, HSPA1A overexpression did not affect microglia activation in the hippocampus. In conclusion, the findings demonstrate that hsp70 can exert pro-convulsant effects promot- ing ictogenesis in naı¨ve animals. The pronounced impact on the response to subsequent stimulations gives first evidence that genetic HSPA1A upregulation may also contribute to epileptogenesis. Thus, strategies inhibiting hsp70 or its expression might be of interest for prevention of seizures and epilepsy. However, conclusions about a putative pro-epileptogenic effect of hsp70 require further investigations in models with development of sponta- neous recurrent seizures. Ó 2018 IBRO. Published by Elsevier Ltd. All rights reserved. Key words: microglia, seizure, heat shock protein, epileptogenesis, pro-epileptogenic. INTRODUCTION Excessive and persistent inflammatory signaling involving Toll-like receptor (TLR)-mediated glia activation is considered as a key factor contributing to the development and manifestation of a permanent hyperexcitability during the course of epileptogenesis (Devinsky et al., 2013; Vezzani et al., 2013). Considering a facilitating impact of inflammatory mediators on excita- tory neurotransmission, inflammatory signaling can also serve as one factor triggering ictogenesis following epilepsy onset (Vezzani, 2014). High-mobility group box 1 (HMGB1) has been intensely studied as a TLR ligand with enhanced release and overexpression following an epileptogenic insult and in the epileptic brain (Dey et al., 2016). A ser- ies of studies has addressed the functional role of HMGB1 in the context of epileptogenesis and ictogene- sis reporting relevant effects of targeting strategies in different rodent epilepsy models (Maroso et al., 2010; Chen et al., 2015; Yang et al., 2017). Whereas a role of HMGB1-triggered TLR signaling has thus been con- firmed, it is still an open question whether further TLR ligands might contribute to the excessive inflammatory signaling and its functional consequences during epileptogenesis and in the epileptic brain. Using a comprehensive proteome analysis, we have recently demonstrated a prominent regulation of inducible heat shock protein 70 (hsp70) in the hippocampus and parahippocampal cortex during the early post-insult phase and the latency phase in a rat post-status epilepticus model of epileptogenesis (Walker et al., 2016). This result raised the question whether HSPA1A https://doi.org/10.1016/j.neuroscience.2018.06.031 0306-4522/Ó 2018 IBRO. Published by Elsevier Ltd. All rights reserved. * Corresponding author. Address: Institute of Pharmacology, Toxicol- ogy, and Pharmacy, Ludwig-Maximilians-University, Ko¨niginstr. 16, D-80539 Munich, Germany. Fax: +49-89-218016556. E-mail address: potschka@pharmtox.vetmed.uni-muenchen.de (H. Potschka). y Both authors contributed equally. Abbreviations: CA1 and CA3, cornu ammonis region 1 and 3; EEG, electroencephalography; HMGB1, high-mobility group box 1; hsp70, heat shock protein 70; Iba1, ionized calcium binding adaptor molecule 1; iNOS, nitric oxide synthase; PTZ, pentylenetetrazol; TG, transgenic; TLR, Toll-like receptor; WT, wildtype. NEUROSCIENCE RESEARCH ARTICLE E.-L. von Ru ¨ den et al. / Neuroscience 386 (2018) 108–120 108